In modular steel construction, volumetric building units are largely completed in the factory before being transported to the site. Their structural framing, interior finishes, plumbing, insulation, and waterproofing are often pre-installed, meaning that inter-module connections must satisfy both structural and construction requirements. They must transfer lateral forces, accommodate erection tolerances, remain accessible for inspection, and avoid damaging pre-installed finishes and envelope layers. These demands are especially important under lateral loading, when adjacent modules must transfer shear forces and accommodate relative translation, gap opening, and local deformation. Many existing inter-module connections depend on field welding, concealed engagement devices, complex components, or large access openings. Although such systems may provide adequate structural resistance, they can slow construction, increase fabrication costs, and interfere with finished floors and walls.

In a recent study published in the Journal of Building Engineering, Dr. Xin Yan, Professor Jingfeng Wang, Tianyang Hu, and Zhengyuan Wu from Hefei University of Technology, together with Mr. Baochun Pan from Hefei Royalstar Electronic & Electrical Appliances Group Co., Ltd., developed an envelope-compatible, all-bolted inter-module connection for low-rise modular steel buildings. The main novelty of the new study is the use of U-bolts and column-end plates to connect adjacent module columns, combined with high-strength bolted plates joining the stacked floor and ceiling beams. Instead of attempting to create full moment-resisting continuity, the system acts as a partial-strength connection that transfers lateral forces while allowing controlled relative movement between modules.

The U-bolts transfer force through clamping and bearing against the column-web bolt holes. This arrangement improves deformation compatibility between adjacent columns during cyclic loading. The connection components are also concentrated in accessible regions of the column and beam webs. No U-bolts are placed at the bases of the upper columns, where installation could disturb pre-installed insulation and waterproofing. The design therefore combines structural performance with practical construction requirements.

Another benefit is the reliance on standard plates, U-bolts, and high-strength bolts rather than proprietary locking mechanisms, sleeves, or grouted components. This simplifies fabrication and procurement, reduces dependence on field welding, and provides clearly visible load-transfer paths that can be inspected after installation.

The researchers tested seven full-scale cruciform joints fabricated from Q355B structural steel. One fully welded specimen served as the reference. The remaining specimens used high-strength bolted beam connections together with either U-bolt–plate or conventional high-strength bolted column connections. The column connectors were placed on the web, on the flange, or at both the upper and lower column levels.

The authors applied a constant axial load through the upper columns while the specimens were subjected to cyclic lateral displacement. The tests measured hysteretic response, peak resistance, stiffness degradation, deformation capacity, energy dissipation, local displacement, and strain development. They also developed a finite element model to examine stress distribution and the force-transfer mechanisms within the joint. The team found that, across the specimens, damage generally began with local buckling of the column walls near the inter-module connection. As drift increased, relative movement and gap opening developed between the upper and lower modules. Final deterioration was commonly associated with column-wall tearing or weld fracture near the interface between the ceiling beam and the lower modular column. Damage was therefore concentrated in the joint region and lower-column segment rather than through widespread yielding of the modular beams.

The main advantage of the U-bolt detail became evident once the drift ratio exceeded approximately 1.0%. The team observed that, at smaller drift levels, the bolted configurations showed similar resistance. At larger drift, however, the U-bolt specimens achieved higher peak loads and sustained greater deformation than comparable specimens using conventional high-strength bolted column connections. In the web-connected comparison, the U-bolt specimen reached 2.0% drift before column-wall tearing, whereas the conventional bolted specimen failed at 1.5% drift because of weld fracture. A similar result was observed for the flange-connected pair. The U-bolt specimen maintained resistance to 2.0% drift, while the conventional bolted specimen experienced sudden strength loss at 1.5%. These results show that the U-bolt assembly provided a more adaptable force-transfer mechanism and delayed abrupt local failure. The location of the lower-column connector on the web or flange had only a limited effect on overall strength and stiffness.

When the authors installed bolted restraints at both the upper and lower columns, a significant change occurred. These double-level arrangements created additional load-transfer paths and allowed the specimens to reach 2.0% drift. However, their hysteresis loops became more asymmetric under load reversal, which indicates that the force-transfer mechanism differed between the two loading directions.

The authors performed strain measurements to better understand the joint response and found the stacked floor and ceiling beams largely behaved as separate flexural members, and most beam-web strains remained below nominal yield before joint deterioration. Much higher strains developed in the beam connection plates, showing that the beam-to-beam interface carried a large share of the local force transfer. Beyond approximately 0.5% drift, deformation increasingly concentrated in the lower-column segment below the inter-module joint. The finite element models reproduced the main hysteretic trends, initial stiffness, peak resistance, and stress development observed experimentally. They identified elevated stresses in the column walls and beam connection plates, consistent with the measured strains and physical damage. The validated finite element model therefore provides a useful tool for investigating local strengthening measures and connection refinements before further full-scale testing.

The connection proposed by Xin Yan et al. provides an accessible, all-bolted load-transfer path made from common components and allows relative movement between stacked modules during cyclic loading. The U-bolt connection better accommodates relative displacement between adjacent modules under repeated loading while maintaining force-transfer capacity at larger drift levels than comparable conventional bolted connections.

Hydrogen storage remains one of the central materials challenges limiting the broader use of hydrogen as an energy carrier. At ambient conditions, hydrogen has a low volumetric energy density, so established storage methods depend on compression or liquefaction. Both approaches add system mass and energy demand. Solid-state storage can achieve high hydrogen density at lower pressure, but its practical value depends on more than the hydrogen content of the material itself. The storage vessel, thermal-management components and fuel cell all contribute to the final system mass. A useful hydride must therefore combine reversible capacity with hydrogen release at temperatures compatible with the surrounding energy system.

Lightweight complex hydrides are attractive because they contain substantial quantities of hydrogen. Their sorption chemistry, however, often requires temperatures that are too high for efficient use of low-grade heat. Lithium borohydride, LiBH₄, illustrates this difficulty: it has a high theoretical hydrogen capacity, yet substantial dehydrogenation and subsequent rehydrogenation occur only under demanding thermal and pressure conditions. Magnesium amide–lithium hydride chemistry offers a more accessible reversible pathway through cooperative reactions that form mixed-metal imides. Its usefulness is still restricted by slow hydrogen-release kinetics at moderate temperature, and ammonia-forming side reactions can contribute to capacity loss during cycling.

Reactive hydride composites seek to overcome these limitations by combining hydrogen-bearing phases that react cooperatively. In the Mg–Li–N–H system, adding LiBH₄ can accelerate sorption and alter the phases formed during dehydrogenation. Earlier studies focused mainly on small or moderate borohydride additions. These compositions reduced the apparent release temperature, but rapid hydrogen delivery near ambient conditions remained difficult because improved thermodynamics did not fully remove the kinetic restrictions of solid-state reactions.

The key unresolved question was whether much higher LiBH₄ contents would continue to produce incremental changes or instead establish a different chemical pathway. In a recently published Nature Communications paper, Professor Martin Dornheim and Professor David Grant from the University of Nottingham, together with an international research team, examined a series of Mg(NH₂)₂–LiH–LiBH₄ composites across a broad range of borohydride concentrations. They investigated how high LiBH₄ loading affects hydrogen-release temperature, gas composition, reversibility and phase evolution, with particular attention to reaction intermediates that are absent from conventional low-borohydride formulations.

The researchers prepared milled composites containing progressively larger amounts of LiBH₄. Coupled thermogravimetric analysis, differential scanning calorimetry and mass spectrometry resolved the temperature, magnitude and gaseous products of successive release events. Temperature-ramped synchrotron powder X-ray diffraction then followed the associated structural changes, allowing hydrogen evolution to be interpreted alongside the consumption and formation of crystalline or poorly ordered phases.

Composition altered both the onset and character of dehydrogenation. The borohydride-rich materials began releasing hydrogen at substantially lower temperatures than the corresponding Mg(NH₂)₂–LiH system without LiBH₄. Among the compositions examined, the intermediate high-LiBH₄ formulation, designated 6-9-18, gave the strongest balance of low-temperature release and reversible storage capacity. It began releasing hydrogen near the lower end of the temperature interval associated with low-grade fuel-cell waste heat and delivered approximately three weight percent hydrogen over the principal operating range.

The authors performed gas analysis and found no ammonia was detected over the main dehydrogenation interval for the higher-LiBH₄ compositions, whereas weak ammonia signals remained in materials containing less borohydride. This distinction suggests that high LiBH₄ loading redirects nitrogen-containing intermediates away from pathways that release ammonia. The change is not simply a reduction in reaction temperature; it also concerns which chemical products become accessible during heating. They also

The research conducted as well calorimetry and showed that the early thermal events could not be explained by the known structural transition of LiBH₄ alone. The measured heat flow was considerably larger than expected for that transformation, indicating that additional chemical or structural rearrangements occurred in the same temperature region as the initial hydrogen release. This observation directed attention toward transient phases that conventional ex situ measurements could easily miss.

Synchrotron diffraction revealed a marked divergence between low- and high-borohydride composites. The low-LiBH₄ material formed the established crystalline imide and borohydride–amide products. In the richer formulations, these familiar phases were replaced by a prominent low-angle diffraction feature associated with a large-period, poorly ordered structure. Its intensity increased during hydrogen release as LiBH₄ was consumed. The researchers therefore assigned it cautiously to a partially decomposed Li–Mg–N–B–H intermediate, possibly with layered or intercalated character.

The magnesium-containing intermediates also changed with composition. In the 6-9-18 material, MgNH appeared during the lower-temperature stage and disappeared as the reaction shifted toward direct interaction between Mg(NH₂)₂ and LiBH₄. At still higher LiBH₄ loading, MgNH was no longer detected, indicating that the borohydride-rich environment controlled the pathway from an earlier stage. This design choice had a clear scientific consequence: increasing LiBH₄ beyond the conventional range changed the reacting partners and the sequence of phase formation, thereby lowering the temperature at which hydrogen became available.

At elevated temperature, the team found the diffraction patterns of the richest formulations became broad and largely non-crystalline, consistent with molten, amorphous or nanocrystalline material. Weak reflections also indicated the formation of a primitive cubic phase, tentatively assigned to Mg₂NH. The authors propose that a partially molten or electrolyte-like borohydride phase may improve ionic transport through the composite and reduce the kinetic restrictions associated with reactions between separate solid particles. Initial cycling measurements confirmed that the 6-9-18 composition remained reversible and retained approximately its original hydrogen capacity, although release became slower after repeated cycling.

The research work of University of Nottingham scientists is the demonstration that LiBH₄ concentration can determine the identity of the dehydrogenation pathway, rather than simply modifying the rate of an established reaction. Small additions support familiar crystalline products. Higher concentrations generate poorly ordered and possibly molten intermediates, accompanied by a different sequence of magnesium nitride-hydride chemistry. The composite therefore enters a distinct reaction regime once the borohydride fraction becomes sufficiently large. This distinction changes the design logic for reactive hydride composites. Their behaviour cannot be predicted by assuming that an additive performs the same role at every concentration. In the borohydride-rich materials, LiBH₄ appears to function as a structurally active reactant. Its abundance is linked to the formation of the large-period intermediate, the weak cubic phase and broad scattering associated with melt-like behaviour. These features provide a coherent explanation for the lower hydrogen-release temperature, although the precise structures and compositions of the transient phases remain provisional.

We believe the 6-9-18 formulation is important because it combines reversible hydrogen storage, release within the temperature range of low-grade fuel-cell waste heat and suppression of detectable ammonia during the principal dehydrogenation interval. The paper does not establish operation within a dynamically loaded fuel-cell system, and the authors distinguish their controlled laboratory measurements from the fluctuating pressures and thermal gradients expected in service. Long-term cycling also remains to be established. Within these boundaries, the new findings provide a clear materials-design principle. Exploring compositions beyond the traditionally studied range can reveal reaction pathways and transport conditions that are inaccessible at lower additive contents. The next scientific task is to resolve the large-period intermediate, the amorphous or molten component and the proposed cubic Mg₂NH phase using complementary structural methods. Their identification would clarify how high borohydride loading couples phase mobility, nitrogen chemistry and reversible hydrogen release.

Solid-state batteries built around lithium-rich manganese oxide positive electrodes bring together two demanding aspects of electrochemical materials design: the use of oxygen redox to access high specific capacity and the need to preserve a stable interface against a solid electrolyte at elevated potential. In lithium-rich manganese oxides, charge compensation extends beyond transition-metal cations to include lattice oxygen associated with the Li–O–Li configuration. This additional redox contribution supports capacities above those of conventional layered oxides and permits operation near 4.6 V versus Li⁺/Li. Yet the same oxygen chemistry that provides this capacity can generate reactive oxidized oxygen species. Their formation may lead to irreversible oxygen release, transition-metal migration, structural rearrangement and chemical oxidation of the adjacent solid electrolyte.

These processes are closely coupled. Oxygen-related changes within the positive-electrode particle alter the near-surface crystal structure, and species reaching the particle boundary can react with the catholyte to form poorly conducting products. The resulting interphase impedes Li⁺ transfer and increases cell resistance, especially during charging above approximately 4.4 V, where oxygen redox becomes prominent. Lithium-rich manganese oxides also contain a Li₂MnO₃-derived component with intrinsically low electronic conductivity. Structural instability and limited transport therefore converge at the same region of the electrode: the particle surface and its contact with the solid electrolyte.

Surface modification offers a means of intervening at this junction, but the requirements are unusually specific. A useful surface layer must restrain oxygen-driven reactions without imposing a prohibitive transport barrier. Chemical passivation alone may protect the electrolyte yet slow Li⁺ exchange, whereas structural reconstruction can alter ion mobility but may not adequately control reactive oxygen species. The scientific problem is consequently one of coordinated interfacial design: stabilizing oxygen redox, limiting irreversible reconstruction and maintaining rapid lithium transport through the outermost region of the active material.

In a recently published research paper in Nature Communications Professor Daniel Rettenwander and colleagues addressed this problem using Li₁.₂Mn₀.₅₄Ni₀.₁₃Co₀.₁₃O₂ modified through immersion in a thiourea-containing aqueous solution followed by annealing. Their central premise was that thiourea processing could produce two chemically and structurally distinct surface features in a single treatment: an ultrathin sulfur-rich layer and a reconstructed Mn-rich spinel-type region beneath it. The investigation was designed to determine whether this coupled modification could regulate oxygen chemistry and interfacial transport simultaneously, and to establish how those effects arise across atomic structure, electrochemical kinetics and extended solid-state battery operation.

 Synchrotron diffraction established that the treatment preserved the predominantly layered interior of the lithium-rich manganese oxide, with only minor changes in lattice parameters and antisite disorder. The principal structural alteration occurred near the surface. The proportion of spinel-type material increased from about 2.3 wt% in the untreated powder to 10.2 wt% after modification, and the broadened spinel reflections indicated nanoscale domains. Electron microscopy resolved the architecture more directly: an approximately 0.7 nm sulfur-containing outer layer covered a Mn-enriched subsurface region consistent with spinel LiMn₂O₄. Sulfite, sulfate and C–S–C species were detected at the surface, whereas nitrogen-containing products were absent. The authors propose that thiourea decomposition generates reducing species during processing, enabling partial conversion of Li₂MnO₃ into LiMn₂O₄ as sulfur is oxidized to sulfite and sulfate.

This surface architecture substantially altered cell behavior. In solid-state cells containing a Li₃InCl₅.₄F₀.₆ catholyte, the modified material delivered an initial discharge capacity of 220.2 mAh g⁻¹ and an initial Coulombic efficiency of 84.83%, compared with 138 mAh g⁻¹ and 75.46% for untreated LRMO. Its capacity remained higher across rates from 0.1 to 2 C. At 0.2 C, 95.6% of the initial capacity was retained after 100 cycles, and at 1 C the cell maintained approximately 147 mAh g⁻¹ with more than 97% capacity retention after 600 cycles. Cells prepared at an areal loading of 15.28 mg cm⁻² produced about 174 mAh g⁻¹ and maintained stable cycling, despite the kinetic constraints associated with the greater loading and secondary-particle morphology.

The authors performed cyclic voltammetry which showed reduced polarization and greater use of the high-voltage redox process. During initial charging, distribution-of-relaxation-time analysis separated the overlapping impedance contributions and showed that interfacial resistance increased far less in the modified cell than in the untreated one. This difference persisted during prolonged cycling, indicating that the coating limited the progressive formation of resistive interfacial products. The spinel-type layer beneath the sulfur-rich coating also had a direct transport consequence: its three-dimensional Li⁺ pathways supported faster motion near the particle boundary than the two-dimensional pathways of the layered bulk. Consistently, the modified material maintained higher lithium diffusion coefficients at high states of charge. Chemical and structural measurements linked these kinetic changes to oxygen stabilization. The modified electrode retained larger fractions of oxidized oxygen species in both delithiated and lithiated states, indicating more reversible oxygen redox. During operando diffraction, untreated LRMO developed high-voltage shoulders associated with oxygen loss, Mn migration and spinel-like reconstruction. These features were absent after thiourea treatment, and the lattice parameters evolved more regularly through charging. Following cycling, Cl–O, In₂O₃, InO⁻ and ClO⁻ products characteristic of catholyte oxidation were prominent beside untreated LRMO but minimal beside the modified particles. Sulfur-containing species and the surface spinel phase remained detectable after prolonged cycling. Density-functional calculations completed the mechanistic account: the lowest-energy peroxide configuration in spinel LiMn₂O₄ was 2.59 eV higher than its counterpart in layered LRMO, making stabilization and migration of oxidized oxygen through the spinel region energetically unfavorable.

 The work of Professor Daniel Rettenwander and colleagues is important in treating oxygen stability and lithium transport as coupled surface phenomena. The sulfur-rich outer layer limits oxygen-mediated reactions with the halide catholyte, and the reconstructed spinel-type region changes the energetic and transport properties of the particle boundary. Neither component is presented as an isolated coating function. Their value follows from their spatial arrangement and complementary roles: one controls interfacial chemistry, while the other provides a more favorable near-surface pathway for Li⁺ and resists the migration of oxidized oxygen toward the electrolyte.

This interpretation clarifies why a nanometre-scale modification can influence both first-cycle reversibility and long-term operation. Preserving oxidized oxygen species within a reversible redox process reduces the loss of active oxygen and the associated transition-metal rearrangement. It also limits formation of resistive oxidation products in the catholyte. Lower interfacial impedance is therefore connected to the stabilization of the active material itself, not simply to improved physical contact. The operando structural data, post-cycling chemical analysis and calculated peroxide energetics converge on this relationship.

The treatment also leaves the layered particle interior largely intact. Capacity continues to arise from the lithium-rich bulk, with the reconstructed region confined to the surface-near volume where oxygen migration and electrolyte oxidation must be controlled. This separation of functions provides a clear materials-design logic: preserve the high-capacity layered phase internally, but give its outer boundary a crystal chemistry better suited to ion transfer and oxygen containment.

Within the cell chemistry and testing conditions examined, the modified electrode combined an initial discharge capacity above 220 mAh g⁻¹ with stable cycling over 600 cycles at 1 C. Performance at increased areal loading further indicates that the engineered interface remains electrochemically stable when more active material is introduced, although the paper confines its demonstrated scope to laboratory solid-state cells and identifies pouch-cell evaluation as future work. The broader implication supported by the evidence is that precursor chemistry can be used to construct a chemically protective layer and a transport-active reconstructed phase in one processing sequence.

Austenitic 316L stainless steel is protected in corrosive environments by a chromium-rich passive film that forms rapidly on its surface. When this film is compact and enriched in Cr₂O₃, it limits charge transfer and helps prevent aggressive species from reaching the underlying metal. In chloride-containing environments, however, even local disturbance of the film can initiate pitting, which make the stability and repair of this surface layer critical under mechanical load. This protection can be weakened by sensitization and in 316L stainless steel, prolonged exposure to humid and elevated-temperature conditions may promote Cr₂₃C₆ carbide precipitation along grain boundaries, producing chromium-depleted regions that are less able to sustain corrosion resistance. Carbide precipitates can be dissolved by pulsed laser treatment without melting the surface, thereby reversing sensitization while preserving the treated surface. The more important question is how this restored surface performs afterward, because the renewed passive film can lose stability when tensile stress and chloride exposure act together.

Previous studies have linked tensile loading with poorer passivity, increased defect density, and altered electrochemical response. What remained less clear was the atomic-scale origin of this deterioration, especially how stress changes the elemental distribution within the passive film. For laser-desensitized 316L stainless steel, the problem therefore extends beyond removing chromium-depleted zones at grain boundaries. The restored surface must also maintain a chemically protective oxide film under mechanical loading. A film may even become thicker without becoming more protective if tensile stress changes its composition, compactness, and ability to resist chloride attack.

In a recently published research paper in Corrosion Science, Dr. Xu-dong Li, Dr. Zi-wen Zhao, Dr. Muhammad Arslan Hafeez, Professor Cheng Zhang, and Professor Lin Liu from Huazhong University of Science and Technology established a multiscale mechanism linking tensile stress to the deterioration of corrosion resistance in laser-desensitized 316L stainless steel. Their multiscale approach connected electrochemical degradation with passive-film chemistry, nanoscale elemental redistribution, and Fe/Cr diffusion.

The researchers prepared pulsed-laser-desensitized 316L specimens and applied increasing elastic tensile stress using a three-point bending arrangement. Electrochemical testing in 3.5 wt% NaCl solution showed a steady decline in corrosion resistance as tensile stress increased. Impedance spectroscopy identified a sharp reduction in total polarization resistance, and circuit fitting showed decreases in both passive-film resistance and charge-transfer resistance under stress. Polarization measurements confirmed this deterioration and that the unstressed and moderately stressed specimens retained a passivation-pitting transition, but the highest-stress condition no longer showed a stable passivation region.

The authors performed Potentiostatic measurements and observed frequent metastable pitting events under high tensile stress, with current transients indicating repeated local rupture of the passive film and slower repassivation. Surface examination after polarization showed that pits became larger and more numerous as stress increased. They were also no longer concentrated mainly near grain boundaries, but appeared increasingly within grain interiors.

The team conducted as well passive-film analysis to explain why the apparent barrier became less effective. Current-decay behaviour showed that tensile stress reduced the efficiency of film densification during growth. Capacitance measurements indicated that the stressed surface became more favourable to chloride adsorption. Mott-Schottky analysis showed n-type semiconducting behaviour in all conditions, but donor defect density increased progressively with tensile stress. XPS then identified the accompanying chemical change: the protective Cr₂O₃ fraction decreased, while FeO and Fe₃O₄ became more prominent. The stressed film therefore contained more lower-valence iron oxides and less protective chromium oxide.

The research team used aberration-corrected TEM and elemental mapping to show that tensile stress did not physically thin the passive film. Under the highest tensile loading, the film near grain boundaries became about 19% thicker, yet its chemical composition shifted in a less protective direction. This finding indicates that mechanical stress degrades the passive film mainly through compositional transformation rather than simple structural thinning. The unstressed passive film was relatively chromium-rich. Under tensile stress, Fe concentration increased toward the outer surface, chromium content was lower across the film thickness, and the Cr/Fe ratio declined substantially. Chlorine content also increased, consistent with the electrochemical evidence for stronger chloride adsorption.

The team’s DFT and AIMD simulations provided the atomic basis for this compositional transformation. Tensile stress made Fe segregation toward the surface more thermodynamically favourable and increased the mobility of both Fe and Cr. Fe nevertheless diffused about 1.5 times faster than Cr under the simulated tensile condition. This preferential Fe migration explains how tensile stress drives the formation of a Fe-enriched, Cr-depleted passive film despite the restored surface condition produced by laser desensitization. It also moves the explanation beyond a general increase in passive-film defects by showing how tensile stress selectively alters Fe and Cr migration during film formation.

The findings of Huazhong University of Science and Technology researchers are important for laser-restored 316L stainless-steel components that operate in chloride-containing environments under sustained elastic loading. For engineering practice, this means that a visually intact surface may still have reduced resistance to localized corrosion. Components restored by pulsed laser treatment may recover protection against sensitization-related attack, but their corrosion performance should be assessed under the loading condition expected in service. Electrochemical testing under pre-applied tensile stress could provide a more realistic basis for qualifying treated material than stress-free corrosion tests alone. Indeed, effective process design should pair Cr₂₃C₆ precipitate removal with control of residual or service-induced tensile stress near exposed surfaces.

Where feasible, reducing high tensile stresses, limiting stress concentrations, or introducing favourable compressive surface states may help preserve the Cr-rich barrier needed for corrosion resistance. Inspection after laser restoration should evaluate localized corrosion across the exposed surface, including grain interiors as well as grain-boundary regions, when the component is expected to experience tensile loading. Although laser desensitization chemically restores the alloy surface, tensile stress can still alter Fe and Cr transport during film formation, leaving the surface layer less protective.

Atomic layer deposition provides precise control over surface coatings by introducing gaseous reactants one at a time, allowing each reaction to stop naturally when the available surface sites are filled. With nanoparticles, however, the very large surface area creates an added challenge: the precursor must travel through porous particle agglomerates to reach active sites buried within the structure. Fluidized bed atomic layer deposition addresses the need for high-throughput particle processing by dispersing nanoparticles in a gas stream while exposing them alternately to precursor and purge gases. Its performance depends on both reaction kinetics at the nanoparticle surface as well as how efficient each precursor moves through the hierarchical structures formed by cohesive particles.

Nanoparticles in a fluidized bed are not isolated objects and adhesive forces cause them to assemble into relatively stable primary agglomerates, typically a few micrometres in diameter. These units can then combine into much larger complex agglomerates with fractal structures extending to hundreds of micrometres or several millimetres. Complex agglomerates may break and recombine during fluidization, whereas the smaller primary structures are more resistant to fragmentation. Precursor transport must therefore proceed through several distinct environments: from the surrounding gas into a dispersion of complex agglomerates, through the outer structure of each complex agglomerate, and finally into the pores of its constituent primary agglomerates before adsorption and surface reaction can occur.

The challenge is to determine how much transport resistance arises at each structural level. Agglomerates have irregular internal structures, so their size, compactness, and fractal dimension determine how easily the precursor can move through them and how far it must travel.  Existing descriptions have treated diffusion within pores, precursor utilization at the reactor scale, or particle coating in fluidized systems. What remained unclear was how the different levels of nanoparticle agglomeration affect precursor transport, surface saturation, and coating uniformity. In a recently published research paper in Chemical Engineering Science, Professor Daoyin Liu’s group from School of Energy and Environment at Southeast University, developed a CFD-DEM-based multiscale model that couples precursor transport with reversible adsorption and self-limiting atomic layer deposition kinetics across primary agglomerates, complex agglomerates, and monodisperse agglomerate systems. They introduced a generalized Thiele modulus that identifies whether reaction or diffusion dominates at each structural level. They also formulated a semi-empirical expression that predicts complex-agglomerate diffusion characteristic time from fractal dimension, agglomerate size, and primary-agglomerate saturation time.

In their modeling work, the trimethylaluminum-water process for alumina deposition served as the reaction system. Within each primary agglomerate, precursor penetration was represented through a lumped diffusion-reaction description. Transport around and between primary agglomerates was calculated directly for complex fractal structures and for systems containing several complex agglomerates. Reversible Langmuir adsorption, desorption, and irreversible surface reactions linked the local gas concentration to surface coverage and film growth. A primary agglomerate provided the reference state for evaluating larger structures. Agreement between the simulated mass-gain evolution and experimental quartz crystal microbalance data from the literature supported the treatment of the reaction kinetics.

After model validation, Zuyang Zhang et al further examined complex agglomerates with different fractal dimensions and numbers of primary agglomerates and found their internal coating patterns changed markedly with structure. In loose agglomerates, saturation depended strongly on position along the direction of precursor flow: upstream particles reacted first, followed by particles farther downstream. As the fractal dimension increased, the agglomerate became denser, and a particle’s position inside it mattered more. Particles near the surface received the precursor first and reached saturation sooner, while particles near the centre coated more slowly. The coating therefore moved gradually from the outside toward the centre. The authors found local resistance increased toward the centre of compact agglomerates and followed an approximately parabolic radial profile, whereas the variation was closer to linear in loose structures. Saturation time increased with both fractal dimension and the number of primary agglomerates. Large, compact agglomerates also developed broader growth-per-cycle distributions and lower mean growth than loose agglomerates containing the same number of primary units. Particles embedded near the centre experienced the greatest precursor depletion.

The team next compared isolated agglomerates with monodisperse systems having the same total surface area. A single-agglomerate calculation reproduced the system saturation time closely when the dispersion was loose or the constituent agglomerates were compact. Dense arrangements increased competition for precursor, particularly for downstream agglomerates. The coating history of one complex agglomerate can therefore represent a monodisperse assembly with useful accuracy under the conditions examined, although the correspondence depends on both agglomerate morphology and inter-agglomerate spacing.

The team pinned the complex agglomerate as the primary culprit for transport resistance. For process designers, this means reactor performance cannot be optimized simply by tracking total solids or surface area. In fact, two powder beds with identical nanoparticle mass will require completely different exposure times if their internal fractal structures and agglomerate sizes do not match. From a practical standpoint, the goal should be tuning fluidization conditions to prevent these dense agglomerates from forming in the first place. Keeping the structures small and open shortens internal diffusion paths, minimizes concentration gradients, and lets surface sites saturate much more uniformly. While the simulations show that longer exposure times can eventually force deep particles to saturate, doing so naturally drags out the entire deposition cycle.

To help navigate these trade-offs, the authors’ generalized Thiele modulus gives engineers a clear way to see whether diffusion or reaction kinetics dominate at any given structural level. In loose agglomerates, for instance, both forces usually come into play, meaning engineers will need to carefully coordinate temperature, precursor concentration, and exposure times to get the best results. The proposed diffusion-time correlation enables agglomerate transport behaviour to be represented in larger-scale reactor models. It estimates the diffusion characteristic time from agglomerate size, fractal dimension, and primary-agglomerate saturation time without resolving every nanoparticle individually. The resulting values can be incorporated into fluidized bed simulations through corrected adsorption rates, linking local agglomerate structure with reactor-scale precursor consumption and coating progress. Finally, the close correspondence between isolated agglomerates and loosely dispersed monodisperse systems indicates that representative single-agglomerate calculations can reduce computational cost.

Matter-wave Sagnac interferometry measures rotation by comparing the phases of atomic wave packets travelling along separate paths that enclose an area. A larger enclosed area produces a stronger rotation signal, increases the rotation scale factor, and can improve sensitivity. Cold-atom gyroscopes can already achieve precise measurements, but improving their sensitivity without increasing the size of the instrument remains difficult. Guided interferometers address this challenge by controlling the atomic paths with optical or magnetic potentials which allow a larger sensing area to be created within a compact system.

For a multi-turn interferometer to work well, the two atomic wave packets must follow stable paths, remain coherent, and meet again at the correct points. This becomes harder as more turns are added. In magnetically guided systems, small changes in trap alignment or field strength can shift the atomic paths and reduce the interference signal. Repeated crossings between the wave packets can also lead to losses. A practical multi-turn gyroscope therefore needs a guide that can control the atoms reliably throughout the full measurement.

Programmable optical dipole potentials offer a different route because the atomic trajectory can be written into the spatial structure of the light field. Spatial light modulators can reshape such fields dynamically, while Bessel-like beams provide a narrow central intensity lobe that can be engineered to follow a prescribed three-dimensional path. For a helical guide, however, the field must do more than trace the desired centerline. It must confine the atoms transversely, transport them along the helix, compensate gravity, and retain a sufficiently stable guiding core over the required propagation distance. These requirements have to be met without introducing excessive photon scattering or an optical configuration whose complexity offsets the advantage of programmable guiding.

 In a recently published research paper in Photonics Research Dr. Xin Lv, Professor Zhaoying Wang, and Professor Qiang Lin from Zhejiang University proposed and numerically analysed a theoretical ultracold-atom gyroscope in which a far-detuned, angular-spectrum-engineered Bessel-like beam is designed to guide a Bose–Einstein condensate along programmable helical trajectories. The same optical field encodes the helix geometry, transverse confinement, and an axial intensity gradient that compensates gravity. A synchronized sequence of Bragg pulses and spatial-light-modulator updates is designed to send two matter-wave packets through reciprocal, opposite-handed multi-turn paths before recombination. Its distinct feature is the use of stable three-dimensional optical guiding to increase effective Sagnac area through repeated orbits within a compact spatial footprint.

The researchers designed the helical guide by engineering the beam’s angular spectrum. Its centre follows a programmed spiral path, while the beam’s intensity changes along the direction of travel to counteract gravity. In the simulations, the atoms can move through the helix at a nearly steady speed while remaining confined close to the bright central core of the Bessel-like beam.

The authors created a simulated beam using a limited optical window, so it is described as Bessel-like instead of the ideal Bessel beam. In numerical propagation tests, its guiding region stayed stable as the beam travelled. In a separate numerical test, when the main lobe was blocked, it quickly formed again, suggesting that the guide could recover from a local disturbance. The intensity change used to balance gravity also caused only a very small shift in the simulated atom position. The team then modelled the motion of ultracold rubidium atoms in the optical potential. The simulated atoms closely followed helical paths with different programmed pitches. Under the representative parameters considered, optical confinement was much stronger than the force caused by photon scattering, indicating that scattering should have little influence on the intended trajectory. A single structured beam could therefore provide both three-dimensional guiding and gravity compensation.

For the interferometer, a Bragg pulse divides the condensate into two wave packets moving in opposite directions. They travel along helices of opposite handedness, while later pulses reverse their momenta and updates to the spatial light modulator switch the direction of the guide. A final pulse is designed to bring the packets back together at their starting point.

In the ideal path-symmetric model, the laser-phase contributions cancel within a single measurement. The calculated phase is therefore mainly determined by propagation through the rotating system. Repeated turns increase the total enclosed area and strengthen the Sagnac response. In the representative eight-turn design, the paper reports an effective area of about 72 mm², corresponding to a large calculated rotation scale factor.

The proposed spiral Bessel-beam gyroscope by Zhejiang University scientists could support several important engineering applications that require accurate rotation sensing in a compact system. Its main advantage is the ability to guide ultracold atoms through several turns inside a programmable helical optical path. Each additional turn increases the effective enclosed area and strengthens the Sagnac phase used to measure rotation, without requiring the instrument to become proportionally larger. This makes the design relevant to compact precision gyroscopes, where sensitivity and physical size often compete with one another.

Another possible engineering application is in inertial navigation. Rotation sensors are essential in systems that must determine their orientation when satellite navigation is weak, interrupted, or unavailable. The proposed concept could contribute to future navigation units for aircraft, ships, underwater vehicles, or other platforms that require stable measurements over extended periods. The paper does not demonstrate such a field-ready device, but it provides a practical optical layout and identifies operating conditions needed for experimental development.

The programmable optical guide also offers engineering flexibility. By changing the spatial-light-modulator pattern, the radius, pitch, and handedness of the atomic trajectory can be adjusted without rebuilding the entire apparatus. This may allow one instrument to be configured for different measurement ranges or experimental conditions. The authors also suggest that tilting the helical axis and repeating the measurement could, in principle, recover all three components of the rotation vector.

Another useful feature is the reduced need for repeated wave-packet crossings. The two atomic packets overlap only at selected points in the interferometer sequence, which may help limit losses and preserve coherence during multi-orbit operation. The reciprocal geometry is also expected to suppress common laser-phase noise and slow common-mode disturbances. From an engineering perspective, the study supplies more than a sensing concept. It defines a beam-generation method, an atom-guiding strategy, a Bragg-pulse sequence, and quantitative limits associated with photon scattering, magnetic noise, optical-intensity fluctuations, and condensate phase diffusion. These elements provide a technical basis for building and testing a compact multi-orbit atom gyroscope.

Nuclear magnetic resonance is powerful because nuclear spins can retain quantum information for relatively long times while remaining sensitive to their local magnetic and structural environment. That same weak coupling, however, also makes nuclear spins difficult to initialize and detect with high sensitivity, especially when one wishes to move from ensemble-averaged spectroscopy toward small, well-defined spin systems. Optical access changes this balance. If a nuclear spin state can be prepared, manipulated, and read through an optical transition, NMR gains a route toward low-field sensitivity, molecular-scale addressability, and direct connection to photonic quantum architectures. The central difficulty is that optical and nuclear degrees of freedom are not naturally linked in most molecular systems in a way that permits coherent control without introducing additional decoherence channels.

A common strategy is to address nuclear spins indirectly through electron spins, using optical transitions connected to magnetic electronic states. This route has been powerful in solid-state defect systems, but it brings a physical compromise: the same electron spin that enables optical access can also add magnetic noise, restrict useful spin density, and limit the nuclear coherence that makes the spin attractive in the first place. Trivalent non-Kramers rare-earth ions offer a different route. In Eu3+, the absence of a net electronic spin allows the nuclear spin to be accessed through ultranarrow optical transitions without relying on a coupled electron spin. That distinction is central to the present paper.

In a recently published research paper in Nature Materials Dr. Evgenij Vasilenko, Vishnu Unni Chorakkunnath, Dr. Jeremias Resch, Nicholas Jobbitt, Dr. Diana Serrano, Dr. Philippe Goldner, Dr. Senthil Kumar Kuppusamy, and led by Professor Mario Ruben & Professor David Hunger from the Karlsruhe Institute of Technology in Germany  developed an optically detected nuclear magnetic resonance approach for coherently controlled 151Eu3+ nuclear spins in a stoichiometric europium molecular crystal. They combined spectral-pit-based optical spin initialization, RF control of two nuclear quadrupole transitions, and optical read-out of spin population changes through ultranarrow 7F0 to 5D0 transitions. The technically distinct advance is the demonstration of Rabi oscillations, Hahn-echo coherence, and CPMG dynamical decoupling in a molecular rare-earth complex with direct optical nuclear spin access. They also established a measurable correlation between optical transition frequency and nuclear spin resonance properties, linking local molecular crystal-field variation to both optical and RF response.

The researchers began with millimetre-sized single crystals of the europium complex grown by slow solvent evaporation, then incorporated an individual crystal into a fibre-based ferrule arrangement operated in liquid helium at 4.2 K. This experimental choice mattered because the optical transition itself served as the entry point to the nuclear spin system. The crystal quality therefore had immediate consequences for how selectively the Eu3+ ions could be addressed. Optical characterization of the 7F0 to 5D0 transition gave an inhomogeneous linewidth of 1.94 GHz, substantially narrower than previously reported for a microcrystalline powder of the same molecular material. Spectral hole burning yielded a homogeneous linewidth of 310 kHz, corresponding to an optical dephasing time just above one microsecond, while optical free-induction decay and photon echo measurements provided a more direct view of instantaneous optical coherence and optical coherence time. They also established that high-quality molecular crystals could provide a sufficiently narrow optical interface for nuclear spin experiments. The optical line was then used to prepare a spin-polarized sub-ensemble by burning a spectral pit through optical pumping. Rather than performing full hyperfine class preparation, the team used a 10 MHz-wide chirped optical burn that depleted one hyperfine ground-state population for a selected class of ions. The consequence of this design choice was a practical one with direct spectroscopic value: the spin preparation was fast enough and produced enough contrast to support repeated optically detected NMR measurements.

The authors obtained nuclear spin lifetime by monitoring recovery of the spectral pit. The decay required two time constants, a shorter component of 4.4 s and a longer component of 120 s. The long persistence of the optically prepared population made it possible to interrogate the quadrupole transitions of 151Eu3+ with radio-frequency pulses and detect the resulting population redistribution optically. Two ground-state nuclear quadrupole resonances were resolved at 21.475 MHz and 33.944 MHz, assigned to the |±1/2〉 to |±3/2〉 and |±3/2〉 to |±5/2〉 transitions, respectively. Their linewidths were not equivalent. The 34 MHz transition showed an 88 kHz inhomogeneous linewidth, while the 21.5 MHz transition was broader but gave stronger signal contrast under the same pulse conditions. They probed the 21.5 MHz transition at different positions across the optical inhomogeneous line, the researchers found that the spin transition frequency shifts with optical probing frequency, with an approximate gradient of −4 kHz GHz−1. The spin linewidth also increased toward the wings of the optical distribution. This correlation tied the nuclear quadrupole environment to the optical transition energy and showed that strain or local ligand-field variation affects both degrees of freedom in a linked, material-specific manner. In a molecular system where the crystal field symmetry differs from common inorganic hosts, this observation is especially informative because it connects the optical read-out channel to the local quadrupolar parameters that set the nuclear resonance.

The team tested coherent manipulation on the 21.5 MHz transition. Radio-frequency driving produced nuclear Rabi oscillations with a Rabi frequency of 14 kHz at 92 W, and the expected square-root dependence of Rabi frequency on RF power was observed. The damping of the oscillations reflected the inhomogeneous distribution of transition frequencies, which is precisely the kind of dephasing that pulsed NMR methods are designed to refocus. A Hahn-echo sequence extended the measurement from driven population oscillations to coherent spin evolution, giving a nuclear spin coherence time of 0.61 ms. Carr–Purcell–Meiboom–Gill dynamical decoupling then increased the observed coherence to 2.0 ms with eight refocusing pulses. The authors afterwards measured exponent, 0.53, differed from the value expected for a simple correlated noise bath of a single spin species. The authors attributed the more complex decoherence environment to a combination of nearby proton spins, randomly distributed 13C spins, possible residual paramagnetic impurities from the europium salt precursor, and quasi-localized low-frequency vibrational modes. The result is a coherent molecular nuclear spin system whose dephasing is not dominated by a single idealized noise source, but by the chemically and structurally specific environment of the molecular crystal.

The importance of the research work of Karlsruhe Institute of Technology scientists is its direct experimental connection between optical spectroscopy and coherent nuclear spin control in a molecular rare-earth complex. Previous molecular europium systems had already shown properties needed for optical nuclear spin access, but the present work completes a more demanding sequence: optical initialization, optically detected nuclear magnetic resonance, coherent RF-driven spin manipulation, spin echo refocusing, and dynamical decoupling. That combination establishes molecular Eu3+ nuclear spins as experimentally controllable quantum objects rather than only long-lived spectroscopic states. The findings also sharpen how molecular design should be viewed in this area. The ligand field is not a passive host environment surrounding an otherwise standard rare-earth ion. It determines the quadrupolar structure, influences the correlation between optical and RF transition frequencies, and contributes to the strain-sensitive inhomogeneous broadening observed across the optical line. Because the molecular complex has a defined coordination environment, these correlations can be treated as part of the material’s controllable physics. The paper therefore supports a design logic in which optical linewidth, nuclear quadrupole structure, spin lifetime, and spin-bath composition are considered together.

The coherence times reported here are measured in an ensemble molecular crystal at liquid-helium temperature, and the authors keep their future expectations tied to specific physical routes: stronger dynamical decoupling, lower temperature operation, magnetic-field polarization of paramagnetic impurities, suppression of low-frequency vibrational modes, isotopic or chemical purification, and ligand deuteration. These are not abstract claims of improvement; they follow from the dephasing sources identified in the measurements. The work also suggests that optically detected NMR in such complexes may become a sensitive probe of material properties, since optical and spin inhomogeneities carry linked information about strain and local crystal-field variation. For molecular quantum technologies, the result is technically meaningful because it brings together atomically defined molecular architecture with direct optical access to coherent nuclear spins. The demonstrated millisecond-scale nuclear coherence, optical spin preparation, and RF control form a platform on which more elaborate molecular spin registers could be explored, especially if future experiments move toward single-molecule read-out or nanophotonic integration.

 

 

Global Navigation Satellite System precise point positioning with ambiguity resolution (PPP-AR) relies on the accurate treatment of hardware-dependent code and carrier-phase delays originating from satellites and receivers. These delays vary across frequencies and signal channels and can destroy the integer properties of carrier-phase ambiguities if they are not properly corrected. Observable-specific bias (OSB) products address this problem by providing satellite- and signal-specific corrections for raw code and phase observations, enabling users to recover integer ambiguities and flexibly process observations from multiple frequencies and constellations. OSB products have therefore become a critical component of modern multi-GNSS PPP-AR services, with their quality directly affecting ambiguity estimation, validation, fixing, positioning convergence, and solution continuity. However, OSB products may contain discontinuities, abnormal fluctuations, missing data, and structured periodic variations arising from datum definitions, clock-reference conventions, satellite operations, and daily processing procedures. These characteristics are not always fully revealed by evaluating positioning accuracy alone.

Most previous OSB assessments have focused on PPP-AR performance, particularly positioning accuracy after ambiguity fixing. Although such tests demonstrate whether a product can support successful positioning, they provide limited insight into the intrinsic behavior of the bias series. An OSB product may produce acceptable positioning results over a short period while still containing day-boundary jumps, unstable intervals, or periodic variations that affect long-term processing and operational reliability. A more comprehensive assessment is therefore required to characterize the continuity, variability, internal consistency, and spectral behavior of OSB products and to support product screening, quality control, adaptive weighting, anomaly detection, and ambiguity recovery after data interruptions.

In a recently published paper in Advances in Space Research, Ge Ge, Zhetao Zhang, Haijun Yuan, and Huaqing Xu established a unified time-space-frequency framework for the comprehensive evaluation of code and phase OSB products. The framework moves beyond conventional positioning-based validation by examining approximately one year of rapid and final OSB series covering GPS, Galileo, BDS-2, and BDS-3. In the time domain, daily stability tests, box-plot distributions, and peak-to-peak variations are used to reveal discontinuities, fluctuations, and long-term stability. In the spatial domain, standard deviations and Pearson correlation coefficients characterize the dispersion and common variation patterns of OSB series across satellites and signals. In the frequency domain, fast Fourier transform analysis identifies periodic components and structured spectral signatures that cannot be readily distinguished through time-domain inspection alone.

Dr. Zhetao Zhang and his colleagues analyzed OSB products from day of year 060 in 2023 to day of year 060 in 2024. They found that most satellites showed high data availability, although interruptions remained in some series. Rather than smoothing out discontinuities caused by reference changes, daily reinitialization, and other practical processing operations, the research team retained these features so that the evaluated series could reflect actual operational behavior. Their results showed that code OSBs were generally more stable, with relatively limited peak-to-peak variations, whereas phase OSBs exhibited wider ranges, stronger fluctuations, and more visible discontinuities. Dr. Zhang and his colleagues also identified several satellite-specific variations, demonstrating that orbital maneuvers, signal characteristics, and processing events may introduce localized anomalies that require targeted monitoring rather than relying solely on product-wide quality indicators.

The spatial- and frequency-domain analyses conducted by Dr. Zhetao Zhang and his colleagues provided further insight into the internal behavior of OSB products. The team found that phase OSBs showed greater dispersion and more complex relationships than code OSBs. Code-bias series generally exhibited clearer common variation patterns, whereas phase-bias series showed weaker correlations and stronger satellite-, signal-, and processing-dependent characteristics. After reducing the influence of missing data through interpolation, the researchers also identified low-frequency draconitic patterns and periodic components associated with orbital resonance. Distinct spectral peaks appeared in some medium Earth orbit bias series, together with low-frequency harmonics. These findings demonstrate that OSB fluctuations are not purely random but may contain structured and physically meaningful periodic components. By revealing such hidden signatures, the work of Dr. Zhang and his colleagues enables monitoring systems to distinguish recurring behavior from isolated anomalies, abrupt product changes, or processing failures.

The findings of Dr. Zhetao Zhang and his colleagues have direct implications for the development of more reliable multi-GNSS PPP-AR services. Phase OSBs are essential for restoring the integer properties of carrier-phase ambiguities, and undetected jumps or unstable corrections may contaminate ambiguity estimates, delay successful fixing, trigger unnecessary reinitialization, or increase the risk of incorrect validation. The multi-domain indicators proposed by the research team provide complementary tools for addressing these risks: time-domain measures can detect jumps and unstable intervals before ambiguity fixing, spatial-domain measures can support satellite- and signal-specific weighting or screening, and frequency-domain characteristics can separate structured periodic behavior from abnormal events. Together, these capabilities provide a foundation for real-time OSB monitoring, adaptive stochastic modeling, ambiguity management, and automated quality control. Although the study focused on OSB product characteristics rather than directly quantifying positioning improvements, the framework developed by Dr. Zhang and his colleagues establishes a clear connection between product-level quality and PPP-AR performance. More stable, continuous, and well-characterized OSB corrections can improve ambiguity-estimation consistency, reduce unnecessary ambiguity resets, support faster recovery of fixed solutions, and ultimately contribute to shorter convergence times, higher ambiguity-fixing reliability, and more continuous centimeter-level positioning. Overall, the study transforms OSB assessment from a simple positioning-result check into a multi-domain product-quality diagnosis, providing an important methodological foundation for more intelligent OSB selection, monitoring, and adaptive use in next-generation multi-GNSS PPP-AR services.

Underwater optical imaging is difficult because light does not travel through water in a simple, direct way. As it passes through suspended particles, part of the light is weakened and part of it is redirected which creates backscattered illumination that can mask the signal from the object being imaged. When the image must reveal boundaries, surface markings, material differences, or quantitative radiometric information, this scattering changes the measured intensity and makes the true scene radiance harder to recover. Polarization is well suited to fix this limitation because underwater backscattering is partially linearly polarized and measurements taken through different analyzer orientations make it possible to extract Stokes parameters and use the degree and angle of linear polarization to help separate direct radiance from scattered light. Classical polarization-difference and Stokes-based descattering methods have already shown that this information can suppress haze more directly than intensity-only enhancement. The central difficulty is that the practical underwater scene rarely follows the clean assumptions that make a simple Stokes inversion stable. Orthogonal analyzer channels may not be balanced. Scattering may be anisotropic. Target surfaces may contribute their own polarization. Multiple scattering, illumination residuals, and sensor response can shift the measured polarization away from an idealized model.

In a recently published research paper in Optics and Lasers in Engineering Dr. Ziqian Chen, Dr. Junkai Wu, Dr. Haofeng Hu, and Professor Xiaobo Li from School of Marine Science and Technology at Tianjin University developed a polarization-guided Stokes descattering method for underwater images acquired from multiple analyzer orientations. The technically distinct element is the joint use of a scene-induced Stokes mixing weight, an effective polarized visibility factor, and an asymptotic airlight scaling parameter, all estimated automatically rather than manually selected. They also developed a DoLP-gated airlight estimation step to reduce foreground polarization leakage into the scattering estimate. The complete method combines physical radiance inversion with a two-stage genetic algorithm and sequential quadratic programming optimization driven by contrast and entropy.

The research team built the method around three analyzer measurements, acquired at 0, 45, and 90 degrees and instead of applying the conventional Stokes relations directly, they introduced a scene-induced mixing parameter to adjust the contribution of the 90-degree channel. This modification preserves the Stokes structure while allowing the measured polarization state to compensate for unequal energy partition caused by anisotropic scattering, target reflection, illumination residuals, alignment effects, or sensor sensitivity. This matters because orthogonal-channel imbalance can affect the polarization parameters and the airlight estimate.

Airlight estimation is handled through a background window selected by high mean degree of linear polarization, which favors regions dominated by coherent backscattering. From that region, the method estimates a representative angle of polarization and intensity scale. A polarized background scale is then obtained using a robust high-quantile statistic, reducing sensitivity to isolated strongly polarized pixels. The new approach also introduces an effective polarized visibility factor, which accounts for the fraction of polarized background actually observable in the measured channel. Since some objects may produce stronger or more heterogeneous polarization than the background scattering itself, the gate suppresses the tendency to assign target-induced polarization to the backscattering term and by reducing foreground leakage into the airlight estimate, the inversion can preserve material and boundary information. The asymptotic airlight scale is also treated adaptively, using a global scaling parameter tied to the representative background intensity.

Because the three central parameters cannot be measured directly, the study estimates them through unsupervised optimization. The objective combines edge contrast with image entropy, so that the restored radiance is encouraged to retain both structural sharpness and gray-level richness. A genetic algorithm first searches the physically admissible parameter space, and sequential quadratic programming then refines the solution. This two-stage strategy reflects the non-smooth, nonconvex nature of the pipeline, where quantiles, clamping, and positivity enforcement make a purely local search unreliable. Experiments in a controlled water tank used semi-skimmed milk to vary turbidity, polarized illumination, a monochrome camera, and objects with different polarization characteristics, including metallic, plastic, paper, and polarizer-film targets. Under moderate turbidity, the proposed method recovered clearer boundaries, stronger contrast, and more visible fine structure than the classical Stokes-based comparison. The distinction between crossed polarizer films was especially informative because it tested whether the restoration preserved polarization-dependent target differences, instead of simply increasing contrast.

Quantitative comparisons using enhancement measure estimation, entropy, and peak signal-to-noise ratio supported the visual observations. The authors found across selected regions and the full image, the proposed method generally produced higher contrast and fidelity measures than the raw images and the classical Stokes approach. Additional comparisons with intensity-only enhancement methods and other polarization-based or learning-based methods showed that the new method retained sharper edges and more uniform background recovery as turbidity increased. Deep learning methods degraded under stronger turbidity in the reported comparisons, which the paper relates to differences between training and testing conditions.

The team extended across milk concentrations from low to high turbidity and noticed as scattering increased, all methods became more challenged, but the proposed method maintained higher contrast and higher peak signal-to-noise values than the alternatives over much of the range. Tests on additional samples showed recovery of structural features in plastic and metallic coins and restoration of printed or surface details across paper, metal, wood, and plastic targets. The researchers also evaluated real seawater data acquired with polarization cameras under active lighting, where fish, coral, seaweed, and rock textures became clearer after restoration. A further comparison under polarized and non-polarized illumination indicated that the method can still operate when ordinary non-polarized lighting is used, although higher turbidity remains associated with reduced signal-to-noise ratio.

The findings of Professor Xiaobo Li  and colleagues have direct engineering relevance for underwater imaging systems that must operate in scattering environments where conventional intensity images lose contrast and structural detail. In ocean observation, inspection, and monitoring tasks, the main requirement is not simply to make an image look clearer, but to recover enough reliable target information for interpretation, identification, or downstream decision-making. The polarization-guided Stokes descattering method addresses this need by combining a physically based imaging model with automatic scene adaptation, allowing the restoration process to respond to changes in turbidity, illumination, and material-dependent polarization behavior. One important application is underwater robotic inspection. Remotely operated vehicles and autonomous underwater platforms often rely on cameras to examine submerged structures, seabed objects, marine organisms, and engineered equipment. In turbid water, backscattering can hide edges, surface markings, cracks, contours, or material boundaries. By improving texture visibility, target-background separation, and structural contrast, the proposed method could support more reliable visual inspection when the water column is not optically clear. The real seawater demonstrations are particularly relevant here because they show that the approach is not limited to a controlled tank environment. The new method is also useful for marine environmental monitoring and biological observation. Underwater scenes often contain low-polarization natural objects, such as fish, coral, rocks, and vegetation-like structures, whose details may be weakened by scattered light. The reported seawater results indicate that polarization-guided descattering can enhance contours and surface texture under practical imaging conditions. This can make visual records more informative for documenting habitats, tracking marine organisms, or supporting image-based ecological analysis. A further engineering implication concerns system design. The procedure can work with polarized measurements and was also tested under non-polarized illumination, suggesting that practical systems may not always require complex polarized lighting arrangements. The use of automatically optimized, physically interpretable parameters also reduces dependence on manual tuning when the imaging scene changes. For maritime security, underwater search, and target discrimination, the ability to preserve fine structures and distinguish objects with different polarization characteristics is valuable. The method’s treatment of scene-induced Stokes imbalance and DoLP-gated airlight estimation gives engineers a more adaptable restoration tool for visually degraded underwater environments.

Aerostatic bearings are widely used in precision motion systems because they support moving components on a thin externally pressurized air film rather than through direct mechanical contact.  In precision manufacturing equipment and high-accuracy measuring instruments, this mode of support is attractive because it can provide clean, smooth, and highly repeatable motion. Pressure must be generated and distributed in a controlled manner, the air film must sustain external load, and the flow introduced through the restrictors must not disturb the stability that the bearing is intended to provide. A conventional aerostatic flat bearing often uses pocketed orifice-type restrictors to feed high-pressure air into the clearance. This arrangement can improve static support, yet it also introduces a difficult fluid-dynamic problem near the inlet region. Air supplied through an orifice perpendicular to the guideway surface impinges on the working surface and then turns sharply as it enters the bearing film. This sudden change in direction is associated with local acceleration, pressure depression, vortex formation, and turbulence. They can contribute to self-excited micro-vibrations, reduce the effective high-pressure region, and influence both load-carrying capacity and stiffness.

It must meter the supplied air so that a supporting pressure field is formed, and it must do so without creating unstable local flow structures that disturb the air film. Previous efforts to improve aerostatic bearing stability have therefore examined the geometry of the orifice chamber, the size and arrangement of orifices, and the influence of recess configuration on vortex behavior and micro-vibration. These studies point to a common physical concern: the flow structure near the restrictor shapes both the local pressure distribution and the dynamic steadiness of the bearing. In a recently published research paper in International Journal of Precision Engineering and Manufacturing Mr. Dong Zhang, PhD candidate  Senyu Yang, Pengfei Cao PhD candidate, Lubin Wang & led by Professor Weishi Li from Hefei University of Technology developed a vortex-type restrictor for aerostatic flat bearings in which two guideway-parallel, tangential orifices drive rotational airflow inside a circular recess before the air enters the bearing clearance. They also developed paired clockwise and counterclockwise restrictor configurations to compensate the torque generated by the rotating recess flow.  They evaluated the new design through CFD modelling and validated experimentally against a pocketed orifice-type bearing with matched main structural parameters.

Briefly, the researchers evaluated how the vortex-type restrictor alters the internal flow field and the bearing response and compared a circular aerostatic bearing with four conventional pocketed orifice-type restrictors against two vortex-type bearing configurations. Both vortex configurations used paired clockwise and counterclockwise restrictors, because a single vortex-generating recess produces torque; arranging opposite vortex directions allows that torque to be compensated while maintaining a symmetric bearing layout.

The flow simulations used ANSYS-Fluent with a realizable k–ε turbulence model and non-equilibrium wall functions. Their choice of modelling aligned with the problem being studied: the restrictor creates rotating and separating flow inside a small recess, and the pressure and velocity gradients near the inlet region are central to the bearing’s dynamic behavior. The computational domain used bearing symmetry to reduce cost while retaining the relevant flow structure, and the researchers treated the air as an ideal gas under supply pressures from 0.4 to 0.6 MPa. They focused in their comparison on bearings with the same main structural parameters except for the restrictor, so that the consequences of changing inlet geometry could be isolated. The simulated pressure field separated the two designs clearly. In the pocketed orifice-type bearing, the authors found the maximum pressure concentrated near the orifice, followed by a pressure depression at the orifice outlet. On the other hand, in the vortex-type bearing, the recess showed a more uniformly distributed high-pressure region, without the sharp local peak and depression seen in the conventional design. The velocity comparison was equally important. In the conventional bearing, the airflow velocity increased abruptly from 26 m/s to 205 m/s near the orifice outlet, whereas the vortex-type bearing kept the recess velocity lower and reached a maximum of 43 m/s at the recess outlet. The design choice of using tangential orifices to generate a controlled recess vortex therefore had the scientific consequence of reducing sudden pressure and velocity changes before the flow entered the bearing film.

The team performed streamline analysis and noticed the pocketed orifice-type restrictor, the jet impinged on the working surface, changed direction abruptly, and produced multiple vortices that were carried away and dissipated by the main flow. In the vortex-type restrictor, the air rotated along the recess wall and then moved into the gap more smoothly. The simulations also showed that torque from a single vortex-type restrictor increased with supply pressure, from 1.24 Nm at 0.4 MPa to 1.90 Nm at 0.6 MPa, which explains why paired opposite vortex directions were built into the bearing configuration rather than treated as an afterthought.

The experimental program tested bearings with four pocketed orifice-type restrictors and four vortex-type restrictors. Tests were taken for load-carrying capacity, stiffness, flow behavior, and micro-vibration under different supply pressures, film thicknesses, recess diameters, recess depths, and orifice heights. The low film thickness region received particular attention because the study identifies it as the operating condition of practical concern in precision equipment. The static results confirmed the main numerical trend. Increasing the recess diameter of the vortex-type restrictor substantially improved load-carrying capacity, especially at low film thickness, and the bearing with a 2.0 mm recess diameter exceeded the pocketed orifice-type bearing. Stiffness also improved under the conditions where the film thickness was below 5 μm, with the maximum reported stiffness increase reaching 286.6% relative to the pocketed orifice-type bearing. Recess depth had a limited effect on load-carrying capacity but influenced stiffness, while orifice height produced almost overlapping curves, indicating little effect on the measured static behavior.

The team also conducted vibration measurements and found that with a 2.0 mm recess diameter, the vortex-type bearing reduced micro-vibration amplitude by more than 60% at film thicknesses of 5 to 6 μm compared with the pocketed orifice-type bearing. With a recess depth of 0.6 mm, the reduction exceeded 70% in the same low film thickness range. Orifice height again had little influence between 3 and 8 μm. No pneumatic hammer phenomenon was observed for either bearing type during testing. The experimental evidence therefore connects the altered recess flow, the reduction in pressure depression, and the improved low-clearance stability in a consistent way.

The findings of Professor Weishi Li and his research team have direct relevance for the design of aerostatic bearings used in high-precision manufacturing equipment and high-precision measuring instruments, where motion stability at very small film thicknesses is essential. The study shows that the restrictor geometry itself can be used as an engineering tool to improve these characteristics, rather than treating the restrictor only as a passive air-supply element. The vortex-type restrictor is especially applicable where self-excited micro-vibration limits the useful operating range of aerostatic flat bearings.  The proposed design changes the inlet condition so that air rotates inside the recess before entering the bearing clearance, producing a smoother transition into the film and reducing the flow instability associated with the conventional configuration. For precision equipment operating at low film thickness, the reported improvements are particularly important. The same design approach also improved static performance: increasing recess diameter enhanced load-carrying capacity, and stiffness increased substantially at film thicknesses below 5 μm. These results suggest that the restrictor can be tuned to support both stability and load performance in the narrow-clearance regime where precision machines often operate. The work also provides practical guidance for bearing design. Recess diameter appears to be the most influential geometric parameter for improving load capacity, stiffness, and vibration suppression, while orifice height has little effect over the tested range.  At the same time, the paper notes that the vortex-type bearing consumes more air because each restrictor contains two orifices. For engineering implementation, this means the design is most suitable where improved stability and stiffness justify the higher air consumption, particularly in precision motion platforms, measuring systems, and manufacturing devices requiring low-vibration noncontact support.

Waste management and carbon mitigation remain major environmental and societal challenges, and integrating them remains difficult. Solid waste produces a significant fraction of global greenhouse gas emissions, and their conventional treatment methods such as landfilling, incineration, or partial recycling displace rather than resolve underlying carbon flows. Landfills introduce long-term environmental liabilities through leachate and methane generation, whereas incineration recovers energy at the expense of releasing stored carbon back into the atmosphere. Even waste-to-energy systems do not eliminate the carbon burden but instead shift how it appears within the system. This structural limitation has motivated researchers to find new approaches that treat waste as a functional carbon resource.

Activated carbon is a porous material capable of selectively adsorbing CO₂ from gas streams, it is already embedded in industrial separation processes. Its synthesis from carbon-rich precursors such as biomass and municipal waste creates the possibility of a closed-loop pathway in which waste-derived carbon is reconfigured into a sorbent that actively removes CO₂ from flue gases. The appeal lies in coupling two otherwise separate systems: waste valorization and carbon capture. Still, that connection must be evaluated at the full process level. The production of activated carbon is itself energy-intensive, involving hydrothermal treatment, carbonization, and activation steps that generate both direct and indirect emissions. Electricity demand, chemical inputs such as potassium hydroxide, and thermal processing all contribute to the environmental footprint. Therefore, proper evaluation of the viability of waste-derived activated carbon requires the emissions incurred during production must be weighed against the CO₂ captured during use.

Previous studies have examined isolated components of this problem but what has been less clear is how these factors interact across different materials and processing strategies, especially when the end-use performance of the activated carbon is included. In a recent research paper published in Environmental Science & Technology, PhD student Beomhui Lee and Assistant Professor Jiajun He from the University of Illinois at Urbana−Champaign developed a new integrated method that combines experimental CO₂ adsorption data, thermodynamic process modeling, and life cycle and techno-economic analysis across multiple waste-derived feedstocks. They implemented this method within a VPSA carbon capture system to quantify both environmental and economic performance. The approach links material properties to system-level outcomes, providing a unified basis for comparing waste-derived activated carbons as CO₂ sorbents.

Beomhui Lee and Jiajun He evaluated six feedstocks—sawdust, jujun grass, Arundo donax, municipal solid waste, coconut shell, and palm kernel shell—each processed through routes tailored to their physical and chemical characteristics. They selected hydrothermal treatment for certain biomass-derived materials because it operates at lower temperatures and yields higher solid carbon fractions, while pyrolysis-based carbonization was applied to others such as municipal waste and shell-based feedstocks. Activation, whether chemical or physical, serves as the defining step in establishing the porous structure necessary for CO₂ adsorption.

The researchers used isotherm data to define working capacities within a vacuum pressure swing adsorption (VPSA) process and this linkage ensured that material performance translates into process behavior. A higher adsorption capacity does not remain an isolated material property—it reduces the required sorbent mass, alters equipment sizing, and affects both capital and operating costs.

Chemically activated carbons consistently have higher CO₂ uptake, but this advantage is offset by increased production costs. Potassium hydroxide emerges as a dominant contributor, because of its unit cost as well as the quantities required during activation. This relationship becomes especially evident in the minimum selling price (MSP), which ranges from approximately $3.63 to $7.97 per kilogram depending on feedstock and process, with chemically activated systems occupying the upper end of that spectrum.

The authors found that across all feedstocks, variable costs especially chemical inputs and electricity have the strongest influence on MSP,  and produced deviations of up to roughly ±33%, on the other hand, fixed capital costs have much less variability which suggests that improvements in economic performance are more likely to arise from material and process optimization than from capital cost reductions alone.

When Lee and He deployed the activated carbons in a VPSA system, they found the performance has capture costs ranging from approximately $42 to $91 per tonne of CO₂, depending on feedstock. These reported values align with reported ranges in the literature, but the variation within the dataset show an important coupling: adsorption capacity influences both system size and energy demand. Higher-performing sorbents reduce equipment requirements but may still incur energy penalties associated with regeneration, leading to a near-parallel scaling of capital and electricity costs across most cases.

Afterward, the authors performed environmental analysis  and observed production-phase emissions range from roughly 2.2 to 6.9 tonnes of CO₂-equivalent per tonne of activated carbon, with electricity consumption accounting for a substantial fraction of the total. Replacing grid electricity with renewable sources such as solar or wind reduces life cycle emissions by as much as 72%, indicating that the carbon intensity of the energy input can dominate the overall environmental profile.  Another important finding was when production and utilization were considered together. Once deployed in carbon capture, the activated carbons offset their production-related emissions within a matter of days—typically between one and four days depending on feedstock. This rapid offset reflects the relatively high daily capture rates achievable in the VPSA system, which, when sustained over longer periods, lead to substantial net CO₂ removal.

Chemical activation enhances adsorption capacity, although it is also associated with higher chemical demand and corresponding cost and emissions contributions. Physical activation, by contrast, lowers some of these inputs but is associated with lower capture efficiency in the systems examined. The choice between these routes cannot be resolved at the material level alone; it depends on how production, energy supply, and operating context interact. By integrating experimental adsorption data with thermodynamic modeling and life cycle accounting, Lee and He shift the evaluation from isolated material metrics to full-system performance. A material with superior adsorption properties may not yield the lowest cost or the smallest carbon footprint once production emissions are included. Conversely, a less efficient sorbent may still perform competitively if its production pathway is less resource-intensive.

Energy sourcing emerges as a critical lever. Because electricity consumption contributes substantially to production emissions, the transition from grid-based to renewable energy fundamentally alters the environmental balance. Under renewable scenarios, even chemically activated carbons—with their higher intrinsic costs—approach more favorable carbon profiles. This dependence suggests that the sustainability of waste-derived activated carbon is not fixed but contingent on broader energy system conditions.

The analysis also highlights the temporal dimension of carbon accounting. The rapid offset of production emissions during operation reframes the initial carbon cost of material synthesis. Rather than representing a long-term penalty, these emissions are effectively amortized over a short operational period. This dynamic becomes particularly relevant when considering large-scale deployment, where cumulative capture over extended lifetimes dominates the overall carbon balance.

At larger scales, the conversion of waste streams into activated carbon introduces a pathway that links material recovery with carbon mitigation. By redirecting carbon from waste into functional sorbents, the system simultaneously addresses waste accumulation and flue gas emissions. The magnitude of this effect, as indicated by scenario analysis across high-waste-generating regions, suggests that the approach is not simply incremental but structurally significant within the bounds examined.

Metal additive manufacturing is increasingly being examined for structural engineering use, where mechanical reliability depends on strength as well as repeatability, ductility, anisotropy, and compatibility with established constitutive descriptions. Selective laser melting is especially relevant for stainless steel components because it can produce geometrically complex parts through layer-by-layer melting of metallic powder. That manufacturing route, however, gives the material a process history very different from conventional forming. Each layer experiences rapid heating, melting, cooling, and solidification, and the final material response is shaped by the interaction of melt pool geometry, interlayer bonding, scan path, build orientation, and local defects. For constructional steel applications, these details cannot be treated as secondary manufacturing features; they become part of the material definition itself.

The main challenge is that SLM 316 L stainless steel does not have a single mechanical identity independent of how it is printed. Earlier studies had examined individual process variables such as laser power, scanning speed, scanning spacing, layer thickness, scanning strategy, specimen thickness, forming method, and printing angle. However, the available experimental basis remained limited when several practical parameters were considered together. This matters because structural design requires material models and design parameters that can represent the actual stress-strain response, not only isolated strength values obtained under one manufacturing condition. A stainless steel part printed at one angle or with one scanning strategy may satisfy strength expectations while showing a different fracture strain, strain-hardening behavior, or directional response from a part produced under another condition.

In a recent research paper published in Journal of Constructional Steel Research, Professor Zhi-Wei Shan from Southeast University working together with Professor Bing-Bing San, Dr. Fang Xu, and Dr. Wen-Hui Zhao from Hohai University developed an experimental dataset for SLM 316 L stainless steel tensile behavior across combined scanning strategies, specimen thicknesses, forming methods, and printing angles. They also evaluated modified two-stage Ramberg-Osgood constitutive descriptions against the measured stress-strain curves and identified the Gardner and Ashraf formulation as the preferred model for this material. They also identified suitable formulas for predicting strain-hardening exponents, ultimate stress, and ultimate strain in the tested material.

The researchers prepared 42 tensile specimens from 316 L stainless steel powder by selective laser melting, arranged across 21 groups with duplicate specimens to improve data reliability. Their experimental design included three scanning strategies, four specimen thicknesses, two forming methods, and three printing angles. The scanning strategies were bidirectional scanning, checkerboard scanning, and bidirectional scanning with 67° interlayer rotation. The forming routes distinguished directly printed specimens from specimens cut from rectangular plates, while the printing angle described the angle between the tensile loading direction and the laser beam reciprocation direction. This design choice mattered scientifically because it allowed the tensile response to be separated into manufacturing-related contributions rather than reduced to a single average material curve. The stress-strain behavior resembled that of conventional stainless steel in one important respect: the curves did not show a distinct yield plateau. However, the mechanical response was strongly shaped by printing direction and processing route. Across the tested specimens, elastic modulus, yield stress, ultimate stress, and fracture strain covered broad ranges, from 164 to 206.9 GPa, 370 to 532 MPa, 539 to 685 MPa, and 16.8% to 68.2%, respectively. These ranges make clear that SLM 316 L stainless steel cannot be described adequately by one nominal tensile value when the printing parameters vary.

The team scanning strategy had a marked effect on strength but a weaker effect on elastic modulus. They found that specimens printed with bidirectional scanning and 67° interlayer rotation showed higher yield and ultimate stresses than those printed with the other two scanning strategies, while their fracture strain was lower. The elastic modulus remained nearly insensitive to scanning strategy. Thickness produced a different pattern: yield stress and ultimate stress increased as specimen thickness increased, while elastic modulus and fracture strain for 4 mm and 5 mm specimens were broadly similar to those for 2 mm and 3 mm specimens. Forming method had little influence on elastic modulus, yield stress, and ultimate stress, but it affected fracture strain, with cut specimens being more susceptible to premature fracture because of internal and surface defects introduced or exposed by the cutting route.

The authors performed printing angle studies and showed the 45° specimens generally showed higher elastic modulus, yield stress, and ultimate stress than the 0° and 90° specimens, while fracture strain increased as the printing angle increased. The fracture observations were consistent with this mechanical trend. Specimens printed at 0° showed sudden fracture without obvious necking, whereas 90° specimens displayed better ductility and a clear necking phenomenon. The link between printing angle and ductility was interpreted through the relation between loading direction and interlayer shear direction: when the interlayer shear direction was parallel to the tensile loading direction, ductility was reduced; when it was perpendicular, ductility improved.

Afterwards, the researchers examined modified two-stage Ramberg-Osgood descriptions for the stress-strain response of SLM 316 L stainless steel. They observed the Gardner and Ashraf model matched the tested curves more across the full strain range than the Rasmussen formulation, particularly for 0° and 45° specimens, where the Rasmussen model tended to overpredict the strain-hardening stage. For material parameter prediction, the two-point formula based on σ0.05 and σ0.2 gave better accuracy for the first strain-hardening exponent, while the EN 1993-1-4 expression was more suitable for the second strain-hardening exponent. Existing formulas for ultimate stress also performed reasonably for SLM 316 L stainless steel, and the ultimate strain prediction remained conservative, partly because the material combined a high yield ratio with a strong printing-angle effect.

The findings of the study are directly relevant to civil and constructional steel applications where selective laser melting can produce complex stainless steel components, customized joints, and geometrically efficient elements whose performance depends on geometry, load direction, and fabrication route.   One important application is in the design of printed stainless steel connectors, nodes, brackets, and transition pieces for truss or cable-supported structures. Specimens printed at 45° achieved higher elastic modulus, yield stress, and ultimate stress than 0° and 90° specimens, while fracture strain increased with printing angle. This means that engineers can use build orientation as a design variable, not just a manufacturing convenience. When strength is the primary concern, a 45° orientation may be advantageous; when ductility and deformation capacity are more critical, the improved fracture strain at higher printing angles becomes important. The results also support process selection for load-bearing SLM stainless steel parts. The bidirectional scanning strategy with 67° interlayer rotation produced higher yield and ultimate stresses than the other scanning strategies, although with lower fracture strain. This has practical value for components where load-bearing resistance is prioritized while also clarifying the associated strength–ductility balance. Thickness effects are also useful for structural detailing, since yield and ultimate stresses increased as specimen thickness increased, whereas elastic modulus and fracture strain were less strongly altered across the tested range. The new work evaluates modified two-stage Ramberg-Osgood models and recommends the Gardner and Ashraf formulation for representing the stress-strain behavior of SLM 316 L stainless steel. This gives engineers a more reliable constitutive description for finite element analysis, nonlinear structural assessment, and performance-based design of printed stainless-steel elements.

In many modern engineered systems, the condition of one component affects the role, loading, or operating status of another component, so the system-level response to failure depends on structural relationships as much as on component reliability. Balanced systems represent a clear example of this type of dependency. Their defining requirement is that operating units must remain arranged in symmetric working positions. A failure in one unit therefore does not simply remove that unit from service; it also forces the corresponding unit in the symmetric position to stop operating so that the system remains balanced. This feature gives balanced systems a distinct reliability and maintenance structure. In a conventional multi-component system, corrective maintenance is usually framed around replacing or repairing the failed component. In a balanced system, maintenance planning must account for more than the failed component itself. A failed unit may create a standby unit on the opposite side, and these standby units may later be rearranged into symmetric positions to restore part of the system’s operating capacity. Replacement remains important, but it is no longer the only route to recovery.

The problem becomes broader when spare-parts availability is included. Balanced systems such as unmanned aerial vehicles may operate from distributed bases, while spare parts are supplied through a two-echelon network consisting of a central depot and multiple bases. If a base has insufficient inventory, replacement actions may be delayed or become more costly. Holding too many spare parts, however, increases inventory cost. The practical decision is therefore not only how to maintain the system after shocks occur, but also how to replenish spare parts so that maintenance actions remain feasible without excessive stock accumulation. Traditional maintenance and inventory models are really not designed for this coupled decision environment. Longitudinal transshipment from a depot to a base is commonly considered, but lateral transshipment among bases may also be valuable because nearby bases can provide faster support when local stock becomes low. At the same time, replacement time, rearrangement time, and order completion time may not follow memoryless distributions, which calls for a formulation beyond simpler Markovian assumptions. These features create a methodological gap: balanced-system maintenance, rearrangement, longitudinal replenishment, and lateral replenishment need to be optimized together under random shocks and general action times.

In a recently published research paper in Reliability Engineering & System Safety, Professor Jingjing Wang, Lingyun Luo, and Yuxue Jin from Qingdao University of Technology, working together with Professor Li Yang from Beihang University, addressed this problem through an integrated optimization framework for maintenance and spare-parts transshipment in balanced systems. The new model treats the base state as a joint description of working units, standby units, and spare-parts inventory, which allows maintenance and replenishment decisions to be optimized together. They also developed a semi-Markov decision process formulation and a modified value-iteration algorithm to handle general action times and compute optimal stationary policies. The technically distinct element is that balanced-system rearrangement and two-way spare-parts transshipment are optimized together, allowing maintenance recovery and spare-parts movement to be coordinated within a single long-run cost framework.

The researchers represented the setting through a base-level state model that links working units, standby units, and inventory level. This state definition is important because it ties the physical condition of the balanced systems directly to the spare-parts situation at the base. A maintenance decision can then depend not only on whether a component has failed, but also on whether standby units are available and whether sufficient inventory exists to support replacement. They represented environmental shocks as a homogeneous Poisson process. When a shock causes a unit failure, the corresponding symmetric unit stops working and becomes a cold standby unit. If two standby units become available, a rearrangement action can place them into symmetric positions and return them to operation. If a failed unit is detected at an inspection epoch and spare parts are available, a replacement action can restore the failed unit and its paired standby unit to service.  For inventory control, the authors combined a longitudinal order policy and a lateral order policy. The longitudinal policy follows an (_s1, S) structure, where a base orders from the depot when its inventory drops below the longitudinal order point and replenishes up to a maximum level. The lateral policy follows a (Q, _s2) structure, where a base receives a fixed quantity from other bases when its inventory falls below a lower lateral order point. The condition _s2 < _s1 reflects the operational logic that lateral transshipment is reserved for a more urgent inventory state, while depot replenishment covers the broader replenishment need.

Because the completion times of replacement, rearrangement, and ordering actions do not provide a simple Markov structure, the researchers used a semi-Markov decision process. They derived transition probabilities for cases in which no activity occurs, one action occurs, or a maintenance action and an order action occur together. Costs were also assigned at the state-action level, including inspection cost, holding cost, replacement cost, rearrangement cost, longitudinal order cost, lateral order cost, failure penalty, and revenue associated with dispatching spare parts from the tagged base to another base. The objective was to minimize the long-run average operation and maintenance cost rate while requiring the probability of normal operation to exceed a specified threshold.

To solve the model, the authors developed a modified value-iteration algorithm. The semi-Markov problem was transformed into an equivalent discrete-time decision problem through a data transformation based on expected sojourn times. They also accounted for reducible Markov chains by removing states not connected with the other states, allowing the algorithm to operate on an irreducible chain. This connects the mathematical formulation to a practical computable policy. The numerical example used a UAV setting with two UAVs at each base and six propellers per UAV. The depot supplied eleven bases, and the lateral dispatch probability for a tagged base was set from the number of other bases. Under the specified cost and time parameters, the modified value-iteration algorithm converged within a finite number of iterations.  The team compared between policies which gave them most direct operational finding and found with only longitudinal ordering, increasing the depot order point raised the average cost rate, although it improved normal operation probability. A low order point reduced cost but could fail to meet the operational probability requirement. When lateral transshipment was added, the model identified policies that lowered the average cost rate while maintaining or improving the probability of operation. Afterward, the authors conducted sensitivity which clarified how order costs and order times shift the optimal balance among replenishment frequency, inventory risk, and operating cost.

The findings of Professor Jingjing Wang et al. have direct engineering value for UAV fleets with symmetrically arranged propellers. In such systems, the failure of one unit can force its paired unit to stop operating, so maintenance planning cannot be limited to replacing the visibly failed component. The proposed framework helps engineers decide when failed units should be replaced, when standby units can be rearranged into useful symmetric positions, and when spare parts should be replenished through either depot supply or nearby bases. For UAV fleet operation, the model can support base-level spare-parts planning. A central depot may hold the main inventory, but individual bases still need enough propellers or equivalent components to respond quickly to environmental shocks. This allows a low-stock base to recover spare-part availability without relying only on the longer depot route. The new approach can also be applied to other balanced engineering systems, such as dual-tire assemblies, shock absorber arrangements, balance bikes, or mechanical platforms where paired components must remain operational in symmetric positions. In these cases, the framework offers a way to coordinate maintenance actions with inventory movement rather than treating them as separate management problems. From an operations perspective, the authors’ proposed method is useful for minimizing long-run maintenance and logistics cost while maintaining a required probability of normal operation. It provides engineers and fleet managers with a structured decision tool for selecting inventory thresholds, lateral transfer quantities, and maintenance actions under random shocks and uncertain action times.

Photonic integrated circuits have become central to the effort to move optical functions from discrete laboratory assemblies into compact, manufacturable chip-scale systems. Much of the strongest progress has occurred in the telecom band, where low propagation loss has enabled high-Q resonators, coherent optical synthesis, microwave generation, lidar architectures, and photonic processing. The shorter-wavelength region, extending from the violet through the visible and into the short near-infrared, presents a more difficult materials problem. As wavelength decreases, surface roughness becomes optically larger and Rayleigh scattering rises; at the same time, absorption becomes more severe as photon energy approaches the Urbach tail of common dielectric materials. These two loss channels are not merely inconvenient. They raise power requirements, degrade resonator performance, and constrain the use of integrated photonics in spectral regions needed for optical clocks, quantum systems, bioimaging, underwater communication, compact lidar, and atomic physics experiments. A useful platform would need to do several things at once. It would have to suppress scattering without distorting waveguide geometry, preserve broad spectral transparency, allow controlled dispersion for nonlinear photonics, and remain suitable for future integration with active or temperature-sensitive components. It would also need to support the physical mechanisms that make resonators useful beyond passive routing: high-Q optical storage, acoustic confinement, low thermorefractive noise, and stable laser feedback.   In a recent research paper published in Nature Journal, Postdoctoral fellow Dr. Hao-Jing Chen, graduate student Kellan Colburn, Peng Liu, Hongrui Yan, Hanfei Hou, Jinhao Ge, Jin-Yu Liu, Phineas Lehan, Qing-Xin Ji, Zhiquan Yuan,  Christopher Holmes, Dr. Henry Blauvelt & Professor Kerry Vahala from California Institute of Technology working together with Professor James Gates from University of Southampton and Professor Dirk Bouwmeester from Leiden University, developed a CMOS-foundry-compatible germano-silicate photonic integrated circuit platform using GeO2-doped silica cores on silicon wafers. The technically distinct element is the combination of fibre-like low material absorption, DUV-defined planar waveguides, ruthenium-assisted deep etching, and surface-tension reflow smoothing to produce ultrahigh-Q resonators from violet to telecom wavelengths. They also showed that the same platform can support dispersion-engineered soliton generation, optical–acoustic confinement for Brillouin lasing, and large-mode-area resonators for low-noise self-injection-locked lasers.

 The researchers developed a germano-silicate photonic integrated circuit platform in which GeO2 doping raises the refractive index of the core relative to silica cladding, allowing optical confinement in a material family closely related to optical fibre. The fabrication route used plasma-enhanced chemical vapour deposition to form a 4-μm-thick germano-silica layer with 25 mol% GeO2 on thermal oxide, followed by ruthenium and silica hard masking, deep-ultraviolet stepper lithography, and inductively coupled plasma etching. The ruthenium mask was important because its selectivity enabled deep, high-fidelity etching of germano-silica. A standard furnace anneal then exploited the low-viscosity reflow behavior of Ge-silica, smoothing etched sidewalls through surface tension while leaving the thermal oxide substrate essentially unaffected. This material feature has a direct scientific consequence: by reducing roughness-induced scattering, the platform addresses one of the major loss mechanisms that becomes increasingly severe at visible wavelengths.

The authors evaluated performance through microring resonators across a wide spectral span. Air-cladded 3-mm-diameter rings were used to avoid substrate leakage and bending loss during measurement. Using tapered-fibre coupling and calibrated tunable lasers, the team measured intrinsic Q factors from 458 nm to 1,550 nm. The resonators exceeded Q values of 180 million across this full range, reaching 463 million at 1,064 nm, corresponding to a waveguide loss of 0.08 dB m−1. At 458 nm, the measured loss was 0.49 dB m−1, reported as a 13-dB improvement over previous integrated-platform records in that wavelength region. The annealed loss values remained below 1 dB m−1 from the violet to the telecom band, which is the central experimental evidence that the platform can carry fibre-like material advantages into a planar chip format. The fabrication results also included an important anneal-free case. Even without reflow smoothing, air-clad resonators reached nearly 200 million Q and a lowest loss of 0.15 dB m−1 at 1,550 nm. The study emphasizes this because many active materials and heterogeneous integration schemes cannot tolerate high-temperature post-processing. In that sense, the anneal-free result is not a side observation; it changes how the platform can be considered for integrated systems that combine passive ultralow-loss routing with III–V materials, organic photonics, thin-film lithium niobate, quartz substrates, or germanium-on-silicon photodetectors.

The device demonstrations then tested whether low loss could coexist with functional photonic behavior. For soliton microcomb generation, the researchers designed a single Ge-silica microring with anomalous dispersion and single-mode transmission. Characterization of the mode family between 1,520 nm and 1,630 nm showed no observable distortion from mode crossings, and soliton triggering produced a spectrum with a sech2 envelope. The repetition rate was near 21.2 GHz, with electrical spectrum analysis supporting pulse-stream stability. For stimulated Brillouin scattering, the platform used the lower longitudinal acoustic velocity of Ge-silica relative to silica to confine both optical and acoustic modes. A 25-mm waveguide with a 4 μm × 6 μm Ge-silica core and thick silica claddings showed a measured SBS gain spectrum that agreed with simulation, with a gain peak at 9.55 GHz and a mechanical quality factor of about 210. Integrated resonators then produced a Brillouin laser with a 9.68 GHz frequency shift and a coherent microwave beatnote. A third demonstration addressed thermorefractive noise in self-injection-locked lasers. The large mode area possible in Ge-silica reduced simulated thermorefractive noise compared with low- and high-confinement silicon nitride resonators of the same diameter. Experimentally, a C-band distributed-feedback laser coupled to a Ge-silica resonator with Q above 100 million showed a 46-dB frequency-noise reduction under self-injection locking and reached a Hz-level fundamental linewidth. The same stabilization concept was extended into the visible using Fabry–Pérot diode lasers locked to high-Q microrings, yielding fundamental linewidths of 15 Hz at 632 nm, 12 Hz at 512 nm, and 90 Hz at 444 nm.

The engineering applications of Professor Kerry Vahala and colleagues are strongest in visible and short-near-infrared integrated photonics, where low loss has been a persistent barrier to compact system design. By achieving ultrahigh-Q germano-silicate resonators from violet to telecom wavelengths, the platform can support chip-scale optical systems that need stable, low-noise, wavelength-specific light in spectral regions that are difficult for conventional integrated platforms. Optical clocks, quantum sensors, quantum computing and networks, atom and ion control, bioimaging, astronomical observation, underwater communication, data-centre links, compact lidar, and atomic physics instruments are all directly aligned with the wavelength range identified in the new work. The practical engineering value is not simply that light can be guided at these wavelengths, but that it can be guided with very low propagation loss, reducing optical power requirements and preserving resonator performance. This matters for miniaturizing systems that currently rely on larger fibre- or free-space optical assemblies. The authors’ schematic concept of combining III–V lasers, germano-silicate resonators, lithium niobate electro-optic modulators, and grating couplers points to integrated visible photonic modules in which light generation, stabilization, modulation, routing, and delivery could be assembled on or near the same chip. The anneal-free ultralow-loss result is also important for engineering, because it makes the platform more compatible with temperature-sensitive active materials, including III–V devices, organic photonics, thin-film lithium niobate, quartz-based substrates, and germanium-on-silicon photodetectors.

The device demonstrations point to more specialized applications in frequency synthesis, precision navigation, microwave photonics, sensing, and low-noise laser engineering. Dispersion-engineered single-ring soliton microcombs could be useful for compact optical frequency comb sources, coherent ranging, portable precision clocks, and photonic systems that require stable multi-wavelength output from a small footprint. The stimulated Brillouin lasing demonstration is especially relevant to chip-scale gyroscopes, integrated microwave photonics, and temperature or strain sensing, because the platform combines ultralow optical loss with optical and acoustic mode confinement. In practical terms, that means the waveguide is not only a passive low-loss channel; it can mediate coherent photon–phonon interactions useful for narrowband signal generation and sensing. The large-mode-area resonators are equally important for low-noise lasers: by reducing thermorefractive noise and enabling self-injection locking of diode lasers, the platform supports Hz-level linewidth operation in the telecom and visible bands. That capability is directly relevant to metrology, coherent optical communication, quantum control, and instrumentation where laser phase noise limits measurement precision. The study also notes possible future use in solid-state gyroscopes, advanced frequency comb systems for portable clocks, large-scale low-loss quantum circuits, high-power amplifiers, and mode-locked lasers if deposition and fabrication continue to improve toward the material-loss limit.

Electric field concentration at nanometer-scale metal edges drives charge carriers into narrow current paths, producing localized current spikes that destabilize organic semiconductor junctions when device dimensions shrink below the wavelength of emitted light. Such behavior becomes unavoidable once conventional organic light-emitting diode architectures approach the submicrometer regime. Organic semiconductors tolerate large exciton binding energies and operate efficiently in multilayer vertical stacks, properties that historically allowed steady downscaling of OLED pixels for display technologies. Yet the physical processes governing charge injection and recombination change markedly when electrode dimensions contract to a few hundred nanometers. Sharp electrode contours intensify the electric field locally, distort the effective injection barriers, and alter the balance of charge transport across the organic layers. Current filaments can form at these locations, destabilizing the junction and frequently triggering irreversible breakdown.  The problem grows acute when pixel densities exceed several thousand pixels per inch, a threshold already pursued in near-eye display technologies where visual artifacts arise from coarse pixel spacing. Conventional micro-OLED structures typically maintain lateral dimensions in the micrometer range, partly because smaller geometries encounter electrical irregularities that degrade performance. Organic semiconductors complicate this scaling effort in another way: their relatively low charge carrier mobilities make them particularly sensitive to variations in injection pathways. Once the injection process concentrates at nanoscale edge defects, transport across the device ceases to remain uniform. The recombination zone shifts unpredictably, and device behavior becomes dominated by uncontrolled conduction paths. Optical constraints emerge simultaneously. The emitted power of a pixel decreases approximately with the square of the ratio between its lateral dimension and the optical wavelength. Once pixel dimensions fall well below the emission wavelength, radiative efficiency declines sharply unless some mechanism redirects or concentrates the generated optical modes. Plasmonic structures offer one possible route. Metallic nanoantennas can couple excitonic emission into radiative modes that propagate into free space. Previous attempts integrated such structures into organic devices, yet these configurations usually relied on lateral device geometries that sacrificed the advantages of established multilayer OLED stacks.

A recent research paper published in Science Advances and conducted by Dr. Cheng Zhang, Dr. Björn Ewald, Dr. Leo Siebigs, Dr. Luca Steinbrecher, Dr. Dr. Maximilian Rödel, Dr. Thomas Fleischmann, Dr. Monika Emmerling, Professor Jens Pflaum, and led by Professor Bert Hecht from the University of Würzburg in Germany, the researchers developed a vertically stacked OLED architecture incorporating gold nanoelectrodes whose edges are insulated while a central nanoaperture defines the charge injection site. This geometry confines carrier injection to a region with uniform electric field distribution, preventing filament formation common in nanoscale electrodes. Integrated plasmonic patch antennas couple excitonic emission from the organic layer into radiative optical modes. The resulting system produces individually addressable OLED pixels with lateral dimensions of 300 nanometers.

Briefly, the research team first examined whether nanoscale gold electrodes could function as reliable charge-injecting contacts when carefully engineered. Electrostatic simulations performed by the investigators revealed a pronounced amplification of the electric field along the edges and corners of square nanoelectrodes, reaching several times the field strength present at the electrode center. Those gradients provided a clear explanation for the erratic behavior commonly reported in nanoscale organic junctions. The researchers addressed this problem by covering the electrode with an insulating hydrogen silsesquioxane layer while leaving a small central opening that exposed only the flat interior region of the metal surface. Through this geometry, charge carriers entered the organic layers exclusively through the nanoaperture, eliminating the high-field injection sites located at the electrode perimeter.  The investigators fabricated these structures using sequential electron-beam lithography steps that defined the gold patch electrodes and then patterned the insulating layer with a controlled gradient exposure. Development of the resist produced a nanoscale aperture positioned at the electrode center. Conductive atomic force microscopy measurements confirmed that electrical current flowed only through the exposed aperture, verifying that the insulating layer effectively blocked the edges. To verify the electrical characteristics of the concept before introducing light emission, the authors constructed hole-only junctions. The device stack incorporated a gold bottom electrode, an ultrathin HAT-CN interfacial layer that promoted hole injection, and an NPB organic transport layer. Measurements comparing nanojunctions with conventional macrojunctions revealed remarkably similar current density levels despite the enormous difference in device area. The research group fitted the electrical behavior using a space-charge-limited current model combined with Poole–Frenkel transport, obtaining hole mobility values consistent with established literature data. Interestingly, the nanoscale junction displayed slightly higher mobility parameters, an observation attributed to the smaller number of trap states present within the minute active volume of the device.

A more revealing comparison emerged when the investigators tested electrodes lacking the insulating aperture. Under repeated voltage cycling those structures displayed abrupt jumps in current, behavior consistent with the formation and rupture of metallic filaments driven by the concentrated electric fields at the electrode edges. Devices containing the nanoaperture remained stable throughout the same tests and exhibited only minor hysteresis during operation. Long-duration measurements under constant voltage reinforced the difference: electrodes without edge passivation failed within minutes, whereas the nanoaperture structures continued operating throughout the full measurement period. Having established stable charge injection, the study advanced to full light-emitting devices. The researchers fabricated vertically stacked nano-OLED pixels measuring 300 by 300 nanometers. Organic layers included a hole-transport region, a thermally activated delayed fluorescence emissive layer, and an electron-transport region, followed by a metal cathode. The gold patch electrode simultaneously acted as a plasmonic antenna. When voltage was applied, excitons formed in the emissive layer and coupled to resonant plasmonic modes supported by the patch antenna beneath the nanoaperture. The research team recorded electroluminescence beginning at approximately five volts and measured external quantum efficiencies approaching one percent. Even at this extreme scale the pixels reached luminance levels around three thousand candela per square meter and switched rapidly enough to exceed video refresh rates. Those observations demonstrated that the stabilized injection geometry preserved balanced charge transport within the multilayer stack while enabling nanoscale optical emission.

To summarize, miniaturization of optoelectronic devices frequently encounters limits that originate from electric field distributions rather than material properties alone. The new work of Professor Bert Hecht and colleagues illustrates how geometric control of the injection interface can redefine those limits. When a nanoelectrode injects carriers uniformly across its central region while the high-field edges remain electrically inactive, the organic semiconductor experiences a nearly planar injection boundary even though the electrode itself remains nanoscale. That geometric intervention changes the physical origin of device instability. Filament formation becomes improbable because the localized field maxima responsible for initiating metallic migration never participate in the conduction path. Such stabilization alters how nanoscale OLED architectures can be designed. Conventional scaling strategies usually attempt to preserve the same layered device structure while shrinking the lateral dimensions. The Würzburg study demonstrates that the injection interface must evolve simultaneously with device size. By confining charge injection to a defined nanoscale aperture, the recombination zone becomes spatially predictable. Excitons form above the aperture and interact consistently with the surrounding optical environment. In the present device that environment includes a plasmonic gold patch antenna, which converts localized excitonic energy into radiative optical modes that propagate through the substrate.

 When emitters couple to resonant antenna modes, the spectral distribution and radiation pattern of the emitted light depend strongly on the geometry of the metal structure. Electromagnetic simulations performed by the research group indicated that vertical and horizontal dipole orientations excite distinct antenna modes, with the dominant resonance occurring near 650 nanometers. Experimental spectra matched the simulated convolution of the molecular emission profile with the antenna outcoupling efficiency, demonstrating that the antenna modes shape the final emission spectrum. This spectral reshaping is not merely an aesthetic effect. It implies that nanoscale OLED pixels could be engineered to tailor their emission profiles through antenna geometry alone, without altering the molecular emitter. Practical implications extend beyond display technology. Individually addressable emitters with dimensions far below the optical wavelength open possibilities for on-chip photonic circuits, nanoscale sensing platforms, and spatially structured optical sources. Integration density becomes a central parameter in those contexts. The devices demonstrated here already operate at pixel dimensions that approach theoretical limits for OLED scaling. Future improvements will likely depend on refinements of the organic stack and antenna geometry. The present prototype exhibits some imbalance between electron and hole transport, leading to charge accumulation at higher voltages. Incorporating doped transport layers and optimized confinement structures—techniques widely used in commercial OLED engineering—should reduce operating voltages and increase efficiency. Scaling to extremely dense pixel arrays introduces additional design constraints. Neighboring antennas may interact optically or electrically if their spacing becomes too small. Any practical implementation must coordinate lithographic patterning, organic layer design, and antenna resonance tuning. Success in that direction could produce emissive arrays exceeding ten thousand pixels per inch, densities appropriate for emerging light-field displays and integrated photonic systems.

RNA stem-loop folding is the process by which a single RNA strand bends back and pairs with itself to produce a short double-helical stem capped by an unpaired loop. It is one of the basic structural events that gives RNA its shape and much of its functional behavior. Complementary bases that are separated along the sequence have to find one another, pair in the correct register, and do so without forcing the intervening nucleotides into an unfavorable geometry. The unpaired segment connects the two sides of the stem and also affects how easily the structure forms, how stable it remains, and how readily it can reorganize. RNA function depends on its sequence, and also on what parts of the chain become paired, which bases stay exposed, how long a given structure survives, and how flexibly it can shift in response to proteins, ligands, ions, or changes in the cellular environment. Stem-loops appear throughout RNA biology. They are found in messenger RNAs, viral RNAs, ribozymes, riboswitches, and many regulatory noncoding RNAs. Sometimes they help protect a region from degradation. Sometimes they control translation or create a recognition surface for a protein. In larger RNAs, they often act as local organizing elements from which more complex structures can grow.

For that reason, stem-loop folding has drawn so much attention in simulation studies. These motifs are small enough to examine in atomic detail, but they are not simple in a physical sense. A model has to reproduce the balance among base pairing, stacking, backbone geometry, and electrostatic interactions well enough for the structure to emerge for the right reasons. That is what makes RNA stem-loop folding scientifically useful: it is both a real biological process and a demanding test of whether current molecular models are actually capturing how RNA structures form. For molecular dynamics, this makes stem-loops useful but rather unforgiving test cases. The stem mainly reports on the balance between base pairing and stacking, whereas the loop tests backbone geometry, noncanonical contacts, and local solvation effects. If stacking is too strong, misfolded compact structures may look artificially stable. If electrostatics or solvent response are treated too coarsely, loop and bulge geometries can move away from the experimental ensemble. Starting from extended chains therefore asks more than whether a model can preserve a known structure. It asks whether the simulation can recover, at least in part, the physical path by which an RNA fold comes into being.

In a recent research paper published in ACS Omega, Professor Tadashi Ando from the Tokyo University of Science examined whether conventional molecular dynamics could fold RNA stem-loops from extended conformations using the DESRES-RNA force field and GB-neck2 implicit solvent. The simulations recovered native stem pairing in all simple stem-loops and in five of eight more complex models. The main technical advance is a benchmark that separates reliable stem-folding behavior from the remaining difficulty of loop and bulge modeling. Briefly, Professor Tadashi Ando performed de novo folding simulations on 26 RNA stem-loops, ranging from 10 to 36 nucleotides, including 18 simple stem-loops and eight structures containing bulges or internal loops. The investigators used conventional molecular dynamics at 298 K, with three independent trajectories for each model, and assessed folding through native base-pair recovery, RMSD values, clustering behavior, and comparison with experimentally determined NMR structures.

For the 18 stem-loops without bulges or internal loops, the authors observed folding into structures retaining all native stem base pairs. Most models reached stem-region RMSD values below 2 Å and whole-molecule RMSD values below 5 Å. The stems behaved as the most reliable structural element: once the correct base-pairing pattern formed, many trajectories maintained the folded state. The loop regions, however, remained less accurately described, with loop RMSD values near 4 Å in many cases. That separation between stem accuracy and loop imperfection is scientifically useful, because it identifies where the force-field and solvent approximation are working well and where local RNA chemistry remains more difficult to reproduce. For the eight stem-loops with bulges or internal loops, the researcher obtained complete native stem pairing in five cases. These more complex molecules often folded through a local route in which the stem adjoining the hairpin loop formed before the more terminal duplex region. The study also showed that several more difficult models sampled misaligned base-pairing arrangements. That behavior is scientifically informative because it reflects the kinetic cost of allowing nonnative contacts to become too stable in a reduced-solvent model.

Professor Tadashi Ando’s work demonstrated that stem formation, at least for many small RNA motifs, can now be recovered from extended conformations with impressive structural fidelity under a computationally efficient implicit-solvent protocol. Loop and bulge modeling still requires caution, especially when noncanonical hydrogen bonds, local base orientation, and solvent-specific contacts determine the experimental structure. These findings are important in RNA biology because many functional RNA interactions depend on single-stranded or partially paired regions, not only on ideal duplex stems. Riboswitches, RNA-protein interfaces, kissing-loop contacts, and ligand-binding pockets all place heavy demands on loop and bulge accuracy. Ando’s study therefore provides a practical benchmark for future simulations: success should be evaluated by whether the model can preserve the local chemistry that makes an RNA motif biologically recognizable. Another implication of the research work is that the DESRES-RNA and GB-neck2 combination which may be useful for exploring broad conformational searches, early folding events, and stem organization in RNA systems where explicit solvent sampling remains expensive. For detailed loop chemistry, explicit solvent treatment or further parameter refinement may still be needed.

 

Ultraviolet-C (UV-C) photonics occupies a distinctive yet historically constrained niche within modern optical science. Spanning wavelengths from 100 to 280 nm, this spectral region enables interactions with matter that are fundamentally inaccessible at longer wavelengths, including strong electronic absorption, bond-specific photochemistry, and nanoscale spatial resolution. These properties underpin applications ranging from sterilization and lithography to ultrafast spectroscopy and non-line-of-sight optical communication. Yet, despite decades of progress in ultrafast optics, UV-C photonics has remained technologically fragmented. The generation and detection of coherent, femtosecond UV-C light have typically evolved along separate and often incompatible trajectories, limiting system-level integration and real-world deployment. The core challenge arises from materials and device constraints at both ends of the photonic chain. On the source side, compact and efficient UV-C lasers remain rare. Excimer lasers, while powerful, are bulky, energy-intensive, and poorly suited to high-repetition-rate ultrafast operation. Semiconductor-based emitters, including AlGaN devices, remain limited by low output power and manufacturing immaturity. Nonlinear frequency conversion from near-infrared femtosecond lasers offers an elegant alternative, yet only a narrow set of nonlinear crystals can support phase-matched processes in the UV-C, and their efficiency is tightly constrained by group-velocity mismatch, absorption, and thermal effects. Detection presents an equally formidable barrier. Conventional UV-C detectors such as photomultiplier tubes and silicon photodiodes either lack temporal resolution, require high operating voltages, or suffer from poor compatibility with scalable integration. Recent advances in two-dimensional semiconductors have opened promising avenues, particularly for wide-bandgap materials capable of room-temperature operation. However, most prior demonstrations rely on continuous-wave illumination, exfoliated flakes, or slow photo-gain mechanisms that obscure true ultrafast response. As a result, the ability to directly sense femtosecond UV-C pulses across a wide dynamic range remains largely unexplored. To this end, new research paper published in Light and conducted by Benjamin  Dewes, Tim Klee, Nathan Cottam, Joseph Broughton, Mustaqeem Shiffa, Tin Cheng, Sergei Novikov, Oleg Makarovsky, & Professor Amalia Patané from the University of Nottingham in collaboration with Professor John Tisch from the Imperial College of London, the researchers developed an integrated femtosecond UV-C photonic platform that combines high-efficiency cascaded harmonic generation with scalable two-dimensional semiconductor detectors. They demonstrated room-temperature detection of femtosecond UV-C pulses with both linear and super-linear photoresponse, depending on material architecture. Crucially, the work reveals new ultrafast carrier dynamics in GaSe and Ga₂O₃ heterostructures that are inaccessible under continuous-wave excitation.

The research team generated femtosecond UV-C pulses via cascaded second-order nonlinear processes and probing their interaction with two-dimensional semiconductor detectors under realistic operating conditions. A near-infrared ytterbium-based femtosecond laser served as the fundamental source, delivering sub-300 fs pulses with adjustable repetition rates extending to tens of kilohertz. These pulses were first frequency-doubled in a bismuth triborate crystal to produce visible light, which was subsequently doubled again in beta-barium borate to yield fourth-harmonic radiation at 256 nm. Careful selection of crystal thickness, phase-matching geometry, and spacing allowed the authors to suppress back-conversion and temporal walk-off, achieving an unusually high conversion efficiency approaching 20 % from the near-infrared to the UV-C regime. The authors confirmed temporal characterization and that the UV-C pulses preserved femtosecond duration, with cross-correlation measurements which showed pulse widths near 240 fs. Spatial profiling showed a near-Gaussian beam matched to the active area of the detectors, ensuring uniform excitation without localized damage. Importantly, the UV-C pulse energy could be continuously tuned from sub-nanojoule to microjoule levels, enabling systematic exploration of detector response across several orders of magnitude. They also examined two complementary material systems: Gallium selenide layers grown by molecular beam epitaxy exhibited exceptionally strong UV-C absorption, with only the top few nanometers participating in carrier generation due to the short absorption length. Interdigitated gold contacts formed planar metal–semiconductor–metal devices that operated reliably at room temperature. Under femtosecond excitation, these GaSe detectors produced sharp electrical pulses whose integrated charge scaled linearly with incident pulse energy. This linearity persisted across a wide range of repetition rates until limited by the RC time constant of the measurement circuit, demonstrating genuine ultrafast detection rather than slow photo-gain effects. The team found when GaSe was intentionally oxidized to form ultrathin β-Ga₂O₃ layers on graphene-terminated silicon carbide. These heterostructures retained low dark current and spectral selectivity in the UV-C, yet displayed a super-linear photocurrent response to pulse energy and average power. Rather than saturating at high excitation levels, the responsivity increased, revealing a non-intuitive amplification mechanism. Analysis ruled out multiphoton absorption at the employed intensities and instead pointed toward power-dependent occupation of defect states and photo-thermionic carrier injection at the graphene interface. The temporal evolution of the signal further suggested dynamic filling of recombination centers, effectively extending carrier lifetimes under intense pulsed illumination.

In conclusion, the research work of Professor Amalia Patané  and her colleagues establishes a practical pathway toward compact, high-speed UV-C photonic systems and indeed developed for the first time, a fully integrated platform capable of generating and sensing UV-C laser pulses on femtosecond timescales. Moreover, the study establishes a foundation for UV-C systems that are no longer confined to laboratory curiosities by showing that compact nonlinear sources and two-dimensional semiconductor detectors can operate coherently within the same ultrafast regime.

Additionally, the observation of linear and super-linear photoresponse under femtosecond excitation challenges conventional assumptions about UV detector behavior. In most photodetectors, increasing optical power leads to recombination-dominated saturation and declining efficiency. Here, the opposite trend is observed in Ga₂O₃-based heterostructures, suggesting that ultrafast excitation accesses carrier dynamics that are invisible under continuous-wave illumination. The implication is profound: detector performance can be enhanced, rather than degraded, by operating in regimes of high peak power but low average heating, a paradigm well-suited to modern ultrafast lasers. Technologically, the use of scalable growth techniques and planar device architectures positions this platform for practical adoption. Unlike photomultiplier tubes or exotic vacuum-based sensors, these detectors function at room temperature, at low bias, and on technologically relevant substrates. The nonlinear source, while high-performance, relies on established crystals and commercially available femtosecond lasers, making miniaturization and ruggedization plausible. Together, these attributes lower the barrier to deploying UV-C photonics beyond specialized research environments. The demonstration of free-space UV-C communication underscores the broader impact of this integration. UV-C wavelengths offer inherent advantages for secure and non-line-of-sight transmission due to strong atmospheric scattering and low background noise. When combined with femtosecond pulse encoding and fast detectors, this opens new possibilities for short-range communication between autonomous systems, robotic platforms, and sensing networks operating in cluttered or hostile environments. We believe the new platform invites reconsideration of how ultraviolet light is used in ultrafast science and applications such as time-resolved spectroscopy, surface chemistry, and nanoscale imaging stand to benefit from reliable femtosecond UV-C sources paired with detectors that faithfully capture pulse-to-pulse dynamics. The work of the British scientists also points toward future device concepts, including monolithically integrated source-sensor chips and engineered heterostructures that exploit defect physics for tailored photoresponse.

FIGURE: Image of GaSe grown by MBE on a 2 inch sapphire wafer. Credit: Light: Science, 2025; 14 (1) DOI: 10.1038/s41377-025-02042-2.