Under ambient conditions, equiatomic zinc pnictides do not naturally form a free-standing monolayer whose atomic network remains both low in energy and resistant to distortion. That difficulty has kept ZnAs, ZnSb, and ZnBi in an uncertain position within the search for useful two-dimensional semiconductors: the bulk compounds already display unusual bonding, with electron-poor valence counts and multicenter connectivity, yet dimensional reduction has not produced a convincingly stable pristine sheet. For ZnSb in particular, prior interest came partly from thermoelectric behavior tied to low lattice thermal conductivity and anisotropic transport, while ZnAs added a related but not identical electronic character through its larger gap and different transport response. ZnBi complicates the family further, because even the bulk phase carries weaker energetic preference at zero temperature and pressure. If the bonding motifs that stabilize the orthorhombic bulk can survive exfoliation in some altered geometric form, one might obtain a two-dimensional phase with electronic behavior very different from the parent crystals. If those motifs cannot survive, the structure falls into the familiar pattern of hypothetical sheets that look plausible until phonons or relaxation break the idea apart.

The motivation here goes beyond the general interest in atomically thin semiconductors. The orthorhombic ZnX (X = As, Sb, Bi) compounds contain quasi-layered rhomboid Zn₂X₂ units embedded in a non-van-der-Waals 3D bulk framework. A bulk crystal without classic layered cleavage does not exclude monolayer design; it simply removes the comfort of obvious exfoliation routes and forces the structural problem back onto bonding topology. In a recent research paper published in ACS Omega, Assistant Professor Dinesh Thapa from Thomas More University working together with Professor Seong-Gon Kim from the Mississippi State University, developed a lattice-engineering framework for deriving and comparing six candidate monolayer structures of ZnAs, ZnSb, and ZnBi extracting from different phases of 3D bulk structures of ZnX using density functional theory (DFT) under periodic boundary conditions. They identified a rectangular 2D-L1 sheet built from relaxed Zn₂X₂ rhomboid units as the lowest-energy and dynamically stable monolayer across the series at zero strain.

The research team examined six monolayer candidates for each compound: the atomic configurations of three sheets obtained from the orthorhombic bulk and labeled L1, L2, and L3, alongside tetragonal, hexagonal (planar honeycomb), and trigonal (puckered honeycomb) symmetries. The investigators relaxed both atomic positions and lattice vectors for every candidate, and this symmetry design is important because fixing the cell too rigid would have hidden the geometry that the material actually preferred. They found that the bulk-derived L1 sheet relaxed into a rectangular monolayer built around quasi-layered rhomboid Zn₂X₂ rings, while L2 and L3 also retained rectangular character but did not match L1 energetically. The authors compared the geometrical stability and integrity of those phases by total energy, phonon behavior, exfoliation energetics, mechanical response, and finite-temperature stability, which made the structural claim rest on more than one criterion.

Thapa and Kim also observed that L1 occupied the lowest-energy position across ZnAs, ZnSb, and ZnBi, with the ordering L1 below L3 below L2 and such ranking alone would not have been enough, because metastable sheets often appear competitive before vibrational analysis exposes the problem. They therefore examined phonon dispersions and found that L1 remained free of imaginary modes at zero strain in all three compounds, whereas L2 and the tetragonal phase carried unstable modes, and L3 stayed fully stable only in ZnAs while showing slight soft-mode behavior in ZnSb and ZnBi. Tetragonal geometry came energetically close in ZnSb and even looked favorable in ZnBi, however, that apparent advantage failed to survive the dynamical test. For synthesis, a low static energy is not sufficient if the lattice still prefers to distort. The authors then reinforced the L1 assignment with ab initio molecular dynamics at 300 K and with elastic analysis, arguing that thermal persistence and mechanical admissibility align with the phonon result instead of contradicting it.

  The authors examined bulk ZnAs and ZnSb as narrow-gap semiconductors and bulk ZnBi as a semimetal, with the orthorhombic network built from edge-sharing tetrahedra and rhomboid multicenter units.  The researchers reported a slightly indirect gap for 2D-L1 ZnAs, but direct gaps for 2D-L1 ZnSb and 2D-L1 ZnBi. L3 remained semiconducting too, though its gap stayed indirect across the series. The investigators also found a more abrupt shift in the tetragonal monolayer, where orbital overlap at the Fermi level produced metallic behavior, thus indicating electronic transition from wide band gap semiconductor to metallic behavior while going from energetically competing 2D-L1 phase to 2D-tetragonal phase. In ZnAs, the team further extracted a negative Poisson ratio for L1, a mechanical response that links the peculiar rhomboid-ring geometry to auxetic behavior. A different local network would not be expected to yield the same coupling between deformation and lateral strain.

Thapa and Kim identified a structural principle for zinc pnictide monolayers: the stable sheet adopts a rectangular lattice inherited from the rhomboid-ring physics of the orthorhombic parent. Many computational searches for new 2D materials begin with familiar structural archetypes, after which chemistry-specific bonding preferences are examined in greater detail but in Thapa and Kim work the bonding chemistry leads to a different structural route. The multicenter bonding character of ZnX pushes the stable monolayer toward a less familiar geometry, and that outcome has consequences well beyond these three compounds. It shows that non-van-der-Waals parents with quasi-layered subunits may still yield viable two-dimensional descendants, but only when the descendant preserves the bonding logic embedded in the bulk.

The authors performed analysis in their paper beyond relaxed structures and band plots to include relative energies, phonons, exfoliation considerations, mechanical checks, thermal trajectories, and hybrid-functional electronic analysis. In the ZnBi case: bulk formation energy remained slightly positive at zero temperature and pressure, but the monolayer question remains open under those conditions. From an applications standpoint, the direct-gap 2D-L1 sheets in ZnSb and ZnBi could become useful where atomically thin semiconductors with larger gaps are needed, especially in optoelectronic settings that do not benefit from metallic leakage. ZnAs is considered interesting for a different reason: a stable auxetic semiconductor is mechanically unusual, and if synthesis catches up, its deformation response could matter in device architectures where strain is not a limitation but part of the operating condition. The new study established a strong theoretical basis, while practical use will depend on experimental validation.  Geometry selected by bond topology can control whether a monolayer survives as well as whether it ends up indirect, direct, or metallic. In zinc pnictides, the sheet that the lattice can actually tolerate appears to be the same sheet that produces the most interesting electronic and mechanical outcomes.

Ultra-wide-bandgap semiconductors are important in power electronics because they offer a route to switching devices that can withstand large electric fields while sustaining efficient operation under demanding voltage conditions. Within this class of materials, β-Ga₂O₃ are attracting a lot of attention because of its wide bandgap and high theoretical breakdown field make it a strong candidate for high-voltage power devices, particularly in settings where the material’s field-handling capability can be translated into practical transistor structures. That possibility has motivated sustained work on β-Ga₂O₃ device design, with both lateral and vertical transistor geometries being explored as researchers try to determine how best to use the material in real high-power operation.  The architectural distinction between lateral and vertical devices is not just geometric. Vertical transistors are especially relevant when the objective is to support both high blocking voltage and substantial current transport, since the current path and drift-region design can be arranged in a way that is more naturally suited to that regime. For β-Ga₂O₃, this has made vertical device development an important scientific and technological goal. Yet the central challenge has been clear for some time: the exceptional material properties of β-Ga₂O₃ do not automatically produce exceptional vertical transistor performance. To realize high-voltage operation in a vertical structure, the device must incorporate a drift region that is both sufficiently thick and sufficiently lightly doped, while the surrounding structure must also suppress electric-field crowding near the device edge. If any of these conditions is not met, the attainable breakdown voltage falls well below what the material itself would appear to allow.

That difficulty has given the field a very specific unresolved problem. Earlier β-Ga₂O₃ vertical transistors had already demonstrated kilovolt-class operation, but pushing the breakdown voltage substantially higher required more than incremental processing refinement. It required progress in the epitaxial platform itself. The paper makes this point in direct materials terms. High-voltage vertical transistors need high-quality epitaxial films with donor concentration at or below about 5 × 10¹⁵ cm⁻³ and thickness on the order of at least several tens of micrometers, yet obtaining such films is not straightforward. During halide vapor phase epitaxy, chlorine can be incorporated into β-Ga₂O₃ and act as a shallow donor, making it difficult to achieve the very low donor concentrations needed for a high-voltage drift layer. At the same time, even with an appropriate drift region, the device still depends on edge-termination measures capable of controlling local electric-field concentration.

In a recent research paper published in Applied Physics Express, Daiki Wakimoto, Dr. Chia-Hung Lin, Dr. Kentaro Ema, Dr. Yuki Ueda, Hironobu Miyamoto, Dr. Kohei Sasaki and Akito Kuramata from Novel Crystal Technology, Inc in Japan, developed a normally-off multi-fin beta-gallium-oxide vertical transistor built on a thick, low-donor-concentration epitaxial layer grown by halide vapor phase epitaxy on a (011) substrate.  Its main technical advance is the demonstration of a beta-gallium-oxide vertical transistor that withstands breakdown voltages above ten kilovolts while still preserving normally-off transistor operation, strong current switching, and low specific on-resistance.

Briefly, the research team fabricated a multi-fin vertical transistor based on beta-gallium oxide using a thick, lightly doped epitaxial layer grown by halide vapor phase epitaxy on a beta-gallium-oxide substrate with the crystallographic orientation chosen to support low donor incorporation. The fabrication sequence established the channel-access and contact structure through silicon implantation, annealing, dielectric formation, dry etching of the fins, planarization, gate formation, and final source and drain metallization. What matters scientifically is not the fabrication sequence alone, but how the device structure was designed to produce the intended electrical behavior: a thick, lightly doped drift region for high-voltage blocking, combined with a fin-based vertical channel and a field-plate-assisted gate arrangement that supports normally-off operation. The authors designed the multi-fin layout with clear attention to geometric control and device uniformity. The active fins were placed within an outer fin arrangement so that the operating channels would behave as consistently as possible and so that variations introduced during dry etching would be reduced. That choice matters because more uniform fin geometry leads to cleaner and more reproducible transistor behavior rather than performance shaped by local structural irregularities. The source electrode was also deliberately pulled back from the fin edge to avoid unintended gate-source contact in regions where etching could distort the fin profile. Electrical measurements showed that the device operated in a normally-off mode. The threshold behavior, strong current modulation, and steep subthreshold response all point to effective control of the channel by the gate. These characteristics are important when considered together, because they show that the fin-channel design and gate-stack integration did not sacrifice switching behavior in the effort to reach high blocking capability. The reported hysteresis remained modest, and the gate current stayed below the measurement limit under the tested conditions, which supports the view that the gate operation was well controlled.

The output characteristics are important for the same reason and the device can block high voltage and also maintains useful conduction performance in the on-state. The authors evaluated the current flow using an effective conductive area that accounts for current spreading in the drift region rather than relying only on the lithographic top-surface geometry.  Within that interpretation, the transistor combined solid current conduction with very high off-state blocking capability.

To prevent premature breakdown through air, the measurements were carried out in an insulating liquid, and the device sustained a breakdown voltage above ten kilovolts. In fact, the measurement was limited by the voltage range of the test system rather than by a confirmed breakdown of the device below that level. The estimated electric field in the trench region was correspondingly very high. The authors state that this is the highest breakdown voltage ever reported for a beta-gallium-oxide vertical transistor, exceeding the previous best result for this device class by more than a factor of two. They also report a strong power figure of merit, reinforcing that this was not a single-metric gain but a meaningful advance in vertical beta-gallium-oxide transistor performance. The authors’ work demonstrated what kind of material-device integration is required for β-Ga₂O₃ vertical transistors to enter a much higher breakdown-voltage regime.   The logic is visible throughout the paper: low donor concentration in a thick epitaxial drift layer, achieved on a (011) substrate where Cl incorporation is suppressed, is paired with a multi-fin normally-off structure and field management at the device edge. The breakdown performance is therefore not an isolated metric but the outcome of a coherent design direction grounded in how the electric field is distributed in the device. There is also a meaningful balance here between voltage blocking and transistor operation. In Daiki Wakimoto and colleagues work, the device still shows threshold control, a large on/off ratio, low measured gate current, and a specific on-resistance that keeps the conduction side of the story in view.   Its contribution is more disciplined than that. It shows that a normally-off β-Ga₂O₃ vertical transistor can be pushed past 10 kV while retaining a credible switching profile and a measurable power figure of merit.  Earlier β-Ga₂O₃ vertical transistors had already shown that kilovolt-class blocking was possible and the new device reported by the authors moves the conversation into a distinctly higher-voltage category and narrows the gap between what the material suggests in principle and what a vertical transistor has actually demonstrated in practice. Just as important, the result reinforces the value of the (011) orientation for HVPE-grown low-doped epitaxial layers when the target is vertical high-voltage operation. The paper’s final implication remains measured: it points to the strong potential of Ga₂O₃ vertical power devices.

Panoramic imaging of closed surfaces sits at the intersection between geometry and optics. Many objects of scientific or practical interest don’t present themselves as open, planar targets, but most optical systems still assume that they do. When the surface wraps back on itself, conventional imaging strategies tend to fragment the view. One records partial perspectives, then stitches them together afterward, hoping the reconstruction doesn’t introduce distortions that matter for measurement. That hope often isn’t well justified, especially when fine spatial correspondence or phase fidelity is required. Current approaches rely heavily on motion, camera arrays, or computational assembly. A camera rotates, or several cameras observe the surface from different angles, and software attempts to reconcile the resulting data. This workflow works tolerably for visualization, but it struggles when accuracy matters. Calibration errors accumulate. Matching subsets of images isn’t trivial. Neural-network-based reconstruction can fill gaps, but it doesn’t enforce physical correspondence in any strict sense. These limitations persist because the optical system itself never acquires a full-pe spective field. It only samples pieces, then asks computation to guess the rest. The underlying difficulty is optical rather than algorithmic. Light propagates according to local material response, and most imaging systems don’t redirect waves from hidden portions of a surface in any systematic way. Without a medium that can guide electromagnetic fields from different orientations onto a single plane while preserving spatial ordering, direct panoramic capture remains out of reach. That’s why improvements in software haven’t resolved the problem. They’re compensating for a missing physical operation. Null media offer an unusual possibility here. In such media, electromagnetic waves propagate along a prescribed axis without reflection or phase delay, effectively projecting fields from one surface to another. Prior demonstrations of this behavior have largely lived in the microwave domain, where material realization is comparatively forgiving. Extending the same concept into the optical band isn’t straightforward. Optical frequencies impose severe constraints on dispersion, loss, and fabrication scale, and simplified implementations that work at longer wavelengths don’t translate automatically.

The motivation behind this work grows from that gap. If a practical optical analogue of a null medium could be constructed, even in an approximate form and for a restricted polarization, it might allow panoramic imaging to be handled optically rather than computationally. That would change how closed-surface imaging is framed. Instead of reconstructing views after the fact, the system could project the entire surface field directly onto a plane, in real time, because the medium itself enforces the mapping.

A recent research paper published in Journal of the Optical Society of America A  and conducted by Mr. Chao Yang, Professor Fei Sun, Ms.  Ran Sun, and Professor Yichao Liu from the Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, College of Physics and Optoelectronics at Taiyuan University of Technology, the researchers developed a direct panoramic optical imaging lens based on a subwavelength silver–glass layered structure acting as a simplified null medium. The system projects optical field distributions from closed surfaces directly onto a flat image plane without reconstruction. Its design relies on spatially varying principal axes to preserve one-to-one correspondence across the surface. The new approach can be considered distinct because the imaging function is enforced by material anisotropy instead of post-processing.

The researchers built an effective optical null medium using a subwavelength silver–glass layered structure and designed a simplified version tailored to TM-polarized waves. The team arranged alternating silver and glass layers with thicknesses well below the operating wavelength, which allowed effective medium theory to describe the composite response. The authors designed the layered structure so that its effective permittivity became highly anisotropic. Along the principal axis, the response remained large, while perpendicular components approached zero. That anisotropy mattered because it forced electromagnetic fields to propagate directionally, projecting surface distributions along predetermined paths. The investigators didn’t treat this structure as uniform. Instead, they divided the lens volume into distinct regions, each with a locally defined principal axis, chosen to map different portions of a closed surface onto a common image plane. Plus, the research team Used numerical simulations to examine how point-like and patterned sources placed on different parts of a closed object surface propagated through the lens. When they positioned TM-polarized sources on the top, sides, and front of the surface, the fields traveled through the layered regions and arrived at corresponding positions on the image plane. The researchers observed that the spatial ordering of peaks and troughs remained intact, even though the propagation paths differed. Loss couldn’t be ignored at optical frequencies, especially with silver. The authors explicitly included material loss and tracked its effect. They found that attenuation occurred, and some broadening appeared, but the directional mapping persisted. That outcome followed directly from the null-medium-like response: loss reduced amplitude, but it didn’t scramble spatial correspondence because the propagation direction was constrained by design.

The study also examined patterned field distributions rather than isolated points. When the investigators imposed oscillatory magnetic-field patterns along the closed surface, the projected patterns on the image plane retained identical spatial frequencies and phase positions. Amplitude variations appeared under lossy conditions, but the structural form of the pattern survived. That distinction matters. It shows that the lens doesn’t just image points; it transfers continuous field information. Bandwidth posed another constraint. The team incorporated dispersion through a Drude description of silver and examined performance away from the design wavelength. Across a broad visible range, the mapping behavior held, with consistent peak locations despite frequency-dependent attenuation. Finally, the researchers successfully extended the design from two dimensions into a finite-height three-dimensional structure and simulations showed that the same projection behavior carried over, which confirmed that their concept wasn’t limited to a planar abstraction.

To sum up, the novel approach of Professor Fei Sun bypasses many sources of error that arise when images are stitched computationally by embedding the mapping operation into the optical medium itself. That matters for applications where spatial correspondence isn’t negotiable, such as surface metrology or biomedical imaging, because post-processing can’t recover information that was never optically acquired. The reliance on effective medium behavior also clarifies where the limits lie. The lens works because the layered structure enforces directional propagation. If fabrication tolerances drift or polarization conditions aren’t maintained, the mapping will degrade. That’s not a weakness of the concept so much as a reminder that the physics is doing the work. The imaging fidelity depends directly on how closely the structure approximates the intended anisotropy. Besides, instead of designing lenses to form images through focusing and interference, this system treats imaging as a transport problem. Fields are moved, not refocused. That distinction opens different design routes, particularly for nonconformal or irregular surfaces where traditional optics struggles. Downstream implications remain bounded by practical considerations. Large-area fabrication of subwavelength metal–dielectric structures isn’t trivial, and maintaining TM polarization in uncontrolled environments isn’t guaranteed. Still, if those constraints can be managed, the approach could support real-time panoramic imaging without heavy computation. Extensions to other frequency ranges or to alternative near-zero-index structures seem plausible, though they’d demand careful material choices.

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.

Fenestration design can influence commercial building energy performance because windows function as architectural features, environmental interfaces, as well as thermal pathways. They provide daylight, view, and façade articulation, but they also create pathways for solar heat gain, conductive heat transfer, and seasonal shifts in heating and cooling demand. The same amount of glazing may perform differently depending on orientation, shape, and position on the façade. A horizontal opening may expose a different solar profile than a vertical one; a south-facing window may be desirable in one climate but burdensome in another; and a larger glazing ratio may reduce one energy load while increasing another. This means a fenestration strategy that reduces energy use in Honolulu or Houston may require a different balance of glazing area, orientation, and shape in Helena or Minneapolis.

Previous studies have examined individual window parameters such as window-to-wall ratio, aspect ratio, orientation, and glazing area, and they have shown that these features can influence building energy performance. However, the practical design problem is more complex than optimizing one variable at a time. Window-to-wall ratio, aspect ratio, and fenestration location interact with one another, and their combined effect determines the balance between heat gain, heat loss, and mechanical conditioning demand. This creates a need for a multi-parameter approach that can search for energy-efficient combinations rather than relying on isolated design rules. In a new research paper published in Journal of Cleaner Production, Associate Professor Reza Foroughi from the Department of Sustainable Technology and the Built Environment at Appalachian State University  developed a genetic-algorithm optimization model coupled with EnergyPlus to identify energy-efficient window-to-wall ratio, aspect ratio, and fenestration location for small commercial buildings.  They applied the model to a two-story commercial building across representative United States climate zones. The output is a climate-specific set of fenestration design parameters intended to reduce total building energy use at the early design stage.

Briefly, the building was square in plan, with eight windows distributed across the four orientations and two floors. The baseline model used centrally placed windows with a relatively large glazing proportion, and provided a consistent reference point for optimization. The envelope, glazing, HVAC system, occupancy schedule, and internal assumptions were specified so that changes in energy performance could be attributed to the geometric fenestration variables rather than to shifting building specifications.

The optimization model coupled a genetic algorithm with EnergyPlus simulations. This choice mattered because the design problem involved many coordinate-based variables and a search space with possible local optima. Instead of limiting the analysis to predefined window configurations, the algorithm repeatedly adjusted window coordinates within practical limits and evaluated the resulting total energy use. The objective function combined heating, cooling, lighting, and equipment energy, although the central trade-off was between heating and cooling loads. A design choice with direct scientific consequence was the decision to allow window coordinates to vary within architectural constraints; this converted window-to-wall ratio, aspect ratio, and placement into linked variables, which make it possible to identify energy-relevant configurations that would not necessarily arise from one-factor comparisons. The team found that hot climates generally favored smaller window-to-wall ratios, keeping glazing more restrained to limit cooling demand. On the other hand, cold climates behaved differently. In colder locations such as Helena and Minneapolis, the optimized designs allowed more south-facing glazing while keeping the other orientations more limited. The optimized aspect ratios also varied strongly by orientation and location. The authors observed although the Memphis case showed that a vertical south-facing window could be favored under specific climate and orientation conditions. In Helena, by contrast, the optimization favored a strongly elongated horizontal opening on the east façade.

These results show that window shape functioned as an energy-relevant design variable; it influenced the balance between incident solar gain and thermal demand. They found the optimized cases reduced total energy consumption in every climate zone and the decrease ranged from 15% in Honolulu to 2% in Helena and Minneapolis. Cooling energy dropped substantially under optimized fenestration, while heating energy increased slightly in several cases. The total balance still improved, meaning the reduction in cooling demand outweighed the added heating burden within the modeled conditions. Primary energy comparisons reinforced the same pattern, with larger gains in hot climates and smaller but still measurable reductions in cold climates.

The economic assessment translated these savings into annual cost terms for the modeled building where Honolulu showed the largest annual saving, while Helena showed the smallest. The authors emphasize that when these decisions are made at the early design stage of new construction, selecting optimized window dimensions and locations does not necessarily add construction cost in the same way that a technology retrofit might. The finding emphasizes the value of informed early-stage design, where placement and proportion can improve energy performance before costly changes are required.

The findings of Professor Reza Foroughi et al. have direct engineering value for early-stage design of small commercial buildings, where fenestration decisions are still flexible and can be changed without major cost penalties. The study shows that window-to-wall ratio, aspect ratio, and window placement should not be selected as independent architectural preferences, but as linked design variables that affect heating and cooling demand together. For engineers, this supports a more climate-responsive approach to envelope design, especially when preparing schematic layouts, façade studies, or energy models for small offices, retail buildings, educational facilities, and similar commercial structures. One practical application is the development of climate-specific fenestration guidelines. In hot locations such as Honolulu, Houston, and Memphis, the optimized results support restrained glazing areas to limit cooling demand. In colder climates such as Helena and Minneapolis, the findings support more selective use of larger south-facing windows while keeping north, east, and west glazing smaller. This gives designers a clearer basis for balancing solar heat gain against envelope heat loss rather than relying on uniform glazing ratios across all façades.

The study is also useful for simulation-driven building design. By coupling a genetic algorithm with EnergyPlus, the authors demonstrate how engineers can use optimization workflows to test many window configurations before construction. This is valuable for projects pursuing reduced operational energy, near-zero energy design, or improved façade performance while complementing later decisions about mechanical systems or renewable energy integration. When existing small commercial buildings undergo envelope renovation, the same logic can help determine whether reducing, reshaping, or relocating glazing would meaningfully reduce cooling or heating loads. Overall, the findings give engineers a practical method for converting fenestration design from a rule-of-thumb decision into a climate-specific energy optimization task.

Viscous dampers are widely used in building structures to reduce dynamic response under earthquake and wind excitation, and their effectiveness depends not only on the constitutive behavior of the damper itself but also on the reliability of the connections through which structural deformation is transmitted. In practical applications, these dampers are commonly connected to the main structural system by shaft-pin joints so that the device can work primarily in axial action. Although this arrangement is mechanically simple and widely accepted in engineering practice, it contains a detail that is usually treated as unavoidable during fabrication and installation: a small gap between the shaft pin and the corresponding hole in the connected plate. Previous studies had already shown, in different structural and mechanical settings, that gaps or clearances can alter stiffness, modify load transfer, and degrade cyclic or dynamic performance. Work on viscous damper systems had also pointed to the detrimental effect of imperfect engagement and the zero-force platform that may appear in hysteretic response when a connection gap is present. Still, those studies largely clarified the consequences of the problem rather than offering a direct mechanical remedy for the shaft-pin joint itself. That left an unresolved question in practical damper design: whether the unavoidable clearance in a pin connection could be removed in a workable way without sacrificing the simplicity and functionality that make such joints attractive in the first place. In their paper published in Engineering Structures, Dr. Yi-Qiong Cui, Professor Yang Xiang, Dr. Bo Yang, Dr. Shi-Li Guo, and Professor Guo-Qiang Li from Tongji University address this issue by proposing a pin-joint configuration that incorporates paired tapered sleeves and thrust flanges to eliminate clearance between the shaft pin and the ear-plate holes. On that basis, they examine the connection behavior of the proposed joint under cyclic loading and then assess, through simplified structural modeling, how the removal of joint gap influences the efficiency of viscous dampers in frame systems subjected to seismic and wind actions.

The authors began with a direct comparison between two joint types: a conventional shaft-pin joint and the proposed tightknit version with tapered sleeves. The conventional specimen had a 20 mm pin and a 23 mm hole, giving a 3 mm assembly clearance chosen deliberately to make the mechanical consequence of the gap visible in testing. The tightknit specimen kept the same basic connection logic but inserted fourteen pairs of tapered sleeves and thrust flanges, with lubrication and machined contact surfaces used to support controlled assembly and sliding during tightening. The internal ear plate also retained an annular partition, which helped divide the sleeves into symmetric groups and improved alignment during installation. That design choice matters because the sleeve system is only useful if the radial expansion that removes the gap can be introduced in a balanced and assembly-friendly way. Under cyclic force-controlled loading, the contrast between the two specimens was immediate. The conventional joint developed a horizontal plateau near load reversal, especially as force passed through the vicinity of zero. Mechanically, that plateau corresponds to relative movement without effective force transmission while the pin traverses the internal clearance. The tightknit joint did not show that feature. Its load-deformation response remained continuous, with a nearly linear slope through reversal, which is exactly the behavior one would expect if the internal gap had been removed and compressive and tensile load transfer could proceed without slack.

The conventional joint showed an initial stiffness of 250 kN/mm, whereas the tightknit joint reached 583.3 kN/mm. Also, in the conventional specimen, plastic deformation began at about 150 kN with a relative displacement of 0.6 mm between the upper and lower end plates. In the tightknit specimen, yielding began at about 175 kN and only 0.3 mm. At 300 kN, the conventional joint reached 3.1 mm in that same displacement measure, while the tightknit joint reached 1.6 mm and the authors attributed this to the tapered sleeve assembly improving contact conditions, restricting shaft deformation, and producing a more uniform stress state along the pin-ear interface. The second displacement measure, taken between the shaft pin and the lower end plate, gave larger values for both specimens, but the qualitative picture did not change. That larger reading captured bending-induced geometric distortion of the pin as the upper and lower portions of the joint moved relative to one another under tension. The post-test pin shape confirmed that combined shear and bending had deformed the shaft. Even there, the tightknit joint retained a mechanical advantage, and the authors also note that by limiting severe deformation of the shaft, the proposed configuration helps maintain the integrity of the connection after heavy loading

Afterward, the researchers used OpenSees, to represent the frame, damper, linkage, and joint within a reduced damper-linkage-joint assembly. For conventional joints, they used bidirectional gap elements built from paired ElasticPPGap materials to reproduce the clearance behavior in both loading directions. For the tightknit case, the gap was taken as negligible. When sinusoidal dynamic loading was applied, the zero-gap assembly produced an ideal elliptical hysteresis loop. Once clearance was introduced, the loops broke into semi-elliptical branches separated by a horizontal no-force segment. As the gap increased from 0.5 mm to 1.5 mm, peak displacement rose and output force fell. Over two seconds of loading at the lower excitation amplitude, cumulative energy dissipation dropped from 19107.4 J in the zero-gap case to 12771.8 J at 1.5 mm, a 26% reduction. Even when the loading amplitude increased and the relative importance of the gap weakened somewhat, the adverse effect remained visible.

The study is important in connection mechanics, and Professor Yang Xiang and colleagues carry the joint model into structural response analyses under both earthquake and wind loading, and that move clarifies why the gap problem matters. In the four-story seismic model, dampers improved performance relative to the uncontrolled structure in every case, but the benefit was consistently strongest when the connection was tightknit. Under the El Centro record, the zero-gap configuration reduced drift, velocity, acceleration, and base shear more than the 1.5 mm-gap case. Across a broader set of 46 ground motions, the same pattern persisted: compared with the idealized tightknit condition, a 1.5 mm joint gap increased average peak inter-story drift by 7.6%, peak velocity by 6.4%, peak acceleration by 4.8%, and base shear by 7.9%. The wind analysis is particularly informative and because wind-induced structural deformations are smaller, a gap that might seem modest from a fabrication perspective can occupy a large fraction of the motion available to activate the damper. That is exactly what the twenty-story model showed. When total wind response was considered, the mean component dominated overall drift, so the difference among models was less dramatic. But once the fluctuating component was isolated, the sensitivity to clearance became unmistakable. A 0.3 mm gap brought the controlled structure much closer to the uncontrolled one, indicating a substantial loss in effective damping contribution. Under 24 synthetic wind histories, the tightknit case gave much stronger reductions in response than the conventional gap cases, including reductions relative to the 0.3 mm-gap model of 23.6% in peak inter-story velocity and 33.8% in roof acceleration. That distinction matters because it shifts the design logic. The issue is not simply that connection clearance is undesirable in an abstract sense. It is that clearance can erase a meaningful portion of the working deformation range of a supplemental damping device, and it does so most severely when the demand itself is small. The paper therefore sharpens the engineering interpretation of damper efficiency: performance depends not only on the constitutive behavior of the damper body, but also on whether the connection transmits motion without loss. In that respect, the tapered-sleeve joint is not treated as a secondary hardware refinement but becomes part of the force-transfer mechanism that strongly influences how effectively the damping system can function.

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.

Optical coherence tomography (OCT) is one of the most widely used imaging technologies in modern medicine and science because it offers micrometer-level resolution, non-invasive depth sectioning, and real-time imaging of tissue microstructure. Its importance and applications span clinical diagnostics, biomedical research, and industrial metrology. However, its theoretical foundation has lagged behind the pace of experimental innovation. As clinicians and researchers push OCT into regimes of higher numerical aperture, broader spectral bandwidths, and increasingly complex optical designs, they often observe image behaviours that do not sit comfortably within classical, three-dimensional approximations. The field has largely relied on simplified treatments that separate lateral and axial resolution, or that implicitly collapse spatial and temporal coordinates into a single depth variable, an approach that works only so long as the optical system operates in a regime where aberrations, dispersion, and coherence gating remain weakly coupled. Once those assumptions are relaxed—which is increasingly the norm in high-performance OCT and OCM—the existing theory struggles to explain why images distort, why coherence gates curve, or why certain spatial frequencies seem irretrievably lost.

To this end and in a new research paper published in Journal of the Optical Society of America A and conducted by Dr. Naoki Fukutake, Dr. Shuichi Makita, Dr. Yoshiaki Yasuno from the University of Tsukuba in Japan and in collaboration with Nikon Corporation, the researchers developed a unified four-dimensional (4D) image-formation theory that treats OCT as a system governed jointly by spatial and temporal coordinates. Their framework introduces 4D pupil functions and a 4D frequency-space aperture that precisely determine which object frequencies contribute to the measured image. They show that all major OCT modalities—time-domain, frequency-domain, and full-field—share the same underlying imaging equation once recast in this 4D space. This formulation explains longstanding imaging distortions and establishes conditions under which perfect refocusing and accurate resolution prediction are possible.

The research team performed a complete mathematical reconstruction of OCT image formation and began with the time-domain system and extended the same logic to frequency-domain and full-field implementations. Instead of treating these as distinct modalities, they derive a unified expression for the detected intensity by tracking how excitation light interacts with the object, propagates through the optical system, and interferes with the reference arm. This leads them to define a four-dimensional point-spread function PSF₄(x, τ), obtained by temporally convolving the excitation field with collection field. In practice, this PSF behaves as the spatial product of two beams—one forward-propagating and one reverse-propagating—whose overlap determines how differently the image is formed depending on the depth of object.

The authors found when they applied this framework to all three major OCT architectures the following: in time-domain systems, the depth coordinate enters explicitly through the physical delay between arms while in frequency-domain systems, the delay reappears mathematically through the Fourier transform of the spectral interferogram. Full-field OCT, despite its incoherent illumination and absence of lateral scanning, yields an equivalent formulation once the illumination coherence function is handled explicitly. According to the authors, all OCT types reduce to the same expression for PSF₄ and therefore share identical imaging properties when experimental conditions are matched.

Moreover, the team performed 4D frequency space analysis, where spatial frequencies (fₓ, fᵧ, f_z) are paired with optical frequency ν. By Fourier transforming PSF₄, the authors obtain a 4D aperture A₄(f, ν) that acts as a window selecting which object frequencies survive the imaging process. When the numerical aperture rises or when the spectrum broadens, this aperture thickens along f_z, meaning that depth-related spatial frequencies overlap and become inseparable. This explains why refocusing fails in high-NA OCT: the instrument itself merges distinct object frequencies before detection. Conversely, when excitation NA approaches zero—as in plane-wave FF-OCT—the aperture collapses into a thin sheet, allowing perfect refocusing and recovery of object structure. Their theoretical predictions extend to aberrations and dispersion. By defining both as manifestations of 4D phase distortions within the pupil, the authors show that spatial aberrations originate from specific combinations of excitation and collection pupils, while temporal aberrations disappear only if both arms share identical dispersion. This generalization clarifies long-standing discrepancies between empirical observations and classical theory, particularly in systems operating outside the paraxial regime.

In conclusion, Dr. Naoki Fukutake and colleagues fundamentally redefined how OCT forms an image by introducing a complete, mathematically rigorous 4D imaging theory. By giving equal weight to spatial and temporal coordinates, the authors illuminate behaviours that were previously treated as experimental nuisances rather than fundamental consequences of the imaging physics. The question of resolution in OCT is often presented as deceptively simple: axial and lateral performance are treated as independent knobs, one governed by spectral bandwidth and the other by numerical aperture. What Fukutake, Makita, and Yasuno demonstrated that this tidy separation only survives in a narrow operating regime. Once the numerical aperture increases or the spectrum broadens, the imaging system begins to behave in ways that traditional theory cannot comfortably explain. Their 4D pupil formulation reveals that spatial and temporal frequencies are inherently entangled, and that this coupling quietly undermines the long-held assumption of independent resolutions. For instrument designers, acknowledging this relationship is not just an academic exercise; it prevents them from leaning on approximations that may have worked a decade ago but become unreliable in the high-performance systems now being built.

Moreover, this new framework also reframes a persistent puzzle around digital refocusing. In practice, refocusing sometimes works beautifully and sometimes stubbornly fails, even with sophisticated algorithms. The authors provide a physical explanation: refocusing does not break down because the computation is lacking, but because the 4D aperture itself blends depth-related object frequencies before detection. Once that mixing happens, the information is simply no longer recoverable. However, the same theory also points to the opposite scenario—when the excitation NA is sufficiently low, the 4D aperture collapses into a thin sheet, and refocusing becomes theoretically perfect. That observation is particularly relevant for full-field OCT, where design choices often involve awkward compromises between illumination geometry, coherence, and lateral resolution. Additionally, their treatment of aberrations follows the same unifying spirit. Spatial aberrations and chromatic dispersion, usually corrected through entirely separate procedures, become aspects of a single 4D aberration in this formulation. Thinking of them together opens a path toward optical designs that handle both simultaneously, something current systems rarely achieve. Taken together, the theory offers more than a refined mathematical model. It lays groundwork for interpreting—and possibly improving—advanced techniques such as inverse scattering reconstructions, computational OCT, and adaptive wavefront shaping. These methods have outpaced the theoretical language used to justify them, and this 4D framework brings the field much closer to understanding how OCT actually manipulates information in space and time.

Liquid droplets interacting with cold solid surfaces appear in an unusually wide range of settings, such as in aircraft icing, but similar processes arise in heat exchangers, power transmission systems, and marine structures operating in cold or polar environments. In all of these cases, the basic event is: a droplet impacts a surface and what follows, however, depends on how inertia, surface tension, viscous losses, and heat transfer compete over very short timescales. If freezing intervenes early enough, even familiar impact scenarios can evolve in unexpected ways. Despite sustained interest over several decades, the coupled dynamics of droplet deformation and liquid–solid phase change are still not fully resolved. Much of the difficulty lies in the timing. Impact-driven spreading and retraction unfold over milliseconds, while solidification may initiate locally on comparable or even shorter timescales when surfaces are strongly supercooled. Once freezing begins, the flow field and thermal field cease to be separable, and intuitive extensions of room-temperature impact theory often fail. Experiments have clarified many aspects of the problem, but their limitations become apparent precisely in the regimes of greatest interest. At modest supercooling, high-speed imaging can track droplet outlines and contact line motion with reasonable confidence. As temperatures decrease further, however, the interior of the droplet rapidly becomes optically inaccessible, and the freezing front itself is difficult to observe directly. Small, uncontrolled variations in surface microstructure or chemistry can also exert an outsized influence on the outcome, particularly on hydrophobic or superhydrophobic substrates where contact times are short. As a result, it is often challenging to disentangle intrinsic physics from experimental variability. Numerical modeling is therefore an attractive complement, though it brings its own complications. Traditional CFD approaches based on the Navier–Stokes equations require explicit interface tracking and empirical representations of the solidifying region. In enthalpy–porosity methods, for instance, momentum suppression in the mushy zone is governed by parameters that are rarely known a priori and are frequently tuned to specific datasets. This undermines confidence when extrapolating beyond the calibration range. Stability is an additional concern: realistic water–air density ratios and low viscosities are notoriously difficult to handle in three-dimensional simulations without numerical damping. For these reasons, the lattice Boltzmann method has gained attention as an alternative framework. Its mesoscopic formulation handles evolving interfaces naturally and couples more cleanly to enthalpy-based phase-change descriptions. That said, much of the existing lattice Boltzmann literature on droplet freezing has relied on reduced density ratios or elevated viscosities to maintain stability. Extending these models to conditions that genuinely reflect droplet impact and freezing in air remains a nontrivial step—and one that motivates the present line of work.

To this end, two closely related studies published in Physics of Fluids and Heat Transfer Engineering by Dr. Yunjie Xu, Pro. Linlin Tian, Pro. Chunling Zhu, and Professor Ning Zhao at Nanjing University of Aeronautics and Astronautics developed a fully three-dimensional lattice Boltzmann framework for investigating droplet impact and freezing. The new framework was designed to operate under near-realistic conditions, resolving large water–air density ratios while maintaining numerical stability at low viscosities. Beyond the flow solver itself, the model accounts explicitly for volumetric expansion during liquid–solid phase change and incorporates a quasi-dynamic contact angle formulation, which allows advancing and receding behaviors to be represented without imposing a single, static wettability condition. In the first study, the authors focused on droplet impact and freezing on cold solid surfaces with moderate wettability. Through systematic validation against experimental observations, the model demonstrated an improved ability to capture contact line motion, interfacial deformation, and freezing-front evolution, addressing limitations that have constrained earlier numerical approaches. Building on this validated foundation, the follow-up work extended the same methodology to ultra-cold superhydrophobic substrates, a regime that remains difficult to probe experimentally. These simulations revealed that freezing can intervene during the retraction stage, fundamentally altering droplet dynamics by suppressing rebound, pinning the contact line, and, under certain conditions, inducing breakup at impact velocities well below those observed at room temperature.

The research team developed numerical framework across the two studies and built upon an enhanced cascaded lattice Boltzmann formulation, specifically designed to maintain stability at large density ratios and low viscosities. They introduced multiple entropic stabilizers to independently relax different orders of kinetic moments, mitigating numerical instabilities that typically arise in high-contrast multiphase flows and that approach enabled the faithful representation of water–air systems without resorting to artificial parameter inflation. The authors captured droplet deformation using a pseudopotential multiphase model, while the freezing process is resolved through an enthalpy-based thermal lattice Boltzmann scheme. It is important to mention that the model incorporates volumetric expansion during solidification, which is an effect that alters local flow fields near the freezing front. Moreover, the team introduced quasi-dynamic contact angle formulation to address contact line dynamics, which allowed the effective wettability to switch between advancing and receding states in response to contact line motion. They found the model to reproduce the canonical stages of spreading, retraction, and eventual arrest due to freezing in simulations of droplet impact on cold hydrophilic and hydrophobic surfaces. Moreover, quantitative comparisons against experimental measurements show close agreement in temporal droplet profiles and contact length evolution across a range of Weber numbers and surface temperatures. Notably, simulations reveal that freezing initiates preferentially near the three-phase contact line, where enhanced heat flux and prolonged residence promote early solidification. This localized freezing progressively pins the contact line, suppressing retraction and altering the final droplet morphology.

The authors extended their research to ultra-cold superhydrophobic surfaces, and found that at modest supercooling, droplets retain the familiar spread–retract–rebound sequence characteristic of superhydrophobic substrates. However, as surface temperatures decrease further, a thin ice rim forms at the droplet periphery during retraction. This rim acts as a mechanical constraint, fundamentally modifying the energy redistribution within the droplet. Under certain conditions, the frozen base induces droplet breakup at impact velocities well below those required on room-temperature surfaces. They also performed parametric studies which demonstrated that maximum spreading is relatively insensitive to surface temperature, remaining primarily governed by inertial and capillary forces. In contrast, retraction dynamics and contact time exhibit strong thermal dependence once freezing becomes appreciable. Increasing Weber number enhances spreading but also accelerates heat transfer at the interface, and lead to earlier freezing onset in ultra-cold regimes. Moreover, they conducted spatially averaged heat flux analyses which further clarified how thermal gradients evolve during impact, and showed distinct signatures associated with rim formation and bottom-up solidification.

The combined contributions of these two studies demonstrate their successful unification of droplet impact hydrodynamics with realistic freezing physics under conditions that challenge both experiment and computation for the first time in LB framework. Indeed, the authors move lattice Boltzmann modeling closer to genuine predictive utility for icing phenomena by demonstrating stable, three-dimensional simulations at large density ratios. Additionally, the work clarifies that freezing actively restructures the pathways through which kinetic and surface energies are redistributed and the emergence of ice rims, contact line pinning, and bottom-up solidification introduces new regimes of behavior that cannot be inferred from room-temperature impact dynamics alone. These findings are especially relevant for the design of anti-icing strategies, where surface coatings or textures are often optimized based on assumptions drawn from non-freezing conditions.

Practically, the findings suggest that superhydrophobicity alone is insufficient to guarantee droplet rebound under extreme cold. Even highly repellent surfaces can lose their effectiveness once freezing intervenes on timescales comparable to retraction. This realization has direct implications for aerospace and energy applications, where surfaces are routinely exposed to ultra-cold environments. Together, the two studies establish an effective coherent numerical framework for examining impact-freezing phenomena across thermal and wettability extremes. Furthermore, this integrated body of work of Dr. Yunjie Xu et al sets the stage for future investigations into surface patterning, inclined geometries, and transient thermal fields and enables systematic exploration of design variables that would be prohibitively difficult to isolate experimentally by establishing a validated numerical foundation.

Dynamic axial strain in lightweight subgrade fills does not remain proportional to repeated loading once pore collapse, interparticle slip, and local damage begin to compete within the same stress cycle. That problem matters acutely in transportation earthworks, where a material may be chosen not only for low unit weight, but for how it stores stiffness and dissipates vibrational energy under thousands of load reversals. Foamed concrete can reduce embankment weight, limit settlement, and provide useful thermal and damping behavior, however, it has environmental burden, since conventional formulations still depend heavily on Portland cement, and the carbon cost of that binder remains substantial. The search for a lighter fill with lower embodied emissions has pushed researchers toward binders that do more than harden the matrix and they also must alter the chemistry of curing itself. This is where serpentine carbon-sequestration foamed concrete has become more interesting to scientists. The material draws on reactive MgO, serpentine powder, silty clay, water, and CO₂ foam, so the gas phase is not just a pore-forming aid but part of the hardening route itself. In that sense, the scientific question is not simply whether a low-density geomaterial can be made from alternative constituents. The harder issue is whether carbonation-based bonding creates a cyclic response that differs in kind from the behavior already documented for cement-based foamed concrete and EPS-modified lightweight soils. A binder system built around magnesium carbonation develops through hydration, mineral precipitation, pore filling, and residual unreacted phases. That history leaves behind a skeleton whose stiffness, damping, and strain accumulation under repeated loading cannot be assumed from older constitutive traditions.

There are practical limitations because dynamic design of subgrades depends heavily on quantities such as dynamic elastic modulus and damping ratio, but those parameters are sensitive to stress state, loading frequency, curing condition, and microstructure. Existing models were largely framed around cement-stabilized soils or polymer-modified lightweight fills. They are useful as a starting point, though they do not automatically carry over to a material whose bonding arises from carbonate formation in a porous, closed-cell matrix. Even the testing is not trivial and a single monotonic strength value says very little about whether cyclic loading first compacts the pore system, then damages it, or does both in alternating sequence across strain levels. In a recent research paper published in Construction and Building Materials, Dr. Mengyao Li, Dr.  Xiang Zhang, and Professor Songyu Liu from the School of Transportation at Southeast University working together with Dr. Zhengcheng Wang from Chongqing Three Gorges University, developed a cement-free serpentine carbon-sequestration foamed concrete formulated with reactive MgO, serpentine powder, silty clay, and CO₂ foam, then characterized its cyclic behavior under multistage triaxial loading. They also developed a modified Darendeli-based model for dynamic elastic modulus evolution, with E_dmax expressed as a function of curing age, confining pressure, and vibration frequency.  The team examined specimens cured for 7 to 28 days under multistage cyclic triaxial loading across a range of confining pressures and frequencies which allowed the investigators trace stiffness and dissipation across a widening strain range within the same specimen, which reduced specimen-to-specimen noise at the very point where nonlinear behavior begins to emerge. The authors also kept the tests in an unsaturated state, consistent with the intended service condition of the material as a protected subgrade fill; saturating such a pore system would have changed the internal structure enough to blur the mechanism they wanted to examine. The researchers observed a clear change in hysteresis morphology as loading intensified. At small dynamic strains, loops remained close to linear and comparatively tight. With rising stress amplitude, the loops became spindle-shaped and later developed concave crescent-like forms, while asymmetry also grew, with tensile-side strain exceeding compressive-side strain. It means the material does not simply cycle elastically around a stable centerline; it accumulates irreversible deformation as pore collapse, contact friction, and microcrack growth begin to separate loading from unloading. The new study examined backbone curves alongside those loops and found a hyperbolic trend that shifted toward smaller strains as curing age, confinement, or frequency increased.

The authors found using SEM that after 28 days, enclosed and broken pores, partially carbonated MgO and serpentine particles, and interlaced dypingite and hydromagnesite, features that help explain the cyclic response. Carbonation products fill voids, cement particles together, and stiffen the internal skeleton; once loading rises far enough, that same carbonate-bonded framework begins to lose local integrity, so the initial compaction benefit gives way to stiffness loss and higher dissipation.  The researchers observed an early increase in E_d with strain amplitude, then a nonlinear drop. The damping ratio moved in the opposite way at first, decreasing to a minimum and then rising before stabilizing. Curing age, confining pressure, and frequency each changed that pattern differently. Longer curing shifted the material toward higher E_d and lower damping after the transitional strain range of about 0.03 to 0.04%, which fits a denser carbonate network and fewer loose particles. Increased confinement produced higher stiffness but also a sharper decline in modulus once degradation began, a reminder that a stiffer skeleton under stronger lateral restraint may carry larger cyclic stresses before it starts to lose integrity. Frequency raised Ed and reduced damping at larger strains without changing loop shape very much, so the rate effect was real but structurally selective. The authors then fitted the data with a modified Darendeli-type framework and showed that confining pressure dominated E_dmax, curing age followed, and vibration frequency contributed the least. Even so, the model showed some deviation under long curing, high confinement, and extreme loading rates, where early hardening and coupled effects become more difficult to capture within a compact equation.

To summarize, Professor Songyu Liu and colleagues demonstrated direct linkage between carbonate mineral formation, hysteretic deformation, and strain-dependent stiffness loss in a lightweight geotechnical material intended for repeated loading service. They showed mineral carbonation changes how a lightweight fill should be read mechanically. SC-FC does not behave like a generic porous filler. Its dynamic response comes from a carbonate-bonded skeleton whose stiffness can rise briefly under early cyclic compaction, then deteriorate once pore collapse and crack growth reach the point where dissipation begins to dominate. The authors treat dynamic elastic modulus and damping ratio not as isolated descriptors but as coupled traces of internal change. When E_d climbs slightly before decaying, and D drops before turning upward, the two curves together reveal a material that first reorganizes and then degrades. That interpretation gives engineers a more discriminating basis for selecting fill materials in rail approaches, embankments, and similar systems exposed to repeated traffic or seismic disturbance. A lightweight material that gains apparent stiffness at low strain but loses it abruptly at higher confinement cannot be judged by a single index and the research work push toward strain-dependent qualification criteria tied to realistic stress paths.

We believe it is important findings that SC-FC replaces Portland cement with reactive MgO and serpentine-derived constituents while incorporating CO₂ during foaming and curing because the combination creates a plausible route toward lower-emission geotechnical fills, but only if mechanical reliability survives the transition from laboratory concept to cyclic service condition. The environmental argument becomes more persuasive once the dynamic behavior is quantified in terms that geotechnical practice already understands. The proposed predictive model offers also a practical description of the tested response within the studied curing ages, confining pressures, and frequencies, although some deviations remain under more demanding conditions. Materials created through carbonation do not always soften from the first increment of cyclic loading; some briefly tighten before damage takes command, and a model that misses that moment also misses part of the physics.

Preparation method and SEM images of serpentine carbon sequestration foamed concrete

Shield tunnelling beneath existing railway subgrades is still a problem in geotechnical engineering, largely because rail infrastructure responds poorly to even small vertical movements. Track systems tolerate very little distortion before operational limits are reached, and relatively minor differential settlement can translate into service restrictions, intensive monitoring, or unplanned reinforcement during construction. With the increase in cities density and heavier use of underground space, tunnelling beneath active rail corridors is now common and this shift has exposed the limitations of prediction methods that focus only on the final settlement profile, without addressing how deformation accumulates as excavation advances.

Although settlement induced by tunnelling has been studied for decades, its temporal development is still not straightforward to predict. Empirical approaches remain widely used, in part because they are easy to implement and grounded in accumulated field experience. However, these methods depend on simplified descriptions of settlement troughs and offer little transparency regarding the underlying mechanics. Their reliability also deteriorates when ground conditions are modified through reinforcement, since key parameters lose their original physical meaning. Numerical simulations provide a more explicit representation of construction sequences and soil–structure interaction, but this comes at the cost of extensive calibration, long runtimes, and sensitivity to modelling choices that are often difficult to justify during preliminary design. Data-driven techniques have attracted attention more recently, yet their reliance on dense monitoring records and limited interpretability restricts their usefulness before construction begins.

Indeed, analytical methods continue to play an important supporting role because   they provide a level of transparency that is often absent from other approaches by expressing settlement directly in terms of mechanical actions and material response. Solutions derived from the Mindlin framework have been especially influential, as they allow forces associated with tunnelling to be treated as distributed loads acting within an elastic ground mass. Extensions of this idea have accounted for face pressure, shield friction, grouting effects, and layered stratigraphy, yielding predictions that compare favourably with observations under controlled conditions. Still, most existing formulations treat settlement as an instantaneous outcome of applied loads. The excavation process, however, unfolds progressively, and the ground responds continuously as stresses are redistributed over time which are not easy to resolve in analytical settlement prediction.

A further difficulty arises from how ground loss is treated. Conventional analytical and semi-empirical models require assumptions regarding soil convergence or volumetric loss ratios, parameters that become uncertain once reinforcement modifies stiffness and stress redistribution. These assumptions hinder accurate description of how settlement accumulates during excavation and consolidation phases. A recent research paper published in Tunnelling and Underground Space Technology and conducted by Professor Yao Shan, Dr. Guankai Wang, Mr. Weifan Lin, Professor. Shunhua Zhou from the Shanghai Key Laboratory of Rail Infrastructure Durability and System Safety, at Tongji University in collaboration with Professor Frank Rackwitz from the Technical University of Berlin, the researchers developed a time-dependent analytical method for predicting railway subgrade settlement during shield tunnelling that integrates construction actions. They introduced a stress-release representation of ground loss that replaces assumed convergence models with an equivalent load framework and the method combines multiple excavation-related effects within a single Mindlin-based formulation while remaining computationally efficient.

The research team formulated an analytical framework that represents shield tunnelling as a sequence of mechanically distinct actions applied to a reinforced, layered soil mass. The authors first translated complex reinforcement schemes into equivalent elastic parameters by drawing on composite material theory, which allowed reinforced strata to be represented without sacrificing directional stiffness effects relevant to vertical deformation. The investigators then simplified the stratigraphy into an equivalent single-layer system so that established elastic solutions remained applicable while preserving the influence of stiffness contrasts above and below the tunnel axis. The authors examined settlement contributions by explicitly associating each construction action with a corresponding stress representation. They also demonstrated how face thrust, shield–soil friction, and synchronous grouting pressure could be expressed as spatially distributed loads whose influence migrated with tunnel advance through coordinate transformation. By embedding tunnel velocity directly into these transformations, the team ensured that settlement at a fixed monitoring point evolved continuously as excavation progressed, rather than appearing as a static superposition.

An important contribution emerged from the treatment of ground loss because instead of prescribing volumetric loss or convergence geometry, the investigators modeled excavation-induced loosening as a gradual release of in situ stress around the tunnel periphery. The team examined how this released stress could be recast as an equivalent load acting on the surrounding soil once the shield tail passed a given section and by linking the stress release rate to tunnel position, the authors aligned settlement development with excavation progress in a manner consistent with observed behaviour. The researchers observed that this formulation naturally reproduced distinct settlement phases reported in monitoring data, including early uplift or minor deformation during cutterhead approach, rapid settlement during shield passage, moderated response during grouting, and continued deformation during post-excavation consolidation. When applied to both a published benchmark case and a coastal railway undercrossing project, the analytical predictions followed measured time histories closely, especially in capturing prolonged settlement after excavation ceased. The study demonstrated that settlement patterns near the tunnel axis were predicted conservatively, while lateral distributions matched observed trough shapes with increasing accuracy away from the centreline.

In conclusion, Professor Yao Shan and colleagues provided a pathway for analytical prediction that remains valid even when reinforcement alters stiffness and load transfer by treating excavation-induced loosening as progressive stress release.  This perspective strengthens the physical basis of settlement analysis and reduces reliance on empirical calibration tied to specific soil conditions. Beyond its immediate application to railway undercrossing, the framework clarifies how time-dependent settlement emerges from the interaction between excavation actions and soil response. The explicit inclusion of tunnel advance allows engineers to anticipate not only peak settlement but also its rate of development, information that is critical for operational decision-making such as speed restrictions or monitoring thresholds. The method’s efficiency makes it suitable for early-stage evaluation, where multiple alignment or reinforcement scenarios must be assessed rapidly. Moreover, the new approach of Professor Yao Shan and co-workers provides a template for extending analytical solutions to other tunnelling contexts where staged construction and stress redistribution dominate ground response. While the formulation remains grounded in elastic theory, it suggests a bridge between short-term excavation effects and longer-term ground behaviour. With the increase in demand transparent, interpretable prediction tools in infrastructure projects the study work reinforces the continuing relevance of analytically grounded models within modern geotechnical practice.

What once worked for single-mode devices becomes awkward when precision, scalability, and wavelength diversity must coexist within the same wafer. Traditionally, producing several emission wavelengths on one chip has relied on either spatially varying the cavity thickness during epitaxy or engineering multiple quantum wells (QWs) with slightly different bandgaps. These strategies, though elegant in principle, suffer from poor scalability and material uniformity. Gradients created across wafers cannot easily yield distinct, well-defined cavities within a confined area, and QW-based emitters possess intrinsically narrow linewidths, requiring numerous meticulously tuned layers to cover even a modest spectral range. Methods based on metal-organic chemical vapor deposition with patterned masks have offered partial wavelength selectivity, but they involve repeated regrowth and lithography steps that complicate processing and reduce yield.

To this account, new research paper was published in Applied Physics Express, conducted by Yuuki Hodson, Tatsuki Yokota, and led by Professor Nobuhiko Ozaki from Wakayama University alongside Dr.  Eiichiro Watanabe and Dr. Naoki Ikeda from the National Institute for Materials Science.The researchers simulated cavity–reflectance framework predicting the relationship between GaAs layer thickness and resonant wavelength and realized fabrications of monolithic vertical cavities

via rotational metal-mask selective-area growth. These cavities incorporated stacked InAs quantum dots with different emission peak wavelengths to achieve broadband near-infrared emission resonating at multiple discrete wavelengths. The innovation lies in producing four distinct vertical cavities during a single uninterrupted molecular beam epitaxy process, eliminating post-growth patterning or regrowth steps while maintaining precise optical control across the wafer.

The team’s central idea was to examine this broadband QD emission while locally controlling the GaAs cavity thickness through selective-area growth. By introducing a rotatable metal mask with asymmetric windows during MBE growth, they could deposit additional GaAs layers only on chosen regions of the wafer, forming cavities of different optical lengths without breaking vacuum or exposing the surface to air. This approach promised a simplified, one-step fabrication process for creating multiple vertical cavities—each tuned to a distinct resonance wavelength—within the same monolithic structure. The motivation was not merely to demonstrate an optical novelty but to propose a realistic fabrication strategy for next-generation, compact, multi-wavelength VCSEL arrays that could serve telecommunication and biosensing applications alike.

The team began with numerical simulations using the Cavity Modeling Framework to predict how the reflectance spectrum of a GaAs-based cavity changes with thickness. A model consisting of 10.5 alternating AlAs/GaAs DBR pairs (96 nm / 82 nm) topped by a GaAs cavity containing stacked InAs QDs was analyzed. The simulation revealed a broad photonic stopband between 1.0 µm and 1.2 µm in wavelength, within which specific dips in reflectance corresponded to resonant cavity modes. Four target cavity thicknesses—347, 362, 377, and 392 nm—were selected to align these resonance wavelengths with the emission spectrum of InAs QDs, ensuring that each cavity would favor a slightly different mode around 1.13–1.18 µm. The researchers grew the structures on n-type GaAs(100) substrates using MBE. The bottom DBR was first deposited, followed by a 347 nm GaAs layer incorporating three stacked QD layers. Each QD layer was formed by supplying 2 monolayers of InAs at 480 °C, but capped differently to tune emission: one with GaAs at 0.5 ML/s, another at 1.0 ML/s, and the third with In₀.₂Ga₀.₈As at 1.25 ML/s. This combination produced broadband emission covering the simulated stopband. The authors then introduced a rotational metal mask containing asymmetric windows mounted on a rotatable holder inside the MBE chamber to generate cavities of variable thickness and by rotating the mask 90° between depositions, additional GaAs layers were selectively grown in four distinct regions, creating the four designed cavity thicknesses in one uninterrupted process. Finally, a three-pair AlAs/GaAs top DBR was deposited across the surface. Afterward, they performed optical characterization through reflectance and micro-photoluminescence (PL) mapping which confirmed the success of this selective-area growth. Distinct dips appeared in the reflectance spectra at 1118, 1129, 1137, and 1157 nm for VC1–VC4, and PL peaks matched these values within experimental error. Each cavity’s emission red-shifted progressively with increasing thickness, exactly as predicted. PL intensity and wavelength mapping further revealed homogeneous emission within each selective-growth area, with minor gradients attributed to natural MBE thickness variation. PL intensity from the MM-SAG sample rose almost linearly and reached nearly 100-fold enhancement relative to a QD reference sample without a cavity. This dramatic gain confirmed that the light was effectively confined and amplified by the vertical cavity modes. The emission remained stable and continuous across all regions, suggesting consistent optical thresholds suitable for future VCSEL operation.

In conclusion, the new study by Professor Nobuhiko Ozaki and colleagues is an important advancement toward practical broadband, multi-wavelength NIR light sources fabricated by a single epitaxial process. The rotational MM-SAG approach eliminates the multi-step lithography and regrowth traditionally required for wavelength multiplexing. By simply varying the GaAs cavity thickness within one continuous MBE run, the team realized four distinct optical resonators—each resonating at a different wavelength yet seamlessly integrated on the same wafer. This efficiency could significantly reduce manufacturing complexity and cost for VCSEL arrays used in compact optical communication modules and biometric sensors. The innovative work also demonstrates the remarkable synergy between InAs quantum dots and the selective-area growth concept. The broadband emission of the stacked QDs allowed simultaneous resonance with multiple cavity modes, achieving roughly 40 nm of wavelength separation—double that of conventional quantum-well-based VCSELs. This capability is critical for expanding data-transmission bandwidths in wavelength-division-multiplexed systems, where precise yet broad coverage of the NIR region is essential. Moreover, the use of excited-state (ES) emissions, which are less susceptible to ground-state reabsorption, provides an intrinsic advantage for achieving efficient lasing once electrical injection is introduced.

Additionally, the MM-SAG method paves the way for dense, chip-scale VCSEL integration. The size of the metal-mask windows can be miniaturized to several hundred micrometers, enabling compact arrays emitting at programmable wavelengths without device-to-device processing variability. Such architecture could underpin future “smart-sensing” platforms—devices capable of multi-spectral illumination for tissue diagnostics, chemical detection, or environmental monitoring. Additionally, the approach is inherently compatible with standard GaAs-based optoelectronic fabrication lines, making industrial translation plausible. We believe the innovative method also offers a new way into cavity–emitter coupling control via geometric confinement rather than compositional tuning. The pronounced photoluminescence enhancement and consistent mode behavior observed across different regions validate the precision of MM-SAG for tailoring optical microcavities. Importantly, the results illustrate that broadband QD ensembles can replace complex multi-QW stacks without sacrificing spectral flexibility. Indeed, such simplification could re-shape the design philosophy of multi-wavelength photonic devices and shift emphasis from material diversification to cavity-geometry engineering. Ultimately, the study establishes a clear pathway for developing compact, broadband, and tunable NIR emitters using rotational selective-area growth, and offers a bridge between fundamental semiconductor optics and applied photonic device engineering.

The controlled folding of single polymer chains into well-defined nanoscale architectures represents one of the most compelling frontiers in polymer chemistry. Inspired by the intricate folding of natural proteins, researchers have long sought to design synthetic macromolecules capable of self-organization through intramolecular interactions. Single-chain polymer nanoparticles (SCNPs) have emerged from this pursuit as a powerful class of materials where individual polymer chains collapse into compact entities via covalent or non-covalent linkages. Their structural precision and tunable functionality render them promising candidates for catalysis, sensing, and drug delivery. Yet, achieving rational control over their folding and unfolding processes remains a substantial challenge, particularly when dynamic, reversible interactions are required. Metal coordination offers a versatile means to guide molecular organization, drawing parallels with the role of metal cofactors in biological systems. However, while metal-mediated folding has been explored in small molecules and peptides, its systematic application in synthetic SCNPs is far less developed. Most previous strategies have relied on covalent crosslinking or rigid ligand–metal bonds that limit reversibility. The ability to drive polymer compaction through transient metal–ligand interactions—strong enough to induce collapse, yet labile enough to reverse upon demand—could open an entirely new dimension of structural control in soft materials.

To this account, new research paper published in Polymer Chemistry and conducted by Dr. Sebastian Gillhuber, Dr. Jochen Kammerer, Dr.  Ada Quinn, Dr. Joshua   Holloway, Kai Mundsinger, Dr. Evelina Liarou, Dr.  Dmitri Golberg, Dr.  Hendrik Frisch, Dr.  Megan   O’Mara and led by Professor Christopher Barner-Kowollik from the Queensland University of Technology (QUT) in Australia and Professor Peter W. Roesky from the Karlsruhe Institute of Technology (KIT) in Germany, the researchers developed two complementary models to elucidate Ba(II)-induced polymer compaction. The first is an experimental model showing that coordination between Ba²⁺ ions and polymeric carboxylates produces reversible, intramolecular nanoparticle folding. The second is a molecular-dynamics model capturing the transient, non-permanent nature of these interactions, where barium ions dynamically bridge distant chain segments. Together, they establish a comprehensive picture of reversible, metal-controlled single-chain folding validated by atomic-scale imaging.

The research team began by synthesizing a statistical copolymer, designated P1, through RAFT polymerization of PEG methyl ether methacrylate and 2-carboxyethyl acrylate. The composition balanced water solubility with a controlled fraction (~14 %) of pendant carboxyl groups, which later served as coordination sites. Upon gradual mixing of an aqueous P1 solution with barium hydroxide octahydrate, intramolecular folding was triggered by complexation between Ba(II) ions and deprotonated carboxylates, producing Ba-functionalized nanoparticles (SCNP1-Ba).

Spectroscopic and hydrodynamic analyses confirmed the transition from an extended coil to a compact entity. Infrared spectra showed the disappearance of the carboxylic C=O stretch and emergence of symmetric and asymmetric COO⁻ vibrations, signaling conversion to barium carboxylates. Diffusion-ordered NMR revealed a measurable increase in diffusion coefficient consistent with reduced hydrodynamic volume, while SEC traces shifted toward lower apparent molar mass, and DLS data indicated a modest but reproducible decrease in particle diameter. Collectively, these results established the successful intramolecular compaction of single polymer chains.

To verify that folding originated from Ba(II) coordination rather than altered hydrogen bonding, a styrene-based analogue lacking polar groups was tested; it too underwent barium-induced compaction, confirming the metal-driven mechanism. Complementary MD simulations provided a dynamic picture of these interactions. Over simulated trajectories, barium ions continuously associated and dissociated from polymer carboxylates, spending roughly two-thirds of their time coordinated yet rarely forming permanent inner-sphere complexes. Instead, the dominant motif involved transient bridging within the second coordination shell, wherein one ion simultaneously contacted multiple carboxylates. This produced momentary intramolecular crosslinks that collectively reduced polymer dimensions without rigidifying the structure. The simulations further revealed that Ba(II) accelerated the collapse of extended chains but did not substantially change the equilibrium size, underscoring a kinetic—rather than purely thermodynamic—role in compaction. The authors demonstrated the reversibility of folding by adding sulfuric acid to precipitate insoluble BaSO₄, thereby removing the coordinating ions and regenerating the original carboxylic acid polymer. SEC and IR spectra of the recovered material were nearly identical to those of the starting P1, and a subsequent re-addition of Ba(II) faithfully re-established the SCNP state. Finally, the heavy-atom contrast of barium enabled direct imaging of individual metal atoms by annular-dark-field STEM. At low magnification, bright clusters marked Ba-rich regions, while at atomic resolution, discrete barium atoms appeared as distinct luminous points. Quantitative image analysis revealed an average of roughly 30 ions per nanoparticle, though cryogenic blotting techniques suggested that isolated SCNPs often contained only one or two Ba atoms, confirming the high sensitivity of preparation conditions. This atomic-level visualization of metal distribution within single polymer chains marks a technical milestone for metallopolymer characterization.

In conclusion, the collaborative research work of Professor Christopher Barner-Kowollik and Professor Peter W. Roesky with their groups, redefines how dynamic metal–polymer interactions can be harnessed to engineer adaptive nanostructures. By exploiting the transient binding of Ba(II) ions, the researchers demonstrated a system where single-chain nanoparticles can fold and unfold reversibly under mild, aqueous conditions. Such control transcends conventional covalent or supramolecular strategies, offering a non-destructive handle over polymer conformation analogous to biological metalloproteins that modulate structure through metal-ion exchange.

The implications extend beyond the specific case of barium. Because the coordinating 2-carboxyethyl groups mimic the side chain chemistry of glutamic acid, the polymer backbone serves as a synthetic analogue for natural systems where Ca²⁺ or Mg²⁺ ions govern folding or catalysis. Thus, the SCNP1-Ba model provides a minimal yet experimentally tractable framework for investigating the thermodynamics and kinetics of metal–carboxylate interactions in biomimetic environments. Moreover, the observed reversibility through BaSO₄ precipitation underscores a general strategy for controlling polymer states by selective removal or introduction of counter-ions—a concept that may inspire switchable materials, recyclable catalysts, or stimuli-responsive delivery carriers.

Equally important is the methodological advance achieved through atomic-level STEM imaging. The ability to detect individual heavy-metal atoms within single polymer chains bridges a long-standing analytical gap, allowing researchers to quantify metal distribution, correlate structure with catalytic or optical properties, and validate computational models with direct visual evidence. When coupled with MD simulations, this dual experimental–computational approach establishes a blueprint for probing dynamic metallopolymer systems that cannot be described by static spectroscopy alone. In a broader context, the study demonstrates that intramolecular compaction does not necessitate permanent crosslinking but can emerge from a dynamic equilibrium of transient coordination events. This insight may influence future design principles in soft-matter chemistry, where achieving mechanical integrity and reversibility often stand at odds. The authors’ integration of reversible metal binding, precise polymer synthesis, and high-resolution imaging thus offers a platform for exploring catalysis, sensing, and self-repair mechanisms at the single-chain level. Ultimately, the work exemplifies how collaboration across synthetic, computational, and analytical disciplines can resolve long-standing questions about structure–function relationships in metallopolymers. The results invite extensions to other ions, ligands, and solvent environments, opening pathways toward artificial materials that emulate the subtle responsiveness of biological macromolecules.

Crossed-beam energy transfer (CBET) has been used as a tuning mechanism in indirect-drive laser fusion, allowing energy to be redistributed between beams with slightly different frequencies in order to improve symmetry. In direct-drive configurations, however, CBET is detrimental. At a mechanistic level, two intersecting laser beams exchange energy through a resonant three-wave interaction mediated by an ion-acoustic wave. However, the dynamic details of this interaction in realistic plasmas—particularly in direct-drive laser fusion—remain unclear. Here, CBET is primarily confined to the region near the critical density surface, where strong laser refraction and reflection dominate. Laser trajectories bend, interference patterns form and dissolve, and small changes in plasma conditions can noticeably alter the coupling strength. Capturing this behavior in a way that remains stable and predictive places heavy demands on numerical models, especially when CBET must be embedded within radiation-hydrodynamics simulations that already strain computational resources. Over time, two broad modeling strategies have taken shape. Ray-based models, which describe laser beams as bundles of geometric rays, are attractive because they are fast and integrate naturally with large-scale fusion codes. Their weakness becomes apparent precisely where CBET is most active. Caustics, phase singularities, and unresolved interference force the introduction of empirical limiters and calibration factors, reducing confidence in quantitative predictions. Wave-based models avoid many of these issues by resolving the electromagnetic field directly, but the price is steep. Resolving optical wavelengths over millimeter-scale plasmas and nanosecond time windows quickly becomes impractical, even on modern computing platforms.  To this end, new research paper published in Physics of Plasmas and conducted by Doctoral student Xiaobao Jia; Dr. Qing Jia; Dr. Jianyuan Xiao; and Professor Jian Zheng from the University of Science and Technology of China, the researchers developed a Hamiltonian reformulation of crossed-beam energy transfer that recasts laser–plasma coupling as a structure-preserving dynamical system. On this basis, they introduced an explicit symplectic numerical algorithm implemented in the BEAM code, achieving wave-level accuracy at dramatically reduced computational cost. They further derived a physically transparent CBET gain formula directly from the Hamiltonian, enabling reliable prediction of energy transfer without empirical tuning.

The research team reformulated the coupled laser–plasma interaction equations governing CBET. Starting from the wave equation for electromagnetic propagation in a plasma and a fluid description of the ion-acoustic response, the system is reduced to two coupled Schrödinger-type equations for the laser envelopes, linked through the ion density perturbation. Rather than treating this coupling as a purely numerical construct, the authors explicitly decompose the complex field variables into real and imaginary components and demonstrate that the resulting evolution equations satisfy canonical Hamiltonian form. This identification is nontrivial: it reveals that the total energy of the interacting laser–ion-acoustic system is conserved in the absence of damping and provides a natural foundation for symplectic time integration. Afterward, the authors implemented symplectic algorithm through Hamiltonian splitting, in which the full Hamiltonian is decomposed into analytically solvable sub-Hamiltonians. Each sub-step advances the system exactly over a finite time increment, and their composition yields a globally stable, structure-preserving scheme. This algorithm is implemented in the BEAM code, with fluid equations for the ion-acoustic wave solved on a coarser time scale and electromagnetic propagation handled with absorbing boundary layers to suppress artificial reflections.

The authors tested the performance of their approach against particle-in-cell simulations across three increasingly demanding scenarios, as is shown in the figure below. In the first, laser reflection near a turning point in a strongly refracting plasma is simulated. The wave-based BEAM results reproduce interference patterns, refraction, and reflection observed in fully kinetic simulations with striking fidelity, despite orders-of-magnitude lower computational cost. In the second case, two intersecting Gaussian beams undergo CBET in a uniform plasma. The spatial redistribution of intensity and the temporal growth of energy transfer agree closely with particle-in-cell results, while BEAM completes the simulation in minutes rather than hundreds of CPU hours. Finally, the model is tested in the strong-coupling regime of Brillouin amplification, where a short probe pulse extracts energy from a long pump pulse. The simulated pulse compression, amplification factors, and pump depletion dynamics quantitatively match established kinetic benchmarks.

Beyond constructing the numerical scheme and developing simulation tools for CBET, the team also found the Hamiltonian formulation to yield an analytical CBET gain expression. They derived a gain formula that remains accurate across a broad range of intensities by relating the energy stored in the ion-acoustic wave to the depletion and amplification of the interacting beams, the predicted gain closely tracks full wave simulations, which provided a compact and physically grounded estimator for CBET strength.

Figure:​ Three benchmark cases for the BEAM code: (i)​ crossed-beam energy transfer, comparing BEAM2D simulations (a-b) with PIC simulations (c-d); (ii)​ laser refraction and reflection at the turning surface; and (iii)​ Brillouin amplification of a short laser pulse.

In conclusion, the new work of Professor Jian Zheng and colleagues unified wave-based accuracy and computational efficiency in a way that has eluded previous approaches. The implications for inertial confinement fusion are substantial and CBET remains one of the dominant uncertainties in direct-drive implosion modeling, where even modest errors in energy redistribution can lead to large deviations in symmetry and yield. The BEAM framework provides a tool that can be deployed at scales relevant to experiments without resorting to empirical correction factors. Its efficiency makes it suitable for parametric studies, design optimization, and integration into larger simulation pipelines where kinetic models are simply infeasible. Moreover, the analytical CBET gain formula derived from the Hamiltonian formalism and this expression provides a rare bridge between first-principles theory and operational modeling. Rather than calibrating ray-based codes against experiments or kinetic simulations in an ad hoc manner, modelers can use the Hamiltonian gain as a physically motivated benchmark. This has direct relevance for facilities seeking to control or mitigate CBET through beam geometry, frequency detuning, or plasma flow tailoring. Furthermore, the work illustrates the power of structure-preserving numerical methods in plasma physics. Symplectic integration is widely appreciated in celestial mechanics and accelerator physics, yet it remains underutilized in laser–plasma interaction modeling. By demonstrating its effectiveness for CBET, the authors invite similar treatments of other laser-plasma instabilities, including Raman scattering and multi-wave coupling processes, where energy conservation and phase coherence are central. Indeed, the new work of Xiaobao Jia etl al reshapes how CBET can be approached, analyzed, and ultimately controlled in fusion-relevant plasmas.