Browse Articles

A stochastic simulation of the dislocation-mediated etching of porous GaN distributed Bragg reflectors

Distributed Bragg reflectors (DBRs) can be fabricated by electrochemically etching nitride epitaxial structures consisting of alternating layers of highly n-type doped and non-intentionally doped (NID) GaN. Threading dislocations (TDs) can be electrochemically etched into transport pipelines that can carry the etchant through the NID layers to access the doped material. Experimentally, this has been shown to involve a mechanism where the etching pathway may follow one TD into a doped layer and then propagate sideways through the doped layer to continue via a different TD. Across multiple layers, this process creates complex pore structures that have been described as “cascades.” Here, we build a stochastic simulation for the DBR etching process that can reproduce some key features of the observed microstructures. By comparing the simulation output to samples etched at a range of voltages, we show that we can reproduce variations in experimental chronoamperometry data with applied bias by varying the probability of etching the doped layers within the simulation. The outputs of the resulting simulations replicate the experimentally observed cascade morphology. At higher voltages, experimental data reveal a lower proportion of cascade features, a trend that is also replicated by the simulations for relevant probability values. Outputs of the simulations also correlate well with experimental chronoamperometry data for samples where—unlike in a DBR—the thicknesses of the doped layers vary through the epitaxial multilayer, suggesting that the probabilistic simulation can be applied to a range of structures to help understand the dislocation-mediated electrochemical etching process.

Deep learning and radiomics models in patients with advanced non-small cell lung cancer treated with immunotherapy combined with stereotactic radiotherapy

Revisiting what we lose by coarse-graining: Modeling cooperative hydrophobic phenomena with short-ranged, pair-additive forces

Water and, in particular, hydrophobic phenomena play a central role in science and technology. Unfortunately, the cooperative, many-body interactions that govern hydrophobic phenomena severely challenge coarse-grained (CG) models. Accordingly, we examine current methods for coarse-graining water. We demonstrate that pair potentials determined via force-matching and iterative Boltzmann inversion provide very similar descriptions of hydrophobic phenomena. By modifying these potentials with relatively long-ranged attractive tails, the corresponding models reasonably stabilize the liquid phase under ambient conditions. However, they significantly overestimate solvation free energies, the width of liquid interfaces, and the magnitude of global and local density (LD) fluctuations. These models also fail to capture the cooperativity of hydrophobic phenomena. More surprisingly, while the local compressibility, χ̃R, of water decreases with length-scale, R, χ̃R actually increases with R in these CG models. This qualitative failure stems from the attractive tails that are commonly used to stabilize liquids. Conversely, by supplementing pair potentials with a global density (GD) potential, CG models accurately reproduce global and LD fluctuations. Nevertheless, this GD model dramatically overestimates solvation free energies and fails to stabilize liquid–vapor coexistence. In contrast, LD potentials that generate pair-additive, environment-dependent forces describe water much more accurately. Although it slightly underestimates the surface tension, this LD model reasonably reproduces the structural and thermodynamic signatures of cooperative hydrophobic phenomena across a wide range of length scales. Our results emphasize the importance of reproducing the local coordination, surface tension, and density fluctuations, while detailed structural correlations appear less important for modeling hydrophobic phenomena.

Advanced Therapy for Intermediate-Risk Pulmonary Embolism

Synergistic damage buildup and helium segregation in helium-accumulated copper under overlapping cascades

The accumulation of transmutant helium (He) poses a major challenge to the structural integrity of materials in the nuclear industry. To elucidate the He effects on microstructural evolution, we performed molecular dynamics simulations of overlapping collision cascades in copper containing pre-existing substitutional He, at concentrations up to 10 000 appm and a cumulative dose of ∼0.24 dpa. Based on statistical analysis across multiple independent simulation runs, the results reveal a synergistic evolution between He atoms and radiation-induced defects. In contrast to the large, localized dislocation loops formed in pristine Cu, He-containing samples developed a distinct damage structure characterized by smaller loops and homogeneously distributed defect clusters. This morphology originates from dominant continuous recombination–replacement reactions between self-interstitials and substitutional He, which eject substantial amounts of He into interstitial sites. These He atoms constitute a significant fraction of the interstitial clusters, and their formation into Cu–He complexes severely restricts cluster mobility. Consequently, the agglomeration and growth of dislocation loops are suppressed. Simultaneously, an interstitial-mediated mechanism drives pronounced He segregation and initial bubble nucleation. The atomic-scale insights provided by this study are crucial for understanding He-induced microstructural degradation under prolonged irradiation.

Meet the biologists deciphering marine-mammal histories from baleen, whiskers and tusks

Body weight variability and mortality in older adults: a nationwide population-based cohort study

Abstract Although body weight variability has been linked to adverse outcomes, its relationship with mortality in older adults remains unclear. We investigated the association between body weight variability and mortality in older adults using a nationwide cohort from the Korean National Health Insurance Service. Adults aged ≥ 75 years who underwent health checkups between 2012 and 2015 were followed until 2022. Body weight variability was assessed using the variability independent of the mean (VIM) based on at least four measurements. Participants were classified by VIM quartiles and weight-change categories. Mortality risks were estimated using multivariable Cox proportional hazards models. Among 616,696 participants, 195,585 deaths occurred during follow-up. Higher VIM was associated with increased all-cause mortality (adjusted HR for highest vs. lowest quartile, 1.62; 95% CI, 1.60–1.64) in a clear dose–response manner ( P for trend < 0.001). This association was consistent across subgroups. High VIM was associated with increased mortality regardless of the direction of weight change. Higher VIM was independently associated with an increased risk of all-cause and cause-specific mortality among older adults. Body weight variability itself, rather than the direction of weight change, may serve as a relevant prognostic marker in this population. Further studies are needed to clarify the clinical implications of body weight variability in older adults.

Classification of interfacial water governed by water–polymer interactions in hydrated polymers: A molecular dynamics simulation study of ethylene-based and acrylate polymers

We perform molecular dynamics simulations to investigate hydration structures and dynamics in seven water-containing polymers: poly(vinyl alcohol) (PVA), poly(2-hydroxyethyl acrylate) (PHEA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(butyl acrylate) (PBA), poly(2-methoxyethyl methacrylate) (PMEMA), poly(ethylene glycol) (PEG), and poly(2-methoxyethyl acrylate) (PMEA). The analysis integrates four perspectives: the water-content dependence of the glass transition temperature Tg, polymer chain fluctuations characterized by dihedral angle distributions, hydrogen-bond lifetimes τHB between water and polymer functional groups, and the localization and exchange dynamics of confined water quantified by the distinct part of the van Hove correlation function. Hydroxyl-containing polymers (PVA, PHEA, and PHEMA) exhibit relatively high dry-state Tg values and a pronounced depression upon hydration. Chain fluctuations are limited, and τHB follows Arrhenius behavior, forming localized hydration shells. In contrast, PMEMA and PBA show low equilibrium water contents and hydrophobic character; although their dry-state Tg values are moderately lower and less sensitive to water content, chain fluctuations remain small, and τHB also obeys Arrhenius behavior, with hydrophobic aggregation promoting water localization. PEG and PMEA display low dry-state Tg values and weak water-content dependence. Greater rotational freedom around ether or methoxy oxygen atoms leads to larger chain fluctuations and loosely bound water. Below Tg, τHB between water and ether or methoxy oxygen atoms exhibits super-Arrhenius behavior. These results clarify three hydration types: highly hydrated (PVA, PHEA, and PHEMA), hydrophobic (PMEMA and PBA), and flexibly hydrated (PEG and PMEA), and provide a molecular-level framework for interpreting interfacial water governed by water–polymer interactions.

When Closure Finds You

Green synthesis of TiO2 nanoparticles using <i>Azadirachta indica</i> flower extract and evaluation of their photocatalytic performance

Industrial dyes such as methylene blue (MB) and methyl orange (MO) pose significant ecological risks when released into aquatic systems. In this study, titanium dioxide nanoparticles (TiO2 NPs) were synthesized via a green synthesis approach using Azadirachta indica flower extract and titanium tetraisopropoxide. The bioactive compounds in the extract acted as reducing and stabilizing agents, promoting the formation of anatase-phase TiO2. The synthesized nanoparticles were characterized using UV–visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and transmission electron microscopy (TEM). UV–vis analysis confirmed a bandgap energy of 3.2 eV, while XRD results indicated a tetragonal anatase structure. FT-IR spectra showed reduced intensities of N—H and C=O functional groups, confirming the role of biomolecules in nanoparticle stabilization. TEM images revealed predominantly spherical nanoparticles with sizes below 20 nm. Photocatalytic degradation studies demonstrated high efficiency, with maximum degradation of 99.30% for MB at pH 8 and 99.17% for MO at pH 5. The degradation followed first-order kinetics, with rate constants of 0.0403 min−1 for MB and 0.00773 min−1 for MO. These findings highlight the potential of green-synthesized TiO2 nanoparticles as an effective and sustainable photocatalyst for wastewater treatment.

Connecting pre-existing digitalization and technology adoption speed with AI-driven business model transformation via employee competencies

Abstract This study investigates how pre-existing digitalization and technology adoption speed shape AI-driven business model transformation, with particular attention to the mediating role of employee competencies. Grounded in the resource-based view and digital transformation theory, the study employs structural equation modeling on survey data collected from 421 employees across various industries operating in Egypt. The results reveal that pre-existing digitalization and technology adoption speed directly and indirectly influence AI-driven business model transformation. Moreover, employee competencies significantly influence AI-driven business model transformation and partially mediate the effects of pre-existing digitalization and technology adoption speed on this outcome. This work contributes to the literature on artificial intelligence and digital transformation by demonstrating that employee competencies constitute a pivotal organizational mechanism linking the technological environment to business model innovation. Further, the study offers empirical insights into an emerging economy where the interplay between human capital and technological advancement has not been adequately studied.

Electronic spectroscopy of the gas-phase H2CCCO+ cation

Resolution of PML after Treatment with Virus-Specific T Cells and HCT

Evaluation of thermal and electrical properties of GaN grown using oxide vapor-phase epitaxy

In this study, we investigated the thermal and electrical properties of gallium nitride (GaN) crystals grown usingthe oxide vapor-phase epitaxy (OVPE) method. We comprehensively evaluated the thermal conductivity and electrical resistivity of OVPE-GaN specimens across the wide oxygen-concentration range of 1019–1021 cm−3, which included a so far uninvestigated ultrahigh doping range beyond 1020 cm−3. The evaluation results demonstrated that the thermal conductivity of the OVPE-GaN specimens decreased monotonically as the oxygen concentration increased, declining to approximately one-fifth of that of specimens composed of unintentionally doped (UID) GaN whose crystals were grown using hydride vapor-phase epitaxy (HVPE) at the highest doping level. Notably, OVPE-GaN specimens with oxygen concentrations in the 1019 cm−3 range exhibited a c axis thermal diffusivity comparable to that of UID-HVPE-GaN specimens. Furthermore, thermal anisotropy was observed in the OVPE-GaN specimens over the mentioned oxygen-concentration range, where c axis thermal diffusivity was higher than in-plane thermal diffusivity because of the unique crystalline structure of the specimens consisting of spatially separated high- and low-oxygen-concentration regions. Although the electrical resistivity also decreased with increasing oxygen concentration, the doping efficiency significantly decreased as the oxygen level increased despite the continued increase in the carrier concentration. Rutherford backscattering spectrometry/channeling measurements provided direct evidence that a large portion of the oxygen impurities in high-concentration OVPE-GaN occupied interstitial positions. The interstitial oxygen atoms functioned as acceptors, resulting in a reduced doping efficiency. Furthermore, the atoms were expected to induce lattice strain, which enhanced phonon scattering, thereby partly reducing the thermal conductivity. These findings are crucial for the thermal management of devices fabricated on OVPE-GaN substrates.

SmartGridDrive: an integrated adaptive Q-learning framework for precision self-parking and reverse navigation in dynamic grid environments—a proof-of-concept study

Ultrafast solvation dynamics of nitrous oxide in alkylmethylimidazolium ionic liquids

Nitrous oxide is a potent greenhouse gas and the leading ozone depleting pollutant. 1-alkyl-3-methylimidazolium bistriflimide based ionic liquids are effective at trapping N2O as well as CO2. Despite being similar to CO2 in many ways, N2O has a permanent dipole moment that allows it to dissolve in both nonpolar and polar solvents. Fourier transform infrared spectroscopy, polarization-controlled two-dimensional infrared spectroscopy, and ultrafast pump–probe spectroscopy of the asymmetric stretch (ν3) band of N2O characterize its solvation structure and dynamics in a series of alkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids ([CnC1Im][Tf2N], n = 2–12). The asymmetric stretch redshifts by 4 cm−1 as the imidazolium alkyl chain increases from 2 to 12 carbons. Vibrational relaxation occurs on a 71–94 ps timescale, decreasing with chain length. Vibrational energy redistribution rates are independent of chain length (14 ps). Rotational correlation times increase with chain length from 20 to 37 ps. Reorientational dynamics are modeled as wobbling in a cone and compared to hydrodynamic and quasihydrodynamic models of rotational diffusion. The polarization-weighted frequency fluctuation correlation functions (PW-FFCFs) decay due to both reorientation-induced spectral diffusion and structural spectral diffusion (SSD). The PW-FFCF is modeled as wobbling in a cone with a first-order Stark effect. The experiments support the solvation of N2O in the charge enhanced domains of the ionic liquids, similar to CO2.

Decompression with or without Duraplasty for Chiari I and Syringomyelia

Near transform-limited single photons from rapid-thermal annealed quantum dots

Single-photon emitters are essential components for quantum communication systems, enabling applications such as secure quantum key distribution and the long-term vision of a quantum internet. Among various candidates, self-assembled InAs/GaAs quantum dots (QDs) remain highly promising due to their ability to emit coherent and indistinguishable photons, as well as their compatibility with photonic integration. In this work, we investigate the impact of post-growth rapid thermal annealing (RTA) on the quantum optical properties of single self-assembled QDs embedded in a p-i-n diode structure. The annealing process induces a controlled blueshift of the emission wavelength by promoting Ga in-diffusion and intermixing. Using resonance fluorescence measurements at cryogenic temperatures (4.2 K), we investigate the single-photon statistics, the emission linewidths, and coherence time T2 of the emitted photons. Our results show that, despite the high annealing temperature of 760 °C, the process does not degrade the optical quality of the quantum dots strongly. Instead, we observe single-photon emission with near transform-limited linewidths, where the dephasing time T2 is only a factor 1.5 above the Fourier-limit T2 = 2T1. These findings demonstrate that rapid thermal annealing (RTA) serves as an effective tuning method that preserves the key single-photon emission properties and may help reduce undesirable effects such as non-radiative Auger recombination in quantum photonic applications.

Design and development of a high-efficiency sustainable wireless charging system for autonomous electric vehicles powered by renewable energy sources for remote locations

Elucidating the structure–property relationships of CL-20/HMX energetic cocrystal materials based on molecular simulation

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)–1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) cocrystal is one of the most promising energy-containing cocrystals. However, the formation mechanism of the CL-20-HMX cocrystal and its effect on the performance of the resulting product remain incompletely understood, which limits the practical application of the cocrystal explosives. In this study, the molecular mechanism of CL-20-HMX cocrystal formation was systematically investigated using density functional theory. The results revealed a substantial disparity in chemical potential between ε-CL-20 and β-HMX, indicating a strong tendency toward cocrystal formation. Moreover, abundant intermolecular interactions favor the formation of cocrystals. Molecular dynamics simulations were used to explore and explain the differences in mechanical and safety properties among cocrystals, mixture systems, and single components. The results indicate that, compared to CL-20, the CL-20-HMX cocrystal exhibits reduced rigidity, enhanced ductility, and improved safety properties.