Browse Articles

Behavioral effects of academic pressure on the risk of adolescent idiopathic scoliosis: a case-control study

Self-diffusion and interface diffusion in crystalline and amorphous Ni/Ti multilayer: A molecular dynamics study

Diffusion phenomena in crystalline and amorphous Ni/Ti binary multilayer systems have been simulated by the molecular dynamics (MD) technique in a wide temperature range of 473–1600 K and compared with the experimental results. Evolution of the diffusion process and crystalline phase formation has been investigated as a function of annealing temperature. Formation of the B2-phase (austenite) of the NiTi alloy has been noticed at the interface for an amorphous multilayer system at a relatively lower temperature compared to the crystalline multilayer system, which corroborates well with our earlier experimental findings on this system. MD simulation has also helped to study the diffusion of Ni and Ti separately and it is observed that the diffusion of Ni and Ti in an amorphous system is higher than the corresponding diffusion in a crystalline system. A very interesting difference has been noticed with self-diffusion being dominant in Ti and interface diffusion in Ni. As a result, the formation of new FCC and BCC Ti phases has been observed in the amorphous Ti layer. Individual diffusion coefficients of Ni and Ti are estimated for both crystalline and amorphous systems, and it is observed that the variation of diffusion coefficients with temperature follows the Arrhenius-type relation, with lower activation energies obtained for the amorphous system over the crystalline system. Furthermore, the diffusion mechanism for both the systems is discussed. The above study gives important insight into the interface diffusion process of a technologically important multilayer system and would be immensely helpful in designing applications of such multilayers.

From predictors and SHAKE toward unified integration scheme for molecular dynamics

Molecular dynamics (MD) simulations applied to various special tasks such as thermostats, barostats, external volume control, or external magnetic fields often require tailored integration methods, complicating software development. Here, we propose a unified integration scheme for solving the common sets of equations of motion in MD. To achieve this, we adapted the traditional SHAKE method for treating rigid bonds to a predictor–corrector integration scheme and combined it with the existing time-reversible velocity predictor and box predictor. This new approach enables using both the time-honored Verlet method and the recently improved Gear methods. The resulting unified integration scheme was tested on two simple models and two MD systems: SPC/E water and ionic liquid (1-ethyl-3-methylimidazolium tetrafluoridoborate). Trajectories in microcanonical, Nosé–Hoover canonical, and MTK isobaric ensembles were generated. The results for Verlet-based methods were in excellent agreement with those obtained using conventional integration methods. For particular tasks, the use of higher-order methods can be beneficial. Overall, in comparison with standard approaches, our universal scheme provides a significantly simpler route to devising new integrators and maintaining existing simulation software. Furthermore, our family of new integrators can be efficiently deployed in massively parallel MD software.

Investigation of sol-gel derived organic inorganic hybrid coatings based on commercial epoxy resin for improved corrosion resistance of 304 stainless steel

Design of a new open-type active electromagnetic metamaterial for magnetic field control based on numerical method

Controlling magnetic field with active electromagnetic metamaterial (AEM) consisting of a group of wires with precise arrangements of currents, essential for a wide range of applications, is limited by the structure where the source is fully surrounded by the concentric cylindrical AEM. We propose an open-type AEM design method based on the transformed medium theory and finite-element calculation method to overcome this stringent limitation. We experimentally demonstrate that an open-type AEM with negative magnetic permeability controls the magnetic field of a straight current wire at a distance outside the AEM. Our strategy leads to focus on the magnetic field in empty space with various structural forms and may broaden the application scope of electromagnetic metamaterials.

Picosecond imaging of dynamics of solvated electrons during femtosecond laser-induced plasma generation in water

The dynamics of solvated electrons were visualized using absorption imaging with sub-picosecond time resolution based on a pump–probe measurement during the early stages of femtosecond laser-induced plasma generation in water. The solvated electrons were generated by the propagation of a femtosecond laser pump pulse. In the area with a pump laser intensity over 2 × 1013 W/cm2, where a high density of free electrons was produced, solvated electrons exhibited an additional rapid increase in optical density (OD) at 800 nm, 7–9 ps after the pump pulse excitation. In contrast, no two-step increase in OD was observed when probed at 400 nm, suggesting that the absorption coefficient of the solvated electrons rapidly changed around 800 nm after femtosecond laser excitation for a few picoseconds. This observation might indicate the structural and electronic modulation of solvated electrons owing to the high density of free electrons in water, accompanied by femtosecond-laser-induced plasma generation.

ChatGPT performance in assessing musculoskeletal MRI scan appropriateness based on ACR appropriateness criteria

Highly transparent smart thermal emitter realized by thin vanadium dioxide

Global energy shortage necessitates enhancing environmentally friendly and energy-saving technologies. This study demonstrates a smart thermal emitter (STE) with high visual transparency and temperature-dependent emissivity to realize smart thermal management in buildings or automobiles. The STE consisting of layered transparent conductive oxide (TCO), zinc sulfide (ZnS), and thin vanadium dioxide (VO2) films was fabricated using the sputtering process. The STE exhibited high transmittance in the visible region owing to the extremely thin VO2 film and the large optical bandgaps of TCO and ZnS. The average transmittance in the wavelength range of 400–800 nm was 0.57. Owing to the metal–insulator transition of VO2, a metal–insulator–metal structure resonating in the infrared region was formed above 70 °C, which increased the thermal emissivity. The thermal emissivity values at 29 and 91 °C in the infrared region within 2.5–15 μm were 0.29 and 0.66, respectively. The appearance of the STE remained almost unchanged even when the emissivity increased with temperature because the refractive index spectra of VO2 in the visible range hardly change by the metal–insulator transition. In addition, W-doped VO2 allowed the STE to operate under summer temperatures (48 °C). This scalable fabrication process and high visual transparency have significant potential in practical applications, such as windows or exterior coatings, for smart thermal management.

Zero-point energies from bond orders and populations relationships

We report two analytical quantum mechanics (QM) models for approximating appropriately scaled harmonic zero-point energies (ZPEs) without Hessian calculations. Following our earlier bond energies from bond orders and populations model that takes a similar form as an extended Hückel model but uses well-conditioned orbital populations, this work demonstrates a proof of concept for approximating ZPEs, an important component in thermochemistry calculations, while eschewing unfavorably scaling algorithms involving Hessian matrices. The ZPE-BOP1 model uses Mulliken orbital populations from hybrid Kohn–Sham density functional theory calculations within an extended Hückel-type model that defines vibrational bond energy terms using two atom-pairwise parameters that are fit to reproduce ZPEs from B3LYP calculations. The more accurate ZPE-BOP2 model uses Mulliken orbital populations from Hartree–Fock calculations within a different extended Hückel-type model that includes a short-range anharmonic energy term and a coupled three-body oscillator energy term with seven atom-pairwise parameters. Both models predict ZPEs in molecules involving first row elements, but ZPE-BOP2 outperforms ZPE-BOP1 in strained and long-chain molecules and provides ZPEs more competitive with those from semi-empirical QM methods (e.g., AM1, PM6, PM7, and XTB-2) that compute ZPEs with Hessian calculations. This work shows progress and an outlook toward computational models that use well-conditioned orbital populations to efficiently predict useful physicochemical properties. It also shows opportunities for approximate QM models that would shift traditional computational bottlenecks away from costly algorithms such as Hessian calculations to others that focus on reliable orbital populations.

RETRACTED: Optimizing light absorption and emission in thermophotovoltaics: A study of tungsten–hafnium dioxide metamaterials

This study presents a theoretical investigation into the spectral performance of a metamaterial structure composed of tungsten (W) and hafnium dioxide (HfO2) layers, which are specifically designed for applications in energy conversion. The proposed metamaterial, which is structured in a multilayer W/HfO2/W configuration, aims to increase light absorption and emission characteristics at targeted wavelengths, thereby improving the efficacy of thermophotovoltaic systems. By utilizing advanced simulation techniques, we analyze the optical properties of the metamaterial, focusing on its ability to achieve high spectral efficiency through tailored emission and absorption mechanisms. Our findings indicate that the designed metamaterial has an average emissivity exceeding 96% in the wavelength range of 0.3–2.2 μm, peaking at 99.9% within the 1.5–2.0 μm range, as evidenced by numerical simulations. Furthermore, significant enhancements in spectral efficiency were observed, reaching optimal values at wavelengths corresponding to the bandgap energy of the targeted InGaAsSb photovoltaic materials. Additionally, the metamaterial maintains high emissivity across a wide range of incident angles (0°–60°) and is insensitive to the polarization of incident light. This investigation underscores the potential of W/HfO2/W metamaterials in advancing energy conversion technologies, highlighting their promising role in enhancing the performance of future thermophotovoltaic devices. The results contribute to a deeper understanding of metamaterial design principles and their implications for efficient energy harvesting systems. AIP Publishing retracted this article on December 22, 2025, due to a high frequency of tortured phrases.

Effects of amino-acid functionalization and pH value on temperature-dependent water dynamics in silica confinement

2H nuclear magnetic resonance (NMR) field-cycling relaxometry and broadband dielectric spectroscopy (BDS) studies show that water dynamics in silica pores with similar diameters (∼6 nm) strongly depend on the functionalization of the inner surfaces. In all studied confinements, we observe two prominent changes in the temperature dependence of water reorientation. Specifically, the activation energy of Ea ∼ 0.3 eV in the fully liquid state more than triples to Ea ∼ 1.0 eV upon partial crystallization at Tm ∼ 258 K. Furthermore, in the partially crystallized state, the liquid fraction shows a dynamical crossover at ∼185 K, where the common low-temperature behavior of confined water with Ea = 0.4–0.5 eV is established. However, the correlation times of water reorientation are up to two orders of magnitude longer in amino-acid functionalized silica pores than in pristine ones. Comparing the results for different functional groups, NMR and BDS consistently show that the slowdown is strongest for basic lysine followed by neutral alanine and, finally, acidic glutamic acid. Based on this order, one may speculate that the changed dynamics are a consequence of different pH values of water in confinements with different functional groups. Although pH measurements confirm that the pH value strongly depends on the amino-acid functionalization, this speculation must be rejected due to the observation that water with very different pH values does not show diverse reorientation dynamics when enclosed in identical pores.

Scaling effects on the microstructure and thermomechanical response of through silicon vias (TSVs)

The dimensional scaling of through silicon vias (TSVs) is critical for the advancement of high-density 3D integration in future logic-on-logic and logic-on-memory computing architectures. Realizing such scaling demands an understanding of the thermomechanical response at the relevant length scales as both the microstructure and properties of the copper making up the majority of the TSV are dependent upon the size. In response, we examine here the residual stress development of the surrounding Si and microstructural evolution of Cu within TSVs as they are scaled from 5 to 1 μm diameter and thermally annealed. Using a combination of Raman spectroscopic and electron backscatter diffraction imaging accompanied by thermomechanical modeling, a non-monotonic trend between equivalent stress and TSV diameter is revealed. The non-monotonic trend is interpreted using an elastic thermomechanical model that accounts for competition between the global bending of the wafer and local Cu shrinkage. The elastic behavior is attributed, in large part, to a decrease in the mean grain size of Cu—and the accompanying increase in strength—that occurs with reduced TSV diameter. Thus, given the consistency of measured stress with the elastic model and the improved mechanical strength with decreased grain size, annealed Cu TSVs are deduced to remain more elastic compared to their larger counterparts as they scale from 5 to 1 μm.

Density fluctuations, solvation thermodynamics, and coexistence curves in grand canonical molecular dynamics simulations

Fluid transport across nanometric channels induced by electric, pressure, and concentration gradients is ubiquitous in biological systems and fosters various applications. In this context, computer simulation setups with well-defined open-boundary equilibrium starting states are essential in understanding and assisting experimental studies. However, open-boundary computational methods are scarce and do not typically satisfy all the equilibrium conditions imposed by reality. Namely, in the absence of external gradients, (1) the system of interest (SoI) must be at thermodynamic and chemical equilibrium with an infinite reservoir of particles; (2) the fluctuations of the SoI in equilibrium should sample the grand canonical ensemble; (3) the local solvation thermodynamics, which is extremely sensitive to finite-size effects due to solvent depletion, should be correctly described. This point is particularly relevant for out-of-equilibrium systems; and (4) finally, the method should be robust enough to deal with phase transitions and coexistence conditions in the SoI. In this study, we demonstrate with prototypical liquid systems embedded into a reservoir of ideal gas particles that the adaptive resolution simulation (AdResS) method, coupled with particle insertion/deletion steps (AdResS+PI), satisfies all these requirements. Therefore, the AdResS+PI setup is suitable for performing grand canonical and stationary non-equilibrium simulations of open systems.

Quantitative analysis of shear band formation around collapsing pores in shocked energetic organic crystals

Shear bands can play a significant role in energy localization in energetic crystals loaded under the high-pressure, high strain-rate conditions of shock waves. While the origin and growth of shear bands have been well studied and visualized in atomic crystalline solids (metals and alloys), as well as in amorphous materials (e.g., metallic glasses), they are less well understood in reactive low-symmetry organic energetic crystals. Recently developed atomistic-consistent material models for commonly studied energetic crystals, HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) and RDX (1,3,5-trinitro-1,3,5-triazinane), have been shown in meso-scale (continuum) simulations to produce shear bands in good agreement with molecular dynamics (MD). Here, by exercising this atomistic-consistent continuum model, we analyze meso-scale simulation-generated shear band patterns during shock-induced pore collapse in HMX and RDX, spanning a wide range of pore sizes and shock strengths. Quantitative pattern analysis of shear bands is performed to extract key metrics, such as spacings at various instants of pore collapse, shear band propagation velocities, etc. These metrics show good agreement with the corresponding MD data for HMX and RDX; we assess the quantitative characteristics of the simulated shear bands against theoretical scaling relationships for shear bands developed mostly in the context of metals. The characteristics of simulated shear bands, such as spacings and growth rates, are found to align well with thermomechanical instability theory. Shear band growth rates display the expected initial slow incipience, intermediate fast growth, and later fast extinction phases seen in experiments. This work indicates that the theory of shear band formation and growth from the surface of pores and defects appears to hold across solids with quite different molecular arrangements. Valuable insights are obtained that enhance our understanding of the contribution of shear banding mechanisms to energy localization in shocked energetic materials.

N-doped MoS2 nanoflowers for the ultrasonic-vibration-driven high piezoelectric catalytic degradation

In this study, N-doped few-layer MoS2 piezocatalysts were successfully prepared by a one-pot hydrothermal method with urea as a nitrogen source. Benefiting from the optimized proportion of minority layers at edge positions and higher conductivity by N doping, the optimal N-doped few-layer MoS2 (120 mg of added urea) sample showed the optimal piezocatalytic activity for Rhodamine B (RhB) and levofloxacin (LEV), reaching 84.6 and 73.1% with the reaction kinetic rate constant of 0.020 86 and 0.017 05 min−1, respectively. In addition, the generation of superoxide radicals (·O2−) from the 120-MoS2 sample was determined to be greater than that from the 0-MoS2 sample in the piezocatalyst process by free radical scavenging experiments and electron paramagnetic resonance tests. Based on experimental data, a potential mechanism has been proposed to explain the enhanced piezocatalyst performance of N-doped few-layer MoS2. This research sheds new light on the development of efficient, cost-effective MoS2 piezoelectric catalysts through the doping of non-metallic dopants.

Electric field-induced domain structures in ferroelectric AlScN thin films

The analog switching properties of wurtzite-type ferroelectrics hold unforeseen potential for future-generation electronic devices, such as neuromorphic memory concepts based on memristive devices. However, investigative studies expanding our detailed knowledge on the physical properties of the ferroelectric domain walls and the modulation of large-scale domain patterns are still very limited. Up to date, the exact atomic configuration of the electric field-induced domain walls has not been identified due to its inclined and wedge-shaped three-dimensional nature. With this contribution, we provide direct experimental evidence on the atomic configuration of electric field-induced vertical inversion domain walls in ferroelectric Al0.85Sc0.15N thin films using advanced scanning transmission electron microscopy techniques. Despite their overall inclined character, the structure of vertical inversion domain walls can be atomically sharp and exhibit laterally facing metal(M)- and nitrogen(N)-polar dimers consistent with low-energy configurations predicted for the Al1−xScxN system. Although nanoscale regions with extended superposition structures are examined, this observation makes it rather unlikely that domain walls in the investigated system are necessarily stabilized by nonpolar supercells. Moreover, by the examination of electric field dependent domain patterns, we evidence the surprising stabilization of N-polar spike domains at the top electrode interface after electrical backswitching to the M-polar state and observed forward growth in the film volume from these residual domains. These results strengthen recent advancements on the realization of memristive devices given the possibility to modulate the density of charged domain walls enabling multi-bit memory operations.

Dynamics of quantum–classical systems in nonequilibrium environments

The dynamics of a quantum system coupled to a classical environment and subject to constraints that drive it out of equilibrium are described. The evolution of the system is governed by the quantum–classical Liouville equation. Rather than evaluating the evolution of the mixed quantum–classical density operator, we derive exact equations of motion for the nonequilibrium average values of a set of operators or variables, along with correlation function expressions for the dissipative coefficients that enter these equations. These equations are obtained by requiring that the exact nonequilibrium averages are equal to local nonequilibrium averages that depend on auxiliary fields whose values satisfy evolution equations obtained using projection operator methods. The results are illustrated by deriving reaction–diffusion equations coupled to fluid hydrodynamic equations for a solution of quantum particles that can exist in two metastable states. Nonequilibrium steady states are discussed along with the reaction rate and diffusion correlation functions that characterize such states.

Electro-mechanical-carrier coupling behaviors of piezoelectric semiconductor fibers with p–n junctions under pull-out loading

Due to their unique properties between carrier redistribution and built-in electric potential induced by external stress, piezoelectric semiconductor (PS) fibers are widely used in intelligent structures. In this paper, electromechanical coupling behaviors of PN junctions in segmented PS fiber under pull-out loading are analytically investigated. Based on the shear-lag model, the stress transfer relationship between the PS fiber and the elastic matrix is established. Closed form solutions of fiber axial stress, interfacial shear stress, electric potential, electric field, and carrier perturbation are obtained. Results show that the initial carrier concentration has a significant influence on the electromechanical coupling behaviors of segmented PS fibers compared with single homogeneous fiber. The interfacial properties of PN homojunction and heterojunction are sensitive to the concentrations of carrier doping. Besides initial doping concentration, the relevant electromechanical coupling fields can be regulated by radius ratio and external stress as well. On the basis of the linearized model, the effect of pull-out stress on the I–V curve plots under small forward-biased voltage has been investigated as well. The fundamental research will be helpful in understanding the physical mechanism of carrier regulation in PN junction fiber composites and guide for designing segmented devices in practical applications.

Comment on “Microcanonical treatment of HCl dissociative chemisorption on Au(111): Reactive dampening through inefficient translational energy coupling and an active surface” [J. Chem. Phys. 160, 084702 (2024)]

Lattice dynamics modeling of thermal transport in solids using machine-learned atomic cluster expansion potentials: A tutorial

Lattice dynamics (LD) plays a crucial role in investigating thermal transport in terms of not only underlying physics but also novel properties and phenomena. Recently, machine learning interatomic potentials (MLIPs) have emerged as powerful tools in computational physics and chemistry, showing great potential in providing reliable predictions of thermal transport properties with high efficiency. This tutorial provides a comprehensive guideline for MLIPs’ development and how they are used for the computational modeling of thermal transport. Using atomic cluster expansion (ACE) as the paradigmatic potential, we introduce the essential fundamentals of MLIPs, including data construction, model training, and hyperparameter optimization. With the developed ACE potentials, we further showcase their applications in the LD modeling of thermal transport for crystalline silicon and amorphous carbon. The corresponding code implementations for MLIP applications in calculating thermal conductivity are also provided for beginners to follow.