Browse Articles

The effects of war-related experiences on mental health symptoms of individuals living in conflict zones: a longitudinal study

Unipolar fields produced by ultrafast optical gating of terahertz pulses

Unipolar (sub-cycle) electromagnetic fields are a subject of current interest as a possible useful tool for light–matter interaction studies and applications. We propose, numerically simulate, and experimentally prove a method to produce unipolar terahertz fields by optical gating of conventional bipolar terahertz pulses in a GaAs wafer. In particular, picosecond long unipolar pulses with the electric field strength of ∼1 kV/cm were detected by electro-optic sampling at the output of the wafer.

A risk prediction model for endometrial hyperplasia/endometrial carcinoma in premenopausal women

Low-pressure CVD grown Si-doped β-Ga2O3 films with promising electron mobilities and high growth rates

In this work, we systematically investigated the growth of Si-doped β-Ga2O3 films using low-pressure chemical vapor deposition (LPCVD) system, achieving high room-temperature Hall mobilities of 162 and 149 cm2/V·s at carrier concentrations of 1.51 × 1017 and 1.15 × 1017 cm−3, respectively, for homoepitaxial (010) β-Ga2O3 film grown on β-Ga2O3 substrates and heteroepitaxial (2¯01) β-Ga2O3 film grown on off-axis c-sapphire substrate with 6° miscut-representing the highest mobilities reported for LPCVD-grown β-Ga2O3 materials. Carrier concentrations were precisely tuned by varying SiCl4 flow rates at a growth temperature of 1000 °C, resulting in concentrations ranging from 1.15 × 1017 to 1.19 × 1019 cm−3 as confirmed by both Hall and capacitance–voltage (C–V) measurements. The films exhibited high crystalline quality, confirmed by high resolution x-ray diffraction and Raman spectroscopy, indicating phase purity and structural integrity. Surface morphologies characterized by field-emission scanning electron microscope and atomic force microscopy showed a strong correlation between carrier concentrations and surface smoothness, with lower concentration resulting in reduced RMS roughness. Secondary Ion Mass Spectrometry analysis revealed uniform Si incorporation, with low carbon, hydrogen, and chlorine impurities below detection limits, indicating high purity of the films. A high low-temperature peak mobility exceeding >843 cm2/V·s was achieved at a carrier concentration of 1.74 × 1016 cm−3 for a (2¯01) β-Ga2O3 heteroepitaxial film at 80 K, highlighting the high purity and low compensation of these films. These findings emphasize the potential of LPCVD growth system for producing high-purity β-Ga2O3 films with thickness ranging between ∼2.3 and 11.7 μm and faster growth rates (∼4.7–17 μm/h), promising transport properties, controllable doping, and scalability for developing high-power vertical devices.

Unifying spatiotemporal and frequential attention for traffic prediction

Abstract Intelligent transportation systems heavily rely on forecasting urban traffic flow, and a variety of approaches have been developed for this purpose. However, most current methods focus on exploring spatial and temporal dependencies in historical traffic data, while often overlooking the inherent spectral characteristics hidden in traffic time series. In this paper, we introduce an approach to analyzing traffic flow in the frequency domain. By integrating attention mechanisms, we comprehensively capture the hidden correlations among space, time, and frequency dimensions. By leveraging deep learning to capture spatial correlations in traffic flow and applying spectral analysis to fuse time series data with underlying periodic correlations in both the time and frequency domains, we develop an innovative traffic prediction model called the Space-Time-Frequency Attention Network (STFAN). The core of this network lies in the application of attention mechanisms, which project the hidden states of current traffic features across the space, time, and frequency domains onto future hidden states. This approach enables a comprehensive learning of the relationships between each dimension and the future states, ultimately allowing for accurate predictions of future traffic flow. We carry out experiments on two publicly available datasets from the California Department of Transportation, PeMS04 and PeMS08, to assess the performance of the proposed model. The results demonstrate that the proposed model outperforms existing baseline models in terms of predictive accuracy, particularly for mid- and long-term traffic flow forecasting. Finally, the ablation study confirmed that the frequency domain characteristics of traffic flow significantly influence future traffic conditions, demonstrating the practical effectiveness of the model.

A 15-Item modification of the PSP rating scale to improve clinical meaningfulness and statistical performance

Torsion-induced rapid switching and tunability of multistable state ferroelectric polarization

The pulse-based rapid domain structure switching method in ferroelectric memristors has stability and other issues, limiting its applications. In this study, we perform atomic simulations to investigate the polarization domain switching behavior of ferroelectric materials under non-pulse torsional loading. During torsion, uniformly distributed spontaneous polarization transitions to predominantly in-plane polarization and finally evolves to predominantly out-of-plane polarization. The out-of-plane polarization remains stable during torsion and can be adjusted through mechanical and electric fields to achieve multistability. This evolution behavior is attributed to the rapid increase in initial normal stress and continuous cyclic variation of shear stress during torsion. The non-pulse control method developed in this study lays the foundation for further research and utilization of polarization regulation in ferroelectric materials, potentially advancing the application of ferroelectric memristors.

Bathymetry estimation for coastal regions using self-attention

Parasitic structure defect blights sustainability of cobalt-free single crystalline cathodes

AbstractRecent efforts to reduce battery costs and enhance sustainability have focused on eliminating Cobalt (Co) from cathode materials. While Co-free designs have shown notable success in polycrystalline cathodes, their impact on single crystalline (SC) cathodes remains less understood due to the significantly extended lithium diffusion pathways and the higher-temperature synthesis involved. Here, we reveal that removing Co from SC cathodes is structurally and electrochemically unfavorable, exhibiting unusual voltage fade behavior. Using multiscale diffraction and imaging techniques, we identify lithium-rich nanodomains (LRNDs) as a heterogeneous phase within the layered structure of Co-free SC cathodes. These LRNDs act as critical tipping points, inducing significant chemo-mechanical lattice strain and irreversible structural degradation, which exacerbates the voltage and capacity loss in electrochemical performance. Our findings highlight the considerable challenges of developing Co-free SC cathodes compared to polycrystalline ones and emphasize the need for new strategies to balance the interplay between cost, sustainability, and performance.

Two-color strong-field terahertz amplification in the non-identical focusing condition

High optical-to-terahertz (THz) conversion efficiency is crucial for generating THz waves. Strong-field ionization using a bi-focal bi-chromatic geometry produces cascading plasmas, leading to amplified THz generation and extended THz bandwidth. We investigate the effect of focal length in this bi-focal geometry on THz intensity. The results show that the THz intensity produced with non-identical focal lengths of the bi-chromatic fields is 25% higher than that of identical focal lengths, and 15 times higher than traditional bi-chromatic THz generation. The electro-optic sampling measurements reveal that the THz-electric-field intensity generated by the bi-focal bi-chromatic field exhibits periodic oscillations, which results from the modulation of the photoelectron's asymptotic velocity by the relative phase of the bi-chromatic pulses, and are consistent with the photocurrent model. The photocurrent simulations indicate that the self-compression of the second harmonic pulse significantly enhances THz amplification and extends the THz bandwidth. These findings deepen understanding of the THz generation mechanism and suggest potential avenues for optimizing THz sources.

Statistical damage constitutive model of soft rock based on Improved Hoek-Brown strength criterion

Optomechanical micro-rheology of complex fluids at ultra-high frequency

Modulating single molecular electron sources with light: Opportunities and challenges

Applying a strong, constant electric field at single-C60 molecule protrusions formed on a metallic substrate can cause electrons to be emitted from individual single molecules into a vacuum. The shapes of such single molecular electron sources reflect the shapes of the molecular orbitals from which the electrons originate. By illuminating the source with light pulses, photo-excited electrons can be emitted from different molecular orbitals, thereby modulating the electron sources at a subnanometric scale. In this context, we discuss the opportunities presented by this light-induced modulation of electron emission for developing a unique scheme to integrate ultrafast switches into a single molecule and for advancing high-resolution, ultrafast electron microscopy. We also discuss the experimental and theoretical challenges associated with this approach, such as the requirements for picoscale stability and controllability of molecular positions, as well as the need for large-scale ab initio calculations under strong constant fields.

Determination of antibacterial and antioxidant potential of organic crude extracts from Malus domestica, Cinnamomum verum and Trachyspermum ammi

Termination-acidity tailoring of molybdenum carbides for alkaline hydrogen evolution reaction

Temperature characteristics of a photoinduced blackbody in intense light fields

A “whitebody” can transform into a “blackbody” under intense light exposure, and the temperature of photoinduced blackbodies deviates significantly from Planck's law. This discovery necessitates the consideration of light excitation's impact on the radiation spectrum of a blackbody when applying Planck's formula. Under the adiabatic approximation, this paper theoretically derives the relationship between the temperature of photoinduced blackbodies and the intensity of excitation light field. The actual temperature of a photoinduced blackbody is directly proportional to the fourth root of the excitation light power. Experimental data demonstrate that this relationship can more accurately describe the temperature characteristics of a photoinduced blackbody in intense light fields. These results provide a theoretical foundation for further investigation into photoinduced blackbody radiation, contribute to an enhanced comprehension of the underlying physical mechanism behind this phenomenon, and may have significant implications for celestial temperature measurements based on Planck's law.

Mental Health and Associated Factors among Bangladeshi Migrants in Thailand: a cross-sectional study

Multi-channel learning for integrating structural hierarchies into context-dependent molecular representation

AbstractReliable molecular property prediction is essential for various scientific endeavors and industrial applications, such as drug discovery. However, the data scarcity, combined with the highly non-linear causal relationships between physicochemical and biological properties and conventional molecular featurization schemes, complicates the development of robust molecular machine learning models. Self-supervised learning (SSL) has emerged as a popular solution, utilizing large-scale, unannotated molecular data to learn a foundational representation of chemical space that might be advantageous for downstream tasks. Yet, existing molecular SSL methods largely overlook chemical knowledge, including molecular structure similarity, scaffold composition, and the context-dependent aspects of molecular properties when operating over the chemical space. They also struggle to learn the subtle variations in structure-activity relationship. This paper introduces a multi-channel pre-training framework that learns robust and generalizable chemical knowledge. It leverages the structural hierarchy within the molecule, embeds them through distinct pre-training tasks across channels, and aggregates channel information in a task-specific manner during fine-tuning. Our approach demonstrates competitive performance across various molecular property benchmarks and offers strong advantages in particularly challenging yet ubiquitous scenarios like activity cliffs.

Electrical control of exchange bias in Fe3GaTe2/Fe3GeTe2 van der Waals heterostructures

Magnetic heterojunctions with large exchange bias have promising applications in magnetic sensing and data storage. Ferromagnetic/antiferromagnetic (FM/AFM) heterojunctions are often used to generate exchange bias. However, the requirement of thermal manipulation makes controlling exchange bias in FM/AFM heterojunctions inconvenient. Herein, a Fe3GeTe2/Fe3GaTe2 FM/FM heterojunction is constructed to generate large exchange bias and reflected magnetic circular dichroism and magneto-optical Kerr effect techniques are used for the magnetic characterization of the heterojunction. The results show that strong magnetic coupling occurs at the Fe3GeTe2/Fe3GaTe2 interface when the temperature is <80 K. By fixing the spin direction of Fe3GaTe2, large exchange bias can be generated in Fe3GeTe2 because of the magnetic pinning effect. Furthermore, the strength of exchange bias can be manipulated by applying an ultralow current between Fe3GeTe2 and Fe3GaTe2 layers without changing the temperature. These results provide potential ways for generating and manipulating exchange bias in two-dimensional (2D) materials and pave the way for implementing the 2D van der Waals exchange bias effect in spintronic devices.

Spin and valley dependent transport and tunneling magnetoresistance in irradiated ferromagnetic WSe2double barrier junctions

AbstractSpin and valley polarizations (Ps and PKK’) and tunneling magnetoresistance (TMR) are demonstrated in the ferromagnetic/barrier/normal/barrier/ferromagnetic WSe2 junction, with the gate voltage and off-resonant circularly polarized light (CPL) applied to the two barrier regions. The minimum incident energy of non-zero spin- and valley-resolved conductance has been derived, which is consistent with numerical calculations and depends on the electric potential U, CPL intensity ΔΩ, exchange field h, and magnetization configuration: parallel (P) or antiparallel (AP). For the P (AP) configuration, the energy region with PKK’ = -1 or Ps = 1 is wider (narrower) and increases with ΔΩ. As h increases, the Ps = 1 (PKK’ = -1 or Ps = 1) plateau becomes wider (narrower) for the P (AP) configuration. As U increases, the energy region with PKK’ = -1 increases first and then moves parallel to the EF-axis, and the energy region with Ps = 1 for the P configuration remains unchanged first and then decreases. The energy region for TMR = 1 increases rapidly with h, remains unchanged first and then decreases as U increases, and has little dependence on ΔΩ. When the helicity of the CPL reverses, the valley polarization will switch. This work sheds light on the design of spin-valley and TMR devices based on ferromagnetic WSe2 double-barrier junctions.