bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo transport analysis to assess intensity dependent response of a carbon-doped GaN photoconductor
Authors: Milestone W. , Guo D. , Sanati M. , Dowling K. M. , Hau-Riege S. , Voss L. F. , Conway A. , Joshi R. P.
Published: May 2021

Evaluation of the photoresponse in wurtzite GaN photoconductive switches is presented based on kinetic Monte Carlo simulations. The focus is on electron transport physics and assessment of high frequency operation. The roles of GaN band structure, Pauli exclusion, and treatment of internal fields based on the fast multipole method are all comprehensively included. The implementation was validated through comparisons of velocity-field characteristics for GaN with computational results in the literature. Photocurrent widths of less than ∼7 ps for the 1 μm device can be expected, which translates into a 100 GHz upper bound. Photocurrent pulse compression below the laser full width at half maxima at high applied fields are predicted based on the interplay of space-charge effects and the negative differential velocity characteristics of GaN.
Real-time signal processing system based on FPGA for motional Stark effect diagnostic on EAST
Authors: Liu D. M. , Yang X. H. , Fu J. , Liu L. C. , Lyu B.
Published: May 2021

The plasma current density profile plays a key role in the development of a high poloidal beta scenario, which is essential for long-pulse and high-performance plasma operation on a tokamak. Based on the polarimetry technique, a Motional Stark Effect (MSE) diagnostic has been built on the Experimental Advanced Superconducting Tokamak. To be prepared for real-time (RT) feedback control of the plasma current density profile in the future, a RT signal processing system has been developed. The RT signal processing system is composed of three functional modules: analog-to-digital conversion (ADC) module, polarization information extraction module, and digital-to-analog conversion (DAC) module. The final objective of this system is to acquire the polarization information of the MSE. Based on the field-programmable gate array unit, fast Fourier transformation is adopted to process the Photoelastic Modulator (PEM) digital signal, which was converted from a PEM signal via the ADC module. By means of frequency spectrum separation, the components around double modulating frequencies are restored through inverse fast Fourier transformation. Furthermore, the two amplitudes of their corresponding components can be obtained through a digital harmonic analyzer technique. Afterward, the ratio of the two amplitudes is calculated by arc tangent so that the polarization angle is obtained. Finally, the information of this polarization angle is converted into a voltage signal by the DAC module and then output in RT. The test results based on the RT signal processing system are in good agreement with those based on the phase lock-in amplifiers. The working cycle of this system is shorter than 10 ms, which meets the requirements of the MSE diagnostic as a RT controller. The algorithm of RT signal processing and the relevant technology applied for building this system are presented in the main body of this paper in detail.
A comprehensive study of secondary and tertiary vortex phenomena of flow past a circular cylinder: A Cartesian grid approach
Authors: Kumar Pankaj , Kalita Jiten C.
Published: May 2021

This study envisages undertaking a comprehensive simulation of the flow past an impulsively started circular cylinder with special emphasis on vortex dynamics in the secondary and tertiary level. A recently developed second order spatially and temporally accurate compact finite difference scheme on a nonuniform Cartesian grid has been used to discretize the transient Navier–Stokes equations governing the flow. The grid is generated in such a way that the cylinder boundary passes through the grid points, thus dispensing with the need to use the immersed interface approach on a Cartesian grid. High quality simulations are accomplished for a wide range of Reynolds numbers (Re) from 5≤Re≤10 000 in the laminar regime, including the periodic flow characterized by von Kármán vortex street. The α, β, sub-α, and sub-β phenomena, which are the trademark of the secondary and tertiary vortex dynamics associated with such flows, are studied in detail. Our results are compared with existing experimental and numerical results, and close comparison is obtained in all the cases exemplifying their accuracy. In the process, for the first time, we also provide a tabular documentation of the early stages of the flow for Re≥700.
The effect of Cu and Mn elements on the mechanical properties of single-crystal CoCrFeNi-based high-entropy alloy under nanoindentation
Authors: Qi Yuming , He Tengwu , Feng Miaolin
Published: May 2021

Considering the impact of chemical compositions, the mechanical properties and microstructure evolution of the single-crystal FCC CoCrFeNi-based high-entropy alloys (HEAs) are investigated by using molecular dynamics simulation in nanoindentation. The addition of Cu and Mn elements would decrease the stacking faults energy resulting in the dislocation-mediated deformation. Moreover, the total number of chemical compositions of CoCrFeNi-based HEAs has critical effects on the results according to the Hertz contact theory. The plastic deformation is studied by correlating the P–h curve with the instantaneous defect structure and dominated by nucleation of Shockley partial dislocations or the motions of stacking faults. Owing to the large amount of Hirth and Stair-rod dislocations, CoCrFeNiCu HEA has the largest indentation force, next followed by CoCrFeNi and CoCrFeNiMn HEAs. Then, the influence of chemical composition on the radial distribution function is explored, and it exhibits that Cu and Mn elements are conducive to amorphization. Finally, the analysis of microstructure evolution reveals that the Mn addition would contribute to the slipping process for CoCrFeNi-based HEAs causing the decrease of indentation force and hardness. In contrast, the Cu addition results in irregular slipping mode accompanying the appearance of dislocation loops. In this simulation, the mechanical properties of single-crystal CoCrFeNi-based HEAs are strongly dependent on the chemical composition, which contributes to the composition design of high entropy alloys in the future.
Dynamical characteristics of the piezotronic ZnO nanowire device in ballistic transport and its MEMS/NEMS resonator hybrid
Authors: Jin Leisheng , Li Zhi , Jiang Zongqing , Li Lijie
Published: May 2021

In this work, the dynamical analysis of carrier transportation in a typical piezoelectric device working in the ballistic regime is conducted. Based on the quantum scatting theory, the Poisson and Schrödinger equations are combined for calculating the dynamical transmission coefficient of the metal–piezoelectric ZnO–metal structure subject to sinusoidal and rectangular external stresses. The roles played by the spanning width of induced piezopotential and incident electron energy in affecting transmission probability are further discussed and clarified, respectively. The cutoff frequency of the piezoelectric device is also studied. Moreover, MEMS/NEMS hybrids specified by double/single-clamped ZnO quantum wire micro/nano-electromechanical resonator hybrids are proposed. Through a comprehensive numerical simulation, it is revealed that the rich nonlinear dynamics of the resonator can be subtly transferred to the piezoelectric device, and the chaotic transmission in the piezoelectric device can arise in two-dimensional parameter space with respect to time and incident electron energy. Therefore, the hybrids are endowed with the ability to detect amplitude changes by measuring ultra-sensitive quantum tunneling current. The study sheds light on developing quantum piezotronics and its related MEMS/NEMS integrations.
On the evolution of the exclusion zone produced by hydrophilic surfaces: A contracted description
Authors: Mercado-Uribe H. , Guevara-Pantoja F. J. , García-Muñoz W. , García-Maldonado J. S. , Méndez-Alcaraz J. M. , Ruiz-Suárez J. C.
Published: May 2021

After exciting scientific debates about its nature, the development of the exclusion zone, a region near hydrophilic surfaces from which charged colloidal particles are strongly expelled, has been finally traced back to the diffusiophoresis produced by unbalanced ion gradients. This was done by numerically solving the coupled Poisson equation for electrostatics, the two stationary Stokes equations for low Reynolds numbers in incompressible fluids, and the Nernst–Planck equation for mass transport. Recently, it has also been claimed that the leading mechanism behind the diffusiophoretic phenomenon is electrophoresis [Esplandiu et al., Soft Matter 16, 3717 (2020)]. In this paper, we analyze the evolution of the exclusion zone based on a one-component interaction model at the Langevin equation level, which leads to simple analytical expressions instead of the complex numerical scheme of previous works, yet being consistent with it. We manage to reproduce the evolution of the exclusion zone width and the mean-square displacements of colloidal particles we measure near Nafion, a perfluorinated polymer membrane material, along with all characteristic time regimes, in a unified way. Our findings are also strongly supported by complementary experiments using two parallel planar conductors kept at a fixed voltage, mimicking the hydrophilic surfaces, and some computer simulations.
Two-dimensional MoS2 reinforced with Cu3N nanoflakes prepared via binder less sputtering route for flexible supercapacitor electrodes
Authors: Sharma Gagan Kumar , Ranjan Bhanu , Kaur Davinder
Published: May 2021

Here, we present a binder less sputtering approach for controllable growth of copper nitride (Cu3N) nanoflakes incorporated into 2D layered molybdenum disulfide (MoS2) nanoworms directly grown on flexible stainless steel (SS) substrate. The formation of the intermixed nanostructure is revealed by surface morphology. Moreover, the porous structure and good conductivity, and the presence of sulfur and N2 edges facilitate the synergistic effect favor more pathways for insertion and desertion of electrolyte ions (Na+). The optimized composite electrode achieves an outstanding specific capacitance (215.47 F/g at 0.5 A/g) along with remarkable elongated cycle life (∼90% retention over 2000 cycles at 9.5 A/g). Additionally, the electrode (of dimensions 3 × 1 cm2) shows high energy density (∼30 Wh/kg at a power density of 138 W/kg), extended potential window (1 V), fair mechanical stability, and pliability (retains ∼91% specific capacitance at 175° bending angle). The contemporary method provides a cathode material for practically applicable supercapacitors with superior flexibility and desirable electrochemical properties.
Motion and deformation of migrating compound droplets in shear-thinning fluids in a microcapillary tube
Authors: Sattari Amirmohammad , Tasnim Nishat , Hanafizadeh Pedram , Hoorfar Mina
Published: May 2021

The deformation dynamics of a moving compound droplet inside a microcapillary tube is investigated in Newtonian and non-Newtonian ambient fluids. The numerical method used is a ternary phase-field model to determine the temporal evolution and the subsequent hydrodynamics of compound droplets traveling inside a microcapillary tube. By solving the axisymmetric momentum equations, the compound droplet movement is identified by tracing the spatiotemporal evolution of a pair of two deformable interfaces. Results indicate that the rheological properties of the continuous phase significantly influence the compound droplet characteristics. The position of the center of the mass of both inner and outer drops along the tube axis increases linearly in a Newtonian ambient fluid while it is nonlinear in a non-Newtonian medium, and the deviation from the linear behavior increases as the concentration of the polymer solution increases. These distinct behaviors occur after a particular normalized time (t*, which is normalized with R/Uavg in which R is the radius of the tube and Uavg is the average inlet velocity) during the early stages of droplet formation (t*∼1). The migration of the compound drop inside a Newtonian fluid approaches a relatively constant velocity after a specific time of the initial movement. Conversely, the movement velocity of both drops increases gradually until the pinch-off moment in non-Newtonian fluids, which means that a moving compound drop has an accelerative motion in all stages of movement in non-Newtonian fluids. The findings presented here are essential for employing compound droplets in droplet microfluidic systems for biological applications.
Role of water model on ion dissociation at ambient conditions
Authors: Wills Alec , Fernández-Serra Marivi
Published: May 2021

We study ion pair dissociation in water at ambient conditions using a combination of classical and ab initio approaches. The goal of this study is to disentangle the sources of discrepancy observed in computed potentials of mean force. In particular, we aim to understand why some models favor the stability of solvent-separated ion pairs vs contact ion pairs. We found that some observed differences can be explained by non-converged simulation parameters. However, we also unveil that for some models, small changes in the solution density can have significant effects on modifying the equilibrium balance between the two configurations. We conclude that the thermodynamic stability of contact and solvent-separated ion pairs is very sensitive to the dielectric properties of the underlying simulation model. In general, classical models are very robust in providing a similar estimation of the contact ion pair stability, while this is much more variable in density functional theory-based models. The barrier to transition from the solvent-separated to contact ion pair is fundamentally dependent on the balance between electrostatic potential energy and entropy. This reflects the importance of water intra- and inter-molecular polarizability in obtaining an accurate description of the screened ion–ion interactions.
W-band circular TM11 mode converter for gyrotrons
Authors: Chao Hsien-Wen , Huang Ren-Jun , Li Yi-Chin , Chang Tsun-Hsu
Published: May 2021

This work proposes a methodology to convert a rectangular TE10 mode to a circular TM11 mode using an H-plane power divider at W-band. The divider evenly splits the input signal into two parts with the same amplitude and phase. One of the waves then goes through a wider rectangular waveguide with a lower cutoff frequency. After propagating through a specific length, the two waves differ by 180°. The two out-of-phase waves can jointly synthesize the circular TM11 mode with high mode purity. This power divider is structurally simple and capable of high-power operation. The full-wave simulation shows that the metal’s conductivity affects the transmission of two-mode converters joined back-to-back. The measured back-to-back transmission agrees with the simulation result except for minor quantitative differences. The measured 3-dB bandwidth is 2.8 GHz with a center frequency of 93.6 GHz, which warrants the success of the TM11 mode gyrotrons.
Chaos-induced resistivity in collisionless reconnection region with magnetic island-chain structure
Authors: Wang Z. , Wu D. J. , Chen L.
Published: May 2021

The mechanism of anomalous resistivity is still an open and unsolved problem in collisionless magnetic reconnection. Studies show that magnetic reconnection regions often have magnetic island-chain structures. By using the test particle simulation, the chaos-induced resistivity is calculated in the regions around X points and O points, respectively. The results show that the chaos-induced resistivity in the X-type region is higher than that in the O-type region by an order of magnitude for the case with a strong guide field or a high magnetic island parameter. For the case of a weak guide field, however, the chaos-induced resistivity in the X-type region sensitively depends on the guide field and may be close to or less than that in the O-type region in the case of a low magnetic island parameter. This work will be helpful for us to understand the magnetic energy dissipation of occurring in collisionless reconnection regions as well as the dynamical evolution of reconnection current sheets.
Normal mode analysis of membrane protein dynamics using the vibrational subsystem analysis
Authors: Zhang Yan , Zhang She , Xing Jianhua , Bahar Ivet
Published: May 2021

The vibrational subsystem analysis is a useful approach that allows for evaluating the spectrum of modes of a given system by integrating out the degrees of freedom accessible to the environment. The approach could be utilized for exploring the collective dynamics of a membrane protein (system) coupled to the lipid bilayer (environment). However, the application to membrane proteins is limited due to high computational costs of modeling a sufficiently large membrane environment unbiased by end effects, which drastically increases the size of the investigated system. We derived a recursive formula for calculating the reduced Hessian of a membrane protein embedded in a lipid bilayer by decomposing the membrane into concentric cylindrical domains with the protein located at the center. The approach allows for the design of a time- and memory-efficient algorithm and a mathematical understanding of the convergence of the reduced Hessian with respect to increasing membrane sizes. The application to the archaeal aspartate transporter GltPh illustrates its utility and efficiency in capturing the transporter’s elevator-like movement during its transition between outward-facing and inward-facing states.
Surface-enhanced Raman scattering nanotags for bioimaging
Authors: Lin Li , Bi Xinyuan , Gu Yuqing , Wang Fu , Ye Jian
Published: May 2021

Surface-enhanced Raman scattering (SERS) technique has shown extraordinary features for biomedical applications. The implementation of SERS nanotags has opened a new era for bioimaging and detections. As a powerful tool, SERS nanotags provide favorable properties such as fingerprint spectrum, narrow peak linewidth, good photostability, and high spatial resolution accompanied by various rational designs of nanoparticles. They have proven as useful imaging agents for in vivo, ex vivo, and in vitro detection of cancerous cells and tissues. This tutorial provides the basic principles of SERS and SERS nanotags, including recent progress of SERS-based bioimaging applications, as well as the outlooks into the future developments toward practical clinical SERS.
Extremely high-efficient activation of acceptor boron introduced by ion implantation at room temperature with various doping concentrations in epitaxially synthesized diamond films by chemical vapor deposition
Authors: Seki Yuhei , Hoshino Yasushi , Nakata Jyoji
Published: May 2021

We homoepitaxially synthesized a pure diamond film on type Ib base substrates by microwave plasma-assisted special chemical vapor deposition method and then doped B impurity atoms by the ion implantation technique with various doping concentrations from 2×1017 to 2×1019 cm−3 at room temperature followed by activation annealing at 1300 °C. The electrical properties of specific resistance, carrier concentration, Hall mobility, and conductive carrier type were analyzed by Hall effect measurements based on the van der Pauw method at sample temperatures from 77 to 873 K. We consequently realized excellent B-doping in the CVD-synthesized diamond film with a low compensation ratio and perfect doping efficiency and confirmed p-type conduction at almost all temperature ranges for the measured samples. In very lightly doped diamond, we observed first the existence of deep acceptor levels located near 1.85 eV with respect to the valence band maximum and proposed a conduction mechanism based on hopping conduction in deep acceptor levels. We showed the availability of this doping process to high-efficient B doping with various acceptor concentrations in diamond. The great success achieved in the activation of acceptor B implanted in diamond with various doping concentrations should definitely contribute to the progress in the application of diamond-based power semiconductor devices.
Triggered emission of indistinguishable photons from an organic dye molecule
Authors: Lombardi Pietro , Colautti Maja , Duquennoy Rocco , Murtaza Ghülam , Majumder Prosenjit , Toninelli Costanza
Published: May 2021

Single molecules in solid state matrices have been proposed as sources of single photon Fock states back 20 years ago. Their success in quantum optics and in many other research fields stems from the simple recipes used in the preparation of samples, with hundreds of nominally identical and isolated molecules. Main challenges as of today for their application in photonic quantum technologies are the optimization of light extraction and the on-demand emission of indistinguishable photons. We here present Hong–Ou–Mandel (HOM) experiments with photons emitted by a single molecule of dibenzoterrylene in an anthracene nanocrystal at 3 K, under continuous wave and also pulsed excitation. A detailed theoretical model is applied, which relies on independent measurements for most experimental parameters, hence allowing for an analysis of the different contributions to the two-photon interference visibility, from residual dephasing to spectral filtering. A HOM interference visibility of more than 75% is reported, which, according to the model, is limited by the residual dephasing present at the operating temperature.
Growth of the lower hybrid drift instability in the plume of a magnetically shielded Hall thruster
Authors: Mikellides Ioannis G. , Lopez Ortega Alejandro
Published: May 2021

Analytical and numerical investigations have been carried out that show the lower hybrid drift instability is active in a region of low-β plasma outside the discharge channel of a magnetically shielded Hall thruster. The region is located downstream of the inner front pole magnet and is contained by the thruster ion beam and hollow cathode plume. It is found that large enough E × B and diamagnetic drifts in the out-of-plane (azimuthal) direction are produced in this region to destabilize lower hybrid waves, even in the presence of electron collisions. The results have been obtained by solving an electrostatic dispersion relation in which the density inhomogeneity is accounted for in the velocity distribution function of the strongly magnetized electrons. Ions in the azimuthal direction have been treated as stationary and unmagnetized. The plasma properties in the dispersion have been provided independently by large-scale 2D multi-fluid/particle-in-cell simulations. The growth rates are found to be even greater than those associated with the modified two-stream instability, which was also predicted recently to be active in this region. The implication of the findings is that ions may be heated anomalously by these instabilities, in both the out-of-plane and in-plane directions perpendicular to the applied magnetic field, thereby altering the velocity field and enhancing the energy of those ions that strike nearby thruster surfaces.
Spatiotemporal linear stability of viscoelastic free shear flows: Nonaffine response regime
Authors: Bansal D. , Ghosh D. , Sircar S.
Published: May 2021

We provide a detailed comparison of the two-dimensional, temporal, and spatiotemporal linearized analyses of the viscoelastic free shear flows (inhomogeneous flows with mean velocity gradients that develop in the absence of boundaries) in the limit of low to moderate Reynolds number and elasticity number obeying four different types of stress–strain constitutive equations: Oldroyd-B, upper convected Maxwell, Johnson–Segalman (JS), and linear Phan-Thien–Tanner (PTT). The resulting fourth-order Orr–Sommerfeld equation is transformed into a set of six auxiliary equations that are numerically integrated via the compound matrix method. The temporal stability analysis suggests (a) elastic stabilization at higher values of elasticity number {shown previously in the dilute regime [Sircar and Bansal, “Spatiotemporal linear stability of viscoelastic free shear flows: Dilute regime,” Phys. Fluids 31, 084104 (2019)]} and (b) a nonmonotonic instability pattern at low to intermediate values of elasticity number for the JS as well as the PTT model. To comprehend the effect of elasticity, Reynolds number, and viscosity on the temporal stability curves of the PTT model, we consider a fourth parameter, the centerline shear rate, ζc. The “JS behavior” is recovered below a critical value of ζc, and above this critical value, the PTT base stresses (relative to the JS model) are attenuated thereby explaining the stabilizing influence of elasticity. The Briggs idea of analytic continuation is deployed to classify regions of temporal stability and absolute and convective instabilities, as well as evanescent modes, and the results are compared with previously conducted experiments for Newtonian as well as viscoelastic flows past a cylinder. The phase diagrams reveal the two familiar regions of inertial turbulence modified by elasticity and elastic turbulence as well as (a recently substantiated) region of elastoinertial turbulence and the unfamiliar temporally stable region for intermediate values of Reynolds and elasticity number.
Analytic gradients for restricted active space second-order perturbation theory (RASPT2)
Authors: Nishimoto Yoshio
Published: May 2021

The computational cost of analytic derivatives in multireference perturbation theory is strongly affected by the size of the active space employed in the reference self-consistent field calculation. To overcome previous limits on the active space size, the analytic gradients of single-state restricted active space second-order perturbation theory (RASPT2) and its complete active space second-order perturbation theory (CASPT2) have been developed and implemented in a local version of OpenMolcas. Similar to previous implementations of CASPT2, the RASPT2 implementation employs the Lagrangian or Z-vector method. The numerical results show that restricted active spaces with up to 20 electrons in 20 orbitals can now be employed for geometry optimizations.
Output characteristics and experimental study of a highly linear and large-range force sensor based on the Villari effect
Authors: Shi Rui , Wang Chuanli , Yu Caofeng , Xiong Meijun , Wang Yu , Chen Zhuo
Published: May 2021

Based on the principle of the Villari effect, a force sensor with a giant magnetostrictive material (GMM) as the sensitive element, high linearity, and a large range was studied. A Hall element integrated into the structure was used to detect the magnetic flux density and measure the external force. First, the finite element method was used to verify the validity of the intended magnetization process. Second, an equation for GMM magnetization was derived based on the Jiles–Atherton (J–A) model and the magneto-mechanical coupling effect. The relationships between magnetization and the biased magnetic field, and magnetization and the external force were analyzed under the dynamic coupling model of positive and negative effects. Finally, the influences of various biased magnetic fields and external forces on the sensor output characteristics were determined experimentally. The sensitivity of the designed force sensor was 0.337 mV/N when the bias current was 1.2 A and the preload was 120 N. When a force of 1000 N was applied, the linearity was 0.82%. The experimental results are consistent with the theoretical design values. These research results aid in the development of a highly linear, large-range force sensor. This study provides the theoretical and technical foundations for a high-performance force sensor that can be used in industrial testing.
A droplet acoustofluidic platform for time-controlled microbead-based reactions
Authors: Liu Zhenhua , Fornell Anna , Tenje Maria
Published: May 2021

Droplet microfluidics is a powerful method used to characterize chemical reactions at high throughput. Often detection is performed via in-line optical readout, which puts high demands on the detection system or makes detection of low concentration substrates challenging. Here, we have developed a droplet acoustofluidic chip for time-controlled reactions that can be combined with off-line optical readout. The principle of the platform is demonstrated by the enzymatic conversion of fluorescein diphosphate to fluorescein by alkaline phosphatase. The novelty of this work is that the time of the enzymatic reaction is controlled by physically removing the enzymes from the droplets instead of using chemical inhibitors. This is advantageous as inhibitors could potentially interact with the readout. Droplets containing substrate were generated on the chip, and enzyme-coupled microbeads were added into the droplets via pico-injection. The reaction starts as soon as the enzyme/bead complexes are added, and the reaction is stopped when the microbeads are removed from the droplets at a channel bifurcation. The encapsulated microbeads were focused in the droplets by acoustophoresis during the split, leaving the product in the side daughter droplet to be collected for the analysis (without beads). The time of the reaction was controlled by using different outlets, positioned at different lengths from the pico-injector. The enzymatic conversion could be measured with fluorescence readout in a separate PDMS based assay chip. We show the ability to perform time-controlled enzymatic assays in droplet microfluidics coupled to an off-line optical readout, without the need of enzyme inhibitors.
Three- and four-site models for heavy water: SPC/E-HW, TIP3P-HW, and TIP4P/2005-HW
Authors: Linse Johanna-Barbara , Hub Jochen S.
Published: May 2021

Heavy water or deuterium oxide, D2O, is used as a solvent in various biophysical and chemical experiments. To model such experiments with molecular dynamics simulations, effective pair potentials for heavy water are required, which reproduce the well-known physicochemical differences relative to light water. We present three effective pair potentials for heavy water, denoted SPC/E-HW, TIP3P-HW, and TIP4P/2005-HW. The models were parameterized by modifying the widely used three- and four-site models for light water, with the aim of maintaining the specific characteristics of the light water models. At room temperature, SPC/E-HW and TIP3P-HW capture the modulations relative to light water of the mass and electron densities, heat of vaporization, diffusion coefficient, and water structure. TIP4P/2005-HW captures, in addition, the density of heavy water over a wide temperature range.
β-Ga2O3 vertical heterojunction barrier Schottky diodes terminated with p-NiO field limiting rings
Authors: Gong H. H. , Yu X. X. , Xu Y. , Chen X. H. , Kuang Y. , Lv Y. J. , Yang Y. , Ren F.-F. , Feng Z. H. , Gu S. L. , Zheng Y. D. , Zhang R. , Ye J. D.
Published: May 2021

In this Letter, high-performance β-Ga2O3 vertical heterojunction barrier Schottky (HJBS) diodes have been demonstrated together with the investigation of reverse leakage mechanisms. In HJBS configurations, NiO/β-Ga2O3 p-n heterojunctions and p-NiO field limiting rings (FLRs) are implemented by using a reactive sputtering technique at room temperature without intentional etching damages. Determined from the temperature-dependent current-voltage characteristics, the reverse leakage mechanism of the HJBS diode is identified to be Poole-Frenkel emission through localized trap sates with an energy level of EC-0.72 eV. With an uniform FLR width/spacing of 2 μm in HJBS, a maximum breakdown voltage (BV) of 1.89 kV and a specific on-resistance (Ron,sp) of 7.7 mΩ·cm2 are achieved, yielding a high Baliga's figure-of-merit (FOM, BV2/Ron,sp) of 0.46 GW/cm2. The electric field simulation and statistical experimental facts indicate that the electric field crowding effect at device edges is greatly suppressed by the shrinkage of p-NiO FLR spacing, and the capability of sustaining high BV is enhanced by the NiO/β-Ga2O3 bipolar structure, both of which contribute to the improved device performance. This work makes a significant step to achieve high performance β-Ga2O3 power devices by implementing alternative bipolar structures to overcome the difficulty in p-type β-Ga2O3.
Design and analysis of shoulder joint exoskeleton rehabilitation mechanism based on gear and rack transmission
Authors: Pang Zaixiang , Wang Tongyu , Yu Junzhi , Wang Zhanli , Liu Shuai , Zhang Xiyu
Published: May 2021

Due to insufficient muscle strength, a novel rehabilitation mechanism of the shoulder joint exoskeleton is proposed and analyzed based on gear and rack transmission, which solves the problem that stroke patients need repetitive exercise rehabilitation training. First, the range of motion angle of the shoulder joint is determined, and the mechanical structure of shoulder joint rehabilitation is designed. The arc rack is engaged with the output shaft gear of the reducer, and the servo motor is utilized as the driving force to realize the internal/external rotation movement of the shoulder joint. The motor connects the horizontal connecting rod and the rotating rod through the cross roller bearing to realize the abduction/adduction and flexion/extension movement of the shoulder joint. Second, the kinematics and dynamics of the shoulder joint exoskeleton are analyzed, investigated, and verified for the rehabilitation mechanism. The simulation analysis of the mechanism is completed in the virtual prototype. The changes in the joint angle and end trajectory and joint moment with time and angular velocity under the given working conditions are obtained, which directly reflect the movement of each joint of the rehabilitation mechanism. Finally, aiming at the nonlinear disturbance in the trajectory tracking control of the rehabilitation mechanism of the shoulder joint exoskeleton, the trajectory tracking approach of the mechanism is achieved aided with the closed-loop PD iterative learning control method. The results demonstrate that the actual trajectories are in good agreement with the desired trajectories, which can achieve effective tracking and improve the control quality of the system.
Diffuse reflectance and machine learning techniques to differentiate colorectal cancer ex vivo
Authors: Fernandes Luís , Carvalho Sónia , Carneiro Isa , Henrique Rui , Tuchin Valery V. , Oliveira Hélder P. , Oliveira Luís M.
Published: May 2021

In this study, we used machine learning techniques to reconstruct the wavelength dependence of the absorption coefficient of human normal and pathological colorectal mucosa tissues. Using only diffuse reflectance spectra from the ex vivo mucosa tissues as input to algorithms, several approaches were tried before obtaining good matching between the generated absorption coefficients and the ones previously calculated for the mucosa tissues from invasive experimental spectral measurements. Considering the optimized match for the results generated with the multilayer perceptron regression method, we were able to identify differentiated accumulation of lipofuscin in the absorption coefficient spectra of both mucosa tissues as we have done before with the corresponding results calculated directly from invasive measurements. Considering the random forest regressor algorithm, the estimated absorption coefficient spectra almost matched the ones previously calculated. By subtracting the absorption of lipofuscin from these spectra, we obtained similar hemoglobin ratios at 410/550 nm: 18.9-fold/9.3-fold for the healthy mucosa and 46.6-fold/24.2-fold for the pathological mucosa, while from direct calculations, those ratios were 19.7-fold/10.1-fold for the healthy mucosa and 33.1-fold/17.3-fold for the pathological mucosa. The higher values obtained in this study indicate a higher blood content in the pathological samples used to measure the diffuse reflectance spectra. In light of such accuracy and sensibility to the presence of hidden absorbers, with a different accumulation between healthy and pathological tissues, good perspectives become available to develop minimally invasive spectroscopy methods for in vivo early detection and monitoring of colorectal cancer.
Identification of multiple influential spreaders on networks by percolation under the SIR model
Authors: Li Xiang , Zhang Xue , Zhao Chengli , Duan Xiaojun
Published: May 2021

Identification of multiple influential spreaders on complex networks is of great significance, which can help us speed up information diffusion and prevent disease from spreading to some extent. The traditional top-k strategy to solve an influence maximization problem based on node centrality is unsuitable for selecting several spreaders simultaneously because of influence overlapping. Besides, other heuristic methods have a poor ability to keep the balance between efficiency and computing time. In this paper, an efficient method is proposed to identify the decentralized influential spreaders on networks by edge percolation under the Susceptible–Infected–Recovered (SIR) model. Thanks to the average size of the connected component where one node is located under the edge percolation equivalent to the final spread range of this node under the SIR model approximately, it inspires us to choose suitable spreaders maximize the spread of influence. The experimental results show that our method has high efficiency compared with other benchmark methods on three synthetic networks and six empirical networks, and it also requires less time and cost.
Reduced variance analysis of molecular dynamics simulations by linear combination of estimators
Authors: Coles S. W. , Mangaud E. , Frenkel D. , Rotenberg B.
Published: May 2021

Building upon recent developments of force-based estimators with a reduced variance for the computation of densities, radial distribution functions, or local transport properties from molecular simulations, we show that the variance can be further reduced by considering optimal linear combinations of such estimators. This control variates approach, well known in statistics and already used in other branches of computational physics, has been comparatively much less exploited in molecular simulations. We illustrate this idea on the radial distribution function and the one-dimensional density of a bulk and confined Lennard-Jones fluid, where the optimal combination of estimators is determined for each distance or position, respectively. In addition to reducing the variance everywhere at virtually no additional cost, this approach cures an artifact of the initial force-based estimators, namely, small but non-zero values of the quantities in regions where they should vanish. Beyond the examples considered here, the present work highlights, more generally, the underexplored potential of control variates to estimate observables from molecular simulations.
Barriers to health care reported by carers of older Australians: new evidence from the 2018 Survey of Disability, Ageing and Carers
Authors: Temple Jeromey , Batchelor Frances , Hwang Kerry , Stiles Jay , Engel Lidia
Published: May 2021

Carers play an important role in assisting older care recipients with their daily lives and attending to their health care. Yet research has largely overlooked the barriers to health care that carers of older Australians themselves experience. This study finds that, among those attempting to access care, approximately 31.2% of carers of older Australians reported a barrier to health care, with one-third of this group reporting barriers at many points in the healthcare system. Barriers to care were considerable for those attempting to access dental, GP and medical specialist services (27.8%, 18.3% and 15.2% respectively), but lower for accessing hospital services (8.6%). People living with a disability or those in high carer distress had a minimum threefold increase in the odds of experiencing a barrier to care, with odds ratios (95% confidence intervals) of 3.35 (2.10–5.36) and 3.37 (2.33–4.88) respectively. Carers of older Australians noted cost as an important barrier to care, but between 20% and 40% cited being too busy or not having enough time to access dental, GP and medical specialist services (21%, 39% and 26% respectively). Addressing the barriers to health care reported by carers is critical not only to their own health and well-being, but also to that of care recipients.
Coal fly ash is a major carbon flux in the Chang Jiang (Yangtze River) basin
Authors: Li Gen K. , Fischer Woodward W. , Lamb Michael P. , West A. Joshua , Zhang Ting , Galy Valier , Wang Xingchen Tony , Li Shilei , Qiu Hongrui , Li Gaojun , Zhao Liang , Chen Jun , Ji Junfeng
Published: May 2021

Significance

Coal combustion releases CO
2
but also leaves behind solid waste, or fly ash, which contains considerable amounts of carbon. The organic carbon sourced from fly ash resists chemical breakdown, and we find that it now contributes nearly half of the fossil organic carbon exported by the Chang Jiang—the largest river in Asia. The fly ash flux in this basin is similar to the natural sediment flux to the oceans because dam building has reduced sediment transport, while increased coal consumption generates abundant fly ash. Our results show that fly ash is an important component of the present-day carbon load in rivers and illustrates that human-driven carbon cycling can match the pace of the geological carbon cycle at decadal timescales.
Resistance of African tropical forests to an extreme climate anomaly
Authors: Bennett Amy C. , Dargie Greta C. , Cuni-Sanchez Aida , Tshibamba Mukendi John , Hubau Wannes , Mukinzi Jacques M. , Phillips Oliver L. , Malhi Yadvinder , Sullivan Martin J. P. , Cooper Declan L. M. , Adu-Bredu Stephen , Affum-Baffoe Kofi , Amani Christian A. , Banin Lindsay F. , Beeckman Hans , Begne Serge K. , Bocko Yannick E. , Boeckx Pascal , Bogaert Jan , Brncic Terry , Chezeaux Eric , Clark Connie J. , Daniels Armandu K. , de Haulleville Thales , Djuikouo Kamdem Marie-Noël , Doucet Jean-Louis , Evouna Ondo Fidèle , Ewango Corneille E. N. , Feldpausch Ted R. , Foli Ernest G. , Gonmadje Christelle , Hall Jefferson S. , Hardy Olivier J. , Harris David J. , Ifo Suspense A. , Jeffery Kathryn J. , Kearsley Elizabeth , Leal Miguel , Levesley Aurora , Makana Jean-Remy , Mbayu Lukasu Faustin , Medjibe Vincent P. , Mihindu Vianet , Moore Sam , Nssi Begone Natacha , Pickavance Georgia C. , Poulsen John R. , Reitsma Jan , Sonké Bonaventure , Sunderland Terry C. H. , Taedoumg Hermann , Talbot Joey , Tuagben Darlington S. , Umunay Peter M. , Verbeeck Hans , Vleminckx Jason , White Lee J. T. , Woell Hannsjoerg , Woods John T. , Zemagho Lise , Lewis Simon L.
Published: May 2021

Significance

The responses of tropical forests to heat and drought are critical uncertainties in predicting the future impacts of climate change. The 2015–2016 El Niño Southern Oscillation (ENSO) resulted in unprecedented heat and low precipitation across the tropics, including in the very poorly studied African tropical forest region. We assess African forest ENSO responses using on-the-ground measurements. Across 100 long-term plots, record high temperatures did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality. Overall, despite the climate anomaly, forests continued to gain live biomass over the ENSO period. Our analyses, while limited to African tropical forests, suggest that they may be more resistant to climate extremes than Amazonian and Asian forests.
Quantifying collective intelligence in human groups
Authors: Riedl Christoph , Kim Young Ji , Gupta Pranav , Malone Thomas W. , Woolley Anita Williams
Published: May 2021

Significance

Collective intelligence (CI) is critical to solving many scientific, business, and other problems. We find strong support for a general factor of CI using meta-analytic methods in a dataset comprising 22 studies, including 5,279 individuals in 1,356 groups. CI can predict performance in a range of out-of-sample criterion tasks. CI, in turn, is most strongly predicted by group collaboration process, followed by individual skill and group composition. The proportion of women in a group is a significant predictor of group performance, mediated by social perceptiveness.
Oligomodal metamaterials with multifunctional mechanics
Authors: Bossart Aleksi , Dykstra David M. J. , van der Laan Jop , Coulais Corentin
Published: May 2021

Significance

Mechanical metamaterials are man-made materials with extraordinary properties that come from their geometrical structure rather than their chemical composition. For instance, they can be engineered to be extremely light and stiff; to shrink sideways when compressed, instead of expanding; or to exhibit programmable shape changes. Such properties often rely on zero-energy modes. In this work, we created a class of mechanical metamaterials with zero-energy modes that can exhibit multiple properties at the same time within a single structure. In particular, we created a metamaterial that can either shrink or expand on the side when compressed, depending on how fast it is compressed. These metamaterials could lead to novel adaptable devices for, for example, robotics and energy absorption applications.
Short hydrogen bonds enhance nonaromatic protein-related fluorescence
Authors: Stephens Amberley D. , Qaisrani Muhammad Nawaz , Ruggiero Michael T. , Díaz Mirón Gonzalo , Morzan Uriel N. , González Lebrero Mariano C. , Jones Saul T. E. , Poli Emiliano , Bond Andrew D. , Woodhams Philippa J. , Kleist Elyse M. , Grisanti Luca , Gebauer Ralph , Zeitler J. Axel , Credgington Dan , Hassanali Ali , Kaminski Schierle Gabriele S.
Published: May 2021

Significance

Intrinsic fluorescence of nonaromatic amino acids is a puzzling phenomenon with an enormous potential in biophotonic applications. The physical origins of this effect, however, remain elusive. Herein, we demonstrate how specific hydrogen bond networks can modulate fluorescence. We highlight the key role played by short hydrogen bonds, present in the protein structure, on the ensuing fluorescence. We provide detailed experimental and molecular evidence to explain these unusual nonaromatic optical properties. Our findings should benefit the design of novel optically active biomaterials for applications in biosensing and imaging.
Global abundance estimates for 9,700 bird species
Authors: Callaghan Corey T. , Nakagawa Shinichi , Cornwell William K.
Published: May 2021

Significance

For the fields of ecology, evolutionary biology, and conservation, abundance estimates of organisms are essential. Quantifying abundance, however, is difficult and time consuming. Using a data integration approach integrating expert-derived abundance estimates and global citizen science data, we estimate the global population of 9,700 bird species (∼92% of all extant bird species). We conclude that there are many rare species, highlighting the need to continue to refine global population estimates for all taxa and the role that global citizen science data can play in this effort.
Plant species richness at archaeological sites suggests ecological legacy of Indigenous subsistence on the Colorado Plateau
Authors: Pavlik Bruce M. , Louderback Lisbeth A. , Vernon Kenneth B. , Yaworsky Peter M. , Wilson Cynthia , Clifford Arnold , Codding Brian F.
Published: May 2021

Significance

Identifying how past human populations altered ecosystems is critical for understanding current ecological diversity and for the management of both natural and cultural resources. This study presents evidence for an enduring ecological legacy of ancient people on the Colorado Plateau, where the complexity of archaeological sites correlates with the richness of culturally important plant species. This suggests the intentional or unintentional transport and cultivation of native plants on a scale that is often overlooked in the American Southwest, where exogenous domesticates (corn, beans, and squash) are emphasized. These results illustrate how even small-scale societies can affect ecosystems and highlight the importance of coupling archaeology, ecology, and tribal expertise for resource management.