bluuebunny/crossref_metadata_2025 huggingface dataset:
Visible-Light-Induced Oxidative Generation of o-Quinone Methides for Inverse-Electron-Demand [4+2] Cycloaddition Reactions
Authors: Tanaka Kenta , Hoshino Yujiro , Nohara Shoya , Iwai Suguru , Yamaguchi Naoya , Asada Yosuke , Kamiyama Yusuke , Tanaka Yuta
Published: August 2023

Organophotoredox-catalyzed oxidative generation of o-quinone methides (o-QMs) for inverse-electron-demand [4+2] cycloaddition reactions has been developed. One-electron oxidation of 2-(sulfanylmethyl)phenols by thioxanthylium photoredox catalyst generated o-QMs, which reacted with various styrenes to produce chromanes with high regioselectivity. This reaction offers a valuable approach for in situ generating o-QMs via one-electron oxidation process under irradiation with mild green light.
Beyond mean-field: Condensate coupled with pair excitations
Authors: Sorokanich Stephen
Published: August 2023

We prove existence results for a system of partial differential equations describing the approximate condensate wavefunction and pair-excitation kernel of a dilute T = 0 Bose gas in the stationary setting, in the presence of a trapping potential and repulsive pairwise atomic interactions. Notably, the Hartree-type equation for the condensate in this system contains contributions from non-condensate particles, and the pair excitation kernel satisfies a nonlinear operator equation. The techniques employed include a direct variational principle and also an iterative procedure for constructing solutions.
National Diagnostic Working Group (NDWG) for inertial confinement fusion (ICF)/high-energy density (HED) science: The whole exceeds the sum of its parts
Authors: Kilkenny J. D. , Hsing W. W. , Batha S. H. , Rochau G. A. , Sangster T. C. , Bell P. M. , Bradley D. K. , Chen H. , Frenje J. A. , Gatu-Johnson M. , Glebov V. Yu. , Leeper R. J. , Mackinnon A. J. , Regan S. P. , Ross J. S. , Weaver J. l.
Published: August 2023

The National Diagnostic Working Group (NDWG) has led the effort to fully exploit the major inertial confinement fusion/high-energy density facilities in the US with the best available diagnostics. These diagnostics provide key data used to falsify early theories for ignition and suggest new theories, recently leading to an experiment that exceeds the Lawson condition required for ignition. The factors contributing to the success of the NDWG, collaboration and scope evolution, and the methods of accomplishment of the NDWG are discussed in this Review. Examples of collaborations in neutron and gamma spectroscopy, x-ray and neutron imaging, x-ray spectroscopy, and deep-ultraviolet Thomson scattering are given. An abbreviated history of the multi-decade collaborations and the present semiformal management framework is given together with the latest National Diagnostic Plan.
Resistive switching conducting filament electroformation with an electrothermal phase field method
Authors: Sevic John F. , Kobayashi Nobuhiko P.
Published: August 2023

A phase field method self-consistently coupled to continuum heat transport and charge conservation is used to simulate conducting filament dynamical evolution and nanostructure of electroformed resistive switching thin films. Our method does not require a pre-defined idealized conducting filament, as previous methods do, instead treating its dynamical evolution as a stochastic diffuse interface problem subject to a variational principle. Our simulation results agree well with available experimental observations, correctly reproducing electroformed conducting filament nanostructure exhibited by a variety of resistive switching thin films.
An optimal capacity allocation method for integrated energy systems considering uncertainty
Authors: Zhang Yuliang , Zhang Jianguo , Chen Yujie
Published: August 2023

The randomness and fluctuation of wind power output will cause certain waste in capacity allocation of integrated energy system. Therefore, a robust chance constrained optimization model is proposed to solve the shortcomings of the traditional model in wind power output analysis, such as weak reliability and conservative results. First, the uncertainty of wind power output is analyzed. Second, a robust chance constrained optimization model combining stochastic programming and robust optimization is established to deal with the uncertainty of the output power of the integrated energy system objectively. Finally, the results are compared with the existing integrated energy system capacity configuration, and the validity of the model is verified. The results show that the robust chance constrained optimization model proposed in this paper can effectively reduce the capacity cost by 38.2% while ensuring the robustness of the system in wind power uncertainty analysis.
Theoretical spectroscopy for unraveling the intensity mechanism of the optical and photoluminescent spectra of chiral Re(I) transition metal complexes
Authors: Shafei Rami , Hamano Ai , Gourlaouen Christophe , Maganas Dimitrios , Takano Keiko , Daniel Chantal , Neese Frank
Published: August 2023

In this work, we present a computational study that is able to predict the optical absorption and photoluminescent properties of the chiral Re(I) family of complexes [fac-ReX(CO)3L], where X is either Cl or I and L is N-heterocyclic carbene extended with π-conjugated [5]-helicenic unit. The computational strategy is based on carefully calibrated time dependent density functional theory calculations and operates in conjunction with an excited state dynamics approach to treat in addition to absorption (ABS) and photoluminescence (PL), electronic circular dichroism (ECD), and circularly polarized luminescence (CPL) spectroscopies, respectively. The employed computational approach provides, an addition, access to the computation of phosphorescence rates in terms of radiative and non-radiative relaxation processes. The chosen molecules consist of representative examples of non-helicenic (NHC) and helicenic diastereomers. The agreement between theoretical and experimental spectra, including absorption (ABS, ECD) and emission (PL, CPL), is excellent, validating a quantitative interpretation of the spectral features on the basis of natural transition orbitals and TheoDore analyses. It is demonstrated that across the set of studied Re(I) diastereomers, the emission process in the case of NHC diastereomers is metal to ligand charge transfer in nature and is dominated by the easy-axis anisotropy of the emissive excited multiplet. On the contrary, in the cases of the helicenic diastereomers, the emission process is intra ligand charge transfer in nature and is dominated by the respective easy-plane anisotropy of the emissive excited multiplet. This affects remarkably the photoluminescent properties of the molecules in terms of PL and CPL spectral band shapes, spin-vibronic coupling, relaxation times, and the respective quantum yields. Spin-vibronic coupling effects are investigated at the level of the state-average complete active space self-consistent field in conjunction with quasi-degenerate second order perturbation theory. It is in fact demonstrated that a spin-vibronic coupling mechanism controls the observed photophysics of this class of Re(I) complexes.
Stochastic simulation of hydrogen–oxygen auto-ignition at the microscale
Authors: Yang C. , Hu Y. , Wang X. Y. , Hong Q. Z. , Sun Q. H.
Published: August 2023

A hybrid stochastic simulation method is developed to study H2–O2 auto-ignition at the microscale. Simulation results show that the discrete and stochastic characteristics of reaction collisions have notable impacts on the ignition process, particularly in the early stages when only a few radicals exist. The statistical properties of ignition delay time, which reflect the accumulated stochasticity during ignition, are obtained and analyzed for different initial temperatures and total molecular numbers. It is found that the average and standard deviation of ignition delay time increase as the total molecular number decreases, with this phenomenon being particularly pronounced near the crossover temperature. When the total molecular number is sufficiently small, the chain initiation reaction becomes crucial to the stochastic properties, as its average firing time exhibits an inverse proportionality to the total molecular number. As the total molecular number increases, the influence of other chain reactions intensifies, causing the power law relation between standard deviation and total molecular number to shift from −1 power to −0.5 power. Owing to different chain reaction paths for high- and low-temperature auto-ignition, the strongest relative fluctuation occurs near the crossover temperature. A theoretical equation for the standard deviation of ignition delay time is obtained based on dimensional analysis, giving excellent agreement with the simulation results in both high- and low-temperature modes.
Laser writing of parabolic micromirrors with a high numerical aperture for optical trapping and rotation
Authors: Plaskocinski T. , Arita Y. , Bruce G. D. , Persheyev S. , Dholakia K. , Di Falco A. , Ohadi H.
Published: August 2023

On-chip optical trapping systems allow for high scalability and lower the barrier to access. Systems capable of trapping multiple particles typically come with high cost and complexity. Here, we present a technique for making parabolic mirrors with micrometer-size dimensions and high numerical apertures (NA > 1). Over 350 mirrors are made by simple CO2 laser ablation of glass followed by gold deposition. We fabricate mirrors of arbitrary diameter and depth at a high throughput rate by carefully controlling the ablation parameters. We use the micromirrors for three-dimensional optical trapping of microbeads in solution, achieving a maximum optical trap stiffness of 52 pN/μm/W. We, then, further demonstrate the viability of the mirrors as in situ optical elements through the rotation of a vaterite particle using reflected circularly polarized light. The method used allows for rapid and highly customizable fabrication of dense optical arrays.
Effect of Mg doping on carrier recombination in GaN
Authors: Marcinkevičius Saulius , Chow Yi Chao , Nakamura Shuji , Speck James S.
Published: August 2023

Time-resolved photoluminescence measurements have been performed on Mg-doped GaN for Mg concentrations in the low- to mid-1019 cm−3. As-grown and annealed (600–675 °C) samples were studied. In the as-grown samples, the nonradiative carrier lifetime was found to be about 200 ps and nearly independent of the Mg concentration. Upon annealing, the carrier lifetimes shorten to ∼150 ps but, again, show little dependence on the annealing temperature. The analysis of possible Shockley–Read–Hall recombination centers and their behavior during doping and annealing suggests that the main nonradiative recombination center is the Mg–nitrogen vacancy complex. The weak dependence of the PL decay times on temperature indicates that carrier capture into this center has a very low potential barrier, and the nonradiative recombination dominates even at low temperatures.
Satellite radio detection via dual-microwave Rydberg spectroscopy
Authors: Elgee Peter K. , Hill Joshua C. , LeBlanc Kermit-James E. , Ko Gabriel D. , Kunz Paul D. , Meyer David H. , Cox Kevin C.
Published: August 2023

Rydberg electric field sensors exploit the large number of Rydberg resonances to provide sensitivity over a broad range of the electromagnetic spectrum. However, due to the difficulty of accessing resonant Rydberg states at ultra-high frequency (UHF) and below, ubiquitous bands in the world's current wireless communications infrastructure, they currently fall, short in sensitivity in this range. We present a resonant Rydberg electric field sensor operating in the UHF band using a dual-optical dual-microwave spectroscopy scheme. Adding an additional microwave photon allows us to access transitions between Rydberg states with higher angular momentum (L=3→4), which have lower resonant frequencies than transitions typically used in Rydberg sensors. We discuss the applicability of this type of sensor across the UHF band and below and measure the resonant sensitivity of our system at 2.3 GHz to be 70(5) μV m−1 Hz−1∕2, 57 times better than the measured sensitivity with a far off-resonant probing scheme at this frequency. We also show the effectiveness of this sensing scheme by measuring Sirius XM satellite radio (2.320–2.345 GHz) received outside the laboratory and rebroadcast onto the atoms.
Inverse distance weighting interpolation-based immersed boundary velocity correction method for incompressible flows
Authors: Du Yinjie , Yang Liming , Shu Chang , Xiao Yang , Song Yuxin
Published: August 2023

In this work, the inverse distance weighting (IDW) interpolation is introduced into the implicit velocity correction-based immersed boundary method (IBM) for simulation of incompressible flows. In the original implicit velocity correction-based IBM, the solid body must be immersed in a uniform mesh region due to the use of the smooth Dirac delta function, which is utilized to associate Lagrangian points with their surrounding Eulerian points and only works with uniform meshes. The IDW method has the advantage that the interpolation range can be set flexibly. The introduction of the IDW interpolation can extend the application of the IBM to non-uniform meshes while reducing the number of Lagrangian points. The numerical test by the decaying vortex problem proves that the IDW interpolation does not significantly affect the overall accuracy of the IBM. In addition, numerical experiments for the flows around a circular cylinder and a NACA0012 airfoil demonstrate the advantages of the proposed method, including allowing fewer Lagrangian points while ensuring no streamline penetration to the solid body, as well as its adaptability to non-uniform meshes which can improve the computational efficiency due to the use of fewer mesh points. Finally, the simulation of the flow past a stationary sphere illustrates that the proposed method can effectively simulate the three-dimensional flow.
Anti-Stokes–Stokes Raman scattering of light from the excited Laughlin liquid
Authors: Kulik L. V. , Zhuravlev A. S. , Larionov A. V. , Zagitova A. A. , Kukushkin I. V.
Published: August 2023

An ensemble of neutral excitations is constructed experimentally in the Laughlin liquid at the electron filling factor 1/3. The excitations are found to induce a nonlinear optical response, manifested as a quadratic dependence of the reflection signal on the excitation power. The reported experimental results indicate that the observed effect is due to the anti-Stokes–Stokes scattering of light from the excited Laughlin liquid.
Estimation time delay from field emission to secondary electron emission avalanche in vacuum surface flashover
Authors: Zhang Jianwei , Wang Hongguang , Li Yongdong , Liu Chunliang , Zhang Jiawei
Published: August 2023

Vacuum surface flashover is the main factor limiting the development of pulsed power system. In this work, a quantitative dynamical model is built to investigate the vacuum surface flashover from field emission to secondary electron emission avalanche (SEEA). The results show that positive charges accumulating on the dielectric surface caused by field emission electrons play a dominant role when the normal electric field on the dielectric surface Edc is small. The growth of the number of positive surface charges exponentially decreases with the distance from the cathode triple junction (CTJ). With the increase in the density of positive surface charges, the growth of positive surface charges mainly depends on the secondary electrons cascade. As a result, the saturation state of Edc will first occur on the dielectric surface at a distance hundreds of micrometers from the CTJ. In addition, the effect of dielectric permittivity on positive surface charges is considered. The density of positive surface charges equals (1+εr) ε0Edc rather than 2ε0Edc. Particle-in-cell simulations are employed to verify the correctness of the theory model, and the agreement of comparisons is favorable. Furthermore, the space charge effect is discussed. When SEEA reaches saturation, electrons can significantly change the spatial distribution of the electric field.
Droplet evaporation on superhydrophobic surfaces
Authors: Erbil H. Y. , McHale G.
Published: August 2023

Over the last decades, a fabulous variety of synthetic superhydrophobic surfaces have been created, offering unique anti-wetting properties. A significant focus for these surfaces has been on their stay-dry and self-cleaning properties. However, unless in a saturated environment, water droplets lose mass through evaporation and this itself is a field of significant interest, which is illustrated by a flood of recent studies on surface contamination and potential surface transmission of infection by evaporating sessile droplets during the Covid-19 pandemic. Superhydrophobic surfaces alter a droplet's contact with a substrate and the surrounding environment, thus changing pinning and heat transfer properties. The droplet shape also alters the space into which vapor can diffuse. Despite the many excellent reviews on superhydrophobic surfaces, there does not appear to have been a focus on the overlap with evaporating sessile droplets. Here, we address this gap by outlining the diffusion-limited sessile droplet evaporation theory, applications on patterned superhydrophobic surfaces, effect of evaporative cooling on drop evaporation rates, and practical applications of drop evaporation on superhydrophobic surfaces, such as nanoparticle assembly, biomedical assay, analytical chemistry, and crystallization applications. Finally, we provide our personal views of possible future directions in these overlapping areas.
Persistent homology-based descriptor for machine-learning potential of amorphous structures
Authors: Minamitani Emi , Obayashi Ippei , Shimizu Koji , Watanabe Satoshi
Published: August 2023

High-accuracy prediction of the physical properties of amorphous materials is challenging in condensed-matter physics. A promising method to achieve this is machine-learning potentials, which is an alternative to computationally demanding ab initio calculations. When applying machine-learning potentials, the construction of descriptors to represent atomic configurations is crucial. These descriptors should be invariant to symmetry operations. Handcrafted representations using a smooth overlap of atomic positions and graph neural networks (GNN) are examples of methods used for constructing symmetry-invariant descriptors. In this study, we propose a novel descriptor based on a persistence diagram (PD), a two-dimensional representation of persistent homology (PH). First, we demonstrated that the normalized two-dimensional histogram obtained from PD could predict the average energy per atom of amorphous carbon at various densities, even when using a simple model. Second, an analysis of the dimensional reduction results of the descriptor spaces revealed that PH can be used to construct descriptors with characteristics similar to those of a latent space in a GNN. These results indicate that PH is a promising method for constructing descriptors suitable for machine-learning potentials without hyperparameter tuning and deep-learning techniques.
Modeling multi-site emission in porous electrosprays resulting from variable electric field and meniscus size
Authors: Whittaker C. B. , Jorns B. A.
Published: August 2023

A model predicting the number of emission sites and total current from a porous conical electrospray emitter as functions of voltage is derived. A pressure balance between capillary and electric forces is used to determine an onset criterion for individual menisci, and an ionic emission scaling law is invoked to predict the current each meniscus emits. These submodels are integrated over a phenomenological meniscus size distribution and the area of the emitter to yield a model for emitter performance as a function of five free parameters, two for the ionic emission submodel and three for the meniscus size distribution. Bayesian inference is applied to determine these model parameters from an existing dataset [Dressler et al., J. Propul. Power 38, 809 (2022)]. The model predictions after training are compared to the experimental data, and it is found that the majority of the data are within a 90% credible interval. The ability of the model to capture key trends in the experimental data is attributed to the interplay of two effects: the distribution over meniscus size on the emitter and the position-dependent electric field. The calibrated model results also suggest that the emitter surface is wetted by a series of large but sparsely distributed pools of propellant. The performance and extensibility of the model are examined within the context of model-based design for porous electrospray array thrusters.
Transport collision integrals for C(5S)-H(2S), C(1S)-H(2S), C(1D)-H(2S), and C(3P)-H(2S) interactions
Authors: Hou Zhenlu , Qin Zhi , Liu Linhua
Published: August 2023

Transport collision integrals of interacting atoms or ions are essential in modeling transport properties of high-temperature gases and plasmas. Here, we obtained the potential energy curves (PECs) of CH using the state-of-the-art ab initio methods. The PECs were also extrapolated to investigate the transport collision integrals for C(3P)-H(2S), C(5S)-H(2S), C(1S)-H(2S), and C(1D)-H(2S) interactions, in which the interactions between the excited C(5S), C(1S), and C(1D) atoms and the ground H(2S) atoms were calculated for the first time. The resulting transport collision integrals were fitted to simple functional forms for ease of use in plasma modeling. Our transport collision integrals can provide data references for computing transport properties of high-temperature plasmas involving C and H atoms.
Droplet dynamics: A phase-field model of mobile charges, polarization, and its leaky dielectric approximation
Authors: Qin Yuzhe , Huang Huaxiong , Song Zilong , Xu Shixin
Published: August 2023

This paper presents a Poisson–Nernst–Planck–Navier–Stokes–Cahn–Hillard (PNP–NS–CH) model for an electrically charged droplet suspended in a viscous fluid under an external electric field. Our model incorporates spatial variations in electric permittivity and diffusion constants, as well as interfacial capacitance. Based on a time scale analysis, we derive two approximations of the original model: a dynamic model for the net charge (assuming unchanged conductance) and a leaky-dielectric model (assuming unchanged conductance and net charge). For the leaky-dielectric model, we perform a detailed asymptotic analysis to demonstrate the convergence of the diffusive-interface leaky-dielectric model to the sharp interface model as the interface thickness approaches zero. Numerical computations are conducted to validate the asymptotic analysis and demonstrate the model's effectiveness in handling topology changes, such as electro-coalescence. Our numerical results from these two approximation models reveal that the polarization force, induced by the spatial variation in electric permittivity perpendicular to the external electric field, consistently dominates the Lorentz force arising from the net charge. The equilibrium shape of droplets is determined by the interplay between these two forces along the direction of the electric field. Moreover, in the presence of interfacial capacitance, a local variation in effective permittivity results in the accumulation of counter-ions near the interface, leading to a reduction in droplet deformation. Our numerical solutions also confirm that the leaky-dielectric model is a reasonable approximation of the original PNP–NS–CH model when the electric relaxation time is sufficiently short. Both the Lorentz force and droplet deformation decrease significantly when the diffusion of net charge increases.
The loading on a vertical cylinder in steep and breaking waves on sheared currents using smoothed particle hydrodynamics
Authors: Yang Yong , Stansby Peter K. , Rogers Benedict D. , Buldakov Eugeny , Stagonas Dimitris , Draycott Samuel
Published: August 2023

Waves and currents coexist in a wide range of natural locations for the deployment of offshore structures and devices. This combined wave–current environment largely determines the loading of vertical surface piercing cylinders, which are the foundations typically used for offshore wind turbines along with many other offshore structures. The smoothed particle hydrodynamics (SPH) code DualSPHysics is used to simulate focused waves on sheared currents and assess subsequent loading on a vertical cylinder. Outputs from another numerical model are used to define the SPH inlet–outlet boundary conditions to generate the wave–current combinations. A modified damping zone is used to damp the waves, but allow the currents to exit the domain. Numerical results are validated against experimental measurements for surface elevation and associated loading on the cylinder. Four phase repeats are used in the SPH model to understand the harmonic structure of the surface elevation at the front face of the cylinder and associated loading. It is shown that the SPH model provides agreement with experimental measurements of harmonic components for both force and elevations. Taking advantage of the SPH method, wave amplitudes were increased up to, and beyond, the breaking threshold highlighting a complex relationship between peak force and wave phase, requiring detailed investigation. The numerical modeling of interactions of steep and breaking waves on sheared currents with the cylinder demonstrates the SPH model's capability for modeling highly nonlinear fluid–structure interaction problems.
GaAs/GaInNAs core-multishell nanowires with a triple quantum-well structure emitting in the telecommunication range
Authors: Nakama Kaito , Yukimune Mitsuki , Kawasaki Naohiko , Higo Akio , Hiura Satoshi , Murayama Akihiro , Jansson Mattias , Chen Weimin M. , Buyanova Irina A. , Ishikawa Fumitaro
Published: August 2023

Semiconducting nanowires (NWs) fabricated from III–V materials have gained significant attention for their application in advanced optoelectronic devices. Here, the growth of GaAs/GaInNAs/GaAs core-multishell NWs with a triple quantum-well structure, having about 2% N and 20% In, is reported. The NWs are grown via selective area plasma-assisted molecular beam epitaxy on patterned Si(111) substrates with SiO2 mask holes. The nucleation and growth of the GaAs nanowires' core are carried out by Ga-induced vapor–liquid–solid growth at the open holes. Finely controlled, vertically aligned, regular core-multishell NWs with uniform wire length and diameter are obtained with a 96% yield and targeted nitrogen concentrations of 0%, 2%, and 3%. The GaInNAs NWs exhibit a spectral red shift relative to the GaAs NWs' peak. Their emission wavelength increases with the N content reaching up to 1.26 μm, which makes them a promising tool in telecommunication light sources.
Toward direct spatial and intensity characterization of ultra-high-intensity laser pulses using ponderomotive scattering of free electrons
Authors: Longman A. , Ravichandran S. , Manzo L. , He C. Z. , Lera R. , McLane N. , Huault M. , Tiscareno G. , Hanggi D. , Spingola P. , Czapla N. , Daskalova R. L. , Roso L. , Fedosejevs R. , Hill W. T.
Published: August 2023

Spatial distributions of electrons ionized and scattered from ultra-low-pressure gases are proposed and experimentally demonstrated as a method to directly measure the intensity of an ultra-high-intensity laser pulse. Analytic models relating the peak scattered electron energy to the peak laser intensity are derived and compared to paraxial Runge–Kutta simulations highlighting two models suitable for describing electrons scattered from weakly paraxial beams (f#>5) for intensities in the range of 1018−1021 W cm−2. Scattering energies are shown to be dependent on gas species, emphasizing the need for specific gases for given intensity ranges. Direct measurements of the laser intensity at full power of two laser systems are demonstrated, both showing a good agreement between indirect methods of intensity measurement and the proposed method. One experiment exhibited the role of spatial aberrations in the scattered electron distribution, motivating a qualitative study on the effect. We propose the use of convolutional neural networks as a method for extracting quantitative information on the spatial structure of the laser at full power. We believe the presented technique to be a powerful tool that can be immediately implemented in many high-power laser facilities worldwide.
Drag reduction study of naturally occurring oscillating axial flow induced by helical corrugated surface in Taylor–Couette flow
Authors: Razzak Md Abdur , Cheong Khoo Boo , Lua Kim Boon , Tay C. M. J.
Published: August 2023

This study investigates drag reduction capability of naturally occurring-oscillating axial secondary flow (ASF) induced by helical-corrugated surface in Taylor–Couette flow (TCFHelical) for three values of pitch to wavelength ratios (P* = 1, 2, and 3) and amplitude to wavelength ratio(A*) of 0.25. As reported in Razzak et al. [“Numerical study of Taylor Couette flow with longitudinal corrugated surface,” Phys. Fluids 32(5), 053606 (2020)], emergence of naturally occurring-oscillating ASF induced by longitudinal-corrugated surface in TCF (TCFLongitudinal) and increasing trend on its magnitude with Reynolds number (Re) results in the occurrence of drag reduction. This has motivated us to study the possibility of enhancing drag reduction by maintaining a consistently increasing trend with Re in the magnitude of naturally occurring-oscillating ASF induced by the helical-corrugated surface on the stationary outer cylinder in TCF. From flow structures, steady ASF with non-zero mean is observed at Re = 60, which suppresses the strength of azimuthal vorticities for Re > 85, and contributed to the occurrence of drag reduction. As Re is increased to 100, 90, and 85 for P* = 1, 2, and 3, respectively, the formation of periodic oscillating ASF with non-zero mean and its increasing trend in magnitude with Re suppresses azimuthal vorticities further, which contributes to the maximum drag reduction of 13%. For Re > 165, 145, and 140 for P* = 1, 2, and 3, respectively, non-periodic oscillating ASF is observed, and its magnitude remains nearly unchanged or decreases slightly with Re, which results in the suppression effect of azimuthal vortices to be weaker. This results in the decrease in the drag reduction. Oscillating ASF observed in TCFHelical is found to occur at earlier Re, and it is stronger than that of TCFLongitudinal, which contributes to the occurrence of higher drag reduction in TCFHelical.
Accelerating and stabilizing the convergence of vibrational self-consistent field calculations via the direct inversion of the iterative subspace (vDIIS) algorithm
Authors: Yang Emily L. , Spencer Ryan J. , Zhanserkeev Asylbek A. , Talbot Justin J. , Steele Ryan P.
Published: August 2023

The vibrational self-consistent field (VSCF) method yields anharmonic states and spectra for molecular vibrations, and it serves as the starting point for more sophisticated correlated-vibration methods. Convergence of the iterative, non-linear optimization in VSCF calculations can be erratic or altogether unsuccessful, particularly for chemical systems involving low-frequency motions. In this work, a vibrational formulation of the Direct Inversion of the Iterative Subspace method of Pulay is presented and investigated. This formulation accounts for distinct attributes of the vibrational and electronic cases, including the expansion of each single-mode vibrational wavefunction in its own basis set. The resulting Direct Inversion of the Iterative Subspace method is shown to substantially accelerate VSCF convergence in all convergent cases as well as rectify many cases where Roothaan-based methods fail. Performance across systems ranging from small, rigid molecules to weakly bound molecular clusters is investigated in this analysis.
Decoupling and reconstruction analysis in a transonic axial compressor using the dynamic mode decomposition method
Authors: An Guangyao , Kang Jiacheng , Wang Longyao , Zhang Lei , Lang Jinhua , Li Hongyang
Published: August 2023

Unsteady flow is highly related to flow loss and aerodynamic performance degradation in the axial compressor. In this paper, the dynamic mode decomposition method was used to investigate in-depth flow structures and related evolutionary mechanisms of the internal flow field. Four main flow structures were observed through flow field decoupling: the oscillation of the tip leakage vortex (TLV) region, the circumferential migration of the leakage-induced vortex (LIV), the axial migration of the rear part of the leakage vortex (RLV), and the oscillation of the leading edge vortex (LEV). All of those four structures indicated the presence of internal high disturbance regions. The reconstruction of the dominant mode flow field revealed that the unsteady evolutionary mechanism of the flow field mainly consisted of two components: the axial evolution of the RLV and the circumferential evolution of the LIV. It was further revealed that the axial evolution of the RLV was the primary reason for the formation of low-energy fluid mass within the passage; under the influence of the “leading edge overflow,” the LIV eventually fused with the LEV. The blocking effect of the LEV led to the formation of a high oscillation region at the leading edge of the adjacent blade pressure surface, resulting in a synchronous moment between the emergence of the LIV and the LEV. The analysis of the two unsteady evolution mechanism components further supported TLV breakdown as the main cause of flow unsteadiness. This study laid the foundation for further accurate flow unsteadiness control.
The separation of one-soliton-shock to multi-soliton-shock of dust-ion acoustic wave using Lax pair and Darboux transformation of Burgers’ equation
Authors: Chatterjee Prasanta , Mandi Laxmikanta
Published: August 2023

Properties of dust-ion acoustic waves (DIAWs) in an unmagnetized dusty plasma consisting of mobile ions, superthermal electrons, and negatively charged dust clouds with charge fluctuation are investigated. Burgers’ equation is derived from the fluid equation of the plasmas by considering the reductive perturbation technique. The Lax pair of the evolution equation is obtained, and the characteristics of the DIAWs are investigated by employing the Darboux transformation. Some new waves (one-soliton, two-soliton-shocks, etc.) other than usual shocks are observed as the Darboux transformation is used through the Lax pair. It is also shown that all the physical plasma parameters have a significant effect on the structure of the nonlinear waves.
Theoretical study on structural and optical properties of β-Ga2O3 with O vacancies via shell DFT-1/2 method
Authors: Hao L. Y. , Du J. L. , Fu E. G.
Published: August 2023

As one of the most common and important defects, O vacancy has a great influence on β-Ga2O3, which has not been studied systematically with appropriate functional approximation. Herein, the effects of O vacancies on the structural, electronic, and optical properties of bulk β-Ga2O3 were systemically investigated by using the shell DFT-1/2 method. For intrinsic β-Ga2O3, the calculated bandgap is 4.77 eV, which corresponds well to the experimental value. Band structures and density of states (DOS) prove that O vacancy will introduce a deeper donor level in the bandgap. Charge density distribution demonstrates the covalent properties of the Ga–O bond and reveals the charge transfer near the O vacancy. Phonon dispersion spectra prove the dynamical instability of the O vacancy systems. The formation energy curves show that the +2 charge state is energetically favorable at low Fermi energy, while the neutral defect is the most stable one at high Fermi energy. The transition energy of ɛ(+2/0) also proves that the O vacancy acts as a deep donor. The introduction of O defects introduces extra peaks in the lower energy regions of the absorption and electron energy loss spectra, and the peak positions are in good agreement with the previous experimental results. This study gives a point of view on the effects of O vacancies on β-Ga2O3 and proves the advantages of shell DFT-1/2 calculation in ultrawide bandgap semiconductors.
Energy and exergy evaluations of solar-aided double reheat coal-fired power generation system
Authors: Wu Junjie , Wu Jiaming , Han Yu
Published: August 2023

In this paper, solar heat with mid- and high-temperature collected by molten salt parabolic trough solar field was integrated into the boiler sub-system of the double reheat coal-fired power generation system. Three typical integration modes were, respectively, evaluated by energy and exergy perspectives in terms of solar-generated electricity and solar energy conversion efficiency. Integration modes I–III utilized solar heat to preheat the inlet superheated steam, inlet reheated steam and inlet double reheated steam, respectively. Based on the case study through energy evaluation, it indicated that integrating solar energy with lower temperature led to higher solar-generated electricity, higher solar-to-solar heat efficiency, and higher solar-to-electricity efficiency. Integration mode I was unreasonably regarded superior to the other two, because the energy evaluation method ignored the quality of solar energy and mistakenly regarded the efficiency of solar heat to solar-generated electricity as the cycle efficiency. As an update, exergy evaluation takes both energy quantity and energy quality into consideration by regarding the efficiency of solar heat exergy to solar-generated electricity as the cycle exergy efficiency. It indicated that integration mode II was more recommended, with the highest solar-to-solar heat exergy efficiency and solar-to-electricity efficiency being 34.0% and 24.7%, respectively. The corresponding aperture area and solar-generated electricity are 5.7 × 105 m2 and 136.1 MW, respectively.
Terahertz bolometric detectors based on graphene field-effect transistors with the composite h-BN/black-P/h-BN gate layers using plasmonic resonances
Authors: Ryzhii M. , Ryzhii V. , Shur M. S. , Mitin V. , Tang C. , Otsuji T.
Published: August 2023

We propose and analyze the performance of terahertz (THz) room-temperature bolometric detectors based on the graphene channel field-effect transistors (GC-FET). These detectors comprise the gate barrier layer (BL) composed of the lateral hexagonal-boron nitride black-phosphorus/hexagonal-boron nitride (h-BN/b-P/h-BN) structure. The main part of the GC is encapsulated in h-BN, whereas a short section of the GC is sandwiched between the b-P gate BL and the h-BN bottom layer. The b-P gate BL serves as the window for the electron thermionic current from the GC. The electron mobility in the GC section encapsulated in h-BN can be fairly large. This might enable a strong resonant plasmonic response of the GC-FET detectors despite relatively lower electron mobility in the GC section covered by the b-P window BL. The narrow b-P window diminishes the Peltier cooling and enhances the detector performance. The proposed device structure and its operation principle promote elevated-temperature GC-FET THz detector responsivity values and other characteristics, especially at the plasmonic resonances.
Laser induced high temperature thermal-mechanical-oxygen coupling experimental system and method
Authors: Wang Jiawei , Feng Guobin , Zhang Jianmin , Wu Lixiong , Wang Na , Zhao Xiaofan , Li Bin
Published: August 2023

In this paper, a thermal–mechanical–oxidation coupling experimental system based on laser heating is developed, containing two modes of Gaussian and flat-top lasers, which has a series of advantages such as high temperature range, rapid heating rate, and convenient observation. The system adopts active illumination and an optical filter to solve the problem where it is difficult for traditional digital-image correlation technology to image clearly under laser heating. A biaxial mechanical test machine is used to simulate the complex load by applying biaxial tension or compression loads on the material. Combined with the radiation temperature measurement and controllable flow field device, the thermal-mechanical-oxygen coupling experiment of high temperature resistant materials under aerobic environment can be carried out. The maximum uniform heat flux output density is 27.2 kW/cm2, and the maximum Gaussian heat flux output density is 105 kW/cm2. The thermal-mechanical-oxygen coupling experimental system and method are of great significance to the development of new high temperature resistant materials and thermal barrier coatings.
Transient effects in the coupling of thermal radiation and non-Fourier heat transport at the nano-scale
Authors: Becerril D. , Camacho de la Rosa A. , Esquivel-Sirvent R.
Published: August 2023

In this work, we study thermalization between two bodies separated by a vacuum gap by coupling the non-Fourier behavior of the materials with the radiative heat transfer in the near-field. Unlike the diffusion-type temperature profile, in non-Fourier materials, the temperature behaves as a wave, changing the thermalization process. Due to the temperature profile induced by the coupling with conduction, we show that the radiative heat flux exchanged between the two bodies differs from the Fourier case and exhibits transient temperature effects at the onset of the thermalization process. These results have important implications in nanoscale thermal management, near-field solid-state cooling, and nanoscale energy conversion.
Numerical investigation on the bubble rising dynamics in ratchet channels filled with viscoelastic liquids
Authors: Li Yunsong , Yuan Wenjun , Ba Qixin , Mei Mei , Wu Weitao
Published: August 2023

In this paper, we investigated the dynamics of a bubble rising inside ratchet channels filled with viscoelastic liquids by means of volume-of-fluid-based direct numerical simulations. The exponential Phan–Thien–Tanner constitutive model was used to describe the rheological behaviors of the nonlinear viscoelastic fluid. The effects of fluid elasticity [characterized by the relaxation time (λ)] and ratchet angle (θ) are mainly discussed in respect of bubble dynamics (e.g., rising velocity, flow field, and stress field, etc.). Our results found that the bubble rise velocity increases with fluid elasticity, and the average bubble velocity can be reduced up to 20% at low elasticity in ratchet channels. In addition, the periodic arrangement of the ratchet influences the distribution of the stress field, the vorticity component, and also the deformation of the entangled polymers in the flow. It was observed that the distributions of the stress field and the trace of the conformation tensor change significantly in a dense ratchet channel compared to a sparse one. Interestingly, the bubble velocity gradually increases after the bubble emerges from the convergent section, whereas it decreases on approaching the convergent section. The dynamical bubbles can be manipulated by the surrounding fluid viscoelasticity and ratchet channels, which will be useful in oil extraction and chemical process involving complex non-Newtonian fluids.
Effect of water content and aging on the elastic properties of extruded pea protein isolate
Authors: Ubbink Job , Muhialdin Belal J.
Published: August 2023

The effects of water on the elastic properties of extruded pea protein isolate (PPI) are investigated transversally to the fiber direction in the water content range between 40% w/w to 60% w/w. Young's modulus of elasticity in the transversal direction was found to decrease linearly with the water content from 2.6 MPa at a water content of 40% w/w to 0.6 MPa at the water content of 60% w/w at T = 21 ± 1 °C. Matrices extruded at different water contents of which the water content was adjusted to 60 ± 1% w/w showed decreasing values of Young's modulus. This variation in the transversal Young's modulus correlates linearly with the specific mechanical energy, confirming the impact of processing on the development of the protein network. The kinetics of aging of the extruded PPI matrices at T = 4 °C were fitted using an exponential equation and were observed to be dependent on the water content. Characteristic aging rates varied from an aging rate of ∼0.1 h−1 for the matrices extruded at a water content of 40% w/w to ∼0.015 h−1 for the matrices extruded at a water content of 60% w/w. The degree of aging was found to be 43.2 ± 7.5%, independent of the protein content of the matrices. The current study is the first systematic investigation of the elastic properties of extruded plant protein matrices in the concentration range that is relevant for meat analogs and may serve in process optimization and product development as well as for fundamental studies into the properties of concentrated protein networks.
From molecular sieving to gas effusion through nanoporous 2D graphenes: Comparison between analytical predictions and molecular simulations
Authors: Guo Juncheng , Galliero Guillaume , Vermorel Romain
Published: August 2023

In this paper, we study the permeation of polyatomic gas molecules through 2D graphene membranes. Using equilibrium molecular dynamics simulations, we investigate the permeation of pure gas compounds (CH4, CO2, O2, N2, and H2) through nanoporous graphene membranes with varying pore sizes and geometries. Our simulations consider the recrossing mechanism, often neglected in previous studies, which has a significant effect on permeation for intermediate pore size to molecular diameter ratios. We find that the permeation process can be decoupled into two steps: the crossing process of gas molecules through the pore plane and the escaping process from the pore region to a neighboring adsorption site, which prevents recrossing. To account for these mechanisms, we use a permeance model expressed as the product of the permeance for the crossing process and the probability of molecule escape. This phenomenological model is extended to account for small polyatomic gas molecules and to describe permeation regimes ranging from molecular sieving to effusion. The proposed model captures the temperature dependence and provides insights into the key parameters of the gas/membrane interaction controlling the permeance of the system. This work lays the foundation for predicting gas permeance and exploring membrane separation factors in 2D materials such as graphene.
Effect of flow channel inclination on void fraction for downward two-phase flows
Authors: Dong Chuanshuai , Hibiki Takashi
Published: August 2023

The drift-flux model (DFM) is of practical importance for analyzing gas–liquid flow in various applications, such as chemical reactors and nuclear power plants. This paper aims at developing an accurate flow-regime-independent DFM for estimating the void fractions of two-phase downward inclined flow. The effect of flow channel inclination on void fraction for downward two-phase flows was investigated comprehensively. First, 2868 data for void fractions of gas–liquid two-phase flows were summarized from 12 sources. The inclination angle ranged from 0° to 90°. Then, the existing drift-flux models were reviewed comprehensively. The existing models had poor predictive performance in terms of the whole experimental database. Therefore, a theoretically supported drift-flux model for downward inclined two-phase flow was established based on a deeper understanding of two-phase flow behavior. The influence of channel inclination angles on the distribution parameters and drift velocities was determined quantitatively. A total of 87.8% of estimated void fractions were within ±20% errors of experimental void fractions. The mean relative deviation, md, was −2.04%.