bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear and nonlinear dynamics of self-consistent collisionless tearing modes in toroidal gyrokinetic simulations
Authors: Widmer F. , Poli E. , Mishchenko A. , Ishizawa A. , Bottino A. , Hayward-Schneider T.
Published: November 2024

We investigate tearing modes (TM) driven by current density gradient in collisionless tokamak plasmas by using the electromagnetic gyrokinetic simulation code ORB5. We elucidate the TM width by simulations for flat profiles, as the absence of background diamagnetic flows implies a small rotation speed, while finite gradients are included to investigate the TM rotation. For flat profiles, the initial saturation width of nonlinearly driven magnetic islands is related to the TM linear growth rate; however, large islands in the initial saturation phase are prone to current density redistribution that reduces the island width in the following evolution. Island-induced E×B and diamagnetic sheared flows develop at the separatrix, able to destabilize the Kelvin–Helmholtz instability (KHI). The KHI turbulence enhances a strong quadrupole vortex flow that reinforces the island decay, resulting in a strong reduction of the island width in an eventual steady state. This process is enhanced by trapped electrons. For finite gradients profile, the TM usually rotates in the electron diamagnetic direction but can change direction when the ion temperature gradient dominates the other gradients. The reduced growth of the TM by diamagnetic effects results in a moderate island size, which remains almost unchanged after the initial saturation. At steady state, strong zonal flows are nonlinearly excited and dominate the island rotation, as expected from previous theoretical and numerical studies. When β is increased, the TM mode is suppressed and a mode with the same helicity but with twisting parity, coupled with the neighboring poloidal harmonics, is destabilized, similar to the kinetic ballooning mode.
Effects of aluminized charge structures on blast wave propagation and the parameters of partially confined explosions
Authors: Wang Feng , Xiao Wei , Tan Lili , Liu Zongwei , Wang Heng , Wang Zecheng
Published: November 2024

The composite charge structure may have the potential to enhance the overall damage capability of the weapon. In this regard, three-dimensional LS-DYNA simulation software (dynamics calculation software from LSTC) was used to simulate the explosion process of charges in a partially confined space. The effects of different aluminized charge structures on the propagation and parameters of blast waves in a cubic cabin structure with a pressure relief port were obtained. The results showed that the reflected waves generated local pressure convergence at the junction and corner areas of adjacent walls in the cabin structure. The numbers of significant reflections of the blast waves at the center and corners of the wall were 3 and 2, respectively. The overpressure of the reflected wave at the corner was more than 3.2 times that at the center of the sidewall. Moreover, the number of reflections, overpressure ratio, and charge structure were not directly related. The advantages of composite structure charges in enhancing the overpressure and wave velocity of incident waves and the overpressure and impulse of reflected waves were not significant. However, the internal and external composite charge structure had more advantages than did the upper and lower structures, and its impulse TNT equivalent reached more than 70% of that of a single-structure explosive. The results can provide theoretical support and technical guidance for the design of charge structures and cabin structures.
Development of soft x-ray absorption spectroscopy technique with simultaneous measurement in electron- and fluorescence-yield modes from high vacuum to ambient pressure for observation of surface adsorbed species
Authors: Shibuya Kohei , Amemiya Kenta
Published: November 2024

To understand the reactions of heterogeneous catalysts at the solid–gas interface under actual reaction conditions, it is important to develop a method to observe the surface-adsorbed species during the reaction, including the changes before and after the adsorption of light elements involved in the surface reaction. We developed a soft x-ray absorption spectroscopy (XAS) technique that allows simultaneous measurements in the electron- and fluorescence-yield modes in the pressure range of 10−4–1 × 105 Pa. In the developed system, the reaction gas near the sample surface is separated from the beamline vacuum by a Si3N4 window and confined to a small area to suppress x-ray absorption by the gas. The electron-yield spectra were obtained by measuring the sample current while applying a bias potential to the Si3N4 window. XAS measurements were performed from high vacuum to ambient pressure by setting the bias potential to 600 and 39 V below and above 100 Pa, respectively. An anatase TiO2 nanoparticle-deposited film was prepared by spin coating, and soft XAS was performed to observe the photocatalytic oxidative decomposition reactions of isopropanol in the presence of water and oxygen. The obtained O K-edge spectra showed that it is possible to observe adsorbed oxygen on solid oxides even under ambient pressure conditions containing 0.1% of oxygen gas.
Hybrid
α
-Ta/
β
-Ta lumped element kinetic inductance detectors with photon noise limited sensitivity and stability
Authors: Chi Tianyuan , Shi Lili , Su Runfeng , Zang Siming , Tan Rui , Yao Shiyi , Zhu Yuwei , Chen Junhua , Wu Jingbo , Tu Xuecou , Jin Biaobing , Wang Hongqiang , Cao Juncheng , Chen Jian , Wu Peiheng
Published: November 2024

The terahertz (THz) band is of immense interest in astronomy as it encompasses significant energy generated following the Big Bang, offering critical insight into processes invisible in other bands, such as the earliest stages of planet, star, and galaxy formation. Kinetic inductance detectors (KIDs) have emerged as a formidable contender in the field of THz astronomy, attributed to their exceptional sensitivity and scalability. In this study, we introduce a kind of KIDs incorporating a lumped element (LE) resonator design, with inductors fabricated on β-Ta film and capacitors on α-Ta film. We characterize the noise of the hybrid α-Ta/β-Ta LEKIDs, achieving an optical noise equivalent power of 8.3 ± 5.7 × 10−19 W/Hz1/2, demonstrating high sensitivity. Additionally, the LEKIDs exhibited stability across multiple thermal cycles. The combination of high sensitivity and stability makes the hybrid LEKIDs promising for the stringent demands of THz astronomy.
A multi-task learning framework for aerodynamic computation of two-dimensional airfoils
Authors: Chen Chao , Zhang Bohan , Huang Hongyu , Xie Zhijiang , Yang Chuan , Meng Dehong , Yue Hao , Liang Lei
Published: November 2024

Accurate and efficient prediction of airfoil aerodynamic coefficients is essential for improving aircraft performance. However, current research often encounters significant challenges in balancing accuracy with computational efficiency when predicting complex aerodynamic coefficients. In this paper, a Multi-Task Learning framework for Aerodynamic parameters Computation (MTL4AC) of two-dimensional (2D) airfoils is proposed. The MTL4AC processes two key subtasks: flow field prediction and pressure coefficient prediction. These two subtasks complement each other to reveal both global and local aerodynamic changes around the airfoil. The flow field prediction provides a coarse-grained global perspective, which focuses on the pressure and velocity variations on and around the airfoil surface. The pressure coefficient prediction offers a fine-grained local perspective, which concentrates on the pressure distribution on the airfoil surface to accurately calculate lift and drag coefficients. The MTL4AC demonstrated substantial improvements in the experiments conducted on the public dataset, achieving significant enhancements in accuracy and stability. This research contributes an accurate and efficient framework for aerodynamic computation, integrating geometric features and advanced multi-task learning techniques to achieve superior performance in predicting aerodynamic coefficients.
Suppression of the coffee-ring effect by controlling the solid particle density
Authors: Liou Guan-Fu , Hsu Chin-Chi , Lin Peng-Wun , Wang Pin-Ya
Published: November 2024

Previous studies show that the coffee-ring effect can be suppressed by altering the droplet's evaporation rate, surface tension, surface properties, and shape of particles. This experiment used five types of particles with different densities to analyze their behavior during the droplet evaporation process. The results showed that when the particle density is close to the fluid density, the particles move within the droplet and accumulate at the edges, forming a pronounced coffee-ring effect. Conversely, with the higher difference between the particle density and the fluid density increases, they tended to deposit uniformly at the bottom of the droplet and were less likely to be pushed to the edges by capillary effects, effectively suppressing the coffee-ring effect. We also observed that the movement speed of high-density particles relatively slowed down through particle image velocimetry tracking technology. By analyzing the Peclet number and the timescale between particle sinking speed and particle movement speed due to capillary flow, we explained how particle density influences the critical factors of particle sinking and suspension, thereby inhibiting the formation of the coffee-ring effect.
Role of cavity strong coupling on single electron transfer reaction rate at electrode–electrolyte interface
Authors: Hayashi Takahiro , Fukushima Tomohiro , Murakoshi Kei
Published: November 2024

The physicochemical properties of molecules can be modulated through polariton formation under strong electromagnetic confinement. Here, we discuss the possibility of exploiting this phenomenon to increase the electron transfer rate at an electrode–electrolyte interface. Electron transfer theory under strong electromagnetic confinement can be extended to the electrode–electrolyte interface, and single-electron transfer reactions can be simulated using Gerischer’s theory. Although single electron transfer in free space is well described using Marcus theory, the vacuum electric field can facilitate an additional electron transfer pathway via virtual photon excitation under cavity strong coupling conditions. Therefore, this binary reaction pathway for single electron transfer can yield a quasi-two-particle electron transfer process. This quantum behavior can dominate when the mode volume is small and when there are a large number of molecules in the vacuum electric field. Exploitation of polaritons in single electron transfer reactions can lead to enhanced electrochemical energy conversion systems.
Size-polydispersity-induced effects on the structure of active Brownian pseudo-hard disks
Authors: Torres-Carbajal Alexis , Sevilla Francisco J.
Published: November 2024

Studies of the effects of particle-size polydispersity or of particle interactions on active matter have been limited to determine and analyze the system short-time dynamics in the high-density regime. On the other hand, the effects of polydispersity on the structural behavior of active systems are of relevance and have received much less attention. In this paper, we comprehensively analyze the effects of size dispersion of pseudo hard-disk active Brownian particles, on its structural behavior at different system densities and different self-propelling velocities, thus elucidating the interplay of these features with the polydispersity. This is introduced into our analysis by well-known particle size distributions in such a manner that the average size is fixed, but with a variance that accounts for different dispersion of the particle size according to: Gaussian, Weibull, uniform and “two point” distribution. Local and global structural properties of the system are determined under these considerations. We observe that activity and size polydisperse effects become relevantly conspicuous at densities above the motility induced phase separation critical point of the monodispersal fluid. We notice that, while the activity promotes a more defined local and global structural arrangement, the polydispersity decreases such structure, observing the greatest effect when the particle size is defined by a uniform distribution.
Evaporating capillary bridges of pure and binary liquids
Authors: Ojha Mradul , Kumar Lalit , Bhardwaj Rajneesh
Published: November 2024

We present a numerical and experimental study on the evaporation of microliter capillary bridges of both pure and binary liquids. Specifically, we focused on capillary bridges of a binary liquid composed of water and isopropanol confined between poly-dimethylsiloxane coated surfaces. We developed a finite-element method-based numerical model to solve Laplace equations for vapor diffusion of the two species present in the capillary bridge, considering quasi-steady and diffusion-limited evaporation. We applied a modified version of Raoult's law, incorporating activity coefficients for binary liquids. The Galerkin finite element method was employed in axisymmetric cylindrical coordinates. The numerical model was validated against in-house experiments of side visualization on an evaporating capillary bridge. We quantified the effect of confinement from the plates on slowing down the diffusion of liquid vapor. The volume evolution of the binary liquid capillary bridge was found to be nonlinear, strongly influenced by the initial concentration of isopropanol in the capillary bridge. This nonlinearity is attributed to the faster diffusion of isopropanol vapor compared to water vapor. We examined the effects of height, substrate radius, contact angle, and composition on the evaporation characteristics. We proposed a computationally efficient reduced-order model for determining evaporation kinetics, which yields predictions very close to those of the numerical model.
Analytical properties and solutions for the synchronous pulsating bubble clusters distributed on a spherical surface
Authors: Qin Yupeng , Wang Zhen , Zou Li
Published: November 2024

The present work concerns with the nonlinear dynamics for the synchronous pulsating bubble clusters uniformly distributed on a spherical surface. First, the governing equation for such clusters with 4/6/8/12/20 coupled bubbles are established. Second, the maximum and minimum radii for the gas-filled bubble clusters are analyzed according to the first integral. Third, by introducing suitable nonlocal transformations, two novel equivalent parametric analytical solutions in the form of Weierstrass elliptic function are constructed for the gas-filled bubble clusters for a specific polytropic exponent κ=3/2 without considering the surface tension, and based on which we immediately derive the parametric analytical solution for the corresponding vapor bubble clusters. Further, to consider the case of arbitrary polytropic exponent and surface tension, we develop a direct approach to construct the parametric analytical solution using Jacobi elliptic function for gas-filled bubble clusters. It is shown that, the behaviors and results for the bubble clusters will degenerate to the corresponding ones for single bubbles as the radius of the bubble cluster approaches infinity. In addition, on the basis of the analytical results, dynamic properties and motion laws of the bubble clusters are also discussed.
Drop impact onto wettability-patterned solid surfaces: A phase field approach
Authors: Ji Linli , Shen Mingguang
Published: November 2024

Drop impact onto wettability-patterned surfaces is of great significance in industries. Self-propulsion, self-splitting, and directional rebounding can be realized when drops impact on such surfaces. This paper established a diffuse interface/phase field model to delve into drop impact onto wettability-patterned surfaces, with two typical surfaces considered, one having a step change in the contact angle and the other having a smooth change in it. The diffuse interface model used the phase field to track the liquid–gas interface, was discretized on a half-staggered grid, and was run in a parallel manner. The model was validated first against an impact onto a uniform surface and then against an impact onto a hydrophilic surface coated with a superhydrophobic strip. A mesh independence study was conducted for the phase field modeling. Grid independence was achieved while the phase field mobility was kept fixed in meshes of varied resolutions. The major findings are as follows. The spreading of a spherical drop on gradient wettability surfaces resembles that of an ellipsoidal drop on a uniform surface, and axis-switching was observed. On the other hand, directional rebounding on multi-region wettability surfaces is enhanced with increased wettability contrast.
Shock compression of crystalline TeO2 to the high-pressure fluid regime: Insights from ab initio molecular dynamics simulations
Authors: Weck Philippe F. , Kim Eunja
Published: November 2024

The shock response of fully-dense and porous crystalline tellurium dioxide (TeO2) to the high-pressure and high-temperature fluid regime was investigated within the framework of density functional theory with Mermin’s generalization to finite temperatures. The principal and porous shock Hugoniot curves were predicted from canonical ab initio molecular dynamics (AIMD) simulations, with the phase space sampled along isotherms up to 80 000 K, for densities ranging from ρ=3 to 17 g/cm3. The polymorphs investigated are α-TeO2 paratellurite (P41212), TeO2 cotunnite (Pnma), and TeO2 post-cotunnite (P21/m). Based on the discontinuity found in the calculated Us−up slope of TeO2 post-cotunnite at a shock velocity of Us≃8.35 km/s and a particle velocity of up≃3.64 km/s, the shock melting temperature and pressure are predicted to be ≃6500 K and ≃170 GPa. Results from the AIMD simulations are in line with the static compression data of TeO2 paratellurite and cotunnite, and with the recent shock Hugoniot data for single-crystal α-TeO2 for pressures up to 85 GPa, obtained using the inclined-mirror method and the velocity interferometer system for any reflector combined with powder gun and two-stage light-gas gun.
Sediment transport on rippled beds
Authors: Guevara O. , Guan L. , Salinas J. S. , Zgheib N. , Balachandar S.
Published: November 2024

We conduct an Euler-Lagrange, direct numerical simulation of a turbulent channel flow at a shear Reynolds number of Reτ=180 over an erodible particle bed. The particle bed consists of approximately 1.3 × 106 monodisperse particles, resulting in a bed thickness of around 12–13 particles. The particle density and size are chosen to achieve a ratio of 4 for the Shields stress to the critical Shields stress necessary for incipient motion such that particle transport occurs primarily as bedload. The simulation is run long enough for ripples to form. We track the temporal evolution of the particle flux and excess Shields stress for the entire bed as well as for the four regions of a ripple, namely, the crest, trough, lee side, and stoss side. We find that the particle flux and excess Shields stress closely match the Wong and Parker correlation when the particle bed is featureless at early time but diverge from the correlation when ripples form. This deviation primarily arises from particle transport in the trough and lee side regions. Conversely, particle transport in the crest and stoss side regions remains largely consistent with the Wong and Parker correlation. A root mean square-based correction for the bed is proposed to be used in conjunction with the Wong and Parker correlation. Additionally, ripples attain a self-similar profile in the shape and near-bed shear stress when they are sufficiently distant from their upstream neighbor. Any departure from self-similarity occurs when the upstream neighbor gets within close proximity.
An open-source, adaptive solver for particle-resolved simulations with both subcycling and non-subcycling methods
Authors: Li Xuzhu , Li Chun , Li Xiaokai , Li Wenzhuo , Tang Mingze , Zeng Yadong , Zhu Zhengping
Published: November 2024

We present the IAMReX (incompressible flow with adaptive mesh refinement for the eXascale), an adaptive and parallel solver for particle-resolved simulations on the multi-level grid. The fluid equations are solved using a finite-volume scheme on the block-structured semi-staggered grids with both subcycling and non-subcycling methods. The particle-fluid interaction is resolved using the multidirect forcing immersed boundary method. The associated Lagrangian markers used to resolve fluid-particle interface only exist on the finest-level grid, which greatly reduces memory usage. The volume integrals are numerically calculated to capture the free motion of particles accurately, and the repulsive potential model is also included to account for the particle–particle collision. We demonstrate the versatility, accuracy, and efficiency of the present multi-level framework by simulating fluid-particle interaction problems with various types of kinematic constraints. The cluster of monodisperse particles case is presented at the end to show the capability of the current solver in handling multiple particles. It is demonstrated that the three-level AMR (Adaptive Mesh Refinement) simulation leads to a 72.46% grid reduction compared with the single-level simulation. The source code and testing cases used in this work can be accessed at https://github.com/ruohai0925/IAMR/tree/development. Input scripts and raw postprocessing data are also available for reproducing all results.
Relaxation and rheology in beam-vibrated granular system
Authors: Hong Guangyang , Li Jian , Zheng Qijun , Yu Aibing , Liu Shuang
Published: November 2024

The yielding transition in dense granular matter under vibrated beams, despite its significance for animal and robotic locomotion on granular surfaces and underground structural engineering, remains underexplored. In this study, we systematically modulate the frequency and amplitude of beam vibrations through experiments and simulations to investigate the granular relaxation dynamics. We uncover dual yielding behaviors: gradual, ductile transitions in the time domain, where the system smoothly stabilizes, and abrupt, brittle transitions in the frequency domain, characterized by sharp shifts between metastable states and pronounced hysteresis, highlighting the dynamic consistency between the behavior of the beam and the granular materials. Through detailed analysis of the mesostructural evolution, encompassing particle motion, and mechanical stability, we unveil the root of the hysteresis as stemming from anomalous diffusion driven by memory effects, where the system's response is influenced by its stress history. These findings lead to the development of a nonmonotonic constitutive law that captures the unique frequency-dependent coupling between the beam and granular material. Our findings pave the way for advanced theoretical models in this domain, offering profound insights into the nuanced behaviors of vibrated granular systems.
Research on laser measurement point cloud preprocessing and 3D reconstruction technology for free-form surfaces
Authors: Sun Bin , Song Junfang , Cao Yi , Zhao Xiaoqian
Published: November 2024

Surface morphology measurement and reconstruction technology based on point cloud data is one of the key technologies for 3D information processing in the digital manufacturing industry and has been widely applied in fields such as reverse engineering, computer vision, and unmanned driving system navigation. A method for 3D modeling of aircraft-engine blade profiles based on laser measurement point cloud data is proposed to address the difficulties in measuring the 3D morphology of aircraft-engine blades and the low modeling accuracy. This method first preprocesses the measured point cloud and then uses Poisson's algorithm to reconstruct the blade surface in three dimensions based on the calculation of the point cloud normal. Through error statistical analysis, the overall reconstruction effect is good. The experimental results further validated the generality and effectiveness of this method.
Magnetic proximity-induced anomalous Hall effect in 2D CrOCl/Pt heterostructure
Authors: Li Zelong , Ali Anwar , Zhao Duo , Tang Wei , Younis Muhammad , Qi Lu , Dai Sichao , Kang Chenxu , Weng Xiaoliang , Wu Xiaokeng , Ramiere Aymeric , Zeng Yu-Jia
Published: November 2024

Two-dimensional (2D) van der Waals antiferromagnetic (AFM) materials boast exceptional properties for spintronics, including high spin-wave speeds and negligible stray fields. Their layer-by-layer assembly into heterostructures enables the exploration of next-generation spintronic devices. However, most 2D AFM materials are semiconductors or insulators. Thus, magneto-transport, a key segment of spintronics, is difficult to obtain especially at low temperatures. Herein, we report the observation of anomalous Hall effect (AHE) in 2D CrOCl/Pt bilayer heterostructure. Magneto-transport measurements supported by density functional theory calculations reveal that the appearance of AHE is generated by spin polarization in Pt due to the magnetic proximity effect. In addition, it is demonstrated that the magnetic easy-axis changes from the z-axis to the xy-plane at the interface of the heterostructure. Our work sheds light on the magneto-transport properties of 2D CrOCl and its potential in emerging spintronic devices.
Dynamic behavior of metal droplets impacting on porous surfaces
Authors: Li Fengchao , Wang Xueren , Sun Zhensheng , Hu Chunbo , Qiang Hongfu
Published: November 2024

During the operation of solid rocket motors, the behavior of condensed particles impacting the wall will have a remarkable influence on the structure and performance of the engine. Especially when the aircraft is under overload flight conditions, the condensed particles will form a local high concentration particle flow under the action of inertia force, continuously scouring the surface of the insulation layer, seriously affecting the thermal protection structure and the work safety of the engine. Therefore, it is an essential issue to master the behavior mode of the condensate particle impinging the wall and clarify its dynamic characteristics and evolutionary mechanism. In this paper, the dynamic behavior of aluminum droplets impacting on the porous surface is experimentally investigated by preparing the porous wall, the influence mechanism of the porous structure on the spreading process of aluminum droplets is clarified, and the effects of the droplet's initial parameters as well as surface environment are analyzed. Combined with the fluid of volume method, the flow process of droplets on the porous surface is simulated. With the variation of the dimensionless parameters M and N, the main behavior patterns of the droplets obtained so far are rebound, adhesion, partial rebound, partial adhesion, and porous seepage. The presence of pore structure enhances the hydrophobicity of the wall and makes the droplets more easily broken during spreading. When the droplet initial energy is certain and the wall structure conditions change, there is a strong competitive relationship between its spreading and penetration. When the droplet initial energy is increased, its spreading and penetration strengths are significantly increased. The research results can provide a reference for the erosion process of condensed-phase droplets impinging on the char layer and provide theoretical basis and data support for the design and optimization of SRMs.
Investigating the effect of finite ionic size and solvent polarization on induced charge electro-osmosis around a perfectly polarizable cylinder
Authors: Das Arka , Bandopadhyay Aditya
Published: November 2024

Many industrially relevant microfluidic applications use concentrated solutions of macro-molecular solutes dissolved in polar solvents like water, which are typically deployed at high voltages. In this study, we investigate the effect of finite ionic sizes and solvent polarization on induced charge electro-osmotic flow around a perfectly polarizable cylinder, at high electric field strengths and ionic concentrations. The flow is actuated by means of a direct current electric field, and the step response of various flow parameters are studied numerically. Finite ionic sizes, defined through a steric factor ν, are modeled using the modified Poisson–Nernst–Planck model. Additionally, a field-dependent permittivity, characterized by a solvent polarization number A, accounts for molecular re-orientation effects. Our findings reveal an ion-size modulated decrement in charge concentration in the electrical double layer and an augmentation in the electric field. Remarkably, the resulting flow velocities increase with ion size. Solvent polarization, on the other hand, results in a marked reduction in flow velocities. Steric effects, however, dominate over a large range of parameter space (applied voltage and bulk ionic concentration) as compared to solvent polarization. Finally, we demonstrate that unequal ionic sizes result in flow asymmetries at the steady-state, thereby generating net electro-phoretic motion of suspended particles.
Interaction between hydrodynamic and morphodynamic processes at the confluence of pipe and channel
Authors: Wang Xuefeng , Li Zhiwei , Sun Bin , Wang Feifei , Gualtieri Carlo , Jia Dongdong , Li Zhiwei
Published: November 2024

Confluences between a pipeline and a channel are commonly found in urban drainage networks. The mechanisms of sediment transport and the coherent structure within the confluence zone remain ambiguous. The hydro-morpho-sedimentary processes at pipe and channel confluences, which are influenced by discharge ratios, are investigated using a laboratory-scale confluence. The pipe current compresses and diverts downstream upon entering the main channel, creating a scour hole that carries sediment downstream. Coarser sediment deposits first, forming the slope of the downstream boundary of the scour hole (D50 = 60.31 μm) and the inner bar (D50 = 62.67 μm). Finer sediments are then deposited in the outer bar (D50 = 53.12 μm), resulting in a bed morphology consisting of the scour hole, outer and inner bars, and corridor. The penetration of the pipe current causes redistribution of the main channel flow, creating two shear layers. The height of the bar is directly related to the intensity of turbulence. Within the range of discharge ratios from 0.06 to 0.09, the shear layers and bars are displaced toward the outer bank by a distance of approximately one pipe diameter (0.05 m). Turbulence in this area is not isotropic, with power-law relations for streamwise and lateral velocity having an exponent of approximately −5/3. Conversely, the separation zone deviates from this pattern. Overall, this study highlights the significant influence of the bed morphology in modifying the flow structure compared to channel confluences and jets into crossflow, which are important in drainage engineering designs and fluvial studies.
Experimental research on nonlinear vibration characteristics of double-layer mining string for deep-sea hydrate extraction under internal and external flow excitation
Authors: Guo Xiaoqiang , Jiang Zhefu , Yang Kelun , Lv Junlin , Xu Jie , Li Xinye
Published: November 2024

The vibration mechanism of the deep-sea hydrate mining string is extremely complex due to the combined effects of internal gas–liquid solid multiphase flow, structural contact collision, soil creep effect, and external ocean random load. Based on this, using the principle of similarity, a simulation experimental platform for the vibration of double-layer mining riser in deep-sea hydrate wells under internal and external flow excitation is developed, considering the vortex-induced effect of external flow field on the mining riser in the ocean section (which can simulate a maximum ocean flow velocity of 0.5 m/s), the three-phase flow-induced effect of gas–liquid–solid inside (which can simulate a maximum flow velocity of 2.0 m/s), and the coupling effect of mining string–conductor anchor node (CAN)–seabed. The influence of particle size, phase ratio, three-phase flow, and external flow velocity on the vibration response characteristics and nonlinear behavior of mining string are investigated. It is found that the vibration of vertical string is significantly affected by external ocean currents and internal three-phase currents. The vibration displacement amplitude of the horizontal section (average 0.08 mm) is significantly smaller than those of the vertical section (average 70 mm). The strong vibration positions of the vertical and horizontal sections of the mining string are different, in that the vertical section is mostly located below the middle section (just at 1800–2400 mm), while the horizontal section is mostly located at the three-phase inlet (just at 500 mm). The vertical section of the mining string presents a motion trajectory of oblique straight line, wide oblique straight line, or approximately wide oblique straight line, while the horizontal section is mostly a chaotic trajectory or an “8”-shaped chaotic trajectory. The decrease in particle mesh size and the increase in solid-phase proportion are reflected in the difficulty and accumulation of particle transport, leading to an increase in vibration displacement, as well as a decrease in vibration displacement amplitude and vibration energy. When the particle size set as 50 mesh, the displacement of mining string is largest, just for 110 mm of vertical section and 0.08 mm of horizontal section. The increase in the proportion of gas phase will lead to changes in the flow state of multiphase flow, which will affect the vibration displacement amplitude of the mining string to varying degrees. The increase in three-phase flow velocity further induces vibration of the mining string, and when the flow velocity is between 1.5 and 1.75 m/s, it will resonate with the string system, resulting in a sudden increase in the amplitude of vibration displacement. The research results can effectively guide operations and improve the service life of deep-sea hydrate mining riser.
General theory of diaphragm rupture in a shock tunnel
Authors: Liu Yang , Ji Feng , Jiang Bo , Li Ruiqu , Sha Xinguo , Xiao Xiang
Published: November 2024

As the flow field starting device is in a shock tunnel, the rupture performance of the diaphragm directly influences the successful formation of the shock wave. The general theory of diaphragm rupture in shock tunnels is proposed first in this paper. The reasons for diaphragm rupture are explained fundamentally. The existing ideologies on diaphragm rupture are unified, and two hypotheses with corresponding methods are introduced. In the ideal diaphragm, diaphragm rupture pressure or rupture time can be predicted by considering the diaphragm opening as a throat through a diaphragm opening aperture. In the non-ideal diaphragm, the control of diaphragm rupture pressure can be realized by considering nominal rupture stress and grooved thickness. The correctness of the general theory of diaphragm rupture is proved through argumentation and based on experimental results of the literature. The general theory of diaphragm rupture can be used to predict the diaphragm rupture behavior of any shock tunnel worldwide and avoid the risk of shearing of petals on the diaphragm caused by the impact load. A new system of diaphragm rupture theory is constituted, and it is of significant importance for the efficient operation of shock tunnel equipment.
Large eddy simulation of a marine propeller with leading edge tubercles
Authors: Posa Antonio , Broglia Riccardo , Shi Weichao , Felli Mario
Published: November 2024

The results of large eddy simulations on a cylindrical grid consisting of 5.8 × 109 points are reported, dealing with marine propellers with leading edge tubercles (LETs). They are compared with the performance and flow fields of the baseline geometry without tubercles. In general, the efficiency of propulsion is not improved, but a substantial effect is produced on the development of the flow across the propeller blades. The minima of pressure on the suction side of the blades are confined in the troughs of the leading edge, with the potential of reducing the overall extent of the area of cavitation (cavitation funneling effect). In addition, local maxima of turbulence are produced on the suction side of the blades by the onset of streamwise vortices at the troughs of the LETs. Although the wake development is slightly modified across blade geometries, no obvious influence of the LETs on the major wake structures is observed. Due to their early breakup, the vortices developing across the span of the propeller blades, including those originating at the LETs, are able to affect indeed a very short extent of the propeller wake. Its dynamics is still dominated by the tip and hub vortices, as for the conventional design of the propeller. Meanwhile, the intensity of the root vortices shed by the conventional propeller is substantially reduced in the wake of the tubercled propellers, thanks to the modified geometry of the blades at their root, resulting also in a slightly slower instability of the hub vortex.
Simple model for the fracture of a polymer chain: Single-bond potential of mean force and tension-based rate constants for chain rupture
Authors: Theodorou D. N.
Published: November 2024

A linear chain of N particles connected by Morse bonds with periodic boundaries in a Brownian bath is considered as a model for polymer fracture. The potential of mean force (pomf) with respect to the length of a bond and its energy and entropic components are computed via Langevin Dynamics simulations at various chain elongations λ > 1. A narrow range of λ values is identified over which equilibrium is established between an intact (i) and a fractured (f) state over a pomf barrier. While the barrier and (f) regions of the pomf are well described by a well-known (N − 1)-bond adiabatic approximation, the shape of the (i) region departs from it, exhibiting a bimodal character. A new, 1-bond adiabatic approximation is proposed to explain this. The lower envelope of the two adiabatic approximations provides an excellent description of the pomf. The relationship between (f) states for individual bonds and for the entire chain is elucidated. A new approach, based on analysis of equilibrium tension autocorrelation functions, is developed to extract rate constants for the fracture and reformation of the chain in dependence of λ. Results from it agree with tension relaxation during nonequilibrium simulations initiated at equispaced configurations of the particles. Rate constants for chain fracture conform to a Boltzmann–Arrhenius–Zhurkov dependence on the tension averaged over the intact state of the chain, the activation length being higher than estimated from pomf extrema. These findings constitute a step toward a predictive multiscale simulation scheme for fracture in polymeric materials.
Numerical investigation into the acid flow and reaction behavior in the tight, naturally fractured carbonate reservoir during acid fracturing
Authors: Gao Budong , Mou Jianye , Lu Panpan , Zhang Shicheng , Sun Xiaoyi , Li Sinan , Zhang Xiong , Wang Xinliang
Published: November 2024

Tight naturally fractured carbonate reservoirs require acid fracturing to build the connectivity between the wellbore and natural fractures (NFs), where hydrocarbon is stored. The high leakoff nature of the NF complicates the acid flow and etching pattern, raising the difficulty in acid fracturing design and optimization. To explore the acid flow and reaction behavior in such reservoirs, an acid fracturing model accounting for the NF distribution is developed, which consists of a fracture surface characterization model, a fracture propagation model, and an acid-etching model. Based on the model, the effects of injection parameters and the NF properties on the effectiveness of acid fracturing are investigated. Then, strategies for acid fracturing the tight naturally fractured carbonate reservoirs are proposed. Results show that high pumping rates and retarded acids with low hydrogen ion (H+) diffusion coefficient is conducive to achieving a long acid penetration distance, while a low pumping rate and acids with a high H+ diffusion coefficient facilitates the NF etching. Therefore, a large stimulated area can be achieved by applying a multi-stage alternating injection of the crosslinked acid with a high pumping rate followed by the gelled acid with a low injection rate. NFs impact acid fracturing in two distinct ways: enhancing the non-uniform etching of the fracture surface and reducing the effective acid-etched fracture length through high leakoff. When NF density is high, leakoff control techniques should be employed; and when the NF inclination is high, non-uniform etching techniques should be used to generate acid-etched channels in flow barriers.
Prescribing pre-exposure prophylaxis for HIV prevention: a cross-sectional survey of general practitioners in Australia
Authors: Wu Jason , Fairley Christopher K. , Grace Daniel , Bavinton Benjamin R. , Fraser Doug , Chan Curtis , Chow Eric P. F. , Ong Jason J.
Published: November 2024

Background Pre-exposure prophylaxis (PrEP) is a safe and effective medication for preventing HIV acquisition. We examined Australian general practitioners’ (GP) knowledge of PrEP efficacy, characteristics associated with ever prescribing PrEP and barriers to prescribing. Methods We conducted an online cross-sectional survey of GPs working in Australia between April and October 2022. We performed univariable and multivariable logistic regression analyses to identify factors associated with: (1) the belief that PrEP was at least 80% efficacious; and (2) ever prescribed PrEP. We asked participants to rate the extent to which barriers affected their prescribing of PrEP. Results A total of 407 participants with a median age of 38 years (interquartile range 33–44) were included in the study. Half of the participants (50%, 205/407) identified how to correctly take PrEP, 63% (258/407) had ever prescribed PrEP and 45% (184/407) felt confident with prescribing PrEP. Ever prescribing PrEP was associated with younger age (AOR 0.97, 95% CI: 0.94–0.99), extra training in sexual health (AOR 2.57, 95% CI: 1.54–4.29) and being a S100 Prescriber (OR 2.95, 95% CI: 1.47–5.90). The main barriers to prescribing PrEP included: ‘Difficulty identifying clients who require PrEP/relying on clients to ask for PrEP’ (76%, 310/407), ‘Lack of knowledge about PrEP’ (70%, 286/407) and ‘Lack of time’ (69%, 281/407). Conclusion Less than half of our GP respondents were confident in prescribing PrEP, and most had difficulty identifying who would require PrEP. Specific training on PrEP, which focuses on PrEP knowledge, identifying suitable clients and making it time efficient, is recommended, with GPs being remunerated for their time.
Enhancing wildfire detection: a novel algorithm for controllable generation of wildfire smoke images
Authors: Huo Yinuo , Zhang Qixing , Wang Chong , Wang Haihui , Zhang Yongming
Published: November 2024

Background The lack of wildfire smoke image data is one of the most important factors hindering the development of image-based wildfire detection. Smoke image generation based on image inpainting techniques is a solution worthy of study. However, it is difficult to generate smoke texture with context consistency in complex backgrounds with current image inpainting methods. Aims This work aims to provide a wildfire smoke image database for specific scenarios. Methods We designed an algorithm based on generative adversarial networks (GANs) to generate smoke images. The algorithm includes a multi-scale fusion module to ensure consistency between the generated smoke and backgrounds. Additionally, a local feature-matching mechanism in the discriminator guides the generator to capture real smoke’s feature distribution. Key results We generated 13,400 wildfire smoke images based on forest background images and early fire simulation from the Fire Dynamics Simulator (FDS). Conclusions A variety of advanced object detection algorithms were trained based on the generated data. The experimental results confirmed that the addition of the generated data to the real datasets can effectively improve model performance. Implications This study paves a way for generating object datasets to enhance the reliability of watchtower or satellite wildfire monitoring.
Exploring the Chinese AWCF Platform’s value in improving CSL learners’ writing performance in a ChatGPT
context
Authors: Yang Yicheng , Tian Ye
Published: November 2024

This study evaluates the efficacy of Chinese Automated Writing Correction Feedback (AWCF) platforms in enhancing
writing performance among Chinese as a Second Language (CSL) learners against the backdrop of emerging generative AI tools like
ChatGPT. Employing data from an intermediate CSL course at an Ivy League university, the paper scrutinizes selected Chinese AWCF
platforms, such as Meta XiezuoCat, for their accuracy, effectiveness, and instructional potential. The analysis juxtaposes AWCF
feedback withChatGPT responses and instructor assessments, revealing both the strengths and limitations of these platforms. The
findings indicate that existing Chinese AWCF platforms exhibit noticeable limitations in CFL writing support but hold considerable
potential for future development. Despite limitations in current corpus and accuracy compared with Generative AI such as ChatGPT,
AWCF’s one-stop service model in error correction significantly reduces the cost of prompt engineering, while its feature of
allowing “noticing” can help enhance students’ metalinguistic awareness. This finding also highlights the critical need for AWCF
platforms to improve their utility by incorporating expansive and authentic CSL learner data.
Stairway to the Golgi: Two paths VPS13B can go by
Authors: Pons Lanau Roger , Campelo Felix
Published: November 2024

VPS13 proteins mediate lipid transfer across membranes. Among them, VPS13B is associated with Golgi membranes, and VPS13B mutations cause Cohen syndrome. In this issue, Ugur et al. (https://doi.org/10.1083/jcb.202311189) and Du et al. (https://doi.org/10.1083/jcb.202402083) reveal new VPS13B interactors and their functions in Golgi organization and trafficking.
Minimum energy principles in electrostatics
Authors: Ivchenko Vladimir
Published: November 2024

We employ the principle of minimum energy of the electrostatic field to derive Laplace’s equation for electric potential in charge-free space. We also apply the principle of minimum electrical potential energy of a system of discrete charges to explain the possibility of the existence of their stable equilibrium configuration on the surface of a conductor.
Four-body semileptonic decays B → D*Pℓ+νℓ with SU(3) flavor symmetry
Authors: Wan Meng-Yuan , Xu Yuan-Guo , Jia Qi-Lin , Liu Yue-Xin , Zhang Yi-Jie
Published: November 2024

We present a complete study of the B → D*Pℓ
+
ν

ℓ
(ℓ = e, μ, τ) decays with the non-resonant, the charmed axial vector resonant, and the charmed tensor resonant contributions using the SU(3) flavor symmetry. The relevant amplitude relations between the different decay modes are obtained by the SU(3) flavor symmetry. We then predict non-measured branching ratios of the B → D*Pℓ
+
ν

ℓ
decays with the non-resonant and the charmed resonant contributions by using the present experimental data of the

B
→
D
*
P
ℓ

′

+

ν

ℓ
′

(
ℓ
′
=
e
,
μ
)

decays within 2σ errors. We have found that B
0,+ → D*ηℓ
+
ν

ℓ
,

B

0
,
+

→
D
*
η
′

ℓ

+

ν

ℓ

,

B

s

0

→

D

s

*

η

ℓ

+

ν

ℓ

,

B

s

0

→

D

s

*

η
′

ℓ

+

ν

ℓ

, and

B

0
,
+

→

D

s

*

K

ℓ

+

ν

ℓ

decays only receive non-resonant contributions. Decays

B

s

0

→

D

s

*
−

π

0

ℓ

+

ν

ℓ

only receive

D

s
1

′

resonant contributions. Other decays receive all three kinds of contributions, and these contributions are important in most decays.