bluuebunny/crossref_metadata_2025 huggingface dataset:
A new measure for drop deformation in extensional flows at low Reynolds number
Authors: Bigio David I. , Sangli Aditya N.
Published: February 2024

The critical capillary number of a drop, which represents the state where the interfacial tension force of the drop cannot overcome the viscous force exerted by a surrounding flow, is usually determined in low Reynolds number [<O(1)] extensional flows by progressively elongating the drop in stagnant extensional flows. Below the critical capillary number, all the elongated states of the drop are steady. The unsteady drop states beyond the critical capillary number, usually seen in practically relevant non-stagnant extensional flows which breakup the drop, provide no information about critical capillary number and are usually studied separately. In this study, we present a new measure—called the semi-minor capillary number—which uniquely describes the drop deformation process at both steady and unsteady states. The measure uses the instantaneous semi-minor dimension of the deforming drop as the length scale in calculating the capillary number. Our experiments at small initial capillary numbers, compared to the critical capillary number, yielded steady drops with a constant value of semi-minor capillary number. For large initial capillary numbers and unsteady states, the drops elongated continuously, and the same constant represented an asymptotic limit of the self-similar deformation. The new measure of semi-minor capillary number rationalized drop behavior at both small and large initial capillary numbers compared to the critical capillary number. More importantly, it provided significance to drop behavior at large initial capillary numbers, which is an unstudied parametric space in the context of determining the critical capillary number. Finally, we discuss the significance of the new measure by presenting the critical semi-minor capillary number at different viscosity ratios.
Excitons in metal-halide perovskites from first-principles many-body perturbation theory
Authors: Leppert Linn
Published: February 2024

Metal-halide perovskites are a structurally, chemically, and electronically diverse class of semiconductors with applications ranging from photovoltaics to radiation detectors and sensors. Understanding neutral electron–hole excitations (excitons) is key for predicting and improving the efficiency of energy-conversion processes in these materials. First-principles calculations have played an important role in this context, allowing for a detailed insight into the formation of excitons in many different types of perovskites. Such calculations have demonstrated that excitons in some perovskites significantly deviate from canonical models due to the chemical and structural heterogeneity of these materials. In this Perspective, I provide an overview of calculations of excitons in metal-halide perovskites using Green’s function-based many-body perturbation theory in the GW + Bethe–Salpeter equation approach, the prevalent method for calculating excitons in extended solids. This approach readily considers anisotropic electronic structures and dielectric screening present in many perovskites and important effects, such as spin–orbit coupling. I will show that despite this progress, the complex and diverse electronic structure of these materials and its intricate coupling to pronounced and anharmonic structural dynamics pose challenges that are currently not fully addressed within the GW + Bethe–Salpeter equation approach. I hope that this Perspective serves as an inspiration for further exploring the rich landscape of excitons in metal-halide perovskites and other complex semiconductors and for method development addressing unresolved challenges in the field.
Field-programmable-gate-array based hardware platform for nitrogen-vacancy center based fast magnetic imaging
Authors: Liang Kaiqing , Zhu Mingdong , Qin Xi , Meng Ziqing , Wang Pengfei , Du Jiangfeng
Published: February 2024

A nitrogen-vacancy center based scanning magnetic microscope can be used to characterize magnetics at the nanoscale with high sensitivity. This paper reports a field-programmable-gate-array based hardware system that is designed to realize control and signal readout for fast scanning magnetic imaging with a nitrogen-vacancy center. A 10-channel 1 Msps @ 20 bit analog signal generator, a 12-channel 50 ps resolution pulse generator, a 300 Msps @ 16 bit lock-in amplifier with proportional integral derivative control function, and a 4-channel 200 Msps counter are integrated on the platform. A customized acceleration algorithm is realized with the re-configurable field-programmable-gate-array chip to accelerate the imaging speed of the nitrogen-vacancy system, and the experimental results prove that the imaging efficiency can be accelerated by five times compared to the system without the acceleration algorithm. The platform has considerable potential for future applications of fast scanning magnetic imaging.
Channel-confined flow-induced rotation of an asymmetrically confined square cylinder in a two-dimensional laminar flow regime
Authors: Rath Subhasisa , Mittal Charu , Abhishek  , Sharma Atul
Published: February 2024

This study focuses on the flow-induced rotational characteristics of an asymmetrically confined square cylinder in a channel for various engineering applications. We consider the classical, fully developed channel flow problem to numerically study the flow-induced rotation (FIR) of a square cylinder in a two-dimensional laminar flow regime. We employ our in-house computational fluid dynamics solver, based on the hybrid Lagrangian–Eulerian method, for the present study. For the very first time, we identify seven distinct rotational modes by investigating FIR for a wide range of Reynolds number Re(1−150) and eccentricity ε (0, 1/3, 2/3). This paper reports the combined effects of Re and ε on the FIR characteristics in terms of rotational modes, accompanying flow structures, and pertinent engineering parameters. At low Re, the shear-induced torque dominates over the pressure-induced torque, whereas with an increase in Re, the pressure-induced torque gradually outweighs the shear-induced torque. Thus, we observe a smooth transition in the direction of rotation from clockwise to counterclockwise with increasing Re. This study involves a detailed discussion of the flow physics and moment-generating mechanisms for four intriguing rotational modes, including Autorotation, Mono-harmonic Oscillation, Bi-harmonic Oscillation, and Reversal Autorotation. The current study has applications in micro energy-harvesting, vortex generation, and microfluidic mixing.
Structural and Na-ion diffusion behavior of O3/P3/P2-type NaNi1/3Mn1/3Fe1/3O2 cathode for Na-ion batteries from first-principles study
Authors: Su Lei , Sun Baozhen , Wu Musheng , Liu Gang , Xu Bo , Ouyang Chuying
Published: February 2024

A layered sodium-ion battery cathode, O3/P3/P2-type NaNi1/3Mn1/3Fe1/3O2, has been systematically investigated by first-principles density functional theory to explore the detailed structural and Na-ion diffusion behavior during desodiation. Our results suggest that the (NaO6) spacing is greatest in the P3 phase and lowest in the O3 phase, with the P2 phase exhibiting intermediate spacing. During desodiation, the intermediate stages have a greater (NaO6) spacing than the initial and final stages. The great (NaO6) spacing facilitates the formation of the P3 phase, resulting in the structural evolution of NaxNi1/3Mn1/3Fe1/3O2 from the O3 to the P3 phase at x ≈ 0.59, finally reaching the O3 structure again at x ≈ 0.12. The electronic structure clearly proves that both Ni and Fe are active in O3/P3/P2-type NaxNi1/3Mn1/3Fe1/3O2. Ni2+ is oxidized to Ni3+ as Na content decreases from x = 1 to x = 0.66, then further oxidized to Ni4+ at x = 0.33, and finally, Fe3+ → Fe4+ oxidation occurs at x = 0. In the Na ion diffusion behavior, the order of the barrier is O3 (0.82 eV) > P2 (0.53 eV) > P3 (0.35 eV) at the initial stage, whereas it is O3 (0.53 eV) > P3 (0.21 eV) > P2 (0.16 eV) at a highly desodiated stage. The former can be traced back to the (NaO6) spacing, but the latter is related to the different Na sites. Our results thus provide a factor of the structural evolution and Na ion diffusion barrier by considering (NaO6) width and Na site changes during desodiation.
Transferability of atomic energies from alchemical decomposition
Authors: Sahre Michael J. , von Rudorff Guido Falk , Marquetand Philipp , von Lilienfeld O. Anatole
Published: February 2024

We study alchemical atomic energy partitioning as a method to estimate atomization energies from atomic contributions, which are defined in physically rigorous and general ways through the use of the uniform electron gas as a joint reference. We analyze quantitatively the relation between atomic energies and their local environment using a dataset of 1325 organic molecules. The atomic energies are transferable across various molecules, enabling the prediction of atomization energies with a mean absolute error of 23 kcal/mol, comparable to simple statistical estimates but potentially more robust given their grounding in the physics-based decomposition scheme. A comparative analysis with other decomposition methods highlights its sensitivity to electrostatic variations, underlining its potential as a representation of the environment as well as in studying processes like diffusion in solids characterized by significant electrostatic shifts.
Blind fit modeling of soft x-ray resonant reflectivity maps in nanoscale epitaxial iron oxide multilayers
Authors: Dvortsova Polina A. , Korovin Alexander M. Mikhailovich , Ukleev Victor , Suturin Sergey M.
Published: February 2024

In the present paper, we apply a blind fitting algorithm to model two-dimensional energy-incidence angle maps of soft x-ray resonant reflectivity measured in nanoscale epitaxial multilayers of multiferroic ε-Fe2O3 grown by pulsed laser deposition. The possibility of fitting the spectral shape of the complex refraction index across the Fe L3 absorption edge without having an initial guess about the optical constants has been demonstrated. The spectral shape fitting of the real (f1) and imaginary (f2) parts of the atomic scattering factor has been carried out by using a specially designed software utilizing OpenCL fast calculations on graphical processing units. The Kramers-Kronig relations between f1 and f2 are automatically taken into account by the fitting algorithm. A reasonable agreement between blindly generated and reference scattering factor spectra derived independently from an x-ray absorption spectroscopy experiment has been demonstrated. The blind fitting has been compared with the alternative refinement routines, in which small free variations of the reference spectral shapes (or no variations at all) have been allowed. The presented approach to the resonant x-ray reflectometry modeling makes it unnecessary to acquire the optical constant spectral shapes in advance and, thus, is especially helpful when such spectra cannot be physically measured, e.g., for a buried layer of a multilayer system.
Polar metals with coexisting ferroelectricity and high-density conduction electrons
Authors: Hou De , Bi Jiachang , Yang Jingkai , Geng Hansong , Wang Zhenzhen , Lin Zeguo , Li Bolin , Ma Zongwei , Liu Caixing , Meng Zhi , Zhang Ruyi , Pei Yujuan , Zhang Guangchao , Xiao Shaozhu , Wu Liang , Zhang Qinghua , Yang Fang , Guo Jiandong , Sheng Zhigao , Cao Yanwei
Published: February 2024

Polar metals, a family of materials with exclusive but coexisting electric polarization and metallicity, have attracted plenty of studies recently. Experimentally, how these two exclusive states interact with each other is still an open question thus far. Here, we report on the existence of ferroelectric metal states with switchable electric polarization and unexpected high carrier density in Ba0.5La0.5TiO3 films. A combination of atomic resolution scanning transmission electron microscopy, high-resolution x-ray diffraction, piezoresponse force microscopy, optical second harmonic generation, and electrical transport was utilized to investigate the crystal and electronic structures of Ba0.5La0.5TiO3 films. Unexpectedly, with the modulation of ferroelectricity, the density of conduction electrons can be tuned from 1019 to 1021 cm−3. Our results provide a way to design polar metals with coexisting switchable electric polarization and high-density conduction electrons.
Ballooning instability in the dipole magnetosphere: The finite transverse wavelength influence
Authors: Petrashchuk Aleksandr V. , Mager Pavel N. , Klimushkin Dmitri Yu.
Published: February 2024

This paper is concerned with the condition for the development of ballooning instability in the dipole Earth's magnetosphere. Under investigation is the dependence of the ratio of the radial and azimuthal wave vector components squared on the wave frequency squared ω2. It is shown that this dependence is depicted by continuous curve (the dispersion curve). The part of the dispersion curve with ω2>0 corresponds to the slow magnetosonic mode modified by the coupling with the Alfvén mode, while the part with ω2<0 corresponds to the ballooning instability. The instability appears at some critical ratio of the radial and azimuthal wave vector components, the growth rate reaches the maximum value where this ratio is zero. The instability threshold is determined depending on the β parameter and the pressure gradient when the coupling of the slow and Alfvén modes is taken into account. On a given magnetic shell, at a given β value, large pressure gradient favors the instability, and vice versa, at a given pressure gradient, a large β favors instability. It is shown that in the unstable mode, the compressional magnetic field component has a phase shift with respect to the radial component. This can be used to detect unstable ballooning modes during observations in the Earth's magnetosphere.
Implementation of a dynamic slip wall model for large eddy simulation in the local domain-free discretization method
Authors: Zhang Dian , Zhou Chunhua
Published: February 2024

Wall-modeling techniques are frequently applied in the extension of immersed boundary methods to large eddy simulation (LES) of turbulent flows. In this paper, a dynamic slip wall model is incorporated into an immersed boundary method named the local domain-free discretization (DFD) method for implicitly filtered LES, which is based on a Robin-type boundary condition and free of a priori specified tunable coefficients and also does not rely on any assumptions about the boundary layer. The present study provides a detailed description of the implementation of the dynamic slip model in the DFD framework, including the evaluation of the velocity components at an exterior dependent node via the Robin-type boundary condition and the dynamic procedure for calculating the slip length. The non-zero slip velocity in the normal direction is imposed in a new way to satisfy on average the non-penetration of the curved wall and maintain the global mass conservation in the implicitly filtered LES. To validate the present wall-modeling LES/DFD method, a series of turbulent channel flows at various Reynolds numbers, the flow over periodic hills, and the high-Reynolds-number flow past a National Advisory Committee for Aeronautics (NACA) 4412 airfoil at near-stall conditions are simulated, and the predicted results agree well with the referenced experimental and numerical results.
Effect of multiply excited states to the EUV emission from yttrium-like tin
Authors: Sasaki A.
Published: February 2024

The spectral emission rate of yttrium-like tin (Sn11+) is investigated as the typical ion, which has a strong emission of extreme ultra-violet (EUV) light near the wavelength of 13.5 nm. The energy level structure of the tin ion is investigated using the non-relativesitic configuration average model to calculate the population in the local thermodynamic equilibrium, and the spectral structure of the unresolved transition array that has EUV emission is investigated based on the calculated atomic data using the HULLAC code. It is shown that the broad main peak is accompanied by the tail structure for shorter and longer wavelengths, which arises from multiply and inner-shell excited levels. The emission channels that significantly contribute to the spectrum are determined from a convergence analysis. The excited states below the ionization limit with a large population are shown to have a significant contribution to the emission.
On a direct method of calculating pressure in the canonical ensemble
Authors: Tanouye Fernando Takeshi , Alves Jozismar Rodrigues
Published: February 2024

Determining fluid pressure in Monte Carlo simulations can be a challenging task due to the reduced arsenal of computational tools available to perform such measurements. In addition, none of these tools is general enough to calculate the equilibrium pressure for a wide variety of models. The Gibbs–Duhem method, for example, is a very useful option, but only for pure (one component) systems. To enrich this arsenal, we propose here a direct method to calculate pressure in the canonical ensemble, which could easily be extended to mixtures at low densities. In analogy with the Widom method, our approach is based on the free energy variation with volume, described in terms of the removal of an empty or particle-occupied lattice column. We tested our approach for the lattice gas model and compared the results with exact Onsager solutions. Furthermore, the appearance of thermodynamic instabilities (loops) in the pressure isotherms during the phase transition and their relationship with interface effects are discussed. Finally, a phase diagram is obtained from these isotherms using the Hill construction.
Fluid classification with dynamic graph convolution network by local linear embedding well logging data
Authors: Sun Youzhuang , Pang Shanchen , Zhang Yongan , Zhang Junhua
Published: February 2024

Fluid prediction is pivotal in exploration, aiding in the identification of targets and estimating reserve potential. To enhance well logging data processing, we employ local linear embedding (LLE) for dimensionality reduction. LLE effectively reduces data dimensionality by identifying local linear relationships and preserving essential local structure in a low-dimensional space, which is particularly advantageous for log data that often contains formation-specific information, including fluid content. The process of dimensionality reduction through LLE retains vital stratigraphic information, which is key for insightful subsequent analyses. Next, we utilize a dynamic graph convolutional network (DGCN) integrated with a multi-scale temporal self-attention (TSA) module for fluid classification on the reduced data. This multi-scale temporal self-attention module is specifically designed to capture time series information inherent in well logging data, allowing the model to autonomously learn and interpret temporal dependencies and evolutionary patterns in the data. This enhances the accuracy of fluid prediction, particularly in the context of varying rock layer characteristics over time. Our methodology, combining LLE with DGCN-TSA, has demonstrated high accuracy in applications such as Tarim Oilfield logging data analysis. It amalgamates advanced technologies with a robust generalization ability. In practical applications, this approach provides steadfast support for oil and gas exploration, significantly contributing to the refinement of fluid prediction accuracy.
Noise performance analysis of PT-symmetric non-reciprocal transmission systems
Authors: Dong Lei , Chen Dong-Yan , Zhou Yi , Huang Qing-An
Published: February 2024

Non-reciprocity is a crucial concept in the field of signal transmission and processing as it protects sensitive elements from the effects of feedback signal. The non-reciprocal components based on ferrite materials are bound to show shortcomings due to incompatibility with chip-level ICs. In recent years, parity-time (PT)-symmetric non-reciprocal transmission in electronic systems has been proposed and analyzed. Here, we propose the simplified noise analysis model based on a PT-symmetric non-reciprocal transmission system. And we verify the theoretical noise model by simulation analysis and experimental demonstrations. The experimental result shows that the noise figure of the proposed PT-symmetric non-reciprocal transmission device is 7.5 dB because of the employment of the active amplifier. This work establishes a noise performance analysis framework, providing guidance for the development of lossless and miniaturized applications of non-reciprocal components.
Designable and unidirectional motion of Leidenfrost droplets on heated asymmetric microgrooves written by femtosecond laser
Authors: Cheng Zilong , Wang Chaowei , Li Xinlei , Xu Tianyu , Chen Zhenrui , Cui Zehang , Cheng Kangru , Zhu Suwan , Wu Dong , Yong Jiale
Published: February 2024

Unidirectional droplet motion is realized on heated asymmetric microgroove arrays prepared by femtosecond laser direct writing. The plasma expansion under laser ablation compresses the two sides of the induced microgroove differently, resulting in the formation of asymmetrical microgrooves. The asymmetry of the microgrooves can rectify the water vapor that ejects from the Leidenfrost droplet and generate a viscous shear force at the bottom of the droplet, causing the droplet to move in a certain direction (where the laser scanning line is added) when the substrate temperature is higher than a certain critical value (the transition temperature of disordered motion and unidirectional motion). The velocity of droplets can exceed 318 mm/s, and the droplets can even climb surfaces that are tilted 14°. With the advantages of femtosecond lasers in the flexible design of surface microstructures and patterns, this unidirectional droplet motion can support a variety of complex droplet-manipulation applications, such as droplet movement along designed trajectories, droplet accelerator devices, fixed-point capture of droplets, and fixed-point cooling of hot solid surfaces. Compared with traditional macroscopic ratchets, laser-written asymmetrical microgrooves make the Leidenfrost droplet motion more designable and controllable.
Simplified dynamics model of a sphere decelerating freely in a fluid
Authors: Velazquez A. , Barrero-Gil A.
Published: February 2024

An experimental/theoretical study has been presented on the problem of the dynamic equation of motion of a close to neutral buoyancy sphere (0.04 m in diameter) decelerating freely in water after an impulsive start. It has been verified, via analysis of the acceleration parameter, that, for the range of parameters that have been considered, the motion is governed by unsteady effects. A model has been developed for this specific problem. It contains three forcing terms in the sphere dynamics equation of motion: (a) unsteady drag, (b) added mass, and (c) buoyancy. This departs from the approach following the standard Basset–Boussinesq–Oseen formulation. In this case, the equation of motion would contain four forcing terms: (a) steady drag, (b) added mass, (c) history, and (d) buoyancy. Comparison between the experimental and model results shows reasonable agreement in terms of trajectory, velocity, and acceleration profiles. The model could be used for practical engineering applications that involve this type of unsteady flow situations.
Vortex-induced vibrations in the presence of moderate freestream turbulence
Authors: Ramesh Nikhilesh Tumuluru , Morton Chris , Yarusevych Serhiy
Published: February 2024

The influence of incoming freestream turbulence on an elastically mounted circular cylinder undergoing vortex-induced vibrations is investigated through simultaneous displacement and flow field measurements at a constant Reynolds number of approximately 4400. The results show that the effects of freestream turbulence are more prominent within the lower branch and desynchronization, where earlier desynchronization is observed with elevated freestream turbulence. Conversely, freestream turbulence minimally affects the structure and wake dynamics within the initial and upper branches. A comparison between a stationary cylinder wake and the wake of a cylinder free to vibrate at very low amplitudes reveals that even minor cylinder vibrations (≈ 1% of cylinder diameter) modify the separated shear layer and near wake dynamics, the result of which is a decreased sensitivity of the near wake to freestream turbulence. Proper orthogonal decomposition is used to identify changes in the vortex shedding characteristics that result in earlier desynchronization.
Rotational dynamics, ionic conductivity, and glass formation in a ZnCl2-based deep eutectic solvent
Authors: Schulz A. , Lunkenheimer P. , Loidl A.
Published: February 2024

Glass formation and reorientational motions are widespread but often-neglected features of deep eutectic solvents although both can be relevant for the technically important ionic conductivity at room temperature. Here, we investigate these properties for two mixtures of ethylene glycol and ZnCl2, which were recently considered superior electrolyte materials for application in zinc-ion batteries. For this purpose, we employed dielectric spectroscopy performed in a broad temperature range, extending from the supercooled state at low temperatures up to the liquid phase around room temperature and beyond. We find evidence for a relaxation process arising from dipolar reorientation dynamics, which reveals the clear signatures of glassy freezing. This freezing also governs the temperature dependence of the ionic dc conductivity. We compare the obtained results with those for deep eutectic solvents that are formed by the same hydrogen-bond donor, ethylene glycol, but by two different salts, choline chloride and lithium triflate. The four materials reveal significantly different ionic and reorientational dynamics. Moreover, we find varying degrees of decoupling of rotational dipolar and translational ionic motions, which can partly be described by a fractional Debye–Stokes–Einstein relation. The typical glass-forming properties of these solvents strongly affect their room-temperature conductivity.
An insight into the solitonic structure of two distinct fractional nonlinear Schrödinger models in optical fiber using conformable fractional derivative
Authors: Alkhidhr Hanan A.
Published: February 2024

The goal of this work was to use conformable fractional derivative sense to create some crucial solitary waves for two models of space–time fractional nonlinear Schrödinger equations. We use the unified solver approach to accomplish this goal in a fully unified way. This solution is robust, practical, dependable, and simple to use. The obtained solutions are extremely important for describing critical complicated phenomena in fractional quantum mechanics, optical fiber communications, and energy applications. Some simulations are provided to demonstrate the behavior of the obtained solutions when appropriate physical parameters are used. It was noted that by increasing the fractal factors, the nonlinear wave propagates with a changing phase and wave frequency. Our research may open up new possibilities for optical manipulation in practical applications. Finally, further fractional physical models can be solved using the suggested technique.
Minimum energy dissipation required for information processing using adiabatic quantum-flux-parametron circuits
Authors: Yamae Taiki , Takeuchi Naoki , Yoshikawa Nobuyuki
Published: February 2024

The reversible quantum-flux-parametron (RQFP) is a reversible logic gate based on an energy-efficient superconductor logic family, namely, the adiabatic quantum-flux-parametron logic. The RQFP can perform logic operations in a thermodynamically reversible manner (i.e., without energy dissipation) in the quasi-static limit due to its logical and physical reversibility. Hence, it can be used for investigating the fundamental relations between information and thermodynamics from a circuit perspective. In the present study, we propose a reversible flip-flop (RFF) comprising an RQFP and investigate the minimum energy dissipation required for general information processing through numerical simulation using an RFF-based circuit. This circuit includes fundamental information processing (combinational logic, sequential logic, and data erasure) and can, thus, be used as a physical model for such an investigation. The numerical simulation of this circuit shows that both combinational and sequential logic operations can be conducted without energy dissipation in the quasi-static limit and that the amount of erased data determines the minimum energy dissipation. These results indicate that general information processing can be conducted in a thermodynamically reversible manner by using RQFP circuits as long as all data, including garbage outputs, are conserved.
Stability of buoyancy–thermocapillary convection in molten silicon liquid bridge between two disks with different radii under gravity
Authors: Tu Yaming , Zeng Zhong , Zhang Liangqi , Wang Yue , Liu Yong , Li Hao , Liu Chengzhao , Yin Linmao , Liu Hao
Published: February 2024

By employing a linear stability analysis based on the spectral element method, we investigated the impact of radius ratio (Γr) on the stability of buoyancy–thermocapillary convection in a molten silicon liquid bridge (Pr = 0.011). This liquid bridge was located between two coaxial disks with different radii under the influence of gravity. The aspect ratio of the liquid bridge was maintained at Γ = 1, with a volume ratio Γv = 1 and a fixed height. To explore the physical mechanisms behind convection instability, a perturbation energy analysis was adopted. The free surface shape was determined using the Young–Laplace equation, and two distinct heating strategies were employed. In a top-heated liquid bridge, the convection stability under gravity is always stronger than under zero-gravity. However, in a bottom-heated liquid bridge, the convection stability under gravity is not consistently stronger than under zero-gravity; specifically, when 0.522 < Γr < 0.673, the convection stability under gravity is weaker than under zero-gravity. Despite the small height of the liquid bridge (approximately 2 mm), the maximum relative difference of the critical Marangoni number (Mac) between gravity and zero-gravity conditions reaches as high as 227.8%. In a bottom-heated liquid bridge, oscillatory instability occurs at larger radius ratios (Γr = 0.8) compared to the zero-gravity condition. Furthermore, all instabilities for various radius ratios and heating strategies were found to be of hydrodynamic in nature.
Statistical analysis of serrated flows in CoNiV medium-entropy alloy
Authors: Liu Bohao , Wang Zhong , Lan Aidong , Yang Huijun , Liaw Peter K. , Qiao Junwei
Published: February 2024

The Portevin–Le Chatelier (PLC) effect induced by dynamic strain aging is commonly observed in various alloys. The stress-drop magnitude of serrations and the critical strain at which serrations occur are two pivotal features characterizing serrated flow. This study investigates the temperature (160–460 °C) and strain rate (6 × 10−4 s−1–2 × 10−2 s−1) dependence of the serrated flow behavior in the CoNiV medium-entropy alloy through uniaxial tensile tests. Under the guidance of the mean-field theory, a scale theory has been applied to derive a scale function and scale indices that can be used to predict the distribution of stress drops. A normal PLC behavior of critical strain is fitted using the dislocation pinning model, demonstrating the presence of specific solute atoms conforming to the dislocation pinning model within medium-entropy alloys.
The preparation and properties of photocatalytic composites based on palygorskite/molybdenum disulfide
Authors: Tian Weidong , Wu Limei , Huang Ritong , Wang Aiqin , Lu Yushen , Tang Ning , Gao Lili
Published: February 2024

The pollution problem resulting from advancements in science and technology is increasingly severe, particularly concerning organic pollution. Photocatalytic technology is considered one of the most effective methods for treating organic pollution due to its cost-effectiveness, simplicity of operation, high efficiency, and versatility. In this study, palygorskite was purified and extracted using techniques such as ultrasonication, high-speed stirring, centrifugation, and others. Molybdenum disulfide (MoS2) was synthesized in situ on the palygorskite surface through hydrothermal synthesis, resulting in palygorskite/MoS2 nanocomposites. The structure and apparent morphology of the palygorskite/MoS2 composites were analyzed using characterization methods such as transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, and others. MoS2 interacted with the hydroxyl groups on the palygorskite surface through amino groups, leading to the dispersion of MoS2 nanosheets on the palygorskite surface, forming a unique nanoflower structure. To assess the photocatalytic degradation performance of palygorskite/MoS2 composites, Rhodamine B was employed as the target pollutant. Under conditions of a pH of 6, a reaction time of 170 min, and a solution concentration of 1500 mg/l, palygorskite/MoS2 composites achieved a Rhodamine B removal amount of 371.73 mg/g. Notably, these composites facilitated the degradation of Rhodamine B into intermediate chain-broken products. The findings of this study hold significant implications for the advancement of clay mineral-based photocatalytic composites and the effective removal of organic pollutants.
Drop impact on a heated liquid bath: Formation of antibubbles
Authors: Wang Wei , Lin Fangye , Wang Pengfei
Published: February 2024

As a ubiquitous phenomenon, drop impact on a liquid bath has been widely studied. This paper demonstrates a systematical study on the collision between the volatile drops and a heated liquid bath. In the experiments, water, alcohol, and hydrogen fluoride ether (HFE-7100) were used to generate drops. The experimental results vary with the impact parameters and liquid properties. Despite the common phenomena, like bouncing and coalescence, antibubble was observed at an intermediate impact velocity with the HFE-7100 drops. A regime map is built based on the experimental results. A qualitative model is proposed to elucidate the stability of the air film separating the impinging droplet and the surrounding liquid during collision. This study should stimulate further investigation on the surfactant-free antibubbles and the control of antibubble lifetime.
A comparative study of the target search of end monomers of real and Rouse chains under spherical confinement
Authors: Chen Ye , Tian Xiaofei , Xu Xiaolei , Xu Wen-Sheng , Chen Jizhong
Published: February 2024

We study the dynamics of the end monomers of a real chain confined in a spherical cavity to search for a small target on the cavity surface using Langevin dynamics simulation. The results are compared and contrasted with those of a Rouse chain to understand the influence of excluded volume interactions on the search dynamics, as characterized by the first passage time (FPT). We analyze how the mean FPT depends on the cavity size Rb, the target size a, and the degree of confinement quantified by Rg/Rb, with Rg being the polymer radius of gyration in free space. As a basic finding, the equilibrium distribution of the end monomers of a real chain in a closed spherical cavity differs from that of a Rouse chain at a given Rg/Rb, which leads to the differences between the mean FPTs of real and Rouse chains. Fitting the survival probability S(t) by a multi-exponential form, we show that the S(t) of real chains exhibits multiple characteristic times at large Rg/Rb. Our simulation results indicate that the search dynamics of a real chain exhibit three characteristic regimes as a function of Rg/Rb, including the transition from the Markovian to non-Markovian process at Rg/Rb ≈ 0.39, along with two distinct regimes at 0.39 < Rg/Rb < 1.0 and Rg/Rb > 1.0, respectively, where S(t) exhibits a single characteristic time and multiple characteristic times.
Effects of wave forces on sediment transport patterns in micro-tidal estuaries
Authors: Zhang Zhaozi , Liang Bingchen , Wang Zhenlu , Shi Luming , Borsje B. W.
Published: February 2024

Estuarine sediment transport is driven by the combined action of a multitude of influencing factors, including astronomical tides, waves dynamics, and river discharges. This study focuses on the effects of wave forces on sediment transport patterns in micro-tidal estuaries near Wanbao Beach, China. Numerical simulations are carried out using Delft3D. Modeling scenarios are configured using different wave characteristics, spanning from typical waves to those with a return period of 50 years. Results show that waves have a positive effect on landward sediment transport, resulting a larger active range of sediment. By comparing the spatial geomorphic variations under varying wave conditions, we find that modifications in significant wave height (Hs) primarily impact the position of erosion and deposition zones, whereas alterations in spectral peak period (Tp) predominantly influence the magnitude of these changes. The finding is further demonstrated by a comparison of residual currents under different wave intensities. Analysis of sediment transport rates in different transects indicates that the sediment transport rate is highest at the mouth transects and lowest at the alongshore transects. Moreover, variations in sediment transport rates exhibit distinctive patterns between the two outlet transects, even when subjected to identical wave conditions. The disparities are attributed to differences in runoff and the topographical features in proximity to the estuaries. Additionally, we find the sediment transport rate becomes insensitive to the variations in Hs when Hs is larger than a threshold value. The threshold decreases with increasing Tp.
Evolution of coherent structures in the flow around a circular pier with a developing scour hole: A numerical study
Authors: Kalidindi Murali Krishnamraju , Khosa Rakesh
Published: February 2024

Large-eddy simulations (LES) were used to simulate the flow features around a circular pier with evolving scour hole. The bathymetry corresponding to four stages of scour hole evolution, published in the previous literature, was used in the flow domain to recreate the flow at a particular stage of scour hole development. The growth of coherent structures and their interactions in a developing scour hole were investigated. The formation of secondary vortices inside the scour hole and their interactions with the primary horseshoe vortex (HV) made the HV system highly dynamic. High-level pressure fluctuations were observed inside the core of HV. The simulation captured the bimodal aperiodic oscillations in the HV at all stages of scour hole development. The mechanisms responsible for the formation of scour hole behind the pier were discussed. High levels of mean and instantaneous bed shear stress values were observed beneath the horseshoe vortex. These values were found to have decreased with an increase in the scour hole depth. The LES also captured the detachment of vortices from the legs of HV and their convection in the pier downstream.
Spatial entanglement in two-dimensional artificial atoms
Authors: Pham Dung N. , Bharadwaj Sathwik , Ram-Mohan L. R.
Published: February 2024

Semiconductor quantum dots (QDs) are one of the leading candidates for realizable qubits, as well as for many other advances in quantum computing and quantum communication. The spatial overlapping of wavefunctions describing each single electron in these nanoscale devices results in tunable spatial entanglement. In this article, we explore the case of two electrons in two-dimensional double quantum dot systems. We compute the two-particle wavefunction through a variational method combined with Hermite finite elements and study the spatial entanglement of electrons. We show that symmetry in the geometry of the double quantum dots plays a role in obtaining optimal entanglement, while a broken symmetry can lead to additional resonances in entanglement that are associated with the crossings of states. We also show that one can finely tune the level of spatial entanglement by altering the geometry of the quantum dots or by applying external fields, which corresponds to an “entanglement spectroscopy.” Finally, we study how impurities in the potential profile of the QDs affect the level of entanglement.
Grating magneto-optical trap optimization and drift-mitigation based on Bayesian learning
Authors: Yu Zhilong , Chen Lang , Duan Junyi , Yao Minghao , Tan Ning , Liu Xiaochi
Published: February 2024

The grating magneto-optical trap (GMOT) is a promising approach for miniaturizing cold-atom systems. We demonstrated a real-time parameter optimization and drift-mitigation method for a GMOT system based on Bayesian learning. In a remarkable short convergence period, optimal numbers of cold atoms reached up to 7.7 × 106, which was nearly four times better than with manual optimization. The parameters included not only physical parameters but also mechanical parameters that can control the critical optical alignment. The results experimentally demonstrate that our work can efficiently optimize multiple parameters for a GMOT system and for the atom-based systems that need fine control. The machine learner employed a dual layer Bayesian learning, which could suppress the cost function drift due to the instability of the experimental parameters and environmental factors of the GMOT. The proposed approach validates the feasibility of Bayesian optimization in multiparameter cold-atom systems and can be applied to rapidly determine optimal parameters and high stability of general cold atom-based physical systems.
Tetracoordinate or tricoordinate? Planar tetracoordinate nitrogen in the NBe4H4− cluster stabilized by multicenter bonds
Authors: Jin Bo , Wang Zai-Ran , Wu Yan-Bo
Published: February 2024

Realization of planar tetracoordinate arrangements of nitrogen atoms is challenging because their preference for localized bonding (caused by its high electronegativity) makes them typically tricoordinate. This is especially true for the more electronegative oxygen atoms. Herein, we computationally designed two clusters NBe4H4− and OBe4H4; they contain a planar tetracoordinate nitrogen (ptN) and planar tetracoordinate oxygen (ptO) atom, respectively. Remarkably, the former is a dynamically stable global minimum, while the latter is not. The bonding analysis proves that planar tetracoordination in NBe4H4− favors over tricoordination because of the presence of multicenter delocalized bonds. In contrast, the planar tricoordination dominates due to its weak delocalized bonding ability of oxygen in the OBe4H4 cluster. Moreover, the 6σ/2π double aromaticity due to multicenter delocalized bonds allows the NBe4H4− cluster to obtain additional stability. This cluster is a promising synthetic due its dynamic and thermodynamic stability.
Sedimentation of two circular particles with different sizes in a vertical channel at low Reynolds numbers
Authors: Huang Tao , Yu Hao , Tang Tingting , Zhao Haibo , Zhang Chengyao , Deng Qiyu , Yu Peng
Published: February 2024

In this study, the generalized finite-difference with singular value decomposition method for fluid–structure interaction problems is used to simulate the sedimentation of the two circular particles with different sizes in a vertical channel. The effects of the Reynolds number (8 ≤ Re ≤ 70) and the size difference (0 ≤ β ≤ 0.1) on the final motions of the two particles are analyzed. Over the ranges of the parameters investigated, three modes in the final state of the two-particle system are identified, i.e., the steady state, the periodic oscillation state, and the period-doubling bifurcation (PDB) state. Depending on the importance of the inertial force, the steady state can be classified as the steady state I and the steady state II. Similarly, the periodic oscillation state can be categorized into the periodic motion I (PMI) and the periodic motion II (PMII) based on the influence of the wake between the two particles. The directions of the limit cycles corresponding to PMI and PMII are counterclockwise and clockwise, respectively. In PMI, the limit cycle at 8 ≤ Re ≤ 9 decreases in size with increasing β, while the limit cycle at 12 ≤ Re < 70 behaves oppositely. The limit cycle in PMII always increases in size with β. PDB, characterized by the limit cycle with two branches, mainly appears at 14 ≤ Re ≤ 30.
Quantitative assessment of acoustic field characteristics in water by radial extracorporeal shockwave therapy
Authors: He Luyao , Guo Anyi , Wang Bo , Liu Qingquan , Liu Yajun , Chen Xiaodong
Published: February 2024

Radial extracorporeal shockwave therapy (rESWT) is a noninvasive medical technique that treats a range of musculoskeletal conditions. To understand its biological effects and develop personalized treatment plans, it is crucial to fully characterize the acoustic field that rESWT generates. This study presents a quantitative assessment of rESWT's acoustic field, achieved through experiments and simulations. The study measures the acoustic fields using a needle-type hydrophone under different machine settings and establishes and calibrates a computational model based on the experimental measurements. The study also determines the spatial distributions of peak pressure and energy flux density for different driving pressures. High-speed photography is used to visualize cavitation bubbles, which correspond to the negative pressure distribution. The study finds that the axial pressure distribution is similar to the acoustic radiation from an oscillating circular piston, whereas the radial pressure distribution cannot be described by acoustic radiation. Furthermore, the study develops a machine learning model that predicts positive pressure distributions for continuous driving pressure. Overall, this study expands our understanding of the acoustic fields generated by rESWT and provides quantitative information to explore underlying biological mechanisms and determine personalized treatment approaches.
Snap-through instability of a high arch of magneto elastomers with a giant magnetic actuation
Authors: Chen Lingling , Tan Kai , Yang Shengyou
Published: February 2024

In our previous work [Chen et al., Int. J. Solids Struct. 246–247, 111607 (2022)], we designed a flat arch structure for hard magnetic soft material. It used snap-through instability for remote actuation and large deformation in a small magnetic field range (25–170 Oe). The ratio of the magnetic-driven deflection to the arch length was about 0.05. To improve this ratio, we designed a high arch of magneto elastomers, which expanded the range of ratio from 0.05 to 0.5, increasing it by an order of magnitude. However, raising the arch height extended the driving range while unintentionally increasing the critical magnetic field for snap-through. To overcome this challenge, we reduced the bending stiffness of the arch-shaped structure, effectively lowering the critical magnetic field. Our goal is to optimize the structure of hard magnetic soft materials to achieve a broader driving range under quasi-static applied magnetic field conditions. This is accomplished by adjusting the arch height and structural stiffness to balance different performance requirements. Our research could have a significant impact on applications and devices that utilize magnetic materials.