bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady flow characteristics during runaway process in Francis turbine: Insights from numerical investigation
Authors: Li Yanyan , Sun Longgang , Guo Pengcheng
Published: February 2024

The runaway process in hydraulic turbines is characterized by unstable flow that results in the formation of vortex structures, pressure fluctuations, and energy dissipation. This study focuses on the unsteady flow characteristics of a Francis turbine during the runaway process using numerical simulations. The obtained runaway speed and discharge align well with the experimental results. The findings reveal that larger openings lead to more rapid attainment of the runaway speed. During the runaway process, extensive flow separation at the runner blade generates a columnar vortex, which obstructs the channel and dissipates energy. High-amplitude pressure fluctuations, with a frequency below 0.5 times the blade frequency, are observed in the flow passage components. These pressure fluctuations are attributed to forming a columnar vortex structure at the hub and a sheet vortex band at the trailing edge of the runner blade. A large opening leads to an earlier occurrence of high-amplitude pressure fluctuations, a gradual increase in the amplitude of low-frequency fluctuations, and a more intense force in the runner. An analysis of the energy dissipation characteristics using the energy balance equation reveals that turbulence plays a dominant role in energy transfer and dissipation during the runaway process. Additionally, the dissipation is caused by the formation of a columnar vortex structure induced by flow separation at the blade hub and the presence of a sheet vortex band at the trailing edge. Furthermore, the findings observe that energy conversion and dissipation within the runner channel intensify with increasing guide vane opening.
Influence of oncoming flow parameters on rotating detonation combustor with supersonic turbine guide vanes
Authors: Wen Fengbo , Su Liangjun , Wang Ying , Han Jiajun , Wang Songtao
Published: February 2024

Rotating detonation combustion can greatly improve the performance of air-breathing turbojet engines due to its self-pressurization and high combustion efficiency. Detonation wave propagation is closely related to oncoming flow parameters. The supersonic turbine guide vane plays a role in weakening the uneven oscillation caused by the propagation of the detonation wave. Therefore, the study of the influence of oncoming flow parameters on the coupling between the rotating detonation combustor and the supersonic turbine plays a key role in the design of the rotating detonation supersonic turbine engine. In this paper, we study the influence of oncoming flow parameters (Aw/At∼25–15, P0∼ 0.5–1.5 MPa, T0∼ 250–350 K, pb∼ 0.5–1.5 atm, and Φ∼ 0.6–1.4) and propagation direction (D ∼ R-L) on the performance and flow mechanism of the coupling of a rotating detonation combustor with supersonic turbine guide vanes; a total of 27 cases are calculated and analyzed. According to the study, the injection parameters mainly determine the premixed fuel injection flow rate and its physical and chemical characteristics, thereby affecting the secondary detonation of the detonation wave. The detonation wave will exhibit four propagation modes: single wave mode, multi-wave mode, multi-wave co-propagation mode, and multi-wave reverse-propagation mode. The formation of multi-wave modes is the result of multi-wave collision, annihilation and secondary detonation of detonation waves. Under different parameter conditions, the intensity of the secondary detonation is different. The single wave mode is due to the low stoichiometric ratio and low total temperature inhibiting the secondary detonation. As for the reverse propagation mode and multi-wave collision, multi-wave co-propagation is caused by the interaction between the new detonation wave caused by the secondary detonation and the detonation wave. The interaction between rotating detonation and supersonic turbine guide vanes is mainly reflected in the interaction between oblique shock waves and supersonic turbine guide vanes, which will generate basic wave structures such as channel shock waves, reflected shock waves, and dovetail waves. The interaction area between the slip lines and the oblique shock waves and the guide vanes of the supersonic turbine will form local high temperature zones, resulting in a large local thermal load. These laws provide reference for the coupling design of rotating detonation and supersonic turbine.
The structure of water: A historical perspective
Authors: Finney John L.
Published: February 2024

Attempts to understand the molecular structure of water were first made well over a century ago. Looking back at the various attempts, it is illuminating to see how these were conditioned by the state of knowledge of chemistry and physics at the time and the experimental and theoretical tools then available. Progress in the intervening years has been facilitated by not only conceptual and theoretical advances in physics and chemistry but also the development of experimental techniques and instrumentation. Exploitation of powerful computational methods in interpreting what at first sight may seem impenetrable experimental data has led us to the consistent and detailed picture we have today of not only the structure of liquid water itself and how it changes with temperature and pressure but also its interactions with other molecules, in particular those relevant to water’s role in important chemical and biological processes. Much remains to be done in the latter areas, but the experimental and computational techniques that now enable us to do what might reasonably be termed “liquid state crystallography” have opened the door to make possible further advances. Consequently, we now have the tools to explore further the role of water in those processes that underpin life itself—the very prospect that inspired Bernal to develop his ideas on the structure of liquids in general and of water in particular.
Surface wave propagation along a narrow transition layer in a slab Voigt geometry
Authors: Girka Igor O. , Tierens Wouter
Published: February 2024

The dispersion properties of electromagnetic surface waves, which propagate along a slab narrow transition layer separating two magnetoactive plasma uniform half spaces, are studied. Voigt geometry is considered, in which the waves propagate perpendicularly to an external uniform static magnetic field, which in turn is parallel to the interfaces between the plasmas and the transition layer. Electromagnetic power absorption within local resonances inside the transition layer is out of scope of the study. The influence of the plasma particle density profile smoothness on the surface wave dispersion properties is emphasized.
A new nano-design of configurable logic module based on coplanar reversible adder and modified Fredkin gates using quantum technology
Authors: Wang Junzhuang , Tan Dongping , Diakina Ekaterina
Published: February 2024

Quantum Dot Cellular Automata (QCA) and reversible logic have emerged as promising alternatives to conventional CMOS technology, offering several advantages, such as ultra-dense structures and ultra-low-power consumption. Among the crucial components of processors, the Arithmetic Logic Unit (ALU) has witnessed significant advancements in reversible computing, leading to energy-efficient and high-speed computing systems, particularly beneficial for Digital Signal Processing (DSP) applications. Conventional ALUs, reliant on irreversible logic, encounter energy inefficiencies due to information loss during computations, resulting in increased power consumption. Moreover, they may face limitations in processing speed, impacting real-time processing capabilities, especially for complex DSP tasks involving intensive arithmetic and logic operations. In response to these challenges, a research paper presents a pioneering approach, proposing a novel reversible ALU design using QCA nanotechnology. The proposed design ingeniously incorporates Modified Fredkin (MF) gates, and a coplanar reversible full adder based on the HNG gate, skillfully leveraging the unique features of QCA nanotechnology to optimize the ALU's energy-efficient and high-speed performance for DSP applications. This revolutionary QCA reversible ALU comprises 330 QCA cells arranged in a compact 0.41 μm2 area, skillfully realized through the coplanar clock-zone-based crossover approach. Its core computational elements, the three MF gates, and the innovative coplanar reversible full adder empower the ALU to execute a remarkable array of 20 distinct arithmetic and logic operations, showcasing its versatility in handling diverse DSP tasks. The proposed structure undergoes extensive simulations utilizing QCADesigner version 2.0.3 to confirm its performance. The evaluation results manifest substantial improvements compared to previous designs, boasting a 30% reduction in area occupancy, a 20% decrement in cell count, a 10% reduction in latency, and a 10% decrease in quantum cost compared to the best-known previous structure. These compelling outcomes solidify the potential of the proposed reversible ALU as a transformative advancement in energy-efficient and high-speed computing for DSP applications.
Thermal simulation and optimization of a Curie-based thermomagnetic motor harnessing concentrated solar energy
Authors: Afenyiveh Serge Dzo Mawuefa , Adanlete Adjanoh Assiongbon , Douti Dam-Bé Lardja , Pakam Tchilabalo
Published: February 2024

This work reports on a numerical study of a thermomagnetic motor with the active material being a Nickel (Ni) plate using the Curie effect. The main goal is to use thermal simulation and parameter optimization to increase the motor’s efficiency. With respect to beam width, heat exposure duration, and rotation frequency, the study focuses on multiparametric simulations of a thermomagnetic wheel exposed to a concentrated sun beam. An efficient configuration for real-world application is found using the finite element-based computational tool COMSOL Multiphysics. The outcomes show that, when taking into account n = 5 cycles, the ideal configuration displays parameter settings with the lowest quadratic deviation around the Curie temperature during the thermal excitation process and the lowest quadratic deviation around the ambient temperature during the thermal relaxation process. Furthermore, a cooling method is presented, which includes supporting the active material with an Aluminum (Al) heat sink. In order to speed up the remagnetization of the Curie wheel, this method seeks to decrease heat accumulation and regulate the deposited thermal flux on the Ni plate. We also found that the reduction in quadratic deviation is most pronounced between zAl = 1 mm and zAl = 2 mm. At zAl = 10 mm, the quadratic deviation achieves its lowest value (σθmin=5.65K) at the end of the thermal relaxation process. The results of this study will forward the design of a high-performance thermomagnetic motor for mechanical and electrical applications.
On the spin-quantization-axis selection for the spin polarization modeling during laser–electron collision
Authors: An Xiangyan , Chen Min , Sheng Zhengming
Published: February 2024

Spin polarized electron beams have wide applications in high energy physics. The generation of such electron beams has recently attracted considerable attention where the collision of intense laser pulses with high energy electron beams is proposed as one of the potential methods. In previous numerical studies, different spin-quantization axes (SQA) are used, which lead to different calculation results in some configurations of laser interaction with an electron beam. To be consistent with the well-known Thomas–Bargmann–Michel–Telegdi (TBMT) equation, we have proposed a new SQA which is along the TBMT precession direction. We clearly show the difference among the three kinds of SQA selections by comparing the temporal evolution of the electron beam's polarization during the perpendicular collision of an electron beam with s-polarized two-color laser pulses, where the magnetic fields have a parallel component along the electron motion direction. Calculation shows that such differences could be experimentally measured by nowadays facilities. To get the maximum electron polarization degree in the two-color laser pulses based schemes, we also find the optimized condition for the two-color laser parameters. Our studies give a better understanding of spin-polarization calculation and will be beneficial for future experimental designs for electron polarization manipulation.
Low-frequency oscillation flow in nitrogen jet condensation
Authors: Zhu Chengfeng , Li Yanzhong , Wang Lei , Yang Jiahui , Li Cui
Published: February 2024

Jet condensation is a complicated two-phase flow phenomenon that occurs in pipe flow, especially in cryogenic fluids. In this study, the condensation flow dynamics of a stream of nitrogen (N2) injected into a subcooled liquid nitrogen (LN2) flow was photographically investigated using a high-speed camera. The pulsating pressure was measured at different observation points using dynamic pressure transducers. Three typical condensation flow patterns were observed and measured under different nitrogen volume fluxes: suck-back flow, transition flow, and oscillation flow. Suck-back flow occurs at a smaller N2 volume flux, where the LN2 is periodically sucked back into the gas chamber. Oscillation flow is encountered at larger N2 volume flux, along with intense pressure fluctuations. Using fast Fourier transform analysis, the frequency of these pressure oscillations was found to be in the range 16–18 Hz with a maximum amplitude of about 10 kPa. An image-processing method was developed to track the fluid motion in the dynamic photographs recorded by the high-speed camera according to the local changes of pixels. The results show the presence of a periodic shrinking of the vapor-plume trail with the same frequency as the pressure oscillation. The mechanism for the low-frequency oscillation flow is, therefore, identified as periodic interfacial condensation. The findings of this study provide strong evidence for the origin of the low-frequency pressure oscillations observed in cryogenic liquid rocket engines. This information can be used to improve the design and operation of such propulsion systems.
Excellent thermoelectric performance of layered trigonal crystals XPt2Se3 (X = K, Rb)
Authors: Zeng Shuming , Shen Qian , Yang Jinpeng , Zhao Yinchang , Li Geng , Gu Zonglin , Tu Yusong , Huang Hao
Published: February 2024

Thermoelectrics (TEs) have been considered a sustainable and eco-friendly energy technology. However, due to limitations in energy conversion efficiency, TE devices have not yet been widely adopted. Here, we proposed a class of TE materials, trigonal XPt2Se3 (X = K, Rb), with the same crystal structure as Bi2Te3. At room temperature, with quartic anharmonicity correction, the lattice thermal conductivity (κL) of KPt2Se3 and RbPt2Se3 in the x-direction is only 0.57 and 0.46 W m−1 K−1, respectively. The ultralow κL arises from their layered structure, strong lattice anharmonicity, weak bonding nature, rattling motion of guest alkali metal atoms, and large scattering space. Simultaneously, the large density of states contributes to large power factors. At 800 K, both under n-type and p-type doping, KPt2Se3 exhibits ZT values that can exceed 4 in specific directions, while RbPt2Se3's ZT values can surpass 3, which is significantly higher than traditional TE materials. Our research not only elucidates that the layered trigonal crystals XPt2Se3 (X = K, Rb) represent a category of potential TE materials with ultralow κL and high TE performance but also provides directions for exploring TE materials.
A novel dynamic subgrid-scale model based on partial-averaged velocity for large eddy simulation
Authors: Sun Yifan , Qi Haiying , Zhang Guihua , Wu Yuxin
Published: February 2024

This study presents an innovative dynamic subgrid-scale model for large eddy simulation based on the partial-averaging method. In this method, the partial-averaged velocity fluctuations, known as drift velocities, were used to formulate subgrid-scale turbulent viscosity. This feature enables the preservation of more comprehensive first-order turbulence information so that the anisotropic turbulent flow can be better predicted. Dynamic coefficient adjustment was adopted to effectively address the sharp change of subgrid-scale viscosity in complex flows. The proposed model was programed and employed to simulate a plane jet, a circular jet, a fully developed pipe flow, and a swirling jet based on OpenFOAM. The results indicate that the model exhibits high predictive accuracy, adapting well to free shear flows and wall-bounded shear flows. The distribution of drift velocities provides direct statistical information of turbulent flows and reveals anisotropic characteristics of turbulent fluctuations.
Experimental realization of tunable exceptional points in a resonant non-Hermitian piezoelectrically coupled waveguide
Authors: Thomes Renan L. , Rosa Matheus I. N. , Erturk Alper
Published: February 2024

This Letter presents an experimental demonstration of tunable exceptional points (EPs) in an electromechanical waveguide. EPs are non-Hermitian singularities typically found in parity-time (PT) symmetric systems with balanced gain and loss. Here, piezoelectric transducers on an aluminum beam (waveguide) are shunted to synthetic impedance circuits that emulate negative and positive resistors (responsible for gain and loss) and inductors (for resonant tunability), whose properties can be programmed digitally. Specifically, an electrical mode is introduced via inductive shunts to electromechanically interact with target structural mode(s) to create degeneracy. While the internal structural damping of the waveguide has the effect of breaking PT symmetry inherently, we show that EPs can still be created by using non-trivial gain and loss combinations. The results in this Letter pave the way for practical realization of EPs in elastic media toward their application in enhanced sensing and asymmetric wave control, among others.
Extended contributions to the pyroelectric effect in ferroelectric thin films
Authors: Arli Cihan , Atilgan Ali Rana , Misirlioglu I. Burc
Published: February 2024

Pyroelectric properties of dielectrics have been occupying the agenda of relevant scientific research groups owing to a number of device designs tailoring this effect, such as energy harvesting and caloric devices. Ferroelectrics come forward probably as the most important class of dielectrics in this regard due to their spontaneous polarization that is strongly dependent on temperature as well as strain and electric field. Here, we rigorously formulate and identify the connection between the experimentally accessible pyroelectric coefficient of a perovskite type ferroelectric and contributions arising from strain and clamping conditions. Secondary pyroelectric coefficient under partial clamping reminiscing a thin film is formulated so as to separate it from the primary coefficient that is conventionally defined at constant volume. The formulation is then applied to a number of ferroelectric compositions to reveal the extent of the variations in the secondary pyroelectric effect. The secondary effect reinforces the primary pyroelectric coefficient for the PMN-PT system, whereas it diminishes the total coefficient for PbZr0.4Ti0.6O3 and BaTiO3 systems. The role of thermal expansion coefficients in these variations is discussed.
Ion–ion association is lost by linearizing the Poisson–Boltzmann equation when deriving the Debye–Hückel equation
Authors: Silva Gabriel M. , Liang Xiaodong , Kontogeorgis Georgios M.
Published: February 2024

In this work, we demonstrate how the ion association constant can be attributed to the difference between the full Poisson–Boltzmann equation and its linearized version in very dilute solutions. We follow a pragmatic approach first by deriving an analytical approximated solution to the Poisson–Boltzmann equation, then calculating its respective Helmholtz free energy and activity coefficient, and then finally comparing it to the contribution from the mass action law principle. The final result is the Ebeling association constant. We conclude that electrostatic ion–ion interaction models miss the ion association contribution naturally introduced in higher-order electrostatic theories. We also demonstrate how the negative deviations from the Debye–Hückel limiting law can be physically attributed to the ion association phenomenon.
Linear NIMROD simulations of n = 0 modes for straight tokamak configuration and comparison with analytic results
Authors: Banerjee Debabrata , Kim Charlson C. , Barberis Tommaso , Porcelli Francesco
Published: February 2024

Comparison between the analytic theory of n = 0 vertical displacement modes in magnetically confined plasmas of fusion interest and numerical simulations using the extended-MHD code NIMROD is presented. Agreement between analytic and numerical results is highly satisfactory. Differences are interpreted to be caused mostly by the different wall shape and by the presence of a halo plasma surrounding the hot plasma adopted in NIMROD. A numerical study of vertical displacement oscillatory modes [Barberis et al., J. Plasma Phys. 88, 905880511 (2022)] is presented. Axisymmetric X-point currents supported by the halo plasma are discussed. The article provides a successful benchmark and a useful starting point for future numerical investigations of n = 0 modes using more realistic tokamak geometry and plasma equilibria.
Elimination of spiral hillocks in AlGaN grown on high-temperature annealed AlN templates by adopting an AlN/AlGaN stress modulation multilayer
Authors: Fang Xuzhou , Wang Jiaming , Xu Fujun , Zhang Lisheng , Lang Jing , Zhang Ziyao , Tan Fuyun , Yang Xuelin , Kang Xiangning , Qin Zhixin , Tang Ning , Wang Xinqiang , Ge Weikun , Shen Bo
Published: February 2024

The formation of spiral hillocks during AlGaN growth is investigated by modulating the residual strain in the underlying AlN templates. It is demonstrated that the high-density hillocks are directly related to the compressive stress, in particular for AlGaN on high-temperature annealed (HTA) AlN. AlN/AlGaN stress modulation multilayer is then introduced and optimized before AlGaN growth, which is revealed to be helpful to release the compressive stress in AlGaN as well as to suppress the hillocks. Eventually, the hillocks in AlGaN/HTA-AlN are eliminated, leading to a great improvement of yield for deep-ultraviolet light-emitting diode (DUV-LED) wafers. This work will definitely promote further industrial development and application of DUV-LEDs.
Ultrafast vibrational energy redistribution in cyclotrimethylene trinitramine (RDX)
Authors: Zhang Lingyu , Song Huajie , Yang Yanqiang , Zhou Zhongjun , Zhang Jilong , Qu Zexing
Published: February 2024

The microscopic mechanism of the energy transfer in cyclotrimethylene trinitramine (RDX) is of particular importance for the study of the energy release process in high-energy materials. In this work, an effective vibrational Hamiltonian based on normal modes (NMs) has been introduced to study the energy transfer process of RDX. The results suggest that the energy redistribution in RDX can be characterized as an ultrafast process with a time scale of 25 fs, during which the energy can be rapidly localized to the –NNO2 twisting mode (vNNO2), the N–N stretching mode (vN–N), and the C–H stretching mode (vC–H). Here, the vNNO2 and vN–N modes are directly related to the cleavage and dissociation of the N–N bond in RDX and, therefore, can be referred to as “active modes.” More importantly, we found that the energy can be rapidly transferred from the vC–H mode to the vNNO2 mode due to their strong coupling. From this perspective, the vC–H mode can be regarded as an “energy collector” that plays a pivotal role in supplying energy to the “active modes.” In addition, the bond order analysis shows that the dissociation of the N–N bonds of RDX follows a combined twisting and stretching path along the N–N bond. This could be an illustration of the further exothermic decomposition triggered by the accumulation of vibrational energy. The present study reveals the microscopic mechanism for the vibrational energy redistribution process of RDX, which is important for further investigation of the energy transfer process in high-energy materials.
Numerical simulation of deformation and breakage of compound droplet in air flow
Authors: Lv Chao , Ji Zhaoxiang , Yang Tao , Zhao Hongliang , Zhang Haiwei
Published: February 2024

The deformation process of compound droplets moving in air flow was studied by using volume of fluid model. In this paper, the kinetic process of air-in-liquid CeO2 compound droplets in air flow is reported by numerical simulation. First, the effects of initial velocity, initial diameter, and internal and external pressure difference on droplet behavior were studied when the compound droplets finally reached the morpho-steady state. The self-compiled program is used to process and analyze the digital image of the simulated broken image. The results show that, under the action of four main forces, namely, external aerodynamic force, internal pressure, viscous force, and surface tension, the inner surface of the hollow droplets gradually begins to break and continues to expand to the outer surface to break. With the increase in the pressure difference between inside and outside of the hollow drops, the pores are severely deformed and cracked. The increase in velocity leads to the imbalance of internal and external surface forces caused by the increase in aerodynamic fluctuation on the outer surface of hollow droplets. With the decrease in the diameter of the hollow droplet, the pressure threshold of the droplet breaking decreases and it is easier to break.
Maximum entropy model of chaotic explosion and implosion of a large gas bubble in liquid
Authors: Waldo G. V.
Published: February 2024

A mathematical model for the chaotic explosion of a large gas bubble in a liquid is presented in which there is a maximum increase in entropy. It is shown that this requires that the acoustic radiation during the chaos must be minimal and that the spherical surface at the end of the chaos must be stable. Also, a model including the acoustic radiation is developed for the spherical phases of the explosion and implosion of the bubble during which there is no change in entropy. The (final) chaotic phase of the implosion is also modeled so that there is a maximum increase in entropy. There might be additional periods of the bubble during which the bubble explodes and implodes in a similar fashion as the first period. The calculations using this model are shown to agree reasonably well with the data. In particular, these calculations determined that the ratio of the duration of the second period of the bubble to the first period imply that the energy lost in the first period during its implosion is about 2/3 of the energy of the first period. Also, these calculations determine that only about 30% of the total energy is radiated and the rest is absorbed by the water for a total of about 2/3 of the total energy. This also agrees with the data. Furthermore, the data appear to scale with initial total energy as in the calculations using this chaos model.
Transient dispersion of a reactive solute in an oscillatory Couette flow through an anisotropic porous medium
Authors: Das Debabrata , Mondal Kajal Kumar , Poddar Nanda , Wang Ping
Published: February 2024

This research discusses the significance of reactive solute dispersion relevant to ecological, biological, and geological contexts. It examines solute movement under oscillatory Couette flow through anisotropic porous media between parallel plates under the effect of heterogeneous boundary reactions. The flow is driven by the combined effect of upper plate oscillation in its plane and time-dependent pressure gradient. The lower plate is assumed rough, which introduces slip velocity. A semi-analytical approach, with the method of moments and finite difference scheme, is utilized to explore the transient dispersion in steady and oscillatory flows with or without a non-zero mean. Using the Hermite polynomial, the mean concentration for purely oscillatory and combined flow is obtained, highlighting notable variations based on flow factors. The results suggest that increment in anisotropic angle ϕ reduces dispersion and enhances mean concentration for permeability ratio K < 1, but this reverses for K > 1. Three dispersion phases emerge: diffusive, anomalous, and Taylor's regimes. Gaussian cloud distribution occurs at small and large times, with intermediate stages displaying anomalous dispersion and asymmetric longitudinal distribution. Effects of boundary absorption stabilize over time. The research focuses on the practical significance of different permeabilities of porous media, emphasizing applications of anisotropic porous media in fields such as chemical engineering and industrial processes.
Effects of electron viscosity on resonant layer responses to non-axisymmetric magnetic perturbations
Authors: Waybright J. C. , Park J.-K.
Published: February 2024

The resonant field penetration to magnetic islands is the central MHD mechanism of non-axisymmetric plasma responses in a tokamak such as disruptive locking or favorable ELM stabilization. The resonant field penetration can be induced by any non-ideal processes as manifested in the delicate balance under the generalized Ohm's law. Here, we show that the viscous effects by electrons are not ignorable in the field penetration unlike previous presumption, even if the electron viscosity is as small as the square root of its mass compared to the ions. It is clear that its effects become only bigger if the electron viscosity becomes anomalously large. The work strictly follows the three-field model in the linear regime targeting the prediction of the onset of the field penetration and successfully extending it with electron viscosity and identifying new regimes. The results also indicate that the error field thresholds become more strongly dependent on plasma density than ones predicted in the linear regimes without the electron viscosity, which is consistent with experimental observations and thus a significant implication.
Flow field interference effect on energy harvesting enhancement of a combined fluid–structure interaction system in channel flow
Authors: Tatar Massoud , Yao Hua-Dong
Published: February 2024

In this paper, the flow field between two vibrating systems and the potential to increase the harvested energy by the interference of flow fields was numerically evaluated. A combined configuration of a cylinder-splitter hyperelastic plate placed at the wake of a vortex-induced oscillating cylinder was studied in a laminar channel flow at a Reynolds number of 200. A finite-volume method was adopted for solving the flow field over polyhedral cells. Overset grid and mesh morpher algorithms were employed to handle different mesh motions. On the other hand, a finite element method was exploited to solve the structural displacement of the hyperelastic plate. Having validated two individual similar systems, the effects of different spacing values and the reduced frequency of the vibrating cylinder on the amount of harvested energy were investigated in the combined configuration. According to results, no flow unsteadiness took place for the small spacing values at low reduced velocity. Increasing the natural frequency, the oscillation of the vibrating cylinder excited its boundary layer, causing it to separate. Moreover, the presence of such oscillations at downstream of the vibrating cylinder altered its response yielding higher energy production. Results showed that at some specific reduced velocities of the oscillating cylinder, the vortex shedding phenomenon did not occur if the spacing between the cylinders was small. However in other cases, the relative power efficiency of the oscillating cylinder in the combined system was increased from 29% to more than five times of the isolated oscillating cylinder depending on the parameters.
Bubble entrainment and underwater noise caused by a single water drop falling on the surface of freshwater and saltwater
Authors: Huang Ching-Jer , Yeh Chih-Hui , Liu Kuan-Wen
Published: February 2024

Bubble entrainment caused by and underwater sound produced by a single water drop falling on the surface of freshwater and saltwater were experimentally investigated in this study. A charge-coupled device camera was employed to photograph the drop's impact and the process of bubble formation. Underwater sound was received using a hydrophone connected to a charge amplifier and a data-acquisition system. To capture the temporal and spectral characteristics of the sound, the time series of the underwater sound was transformed into the time–frequency domain by using the Gabor transform. The diameter of the drops was varied from 2.6 to 5.66 mm, and the release heights investigated were 10–150 cm. The experimental results revealed three distinct bubble formation processes following the impact of a water drop. Type-I bubbling was the formation of a singular bubble at the apex of the contracting crater produced by the initial drop impact. Type-II bubbling was the formation of one or multiple bubbles entrained by the downward motion of the water column produced during the initial drop impact. Type-III bubbling was the formation of a singular bubble generated due to the impact of a secondary water drop above the water column. The effects of salinity on bubble entrainment and underwater noise were also studied. For the same experimental parameters, bubbles entrained in saltwater were discovered to be larger than those entrapped in freshwater; moreover, the saltwater bubbles collapsed into two bubbles.
Scale filtering analysis of kinetic reconnection and its associated turbulence
Authors: Adhikari Subash , Yang Yan , Matthaeus William H. , Cassak Paul A. , Parashar Tulasi N. , Shay Michael A.
Published: February 2024

Previously, using an incompressible von Kármán–Howarth formalism, the behavior of cross-scale energy transfer in magnetic reconnection and turbulence was found to be essentially identical to each other, independent of an external magnetic (guide) field, in the inertial and energy-containing ranges [Adhikari et al., Phys. Plasmas 30, 082904 (2023)]. However, this description did not account for the energy transfer in the dissipation range for kinetic plasmas. In this Letter, we adopt a scale-filtering approach to investigate this previously unaccounted-for energy transfer channel in reconnection. Using kinetic particle-in-cell simulations of antiparallel and component reconnection, we show that the pressure–strain interaction becomes important at scales smaller than the ion inertial length, where the nonlinear energy transfer term drops off. Also, the presence of a guide field makes a significant difference in the morphology of the scale-filtered energy transfer. These results are consistent with kinetic turbulence simulations, suggesting that the pressure strain interaction is the dominant energy transfer channel between electron scales and ion scales.
Predicting the upper bound of two-dimensional flow regimes of symmetric objects through two-dimensional computations
Authors: Yadav Pavan Kumar , Sen Subhankar
Published: February 2024

The onset of secondary wake instability is generally predicted via experiments, linear stability analysis, and three-dimensional direct numerical simulations. The current work stems from an open question that is very intriguing and fundamental: Can the upper bound of a two-dimensional flow be predicted purely on the basis of two-dimensional computational results? It is found that spatial distribution of a field variable, i.e., streamwise velocity in the vortex formation region, aids in determining the upper limit of a two-dimensional flow regime of a symmetric object. The vortex formation length attains its least value at the second critical Reynolds number. In addition, streamwise extents of mean wake and vortex formation region along wake axis become the same. Under this circumstance, the streamwise velocity at the terminal point of vortex formation region is such that its mean value vanishes while intensity of fluctuations or corresponding Reynolds stress becomes the maximum. The predicted values of critical Reynolds numbers for circular, square, and diamond cross sections exhibit excellent agreement with the results available in the literature.
Machine learning-based vorticity evolution and super-resolution of homogeneous isotropic turbulence using wavelet projection
Authors: Asaka Tomoki , Yoshimatsu Katsunori , Schneider Kai
Published: February 2024

A wavelet-based machine learning method is proposed for predicting the time evolution of homogeneous isotropic turbulence where vortex tubes are preserved. Three-dimensional convolutional neural networks and long short-term memory are trained with a time series of direct numerical simulation (DNS) data of homogeneous isotropic turbulence at the Taylor microscale Reynolds number 92. The predicted results are assessed by using the flow visualization of vorticity and statistics, e.g., probability density functions of vorticity and enstrophy spectra. It is found that the predicted results are in good agreement with DNS results. The small-scale flow topology considering the second and the third invariants of the velocity gradient tensor likewise shows an approximate match. Furthermore, we apply the pre-trained neural networks to coarse-grained vorticity data using super-resolution. It is shown that the super-resolved flow field well agrees with the reference DNS field, and thus small-scale information and vortex tubes are well regenerated.
Effects of plasmon coupling on circular dichroism of chiral nanoparticle arrays
Authors: Kuroki Shuki , Ishida Takuya , Tatsuma Tetsu
Published: February 2024

Arrays and ensembles of chiral nanostructures have potential applications in the field of enantioselective sensors, metamaterials, and metasurfaces. In particular, chiral nanostructures fabricated through chemical and bottom-up approaches have attracted much attention from the viewpoint of cost and scalability, but the heterogeneity of the unit nanostructure constituting the array or ensemble often deteriorates its chiroptical responses. Here, we report that their deteriorated responses can be recovered or even enhanced further by interparticle plasmon coupling. We employed chiral silver (Ag) hexamers as models for electromagnetic simulations and investigated the effect of their parameters, such as interparticle spacing, chiral purity, and enantiomeric excess, on their g-factor, which is an index for chiroptical responses. The maximum value of g-factor (gmax) of the Ag hexamer surpasses that of the chiral monomer and augments with decreasing interparticle spacing. This enhancement in g-factor is observed even when chiral purity and enantiomeric excess are less than 100%, showing the potent role of plasmon coupling in amplifying chiroptical responses. Furthermore, our research highlights the amplification of the effect of plasmon coupling on the gmax value of infinite periodic chiral nanostructures. These results corroborate the potential of plasmon coupling to improve chiroptical responses by precisely controlling the interparticle spacing of chiral plasmonic nanostructures, thus mitigating the loss of g-factor caused by low purity and enantiomeric excess of the nanostructures fabricated by chemical and bottom-up approaches.
Measuring arrangement and size distributions of flowing droplets in microchannels through deep learning using DropTrack
Authors: Durve Mihir , Orsini Sibilla , Tiribocchi Adriano , Montessori Andrea , Tucny Jean-Michel , Lauricella Marco , Camposeo Andrea , Pisignano Dario , Succi Sauro
Published: February 2024

In microfluidic systems, droplets undergo intricate deformations as they traverse flow-focusing junctions, posing a challenging task for accurate measurement, especially during short transit times. This study investigates the physical behavior of droplets within dense emulsions in diverse microchannel geometries, specifically focusing on the impact of varying opening angles within the primary channel and injection rates of fluid components. Employing a sophisticated droplet tracking tool based on deep-learning techniques, we analyze multiple frames from flow-focusing experiments to quantitatively characterize droplet deformation in terms of ratio between maximum width and height and propensity to form liquid with hexagonal spatial arrangement. Our findings reveal the existence of an optimal opening angle where shape deformations are minimal and hexagonal arrangement is maximal. Variations of fluid injection rates are also found to affect size and packing fraction of the emulsion in the exit channel. This paper offers insight into deformations, size, and structure of fluid emulsions relative to microchannel geometry and other flow-related parameters captured through machine learning, with potential implications for the design of microchips utilized in cellular transport and tissue engineering applications.
Metal–insulator transition in ScxSb2Te3 phase-change memory alloys
Authors: Song Tao , Chen Bin , Xie Jiatao , Liu Zhaoyang , Gong Huang , Ding Keyuan , Rao Feng
Published: February 2024

The scandium doped antimony tellurides (ScxSb2Te3), as promising phase-change memory materials, possess the merits of ultrafast crystallization speed and ultralow resistance drift, of the amorphous phases, ensuring the development of cache-type universal memory and high-accuracy computing chip. There is keenness to further explore the annealing effect in the crystalline ScxSb2Te3 phases to seek a potential metal–insulator transition (MIT) in electrical conduction, by which more intermediate resistance states of superior stability can be generated to enhance the programming contrast and accuracy. In this work, we have identified the metastable rock salt ScxSb2Te3 as an Anderson-type insulator and verified that the MIT occurs in its stable rhombohedral grains when lattice vacancies are highly ordered into the van der Waals-like gaps. The Sc dopant can exert profound influence on retarding the vacancy-ordering procedure, even completely prohibiting the MIT for the Sc-rich compounds. Our work suggests that tuning Sc content in ScxSb2Te3 alloys provides a simple route to engineer the material microstructures and electrical properties for the desired memory and computing performances.
Harnessing collective radiative phenomena on a photonic Kagome lattice
Authors: Salinas Ignacio , Cornejo Javier Cubillos , Szameit Alexander , Solano Pablo , Vicencio Rodrigo A.
Published: February 2024

Photonic lattices enable experimental exploration of transport and localization phenomena, two of the major goals in physics and technology. In particular, the optical excitation of some lattice sites, which evanescently couple to a lattice array, emulates radiation processes in structured reservoirs, a fundamental subject in quantum optics. Moreover, the simultaneous excitation of two sites simulates collective phenomena, leading to phase-controlled enhanced or suppressed radiation, namely super- and subradiance. This work presents an experimental study of collective radiative processes on a photonic Kagome lattice. A single or simultaneous—in-phase or out-of-phase—excitation of the outlying sites controls the radiation dynamics. Specifically, we demonstrate a controllable transition between a fully localized profile at the two outlying sites and a completely dispersed state into the quasi-continuum. Our result presents photonic lattices as a platform to emulate and experimentally explore quantum optical phenomena in two-dimensional structured reservoirs, while harnessing such phenomena for controlling transport dynamics and implementing all-optical switching devices.
Mechanical C–C, C–O, and O–O bond formation between methanol molecules by laser-driven shock wave
Authors: Ishikawa Wakako , Sato Shunichi
Published: February 2024

In this paper, all molecules (1,2-ethanediol, ethanol, methoxymethanol, dimethyl ether, and dimethyl peroxide) predicted to be produced as a result of C–C, C–O, or O–O bond formation between methanol molecules induced by laser-driven shock wave were detected and identified by gas chromatography-mass spectroscopy. In this process, the ultrahigh pressure resulting from the shock wave is considered to reduce the interatomic distance between molecules to mechanically create a new chemical bond. Methoxymethanol production was further verified by infrared absorption spectroscopy of the laser-irradiated methanol concentrated by vacuum distillation. In the concentrated sample, polyoxymethylene hemiformals, which are presumably produced by the polymerization of methoxymethanol, were also found.
Investigation of the influence of different liquid temperatures on the dynamics of long-pulse laser-induced cavitation bubbles
Authors: Wang D. , Bi Y.
Published: February 2024

Long-Pulse Laser-induced cavitation bubbles have been identified to hold significant applications in various fields, such as industry and medicine. In this study, the dynamics of cavitation bubbles, induced by a 2.94 μm wavelength Er:YAG laser with an energy of 20 ±1 mJ and transmitted via sapphire fiber optics into distilled water at different temperatures, were investigated. The adiabatic expansion theory was utilized to predict the maximum length (Lmax) and the maximum width (Wmax) of the cavitation bubbles at different liquid temperatures. Excellent alignment was observed between the theoretical predictions and the experimental data. Using this theory, the local overheated liquid temperature was deduced to be ∼180 °C during the formation of cavitation bubbles. It was found that as the liquid temperature increased, the collapse position of the cavitation bubbles, relative to the normalized distance (γ) from the fiber end face, decreased. This study reveals the importance of considering the potential risk of damage to fiber optics from the shockwaves and microjet streams generated by cavitation bubbles in high-temperature conditions.
Mode transformation of dynamic spin wave well modes in the magnetic stripes
Authors: Li Xiling , Yao Yuping , Ma Fusheng , Wang Jianbo , Chai Guozhi
Published: February 2024

In this work, we present an experimental and micromagnetic simulation study of the mode transformation of dynamic spin wave well modes in the magnetic stripes. With a highly precise lock-in ferromagnetic resonance measurement system, the spin wave modes, including the quantized backward volume magnetostatic spin waves and the spin wave well modes, can both be clearly detected in the transversely magnetized stripes. The mode transformations of dynamic spin wave well modes are detected in a field range that the moments near the edge of the stripe are not fully magnetized. Further micromagnetic simulation and analyzation show that the boundary condition change in the potential well might be the main reason for the mode transformation of spin wave well modes. These results might be helpful for the further understanding of the spin wave dynamics in the finite ferromagnets.
Giant microwave photoconductance of short channel MOSFETs
Authors: Jaroshevich A. S. , Kvon Z. D. , Tkachenko V. A. , Tkachenko O. A. , Baksheev D. G. , Antonov V. A. , Popov V. P.
Published: February 2024

We study microwave photoresponse of a short p-channel MOSFET in the subthreshold regime at temperatures from room to helium. We observe large (several times) enhancement of the MOSFET conductance at 300 K, an order at 77 K, and giant (up to 4–5 orders of magnitude) at 4.2 K. It is shown that this giant enhancement is mainly due to microwave-induced hole tunneling between the MOSFET source and drain. The result obtained exhibits real possibility of developing substantially different kind of microwave radiation detectors fabricated on the basis of ordinary MOS-technology.