bluuebunny/crossref_metadata_2025 huggingface dataset:
Control system and process optimization for electroless nickel plating
Authors: Qiao Yingtai , Hou Jian , Lai Min , Fang Fengzhou
Published: November 2024

A novel method based on mid-frequency vibration is proposed to eliminate coating defects such as bubbles during electroless nickel plating. An automated control system for the plating, enabling precise and stable measurements and adjustments of critical parameters such as plating solution temperature, pH, and nickel ion concentration, is also established, which significantly improves process efficiency and coating quality. Experimental results indicate that the system is capable of realizing stable operation over extended periods. A nonporous nickel–phosphorus coating with a thickness greater than 200 μm is successfully obtained, with high phosphorus content, robust adhesion, and superior machinability.
An automatic multi-precursor flow-type atomic layer deposition system
Authors: Rodriguez Daniel J. , Her Mai A. , Usov Igor O. , Safarik D. J. , Jones Rommel , Heidlage Michael G. , Gorey Timothy J.
Published: November 2024

Designs for two automated atomic layer deposition (ALD) flow reactors are presented, and their capabilities for coating additively manufactured (AM) metal prints are described. One instrument allows the coating of several AM parts in batches, while the other is useful for single part experiments. To demonstrate reactor capabilities, alumina (Al2O3) was deposited onto AM 316L stainless steel by dosing with water (H2O) vapor and trimethylaluminum (TMA) and purging with nitrogen gas (N2). Both instruments are controlled by custom-programmed LabVIEW software that enables in situ logging of temperature, total pressure, and film thickness using a quartz crystal microbalance. An initial result shows that 150 ALD cycles led to a film thickness of ∼55 nm, which was verified with Rutherford backscattering spectroscopy. This indicates that the reactors were indeed depositing single atomic layers of Al2O3 per ALD cycle, as intended.
Scientific machine learning based reduced-order models for plasma turbulence simulations
Authors: Gahr Constantin , Farcaş Ionuţ-Gabriel , Jenko Frank
Published: November 2024

This paper investigates non-intrusive Scientific Machine Learning (SciML) Reduced-Order Models (ROMs) for plasma turbulence simulations. In particular, we focus on Operator Inference (OpInf) to build low-cost physics-based ROMs from data for such simulations. As a representative example, we consider the (classical) Hasegawa–Wakatani (HW) equations used for modeling two-dimensional electrostatic drift-wave turbulence. For a comprehensive perspective of the potential of OpInf to construct predictive ROMs, we consider three setups for the HW equations by varying a key parameter, namely, the adiabaticity coefficient. These setups lead to the formation of complex and nonlinear dynamics, which makes the construction of predictive ROMs of any kind challenging. We generate the training datasets by performing direct numerical simulations of the HW equations and recording the computed state data and outputs over a time horizon of 100 time units in the turbulent phase. We then use these datasets to construct OpInf ROMs for predictions over 400 additional time units, that is, 400% more than the training horizon. Our results show that the OpInf ROMs capture important statistical features of the turbulent dynamics and generalize beyond the training time horizon while reducing the computational effort of the high-fidelity simulation by up to five orders of magnitude. In the broader context of fusion research, this shows that non-intrusive SciML ROMs have the potential to drastically accelerate numerical studies, which can ultimately enable tasks such as the design of optimized fusion devices.
Direct measurement of the real strength of near-field electric field
Authors: Fan Yihang , Zhao Jianqiao , Yang Fei , Xue Xiaotian , Wang Weipeng , Zhou Ji , Zhang Zhengjun
Published: November 2024

Measurement of the real strength value of near-field electric fields is of great importance for understanding light–matter interactions in nanophotonics, which is a big challenge in the field. We developed in this study a theory and approaches for directly measuring the real strength of near-field electric fields by scattering type scanning near-field optical microscope (s-SNOM). The validity of the theory and approaches was confirmed by comparing s-SNOM measurement results with the finite element method simulations. Our efforts enable s-SNOM as a quantitative tool in clarifying light–matter interactions in a variety of fields, such as all-optical chips, plasmon-induced catalysis, metamaterials and metasurfaces, enhanced spectroscopy, and van der Waals materials, etc.
Laser Thomson scattering measurements indicate non-isothermal magnetic field lines in magnetically shielded Hall effect thrusters
Authors: Betancourt Jean Luis Suazo , Butler-Craig Naia , Lopez-Uricoechea Julian , Steinberg Adam M. , Walker Mitchell L. R.
Published: November 2024

Expected high electron mobility and low resistivity along magnetic field lines—as compared to across magnetic field lines—have led to the assumption, or the reproduction through a solution to the electron energy equation, that magnetic field lines are isothermal in typical plasma simulations for Hall effect thrusters (HETs). However, the inaccessibility of the near-field plasma region and perturbative nature of electrostatic probes have prevented validation of these assumptions in HETs. This manuscript presents non-intrusive measurements of the electron number density and electron temperature along two distinct magnetic field lines in the near-field discharge of a magnetically shielded HET operating at 150 V and 40 A on krypton based on incoherent laser Thomson scattering. The resulting electron temperature and density profiles indicate that the magnetic field lines are not isothermal or isopotential, with percent changes exceeding 100% of the channel centerline electron temperature along each magnetic field line. This observation brings into question the current state of electron models in simulations and what physics are included, or neglected, to produce isothermal magnetic field lines in certain regions.
Effective phonon dispersion and low field transport in AlxGa1−xN alloys using supercells: An ab initio approach
Authors: Datta Animesh , Sharma Ankit , Hosseinigheidari Matinehsadat , Singisetti Uttam
Published: November 2024

To investigate the transport properties in random alloys, it is important to model the alloy disorder using supercells. Although computationally expensive, the local disorder in the system is accurately captured as translational symmetry that is imposed on the system over larger length scales. Additionally, in supercells, the error introduced by self-image interaction between the impurities is reduced. In this work, we have investigated the Effective Phonon Dispersion (EPD) and transport properties, from first principle calculations using supercells in AlxGa1−xN alloy systems. Using an in-house developed code for phonon-band unfolding, the EPD of AlGaN is obtained and the individual phonon modes are identified with good agreement with experimental values. Moreover, we report an in-house developed method to calculate low-field transport properties directly from supercells without phonon band unfolding. First, to validate our methods, we have solved the Boltzmann transport equation using Rode’s method to compare the phonon limited mobility in the 4 atom GaN primitive cell and 12 atom GaN supercell. Using the same technique, we have investigated the low field transport in random AlxGa1−xN alloy systems. The quadrupole interaction is included for transport properties of GaN and AlN to accurately capture the physics in these materials. Our calculations show that along with alloy scattering, electron–phonon scattering may also play an important role at room temperature and high-temperature device operation. This technique opens up the path for calculating phonon-limited transport properties in random alloy systems.
Theoretical investigation of wave transmission and reflection in a 1D dusty plasma chain with impurities
Authors: Shi Lan-Xin , Wei Lin , Yang Yang-Yang , Yang Lei , Duan Wen-Shan
Published: November 2024

The present paper investigates how an envelope solitary wave reflected and transmitted by one or several impurities in an inhomogeneous dusty plasma. By using the nonlinear Schrödinger equation and the molecular dynamics method, both the reflected waves and the transmitted waves due to impurities produced by an incident envelope solitary waves are given in the present paper. The results show that both the reflection and the transmission are usually envelope solitary waves if incident wave is an envelope solitary wave. The numbers of both the reflected and transmitted envelope solitary wave and the amplitudes of each reflected and the transmitted envelope waves depend on both the mass ratio of impurity to the dust particle and the impurity numbers in dust particle chain. This result may have potential applications. For example, both the reflection and the transmission produced by a given incident envelope solitary wave have the information of the number and the mass of the impurity.
Coexistence of analog and digital resistive switching behaviors in TiN/SiNx resistive random access memory device
Authors: Gao Haixia , Zhao Yang , Zhu Shilong , Qiu Xuan , Wang Rui , Guo Jingli , Ma Xiaohua , Yang Yintang
Published: November 2024

The digital–analog hybrid resistive random access memory can not only be used in computing in memory integrated circuits but also adapt to various requirements, such as achieving lower integration complexity. In this work, resistive memory devices with Ta/SiNx/TiN/Pt structures were fabricated, which exhibit a gradual analog or abrupt digital resistive state (DRS) characteristic depending on the different applied voltage range. The experimental results indicate that different RS switching of these devices is due to the change in the conductive mechanism in the SiNx/TiN double-layer structure. The Schottky barrier at the SiNx/TiN interface is the cause of analog resistive state characteristics under low sweeping voltage, while the formation/rupture of the conductive filaments formed under large voltage is the reason for the device to exhibit DRS characteristics.
A data assimilation pressure field measurement method for linear turbine cascades based on compressed sensing
Authors: Yang Yi , Ma Hongwei
Published: November 2024

One of the most dominant measuring techniques for linear turbine cascades is to obtain the high spatial resolution pressure field by a discrete point array. In this work, a compressed sensing (CS) based data assimilation methodology is proposed, by which a set of optimal sparse measuring points can be derived through an optimization procedure. Combined with numerical simulations and the data-driven modal decomposition, the high spatial resolution pressure distribution can be reconstructed accurately with sparse random sampling. To this end, detailed comparative research is conducted. First, the impacts of different sparse bases, including the discrete Fourier transform (DFT), the discrete cosine transform (DCT), and the proper orthogonal decomposition (POD) matrices, and the compression ratio on the reconstruction performance are compared and analyzed systematically under different incidence angles and cascade exit isentropic Mach numbers. Results reveal that a CS approach on POD subspace (CS-POD) performs remarkably better than the CS-DFT and CS-DCT in capturing the spatially continuous pressure distribution, even with a small number of measuring points. Furthermore, effects of the order of truncated POD modes and the number of training dataset required to conduct POD on the error are also investigated that exhibits a downward trend with the rise in these two elements. To overcome the deficiency of randomly selected sparse observation sites with this methodology and the resulting high measuring cost under different conditions, a vectorized CS-POD (Vec-CS-POD) model is constructed to obtain one set of measuring distribution that could satisfy the multi-conditional measurements simultaneously, and its reliability and robustness are validated through cascade experiments. With the aid of the Vec-CS-POD based data fusion framework, spatially resolved end wall pressure fields can be acquired by only a few measuring ports, the number of which can be reduced by 77% compared to the conventional uniform arrangement. The generalization ability of the proposed framework is also validated and evaluated; thus, it exhibits broad potential in other flow field measurements.
Coriolis forces modify magnetostatic ponderomotive potentials
Authors: Kolmes E. J. , Fisch N. J.
Published: November 2024

It is possible to produce a ponderomotive effect in a plasma system without time-varying fields, if the plasma flows over spatial oscillations in the field. This can be achieved by superimposing a spatially oscillatory perturbation on a guide field, then setting up an electric field perpendicular to the guide field to drive flow over the perturbation. However, subtle distinctions in the structure of the resulting electric field can entirely change the behavior of the resulting ponderomotive force. Previous work has shown that, in slab models, these distinctions can be explained in terms of the polarization of the effective wave that appears in the co-moving frame. Here, we consider what happens to this picture in a cylindrical system, where the transformation to the co-moving (rotating) frame is not inertial. It turns out that the non-inertial nature of this frame transformation can lead to counterintuitive behavior, partly due to the appearance of parallel (magnetic-field-aligned) electric fields in the rotating frame even in cases where none existed in the laboratory frame. Apart from the academic interest of this study, the practical impact lies in being better able to anticipate the antenna configuration on the plasma periphery of a cylindrical plasma that will lead to optimal ponderomotive barrier formation in the interior plasma.
High-pressure exciton engineering in two-dimensional metal halide perovskite toward intense deep-blue emission and regulated photocurrent property
Authors: Wei Lin , You Zhaojiang , Meng Xinmiao , Fang Yuanyuan , Li Aisen , Li Shourui , Wang Kai , Li Qian
Published: November 2024

Exciton engineering in two-dimensional (2D) hybrid metal halide perovskites (HMHPs) is crucial for optimizing photoluminescent (PL) and photocurrent (PC) properties, yet it remains a great challenge. In this work, high pressure is applied to accurately control the conversion equilibrium among free carriers (FCs), free excitons (FEs), and trapped excitons in 2D HMHPs of 10% Pb2+-doped BDACdBr4 (BDA = 1, 4-butanediamine). Initial compression induces noticeable interlayer approach and limited intralayer distortion. Reduced self-trapping energy facilitates reverse intersystem crossing of self-trapped excitons (STEs), leading to visible PL transformation from STE to FE emission. Under sufficient compression, phase transition occurs, and significant structural distortions are accompanied by further exciton release. The FE emission is enhanced with more symmetric line shape, achieving intense deep-blue emission that meets the international specification of deep-blue display. Sufficiently decreased binding energy also promotes the dissociation of FEs to simultaneously enhance PC property.
A conditional deep learning model for super-resolution reconstruction of small-scale turbulent structures in particle-Laden flows
Authors: Tofighian Hesam , Denev Jordan A. , Kornev Nikolai
Published: November 2024

Super-resolution reconstruction of turbulent flows using deep learning has gained significant attention, yet challenges remain in accurately capturing physical small-scale structures. This study introduces the Conditional Enhanced Super-Resolution Generative Adversarial Network (CESRGAN) for reconstructing high-resolution turbulent velocity fields from low-resolution inputs. CESRGAN consists of a conditional discriminator and a conditional generator, the latter being called CoGEN. CoGEN incorporates subgrid-scale (SGS) turbulence kinetic energy as conditional information, improving the recovery of small-scale turbulent structures with the desired level of energy. By being aware of SGS turbulence kinetic energy, CoGEN is relatively insensitive to the degree of detail in the input. As shown in the paper, its advantages become more pronounced when the model is applied to heavily filtered input. We evaluate the model using direct numerical simulation (DNS) data of forced homogeneous isotropic turbulence. The analysis of Q-criterion isosurfaces, energy spectra, and probability density functions shows that the proposed CoGEN reconstructs fine-scale vortical structures more precisely and captures turbulent intermittency better compared to the traditional generator. Particle-pair dispersion simulations validate the physical fidelity of CoGEN-reconstructed fields, closely matching DNS results across various Stokes numbers and filtering levels. This paper demonstrates how incorporating available physical information enhances super-resolution models for turbulent flows.
Kinetic of the development of a quantum vortex tangle in superfluids under the influence of thermal activation
Authors: Nemirovskii Sergey
Published: November 2024

The study explores the development of a thermally equilibrated quantum vortex tangle in superfluid liquids under the influence of thermal activation. This problem is of interest to both applied and fundamental research and has been investigated by many authors in various aspects. Despite the important and impressive results obtained, a significant part of the process, namely, the kinetics of processes leading to equilibrium state, remained unexplored. In this article, we conduct a study of kinetic phenomena and focus our attention on the evolution of the vortex line density (VLD) L(t), the total length of the filament per unit volume. The initial development of VLD is due to random thermal fluctuations. The increase in the vortex line length L(t) can be obtained based on the famous Novikov–Furutsu theorem, which shows that the growth rate of L(t) is proportional to a random force correlator. As the length of the vortex filaments increases, the interaction between the vortices becomes significant and affects the dynamics process. At this point, we turn to the phenomenological Feynman–Vinen theory, which offers various models for the evolution of the quantity L(t). Next, we examine the evolution of a vortex tangle as a combination of growth due to random thermal excitations and decay in the Feynman–Vinen theory. Several applications leading to significant and remarkable results are considered.
Transmission electron microscopic study on rutile-type GeO2 film on TiO2 (001) substrate
Authors: Takane Hitoshi , Konishi Shinya , Ota Ryo , Hayasaka Yuichiro , Wakamatsu Takeru , Isobe Yuki , Kaneko Kentaro , Tanaka Katsuhisa
Published: November 2024

Rutile-type GeO2 (r-GeO2) with an ultrawide bandgap of ∼4.7 eV has emerged as a promising material for next-generation power-electronic and optoelectronic devices. We performed transmission electron microscopy (TEM) observation to analyze the structural properties of r-GeO2 film on r-TiO2 (001) substrate at an atomic level. The r-GeO2 film exhibits a threading dislocation density of 3.6 × 109 cm−2 and there exist edge-, screw-, and mixed-type dislocations in the film as demonstrated by two-beam TEM. The edge-type dislocations have Burgers vectors of [100] and/or [110]. The bandgap of the r-GeO2 film is 4.74 ± 0.01 eV as determined by electron energy loss spectroscopy.
Mid-infrared characterization of NbTiN superconducting nanowire single-photon detectors on silicon-on-insulator
Authors: Azem Adan , Morozov Dmitry V. , Kuznesof Daniel , Bruscino Ciro , Hadfield Robert H. , Chrostowski Lukas , Young Jeff F.
Published: November 2024

Superconducting nanowire single-photon detectors are widely used for detecting individual photons across various wavelengths from ultraviolet to near-infrared range. Recently, there has been increasing interest in enhancing their sensitivity to single photons in the mid-infrared spectrum, driven by applications in quantum communication, spectroscopy, and astrophysics. Here, we present our efforts to expand the spectral detection capabilities of U-shaped NbTiN-based superconducting nanowire single-photon detectors, fabricated in a 2-wire configuration on a silicon-on-insulator substrate, into the mid-infrared range. We demonstrate saturated internal detection efficiency extending up to a wavelength of 3.5 μm for a 5 nm thick and 50 nm wide NbTiN nanowire with a dark count rate less than 10 counts per second at 0.9 K and a rapid recovery time of 4.3 ns. The detectors are engineered for integration on waveguides in a silicon-on-insulator platform for compact, multi-channel device applications.
On turning maneuverability in self-propelled burst-and-coast swimming
Authors: Chao Li-Ming , Couzin Iain D. , Li Liang
Published: November 2024

Fish have evolved remarkable underwater turning maneuverability, primarily under active control. This allows them to execute turns within confined spaces, such as during C-start rapid turning. In our study, conducted through computational fluid dynamics simulations of a self-propelled swimmer, we revealed that burst-and-coast swimming patterns can generate various turning behaviors purely through passive fluid–body interactions. The burst-and-coast swimming is characterized by the alternating tail movements between continuous undulating burst phases (bp) and non-undulating or gliding coast phases (cp). Through extensive systematic three-dimensional (3D) simulations, we found that both the burst-and-coast duty cycle—the ratio of burst duration to the total cycle duration—and the swimmer's undulation frequency inhibit turning maneuverability, which is quantified by the curvature of swimming trajectories. We also found there is an optimal Reynolds number that maximizes turning maneuverability. Further analysis suggests that the turning maneuverability is probably due to the persistent presence of the Wagner effect during burst phases and the Magnus effect during coast phases, which differs from the mechanism of actively generating lateral forces by asymmetric continuous flapping. These insights not only advance our understanding of fish locomotion control mechanisms but also provide guidelines for designing underwater robots with improved navigational capabilities.
Numerical investigation of the labyrinth leakage flow on the performance of a compressor cascade
Authors: Xu Wenfeng , Zou Shilong , Li Ao , Zhao Huan , Ren Guozhe , Wang Shengyuan
Published: November 2024

This paper examines the effect of labyrinth seal structure on the evolution of vortex systems and the performance of the cascade. It is found that the labyrinth seal leakage leads to the circumferential development of the separation vortex, and the axial influence region of the concentrated shedding vortex also expands, which increases the flow loss and reduces the diffuser capacity. Among all the cases, the deteriorating effect of the cavity without a labyrinth seal is the most significant. This results in an 83% increase in total pressure loss compared to the prototype cascade. The straight tooth labyrinth and the straight tooth labyrinth with block structures can effectively reduce the leakage from the sealing cavity and weaken the deterioration caused by labyrinth seal leakage. Among these schemes, the straight tooth with block scheme has the most considerable effect, resulting in a 19% reduction in total pressure loss. As the incidence angle increases, the recirculation zone on the end wall of each scheme gradually shrinks toward the leading edge. Meanwhile, the static pressure rises, and the velocity decreases near the leading edge. Compared with the straight tooth scheme, the straight tooth with block scheme can reduce the high-loss zone by 14% at most. In addition, as the sealing clearance gradually increases, the inhibitory effect of the straight tooth with block scheme on the deterioration of cascade performance caused by the labyrinth sealing cavity is gradually enhanced compared to the straight tooth structure. The improvement effect is optimal under 0.5 mm sealing clearance.
Revealing the correlation between asymmetric structure and low thermal conductivity in Janus-graphene via machine learning force constant potential
Authors: Yu Linfeng , Dong Kexin , Yang Qi , Zhang Yi , Zheng Xiong , Wang Huimin , Qin Zhenzhen , Qin Guangzhao
Published: November 2024

Understanding the fundamental link between structure and functionalization is crucial for designing and optimizing functional materials, since different structural configurations could trigger materials to demonstrate diverse physical and chemical properties. However, the correlation between crystal structure and thermal conductivity (κ) remains unclear. In this study, taking two-dimensional (2D) carbon allotropes Janus-graphene and graphene as study cases, we utilize phonon Boltzmann transport equation combined with machine learning potential to thoroughly investigate the complex folding structure of pure sp2 hybridized Janus-graphene from the perspective of crystal structure, phonon modal resolved thermal transport, and atomic interactions, with the goal of identifying the underlying relationship between 2D geometry and κ. The results reveal that the folded structure in Janus-graphene causes strong symmetry breaking, significantly reduces phonon group velocities, increases phonon–phonon scattering, and ultimately leads to low κ. These findings enhance our understanding of how atomic structure folding affects thermal transport and the relationship between structure and functionalization.
Topological insulating phase in nonsymmorphic bulk AX2 (A = Ca, Sr, or Ba; and X = As, Sb, or Bi) compounds
Authors: Purwitasari Winda , Sufyan Ali , Villaos Rovi Angelo B. , Huang Zhi-Quan , Bansil Arun , Lin Hsin , Chuang Feng-Chuan
Published: November 2024

Owing to their unique topologically protected gapless boundary states, topological insulators (TIs) are attracting substantial interest in spintronics and quantum computing. Here, we discuss the structural, electronic, and topological properties of bulk alkaline earth di-pnictides AX2 (where A= Ca, Sr, or Ba and X= As, Sb, or Bi) using first-principles calculations under the hybrid functional approach. Our structural analysis based on phonon dispersion and molecular dynamics calculations establishes the thermodynamic stability of these materials and indicates their potential for synthesis. All investigated compounds are shown to host nontrivial phases upon including spin–orbit coupling. CaAs2, SrSb2, and BaSb2 are found to be strong TIs with sizable bandgaps of up to 213 meV. Nontrivial topology in the case of SrSb2 was further confirmed through surface state computations which showed the presence of gapless surface states. In addition, we demonstrate that using the hybrid functional approach can enhance the accuracy of the calculations to predict experimental findings. Finally, our study suggests that the alkaline earth di-pnictide family would provide a promising materials platform for developing applications of TIs.
Analysis of transition rates from variational flooding using analytical theory
Authors: Cummins David , Longstreth Carter , McCarty James
Published: November 2024

Variational flooding is an enhanced sampling method for obtaining kinetic rates from molecular dynamics simulations. This method is inspired by the idea of conformational flooding that employs a boost potential acting along a chosen reaction coordinate to accelerate rare events. In this work, we show how the empirical distribution of crossing times from variational flooding simulations can be modeled with analytical Kramers’ time-dependent rate (KTR) theory. An optimized bias potential that fills metastable free energy basins is constructed from the variationally enhanced sampling (VES) method. This VES-derived flooding potential is then augmented by a switching function that determines the fill level of the boost. Having a prescribed time-dependent fill rate of the flooding potential gives an analytical expression for the distribution of crossing times from KTR theory that is used to extract unbiased rates. In the case of a static boost potential, the distribution of barrier crossing times follows an expected exponential distribution, and unbiased rates are extracted from a series of boosted simulations at discrete fill levels. Introducing a time-dependent boost that increases the fill level gradually over the simulation time leads to a simplified procedure for fitting the biased distribution of crossing times to analytical theory. We demonstrate the approach for the paradigmatic cases of alanine dipeptide in vacuum, the asymmetric SN2 reaction, and the folding of chignolin in explicit solvent.
High-order discontinuous Galerkin method with immersed boundary treatment for compressible flows on parallel adaptive Cartesian grids
Authors: Qi Xinyu , Wang Zhenming , Zhu Jun , Tian Linlin , Zhao Ning
Published: November 2024

Adaptive mesh refinement (AMR) technology and high-order methods are important means to improve the quality of simulation results and have been hotspots in the computational fluid dynamics community. In this paper, high-order discontinuous Galerkin (DG) and direct DG (DDG) finite element methods are developed based on a parallel adaptive Cartesian grid to simulate compressible flow. On the one hand, a high-order multi-resolution weighted essentially nonoscillatory limiter is proposed for DG and DDG methods. This limiter can enhance the stability of DG/DDG methods for compressible flows dominated by shock waves. It is also compact, making it suitable for the implementation of AMR with frequent refinement/coarsening. On the other hand, a coupling method of DG and immersed boundary method is proposed to simulate flow around objects. Due to the compactness of DG, the physical quantities of image points can be directly obtained through the DG/DDG polynomial of the corresponding cells. It avoids the wide interpolation stencil of traditional IBM and makes it more suitable for the parallel adaptive Cartesian grid framework in this paper. Finally, the performance of the proposed method is verified through typical two- and three-dimensional cases. The results indicate that the method proposed in this paper has low numerical dissipation in smooth areas and can effectively handle compressible flow dominated by discontinuities. Moreover, for transonic flow over a sphere, the error of results between the proposed method and direct numerical simulation is within 1%, fully validating the accuracy of the method presented in this paper.
Streaming flows within ultrasonic levitators
Authors: Wang Tianyi , Lv Qimeng , Hardalupas Yannis
Published: November 2024

The streaming flows inside a single-axis ultrasonic levitator are experimentally investigated using particle imaging velocimetry (PIV). Detailed quantification of the flow motion within the levitator is provided for both scenarios, with and without a suspended droplet. In the case of suspended droplets, both water and ethanol are studied to investigate the varying external streaming around droplets with different volatilities. The quantified PIV results reveal two acoustically induced jet flows, originating from the transducer and reflector, within the empty levitator in the absence of a suspended droplet. These flows, identified as Eckart streaming, dominate the external streaming around less-volatile water droplets by directly interacting with their surfaces. For highly volatile ethanol droplets, the Stefan flow, which carries ethanol vapor away from the droplet surface, is clearly observed. This flow counteracts the motion of Eckart streaming within the levitator, preventing it from reaching the surface of the ethanol droplet. This observation confirms the presence of Stefan flow around a highly volatile droplet in the ultrasonic levitator. The interaction between Stefan flow and Eckart streaming determines the external streaming patterns of the ethanol droplet, which significantly differ from those around water droplets. Additionally, boundary-driven acoustic streaming near the droplet surface, also known as Rayleigh–Schlichting streaming, can only develop in the presence of a strong Stefan flow leaving from the highly volatile ethanol droplets. In contrast, without the “protection” of this robust Stefan flow, the boundary-driven streaming around less volatile water droplets are swept away by Eckart streaming within the levitator. This study emphasizes the importance of considering both Eckart streaming and Stefan flow when modeling the transport phenomena of droplets suspended in single-axis ultrasonic levitators. The differences in external streaming patterns between less volatile and highly volatile droplets may influence their corresponding heat and mass transfer processes in the levitator.
Effect of temperature on the performance of ScAlN/GaN high-electron mobility transistor
Authors: Hasan Md Tanvir , Liu Jiangnan , Wang Ding , Mondal Shubham , Tanim Md Mehedi Hasan , Yang Samuel , Mi Zetian
Published: November 2024

We have studied the operation of the ScAlN/GaN high-electron mobility transistor (HEMT) at high temperatures up to 700 K (423 °C). A maximum drain current density of ∼2 A/mm and an on-resistance of ∼1.5 Ω·mm was measured at room temperature (RT). The epi-structure exhibited a very high two-dimensional electron gas (2DEG) density of 6 × 1013 cm−2 at RT using Hall measurement. The Sc0.15Al0.85N barrier, nearly lattice matched to the GaN channel, showed a drain current reduction of ∼50% at 700 K. The decrease in 2DEG mobility, which leads to an increase in sheet resistance, is mostly responsible for this reduction in drain current. However, an excellent electrostatic control was achieved at 700 K with the drain current value exceeding 1 A/mm, which is 2 times higher compared to that of AlGaN/GaN HEMTs reported previously. These results indicate that ScAlN/GaN HEMTs are a promising candidate for high-temperature and high-power electronic applications.
Heat transport enhancement by rotating bottom endwall in a cylindrical Rayleigh–Bénard convection
Authors: Yang Wen , Deng Pei-Yan , Wu Jian-Zhao
Published: November 2024

Rotating thermal convection, commonly encountered in natural and industrial environments, is typically influenced by both buoyancy forces and boundary rotation. In this study, we conduct direct numerical simulations to explore the effect of rotating bottom on the flow structure and heat transport of Rayleigh–Bénard convection (RBC) in a cylindrical cavity. This cavity has a radius-to-height ratio of 1 and is filled with an incompressible fluid with a Prandtl number of 0.7. Our results show that the axisymmetric convection pattern, observed in RBC for Ra∈[4000,8000] without rotation, transitions into a double roll structure at low rotating speeds (ω), while for Ra≤4000, the pattern remains axisymmetric, independent of ω. We then focus on the impact of bottom rotation on heat transport in the axisymmetric regime. Based on the variation in the Nusselt number (Nu) with ω, two distinct regimes are identified: a convection-dominated regime at low ω, where Nu closely resembles that of standard RBC, and a rotation-dominated regime at high ω, where strong shear induced by the rotating bottom intensifies the meridional circulation, significantly boosting global heat flux. The critical rotating speed, ω*, marking the transition between these regimes, follows different power-law relations below and above the buoyant convection onset (Rac): ω*∼Ra−0.64 for RaRac. As ω increases, the exponents for Nu∼Raλ and Re∼Raγ evolve before converging to λ≈0.3 and γ=0.5, respectively. Scaling laws for Nu and Re as functions of ω and Ra in the rotation-dominated regime are finally derived: Nu∼Ra0.3ω0.64 and Re∼Ra0.5ω.
Internal energy consumption analysis of counter-rotating axial-flow compressor based on entropy production theory
Authors: Zhang Jinya , Tan Zheng , Xue Zhicheng
Published: November 2024

Counter-rotating wet gas compressor is an ideal equipment for pressurizing natural gas in offshore gas fields. It has a compact structure, a wide range of operating conditions, and a certain liquid tolerance in the process of gas pressurization. However, due to the opposite rotation of the adjacent rotors, and the characteristics of the flow containing liquid, it is also easy to lead to flow separation in its interior and then produce obvious energy dissipation. In this paper, the numerical simulation of the internal flow field of counter-rotating axial-flow compressor under dry and wet conditions is carried out. The entropy production theory based on the second law of thermodynamics is introduced to analyze the energy consumption of the compressor, and the high energy consumption area in the internal flow field of the compressor is accurately located. Then, the energy consumption of this area is evaluated quantitatively and qualitatively. The entropy production and its proportion of each component under different working conditions, the distribution of the entropy production of each rotor along the flow direction, and the radial distribution under the near-stall state are obtained. The calculation results show that the entropy production of upstream rotor and downstream rotor in the total entropy production is 29.19%–31.41% and 59.48%–62.61% under dry gas conditions, respectively. Under wet conditions, the proportions are 28.20%–30.67% and 60.02%–63.33%, respectively. The wet gas droplets can increase the momentum input to the low energy region of 0.7–0.9 relative position of the suction surface of the upstream rotor and improve the flow field in this region. However, it can also exacerbate flow separation in the front middle of the downstream rotor, causing additional energy loss.
Calculation of divergenceless magnetically induced current density in molecules
Authors: Monaco Guglielmo , Summa Francesco F. , Zanasi Riccardo , Berger Raphael J. F.
Published: November 2024

A method for the calculation of divergenceless, magnetically induced quantum mechanical current densities in molecules that approximates the exact current is presented. This was achieved by adding to the calculated conventional current density, i.e., a current that typically has a non-zero divergence, a corrective term that is the negative of the irrotational field of its Helmholtz decomposition. The solenoidal field of the decomposition is the divergence-free current density, which is still an approximation of the exact current but which now satisfies the continuity requirement regardless of the quality of the basis set. Based on calculations performed on several simple molecules (LiH, H2O, benzene, and zethrene), adopting different kinds of low-level theoretical approaches, clear improvements are observed in the correspondence of vortices, sources, and sinks for which the conventional current density shows a lack of continuity. A little improvement is also observed for the calculated diagonal components of the magnetizability tensor.
Evolution and propagation characteristics of the wake induced by an underwater vehicle moving in two layers of fluid: A parametric study
Authors: Gao Gang , Pan Yanyan , Wang Yun , Shen Zhiben , Cao Liushuai , Wan Decheng
Published: November 2024

This paper utilizes overlapping grids and large eddy simulation to numerically investigate the self-propulsion of an underwater vehicle in a two-layer fluid. The study focuses on the evolution and propagation of the flow field at both fluid interfaces and conducts a parametric analysis of the Froude number (Fr), submergence depth (h), and density ratio (γ). Particular attention is paid to variations in wave height at the free surface (η1) and internal interface (η2), and surface divergence (div). The distribution of the pressure coefficient on the hull surface and the vortex structures behind the vehicle are also examined. The findings show that as Fr increases from 0.221 to 0.886 and h decreases from 0.09 m to 0.02 m, the wave pattern at the free surface shifts from transverse to predominantly divergent wave, with more rapid lateral propagation. At h = 0.02 and 0.03 m, the surface divergence forms a distinct spindle-shaped pattern, and internal waves occupy a significant region behind the vehicle. Regarding γ, the results vary with the vehicle's position. In the upper fluid layer, η1max, η1min, η2max, η2min, divmax, and divmin show a strong positive correlation with γ. Conversely, in the lower fluid layer, these parameters exhibit an almost linear negative correlation, and the relationships η1min = −1.51γ + 1.94, η2max = −0.55γ + 2.81, η2min = −3.40γ + 4.66, and divmin = −1.38γ + 1.90 are satisfied. Specifically, from γ  =  0.50 to γ  =  1.00, η1max, η1min, divmax, and divmin decrease by 62.84%, 62.55%, 9.04%, and 47.89%, respectively.
Temporal variation in utilisation distribution and direction distribution of dugong feeding trails in intertidal seagrass beds in Talibong Island, Thailand: an insight into dugong feeding routes
Authors: Yamato Chiaki , Ichikawa Kotaro , Kittiwattanawong Kongkiat , Arai Nobuaki
Published: November 2024

Context A better understanding of animal habitat use informs fundamental ecology and can provide underpinnings for effective management. Aims This study explored the temporal variation in feeding ground utilisation by dugongs (Dugong dugon) in two intertidal seagrass beds in Talibong Island, Thailand (Sites A and B), focusing on the distribution and direction of dugong feeding trails. Methods Drone-based aerial photography was conducted quarterly over 1 year and daily over 2 weeks to observe feeding trails and behaviour. Key results During five and seven separate photography periods over 1 year, 0.04 ± 0.01% (range: 0.03–0.06%) of Site A (200,000 m2) was covered with new feeding trails daily, while 0.35 ± 0.31% (range: 0.07–0.96%) of Site B (278,000 m2) was covered daily. This temporal variation in the feeding trail area corresponded to that in seagrass coverage. Daily observations over 2 weeks during six separate photography periods revealed a significant decrease in overlapping rates (intersection over union) of the core areas (50% kernel density estimation [KDE]) as time elapsed. The 1-year observation highlighted relatively higher overlapping rates of home ranges (95% KDE) (Site A: 0.27 ± 0.09; Site B: 0.49 ± 0.08) and low overlapping rates of core areas (Site A: 0.02 ± 0.03; Site B: 0.09 ± 0.09). The relative frequencies of the feeding trail direction remained consistent across survey seasons, and the most and least dominant directions were common across all survey seasons and sites. The circular correlation coefficient between the directions of dugong body axis and the estimated tidal current was 0.45, suggesting that feeding generally occurred in the upstream direction. The direction and spatial range of dugong feeding may be affected by temporally consistent factors. One factor that can affect the feeding direction is the tidal current. Conclusions Overall, dugongs may feed and move within seagrass beds in a temporally consistent manner, even when there are shifts in feeding hotspots. Implications This research enhances our understanding of how dugongs utilise their feeding grounds and highlights the importance of not only identifying feeding hotspots but also predicting their feeding routes by considering the direction and distribution of feeding trails.
Cultural evolution: Where we have been and where we are going (maybe)
Authors: Boyd Robert , Richerson Peter J.
Published: November 2024

The study of cultural evolution using ideas from population biology began about 50 y ago, with the work of L.L. Cavalli-Sforza, Marcus Feldman, and ourselves. It has grown from this small beginning into a vital field with many publications and its own scientific society. In this essay, we give our perspective on the origins of the field and current unanswered questions.
Forward and backward modeling of cultural evolutionary processes
Authors: Wakano Joe Y. , Aoki Kenichi
Published: November 2024

Modern cultural evolution theory adopts a variety of concepts and methods developed in mathematical biology, in particular population genetics theory. In addition to forward-looking approaches such as two-locus models, backward-looking approaches such as coalescent theory, which describe ancestral states of the current population, have played an important role in population genetics. Here, we show how forward and backward approaches can be applied to two examples in cultural evolution. The first example deals with the number of cultural traits, which can be analyzed by a backward approach. Cultural coalescent theory illustrates many unique aspects of cultural processes such as information transfer (i.e., social learning) from many donors (“cultural parents”), including or excluding the biological parents. Theory predicts that many cultural traits of intermediate (or higher) frequency (popularity) can exist that are surprisingly old. Many unsolved issues remain, however, such as how to incorporate social structure as well as natural and/or cultural selection, which we believe to be an urgent agenda. The second example is the punishment of sibling incest, a problem to which cultural coalescent theory cannot currently be usefully applied. By analyzing forward recursions, we show that punishment is ineffective in suppressing incest, unless the incestuous inclination is diminished by the presence of punishers. Based on these examples, we discuss the merits and demerits of forward and backward approaches.
How cultural innovations trigger the emergence of new pathogens
Authors: Pooladvand Pantea , Kendal Jeremy R. , Tanaka Mark M.
Published: November 2024

Cultural practices perceived to be adaptive—from clearing land for food production to medical innovations—can disseminate quickly through human populations. However, these same practices often have unintended maladaptive effects. A particularly consequential effect is the emergence of diseases. In numerous instances, a cultural change is followed by the appearance of a new pathogen. Here, we develop mathematical models to analyze the population processes through which cultural evolution precipitates the emergence of a new disease. We find that when a risk-bearing cultural practice spreads, emergence can be an unavoidable cost even if a safer alternative practice eventually evolves from the original. Social learning and a fitness advantage associated with the evolving practice drive early disease emergence but the two factors have distinct effects on the time to mutation of the pathogen and significant stochastic variation is observed. For example, a disease can take longer to emerge in a population that adopts the risk-bearing practice quickly than in a population that is slow to transition. Extending the model to explore the effects of an alternative practice evolving from the original, we find a nonmonotonic relationship between relative risk of the two practices and the median time to disease emergence. Our findings contribute to understanding how cultural evolution can shape pathogen evolution and highlight the unpredictability of disease emergence.