bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient skin friction behavior associated with hemisphere-based vortex ring collisions
Authors: New T. H. , Xu Bowen , Shi Shengxian
Published: May 2024

Global and local transient skin friction variations resulting from a large-eddy simulation study on ReΓ0=3000 vortex rings colliding with surface-mounted hemispheres of hemisphere-to-vortex-ring diameter-ratios of 0.5≤D/d≤2 are investigated here. Skin friction distribution changes due to the approaching primary vortex ring, formation of secondary/tertiary vortex rings, subsequent mutual interactions between various vortex ring structures, and azimuthal instabilities are clarified with a view to better establish their relationships when the relative hemisphere size varies. Results show that the primary vortex ring produces the highest skin friction levels when it is close to or collides with the hemisphere/flat wall. Additionally, entrainment of wavy secondary/tertiary vortex rings leads to them entangling around the primary vortex ring and resulting in segmented skin friction regions at later stages of the collision process, regardless of the diameter-ratio. Unlike smaller hemispheres, the largest D/d=2 hemisphere here restricts all skin friction changes along its surface with the flat wall unaffected. It is also revealed here that while the diameter-ratio governs the global skin friction distributions, how secondary/tertiary vortex rings interact with the primary vortex ring and how azimuthal instabilities manifest and evolve for all the various vortex rings confer strong influences on the breaking-up and dissipation of regions with high skin friction levels.
Boosting radio frequency radiation with collisional processes in picosecond laser filamentation
Authors: Thornton E. , Garrett T. , Elle J.
Published: May 2024

When focused in air, ultrashort pulse lasers generate a plasma that produces ultrabroadband radio frequency (RF) radiation via both ponderomotive and plasma wake field current mechanisms. We have performed experiments with high energy pulses and pulse durations up to 5 ps, while holding the power constant. These longer pulses drive much higher electron densities and temperatures, especially as collisional processes become important, and we in turn have measured substantially increased RF generation. We have also developed a Drude numerical model of the ionization within the laser pulse, the heating due to collisions, and the ensuing current density evolution. We find that the low frequency scaling of the simulated current matches the experimental data, which indicates that the ponderomotive currents dominate the RF generation for these atmospheric pressure plasmas. However, the experimentally measured spectra also show an additional low frequency (1–10 GHz) component that grows with laser pulse length, which is consistent with the plasma wake surface wave RF also becoming important as the plasma temperature approaches 100 eV.
Influence of rheological parameters on the performance of the aerated coaxial mixer containing a pseudoplastic fluid
Authors: Rahimzadeh Ali , Ein-Mozaffari Farhad , Lohi Ali
Published: May 2024

Gas dispersion in non-Newtonian fluids has numerous applications in many chemical and biochemical applications. However, the effect of the power-law model constants describing the rheological behavior of the pseudoplastic fluid has never been investigated. Thus, a numerical model was developed to simulate the hydrodynamics of gas dispersion in non-Newtonian fluids with a coaxial mixer. Then, a set of experiments was conducted to assess the mass transfer efficacy of a coaxial mixer to benchmark the numerical model. In this regard, various methods, including dynamic gassing-in and electrical resistance tomography methods, were used to quantify the mass transfer and gas hold-up profiles. The influence of fluid rheological properties, gas flow number, and rotating mode on the power consumption, mass transfer coefficient, bubble size profile, and hydrodynamics were examined both experimentally and numerically. The response surface model (RSM) was employed to explore the individual effects of power-law model constants on mass transfer. The RSM model utilized five levels for the consistency index (k), five levels for the flow index (n), and three levels for the gas flow number. The statistical model proposed that the absolute model constants for the flow and consistency indices were 0.0012 and 0.0010, respectively, for the co-rotating mixer. Conversely, for the counter-rotating mixer, these constants were 0.0010 and 0.0013, respectively. Therefore, this study revealed that the co-rotating coaxial mixer was well-suited for dispersing gas within a fluid with high consistency. In contrast, the counter-rotating mixer proved effective in enhancing gas dispersion within a fluid with a lower flow index.
High performance CH3NH3PbI3 perovskite photodetector functionalized by T-Ag plasmonic nanostructure
Authors: Jiang Jianwei , Ye Xinyi , Ma Chi , Lou Huan
Published: May 2024

Photodetectors with ultrathin thickness and high efficiency are increasingly needed in the developing of wearable devices. However, the very limited active layer thickness has seriously restricted the photoelectric conversion efficiency. Here, the optical nanostructure fabricated with the assistance of self-assembly polystyrene mask layer has been integrated to increase the light absorption capacity by simultaneously utilizing the local surface plasma resonance, gap plasma, and the microcavity resonance effect. With the incorporation of triangular silver (T-Ag) nanostructure, the photogenerated current and response speed have significantly enhanced 481.25% and 26.30%, respectively. This strategy provides a viable way to design high-efficiency ultra-thin photodetectors.
Numerical study on the effect of smoke emitted from the vents on the roof of a diesel train on the intake of downstream air-conditioning units
Authors: Chen Chunjiang , Zhang Qiyue , Li Zhuojun , Ma Yamin , Xu Liangzhong , Gong Weisi , Niu Jiqiang
Published: May 2024

Constrained by economic development and geographical features, numerous railway lines remain unelectrified, underscoring the expansive potential of diesel trains. Diesel engine emissions discharged from the roof of trains pose a challenge as some of the smoke infiltrates the cabin through the intake of roof-mounted air-conditioning units (ACUs). This intrusion diminishes the indoor air quality, posing health risks to passengers and potentially jeopardizing their safety. This study employs the shear stress transport k-omega turbulence model to formulate a multiphase flow model for simulating smoke diffusion in diesel trains. Additionally, we conducted an optimization design to minimize smoke entry into the ACUs. This study defined six cases based on variations in the shape and height of the cover and the spacing of the smoke vents. The results show that the effect of the diffusion characteristics decreased with the cover height. With the progression of airflow diffusion, the effect of the smoke vent structure on the concentration diminished farther from the vents. The minimum smoke mass flow rate into the intake occurred with the vent spacing of 2.14 m and without a cover, resulting in a 57.0% decrease compared with the maximum. Thus, a smoke vent spacing of 2.14 m without a cover was deemed to be the optimal configuration. The research results provide certain engineering guidance significance for the design and operation of train-smoke vent structures.
An improved continuum model for hypersonic thermal nonequilibrium flow in the near-continuum regime
Authors: Jia Yubin , Chen Jie , Ou Jihui
Published: May 2024

In this work, the rarefied Couette flow of diatomic gases with thermal nonequilibrium effects is investigated by the direct simulation Monte Carlo (DSMC) method, and a macroscopic computational model is developed to consider the local rarefaction effects for diatomic gases in the near-continuum regime. The nonlinear transport properties of the diatomic gases are studied, indicating that effective viscosity and effective translational thermal conductivity in the shear nonequilibrium state are affected by translational nonequilibrium effects, which obey the same laws for both monatomic and diatomic gases. The transport coefficients of internal energy modes are affected by both translational nonequilibrium and internal energy relaxation, therefore, the effective rotational and vibrational thermal conductivities are related to the effective viscosity through a modified Eucken relation that accounts for internal energy relaxation. Conclusively, effective constitutive relations are newly established as a function of the shear nonequilibrium parameter and the modified Eucken factors for thermal nonequilibrium flows, and these are integrated into the macroscopic two-temperature model. Subsequently, it is assessed in the simulation of hypersonic flows over flat plates and cylinders at various Knudsen numbers. The results show that the surface shear stress and heat flux obtained by the proposed model agree well with the DSMC results, indicating significantly improved performance compared to the conventional Navier–Stokes two-temperature model for hypersonic flows in the near-continuum regime.
Variation of vortical structures across shock-wave/turbulent boundary-layer interaction region in a compression ramp flow
Authors: Dong Zhen-xun , Pan Chong , Tong Fu-lin , Yuan Xian-xu
Published: May 2024

This paper describes direct numerical simulations of a shock-wave/turbulent boundary-layer interaction (STBLI) process in a compression-ramp flow with a ramp angle of 24° and a free-stream Mach number of Ma∞=2.9. Spectral analysis, two-point cross correlation, convection velocity statistics, and individual vortex identification are used to elucidate the streamwise variation of multiscale turbulent structures in the STBLI process. Typical Lagrangian coherent structures in the turbulent boundary layer before the STBLI region are characterized as hairpin-like vortical structures, with heads that rise together with the separated mean flow in the STBLI region. In the downstream region, the reattached turbulent boundary layer has a two-layer structure. The outer layer is characterized as an intensification of large-scale velocity structures, which is attributed to the shock-wave-induced compression effect on vortical structures. A viscous-dominated layer develops independently in the vicinity of the wall, leading to a gradual restoration of the wall-shear effect that accumulates the inner-layer dynamics of small-to-moderate-scale turbulent motions.
Extreme near-field heat transfer between silica surfaces
Authors: Rajabpour Ali , El Hajj Julien , Gómez Viloria Mauricio , Messina Riccardo , Ben-Abdallah Philippe , Guo Yangyu , Merabia Samy
Published: May 2024

Despite recent experiments exhibiting an impressive enhancement in radiative heat flux between parallel planar silica surfaces with gap sizes of about 10 nm, the exploration of sub-nanometric gap distances remains unexplored. In this work, by employing non-equilibrium molecular dynamics (NEMD) simulations, we study the heat transfer between two SiO2 plates in both their amorphous and crystalline forms. When the gap size is 2 nm, we find that the heat transfer coefficient experiences a substantial ∼30-fold increase compared to the experimental value at the gap size of 10 nm confirming the dependence on the distance inversely quadratic as predicted by the fluctuational electrodynamics (FE) theory. Comparative analysis between NEMD and FE reveals a generally good agreement, particularly for amorphous silica. Spectral heat transfer analysis demonstrates the profound influence of gap size on heat transfer, with peaks corresponding to the resonances of dielectric function. Deviations from the fluctuational electrodynamics theory at smaller gap sizes are interpreted in the context of acoustic phonon tunneling and the effects of a gradient of permittivity close to the surfaces.
Core release dynamics of double-emulsion droplets induced by temperature gradient
Authors: Wang Zhibin , Wang Yilin , Qin Jingyi , Chen Zhanzhu , Ding Bin , Chen Ying
Published: May 2024

The thermocapillary-driven core release of double-emulsion droplets offers advantages such as simplicity in implementation and a broad range of applications, providing unique strengths in the field of core component release. However, the characteristics and mechanisms related to thermocapillary-driven core release were still unknown. This article employed the Volume of Fluid method to investigate the core release characteristics of double-emulsion droplets driven by thermocapillary. The range of Marangoni (Ma) numbers is from 10 to 500. The results indicate that effective control of the migration and release dynamics of double-emulsion droplets can be achieved through viscosity regulation, which induces the obvious difference between the two types of double-emulsion droplets. The regulation of both viscosity and surface tension is efficient in controlling the release type of the core. A phase diagram distinguishing between one-off and two-off release types is presented. Additionally, by characterizing dimensionless numbers, a formula for the characteristic release time of double-emulsion droplets is derived. The current study contributes to achieving precise control of double-emulsion droplets, expanding the scope of applications for double-emulsion droplets and establishing a fundamental groundwork for subsequent investigations into the release methods of double-emulsion droplets driven by thermocapillary.
Two-dimensional electron gases in AlYN/GaN heterostructures grown by metal–organic chemical vapor deposition
Authors: Streicher Isabel , Straňák Patrik , Kirste Lutz , Prescher Mario , Müller Stefan , Leone Stefano
Published: May 2024

Wurtzite AlN alloyed with group 3 elements Sc and Y boosts the performance of GaN-based high-electron-mobility transistors (HEMTs) significantly as they increase the spontaneous polarization of the barrier layer and, thus, enhance the charge carrier density ns in the two-dimensional electron gas (2DEG) formed at the interface with the GaN channel. The emerging nitride Al1−xYxN additionally features an a lattice parameter matching to that of GaN at x = 0.07–0.11, allowing for the growth of strain-free barriers. Here, we demonstrate the growth of Al1−xYxN/GaN heterostructures for HEMTs by metal–organic chemical vapor deposition for the first time. The effect of the Y concentrations on the 2DEG is investigated in a Y concentration range from 3% to 15%. At 8% Y, a record mobility of 3200 cm2/(Vs) was measured at a low temperature (7 K). Room and low-temperature ns was at 1–2 × 1013 cm−2. Al0.92Y0.08N barriers were coherently strained to the GaN channel for barrier thicknesses from 5 to 15 nm. Finally, the deposition of Al1−xYxN/GaN heterostructures deposited on 4″ 4H–SiC wafers had a room-temperature mobility close to 1400 cm2/(Vs). AlYN/GaN heterostructures may offer advantages over AlScN/GaN heterostructures not only for the lower price and higher abundance of the raw material but also in terms of electrical characteristics and may be more suitable for power amplifying applications due to increased electron mobility.
Stochastic distinguishability of Markovian trajectories
Authors: Pagare Asawari , Zhang Zhongmin , Zheng Jiming , Lu Zhiyue
Published: May 2024

The ability to distinguish between stochastic systems based on their trajectories is crucial in thermodynamics, chemistry, and biophysics. The Kullback–Leibler (KL) divergence, DKLAB(0,τ), quantifies the distinguishability between the two ensembles of length-τ trajectories from Markov processes A and B. However, evaluating DKLAB(0,τ) from histograms of trajectories faces sufficient sampling difficulties, and no theory explicitly reveals what dynamical features contribute to the distinguishability. This work provides a general formula that decomposes DKLAB(0,τ) in space and time for any Markov processes, arbitrarily far from equilibrium or steady state. It circumvents the sampling difficulty of evaluating DKLAB(0,τ). Furthermore, it explicitly connects trajectory KL divergence with individual transition events and their waiting time statistics. The results provide insights into understanding distinguishability between Markov processes, leading to new theoretical frameworks for designing biological sensors and optimizing signal transduction.
Advancements in predicting scour depth induced by turbulent wall jets: A comparative analysis of mathematical formulations and machine learning models
Authors: Devi Kamalini , Khuntia Jnana Ranjan , Mumtaz Mohd Aamir , Elgamal Mohamed H. , Shankar Das Bhabani
Published: May 2024

This study examines the scour depth induced by turbulent wall jets and proposes novel mathematical formulations to predict the depth of scouring. Through a comprehensive gamma test, key parameters influencing the scour depth are identified, including the apron length, densimetric Froude number, median sediment size, tailwater level, Reynolds number, and Froude number of the jet. Regression analysis is subsequently conducted to establish relationships between the dependent parameter and the aforementioned independent variables. A comparative analysis is then undertaken between the measured scour depths and those predicted by existing equations from previous studies. Furthermore, predictive models leveraging the support vector machine, artificial neural network with particle swarm optimization, M5 tree algorithm, gene expression programming, and adaptive neuro-fuzzy inference system (ANFIS) are developed using the collected data. Statistical metrics are employed to evaluate the performance of each model and the regression equation. The effectiveness of each model in predicting scour depth is demonstrated. Notably, ANFIS yields a coefficient of determination of 0.809 and a root mean square error (RMSE) of 1.585. Multi-nonlinear regression analysis exhibits a coefficient of determination of 0.752 and an RMSE of 0.421, while the M5 tree achieves a coefficient of determination of 0.739 and an RMSE of 1.874, demonstrating superior performance compared to other machine learning techniques and regression equations employed in this study.
A bionic mimosa soft robot based on a multi-responsive PNIPAM-PEGDA hydrogel composition
Authors: Yang Wenguang , Wang Xiaowen , Teng Xiangyu , Qiao Zezheng , Yu Haibo , Yuan Zheng
Published: May 2024

Deformation plays a vital role in the survival of natural organisms. One example is that plants deform themselves to face the sun for sufficient sunlight exposure, which allows them to produce nutrients through photosynthesis. Drawing inspiration from nature, researchers have been exploring the development of 3D deformable materials. However, the traditional approach to manufacturing deformable hydrogels relies on complex technology, which limits their potential applications. In this study, we simulate the stress variations observed in the plant tissue to create a 3D structure from a 2D material. Using UV curing technology, we create a single-layer poly(N-isopropylacrylamide) hydrogel sheet with microchannels that exhibit distinct swelling rates when subjected to stimulation. After a two-step curing process, we produce a poly(N-isopropylacrylamide)–polyethylene glycol diacrylatedouble-layer structure that can be manipulated to change its shape by controlling the light and solvent content. Based on the double-layer structure, we fabricate a dual-response driven bionic mimosa robot that can perform a variety of functions. This soft robot can not only reversibly change its shape but also maintain a specific shape without continuous stimulation. Its capacity for reversible deformation, resulting from internal stress, presents promising application prospects in the biomedical and soft robotics domain. This study delivers an insightful framework for the development of programmable soft materials.
Nanofluid cooling of a hot rotating circular cylinder employing cross-flow channel cooling on the upper part and multi-jet impingement cooling on the lower part
Authors: Selimefendigil Fatih , Larguech Samia , Ghachem Kaouther , Albalawi Hind , Alshammari Badr M. , Labidi Taher , Kolsi Lioua
Published: May 2024

This study explores the convective cooling features of a hot rotating cylinder by using the combined utilization of cross-flow on the upper part and multi-jet impingement on the bottom part. The analysis is performed for a range of jet Reynolds number (Re) values (between 100 and 500), cross-flow Re values (between 100 and 1000), rotational Re values (between −1000 and 1000), cylinder size (between 0.25wj and 3wj in radius), and center placement in the y direction (between −1.5wj and 1.5wj). When the cylinder is not rotating, the average Nu increment becomes 102% at the highest jet Re, while it becomes 140.82% at the highest cross-flow Re. When rations become active, the impacts of cross-flow and jet impingement cooling become slight. As compared to a motionless cylinder, at the highest speed of the rotating cylinder, the average Nu rises by about 357% to 391%. For clockwise rotation of the cylinder, a lager cylinder results an increase in the average Nu by about 86.3%. At the lowest and highest cross-flow impinging jet Re value combinations, cooling performance improvement becomes a factor of 8.1 and 2, respectively. When the size of the cylinder changes, entropy generation becomes significant, while the vertical location of the cylinder has a slight impact on entropy generation.
A unified quantification of synchrony in globally coupled populations with the Wiener order parameter
Authors: Pikovsky Arkady , Rosenblum Michael
Published: May 2024

We tackle the quantification of synchrony in globally coupled populations. Furthermore, we treat the problem of incomplete observations when the population mean field is unavailable, but only a small subset of units is observed. We introduce a new order parameter based on the integral of the squared autocorrelation function and demonstrate its efficiency for quantifying synchrony via monitoring general observables, regardless of whether the oscillations can be characterized in terms of the phases. Under condition of a significant irregularity in the dynamics of the coupled units, this order parameter provides a unified description of synchrony in populations of units of various complexities. The main examples include noise-induced oscillations, coupled strongly chaotic systems, and noisy periodic oscillations. Furthermore, we explore how this parameter works for the standard Kuramoto model of coupled regular-phase oscillators. The most significant advantage of our approach is its ability to infer and quantify synchrony from the observation of a small percentage of the units and even from a single unit, provided the observations are sufficiently long.
Spatially resolved work-function manipulation of azobenzene-functionalized self-assembled monolayers by optical stimulation
Authors: Böhnke Jan , Andres Beatrice , Boie Larissa , Richter Angela , Gahl Cornelius , Weinelt Martin , Bronsch Wibke
Published: May 2024

Strongly differing static dipole moments of the trans and cis isomers of photochromic azobenzene allow for optical switching of the work function of azobenzene-functionalized self-assembled monolayers (SAMs). We apply these properties in a fundamental experiment to manipulate the area size of the switched SAM. Azobenzene molecules were excited by ultraviolet laser illumination, and the transient isomerization profile of the SAM was spatially resolved recording photoemission electron microscopy images. Thereby, we demonstrate the spatial tuning of the SAM's work function and discuss the role of the laser spot profile in generating sharp edges or gradual changes of the work function.
Analytical solutions for hydrodynamic responses of arrays of floating truncated cylinders using multi-term Galerkin method and its application to a new wave energy converter device
Authors: Kang Yuanshun , Zeng Xiaohui , Cui Zhehua , Chen Jiahao
Published: May 2024

In the context of linear water wave theory, the analytical solutions for the diffraction and radiation of a truncated cylinder array are developed in the presence of ambient incident waves. Each cylinder in the array can oscillate with five degrees of freedom (DOFs), i.e., surge, sway, heave, roll, and pitch. This paper adopts the multi-term Galerkin method to expand the fluid velocity at the interface of different regions into a set of basis functions containing Gegenbauer polynomials, which accurately and efficiently characterizes the cube root singularity of the fluid velocity near the edges of the truncated cylinders. Using the dynamic equilibrium equations, the amplitudes of each DOF of the cylinders in the array are solved. The analytical solution presented in this paper converges rapidly, and high-precision hydrodynamic response results can be obtained using just a few truncated terms (e.g., the upper bounds of m0 = 5 and p0 = 22 can yield results of five-figure accuracy). For the 4-cylinder array, under the same accuracy conditions (the error less than 1%), the computation time of the conventional method developed by Zeng et al. [“Hydrodynamic interactions between waves and cylinder arrays of relative motions composed of truncated floating cylinders with five degrees of freedom,” J. Fluids Struct. 115, 103785 (2022d)] based on the exact algebraic method [Kagemoto and Yue, “Interactions among multiple three-dimensional bodies in water waves: An exact algebraic method,” J. Fluid Mech. 166, 189–209 (1986)] is 3.9 times longer than that of the present method. As the number of cylinders increases, the advantage of the present method in terms of convergence speed becomes more apparent, e.g., for the 16-cylinder array, the conventional solution takes 6.3 times longer than the present solution. To extract wave energy more efficiently, a new 5DOF wave energy converter (WEC) device that can extract energy in 5DOFs is proposed. The present method is adopted to investigate the hydrodynamic performance of the 5DOF WEC arrays. Compared with the traditional 1DOF (heave) WEC, the 5DOF WEC can significantly improve the energy capture performance of arrays, especially in the high-frequency wave region.
Revealing the reconstruction mechanism of AgPd nanoalloys under fluorination based on a multiscale deep learning potential
Authors: Guo Longfei , Shan Shuang , Liu Xiaoqing , Zhang Wanxuan , Xu Peng , Ma Fanzhe , Li Zhen , Wang Chongyang , Wang Junpeng , Chen Fuyi
Published: May 2024

The design of heterogeneous catalysts generally involves optimizing the reactivity descriptor of adsorption energy, which is inevitably governed by the structure of surface-active sites. A prerequisite for understanding the structure–properties relationship is the precise identification of real surface-active site structures, rather than relying on conceived structures derived from bulk alloy properties. However, it remains a formidable challenge due to the dynamic nature of nanoalloys during catalytic reactions and the lack of accurate and efficient interatomic potentials for simulations. Herein, a generalizable deep-learning potential for the Ag–Pd–F system is developed based on a dataset encompassing the bulk, surface, nanocluster, amorphous, and point defected configurations with diverse compositions to achieve a comprehensive description of interatomic interactions, facilitating precise prediction of adsorption energy, surface energy, formation energy, and diffusion energy barrier and is utilized to investigate the structural evolutions of AgPd nanoalloys during fluorination. The structural evolutions involve the inward diffusion of F, the outward diffusion of Ag in Ag@Pd nanoalloys, the formation of surface AgFx species in mixed and Janus AgPd nanoalloys, and the shape deformation from cuboctahedron to sphere in Ag and Pd@Ag nanoalloys. Moreover, the effects of atomic diffusion and dislocation formation and migration on the reconstructing pathway of nanoalloys are highlighted. It is demonstrated that the stress relaxation upon F adsorption serves as the intrinsic driving factor governing the surface reconstruction of AgPd nanoalloys.
Oblique impingement of binary droplets at the nanoscale on superhydrophobic surfaces: A molecular dynamics study
Authors: Zhang Aiping , Cui Kai , Tian Yuanyuan , Zhang Benxi , Wang Tieying , He Xin
Published: May 2024

The impacting phenomenon of nanodroplets has received much attention due to their importance in various industrial applications. The oblique impingement of single droplets is well understood; however, the effect of oblique angle on impacting the dynamics of multiple droplets at the nanoscale is very limited. To address this gap, we perform molecular dynamics (MD) simulations to study the impacting dynamics of binary nanodroplets with various oblique angles (αob) and Weber numbers (We). Using MD simulations, we directly capture the detailed morphological evolution of the impacting binary droplets with various given conditions. Compared to the oblique impingement of a single droplet, the evolution of impacting binary droplets involves two novel dynamic characteristics: the asymmetric dynamics with droplet preferential spreading in the y direction and the rotating of the coalescing droplet. The mechanisms underlying are well studied. The asymmetric dynamics is a result of the velocity gradient of the outer edge of the spreading droplet, and the rotating effect is due to the change in angular momentum induced by surface force. The analysis and study of these phenomena have never been mentioned in previous studies of single droplet. Finally, we investigate the effect of αob and We on normalized moving distance (L/Dsin) and contact time (tc). This work paves the way for offering a comprehensive understanding of the oblique impingement of binary nanodroplets.
Dynamics of carrier injection through V-defects in long wavelength GaN LEDs
Authors: Marcinkevičius Saulius , Tak Tanay , Chow Yi Chao , Wu Feng , Yapparov Rinat , DenBaars Steven P. , Nakamura Shuji , Speck James S.
Published: May 2024

The efficiency of high-power operation of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on the realization of uniform hole distribution between the QWs. In long wavelength InGaN/GaN QW LEDs, the thermionic interwell hole transport is hindered by high GaN barriers. However, in polar LED structures, these barriers may be circumvented by the lateral hole injection via semipolar 101¯1 QWs that form on the facets of V-defects. The efficiency of such carrier transfer depends on the transport time since transport in the semipolar QWs is competed by recombination. In this work, we study the carrier transfer from the semipolar to polar QWs by time-resolved photoluminescence in long wavelength (green to red) LEDs. We find that the carrier transfer through the semipolar QWs is fast, a few tens of picoseconds with the estimated room temperature ambipolar diffusion coefficient of ∼5.5 cm2/s. With diffusion much faster than recombination, the hole transport from the p-side of the structure to the polar QWs should proceed without a substantial loss, contributing to the high efficiency of long wavelength GaN LEDs.
Blasting damage mechanism and excavation stability of surrounding rock of shallow-buried metro station
Authors: Li Wei , Zhang Qingsong , Bai Jiwen , Zhang Jie , Yu Liyuan , Liu Jingwei , Liu Yankai
Published: May 2024

Given the significant impact of damage on the deformation and stability of surrounding rock in shallowly buried metro stations, understanding the behaviors of rocks, with the blasting vibration effect considered, is crucial. This study examines the blasting damage mechanism, including an analysis of damage factors and radii. The results revealed a nonlinear decreasing relationship between the damage factor and the distance from the blasting source. Hence, equations for the radii of the surrounding rock's crushing and crack zones are established under the influence of blasting shock and stress waves. On-site acoustic testing indicated that the surrounding rock suffers severe damage within a 0–0.6 m range from the blasting source. A damage disturbance zone exists within a 0.7–1.7 m range while the rock remains intact within a 1.7–4.7 m range. The on-site measured radius of the crushing zone differs by 9.59% from the theoretical value, and the crack zone's radius deviates by 16.47%. In addition, a simulation model is developed to investigate the stability of surrounding rock under different rock span ratio (RSR). For shallowly buried, large-span hard rock stations, the findings suggested that with RSR between 0.15 and 0.25, a smaller ratio correlates with increased settlement of the surrounding rock, higher horizontal stress values, and larger plastic zone areas post-excavation, confirming the evaluation index's rationality and scientific validity.
Impact of white noise in artificial neural networks trained for classification: Performance and noise mitigation strategies
Authors: Semenova N. , Brunner D.
Published: May 2024

In recent years, the hardware implementation of neural networks, leveraging physical coupling and analog neurons has substantially increased in relevance. Such nonlinear and complex physical networks provide significant advantages in speed and energy efficiency, but are potentially susceptible to internal noise when compared to digital emulations of such networks. In this work, we consider how additive and multiplicative Gaussian white noise on the neuronal level can affect the accuracy of the network when applied for specific tasks and including a softmax function in the readout layer. We adapt several noise reduction techniques to the essential setting of classification tasks, which represent a large fraction of neural network computing. We find that these adjusted concepts are highly effective in mitigating the detrimental impact of noise.
Effect of bonding description and strain regulation on the conductive transition of Bi semimetal
Authors: Yang Xing-Yu , Cao Jia-Ying , Ma Xiao-hang , Ren Shi-Hao , Liu Yong-Li , Meng F. S. , Qi Yang
Published: May 2024

Due to the differences in the treatment methods of the electron–ion interaction and the critical strain mode of the transition from semimetals to semiconductors, the corresponding strain modulation mechanism in layered bismuth (Bi) crystals remains elusive. In this work, the effects of van der Waals (vdW) correction on the crystal structure and electrical properties of Bi in an equilibrium/strained state are comparatively studied based on the density functional theory. It is found that vdW corrections can better describe the layered crystal and bandgap structure of Bi under equilibrium/strain conditions. With the vdW modification, bismuth can be converted from a semimetal to a semiconductor within a small compression range that is experimentally available. This transition is induced by the transfer of the conduction band minimum and the valence band maximum and is related to the competition of the near-band edge energy state near the Fermi level of bismuth. The present results not only provide guidance for the accurate study of the crystal structure and electronic properties of complex model systems, such as Bi or Bi-based inherently nanostructured materials, but also reveal strain regulation mechanism of Bi and predict its potential application in the semiconductor electronic devices.
Field inversion machine learning augmented turbulence modeling for time-accurate unsteady flow
Authors: Fang Lean , He Ping
Published: May 2024

Field inversion machine learning (FIML) has the advantages of model consistency and low data dependency and has been used to augment imperfect turbulence models. However, the solver-intrusive field inversion has a high entry bar, and existing FIML studies focused on improving only steady-state or time-averaged periodic flow predictions. To break this limit, this paper develops an open-source FIML framework for time-accurate unsteady flow, where both spatial and temporal variations of flow are of interest. We augment a Reynolds-Averaged Navier–Stokes (RANS) turbulence model's production term with a scalar field. We then integrate a neural network (NN) model into the flow solver to compute the above augmentation scalar field based on local flow features at each time step. Finally, we optimize the weights and biases of the built-in NN model to minimize the regulated spatial-temporal prediction error between the augmented flow solver and reference data. We consider the spatial-temporal evolution of unsteady flow over a 45° ramp and use only the surface pressure as the training data. The unsteady-FIML-trained model accurately predicts the spatial-temporal variations of unsteady flow fields. In addition, the trained model exhibits reasonably good prediction accuracy for various ramp angles, Reynolds numbers, and flow variables (e.g., velocity fields) that are not used in training, highlighting its generalizability. The FIML capability has been integrated into our open-source framework DAFoam. It has the potential to train more accurate RANS turbulence models for other unsteady flow phenomena, such as wind gust response, bubbly flow, and particle dispersion in the atmosphere.
Robust and adaptive deep reinforcement learning for enhancing flow control around a square cylinder with varying Reynolds numbers
Authors: Jia Wang , Xu Hang
Published: May 2024

The present study applies a Deep Reinforcement Learning (DRL) algorithm to Active Flow Control (AFC) of a two-dimensional flow around a confined square cylinder. Specifically, the Soft Actor-Critic (SAC) algorithm is employed to modulate the flow of a pair of synthetic jets placed on the upper and lower surfaces of the confined squared cylinder in flow configurations characterized by Re of 100, 200, 300, and 400. The investigation starts with an analysis of the baseline flow in the absence of active control. It is observed that at Re = 100 and Re = 200, the vortex shedding exhibits mono-frequency characteristics. Conversely, at Re = 300 and Re = 400, the vortex shedding is dominated by multiple frequencies, which is indicative of more complex flow features. With the application of the SAC algorithm, we demonstrate the capability of DRL-based control in effectively suppressing vortex shedding, while significantly diminishing drag and fluctuations in lift. Quantitatively, the data-driven active control strategy results in a drag reduction of approximately 14.4%, 26.4%, 38.9%, and 47.0% for Re = 100, 200, 300, and 400, respectively. To understand the underlying control mechanism, we also present detailed flow field comparisons, which showcase the adaptability of DRL in devising distinct control strategies tailored to the dynamic conditions at varying Re. These findings substantiate the ability of DRL to control chaotic, multi-frequency dominated vortex shedding phenomena, underscoring the robustness of DRL in complex AFC problems.
Investigation of a rotating stall in a supercritical CO2 centrifugal compressor
Authors: Zhang Lei , Yang Fan , An Guangyao , Lang Jinhua , Yuan Wei , Zhang Qian
Published: May 2024

Due to the nonlinear behavior of carbon dioxide properties at its critical point and the size effect of the supercritical carbon dioxide (S-CO2) centrifugal compressor, the stall causation mechanism differs between the S-CO2 centrifugal compressor and a conventional air compressor. The comprehension of the induced principle of the S-CO2 compressor rotating stall holds immense significance in enhancing stall margin and efficiency. This paper employs unsteady simulations to investigate the causes of the impeller rotating stall in the S-CO2 centrifugal compressor. The results show that the leading edge breakdown vortex (LEBV) formed by the tip leakage vortex (TLV) breakdown and the reverse flow in the passage are the reasons for blocking the passage and ultimately causing the rotating stall of the impeller. The migration motion of the LEBV not only induces the leading edge spillage phenomenon but also influences the intensity of the tip leakage flow (TLF) in adjacent passages, causing the propagation of the TLV breakdown phenomenon in the opposite direction to that of impeller rotation. The TLV undergoes intermittent breakdown in flow field, which is influenced by variations in TLF intensity. Additionally, there is a preceding process of breakdown-induced vortex formation and disappearance prior to TLV fragmentation.
Facile compliance-based pump for blood physiometer
Authors: Kang Yang Jun
Published: May 2024

The biomechanical properties of blood are considered promising label-free biomarkers for early disease detection. Disposable pumps have been suggested as replacements for bulky and expensive syringe pumps. However, they have limitations, including initial air bubble removal, simple stop-and-run flow control, and quantification of many rheological properties. In this study, a compliance-based pump (CP) is developed by fitting a blood-loaded syringe, an air-compliance unit, and a needle into each port of a three-way valve. When blood is loaded into the microfluidic channel from the CP, the initial air bubbles are removed from the channels. By manipulating the three-way valve, blood flow is stopped immediately. Red blood cell (RBC) aggregation index (AI) is obtained by analyzing microscopic blood images. The air-compliance unit induces a transient blood flow. The time-resolved micro-particle image velocimetry technique is employed to obtain the blood velocity. The flow rate and time constant are obtained by assuming the flow rate as Q (t) = Q1 exp(−t/λ1) + Q2 exp(t/λ2) and conducting nonlinear regression analysis. The proposed method is employed to obtain the properties (AI, Q1, Q2, λ1, and λ2) of suspended bloods (hematocrit = 30%–70%, 5–30 mg/ml dextran solution, and heat-shocked RBCs). It is also used to detect four different types of suspended blood prepared by adding two types of RBCs (normal or hardened RBCs) to two types of diluents (1 × phosphate-buffered saline or dextran). In conclusion, the proposed method can be used to detect differences in suspended blood by manipulating the CP and consistently analyzing microscopic blood images.
Research on development and quantitative control preparation technology of array-type microfine bubbles generator
Authors: Huang Zhijie , Zhang Yufeng , Sun Lixia , Wang Zheng , Wang Qin , Liu Yang
Published: May 2024

In traditional wastewater treatment, ozone injection efficiency is low. There is a need for the quantitative preparation of ozone-based microfine bubbles to balance bubble stability and ozone reactivity. To address this, we developed coaxial and T-type ozone-based microfine bubble generators and conducted experiments to compare their bubble production effects. The more effective generator was then compared with the traditional aeration method. The results indicate the following: 1. The coaxial type is more effective in producing ozone-based microfine bubbles. 2. The bubbles produced by the coaxial type have an average diameter of 0.2–0.4 mm and a residence time of ∼2 min, meeting microfine bubble standards. Experimental data analysis shows compliance with the force process and bubble growth mechanism under coaxial flow, meeting the requirements for quantitative and controllable ozone-based microfine bubble production. 3. Ozone bubbles from the coaxial method surpass those from traditional aeration in volume and concentration. More than 99.73% are microfine bubbles, with an ozone concentration of ∼84.5%. 4. The coaxial method more effectively reduces COD values in water, contributing to efficient wastewater treatment. This research presents new avenues for efficient sewage treatment.
Bioengineering solutions for expansive soil stabilization using waste materials: An experimental evaluation
Authors: Randhawa Karanbir Singh , Kumar Raman , Alkaabi Hamad , Alkahtani Meshel Q. , Islam Saiful , Prakash Chander , Kumar Rahul , Ammarullah Muhammad Imam
Published: May 2024

Municipal solid waste incineration ash is the outcome/product of bioengineering science. The incineration or burning of municipal solid waste (MSW) reduces the volume of this biomass by 90%, and the residual ash can be used in several applications. In this study, the potential of municipal solid waste incineration (MSWI) ash and calcium carbide residue (CCR) waste for stabilization of expansive soil has been experimentally evaluated. The abnormal shrink–swell characteristics of expansive soils pose several problems for civil engineering structures when these soils are used for construction in their original form. The study presents an experimental set-up to determine the best combination of additives to achieve the most favorable technical characteristics of expansive soil for civil engineering activities. The percentage of expansive soil has been kept fixed at 60% of the total weight of the mix for varying ratios of stabilizing agents. The optimization of the stabilizing materials is based on the highest strength parameters of the mix achieved for a particular ratio of additives and soil. The two stabilizing agents are waste materials, and their disposal through landfilling has become costly due to a scarcity of space and handling mechanisms. The values of strength parameters, unconfined compressive strength (UCS), and split tensile strength (STS) of a treated mix are found to be highest for a unique combination of 60% lime stabilized expansive soil and 20% MSWI ash and an equal quantity (20%) of CCR. The cumulative effect of adding the best mix of additives to soil and curing time depicts an improvement of 526.03% in UCS and 463.41% in STS of the mix compared to one day and 28 days of curing time. There is scope for further study, such as adding some fibers to the finalized mix to reinforce the soil mix.
An investigation of self-interstitial diffusion in α-zirconium by an on-the-fly machine learning force field
Authors: Shi Tan , Liu Wenlong , Zhang Chen , Lyu Sixin , Sun Zhipeng , Peng Qing , Li Yuanming , Meng Fanqiang , Tang Chuanbao , Lu Chenyang
Published: May 2024

The on-the-fly machine learning force field approach, based on the Gaussian approximation potential and Bayesian error estimation, was used to study the diffusion of self-interstitial atoms in α-zirconium. Ab initio molecular dynamics simulations of lattice vibration and interstitial diffusion at different temperatures were employed to develop the force field. The radial and angular descriptors of the potential were further optimized to achieve better agreement with first-principles results. Subsequent long-term diffusion simulations were performed to assess the diffusion behavior based on the obtained force field. Tracer diffusion coefficients and diffusion anisotropy were studied at temperatures of 600–1200 K, and the Bayesian errors were estimated throughout the diffusion simulations. The mean and maximum estimated Bayesian errors of atomic force were approximately twice as large as those observed during the learning period. The basal diffusion was greatly favored compared to the interstitial diffusion along the c-axis, consistent with previous simulations based on first-principles results and classical potentials. The accuracy and applicability of the current on-the-fly machine learning approach were critically evaluated.