bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy loss analyses of amorphous magnetic ribbons by multi-frequency single sheet tester
Authors: Pfützner Helmut , Shilyashki Georgi , Bengtsson Claes
Published: March 2024

Due to low values of both thickness and conductivity, Fe-based amorphous soft magnetic ribbon (AR) is an attractive alternative to crystalline silicon steel (CS) for elevated frequencies f up to several kHz. On the other hand, for corresponding tests of losses P, the only standardized method is restricted to just 400 Hz. Recently, we reported “Physically Consistent Loss Testing” (CLT) for loss tests of CS for f up to 10 kHz. Here, we describe an adaptation of a corresponding multi-frequency single sheet tester for AR-applications. The CS single sheet is replaced by six 50 cm long and 17 cm wide ARs, loosely inserted into a paper envelope. This “envelope technique” provides (i) simple sample arrangement in an absolutely flat state, (ii) high repeatability, (iii) robust sensor signals, (iv) avoidance of loss increases due to magneto-mechanical effects, and (v) averaging over thickness variations of ARs through as much as 100 g of sample mass. Here, we report the results of frequency analyses for sinusoidal magnetization in the longitudinal direction for induction up to 1.5 T for f < 1 kHz and 0.4 T for 10 kHz, with P up to 50 W/kg. Anisotropy tests confirm a very weak dominance of the transverse direction. In conclusion, CLT proves to be an effective tool for loss tests on both CS and AR as a physically consistent principle. Therefore, for the ongoing standardization of SST with H-coil, we recommend considering the integration of the “envelope technique” in order to establish rapid and universal multi-frequency loss testing.
Synthesizing impurity clustering in the edge plasma of tokamaks using neural networks
Authors: Lin Zetao , Maurel-Oujia Thibault , Kadoch Benjamin , Krah Philipp , Saura Nathaniel , Benkadda Sadruddin , Schneider Kai
Published: March 2024

This work investigates the behavior of impurities in edge plasma of tokamaks using high-resolution numerical simulations based on Hasegawa–Wakatani equations. Specifically, it focuses on the behavior of inertial particles, which has not been extensively studied in the field of plasma physics. Our simulations utilize one-way coupling of a large number of inertial point particles, which model plasma impurities. We observe that with Stokes number (St), which characterizes the inertia of particles being much less than one, such light impurities closely track the fluid flow without pronounced clustering. For intermediate St values, distinct clustering appears, with larger Stokes values, i.e., heavy impurities even generating more substantial clusters. When St is significantly large, very heavy impurities tend to detach from the flow and maintain their trajectory, resulting in fewer observable clusters and corresponding to random motion. A core component of this work involves machine learning techniques. Applying three different neural networks—Autoencoder, U-Net, and Generative Adversarial Network (GAN)—to synthesize preferential concentration fields of impurities, we use vorticity as input and predict impurity number density fields. GAN outperforms the two others by aligning closely with direct numerical simulation data in terms of probability density functions of the particle distribution and energy spectra. This machine learning technique holds the potential to reduce computational costs by eliminating the need to track millions of particles modeling impurities in simulations.
Study on the effect of wall roughness on the flow characteristics of liquid film in airflow
Authors: Dai Xinbo , Zeng Yiyi , Liu Senyun , Yi Xian
Published: March 2024

During the flight, water flows under the action of shear force to form the overflow liquid film and freezes to form overflow ice. Overflow ice will change the aerodynamic shape of the aircraft and affect the safety and stability. In this paper, the three-dimensional structure of the liquid film in airflow was measured transiently with the digital image projection technology. The effects of different flat wall roughnesses, airflow velocities, and liquid film flow rates on the flow characteristics of the liquid film were analyzed. The experimental results show that the lower the wall roughness, the more pronounced the liquid film contraction toward the central axis. When the liquid flow rate drops to 0.228 l/min, the continuous liquid film transforms into rivulets on the surface of a large contact angle or low roughness. The average thickness of the liquid film on the flat is greater than that on the rough flat at low airflow velocity and low liquid flow rate, but smaller than that on the rough flat at high airflow velocity and high liquid flow rate. The wave near the inlet has an obvious acceleration process, and after reaching the peak speed, it gradually decreases and stabilizes near a certain value. The smoother the surface, the faster the acceleration of the wave at the inlet, and the greater the final stable wave speed.
Modification of the resistive tearing instability with Joule heating by shear flow
Authors: De Jonghe J. , Keppens R.
Published: March 2024

We investigate the influence of background shear flow on linear resistive tearing instabilities with Joule heating for two compressible plasma slab configurations: a Harris current sheet and a force-free, shearing magnetic field that varies its direction periodically throughout the slab, possibly resulting in multiple magnetic nullplanes. To do so, we exploit the latest version of the open-source, magnetohydrodynamic spectroscopy tool Legolas. Shear flow is shown to dramatically alter tearing behavior in the presence of multiple magnetic nullplanes, where the modes become propagating due to the flow. Finally, the tearing growth rate is studied as a function of resistivity, showing where it deviates from analytic scaling laws, as well as the Alfvén speed, the plasma-β, and the velocity parameters, revealing surprising nuance in whether the velocity acts stabilizing or destabilizing. We show how both slab setups can produce growth rate regimes, which deviate from analytic scaling laws, such that systematic numerical spectroscopic studies are truly necessary, for a complete understanding of linear tearing behavior in flowing plasmas.
Trapping and actively transporting single particles of arbitrary properties in low-pressure rf plasmas with and without a magnetic field
Authors: Ekanayaka Pubuduni , Wang Chuji , Thakur Saikat Chakraborty , Thomas Edward
Published: March 2024

We report the experimental realization of optical trapping and controlled manipulations of single particles of arbitrary properties, e.g., nano- to micrometer in size, transparent spheres to strongly light absorbing nonspherical particles, in low-pressure rf plasmas. First, we show optical trapping and transport of single particles in an unmagnetized rf plasma. Then, we show similar observations in a weakly magnetized rf plasma. This is the first demonstration of actively transporting (pushing and pulling) light-absorbing, nonspherical single particles in plasmas. The result suggests that optically trapped, actively controlled, single plasma dust particles (not limited to those externally sampled spheres) could be an in situ micro-probe for dusty plasma and magnetized dusty plasma diagnostics.
Advances in high-pressure laser floating zone growth: The Laser Optical Kristallmacher II (LOKII)
Authors: Gomez Alvarado Steven J. , Zoghlin Eli , Jackson Azzedin , Kautzsch Linus , Plumb Jayden , Aling Michael , Capa Salinas Andrea N. , Pokharel Ganesh , Pang Yiming , Gomez Reina M. , Daly Samantha , Wilson Stephen D.
Published: March 2024

The optical floating zone crystal growth technique is a well-established method for obtaining large, high-purity single crystals. While the floating zone method has been constantly evolving for over six decades, the development of high-pressure (up to 1000 bar) growth systems has only recently been realized via the combination of laser-based heating sources with an all-metal chamber. While our inaugural high-pressure laser floating zone furnace design demonstrated the successful growth of new volatile and metastable phases, the furnace design faces several limitations with imaging quality, heating profile control, and chamber cooling power. Here, we present a second-generation design of the high-pressure laser floating zone furnace, “Laser Optical Kristallmacher II” (LOKII), and demonstrate that this redesign facilitates new advances in crystal growth by highlighting several exemplar materials: α-Fe2O3, β-Ga2O3, and La2CuO4+δ. Notably, for La2CuO4+δ, we demonstrate the feasibility and long-term stability of traveling solvent floating zone growth under a record pressure of 700 bar.
Droplet coalescence kinetics: Thermodynamic non-equilibrium effects and entropy production mechanism
Authors: Sun Guanglan , Gan Yanbiao , Xu Aiguo , Shi Qingfan
Published: March 2024

The thermodynamic non-equilibrium (TNE) effects and the relationships between various TNE effects and entropy production rate, morphology, kinematics, and dynamics during two initially static droplet coalescences are studied in detail via the discrete Boltzmann method. Temporal evolutions of the total TNE strength D¯* and the total entropy production rate can both provide concise, effective, and consistent physical criteria to distinguish different stages of droplet coalescence. Specifically, when the total TNE strength D¯* and the total entropy production rate reach their maxima, it corresponds to the time when the liquid–vapor interface length changes the fastest; when the total TNE strength D¯* and the total entropy production rate reach their valleys, it corresponds to the moment of the droplet being the longest elliptical shape. Throughout the merging process, the force contributed by surface tension in the coalescence direction acts as the primary driving force for droplet coalescence and reaches its maximum simultaneously with coalescent acceleration. In contrast, the force arising from non-organized momentum fluxes (NOMFs) in the coalescing direction inhibits the merging process and reaches its maximum at the same time as the total TNE strength D¯*. In the coalescence of two unequal-sized droplets, contrary to the larger droplet, the smaller droplet exhibits higher values for total TNE strength D¯*, merging velocity, driving force contributed by surface tension, and resistance contributed by the NOMFs. Moreover, these values gradually increase with the initial radius ratio of the large and small droplets due to the stronger non-equilibrium driving forces stemming from larger curvature. However, non-equilibrium components and forces related to shear velocity in the small droplet are consistently smaller than those in the larger droplet and diminish with the radius ratio. This study offers kinetic insights into the complexity of thermodynamic non-equilibrium effects during the process of droplet coalescence, advancing our comprehension of the underlying physical processes in both engineering applications and the natural world.
Drag force and heat transfer characteristics of deformable alumina droplets in compressible flows
Authors: Ding Shuai , Hu Haiyang , Wang Qiang
Published: March 2024

This paper investigates the force and heat transfer characteristics of deformable alumina droplets in compressible flow. The numerical scheme couples the Navier–Stokes equations with the volume-of-fluid method, fuzzy theory, and a proportional–derivative controller. The effects of the Reynolds number, Weber number, and relative Mach number on the droplet deformation and the drag and heat transfer characteristics are studied. The results show that the fuzzy theory coupled with the proportional–derivative controller allow the droplet to reach the quasi-steady state more efficiently and robustly. The drag coefficient and Nusselt number of the droplet increase with the degree of deformation and the relative Mach number between the flow field and the droplet. The relative Mach number and the Weber number are weakly coupled with the drag coefficient and the Nusselt number. Finally, the inner two-phase flow fields of a solid rocket motor are calculated. The mechanisms whereby particle deformation influence the inner flow field of the solid rocket motor are analyzed.
The change in inertial particle clustering in turbulent flow due to collision-coagulation: A Voronoi analysis
Authors: Feng Jun , Meng Xiaohui , Saw Ewe-Wei
Published: March 2024

Two-dimensional Voronoi analysis is used to quantify the preferential concentration (clustering) of inertial particles in homogeneous isotropic turbulence. The diameter of particles is one order of magnitude smaller than the Kolmogorov length scale of turbulent flow, and the density of particle is more than one order of magnitude larger than that of the fluid. We study the influence of particle collision-coagulation on particle clustering and how it relates to particle and turbulent parameters (particle Stokes number St, particle diameter d, and turbulent Reynolds number Reλ). The probability density function (PDF) of Voronoi area (of particles) normalized by its average shows different properties due to particle collision-coagulation. The influence of particle collision-coagulation on particle clustering is mainly in the small scale (area) range, with the changes in PDF limited in the large area regime. In the small area regime, the PDF decreases as a result of particle collision-coagulation when compared to the control case with non-colliding particles. This decrease is noticeable in the range of A/A¯≲2×10−2. The decrease in the PDF becomes more significant with increasing particles Stokes number until a turning point at St∼0.5, after which the effect diminishes gradually. The influence of particle collision-coagulation on particle preferential concentration is also related to the particle diameter d. As d increases, the PDF value decreases obviously at small areas. When the particle diameter is made three times larger, the range where PDF decreases extends to A/A¯≲10−1. We also study the influence of turbulent Reynolds number. For Reynolds number in the range of Reλ=84–189, we find that the decrease in the PDF due to particle collision-coagulation is independent of Reλ for particle with St = 0.1 and St = 1.0. In the large area regime, the PDF increases slightly, indicating an increasing void region due to particle collision-coagulation.
Realization of a composite ferroelectric characterization test system using a modified constant current method and a modified virtual ground method
Authors: Wang Ding-Yeong
Published: March 2024

A composite ferroelectric characterization test system constructed using a modified constant current method (CCM) and a modified virtual ground method (VGM) has been successfully designed and implemented. By sending instructions to the microcontroller through software, the system’s test mode can be easily changed by arranging the switching status of six switching elements. When validating the system, a dual-channel precision source/measure unit B2912B was used to verify this design. There is also parasitic capacitance that cannot be ignored in this commercial machine. This parasitic capacitance affects the appearance of the entire hysteresis curve. However, the parasitic capacitance values also differ in various test current ranges. In addition, to confirm the data credibility of this composite ferroelectric test system, Keysight B1530A and Radiant Premier II were used to conduct cross-verification between different systems. The results obtained between different systems show good consistency. Furthermore, reproducible and recoverable imprint phenomena were found in this composite system during interactive validation using VGM and CCM methods. After designing different voltage profiles for verification, it was found that the root cause of this imprint phenomenon was the difference between the final polarization state of the previous test and the pre-initialized polarization state. This imprint phenomenon exists in traditional Pb(Zr, Ti)O3 (PZT) ferroelectric capacitors and Hf0.5Zr0.5O2-based ferroelectric capacitors. Fortunately, this imprint phenomenon is reversible. Moreover, this imprint phenomenon disappears through the design of the time-varying voltage profile on the ferroelectric capacitor of the CCM method.
The causality measure of partial mutual information from mixed embedding (PMIME) revisited
Authors: Fotiadis Akylas , Vlachos Ioannis , Kugiumtzis Dimitris
Published: March 2024

The measure of partial mutual information from mixed embedding (PMIME) is an information theory-based measure to accurately identify the direct and directional coupling, termed Granger causality or simply causality, between the observed variables or subsystems of a high-dimensional dynamical and complex system, without any a priori assumptions about the nature of the coupling relationship. In its core, it is a forward selection procedure that aims to iteratively identify the lag-dependence structure of a given observed variable (response) to all the other observed variables (candidate drivers). This model-free approach is capable of detecting nonlinear interactions, abundantly present in real-world complex systems, and it was shown to perform well on multivariate time series of moderately high dimension. However, the PMIME presents some inefficiencies in its performance mainly when applied on strongly stochastic (linear or nonlinear) systems as it may falsely detect non-existent relationships. Moreover, and by construction, the measure cannot extract purely synergetic relationships present in a system. In the current work, the issue of false detections is addressed by introducing an improved resampling significance test and a procedure of rechecking the identified drivers (backward revision). Regarding the inability to detect synergetic relationships, the PMIME is further enhanced by checking pairs as candidate drivers for the response variable after having considered all drivers individually. The effects of these modifications are investigated in a systematic simulation study on properly designed systems involving strong stochasticity, regressor terms with synergetic effects, and a system dimension ranging from 3 to 30. The overall results of the simulations indicate that these modifications indeed improve the performance of PMIME and alleviate to a significant degree the issues of the original algorithm. Guidelines for balancing between accuracy and computational efficiency are also given, particularly relevant for real-world applications. Finally, the measure performance is investigated in the study of futures of various government bonds and stock market indices in the period around COVID-19 pandemic.
ReaxFF molecular dynamics simulations of methane clathrate combustion
Authors: Bai Dongsheng , Zhang Jie
Published: March 2024

Understanding the ignition and dynamic processes for the combustion of hydrate is crucial for efficient energy utilization. Through reactive force field molecular dynamics simulations, we studied the high-temperature decomposition and combustion processes of methane hydrates in a pure oxygen environment. We found that at an ignition temperature of 2800 K, hydrates decomposed from the interface to the interior, but the layer-by-layer manner was no longer strictly satisfied. At the beginning of combustion, water molecules reacted first to generate OH•, followed by methane oxidation. The combustion pathway of methane is CH4→CH3•→CH3O•→CH2O→HC•O→HCOO•→CO(CO2). During the combustion process, a liquid water layer was formed between melted methane and oxygen, which hindered the reaction’s progress. When there is no heat resistance, oxygen will transform into radicals such as OH• and O•, which have faster diffusion rates, allowing oxygen to conveniently cross the mass transfer barrier of the liquid water layer and participate in the combustion process. Increasing the amount of OH• may cause a surge in the reaction. On the other hand, when significant heat resistance exists, OH• is difficult to react with low-temperature hydrate components, but it can transform into O• to trigger the oxidation of methane. The H• generated has a sufficient lifetime to contact high-temperature oxygen molecules, converting oxygen into radicals that easily cross the water layer to achieve mass transfer. Therefore, finding ways to convert oxygen into various radicals is the key to solving the incomplete combustion of hydrates. Finally, the reaction pathways and microscopic reaction mechanisms of each species are proposed.
Two-dimensional temperature field inversion of turbine blade based on physics-informed neural networks
Authors: Mai Jieai , Li Yang , Long Lian , Huang Yue , Zhang Huiliu , You Yancheng
Published: March 2024

Correct evaluation of the blades' surface temperature field is crucial to the structural design and operational safety of aero-engine turbine blades. Current high-temperature measurement technology can only measure the limited discrete points temperature of the hot-end turbine blades. If the boundary conditions are completely unknown, it is still difficult to solve equations through traditional computational fluid dynamics methods. It is an inverse problem to predict the temperature field of the turbine engine blade with unknown boundary conditions. This paper proposes a two-dimensional temperature field inversion of turbine blades based on physics-informed neural networks (PINN) and finite discrete temperature measurement points. The PINN is used to model the nonlinear mapping of input variables and output variables. Only a small amount of data is used to train the neural network. It can be found that adding the loss term of the physical governing equation during training can make the neural network better predict the temperature field of the turbine blade, which can also avoid anomalies such as large temperature errors in some areas that may occur when training with only a small amount of data. When the boundary conditions are completely unknown, the average relative error of PINN trained with only 62 points of temperature data on the test set is below 2%, and the R2−Score is above 0.95. When the training data reaches 122 points of temperature data, the average relative error of PINN on the test set is less than 1%, and the R2−Score reaches 0.99.
An efficient framework for controllable micromixer design through the fusion of data-driven modeling and machine learning insights: Numerical and experimental analysis
Authors: Hassani Faridoddin , Sadegh Moghanlou Farhad , Minaei Asgar , Vajdi Mohammad , Golshani Ali , Kouhkord Afshin , Dehghani Tohid
Published: March 2024

Micromixers are inevitable components in microfluidics, micro-electro-mechanical devices, and numerous bio-chemical assays. By assays, we mean diverse analytical procedures encompassing gene engineering, the manipulation of genetic material; nanoparticle synthesis, focusing on the controlled creation of nanoparticles; and cell lysis, involving cell membranes disruption for the release of intracellular substances for diagnostic purposes. In these assays, the homogeneous mixture of two or more fluids is crucial. However, designing an efficient micromixer providing high homogeneity and low pressure drop, while maintaining controllability, is challenging. Controllability refers to the design of a micro-system tailored to meet the specific requirements of a given assay. This study proposes a controllable framework, combining machine learning and statistical modeling. The framework begins with the generation of a reference parametric micro-structure, herein a microchannel with L-shaped baffles and featuring seven variables. A response surface method, a data-driven modeling scheme, is used to establish functional relationships between design variables and objective functions. The study reveals that the baffle height significantly impacts the system functionality, increasing the mixing index by over 40% and the pressure drop by more than 220% when reaching its upper limit. Dean-like secondary vortexes are generated in the microchannel at Re = 10, demonstrating the efficiency of the implemented baffles. Subsequently, multi-objective optimization methods, non-dominated sorting genetic algorithm (NSGA-II) and differential evolution (DE), are employed, with adaptable variable constraints. Comparative analysis of the methods shows that DE finds superior optimum solutions in fewer iterations. Finally, an optimum structure is fabricated using soft lithography, and experimental tests are conducted for validation.
Impact of Co2C nanoparticles on enhancing the critical current density of Bi-2223 superconductor
Authors: Ali Md Arif , Karan Sourav M. , Roy Nirmal , Banerjee S. S.
Published: March 2024

We have investigated the superconducting properties of nanocomposite pellets made from Bi-2223 and Co2C powders. Our measurements reveal loss of superconducting fraction in the nanocomposites. However, the retained superconducting fraction exhibits robust bulk superconducting properties. The Tc of the retained superconducting fraction was 109 K, which was found to be comparable to that of the pure Bi-2223 pellet. We found that the composite’s net magnetization response is a superposition of the contributions of ferromagnetic and superconducting fractions. Analysis revealed that the surviving superconducting fraction exhibits a robust Meissner response. In the nanocomposite, the irreversibility field of the superconducting fraction at 77 K is found to increase by almost three times compared to the pristine material, thereby showing strong vortex pinning features. We also find a broadened magnetic field regime over which we observe that a single vortex pinning regime sustained in the nanocomposite. The critical current density, Jc, of the nanocomposite was found to be approximately five times higher than that of the pristine Bi-2223 pellet at low T. In fact, the enhancement in Jc is most significant in the high T regime, where at temperatures close to Tc in the nanocomposite, we see almost two orders of magnitude increase in Jc compared to the pristine Bi-2223 pellet. Our study suggests that larger sized agglomeration of magnetic nanoparticles of Co2C leads to loss of superconductivity in the nanocomposite. However, there are also unagglomerated Co2C nanoparticles distributed uniformly throughout the nanocomposite, which act as efficient pinning centers that allow for collective vortex pinning centers to be retained, even up to temperatures near Tc, and these nanoparticles also do not compromise the bulk Tc of the superconducting fraction. Our study shows that these nanocomposites that exhibit enhanced Jc especially in the high T regime are potentially useful for high current applications.
A hybrid solar-driven vacuum thermionic generator and looped multi-stage thermoacoustically driven cryocooler system: Exergy- and emergy-based analysis and optimization
Authors: Yousefi Yasaman , Noorpoor Arshiya , Boyaghchi Fateme Ahmadi
Published: March 2024

Significant high-quality heat is wasted in the vacuum thermionic generator (VTIG), which can be efficiently utilized as a prime mover of a bottoming system for cogeneration applications. For this purpose, a new environmental-friendly hybrid system composed of a heliostat solar field, VTIG, and looped multi-stage thermoacoustically driven cryocooler (LMTC) is established, in which the high-temperature heat source of the solar receiver runs the VTIG to generate power, and the LMTC recovers the waste heat of the VTIG to produce a cooling load. Thermodynamic, economic, and environmental analyses of the system are carried out based on exergy and emergy concepts. Moreover, a parametric study is performed to assess the effect of design parameters on the system's thermodynamic, economic, and environmental criteria. Finally, the multi-criteria salp swarm optimization algorithm and decision-making procedures are conducted to improve the exergetic performance and decrease the system's cost and monetary emergy rates along with the environmental impact and ecological emergy rate. Findings depict that at the reliable, optimal operation of the system, the exergetic efficiency can reach 29.36% with a maximum power of 17.2 MW and cooling load of 0.260 MW. The system's cost and monetary emergy rate can be reduced to 0.059 $/s and 5.94 × 1010 seJ/s, with 10.6% and 10% reductions, respectively. Moreover, the environmental impact and ecological emergy rates decline by 6% and 7.4%, respectively. The theoretical findings may offer guidance for the optimum designing and practical running of such a solar solid-state cogeneration system.
Macroscopic and stable gas film obtained by superhydrophobic step and its drag reduction performance
Authors: Zhang Zheng , Hou Yacong , Ma Liran , Tian Yu
Published: March 2024

Drag reduction technology has a promising application in marine fields and has drawn much interest in scientific fields. Superhydrophobic surface has been proven to be effective in drag reduction due to thin film of gas adsorbed on surface because of its low friction drag and large slip length. Here, macroscopic and stable gas film was observed when water flowed over superhydrophobic surface with step without additional gas injection under laminar flow and turbulent flow. Superhydrophobic surface was prepared with contact angle more than 150° and roll-off angle nearly 0°. Macroscopic gas film could maintain under laminar flow and turbulent flow and keep up to 80% after 1 h water flowing with optimized parameters of step, showing different morphological deformations under different velocities and Reynolds numbers. Compared with untreated hydrophilic surface, superhydrophobic surface with step exhibited good drag reduction performance with maximum drag reduction rate 20% under laminar flow and turbulent flow, after optimizing of height of step and distance between steps. Mechanisms of gas film drag reduction were the ultra-low skin friction drag force between liquid–gas interface, large slip length on liquid–gas interface, and flexible gas film surface acted like compliant wall. Gas film of millimeter scale was much larger than thickness of boundary layer and reduced turbulence intensity near wall. This work provides a new way to obtain macroscopic gas film and analyze liquid–gas interface.
Vanishing in fractal space: Thermal melting and hydrodynamic collapse
Authors: Phan Trung V. , Cai Truong H. , Do Van H.
Published: March 2024

Fractals emerge everywhere in nature, exhibiting intricate geometric complexities through the self-organizing patterns that span across multiple scales. Here, we investigate beyond steady-states the interplay between this geometry and the vanishing dynamics, through phase-transitional thermal melting and hydrodynamic void collapse, within fractional continuous models. We present general analytical expressions for estimating vanishing times with their applicability contingent on the fractality of space. We apply our findings on the fractal environments crucial for plant growth: natural soils. We focus on the transport phenomenon of cavity shrinkage in incompressible fluid, conducting a numerical study beyond the inviscid limit. We reveal how a minimal collapsing time can emerge through a non-trivial coupling between the fluid viscosity and the surface fractal dimension.
Miniaturized time-correlated single-photon counting module for time-of-flight non-line-of-sight imaging applications
Authors: Wu Jie , Yu Chao , Zeng Jian-Wei , Dai Chen , Xu Feihu , Zhang Jun
Published: March 2024

Single-photon time-of-flight (TOF) non-line-of-sight (NLOS) imaging enables the high-resolution reconstruction of objects outside the field of view. The compactness of TOF NLOS imaging systems, entailing the miniaturization of key components within such systems, is crucial for practical applications. Here, we present a miniaturized four-channel time-correlated single-photon counting module dedicated to TOF NLOS imaging applications. The module achieves excellent performance with a 10 ps bin size and 27.4 ps minimum root-mean-square time resolution. We present the results of the TOF NLOS imaging experiment using an InGaAs/InP single-photon detector and the time-correlated single-photon counting module and show that a 6.3 cm lateral resolution and 2.3 cm depth resolution can be achieved under the conditions of 5 m imaging distance and 1 ms pixel dwell time.
Revised Fowler–Dubridge model for multiphoton over-barrier electron emission from two-dimensional materials
Authors: Luo Yi , Er Chen-Chen , Ang Yee Sin , Ang L. K.
Published: March 2024

We revise the Fowler–Dubridge model for multiphoton over-barrier photoemission from two-dimensional (2D) materials to include the effects of reduced dimensionality, non-parabolic, and anisotropic energy dispersion of 2D materials. Two different directions of electron emission are studied, namely, vertical emission from the surface and lateral emission from the edge. Our analytical model reveals a universal temperature scaling of Tβ with β = 1 for the surface emission over a wide class of 2D materials and β = 3/2 for the edge emission from the 2D material with anisotropic parabolic energy dispersion, which are distinct from the traditional scaling of β = 2 originally derived for the traditional bulk materials. Our comparison shows good agreement with two experiments of photoelectron emitted from graphene for both surface and edge emission. Our calculations also show that the photoelectron emission is more pronounced than the coexisting thermionic emission for materials with low temperature and Fermi energy. This model provides helpful guidance in choosing proper combinations of light intensity, temperature range, and type of 2D materials for the design of photoemitters, photodetectors and other optoelectronics.
Stability and instability of thermosolutal convection in a Brinkman–Darcy–Kelvin–Voigt fluid with couple stress effect
Authors: Afluk Zaid Abbas , Harfash Akil J.
Published: March 2024

In this article, the phenomenon of thermosolutal convection within a fluid characterized by the Brinkman–Darcy–Kelvin–Voigt (BDKV) model is delved into, while the impact of couple stresses on this process is considered. Both linear instability and nonlinear stability analyses are encompassed in our investigation. Several noteworthy observations have been made. When the fluid layer is heated from below and salt is introduced from above, it is found that the points at which stability and instability thresholds are reached coincide. This alignment is supported by the validity of the linear theory in predicting the initiation of convection under these conditions. However, the scenario changes when the layer is salted from the bottom while being heated. In this case, the stability thresholds remain constant, regardless of variations in the salt Rayleigh number. This discrepancy between the thresholds of linear instability and nonlinear stability is deemed significant. To gain a deeper understanding, numerical computations were conducted to identify and thoroughly discuss the thresholds of linear instability. These findings offer valuable insights into the behavior of the system under study. It is indicated by our results that parameters such as Brinkman, couple stresses, and Kelvin–Voigt contribute to stabilizing the system. Additionally, it was noted that the salt Rayleigh number has a stabilizing effect when the layer is salted from below, whereas it has a destabilizing effect when salt is introduced from above.
Design and characterization of a virtual-dimple plasma actuator for turbulent skin-friction drag reduction
Authors: Fang Ziqi , Zong Haohua , Wu Yun , Liang Hua , Cao Rui , Su Zhi , Hua Weizhuo
Published: March 2024

A virtual-dimple plasma actuator (VDPA), capable of producing suction flow above a staggered array of circular anodes, is proposed for turbulent skin-friction drag reduction. Characteristics of the VDPA at different discharge voltages are studied using multi-slice stereoscopic particle image velocimetry and electrical measurements. Results indicate that the VDPA induces a downwash suction flow above the cathode, a wall-normal jet flow above the anode, and a counter-rotating vortex pair caused by near-wall jet impingement. With increasing discharge voltage, both the peak blowing velocity and centerline-jet decay rate increase, while the dimensionless total circulation decreases linearly. For different cases, the vortex-core spacing remains approximately unchanged at 0.43D.
Coherent structure analysis of cavitation waterjets using dynamic mode decomposition
Authors: Fang Zhenlong , Hou Wenjiang , Fan Shidong , Guo Xiaofeng , Chen Yong
Published: March 2024

This study analyzes the influence of nozzle geometry on the vortex and cavitation cloud structures. The differences between the coherent structures of the Helmholtz nozzle, organ pipe nozzle, and venturi nozzle jets are investigated through large eddy simulation. The vorticity transport equation is used to investigate the relationship between the cavitation cloud and diagonal pressure torque terms. The cavitation and vortex structure shedding frequencies of the jets are investigated using the dynamic mode decomposition method. Three distinct stages of the cavitation bubbles are illustrated: priming, expansion, and collapse. The nozzle structure determines the shape of the primary cavitation bubbles. Moreover, turbulent kinetic energy convergence facilitates the maintenance of the coherent structure. Organ pipe nozzle jets have a high peak velocity at the center axis. Their vortex structure only exhibits a stretched state in the downstream and collapses later than the vortex structures of other nozzles. Advantageously, organ pipe nozzles maintain the stability of the coherent structure. The jets generated by the three nozzles have similar static modes. Helmholtz nozzles produce jets with higher energy and periodically shedding small-scale vortex structural modes. These modes are coupled to the static flow field, resulting in quasi-periodic oscillations of the Helmholtz nozzle jets. The periodic oscillation effect of the Helmholtz nozzle jets is superior to that of the other nozzle jets. The high-energy modes of the venturi nozzle jets have anisotropic and small-scale vortex structures. Furthermore, the venturi nozzle jets exhibit good dispersion and cavitation properties. This study provides guidance for the use of jets with different properties in the respective engineering fields.
Lost circulation detection method based on cepstrum analysis of transient pressure waves
Authors: Zhu Zhongxi , Liu Hong , Lei Wanneng , Xue Youqiang
Published: March 2024

Encountering natural fractures or unbalanced formation pressure during oil drilling can result in economic loss and environmental pollution due to well leakage. Existing detection methods encounter challenges such as high costs, complex downhole environments, and difficult data acquisition. To address these issues, we propose a well leakage detection method using cepstrum for analyzing transient pressure waves. Cepstrum is a signal Fourier transform after logarithmic operation and then Fourier inverse spectrum obtained. By studying the propagation of transient pressure waves in the wellbore, we identify drilling fluid leakage location and amount based on time-dependent and amplitude changes of pressure wave signal characteristic peaks. To handle noise in the pressure wave signal, we employ adaptive noise-complete ensemble empirical modal decomposition (CEEMDAN) and wavelet threshold (WT) joint denoising. Correlation coefficient (CCF) with the Hilbert joint spectrum (HJS) is used to extract main frequency components, achieving denoising. Experimental results confirm: ① Noise interference in transient pressure waves is effectively suppressed using the CEEMDAN-WT-CCF-HJS denoising method. ② Cepstrum analysis of the pressure wave signal during wellbore annulus system leakage reveals distinct reflected wave characteristic peaks, aiding in locating different leakage points, with the amplitude of these peaks reflecting the size of the leakage. ③ This method efficiently utilizes time-frequency information from the excitation pressure wave signal, offering advantages over traditional time-domain and frequency-domain analysis. Experiments covering various leakage scenarios, amounts, and borehole sizes yielded controlled experimental errors (2.25%–9.10%), within a reasonable range. The method's validity and reliability were confirmed, providing theoretical support and technical guidance for well leakage detection in oil drilling.
Clinical research imperatives: principles and priorities from the perspective of Allied Health executives and managers
Authors: Hillier Susan , Lodge Duncan , Nolan Jo , Yandell Rosalie , Chur-Hansen Anna , George Stacey , Lynch Elizabeth
Published: March 2024

Objective It is widely understood that a key means of improving health systems and patient outcomes is through research – accessing, understanding, generating and applying research evidence-based practice. To promote more targeted and strategic research in Allied Health practice, this study sought to establish the principles, areas and priorities for clinical research as perceived by Allied Health leaders in the South Australian public health system. Methods The study used a mixed-methods design (full, sequential and equal model). Participants were recruited from the South Australian Department of Health and Wellbeing employment lists for Allied Health senior leaders. Consenting participants attended face-to-face focus groups; after an overview presentation, they discussed the principles for Allied Health research, followed by areas and priorities for research. Summaries of the responses were themed descriptively and circulated electronically so participants could confirm the research areas and ascribe priority ratings, clinical populations and services. Results A total of 28 people attended the stakeholder forum (5 online); 20 responded to the second-round electronic summary. Nine principles of research action were agreed. Fourteen research areas were identified and prioritised. There was a relatively consistent prioritisation of measuring Allied Health value, Allied Health workforce, hospital avoidance and closing the gap for Aboriginal and Torres Strait Islander peoples health outcomes – whether the individuals were thinking about their own service or the state as a whole. Conclusions Allied Health leadership identified key principles and priorities for research to improve service delivery and patient outcomes. These priorities should generate further discussion and interest for novice and experienced researchers and leaders and can be used to inform granting and project plans.
Antibiotics in semen extenders – a multiplicity of paradoxes
Authors: Morrell Jane M. , Cojkic Aleksandar , Malaluang Pongpreecha , Ntallaris Theodoros , Lindahl Johanna , Hansson Ingrid
Published: March 2024

Addition of antibiotics to semen extenders was taken for granted for many years, from the time that commercial artificial insemination in livestock first began many decades ago. However, there is now a growing realisation that this non-therapeutic utilisation of antibacterial agents is contrary to current recommendations for prudent use that medical and veterinary professionals are advised to follow. Furthermore, antibiotics are not benign, having negative effects on sperm samples, the inseminated female, personnel and potentially the environment. The purpose of this review is three-fold: to highlight the fact that antibiotics are used in semen extenders, with the result that considerable amounts are used globally in animal breeding, to review recent studies on the negative aspects of using antibiotics for this purpose, and to look at possible alternatives. Recent changes in the legislation regarding semen extenders occurred in some, but not all, countries, leaving question marks for semen producers as to whether antibiotics should be added to semen extenders or not.
Direct-write 3D printing of plasmonic nanohelicoids by circularly polarized light
Authors: Kim Ji-Young , McGlothin Connor , Cha Minjeong , Pfaffenberger Zechariah J. , Turali Emre Emine Sumeyra , Choi Wonjin , Kim Sanghoon , Biteen Julie S. , Kotov Nicholas A.
Published: March 2024

Chiral plasmonic surfaces with 3D “forests” from nanohelicoids should provide strong optical rotation due to alignment of helical axis with propagation vector of photons. However, such three-dimensional nanostructures also demand multi-step nanofabrication, which is incompatible with many substrates. Large-scale photonic patterns on polymeric and flexible substrates remain unattainable. Here, we demonstrate the substrate-tolerant direct-write printing and patterning of silver nanohelicoids with out-of-plane 3D orientation using circularly polarized light. Centimeter-scale chiral plasmonic surfaces can be produced within minutes using inexpensive medium-power lasers. The growth of nanohelicoids is driven by the symmetry-broken site-selective deposition and self-assembly of the silver nanoparticles (NPs). The ellipticity and wavelength of the incident photons control the local handedness and size of the printed nanohelicoids, which enables on-the-fly modulation of nanohelicoid chirality during direct writing and simple pathways to complex multifunctional metasurfaces. Processing simplicity, high polarization rotation, and fine spatial resolution of the light-driven printing of stand-up helicoids provide a rapid pathway to chiral plasmonic surfaces, accelerating the development of chiral photonics for health and information technologies.
Assessment of an NTP service calibration over a Local Area Network
Authors: Vélez Carmen , Díaz Javier , Osuna Alfonso , Álvarez-Martínez Héctor , Esteban Héctor
Published: March 2024

Nowadays, timekeeping is an essential component in modern computing. The Network Time Protocol (NTP) is a distributed service based on a hierarchical network protocol used to synchronize computer clocks over a network in an easy and scalable manner. Currently, this protocol is the main mechanism used on the internet to provide a common notion of time to all computers. The Real Instituto y Observatorio de la Armada (ROA) realizes Spanish legal time and disseminates it via the internet from two publicly accessible NTP time servers. In this study, it is assessed the implementation and characterization of two NTP time servers over a Local Area Network in client-to-server and server-to-server modes from the side of NTP protocol and all its functionalities. These measurements aim to analyze the client-to-server mode operation, forcing the polling interval at different values, and to verify the consistency of the results by employing the ppstest tool to compare one pulse‐per‐second from the UTC (ROA) with the client time offset. This comparison corroborates the proper operation of the NTP time server configured as stratum 1 and referred directly to UTC (ROA), and shows how a real deployment can be professionally deployed with the aim of distributing time over a public service using NTP.