bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of MNE strategies amid China’s changing institutions: a thematic review
Authors: Tse Caleb H. , Meyer Klaus E. , Pan Yigang , Chi Tailan
Published: July 2024

As China’s economy rose to become the second largest in the world, its institutions did not converge with those of other advanced economies as predicted by many Western observers; instead, China developed a distinct form of state-led capitalism. As a result, how multinational enterprises (MNEs) engage with China’s changing institutional context needs to be revisited. To this end, we review 331 papers on MNE strategies and operations in China published in top international business and management journals between 2001 and 2022. We first introduce the path of institutional change and the opportunities and challenges it created for MNEs in China. We focus on six aspects of MNE strategies and operations: market entry, strategic alliances, innovation and knowledge sharing, global value chain strategies, guanxi and relationship management, and non-market strategies. Our analysis of China’s institutional trajectory and of MNE strategies and operations points to three persistent institutional mechanisms of concern for MNEs: challenges to organizational legitimacy, protection of property rights, and the enabling and directing aspect of institutions created by industrial policies. Insights from this analysis point to future research needs on institutional nonlinearities and discontinuities, linkages between inward and outward investments, and geopolitical influences on national institutions.
Exploring loyalty drivers for smartphone and mobile carriers
Authors: Jo Hyeon , Park Do-Hyung
Published: July 2024

Smartphones have permeated daily human life and play a role in various areas. Loyalty to smartphones holds significant implications for both businesses and customers. This study constructed a research model that considers smartphones as parallel to telecom services. The model comprises devices and mobile carriers as the main axes. The study designates exogenous variables as symmetric factors and common factors. The research collected empirical questionnaire responses from 357 smartphone users. Data analysis was conducted using partial least squares structural equation modeling. The findings revealed that brand image and apps are significantly related to device satisfaction. The results demonstrated that apps, corporate image, and perceived fees are crucial determinants of carrier satisfaction. The analysis also showed that both device satisfaction and mobile carrier satisfaction influence loyalty.
Grade inflation effects of capacity expansion in higher education: a longitudinal study in undergraduate teacher education programs from 2003 to 2022
Authors: Ciftci S. Koza , Karadag Engin
Published: July 2024

This study examined the change in the rate of graduates with high honors (>3.50) in teacher training programs and the factors affecting grade inflation and graduation GPAs over a 20-year period. In the study, the weighted grade point average of 173,232 student-teachers who had graduated from 32 teacher training institutions between 2003 and 2022 was analyzed using the random effects estimator, ANOVA, t test, and ANCOVA. The findings suggest that their grade point averages increased from 2.83 to 3.34 within this period. The highest-grade averages were found in 2012, when the number of teacher training institutions was expanded; as well as in 2021–2022, during the COVID-19 pandemic. In addition, the gender of the students, their university admission scores, the teaching field, the establishment year of the program, and the ratio of students per faculty member were found to be important determinants of graduation GPAs. Based on our results, it can be argued that the rapid growth of teacher training programs in Türkiye has caused a decrease in quality, which has triggered an increase in grade averages. One of the most important findings supporting this idea is that programs with lower university admission scores have more students graduating with honors.
A control theoretic analysis of oscillator Ising machines
Authors: Cheng Yi , Khairul Bashar Mohammad , Shukla Nikhil , Lin Zongli
Published: July 2024

This work advances the understanding of oscillator Ising machines (OIMs) as a nonlinear dynamic system for solving computationally hard problems. Specifically, we classify the infinite number of all possible equilibrium points of an OIM, including non-0/π ones, into three types based on their structural stability properties. We then employ the stability analysis techniques from control theory to analyze the stability property of all possible equilibrium points and obtain the necessary and sufficient condition for their stability. As a result of these analytical results, we establish, for the first time, the threshold of the binarization in terms of the coupling strength and strength of the second harmonic signal. Furthermore, we provide an estimate of the domain of attraction of each asymptotically stable equilibrium point by employing the Lyapunov stability theory. Finally, we illustrate our theoretical conclusions by numerical simulation.
On lattice hexagonal crystallization for non-monotone potentials
Authors: Luo Senping , Wei Juncheng
Published: July 2024

We prove that for α ≥ 1, among 2d unit density lattices, minL∑P∈L(|P|2−β)e−πα|P|2 is achieved at hexagonal lattice for β≤12πα and does not exist for β>12πα. Here the hexagonal lattice with unit density can be expressed by Λ1=132[Z(1,0)⊕Z(12,32)]. This leads to two applications as follows. (1) Assume that α ≥ 1. Then, among 2d unit density lattices, minL∑P∈L|P|2e−πα|P|2 is achieved at hexagonal lattice. (2) Assume that β > α ≥ 1. Then minz∈Hθ(α;z)−bθ(β;z) is achieved at z=eiπ3 (corresponding to hexagonal lattice) for b≤βα and does not exist for b>βα. Here θ(α; z) is the two-dimensional Theta function.
Modeling interactions between rubidium atom and magnetometer cell wall molecules
Authors: David Grégoire , Wibowo-Teale Andrew M. , Rogers David M.
Published: July 2024

Magnetometer cell wall coat molecules play an important role in preserving the lifetime of pumped alkali metal atoms for use in magnetometers that are capable of measuring very small magnetic fields. The goal of this study is to help rationalize the design of the cell coat molecules. Rubidium-87 is studied in terms of its interaction with three template cell coat molecules: ethane, ethene, and methyltrichlorosilane (MeTS). Ab initio electronic structure methods are applied to investigate the effect that the coat molecules have on the 2S ground state and 2P excited state of 87Rb. We find that, from the ab initio results, the three template molecules have differing effects, with MeTS having the largest effect on the ground state and ethane or ethene having the largest effect on the non-degenerate excited states.
Comparison of type II superlattice InAs/InAsSb barrier detectors operating in the mid-wave infrared range
Authors: Kopytko Małgorzata , Madejczyk Paweł , Murawski Krzysztof , Kubiszyn Łukasz , Michalczewski Krystian , Seredyński Bartłomiej , Szlachetko Kamil , Jureńczyk Jarosław , Gawron Waldemar , Rutkowski Jarosław
Published: July 2024

Four types of barrier detectors based on a type II InAs/InAsSb superlattice with a wide-gap barrier made of a solid AlInAsSb lattice matched to the GaSb buffer were compared. The tested detectors differed in the type of doping of the active layer and the level and type of doping of the contact layer at the barrier. The epitaxial layers were deposited on GaAs (100) substrates using the molecular beam epitaxy method. The spectral and current–voltage characteristics of the analyzed detectors were compared. The highest current responsivities were observed in the structure with a p-type absorber (p+BpN+). Detectors with an n-type absorber (p+Bnn+, n+Bnn+, and nBnn+) show an increase in the current responsivity with an increase in the reverse bias voltage due to the reduction in the undesirable barrier in the valence band. Arrhenius characteristics for the dark current show that only in nBnn+ detectors, it was possible to limit the generation–recombination current. These detectors at 150 K were characterized by the highest normalized detectivity of approximately 3 × 1011 cm · Hz1/2/W. The obtained results were compared with literature data, showing that the parameters of type II superlattice photodetectors are close to those of HgCdTe photodiodes according to the “Rule 07” and “Rule 22” principles.
Tipping points, multistability, and stochasticity in a two-dimensional traffic network dynamics
Authors: Narayan Chattopadhyay Shankha , Kumar Gupta Arvind
Published: July 2024

Mitigating traffic jams is a critical step for the betterment of the urban transportation system, which comprises a large number of interconnected routes to form an intricate network. To understand distinct features of vehicular traffic flow on a network, a macroscopic two-dimensional traffic network model is proposed incorporating intra-nodal and inter-nodal vehicular interaction. Utilizing the popular techniques of nonlinear dynamics, we investigate the impact of different parameters like occupancy, entry rates, and exit rates of vehicles. The existence of saddle-node, Hopf, homoclinic, Bogdanov–Takens, and cusp bifurcations have been shown using single or biparametric bifurcation diagrams. The occurrences of different multistability (bistability/tristability) phenomena, stochastic switching, and critical transitions are explored in detail. Further, we calculate the possibility of achieving each alternative state using the basin stability metric to characterize multistability. In addition, critical transitions from free flow to congestion are identified at different magnitudes of stochastic fluctuations. The applicability of critical slowing down based generic indicators, e.g., variance, lag-1 autocorrelation, skewness, kurtosis, and conditional heteroskedasticity are investigated to forewarn the critical transition from free flow to traffic congestion. It is demonstrated through the use of simulated data that not all of the measures exhibit sensitivity to rapid phase transitions in traffic flow. Our study reveals that traffic congestion emerges because of either bifurcation or stochasticity. The result provided in this study may serve as a paradigm to understand the qualitative behavior of traffic jams and to explore the tipping mechanisms occurring in transport phenomena.
Energy and mass flow in photocatalytic water splitting by coupling photothermal effect
Authors: Wang Shujian , Si Yitao , Lu Kejian , Liu Feng , Wang Biao , Zhao Shidong , Wang Yi , Zhang Shiyue , Lu Youjun , Li Naixu , Liu Maochang
Published: July 2024

Solar photocatalytic water splitting for hydrogen production represents an ideal approach to address the current energy and environmental challenges, while also achieving “carbon peak and carbon neutrality” goals. The incorporation of photothermal effect into photocatalysis enables dual utilization of both light and heat energies, resulting in improved solar-to-hydrogen efficiency. In this review, we first discussed the behavior of energy flow and mass flow, and the characteristics of photogenerated carrier throughout the photocatalytic water splitting process, with particular focus on the behaviors induced by photothermal effect. Subsequently, we elaborate on strategies for designing high-efficiency photothermal catalytic systems and novel photothermal–photocatalytic integrated systems based upon concentrating-photothermal coupling effects. We then illustrate the development and large-scale demonstrations that utilize concentrated solar irradiation. Finally, we outline the challenges and highlight the future research directions of photothermal catalysis toward hydrogen production from water. This review aims to provide fundamental references and principal strategies for efficient utilization of solar energy in photothermal catalytic processes.
Extending femtosecond laser superfilamentation in air with a multifocal phase mask
Authors: Fu Silin , Mysyrowicz André , Arantchouk Leonid , Lozano Magali , Houard Aurélien
Published: July 2024

Laser filamentation is a spectacular phenomenon where the self-focusing of the laser pulse generates ionizing light channels. Many applications of filamentation, such as the laser lightning rod, require the generation of superfilaments, long plasma channels of higher electron density than normal filaments. Using a multifocal phase mask, we demonstrate an extension of the superfilamentation length of a focused terawatt laser beam. Optimized superfilaments show increased energy deposition compared to a normal gaussian beam and an extension of their length by at least a factor two. When put in contact with a high voltage electrode, the guiding of a single plasma column with a length of ∼1 m is observed. The length of an air waveguide generated by a vortex laser pulse is also increased by a factor 2 in the presence of the phase mask.
Wafer-scale CMOS-compatible graphene Josephson field-effect transistors
Authors: Generalov Andrey A. , Viisanen Klaara L. , Senior Jorden , Ferreira Bernardo R. , Ma Jian , Möttönen Mikko , Prunnila Mika , Bohuslavskyi Heorhii
Published: July 2024

Electrostatically tunable Josephson field-effect transistors (JoFETs) are one of the most desired building blocks of quantum electronics. Applications of JoFETs range from parametric amplifiers and superconducting qubits to a variety of integrated superconducting circuits. Here, we report on graphene JoFET devices fabricated with wafer-scale complementary metal-oxide-semiconductor (CMOS)-compatible processing based on chemical-vapor-deposited monolayer graphene encapsulated with atomic-layer-deposited Al2O3 gate oxide, lithographically defined top gate, and evaporated superconducting Ti/Al source, drain, and gate contacts. By optimizing the contact resistance down to ∼170 Ω μm, we observe proximity-induced superconductivity in the JoFET channels with different gate lengths of 150–350 nm. The Josephson junction devices show reproducible critical current Ic tunablity with the local top gate. Our JoFETs are in the short diffusive limit with the Ic reaching up to ∼3 µA for a 50 µm channel width. Overall, our demonstration of CMOS-compatible two-dimensional (2D) material-based JoFET fabrication process is an important step toward graphene-based integrated quantum circuits.
Interacting dust grains in complex plasmas: Ion wake formation and the electric potential
Authors: Vermillion K. , Banka R. , Mendoza A. , Wyatt B. , Matthews L. , Hyde T.
Published: July 2024

Dust grains have been used as minimally invasive probes to determine plasma parameters including the plasma density, temperature, and electric field in a plasma discharge. However, the dust grains in a plasma generate local potential disturbances due to the collection of charge and the subsequent electrostatic interactions between the dust and charged plasma particles. Dust grains in close proximity to one another exhibit interesting non-reciprocal interactions and self-organize into structures such as one-dimensional filamentary chains, two-dimensional “zigzags,” and three-dimensional helices, among others. The formation of these structures suggests that although the dust grains may be less invasive than traditional plasma probes, the disturbance to the local plasma environment introduced by dust grains is non-trivial. Commonly used analytic forms of the electric potential describing complex plasmas have failed to resolve the near-dust region, and as a result are insufficient to provide insight about the formation of complex dust structures. Here, we use an N-body simulation to compute the electric potential from ion densities near various dust grain configurations. We provide an alternative description to the standard analytic model for the electric potential of dust and ion wakes based on a Gaussian shaped cloud of ions. The electric potential obtained from simulations is used to identify minimum energy configurations for two and three dust grains. It is further demonstrated that the minimum potential region identified for N dust grains and their associated ion wakes does not predict the minimum-energy configuration of N + 1 dust grains.
Electronically controlled left-handed metamaterial based on memristor/ferrite multilayer at microwaves
Authors: Girich Aleksey , Kazan Sinan , Rameev Bulat , Tarapov Sergey
Published: July 2024

The paper focuses on exploring the left-handed microwave properties of a double negative metamaterial formed by utilizing elements from two natural materials: (a) thin-layer ferrite, which exhibits effective negative permeability, and (b) thin-layer TiO2 (memristor), which exhibits effective negative permittivity. Both of these natural materials possess negative constitutive parameters within the frequency band where they exhibit left-handed properties. We have defined the conditions under which a backward wave appears in the double negative frequency band. We analyze a left-handed metamaterial (LHM) for the microwave frequency band formed by a multilayer structure from the above-mentioned materials. We have theoretically demonstrated the transparency of this LHM. Furthermore, we demonstrate the ability to control the electromagnetic properties of the metamaterial. This can be achieved not only by applying both static magnetic and static electric fields but also by solely using a static electric field. The latter is one of the main advantages of this structure for technological implementation. We discuss potential applications of the designed structure as a component of microwave electronics. The capability to control various resistance states of nanoscaled TiOX with low voltage offers further control over the properties of the left-handed metamaterial.
Fast-forwarding molecular ground state preparation with optimal control on analog quantum simulators
Authors: Castaldo Davide , Rosa Marta , Corni Stefano
Published: July 2024

We show that optimal control of the electron dynamics is able to prepare molecular ground states, within chemical accuracy, with evolution times approaching the bounds imposed by quantum mechanics. We propose a specific parameterization of the molecular evolution only in terms of interaction already present in the molecular Hamiltonian. Thus, the proposed method solely utilizes quantum simulation routines, retaining their favorable scalings. Due to the intimate relationships between variational quantum algorithms and optimal control, we compare, when possible, our results with state-of-the-art methods in the literature. We found that the number of parameters needed to reach chemical accuracy and algorithmic scaling is in line with compact adaptive strategies to build variational Ansätze. The algorithm, which is also suitable for quantum simulators, is implemented by emulating a digital quantum processor (up to 16 qubits) and tested on different molecules and geometries spanning different degrees of electron correlation.
Modeling two-dimensional ice shape based on fractal interpolation
Authors: Nong Li , Hu Zhanwei , Sheng Zishuai , Zhang Huaibao , Yi Xian
Published: July 2024

The ice accretion data obtained from ice wind tunnel tests reveal a multiscale structure and rough surface. In the follow-up aerodynamic evaluation of icing airfoils, simplified two-dimensional ice shapes are generally used as substitutes, but this simplification changes the aerodynamic effects of the original ice shape. Therefore, finding a simple and effective two-dimensional ice shape simulation method is urgent. Due to the self-similarity characteristics of ice shape surfaces, fractal interpolation is proposed for ice shape simulation. First, the geometric characteristics of the ice shapes are analyzed to determine interpolation points, and an iterative function system is constructed for interpolation simulation. Considering the influence of various characteristics of ice shapes on aerodynamics, interpolation parameters are limited to simulating more realistic ice shapes. High-order numerical simulation methods were utilized to numerically simulate and analyze the aerodynamic characteristics of icing airfoil while also verifying the feasibility of fractal interpolation for simulating ice shapes. The analysis revealed that this method could effectively simulate ice profiles of various feature scales with minimal ice shape data. These simulated shapes closely resemble real ice formations and maintain the original aerodynamic characteristics of the icing airfoil. This method can be used to improve the computational accuracy of ice accretion codes and provide improvement strategies for complex ice shape prediction; thus, this method has great application prospects in engineering.
Enhancement of visible light response of TiO2 photocatalyst by 3D-deposited Ag nanowires and its charge separation mechanism
Authors: Murase Masaki , Matsuoka Yuki , Sugano Satoshi , Katayama Tetsuro , Furube Akihiro
Published: July 2024

In 3D-deposited AgNW/TiO2, which is prepared by spray-applying titanium dioxide suspension to deposited silver nanowire sheets, the synergistic effects of increased crossing points of AgNWs to enhance localized surface plasmon resonance excitation and longer-lived electrons in the conduction band of TiO2 generated by plasmon-induced charge transfer have successfully resulted in photocatalytic activity in the visible light range. We have developed photocatalytic sheets in which TiO2 particles are uniformly attached to 3D-deposited AgNWs. Regarding the prepared sheet, it was confirmed that TiO2 was indeed well adhered to the AgNWs, and electron transfer was efficient at the interface. This sheet solves the problem that the response wavelength range of the photocatalytic reaction using TiO2 is only in the ultraviolet region and exhibits sufficient photocatalytic effect in the visible light region. Transient absorption spectroscopy measurements in the diffuse reflectance configuration confirmed that the electrons of AgNWs actually move into the conduction band of TiO2 under visible light and that the interaction is independent of the excitation light intensity, thereby extending the lifetime of the electrons.
Electric field control of the energy gap in ZnO and BaSnO3 films grown on PMN-PT
Authors: Bridoux G. , Mogensen G. A. , Nieva G. , Guimpel J. , Ferreyra J. M. , Tolosa M. R. , Villafuerte M.
Published: July 2024

ZnO and BaSnO3 (BSO) thin films grown on Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) substrates have been studied using electrical resistance and photoconductivity (PC) spectra measurements under different applied electric fields on the substrate. The behavior of the resistance and the energy gap (EG) extracted from the PC spectra are modified by the polarization state of the substrate in the case of the ZnO film, while for BSO, these physical parameters depend on the strain imposed by the substrate when a voltage is applied on the PMN-PT. In the latter case, an in-plane tensile (compressive) strain leads to a reduction (increase) in the resistance and the energy gap when an external electric field is applied on the substrate. The behavior of ZnO and BSO can be explained by the different crystalline structure in both films and by the fact that ZnO is also a piezoelectric material. In ZnO, a change in the polarization state of the substrate is associated with an imposed strain and an induced polarization on the film that leads to a modification of the band bending and hence of the energy gap. In the case of BSO, a shift of the impurity and conduction band generates a modification of the energy gap for the different types of strain.
Strained single crystal high entropy oxide manganite thin films
Authors: Zhao Zhibo , Waqar Moaz , Jaiswal Arun Kumar , Raghavan Aaditya Rangan , Fuchs Dirk , Lin Jing , Brezesinski Torsten , Bhattacharya Subramshu S. , Hahn Horst , Pan Xiaoqing , Kruk Robert , Sarkar Abhishek
Published: July 2024

The ability to accommodate multiple principal cations within a single crystallographic structure makes high entropy oxides (HEOs) ideal systems for exploring new composition–property relationships. In this work, the high-entropy design strategy is extended to strained single-crystal HEO-manganite (HEO-Mn) thin films. Phase-pure orthorhombic films of (Gd0.2La0.2Nd0.2Sm0.2Sr0.2)MnO3 were deposited on three different single-crystal substrates: SrTiO3 (STO) (100), NdGaO3 (110), and LaAlO3 (LAO) (100), each inducing different degrees of epitaxial strain. Fully coherent growth of the thin films is observed in all cases, despite the high degree of lattice mismatch between HEO-Mn and LAO. Magnetometry measurements reveal distinct differences in the magnetic properties between epitaxially strained HEO-Mn thin films and their bulk crystalline HEO counterparts. In particular, the bulk polycrystalline HEO-Mn shows two magnetic transitions as opposed to a single one observed in epitaxial thin films. Moreover, the HEO-Mn film deposited on LAO exhibits a significant reduction in the Curie temperature, which is attributed to the strong variation of the in-plane lattice parameter along the thickness of the film and the resulting changes in the Mn–O–Mn bond geometry. Thus, this preliminary study demonstrates the potential of combining high entropy design with strain engineering to tailor the structure and functionality of perovskite manganites.
BubbleID: A deep learning framework for bubble interface dynamics analysis
Authors: Dunlap C. , Li C. , Pandey H. , Le N. , Hu H.
Published: July 2024

This paper presents BubbleID, a sophisticated deep learning architecture designed to comprehensively identify both static and dynamic attributes of bubbles within sequences of boiling images. By amalgamating segmentation powered by Mask R-CNN with SORT-based tracking techniques, the framework is capable of analyzing each bubble's location, dimensions, interface shape, and velocity over its lifetime and capturing dynamic events such as bubble departure. BubbleID is trained and tested on boiling images across diverse heater surfaces and operational settings. This paper also offers a comparative analysis of bubble interface dynamics prior to and post-critical heat flux conditions.
Theoretical study of short-range exchange interaction based on semiconductor dielectric function model toward time-dependent dielectric density functional theory
Authors: Shimazaki Tomomi , Tachikawa Masanori
Published: July 2024

This study explores various models of semiconductor dielectric functions, with a specific emphasis on the large wavenumber spectrum and the derivation of the screened exchange interaction. Particularly, we discuss the short-range effect of the screened exchange potential. Our investigation reveals that the short-range effect originating from the high wavenumber spectrum is contingent upon the dielectric constant of the targeted system. To incorporate dielectric-dependent behaviors concerning the short-range aspect into the dielectric density functional theory (DFT) framework, we utilize the local Slater term and the Yukawa-type term, adjusting the ratio between these terms based on the dielectric constant. Additionally, we demonstrate the efficacy of the time-dependent dielectric DFT method in accurately characterizing the electronic structure of excited states in dyes and functional molecules. Several theoretical approaches have incorporated parameters dependent on the system to elucidate short-range exchange interactions. Our theoretical analysis and discussions will be useful for those studies.
Consistent and reproducible computation of the glass transition temperature from molecular dynamics simulations
Authors: Carmona Esteva Fernando J. , Zhang Yong , Maginn Edward J. , Colón Yamil J.
Published: July 2024

In many fields, from semiconductors for opto-electronic applications to ionic liquids (ILs) for separations, the glass transition temperature (Tg) of a material is a useful gauge for its potential use in practical settings. As a result, there is a great deal of interest in predicting Tg using molecular simulations. However, the uncertainty and variation in the trend shift method, a common approach in simulations to predict Tg, can be high. This is due to the need for human intervention in defining a fitting range for linear fits of density with temperature assumed for the liquid and glass phases across the simulated cooling. The definition of such fitting ranges then defines the estimate for the Tg as the intersection of linear fits. We eliminate this need for human intervention by leveraging the Shapiro–Wilk normality test and proposing an algorithm to define the fitting ranges and, consequently, Tg. Through this integration, we incorporate into our automated methodology that residuals must be normally distributed around zero for any fit, a requirement that must be met for any regression problem. Consequently, fitting ranges for realizing linear fits for each phase are statistically defined rather than visually inferred, obtaining an estimate for Tg without any human intervention. The method is also capable of finding multiple linear regimes across density vs temperature curves. We compare the predictions of our proposed method across multiple IL and semiconductor molecular dynamics simulation results from the literature and compare other proposed methods for automatically detecting Tg from density–temperature data. We believe that our proposed method would allow for more consistent predictions of Tg. We make this methodology available and open source through GitHub.
Multi-delay coherence imaging spectroscopy optimized for ion temperature measurements in the divertor plasma of the Wendelstein 7-X stellarator
Authors: Kriete David M. , Perseo Valeria , Gradic Dorothea , Ennis David A. , König Ralf , Maurer David A. ,   W7-X Team
Published: July 2024

A new coherence imaging spectroscopy (CIS) diagnostic optimized to measure the C2+ impurity ion temperature Ti spatial distribution in the divertor plasma of the W7-X stellarator is designed, tested, and validated. Using CIS to obtain Ti in the edge of magnetically confined plasmas has historically been challenging because Doppler broadening and Zeeman splitting have comparable effects on the shape of spectral emission lines. To distinguish between these two mechanisms, a novel approach to birefringent crystal design is employed to minimize the diagnostic’s sensitivity to Zeeman splitting. The recently developed pixelated multi-delay CIS approach is also used to obtain four times as much spectral information as traditional CIS approaches. The Ti-optimized CIS diagnostic is validated in a long-pulse W7-X plasma by comparison with a high-resolution spectrometer whose sightlines overlap with the CIS field of view. The CIS and spectrometer Ti profiles have the same shape and agree to within 10% on average and 25% in the worst case. Images of the Ti distribution near the divertor show toroidally elongated bands aligned with the magnetic field, with Ti ranging between 10 and 40 eV.
Utilizing lagging-phase analysis to identify topological phase transitions in 1D chains
Authors: Qiao Shizhu
Published: July 2024

The Zak phase serves as a reliable index for pinpointing topological phase transitions within one-dimensional chains, typically ascertained through numerical methods in complex situations. Nonetheless, in proximity to the transition threshold, the numerical Zak phase may become ambiguous. This ambiguity arises from the discrete nature of numerical approaches and the nonlinear relationship between the wave function's phase and the wave vector (k). In response, this paper presents an innovative method aimed at accurately determining the winding number, thereby facilitating the identification of topological phase transitions. Our approach hinges on analyzing the evolution of the phase difference between the projections of the Bloch wave function onto two distinct sublattices. We demonstrate the efficacy of this method through three illustrative examples: the Su–Schrieffer–Heeger model, a magnetic vortex chain, and a trimer lattice chain. The results indicate that our proposed numerical lagging-phase examination method achieves superior precision in identifying topological phase transitions, particularly at critical junctures, compared to the conventional numerical Zak phase approach.
Numerical and experimental studies on the effects of molten steel viscosity on fluid flow, inclusion motion, and temperature distribution in a tundish
Authors: Li Yihong , Hu Xin , Wang Liyong , Zhang Hongxu , He Yibo , Zhang Wenjie , Hua Chengjian
Published: July 2024

Tundishes are refractory vessels that are used to control the flow of molten steel, promote the removal of inclusions, and increase the homogeneity of temperature and composition during continuous casting processes by optimizing their geometric shape. The flow of molten steel in tundishes is a high-temperature process, and the optimization of the tundish structure is carried out by numerical and physical simulations. In numerical simulations, the viscosity of molten steel is generally set to a constant value; however, in industrial scenarios, the molten steel viscosity is variable with temperature. In the present work, the effects of molten steel viscosity varying with temperature on fluid flow, inclusion motion, and temperature distribution in a tundish were investigated by numerical simulations based on the modification of the top heat flux of the tundish, and the results were further verified by an industrial experiment. The removal rate of inclusions obtained from the industrial experiment was 40.40%. In numerical simulations, the inclusion removal rates were 50.85% and 40.67% when the fluid viscosity was constant and variable, respectively. Hence, when the molten steel viscosity was variable, the numerical simulation result was closer to the experimental one. The industrial experiment revealed that the temperature difference between the edge flow and the middle flow on the tundish liquid surface was 0 K. In numerical simulations, when the top heat fluxes of the tundish were 15 000 and 100 W/m2, the temperature differences on the tundish liquid surface were 5.95 and 0.16 K, respectively.
An optimization approach to establish dynamical equivalence for soft and rigid impact models
Authors: Tian Bo , Yin Shan , Páez Chávez Joseph , Liu Yang
Published: July 2024

This paper studies a computational approach aimed at establishing equivalent dynamical responses within oscillatory impacting systems subject to soft and rigid constraints. The proposed method incorporates an adaptive differential evolution algorithm with the Metropolis criterion to determine the stiffness and damping parameters of the soft constraint for a prescribed coefficient of restitution governing the rigid constraint. The proposed algorithm aims to establish an equivalent dynamical response of the two models based on constraints regarding energy dissipation and contact time duration. Upon examining the dynamical responses of the two impact cases, they exhibit nearly identical outcomes in the two-parameter bifurcation diagrams when subjected to a large restitution coefficient. However, discrepancies arise between the results of the two models when the restitution coefficient is low. Detailed numerical tests, conducted using the proposed method, demonstrate enhanced effectiveness compared to previous techniques, such as the prediction formulas for the different related soft impact model outlined by Okolewski and Blazejczyk-Okolewska [Chaos 31(8), 083110 (2021)]. This method not only finds application in experimentally identifying the physical properties of an impact surface but also provides convenience in employing soft models within impacting systems, which could then avoid potential inaccuracies in handling discontinuities by some integrator during velocity jumps before and after impacts.
Heated-H3PO4 etching of (001) β-Ga2O3
Authors: Rebollo Steve , Itoh Takeki , Krishnamoorthy Sriram , Speck James S.
Published: July 2024

β-Ga2O3 is a promising ultra-wide bandgap semiconductor with melt-grown substrates that are scalable, particularly in the (001) orientation. In this study, we report on the heated-phosphoric acid etching of (001) β-Ga2O3. A wagon wheel pattern with spokes aligned to a range of specific crystallographic directions was fabricated on (001) β-Ga2O3. At 160 °C, the (001) etch rate was 1.47 μm/h, which is comparable to etch rates obtained via dry etch techniques. The etched (001) surface had a morphology that was smoother than an inductively coupled plasma etched surface. All spokes possessed relatively smooth sidewalls. Spokes oriented along the [100] direction exhibited minimal SiO2 mask undercut rates at lower etch temperatures and symmetric trapezoidal profiles with near vertical (010)-like sidewalls, which are ideal for device structures with a trench geometry. Spokes oriented along the [010] direction exhibited significant SiO2 mask undercut rates and asymmetric trapezoidal profiles with different sidewall angles. These spokes also possessed reduced sidewall angles, which is favorable for field management at device corners and edges. The etch process was used to realize a dense array of [100]-oriented trenches with a height of 1.5 μm, a base width of 2.0 μm, and a mask width of 0.8 μm. The work highlights the potential for ion damage-free, standalone heated-H3PO4 etching as a viable alternative to the dry etching of (001) β-Ga2O3 for high-performance device applications.
Modeling wave attenuation through vegetation patches: The overlooked role of spatial heterogeneity
Authors: Zhang Jing , Wu Guoxiang , Liang Bingchen , Shi Luming
Published: July 2024

Coastal wetlands serve as vital buffers against extreme hazards due to the wave-dissipating capacity of vegetation. While most studies assume a spatial-uniform vegetation cover when modeling wave attenuation through wetlands, they are far from homogeneous in reality due to life-stage dependent growths, die-offs, and zonation of different vegetation species. In the present study, the XBeach model was applied to explore the role of vegetation spatial heterogeneity on wave attenuations. Random distributed vegetation maps with the same coverage but diverse patch sizes are generated to replicate the complex patterns of real wetland vegetations. We focus on the attenuation of solitary waves and wave groups, representing tsunami and storm waves, respectively. Different wave heights, vegetation densities, and land slopes are considered. For solitary wave cases, it is found that smaller patch sizes lead to higher wave attenuation rates, lower run-up, and less inundation extents. For wave group cases, it is found that the attenuation rates are dependent not only on patch sizes but also wave frequencies; while the higher frequency wave components are attenuated at similar magnitudes by different patch sizes, the infragravity waves are much less attenuated by larger patch sizes due to the penetrating effects through the major gaps between patches. Both cases revealed that under the same vegetation coverage, smaller patch sizes outperform their larger counterparts in terms of wave attenuation capacity. Out study highlights the importance of vegetation spatial heterogeneity, which are seldom considered in evaluating the wetlands' capacity of attenuating extreme waves.
Heteroepitaxial growth of Ga2O3 thin films on Al2O3(0001) by ion beam sputter deposition
Authors: Kalanov Dmitry , Gerlach Jürgen W. , Bundesmann Carsten , Bauer Jens , Lotnyk Andriy , von Wenckstern Holger , Anders André , Unutulmazsoy Yeliz
Published: July 2024

Deposition of epitaxial oxide semiconductor films using physical vapor deposition methods requires a detailed understanding of the role of energetic particles to control and optimize the film properties. In the present study, Ga2O3 thin films are heteroepitaxially grown on Al2O3(0001) substrates using oxygen ion beam sputter deposition. The influence of the following relevant process parameters on the properties of the thin films is investigated: substrate temperature, oxygen background pressure, energy of primary ions, ion beam current, and sputtering geometry. The kinetic energy distributions of ions in the film-forming flux are measured using an energy-selective mass spectrometer, and the resulting films are characterized regarding crystalline structure, microstructure, surface roughness, mass density, and growth rate. The energetic impact of film-forming particles on the thin film structure is analyzed, and a noticeable decrease in crystalline quality is observed above the average energy of film-forming Ga+ ions around 40 eV for the films grown at a substrate temperature of 725 °C.
Multichannel direct communication based on a programmable topological plasmonic metasurface
Authors: Xiao Qiang , Ma Qian , Qin Shi Long , Chen Long , Ning Yu Ming , You Jian Wei
Published: July 2024

With the gradual improvement of the future wireless communication technology, the demand for high information capacity and reliable links in communication systems is also ever-increasing. Programmable topological plasmonic metasurfaces, consisting of artificially engineered structures with robust propagation pathways control, have emerged as a revolutionary technology for stable microwave and on-chip communication systems. Programmable topological plasmonic metasurfaces offer unprecedented flexibility and adaptability in managing multiple communication channels as the propagation paths can be easily reconfigured to meet specific communication requirements. Here, we have experimentally demonstrated the ability to dynamically manipulate electromagnetic waves along eight distinct topological pathways for a multichannel direct communication system. The simulation results of topological plasmonic metasurfaces with different coding schemes have showcased their excellent performance in multichannel wavefront control. Experimental results have consistently aligned with the simulation findings, validating the effectiveness of multichannel topological routes. Furthermore, an eight-channel direct communication system based on a programmable topological plasmonic metasurface is designed and implemented to transmit different information. The proposed multichannel communication system based on a programmable topological plasmonic metasurface opens up new possibilities for high-capacity, efficient, and adaptive communication systems, which hold great potential in transformative applications in areas such as 6G, Internet of Things, and beyond.
Thermal optimization of two-terminal SOT-MRAM
Authors: Su Haotian , Kwon Heungdong , Hwang William , Xue Fen , Köroğlu Çağıl , Tsai Wilman , Asheghi Mehdi , Goodson Kenneth E. , Wang Shan X. , Pop Eric
Published: July 2024

While magnetoresistive random-access memory (MRAM) stands out as a leading candidate for embedded nonvolatile memory and last-level cache applications, its endurance is compromised by substantial self-heating due to the high programming current density. The effect of self-heating on the endurance of the magnetic tunnel junction (MTJ) has primarily been studied in spin-transfer torque (STT)-MRAM. Here, we analyze the transient temperature response of two-terminal spin–orbit torque (SOT)-MRAM with a 1 ns switching current pulse using electro-thermal simulations. We estimate a peak temperature range of 350–450 °C in 40 nm diameter MTJs, underscoring the critical need for thermal management to improve endurance. We suggest several thermal engineering strategies to reduce the peak temperature by up to 120 °C in such devices, which could improve their endurance by at least a factor of 1000× at 0.75 V operating voltage. These results suggest that two-terminal SOT-MRAM could significantly outperform conventional STT-MRAM in terms of endurance, substantially benefiting from thermal engineering. These insights are pivotal for thermal optimization strategies in the development of MRAM technologies.
A piezoelectric vibration sensor with excellent performance based on Bi12SiO20 crystal for high-temperature applications
Authors: Wu Guangda , Yao Qingkai , Liu Xueliang , Yu Fapeng , Zhao Xian
Published: July 2024

High-temperature piezoelectric vibration sensors play a crucial role in the accurate monitoring of the dynamic mechanical conditions in aerospace, automotive, and energy generation systems. However, the use of conventional piezoelectric materials in high-temperature environments is restricted owing to their limited Curie temperatures. In this study, we grew a piezoelectric crystal Bi12SiO20 (BSO) with the crystal cut optimized for high longitudinal piezoelectric coefficient and low piezoelectric crosstalk behaviors. Subsequently, a compression-type piezoelectric vibration sensor utilizing the BSO bulk crystal was developed and fabricated for structural health monitoring under high temperatures. The impact of pre-tightening torques on the sensor performance was investigated. Moreover, the sensor performance was analyzed under temperatures up to 650 °C. The BSO-based sensor exhibited an average sensitivity of ∼3.89 pC/g between 25 and 650 °C under 160 Hz frequency, with a variation of 5.5%. Additionally, the BSO-based sensor demonstrated ultra-stable sensitivity at 600 °C, highlighting its strong sensing capabilities and reliability under high temperatures. Thus, the BSO-based vibration sensor is a promising option for structural health monitoring applications under high temperatures.
Numerical investigation of non-uniform inflow effects on internal and external characteristics of an axial-flow pump
Authors: Xu Chenxi , Liu Dong , Liu Benqing , Liu Zhuqing , Yang Wei
Published: July 2024

This paper investigates the effects of non-uniform inflow on the internal and external characteristics of an axial-flow pump. Numerical simulation is employed to study two different configurations: one with an intake sump (referred to as the intake system) and another without an intake sump (referred to as the pump system), where the intake sump introduces non-uniform inflow conditions. First, under low flow conditions, typical unstable flow phenomena are observed in the impeller, including leading edge spillage and tip leakage vortex, which are consistent with previous research findings. Second, the analysis reveals that the non-uniform inflow causes the pump system to enter the hump zone earlier, as indicated by the external characteristic curves. Energy loss analysis identifies the increased energy loss at the bell mouth due to backflow from the impeller as the main contributor to the head drop. Finally, it is observed that submerged vortices exist at the bottom of the intake sump; however, their swirling strength is insufficient to significantly affect the hump characteristics of the intake system under low flow conditions. The distinguishing factor between the two systems is the distribution of axial velocity along the radial direction in the bell mouth. The higher axial velocity near the casing of the bell mouth in the pump system supplements the energy of the liquid near the shroud side of the impeller, thus delaying the occurrence of backflow.
Responsive refractive index sensor based on actively tuning liquid crystal topological edge states
Authors: Ye Hai-Ning , Wan Bao-Fei , Zhao Yu-Qi , Li Bing-Xiang , Zhang Hai-Feng
Published: July 2024

In this paper, using the electric field regulation and low loss properties of liquid crystal materials, a tunable polarization-separated liquid crystal (LC) topological edge state is proposed, whose potential in responsive sensors (RSs) is explored. Adjustment of the measuring range and sensitivity of the RS can be realized by controlling the orientation angle of LC and the analyte proportion. In the case of a low ratio of analytes, as the LC orientation angle changes from 18° to 0°, the measurement range will also vary from 1–1.8 RIU (refractive index unit) to 1.8–2.3 RIU. When adding the proportion of analytes and the number of periods, the normalized sensitivity will be increased from 0.0759 c/d/RIU (c is the propagation speed of light in vacuum, and d is the normalized thickness) to 0.299 c/d/RIU, leading to a reduction in the detection limit from 2.75 × 10−4 to 5 × 10−6 RIU, so biological indicators such as bacteria Leptospira in rodent urine can be detected.