bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed discharge in a large diameter tube with long-lasting pre-ionization
Authors: Jancarek A. , Bobrova N. A. , Nevrkla M. , Sasorov P. V. , Sisma J. , Vrba P. , Hübner J. , Vrbova M.
Published: February 2025

The evolution of a nitrogen plasma discharge in a tube with an inner diameter of 9.2 mm, excited by a particular pulse shape, is studied to suppress ablation from the inner wall. Excitation is realized by two current pulses. The first one is a long pre-ionization pulse, which guarantees the stability of the plasma column, and the second one is a higher current pulse, which causes the detachment of the discharge plasma from the wall. The evolution of plasma in the tube is modeled using the magneto-hydrodynamic code NPINCH in two approximations: (1) non-ablative and (2) strongly ablative walls. The time dependences of the optical radiation power in the direction along the discharge tube axis are measured and compared with simulated experimental results in non-ablative and ablative approaches. Time dependence of the measured optical radiation emission corresponds to the non-ablative model. In the selected large diameter capillary, the development of the pinching plasma is not significantly affected by the ablation of the material from the capillary walls.
Analysis of two-step photocurrent generation in GaAs:N-based intermediate band solar cells with utilization of device simulation
Authors: Hossain Md Faruk , Yagi Shuhei , Yaguchi Hiroyuki
Published: February 2025

We developed a novel approach to analyze the two-step photocurrent generation process in intermediate band solar cells (IBSCs) by means of numerical device simulation combined with rate equation analysis. An IBSC having a GaAs:N intermediate band (IB) absorber with the same layered structure as experimentally investigated in our previous work is modeled, and its characteristic behavior of external quantum efficiency (EQE) is successfully simulated with the utilization of Silvaco-Atlas software. The simulated results gave new insights into the material parameters of the device, such as trap states and interface recombination velocity, and revealed that an electron-blocking layer adjacent to the IB absorber plays a significant role in confining the electrons in the IB state, which is the main prerequisite for efficient two-step photocurrent generation. Change in EQE (ΔEQE) induced by additional light illumination of which energy is below the valence band–IB gap is analyzed as an evaluation metric of two-step photocurrent generation based on a rate equation analysis. The integrated electron concentration in the GaAs:N absorber layer is calculated from the simulation results and is used as an input parameter for the rate equation analysis. As a result, the bias voltage-dependent ΔEQE of experimentally investigated IBSC is well reproduced, indicating that the proposed method can be a useful approach for a better understanding of IBSC operation physics and designing more efficient devices.
Enhancing contact triboelectrification by coupling interfacial spontaneous polarization and permittivity manipulation
Authors: Li Haozhen , Zhao Xin , Xie Guangzhong , Su Yuanjie
Published: February 2025

The electricity generation of triboelectric nanogenerators (TENGs) originates from charge transfer enabled by contact electrification. However, the inherent barrier between two contacting surfaces hampers the triboelectric charge transfer. There are mainly four ways to promote the triboelectrification of TENGs. While synergy among them has never been achieved. Herein, we reported an effective strategy to boost the triboelectric charge transfer efficiency by synergizing the strong ferroelectric polarization and high permittivity of embedded lead zirconate titanate fillers. The influence of interfacial polarization intensity and the dielectric permittivity, as well as corona poling, on the triboelectrification of composite film was systematically investigated. Notably, the switching of interfacial polarization direction renders an increase (207%) or a decrease (71%) in the triboelectric output in comparison with the non-poled counterpart. Theoretical modeling was established by combining Kelvin probe force microscopy characterization with the electron cloud overlap energy band derivation. This work not only offers unprecedented insight into the fundamental mechanism of triboelectrification but also opens up a possibility in the development of next-generation wearable electronics.
Nonlocal strain gradient modeling of vibration energy harvesting in fluid-immersed bimorph sandwich nanoplates under thermal environment
Authors: Roodgar Saffari Pouyan , Senjuntichai Teerapong , Rajapakse Nimal
Published: February 2025

This research details a method for mathematically simulating and assessing thermal vibration energy harvesting in laminated bimorph nanoplates in fluid contact. The model uses the piezoelectric characteristics of the outer layers and the functionally graded (FG) core material to transform thermal stresses into electrical energy efficiently. Nanostructures' size effects and nonclassical behavior are captured by the nonlocal strain gradient theory (NSGT). Combining the Navier–Stokes equations with the electromechanical equations obtained from Hamilton's principle, first-order shear deformation theory (FSDT), and Gauss's law yields an advanced multi-physics model. The FG core exhibits variations by the power law principle and is composed of both ceramic and metal components. Analytical solutions are obtained for the frequency response functions that relate the electrical power output to the external circuit load resistance by solving the coupled electromechanical-fluid equations. A thorough investigation is conducted to analyze how different elements impact energy harvesting performance using parametric studies. These factors include the configuration of the harvester (either parallel or series piezoelectric connections), nonlocal and strain gradient effects, temperature gradients, fluid depth, electrical load, geometric dimensions, and the material properties of the piezoelectric layers, and functionally graded core.
Research on the regulation of lithium-ion battery electrode coating stability
Authors: Lu Qian , Ye Xin , Wu Lutong , Jiang Fengze
Published: February 2025

The electrode slot die coating for lithium-ion batteries is characterized by its large scale and high efficiency, with significant advancements in recent years. Coating stability, a critical factor of lithium-ion batteries quality, is significantly influenced by numerous factors. To address this, a computational model for slot die coating has been developed to ensure stable electrode coatings. The model examines the impact of slurry speed at the slot exit (Vslurry) and substrate movement speed (V) on both coating stability and coating thickness (h), aiming to create a prediction model. The electrode coating state is classified into three distinct categories: fluid weeping, stable coating, and bead breakup, based on the meniscus position of the coating. By effectively managing the process parameters, this prediction model can mitigate defects during the coating, facilitating efficient, and stable electrode coatings. Moreover, the model enables adjustments to coating thickness at different coating speeds. Specifically, when the Vslurry ranges from 0.250 and 0.750 m/s, the corresponding stable V spans 0.255–1.800 m/s, with h varying from 0.200 to 0.480 mm under these conditions. This study provides theoretical guidance for regulating the stability of slot die coating in lithium-ion battery electrodes and establishes a theoretical foundation for the selecting optimal process parameters in practical applications, which holds considerable significance.
Thermal effects on the dynamics of vortex breakdown in spherical Couette flow
Authors: J. P. Ananthu , Narayanan Vinod
Published: February 2025

This study investigates the effect of heating on the topology of vortex breakdown in spherical Couette flow under unstable thermal stratification. A three-dimensional spectral direct numerical solver is employed to solve the non-dimensionalised Navier–Stokes and energy equations. The inner sphere is rotated with constant angular velocity, while the outer sphere remains stationary. A constant temperature difference is maintained between the inner and outer spheres. The rotational effects are characterized by the Reynolds number (Re), while buoyancy-driven forces are quantified by the Rayleigh number (Ra). At low Ra, rotational forces dominate, resulting in steady, axisymmetric flow with well-defined vortex-detection bubbles and an equatorial jet. As Re increases, centrifugal instabilities lead to periodic oscillations and the formation of complex bubble structures. For higher Ra values, buoyancy-induced convection destabilizes the flow, transitioning it to nonaxisymmetric and chaotic states dominated by convective cells and large-scale circulation. The evolution of the vortex breakdown topology is characterized using streamlines and velocity magnitude distributions. Time series and their fast Fourier transform illustrate the transition from periodic oscillations to high-frequency complex unsteady flow. Dynamic mode decomposition analysis reveals the dominant spatiotemporal modes, providing insight into the interplay between rotational and buoyancy-driven instabilities. Thermal plumes, driven by buoyancy forces, enhance radial mixing and heat transfer, with their coherence and complexity increasing with Ra and Re.
Vortex-driven nanogenerators for marine energy harvesting and flow velocity sensing
Authors: Xu Peng , Hong Mingjie , Li He , Song Chenlu , el Moctar Ould , Jiang Changqing
Published: February 2025

With the growing focus on clean and sustainable energy, ocean currents have emerged as a promising source. Traditional hydraulic turbines perform poorly in low-velocity ocean currents, limiting efficient energy extraction. This study introduces a novel multi-grating triboelectric nanogenerator (MG-TENG) that harnesses vortex-induced vibrations for energy harvesting, particularly effective in low-velocity marine environments. Our device not only converts ocean current energy into electricity but also measures flow velocity, addressing two critical needs. Structural improvements to the MG-TENG have boosted its output power by 33.5 times over conventional designs, while durability tests confirm its reliability under sustained operation. A new double-cylinder configuration extends the range of measurable velocities from 0.3 to 0.65 m/s, enhancing the device's versatility. These findings suggest that MG-TENG could serve as both a power supply and a velocity sensor, presenting an innovative solution for energy harvesting in low-velocity ocean currents.
Morphology and wetting characteristics of micrometer-sized droplets impacting rough wall surfaces
Authors: Yang Yinkai , Tian Shixiang , Zhao Jiajia , Yan Minghai , Zhang Xuan
Published: February 2025

Droplet impact on rough walls is a prevalent phenomenon in engineering applications, including surface spraying and spray wetting, and understanding the morphology and wetting characteristics of such impacts is crucial for industrial processes. This study utilizes computational fluid dynamics to examine the effects of velocity, surface tension, and their interactions on the behavior of micrometer-sized droplets impacting rough walls. The findings reveal five morphological changes during droplet impact: oscillation, rebound, bubble formation/rebound, tearing/bubble formation/rebound, and rupture/localized rebound. Droplets with lower surface tension are more likely to rebound in low-speed impacts compared to those with higher surface tension. Surface tension has minimal influence on droplet spreading at the initial stage of impact but significantly affects spreading and retraction prior to the liquid reaching its residual diameter after impact. Lowering surface tension and increasing impact velocity intensify morphological changes and enhance wetting performance on rough wall surfaces. The interaction between surface tension and velocity influences the droplet's behavior, as increased surface tension reduces the enhancement of spreading caused by higher impact velocity, while higher velocity decreases the disparity in the minimum height values of droplets with varying surface tensions. This analysis of droplet morphology and wetting characteristics provides valuable insights for applications involving micrometer-sized droplets interacting with rough wall surfaces in engineering practices.
Numerical investigation of flow and heat transfer characteristics in buoyancy-driven convection around cylinder arrays within an enclosure
Authors: Xu Tiantian , Choi Jung-Il
Published: February 2025

This study examines the flow and heat transfer characteristics of buoyancy-driven convection around cylindrical arrays within an enclosure, employing a monolithic immersed boundary projection method. The effects of Rayleigh numbers, volume fraction, and cylinder count on flow regimes and heat transfer are systematically analyzed, identifying three distinct regimes: steady, periodic unsteady, and chaotic unsteady. Transitions between these regimes are strongly influenced by interactions among the parameters, with odd-count cylinder configurations promoting flow instability and broadening the range of periodic flow. Flow and temperature field analyses reveal that the flow regime is governed by the available space for fluid motion (determined by cylinder count and volume fraction) and thermal driving forces (determined by Rayleigh numbers). Time- and surface-averaged Nusselt numbers demonstrate heat transfer enhancement with increasing Rayleigh numbers and decreasing cylinder counts. At lower Rayleigh numbers, a linear increase in Nusselt numbers with total surface area is observed, while at higher Rayleigh numbers, the increase exhibits a gradually decreasing slope, providing insight for optimizing thermal performance. These findings underscore the critical roles of Rayleigh numbers, volume fraction, and cylinder count in influencing heat transfer characteristics in buoyancy-driven convection systems.
Gap ratio effect on the nearstream behavior of a confined jet flow
Authors: Nwoye Chukwunonso , Oko Eni , Okoro Humphrey O. , Nwaji Godswill N. , Okoronkwo Chukwunenye A. , Anyanwu Emmanuel E.
Published: February 2025

This work investigated the near stream behavior of a confined jet flow when passive rings were placed at the nozzle exit plane at different gap ratios (β). β is the gap (da) between the ring and the inner nozzle wall, normalized by the ring thickness (drc) and ranged from  0.2≤da/drc≤1.0. The results show that the shedding of vortices behind the ring depends strongly on β. The suppression of the vortices was complete and partially at β=0.2 and 0.6, respectively, but negligible at β=1.0. The vortex suppression was associated with flow deflection due to delayed separation. The normal Reynolds stress Uu at the center of the gap was 1.255m2s−2 at β=0.2 and 3.083e−5m2s−2 at β=1.0. The increase in stress across the gap at small β values enhanced the momentum transfer between the fluid layers. This sustained the flow on the ring surface against an adverse pressure gradient and delayed the flow separation. The ring generally suppressed the jet spread. However, the mean velocity spread suppression only correlated strongly with β at the nozzle exit because the negative forcing on the shear layer coherent structure by the wake vortices was local. At 0.3 nozzle diameter downstream of the origin, the velocity spread became independent of β because of the decay of the wake vortices.
Effect of nozzle translation on a bounded vortex flow
Authors: DesRoberts Ben , Marshall Jeffrey S.
Published: February 2025

A bounded vortex flow is generated by a nozzle that combines azimuthally tilted downward jets in a circular array and a central suction port. When the nozzle is directed toward a bottom surface (called the impingement surface), the flow develops a strong intake vortex spanning from the impingement surface to the suction port, which acts to generate strong shear stress on the impingement surface. This strong shear stress can aid in removing particles attached to the impingement surface or in enhancement of heat or mass transfer, where in typical applications, the nozzle would be translated along the impingement surface. This paper reports on a computational study of the effect of nozzle translation on the bounded vortex flow field. The nozzle translation induces a bending of the bounded vortex in the downstream flow direction, which becomes larger with increase in the nozzle translation speed. We identify an interesting oscillatory phenomenon by which the bounded vortex can resist the bending induced by the translational flow and rotate about a mean position downstream of the suction port. At sufficiently high translation speeds, the oscillatory process can no longer resist the downwash effect from nozzle translation and the vortex eventually detaches from the impingement surface, limiting the effectiveness of this flow device.
Method of characteristics with thermo-chemical non-equilibrium for high Mach number inlet
Authors: Li Dengke , Dai Chunliang , Sun Bo , Chen Xiong
Published: February 2025

A method of characteristics (MOC) plays a crucial role in the inviscid design of conventional hypersonic inlets. However, thermo-chemical non-equilibrium effect caused by the high total temperature makes it arduous to accurately predict the flow inside a high Mach number inlet by employing the traditional MOC method. To bridge this gap, this study intends to proposed the method of non-equilibrium characteristics (MONC), a novel approach grounded in the governing equations of inviscid and thermo-chemical non-equilibrium flow. Different from the previous MOC for non-equilibrium flows, the specific heat ratio of translational–rotational energy is derived to execute the solution processes of MONC rather than a frozen specific heat ratio. In addition, the strategy based on a streamline and a Mach line is employed to reduce the errors in the interpolation. As for capturing the shock wave and predicting the vibration relaxation and chemical reactions in the high-temperature flow fields of the high Mach number inlet, the MONC code based on Python language is capable of predicting numerical results with a deviation of less than 2% from computational fluid dynamics (CFD). In the expansion flow of the high-enthalpy nozzle, our MONC code can also well calculate the vibrational temperature, with the maximum error of 1.4% compared to the closest experimental data. Moreover, the MONC method demonstrates a significant improvement in the computational efficiency, being approximately 353 times faster than the CFD method in the case of curve surface compression flow. The MONC demonstrates the outstanding potential for solving shock capture problems in the inviscid flow with the high enthalpy. Thereby, the current study should supply the theoretical tool for the aerodynamic design of the high Mach number inlets.
Particle weight spatial distribution and force chain network evolution in flat-bottomed silos using the discrete element method
Authors: You Minghao , Wang Xin , Liang Cai , Liu Daoyin , Ma Jiliang , Chen Xiaoping
Published: February 2025

In industrial-scale powder storage facilities, abnormal stress distribution on silo walls can lead to severe safety accidents, including structural deformation and collapses. The powder weight distribution in three-dimensional flat-bottomed silos was studied from the force chain network rearrangement of the micro-mechanism to the wall stress distribution of the macro-behavior. The effects of particle size, silo diameter, and powder type were considered using the discrete element method. At a constant filling height-to-diameter ratio (Hfilling/D), increasing particle size slightly raises the bottom load-bearing percentage, while maintaining a constant filling height significantly increases this percentage as silo diameter increases. The size effect notably affects load-bearing distribution and pressure accumulation on the silo wall. The bottom effect weakens the sidewall load-bearing capacity near the bottom. The average particle–wall friction coefficient in static packing is lower than the predefined value, indicating insufficient wall friction mobilization. Shallow silos primarily support powder weight from the bottom. As Hfilling/D increases, strong force chains develop, enhancing force transmission and uniformity, while enhancing the sidewall load-bearing capacity.
Vertical vortex-induced vibration performance of split triple-box girders with various ancillary facility configurations
Authors: Yang Han , Zheng Shixiong , Ma Cunming
Published: February 2025

Wind tunnel tests were conducted to systematically investigate the effects of maintenance rails, individual auxiliary facilities, and various combinations on the vertical vortex-induced vibration (VIV) of triple-box girders. Results indicate that highway wind barriers intensify vertical VIV, while railway wind barriers and crash barriers help to mitigate it. Computational fluid dynamics (CFD) was utilized to analyze the aerodynamic pressure distribution and flow field characteristics of the triple-box girder. Flow separation at the top of the highway wind barrier was identified as a primary driver of VIV. Railway wind barriers effectively reduce VIV by creating low-pressure regions on the railway box's top surface, preventing the main girder from generating periodic aerodynamic forces. Additionally, crash barriers reduce VIV by suppressing vortex formation at the trailing edge of the upstream box. The two vibration suppression measures were proposed based on the VIV-inducing mechanism and validated through experiments and flow field analysis.
Effect of particle shape on particle flow and heat transfer behavior based on computational fluid dynamics-discrete element modeling
Authors: Gou Qiuqin , Wang Xinglin , Chen Guoding , Liu Surong
Published: February 2025

Particle fluidization technology is often involved in biomass industrial applications. However, the utilization of biomass particles requires gas–solid flow and processes, such as heat transfer and reaction transformation. Therefore, in this paper, biomass pellets were processed into cylindrical particles and designed with five aspect ratios (AR = 0.5, 1.0, 1.5, 2.0, and 3.0). The kinetic and heat transfer characteristics of cylindrical particles with different aspect ratios in a bubbling fluidized bed were analyzed from macroscopic and microscopic perspectives using the Computational Fluid Dynamics-Discrete Element Method. The simulation results show that the higher the sphericity of cylindrical particles (AR = 1), there is obvious particle aggregation near the wall, and the higher the bed height, the more asymmetric the particle flux distribution. Increasing the gas superficial velocity helps to improve the mixing quality of the particles, convective heat transfer, particle temperature cooling rate, and uniformity of particle temperature distribution. The contact force between particles is much larger than the gas–particle interaction force, and the particle contact force is mainly concentrated on both sides of the wall. The larger the aspect ratio of cylindrical particles, the smaller and more uniformly distributed the particle contact force at the wall. Furthermore, when AR > 1, the drag force and lift force gradually increase with the increase in particle aspect ratio, the faster the particle temperature decreases, the larger the particle convective heat transfer, and the larger the standard deviation of temperature.
Peristaltic transport of mixed convective two-phase nanofluid with Ohmic heating used in drug delivery systems: Adomian decomposition method
Authors: Mishra S. R. , Panda Subhajit , Baithalu Rupa , Shah Nehad Ali
Published: February 2025

Flow through flexible wavy walls, the peristaltic transport has widespread applications in various sectors such as biomedical engineering, particularly in drug delivery systems, dialysis, etc., where the role of flexible conduits is crucial in controlling fluid flow. Peristaltic phenomena are utilized in several industrial processes like microfluidic devices. The proposed study focuses on the peristaltic flow of two-phase nanofluid within flexible wavy walls by including thermal radiation and Ohmic heating. The interaction of both the flow properties influences the temperature distributions and flow characteristics within the channel. The heat transfer rate increases due to the inclusion of the thermal radiation; however, Ohmic heating contributes a significant augmentation in the fluid temperature due to the electrical conducting nature of the fluid. A comparative analysis is presented using the Adomian decomposition method, as semi-analytical method. The behavior of several characterizing factors is presented briefly and described in the discussion section. However, the important findings are the buoyant forces accumulated with both thermal and solutal Grashof number that enhance the fluid velocity; however, a smooth retardation occurs at both the walls for the increase in inertial drag.
Assessment and L2 pragmatics
Authors: Roever Carsten
Published: February 2025

Pragmatic and interactional abilities are represented in major models of second language (L2) communicative competence (Bachman & Palmer, 2010; Canale & Swain, 1980), which provide the framework for L2 assessment. However, pragmatics and interaction are only rarely tested in major operational tests. This is despite a significant amount of work in the testing of L2 pragmatics and interaction since the mid-1990s. This paper outlines current work on testing of L2 pragmatics, which broadly follows two traditions, one informed by speech act theory, politeness theory and philosophical pragmatics, and the other by conversation analysis and sociology. It also discusses reasons for the limited uptake of pragmatics assessment by large-scale tests, including low practicality, limited stakeholder test literacy, and broader challenges in testing pragmatics. It concludes by suggesting ways of overcoming these obstacles and thereby achieving better construct representation in L2 tests.
Heritage learner pragmatics
Authors: Xiao-Desai Yang , Wong Ka F.
Published: February 2025

The diversity of heritage language learners and inclusivity of pragmatics usher in a new era of research that explores the unique nature of “heritage learner pragmatics.” This article provides a review of this emerging field, drawing on a thematic analysis of the literature over the past decade. Major findings reveal that a high degree of hybridity underlies heritage learners’ pragmatic competence and performance and that the reasons for this hybridity are complex. The hegemony of the majority language, the assimilative pressure from the host society, the status of the heritage language in the home country, and access to formal education, together with learner factors such as proficiency, attitude, and agency, all appear to have meaningful impacts. We propose that the research of heritage learner pragmatics needs an extension beyond the binary convention of monolingualism and bilingualism to embrace intersectional inquiries that focus on identity, multiculturalism, translanguaging, and social justice for minoritized communities and their languages.
Antiferromagnetic spin fluctuations and structural transition in cluster Mott insulator candidate Nb3Cl8 revealed by 93Nb- and 35Cl-NMR
Authors: Zhou Y. Z. , Han X. , Luo J. , Wu D. T. , Fang A. F. , Shen B. , Feng B. J. , Shi Y. G. , Yang J. , Zhou R.
Published: February 2025

Motivated by recent studies on the cluster mott insulator candidate compound Nb3Cl8, we perform 93Nb and 35Cl nuclear magnetic resonance (NMR) measurements to investigate its electron correlations. Below the structural transition temperature Ts
~ 97 K, all the satellites of the 93Nb NMR spectra split into three distinct peaks, which suggest a symmetry lowering due to the structural transiton and could be attribute to the change of the Nb-Nb bond-lengths of Nb3 clusters. The spin-lattice relaxation rate 1/T
1 devided by temperature T, 1/T
1
T, increases upon cooling down to Ts
for all Cl sites, whereas only the Knight shift K of Cl located at the center of Nb3 clusters exhibits a similar temperature dependence as observed in magnetic susceptibility. These findings collectively demonstrate the existence of strong spin correlations between Nb atoms in Nb3Cl8, which should be closely associated with its Mottness.
Effect of polydimethylsiloxane strain on its contact electrification characteristic: a first-principles investigation
Authors: Wu Jun , Zhu Wenming , Wen Qing , Cao Jiapeng
Published: February 2025

Material strain is one of the factors affecting contact electrification. Previous works have investigated the influence of polymer strain on contact electrification from the perspective of material transfer by means of experimental methods. However, the detailed electron transfer mechanism, which is the most fundamental form of contact electrification mechanism, is still unclear. In this work, the effect and its mechanism of polydimethylsiloxane (PDMS) tensile strain on contact electrification with polytetrafluoroethylene (PTFE) are investigated via first-principles calculations. The results show that the number of electrons transferred from the PDMS to the PTFE increases with the stretched ratio. In addition, the possibility of breakage on the PDMS main chain caused by tensile strain is considered. The result shows that the total number of transferred electrons from the broken fragments is much less than that of the original PDMS molecule. Moreover, the fragment of PDMS molecules with the oxygen dangling bond can even obtain electrons from the PTFE molecule. This work can provide a theoretical basis for understanding the influence mechanism of polymer strain on contact electrification from the perspective of electron transfer.
Spatial charge transport model driven by Kerr optic-electric measurement in transformer oil under switching overvoltage conditions
Authors: Zhang Zhaotian , Duan Pan , Wan Haibo , He Wenkai , Wu Shilin , Xing Zhaoliang , Yang Qing
Published: February 2025

The accumulation of space charge in transformer oil under switching overvoltage considerably influenced its insulation performance, representing a critical factor in transformer insulation design. This study examined the electric field and space charge distribution in transformer oil under varying switching overvoltages, utilizing a Kerr effect electro-optical measurement platform integrated with a novel optical path multiplier device. The results indicated that the maximum electric field distortion rate consistently occurred within the 250–500 μs range for different voltage levels. Moreover, increasing the applied voltage led to a corresponding rise in electric field distortion within the oil gap, with the maximum distortion rate exceeding 90%. Under switching overvoltage conditions, the space charge in transformer oil displayed a bipolar homogeneous charge distribution, characterized by notable charge injection. With increasing voltage, both the electrode’s charge injection capacity and the average charge mobility were enhanced. Based on the observed space charge distribution patterns and key physical parameters, a bipolar charge transport model was developed, shedding light on the mechanisms of space charge accumulation in transformer oil. Overall, this study provided valuable experimental data and theoretical insights for the insulation design of transformers.
Bandgaps and damping of four-component phononic crystals with planar tension–torsion coupling effect
Authors: Tang Haishan , Li Xiaobai , Mei Chaosheng , Hu Yujin , Ling Ling , Li Li
Published: February 2025

In the conventional phononic crystal, the torsion local resonance cannot open new bandgaps due to the absence of coupling between the torsion of core and the tension/compression of matrix. Also, the soft coating may greatly reduce the overall stiffness due to the direct contact between the coating and the matrix. By introducing the planar tension–torsion coupling (TTC) effect and the rigid strain isolation interphase, the four-component phononic crystal with higher stiffness and damping properties is developed in this study, and the general mechanism of the TTC effect on the bandgap and energy attenuation properties of TTC phononic crystal is investigated based on Bloch–Floquet theory. The effects of stiffness coefficients including tension stiffness, torsion stiffness and TTC stiffness on the location and width of bandgaps in the TTC phononic crystals are presented, it is found that the introduced TTC effect is beneficial for opening new bandgaps that cannot be created in the conventional locally resonant phononic crystals (LRPCs). The spatial and temporal energy attenuation properties of TTC phononic crystal are evaluated via ‘harmonic wave’ approach (

q
(
ω
)

) and ‘free wave’ approach (

ω
(
q
)

), respectively. Meanwhile, the TTC effect can help some damping phononic crystals to increase the temporal energy attenuation via the modal strain energy approach. Furthermore, the maximum spatial energy attenuation of TTC phononic crystal is triggered by the TTC local resonance of the core. This study provides some guidelines for high-damping and high-stiffness phononic crystals, which are ideal candidates for vibration reduction of engineering structures.
A mathematical model for thermal radiation between non-continuous periodic structures and its application in near-field radiation between split ring resonators
Authors: Wen Sy-Bor , Khazaee Saeed
Published: February 2025

A mathematical model has been developed to study far-field and near-field thermal emission from non-continuous periodic structures. Non-continuous periodic structures with appropriate geometries and materials can support electric or magnetic resonance, idealized for designing far-field perfect absorbers and near-field emitters/absorbers supporting long-distance photon tunneling. However, these structures do not have close format dyadic Green’s function to describe the thermal radiation from randomly fluctuating thermal current. Thus, simulating the near-field radiation spectrum between emitters and collectors patterned with these non-continuous periodic structures is challenging. Though finding eigenmodes of white-noise-like fluctuating thermal current satisfying this specific geometry, we extended the Wiener-Chaotic expansion type of near-field simulation to study far-field and near-field thermal emission from non-continuous periodic structures. After verifications with reference cases, the new mathematical method is applied to study photon tunneling between the emitter and the collector patterned with single-ring split ring resonance rings (SRR) supporting magnetic field resonance. It is observed from the new mathematical model that long photon tunneling can occur under such a configuration through magnetic field coupling between the emitter and collector at the magnetic resonance frequency of SRRs.
Experimental study of flute instability by even/odd-parity quadrupole fields in Keda Mirror with AXisymmetricity (KMAX)
Authors: Li Qing , Teng Xiaotian , Qin Weijian , Xu Zelin , Ying Jiacheng , Chen Yutao , Zhang Yichi , Li Yilin , Wen Jingran , Yang Zhida , Liu Ming , Ren Baoming , Sun Xuan
Published: February 2025

This study investigates the stabilization of flute mode instabilities in the Keda Mirror with AXisymmetry device, specifically focusing on the m = 1 mode that propagates in the direction of electron diamagnetism due to the
E
×
B
force. To mitigate this instability, quadrupole field (QPF) antennas were designed with either even or odd parity, depending on the direction of the induced current. Experimental results reveal that even parity significantly enhances stability, reducing fluctuation values at the plasma boundary by approximately 50%, while odd parity achieves only a 10% to 20% reduction. Radial particle flux measurements indicate a decrease to one-tenth of the original value when the even-parity QPF is applied during the wash-gun injection phase, with no correlation observed between ion saturation current and angular electric field fluctuations. The stability enhancement is attributed to the positive magnetic pressure gradient generated by the QPF. Further analysis incorporating magnetic field curvature reveals that the beneficial effects are more pronounced with even parity. However, the density measured by the interferometer decreases significantly with increasing even-parity QPF current, while the density with odd parity remains largely unchanged.
Impact monitoring based on domain adversarial transfer learning strategies
Authors: Zhao Bowen , Qing Xinlin , Wang Yishou , Liu Qijian , Yan Jiajia , Wang Yihan , Liao Yunlai
Published: February 2025

Impact events may cause some damage to aerospace composite structures that are difficult to inspect on the surface, thus threatening the operational safety of the aircraft. Therefore, estimating the impact location and the original impact force is necessary. This paper proposes a deep-learning model for impact monitoring based on feature extraction. The first step employs a convolutional neural network to localize the impact region, initially narrowing it to a specific area and then determining a precise location using a weighted center algorithm. In the second part, the temporal convolutional network is first utilized for feature extraction, and then the gated recurrent unit is used for impact force estimation. During the training of the impact monitoring model, a domain-adversarial transfer learning strategy is employed to extract domain-invariant features between the source and target domains, reducing the data needed for training. This method can monitor impacts on large, complex composite structures using sparse sensor arrays.
Enhancement of electrochemical energy storage performance of MOF-5 and Eucalyptus plant bark derived rGO composite
Authors: Saini Robin , Wadhwa Priyanka , Jain Karuna , Pathak Mayank , Singh Pratap , Dhaka Rahul Kumar , Kumar Sandeep , Singh Manoj Kumar
Published: February 2025

Metal Organic Frameworks (MOFs) and carbon derivatives based composites are an interesting class of materials having complementary properties, with the high surface area and tunable porosity of MOFs together with excellent electrical conductivity of carbon based materials. Here in, we report a facile one step solvothermal synthesis of composite made of MOF-5 and Eucalyptus bark derived rGO. MOF-5/rGO composite (MRG) has a high specific surface area (1150 m2 g−1). MRG was studied for electrochemical energy storage application using Cycle Voltammetry (CV), Galvanostatic Charge Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The MRG has high specific capacitance of 1366.6 F g−1 as calculated by GCD at 1 A g−1 current density, Energy density of 150.7 W h kg−1 and Power density of 450.3 W kg−1 at a current density of 1 A g−1 as calculated by GCD with 1 M H2SO4. The coulombic efficiency for the MRG composite was found to be 89.3% at higher current density. The cyclic stability data shown that composite material is retaining ∼80.9% capacitance even after 10000 cycles. Moreover, symmetrical two electrode device of MRG shown a specific capacitance of 262.4 F g−1 at a current density of 1 A g−1, while the device retained 83.7% capacitance after 10000 charging discharging cycles. The energy density and power density of device were found to be 36.4 W h kg−1 and 498.6 W kg−1 at a current of 1 A g−1. The enhanced electrochemical performance of MRG is attributed to the synergistic effect between MOF-5 and rGO leading to the enhanced conductivity and provides larger surface area for charge storage.
Topological bulk and edge correlations in a Kitaev model on a square lattice
Authors: Ma E S , Zhang K L , Song Z
Published: February 2025

We study the topological bulk and edge correlations of condensed ground state in a p-wave Kitaev model on a square lattice. It is shown that the ground state of the system has the form of the condensate of the Bardeen-Cooper-Schrieffer pair, and the topological transition is associated with the nonanalytic behavior of the pairing order parameters. A real space correlation function is proposed to characterizing the topological phase of the many-body ground state. Numerical results demonstrate that this method works well in the presence of disordered perturbation, lattice defects, or irregular boundary conditions. In addition, the real space correlation function between two edges of the system is investigated, which directly reflects the existence of topological edge modes in the many-body ground state.
Enhanced multi-mode squeezing via a balanced regime in dual-four-wave mixing
Authors: Heng Xing , Wang Weiyi , Wang Fan , Liu Wei , Xia Mingming , Zhai Yueyang , Wei Kai
Published: February 2025

The generation of multi-mode squeezing using four-wave mixing process has attracted considerable attention, offering significant potential for advancements in quantum communication, quantum key distribution, and quantum-enhanced sensing. In this paper, we propose a balanced regime within the dual-four-wave mixing (DFWM) process to theoretically generate quantum-enhanced multi-mode squeezed light. By operating at a plane-balanced regime, the relative intensity squeezing noise factor of the multi-mode beams can be made to approach zero theoretically, thus achieving perfect multi-mode squeezed states. Moreover, the generated beams at the plane-balanced regime exhibit quantum-enhanced entanglement superior to that of conventional four-wave mixing processes, offering significant implications for quantum information processing. The DFWM process can also be extended to multi-spatial-mode squeezing with a spatial-balanced regime, where the attainable squeezing degree is enhanced by a factor of G

N
, where N denotes mode numbers and G denotes the gain, facilitating simply experimental implementation within a single atomic system. The proposed method paves the way for practical applications in high-precision measurements, robust quantum communication networks, and advanced quantum information processing systems.
Scanning tunneling microscopy study on symmetry breaking of charge density wave in FeGe
Authors: Zhang Jiakang , Chen Ziyuan , Wu Xueliang , Li Mingzhe , Li Yuanji , Yin Ruotong , Gong Jiashuo , Wang Shiyuan , Wang Aifeng , Feng Dong-Lai , Yan Ya-Jun
Published: February 2025

The complex symmetry breaking states in AV3Sb5 family have attracted extreme research attention, but controversy still exists, especially in the question of time reversal symmetry breaking of the charge density wave (CDW). Most recently, a chiral CDW has been suggested in Kagome magnet FeGe, but the related study is very rare. Here, we use a scanning tunneling microscope to study the symmetry breaking behavior of both the short- and long-ranged CDWs in FeGe. Different from previous studies, our study revealed an isotropic long-ranged CDW without obvious symmetry breaking, while local rotational symmetry breaking appears in the short-ranged CDW, which may be related to the existence of strong structural disorders. Moreover, the charge distribution of the short-ranged CDW is inert to the applied external magnetic fields and the detailed spin arrangements of FeGe, inconsistent to the expectation of a chiral CDW associated with chiral flux. Our results rule out the existence of spontaneous chiral and rotational symmetry breaking in the CDW state of FeGe, putting strong constrains on the further understanding of CDW mechanism.
Study on the Corrosion Failure Mechanism and Protective Materials of AC Charging Piles in Tropical Island Environment
Authors: Pang Songling , Wang Jun , Li Zhi , Huo Meiyi
Published: February 2025

This paper first analyses the corrosion of AC charging piles in tropical island environments in detail through field investigation and laboratory simulation. The survey results show that the corrosion of the charging pile shell and internal connectors is the most serious, especially in the area close to the coastline, where the corrosion rate is more than 3 times higher than that in inland areas. The laboratory test uses an artificial seawater environment to simulate the actual island environment and study the corrosion resistance of different materials. Through the electrochemical impedance spectroscopy (EIS) test, this paper analyses the electrochemical behavior of different materials in the simulated environment. The results show that the corrosion rates of nano-silver-coated steel and stainless steel are 0.12 mm and 0.38 mm per year, respectively. This paper introduces finite element analysis (FEA) to simulate and analyze the stress distribution and fatigue life of different protective materials in a corrosive environment. The results show that after three years of service, the unprotected stainless-steel material has obvious cracks in the structural stress concentration area, while the stainless steel with nano-silver coating effectively extends the service life of the material, and the cracks are delayed until six years after service. In addition, FEA analysis found that the uniformity and adhesion of the surface coating are the key factors affecting the protective effect. If the coating thickness is uneven or there is a problem of insufficient adhesion, corrosion points are likely to form at the microscopic level, eventually leading to local failure of the material.
Numerical Simulation Study of PM2.5 Diffusion and Distribution in Building Cluster Microenvironment
Authors: Zhang Jingjing
Published: February 2025

In order to improve the quality of the micro-environment of the architectural complex and ensure that residents enjoy a healthy and comfortable living experience, this paper uses Fluent simulation software to simulate the wind environment under the three common layouts of the architectural complex and the diffusion status of PM2.5. On this basis, green trees are added around the pollution sources to compare and analyze the adsorption and blocking effect of green trees on particulate matter. The results showed that after the addition of green trees, the wind environment of the community was optimized, and the concentration of PM2.5 also decreased significantly. These results provide a reference for improving the micro-environment air quality of the building complex.
Comparison of continuum and lattice particle distribution on the percolation threshold for spherical particles in 3D
Authors: Ruiz Vargas Arturo , García Pacheco Georgina , López Monroy Alfredo , Esteban Munguía Cervantes Jacobo , Hiram Calvo Castro Francisco
Published: February 2025

Percolation theory is relevant in research on composite materials because it allows the estimation of the percolation threshold, fc
, which is the critical volumetric fraction at which the phase transition occurs, where they begin to dominate the properties of the filler material over those of the matrix.

There are two main focuses for modelling percolation: continuum or lattice percolation. In the first, the particles are distributed freely in space, and in the second, they are positioned on the sites of a lattice, which could influence the calculated percolation threshold.

Given that in composite materials, particles of the filler are distributed freely on the matrix, in this study, we developed a computational model for estimating the percolation threshold for spherical particles in 3D, under the continuum percolation approach. The results are compared with those obtained with a previous model for lattice percolation, to observe the effect of the modelling focus on the percolation threshold.