bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimizing reduced frequency using genetic algorithms for plasma flow control to achieve drag reduction on a circular cylinder
Authors: Ran Zhuoling , Yu Yi , Nawaz Fahad , Ju Enbo , Meng Xuanshi
Published: December 2024

A closed-loop parameter optimization system around a cylinder is built by integrating the plasma actuation and genetic algorithms in this research, employing numerical simulations and experimental methods. The study aims to minimize the total drag on the cylinder by optimizing the reduced frequency. A pair of surface dielectric barrier discharge plasma actuators, powered by alternating-current high-voltage sources, is symmetrically positioned at ±90° azimuth angles on the two sides of a circular cylinder, and the Reynolds (Re) number is 1.5×104 based on the cylinder diameter. Numerical simulations were first used to determine the optimization space for the reduced frequency, followed by wind tunnel experiments to further search for the optimal research within this space. Particle image velocimetry and hot-wire anemometry were used to investigate the flow field's instantaneous and time-averaged characteristics. Ultimately, the optimal reduced frequency was identified based on duty-cycle frequency, free-stream velocity, and cylinder diameter. The results show that the optimal duty-cycle frequency obtained through genetic algorithm optimization in numerical simulations and wind tunnel experiments is the same, at 140 Hz, corresponding to a reduced frequency of approximately 1.372. The drag reduction rates are also similar, at 73.9% and 73.6%, respectively. During plasma flow control with the optimal reduced frequency, the dominant frequency of the overall motion of the separated vortex field is no longer the natural shedding frequency of the baseline flow. Still, it is instead controlled by the plasma duty-cycle frequency. Compared to the baseline flow, the plasma flow control at the optimal reduced frequency transforms the large-scale alternating vortices into small-scale shedding vortices, resulting in a time-averaged narrow and stable velocity deficit region, leading to reduced energy loss and significantly lower time-averaged drag coefficient. Meanwhile, the interaction between plasma-induced vortices and the Kármán vortex street in the cylinder wake enhances mixing, significantly suppressing turbulence intensity. The results demonstrate the effectiveness of genetic algorithms in identifying the global optimal reduced frequency of plasma actuation, achieving maximum drag reduction.
Computing the multimodal stochastic dynamics of a nanobeam in a viscous fluid
Authors: Barbish J. , Paul M. R.
Published: December 2024

The stochastic dynamics of small elastic objects in fluid are central to many important and emerging technologies. It is now possible to measure and use the higher modes of motion of elastic structures when driven by Brownian motion alone. Although theoretical descriptions exist for idealized conditions, computing the stochastic multimodal dynamics for the complex conditions of an experiment is very challenging. We show that this is possible using deterministic finite-element calculations with the fluctuation dissipation theorem by exploring the multimodal stochastic dynamics of a doubly clamped nanobeam. We use a very general, and flexible, finite-element computational approach to quantify the stochastic dynamics of multiple modes simultaneously using only a single deterministic simulation. We include the experimentally relevant features of an intrinsic tension in the beam and the influence of a nearby rigid boundary on the dynamics through viscous fluid interactions. We quantify the stochastic dynamics of the first 11 flexural modes of the beam when immersed in air or water. We compare the numerical results with theory, where possible, and find excellent agreement. We quantify the limitations of the computational approach and describe its range of applicability. These results pave the way for computational studies of the stochastic dynamics of complex 3D elastic structures in a viscous fluid where theoretical descriptions are not available.
Modification of the uniform momentum zones in the turbulent boundary layer by superhydrophobic surface
Authors: Cheng Xiaoqi , Jiang Nan
Published: December 2024

Experimental investigation is carried out in a water tunnel to study the influence of the superhydrophobic (SHPo) surface on the coherent structures, especially the uniform momentum zones (UMZs) and their edges, in a zero-pressure gradient turbulent boundary layer (TBL) at the friction Reynolds number of 650. Particle image velocimetry (PIV) technique is applied to capture the instantaneous velocity field in the streamwise-wall-normal plane. The UMZs are detected based on the probability density function of the PIV-measured instantaneous streamwise velocity. The mean value of the UMZ number is reduced by the SHPo surface, indicating the more organized coherent structures. The modal velocity of the UMZs under SHPo surface is always higher than that with smooth wall at the same wall-normal location, which may directly result from the velocity slip on the wall. The internal interfaces between the neighboring UMZs are further examined. The area fraction of the internal interfaces relative to the total TBL is reduced by the SHPo surface, consistent with the smaller number of the detected UMZs. Conditional average is carried out based on the internal interfaces and the statistical characteristics of the velocity gradient at the interface are compared. Both the mean and root mean square values of the velocity gradient are reduced for the SHPo surface, resulting from the weakened spanwise vortices at the internal interfaces.
An experimental study of the solid–liquid interface for an elasto-viscoplastic fluid flow in benchmark geometry: 4 to 1 planar contraction
Authors: Hadj Arab Belaid , Louna Zineeddine , Mahfoud Mohamed , de Souza Mendes Paulo R. , Garcia-Blanco Yamid J. , Franco Admilson T.
Published: December 2024

This paper presents an experimental study of the flow of an elasto-viscoplastic fluid (Carbopol) in a rectangular duct with an abrupt contraction of an aspect ratio of 4:1. At the corners of the contraction, a dead zone appears with no recirculation zone. The hydrodynamics of the flow is studied using high-resolution laser Doppler velocimetry (LDV). We focus, in particular, on velocity and shear rate profiles within and above the dead zone. The position of the solid–liquid interface is provided for different flow rates. The velocity profiles show a line where they overlap at the same point, known as the “slip line.” The position of this line is independent of the flow rate, but its velocity evolves with the flow rate, for which we have proposed a correlation. The position of this line aligns with the level of contraction for all flow rates. Shear rate profiles show a non-monotonic evolution: from zero at the solid–liquid interface to a peak, then decreasing to zero again in the plug zone at the core of the pipe, indicating the presence of different layers between the solid–liquid interface and the slip line. The line of maximum shear rate is independent of the flow rate, suggesting that the width of the zone between the slip line and this line remains constant at all flow rates. The study is completed by establishing correlations between the friction factor (f) and the Euler number (Eu) as a function of the generalized Reynolds number Regen upstream, downstream, and at the level of contraction.
Pressure-induced tunable luminescence of Mn2+–Mn2+ dimers in Mn-based metal halides (C6H9N2)2MnBr4
Authors: Luo Hang , Wang Wei , Wu Tengfei , Yang Chuanlu , Jiao Mengmeng , Wang Kai , Xu Qinfeng
Published: December 2024

The super-exchange coupled Mn2+–Mn2+ dimer can be formed by doping high concentrations of Mn2+ ions. However, since the distribution of Mn2+ ions strongly depends on the crystal structure of the host lattice, the tuning of Mn2+ ion related emission properties remains limited. Here, a pressure-treated strategy is reported to induce a new red emission band of Mn2+–Mn2+ dimers in the Mn-based metal halide (C6H9N2)2MnBr4. The red and green emission bands generated by Mn2+–Mn2+ dimers and isolated Mn2+ ions exhibit different emission behaviors under pressure. Notably, the emission of the Mn2+–Mn2+ dimer exhibits a wide tunability range from 660 to 770 nm, which is attributed to the increased crystal field splitting energy resulting from the reduced Mn–Br bond length under pressure. Our findings highlight the important role of Mn2+–Mn2+ dimers in pressure-tuned optoelectronic properties and provide guidance for the design of novel optoelectronic devices with desired emission characteristics.
Long-range hot carrier transport in lead-free cesium tin halide perovskite microplates
Authors: Tan Jiayu , Zhou Yixuan , Feng Xukun , Cao Xueqin , Xi Yayan , Wu Yue , Lu De , Han Tao , Huang Yuanyuan , Xu Xinlong
Published: December 2024

The carrier dynamics of lead-free cesium tin halide perovskites are crucial for evaluating their potential as substitutes for lead-based perovskites. Herein, we investigate the ultrafast transport of hot carriers in CsSnBr3 microplates synthesized via chemical vapor deposition. We observe a significantly prolonged hot carrier cooling process lasting ∼50 ps, due to the hot-phonon bottleneck effect and the formation of large polarons. By employing transient absorption microscopy, we detect a time-dependent diffusion coefficient of hot carriers initially reaching up to 257.8 cm2·s−1, leading to a long average travel distance of ∼600 nm. Subsequently, it reveals a remarkable equilibrium carrier diffusion coefficient ranging from 12.7 to 16.5 cm2·s−1. These findings establish a fundamental basis for designing and advancing lead-free perovskite-based optoelectronic applications involving hot carriers.
Multiple scale method integrated physics-informed neural networks for reconstructing transient natural convection
Authors: Ohashi Nagahiro , Nguyen Nam Phuong , Hwang Leslie K. , Kwon Beomjin
Published: December 2024

This study employs physics-informed neural networks (PINNs) to reconstruct multiple flow fields in a transient natural convection system solely based on instantaneous temperature data at an arbitrary moment. Transient convection problems present reconstruction challenges due to the temporal variability of fields across different flow phases. In general, large reconstruction errors are observed during the incipient phase, while the quasi-steady phase exhibits relatively smaller errors, reduced by a factor of 2–4. We hypothesize that reconstruction errors vary across different flow phases due to the changing solution space of a PINN, inferred from the temporal gradients of the fields. Furthermore, we find that reconstruction errors tend to accumulate in regions where the spatial gradients are smaller than the order of 10−6, likely due to the vanishing gradient phenomenon. In convection phenomena, field variations often manifest across multiple scales in space. However, PINN-based reconstruction tends to preserve larger-scale variations, while smaller-scale variations become less pronounced due to the vanishing gradient problem. To mitigate the errors associated with vanishing gradients, we introduce a multi-scale approach that determines scaling constants for the PINN inputs and reformulates inputs across multiple scales. This approach improves the maximum and mean errors by 72.2% and 6.4%, respectively. Our research provides insight into the behavior of PINNs when applied to transient convection problems with large solution space and field variations across multiple scales.
Research on intelligent identification algorithm of flame states to judge flame stabilization in a scramjet combustor
Authors: Meng Liang , Tian Ye , Le Jialing , Wu Fan
Published: December 2024

The supersonic combustor is a critical component of a scramjet, and it is essential to monitor the combustion states within the combustor to ensure the safe and stable operation of the scramjet. Hence, we propose an intelligent combustion state recognition model called the parallel Kolmogorov–Arnold transformer (PKAT). In this model, we construct a Kolmogorov–Arnold linear layer based on Kolmogorov–Arnold theory to enhance the model's ability to approximate flame-stable combustion features. To enable different levels of feature recognition through various backbone networks, we build a parallel structure. The PKAT model performs multi-level and comprehensive recognition of flame combustion features, considering both global and local perspectives. To validate the robustness and generalization capability of the PKAT, we collect data on the stable combustion process of a hydrogen-fueled scramjet engine in a direct-connect supersonic pulse combustion wind tunnel. Experimental results show that the proposed model accurately identifies stable combustion states under different operating conditions, achieving precision, recall, and accuracy rates of 98.31%, 98.36%, and 98.76%, respectively. Furthermore, the PKAT model demonstrates a certain level of generalization capability. When compared to traditional convolutional neural network-based and transformer-based models, the PKAT model exhibits higher recognition performance and robustness in accurately identifying combustion characteristics.
Characterization of interactions in battery slurry via MD simulation: Influence on miscibility, morphology, and dispersion with varying ACN content in HNBR
Authors: Park Anseong , Kim Seungtae , Jung Je-Yeon , Kim WooJin , Seo Min Young , Kim Sangdeok , Nam Chongyong , Lee Won Bo , Kim YongJoo
Published: December 2024

This paper investigates the phase behaviors, morphology changes, and degree of dispersion of a multi-component cathode battery slurry system. The slurry comprises polyvinylidene fluoride (PVDF) as the binder, hydrogenated nitrile butadiene rubber (HNBR) as the dispersant with varying acrylonitrile (ACN) content, N-methyl-2-pyrrolidone (NMP) as the solvent, and carbon nanotubes/graphene (CNTs/GRA) as the conductive agent. Several analytical methods, including visualized imaging, solubility parameters, radial distribution function (RDF) analysis, β phase PVDF analysis, near-atom analysis, and potential of mean force (PMF) analysis, were employed to compare the slurry’s characteristics. The results indicate that an increase in ACN content in HNBR improves the miscibility between HNBR and PVDF, while HNBR with low ACN content results in a crystalline structure and phase separation of HNBR and PVDF. Conversely, increasing the ACN content in HNBR has a negative impact, making it a poorer dispersant itself. These findings provide essential insights into effectively regulating the phase behavior, miscibility, and dispersion ability of multi-component slurry systems, thereby enhancing the performance of lithium-ion batteries.
Phase diagram and boundary of impact outcomes
Authors: Wei Bo-Jian , Shi Lian-Kai , Gao Shu-Rong , Shi Shi-Hua , Liu Zhe , Wang Yi-Feng , Yang Yan-Ru , Wang Xiao-Dong
Published: December 2024

This study investigates the outcomes of droplet impact under varying impact velocities (Weber numbers) and surface wettability, using experimental methods, with a particular focus on the boundaries between these outcomes. Three primary outcomes were identified at lower Weber numbers (We ≤ 100): deposition, partial rebound, and complete rebound. Discrepancies were observed between existing boundary models for rebound (partial and complete) and deposition, and the actual experimental results. To address this, a new model was developed based on the “water spring model” proposed by Balance et al., incorporating the effects of contact line dissipation and adhesion forces. This model showed improved accuracy in predicting these outcomes. At higher Weber numbers (We > 100) and contact angles (θ > 100°), two main outcomes, receding breakup and prompt splash, were observed. By comparing the instability stresses driving these outcomes, a novel predictive boundary for receding breakup and prompt splash was proposed. This model's accuracy was validated through experimental data from phase diagrams. This research offers new insights into understanding droplet impact behavior under different surface wettability conditions.
Compression fracture, heat transfer, and uncertain optimization of launch propellant charge
Authors: He Xinjia , Rui Xiaoting , Wang Yan , Li Chao
Published: December 2024

In response to the abnormal phenomenon of a certain large caliber artillery having a maximum chamber pressure at low temperatures higher than normal temperature, and the maximum chamber pressure at low temperatures exceeding the allowable pressure of the index, this large caliber artillery is taken as the research object. The interval uncertain optimization method is used to conduct uncertain optimization research on the interior ballistic parameters, to improve the firing safety of the propellant under uncertain conditions. First, an interior ballistic model was established without considering the fracture of the propellant at room temperature, as well as an interior ballistic model considering the compression fracture of the propellant under low temperature conditions. Then, numerical solutions were carried out using dispersion controllable schemes. The variation curve of the bottom pressure of the chamber showed good consistency with the measured results. At the same time, simulation and experimental results jointly proved that the propagation speed of stress waves between particles of the propellant at low temperature was greater than that of flame waves, resulting in the compression stress acting on the propellant at the bottom of the projectile and causing it to fracture before ignition. Finally, based on the interval uncertainty optimization method, an interior ballistic interval uncertainty optimization model considering the compression and fracture of the launching charge was established. A two-layer nested optimization strategy and a backpropagation neural network approximation model were used to solve the problem. The calculation results showed that after optimization, the maximum breech pressure decreased from 526.40 MPa to within the range of [478.86, 502.29] MPa, meeting the requirements of the design indicators. The lower limit of the optimized muzzle velocity was 1616.64 m/s, meeting the minimum muzzle velocity requirement. At the same time, the compression stress at the ignition time of the bottom area of the projectile was reduced by 16.8%, reducing the degree of fracture of the launching charge in the bottom area and suppressing the rapid increase in gas generation rate. The optimization results obtained provide reference for improving the launch safety of large caliber artillery in uncertain environments.
Implicit near-wall domain decomposition approach for large eddy simulation of turbulent flow separation
Authors: Lyu Shiyu , Fard Amir E. , Utyuzhnikov Sergey , Adams Nikolaus A.
Published: December 2024

To mitigate the high computational cost associated with resolving small near-wall eddies in large eddy simulation (LES) while achieving acceptable accuracy, this work extends the implicit near-wall domain decomposition (INDD) method to a hybrid Reynolds-averaged Navier–Stokes (RANS)/LES zonal decomposition approach. In this framework, the LES solution is first computed using a Robin-type (slip) wall boundary condition on a coarse mesh. This solution is then iteratively corrected in the near-wall region based on an updated solution derived from simplified one-dimensional (1D) RANS equations. It is important that the composite solution is smooth thanks to the specially designed slip boundary conditions. The performance of the proposed approach is assessed for flow over a plain channel at different Reynolds numbers and for a periodic hill at ReH=10,595, using very coarse meshes. Applying the INDD technique to both flows results in a significant accuracy improvement compared to unresolved LES, demonstrating good generalization capability across different turbulent viscosity models, such as algebraic or RANS turbulence models. Meanwhile, when applying the k – l RANS model to channel flow cases, the quality of predictions by INDD remains relatively independent of interface locations. Compared to reference wall-resolved LES, the INDD technique significantly reduces the overall computational cost by using simplified RANS equations and more importantly, by requiring far fewer grid points.
Model of inhibited surface adsorption: Application to foam stabilization and destabilization
Authors: Tran Tuong , MacLeod Katarin A. , Razul M. Shajahan G. , Marangoni Alejandro G. , Pink David
Published: December 2024

A classic statistical mechanical model of surface adsorption of an object that interacts with another component present in a medium was developed in this work. The effective Hamiltonian for the process is proposed and developed here, which takes into consideration the interactions between one of the objects with a surface and the interaction with another object in the medium. This model allowed for the prediction of the binding isotherm for the object. Monte Carlo computer simulations were employed to model the behavior of the system, which was in good agreement with the theory. This model was complemented with an equilibrium kinetic model of the same system and simulations. Qualitative agreement between the two approaches was achieved by introducing a degeneracy in the cooperative interaction between the object and the component, namely simultaneous positive and negative binding cooperativity of the same process. The model developed and the results obtained will help explain the variability in the foamability of barista milk, where free fatty acids are known to inhibit the adsorption of proteins to the air bubble surface. Here, we suggest that the variability observed could be due to the ratio of free fatty acids to protein, which was never considered before.
Density of molten oxides measured in an aero-acoustic levitator
Authors: Wilke Stephen K. , Rafferty Jared , Al-Rubkhi Abdulrahman , Weber Richard
Published: December 2024

Knowing the thermophysical properties of high-temperature melts can aid the design of melt processes and validate atomic structural models, such as those used in studying glass formation. Property measurements on such melts are challenging, however, due to container-related contamination and heterogeneous nucleation. Containerless processing techniques that employ levitation can be used to avoid these obstacles. In that context, we demonstrate here the application of silhouette imaging to measure the density of molten oxides in an aero-acoustic levitation instrument (AAL). The AAL combines gas jet levitation with actively controlled acoustic positioning to enable full optical access to samples ca. 2–4 mm in diameter, which are laser beam heated and melted. The cross sections of molten drops are imaged using a monochromatic light source and narrowband-filtered camera. Melt volume is calculated from the cross sections and used to find density at several temperatures ranging 1530–1920 K, including up to 350 K of supercooling. We report densities for CaAl2O4, Ca12Al14O33, CaSiO3, their Fe2O3-bearing analogs, and 83TiO2-17RE2O3 (RE = La or Nd). These provide important benchmarks of the capabilities, measurement uncertainties, and future outlook for this technique.
Effects of pre-injection parameters on spray characteristics of high-pressure common rail diesel engines
Authors: Song Yang , Li Ruina , Wang Zhong , Liu Shuai , Liu Haoye
Published: December 2024

A verified hydrodynamic spray model was used to investigate the effects of multiple injection strategies on fuel bundle development and atomization characteristics of diesel fuel under typical conditions of direct-injection, turbocharged, and high-speed automotive diesel engines. Emphasis is placed on the effect of injecting a small amount of pre-injection fuel prior to the main injection on the spray development process. In addition, the effect and degree of influence of pre/main-injection interval time and pre-injection fuel ratio on spray macro- and micro-parameters in the two-injection strategies. The results show that at the end of the injection process, as the pre/main-injection interval time increases, the spray gas phase penetration distance increases, the spray width and the spray volume of the high-temperature region decrease, and the fuel concentration in the vicinity of the nozzle is in a decreasing trend. As the pre-injection ratio increases, the spray gas phase penetration distance decreases, the spray width, the spray volume of the high-temperature region increases, the spray volume between the fuel equivalence ratio of 0.8–1.2 decreases, and the fuel concentration at the front end of the spray tends to increase. The effect of the proportion of pre-injection fuel on spray width, spray volume of the high-temperature region, and spray volume between the fuel equivalence ratio of 0.8–1.2 was 4.88, 4.56, and 11.5 times that of changing the pre/main-injection interval time, respectively. The research provides a basis for optimizing the injection strategy and applying multiple injection technology in high-pressure common rail diesel engines.
Flow field generated by a plasma actuator at different elevations in quiescent air
Authors: Zhang Xin , Zuo Zhengyu
Published: December 2024

Motivated by the need for improving the lift of unmanned aerial vehicle and replacing the trailing-edge flap under high-altitude environment, the electrical and the flow characteristics of an asymmetrical plasma actuator for a range of elevations [0.2 km ≤ E (elevations) ≤ 4 km] in quiescent air were studied in the present work. In general, compared with the plasma actuator under normal environment, the disturbance capability of the plasma actuator can be enhanced in high-elevation environments and more beneficial to flow control. Initially, the average total power consumption and the maximum amplitude of the induced current increase monotonously with the elevation. Meanwhile, the maximum velocity, Vmax, of the wall jet created by the plasma actuator increases with increasing the elevation and Vmax (velocity) ∼ E0.36. The velocity profile becomes irregular at E ≥ 2 km. Moreover, the relationship between the electrical and the flow characteristics of the plasma actuator is revealed based on the body force and the power consumption. In addition, compared with the case of normal condition, the starting vortex travels further from the upper electrode and the traveling angle is lower at higher elevation, which is benefit for momentum transfer and mixing. It is of great importance that a series of coherent structures in the vicinity of the wall surface were first observed at higher elevation, which is quite different from the case with normal condition.
Control of turbulent coherent structures on flat panel by porous medium
Authors: He Yunao , Zhang Kaiyuan , Du Hai , Zhang Tonghao , Ma Junyu , Zhang Xiaodong
Published: December 2024

Due to the unique internal structure of porous medium, the disturbance to the boundary layer involves both changing the dynamic behavior of the physical quantity in the conservation equation and changing the boundary conditions. In order to investigate the effect and mechanism of porous medium on the coherent structure near the wall of a flat panel, particle image velocimetry experiments of a flat panel and a flat panel with porous medium were carried out in a low turbulence return flow wind tunnel. The coherent structures of flat panel and porous medium-laden flat panel were compared in the study. The flow-normal plane flow display results show that porous medium can significantly lower the near-wall flow velocity, lift up the vortex structure in the near-wall region, reduce the vorticity, and effectively reduce the shear stress. Meanwhile, the velocity statistical quantities were extracted and fitted using the velocity profile method to show that at a wind velocity of 5.8 m/s and a porosity of 10 pores per inch (ppi), the maximum resistance reduction rate reaches 23.1%. The flow-spanwise plane flow display results show that the porous medium can destroy large-scale streak structures.
Charge-storage behaviors in quantum-dot light-emitting diodes
Authors: Cui Yeguang , Wang Ting , Zhu Bingyan , Yuan Xitong , Wang Song , Zhang Hanzhuang , Chi Xiaochun , Ji Wenyu
Published: December 2024

Understanding the charge dynamics in the quantum-dot light-emitting diodes (QLEDs) is essential to further improve their performance. Here we demonstrate that the holes can be stored for over 30 ms in QLEDs based Cd-based quantum dot (QD) emission layer. This ultralong-term hole storage is examined by inserting an electron-capturing unit (ECU) in the hole-transport layer. Through superimposing a negative offset voltage during transient electroluminescence measurements, the electrons captured by the ECU were transported back to the QDs, where holes are stored during the typical operation for the QLED. Then, excitons are formed and electroluminescence signal is detected. We found that the electroluminescence signal can be detected until 30 ms after turning off the driving voltage for the QLED. Given the limited electron capturing time in the ECU, this should be the lower limit for hole storage time. It is abnormal and unanticipated for the QLEDs based on the ZnO electron-transport layer, for which electrons are widely considered as the majority charge carriers. We believe our results can offer significant insights into the working mechanism and degradation of the QLEDs.
Optimization of swim depth across diverse taxa during horizontal travel
Authors: Stokes Kimberley L. , Esteban Nicole , Casale Paolo , Chiaradia André , Kaska Yakup , Kato Akiko , Luschi Paolo , Ropert-Coudert Yan , Stokes Holly J. , Hays Graeme C.
Published: December 2024

Semiaquatic taxa, including humans, often swim at the air–water interface where they waste energy generating surface waves. For fully marine animals however, theory predicts the most cost-efficient depth-use pattern for migrating, air-breathing species that do not feed in transit is to travel at around 2 to 3 times the depth of their body diameter, to minimize the vertical distance traveled while avoiding wave drag close to the surface. This has rarely been examined, however, due to depth measurement resolution issues at the surface. Here, we present evidence for the use of this strategy in the wild to the nearest centimeter and document the switch to shallow swimming during naturally occurring long-distance migrations. Using high-resolution depth-accelerometry and video data for little penguins (
Eudyptula minor
) and loggerhead turtles (
Caretta caretta
), satellite-relayed data for green turtles (
Chelonia mydas
), and literature data for further sea turtle, penguin, and whale species, we show that near-surface swimming is likely used broadly across nonforaging diving animals to minimize the cost of transport.
Linguistic variation beyond the Indo-European web
Authors: Erten-Johansson Selcen , Skantsi Valtteri , Pyysalo Sampo , Laippala Veronika
Published: December 2024

A register, defined as a text variety with specific situational characteristics and a communicative purpose (Biber & Conrad 2019), is also recognized as a cultural construct (Biber & Egbert 2023). Registers merit thorough investigation due to their pivotal role in reflecting linguistic and cultural landscapes. However, existing studies predominantly focus on Indo-European languages. This study investigates Turkish web registers through the introduction of the Turkish Corpus of Online Registers (TurCORE). Comprising 2,780 web texts, TurCORE was manually annotated using a register taxonomy targeting the entire unrestricted web and identifying 24 web register categories. By employing Text Dispersion Keyword Analysis (Egbert & Biber 2019), the research examines the register characteristics with a specific focus on news reports, interactive discussions, and recipes, drawing comparisons with their English equivalents. Results reveal parallels between Turkish and English news reports while Turkish interactive discussions and recipes exhibit distinctive language- and culture specific features.
An Off-Resonant Quantum Collision Model: Realizing a Qubit Coupled with an Effective Negative-Temperature Bath
Authors: Yan 闫 Wei-Bin 伟斌 , Man 满 Zhong-Xiao 忠晓 , Zhang 张 Ying-Jie 英杰 , Xia 夏 Yun-Jie 云杰
Published: December 2024

The quantum collision model provides a promising tool for investigating system-bath dynamics. Most studies of quantum collision models, however, are in the resonant regime. In quantum dynamics, the off-resonant interactions often result in exciting effects. Therefore, it is important to investigate the quantum collision models in the off-resonant regime. A bath with a negative absolute temperature is expected to be instrumental in the development of thermal devices. The design of an effective bath with negative absolute temperature coupled to a qubit is a significant component for developing such thermal devices. In this study, we establish an effective negative-absolute-temperature bath coupled to a qubit with a quantum collision model in the far-off-resonant regime. We conduct a detailed systematic investigation of the off-resonant collision model and determine the presence of an additional constraint on the collision duration resulting from the far-off resonant collision. The dynamics of the collision model in the far-off-resonant regime are different from those beyond the far-off-resonant regime. Numerical simulations are used to confirm the validity of the proposed approach.
Electrically Tunable Graphene Terahertz Isolator Assisted by Nonreciprocal Plasmon
Authors: Xu 徐 Chen-Ran 晨燃 , Fan 范 Weiru 伟如 , Tang 汤 Yanhao 衍浩 , Wang 王 Dawei 大伟
Published: December 2024

Nonreciprocal isolators enable unidirectional light propagation without back-reflection. Typical terahertz isolators require magnetic fields to break the time-reversal symmetry. Herein, we propose a nonmagnetic isolator in the terahertz range based on nonreciprocal graphene plasmons operated in a reflection configuration. The bias voltage generates a drift current in graphene, which breaks the time-reversal symmetry and induces nonreciprocal reflection. The isolator device exhibited a high isolation exceeding 20 dB with an insertion loss of less than 3 dB. Moreover, the bandwidth wit isolation exceeding 20 dB can be broadened five times to 1.7 THz by tuning the carrier density. The indexes, including the isolation, insertion loss and bandwidth of the isolator, show a strong dependence on the drift velocity and mobility of graphene, as well as the air-gap thickness. Our study shows great potential in the burgeoning terahertz technology, where nonmagnetic and electrically tunable isolators are still lacking.
Quantifying the Driving Effect of Colored Noise in Brownian Motors
Authors: Zhang Zhichao , Liu Yue , Wu Congmin , He Dahai
Published: December 2024

The colored noise disrupts the detailed balance, enabling directed transport in ratchet systems without additional driving forces. Despite a well-established understanding of the conditions for Brownian motors, quantification of the driving effect of colored noise and its connection to deviations from equilibrium remains unexplored. In this study, we examined the directed motion of an overdamped Brownian motor within an asymmetric traveling potential subjected to Ornstein–Uhlenbeck colored noise. We propose a scheme to quantify the driving effect of colored noise by defining an effective force based on the stopping velocity of the traveling potential where directed transport halts. Our results revealed a nonmonotonic dependence of the effective force on the noise correlation time and a monotonic dependence on the noise strength, corresponding to double and single current reversals, respectively. The nonmonotonicity of the current is attributed to the interplay between the fluctuating characteristics and the driving effects of colored noise.
Atomic Level Insight into the Variation and Tunability of Band Alignment between Si and Amorphous SiO2/HfO2
Authors: Li 李 Wen-Feng 文峰 , Liu 刘 Ting-Wei 亭炜 , Yang 杨 Zheng-Mei 正美 , Wang 汪 Lin-Wang 林望 , Liu 刘 Yue-Yang 岳阳
Published: December 2024

The band alignment between silicon and high-k dielectrics, which is a key factor in device operation and reliability, still suffers from uncontrolled fluctuations and ambiguous understanding. In this study, by conducting atomic-level ab initio calculations on realistic Si/SiO2/HfO2 stacks, we reveal the physical origin of band alignment fluctuations, i.e., the oxygen density-dependent interface and surface dipoles, and demonstrate that band offsets can be tuned without introducing other materials. This is instructive for reducing the gate tunneling current, alleviating device-to-device variation, and tuning the threshold voltage. Additionally, this study indicates that significant attention should be focused on model construction in emerging atomistic studies on semiconductor devices.
Quantum-fluid correspondence in relativistic fluids with spin: from Madelung form to gravitational coupling
Authors: Sato Naoki
Published: December 2024

This paper explores the quantum-fluid correspondence in a charged relativistic fluid with intrinsic spin. We begin by examining the nonrelativistic case, showing that the inclusion of spin introduces a quantum correction to the classical fluid energy. This correction, coupled with Maxwell’s equations, naturally leads to the Schrödinger equation in Madelung form. Building on this foundation, we extend the formalism to a relativistic perfect fluid, identifying the system’s stress-energy-momentum tensor. Our analysis reveals that the trace of the quantum correction to this tensor corresponds to the energy density of an oscillator, with its frequency determined by the vorticity of the spin motion. We then use the stress-energy-momentum tensor to establish the relationship between the Ricci scalar curvature, as dictated by the Einstein field equations, and the fluid density in a static, spherically symmetric configuration. Lastly, we generalize the Madelung transformation to compressible Navier–Stokes flows with vorticity and viscosity by developing a tailored Clebsch representation of the velocity field. This theoretical framework offers potential applications for studying fluid-like systems with internal rotational degrees of freedom, commonly encountered in astrophysical settings.
Testing Newtonian gravitation in educational context
Authors: Giudici Sergio
Published: December 2024

In both Upper Secondary School and first-level university courses, Newtonian gravitation is typically taught with a primary focus on theoretical aspects, particularly on solving the two-body problem. The solution is claimed reproduce Kepler's empirical laws, but little attention is given to the details of the validation. In the past, the emphasis on theory could be justified by the technical difficulties associated with accessing and analyzing data. Today, however, the availability of open-access data and advanced computational tools makes it feasible to construct empirical evidence for Newtonian gravitation, even within classroom settings. This work revisits the arguments Newton himself used to support his theory and replicate the validation process through a series of activities designed for educational purposes. This approach includes analyzing astrophotographic and mareographic data, along with revisiting Aristarchus of Samos's method for measuring the distance to the Moon through eclipse analysis.
Photon-assisted tunneling resonantly controlling spin current of a spin–orbit-coupled atom in a toroidal trap
Authors: Li Zhiqiang , Hu Xiaoxiao , Zeng Zhao-Yun , Chen Ai-Xi , Luo Xiaobing
Published: December 2024

The periodic flashing potential has proven to be a powerful tool for investigating directed atomic currents. By applying the flashing ring-shaped potential to spin–orbit (SO) coupled, noninteracting Bose–Einstein condensate (BEC) systems, through photon-assisted tunneling (resonance) techniques, we demonstrate the generation of tunable alternating (AC) spin and atomic mass currents that can be precisely controlled in terms of direction and strength. The underlying mechanism behind this phenomenon is that the flashing potential supplies enough photons to induce Rabi oscillations and provides momentum transfer for spin and atomic transport. As the single-particle ground state of the unperturbed SO-coupled BEC depends on the Raman coupling strength, we demonstrate how to generate and control AC spin currents in the cases where the initial state resides in a single-well or double-well phase. In particular, we realize and explain the mechanism of generating a net AC spin current without mass current through single-photon resonance processes. It is shown that these interesting resonance phenomena can be analytically described only by the simple three-level model, which creates the possibility of transparent controls of spin dynamics.
Structural and spectroscopic characterization of Ba3RE2(Ge3O9)2 (RE = La, Pr, Nd) and Ba3La2−
xEux(Ge3O9)2 cyclogermanates
Authors: Lipina Olga A , Baklanova Yana V , Popov Ilya S , Surat Lyudmila L , Chufarov Alexander Yu , Tyutyunnik Alexander P , Rybnikova Anna A , Zubkov Vladimir G
Published: December 2024

Ba3RE2(Ge3O9)2 (RЕ = La, Pr, Nd) and Ba3La2−x
Eu
x
(Ge3O9)2 germanates were prepared via solid-state reaction for the first time. The crystal structure of the compounds was identified using x-ray powder diffraction. The obtained results indicate that all germanates are isostructural and crystallize in a monoclinic crystal system with the space group С2/c, Z = 4. The crystal lattice consists of two kinds of layers, formed from [Ge3O9]6− rings or from Ba2+/RE3+ cations. The density functional theory calculations performed on a rich set of Ba3RE2(Ge3O9)2 compounds have approved a high thermodynamic stability of monoclinic modification and chair conformation of [Ge3O9]6− rings. The luminescence properties of Ba3La2−x
Eu
x
(Ge3O9)2 phosphors have been studied under 239 nm and 393 nm excitation. The spectra contain narrow lines in the orange–red spectral region, associated with the intraconfiguration f‒f transitions in Eu3+. The most intensive lines are located at 603–635 nm and are caused by 5D0 → 7F2 transition in Eu3+. The concentration dependence indicates an effective energy transfer due to dipole–dipole interaction. The Ba3La2−x
Eu
x
(Ge3O9)2 phosphors possess a high color purity and thermal stability of luminescence that allows one to predict that they may be successfully used in solid state lighting.
Effects of anode voltage and mass flow rate on the erosion of inner permanent magnet conducting cover in a 100 W Hall thruster
Authors: Wang Lei , Li Zijie , Ding Rui , Hou Ernan , Wei Liqiu , Li Hong , Ding Yongjie
Published: December 2024

The effects of anode voltage and mass flow rate on the erosion of the inner permanent magnet conducting cover in a 100 W Hall thruster were studied in this paper. To accelerate erosion, an inner permanent magnet conducting cover made of aluminum alloy was employed. Experimental results indicate that the erosion rate of the inner conducting cover increases with higher anode voltage and mass flow rate. When the anode mass flow rate is set at 3.8 sccm and the anode voltage increases from 200 V to 300 V and 350 V, the erosion rate at the center of the inner conducting cover increases from 6.54 mm kh−1 to 9.29 mm kh−1 and 13.79 mm kh−1, respectively, reflecting increases of 42.0% and 110.8% compared to the initial erosion rate. When the anode voltage is 200 V and the anode mass flow rate increases from 3.8 sccm to 5.4 sccm and 6.9 sccm, the erosion rate at the center of the cover increases from 6.54 mm kh−1 to 9.00 mm kh−1 and 10.91 mm kh−1, indicating increases of 37.6% and 66.9%, respectively. These findings underscore the challenges of maintaining the lifespan of the inner conducting cover when thruster is operated under the conditions of high specific impulse and high thrust discharge. Further investigation reveals that the potential difference between the channel exit and the inner conducting cover is a significant factor driving ions near the channel exit bombardment of the inner conducting cover. Increased anode voltage and mass flow rate enhance this potential difference and increase the ion density near the channel exit, resulting in greater current density and energy of ions bombarding the inner conducting cover, thereby accelerating its erosion. This study provides a reference for the lifespan analysis of the inner conducting cover in low-power thrusters operating under multi-mode conditions.
Descriptive overview of AI applications in x-ray imaging and radiotherapy
Authors: Damilakis John , Stratakis John
Published: December 2024

Artificial intelligence (AI) is transforming medical radiation applications by handling complex data, learning patterns, and making accurate predictions, leading to improved patient outcomes. This article examines the use of AI in optimising radiation doses for x-ray imaging, improving radiotherapy outcomes, and briefly addresses the benefits, challenges, and limitations of AI integration into clinical workflows. In diagnostic radiology, AI plays a pivotal role in optimising radiation exposure, reducing noise, enhancing image contrast, and lowering radiation doses, especially in high-dose procedures like computed tomography (CT). Deep learning (DL)-powered CT reconstruction methods have already been incorporated into clinical routine. Moreover, AI-powered methodologies have been developed to provide real-time, patient-specific radiation dose estimates. These AI-driven tools have the potential to streamline workflows and potentially become integral parts of imaging practices. In radiotherapy, AI’s ability to automate and enhance the precision of treatment planning is emphasised. Traditional methods, such as manual contouring, are time-consuming and prone to variability. AI-driven techniques, particularly DL models, are automating the segmentation of organs and tumours, improving the accuracy of radiation delivery, and minimising damage to healthy tissues. Moreover, AI supports adaptive radiotherapy, allowing continuous optimisation of treatment plans based on changes in a patient’s anatomy over time, ensuring the highest accuracy in radiation delivery and better therapeutic outcomes. Some of these methods have been validated and integrated into radiation treatment systems, while others are not yet ready for routine clinical use mainly due to challenges in validation, particularly ensuring reliability across diverse patient populations and clinical settings. Despite the potential of AI, there are challenges in fully integrating these technologies into clinical practice. Issues such as data protection, privacy, data quality, model validation, and the need for large and diverse datasets are crucial to ensuring the reliability of AI systems.