bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oscillations of subcritical fast magnetosonic shock boundaries caused by shock reformation
Authors: Dieckmann M E , Bret A , Folini D , Walder R 
Published: November 2024

Abstract
The evolution of a deformed subcritical fast magnetosonic shock front is compared between two two-dimensional particle-in-cell simulations with different orientations of the magnetic field relative to the simulation box. All other initial and simulation conditions are kept identical. Shock boundary oscillations are observed in the simulation where the magnetic field direction is resolved. This oscillation is caused by the reformation of the shock front. One part of the front acts as a shock, while the other functions as a magnetic piston, with both halves changing their states in antiphase. The oscillation period corresponds to the time required for one shock wave to grow as the other collapses. In contrast, the corrugated fast magnetosonic shock does not oscillate in the second simulation, where the magnetic field is oriented out of the simulation plane. This dependence on magnetic field orientation suggests that the shock oscillation is induced by magnetic tension, which is only effective in the first simulation. In both simulations, the shock perturbation does not grow over time, indicating that the shocks are stable. The potential relevance of these findings for the Alfvénic oscillations of the supercritical Earth’s bow shock, detected by the MMS multi-spacecraft mission, is also discussed.
Equilibrium reconstruction of axisymmetric plasmas by combining Gaussian process regression and Markov chain Monte Carlo sampling
Authors: Nishizawa T , Tokuda S , Sanpei A , Hasegawa M , Yamasaki K , Fujisawa A 
Published: November 2024

Abstract
Reliable equilibrium reconstruction is indispensable for understanding and controlling hot magnetized plasmas to achieve fusion reactors. In axisymmetric systems, current and pressure profiles that satisfy the force balance conditions are given by the Grad–Shafranov (GS) equation. While many novel approaches have been developed to swiftly and robustly find an optimum solution of the GS equation, approaches based on a single solution search may not be adaptable if diagnostics fail to provide sufficient constraints. Here, we investigate the solution space of the GS equation when only basic edge magnetic measurements are available. By combining Gaussian process regression and Markov chain Monte Carlo sampling within the Bayesian framework, we treat each current element as an independent variable and evaluate the probability distribution that describes all possible solutions. We have applied this inference frame to the geometry of the PLATO tokamak and shown that the flux surface locations can be determined relatively well only from 16 pick-up coils, 4 flux loops and a diamagnetic loop. On the other hand, the toroidal current density is inferred with limited success, and the inferences of the safety factor and pressure profiles are difficult. The characterization of possible choices of equilibria realized by this inference framework will help optimize diagnostic setups for equilibrium reconstruction.
Suppression of core temperature fluctuations by edge cooling in the J-TEXT tokamak
Authors: Xie Y Y , Zhao K J , Yang Z J , Chen Z P , Dong J Q , Chen Z Y , Shi Yuejiang , Tan M Z , Gao L , Ding Y H , Chen Y Q , Zhang H Q , Li R , Cao X G , Du J J , Jiang J M , Zhang G S , Cheng J , Xu J Q , Zhang J Y , Xiang L , Wang N C , Wang L , Liang Y F 
Published: November 2024

Abstract
The suppression of core temperature fluctuations due to edge cooling in the J-TEXT tokamak is presented. The supersonic molecular beam is injected into the low density plasmas and the core temperature rise appears. The staggered time correlation technique is utilized to infer the temperature fluctuations from an electron cyclotron emission radiometer (ECE). The existing correlation ECE (CECE) also enables the observation of the temperature fluctuations simultaneously. A significant flattening of the density gradients appears almost in the whole plasmas after the cold pulse injection. The behaviors of the temperature fluctuations from both ECE and CECE show a good agreement, except for the fluctuation level, which exhibits a relative variation of approximately 10%

−

50%. The relative intensity of temperature fluctuations decreases within the surface of

r

/

a
∼

0.8 due to the edge cooling. The cross-power analysis and the agreement in measurements suggest that temperature fluctuations from turbulence inferred from a single ECE channel may be possible. Linear simulations suggest the drop in temperature fluctuation intensity may relate to the trapped electron mode turbulence stabilization. This paper also demonstrates the evolution of both gradients and fluctuations before and after supersonic molecular beam injection with density scans.
Development of magnetically driven contactless piezoelectric nanogenerators utilizing ZnO nanowires with different shaped top electrodes
Authors: Ucar E F , Ilbay A , Simsek T , Kaynar M B , Ozbay E , Ozcan S 
Published: November 2024

Abstract
In this research, ZnO nanorod (NR)-based contactless piezoelectric nanogenerators (C-PENGs) with pyramidal and zigzag-shaped top electrodes were fabricated. ZnO NRs with different aspect ratios were grown on a Si (100) wafer, which acts as the bottom electrode. Two different top electrode architectures, zigzag-trenched and pyramidal cavity, were used. Additionally, different work function metallic coatings, platinum and nickel (as a cheaper alternative to noble metals) were applied to the architecturally shaped surfaces to achieve a Schottky contact between the top and bottom electrodes. A magnetic field ranging from 3.5 Oe to 55 Oe with a frequency range between 0.5 and 2 Hz was applied to drive the nanogenerator. The results showed that a maximum output voltage of 75 mV and a maximum power density of 20.7 pW cm−2 were successfully generated. The measurement of output power densities revealed that C-PENGs are a promising candidate for future nanorobotics applications.
Wearable chairless exoskeleton capable of flexible support to relieve muscle fatigue for industrial workers
Authors: Wang Wenpan , Liang Xianhao , Li Lei , Gong Liping , Deng Lei , Hu Xuanrui , Zhang Shiwu , Sun Shuaishuai 
Published: November 2024

Abstract
Currently, workers who need to maintain specific postures for prolonged periods, such as assemblers, builders, and operators, often suffer from work-related musculoskeletal disorders, resulting in muscle fatigue and joint injuries. Although exoskeleton-assisted technologies have been widely explored to assist workers with posture support, existing chairless exoskeletons cannot reinforce all the joints of the lower extremities at multiple angles or involve bulky additional legs, incapable of agile and flexible support. Here, we develop a wearable chairless exoskeleton that can strengthen the hip, knee, and ankle joints by integrating six magnetorheological (MR) actuators. It is flexible with 5 degrees of freedom (DOFs) on each leg, avoiding unfavorable effects on leg movements and allowing various large-scale, multi-DOF maneuvers. The MR actuators are compact with a high torque density of 126.32 Nm kg−1. The actuator, with a power consumption of 7.0 W, can provide a damping resistance torque of 120 Nm to lock the joint at any angle. Therefore, the chairless exoskeleton can provide stable support for the wearer in a wide range of postures. We modeled the human–exoskeleton system and theoretically analyzed the support force required for posture maintenance. Moreover, the safety margins for the hip, knee, and ankle joints in our configuration are 41.54%, 42.89%, and 39.51%, respectively, enhancing both safety and reliability for the user by protecting against potential overloading or instability. The individual-wearing experiments and demonstrations exhibited the exoskeleton’s capabilities, including an average reduction of 74.24% in muscle electromyographic and enhanced endurance during posture sustain tasks.
Energy harvesting of a metamaterial beam with acoustic black holes
Authors: Jia Yuhang , Wang Chuankui , Tong Weihao , Moshrefi-Torbati Mohamed , Yurchenko Daniil , Yang Kai 
Published: November 2024

Abstract
This paper proposed an improved metamaterial piezoelectric beam with the acoustic black holes (ABHs) for low-frequency energy harvesting. The ABHs are embedded in the local resonant beams distributed on both sides of the primary beam. Piezoelectric plates are attached to the ABHs, leveraging the energy-focusing effect to enhance the energy harvesting performance. Finite element simulation results indicate that the energy harvesting electrical energy has improved by 6.92 times compared to the traditional metamaterial resonant beam without ABHs. Parameter analysis indicates that increasing the number of local resonators and extending the length of the piezoelectric patches can further enhance energy harvesting performance. However, reducing the truncation thickness of the ABH boosts energy harvesting but compromises structural strength. Extending the ABH length and increasing load resistance within the appropriate range are conducive to energy harvesting. Besides, the optimal load resistance varies with frequency. These findings provide useful guidance for future applications of improved metamaterial beam.
Three degrees of freedom rigid-soft coupling biomimetic hip joint driven by dielectric elastomer
Authors: Jinzhu Zhang , Yang Liu , Xiaoyan Xiong , Qi Shen , Chenguang Niu 
Published: November 2024

Abstract
Dielectric elastomer (DE) has an attractive combination of high energy density, large strain, and fast response. A growing number of DE actuators are being used as driving materials in rigid-soft coupling joints. For better structural design, the mapping relations from the musculoskeletal system of the human hip joint to the biomimetic hip joint mechanism have been established. Inspired by the human musculoskeletal system, the configuration of the three-degree-of-freedom rigid-soft coupling hip joint based on DE is proposed. The configuration includes six soft-driving limbs and one passive rigid limb. The soft-driving limb driven by the fiber-constrained dielectric elastomer actuator (FCDEA) does not contain passive rigid joints. Based on the Gent material model, the electromechanical coupling model of FCDEA is established. A mapping model is established between the voltage applied to the soft-driving limb of the biomimetic hip joint and the posture of the moving platform in the case of deflection and torsion. A single FCDEA is prepared and its electro-responsive deformation performance is tested through experiments. As a demonstration, a prototype of the biomimetic hip joint is developed. After applying voltage, the deflection angle and the torsion angle of the biomimetic hip joint are tested and the curve of voltage and rotation angle is drawn. The experimental results agree well with the theoretical predictions. This article can provide theoretical references for improving the performance of rigid-soft coupling hip joints.
Full-field dynamic strain reconstruction of rotating compressor blades based on FBG sensors
Authors: Huang Meiao , Liu Hailong , Zhang Qingchen , Wen Jinshan , Liu Qijian , Qing Xinlin 
Published: November 2024

Abstract
Rotating compressor blades experience complex alternating loads during service, altering their stress–strain distributions and peak stress positions over time. Accurate measurement of these strains is crucial for identifying the areas of stress concentration. This paper presents a structural health monitoring system using fiber Bragg grating (FBG) sensors to record dynamic strains on laboratory-scale rotating blades, and a tailored full-field strain reconstruction methodology, which successfully identifies the magnitude of the strains and the areas of stress concentration of the blades at different rotational speeds. First, dynamic strain at selected blade points was monitored using FBG sensors, with raw signal data enhanced by the empirical wavelet transform method to reduce noise and clarify signals. An analytical framework was developed to relate blade rotational velocity to signal period, enabling precise speed calculation and accurate strain analysis. The improved-Kriging interpolation technique was then used to reconstruct comprehensive strain profiles. A comparative analysis showed an average strain relative error of 7.4% between predicted and actual values, demonstrating the methodology’s robustness and precision.
Constraints on Testing Post-Newtonian Gravity with Scanning Space Astrometry
Authors: Butkevich Alexey G. , Vecchiato Alberto , Bucciarelli Beatrice , Gai Mario , Crosta Mariateresa , Lattanzi Mario G. , Riva Alberto 
Published: November 2024

Abstract
High-precision astrometry has the capability of testing General Relativity in the framework of the parametrized post-Newtonian formalism (PPN). Accurate measurements of gravitational light deflection over the entire celestial sphere open up a potential opportunity for determining the post-Newtonian parameter γ, which governs the deflection strength. We examine both analytically and numerically the coupling between a global parallax shift and the PPN parameter γ in Gaia-like astrometry. We also study effect of a parallax zero point on PPN γ estimation is scanning space astrometry. Least squares technique is applied to a direct astrometric solution including PPN γ and astrometric parameters (positions, parallax and proper motions). Analytical solution of the normal equations provides covariance information for the parameter γ and parallaxes. We present a new treatment of the correlation between parallax zero point and PPN γ, based on a statistical approach. We also derive a formula describing the bias in PPN γ estimation resulting from a global parallax offset. These theoretical results are verified by Monte Carlo experiments using astrometric solutions with simulated Gaia observations. Parallax zero point at a sub-μas level is needed to obtain a PPN γ estimate comparable with today’s best determination. We generalize the problem to two-dimensional observations and derive formula for the correlation between parallax zero point and PPN γ in the case when both along- and across-scan measurements are used for PPN γ determination.
Stokes–Einstein–Debye relation in TIP5P water
Authors: Ren 任 Gan 淦 
Published: November 2024

Abstract
The Stokes–Einstein–Debye (SED) relation in TIP5P water is tested with the original formula and its variants within the temperature range 240–390 K. The results indicate that although the variants explicitly break down, the original SED relation is almost valid. Compared with the Stokes–Einstein relation, no explicit decoupling is observed in translational and rotational motion. Variation of the effective hydrodynamic radius is critical to testing the validity of the SED relation.
One-step synthesis of cubic gauche polymeric nitrogen with high yield just by heating
Authors: Wu 吴 Liangfei 良飞 , Xu 徐 Yuxuan 宇轩 , Chen 陈 Guo 果 , Ding 丁 Junfeng 俊峰 , Li 李 Ming 明 , Zeng 曾 Zhi 雉 , Wang 王 Xianlong 贤龙 
Published: November 2024

Abstract
A high-efficient one-step synthesis of cubic gauche polymeric nitrogen was developed just by thermal treatment of KN3 powders. Raman and infrared spectra confirm the formation of cubic gauche polymeric nitrogen. Further thermogravimetric differential scanning calorimeter measurements show that the content of cubic gauche polymeric nitrogen is as high as 1.5 wt% with high thermal stability, which is the highest content value reported so far.
Demonstration of irradiation-resistant 4H-SiC based photoelectrochemical water splitting
Authors: Pei Yan , Geng Wenhao , Xu Lingbo , Cui Can , Pi Xiaodong , Yang Deren , Wang Rong 
Published: November 2024

Abstract
4H silicon carbide (4H-SiC) has gained a great success in high-power electronics, owing to its advantages of wide bandgap, high breakdown electric field strength, high carrier mobility, and high thermal conductivity. Considering the high carrier mobility and high stability of 4H-SiC, 4H-SiC has great potential in the field of photoelectrochemical (PEC) water splitting. In this work, we demonstrate the irradiation-resistant PEC water splitting based on nanoporous 4H-SiC arrays. A new two-step anodizing approach is adopted to prepare 4H-SiC nanoporous arrays with different porosity, that is, a constant low-voltage etching followed by a pulsed high-voltage etching. The constant-voltage etching and pulsed-voltage etching are adopted to control the diameter of the nanopores and the depth of the nanoporous arrays, respectively. It is found that the nanoporous arrays with medium porosity has the highest PEC current, because of the enhanced light absorption and the optimized transportation of charge carriers along the walls of the nanoporous arrays. The performance of the PEC water splitting of the nanoporous arrays is stable after the electron irradiation with the dose of 800 and 1600 kGy, which indicates that 4H-SiC nanoporous arrays has great potential in the PEC water splitting under harsh environments.
Selection of dopants and doping sites in semiconductors: the case of AlN
Authors: Zheng Yi-Feng , Cai Xuefen , Wei Su-Huai 
Published: November 2024

Abstract
The choices of proper dopants and doping sites significantly influence the doping efficiency. In this work, using doping in AlN as an example, we discuss how to choose dopants and doping sites in semiconductors to create shallow defect levels. By comparing the defect properties of CN, ON, MgAl, and SiAl in AlN and analyzing the pros and cons of different doping approaches from the aspects of size mismatch between dopant and host elements, electronegativity difference and perturbation to the band edge states after the substitution, we propose that MgAl and SiAl should be the best dopants and doping sites for p-type and n-type doping, respectively. Further first-principles calculations verify our predictions as these defects present lower formation energies and shallower defect levels. The defect charge distributions also show that the band edge states, which mainly consist of N- s and p orbitals, are less perturbed when Al is substituted, therefore, the derived defect states turn out to be delocalized, opposite to the situation when N is substituted. This approach of analyzing the band structure of the host material and choosing dopants and doping sites to minimize the perturbation on the host band structure is general and can provide reliable estimations for finding shallow defect levels in semiconductors.
An SI for humans and a digital-SI for machines
Authors: Valdés Joaquín , Laiz Héctor M 
Published: November 2024

Abstract
The international metrology community is focusing on the digitalization of the International System of Units (SI). A digital SI does not necessarily have to be a digital version of the present SI designed for communication between humans, or between humans and machines. This contribution reviews a proposed Digital System of Units (D-SI) for communication between machines using only the seven SI base units. We analyze the convenience of including in a future D-SI the conversion to the seven SI base units of most of the non SI units used worldwide for machine-to-machine communication, being machine accessible at the International Bureau of Weights and Measures website. This needs authoritative agreement of the corresponding conversion factors to be used. In this way, the dream of managing a single system of units could be achieved by machines before humans. Some causes of ambiguity in the present SI that may be overcome in the D-SI are also considered.
Improved weighted sum estimation of total radiated power at W7-X
Authors: Partesotti G. , Reimold F. , Tsikouras A. , Zhang D. , Kawamura G. , Peterson B.J. ,   the W7-X Team
Published: November 2024

AbstractAs magnetic confinement devices move toward higher fusion powers, moderating the heat load to the plasma-facing components becomes increasingly challenging. Efficient power dissipation can be achieved through control of the plasma radiation. However, defining a reliable proxy for the total radiated power is particularly challenging for non-axisymmetric devices such as stellarators. To address this problem, the radiated power can be estimated through a sum of the individual line-integrated bolometer measurements with weights properly calculated to account for the three-dimensional magnetic geometry. The present contribution aims to apply this weighted sum approach to Wendelstein 7-X (W7-X) and quantitatively validate it. First, we generate synthetic radiated power phantoms with characteristic W7-X radiation features to derive a set of optimized line-of-sight weights. Then, we test the weights on mock-ups and EMC3-EIRENE radiation patterns, including acquisition and analysis errors such as random noise fluctuations, camera misalignments, and field errors. Compared to other methods, the optimized weighted sum technique exhibited the best performance in all the presented synthetic test cases. When applied to experimental bolometer data, the optimized weights provided a proxy that is both reliable and real-time capable. Further validation is foreseen for the next experimental campaign.
Frequency comb for 88Sr+ clock frequency comparison with Cs fountain clock at the NRC
Authors: Marceau Claude , Beattie Scott , Pakulski Wojciech , Gertsvolf Marina 
Published: November 2024

Abstract
We describe a polarization maintaining erbium fibre optical frequency comb that was used to link NRC-FCs2 to an ultrastable laser, generating ultrastable microwaves (MW) that are shown to significantly shorten the fountain clock averaging time. A detailed experimental setup for our next measurement linking NRC 88Sr+ clock to the NRC-FCs2 Cs fountain clock is also presented.
Compact clocks & cavities for space and ground applications
Authors: Gill P , Mulholland S , Klein H , Huang G , Hill I , Allen B , Haji M , Stacey J , Spampinato A , Tsoulos P , Hockley G , Vincent N , Knapp M , Trigatzis M , Barwood G 
Published: November 2024

Abstract
Position, navigation and timing capability worldwide is predominantly underpinned by global navigation satellite systems (GNSS), which provide the underlying capability for critical national infrastructures, science, industry, commerce and society. Recently, the vulnerability of such systems to interference, whether intentional or not, instrument failure or space weather, has been recognised, pointing to the need for alternative independent navigation and timing solutions. In particular, the availability of low size, weight and power (low-SWaP) traceable portable clocks with extended holdover times for use both in space and on ground is seen as paramount. We report on progress in the development of compact cold ion microwave and optical clocks at NPL that point to capability to out-perform existing commercial clock systems and identify future space applications that could benefit from this technology.