bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural width of the superconducting transition in epitaxial TiN films
Authors: Baeva Elmira , Kolbatova Anna , Titova Nadezhda , Saha Soham , Boltasseva Alexandra , Bogdanov Simeon , Shalaev Vladimir M , Semenov Alexander , Goltsman Gregory N , Khrapai Vadim 
Published: August 2024

AbstractWe investigate the effect of various fluctuation mechanisms on the DC resistance in superconducting (SC) devices based on epitaxial titanium nitride (TiN) films. The samples we studied show a relatively steep resistive transition (RT), with a transition widthΔT/Tc∼0.002−0.025, depending on the film thickness (20 nm, 9 nm, and 5 nm) and device dimensions. This value is significantly broader than expected due to conventional SC fluctuations (ΔT/Tc≪10−3). The shape and width of the RT can be perfectly described by the well-known effective medium theory, which allows us to understand the origin of the inhomogeneity in the SC properties of TiN films. We propose that this inhomogeneity can have both dynamic and static origins. The dynamic mechanism is associated with spontaneous fluctuations in electron temperature (T-fluctuations), while the static mechanism is due to a random spatial distribution of surface magnetic disorder (MD). Our analysis has revealed clear correlations between the transition width and material parameters as well as device size for both proposed mechanisms. While T-fluctuations may contribute significantly to the observed transition width, our findings suggest that the dominant contribution comes from the MD mechanism. Our results provide new insights into the microscopic origin of broadening of the SC transition and inhomogeneity in thin SC films.
A full-bridge flux pump using two switches: numerical model and experimental prototype
Authors: Li Chao , Li Gengyao , Xin Ying , Li Bin 
Published: August 2024

Abstract
High-temperature superconducting (HTS) magnets are promising in high field applications. However, due to inevitable joint resistance and flux creep, HTS magnets still face challenges in maintaining field stability in their closed-loop operation. HTS flux pumps can charge closed HTS magnets wirelessly, thus allowing lower cryogenic loading and more flexible arrangements in HTS magnet systems. In this work, a full-bridge flux pump using two AC field-controlled switches is proposed, which can charge HTS magnets during whole cycles. Therefore, the charging speed of the proposed full-bridge flux pump is at least one time larger than half-bridge flux pumps. A numerical model and an experimental prototype are developed to verify the working principle of the proposed full-bridge flux pump. Simulation and experimental tests are carried out to investigate the working characteristics of the proposed flux pump. The proposed flux pump has huge potential in the application scenarios where high charging speed is required.
The mechanism of adjusting the low-frequency ultra-wide band gap within lightweight spherical superstructue
Authors: Zhang Yongyan , Zhao Zebo , Miao Xiangjie , Wu Jiuhui , Chen Liming , Li Biao , Liu Hui , Yang Leipeng , Liu Qinglong , Chen Tao , Li Suobin 
Published: August 2024

Abstract
Conventional resonant structures can be effective in obtaining broadband, but it is still a challenge to design small-sized and lightweight acoustic metamaterials with a low-frequency ultra-wideband. This paper proposes a new approach of designing a lightweight spherical localized resonance superstructure with adjustable stiffness ratio, and the mechanism of adjusting the low-frequency ultra-wide forbidden band is revealed. Then, the correlation between the zero value of its dynamic equivalent mass and the stiffness ratio of the system is studied. It is found that not only is the upper bound of the negative mass effectively broadened, but also the lower bound is successfully lowered only by adjusting the stiffness ratio of the sphere. Most importantly, based on the regulation mechanism with adjustable stiffness ratio, the lower boundary of the band gap is lowered from 171 Hz to 141 Hz, and the upper boundary is increased from 445 Hz to 710 Hz. Therefore, the low-frequency ultra-wideband of 141–710 Hz is obtained only by adjusting the stiffness ratio of the system and the Finite Element Method, which is highly consistent with theoretical analyses. Obviously, the mechanism of obtaining the low-frequency wideband through adjusting the stiffness ratio not only provides a novel idea for adjusting the low-frequency ultra-wideband, but also provides theoretical guidance for the developing the small-size and lightweight acoustic devices, so it would have potential application in the field of vibration and noise reduction.
Reconstruction of bandlimited graph signals from random local sampling
Authors: Shen Lili , Xian Jun , Cheng Cheng 
Published: August 2024

Abstract
Sampling and reconstruction on the spatially distributed networks is an innovative topic in graph signal processing. Recently, it has been shown that k-bandlimited graph signals can be reconstructed from a random collection of physically constrained sampled data. In this paper, we first study the random sampling scheme of k-bandlimited signals from a general local measurement, and then an iterative reconstruction algorithm based on frame theory is proposed with exponential convergence. It can yield a distributed implementation at a vertex level, which enables the devices that are limited by storage and computing power to recover signals more effectively. Numerical experiments on synthetic and real-world data are performed to validate the effectiveness of the proposed approach.
Near-zero magnetic field disturbance suppression method based on adaptive filtering and quasi-proportional resonance control
Authors: Wu Haoting , Zhang Haifeng , Tian Pengtao , Zhao Xiuqi , Zheng Shiqiang 
Published: August 2024

Abstract
The cardiac magnetic field used for magnetocardiographic (MCG) imaging must be detected in a stable near-zero magnetic field environment. In the hospital environment, there are mainly two kinds of magnetic field disturbances that affect the signal-to-noise ratio of cardiac magnetic field detection. One is the magnetic field disturbance with high power spectral density at a specific frequency, and the other is the random magnetic field disturbance with low frequency. To suppress magnetic field disturbances, this paper proposed a near-zero magnetic field disturbance suppression method that combined a PI controller with adaptive filtering and quasi-proportional resonance control (PI-APF-QPR). The magnetic field disturbance with high amplitude and specific frequency was extracted by the adaptive filter (APF) and suppressed by the quasi-proportional resonance (QPR) controller. Additionally, the low-frequency random disturbance was suppressed by the PI controller. The experimental results showed that compared with the PI controller, the peak-to-peak value of the magnetic field by the PI-APF-QPR controller was reduced by 39.1%, and the suppression ratio of the magnetic field noise by the PI-APF-QPR controller was improved by 29.5%, which verified the effectiveness of the proposed magnetic field disturbance suppression method.
A capillary fiber-based liquid metal pressure sensor
Authors: Zhou Xiao-Ping , Zhang Qi 
Published: August 2024

Abstract
The capillary fibers can easily be prefabricated in the factory, and their production cost is reduced. Moreover, the liquid metal fibers have the advantages of good integrity, excellent electrical conductivity, inherent stretchability, easy phase transition, and can be woven or knitted into smart fabrics. To solve the problems of the complex manufacture process and low integrity of lithographic sensors, capillary fibers replace the lithographic microfluidic channel to fill liquid metal to manufacture the pressure sensor in this paper. The prefabricated fiber is poured directly to produce the flexible chip. The steel shell is employed to increase the sensor’s measuring range and to enhance its overall performance. Compression experiments on the developed sensor are conducted, and pressure-resistance curves of the developed pressure sensor are obtained. The analytical solution of the pressure for the developed sensor is derived, and the analytical results are in good agreement with the experimental data. The cyclic loading experimental result shows that the measuring range of the chip is from 0 kPa to 1900 kPa with a full-scale output value of 1644 mΩ, linearity varying from 0.14 to 1.22 mΩ kPa−1, curve coincidence of 48.2%, repeatability of 2.77% and hysteresis of 5.26%. The measuring range of the developed pressure sensor is from 0 MPa to 20 MPa with a full-scale output value of 1046 mΩ, linearity ranging from 35.63 to 70.20 mΩ MPa−1, curve coincidence of 7.5%, repeatability of 2.35% and hysteresis of 4.53%. The comparison of performance indexes shows that the capillary fiber-based chip has good measurement performance, and the introduction of steel shell further improves the measurement performance.
High-Q resonances based on BIC in graphene-dielectric hybrid double-T metasurfaces for terahertz modulation and sensing
Authors: Wang Yaqi , Qi Yunping , Zhou Zihao , Li Zhexian , Wang Xiangxian 
Published: August 2024

Abstract
In recent years, there has been a growing interest in bound states in the continuum (BIC) in metasurfaces. One particular area of focus is achieving high-quality (Q) factor resonance, as this is crucial for enhancing the performance of refractive index sensors. In this study, a graphene-dielectric hybrid metasurface that supports the bound states in the continuum is proposed. By varying the width of the dielectric rectangle, quasi-BIC resonances with a high Q factor can be excited, and the Q factor can reach 752724.95 and 272004.759 respectively. The analysis of multipole decomposition reveals that the two quasi-BIC resonances are predominantly influenced by the electric quadrupole and magnetic dipole, respectively. Moreover, the transmittance of the resonance point can be changed rapidly with the change of the chemical potential of graphene, so the function of modulation can be realized by changing the chemical potential of graphene. Based on these findings, we have designed a terahertz wave modulator, which exhibits modulation depths of 98.1% and 99.9% at the two resonance peaks, respectively. The corresponding chemical potential shifts are 50 meV and 0.5 eV. Additionally, we have investigated the sensing performance of the metasurface. By analyzing the magnitude of the frequency shifts of the quasi-BIC resonance peaks at different gas refractive indexes, we have determined sensitivities of 740 GHz RIU−1 and 630 GHz RIU−1 at the two resonance peaks. The maximum figure of merit (FOM) values are 132911.39 RIU−1 and 45000 RIU−1, respectively. This research serves as a valuable reference for the design of dynamic optical modulators and sensors operating in the terahertz band.
Design of short-focus near-eye optical system for virtual reality using polarization-insensitive metasurface
Authors: Li Yangyang , Hu Yanhong , Zhang Chao , Yuan Ying , Li Qiang , Wang Xiaorui 
Published: August 2024

Abstract
Near-eye optical systems, as an important component of virtual reality displays, have attracted great research interest recently. However, current systems have complex structures and face the design challenge of combining compact, short-focus design with wide field of view and high angular resolution. In this paper, we propose a short-focus near-eye optical system with wide field of view and high angular resolution, referred to as a meta-eyepiece, by patterning a single-layer polarization-insensitive metasurface on a substrate. The metasurface, featuring a quasi-periodic nanopillar arrangement, enables precise phase modulation and enhances design flexibility. The desired metaform phase can be obtained by modeling the light propagation of the meta-eyepiece to determine key design parameters, utilizing metaform phase polynomials, customizing the objective merit function and employing advanced optimization algorithms. Our system achieves a short focal length of approximately 22 mm with an 80° field of view, offering compactness superior to conventional virtual reality optics and a minimum resolvable angle less than 1.25 arcminutes, ensuring high angular resolution. It also exhibits excellent imaging performance with full-field modulation transfer function values exceeding 0.5 at 62.5 lp/mm. Although the initial system utilizes ray optics, the scaled version is validated for its feasibility and scalability through full-wave simulations. Our meta-eyepiece structure and design method show the potential of metasurfaces for applications in virtual reality, offering valuable support for technological development in this field.
Tuning of optical, thermodynamic, and thermoelectric properties of Cs2CuBiX6 (X = Cl, Br, I) halide perovskites for solar cells and energy harvesting applications
Authors: Al-Daraghmeh Tariq M , Nazir Ghazanfar , Zayed Omar , Kattan Nessrin A , Rouf Syed Awais , Albalawi Hind , Aljameel A I , Boukhris Imed 
Published: August 2024

Abstract
The double perovskites are outstanding materials for solar cells and transport applications to clean harvest energy. Therefore, the Cs2CuBiX6 (X = Cl, Br, I) are discussed comprehensively for energy harvesting by modified Becke and Johnson (mBJ) potential. The studied DPs fit the structural, mechanical, and dynamic stability scale by tolerance factor, Born–Huang criteria, and phonon dispersion band structures. The band gaps (1.20, 1.0, 0.70) eV for (Cl, Br, I) based DPs ensure the Cs2CuBiCl6 has an absorption band in the visible region while Cs2CuBiBr6 and Cs2CuBiI6 has an absorption band in the infrared region. Heavy elements’ spin–orbit coupling effect (Cs, Bi) reduces the band gap to 0.08 eV. Thermoelectric behavior regarding the merit scale against dopant carriers and temperature has been elaborated. The ultralow lattice thermal conductivity, large Debye temperature, hardness, and melting temperature increase their implication for thermoelectric and other thermodynamic applications. The variation in band gap makes them important for diverse optoelectric and thermoelectric applications. The Cs2CuBiCl6 with a band gap of 1.20 eV is suitable for solar cells, while Cs2CuBiBr6 and Cs2CuBiI6 with band gaps of 1.0 eV and 0.70 eV are significant for thermoelectric generators.
Fitting the DESI BAO data with dark energy driven by the Cohen-Kaplan-Nelson bound
Authors: Adolf Patrick , Hirsch Martin , Krieg Sara , Päs Heinrich , Tabet Mustafa 
Published: August 2024

AbstractGravity constrains the range of validity of quantum field theory. As has been pointed out by Cohen, Kaplan, and Nelson (CKN), such effects lead to interdependent ultraviolet (UV) and infrared (IR) cutoffs that may stabilize the dark energy of the universe against quantum corrections, if the IR cutoff is set by the Hubble horizon. As a consequence of the cosmic expansion, this argument implies a time-dependent dark energy density. In this paper we confront this idea with recent data from DESI BAO, Hubble and supernova measurements. We find that the CKN model provides a better fit to the data than the ΛCDM model and can compete with other models of time-dependent dark energy that have been studied so far.
Standard siren cosmology in the era of the 2.5-generation ground-based gravitational wave detectors: bright and dark sirens of LIGO Voyager and NEMO
Authors: Jin Shang-Jie , Zhu Rui-Qi , Song Ji-Yu , Han Tao , Zhang Jing-Fei , Zhang Xin 
Published: August 2024

AbstractThe 2.5-generation (2.5G) ground-based gravitational wave (GW) detectors LIGO Voyager and NEMO are expected to be operational in the late 2020s and early 2030s. In this work, we explore the potential of GW standard sirens observed by the 2.5G GW detectors in measuring cosmological parameters, especially for the Hubble constant. Using GWs to measure cosmological parameters is inherently challenging, especially for 2.5G detectors, given their limited capability, which results in weaker constraints on cosmological parameters from the detected standard sirens. However, the measurement of the Hubble constant using standard siren observations from Voyager and NEMO is still promising. For example, using bright sirens from Voyager and NEMO can measure the Hubble constant with a precision of about 2% and 6% respectively, and using the Voyager-NEMO network can improve the precision to about 1.6%. Moreover, bright sirens can be used to break the degeneracy of cosmological parameters generated by CMB data, and to a certain extent, 2.5G detectors can also play a role in this aspect. Observations of dark sirens by 2.5G detectors can achieve relatively good results in measuring the Hubble constant, with a precision of within 2%, and if combining observations of bright and dark sirens, the precision of the Hubble constant measurement can reach about 1.4%. Finally, we also discussed the impact of the uncertainty in the binary neutron star merger rate on the estimation of cosmological parameters. We conclude that the magnificent prospect for solving the Hubble tension is worth expecting in the era of the 2.5G ground-based GW detectors.
Operators of quantum theory of Dirac's free field
Authors: Cotăescu Ion I. 
Published: August 2024

Abstract
The Pryce (e) spin and position operators of the quantum theory of Dirac's free field were re-defined and studied recently with the help of a new spin symmetry and suitable spectral representations [Eur. Phys. J. C 82, 1073 (2022)]. This approach is generalized here, associating a pair of integral operators acting directly on particle and antiparticle wave spinors in momentum representation to any integral operator in configuration representation, acting on mode spinors. This framework allows an effective quantization procedure, giving a large set of one-particle operators with physical meaning as the spin and orbital parts of the isometry generators, the Pauli-Lubanski and position operators, or other spin-type operators proposed to date. Special attention is paid to the operators that mix the particle and antiparticle sectors whose off-diagonal associated operators have oscillating terms producing Zitterbevegung. The principal operators of this type, including the usual coordinate operator, are derived here for the first time. As an application, it is shown that an apparatus measuring these new observables may prepare and detect one-particle wave packets moving uniformly without Zitterbewegung or spin dynamics, spreading in time normally as any other relativistic or even non-relativistic wave packet.
The Effect of External Magnetic Field on Electron Scale Kelvin–Helmholtz Instability
Authors: Tsiklauri D. 
Published: August 2024

Abstract
We use particle-in-cell, fully electromagnetic, plasma kinetic simulation to study the effect of external magnetic field on electron scale Kelvin–Helmholtz instability (ESKHI). The results are applicable to collisionless plasmas when, e.g., solar wind interacts with planetary magnetospheres or a magnetic field is generated in AGN jets. We find that as in the case of magnetohydrodynamic (MHD) KHI, in the kinetic regime, the presence of an external magnetic field reduces the growth rate of the instability. In the MHD case, there is a known threshold magnetic field for KHI stabilization, while for ESKHI this is to be analytically determined. Without a kinetic analytical expression, we use several numerical simulation runs to establish an empirical dependence of ESKHI growth rate, Γ(B
0)ω
pe, on the strength of the applied external magnetic field. We find the best fit is hyperbolic,

Γ
(

B

0

)

ω

pe

=

Γ

0

ω

pe

/

(
A
+
B

B

¯

0

)

, where Γ0 is the ESKHI growth rate without an external magnetic field and

B

¯

0

=

B

0

/

B

MHD

is the ratio of external and two-fluid MHD stability threshold magnetic field, derived here. An analytical theory to back up this growth rate dependence on the external magnetic field is needed. The results suggest that in astrophysical settings where a strong magnetic field pre-exists, the generation of an additional magnetic field by the ESKHI is suppressed, which implies that nature provides a “safety valve”—natural protection not to “over-generate” magnetic field by the ESKHI mechanism. Remarkably, we find that our two-fluid MHD threshold magnetic field is the same (up to a factor

γ

0

) as the DC saturation magnetic field, previously predicted by fully kinetic theory.
Enhancing facial nerve regeneration with scaffold-free conduits engineered using dental pulp stem cells and their endogenous, aligned extracellular matrix
Authors: Drewry Michelle D , Shi Delin , Dailey Matthew T , Rothermund Kristi , Trbojevic Sara , Almarza Alejandro J , Cui Xinyan T , Syed-Picard Fatima N 
Published: August 2024

Abstract

Objective. Engineered nerve conduits must simultaneously enhance axon regeneration and orient axon extension to effectively restore function of severely injured peripheral nerves. The dental pulp contains a population of stem/progenitor cells that endogenously express neurotrophic factors (NTFs), growth factors known to induce axon repair. We have previously generated scaffold-free dental pulp stem/progenitor cell (DPSC) sheets comprising an aligned extracellular matrix (ECM). Through the intrinsic NTF expression of DPSCs and the topography of the aligned ECM, these sheets both induce and guide axon regeneration. Here, the capacity of bioactive conduits generated using these aligned DPSC sheets to restore function in critical-sized nerve injuries in rodents was evaluated. Approach. Scaffold-free nerve conduits were formed by culturing DPSCs on a substrate with aligned microgrooves, inducing the cells to align and deposit an aligned ECM. The sheets were then detached from the substrate and assembled into scaffold-free cylindrical tissues. Main results. In vitro analyses confirmed that scaffold-free DPSC conduits maintained an aligned ECM and had uniformly distributed NTF expression. Implanting the aligned DPSC conduits across critical-sized defects in the buccal branch of rat facial nerves resulted in the regeneration of a fascicular nerve-like structure and myelinated axon extension across the injury site. Furthermore, compound muscle action potential and stimulated whisker movement measurements revealed that the DPSC conduit treatment promoted similar functional recovery compared to the clinical standard of care, autografts. Significance. This study demonstrates that scaffold-free aligned DPSC conduits supply trophic and guidance cues, key design elements needed to successfully promote and orient axon regeneration. Consequently, these conduits restore function in nerve injuries to similar levels as autograft treatments. These conduits offer a novel bioactive approach to nerve repair capable of improving clinical outcomes and patient quality of life.