bluuebunny/crossref_metadata_2025 huggingface dataset:
Decay properties for a density-dependent liquid crystal system
Authors: Han Pigong , Lei Keke , Liu Chenggang , Wang Xuewen
Published: September 2022

The purpose of this paper is to establish the optimal temporal decay properties for nonhomogeneous incompressible liquid crystal flows in Rn, n = 2, 3. Under a weaker smallness assumption on the initial datum d0, we construct a uniform (in t) energy estimate for the director field d, which plays a crucial role in giving the optimal L2-decay rates for the liquid crystal flows. If the initial data are more regular, the optimal decay rates for the higher spatial derivatives are also obtained.
Evidence of the nontrivial Berry phase at
γ
-Al2O3/SrTiO3 heterointerfaces
Authors: Niu Wei , Wu Zhenqi , Chen Yongda , Gan Yulin , Chen Yequan , Hu Hongqi , Zhang Xiaoqian , Xu Yongbing , Zou Youming , Pu Yong , Wang Xuefeng
Published: September 2022

The nontrivial Berry phase in correlated oxide heterostructures has been highly attractive due to the Rashba spin–orbit interactions originating from the inversion symmetry breaking at the heterointerfaces. Despite the theoretically predicated nontrivial π Berry phase in Rashba systems, its experimental detection among all Rashba oxide interfaces remains elusive. Here, we report a nontrivial Berry phase at the interface between γ-Al2O3 and SrTiO3 as evidenced by the quantum oscillations. Analysis of transport properties under the high magnetic field up to 32 T reveals the weak anti-localization (WAL) effect and Shubnikov–de Haas (SdH) oscillations. Both the WAL effect and the nontrivial π Berry phase extracted from the SdH oscillations manifest the significance of the Rashba spin–orbit coupling in γ-Al2O3/SrTiO3. Physical quantities concerning the Fermi surface, such as effective mass, scattering time, etc., are experimentally accessed as well. Our work provides insights into the nontrivial Berry phase in correlated oxide interfaces.
High resolution in non-destructive testing: A review
Authors: Kumar Anish , Arnold Walter
Published: September 2022

Since the beginning of the applications of non-destructive testing/evaluation (NDT/NDE) techniques, efforts have been made consistently to improve their detection sensitivity and resolution. In the present paper, factors governing lateral resolution in three major NDT techniques, viz., ultrasonic testing (UT), x-ray radiographic testing (XRT), and eddy current testing (ECT) are presented. Furthermore, a review of recent advances in these NDT techniques to reach the theoretically achievable resolution limit or even surpassing the same using alternate approaches is also discussed. For example, resolution in UT is theoretically limited to half the wavelength by the Rayleigh limit; however, subwavelength resolutions have been achieved through the applications of near field methods by capturing the evanescent field. On the other hand, the resolution achieved in XRT is primarily limited to half the source/focal spot size, which is many orders of magnitude larger than the wavelength. Over the years, the reduction in the focal spot from macro-focus to micro-focus and now to nano-focus has led to improvement in the resolution to a few nanometers, of course, in combination with suitable magnification required due to detectors with limited pixel size (a few μm to a few 10 s of μm). Similarly, innovations in electromagnetic/magnetic sensors have significantly improved the resolution achieved in ECT. Atomic force microscopy, metamaterials, and artificial neural network-based methods have been employed for obtaining high-resolution NDE images. At the end, authors' perspective toward possible directions for high-resolution NDT is presented.
Spin Seebeck effect at low temperatures in the nominally paramagnetic insulating state of vanadium dioxide
Authors: Luo Renjie , Zhao Xuanhan , Chen Liyang , Legvold Tanner J. , Navarro Henry , Schuller Ivan K. , Natelson Douglas
Published: September 2022

The low temperature monoclinic, insulating phase of vanadium dioxide is ordinarily considered nonmagnetic, with dimerized vanadium atoms forming spin singlets, though paramagnetic response is seen at low temperatures. We find a nonlocal spin Seebeck signal in VO2 films that appears below 30 K and that increases with a decrease in temperature. The spin Seebeck response has a nonhysteretic dependence on the in-plane external magnetic field. This paramagnetic spin Seebeck response is discussed in terms of prior findings on paramagnetic spin Seebeck effects and expected magnetic excitations of the monoclinic ground state.
Simulated experiments for removal of odorous gases by wire-mesh electrode dielectric barrier discharge
Authors: Yang Geon W. , Chun Se M. , Kim Kang I. , Lee Hee J. , Hong Yongcheol
Published: September 2022

The emission of odorous gases from various industrial processes such as factories and wastewater treatment, in addition to emissions from landfills and livestock, has become a public concern because of their negative effect on air quality and human health. This study presents a technology based on dielectric barrier discharge (DBD) of wire-mesh type with a high-voltage electric wire as the electrode. This system was used to experimentally assess the removal efficiency of odorous gases. The plasma system consists of a wire electrode with a mesh-type configuration, a small blower (1.6 N m3/min, compressed air) for the plasma discharge or to supply cooling gas, and an AC high-voltage power supply. The plasma system offers the advantages of low power consumption and a large discharge area for ozone production. The wire-mesh electrode DBD comprises 64 discharge nodes, and the large amount of ozone generated from these nodes is used to oxidize odorous gases. Under optimized conditions, ozone is stably generated at the rate of 5.1 g/h for a specific input energy of 3.7 J/L. The ozone and odorous compounds (H2S: 4.5 ppm, CH3SH: 6.7 ppm, NH3: 3 ppm, outlet concentration) are injected into the main blower (20 N m3/min, compressed air). Finally, the experiments designed to simulate the removal of odorous gases confirmed that 99% of odorous compounds were removed using the wire-mesh electrode DBD. The cost-effectiveness and scalability of this system make it highly suitable for use in industrial environments where odorous gases are produced.
Multi-harmonic Rutherford island theory
Authors: Fitzpatrick R.
Published: September 2022

Rutherford island theory, which governs the nonlinear evolution of tearing modes in tokamak plasmas, is generalized to take into account situations in which the conventional one-harmonic approximation is not valid. The analysis incorporates non-inductive currents driven by radio frequency (RF) electromagnetic waves injected into the plasma. A multi-harmonic tearing mode dispersion relation is derived that takes the form of a nonlinear inhomogeneous matrix eigenvalue problem. The dispersion relation is solved in the so-called two-harmonic approximation, in which only the principal Fourier harmonic of the perturbed magnetic flux and its first overtone are included in the calculation. In the absence of RF current drive, the nonlinear behavior of a tearing mode predicted in the two-harmonic approximation does not differ substantially from that predicted in the one-harmonic approximation. On the other hand, RF current drive that is sufficiently localized in the vicinity of the O-points of the mode's magnetic island chain is capable of triggering bifurcations of the O-points (which is impossible in the one-harmonic approximation). However, the current drive is incapable of triggering bifurcations of the island X-points. This finding is significant because Bardóczi and Evans [Phys. Rev. Lett. 126, 085003 (2021)] recently observed bifurcations of magnetic island chain O-points in the presence of RF current drive in the DIII-D tokamak but did not observe bifurcations of the X-points. Finally, the changes in the topology of the magnetic island flux-surfaces induced by RF current drive are found to facilitate the stabilization of the tearing mode.
Dynamics of plasmas produced by a laser pulse, inside a dense gaseous target, formed in an ambient gas
Authors: Bartnik Andrzej , Jach Karol , Świerczyński Robert , Majszyk Mateusz , Fok Tomasz , Węgrzyński Łukasz , Wachulak Przemysław , Fiedorowicz Henryk
Published: September 2022

In this work, the time development of plasmas produced by interaction of laser pulses, with a nitrogen gas, was investigated. The interaction took place inside a small portion of dense nitrogen gas injected temporarily into a chamber filled with the gas under low pressure. High-temperature plasmas produced directly by the laser pulse were a source of soft x rays and charged particles, ionizing and exciting the surrounding gas. In this way, low-temperature plasmas were produced. The formation of high-temperature plasmas was studied using soft x-ray spectroscopy and x-ray streak imaging. Low-temperature plasmas formed at various distances from the laser focus were investigated using an optical streak camera. Interpretation of the experimental data was supported by numerical modeling of the laser-produced plasma hydrodynamics. It was concluded that depending on the distance from the focal spot, the formation of the low-temperature plasmas was dominated by ion streams or by soft x-ray radiation.
Influence of depolarization field on temperature-misfit strain phase diagram of PbZr0.4Ti0.6O3 ultrathin films
Authors: Ma Wenbo , Yuan Shuai , Ma Lele , Liu Yulan , Wang Biao , Chen Zuhuang
Published: September 2022

Phase-field simulations are performed to study domain structures in (001)-oriented PbZr0.4Ti0.6O3 epitaxial thin films. Temperature-misfit strain phase diagrams of the domain structures are constructed under various depolarization fields by adjusting surface screening conditions and film thickness. We find that the vortex-array state area in the phase diagram enlarges with the decrement of the depolarization field, which is contrary to the general view of depolarization field conductive to vortex formation. Moreover, a strain-mediated ferroelectric failure mechanism is found, wherein the ferroelectric characteristics of an ultrathin film with a thickness of 4 nm completely disappear (Curie temperature drops to 0 K) under the open-circuit condition when the compressive misfit strain drops to −2.69%. The results guide further understanding and manipulation of domain structures in ferroelectric nanomaterials.
Carrier dynamics in quantum-dot tunnel-injection structures: Microscopic theory and experiment
Authors: Lorke Michael , Khanonkin Igor , Michael Stephan , Reithmaier Johann Peter , Eisenstein Gadi , Jahnke Frank
Published: September 2022

Tunneling-injection structures are incorporated in semiconductor lasers in order to overcome the fundamental dynamical limitation due to hot carrier injection by providing a carrier transport path from a cold carrier reservoir. The tunneling process itself depends on band alignment between quantum-dot levels and the injector quantum well, especially as in these devices LO-phonon scattering is dominant. Quantum dots with their first excited state near the quantum well bottom profit the most from tunnel coupling. As inhomogeneous broadening is omnipresent in quantum dot structures, this implies that individual members of the ensemble couple differently to the injector quantum well. Quantum dots with higher energy profit less, as the phonon couples to higher, less occupied states. Likewise, if the energy difference between ground state and quantum well exceeds the LO-phonon energy, scattering becomes increasingly inefficient. Therefore, within 20–30 meV, we find quantum dots that benefit substantially different from the tunnel coupling. Furthermore, in quantum dots with increasing confinement depth, excited states become successively confined. Here, scattering gets more efficient again, as subsequent excited states reach the phonon resonance with the quantum well bottom. Our results provide guidelines for the optimization of tunnel-injection lasers. Theoretical results for electronic state calculations in connection with carrier–phonon and carrier–carrier scattering are compared to the experimental results of the temporal gain recovery after a short pulse perturbation.
Evaluation of a collisional radiative model for electron temperature determination in hydrogen plasma
Authors: Vinoth S. P. , Evans E. S. , Swanson C. P. S. , Palmerduca E. , Cohen S. A.
Published: September 2022

A collisional-radiative (CR) model that extracts the electron temperature, Te, of hydrogen plasmas from Balmer-line-ratio measurements is examined for the plasma electron density, ne, and Te ranges of 1010–1015 cm−3 and 5–500 eV, respectively. The CR code, developed and implemented in Python, has a forward component that computes the densities of excited states up to n = 15 as functions of Te, ne, and the molecular-to-atomic neutral ratio r(H2/H). The backward component provides ne and r(H2/H) as functions of the Balmer ratios to predict the Te. The model assumes Maxwellian electrons. The density profiles of the electrons and of the molecular and atomic hydrogen neutrals are shown to be of great importance, as is the accuracy of the line-ratio measurement method.
A virtual platform of electrical tomography for multiphase flow imaging
Authors: Wang Sheng-Nan , Giorgio-Serchi Francesco , Yang Yun-Jie
Published: September 2022

This paper reports a new approach to quantitatively evaluate the performance of Electrical Tomography (ET) in measuring dynamic multiphase flows. A virtual multiphase flow imaging platform based on ET is constructed and demonstrated on two typical gas–liquid flows, i.e., water–gas flow and oil–gas flow. Two coupling simulation cases, i.e., water–gas flow field and electric currents field coupling simulation and oil–gas flow field and electrostatics field coupling simulation, are performed to simulate multiphase flow sensing of Electrical Impedance Tomography (EIT) and Electrical Capacitance Tomography (ECT). We quantitatively evaluated the representative EIT and ECT image reconstruction algorithms on the virtual evaluation platform bringing evidence of the improved capability to capture the key flow features of the fluid mixture with respect to traditional static phantoms. Ad-hoc treatment of the signal noise enables one to better capture dynamic responses of the fluid phase volume fractions and their spatial gradients throughout their mixing along the conduit, ultimately demonstrating unprecedented potential in the quantitative characterization of complex, unsteady multi-phase systems. The proposed image reconstruction constitutes a highly effective platform for quantitative performance evaluation of ET, parameter optimization of model-based ET image reconstruction algorithms, and for the development of data-driven ET algorithms in multiphase flow imaging.
Nanostructured back surface amorphization of silicon with picosecond laser pulses
Authors: Blothe Markus , Chambonneau Maxime , Nolte Stefan
Published: September 2022

Laser-based amorphization on the back surface of a 525-μm thick crystalline silicon sample is studied. To deposit sufficient energy for a local change from a crystalline to an amorphous state, laser irradiation at 2-μm wavelength with 25-ps pulse duration is combined with Bessel beam shaping. Deterministic single-site modifications and homogeneous continuous lines of amorphous silicon are demonstrated. Optical and electron microscopy together with Raman spectroscopy measurements highlight the material transformations featuring the formation of subwavelength periodic surface structures. The investigations open up possibilities for processing in-built microelectronic devices.
Non-resonant recirculating light phase modulator
Authors: Huang Haijin , Han Xu , Balčytis Armandas , Dubey Aditya , Boes Andreas , Nguyen Thach G. , Ren Guanghui , Tan Mengxi , Tian Yonghui , Mitchell Arnan
Published: September 2022

High efficiency and a compact footprint are desired properties for electro-optic modulators. In this paper, we propose, theoretically investigate, and experimentally demonstrate a recirculating phase modulator, which increases the modulation efficiency by modulating the optical field several times in a non-resonant waveguide structure. The “recycling” of light is achieved by looping the optical path that exits the phase modulator back and coupling it to a higher order waveguide mode, which then repeats its passage through the phase modulator. By looping the light back twice, we were able to demonstrate a recirculating phase modulator that requires nine times lower power to generate the same modulation index of a single pass phase modulator. This approach to modulation efficiency enhancement is promising for the design of advanced tunable electro-optical frequency comb generators and other electro-optical devices with defined operational frequency bandwidths.
Photophoresis of spherical particles in slip-flow regime
Authors: Pereira D. J. S. , Panão M. R. O.
Published: September 2022

Photophoresis is a particle-light-induced phenomenon with several applications, such as spectroscopy, three-dimensional displays, and nanomanufacturing, to name a few. This work synthesizes, criticizes, and compares the main hydrodynamic and gas-kinetic models developed to quantify photophoretic forces in the slip-flow regime for uniform light beams, contrasting their predictions with experimental data available in the literature. The results comparing the different models evidence the simplicity and accuracy of Loesche and Husmann's model, which is then confronted with the experimental data available in the literature. However, considering the noticeable effect of high irradiance levels on photophoretic forces, namely, when temperature variations significantly change the thermofluid properties of the gaseous layer around the particle, more experiments are recommended to validate theoretical models. Finally, considering the photophoretic models that depend on two asymmetry factors, J0 and J1, a physical interpretation of their meaning is provided, especially for the oscillations in the latter argued as the result of Mie resonance effects.
The melt-back etching effect of the residual Ga in the reactor for GaN grown on (111) Si
Authors: Zhang Zhenzhuo , Yang Jing , Zhao Degang , Wang Baibin , Zhang Yuheng , Liang Feng , Chen Ping , Liu Zongshun , Ben Yuhao
Published: September 2022

The reaction between gallium (Ga) and silicon (Si), termed melt-back etching, greatly deteriorates the quality of GaN grown on a Si substrate. In this paper, the mechanism of melt-back etching was investigated layer-by-layer in a GaN/AlN/Si system. It is found that the environment of the reactor plays a critical role in melt-back etching, which may happen as early as during the baking process. Drawing on experimental evidence and analyses, a two-step melt-back etching model is proposed. Finally, optimized pretreatments including an AlN precoating process and reduction in baking temperature were used to successfully solve the etching problem and verify the model.
The control mechanism of the soft trailing fringe on the flow characteristics over an airfoil
Authors: Deng Zhi , Chen Wen-Li , Yang Zifeng
Published: September 2022

Inspired by the owl’s silent flight, we experimentally investigated the flow control mechanism of the soft trailing fringes (STFs) on the wake of the S833 airfoil at the Reynolds number of Re = 2 × 104. A high-speed Particle Image Velocimetry (PIV) system is employed to visualize and analyze the flow structures in the wake of the airfoil at different angles of attack (AOA). Furthermore, spectral proper orthogonal decomposition and bispectral mode decomposition are carried out to identify the coherent flow structures and reveal the control mechanism from the perspective of simplified models. PIV measurements’ results demonstrate that the STFs evidently suppress the turbulent quantities including turbulent kinetic energy and Reynolds shear stress in the airfoil wake. On the one hand, the STFs at low AOAs prevent the interaction between the upper and lower shear layers, and the leading- and trailing-edge vortices (TEVs) are significantly suppressed, thus destructing the von Karman vortex streets. On the other hand, the STFs at high AOAs divide the lower shear layer into two parts, markedly attenuating the TEVs and modifying the vortical structures in the wake. Besides, the quadrant analysis reveals that the STFs can mitigate the high-amplitude wall-pressure peaks, indicating that the STFs may manipulate the trailing-edge noise. However, the control effect is limited at median AOAs because the region with high triadic interactions moves upward in the interaction maps, which limits the impact of the STFs.
Cross-correlation effects in the solution NMR spectra of near-equivalent spin-1/2 pairs
Authors: Whipham James W. , Moustafa Gamal A. I. , Sabba Mohamed , Gong Weidong , Bengs Christian , Levitt Malcolm H.
Published: September 2022

The nuclear magnetic resonance (NMR) spectra of spin-1/2 pairs contain four peaks, with two inner peaks much stronger than the outer peaks in the near-equivalence regime. We have observed that the strong inner peaks have significantly different linewidths when measurements were performed on a 13C2-labelled triyne derivative. This linewidth difference may be attributed to strong cross-correlation effects. We develop the theory of cross-correlated relaxation in the case of near-equivalent homonuclear spin-1/2 pairs, in the case of a molecule exhibiting strongly anisotropic rotational diffusion. Good agreement is found with the experimental NMR lineshapes.
A Weyl semimetal WTe2/GaAs 2D/3D Schottky diode with high rectification ratio and unique photocurrent behavior
Authors: Wang Jina , Wang Hanyu , Chen Quan , Qi Ligan , Zheng Zhaoqiang , Huo Nengjie , Gao Wei , Wang Xiaozhou , Li Jingbo
Published: September 2022

Since the discovery of Dirac semimetal graphene, two-dimensional (2D) Weyl semimetals (WSMs) have been widely used in low-energy photon detection, polarization imaging, and other systems due to their rich physical characteristics, such as unique nonlinear optical structure, topological nontrivial electronic structure, thickness-tunable bandgap, high electric conductivity, and so on. However, it is difficult to detect the photocurrent signal at room temperature because of its large intrinsic background current. Fortunately, the fabrication of a van der Waals (vdW) heterojunction based on WSM can effectively suppress the background current, greatly extend the detection range, improve the light absorption efficiency, and increase the response speed. Herein, the 2D type-II WSM 1T′-WTe2/bulk GaAs vdW vertical Schottky diode is investigated. Benefiting from the lateral built-in electric field of 260 meV and zero-bandgap structure of 52 nm 1T′-WTe2, it delivers a rectifying ratio over 103 and can respond to the wavelength range of 400–1100 nm. Particularly, when the light power density is 0.02 mW/cm2, the maximum photoresponsivity (R) and specific detectivity (D*) under 808 nm are 298 mA/W and 1.70 × 1012 Jones, respectively. Meanwhile, the Ilight/Idark ratio and response time are 103 and 520/540 μs, respectively. Moreover, an abnormal negative response behavior can be observed with thin WTe2 (11 nm) under 1064 nm illumination because of the open surface bandgap. It is suggested that such 2D WTe2/GaAs mixed-dimensional vdW structure can be extended to other WSM/3D semiconductor junctions and used in fast response and wide broadband spectrum photodetectors' arrays.
Well-pattern optimization of CH4 transport associated with supercritical CO2 flooding
Authors: Deng Jia , He Jiujiu , Li Jiujiang , Zhang Lan , Song Fuquan
Published: September 2022

Injecting supercritical CO2 into depleted gas reservoirs enables additional CH4 to be extracted, a process known as CO2 enhanced gas recovery (CO2-EGR). Optimization of the well pattern is another method used to enhance gas reservoir exploitation. The focus of the present work is to address the arrangement of the well pattern when using CO2-EGR. For this purpose, mathematical models with five-spot and seven-spot well patterns are established in steady and unsteady conditions, and their results are validated against previously published models. For the first time, equipotential and streamline charts of the well pattern in CO2-EGR are derived from these models. As a result, the main flow channel of the well pattern is clarified, and the distributions of formation pressure and seepage velocity are determined. Moreover, the relationships between the gas production rate and well pattern parameters such as the producing pressure drop, permeability, formation pressure, temperature, and well spacing are investigated and the factors that influence the recovery ratio are examined. Finally, an optimization strategy for the well pattern parameters in CO2-EGR is proposed to enhance the gas production rate and recovery factor.
Corrigendum to: A method for soil management assessment in an unreplicated commercial field
Authors: Lee Juhwan , Plant Richard E.
Published: September 2022

 Context: Unreplicated trials are common in agriculture. However, statistical inferences differ from those of traditional experiments based on small, replicated plots.

 Aims: To present a method to assess management effects on soil carbon (C) storage from unreplicated, side-by-side field trials.

 Methods: Two estimates of means with spatially correlated errors are compared using a corrected t-statistic. Then causal inference is made by analysing a significant difference between the means (P<0.05) and its changes over time. The use of the method is described in comparing yield and organic C stocks between two large fields. Yield was measured during 1997–2005 with a commercial yield monitor, and soil organic C stocks during 2003–2005. The fields experienced the same tillage practice until autumn 2003 and then with different tillage intensity.

 Key results: The results show that crop C yield did not differ between the fields when using the same tillage practice but was greater in the tilled than the no-till field. The results also suggest that total and particulate organic matter-C contents depend on tillage history. For comparative purposes, the data were also analysed using standard mixed model analysis with a semivariogram model for spatial autocorrelation among the residuals. The mixed model results were generally similar to those of the corrected t-statistic method. The mixed model was often, but not always, less conservative than the corrected t-statistic model.

 Conclusions: The method allows analysis of whole-field data and improves our understanding of soil C processes in commercial fields, where agricultural assessment cannot involve replication due to agronomic and economic constraints.

 Implications: The method complements observational data analyses and can offer a direction towards whole-field management.
PP1 phosphatases control PAR-2 localization and polarity establishment in C. elegans embryos
Authors: Calvi Ida , Schwager Françoise , Gotta Monica
Published: September 2022

Cell polarity relies on the asymmetric distribution of the conserved PAR proteins, which is regulated by phosphorylation/dephosphorylation reactions. While the kinases involved have been well studied, the role of phosphatases remains poorly understood. In Caenorhabditis elegans zygotes, phosphorylation of the posterior PAR-2 protein by the atypical protein kinase PKC-3 inhibits PAR-2 cortical localization. Polarity establishment depends on loading of PAR-2 at the posterior cortex. We show that the PP1 phosphatases GSP-1 and GSP-2 are required for polarity establishment in embryos. We find that codepletion of GSP-1 and GSP-2 abrogates the cortical localization of PAR-2 and that GSP-1 and GSP-2 interact with PAR-2 via a PP1 docking motif in PAR-2. Mutating this motif in vivo, to prevent binding of PAR-2 to PP1, abolishes cortical localization of PAR-2, while optimizing this motif extends PAR-2 cortical localization. Our data suggest a model in which GSP-1/-2 counteracts PKC-3 phosphorylation of PAR-2, allowing its cortical localization at the posterior and polarization of the one-cell embryo.
Fundamental asymmetry between space and time in quantum field theory
Authors: Gavassino L
Published: September 2022

In 1 + 1 dimensions, space and time are geometrically interchangeable. The reason is that, if we switch the roles of the spacelike and the timelike dimensions, this only amounts to redefining the signature convention of the metric tensor. This establishes a mathematical duality between classical Klein–Gordon fields and classical tachyonic fields: one is the ‘space/time swapped’ version of the other. Here, we show that this duality breaks down completely in a quantum world. In quantum field theory, if we exchange space with time, we end up with non-canonical field theories that exhibit all sorts of paradoxical behaviours. Theories that should be stable are, instead, unstable, while theories that should be unstable are stable. Theories that should be causal are, instead, acausal. This formalizes a widespread (but often neglected) intuition: there is a fundamental (non-geometrical) asymmetry between space and time, which has a purely quantum origin, and does not exist in a classical world. Such asymmetry exists independently from the measurement problem, as it is encoded directly in the algebraic properties of the field operators.
The factorization method and Capon’s method for random source identification in experimental aeroacoustics
Authors: Griesmaier Roland , Raumer Hans-Georg
Published: September 2022

Experimental aeroacoustics is concerned with the estimation of acoustic source power distributions, which are for instance caused by fluid structure interactions on scaled aircraft models inside a wind tunnel, from microphone array measurements of associated sound pressure fluctuations. In the frequency domain aeroacoustic sound propagation can be modeled as a random source problem for a convected Helmholtz equation. This article is concerned with the inverse random source problem to recover the support of an uncorrelated aeroacoustic source from correlations of observed pressure signals. We show that a variant of the factorization method from inverse scattering theory can be used for this purpose. We also discuss a surprising relation between the factorization method and a commonly used beamforming algorithm from experimental aeroacoustics, which is known as Capon’s method or as the minimum variance method. Numerical examples illustrate our theoretical findings.
A novel ultra-broadband absorber based on carbon-coated honeycomb panels combined with metamaterials
Authors: Wang Yang , Chen Shiju , Liu Shanshan , Wu Jiong , Wang Youcheng , Ding Xiaoxia , Yang Helin
Published: September 2022

In this paper, a radar absorber with composite structure of metasurface/honeycomb is proposed. Carbon coating is used as a loss material, and honeycomb sandwich structure is used as a support layer to enhance mechanical strength. Introducing impedance matching layer in the top layer of honeycomb absorber can significantly improve the low-frequency absorption performance. The simulation results show that the absorption efficiency of the combined structure absorber can reach more than 90% in the frequency range of 3.65–17.3 GHz. We verified the simulation results through experiments. This method provides an idea for the design of ultra-wideband absorber and has a potential application prospect in stealth material design.
KATRIN: status and prospects for the neutrino mass and beyond
Authors: Aker M , Balzer M , Batzler D , Beglarian A , Behrens J , Berlev A , Besserer U , Biassoni M , Bieringer B , Block F , Bobien S , Bombelli L , Bormann D , Bornschein B , Bornschein L , Böttcher M , Brofferio C , Bruch C , Brunst T , Caldwell T S , Carminati M , Carney R M D , Chilingaryan S , Choi W , Cremonesi O , Debowski K , Descher M , Díaz Barrero D , Doe P J , Dragoun O , Drexlin G , Edzards F , Eitel K , Ellinger E , Engel R , Enomoto S , Felden A , Fink D , Fiorini C , Formaggio J A , Forstner C , Fränkle F M , Franklin G B , Friedel F , Fulst A , Gauda K , Gavin A S , Gil W , Glück F , Grande A , Grössle R , Gugiatti M , Gumbsheimer R , Hannen V , Hartmann J , Haußmann N , Helbing K , Hickford S , Hiller R , Hillesheimer D , Hinz D , Höhn T , Houdy T , Huber A , Jansen A , Karl C , Kellerer J , King P , Kleifges M , Klein M , Köhler C , Köllenberger L , Kopmann A , Korzeczek M , Kovalík A , Krasch B , Krause H , Lasserre T , La Cascio L , Lebeda O , Lechner P , Lehnert B , Le T L , Lokhov A , Machatschek M , Malcherek E , Manfrin D , Mark M , Marsteller A , Martin E L , Mazzola E , Melzer C , Mertens S , Mostafa J , Müller K , Nava A , Neumann H , Niemes S , Oelpmann P , Onillon A , Parno D S , Pavan M , Pigliafreddo A , Poon A W P , Poyato J M L , Pozzi S , Priester F , Puritscher M , Radford D C , Ráliš J , Ramachandran S , Robertson R G H , Rodejohann W , Rodenbeck C , Röllig M , Röttele C , Ryšavý M , Sack R , Saenz A , Salomon R W J , Schäfer P , Schimpf L , Schlösser K , Schlösser M , Schlüter L , Schneidewind S , Schrank M , Schütz A-K , Schwemmer A , Sedlak A , Šefčík M , Sibille V , Siegmann D , Slezák M , Spanier F , Spreng D , Steidl M , Sturm M , Telle H H , Thorne L A , Thümmler T , Titov N , Tkachev I , Trigilio P , Urban K , Valerius K , Vénos D , Vizcaya Hernández A P , Voigt P , Weinheimer C , Weiss E , Welte S , Wendel J , Wiesinger C , Wilkerson J F , Wolf J , Wunderl L , Wüstling S , Wydra J , Xu W , Zadoroghny S , Zeller G
Published: September 2022

The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to measure a high-precision integral spectrum of the endpoint region of T2 β decay, with the primary goal of probing the absolute mass scale of the neutrino. After a first tritium commissioning campaign in 2018, the experiment has been regularly running since 2019, and in its first two measurement campaigns has already achieved a sub-eV sensitivity. After 1000 days of data-taking, KATRIN’s design sensitivity is 0.2 eV at the 90% confidence level. In this white paper we describe the current status of KATRIN; explore prospects for measuring the neutrino mass and other physics observables, including sterile neutrinos and other beyond-Standard-Model hypotheses; and discuss research-and-development projects that may further improve the KATRIN sensitivity.
Free-standing hybrid material of Cu/Cu2O/CuO modified by graphene with commercial Cu foil using for non-enzymatic glucose detection
Authors: Ren Zhaodi , Dong Rui , Liu Yuanan
Published: September 2022

Free-standing Cu/Cu2O/CuO modified by graphene was formed through two steps: Firstly, the commercial Cu foil was thermal annealed to form Cu/Cu2O/CuO; Secondly, the Cu/Cu2O/CuO was modified by graphene through electrochemical exfoliated method. The SEM, XRD, TEM and XPS have been used to characterize the morphology, the crystalline phase, and the surface composition of the hybrid electrode as-prepared. The effects of Cu and its oxides on graphene has been uncovered by the Raman results. The sensitivity of the glucose sensor in 0.1 M NaOH by using the as-prepared hybrid material reaches 3102 μA·mM−1 cm−2 within a linear range of 0.002–2.88 mM, which is better than that of the Cu/graphene and the Cu/Cu2O/CuO prepared at the same conditions. The sensor also shows excellent anti-interference ability, good cycling stability and time stability. The advantage of the sensor is caused by the strengthened synergistic effects between the graphene and the Cu/Cu2O/CuO due to the alleviated detrimental effects of the metal on the property of the graphene through using oxides middle layer as well as the large active area that obtained. This work provides a new way to study the effects of graphene in improving the property of the metal oxide especially in using for glucose sensor.
A literature review on the definition of the concept of weight
Authors: Taşkın Tuğba , Karadag Mustafa
Published: September 2022

The weight, one of the key concepts of physics education, still continues to be discussed among physics educators. Today, there are two main definitions as the ‘gravitational’ and ‘operational’, but there are differences even between them. It is important to know the different approaches found in textbooks in eliminating misconceptions and organizing the learning environment. Therefore, in this study, we examined the basic physics textbooks used as reliable sources in different universities in the world and aimed to reveal the differences of opinion in the literature in a single source. We examined the definitions in the textbooks for the concept of weight by using content analysis method in terms of vector and scalar characteristics. As a result of the analysis, we saw that the textbooks mostly (69.8%) define weight as a vector quantity. In addition, we determined that the definitions for being scalar started to be preferred after 2004. Moreover, we have determined that the gravitational and operational definitions have different interpretations, both as vectors and scalars, but the textbooks offer a single perspective for weight and do not include these different interpretations. We encountered the explanation of the differences of opinion in the literature only in one textbook.
Currents induced in a circular loop by an oscillating magnet
Authors: Ha Hye Jin , Jang Taehun , Sohn Sang Ho
Published: September 2022

In this study, we derived several formulas for the currents induced in a circular loop by a magnet connected to a spring-based simple harmonic oscillation system. In addition, we conducted an experiment for measuring the induced currents and compared the results with the theoretical prediction. It was confirmed that the prediction from the derived formulas fits well with experimental results. Via derived formulas and a simple experiment, Faraday’s Law and Lenz’s Law could be easily explained.
Electron cyclotron drift instability and anomalous transport: two-fluid moment theory and modeling
Authors: Wang Liang , Hakim Ammar , Juno James , Srinivasan Bhuvana
Published: September 2022

In the presence of a strong electric field perpendicular to the magnetic field, the electron cross-field (E × B) flow relative to the unmagnetized ions can cause the so-called electron cyclotron drift instability (ECDI) due to resonances of the ion acoustic mode and the electron cyclotron harmonics. This occurs in, for example, collisionless shock ramps in space, and in E × B discharge devices such as Hall thrusters. A prominent feature of ECDI is its capability to induce an electron flow parallel to the background E field at a speed greatly exceeding predictions by classical collision theory. Such anomalous transport is important due to its role in particle thermalization at space shocks, and in causing plasma flows towards the walls of E × B devices, leading to unfavorable erosion and performance degradation, etc. The development of ECDI and anomalous transport is often considered requiring a fully kinetic treatment. In this work, however, we demonstrate that a reduced variant of this instability, and more importantly, the associated anomalous transport, can be treated self-consistently in a collisionless two-fluid framework without any adjustable collision parameter. By treating both electron and ion species on an equal footing, the free energy due to the inter-species velocity shear allows the growth of an anomalous electron flow parallel to the background E field. We will first present linear analyses of the instability in the two-fluid five- and ten-moment models, and compare them against the fully-kinetic theory. At low temperatures, the two-fluid models predict the fastest-growing mode in good agreement with the kinetic result. Also, by including more

(

>

=
10

)

moments, secondary (and possibly higher) unstable branches can be recovered. The dependence of the instability on ion-to-electron mass ratio, plasma temperature, and background B field strength is also thoroughly explored. We then carry out direct numerical simulations of the cross-field setup using the five-moment model. The development of the instability, as well as the anomalous transport, is confirmed and in excellent agreement with theoretical predictions. The force balance properties are also studied using the five-moment simulation data. This work casts new insights into the nature of ECDI and the associated anomalous transport and demonstrates the potential of the two-fluid moment model in efficient modeling of E × B plasmas.
Characterisation of surface charge density and net electric field during parallel-plate dielectric barrier discharge generated in atmospheric-pressure air
Authors: Natsume China , Komuro Atsushi , Ando Akira
Published: September 2022

We measured the surface charge density in a parallel-plate dielectric barrier discharge (DBD) using the Pockels effect, and the axial and lateral components of the net electric field were evaluated for different gap lengths and applied voltages. The DBD was driven by a 5 kHz sinusoidal voltage in gap lengths of 0.5, 0.3, and 0.1 mm at atmospheric pressure with Bi4Ge3O12 crystal as a dielectric. Typical microdischarges (MDs) were observed for every gap length, and the number of MDs increased with the increasing applied voltage. As the gap length decreased, the spot radius of a single MD decreased, whereas the peaks of charge density were almost the same, indicating that the amount of charge transported per unit MD is limited for short gaps. The spatial memory effect, in which MDs occur at the same position in successive cycles, was not always observed under the experimental conditions, and it was evaluated considering the surface charge density distributions. Whether the memory effect works is determined by the surface charge density, and it is likely to occur under a balance between positive and negative charges across successive half-cycles. The net electric field was estimated from surface charge measurements. The axial component of the net electric field strength increased up to 150–170 Td before the MD occurred, and it decreased below 100 Td by the surface charge deposited by MD, being approximately 50%–60% of the external field amplitude. The maximum value of the lateral component of the electric field was approximately 150 Td at the edge of the MD spot with a gap length of 0.5 mm, and it decreased as the gap length decreased. As a negative surface charge generated a weaker lateral field than a positive one, the electric field distribution differed between anodic and cathodic dielectrics.
Low-frequency vibration energy harvesting: a comprehensive review of frequency up-conversion approaches
Authors: Tang Hao , Hua Chunrong , Huang Heng , Liu Weiqun , Yang Zhengbao , Yuan Yanping , Zhang Zutao
Published: September 2022

Along with the rapid development of low-power electronics and the Internet of Things, vibration energy harvesting is attracting increasingly attention from both industry and academia. However, most reported energy harvesters are inefficient in real applications where excitation sources mostly are unpredictable and low frequency. To harness low-frequency vibration energy, the concept of frequency up-conversion is proposed and a variety of designs and analysis has been reported. This article presents a critical review on frequency up-conversion vibration energy harvesters (FUCHs) based on two classification principles: (a) interaction mechanisms as contact and noncontact types; and (b) excitations as type of inertial vibration and type of direct loading. Furthermore, we illustrate the applications of FUCHs designed for harvesting energy from the low-frequency human motions and propose the feasible future research directions of FUCHs.
Single-photon induced symmetry breaking of the electron localization and photoelectron directional emission in the dissociative ionization of H2
Authors: Wang Jun-Ping , Zhang Zhao-Han , He Feng
Published: September 2022

By numerically solving the non-Born–Oppenheimer time-dependent Schrödinger equation of H2 exposed to an isolated EUV laser pulse, we demonstrate the photoionization associated with the 2sσ

g
and 3pσ

u
dissociative states of

H

2

+

. The two asymptotically degenerate pathways with opposite parities may interfere and end up with the same kinetic energy release, resulting in the asymmetric electron localization on two nuclei. Due to dipole selection rule, the emitted photoelectron has the opposite parity with the associated

H

2

+

, and thus is also on the coherent superposition of states with odd and even parities, leading to the asymmetric directional emission of the photoelectron. The asymmetry is fundamentally determined by the phase difference of the 2sσ

g
and 3pσ

u
dissociation channels.
Generation of gravitational waves from freely decaying turbulence
Authors: Auclair Pierre , Caprini Chiara , Cutting Daniel , Hindmarsh Mark , Rummukainen Kari , Steer Danièle A. , Weir David J.
Published: September 2022

We study the stochastic gravitational wave background (SGWB) produced by freely decaying vortical turbulence in the early Universe. We thoroughly investigate the time correlation of the velocity field, and hence of the anisotropic stresses producing the gravitational waves. With hydrodynamical simulations, we show that the unequal time correlation function (UETC) of the Fourier components of the velocity field is Gaussian in the time difference, as predicted by the “sweeping” decorrelation model. We introduce a decorrelation model that can be extended to wavelengths around the integral scale of the flow. Supplemented with the evolution laws of the kinetic energy and of the integral scale, this provides a new model UETC of the turbulent velocity field consistent with the simulations. We discuss the UETC as a positive definite kernel, and propose to use the Gibbs kernel for the velocity UETC as a natural way to ensure positive definiteness of the SGWB. The SGWB is given by a 4-dimensional integration of the resulting anisotropic stress UETC with the gravitational wave Green's function. We perform this integration using a Monte Carlo algorithm based on importance sampling, and find that the result matches that of the simulations. Furthermore, the SGWB obtained from the numerical integration and from the simulations show close agreement with a model in which the source is constant in time and abruptly turns off after a few eddy turnover times. Based on this assumption, we provide an approximate analytical form for the SGWB spectrum and its scaling with the initial kinetic energy and integral scale. Finally, we use our model and numerical integration algorithm to show that including an initial growth phase for the turbulent flow heavily influences the spectral shape of the SGWB. This highlights the importance of a complete understanding of the turbulence generation mechanism.
Hierarchical merger of primordial black holes in dwarf galaxies
Authors: Erfani Encieh , Gomez-Aguilar Tadeo D. , Hidalgo Juan Carlos
Published: September 2022

We study the merger history of primordial black holes (PBHs) in a scenario where they represent the dominant dark matter component of a typical dwarf galaxies' core. We investigate the possibility of a sequence of collisions resulting in a hierarchical merger of black holes, and look at the final mass spectrum in such clusters, which initially present a monochromatic (single-mass) PBH population. Our study shows that the merging process results in the transfer of about 40% of the total mass of the core to the merger products regardless of the initial mass of PBHs, with about 5% of energy radiated out in the form of gravitational waves. We find that, in the lighter mass limit, black holes up to eight times more massive than the original population can be formed within a Hubble time.