bluuebunny/crossref_metadata_2025_split huggingface dataset:
All conformally flat Einstein–Gauss–Bonnet static metrics
Authors: Hansraj Sudan , Megandhren Govender , Banerjee Ayan , Mkhize Njabulo 
Published: February 2021

Abstract
It is known that the standard Schwarzschild interior metric is conformally flat and generates a constant density sphere in any spacetime dimension in Einstein and Einstein–Gauss–Bonnet (EGB) gravity. This motivates the questions: in EGB does the conformal flatness criterion yield the Schwarzschild metric? Does the assumption of constant density generate the Schwarzschild interior spacetime? The answer to both questions turn out in the negative in general. In the case of the constant density sphere, a generalised Schwarzschild metric emerges. When we invoke the conformal flatness condition the Schwarschild interior solution is obtained as one solution and another metric which does not yield a constant density hypersphere in EGB theory is found. For the latter solution one of the gravitational metrics is obtained explicitly while the other is determined up to quadratures in 5 and 6 dimensions. The physical properties of these new solutions are studied with the use of numerical methods and a parameter space is located for which both models display pleasing physical behaviour.
Inquiring the Unruh–DeWitt detector about the global property of spacetime
Authors: Sun Hongsong , Zhang Kaituo , Cai Huabing 
Published: February 2021

Abstract
We investigate the effect of spatial compactification on the transition rate of an inertial or accelerated Unruh–Dewitt detector coupled to an untwisted or twisted massless quantum scalar field. Four typical cases of the detector’s motion in the compactified Minkowski spacetime are considered respectively. Our results indicate that the detector’s transition rates are crucially dependent on the spatial compactification length, the magnitude and direction of detector’s velocity, the detector’s acceleration, and the field structure. As these factors change, the detector’s spontaneous emission and absorption processes can be enhanced or weakened at different degrees. In particular, when the compact length is small, the behavior of transition rate in the case of the twisted field is quite distinct from that of the untwisted field. Notably, when the detector moves at a constant velocity with nonzero components along the compact and non-compact directions, our study finds that the spontaneous emission rate depends on the component of velocity along the non-compact direction besides that along the compact direction. This is in sharp contrast with the case of the free Minkowski spacetime. Moreover, for the uniformly accelerated detector along the non-compact direction, the spatial compactification clearly modifies both the spontaneous emission and absorption rates, as the modifying factors depend on the compact length and the detector’s acceleration. Our work indirectly but comprehensively examines the nonequivalence of inertial frames in the compactified Minkowski spacetime, and meanwhile provides a theoretical way to identify the orientation and the size of the compact spatial dimension.
Solving an inverse heat convection problem with an implicit forward operator by using a projected quasi-Newton method
Authors: Rothermel Dimitri , Schuster Thomas 
Published: February 2021

Abstract
We consider the quasilinear 1D inverse heat convection problem of determining the enthalpy-dependent heat fluxes from noisy internal enthalpy measurements. This problem arises in the accelerated cooling process of producing thermomechanically controlled processed heavy plates made of steel. In order to adjust the complex microstructure of the underlying material, the Leidenfrost behavior of the hot surfaces with respect to the application of the cooling fluid has to be studied. Since the heat fluxes depend on the enthalpy and hence on the solution of the underlying initial boundary value problem (IBVP), the parameter-to-solution operator, and thus the forward operator of the inverse problem, can only be defined implicitly. To guarantee well-defined operators, we study two approaches for showing existence and uniqueness of solutions of the IBVP. One approach deals with the theory of pseudomonotone operators and so-called strong solutions in Sobolev–Bochner spaces. The other theory uses classical solutions in Hölder spaces. Whereas the first approach yields a solution under milder assumptions, it fails to show the uniqueness result in contrast to the second approach. Furthermore, we propose a convenient parametrization approach for the nonlinear heat fluxes in order to decouple the parameter-to-solution relation and use an iterative solver based on a projected quasi-Newton (PQN) method together with box-constraints to solve the inverse problem. For numerical experiments, we derive the necessary gradient information of the objective functional and use the discrepancy principle as a stopping rule. Numerical tests show that the PQN method outperforms the Landweber method with respect to computing time and approximation accuracy.
A particle-capturing and -separating, sheathless chip in series with microfilters and planar interdigital electrodes
Authors: Zhang Binzhen , Wang Yangyang , Liu Yunpeng , Li Huan , Zang Wenxuan , Duan Junping 
Published: February 2021

Abstract
Research on microfluidic chips is becoming more and more important in life sciences, medical testing, and chemical reactions. In the process of separating particles by dielectrophoresis (DEP), focusing of mixed particles is essential. The commonly used focusing method is sheath flow which dilutes the particle samples. However, it requires an additional injector which precludes development of an integrated system for chemical analysis and biological detection. In this paper, we propose a novel sheathless, shunt-focusing approach using microfilters (MFs) and interdigital electrodes to achieve particle capture and separation. By passing through a shrinking channel, most of the flowing small particles pass through the MFs, generating an artificial sheath flow in the channels to achieve focusing. Subsequently, interdigital electrodes provide DEP force to separate the particles. Separation efficiency was assessed by collecting polystyrene (20 μm diameter) from silica (4 μm diameter) at various flow rates. From the experimental results, the efficiency of capture reached 71%–86% and that of separation was over 98.6%. This chip is expected to be applied to the separation of circulating tumor cells in blood samples.
Remote epitaxy of GaN via graphene on GaN/sapphire templates
Authors: Badokas Kazimieras , Kadys Arūnas , Mickevičius Jūras , Ignatjev Ilja , Skapas Martynas , Stanionytė Sandra , Radiunas Edvinas , Juška Giedrius , Malinauskas Tadas 
Published: February 2021

Abstract
Remote epitaxy via graphene has recently attracted significant attention, since it provides the possibility to lift-off the grown epitaxial layer, reuse the substrate, and produce flexible devices. However, extensive research is still necessary to fully understand the III-nitride formation on the van der Waals surface of a two-dimensional material and utilize remote epitaxy to its full potential. In this work, the growth of a GaN epilayer using a GaN/sapphire template covered with monolayer graphene is presented. Metalorganic vapor phase epitaxy is chosen to fabricate both the template and the nitride epilayer on top as a cost-effective approach toward GaN homoepitaxy. One-step and multi-step growth temperature protocols are demonstrated while paying particular attention to the graphene interface. GaN seed formation on graphene is analyzed to identify remote epitaxy. Crystalline quality improvement of the epilayer by adjusting the growth parameters is further discussed to provide useful insights into GaN growth on a GaN/sapphire template via monolayer graphene.
High performance perovskite LEDs via SPR and enhanced hole injection by incorporated MoS2
Authors: Sun Dongwei , Zhang Ke , Mei Sijiong , Xu Jinxia , Jiang Yan , Xiao Xiangheng , Zhou Yuanming , Mei Fei 
Published: February 2021

Abstract
Organic–inorganic hybrid perovskites have attracted widespread attention in relation to light-emitting diodes (LEDs) due to their excellent properties. However, the imperfect energy band alignment between the perovskite and poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) limits the device’s performance. Here, we have investigated the effect of blending MoS2 in PEDOT:PSS and the resulting performance of perovskite LEDs (PeLEDs). We found that the doping of MoS2 can optimize the energy barrier and promote hole injection, significantly improving the current efficiency (CE) of PeLEDs, which can be attributed to the distinguished electrical conductivity and improved charge injection balance. At the same time, the local surface plasmon resonance effect with Au nanoparticles (NPs) is also introduced to reduce the nonradiative recombination and effectively promote light emission to further improve the performance of PeLED devices. Compared to the control PeLEDs device with undoped PEDOT:PSS as the hole transport layer, a 223% enhancement in maximum CE and a 130% enhancement in maximum luminance are achieved, with an optimal volume ratio for the PEDOT:PSS:MoS2 of 1:0.4 and Au NPs of 10%. Thus, the optimization combination of MoS2 and Au NPs is an excellent approach to improve the performance of PeLEDs, thereby increasing the potential applications of PeLED devices.
High-pressure monoclinic–monoclinic transition in fergusonite-type HoNbO4
Authors: Garg A B , Errandonea D , Rodríguez-Hernández P , Muñoz A 
Published: February 2021

Abstract
In this paper we perform a high-pressure (HP) study of fergusonite-type HoNbO4. Powder x-ray diffraction experiments and ab initio density-functional theory (DFT) simulations provide evidence of a phase transition at 18.9(1.1) GPa from the monoclinic fergusonite-type structure (space group I2/a) to another monoclinic polymorph described by space group P21/c. The phase transition is reversible and the HP structural behavior is different than the one previously observed in related niobates. The HP phase remains stable up to 29 GPa. The observed transition involves a change in the Nb coordination number from 4 to 6, and it is driven by mechanical instabilities. We have determined the pressure dependence of unit-cell parameters of both phases and calculated their room-temperature equation of state. For the fergusonite-phase we have also obtained the isothermal compressibility tensor. In addition to the HP studies, we report ambient-pressure Raman and infrared (IR) spectroscopy measurements. We have been able to identify all the active modes of fergusonite-type HoNbO4, which have been assigned based upon DFT calculations. These simulations also provide the elastic constants of the different structures and the pressure dependence of the Raman and IR modes of the two phases of HoNbO4. According to ab initio calculations, the reported phase transition is related to a mechanical instability and a phonon softening.
Emergence of magnetic anisotropy by surface adsorption of transition metal dimers on γ-graphyne framework
Authors: Jana Susmita , Chowdhury Suman , Jana Debnarayan , Chakrabarti Aparna , Banerjee Arup 
Published: February 2021

Abstract
In this paper a systematic study is carried out to demonstrate the structural stability and magnetic novelty of adsorbing transition metal (TM) dimers (A-B) on graphyne (GY) surface, GY@A-B. Our research points out that the dimers are strongly adsorbed onto GY due to their large natural pores and the electron affinity of the sp-hybridized carbon atoms. Electronic properties of these dimer-graphyne composite systems are of particular importance as they behave as degenerate semiconductors with partial occupation of states at E
F. Furthermore, their remarkable spin polarization (>80%) at Fermi energy (E
F) can be of paramount importance in spintronics applications. Most of the GY@A-B structures exhibit large magnetic anisotropies as well as magnetic moments along the out-of-plane direction with respect to the GY surface. Particularly, GY@Co–Ir, GY@Ir–Ir and GY@Ir–Os structures possess positive magnetic anisotropic energies (MAE) of 121 meV, 81 meV and 137 meV, respectively, which are comparable to other well-known TM dimer doped systems. The emergence of high MAE can be understood using the second-order perturbation theory on the basis of the strong spin–orbit coupling (SOC) between the two TMs and the degeneracy of their d-orbitals near E
F. A close correspondence between the simulated and the analytical results has been established through our work. Further, a simple estimation shows that, GY@A-B structures have the potential to store data up to 64 PB m−2. These intriguing electronic characteristics along with magnetism suggest GY@A-B to be a promising material for future magnetic storage devices.
Foundations of measurement of electrons, ions and species fluxes toward surfaces in low-temperature plasmas
Authors: Benedikt Jan , Kersten Holger , Piel Alexander 
Published: February 2021

Abstract
This foundation article discusses the diagnostics of electrons and ions in plasmas and fluxes of charged and neutral species toward plasma-facing surfaces by non-optical methods. The focus is laid on the fundamentals of the most common methods and their application to non-equilibrium low-pressure electropositive plasmas and ion beams. The key topics are Langmuir probes (LPs), Faraday cups (FCs) and energy analyzers, mass spectrometry, as well as novel calorimetric and force probes (FPs). For each method, the concepts are introduced, hints at best practice are given, and a survey of the recently published literature is included. Starting with the sheath–plasma boundary, the principles of plane and cylindrical LPs and the measurement of electron temperature and density are discussed. Beyond standard textbooks, double, triple and emissive probes are described and modulation techniques for obtaining the electron energy distribution function are presented. More technical issues related to probe compensation in radio-frequency plasmas, probe contamination, and the influence of a magnetic field are also included. The presentation is completed by modern radio-frequency techniques, such as impedance probes, multipole resonance probes, and self-excited electron resonance spectroscopy. FCs, retarding field analyzers (RFAs) as well as novel calorimetric and FPs are useful tools for the measurement of overall, not species resolved, ions and neutral species fluxes toward surfaces. RFAs provide overall ion energy distribution functions, whereas calorimetric and FPs can deliver information about fluxes of fast neutrals. The issues related to secondary electron emission, absolute signal calibration, and analysis of plasmas with complex chemistry are discussed. Mass spectrometry diagnostics is capable of mass and energy-resolved detection of ions and neutral species at the plasma-facing surfaces. Detection, identification and absolute density calibration of neutral stable and radical species are treated in detail and peculiarities of ion mass spectrometry, such as detection of negative ions, ion measurements in front of powered electrodes, or chromatic aberration and acceptance angle limitations in energy spectrum measurements are introduced.
Remote streamer initiation on dielectric surface
Authors: Kusýn L , Synek P , Becker M M , Hoder T 
Published: February 2021

Abstract
We study the origin of filamentary patterns in a sinusoidally driven surface barrier discharge at high over-voltage in atmospheric pressure air. Using a time-correlated single-photon counting based optical emission spectroscopy, we reveal ultrafast processes within generated discharges in both polarities of the applied voltage. For negative polarity, we observe initiation of complex streamer cascade which emerges far from the bare cathode. This event is responsible for long filamentary structure detected by an intensified CCD camera and transfers an exceptionally large electrical charge. It constitutes another, previously unknown, mechanism contributing to the charge-transfer equilibrium in studied periodical discharge. The revealed process leads to the formation of an intense cathode spot, a critical condition for plasma-transition into a highly ionised state.
Formulation of UV curable nano-silver conductive ink for direct screen-printing on common fabric substrates for wearable electronic applications
Authors: Hong Hong , Jiang Lihong , Tu Huating , Hu Jiyong , Yan Xiong 
Published: February 2021

Abstract
One-step printing of electrically conductive inks on textiles is one of the simplest and most prospective methods to manufacture functional wearable electronics. However, the high surface roughness and porous structure as well as poor temperature endurance of most textiles have become the major challenges for the realization of printed electronic textiles (E-textiles). To solve these issues, the UV curable conductive ink with fast curing and low temperature characteristics was formulated to fabricate the flexible fabric-based conductive patterns using screen printing method. The specific focus was spent on investigating the effect of ink composition on curing speed, film forming ability, morphological characteristics and electrical properties of conductive patterns directly printed on fabric substrates. Firstly, we determined the necessity of defoamer for the formation of uniform and continuous printed textile-based patterns, and optimized the film forming ability of UV-curing ink by exploring the defoamer performance. Then, the ink curing speed was found heavily depending on the different types and contents of photoinitiators. Finally, the nano-silver loading showed critical influence to the screen-printability and the electrical properties of printed patterns. An ink formulation with 60 wt% nano-silver, 4 wt% photoinitiator (1173), and 0.2 wt% defoamer (BYK-555) showed satisfactory screen printability, and the conductive patterns with 1.0 mm width exhibited a remarkably low resistivity of 4.04 × 10−5 Ω cm. Moreover, the high performance of the conductive pattern screen-printed on four different fabrics by the formulated UV curable conductive ink further demonstrated its application potential. The results showed that uniformity and electrical properties of printed patterns were directly
related to the weaving method, texture characteristic, and roughness of the
textiles. We believe these results will provide basic guidance for the formulation design of conductive ink and facilitate the utility of textiles-based wearable electronics.
Electromagnetic properties of curved HTS trapped field stacks under high-frequency cross fields for high-speed rotating machines
Authors: Zhang Hongye , Mueller Markus 
Published: February 2021

Abstract
Superconducting electric propulsion systems, characterized by high power densities and efficiencies, provide a possibility to zero carbon emission for future aviation. Stacks of high temperature superconducting (HTS) coated conductors (CCs) have become an alternative for high field magnets applied to superconducting machines, given their excellent field trapping ability and thermal stability. High-frequency ripple fields always exist in high-speed electric machines. Most research work regarding HTS trapped field stacks (TFSs) was focused on their magnetization methods and amplitude of trapped flux density; however, their performance in the high-frequency environment remains unclear. Despite several numerical models established for flat HTS TFSs, a comprehensive analysis of curved ones is still lacking, which possess geometrical applicability for cylindrical rotating shafts. Aimed at exploring the electromagnetic properties of curved HTS TFSs applied to high-speed rotating machines, a 3D numerical model considering both the multilayer structure and the Jc
(B) dependence of HTS CCs has been built. Current and magnetic flux density distributions, as well as loss properties of a curved HTS TFS have been studied in detail, under perpendicular and cross fields with varying frequencies ranging from 50 Hz to 20 kHz. Results have shown that, the widely adopted two-dimensional-axisymmetric models are inapplicable to study the electromagnetic distributions of TFSs because of the emergence of the electromagnetic criss-cross defined in this paper. High-frequency ripple fields can drive induced current towards the periphery of the HTS TFS due to the skin effect, leading to a fast rise of AC loss and even an irreversible demagnetization of the stack. This paper has qualified and quantified the high-frequency electromagnetic behaviours of curved HTS TFSs, providing a useful reference for their loss controlling and anti-demagnetization design in high-speed propulsion machines.
Superconducting properties of the non-centrosymmetric superconductors TaXSi (X = Re, Ru)
Authors: P Sajilesh K , Singh R P 
Published: February 2021

Abstract
Ternary noncentrosymmetric superconductors TaXSi (X = Re, Ru) investigated by magnetization, resistivity, and specific heat measurements. It crystallize in the orthorhombic TiFeSi-type structure with superconducting transition

T

c

= 5.32 K and 3.91 K for TaReSi and TaRuSi, respectively. A low value of specific heat jump and the upper critical field concave nature suggests a nontrivial superconducting gap.
Zero-energy modes of two-component Bose–Bose droplets
Authors: Zin Paweł , Pylak Maciej , Gajda Mariusz 
Published: February 2021

Abstract
Bose–Bose droplets are self-bound objects emerging from a mixture of two interacting Bose–Einstein condensates when their interactions are appropriately tuned. During droplet formation three continuous symmetries of the system’s Hamiltonian are broken: translational symmetry and two U(1) symmetries, allowing for arbitrary choice of phases of the mean-field wavefunctions describing the two components. Breaking of these symmetries must be accompanied by appearance of zero-energy excitations in the energy spectrum of the system recovering the broken symmetries. Normal modes corresponding to these excitations are the zero-energy modes. Here we find analytic expressions for these modes and introduce Hamiltonians generating their time evolution—dynamics of the droplet’s centers of mass as well as dynamics of the phases of the two droplet’s wavefunctions. When internal types of excitations (quasiparticles) are neglected then the very complex system of a quantum droplet is described using only a few ‘global’ degrees of freedom—the position of the center of mass of the droplet and two phases of two wave-functions, all these being quantum operators. We believe that our work might be useful in describing in a relatively easy way the low energy collisions of quantum droplets in situations where coherent flow of atoms between the droplets takes place.