bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lorentzian spectral geometry with causal sets
Authors: Yazdi Yasaman K , Letizia Marco , Kempf Achim 
Published: October 2020

Abstract
We study discrete Lorentzian spectral geometry by investigating to what extent causal sets can be identified through a set of geometric invariants such as spectra. We build on previous work where it was shown that the spectra of certain operators derived from the causal matrix possess considerable but not complete power to distinguish causal sets. We find two especially successful methods for classifying causal sets and we computationally test them for all causal sets of up to 9 elements. One of the spectral geometric methods that we study involves holding a given causal set fixed and collecting a growing set of its geometric invariants such as spectra (including the spectra of the commutator of certain operators). The second method involves obtaining a limited set of geometric invariants for a given causal set while also collecting these geometric invariants for small ‘perturbations’ of the causal set, a novel method that may also be useful in other areas of spectral geometry. We show that with a suitably chosen set of geometric invariants, this new method fully resolves the causal sets we considered. Concretely, we consider for this purpose perturbations of the original causal set that are formed by adding one element and a link. We discuss potential applications to the path integral in quantum gravity.
Instructor’s dilemma: requiring two-dimensional measurements to describe one-dimensional motion, applied to a person walking
Authors: Diener J P W , Kriek J 
Published: October 2020

Abstract
Introductory physics courses uses simplified models and approximations to convey fundamental concepts. Many of these simplifications are introduced without explanation. When considering motion, one such simplification is the point particle approximation. That is to assume that the motion of an extended object can be represented by the motion of a single point, generally the object’s centre of mass. For some objects the exact position of the centre of mass could be difficult to locate and the procedure beyond the scope of an introductory course. Furthermore, if the object changes its shape while in motion, thereby redistributing its mass, the relative position of the centre of mass also changes. In such instances the physical measurements of the object’s position could be rather complicated, especially if the task is to choose one physical marker on the object that best represents its motion. If the object is travelling in a straight line [one-dimensional (1D) motion] and the motion of physical marker does not closely match that of the object, a two-dimensional measurement would be required to describe 1D motion. Hereby instructors might be challenged to explain seemingly simple phenomena, like determining the position of an object, within the confines of the introductory course. In order to assist instructors in this regard, we present an experimental measurement procedure which aims to minimize the error in position measurements of objects that changes their shape while in motion. We apply the procedure to determine the position of a walking person.
Shock waves in pulsed electrical discharges in liquids: numerical simulation and comparison to experiment
Authors: Jimenez Francisco J , Radfar Marjan , Kirk Braedan , Sydora Richard D , Hunter Trent S 
Published: October 2020

Abstract
In this paper a computational model for the post-breakdown phase of an electrical discharge in liquids is presented and validated through comparison with data from a high voltage pulsed power discharge in a water-filled crucible. The numerical framework consists of an arc plasma channel modeled by equivalent resistor-inductor-capacitor circuit equations coupled to a computational fluid dynamics (CFD) model (based on OpenFOAM) that solves the compressible fluid equations for describing the shock waves associated with the rapid development of the plasma channel. The circuit model equations evolve the initial discharge plasma expansion which are then used to initialize the pressure pulse in the CFD model. Both single-phase (liquid) and two-phase (gas–liquid) CFD solvers were implemented and compared. The dynamics and magnitude of the simulated pressure pulse perturbations at the boundaries of the crucible were validated with the pressure sensor measurements made in an experiment of a pulsed electrical discharge in liquid water.
One-dimensional nanomaterials in lithium-ion batteries
Authors: Jaramillo-Cabanzo D F , Ajayi B P , Meduri P , Sunkara M K 
Published: October 2020

Abstract
A lot of progress has been made in rechargeable lithium-ion battery (LIB) technology research in the last decade, even so, renewed developmental efforts must be pursued to better improve energy density, capacity retention and rate capability. This review discusses the role that one-dimensional (1D) nanomaterials can play towards development of next-generation LIBs. Electrode nanoengineering, interfacial kinetics and high-volume manufacturing are critical issues limiting energy density, electrochemical performance and material viability. These points are discussed, as are the advantages of deploying these nanomaterials in rechargeable LIB devices. Current data from literature is indicative of laboratory-scale success as these 1D nanomaterials display excellent capacity retention, high-rate capability and long cycle life emanating from high mechanical strength, resilience and short charge carrier diffusion distance. However, significant advances are required to translate these achievements into commercial scale deployment.
A high numerical aperture terahertz all-silicon metalens with sub-diffraction focus and long depth of focus
Authors: Wang Zewen , Li Qi , Yan Fei 
Published: October 2020

Abstract
A high numerical aperture (NA = 0.92) square all-silicon metalens is designed for a wavelength of λ= 0.11883 mm with a focal length of 16.8λ and a side length of 104.4λ. Based on the waveguide effect, anisotropic rectangular silicon pillars with different dimensions are arranged on the silicon substrate according to the conical phase distribution, and then the rotation angle of each rectangular pillar is adjusted to realize the polarization conversion. Furthermore, a polarization-independent square antireflection silicon pillar array is proposed to be patterned at the other side of the substrate. The metalens can efficiently convert the normally incident x- (or y-) polarized plane wave into the radially (or azimuthally) polarized beam and conduct the sub-diffraction tight-focusing simultaneously, thus the shape of the focus can be flexibly switched. The numerical simulation results show that, under high-NA conditions, our metalens can obtain a tighter focus compared with linearly polarized metalens and a longer depth of focus (DOF) compared with metalens based on the hyperboloidal phase distribution. Under x- (or y-) polarized plane wave incidence, a circular-spot-shaped (or doughnut-shaped) focus with a full width at half maximum of 0.4λ (or 0.3λ) is obtained and the DOF is 26.509λ (or 18.935λ). In addition, under x-polarized beam incidence, the influence of the incident beam intensity distribution on the focusing results is also discussed. The use of a single material makes our metalens more favorable in fabrication and it is expected that our study is of great significance for applying terahertz wave in imaging and communication systems, high-resolution microscopy, optical coherence tomography and manipulation of particles.
Pseudo-spin rotation symmetry breaking by Coulomb interaction terms in spin–orbit coupled systems
Authors: Mohapatra Shubhajyoti , Singh Avinash 
Published: October 2020

Abstract
By transforming from the pure-spin-orbital (t
2g) basis to the spin-orbital entangled pseudo-spin-orbital basis, the pseudo-spin rotation symmetry of the different Coulomb interaction terms is investigated under SU(2) transformation in pseudo-spin space. While the Hubbard and density interaction terms are invariant, the Hund’s coupling and pair-hopping interaction terms explicitly break pseudo-spin rotation symmetry systematically. The form of the symmetry-breaking terms obtained from the transformation of the Coulomb interaction terms accounts for the easy x–y plane anisotropy and magnon gap for the out-of-plane mode, highlighting the importance of mixing with the nominally non-magnetic J = 3/2 sector, and providing a physically transparent approach for investigating magnetic ordering and anisotropy effects in perovskite (Sr2IrO4) and other d
5 pseudo-spin compounds.
Magnetic properties of γ-Fe2O3 nanoparticles in a porous SiO2 shell for drug delivery
Authors: Kamali S , Yu E , Bates B , McBride J R , Johnson C E , Taufour V , Stroeve P 
Published: October 2020

Abstract
A method is presented for synthesizing core–shell nanoparticles with a magnetic core and a porous shell suitable for drug delivery and other medical applications. The core contains multiple γ-Fe2O3 nanoparticles (∼15 nm) enclosed in a SiO2 (∼100–200 nm) matrix using either methyl (denoted TMOS-γ-Fe2O3) or ethyl (TEOS-γ-Fe2O3) template groups. Low-temperature Mössbauer spectroscopy showed that the magnetic nanoparticles have the maghemite structure, γ-Fe2O3, with all the vacancies in the octahedral sites. Saturation magnetization measurements revealed that the density of γ-Fe2O3 was greater in the TMOS-γ-Fe2O3 nanoparticles than TEOS-γ-Fe2O3 nanoparticles, presumably because of the smaller methyl group. Magnetization measurements showed that the blocking temperature is around room temperature for the TMOS-γ-Fe2O3 and around 250 K for the TEOS-γ-Fe2O3. Three dimensional topography analysis shows clearly that the magnetic nanoparticles are not only at the surface but have penetrated deep in the silica to form the core–shell structure.
Electronic, phononic and superconducting properties of trigonal Li2
MSi2 (M
= Ir, Rh)
Authors: Tayran C , Çakmak M 
Published: October 2020

Abstract
We have used ab initio density functional theory to study electronic, mechanical, phononic, and superconducting properties of Li2
MSi2 (M = Ir, Rh), which has recently been produced as a new type of transition metal–based ternary compound in the trigonal structure (Horigane et al 2019 New J. Phys.
21 093056). The calculated electronic band structure and the density of states indicate that the Li2IrSi2 and Li2RhSi2 compounds are in metallic character. Mechanical properties such as elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and Debye temperature were calculated for these compounds. The calculated results suggest that the compounds are mechanically stable and behave in a ductile manner. The phonon spectra have no imaginary frequency, which proves that these compounds are dynamically stable. Electron–phonon coupling parameters confirm that they are weak–coupling superconductors. Although the influence of spin–orbit coupling in superconductivity is not significant for these compounds, it has a very small influence on electronic structure for Li2IrSi2. The calculated critical temperature (

T

c

μ

⋆

=
0.11

) values of 3.29 K for Li2IrSi2 and 2.82 K for Li2RhSi2 agree well with experimental estimates.
Anion ordering transition and Fermi surface electron–hole instabilities in the (TMTSF)2ClO4 and (TMTSF)2NO3 Bechgaard salts analyzed through the first-principles Lindhard response function
Authors: Guster Bogdan , Pruneda Miguel , Ordejón Pablo , Canadell Enric , Pouget Jean-Paul 
Published: October 2020

Abstract
The first-principles electron–hole Lindhard response function has been calculated and analyzed in detail for two (TMTSF)2
X (X = ClO4 and NO3) Bechgaard salts undergoing different anion-ordering (AO) transitions. The calculation was carried out using the real triclinic low-temperature structures. The evolution of the electron–hole response with temperature for both relaxed and quenched salts is discussed. It is shown that the 2k
F response of the quenched samples of both salts display a low temperature curved and tilted triangular continuum of maxima. This is not the case for the relaxed samples. (TMTSF)2ClO4 in the AO state exhibits a more quasi-1D response than in the non AO state and relaxed (TMTSF)2NO3 shows a sharp maximum. The curved triangular plateau of the quenched samples results from multiple nesting of the warped quasi-1D Fermi surface which implies the existence of a large q range of electron–hole fluctuations. This broad maxima region is around 1% of the Brillouin zone area for the X = ClO4 salt (and X = PF6) but only 0.1% for the X = NO3 salt. It is suggested that the strong reduction of associated SDW fluctuations could explain the non detection of the SDW-mediated superconductivity in (TMTSF)2NO3. The calculated maxima of the Lindhard response nicely account for the modulation wave vector experimentally determined by NMR in the SDW ground state of the two salts. The critical AO wave vector for both salts is located in regions where the Lindhard response is a minimum so that they are unrelated to any electron–hole instability. The present first-principles calculation reveals 3D effects in the Lindhard response of the two salts at low temperature which are considerably more difficult to model in analytical approaches.
Quantitative identification of independent and dependent sources based on bounded component analysis
Authors: Gong Teng , Zhang Zhousuo , Luo Xin , Li Yongjie 
Published: October 2020

Abstract
The quantitative identification of vibration sources can provide the basis and guidance for the vibration and noise reduction of mechanical systems. Since the vibration sources in a mechanical system are not necessarily mutually independent, this paper proposes a quantitative identification method suitable for both independent and dependent sources based on bounded component analysis (BCA). Firstly, the new BCA algorithm is adopted to separate source signals and normalized boundary minimization is used as the objective function, which is optimized by a modified subgradient method with the introduction of the probability mass function and an adaptive step size, and thus the noise resistance and convergence performance are enhanced. Secondly, the source contribution is extracted by taking the separated signal as the input and boundary minimization of the residual signal as the criterion. Thirdly, the projection of the source contribution in the mixed signal is calculated by the inner product and the proportion of the calculated projection on the mixed signal is taken as the contribution index to evaluate the influence of the vibration source on the vibration of the observation point of the system. Finally, the effectiveness and superiority of the proposed method are tested by simulation analysis and experimental verification. The results show that the proposed method has high accuracy in the quantitative identification of both independent and dependent sources.
Assembling your nanowire: an overview of composition tuning in ternary III–V nanowires
Authors: Ghasemi Masoomeh , Leshchenko Egor D , Johansson Jonas 
Published: October 2020

Abstract
The ability to grow defect-free nanowires in lattice-mismatched material systems and to design their properties has made them ideal candidates for applications in fields as diverse as nanophotonics, nanoelectronics and medicine. After studying nanostructures consisting of elemental and binary compound semiconductors, scientists turned their attention to more complex systems—ternary nanowires. Composition control is key in these nanostructures since it enables bandgap engineering. The use of different combinations of compounds and different growth methods has resulted in numerous investigations. The aim of this review is to present a survey of the material systems studied to date, and to give a brief overview of the issues tackled and the progress achieved in nanowire composition tuning. We focus on ternary III
x
III1−x
V nanowires (AlGaAs, AlGaP, AlInP, InGaAs, GaInP and InGaSb) and IIIV
x
V1−x
nanowires (InAsP, InAsSb, InPSb, GaAsP, GaAsSb and GaSbP).
Facile one-step hydrothermal synthesis of single-crystalline SnNb2O6 nanosheets with greatly extended visible-light response for enhanced photocatalytic performance and mechanism insight
Authors: Liu Qianqian , Zhang Quan , Liu Bo , Dai Wei-Lin 
Published: October 2020

Abstract
The conventional preparation of SnNb2O6 invariably involves complex and laborious steps, which unavoidably introduces defect into the host lattice and also increases the reaction period and costs, resulting in undesired recombination of photo-generated electron–hole pairs. For the first time in this work, we manage to synthesize single-crystalline two-dimensional (2D) SnNb2O6 nanosheets with ultrathin structure through a facile one-step hydrothermal method. Comparative studies were explored to analyze the structure and phase evolution during the preparation course. The synthesized 2D structure demonstrated a narrower band gap of 2.09 eV and specific surface area of 76.1 m2 g−1, which exhibited significantly extended visible-light-responsive range and larger surface area by contrast with the state-of-the-art reports, resulting in excellent visible-light-driven photoactivity towards H2 production and water purification as well. Additionally, further enhanced photocatalytic performance was achieved by the incorporation of Pt as co-catalyst to indirectly indicate the advantage of the SnNb2O6 nanosheets in this method over other reported counterparts. It was found that, a very small amount of Pt loaded on the surface of SnNb2O6 nanosheets would contribute to remarkably higher activity than pure SnNb2O6 nanosheets and exhibit superior stability as well. Moreover, a deep insight into the underlying photocatalytic mechanism was proposed. This work sheds light on a new facile way to fabricate high-performance photocatalytic materials and provided new opportunities for solar-energy conversion.
All-dielectric multifunctional transmittance-tunable metasurfaces based on guided-mode resonance and ENZ effect
Authors: Qiu Xiaoming , Shi Jian , Li Yanping , Zhang Fan 
Published: October 2020

Abstract
Electrically tunable metasurfaces open new doors for manipulating the phase, amplitude and polarization of light in ultrathin layers. Compared with metal assisted metasurfaces, all-dielectric transmission metasurfaces—with outstanding feature of low loss, especially incorporating with new electro-optical materials—show great potential for the next generation flat optics. In this study, by combining the epsilon-near-zero effect in indium tin oxide (ITO) with guided-mode resonance, we propose novel electrically tunable all-dielectric metasurface architectures with versatile functions for widespread potential application. The inserted periodic ITO and hafnium oxide layers sandwiched in silicon act as two metal-oxide-semiconductor capacitors in a single period to disturb the resonance wavelength in the near-infrared spectral range under the voltage applied. For the one-dimensional structure, the transmittances of this metasurface at 1512 and 1510 nm change 20 and −14 dB under 0∼5 V bias voltage, respectively. In addition, the bilayer structure performs well in double-waveband applications, indicating that more layers can support more operation wavebands. Meanwhile, the two-dimensional structure works as a polarization insensitive device when setting the same structural parameters in both orthogonal directions. The proposed architecture, with various merits including ultra-compact size, high-speed and complementary metal-oxide-semiconductor compatibility, provides a multifunctional and multi-degree-of-freedom design, as well as enormous potential applications in more complicated flat optics.
Existence of stationary stochastic Burgers evolutions on R
2 and R
3

*
Authors: Dunlap Alexander 
Published: October 2020

Abstract
We prove that the stochastic Burgers equation on R

d
, d < 4, forced by gradient noise that is white in time and smooth in space, admits spacetime-stationary solutions. These solutions are thus the gradients of solutions to the KPZ equation on R

d
with stationary gradients. The proof works by proving tightness of the time-averaged laws of the solutions in an appropriate weighted space.
The mean-field equation of a leaky integrate-and-fire neural network: measure solutions and steady states
Authors: Dumont Grégory , Gabriel Pierre 
Published: October 2020

Abstract
Neural network dynamics emerge from the interaction of spiking cells. One way to formulate the problem is through a theoretical framework inspired by ideas coming from statistical physics, the so-called mean-field theory. In this document, we investigate different issues related to the mean-field description of an excitatory network made up of leaky integrate-and-fire neurons. The description is written in the form a nonlinear partial differential equation which is known to blow up in finite time when the network is strongly connected. We prove that in a moderate coupling regime the equation is globally well-posed in the space of measures, and that there exist stationary solutions. In the case of weak connectivity we also demonstrate the uniqueness of the steady state and its global exponential stability. The method to show those mathematical results relies on a contraction argument of Doeblin’s type in the linear case, which corresponds to a population of non-interacting units.
Semiclassical states for Choquard type equations with critical growth: critical frequency case
*
Authors: Ding Yanheng , Gao Fashun , Yang Minbo 
Published: October 2020

Abstract
In this paper we are interested in the existence of semiclassical states for the Choquard type equation

−

ε

2

Δ
u
+
V

(

x

)

u
=

∫

R

N

G

(

u

(

y

)

)

|
x
−
y
|

μ

d
y

g

(

u

)

in

R

N

,

where 0 < μ < N, N ⩾ 3, ɛ is a positive parameter and G is the primitive of g which is of critical growth due to the Hardy–Littlewood–Sobolev inequality. The potential function V(x) is assumed to be nonnegative with V(x) = 0 in some region of

R

N

, which means it is of the critical frequency case. Firstly, we study a Choquard equation with double critical exponents and prove the existence and multiplicity of semiclassical states by the mountain-pass lemma and the genus theory. Secondly, we consider a class of critical Choquard equation without lower perturbation, by establishing a global compactness lemma for the nonlocal Choquard equation, we prove the multiplicity of high energy semiclassical states by the Lusternik–Schnirelman theory.