bluuebunny/crossref_metadata_2025 huggingface dataset:
The complex time and energy evolution of quasi-periodic eruptions in eRO-QPE1
Authors: Arcodia R. , Miniutti G. , Ponti G. , Buchner J. , Giustini M. , Merloni A. , Nandra K. , Vincentelli F. , Kara E. , Salvato M. , Pasham D.
Published: April 2022

Quasi-periodic eruptions (QPEs) are recurrent X-ray bursts found in the nuclei of low-mass galaxies. Their trigger mechanism is still unknown, but recent models involving one or two stellar-mass companions around the central massive (≈105 − 106 M⊙) black hole have gathered significant attention. While these models have been compared only qualitatively with observations, the phenomenology of QPEs is developing at a fast pace, and has the potential to reveal new insights. Here we report two new observational results found in eRO-QPE1, the brightest QPE source discovered so far. First, the eruptions in eRO-QPE1 sometimes occur as single isolated bursts, and at others as chaotic mixtures of multiple overlapping bursts with very different amplitudes. Second, we confirm that QPEs peak at later times and are broader at lower energies than at higher energies, while we find for the first time that QPEs also start earlier at lower energies. Furthermore, eruptions appear to undergo a counterclockwise hysteresis cycle in a plane of hardness ratio versus total count rate. The first behavior has not been found in any other QPE source, and implies that if a common trigger mechanism is in place for all QPEs, it must be able to produce both types of timing properties, regular and complex. The second result implies that the X-ray emitting component does not have an achromatic evolution even during the start of QPEs, and that the rise is harder than the decay at a given total count rate. This specific energy dependence could be qualitatively compatible with inward radial propagation during the rise within a compact accretion flow, the presence of which is suggested by the stable quiescence spectrum observed in general for QPE sources.
Optimality conditions, approximate stationarity, and applications – a story beyond lipschitzness
Authors: Kruger Alexander Y. , Mehlitz Patrick
Published: April 2022

Approximate necessary optimality conditions in terms of Frechet subgradients and normals for a rather general optimization problem with a potentially non-Lipschitzian objective function are established with the aid of Ekeland’s variational principle, the fuzzy Frechet subdifferential sum rule, and a novel notion of lower semicontinuity relative to a set-valued mapping or set. Feasible points satisfying these optimality conditions are referred to as approximately stationary. As applications, we derive a new general version of the extremal principle. Furthermore, we study approximate stationarity conditions for an optimization problem with a composite objective function and geometric constraints, a qualification condition guaranteeing that approximately stationary points of such a problem are M-stationary, and a multiplier-penalty-method which naturally computes approximately stationary points of the underlying problem. Finally, necessary optimality conditions for an optimal control problem with a non-Lipschitzian sparsity-promoting term in the objective function are established.
A LWR model with constraints at moving interfaces
Authors: Sylla Abraham
Published: April 2022

We propose a mathematical framework to the study of scalar conservation laws with moving interfaces. This framework is developed on a LWR model with constraint on the flux along these moving interfaces. Existence is proved by means of a finite volume scheme. The originality lies in the local modification of the mesh and in the treatment of the crossing points of the trajectories.
Vacuum ultraviolet photodissociation dynamics of OCS via the F Rydberg state: The S(3PJ = 2, 1, 0) product channels
Authors: Tang Ling , Chen Wentao , Yuan Daofu , Yu Shengrui , Yang Xueming , Wang Xingan
Published: April 2022

Vacuum ultraviolet (VUV) photodissociation dynamics of carbonyl sulfide was investigated experimentally by using a tunable photolysis light source and the time-sliced velocity map ion imaging technique. Ion images of S(3PJ =2, 1, 0) dissociation products were measured at five photolysis wavelengths from 133.26 nm to 139.96 nm, corresponding to the F Rydberg state of OCS. Two dissociation channels: S(3PJ)+CO(X1Σ+) and S(3PJ)+CO(A3Π) were observed with the former being dominant. The vibrational states of CO co-products were partially resolved in the ion images. The product total kinetic energy releases, anisotropy parameters (β), and the branching ratios of high-lying CO vibrational states were determined for the S(3PJ )+CO(X1Σ+) channel. We found that the anisotropy parameters suddenly changed from negative to positive when OCS was excited to the higher vibrational levels of the F state. Furthermore, the anisotropy parameters for S(3PJ) products of J = 2, 1, 0 were even different. These anomalous phenomena may result from the simultaneous existence of both parallel and perpendicular dissociation mechanisms, suggesting the involvement of other electronic states with different symmetry in the initially-excited energy region. This work provides a further understanding of the nonadiabatic couplings in the VUV photodissociation process of OCS.
Excess-electron attachment and ionization of aqueous uridine monophosphate anion
Authors: Zhang Yan , Chen Xuan-ning , Yin Shu-hui , Yang Song-qiu
Published: April 2022

We applied quantum mechanics/classical mechanics simulations to study excess-electron attachment and ionization of uridine monophosphate anion (dUMP−) in explicit aqueous solutions. We calculated vertical electron affinities (VEAs), adiabatic electron affinities (AEAs), vertical detachment energies (VDEs), vertical ionization energies (VIEs), and adiabatic ionization energies (AIEs) of the 40 structures obtained from molecular dynamic trajectory. The excess-electron and hole distributions were analyzed in electron attachment and ionization of aqueous dUMP−. The converged mean VEA (−0.31 eV) and AEA (2.13 eV) suggest that excess-electron can easily attach to dUMP−. The mean vertical (−0.50 e) and adiabatic (−0.62 e) excess-electron on uracil reveal that main excess-electrons are localized on nucleobases at the most snapshots. The distributions at several special snapshots demonstrate the excess-electron delocalization over nucleobases/ribose or ribose/phosphate group after the structural relaxations of dUMP2− dianion. The VDE value (2.78 eV) indicates that dUMP2− dianion could be very stable. Moreover, the mean VIE is 8.13 eV which is in agreement with the previous calculation using solvation model. The hole distributions on uracil suggest that the nucleobases are easily ionized after the irradiation of high-energy rays. In vertical ionizations, the holes would be delocalized over uracil and ribose at several snapshots. Observing the adiabatic hole distributions, it can be found that electrons on phosphate group and holes on nucleobases can be transferred to ribose at the special snapshots in the structural relaxation of neutral species.
A rapidly convergent method for solving third-order polynomials
Authors: Fernández Molina Ramón A. , Sigalotti Leonardo Di G. , Rendón Otto , Mejias Antonio J.
Published: April 2022

We present a rapidly convergent method for solving cubic polynomial equations with real coefficients. The method is based on a power series expansion of a simplified form of Cardano’s formula using Newton’s generalized binomial theorem. Unlike Cardano’s formula and semi-analytical iterative root finders, the method is free from round-off error amplification when the polynomial coefficients differ by several orders of magnitude or when they do not differ much from each other, but are all large or small by many orders of magnitude. Validation of the method is assessed by casting a cubic equation of state as a polynomial in terms of the compressibility factor and the reduced molar volume for propylene at temperature and pressure conditions where Cardano’s formula and iterative root finders fail.
A new concept of acousto-optic tunable filter-based near-infrared hyperspectral imager for planetary surface exploration
Authors: Royer Clément , Pilorget C. , Hamm V. , Bibring J.-P. , Poulet F.
Published: April 2022

In the past two decades, near-infrared (NIR) hyperspectral imaging instruments have revolutionized our conception of planetary surfaces in terms of evolution, geology, mineralogy, and alteration processes. The cornerstone of this remote analysis technique is the synergy between imagery, giving the geomorphological context of the observations, and NIR spectroscopy whose spectral range is sensitive to the main absorption features of most of the minerals present on planetary surfaces. The development of a generation of space instrument based on Acousto-Optic Tunable Filters (AOTFs) increases the capacity of these spectrometers to be set up in a variety of space probes. The ExoCam concept, developed at Institut d’Astrophysique Spatiale and profiting from the lab’s previous experience (MicrOmega onboard Phobos-Grunt, Hayabusa 2 and ExoMars), thus, proposes for the first time to do hyperspectral imagery through a wide aperture AOTF (15 × 15 mm2) in the 0.95–3.6 µm spectral range. The characterization of this instrumental concept, led on a representative breadboard built for this purpose, showed that the acousto-optic diffraction preserves the image quality up to the diffraction/resolution limit over the whole field of view. The spectral resolution (from 2 to 25 nm over the spectral range) and accuracy of the instrument are also consistent with the identification of planetary surface minerals. This paper describes the ExoCam concept and objectives, the setup of an optical breadboard representative of a space instrument based on this concept, and the results of performance characterizations realized on the breadboard.
On the mean density of states of some matrices related to the beta ensembles and an application to the Toda lattice
Authors: Mazzuca G.
Published: April 2022

In this paper, we study tridiagonal random matrix models related to the classical β-ensembles (Gaussian, Laguerre, and Jacobi) in the high-temperature regime, i.e., when the size N of the matrix tends to infinity with the constraint that βN = 2α constant, α > 0. We call these ensembles the Gaussian, Laguerre, and Jacobi α-ensembles, and we prove the convergence of their empirical spectral distributions to their mean densities of states, and we compute them explicitly. As an application, we explicitly compute the mean density of states of the Lax matrix of the Toda lattice with periodic boundary conditions with respect to the Gibbs ensemble.
Quantum information processing with integrated silicon carbide photonics
Authors: Majety Sridhar , Saha Pranta , Norman Victoria A. , Radulaski Marina
Published: April 2022

Color centers in wide bandgap semiconductors are prominent candidates for solid-state quantum technologies due to their attractive properties including optical interfacing, long coherence times, and spin–photon and spin–spin entanglement, as well as the potential for scalability. Silicon carbide color centers integrated into photonic devices span a wide range of applications in quantum information processing in a material platform with quantum-grade wafer availability and advanced processing capabilities. Recent progress in emitter generation and characterization, nanofabrication, device design, and quantum optical studies has amplified the scientific interest in this platform. We provide a conceptual and quantitative analysis of the role of silicon carbide integrated photonics in three key application areas: quantum networking, simulation, and computing.
Approximate bounds and temperature dependence of adiabatic connection integrands for the uniform electron gas
Authors: Harding Brittany P. , Mauri Zachary , Pribram-Jones Aurora
Published: April 2022

Thermal density functional theory is commonly used in simulations of warm dense matter, a highly energetic phase characterized by substantial thermal effects and by correlated electrons demanding quantum mechanical treatment. Methods that account for temperature dependence, such as Mermin–Kohn–Sham finite-temperature density functional theory and free energy density functional theory, are now employed with more regularity and available in many standard code packages. However, approximations from zero-temperature density functional theory are still often used in temperature-dependent simulations using thermally weighted electronic densities as an input to exchange–correlation functional approximations, a practice known to miss temperature-dependent effects in the exchange–correlation free energy of these systems. In this work, the temperature-dependent adiabatic connection is demonstrated and analyzed using a well-known parameterization of the uniform electron gas free energy. Useful tools based on this formalism for analyzing and constraining approximations of the exchange–correlation at zero temperature are leveraged for the finite-temperature case. Inspired by the Lieb–Oxford inequality, which provides a lower bound for the ground-state exchange–correlation energy, bounds for the exchange–correlation at finite temperatures are approximated for various degrees of electronic correlation.
Assessing physics of ion temperature gradient turbulence via hierarchical reduced-model representations
Authors: Li P.-Y. , Terry P. W.
Published: April 2022

The saturation physics of ion temperature gradient (ITG) turbulence is probed by studying how amplitudes and scalings with key parameters vary across a hierarchy of reduced models. The models derive from nonlinear fluid equations for toroidal ITG turbulence under approximations to the mode coupling interactions in wavenumber space and the representation of turbulent decorrelation. Mode coupling approximations include local-in-wavenumber treatments like the spectral density of flux in quasilinear theory, a truncation to three nonlinearly interacting waves, and the interactions in a cascade to high radial wavenumber mediated by a single zonal flow. Turbulent decorrelation treatments are based on the triplet correlation time with and without eddy damping. Model fidelity is assessed by the scalings and magnitudes of the squared amplitudes of unstable mode, stable mode, and zonal flow with respect to the flow-damping rate and temperature gradient. It is shown that all models reproduce fundamental scalings, provided they incorporate the coupling of unstable mode, stable mode, and zonal flow. Accurate amplitude prediction requires eddy damping in the triplet correlation time and proper representation of the zonal-flow drive by interactions associated with the radial wavenumber cascade.
Multiband transport enables thermoelectric enhancements in the SrMg2Bi2 compound
Authors: Zhang Yin , Deng Yushan , Xiong Rui , Cheng Kun , Chen Bo , Wen Cuilian , Cao Kaiyan , Li Wen
Published: April 2022

A small energy offset (ΔE < 0.2 eV) between Γ(pxy) and Γ(pz) band orbitals in AB2X2 Zintl compounds enables the realization of band alignment for an increased band degeneracy as well as an enhanced electronic performance. The SrMg2Bi2 Zintl compound has been theoretically illustrated to have a small ΔE, suggesting an approximately inherent convergence of two band orbitals. Therefore, this work is devoted to the revelation of the thermoelectric potential of the SrMg2Bi2 Zintl compound in a broad Hall carrier concentration of 0.3–5 × 1019 cm−3 by Ag-doping at the Sr site. The electrical transport properties can be well predicted by the single parabolic band model with acoustic phonon scattering, which reveals a multi-band transporting behavior in the heavily doped samples due to Fermi level deepening, leading to a significant zT-enhancement. In terms of the model, a peak zT of up to 1.0 is achievable by assuming the amorphous minimum lattice thermal conductivity, which demonstrates this compound as a promising thermoelectric material.
Hyperfine-resolved optical spectroscopy of the A2Π ← X2Σ+ transition in MgF
Authors: Doppelbauer M. , Wright S. C. , Hofsäss S. , Sartakov B. G. , Meijer G. , Truppe S.
Published: April 2022

We report on hyperfine-resolved laser spectroscopy of the A2Π ← X2Σ+ transition of magnesium monofluoride (MgF), relevant for laser cooling. We recorded 25 rotational transitions with an absolute accuracy of better than 20 MHz, assigned 56 hyperfine lines, and determined precise rotational, fine, and hyperfine structure parameters for the A2Π state. The radiative lifetime of the A2Π state was determined to be 7.2(3) ns, in good agreement with ab initio calculations. The transition isotope shift between bosonic isotopologues of the molecule is recorded and compared to predicted values within the Born–Oppenheimer approximation. We measured the Stark effect of selected rotational lines of the A2Π ← X2Σ+ transition by applying electric fields of up to 10.6 kV cm−1 and determined the permanent electric dipole moments of 24MgF in its ground X2Σ+ and first excited A2Π states to be μX = 2.88(20) D and μA = 3.20(22) D, respectively. Based on these measurements, we caution for potential losses from the optical cycling transition due to electric field induced parity mixing in the excited state. In order to scatter 104 photons, the electric field must be controlled to below 1 V cm−1.
Low-pressure gas flow properties of sintered stainless steel microporous media
Authors: Johansson M. V. , Wüest M. , Perrier P. , Graur I.
Published: April 2022

The gas flows through the low permeable porous media are of great interest, especially in vacuum technology for filtering, separation processes, protection, and flow control. They can combine a high mass flow rate and a high level of rarefaction. The transient experimental technique, developed previously for the mass flow rate measurements through the microchannels [Rojas Cardenas et al., Phys. Fluids 23, 031702 (2011)], is generalized to obtain the permeability and conductance directly from the pressure variation measurements. The present experimental methodology, allowing for step by step data verification, leads to higher accuracy than the similar and commonly used method such as “pulse-decay” techniques [W. F. Brace and R. J. Martin, Int. J. Rock Mech. Min. Sci. 5, 415–426 (1968)]. The measured data are fitted according to the exponential function with the pressure relaxation time as a single fitting parameter. The permeability and conductance of the sintered stainless steel microporous medium are measured for different gases. By using the methodology proposed by Johansson et al. [Int. J. Heat Mass Transfer 142, 118412 (2019)], the characteristic pore size of the sample was determined to be equal to 1.5 micrometers. It was found that free molecular flow constant conductance is achieved at a pressure below 30 mbar for helium. This property makes this kind of porous media particularly suitable as a leak element by taking advantage of the constancy of conductance in the free molecular flow regime, for example, for calibration of ionization gauges or mass spectrometers [Yoshida et al., Measurement 45(10), 2452–2455 (2012)].
Molecular dynamics study of the impact of a solid drop on a solid target
Authors: Soulard L. , Carrard Th. , Durand O.
Published: April 2022

The impact of a drop on a surface can result in bouncing, bonding, or erosion of the drop and the target. The occurrence of these processes is important in many industrial applications such as cold-spray. An experiment indicates that erosion is preceded by jet formation, which is closely related to the bonding/erosion boundary, but a detailed description accounting for jet fragmentation is still lacking. We propose in this article to combine the theoretical analysis and molecular dynamics simulations to explore these complex processes. In a previous article [L. Soulard et al., J. Appl. Phys. 129, 205104 (2021)], we analyzed the simplest case: a drop of liquid on a rigid surface. In this article, we address a more complex case: a solid drop and a solid surface. A detailed analysis of the impact processes allows us to establish simple formulas to calculate the velocity and orientation of the jet and to propose criteria for the appearance of the jet. These theoretical results are then evaluated by comparison to large-scale molecular dynamics simulations. The agreement is partially satisfactory and gives the limits of the theory. The results make it possible to specify the criteria of formation of the jet used in the literature.
Turbulence suppression and regeneration in a magnetohydrodynamic duct flow due to influence of arbitrary electrically conductive walls
Authors: Blishchik Artem , Kenjereš Saša
Published: April 2022

In the current study, we present a series of numerical simulations describing a turbulent magnetohydrodynamic flow subjected to a transverse magnetic field in a square duct with arbitrary electrically conductive walls. The characteristic flow and electromagnetic non-dimensional parameters (Reynolds and Hartmann number, respectively) were fixed, while the wall conductivity ratio (Cd) was varied from the perfectly electrically insulated (Cd = 0) to perfectly electrically conducting (Cd→∞). We have assumed the one-way coupling between the flow of an electrically conducting fluid and the imposed magnetic field. The influence of the electrically conducting walls was imposed by simulating additional finite solid domains coupled with the channel interior. The turbulence was simulated by applying the large eddy simulation approach with the dynamic Smagorinsky sub-grid scale model. The obtained results confirmed a significant impact of the conductivity of the surrounding walls on the flow and turbulence reorganization. We have observed that the initially fully developed turbulence regime was gradually suppressed in the 0≤Cd<0.15 range, while the fully laminarized state was obtained at Cd=0.15. We found that the process of turbulence suppression was accompanied by the appearance of the patterned turbulence phenomenon in the proximity of the walls parallel to the magnetic field direction. With a further increase in the wall conductivity parameter (0.15<Cd<∞), we have observed a complete turbulence regeneration. We found that this turbulence regeneration was caused by the local reorganization of the total current density loops near the electrically conducting walls.
Multi-order resonators for acoustic multiband asymmetric absorption and reflection
Authors: Yu Yuchi , Jia Han , Yang Yuzhen , Zhao Han , Shi Quanquan , Kong Peng , Yang Jun , Deng Ke
Published: April 2022

We propose a multiband asymmetric acoustic absorption and reflection system constructed from a waveguide and multi-order resonators with different radiant modes. Theoretical and experimental results confirm that the coupling of the dark and bright modes at each resonant frequency enables multiband high-efficiency absorption requiring only two functional units. More interestingly, we demonstrate a hybrid multiband asymmetric system based on customized multi-mode pairs. One side of the hybrid multiband system almost completely absorbs the lower frequency incident sound waves while reflecting the higher frequency ones; conversely, the other side effectively reflects the lower frequency ones and absorbs the higher frequency ones. Our design showcases the flexibility of customized multiband asymmetric absorption and also provides an approach for the design of bidirectional wave-manipulation devices.
Calculation of the T-X phase diagram for the first-order smectic–hexatic transitions in binary mixtures
Authors: Kilit Dogan E. , Yurtseven H.
Published: April 2022

This work gives the T-X phase diagram calculated from the Landau mean field model for the smectic–hexatic transitions in binary mixtures, particularly, in THI-13+THI-17. It is calculated near the SmC-SmF (Hex F)–Hex B triple point by considering transitions of SmC-SmF, SmF-HexB, and SmC-Hex B as the first order. The phase line equations are fitted to the experimental T-X phase diagram from the literature for this binary mixture by assuming the temperature and concentration dependence of the coefficients in the Landau free energy expansion. Calculations are given in some detail to describe the smectic–hexatic transitions in the THI-13+THI-17, which can also be considered for other binary mixtures under the Landau mean field model studied here.
Slow manifold reduction as a systematic tool for revealing the geometry of phase space
Authors: Burby J. W.
Published: April 2022

Many non-dissipative reduced plasma models can be derived from more fundamental non-dissipative models by restricting to an approximate invariant manifold. I present a general systematic procedure for finding the Hamiltonian formulation of a plasma model that can be derived in this manner. Several illustrative examples are considered in detail.
There exist infinitely many kinds of partial separability/entanglement
Authors: Ha Kil-Chan , Han Kyung Hoon , Kye Seung-Hyeok
Published: April 2022

In tri-partite systems, there are three basic biseparability, A-BC, B-CA, and C-AB, according to bipartitions of local systems. We begin with three convex sets consisting of these basic biseparable states in the three-qubit system, and consider arbitrary iterations of intersections and/or convex hulls of them to get convex cones. One natural way to classify tri-partite states is to consider those convex sets to which they belong or do not belong. This is especially useful to classify partial entanglement of mixed states. We show that the lattice generated by those three basic convex sets with respect to convex hull and intersection has infinitely many mutually distinct members to see that there are infinitely many kinds of three-qubit partial entanglement. To do this, we consider an increasing chain of convex sets in the lattice and exhibit three-qubit Greenberger–Horne–Zeilinger diagonal states distinguishing those convex sets in the chain.
Localization analysis of intercellular materials of living diatom cells studied by tomographic phase microscopy
Authors: Hamano Ryo , Mayama Shigeki , Umemura Kazuo
Published: April 2022

We demonstrated tomographic phase microscopy (TPM) of living diatoms in liquid in order to quantitatively analyze localization of cell components of symmetric shape cells. One TPM image includes several millions of pixel data of three-dimensional optical information such as refractive index (RI) values of cell components. In this work, the obtained TPM data of living cells were analyzed using X–Y cross sections to visualize the localization of cell components. Distribution of RI values at the cell surfaces and inside the cells were quantified. The results showed that the RI values were slightly lower at the cell center (RI ∼ 1.400) than the cell boundary (RI ∼ 1.420). RI values were fluctuated according to the depth measured from the cell surface also. Furthermore, statistical analysis by root mean square and Moran's I methods revealed unique localization of RI values for several cells among 25 individuals. In addition, the volumes of the cells estimated using TPM data corresponded to the cell volumes obtained via scanning electron microscopy. Our work proposed an effective procedure to quantitatively/statistically investigate intracellular materials of living cells based on physical information of TPM data.
Large piezoelectricity response in Li and Ti (or Zr) co-alloyed w-AlN
Authors: Tao Zechao , Hu Zhibin , Xie Liu , Sun Chengliang , Tang Qiang , Liu Yonghui , Jia Jun , Guo YuZheng , Wang Jun , Wu Guoqiang
Published: April 2022

As one of the most important piezoelectric materials for piezoelectricity related devices, the performance of wurtzite-type aluminum nitride (w-AlN) is still inhibited by its low piezoelectric coefficients. Herein, we have proposed a new co-alloying w-AlN system by Li+ and Ti4+ (or Zr4+) in a ratio of 1:2 and systematically compared its piezoelectric properties with state-of-the-art Sc-alloyed w-AlN via the first-principle method. It is found that the co-alloyed w-AlN shows obvious advantages over Sc-alloyed w-AlN in nearly all aspects of piezoelectric performance. The piezoelectric strain coefficient (d33) of (LiTi2)0.375Al0.625N reaches 213.25 pC/N, about 8 times and 41 times that of Sc0.375Al0.625N and pure w-AlN, respectively. Additionally, the large enhancement of piezoelectricity of co-alloyed w-AlN was successfully related to the elastic softening, the increased Born effective charge (Z∗), and the decreased internal strain sensitivity (dudδ). This work provides a new way to enhance the performance of incumbent piezoelectric materials by accessible elements instead of Sc.
Mach and Reynolds number dependency of the unsteady shock-induced drag force on a sphere
Authors: Osnes Andreas Nygård , Vartdal Magnus
Published: April 2022

Shock–particle interaction is an important phenomenon in a wide range of technological applications and natural phenomena, and the development of accurate models for this interaction is therefore of interest. This study investigates the transient forces during shock–particle interaction at particle Reynolds numbers between 100 and 1000, and incident shock wave Mach numbers between 1.22 and 2.51. This is achieved with the aid of particle-resolved large-eddy simulations. The simulation results show that shock–particle interaction differs qualitatively for subcritical and supercritical incident flow conditions. By decomposing the total force, the inviscid and viscous unsteady forces are estimated. The inviscid unsteady component is significantly larger than the viscous contribution, but the magnitude of the viscous component is comparable to steady-state drag. The predictions of current state of the art force models are compared to the computed particle forces. For subcritical flows, the models are quite successful in predicting the drag. For these conditions, the magnitudes of both the inviscid and viscous unsteady force models agree well with the simulation results, but the transient nature of the viscous unsteady force history is not well captured. For supercritical flows, the inviscid unsteady force model is not able to capture the force dynamics. This highlights the need for the development of unsteady force models for supercritical flow conditions.
Fluid mixing behind a branched elastic flag connecting to a cylinder in channel flow
Authors: Jing Dalei , Zhan Xuekuan
Published: April 2022

This paper proposes a mixer with an elastic vortex generator consisting of a branched elastic flag connected to the rear of a cylinder in the mixing channel and studies the effects of the branching angle of the branching elastic flag and Reynolds number based on the cylinder diameter Red on the mixing modes of the fluid flow in the mixer. One free diffusion-induced mixing mode and two different vortex-induced mixing modes are found, and a phase diagram regarding the mixing modes of the fluid flow behind the elastic vortex generator is established. It is found that the elastic vortex generator is helpful for the transition of the mixing mode from free diffusion-induced mixing to vortex-induced mixing with the increasing branching angle. Furthermore, the rising Reynolds number results in the transition of mixing mode from free diffusion-induced mixing to vortex-induced mixing. In addition, the present work quantitatively studies the effects of the branching angle of the branched elastic flag and Reynolds number on the pressure loss and the outlet mixing efficiency of the mixer. It is found that the increase in pressure loss and the outlet mixing efficiency are 141.41% and 613.70% as the branching angle increases from 0° to 180° when Red = 90. In addition, the pressure loss and outlet mixing efficiency of the mixer with the branched elastic flag of branching angle θ = 180° can be 227.66% and 601.36% higher than those of the fluid flow around the cylinder without the elastic flag in the mixing channel when Red = 50.
Origin of magnetic field-induced magnetic anisotropy in amorphous CoFeB thin films
Authors: Yuan Lu , Wang Baomin , Zha Dezhi , Liu Chenxu , Li Mengchao , Xie Yali , Yang Huali , Cao Yanwei , Xu Hui , Li Run-Wei
Published: April 2022

Magnetic anisotropy (MA) is an important property of magnetic materials, which not only determines the orientation of the magnetic moment in the magnetic material but also influences the working frequency of magnetoelectric devices. Unrevealing the origin of MA has become an important topic and attracts lasting interest. Here, we report a quite significant magnetic field-induced uniaxial MA in amorphous CoFeB thin films containing double ferromagnetic atoms. The thickness independence of MA was obtained by observing a series of hysteresis loops and magnetic domains. The MA is proved subtly to be related to the variation of orbital magnetic moment acquired by ferromagnetic resonance. Furthermore, we found that atoms combine into clusters and incline to an order in amorphous CoFeB thin films with field-induced MA. Based on these experimental results, we proposed a direction-like order model to interpret the origin of magnetic field-induced MA in amorphous CoFeB thin films well.
Enhanced magnetic properties of NiFe2O4 thin films deposited on BCZT-buffered SrTiO3 substrate
Authors: Wang Chuanbin , Liu Shihang , Shi Junwei , Shen Qiang
Published: April 2022

In this study, NiFe2O4 films were deposited on the Ba0.85Ca0.15Zr0.9Ti0.1O3 (BCZT)-buffered SrTiO3 substrate by pulsed laser deposition, and the effect of the thickness of the layer on the rearrangement of cations and magnetic property of the NiFe2O4 films was explored. All NiFe2O4 films were grown epitaxially along the c-axis orientation and exhibited a smooth surface. When the buffer layer was 30 nm thick, the proportion of Ni2+ cations at the Td site in NiFe2O4 reached the maximum. Accordingly, the obtained film exhibited the highest saturation magnetization of 113 emu/cm3. This work demonstrates that introducing the BCZT buffer layer between the NiFe2O4 thin film and the SrTiO3 substrate is an effective approach to tailor the magnetic properties of NiFe2O4 thin films.
An analysis of the long-term trends in the records of Friends of the Koala in north-east New South Wales: I. Cause and fate of koalas admitted for rehabilitation (1989–2020)
Authors: Lunney Daniel , Cope Holly , Sonawane Indrie , Stalenberg Eleanor , Haering Ron
Published: April 2022

Context The koala is a threatened species in New South Wales and long-term datasets of koala rehabilitation provide a valuable source of insight into local threats. Aims To examine the long-term trends of the cause and fate of koalas admitted for rehabilitation to assist monitoring the recovery of koala populations and provide a new outlook on the limitations and strengths of rehabilitation records for koala conservation. Methods We used data from long-term records (1989–2020) of the Friends of the Koala wildlife rehabilitation group in north-east New South Wales to identify spatial and temporal trends in 5051 koala admissions. Key results Chlamydiosis was the most common cause of admission, affecting female koalas more often than males. Admissions of female koalas with chlamydiosis showed a two-fold increase over summer, and admissions for motor vehicle collisions and unsuitable environment increased in spring. The rescue locations of admissions show an increasing geographic spread over time, as well as an increasing density of records. Admission body scores were higher in koalas that were eventually released than in non-released koalas. Other main causes of admission were unsuitable environments, dog attacks, abandonment/orphaning and attacks from other species. Conclusions We have produced an analysis and interpretation of a long-term dataset of the relative importance of various threats facing the koala population in north-east New South Wales. However, admissions to rehabilitation do not capture all the landscape-scale problems confronting koalas locally, particularly climate change and habitat loss. Implications We have provided the baseline necessary to detect future changes in the causes for admission, rates of rehabilitation and post-release survival.
The Caputo–Fabrizio time-fractional Sharma–Tasso–Olver–Burgers equation and its valid approximations
Authors: Hosseini Kamyar , Ilie Mousa , Mirzazadeh Mohammad , Baleanu Dumitru , Park Choonkil , Salahshour Soheil
Published: April 2022

Studying the dynamics of solitons in nonlinear time-fractional partial differential equations has received substantial attention, in the last decades. The main aim of the current investigation is to consider the time-fractional Sharma–Tasso–Olver–Burgers (STOB) equation in the Caputo–Fabrizio (CF) context and obtain its valid approximations through adopting a mixed approach composed of the homotopy analysis method (HAM) and the Laplace transform. The existence and uniqueness of the solution of the time-fractional STOB equation in the CF context are investigated by demonstrating the Lipschitz condition for

φ

x
,
t
;
u

as the kernel and giving some theorems. To illustrate the CF operator effect on the dynamics of the obtained solitons, several two- and three-dimensional plots are formally considered. It is shown that the mixed approach is capable of producing valid approximations to the time-fractional STOB equation in the CF context.
Product and sum uncertainty relations based on metric-adjusted skew information
Authors: Ma Xiaoyu , Zhang Qing-Hua , Fei Shao-Ming
Published: April 2022

The metric-adjusted skew information establishes a connection between the geometrical formulation of quantum statistics and the measures of quantum information. We study uncertainty relations in product and summation forms of metric-adjusted skew information. We present lower bounds on product and summation uncertainty inequalities based on metric-adjusted skew information via operator representation of observables. Explicit examples are provided to back our claims.
Deep-learning-based cryptanalysis of two types of nonlinear optical cryptosystems
Authors: Wang Xiao-Gang , Wei Hao-Yu
Published: April 2022

The two types of nonlinear optical cryptosystems (NOCs) that are respectively based on amplitude-phase retrieval algorithm (APRA) and phase retrieval algorithm (PRA) have attracted a lot of attention due to their unique mechanism of encryption process and remarkable ability to resist common attacks. In this paper, the securities of the two types of NOCs are evaluated by using a deep-learning (DL) method, where an end-to-end densely connected convolutional network (DenseNet) model for cryptanalysis is developed. The proposed DL-based method is able to retrieve unknown plaintexts from the given ciphertexts by using the trained DenseNet model without prior knowledge of any public or private key. The results of numerical experiments with the DenseNet model clearly demonstrate the validity and good performance of the proposed the DL-based attack on NOCs.
Integral cross sections for electron impact excitations of argon and carbon dioxide
Authors: Wang Shu-Xing , Zhu Lin-Fan
Published: April 2022

Electron-impact excitation integral cross sections play an important role in understanding the energy transfer processes in many applied physics. Practical applications require integral cross sections in a wide collision energy range from the excitation threshold to several keV. The recently developed BE-scaling method is able to meet the demands of integral cross sections for dipole-allowed transitions while the prerequisite relies on the accurate generalized oscillator strengths. Fast electron and x-ray scatterings are the conventional experimental techniques to approach the generalized oscillator strengths, and the joint study by both methods can provide credible cross-checks. The validated generalized oscillator strengths can then be used to extrapolate optical oscillator strengths by fitting the data with the Lassettre formula. The fitted curve also enables the integration of generalized oscillator strengths over the whole momentum transfer region to obtain the BE-scaled integral excitation cross sections. Here, experimental measurements by both fast electron and x-ray scattering of argon and carbon dioxide are reviewed. The integral cross sections for some low-lying states are derived from the cross-checked generalized oscillator strengths for the first time. The integral cross sections presented in this paper are openly available at https://doi.org/10.11922/sciencedb.01466.
Effects of oxygen concentration and irradiation defects on the oxidation corrosion of body-centered-cubic iron surfaces: A first-principles study
Authors: Ye Zhiqiang , Lei Yawei , Zhang Jingdan , Zhang Yange , Li Xiangyan , Xu Yichun , Wu Xuebang , Liu C. S. , Hao Ting , Wang Zhiguang
Published: April 2022

Oxidation corrosion of steels usually occurs in contact with the oxygen-contained environment, which is accelerated by high oxygen concentration and irradiation. The oxidation mechanism of steels is investigated by the adsorption/solution of oxygen atoms on/under body-centered-cubic (bcc) iron surfaces, and diffusion of oxygen atoms on the surface and in the near-surface region. Energetic results indicate that oxygen atoms prefer to adsorb at hollow and long-bridge positions on the Fe(100) and (110) surfaces, respectively. As the coverage of oxygen atoms increases, oxygen atoms would repel each other and gradually dissolve in the near-surface and bulk region. As vacancies exist, oxygen atoms are attracted by vacancies, especially in the near-surface and bulk region. Dynamic results indicate that the diffusion of O atoms on surfaces is easier than that into near-surface, which is affected by oxygen coverage and vacancies. Moreover, the effects of oxygen concentration and irradiation on oxygen density in the near-surface and bulk region are estimated by the McLean’s model with a simple hypothesis.
A new transition metal diphosphide α-MoP2 synthesized by a high-temperature and high-pressure technique
Authors: Liu Xiaolei , Yu Zhenhai , Li Jianfu , Xu Zhenzhen , Zhou Chunyin , Dong Zhaohui , Zhang Lili , Wang Xia , Yu Na , Zou Zhiqiang , Wang Xiaoli , Guo Yanfeng
Published: April 2022

Monoclinic α-MoP2, with the OsGe2-type structure (space group C2/m, Z = 4) and lattice parameters a = 8.7248(11) Å, b = 3.2322(4) Å, c = 7.4724(9)Å, and β = 119.263°, was synthesized under a pressure of 4~GPa at a temperature between 1100 °C and 1200 °C. The structure of α-MoP2 and its relationship to other transition metal diphosphides are discussed. Surprisingly, the ambient pressure phase orthorhombic β-MoP2 (space group Cmc21) is denser in structure than α-MoP2. Room-temperature high-pressure x-ray diffraction studies exclude the possibility of phase transition from β-MoP2 to α-MoP2, suggesting that α-MoP2 is a stable phase at ambient conditions; this is also supported by the total energy and phonon calculations.
Algebra of discrete symmetries in the extended Poincaré group
Authors: Dvoeglazov Valeriy V.
Published: April 2022

We begin with the comprehensible review of the basics of the Lorentz, (extended) Poincare Groups and O(3,2) and O(4,1). On the basis of the Gelfand-Tsetlin-Sokolik-Silagadze research [1-3], we investigate the definitions of the discrete symmetry operators both on the classical level, and in the secondary-quantization scheme. We studied the physical content within several bases: light-front form formulation, helicity basis, angular momentum basis, on several practical examples. The conclusion is that we have ambiguities in the definitions of the the corresponding operators P, C; T, which lead to different physical consequences.
Michelson-Morley experiment explained by means of five methods
Authors: Klinaku Shukri
Published: April 2022

The Michelson-Morley experiment (MME) is still important to physics, and not just to the history of physics. The hypothesis of contraction of bodies in the direction of their motion arose as an ad hoc hypothesis about the “contraction” of the Michelson’s interferometer arm in the direction of its motion. Even today this experiment is the “strongest argument” of this hypothesis, and of time dilation too. This work will present the explanation of the MME through five methods. The first method can be called the traditional method, which was applied by Michelson, but not correctly. The other methods are the explanation of the MME with the interferometer located at an acute angle to the direction of Earth’s motion; with the light clock; using Galilean transformation in polar coordinates and using the Doppler effect formula. All these methods give the same solution, and this solution is in accordance with the experiment’s result. Solutions derived from these five methods represent a natural explanation for the result of the MME – without weird terms and without unscientific assumptions.
The universal rewrite system coded
Authors: Rowlands Sydney , Rowlands Peter
Published: April 2022

The universal rewrite system (URS), first formulated by Rowlands and Diaz [2002], which may well be the meta-pattern driving the systems of the physical universe, has been realized, in the companion paper, in the deterministic Turing machine and other devices foundational to computational theory. Here, we show that we can extend the results to actual coding of a given finite section of the fundamentally infinite system. We also apply the principle of the URS to the universal Turing machine and to variable finite automata over an infinite alphabet, and explain its use in cryptography and the decision problem.
Double photon coincidence crosstalk reduction method for multi-nuclide Compton imaging
Authors: Uenomachi M. , Shimazoe K. , Takahashi H.
Published: April 2022

Compton imaging based on Compton scattering kinematics has the potential to visualize multi-nuclides by discriminating the total energy of Compton scattering and photoelectric absorption events. This feature enables us to perform multi-tracer imaging that reflects different functional information in nuclear medicine, resulting in a definitive diagnosis and being useful for biological and medical research. One of the challenges with multi-nuclide imaging is the crosstalk artifacts caused by scattered photons of higher energy gamma-rays. In this study, we investigated the potential benefits of the double photon coincidence detection as a drastic crosstalk reduction method. Coincidence detection of successive gamma-rays can differentiate nuclides and reduce the background caused by other nuclides' gamma-rays because some nuclides emit two or more gamma-rays in rapid succession. In this study, we focused on the coincidence detection of a Compton event and a photoelectric absorption event, and we showed simultaneous double photon emitter imaging of 111In and 177Lu with a ring-type Compton imaging system. The artifacts caused by other nuclides' gamma-rays were reduced by extracting Compton events coincident with photoelectric absorption events. The coincidence Compton images demonstrated a signal-to-background ratio improvement of 1.1–1.7 times over the one of no-coincidence Compton images, despite a drop in intrinsic detection efficiency of the order of 10-2. This strategy of directly reducing crosstalk will be useful in other combinations imaging such as of 111In (or 177Lu) and a positron emission tomography nuclide.