bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonadiabatic simulations of photoisomerization and dissociation in ethylene using ab initio classical trajectories
Authors: Miyazaki K. , Ananth N.
Published: September 2023

We simulate the nonadiabatic dynamics of photo-induced isomerization and dissociation in ethylene using ab initio classical trajectories in an extended phase space of nuclear and electronic variables. This is achieved by employing the linearized semiclassical initial value representation method for nonadiabatic dynamics, where discrete electronic states are mapped to continuous classical variables using either the Meyer–Miller–Stock–Thoss representation or a more recently introduced spin mapping approach. Trajectory initial conditions are sampled by constraining electronic state variables to a single initial excited state and by drawing nuclear phase space configurations from a Wigner distribution at a finite temperature. An ensemble of classical ab initio trajectories is then generated to compute thermal population correlation functions and analyze the mechanisms of isomerization and dissociation. Our results serve as a demonstration that this parameter-free semiclassical approach is computationally efficient and accurate, identifying mechanistic pathways in agreement with previous theoretical studies and also uncovering dissociation pathways observed experimentally.
Nuclear induction lineshape modeling via hybrid SDE and MD approach
Authors: Niknam Mohamad , Bouchard Louis-S.
Published: September 2023

The temperature dependence of the nuclear free induction decay in the presence of a magnetic-field gradient was found to exhibit motional narrowing in gases upon heating, a behavior that is opposite to that observed in liquids. This has led to the revision of the theoretical framework to include a more detailed description of particle trajectories since decoherence mechanisms depend on histories. In the case of free diffusion and single components, the new model yields the correct temperature trends. The inclusion of boundaries in the current formalism is not straightforward. We present a hybrid SDE-MD (stochastic differential equation - molecular dynamics) approach whereby MD is used to compute an effective viscosity and the latter is fed to the SDE to predict the line shape. The theory is in agreement with the experiments. This two-scale approach, which bridges the gap between short (molecular collisions) and long (nuclear induction) timescales, paves the way for the modeling of complex environments with boundaries, mixtures of chemical species, and intermolecular potentials.
Robust measurement of angular velocity based on rotational Doppler effect in misaligned illumination
Authors: Lü Jia-Qi , Cheng Tian-Yu , Guo Ji-Xiang , Li Jin-Song , Wang Yulei , Lu Zhiwei
Published: September 2023

The discovery of the rotational Doppler effect (RDE) provides opportunities to achieve fast, accurate, and contactless measurement of angular velocity. As the RDE signal is sensitive to the illumination light and its scattering characteristic, how to effectively extract the angular velocity of a detected target becomes one of the key difficulties in this measurement technique. Here, we put forward a scattering modified RDE model to fully understand the frequency-domain behavior of an RDE signal in misaligned illumination. A robust strategy based on the peak-to-peak intervals in a wideband spectrum of the RDE signal is demonstrated to acquire accurate angular velocity, without strict requirement to the alignment of illumination and roughness of the detected surface. Furthermore, the feasibility to extract the spin angular velocity from a composite motion of spin and translation is discussed.
Eliminating finite-size effects on the calculation of x-ray scattering from molecular dynamics simulations
Authors: Dohn A. O. , Markmann V. , Nimmrich A. , Haldrup K. , Møller K. B. , Nielsen M. M.
Published: September 2023

Structural studies using x-ray scattering methods for investigating molecules in solution are shifting focus toward describing the role and effects of the surrounding solvent. However, forward models based on molecular dynamics (MD) simulations to simulate structure factors and x-ray scattering from interatomic distributions such as radial distribution functions (RDFs) face limitations imposed by simulations, particularly at low values of the scattering vector q. In this work, we show how the value of the structure factor at q = 0 calculated from RDFs sampled from finite MD simulations is effectively dependent on the size of the simulation cell. To eliminate this error, we derive a new scheme to renormalize the sampled RDFs based on a model of the excluded volume of the particle-pairs they were sampled from, to emulate sampling from an infinite system. We compare this new correction method to two previous RDF-correction methods, developed for Kirkwood–Buff theory applications. We present a quantitative test to assess the reliability of the simulated low-q scattering signal and show that our RDF-correction successfully recovers the correct q = 0 limit for neat water. We investigate the effect of MD-sampling time on the RDF-corrections, before advancing to a molecular example system, comprised of a transition metal complex solvated in a series of water cells with varying densities. We show that our correction recovers the correct q = 0 behavior for all densities. Furthermore, we employ a simple continuum scattering model to dissect the total scattering signal from the solvent–solvent structural correlations in a solute–solvent model system to find two distinct contributions: a non-local density-contribution from the finite, fixed cell size in NVT simulations, and a local contribution from the solvent shell. We show how the second contribution can be approximated without also including the finite-size contribution. Finally, we provide a “best-practices”-checklist for experimentalists planning to incorporate explicit solvation MD simulations in future work, offering guidance for improving the accuracy and reliability of structural studies using x-ray scattering methods in solution.
Metasurface characterization based on eigenmode analysis and averaging of electromagnetic fields
Authors: Nitas Michalis , Kafesaki Maria , Arslanagic Samel
Published: September 2023

A fully numerical homogenization technique for the retrieval of the effective surface susceptibilities of a periodic composite metasurface is developed in this work. We utilize the so-called dual field-flux finite element formulation scheme to accurately calculate the eigenmodes of a composite periodic metasurface, a scheme that possesses a crucial advantage: The capability of evaluating all field components and their derivatives accurately and with the same order of approximation is a requirement for our proposed technique. Next, we derive the generalized sheet transition condition equations for a general bianisotropic metasurface, which correlate the field components on either sides of the metasurface with its surface susceptibilities. At this point, we establish a new field averaging scheme for the acquisition of the average field components of the modes supported by the metasurface. Combining this computational information, we derive a set of linear algebraic equations based on the GSTCs and the average electromagnetic fields and numerically solve it, so as to obtain the effective surface susceptibilities of a bianisotropic metasurface. Comparison with the results of other techniques in the literature shows very good agreement, relatively to the resonance behavior of the returned values and their position at the frequency spectrum. The advantages that distinguish the proposed technique over other related methods are its foundation on the intrinsic modal information of the eigenmodes supported by the metasurface and its independence of any wave excitation schemes or involvement of analytical polarizability calculations.
Modeling and simulation of flow–osteocyte interaction in a lacuno-canalicular network
Authors: Barber Jared , Manring Isaac , Boileau Sophie , Zhu Luoding
Published: September 2023

Osteocytes are bone cells that can sense mechanical cues (stress and strain) and respond by releasing biochemical signals that direct bone remodeling. This process is called mechanotransduction which, in osteocytes, is not well understood yet because in vivo studies have proven difficult due to the complexity and inaccessibility of the flow–osteocyte lacuna-canaliculi system. While in silico studies (modeling and simulation) have become powerful, currently computational studies for the system often omit the fluid–structure interaction (FSI) between the cell and the surrounding fluids. To investigate the role of FSI in osteocyte mechanotransduction, we introduce a two-dimensional coarse-grained yet integrative model for flow–osteocyte interaction in a lacuno-canalicular network. The model uses the lattice Boltzmann immersed boundary framework to incorporate the flexible osteocyte (membrane, cytoskeleton, and cytosol), its processes, the interstitial fluid, and the rigid extracellular matrix that encases the system. One major result of our model is that the stress and strain tend to attain their local maxima near the regions where the processes meet the membrane of the main body.
Reduced thermal resistance of amorphous Al2O3 thin films on β-Ga2O3 and amorphous SiO2 substrates via rapid thermal annealing
Authors: Aller Henry T. , McGaughey Alan J. H. , Malen Jonathan A.
Published: September 2023

The impact of rapid thermal annealing (1000 °C for 1 min) on the thermal transport properties of amorphous alumina (a-Al2O3) thin films grown by atomic layer deposition on β−Ga2O3 and amorphous silica (a-SiO2) substrates is determined using frequency-domain thermoreflectance measurements. The annealing more than doubles the a-Al2O3 thermal conductivity for both substrates (1.54 ± 0.13 to 3.14 ± 0.27 W m−1 K−1 for β−Ga2O3 and 1.60 ± 0.14 to 3.87 ± 0.33 W m−1 K−1 for a-SiO2) while keeping the film amorphous. The thermal conductivity increase is attributed to partial recrystallization and off-gassing of embedded impurities. Annealing halves the thermal boundary resistance of the a-Al2O3/a-SiO2 interface (10.5 ± 1.0 to 4.47 ± 0.42 m2 K GW−1), which is attributed to compositional mixing and structural reorganization that are enabled by the elastic matching of these two materials. The thermal boundary resistance of the a-Al2O3/β−Ga2O3 interface is not affected by annealing due to the elastic mismatch. Reducing the thermal resistance of a-Al2O3 dielectric films and adjacent interfaces by annealing will promote lateral heat spreading adjacent to hot spots and improve device longevity.
Theoretical investigation of magnetic and thermal properties in Dy1−x
Sc
x
Ni2 series
Authors: Clemente P. C. M. , da Silva J. M. N. , De Oliveira R. S. , Alho B. P. , Nóbrega E. P. , de Sousa V. S. R. , von Ranke P. J. , Ribeiro P. O.
Published: September 2023

We report on the thermal and magnetic properties of Dy1−xScxNi2 series compounds (x=0.1,0.3,0.5,and0.7), which were investigated through a model Hamiltonian including the exchange, Zeeman, and crystalline electric field interactions. We investigated the effect of Sc substitution on the Dy site on the magnetic and magnetocaloric properties of these compounds. Theoretical results were simulated for heat capacity, entropy, and the magnetocaloric effect quantities. Our model reproduced the decrease of the magnetic ordering temperature and of the isothermal entropy change peaks as Sc concentration increases. Our theoretical results were confronted with experimental data from the literature, showing good agreement.
Numerical study of rectified electroosmotic flow in nanofluidics: Influence of surface charge and geometrical asymmetry
Authors: Mai Thanh Dam , Lee Choongyeop , Ryu Jaiyoung
Published: September 2023

The transport of ions in nanofluidic systems, specifically the rectified ion transport or the ionic diode phenomenon occurring in the presence of asymmetrical geometry and/or charge distribution, has drawn considerable attention due to its relevance in energy conversion and biosensing applications. However, previous numerical research has frequently overlooked the concurrent liquid flow within these systems, even though multiple experimental studies have highlighted intriguing flow patterns in ionic diode configurations. In the present study, we employ comprehensive numerical simulations to probe the influence of geometrical or charge asymmetry in a nanofluidic system on electroosmotic flow and ion transport. These simulations employ the Poisson–Nernst–Planck equation in conjunction with the Navier–Stokes equation. Our findings reveal that even when the current rectification trend is consistent between conical and straight nanopores, charge asymmetry and geometric asymmetry can generate significant variations in the rectification effects of electroosmotic flow. Furthermore, our research indicates that the direction of ion rectification and flow rectification can be independently manipulated by utilizing charge asymmetry in conjunction with geometric asymmetry, thereby facilitating advanced control of ions and flows within nanofluidic systems. Collectively, our findings contribute to a more profound understanding of the mechanisms underlying osmotic flow rectification and propose a novel approach for developing efficient ion and flow rectification systems.
Bandgaps of long-period polytypes of IV, IV-IV, and III-V semiconductors estimated with an Ising-type additivity model
Authors: Ramakrishnan Raghunathan , Jain Shruti
Published: September 2023

We apply an Ising-type model to estimate the bandgaps of the polytypes of group IV elements (C, Si, and Ge) and binary compounds of groups: IV–IV (SiC, GeC, and GeSi), and III–V (nitride, phosphide, and arsenide of B, Al, and Ga). The models use reference bandgaps of the simplest polytypes comprising 2–6 bilayers calculated with the hybrid density functional approximation, HSE06. We report four models capable of estimating bandgaps of nine polytypes containing 7 and 8 bilayers with an average error of ≲0.05 eV. We apply the best model with an error of <0.04 eV to predict the bandgaps of 497 polytypes with up to 15 bilayers in the unit cell, providing a comprehensive view of the variation in the electronic structure with the degree of hexagonality of the crystal structure. Within our enumeration, we identify four rhombohedral polytypes of SiC—9R, 12R, 15R(1), and 15R(2)—and perform detailed stability and band structure analysis. Of these, 15R(1) that has not been experimentally characterized has the widest bandgap (>3.4 eV); phonon analysis and cohesive energy reveal 15R(1)-SiC to be metastable. Additionally, we model the energies of valence and conduction bands of the rhombohedral SiC phases at the high-symmetry points of the Brillouin zone and predict band structure characteristics around the Fermi level. The models presented in this study may aid in identifying polytypic phases suitable for various applications, such as the design of wide-gap materials, that are relevant to high-voltage applications. In particular, the method holds promise for forecasting electronic properties of long-period and ultra-long-period polytypes for which accurate first-principles modeling is computationally challenging.
Correlation between the rheology of electronic inks and the droplet size generated from a capillary nozzle in dripping regime
Authors: Rijo Pedro C. , Cremonezzi Josué M. O. , Andrade Ricardo J. E. , Galindo-Rosales Francisco J.
Published: September 2023

This study provides a complete rheological characterization of bidimensional (2D) nanomaterial dispersions, employed as 2D-inks precursors in printed electronics. Three different 2D nanomaterials [molybdenum disulfide (MoS2), graphene, and hexagonal boron nitride (hBN)] were dispersed in a Newtonian fluid (toluene) and a viscoelastic fluid (toluene + ethyl cellulose) with different polymer concentrations. The presence of nanosheets does not change the shear rheology of the carrier fluid. Regarding the extensional rheology, the results showed that the pinch-off phenomenon is present in all toluene suspensions; however, the presence of the ethyl cellulose introduces elasticity in the system, even leading to the formation of beads-on-a-string, and the relaxation times of the suspensions depend on the kind of nanosheets present in the fluid. As controlling the droplet size when dispensing 2D-inks is of paramount importance for printed electronics as well as for many other applications, here it is presented a correlation between the rheological properties of these 2D-inks precursors and their droplet size when generated from a capillary nozzle in the dripping regime.
High expectations on phase locking: Better quantifying the concentration of circular data
Authors: Andrzejak Ralph G. , Espinoso Anaïs , García-Portugués Eduardo , Pewsey Arthur , Epifanio Jacopo , Leguia Marc G. , Schindler Kaspar
Published: September 2023

The degree to which unimodal circular data are concentrated around the mean direction can be quantified using the mean resultant length, a measure known under many alternative names, such as the phase locking value or the Kuramoto order parameter. For maximal concentration, achieved when all of the data take the same value, the mean resultant length attains its upper bound of one. However, for a random sample drawn from the circular uniform distribution, the expected value of the mean resultant length achieves its lower bound of zero only as the sample size tends to infinity. Moreover, as the expected value of the mean resultant length depends on the sample size, bias is induced when comparing the mean resultant lengths of samples of different sizes. In order to ameliorate this problem, here, we introduce a re-normalized version of the mean resultant length. Regardless of the sample size, the re-normalized measure has an expected value that is essentially zero for a random sample from the circular uniform distribution, takes intermediate values for partially concentrated unimodal data, and attains its upper bound of one for maximal concentration. The re-normalized measure retains the simplicity of the original mean resultant length and is, therefore, easy to implement and compute. We illustrate the relevance and effectiveness of the proposed re-normalized measure for mathematical models and electroencephalographic recordings of an epileptic seizure.
Coupling high-overtone bulk acoustic wave resonators via superconducting qubits
Authors: Crump Wayne , Välimaa Alpo , Sillanpää Mika A.
Published: September 2023

In this work, we present a device consisting of two coupled transmon qubits, each of which are coupled to an independent high-overtone bulk acoustic wave resonator (HBAR). Both HBAR resonators support a plethora of acoustic modes, which can couple to the qubit near resonantly. We first show qubit–qubit interaction in the multimode system and, finally, quantum state transfer where an excitation is swapped from an HBAR mode of one qubit to an HBAR mode of the other qubit.
An effective control strategy for transitional hypersonic boundary layers
Authors: Yu Jiaming , Chen Wangqiao , Huang Xun , Zhu Yiding , Lee Cunbiao
Published: September 2023

An effective control strategy is studied in this work to reduce aerodynamic heating inside transitional hypersonic boundary layers, which is of both scientific significance and practical importance. The experiments show that the use of grooved wavy walls covered with an acoustic transparent film can successfully reduce the growth of Mack's second mode, which delays transition and results in significant reduction of aerodynamic heating.
Non-uniform orientation of H2 molecules in a magnetic field as a critical condition for the appearance of partially negative NMR lines of o-H2 in hyperpolarization experiments using p-H2
Authors: Bernatowicz P. , Ratajczyk T. , Szymański S.
Published: September 2023

In hyperpolarization experiments using parahydrogen, a partially negative line (PNL) of o-H2 is occasionally spotted in the nuclear magnetic resonance (NMR) spectra. This is a manifestation of the two-spin order (TSO) of the proton spins, appearing transiently in o-H2 molecules freshly derived from p-H2. For the TSO to be observable, the o-H2 NMR signal must be split into a doublet. In the literature, the splitting is believed to originate from a slow exchange of the dissolved dihydrogen with the dihydride moiety bound to a catalyst present in the reaction mixture. Because this hypothesis may be debatable, in this work a different splitting mechanism is proposed. It employs a residual dipolar coupling (RDC) between the hydrogen protons, originating from a partial orientation of the H2 molecules by the external magnetic field. The orientation effect is due to the anisotropic magnetic polarizability of H2. In a magnetic field of 11.74 T at room temperature, the currently predicted value of the RDC is −0.0024 Hz. Even such small RDC values are sufficient for the PNL effect to be clearly visible in NMR spectra for physically reasonable levels of the TSO in the o-H2 molecules. For RDC values much smaller than the natural linewidth of o-H2, the theoretical frequency distance between the minimum and maximum of PNL proves to be practically independent of the RDC and is of the order of the linewidth. The calculated amplitudes of the PNLs are proportional to the RDC values used in the calculations.
Channeling the exchanges of eg electrons by Co-implantation for magnetism enhancement in CrI3 monolayer
Authors: Xu Jinlin , Huang Xiaokun , Mo Yunying , Nie Xin , Chen Chao , Jiang Xiangping , Liu Jun-Ming
Published: September 2023

In recent few years, the two-dimensional (2D) magnets have emerged as one of the most important frontiers in materials physics and attracted much attention. As one of the earliest experimentally discovered 2D magnets, CrI3 shows a wealth of properties and has been extensively studied. In particular, an intriguing characteristic of the CrI3 monolayer is its octahedrally coordinated hollow within the unit-cell, which enables the implantation of a magnetic atom, thereby resulting in an artificial 2D superlattice with fertile physics to explore. In this work, using first-principles calculations, we investigate the Co-implanted CrI3 monolayer, denoted as Co-(CrI3)2, and demonstrate the vital roles of the exchange channels of eg electrons in enhancing magnetism. It is shown that the Co-(CrI3)2 monolayer has a half-metallic ferrimagnetic (FiM) ground-state with a net in-plane magnetic moment of 5.0μB/f.u. and a relatively high Curie point (TC) of ∼195 K, noting that TC of pristine CrI3 is only 45–61 K. The FiM ordering is established by the strong anti-ferromagnetic coupling in the t2g-eg exchange channels of the nearest-neighbor (NN) Cr–Co pair and the sizeable ferromagnetic coupling of the third NN Cr–Cr pair mediated by the itinerant eg electrons. In addition, an in-plane biaxial tensile strain of ∼2% may further enhance TC up to ∼210 K. This work offers unique insights into the magnetism enhancement of the CrI3 monolayer by atom-implantation, paving the way for the development of 2D magnets.
Antiferromagnetic second-order topology in two-dimensional NiRuCl6
Authors: Li Jianghua , Xie Chengwu , Wang Wenhong , Li Xiao-Ping , Zhang Gang , Wang Xiaotian
Published: September 2023

In recent years, 2D second-order topological insulators (SOTIs) have garnered considerable interest because of their unique properties. However, only the FeSe monolayer with four corner states (two occupied and two unoccupied states) near the Fermi level has been reported to be a candidate for 2D intrinsic antiferromagnetic SOTIs in theory. The limited amount of antiferromagnetic SOTIs has hindered future research, and corner states should be at the Fermi level in order to manifest interesting physics. Herein, we propose NiRuCl6 as a candidate for 2D antiferromagnetic SOTIs with corner states strictly at the Fermi level. Without spin–orbit coupling (SOC), NiRuCl6 is an antiferromagnetic half-metal with a compensating magnetic moment and decoupled spin bands. In the spin-up channel, NiRuCl6 hosts a nontrivial gap of 1.11 eV, where zero-dimensional corner states appear. In the spin-down channels, NiRuCl6 hosts metallically behaved bands, where a spin-polarized quadratic Weyl point emerges. With SOC, two spin bands are coupled, and NiRuCl6 becomes an antiferromagnetic SOTI with three degenerate corner states at the Fermi level inside the SOC-induced gap with a value of 0.11 eV. Remarkably, the corner states in NiRuCl6 are resistant to changes in SOC strength and magnetization orientation. We also reveal that the phononic second-order topology and corner vibrational modes appear in the phonon dispersion curves of NiRuCl6. The presented results improve the general understanding of antiferromagnetic SOTIs and contribute to the prediction of materials with ideal corner states at the Fermi level, thereby advancing the field of topological antiferromagnetic spintronics.
Broadband RCS reduction by means of disordered coding metasurfaces
Authors: Mourad A. , Burgnies L. , Lheurette É.
Published: September 2023

Pattern Search (PS) optimization algorithm has been used for the design of disordered coding metasurfaces with the aim of reducing both monostatic and bistatic Radar Cross Section (RCS) in the 26–40 GHz frequency range. On this basis, high and low phase-state unit-cells have been defined with special attention to the minimization of coupling between the elementary patterns, thus allowing a quasi-constant 180° phase difference over a broad frequency range. Then, finite size metasurfaces have been designed and fabricated using the printed circuit board technological process. Finally, the experimental characterization of various disordered samples leads to −10 dB monostatic RCS reduction over a relative frequency band broader than 35% with a good agreement with both simulated and analytic theoretical predictions. This illustrates the relevance of disordered coded patterns for RCS reduction as well as the PS optimization approach as a design method of coding metasurfaces.
A new generation of non-diagonal, renormalized self-energies for calculation of electron removal energies
Authors: Opoku Ernest , Pawłowski Filip , Ortiz J. V.
Published: September 2023

A new generation of diagonal self-energies for the calculation of electron removal energies of molecules and molecular ions that has superseded its predecessors with respect to accuracy, efficiency, and interpretability is extended to include non-diagonal self-energies that permit Dyson orbitals to be expressed as linear combinations of canonical Hartree–Fock orbitals. In addition, an improved algorithm for renormalized methods eliminates the convergence difficulties encountered in the first studies of the new, diagonal self-energies. A dataset of outer-valence, vertical ionization energies with almost full-configuration-interaction quality serves as a standard of comparison in numerical tests. The new non-diagonal, renormalized methods are slightly more accurate than their diagonal counterparts, with mean absolute errors between 0.10 and 0.06 eV for outer-valence final states. This advantage is procured at the cost of an increase in the scaling of arithmetic bottlenecks that accompany the inclusion of non-diagonal self-energy terms. The new, non-diagonal, renormalized self-energies are also more accurate and efficient than their non-diagonal predecessors.
Impact of the crystallographic variants of VO2 thin films on c- and r-cut sapphire on structural phase transition and radiofrequency properties
Authors: Diebold Laura , Maroutian Thomas , Largeau Ludovic , Guiblin Nicolas , Bude Romain , Garry Guy , Ishchenko Olga M. , Aubert Pascal
Published: September 2023

Vanadium dioxide exhibits a metal to insulator transition close to room temperature, making it very interesting in particular for radio frequency (RF) device applications. Here, we compare the structural and RF properties of VO2 thin films grown by magnetron sputtering on c-cut and r-cut sapphire substrates. The epitaxial growth of VO2 on c-cut sapphire gives rise to several crystallographic variants for the insulating M1 phase. Moreover, during the structural transition, simultaneous presence of both metallic and insulating phases is evidenced by x-ray diffraction over a large temperature range. Films grown on r-cut sapphire exhibit only two variants and present a very narrow temperature range of their structural transition. Interestingly, such structural differences of the films grown on c- and r-cut sapphire substrates have very little influence on their dc resistivity, while the transmission of the RF signal through the metallic phase was found much lower on c-cut than on r-cut sapphire. This supports the fact that r-cut sapphire is preferable for VO2-based RF device fabrication.
Resonant excitation of vortex gyrotropic mode via surface acoustic waves
Authors: Koujok A. , Riveros A. , Rodrigues D. R. , Finocchio G. , Weiler M. , Hamadeh A. , Pirro P.
Published: September 2023

Finding new energy-efficient methods for exciting magnetization dynamics is one of the key challenges in magnonics. In this work, we present an approach to excite the gyrotropic dynamics of magnetic vortices through the phenomenon of inverse magnetostriction, also known as the Villari effect. We develop an analytical model based on the Thiele formalism that describes the gyrotropic motion of the vortex core including the energy contributions due to inverse magnetostriction. Based on this model, we predict excitations of the vortex core resonances by surface acoustic waves whose frequency is resonant with the frequency of the vortex core. We verify the model's prediction using micromagnetic simulations and show the dependence of the vortex core's oscillation radius on the surface acoustic wave amplitude and the static bias field. Our study contributes to the advancement of energy-efficient magnetic excitations by relying on voltage-induced driven dynamics, which is an alternative to conventional current-induced excitations.
Double-floating-gate memory device based on energy band engineered van der Waals heterostructure
Authors: Tang Fei , Liu Xiaochi , Dai Xianfu , Yuan Yahua , Jing Yumei , Sun Jian
Published: September 2023

Floating-gate memory devices based on two-dimensional van der Waals heterostructures are considered as promising candidates for next-generation nonvolatile memories. Here, we report a nonvolatile double-floating-gate (DFG) memory device based on a ReS2/boron nitride/black phosphorus (BP)/boron nitride/graphene heterostructure. By comparing with a single-floating-gate device we fabricated, the device shows enlarged memory window, high on–off ratio, and improved retention performance. Based on these findings, we propose energy band diagrams showing how the memory performance can be improved by energy band engineering through designing the van der Waals heterostructure. In the DFG structure, electrons could transfer between the ReS2 channel and BP as well as between BP and graphene, providing greater controllability for electron tunneling and injection. By choosing graphene and BP as two floating gates, an energy barrier rising from the conduction-band offset between multilayer graphene and BP is set up to efficiently prevent charge leakage from the graphene floating gate and, thus, improve the memory performance. Our work demonstrates an effective way for future designs of high-performance nonvolatile flash memories.
HASR-TAI: Hybrid model-based interpretable network and super-resolution network for thermoacoustic imaging
Authors: Liu Shuangli , Wan Pengcheng , Shang Xin
Published: September 2023

Microwave induced thermoacoustic tomography has shown promise for noninvasive and non-ionizing early tumor detection. Nowadays, thermoacoustic reconstruction methods based on deep learning have achieved good and time-efficient results. However, both deep learning methods based on the initial thermoacoustic image and end-to-end methods lack interpretability due to the black-box property of neural networks. In this Letter, we propose an interpretable end-to-end network structure comprising an unrolling part and a super-resolution part. In the unrolling part, a deep unfolding network interprets the iterations of the model-based algorithm based on compressed sensing as layers of the network. Subsequently, a fast and efficient super-resolution neural network maps the low-resolution image into the super-resolution space. Two breast models with different sizes of tumor targets are used for validation. By comparing with the traditional method and the deep learning method, the proposed method demonstrates superior performance in image quality and imaging time. Moreover, the parameters in the network hold physical significance, offering the potential for the interpretable end-to-end network in thermoacoustic imaging.
Ultrathin superconducting TaCxN1−x films prepared by plasma-enhanced atomic layer deposition with ion-energy control
Authors: Peeters Silke A. , Lennon Ciaran T. , Merkx Marc J. M. , Hadfield Robert H. , Kessels W. M. M. (Erwin) , Verheijen Marcel A. , Knoops Harm C. M.
Published: September 2023

This work demonstrates that plasma-enhanced atomic layer deposition (PEALD) with substrate biasing enables the preparation of ultrathin superconducting TaCxN1−x films. By comparing with films grown without substrate biasing, the enhanced ion energies yield a hundredfold reduction in room-temperature resistivity: a comparably low value of 217 μΩ cm is obtained for a 40 nm film. The ion-energy control enables tuning of the composition, counteracts oxygen impurity incorporation, and promotes a larger grain size. Correspondingly, the critical temperature of superconductivity (Tc) displays clear ion-energy dependence. With optimized ion energies, a consistently high Tc around 7 K is measured down to 11 nm film thickness. These results demonstrate the high ultrathin-film quality achievable through PEALD combined with substrate biasing. This process is particularly promising for the fabrication of low-loss superconducting quantum devices.
Efficient scheme for implementing a hybrid Toffoli gate with two NV ensembles simultaneously controlling a single superconducting qubit
Authors: Liu Tong , Xu Jin , Zhang Yu , Yu Yang , Su Qi-Ping , Zhou Yan-Hui , Yang Chui-Ping
Published: September 2023

The Toffoli gate is a three-qubit controlled-controlled-NOT gate, which plays a central role in quantum information processing and quantum computing. Recently, hybrid systems and hybrid quantum gates have attracted much attention. We propose an efficient scheme to implement a hybrid Toffoli gate with two nitrogen-vacancy center ensembles (NV ensembles) as the control qubits and a single superconducting flux qubit as the target qubit. This hybrid Toffoli gate is realized by employing two NV ensembles coupled to a superconducting qutrit. The hybrid Toffoli gate is constructed by a controlled-controlled-phase (CCPHASE) gate sandwiched between two Hadamard gates applied on the target qubit. Since the CCPHASE gate is realized using only a single-step operation and no conventional gate decomposition protocol is applied, the Toffoli-gate implementation is greatly simplified. Because the higher energy level of the flux qutrit is not populated, the decoherence of this level is greatly suppressed. In addition, our hybrid Toffoli gate can be used to generate a hybrid Greenberger–Horne–Zeilinger entangled state of a flux qubit and two NV ensembles. Numerical simulations demonstrate that high-fidelity implementation of a hybrid Toffoli gate is feasible within current experimental technology. This proposal is universal and can be applied to accomplish the same task in a wide range of physical systems.
Subwavelength pulse focusing and perfect absorption in the Maxwell fish-eye
Authors: Lefebvre Gautier , Dubois Marc , Achaoui Younes , Ing Ros Kiri , Fink Mathias , Guenneau Sébastien , Sebbah Patrick
Published: September 2023

Maxwell's fish-eye is a paradigm for an absolute optical instrument with a refractive index deduced from the stereographic projection of a sphere on a plane. We investigate experimentally the dynamics of flexural waves in a thin plate with a thickness varying according to the Maxwell fish-eye index profile and a clamped boundary. We demonstrate subwavelength focusing and temporal pulse compression at the image point. This is achieved by introducing a sink emitting a cancelling signal optimally shaped using a time-reversal procedure. Perfect absorption and outward going wave cancellation at the focus point are demonstrated. The time evolution of the kinetic energy stored inside the cavity reveals that the sink absorbs energy out of the plate ten times faster than the natural decay rate.
Development of high-reflectivity polymer/air-Bragg micromirror structures for nanophotonic applications
Authors: Palekar Chirag Chandrakant , Shah Manan , Reitzenstein Stephan , Rahimi-Iman Arash
Published: September 2023

We report the design, nanofabrication, and characterization of high-quality polymer-based micromirror structures employing the 3D two-photon polymerization lithography technique. Compared to conventional microcavity approaches, our innovative concept provides microstructures, which allow fast prototyping. Moreover, our polymer-based mirrors are cost effective and environmentally sensitive, as well as compatible with a wide range of wavelengths from near-infrared to the telecom C-band. We demonstrate polymer/air distributed Bragg reflectors and full microcavity structures with up to 14 mirror pairs with a target wavelength of 1550 nm and a reflectivity close to 99%. Additionally, our 3D printed micromirrors are reproducible and mechanically stable, and enable hybrid nanophotonic devices based on quantum dots, molecules, or 2D quantum materials as the active medium.
Discoveries on the link between the properties of thermoelectric and infrared radiation
Authors: Du Ya-Qian , Zhang Lei , Zhang Gui-Bin , Fang Bing-Bing , Luan Xin-Peng , Li Yan-Nan , La Ta , Liu Jun-Jie , Wang Jun
Published: September 2023

Both thermoelectric conversion materials and infrared (IR) radiation materials enjoy broad applicability in energy utilization and aerospace. Therefore, it is essential to study the relationship between the physical properties of these two materials. This paper investigates the connection between the thermoelectric properties and the IR radiation properties using a SrTiO3-based thermoelectric material. As a result, we have demonstrated the correlation between a material's Seebeck coefficient and IR emissivity using experimental data and theoretical calculations. With increasing Seebeck coefficient, the IR emissivity increases. The material's IR emissivity falls as its electrical conductivity rises, and vice versa. When the material's thermal gradient is low, its IR emissivity influences its IR radiation energy. As the thermal gradient of the material increases, the IR radiation energy incident on the material surface is mainly influenced by the material's thermal conductivity. This work provides a fresh perspective on modulating the IR radiation and thermoelectric properties using the connection found in this study. The results provide theoretical guidance for studies at the intersection of thermoelectric and IR materials.
Nonreciprocal interactions give rise to fast cilium synchronization in finite systems
Authors: Hickey David J. , Golestanian Ramin , Vilfan Andrej
Published: September 2023

Motile cilia beat in an asymmetric fashion in order to propel the surrounding fluid. When many cilia are located on a surface, their beating can synchronize such that their phases form metachronal waves. Here, we computationally study a model where each cilium is represented as a spherical particle, moving along a tilted trajectory with a position-dependent active driving force and a position-dependent internal drag coefficient. The model thus takes into account all the essential broken symmetries of the ciliary beat. We show that taking into account the near-field hydrodynamic interactions, the effective coupling between cilia even over an entire beating cycle can become nonreciprocal: The phase of a cilium is more strongly affected by an adjacent cilium on one side than by a cilium at the same distance in the opposite direction. As a result, synchronization starts from a seed at the edge of a group of cilia and propagates rapidly across the system, leading to a synchronization time that scales proportionally to the linear dimension of the system. We show that a ciliary carpet is characterized by three different velocities: the velocity of fluid transport, the phase velocity of metachronal waves, and the group velocity of order propagation. Unlike in systems with reciprocal coupling, boundary effects are not detrimental for synchronization, but rather enable the formation of the initial seed.
Fatal architectures and death by design: the infrastructures of state-sponsored climate disasters in Angola and Mozambique
Authors: Blanes Ruy Llera
Published: September 2023

This article addresses how African states respond to climate crisis, arguing that, beyond the agency and impact of climate phenomena such as drought and cyclones, they are active participants in the production of climate disasters and emergencies, mostly through infrastructural processes that affect land and resource use, and subsequently livelihoods. To demonstrate this, it uses the cases of the drought in southwestern Angola and cyclones in northern and central Mozambique, where such climate phenomena have exposed ‘fatal architectures’ that have dramatically raised the toll of climate victims and refugees. Both extractivist, agro-industrial and hydroelectric projects, as well as other, more deferred infrastructural designs (roads, communication networks, etc.) have challenged the traditional agency and resilience of local communities. Such new infrastructural projects also illustrate how certain perceived long-term solutions to address the climate crisis with industrial and energy reconversion towards greener energies can still become fatal architectures in the context of climate emergencies.
Dependence of myosin filament structure on intracellular calcium concentration in skeletal muscle
Authors: Caremani Marco , Fusi Luca , Reconditi Massimo , Piazzesi Gabriella , Narayanan Theyencheri , Irving Malcolm , Lombardi Vincenzo , Linari Marco , Brunello Elisabetta
Published: September 2023

Contraction of skeletal muscle is triggered by an increase in intracellular calcium concentration that relieves the structural block on actin-binding sites in resting muscle, potentially allowing myosin motors to bind and generate force. However, most myosin motors are not available for actin binding because they are stabilized in folded helical tracks on the surface of myosin-containing thick filaments. High-force contraction depends on the release of the folded motors, which can be triggered by stress in the thick filament backbone, but additional mechanisms may link the activation of the thick filaments to that of the thin filaments or to intracellular calcium concentration. Here, we used x-ray diffraction in combination with temperature-jump activation to determine the steady-state calcium dependence of thick filament structure and myosin motor conformation in near-physiological conditions. We found that x-ray signals associated with the perpendicular motors characteristic of isometric force generation had almost the same calcium sensitivity as force, but x-ray signals associated with perturbations in the folded myosin helix had a much higher calcium sensitivity. Moreover, a new population of myosin motors with a longer axial periodicity became prominent at low levels of calcium activation and may represent an intermediate regulatory state of the myosin motors in the physiological pathway of filament activation.
GiftBTE: an efficient deterministic solver for non-gray phonon Boltzmann transport equation
Authors: Hu Yue , Jia Ru , Xu Jiaxuan , Sheng Yufei , Wen Minhua , Lin James , Shen Yongxing , Bao Hua
Published: September 2023

Advances in nanotechnology have facilitated the exploration of submicron thermal transport. At this scale, Fourier’s law is no longer applicable, and the governing equation for thermal transport is the phonon Boltzmann transport equation (BTE). However, the availability of open-source solvers for the phonon BTE is limited, impeding progress in this field. This study introduces an open-source package, GiftBTE, for numerically solving the non-gray phonon BTE. GiftBTE employs deterministic solutions and provides both steady-state and transient solvers. For the steady-state solver, GiftBTE employs the implicit discrete ordinates method (DOM) with second-order spatial accuracy and the synthetic iterative scheme. For the transient solver, GiftBTE employs the explicit DOM with second-order spatial accuracy. This package demonstrates excellent computational efficiency, enabling realistic three-dimensional simulations of devices and materials. By interfacing with first-principles calculations, this solver enables parameter-free computation of submicron thermal transport. The application of GiftBTE includes, but is not limited to, computing the thermal conductivity of nanostructures, predicting temperature rises in transistors, and simulating laser heating processes.
Multiple-order singularity expansion method
Authors: Ben Soltane I , Colom R , Dierick F , Stout B , Bonod N
Published: September 2023

Physical systems and signals are characterized by complex functions of the frequency in the harmonic domain. The extension of such functions to the complex frequency plane, and in particular expansions and factorized forms of the harmonic-domain functions in terms of their poles and zeros, is of high interest to describe the physical properties of a system, and study its response dynamics in the temporal and harmonic domains. In this work, we start from a general property of continuity and differentiability of the complex functions to derive the multiple-order singularity expansion method. We rigorously derive the common singularity and zero expansion and factorization expressions, and generalize them to the case of singularities of arbitrary order, while deducing the behavior of these complex frequencies from the simple hypothesis that we are dealing with physically realistic signals.
Some classes of topological spaces extending the class of Δ-spaces
Authors: Ka̧kol Jerzy , Kurka Ondřej , Leiderman Arkady
Published: September 2023

A study of the class

Δ
\Delta

consisting of topological

Δ
\Delta

-spaces was originated by Jerzy Ka̧kol and Arkady Leiderman [Proc. Amer. Math. Soc. Ser. B 8 (2021), pp. 86–99; Proc. Amer. Math. Soc. Ser. B 8 (2021), pp. 267–280]. The main purpose of this paper is to introduce and investigate new classes

Δ
2

⊂

Δ
1

\Delta _2 \subset \Delta _1

properly containing

Δ
\Delta

.

We observe that for every first-countable

X
X

the following equivalences hold:

X
∈

Δ
1

X\in \Delta _1

iff

X
∈

Δ
2

X\in \Delta _2

iff each countable subset of

X
X

is

G

δ

G_{\delta }

. Thus, new proposed concepts provide a natural extension of the family of all

λ
\lambda

-sets beyond the separable metrizable spaces.

We prove that (1) A pseudocompact space

X
X

belongs to the class

Δ
1

\Delta _1

iff countable subsets of

X
X

are scattered. (2) Every regular scattered space belongs to the class

Δ
2

\Delta _2

.

We investigate whether the classes

Δ
1

\Delta _1

and

Δ
2

\Delta _2

are invariant under the basic topological operations. Similarly to

Δ
\Delta

, both classes

Δ
1

\Delta _1

and

Δ
2

\Delta _2

are invariant under the operation of taking countable unions of closed subspaces. In contrast to

Δ
\Delta

, they are not preserved by closed continuous images.

Let

Y
Y

be

l
l

-dominated by

X
X

, i.e.

C
p

(
X
)

C_p(X)

admits a continuous linear map onto

C
p

(
Y
)

C_p(Y)

. We show that

Y
∈

Δ
1

Y \in \Delta _1

whenever

X
∈

Δ
1

X \in \Delta _1

. Moreover, we establish that if

Y
Y

is

l
l

-dominated by a compact scattered space

X
X

, then

Y
Y

is a pseudocompact space such that its Stone–Čech compactification

β
Y

\beta Y

is scattered.