First-order Ones Research Articles

Biaxial Strain Transfer in Monolayer MoS2 and WSe2 Transistor Structures.

Monolayer transition metal dichalcogenides are intensely explored as active materials in 2D material-based devices due to their potential to overcome device size limitations, sub-nanometric thickness, and robust mechanical properties. Considering their large band gap sensitivity to mechanical strain, single-layered TMDs are well-suited for strain-engineered devices. While the impact of various types of mechanical strain on the properties of a variety of TMDs has been studied in the past, TMD-based devices have rarely been studied under mechanical deformations, with uniaxial strain being the most common one. Biaxial strain on the other hand, which is an important mode of deformation, remains scarcely studied as far as 2D material devices are concerned. Here, we study the strain transfer efficiency in MoS2- and WSe2-based flexible transistor structures under biaxial deformation. Utilizing Raman spectroscopy, we identify that strains as high as 0.55% can be efficiently and homogeneously transferred from the substrate to the material in the transistor channel. In particular, for the WSe2 transistors, we capture the strain dependence of the higher-order Raman modes and show that they are up to five times more sensitive compared to the first-order ones. Our work demonstrates Raman spectroscopy as a nondestructive probe for strain detection in 2D material-based flexible electronics and deepens our understanding of the strain transfer effects on 2D TMD devices.

A class of polynomial approximation methods to second-order delay differential equations

This paper studies special high-order methods to numerically solve special second-order ordinary differential equations and second-order differential equations with constant delay, which are based on vector field expansion along the shifted and scaled Legendre polynomial orthonormal basis. In the framework of method design, we obtain the second-order perturbation results by transforming the second-order differential equations into first-order ones, and the error accuracy estimation of numerical solutions is achieved by using perturbation results for the problem under consideration. In addition, some numerical tests on specific second-order delay Hamiltonian systems are shown, the purpose of which is to verify the effectiveness of the theoretical findings.

Microstructure evolution of carbon films, grown by physical vapor deposition, when substrate temperature is increased

We study how the increases of substrate temperature influence the structural properties of carbon films deposited by physical vapor deposition (PVD) techniques. We installed and adapted a heating system inside the deposition chamber, which can reach temperatures as high as 700 °C. Here we develop an experimental setup that allows us to obtain large films of the desired material on any substrate, with deposition times of the order of a minute. The characterization is based mainly on the analysis of the Raman spectra, where the evolution of the G and D peaks corresponding to the material in its amorphous phase is observed. With the increase of substrate temperature, the sp2 zones grow. A displacement to the right of the G peak and an increase in the ID/IG ratio is seen. At 700 °C a 2D zone at a frequency greater than 2000 cm−1 appears. Four Lorentzian-shaped bands are necessary to account for the peaks at this zone, whose centers correspond to different combinations of first-order ones. This shows that we are transitioning from an amorphous to a carbon phase with more ordered or graphitic zones and that we are near the crystallization point. This opens the path to produce structures similar to graphene using this method of deposition. The Tauc gap energy ratio decreases as temperature increases indicating that there is a graphitization of the sample. Transmission FTIR study is carried out at some of the intermediate temperatures, determining the type of bond at low frequencies. These bonds are consistent with the ones of the hydrogenated amorphous carbon (a-C:H) structure.

Scaled Position Consensus of High-Order Uncertain Multiagent Systems Over Switching Directed Graphs.

We investigate the scaled position consensus of high-order multiagent systems with parametric uncertainties over switching directed graphs, where the agents' position states reach a consensus value with different scales. The intricacy arises from the asymmetry inherent in information interaction. Achieving scaled position consensus in high-order multiagent systems over directed graphs remains a significant challenge, particularly when confronted with the following complex features: 1) uniformly jointly connected switching directed graphs; 2) complex agent dynamics with unknown inertias, unknown control directions, parametric uncertainties, and external disturbances; 3) interacting with each other via only relative scaled position information (without high-order derivatives of relative position); and 4) fully distributed in terms of no shared gains and no global gain dependency. To address these challenges, we propose a distributed adaptive algorithm based on a acrlong MRACon scheme, where a linear high-order reference model is designed for every individual agent employing relative scaled position information as input. A new transformation is proposed which converts the scaled position consensus of high-order linear reference models to that of first-order ones. Theoretical analysis is presented where agents' positions achieve the scaled consensus over switching directed graphs. Numerical simulations are performed to validate the efficacy of our algorithm and some collective behaviors on traditional consensus, bipartite consensus, and cluster consensus are shown by precisely choosing the scales of the agents.

Ensemble inequivalence in an extended spin-1 Nagle-Kardar model

We conduct a comprehensive investigation of an extended spin-1 Nagle-Kardar model in the microcanonical ensemble, focusing on exploring the inequivalence between the canonical and microcanonical ensembles in this generalized model. Our results reveal that the general trends of the microcanonical phase diagram align with those in the canonical ensemble. The continuous phase transition lines of these two ensembles largely coincide, yet the first-order ones in the microcanonical ensemble exhibit greater complexity, showing various examples of ensemble inequivalence, particularly in cases involving the triple points.

Bayesian second-order sensitivity of longitudinal inferences to non-ignorability: an application to antidepressant clinical trial data.

Incomplete data is a prevalent complication in longitudinal studies due to individuals' drop-out before intended completion time. Currently available methods via commercial software for analyzing incomplete longitudinal data at best rely on the ignorability of the drop-outs. If the underlying missing mechanism was non-ignorable, potential bias arises in the statistical inferences. To remove the bias when the drop-out is non-ignorable, joint complete-data and drop-out models have been proposed which involve computational difficulties and untestable assumptions. Since the critical ignorability assumption is unverifiable based on the observed part of the sample, some local sensitivity indices have been proposed in the literature. Specifically, Eftekhari Mahabadi (Second-order local sensitivity to non-ignorability in Bayesian inferences. Stat Med 2018;59:55-95) proposed a second-order local sensitivity tool for Bayesian analysis of cross-sectional studies and show its better performance for handling bias compared with the first-order ones. In this paper, we aim to extend this index for the Bayesian sensitivity analysis of normal longitudinal studies with drop-outs. The index is driven based on a selection model for the drop-out mechanism and a Bayesian linear mixed-effect complete-data model. The presented formulas are calculated using the posterior estimation and draws from the simpler ignorable model. The method is illustrated via some simulation studies and sensitivity analysis of a real antidepressant clinical trial data. Overall, the numerical analysis showed that when repeated outcomes are subject to missingness, regression coefficient estimates are nearly approximated well by a linear function in the neighbourhood of MAR model, but there are a considerable amount of second-order sensitivity for the error term and random effect variances in Bayesian linear mixed-effect model framework.

High-order paired-ASPP for deep semantic segmentation networks

Current semantic segmentation models only exploit first-order information, while rarely exploring high-order semantics. However, traditional first-order statistics are insufficient to support a solid unanimous representation. In this paper, we propose High-Order Paired-ASPP (Atrous Spatial Pyramid Pooling) Network to exploit high-order statistics from various feature levels. The network first introduces a High-Order Representation module to extract the contextual high-order information from all stages of the backbone. They can provide more semantic clues and discriminative information than the first-order ones. Besides, a Paired-ASPP module is proposed to embed high-order statistics of the early stages into the last stage. It can further preserve the boundary-related and spatial context in the low-level features for final prediction. Our experiments show that the high-order semantics significantly boost the performance on confusing objects. Our method achieves competitive performance without bells and whistles on three benchmarks, i.e., Cityscapes, ADE20K and Pascal-Context.

Multicomponent gauge-Higgs models with discrete Abelian gauge groups

We consider a variant of the charge-Q compact Abelian-Higgs model, in which an N f -dimensional complex vector is coupled with an Abelian gauge field. For and Q = 1 we observe several transition lines that belong to the O(4), O(3), and O(2) vector universality classes, depending on the symmetry breaking pattern at the transition. The universality class is independent of q as long as . The universality class of the transition is uniquely determined by the behavior of the scalar fields; gauge fields do not play any role. We also investigate the system for and Q = 2. In the presence of U(1) gauge fields, the system undergoes transitions associated with charged fixed points of the Abelian-Higgs field theory. These continuous transitions turn into first-order ones when the U(1) gauge fields are replaced by the discrete fields: in the present compact model charged transitions appear to be very sensitive to the nature of the gauge fields.

Phase transitions in the Haldane-Hubbard model with ionic potentials

By employing the exact-diagonalization method, we revisit the ground-state phase diagram of the Haldane-Hubbard model on the honeycomb lattice with staggered sublattice potentials. The phase diagram includes the band insulator, Mott insulator, and two Chern insulator phases with Chern numbers C=2 and C=1, respectively. The character of transitions between different phases is studied by analyzing the lower-lying energy levels, excitation gaps, structure factors, and fidelity metric. We find that the C=1 phase can be continuously deformed into the C=2 phase without a gap closure in the periodic boundary condition, while a further analysis on the Berry curvatures indicates that the excitation gap closes at the phase boundary in a twisted boundary condition, accompanied by the discontinuities of structure factors. All the other phase transitions are found to be first-order ones as expected.

Asymptotic dynamics of higher-order lumps in the Davey–Stewartson II equation

A family of higher-order rational lumps on non-zero constant background of Davey–Stewartson (DS) II equation are investigated. These solutions have multiple peaks whose heights and trajectories are approximately given by asymptotical analysis. It is found that the heights are time-dependent and for large time they approach the same constant height value of the first-order fundamental lump. The resulting trajectories are considered and it is found that the scattering angle can assume arbitrary values in the interval of which is markedly distinct from the necessary orthogonal scattering for the higher-order lumps on zero background. Additionally, it is illustrated that the higher-order lumps containing multi-peaked n-lumps can be regarded as a nonlinear superposition of n first-order ones as .

A Hybridizable Discontinuous Galerkin Time-Domain Method With Robin Transmission Condition for Transient Thermal Analysis of 3-D Integrated Circuits

In this article, a discontinuous Galerkin time-domain (DGTD) method hybridized with Robin transmission condition (RTC-DGTD) is proposed for the transient thermal analysis of 3-D integrated circuits (ICs). As a kind of domain decomposition method (DDM), the DGTD method employs a term named numerical flux for the information exchange of solutions between neighboring subdomains. The numerical flux is a function of both temperature <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> and heat flux q, and thus for the heat equation, apart from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> , the variable q has to be solved as well. To reach this, the traditional DGTD method decomposes the second-order partial-differential thermal equation into two first-order ones, which results that both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> and q need to be solved in the whole computational domain, thereby the computational cost is extremely expensive. In this work, to get this trouble-treated, the proposed DGTD method is directly applied to discretize the second-order heat equation. An RTC is established at the interfaces of subdomains, which serves as the second governing equation and meanwhile bridges another connection of solutions in adjacent subdomains. In this way, the new variable q is now only present at the interfaces of subdomains. Consequently, the total number of unknowns is significantly reduced compared with that in the traditional DGTD method. To further speed up the time-marching scheme, an adaptive time-stepping method in terms of the proportional–integral–derivative (PID) control algorithm is employed. Besides, by introducing a restriction operator, the globally coupled matrix equation is torn into a number of small matrix equations pertinent to each subdomain, which is later solved via a finite-element tearing and interconnecting (FETI)-like method. To validate and verify the accuracy and efficiency of the proposed algorithm, several representative examples are studied and compared with COMSOL simulations.

Curved node-to-face contact schemes for higher-order finite elements in lumped-mass explicit methods

Contact is crucial in many lumped-mass explicit analyses, such as for high-rate impact, and enforcement methods for higher-order elements are generally less mature than for first-order ones. In this paper, basic lumped-mass explicit capabilities are pursued for three-dimensional contact/impact that account for arbitrary-order elemental curvature but with reasonable computational costs. Deformable-to-rigid and deformable-to-deformable surface-to-surface contact are considered with both triangular and/or quadrilateral faces for large deformation/sliding. Double-pass node-to-face contact searching and enforcement approaches are presented for general three-dimensional C0 higher-order Lagrange type elements in nonlinear solid dynamics using typical lumped-mass central difference time integration. This study uses classical kinematically compliant and penalty methods as well as presents modified versions better suited for higher-order Lagrange type elements. It also presents a general outer-loop iterative framework for increased accuracy and examines the simplifying practice of partitioning (subdivision) of higher-order element faces into first-order ones. Assessments are made with benchmark and practical high-rate impact applications involving elastic, hyperelastic, and elastic–plastic material models. Although subdivision into bilinear elements can sometimes be effective, it is demonstrated that they can also fail and that more precise treatment of even only modest amounts of curvature can be more reliable and improve performance.

Entrainment, stopping, and transmission of microwave solitons of self-induced transparency in counter-propagating magnetized electron beam.

Based on numerical simulations of a boundary problem, we study various scenarios of microwave soliton formation in the process of cyclotron resonance interaction of a short electromagnetic pulse with a counter-propagating initially rectilinear electron beam taking into account the relativistic dependence of the cyclotron frequency on the electrons' energy. When a certain threshold in the pulse energy is exceeded, the incident pulse can propagate without damping in the absorbing beam, similar to the effect of self-induced transparency in optics. However, mutual motion of the wave and electrons can lead to some novel effects. For relatively small energy of the incident pulse, the microwave soliton is entrained by the electron beam opposite to the direction of the wave's group velocity. With an increase in the pulse energy, soliton stopping occurs. This regime is characterized by the close-to-zero pulse velocity and can be interpreted as a variety of the "light stopping." High-energy microwave solitons propagate in the direction of the unperturbed group velocity. Their amplitude may exceed the amplitude of the incident pulse, i.e., nonlinear self-compression takes place. A further increase in the incident energy leads to the formation of additional high-order solitons whose behavior is similar to that of the first-order ones. The characteristics of each soliton (its amplitude and duration) correspond to analytical two-parametric soliton solutions that are to be found from consideration of the unbounded problem.

Bilinear form and nonlinear waves of a (1+1)-dimensional generalized Boussinesq equation for the gravity waves over water surface

Gravity waves are studied in, e.g., the oceanic and atmospheric sciences. In this paper, for the head-on interaction of oblique gravity wave profiles over the water surface, we investigate a (1+1)-dimensional generalized Boussinesq equation. Bilinear form is derived, and the higher-order rogue waves, breather and hybrid solutions in the determinant form are constructed via the Hirota bilinear method and Kadomtsev–Petviashvili hierarchy reduction. Influence of α, β and γ on the solutions is discussed, where α, β and γ are the nonzero coefficients in that equation. For the first-order rogue-wave solutions, we find that the wave widths and amplitudes are related to α and β, and the locations of the extreme points depend on α, β and γ. Structures of the higher-order rogue waves are also given. We construct three types of the first-order breathers, and the second-order breathers are obtained through the combinations of the first-order ones. α, β and γ are found to influence the amplitudes and locations of the first-order breathers. Hybrid solutions comprising the one rogue wave, the higher-order breathers and solitons are discussed graphically. Those results reveal the nonlinear properties of oblique gravity waves over the water surface, which can help the study on nonlinear waves in fluid mechanics, plasma physics and fiber optics.

Statistical spatial analysis for cryo-electron tomography

Cryo-electron tomography (cryo-ET) is uniquely suited to precisely localize macromolecular complexes in situ, that is in a close-to-native state within their cellular compartments, in three-dimensions at high resolution. Point pattern analysis (PPA) allows quantitative characterization of the spatial organization of particles. However, current implementations of PPA functions are not suitable for applications to cryo-ET data because they do not consider the real, typically irregular 3D shape of cellular compartments and molecular complexes. Here, we designed and implemented first and the second-order, uni- and bivariate PPA functions in a Python package for statistical spatial analysis of particles located in three dimensional regions of arbitrary shape, such as those encountered in cellular cryo-ET imaging (PyOrg).To validate the implemented functions, we applied them to specially designed synthetic datasets. This allowed us to find the algorithmic solutions that provide the best accuracy and computational performance, and to evaluate the precision of the implemented functions. Applications to experimental data showed that despite the higher computational demand, the use of the second-order functions is advantageous to the first-order ones, because they allow characterization of the particle organization and statistical inference over a range of distance scales, as well as the comparative analysis between experimental groups comprising multiple tomograms.Altogether, PyOrg is a versatile, precise, and efficient open-source software for reliable quantitative characterization of macromolecular organization within cellular compartments imaged in situ by cryo-ET, as well as to other 3D imaging systems where real-size particles are located within regions possessing complex geometry.

Quantum criticality at finite temperature for two-dimensional [formula omitted] models on the square and the honeycomb lattices

We study the quantum criticality at finite temperature for three two-dimensional (2D) JQ3 models using the first principles quantum Monte Carlo calculations (QMC). In particular, the associated universal quantities are obtained, and their inverse temperature dependence is investigated. The considered models are known to have quantum phase transitions from the Néel order to the valence-bond solid, and these transitions are shown to be possibly of second order for two of the studied models, with the remaining one being of first order. When the temperature dependence of the studied universal quantities is considered, we observe substantial differences between the two models likely possessing second-order phase transitions and the remaining model. Moreover, by using the associated data from both the models that may have continuous transitions, good data collapses are obtained for a number of the considered universal quantities. The findings presented here provide numerical evidence to support particular results established in the literature regarding the nature of the phase transitions of these JQ3 models, and can be employed as useful criterions to distinguish second-order phase transitions from first-order ones for the exotic criticalities of the JQ-type models.

Topological quantum critical points in strong coupling limits: Global symmetries and strongly interacting Majorana fermions

In this paper, we discuss strong coupling limits of topological quantum critical points (TQCPs) where quantum phase transitions between two topological distinct superconducting states take place. We illustrate that while superconducting phases on both sides of TQCPs spontaneously break the same symmetries, universality classes of critical states can be identified only when global symmetries in topological states are further specified. In dimensions $d=2\phantom{\rule{4.pt}{0ex}}\text{and}\phantom{\rule{4.pt}{0ex}}3$, we find that continuous $(d+1)\mathrm{th}$-order transitions at weakly interacting TQCPs that were pointed out previously in the presence of the emergent Lorentz symmetry can be terminated by strongly interacting fixed points of Majorana fields. For $2d$ time reversal symmetry breaking TQCPs, termination points are supersymmetric with $\mathcal{N}=4{N}_{f}=1$ (where ${N}_{f}$ is the number of four-component Dirac fermions and $\mathcal{N}$ is the number of two-component real fermions) beyond which transitions are discontinuous first-order ones. For $2d$ time reversal symmetric TQCPs without other global symmetries, termination points of $(d+1)\mathrm{th}$-order continuous transition lines are generically conformal invariant without supersymmetry. Beyond these strong coupling fixed points, there are first-order discontinuous transitions as far as the protecting symmetry is not spontaneously broken but no direct transitions if the protecting symmetry is spontaneously broken in the presence of strong interactions. In this case, termination points can become supersymmetric with $\mathcal{N}=4{N}_{f}=2$ only when interacting Majorana fermions further display an emergent global $\text{U}(1)$ symmetry. In $3d$, strong coupling termination points can be further effectively represented by new emergent gapless real bosons weakly coupled with free gapless Majorana fermions. However, in $1d$, time reversal symmetric $(d+1)\mathrm{th}$ continuous transition lines of TQCPs are terminated by simple free Majorana fermion fixed points.

Environmental Fragility in a Permanent Preservation Area

Permanent preservation areas reduce the exposure of sediments and nutrients in aquatic medium and improve the quality of water. The analysis of natural features and anthropic use in rivers’ surroundings makes it possible detecting potential ecological unbalance. This study analyzed the potential and emerging environmental fragility in Permanent Preservation Areas (PPA). Environmental fragilities around drainage areas composing the sub-basin were assessed based on soil, relief, rainfall, land use/land cover (LULC) features. The degrees of emerging environmental fragility observed in the second-order stream were lower than those in first-order ones: 3.07 and 2.68, on average, respectively; and standard deviation of approximately 0.7 was recorded in each group. First-order streams are more closely associated with high slopes, and it increases their fragility. Then reduction of fragility levels around water springs due to conservationist practices will decrease material and energy transfer throughout network connections and rebalance the assessed aquatic ecosystem.

A second-order accelerated neurodynamic approach for distributed convex optimization

Based on the theories of inertial systems, a second-order accelerated neurodynamic approach is designed to solve a distributed convex optimization with inequality and set constraints. Most of the existing approaches for distributed convex optimization problems are usually first-order ones, and it is usually hard to analyze the convergence rate for the state solution of those first-order approaches. Due to the control design for the acceleration, the second-order neurodynamic approaches can often achieve faster convergence rate. Moreover, the existing second-order approaches are mostly designed to solve unconstrained distributed convex optimization problems, and are not suitable for solving constrained distributed convex optimization problems. It is acquired that the state solution of the designed neurodynamic approach in this paper converges to the optimal solution of the considered distributed convex optimization problem. An error function which demonstrates the performance of the designed neurodynamic approach, has a superquadratic convergence. Several numerical examples are provided to show the effectiveness of the presented second-order accelerated neurodynamic approach.

An analytical state-space solution for free vibration of sandwich piezoelectric plate with functionally graded core

The purpose of this paper is to develop an analytical solution for free vibration analysis of smart functionally graded (FG) plates by the Levy solution in conjunction with the state-space approach. The FG substrate is sandwiched between two piezoelectric layers. The rectangular structure has two simply-supported opposite edges while the boundary conditions of the other two edges are arbitrary. Based on the simple but efficient four-variable refined plate theory, the governing equations are extracted employing Maxwell’s equation and Hamilton’s principle. The achieved fourth-order partial differential equations are transformed to first-order ordinary ones using the Levy solution along with the state-space approach and then, they are solved by applying the eigenvalue method. Meanwhile, an iterative algorithm is proposed to obtain the natural frequencies of the structure with various boundary conditions. A comparison is made between the obtained results and those available in the literature which verifies the accuracy of the solution method and numerical algorithm proposed in this study. Finally, the effect of several parameters such as type of boundary conditions, aspect ratio, power-law index, piezoelectric layer thickness, and thickness-to-side ratio is examined on the obtained results.