Boundary Stability Research Articles

High strength CuAg foil with a nano-lamellar structure prepared via pulse electrodeposition in an environmental-friendly methanesulfonic acid-based bath

In this study, high strength CuAg foils with nano-lamellar structures were prepared using a pulse electrodeposition method in an environmental-friendly methanesulfonic acid (MSA)-based solution. In an MSA-based bath, the Ag+ ion acted as the source for solute atoms and as a brightening agent, which allowed the formation of compact and bright CuAg structures in an additive-free bath. The application of pulse plating led to the formation of a nano-lammellar structure, in which Cu-rich and Ag layers were repeatedly stacked. Because of the contribution of the Ag layer, the as-deposited CuAg foil exhibited a high ultimate tensile strength (927 MPa) even at a low Ag content (2.37 wt%). The strength of the CuAg foil was further improved with annealing at 100–250 °C owing to the stabilization of the phase boundary. Despite a high fraction of the phase boundary, the nanostructure was stably maintained even after annealing at 250 °C for 1 h.

Boundary Stability Criterion for a Nonlinear Axially Moving Beam

This article deals with, in the framework of absolute stability, boundary stabilization for a nonlinear axially moving beam under boundary velocity feedback controls. The nonlinear boundary control that satisfies a slope-sector condition covering many types of nonlinear control schemes is a negative feedback of the transverse velocity at the right eyelet of the moving beam. Under the nonlinear control scheme, the well-posedness of the nonlinear partial differential equation, which depends continuously on the initial value is investigated by means of the Faedo–Galerkin approximation and priori estimates. By exploiting the integral-type multiplier method, the exponential stability of the closed-loop system is established, where a novel energy like function is constructed. The numerical simulation examples using the finite element method are presented to illustrate the effectiveness of the established criterion of the controller.

The effect of solute segregation on stability and strength of Cu symmetrical tilt grain boundaries from the first-principles study

Grain boundary (GB) stability and strength are two essential points for nanocrystalline materials. In this study, the effects and underlying mechanisms of segregation-induced GB stabilization and GB strengthening in various Cu GBs for selected 8 alloying elements (Mg, Ca, Cr, Ni, Zn, Zr, Ag and Sn) were investigated through first-principles total energy calculations. The segregation energy results show that all other elements excluding Ni can segregate to GB thus improving the GB stability. The segregation driving force is associated with the volume of Voronoi cell of solute, in the trend that increases along with the volume of Voronoi cell growth. The stabilizing mechanism should attribute to the decrease in the number of antibonding electrons. As to GB strength, the embrittling potency results show that Mg, Cr, Zr and Ag are enhancers in Σ5 [001](310) GB, while for Σ5 [001](210) and Σ11 [110](113) GBs, only Cr and Zr are enhancers. The embrittling potency is concerned with segregation energy and the volume of Voronoi cell of solute, in a trend that increases with the segregation energy decline and the volume of Voronoi cell growth. The enhancing mechanism lies in the formation of covalent-like bonds between solute and matrix atoms. Furthermore, by comparing the stabilizing and strengthening effectiveness of alloying elements in various Cu GBs. The trend that the worse the stability and strength of GBs, the better the stabilizing and strengthening effects of alloying elements were revealed.

Atomistic simulations of ∑3 [110](111) grain boundary in diamond: Structure, stability, and properties

AbstractGrain boundaries play a pivotal role to influence the stability and mechanical properties of the diamond derived from chemical vapor deposition; therefore, the scrutiny of grain boundaries has aroused intensive research attention. In the present study, the structure, stability, mechanical, electronic properties, and concentration effect of the ∑3 [110](111) grain boundary in diamond has been investigated using density functional theory calculations. The grain boundary energy (), phonon dispersion relation, and charge density distribution clearly indicate that the ∑3 [110](111) grain boundary in diamond is stable. The elasticity and electronic properties of the diamond with the ∑3 [110](111) grain boundary closely resemble the pristine diamond. En route to determining the thermal stability of the grain boundary, molecular dynamics simulations using ReaxFF were performed at various temperatures. In addition, Young's modulus was calculated by applying an increasing 5.6% uniaxial strain along the z‐direction during the molecular dynamics simulations using ReaxFF. The ReaxFF simulations further demonstrate that the grain boundary is found to be thermally stable even at 1773.15 K.

A Novel Perspective on Surface Modification of LiNi0.5Co0.2Mn0.3O2 Cathode Material for Lithium‐Ion Batteries

AbstractHigh nickel ternary cathode materials have caught much consideration because of their remarkable energy density, cycling stability, and low pollution. However, the materials with the instability of nickel are prone to crack during long‐term cycling processes; secondly, the residual alkali on the surface of materials would react with the electrolyte to corrode the electrode. To solve the above problems, the particle surface is usually coated with a protective layer of Al2O3 with good compatibility and thermal stability. But this method is relatively complicated and produces toxic organic solvents. In addition, the thick coating layer increases the charge transport resistance and decreases the lithium‐ion transport rate. Herein, we design a novel surface modification strategy: nano‐Al2O3 is loaded on the micro‐particles to form a series of stable points to improve the stability of the interface boundary, while the charge transmission impedance does not change significantly. As a result, the lithium‐ion transmission coefficient is greatly improved, whose capacity retention rate is still up to 86.17 % at 1 C after 100 cycles. This surface modification strategy is simple to operate and low in cost, which could meet industrial mass production.

Interface dynamics and flow fields’ structure under thermal heat flux, thermal conductivity, destabilizing acceleration and inertial stabilization

Interfaces and interfacial mixing are omnipresent in fluids, plasmas, materials in vastly different environments. A thorough understanding of their fundamentals is essential in many areas of science, mathematics, and technology. This work focuses on the classical problem of stability of a phase boundary that is a subject to fluxes of heat and mass across it for non-ideal thermally conducting fluids. We develop a rigorous theory resolving challenges not addressed before, including boundary conditions for thermal heat flux, structure of perturbation waves, and dependence of waves coupling on system parameters in a broad range of conditions. We discover the novel class of fluid instabilities in the three regimes—advection, diffusion, and low Mach—with properties that were never earlier discussed and that are defined by the interplay of the thermal heat flux, thermal conductivity and destabilizing acceleration with the inertial stabilization. We reveal the parameter controlling transitions between the regimes through varying the initial conditions. We find that the interface stability is set primarily by the macroscopic inertial mechanism balancing the destabilizing acceleration. The thermal heat flux and the microscopic thermodynamics create vortical fields in the bulk. By linking micro to macro scales, the interface is the place where balances are achieved.Article highlightsThis work yields the general theory of interface dynamics in a broad range of conditions.The interplay is explored of inertial stabilization, destabilizing acceleration, thermal conductivity and heat flux.We discover that interface is the place where balances are achieved through linking micro to macro scales.

Experimental Studies of Nonlinear Dynamics of Asynchronous Electric Drives with Variable Load

This article presents the results of the analysis of experimental data that were obtained during industrial tests of an adjustable asynchronous traction electric drive of a shuttle car for the mining industry. During these tests, by changing the parameters of the stator voltage, the stator currents of the induction motor were optimized when the load changes over a wide range (from −1.5 Tn to + 1.5 Tn). The authors managed to significantly reduce the effective values of the stator currents of the motor, but at the same time it was found that, with the load and even the rate of its change, oscillations of the effective values of currents with variable amplitude and frequency occur. It turned out to be very difficult to explain these oscillations and the variability of their parameters using traditional mathematical methods for describing processes in asynchronous electric motors. Vector equations and diagrams are valid only at constant frequencies of the stator voltage and, in the modes of their significant changes, which exist during self-oscillations of the effective values of the motor stator current, their error is very large. To analyze the conditions of the self-oscillations, it was proposed to use nonlinear continuous transfer functions that describe the formation of torque in induction motors. The article shows how such transfer functions make it possible to take into account the influence of the load torque and the speed of its change on the parameters of the self-oscillations of the effective values of the stator current of asynchronous electric drives experiencing such loads. The article proposes a qualitative analysis of the results of experiments carried out on real tracks of the movement of the shuttle car. The analysis of experimental data confirmed the effectiveness of using nonlinear transfer functions to evaluate the dynamics of asynchronous electric drives and the sufficient accuracy of the proposed method. In the course of research, it is shown how the conditions of the boundary stability of the drive depend on external loads that change the nonlinear transfer function of the induction motor. As a result, it was found that the condition of boundary stability and the parameters of the self-oscillations are affected not only by the magnitude, but also by the rate of load change. The article made assumptions about possible options for the effective correction of asynchronous electric drives experiencing variable loads.

Uncovering the softening mechanism and exploring the strengthening strategies in extremely fine nanograined metals: A molecular dynamics study

• Softening and strengthening in extremely fine nanograined metals are governed by grain boundary (GB) stability. • Atomic sliding in GB layer induces the softening while dislocation activity in grain interior plays the role of coordinator to fit the deformation dominated by GBs. • The solid solution exerts the negative strengthening (the softening) effect to the nanoscale metals. • The GB segregation gives rise to a notable improvement in strength, and this improvement can be further enhanced by optimizing solute concentration and GB excess. The strength of polycrystalline metals increases with decreasing grain size, following the classical Hall-Petch relationship. However, this relationship fails when softening occurs at very small grain sizes (typically less than 10 to 20 nm), which limits the development of ultrahigh-strength materials. In this work, using columnar-grained nanocrystalline Cu-Ag ‘samples’, molecular dynamics simulations were performed to investigate the softening mechanism and explore the strengthening strategies (e.g., formation of solid solution or grain boundary (GB) segregation) in extremely fine nanograined metals. Accordingly, the softening of pure metals is induced by atomic sliding in the GB layer, rather than dislocation activities in the grain interior, although both occur during deformation. The solid solution lowers the stacking fault energy and increases the GB energy, which leads to the softening of NC metals. GB segregation stabilizes GB structures, which causes a notable improvement in strength, and this improvement can be further enhanced by optimizing the solute concentration and GB excess. This work deepens the understanding of the softening mechanism due to atomic sliding in the GB layer and the strengthening mechanism arising from tailoring the GB stability of immiscible alloys and provides insights into the design of ultrahigh-strength materials.

Stability of phase boundary between L12-Ni3Al phases: A phase field study

The evolution and stability of phase boundaries (PBs) between L12-Ni3Al phases in Ni75Al11V14 alloy aged at 1050k was studied using the microscopic equation phase-field method (MPFM). Four types of L12 PBs were found through atomic configuration, migration and occupation probability (OP). The evolution of metastable PBs and formation of stable PBs were tracked and explored, the effect of coherent elastic strain energy on the evolution and stability of PBs is also investigated by coupling the micro elastic theory with MPFM. In addition, the formation enthalpy, interface energy and electron distribution function of PBs are calculated by FP method, and the stability of PBs is further quantitatively predicted from the perspective of thermodynamic energy and gaining or losing electrons. FP calculation results are consistent with MPFM prediction, and the essence of the transition and stability of PBs is revealed based on the atomic migration dynamics, interface evolution morphology and thermodynamic energy. This is an effective method to further explore the formation and structure of PBs and design high stability PBs.

Rainfall infiltration boundary conditions and stability of a fractured-rock slope based on a dual-continuum model

Rainfall infiltration boundary conditions and stability of a fractured-rock slope based on a dual-continuum model

Boundary regularity and stability for spaces with Ricci bounded below

This paper studies the structure and stability of boundaries in noncollapsed {{,mathrm{RCD},}}(K,N) spaces, that is, metric-measure spaces (X,{mathsf {d}},{mathscr {H}}^N) with Ricci curvature bounded below. Our main structural result is that the boundary partial X is homeomorphic to a manifold away from a set of codimension 2, and is N-1 rectifiable. Along the way, we show effective measure bounds on the boundary and its tubular neighborhoods. These results are new even for Gromov–Hausdorff limits (M_i^N,{mathsf {d}}_{g_i},p_i) rightarrow (X,{mathsf {d}},p) of smooth manifolds with boundary, and require new techniques beyond those needed to prove the analogous statements for the regular set, in particular when it comes to the manifold structure of the boundary partial X. The key local result is an varepsilon -regularity theorem, which tells us that if a ball B_{2}(p)subset X is sufficiently close to a half space B_{2}(0)subset {mathbb {R}}^N_+ in the Gromov–Hausdorff sense, then B_1(p) is biHölder to an open set of {mathbb {R}}^N_+. In particular, partial X is itself homeomorphic to B_1(0^{N-1}) near B_1(p). Further, the boundary partial X is N-1 rectifiable and the boundary measure is Ahlfors regular on B_1(p) with volume close to the Euclidean volume. Our second collection of results involve the stability of the boundary with respect to noncollapsed mGH convergence X_irightarrow X. Specifically, we show a boundary volume convergence which tells us that the N-1 Hausdorff measures on the boundaries converge to the limit Hausdorff measure on partial X. We will see that a consequence of this is that if the X_i are boundary free then so is X.

A State-Dependent Impulsive Nonlinear System with Ratio-Dependent Action Threshold for Investigating the Pest-Natural Enemy Model

Based on the Lotka–Volterra system, a pest-natural enemy model with nonlinear feedback control as well as nonlinear action threshold is introduced. The model characterizes the implementation of comprehensive prevention and control measures when the pest density reaches the nonlinear action threshold level depending on the pest density and its change rate. The mortality rate of the pest is a saturation function that strictly depends on their density while the release of natural enemies is also a nonlinear pulse term depending on the density of real-time natural enemies. The exact impulsive and phase sets are given. The definition and properties of the Poincaré map corresponding to the pulse points on the phase set are provided. We investigate the existence and stability of boundary and interior order-1 periodic solution. The theoretical analysis developed in the present paper combined with nonlinear controlling measures as well as nonlinear action threshold methods and techniques laid the foundation for the establishment and analysis of other state-dependent feedback control models.

Широтная и амплитудная модуляция тока пучка для управления его мощностью в течение импульса субмиллисекундной длительности

Methods for controlling the power electron beam in a source based on a low-pressure arc discharge with layer stabilization of the emission plasma boundary are described. The control is carried out by the method of amplitude and latitude modulation within the duration of the beam current pulse with a time resolution of 10 μs at a submillisecond pulse duration. Two ways to control the power of the electron beam are implemented: the first one is based on changing the concentration of the emission plasma by modulating the arc discharge current, the second method uses grid control (the mode of operation of the plasma triode) at the constant discharge current. Simplified diagrams of the power supply sources of the discharge and intergrid control voltage, typical oscillograms of the main currents of the discharge system, a graph of a quick-acting power change, and a control characteristic of a plasma triode are presented.

Interface dynamics with heat and mass fluxes

Unstable interfaces ubiquitously occur in fluids, plasmas and materials, from the celestial event of supernova to the atomic level of plasma fusion. Knowledge of their fundamentals is in demand in science, mathematics, and engineering. Our work considers the classical problem of stability of a phase boundary having heat and mass fluxes across it and yields a rigorous theory resolving challenges not addressed before. By employing self-consistent boundary conditions for thermal heat flux, by identifying the perturbation waves' structure, and by thoroughly investigating the dependence of waves' coupling on system parameters, we discover new fluid instabilities in the advection, diffusion and low Mach regimes. We find that the interface stability is set primarily by the interplay of macroscopic inertial stabilization with destabilizing acceleration, and the microscopic thermodynamics and thermal heat flux creates vortical fields in the bulk.

Coexistence of the Three Trophic Levels in a Model with Intraguild Predation and Intraspecific Competition of Prey

The model of a three-trophic community with intraguild predation is considered. The system consists of three coupled ordinary differential equations describing the dynamics of resource, prey and predator. Models with intraguild predation are characterized by predators that feed on resource of its own prey. A number of similar models with different functional responses have been proposed. In contrast to previous works, in the present model, the predator functional response to the resource is differed from that to the prey. The model takes into account an intraspecific competition of prey to stabilize the system in resource-rich environment. Conditions of existence and local stability of non-negative solutions are established. The possibility of Hopf bifurcation around positive equilibrium with consumption rate as bifurcation parameter is studied. For the model, in the plane of the consumption and predation rates, the regions of existence and stability of boundary and internal equilibria are constructed. Numerical simulations show that the region of equilibrium coexistence of populations is increased due to the inclusion of prey self-limitation in the model. Bifurcation diagrams confirm the stabilizing effect of intraspecific competition of prey on the system dynamics in resource-rich environment.

Effects of impurity elements on SiC grain boundary stability and corrosion

Effects of impurity elements on SiC grain boundary stability and corrosion

Electromagnetic Wave Equation Approximation using FDTD method on Conductivity Material

FDTD is a method that is applied in the simulation of electromagnetic waves. This study aims to simulate the propagation of electromagnetic waves on a material with conductivity and permittivity on the plate. The approximate form of Maxwell’s equations can be used to describe discrete electromagnetic waves. Signal analysis in the form of electromagnetic waves using position domains for magnetic field H and electric field E. By taking into consideration boundary conditions, stability, and boundary conditions, the proposed research employs the basic concept of differential equation method. The simulation results show that materials with high conductivity will cause the waves to decay. Under certain conditions, the relationship between the shape of the field to changes in conductivity and permittivity of the material is needed in the analysis process.

Effects of Grain Size and Grain Boundary Stability on Mechanical and Fatigue Properties of Nanocrystalline Nickel Thin Films

Effects of Grain Size and Grain Boundary Stability on Mechanical and Fatigue Properties of Nanocrystalline Nickel Thin Films

3D Wavelet Finite-Element Modeling of Frequency-Domain Airborne EM Data Based on B-Spline Wavelet on the Interval Using Potentials

We present a wavelet finite-element method (WFEM) based on B-spline wavelets on the interval (BSWI) for three-dimensional (3D) frequency-domain airborne EM modeling using a secondary coupled-potential formulation. The BSWI, which is constructed on the interval (0, 1) by joining piecewise B-spline polynomials between nodes together, has proved to have excellent numerical properties of multiresolution and sparsity and thus is utilized as the basis function in our WFEM. Compared to conventional basis functions, the BSWI is able to provide higher interpolating accuracy and boundary stability. Furthermore, due to the sparsity of the wavelet, the coefficient matrix obtained by BSWI-based WFEM is sparser than that formed by general FEM, which can lead to shorter solution time for the linear equations system. To verify the accuracy and efficiency of our proposed method, we ran numerical experiments on a half-space model and a layered model and compared the results with one-dimensional (1D) semi-analytic solutions and those obtained from conventional FEM. We then studied a synthetic 3D model using different meshes and BSWI basis at different scales. The results show that our method depends less on the mesh, and the accuracy can be improved by both mesh refinement and scale enhancement.

Subsidence Monitoring Base on SBAS-InSAR and Slope Stability Analysis Method for Damage Analysis in Mountainous Mining Subsidence Regions

Surface subsidence caused by coal mining has a great impact on the geological and ecological environments and causes damage to houses, roads, and industrial buildings. In order to understand the subsidence pattern in the mountainous mining regions, three mining faces of the Zhangjiamao mining area in the north of Shaanxi province, northwestern China are taken as case study. Firstly, the small baseline subset (SBAS) technology is used to process 12 images obtained in the mining area to investigate the subsidence data from December 2019 to April 2020. The boundary of surface deformation of the mining area interpreted by the SBAS-InSAR technology is inconsistent with the theoretical boundary suggested by coal mine subsidence theories. Especially, there are some areas in which the real subsidence are larger than estimated area. This discrepancy must be corrected as steep slopes near the theoretical boundary may increase the likelihood of landslides. Our research indicates that: (1) The accumulated displacement and the maximum deformation rate reached −120.759 mm and −270.012 mm/yr in the study area, and the subsidence boundary of the three mining faces is revealed; (2) the combination of the predicted boundary and slope stability analysis can effectively identify the landslide region at the edge of subsidence boundary; (3) the field surveys have proved the effectiveness of this method. The mining area subsidence revealed by our research helps to further understand the impact of land subsidence caused by mining in the mountainous areas and provides a practical method to predict subsidence boundaries and the likelihood for landslides.