Contact Boundary Research Articles

Electron acceleration driven by the lower-hybrid-drift instability

Context.Density inhomogeneities are ubiquitous in space and astrophysical plasmas, particularly at contact boundaries between different media. They often correspond to regions that exhibit strong dynamics across a wide range of spatial and temporal scales. Indeed, density inhomogeneities are a source of free energy that can drive various instabilities such as the lower-hybrid-drift instability, which, in turn, transfers energy to the particles through wave-particle interactions and eventually heats the plasma.Aims.Our study is aimed at quantifying the efficiency of the lower-hybrid-drift instability to accelerate or heat electrons parallel to the ambient magnetic field.Methods.We combine two complementary methods: full-kinetic and quasilinear models.Results.We report self-consistent evidence of electron acceleration driven by the development of the lower-hybrid-drift instability using 3D-3V full-kinetic numerical simulations. The efficiency of the observed acceleration cannot be explained by standard quasilinear theory. For this reason, we have developed an extended quasilinear model that is able to quantitatively predict the interaction between lower-hybrid fluctuations and electrons on long time scales, which is now in agreement with full-kinetic simulations results. Finally, we apply this new, extended quasilinear model to a specific inhomogeneous space plasma boundary, namely, the magnetopause of Mercury. Furthermore, we discuss our quantitative predictions of electron acceleration to support future BepiColombo observations.

A numerical study of the expansion of a gas-particles mixture with axial symmetry

The article deals with the study of new phenomena that accompany the free or wall-bounded expansion of a nonequilibrium in terms of velocities and temperatures mixture of gas and particles of various sizes with axial symmetry. The dynamics of the gas suspension is considered in the multifluid model of a calorically perfect inviscid gas and incompressible monodisperse spherical particles. The Eulerian approach is used to describe the motion of each phase of the mixture. For numerical simulation, a hybrid large-particle method of the second order of approximation in space and time with nonlinear correction of artificial viscosity, an additive combination of fluxes, and a semi-implicit scheme for calculating interfacial friction and heat transfer are implemented. The efficiency and accuracy of the method for a two-dimensional problem with axial symmetry are confirmed by comparing the solutions obtained in a one-dimensional formulation in a cylindrical coordinate system. In the case of small particles (with a diameter of d = 0.1 µm), the relaxation time of the phases is much less than the characteristic time of the problem and the gas and particles mixture behaves as a homogeneous medium similar to the gas flow. For sufficiently large particles (d = 20 µm), the effects of the difference in the inertia of the phases and nonequilibrium, associated with the mismatch of the velocities and temperatures of the gas and particles, are manifested. These effects cause the splitting of the initial interface of the media into a contact discontinuity in the gaseous phase and the surface between the suspension and the pure gas (a jump in porosity). At subsequent moments, the flow pattern changes to the opposite, which is explained by the deceleration of the gas, the appearance of a reverse flow to the center of expansion due to rarefaction in the vicinity of the axis of symmetry, and the formation of a secondary shock wave. Then there are fluctuations with a change in the relative position of the phase boundaries. In this case, fractures of the gas contact trajectories (the break of the first derivative) are observed, which are associated with the passage of the shock wave reflected from the wall and the plane of symmetry. Over time, due to baroclinic instability (the mismatch of density and pressure gradients), vortex structures begin to appear at the interface boundaries. In addition, in the case of expansion of the gas suspension in a closed volume, a complex shock-wave structure is formed, due to multiple reflections of shock waves from the walls and their interaction with the contact surfaces. The practical significance of the results obtained is to identify the fundamental physical effects that should be taken into account when setting and solving problems in chemical technologies, pneumatic transport, and other areas. In addition, the numerical solutions can be useful in testing the resolution of other difference schemes for reproducing the vortex instability of contact boundaries and shock wave structures in the flows of relaxing gas suspensions.

Multilevel augmented Lagrangian solvers for overconstrained contact formulations

Multigrid methods for two-body contact problems are mostly based on special mortar discretizations, nonlinear Gauss-Seidel solvers, and solution-adapted coarse grid spaces. Their high computational efficiency comes at the cost of a complex implementation and a nonsymmetric master-slave discretization of the nonpenetration condition. Here we investigate an alternative symmetric and overconstrained segment-to-segment contact formulation that allows for a simple implementation based on standard multigrid and a symmetric treatment of contact boundaries, but leads to nonunique multipliers. For the solution of the arising quadratic programs, we propose augmented Lagrangian multigrid with overlapping block Gauss-Seidel smoothers. Approximation and convergence properties are studied numerically at standard test problems.

Influence of distinct type of imperfect interfaces on reflection and transmission phenomena of triclinic thermoelastic structure

This article is intended to observe the reflection and transmission phenomena of three-dimensional plane waves at the interfaces of two distinct anisotropic triclinic media under the context of the three-phase-lag model and Green-Naghdi theory. Distinct interfaces, viz. normal stiffness, transverse stiffness, thermal contact conductance, welded contact and slip boundaries have been considered to examine the impact of boundaries on the reflection and transmission phenomena of the thermoelastic waves. Mathematical expressions for the reflection and transmission coefficients of the waves have been acquired in the context of generalized thermoelasticity. Energy ratios for each of the reflected and transmitted waves have been derived to establish the energy conservation law at each of the incident angles. The findings of this study are elaborated in the form of graphical means.

Self-contact in closed and open Kirchhoff rods

We consider the problem of an impenetrable Kirchhoff rod in self-contact. The contact is assumed to be frictionless and of point-contact type. The self-contacted rod is modeled as a set of contact-free segments each having unknown length and connected in series with each other through frictionless hard-contact condition. The Landau–Lifshitz approach is used to express analytically the centerline of each contact-free segment in terms of unknown parameters which are obtained using the hard-contact condition at each contact point and boundary condition on the full rod. The presented formulation is applicable to both closed and open rods. For the open rod case, its two end cross-sections need not be parallel either. Numerical solution of following three example problems are presented both before and after self-contact: (i) twisting of a closed rod (ii) compression and twisting of a straight rod (iii) compression and twisting of a rod with opening angle. For the case of twisting of a closed rod in the pre-self-contact regime, we also derive a minimal set of three integral equations to obtain the ring’s buckled spatial configuration. We also point to a difficulty in numerical integration of the rod’s centerline torsion over the rod length whenever the torsion value becomes large locally: a finer discretization of the rod’s length is necessitated in such regions to obtain an accurate integral value. An analytical approximation of the torsion integral is derived in such regions to make the full numerical integration computationally efficient.

АППРОКСИМИРОВАННАЯ ОЦЕНОЧНАЯ ЗАВИСИМОСТЬ КАК ПАРАДИГМА ЭКСПЛУАТАЦИОННОЙ-РЫНОЧНОЙ СТОИМОСТИ

From the first days of operation, buildings and structures change under the influence of physical, mechanical and chemical factors, systematically reducing their operational characteristics, and therefore, it becomes necessary to determine the contact boundary, the area of ​​interaction of the effect of aging on cost and determine the parameters of compensation for operational and cost characteristics. The results of the research showed that, taking into account the cost of operating costs accumulated in the compensation fund, we get the opportunity to systematically regulate the technical condition, reduce the likelihood of accidents and reduce investment in operating costs, which are the loss of qualitative and quantitative building structures and engineering equipment of buildings. physical properties of the material of manufacture, for which it was justified the need to create, in appraisal practice, a type of - operating-market value to determine the true probable cost in the existing development, which is the sum of operating costs-aging to residual suitability.

Unmasking the Role of an Amorphous/Amorphous Interface and a Crystalline/Amorphous Interface in the Transition of Charge Carriers on the CN/SiO2/WO3 Photocatalyst.

Making heterojunctions between semiamorphous carbon nitride (CN) and other well-matched semiconductors (or even insulators) can solve many photocatalytic problems such as the recombination of charge carriers. However, many researchers encounter intrinsic problems including the lack of detailed information on contact boundaries in their heterojunctions, particularly in the amorphous/amorphous interface. In addition, the roles of contact boundaries in the photocatalytic mechanisms of many heterojunctions are still obscure. This study synthesized a novel CN/SiO2/WO3 photocatalyst having two different contact features by constructing an amorphous/amorphous (CN/SiO2) interface and a crystalline/amorphous (WO3/CN) interface to provide deep insights into heterojunction interfaces. SiO2 plays an exceptional role as a major component in the separation and migration of charge carriers. It not only modifies the texture but also transfers electrons. Surprisingly, the amorphous/amorphous interface shows an unpredicted capability for decreasing the recombination of electron-hole pairs. Based on capturing experiments and photoluminescence investigations, the amorphous/amorphous interface is unprecedently present in the production of hydroxyl radicals, while the crystalline/amorphous interface gives more superoxide radicals. This work provides a platform that opens a new perspective on the selection of mutual photocatalysts. It extends boundaries of conventional heterojunctions.

Effect of DC Bias on Dielectric Properties of NdFeO3

The solid-state synthesis method was used to prepare polycrystalline samples of NdFeO3. The effect of dc bias was observed on the dielectric properties of prepared NdFeO3 samples. Impedance was found to be comprised of three contributions corresponding to grains, grain boundaries, and sample-electrode contact. Temperature and frequency-dependent dielectric measurements revealed that the sample electrode contact and grain boundary responses get modified, while grain response remains unaltered under dc bias. Large dielectric permittivity (of the order of ∼103) in the entire studied temperature range (100 K–450 K) and at high frequencies (∼5 MHz) was found to remain unaffected under dc bias, suggesting that the large dielectric constant is an intrinsic property of NdFeO3.

Influence of technological modes of well operation on the efficiency of regulation of the process of waterflooding of gas condensate reservoirs by carbon dioxide

Using the main tools of hydrodynamic modeling, the study of the influence of production well operating parameters on the regulation effectiveness of the gas condensate reservoirs’ flooding process by injection of carbon dioxide at the initial gas-water contact has been carried out. The study has been undertaken for various values ​​of gas flow rate. The simulation results indicate a high technological efficiency of using carbon dioxide as an injection agent. High displacing properties of carbon dioxide provide an increase in the mobility of formation fluids (condensate, oil) and a decrease in the mobility of formation water. The introduction of the technology for injecting carbon dioxide into productive reservoirs at the initial gas-water contact provides the creation of additional hydrodynamic and filtration resistance on the path of formation water movement. Due to which the inflow of formation water into gas-saturated horizons is partially blocked and waterless operation of production wells is ensured during a longer period of further field development. Based on the results of processing the calculated data, the optimal value of the rate of natural gas production has been determined under the carbon dioxide injection into the productive reservoir at the boundary of the gas-water contact, outside of which the gas recovery factor changes insignificantly. At the time of the carbon dioxide breakthrough into the production wells, the optimal production rate of the production well is 55.93 th.m3/day. The predicted gas recovery factor for the given optimal value of the gas production rate is 64.99 %, and when developing for depletion it is 58.34 %. The results of the studies carried out indicate the technological efficiency of the introduction of technologies for injecting carbon dioxide into reservoirs, which are developed in a water drive in order to regulate the process of formation water flow into productive reservoirs and increase the final gas recovery factor.

High Order Godunov Type Multimesh Method for 3d Impact Problems of Elastoplastic Media

A numerical method for calculating the three-dimensional processes of impact interaction of elastoplastic bodies under large displacements and deformations based on the multi mesh sharp interface method and modified Godunov scheme is presented. To integrate the equations of dynamics of an elastoplastic medium, the principle of splitting in space and in physical processes is used. The solutions of the Riemann problem for first and second order accuracy for compact stencil for an elastic medium in the case of an arbitrary stress state are obtained and presented, which are used at the “predictor” step of the Godunov scheme. A modification of the scheme is described that allows one to obtain solutions in smoothness domains with a second order of accuracy on a compact stencil for moving Eulerian-Lagrangian grids. Modification is performed by converging the areas of influence of the differential and difference problems for the Riemann’s solver. The “corrector” step remains unchanged for both the first and second order accuracy schemes. Three types of difference grids are used. The first – a moving surface grid – consists of a continuous set of triangles that limit and accompany the movement of bodies; the size and number of triangles in the process of deformation and movement of the body can change. The second – a regular fixed Eulerian grid – is limited to a surface grid; separately built for each body; integration of equations takes place on this grid; the number of cells in this grid can change as the body moves. The third grid is a set of local Eulerian-Lagrangian grids attached to each moving triangle of the surface from the side of the bodies and allowing obtain the parameters on the boundary and contact surfaces. The values of the underdetermined parameters in cell’s centers near the contact boundaries on all types of grids are interpolated. Comparison of the obtained solutions with the known solutions by the Eulerian-Lagrangian and Lagrangian methods, as well as with experimental data, shows the efficiency and sufficient accuracy of the presented three-dimensional methodology.

Analysis of reflection and transmission phenomenon at distinct bonding interfaces in a rotating pre-stressed functionally graded piezoelectric-orthotropic structure

The present mathematical study analyzes the reflection and transmission phenomenon of a plane wave being incident at the distinct types of separating interfaces in a rotating pre-stressed structure with two semi-infinite media comprised of functionally graded piezoelectric-orthotropic (FGPO) materials. The effects of pre-stresses, rotation, and functional gradients along with six different types of boundaries viz. Normal stiffness boundary (NSB), Transverse stiffness boundary (TSB), Electric imperfection boundary (EIB), Complete debonded boundary (CDB), Slip boundary (SB), and Welded contact boundary (WCB) on reflection coefficients (RCs) of reflected qP, qSV, and EA waves and transmission coefficients (TCs) of transmitted qP, qSV, and EA waves have been examined with a comparative approach. Comparison of the obtained result with that of the case when rotating pre-stressed structure with two semi-infinite media is constituted of lesser anisotropic functionally graded transversely isotropic piezoelectric (FGTIP) materials is also carried out. To validate the findings energy-partitions of reflected and transmitted waves for both the cases of the structures have been computed and shown to observe the Law of conservation of energy. Further, on considering a grazing incident of qP wave in both the cases of structure, RCs and TCs for reflected and transmitted qSV waves and EA waves become zero, whereas the RC for reflected and TC of transmitted qP wave gets out of phase. Some important peculiarities have also been highlighted through numerical results, which serve as a salient feature of the study.

Fabrication and Characterization of Collagen/PVA Dual-Layer Membranes for Periodontal Bone Regeneration.

Guided tissue regeneration (GTR) is a promising treatment for periodontal tissue defects, which generally uses a membrane to build a mechanical barrier from the gingival epithelium and hold space for the periodontal regeneration especially the tooth-supporting bone. However, existing membranes possess insufficient mechanical properties and limited bioactivity for periodontal bone regenerate. Herein, fish collagen and polyvinyl alcohol (Col/PVA) dual-layer membrane were developed via a combined freezing/thawing and layer coating method. This dual-layer membrane had a clear but contact boundary line between collagen and PVA layers, which were both hydrophilic. The dual membrane had an elongation at break of 193 ± 27% and would undergo an in vitro degradation duration of more than 17 days. Further cell experiments showed that compared with the PVA layer, the collagen layer not only presented good cytocompatibility with rat bone marrow-derived mesenchymal stem cells (BMSCs), but also promoted the osteogenic genes (RUNX2, ALP, OCN, and COL1) and protein (ALP) expression of BMSCs. Hence, the currently developed dual-layer membranes could be used as a stable barrier with a stable degradation rate and selectively favor the bone tissue to repopulate the periodontal defect. The membranes could meet the challenges encountered by GTR for superior defect repair, demonstrating great potential in clinical applications.

Active source seismic imaging on near-surface granite body: case study of siting a geological disposal repository for high-level radioactive nuclear waste

In order to research whether it is suitable to set a geological disposal repository for high-level radioactive nuclear waste into one target granite body, two active source seismic profiles were arranged near a small town named Tamusu, Western China. The study area is with complex surface conditions, thus the seismic exploration encountered a variettraveltimey of technical difficulties such as crossing obstacles, de-noising harmful scattered waves, and building complex near-surface velocity models. In order to address those problems, techniques including cross-obstacle seismic geometry design, angle-domain harmful scattered noise removal, and an acoustic wave equation-based inversion method jointly utilizing both the and waveform of first arrival waves were adopted. The final seismic images clearly exhibit the target rock’s unconformable contact boundary and its top interface beneath the sedimentary and weathered layers. On this basis, it could be confirmed that the target rock is not thin or has been transported by geological process from somewhere else, but a native and massive rock. There are a few small size fractures whose space distribution could be revealed by seismic images within the rock. The fractures should be kept away. Based on current research, it could be considered that active source seismic exploration is demanded during the sitting process of the geological disposal repository for nuclear waste. The seismic acquisition and processing techniques proposed in the present paper would offer a good reference value for similar researches in the future.

О расчете размывающих скоростей при проектировании фильтрующих сооружений в связных грунтах

Objective: To develop a method for calculating erosion rates in the place of contact of filtering structures with cohesive soils. Methods: Previously at the VNIIG n. a. B. E. Vedeneev, hydrodynamic and strength criteria of contact suffusion were established concerning hydraulic structures. However, there were no calculated dependencies for determining the critical Reynolds number and, accordingly, the critical velocity for coarse-grained materials. Through special processing of experimental data on filtration in non-cavity drain fillers of various grades, it was possible to integrate numerous curves into a single one, making it possible to isolate the transient regime boundaries and obtain a formula for the critical Reynolds number. This made it possible to calculate the critical rate. As a result, a formula was obtained for calculating the erosion rate. Results: The calculated dependencies made it possible to determine the critical rate for the filler material and the erosion rate at the contact boundary between the filtering structure and the soil, based on the initial data of the coarse-grained material from which the filtering structures are made, and the characteristics of the soils in which they are built. Practical importance: The proposed calculation method made it possible to: 1) establish whether the manifestations of erosion by the filtration flow are possible in the place of contact of the filtering structure with the soil; 2) develop measures to eliminate erosion. Geotextile material can be laid along the border of the contact of the filtering structure with the soil, or a finer material can be used as a filler in the filtering structure, the actual filtration flow rates in which will be less than the erosional rates. In this case, the erosion rates in the place of contact with the finer material will increase.

Distinguishing open symplectic mapping tori via their wrapped Fukaya categories

In this paper, we present partial results towards a classification of symplectic mapping tori using dynamical properties of wrapped Fukaya categories. More precisely, we construct a symplectic manifold $T_\phi$ associated to a Weinstein domain $M$, and an exact, compactly supported symplectomorphism $\phi$. $T_\phi$ is another Weinstein domain and its contact boundary is independent of $\phi$. In this paper, we distinguish $\phi$ from $T_{1_M}$, under certain assumptions (Theorem 1.1). As an application, we obtain pairs of diffeomorphic Weinstein domains with the same contact boundary and whose symplectic cohomology groups are the same, as vector spaces, but that are different as Liouville domains. To our knowledge, this is the first example of such pairs that can be distinguished by their wrapped Fukaya category. Previously, we have suggested a categorical model $M_\phi$ for the wrapped Fukaya category $\mathcal{W}(T_\phi)$, and we have distinguished $M_\phi$ from the mapping torus category of the identity. In this paper, we prove $\mathcal{W}(T_\phi)$ and $M_\phi$ are derived equivalent (Theorem 1.9); hence, deducing the promised Theorem 1.1. Theorem 1.9 is of independent interest as it preludes an algebraic description of wrapped Fukaya categories of locally trivial symplectic fibrations as twisted tensor products.

A probabilistic optimal sensor design approach for structural health monitoring using risk-weighted [formula omitted]-divergence

This paper presents a new approach to optimal sensor design for structural health monitoring (SHM) applications using a modified f-divergence objective functional. One of the primary goals of SHM is to infer the unknown and uncertain damage state parameter(s) from the acquired data or features derived from the data. In this work, we consider the loss of boundary contact (a “gap”) between a navigation lock miter gate and the supporting wall quoin block at the bottom of the gate to be the damage state parameter of concern. The design problem requires the optimal sensor placement of strain gages to obtain the best possible inference of the probability distribution of the gap length using the data from the multi-dimensional strain-gauge array. Using the notion of f-divergences (measures of difference between probability distributions), a risk-adjustment is made by using functions that weigh the importance of acquiring useful information for a given true value of the state-parameter and using Bayesian optimization. For this case study of miter gate monitoring, a computationally expensive high-fidelity finite element model and its digital surrogate is employed to provide efficient, previously-validated data.

Analysis of the Heat Resistance of Multilayer Clothing Packages

Clothing fabrics are rarely used individually as the only layer protecting the body against different outer factors. Especially in cold climates, human attire is usually composed of several layers constituting together a multilayer set of textile materials. The purpose of this work was to analyse the impact of the number of layers on the thermal resistance of multi-layer clothing packages. Two-, three- and four-layer packages were made from woven fabrics of different structure. The packages were tested for thermal resistance by means of a Permetest instrument, made by Sensora (Czech Republic). The tests were carried out for individual materials forming the layers of the packages and for entire packages. Based on the research conducted and analysis of the results, it was found that the number of layers has a significant impact on the thermal resistance of multi-layer clothing packages. The thermal resistance of the multilayer textile packages measured was a little lower than the sum of the thermal resistance of the particular layers creating the packages. On the basis of the results, the thermal contact resistance and boundary effect were also discussed.

Highly Swollen Adsorption Layer Formed by Polymeric Friction Modifier Providing Low Friction at Higher Temperature

To reduce friction, especially under high-temperature conditions, an oil-soluble polymeric friction modifier (polymeric FM) with a methacrylate backbone and hydroxyl groups has been developed. It was designed to have high adsorption performance and to increase in size when dissolved in base oil as the temperature is increased. To investigate the temperature dependence of the structural and tribological characteristics of the adsorbed layer formed on a metal surface by the polymeric FM, neutron reflectometry measurements and nano-to-macro tribological tests were conducted. The measurements revealed that the polymeric FM adsorbed efficiently on a Cu surface and formed a 6.0-nm-thick adsorbed layer at 23 °C. This adsorbed layer was highly swollen, and its thickness became about three times larger at 100 °C. Nanoscale friction tests using an atomic force microscope showed that the swollen-state adsorbed polymeric FM layer exhibited low-friction and surface-protection performance at 100 °C. Macroscale friction tests revealed the tribological behaviour of an adsorbed polymeric FM layer in elastohydrodynamic lubrication and mixed lubrication regimes. At higher temperatures, the increase in shear resistance due to the effect of thin-film lubrication was suppressed by the weaker segment–segment interaction, causing the boundary contact of the adsorbed polymeric FM layer to have low frictional properties on both ball and disc surfaces. The low-friction mechanism of the adsorbed polymeric FM layer at higher temperatures was justified by associating the temperature with the layer thickness.

Laboratory earthquakes along faults with a low velocity zone: Directionality and pulse-like ruptures

Low velocity zone (LVZ) is a common structural feature in geological faults. To examine the effect of LVZ on faulting, a laboratory fault model considering the LVZ is constructed and loaded to different levels. Subsequently ruptures are triggered on one of its contact boundaries with the host rock. The bilateral rupture propagation along this laboratory fault that separates different materials shows distinct directionality in both rupture speeds and rupture modes. The rupture in the positive direction with respect to the fault is always crack-like growing at the Generalized Rayleigh (GR) wave speed. However, in the negative direction both stable and unstable slip pulses are observed. Higher load and thinner LVZ facilitate the unstable slip pulses. The trailing tip for both types of pulses propagates at the GR wave speed, the leading tip of the stable pulse propagates with the GR wave speed while that of the unstable pulse features a supershear speed.

Lattice-Preferred Orientation and Seismic Anisotropy of Minerals in Retrograded Eclogites from Xitieshan, Northwestern China, and Implications for Seismic Reflectance of Rocks in the Subduction Zone

Various rock phases, including those in subducting slabs, impact seismic anisotropy in subduction zones. The seismic velocity and anisotropy of rocks are strongly affected by the lattice-preferred orientation (LPO) of minerals; this was measured in retrograded eclogites from Xitieshan, northwest China, to understand the seismic velocity, anisotropy, and seismic reflectance of the upper part of the subducting slab. For omphacite, an S-type LPO was observed in three samples. For amphibole, the <001> axes were aligned subparallel to the lineation, and the (010) poles were aligned subnormal to foliation. The LPOs of amphibole and omphacite were similar in most samples. The misorientation angle between amphibole and neighboring omphacite was small, and a lack of intracrystalline deformation features was observed in the amphibole. This indicates that the LPO of amphibole was formed by the topotactic growth of amphibole during retrogression of eclogites. The P-wave anisotropy of amphibole in retrograded eclogites was large (approximately 3.7–7.3%). The seismic properties of retrograded eclogites and amphibole were similar, indicating that the seismic properties of retrograded eclogites are strongly affected by the amphibole LPO. The contact boundary between serpentinized peridotites and retrograded eclogites showed a high reflection coefficient, indicating that a reflected seismic wave can be easily detected at this boundary.