Effect Of Structural Inhomogeneity Research Articles

Effects of structural inhomogeneity on equilibration processes in Langevin dynamics.

In recent decades, computer experiments have led to an accurate and fundamental understanding of atomic and molecular mechanisms in fluids, such as different kinds of relaxation processes toward steady physical states. In this paper, we investigate how exactly the configuration of initial states in a molecular-dynamics simulation can affect the rates of decay toward equilibrium for the widely known Langevin canonical ensemble. For this purpose, we derive an original expression relating the system relaxation time τ_{sys} and the radial distribution function g(r) in the near-zero and high-density limit. We found that, for an initial state which is slightly marginally inhomogeneous in the number density of atoms, the system relaxation time τ_{sys} is much longer than that for the homogeneous case and an increasing function of the Langevin coupling constant, γ. We also found, during structural equilibration, g(r) at large distances approaches 1 from above for the inhomogeneous case and from below for the macroscopically homogeneous one.

Effect of Structural Inhomogeneity and Nonreciprocal Effects in the Interaction of Macroparticles on the Dynamic Properties of a Dusty Plasma Monolayer

Effect of Structural Inhomogeneity and Nonreciprocal Effects in the Interaction of Macroparticles on the Dynamic Properties of a Dusty Plasma Monolayer

Формирование Ферми-дуг при T<< T-=SUB=-c-=/SUB=- в окрестности d-волновых узлов структурно неоднородных ВТСП YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-6.92-=/SUB=-

The effect of structural inhomogeneity on the superconducting gap near d-wave for optimally doped high-Tc superconductors YBa2Cu3O6.92 sites is considered. For this purpose, the heat capacity was investigated in the temperature range T = 2-10 K and in magnetic fields H = 0-9 T for a series of fine-crystalline samples with different degrees of controlled structural disordering. The information on the features of superconducting gap near d-wave sites in structurally disordered samples is obtained. It is shown that the d-wave sites inherent in an ideal crystal structure under the influence of structural disorder are modified with the formation of small Fermi arcs in the vicinity of nodal points at T << Tc, not covered by a superconducting gap. In this case, the gap itself remains at T ≤ Tc in other directions of the Brillouin zone and coexists with the Fermi arcs. This transformation is accompanied by an increase in the steepness of the nodal slope, a decrease of the Volovik effect, and the generation of a linear term γ (0) T of the metallic type in the temperature dependence of heat capacity, which should not be present in superconductors with an ideal crystal structure and the nature of which has not yet been established.

Effects of structural inhomogeneities on the steel balls resistance to loading

When conducting impact tests of protective glasses, nonunique cases of destruction of balls made of bearing steel ShKh15 were recorded. The causes of their destruction were determined. The state of the material was studied by fractographic and metallographic analysis, hardness and microhardness measurement. In the structure of the metal of all the balls, no critical defects were found such as flockens, shells and microcracks, but adverse factors were detected in the microstructure of the material, namely, the presence of fineneedle martensite with excessive carbides. It is established that the detected structural factors lead to liability to brittle fracture, an increase in the hardness of the material, a decrease in plasticity. To prevent brittle fracture of the balls and provide a reserve of plasticity of steel ShKh15 at high shock loads assessment calculations of ductility coefficient were made; and it was recommended to limit the maximum hardness of the material critical value HV=5.70 HPa (54 HRC), with the corresponding plasticity coefficient equal to 0.8.

Effect of Structural Inhomogeneities on the Spin-Wave and Magnetic Properties of Monocrystalline Spinel Ferrite Films in the Microwave Range

We have studied magnetic parameters of monocrystalline manganese spinel ferrite films differing in composition and structural perfection and assessed the effect of dislocation distribution on the frequency dependence of the ferromagnetic resonance (FMR) linewidth in the microwave range. The results demonstrate that, if an external magnetic field is perpendicular to the film surface, electron paramagnetic resonance (EPR) absorption lines correspond to ferromagnetic and spin wave resonances (SWRs). SWR is due to nanostructural surface inhomogeneities. The EPR spectrum of a tangently magnetized film represents a single dipole exchange oscillation spectrum. Parameters of dipole and exchange modes have been determined.

Design of monomeric units for rigid aromatic polymers

The effect of structural inhomogeneities on the equilibrium flexibility of rigid-chain aromatic polymers containing complex condensed cycles in the main chain has been studied. The non-flatness of complex condensed cycles leads to a significant decrease in the equilibrium flexibility of rigid-chain polymers based on them and, consequently, to a deterioration of their mechanical properties. It is shown that the non-planarity of these cycles can reduce the Kuhn segment by several times. The introduction of phenyl substituents into condensed cycles reduces the non-planarity of such cycles and makes it possible to obtain a polymer with sufficiently high physical characteristics.

Role of structural inhomogeneities in resting-state brain dynamics.

Brain imaging methods allow a non-invasive assessment of both structural and functional connectivity. However, the mechanism of how functional connectivity arises in a structured network of interacting neural populations is as yet poorly understood. Here we use a modeling approach to explore the way in which functional correlations arise from underlying structural connections taking into account inhomogeneities in the interactions between the brain regions of interest. The local dynamics of a neural population is assumed to be of phase-oscillator type. The considered structural connectivity patterns describe long-range anatomical connections between interacting neural elements. We find a dependence of the simulated functional connectivity patterns on the parameters governing the dynamics. We calculate graph-theoretic measures of the functional network topology obtained from numerical simulations. The effect of structural inhomogeneities in the coupling term on the observed network state is quantified by examining the relation between simulated and empirical functional connectivity. Importantly, we show that simulated and empirical functional connectivity agree for a narrow range of coupling strengths. We conclude that identification of functional connectivity during rest requires an analysis of the network dynamics.

Magnetocaloric properties of distilled gadolinium: Effects of structural inhomogeneity and hydrogen impurity

High-purity Gd prepared by distillation is a structurally inhomogeneous system consisting of needle-shaped crystals of cross section 0.5–2.5 μm with near-c-axis orientation embedded in a matrix of nanosized (30–100 nm) grains. By measuring the magnetocaloric effect (MCE) directly, we find that the MCE values differ markedly for the plate-shaped samples cut out of a distillate along and perpendicular to the crystals. The effect of small controlled amounts of impurity (hydrogen) on the properties of distilled Gd is further studied. We observe opposite trends in the MCE response to hydrogen charging with respect to the crystal's orientation within the samples and discuss mechanisms interrelating the unique structural morphology with the impurity behavior. As an overall assessment, the Curie temperatures of α-GdHx solid solutions increase from 291 K up to 294 K when increasing hydrogen concentration x from 0 to 0.15. Hydrogenation is found to broaden the ferromagnetic-to-paramagnetic phase transition. Hydrogen-containing specimens demonstrate reversibility of MCE at these temperatures.

Effect of Structural Inhomogeneity on Mechanical Behavior of Injection Molded Polypropylene Investigated with Microbeam X-ray Scattering

Relationship between the structure of injection-molded isotactic polypropylene and its tensile mechanical properties, necking and fracture behaviors in particular, was investigated in terms of micrometer-scale structural inhomogeneity of nanometer- and subnanometer-scale structures. To clarify the micrometer-scale inhomogeneity, we employed scanning microbeam wide-angle X-ray diffraction and small-angle X-ray scattering technique. Four isotactic polypropylene samples were studied, produced using different injection-condition and thermal treatments. The results of scanning microbeam X-ray scattering measurements showed the presence of two types of micrometer-scale structural inhomogeneity in addition to the orientation of molecules: the distribution of polymorphs and of crystalline ordering. The results of scanning microbeam X-ray scattering of deformed sample showed the disappearance of the β-form isotactic polypropylene crystals at the outer regions accompanied by the plastic deformation. It is indicated that the inhomogeneous distribution of crystalline ordering and the existence of different polymorphs are highly related to the tensile mechanical behavior.

Effect of resistive barrier location on the relationship between T-wave alternans and cellular repolarization alternans: a 1-D modeling study

Structural inhomogeneities in cardiac tissue have been associated with increased cellular repolarization alternans in animal experiments and increased T-wave alternans (TWA) in clinical studies. However, the effect of structural inhomogeneities on the relationship between cellular alternans and TWA has not been thoroughly investigated. We created 1-dimensional multicellular fiber models with and without a resistive barrier in various fiber regions and paced each model to induce cellular alternans. The models demonstrate that a resistive barrier in one fiber region substantially alters cellular repolarization alternans throughout the fiber. A midmyocardial or subepicardial barrier increase both TWA amplitude and maximum cellular alternans magnitude, relative to a fiber without a barrier. In addition, a direct relationship exists between TWA amplitude and maximum cellular alternans magnitude, which was highly dependent on barrier location. These results suggest that the position of a structural inhomogeneity within the myocardium may have substantial effects on dynamic repolarization instability and arrhythmogenicity.

Structural defects in CVD ZnS

The structure of polycrystalline zinc sulfide grown by chemical vapor deposition has been studied, and stacking faults have been revealed in the cubic matrix of crystals, which lead to a striated subgranular structure. During synthesis, mixed-phase crystals are formed as a result of the characteristic polymorphism. The effect of structural inhomogeneities on the optical loss in the material in the visible range is analyzed.

A study of deformation and disruption in category X80 strip and tube metal fabricated by thermomechanical treatment

We perform an analysis of the requirements of domestic and international standards regarding Category X80 high-strength pipe steel, as well as a comprehensive assessment of the mechanical properties and functional characteristics of 27.7-mm-thick metal strip and arc-welded pipe made from steel in this strength category. We show that substantial improvement of test methods and test result assessment criteria is reqiured. Important items include an analysis of resistance to brittle fracture and the effect of structural inhomogeneity of the material on fracture resistance.

Effect of structural inhomogeneities on the dynamic stability of the photoelectric response of Cd0.9Zn0.1Te crystals

I(t)-dI/dt phase diagrams obtained under local and integral photoexcitation have been used to investigate the stability of the dynamic photoresponse of Cd0.9Zn0.1Te crystals containing two-dimensional structural defects and defect complexes. The results demonstrate that the diagrams shed light on the development and loss of the dynamic stability of the photoelectric response under photoexcitation with rectangular light pulses in combination with linear heating in the temperature range 293–450 K.

Prepeak in the structural factor. Inhomogeneous packings of Lennard-Jones atoms

This work reports on the effects of structural inhomogeneities within the models of spherical atomic packings on the radial distribution function (RDF) and the structural factor (SF). Models of inhomogeneous packings were constructed by removing some atoms from homogeneous packing according to a predetermined template. Thus various additional voids, leading to specific structural correlations of atoms on a middle scale (several atomic sizes), are introduced in the model. A dense noncrystalline packing of 27,000 Lennard-Jones atoms serves as the initial system. Three various templates were used, and models containing different fractions of additional voids were constructed with each of these templates. It is demonstrated that RDF is only slightly sensitive to such inhomogeneities; in contrast, the SF has additional peaks at small q, these peaks being notable even after removal of a small fraction of atoms. Some models yield a single narrow prepeak, which is akin to that observed in diffraction experiment for some glasses.

Developing Algorithms for Estimating Strength on the Base of Imitating Structural Model of Acoustic Emission. II. Effect of Structural Inhomogeneity of a Material

The first part was dedicated to the theoretical basis for estimating strength characteristics of materials developed from the ideas that had been put forth in the earlier publications [1–5]. A formalized technique based on the earlier studies [2, 3] was also discussed. Its main assumption was that the material was homogeneous, and it enabled one to process real experimental data on a computer. This paper is devoted to the effect of structural inhomogeneities of materials, which is identified with a large spread of the parameter \(\overline \omega \). This factor must be taken into account in a number of cases when the assumption that a tested body is structurally homogeneous does not apply.

Transition from thermally activated to regular flow of magnetic flux vortices in HTSC

The effect of structural inhomogeneities in a superconductor on a vortex medium flow in weak magnetic fields at temperatures varying from 78 to 83 K for various bias current densities is investigated by using transport measurements of Bi2Sr2CaCu2O8+x thin-film microbridges. The results obtained are analyzed on the basis of the theories of flux creep and the regular flow of vortices. It is shown that the current dependences of the effective potential for vortex pinning can be satisfactorily described in the framework of two statistical models, one of which was proposed earlier by the authors. Both models cover the regimes of thermally activated and regular flow of vortices as limiting cases. The wide transition region in which the creep and regular vortex flow processes simultaneously occur due to a large dispersion in the pinning energy distribution. It is found that when the magnetic field exceeds a certain value, the average value and dispersion of the pinning potential decrease sharply, so that the conditions of regular flow set in even for small values of the bias current. This fact is attributed to the destruction of vortex lines into two-dimensional segments.

Effect of structural inhomogeneity of material on the strength of soldered joints

1. The inhomogeneity of the chemical composition that appears in steel on the boundary with the soldered joint markedly worsens the strength of the soldered joint. 2. In order to prevent early fracture of the soldered structure, we developed theoretical and experimental substantiation for designing the soldering process, which consists of allowance for the special features of the design of the structure and the mechanical, thermophysical, and rheological properties of the materials and the solder.

Beyond the Fisher model of grain boundary diffusion: effect of structural inhomogeneity in the bulk

An extension of the Fisher model of grain boundary diffusion is suggested, in which the diffusion along the short-circuit paths in the bulk of the crystalline grains (dislocations, subgrain boundaries, interphase boundaries in the lamellar structures) is taken into account. In the framework of the suggested model the bulk is treated as a stochastic mixture of defect-free crystalline regions and regions of bad material inside the short-circuit paths. The Harrison classification of the diffusion regimes is extended to the new D-regime, in which the kinetics of the penetration of the diffusing element along the grain boundaries is dominated by diffusion along these short-circuit paths. Three different kinetic modes during the grain boundary diffusion in the D-regime are uncovered: for the short annealing times the penetration kinetics follows the Whipple law, but with the bulk diffusion coefficient substituted by g 2 D d, for the intermediate annealing times the penetration distance along the grain boundary is a weak function of time and for the long times the Whipple law is valid again, but with the bulk diffusion coefficient substituted by gD d, where g and D d are the volume fraction of the material inside the short-circuit paths and the diffusion coefficient along them, respectively. The applications of the suggested model to the analysis of experimental data are discussed.

Inhomogenous broadening in quantum well lasers

The effect of structural inhomogeneities in multi-quantum-well lasers caused by composition and well width fluctuations on the line-shape and gain of the lasers is discussed based on gaussian and uniform distribution models. Quantitative results of wide applicability are deduced. The results show that the structural inhomogeneities will reduce the gain and broaden the lineshape.

Lifetime Prediction and Reliability Evaluation of Si3N4 Ceramic

In this study, non-equilibrium statistical physics is used to estimate the time-dependent fracture of inhomogeneous Si3N4 ceramic. The effects of structural inhomogeneity on mechanical properties of the Si3N4 ceramic are discussed. The numerical calculations show that the average lifetime will increase by means of introducing suitable inhomogeneity in materials, but it is not monotonous.