Effect Of Spatial Inhomogeneity Research Articles

Effect of Highly Crosslinked Domains on the Dimensions of Network Polymers

AbstractThe effect of spatial inhomogeneity on the dimensions of network polymers is investigated by using model networks containing highly crosslinked domains. It is found that the dimensions of network architecture consisting of densely crosslinked domains connected by long chains are larger than those of loosely crosslinked domains connected by short chains, given the cycle rank is the same. The cases with the domains connected by the domains are also investigated. In all cases, the dimensions are larger than the corresponding randomly crosslinked homogeneous networks. This is because the loosely crosslinked regions dominate the dimensions of network polymers. The master curve relationship found for the statistical networks is applicable also for the present types of spatial inhomogeneous network polymers when the cycle rank is increased to make the network well‐developed in a homologous series of networks.

On the Effects of Spatial Inhomogeneities of Buoyancy on the Dynamics of a Rotating Medium

On the Effects of Spatial Inhomogeneities of Buoyancy on the Dynamics of a Rotating Medium

Sea surface short-period roughness unsteadiness

The effect of spatial inhomogeneity of sea waves on the accuracy of determining the level of the sea surface is studied. Based on the data of direct wave measurements, the variability of statistical characteristics of sea waves on scales smaller than the size of the area illuminated by the radar was analyzed. The case is considered when radio sounding is carried out at low angles of incidence by radar located on a spacecraft. It is shown that the displacement of the distribution median of surface elevations, which determines the skewness bias, is alternating. The absolute value of the median shift reaches two percent of the significant wave height. In most cases, the signs of skewness bias and electromagnetic bias coincide.

Impurity bands in magnetic superconductors with spin density wave

Magnetic superconductors define a broad class of strongly correlated materials in which superconductivity may coexist with either localized or itinerant long-range magnetic order. In this work we consider a multiband model of a disordered magnetic superconductor which realizes coexistence of unconventional superconductivity and a spin-density-wave. We derive an exact T-matrix and compute a single particle density of states in this system. In a purely superconducting state the interband scattering potential leads to an appearance of the localized Yu–Shiba–Rusinov bound states. Our main finding is that in the fairly broad swath of the coexistence region superconductivity remains fully gapped despite the presence of the impurity bands. We also discuss the effects of spatial inhomogeneities on the density of states in strongly contaminated superconductors.

The quantum vortex states in extended Bose–Hubbard model: effects of lattice geometries, inter-particle interactions and spatial inhomogeneity

We study quantum vortex states of strongly interacting bosons in a two-dimensional rotating optical lattice. The system is modeled by Bose-Hubbard Hamiltonian with rotation. We consider lattices of different geometries, such as square, rectangular and triangular. Using numerical exact diagonalization method we show how the rotation introduces vortex states of different ground-state symmetries and the transition between these states at discrete rotation frequencies. We show how the geometry of the lattice plays crucial role in determining the maximum number of vortex states as well as the general characteristics of these states such as, the average angular momentum $<L_z>$, the current at the perimeter of the lattice, phase winding, the relation between the maximum phase difference, the maximum current and also the saturation of the current between the two neighboring lattice points. The effect of the two- and three-body interactions between the particles, both attractive and repulsive, also depends on the geometry of the lattice as the current flow or the lattice current depends on the interactions. We also consider the effect of the spatial inhomogeneity introduced by the presence of an additional confining harmonic trap potential. It is shown that the curvature of the trap potential and the position of the minimum of the trap potential with respect to the axis of rotation or the center of the lattice have a significant effect on the general characteristics these vortex states.

Effects of spatial inhomogeneity of wave excitations on structural behaviors of multi-span floating bridges

Floating bridges have wide application prospect in deep-water transportation infrastructures. However, limited research works have been conducted to study the structural behaviors of such type of structure under various wave conditions. In this paper, a novel time domain approach, which combines dynamic finite element method and state-space model, is proposed for the refined analysis of floating bridges. High-precision fitted state-space models are established to enhance the calculation efficiency of motion-induced radiation forces. The presented method is verified by applying it to simulate a physical scaled model test. Upon verification, the developed approach is further employed to investigate the effects of spatial inhomogeneity of waves on the dynamic behaviors of multi-span floating bridges, where two bridges with five and seven spans as well as four wave conditions of different wave height distributions, are considered for comparative analyses. It is shown that inhomogeneous waves could mitigate the horizontal responses of multi-span floating bridges, while the structural responses in vertical direction could be enhanced. The dynamic responses of multi-span floating bridges could be more sensitive to the wave inhomogeneity as the bridge length increases. Furthermore, the effects of short-crested and long-crested waves on the structural responses are also compared in this study.

Synchronisation of glycolytic activity in yeast cells.

Glycolysis is the central metabolic pathway of almost every cell and organism. Under appropriate conditions, glycolytic oscillations may occur in individual cells as well as in entire cell populations or tissues. In many biological systems, glycolytic oscillations drive coherent oscillations of other metabolites, for instance in cardiomyocytes near anorexia, or in pancreas where they lead to a pulsatile release of insulin. Oscillations at the population or tissue level require the cells to synchronize their metabolism. We review the progress achieved instudying a model organism for glycolytic oscillations, namely yeast. Oscillations may occur on the level of individual cells as well as on the level of the cell population. In yeast, the cell-to-cell interaction is realized by diffusion-mediated intercellular communication via a messenger molecule. The present mini-review focuses on the synchronisation of glycolytic oscillations in yeast. Synchronisation is a quorum-sensing phenomenon because the collective oscillatory behaviour of a yeast cell population ceases when the cell density falls below a threshold. We review the question, under which conditions individual cells in a sparse population continue or cease to oscillate. Furthermore, we provide an overview of the pathway leading to the onset of synchronized oscillations. We also address the effects of spatial inhomogeneities (e.g., the formation of spatial clusters) on the collective dynamics, and also review the emergence of travelling waves of glycolytic activity. Finally, we briefly review the approaches used in numerical modelling of synchronized cell populations.

Schottky barrier inhomogeneity in (Pd / Au) Al0.22 Ga0.78N/GaN/SiC HEMT: Triple Gaussian distributions

The temperature dependence of electrical properties of (Au/Pd)/Al0.22 Ga0.78N/ GaN Schottky barrier diodes (SBDs) have been deeply analyzed by means of forward Igs (Vgs) measurements over the temperature range of 60-320 K. First results indicate that the barrier height (ϕb), ideality factor (n) and series resistance (Rs) have demonstrated a strongly temperature dependence which suggesting the presence of barrier inhomogeneities at the interface. The effect of spatial inhomogeneity causes fluctuations in the barrier height around an average value. The series resistances obtained from Cheung's function are increasing with increasing temperature. Werner's model consisted in the Schottky contact modeling through inhomogeneities of the barrier which induces the presence of three different average barrier heights each associated with a standard deviation σ. Such abnormal behavior is indeed due to the lateral inhomogeneity of the Schottky barrier, assuming three Gaussian distributions of the barrier height (BH) in three different temperature ranges of 220-320K, 120-200K, and 60-100K, respectively. The (Au/Pd)/ GaN Schottky barrier diode have been shown a Gaussian distribution giving mean s (ϕb) of 0.83, 0.43 and 0.20 eV and standard deviation σ of 139, 74.18 and 35.15 mV for the three temperature regions, respectively. A modified Richardson plot ln (I0/T2) − q2σ2/2k2T2 vs. 1/kT have given ϕb and A* as 0.95 eV and 10.56 A/cm2K2, 0.45 eV and 24.45A/cm2 K2, 0.20 eV and 28.18 A/cm2 K2, respectively. Moreover, the determination of the energy characteristic relating to the transmission probability by tunneling effect E00 made it possible to highlight two conduction modes: conduction by tunnel effect (FE) and a thermionic conduction assisted by field effect (TFE).

Emergent failure patterns at sub-critical fields in polymeric dielectrics

A generalized physical framework is presented for the simulation of electro-thermal ageing in large-size samples of polymeric dielectric by discretizing them into small-size elements using an orthogonal matrix. The individual elements are treated as thin-film samples with assigned generic morphological parameters, whose distribution in the matrix obeys their fitted thin-film distribution probabilities obtained from experiments. This allows the effect of spatial inhomogeneity in large-size samples to be included in the model. Quantitative simulations of the evolution of direct-current ageing up to eventual catastrophic failure are studied at sub-critical fields, and it is shown that the criterion for the onset of a deterministic runaway event is the enhancement of the local field, caused by self-organized degradation, to a temperature-dependent critical value. The lifetime is effectively the time taken to reach the critical value, and its statistics are fitted to the Weibull distribution. The failure patterns produced during ageing were found to be strongly dependent on the applied electric field, but not on temperature whose increases accelerated the ageing process instead. The global inhomogeneous properties of the dielectric were found to control the ageing process with stochastic percolation behaviour below the critical point at low applied fields. Increasing the applied field gradually strengthened the influence of local deterministic factors.

Analytical Model for Determining The Effective Size of an Evaporation Region in Pulsed Laser Ablation

This paper describes the study of the effect of spatial inhomogeneity of surface temperature on the size of a crater forming in the case of pulsed laser ablation. It is assumed that the surface temperature is linearly dependent on laser radiation energy. Analytical expressions determining the effective radius of an evaporation region, characteristic temperatures of the surface on which evaporation occurs, and evaporation depths in the case of the Gaussian distribution of laser radiation energy are derived. It is shown that the analytical dependences obtained are in good agreement with known numerical calculation results.

Effect of spatial inhomogeneities on detonation propagation with yielding confinement

The propagation of detonations in layers of reactive gas bounded by inert gas is simulated computationally in both homogeneous and inhomogeneous systems described by the two-dimensional Euler equations with the energy release governed by an Arrhenius rate equation. The thickness of the reactive layer is varied and the detonation velocity is recorded as the layer thickness approaches the critical value necessary for successful propagation. In homogeneous systems, as activation energy is increased, the detonation wave exhibits increasingly irregular cellular structure characteristic of the inherent multidimensional instability. The critical layer thickness necessary to observe successful propagation increases rapidly, by a factor of five, as the activation energy is increased from $$E_\mathrm{a}/RT_0 = 20$$ –30; propagation could not be observed at higher activation energies due to computational limitations. For simulations of inhomogeneous systems, the source energy is concentrated into randomly positioned squares of reactive medium embedded in inert gas; this discretization is done in such a way that the average energy content and the theoretical Chapman–Jouguet (CJ) speed remain the same. In the limit of highly discrete systems with layer thicknesses much greater than critical, velocities greater than the CJ speed are obtained, consistent with our prior results in effectively infinite width systems. In the limit of highly discretized systems wherein energy is concentrated into pockets representing 10% or less of the area of the reactive layer, the detonation is able to propagate in layers much thinner (by an order of magnitude) than the equivalent homogeneous system. The critical layer thickness increases only gradually as the activation energy is increased from $$E_\mathrm{a}/R T_0 = 20{-}55$$ , a behavior that is in sharp contrast to the homogeneous simulations. The dependence of the detonation velocity on layer thickness and the critical layer thickness is remarkably well described by a front curvature model derived from the classic, ZND-based model of Wood and Kirkwood. The results of discrete sources are discussed as a conceptual link to the behavior that is experimentally observed in cellular detonations with highly irregular cellular structure in which intense turbulent burning rapidly consumes detached pockets behind the main shock front. The fact that highly discrete systems are well described by classical, curvature-based mechanisms is offered as a possible explanation as to why curvature-based models are successful in describing heterogeneous, condensed-phase explosives.

The Effect of Spatial Inhomogeneity of the Cornea on the Deformation Properties of the Eyeball and the Results of Maklakoff Applanation Tonometry

A two-component model of the eyeball that represents the cornea as a momentless, linearly elastic deformable surface and the scleral region, as an elastic element that responds to intraocular pressure changes by volume changes, has been used to analyze the effect of spatial inhomogeneity in the distribution of effective corneal stiffness on the mechanical properties of the eye. The effective stiffness of the cornea characterized both the elastic properties and the thickness of the cornea within the framework of the model. Various axisymmetric forms of the effective stiffness distribution characterized by monotonic increase along the arc between a point on the corneal surface and the apex of the cornea were studied. The considered distributions simulated both natural inhomogeneity and apical region weakening due to surgical interventions. Numerical simulation yielded the dependences of deformation parameters on intraocular pressure changes. These parameters characterized the deformation properties of both the cornea (apex displacement) and the eyeball as a whole (intraocular volume change). In the case of moderate inhomogeneity, the dependences were only slightly different from those for a homogeneous cornea with an effective stiffness equal to the mean value for the corresponding inhomogeneous distribution. A noticeable increase in the integral response of the cornea and the eyeball as a whole to changes in pressure was observed if the effective stiffness amplitude was very high (two or more times higher than the mean value). The effect of inhomogeneity on the results of tonometric measurements with a Maklakoff tonometer (flat stamp) was studied. The tonometric difference, that is, the difference between the tonometric pressure (in the loaded eye) and the true pressure (before loading), mainly depended on the average stiffness of the cornea in this case as well, with a substantial increase observed at very high stiffness amplitudes only. Apical weakening of the cornea led to an increase (although not very pronounced) of the tonometric difference.

Local photoemission spectra and effects of spatial inhomogeneity in the BCS-BEC-crossover regime of a trapped ultracold Fermi gas

We theoretically investigate single particle excitations in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein-Condensation) crossover regime of an ultracold Fermi gas. Including strong pairing fluctuations within a $T$-matrix approximation, as well as effects of a harmonic trap potential in the local density approximation, we calculate the local photoemission spectrum in the normal state. Recently, JILA group has measured this quantity in a $^{40}$K Fermi gas, in order to examine homogeneous single-particle properties of this system. Comparing our results with this experiment, we show that, this attempt indeed succeeds under the JILA's experimental condition. However, we also find that the current local photoemission spectroscopy still has room for improvement, in order to examine the pseudogap phenomenon predicted in the BCS-BEC crossover region. Since ultracold Fermi gases are always in a trap, our results would be useful in applying this system to various homogeneous Fermi systems, as a quantum simulator.

Modeling of natural acoustic frequencies of a gas-turbine plant combustion chamber

The paper presents results of determination of natural acoustic frequencies of a gas-turbine plant annular combustion chamber model using 3D-simulation. At the beginning, a calculation procedure for determining natural acoustic frequencies of the gas-turbine plant combustion chamber was worked out. The effect of spatial inhomogeneity of the flow parameters (fluid composition, pressure, temperature) arising in combustion and some geometrical parameters (cooling holes of the flame tube walls) on the calculation results is studied. It is found that the change of the fluid composition in combustion affects the acoustic velocity not more than 5%; therefore, the air with a volume variable temperature can be taken as a working fluid in the calculation of natural acoustic frequencies. It is also shown that the cooling holes of the flame tube walls with diameter less than 2 mm can be neglected in the determination of the acoustic modes in the frequency range of up to 1000 Hz. This reduces the number of the grid-model elements by a factor of six in comparison with a model that considers all of the holes. Furthermore, a method of export of spatial inhomogeneity of the flow parameters from a CFD solver sector model to the annular combustion chamber model in a modal solver is presented. As a result of the obtained model calculation, acoustic modes of the combustion chamber in the frequency range of up to 1000 Hz are determined. For a standard engine condition, a potentially dangerous acoustic mode with a frequency close to the ripple frequency of the precessing vortex core, which is formed behind the burner device of this combustion chamber, is detected.

Effect of Spatial Inhomogeneities on the Membrane Surface on Receptor Dimerization and Signal Initiation

Important signal transduction pathways originate on the plasma membrane, where microdomains may transiently entrap diffusing receptors. This results in a non-random distribution of receptors even in the resting state, which can be visualized as “clusters” by high resolution imaging methods. Here, we explore how spatial in-homogeneities in the plasma membrane might influence the dimerization and phosphorylation status of ErbB2 and ErbB3, two receptor tyrosine kinases that preferentially heterodimerize and are often co-expressed in cancer. This theoretical study is based upon spatial stochastic simulations of the two-dimensional membrane landscape, where variables include differential distributions and overlap of transient confinement zones (“domains”) for the two receptor species. The in silico model is parameterized and validated using data from single particle tracking experiments. We report key differences in signaling output based on the degree of overlap between domains and the relative retention of receptors in such domains, expressed as escape probability. Results predict that a high overlap of domains, which favors transient co-confinement of both receptor species, will enhance the rate of hetero-interactions. Where domains do not overlap, simulations confirm expectations that homo-interactions are favored. Since ErbB3 is uniquely dependent on ErbB2 interactions for activation of its catalytic activity, variations in domain overlap or escape probability markedly alter the predicted patterns and time course of ErbB3 and ErbB2 phosphorylation. Taken together, these results implicate membrane domain organization as an important modulator of signal initiation, motivating the design of novel experimental approaches to measure these important parameters across a wider range of receptor systems.

Spatial attraction in migrants' settlement patterns in the city of Catania

(ProQuest: ... denotes formulae omitted.)1. IntroductionResidential location influences individuals' proximity to important resources (such as schools, hospitals, child care facilities, labor markets, and employment opportunities) and to potential risks, including environmental threats and social hazards (such as exposure to crime and violence) (Reardon 2006). Furthermore, it impacts access to social networks and other forms of social capital; overall, it shapes human interaction and the demographic processes that originate from it, such as mortality, fertility and mobility (Almquist and Butts 2012).A minority ethnic group is spatially clustered when the spatial arrangement of minority households departs from expectations based upon a random spatial allocation (Freeman, Pilger, and Alexander 1971).In broad terms, and apart from ethnic discriminatory rules enforced by law or traditions in some places and at some times, we may distinguish between two sources of spatial clustering. One source is spatial inhomogeneity or apparent contagion. Typically, the different parts of a city exhibit large variations in the price of residential property, in the accessibility of low cost public infrastructures, and in the availability of certain types of jobs; these inhomogeneities may lead to a mostly economically induced segregation. As Schelling (1971) observes, ethnicity is often correlated with income, and income with residence; so even if residential choices were unconstrained by ethnic discrimination, the different ethnic groups would not be randomly distributed among residences.The second source is spatial attraction or true contagion. Survey data on the ideal neighborhood composition for different ethnic groups in the USA, reported in Clark and Fossett (2008), show that all groups prefer living in areas where their group is a majority or near-majority. These preferences have complex origins and may reflect attachment to group identity and culture (e.g., language, religion, customs, etc.). Newly arrived minority migrants may benefit from positive spillovers in settling close to their compatriots, in terms of reciprocal acceptance, common language, and support. Transnational social networks play an important role in channeling arriving migrants into specific neighborhoods and also into particular occupations (Gelderblom and Adams 2006).However, regardless of what the basis of the individual preferences for coethnic contact is, they produce identical patterns of residential segregation (Clark and Fossett 2008). The Schelling (1971) model provides an analysis of the implications of individual preferences and shows that when a household enters a neighborhood, that neighborhood becomes more attractive to members of the household's own group and less attractive to members of other groups. In other words, the presence of a household in a given area increases the probability of others of the same group to locating nearby.It is relevant in social research to be able to distinguish between these two sources of clustering. Whereas economic induced segregation might explain some initial degree of segregation and raises questions of social equity, the Schelling model highlights the importance of individually motivated segregation and posits that even mild preferences for living with similar neighbors carry the potential of being strong determinants for residential segregation (Clark and Fossett 2008). The spatial distribution of households may be represented by a point pattern, i.e.,a set of points in a map. Ripley's K-function (Ripley 1981) is widely used to detect clustering in point processes. The inhomogeneous K-function is a version of Ripley's K-function conceived for assessing the effects of spatial attraction (or inhibition), while adjusting for the effects of spatial inhomogeneity. In other words, this approach allows us to distinguish between the two sources of clustering, by assessing clustering above and beyond that due to apparent contagion. …

Diagnostics of inhomogeneous plasmas: correction coefficients of the self-absorption and of the effect of spatial inhomogeneity

A plasma spatial distribution model for a cylindrical geometry was developed to study the dependence of the spectral lines in the plasma emission spectra on plasma inhomogeneity and on the self-absorption effect. In this work, we consider a particular spatial distribution of a plasma. This distribution has allowed us to establish new correction coefficients of spectral lines on the self-absorption effect and to consider the media inhomogeneity effect. These coefficients are then used to analyse experimental spectral lines of emission of a single laser breakdown in an underwater medium. A spatial and time resolved spectroscopic method was used to study the spectrum. For the electron temperature and electron density measurements, trace impurities of Ca and K are added to the water.

Mesh-Free Simulation of Aerosol Evolution

The nuclear source term is greatly affected by the formation and presence of aerosols in the reactor primary vessel and the containment. In simulations, the aerosol distribution is often assumed spatially homogeneous (well mixed), and there have been relatively few studies of the effects of spatial inhomogeneity on aerosol evolution in nuclear accidents. We have explored here an extension of some of our recent work on the Direct Simulation Monte Carlo (DSMC) method to spatially inhomogeneous aerosol. In doing so, we have also departed from the traditional applications of the DSMC method where the computational domain is divided into fixed cells. We have explored here an alternative, mesh-free method by utilizing a clustering technique. This technique associates particles according to a distance parameter and is commonly used in group theory and machine learning. To benchmark this mesh-free modeling, we have verified the DSMC results against those obtained from the use of the cell balanced sectional technique for a spherical geometry where both coagulation and diffusion take place.

(Invited) Density Functional Theory Modeling of Coupled Mechanical/Electrochemical Interfacial Processes during Li-Insertion into Silicon Anode

Silicon anodes, unlike graphite widely used in commercial batteries, experience large (up to 400%) volumetric expansion after Li insertion during charging. This likely leads to unique SEI structures and formation mechanisms, especially at atomic lengthscales not readily probed using existing experimental techniques. We apply DFT modeling to model the incremental expansion of amorphous LixSi as the Li-content (“x”) increases; examine how such expansion stretches or even cracks the model passivating layers; and how such SEI evolution/degradation leads to additional electrolyte decomposition. First we create a series of amorphous LixSi slabs by incrementally increasing the Li content. The stoichiometry can range from LiSi to Li13Si4. The slabs are coated by a thin passivating layer (e.g., LiFz, which should form rapidly in the presence of FEC additives). During expansion, the surface films evolve, become stretched, or even crack. AIMD simulations of liquid ethylene carbonate (EC) films are then conducted on expanded LixSiy with stretched passivating LiFx layers. The instantaneous, electronic voltage, responsible for SEI formation, is periodically computed to ensure the modeling conditions conform to the experimental voltage window. The effect of spatial inhomogeneity, e.g., holes in the passivating layer, on inducing voltage ”hot-spots” that can accelerate electrolyte decomposition, are highlighted. To some extent, the modeling work represents very fast Li insertion, on the time scale of SEI formation. Despite this, studying the stretching and potential breaking of model SEI layers can provide valuable insight concernin potentially unique SEI behavior on Si anode surfaces. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract No. 7060634 under the Batteries for Advanced Transportation Technologies (BATT) Program. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corpo ration, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Figure 1

From invasion to latency: intracellular noise and cell motility as key controls of the competition between resource-limited cellular populations.

In this paper we analyse stochastic models of the competition between two resource-limited cell populations which differ in their response to nutrient availability: the resident population exhibits a switch-like response behaviour while the invading population exhibits a bistable response. We investigate how noise in the intracellular regulatory pathways and cell motility influence the fate of the incumbent and invading populations. We focus initially on a spatially homogeneous system and study in detail the role of intracellular noise. We show that in such well-mixed systems, two distinct regimes exist: In the low (intracellular) noise limit, the invader has the ability to invade the resident population, whereas in the high noise regime competition between the two populations is found to be neutral and, in accordance with neutral evolution theory, invasion is a random event. Careful examination of the system dynamics leads us to conclude that (i) even if the invader is unable to invade, the distribution of survival times, PS(t), has a fat-tail behaviour (PS(t) ∼ t(-1)) which implies that small colonies of mutants can coexist with the resident population for arbitrarily long times, and (ii) the bistable structure of the invading population increases the stability of the latent population, thus increasing their long-term likelihood of survival, by decreasing the intensity of the noise at the population level. We also examine the effects of spatial inhomogeneity. In the low noise limit we find that cell motility is positively correlated with the aggressiveness of the invader as defined by the time the invader takes to invade the resident population: the faster the invasion, the more aggressive the invader.