Influence Of Spatial Inhomogeneity Research Articles

Matched Filtering of Small-Sized Objects in Images Containing Constant Spatial Interference

The influence of spatial inhomogeneity of the photoelectric characteristics of a matrix photodetector (PDD) on the quality of detection of small-sized objects in the image formed by it is considered. It is shown that in the conditions of spatially inhomogeneous natural noise of the PDD, the traditionally applied two-point correction is not optimal for subsequent matched image filtering performed in order to increase the reliability of object detection. A two-stage algorithm for constructing a linear spatially invariant matched filter is proposed, which provides a significant increase in the reliability of detecting weak small-sized objects against the background of uncorrelated noise in images containing interference due to the spatial heterogeneity of the PDD characteristics.

Analysis of unsteady flow of second grade fluid with power law spatially distributed viscosity

This paper investigates the influence of spatial inhomogeneity of fluid viscosity in an unsteady channel flow of a viscous second grade fluid. The viscosity model is assumed to follow a power-law spatial relation which may arise from concentration gradient, thermal gradient or boundary induced phase transition in the weakly elastic fluid. Two flow problems are considered (i) the Generalized Couette and (ii) the time-periodic plane Poiseuille flows. The associated partial differential equation governing each flow setup is decoupled into steady and transient state problems which are analyzed for possible closed form solutions. The analytical technique explored in this study is premised on theoretical analysis of the resulting ordinary differential equations. Corresponding results to the deduced ordinary differential equations with variable coefficient are presented as trigonometric and hyperbolic functions. In cases where analytical results are not attainable, numerical solutions are obtained via finite volume techniques. On comparing instances with the same parameter values, both the numerical and analytical solutions show good agreement. The spatial variation in the viscosity results in either a plug flow for cases where the viscosity index is negative or a fast flow throw the axis in instances where the index is positive. With graphical and tabular illustrations the influence of associated material parameters on the flow are presented and discussed.

Influence of Spatial Inhomogeneity on the Formation of Chaotic Modes at the Self-Organization Process

The Lorentz system of equations, in which gradient terms are taken into account, has been solved numerically. Three fundamentally different modes of evolution are considered. In the first mode, the spatial distribution of the order parameter permanently changes in time, and domains of two types with positive and negative order parameter values are formed. In the second mode, the order parameter distribution is close to the stationary one. Finally, in the third mode, the order parameter is identical over the whole space. The dependences of the average area of domains, their number, and their total area on the time are calculated in the first two cases. In the third case, the contribution of gradient terms completely vanishes, and a classical Lorenz attractor is realized.

Influence of spatial inhomogeneity of environment temperature on temperature oscillations and thermocyclic stresses in elastic half-space

Elastic half-space on which surface the heat transfer follows the Newton-Richmann law where enviroment temperature is a periodic function of time and spatial variable is investigated. A temperature field and a stressed deformed state of half-space is found after the solution of a quasistatic problem of thermoelasticity. The solution is received in the form of double Fourier series.

Hardware-in-the-Loop Simulation on Fault Current Limiting Operation of RE-123 Coated Conductors Under the Influence of Spatial Inhomogeneity

We have investigated transient behavior of RE-123 coated conductors in fault current limiting operation based on experimental hardware-in-the-loop simulation (HILS). Fault current limiting function of superconducting electric power application is attractive to maximize the potential of power system; such a function can be realized by the transition to the resistive state of superconducting wire. However, the phenomena is relatively complicated: nonlinear current transport properties varying with time-dependent temperature rise. Furthermore, from practical point of view, the influence of spatially homogeneity of cooling and local critical current properties in RE-123 coated conductors must be clarified for reliable operation. To demonstrate this, we developed HILS system using real-time digital simulator. Fault current limiting operation was successfully demonstrated for dc electric railway system. This method enabled us to evaluate the real-time responses of RE-123 coated conductors such as nonlinear properties and thermal behaviors under a power grid network. In particular, we applied RE-123 coated conductors with spatially inhomogeneous cooling and local critical currents to the experiment to understand the influences of them on the fault current limiting and recovery functions. Furthermore, such transient phenomena were successfully described by an electrically and thermally coupled analysis taking into account of temperature dependent nonlinear transport properties of the RE-123 coated conductors based on the percolation transition model. The method and findings will become crucial for effective and reliable designs of superconducting fault current limiters.

Comparison between Bi-2223 tape and RE-123 coated conductor from the view point of current transport properties influencing thermal stability

We have investigated flux flow dissipation in typical two kinds of HTS tapes, i.e., a Bi-2223 multi-filamentary tape and a RE-123 coated conductor (CC) from the view point of heat load under over current conditions. Based on systematic measurements on current-voltage characteristics, the nonlinear flux flow dissipation has been described analytically by taking into account current sharing in metallic sheath or stabilization layer. Flux flow dissipation in the RE-123 CC shows much steeper temperature dependence than that of the Bi-2223 tape. As a result, attainable cooling power becomes smaller in the RE-123 CC in comparison with that of Bi-2223 tape even if the same cooling condition. In other word, acceptable temperature rise in the RE-123 CC is small at over current condition, whereas moderate temperature dependence in the Bi-2223 tape allows stable operation even if the bias current exceeds the critical current. Influence of spatial inhomogeneity in the both HTS tapes has also been investigated. Longitudinal variation of local critical current, Ic, and its statistical behavior have been characterized by use of reel-to-reel scanning Hall probe microscopy. It has been found that the flux flow dissipation is possibly localized more than one order higher than that of the average value due to discrete local Ic drops.

Influence of spatial inhomogeneity on electronic and magnetotransport in graphene

We present room temperature electronic and magnetotransport measurements of polycrystalline graphene, grown by chemical vapor deposition, on a $\mathrm{Si}{\mathrm{O}}_{2}$ dielectric. The measured graphene devices are intentionally spatially inhomogeneous such that the length of the sample is much greater (g1000 times) than the average grain size. At magnetic field $B=0\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ the electronic transport is well described by a diffusive transport model with contributions from grain boundary scattering significantly larger in the high charge carrier density limit. We find the largest percent change in the magnetoresistivity occurs at the film's Dirac point where the magnetotransport is largely dependent upon charge disorder. Away from the Dirac point we find a modified expression for the charge carrier density dependence of the magnetoresistivity with respect to the case of single-crystal graphene.

Tidal dynamics in cosmological spacetimes

We study the relative motion of nearby free test particles in cosmological spacetimes, such as the FLRW and LTB models. In particular, the influence of spatial inhomogeneities on local tidal accelerations is investigated by means of simple spherically symmetric models. The implications of our results for the dynamics of the solar system are briefly discussed. That is, on the basis of the models studied in this paper, we estimate the tidal influence of the cosmic gravitational field on the orbit of the Earth around the Sun and show that the corresponding temporal rate of variation of the astronomical unit is negligibly small.

Effects of spatial inhomogeneities on the dynamics of cavity solitons in quadratically nonlinear media.

We study the dynamics of cavity solitons under the influence of spatial inhomogeneities and derive generalized equations of motions. For perturbations large compared to the soliton size we find the modulus of the soliton velocity to be proportional to the gradient of the respective perturbation and that the proportionality coefficient changes sign when the soliton peak power drives the cavity beyond the resonance. For short scale perturbations solitons may be trapped at the extrema of the inhomogeneities. Shape and stability of these trapped solitons can be quasianalytically described by means of a perturbation theory. If both types of perturbations act solitons are either trapped or move depending on the strength of the respective perturbation. In the framework of a quasiparticle approach this dynamics is governed by a differential equation that holds for particle motion in a strongly viscous fluid under the action of a constant and harmonically varying force. We also show that in addition to acquiring a velocity the very existence conditions of the solitons (hysteresis curve) are affected by both kinds of perturbations. We find good quantitative agreement between our analytical results and numerical findings, which were obtained for a two wave interaction in a cavity filled with a quadratically nonlinear material.

LINE RADIATION SPECTRA OF INHOMOGENEOUS FLUCTUATING PLASMA VOLUMES

The influence of spatial inhomogeneity and temporal fluctuations of the parameters of equilibrium plasma on the intensity and shape of the lines in the spectrum of its radiation was investigated. A closed mathematical model based on the solution of the radiation transfer equation, which describes the formation of the emission spectrum of the plasma volume with given characteristics, has been constructed. A semianalytical approximation that permits adequate description of the line radiation spectra of optically transparent plasma has been developed. The laws of formation of the line radia- tion spectra of inhomogeneous fluctuating plasma volumes and the relations relating the charac- teristics of these spectra to the emissivity and local parameters of the plasma have been found. For the presentation of the results, we have chosen atmospheric-pressure argon plasma. Introduction. Analysis of the intensity and the profiles of spectral lines in the radiation spectrum of plasma is one of the most effective methods of its diagnostics with the use of optical emission spectroscopy (OES). Plasma diagnostics by OES methods is based on the relation between the emissivity of the plasma and its local parameters, which is usually nonlinear. The OES diagnostics involves the recording of the spec- tral line profile and the intensity summed over the line and the observation period. To determine the emissiv- ity of an inhomogeneous plasma, it is necessary to solve the inverse problem. This problem is formally considered as incorrect: a small error in measured data can cause marked errors in the determination of the desired quantities (1). In the general case, it is solved by tomography methods. In so doing, the number of rays of observation and their directions are determined by the character of inhomogeneity, and their number can be very large. In the simplest case of axisymmetric inhomogeneities, the problem reduces to the inverse Abelian transform (2−4). The amount of recorded data increases significantly when the spectral line profiles obtained by scanning the radiation spectrum are used for diagnostics. The instability of plasma imposes addi- tional requirements on the measurement system: the recording time of plasma radiation should be shorter than the characteristic time of fluctuations. Therefore, there is often no point in solving traditionally the inverse problems in plasma OES or such a solution is impossible because of the large errors, excessive complexity of the recording systems, and stringent requirements imposed on them. As a consequence, there are practi- cally no OES methods for measuring local parameters in space and time of the low-temperature plasma of

The Influence of Spatial Inhomogeneities on Neutral Models of Geographical Variation IV. Discontinuities in the Population Density and Migration Rate

The equilibrium structure of the infinite, one-dimensional stepping-stone model with coincident discontinuities in the population density and migration rate is investigated in the diffusion approximation. The monoecious, diploid population is subdivided into an infinite linear array of equally large, panmictic colonies that exchange gametes isotropically. The population density and the migration rate have a discontinuity at the origin, but are elsewhere uniform. Generations are discrete and nonoverlapping; the analysis is restricted to a single locus without selection; every allele mutates to new alleles at the same rate. The three dimensionless parameters in the theory are α=(ρ+/ρ−)2 (V+/V−)3/2, and β±=4ρ±2uV± , where ρ+ (ρ−) and V+ (V−) designate the population density and variance of gametic dispersion per generation to the right (left) of the discontinuity, respectively, and u denotes the mutation rate. The characteristic length on the right (left) is V+/(2u) (V−/(2u)). The probability of identity is continuous at the origin, but its partial derivatives have a discontinuity unless migration is conservative (ρ−V−=ρ+V+). At least for nonconservative migration, the probability of identity (including the expected homozygosity) can be nonmonotonic even if the migration rate is uniform and the population density is monotonic. Thus, there can be a nonmonotonic genetic response in a neutral model to a monotonic environment.

Modeling of optical pumping experiments in CO: II. Steady conditions

Results of continuous optical pumping experiments in CO-rare gas mixtures are presented. A kinetic modeling is carried out taking spatial non-uniformity, heat transfer, forced convection and molecular diffusion into account. The influence of spatial inhomogeneity is studied. It is found that kinetic calculations substantially overestimate vibrational populations in high levels if VE transfers are not taken into account.

Small and large deformation studies of protein gels

The rheological behavior of protein gels with different network and strand structures has in a series of studies been investigated to elucidate how the structure of the gel influences its rheological properties. Nondestructive viscoelastic measurements and fracture techniques were used and the different types of structures studied were fine-stranded gels and particulate gels. The influence of spatial inhomogeneities in the network structure was also investigated. The protein gel chosen as the model system was β-lactoglobulin which forms gels on heating and develops different structures depending on pH: a particulate network at intermediate pH (4–6) and a fine-stranded network below and above this interval. It can also form inhomogeneous networks depending on pH or heating rate. The fine-stranded and the particulate gels had totally different mechanical properties. It was shown that the strand structure influenced both the modulus as well as the fracture properties of both fine-stranded and particulate gels. Inhomogeneities induced by a slow heating rate also changed the mechanical properties the gels.

On the influence of inhomogeneities in a reaction-diffusion system

We compare experimental and analytical results concerning the influence of spatial inhomogeneities on front dynamics in the case of a one-component reaction-diffusion system represented by a chain of bistable electrical relaxation elements. Spatial variation of the front velocity, especially the pinning behavior, is in quantitative agreement with predictions of multiple scale perturbation theory.

Effects of interfaces on magnetic properties of Co-based multilayers

Abstract The determination of the anisotropy constants and of the electronic structure of single, epitaxially grown interfaces as building blocks of magnetic multilayers has been carried out by means of in situ Brillouin light scattering from spin waves and of spin-resolved photoemission, respectively. Multilayer structures have also been studied using ex situ Brillouin light scattering with emphasis on the influence of spatial inhomogeneities on the magnetic anisotropies of the multilayered structures.

The influence of spatial inhomogeneities on neutral models of geographical variation: II. The semi-infinite linear habitat

The equilibrium structure of the semi-infinite, one-dimensional stepping-stone model is investigated in the diffusion approximation. The monoecious, diploid population is subdivided into a semi-infinite linear array of equally large, panmictic colonies that exchange gametes uniformly and symmetrically. Generations are discrete and nonoverlapping; the analysis is restricted to a single locus in the absence of selection; every allele mutates to new alleles at the same rate. Boundaries corresponding to an impenetrable geographical barrier and to contact with a region of extremely high population density or dispersal rate (a “density-mobility boundary”) are both treated. Relative to a homogeneous infinite habitat, a geographical barrier raises, and a density-mobility boundary lowers, the probability of identity. For fixed average position of the two points of observation, the probability of identity decreases with increasing separation. For fixed separation, the probability of identity decreases (increases) as the average position recedes from the barrier (density-mobility boundary). The sole dimensionless parameter in the theory is β = 4 ρo √2 uV o , where ρ o , u, and V o represent the population density, mutation rate, and variance of gametic dispersion per generation, respectively. The characteristic length is √ V o (2u) . Lower and upper bounds on the probability of identity are established; these yield a simple approximation for β ⪢ 1. The probability of identity is obtained as an integral; from this solution, approximations close to and far from the boundary are derived and the exact mean homozygosity at a geographical barrier is evaluated.

The influence of spatial inhomogeneities on neutral models of geographical variation: I. Formulation

The influence of spatial variation in the carrying capacity and migration rate of a geographical barrier on the one-dimensional stepping-stone model is studied. The monoecious, diploid population is subdivided into an infinite linear array of panmictic colonies that exchange gametes. In each deme, the rate of self-fertilization is equal to the reciprocal of the number of individuals in that deme. Generations are discrete and nonoverlapping; the analysis is restricted to a single locus in the absence of selection; every allele mutates to new alleles at the same rate. In the diffusion approximation, a partial differential equation that incorporates spatial (and temporal) variation in the carrying capacity and migration rate is derived for the probability of identity. Transition conditions that simultaneously take into account discontinuities in the carrying capacity and migration rate are established: the probability of identity is continuous, but its partial derivatives are not, their ratio being a simple function of the carrying capacities and migrational variance on the two sides of the inhomogeneity. The partial derivatives of the probability of identity are continuous across a geographical barrier, whereas the probability of identity itself has a discontinuity proportional to the partial derivative at the barrier, the constant of proportionality being a measure of the difficulty of crossing the barrier.

Foveal information processing at photopic luminances.

A tentative model of information processing in the human fovea at photopic luminances is described, that handles both luminosity and chromaticity signals. The model consists of a “scaling-ensemble”, a group of sealers with common scaling-factor that provide an effective compression of the dynamic range of the input signals. The scaling factor adapts in such a way that the model conforms to Weber's law for the detection of short, small flashes on a bright background. The dynamics of the adaptation is such that the model effectively computes the logarithmic time derivative of the input signal. The model predicts the outcome of several psychophysical experiments. The predictions include Weber's law, Bloch's law, the apparent brightness of suprathreshold flashes as a function of adaptation level, the influence of spatial inhomogeneities on the perception of flicker, and the transfer function for moving sinusoidal bar patterns for both luminosity and chromaticity modulations. The influence of involuntary eye-movements on the perception of spatial patterns is also discussed. Finally an attempt is made to locate the components of the model in the anatomical structure of the retina. A tentative scheme of neural connections in the human fovea is presented.

Influence of Spatial Inhomogeneities on the Nuclear Polarization Due to Direct Current in Semiconductors

Influence of Spatial Inhomogeneities on the Nuclear Polarization Due to Direct Current in Semiconductors