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Heterogeneous Structure (heterogeneous + structure)
Selected AbstractsHeterogeneous Plasma-Producing Structures at Current Implosion of a Wire ArrayCONTRIBUTIONS TO PLASMA PHYSICS, Issue 8 2005E. V. Grabovsky Abstract Characteristic properties of the plasma production process have been considered for the case of megampere currents flowing through hollow cylindrical wire arrays of the Angara-5-1 facility. In 3-4 nanoseconds after voltage applying to the wire surfaces there appear a plasma layer. The system becomes heterogeneous, i.e. consisting of a kernel of metal wires and a plasma layer. In several nanoseconds the current flow goes from metal to plasma, which results in reducing the electric field strength along the wire. The Joule heat energy delivered to the metal before the moment of complete current trapping by plasma is insufficient for the whole mass transition to a hot plasma state. The X-ray radiography techniques made it possible to detect and study dense clusters of substance of ,1g/cm3 at a developed discharge stage. The radial expansion velocity of ,104 cm/s measured at the 70-th nanosecond after the current start allows treating the dense core at a late stage in the form of a submicron heterogeneous structure from its liquid and slightly ionized gas phase. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Regional tomographic inversion of the amplitude and phase of Rayleigh waves with 2-D sensitivity kernelsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Yingjie Yang SUMMARY In this study, we test the adequacy of 2-D sensitivity kernels for fundamental-mode Rayleigh waves based on the single-scattering (Born) approximation to account for the effects of heterogeneous structure on the wavefield in a regional surface wave study. The calculated phase and amplitude data using the 2-D sensitivity kernels are compared to phase and amplitude data obtained from seismic waveforms synthesized by the pseudo-spectral method for plane Rayleigh waves propagating through heterogeneous structure. We find that the kernels can accurately predict the perturbation of the wavefield even when the size of anomaly is larger than one wavelength. The only exception is a systematic bias in the amplitude within the anomaly itself due to a site response. An inversion method of surface wave tomography based on the sensitivity kernels is developed and applied to synthesized data obtained from a numerical simulation modelling Rayleigh wave propagation over checkerboard structure. By comparing recovered images to input structure, we illustrate that the method can almost completely recover anomalies within an array of stations when the size of the anomalies is larger than or close to one wavelength of the surface waves. Surface wave amplitude contains important information about Earth structure and should be inverted together with phase data in surface wave tomography. [source] Scattering behaviour at Merapi volcano (Java) revealed from an active seismic experimentGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Ulrich Wegler SUMMARY The seismic structure of the stratovolcano Merapi (Java, Indonesia) was studied using an active seismic experiment. Three 3 km long seismic profiles each consisting of up to 30 three-component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level. The detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting. The seismic experiment at Merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome, where the sources of most of the natural volcanic seismic events are located. The cone of Merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material. Additionally, the topography of the erosion valleys leads to an irregular deposition, which cannot be described by a simple 1-D layering. These inhomogeneities have a strong influence on seismic signals. The direct P and S waves are attenuated quickly and show only small amplitudes on seismograms. The energy lost from the direct waves, however, is not changed into heat but scattered and can be observed as seismic coda following the direct waves. The observed seismograms show a spindle-like amplitude increase after the direct P phase. This shape of the envelope can be explained by the diffusion model. According to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves. Besides the envelope, the coherence and polarization properties of the wavefield also indicate strong scattering. Only the first onset shows coherence over a station spacing of 100 m, whereas the late phases carrying the major part of the energy are mainly incoherent. The horizontal components of the seismograms have larger amplitudes than the vertical component, but within the horizontal plane the polarization is almost arbitrary, corresponding to waves arriving from scatterers located arbitrarily in space. As a result of the inversion using the diffusion model we obtain values of the S -wave scattering attenuation coefficient, ,s, and the S -wave intrinsic absorption coefficient, ,i. In the frequency range of 4,20 Hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption (,s,,i). The mean free path of S waves is as low as 100 m (,s,1,100 m). The scattering coefficient is independent of frequency (,s,f0.0), whereas the coefficient of intrinsic attenuation increases with increasing frequency (,i,f1.6). The natural seismic signals at Merapi volcano show similar characteristics to the artificial shots. The first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves. Therefore, these signals appear to be strongly affected by multiple scattering also. [source] The regulation of brood reduction in Booted Eagles Hieraaetus pennatus through habitat heterogeneityIBIS, Issue 4 2008EVA CASADO Brood reduction, the death of one or more chicks through siblicide or starvation, can occur through density-dependence in fecundity. Brood reduction may arise in territorial breeding systems either as a response to a high level of territorial interference in a situation of high density or as a result of habitat heterogeneity. To test the predictions of the two main hypotheses that attempt to explain how density-dependent fecundity is generated, the Habitat Heterogeneity Hypothesis (HHH) and the Individual Adjustment Hypothesis (IAH), we analysed the relationship between density and fecundity in an expanding population of Booted Eagles in Dońana National Park, Spain, using an 18-year data series. We also studied the occurrence and frequency of brood reduction in the same Booted Eagle population to appreciate further its effects and the factors that influence its occurrence and frequency. Our results support the HHH in the present situation of high density, as fecundity in the better territories (older and more frequently occupied) was higher than in low quality territories and was not affected by population density in high density periods. Nevertheless, the fecundity of high quality territories was affected (although not significantly) by population density in periods of low density, suggesting that the IAH was supported when only high quality territories were occupied. Older territories were used more frequently and chicks in these areas hatched earlier and suffered lower mortality than in new territories. We found a significant negative relationship between mean fecundity and its skewness, a finding that also supports HHH. During years of food shortage, less frequently occupied territories suffered higher rates of brood reduction. Brood reduction in this Booted Eagle population was a consequence of the heterogeneous structure of the habitat, with some territories having a higher probability of brood reduction than others. Parental nutritional condition did not affect brood reduction. The effect of brood reduction on nestling quality and population dynamics is also discussed. [source] Aspects of a direct homogenization procedure for electro-mechanically coupled problemsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Marc-André Keip The aim of this work is to discuss a micro,macro homogenization procedure for electro,mechanically coupled problems. In this context a two,scale homogenization ansatz for ferroelectric ceramics based on an FE2 -approach is presented. The microscopic discretization of the heterogeneous structure of the polycrystalline material allows for the incorporation of microscopic effects, which are necessary to determine the corresponding overall macroscopic material response. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sampling subproblems of heterogeneous Max-Cut problems and approximation algorithms,RANDOM STRUCTURES AND ALGORITHMS, Issue 3 2008Petros Drineas Abstract Recent work in the analysis of randomized approximation algorithms for NP -hard optimization problems has involved approximating the solution to a problem by the solution of a related subproblem of constant size, where the subproblem is constructed by sampling elements of the original problem uniformly at random. In light of interest in problems with a heterogeneous structure, for which uniform sampling might be expected to yield suboptimal results, we investigate the use of nonuniform sampling probabilities. We develop and analyze an algorithm which uses a novel sampling method to obtain improved bounds for approximating the Max-Cut of a graph. In particular, we show that by judicious choice of sampling probabilities one can obtain error bounds that are superior to the ones obtained by uniform sampling, both for unweighted and weighted versions of Max-Cut. Of at least as much interest as the results we derive are the techniques we use. The first technique is a method to compute a compressed approximate decomposition of a matrix as the product of three smaller matrices, each of which has several appealing properties. The second technique is a method to approximate the feasibility or infeasibility of a large linear program by checking the feasibility or infeasibility of a nonuniformly randomly chosen subprogram of the original linear program. We expect that these and related techniques will prove fruitful for the future development of randomized approximation algorithms for problems whose input instances contain heterogeneities. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008 [source] Simulation of water flow and solute transport in free-drainage lysimeters and field soils with heterogeneous structuresEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2004H. M. Abdou Summary Lysimeters are valuable for studying the fate and transport of chemicals in soil. Large-scale field lysimeters are used to assess pesticide behaviour and radionuclide transport, and are assumed to represent natural field conditions better than laboratory columns. Field lysimeters are usually characterized by a free-draining lower boundary. As a result, the hydraulic gradient is disrupted, and leachate cannot be collected until the bottom of the lysimeter becomes saturated. We compared heterogeneously structured, free-drainage lysimeters and field soils with respect to water flow and solute transport. Numerical simulations were carried out in a two-dimensional heterogeneous sandy soil under unsaturated water flow conditions with the CHAIN_2D code. Three different soil structures (isotropic, horizontal, and vertical) were generated, and Miller,Miller similitude was used to scale the hydraulic properties of the soil. The results showed that ponding occurs at the bottom of the lysimeter for the three soil structures and that it occurred faster and was more pronounced with the vertical structure (preferential flow effect). Breakthrough curves of a conservative solute (bromide) showed that solutes are moving faster in the field than in the lysimeters. Fewer differences between lysimeters and field soils were found with the horizontal soil structure than with the isotropic and vertical structures. [source] Coaxial Metal Nano-/Microcables with Isolating Sheath: Synthetic Methodology and Their Application as InterconnectsADVANCED MATERIALS, Issue 17 2010Min-Rui Gao Abstract Synthesis of coaxial nano-/microcables has been an intensive research subject due to their heterogeneous structures, tuneable properties, and important applications in nano-/micrometer-scale electronic and optoelectronic devices. Research on the fabrication of nanocables via solution strategies has made great progress in the past few years. In this Research News article, rapidly emerging new solution strategies such as hydrothermal carbonization (HTC) and synergistic soft,hard templates (SSHTs) are highlighted. Unique and flexible coaxial nano-/microcables synthesized by those methods have obvious advantages such as long-term stability and their electrical transport properties, compared with bare counterparts, suggesting that they are potential candidates as interconnects in the future. [source] Analysis of scattering from polydisperse structure using Mellin convolutionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006Norbert Stribeck This study extends a mathematical concept for the description of heterogeneity and polydispersity in the structure of materials to multiple dimensions. In one dimension, the description of heterogeneity by means of Mellin convolution is well known. In several papers by the author, the method has been applied to the analysis of data from materials with one-dimensional structure (layer stacks or fibrils along their principal axis). According to this concept, heterogeneous structures built from polydisperse ensembles of structural units are advantageously described by the Mellin convolution of a representative template structure with the size distribution of the templates. Hence, the polydisperse ensemble of similar structural units is generated by superposition of dilated templates. This approach is particularly attractive considering the advantageous mathematical properties enjoyed by the Mellin convolution. Thus, average particle size, and width and skewness of the particle size distribution can be determined from scattering data without the need to model the size distributions themselves. The present theoretical treatment demonstrates that the concept is generally extensible to dilation in multiple dimensions. Moreover, in an analogous manner, a representative cluster of correlated particles (e.g. layer stacks or microfibrils) can be considered as a template on a higher level. Polydispersity of such clusters is, again, described by subjecting the template structure to the generalized Mellin convolution. The proposed theory leads to a simple pathway for the quantitative determination of polydispersity and heterogeneity parameters. Consistency with the established theoretical approach of polydispersity in scattering theory is demonstrated. The method is applied to the best advantage in the field of soft condensed matter when anisotropic nanostructured materials are to be characterized by means of small-angle scattering (SAXS, USAXS, SANS). [source] Microbial composition and structure of a multispecies biofilm from a trickle-bed reactor used for the removal of volatile aromatic hydrocarbons from a waste gasJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2004Dariusch Hekmat Abstract The microbial composition and structure of a multispecies biofilm of a laboratory-scale trickle-bed bioreactor for the treatment of waste gas was examined. The model pollutant was a volatile organic compound-mixture of polyalkylated benzenes called Solvesso 100®. Fluorescent in-situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) were applied. Two new Solvesso 100® -degrading Pseudomonas sp strains were isolated from the multispecies biofilm. Corresponding isolate-specific oligonucleotide probes were designed and applied successfully. A major finding was that the fraction of Solvesso 100® -degrading bacteria in the biofilm was low (about 3,6% during long-term operation). The majority of the active cells were saprophytes which utilized intermediates and cell lysis products. The measured fraction of extracellular polymeric substances of the mature biofilm was 89,93% of the total biomass. The CLSM examinations of a 3-days-old approx 10 µm thick biofilm revealed highly heterogeneous structures with distinguished three-dimensional matrix-enclosed microcolony bodies spread across the substratum surface. The 28-days-old 80,960 µm thick biofilm exhibited voids, cell-free channels, and pores of variable sizes. In both cases, an even distribution of active cells and pollutant-degrading bacteria throughout the biofilm cross-section as well as through the biofilm depth was observed. Copyright © 2003 Society of Chemical Industry [source] Multi-scale study on the secondary reactions of fluid catalytic cracking gasolineAICHE JOURNAL, Issue 8 2009Bo-lun Yang Abstract Multi-scale model considered the heat transfer, mass transfer, momentum transfer, fluid flow with reactions together at different spatiotemporal scales for the riser reactor of secondary reactions of fluid catalytic cracking gasoline (SRFCCG) process has been preformed in this work. Micro-scale of kinetics in catalyst particles, meso-scale of clusters, voids, dense phase, dilute phases, and heterogeneous structures in gas,solid flow, and the macro-scale of product distribution over riser reactor have been established using multi-scale modeling method and integrated by the multi-domain strategy. The proposed model was solved with the software of EQUATRAN-G. Good agreement between simulation results and the experimental data suggested that the proposed model was well constructed and simulation exercise was successful. The multi-scale model was capable of predicting heterogeneous structures of multi-phase flow, reactor temperature profile, and product distribution of SRFCCG process. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | |||||||||||||