Primordial inhomogeneities from massive defects during inflation
NASA Astrophysics Data System (ADS)
Firouzjahi, Hassan; Karami, Asieh; Rostami, Tahereh
2016-10-01
We consider the imprints of local massive defects, such as a black hole or a massive monopole, during inflation. The massive defect breaks the background homogeneity. We consider the limit that the physical Schwarzschild radius of the defect is much smaller than the inflationary Hubble radius so a perturbative analysis is allowed. The inhomogeneities induced in scalar and gravitational wave power spectrum are calculated. We obtain the amplitudes of dipole, quadrupole and octupole anisotropies in curvature perturbation power spectrum and identify the relative configuration of the defect to CMB sphere in which large observable dipole asymmetry can be generated. We observe a curious reflection symmetry in which the configuration where the defect is inside the CMB comoving sphere has the same inhomogeneous variance as its mirror configuration where the defect is outside the CMB sphere.
EFG Component Distribution Functions in Inhomogeneous Broadening in PAC Spectroscopy
NASA Astrophysics Data System (ADS)
Adams, Mike; Matheson, P.; Evenson, W. E.; Zacate, M. O.
2010-10-01
Perturbed Angular Correlation (PAC) spectroscopy is used to study the distribution and mobility of defects within crystals. The angular correlation of multiple gamma rays emitted from probe nuclei, affected by the net electric field gradient (EFG) in a probe's vicinity, are used to produce the PAC spectrum, G2(t). The distribution of EFGs from many random defects in a crystal, results in inhomogeneous broadening (IHB) of G2(t). Our EFG component probability distribution functions are found by summing 20,000 net EFGs, each found from taking a random distribution of vacancies of a particular concentration, combined with a single trapped vacancy in a near neighbor position to a probe nucleus. The derived EFG component distributions allow us to reconstruct the G2(t) as a function of defection concentration. The EFG component distribution functions are characterized by weighted sums of either Gamma, Lorenztian or Gaussian distributions. A systematic change in the type and number of distribution functions required to model IHB is apparent as defect concentration increases. In particular, the EFG distributions become increasingly skewed with increasing defect concentration. Results for the EFG components in simple cubic (SC), face-centered cubic (FCC) and body-centered cubic (BCC) lattices are presented.
Kurai, Satoshi Ushijima, Fumitaka; Yamada, Yoichi; Miyake, Hideto; Hiramatsu, Kazumasa
2014-02-07
The spatial distribution of luminescence in Si-doped AlGaN epitaxial layers that differ in Al content and Si concentration has been studied by cathodoluminescence (CL) mapping in combination with scanning electron microscopy. The density of surface hillocks increased with decreasing Al content and with increasing Si concentration. The mechanisms giving rise to those hillocks are likely different. The hillocks induced surface roughening, and the compositional fluctuation and local donor-acceptor-pair (DAP) emission at hillock edges in AlGaN epitaxial layers were enhanced irrespective of the origin of the hillocks. The intensity of local DAP emission was related to Si concentration, as well as to hillock density. CL observation revealed that DAP emission areas were present inside the samples and were likely related to dislocations concentrated at hillock edges. Possible candidates for acceptors in the observed DAP emission that are closely related in terms of both Si concentration and hillock edges with large deformations are a V{sub III}-Si{sub III} complex and Si{sub N}, which are unfavorable in ordinary III-nitrides.
Inhomogeneous distribution of organic molecules adsorbed in sol gel glasses
NASA Astrophysics Data System (ADS)
Meneses-Nava, M. A.; Chávez-Cerda, S.; Sánchez-Villicaña, V.; Sánchez-Mondragón, J. J.; King, T. A.
1999-09-01
The effects of the porous matrix upon the radiative characteristics of quinine sulphate doped sol-gel glasses are investigated. The broadenings of the absorption and fluorescence spectra are explained by the attachment of the molecules on distorted sites or in a non-planar fashion, creating an inhomogeneous distribution of adsorbed molecules. For this reason, each emitting center relaxes with its own characteristics. This inhomogeneous distribution is also supported by the non-exponential and the wavelength dependence of the fluorescence decay.
NASA Astrophysics Data System (ADS)
Park, Tyler; Adams, Mike; Bunker, Austin; Hodges, Jeffery; Stufflebeam, Michael; Evenson, William; Matheson, Phil; Zacate, Matthew
2009-10-01
Materials contain defects, which affect crystal properties such as damping of the correlation signal,G2(t), in time and broadening of the frequency spectrum in perturbed angular correlation (PAC) experiments. We attribute this inhomogeneous broadening (IHB) to the random static defects that produce a distribution of electric field gradients (EFGs). Our goal is to find a relationship between the amount of broadening and the concentration of defects. After simulating the EFGs from random configurations of defects, we map our results from the Vzz-Vxx plane to a coordinate system optimized for the EFG distribution through a Czjzek transformation, followed by a conformal mapping. From histograms in this space, we can define probability distribution functions with parameters that vary according to defect concentration. This allows us to calculate the broadened G2(t) spectrum for any concentration, and, in reverse, identify concentrations given a broadened G2(t) spectrum.
Inhomogeneous broadening of PAC spectra with V zz and η joint probability distribution functions
NASA Astrophysics Data System (ADS)
Evenson, W. E.; Adams, M.; Bunker, A.; Hodges, J.; Matheson, P.; Park, T.; Stufflebeam, M.; Zacate, M. O.
2013-05-01
The perturbed angular correlation (PAC) spectrum, G 2( t), is broadened by the presence of randomly distributed defects in crystals due to a distribution of electric field gradients (EFGs) experienced by probe nuclei. Heuristic approaches to fitting spectra that exhibit such inhomogeneous broadening (ihb) consider only the distribution of EFG magnitudes V zz , but the physical effect actually depends on the joint probability distribution function (pdf) of V zz and EFG asymmetry parameter η. The difficulty in determining the joint pdf leads us to more appropriate representations of the EFG coordinates, and to express the joint pdf as the product of two approximately independent pdfs describing each coordinate separately. We have pursued this case in detail using as an initial illustration of the method a simple point defect model with nuclear spin I = 5/2 in several cubic lattices, where G 2( t) is primarily induced by a defect trapped in the first neighbor shell of a probe and broadening is due to defects distributed at random outside the first neighbor shell. Effects such as lattice relaxation are ignored in this simple test of the method. The simplicity of our model is suitable for gaining insight into ihb with more than V zz alone. We simulate ihb in this simple case by averaging the net EFGs of 20,000 random defect arrangements, resulting in a broadened average G 2( t). The 20,000 random cases provide a distribution of EFG components which are first transformed to Czjzek coordinates and then further into the full Czjzek half plane by conformal mapping. The topology of this transformed space yields an approximately separable joint pdf for the EFG components. We then fit the nearly independent pdfs and reconstruct G 2( t) as a function of defect concentration. We report results for distributions of defects on simple cubic, face-centered cubic, and body-centered cubic lattices. The method explored here for analyzing ihb is applicable to more realistic cases.
Ross, Michael B.; Ku, Jessie C.; Blaber, Martin G.; Mirkin, Chad A.; Schatz, George C.
2015-01-01
Bottom-up assemblies of plasmonic nanoparticles exhibit unique optical effects such as tunable reflection, optical cavity modes, and tunable photonic resonances. Here, we compare detailed simulations with experiment to explore the effect of structural inhomogeneity on the optical response in DNA-gold nanoparticle superlattices. In particular, we explore the effect of background environment, nanoparticle polydispersity (>10%), and variation in nanoparticle placement (∼5%). At volume fractions less than 20% Au, the optical response is insensitive to particle size, defects, and inhomogeneity in the superlattice. At elevated volume fractions (20% and 25%), structures incorporating different sized nanoparticles (10-, 20-, and 40-nm diameter) each exhibit distinct far-field extinction and near-field properties. These optical properties are most pronounced in lattices with larger particles, which at fixed volume fraction have greater plasmonic coupling than those with smaller particles. Moreover, the incorporation of experimentally informed inhomogeneity leads to variation in far-field extinction and inconsistent electric-field intensities throughout the lattice, demonstrating that volume fraction is not sufficient to describe the optical properties of such structures. These data have important implications for understanding the role of particle and lattice inhomogeneity in determining the properties of plasmonic nanoparticle lattices with deliberately designed optical properties. PMID:26240356
Defect imaging with elastic waves in inhomogeneous-anisotropic materials with composite geometries.
Shlivinski, A; Langenberg, K J
2007-03-01
Imaging of defects in composite structures plays an important role in non-destructive testing (NDT) with elastic waves, i.e., ultrasound. Traditionally the imaging of such defects is performed using the synthetic aperture focusing technique (SAFT) algorithm assuming homogeneous isotropic materials. However, if parts of the structure are inhomogeneous and/or anisotropic, this algorithm fail to produce correct results that are needed in order to asses the lifetime of the part under test. Here we present a modification of this algorithm which enables a correct imaging of defects in inhomogeneous and/or anisotropic composite structures, whence it is termed InASAFT. The InASAFT is based on the exact modelling of the structure in order to account for the true nature of the elastic wave propagation using travel time ray tracing techniques. The algorithm is validated upon several numerical and real life examples yielding satisfactory results for imaging of cracks. The modified algorithm suffers, though, from the same difficulties encountered in the SAFT algorithm, namely "ghost" images and eventual lack of clear focused images. However, these artifacts can be identified using a forward wave propagation analysis of the structure.
NASA Astrophysics Data System (ADS)
Li, Yao; Qian, Dan; Xue, Jiawei; Wan, Jingchun; Zhang, Anfeng; Tamura, Nobumichi; Song, Zhongxiao; Chen, Kai
2015-11-01
Synchrotron X-ray microdiffraction was employed to investigate the inhomogeneous distribution of defect and residual strain in the transitional region between the dendritic and stray grains in a laser-assisted 3D printed Ni-based superalloy. The dendritic region was found to be under tensile strain transversely to the primary dendrite arm directions. The dendrite edges, where high level of strains and geometrically necessary dislocations were detected, were discerned as low angle grain boundaries. High angle grain boundaries were observed in the stray grain region, and the orientation of the strain tensor in this region varied dramatically at the micron scale, in contrast with the more or less homogeneous distribution in the dendritic region.
Inhomogeneity Based Characterization of Distribution Patterns on the Plasma Membrane
Paparelli, Laura; Corthout, Nikky; Wakefield, Devin L.; Sannerud, Ragna; Jovanovic-Talisman, Tijana; Annaert, Wim; Munck, Sebastian
2016-01-01
Cell surface protein and lipid molecules are organized in various patterns: randomly, along gradients, or clustered when segregated into discrete micro- and nano-domains. Their distribution is tightly coupled to events such as polarization, endocytosis, and intracellular signaling, but challenging to quantify using traditional techniques. Here we present a novel approach to quantify the distribution of plasma membrane proteins and lipids. This approach describes spatial patterns in degrees of inhomogeneity and incorporates an intensity-based correction to analyze images with a wide range of resolutions; we have termed it Quantitative Analysis of the Spatial distributions in Images using Mosaic segmentation and Dual parameter Optimization in Histograms (QuASIMoDOH). We tested its applicability using simulated microscopy images and images acquired by widefield microscopy, total internal reflection microscopy, structured illumination microscopy, and photoactivated localization microscopy. We validated QuASIMoDOH, successfully quantifying the distribution of protein and lipid molecules detected with several labeling techniques, in different cell model systems. We also used this method to characterize the reorganization of cell surface lipids in response to disrupted endosomal trafficking and to detect dynamic changes in the global and local organization of epidermal growth factor receptors across the cell surface. Our findings demonstrate that QuASIMoDOH can be used to assess protein and lipid patterns, quantifying distribution changes and spatial reorganization at the cell surface. An ImageJ/Fiji plugin of this analysis tool is provided. PMID:27603951
Inhomogeneity Based Characterization of Distribution Patterns on the Plasma Membrane.
Paparelli, Laura; Corthout, Nikky; Pavie, Benjamin; Wakefield, Devin L; Sannerud, Ragna; Jovanovic-Talisman, Tijana; Annaert, Wim; Munck, Sebastian
2016-09-01
Cell surface protein and lipid molecules are organized in various patterns: randomly, along gradients, or clustered when segregated into discrete micro- and nano-domains. Their distribution is tightly coupled to events such as polarization, endocytosis, and intracellular signaling, but challenging to quantify using traditional techniques. Here we present a novel approach to quantify the distribution of plasma membrane proteins and lipids. This approach describes spatial patterns in degrees of inhomogeneity and incorporates an intensity-based correction to analyze images with a wide range of resolutions; we have termed it Quantitative Analysis of the Spatial distributions in Images using Mosaic segmentation and Dual parameter Optimization in Histograms (QuASIMoDOH). We tested its applicability using simulated microscopy images and images acquired by widefield microscopy, total internal reflection microscopy, structured illumination microscopy, and photoactivated localization microscopy. We validated QuASIMoDOH, successfully quantifying the distribution of protein and lipid molecules detected with several labeling techniques, in different cell model systems. We also used this method to characterize the reorganization of cell surface lipids in response to disrupted endosomal trafficking and to detect dynamic changes in the global and local organization of epidermal growth factor receptors across the cell surface. Our findings demonstrate that QuASIMoDOH can be used to assess protein and lipid patterns, quantifying distribution changes and spatial reorganization at the cell surface. An ImageJ/Fiji plugin of this analysis tool is provided. PMID:27603951
Wavenumber and Defect Distributions in Undulation Chaos
NASA Astrophysics Data System (ADS)
Daniels, Karen E.; Bodenschatz, Eberhard
2000-11-01
We report experimental results on thermally driven convection in a large aspect ratio inclined layer with a fluid of Prandtl number σ ≈ 1. Very close to the onset of convection for inclination angles between 20 and 70 degrees, we find the defect turbulent state of undulation chaos (Daniels, Plapp, and Bodenschatz. Phys. Rev. Lett. 84:5320). We characterize this state by determining the defect locations and the wavenumber distribution. A snapshot of the pattern, as well as its wavenumber distribution, can be well-reconstructed from a perfect underlying undulation pattern and the phase field given by the point defects. The defect density distribution shows a crossover from a Poisson to a squared Poisson distribution. By measuring the creation, annihilation, inflow, and outflow rates of defects we can quantitatively explain this behavior. This work is supported by the National Science Foundation DMR-0072077.
Shkilev, V. P.
2012-01-15
Based on the random-trap model and using the mean-field approximation, we derive an equation that allows the distribution of a functional of the trajectory of a particle making random walks over inhomogeneous-lattice site to be calculated. The derived equation is a generalization of the Feynman-Kac equation to an inhomogeneous medium. We also derive a backward equation in which not the final position of the particle but its position at the initial time is used as an independent variable. As an example of applying the derived equations, we consider the one-dimensional problem of calculating the first-passage time distribution. We show that the average first-passage times for homogeneous and inhomogeneous media with identical diffusion coefficients coincide, but the variance of the distribution for an inhomogeneous medium can be many times larger than that for a homogeneous one.
Effect of tissue inhomogeneities on dose distributions from Cf-252 brachytherapy source.
Ghassoun, J
2013-01-01
The Monte Carlo method was used to determine the effect of tissue inhomogeneities on dose distribution from a Cf-252 brachytherapy source. Neutron and gamma-ray fluences, energy spectra and dose rate distributions were determined in both homogenous and inhomogeneous phantoms. Simulations were performed using the MCNP5 code. Obtained results were compared with experimentally measured values published in literature. Results showed a significant change in neutron dose rate distributions in presence of heterogeneities. However, their effect on gamma rays dose distribution is minimal.
NASA Astrophysics Data System (ADS)
Takahashi, T.; Obana, K.; Yamamoto, Y.; Nakanishi, A.; Kodaira, S.; Kaneda, Y.
2011-12-01
In the Nankai trough, there are three seismogenic zones of megathrust earthquakes (Tokai, Tonankai and Nankai earthquakes). Lithospheric structures in and around these seismogenic zones are important for the studies on mutual interactions and synchronization of their fault ruptures. Recent studies on seismic wave scattering at high frequencies (>1Hz) make it possible to estimate 3D distributions of random inhomogeneities (or scattering coefficient) in the lithosphere, and clarified that random inhomogeneity is one of the important medium properties related to microseismicity and damaged structure near the fault zone [Asano & Hasegawa, 2004; Takahashi et al. 2009]. This study estimates the spatial distribution of the power spectral density function (PSDF) of random inhomogeneities the western part of Nankai subduction zone, and examines the relations with crustal velocity structure and seismic activity. Seismic waveform data used in this study are those recorded at seismic stations of Hi-net & F-net operated by NIED, and 160 ocean bottom seismographs (OBSs) deployed at Hyuga-nada region from Dec. 2008 to Jan. 2009. This OBS observation was conducted by JAMSTEC as a part of "Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes" funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. Spatial distribution of random inhomogeneities is estimated by the inversion analysis of the peak delay time of small earthquakes [Takahashi et al. 2009], where the peak delay time is defined as the time lag from the S-wave onset to its maximal amplitude arrival. We assumed the von Karman type functional form for the PSDF. Peak delay times are measured from root mean squared envelopes at 4-8Hz, 8-16Hz and 16-32Hz. Inversion result can be summarized as follows. Random inhomogeneities beneath the Quaternary volcanoes are characterized by strong inhomogeneities at small spatial scale (~ a few hundreds meter) and weak spectral gradient
NASA Astrophysics Data System (ADS)
Unruh, Oliver
2016-09-01
In order to reduce noise emitted by vibrating structures additional damping treatments such as constraint layer damping or embedded elastomer layers can be used. To save weight and cost, the additional damping is often placed at some critical locations of the structure, what leads to spatially inhomogeneous distribution of damping. This inhomogeneous distribution of structural damping leads to an occurrence of complex vibration modes, which are no longer dominated by pure standing waves, but by a superposition of travelling and standing waves. The existence of complex vibration modes raises the question about their influence on sound radiation. Previous studies on the sound radiation of complex modes of rectangular plates reveal, that, depending on the direction of travelling waves, the radiation efficiency of structural modes can slightly decrease or significantly increase. These observations have been made using a rectangular plate with a simple inhomogeneous damping configuration which includes a single plate boundary with a higher structural damping ratio. In order to answer the question about the influence of other possible damping configurations on the sound radiation properties, this paper addresses the self- and mutual-radiation efficiencies of the resulting complex vibration modes. Numerical simulations are used for the calculation of complex structural modes of different inhomogeneous damping configurations with varying geometrical form and symmetry. The evaluation of self- and mutual-radiation efficiencies reveals that primarily the symmetry properties of the inhomogeneous damping distribution affect the sound radiation characteristics. Especially the asymmetric distributions of inhomogeneous damping show a high influence on the investigated acoustic metrics. The presented study also reveals that the acoustic cross-coupling between structural modes, which is described by the mutual-radiation efficiencies, generally increases with the presence of
NASA Astrophysics Data System (ADS)
Takahashi, T.; Obana, K.; Yamamoto, Y.; Nakanishi, A.; Kaiho, Y.; Kodaira, S.; Kaneda, Y.
2012-12-01
The Nankai trough in southwestern Japan is a convergent margin where the Philippine sea plate is subducted beneath the Eurasian plate. There are major faults segments of huge earthquakes that are called Tokai, Tonankai and Nankai earthquakes. According to the earthquake occurrence history over the past hundreds years, we must expect various rupture patters such as simultaneous or nearly continuous ruptures of plural fault segments. Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted seismic surveys at Nankai trough in order to clarify mutual relations between seismic structures and fault segments, as a part of "Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes" funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. This study evaluated the spatial distribution of random velocity inhomogeneities from Hyuga-nada to Kii-channel by using velocity seismograms of small and moderate sized earthquakes. Random velocity inhomogeneities are estimated by the peak delay time analysis of S-wave envelopes (e.g., Takahashi et al. 2009). Peak delay time is defined as the time lag from the S-wave onset to its maximal amplitude arrival. This quantity mainly reflects the accumulated multiple forward scattering effect due to random inhomogeneities, and is quite insensitive to the inelastic attenuation. Peak delay times are measured from the rms envelopes of horizontal components at 4-8Hz, 8-16Hz and 16-32Hz. This study used the velocity seismograms that are recorded by 495 ocean bottom seismographs and 378 onshore seismic stations. Onshore stations are composed of the F-net and Hi-net stations that are maintained by National Research Institute for Earth Science and Disaster Prevention (NIED) of Japan. It is assumed that the random inhomogeneities are represented by the von Karman type PSDF. Preliminary result of inversion analysis shows that spectral gradient of PSDF (i.e., scale dependence of
NASA Astrophysics Data System (ADS)
Neville, D. J.; Knott, J. F.
THE FIRST part of this paper deals with the fracture behaviour of material that is sensibly homogeneous. The statistical distributions of toughness and fracture stress for this case are determined, and the accuracies of the methods used of measuring toughness and fracture stress are assessed. Subsequently, the second part deals with the fracture of microstructurally inhomogeneous (two-phase) materials. The statistical distributions obtained for fracture stress, fracture toughness and critical crack opening displacement are assessed, and the relationships between them for inhomogeneous materials are discussed. A model is developed which explains the shapes of the distributions obtained in terms of a sampling argument. In Part III the model is applied to data for metallurgically inhomogeneous material. This is material which has a homogeneous microstructure but has chemical inhomogeneity due to segregation of alloy elements. These data are from the transition region and the lower shelf and the model predicts accurately the effect of specimen size. The model is also faithful to the change of distribution shape with proximity to the sharp transition in toughness and this too is explainable by the sampling argument.
Inhomogeneous distribution of Chlamydomonas in a cylindrical container with a bubble plume.
Nonaka, Yuki; Kikuchi, Kenji; Numayama-Tsuruta, Keiko; Kage, Azusa; Ueno, Hironori; Ishikawa, Takuji
2016-01-19
Swimming microalgae show various taxes, such as phototaxis and gravitaxis, which sometimes result in the formation of a cell-rich layer or a patch in a suspension. Despite intensive studies on the effects of shear flow and turbulence on the inhomogeneous distribution of microalgae, the effect of a bubble plume has remained unclear. In this study, we used Chlamydomonas as model microalgae, and investigated the spatial distribution of cells in a cylindrical container with a bubble plume. The results illustrate that cells become inhomogeneously distributed in the suspension due to their motility and photo-responses. A vortical ring distribution was observed below the free surface when the bubble flow rate was sufficiently small. We performed a scaling analysis on the length scale of the vortical ring, which captured the main features of the experimental results. These findings are important in understanding transport phenomena in a microalgae suspension with a bubble plume.
Inhomogeneous distribution of Chlamydomonas in a cylindrical container with a bubble plume.
Nonaka, Yuki; Kikuchi, Kenji; Numayama-Tsuruta, Keiko; Kage, Azusa; Ueno, Hironori; Ishikawa, Takuji
2016-01-01
Swimming microalgae show various taxes, such as phototaxis and gravitaxis, which sometimes result in the formation of a cell-rich layer or a patch in a suspension. Despite intensive studies on the effects of shear flow and turbulence on the inhomogeneous distribution of microalgae, the effect of a bubble plume has remained unclear. In this study, we used Chlamydomonas as model microalgae, and investigated the spatial distribution of cells in a cylindrical container with a bubble plume. The results illustrate that cells become inhomogeneously distributed in the suspension due to their motility and photo-responses. A vortical ring distribution was observed below the free surface when the bubble flow rate was sufficiently small. We performed a scaling analysis on the length scale of the vortical ring, which captured the main features of the experimental results. These findings are important in understanding transport phenomena in a microalgae suspension with a bubble plume. PMID:26787679
Inhomogeneous distribution of Chlamydomonas in a cylindrical container with a bubble plume
Nonaka, Yuki; Kikuchi, Kenji; Numayama-Tsuruta, Keiko; Kage, Azusa; Ueno, Hironori; Ishikawa, Takuji
2016-01-01
ABSTRACT Swimming microalgae show various taxes, such as phototaxis and gravitaxis, which sometimes result in the formation of a cell-rich layer or a patch in a suspension. Despite intensive studies on the effects of shear flow and turbulence on the inhomogeneous distribution of microalgae, the effect of a bubble plume has remained unclear. In this study, we used Chlamydomonas as model microalgae, and investigated the spatial distribution of cells in a cylindrical container with a bubble plume. The results illustrate that cells become inhomogeneously distributed in the suspension due to their motility and photo-responses. A vortical ring distribution was observed below the free surface when the bubble flow rate was sufficiently small. We performed a scaling analysis on the length scale of the vortical ring, which captured the main features of the experimental results. These findings are important in understanding transport phenomena in a microalgae suspension with a bubble plume. PMID:26787679
Inhomogeneous distribution of water droplets in cloud turbulence.
Fouxon, Itzhak; Park, Yongnam; Harduf, Roei; Lee, Changhoon
2015-09-01
We consider sedimentation of small particles in the turbulent flow where fluid accelerations are much smaller than acceleration of gravity g. The particles are dragged by the flow by linear friction force. We demonstrate that the pair-correlation function of particles' concentration diverges with decreasing separation as a power law with negative exponent. This manifests fractal distribution of particles in space. We find that the exponent is proportional to ratio of integral of energy spectrum of turbulence times the wave number over g. The proportionality coefficient is a universal number independent of particle size. We derive the spectrum of Lyapunov exponents that describes the evolution of small patches of particles. It is demonstrated that particles separate dominantly in the horizontal plane. This provides a theory for the recently observed vertical columns formed by the particles. We confirm the predictions by direct numerical simulations of Navier-Stokes turbulence. The predictions include conditions that hold for water droplets in warm clouds thus providing a tool for the prediction of rain formation.
Inhomogeneous snow distribution and depletion patterns at grid scale in a shallow snowpack region
NASA Astrophysics Data System (ADS)
Li, H.; Wang, J.; Tang, Z.; Wang, J.
2012-10-01
Understanding inhomogeneous snow processes at the grid scale is crucial for distributed snow hydrology research. Many studies on inhomogeneous snow processes focus on the annual similarity of snow distribution and depletion and the roles of topography and other environmental conditions. In contrast, this study examines the snow distribution and depletion patterns at a small grid scale in a shallow snowpack region and analyzes how meteorological factors influence these patterns by using the SNOWPACK model for scenario simulations. These simulations enable quantification of the role of three main meteorological factors: shortwave radiation, longwave radiation, and air temperature. The study region is located in the Northeastern Qinghai-Tibet plateau. The results of the study indicate the following two points. (1) During different snowmelt periods, spatial similarity exists between the periodical cumulative snow distributions, and the relationships between snow cover fraction and mean snow water equivalent are similar. However, this similarity is not applicable to the period before snowmelt. (2) Shortwave radiation has a~major impact on the snow distribution and depletion patterns at the small grid scale. Increasing shortwave radiation can greatly promote the heterogeneity of the snow distribution. The contributions of longwave radiation and air temperature to the heterogeneity of snow distribution are minor. Moreover, there are similarities between the simulated snow distributions when considering the scenarios of increases in longwave radiation or in air temperature.
NASA Astrophysics Data System (ADS)
Zólyomi, V.; Simon, F.; Rusznyák, Á.; Pfeiffer, R.; Peterlik, H.; Kuzmany, H.; Kürti, J.
2007-05-01
Vibrational modes of C13 isotope enriched single-walled carbon nanotubes are inhomogeneously broadened due to the random distribution of isotopes. We study this effect on the radial breathing mode theoretically using density-functional theory within the local-density approximation and compare the result with experiments on inner tubes in double-walled carbon nanotubes grown from C13 -enriched fullerenes. Increased inhomogeneity was achieved by growing inner tubes from a mixture of enriched and natural fullerenes, which is explained by the calculations. This shows the absence of carbon diffusion along the tube axis during inner tube growth, supporting the theory of inner tube growth by Stone-Wales transformations from interconnected fullerenes.
Defect distribution near the surface of electron-irradiated silicon
NASA Technical Reports Server (NTRS)
Wang, K. L.; Lee, Y. H.; Corbett, J. W.
1978-01-01
The surface-defect distributions of electron-irradiated n-type silicon have been investigated using a transient capacitance technique. Schottky, p-n junction, and MOS structures were used in profiling the defect distributions. Surface depletions of defects observed were attributed to the vacancy distribution, but not that of oxygen, and other capture centers' distributions. The vacancy diffusion length at 300 K was estimated to be about 3-6 microns.
Serov, A.V.
1995-12-31
The time variation of the spartial distribution of an electron beam reflected by an inhomogeneous wave or traverse the wave was investigated. The injected beam is perpendicular to the direction of propagation of the wave. The interaction between an electron beam and an electromagnetic wave not only produces electron oscillation but also substantially changes the electron phase and energy distribution. It is shown that under specific conditions one part of particles are reflected by an electromagnetic wave and other part of particles traverse the wave.
Expansion-free evolving spheres must have inhomogeneous energy density distributions
Herrera, L.; Le Denmat, G.; Santos, N. O.
2009-04-15
In a recent paper a systematic study on shearing expansion-free spherically symmetric distributions was presented. As a particular case of such systems, the Skripkin model was mentioned, which corresponds to a nondissipative perfect fluid with a constant energy density. Here we show that such a model is inconsistent with junction conditions. It is shown that in general for any nondissipative fluid distribution, the expansion-free condition requires the energy density to be inhomogeneous. As an example we consider the case of dust, which allows for a complete integration.
NASA Astrophysics Data System (ADS)
Carvalho, C. Sofia; Basilakos, Spyros
2016-08-01
We use a kinematic parametrisation of the luminosity distance to measure the angular distribution on the sky of time derivatives of the scale factor, in particular the Hubble parameter H0, the deceleration parameter q0, and the jerk parameter j0. We apply a recently published method to complement probing the inhomogeneity of the large-scale structure by means of the inhomogeneity in the cosmic expansion. This parametrisation is independent of the cosmological equation of state, which renders it adequate to test interpretations of the cosmic acceleration alternative to the cosmological constant. For the same analytical toy model of an inhomogeneous ensemble of homogenous pixels, we derive the backreaction term in j0 due to the fluctuations of { H0,q0 } and measure it to be of order 10-2 times the corresponding average over the pixels in the absence of backreaction. In agreement with that computed using a ΛCDM parametrisation of the luminosity distance, the backreaction effect on q0 remains below the detection threshold. Although the backreaction effect on j0 is about ten times that on q0, it is also below the detection threshold. Hence backreaction remains unobservable both in q0 and in j0.
Angular distribution of cosmological parameters as a probe of space-time inhomogeneities
NASA Astrophysics Data System (ADS)
Carvalho, C. Sofia; Marques, Katrine
2016-08-01
We develop a method based on the angular distribution on the sky of cosmological parameters to probe the inhomogeneity of large-scale structure and cosmic acceleration. We demonstrate this method on the largest type Ia supernova (SN) data set available to date, as compiled by the Joint Light-curve Analysis (JLA) collaboration and, hence, consider the cosmological parameters that affect the luminosity distance. We divide the SN sample into equal surface area pixels and estimate the cosmological parameters that minimize the chi-square of the fit to the distance modulus in each pixel, hence producing maps of the cosmological parameters {ΩM,ΩΛ,H0} . In poorly sampled pixels, the measured fluctuations are mostly due to an inhomogeneous coverage of the sky by the SN surveys; in contrast, in well-sampled pixels, the measurements are robust enough to suggest a real fluctuation. We also measure the anisotropy of the parameters by computing the power spectrum of the corresponding maps of the parameters up to ℓ = 3. For an analytical toy model of an inhomogeneous ensemble of homogeneous pixels, we derive the backreaction term in the deceleration parameter due to the fluctuations of H0 across the sky and measure it to be of order 10-3 times the corresponding average over the pixels in the absence of backreaction. We conclude that, for the toy model considered, backreaction is not a viable dynamical mechanism to emulate cosmic acceleration.
The permselectivity of membrane systems with an inhomogeneous distribution of fixed charge groups
Sokirko, A.V. . Dept. of Hydromechanics); Manzanares, J.A.; Pellicer, J. . Dept. de Termodinamica)
1994-11-01
The influence of the inhomogeneities in the fixed charge distribution on the transport properties (permselectivity and current-voltage characteristics) of ion-exchange membranes is theoretically studied. A simple, approximate method for the analytical solution of the Nernst-Planck equations with the assumption of local electroneutrality is presented. Special attention is paid to the effect of the diffusion boundary layers on the permselectivity of the membrane system. Two fixed charge distributions (linear and exponential) are considered in detail. It is predicted that these distributions could show higher permselectivities than a homogeneous distribution with the same average concentration. Still, the membrane permselectivity is mainly determined by the average fixed charge concentration and the thickness of the boundary layers.
Effects of inhomogeneous irradiation distribution on a PV array in an urban environment
Kovach, A.
1994-12-31
The effect of inhomogeneous irradiation on building-integrated photovoltaic arrays is studied with the help of the simulation program, PVPACK, developed in this work. Particular attention is paid to the effect of partial shading and reflection on photovoltaic (PV) arrays from the surrounding environment. By incorporating the raytracing program, RADIANCE, the irradiation distribution on the building surface can be calculated with a high resolution. Simulation results show that a poorly planned lay-out design of a PV array on a building can lead to large energy losses. Such a simulation tool is a helpful aid for successful incorporation of PV in the building sector.
Thermal rectification in silicon by a graded distribution of defects
NASA Astrophysics Data System (ADS)
Dettori, Riccardo; Melis, Claudio; Rurali, Riccardo; Colombo, Luciano
2016-06-01
We discuss about computer experiments based on nonequilibrium molecular dynamics simulations providing evidence that thermal rectification can be obtained in bulk Si by a non-uniform distribution of defects. We consider a graded population of both Ge substitutional defects and nanovoids, distributed along the direction of an applied thermal bias, and predict a rectification factor comparable to what is observed in other low-dimensional Si-based nanostructures. By considering several defect distribution profiles, thermal bias conditions, and sample sizes, the present results suggest that a possible way for tuning the thermal rectification is by defect engineering.
NASA Astrophysics Data System (ADS)
Brauer, R.; Wolf, S.
2016-01-01
Context. Analysis of observations of circumstellar disks around young stellar objects is often based on disk models with smooth and continuous density distribution. However, spatially resolved observations with increasing angular resolution and dynamical models indicate that circumstellar disks are highly structured. Aims: We investigate the influence of different clumpy density distributions on selected physical properties and on the observable characteristics of circumstellar disks. In particular, these are the temperature distribution, the spectral energy distribution (SED), the radial brightness profile and the degree of polarization of scattered stellar radiation. Methods: Based on radiative transfer modeling we calculated the temperature structure of the disk and simulate observational quantities in the thermal re-emission and scattering regime. The clumpy density distributions are realized using a two-phase medium approach with phases for the clumps and the medium in between. We compared our results to those obtained for a smooth and continuous density distribution to quantify the influence of clumps on internal physical parameters and observable quantities of circumstellar disks. Results: Within the considered model space, the clumpiness has a significant impact on the disk temperature distribution. For instance, in the transition region from the optically thin upper disk layers to the disk interior, it causes a decrease in the mean temperature by up to 12 K (corresponding to ~15%), if compared to continuous disks. In addition, circumstellar disks with clumpy density distributions generally feature a lower spectral index in the submm/mm range of the SED than continuous disks. The strength of this decrease can be varied by changing the dust mass or grain size, but not by changing the inclination of the disk. As a consequence of the lower spectral index, the dust grain size derived from the submm/mm-slope of the SED may be overestimated, if the inhomogeneity
McCallum, Kenneth Jordan; Wang, Ji-Ping
2013-07-01
Copy number variations (CNVs) are a significant source of genetic variation and have been found frequently associated with diseases such as cancers and autism. High-throughput sequencing data are increasingly being used to detect and quantify CNVs; however, the distributional properties of the data are not fully understood. A hidden Markov model (HMM) is proposed using inhomogeneous emission distributions based on negative binomial regression to account for the sequencing biases. The model is tested on the whole genome sequencing data and simulated data sets. An algorithm for CNV detection is implemented in the R package CNVfinder. The model based on negative binomial regression is shown to provide a good fit to the data and provides competitive performance compared with methods based on normalization of read counts. PMID:23428932
NASA Astrophysics Data System (ADS)
Vasilevskaya, Valentina V.; Aerov, Artem A.; Khokhlov, Alexei R.
2004-05-01
"Swiss-cheese" polyelectrolyte gels (i.e., gels containing a regular set of closed spherical pores) are considered as a suitable system for modeling of a medium with extremely inhomogeneous distribution of charged species. It is shown that the inhomogeneous distribution of ions in Swiss-cheese polyelectrolyte gels can be reached simply by immersion of the gels in an aqueous solution of charged species (e.g., low-molecular 1-1 salt or multivalent ions and macroions charged likely to the gel chains). If a polymer gel is kept in such a solution for a long time, the concentration of ions within relatively big voids becomes equal to that in external solution. On the other hand, due to the Donnan effect the ion's concentration in polymer matrix is always lower than that in external solution. As a result the multivalent ions distribute between water voids and polymer matrix. The extent of this distribution is characterized by partition coefficient kD (determined as ratio kD=nsvoid/nsmat of the concentrations nsvoid and nsmat of ions in water voids and in polymer matrix, correspondingly). It is shown that the partition coefficient kD can be larger than 10 for low-molecular salt, reaches 103 for bivalent ions, and is higher than 106 for tetravalent ions. In the case of polymer macroions the partition coefficient kD tends to infinity. Our calculations show that the lower limit of characteristic scales of heterogeneity (determined by water voids size starting from which the condition of total electroneutrality is fulfilled and effect of partition is the most pronounced) can be equal to tens of nanometers.
Positron sensing of distribution of defects in depth materials
NASA Astrophysics Data System (ADS)
Kupchishin, A. I.; Kupchishin, A. A.; Voronova, N. A.; Kirdyashkin, V. I.
2016-02-01
It was developed a non-destructive method of positron sensing, which allows to determine the distribution of defects in the depth of the material. From the analysis we can conclude that the angular distribution curves of annihilation photons (well as and on the characteristics in experiments on the lifetime, 3γ - angular correlation, Doppler effect) is influenced by three main factors: a) The distribution of defects in the depth of the material, their dimensions as well as parameters of the interaction of positrons with defects. With increasing the concentration of defects the intensity Jγ(a, ξ) varies more; b) Modification of the energy spectrum of slow positrons due to the influence of defects, wherein the spectrum of positrons becomes softer, and the average energy of the positron annihilation is reduced; c) Deformation of the momentum distribution of the electrons in the region of defect. The energy spectrum of electrons is also becomes softer, and the average energy of the electrons (on which positrons annihilate) is less. The experimentally were measured spectra of photons in the zone of annihilation and were calculated the distribution of defects in depth for a number of metals.
Graphene materials having randomly distributed two-dimensional structural defects
Kung, Harold H; Zhao, Xin; Hayner, Cary M; Kung, Mayfair C
2013-10-08
Graphene-based storage materials for high-power battery applications are provided. The storage materials are composed of vertical stacks of graphene sheets and have reduced resistance for Li ion transport. This reduced resistance is achieved by incorporating a random distribution of structural defects into the stacked graphene sheets, whereby the structural defects facilitate the diffusion of Li ions into the interior of the storage materials.
Graphene materials having randomly distributed two-dimensional structural defects
Kung, Harold H.; Zhao, Xin; Hayner, Cary M.; Kung, Mayfair C.
2016-05-31
Graphene-based storage materials for high-power battery applications are provided. The storage materials are composed of vertical stacks of graphene sheets and have reduced resistance for Li ion transport. This reduced resistance is achieved by incorporating a random distribution of structural defects into the stacked graphene sheets, whereby the structural defects facilitate the diffusion of Li ions into the interior of the storage materials.
Monte Carlo N Particle code - Dose distribution of clinical electron beams in inhomogeneous phantoms
Nedaie, H. A.; Mosleh-Shirazi, M. A.; Allahverdi, M.
2013-01-01
Electron dose distributions calculated using the currently available analytical methods can be associated with large uncertainties. The Monte Carlo method is the most accurate method for dose calculation in electron beams. Most of the clinical electron beam simulation studies have been performed using non- MCNP [Monte Carlo N Particle] codes. Given the differences between Monte Carlo codes, this work aims to evaluate the accuracy of MCNP4C-simulated electron dose distributions in a homogenous phantom and around inhomogeneities. Different types of phantoms ranging in complexity were used; namely, a homogeneous water phantom and phantoms made of polymethyl methacrylate slabs containing different-sized, low- and high-density inserts of heterogeneous materials. Electron beams with 8 and 15 MeV nominal energy generated by an Elekta Synergy linear accelerator were investigated. Measurements were performed for a 10 cm × 10 cm applicator at a source-to-surface distance of 100 cm. Individual parts of the beam-defining system were introduced into the simulation one at a time in order to show their effect on depth doses. In contrast to the first scattering foil, the secondary scattering foil, X and Y jaws and applicator provide up to 5% of the dose. A 2%/2 mm agreement between MCNP and measurements was found in the homogenous phantom, and in the presence of heterogeneities in the range of 1-3%, being generally within 2% of the measurements for both energies in a "complex" phantom. A full-component simulation is necessary in order to obtain a realistic model of the beam. The MCNP4C results agree well with the measured electron dose distributions. PMID:23533162
NASA Astrophysics Data System (ADS)
Takahashi, Tsutomu; Obana, Koichiro; Yamamoto, Yojiro; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki
2013-05-01
waves at high frequencies (>1 Hz) show collapsed and broadened wave trains caused by multiple scattering in the lithosphere. This study analyzed the envelopes of direct S waves in southwestern Japan and on the western side of the Nankai trough and estimated the spatial distribution of random inhomogeneities by assuming a von Kármán type power spectral density function (PSDF). Strongly inhomogeneous media have been mostly imaged at shallow depth (0-20 km depth) in the onshore area of southwestern Japan, and their PSDF is represented as P(m) ≈ 0.05m-3.7 km3, with m being the spatial wave number, whereas most of the other area shows weak inhomogeneities of which PSDF is P(m) ≈ 0.005m-4.5 km3. At Hyuga-nada in Nankai trough, there is an anomaly of inhomogeneity of which PSDF is estimated as P(m) ≈ 0.01m-4.5 km3. This PSDF has the similar spectral gradient with the weakly inhomogeneous media, but has larger power spectral density than other offshore areas. This anomalous region is broadly located in the subducted Kyushu Palau ridge, which was identified by using velocity structures and bathymetry, and it shows no clear correlation with the fault zones of large earthquakes in past decades. These spatial correlations suggest that possible origins of inhomogeneities at Hyuga-nada are ancient volcanic activity in the oceanic plate or deformed structures due to the subduction of the Kyushu Palau ridge.
Zhang, Yanni; Pan, Jie
2015-05-01
This paper studies the effects of an embedded and distributed inhomogeneity on the underwater sound radiation from an elastically coated plate. Embedding a signal conditioning plate (SCP) in the coating material provides an extra parameter for controlling the sound radiation of the plate, as compared with the previous design with an SCP on the coating surface [Y. Zhang and J. Pan, J. Acoust. Soc. Am. 133(1), 173-185 (2013)]. For such a configuration, the vibration and sound responses of the coated plate to a point force excitation are described by three coupled Fredholm integral equations of the second kind. Its acoustical properties are examined by comparing the radiation powers from plates without an SCP, with a surface SCP, and with an embedded SCP. The differences in the sound powers are explained through resonance and scattering caused by the interaction of the embedded SCP with structural waves. The effects of the depth of the embedded SCP in the coating material on the sound radiation properties of the plate are discussed in detail.
NASA Astrophysics Data System (ADS)
Chen, Dongyue; Murakami, Kenta; Dohi, Kenji; Nishida, Kenji; Soneda, Naoki; Li, Zhengcao; Liu, Li; Sekimura, Naoto
2015-12-01
Although heavy ion irradiation is a good tool to simulate neutron irradiation-induced damages in light water reactor, it produces inhomogeneous defect distribution. Such difference in defect distribution brings difficulty in comparing the microstructure evolution and mechanical degradation between neutron and heavy ion irradiation, and thus needs to be understood. Stainless steel is the typical structural material used in reactor core, and could be taken as an example to study the inhomogeneous defect depth distribution in heavy ion irradiation and its influence on the tested irradiation hardening by nano-indentation. In this work, solution annealed stainless steel model alloys are irradiated by 3 MeV Fe2+ ions at 400 °C to 3 dpa to produce Frank loops that are mainly interstitial in nature. The silicon content of the model alloys is also tuned to change point defect diffusion, so that the loop depth distribution influenced by diffusion along the irradiation beam direction could be discussed. Results show that in low Si (0% Si) and base Si (0.42% Si) samples the depth distribution of Frank loop density quite well matches the dpa profile calculated by the SRIM code, but in high Si sample (0.95% Si), the loop number density in the near-surface region is very low. One possible explanation could be Si's role in enhancing the effective vacancy diffusivity, promoting recombination and thus suppressing interstitial Frank loops, especially in the near-surface region, where vacancies concentrate. By considering the loop depth distribution, the tested irradiation hardening is successfully explained by the Orowan model. A hardening coefficient of around 0.30 is obtained for all the three samples. This attempt in interpreting hardening results may make it easier to compare the mechanical degradation between different irradiation experiments.
Simulated models of inhomogeneous broadening in perturbed angular correlation spectroscopy (PAC)
NASA Astrophysics Data System (ADS)
Stufflebeam, Michael A.; Hodges, Jeffery A.; Evenson, William E.; Matheson, P.; Zacate, M. O.
2007-10-01
All real crystals have defects: missing atoms (vacancies), impurities, atoms out of place, etc. In perturbed angular correlation (PAC), these defects produce damping of the correlation signal in time and broadening of the frequency spectrum. This broadening is termed ``inhomogeneous broadening'' since it is due to the inhomogeneities (i.e. defects) in the crystal. We have simulated PAC spectra for various concentrations (0.1% to 5%) of distant randomly distributed defects plus a near-neighbor vacancy in simple cubic and face-centered cubic crystal structures. For every particular set of defects, the randomly distributed defects and the near-neighbor vacancy together produce a net electric field gradient (EFG), from which we obtain the PAC spectrum. We fit average PAC spectra to study the effects of defect concentration and crystal structure on inhomogeneous broadening as an aid to analyzing experimental data.
Li, Xiaoqi; Jiang, Huabei
2013-02-21
We present a study through extensive simulation that considers the impact of inhomogeneous optical scattering coefficient distribution on recovery of optical absorption coefficient maps using tomographic photoacoustic data collected from media mimicking breast tissue. We found that while the impact of scattering heterogeneities/targets is modest on photoacoustic recovery of optical absorption coefficients, the impact of scattering contrast caused by adipose tissue, a layer of normal tissue along the boundary of the breast, is dramatic on reconstruction of optical absorption coefficients using photoacoustic data-up to 25.8% relative error in recovering the absorption coefficient is estimated in such cases. To overcome this problem, we propose a new method to enhance photoacoustic recovery of the optical absorption coefficient in heterogeneous media by considering inhomogeneous scattering coefficient distribution provided by diffuse optical tomography (DOT). Results from extensive simulations show that photoacoustic recovery of absorption coefficient maps can be improved considerably with a priori scattering information from DOT.
Zeng Chuan; Giantsoudi, Drosoula; Grassberger, Clemens; Goldberg, Saveli; Niemierko, Andrzej; Paganetti, Harald; Efstathiou, Jason A.; Trofimov, Alexei
2013-05-15
Purpose: Biological effect of radiation can be enhanced with hypofractionation, localized dose escalation, and, in particle therapy, with optimized distribution of linear energy transfer (LET). The authors describe a method to construct inhomogeneous fractional dose (IFD) distributions, and evaluate the potential gain in the therapeutic effect from their delivery in proton therapy delivered by pencil beam scanning. Methods: For 13 cases of prostate cancer, the authors considered hypofractionated courses of 60 Gy delivered in 20 fractions. (All doses denoted in Gy include the proton's mean relative biological effectiveness (RBE) of 1.1.) Two types of plans were optimized using two opposed lateral beams to deliver a uniform dose of 3 Gy per fraction to the target by scanning: (1) in conventional full-target plans (FTP), each beam irradiated the entire gland, (2) in split-target plans (STP), beams irradiated only the respective proximal hemispheres (prostate split sagittally). Inverse planning yielded intensity maps, in which discrete position control points of the scanned beam (spots) were assigned optimized intensity values. FTP plans preferentially required a higher intensity of spots in the distal part of the target, while STP, by design, employed proximal spots. To evaluate the utility of IFD delivery, IFD plans were generated by rearranging the spot intensities from FTP or STP intensity maps, separately as well as combined using a variety of mixing weights. IFD courses were designed so that, in alternating fractions, one of the hemispheres of the prostate would receive a dose boost and the other receive a lower dose, while the total physical dose from the IFD course was roughly uniform across the prostate. IFD plans were normalized so that the equivalent uniform dose (EUD) of rectum and bladder did not increase, compared to the baseline FTP plan, which irradiated the prostate uniformly in every fraction. An EUD-based model was then applied to estimate tumor
Defect distribution model validation and effective process control
NASA Astrophysics Data System (ADS)
Zhong, Lei
2003-07-01
Assumption of the underlying probability distribution is an essential part of effective process control. In this article, we demonstrate how to improve the effectiveness of equipment monitoring and process induced defect control through properly selecting, validating and using the hypothetical distribution models. The testing method is based on probability plotting, which is made possible through order statistics. Since each ordered sample data point has a cumulative probability associated with it, which is calculated as a function of sample size, the assumption validity is readily judged by the linearity of the ordered sample data versus the deviate predicted by the assumed statistical model from the cumulative probability. A comparison is made between normal and lognormal distributions to illustrate how dramatically the distribution model could affect the control limit setting. Examples presented include defect data collected on SP1 the dark field inspection tool on a variety of deposited and polished metallic and dielectric films. We find that the defect count distribution is in most cases approximately lognormal. We show that normal distribution is an inadequate assumption, as clearly indicated by the non-linearity of the probability plots. Misuse of normal distribution leads to a too optimistic process control limit, typically 50% tighter than suggested by the lognormal distribution. The inappropriate control limit setting consequently results in an excursion rate at a level too high to be manageable. Lognormal distribution is a valid assumption because it is positively skewed, which adequately takes into account the fact that defect count distribution is typically characteristic of a long tail. In essence, use of lognormal distribution is a suggestion that the long tail be treated as part of the process entitlement (capability) instead of process excursion. The adjustment of the expected process entitlement is reflected and quantified by the skewness of
Concentration dependence of inhomogeneous broadening in perturbed angular correlation spectroscopy
NASA Astrophysics Data System (ADS)
Moreno, Carlos; Hodges, Jeffery A.; Park, Tyler; Stufflebeam, Michael; Evenson, W.; Matheson, P.; Zacate, M. O.
2008-10-01
Since real crystals always include defects, the effect of the defects on crystal properties depends on how many defects are present, i.e. on defect concentration. In perturbed angular correlation (PAC), these defects produce damping of the correlation signal in time and broadening of the frequency spectrum. This ``inhomogeneous broadening'' depends quantitatively on defect concentration, so the size of the broadening in a PAC spectrum can be a measure of the concentration of defects. Using simulated PAC spectra and independent component analysis to obtain the probability distribution function for electric field gradient (EFG) components, we have found defect concentration-dependent parameters for the probability functions. This allows us to calculate broadened PAC spectra for any selected defect concentration. It also allows us to fit defect concentration from an experimental PAC spectrum. This work will be applied initially to broadened PAC data from β-Mn, Al-doped β-Mn, and Sr2RuO4.
Evolution of the statistical distribution in a topological defect network
NASA Astrophysics Data System (ADS)
Xue, Fei; Wang, Xueyun; Socolenco, Ion; Gu, Yijia; Chen, Long-Qing; Cheong, Sang-Wook
2015-11-01
The complex networks of numerous topological defects in hexagonal manganites are highly relevant to vastly different phenomena from the birth of our cosmos to superfluidity transition. The topological defects in hexagonal manganites form two types of domain networks: type-I without and type-II with electric self-poling. A combined phase-field simulations and experimental study shows that the frequencies of domains with N-sides, i.e. of N-gons, in a type-I network are fitted by a lognormal distribution, whereas those in type-II display a scale-free power-law distribution with exponent ∼2. A preferential attachment process that N-gons with a larger N have higher probability of coalescence is responsible for the emergence of the scale-free networks. Since the domain networks can be observed, analyzed, and manipulated at room temperature, hexagonal manganites provide a unique opportunity to explore how the statistical distribution of a topological defect network evolves with an external electric field.
Chelcea, R I; Fechete, R; Culea, E; Demco, D E; Blümich, B
2009-02-01
The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG (1)H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/T(2,short) and 1/T(2,long) were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T(1)/T(2) ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T(2)/T(2,eff) is derived as a function of the T(1)/T(2) ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T(1)-T(2) correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T(1)-T(2) experimental correlations maps were corrected for the T(1)/T(2) effect using the derived T(2)/T(2,eff) correction factor.
Simulated models of inhomogeneous broadening in perturbed angular correlation spectroscopy
NASA Astrophysics Data System (ADS)
Hodges, Jeffery A.; Park, Tyler; Stufflebeam, Michael; Evenson, W.; Matheson, P.; Zacate, M. O.
2008-10-01
All real crystals have defects such as impurities and vacancies which affect their properties. In perturbed angular correlation (PAC), these defects produce damping of the correlation signal in time and broadening of the frequency spectrum. This broadening is termed ``inhomogeneous broadening'' since it is due to the inhomogeneities (i.e. defects) in the crystal. We have simulated PAC spectra for various concentrations (0.1% to 15%) of randomly distributed defects with a near-neighbor vacancy in simple cubic and face-centered cubic crystal structures. For every particular set of defects, the randomly distributed defects and the near-neighbor vacancy together produce a net electric field gradient (EFG), from which we obtain the PAC spectrum. We then average PAC spectra to study the effects of defect concentration and crystal structure on inhomogeneous broadening as an aid to analyzing experimental data. This work will be applied initially to broadened PAC data from β-Mn, Al-doped β-Mn, and Sr2RuO4.
NASA Astrophysics Data System (ADS)
Yan, Jianfeng; Zou, Guisheng; Wu, Aiping; Ren, Jialie; Hu, Anming; Zhou, Y. Norman
2012-07-01
Low-temperature bonding by sintering of Ag nanoparticles (NPs) is a promising lead-free bonding technique used in the electronic packaging industry. In this work, we prepare Ag nanoparticle (NP) paste using both an aqueous method and a polyol method. Sintering bonding trials were then conducted using different forms of Ag NPs. The results showed that use of the aqueous-based Ag NP paste led to inhomogeneous distribution of NPs, known as the "coffee-ring effect." This led to low strength of fabricated joints. We investigated the influence of the coffee-ring effect and ways to depress it by changing the bonding material composition. Our results show that, when using polyol-based Ag NP paste as the bonding material, the coffee-ring effect was successfully depressed due to increased Marangoni flow. The corresponding shear strength of joints was increased significantly to 50 MPa at bonding temperature of 250°C.
NASA Astrophysics Data System (ADS)
Xue, Hong-Tao; Tang, Fu-Ling; Zhang, Fu-Zhen; Lu, Wen-Jiang; Feng, Yu-Dong
2016-01-01
The distribution morphologies and inhomogeneity degrees of Se-S atoms in CuIn(Se1-x S x )2 (CISS) alloys with seven concentrations of sulphur atoms were studied at the temperature range from 23 K to 973 K using Monte Carlo simulations based on the cluster expansion method and first-principles calculations. We found the S(Se) atoms in CISS alloys cluster in a form of ellipsoid or lamella at low temperatures as the concentration of S atoms changes. And the Se-S distribution in CISS alloys becomes more and more homogeneous as the temperature increases. A sharp decline in the inhomogeneity degree σ within a certain temperature range for CISS alloys indicates a phase transition from an inhomogeneous state to a homogeneous state is occurring. And the homogeneous state here is not a totally homogeneous state due to the unavoidable inhomogeneity of CISS alloys. The relation between the inhomogeneity degree and temperature follows well the Boltzmann function model. Finally, a reliable method for predicting the phase transition temperature of similar alloys was proposed.
Vortex lattice inhomogeneity in spatially inhomogeneous superfluids
NASA Astrophysics Data System (ADS)
Sheehy, Daniel E.; Radzihovsky, Leo
2004-11-01
A trapped degenerate Bose gas exhibits superfluidity with spatially nonuniform superfluid density. We show that the vortex distribution in such a highly inhomogeneous rotating superfluid is nevertheless nearly uniform. The inhomogeneity in vortex density, which diminishes in the rapid-rotation limit, is driven by the discrete way vortices impart angular momentum to the superfluid. This effect favors the highest vortex density in regions where the superfluid density is most uniform (e.g., the center of a harmonically trapped gas). A striking consequence of this is that the boson velocity deviates from a rigid-body form exhibiting a radial-shear flow past the vortex lattice.
Lunnemann, Per; Rabouw, Freddy T; van Dijk-Moes, Relinde J A; Pietra, Francesca; Vanmaekelbergh, Daniël; Koenderink, A Femius
2013-07-23
We demonstrate that a simple silver coated ball lens can be used to accurately measure the entire distribution of radiative transition rates of quantum dot nanocrystals. This simple and cost-effective implementation of Drexhage's method that uses nanometer-controlled optical mode density variations near a mirror, not only allows an extraction of calibrated ensemble-averaged rates, but for the first time also to quantify the full inhomogeneous dispersion of radiative and non radiative decay rates across thousands of nanocrystals. We apply the technique to novel ultrastable CdSe/CdS dot-in-rod emitters. The emitters are of large current interest due to their improved stability and reduced blinking. We retrieve a room-temperature ensemble average quantum efficiency of 0.87 ± 0.08 at a mean lifetime around 20 ns. We confirm a log-normal distribution of decay rates as often assumed in literature, and we show that the rate distribution-width, that amounts to about 30% of the mean decay rate, is strongly dependent on the local density of optical states.
NASA Astrophysics Data System (ADS)
Tranchida, Davide; Piccarolo, Stefano
2007-04-01
A nanoindentation technique using an Atomic Force Microscope (AFM) was applied to characterize the mechanical behaviour of several polymeric samples. Samples with well-defined morphologies, spanning from amorphous to rubbery and semi-crystalline ones, were studied for identifying experimental conditions determining contact mechanics within the elastic range such that Young's moduli could be drawn by the Sneddon's elastic contact model. Structure homogeneity, up to the scale of macroscopic samples used to evaluate the elastic moduli, allowed a successful comparison of these values with those determined by macroscopic tension test on full size samples (a few mm), provided that comparable "overall" deformation rates are used (approx. 10∧-5 m/s). Therefore, it is possible to scale down the measurement of mechanical properties by AFM to the typical resolution of nanoindentations. With this method the distribution of mechanical properties on systems with a spatial distribution of morphology (injection moulded samples) is presented..
Effect of tissue inhomogeneity on dose distribution of point sources of low-energy electrons.
Kwok, C S; Bialobzyski, P J; Yu, S K; Prestwich, W V
1990-01-01
Perturbation in dose distributions of point sources of low-energy electrons at planar interfaces of cortical bone (CB) and red marrow (RM) was investigated experimentally and by Monte Carlo codes EGS and the TIGER series. Ultrathin LiF thermoluminescent dosimeters were used to measure the dose distributions of point sources of 204Tl and 147Pm in RM. When the point sources were at 12 mg/cm2 from a planar interface of CB and RM equivalent plastics, dose enhancement ratios in RM averaged over the region 0-12 mg/cm2 from the interface were measured to be 1.08 +/- 0.03 (SE) and 1.03 +/- 0.03 (SE) for 204Tl and 147Pm, respectively. The Monte Carlo codes predicted 1.05 +/- 0.02 and 1.01 +/- 0.02 for the two nuclides, respectively. However, EGS gave consistently 3% higher dose in the dose scoring region than the TIGER series when point sources of monoenergetic electrons up to 0.75 MeV energy were considered in the homogeneous RM situation or in the CB and RM heterogeneous situation. By means of the TIGER series, it was demonstrated that aluminum, which is normally assumed to be equivalent to CB in radiation dosimetry, leads to an overestimation of backscattering of low-energy electrons in soft tissue at a CB-soft-tissue interface by as much as a factor of 2.
NASA Astrophysics Data System (ADS)
Hasegawa, M.; Tashima, K.; Kotsugi, M.; Ohkochi, T.; Suemitsu, M.; Fukidome, H.
2016-09-01
The intrinsic transport properties, such as carrier mobility and saturation velocity, of graphene are the highest among materials owing to its linear band dispersion and weak backscattering. However, the reported field-effect mobility of transistors using graphene as a channel is much lower than the intrinsic channel mobility. One of the reasons for this low mobility is the high contact resistance between graphene and metals used for the source and drain electrodes, which results from the interfacial roughness. Even Ni, which is a promising contact metal for many materials because of its high adhesion and lower contact resistance, does not meet the requirement as a contact metal for graphene. Noticing that the interfacial roughness between the a metal and graphene is strongly related to the onset of the contact resistance, we performed transmission electron microscopy and photoemission electron microscopy measurements to evaluate the microscopic lateral and longitudinal distributions of Ni atoms at the Ni/graphene interface formed on epitaxial graphene (EG) on 4H-SiC(0001). Our data revealed that the deposited Ni atoms diffused into the EG layers, but they did not reach the EG/SiC interface, and the diffusion was stronger on bilayered graphene than on monolayered graphene. We thus ascribe the layer-number-dependent internal diffusion of Ni atoms in EG as a cause of the microscopic interfacial roughness between graphene and the metal. Ensuring homogeneous distribution of the number of EG layers should be key to lowering the contact resistance.
NASA Astrophysics Data System (ADS)
Ebrahimi, Farzad; Barati, Mohammad Reza
2016-10-01
In this paper, thermo-mechanical buckling analysis of curved functionally graded (FG) nanobeams is carried out via an analytical solution method. Curved FG nanobeam is subjected to uniform, linear and nonlinear temperature distributions across the thickness. Three kinds of boundary condition namely, simply supported-simply supported, simply supported-clamped and clamped-clamped are investigated. Thermo-elastic properties of curved FG beam change in radial direction according to the power-law model. Nonlocal elasticity theory is adopted to capture the size effects. Nonlocal governing equations of curved FG nanobeam are obtained from Hamilton's principle based on Euler-Bernoulli beam model. Finally, the influences of thermal loadings, nonlocal parameter, opening angle, material composition, slenderness ratio and boundary conditions on the thermal buckling behavior of nanosize curved FG beams are explored.
Gaussian distribution of inhomogeneous barrier height in Al/SiO2/p-Si Schottky diodes
NASA Astrophysics Data System (ADS)
Yıldız, D. E.; Altındal, Ş.; Kanbur, H.
2008-06-01
The forward and reverse bias current-voltage (I-V) characteristics of Al/SiO2/p-Si (metal-insulator-semiconductor) type Schottky diodes (SDs) were measured in the temperature range of 200-400 K. Evaluation of the experimental I-V data reveals a decrease in ΦB0 and Rs but an increase in n, with a decrease in temperature. To explain this behavior of ΦB0 with temperature, we have reported a modification which included n and the tunneling parameter αχ1/2δ in the expression of reverse saturation current I0. Thus, a corrected effective barrier height ΦB eff(I -V) vs T has a negative temperature coefficient (α ≈-5×10-4 eV/K), and it is in good agreement with α=-4.73×10-4 eV/K of Si band gap. Such behavior of Rs estimated from Cheung's method could be expected for semiconductors in the temperature region, where there is no carrier freezing out, which is non-negligible at low temperatures. Also, there is a linear correlation between ΦB0(I -V) and n due to the inhomogeneities of the barrier heights (BHs). The conventional activation energy (Ea) plot exhibits nonlinearity below 320 K with the linear portion corresponding to Ea of 0.275 eV. An A∗ value of 1.45×10-5 A cm-2 K-2,which is much lower than the known value of 32 A cm-2 K-2 for p-type Si, is determined from the intercept at the ordinate of this experimental plot. Such behavior is attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution (GD) of BHs due to BH inhomogeneities that prevail at the interface. We attempted to draw a ΦB0 vs q /2kT plot to obtain evidence of a GD of the BHs, and the values of Φ¯B0=1.136 eV and σ0=0.159 V for the mean BH and standard deviation at zero bias have been obtained from this plot. Therefore, the modified ln (I0/T2)-q2σ02/2k2T2 vs q /kT plot gives Φ¯B0 and A∗ values of 1.138 eV and 37.23 A cm-2 K-2, respectively, without using the temperature coefficient of the BH. This A∗ value of 37.23 A cm-2 K-2 is very close to the theoretical
Effects of macroscopic inhomogeneities on electron mobility in semi-insulating GaAs
NASA Technical Reports Server (NTRS)
Walukiewicz, W.; Wang, L.; Pawlowicz, L. M.; Lagowski, J.; Gatos, H. C.
1986-01-01
It is shown that defect inhomogeneities of sizes larger than the electron mean free path are responsible for the low values and anomalous temperature dependence of the electron mobility in semi-insulating (SI) GaAs. The room-temperature electron mobility values below about 6000 sq cm/V s cannot be uniquely used for the determination of the concentration of ionized defects, since the contribution from inhomogeneities usually exceeds that from scattering by ionized impurities. The effects of the macroscopically inhomogeneous distribution of residual acceptors and the major deep donor EL2 diminish at elevated temperatures between 600 and 900 K, which offers a means for identification of inhomogeneities, and furthermore explains recently reported steplike mobility versus temperature behavior in SI-GaAs.
NASA Technical Reports Server (NTRS)
Yang, P.; Gao, B.-C.; Baum, B. A.; Wiscombe, W.; Hu, Y.; Nasiri, S. L.; Soulen, P. F.; Heymsfield, A. J.; McFarquhar, G. M.; Miloshevich, L. M.
2000-01-01
A common assumption in satellite imager-based cirrus retrieval algorithms is that the radiative properties of a cirrus cloud may be represented by those associated with a specific ice crystal shape (or habit) and a single particle size distribution. However, observations of cirrus clouds have shown that the shapes and sizes of ice crystals may vary substantially with height within the clouds. In this study we investigate the sensitivity of the top-of-atmosphere bidirectional reflectances at two MODIS bands centered at 0.65 micron and 2.11 micron to the cirrus models assumed to be either a single homogeneous layer or three distinct but contiguous, layers. First, we define the single- and three-layer cirrus cloud models with respect to ice crystal habit and size distribution on the basis of in situ replicator data acquired during the First ISCCP Regional Experiment (FIRE-II), held in Kansas during the fall of 1991. Subsequently, fundamental light scattering and radiative transfer theory is employed to determine the single scattering and the bulk radiative properties of the cirrus cloud. Regarding the radiative transfer computations, we present a discrete form of the adding/doubling principle by introducing a direct transmission function, which is computationally straightforward and efficient an improvement over previous methods. For the 0.65 micron band, at which absorption by ice is negligible, there is little difference between the bidirectional reflectances calculated for the one- and three-layer cirrus models, suggesting that the vertical inhomogeneity effect is relatively unimportant. At the 2.11 micron band, the bidirectional reflectances computed for both optically thin (tau = 1) and thick (tau = 10) cirrus clouds show significant differences between the results for the one- and three-layer models. The reflectances computed for the three-layer cirrus model are substantially larger than those computed for the single-layer cirrus. Finally, we find that cloud
Lake, Spencer P.; Miller, Kristin S.; Elliott, Dawn M.; Soslowsky, Louis J.
2010-01-01
Tendon exhibits nonlinear stress-strain behavior that may be due, in part, to movement of collagen fibers through the extracellular matrix. While a few techniques have been developed to evaluate the fiber architecture of other soft tissues, the organizational behavior of tendon under load has not been determined. The supraspinatus tendon (SST) of the rotator cuff is of particular interest for investigation due to its complex mechanical environment and corresponding inhomogeneity. In addition, SST injury occurs frequently with limited success in treatment strategies, illustrating the need for a better understanding of SST properties. Therefore, the objective of this study was to quantitatively evaluate the inhomogeneous tensile mechanical properties, fiber organization and fiber realignment under load of human SST utilizing a novel polarized light technique. Fiber distributions were found to become more aligned under load, particularly during the low stiffness toe-region, suggesting that fiber realignment may be partly responsible for observed nonlinear behavior. Fiber alignment was found to correlate significantly with mechanical parameters, providing evidence for strong structure-function relationships in tendon. Human SST exhibits complex, inhomogeneous mechanical properties and fiber distributions, perhaps due to its complex loading environment. Surprisingly, histological grade of degeneration did not correlate with mechanical properties. PMID:19544524
Cloud Inhomogeneity from MODIS
NASA Technical Reports Server (NTRS)
Oreopoulos, Lazaros; Cahalan, Robert F.
2004-01-01
Two full months (July 2003 and January 2004) of MODIS Atmosphere Level-3 data from the Terra and Aqua satellites are analyzed in order to characterize the horizontal variability of cloud optical thickness and water path at global scales. Various options to derive cloud variability parameters are discussed. The climatology of cloud inhomogeneity is built by first calculating daily parameter values at spatial scales of l degree x 1 degree, and then at zonal and global scales, followed by averaging over monthly time scales. Geographical, diurnal, and seasonal changes of inhomogeneity parameters are examined separately for the two cloud phases, and separately over land and ocean. We find that cloud inhomogeneity is weaker in summer than in winter, weaker over land than ocean for liquid clouds, weaker for local morning than local afternoon, about the same for liquid and ice clouds on a global scale, but with wider probability distribution functions (PDFs) and larger latitudinal variations for ice, and relatively insensitive to whether water path or optical thickness products are used. Typical mean values at hemispheric and global scales of the inhomogeneity parameter nu (roughly the mean over the standard deviation of water path or optical thickness), range from approximately 2.5 to 3, while for the inhomogeneity parameter chi (the ratio of the logarithmic to linear mean) from approximately 0.7 to 0.8. Values of chi for zonal averages can occasionally fall below 0.6 and for individual gridpoints below 0.5. Our results demonstrate that MODIS is capable of revealing significant fluctuations in cloud horizontal inhomogenity and stress the need to model their global radiative effect in future studies.
NASA Astrophysics Data System (ADS)
Taylor, Marika; Woodhead, William
2014-12-01
We study models of translational symmetry breaking in which inhomogeneous matter field profiles can be engineered in such a way that black-brane metrics remain isotropic and homogeneous. We explore novel Lagrangians involving square root terms and show how these are related to massive gravity models and to tensionless limits of branes. Analytic expressions for the DC conductivity and for the low frequency scaling of the optical conductivity are derived in phenomenological models, and the optical conductivity is studied in detail numerically. The square root Lagrangians are associated with linear growth in the DC resistivity with temperature and also lead to minima in the optical conductivity at finite frequency, suggesting that our models may capture many features of heavy fermion systems.
Modeling the defect distribution and degradation of CdTe ultrathin films
NASA Astrophysics Data System (ADS)
Gorji, Nima E.
2014-12-01
The defect distribution across an ultrathin film CdTe layer of a CdS/CdTe solar cell is modelled by solving the balance equation in steady state. The degradation of the device parameters due to the induced defects during ion implantation is considered where the degradation rate is accelerated if the defect distribution is considerable. The defect concentration is maximum at the surface of the CdTe layer where implantation is applied and it is minimum at the junction with the CdS layer. It shows that ultrathin devices degrade faster if the defect concentration is high at the junction rather than the back region (CdTe/Metal). Since the front and back contacts of the device are close in ultrathin films and the electric field is strong to drive the defects into the junction, the p-doping process might be precisely controlled during ion implantation. The modeling results presented here are in agreement with the few available experimental reports in literature about the degradation and defect configuration of the ultrathin CdTe films.
Chung, Sung-Yoon; Choi, Si-Young; Kim, Tae-Hwan; Lee, Seongsu
2015-01-27
Atomic-scale exchange between two different cations of similar size in crystalline oxides is one of the major types of point defects when multiple cations in oxygen interstitials are arrayed in an ordered manner. Although a number of studies have been performed on a variety of Li-intercalation olivine phosphates to determine the distribution of exchange defects in bulk, understanding of the thermodynamic stability of the defects in subsurface regions and its dependency on the crystallographic orientation at the surface has remained elusive. Through a combination of small-angle neutron scattering, atomic-scale direct probing with scanning transmission electron microscopy, and theoretical ab initio calculations, we directly demonstrate that the antisite exchange defects are distributed in a highly anisotropic manner near the surfaces of LiFePO4 crystals. Moreover, a substantial amount of cation exchanges between Li and Fe sites is identified as an energetically favorable configuration in some surface regions, showing excellent agreement with the calculation results of negative defect formation energies. The findings in this study provide insight into developing better ways to avoid degradation of lithium mobility through the surface as well as scientifically notable features regarding the distribution of exchange defects in olivine phosphates.
Local Inhomogeneity and Filamentary Superconductivity in Pr-Doped CaFe2As2
NASA Astrophysics Data System (ADS)
Gofryk, Krzysztof; Pan, Minghu; Cantoni, Claudia; Saparov, Bayrammurad; Mitchell, Jonathan E.; Sefat, Athena S.
2014-01-01
We use multiscale techniques to determine the extent of local inhomogeneity and superconductivity in Ca0.86Pr0.14Fe2As2 single crystal. The inhomogeneity is manifested as a spatial variation of the praseodymium concentration, local density of states, and superconducting order parameter. We show that the high-Tc superconductivity emerges from cloverlike defects associated with Pr dopants. The highest Tc is observed in both the tetragonal and collapsed tetragonal phases, and its filamentary nature is a consequence of nonuniform Pr distribution that develops localized, isolated superconducting regions within the crystals.
Local inhomogeneity and filamentary superconductivity in Pr-doped CaFe2As2.
Gofryk, Krzysztof; Pan, Minghu; Cantoni, Claudia; Saparov, Bayrammurad; Mitchell, Jonathan E; Sefat, Athena S
2014-01-31
We use multiscale techniques to determine the extent of local inhomogeneity and superconductivity in Ca0.86Pr0.14Fe2As2 single crystal. The inhomogeneity is manifested as a spatial variation of the praseodymium concentration, local density of states, and superconducting order parameter. We show that the high-Tc superconductivity emerges from cloverlike defects associated with Pr dopants. The highest Tc is observed in both the tetragonal and collapsed tetragonal phases, and its filamentary nature is a consequence of nonuniform Pr distribution that develops localized, isolated superconducting regions within the crystals. PMID:24580484
NASA Astrophysics Data System (ADS)
Yathapu, Nithin; McGarvey, Steve; Brown, Justin; Zhivotovsky, Alexander
2016-03-01
This study explores the feasibility of Automated Defect Classification (ADC) with a Surface Scanning Inspection System (SSIS). The defect classification was based upon scattering sensitivity sizing curves created via modeling of the Bidirectional Reflectance Distribution Function (BRDF). The BRDF allowed for the creation of SSIS sensitivity/sizing curves based upon the optical properties of both the filmed wafer samples and the optical architecture of the SSIS. The elimination of Polystyrene Latex Sphere (PSL) and Silica deposition on both filmed and bare Silicon wafers prior to SSIS recipe creation and ADC creates a challenge for light scattering surface intensity based defect binning. This study explored the theoretical maximal SSIS sensitivity based on native defect recipe creation in conjunction with the maximal sensitivity derived from BRDF modeling recipe creation. Single film and film stack wafers were inspected with recipes based upon BRDF modeling. Following SSIS recipe creation, initially targeting maximal sensitivity, selected recipes were optimized to classify defects commonly found on non-patterned wafers. The results were utilized to determine the ADC binning accuracy of the native defects and evaluate the SSIS recipe creation methodology. A statistically valid sample of defects from the final inspection results of each SSIS recipe and filmed substrate were reviewed post SSIS ADC processing on a Defect Review Scanning Electron Microscope (SEM). Native defect images were collected from each statistically valid defect bin category/size for SEM Review. The data collected from the Defect Review SEM was utilized to determine the statistical purity and accuracy of each SSIS defect classification bin. This paper explores both, commercial and technical, considerations of the elimination of PSL and Silica deposition as a precursor to SSIS recipe creation targeted towards ADC. Successful integration of SSIS ADC in conjunction with recipes created via BRDF
On the origin of the spatial inhomogeneity of photoluminescence in thin-film CIGS solar devices
NASA Astrophysics Data System (ADS)
El-Hajje, Gilbert; Ory, Daniel; Guillemoles, Jean-François; Lombez, Laurent
2016-07-01
In this letter, we investigate the origin of the spatial inhomogeneity of the photoluminescence (PL) intensity maps obtained on thin-film solar cells. Based on a hyperspectral imager setup, we record an absolute map of the quasi-Fermi level splitting Δμ by applying the generalized Planck's law. Then, using scanning confocal microscopy, we perform spatially and time-resolved photoluminescence measurements. This allowed us to quantify and map the micrometric fluctuations of the trapping defect density within these solar cells. Finally, we demonstrate the existence of a direct correlation between the spatial fluctuations of the quasi-Fermi level splitting and the trapping defect density. The latter was found to be correlated with the frequently reported spatially inhomogeneous PL maps of thin-film solar cells. Based on the observed correlation, we can quantify the local losses in quasi-Fermi level splitting induced by the spatial distribution of the trapping defects.
Muntasir, Tanvir E-mail: sumitc@iastate.edu; Chaudhary, Sumit E-mail: sumitc@iastate.edu
2015-11-28
Organic photovoltaics (OPVs) are regarded as promising for solar-electric conversion with steadily improving power conversion efficiencies. For further progress, it is crucial to understand and mitigate defect states (traps) residing in the band-gap of OPV materials. In this work, using capacitance measurements, we analyzed two major bands in the density of states (DOS) energy spectra of defects in poly(3-hexylthiophene) (P3HT); regio-regular and regio-random species of P3HT were compared to elucidate the role of morphological disorder. To accurately interpret the obtained DOS profile, trap emission prefactors and activation energy were extracted from temperature dependent capacitance-frequency measurements, while doping, Fermi energy, built-in voltage, and energy levels of the defects were extracted from capacitance-voltage measurements. We identified that the lower energy band—misinterpreted in literature as a defect distribution—stems from free carrier response. The higher energy defect distribution band for regio-random P3HT was an order of magnitude higher than region-regular P3HT, thus stemming from morphological disorder. Impedance spectroscopy was also employed for further comparison of the two P3HT species.
NASA Astrophysics Data System (ADS)
Muntasir, Tanvir; Chaudhary, Sumit
2015-11-01
Organic photovoltaics (OPVs) are regarded as promising for solar-electric conversion with steadily improving power conversion efficiencies. For further progress, it is crucial to understand and mitigate defect states (traps) residing in the band-gap of OPV materials. In this work, using capacitance measurements, we analyzed two major bands in the density of states (DOS) energy spectra of defects in poly(3-hexylthiophene) (P3HT); regio-regular and regio-random species of P3HT were compared to elucidate the role of morphological disorder. To accurately interpret the obtained DOS profile, trap emission prefactors and activation energy were extracted from temperature dependent capacitance-frequency measurements, while doping, Fermi energy, built-in voltage, and energy levels of the defects were extracted from capacitance-voltage measurements. We identified that the lower energy band—misinterpreted in literature as a defect distribution—stems from free carrier response. The higher energy defect distribution band for regio-random P3HT was an order of magnitude higher than region-regular P3HT, thus stemming from morphological disorder. Impedance spectroscopy was also employed for further comparison of the two P3HT species.
Influence of defect distribution on the reducibility of CeO2-x nanoparticles
NASA Astrophysics Data System (ADS)
Chiara Spadaro, Maria; Luches, Paola; Bertoni, Giovanni; Grillo, Vincenzo; Turner, Stuart; Van Tendeloo, Gustaaf; Valeri, Sergio; D'Addato, Sergio
2016-10-01
Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution- and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties.
Influence of defect distribution on the reducibility of CeO2-x nanoparticles.
Spadaro, Maria Chiara; Luches, Paola; Bertoni, Giovanni; Grillo, Vincenzo; Turner, Stuart; Van Tendeloo, Gustaaf; Valeri, Sergio; D'Addato, Sergio
2016-10-21
Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution- and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties. PMID:27631569
Influence of defect distribution on the reducibility of CeO2-x nanoparticles.
Spadaro, Maria Chiara; Luches, Paola; Bertoni, Giovanni; Grillo, Vincenzo; Turner, Stuart; Van Tendeloo, Gustaaf; Valeri, Sergio; D'Addato, Sergio
2016-10-21
Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution- and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties.
NASA Astrophysics Data System (ADS)
Ferris, Kim; Jones, Dumont
2014-03-01
Local electric fields reflect the structural and dielectric fluctuations in a semiconductor, and affect the material performance both for electron transport and carrier lifetime properties. In this paper, we use the LOCALF methodology with periodic boundary conditions to examine the local electric field distributions and its perturbations for II-VI (CdTe, Cd(1-x)Zn(x)Te) semiconductors, containing Te inclusions and small fluctuations in the local dielectric susceptibility. With inclusion of the induced-field term, the electric field distribution shows enhancements and diminishments compared to the macroscopic applied field, reflecting the microstructure characteristics of the dielectric. Learning methods are applied to these distributions to assess the spatial extent of the perturbation, and determine an electric field defined defect size as compared to its physical dimension. Critical concentrations of defects are assessed in terms of defect formation energies. This work was supported by the US Department of Homeland Security, Domestic Nuclear Detection Office, under competitively awarded contract/IAA HSHQDC-08-X-00872-e. This support does not constitute an express or implied endorsement on the part of the Gov't.
Uchitomi, Naotaka Inoue, Hiroaki; Kato, Takahiro; Toyota, Hideyuki; Uchida, Hiroshi
2015-05-07
Atomic-scale Mn distributions in ferromagnetic ZnSnAs{sub 2}:Mn thin films grown on InP substrates have been studied by applying three-dimensional atom probe (3DAP) microscopy. It is found that Mn atoms in cross-sectional 3DAP maps show the presence of inhomogeneities in Mn distribution, which is characteristic patterns of a spinoidal decomposition phase with slightly high and low concentration regions. The high Mn concentration regions are expected to be coherently clustered MnAs in the zinc-blende structure, resulting in the formation of Mn-As random connecting patterns. The origin of room-temperature ferromagnetism in ZnSnAs{sub 2}:Mn on InP can be well explained by the formation of atomic-scale magnetic clustering by spinoidal decomposition without breaking the continuity of the zinc-blende structure, which has been suggested by previous theoretical works. The lattice-matching between magnetic epi-layers and substrates should be one of the most important factors to avoid the formation of secondary hexagonal MnAs phase precipitates in preparing ferromagnetic semiconductor thin films.
Conn, A. R.; Parker, Q. A.; Zucker, D. B.; Lewis, G. F.; Ibata, R. A.; Martin, N. F.; McConnachie, A. W.; Valls-Gabaud, D.; Tanvir, N.; Irwin, M. J.; Ferguson, A. M. N.; Chapman, S. C.
2013-04-01
We undertake an investigation into the spatial structure of the M31 satellite system utilizing the distance distributions presented in a previous publication. These distances make use of the unique combination of depth and spatial coverage of the Pan-Andromeda Archaeological Survey to provide a large, homogeneous sample consisting of 27 of M31's satellites, as well as M31 itself. We find that the satellite distribution, when viewed as a whole, is no more planar than one would expect from a random distribution of equal size. A disk consisting of 15 of the satellites is however found to be highly significant, and strikingly thin, with an rms thickness of just 12.34{sup +0.75}{sub -0.43} kpc. This disk is oriented approximately edge-on with respect to the Milky Way and almost perpendicular to the Milky Way disk. It is also roughly orthogonal to the disk-like structure regularly reported for the Milky Way satellite system and in close alignment with M31's Giant Stellar Stream. A similar analysis of the asymmetry of the M31 satellite distribution finds that it is also significantly larger than one would expect from a random distribution. In particular, it is remarkable that 20 of the 27 satellites most likely lie on the Milky Way side of the galaxy, with the asymmetry being most pronounced within the satellite subset forming the aforementioned disk. This lopsidedness is all the more intriguing in light of the apparent orthogonality observed between the satellite disk structures of the Milky Way and M31.
Special pinning phenomena in arrays of defects with gradient spatial distributions on niobium film
Wu, Tian-Chiuan; Horng, Lance Wu, Jong-Ching
2015-05-07
Flux pinning effect is related to the strong influence by the presence of defects that act as pinning centers. We present transport experiments that investigate the pinning properties in a spacing-graded array of pinning sites. We have found the asymmetric pinning by arrays of defects with modulated gradient spatial distributions on niobium film. One can clearly see the asymmetric pinning effect for the vortex motion. The dc voltage depends on the amplitude of the ac current and that there is a sharp maximum at matching fields. This curve, however, has an interesting sign reversal phenomenon below the first matching field, which will be investigated more in the future. The dc voltage as a function of dc and ac applied current gives evidence that the artificial arrays of gradient pinning site density induce ratchet effect. This effect can be used to control the vortex motion, which will be important for the application of vortex based on electronic devices.
Direct optical imaging of structural inhomogeneities in crystalline materials.
Grigorev, A M
2016-05-10
A method for optical imaging of structural inhomogeneities in crystalline materials is proposed, based on the differences in the optical properties of the structural inhomogeneity and the homogeneous material near the fundamental absorption edge of the crystalline material. The method can be used to detect defects in both semiconductors and insulators.
NASA Technical Reports Server (NTRS)
Kuczmarski, Maria A.; Neudeck, Philip G.
2000-01-01
Most solid-state electronic devices diodes, transistors, and integrated circuits are based on silicon. Although this material works well for many applications, its properties limit its ability to function under extreme high-temperature or high-power operating conditions. Silicon carbide (SiC), with its desirable physical properties, could someday replace silicon for these types of applications. A major roadblock to realizing this potential is the quality of SiC material that can currently be produced. Semiconductors require very uniform, high-quality material, and commercially available SiC tends to suffer from defects in the crystalline structure that have largely been eliminated in silicon. In some power circuits, these defects can focus energy into an extremely small area, leading to overheating that can damage the device. In an effort to better understand the way that these defects affect the electrical performance and reliability of an SiC device in a power circuit, the NASA Glenn Research Center at Lewis Field began an in-house three-dimensional computational modeling effort. The goal is to predict the temperature distributions within a SiC diode structure subjected to the various transient overvoltage breakdown stresses that occur in power management circuits. A commercial computational fluid dynamics computer program (FLUENT-Fluent, Inc., Lebanon, New Hampshire) was used to build a model of a defect-free SiC diode and generate a computational mesh. A typical breakdown power density was applied over 0.5 msec in a heated layer at the junction between the p-type SiC and n-type SiC, and the temperature distribution throughout the diode was then calculated. The peak temperature extracted from the computational model agreed well (within 6 percent) with previous first-order calculations of the maximum expected temperature at the end of the breakdown pulse. This level of agreement is excellent for a model of this type and indicates that three
Vortices in spatially inhomogeneous superfluids
NASA Astrophysics Data System (ADS)
Sheehy, Daniel E.; Radzihovsky, Leo
2004-12-01
We study vortices in a radially inhomogeneous superfluid, as realized by a trapped degenerate Bose gas in a uniaxially symmetric potential. We show that, in contrast to a homogeneous superfluid, an off-axis vortex corresponds to an anisotropic superflow whose profile strongly depends on the distance to the trap axis. One consequence of this superflow anisotropy is vortex precession about the trap axis in the absence of an imposed rotation. In the complementary regime of a finite prescribed rotation, we compute the minimum-energy vortex density, showing that in the rapid-rotation limit it is extremely uniform, despite a strongly inhomogeneous (nearly) Thomas-Fermi condensate density ρs(r) . The weak radially dependent contribution [∝∇2lnρs(r)] to the vortex distribution, that vanishes with the number of vortices Nv as 1/Nv , arises from the interplay between vortex quantum discreteness (namely their inability to faithfully support the imposed rigid-body rotation) and the inhomogeneous superfluid density. This leads to an enhancement of the vortex density at the center of a typical concave trap, a prediction that is in quantitative agreement with recent experiments. One striking consequence of the inhomogeneous vortex distribution is an azimuthally directed, radially shearing superflow.
Bergman, J E H; Otten, E; Verheij, J B G M; de Walle, H E K
2016-01-01
Periconceptional folic acid (FA) reduces neural tube defect (NTD) risk, but seems to have a varying effect per NTD subtype. We aimed to study the effect of FA supplementation on NTD subtype distribution using data from EUROCAT Northern Netherlands. We included all birth types with non-syndromal NTDs born in 1997-2012. By Fisher's exact test we analyzed possible differences in NTD subtype distribution between a correct FA supplementation group and incorrect FA supplementation group. We found proportionally fewer cervical/thoracic spina bifida cases and more lumbar/sacral spina bifida cases in the correct FA supplementation group, irrespective of the presence of the main NTD risk factors. The effect on NTD subtype distribution was only seen when FA supplementation was started before conception. We conclude that FA not only prevents the occurrence of a significant proportion of NTDs, but might also decrease the severity of NTDs, as long as supplementation is started before conception. PMID:26627544
NASA Astrophysics Data System (ADS)
Ilyushin, Yaroslaw; Kutuza, Boris
Observations and mapping of the upwelling thermal radiation of the Earth is the very promising remote sensing technique for the global monitoring of the weather and precipitations. For reliable interpretation of the observation data, numerical model of the microwave radiative transfer in the precipitating atmosphere is necessary. In the present work, numerical simulations of thermal microwave radiation in the rain have been performed at three wavelengths (3, 8 and 22 mm). Radiative properties of the rain have been simulated using public accessible T-matrix codes (Mishchenko, Moroz) for non-spherical particles of fixed orientation and realistic raindrop size distributions (Marshall-Palmer) within the range of rain intensity 1-100 mm/h. Thermal radiation of infinite flat slab medium and isolated rain cell of kilometer size has been simulated with finite difference scheme for the vectorial radiative transfer equation (VRTE) in dichroic scattering medium. Principal role of cell structure of the rain field in the formation of angular and spatial distribution of the intensity and polarization of the upwelling thermal radiation has been established. Possible approaches to interpretation of satellite data are also discussed. It is necessary that spatial resolution of microwave radiometers be less than rain cell size. At the present time the resolution is approximately 15 km. It can be considerably improved, for example by two-dimensional synthetic aperture millimeter-wave radiometric interferometer for measuring full-component Stokes vector of emission from hydrometeors. The estimates show that in millimeter band it is possible to develop such equipment with spatial resolution of the order of 1-2 km, which is significantly less than the size of rain cell, with sensitivity 0.3-0.5 K. Under this condition the second Stokes parameter may by successfully measured and may be used for investigation of precipitation regions. Y-shaped phased array antenna is the most promising to
Akimoto, Takuma; Seki, Kazuhiko
2015-08-01
Diffusion of molecules in cells plays an important role in providing a biological reaction on the surface by finding a target on the membrane surface. The water retardation (slow diffusion) near the target assists the searching molecules to recognize the target. Here, we consider effects of the surface diffusivity on the effective diffusivity, where diffusion on the surface is slower than that in bulk. We show that the ensemble-averaged mean-square displacements increase linearly with time when the desorption rate from the surface is finite, which is valid even when the diffusion on the surface is anomalous (subdiffusion). Moreover, this slow diffusion on the surface affects the fluctuations of the time-averaged mean-square displacements (TAMSDs). We find that fluctuations of the TAMSDs remain large when the measurement time is smaller than a characteristic time, and decays according to an increase of the measurement time for a relatively large measurement time. Therefore, we find a transition from nonergodic (distributional) to ergodic diffusivity in a target search process. Moreover, this fluctuation analysis provides a method to estimate an unknown surface diffusivity.
NASA Technical Reports Server (NTRS)
Thomas, J. L.; Diskin, B.; Brandt, A.
1999-01-01
The distributed-relaxation multigrid and defect- correction methods are applied to the two- dimensional compressible Navier-Stokes equations. The formulation is intended for high Reynolds number applications and several applications are made at a laminar Reynolds number of 10,000. A staggered- grid arrangement of variables is used; the coupled pressure and internal energy equations are solved together with multigrid, requiring a block 2x2 matrix solution. Textbook multigrid efficiencies are attained for incompressible and slightly compressible simulations of the boundary layer on a flat plate. Textbook efficiencies are obtained for compressible simulations up to Mach numbers of 0.7 for a viscous wake simulation.
Simulation of external contamination into water distribution systems through defects in pipes
NASA Astrophysics Data System (ADS)
López, P. A.; Mora, J. J.; García, F. J.; López, G.
2009-04-01
Water quality can be defined as a set of properties (physical, biological and chemical) that determine its suitability for human use or for its role in the biosphere. In this contribution we focus on the possible impact on water distribution systems quality of external contaminant fluids entering through defects in pipes. The physical integrity of the distribution system is a primary barrier against the entry of external contaminants and the loss in quality of the treated drinking water, but this integrity can be broken. Deficiencies in physical and hydraulic integrity can lead into water losses, but also into the influx of contaminants through pipes walls, either through breaks coming from external subsoil waters, or via cross connections coming from sewerage or other facilities. These external contamination events (the so called pathogen intrusion phenomenon) can act as a source of income by introducing nutrients and sediments as well as decreasing disinfectant concentrations within the distribution system, thus resulting in a degradation of the distribution water quality. The objective of this contribution is to represent this pathogen intrusion phenomenon. The combination of presence of defects in the infrastructures (equipment failure), suppression and back-siphonage and lack of disinfection is the cause of propagation of contamination in the clean current of water. Intrusion of pathogenic microorganisms has been studied and registered even in well maintained services. Therefore, this situation can happen when negative pressure conditions are achieved in the systems combined with the presence of defects in pipes nearby the suppression. A simulation of the process by which the external fluids can come inside pipes across their defects in a steady-state situation will be considered, by using different techniques to get such a successful modeling, combining numerical and experimental simulations. The proposed modeling process is based on experimental and
Localization of resistive domains in inhomogeneous superconductors
Gurevich, A.V.; Mints, R.G.
1981-01-01
The properties of resistive domains due to the Joule heating in inhomogeneous superconductors with transport currents are studied. The equilibrium of a domain at an inhomogeneity of arbitrary type and with dimensions much smaller than the dimensions of the domain is investigated. It is shown that resistive domains can become localized at inhomogeneities. The temperature distribution in a domain and the current--voltage characteristic of the domain are determined. The stability of localized domains is discussed. It is shown that such domains give rise to a hysteresis in the destruction (recovery) of the superconductivity by the transport current.
Defect distribution and Schottky barrier at metal/Ge interfaces: Role of metal-induced gap states
NASA Astrophysics Data System (ADS)
Sasaki, Shogo; Nakayama, Takashi
2016-11-01
The defect distribution and Schottky barrier at metal/Ge interfaces were studied using first-principles calculation. It was shown that the defect density markedly increases around the interface owing to the stabilization caused by the hybridization of defect electronic states with metal-induced gap states (MIGS) and by the associated small elastic energy loss around the interface. By comparing the formation energies of various defects at a variety of metal/substrate interfaces, we showed that MIGS not only control the Schottky barrier but also promote a defect-density increase at most metal/semiconductor interfaces. Moreover, we showed that interface oxide layers block MIGS penetration into the Ge substrate and promote the observed breakdown of Fermi-level pinning.
Inflating an inhomogeneous universe
Easther, Richard; Price, Layne C.; Rasero, Javier E-mail: lpri691@aucklanduni.ac.nz
2014-08-01
While cosmological inflation can erase primordial inhomogeneities, it is possible that inflation may not begin in a significantly inhomogeneous universe. This issue is particularly pressing in multifield scenarios, where even the homogeneous dynamics may depend sensitively on the initial configuration. This paper presents an initial survey of the onset of inflation in multifield models, via qualitative lattice-based simulations that do not include local gravitational backreaction. Using hybrid inflation as a test model, our results suggest that small subhorizon inhomogeneities do play a key role in determining whether inflation begins in multifield scenarios. Interestingly, some configurations which do not inflate in the homogeneous limit ''succeed'' after inhomogeneity is included, while other initial configurations which inflate in the homogeneous limit ''fail'' when inhomogeneity is added.
Experimental study on structural defect detection by monitoring distributed dynamic strain
NASA Astrophysics Data System (ADS)
Liu, R. M.; Babanajad, S. K.; Taylor, T.; Ansari, F.
2015-11-01
A defect detection method of civil structures is studied. In order to complete the task, the proposed detection method is based on the analysis of distributed dynamic strains using Brillouin scattering based fiber optic sensors along large span structures. The current challenges in the detection of localized damage fundamentally include monitoring the dynamic strain as well as eliminating the system noise and the distortion of the changing distributed strain. Due to the capability of Brillouin scattering based methods in distributed monitoring of large structures, Brillouin optical time-domain analysis approach is implemented for assessing damage. In order to highlight the singularity at the damage location, Fourier as well as dual tree complex wavelet transform approaches were conducted. During the processing, the dynamic distributed strain in the time domain was transformed into the frequency domain for extraction of natural and forced frequencies. Then, the data was decomposed, filtered for extraction of crack features and reconstructed. The feasibility of the proposed method is evaluated through an experimental program involving the use of pulse-pre-pump Brillouin optical time domain analysis for the distributed measurement of dynamic strain with 13 Hz sampling speed and detection of simulated cracks in a 15 m long steel beam. The beam mimics a bridge girder with two artificial cracks along its length subjected to free and forced vibrations. The results indicate that the method based on the discontinuities in the strain distribution is applicable in the detection of very small damage as small as 40 micro strains. A crack gauge independently monitored the crack opening displacements during the experiments, and the limit of detected crack openings based on the first appearance of strain singularities was 30 μm.
Radially inhomogeneous bounded plasmas
NASA Astrophysics Data System (ADS)
Zakeri-Khatir, H.; Aghamir, F. M.
2016-07-01
On the basis of kinetic theory along with self-consistent field equations, the expressions for dielectric tensor of radially inhomogeneous magnetized plasma columns are obtained. The study of dielectric tensor characteristics allows the accurate analysis of the inhomogeneous properties, beyond limitations that exist in the conventional method. Through the Bessel-Fourier transformation, the localized form of material equations in a radially inhomogeneous medium are obtained. In order to verify the integrity of the model and reveal the effect of inhomogeneity, a special case of a cylindrical plasma waveguide completely filled with inhomogeneous magnetized cold plasma was considered. The dispersion relation curves for four families of electromagnetic (EH and HE) and electrostatic (SC and C) modes are obtained and compared with the findings of the conventional model. The numerical analysis indicates that the inhomogeneity effect leads to coupling of electromagnetic and electrostatic modes each having different radial eigen numbers. The study also reveals that the electrostatic modes are more sensitive to inhomogeneous effects than the electromagnetic modes.
Radially inhomogeneous bounded plasmas
NASA Astrophysics Data System (ADS)
Zakeri-Khatir, H.; Aghamir, F. M.
2016-07-01
On the basis of kinetic theory along with self-consistent field equations, the expressions for dielectric tensor of radially inhomogeneous magnetized plasma columns are obtained. The study of dielectric tensor characteristics allows the accurate analysis of the inhomogeneous properties, beyond limitations that exist in the conventional method. Through the Bessel–Fourier transformation, the localized form of material equations in a radially inhomogeneous medium are obtained. In order to verify the integrity of the model and reveal the effect of inhomogeneity, a special case of a cylindrical plasma waveguide completely filled with inhomogeneous magnetized cold plasma was considered. The dispersion relation curves for four families of electromagnetic (EH and HE) and electrostatic (SC and C) modes are obtained and compared with the findings of the conventional model. The numerical analysis indicates that the inhomogeneity effect leads to coupling of electromagnetic and electrostatic modes each having different radial eigen numbers. The study also reveals that the electrostatic modes are more sensitive to inhomogeneous effects than the electromagnetic modes.
NASA Astrophysics Data System (ADS)
Do, D. D.; Nicholson, D.; Do, H. D.
2007-04-01
The adsorption behavior (capacity, density distribution and packing density) and the isosteric heat versus loading in a slit pore whose walls contain defective graphene layers are investigated in this paper. The defective wall is characterized by the extent and size of the defect. Simulation results obtained with the Grand Canonical Monte Carlo method reveal complex patterns of isosteric heat, and this complex behavior is a result of the interplay between three factors: (i) the surface heterogeneity (solid-fluid interaction, sites with varying degree of affinity), (ii) fluid-fluid interaction and (iii) the overlapping of potentials exerted by the two defective walls. We illustrate this with argon adsorption in pores of various sizes, and results obtained from the simulation agree qualitatively with the experimental data at 77 K on Saran microporous S600H and micro-mesoporous S84 charcoals of Beebe et al. [R.A. Beebe, B. Millard, J. Cynarski, J. Am. Chem. Soc. 75 (1953) 839]. The S600H was found to contain pores predominantly in the neighborhood of 7 Å with 30% of defect and a defective size of 2.84 Å. This is consistent with the argument made by Beebe et al. that this sample is a microporous solid and most pores can accommodate only one layer. The other sample, S84, has larger pores than S600H, and it is found that it has a wider pore size distribution and the pore width is centered at about 12 Å.
Mahdavi, Hoda; Jabbari, Keyvan; Roayaei, Mahnaz
2016-01-01
Delivering radiotherapy to the postmastectomy chest wall can be achieved using matched electron fields. Surgical defects of the chest wall change the dose distribution of electrons. In this study, the improvement of dose homogeneity using simple, nonconformal techniques of thermoplastic bolus application on a defect is evaluated. The proposed phantom design improves the capability of film dosimetry for obtaining dose profiles of a patient's anatomical condition. A modeled electron field of a patient with a postmastectomy inward surgical defect was planned. High energy electrons were delivered to the phantom in various settings, including no bolus, a bolus that filled the inward defect (PB0), a uniform thickness bolus of 5 mm (PB1), and two 5 mm boluses (PB2). A reduction of mean doses at the base of the defect was observed by any bolus application. PB0 increased the dose at central parts of the defect, reduced hot areas at the base of steep edges, and reduced dose to the lung and heart. Thermoplastic boluses that compensate a defect (PB0) increased the homogeneity of dose in a fixed depth from the surface; adversely, PB2 increased the dose heterogeneity. This study shows that it is practical to investigate dose homogeneity profiles inside a target volume for various techniques of electron therapy. PMID:27051169
NASA Technical Reports Server (NTRS)
Cusano, C.; Wedeven, L. D.
1981-01-01
The effects of artificially produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact were investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, were held stationary at various locations within and in the vicinity of the contact region while the disk was rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.
NASA Astrophysics Data System (ADS)
Paliwal, Bhasker
brittle materials. The model incorporates pre-existing defect distributions and a crack growth law. The damage is defined as a scalar parameter which is a function of the micro-crack density, the evolution of which is a function of the existing defect distribution and the crack growth dynamics. A specific case of a uniaxial compressive loading under constant strain-rate has been studied to predict the effects of the strain-rate, defect distribution and the crack growth dynamics on the constitutive response and failure behavior of brittle materials. Finally, the effects of crack growth dynamics on the strain-rate sensitivity of brittle materials are studied with the help of the micro-mechanical damage model. The results are compared with the experimentally observed damage evolution and the rate-sensitive behavior of the compressive strength of several engineering ceramics. The dynamic failure of armor-grade hot-pressed boron carbide (B 4C) under loading rates of ˜ 5X10-6 to 200 MPa/mus is also discussed.
Lee, Keundong; Hwang, Inrok; Lee, Sangik; Oh, Sungtaek; Lee, Dukhyun; Kim, Cheol Kyeom; Nam, Yoonseung; Hong, Sahwan; Yoon, Chansoo; Morgan, Robert B.; Kim, Hakseong; Seo, Sunae; Seo, David H.; Lee, Sangwook; Park, Bae Ho
2015-01-01
Resistive random access memory (ReRAM) devices have been extensively investigated resulting in significant enhancement of switching properties. However fluctuations in switching parameters are still critical weak points which cause serious failures during ‘reading’ and ‘writing’ operations of ReRAM devices. It is believed that such fluctuations may be originated by random creation and rupture of conducting filaments inside ReRAM oxides. Here, we introduce defective monolayer graphene between an oxide film and an electrode to induce confined current path distribution inside the oxide film, and thus control the creation and rupture of conducting filaments. The ReRAM device with an atomically thin interlayer of defective monolayer graphene reveals much reduced fluctuations in switching parameters compared to a conventional one. Our results demonstrate that defective monolayer graphene paves the way to reliable ReRAM devices operating under confined current path distribution. PMID:26161992
NASA Astrophysics Data System (ADS)
Schön, Jonas; Youssef, Amanda; Park, Sungeun; Mundt, Laura E.; Niewelt, Tim; Mack, Sebastian; Nakajima, Kazuo; Morishita, Kohei; Murai, Ryota; Jensen, Mallory A.; Buonassisi, Tonio; Schubert, Martin C.
2016-09-01
Identification of the lifetime limiting defects in silicon plays a key role in systematically optimizing the efficiency potential of material for solar cells. We present a technique based on temperature and injection dependent photoluminescence imaging to determine the energy levels and capture cross section ratios of Shockley-Read-Hall defects. This allows us to identify homogeneously and inhomogeneously distributed defects limiting the charge carrier lifetime in any silicon wafer. The technique is demonstrated on an n-type wafer grown with the non-contact crucible (NOC) method and an industrial Czochralski (Cz) wafer prone to defect formation during high temperature processing. We find that the energy levels for the circular distributed defects in the Cz wafer are in good agreement with literature data for homogeneously grown oxide precipitates. In contrast, the circular distributed defects found in NOC Si have significantly deeper trap levels, despite their similar appearance.
Defect distribution in ion-irradiated pure tungsten at different temperatures
NASA Astrophysics Data System (ADS)
Zhang, Zhexian; Yabuuchi, Kiyohiro; Kimura, Akihiko
2016-11-01
Tungsten (W) has been selected as the armor materials for divertor in fusion reactors. To investigate the temperature dependent microstructural evolution under fusion relevant environment, pure W was irradiated with dual beam of 6.4 MeV Fe3+ and 1 MeV energy degraded He+ at 300 °C, 500 °C, 700 °C and 1000 °C. The overall distribution of microstructures were observed. At 300 °C, a high dislocation density zone (HDDZ) appeared at the end of radiation area. The HDDZ gradually disappeared with increasing irradiation temperature, instead, a low dislocation density zone (LDDZ) appeared between the front zone (FZ) and diffusion zone (DZ). At all the irradiation temperatures, both dislocation lines and loops were observed, while bubbles were observed only at 500 °C and above. Loop rafts appeared in the whole irradiated area from 300 °C to 700 °C, but only in the defect diffusion zone (DZ) at 1000 °C. Dislocation loop denuded zone was formed along grain boundaries, suggesting that grain boundaries suppress the formation of dislocation loops. Bubbles at grain boundaries tended to have a larger size than those in the matrix, indicating that bubble growth was accelerated in grain boundaries.
Meissner response of superconductors with inhomogeneous penetration depths
Kogan, V. G.; Kirtley, J. R.
2011-03-24
We discuss the Meissner response to a known field source of superconductors having inhomogeneities in their penetration depth. We simplify the general problem by assuming that the perturbations of the fields by the penetration depth inhomogeneities are small. We present expressions for inhomogeneities in several geometries, but concentrate for comparison with experiment on planar defects, perpendicular to the sample surfaces, with superfluid densities different from the rest of the samples. These calculations are relevant for magnetic microscopies, such as Scanning Superconducting Quantum Interference Device (SQUID) and Magnetic Force Microscope, which image the local diamagnetic susceptibility of a sample.
Effect of layerwise structural inhomogeneity on stress- corrosion cracking of steel tubes
NASA Astrophysics Data System (ADS)
Perlovich, Yu A.; Krymskaya, O. A.; Isaenkova, M. G.; Morozov, N. S.; Fesenko, V. A.; Ryakhovskikh, I. V.; Esiev, T. S.
2016-04-01
Based on X-ray texture and structure analysis data of the material of main gas pipelines it was shown that the layerwise inhomogeneity of tubes is formed during their manufacturing. The degree of this inhomogeneity affects on the tendency of tubes to stress- corrosion cracking under exploitation. Samples of tubes were cut out from gas pipelines located under various operating conditions. Herewith the study was conducted both for sections with detected stress-corrosion defects and without them. Distributions along tube wall thickness for lattice parameters and half-width of X-ray lines were constructed. Crystallographic texture analysis of external and internal tube layers was also carried out. Obtained data testifies about considerable layerwise inhomogeneity of all samples. Despite the different nature of the texture inhomogeneity of gas pipeline tubes, the more inhomogeneous distribution of texture or structure features causes the increasing of resistance to stress- corrosion. The observed effect can be explained by saturation with interstitial impurities of the surface layer of the hot-rolled sheet and obtained therefrom tube. This results in rising of lattice parameters in the external layer of tube as compared to those in underlying metal. Thus, internal layers have a compressive effect on external layers in the rolling plane that prevents cracks opening at the tube surface. Moreover, the high mutual misorientation of grains within external and internal layers of tube results in the necessity to change the moving crack plane, so that the crack growth can be inhibited when reaching the layer with a modified texture.
Light propagation and large-scale inhomogeneities
Brouzakis, Nikolaos; Tetradis, Nikolaos; Tzavara, Eleftheria E-mail: ntetrad@phys.uoa.gr
2008-04-15
We consider the effect on the propagation of light of inhomogeneities with sizes of order 10 Mpc or larger. The Universe is approximated through a variation of the Swiss-cheese model. The spherical inhomogeneities are void-like, with central underdensities surrounded by compensating overdense shells. We study the propagation of light in this background, assuming that the source and the observer occupy random positions, so that each beam travels through several inhomogeneities at random angles. The distribution of luminosity distances for sources with the same redshift is asymmetric, with a peak at a value larger than the average one. The width of the distribution and the location of the maximum increase with increasing redshift and length scale of the inhomogeneities. We compute the induced dispersion and bias of cosmological parameters derived from the supernova data. They are too small to explain the perceived acceleration without dark energy, even when the length scale of the inhomogeneities is comparable to the horizon distance. Moreover, the dispersion and bias induced by gravitational lensing at the scales of galaxies or clusters of galaxies are larger by at least an order of magnitude.
NASA Astrophysics Data System (ADS)
Ma, Xiao-Bo; Wang, Fei; Chen, De-Zhen
2014-05-01
The recognition of subsurface defects is an important aspect of inverse heat transfer problems. The solution of direct problems is the basis of the inverse problems. In this paper, based on the non-Fourier heat conduction equation and using the image method and the wave function expansion method, an analytical method to study the multiple scattering of thermal waves and temperatures from the subsurface defect in semi-infinite functionally graded materials (FGMs) is presented. A general solution of the scattered fields of thermal waves is obtained. Without loss of generality, the incidence of thermal waves excited by the periodically modulated laser and the subsurface defect are treated as the line heat source and a cylindrical cavity with thermal insulation in the modelling, respectively. The amplitude of the changes in temperature at the frontal surface in the cylindrical defect due to different physical and geometrical parameters is analysed, discussed, and presented graphically using the analytical method. The significant changes in the temperature were found to occur at the frontal surface because of the existence of conducting defects. In addition, the influence of the defect state on the temperature was found to also be related to the nonhomogeneous parameters of FGMs, the wavenumber, the frequency of the thermal waves, and the depth of the buried defects. The numerical results and method proposed in this paper are expected to be applied for the analysis of infrared thermal waves in non-destructive evaluations of functionally graded materials and inverse problems of mathematical physics.
Cavell, R.G.; Feng, R.; Barnes, E.M.; Cavell, P.A.; McCready, A.J.; Webb, M.A.
2007-06-08
The hard X-ray microprobe provides an effective methodology for the non-destructive analysis of inhomogeneous materials. Application of X-ray absorption/fluroescence spectroscopy techniques (XANES and EXAFS) permits the speciation of the elements and yields information about the local structural environment. Microfocussed, monochromatic, tunable X-rays allows examination of small areas of micrometer dimensions with spectroscopic procedures. Typically the materials which are presented are thick and cannot be altered for the experiment. This condition introduces difficulties which may compromise the results. Herein we discuss those difficulties and show that the system can yield reliable results in spite of the compromises. Some results are presented on the two iron meteorites we have examined. These specimens are representative of highly inhomogeneous materials and illustrate the difficulties encountered with compositional variations which may occur at sub-millimeter dimensions and also illustrate the difficulties presented by the need to analyze components present at ppm concentration levels in a concentrated matrix. In these particular samples the major constituent is Fe which ranges from 90% to 70%, balanced by Ni which ranges from 10% to 30%. The critical diagnostic trace elements Ga and Ge which must also be analyzed are present at the 80 and 340 ppm level respectively. These diagnostic elements have been shown by EXAFS to be substitutionally placed in the matrix of the major element species in these meteorite samples.
Energy level broadening of defects causing nonideality in nearly ideal Si Schottky barriers
NASA Astrophysics Data System (ADS)
Maeda, Keiji
2004-10-01
We have proposed a mechanism of the local Schottky barrier height (SBH) lowering to explain the nonideal characteristics in Si SBs. Positively charged defects close to the M/S interface induce image charge in the metal-induced gap states (MIGS) and lower the SBH. Based on this mechanism, the inhomogeneous potential distributions in the proximity of the MIGS are calculated in agreement with the I- V characteristics. The energy level of the defect, identified with Si self-interstitial, is in agreement with the theoretical value. The energy width of the defect is nearly equal to the standard deviation in the Gaussian distribution describing the SBH inhomogeneity. Thus, the propriety of the model is confirmed.
Theoretical understanding of chromospheric inhomogeneities
NASA Technical Reports Server (NTRS)
Delache, P.
1973-01-01
Detailed theoretical studies of chromospheric inhomogeneities consider dynamics as well as radiative transfer of mass flow as a consequence of energy deposition. It is shown that pressure is exerted by the heating waves, especially in inhomogeneous structures, where they can be defracted. A dynamical model is formulated that depicts the inhomogeneous structure of the chromosphere-corona transition region through mass flow regimes.
Electromagnetic effects on the inhomogeneity of planar symmetry
NASA Astrophysics Data System (ADS)
Sharif, M.; Bhatti, M. Zaeem Ul Haq
2014-08-01
In this work, we aim to identify the effects of electromagnetic field on the energy density inhomogeneity in self-gravitating plane symmetric spacetime filled with imperfect matter in terms of dissipation and anisotropic pressure. We formulate the Einstein-Maxwell field equation, conservation laws, evolution equations for the Weyl tensor and the transport equation for diffusion approximation. Inhomogeneity factors are identified for some particular cases of non-dissipative and dissipative fluids. For non-dissipative case, we analyze the inhomogeneity factor for dust, isotropic and anisotropic matter distributions while dissipative matter distribution includes the inhomogeneity factor only for geodesic dust fluid. We conclude that electric charge increases the inhomogeneity in the energy density which is due to shear, anisotropy and dissipation.
Byrnes, Christian T.; Nurmi, Sami; Tasinato, Gianmassimo; Wands, David E-mail: s.nurmi@thphys.uni-heidelberg.de E-mail: david.wands@port.ac.uk
2012-03-01
We propose a method to probe higher-order correlators of the primordial density field through the inhomogeneity of local non-Gaussian parameters, such as f{sub NL}, measured within smaller patches of the sky. Correlators between n-point functions measured in one patch of the sky and k-point functions measured in another patch depend upon the (n+k)-point functions over the entire sky. The inhomogeneity of non-Gaussian parameters may be a feasible way to detect or constrain higher- order correlators in local models of non-Gaussianity, as well as to distinguish between single and multiple-source scenarios for generating the primordial density perturbation, and more generally to probe the details of inflationary physics.
Process-induced defects and potential distribution in nearly ideal Au/Si Schottky barriers
NASA Astrophysics Data System (ADS)
Maeda, Keiji
2003-06-01
We have proposed a mechanism of nonideality in nearly ideal Au/ n-Si Schottky barriers (SBs), which explains various experimental observations called the To anomaly. Because of the nature of the metal-induced gap states (MIGS), positively ionized defects induced by the process very close to the interface are considered to cause local lowering of the Schottky barrier height (SBH) due to filling-up of the MIGS. The formulation of the defect density is revised to be consistent with the experimental observations. There is a potential drop of more than 100 mV at about 20 Å from the interface due to the space-charge of the defects. The saddle potential for the low-SBH spot is lowered by this potential drop. Therefore, the local SBH lowering is observable in the I- V characteristics.
Quantifying uncertainty from material inhomogeneity.
Battaile, Corbett Chandler; Emery, John M.; Brewer, Luke N.; Boyce, Brad Lee
2009-09-01
Most engineering materials are inherently inhomogeneous in their processing, internal structure, properties, and performance. Their properties are therefore statistical rather than deterministic. These inhomogeneities manifest across multiple length and time scales, leading to variabilities, i.e. statistical distributions, that are necessary to accurately describe each stage in the process-structure-properties hierarchy, and are ultimately the primary source of uncertainty in performance of the material and component. When localized events are responsible for component failure, or when component dimensions are on the order of microstructural features, this uncertainty is particularly important. For ultra-high reliability applications, the uncertainty is compounded by a lack of data describing the extremely rare events. Hands-on testing alone cannot supply sufficient data for this purpose. To date, there is no robust or coherent method to quantify this uncertainty so that it can be used in a predictive manner at the component length scale. The research presented in this report begins to address this lack of capability through a systematic study of the effects of microstructure on the strain concentration at a hole. To achieve the strain concentration, small circular holes (approximately 100 {micro}m in diameter) were machined into brass tensile specimens using a femto-second laser. The brass was annealed at 450 C, 600 C, and 800 C to produce three hole-to-grain size ratios of approximately 7, 1, and 1/7. Electron backscatter diffraction experiments were used to guide the construction of digital microstructures for finite element simulations of uniaxial tension. Digital image correlation experiments were used to qualitatively validate the numerical simulations. The simulations were performed iteratively to generate statistics describing the distribution of plastic strain at the hole in varying microstructural environments. In both the experiments and simulations, the
Surface defect detection of magnetic microwires by miniature rotatable robot inside SEM
NASA Astrophysics Data System (ADS)
Wan, Wenfeng; Lu, Haojian; Zhukova, Valentina; Ipatov, Mihail; Zhukov, Arcady; Shen, Yajing
2016-09-01
Surface defect is regarded as one critical factor that affects magnetic properties of magnetic microwires. However, current imaging techniques only allow to observe samples from one fixed direction, and thereby most of surface defects on microwire cannot be detected. Herein, we firstly develop a miniature rotatable robot inside scanning electron microscopy (SEM) and propose a relevant control strategy to align the microwire onto the rotation axis of the robot. After that, the microwire is rotated continuously by 360o and all the surface defects on the microwire are observed from different directions successfully. Multidirectional observation results can be used to located heating inhomogeneity, which is the main cause of defects. Magnetic measurement results show that the effect of defects on domain wall (DW) should be considered in device design. This research provides the direct evidence for surface defects' distribution and effect, which can be adopted to provide guidance for improving magnetic wire's fabrication process and designing logic circuits made from those magnetic wires.
Size distribution of black spot defects and their contribution to swelling in irradiated SiC
NASA Astrophysics Data System (ADS)
Tyburska-Püschel, B.; Zhai, Y.; He, L.; Liu, C.; Boulle, A.; Voyles, P. M.; Szlufarska, I.; Sridharan, K.
2016-08-01
Experimental and modeling efforts were combined to investigate the role of black spot defects (BSD) in swelling of carbon- and krypton-irradiated 4H-SiC. Samples were exposed to conditions favoring BSD formation: irradiation at temperatures 600-950 °C and damage levels of 0.4-0.8 dpa. The maximum XRD swelling values, corrected for the effect of the rigid substrate, of 0.58% for C and 0.75% for Kr-irradiation were measured at the lowest irradiation temperature of 600 °C and decreased with increasing temperature. The swelling values estimated from TEM are on the same order of magnitude, but usually 40-70% lower than those measured by XRD. The contribution of BSDs to the overall swelling is 62% and the remainder of the swelling is caused by isolated point defects. The obtained results contribute to understanding of what defect types account for swelling and how their concentration evolves with the irradiation temperature and damage level.
Stabilizing synchrony by inhomogeneity
Bolhasani, Ehsan; Valizadeh, Alireza
2015-01-01
We show that for two weakly coupled identical neuronal oscillators with strictly positive phase resetting curve, isochronous synchrony can only be seen in the absence of noise and an arbitrarily weak noise can destroy entrainment and generate intermittent phase slips. Small inhomogeneity–mismatch in the intrinsic firing rate of the neurons–can stabilize the phase locking and lead to more precise relative spike timing of the two neurons. The results can explain how for a class of neuronal models, including leaky integrate-fire model, inhomogeneity can increase correlation of spike trains when the neurons are synaptically connected. PMID:26338691
NASA Astrophysics Data System (ADS)
Bai, Xiaogong; Shi, Yantao; Guo, Jiahao; Gao, Liguo; Wang, Kai; Du, Yi; Ma, Tingli
2016-02-01
N-doped graphene (NG) is a promising candidate for oxygen reduction reaction (ORR) in the cathode of fuel cells. However, the catalytic activity of NG is lower than that of commercial Pt/C in alkaline and acidic media. In this study, NG samples were obtained using urea as N source. The structural defects and N distribution in the samples were adjusted by regulating the pyrolysis temperature. The new NG type exhibited remarkable catalytic activities for ORR in both alkaline and acidic media.
Inhomogeneous anisotropic cosmology
NASA Astrophysics Data System (ADS)
Kleban, Matthew; Senatore, Leonardo
2016-10-01
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with ``flat'' (including toroidal) and ``open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are ``flat'' or ``open''. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with ``flat'' or ``open'' topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
NASA Astrophysics Data System (ADS)
Popov, M. V.; Andrianov, A. S.; Bartel, N.; Gwinn, C.; Joshi, B. C.; Jauncey, D.; Kardashev, N. S.; Rudnitskii, A. G.; Smirnova, T. V.; Soglasnov, V. A.; Fadeev, E. N.; Shishov, V. I.
2016-09-01
The RadioAstron ground-space interferometer has been used to measure the angular sizes of the scattering disks of the three distant pulsars B1641-45, B1749-28, and B1933+16. The observations were carried out with the participation of the Westerbork Synthesis Radio Telescope; two 32-m telescopes at Torun, Poland and Svetloe, Russia (the latter being one antenna of the KVAZAR network); the Saint Croix VLBA antenna; the Arecibo radio telescope; the Parkes, Narrabri (ATCA), Mopra, Hobart, and Ceduna Australian radio telescopes; and the Hartebeesthoek radio telescope in South Africa. The full widths at half maximum of the scattering disks were 27 mas at 1668 MHz for B1641-45, 0.5 mas at 1668 MHz for B1749-28, and 12.3 at 316 MHz and 0.84 mas at 1668 MHz for B1933+16. The characteristic time scales for scatter-broadening of the pulses on inhomogeneities in the interstellar plasma τsc were also measured for these pulsars using various methods. Joint knowledge of the size of the scattering disk and the scatter-broadening time scale enables estimation of the distance to the effective scattering screen d. For B1641-45, d = 3.0 kpc for a distance to the pulsar D = 4.9 kpc, and for B1749-28, d = 0.95 kpc for D = 1.3 kpc. Observations of B1933+16 were carried out simultaneously at 316 and 1668 MHz. The positions of the screen derived using the measurements at the two frequencies agree: d 1 = 2.6 and d 2 = 2.7 kpc, for a distance to the pulsar of 3.7 kpc. Two screens were detected for this pulsar from an analysis of parabolic arcs in the secondary dynamic spectrum at 1668 MHz, at 1.3 and 3.1 kpc. The scattering screens for two of the pulsars are identified with real physical objects located along the lines of sight toward the pulsars: G339.1-04 (B1641-45) and G0.55-0.85 (B1749-28).
Johnsen, D; Krejci, C; Hack, M; Fanaroff, A
1984-01-01
Although dental defects have long been observed among surviving pre-term infants, only few systematic studies address this problem. In a clinic limited to recall of infants of very low birthweight (less than 1.5 kg), enamel hypoplasia of primary incisors was found in 14/67 (21%) children, and enamel opacities were found in an additional 31% of the children. In contrast, enamel hypoplasia and opacities were found in 4% and 22%, respectively, of a control group of 46 normal birthweight children. The difference was significant (p less than 0.05) for the hypoplasia but not for the opacities. Primary incisor enamel hypoplasia was more commonly noted in maxillary central incisors than in lateral incisors (X2 = 28.0, p less than 0.01). Furthermore, hypoplasia was more common in maxillary incisors than in mandibular incisors (X2 = 48.4, p less than 0.01). In infants with dental defects, there was no significant correlation with pregnancy risk factors, gestational age, birthweight, septicemia, first-week caloric intake, serum bilirubin, or calcium. Infants with enamel hypoplasia were more likely, however, to have severe respiratory distress syndrome (X2 = 7.2, p less than 0.01), than infants with unaltered enamel. Central incisor edge involvement may indicate post-natal processes and/or a systemic disturbance extending back to the middle trimester of pregnancy.
Short communication: Distribution of recessive genetic defect carriers in Chinese Holstein.
Sun, D X; Fan, X H; Xie, Y; Chu, Q; Sun, Y; Zhang, Y; Zhang, S L; Gong, W J; Chen, S H; Li, Y H; Shi, W H; Zhang, Y
2011-11-01
In dairy cattle, 4 important recessive hereditary diseases exist: complex vertebral malformation (CVM), bovine leukocyte adhesion deficiency (BLAD), citrullinemia (CTLN), and deficiency of uridine monophosphate synthase (DUMPS). Holstein Associations in developed countries have established monitoring systems for such disorders in Holstein bulls for decades. Over the past decades, China has continuously imported Holstein semen and embryos, mainly from North America but also from Europe. The dissemination of such genetic defects was undetermined until now, although efforts were taken to develop molecular techniques and detect carriers for CVM and BLAD in small populations of Chinese dairy cattle. Thus, herein we extensively screened 732 proven bulls participating in artificial insemination programs and 136 young bulls entering progeny test from 15 bull stations in China for CVM, BLAD, CTLN, and DUMPS. The proportion of carriers of the defects was found to be 7.72, 1.38, 0.23, and 0.12%, respectively. Given our findings, early diagnostic and monitoring systems on recessive inherited disorders among proven and young bulls entering the national genetic improvement programs for dairy cattle of China should be established immediately, in which a series of measures will be taken to prevent further spreading of such disorders and gradually eliminate them in the dairy cattle population in China. PMID:22032394
NASA Technical Reports Server (NTRS)
Su, Ching-Hua; Feth, S.; Hirschfeld, D.; Smith, T. M.; Wang, Ling Jun; Volz, M. P.; Lehoczky, S. L.
1999-01-01
ZnSe crystals were grown by the physical vapor transport technique under horizontal and vertical (stabilized and destabilized) configurations. Secondary ion mass spectroscopy and photoluminescence measurements were performed on the ZnSe samples to map the distributions of [Si], [Fe], [Cu], [Al] and [Li or Na] impurities as well as Zn vacancy, [V(zn)]. The annealings of ZnSe under controlled Zn pressures were studied to correlate the measured photoluminescence emission intensity to the equilibrium Zn partial pressure. In the horizontal grown crystals the segregations of [Si], [Fe], [Al] and [V(zn)] along the gravity vector direction were observed whereas in the vertically stabilized grown crystal the segregations of these point defects were radially symmetrical. No apparent pattern was observed on the measured distributions in the vertically destabilized grown crystal. The observed segregations in the three growth configurations were interpreted based on the possible buoyancy-driven convection in the vapor phase.
NASA Technical Reports Server (NTRS)
Su, Ching-Hua; Feth, S.; Hirschfeld, D.; Smith, T. M.; Wang, Ling Jun; Volz, M. P.; Lehoczky, S. L.
1999-01-01
ZnSe crystals were grown by the physical vapor transport technique under horizontal and vertical (stabilized and destabilized) configurations. Secondary ion mass spectroscopy and photoluminescence measurements were performed on the grown ZnSe samples to map the distributions of [Si], [Fe], [Cu], [Al] and [Li or Na] impurities as well as Zn vacancy, [V (sub Zn)]. Annealings of ZnSe under controlled Zn pressures were studied to correlate the measured photoluminescence emission intensity to the equilibrium Zn partial pressure. In the horizontal grown crystals the segregations of [Si], [Fe], [Al] and [V (sub Zn)] were observed along the gravity vector direction whereas in the vertically stabilized grown crystal the segregation of these point defects was radially symmetrical. No apparent pattern was observed on the measured distributions in the vertically destabilized grown crystal. The observed segregations in the three growth configurations were interpreted based on the possible buoyancy-driven convection in the vapor phase.
NASA Astrophysics Data System (ADS)
Uglov, A. A.; Smurov, I. Yu; Gus'kov, A. G.; Aksenov, L. V.
1990-08-01
A theoretical study is reported of melting and thermocapillary convection under the action of laser radiation with a nonmonotonic spatial distribution of the power density. An analysis is made of changes in the geometry of the molten bath with time. The transition from a nonmonotonic boundary of a melt, corresponding to the spatial distribution of the radiation, to a monotonic one occurs in a time of the order of 1 ms when the power density of laser radiation is 105 W/cm2. The vortex structure of the flow in the molten bath is governed by the spatial distribution of the laser radiation in such a way that each local power density maximum corresponds to two vortices with oppositely directed velocity components.
NASA Astrophysics Data System (ADS)
Mokrý, Pavel; Sluka, Tomáš
2016-02-01
The motion of ferroelectric domain walls greatly contributes to the macroscopic dielectric and piezoelectric response of ferroelectric materials. The domain-wall motion through the ferroelectric material is, however, hindered by pinning on crystal defects, which substantially reduces these contributions. Here, using thermodynamic models based on the Landau-Ginzburg-Devonshire theory, we find a relation between the microscopic reversible motion of nonferroelastic 180∘ domain walls interacting with a periodic array of pinning centers and the nonlinear macroscopic permittivity. We show that the reversible motion of domain walls can be split into two basic modes: first, the bending of a domain wall between pinning centers, and, second, the uniform movement of the domain-wall plane. We show that their respective contributions may change when the distribution of pinning centers is rearranged during the material aging. We demonstrate that it is possible to indicate which mechanism of the domain-wall motion is affected during material aging. This allows one to judge whether the defects only homogeneously accumulate at domain walls or prefer to align in certain directions inside the domain-wall plane. We suggest that this information can be obtained using simple macroscopic dielectric measurements and a proper analysis of the nonlinear response. Our results may therefore serve as a simple and useful tool to obtain details on domain-wall pinning in an aging process.
Aliev, V. Sh.; Bortnikov, S. G. Mzhelskiy, I. V.; Badmaeva, I. A.
2014-10-06
A spatial temperature distribution in VO{sub 2} film was first investigated at current oscillations using infrared microscope. The oscillations are revealed to arise from the periodic formation and disappearance of a narrow high-temperature channel in VO{sub 2} film. The nature of the oscillations in VO{sub 2} films is considered from the standpoint of a well-known phenomenon: spatio-temporal instability of current flow in homogeneous semiconductors. The temperature of the channel significantly exceeds the semiconductor-metal transition temperature being the cause of film destruction and oscillations cessation.
Homogeneous and inhomogeneous eddies
Pavia, E.G.
1994-12-31
This work deals with mesoscale warm oceanic eddies; i.e., self-contained bodies of water which transport heat, among other things, for several months and for several hundreds of kilometers. This heat transport is believed to play an important role in the atmospheric and oceanic conditions of the region where it is being transported. Here the author examines the difference in evolution between eddies modeled as blobs of homogeneous water and eddies in which density varies in the horizontal. Preliminary results suggest that instability is enhanced by inhomogeneities, which would imply that traditional modeling studies, based on homogeneous vortices have underestimated the rate of heat-release from oceanic eddies to the surroundings. The approach is modeling in the simplest form; i.e., one single active layer. Although previous studies have shown the drastic effect on stability brought by two or more dynamically-relevant homogeneous layers, the author believes the single-layer eddy-model has not been investigated thoroughly.
Scaling of earthquake models with inhomogeneous stress dissipation.
Dominguez, Rachele; Tiampo, Kristy; Serino, C A; Klein, W
2013-02-01
Natural earthquake fault systems are highly nonhomogeneous. The inhomogeneities occur because the earth is made of a variety of materials which hold and dissipate stress differently. In this work, we study scaling in earthquake fault models which are variations of the Olami-Feder-Christensen and Rundle-Jackson-Brown models. We use the scaling to explore the effect of spatial inhomogeneities due to damage and inhomogeneous stress dissipation in the earthquake-fault-like systems when the stress transfer range is long, but not necessarily longer than the length scale associated with the inhomogeneities of the system. We find that the scaling depends not only on the amount of damage, but also on the spatial distribution of that damage.
Inhomogeneous cosmology. III - Primordial gravitational waves and dust
NASA Technical Reports Server (NTRS)
Adams, P. J.; Hellings, R. W.; Zimmerman, R. L.
1987-01-01
In this paper, the properties of a special class of inhomogeneous cosmological models and the interaction of the inhomogeneities with the evolution of the background geometry and matter are studied. The cosmological model is chosen so that the initial inhomogeneities evolve into 'plane' gravitational waves propagating through a smooth Bianchi I dust background. It is shown how the inhomogeneities interact with matter, 3 K radiation, and the background geometry, causing the expansion to slow down in some regions and speed up in others. It is also shown how the gravitational waves can produce a 'dragging of the inertial frame' which will affect the observed distribution of matter and 3 K radiation. In particular, this frame-dragging effect can account for a major fraction of the obsserved dipole component between the 3 K background radiation and the rest frame of global matter, an effect usually assumed to have been produced by large-scale local motion.
Sampling-based learning control of inhomogeneous quantum ensembles
NASA Astrophysics Data System (ADS)
Chen, Chunlin; Dong, Daoyi; Long, Ruixing; Petersen, Ian R.; Rabitz, Herschel A.
2014-02-01
Compensation for parameter dispersion is a significant challenge for control of inhomogeneous quantum ensembles. In this paper, we present the systematic methodology of sampling-based learning control (SLC) for simultaneously steering the members of inhomogeneous quantum ensembles to the same desired state. The SLC method is employed for optimal control of the state-to-state transition probability for inhomogeneous quantum ensembles of spins as well as Λ-type atomic systems. The procedure involves the steps of (i) training and (ii) testing. In the training step, a generalized system is constructed by sampling members according to the distribution of inhomogeneous parameters drawn from the ensemble. A gradient flow based learning and optimization algorithm is adopted to find an optimal control for the generalized system. In the process of testing, a number of additional ensemble members are randomly selected to evaluate the control performance. Numerical results are presented, showing the effectiveness of the SLC method.
Inhomogeneous Broadening in Perturbed Angular Correlation Spectroscopy
NASA Astrophysics Data System (ADS)
Bunker, Austin; Adams, Mike; Hodges, Jeffery; Park, Tyler; Stufflebeam, Michael; Evenson, William; Matheson, Phil; Zacate, Matthew
2009-10-01
Our research concerns the effect of a static distribution of defects on the net electric field gradient (EFG) within crystal structures. Defects and vacancies perturb the distribution of gamma rays emitted from radioactive probe nuclei within the crystal. These defects and vacancies produce a net EFG at the site of the probe which causes the magnetic quadrupole moment of the nucleus of the probe to precess about the EFG. The net EFG, which is strongly dependent upon the defect concentration, perturbs the angular correlation (PAC) of the gamma rays, and is seen in the damping of the perturbation function, G2(t), in time and broadening of the spectral peaks in the Fourier transform. We have used computer simulations to study the probability distribution of EFG tensor components in order to uncover the concentration dependence of G2(t). This in turn can be used to analyze experimental PAC data and quantitatively describe properties of the crystal.
Ahrens, Michael J; Depree, Craig V
2004-02-01
Polycyclic aromatic hydrocarbons (PAHs) in sediment from Auckland Harbour (New Zealand) are not distributed evenly throughout bulk sediment, but highly concentrated in coarser, low-density fractions. Concentrations of 24 PAHs, measured in sediment that was separated into six size fractions that were furthermore separated into two density sub-fractions by flotation in sodium-polytungstate solution (rho = 2.15 g cm(-3)), varied between 4-103 microg g(-1)dw among grain size fractions and 2-998 microg g(-1)dw for density sub-fractions. Highest PAH concentrations were measured in the low density, 125-250 microm fraction. All sediment fractions had a similar relative PAH composition, dominated by >3-ring PAHs, suggesting a common pyrogenic origin. Low density material had 10-200 times higher PAH concentrations and 10-100 times higher organic carbon (OC) content, yet differences in OC content only partially accounted for variations in PAH concentration. Low density particles contributed more than 75% of the Sigma PAH, while comprising only 3% of bulk sediment dry weight. This may have significant utility for contaminant mitigation efforts in Auckland Harbour. PMID:14972587
The Signature of Inhomogeneous Superconductivity
NASA Astrophysics Data System (ADS)
Agosta, Charles C.; Bishop-Van Horn, Logan; Newman, Max
2016-11-01
Superconductivity can be inhomogeneous, having a periodically modulated order parameter, in materials that have long electronic mean free paths and where the effects of vortices are suppressed. One class of materials that has these properties is crystalline organic superconductors. They are stoichiometric compounds and highly anisotropic crystals such that the vortices that form can hide in the least conducting layers. We analyze recent data to look for complexity in the inhomogeneous states, such as changes in the order parameter nodal structure.
The Signature of Inhomogeneous Superconductivity
NASA Astrophysics Data System (ADS)
Agosta, Charles C.; Bishop-Van Horn, Logan; Newman, Max
2016-09-01
Superconductivity can be inhomogeneous, having a periodically modulated order parameter, in materials that have long electronic mean free paths and where the effects of vortices are suppressed. One class of materials that has these properties is crystalline organic superconductors. They are stoichiometric compounds and highly anisotropic crystals such that the vortices that form can hide in the least conducting layers. We analyze recent data to look for complexity in the inhomogeneous states, such as changes in the order parameter nodal structure.
Inhomogeneous neutrino degeneracy and big bang nucleosynthesis
Whitmire, Scott E.; Scherrer, Robert J.
2000-04-15
We examine big bang nucleosynthesis (BBN) in the case of inhomogeneous neutrino degeneracy, in the limit where the fluctuations are sufficiently small on large length scales that the present-day element abundances are homogeneous. We consider two representative cases: degeneracy of the electron neutrino alone and equal chemical potentials for all three neutrinos. We use a linear programming method to constrain an arbitrary distribution of the chemical potentials. For the current set of (highly restrictive) limits on the primordial element abundances, homogeneous neutrino degeneracy barely changes the allowed range of the baryon-to-photon ratio {eta}. Inhomogeneous degeneracy allows for little change in the lower bound on {eta}, but the upper bound in this case can be as large as {eta}=1.1x10{sup -8} (only {nu}{sub e} degeneracy) or {eta}=1.0x10{sup -9} (equal degeneracies for all three neutrinos). For the case of inhomogeneous neutrino degeneracy, we show that there is no BBN upper bound on the neutrino energy density, which is bounded in this case only by limits from structure formation and the cosmic microwave background. (c) 2000 The American Physical Society.
Success-driven distribution of public goods promotes cooperation but preserves defection
NASA Astrophysics Data System (ADS)
Perc, Matjaž
2011-09-01
Established already in Biblical times, the Matthew effect refers to the fact that in societies the rich tend to get richer and the potent even more powerful. Here we investigate a game theoretical model describing the evolution of cooperation on structured populations where the distribution of public goods is driven by the reproductive success of individuals. Phase diagrams reveal that cooperation is promoted irrespective of the uncertainty by strategy adoptions and the type of interaction graph, yet the complete dominance of cooperators is elusive due to the spontaneous emergence of superpersistent defectors that owe their survival to extremely rare microscopic patterns. This indicates that success-driven mechanisms are crucial for effectively harvesting benefits from collective actions but that they may also account for the observed persistence of maladaptive behavior.
Inhomogeneities in single crystals of cuprate oxide superconductors
NASA Technical Reports Server (NTRS)
Moorjani, K.; Bohandy, J.; Kim, B. F.; Adrian, F. J.
1991-01-01
The next stage in the evolution of experimental research on the high temperature superconductors will require high quality single crystals and epitaxially grown crystalline films. However, inhomogeneities and other defects are not uncommon in single crystals of cuprate oxide superconductors, so a corollary requirement will be a reliable method for judging the quality of these materials. The application of magnetically modulated resistance methods in this task is briefly described and illustrated.
Zhang, Yanni; Huang, Hai; Zheng, Jing; Pan, Jie
2015-11-01
This paper extends previous work of Zhang and Pan [J. Acoust. Soc. Am. 133(4), 2082-2096 (2013)] on sound scattering and absorption by an underwater coated plate with a single attached distributed-inhomogeneity to that with periodically located distributed-inhomogeneities. A comparison is made among cases of a plate without inhomogeneities, a plate with inhomogeneities, and one with inhomogeneities ignoring the mutual coupling. Results show that coupling of the structural waves scattered by the inhomogeneities plays an important role in modifying the sound absorption and scattering of surface sound pressure, especially at low frequencies and/or the resonance frequencies of the trapped modes of the plate. The sound absorption of the plate is dependent on the distance between the adjacent inhomogeneities, the length of the inhomogeneity, and the angle of the incident sound. On the surface of the inhomogeneities, the scattered/total sound pressure is generally enhanced. On the surface in between the inhomogeneities, the pressure is also enhanced at low frequencies but is nearly unchanged at higher frequencies. Results also show that the coupling-induced variation of scattered/total pressure is significant only at the resonance frequencies of the global modes and trapped modes. The surface normal velocity is presented to explain the coupling-induced variations in the vibration and pressure fields.
Zhang, Yanni; Huang, Hai; Zheng, Jing; Pan, Jie
2015-11-01
This paper extends previous work of Zhang and Pan [J. Acoust. Soc. Am. 133(4), 2082-2096 (2013)] on sound scattering and absorption by an underwater coated plate with a single attached distributed-inhomogeneity to that with periodically located distributed-inhomogeneities. A comparison is made among cases of a plate without inhomogeneities, a plate with inhomogeneities, and one with inhomogeneities ignoring the mutual coupling. Results show that coupling of the structural waves scattered by the inhomogeneities plays an important role in modifying the sound absorption and scattering of surface sound pressure, especially at low frequencies and/or the resonance frequencies of the trapped modes of the plate. The sound absorption of the plate is dependent on the distance between the adjacent inhomogeneities, the length of the inhomogeneity, and the angle of the incident sound. On the surface of the inhomogeneities, the scattered/total sound pressure is generally enhanced. On the surface in between the inhomogeneities, the pressure is also enhanced at low frequencies but is nearly unchanged at higher frequencies. Results also show that the coupling-induced variation of scattered/total pressure is significant only at the resonance frequencies of the global modes and trapped modes. The surface normal velocity is presented to explain the coupling-induced variations in the vibration and pressure fields. PMID:26627747
Ice, G.E.; Barabash, R.I.; Pang, J.W. L.
2007-12-19
Three-dimensional (3D), nondestructive, spatially resolved characterization of local crystal structure is conveniently made with polychromatic x-ray microdiffraction. In general, polychromatic microdiffraction provides information about the local (subgrain) orientation, unpaired-dislocation density, and elastic strain. This information can be used for direct comparison to theoretical models. Practical microbeams use intense synchrotron x-ray sources and advanced x-ray focusing optics. By employing polychromatic x-ray beams and a virtual pinhole camera method, called differential aperture microscopy, 3D distributions of the local crystalline phase, orientation (texture), and elastic and plastic strain tensors can be measured with submicron 3D resolution. The local elastic strain tensor elements can typically be determined with uncertainties less than 100 ppm. Orientations can be quantified to {approx} 0.01{sup o} and the local unpaired dislocation-density tensor can be simultaneously characterized. The spatial resolution limit for hard x-ray polychromatic microdiffraction is < 40nm and existing instruments operate with {approx} 500 to 1000nm resolution. Because the 3D x-ray crystal microscope is a penetrating nondestructive tool, it is ideal for studies of mesoscale evolution in materials.
Defect causing nonideality in nearly ideal Au/Si Schottky barrier
NASA Astrophysics Data System (ADS)
Maeda, Keiji
2000-06-01
Previously we have proposed a model of lattice defect, positively charged defect close to the M/S interface, which causes nonideality in nearly ideal Au/Si Schottky barrier. This model is elaborated in this paper. The To anomaly is caused by the spatial inhomogeneity of Schottky barrier height (SBH) due to the same defect, which is expressed by a Gaussian distribution with standard deviation σ. The ideality factor n is related with σ2, which depends on applied voltage. Utilizing a relation between the local SBH lowering and the distance of defect from metal-induced gap state (MIGS), the defect distribution, 6×10 13 cm -2 in total, is obtained to be confined close (about 10 Å) to the MIGS. Changes of the distribution with applied bias indicate that the defect is an ionized donor in an equilibrium with neutral state in a low SBH region. The defect is induced by the Au evaporation process which produces Au silicide. Si self-interstitial induced by the process has appropriate atomic and electronic properties as the defect with deep donor levels of the negative-U property.
Optimum inhomogeneity of local lattice distortions in La2CuO4+y
Poccia, Nicola; Ricci, Alessandro; Campi, Gaetano; Fratini, Michela; Puri, Alessandro; Gioacchino, Daniele Di; Marcelli, Augusto; Reynolds, Michael; Burghammer, Manfred; Saini, Naurang Lal; Aeppli, Gabriel; Bianconi, Antonio
2012-01-01
Electronic functionalities in materials from silicon to transition metal oxides are, to a large extent, controlled by defects and their relative arrangement. Outstanding examples are the oxides of copper, where defect order is correlated with their high superconducting transition temperatures. The oxygen defect order can be highly inhomogeneous, even in optimal superconducting samples, which raises the question of the nature of the sample regions where the order does not exist but which nonetheless form the “glue” binding the ordered regions together. Here we use scanning X-ray microdiffraction (with a beam 300 nm in diameter) to show that for La2CuO4+y, the glue regions contain incommensurate modulated local lattice distortions, whose spatial extent is most pronounced for the best superconducting samples. For an underdoped single crystal with mobile oxygen interstitials in the spacer La2O2+y layers intercalated between the CuO2 layers, the incommensurate modulated local lattice distortions form droplets anticorrelated with the ordered oxygen interstitials, and whose spatial extent is most pronounced for the best superconducting samples. In this simplest of high temperature superconductors, there are therefore not one, but two networks of ordered defects which can be tuned to achieve optimal superconductivity. For a given stoichiometry, the highest transition temperature is obtained when both the ordered oxygen and lattice defects form fractal patterns, as opposed to appearing in isolated spots. We speculate that the relationship between material complexity and superconducting transition temperature Tc is actually underpinned by a fundamental relation between Tc and the distribution of ordered defect networks supported by the materials. PMID:22961255
Optimum inhomogeneity of local lattice distortions in La2CuO(4+y).
Poccia, Nicola; Ricci, Alessandro; Campi, Gaetano; Fratini, Michela; Puri, Alessandro; Di Gioacchino, Daniele; Marcelli, Augusto; Reynolds, Michael; Burghammer, Manfred; Saini, Naurang Lal; Aeppli, Gabriel; Bianconi, Antonio
2012-09-25
Electronic functionalities in materials from silicon to transition metal oxides are, to a large extent, controlled by defects and their relative arrangement. Outstanding examples are the oxides of copper, where defect order is correlated with their high superconducting transition temperatures. The oxygen defect order can be highly inhomogeneous, even in optimal superconducting samples, which raises the question of the nature of the sample regions where the order does not exist but which nonetheless form the "glue" binding the ordered regions together. Here we use scanning X-ray microdiffraction (with a beam 300 nm in diameter) to show that for La(2)CuO(4+y), the glue regions contain incommensurate modulated local lattice distortions, whose spatial extent is most pronounced for the best superconducting samples. For an underdoped single crystal with mobile oxygen interstitials in the spacer La(2)O(2+y) layers intercalated between the CuO(2) layers, the incommensurate modulated local lattice distortions form droplets anticorrelated with the ordered oxygen interstitials, and whose spatial extent is most pronounced for the best superconducting samples. In this simplest of high temperature superconductors, there are therefore not one, but two networks of ordered defects which can be tuned to achieve optimal superconductivity. For a given stoichiometry, the highest transition temperature is obtained when both the ordered oxygen and lattice defects form fractal patterns, as opposed to appearing in isolated spots. We speculate that the relationship between material complexity and superconducting transition temperature T(c) is actually underpinned by a fundamental relation between T(c) and the distribution of ordered defect networks supported by the materials. PMID:22961255
Fusion Reaction Rate in an Inhomogeneous Plasma
S. Son; N.J. Fisch
2004-09-03
The local fusion rate, obtained from the assumption that the distribution is a local Maxwellian, is inaccurate if mean-free-paths of fusing particles are not sufficiently small compared with the inhomogeneity length of the plasma. We calculate the first order correction of P0 in terms of the small spatial gradient and obtain a non-local modification of P(sub)0 in a shock region when the gradient is not small. Use is made of the fact that the fusion reaction cross section has a relatively sharp peak as a function of energy.
NASA Astrophysics Data System (ADS)
Maekawa, M.; Kawasuso, A.
2013-06-01
A complementary study of vacancy defects in Si substrates by using scanning positron microscope (SPM) and electron beam induced current (EBIC) method were demonstrated for the same samples and in the same chamber. Both the S parameter and EBIC contrast were found to be enhanced in the regions containing vacancy defects introduced by ion implantation. That is, the SPM provides a criterion if the spatially resolved carrier recombination centres by the EBIC method are originating from vacancy defects or not.
Chang, Huibo; Zhang, Ting; Zhang, Zhiping; Bao, Rui; Fu, Chengbo; Wang, Zhigang; Bao, Yihua; Li, Yuanyuan; Wu, Lihua; Zheng, Xiaoying; Wu, Jianxin
2011-12-01
This study compares the density and tissue-specific distribution of 5-methyl cytosine (5mC) in genomic DNA from human fetuses with or without neural tube defects (NTD) and examines whether low maternal serum folate is a possible correlate and/or risk factor for NTD. The results demonstrate significant hypomethylation of brain genomic DNA in NTD fetuses relative to controls (P<.01), as well as relative hypermethylation of skin and heart in NTD fetuses. In normal fetuses, the level of 5mC in liver genomic DNA decreased from fetal week 18 to 28 and increased over the same developmental period in kidney genomic DNA, but these trends were absent in genomic DNA from NTD fetuses. Mean maternal serum folate was significantly lower in NTD fetuses than in controls (P<.01), and maternal serum folate correlated with density of 5mC in genomic brain DNA from NTD fetuses (r=0.610). The results indicate that aberrant DNA methylation in NTD may be due to maternal folate deficiency and may be involved in the pathogenesis of NTD in humans. PMID:21333513
Remarks on inhomogeneous anisotropic cosmology
NASA Astrophysics Data System (ADS)
Kaya, Ali
2016-08-01
Recently a new no-global-recollapse argument was given for some inhomogeneous and anisotropic cosmologies that utilizes surface deformation by the mean curvature flow. In this paper we discuss important properties of the mean curvature flow of spacelike surfaces in Lorentzian manifolds. We show that singularities may form during cosmic evolution, and the theorems forbidding the global recollapse lose their validity. The time evolution of the spatial scalar curvature that may kinematically prevent the recollapse is determined in normal coordinates, which shows the impact of inhomogeneities explicitly. Our analysis indicates a caveat in numerical solutions that give rise to inflation.
Inhomogeneous diffusion-limited aggregation
NASA Technical Reports Server (NTRS)
Selinger, Robin Blumberg; Nittmann, Johann; Stanley, H. E.
1989-01-01
It is demonstrated here that inhomogeneous diffusion-limited aggregation (DLA) model can be used to simulate viscous fingering in a medium with inhomogeneous permeability and homogeneous porosity. The medium consists of a pipe-pore square-lattice network in which all pores have equal volume and the pipes have negligible volume. It is shown that fluctuations in a DLA-based growth process may be tuned by noise reduction, and that fluctuations in the velocity of the moving interface are multiplicative in form.
Jaramillo-Fernandez, J; Ordonez-Miranda, J; Ollier, E; Volz, S
2015-03-28
The effect of the structural inhomogeneity and oxygen defects on the thermal conductivity of polycrystalline aluminum nitride (AlN) thin films deposited on single-crystal silicon substrates is experimentally and theoretically investigated. The influence of the evolution of crystal structure, grain size, and out-of plane disorientation along the cross plane of the films on their thermal conductivity is analyzed. The impact of oxygen-related defects on thermal conduction is studied in AlN/AlN multilayered samples. Microstructure, texture, and grain size of the films were characterized by X-ray diffraction and scanning and transmission electron microscopy. The measured thermal conductivity obtained with the 3-omega technique for a single and multiple layers of AlN is in fairly good agreement with the theoretical predictions of our model, which is developed by considering a serial assembly of grain distributions. An effective thermal conductivity of 5.92 W m(-1) K(-1) is measured for a 1107.5 nm-thick multilayer structure, which represents a reduction of 20% of the thermal conductivity of an AlN monolayer with approximately the same thickness, due to oxygen impurities at the interface of AlN layers. Our results show that the reduction of the thermal conductivity as the film thickness is scaled down, is strongly determined by the structural inhomogeneities inside the sputtered films. The origin of this non-homogeneity and the effect on phonon scattering are also discussed.
Inhomogeneous turbulence in magnetic reconnection
NASA Astrophysics Data System (ADS)
Yokoi, Nobumitsu
2016-07-01
Turbulence is expected to play an essential role in enhancing magnetic reconnection. Turbulence associated with magnetic reconnection is highly inhomogeneous: it is generated by inhomogeneities of the field configuration such as the velocity shear, temperature gradient, density stratification, magnetic shear, etc. This self-generated turbulence affects the reconnection through the turbulent transport. In this reconnection--turbulence interaction, localization of turbulent transport due to dynamic balance between several turbulence effects plays an essential role. For investigating inhomogeneous turbulence in a strongly nonlinear regime, closure or turbulence modeling approaches provide a powerful tool. A turbulence modeling approach for the magnetic reconnection is introduced. In the model, the mean-field equations with turbulence effects incorporated are solved simultaneously with the equations of turbulent statistical quantities that represent spatiotemporal properties of turbulence under the effect of large-scale field inhomogeneities. Numerical simulations of this Reynolds-averaged turbulence model showed that self-generated turbulence enhances magnetic reconnection. It was pointed out that reconnection states may be divided into three category depending on the turbulence level: (i) laminar reconnection; (ii) turbulent reconnection, and (iii) turbulent diffusion. Recent developments in this direction are also briefly introduced, which includes the magnetic Prandtl number dependence, spectral evolution, and guide-field effects. Also relationship of this fully nonlinear turbulence approach with other important approaches such as plasmoid instability reconnection will be discussed.
(Fracture mechanics of inhomogeneous materials)
Bass, B.R.
1990-10-01
Discussions were held with Japanese researchers concerning (1) the Elastic-Plastic Fracture Mechanics in Inhomogeneous Materials and Structures (EPI) Program, and (2) ongoing large-scale pressurized- thermal-shock (PTS) experiments in Japan. In the EPI Program, major activities in the current fiscal year include round-robin analyses of measured data from inhomogeneous base metal/weld metal compact- tension (CT) specimens fabricated from welded plates of A533 grade B class 1 steel. The round-robin task involves participants from nine research organizations in Japan and is scheduled for completion by the end of 1990. Additional experiments will be performed on crack growth in inhomogeneous CT specimens and three-point bend (3PB) specimens 10 mm thick. The data will be compared with that generated previously from 19-mm-thick-specimens. A new type of inhomogeneous surface-cracked specimen will be tested this year, with ratio of crack depth to surface length (a/c) satisfying 0.2 {le} (a/c) {le} 0. 8 and using a 3PB type of applied load. Plans are under way to fabricate a new welded plate of A533 grade B class 1 steel (from a different heat than that currently being tested) in order to provide an expanded fracture-toughness data base. Other topics concerning fracture-prevention issues in reactor pressure vessels were discussed with each of the host organizations, including an overview of ongoing work in the Heavy-Section Steel Technology (HSST) Program.
Averaging inhomogeneous cosmologies - a dialogue.
NASA Astrophysics Data System (ADS)
Buchert, T.
The averaging problem for inhomogeneous cosmologies is discussed in the form of a disputation between two cosmologists, one of them (RED) advocating the standard model, the other (GREEN) advancing some arguments against it. Technical explanations of these arguments as well as the conclusions of this debate are given by BLUE.
Averaging inhomogenous cosmologies - a dialogue
NASA Astrophysics Data System (ADS)
Buchert, T.
The averaging problem for inhomogeneous cosmologies is discussed in the form of a disputation between two cosmologists, one of them (RED) advocating the standard model, the other (GREEN) advancing some arguments against it. Technical explanations of these arguments as well as the conclusions of this debate are given by BLUE.
Simple inhomogeneous cosmological (toy) models
NASA Astrophysics Data System (ADS)
Chirinos Isidro, Eddy G.; Zuñiga Vargas, Cristofher; Zimdahl, Winfried
2016-05-01
Based on the Lemaître-Tolman-Bondi (LTB) metric we consider two flat inhomogeneous big-bang models. We aim at clarifying, as far as possible analytically, basic features of the dynamics of the simplest inhomogeneous models and to point out the potential usefulness of exact inhomogeneous solutions as generalizations of the homogeneous configurations of the cosmological standard model. We discuss explicitly partial successes but also potential pitfalls of these simplest models. Although primarily seen as toy models, the relevant free parameters are fixed by best-fit values using the Joint Light-curve Analysis (JLA)-sample data. On the basis of a likelihood analysis we find that a local hump with an extension of almost 2 Gpc provides a better description of the observations than a local void for which we obtain a best-fit scale of about 30 Mpc. Future redshift-drift measurements are discussed as a promising tool to discriminate between inhomogeneous configurations and the ΛCDM model.
Theoretical study of inhomogenous fluids
NASA Astrophysics Data System (ADS)
Noworyta, Jerzy Piotr
1998-07-01
Binary, additive mixtures of hard spheres near the structureless 'hard' walls are studied with the grand canonical Monte Carlo (MC) simulation method. Binary mixtures of hard spheres and hard sphere systems in the neighborhood of hard walls had been studied separately before. This research for the first time incorporates both elements. A brief survey of the alternative methods that can be applied to study inhomogenous fluid systems is presented, with special attention paid to the integral equation theory. Well-known formulas utilizing the idea of a radial distribution function and a direct correlation function to describe the thermodynamics of the uniform hard sphere fluid through the solution of the Ornstein- Zernike (OZ) integral equation within the Percus-Yevick (PY) closure are given, as well as their generalization to the mixtures. Also presented are the empirical expressions (BMCSL), based on the PY and the scaled particle theory (SPT). The main features of the model assumed for the purpose of this study are hard spheres of two sizes, the conditions of the grand canonical ensemble and the existence of two parallel flat and structureless walls. In contrast to some recently published results, chemical potential is held constant for both species. Some details of the application of the classical Monte Carlo method to the investigated model are presented, including the procedure to ensure an unbiased Markov chain of states. The results of the simulation are analyzed with special attention to the choice of the equilibration point and the extrapolation of the density to the contact separation from the wall. The standard deviation is estimated through the block average method. Results are presented for the mixtures of hard spheres with a 3:5 and 1:3 diameter ratio. The applied range of chemical potentials allowed the simulation of moderately high densities, below the packing fraction of 0.4. Generally, the plots of the obtained reduced density profiles show good
Alnoor, Hatim Chey, Chan Oeurn; Pozina, Galia; Willander, Magnus; Nur, Omer; Liu, Xianjie; Khranovskyy, Volodymyr
2015-08-15
Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.
Impact of Inhomogeneities in HTS Coated Conductors for Resistive FCLs
NASA Astrophysics Data System (ADS)
Colangelo, Daniele; Memiaghe, Steeve; Lacroix, Christian; Sirois, Frédéric; Dutoit, Bertrand
Several issues remain to be addressed for the commercial development of ResistiveFault Current Limiters based on superconducting technologies (RFCL). In particular, the inhomogeneity of high temperature superconducting coated conductors (HTS-CC) combined with the diffculty to predict RFCLs behaviour when interfaced with the existing electrical grid represents an important bottleneck that limits their competitiveness on the electrical market. In order to study the influence of the local inhomogeneity of the HTS tape on the global effective performance of an RFCL, a modular equivalent circuit model has been developed using SimPowerSystemsTM. The model implements an inhomogeneity distribution based on statistical data and takes into account the thermal conduction between different zones of the HTS-CC. It has been calibrated with experimental measurements and finite element simulations. The model can be used to study various scenarios common to power systems, such as transformer in-rush currents, motor starts, etc.
Solutions of the chemical kinetic equations for initially inhomogeneous mixtures.
NASA Technical Reports Server (NTRS)
Hilst, G. R.
1973-01-01
Following the recent discussions by O'Brien (1971) and Donaldson and Hilst (1972) of the effects of inhomogeneous mixing and turbulent diffusion on simple chemical reaction rates, the present report provides a more extensive analysis of when inhomogeneous mixing has a significant effect on chemical reaction rates. The analysis is then extended to the development of an approximate chemical sub-model which provides much improved predictions of chemical reaction rates over a wide range of inhomogeneities and pathological distributions of the concentrations of the reacting chemical species. In particular, the development of an approximate representation of the third-order correlations of the joint concentration fluctuations permits closure of the chemical sub-model at the level of the second-order moments of these fluctuations and the mean concentrations.
Nonideality of Au/Si and Au/GaAs Schottky barriers due to process-induced defects
NASA Astrophysics Data System (ADS)
Maeda, Keiji
2006-06-01
A mechanism of local lowering of the Schottky barrier height (SBH) is proposed, which causes nonideality in nearly ideal Au/ n-Si and Au/ n-GaAs Schottky barriers. Positively ionized defects generated by the process very close to the interface induce electrons in the metal-induced gap states (MIGS) and lower the SBH locally. The spatial density distribution of the ionized defects obtained from the SBH distribution is determined by the unique interaction with the MIGS. The defects are considered to have the negative-U property and are neutralized at very close positions to the MIGS. The potential distributions close to the interface have a considerable potential drop due to the large defect density. These inhomogeneous potentials are coincident with the energy level scheme of the defect identified as the defect causing the nonideality. This defect is Si self-interstitial in Au/Si SB, and As antisite in Au/ n-GaAs SB. This MIGS with process-induced defect model supersedes the previously proposed two major Fermi level pinning models. The mystery of the T0 effect is solved. The thermionic-field emission current taking place in the strong electric field has influence on the I- V characteristics at low temperatures. Regarding the C- V characteristics of Au/Si SB, the observed extra capacitance under the forward bias is an experimental evidence in accordance with the proposed model.
Li NMR study of heavy-fermion LiV2O4 containing magnetic defects
Zong, X.; Das, S.; Borsa, F.; Vannette, M.; Prozorov, R.; Schmalian, J.; Johnston, D.
2008-04-21
We present a systematic study of the variations of the {sup 7}Li NMR properties versus magnetic defect concentration up to 0.83 mol% within the spinel structure of polycrystalline powder samples and a collection of small single crystals of LiV2O4 in the temperature range from 0.5 to 4.2 K. We also report static magnetization measurements and ac magnetic susceptibility measurements at 14 MHz on the samples at low temperatures. Both the NMR spectrum and nuclear spin-lattice relaxation rate are inhomogeneous in the presence of the magnetic defects. The NMR data for the powders are well explained by assuming that (i) there is a random distribution of magnetic point defects, (ii) the same heavy Fermi liquid is present in the samples containing the magnetic defects as in magnetically pure LiV2O4, and (iii) the influences of the magnetic defects and of the Fermi liquid on the magnetization and NMR properties are separable. In the single crystals, somewhat different behaviors are observed. Remarkably, the magnetic defects in the powder samples show evidence of spin freezing below T {approx} 1.0 K, whereas in the single crystals with similar magnetic defect concentration no spin freezing was found down to 0.5 K. Thus different types of magnetic defects and/or interactions between them appear to arise in the powders versus the crystals, possibly due to the substantially different synthesis conditions of the powders and crystals.
Study of structural inhomogeneity of commercial oxide-dispersion-strengthened steels
NASA Astrophysics Data System (ADS)
Veternikova, J.; Degmova, J.; Skraba, M.; Petriska, M.; Sojak, S.; Slugen, V.
2014-04-01
Oxide-dispersion-strengthened steels, candidate materials for construction of new generation of nuclear reactors, can have inhomogeneous structure and anisotropic mechanical properties due to their fabrication, especially by process of mechanical alloying. This paper examines two similar commercial oxide-dispersion-strengthened steels MA 956 and PM 2000 in two different orientations of samples in order to study inhomogeneity of defect presence using positron annihilation techniques. Positron data showed small or negligible differences between samples of individual steels (up to 4 % for average lifetime). Moreover, structural divergence between two orientations (transversal cut and longitudinal cut) of the same steel was also not apparent. However, higher presence of defects and also bigger defects were found for both orientations of MA 956 samples. The structure of PM 2000 probably contains fewer defects with smaller size, though their occurrence in surface and subsurface layers up to 1.6 μm (from Doppler broadening spectroscopy) seem to be less homogeneous than in MA 956.
NASA Astrophysics Data System (ADS)
Stufflebeam, Michael; Hodges, Jeffery A.; Park, Tyler; Evenson, W.; Matheson, P.; Zacate, M. O.
2008-10-01
Independent component analysis (ICA) of electric field gradient (EFG) tensor components has proven useful in analysis of inhomogeneous broadening in perturbed angular correlation (PAC). We have simulated PAC spectra for various concentrations (0.1% to 15%) of randomly distributed defects with a near- neighbor vacancy in simple cubic and face-centered cubic crystal structures. In analyzing this simulation, we used ICA to transform the Vxx and Vzz EFG components to find a joint probability distribution function for the EFGs. ICA allowed us to separate the components and develop the joint probability function as a product of the probability distributions for two independent coordinates. Then we found the broadened G2(t) by integration over the joint probability distribution function. We have compared these results to simulated G2(t) functions, allowing us to analyze the concentration dependence of the broadened PAC spectrum. This work will be applied initially to broadened PAC data from β-Mn, Al-doped β-Mn, and Sr2RuO4.
Insights into Ventilatory Inhomogeneity from Respiratory Measurements on Spacelab Mission D-2
NASA Technical Reports Server (NTRS)
Paiva, Manuel; Verbanck, Sylvia; Linnarsson, Dag; Prisk, Kim; West, John B.
1996-01-01
The relative contributions of inter-regional and intra-regional ventilation inhomogeneities of Spacelab astronauts are studied. The classical theory of ventilation distribution in the lung is that the top-to-bottom (inter-regional) ventilation inhomogeneities are primarily gravity dependent, whereas the peripheral (intra-regional) ventilation distribution is gravity independent. Argon rebreathing tests showed that gravity independent specific ventilation (ventilation per unit volume) inhomogeneities are at least as large as gravity dependent ones. Single breath tests with helium and sulfur hexafluoride showed the different sensitivity of these gases to microgravity.
Measurement of the microwave emitter's inhomogeneity using optical fiber DTS
NASA Astrophysics Data System (ADS)
Jaros, Jakub; Papes, Martin; Liner, Andrej; Vašinek, Vladimir; Smira, Pavel; Nasswettrova, Andrea; Cubik, Jakub; Kepak, Stanislav
2014-06-01
Researcher's teams were dealing with the microwave emitter's inhomogeneity problem since the microwaves were used. One possible way, how to measure electromagnetic field is the measurement on inhomogeneous temperature distribution on the irradiated sample, which can cause problems as in other material processing, so in the undesirable change of properties and even security. Inhomogeneity of electromagnetic field is specific by creating spots with higher or lower temperature called "hot spots". This inhomogeneity strongly affects the temperature distribution in the cross section of the material and its resultant heating. Given the impossibility of using classical electronic devices with metal temperature sensors were various indirect methods used in the past. This paper deals with experimental measurement of the microwave emitter's inhomogeneity (2.45 GHz) using the optical fiber DTS. The greatest advantage of this sensor system is just in using of the optical fiber (electromagnetic resistance, small size, safety using in inflammable and explosive area, easy installation). Due to these properties of the optical fiber sensor it's possible to measure the temperature of the sample in real time. These sensor are able to measure the temperature along the fiber, in some cases they use nonlinear effect in optical fiber (Raman nonlinear effect). The verification of non-homogeneity consists in experimental measuring of the temperature distribution within the wooden sample. The method is based on heat exchange in an isolated system where wooden sample serves as an absorber of the irradiated energy. To identify locations with different power density was used DTS system, based on nonlinear phenomena in optical fibers.
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Yang, Guangtao Swaaij, R. A. C. M. M. van; Dobrovolskiy, S.; Zeman, M.
2014-01-21
In this contribution, we demonstrate the application temperature dependent capacitance-frequency measurements (C-f) to n-i-p hydrogenated amorphous silicon (a-Si:H) solar cells that are forward-biased. By using a forward bias, the C-f measurement can detect the density of defect states in a particular energy range of the interface region. For this contribution, we have carried out this measurement method on n-i-p a-Si:H solar cells of which the intrinsic layer has been exposed to a H{sub 2}-plasma before p-type layer deposition. After this treatment, the open-circuit voltage and fill factor increased significantly, as well as the blue response of the solar cells as is concluded from external quantum efficiency. For single junction, n-i-p a-Si:H solar cells initial efficiency increased from 6.34% to 8.41%. This performance enhancement is believed to be mainly due to a reduction of the defect density in the i-p interface region after the H{sub 2}-plasma treatment. These results are confirmed by the C-f measurements. After H{sub 2}-plasma treatment, the defect density in the intrinsic layer near the i-p interface region is lower and peaks at an energy level deeper in the band gap. These C-f measurements therefore enable us to monitor changes in the defect density in the interface region as a result of a hydrogen plasma. The lower defect density at the i-p interface as detected by the C-f measurements is supported by dark current-voltage measurements, which indicate a lower carrier recombination rate.
Sopori, B.; Tan, T.Y.
1994-08-01
This report is the summary of the third workshop on the role of point defects and defect complexes in silicon device processing. The workshop was organized: (1) to discuss recent progress in the material quality produced by photovoltaic Si manufacturers, (2) to foster the understanding of point defect issues in Si device processing, (3) to review the effects of inhomogeneities on large- area solar cell performance, (4) to discuss how to improve Si solar cell processing, and (5) to develop a new understanding of gettering, defect passivation, and defect annihilation. Separate abstract were prepared for the individual papers, for the database.
Transdimensional imaging of random velocity inhomogeneities in Nankai subduction zone
NASA Astrophysics Data System (ADS)
Takahashi, T.; Obana, K.; Yamamoto, Y.; Kaiho, Y.; Nakanishi, A.; Kodaira, S.; Kaneda, Y.
2014-12-01
The Nankai trough in southwestern Japan is a convergent margin where the Philippine Sea plate is subducting beneath the Eurasian plate. We have conducted five seismic observations with ocean bottom seismograms (OBSs) from 2008 to 2012 to elucidate detailed seismic structures and its relations with fault segments of large earthquakes. These observations covered the entire area of the Nankai trough, but quantity and quality of data are not spatially uniform because of different observing lengths and various noises. Waveform data of OBSs suggests variously-sized anomalies of random velocity inhomogeneity (i.e., scattering strength) in this subduction zone. To clarify details of random inhomogeneity structures, we conducted a transdimensional imaging of random inhomogeneities by means of the reversible jump Markov Chain Monte Carlo (rjMCMC) without assuming smooth spatial distributions of unknown parameters. We applied the rjMCMC for the inversion of peak delay times of S-wave envelopes at 4-8, 8-16, and 16-32 Hz, where the peak delay time is defined as the time lag from the S-wave onset to its maximal amplitude arrival. This delay time mainly reflects the accumulated multiple forward scattering effect due to random inhomogeneities. We assumed the von Karman type power spectral density function (PSDF) for random velocity fluctuation, and estimated two parameters related with the PSDF at large wavenumber. Study area is partitioned by discrete Voronoi cells of which number and spatial sizes are variable. Estimated random inhomogeneities show clear lateral variations along the Nankai trough. The strongest inhomogeneity on the Nankai trough was found near the subducted Kyushu-Palau ridge that is located at the western margin of the fault segments. We also find a horizontal variation of inhomogeneity along the non-volcanic tremor zone. Relatively strong inhomogeneities in this tremor zone were imaged beneath west Shikoku and Kii-Peninsula. These anomalies were not clearly
Casimir stress in an inhomogeneous medium
Philbin, T.G. Xiong, C.; Leonhardt, U.
2010-03-15
The Casimir effect in an inhomogeneous dielectric is investigated using Lifshitz's theory of electromagnetic vacuum energy. A permittivity function that depends continuously on one Cartesian coordinate is chosen, bounded on each side by homogeneous dielectrics. The result for the Casimir stress is infinite everywhere inside the inhomogeneous region, a divergence that does not occur for piece-wise homogeneous dielectrics with planar boundaries. A Casimir force per unit volume can be extracted from the infinite stress but it diverges on the boundaries between the inhomogeneous medium and the homogeneous dielectrics. An alternative regularization of the vacuum stress is considered that removes the contribution of the inhomogeneity over small distances, where macroscopic electromagnetism is invalid. The alternative regularization yields a finite Casimir stress inside the inhomogeneous region, but the stress and force per unit volume diverge on the boundaries with the homogeneous dielectrics. The case of inhomogeneous dielectrics with planar boundaries thus falls outside the current understanding of the Casimir effect.
A Chebychev propagator for inhomogeneous Schroedinger equations
Ndong, Mamadou; Koch, Christiane P.; Tal-Ezer, Hillel; Kosloff, Ronnie
2009-03-28
A propagation scheme for time-dependent inhomogeneous Schroedinger equations is presented. Such equations occur in time dependent optimal control theory and in reactive scattering. A formal solution based on a polynomial expansion of the inhomogeneous term is derived. It is subjected to an approximation in terms of Chebychev polynomials. Different variants for the inhomogeneous propagator are demonstrated and applied to two examples from optimal control theory. Convergence behavior and numerical efficiency are analyzed.
Inhomogeneous viscous fluid in anisotropic inflationary universe
NASA Astrophysics Data System (ADS)
Sharif, M.; Mohsaneen, Sidra
2015-06-01
In this paper, we study inhomogeneous viscous fluid for inflation in the framework of locally rotationally symmetric Bianchi type I universe model. We consider an inhomogeneous equation of state with viscosity term to ensure a graceful exit from inflationary period. In order to study inflationary perturbations, we evaluate slow-roll parameters, scalar and tensor power spectra, scalar spectral index, tensor to scalar ratio for scalar field and inhomogeneous viscous fluid. It is concluded that our anisotropic inflationary universe model with inhomogeneous viscous fluid is consistent with recent data in a specific range of the model parameters.
Moving inhomogeneous envelopes of stars
NASA Astrophysics Data System (ADS)
Oskinova, Lidia M.; Kubátová, Brankica; Hamann, Wolf-Rainer
2016-11-01
Massive stars are extremely luminous and drive strong winds, blowing a large part of their matter into the galactic environment before they finally explode as a supernova. Quantitative knowledge of massive star feedback is required to understand our Universe as we see it. Traditionally, massive stars have been studied under the assumption that their winds are homogeneous and stationary, largely relying on the Sobolev approximation. However, observations with the newest instruments, together with progress in model calculations, ultimately dictate a cardinal change of this paradigm: stellar winds are highly inhomogeneous. Hence, we are now advancing to a new stage in our understanding of stellar winds. Using the foundations laid by V.V. Sobolev and his school, we now update and further develop the stellar spectral analysis techniques. New sophisticated 3-D models of radiation transfer in inhomogeneous expanding media elucidate the physics of stellar winds and improve classical empiric mass-loss rate diagnostics. Applications of these new techniques to multiwavelength observations of massive stars yield consistent and robust stellar wind parameters.
Thomson scattering on inhomogeneous targets
Thiele, R.; Sperling, P.; Bornath, Th.; Kraeft, W.-D.; Redmer, R.; Chen, M.; Faeustlin, R. R.; Toleikis, S.; Fortmann, C.; Glenzer, S. H.; Pukhov, A.; Tschentscher, Th.
2010-11-15
The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm dense matter states. For instance, a short-pulse optical laser irradiates a liquid hydrogen jet that is subsequently probed with brilliant soft x-ray radiation. The strongly inhomogeneous plasma prepared by the optical laser is characterized with particle-in-cell simulations. The interaction of the soft x-ray probe radiation for different time delays between pump and probe with the inhomogeneous plasma is also taken into account via radiative hydrodynamic simulations. We calculate the respective scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We can identify plasmon modes that are generated in different target regions and monitor their temporal evolution. Therefore, such pump-probe experiments are promising tools not only to measure the important plasma parameters density and temperature but also to gain valuable information about their time-dependent profile through the target. The method described here can be applied to various pump-probe scenarios by combining optical lasers and soft x ray, as well as x-ray sources.
Quasiadiabatic modes from viscous inhomogeneities
NASA Astrophysics Data System (ADS)
Giovannini, Massimo
2016-04-01
The viscous inhomogeneities of a relativistic plasma determine a further class of entropic modes whose amplitude must be sufficiently small since curvature perturbations are observed to be predominantly adiabatic and Gaussian over large scales. When the viscous coefficients only depend on the energy density of the fluid the corresponding curvature fluctuations are shown to be almost adiabatic. After addressing the problem in a gauge-invariant perturbative expansion, the same analysis is repeated at a nonperturbative level by investigating the nonlinear curvature inhomogeneities induced by the spatial variation of the viscous coefficients. It is demonstrated that the quasiadiabatic modes are suppressed in comparison with a bona fide adiabatic solution. Because of its anomalously large tensor to scalar ratio the quasiadiabatic mode cannot be a substitute for the conventional adiabatic paradigm so that, ultimately, the present findings seems to exclude the possibility of a successful accelerated dynamics solely based on relativistic viscous fluids. If the dominant adiabatic mode is not affected by the viscosity of the background a sufficiently small fraction of entropic fluctuations of viscous origin cannot be a priori ruled out.
Lensing effects in an inhomogeneous universe
NASA Astrophysics Data System (ADS)
Bergström, L.; Goliath, M.; Goobar, A.; Mörtsell, E.
2000-06-01
Recently, Holz & Wald have presented a new method for determining gravitational lensing effects on, e.g., supernova luminosity versus redshift measurements in inhomogeneous universes. In this paper, their method is generalized in several ways: First, the matter content is allowed to consist of several different types of fluids, possibly with non-vanishing pressure. Second, besides lensing by simple point masses and singular isothermal spheres, the more realistic halo dark matter distribution proposed by Navarro, Frenk & White (NFW), based on N-body simulation results, is treated. We discuss various aspects of the accuracy of the method, such as luminosity corrections, and statistics, for multiple images. We find in agreement with other recent work that a large sample of supernovae at large redshift could be used to extract gross features of the mass distribution of the lensing dark matter halos, such as the existence of a large number of point-like objects. The results for the isothermal sphere and the NFW model are, however, very similar if normalized to the observed luminosity distribution of galaxies. We give convenient analytical fitting formulas for our computed lensing probabilites as a function of magnification, for several redshifts.
Optimality of Spatially Inhomogeneous Search Strategies
NASA Astrophysics Data System (ADS)
Schwarz, Karsten; Schröder, Yannick; Qu, Bin; Hoth, Markus; Rieger, Heiko
2016-08-01
We consider random search processes alternating stochastically between diffusion and ballistic motion, in which the distribution function of ballistic motion directions varies from point to point in space. The specific space dependence of the directional distribution together with the switching rates between the two modes of motion establishes a spatially inhomogeneous search strategy. We show that the mean first passage times for several standard search problems—narrow escape, reaction partner finding, reaction escape—can be minimized with a directional distribution that is reminiscent of the spatial organization of the cytoskeleton filaments of cells with a centrosome: radial ballistic transport from the center to the periphery and back, and ballistic transport in random directions within a concentric shell of thickness Δopt along the domain boundary. The results suggest that living cells realize efficient search strategies for various intracellular transport problems economically through a spatial cytoskeleton organization that involves radial microtubules in the central region and only a narrow actin cortex rather than a cell body filled with randomly oriented actin filaments.
Optimality of Spatially Inhomogeneous Search Strategies.
Schwarz, Karsten; Schröder, Yannick; Qu, Bin; Hoth, Markus; Rieger, Heiko
2016-08-01
We consider random search processes alternating stochastically between diffusion and ballistic motion, in which the distribution function of ballistic motion directions varies from point to point in space. The specific space dependence of the directional distribution together with the switching rates between the two modes of motion establishes a spatially inhomogeneous search strategy. We show that the mean first passage times for several standard search problems-narrow escape, reaction partner finding, reaction escape-can be minimized with a directional distribution that is reminiscent of the spatial organization of the cytoskeleton filaments of cells with a centrosome: radial ballistic transport from the center to the periphery and back, and ballistic transport in random directions within a concentric shell of thickness Δ_{opt} along the domain boundary. The results suggest that living cells realize efficient search strategies for various intracellular transport problems economically through a spatial cytoskeleton organization that involves radial microtubules in the central region and only a narrow actin cortex rather than a cell body filled with randomly oriented actin filaments. PMID:27541477
Analysis of interferograms of refractive index inhomogeneities produced in optical materials
NASA Astrophysics Data System (ADS)
Tarjányi, N.
2014-12-01
Optical homogeneity of materials intended for optical applications is one of the criterions which decide on an appropriate application method for the material. The existence of a refractive index inhomogeneity inside a material may disqualify it from utilization or by contrary, provide an advantage. For observation of a refractive index inhomogeneity, even a weak one, it is convenient to use any of interferometric methods. They are very sensitive and provide information on spatial distribution of the refractive index, immediately. One can use them also in case when the inhomogeneity evolves in time, usually due to action of some external fields. Then, the stream of interferograms provides a dynamic evolution of a spatial distribution of the inhomogeneity. In the contribution, there are presented results of the analysis of interferograms obtained by observing the creation of a refractive index inhomogeneity due to illumination of thin layers of a polyvinyl-alcohol/acrylamide photopolymer and a plate of photorefractive crystal, lithium niobate, by light and a refractive index inhomogeneity originated at the boundary of two layers of polydimethylsiloxane. The obtained dependences can be used for studying of the mechanisms responsible for the inhomogeneity creation, designing various technical applications or for diagnostics of fabricated components.
Integration of inhomogeneous cosmological spacetimes in the BSSN formalism
NASA Astrophysics Data System (ADS)
Mertens, James B.; Giblin, John T.; Starkman, Glenn D.
2016-06-01
We present cosmological-scale numerical simulations of an evolving universe in full general relativity and introduce a new numerical tool, cosmograph, which employs the Baumgarte-Shapiro-Shibata-Nakamura formalism on a three-dimensional grid. Using cosmograph, we calculate the effect of an inhomogeneous matter distribution on the evolution of a spacetime. We also present the results of a set of standard stability tests to demonstrate the robustness of our simulations.
Inhomogeneous width of oxygen-deficient centers induced by electron irradiation of silica
D'Amico, Michele; Leone, Maurizio; Messina, Fabrizio; Cannas, Marco; Boscaino, Roberto
2009-02-01
We report a study of the luminescence activity of oxygen-deficient centers stabilized in as-grown synthetic silica, as compared with the same defects induced by {beta} irradiation at increasing doses, ranging from 1.2x10{sup 3} to 5x10{sup 6} kGy. We experimentally observe a progressive broadening of the luminescence band with increasing total electron dose released on samples. By analyzing our data within a theoretical model capable of separating homogeneous and inhomogeneous contribution to the total luminescence linewidth, we observe that the increasing of the width is entirely ascribable to the inhomogeneous component which increases, in the most irradiated sample, of 60% with respect to the value in the as-grown sample. This effect can be due either to the progressive creation of new defects statistically exploring different sites of the matrix, or to a progressive structural transformation of silica host which affects the optical properties of induced point defects.
Theoretical model for forming limit diagram predictions without initial inhomogeneity
NASA Astrophysics Data System (ADS)
Gologanu, Mihai; Comsa, Dan Sorin; Banabic, Dorel
2013-05-01
We report on our attempts to build a theoretical model for determining forming limit diagrams (FLD) based on limit analysis that, contrary to the well-known Marciniak and Kuczynski (M-K) model, does not assume the initial existence of a region with material or geometrical inhomogeneity. We first give a new interpretation based on limit analysis for the onset of necking in the M-K model. Considering the initial thickness defect along a narrow band as postulated by the M-K model, we show that incipient necking is a transition in the plastic mechanism from one of plastic flow in both the sheet and the band to another one where the sheet becomes rigid and all plastic deformation is localized in the band. We then draw on some analogies between the onset of necking in a sheet and the onset of coalescence in a porous bulk body. In fact, the main advance in coalescence modeling has been based on a similar limit analysis with an important new ingredient: the evolution of the spatial distribution of voids, due to the plastic deformation, creating weaker regions with higher porosity surrounded by sound regions with no voids. The onset of coalescence is precisely the transition from a mechanism of plastic deformation in both regions to another one, where the sound regions are rigid. We apply this new ingredient to a necking model based on limit analysis, for the first quadrant of the FLD and a porous sheet. We use Gurson's model with some recent extensions to model the porous material. We follow both the evolution of a homogeneous sheet and the evolution of the distribution of voids. At each moment we test for a potential change of plastic mechanism, by comparing the stresses in the uniform region to those in a virtual band with a larger porosity. The main difference with the coalescence of voids in a bulk solid is that the plastic mechanism for a sheet admits a supplementary degree of freedom, namely the change in the thickness of the virtual band. For strain ratios close to
Pair production in inhomogeneous fields
Gies, Holger; Klingmueller, Klaus
2005-09-15
We employ the recently developed worldline numerics, which combines string-inspired field theory methods with Monte Carlo techniques, to develop an algorithm for the computation of pair-production rates in scalar QED for inhomogeneous background fields. We test the algorithm with the classic Sauter potential, for which we compute the local production rate for the first time. Furthermore, we study the production rate for a superposition of a constant E field and a spatially oscillating field for various oscillation frequencies. Our results reveal that the approximation by a local derivative expansion already fails for frequencies small compared to the electron-mass scale, whereas for strongly oscillating fields a derivative expansion for the averaged field represents an acceptable approximation. The worldline picture makes the nonlocal nature of pair production transparent and facilitates a profound understanding of this important quantum phenomenon.
Electromagnetic inhomogeneous waves at planar boundaries: tutorial.
Frezza, Fabrizio; Tedeschi, Nicola
2015-08-01
In this review paper, we summarize the fundamental properties of inhomogeneous waves at the planar interface between two media. We point out the main differences between the wave types: lateral waves, surface waves, and leaky waves. We analyze each kind of inhomogeneous wave, giving a quasi-optical description and explaining the physical origin of some of their properties.
Inhomogeneities of stratocumulus liquid water
NASA Technical Reports Server (NTRS)
Cahalan, Robert F.; Snider, Jack B.
1990-01-01
There is a growing body of observational evidence on inhomogeneous cloud structure, most recently from the extensive measurements of the FIRE field program. Knowledge of cloud structure is important because it strongly influences the cloud radiative properties, one of the major factors in determining the global energy balance. Current atmospheric circulation models use plane-parallel radiation, so that the liquid water in each gridbox is assumed to be uniform, which gives an unrealistically large albedo. In reality cloud liquid water occupies only a subset of each gridbox, greatly reducing the mean albedo. If future climate models are to treat the hydrological cycle in a manner consistent with energy balance, a better treatment of cloud liquid is needed. FIRE concentrated upon two cloud types of special interest: cirrus and marine stratocumulus. Cirrus tend to be high and optically thin, thus reducing the effective radiative temperature without increasing the albedo significantly, leading to an enhanced greenhouse heating. In contrast, marine stratocumulus are low and optically thick, thus producing a large increase in reflected radiation with a small change in emitted radiation, giving a net cooling which could potentially mitigate the expected greenhouse warming. The FIRE measurements in California stratocumulus during June and July of 1987 show variations in cloud liquid water on all scales. Such variations are associated with inhomogeneous entrainment, in which entrained dry air, rather than mixing uniformly with cloudy air, remains intact in blobs of all sizes, which decay only slowly by invasion of cloudy air. Two important stratocumulus observations are described, followed by a simple fractal model which reproduces these properties, and finally, the model radiative properties are discussed.
Modelling of the inhomogeneous interior of polymer gels
NASA Astrophysics Data System (ADS)
Shew, Chwen-Yang; Iwaki, Takafumi
2006-04-01
A simple model has been investigated to elucidate the mean squared displacement (MSD) of probe molecules in cross-linked polymer gels. In the model, we assume that numerous cavities distribute in the inhomogeneous interior of a gel, and probe molecules are confined within these cavities. The individual probe molecules trapped in a gel are treated as Brownian particles confined to a spherical harmonic potential. The harmonic potential is chosen to model the effective potential experienced by the probe particle in the cavity of a gel. Each field strength is corresponding to the characteristic of one type of effective cavity. Since the statistical distribution of different effective cavity sizes is unknown, several distribution functions are examined. Meanwhile, the calculated averaged MSDs are compared to the experimental data by Nisato et al (2000 Phys. Rev. E 61 2879). We find that the theoretical results of the MSD are sensitive to the shape of the distribution function. For low cross-linked gels, the best fit is obtained when the interior cavities of a gel follow a bimodal distribution. Such a result may be attributed to the presence of at least two distinct classes of cavity in gels. For high cross-linked gels, the cavities in the gel can be depicted by a single-modal uniform distribution function, suggesting that the range of cavity sizes becomes smaller. These results manifest the voids inside a gel, and the shape of distribution functions may provide the insight into the inhomogeneous interior of a gel.
... defects happen during the first 3 months of pregnancy. One out of every 33 babies in the ... abuse can cause fetal alcohol syndrome. Infections during pregnancy can also result in birth defects. For most ...
The magnitude-redshift relation in a realistic inhomogeneous universe
Hada, Ryuichiro; Futamase, Toshifumi E-mail: tof@astr.tohoku.ac.jp
2014-12-01
The light rays from a source are subject to a local inhomogeneous geometry generated by inhomogeneous matter distribution as well as the existence of collapsed objects. In this paper we investigate the effect of inhomogeneities and the existence of collapsed objects on the propagation of light rays and evaluate changes in the magnitude-redshift relation from the standard relationship found in a homogeneous FRW universe. We give the expression of the correlation function and the variance for the perturbation of apparent magnitude, and calculate it numerically by using the non-linear matter power spectrum. We use the lognormal probability distribution function for the density contrast and spherical collapse model to truncate the power spectrum in order to estimate the blocking effect by collapsed objects. We find that the uncertainties in Ω{sub m} is ∼ 0.02, and that of w is ∼ 0.04 . We also discuss a possible method to extract these effects from real data which contains intrinsic ambiguities associated with the absolute magnitude.
A Study of Effects of Tissue Inhomogeneity on HIFU Beam
NASA Astrophysics Data System (ADS)
Amin, Viren; Roberts, Ron; Long, Tao; Thompson, R. B.; Ryken, Timothy
2006-05-01
The potential of high-intensity focused ultrasound (HIFU) will not be realized unless the effects of overlaying tissues are understood in such a way that allows for estimation of HIFU dose distribution at a target tissue. We employ computational models to examine the impact of phase aberration on tissue ablation. Thompson and Roberts have recently studied the effects of phase aberration on ultrasound focusing in aerospace engine materials such as titanium alloy, and have developed a computational model to examine these effects. The ultrasound beam observed after transmission through the fused quartz (homogeneous) and that observed after transmission through the titanium (inhomogeneous) demonstrate the severe beam wavefield amplitude distortion introduced by the velocity inhomogeneity-induced phase aberration. We study applicability of this approach to model phase aberration in inhomogeneous tissues and its effect on HIFU dose distribution around the focus. It is hypothesized that the ill-effects of phase aberration accumulate during propagation through intervening tissue in which field intensities are substantially lower than that in the focal zone, and it is therefore appropriate to use a linear acoustic model to describe the transport of energy from the transducer to the volume targeted for ablation. We present initial results of the simulation and experiments of beam measurements under water without and with different tissue layers.
Metal-induced gap states model of nonideal Au/Si Schottky barrier with low defect density
NASA Astrophysics Data System (ADS)
Maeda, Keiji; Kitahara, Eiji
1998-06-01
Temperature dependence of current-voltage characteristics was investigated on Au/n-Si Schottky barrier. The experimental current density can be represented by a modified equation of the thermionic emission, in which nearly the same ideality factors nΦ and nv appear in the temperature dependent exponential term of the barrier height ΦB and in that of the applied voltage V, respectively. Origin of nΦ is considered to be spatially inhomogeneous Schottky barrier height distribution. Origin of nv is considered to be applied bias dependence of the effective barrier height. A microscopic model of the inhomogeneity based on the MIGS model is proposed. Positively charged defects close to interface but outside the evanescent tail of MIGS produce local lowering of barrier height due to induced charge density, which depends on a distance of the defect from interface. The local barrier height lowering is restored by disappearance of the defect charge under forward bias. This model is applicable to interfaces of defect density lower than 10 14 cm -2, which has been considered to be necessary for the Fermi level pinning.
Sahu, R.; Dileep, K.; Loukya, B.; Datta, R.
2014-02-03
It is found that the oxygen vacancy (V{sub O}) defect concentration affecting the separation between individual species in Li{sub Zn}-Li{sub i} complex influences the optical emission property of Li{sub 0.06}Zn{sub 0.94}O epitaxial thin film grown by pulsed laser deposition. The film grown under low oxygen partial pressure (n-type conductivity)/higher partial pressure (resistive-type) has broad emission at ∼2.99 eV/∼2.1 eV and a narrower emission at 3.63 eV/3.56 eV, respectively. First principle based mBJLDA electronic structure calculation suggests that the emission at 2.99 eV is due to the Li{sub Zn}-Li{sub i} pair complex and the emission at 2.1 eV is when the component species are away from each other.
Holographic confinement in inhomogeneous backgrounds
NASA Astrophysics Data System (ADS)
Marolf, Donald; Wien, Jason
2016-08-01
As noted by Witten, compactifying a d-dimensional holographic CFT on an S 1 gives a class of ( d - 1)-dimensional confining theories with gravity duals. The proto-typical bulk solution dual to the ground state is a double Wick rotation of the AdS d+1 Schwarzschild black hole known as the AdS soliton. We generalize such examples by allowing slow variations in the size of the S 1, and thus in the confinement scale. Coefficients governing the second order response of the system are computed for 3 ≤ d ≤ 8 using a derivative expansion closely related to the fluid-gravity correspondence. The primary physical results are that i) gauge-theory flux tubes tend to align orthogonal to gradients and along the eigenvector of the Hessian with the lowest eigenvalue, ii) flux tubes aligned orthogonal to gradients are attracted to gradients for d ≤ 6 but repelled by gradients for d ≥ 7, iii) flux tubes are repelled by regions where the second derivative along the tube is large and positive but are attracted to regions where the eigenvalues of the Hessian are large and positive in directions orthogonal to the tube, and iv) for d > 3, inhomogeneities act to raise the total energy of the confining vacuum above its zeroth order value.
The effects of plasma inhomogeneity on the nanoparticle coating in a low pressure plasma reactor
Pourali, N.; Foroutan, G.
2015-10-15
A self-consistent model is used to study the surface coating of a collection of charged nanoparticles trapped in the sheath region of a low pressure plasma reactor. The model consists of multi-fluid plasma sheath module, including nanoparticle dynamics, as well as the surface deposition and particle heating modules. The simulation results show that the mean particle radius increases with time and the nanoparticle size distribution is broadened. The mean radius is a linear function of time, while the variance exhibits a quadratic dependence. The broadening in size distribution is attributed to the spatial inhomogeneity of the deposition rate which in turn depends on the plasma inhomogeneity. The spatial inhomogeneity of the ions has strong impact on the broadening of the size distribution, as the ions contribute both in the nanoparticle charging and in direct film deposition. The distribution width also increases with increasing of the pressure, gas temperature, and the ambient temperature gradient.
Microwaves Scattering by Underdense Inhomogeneous Plasma Column
NASA Astrophysics Data System (ADS)
Zhang, Lin; Ouyang, Jiting
2016-03-01
The scattering characteristics of microwaves (MWs) by an underdense inhomogeneous plasma column have been investigated. The plasma column is generated by hollow cathode discharge (HCD) in a glass tube filled with low pressure argon. The plasma density in the column can be varied by adjusting the discharge current. The scattering power of X-band MWs by the column is measured at different discharge currents and receiving angles. The results show that the column can affect the properties of scattering wave significantly regardless of its plasma frequency much lower than the incident wave frequency. The power peak of the scattering wave shifts away from 0° to about ±15° direction. The finite-different time-domain (FDTD) method is employed to analyze the wave scattering by plasma column with different electron density distributions. The reflected MW power from a metal plate located behind the column is also measured to investigate the scattering effect on reducing MW reflectivity of a metal target. This study is expected to deepen the understanding of plasma-electromagnetic wave interaction and expand the applications concerning plasma antenna and plasma stealth.
Mathematical Modeling of Extinction of Inhomogeneous Populations
Karev, G.P.; Kareva, I.
2016-01-01
Mathematical models of population extinction have a variety of applications in such areas as ecology, paleontology and conservation biology. Here we propose and investigate two types of sub-exponential models of population extinction. Unlike the more traditional exponential models, the life duration of sub-exponential models is finite. In the first model, the population is assumed to be composed clones that are independent from each other. In the second model, we assume that the size of the population as a whole decreases according to the sub-exponential equation. We then investigate the “unobserved heterogeneity”, i.e. the underlying inhomogeneous population model, and calculate the distribution of frequencies of clones for both models. We show that the dynamics of frequencies in the first model is governed by the principle of minimum of Tsallis information loss. In the second model, the notion of “internal population time” is proposed; with respect to the internal time, the dynamics of frequencies is governed by the principle of minimum of Shannon information loss. The results of this analysis show that the principle of minimum of information loss is the underlying law for the evolution of a broad class of models of population extinction. Finally, we propose a possible application of this modeling framework to mechanisms underlying time perception. PMID:27090117
Pair-production in inhomogeneous electric fields
Xue Shesheng
2008-01-03
This is a preliminary study on the rate of electron-positron pair production in spatially inhomogeneous electric fields. We study the rate in the Sauter field and compare it to the rate in the homogeneous field.
Vacuum bubble in an inhomogeneous cosmology
NASA Astrophysics Data System (ADS)
Fischler, W.; Paban, S.; Žanić, M.; Krishnan, C.
2008-05-01
We study the propagation of bubbles of new vacuum in a radially inhomogeneous Lemaître-Tolman-Bondi background that includes a cosmological constant. This exemplifies the classical evolution of a tunneling bubble through a metastable state with curvature inhomogeneities, and will be relevant in the context of the Landscape. We demand that the matter profile in the LTB background satisfy the weak energy condition. For sample profiles that satisfy this restriction, we find that the evolution of the bubble (in terms of the physically relevant coordinates intrinsic to the shell) is largely unaffected by the presence of local inhomogeneities. Our setup should also be a useful toy model for capturing the effects of ambient inhomogeneities on an inflating region.
Diffraction by spherically symmetric inhomogeneous scatterers
Perel`man, A.Y.
1995-05-01
The problem of diffraction by scatterers optically inhomogeneous in the radial direction illuminated by sources with a fixed azimuthal structure is solved. Standard models are proposed for approximating the exact solution of the problem, in which partial potentials are represented in terms of exponential and exponential and cylindrical functions, and the corresponding algorithms for solving the problem are developed. A formula is deduced for the scattering cross section of a radially inhomogeneous sphere. 8 refs.
Inhomogeneous Einstein-Rosen string cosmology
NASA Astrophysics Data System (ADS)
Clancy, Dominic; Feinstein, Alexander; Lidsey, James E.; Tavakol, Reza
1999-08-01
Families of anisotropic and inhomogeneous string cosmologies containing non-trivial dilaton and axion fields are derived by applying the global symmetries of the string effective action to a generalized Einstein-Rosen metric. The models exhibit a two-dimensional group of Abelian isometries. In particular, two classes of exact solutions are found that represent inhomogeneous generalizations of the Bianchi type VIh cosmology. The asymptotic behavior of the solutions is investigated and further applications are briefly discussed.
Inhomogeneities Between and Within Moldavites
NASA Astrophysics Data System (ADS)
Lange, J.-M.; Meisel, T.
1995-09-01
Tektites of unusual chemical or textural composition can give us clues to a range of source materials involved in the formation of the whole population of ejected glasses. Inhomogeneities of moldavites are well known [e.g. 1, 2]. There have been several reports on Muong Nong or layered tektites in the moldavite strewn field [e.g. 3]. In a systematical study of 69 specimens of Lusatia and also from the Czech subfields (Moravia, Bohemia, Radomilice) new glasses were discovered with unusual composition. To the etablished groups of: Normal moldavites (SiO2 76-80 wt%, CaO/MgO about 1.3) including the Bohemian (MgO > 1.5 wt%, CaO > 2 wt%) and Moravian (MgO < 1.5 wt%, CaO < 2 wt%) types, HSi-moldavites (> 80 wt% SiO2) which is common in the Radomilice subfield, HCa/Mg-moldavites (CaO/MgO > 2) first described by [4], HFe-moldavites (Fe-rich moldavites FeO > 2 wt% and SiO2 typically < 76 wt% reported by [5] and layered moldavite (one specimen described by [3], with textural similiarities to Muong Nong-type tektites),we want to add new types found at Jankov (Bohemia) and Trebic (Moravia), "MB-JKV12", which is characterized by two optically distinct components of distinct chemical composition: 1. low SiO2 and high FeO (dark colored) areas and 2. areas of normal moldavite composition (pale areas). The halogen content and Cl/Br ratio are similiar to layered tektites from Indochina [6]. Figure 1 displays the inhomogeneity of this sample in the chemical composition of the two areas and "MM-TRB1" a LCa/Mg-moldavite with an low CaO/MgO-ratio of 0.5. In a diagram Eu versus CaO most of the groups above can be discriminated. New REE-analysis of MB-CLM1 (a HCa/Mg type) done with ID-MS display a less pronounced negative Eu anomaly compared to a normal moldavite from the same locality (MB-CLM2). The high Ca and higher Eu content could be indicative of a higher proportion of plagioclas in the source of this specimen. Whereas the Moravia specimens are very homogenous in their element
How Forest Inhomogeneities Affect the Edge Flow
NASA Astrophysics Data System (ADS)
Boudreault, Louis-Étienne; Dupont, Sylvain; Bechmann, Andreas; Dellwik, Ebba
2016-09-01
Most of our knowledge on forest-edge flows comes from numerical and wind-tunnel experiments where canopies are horizontally homogeneous. To investigate the impact of tree-scale heterogeneities ({>}1 m) on the edge-flow dynamics, the flow in an inhomogeneous forest edge on Falster island in Denmark is investigated using large-eddy simulation. The three-dimensional forest structure is prescribed in the model using high resolution helicopter-based lidar scans. After evaluating the simulation against wind measurements upwind and downwind of the forest leading edge, the flow dynamics are compared between the scanned forest and an equivalent homogeneous forest. The simulations reveal that forest inhomogeneities facilitate flow penetration into the canopy from the edge, inducing important dispersive fluxes in the edge region as a consequence of the flow spatial variability. Further downstream from the edge, the forest inhomogeneities accentuate the canopy-top turbulence and the skewness of the wind-velocity components while the momentum flux remains unchanged. This leads to a lower efficiency in the turbulent transport of momentum within the canopy. Dispersive fluxes are only significant in the upper canopy. Above the canopy, the mean flow is less affected by the forest inhomogeneities. The inhomogeneities induce an increase in the mean wind speed that was found to be equivalent to a decrease in the aerodynamic height of the canopy. Overall, these results highlight the importance of forest inhomogeneities when looking at canopy-atmosphere exchanges in forest-edge regions.
Modelling of of hydraulic fractures trajectories in inhomogeneous stress field
NASA Astrophysics Data System (ADS)
Andreev, A. A.; Galybin, A.
2013-05-01
The paper examines an actual problem of oil and gas production -- modelling of the hydro-fracture trajectories depending on ihomogeneous distributions of pore pressure. The results could serve for improvement of the design of hydraulic fracturing in the oil/gas fields. The methods of the plane elasticity theory and fracture mechanics are employed. It is assumed, that in addition to the homogeneous field of natural stress the reservoir is also subjected to additional stresses caused by technological reasons, which makes the total stress field to be inhomogeneous. Therefore, the objective is to model a curvilinear crack path in an elastic inhomogeneous-loaded plane depending on the different mechanical parameters that control the stress state of the reservoir. For the simulation of the trajectory of a crack the method of boundary integral equation is used. The algorithms of step-by-step determination of the crack's trajectory development using the criterion of maximum tensile stresses at the end of the cracks have been developed. For the numerical realization of the solution we used a special modification of the method of mechanical quadratures providing effective and fast solution of the corresponding system of singular integral equation. The solution for the hydro-fracture path have been simulated for the case of inhomogeneous stress field due to presence of injection well for several physical models.
Otsuka, Teppei; Hanada, Hitoshi; Nakashima, Hidehiko; Sakamoto, Kan; Hayakawa, Masao; Hashizume, Kenichi; Sugisaki, Masayasu
2005-07-15
Hydrogen distributions around non-metallic inclusions in steels are successfully characterized with high-resolution tritium autoradiography. The autoradiographs show that hydrogen accumulation characteristics around the inclusions depend on types of the inclusions. In the case of MnS, hydrogen was inhomogeneously distributed in the ferrite matrix surrounding the MnS inclusion, probably because hydrogen is trapped in defects formed around MnS. The inhomogeneous distribution of hydrogen may be originated from the asymmetric stress field produced by a contraction of the MnS phase in the heat treatment, i.e. the inhomogeneous volumetric change of MnS owing to its larger thermal expansion than that of the ferrite phase. In the case of Al{sub 2}O{sub 3}, hydrogen was intensely localized at boundary layers of the ferrite matrix surrounding the Al{sub 2}O{sub 3} inclusion. This could be attributed to hydrogen trapping at defects introduced by a residual stress in the boundary layers of the ferrite matrix due to larger contraction of the ferrite phase than that of the Al{sub 2}O{sub 3} phase on cooling. Similarly hydrogen was accumulated in the surrounding ferrite matrix but more widely distributed around Cr carbide probably because difference in the thermal expansion between the Cr carbide and ferrite phases is less than that between the Al{sub 2}O{sub 3} and ferrite phases.
Laser-driven electron acceleration in an inhomogeneous plasma channel
Zhang, Rong; Cheng, Li-Hong; Xue, Ju-Kui
2015-12-15
We study the laser-driven electron acceleration in a transversely inhomogeneous plasma channel. We find that, in inhomogeneous plasma channel, the developing of instability for electron acceleration and the electron energy gain can be controlled by adjusting the laser polarization angle and inhomogeneity of plasma channel. That is, we can short the accelerating length and enhance the energy gain in inhomogeneous plasma channel by adjusting the laser polarization angle and inhomogeneity of the plasma channel.
NASA Technical Reports Server (NTRS)
Cusano, C.; Wedeven, L. D.
1981-01-01
Effects of artificially produced dents and grooves on the elastohydrodynamic film thickness profile in a sliding point contact are investigated using optical interferometry. Defects on the surface of a highly polished ball are held stationary at various locations within the vicinity of the contact region while the disk is rotating. It is shown that defects can dramatically change the film thickness which exists when no defects are present in or near the contact, and it is shown that the change in thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.
NASA Astrophysics Data System (ADS)
Ofman, Leon; Ozak, Nataly; Viñas, Adolfo F.
2016-03-01
Near the Sun (< 10Rs) the acceleration, heating, and propagation of the solar wind are likely affected by the background inhomogeneities of the magnetized plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects of background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super-Alfvénic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.
Corrections to the apparent value of the cosmological constant due to local inhomogeneities
Romano, Antonio Enea; Chen, Pisin E-mail: pisinchen@phys.ntu.edu.tw
2011-10-01
Supernovae observations strongly support the presence of a cosmological constant, but its value, which we will call apparent, is normally determined assuming that the Universe can be accurately described by a homogeneous model. Even in the presence of a cosmological constant we cannot exclude nevertheless the presence of a small local inhomogeneity which could affect the apparent value of the cosmological constant. Neglecting the presence of the inhomogeneity can in fact introduce a systematic misinterpretation of cosmological data, leading to the distinction between an apparent and true value of the cosmological constant. We establish the theoretical framework to calculate the corrections to the apparent value of the cosmological constant by modeling the local inhomogeneity with a ΛLTB solution. Our assumption to be at the center of a spherically symmetric inhomogeneous matter distribution correspond to effectively calculate the monopole contribution of the large scale inhomogeneities surrounding us, which we expect to be the dominant one, because of other observations supporting a high level of isotropy of the Universe around us. By performing a local Taylor expansion we analyze the number of independent degrees of freedom which determine the local shape of the inhomogeneity, and consider the issue of central smoothness, showing how the same correction can correspond to different inhomogeneity profiles. Contrary to previous attempts to fit data using large void models our approach is quite general. The correction to the apparent value of the cosmological constant is in fact present for local inhomogeneities of any size, and should always be taken appropriately into account both theoretically and observationally.
NASA Astrophysics Data System (ADS)
Gertsch, A. G.; Jaeger, M.; Bush, N. L.; Frenz, M.; Bamber, J. C.
2009-02-01
Optoacoustic (OA) imaging allows optical absorption contrast to be visualised using thermoelastically generated ultrasound. To date, optoacoustic theory has been applied to homogeneously absorbing tissue models that may describe, for example, large vessels filled with blood, where the whole target will act as a coherent source of sound. Here we describe a new model in which the optical absorbers are distributed inhomogeneously, as appropriate to describe microvasculature, or perhaps the distribution of molecularly targeted OA contrast agents inside a tumour. The degree of coherence over the resulting distributed acoustic source is influenced by parameters that describe the scale of the inhomogeneity, such as the sizes of the absorbers and the distances between them. To investigate the influence of these parameters on OA image appearance, phantoms with homogeneously and imhomogeneously absorbing regions were built and imaged. Simulations of the same situation were conducted using a time domain acoustic propagation method. Both simulations and experiments showed that introducing inhomogeneity of absorption produces more complete images of macroscopic targets than are obtained with a homogeneous absorption. Image improvement and target detectability were found to reach a maximum at an intermediate value of the length-scale of the inhomogeneity that was similar to the axial resolution of the acoustic receiver employed. As the scale of inhomogeneity became finer than this the target's detectability and appearance began to revert to that for homogeneous absorption. Further understanding of this topic is believed to be important for optimising the design of clinical optoacoustic imaging systems.
Energy density inhomogeneities in charged radiating stars with generalized CDTT model
NASA Astrophysics Data System (ADS)
Sharif, M.; Yousaf, Z.
2014-12-01
In this paper, we analyze the role of electromagnetic field and generalized Carrol-Duvvuri-Trodden-Turner (CDTT) model on the existence of homogeneous energy density. For this purpose, we model spherical star with anisotropic matter distribution dissipating in the mode of heat and radiation density. To develop a relationship between the Weyl tensor and matter parameters, we construct two evolution equations. We explore inhomogeneity parameters for particular cases of non-dissipative and dissipative matter distributions. It is concluded that in addition to other fluid variables higher order f( R) corrections, relaxation processes and electromagnetic field affect the energy density inhomogeneity of spherical stars.
Influence of interfacial properties and inhomogeneity on formation of microdamage in bone
NASA Astrophysics Data System (ADS)
Nakade, Rugved
Microdamage accumulation at the nanoscopic level of bone affects the overall mechanical behavior of the bone. This makes it necessary to study the mechanisms through which microdamage accumulation can take place at the nanoscopic level. Experiments on bone's different hierarchy are difficult because of the small sizes of these hierarchical structures. Prevention of bone fractures is greatly enhanced with the help of predictive computational tools and hence used to evaluate the effects of microdamage in bone. There are two main types of microdamage that can form in the bone; linear cracks and diffuse damage. The bone nanostructure consists of mineral platelets embedded in soft protein called collagen and can be treated as a composite material. In this study, a two-dimensional probabilistic finite element model of the bone nanostructure was developed to evaluate the likely formation of the microdamage in the nanostructure due to changes in material properties of the nanostructure. The influence of the microdamage formation due to the collagen-mineral interface strength and also the effects of inhomogeneity were studied. To study interfacial strength effects, cohesive elements using bilinear traction separation laws were used to simulate the behavior of the interface (by way of interfacial debonding) between the collegen-mineral layers. Random field theory was used to assign spatially correlated random variables in order to assign inhomogeneous material properties to the bone. Correlation lengths were used to control the level of inhomogeneity in the model. The analysis showed that the type of microdamage was significantly influenced by the strength of the mineral-collagen interface. Probabilistic failure analyses indicated that strong interfaces resulted in limited interfacial debonding and narrow stress concentrations around an initial defect in the mineral-collagen composite, thereby suggesting that the likely location of failure was in same plane of the initial
Inhomogeneities in the use of orbit - Impact of earth stations
NASA Astrophysics Data System (ADS)
Sane, C. K.
The paper highlights rapid increase in demand for the two limited natural resources, the geostationary satellite orbit (GSO) and radio frequency spectrum, arising from spectacular growth of satellite communication systems in the recent years. Certain parts of the GSO are relatively more congested due to uneven distribution of countries, their sizes, population, geographical factors and telecommunication requirements over the surface of the earth. Consideration for the selection of the orbit slots, inhomogeneity in the use of GSO and technical factors relating to intersatellite spacing are presented. Uneven use of GSO, intersatellite interference and impact of earth station parameters has been discussed. Techno-economic factors influencing earth station subsystems are given.
Vortices in Spatially Inhomogeneous Superfluids
NASA Astrophysics Data System (ADS)
Sheehy, Daniel E.; Radzihovsky, Leo
2004-03-01
Trapped degenerate Bose gases exhibit superfluidity with spatially nonuniform superfluid density. We study the vortex distribution in such rotating nonuniform superfluids, focusing particularly on deviations from a uniform distribution corresponding to an average rigid-body rotation. The origin of such deviations is the discrete way in which vortices impart angular momentum to the superfluid. This effect favors highest vortex density in regions where the superfluid density is most uniform, i.e., at the center of a trap, while tending to decrease the overall number of vortices. Supported by NSF DMR-0321848 and the Packard Foundation.
Beginning inflation in an inhomogeneous universe
NASA Astrophysics Data System (ADS)
East, William E.; Kleban, Matthew; Linde, Andrei; Senatore, Leonardo
2016-09-01
Using numerical solutions of the full Einstein field equations coupled to a scalar inflaton field in 3+1 dimensions, we study the conditions under which a universe that is initially expanding, highly inhomogeneous and dominated by gradient energy can transition to an inflationary period. If the initial scalar field variations are contained within a sufficiently flat region of the inflaton potential, and the universe is spatially flat or open on average, inflation will occur following the dilution of the gradient and kinetic energy due to expansion. This is the case even when the scale of the inhomogeneities is comparable to the initial Hubble length, and overdense regions collapse and form black holes, because underdense regions continue expanding, allowing inflation to eventually begin. This establishes that inflation can arise from highly inhomogeneous initial conditions and solve the horizon and flatness problems, at least as long as the variations in the scalar field do not include values that exceed the inflationary plateau.
FAST TRACK COMMUNICATION: Big Bounce and inhomogeneities
NASA Astrophysics Data System (ADS)
Brizuela, David; Mena Marugán, Guillermo A.; Pawłowski, Tomasz
2010-03-01
The dynamics of an inhomogeneous universe is studied with the methods of loop quantum cosmology, via a so-called hybrid quantization, as an example of the quantization of vacuum cosmological spacetimes containing gravitational waves (Gowdy spacetimes). The analysis of this model with an infinite number of degrees of freedom, performed at the effective level, shows that (i) the initial Big Bang singularity is replaced (as in the case of homogeneous cosmological models) by a Big Bounce, joining deterministically two large universes, (ii) the universe size at the bounce is at least of the same order of magnitude as that of the background homogeneous universe and (iii) for each gravitational wave mode, the difference in amplitude at very early and very late times has a vanishing statistical average when the bounce dynamics is strongly dominated by the inhomogeneities, whereas this average is positive when the dynamics is in a near-vacuum regime, so that statistically the inhomogeneities are amplified.
Refraction in electrically thin inhomogeneous media.
Ruphuy, Miguel; Ramahi, Omar M
2016-04-01
This work presents a new formulation for refraction from flat electrically thin lenses and reflectors comprised of inhomogeneous material. Inhomogeneous electrically thin flat lenses and reflectors cannot make use of the Snell law since this classical formulation works solely at interfaces of planar homogeneous media. The refraction of a perpendicularly incident plane wave at a planar interface is physically explained through the phase advance of the rays within the medium. The Huygens principle is then used to construct the refracted wavefront. The formulation is validated using numerical full wave simulation for several examples where the refractive angle is predicted with good accuracy. Furthermore, the formulation gives a physical insight of the phenomenon of refraction from electrically thin inhomogeneous media.
Exact sum rules for inhomogeneous strings
Amore, Paolo
2013-11-15
We derive explicit expressions for the sum rules of the eigenvalues of inhomogeneous strings with arbitrary density and with different boundary conditions. We show that the sum rule of order N may be obtained in terms of a diagrammatic expansion, with (N−1)!/2 independent diagrams. These sum rules are used to derive upper and lower bounds to the energy of the fundamental mode of an inhomogeneous string; we also show that it is possible to improve these approximations taking into account the asymptotic behavior of the spectrum and applying the Shanks transformation to the sequence of approximations obtained to the different orders. We discuss three applications of these results. -- Highlights: •We derive an explicit expression for the sum rules of an inhomogeneous string. •We obtain a diagrammatic representation for the sum rules of a given order. •We obtain precise bounds on the lowest eigenvalue of the string.
Investigating inhomogeneous Szekeres models and their applications to precision cosmology
NASA Astrophysics Data System (ADS)
Peel, Austin Chandler
Exact solutions of Einstein's field equations that can describe the evolution of complex structures in the universe provide complementary frameworks to standard perturbation theory in which to analyze cosmological and astrophysical phenomena. The flexibility and generality of the inhomogeneous and anisotropic Szekeres metric make it the best known exact solution to explore nonlinearities in the universe. We study applications of Szekeres models to precision cosmology, focusing on the influence of inhomogeneities in two primary contexts---the growth rate of cosmic structures and biases in distance determinations to remote sources. We first define and derive evolution equations for a Szekeres density contrast, which quantifies exact deviations from a smooth background cosmology. Solving these equations and comparing to the usual perturbative approach, we find that for models with the same matter content, the Szekeres growth rate is larger through the matter-dominated cosmic era. Including a cosmological constant, we consider exact global perturbations, as well as the evolution of a single extended structure surrounded by an almost homogeneous background. For the former, we use growth data to obtain a best fit Szekeres model and find that it can fit the data as well as the standard Lambda-Cold Dark Matter (LCDM) cosmological model but with different cosmological parameters. Next, to study effects of inhomogeneities on distance measures, we build an exact relativistic Swiss-cheese model of the universe, where a large number of non-symmetric and randomly placed Szekeres structures are embedded within a LCDM background. Solving the full relativistic propagation equations, light beams are traced through the model, where they traverse the inhomogeneous structures in a way that mimics the paths of real light beams in the universe. For beams crossing a single structure, their magnification or demagnification reflects primarily the net density encountered along the path
Polarization and adiabatic pumping in inhomogeneous crystals.
Xiao, Di; Shi, Junren; Clougherty, Dennis P; Niu, Qian
2009-02-27
We develop a general theory of electric polarization in crystals with inhomogeneous order. We show that the inhomogeneity-induced polarization can be classified into two parts: a perturbative contribution stemming from a correction to the basis functions and a topological contribution described in terms of the Chern-Simons form of the Berry gauge fields. The latter is determined up to an uncertainty quantum, which is the second Chern number in appropriate units. Our theory provides an exhaustive link between microscopic models and the macroscopic polarization. PMID:19257787
Polarization and Adiabatic Pumping in Inhomogeneous Crystals
NASA Astrophysics Data System (ADS)
Xiao, Di; Shi, Junren; Clougherty, Dennis P.; Niu, Qian
2009-02-01
We develop a general theory of electric polarization in crystals with inhomogeneous order. We show that the inhomogeneity-induced polarization can be classified into two parts: a perturbative contribution stemming from a correction to the basis functions and a topological contribution described in terms of the Chern-Simons form of the Berry gauge fields. The latter is determined up to an uncertainty quantum, which is the second Chern number in appropriate units. Our theory provides an exhaustive link between microscopic models and the macroscopic polarization.
Annealed and quenched inhomogeneous cellular automata (INCA)
Vichniac, G.Y.; Tamayo, P.; Hartman, H.
1986-12-01
A probabilistic one-dimensional cellular automaton model by Domany and Kinzel is mapped into an inhomogeneous cellular automaton with the Boolean functions XOR an AND as transition rules. Wolfram's classification is recovered by varying the frequency of these two simple rules and by quenching or annealing the inhomogeneity. In particular, ''class 4'' is related to critical behavior in directed percolation. Also, the critical slowing down of second-order phase transitions is related to a stochastic version of the classical ''halting problem'' of computation theory.
On electromagnetic field problems in inhomogeneous media
NASA Technical Reports Server (NTRS)
Mohsen, A.
1973-01-01
Analysis of electromagnetic fields in inhomogeneous media is of practical interest in general scattering and propagation problems and in the study of lenses. For certain types of inhomogeneities, the fields may be represented in terms of two scalars. In a general orthogonal coordinate system, these potentials satisfy second order differential equations. Exact solutions of these equations are known only for a few particular cases and in general, an approximate or numerical technique must be employed. The present work reviews and generalizes some of the main methods of attack of the problem. The results are presented in a form appropriate for numerical computation.
NASA Astrophysics Data System (ADS)
Boyadjiev, T. L.; Semerdjieva, E. G.; Shukrinov, Yu. M.
2007-09-01
We study the vortex structure in three different models of the long Josephson junction: the exponentially shaped Josephson junction and the Josephson junctions with the resistor and the shunt inhomogeneities in the barrier layer. For these three models the critical curves “critical current-magnetic field” are numerically constructed. We develop the idea of the equivalence of the exponentially shaped Josephson junction and the rectangular junction with the distributed inhomogeneity and demonstrate that at some parameters of the shunt and the resistor inhomogeneities in the ends of the junction the corresponding critical curves are very close to the exponentially shaped one.
Inhomogeneous feed gas processing in industrial ozone generation.
Krogh, Fabio; Merz, Reto; Gisler, Rudolf; Müller, Marco; Paolini, Bernhard; Lopez, Jose L; Freilich, Alfred
2008-01-01
The synthesis of ozone by means of dielectric barrier discharge (DBD) is extensively used in industry. Ozone generators available on the market differ in ozone production capacities, electrode arrangements and working parameters, but operate with a uniformly distributed filamentary discharge plasma pattern.In the presented work the benefits of inhomogeneous feed gas processing are explored. Causality between power induction, production efficiency and working parameters are investigated. Different electrode arrangements, evenly distributed within a given space parameter, were designed, simulated, manufactured and tested on a representative scale. A finite element model was utilized to simulate an inhomogeneous power induction pattern along the ozone generator tube. The simulation yielded the local power density, the local gas temperature gradient and the relative DBD packing density.Results show that the degree of filamentation turns out to be decisive, indicating a new potential by means of plasma tailoring. An arrangement with a pronounced power induction at the inlet of the ozone generator revealed several advantages over homogeneous plasma processing arrangements, for which an increase in robustness and a reduction in electrical power consumption are achieved. PMID:19092182
A Simple Model of Cirrus Horizontal Inhomogeneity and Cloud Fraction
NASA Technical Reports Server (NTRS)
Smith, Samantha A.; DelGenio, Anthony D.
1998-01-01
A simple model of horizontal inhomogeneity and cloud fraction in cirrus clouds has been formulated on the basis that all internal horizontal inhomogeneity in the ice mixing ratio is due to variations in the cloud depth, which are assumed to be Gaussian. The use of such a model was justified by the observed relationship between the normalized variability of the ice water mixing ratio (and extinction) and the normalized variability of cloud depth. Using radar cloud depth data as input, the model reproduced well the in-cloud ice water mixing ratio histograms obtained from horizontal runs during the FIRE2 cirrus campaign. For totally overcast cases the histograms were almost Gaussian, but changed as cloud fraction decreased to exponential distributions which peaked at the lowest nonzero ice value for cloud fractions below 90%. Cloud fractions predicted by the model were always within 28% of the observed value. The predicted average ice water mixing ratios were within 34% of the observed values. This model could be used in a GCM to produce the ice mixing ratio probability distribution function and to estimate cloud fraction. It only requires basic meteorological parameters, the depth of the saturated layer and the standard deviation of cloud depth as input.
Functional integral approach to the kinetic theory of inhomogeneous systems
NASA Astrophysics Data System (ADS)
Fouvry, Jean-Baptiste; Chavanis, Pierre-Henri; Pichon, Christophe
2016-10-01
We present a derivation of the kinetic equation describing the secular evolution of spatially inhomogeneous systems with long-range interactions, the so-called inhomogeneous Landau equation, by relying on a functional integral formalism. We start from the BBGKY hierarchy derived from the Liouville equation. At the order 1 / N, where N is the number of particles, the evolution of the system is characterised by its 1-body distribution function and its 2-body correlation function. Introducing associated auxiliary fields, the evolution of these quantities may be rewritten as a traditional functional integral. By functionally integrating over the 2-body autocorrelation, one obtains a new constraint connecting the 1-body DF and the auxiliary fields. When inverted, this constraint allows us to obtain the closed non-linear kinetic equation satisfied by the 1-body distribution function. This derivation provides an alternative to previous methods, either based on the direct resolution of the truncated BBGKY hierarchy or on the Klimontovich equation. It may turn out to be fruitful to derive more accurate kinetic equations, e.g., accounting for collective effects, or higher order correlation terms.
Charge and Spin Inhomogeneity in Cuprate Superconductors Characterized by NMR
NASA Astrophysics Data System (ADS)
Haase, J.; Slichter, C. P.; Milling, C. T.; Hinks, D.; Yoshimura, Kazuyoshi
2002-03-01
The characterization of spatial inhomogeneities in the electronic structure of cuprate superconductors is of great interest since the relation of such inhomogeneities to superconductivity is unknown. We use nuclear magnetic resonance (NMR) to investigate the magnetic and electric fields at various nuclear sites in the unit cell of La2-xSrxCuO4 and address one of the long standing mysteries in NMR: what causes the rather large distributions of local fields? We will show that the found large linewidths are due to short wavelength spatial modulations in the Cu-O plane, that comprise the electric field gradients and magnetic fields. Both quantities are correlated. The data are consistent with a non-uniform electronic spin polarization induced by a homogeneous magnetic field. The resulting width of the distribution of the electronic spin polarization at the Cu sites follows Curie laws. The correlation functions between neighboring electronic spins was determined and found to be sample and temperature dependent. Below optimal doping (x=0.10 and x=0.15) it approaches at lower temperatures a value expected from (commensurate) antiferromagnetic behavoir, whereas for x = 0.2 it is temperature independent and in agreement with incommensurate behavior found from INS experiments.
NASA Astrophysics Data System (ADS)
Izyumskaya, N.; Zhang, F.; Okur, S.; Selden, T.; Avrutin, V.; Özgür, Ü.; Metzner, S.; Karbaum, C.; Bertram, F.; Christen, J.; Morkoç, H.
2013-09-01
Formation of defects in semipolar (11¯01)-oriented GaN layers grown by metal-organic chemical vapor deposition on patterned Si (001) substrates and their effects on optical properties were investigated by steady-state and time-resolved photoluminescence (PL) and spectrally and spatially resolved cathodoluminescence (CL). Near-band edge emission is found to be dominant in the c+-wings of semipolar (11¯01)GaN, which are mainly free from defect-related emission lines, while the c- wings contain a large number of basal stacking faults. When the advancing c+ and c— fronts meet to coalesce into a continuous film, the existing stacking faults contained in c— wings continue to propagate in the direction perpendicular to the c-axis and, as a result, the region dominated by stacking fault emission is extended to the film surface. Additional stacking faults are observed within the c+ wings, where the growing c+ wings of GaN are in contact with the SiO2 masking layer. Out-diffusion of oxygen/silicon species and concentration of strain near the contact region are considered as possible causes of the stacking fault formation. CL linescans performed along the surface and across the thickness of the non-coalesced and coalesced layers revealed that, while most of the material in the near-surface region of the non-coalesced layers is relaxed, coalescence results in nonuniform strain distribution over the layer surface. Red-shifted near-band-edge emission from the near-surface region indicates tensile stress near the surface of a coalesced layer, reaching a value of 0.3 GPa. The regions near the GaN/AlN/Si(111) interface show slightly blue shifted, broadened near-band-edge emission, which is indicative of a high concentration of free carriers possibly due to incorporation of shallow-donor impurities (Si and/or O) from the substrate or SiO2 mask. Steady-state and time-resolved PL results indicate that semipolar (11¯01)GaN on patterned Si exhibits optical properties (PL
Inhomogeneous generalization of some Bianchi models
NASA Astrophysics Data System (ADS)
Carmeli, M.; Charach, Ch.
1980-02-01
Vacuum Bianchi models which can be transformed to the Einstein-Rosen metric are considered. The models are used in order to construct new inhomogeneous universes, which are generalizations of Bianchi cosmologies of types III, V and VIh. Recent generalizations of these Bianchi models, considered by Wainwright et al., are also discussed.
Optical properties of nonextensive inhomogeneous plasma sheath
NASA Astrophysics Data System (ADS)
Mousavi, A.; Esfandiari-Kalejahi, A.; Akbari-Moghanjoughi, M.
2016-07-01
Propagation of electromagnetic wave through an inhomogeneous magnetized nonextensive plasma sheath is numerically examined for a realistic density profile of a reentry problem around a hypersonic vehicle. The effect of nonextensivity and inhomogeneity on radio wave communication is studied parametrically. Variation of reflection and transmission coefficients, total attenuation, and total phase shift over the plasma sheath with respect to the strength of applied magnetic field are derived and compared for different values of q-nonextensive parameter. The obtained results for inhomogeneous plasma sheath are compared with previously obtained results of authors for homogeneous plasma sheath. The comparison shows that radio communication in the inhomogeneous plasma sheath is more advantageous than that in the homogeneous case. The transmission coefficient of a plasma sheath with superthermal electrons ( /1 3 < q < 1 ) has larger value compared to that with q > 1. Moreover, for ω c e > ω , the minimum value of total attenuation corresponds to the range /1 3 < q < 1 . An interesting result is that nonextensivity effect on wave propagation in plasma sheath depends on the strength of the ambient magnetic field. The effect of nonextensivity on attenuation coefficient is found to be negligible for ω c e < ω while it is significant for ω c e > ω .
Mesoscale inhomogeneities in an aqueous ternary system
NASA Astrophysics Data System (ADS)
Subramanian, Deepa; Hayward, Stephen; Altabet, Elia; Collings, Peter; Anisimov, Mikhail
2012-02-01
Aqueous solutions of certain low-molecular-weight organic compounds, such as alcohols, amines, or ethers, which are considered macroscopically homogeneous, show the presence of mysterious mesoscale inhomogeneities, order of a hundred nm in size. We have performed static and dynamic light scattering experiments in an aqueous ternary system consisting of tertiary butyl alcohol and propylene oxide. Tertiary butyl alcohol is completely soluble in water and in propylene oxide, and forms strong hydrogen bonds with water molecules. Based on results of the study, we hypothesize that the mesoscale inhomogeneities are akin to a micro phase separation, resulting from a competition between water molecules and propylene oxide molecules, wanting to be adjacent to amphiphilic tertiary butyl alcohol molecules. Coupling between two competing order parameters, super-lattice binary-alloy-like (``antiferromagnetic'' type) and demixing (``ferromagnetic'' type) may explain the formation of these inhomogeneities. Long-term stability investigation of this supramolecular structure has revealed that these inhomogeneities are exceptionally long-lived non-equilibrium structures that persist for weeks or even months.
No hair theorem for inhomogeneous cosmologies
Jensen, L.G.; Stein-Schabes, J.A.
1986-03-01
We show that under very general conditions any inhomogeneous cosmological model with a positive cosmological constant, that can be described in a synchronous reference system will tend asymptotically in time towards the de Sitter solution. This is shown to be relevant in the context of inflationary models as it makes inflation very weakly dependent on initial conditions. 8 refs.
Cylindrically symmetric inhomogeneous cosmological models with viscous fluid and varying Λ
NASA Astrophysics Data System (ADS)
Pradhan, Anirudh; Singh, Prashant Kumar; Jotania, R. Kanti
2006-06-01
Cylindrically symmetric non-static cosmological models representing a bulk viscous fluid distribution have been obtained which are inhomogeneous and anisotropic. Without assuming any adhoc law, we obtain a cosmological constant as a decreasing function of time. Various physical and geometrical features of the models are also discussed.
Effect of inhomogeneity of light from light curing units on the surface hardness of composite resin.
Arikawa, Hiroyuki; Kanie, Takahito; Fujii, Koichi; Takahashi, Hideo; Ban, Seiji
2008-01-01
This study investigated the characteristics of output light from different types of light curing units, and their effects on polymerization of light-activated composite resin. Three quartz-tungsten-halogen lamps, one plasma arc lamp, and one LED light curing unit were used. Intensity distribution of light emitted from the light guide tip was measured at 1.0-mm intervals across the guide tip. Distribution of Knoop hardness number on the surface of resin irradiated with the light curing units was also measured. For all units, inhomogeneous distribution of light intensity across the guide tip was observed. Minimum light intensity values were 19-80% of the maximum values. In terms of surface hardness, inhomogeneous distribution was also observed for the materials irradiated with the tested units. Minimum values were 53-92% of the maximum values. Our results indicated that markedly inhomogeneous light emitted from light curing unit could result in inhomogeneous polymerization in some areas of the restoration below the light guide tip. PMID:18309608
Sustainable Development and Spatial Inhomogeneities
NASA Astrophysics Data System (ADS)
Weisbuch, Gérard
2013-05-01
Historical data, theory and computer simulations support a connection between growth and economic inequality. Our present world with large regional differences in economic activity is a result of fast economic growth during the last two centuries. Because of limits to growth we might expect a future world to develop differently with far less growth. The question that we here address is: "Would a world with a sustainable economy be less unequal?" We then develop integrated spatial economic models based on limited resources consumption and technical knowledge accumulation and study them by the way of computer simulations. When the only coupling between world regions is diffusion we do not observe any spatial unequality. By contrast, highly localized economic activities are maintained by global market mechanisms. Structures sizes are determined by transportation costs. Wide distributions of capital and production are also predicted in this regime.
Chromospheric Circulation Driven by Horizontally Inhomogeneous Heating
NASA Astrophysics Data System (ADS)
Vasyliunas, V. M.; Song, P.
2013-12-01
The rate of chromospheric heating by damping of Alfvén waves propagating upward from below the photosphere (Song and Vasyliunas, 2011) depends on the strength of the magnetic field. In regions of locally confined very strong magnetic field, particularly at the boundaries of the chromospheric network, the heating rate is greatly enhanced, and the heating per unit mass is concentrated toward higher altitudes. Song and Vasyliunas (2012) proposed that the resulting inhomogeneity of pressure may drive circulating flows in the chromosphere, horizontally away from the strong-field region at one altitude and returning at another. We investigate this circulation further, with particular attention to the flow patterns and to the question to what extent the circulation might be impeded by MHD effects. The heating process acts equally on the plasma and on the neutral gas, but because most of the chromosphere is weakly ionized, the flow is predominantly that of the neutral gas. Below the altitude he at which electron collision frequency equals electron gyrofrequency, all the species (electrons, ions, neutrals) flow together; the magnetic field can change relative to the flow only by diffusion. In the altitude range above he but below the altitude hi at which ion collision frequency equals ion gyrofrequency, ions and neutrals flow together, but electron flow is decoupled from neutral flow; the magnetic field is frozen to the motion of electrons. Above hi neutrals are decoupled from ions, while electrons and ions flow nearly together with the common plasma flow; the magnetic field is frozen to the plasma flow. (This is analogous to the well-studied neutral-wind dynamo process in the terrestrial ionosphere and thermosphere, except that at the Sun there is no counterpart to the non-conducting terrestrial atmosphere.) The circulation, confined to altitudes above he, consists of neutral and ion flow between he and hi; above hi, there is only neutral flow, with ions at rest, while
NASA Astrophysics Data System (ADS)
Yani, S.; Rhani, M. F.; Haryanto, F.; Arif, I.
2016-08-01
Treatment fields consist of tissue other than water equivalent tissue (soft tissue, bones, lungs, etc.). The inhomogeneity effect can be investigated by Monte Carlo (MC) simulation. MC simulation of the radiation transport in an absorbing medium is the most accurate method for dose calculation in radiotherapy. The aim of this work is to evaluate the effect of inhomogeneity phantom on dose calculations in photon beam radiotherapy obtained by different MC codes. MC code system EGSnrc and Geant4 was used in this study. Inhomogeneity phantom dimension is 39.5 × 30.5 × 30 cm3 and made of 4 material slices (12.5 cm water, 10 cm aluminium, 5 cm lung and 12.5 cm water). Simulations were performed for field size 4 × 4 cm2 at SSD 100 cm. The spectrum distribution Varian Trilogy Clinac iX 10 MV was used. Percent depth dose (PDD) and dose profile was investigated in this research. The effects of inhomogeneities on radiation dose distributions depend on the amount, density and atomic number of the inhomogeneity, as well as on the quality of the photon beam. Good agreement between dose distribution from EGSnrc and Geant4 code system in inhomogeneity phantom was observed, with dose differences around 5% and 7% for depth doses and dose profiles.
Light propagation in inhomogeneous universes - The ray-shooting method
NASA Technical Reports Server (NTRS)
Schneider, Peter; Weiss, Achim
1988-01-01
The propagation of light in a clumpy universe is studied using the ray-shooting method. It is found that 'empty cones' in a clumpy universe are rare, which points out the limitation of frequently used distance measures in an inhomogeneous universe. The results show some qualitatively new features of multiple-gravitational-lens geometry, and a likely explanation for these features is presented. A statistical analysis of the simulations give amplification probability distributions for extended sources, as well as the distribution for the ratio of amplifications of compact sources to amplifications of more extended sources. Sample light curves of individual sources are obtained. Finally, the results support the validity of recent investigations on the influence of gravitational light deflection on source counts of compact extragalactic objects.
Holographic measurements of inhomogeneous cloud mixing at the centimeter scale.
Beals, Matthew J; Fugal, Jacob P; Shaw, Raymond A; Lu, Jiang; Spuler, Scott M; Stith, Jeffrey L
2015-10-01
Optical properties and precipitation efficiency of atmospheric clouds are largely determined by turbulent mixing with their environment. When cloud liquid water is reduced upon mixing, droplets may evaporate uniformly across the population or, in the other extreme, a subset of droplets may evaporate completely, leaving the remaining drops unaffected. Here, we use airborne holographic imaging to visualize the spatial structure and droplet size distribution at the smallest turbulent scales, thereby observing their response to entrainment and mixing with clear air. The measurements reveal that turbulent clouds are inhomogeneous, with sharp transitions between cloud and clear air properties persisting to dissipative scales (<1 centimeter). The local droplet size distribution fluctuates strongly in number density but with a nearly unchanging mean droplet diameter.
Probing the Surface Defect States of Gallium Nitride Nanowires
NASA Astrophysics Data System (ADS)
Simonsen, Lauren; Yang, Yuchen; Borys, Nicholas; Ghimire, Anil; Schuck, James; Aloni, Shaul; Gerton, Jordan
In this work, we investigate gallium nitride nanowires (NWs) as a potential system for solar-driven water splitting. Although bulk GaN has a UV bandgap, the synthesized NWs exhibit strong absorption and fluorescence emission across the visible spectrum. Density functional theory calculations suggest that this visible fluorescence originates from mid-gap surface-defect states along the triangular facets of the NWs. The orientation of the NWs can be controlled during MOCVD growth, leading to different exposed crystallographic surface terminations with different electronic structures. High resolution microscopy techniques using AFM and confocal hyper-spectral imaging show spectral inhomogeneity across the widths of the NWs, providing evidence that various crystallographic terminations produce different surface states. These NWs also exhibit wave guiding properties, leading to Fabry-Perot fringes and high intensity spectra and the ends of the wires. Photoluminescence excitation spectroscopy reveals a non-linear dependence of the emission spectral features on excitation wavelength, indicating a complex distribution of mid-gap defect states. Time-resolved spectroscopy reveals non-exponential decay dynamics through a complicated manifold of mid-gap states.
Probing the Surface Defect States of Gallium Nitride Nanowires
NASA Astrophysics Data System (ADS)
Simonsen, Lauren; Yang, Yuchen; Borys, Nicholas; Ghimire, Anil; Schuck, James; Aloni, Shaul; Gerton, Jordan
2016-03-01
In this work, we investigate gallium nitride nanowires (NWs) as a potential system for solar-driven water splitting. Although bulk GaN has a UV bandgap, the synthesized NWs exhibit strong absorption and fluorescence emission across the visible spectrum. Density functional theory calculations suggest that this visible fluorescence originates from mid-gap surface-defect states along the triangular facets of the NWs. The orientation of the NWs can be controlled during MOCVD growth, leading to different exposed crystallographic surface terminations with various electronic structures. High resolution microscopy techniques using AFM and confocal hyper-spectral imaging show spectral inhomogeneity across the widths of the NWs, providing evidence that various crystallographic terminations produce different surface states. These NWs also exhibit wave guiding properties, leading to Fabry-Perot fringes and high intensity spectra at the ends of the wires. Photoluminescence excitation spectroscopy reveals a non-linear dependence of the emission spectral features on excitation wavelength, indicating a complex distribution of mid-gap defect states. Time-resolved spectroscopy reveals non-exponential decay dynamics through a complicated manifold of mid-gap states.
NASA Astrophysics Data System (ADS)
Konovalov, Alexander B.; Vlasov, Vitaly V.
2016-04-01
The important advantage of diffuse optical tomography (DOT) is the possibility of tissue functional diagnosis. However the possibility implements if only we separately reconstruct the spatial distributions of optical parameters, specifically the absorption and scattering coefficients. We have recently demonstrated that time-domain DOT based on the perturbation model by Lyubimov is capable of reconstructing absorbing inhomogeneities in tissue with a DOT high spatial resolution (better than 3 mm at a depth of 4 cm). This paper continues our research and focuses on the reconstruction of scattering inhomogeneities. We consider the flat layer transmission geometry which is traditional for optical mammography, and use diffusion approximation to derive analytical expressions for weight functions responsible for the reconstruction of scattering inhomogeneities. To confirm that our calculations are correct we perform a numerical experiment where we reconstruct a rectangular scattering object 10×8 cm in size with 4 circular scattering macroinhomogeneities 4 mm in diameter each, and a randomly inhomogeneous scattering structure. The inverse DOT problem is solved with a multiplicative algebraic reconstruction technique where interim iterations are processed through total variation norm minimization. The results suggest that our DOT method reliably resolves the scattering macroinhomogeneities of mentioned size against a randomly inhomogeneous structure.
NASA Technical Reports Server (NTRS)
Fu, L. S. W.
1982-01-01
The scattering of a single ellipsoidal inhomogeneity is studied via an eigenstrain approach. The displacement field is given in terms of volume integrals that involve eigenstrains that are related to mismatch in mass density and that in elastic moduli. The governing equations for these unknown eigenstrains are derived. Agreement with other approaches for the scattering problem is shown. The formulation is general and both the inhomogeneity and the host medium can be anisotrophic. The axisymmetric scattering of an ellipsoidal inhomogeneity in a linear elastic isotropic medium is given as an example. The angular and frequency dependence of the scattered displacement field, the differential and total cross sections are formally given in series expansions for the case of uniformly distributed eigenstrains.
ERIC Educational Resources Information Center
Goldman, Allen S.; And Others
There are two general categories (not necessarily mutually exclusive) of congenital defects: (1) abnormalities that have an hereditary basis, such as single and multiple genes, or chromosomal abberration; and (2) abnormalities that are caused by nonhereditary factors, such as malnutrition, maternal disease, radiation, infections, drugs, or…
A blind test of correction algorithms for daily inhomogeneities
NASA Astrophysics Data System (ADS)
Stepanek, Petr; Venema, Victor; Guijarro, Jose; Nemec, Johanna; Zahradnicek, Pavel; Hadzimustafic, Jasmina
2013-04-01
As part of the COST Action HOME (Advances in homogenisation methods of climate series: an integrated approach), a dataset was generated that serves as a validation tool for correction of daily inhomogeneities. The dataset contains daily air temperature data and was generated based on the temperature series from the Czech Republic. The validation dataset has three different types of series: network, pair and pair-dedicated data. Different types of inhomogeneities have been inserted into the series. Parametric breaks in the first three moments were introduced and the influence of relocation was simulated by exchanging the distribution of two nearby stations. The participants have returned several contributions, including methods that are currently used: HOM, SPLIDHOM (with various modifications like HOMAD and bootstrapped SPLIDHOM), QM (RHtestsV3 software), DAP (ProClimDB), HCL (Climatol), MASH and also simple delta method. The quality of the homogenised data was measured by a large range of metrics, the most important ones are the RMSE and the trends in the moments. Thanks to RHtestsV3 algorithms we could also assess relative and absolute homogenization results. As expected, the simpler methods, correcting only the mean, are best at reducing the RMSE. For more information on the COST Action on homogenisation see: http://www.homogenisation.org/
NASA Astrophysics Data System (ADS)
Osswald, P. J.; Erhard, S. V.; Rheinfeld, A.; Rieger, B.; Hoster, H. E.; Jossen, A.
2016-10-01
The influence of cell temperature on the current density distribution and accompanying inhomogeneities in state of charge (SOC) during cycling is analyzed in this work. To allow for a detailed insight in the electrochemical behavior of the cell, commercially available 26650 cells were modified to allow for measuring local potentials at four different, nearly equidistant positions along the electrodes. As a follow-up to our previous work investigating local potentials within a cell, we apply this method for studying SOC deviations and their sensitivity to cell temperature. The local potential distribution was studied during constant current discharge operations for various current rates and discharge pulses in order to evoke local inhomogeneities for temperatures ranging from 10 °C to 40 °C. Differences in local potentials were considered for estimating local SOC variations within the electrodes. It could be observed that even low currents such as 0.1C can lead to significant inhomogeneities, whereas a higher cell temperature generally results in more pronounced inhomogeneities. A rapid SOC equilibration can be observed if the variation in the SOC distribution corresponds to a considerable potential difference defined by the open circuit voltage of either the positive or negative electrode. With increasing temperature, accelerated equalization effects can be observed.
Vortex structure in a long Josephson junction with two inhomogeneities
NASA Astrophysics Data System (ADS)
Andreeva, O. Yu.; Boyadjiev, T. L.; Shukrinov, Yu. M.
2007-09-01
We study the vortex structure in the long Josephson junctions with one and two rectangular inhomogeneities in the barrier layer. In case of one inhomogeneity we demonstrate the existence of the asymmetric fluxon states. The disappearance of the mixed fluxon-antifluxon states is shown when the position of the inhomogeneity shifted to the end of the junction. In case of two inhomogeneities the change of the amplitude of Josephson current through the inhomogeneity in the end of the junction makes strong effect on the stability of the fluxon states and smoothes the maximums on the dependence “critical current-magnetic field”.
Theory of Thomson scattering in inhomogeneous media
NASA Astrophysics Data System (ADS)
Kozlowski, P. M.; Crowley, B. J. B.; Gericke, D. O.; Regan, S. P.; Gregori, G.
2016-04-01
Thomson scattering of laser light is one of the most fundamental diagnostics of plasma density, temperature and magnetic fields. It relies on the assumption that the properties in the probed volume are homogeneous and constant during the probing time. On the other hand, laboratory plasmas are seldom uniform and homogeneous on the temporal and spatial dimensions over which data is collected. This is particularly true for laser-produced high-energy-density matter, which often exhibits steep gradients in temperature, density and pressure, on a scale determined by the laser focus. Here, we discuss the modification of the cross section for Thomson scattering in fully-ionized media exhibiting steep spatial inhomogeneities and/or fast temporal fluctuations. We show that the predicted Thomson scattering spectra are greatly altered compared to the uniform case, and may lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous systems.
Generating matter inhomogeneities in general relativity.
Coley, A A; Lim, W C
2012-05-11
In this Letter we discuss a natural general relativistic mechanism that causes inhomogeneities and hence generates matter perturbations in the early Universe. We concentrate on spikes, both incomplete spikes and recurring spikes, that naturally occur in the initial oscillatory regime of general cosmological models. In particular, we explicitly show that spikes occurring in a class of G2 models lead to inhomogeneities that, due to gravitational instability, leave small residual imprints on matter in the form of matter perturbations. The residual matter overdensities from recurring spikes are not local but form on surfaces. We discuss the potential physical consequences of the residual matter imprints and their possible effect on the subsequent formation of large-scale structure.
Theory of Thomson scattering in inhomogeneous media.
Kozlowski, P M; Crowley, B J B; Gericke, D O; Regan, S P; Gregori, G
2016-01-01
Thomson scattering of laser light is one of the most fundamental diagnostics of plasma density, temperature and magnetic fields. It relies on the assumption that the properties in the probed volume are homogeneous and constant during the probing time. On the other hand, laboratory plasmas are seldom uniform and homogeneous on the temporal and spatial dimensions over which data is collected. This is particularly true for laser-produced high-energy-density matter, which often exhibits steep gradients in temperature, density and pressure, on a scale determined by the laser focus. Here, we discuss the modification of the cross section for Thomson scattering in fully-ionized media exhibiting steep spatial inhomogeneities and/or fast temporal fluctuations. We show that the predicted Thomson scattering spectra are greatly altered compared to the uniform case, and may lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous systems. PMID:27068215
Anomalous Maxwell equations for inhomogeneous chiral plasma
NASA Astrophysics Data System (ADS)
Gorbar, E. V.; Shovkovy, I. A.; Vilchinskii, S.; Rudenok, I.; Boyarsky, A.; Ruchayskiy, O.
2016-05-01
Using the chiral kinetic theory we derive the electric and chiral current densities in inhomogeneous relativistic plasma. We also derive equations for the electric and chiral chemical potentials that close the Maxwell equations in such a plasma. The analysis is done in the regimes with and without a drift of the plasma as a whole. In addition to the currents present in the homogeneous plasma (Hall current, chiral magnetic, chiral separation, and chiral electric separation effects, as well as Ohm's current) we derive several new terms associated with inhomogeneities of the plasma. Apart from various diffusionlike terms, we find also new dissipationless terms that are independent of relaxation time. Their origin can be traced to the Berry curvature modifications of the kinetic theory.
Theory of Thomson scattering in inhomogeneous media
Kozlowski, P. M.; Crowley, B. J. B.; Gericke, D. O.; Regan, S. P.; Gregori, G.
2016-01-01
Thomson scattering of laser light is one of the most fundamental diagnostics of plasma density, temperature and magnetic fields. It relies on the assumption that the properties in the probed volume are homogeneous and constant during the probing time. On the other hand, laboratory plasmas are seldom uniform and homogeneous on the temporal and spatial dimensions over which data is collected. This is particularly true for laser-produced high-energy-density matter, which often exhibits steep gradients in temperature, density and pressure, on a scale determined by the laser focus. Here, we discuss the modification of the cross section for Thomson scattering in fully-ionized media exhibiting steep spatial inhomogeneities and/or fast temporal fluctuations. We show that the predicted Thomson scattering spectra are greatly altered compared to the uniform case, and may lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous systems. PMID:27068215
Efficient modeling in transversely isotropic inhomogeneous media
Alkhalifah, T.
1993-11-01
An efficient modeling technique for transversely isotropic, inhomogeneous media, is developed using a mix of analytical equations and numerical calculations. The analytic equation for the raypath in a factorized transversely isotropic (FTI) media with linear velocity variation, derived by Shearer and Chapman, is used to trace between two points. In addition, I derive an analytical equation for geometrical spreading in FTI media that aids in preserving program efficiency; however, the traveltime is calculated numerically. I then generalize the method to treat general transversely isotropic (TI) media that are not factorized anisotropic inhomogeneous by perturbing the FTI traveltimes, following the perturbation ideas of Cerveny and Filho. A Kirchhoff-summation-based program relying on Trorey`s (1970) diffraction method is used to generate synthetic seismograms for such a medium. For the type of velocity models treated, the program is much more efficient than finite-difference and general ray-trace modeling techniques.
Single-file diffusion through inhomogeneous nanopores.
Bandyopadhyay, Tusar
2008-03-21
Strict one-dimensional diffusion, due to geometrical confinement in a nanopore, of an assembly of particles forbids overtaking by each other, giving rise to single-file diffusion (SFD). Smooth carbon nanotube is the epitome of SFD. However, natural nanoporous materials are far from smooth; morphologically, the nanopores' inner surface may provide an inhomogeneous environment for diffusion to occur, giving rise to subnormal diffusion even for an isolated particle diffusing through this fractal landscape. The realm of fractional diffusion (FD) falls under this paradigm. In order to understand the characteristics of SFD through inhomogeneous nanopores, here, we introduce a fractional SFD (FSFD) formalism that deals with a combination of these two phenomena, namely, SFD of particles, each of which are moving subdiffusively in one dimension. For an infinite system, we obtain the mean square displacement (MSD) of the combined entity and our analysis is based on FD equation for particles moving in concert where the single-file correlation is established through reflection principle. For a finite system, we calculate the transport probabilities based on continuous time random walk model. While both the diffusion mechanisms (SFD and FD) acting separately are responsible for slow dynamics at long times, their combined effect leads to ultraslow diffusion. For example, while the long time asymptote of MSD of SFD scales as sqr rt of t, that for FSFD is sqr rt of t(alpha), where alpha is the measure of the extent of inhomogeneity. These findings, which are believed to occur in a natural inhomogeneous nanopore, is also important for design and fabrication of nanofluidic devices through which the fluid delivery can be engineered.
Inversion identities for inhomogeneous face models
NASA Astrophysics Data System (ADS)
Frahm, Holger; Karaiskos, Nikos
2014-10-01
We derive exact inversion identities satisfied by the transfer matrix of inhomogeneous interaction-round-a-face (IRF) models with arbitrary boundary conditions using the underlying integrable structure and crossing properties of the local Boltzmann weights. For the critical restricted solid-on-solid (RSOS) models these identities together with some information on the analytical properties of the transfer matrix determine the spectrum completely and allow to derive the Bethe equations for both periodic and general open boundary conditions.
Controlling Charged Particles with Inhomogeneous Electrostatic Fields
NASA Technical Reports Server (NTRS)
Herrero, Federico A. (Inventor)
2016-01-01
An energy analyzer for a charged-particle spectrometer may include a top deflection plate and a bottom deflection plate. The top and bottom deflection plates may be non-symmetric and configured to generate an inhomogeneous electrostatic field when a voltage is applied to one of the top or bottom deflection plates. In some instances, the top and bottom deflection plates may be L-shaped deflection plates.
Spiral laser beams in inhomogeneous media.
Mahalov, Alex; Suazo, Erwin; Suslov, Sergei K
2013-08-01
Explicit solutions of the inhomogeneous paraxial wave equation in a linear and quadratic approximation are applied to wave fields with invariant features, such as oscillating laser beams in a parabolic waveguide and spiral light beams in varying media. A similar effect of superfocusing of particle beams in a thin monocrystal film, harmonic oscillations of cold trapped atoms, and motion in magnetic field are also mentioned. PMID:23903135
Qiu, Wenqi; Wei, Zhiliang; Ding, Nan; Yang, Yu; Ye, Qimiao; Lin, Yulan; Chen, Zhong
2016-05-18
High-resolution multidimensional nuclear magnetic resonance (NMR) spectroscopy serves as an irreplaceable and versatile tool in various chemical investigations. In this study, a method based on the concept of partial homogeneity is developed to offer two-dimensional (2D) high-resolution NMR spectra under inhomogeneous fields. Oscillating gradients are exerted to encode the high-resolution information, and a field-inhomogeneity correction algorithm based on pattern recognition is designed to recover high-resolution spectra. Under fields where inhomogeneity primarily distributes along a single orientation, the proposed method will improve performances of 2D NMR spectroscopy without increasing the experimental duration or significant loss in sensitivity, and thus may open important perspectives for studies of inhomogeneous chemical systems.
Wealth inhomogeneity applied to crash rate theory.
Shuler, Robert L
2015-11-01
A crash rate theory based on corporate economic utility maximization is applied to individual behavior in U.S. and German motorway death rates, by using wealth inhomogeneity data in ten-percentile bins to account for variations of utility maximization in the population. Germany and the U.S. have similar median wealth figures, a well-known indicator of accident risk, but different motorway death rates. It is found that inhomogeneity in roughly the 10(th) to 30(th) percentile, not revealed by popular measures such as the Gini index which focus on differences at the higher percentiles, provides a satisfactory explanation of the data. The inhomogeneity analysis reduces data disparity from a factor of 2.88 to 1.75 as compared with median wealth assumed homogeneity, and further to 1.09 with average wealth assumed homogeneity. The first reduction from 2.88 to 1.75 is attributable to inequality at lower percentiles and suggests it may be as important in indicating socioeconomic risk as extremes in the upper percentile ranges, and that therefore the U.S. socioeconomic risk may be higher than generally realized. PMID:27441226
Beginning inflation in an inhomogeneous universe
East, William E.; Kleban, Matthew; Linde, Andrei; Senatore, Leonardo
2016-09-06
Using numerical solutions of the full Einstein field equations coupled to a scalar inflaton field in 3+1 dimensions, we study the conditions under which a universe that is initially expanding, highly inhomogeneous and dominated by gradient energy can transition to an inflationary period. If the initial scalar field variations are contained within a sufficiently flat region of the inflaton potential, and the universe is spatially flat or open on average, inflation will occur following the dilution of the gradient and kinetic energy due to expansion. This is the case even when the scale of the inhomogeneities is comparable to themore » initial Hubble length, and overdense regions collapse and form black holes, because underdense regions continue expanding, allowing inflation to eventually begin. In conclusion, this establishes that inflation can arise from highly inhomogeneous initial conditions and solve the horizon and flatness problems, at least as long as the variations in the scalar field do not include values that exceed the inflationary plateau.« less
Viscosity of confined inhomogeneous nonequilibrium fluids
NASA Astrophysics Data System (ADS)
Zhang, Junfang; Todd, B. D.; Travis, Karl P.
2004-12-01
We use the nonlocal linear hydrodynamic constitutive model, proposed by Evans and Morriss [Statistical Mechanics of Nonequilibrium Liquids (Academic, London, 1990)], for computing an effective spatially dependent shear viscosity of inhomogeneous nonequilibrium fluids. The model is applied to a simple atomic fluid undergoing planar Poiseuille flow in a confined channel of several atomic diameters width. We compare the spatially dependent viscosity with a local generalization of Newton's law of viscosity and the Navier-Stokes viscosity, both of which are known to suffer extreme inaccuracies for highly inhomogeneous systems. The nonlocal constitutive model calculates effective position dependent viscosities that are free from the notorious singularities experienced by applying the commonly used local constitutive model. It is simple, general, and has widespread applicability in nanofluidics where experimental measurement of position dependent transport coefficients is currently inaccessible. In principle the method can be used to predict approximate flow profiles of any arbitrary inhomogeneous system. We demonstrate this by predicting the flow profile for a simple fluid undergoing planar Couette flow in a confined channel of several atomic diameters width.
Wealth inhomogeneity applied to crash rate theory.
Shuler, Robert L
2015-11-01
A crash rate theory based on corporate economic utility maximization is applied to individual behavior in U.S. and German motorway death rates, by using wealth inhomogeneity data in ten-percentile bins to account for variations of utility maximization in the population. Germany and the U.S. have similar median wealth figures, a well-known indicator of accident risk, but different motorway death rates. It is found that inhomogeneity in roughly the 10(th) to 30(th) percentile, not revealed by popular measures such as the Gini index which focus on differences at the higher percentiles, provides a satisfactory explanation of the data. The inhomogeneity analysis reduces data disparity from a factor of 2.88 to 1.75 as compared with median wealth assumed homogeneity, and further to 1.09 with average wealth assumed homogeneity. The first reduction from 2.88 to 1.75 is attributable to inequality at lower percentiles and suggests it may be as important in indicating socioeconomic risk as extremes in the upper percentile ranges, and that therefore the U.S. socioeconomic risk may be higher than generally realized.
Inhomogeneity of pulmonary perfusion during sustained microgravity
NASA Technical Reports Server (NTRS)
Prisk, G. Kim; Guy, Harold J. B.; Elliott, Ann R.; West, John B.
1994-01-01
The effects of gravity on the inhomogeneity of pulmonary perfusion in man were studied by performing hyperventilation-breathhold single-breath measurements before, during and after 9 days of continuous exposure to microgravity. In microgravity the indicators of inhomogeneity of perfusion, especially the size of cardiogenic oscillations in expired CO2 and the height of phase 4, were both markedly reduced. Cardiogenic oscillations were reduced to approximately 60 of their preflight standing size, while the height of phase 4 was between 0 and -8% (a terminal fall became a small terminal rise) of preflights standing. The terminal change in CO2 was nearly abolished in microgravity indicating more uniformity of blood flow between lung units that close at the end of expiration and units that remain open. This may result from the disappearance of gravity-dependent topographical inequality of blood flow. The residual cardiographic oscillations in expired CO2 imply a persisting inhomogeneity of perfusion in the absence of gravity at a level larger than acinar.
Scattering of electromagnetic wave by the layer with one-dimensional random inhomogeneities
NASA Astrophysics Data System (ADS)
Kogan, Lev; Zaboronkova, Tatiana; Grigoriev, Gennadii., IV.
A great deal of attention has been paid to the study of probability characteristics of electro-magnetic waves scattered by one-dimensional fluctuations of medium dielectric permittivity. However, the problem of a determination of a density of a probability and average intensity of the field inside the stochastically inhomogeneous medium with arbitrary extension of fluc-tuations has not been considered yet. It is the purpose of the present report to find and to analyze the indicated functions for the plane electromagnetic wave scattered by the layer with one-dimensional fluctuations of permittivity. We assumed that the length and the amplitude of individual fluctuations as well the interval between them are random quantities. All of indi-cated fluctuation parameters are supposed as independent random values possessing Gaussian distribution. We considered the stationary time cases both small-scale and large-scale rarefied inhomogeneities. Mathematically such problem can be reduced to the solution of integral Fred-holm equation of second kind for Hertz potential (U). Using the decomposition of the field into the series of multiply scattered waves we obtained the expression for a probability density of the field of the plane wave and determined the moments of the scattered field. We have shown that all odd moments of the centered field (U-¡U¿) are equal to zero and the even moments depend on the intensity. It was obtained that the probability density of the field possesses the Gaussian distribution. The average field is small compared with the standard fluctuation of scattered field for all considered cases of inhomogeneities. The value of average intensity of the field is an order of a standard of fluctuations of field intensity and drops with increases the inhomogeneities length in the case of small-scale inhomogeneities. The behavior of average intensity is more complicated in the case of large-scale medium inhomogeneities. The value of average intensity is the
Ilyasov, Askar A.; Chernyshov, Alexander A. Mogilevsky, Mikhail M.; Golovchanskaya, Irina V. Kozelov, Boris V.
2015-03-15
Inhomogeneities of plasma density and non-uniform electric fields are compared as possible sources of a sort of electrostatic ion cyclotron waves that can be identified with broadband extremely low frequency electrostatic turbulence in the topside auroral ionosphere. Such waves are excited by inhomogeneous energy-density-driven instability. To gain a deeper insight in generation of these waves, computational modeling is performed with various plasma parameters. It is demonstrated that inhomogeneities of plasma density can give rise to this instability even in the absence of electric fields. By using both satellite-observed and model spatial distributions of plasma density and electric field in our modeling, we show that specific details of the spatial distributions are of minor importance for the wave generation. The solutions of the nonlocal inhomogeneous energy-density-driven dispersion relation are investigated for various ion-to-electron temperature ratios and directions of wave propagation. The relevance of the solutions to the observed spectra of broadband extremely low frequency emissions is shown.
Spatial structure of a collisionally inhomogeneous Bose-Einstein condensate
Li, Fei; Zhang, Dongxia; Rong, Shiguang; Xu, Ying
2013-11-15
The spatial structure of a collisionally inhomogeneous Bose-Einstein condensate (BEC) in an optical lattice is studied. A spatially dependent current with an explicit analytic expression is found in the case with a spatially dependent BEC phase. The oscillating amplitude of the current can be adjusted by a Feshbach resonance, and the intensity of the current depends heavily on the initial and boundary conditions. Increasing the oscillating amplitude of the current can force the system to pass from a single-periodic spatial structure into a very complex state. But in the case with a constant phase, the spatially dependent current disappears and the Melnikov chaotic criterion is obtained via a perturbative analysis in the presence of a weak optical lattice potential. Numerical simulations show that a strong optical lattice potential can lead BEC atoms to a state with a chaotic spatial distribution via a quasiperiodic route.
A hybrid method with deviational particles for spatial inhomogeneous plasma
NASA Astrophysics Data System (ADS)
Yan, Bokai
2016-03-01
In this work we propose a Hybrid method with Deviational Particles (HDP) for a plasma modeled by the inhomogeneous Vlasov-Poisson-Landau system. We split the distribution into a Maxwellian part evolved by a grid based fluid solver and a deviation part simulated by numerical particles. These particles, named deviational particles, could be both positive and negative. We combine the Monte Carlo method proposed in [31], a Particle in Cell method and a Macro-Micro decomposition method [3] to design an efficient hybrid method. Furthermore, coarse particles are employed to accelerate the simulation. A particle resampling technique on both deviational particles and coarse particles is also investigated and improved. This method is applicable in all regimes and significantly more efficient compared to a PIC-DSMC method near the fluid regime.
NASA Technical Reports Server (NTRS)
Prisk, G. Kim; Guy, Harold J. B.; Elliott, Ann R.; Paiva, Manuel; West, John B.
1995-01-01
We used multiple-breath N2 washouts (MBNW) to study the homogeneity of ventilation in four normal humans (mean age 42.5 yr) before, during, and after 9 days of exposure to microgravity on Spacelab Life Sciences-1. Subjects performed 20-breath MBNW at tidal volumes of approximately 700 ml and 12-breath MBNW at tidal volumes of approximately 1,250 ml. Six indexes of ventilatory inhomogeneity were derived from data from (1) distribution of specific ventilation (SV) from mixed-expired and (2) end-tidal N2, (3) change of slope of N2 washout (semilog plot) with time, (4) change of slope of normalized phase III of successive breaths, (5) anatomic lead dead space, and (6) Bohr dead space. Significant ventilatory inhomogeneity was seen in the standing position at normal gravity (1 G). When we compared standing 1 G with microgravity, the distributions of SV became slightly narrower, but the difference was not significant. Also, there were no significant changes in the change of slope of the N2 washout, change of normalized phase III slopes, or the anatomic and Bohr dead spaces. By contrast, transition from the standing to supine position in 1 G resulted in significantly broader distributions of SV and significantly greater changes in the changes in slope of the N2 washouts, indicating more ventilatory inhomogeneity in that posture. Thus these techniques can detect relatively small changes in ventilatory inhomogeneity. We conclude that the primary determinants of ventilatory inhomogeneity during tidal breathing in the upright posture are not gravitational in origin.
Evidence of deep traps in overgrown v-shaped defects in epitaxial GaN layers
NASA Astrophysics Data System (ADS)
Weidlich, P. H.; Schnedler, M.; Eisele, H.; Strauß, U.; Dunin-Borkowski, R. E.; Ebert, Ph.
2013-08-01
The geometric and electronic structure of overgrown v-shaped defects in GaN epitaxial layers are investigated by cross-sectional scanning tunneling microscopy and spectroscopy. The v-defects are found to be hexagonal pit structures delimited by six {112¯2} planes. The electronic properties are inhomogeneous. In some areas the center of the v-defects exhibits a strongly inhibited tunneling current, indicating the presence of deep traps.
Degradation of the Bragg peak due to inhomogeneities.
Urie, M; Goitein, M; Holley, W R; Chen, G T
1986-01-01
The rapid fall-off of dose at the end of range of heavy charged particle beams has the potential in therapeutic applications of sparing critical structures just distal to the target volume. Here we explored the effects of highly inhomogeneous regions on this desirable depth-dose characteristic. The proton depth-dose distribution behind a lucite-air interface parallel to the beam was bimodal, indicating the presence of two groups of protons with different residual ranges, creating a step-like depth-dose distribution at the end of range. The residual ranges became more spread out as the interface was angled at 3 degrees, and still more at 6 degrees, to the direction of the beam. A second experiment showed little significant effect on the distal depth-dose of protons having passed through a mosaic of teflon and lucite. Anatomic studies demonstrated significant effects of complex fine inhomogeneities on the end of range characteristics. Monoenergetic protons passing through the petrous ridges and mastoid air cells in the base of skull showed a dramatic degradation of the distal Bragg peak. In beams with spread out Bragg peaks passing through regions of the base of skull, the distal fall-off from 90 to 20% dose was increased from its nominal 6 to well over 32 mm. Heavy ions showed a corresponding degradation in their ends of range. In the worst case in the base of skull region, a monoenergetic neon beam showed a broadening of the full width at half maximum of the Bragg peak to over 15 mm (compared with 4 mm in a homogeneous unit density medium). A similar effect was found with carbon ions in the abdomen, where the full width at half maximum of the Bragg peak (nominally 5.5 mm) was found to be greater than 25 mm behind gas-soft-tissue interfaces. We address the implications of these data for dose computation with heavy charged particles.
Degradation of the Bragg peak due to inhomogeneities.
Urie, M; Goitein, M; Holley, W R; Chen, G T
1986-01-01
The rapid fall-off of dose at the end of range of heavy charged particle beams has the potential in therapeutic applications of sparing critical structures just distal to the target volume. Here we explored the effects of highly inhomogeneous regions on this desirable depth-dose characteristic. The proton depth-dose distribution behind a lucite-air interface parallel to the beam was bimodal, indicating the presence of two groups of protons with different residual ranges, creating a step-like depth-dose distribution at the end of range. The residual ranges became more spread out as the interface was angled at 3 degrees, and still more at 6 degrees, to the direction of the beam. A second experiment showed little significant effect on the distal depth-dose of protons having passed through a mosaic of teflon and lucite. Anatomic studies demonstrated significant effects of complex fine inhomogeneities on the end of range characteristics. Monoenergetic protons passing through the petrous ridges and mastoid air cells in the base of skull showed a dramatic degradation of the distal Bragg peak. In beams with spread out Bragg peaks passing through regions of the base of skull, the distal fall-off from 90 to 20% dose was increased from its nominal 6 to well over 32 mm. Heavy ions showed a corresponding degradation in their ends of range. In the worst case in the base of skull region, a monoenergetic neon beam showed a broadening of the full width at half maximum of the Bragg peak to over 15 mm (compared with 4 mm in a homogeneous unit density medium). A similar effect was found with carbon ions in the abdomen, where the full width at half maximum of the Bragg peak (nominally 5.5 mm) was found to be greater than 25 mm behind gas-soft-tissue interfaces. We address the implications of these data for dose computation with heavy charged particles. PMID:3952143
Zhou, Lian; Zhu, Shanan
2014-01-01
Magnetoacoustic tomography with Magnetic Induction (MAT-MI) is a noninvasive electrical conductivity imaging approach that measures ultrasound wave induced by magnetic stimulation, for reconstructing the distribution of electrical impedance in biological tissue. Existing reconstruction algorithms for MAT-MI are based on the assumption that the acoustic properties in the tissue are homogeneous. However, the tissue in most parts of human body, has heterogeneous acoustic properties, which leads to potential distortion and blurring of small buried objects in the impedance images. In the present study, we proposed a new algorithm for MAT-MI to image the impedance distribution in tissues with inhomogeneous acoustic speed distributions. With a computer head model constructed from MR images of a human subject, a series of numerical simulation experiments were conducted. The present results indicate that the inhomogeneous acoustic properties of tissues in terms of speed variation can be incorporated in MAT-MI imaging. PMID:24845284
Critical depinning current of elastic vortex strings in superconductors with extended linear defects
NASA Astrophysics Data System (ADS)
Fedirko, V. A.; Kasatkin, A. L.; Polyakov, S. V.
2016-09-01
The problem of the depinning of an Abrikosov elastic vortex string from an extended linear defect in the plate of a 3 D anisotropic superconductor of thickness d > 2λ (where λ is the London penetration depth) under the action of an inhomogeneously distributed transport current that flows in the surface shielding layer has been solved using classical mechanics approach. Conditions for the appearance of the instability of the pinned state of a vortex have been investigated and calculations of the corresponding critical current density on the surface at which the depinning of the vortex string occurs have been carried out. The dependence of the average of the critical current density on the thickness of the plate has been determined.
Diffusion of rotating inhomogeneities in ionospheric plasma
NASA Astrophysics Data System (ADS)
Erukhimov, L. M.; Myasnikov, E. N.
1998-02-01
We consider the problem of generation of small-scale quasistatic electric fields that can lead to establishment of the bipolar regime of inhomogeneity relaxation observed in experimental studies of the properties of an artificial turbulence excited in the upper ionosphere by high-power shortwave radio emission [1 8], which is slower than the regime of unipolar diffusion of quasineutral fluctuations of density in a homogeneous strongly magnetized plasma [9 11]. We show that necessary conditions for the existence of this mode are disruption of the symmetry of the initial disturbance in the plasma density with respect to the direction of the field ěc B_0 and its differential rotation with the drift frequency in the plane orthogonal to ěc B_0 . Assuming that the initial disturbance of the plasma has the form of a plane wave whose wave vector ěc k makes an angle θ = k_allel /k_ bot ≪ 1 with the normal to ěc B_0 , we obtain an expression for the drift frequency and study the relations between the fluctuational electric and magnetic fields and the drift velocity of the disturbed plasma in, the linear approximation. We discuss the properties of the nonlinear solution, which, in particular, can describe generation of small-scale plasma inhomogeneities that have a helical structure in the plane orthogonal to ěc B_0 . The phenomenon of frequency broadening of the Doppler spectra of signals of field-aligned SW and USW scattering observed in the case of field-aligned scattering of short and ultrashort radio waves by artificial ionospheric inhomogeneities [4 7] is interpreted.
Landau damping and inhomogeneous reference states
NASA Astrophysics Data System (ADS)
Barré, Julien; Olivetti, Alain; Yamaguchi, Yoshiyuki Y.
2015-10-01
Landau damping is a fundamental phenomenon in plasma physics, which also plays an important role in astrophysics, and sometimes under different names, in fluid dynamics, and other fields. Its theoretical discussion in the framework of the Vlasov equation often assumes that the reference stationary state is homogeneous in space. However, Landau damping around an inhomogeneous reference stationary state, a natural setting in astrophysics for instance, induces new mathematical difficulties and physical phenomena. The goal of this article is to provide an introduction to these problems and the questions they raise. xml:lang="fr"
Inhomogeneous thermal conductivity enhances thermoelectric cooling
NASA Astrophysics Data System (ADS)
Lu, Tingyu; Zhou, Jun; Li, Nianbei; Yang, Ronggui; Li, Baowen
2014-12-01
We theoretically investigate the enhancement of thermoelectric cooling performance in thermoelectric refrigerators made of materials with inhomogeneous thermal conductivity, beyond the usual practice of enhancing thermoelectric figure of merit (ZT) of materials. The dissipation of the Joule heat in such thermoelectric refrigerators is asymmetric which can give rise to better thermoelectric cooling performance. Although the thermoelectric figure of merit and the coefficient-of-performance are slightly enhanced, both the maximum cooling power and the maximum cooling temperature difference can be enhanced significantly. This finding can be used to increase the heat absorption at the cold end. We further find that the asymmetric dissipation of Joule heat leads to thermal rectification.
Modeling Electromagnetic Scattering From Complex Inhomogeneous Objects
NASA Technical Reports Server (NTRS)
Deshpande, Manohar; Reddy, C. J.
2011-01-01
This software innovation is designed to develop a mathematical formulation to estimate the electromagnetic scattering characteristics of complex, inhomogeneous objects using the finite-element-method (FEM) and method-of-moments (MoM) concepts, as well as to develop a FORTRAN code called FEMOM3DS (Finite Element Method and Method of Moments for 3-Dimensional Scattering), which will implement the steps that are described in the mathematical formulation. Very complex objects can be easily modeled, and the operator of the code is not required to know the details of electromagnetic theory to study electromagnetic scattering.
Albedo and transmittance of inhomogeneous stratus clouds
Zuev, V.E.; Kasyanov, E.I.; Titov, G.A.
1996-04-01
A highly important topic is the study of the relationship between the statistical parameters of optical and radiative charactertistics of inhomogeneous stratus clouds. This is important because the radiation codes of general circulation models need improvement, and it is important for geophysical information. A cascade model has been developed at the Goddard Space Flight Center to treat stratocumulus clouds with the simplest geometry and horizontal fluctuations of the liquid water path (optical thickness). The model evaluates the strength with which the stochastic geometry of clouds influences the statistical characteristics of albedo and the trnasmittance of solar radiation.
Curvaton and the inhomogeneous end of inflation
Assadullahi, Hooshyar; Wands, David; Firouzjahi, Hassan; Namjoo, Mohammad Hossein E-mail: firouz@mail.ipm.ir E-mail: david.wands@port.ac.uk
2012-12-01
We study the primordial density perturbations and non-Gaussianities generated from the combined effects of an inhomogeneous end of inflation and curvaton decay in hybrid inflation. This dual role is played by a single isocurvature field which is massless during inflation but acquire a mass at the end of inflation via the waterfall phase transition. We calculate the resulting primordial non-Gaussianity characterized by the non-linearity parameter, f{sub NL}, recovering the usual end-of-inflation result when the field decays promptly and the usual curvaton result if the field decays sufficiently late.
Curvaton and the inhomogeneous end of inflation
NASA Astrophysics Data System (ADS)
Assadullahi, Hooshyar; Firouzjahi, Hassan; Namjoo, Mohammad Hossein; Wands, David
2012-12-01
We study the primordial density perturbations and non-Gaussianities generated from the combined effects of an inhomogeneous end of inflation and curvaton decay in hybrid inflation. This dual role is played by a single isocurvature field which is massless during inflation but acquire a mass at the end of inflation via the waterfall phase transition. We calculate the resulting primordial non-Gaussianity characterized by the non-linearity parameter, fNL, recovering the usual end-of-inflation result when the field decays promptly and the usual curvaton result if the field decays sufficiently late.
On reflected interactions in elastic solids containing inhomogeneities
NASA Astrophysics Data System (ADS)
Rodin, Gregory J.; Weng, George J.
2014-08-01
Interactions in linear elastic solids containing inhomogeneities are examined using integral equations. Direct and reflected interactions are identified. Direct interactions occur simply because elastic fields emitted by inhomogeneities affect each other. Reflected interactions occur because elastic fields emitted by inhomogeneities are reflected by the specimen boundary back to the individual inhomogeneities. It is shown that the reflected interactions are of critical importance to analysis of representative volume elements. Further, the reflected interactions are expressed in simple terms, so that one can obtain explicit approximate expressions for the effective stiffness tensor for linear elastic solids containing ellipsoidal and non-ellipsoidal inhomogeneities. For ellipsoidal inhomogeneities, the new approximation is closely related to that of Mori and Tanaka. In general, the new approximation can be used to recover Ponte Castañeda-Willis' and Kanaun-Levin's approximations. Connections with Maxwell's approximation are established.
Diniz, I.; Portolan, S.; Auffeves, A.
2011-12-15
We investigate theoretically the coupling of a cavity mode to a continuous distribution of emitters. We discuss the influence of the emitters' inhomogeneous broadening on the existence and on the coherence properties of the polaritonic peaks. We find that their coherence depends crucially on the shape of the distribution and not only on its width. Under certain conditions the coupling to the cavity protects the polaritonic states from inhomogeneous broadening, resulting in a longer storage time for a quantum memory based on emitter ensembles. When two different ensembles of emitters are coupled to the resonator, they support a peculiar collective dark state, which is also very attractive for the storage of quantum information.
Effective quantum dynamics of interacting systems with inhomogeneous coupling
Lopez, C. E.; Retamal, J. C.; Christ, H.; Solano, E.
2007-03-15
We study the quantum dynamics of a single mode (particle) interacting inhomogeneously with a large number of particles and introduce an effective approach to find the accessible Hilbert space, where the dynamics takes place. Two relevant examples are given: the inhomogeneous Tavis-Cummings model (e.g., N atomic qubits coupled to a single cavity mode, or to a motional mode in trapped ions) and the inhomogeneous coupling of an electron spin to N nuclear spins in a quantum dot.
Local Equilibrium in Inhomogeneous Stochastic Models of Heat Transport
NASA Astrophysics Data System (ADS)
Nándori, Péter
2016-07-01
We extend the duality of Kipnis et al. (J Stat Phys 27:65-74, 1982) to inhomogeneous lattice gas systems where either the components have different degrees of freedom or the rate of interaction depends on the spatial location. Then the dual process is applied to prove local equilibrium in the hydrodynamic limit for some inhomogeneous high dimensional systems and in the nonequilibrium steady state for one dimensional systems with arbitrary inhomogeneity.
Simulation of EUV multilayer mirror buried defects
NASA Astrophysics Data System (ADS)
Brukman, Matthew J.; Deng, Yunfei; Neureuther, Andrew R.
2000-07-01
A new interface has been created to link existing deposition/etching and electromagnetic simulation software, allowing the user to program deposition and etching conditions and then find the reflective properties of the resultant structure. The application studied in this paper is the problem of three-dimensional defects which become buried during fabrication of multilayer mirrors for extreme ultraviolet lithography. The software link reads in surface information in the form of linked triangles, determines all nodes within the triangles, and then creates nodes lying between triangles of different layers to create a 3- dimensional inhomogeneous matrix containing the materials' indices of refraction. This allows etching and depositions to be input into SAMPLE-3D, a multi-surface topology to be generated, and then the electromagnetic properties of the structure to be assessed with TEMPEST. This capability was used to study substrate defects in multilayer mirrors by programming a defect and then sputter-depositing some forty layers on top of the defect. Specifically examined was how the topography depended on sputter conditions and determined the defects' impact on the mirrors' imaging properties. While this research was focused on application to EUV lithography, the general technique may be extended to other optical processes such as alignment and mask defects.
NASA Astrophysics Data System (ADS)
Kolokolova, L.; Gustafson, B. A. S.
2001-08-01
It is common practice to use effective medium theories (EMT) to estimate average, "effective" optical constants of inhomogeneous materials. A variety of EMTs were developed for different internal structures of the medium and for a variety of shapes, size distributions and physical properties of the inhomogeneities. The most popular EMTs (Maxwell Garnett, Bruggeman, Looyenga, etc.) consider inhomogeneities that are much smaller than the wavelength. The so-called extended EMTs were developed to find effective optical constants in the case of inhomogeneities comparable and slightly larger than the wavelength. This paper compares angular distribution and wavelength dependence of intensity and polarization of scattered light obtained from calculations using the most popular EMTs and extended EMTs with the results of microwave analog measurements at the microwave facilities of the University of Florida. We simulated the light scattering by organic grains with silicate inclusions of size parameter View the MathML source, View the MathML source, and 1.24 View the MathML source). The conclusion is that for inclusions of a small size and for a small volume fraction of them in the mixture all EMTs yield similar results and show reasonable agreement with experimental results. The accuracy is better for the angular dependencies of the intensity and of the polarization of the scattered light than for their wavelength dependencies. For inhomogeneities comparable and larger than the wavelength extended EMTs work better but for smaller inclusions non-extended EMTs show more accurate results. Large volume fractions of the inclusions in the mixture (>10%) essentially reduce the accuracy of the results obtained with EMTs. Based on our study we do not recommend to use EMTs in the back-scattering domain and at the scattering angles 30°<θ<70°.
Study of the Radiative Properties of Inhomogeneous Stratocumulus Clouds
NASA Technical Reports Server (NTRS)
Batey, Michael
1996-01-01
Clouds play an important role in the radiation budget of the atmosphere. A good understanding of how clouds interact with solar radiation is necessary when considering their effects in both general circulation models and climate models. This study examined the radiative properties of clouds in both an inhomogeneous cloud system, and a simplified cloud system through the use of a Monte Carlo model. The purpose was to become more familiar with the radiative properties of clouds, especially absorption, and to investigate the excess absorption of solar radiation from observations over that calculated from theory. The first cloud system indicated that the absorptance actually decreased as the cloud's inhomogeneity increased, and that cloud forcing does not indicate any changes. The simplified cloud system looked at two different cases of absorption of solar radiation in the cloud. The absorptances calculated from the Monte Carlo is compared to a correction method for calculating absorptances and found that the method can over or underestimate absorptances at cloud edges. Also the cloud edge effects due to solar radiation points to a possibility of overestimating the retrieved optical depth at the edge, and indicates a possible way to correct for it. The effective cloud fraction (Ne) for a long time has been calculated from a cloud's reflectance. From the reflectance it has been observed that the N, for most cloud geometries is greater than the actual cloud fraction (Nc) making a cloud appear wider than it is optically. Recent studies we have performed used a Monte Carlo model to calculate the N, of a cloud using not only the reflectance but also the absorptance. The derived Ne's from the absorptance in some of the Monte Carlo runs did not give the same results as derived from the reflectance. This study also examined the inhomogeneity of clouds to find a relationship between larger and smaller scales, or wavelengths, of the cloud. Both Fourier transforms and wavelet
Intensity inhomogeneity correction of magnetic resonance images using patches
NASA Astrophysics Data System (ADS)
Roy, Snehashis; Carass, Aaron; Bazin, Pierre-Louis; Prince, Jerry L.
2011-03-01
This paper presents a patch-based non-parametric approach to the correction of intensity inhomogeneity from magnetic resonance (MR) images of the human brain. During image acquisition, the inhomogeneity present in the radio-frequency coil, is usually manifested on the reconstructed MR image as a smooth shading effect. This artifact can significantly deteriorate the performance of any kind of image processing algorithm that uses intensities as a feature. Most of the current inhomogeneity correction techniques use explicit smoothness assumptions on the inhomogeneity field, which sometimes limit their performance if the actual inhomogeneity is not smooth, a problem that becomes prevalent in high fields. The proposed patch-based inhomogeneity correction method does not assume any parametric smoothness model, instead, it uses patches from an atlas of an inhomogeneity-free image to do the correction. Preliminary results show that the proposed method is comparable to N3, a current state of the art method, when the inhomogeneity is smooth, and outperforms N3 when the inhomogeneity contains non-smooth elements.
Model of non-stationary, inhomogeneous turbulence
NASA Astrophysics Data System (ADS)
Bragg, Andrew D.; Kurien, Susan; Clark, Timothy T.
2016-07-01
We compare results from a spectral model for non-stationary, inhomogeneous turbulence (Besnard et al. in Theor Comp Fluid Dyn 8:1-35, 1996) with direct numerical simulation (DNS) data of a shear-free mixing layer (SFML) (Tordella et al. in Phys Rev E 77:016309, 2008). The SFML is used as a test case in which the efficacy of the model closure for the physical-space transport of the fluid velocity field can be tested in a flow with inhomogeneity, without the additional complexity of mean-flow coupling. The model is able to capture certain features of the SFML quite well for intermediate to long times, including the evolution of the mixing-layer width and turbulent kinetic energy. At short-times, and for more sensitive statistics such as the generation of the velocity field anisotropy, the model is less accurate. We propose two possible causes for the discrepancies. The first is the local approximation to the pressure-transport and the second is the a priori spherical averaging used to reduce the dimensionality of the solution space of the model, from wavevector to wavenumber space. DNS data are then used to gauge the relative importance of both possible deficiencies in the model.
Inhomogeneous radiative forcing of homogeneous greenhouse gases
NASA Astrophysics Data System (ADS)
Huang, Yi; Tan, Xiaoxiao; Xia, Yan
2016-03-01
Radiative forcing of a homogeneous greenhouse gas (HGG) can be very inhomogeneous because the forcing is dependent on other atmospheric and surface variables. In the case of doubling CO2, the monthly mean instantaneous forcing at the top of the atmosphere is found to vary geographically and temporally from positive to negative values, with the range (-2.5-5.1 W m-2) being more than 3 times the magnitude of the global mean value (2.3 W m-2). The vertical temperature change across the atmospheric column (temperature lapse rate) is found to be the best single predictor for explaining forcing variation. In addition, the masking effects of clouds and water vapor also contribute to forcing inhomogeneity. A regression model that predicts forcing from geophysical variables is constructed. This model can explain more than 90% of the variance of the forcing. Applying this model to analyzing the forcing variation in the Climate Model Intercomparison Project Phase 5 models, we find that intermodel discrepancy in CO2 forcing caused by model climatology leads to considerable discrepancy in their projected change in poleward energy transport.
Resistance switching in oxides with inhomogeneous conductivity
NASA Astrophysics Data System (ADS)
Shang, Da-Shan; Sun, Ji-Rong; Shen, Bao-Gen; Wuttig, Matthias
2013-06-01
Electric-field-induced resistance switching (RS) phenomena have been studied for over 60 years in metal/dielectrics/metal structures. In these experiments a wide range of dielectrics have been studied including binary transition metal oxides, perovskite oxides, chalcogenides, carbon- and silicon-based materials, as well as organic materials. RS phenomena can be used to store information and offer an attractive performance, which encompasses fast switching speeds, high scalability, and the desirable compatibility with Si-based complementary metal—oxide—semiconductor fabrication. This is promising for nonvolatile memory technology, i.e., resistance random access memory (RRAM). However, a comprehensive understanding of the underlying mechanism is still lacking. This impedes faster product development as well as accurate assessment of the device performance potential. Generally speaking, RS occurs not in the entire dielectric but only in a small, confined region, which results from the local variation of conductivity in dielectrics. In this review, we focus on the RS in oxides with such an inhomogeneous conductivity. According to the origin of the conductivity inhomogeneity, the RS phenomena and their working mechanism are reviewed by dividing them into two aspects: interface RS, based on the change of contact resistance at metal/oxide interface due to the change of Schottky barrier and interface chemical layer, and bulk RS, realized by the formation, connection, and disconnection of conductive channels in the oxides. Finally the current challenges of RS investigation and the potential improvement of the RS performance for the nonvolatile memories are discussed.
Structural inhomogeneities in glasses via cavitation
NASA Astrophysics Data System (ADS)
Chaudhuri, Pinaki; Horbach, Jürgen
2016-09-01
Using large-scale molecular-dynamics simulations for a system of 106 particles, the response of a dense amorphous solid to the continuous expansion of its volume is investigated. We find that the spatially uniform glassy state becomes unstable via the formation of cavities, which eventually leads to failure. By scanning through a wide range of densities and temperatures, we determine the state points at which the instability occurs and thereby provide estimates of the coexistence density of the resultant glass phase. Evidence for long-lived, inhomogeneous configurations with a negative pressure is found, where the frozen-in glass structure contains spherical cavities or a network of void space. Furthermore, we demonstrate the occurrence of hysteretic effects when the cavitated solid is compressed to regain the dense glassy state. As a result, a new glass state is obtained, the pressure of which is different from the initial one due to small density inhomogeneities that are generated by the dilation-compression cycle.
Coupling dark energy to dark matter inhomogeneities
NASA Astrophysics Data System (ADS)
Marra, Valerio
2016-09-01
We propose that dark energy in the form of a scalar field could effectively couple to dark matter inhomogeneities. Through this coupling energy could be transferred to/from the scalar field, which could possibly enter an accelerated regime. Though phenomenological, this scenario is interesting as it provides a natural trigger for the onset of the acceleration of the universe, since dark energy starts driving the expansion of the universe when matter inhomogeneities become sufficiently strong. Here we study a possible realization of this idea by coupling dark energy to dark matter via the linear growth function of matter perturbations. The numerical results show that it is indeed possible to obtain a viable cosmology with the expected series of radiation, matter and dark-energy dominated eras. In particular, the current density of dark energy is given by the value of the coupling parameters rather than by very special initial conditions for the scalar field. In other words, this model-unlike standard models of cosmic late acceleration-does not suffer from the so-called "coincidence problem" and its related fine tuning of initial conditions.
Inhomogeneous chemical enrichment in the Galactic Halo
NASA Astrophysics Data System (ADS)
Kobayashi, Chiaki
2016-08-01
In a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances originate from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relation. This means that the most metal-poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant branch stars or neutron star mergers can contribute at low metallicities. The intrinsic variation of yields are important in the early Universe or metal-poor systems such as in the Galactic halo. The carbon enhancement of extremely metal-poor (EMP) stars can be best explained by faint supernovae, the low [α/Fe] ratios in some EMP stars naturally arise from low-mass (~ 13 - 15M ⊙) supernovae, and finally, the [α/Fe] knee in dwarf spheroidal galaxies can be produced by subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions.
Covariant constitutive relations and relativistic inhomogeneous plasmas
Gratus, J.; Tucker, R. W.
2011-04-15
The notion of a 2-point susceptibility kernel used to describe linear electromagnetic responses of dispersive continuous media in nonrelativistic phenomena is generalized to accommodate the constraints required of a causal formulation in spacetimes with background gravitational fields. In particular the concepts of spatial material inhomogeneity and temporal nonstationarity are formulated within a fully covariant spacetime framework. This framework is illustrated by recasting the Maxwell-Vlasov equations for a collisionless plasma in a form that exposes a 2-point electromagnetic susceptibility kernel in spacetime. This permits the establishment of a perturbative scheme for nonstationary inhomogeneous plasma configurations. Explicit formulae for the perturbed kernel are derived in both the presence and absence of gravitation using the general solution to the relativistic equations of motion of the plasma constituents. In the absence of gravitation this permits an analysis of collisionless damping in terms of a system of integral equations that reduce to standard Landau damping of Langmuir modes when the perturbation refers to a homogeneous stationary plasma configuration. It is concluded that constitutive modeling in terms of a 2-point susceptibility kernel in a covariant spacetime framework offers a natural extension of standard nonrelativistic descriptions of simple media and that its use for describing linear responses of more general dispersive media has wide applicability in relativistic plasma modeling.
Ising Critical Behavior of Inhomogeneous Curie-Weiss Models and Annealed Random Graphs
NASA Astrophysics Data System (ADS)
Dommers, Sander; Giardinà, Cristian; Giberti, Claudio; van der Hofstad, Remco; Prioriello, Maria Luisa
2016-11-01
We study the critical behavior for inhomogeneous versions of the Curie-Weiss model, where the coupling constant {J_{ij}(β)} for the edge {ij} on the complete graph is given by {J_{ij}(β)=β w_iw_j/( {sum_{kin[N]}w_k})}. We call the product form of these couplings the rank-1 inhomogeneous Curie-Weiss model. This model also arises [with inverse temperature {β} replaced by {sinh(β)} ] from the annealed Ising model on the generalized random graph. We assume that the vertex weights {(w_i)_{iin[N]}} are regular, in the sense that their empirical distribution converges and the second moment converges as well. We identify the critical temperatures and exponents for these models, as well as a non-classical limit theorem for the total spin at the critical point. These depend sensitively on the number of finite moments of the weight distribution. When the fourth moment of the weight distribution converges, then the critical behavior is the same as on the (homogeneous) Curie-Weiss model, so that the inhomogeneity is weak. When the fourth moment of the weights converges to infinity, and the weights satisfy an asymptotic power law with exponent {τ} with {τin(3,5)}, then the critical exponents depend sensitively on {τ}. In addition, at criticality, the total spin {S_N} satisfies that {S_N/N^{(τ-2)/(τ-1)}} converges in law to some limiting random variable whose distribution we explicitly characterize.
NASA Astrophysics Data System (ADS)
Harada, Y.; Fujii, K.; Ohyama, T.; Itoh, K. M.; Haller, E. E.
1996-06-01
Stark broadening of Zeeman absorption lines caused by inhomogeneous electric fields in highly compensated Ge has been studied by means of far-infrared magneto-optical absorption spectroscopy measurements. A number of transmutation-doped Ge single crystals with a systematically varying compensation ratio were employed. The broadening of the full width at half maximum (FWHM) of an absorption line of the Ga acceptor is studied as a function of excitation light intensity with above-band-gap energy. The FWHM increases with decreasing intensity of the band-edge light excitation. Observation of the theoretically predicted 4/3-power law of Stark broadening, due to ionized impurities, is reported. The line broadening originates in the Stark effect, due to inhomogeneous electric fields caused by the random distribution of ionized impurities. In order to understand the mechanism for the line broadening in detail, a numerical approach based on a Monte Carlo simulation has been performed. The results of this simulation show that the inhomogeneity of the field distribution becomes larger with increasing concentration of ionized impurities. The simulation based on a perfectly random distribution for an initial impurity arrangement gives a fairly good agreement with the experimental results. We conclude that the distribution of impurities in transmutation-doped Ge samples is close to random.
NASA Technical Reports Server (NTRS)
Kummerow, Christian; Poyner, Philip; Berg, Wesley; Thomas-Stahle, Jody
2007-01-01
Passive microwave rainfall estimates that exploit the emission signal of raindrops in the atmosphere are sensitive to the inhomogeneity of rainfall within the satellite field of view (FOV). In particular, the concave nature of the brightness temperature (T(sub b)) versus rainfall relations at frequencies capable of detecting the blackbody emission of raindrops cause retrieval algorithms to systematically underestimate precipitation unless the rainfall is homogeneous within a radiometer FOV, or the inhomogeneity is accounted for explicitly. This problem has a long history in the passive microwave community and has been termed the beam-filling error. While not a true error, correcting for it requires a priori knowledge about the actual distribution of the rainfall within the satellite FOV, or at least a statistical representation of this inhomogeneity. This study first examines the magnitude of this beam-filling correction when slant-path radiative transfer calculations are used to account for the oblique incidence of current radiometers. Because of the horizontal averaging that occurs away from the nadir direction, the beam-filling error is found to be only a fraction of what has been reported previously in the literature based upon plane-parallel calculations. For a FOV representative of the 19-GHz radiometer channel (18 km X 28 km) aboard the Tropical Rainfall Measuring Mission (TRMM), the mean beam-filling correction computed in this study for tropical atmospheres is 1.26 instead of 1.52 computed from plane-parallel techniques. The slant-path solution is also less sensitive to finescale rainfall inhomogeneity and is, thus, able to make use of 4-km radar data from the TRMM Precipitation Radar (PR) in order to map regional and seasonal distributions of observed rainfall inhomogeneity in the Tropics. The data are examined to assess the expected errors introduced into climate rainfall records by unresolved changes in rainfall inhomogeneity. Results show that global
Evaluation of inhomogeneous model and the LCS based investigation in multiphase flows
NASA Astrophysics Data System (ADS)
Y Bai, Z.; Y Wang, G.; Wu, Q.; Huang, X.; Huang, B.
2013-12-01
In this paper, an evaluation of inhomogeneous model for computations of gas-liquid two-phase flow is presented, and the mechanism of gas-liquid two-phase flow in a bubble column is studied based on Finite-Time Lyapunov Exponents (FTLE) and Lagrangian Coherent Structures (LCS). The simulation is conducted with the homogeneous and inhomogeneous models respectively, and the numerical results are compared with the experimental data. It is shown that the inhomogeneous model can calculate the force of the gas more accurately and simulates the details of transient flows well due to the consideration of the interaction between the two phases. With inhomogeneous model, the periodic fluctuation of the bubble hose is captured and the velocity distribution coincides exactly with the experimental data. For the gas-liquid two-phase flow in the bubble column, the process of gaseous flow injected into water can be divided into two stages: the gas rising and gas fluctuation. The Lagrangian Coherent Structures (LCS) which consist of the ridges of the FTLE field can capture the boundary of vortex and the interface between the forward and backward flows in the liquid region, and the LCS have unique value for representing the divergence extent of neighboring particles in regions with different dynamics characteristics.
Inhomogeneity effects in HTS coated conductors used as resistive FCLs in medium voltage grids
NASA Astrophysics Data System (ADS)
Colangelo, Daniele; Dutoit, Bertrand
2012-09-01
For resistive fault current limiters (RFCLs) based on high temperature superconducting coated conductors (HTS-CCs), inhomogeneity, in terms of critical current and geometrical imperfections such as stabilizer and substrate thicknesses, plays a very important role and it may limit the penetration of such devices into the electrical market. This paper presents an electrothermal model, developed in SimPowerSystem™, able to describe the transient response of HTS-CC candidates with different degrees of inhomogeneity, both in terms of critical current and of stabilizer thickness. Critical current inhomogeneity has been modeled with Gaussian distributions. The layer thicknesses used in the simulations have been chosen by fitting the temperature dependence of real tape resistances. Our approach considers relative inhomogeneity positions as well as thermal conduction along the HTS-CC length. The model is tuned using experimental measurements made on ReBaCuO coated conductors. A new dynamical thermal calibration of the model is proposed using finite element method calculations. Inhomegeneity effects with different possible faults (e.g. three phase and single phase short-circuit) are presented.
NASA Astrophysics Data System (ADS)
Reese, Erik D.; Kawahara, H.; Kitayama, T.; Sasaki, S.; Suto, Y.
2009-01-01
Motivated by cosmological hydrodynamic simulations, the intracluster medium (ICM) inhomogeneity of galaxy clusters is modeled statistically with a lognormal model for density inhomogeneity. Through mock observations of synthetic clusters the relationship between density inhomogeneities and that of the X-ray surface brightness has been developed. This enables one to infer the statistical properties of the fluctuations of the underlying three-dimensional density distribution of real galaxy clusters from X-ray observations. We explore inhomogeneity in the intracluster medium by applying the above methodology to Chandra observations of a sample of nearby galaxy clusters. We also consider extensions of the model, including Poissonian effects and compare this hybrid lognormal-Poisson model to the nearby cluster Chandra data. EDR gratefully acknowledges support from JSPS (Japan Society for the Promotion of Science) Postdoctoral Fellowhip for Foreign Researchers award P07030. HK is supported by Grands-in-Aid for JSPS of Science Fellows. This work is also supported by Grant-in-Aid for Scientific research of Japanese Ministry of Education, Culture, Sports, Science and Technology (Nos. 20.10466, 19.07030, 16340053, 20340041, and 20540235) and by JSPS Core-to-Core Program "International Research Network for Dark Energy".
NASA Astrophysics Data System (ADS)
Zhang, Ling; Min, Junying; Wang, Bin; Lin, Jianping; Li, Fangfang; Liu, Jing
2016-03-01
In practical engineering, finite element(FE) modeling for weld seam is commonly simplified by neglecting its inhomogeneous mechanical properties. This will cause a significant loss in accuracy of FE forming analysis, in particular, for friction stir welded(FSW) blanks due to the large width and good formability of its weld seam. The inhomogeneous mechanical properties across weld seam need to be well characterized for an accurate FE analysis. Based on a similar AA5182 FSW blank, the metallographic observation and micro-Vickers hardness analysis upon the weld cross-section are performed to identify the interfaces of different sub-zones, i.e., heat affected zone(HAZ), thermal-mechanically affected zone(TMAZ) and weld nugget(WN). Based on the rule of mixture and hardness distribution, a constitutive model is established for each sub-zone to characterize the inhomogeneous mechanical properties across the weld seam. Uniaxial tensile tests of the AA5182 FSW blank are performed with the aid of digital image correlation(DIC) techniques. Experimental local stress-strain curves are obtained for different weld sub-zones. The experimental results show good agreement with those derived from the constitutive models, which demonstrates the feasibility and accuracy of these models. The proposed research gives an accurate characterization of inhomogeneous mechanical properties across the weld seam produced by FSW, which provides solutions for improving the FE simulation accuracy of FSW sheet forming.
Threshold Clustering Functions and Thermal Inhomogeneities in the Lyman-Alpha Forest
NASA Astrophysics Data System (ADS)
Lee, Khee-Gan
2011-01-01
We introduce to astrophysics the threshold clustering function S2 first derived by Torquato et al. (1988), which effectively samples the flux probability distribution (PDF) of the Lyα forest at different spatial scales. These statistics are tested on mock Lyα forest spectra based on various toy models for He II reionization, with homogeneous models with various temperature-density relations as well as inhomogeneous models with temperature differences of 10,000K and different equations of state T Δ(γ-1). These mock samples have systematics and noise added to simulate the latest Sloan Digital Sky Survey Data Release 7 (SDSS DR7) data. The traditional flux PDF is degenerate to temperature inhomogeneities in the IGM arising from He II reionization, but we find S2 can detect these inhomogeneities at 5σ, with the assumption that the flux continuum of the Lyα forest can be determined to 10% accuracy, approximately the error from current fitting methods. If the flux continuum can be determined to 3% accuracy, then S2 is capable of constraining the characteristic scale of temperature inhomogeneities, with 4σ differentiation between toy models with hot bubble radii of 50 Mpc/h and 100 Mpc/h.
Threshold Probability Functions and Thermal Inhomogeneities in the Lyα Forest
NASA Astrophysics Data System (ADS)
Lee, Khee-Gan; Spergel, David N.
2011-06-01
We introduce to astrophysics the threshold probability functions S 2, C 2, and D 2 first derived by Torquato et al., which effectively samples the flux probability distribution function (PDF) of the Lyα forest at different spatial scales. These statistics are tested on mock Lyα forest spectra based on various toy models for He II reionization, with homogeneous models with various temperature-density relations as well as models with temperature inhomogeneities. These mock samples have systematics and noise added to simulate the latest Sloan Digital Sky Survey Data Release 7 (SDSS DR7) data. We find that the flux PDF from SDSS DR7 can be used to constrain the temperature-density relation γ (where Tvprop(1 + Δ)γ - 1) of the intergalactic medium (IGM) at z = 2.5 to a precision of Δγ = 0.2 at ~4σ confidence. The flux PDF is degenerate to temperature inhomogeneities in the IGM arising from He II reionization, but we find S 2 can detect these inhomogeneities at ~3σ, with the assumption that the flux continuum of the Lyα forest can be determined to 9% accuracy, approximately the error from current fitting methods. If the flux continuum can be determined to 3% accuracy, then S 2 is capable of constraining the characteristic scale of temperature inhomogeneities, with ~4σ differentiation between toy models with hot bubble radii of 50 h -1 Mpc and 25 h -1 Mpc.
Defeating radiation damping and magnetic field inhomogeneity with spatially encoded noise.
Michal, Carl A
2010-11-15
A simple NMR experiment capable of providing well resolved spectra under conditions where either radiation damping or static magnetic field inhomogeneity would broaden otherwise high-resolution NMR spectra is introduced. The approach involves using a strong pulsed magnetic field gradient and a selective radio-frequency pulse to encode a predetermined noise pattern into the spatial distribution of magnetization. Following readout in a much smaller field gradient, the noise sequence may be deconvolved from the acquired data and a high-resolution spectrum is obtained, eliminating the effects of either radiation damping or the static field inhomogeneity. In the presence of field inhomogeneity a field map is also obtained from the same single transient. A quasi-two-dimensional version of the experiment eliminates the need for deconvolution and produces improved results with simplified processing, but without requiring a full two-dimensional experiment. Example spectra are shown for both radiation damping and one-dimensional field inhomogeneity with improvement in linewidths of more than a factor of 40.
Predicting surface vibration from underground railways through inhomogeneous soil
NASA Astrophysics Data System (ADS)
Jones, Simon; Hunt, Hugh
2012-04-01
Noise and vibration from underground railways is a major source of disturbance to inhabitants near subways. To help designers meet noise and vibration limits, numerical models are used to understand vibration propagation from these underground railways. However, the models commonly assume the ground is homogeneous and neglect to include local variability in the soil properties. Such simplifying assumptions add a level of uncertainty to the predictions which is not well understood. The goal of the current paper is to quantify the effect of soil inhomogeneity on surface vibration. The thin-layer method (TLM) is suggested as an efficient and accurate means of simulating vibration from underground railways in arbitrarily layered half-spaces. Stochastic variability of the soil's elastic modulus is introduced using a K-L expansion; the modulus is assumed to have a log-normal distribution and a modified exponential covariance kernel. The effect of horizontal soil variability is investigated by comparing the stochastic results for soils varied only in the vertical direction to soils with 2D variability. Results suggest that local soil inhomogeneity can significantly affect surface velocity predictions; 90 percent confidence intervals showing 8 dB averages and peak values up to 12 dB are computed. This is a significant source of uncertainty and should be considered when using predictions from models assuming homogeneous soil properties. Furthermore, the effect of horizontal variability of the elastic modulus on the confidence interval appears to be negligible. This suggests that only vertical variation needs to be taken into account when modelling ground vibration from underground railways.
Analyzing the impact of ISO on digital imager defects with an automatic defect trace algorithm
NASA Astrophysics Data System (ADS)
Leung, Jenny; Chapman, Glenn H.; Choi, Yong H.; Thomas, Rohit; Koren, Israel; Koren, Zahava
2010-01-01
Reliability of image sensors is limited by the continuous development of in-field defects. Laboratory calibration on 21 DSLRs has revealed hot pixels as the main defect type found in all tested cameras, with 78% of the identified defects having a time-independent offset. The expanded ISO range that exists in new cameras enables natural light photography. However, the gain applied to all pixels also enhances the appearance of defects. Analysis of defects at varying ISO levels shows that compared to the number of defects at ISO 400, the number of defects at ISO 1600 is 2-3 times higher. Amplifying the defect parameters helps differentiate faults from noise, thus detecting larger defect sets and causes some hot pixels to become saturated. The distribution of defect parameters at various ISO levels shows that the gain applied to faults with moderate defect magnitude caused 2-10% of the defects to saturate at short exposure times (0.03-0.5s). With our expanded defect collection, spatial analysis confirmed the uniform distribution of defects, indicating a random defect source. In our extended study, the temporal growth of defects is analyzed using our defecttracing algorithm. We introduce an improved defect model which incorporates the ISO gain, allowing the detection of defects even in short exposure images at high ISO and thus providing a wider selection of historical images and more accurate defect tracing. Larger area sensors show more hot pixels, while hot pixel rates strongly grow as the pixel size decreases to 2.2 microns.
Kosevich, Yuriy A; Gann, Vladimir V
2013-06-19
We study the localization of magnon states in finite defect-free Heisenberg spin-1/2 ferromagnetic chains placed in an inhomogeneous magnetic field with a constant spatial gradient. Continuous transformation from the extended magnon states to the localized Wannier-Zeeman states in a finite spin chain placed in an inhomogeneous field is described both analytically and numerically. We describe for the first time the non-monotonic dependence of the energy levels of magnons, both long and short wavelength, on the magnetic field gradient, which is a consequence of magnon localization in a finite spin chain. We show that, in contrast to the destruction of the magnon band and the establishment of the Wannier-Stark ladder in a vanishingly small field gradient in an infinite chain, the localization of magnon states at the chain ends preserves the memory of the magnon band. Essentially, the localization at the lower- or higher-field chain end resembles the localization of the positive- or negative-effective-mass band quasiparticles. We also show how the beat dynamics of coherent superposition of extended spin waves in a finite chain in a homogeneous or weakly inhomogeneous field transforms into magnon Bloch oscillations of the superposition of localized Wannier-Zeeman states in a strongly inhomogeneous field. We provide a semiclassical description of the magnon Bloch oscillations and show that the correspondence between the quantum and semiclassical descriptions is most accurate for Bloch oscillations of the magnon coherent states, which are built from a coherent superposition of a large number of the nearest-neighbour Wannier-Zeeman states.
Effects of in-cascade defect clustering on near-term defect evolution
Heinisch, H.L.
1997-08-01
The effects of in-cascade defect clustering on the nature of the subsequent defect population are being studied using stochastic annealing simulations applied to cascades generated in molecular dynamics (MD) simulations. The results of the simulations illustrates the strong influence of the defect configuration existing in the primary damage state on subsequent defect evolution. The large differences in mobility and stability of vacancy and interstitial defects and the rapid one-dimensional diffusion of small, glissile interstitial loops produced directly in cascades have been shown to be significant factors affecting the evolution of the defect distribution. In recent work, the effects of initial cluster sizes appear to be extremely important.
Topological end states due to inhomogeneous strains in wrinkled semiconducting ribbons
NASA Astrophysics Data System (ADS)
Pandey, Sudhakar; Ortix, Carmine
2016-05-01
We show that curvature-induced inhomogeneous strain distributions in nanoscale buckled semiconducting ribbons lead to the existence of end states which are topologically protected by inversion symmetry. These end-state doublets, corresponding to the so-called Maue-Shockley states, are robust against weak disorder. By identifying and calculating the corresponding topological invariants, we further show that a buckled semiconducting ribbon undergoes topological phase transitions between trivial and nontrivial insulating phases by varying its real-space geometry.
Tests of Cosmological Inhomogeneity Using WMAP
NASA Astrophysics Data System (ADS)
Shubert, Richard; Tatineni, Mahidhar
2016-06-01
This paper reports on the latest results obtained from studies of the calibrated Time-Ordered Data of the Wilkinson Microwave Anisotropy Probe (9-yr) mission that has in the past been used to determine the anisotropy of the Cosmic Microwave Background Radiation, although with a novel objective. The purpose of this work has been to examine what can be inferred from these data about the local inhomogeneity of the CMBR, which would be in this case an apparent radial variation of the brightness (or effective temperature) at the same point of the celestial sky as seen by the WMAP spacecraft instruments from the center of observation, namely the Sun. The usual studies of anisotropy normally have averaged the observed temperature of any given point on the celestial sky over one full annual orbit of the WMAP spacecraft around the Sun to produce the well-known maps. Inhomogeneity of the kind being sought here, however, would manifest itself as a systematic variation of the apparent temperature at that point as a function of the orbital position of the spacecraft. The detection of such inhomogeneity, if it could be confirmed by subsequent observations, could significantly impact the standard cosmological paradigm. The computational approach used thus far in that search, over the last four years of study by supercomputer facilities at UCSD, has been to examine the differences of temperature seen of the same points on the sky, taken in pairs corresponding to the pointing directions of the A and B radiometer horns of the instrument, from different orbital positions of the spacecraft. From those observed differences of temperature and the corresponding angular separations of the respective orbital positions — here limited to values greater than or equal to 44 degrees out of a maximum available range of 1 - 45 degrees — an apparent radial gradient of temperature could be computed with lowest uncertainties. A small but significant gradient of temperature tentatively has been
Tests of Cosmological Inhomogeneity Using WMAP
NASA Astrophysics Data System (ADS)
Shubert, Richard; Tatineni, Mahidhar
2016-06-01
This paper reports on the latest results obtained from studies of the calibrated Time-Ordered Data of the Wilkinson Microwave Anisotropy Probe (9-yr) mission that has in the past been used to determine the anisotropy of the Cosmic Microwave Background Radiation, although with a novel objective. The purpose of this work has been to examine what can be inferred from these data about the local inhomogeneity of the CMBR, which would be in this case an apparent radial variation of the brightness (or effective temperature) at the same point of the celestial sky as seen by the WMAP spacecraft instruments from the center of observation, namely the Sun. The usual studies of anisotropy normally have averaged the observed temperature of any given point on the celestial sky over one full annual orbit of the WMAP spacecraft around the Sun to produce the well-known maps. Inhomogeneity of the kind being sought here, however, would manifest itself as a systematic variation of the apparent temperature at that point as a function of the orbital position of the spacecraft. The detection of such inhomogeneity, if it could be confirmed by subsequent observations, could significantly impact the standard cosmological paradigm. The computational approach used thus far in that search, over the last four years of study by supercomputer facilities at UCSD, has been to examine the differences of temperature seen of the same points on the sky, taken in pairs corresponding to the pointing directions of the A and B radiometer horns of the instrument, from different orbital positions of the spacecraft. From those observed differences of temperature and the corresponding angular separations of the respective orbital positions — here limited to values greater than or equal to 44 degrees out of a maximum available range of 1 – 45 degrees — an apparent radial gradient of temperature could be computed with lowest uncertainties. A small but significant gradient of temperature tentatively has been
Effect of inhomogeneities on high precision measurements of cosmological distances
NASA Astrophysics Data System (ADS)
Peel, Austin; Troxel, M. A.; Ishak, Mustapha
2014-12-01
We study effects of inhomogeneities on distance measures in an exact relativistic Swiss-cheese model of the Universe, focusing on the distance modulus. The model has Λ CDM background dynamics, and the "holes" are nonsymmetric structures described by the Szekeres metric. The Szekeres exact solution of Einstein's equations, which is inhomogeneous and anisotropic, allows us to capture potentially relevant effects on light propagation due to nontrivial evolution of structures in an exact framework. Light beams traversing a single Szekeres structure in different ways can experience either magnification or demagnification, depending on the particular path. Consistent with expectations, we find a shift in the distance modulus μ to distant sources due to demagnification when the light beam travels primarily through the void regions of our model. Conversely, beams are magnified when they propagate mainly through the overdense regions of the structures, and we explore a small additional effect due to time evolution of the structures. We then study the probability distributions of Δ μ =μΛ CDM-μSC for sources at different redshifts in various Swiss-cheese constructions, where the light beams travel through a large number of randomly oriented Szekeres holes with random impact parameters. We find for Δ μ the dispersions 0.004 ≤σΔ μ≤0.008 mag for sources with redshifts 1.0 ≤z ≤1.5 , which are smaller than the intrinsic dispersion of, for example, magnitudes of type Ia supernovae. The shapes of the distributions we obtain for our Swiss-cheese constructions are peculiar in the sense that they are not consistently skewed toward the demagnification side, as they are in analyses of lensing in cosmological simulations. Depending on the source redshift, the distributions for our models can be skewed to either the demagnification or the magnification side, reflecting a limitation of these constructions. This could be the result of requiring the continuity of Einstein
Saleh, Navid B; Milliron, Delia J; Aich, Nirupam; Katz, Lynn E; Liljestrand, Howard M; Kirisits, Mary Jo
2016-10-15
Metal oxide nanoparticles (MONPs) are considered to have the potency to generate reactive oxygen species (ROS), one of the key mechanisms underlying nanotoxicity. However, the nanotoxicology literature demonstrates a lack of consensus on the dominant toxicity mechanism(s) for a particular MONP. Moreover, recent literature has studied the correlation between band structure of pristine MONPs to their ability to introduce ROS and thus has downplayed the ROS-mediated toxicological relevance of a number of such materials. On the other hand, material science can control the band structure of these materials to engineer their electronic and optical properties and thereby is constantly modulating the pristine electronic structure. Since band structure is the fundamental material property that controls ROS-producing ability, band tuning via introduction of dopants and defects needs careful consideration in toxicity assessments. This commentary critically evaluates the existing material science and nanotoxicity literature and identifies the gap in our understanding of the role of important crystal structure features (i.e., dopants and defects) on MONPs' electronic structure alteration as well as their ROS-generation capability. Furthermore, this commentary provides suggestions on characterization techniques to evaluate dopants and defects on the crystal structure and identifies research needs for advanced theoretical predictions of their electronic band structures and ROS-generation abilities. Correlation of electronic band structure and ROS will not only aid in better mechanistic assessment of nanotoxicity but will be impactful in designing and developing ROS-based applications ranging from water disinfection to next-generation antibiotics and even cancer therapeutics.
Saleh, Navid B; Milliron, Delia J; Aich, Nirupam; Katz, Lynn E; Liljestrand, Howard M; Kirisits, Mary Jo
2016-10-15
Metal oxide nanoparticles (MONPs) are considered to have the potency to generate reactive oxygen species (ROS), one of the key mechanisms underlying nanotoxicity. However, the nanotoxicology literature demonstrates a lack of consensus on the dominant toxicity mechanism(s) for a particular MONP. Moreover, recent literature has studied the correlation between band structure of pristine MONPs to their ability to introduce ROS and thus has downplayed the ROS-mediated toxicological relevance of a number of such materials. On the other hand, material science can control the band structure of these materials to engineer their electronic and optical properties and thereby is constantly modulating the pristine electronic structure. Since band structure is the fundamental material property that controls ROS-producing ability, band tuning via introduction of dopants and defects needs careful consideration in toxicity assessments. This commentary critically evaluates the existing material science and nanotoxicity literature and identifies the gap in our understanding of the role of important crystal structure features (i.e., dopants and defects) on MONPs' electronic structure alteration as well as their ROS-generation capability. Furthermore, this commentary provides suggestions on characterization techniques to evaluate dopants and defects on the crystal structure and identifies research needs for advanced theoretical predictions of their electronic band structures and ROS-generation abilities. Correlation of electronic band structure and ROS will not only aid in better mechanistic assessment of nanotoxicity but will be impactful in designing and developing ROS-based applications ranging from water disinfection to next-generation antibiotics and even cancer therapeutics. PMID:27350094
Lensing effects in inhomogeneous cosmological models
Ghassemi, Sima; Khoeini-Moghaddam, Salomeh; Mansouri, Reza
2009-05-15
Concepts developed in the gravitational lensing techniques such as shear, convergence, tangential, and radial arcs maybe used to see how tenable inhomogeneous models proposed to explain the acceleration of the universe models are. We study the widely discussed Lemaitre-Tolman-Bondi (LTB) cosmological models. It turns out that for the observer sitting at origin of a global LTB solution the shear vanishes as in the Friedmann-Robertson-Walker models, while the value of convergence is different, which may lead to observable cosmological effects. We also consider Swiss-cheese models proposed recently based on LTB with an observer sitting in the Friedmann-Robertson-Walker part. It turns out that they have different behavior as far as the formation of radial and tangential arcs are concerned.
Inhomogeneous high harmonic generation in krypton clusters.
Ruf, H; Handschin, C; Cireasa, R; Thiré, N; Ferré, A; Petit, S; Descamps, D; Mével, E; Constant, E; Blanchet, V; Fabre, B; Mairesse, Y
2013-02-22
High order harmonic generation from clusters is a controversial topic: conflicting theories exist, with different explanations for similar experimental observations. From an experimental point of view, separating the contributions from monomers and clusters is challenging. By performing a spectrally and spatially resolved study in a controlled mixture of clusters and monomers, we are able to isolate a region of the spectrum where the emission purely originates from clusters. Surprisingly, the emission from clusters is depolarized, which is the signature of statistical inhomogeneous emission from a low-density source. The harmonic response to laser ellipticity shows that this generation is produced by a new recollisional mechanism, which opens the way to future theoretical studies.
Probing dark energy inhomogeneities with supernovae
Blomqvist, Michael; Moertsell, Edvard; Nobili, Serena E-mail: edvard@physto.se
2008-06-15
We discuss the possibility of identifying anisotropic and/or inhomogeneous cosmological models using type Ia supernova data. A search for correlations in current type Ia peak magnitudes over a large range of angular scales yields a null result. However, the same analysis limited to supernovae at low redshift shows a feeble anticorrelation at the 2{sigma} level at angular scales {theta} Almost-Equal-To 40 Degree-Sign . Upcoming data from, e.g., the SNLS (Supernova Legacy Survey) and the SDSS-II (SDSS: Sloan Digital Sky Survey) supernova searches will improve our limits on the size of-or possibly detect-possible correlations also at high redshift at the per cent level in the near future. With data from the proposed SNAP (SuperNova Acceleration Probe) satellite, we will be able to detect the induced correlations from gravitational lensing on type Ia peak magnitudes on scales less than a degree.
AFE dynamic effects in inhomogeneous plasmas
NASA Technical Reports Server (NTRS)
Juang, Jeng-Nan
1989-01-01
The Microwave Reflectometer Ionization Sensor (MRIS) is an instrument on the Aeroassist Flight Experiment (AFE) satellite which will be deployed from the space shuttle. The flow characteristic around a hypersonic bluff reentry vehicle will be measured by the AFE. The general mission of the MRIS is to measure the electron density within the range from 10(exp12) to 10(exp 15) electrons per cu cm and determine the distance to the location of each measured from the surface of the aerobrake. These measurements will be compared with prior aerothermodynamic computer code predictions. Since a knowledge of plasma dynamic effects is important for MRIS design and post flight analysis, it is of interest to consider any possibility of plasma dynamic effects and especially in inhomogeneous plasmas. Of particular interest is the need to study plasma dynamic effects that may emerge from a flow field stationary state that was determined without regard to electric or magnetic fields.
Dielectric elastomer membranes undergoing inhomogeneous deformation
NASA Astrophysics Data System (ADS)
He, Tianhu; Zhao, Xuanhe; Suo, Zhigang
2009-10-01
Dielectric elastomers are capable of large deformation subject to an electric voltage and are promising for use as actuators, sensors, and generators. Because of large deformation, nonlinear equations of states, and diverse modes of failure, modeling the process of electromechanical transduction has been challenging. This paper studies a membrane of a dielectric elastomer deformed into an out-of-plane axisymmetric shape, a configuration used in a family of commercial devices known as the universal muscle actuators. The kinematics of deformation and charging, together with thermodynamics, leads to equations that govern the state of equilibrium. Numerical results indicate that the field in the membrane can be very inhomogeneous, and that the membrane is susceptible to several modes of failure, including electrical breakdown, loss of tension, and rupture by stretch. Care is needed in the design to balance the requirements of averting various modes of failure while using the material efficiently.
Mass spectrometry and inhomogeneous ion optics
NASA Technical Reports Server (NTRS)
White, F. A.
1973-01-01
Work done in several areas to advance the state of the art of magnetic mass spectrometers is described. The calculations and data necessary for the design of inhomogeneous field mass spectrometers, and the calculation of ion trajectories through such fields are presented. The development and testing of solid state ion detection devices providing the capability of counting single ions is discussed. New techniques in the preparation and operation of thermal-ionization ion sources are described. Data obtained on the concentrations of copper in rainfall and uranium in air samples using the improved thermal ionization techniques are presented. The design of a closed system static mass spectrometer for isotopic analyses is discussed. A summary of instrumental aspects of a four-stage mass spectrometer comprising two electrostatic and two 90 deg. magnetic lenses with a 122-cm radius used to study the interaction of ions with solids is presented.
On Isospectral Deformations of an Inhomogeneous String
NASA Astrophysics Data System (ADS)
Colville, Kale; Gomez, Daniel; Szmigielski, Jacek
2016-07-01
In this paper we consider a class of isospectral deformations of the inhomogeneous string boundary value problem. The deformations considered are generalizations of the isospectral deformation that has arisen in connection with the Camassa-Holm equation for the shallow water waves. It is proved that these new isospectral deformations result in evolution equations on the mass density whose form depends on how the string is tied at the endpoints. Moreover, it is shown that the evolution equations in this class linearize on the spectral side and hence can be solved by the inverse spectral method. In particular, the problem involving a mass density given by a discrete finite measure and arbitrary boundary conditions is shown to be solvable by Stieltjes' continued fractions.
Dielectric fluid in inhomogeneous pulsed electric field.
Shneider, M N; Pekker, M
2013-04-01
We consider the dynamics of a compressible fluid under the influence of electrostrictive ponderomotive forces in strong inhomogeneous nonstationary electric fields. It is shown that if the fronts of the voltage rise at a sharp, needlelike electrode are rather steep (less than or about nanoseconds), the region of negative pressure arises, which can reach values at which the fluid loses its continuity with the formation of cavitation ruptures. If the voltage on the electrode is not large enough or the front is flatter, the cavitation in the liquid does not occur. However, a sudden shutdown of the field results in a reverse flow of liquid from the electrode, which leads to appearance of negative pressure, and, possibly, cavitation.
Topological defects from the multiverse
Zhang, Jun; Blanco-Pillado, Jose J.; Garriga, Jaume; Vilenkin, Alexander
2015-05-28
Many theories of the early universe predict the existence of a multiverse where bubbles continuously nucleate giving rise to observers in their interior. In this paper, we point out that topological defects of several dimensionalities will also be produced in de Sitter like regions of the multiverse. In particular, defects could be spontaneously nucleated in our parent vacuum. We study the evolution of these defects as they collide with and propagate inside of our bubble. We estimate the present distribution of defects in the observable part of the universe. The expected number of such nearby defects turns out to be quite small, even for the highest nucleation rate. We also study collisions of strings and domain walls with our bubble in our past light cone. We obtain simulated full-sky maps of the loci of such collisions, and find their angular size distribution. Similarly to what happens in the case of bubble collisions, the prospect of detecting any collisions of our bubble with ambient defects is greatly enhanced in the case where the cosmological constant of our parent vacuum is much higher than the vacuum energy density during inflation in our bubble.
Topological defects from the multiverse
Zhang, Jun; Vilenkin, Alexander; Blanco-Pillado, Jose J.
2015-05-01
Many theories of the early universe predict the existence of a multiverse where bubbles continuously nucleate giving rise to observers in their interior. In this paper, we point out that topological defects of several dimensionalities will also be produced in de Sitter like regions of the multiverse. In particular, defects could be spontaneously nucleated in our parent vacuum. We study the evolution of these defects as they collide with and propagate inside of our bubble. We estimate the present distribution of defects in the observable part of the universe. The expected number of such nearby defects turns out to be quite small, even for the highest nucleation rate. We also study collisions of strings and domain walls with our bubble in our past light cone. We obtain simulated full-sky maps of the loci of such collisions, and find their angular size distribution. Similarly to what happens in the case of bubble collisions, the prospect of detecting any collisions of our bubble with ambient defects is greatly enhanced in the case where the cosmological constant of our parent vacuum is much higher than the vacuum energy density during inflation in our bubble.
Generalized Langevin Theory for Inhomogeneous Fluids.
NASA Astrophysics Data System (ADS)
Grant, Martin Garth
This thesis presents a molecular theory of the dynamics of inhomogeneous fluids. Dynamical correlations in a nonuniform system are studied through the generalized Langevin approach. The equations of motion (formally exact) are obtained for the number density, momentum density, energy density, stress tensor and heat flux. We evaluate all the relevant sum rules appearing in the frequency matrix exactly in terms of microscopic pair potentials and an external field. We show using functional derivatives how these microscopic sum rules relate to more familiar, though now nonlocal, hydrodynamic-like quantities. The set of equations is closed by a Markov approximation in the equations for stress tensor and heat flux. As a result, these equations become analogous to Grad's 13-moment equations for low density fluids and constitute a generalization to inhomogeneous fluids of the work of Schofield and Akcasu-Daniels. We apply this formalism to several problems. We study the correlation of currents orthogonal to a diffuse planar, liquid-vapour, interface, introducing new nonlocal elastic moduli and new nonlocal, frequency dependent, viscosities. Novel symmetry breaking contributions are obtained, which are related to the Young-Laplace equation for pressure balance. The normal modes, associated with the symmetry breaking interface in the liquid-vapour system, are analyzed, taking into account the nonlocal nature of the diffuse planar interface. We obtain the classical dispersion relation for capillary waves, observed in light scattering experiments, from an adiabatic (molecular) approach. We consider the 'capillary wave model' (CWM) of the equilibrium liquid-vapour interface. CWM is reformulated to be consistent with capillary waves; corrections to the standard CWM results, due to self-consistent long range coupling, are obtained for finite surface area and nonzero gravitational acceleration. Finally, we obtain the Landau-Lifshitz theory of fluctuating hydrodynamics from the
Problem of time in slightly inhomogeneous cosmology
NASA Astrophysics Data System (ADS)
Anderson, Edward
2016-07-01
The problem of time (PoT) is a multi-faceted conceptual incompatibility between various areas of Theoretical Physics. While usually stated as between GR and QM, in fact 8/9ths of it is already present at the classical level. Thus we adopt a ‘top-down’ classical and then quantum approach. I consider a local resolution to the PoT that is Machian, which was previously realized for relational triangle and minisuperspace models. This resolution has three levels: classical, semiclassical and combined semiclassical-histories-records. This article’s specific model is a slightly inhomogeneous cosmology considered for now at the classical level. This is motivated by how the inhomogeneous fluctuations that underlie structure formation—galaxies and CMB hotspots—might have been seeded by quantum cosmological fluctuations, as magnified by some inflationary mechanism. In particular, I consider the perturbations about {{{S}}}3 case of this involving up to second order, which has a number of parallels with the Halliwell-Hawking model but has a number of conceptual differences and useful upgrades. The article’s main features are that the elimination part of the model’s thin sandwich is straightforward, but the modewise split of the constraints fail to be first-class constraints. Thus the elimination part only arises as an intermediate geometry between superspace and Riem. The reduced geometries have surprising singularities influenced by the matter content of the Universe, though the N-body problem anticipates these with its collinear singularities. I also give a ‘basis set’ of Kuchař beables for this model arena.
The Hyades open cluster is chemically inhomogeneous
NASA Astrophysics Data System (ADS)
Liu, F.; Yong, D.; Asplund, M.; Ramírez, I.; Meléndez, J.
2016-04-01
We present a high-precision differential abundance analysis of 16 solar-type stars in the Hyades open cluster based on high-resolution, high signal-to-noise ratio (S/N ≈ 350-400) spectra obtained from the McDonald 2.7-m telescope. We derived stellar parameters and differential chemical abundances for 19 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ba) with uncertainties as low as ˜0.01-0.02 dex. Our main results include: (1) there is no clear chemical signature of planet formation detected among the sample stars, i.e. no correlations in abundances versus condensation temperature; (2) the observed abundance dispersions are a factor of ≈1.5-2 larger than the average measurement errors for most elements; (3) there are positive correlations, of high statistical significance, between the abundances of at least 90 per cent of pairs of elements. We demonstrate that none of these findings can be explained by errors due to the stellar parameters. Our results reveal that the Hyades is chemically inhomogeneous at the 0.02 dex level. Possible explanations for the abundance variations include (1) inhomogeneous chemical evolution in the proto-cluster environment, (2) supernova ejection in the proto-cluster cloud and (3) pollution of metal-poor gas before complete mixing of the proto-cluster cloud. Our results provide significant new constraints on the chemical composition of open clusters and a challenge to the current view of Galactic archaeology.
Local dissipation scales in strongly inhomogeneous turbulent shear flows
NASA Astrophysics Data System (ADS)
Morshed, Khandakar; Dasi, Lakshmi
2014-11-01
We have previously shown that the distribution of dissipation scales, Q (η) , is dependent on the shear-dissipation Reynolds number Res ≡ < ɛ > / (S2 ν) along the streamwise homogeneous direction. This dependency is further explored through a generalized theoretical framework linking Q (η) , with the two-point correlation function, as well as the Reynolds stress tensor orientation relative to the mean axes of principal deformation. Time-resolved particle image velocimetry measurements were performed in a stationary turbulent flow past a backward facing step at Reynolds numbers 13,600, 9,000, and 5,500 based on the maximum velocity and step size. Q (η) were measured in all directions at different points in the measurement region with varying mean shear magnitude. Results show anisotropic Q (η) distributions strongly reflecting the anisotropy in the two-point correlation function and the Reynolds stress tensor. Based on these results the previous Res dependency is generalized to inhomogeneous directions while discussing the physical role of strong mean shear in inducing local anisotropy.
Local and average behaviour in inhomogeneous superdiffusive media
NASA Astrophysics Data System (ADS)
Vezzani, Alessandro; Burioni, Raffaella; Caniparoli, Luca; Lepri, Stefano
2011-05-01
We consider a random walk on one-dimensional inhomogeneous graphs built from Cantor fractals. Our study is motivated by recent experiments that demonstrated superdiffusion of light in complex disordered materials, thereby termed Lévy glasses. We introduce a geometric parameter α which plays a role analogous to the exponent characterising the step length distribution in random systems. We study the large-time behaviour of both local and average observables; for the latter case, we distinguish two different types of averages, respectively over the set of all initial sites and over the scattering sites only. The 'single long-jump approximation" is applied to analytically determine the different asymptotic behaviour as a function of α and to understand their origin. We also discuss the possibility that the root of the mean square displacement and the characteristic length of the walker distribution may grow according to different power laws; this anomalous behaviour is typical of processes characterised by Lévy statistics and here, in particular, it is shown to influence average quantities.
Propagation of a finite optical beam in an inhomogeneous medium.
Lutomirski, R F; Yura, H T
1971-07-01
The first part of this paper is devoted to extending the Huygens-Fresnel principle to a medium that exhibits a spatial (but not temporal) variation in index of refraction. Utilizing a reciprocity theorem for a monochromatic disturbance in a weakly inhomogeneous medium, it is shown that the secondary wave-front will be determined by the envelope of spherical wavelets from the primary wavefront, as in the vacuum problem, but that each wavelet is now determined by the propagation of a spherical wave in the refractive medium. In the second part, the above development is applied to the case in which the index of refraction is a random variable; a further application of the reciprocity theorem results in a formula for the mean intensity distribution from a finite aperture in terms of the complex disturbance in the aperture and the modulation transfer function (MTF) for a spherical wave in the medium. The results are applicable for an arbitrary complex disturbance in the transmitting aperture in both the Fresnel and Fraunhofer regions of the aperture. Using a Kolmogorov spectrum for the index of refraction fluctuations and a second-order expression for the MTF, the formula is used to calculate the mean intensity distribution for a plane wave diffracting from a circular aperture and to give approximate expressions for the beam spreading at various ranges. PMID:20111181
NASA Astrophysics Data System (ADS)
Shao, Lin; Wei, C.-C.; Gigax, J.; Aitkaliyeva, A.; Chen, D.; Sencer, B. H.; Garner, F. A.
2014-10-01
Ion irradiation has been widely used to simulate neutron-induced radiation damage. There are a number of features of ion-induced damage that differ from neutron-induced damage, however, and these differences require investigation before ion data can be confidently used to predict behavior arising from neutron bombardment. In this study 3.5 MeV self-ion irradiation of pure iron was used to study the influence on void swelling of the depth-dependent defect imbalance between vacancies and interstitials that arises from various surface effects, forward scattering of displaced atoms, and especially the injected interstitial effect. It was observed that the depth dependence of void swelling does not follow the behavior anticipated from the depth dependence of the damage rate. Void nucleation and growth develop first in the lower-dose, near-surface region, and then moves to progressively deeper and higher-damage depths during continued irradiation. This indicates a strong initial suppression of void nucleation in the peak damage region that is eventually overcome with continued irradiation. Using the Boltzmann transport equation method, this phenomenon is shown to be due to depth-dependent defect imbalances created under ion irradiation. These findings demonstrate that void swelling does not depend solely on the local dose level and that this sensitivity of swelling to depth must be considered in extraction and interpretation of ion-induced swelling data.
Shao, Lin; Wei, C. -C.; Gigax, J.; Aitkaliyeva, A.; Chen, D.; Sencer, B. H.; Garner, F. A.
2014-06-10
Ion irradiation has been widely used to simulate radiation damage induced by neutrons. However, there are a number of features of ion-induced damage that differ from neutron-induced damage, and these differences require investigation before behavior arising from neutron bombardment can be confidently predicted from ion data. In this study 3.5 MeV self-ion irradiation of pure iron was used to study the influence on void swelling of the depth-dependent defect imbalance between vacancies and interstitials that arises from various surface effects, forward scattering of displaced atoms, and especially the injected interstitial effect. The depth dependence of void swelling was observed notmore » to follow the behavior anticipated from the depth dependence of the damage rate. Void nucleation and growth develop first in the lower-dose, near-surface region, and then, during continued irradiation, move to progressively deeper and higher-damage depths. This indicates a strong initial suppression of void nucleation in the peak damage region that continued irradiation eventually overcomes. This phenomenon is shown by the Boltzmann transport equation method to be due to depth-dependent defect imbalances created under ion irradiation. These findings thus demonstrate that void swelling does not depend solely on the local dose level and that this sensitivity of swelling to depth must be considered in extracting and interpreting ion-induced swelling data.« less
Shao, Lin; Wei, C. -C.; Gigax, J.; Aitkaliyeva, A.; Chen, D.; Sencer, B. H.; Garner, F. A.
2014-06-10
Ion irradiation has been widely used to simulate radiation damage induced by neutrons. However, there are a number of features of ion-induced damage that differ from neutron-induced damage, and these differences require investigation before behavior arising from neutron bombardment can be confidently predicted from ion data. In this study 3.5 MeV self-ion irradiation of pure iron was used to study the influence on void swelling of the depth-dependent defect imbalance between vacancies and interstitials that arises from various surface effects, forward scattering of displaced atoms, and especially the injected interstitial effect. The depth dependence of void swelling was observed not to follow the behavior anticipated from the depth dependence of the damage rate. Void nucleation and growth develop first in the lower-dose, near-surface region, and then, during continued irradiation, move to progressively deeper and higher-damage depths. This indicates a strong initial suppression of void nucleation in the peak damage region that continued irradiation eventually overcomes. This phenomenon is shown by the Boltzmann transport equation method to be due to depth-dependent defect imbalances created under ion irradiation. These findings thus demonstrate that void swelling does not depend solely on the local dose level and that this sensitivity of swelling to depth must be considered in extracting and interpreting ion-induced swelling data.
Azough, Feridoon; Cernik, Robert Joseph; Schaffer, Bernhard; Kepaptsoglou, Demie; Ramasse, Quentin Mathieu; Bigatti, Marco; Ali, Amir; MacLaren, Ian; Barthel, Juri; Molinari, Marco; Baran, Jakub Dominik; Parker, Stephen Charles; Freer, Robert
2016-04-01
We investigated the structure of the tungsten bronze barium neodymium titanates Ba(6-3n)Nd(8+2n)Ti(18)O(54), which are exploited as microwave dielectric ceramics. They form a complex nanostructure, which resembles a nanofilm with stacking layers of ∼12 Å thickness. The synthesized samples of Ba(6-3n)Nd(8+2n)Ti(18)O(54) (n = 0, 0.3, 0.4, 0.5) are characterized by pentagonal and tetragonal columns, where the A cations are distributed in three symmetrically inequivalent sites. Synchrotron X-ray diffraction and electron energy loss spectroscopy allowed for quantitative analysis of the site occupancy, which determines the defect distribution. This is corroborated by density functional theory calculations. Pentagonal columns are dominated by Ba, and tetragonal columns are dominated by Nd, although specific Nd sites exhibit significant concentrations of Ba. The data indicated significant elongation of the Ba columns in the pentagonal positions and of the Nd columns in tetragonal positions involving a zigzag arrangement of atoms along the b lattice direction. We found that the preferred Ba substitution occurs at Nd[3]/[4] followed by Nd[2] and Nd[1]/[5] sites, which is significantly different to that proposed in earlier studies. Our results on the Ba(6-3n)Nd(8+2n)Ti(18)O(54) "perovskite" superstructure and its defect distribution are particularly valuable in those applications where the optimization of material properties of oxides is imperative; these include not only microwave ceramics but also thermoelectric materials, where the nanostructure and the distribution of the dopants will reduce the thermal conductivity. PMID:26998674
Azough, Feridoon; Cernik, Robert Joseph; Schaffer, Bernhard; Kepaptsoglou, Demie; Ramasse, Quentin Mathieu; Bigatti, Marco; Ali, Amir; MacLaren, Ian; Barthel, Juri; Molinari, Marco; Baran, Jakub Dominik; Parker, Stephen Charles; Freer, Robert
2016-04-01
We investigated the structure of the tungsten bronze barium neodymium titanates Ba(6-3n)Nd(8+2n)Ti(18)O(54), which are exploited as microwave dielectric ceramics. They form a complex nanostructure, which resembles a nanofilm with stacking layers of ∼12 Å thickness. The synthesized samples of Ba(6-3n)Nd(8+2n)Ti(18)O(54) (n = 0, 0.3, 0.4, 0.5) are characterized by pentagonal and tetragonal columns, where the A cations are distributed in three symmetrically inequivalent sites. Synchrotron X-ray diffraction and electron energy loss spectroscopy allowed for quantitative analysis of the site occupancy, which determines the defect distribution. This is corroborated by density functional theory calculations. Pentagonal columns are dominated by Ba, and tetragonal columns are dominated by Nd, although specific Nd sites exhibit significant concentrations of Ba. The data indicated significant elongation of the Ba columns in the pentagonal positions and of the Nd columns in tetragonal positions involving a zigzag arrangement of atoms along the b lattice direction. We found that the preferred Ba substitution occurs at Nd[3]/[4] followed by Nd[2] and Nd[1]/[5] sites, which is significantly different to that proposed in earlier studies. Our results on the Ba(6-3n)Nd(8+2n)Ti(18)O(54) "perovskite" superstructure and its defect distribution are particularly valuable in those applications where the optimization of material properties of oxides is imperative; these include not only microwave ceramics but also thermoelectric materials, where the nanostructure and the distribution of the dopants will reduce the thermal conductivity.
Ventricular septal defect (image)
Ventricular septal defect is a congenital defect of the heart, that occurs as an abnormal opening in ... wall that separates the right and left ventricles. Ventricular septal defect may also be associated with other ...
Neural tube defects are birth defects of the brain, spine, or spinal cord. They happen in the first month ... she is pregnant. The two most common neural tube defects are spina bifida and anencephaly. In spina ...
Modification of light transmission channels by inhomogeneous absorption in random media.
Liew, Seng Fatt; Cao, Hui
2015-05-01
Optical absorption is omnipresent and often distributed non-uniformly in space. We present a numerical study on the effects of inhomogeneous absorption on transmission eigenchannels of light in highly scattering media. In the weak absorption regime, the spatial profile of a transmission channel remains similar to that without absorption, and the effect of inhomogeneous absorption can be stronger or weaker than homogeneous absorption depending on the spatial overlap of the localized absorbing region with the field intensity maximum of the channel. In the strong absorption regime, the high transmission channels redirect the energy flows to circumvent the absorbing regions to minimize loss. The attenuation of high transmission channels by inhomogeneous absorption is lower than that by homogeneous absorption, regardless of the location of the absorbing region. The statistical distribution of transmission eigenvalues in the former becomes broader than that in the latter, due to a longer tail at high transmission. The maximum enhancement factor of total transmission increases with absorption, eventually exceeds that without absorption.
Causality and non-equilibrium second-order phase transitions in inhomogeneous systems
NASA Astrophysics Data System (ADS)
del Campo, A.; Kibble, T. W. B.; Zurek, W. H.
2013-10-01
When a second-order phase transition is crossed at a finite rate, the evolution of the system stops being adiabatic as a result of the critical slowing down in the neighborhood of the critical point. In systems with a topologically nontrivial vacuum manifold, disparate local choices of the ground state lead to the formation of topological defects. The universality class of the transition imprints a signature on the resulting density of topological defects: it obeys a power law in the quench rate, with an exponent dictated by a combination of the critical exponents of the transition. In inhomogeneous systems the situation is more complicated, as the spontaneous symmetry breaking competes with bias caused by the influence of the nearby regions that already chose the new vacuum. As a result, the choice of the broken symmetry vacuum may be inherited from the neighboring regions that have already entered the new phase. This competition between the inherited and spontaneous symmetry breaking enhances the role of causality, as the defect formation is restricted to a fraction of the system where the front velocity surpasses the relevant sound velocity and phase transition remains effectively homogeneous. As a consequence, the overall number of topological defects can be substantially suppressed. When the fraction of the system is small, the resulting total number of defects is still given by a power law related to the universality class of the transition, but exhibits a more pronounced dependence on the quench rate. This enhanced dependence complicates the analysis but may also facilitate experimental testing of defect formation theories.
Konovalov, A B; Vlasov, V V
2014-08-31
We report a new method for determining the weighting functions to reconstruct absorbing inhomogeneities in tissue by perturbation time-domain diffuse optical tomography using the transmission geometry of a flat layer. The method is based on an analytical approach to the calculation of the weighting functions for a semi-infinite scattering medium and on the use of the original method of an equivalent inverse source in order to obtain weight distributions for the flat layer geometry. The correctness of the proposed method of the weighting function calculation is evaluated by a numerical experiment on the reconstruction of absorbing inhomogeneities. It is shown that the perturbation reconstruction model based on the proposed weighting function calculation method allows the inhomogeneities smaller than 0.3 cm and ∼0.4 cm, located respectively in the transverse and longitudinal directions to the probe light direction, to be resolved in the centre of an 8-cm-thick object. (laser biophotonics)
Zhang, Neng-Hui; Meng, Wei-Lie; Tan, Zou-Qing
2013-02-01
In nanoscale diagnostic systems, inhomogeneity in near-surface systems and flexibility in biostructures greatly influence the mechanical/electrical/thermal properties of biosensors and resultant detection signals. This study focuses on inhomogeneity and flexibility of DNA biofilm and characterizes its local interactions and mechanical properties. First, a flexible cylinder model of DNA chain is employed to capture the local geometric deformation characteristics of DNA molecules on microcantilever. In order to describe the inhomogeneous properties of DNA biofilm at thickness direction, the Strey's empirical formula for mesoscopic DNA liquid crystal theory is improved with the assumption of a net charge distribution in film. The model parameters are obtained by curve fitting with experimental data. Second, the biaxial iso-strain compression of thought experiment and the energy conservation law are used to predict macroscopic effective tangent modulus of DNA biofilm in terms of nanoscopic properties of dsDNA, buffer salt concentration. PMID:23228426
The effect of compositional inhomogeneities on the enthalpies of hydrogen absorption by Pd-Ni alloys
NASA Astrophysics Data System (ADS)
Flanagan, Ted; Park, C.-N.; Luo, Suifang
2004-03-01
A substitutional solution fcc Pd-Ni(15 atbeen prepared by arc-melting without a subsequent high temperature annealing treatment. It is inhomogeneous and its "plateau" region is very sloping. This sloping is used to determine a distribution function for the composition of the Ni according to a model developed by the authors. Enthalpies determined along this region from p-c-T(pressure-composition-temperature) measurements, i.e., van't Hoff plots, decrease in magnitude accounting for the sloping. On the other hand, enthalpies measured calorimetrically along the sloping plateau are closely constant while the entropies increase in magnitude. An explanation for this is given and it should be noted that this phenomenon may be quite general for compositionally inhomogeneous metal alloys or intermetallic hydride systems.
Dynamic Self-Consistent Field Theory of Inhomogeneous Complex Fluids Under Shear
NASA Astrophysics Data System (ADS)
Mihajlovic, Maja; Lo, Tak Shing; Shnidman, Yitzhak
2003-03-01
Understanding and predicting the interplay between morphology and rheology of sheared, inhomogeneous, complex fluids is of great importance. Yet modeling of such phenomena is in its infancy. We have developed a novel dynamic self-consistent field (DSCF) theory that makes possible detailed computational study of such phenomena. Our DSCF theory couples the time evolution of chain conformation statistics with probabilistic transport equations for volume fractions and momenta, based on local conservation laws formulated on a segmental scale. To generate chain conformation statistics, we are using a modification of the lattice random walk formalism of Scheutjens and Fleer. Their static SCF theory is limited to equilibrium systems, since probability distributions are obtained by free energy minimization, assuming isotropic Gaussian chain conformations. In contrast, our DSCF approach accounts for explicit time evolution of the segmental and (anisotropic) stepping probabilities used for generating chain conformations. We will present highlights of DSCF studies of a variety of inhomogenous fluids containing homopolymers, block copolymers and nanoparticles.
Spatial discrimination of Rydberg tagged molecular photofragments in an inhomogeneous electric field
NASA Astrophysics Data System (ADS)
Monti, O. L. A.; Cruse, H. A.; Softley, T. P.; Mackenzie, S. R.
2001-11-01
A new approach to detecting the spatial and energetic distribution of photodissociation products is demonstrated, in which an inhomogeneous electric field is used for spatially selective field ionization of Rydberg molecules. State-selected NO fragments from NO2 photodissociation in a supersonic beam are excited to high-n Rydberg states and allowed to expand through the inhomogeneous field provided by an octopole. The field in the octopole results in the field ionization of those fragments that have moved to large radial distances (˜5 mm) from the beam axis, and therefore this device transmits only those Rydberg molecules with a low velocity component in the direction perpendicular to the beam. A detailed characterization of the properties of this "steradiancy analyzer" is carried out and factors limiting the energy resolution (currently approximately 100 cm-1 at an excess energy of 250 cm-1), along with possible improvements, are discussed in detail.
Temperature-Dependent Exciton Hopping in an Array of Inhomogeneously Broadened Quantum Dots
NASA Astrophysics Data System (ADS)
Miyazaki, Jun; Kinoshita, Shuichi
2012-07-01
The dynamics of exciton hopping in an array of inhomogeneously broadened CdSe/ZnS quantum dot (QD) ensembles is examined by measuring time- and spectrally resolved fluorescence intensities. We have found a decrease in the fluorescence decay time as well as a dynamic redshift of the fluorescence spectrum originating from exciton transfer. Both show the characteristic temperature dependence reflecting the peculiar exciton dynamics in the QD ensemble. We propose a model of coupled QD arrays where inhomogeneous distribution and dark QDs that are related to a long-lasting off-state of blinking QDs are taken into account. Experimental results together with numerical calculations based on this model suggest that at low temperatures, an exciton transfers to a local low-energy site and tends to be trapped, whereas at high temperatures, thermally activated hopping of the exciton occurs repeatedly. Furthermore, we show that the decay time decrease of the QD array is attributable to exciton hopping to dark QDs.
Propagator-resolved 2D exchange in porous media in the inhomogeneous magnetic field.
Burcaw, Lauren M; Hunter, Mark W; Callaghan, Paul T
2010-08-01
We present a propagator-resolved 2D exchange spectroscopy technique for observing fluid motion in a porous medium. The susceptibility difference between the matrix and the fluid is exploited to produce an inhomogeneous internal magnetic field, causing the Larmor frequency to change as molecules migrate. We test our method using a randomly packed monodisperse 100 microm diameter glass bead matrix saturated with distilled water. Building upon previous 2D exchange spectroscopy work we add a displacement dimension which allows us to obtain 2D exchange spectra that are defined by both mixing time and spatial displacement rather than by mixing time alone. We also simulate our system using a Monte Carlo process in a random nonpenetrating monodisperse bead pack, finding good agreement with experiment. A simple analytic model is used to interpret the NMR data in terms of a characteristic length scale over which molecules must diffuse to sample the inhomogeneous field distribution. PMID:20554230
Analytical expression of the potential generated by a massive inhomogeneous straight segment
NASA Astrophysics Data System (ADS)
Najid, N.-E.; Elourabi, E.
2011-12-01
Potential calculation is an important task to study dynamical behavior of test particles around celestial bodies. Gravitational potential of irregular bodies is of great importance since the discoveries of binary asteroids, this opened a new field of research. A simple model to describe the motion of a test particle, in that case, is to consider a finite homogeneous straight segment. In our work, we take this model by adding an inhomogeneous distribution of mass. To be consistent with the geometrical shape of the asteroid, we explore a parabolic profile of the density. We establish the closet analytical form of the potential generated by this inhomogeneous massive straight segment. The study of the dynamical behavior is fulfilled by the use of Lagrangian formulation, which allowed us to give some two and three dimensional orbits.
Average luminosity distance in inhomogeneous universes
Kostov, Valentin
2010-04-01
Using numerical ray tracing, the paper studies how the average distance modulus in an inhomogeneous universe differs from its homogeneous counterpart. The averaging is over all directions from a fixed observer not over all possible observers (cosmic), thus is more directly applicable to our observations. In contrast to previous studies, the averaging is exact, non-perturbative, and includes all non-linear effects. The inhomogeneous universes are represented by Swiss-cheese models containing random and simple cubic lattices of mass-compensated voids. The Earth observer is in the homogeneous cheese which has an Einstein-de Sitter metric. For the first time, the averaging is widened to include the supernovas inside the voids by assuming the probability for supernova emission from any comoving volume is proportional to the rest mass in it. Voids aligned along a certain direction give rise to a distance modulus correction which increases with redshift and is caused by cumulative gravitational lensing. That correction is present even for small voids and depends on their density contrast, not on their radius. Averaging over all directions destroys the cumulative lensing correction even in a non-randomized simple cubic lattice of voids. At low redshifts, the average distance modulus correction does not vanish due to the peculiar velocities, despite the photon flux conservation argument. A formula for the maximal possible average correction as a function of redshift is derived and shown to be in excellent agreement with the numerical results. The formula applies to voids of any size that: (a)have approximately constant densities in their interior and walls; and (b)are not in a deep nonlinear regime. The average correction calculated in random and simple cubic void lattices is severely damped below the predicted maximal one after a single void diameter. That is traced to cancellations between the corrections from the fronts and backs of different voids. The results obtained
Inhomogeneous Lens Structures for Integrated Optics.
NASA Astrophysics Data System (ADS)
Finlayson, Neil
Available from UMI in association with The British Library. Requires signed TDF. The thesis is concerned with the design, analysis, fabrication and evaluation of integrated optic lenses which are inhomogeneous either in physical shape or in refractive index profile. Connections are made between the study of these lenses and the exciting new field of optical computing. A special class of non-uniform lenses forms the main area of interest in the present study. Historically, the development of these lenses has followed two distinct lines. In one method the optical path is made to vary directly, whilst the other method involves controlling the physical path, and thus the optical path, through the principle of equivalence. The dual development has been continued in the field of integrated optics, where lenses based on direct control of the optical path are termed variable-index lenses and those based on physical path control are termed geodesic lenses. The perfect variable -index lens studied in this work was the well-known Luneburg lens. The design formulae for both types of lens are presented. A simpler lens, of spherical geometry, is also presented. Chapter three investigates the problems involved in modelling fabrication conditions in a thermal-evaporation -in-vacuum environment so that lens profiles can actually be constructed. Chapter four goes into methods of tracing rays through these lenses in some detail. The beam-propagation method (BPM) is used to study diffraction and associated effects in inhomogeneous lenses. Negative focal shifts are reported which are not predicted by geometrical optics or the usual approximate diffraction theories. The fabrication of lenses is considered. Planar waveguide measurements carried out on the various materials used in the study are presented. A major problem in the fabrication of geodesic lenses, that of obtaining a uniform waveguide layer over the complete lens area, is dealt with in some detail. Extensive tests on the
Average luminosity distance in inhomogeneous universes
NASA Astrophysics Data System (ADS)
Kostov, Valentin Angelov
Using numerical ray tracing, the paper studies how the average distance modulus in an inhomogeneous universe differs from its homogeneous counterpart. The averaging is over all directions from a fixed observer not over all possible observers (cosmic), thus it is more directly applicable to our observations. Unlike previous studies, the averaging is exact, non-perturbative, an includes all possible non-linear effects. The inhomogeneous universes are represented by Sweese-cheese models containing random and simple cubic lattices of mass- compensated voids. The Earth observer is in the homogeneous cheese which has an Einstein - de Sitter metric. For the first time, the averaging is widened to include the supernovas inside the voids by assuming the probability for supernova emission from any comoving volume is proportional to the rest mass in it. For voids aligned in a certain direction, there is a cumulative gravitational lensing correction to the distance modulus that increases with redshift. That correction is present even for small voids and depends on the density contrast of the voids, not on their radius. Averaging over all directions destroys the cumulative correction even in a non-randomized simple cubic lattice of voids. Despite the well known argument for photon flux conservation, the average distance modulus correction at low redshifts is not zero due to the peculiar velocities. A formula for the maximum possible average correction as a function of redshift is derived and shown to be in excellent agreement with the numerical results. The formula applies to voids of any size that: (1) have approximately constant densities in their interior and walls, (2) are not in a deep nonlinear regime. The actual average correction calculated in random and simple cubic void lattices is severely damped below the predicted maximum. That is traced to cancelations between the corrections coming from the fronts and backs of different voids at the same redshift from the
Meandering of overgrown v-shaped defects in epitaxial GaN layers
NASA Astrophysics Data System (ADS)
Weidlich, P. H.; Schnedler, M.; Portz, V.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.
2014-07-01
The meandering of v-shaped defects in GaN(0001) epitaxial layers is investigated by cross-sectional scanning tunneling microscopy. The spatial position of v-shaped defects is mapped on ( 10 1 ¯ 0 ) cleavage planes using a dopant modulation, which traces the overgrown growth front. Strong lateral displacements of the apex of the v-shaped defects are observed. The lateral displacements are suggested to be induced by the meandering of threading dislocations present in the v-shaped defects. The meandering of the dislocation is attributed to interactions with inhomogeneous strain fields.
Reflection and interference of electromagnetic waves in inhomogeneous media
NASA Technical Reports Server (NTRS)
Geiger, F. E.; Kyle, H. L.
1973-01-01
Solutions were obtained of the wave equation for a plane horizontally polarized electro-magnetic wave incident on a semi infinite two dimensional inhomogeneous medium. Two problems were considered: An inhomogeneous half space, and an inhomogeneous layer of arbitrary thickness. Solutions of the wave equation were obtained in terms of Hankel functions with complex arguments. Numerical calculations were made of the reflection coefficient R at the interface of the homogeneous medium. The startling results show that the reflection coefficient for a complex dielectric constant with gradient, can be less than that of the same medium with zero gradient.
Modelling of hydraulic fracture propagation in inhomogeneous poroelastic medium
NASA Astrophysics Data System (ADS)
Baykin, A. N.; Golovin, S. V.
2016-06-01
In the paper a model for description of a hydraulic fracture propagation in inhomogeneous poroelastic medium is proposed. Among advantages of the presented numerical algorithm, there are incorporation of the near-tip analysis into the general computational scheme, account for the rock failure criterion on the base of the cohesive zone model, possibility for analysis of fracture propagation in inhomogeneous reservoirs. The numerical convergence of the algorithm is verified and the agreement of our numerical results with known solutions is established. The influence of the inhomogeneity of the reservoir permeability to the fracture time evolution is also demonstrated.
NASA Astrophysics Data System (ADS)
Vikram, Ajit; Chowdhury, Prabudhya Roy; Phillips, Ryan K.; Hoorfar, Mina
2016-07-01
This paper describes a measurement technique developed for the determination of the effective electrical bulk resistance of the gas diffusion layer (GDL) and the contact resistance distribution at the interface of the GDL and the bipolar plate (BPP). The novelty of this study is the measurement and separation of the bulk and contact resistance under inhomogeneous compression, occurring in an actual fuel cell assembly due to the presence of the channels and ribs on the bipolar plates. The measurement of the electrical contact resistance, contributing to nearly two-third of the ohmic losses in the fuel cell assembly, shows a non-linear distribution along the GDL/BPP interface. The effective bulk resistance of the GDL under inhomogeneous compression showed a decrease of nearly 40% compared to that estimated for homogeneous compression at different compression pressures. Such a decrease in the effective bulk resistance under inhomogeneous compression could be due to the non-uniform distribution of pressure under the ribs and the channels. This measurement technique can be used to identify optimum GDL, BPP and channel-rib structures based on minimum bulk and contact resistances measured under inhomogeneous compression.
Inhomogeneous cloud measurements during bbc-2001
NASA Astrophysics Data System (ADS)
Venema, V.; Simmer, C.; Crewell, S.; 4D-Clouds Team
2003-04-01
The 4D-clouds project aims at capturing the radiative influence of inhomogeneous clouds and at implementing these influences in the modelling of transport and exchange processes in dynamical atmospheric models. The measurement component of this project was executed together with the EU-project CLIWA-NET in the Baltex Bridge Campaign (BBC), which was held in the Netherlands around Cabauw in August and September 2001. It encompassed satellite and diverse ground based remote sensing measurements and simultaneous in situ measurements of the microphysical and radiative properties with three airplanes. The airplanes complement one another very well: The Merlin IV (Meteo France, CAATER) carried microphysical probes, the Cessna (TU Berlin) imaging remote sensing instruments and the Partenavia (IfT Leipzig) mainly radiation equipment. In total seven remote sensing stations with a lidar ceilometer, an infrared-radiometer and a microwave radiometer, were scattered over a region of 100 by 100 km. Furthermore, 3D cloud fields have been measured at Cabauw by making scanning measurements with a microwave radiometer and a cloud radar. In total four radars were present, an UHF windprofiler/RASS, an S-band Radar (TARA), and two cloud radars (K and W band). The paper will describe the 4D-clouds project and the instrumentation of the BBC campaign. Furthermore, it will show some first results of the campaign.
First artificial periodic inhomogeneity experiments at HAARP
NASA Astrophysics Data System (ADS)
Hysell, D. L.; McCarrick, M. J.; Fallen, C. T.; Vierinen, J.
2015-03-01
Experiments involving the generation and detection of artificial periodic inhomogeneities have been performed at the High Frequency Active Auroral Research Program (HAARP) facility. Irregularities were created using powerful X-mode HF emissions and then probed using short (10 μs) X- and O-mode pulses. Reception was performed using a portable software-defined receiver together with the crossed rhombic antenna from the local ionosonde. Echoes were observed reliably between about 85 and 140 km altitude with signal-to-noise ratios as high as about 30 dB. The Doppler shift of the echoes can be associated with the vertical neutral wind in this altitude range. Small but persistent Doppler shifts were observed. The decay time constant of the echoes is meanwhile indicative of the ambipolar diffusion coefficient which depends on the plasma temperature, composition, and neutral gas density. The measured time constants appear to be consistent with theoretical expectations and imply a methodology for measuring neutral density profiles. The significance of thermospheric vertical neutral wind and density measurements which are difficult to obtain using ground-based instruments by other means is discussed.
Inhomogeneous field theory inside the arctic circle
NASA Astrophysics Data System (ADS)
Allegra, Nicolas; Dubail, Jérôme; Stéphan, Jean-Marie; Viti, Jacopo
2016-05-01
Motivated by quantum quenches in spin chains, a one-dimensional toy-model of fermionic particles evolving in imaginary-time from a domain-wall initial state is solved. The main interest of this toy-model is that it exhibits the arctic circle phenomenon, namely a spatial phase separation between a critically fluctuating region and a frozen region. Large-scale correlations inside the critical region are expressed in terms of correlators in a (euclidean) two-dimensional massless Dirac field theory. It is observed that this theory is inhomogenous: the metric is position-dependent, so it is in fact a Dirac theory in curved space. The technique used to solve the toy-model is then extended to deal with the transfer matrices of other models: dimers on the honeycomb and square lattice, and the six-vertex model at the free fermion point (Δ =0 ). In all cases, explicit expressions are given for the long-range correlations in the critical region, as well as for the underlying Dirac action. Although the setup developed here is heavily based on fermionic observables, the results can be translated into the language of height configurations and of the gaussian free field, via bosonization. Correlations close to the phase boundary and the generic appearance of Airy processes in all these models are also briefly revisited in the appendix.
Spin generation by strong inhomogeneous electric fields
NASA Astrophysics Data System (ADS)
Finkler, Ilya; Engel, Hans-Andreas; Rashba, Emmanuel; Halperin, Bertrand
2007-03-01
Motivated by recent experiments [1], we propose a model with extrinsic spin-orbit interaction, where an inhomogeneous electric field E in the x-y plane can give rise, through nonlinear effects, to a spin polarization with non-zero sz, away from the sample boundaries. The field E induces a spin current js^z= z x(αjc+βE), where jc=σE is the charge current, and the two terms represent,respectively, the skew scattering and side-jump contributions. [2]. The coefficients α and β are assumed to be E- independent, but conductivity σ is field dependent. We find the spin density sz by solving the equation for spin diffusion and relaxation with a source term ∇.js^z. For sufficiently low fields, jc is linear in E, and the source term vanishes, implying that sz=0 away from the edges. However, for large fields, σ varies with E. Solving the diffusion equation in a T-shaped geometry, where the electric current propagates along the main channel, we find spin accumulation near the entrance of the side channel, similar to experimental findings [1]. Also, we present a toy model where spin accumulation away from the boundary results from a nonlinear and anisotropic conductivity. [1] V. Sih, et al, Phys. Rev. Lett. 97, 096605 (2006). [2] H.-A. Engel, B.I. Halperin, E.I.Rashba, Phys. Rev. Lett. 95, 166605 (2005).
Polydispersity-driven topological defects as order-restoring excitations.
Yao, Zhenwei; Olvera de la Cruz, Monica
2014-04-01
The engineering of defects in crystalline matter has been extensively exploited to modify the mechanical and electrical properties of many materials. Recent experiments on manipulating extended defects in graphene, for example, show that defects direct the flow of electric charges. The fascinating possibilities offered by defects in two dimensions, known as topological defects, to control material properties provide great motivation to perform fundamental investigations to uncover their role in various systems. Previous studies mostly focus on topological defects in 2D crystals on curved surfaces. On flat geometries, topological defects can be introduced via density inhomogeneities. We investigate here topological defects due to size polydispersity on flat surfaces. Size polydispersity is usually an inevitable feature of a large variety of systems. In this work, simulations show well-organized induced topological defects around an impurity particle of a wrong size. These patterns are not found in systems of identical particles. Our work demonstrates that in polydispersed systems topological defects play the role of restoring order. The simulations show a perfect hexagonal lattice beyond a small defective region around the impurity particle. Elasticity theory has demonstrated an analogy between the elementary topological defects named disclinations to electric charges by associating a charge to a disclination, whose sign depends on the number of its nearest neighbors. Size polydispersity is shown numerically here to be an essential ingredient to understand short-range attractions between like-charge disclinations. Our study suggests that size polydispersity has a promising potential to engineer defects in various systems including nanoparticles and colloidal crystals.
Quantum Brownian motion with inhomogeneous damping and diffusion
NASA Astrophysics Data System (ADS)
Massignan, Pietro; Lampo, Aniello; Wehr, Jan; Lewenstein, Maciej
2015-03-01
We analyze the microscopic model of quantum Brownian motion, describing a Brownian particle interacting with a bosonic bath through a coupling which is linear in the creation and annihilation operators of the bath, but may be a nonlinear function of the position of the particle. Physically, this corresponds to a configuration in which damping and diffusion are spatially inhomogeneous. We derive systematically the quantum master equation for the Brownian particle in the Born-Markov approximation and we discuss the appearance of additional terms, for various polynomials forms of the coupling. We discuss the cases of linear and quadratic coupling in great detail and we derive, using Wigner function techniques, the stationary solutions of the master equation for a Brownian particle in a harmonic trapping potential. We predict quite generally Gaussian stationary states, and we compute the aspect ratio and the spread of the distributions. In particular, we find that these solutions may be squeezed (superlocalized) with respect to the position of the Brownian particle. We analyze various restrictions to the validity of our theory posed by non-Markovian effects and by the Heisenberg principle. We further study the dynamical stability of the system, by applying a Gaussian approximation to the time-dependent Wigner function, and we compute the decoherence rates of coherent quantum superpositions in position space. Finally, we propose a possible experimental realization of the physics discussed here, by considering an impurity particle embedded in a degenerate quantum gas.
Laser transmission-backscattering through inhomogeneous cirrus clouds.
Ou, Szu-Cheng; Takano, Yoshihide; Liou, Kuo-Nan; Lefevre, Randy J; Johnson, Michael W
2002-09-20
We have developed a two-dimensional (2D) model for inhomogeneous cirrus clouds in plane-parallel and spherical geometries for the analysis of the transmission and backscattering of high-energy laser beams. The 2D extinction-coefficient and mean effective ice-crystal size fields for cirrus clouds can be determined from a combination of the remote sensing of cirrus clouds by use of the Advanced Very High Resolution Radiometer on board National Oceanic and Atmospheric Administration satellites and the vertical profiling of ice-crystal size distributions available from limited measurements. We demonstrate that satellite remote sensing of the position and the composition of high cirrus can be incorporated directly in the computer model developed for the transmission and backscattering of high-energy laser beams in realistic atmospheres. The results of laser direct transmission, forward scattering, and backscattering are analyzed carefully with respect to aircraft height, cirrus cloud optical depth, and ice-crystal size and orientation. Uncertainty in laser transmission that is due to errors in the retrieved ice-crystal size is negligible. But uncertainty of the order of 2% can be produced if the retrieved optical depth has errors of +/-0.05. With both the aircraft and the target near the cloud top, the direct transmission decreases, owing to the propagation of the laser beam through the curved portion of the cloud top. This effect becomes more pronounced as the horizontal distance between the aircraft and the target increases.
Characterizing Electronic Inhomogeneities of Nanoscale Materials for Printable Electronics
NASA Astrophysics Data System (ADS)
Schlitz, Ruth Anne S.
Inhomogeneities in the electronic properties of boron-doped silicon nanowires and self-assembled nanodielectrics were characterized quantitatively. For silicon nanowires grown by the vapor-liquid-solid mechanism, radial and axial gradients in boron concentration due to preferentially-doped vapor-solid (VS) deposition on the nanowire side wall lead to significant intra- and inter- nanowire variability. Devices fabricated along the length of a single nanowire transition from behavior dominated by Schottky barriers at the Ni2Si source and drain contacts to linear behavior as the thickness of the VS material increases. For self-assembled nanodielectrics (SANDs), Weibull analysis demonstrates that a high degree of uniformity is achievable with molecular self-assembly. The dielectric breakdown voltage distribution for metal-insulator-semiconductor parallel-plate capacitors containing two types of SAND, Type III and Zr-SAND, were characterized. These devices exhibit a high degree of uniformity (beta ≥ 16 for some samples), and annealing at ≥ 300 °C does not degrade SAND properties. SANDs are also demonstrated to be compatible with electron-beam lithography, and attempts to fabricate Si nanowire SAND field-effect transistors are discussed. Finally, a simple strain platform for one-dimensional nanostructures is presented, and shifts in the Raman peaks of vanadium dioxide nanobeams under varying amounts of uniaxial tension are observed.
Statistical field theory description of inhomogeneous polarizable soft matter
NASA Astrophysics Data System (ADS)
Martin, Jonathan M.; Li, Wei; Delaney, Kris T.; Fredrickson, Glenn H.
2016-10-01
We present a new molecularly informed statistical field theory model of inhomogeneous polarizable soft matter. The model is based on fluid elements, referred to as beads, that can carry a net monopole of charge at their center of mass and a fixed or induced dipole through a Drude-type distributed charge approach. The beads are thus polarizable and naturally manifest attractive van der Waals interactions. Beyond electrostatic interactions, beads can be given soft repulsions to sustain fluid phases at arbitrary densities. Beads of different types can be mixed or linked into polymers with arbitrary chain models and sequences of charged and uncharged beads. By such an approach, it is possible to construct models suitable for describing a vast range of soft-matter systems including electrolyte and polyelectrolyte solutions, ionic liquids, polymerized ionic liquids, polymer blends, ionomers, and block copolymers, among others. These bead models can be constructed in virtually any ensemble and converted to complex-valued statistical field theories by Hubbard-Stratonovich transforms. One of the fields entering the resulting theories is a fluctuating electrostatic potential; other fields are necessary to decouple non-electrostatic interactions. We elucidate the structure of these field theories, their consistency with macroscopic electrostatic theory in the absence and presence of external electric fields, and the way in which they embed van der Waals interactions and non-uniform dielectric properties. Their suitability as a framework for computational studies of heterogeneous soft matter systems using field-theoretic simulation techniques is discussed.
Inhomogeneous deformation in INCONEL 718 during monotonic and cyclic loadings
NASA Astrophysics Data System (ADS)
Worthem, D. W.; Robertson, I. M.; Leckie, F. A.; Socie, D. F.; Altstetter, C. J.
1990-12-01
The deformation microstructures produced by room-temperature monotonie tensile and uniaxial low-cycle fatigue tests in aged (precipitate-hardened) INCONEL 718 were examined by transmission electron microscopy (TEM). Regularly spaced arrays of deformation bands on {111} slip planes were observed. Under monotonie loading, the dislocation structure within a deformation band formed an inverse pileup at a grain boundary, indicating that the boundary was the probable dislocation source. Under fatigue loading, the bands contained a high density of dislocations in a complex arrangement, which was attained after relatively few cycles. Samples of homogenized (precipitate-free) material were deformed monotonically in tension for comparison with the aged material. Early in the deformation, there was only one deformation band per grain and little evidence of work hardening; that is, there was a region of constant flow stress. With increased deformation, work hardening began, more bands nucleated, and their spacing became similar to that in the aged material. This result demonstrates that the degree of coarseness of inhomogeneous deformation in this material was not necessarily a result of a softening process within the bands because of precipitate shearing, but rather, it was primarily a function of the amount of work hardening within the bands. The regularity of the bands and the dislocation structure can be rationalized in terms of a periodic resistance to glide of the dislocations due to the presence of the precipitates and a distribution of dislocation sources along the grain boundaries.
Inhomogeneous field in cavities of zero index metamaterials
Fu, Yangyang; Xu, Yadong; Chen, Huangyang
2015-01-01
In common media, electromagnetic wave always possesses a fluctuant field variation, analogous to an undulant surface of sea. While electromagnetic wave in the media with zero index metamaterials (ZIMs), whose refractive indices are near zero, homogeneous or constant field distribution will emerge, resembling a tranquil surface of lake. Such impression almost could be found in all previous literatures related to ZIMs. However, in this letter, we theoretically and numerically find that, in a cavity structure with ZIMs, when higher order modes (e.g., dipole modes) are excited inside cavity, inhomogeneous field could take place in ZIMs. Such a finding challenges the common perception in ZIMs: It is generally considered that homogeneous or constant field is generated in ZIMs. In addition, the proposed cavity structure herein could be used to manipulate radiation of light, such as enhancing or suppressing radiation, controlling radiation pattern and achieving isotropic or directive radiation, thereby potential applications are expected. These effects are well confirmed by numerical simulations. PMID:26080276
NASA Astrophysics Data System (ADS)
Hafiz, Shopan; Andrade, Nicolas; Monavarian, Morteza; Izyumskaya, Natalia; Das, Saikat; Zhang, Fan; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit
2016-02-01
Near-field scanning optical microscopy was applied to investigate the spatial variations of extended defects and their effects on the optical quality for semi-polar (1-101) and (11-22) InGaN light emitting diodes (LEDs). (1-101) and (11-22) oriented InGaN LEDs emitting at 450-470 nm were grown on patterned Si (001) 7° offcut substrates and m-sapphire substrates by means of nano-epitaxial lateral overgrowth (ELO), respectively. For (1-101) structures, the photoluminescence (PL) at 85 K from the near surface c+ wings was found to be relatively uniform and strong across the sample. However, emission from the c- wings was substantially weaker due to the presence of high density of threading dislocations (TDs) and basal plane stacking faults (BSFs) as revealed from the local PL spectra. In case of (11-22) LED structures, near-field PL intensity correlated with the surface features and the striations along the direction parallel to the c-axis projection exposed facets where the Indium content was higher as deduced from shift in the PL peak energy.
Kim, Kihong; Lee, Dong-Hun
2006-04-15
A new version of the invariant imbedding theory for the propagation of coupled waves in inhomogeneous media is applied to the mode conversion of high frequency electromagnetic waves into electrostatic modes in cold, magnetized, and stratified plasmas. The cases where the external magnetic field is applied perpendicularly to the direction of inhomogeneity and the electron density profile is linear are considered. Extensive and numerically exact results for the mode conversion coefficients, the reflectances, and the wave electric and magnetic field profiles inside the inhomogeneous plasma are obtained. The dependencies of mode conversion phenomena on the magnitude of the external magnetic field, the incident angle, and the wave frequency are explored in detail.
Alternative field representations and integral equations for modeling inhomogeneous dielectrics
NASA Technical Reports Server (NTRS)
Volakis, John L.
1992-01-01
New volume and volume-surface integral equations are presented for modeling inhomogeneous dielectric regions. The presented integral equations result in more efficient numerical implementations and should, therefore, be useful in a variety of electromagnetic applications.
Inhomogeneous Fermi and quantum spin systems on lattices
NASA Astrophysics Data System (ADS)
Bru, J.-B.; de Siqueira Pedra, W.
2012-12-01
We study the thermodynamic properties of a certain type of space-inhomogeneous Fermi and quantum spin systems on lattices. We are particularly interested in the case where the space scale of the inhomogeneities stays macroscopic, but very small as compared to the side-length of the box containing fermions or spins. The present study is however not restricted to "macroscopic inhomogeneities" and also includes the (periodic) microscopic and mesoscopic cases. We prove that - as in the homogeneous case - the pressure is, up to a minus sign, the conservative value of a two-person zero-sum game, named here thermodynamic game. Because of the absence of space symmetries in such inhomogeneous systems, it is not clear from the beginning what kind of object equilibrium states should be in the thermodynamic limit. However, we give rigorous statements on correlations functions for large boxes.
Zero-Lag Synchronization Despite Inhomogeneities in a Relay System
Ghasemi Esfahani, Zahra; Valizadeh, Alireza
2014-01-01
A novel proposal for the zero-lag synchronization of the delayed coupled neurons, is to connect them indirectly via a third relay neuron. In this study, we develop a Poincaré map to investigate the robustness of the synchrony in such a relay system against inhomogeneity in the neurons and synaptic parameters. We show that when the inhomogeneity does not violate the symmetry of the system, synchrony is maintained and in some cases inhomogeneity enhances synchrony. On the other hand if the inhomogeneity breaks the symmetry of the system, zero lag synchrony can not be preserved. In this case we give analytical results for the phase lag of the spiking of the neurons in the stable state. PMID:25486522
Defect interactions within a group of subcascades
Heinisch, H.L.
1996-10-01
The evolution of the defect distributions within high energy cascades that contain multiple subcascades is studied as a function of temperature for cascades in copper. Low energy cascades generated with molecular dynamics are placed in close proximity to simulate the arrangement of subcascades within a high energy event, then the ALSOME code follows the evolution of the cascade damage during short term annealing. The intersubcascade defect interactions during the annealing stage are found to be minimal. However, no conclusions regarding effects of subcascades on defect production should be drawn until intersubcascade defect interactions during the quenching stage are examined.
Stochastic gene expression: Density of defects frozen into permanent Turing patterns
NASA Astrophysics Data System (ADS)
Dziarmaga, Jacek
2001-01-01
We estimate density of defects frozen into a biological Turing pattern which was turned on at a finite rate. Self-locking of gene expression in individual cells, which makes the Turing transition discontinuous, stabilizes the pattern together with its defects. Defects frozen into the pattern are a permanent record of the transition-they give an animal its own characteristic lifelong ``fingerprints'' or, as for vital organ formation, they can be fatal. Density of defects scales like the fourth root of the transition rate. This dependence is so weak that there is not enough time during morphogenesis to get rid of defects simply by slowing down the rate. A defect-free pattern can be obtained by spatially inhomogeneous activation of the genes. If the supercritical density of activator spreads slower than certain threshold velocity, then the Turing pattern is expressed without any defects.
Towards collisions of inhomogeneous shockwaves in AdS
NASA Astrophysics Data System (ADS)
Fernández, Daniel
2015-07-01
We perform a numerical simulation of the evolution of inhomogeneities with transverse profile in a collision of gravitational shockwaves in asymptotically anti-de Sitter spacetime. This constitutes a step closer towards an accurate holographic description of the thermalization of a strongly coupled plasma, which can model the dynamics of heavy ion collisions. The results indicate that the considered inhomogeneities typically become hydrodynamical earlier or at the same moment when hydrodynamics applies to the background, even though they decay slowly.
Defects and inhomogeneities in Fe3O4(111) thin film growth on Pt(111)
NASA Astrophysics Data System (ADS)
Sala, A.; Marchetto, H.; Qin, Z.-H.; Shaikhutdinov, S.; Schmidt, Th.; Freund, H.-J.
2012-10-01
Growth and surface termination of a Fe3O4(111) thin film on a Pt(111) surface were examined by a combination of low-energy electron microscopy, selected area low-energy electron diffraction (LEED), and x-ray-induced photoemission electron microscopy. The film exhibits the predominance of one out of two possible rotational domains, independent of film thickness. The morphology strongly depends on preparation conditions, e.g., at high oxidation temperature FeO/Pt(111) domains are formed that prevent the closure of the thin film. Dynamical LEED analysis and spot-profile analysis LEED (SPA-LEED) show that the surface exposes ¼ monolayer of Fe over a close-packed oxygen layer only when the sample is subsequently annealed in ultrahigh vacuum at 900 K. In contrast, the as-prepared films grown by oxidation at 1000 K and subsequent cooling down in oxygen, additionally exhibit small FeOx agglomerates that rest upon the canonical surface termination. Their formation as a function of the various preparation conditions of the thin film is discussed.
NASA Astrophysics Data System (ADS)
Stockmann, Jason P.; Cooley, Clarissa Z.; Guerin, Bastien; Rosen, Matthew S.; Wald, Lawrence L.
2016-07-01
the even and odd-echo coherence pathways due to defects in the refocusing pulse. In this paper, we describe this needed methodology and demonstrate the ability of TRASE to Fourier encode in an inhomogeneous field (ΔB0/B0 ∼ 1% over the full FOV).
A Gravitational Experiment Involving Inhomogeneous Electric Fields
Datta, T.; Yin Ming; Vargas, Jose
2004-02-04
Unification of gravitation with other forms of interactions, particularly with electromagnetism, will have tremendous impacts on technology and our understanding of nature. The economic impact of such an achievement will also be unprecedented and far more extensive than the impact experienced in the past century due to the unification of electricity with magnetism and optics. Theoretical unification of gravitation with electromagnetism using classical differential geometry has been pursued since the late nineteen twenties, when Einstein and Cartan used teleparallelism for the task. Recently, Vargas and Torr have followed the same line of research with more powerful mathematics in a more general geometric framework, which allows for the presence of other interactions. Their approach also uses Kaehler generalization of Cartan's exterior calculus, which constitutes a language appropriate for both classical and quantum physics. Given the compelling nature of teleparallelism (path-independent equality of vectors at a distance) and the problems still existing with energy-momentum in general relativity, it is important to seek experimental evidence for such expectations. Such experimental programs are likely to provide quantitative guidance to the further development of current and future theories. We too, have undertaken an experimental search for potential electrically induced gravitational (EIG) effects. This presentation describes some of the practical concerns that relates to our investigation of electrical influences on laboratory size test masses. Preliminary results, appear to indicate a correlation between the application of a spatially inhomogeneous electric field and the appearance of an additional force on the test mass. If confirmed, the presence of such a force will be consistent with the predictions of Vargas-Torr. More importantly, proven results will shed new light and clearer understanding of the interactions between gravitational and electromagnetic
A Gravitational Experiment Involving Inhomogeneous Electric Fields
NASA Astrophysics Data System (ADS)
Datta, T.; Yin, Ming; Vargas, Jose
2004-02-01
Unification of gravitation with other forms of interactions, particularly with electromagnetism, will have tremendous impacts on technology and our understanding of nature. The economic impact of such an achievement will also be unprecedented and far more extensive than the impact experienced in the past century due to the unification of electricity with magnetism and optics. Theoretical unification of gravitation with electromagnetism using classical differential geometry has been pursued since the late nineteen twenties, when Einstein and Cartan used teleparallelism for the task. Recently, Vargas and Torr have followed the same line of research with more powerful mathematics in a more general geometric framework, which allows for the presence of other interactions. Their approach also uses Kähler generalization of Cartan's exterior calculus, which constitutes a language appropriate for both classical and quantum physics. Given the compelling nature of teleparallelism (path-independent equality of vectors at a distance) and the problems still existing with energy-momentum in general relativity, it is important to seek experimental evidence for such expectations. Such experimental programs are likely to provide quantitative guidance to the further development of current and future theories. We too, have undertaken an experimental search for potential electrically induced gravitational (EIG) effects. This presentation describes some of the practical concerns that relates to our investigation of electrical influences on laboratory size test masses. Preliminary results, appear to indicate a correlation between the application of a spatially inhomogeneous electric field and the appearance of an additional force on the test mass. If confirmed, the presence of such a force will be consistent with the predictions of Vargas-Torr. More importantly, proven results will shed new light and clearer understanding of the interactions between gravitational and electromagnetic
Inverse Scattering Problems for Acoustic Waves in AN Inhomogeneous Medium.
NASA Astrophysics Data System (ADS)
Kedzierawski, Andrzej Wladyslaw
1990-01-01
This dissertation considers the inverse scattering problem of determining either the absorption of sound in an inhomogeneous medium or the surface impedance of an obstacle from a knowledge of the far-field patterns of the scattered fields corresponding to many incident time -harmonic plane waves. First, we consider the inverse problem in the case when the scattering object is an inhomogeneous medium with complex refraction index having compact support. Our approach to this problem is the orthogonal projection method of Colton-Monk (cf. The inverse scattering problem for time acoustic waves in an inhomogeneous medium, Quart. J. Mech. Appl. Math. 41 (1988), 97-125). After that, we prove the analogue of Karp's Theorem for the scattering of acoustic waves through an inhomogeneous medium with compact support. We then generalize some of these results to the case when the inhomogeneous medium is no longer of compact support. If the acoustic wave penetrates the inhomogeneous medium by only a small amount then the inverse medium problem leads to the inverse obstacle problem with an impedance boundary condition. We solve the inverse impedance problem of determining the surface impedance of an obstacle of known shape by using both the methods of Kirsch-Kress and Colton-Monk (cf. R. Kress, Linear Integral Equations, Springer-Verlag, New York, 1989).
Local nonlinear rf forces in inhomogeneous magnetized plasmas
Chen, Jiale; Gao, Zhe
2014-06-15
The local nonlinear forces induced by radio frequency (rf) waves are derived in inhomogeneous magnetized plasmas, where the inhomogeneity exists in the rf fields, in the static magnetic field as well as in the equilibrium density and temperature. The local parallel force is completely resonant, but a novel component dependent on those inhomogeneities is obtained as the result of the inhomogeneous transport of parallel resonant-absorbed momentum by the nonlinear perpendicular drift flux. In the local poloidal force, the component induced by the inhomogeneity of rf power absorption is also confirmed and it can be recognized as the residual effect from the incomplete cancellation between the rate of the diamagnetic poloidal momentum gain and the Lorentz force due to the radial diffusion-like flux. The compact expression for radial force is also obtained for the first time, whose nonresonant component is expressed as the sum of the ponderomotive force on particles and the gradients of the nonresonant perpendicular pressure and of the nonresonant momentum flux due to the finite temperature effect. Numerical calculations in a 1-D slab model show that the resonant component dependent on the inhomogeneities may be significant when the ion absorption dominates the resonant wave-particle interaction. A quantitative estimation shows that the novel component in the parallel force is important to understand the experiments of the ion-cyclotron-frequency mode-conversion flow drive.
Defect formation and coarsening in hexagonal 2D curved crystals.
García, Nicolás A; Pezzutti, Aldo D; Register, Richard A; Vega, Daniel A; Gómez, Leopoldo R
2015-02-01
In this work we study the processes of defect formation and coarsening of two-dimensional (2D) curved crystal structures. These processes are found to strongly deviate from their counterparts in flat systems. In curved backgrounds the process of defect formation is deeply affected by the curvature, and at the onset of a phase transition the early density of defects becomes highly inhomogeneous. We observe that even a single growing crystal can produce varying densities of defects depending on its initial position and local orientation with regard to the substrate. This process is completely different from flat space, where grain boundaries are formed due to the impingement of different propagating crystals. Quenching the liquid into the crystal phase leads to the formation of a curved polycrystalline structure, characterized by complex arrays of defects. During annealing, mechanisms of geodesic curvature-driven grain boundary motion and defect annihilation lead to increasing crystalline order. Linear arrays of defects diffuse to regions of high curvature, where they are absorbed by disclinations. At the early stage of coarsening the density of dislocations is insensitive to the geometry while the population of isolated disclinations is deeply affected by curvature. The regions with high curvature act as traps for the diffusion of different structures of defects, including disclinations and domain walls.
Two and Three-Dimensional Nonlocal DFT for Inhomogeneous Fluids I: Algorithms and Parallelization
Frink, Laura J. Douglas; Salinger, Andrew
1999-08-09
Fluids adsorbed near surfaces, macromolecules, and in porous materials are inhomogeneous, inhibiting spatially varying density distributions. This inhomogeneity in the fluid plays an important role in controlling a wide variety of complex physical phenomena including wetting, self-assembly, corrosion, and molecular recognition. One of the key methods for studying the properties of inhomogeneous fluids in simple geometries has been density functional theory (DFT). However, there has been a conspicuous lack of calculations in complex 2D and 3D geometries. The computational difficulty arises from the need to perform nested integrals that are due to nonlocal terms in the free energy functional These integral equations are expensive both in evaluation time and in memory requirements; however, the expense can be mitigated by intelligent algorithms and the use of parallel computers. This paper details our efforts to develop efficient numerical algorithms so that no local DFT calculations in complex geometries that require two or three dimensions can be performed. The success of this implementation will enable the study of solvation effects at heterogeneous surfaces, in zeolites, in solvated (bio)polymers, and in colloidal suspensions.
From random inhomogeneities to periodic nanostructures induced in bulk silica by ultrashort laser
NASA Astrophysics Data System (ADS)
Rudenko, Anton; Colombier, Jean-Philippe; Itina, Tatiana E.
2016-02-01
Femtosecond laser-induced volume nanograting formation is numerically investigated. The developed model solves nonlinear Maxwell's equations coupled with multiple rate free carrier density equations in the presence of randomly distributed inhomogeneities in fused silica. As a result of the performed calculations, conduction band electron density is shown to form nanoplanes elongated perpendicular to the laser polarization. Two types of nanoplanes are identified. The structures of the first type have a characteristic period of the laser wavelength in glass and are attributed to the interference of the incident and the inhomogeneity-scattered light waves. Field components induced by coherent multiple scattering in directions perpendicular to the laser polarization are shown to be responsible for the formation of the second type of structures with a subwavelength periodicity. In this case, the influence of the inhomogeneity concentration on the period of nanoplanes is shown. The calculation results not only help to identify the physical origin of the self-organized nanogratings, but also explain their period and orientation.
Debonding of an elastic inhomogeneity of arbitrary shape in anti-plane shear
NASA Astrophysics Data System (ADS)
Wang, Xu; Yang, Moxuan; Schiavone, Peter
2016-08-01
We investigate the anti-plane shear problem of a curvilinear crack lying along the interface of an arbitrarily shaped elastic inhomogeneity embedded in an infinite matrix subjected to uniform stresses at infinity. Complex variable and conformal mapping techniques are used to derive an analytical solution in series form. The problem is first reduced to a non-homogeneous Riemann-Hilbert problem, the solution of which can be obtained by evaluating the associated Cauchy integral. A set of linear algebraic equations is obtained from the compatibility condition imposed on the resulting analytic function defined in the inhomogeneity and its Faber series expansion. Each of the unknown coefficients in the corresponding analytic functions can then be uniquely determined by solving the linear algebraic equations, which are written concisely in matrix form. The resulting analytical solution is then used to quantify the displacement jump across the debonded section of the interface as well as the traction distribution along the bonded section of the interface. In addition, our solution allows us to obtain mode-III stress intensity factors at the two crack tips. The solution to the anti-plane problem of a partially debonded elliptical inhomogeneity containing a confocal crack is also derived using a similar method.
Elastic fields and moduli in defected graphene.
Dettori, Riccardo; Cadelano, Emiliano; Colombo, Luciano
2012-03-14
By means of tight-binding atomistic simulations we study a family of native defects in graphene which have recently been detected experimentally. Their formation energy is found to be as large as several electronvolts, consistent with the empirical evidence of high crystalline quality in most graphene samples. Defects, especially if associated with bond reconstructions, induce sizable deformation and stress fields with a spatial distribution closely related to their actual symmetry. The description of such fields proposed here is believed to be useful for the unambiguous characterization of images obtained by electron microscopy. We also argue that they define the basin of mutual interaction between two nearby defects. Finally, we provide evidence that defects differently affect the linear elastic moduli of monolayer graphene. In general, both the Young modulus and the Poisson ratio are decreased, but their dependence upon the defect surface density is remarkably more pronounced for vacancy-like than for number-like defects.
Surface defects and temperature on atomic friction.
Fajardo, O Y; Mazo, J J
2011-09-01
We present a theoretical study of the effect of surface defects on atomic friction in the stick-slip dynamical regime of a minimalistic model. We focus on how the presence of defects and temperature change the average properties of the system. We have identified two main mechanisms which modify the mean friction force of the system when defects are considered. As expected, defects change the potential profile locally and thus affect the friction force. But the presence of defects also changes the probability distribution function of the tip slip length and thus the mean friction force. We corroborated both effects for different values of temperature, external load, dragging velocity and damping. We also show a comparison of the effects of surface defects and surface disorder on the dynamics of the system. PMID:21846940
Wafer Mapping Using Deuterium Enhanced Defect Characterization
NASA Astrophysics Data System (ADS)
Hossain, K.; Holland, O. W.; Hellmer, R.; Vanmil, B.; Bubulac, L. O.; Golding, T. D.
2010-07-01
Deuterium (as well as other hydrogen isotopes) binds with a wide range of morphological defects in semiconductors and, as such, becomes distributed similarly to those defects. Thus, the deuterium profile within the sample serves as the basis of a technique for defect mapping known as amethyst wafer mapping (AWM). The efficiency of this technique has been demonstrated by evaluation of ion-induced damage in implanted Si, as well as as-grown defects in HgCdTe (MCT) epilayers. The defect tagging or decoration capability of deuterium is largely material independent and applicable to a wide range of defect morphologies. A number of analytical techniques including ion channeling and etch pit density measurements were used to evaluate the AWM results.
Defects formation and wave emitting from defects in excitable media
NASA Astrophysics Data System (ADS)
Ma, Jun; Xu, Ying; Tang, Jun; Wang, Chunni
2016-05-01
Abnormal electrical activities in neuronal system could be associated with some neuronal diseases. Indeed, external forcing can cause breakdown even collapse in nervous system under appropriate condition. The excitable media sometimes could be described by neuronal network with different topologies. The collective behaviors of neurons can show complex spatiotemporal dynamical properties and spatial distribution for electrical activities due to self-organization even from the regulating from central nervous system. Defects in the nervous system can emit continuous waves or pulses, and pacemaker-like source is generated to perturb the normal signal propagation in nervous system. How these defects are developed? In this paper, a network of neurons is designed in two-dimensional square array with nearest-neighbor connection type; the formation mechanism of defects is investigated by detecting the wave propagation induced by external forcing. It is found that defects could be induced under external periodical forcing under the boundary, and then the wave emitted from the defects can keep balance with the waves excited from external forcing.
SU-E-T-536: Inhomogeneity Correction in Planning of Gamma Knife Treatments for Acoustic Schwannoma
Lu, L; Gupta, N; Hessler, J; Liu, A; Weldon, M; McGregor, J; Ammirati, M; Guiou, M; Xia, F; Grecula, J
2014-06-01
Purpose: To find out the dose difference on targets and organs at risk for the treatment of acoustic schwannoma if the inhomogeneity correction (Convolution algorithm) is applied. Methods: Images of patients treated for acoustic schwannoma with Gamma Knife using TMR 10 algorithm were retrieved from database and replanned with Convolution and TMR 10 algorithm respectively. These patients were treated using a preplan scheme in following: (1) Before the actual treatment day, using the MRI image that was taken without a head frame on the patient's skull, a pre-treatment plan was made based on the default skull coordinates in the Gamma Knife treatment planning system (LGP); (2) then on treatment day, a head frame was placed on the patient's skull, and a CT image was taken. The CT image with head frame was registered and fused with the completed preplan; (3) the treatment plan was finalized and the treatment was delivered. To find out the dosimetry impact of inhomogeneity correction, we used the retrieved CT images to replan the treatment using Convolution algorithm in LGP software version 10.1.1. The dose distributions and the dose volume histograms for targets and OARs were compared for these two dose calculation algorithms. Results: The dose calculated with the Convolution algorithm in general is slightly lower than the one from TMR 10 around the boney area. The effect from the inhomogeneity correction is observable but not significant, and varies with the location of the tumor. Conclusion: Inhomogeneity correction slightly improve the dose accuracy for acoustic schwannoma Gamma Knife treatments although the correction may not be very significant. Our Result provides evidence for dose prescription adjustment to treat acoustic schwannoma. The actual clinical outcome of switching from using TMR10 to using Convolution needs to be further investigated.
THRESHOLD PROBABILITY FUNCTIONS AND THERMAL INHOMOGENEITIES IN THE Ly{alpha} FOREST
Lee, Khee-Gan; Spergel, David N. E-mail: dns@astro.princeton.edu
2011-06-10
We introduce to astrophysics the threshold probability functions S{sub 2}, C{sub 2}, and D{sub 2} first derived by Torquato et al., which effectively samples the flux probability distribution function (PDF) of the Ly{alpha} forest at different spatial scales. These statistics are tested on mock Ly{alpha} forest spectra based on various toy models for He II reionization, with homogeneous models with various temperature-density relations as well as models with temperature inhomogeneities. These mock samples have systematics and noise added to simulate the latest Sloan Digital Sky Survey Data Release 7 (SDSS DR7) data. We find that the flux PDF from SDSS DR7 can be used to constrain the temperature-density relation {gamma} (where T{proportional_to}(1 + {Delta}){sup {gamma}-1}) of the intergalactic medium (IGM) at z = 2.5 to a precision of {Delta}{gamma} = 0.2 at {approx}4{sigma} confidence. The flux PDF is degenerate to temperature inhomogeneities in the IGM arising from He II reionization, but we find S{sub 2} can detect these inhomogeneities at {approx}3{sigma}, with the assumption that the flux continuum of the Ly{alpha} forest can be determined to 9% accuracy, approximately the error from current fitting methods. If the flux continuum can be determined to 3% accuracy, then S{sub 2} is capable of constraining the characteristic scale of temperature inhomogeneities, with {approx}4{sigma} differentiation between toy models with hot bubble radii of 50 h{sup -1} Mpc and 25 h{sup -1} Mpc.
Theoretical analysis of mixing in liquid clouds - Part 3: Inhomogeneous mixing
NASA Astrophysics Data System (ADS)
Pinsky, M.; Khain, A.; Korolev, A.
2015-11-01
An idealized model of time-dependent mixing between cloud and non-cloud volumes is analyzed. Initial droplet size distribution (DSD) in cloud volume is assumed to be monodisperse. Both analytical investigation and parcel model investigation are used to study mixing processes and solve diffusion-evaporation equations. It is shown that the evolution of microphysical variables and the final equilibrium stage are unambiguously determined by two non-dimensional parameters. The first parameter, R, which is proportional to the ratio of the saturation deficit to the liquid water content in a cloud volume, determines whether the equilibrium stage is reached at 100 % relative humidity, or, rather, leads to a full evaporation of cloud droplets. The second parameter, Da, is the Damkölher number, which is equal to the ratio of the characteristic mixing time and phase relaxation time. This parameter (together with parameter R) determines whether mixing takes place according to a homogeneous or an inhomogeneous scenario. An analysis of the results obtained within a wide range of parameters R and Da is presented. It is shown that there is no pure homogeneous mixing, since the first stage of mixing is always inhomogeneous. Turbulent mixing between different volumes always starts as inhomogeneous and the mixing type can change during the mixing process. At any values of governing parameters, mixing leads to the formation of a tail of small droplets in the DSD and therefore to DSD broadening. The broadening depends onDa and the final DSD dispersion can be as large as 0.2 at large Da. The total duration of the mixing process varies from several to one hundred phase relaxation times, depending on R and Da. Delimitation between the types of mixing on the Da-R plane is carried out. The definitions of homogeneous and inhomogeneous mixings are reconsidered and clarified. The paper also compares the results of the current study with those obtained with classical mixing concepts.
Ardakani, Abbas Ghasempour; Mahdavi, Seyed Mohammad; Bahrampour, Ali Reza
2013-02-20
Time-dependent model is presented to simulate random lasers in the presence of an inhomogeneous gain medium. PbSe quantum dots (QDs) with an arbitrary size distribution are treated as an inhomogeneous gain medium. By introducing inhomogeneity of the PbSe QDs in polarization, rate, and Maxwell's equations, our model is constructed for a one-dimensional disordered system. By employing the finite difference time-domain method, the governing equations are numerically solved and lasing spectra and spatial distribution of the electric field are calculated. The effect of increasing the pumping rate on the laser characteristics is investigated. The results show that the number of lasing modes and their intensities increase with pumping rate. It is also demonstrated that the emission spectra depend on the standard deviation of the Gaussian distribution function. Increasing the standard deviation leads to reduction of the laser intensity.
... chromosomal disorder or heart defect in the baby. Second Trimester Screening Second trimester screening tests are completed between weeks 15 ... look for certain birth defects in the baby. Second trimester screening tests include a maternal serum screen ...
NASA Astrophysics Data System (ADS)
Fujita, Kohei; Egami, Chikara
2015-06-01
Polarization interferometric confocal microscope has been developed for high-precision measurement, especially for inhomogeneous organic media doped with nonlinear chromophores. The microscope has a novel contrast-enhancing technique: suppressing the background electric field with polarization interferometer. With this technique, the microscope has allowed optical anisotropy detection in a submicron area (400 nm × 400 nm), even with a low-cost and low-power continuous-wave (CW) laser light source. In particular, the microscope clearly distinguishes between isotropic and anisotropic regions. According to polarization interferometric ellipsometry, the microscope produces inspection images showing planer distribution of the optical parameter directly.
Windowed and Wavelet Analysis of Marine Stratocumulus Cloud Inhomogeneity
NASA Technical Reports Server (NTRS)
Gollmer, Steven M.; Harshvardhan; Cahalan, Robert F.; Snider, Jack B.
1995-01-01
To improve radiative transfer calculations for inhomogeneous clouds, a consistent means of modeling inhomogeneity is needed. One current method of modeling cloud inhomogeneity is through the use of fractal parameters. This method is based on the supposition that cloud inhomogeneity over a large range of scales is related. An analysis technique named wavelet analysis provides a means of studying the multiscale nature of cloud inhomogeneity. In this paper, the authors discuss the analysis and modeling of cloud inhomogeneity through the use of wavelet analysis. Wavelet analysis as well as other windowed analysis techniques are used to study liquid water path (LWP) measurements obtained during the marine stratocumulus phase of the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment. Statistics obtained using analysis windows, which are translated to span the LWP dataset, are used to study the local (small scale) properties of the cloud field as well as their time dependence. The LWP data are transformed onto an orthogonal wavelet basis that represents the data as a number of times series. Each of these time series lies within a frequency band and has a mean frequency that is half the frequency of the previous band. Wavelet analysis combined with translated analysis windows reveals that the local standard deviation of each frequency band is correlated with the local standard deviation of the other frequency bands. The ratio between the standard deviation of adjacent frequency bands is 0.9 and remains constant with respect to time. This ratio defined as the variance coupling parameter is applicable to all of the frequency bands studied and appears to be related to the slope of the data's power spectrum. Similar analyses are performed on two cloud inhomogeneity models, which use fractal-based concepts to introduce inhomogeneity into a uniform cloud field. The bounded cascade model does this by iteratively redistributing LWP at each scale
Duralumin - Defects and Failures
NASA Technical Reports Server (NTRS)
Nelson, WM
1927-01-01
It is proposed in this paper to identify some of the defects and failures in duralumin most frequently encountered by the aircraft industry with a view to indicate their importance. The defects and failures in duralumin may be classified into the following groups: 1) defects produced during manufacture; 2) defects produced during fabrication; 3) corrosion and erosion; and 4) fatigue failures. Only the first two will be covered in this report.
SPIN-TORQUE IN SYSTEMS WITH INHOMOGENEOUS MAGETIZATION
Zangwill, Andrew
2013-04-23
The work performed during the grant period focused on the phenomenon of spin-transfer torque. This is a quantum mechanical effect whereby the angular momentum of conduction electrons is transferred to the magnetization of ferromagnetic structures. Our work on this subject began with phenomenological drift-diffusion and Landau-Lifshitz-Gilbert equations to demonstrate unambiguously that unpolarized current flow from a nonmagnet into a ferromagnet can produce a precession-type instability of the magnetization. We then used Boltzmann calculations appropriate to spin-valve type magnetic heterostructures composed of a non-magnetic thin film sandwiched between two thin film layers with uniform magnetization. Perhaps our most important paper dealt with quantum and semi-classical calculations of spin-transfer torque in systems with domain walls and other inhomogeneous distributions of magnetization. The latter work caused us to suggest that the Landau-Lifshitz approach to magnetic damping provided a clearer picture of the physics than the more popular (but formally equivalent) Gilbert approach to damping. Finally, we returned to our Boltzmann calculations and made a serious effort to analyze experimental data on current-induced magnetization in switching in magnetic spin-valve structures. Our work was part of a world-wide effort to study and harness the transport of the electron's spin and was one of the first sustained theoretical efforts in this direction in the United States. The payoff is just now being seen. In November of 2012, the Everspin Corporation announced the release of the first commercial spin-torque magnetoresistive random access memory.
Microstructural Inhomogeneity of Electrical Conductivity in Subcutaneous Fat Tissue
Kruglikov, Ilja L.
2015-01-01
Microscopic peculiarities stemming from a temperature increase in subcutaneous adipose tissue (sWAT) after applying a radio-frequency (RF) current, must be strongly dependent on the type of sWAT. This effect is connected with different electrical conductivities of pathways inside (triglycerides in adipocytes) and outside (extra-cellular matrix) the cells and to the different weighting of these pathways in hypertrophic and hyperplastic types of sWAT. The application of the RF current to hypertrophic sWAT, which normally has a strongly developed extracellular matrix with high concentrations of hyaluronan and collagen in a peri-cellular space of adipocytes, can produce, micro-structurally, a highly inhomogeneous temperature distribution, characterized by strong temperature gradients between the peri-cellular sheath of the extra-cellular matrix around the hypertrophic adipocytes and their volumes. In addition to normal temperature effects, which are generally considered in body contouring, these temperature gradients can produce thermo-mechanical stresses on the cells’ surfaces. Whereas these stresses are relatively small under normal conditions and cannot cause any direct fracturing or damage of the cell structure, these stresses can, under some supportive conditions, be theoretically increased by several orders of magnitude, causing the thermo-mechanical cell damage. This effect cannot be realized in sWAT of normal or hyperplastic types where the peri-cellular structures are under-developed. It is concluded that the results of RF application in body contouring procedures must be strongly dependent on the morphological structure of sWAT. PMID:25734656
Inverse scattering problems for acoustic waves in an inhomogeneous medium
NASA Astrophysics Data System (ADS)
Kedzierawski, Andrzej Wladyslaw
The inverse scattering problem is considered of determining either the absorption of sound in an inhomogeneous medium or the surface impedance of an obstacle from a knowledge of the far field patterns of the scattered field corresponding to many incident time-harmonic plane waves. First, the inverse problem is studied in the case when the scattering object is an inhomogeneous medium with complex refractive index having compact support. The approach to this problem is the orthogonal projection method of Colton-Monk (1988). After that, the analogue is proven of Karp's Theorem for the scattering of acoustic waves through an inhomogeneous medium with compact support. Some of these results are then generalized to the case when the inhomogeneous medium is no longer of compact support. If the acoustic wave penetrates the inhomogeneous medium by only a small amount then the inverse medium problem leads to the inverse obstacle problem with an impedance boundary condition. The inverse impedance problem is solved of determining the surface impedance of an obstacle of known shape by using both the methods of Kirsch-Kress and Colton-Monk (1989).
Interaction between noise suppression and inhomogeneity correction in MRI
NASA Astrophysics Data System (ADS)
Montillo, Albert; Udupa, Jayaram K.; Axel, Leon; Metaxas, Dimitri N.
2003-05-01
While cardiovascular disease is the leading cause of death in most developed countries, SPAMM-MRI can reduce morbidity by facilitating patient diagnosis. An image analysis method with a high degree of automation is essential for clinical adoption of SPAMM-MRI. The degree of this automation is dependent on the amount of thermal noise and surface coil-induced intensity inhomogeneity that can be removed from the images. An ideal noise suppression algorithm removes thermal noise yet retains or enhances the strength of the edges of salient structures. In this paper, we quantitatively compare and rank several noise suppression algorithms in images from both normal and diseased subjects using measures of the residual noise and edge strength and the statistical significance levels and confidence intervals of these measures. We also investigate the interrelationship between inhomogeneity correction and noise suppression algorithms and compare the effect of the ordering of these algorithms. The variance of thermal noise does not tend to change with position, however, inhomogeneity correction increases noise variance in deep thoracic regions. We quantify the degree to which an inhomogeneity estimate can improve noise suppression and how well noise suppression can facilitate the identification of homogeneous tissue regions and thereby, assist in inhomogeneity correction.
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Studying post-etching silicon crystal defects on 300mm wafer by automatic defect review AFM
NASA Astrophysics Data System (ADS)
Zandiatashbar, Ardavan; Taylor, Patrick A.; Kim, Byong; Yoo, Young-kook; Lee, Keibock; Jo, Ahjin; Lee, Ju Suk; Cho, Sang-Joon; Park, Sang-il
2016-03-01
Single crystal silicon wafers are the fundamental elements of semiconductor manufacturing industry. The wafers produced by Czochralski (CZ) process are very high quality single crystalline materials with known defects that are formed during the crystal growth or modified by further processing. While defects can be unfavorable for yield for some manufactured electrical devices, a group of defects like oxide precipitates can have both positive and negative impacts on the final device. The spatial distribution of these defects may be found by scattering techniques. However, due to limitations of scattering (i.e. light wavelength), many crystal defects are either poorly classified or not detected. Therefore a high throughput and accurate characterization of their shape and dimension is essential for reviewing the defects and proper classification. While scanning electron microscopy (SEM) can provide high resolution twodimensional images, atomic force microscopy (AFM) is essential for obtaining three-dimensional information of the defects of interest (DOI) as it is known to provide the highest vertical resolution among all techniques [1]. However AFM's low throughput, limited tip life, and laborious efforts for locating the DOI have been the limitations of this technique for defect review for 300 mm wafers. To address these limitations of AFM, automatic defect review AFM has been introduced recently [2], and is utilized in this work for studying DOI on 300 mm silicon wafer. In this work, we carefully etched a 300 mm silicon wafer with a gaseous acid in a reducing atmosphere at a temperature and for a sufficient duration to decorate and grow the crystal defects to a size capable of being detected as light scattering defects [3]. The etched defects form a shallow structure and their distribution and relative size are inspected by laser light scattering (LLS). However, several groups of defects couldn't be properly sized by the LLS due to the very shallow depth and low
NASA Astrophysics Data System (ADS)
Zinchik, Alexander A.; Muzychenko, Yana B.
2015-06-01
This paper discusses theoretical and experimental results of the investigation of light beams that retain their intensity structure during propagation and focusing. Spiral laser beams are a family of laser beams that preserve the structural stability up to scale and rotation with the propagation. Properties of spiral beams are of practical interest for laser technology, medicine and biotechnology. Researchers use a spiral beams for movement and manipulation of microparticles. Functionality laser manipulators can be significantly enhanced by using spiral beams whose intensity remains invariable. It is well known, that these beams has non-zero orbital angular momentum. Spiral beams have a complicated phase distribution in cross section. In this paper we investigate the structural stability of the laser beams having a spiral phase structure by passing them through an inhomogeneous phase medium. Laser beam is passed through a medium is characterized by a random distribution of phase in the range 0..2π. The modeling was performed using VirtualLab 5.0 (manufacturer LightTrans GmbH). Compared the intensity distribution of the spiral and ordinary laser beam after the passage of the inhomogeneous medium. It is shown that the spiral beams exhibit a significantly better structural stability during the passage phase heterogeneous environments than conventional laser beams. The results obtained in the simulation are tested experimentally. Experimental results show good agreement with the theoretical results.
Reduction of solar cell efficiency by bulk defects across the back-surface-field junction
NASA Technical Reports Server (NTRS)
Sah, C. T.; Yamakawa, K. A.; Lutwack, R.
1982-01-01
The degradation of solar cell performance due to bulk defects distributed across the back-surface field junction is analyzed in terms of a three-region developed-perimeter model. Families of curves are computed and their physical significance is discussed in detail with reference to three parameters used to characterize the defects: defect area, defect density, and defect surface recombination velocity. A reduction in the open-circuit voltage due to the presence of a defect is expressed as a function of the defect area, density, cell thickness, and defect surface recombination velocity. Numerical examples are presented to illustrate the importance of the particular defect parameters.
NASA Astrophysics Data System (ADS)
Caineta, Júlio; Ribeiro, Sara; Costa, Ana Cristina; Henriques, Roberto; Soares, Amílcar
2014-05-01
Climate data homogenisation is of major importance in monitoring climate change, the validation of weather forecasting, general circulation and regional atmospheric models, modelling of erosion, drought monitoring, among other studies of hydrological and environmental impacts. This happens because non-climate factors can cause time series discontinuities which may hide the true climatic signal and patterns, thus potentially bias the conclusions of those studies. In the last two decades, many methods have been developed to identify and remove these inhomogeneities. One of those is based on geostatistical simulation (DSS - direct sequential simulation), where local probability density functions (pdf) are calculated at candidate monitoring stations, using spatial and temporal neighbouring observations, and then are used for detection of inhomogeneities. This approach has been previously applied to detect inhomogeneities in four precipitation series (wet day count) from a network with 66 monitoring stations located in the southern region of Portugal (1980-2001). This study revealed promising results and the potential advantages of geostatistical techniques for inhomogeneities detection in climate time series. This work extends the case study presented before and investigates the application of the geostatistical stochastic approach to ten precipitation series that were previously classified as inhomogeneous by one of six absolute homogeneity tests (Mann-Kendall test, Wald-Wolfowitz runs test, Von Neumann ratio test, Standard normal homogeneity test (SNHT) for a single break, Pettit test, and Buishand range test). Moreover, a sensibility analysis is implemented to investigate the number of simulated realisations that should be used to accurately infer the local pdfs. Accordingly, the number of simulations per iteration is increased from 50 to 500, which resulted in a more representative local pdf. A set of default and recommended settings is provided, which will help
Orientational defects near colloidal particles in a nematic liquid crystal.
Feng, James J; Zhou, Chixing
2004-01-01
We study the interaction between a surface-anchoring colloidal particle and a liquid-crystalline host, and in particular the formation of orientational defects near the particle. A mean-field theory based on the nonlocal Marrucci-Greco nematic potential is used to represent molecular interactions in an inhomogeneous orientational field. An evolution equation for the molecular configuration tensor is solved numerically whose steady state minimizes the total free energy of the system. With strong homeotropic anchoring on the particle surface, three types of solutions may appear depending on initial conditions and particle size: Saturn rings, satellite point defects, and polar rings. The Saturn ring remains stable on micrometer-sized particles, contrary to previous calculations but consistent with experiments. A phase diagram is constructed for the three regimes. Based on the free energy, the most stable state is the Saturn ring for smaller particles and the satellite defect for larger ones.
Characteristics of inhomogeneous jets in confined swirling air flows
NASA Technical Reports Server (NTRS)
So, R. M. C.; Ahmed, S. A.
1984-01-01
An experimental program to study the characteristics of inhomogeneous jets in confined swirling flows to obtain detailed and accurate data for the evaluation and improvement of turbulent transport modeling for combustor flows is discussed. The work was also motivated by the need to investigate and quantify the influence of confinement and swirl on the characteristics of inhomogeneous jets. The flow facility was constructed in a simple way which allows easy interchange of different swirlers and the freedom to vary the jet Reynolds number. The velocity measurements were taken with a one color, one component DISA Model 55L laser-Doppler anemometer employing the forward scatter mode. Standard statistical methods are used to evaluate the various moments of the signals to give the flow characteristics. The present work was directed at the understanding of the velocity field. Therefore, only velocity and turbulence data of the axial and circumferential components are reported for inhomogeneous jets in confined swirling air flows.
Inhomogeneous models of the Venus clouds containing sulfur
NASA Technical Reports Server (NTRS)
Smith, S. M.; Pollack, J. B.; Giver, L. P.; Cuzzi, J. N.; Podolak, M.
1979-01-01
Based on the suggestion that elemental sulfur is responsible for the yellow color of Venus, calculations are compared at 3.4 microns of the reflectivity phase function of two sulfur containing inhomogeneous cloud models with that of a homogeneous model. Assuming reflectivity observations with 25% or less total error, comparison of the model calculations leads to a minimum detectable mass of sulfur equal to 7% of the mass of sulfuric acid for the inhomogeneous drop model. For the inhomogeneous cloud model the comparison leads to a minimum detectable mass of sulfur between 17% and 38% of the mass of the acid drops, depending upon the actual size of the large particles. It is concluded that moderately accurate 3.4 microns reflectivity observations are capable of detecting quite small amounts of elemental sulfur at the top of the Venus clouds.
Symmetry Analysis of Thermoelectric Energy Converters with Inhomogeneous Legs
NASA Astrophysics Data System (ADS)
Korzhuev, M. A.
2010-09-01
Symmetry analysis has been applied to thermoelectric energy converters [thermoelectric generators (TEG), coolers (TEC), and heaters (TEH)] with inhomogeneous legs. The features of the crystallographic symmetry of thermoelectric materials and the symmetry of legs, thermocouples, and modules are studied. The effect of symmetry on the figure of merit Z of thermoelectric energy converters is considered. A general rule for proper placement of legs in thermoelectric converters is developed. A modified tetratomic classification for thermoelectric energy converters with inhomogeneous legs (TEGa, TEGb, TEC, and TEH) is proposed. An increase in Z for thermoelectric energy converters with inhomogeneous legs is due to the bulk thermoelectric effect. An increase in Z gives the reduction of irreversible processes in the modules (Joule heating and thermal conductivity), accompanying breaking of the symmetry of the legs. It is found that violations of the symmetry requirements can lead to significant energy losses in converters.
Generalized Langevin theory for inhomogeneous fluids: The equations of motion
NASA Astrophysics Data System (ADS)
Grant, Martin; Desai, Rashmi C.
1982-05-01
We use the generalized Langevin approach to study the dynamical correlations in an inhomogeneous system. The equations of motion (formally exact) are obtained for the number density, momentum density, energy density, stress tensor, and heat flux. We evaluate all the relevant sum rules appearing in the frequency matrix exactly in terms of microscopic pair potentials and an external field. We show using functional derivatives how these microscopic sum rules relate to more familiar, though now nonlocal, hydrodynamiclike quantities. The set of equations is closed by a Markov approximation in the equations for stress tensor and heat flux. As a result, these equations become analogous to Grad's 13-moment equations for low-density fluids and constitute a generalization to inhomogeneous fluids of the work of Schofield and Akcasu-Daniels. We also indicate how the resulting general set of equations would simplify for systems in which the inhomogeneity is unidirectional, e.g., a liquid-vapor interface.
Inhomogeneous stationary and oscillatory regimes in coupled chaotic oscillators.
Liu, Weiqing; Volkov, Evgeny; Xiao, Jinghua; Zou, Wei; Zhan, Meng; Yang, Junzhong
2012-09-01
The dynamics of linearly coupled identical Lorenz and Pikovsky-Rabinovich oscillators are explored numerically and theoretically. We concentrate on the study of inhomogeneous stable steady states ("oscillation death (OD)" phenomenon) and accompanying periodic and chaotic regimes that emerge at an appropriate choice of the coupling matrix. The parameters, for which OD occurs, are determined by stability analysis of the chosen steady state. Three model-specific types of transitions to and from OD are observed: (1) a sharp transition to OD from a nonsymmetric chaotic attractor containing random intervals of synchronous chaos; (2) transition to OD from the symmetry-breaking chaotic regime created by negative coupling; (3) supercritical bifurcation of OD into inhomogeneous limit cycles and further evolution of the system to inhomogeneous chaotic regimes that coexist with complete synchronous chaos. These results may fill a gap in the understanding of the mechanism of OD in coupled chaotic systems.
Automatic determination of the optical constants of inhomogeneous thin films.
Borgogno, J P; Lazarides, B; Pelletier, E
1982-11-15
The refractive index of a layer is a sensitive function of the preparation conditions. Normal incidence measurement of the optical properties can reveal possible inhomogeneity of index. We propose a method of automatic determination of the complex refractive index and thickness of a layer which includes systematic measurement of the degree of inhomogeneity which is represented by a simple model. The usefulness of the technique is demonstrated by examples that form part of an experimental study of a number of useful optical materials including Y(2)O(3), TiO(2), MgF(2), HfO(2), and SiO(2). The dispersions of the refractive index, the extinction coefficient, and of the inhomogeneity are represented by Cauchy formulas with accurately determined coefficients. The results can therefore be readily used in computing the optical properties of thin-film multilayers.
Radiation from accelerated Alfven solitons in inhomogeneous plasmas
NASA Technical Reports Server (NTRS)
Lakhina, G. S.; Buti, B.; Tsintsadze, N. L.
1990-01-01
In a weakly inhomogeneous plasma, the large-amplitude Alfven waves propagating parallel to the ambient magnetic field are shown to evolve into accelerated Alfven solitons. Nonlinear interaction of the accelerated Alfven solitons with the Langmuir waves results in the emission of coherent radiations. Analytical expression for the power radiated per unit solid angle from a soliton is derived for two inhomogeneity profiles, namely the linear profile and the parabolic profile. For the case of uniform plasmas, the emission occurs via a decay-type process or resonant modes. In the presence of inhomogeneity, nonresonant modes provide a new channel for the emission of radiation. The power radiated per unit solid angle is computed for the parameters relevant to Comet Halley's plasma environment. For the nonresonant modes it is found to be several orders of magnitude higher than that for the case of resonant modes.
Zinkle, S.J.; Kinoshita, C.
1997-08-01
A review is given of several important defect production and accumulation parameters for irradiated ceramics. Materials covered in this review include alumina, magnesia, spinel silicon carbide, silicon nitride, aluminum nitride and diamond. Whereas threshold displacement energies for many ceramics are known within a reasonable level of uncertainty (with notable exceptions being AIN and Si{sub 3}N{sub 4}), relatively little information exists on the equally important parameters of surviving defect fraction (defect production efficiency) and point defect migration energies for most ceramics. Very little fundamental displacement damage information is available for nitride ceramics. The role of subthreshold irradiation on defect migration and microstructural evolution is also briefly discussed.
Postdevelopment defect evaluation
NASA Astrophysics Data System (ADS)
Miyahara, Osamu; Kiba, Yukio; Ono, Yuko
2001-08-01
Reduction of defects after development is a critical issue in photolithography. A special category of post development defects is the satellite defect which is located in large exposed areas generally in proximity to large unexposed regions of photoresist. We have investigated the formation of this defect type on ESCAP and ACETAL DUV resists with and without underlying organic BARCs, In this paper, we will present AFM and elemental analysis data to determine the origin of the satellite defect. Imaging was done on a full-field Nikon 248nm stepper and resist processing was completed on a TEL CLEAN TRACK ACT 8 track. Defect inspection and review were performed on a KLA-Tencor and Hitachi SEM respectively. Results indicate that the satellite defect is generated on both BARC and resist films and defect counts are dependent on the dark erosion. Elemental analysis indicates that the defects are composed of sulfur and nitrogen compounds. We suspect that the defect is formed as a result of a reaction between PAG, quencher and TMAH. This defect type is removed after a DIW re-rinse.
Cosmological structure formation from soft topological defects
NASA Technical Reports Server (NTRS)
Hill, Christopher T.; Schramm, David N.; Fry, J. N.
1988-01-01
Some models have extremely low-mass pseudo-Goldstone bosons that can lead to vacuum phase transitions at late times, after the decoupling of the microwave background.. This can generate structure formation at redshifts z greater than or approx 10 on mass scales as large as M approx 10 to the 18th solar masses. Such low energy transitions can lead to large but phenomenologically acceptable density inhomogeneities in soft topological defects (e.g., domain walls) with minimal variations in the microwave anisotropy, as small as delta Y/T less than or approx 10 to the minus 6 power. This mechanism is independent of the existence of hot, cold, or baryonic dark matter. It is a novel alternative to both cosmic string and to inflationary quantum fluctuations as the origin of structure in the Universe.
NASA Astrophysics Data System (ADS)
da Silva-Araújo, Joice; Nascimento, A. J. M.; Chacham, Hélio; Nunes, R. W.
2013-01-01
We perform ab initio calculations for the strain-induced formation of non-hexagonal-ring defects in graphene, graphane (hydrogen-functionalized graphene) and graphenol (hydroxyl-functionalized graphene). We find that the simplest of such topological defects, the Stone-Wales defect, acts as a seed for strain-induced dissociation and multiplication of topological defects. Through the application of inhomogeneous deformations to graphene, graphane and graphenol with varying initial concentrations of pentagonal and heptagonal rings and small-sized voids, we obtain several novel stable structures that possess, at the same time, large concentrations of non-hexagonal rings (from fourfold to elevenfold) and small formation energies.
Identification of the topological defects of optical indicatrix orientation in CaB4O7 glasses
NASA Astrophysics Data System (ADS)
Vasylkiv, Yu; Skab, I.; Vlokh, R.
2016-08-01
We develop an experimental method for the identification of the topological defects of optical indicatrix orientation, which appear in glass samples with residual mechanical stresses. The criteria needed to determine the sign of the strength of topological defects are formulated. The method is verified on the example of a non-annealed CaB4O7 glass sample that manifests spatially inhomogeneous residual stresses. We have found that at least seven topological defects of optical indicatrix orientation exist under the condition when a light beam propagates through a parallelepiped-shaped glass sample. The strengths of all the defects detected by us are equal to +1/2.
Bending of solitons in weak and slowly varying inhomogeneous plasma
Mukherjee, Abhik Janaki, M. S. Kundu, Anjan
2015-12-15
The bending of solitons in two dimensional plane is presented in the presence of weak and slowly varying inhomogeneous ion density for the propagation of ion acoustic soliton in unmagnetized cold plasma with isothermal electrons. Using reductive perturbation technique, a modified Kadomtsev-Petviashvili equation is obtained with a chosen unperturbed ion density profile. The exact solution of the equation shows that the phase of the solitary wave gets modified by a function related to the unperturbed inhomogeneous ion density causing the soliton to bend in the two dimensional plane, while the amplitude of the soliton remains constant.
Heteronuclear J-coupling measurements in grossly inhomogeneous magnetic fields.
Mandal, S; Song, Y-Q
2015-06-01
It is difficult to measure chemical shifts in the small and inhomogeneous magnetic fields found in ex situ and single-sided NMR systems, such as those used for well-logging. However, it is still possible to obtain chemical information from J-coupling constants, which are independent of static field strength and temperature. We describe and analyze (1)H-(13)C double-resonance pulse sequences that are suitable for measuring heteronuclear J-coupling in grossly inhomogeneous fields. We also present preliminary experimental results from a low-frequency fringe-field system. PMID:25898398
Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields.
Karlsen, Jonas T; Augustsson, Per; Bruus, Henrik
2016-09-01
We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip. PMID:27661695
Possible effect of subsurface inhomogeneities on the lunar microwave spectrum
NASA Technical Reports Server (NTRS)
Fisher, A. D.; Staelin, D. H.
1977-01-01
Inhomogeneities beneath the lunar surface could alter the average microwave emission spectrum of the moon in a fashion generally consistent with observations, even in the absence of an average heat flux or density gradients with depth. The lunar subsurface was modeled as an inhomogeneous lossy dielectric with three-dimensional refractive-index fluctuations characterized by independent horizontal and vertical correlation lengths. The model suggests that attempts to infer the physical properties of the moon from the lunar microwave spectrum could be significantly inaccurate if subsurface scattering were neglected.
A theoretical model of barriers having inhomogeneous impedance surfaces.
Wang, Xu; Wang, Xiaonan; Yu, Wuzhou; Jiang, Zaixiu; Mao, Dongxing
2016-03-01
When barriers are placed in parallel on opposite sides of a source, their performance deteriorates markedly. However, barriers made from materials of inhomogeneous impedance eliminate this drawback by altering the behavior of sound as it undergoes multiple reflections between the barriers. In this paper, a theoretical approach is carried out to estimate the performance of the proposed barriers. By combining the ray-tracing method and sound diffraction theory, the existence of different ray paths between the proposed barriers is revealed. Compared to conventional rigid-walled barriers, barriers having inhomogeneous surfaces may have the potential to be widely used in environmental noise control. PMID:27036289
Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields.
Karlsen, Jonas T; Augustsson, Per; Bruus, Henrik
2016-09-01
We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip.
Deep and Clear Optical Imaging of Thick Inhomogeneous Samples
Andilla, Jordi; Maandhui, Amina; Frongia, Céline; Lobjois, Valérie; Ducommun, Bernard; Lorenzo, Corinne
2012-01-01
Inhomogeneity in thick biological specimens results in poor imaging by light microscopy, which deteriorates as the focal plane moves deeper into the specimen. Here, we have combined selective plane illumination microscopy (SPIM) with wavefront sensor adaptive optics (wao). Our waoSPIM is based on a direct wavefront measure using a Hartmann-Shack wavefront sensor and fluorescent beads as point source emitters. We demonstrate the use of this waoSPIM method to correct distortions in three-dimensional biological imaging and to improve the quality of images from deep within thick inhomogeneous samples. PMID:22558226
Sublattice model of atomic scale pairing inhomogeneity in a superconductor
NASA Astrophysics Data System (ADS)
Mishra, Vivek; Hirschfeld, P. J.; Barash, Yuri S.
2008-03-01
We study a toy model for a superconductor on a bipartite lattice, where intrinsic microscopic inhomogeneity is produced by two different pairing coupling constants on each sublattice. We consider effects of the inhomogeneity on the transition temperature, the density of states, the specific heat and superfluid density in the framework of the Bogoliubov-de Gennes equations, which may be solved analytically in several interesting cases. The phase diagram in the plane of two pairing coupling constants is found to include a state of gapless superconductivity.
Optical Dephasing by Defects in Crystalline Solids
NASA Astrophysics Data System (ADS)
Jang, Ki-Wan
Two pulse photon echo (TPPE) and hole burning techniques are used in the study of the effect of defects on the optical dephasing in crystalline materials for various types of defects. From a optical dephasing study of the ^7F_0 rightarrow ^5D_0 transition of Eu^ {3+} ions doped in a number of crystalline fibers of rm Y_2O_3 prepared by three different crystal-growth techniques, it is shown that the optical dephasing rate, 1/T _{m} (T_{m}: phase memory time), of crystals prepared by laser heated pedestal growth (LHPG) or arc-imaging furnace at 1.4K is up to two orders of magnitude faster than that of a crystal grown by the flame fusion and that its linear temperature dependence is similar to that in highly disordered system such as glass. However, other optical spectroscopic properties such as the lifetime, or inhomogeneous linewidth are similar to that of the flame fusion crystal. Nevertheless, the fact that the optical dephasing depends linearly on temperature suggests that the optical dephasing may be attributed to disorder present in the samples resulting in an additional dephasing due to local configurational changes. In relation to defects in samples, the study of the optical dephasing of the ^7F _0 rightarrow ^5D_0 transition of Eu^{3+} ions doped in the disordered system rm Y_{2-x}Sc_{x}O_3 (2% Eu, x = 0.04, 0.3, 1 and 0.2% Eu, x = 0.04) shows that the optical dephasing and its temperature behavior are similar to that in the flame fusion crystal and that the optical dephasing is uncorrelated with the inhomogeneous linewidth of the samples studied. This means that Sc ^{3+} ions may remove the TLS type of the optical dephasing observed in pure rm Y_2O_3 fibers, perhaps by stabilizing the stoichiometry. The optical dephasing in YSZ with a high concentration of defects due to oxygen vacancies is faster, by up to three orders of magnitude, than that of YScO_3 (x = 1) in spite of a similar inhomogeneous linewidth. Hole spectra via a hole burning experiment shows
NASA Astrophysics Data System (ADS)
Kol'tsov, A. V.; Serov, Alexander V.
1995-03-01
A theoretical investigation is made of the time dependence of the spatial distribution of particles injected perpendicular to the direction of propagation of a linearly polarised inhomogeneous electromagnetic wave and reflected by this wave. It is shown that such reflection modulates the particle density in a beam which is homogeneous at injection. Stimulated emission of radiation from a ribbon electron beam reflected by a wave is considered. The spectral—angular and polarisation characteristics of such radiation are investigated.
Koltsov, A.V.; Serov, A.V.
1995-12-31
The generation of frequency harmonics of a radiation when the electron beam traverse the inhomogeneous electromagnetic wave was investigated. The electromagnetic wave are linearly polarized. The plane beam of particles enters the wave at right angle with respect to the direction of propogation of the wave and the vector E of the wave. The spartial distribution of radiation from the higher harmonics and the power density contours are caculated.
NASA Astrophysics Data System (ADS)
Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W.
2016-06-01
Photoluminescence (PL) properties of semi-insulating Tl6SeI4 have been investigated. A broad emission band centered at 1.63 ± 0.02 eV was observed in all samples. The PL emission band is excitonic in nature and is tentatively attributed to a bound exciton emission. PL fatigue (a reduction in PL intensity under prolonged laser excitation) was always observed. The amount of PL fatigue depended on excitation power and temperature. PL fatigue kinetics are described by a stretched exponential with nominal lifetimes in the 10–265 s range. The recovery of the PL occurred within a few seconds of light cessation. The magnitude of PL fatigue in different samples correlated with inhomogeneous line broadening of the 1.63 eV emission band, such that broader bands exhibited more fatigue. An additional luminescence band centered at 1.78 eV was observed which increased in intensity under prolonged laser irradiation. The fatigue phenomenon is tentatively attributed to two mechanisms—the formation of photo-induced defects and the formation of quasi-stable particles. Both of these mechanisms introduce additional radiative and non-radiative recombination channels that lead to a decrease in the PL intensity under prolonged laser irradiation. Since inhomogeneous line broadening and PL fatigue are related to the concentration of defects or impurities, the measurement of these two parameters is an effective method to screen sample quality.
NASA Astrophysics Data System (ADS)
Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W.
2016-06-01
Photoluminescence (PL) properties of semi-insulating Tl6SeI4 have been investigated. A broad emission band centered at 1.63 ± 0.02 eV was observed in all samples. The PL emission band is excitonic in nature and is tentatively attributed to a bound exciton emission. PL fatigue (a reduction in PL intensity under prolonged laser excitation) was always observed. The amount of PL fatigue depended on excitation power and temperature. PL fatigue kinetics are described by a stretched exponential with nominal lifetimes in the 10-265 s range. The recovery of the PL occurred within a few seconds of light cessation. The magnitude of PL fatigue in different samples correlated with inhomogeneous line broadening of the 1.63 eV emission band, such that broader bands exhibited more fatigue. An additional luminescence band centered at 1.78 eV was observed which increased in intensity under prolonged laser irradiation. The fatigue phenomenon is tentatively attributed to two mechanisms—the formation of photo-induced defects and the formation of quasi-stable particles. Both of these mechanisms introduce additional radiative and non-radiative recombination channels that lead to a decrease in the PL intensity under prolonged laser irradiation. Since inhomogeneous line broadening and PL fatigue are related to the concentration of defects or impurities, the measurement of these two parameters is an effective method to screen sample quality.
Charge transport through inhomogeneous polymeric materials
NASA Astrophysics Data System (ADS)
Vakhshouri, Kiarash
The generation of unique properties through mixing of organic semiconductors has enabled improved performance and novel functionalities in organic electronic devices. In organic light emitting diodes (OLEDs), isolated phases of a second material within the photoactive layer can act as recombination centers, enhancing the overall device performance. Mixing of flexible polymer semiconductors with high-mobility small organic molecules can yield high-performance flexible thin film transistors. Solution-processed, bulk-heterojunction (BHJ), thin-film organic solar cells rely on the self-assembly of polymer/fullerene donor/acceptor mixtures to create the necessary morphology with a high interfacial area for efficient photocurrent generation. Efficient conversion of absorbed photons into photocurrent requires sufficiently intimate mixing of the donor and acceptor phases such that photogenerated excitons can easily find an interface, as well as a sufficiently large thermodynamic driving force for charge separation at the interface. At the same time, efficient transport of separated charges towards the electrodes requires a certain degree of phase segregation between the two materials, to enable ordered molecular packing within each phase and also minimize interfacial recombination. Despite the importance of creating inhomogeneous mixtures of organic semiconductors and the tremendous recent advances in the performance of the aforementioned devices, it remains a challenge to fully describe the optoelectronic properties of organic semiconductor mixtures and understand the effects of structural and morphological parameters on charge transport. Recently, it has been shown that highly regioregular poly(3-hexylthiophene) (RR-P3HT) and poly[2,5-bis(3-hexadecylthiophen-2-yl)thieno(3,2-b)thiophene] (PBTTT) are promising materials for organic electronic applications due to the relatively high charge carrier mobility, high solubility in different organic solvents and acceptable film
Nishizawa, Shinichiro; Ruoss, Hans-Oliver; Landstorfer, Friedrich M; Hashimoto, Osamu
2004-04-01
A new equivalent numerical source model is proposed for efficient dosimetric investigations in the low-frequency range. This approach allows the reproduction of complicated inhomogeneous magnetic field distributions around electronic appliances with full generality (i.e., supports three-dimensional vector fields). This paper investigates the accuracy of the equivalent source model using the geometry-based numerical reference model of a current loop to simulate the magnetic field distribution of a real electronic appliance. Good agreement between the equivalent source model and the reference is obtained with regard to the magnetic field distribution and the induced electric current density in a homogeneous human body model, respectively.
The effect of a defective BSF layer on solar cell open circuit voltage. [Back Surface Field
NASA Technical Reports Server (NTRS)
Weizer, V. G.
1985-01-01
A straightforward analysis of special limiting cases has permitted the determination of the range of possible open circuit voltage losses due to a defective BSF (back surface field) layer. An important result of the analysis is the finding that it is possible to have a fully effective BSF region, regardless of the spatial distribution of the defective areas, as long as the total defective area is reduced below certain limits. Distributed defects were found to be much more harmful than lumped defects.
Delamination initiated by a defect
NASA Astrophysics Data System (ADS)
Biel, A.; Toftegaard, H.
2016-07-01
Composite materials in wind turbines are mainly joined with adhesives. Adhesive joining is preferable since it distributes the stresses over a larger area. This study shows how a defect can influence the fracture behaviour of adhesively joined composite. Repeated experiments are performed using double cantilever beam specimens loaded with bending moments. The specimens consist of two 8 mm thick GFRP-laminates which are joined by a 3 mm thick epoxy adhesive. A thin foil close to one of the laminates is used to start the crack. For some of the specimens a defect is created by an initial load-unload operation. During this operation, a clamp is used in order to prevent crack propagation in the main direction. For the specimens without defect, the crack propagates in the middle of the adhesive layer. For the specimens with defect, the crack directly deviates into the laminate. After about 25 mm propagation in the laminate, the crack returns to the adhesive. Compared to the adhesive the fracture energy for the laminate is significantly higher.
Characterizing cosmic inhomogeneity with anomalous diffusion
NASA Astrophysics Data System (ADS)
Kraljic, D.
2015-08-01
Dark matter (DM) clustering at the present epoch is investigated from a fractal viewpoint in order to determine the scale where the self-similar scaling property of the DM halo distribution transits to homogeneity. Methods based on well-established `counts-in-cells' as well as new methods based on anomalous diffusion and random walks are investigated. Both are applied to DM haloes of the biggest N-body simulation in the `Dark Sky Simulations' (DS) catalogue and an equivalent randomly distributed catalogue. Results based on the smaller `Millennium Run' (MR) simulation are revisited and improved. It is found that the MR simulation volume is too small and prone to bias to reliably identify the onset of homogeneity. Transition to homogeneity is defined when the fractal dimension of the clustered and random distributions cannot be distinguished within the associated uncertainties. The `counts-in-cells' method applied to the DS then yields a homogeneity scale roughly consistent with previous work (˜150 h-1 Mpc). The characteristic length-scale for anomalous diffusion to behave homogeneously is found to be at about 250 h-1 Mpc. The behaviour of the fractal dimensions for a halo catalogue with the same two-point function as the original but with shuffled Fourier phases is investigated. The methods based on anomalous diffusion are shown to be sensitive to the phase information, whereas the `counts-in-cells' methods are not.
Power spectra in totally asymmetric simple exclusion process (TASEP) with local inhomogeneity
NASA Astrophysics Data System (ADS)
Dong, Jiajia; Zia, Royce K. P.
2010-03-01
As a paradigmatic system in non-equilibrium statistical mechanics, TASEP has been extensively studied in the abstract and also applied to model many complex phenomena such as traffic flow and protein synthesis. We focus on a rather less studied aspect of TASEP: the total number of particles on a one-dimension open TASEP at time t, N(t), and its power spectra I(φ), especially when there are local inhomogeneities. Motivated by the protein synthesis process where messenger RNA, codons and ribosomes are associated with the underlying lattice, sites and particles transported in TASEP, we investigate the effect on the power spectrum due to one defect (slower hopping rate) at different positions along the lattice. Using Monte Carlo simulation, we measure I(φ) for both the entire system and the subsystems separated by the defect. As in previous studies, oscillations are found. Here, however, more interesting characteristics emerge, depending on the location and the ``strength'' of the slow site. The biological implication of these results is also discussed.
Behavior of chemically amplified resist defects in TMAH solution: III
NASA Astrophysics Data System (ADS)
Ono, Yuko; Shimoaoki, Takeshi; Naito, Ryoichiro; Kitano, Junichi
2004-05-01
As the minimum feature size of electronic devices shrinks to less than 0.25 μm, it is critically important that we reduce the defects that occur in lithography processes. Moreover, as the defects to be controlled become ever smaller, this makes them increasingly difficult to detect by conventional fault detection equipment. In order to detect these minute defects in the context of shrinking device geometries, it is essential that we develop a clear understanding of the behavior of micro defects in developer. In principle, there are three ways in which these defects might be dealt with: (1) defects can be prevented from occurring in the first place, (2) defects can be prevented from adhering to the device, or (3) defects can be eliminated after they occur. Our recent work has mainly been concerned with the first and most effective approach of preventing defects from occurring in the first place, and this motivated the present study to investigate the mechanisms by which defects occur. We believe that defects occur in chemically amplified (CA) resists that are insufficiently unprotected at boundary regions between unexposed and exposed areas or in unexposed areas, so that the de-protection reaction in the resist suns to different degrees of completion due to varying exposure doses. In this study we investigate the number of defects in various developers, and determine the size distribution of the defects. Based on analysis of the behavior of defects from their size distribution in develop we conclude that: (1) the size of defects increases when the exposure dose is reduced by appropriate Eops, (2) defects originate in the boundary area between unexposed and exposed areas, and (3) a portion of CA resist polymer that is insufficiently deprotected is dispersed in the developer, coalesces and is deposited in a form that is not very soluble, and is manifested as relatively large particle defects.
NASA Astrophysics Data System (ADS)
Manfreda, G.; Bellina, F.; Volpini, G.
2014-12-01
Type II superconductors, like Nb-Ti and Nb3Sn, play a central role in the design of magnets for fusion and particle accelerators. These materials show experimentally a longitudinal electric field which depends in a nonlinear way on the current. Different models have been developed to analyse this phenomenon, mainly based on the role of defects and inhomogeneities in the superconducting sample. Some of these models are based on a statistical description of the critical current distribution along the wire, that can explain the presence of a curvature in the volt-ampere characteristic (VAC). In the work we have studied the impact of different critical current statistical distributions on the VAC and their implications, and compared some experimental data with our theoretical results.
Matrix algorithms for solving (in)homogeneous bound state equations
Blank, M.; Krassnigg, A.
2011-01-01
In the functional approach to quantum chromodynamics, the properties of hadronic bound states are accessible via covariant integral equations, e.g. the Bethe–Salpeter equation for mesons. In particular, one has to deal with linear, homogeneous integral equations which, in sophisticated model setups, use numerical representations of the solutions of other integral equations as part of their input. Analogously, inhomogeneous equations can be constructed to obtain off-shell information in addition to bound-state masses and other properties obtained from the covariant analogue to a wave function of the bound state. These can be solved very efficiently using well-known matrix algorithms for eigenvalues (in the homogeneous case) and the solution of linear systems (in the inhomogeneous case). We demonstrate this by solving the homogeneous and inhomogeneous Bethe–Salpeter equations and find, e.g. that for the calculation of the mass spectrum it is as efficient or even advantageous to use the inhomogeneous equation as compared to the homogeneous. This is valuable insight, in particular for the study of baryons in a three-quark setup and more involved systems. PMID:21760640
Inhomogeneous particle model for light-scattering by cometary dust
NASA Astrophysics Data System (ADS)
Markkanen, Johannes; Penttilä, Antti; Peltoniemi, Jouni; Muinonen, Karri
2015-12-01
We introduce an inhomogeneous irregular-particle model for reproducing the typical light-scattering features of cometary dust such as the negative polarization near the backscattering direction, and the weak increase of the backscattering intensity. The model is based on the hierarchical Voronoi-partitioning and the algorithm provides fast generation of irregular particles with a flexible control of inhomogeneity. The input parameters of the model are refractive indices, their volumetric abundances, and the number of constituents on each level. The light-scattering properties of these particles with parameters relevant to cometary dust are solved by the volume-integral-equation method. The light-scattering features of inhomogeneous particles are compared with the mixtures of homogeneous particles, and particles with the refractive index obtained by the effective-medium approximation. We show that with the inhomogeneity size of order 0.2 μm, the different models produce qualitatively similar scattering features while some quantitative differences are observed which have an effect on the retrieved material composition of dust.
Inhomogeneous generalizations of Bianchi type VIh models with perfect fluid
NASA Astrophysics Data System (ADS)
Roy, S. R.; Prasad, A.
1991-07-01
Inhomogeneous universes admitting an Abelian G2 of isometry and filled with perfect fluid have been derived. These contain as special cases exact homogeneous universes of Bianchi type VIh. Many of these universes asymptotically tend to homogeneous Bianchi VIh universes. The models have been discussed for their physical and kinematical behaviors.
Achieving illusion and invisibility of inhomogeneous cylinders and spheres
NASA Astrophysics Data System (ADS)
Zhang, Lin; Shi, Yan; Liang, Chang-Hong
2016-08-01
This paper has developed a scattering cancellation technique to achieve illusion and invisibility of inhomogeneous cylinders and spheres. The inhomogeneous cylinders and spheres are modelled as many thin layers of piecewise homogeneous layers. For the two-layer cylindrical and spherical objects with the isotropic coatings, Mie series solutions to the resulting scattered fields are analyzed in the quasistatic limit, and thus geometric and electromagnetic parameters of the coatings are derived to realize the illusion and invisibility of the two-layer cylindrical and spherical objects. Following a further generalization step, the coating parameters are determined for the illusion and invisibility of the inhomogeneous cylinders and spheres composed of N piecewise homogeneous layers. With the proposed method, the electrically small inhomogeneous cylindrical and spherical objects with arbitrary media and conductor core can be hidden, and have illusion images generated by the objects with similar shapes but different electromagnetic parameters and geometric sizes. Numerical results are given to verify correctness and effectiveness of the proposed method.
Tracking inhomogeneity in high-capacity lithium iron phosphate batteries
NASA Astrophysics Data System (ADS)
Paxton, William A.; Zhong, Zhong; Tsakalakos, Thomas
2015-02-01
Energy-dispersive x-ray diffraction (EDXRD) is one of the few techniques that can internally probe a sealed battery under operating conditions. In this paper, we use EDXRD with ultrahigh energy synchrotron radiation to track inhomogeneity in a cycled high-capacity lithium iron phosphate cell under in-situ and operando conditions. A sequence of depth-profile x-ray diffraction spectra are collected with 40 μm resolution as the cell is discharged. Additionally, nine different locations of the cell are tracked independently throughout a second discharge process. In each case, a two-peak reference intensity ratio analysis (RIR) was used on the LiFePO4 311 and the FePO4 020 reflections to estimate the relative phase abundance of the lithiated and non-lithiated phases. The data provide a first-time look at the dynamics of electrochemical inhomogeneity in a real-world battery. We observe a strong correlation between inhomogeneity and overpotential in the galvanic response of the cell. Additionally, the data closely follow the behavior that is predicted by the resistive-reactant model originally proposed by Thomas-Alyea. Despite a non-linear response in the independently measured locations, the behavior of the ensemble is strikingly linear. This suggests that effects of inhomogeneity can be elusive and highlights the power of the EDXRD technique.
Drift-Alfven eigenmodes in inhomogeneous plasma
Vranjes, J.; Poedts, S.
2006-03-15
A set of three nonlinear equations describing drift-Alfven waves in a nonuniform magnetized plasma is derived and discussed both in linear and nonlinear limits. In the case of a cylindric radially bounded plasma with a Gaussian density distribution in the radial direction the linearized equations are solved exactly yielding general solutions for modes with quantized frequencies and with radially dependent amplitudes. The full set of nonlinear equations is also solved yielding particular solutions in the form of rotating radially limited structures. The results should be applicable to the description of electromagnetic perturbations in solar magnetic structures and in astrophysical column-like objects including cosmic tornados.
Dissociation and recombination in an inhomogeneous gas
NASA Astrophysics Data System (ADS)
Kuščer, Ivan
1991-09-01
The system of Boltzmann equations of Ludwig and Heil for a dissociating gas mixture is reviewed and reformulated in terms of differential cross sections. For the purpose of Monte Carlo simulations, collision models of the type of Borgnakke and Larsen are proposed. In case of short-lived transient flows of molecular gases and at not too high temperatures, simulation of scattering collisions is expected to suffice; the distribution function of the dissociated particles can be evaluated afterwards by integration, and recombination can be ignored.
Probing large scale homogeneity and periodicity in the LRG distribution using Shannon entropy
NASA Astrophysics Data System (ADS)
Pandey, Biswajit; Sarkar, Suman
2016-08-01
We quantify the degree of inhomogeneity in the Luminous Red Galaxy (LRG) distribution from the SDSS DR7 as a function of length scales by measuring the Shannon entropy in independent and regular cubic voxels of increasing grid sizes. We also analyse the data by carrying out measurements in overlapping spheres and find that it suppresses inhomogeneities by a factor of 5-10 on different length scales. Despite the differences observed in the degree of inhomogeneity both the methods show a decrease in inhomogeneity with increasing length scales which eventually settle down to a plateau at ˜150 h-1 Mpc. Considering the minuscule values of inhomogeneity at the plateaus and their expected variations we conclude that the LRG distribution becomes homogeneous at 150 h-1 Mpc and beyond. We also use the Kullback-Leibler divergence as an alternative measure of inhomogeneity which reaffirms our findings. We show that the method presented here can effectively capture the inhomogeneity in a truly inhomogeneous distribution at all length scales. We analyse a set of Monte Carlo simulations with certain periodicity in their spatial distributions and find periodic variations in their inhomogeneity which helps us to identify the underlying regularities present in such distributions and quantify the scale of their periodicity. We do not find any underlying regularities in the LRG distribution within the length scales probed.
Astrocyte signaling in the presence of spatial inhomogeneities
NASA Astrophysics Data System (ADS)
Stamatakis, Michail; Mantzaris, Nikos V.
2007-09-01
Astrocytes, a special type of glial cells, were considered to have just a supporting role in information processing in the brain. However, several recent studies have shown that they can be chemically stimulated by various neurotransmitters, such as ATP, and can generate Ca2+ and ATP waves, which can propagate over many cell lengths before being blocked. Although pathological conditions, such as spreading depression and epilepsy, have been linked to abnormal wave propagation in astrocytic cellular networks, a quantitative understanding of the underlying characteristics is still lacking. Astrocytic cellular networks are inhomogeneous, in the sense that the domain they occupy contains passive regions or gaps, which are unable to support wave propagation. Thus, this work focuses on understanding the complex interplay between single-cell signal transduction, domain inhomogeneity, and the characteristics of wave propagation and blocking in astrocytic cellular networks. The single-cell signal transduction model that was employed accounts for ATP-mediated IP3 production, the subsequent Ca2+ release from the ER, and ATP release into the extracellular space. The model is excitable and thus an infinite range of wave propagation is observed if the domain of propagation is homogeneous. This is not always the case for inhomogeneous domains. To model wave propagation in inhomogeneous astrocytic networks, a reaction-diffusion framework was developed and one-gap as well as multiple-gap cases were simulated using an efficient finite-element algorithm. The minimum gap length that blocks the wave was computed as a function of excitability levels and geometric characteristics of the inhomogeneous network, such as the length of the active regions (cells). Complex transient patterns, such as wave reflection, wave trapping, and generation of echo waves, were also predicted by the model, and their relationship to the geometric characteristics of the network was evaluated. Therefore, the
Role of Inhomogeneity in Mechanochemically Active Polymers
NASA Astrophysics Data System (ADS)
Silberstein, Meredith
2013-03-01
Mechanically-induced reactivity is a promising means for designing self sensing and autonomous materials. Mechanically sensitive chemical groups termed mechanophores can be covalently linked into polymers in order to trigger specific chemical reactions upon mechanical loading. The mechanophore reaction kinetics, as determined by ab initio steered molecular dynamics, are exponential in force. As such the mechanochemical behavior of a solid-state polymer is highly sensitive to stress carried by that polymer, including local spatial and temporal fluctuations. Previously we developed microstructurally-based continuum models for fluorescence response in spiropyran-linked rubbery (poly methacrylate) and glassy (poly methylmethacrylate) polymers. The homogenization scheme in each relied on assigning mean effective forces acting on the mechanophores. Here we explore the theoretical influence of nanoscale spatial force distributions and fast temporal force fluctuations on the mechanochromic response of these systems. The effect of each is found to be significant and highly dependent on the intrinsic polymer mechanical behavior.
Vacuum birefringence in strong inhomogeneous electromagnetic fields
NASA Astrophysics Data System (ADS)
Karbstein, Felix; Gies, Holger; Reuter, Maria; Zepf, Matt
2015-10-01
Birefringence is one of the fascinating properties of the vacuum of quantum electrodynamics (QED) in strong electromagnetic fields. The scattering of linearly polarized incident probe photons into a perpendicularly polarized mode provides a distinct signature of the optical activity of the quantum vacuum and thus offers an excellent opportunity for a precision test of nonlinear QED. Precision tests require accurate predictions and thus a theoretical framework that is capable of taking the detailed experimental geometry into account. We derive analytical solutions for vacuum birefringence which include the spatio-temporal field structure of a strong optical pump laser field and an x-ray probe. We show that the angular distribution of the scattered photons depends strongly on the interaction geometry and find that scattering of the perpendicularly polarized scattered photons out of the cone of the incident probe x-ray beam is the key to making the phenomenon experimentally accessible with the current generation of FEL/high-field laser facilities.
Observation of structural inhomogeneity at degraded Fe-doped SrTiO3 interfaces
NASA Astrophysics Data System (ADS)
Ascienzo, D.; Greenbaum, S.; Bayer, T. J. M.; Maier, R.; Randall, C. A.; Ren, Y. H.
2016-07-01
We report on the detection of structural inhomogeneity across anode and cathode interfaces in electrically degraded reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals by optical second harmonic generation (SHG) spectroscopy. SHG spectra were collected from several regions across the anode and cathode interfaces in both degraded reduced and oxidized Fe:STO crystals. We identify the formation of defect concentration gradients along both degraded reduced and oxidized anode interfaces. While the broken symmetries decrease from the outer region towards the central region of the reduced anode, the opposite trend is seen in the degraded oxidized anode. These results are attributed to the formation of centrosymmetric Fe4+:Ti4+-O6 octahedral structures in the central region of the reduced sample's degraded anode and non-centrosymmetric Jahn-Teller distortions in the central region of the oxidized sample's degraded anode. The observed changes in SHG intensity from the outer region towards the central region of the degraded cathode interfaces is accompanied by a structural phase transition in the inner and outer regions, marked by strong changes to the s-polarized intensity spectra. We explain the SHG intensity changes by the formation of lower order symmetry Fe3+:Ti3+-O6 structures in the outer region and a modification of the second-order nonlinear susceptibility near the central regions due to the clustering of dissociated oxygen vacancies. These significant structural and spatial inhomogeneities are linked directly to the field-driven migration of oxygen ions and vacancies.
Dopant Distribution in NIF Beryllium Ablator Capsules
NASA Astrophysics Data System (ADS)
Huang, H.; Xu, H. W.; Youngblood, K. P.; Wall, D. R.; Stephens, R. B.; Moreno, K. A.; Nikroo, A.; Salmonson, J. D.; Haan, S. W.; Wu, K. J.; Wang, Y. M.; Hamza, A. V.
2012-10-01
Good implosion performance requires capsule ablator material with spherically uniform x-ray opacity, which is controlled by one of several dopants (Cu, Si, Al, etc.) in the Be shell. During production, the dopant concentration is radially stepped. However, the various Be-dopant interactions result in vastly different dopant distribution patterns, some quite inhomogeneous. We have characterized these structures and established the phenomenological basis and the magnitudes of the inhomogeneity both in spatial length scales and in atomic percent. We will discuss the case of inhomogeneous Cu diffusion in detail, followed by discussions of other dopants and the estimate of the impact of these structures on target implosion.
NASA Astrophysics Data System (ADS)
Kaurov, Alexander A.
2016-06-01
We explore a time-dependent energy dissipation of the energetic electrons in the inhomogeneous intergalactic medium (IGM) during the epoch of cosmic reionization. In addition to the atomic processes, we take into account the inverse Compton (IC) scattering of the electrons on the cosmic microwave background photons, which is the dominant channel of energy loss for electrons with energies above a few MeV. We show that: (1) the effect on the IGM has both local (atomic processes) and non-local (IC radiation) components; (2) the energy distribution between hydrogen and helium ionizations depends on the initial energy of an electron; (3) the local baryon overdensity significantly affects the fractions of energy distributed in each channel; and (4) the relativistic effect of the atomic cross-section becomes important during the epoch of cosmic reionization. We release our code as open source for further modification by the community.
Sukstanskii, A.L.; Ackerman, J.J.H.; Yablonskiy, D.A.
2007-01-01
The spatial distribution of the transverse nuclear spin magnetization, appearing in a single compartment with impermeable boundaries in a Stejskal-Tanner gradient pulse MR experiment, is analyzed in detail. At short diffusion times the presence of diffusion-restrictive barriers (membranes) reduces effective diffusivity near the membranes and leads to an inhomogeneous spin magnetization distribution (the edge-enhancement effect). In this case, the signal reveals a quasi-two-compartment behavior and can be empirically modeled remarkably well by a biexponential function. The current results provide a framework for interpreting experimental MR data on various phenoma, including water diffusion in giant axons, metabolite diffusion in the brain, and hyperpolarized gas diffusion in lung airways. PMID:14523959
Effects of charge inhomogeneities on elementary excitations in La2-xSrxCuO₄
Park, S. R.; Hamann, A.; Pintschovius, L.; Lamago, D.; Khaliullin, G.; Fujita, M.; Yamada, K.; Gu, G. D.; Tranquada, J. M.; Reznik, D.
2011-12-12
Purely local experimental probes of many copper oxide superconductors show that their electronic states are inhomogeneous in real space. For example, scanning tunneling spectroscopic imaging shows strong variations in real space, and according to nuclear quadrupole resonance (NQR) studies, the charge distribution in the bulk varies on the nanoscale. However, the analysis of the experimental results utilizing spatially averaged probes often ignores this fact. We have performed a detailed investigation of the doping dependence of the energy and linewidth of the zone-boundary Cu-O bond-stretching vibration in La2-xSrxCuO₄ by inelastic neutron scattering. Both our results as well as previously reported angle-dependentmore » momentum widths of the electronic spectral function detected by angle-resolved photoemission can be reproduced by including the same distribution of local environments extracted from the NQR analysis.« less
Stressed states and persistent defects in confined nematic elastica
NASA Astrophysics Data System (ADS)
Köpf, M. H.; Pismen, L. M.
2015-10-01
We analyse the variety of solutions, both defect-free and containing defects in a confined nematic elastomer, arising as a result of competition between nematic ordering and elastic stresses. Phase field analysis predicts bifurcation of solutions with symmetric and antisymmetric distribution of nematic alignment from a perfectly aligned stressed state. The antisymmetric branch always has a lower energy, as confirmed by numerical computations away from the bifurcation point. At still higher deviations, states containing persistent defect pairs become preferable but defect-free states and states with defects coexist in a wide parametric range.
Defect depth measurement of carbon fiber reinforced polymers by thermography
NASA Astrophysics Data System (ADS)
Chen, Terry Y.; Chen, Jian-Lun
2016-01-01
Carbon fiber reinforced polymers has been widely used in all kind of the industries. However the internal defects can result in the change of material or mechanical properties, and cause safety problem. In this study, step-heating thermography is employed to measure the time series temperature distribution of composite plate. The principle of heat conduction in a flat plate with defect inside is introduced. A temperature separation criterion to determine the depth of defect inside the specimen is obtained experimentally. Applying this criterion to CFRP specimens with embedded defects, the depth of embedded defect in CFRP can be determined quite well from the time series thermograms obtained experimentally.
Mehdian, H. Kargarian, A.; Hajisharifi, K.
2015-06-15
In this paper, the effect of an external inhomogeneous magnetic field on the high intensity laser absorption rate in a sub-critical plasma has been investigated by employing a relativistic electromagnetic 1.5 dimensional particle-in-cell code. Relying on the effective nonlinear phenomena such as phase-mixing and scattering, this study shows that in a finite-size plasma the laser absorption increases with inhomogeneity of the magnetic field (i.e., reduction of characteristic length of inhomogeneous magnetic field, λ{sub p}) before exiting a considerable amount of laser energy from the plasma due to scattering process. On the other hand, the presence of the external inhomogeneous magnetic field causes the maximum absorption of laser to occur at a shorter time. Moreover, study of the kinetic results associated with the distribution function of plasma particles shows that, in a special range of the plasma density and the characteristic length of inhomogeneous magnetic field, a considerable amount of laser energy is transferred to the particles producing a population of electrons with kinetic energy along the laser direction.
Kim, Kihong; Lee, Dong-Hun
2005-06-15
This is the first of a series of papers devoted to the development of the invariant imbedding theory of mode conversion in inhomogeneous plasmas. A new version of the invariant imbedding theory of wave propagation in inhomogeneous media allows one to solve a wide variety of coupled wave equations exactly and efficiently, even in the cases where the material parameters change discontinuously at the boundaries and inside the inhomogeneous medium. In this paper, the invariant imbedding method is applied to the mode conversion of the simplest kind, that is, the conversion of p-polarized electromagnetic waves into electrostatic modes in cold, unmagnetized plasmas. The mode conversion coefficient and the field distribution are calculated exactly for linear and parabolic plasma density profiles and compared quantitatively with previous results.
None, None
2012-10-11
Micrograph image defect identifier is a computer code written in MATLAB to automatically detect defects on scanned image of thin film membrane samples employing three methods: global threshold, line detection and k-means segmentation. The results are segmented binary images of thin film with defects identified. Defect area fractions are also calculated. The users may use default functional variables calculated by program, or input preferred value from users experience. This will empower the user to processing the image with more flexibility. MDI was designed to identify defects of thin films fabricated. It is also used in phase identification, porosity study on SEM, OM, TEM images. Different methods were applied in this software package: global threshold, line detection and k-means segmentation.
2012-10-11
Micrograph image defect identifier is a computer code written in MATLAB to automatically detect defects on scanned image of thin film membrane samples employing three methods: global threshold, line detection and k-means segmentation. The results are segmented binary images of thin film with defects identified. Defect area fractions are also calculated. The users may use default functional variables calculated by program, or input preferred value from users experience. This will empower the user to processingmore » the image with more flexibility. MDI was designed to identify defects of thin films fabricated. It is also used in phase identification, porosity study on SEM, OM, TEM images. Different methods were applied in this software package: global threshold, line detection and k-means segmentation.« less
Li, Xun; Hu, Sanqing; Li, Lihua; Zhu, Shanan
2013-01-01
Magnetoacoustic tomography with magnetic induction (MAT-MI) is a noninvasive imaging modality for generating electrical conductivity images of biological tissues with high spatial resolution. In this paper, we create a numerical model, including a permanent magnet, a coil, and a two-layer coaxial cylinder with anisotropic electrical conductivities, for the MAT-MI forward problem. We analyze the MAT-MI sources in two cases, on a thin conductive boundary layer and in a homogeneous medium, and then develop a feasible numerical approach to solve the MAT-MI sound source densities in the anisotropic conductive model based on finite element analysis of electromagnetic field. Using the numerical finite element method, we then investigate the magnetoacoustic effect of anisotropic conductivity under the inhomogeneous static magnetic field and inhomogeneous magnetic field, quantitatively compute the boundary source densities in the conductive model, and calculate the sound pressure. The anisotropic conductivity contributes to the distribution of the eddy current density, Lorentz force density, and acoustic signal. The proposed models and approaches provide a more realistic simulation environment for MAT-MI.
Dephasing of Hahn echo in rocks by diffusion in susceptibility-induced field inhomogeneities.
Hürlimann, M D; Helmer, K G; Sotak, C H
1998-01-01
The decay of the Hahn spin echo of water in the pore space of many porous media is dominated by the dephasing of spins in internal-field inhomogeneities, produced by susceptibility contrasts, rather than surface or bulk relaxation. This is particularly the case for measurements at moderate and high fields in samples such as fluid-saturated sedimentary rocks and some biological materials. Here, we study the behavior of the Hahn-echo decay in rocks with grains much larger and smaller than the average dephasing length, which is typically of the order of a few microns. It is shown that the decay in these two cases is qualitatively different. For coarse-grained rocks, the decay can be modeled to first order by a distribution of local, effective field gradients. This is in contrast to the case of fine-grained rocks, where motional narrowing of the field inhomogeneities occurs. These interpretations are supported by measurements of the temperature dependence of the Hahn echo decay and the diffusion time dependence of the diffusion coefficient.
Boundary effect on the elastic field of a semi-infinite solid containing inhomogeneities
Liu, Y. J.; Song, G.; Yin, H. M.
2015-01-01
The boundary effect of one inhomogeneity embedded in a semi-infinite solid at different depths has firstly been investigated using the fundamental solution for Mindlin's problem. Expanding the eigenstrain in a polynomial form and using the Eshelby's equivalent inclusion method, one can calculate the eigenstrain and thus obtain the elastic field. When the inhomogeneity is far from the boundary, the solution recovers Eshelby's solution. The method has been extended to a many-particle system in a semi-infinite solid, which is first demonstrated by the cases of two spheres. The comparison of the asymptotic form solution with the finite-element results shows the accuracy and capability of this method. The solution has been used to illustrate the boundary effects on its effective material behaviour of a semi-infinite simple cubic lattice particulate composite. The local field of a semi-infinite composite has been calculated at different volume fractions. A representative unit cell has been taken with different depths to the surface. The average stress and strain of the unit cell have been calculated under uniform loading conditions of normal or shear force on the surface, respectively. The effective elastic moduli of the unit cell not only depend on the material proportion, but also on its distance to the surface. The present model can be extended to other types of particle distribution and ellipsoidal particles. PMID:26345084
Electron holes in inhomogeneous magnetic field: Electron heating and electron hole evolution
NASA Astrophysics Data System (ADS)
Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; Artemyev, A. V.; Drake, J. F.
2016-05-01
Electron holes are electrostatic non-linear structures widely observed in the space plasma. In the present paper, we analyze the process of energy exchange between electrons trapped within electron hole, untrapped electrons, and an electron hole propagating in a weakly inhomogeneous magnetic field. We show that as the electron hole propagates into the region with stronger magnetic field, trapped electrons are heated due to the conservation of the first adiabatic invariant. At the same time, the electron hole amplitude may increase or decrease in dependence on properties of distribution functions of trapped and untrapped resonant electrons. The energy gain of trapped electrons is due to the energy losses of untrapped electrons and/or decrease of the electron hole energy. We stress that taking into account the energy exchange with untrapped electrons increases the lifetime of electron holes in inhomogeneous magnetic field. We illustrate the suggested mechanism for small-amplitude Schamel's [Phys. Scr. T2, 228-237 (1982)] electron holes and show that during propagation along a positive magnetic field gradient their amplitude should grow. Neglect of the energy exchange with untrapped electrons would result in the electron hole dissipation with only modest heating factor of trapped electrons. The suggested mechanism may contribute to generation of suprathermal electron fluxes in the space plasma.
Thermal depth profiling of materials for defect detection using hot disk technique
NASA Astrophysics Data System (ADS)
Mihiretie, B. M.; Cederkrantz, D.; Sundin, M.; Rosén, A.; Otterberg, H.; Hinton, Å.; Berg, B.; Karlsteen, M.
2016-08-01
A novel application of the hot disk transient plane source technique is described. The new application yields the thermal conductivity of materials as a function of the thermal penetration depth which opens up opportunities in nondestructive testing of inhomogeneous materials. The system uses the hot disk sensor placed on the material surface to create a time varying temperature field. The thermal conductivity is then deduced from temperature evolution of the sensor, whereas the probing depth (the distance the heat front advanced away from the source) is related to the product of measurement time and thermal diffusivity. The presence of inhomogeneity in the structure is manifested in thermal conductivity versus probing depth plot. Such a plot for homogeneous materials provides fairly constant value. The deviation from the homogeneous curve caused by defects in the structure is used for inhomogeneity detection. The size and location of the defect in the structure determines the sensitivity and possibility of detection. In addition, a complementary finite element numerical simulation through COMSOL Multiphysics is employed to solve the heat transfer equation. Temperature field profile of a model material is obtained from these simulations. The average rise in temperature of the heat source is calculated and used to demonstrate the effect of the presence of inhomogeneity in the system.
Residual Defect Density in Random Disks Deposits
NASA Astrophysics Data System (ADS)
Topic, Nikola; Pöschel, Thorsten; Gallas, Jason A. C.
2015-08-01
We investigate the residual distribution of structural defects in very tall packings of disks deposited randomly in large channels. By performing simulations involving the sedimentation of up to 50 × 109 particles we find all deposits to consistently show a non-zero residual density of defects obeying a characteristic power-law as a function of the channel width. This remarkable finding corrects the widespread belief that the density of defects should vanish algebraically with growing height. A non-zero residual density of defects implies a type of long-range spatial order in the packing, as opposed to only local ordering. In addition, we find deposits of particles to involve considerably less randomness than generally presumed.
Residual Defect Density in Random Disks Deposits
Topic, Nikola; Pöschel, Thorsten; Gallas, Jason A. C.
2015-01-01
We investigate the residual distribution of structural defects in very tall packings of disks deposited randomly in large channels. By performing simulations involving the sedimentation of up to 50 × 109 particles we find all deposits to consistently show a non-zero residual density of defects obeying a characteristic power-law as a function of the channel width. This remarkable finding corrects the widespread belief that the density of defects should vanish algebraically with growing height. A non-zero residual density of defects implies a type of long-range spatial order in the packing, as opposed to only local ordering. In addition, we find deposits of particles to involve considerably less randomness than generally presumed. PMID:26235809
The Effect of Habitat Inhomogeneities and Fragmentation on Population Density and Time to Extinction
Kostova, T; Carlsen, T
2003-12-22
We present a study, based on simulations with SERDYCA, a spatially-explicit individual based model of rodent dynamics, on the connection between population persistence and the presence of inhomogeneities in the habitat. We are specifically interested on the effect that inhomogeneities that do not fragment the environment, have on population persistence. Our results suggest that a certain percentage of inhomogeneities can increase the average time to extinction of the population. Inhomogeneities decrease the population density and can increase the ratio of juveniles in the population thus providing a better chance for the population to restore itself after a severe period with critically low population density. We call this the ''inhomogeneity localization effect''.
Critical role of inhomogeneities in pacing termination of cardiac reentry
NASA Astrophysics Data System (ADS)
Sinha, Sitabhra; Stein, Kenneth M.; Christini, David J.
2002-09-01
Reentry around nonconducting ventricular scar tissue, a cause of lethal arrhythmias, is typically treated by rapid electrical stimulation from an implantable cardioverter defibrillator. However, the dynamical mechanisms of termination (success and failure) are poorly understood. To elucidate such mechanisms, we study the dynamics of pacing in one- and two-dimensional models of anatomical reentry. In a crucial realistic difference from previous studies of such systems, we have placed the pacing site away from the reentry circuit. Our model-independent results suggest that with such off-circuit pacing, the existence of inhomogeneity in the reentry circuit is essential for successful termination of tachycardia under certain conditions. Considering the critical role of such inhomogeneities may lead to more effective pacing algorithms.
Inhomogeneous spin diffusion in traps with cold atoms.
Heiselberg, H
2012-06-15
The spin diffusion and damped oscillations are studied in the collision of two spin polarized clouds of cold atoms with resonant interactions. The strong density dependence of the diffusion coefficient leads to inhomogeneous spin diffusion that changes from central to surface spin flow as the temperature increases. The inhomogeneity and the smaller finite trap size significantly reduce the spin diffusion rate at low temperatures. The resulting spin diffusion rates and spin drag at longer time scales are compatible with measurements at low to high temperatures for resonant attractive interactions but are incompatible with a metastable ferromagnetic phase. This does not exclude that the colliding clouds can evolve into a repulsive initial state which subsequently decays during the bounce and the initial damped oscillations. PMID:23004287
Inhomogeneous spin diffusion in traps with cold atoms.
Heiselberg, H
2012-06-15
The spin diffusion and damped oscillations are studied in the collision of two spin polarized clouds of cold atoms with resonant interactions. The strong density dependence of the diffusion coefficient leads to inhomogeneous spin diffusion that changes from central to surface spin flow as the temperature increases. The inhomogeneity and the smaller finite trap size significantly reduce the spin diffusion rate at low temperatures. The resulting spin diffusion rates and spin drag at longer time scales are compatible with measurements at low to high temperatures for resonant attractive interactions but are incompatible with a metastable ferromagnetic phase. This does not exclude that the colliding clouds can evolve into a repulsive initial state which subsequently decays during the bounce and the initial damped oscillations.
Gilbert damping of ferromagnetic metals incorporating inhomogeneous spin dynamics
Umetsu, Nobuyuki Miura, Daisuke; Sakuma, Akimasa
2015-05-07
The effects of inhomogeneous spin dynamics on magnetic damping in ferromagnetic metals are studied. On the basis of linear response theory, we derive the microscopic expression for the Gilbert damping term in a two-dimensional electron gas interacting with the magnetization via exchange coupling in the presence of Rashba spin-orbit coupling (SOC). In the spin wave propagating with the wave vector, q, the behavior of q-dependent damping can be explained in terms of both inter- and intra-band spin excitations. The spatially dependent damping torques originating from Rashba SOC that cancel out in a uniform precession system distort the circular orbit of a magnetization-precession trajectory in the presence of inhomogeneous spin dynamics.
Effects of dipole magnet inhomogeneities on the beam ellipsoid
Tsoupas, N.; Colman, J.; Levine, M.; McKenzie-Wilson, R.; Ward, T.; Grand, P.
1986-01-01
The RAYTRACE computer code has been modified to accept magnetic fields measured in the median plane of a dipole magnet. This modification allows one to study the effects of a non-ideal dipole magnet on the beam ellipsoid (as defined by the TRANSPORT code manual). The effects on the beam ellipsoid are due to: field inhomogeneities in the interior region of the dipole, and discrepancies from design conditions of the magnetic field values in the fringe field region. The results of the RAYTRACE code calculations based on experimentally measured fields will be compared with the results derived using both an ideal (no inhomogeneities) dipole with SCOFF boundaries and an ideal dipole with perfect (according to design) fringe fields.
Trace element evidence for a laterally inhomogeneous moon
NASA Technical Reports Server (NTRS)
Jovanovic, S.; Reed, G. W., Jr.
1978-01-01
A number of trace element interrelationships support the concept of a laterally inhomogeneous moon based originally on Clr/P2O5 ratios. The correspondence between Clr/P2O3 and Rb/Sr ratios in basalts are of special interest since the isotropic evolution of the latter pair of elements relates to the earliest history of the moon. This implies the times when the Clr/P2O5 relationships were established. The early magma ocean is conjectured to have been made up of non-intermixing seas resulting either from large convection cells or large body accretion. These mutually exclusive regions could be lunar geological provinces. It is proposed that the diversity of basalts from the Apollo 17 site is related to the lateral inhomogeneity of the moon. Ca/Na ratios in basalts show a trend which parallels that of Ru/Os and in a corresponding fashion may serve as a depth indicator.
Sublattice model of atomic scale pairing inhomogeneity in a superconductor
NASA Astrophysics Data System (ADS)
Mishra, Vivek; Hirschfeld, P. J.; Barash, Yu. S.
2008-10-01
We study a toy model for a superconductor on a bipartite lattice where intrinsic pairing inhomogeneity is produced by two different coupling constants on the sublattices. The simplicity of the model allows for analytical solutions and tests of the consequences of atomic scale variations in pairing interactions, which have been considered recently in the cuprates. We present results for the transition temperature, density of states, and thermodynamics of the system over a phase diagram in the plane of two pairing coupling constants. For coupling constants of alternating sign, a gapless superconducting state is stable. Inhomogeneity is generally found to enhance the critical temperature, and at the same time the superfluid density is remarkably robust; at T=0 , it is suppressed only in the gapless phase.
Multi-echo imaging in highly inhomogeneous magnetic fields.
Casanova, F; Perlo, J; Blümich, B; Kremer, K
2004-01-01
A new pulsed field gradient multi-echo imaging technique to encode position in the phase of every echo generated by a CPMG sequence in the presence of a strongly inhomogeneous static magnetic field is presented. It was applied to improve the sensitivity in an imaging experiment by adding the echo train acquired during the CPMG sequence and to spatially resolve relaxation times of inhomogeneous specimens using single-sided probes. The sequence was implemented in a new bar-magnet MOUSE equipped with a gradient coil system to apply a pulsed magnetic field with a constant gradient along one spatial coordinate. An important reduction by a factor larger than two orders of magnitude in the acquisition time was obtained compared to the previously published single-point imaging technique. PMID:14675822
Defect Detection in Correlated Noise
NASA Astrophysics Data System (ADS)
Dogandžić, Aleksandar; Eua-Anant, Nawanat
2004-02-01
We present methods for detecting NDE defect signals in correlated noise having unknown covariance. The proposed detectors are derived using the statistical theory of generalized likelihood ratio (GLR) tests and multivariate analysis of variance (MANOVA). We consider both real and complex data models. To allow accurate estimation of the noise covariance, we incorporate secondary data containing only noise into detector design. Probability distributions of the GLR test statistics are derived under the null hypothesis, i.e. assuming that the signal is absent, and used for detector design. We apply the proposed methods to simulated and experimental data and demonstrate their superior performance compared with the detectors that neglect noise correlation.
Cavity-Enhanced Measurements of Defect Spins in Silicon Carbide
NASA Astrophysics Data System (ADS)
Calusine, Greg; Politi, Alberto; Awschalom, David D.
2016-07-01
The identification of new solid-state defect-qubit candidates in widely used semiconductors has the potential to enable the use of nanofabricated devices for enhanced qubit measurement and control operations. In particular, the recent discovery of optically active spin states in silicon carbide thin films offers a scalable route for incorporating defect qubits into on-chip photonic devices. Here, we demonstrate the use of 3C silicon carbide photonic crystal cavities for enhanced excitation of color-center defect spin ensembles in order to increase measured photoluminescence signal count rates, optically detected magnetic-resonance signal intensities, and optical spin initialization rates. We observe an up to a factor of 30 increase in the photoluminescence and optically detected magnetic-resonance signals from Ky5 color centers excited by cavity-resonant excitation and increase the rate of ground-state spin initialization by approximately a factor of 2. Furthermore, we show that the 705-fold reduction in excitation mode volume and enhanced excitation and collection efficiencies provided by the structures can be used to overcome inhomogenous broadening in order to facilitate the study of defect-qubit subensemble properties. These results highlight some of the benefits that nanofabricated devices offer for engineering the local photonic environment of color-center defect qubits to enable applications in quantum information and sensing.
Scatter of elastic waves by a thin flat elliptical inhomogeneity
NASA Technical Reports Server (NTRS)
Fu, L. S.
1983-01-01
Elastodynamic fields of a single, flat, elliptical inhomogeneity embedded in an infinite elastic medium subjected to plane time harmonic waves are studied. Scattered displacement amplitudes and stress intensities are obtained in series form for an incident wave in an arbitrary direction. The cases of a penny shaped crack and an elliptical crack are given as examples. The analysis is valid for alpha a up to about two, where alpha is longitudinal wave number and a is a typical geometric parameter.
Structural inhomogeneity and magnetic properties of strontium hexaferrites
Pashchenko, V.P.; Samoilenko, Z.A.; Vintonyak, V.M.
1995-07-01
The clustered inhomogeneity observed in ferromagnetic materials deepens our concepts of the actual structure of solids and opens new possibilities for controlling their properties. These investigations were made for the purpose of establishment of the relationship between clusterization and magnetic properties of SrO-nFe{sub 2}O{sub 3}, where 5.4 < n < 6.2, metal oxide magnetically hard strontium ferrites.
Comment on 'Heavy element production in inhomogeneous big bang nucleosynthesis'
Rauscher, Thomas
2007-03-15
The work of Matsuura et al. [Phys. Rev. D 72, 123505 (2005)] claims that heavy nuclei could have been produced in a combined p- and r-process in very high baryon density regions of an inhomogeneous big bang. However, they do not account for observational constraints and previous studies which show that such high baryon density regions did not significantly contribute to big bang abundances.
Phase transformation kinetics in finite inhomogeneously nucleated systems
NASA Technical Reports Server (NTRS)
Weinberg, Michael; Kapral, Raymond
1989-01-01
Phase transformation kinetics that occur by a nucleation and growth process are investigated. A simple discrete space and time model is used for the dynamics and analytical results are obtained for the volume fraction of the material transformed for both finite systems and a special example of an inhomogeneously nucleated system. The theory is developed for two cases, initial nucleation, and continuous nucleation. The results are compared with simulations of the model.
Detection of detachments and inhomogeneities in frescos by Compton scattering
NASA Astrophysics Data System (ADS)
Castellano, A.; Cesareo, R.; Buccolieri, G.; Donativi, M.; Palamà, F.; Quarta, S.; De Nunzio, G.; Brunetti, A.; Marabelli, M.; Santamaria, U.
2005-07-01
A mobile instrument has been developed for the detection and mapping of detachments in frescos by using Compton back scattered photons. The instrument is mainly composed of a high energy X-ray tube, an X-ray detection system and a translation table. The instrument was first applied to samples simulating various detachment situations, and then transferred to the Vatican Museum to detect detachments and inhomogeneities in the stanza di Eliodoro, one of the "Raphael's stanze".
Variational calculations for resonance oscillations of inhomogeneous plasmas
NASA Technical Reports Server (NTRS)
Peng, Y. K. M.; Crawford, F. W.
1973-01-01
The electrostatic resonance properties of an inhomogeneous plasma column are reported by application of the Rayleigh-Ritz method. A description of the rf equation of motion and pressure term that expresses the system of equations in Euler-Lagrange form is presented. The Rayleigh-Ritz procedure is applied to the corresponding Lagrangian to obtain approximate resonance frequencies and eigenfunctions. An appropriate set of trial coordinate functions is defined, which leads to frequency and eigenfunction estimates.
Nondestructive evaluation of weld defects by infrared thermography
Satonaka, Shinobu; Ohba, Hiroyasu; Shinozaki, Kenya
1995-12-31
In order to clarify the applicability of infrared thermography to the nondestructive evaluation of weld defects, an infrared measurement was conducted on the welds with various artificial defects. Two heating methods, a moving gas flame and a Joule effect by electric current flow, were used for the fast and large area inspection with readily interpretable images of defects. Finite element analysis was also used for the theoretical analyses of beat conduction and electric current flow, together with the development of imaging technique for the evaluation of the shape and size of defects. As the results of infrared measurements and theoretical analyses, the selection of heating method and the acquisition of infrared images were important for the clear image and precise measurement of weld defects. As for the clear images, the Joule effect heating was useful for the detection of open-to-the-surface defects, while the moving gas flame heating was available to the inner defect parallel to the surface. It was also clarified that the types of defects were identified by the distribution of high and low temperature regions. In the measurement of defect size, defect edges were evaluated by the positions with maximum temperature gradient in the moving gas flame heating, and with minimum second derivative of temperature in the Joule effect heating. The effective images for the precise measurement of defect size were obtained from the ones immediately after current flow in the Joule effect heating, and just before the arrival of gas flame beneath the defect.
Defect Chemistry of Nanocarbon
NASA Astrophysics Data System (ADS)
Wang, Yuhuang
2015-03-01
Defects can rule the properties of a crystal. This effect is particularly intriguing in atom-thick materials such as single-walled carbon nanotubes and graphene, where electrons, excitons, phonons, and spin may strongly couple at the defect sites due to reduced dimensionality. In this talk, we will discuss our recent progress in fundamental understanding and molecular control of sp3 defects in sp2 carbon lattices, and their applications. An sp3 defect (tetrahedral bonding, diamond-like) is created by covalently attaching a functional group to the sp2 carbon lattice (trigonal planar, honeycomb-like) of a carbon nanotube or graphene. The beauty of this type of defect is its well-defined structure and chemical tunability at the molecular level. Our experimental results have unraveled a series of intriguing and surprising roles of defects. Specific examples will be given to illustrate how defects may be used to drive reaction propagation on sp2 carbon lattices, brighten carbon nanotube photoluminescence, and create selective chemical sensors.
Dispersion properties of helical waves in radially inhomogeneous elastic media.
Syresin, D E; Zharnikov, T V; Tyutekin, V V
2012-06-01
In this paper, a method describing dispersion curve calculation for waves propagating in radially layered, inhomogeneous isotropic elastic waveguides is developed. Particular emphasis is placed on the helical waves with noninteger azimuthal wavenumbers, which can be potentially applied in such fields as nondestructive evaluation, acoustic tomography, etc., stipulating their practical importance. To solve the problem under consideration, the matrix Riccati equation is formulated for an impedance matrix. The use of the latter yields a simple form of the dispersion equation. Numerical computation of dispersion curves can encounter difficulties, which are due to potential singularities of the impedance matrix and the necessity to separate roots of the dispersion equation. These difficulties are overcome by employing the Cayley transform and invoking the parametric continuation method. The method developed by the authors is demonstrated by calculating dispersion diagrams in support of helical waves for several models of practical interest. Such computations for an inhomogeneous layer and its approximation by a set of homogeneous layers using a transfer matrix and Riccati equation methods revealed higher computational accuracy of the latter. Dispersion curves calculated for layers with different types of inhomogeneity demonstrated significant discrepancies at low frequencies. PMID:22712901
Inhomogeneous chiral symmetry breaking in dense neutron-star matter
NASA Astrophysics Data System (ADS)
Buballa, Michael; Carignano, Stefano
2016-03-01
An increasing number of model results suggests that chiral symmetry is broken inhomogeneously in a certain window at intermediate densities in the QCD phase diagram. This could have significant effects on the properties of compact stars, possibly leading to new astrophysical signatures. In this contribution we discuss this idea by reviewing recent results on inhomogeneous chiral symmetry breaking under an astrophysics-oriented perspective. After introducing two commonly studied spatial modulations of the chiral condensate, the chiral density wave and the real kink crystal, we focus on their properties and their effect on the equation of state of quark matter. We also describe how these crystalline phases are affected by different elements which are required for a realistic description of a compact star, such as charge neutrality, the presence of magnetic fields, vector interactions and the interplay with color superconductivity. Finally, we discuss possible signatures of inhomogeneous chiral symmetry breaking in the core of compact stars, considering the cases of mass-radius relations and neutrino emissivity explicitly.
Electromagnetic scattering from an inhomogeneous object by ray tracing
NASA Technical Reports Server (NTRS)
Kim, Hyeongdong; Ling, Hao
1992-01-01
A 'shooting and bouncing ray' (SBR) formulation is presented for treating the electromagnetic scattering from electrically large, inhomogeneous objects. A dense grid of rays representing the incident plane wave is shot toward the inhomogeneous object. At the scatterer boundary, reflected rays and refracted rays are generated due to discontinuity of the medium parameters. The trajectory, amplitude, phase and polarization of the rays inside the inhomogeneous object are traced based on geometrical optics. Whenever the rays cross the scatterer surface, additional reflected/refracted rays are generated and are tracked. This process is repeated until the intensities of the refracted/reflected rays become negligible. The contributions of the exiting rays to the total scattered field are calculated by using the equivalence principle in conjunction with a ray-tube integration scheme. The ray formulation is applied to calculate the backscattering from cylinders and spheres and good agreement with the exact series solutions is observed in the high frequency range. In addition, the backscattering mechanisms in penetrable objects are interpreted in terms of simple ray pictures.
Density functional theory for systems with mesoscopic inhomogeneities
NASA Astrophysics Data System (ADS)
Ciach, A.; Gozdz, W. T.
2016-06-01
We study the effects of fluctuations on the mesoscopic length scale on systems with mesoscopic inhomogeneities. Equations for the correlation function and for the average volume fraction are derived in the self-consistent Gaussian approximation. The equations are further simplified by postulating the expression for the structure factor consistent with scattering experiments for self-assembling systems. Predictions of the approximate theory are verified by a comparison with the exact results obtained earlier for the one-dimensional lattice model with first-neighbor attraction and third-neighbor repulsion. We find qualitative agreement for the correlation function, the equation of state and the dependence of the chemical potential μ on the volume fraction ζ. Our results confirm also that strong inhomogeneities in the disordered phase are found only in the case of strong repulsion. The inhomogeneities are reflected in an oscillatory decay of the correlation function with a very large correlation length, three inflection points in the μ ≤ft(\\zeta \\right) curve and a compressibility that for increasing ζ takes very large, very small and again very large values.
Segmentation of intensity inhomogeneous brain MR images using active contours.
Akram, Farhan; Kim, Jeong Heon; Lim, Han Ul; Choi, Kwang Nam
2014-01-01
Segmentation of intensity inhomogeneous regions is a well-known problem in image analysis applications. This paper presents a region-based active contour method for image segmentation, which properly works in the context of intensity inhomogeneity problem. The proposed region-based active contour method embeds both region and gradient information unlike traditional methods. It contains mainly two terms, area and length, in which the area term practices a new region-based signed pressure force (SPF) function, which utilizes mean values from a certain neighborhood using the local binary fitted (LBF) energy model. In turn, the length term uses gradient information. The novelty of our method is to locally compute new SPF function, which uses local mean values and is able to detect boundaries of the homogenous regions. Finally, a truncated Gaussian kernel is used to regularize the level set function, which not only regularizes it but also removes the need of computationally expensive reinitialization. The proposed method targets the segmentation problem of intensity inhomogeneous images and reduces the time complexity among locally computed active contour methods. The experimental results show that the proposed method yields better segmentation result as well as less time complexity compared with the state-of-the-art active contour methods. PMID:25143780
Off-center observers versus supernovae in inhomogeneous pressure universes
Balcerzak, Adam; Dabrowski, Mariusz P.; Denkiewicz, Tomasz
2014-09-10
Exact luminosity distance and apparent magnitude formulae are applied to the Union2 557 supernovae sample in order to constrain the possible position of an observer outside of the center of symmetry in spherically symmetric inhomogeneous pressure Stephani universes, which are complementary to inhomogeneous density Lemaître-Tolman-Bondi (LTB) void models. Two specific models are investigated. The first allows a barotropic equation of state at the center of symmetry without the need to specify a scale factor function (model IIA). The second has no barotropic equation of state at the center, but has an explicit dust-like scale factor evolution (model IIB). It is shown that even at 3σ CL, an off-center observer cannot be further than about 4.4 Gpc away from the center of symmetry, which is comparable to the reported size of a void in LTB models with the most likely value of the distance from the center at about 341 Mpc for model IIA and 68 Mpc for model IIB. The off-center observer cannot be farther away from the center than about 577 Mpc for model IIB at 3σ CL. It is determined that the best-fit parameters which characterize inhomogeneity are Ω{sub inh} = 0.77 (dimensionless: model IIA) and α = 7.31 × 10{sup –9} (s km{sup –1}){sup 2/3} Mpc{sup –4/3} (model IIB).
Correcting radiofrequency inhomogeneity effects in skeletal muscle magnetisation transfer maps.
Sinclair, C D J; Morrow, J M; Hanna, M G; Reilly, M M; Yousry, T A; Golay, X; Thornton, J S
2012-02-01
The potential of MRI to provide quantitative measures of neuromuscular pathology for use in therapeutic trials is being increasingly recognised. Magnetisation transfer (MT) imaging shows particular promise in this context, being sensitive to pathological changes, particularly in skeletal muscle, where measurements correlate with clinically measured muscle strength. Radiofrequency (RF) transmit field (B(1)) inhomogeneities can be particularly problematic in measurements of the MT ratio (MTR) and may obscure genuine muscle MTR changes caused by disease. In this work, we evaluate, for muscle imaging applications, a scheme previously proposed for the correction of RF inhomogeneity artefacts in cerebral MTR maps using B(1) information acquired in the same session. We demonstrate the theoretical applicability of this scheme to skeletal muscle using a two-pool model of pulsed quantitative MT. The correction scheme is evaluated practically in MTR imaging of the lower limbs of 28 healthy individuals and in two groups of patients with representative neuromuscular diseases: Charcot-Marie-Tooth disease type 1A and inclusion body myositis. The correction scheme was observed to reduce both the within-subject and between-subject variability in the calf and thigh muscles of healthy subjects and patient groups in histogram- and region-of-interest-based approaches. This method of correcting for RF inhomogeneity effects in MTR maps using B(1) data may markedly improve the sensitivity of MTR mapping indices as measures of pathology in skeletal muscle.
Advanced parameter retrievals for metamaterial slabs using an inhomogeneous model
NASA Astrophysics Data System (ADS)
Li Hou, Ling; Chin, Jessie Yao; Yang, Xin Mi; Lin, Xian Qi; Liu, Ruopeng; Xu, Fu Yong; Cui, Tie Jun
2008-03-01
The S-parameter retrieval has proved to be an efficient approach to obtain electromagnetic parameters of metamaterials from reflection and transmission coefficients, where a slab of metamaterial with finite thickness is regarded as a homogeneous medium slab with the same thickness [D. R. Smith and S. Schultz, Phys. Rev. B 65, 195104 (2002)]. However, metamaterial structures composed of subwavelength unit cells are different from homogeneous materials, and the conventional retrieval method is, under certain circumstances, not accurate enough. In this paper, we propose an advanced parameter retrieval method for metamaterial slabs using an inhomogeneous model. Due to the coupling effects of unit cells in a metamaterial slab, the roles of edge and inner cells in the slab are different. Hence, the corresponding equivalent medium parameters are different, which results in the inhomogeneous property of the metamaterial slab. We propose the retrievals of medium parameters for edge and inner cells from S parameters by considering two- and three-cell metamaterial slabs, respectively. Then we set up an inhomogeneous three-layer model for arbitrary metamaterial slabs, which is much more accurate than the conventional homogeneous model. Numerical simulations verify the above conclusions.
Inhomogeneity of pulmonary perfusion during sustained microgravity on SLS-1
NASA Technical Reports Server (NTRS)
Prisk, G. Kim; Guy, Harold J. B.; Elliott, Ann R.; West, John B.
1994-01-01
We studied the effects of gravity on the inhomogeneity of pulmonary perfusion in humans by performing hyperventilation-breath-hold single-breath measurements before, during, and after 9 days of continuous exposure to microgravity during the Spacelab Life Sciences-1 (SLS-1) mission. In microgravity the indicators of inhomogeneity of perfusion, especially the size of cardiogenic oscillations in expired CO2 and the height of phase IV, were markedly reduced. Cardiogenic oscillations were reduced to approximately 60% of their preflight standing size, and the height of phase IV was between 0 and -8% (a terminal fall became a small terminal rise) of the preflight standing value. The terminal change in expired CO2 was nearly abolished in microgravity, indicating more uniformity of blood flow between lung units that close and those that remain open at the end of expiration. A possible explanation of this observation is the disappearance of gravity-dependent topographic inequality of blood flow. The residual cardiogenic oscillations in expired CO2 imply a persisting inhomogeneity of perfusion in the absence of gravity, probably in lung regions that are not within the same acinus.
Dispersion properties of helical waves in radially inhomogeneous elastic media.
Syresin, D E; Zharnikov, T V; Tyutekin, V V
2012-06-01
In this paper, a method describing dispersion curve calculation for waves propagating in radially layered, inhomogeneous isotropic elastic waveguides is developed. Particular emphasis is placed on the helical waves with noninteger azimuthal wavenumbers, which can be potentially applied in such fields as nondestructive evaluation, acoustic tomography, etc., stipulating their practical importance. To solve the problem under consideration, the matrix Riccati equation is formulated for an impedance matrix. The use of the latter yields a simple form of the dispersion equation. Numerical computation of dispersion curves can encounter difficulties, which are due to potential singularities of the impedance matrix and the necessity to separate roots of the dispersion equation. These difficulties are overcome by employing the Cayley transform and invoking the parametric continuation method. The method developed by the authors is demonstrated by calculating dispersion diagrams in support of helical waves for several models of practical interest. Such computations for an inhomogeneous layer and its approximation by a set of homogeneous layers using a transfer matrix and Riccati equation methods revealed higher computational accuracy of the latter. Dispersion curves calculated for layers with different types of inhomogeneity demonstrated significant discrepancies at low frequencies.
Magnetostatic modes in ferromagnetic samples with inhomogeneous internal fields
NASA Astrophysics Data System (ADS)
Arias, Rodrigo
2015-03-01
Magnetostatic modes in ferromagnetic samples are very well characterized and understood in samples with uniform internal magnetic fields. More recently interest has shifted to the study of magnetization modes in ferromagnetic samples with inhomogeneous internal fields. The present work shows that under the magnetostatic approximation and for samples of arbitrary shape and/or arbitrary inhomogeneous internal magnetic fields the modes can be classified as elliptic or hyperbolic, and their associated frequency spectrum can be delimited. This results from the analysis of the character of the second order partial differential equation for the magnetostatic potential under these general conditions. In general, a sample with an inhomogeneous internal field and at a given frequency, may have regions of elliptic and hyperbolic character separated by a boundary. In the elliptic regions the magnetostatic modes have a smooth monotonic character (generally decaying form the surfaces (a ``tunneling'' behavior)) and in hyperbolic regions an oscillatory wave-like character. A simple local criterion distinguishes hyperbolic from elliptic regions: the sign of a susceptibility parameter. This study shows that one may control to some extent magnetostatic modes via external fields or geometry. R.E.A. acknowledges Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia under Project No. FB 0807 (Chile), Grant No. ICM P10-061-F by Fondo de Innovacion para la Competitividad-MINECON, and Proyecto Fondecyt 1130192.
Defect passivation in multicrystalline silicon for solar cells
NASA Astrophysics Data System (ADS)
Tarasov, I.; Ostapenko, S.; Nakayashiki, K.; Rohatgi, A.
2004-11-01
We report on the effect of hydrogen passivation in ribbon multicrystalline silicon (mc-Si) wafers from SiNx:H anti-reflecting layer using simultaneous rapid thermal annealing of Al back-contact and SiNx anti-reflection coating on the front (RTP-Al /SiNx). Scanning room-temperature photoluminescence spectroscopy revealed a strong inhomogeneity in the increase of minority carrier lifetime caused by the hydrogen defect passivation in mc-Si. We present experimental evidence that RTP-Al /SiNx processing leads to strong lifetime enhancement caused by hydrogen defect passivation in low-lifetime regions of mc-Si wafers. Additional details on the hydrogenation mechanism are revealed in a course of the dehydrogenation study. Hydrogen out-diffusion shows a different rate or activation energy between high and low lifetime regions of the wafers.
Surface defects and symmetries
NASA Astrophysics Data System (ADS)
Fuchs, Jürgen; Schweigert, Christoph
2015-04-01
In quantum field theory, defects of various codimensions are natural ingredients and carry a lot of interesting information. In this contribution we concentrate on topological quantum field theories in three dimensions, with a particular focus on Dijkgraaf-Witten theories with abelian gauge group. Surface defects in Dijkgraaf-Witten theories have applications in solid state physics, topological quantum computing and conformal field theory. We explain that symmetries in these topological field theories are naturally defined in terms of invertible topological surface defects and are thus Brauer-Picard groups.
Defect solitons in photonic lattices.
Yang, Jianke; Chen, Zhigang
2006-02-01
Nonlinear defect modes (defect solitons) and their stability in one-dimensional photonic lattices with focusing saturable nonlinearity are investigated. It is shown that defect solitons bifurcate out from every infinitesimal linear defect mode. Low-power defect solitons are linearly stable in lower bandgaps but unstable in higher bandgaps. At higher powers, defect solitons become unstable in attractive defects, but can remain stable in repulsive defects. Furthermore, for high-power solitons in attractive defects, we found a type of Vakhitov-Kolokolov (VK) instability which is different from the usual VK instability based on the sign of the slope in the power curve. Lastly, we demonstrate that in each bandgap, in addition to defect solitons which bifurcate from linear defect modes, there is also an infinite family of other defect solitons which can be stable in certain parameter regimes. PMID:16605473
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Atrial Septal Defect (For Teens)
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Characteristic Work Function Variations of Graphene Line Defects.
Long, Fei; Yasaei, Poya; Sanoj, Raj; Yao, Wentao; Král, Petr; Salehi-Khojin, Amin; Shahbazian-Yassar, Reza
2016-07-20
Line defects, including grain boundaries and wrinkles, are commonly seen in graphene grown by chemical vapor deposition. These one-dimensional defects are believed to alter the electrical and mechanical properties of graphene. Unfortunately, it is very tedious to directly distinguish grain boundaries from wrinkles due to their similar morphologies. In this report, high-resolution Kelvin potential force microscopy (KPFM) is employed to measure the work function distribution of graphene line defects. The characteristic work function variations of grain boundaries, standing-collapsed wrinkles, and folded wrinkles could be clearly identified. Classical and quantum molecular dynamics simulations reveal that the unique work function distribution of each type of line defects is originated from the doping effect induced by the SiO2 substrate. Our results suggest that KPFM can be an easy-to-use and accurate method to detect graphene line defects, and also propose the possibility to tune the graphene work function by defect engineering. PMID:27356179