NASA Astrophysics Data System (ADS)
Mogilatenko, A.; Knauer, A.; Zeimer, U.; Weyers, M.
2016-02-01
This study reports on defect distribution and compositional homogeneity of Al x Ga1-x N layers with a nominal composition x of 0.5 grown on AlN by metal organic vapor phase epitaxy. The AlN layers with a low threading dislocation density (TDD) of a few 108 cm-2 were obtained by ELO and showed periodic surface macrosteps. Al x Ga1-x N growth on these AlN surfaces results in inhomogeneous Ga distribution due to enhanced Ga incorporation on the macrostep sidewalls. Variation of AlGaN deposition rate strongly influences the Ga distribution as well as the defect structure in the layers. Low growth rates (0.2 μm h-1) result in an inhomogeneous TD distribution with formation of alternating stripes with lower and higher defect densities. Additionally, self-organized formation of additional Ga-rich areas at the top edge of the steps is observed. In contrast, at a higher growth rate of 1 μm h-1 the formation of additional Ga-rich areas can be completely suppressed, but the defect density increases. This leads to an optimum growth rate to minimize the TDD.
Phase Diagram of Inhomogeneous Percolation with a Defect Plane
NASA Astrophysics Data System (ADS)
Iliev, G. K.; Janse van Rensburg, E. J.; Madras, N.
2015-01-01
Let be the -dimensional hypercubic lattice and let be an -dimensional sublattice, with . We consider a model of inhomogeneous bond percolation on at densities and , in which edges in are open with probability , and edges in open with probability . We generalize several classical results of (homogeneous) bond percolation to this inhomogeneous model. The phase diagram of the model is presented, and it is shown that there is a subcritical regime for and (where is the critical probability for homogeneous percolation in ), a bulk supercritical regime for , and a surface supercritical regime for and . We show that is a strictly decreasing function for , with a jump discontinuity at . We extend the Aizenman-Barsky differential inequalities for homogeneous percolation to the inhomogeneous model and use them to prove that the susceptibility is finite inside the subcritical phase. We prove that the cluster size distribution decays exponentially in the subcritical phase, and sub-exponentially in the supercritical phases. For a model of lattice animals with a defect plane, the free energy is related to functions of the inhomogeneous percolation model, and we show how the percolation transition implies a non-analyticity in the free energy of the animal model. Finally, we present simulation estimates of the critical curve.
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.
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
Ross, Michael B; Ku, Jessie C; Blaber, Martin G; Mirkin, Chad A; Schatz, George C
2015-08-18
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
Weigmann, H-J; Schanzer, S; Vergou, T; Antoniou, C; Sterry, W; Lademann, J
2012-01-01
The inhomogeneous distribution of topically applied substances due to decisive differences in the skin structure (furrows and wrinkles) affects the efficacy of cosmetic products, in particular sunscreens. The combination of tape stripping and optical spectroscopy results in absorption data, which reflect ex vivo the inhomogeneity of the in vivo distribution of topically applied substances. Based on these data, a factor of inhomogeneity is defined describing the individual distribution of formulations on the skin surface of volunteers. Thus, the influence of different skin surface structures and the influence of different formulations on the distribution of the topically applied substances can be determined. Analyzing the inhomogeneity data on 6 volunteers (5 sunscreens per volunteer), it was found that the influence on the distribution of sunscreens caused by the formulation was higher than the inhomogeneity originating from the differences in the skin surface structure of the volunteers. The method is well suited to characterize, for example, sunscreens and antiaging creams in the process of development, as well as for the evaluation of the final products. PMID:22343548
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.
Temperature Anisotropy Distribution and Evolution in Inhomogeneous Solar Wind
NASA Astrophysics Data System (ADS)
Yoon, P. H.; Seough, J.; Kim, S.
2015-12-01
The solar wind displays temperature anisotropy associated with the protons, which is often represented as a rhombic shape data distribution in (Tperp/Tll, βll) space. The upper-right and lower-right boundaries of such a data distribution appear to be limited by various kinetic plasma instabilities driven by the proton temperature anisotropy. To understand such boundaries, the present authors developed a quasi-linear model in inhomogeneous solar wind plasma in which the instability-driven dissipation terms appear on the right-hand sides of the equations for Tperp and Tll, while self-consistently computing for the wave intensities. Such a formalism successfully reproduced the upper-right and lower-right boundaries. However, in order to explain the vast majority of data points within the distribution that are found well away from the boundaries and possessing near isotropy, Tperp ≈ Tll, one must include effects other than the collisionless dissipations, i.e., other than dissipations due to instabilities. The present paper employs an improved quasi-linear theory that incorporates not only the instability-driven collisionless dissipation terms, but also the dissipations due to binary collisions (which is often called the collisional age) as well as the dissipations due to spontaneous thermal emissions. The set of equations for Tperp and Tll as well as for the waves are solved over inhomogeneous solar wind model, and the results will be discussed. The present approach may help in interpreting existing and future satellite data, including those from the near future Solar Probe Plus and Solar Orbiter Missions.
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
NASA Astrophysics Data System (ADS)
Yan, Dandan; Zhang, Jianwei; Wu, Weijuan; Ying, Xiaoyan; Wu, Xiangping
2009-10-01
This paper is focused on the sophisticated realistic head modeling based on inhomogeneous and anisotropic conductivity distribution of the head tissues. The finite element method (FEM) was used to model the five-layer head volume conductor models with hexahedral elements from segmentation and mapping of DT-MRI data. Then the inhomogeneous conductivities of the scalp, CSF and gray matter tissue were distributed according a normal distribution based on the mean value of respective tissues. The electric conductivity of the brain tissues dictates different inhomogeneous and anisotropic at some different microscopic levels. Including the inhomogeneous and anisotropy of the tissue would improve the accuracy of the MREIT, EEG and MEG problems in the simulation research.
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. PMID:23069196
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
The influence of inhomogeneity of the reflectivity distribution on the accuracy of its measurement
NASA Technical Reports Server (NTRS)
Salman, Y. M.
1975-01-01
The influence of pulse volume dimensions on the accuracy of reflectivity from various clouds is considered. It is shown that due to the spatial averaging and the inhomogeneities of the clouds, the dependence frequently breaks down, which is a cause of lower values of the spatial distribution estimate. Values of the corrections calculated for various conditions are presented.
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
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.
X7R Lead-Complex Perovskite Dielectrics with Inhomogeneous Compositional Distribution
NASA Astrophysics Data System (ADS)
Uchikoba, Fumio; Ito, Takashi; Nakajima, Shigeyuki
1995-05-01
Excess- WO3 Pb(Mg1/2W1/2)O3-PbTiO3-Pb(Ni2/3Nb2/3)O3 polycrystalline dielectric material was investigated. This material met EIA X7R specifications (the change of the capacitance is less than 15% over the temperature range from -55° C to +125° C). The material showed inhomogeneous compositional distributions within grains that consisted of three main parts, each possessing a different temperature dependence of the dielectric constant. It was found that the flat-temperature dependence of the dielectric constant in this system could be attributed to this inhomogeneous compositional distribution. Using this material, multilayer ceramic capacitors were fabricated.
NASA Astrophysics Data System (ADS)
Ciappina, M. F.; Pérez-Hernández, J. A.; Shaaran, T.; Roso, L.; Lewenstein, M.
2013-06-01
We use the three-dimensional time-dependent Schrödinger equation (3 D-TDSE) to calculate angular electron momentum distributions and photoelectron spectra of atoms driven by spatially inhomogeneous fields. An example for such inhomogeneous fields is the locally enhanced field induced by resonant plasmons, appearing at surfaces of metallic nanoparticles, nanotips, and gold bow-tie shaped nanostructures. Our studies show that the inhomogeneity of the laser electric field plays an important role on the above-threshold ionization process in the tunneling regime, causing significant modifications on the electron momentum distributions and photoelectron spectra, while its effects in the multiphoton regime appear to be negligible. Indeed, through the tunneling above-threshold ionization (ATI) process, one can obtain higher energy electrons as well as a high degree of asymmetry in the momentum space map. In this study we consider near infrared laser fields with intensities in the mid- 1014 W/cm2 range and we use a linear approximation to describe their spatial dependence. We show that in this case it is possible to drive electrons with energies in the near-keV regime. Furthermore, we study how the carrier envelope phase influences the emission of ATI photoelectrons for few-cycle pulses. Our quantum mechanical calculations are fully supported by their classical counterparts.
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.
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.
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.
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.
Gamma Knife 3-D dose distribution near the area of tissue inhomogeneities by normoxic gel dosimetry
Isbakan, Fatih; Uelgen, Yekta; Bilge, Hatice; Ozen, Zeynep; Agus, Onur; Buyuksarac, Bora
2007-05-15
The accuracy of the Leksell GammaPlan registered , the dose planning system of the Gamma Knife Model-B, was evaluated near tissue inhomogeneities, using the gel dosimetry method. The lack of electronic equilibrium around the small-diameter gamma beams can cause dose calculation errors in the neighborhood of an air-tissue interface. An experiment was designed to investigate the effects of inhomogeneity near the paranosal sinuses cavities. The homogeneous phantom was a spherical glass balloon of 16 cm diameter, filled with MAGIC gel; i.e., the normoxic polymer gel. Two hollow PVC balls of 2 cm radius, filled with N{sub 2} gas, represented the air cavities inside the inhomogeneous phantom. For dose calibration purposes, 100 ml gel-containing vials were irradiated at predefined doses, and then scanned in a MR unit. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. Dose distributions are the results of a single shot of irradiation, obtained by collimating all 201 cobalt sources to a known target in the phantom. Both phantoms were irradiated at the same dose level at the same coordinates. Stereotactic frames and fiducial markers were attached to the phantoms prior to MR scanning. The dose distribution predicted by the Gamma Knife planning system was compared with that of the gel dosimetry. As expected, for the homogeneous phantom the isodose diameters measured by the gel dosimetry and the GammaPlan registered differed by 5% at most. However, with the inhomogeneous phantom, the dose maps in the axial, coronal and sagittal planes were spatially different. The diameters of the 50% isodose curves differed 43% in the X axis and 32% in the Y axis for the Z=90 mm axial plane; by 44% in the X axis and 24% in the Z axis for the Y=90 mm coronal plane; and by 32% in the Z axis and 42% in the Y axis for the X=92 mm sagittal plane. The lack of ability of the GammaPlan registered to predict the rapid dose fall off, due
Gamma Knife 3-D dose distribution near the area of tissue inhomogeneities by normoxic gel dosimetry.
Isbakan, Fatih; Ulgen, Yekta; Bilge, Hatice; Ozen, Zeynep; Agus, Onur; Buyuksarac, Bora
2007-05-01
The accuracy of the Leksell GammaPlan, the dose planning system of the Gamma Knife Model-B, was evaluated near tissue inhomogeneities, using the gel dosimetry method. The lack of electronic equilibrium around the small-diameter gamma beams can cause dose calculation errors in the neighborhood of an air-tissue interface. An experiment was designed to investigate the effects of inhomogeneity near the paranosal sinuses cavities. The homogeneous phantom was a spherical glass balloon of 16 cm diameter, filled with MAGIC gel; i.e., the normoxic polymer gel. Two hollow PVC balls of 2 cm radius, filled with N2 gas, represented the air cavities inside the inhomogeneous phantom. For dose calibration purposes, 100 ml gel-containing vials were irradiated at predefined doses, and then scanned in a MR unit. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. Dose distributions are the results of a single shot of irradiation, obtained by collimating all 201 cobalt sources to a known target in the phantom. Both phantoms were irradiated at the same dose level at the same coordinates. Stereotactic frames and fiducial markers were attached to the phantoms prior to MR scanning. The dose distribution predicted by the Gamma Knife planning system was compared with that of the gel dosimetry. As expected, for the homogeneous phantom the isodose diameters measured by the gel dosimetry and the GammaPlan differed by 5% at most. However, with the inhomogeneous phantom, the dose maps in the axial, coronal and sagittal planes were spatially different. The diameters of the 50% isodose curves differed 43% in the X axis and 32% in the Y axis for the Z =90 mm axial plane; by 44% in the X axis and 24% in the Z axis for the Y=90 mm coronal plane; and by 32% in the Z axis and 42% in the Y axis for the X=92 mm sagittal plane. The lack of ability of the GammaPlan to predict the rapid dose fall off, due to the air cavities behind or near the
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.
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
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.
NASA Astrophysics Data System (ADS)
Uenoyama, T.; Miyahara, R.; Katayama, M.; Inada, Y.
2016-05-01
The spatial distribution of the oxidation state for the nickel species in the LiNiO2 cathode was analyzed by means of the in-situ XAFS imaging technique during the charging and discharging processes. The inhomogeneous reaction for the LiNiO2 cathode was observed under the operating condition. The pattern in the 2-dimensional map of the oxidation state of the active material in the discharging process was similar to that in the charging process. It means that the areas preceding the discharging reaction agree with the areas delaying the charging reaction. It was suggested that the diffusion of Li+ was restricted by the surface product of the LiNiO2 electrode, and the concentration gradient of Li+ delayed the charging reaction at the reaction channel of the discharging reaction.
Cho, Yong-Hee Shim, Mun-Bo; Hwang, Sangheum; Kim, Sungjin; Kim, Jun-Youn; Kim, Jaekyun; Park, Young-Soo; Park, Seoung-Hwan
2013-12-23
It is known that due to the formation of in-plane local energy barrier, V-defects can screen the carriers which non-radiatively recombine in threading dislocations (TDs) and hence, enhance the internal quantum efficiency in GaN based light-emitting diodes. By a theoretical modeling capable of describing the inhomogeneous carrier distribution near the V-defect in GaN based quantum wells, we show that the efficient suppression of non-radiative (NR) recombination via TD requires the local energy barrier height of V-defect larger than ∼80 meV. The NR process in TD combined with V-defect influences the quantum efficiency mainly in the low injection current density regime suitably described by the linear dependence of carrier density. We provide a simple phenomenological expression for the NR recombination rate based on the model result.
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.
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.
Fault-induced delayed voltage recovery in a long inhomogeneous power-distribution feeder
NASA Astrophysics Data System (ADS)
Stolbova, Irina; Backhaus, Scott; Chertkov, Michael
2015-02-01
We analyze the dynamics of a distribution circuit loaded with many induction motors and subjected to sudden changes in voltage at the beginning of the circuit. As opposed to earlier work by Duclut et al. [Phys. Rev. E 87, 062802 (2013), 10.1103/PhysRevE.87.062802], the motors are disordered, i.e., the mechanical torque applied to the motors varies in a random manner along the circuit. In spite of the disorder, many of the qualitative features of a homogeneous circuit persist, e.g., long-range motor-motor interactions mediated by circuit voltage and electrical power flows result in coexistence of the spatially extended and propagating normal and stalled phases. We also observed a new phenomenon absent in the case without inhomogeneity or disorder. Specifically, the transition front between the normal and stalled phases becomes somewhat random, even when the front is moving very slowly or is even stationary. Motors within the blurred domain appear in a normal or stalled state depending on the local configuration of the disorder. We quantify the effects of the disorder and discuss the statistics of distribution dynamics, e.g., the front position and width, total active and reactive consumption of the feeder, and maximum clearing time.
Fault-induced delayed voltage recovery in a long inhomogeneous power-distribution feeder.
Stolbova, Irina; Backhaus, Scott; Chertkov, Michael
2015-02-01
We analyze the dynamics of a distribution circuit loaded with many induction motors and subjected to sudden changes in voltage at the beginning of the circuit. As opposed to earlier work by Duclut et al. [Phys. Rev. E 87, 062802 (2013)], the motors are disordered, i.e., the mechanical torque applied to the motors varies in a random manner along the circuit. In spite of the disorder, many of the qualitative features of a homogeneous circuit persist, e.g., long-range motor-motor interactions mediated by circuit voltage and electrical power flows result in coexistence of the spatially extended and propagating normal and stalled phases. We also observed a new phenomenon absent in the case without inhomogeneity or disorder. Specifically, the transition front between the normal and stalled phases becomes somewhat random, even when the front is moving very slowly or is even stationary. Motors within the blurred domain appear in a normal or stalled state depending on the local configuration of the disorder. We quantify the effects of the disorder and discuss the statistics of distribution dynamics, e.g., the front position and width, total active and reactive consumption of the feeder, and maximum clearing time. PMID:25768557
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
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)
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.
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. PMID:25994718
Experimetal study of a freely falling plate with an inhomogeneous mass distribution
NASA Astrophysics Data System (ADS)
Huang, Wentao; Liu, Hong; Wang, Fuxin; Wu, Junqi; Zhang, H. P.
2013-11-01
A homogeneous thin plate often flutters while falling through a fluid under gravity. The center of gravity of the plate moves back-and-forth horizontally and the plate tilting angle oscillates symmetrically from the horizontal. Here we show that such a scenario is qualitatively changed for a plate with noncoinciding centers of gravity and buoyancy due to an inhomogeneous mass distribution. Mismatch of the centers causes an external torque that breaks the symmetry of rotational motion, shifts the mean tilting position from the horizontal, and leads to a net horizontal plate displacement. In laboratory experiments with a Reynolds number around 1500, we found that the net horizontal displacement scales linearly with the separation between the centers up to a critical value, beyond which the plate falls vertically in an edge-on configuration with the heavier side downward. Experimental results are compared to predictions of a quasi-steady numerical model. Our work demonstrates that motion of freely moving objects in a fluid depends sensitively on external torques, which potentially can be used as an effective control method.
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.
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
NASA Astrophysics Data System (ADS)
Li, Xiaoqi; Jiang, Huabei
2013-02-01
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.
Spatial distribution of defect luminescence in GaN nanowires.
Li, Qiming; Wang, George T
2010-05-12
The spatial distribution of defect-related and band-edge luminescence from GaN nanowires grown by metal-organic chemical vapor deposition was studied by spatially resolved cathodoluminescence imaging and spectroscopy. A surface layer exhibiting strong yellow luminescence (YL) near 566 nm in the nanowires was revealed, compared to weak YL in the bulk. In contrast, other defect-related luminescence near 428 nm (blue luminescence) and 734 nm (red luminescence), in addition to band-edge luminescence (BEL) at 366 nm, were observed in the bulk of the nanowires but were largely absent at the surface. As the nanowire width approaches a critical dimension, the surface YL layer completely quenches the BEL. The surface YL is attributed to the diffusion and piling up of mobile point defects, likely isolated gallium vacancies, at the surface during growth. PMID:20392110
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
Evolution of the statistical distribution in a topological defect network
Xue, Fei; Wang, Xueyun; socolenco, Ion; Gu, Yijia; Chen, Long-Qing; Cheong, Sang-Wook
2015-01-01
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. PMID:26586339
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.
Evolution of the statistical distribution in a topological defect network.
Xue, Fei; Wang, Xueyun; Socolenco, Ion; Gu, Yijia; Chen, Long-Qing; Cheong, Sang-Wook
2015-01-01
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. PMID:26586339
Hesse, Markus C; Salehi, Leili; Schmitz, Georg
2013-09-01
In diagnostic ultrasound imaging, the image reconstruction quality is crucial for reliable diagnosis. Applying reconstruction algorithms based on the acoustic wave equation, the obtained image quality depends significantly on the physical material parameters accounted for in the equation. In this contribution, we extend a proposed iterative nonlinear one-parameter compressibility reconstruction algorithm by the additional reconstruction of the object's inhomogeneous mass density distribution. The improved iterative algorithm is able to reconstruct inhomogeneous maps of the object's compressibility and mass density simultaneously using only one conventional linear transducer array at a fixed location for wave transmission and detection. The derived approach is based on an acoustic wave equation including spatial compressibility and mass density variations, and utilizes the Kaczmarz method for iterative material parameter reconstruction. We validate our algorithm numerically for an unidirectional pulse-echo breast imaging application, and thus generate simulated measurements acquired from a numerical breast phantom with realistic compressibility and mass density values. Applying these measurements, we demonstrate with two reconstruction experiments the necessity to calculate the mass density in case of tissues with significant mass density inhomogeneities. When reconstructing spatial mass density variations, artefacts in the breast's compressibility image are reduced resulting in improved spatial resolution. Furthermore, the compressibility relative error magnitude within a diagnostically significant region of interest (ROI) decreases from 3.04% to 2.62%. Moreover, a second image showing the breast's inhomogeneous mass density distribution is given to provide additional diagnostic information. In the compressibility image, a spatial resolution moderately higher than the classical half-wavelength limit is observed. PMID:23948675
NASA Astrophysics Data System (ADS)
Starikov, F. A.
1993-05-01
This paper investigates the dynamics of amplified spontaneous x-ray emission escaping from a randomly inhomogeneous plasma active medium through its ends and lateral surface. It is shown that the scattering of radiation by fluctuations in the dielectric permittivity, ɛ˜, can be utilized to extract energy through the lateral surface of the active medium. The radiant intensity is maximal in an off-axis direction in this case. When both regular refraction and scattering by ɛ˜ are operating, the distributed extraction of the light is determined by that effect which has the smaller characteristic length (i.e., the scattering length or the refraction length).
NASA Astrophysics Data System (ADS)
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 1H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/ T2,short and 1/ T2,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 T1/ T2 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 T2/ T2,eff is derived as a function of the T1/ T2 ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T1- T2 correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T1- T2 experimental correlations maps were corrected for the T1/ T2 effect using the derived T2/ T2,eff correction factor.
Two new defective distributions based on the Marshall-Olkin extension.
Rocha, Ricardo; Nadarajah, Saralees; Tomazella, Vera; Louzada, Francisco
2016-04-01
The presence of immune elements (generating a fraction of cure) in survival data is common. These cases are usually modeled by the standard mixture model. Here, we use an alternative approach based on defective distributions. Defective distributions are characterized by having density functions that integrate to values less than 1, when the domain of their parameters is different from the usual one. We use the Marshall-Olkin class of distributions to generalize two existing defective distributions, therefore generating two new defective distributions. We illustrate the distributions using three real data sets. PMID:25951911
NASA Astrophysics Data System (ADS)
Roy, Suparna; Patra, Sudipta; Neogy, S.; Laik, A.; Choudhary, S. K.; Chakrabarti, Debalay
2012-06-01
Spatial distribution in size and frequency of microalloy precipitates have been characterized in two continuous-cast high-strength, low-alloy steel slabs, one containing Nb, Ti, and V and the other containing only Ti. Microsegregation during casting resulted in an inhomogeneous distribution of Nb and Ti precipitates in as-cast slabs. A model has been proposed in this study based on the detailed characterization of cast microalloy precipitates for predicting the spatial distribution in size and volume fraction of precipitates. The present model considers different models, which have been proposed earlier. Microsegregation during solidification has been predicted from the model proposed by Clyne and Kurz. Homogenization of alloying elements during cooling of the cast slab has been predicted following the approach suggested by Kurz and Fisher. Thermo-Calc software predicted the thermodynamic stability and volume fraction of microalloy precipitates at interdendritic and dendritic regions. Finally, classical nucleation and growth theory of precipitation have been used to predict the size distribution of microalloy precipitates at the aforementioned regions. The accurate prediction and control over the precipitate size and fractions may help in avoiding the hot-cracking problem during casting and selecting the processing parameters for reheating and rolling of the slabs.
Nonequilibrium inhomogeneous steady state distribution in disordered, mean-field rotator systems
NASA Astrophysics Data System (ADS)
Campa, Alessandro; Gupta, Shamik; Ruffo, Stefano
2015-05-01
We present a novel method to compute the phase space distribution in the nonequilibrium stationary state of a wide class of mean-field systems involving rotators subject to quenched disordered external drive and dissipation. The method involves a series expansion of the stationary distribution in inverse of the damping coefficient; the expansion coefficients satisfy recursion relations whose solution requires computing a matrix where about three quarters of the elements vanish, making numerical evaluation simple and efficient. We illustrate our method for the paradigmatic Kuramoto model of spontaneous collective synchronization and for its two mode generalization, in the presence of noise and inertia, and demonstrate an excellent agreement between simulations and theory for the phase space distribution.
Nilsson, Henrik; Karlgren, Silja; Blomqvist, Lennart; Jonas, Eduard
2015-01-01
Background Previous studies have shown that liver function is inhomogeneously distributed in diseased livers, and this uneven distribution cannot be compensated for if a global liver function test is used for the prediction of post-operative remnant liver function. Dynamic Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) can assess segmental liver function, thus offering the possibility to overcome this problem. Methods In 10 patients with liver cirrhosis and 10 normal volunteers, the contribution of individual liver segments to total liver function and volume was calculated using dynamic Gd-EOB-DTPA-enhanced MRI. Remnant liver function predictions using a segmental method and global assessment were compared for a simulated left hemihepatectomy. For the prediction based on segmental functional MRI assessment, the estimated function of the remnant liver segments was added. Results Global liver function assessment overestimated the remnant liver function in 9 out of 10 patients by as much as 9.3% [median −3.5% (−9.3–3.5%)]. In the normal volunteers there was a slight underestimation of remnant function in 9 out of 10 cases [median 1.07% (−0.7–2.5%)]. Discussion The present study underlines the necessity of a segmental liver function test able to compensate for the non-homogeneous nature of liver function, if the prediction of post-operative remnant liver function is to be improved. PMID:25297934
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..
NASA Astrophysics Data System (ADS)
Doucet, R.; Olivares, M.; DeBlois, F.; Podgorsak, E. B.; Kawrakow, I.; Seuntjens, J.
2003-08-01
Calculations of dose distributions in heterogeneous phantoms in clinical electron beams, carried out using the fast voxel Monte Carlo (MC) system XVMC and the conventional MC code EGSnrc, were compared with measurements. Irradiations were performed using the 9 MeV and 15 MeV beams from a Varian Clinac-18 accelerator with a 10 × 10 cm2 applicator and an SSD of 100 cm. Depth doses were measured with thermoluminescent dosimetry techniques (TLD 700) in phantoms consisting of slabs of Solid WaterTM (SW) and bone and slabs of SW and lung tissue-equivalent materials. Lateral profiles in water were measured using an electron diode at different depths behind one and two immersed aluminium rods. The accelerator was modelled using the EGS4/BEAM system and optimized phase-space files were used as input to the EGSnrc and the XVMC calculations. Also, for the XVMC, an experiment-based beam model was used. All measurements were corrected by the EGSnrc-calculated stopping power ratios. Overall, there is excellent agreement between the corrected experimental and the two MC dose distributions. Small remaining discrepancies may be due to the non-equivalence between physical and simulated tissue-equivalent materials and to detector fluence perturbation effect correction factors that were calculated for the 9 MeV beam at selected depths in the heterogeneous phantoms.
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. PMID:2233564
NASA Astrophysics Data System (ADS)
Prikhna, T. A.; Gawalek, W.; Tkach, V. M.; Danilenko, N. I.; Savchuk, Ya M.; Dub, S. N.; Moshchil, V. E.; Kozyrev, A. V.; Sergienko, N. V.; Wendt, M.; Melnikov, V. S.; Dellith, J.; Weber, H.; Eisterer, M.; Schmidt, Ch; Habisreuther, T.; Litzkendorf, D.; Vajda, J.; Shapovalov, A. P.; Sokolovsky, V.; Nagorny, P. A.; Sverdun, V. B.; Kosa, J.; Karau, F.; Starostina, A. V.
2010-06-01
The effect of doping with Ti, Ta, SiC in complex with synthesis temperature on the amount and distribution of structural inhomogeneities in MgB2 matrix of high-pressure-synthesized-materials (2 GPa) which can influence pinning: higher borides (MgB12) and oxygen-enriched Mg-B-O inclusions, was established and a mechanism of doping effect on jc increase different from the generally accepted was proposed. Near theoretically dense SiC-doped material exhibited jc= 106 A/cm2 in 1T field and Hirr =8.5 T at 20 K. The highest jc in fields above 9, 6, and 4 T at 10, 20, and 25 K, respectively, was demonstrated by materials synthesized at 2 GPa, 600 °C from Mg and B without additions (at 20 K jc= 102 A/cm2 in 10 T field). Materials synthesized from Mg and B taken up to 1:20 ratio were superconductive. The highest jc (6×104 A/cm2 at 20 K in zero field, Hirr= 5 T) and the amount of SC phase (95.3% of shielding fraction), Tc being 37 K were demonstrated by materials having near MgB12 composition of the matrix. The materials with MgB12 matrix had a doubled microhardness of that with MgB2 matrix (25±1.1 GPa and 13.08±1.07 GPa, at a load of 4.9 N, respectively).
Distribution Features of Small Defects in Precision Weldments of Titanium Alloy
NASA Astrophysics Data System (ADS)
Gang, T.; Shi, D. H.; Yuan, Y.; Yang, S. Y.
2006-10-01
The detection method of real time radioscopy was adopted to test titanium alloys precision weldments with complex structure non-destructively. The location of small defects in the line grey distribution curve was determined based on the analysis of X-ray detection images and the geometry relationship of precision weldments components, and a formula which can calculate the depth of defects was deduced. In order to improve the accuracy of defect locating a formula which can calculate the deviation of defects was deduced also by adopting the method of rotation weldments in this paper. Automated extraction algorithm of projection distance was developed according to the characteristic of the typical defects — peak anomaly and slant concave anomaly in the line grey distribution curve. The experimental results show that the defect depth, deviation and distribution along the longitudinal direction of weld can be figured out, and the spatial distribution features of defects can be determined, the above features will provide better basis for further structural integrity evaluation of the precision weldments.
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
Distribution pattern and allocation of defects in hydrogenated ZnO thin films.
Gurylev, Vitaly; Su, Chung-Yi; Perng, Tsong-Pyng
2016-06-21
A polycrystalline ZnO thin film prepared by atomic layer deposition was annealed in hydrogen at 10 bar and 350-450 °C. Hydrogenation induced simultaneous formation of oxygen and zinc vacancies whose concentrations were closely related to the temperature of treatment. Spatial distributions of these defects were analyzed by photoluminescence confocal mapping which revealed that their localized appearances are linked to each other. It was also demonstrated that nanomechanical mapping of elastic modulus distribution could be used to assess the allocation of accumulated defects on the topmost surface of ZnO with a depth resolution of only several atomic layers. The higher the temperature of hydrogenation, the higher the concentration, and more uniform the distribution of surface defects. In addition, the correlation between the surface morphology and the accumulated defects was established. PMID:27244648
NASA Astrophysics Data System (ADS)
Pastor, K.; Goiran, M.; Kim, D. J.; Madhukar, A.; Leotin, J.; Bouchelaghem, M.; Askenazy, S.
1990-12-01
Cyclotron resonance in an inverted GaAs/Ga1-xAlxAs heterostructure and/or single quantum well (GaAs is grown on a Ga1-xAlxAs-doped layer rather than vice versa) was studied in the far infrared. A large splitting was found and is attributed to inhomogeneous charge-distribution-induced coupling to the intersubband resonance. A simple model accounting for the coupling in the presence of the inhomogeneous charge at the interface has been developed. From the fit to the experimental data, the value of the average electric field gradients at the inverted interface G=1.2×109 V/cm2 was obtained.
NASA Technical Reports Server (NTRS)
Lacis, Andrew A.; Oinas, Valdar
1991-01-01
A radiative transfer method for treating nongray gaseous absorption and thermal emission in vertically inhomogeneous multiple scattering atmospheres is described. Probability density distributions of absorption coefficient strength are derived from line-by-line calculations to construct line-by-line and band model based k distributions. The monotonic ordering of absorption coefficient strengths in these k distributions implicitly preserves the monochromatic structure of the atmosphere at different pressure levels, thus simulating monochromatic spectral integration at a fraction of the line-by-line computing cost. The k distribution approach also permits accurate modeling of overlapping absorption by different atmospheric gases and accurate treatment of nongray absorption in multiple scattering media. It is shown that the correlated k distribution method is capable of achieving numerical accuracy to within 1 percent of cooling rates obtained with line-by-line calculations throughout the troposphere and most of the stratosphere.
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.
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. PMID:25565086
Lithographic analysis of distributed photomask defects: II. Random mask CD errors
NASA Astrophysics Data System (ADS)
Karklin, Linard
2002-07-01
With constant push for smaller and faster devices photo mask technology has become the most critical part of the entire integrated circuit (IC) production flow. Mask inspection and mask defect repair are increasingly important components of advanced photo mask technology. The low cost of mask manufacturing and the necessity of delivering photo masks to production floor in the shortest possible time require new photo mask specs and acceptance criteria. It is no longer economically viable to reject a photo mask because some mask anomalies were found, or repair all the defects detected by state of the art inspection tool. One should use a smart approach to separate tolerable mask anomalies from real mask defects that might negatively affect device yield. However, this is not a trivial task. With rising mask complexity (e.g., binary masks with aggressive optical proximity correction or phase-shifting masks (PSM)-attenuated and alternating) and inspection and metrology tools running out of steam, new technologies such as the AIMSTMand Virtual Stepper® system must be used to sort nuisance mask defects from real ones. This will help to reduce the number of required defect repairs and shorten mask manufacturing cycle time. However, it is very difficult to utilize AIMS in the production environment because of its low operational speed; the Virtual Stepper software, in its turn, relies on mask data captured by inspection/metrology hardware. In the case of phase masks, such as Attenuated PSM (especially high transmission EAPSM) and Alternating PSM, inspection tools are not able to accurately retrieve optical properties of mask materials; as a result defect analysis is becoming very difficult and unreliable task. Very common types of PSM defects that occur during mask manufacturing and repair processes are the so-called distributed defects, such as gallium stains, riverbeds, pinhole clusters, and large chrome residuals (on EAPSM). It is very difficult to get accurate
Oddstig, Jenny; Bernhardt, Peter; Lizana, Helena; Nilsson, Ola; Ahlman, Håkan; Kölby, Lars; Forssell-Aronsson, Eva
2012-02-01
The aim of this study was to investigate the activity distribution in neouroendocrine tumors after diagnostic, or therapeutic, amounts of [(177)Lu-DOTA(0)-Tyr(3)]-octreotate and to investigate how the activity distribution influences the absorbed dose. Furthermore, the activity distribution of a second administration of radiolabeled octreotate was studied. Nude mice with subcutaneously grown human midgut carcinoid (GOT1) were injected intravenously with different amounts of (177)Lu-octreotate. At different time points thereafter (4 h to 13 days), a second injection of [(111)In-DOTA(0)-Tyr(3)]-octreotate was given to estimate the somatostatin receptor (sstr) expression. The activity distribution in the tumors was then determined. Monte Carlo simulations with PENELOPE were performed for dosimetry. Fifty-one out of 58 investigated tumors showed a lower activity concentration in the peripheral part than in the central part of the tumor. The amount of activity injected, or time after administration, did neither influence the relative activity nor the sstr distribution in the tumor. After an initial down-regulation (at 4-24 h), there was an up-regulation of sstr (1.5-2 times, at 7-14 days). Monte Carlo simulations demonstrated an inhomogeneous absorbed dose distribution in the tumor using (177)Lu, with twice as high absorbed dose centrally than peripherally. The high activity concentration centrally and the up-regulation of sstr demonstrated will facilitate fractionated therapy using radiolabeled somatostatin analogues if similar results will be obtained also in patients. The inhomogeneous activity distribution in the tumor has to be taken into account when the absorbed dose distribution in tumor is calculated. PMID:22108870
NASA Astrophysics Data System (ADS)
Wang, Tao; Diao, Xungang; Wang, Xuan
2011-09-01
Aluminum doped zinc oxide (ZAO) films were deposited by direct current (DC) reactive magnetron sputtering from a ZnO:Al2O3 (3 wt.% Al2O3) ceramic target at room temperature. In order to explore the inhomogeneous property distribution across the substrate, the films were deposited with varied substrate-target distances (Ds) ranging from 2 cm to 9 cm. The experimental results obtained from four-point probe, spectrophotometer, scanning electron microscope, X-ray diffractometer and Auger electronic spectrometer were analyzed to explore the nonuniform property distribution of the obtained ZAO films. The results confirmed that the films' optoelectronic properties, crystallinity and surface morphology, etc., which were obtained from different substrate areas facing the target were remarkably different. It was revealed that the inhomogeneous property distribution was noticeably dependent on the Ds. It was also suggested that the great difference of electrical conductivity among films from different substrate areas could not be ascribed to the difference of chemical composition, but might be explained by the distinctive crystallinity correspondingly. Films from different substrate regions with distinctive electrical characteristics were either (0 0 2) or (1 1 0) textured.
Odedra, Smita; Wimperis, Stephen
2013-06-01
Several widely used methods for suppressing the "background" signal in (1)H magic angle spinning (MAS) NMR spectroscopy are based on the assumption of a significant difference between the B1 radiofrequency field experienced by the sample (within the MAS rotor) and that felt by static components of the probehead (where the background signal is believed to originate). In this work, a two-dimensional correlation experiment employing inhomogeneous B0 and B1 fields is used to image the B1 distribution in a MAS NMR probehead. The experiment, which can be performed on any spectrometer, allows the distribution of the B1 field to be measured and also correlated with the spatial location of the NMR signal within the probehead. The method can also readily be combined with various "depth pulse" techniques for background suppression, allowing their performances to be more rigorously evaluated. PMID:23644349
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
Point defect distribution in high-mobility conductive SrTiO{sub 3} crystals
Gentils, A.; Copie, O.; Bibes, M.; Bouzehouane, K.; Jacquet, E.; Carretero, C.; Barthelemy, A.; Fortuna, F.; Basletic, M.; Tafra, E.; Hamzic, A.
2010-04-01
We have carried out positron-annihilation spectroscopy to characterize the spatial distribution and the nature of vacancy defects in insulating as-received as well as in reduced SrTiO{sub 3} substrates exhibiting high-mobility conduction. The substrates were reduced either by ion etching the substrate surfaces or by doping with vacancies during thin-film deposition at low pressure and high temperature. We show that Ti vacancies are native defects homogeneously distributed in as-received substrates. In contrast, the dominant vacancy defects are the same both in ion etched crystals and substrates reduced during the film growth, and they consist of nonhomogeneous distributions of cation-oxygen vacancy complexes. Their spatial extension is tuned from a few microns in ion-etched samples to the whole substrate in specimens reduced during film deposition. Our results shed light on the transport mechanisms of conductive SrTiO{sub 3} crystals and on strategies for defect-engineered oxide quantum wells, wires, and dots.
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.
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
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.
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.
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.
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
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.
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
Radiation transport in inhomogeneous media
Keiter, Paul; Gunderson, Mark; Foster, John; Rosen, Paula; Comley, Andrew; Taylor, Mark; Perry, Ted
2008-05-15
Calculations of radiation transport in heated materials are greatly complicated by the presence of regions in which two or more materials are inhomogeneously mixed. This phenomenon is important in many systems, such as astrophysical systems where density clumps can be found in star-forming regions and molecular clouds. Laboratory experiments have been designed to test the modeling of radiation transport through inhomogeneous plasmas. A laser-heated hohlraum is used as a thermal source to drive radiation through polymer foam containing randomly distributed gold particles. Experimental measurements of radiation transport in foams with gold particle sizes ranging from 5-9 {mu}m to submicrometer diameters as well as the homogeneous foam case are presented. The simulation results of the radiation transport are compared to the experiment and show that an inhomogeneous transport model must be applied to explain radiation transport in foams loaded with 5 {mu}m diameter gold particles.
NASA Astrophysics Data System (ADS)
Coraddu, Massimo; Lissia, Marcello; Quarati, Piero
2009-09-01
Non-resonant fusion cross-sections significantly higher than corresponding theoretical predictions are observed in low-energy experiments with deuterated matrix target. Models based on thermal effects, electron screening, or quantum-effect dispersion relations have been proposed to explain these anomalous results: none of them appears to satisfactory reproduce the experiments. Velocity distributions are fundamental for the reaction rates and deviations from the Maxwellian limit could play a central role in explaining the enhancement. We examine two effects: an increase of the tail of the target Deuteron momentum distribution due to the Galitskii-Yakimets quantum uncertainty effect, which broadens the energy-momentum relation; and spatial fluctuations of the Debye-Hückel radius leading to an effective increase of electron screening. Either effect leads to larger reaction rates especially large at energies below a few keV, reducing the discrepancy between observations and theoretical expectations.
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
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
Zhang, X. B.; Pei, Z. L.; Gong, J.; Sun, C.
2007-01-01
A study of the electrical properties and spatial distribution of the ZnO:Al (AZO) thin films prepared by dc magnetron sputtering at low deposition temperature was presented, with emphasis on the origin of the resistivity inhomogeneity across the substrate. Various growth conditions were obtained by manipulating the growth temperature T{sub S}, total pressure P{sub T}, and ion-to-neutral ratio J{sub i}/J{sub n}. The plasma characteristics such as radial ion density and floating/plasma potential distribution over the substrate were measured by Langmuir probe, while the flux and energy distribution of energetic species were estimated through Monte Carlo simulations. The crystalline, stress and electrical properties of the films were found to be strongly dependent on T{sub S} and J{sub i}/J{sub n}. Under the low J{sub i}/J{sub n} (<0.3) conditions, the T{sub S} exerted a remarkable influence on film quality. The films prepared at 90 deg. C were highly compressed, exhibiting poor electrical properties and significant spatial distribution. High quality films with low stress and resistivity were produced at higher T{sub S} (200 deg. C). Similarly, at lower T{sub S} (90 deg. C), higher J{sub i}/J{sub n} ({approx}2) dramatically improved the film resistivity as well as its lateral distribution. Moreover, it indicated that the role of ion bombardment is dependent on the mechanism of dissipation of incident species. Ion bombardment is beneficial to the film growth if the energy of incident species E{sub i} is below the penetration threshold E{sub pet} ({approx}33 eV for ZnO); on the other hand, the energy subimplant mechanism would work, and the bombardment degrades the film quality when E{sub i} is over the E{sub pet}. The energetic bombardment of negative oxygen ions rather than the positives dominated the resistivity distribution of AZO films, while the nonuniform distribution of active oxygen played a secondary role which was otherwise more notable under conditions of
Spatial distribution of defects in ultra fine grained copper prepared by high pressure torsion
NASA Astrophysics Data System (ADS)
Čížek, J.; Melikhova, O.; Procházka, I.; Janeček, M.; Hruška, P.; Dobatkin, S.
2016-01-01
Bulk materials with ultra fine grain structure can be fabricated by severe plastic deformation. Among variety of techniques based on severe plastic deformation high pressure torsion is the most efficient method for grain refinement down to nano-scale. In torsion deformation the strain distribution across the sample is non-uniform and increases with increasing radial distance from the centre of the sample corresponding to the axis of torsional straining. Due to this reason it is very important to examine homogeneity of ultra fine grained structure of samples prepared by high pressure torsion. In the present work positron annihilation spectroscopy was employed for mapping of spatial distribution of defects in ultra fine grained copper prepared by high pressure torsion. Spatial distribution of defects was examined by means of (i) Doppler broadening using S parameter for mapping of defect density and (ii) positron lifetime spectroscopy. Spatially resolved positron annihilation studies were combined with mapping by microhardness testing. Hardness is sensitive to dislocation density due to work hardening but is practically not affected by vacancies while positron annihilation is sensitive both to dislocations and vacancies. Our investigations revealed that ultra fine grained copper contains dislocations and vacancy clusters created by agglomeration of deformation-induced vacancies. Average size of vacancy clusters increases with increasing radial distance from the centre of the sample due to higher production rate of vacancies resulting in larger clusters. During high pressure torsion deformation microhardness increases firstly at the periphery of the sample due to the highest imposed strain. With increasing number of high pressure torsion revolutions the hardness increases also in the centre and finally becomes practically uniform across the whole sample indicating the homogeneous distribution of dislocations. Doppler broadening mapping revealed a remarkable increase of
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
Relationship between Defect Size and Fatigue Life Distributions in Al-7 Pct Si-Mg Alloy Castings
NASA Astrophysics Data System (ADS)
Tiryakioğlu, Murat
2009-07-01
A new method for predicting the variability in fatigue life of castings was developed by combining the size distribution for the fatigue-initiating defects and a fatigue life model based on the Paris-Erdoğan law for crack propagation. Two datasets for the fatigue-initiating defects in Al-7 pct Si-Mg alloy castings, reported previously in the literature, were used to demonstrate that (1) the size of fatigue-initiating defects follow the Gumbel distribution; (2) the crack propagation model developed previously provides respectable fits to experimental data; and (3) the method developed in the present study expresses the variability in both datasets, almost as well as the lognormal distribution and better than the Weibull distribution.
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.
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.
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.
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.
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)
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
2015-07-01
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.
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
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)
Knitter, Sebastian; Fatt Liew, Seng; Xiong, Wen; Guy, Mikhael I.; Solomon, Glenn S.; Cao, Hui
2016-01-01
We introduce a topological defect to a regular photonic crystal defect cavity with anisotropic unit cell. Spatially localized resonances are formed and have high quality factor. Unlike the regular photonic crystal defect states, the localized resonances in the topological defect structures support powerflow vortices. Experimentally we realize lasing in the topological defect cavities with optical pumping. This work shows that the spatially inhomogeneous variation of the unit cell orientation adds another degree of freedom to the control of lasing modes, enabling the manipulation of the field pattern and energy flow landscape.
Inhomogeneous Polyakov loop induced by inhomogeneous chiral condensates
NASA Astrophysics Data System (ADS)
Hayata, Tomoya; Yamamoto, Arata
2015-05-01
We study the spatial inhomogeneity of the Polyakov loop induced by inhomogeneous chiral condensates. We formulate an effective model of gluons on the background fields of chiral condensates, and perform its lattice simulation. On the background of inhomogeneous chiral condensates, the Polyakov loop exhibits an in-phase spatial oscillation with the chiral condensates. We also analyze the heavy quark potential and show that the inhomogeneous Polyakov loop indicates the inhomogeneous confinement of heavy quarks.
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.
Wakes in inhomogeneous plasmas.
Kompaneets, Roman; Ivlev, Alexei V; Nosenko, Vladimir; Morfill, Gregor E
2014-04-01
The Debye shielding of a charge immersed in a flowing plasma is an old classic problem. It has been given renewed attention in the last two decades in view of experiments with complex plasmas, where charged dust particles are often levitated in a region with strong ion flow. Efforts to describe the shielding of the dust particles in such conditions have been focused on the homogeneous plasma approximation, which ignores the substantial inhomogeneity of the levitation region. We address the role of the plasma inhomogeneity by rigorously calculating the point charge potential in the collisionless Bohm sheath. We demonstrate that the inhomogeneity can dramatically modify the wake, making it nonoscillatory and weaker. PMID:24827356
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.
Quantifying properties of ICM inhomogeneities
NASA Astrophysics Data System (ADS)
Zhuravleva, I.; Churazov, E.; Kravtsov, A.; Lau, E. T.; Nagai, D.; Sunyaev, R.
2013-02-01
We present a new method to identify and characterize the structure of the intracluster medium (ICM) in simulated galaxy clusters. The method uses the median of gas properties, such as density and pressure, which we show to be very robust to the presence of gas inhomogeneities. In particular, we show that the radial profiles of median gas properties in cosmological simulations of clusters are smooth and do not exhibit fluctuations at locations of massive clumps in contrast to mean and mode properties. Analysis of simulations shows that distribution of gas properties in a given radial shell can be well described by a log-normal probability density function and a tail. The former corresponds to a nearly hydrostatic bulk component, accounting for ˜99 per cent of the volume, while the tail corresponds to high-density inhomogeneities. The clumps can thus be easily identified with the volume elements corresponding to the tail of the distribution. We show that this results in a simple and robust separation of the diffuse and clumpy components of the ICM. The full width at half-maximum of the density distribution in simulated clusters is a growing function of radius and varies from ˜0.15 dex in cluster centre to ˜0.5 dex at 2 r500 in relaxed clusters. The small scatter in the width between relaxed clusters suggests that the degree of inhomogeneity is a robust characteristic of the ICM. It broadly agrees with the amplitude of density perturbations found in the Coma cluster core. We discuss the origin of ICM density variations in spherical shells and show that less than 20 per cent of the width can be attributed to the triaxiality of the cluster gravitational potential. As a link to X-ray observations of real clusters we evaluated the ICM clumping factor, weighted with the temperature-dependent X-ray emissivity, with and without high-density inhomogeneities. We argue that these two cases represent upper and lower limits on the departure of the observed X-ray emissivity
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.
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.
Sarkar, Subrata; Mukherjee, Ananya
2014-01-01
Introduction: Developmental defects of the enamel (D.D.E.) are changes in the deciduous dentition may lead to aesthetic problems, dental sensitivity and may be predictors of dental caries. The aim of this study was to estimate the prevalence and distribution of D.D.E. in the deciduous dentition of IVF children of West Bengal. Materials and Methods: A cross-sectional study was carried out with a sample of 153 IVF children aged three to five enrolled in institute of reproductive medicine Kolkata, West Bengal, India. One hundred fifty three spontaneously conceived matched controlled children also examined as control group. All of the teeth were examined and the enamel defects were assessed according to the Modified D.D.E Index. The differences were tested for statistical significance by using the Chi-Square test & z-test. Results: The prevalence of D.D.E. was 7.18% in IVF Children and 8.49% in spontaneously conceived children. Diffuse opacities was the common defect found (2.61%) in both group. The most affected teeth were the deciduous maxillary central incisors (12.82% and 13.63% found in IVF and spontaneously conceived group respectively). Defects were observed more frequently in the maxillary arch than in mandibular arch in both groups. Conclusion: There is no significant difference found in IVF & spontaneously conceived children group. PMID:25177644
Transient analysis of 1D inhomogeneous media by dynamic inhomogeneous finite element method
NASA Astrophysics Data System (ADS)
Yang, Zailin; Wang, Yao; Hei, Baoping
2013-12-01
The dynamic inhomogeneous finite element method is studied for use in the transient analysis of onedimensional inhomogeneous media. The general formula of the inhomogeneous consistent mass matrix is established based on the shape function. In order to research the advantages of this method, it is compared with the general finite element method. A linear bar element is chosen for the discretization tests of material parameters with two fictitious distributions. And, a numerical example is solved to observe the differences in the results between these two methods. Some characteristics of the dynamic inhomogeneous finite element method that demonstrate its advantages are obtained through comparison with the general finite element method. It is found that the method can be used to solve elastic wave motion problems with a large element scale and a large number of iteration steps.
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.
Inhomogeneous screening near the dielectric interface
NASA Astrophysics Data System (ADS)
Wang, Rui; Wang, Zhen-Gang
2016-04-01
Screening is one of the most important concepts in the study of charged systems. Near a dielectric interface, the ion distribution in a salt solution can be highly nonuniform. Here, we develop a theory that self-consistently treats the inhomogeneous screening effects. At higher concentrations when the bulk Debye screening length is comparable to the Bjerrum length, the double layer structure and interfacial properties are significantly affected by the inhomogeneous screening. In particular, the depletion zone is considerably wider than that predicted by the bulk screening approximation or the WKB approximation. The characteristic length of the depletion layer in this regime scales with the Bjerrum length, resulting in a linear increase of the negative adsorption of ions with concentration, in agreement with experiments. For asymmetric salts, inhomogeneous screening leads to enhanced charge separation and surface potential.
Dendritic inhomogeneity of stainless maraging steels
Krasnikova, S.I.; Drobot, A.V.; Shmelev, A.Y.; Vukelich, S.B.
1986-03-01
The authors investigated dendritic inhomogeneity in industrial ingots 630 mm (steel I) in diameter and 500 mm (steel II) in diameter. The variation in the degree of dendritic inhomogeneity was investigated over the height of the ingots and across the sections on an MS-46 microprobe. It was established that the elements can be placed in the following order in accordance with the degree of reduction in the liquation factor: titanium, molybdenum, nickel, chromium, and cobalt. Titanium and molybdenum exhibit forward liquation in both steels, and chromium in steel II. The distribution of nickel and chromium in the steel I ingots and cobalt in the steel II ingots is unconventional. Dendritic inhomogeneity, which must be considered in assigning the heat treatment for finished articles, develops during the crystallization of stainless maraging steels.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Chen, Jenn‑Fang; Hsiao, Ru‑Shang; Hsieh, Pei‑Chen; Chen, Yu‑Chih; Wang, Jyh‑Shyang; Chi, Jim‑Y
2006-07-01
Carrier distribution and defect induction in In0.34Ga0.66As0.98N0.02/GaAs single quantum wells grown by molecular beam epitaxy at low growth rates are investigated by frequency-dependent capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS). The C-V studies show that lowering the growth rate of the InGaAsN layer splits the carrier accumulation in the well into a central and two side peaks with different frequency dispersions. The DLTS studies show that a continuum of states (0-0.083 eV) and a deep trap at 0.21-0.25 eV are responsible for the central and the side peaks, respectively. A comparison with photoluminescence (PL) spectra shows that these defects are induced by composition fluctuation. Lowering the growth rate degrades composition fluctuation by segregating the material into an InGaAsN phase and an N-depleted phase. Post-growth annealing can remove the deep trap and improve the InGaAsN emission, confirming that the deep trap degrades the InGaAsN phase. The feature of the continuum of states suggests that it may be the structural defects associated with lattice expansion or localized states introduced by composition fluctuation.
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
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
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.
Bitoun, Emmanuelle; Micheloni, Alessia; Lamant, Laurence; Bonnart, Chrystelle; Tartaglia-Polcini, Alessandro; Cobbold, Christian; Al Saati, Talal; Mariotti, Feliciana; Mazereeuw-Hautier, Juliette; Boralevi, Franck; Hohl, Daniel; Harper, John; Bodemer, Christine; D'Alessio, Marina; Hovnanian, Alain
2003-10-01
SPINK5, encoding the putative multi-domain serine protease inhibitor LEKTI, was recently identified as the defective gene in the severe autosomal recessive ichthyosiform skin condition, Netherton syndrome (NS). Using monoclonal and polyclonal antibodies, we show that LEKTI is a marker of epithelial differentiation, strongly expressed in the granular and uppermost spinous layers of the epidermis, and in differentiated layers of stratified epithelia. LEKTI expression was also demonstrated in normal differentiated human primary keratinocytes (HK) through detection of a 145 kDa full-length protein and a shorter isoform of 125 kDa. Both proteins are N-glycosylated and rapidly processed in a post-endoplasmic reticulum compartment into at least three C-terminal fragments of 42, 65 and 68 kDa, also identified in conditioned media. Processing of the 145 and 125 kDa precursors was prevented in HK by treatment with a furin inhibitor. In addition, in vitro cleavage of the recombinant 145 kDa precursor by furin generated C-terminal fragments of 65 and 68 kDa, further supporting the involvement of furin in LEKTI processing. In contrast, LEKTI precursors and proteolytic fragments were not detected in differentiated HK from NS patients. Defective expression of LEKTI in skin sections was a constant feature in NS patients, whilst an extended reactivity pattern was observed in samples from other keratinizing disorders, demonstrating that loss of LEKTI expression in the epidermis is a diagnostic feature of NS. The identification of novel processed forms of LEKTI provides the basis for future functional and structural studies of fragments with physiological relevance. PMID:12915442
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
Manzano, Hegoi; Moeini, Sina; Marinelli, Francis; Van Duin, Adri C. T.; Ulm, Franz-Josef; Pellenq, Roland J. M.
2012-01-01
Interest in microporous materials has risen in recent years, as they offer a confined environment that is optimal to enhance chemical reactions. Calcium silicate hydrate (C-S-H) gel, the main component of cement, presents a layered structure with sub-nanometer-size disordered pores filled with water and cations. The size of the pores and the hydrophilicity of the environment make C-S-H gel an excellent system to study the possibility of confined water reactions. To investigate it, we have performed molecular dynamics simulations using the ReaxFF force field. The results show that water does dissociate to form hydroxyl groups. We have analyzed the water dissociation mechanism, as well as the changes in the structure and water affinity of the C-S-H matrix and water polarization, comparing the results with the behavior of water in a defective zeolite. Finally, we establish a relationship between water dissociation in C-S-H gel and the increase of hardness due to a transformation from a two- to a three-dimensional structure.
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.
Inhomogeneous Monte Carlo simulations of dermoscopic spectroscopy
NASA Astrophysics Data System (ADS)
Gareau, Daniel S.; Li, Ting; Jacques, Steven; Krueger, James
2012-03-01
Clinical skin-lesion diagnosis uses dermoscopy: 10X epiluminescence microscopy. Skin appearance ranges from black to white with shades of blue, red, gray and orange. Color is an important diagnostic criteria for diseases including melanoma. Melanin and blood content and distribution impact the diffuse spectral remittance (300-1000nm). Skin layers: immersion medium, stratum corneum, spinous epidermis, basal epidermis and dermis as well as laterally asymmetric features (eg. melanocytic invasion) were modeled in an inhomogeneous Monte Carlo model.
REVIEWS OF TOPICAL PROBLEMS: Defects in liquid crystals: homotopy theory and experimental studies
NASA Astrophysics Data System (ADS)
Kurik, Mikhail V.; Lavrentovich, O. D.
1988-03-01
The fundamental concepts of the homotopy theory of defects in liquid crystals and the results of experimental studies in this field are presented. The concepts of degeneracy space, homotopy groups, and topological charge, which are used for classifying the topologically stable inhomogeneous distributions in different liquid-crystalline phases are examined (uni and biaxial nematics, cholesterics, smectics, and columnar phases). Experimental data are given for the different mesophases on the structure and properties of dislocations, disclinations, point defects in the volume (hedgehogs) and on the surface of the medium (boojums), monopoles, domain formations, and solitons. Special attention is paid to the results of studies of defects in closed volumes (spherical drops, cylindrical capillaries), and to the connection between the topological charges of these defects and the character of the orientation of the molecules of the liquid crystal at the surface. A set of fundamentally new effects that can occur in studying the topological properties of defects in liquid crystals is discussed.
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.
NASA Astrophysics Data System (ADS)
Tung, L. D.; Lees, M. R.; Balakrishnan, G.; McK. Paul, D.
2007-03-01
We report on a study of various RVO3 single-crystal samples ( R=La , Nd, Sm, Gd, Er, and Y) which show temperature-induced magnetization reversal. For compounds with lighter rare earths ( R=La , Nd, and Sm), magnetization reversal can be observed for a magnetic field applied in the ab plane and along the c axis, whereas for the heavy rare earths ( R=Gd and Er), magnetization reversal is only observed when the field is applied along the a axis. YVO3 has a magnetization reversal along all the main crystallographic axes in a modest applied field. We have found that some compounds are very sensitive to small trapped fields present in the superconducting solenoid of the magnetometer during the cooling. Based on the observed results, we argue that inhomogeniety caused by defects in the orbital sector in the quasi-one-dimensional orbital systems could account for the unusual magnetization reversal.
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.
NASA Astrophysics Data System (ADS)
Al-Dweri, Feras M. O.; Rojas, E. Leticia; Lallena, Antonio M.
2005-12-01
Monte Carlo simulation with PENELOPE (version 2003) is applied to calculate Leksell Gamma Knife® dose distributions for heterogeneous phantoms. The usual spherical water phantom is modified with a spherical bone shell simulating the skull and an air-filled cube simulating the frontal or maxillary sinuses. Different simulations of the 201 source configuration of the Gamma Knife have been carried out with a simplified model of the geometry of the source channel of the Gamma Knife recently tested for both single source and multisource configurations. The dose distributions determined for heterogeneous phantoms including the bone- and/or air-tissue interfaces show non-negligible differences with respect to those calculated for a homogeneous one, mainly when the Gamma Knife isocentre approaches the separation surfaces. Our findings confirm an important underdosage (~10%) nearby the air-tissue interface, in accordance with previous results obtained with the PENELOPE code with a procedure different from ours. On the other hand, the presence of the spherical shell simulating the skull produces a few per cent underdosage at the isocentre wherever it is situated.
Lammers, W J; Schalij, M J; Kirchhof, C J; Allessie, M A
1990-10-01
In isolated superfused left atria of the rabbit, inhomogeneity in conduction was quantified using the activation times measured with a high-density mapping system. At each recording site, the maximal difference with neighboring activation times (i.e., phase difference) was calculated. Local phase differences were plotted in a phase map, revealing the spatial distribution of inhomogeneities in conduction, and from each map a total index of inhomogeneity was calculated. During slow pacing (2 Hz) local differences in conduction velocity, depending on the direction of propagation, were found already. Inhomogeneity in conduction increased significantly during single early premature beats (inhomogeneity index increased from 2.3 to 3.1; P less than 0.001). The application of multiple premature beats further increased inhomogeneity in conduction, whereas rapid pacing induced the highest level of inhomogeneity (inhomogeneity index 5.3; P less than 0.001). An analysis of the spatial distribution of maximal phase differences revealed that during premature beats inhomogeneities in conduction were limited to an area of 6 mm around the point of origin of the premature impulse, whereas during rapid pacing inhomogeneities in conduction were found throughout the whole preparation. Phase maps constructed during the initiation of reentrant tachyarrhythmias showed that reentry occurred at sites with the highest phase differences. Quantification of spatial inhomogeneities in conduction is a useful tool to evaluate the vulnerability of the myocardial substrate for reentrant arrhythmias. PMID:1699438
Large-scale inhomogeneities and galaxy statistics
NASA Technical Reports Server (NTRS)
Schaeffer, R.; Silk, J.
1984-01-01
The density fluctuations associated with the formation of large-scale cosmic pancake-like and filamentary structures are evaluated using the Zel'dovich approximation for the evolution of nonlinear inhomogeneities in the expanding universe. It is shown that the large-scale nonlinear density fluctuations in the galaxy distribution due to pancakes modify the standard scale-invariant correlation function xi(r) at scales comparable to the coherence length of adiabatic fluctuations. The typical contribution of pancakes and filaments to the J3 integral, and more generally to the moments of galaxy counts in a volume of approximately (15-40 per h Mpc)exp 3, provides a statistical test for the existence of large scale inhomogeneities. An application to several recent three dimensional data sets shows that despite large observational uncertainties over the relevant scales characteristic features may be present that can be attributed to pancakes in most, but not all, of the various galaxy samples.
The influence of defects on the effective Young's modulus of a defective solid
NASA Astrophysics Data System (ADS)
Shen, Wei; Fan, Qun-Bo; Wang, Fu-Chi; Ma, Zhuang
2013-04-01
It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young's modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young's modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young's modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method (FEM) and strict analytical calculation show that the influence of pore radius and crack length on the effective Young's modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young's modulus in the vertical direction of the crack.
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
Averaging the inhomogeneous universe
NASA Astrophysics Data System (ADS)
Paranjape, Aseem
2012-03-01
A basic assumption of modern cosmology is that the universe is homogeneous and isotropic on the largest observable scales. This greatly simplifies Einstein's general relativistic field equations applied at these large scales, and allows a straightforward comparison between theoretical models and observed data. However, Einstein's equations should ideally be imposed at length scales comparable to, say, the solar system, since this is where these equations have been tested. We know that at these scales the universe is highly inhomogeneous. It is therefore essential to perform an explicit averaging of the field equations in order to apply them at large scales. It has long been known that due to the nonlinear nature of Einstein's equations, any explicit averaging scheme will necessarily lead to corrections in the equations applied at large scales. Estimating the magnitude and behavior of these corrections is a challenging task, due to difficulties associated with defining averages in the context of general relativity (GR). It has recently become possible to estimate these effects in a rigorous manner, and we will review some of the averaging schemes that have been proposed in the literature. A tantalizing possibility explored by several authors is that the corrections due to averaging may in fact account for the apparent acceleration of the expansion of the universe. We will explore this idea, reviewing some of the work done in the literature to date. We will argue however, that this rather attractive idea is in fact not viable as a solution of the dark energy problem, when confronted with observational constraints.
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.
Wu, Po-Chang; Yeh, En-Rong; Zyryanov, Victor Ya; Lee, Wei
2014-08-25
This paper investigates the spectral properties of a one-dimensional photonic crystal (PC) containing an inhomogeneous polymer- dispersed liquid crystal (PDLC) as a defect layer. Experimental results indicate that the voltage-induced reorientation of LC molecules between the light-scattering and transparent states in the PDLC enables the electrical tuning of the transmittance of defect-mode peaks in the spectrum of the PC/PDLC cell. Specifically, owing to the unique configuration of the spatial distribution of LC droplet sizes in the defect layer, a concept concerning the spatial switching in the wavelength of defect modes is proposed. As a result, the PC/PDLC hybrid cell is suggested as a potential element for realizing an electrically tunable and spatially switchable photonic bandgap device, which is polarizer-free and requires no alignment layers in the fabrication process. PMID:25321237
A distributed axis electron beam system for high-speed lithography and defect inspection
NASA Astrophysics Data System (ADS)
Pickard, Daniel S.
Electron beam lithography can delineate features 10 nm and smaller. However the throughput is slow, limited by space charge blurring when writing with large currents. One way to overcome this limit is to employ multiple beamlets distributed over a large area. The approach described here employs a uniform axial magnetic field to focus thousands of electron beams simultaneously. The source must be at least as small as the beam at the wafer. Fabrication and operation of an aperture source with a diameter of 50nm or less was demonstrated. To prevent contamination, the beam heats the aperture to 200°C. Successful operation was demonstrated by building a test-bed featuring a region of uniform magnetic field and building, inside this region, a miniature scanning electron microscope. We observed resolution between 30nm and 50nm at 10kV and better than 75nm at 1kV. This SEM can image at landing energies as low as 260 Volts. The detection and separation of the secondary electrons generated by adjacent beamlets is achieved by spacing the beamlets by more than the cyclotron diameter of the secondary electrons (250 microns is sufficient). Detection was demonstrated with a custom-designed and built, monolithic, PIN detector with 40 detector elements. The system requires a sparse array of matched electron sources with current densities exceeding 10A/cm2, and electron energy spread less than 0.5 eV. Two new configurations were investigated to meet this requirement. The first, the electron bombardment source features a thin semiconductor membrane with a negative electron affinity emission surface. Free carriers are generated by high-energy electrons impinging on the back surface. We demonstrated the first scanning electron microscope images employing this cathode. The other configuration, the plasmon enhanced photocathode, couples the incident light to surface plasmons on a metallic film. This yields quantum efficiencies 100 times larger than conventional photoemission from a
NASA Technical Reports Server (NTRS)
Vasquez, R. P.; Madhukar, A.; Grunthaner, F. J.; Naiman, M. L.
1986-01-01
Previously reported nitrogen distributions in SiO2 films on Si which have been thermally nitrided at 1000 C have been explained by a kinetic model of the nitridation process which rests upon the effects of interfacial strain. A critical test of this kinetic model is the validity of the predictions regarding nitrogen distributions obtained at other nitridation temperatures. In this work, nitrogen distributions determined via X-ray photoelectron spectroscopy are reported for samples nitrided at 800 and 1150 C, and are shown to be consistent with the kinetic model. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen distribution, and is postulated to be related to kinetically generated defects in the dielectric film, consistent with the strain-dependent energy of formation of defects proposed recently to explain electrical data.
NASA Astrophysics Data System (ADS)
Dudorov, V. V.; Kolosov, V. V.; Kolosova, O. A.
2001-09-01
Based on the equation for the second-order coherence function, the propagation of partially coherent radiation is studied under the combined action of diffraction and refraction caused by the inhomogeneous distribution of the real and imaginary parts of the perturbation of the permittivity of a medium in the case of inhomogeneous absorption (amplification). The limits of application of the method of geometrical optics for inhomogeneously absorbing (amplifying) media are studied, as well as of the methods that neglect refraction caused by the inhomogeneous distribution of the imaginary part of the permittivity of the medium.
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
NASA Astrophysics Data System (ADS)
Souidi, A.; Hou, M.; Becquart, C. S.; Domain, C.; De Backer, A.
2015-06-01
We have used an Object Kinetic Monte Carlo (OKMC) model to simulate the long term evolution of the primary damage in Fe70Cr20Ni10 alloys. The mean number of Frenkel pairs created by different Primary Knocked on Atoms (PKA) was estimated by Molecular Dynamics using a ternary EAM potential developed in the framework of the PERFORM-60 European project. This number was then used to obtain the vacancy-interstitial recombination distance required in the calculation of displacement cascades in the Binary Collision Approximation (BCA) with code MARLOWE (Robinson, 1989). The BCA cascades have been generated in the 10-100 keV range with the MARLOWE code and two different screened Coulomb potentials, namely, the Molière approximation to the Thomas-Fermi potential and the so-called "Universal" potential by Ziegler, Biersack and Littmark (ZBL). These cascades have been used as input to the OKMC code LAKIMOCA (Domain et al., 2004), with a set of parameters for describing the mobility of point defect clusters based on ab initio calculations and experimental data. The cluster size distributions have been estimated for irradiation doses of 0.1 and 1 dpa, and a dose rate of 10-7 dpa/s at 600 K. We demonstrate that, like in the case of BCC iron, cluster size distributions in the long term are independent of the cascade energy and that the recursive cascade model suggested for BCC iron in Souidi et al. (2011) also applies to FCC Fe70Cr20Ni10. The results also show that the influence of the BCA potential is sizeable but the qualitative correspondence in the predicted long term evolution is excellent.
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. PMID:26627747
Spin transfer into an inhomogeneous magnetization distribution
Miltat, J.; Albuquerque, G.; Thiaville, A.; Vouille, C.
2001-06-01
Based on specific examples, we examine the consequence of spin-polarized current injection into confined model micromagnetic configurations, namely a high remanence state known as the S state and a low, though nonzero, remanence state called the Leaf state. Magnetization dynamics is solved in the space and time domain owing to the Landau{endash}Lifshitz{endash}Gilbert equation. It is shown that, within model bounds, the S state is not propitious to fast switching under the sole influence of a polarized current, even if disregarding the current induced field, whereas Leaf state switching characteristics become extremely complex as soon as due account is made for the latter. {copyright} 2001 American Institute of Physics.
Inhomogeneous models of Titan's aerosol distribution
NASA Technical Reports Server (NTRS)
Podolak, M.; Bar-Nun, A.; Noy, N.; Giver, L. P.
1984-01-01
A model of Titan's aerosol is presented which allows the particle size to vary with height. The model assumes a refractive index appropriate to an ethylene polymer and a mass flux independent of height equal to the value derived from laboratory measurements. The free parameters of the model are determined by fitting to the observed geometric albedo at 4000 and 6000 A. A methane spectrum is derived which is in excellent agreement with observations. An aerosol optical depth of about 5 is found in the visible, with the particle radius varying from 0.01 to 8 microns. The presence of an optically thick methane cloud at the temperature minimum is indicated.
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)
Hunt, Steven R.; Collins, Phillip G.
2010-03-01
The electronic properties of graphitic carbon devices are primarily determined by the contact metal and the carbon band structure. However, inhomogeneities such as substrate imperfections, surface defects, and mobile contaminants also contribute and can lead to transistor-like behaviors. We experimentally investigate this phenomena in the 1-D limit using metallic single-walled carbon nanotubes (SWCNTs) before and after the electrochemical creation of sidewall defects. While scanning gate microscopy readily identifies the defect sites, the energy-dependence of the technique allows quantitative analysis of the defects and discrimination of different defect types. This research is partly supported by the NSF (DMR 08-xxxx).
Damjanovic, Daniela; Zhang, Xizhong; Mu, Jingyu; Fe Medina, Maria; Xing, Zhou
2008-01-01
It is believed that respiratory mucosal immunization triggers more effective immune protection than parenteral immunization against respiratory infection caused by viruses and intracellular bacteria. Such understanding has led to the successful implementation of intranasal immunization in humans with a live cold-adapted flu virus vaccine. Furthermore there has been an interest in developing effective mucosal-deliverable genetic vaccines against other infectious diseases. However, there is a concern that intranasally delivered recombinant viral-based vaccines may disseminate to the CNS via the olfactory tissue. Initial experimental evidence suggests that intranasally delivered recombinant adenoviral gene transfer vector may transport to the olfactory bulb. However, there is a lack of quantitative studies to compare the relative amounts of transgene products in the respiratory tract, lung, olfactory bulb and brain after intranasal mucosal delivery of viral gene transfer vector. To address this issue, we have used fluorescence macroscopic imaging, luciferase quantification and PCR approaches to compare the relative distribution of transgene products or adenoviral gene sequences in the respiratory tract, lung, draining lymph nodes, olfactory bulb, brain and spleen. Intranasal mucosal delivery of replication-defective recombinant adenoviral vector results in gene transfer predominantly in the respiratory system including the lung while it does lead to a moderate level of gene transfer in the olfactory bulb. However, intranasal inoculation of adenoviral vector leads to little or no viral dissemination to the major region of the CNS, the brain. These experimental findings support the efficaciousness of intranasal adenoviral-mediated gene transfer for the purpose of mucosal immunization and suggest that it may not be of significant safety concern. PMID:18261231
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.
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.
NASA Astrophysics Data System (ADS)
Wang, Xu; Schiavone, Peter
2016-07-01
Using complex variable methods and conformal mapping techniques, we demonstrate rigorously that two inhomogeneities of irregular shape interacting with a screw dislocation can indeed maintain uniform internal stress distributions. Our analysis indicates that while the internal uniform stresses are independent of the existence of the screw dislocation, the shapes of the two inhomogeneities required to achieve this uniformity depend on the Burgers vector, the location of the screw dislocation, and the size of the inhomogeneities. In addition, we find that this uniformity of the internal stress field is achievable also when the two inhomogeneities interact with an arbitrary number of discrete screw dislocations in the matrix.
Direct observation of defect-mediated cluster nucleation
NASA Astrophysics Data System (ADS)
Kaiser, U.; Muller, D. A.; Grazul, J. L.; Chuvilin, A.; Kawasaki, M.
2002-10-01
Ion implantation is widely used to introduce electrically or optically active dopant atoms into semiconductor devices. At high concentrations, the dopants can cluster and ultimately form deactivating precipitates, but deliberate nanocrystal formation offers an approach to self-assembled device fabrication. However, there is very little understanding of the early stages of how these precipitates nucleate and grow, in no small part because it requires imaging an inhomogenous distribution of defects and dopant atoms buried inside the host material. Here we demonstrate this, and address the long-standing question of whether the cluster nucleation is defect-mediated or spontaneous. Atomic-resolution illustrations are given for the chemically dissimilar cases of erbium and germanium implanted into silicon carbide. Whereas interstitial loops act as nucleation sites in both cases, the evolution of nanocrystals is strikingly different: Erbium is found to gather in lines, planes and finally three-dimensional precipitates, whereas germanium favours compact, three-dimensional structures.
Direct observation of defect-mediated cluster nucleation.
Kaiser, U; Muller, D A; Grazul, J L; Chuvilin, A; Kawasaki, M
2002-10-01
Ion implantation is widely used to introduce electrically or optically active dopant atoms into semiconductor devices. At high concentrations, the dopants can cluster and ultimately form deactivating precipitates, but deliberate nanocrystal formation offers an approach to self-assembled device fabrication. However, there is very little understanding of the early stages of how these precipitates nucleate and grow, in no small part because it requires imaging an inhomogenous distribution of defects and dopant atoms buried inside the host material. Here we demonstrate this, and address the long-standing question of whether the cluster nucleation is defect-mediated or spontaneous. Atomic-resolution illustrations are given for the chemically dissimilar cases of erbium and germanium implanted into silicon carbide. Whereas interstitial loops act as nucleation sites in both cases, the evolution of nanocrystals is strikingly different: Erbium is found to gather in lines, planes and finally three-dimensional precipitates, whereas germanium favours compact, three-dimensional structures. PMID:12618823
Multidimensional Plasma Sheaths over Electrically Inhomogeneous Surfaces
NASA Astrophysics Data System (ADS)
Economou, Demetre
2004-09-01
Multidimensional plasma sheaths are encountered in a number of applications including plasma immersion ion implantation, extraction of ions (or plasma) through grids, MEMS fabrication, neutral beam sources, and plasma in contact with internal reactor parts (e.g., wafer chuck edge). The sheath may be multidimensional when: (a) plasma is in contact with surface topography, and the size of the topographical features is comparable to or larger than the plasma sheath thickness, or (b) the surface is flat but inhomogeneous, i.e., a conducting surface next to an insulating surface. In either case, the flux, energy and angular distributions of energetic species incident on the substrate are of primary importance. These quantities depend critically on the shape of the meniscus (plasma-sheath boundary) formed over the surface. A two-dimensional fluid/Monte Carlo simulation model was developed to study multidimensional sheaths. The radio frequency (RF) sheath potential evolution, and ion density and flux profiles over the surface were predicted with a self-consistent fluid simulation. The trajectories of ions and energetic neutrals (resulting by ion neutralization on surfaces or charge exchange collisions in the gas phase) were then followed with a Monte Carlo simulation. Ion flow and energy and angular distributions of ions bombarding a flat but electrically inhomogeneous surface will be reported in detail. Ion flow over trenches and holes will also be reported. Work supported by the NSF, Sandia National Laboratories and NIST.
The use of correlation interferometry for analysis of phase inhomogeneous environments and surfaces
NASA Astrophysics Data System (ADS)
Derzhypolska, L.; Gnatovskiy, O.; Negriyko, A.
2015-12-01
In the paper investigated are optically inhomogeneous objects using holographic interferometry, speckle-interferometry and optical correlation. A non-interferometricshift of interference fringes is observed. Shown is that the shift is related to the statistical distribution that describes the optical inhomogeneity of the objects of study.
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.
(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.
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.
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.
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.
Chemical substructure and inhomogeneous mixing in Local Group dwarf galaxies
NASA Astrophysics Data System (ADS)
Venn, K. A.
Evidence for inhomogeneous mixing in the Carina, Draco, and Sculptor dwarf galaxies is examined from chemical abundance patterns. Inhomogeneous mixing at early times is indicated in the classical dwarf galaxies, though cannot be ascertained in ultra faint dwarfs. Mixing efficiencies can affect the early metallicity distribution function, the pre-enrichment levels in globular clusters, and also have an impact on the structure of dwarf systems at early times. Numerical models that include chemical evolution explicitly do a better job in reproducing the observations, and make interesting predictions for the nature of dwarf galaxies and their first stars at the earliest times.
Tilted Gaussian beam propagation in inhomogeneous media.
Hadad, Yakir; Melamed, Timor
2010-08-01
The present work is concerned with applying a ray-centered non-orthogonal coordinate system which is a priori matched to linearly-phased localized aperture field distributions. The resulting beam-waveobjects serve as the building blocks for beam-type spectral expansions of aperture fields in 2D inhomogeneous media that are characterized by a generic wave-velocity profile. By applying a rigorous paraxial-asymptotic analysis, a novel parabolic wave equation is obtained and termed "Non-orthogonal domain parabolic equation"--NoDope. Tilted Gaussian beams, which are exact solutions to this equation, match Gaussian aperture distributions over a plane that is tilted with respect to the beam-axes initial directions. A numerical example, which demonstrates the enhanced accuracy of the tilted Gaussian beams over the conventional ones, is presented as well. PMID:20686589
Fujita phenomenon in inhomogeneous fast diffusion system
NASA Astrophysics Data System (ADS)
Yang, Jinge; Zheng, Sining; Qu, Chengyuan
2013-04-01
This paper deals with the Fujita phenomenon for the Cauchy problem of an inhomogeneous fast diffusion system. Both the critical exponent and the second exponent are obtained. We observe that the inhomogeneous terms in the system substantially contribute to the critical exponent, in that the blow-up exponent region is obviously enlarged, with keeping the second critical exponent unchanged for small inhomogeneous sources.
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.
Danaeifar, Mohammad; Granpayeh, Nosrat
2015-12-01
The analytical method to study the multi-spectral inhomogeneous metasurfaces with various components is presented. Because of symmetrical distribution of different components, we can find the effective polarizability of the inhomogeneous metasurfaces. This polarizability provides equivalent conductivity of each metasurface with two and three different nanodisk arrays. Full-wave simulations confirm the analysis of inhomogeneous metasurfaces. In a metasurface, symmetrical distribution of components with a unique periodicity is limited to three types in a hexagonal combination. Then we extend the proposed approach to partly symmetric inhomogeneous metasurfaces in subwavelength scale for four different nanodisks. Also, monolayer and multi-layer absorbers consisting of inhomogeneous metasurfaces with graphene nanodisks are designed as the examples of wideband applications of this method in infrared regime. PMID:26625077
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.
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Multiscale approach to inhomogeneous cosmologies
NASA Astrophysics Data System (ADS)
Wiegand, Alexander
The backreaction of inhomogeneities on the global expansion history of the Universe suggests a possible link of the formation of structures to the recent accelerated expansion. In this paper, the origin of this conjecture is illustrated and a model without Dark Energy that allows for a more explicit investigation of this link is discussed. Additionally to this conceptually interesting feature, the model leads to a LCDM-like distance-redshift relation that is consistent with SN data.
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.
NASA Astrophysics Data System (ADS)
Yokogawa, Shinji
2015-05-01
The statistical characteristics of the lifetime distribution based on defect clustering were investigated for middle- and back-end-of-line time-dependent dielectric breakdown. The statistical precision of lifetime estimation was investigated. The maximum likelihood estimators of distribution parameters and their variations were developed by using asymptotic theory. The calculated asymptotic variation coefficient indicates that larger numbers of data are required to maintain the statistical precision of lifetime estimation for highly clustering conditions. However, the censoring of the test time to eliminate the tail of the lifetime distribution has a low impact on the asymptotic variation coefficient of the lifetime. These results provide valuable information for the experimental design of lifetime testing.
Gritsyna, V. T.; Kazarinov, Y. G.; Kobyakov, V. A.; Sickafus, K.
2001-01-01
Kinetic studies of optical center accumulation and decay, together with the growth and decay of radioluminescence (RL) in magnesium aluminate spinel MgAl{sub 2}O{sub 4}, were performed at room temperature. We observed two stages of defect accumulation during prolonged X-ray irradiation, as evidenced by changes in absorption bands at 3.78 and 4.15 eV related to antisite defects, and bands at 4.75 and 5.3 eV due to F-type centers. A correlation was found between optical absorption band growth and the intensities of RL bands at 4.86 and 5.02 eV, the latter of which originate: from electron-hole recombination processes. The rate of decay of absorption centers and RL intensities is dependent on time after X-ray irradiation. Also both decay rates could be described by a two-stage exponential law. Results are discussed using a model that includes tunneling and recombination of electron and hole centers on spatially correlated defects located at different distances from one another.
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.
Mezdrogina, M. M. Krivolapchuk, V. V.; Kozhanova, Yu. V.
2008-02-15
By analyzing time-resolved and steady-state photoluminescence spectra, it is established that the spatial distribution of rare-earth ion dopants in wurtzite GaN crystals doped with Sm, Eu, Er, or Tm is governed by the type and concentration of defects in the initial semiconductor matrix as well as by the type of the impurity (its capacity for segregation). Doping with multicharged rare-earth impurities and additionally introduced Zn impurity leads to an intensification of emission. The effect of intensification of emission in the case of n-and p-GaN crystals is considered with the use of the model of isoelectronic traps.
Inhomogeneous halo collapse and early Galactic chemical evolution - Globular cluster metallicities
NASA Technical Reports Server (NTRS)
Malinie, G.; Hartmann, D. H.; Mathews, G. J.
1991-01-01
A new solution to the observed Galactic globular cluster metallicity distribution is proposed by considering inhomogeneous collapse of a centrally condensed proto-Galaxy. In contrast to the standard one-zone model, it is shown that, for inhomogeneous models, the metallicity distribution can be reproduced without the need to decrease the nucleosynthetic yield for metal-poor stars. Chemical evolution in free fall is calculated analytically. A hybrid hydroparticle code is developed to study the effect of supernova induced pressure.
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.
A birth defect is a problem that happens while a baby is developing in the mother's body. Most birth defects happen during the first 3 months of ... in the United States is born with a birth defect. A birth defect may affect how the ...
Structural inhomogeneities in crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}
Osofsky, M.S.; Qadri, S.B.; Skelton, E.F.; Vanderah, T.A.
1996-12-31
Structural inhomogeneities in crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} are characterized using high resolution x-ray diffraction. Rocking curves and a high resolution specular radial scan show features indicating that the crystals are not truly single. The high resolution radial scan of a crystal that had a superconducting transition width of only one-half Kelvin, as determined by ac susceptibility, and appeared to be free of gross defects, when examined with conventional x-ray diffraction techniques, shows a distribution in the c-axis lattice parameter. These results suggest that crystals with sharp transitions should be carefully examined for the presence of structural anomalies which might influence the superconductive properties.
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
Backflow transformations in inhomogeneous systems
NASA Astrophysics Data System (ADS)
Lopez Rios, Pablo; Ma, Andrea; Drummond, Neil D.; Needs, Richard J.
2006-03-01
The quality of trial wave-functions, and of their nodal surface in particular, determines the accuracy of the results obtained within the Fixed-Node Diffusion Monte Carlo (DMC) method. Backflow transformations have been proven capable of improving the nodal surface of Slater-Jastrow (SJ) wave-functions in homogeneous systems. In this work we will present the extension of backflow to inhomogeneous systems, along with DMC results for atoms, molecules and solids which show the improved accuracy of this form of trial wave-function. We will also discuss the advantages of using electron-by-electron algorithms to enhance the computational efficiency of QMC with backflow wave-functions.
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.
Lesage, F; Hugnot, J P; Amri, E Z; Grimaldi, P; Barhanin, J; Lazdunski, M
1994-01-01
The rat HBP1 cDNA was cloned by its capacity to suppress the potassium transport-defective phenotype of mutant Saccharomyces cerevisiae cells. HBP1 cDNA encodes a 513 amino acids protein which, unexpectedly, does not share any homology with K+ transporters or K+ channels. However, a search in protein databases reveals that HBP1 contains a putative DNA-binding domain called HMG-box. Northern blot analysis shows that HBP1 is expressed in a variety of tissues and that in adipocyte and myogenic cell lines, its expression is directly related to differentiation. Taken together, the results suggest that the rat HBP1 is a new member of the HMG class of transcriptional regulators involved in cell differentiation pathways. Images PMID:7937077
NASA Astrophysics Data System (ADS)
Sahu, R.; Dileep, K.; Loukya, B.; Datta, R.
2014-02-01
It is found that the oxygen vacancy (VO) defect concentration affecting the separation between individual species in LiZn-Lii complex influences the optical emission property of Li0.06Zn0.94O 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 LiZn-Lii pair complex and the emission at 2.1 eV is when the component species are away from each other.
Vacancy-driven anisotropic defect distribution in the battery-cathode material LiFePO4.
Lee, Jaekwang; Zhou, Wu; Idrobo, Juan C; Pennycook, Stephen J; Pantelides, Sokrates T
2011-08-19
Li-ion mobility in LiFePO(4), a key property for energy applications, is impeded by Fe antisite defects (Fe(Li)) that form in select b-axis channels. Here we combine first-principles calculations, statistical mechanics, and scanning transmission electron microscopy to identify the origin of the effect: Li vacancies (V(Li)) are confined in one-dimensional b-axis channels, shuttling between neighboring Fe(Li). Segregation in select channels results in shorter Fe(Li)-Fe(Li) spans, whereby the energy is lowered by the V(Li)'s spending more time bound to end-point Fe(Li)'s. V(Li)-Fe(Li)-V(Li) complexes also form, accounting for observed electron energy loss spectroscopy features. PMID:21929178
Vacancy-driven anisotropic defect distribution in the battery-cathode material LiFePO4
Lee, Jaekwang; Zhou, Wu; Idrobo Tapia, Juan C; Pennycook, Stephen J; Pantelides, Sokrates T.; Biegalski, Michael D
2011-01-01
Li-ion mobility in LiFePO{sub 4}, a key property for energy applications, is impeded by Fe antisite defects (Fe{sub Li}) that form in select b-axis channels. Here we combine first-principles calculations, statistical mechanics, and scanning transmission electron microscopy to identify the origin of the effect: Li vacancies (V{sub Li}) are confined in one-dimensional b-axis channels, shuttling between neighboring Fe{sub Li}. Segregation in select channels results in shorter Fe{sub Li}-Fe{sub Li} spans, whereby the energy is lowered by the V{sub Li}'s spending more time bound to end-point Fe{sub Li}'s. V{sub Li}-Fe{sub Li}-V{sub Li} complexes also form, accounting for observed electron energy loss spectroscopy features.
Transport in partially equilibrated inhomogeneous quantum wires.
Levchenko, A.; Micklitz, T.; Rech, J.; Matveev, K. A.; Materials Science Division; Freie Univ. Berlin; Centre de Physique Theorique
2010-01-01
We study transport properties of weakly interacting one-dimensional electron systems including on an equal footing thermal equilibration due to three-particle collisions and the effects of large-scale inhomogeneities. We show that equilibration in an inhomogeneous quantum wire is characterized by the competition of interaction processes which reduce the electrons total momentum and such which change the number of right- and left-moving electrons. We find that the combined effect of interactions and inhomogeneities can dramatically increase the resistance of the wire. In addition, we find that the interactions strongly affect the thermoelectric properties of inhomogeneous wires and calculate their thermal conductance, thermopower, and Peltier coefficient.
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.
Inhomogeneities in the early universe
NASA Technical Reports Server (NTRS)
Canuto, V.
1976-01-01
The paper investigates certain nonlinear processes that are viable candidates for the mechanisms which produced large-scale inhomogeneities in the early Universe. Several nonlinear Lagrangians are presented for matter, the Korteweg-de Vries equation is analyzed, and the existence of solitons among its solutions is noted. A model based on the possibility of generating a cascade of solitons from an initial perturbation is proposed, and it is shown how large-scale inhomogeneities can be generated when an initial soliton fragments into many others through the nonlinear action of the terms in the Korteweg-de Vries equation. A second model is examined which is based on the interaction of matter with a strong radiation field (an almost monochromatic photon gas) and which involves changes in the refractive index of the vacuum. It is found that matter and radiation will not mix if the radiation field has a nonuniform intensity and that the matter will separate into dense portions or 'cosmological protogalaxies'. The evolution of these portions of matter is studied, and it is found that conditions would be appropriate for the interface between them and the surrounding radiation field to become unstable, giving rise to a turbulent layer.
Thomson scattering on inhomogeneous targets.
Thiele, R; Sperling, P; Chen, M; Bornath, Th; Fäustlin, R R; Fortmann, C; Glenzer, S H; Kraeft, W-D; Pukhov, A; Toleikis, S; Tschentscher, Th; Redmer, R
2010-11-01
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. PMID:21230599
The local value of H0 in an inhomogeneous universe
NASA Astrophysics Data System (ADS)
Odderskov, I.; Koksbang, S. M.; Hannestad, S.
2016-02-01
The effects of local inhomogeneities on low redshift H0 determinations are studied by estimating the redshift-distance relation of mock sources in N-body simulations. The results are compared to those obtained using the standard approach based on Hubble's law. The comparison shows a clear tendency for the standard approach to yield lower values of H0 than the approach based on the scheme using light rays. The difference is, however, small. More precisely, it is found that the overall effect of inhomogeneities on the determination of H0 is a small increase in the local estimates of about 0.3% compared to the results obtained with Hubble's law, when based on a typical distribution of supernovae in the redshift range 0.01 < z < 0.1. The overall conclusion of the study is a verification of the results that have earlier been obtained by using Hubble's law: the effects of inhomogeneities on local H0 estimates are not significant enough to make it plausible that differences in high- and low-redshift estimates of H0 are due to small inhomogeneities within the setting of standard cosmology.
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.
Imaging Inhomogeneities From Dry-Coupled Ultrasonic Scans
NASA Technical Reports Server (NTRS)
Roth, Don J.
1995-01-01
Method of imaging spatial distribution of selected physical properties and microstructure of specimen of material based on dry-coupled contact ultrasonic pulse/echo scanning. Ultrasonic transducer scanned across top surface of specimen. At each of many positions on two-dimensional grid on top surface, ultrasonic pulse/echo measurements taken and processed. Offers rapid, nondestructive alternative to destructive metallographic sectioning to obtain picture of inhomogeneity of specimen.
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
Numerical analysis of inhomogeneous Schottky diode with discrete barrier height patches
NASA Astrophysics Data System (ADS)
Kaushal, Priyanka; Chand, Subhash
2016-06-01
The potential profile inside the semiconductor at the metal-semiconductor contact is simulated by numerically solving the Poisson equation and the drift diffusion equations for inhomogeneous Schottky diode. From the simulated potential and the electron and hole concentrations, the drift-diffusion current as a function of bias is calculated. The simulation is carried out for various distribution patterns of barrier height patches at the metal-semiconductor contact to study the effect of barrier inhomogeneities on the Schottky diode parameters, namely barrier height and ideality factor and their temperature dependence. It is found that barrier height decreases and ideality factor increases with increase in the deviation of discrete barrier height patches in the distribution. The resulting barrier parameters are studied to understand the effect of barrier inhomogeneities on the current-voltage characteristics of inhomogeneous Schottky contact.
Statistical Mechanics of Inhomogeneous Fluids
NASA Astrophysics Data System (ADS)
Schofield, P.; Henderson, J. R.
1982-01-01
The nature of the microscopic stress tensor in an inhomogenous fluid is discussed, with emphasis on the statistical mechanics of drops. Changes in free energy for isothermal deformations of a fluid are expressible as volume integrals of the stress tensor 'times' a strain terror. A particular radial distortion of a drop leads to statistical mechanical expressions for the pressure difference across the surface of the drop. We find that the stress tensor is not uniquely defined by the microscopic laws embodying conservation of momentum and angular momentum and that the ambiguity remains in the ensemble average, or pressure tensor, in regions of inhomomogeneity. This leads to difficulties in defining statistical mechanical expressions for the surface tension of a drop.
Inhomogeneous strains in small particles
NASA Astrophysics Data System (ADS)
Marks, L. D.
1985-02-01
This paper considers the evidence for strains in small particles. Firstly, the dynamical electron diffraction theory for dark field imaging of small particles is briefly reviewed, considering primarily the effects of strain on wedge crystals and identifying the fingerprint of strain contrast effects under strong beam conditions. Evidence included herein and from published papers by other authors clearly shows inhomogeneous strain effects in both multiply twinned particles and single crystals. Considering these results and earlier reports of lattice parameter changes, there are problems with the uniqueness of these analyses, and the strains in the small single crystals are thought more likely to be due to interfacial stresses or contaminants than any intrinsic particle effect; there are so many different origins of this type of strain that we cannot with confidence isolate a unique source. It is emphasised that the uniqueness of any interpretation of experimental results from small particles must be very carefully considered.
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.
Shonka, David C; Park, Stephen S
2009-08-01
The projection and exposure of the auricle make it particularly susceptible to actinic injury and thus to cutaneous malignancies. Auricular reconstruction is challenging because of its unique surface anatomy and undulating topography. This article organizes auricular defects into different categories based on anatomic location and extent of tissue loss, including skin-only defects, small composite defects, full-thickness defects involving or sparing the upper third of the ear, and total auricular loss. The authors share an algorithm for repair of the array of auricular defects. PMID:19698921
Isotropic expansion of an inhomogeneous universe
NASA Astrophysics Data System (ADS)
Geng, Wei-Jian; Lü, H.
2014-10-01
We propose a cosmological model that describes isotropic expansion of an inhomogeneous universe. The energy-momentum tensor that creates the spatial inhomogeneity may not affect the uniform expansion scaling factor a(t) in the Friedmann-Lemaître-Robertson-Walker-like metrics. Such an energy-momentum tensor may not be exotic; in fact any linear or nonlinear σ model has this feature. We show that the classical spatial inhomogeneity can be embedded in both inflation models and the traditional cosmological expansion by perfect fluid. The spatial inhomogeneity resembles the primordial quantum perturbation that was frozen in the comoving frame. We obtain some exact inhomogeneous solutions with spherical or axial symmetries. We also show that some of our cosmological models can be viewed as the dynamical black hole formation.
NASA Astrophysics Data System (ADS)
Pikulev, A. A.
2001-09-01
The propagation of Hermitian beams in a medium with a distributed quadratic inhomogeneity is studied and is shown that any solution can be represented as a function of some particular solution. This is accomplished by establishing a one-to-one correspondence between optical fields in a homogeneous medium and in a medium with an arbitrary quadratic inhomogeneity. The stability of optical resonators is studied and the condition for their stability is found. Several solutions are found using the method developed.
Kumar, A. Bran, J. Melkonyan, D. Shimura, Y. Vandervorst, W.; Demeulemeester, J. Bogdanowicz, J. Fleischmann, C. Loo, R.; Gencarelli, F. Wang, W.
2015-07-14
Ge{sub (1−x)}Sn{sub (x)} has received a lot of interest for opto-electronic applications and for strain engineering in advanced complementary-metal-oxide-semiconductor technology, because it enables engineering of the band gap and inducing strain in the alloy. To target a reliable technology for mass application in microelectronic devices, the physical problem to be addressed is to unravel the complex relationship between strain relaxation (as induced by the growth of large layer thicknesses or a thermal anneal) and defect formation, and/or stable Sn-cluster formation. In this paper, we study the onset of Sn-cluster formation and its link to strain relaxation using Atom Probe Tomography (APT). To this end, we also propose a modification of the core-linkage [Stephenson et al., Microsc. Microanal. 13, 448 (2007)] cluster analysis method, to overcome the challenges of limited detection efficiency and lateral resolution of APT, and the quantitative assessment for very small clusters (<40 atoms) embedded in a random distribution of Sn-atoms. We concluded that the main relaxation mechanism for these layers is defect generation (misfit dislocations, threading dislocations, etc.), irrespective of the cause (thickness of layer or thermal anneal) of relaxation and is independent of the cluster formation. The low thermodynamic solubility limit of Sn in Ge seems to be the driving force for Sn-cluster formation. Finally, we also discuss the spatial distribution of Sn in clusters and relate them to the theoretically predicted stable Sn clusters [Ventura et al., Phys. Rev. B 79, 155202 (2009)].
NASA Astrophysics Data System (ADS)
Wang, Yinshun; Dai, Shaotao; Zhao, Xiang; Xiao, Liye; Lin, Liangzhen; Hui, Dong
2006-12-01
The effect of the local critical current on the self-field loss in single tapes and multi-parallel tapes is investigated computationally. Generally, the self-AC loss of a superconductor can be described using the Norris equation based on Bean's critical state model with elliptical, circular or strip cross-sections. However, because of its intrinsic characteristics, the critical current of high-temperature superconducting (HTS) tape is inhomogeneous. It is reasonable to expect the local critical currents to have a Gaussian statistical distribution, according to the central limit theorem; a detailed analysis of self-AC loss is made to develop an interesting calculation procedure for both single tapes and multi-parallel tapes. The results show that the inhomogeneity of local critical currents has an important effect on the self-field loss. One of the goals in this paper is to provide an accurate method for estimating quality, or what level of critical current inhomogeneity in HTS tape is permissible in practical application. As manufacturing processes are refined through powder in tube and coating technologies, and the sources of extrinsic macroscopic defects are decreased, electromagnetic and mechanical performances of Bi2223 and YBCO tapes are greatly improved. Nevertheless, intrinsic microscopic defects such as weak links, microcracks and small second-phase formations still exist in the tapes, which will lead to statistically local critical current variations. Therefore, it is very important to study the effect that variation in local critical currents may have on the self-field losses of practical long single and multi-parallel HTS tapes.
Zhao, C.; Muehlaus, H.B.; Hobbs, B.E.
1998-03-01
A parametric study is carried out to investigate how geological inhomogeneity affects the pore-fluid convective flow field, the temperature distribution, and the mass concentration distribution in a fluid-saturated porous medium. The related numerical results have demonstrated that (1) the effects of both medium permeability inhomogeneity and medium thermal conductivity inhomogeneity are significant on the pore-fluid convective flow and the species concentration distribution in the porous medium; (2) the effect of medium thermal conductivity inhomogeneity is dramatic on the temperature distribution in the porous medium, but the effect of medium permeability inhomogeneity on the temperature distribution may be considerable, depending on the Rayleigh number involved in the analysis; (3) if the coupling effect between pore-fluid flow and mass transport is weak, the effect of the Lewis number is negligible on the pore-fluid convective flow and temperature distribution, but it is significant on the species concentration distribution in the medium.
NASA Astrophysics Data System (ADS)
Xie, Xin; Zhang, Minghua
2015-08-01
Using long-term radar-based ground measurements from the Atmospheric Radiation Measurement Program, we derive the inhomogeneity of cloud liquid water as represented by the shape parameter of a gamma distribution. The relationship between the inhomogeneity and the model grid size as well as atmospheric condition is presented. A larger grid scale and more unstable atmosphere are associated with larger inhomogeneity that is described by a smaller shape parameter. This relationship is implemented as a scale-aware parameterization of the liquid cloud inhomogeneity in the Community Earth System Model (CESM) in which the shape parameter impacts the cloud microphysical processes. When used in the default CESM1 with the finite-volume dynamic core where a constant liquid inhomogeneity parameter was assumed, it reduces the cloud inhomogeneity in high latitudes and increases it in low latitudes. This is due to both the smaller (larger) grid size in high (low) latitudes in the longitude-latitude grid setting of CESM and the more stable (unstable) atmosphere. The single-column model and general circulation model sensitivity experiments show that the new parameterization increases the cloud liquid water path in polar regions and decreases it in low latitudes. An advantage of the parameterization is that it can recognize the spatial resolutions of the CESM without special tuning of the cloud water inhomogeneity parameter.
Large-scale electromagnetic modeling for multiple inhomogeneous domains
NASA Astrophysics Data System (ADS)
Zhdanov, M. S.; Endo, M.; Cuma, M.
2008-12-01
We develop a new formulation of the integral equation (IE) method for three-dimensional (3D) electromagnetic (EM) field computation in large-scale models with multiple inhomogeneous domains. This problem arises in many practical applications including modeling the EM fields within the complex geoelectrical structures in geophysical exploration. In geophysical applications, it is difficult to describe an earth structure using a horizontally layered background conductivity model, which is required for the efficient implementation of the conventional IE approach. As a result, a large domain of interest with anomalous conductivity distribution needs to be discretized, which complicates the computations. The new method allows us to consider multiple inhomogeneous domains, where the conductivity distribution is different from that of the background, and to use independent discretizations for different domains. This reduces dramatically the computational resources required for large-scale modeling. In addition, by using this method, we can analyze the response of each domain separately without an inappropriate use of the superposition principle for the EM field calculations. The method was carefully tested for modeling the marine controlled-source electromagnetic (MCSEM) fields for complex geoelectrical structures with multiple inhomogeneous domains, such as a seafloor with rough bathymetry, salt domes, and reservoirs. We have also used this technique to investigate the return induction effects from regional geoelectrical structures, e.g., seafloor bathymetry and salt domes, which can distort the EM response from the geophysical exploration target.
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.
Hydrogen solubility in inhomogeneous Pd alloys
Flanagan, T.B.; Wang, D.; Clewley, J.D.
1998-12-31
As-cast, arc-melted Pd-Ni alloys are inhomogeneous and the H{sub 2} isotherms for these differ from their homogeneous counterparts in the two phase, (dilute + hydride), regions but not in the dilute phase regions. Pd-Ni alloys, which become inhomogeneous via a ternary (Pd + Ni + H) equilibrium phase change, have H{sub 2} isotherms which differ from those of the homogeneous alloy in both the two-phase and the dilute phase regions. These results are discussed with respect to the expected type of inhomogeneities.
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.
NASA Astrophysics Data System (ADS)
Wang, Yu-Feng; Tian, Bo
2015-09-01
Under investigation in this paper is an inhomogeneous nonlinear Schrödinger equation, which describes the propagation of a large-wavelength small-amplitude electron plasma wave in a parabolic-distributed and constant-interactional-damping inhomogeneous plasma. Via the Hirota method, Bell-polynomial approach and symbolic computation, bilinear form, Bäcklund transformation and N-soliton solutions are obtained. Influence of the linear density coefficient α and damping coefficient β on the soliton envelopes is also discussed, i.e. α can affect the soliton position, while β is related to the soliton intensity, velocity and phase shift. Periodically attractive and repulsive interactions are shown. Asymptotic analysis shows that the interactions between/among the solitons are elastic.
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.
Inhomogeneous recombinations during cosmic reionization
NASA Astrophysics Data System (ADS)
Sobacchi, Emanuele; Mesinger, Andrei
2014-05-01
By depleting the ionizing photon budget available to expand cosmic H II regions, recombining systems (or Lyman limit systems) can have a large impact during (and following) cosmic reionization. Unfortunately, directly resolving such structures in large-scale reionization simulations is computationally impractical. Instead, here we implement a subgrid prescription for tracking inhomogeneous recombinations in the intergalactic medium. Building on previous work parametrizing photoheating feedback on star formation, we present large-scale, seminumeric reionization simulations which self-consistently track the local (subgrid) evolution of both sources and sinks of ionizing photons. Our simple, single-parameter model naturally results in both an extended reionization and a modest, slowly evolving emissivity, consistent with observations. Recombinations are instrumental in slowing the growth of large H II regions, and damping the rapid rise of the ionizing background in the late stages of (and following) reionization. As a result, typical H II regions are smaller by factors of ˜2 to 3 throughout reionization. The large-scale (k ≲ 0.2 Mpc-1) ionization power spectrum is suppressed by factors of ≳2-3 in the second half of reionization. Therefore properly modelling recombinations is important in interpreting virtually all reionization observables, including upcoming interferometry with the redshifted 21cm line. Consistent with previous works, we find the clumping factor of ionized gas to be C H II ˜ 4 at the end of reionization.
Mathematical Modeling of Extinction of Inhomogeneous Populations.
Karev, G P; Kareva, I
2016-04-01
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 of 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
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.
Inhomogeneous chemical evolution of the Galactic disk
NASA Technical Reports Server (NTRS)
Malinie, Guy; Hartmann, Dieter H.; Clayton, Donald D.; Mathews, Grant J.
1993-01-01
We present analytical models for inhomogeneous chemical evolution (ICE) of systems in which the star formation history resembles a series of bursts, localized in space and/or time, with intermittent periods of remixing. The additional parameter of this model is the metallicity increment of bursting subsystems, but this parameter is constrained by the spread in the age-metallicity relation. We apply this model to the solar annulus in the Galactic disk and show that ICE models yield an improved fit to the observed shape of the stellar abundance distribution function (ADF). The G-dwarf problem can be alleviated with ICE models, but infall of metal poor gas and/or some preenrichment of the disk during the epoch of protogalactic evolution is still required to explain the paucity of low-metallicity dwarfs. ICE models also suggest an explanation of the reduced frequency of metal-rich G-dwarfs relative to the predictions of the simple model. It does not seem likely that chemical evolution of the solar annulus proceeded in a medium that was well-mixed at all times.
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
The fluctuating gravitational field in inhomogeneous and clustered self-gravitating systems.
NASA Astrophysics Data System (ADS)
Del Popolo, A.
1996-07-01
In this paper I extend the results of Ahmad & Cohen (1973), regarding the study of the probability distribution of the stochastic force in homogeneous gravitational systems, to inhomogeneous gravitational ones. To this aim, I study the stochastic force distribution using N-body realizations of Plummer's spherically symmetric models. I find that the stochastic force distribution obtained for the evolved system is in good agreement with Kandrup's (1980) theory of stochastic force in inhomogeneous systems. Correlation effects that arise during the evolution of the system of particles are well described by Antonuccio-Delogu & Atrio-Barandela's (1992) theory.
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.
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.
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.
SURFACE INHOMOGENEITY EFFECTS ON CONVECTIVE DIFFUSION
It is suggested that convectlve scaling, with appropriate extensions, provides the most useful framework for estimating the effects of urban-scale surface inhomogeneities on diffusion in convective conditions. trong contrasts in surface heat flux exist between cropland, forests, ...
... with birth defects may need surgery or other medical treatments. Today, doctors can diagnose many birth defects in the womb. This enables them to treat or even correct some problems before the baby is born. Centers for Disease Control and Prevention
Micro-probe Raman spectroscopy for detection of inhomogeneities in YVO4 single crystals
NASA Astrophysics Data System (ADS)
Erdei, S.; Jin, B.; Ainger, F. W.; Bhalla, A. S.; Keszei, B.; Vandlik, J.; Süveges, A.
1996-03-01
Several near quasicongruent undoped YVO4 single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO4 single crystals grown by the top-seeded solution growth technique, were investigated by micro-probe Raman spectroscopy using unpolarized argon-ion laser light. The line broadening effects of the Raman active mode at 379 cm-1 indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO4. In the latter case a value of 9.23 cm-1 was measured for full width at half-maximum. Although the annealing process in O2 can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO4 crystals, certain remaining peak broadening effects demonstrate a Y-V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm-1 frequencies. In addition, nonassigned low intensity extra Raman peaks appeared over 1000 cm-1 frequencies in all CZ grown samples. The above detected changes in Y-V-O stoichiometry demonstrate a complex phase system around the homogeneity region of quasicongruent YVO4 specimens and enable a more realistic and unified interpretation of the segregated defects and stoichiometry changes in CZ grown YVO4 single crystals than previously available.
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
Large-scale flow generation by inhomogeneous helicity
NASA Astrophysics Data System (ADS)
Yokoi, N.; Brandenburg, A.
2016-03-01
The effect of kinetic helicity (velocity-vorticity correlation) on turbulent momentum transport is investigated. The turbulent kinetic helicity (pseudoscalar) enters the Reynolds stress (mirror-symmetric tensor) expression in the form of a helicity gradient as the coupling coefficient for the mean vorticity and/or the angular velocity (axial vector), which suggests the possibility of mean-flow generation in the presence of inhomogeneous helicity. This inhomogeneous helicity effect, which was previously confirmed at the level of a turbulence- or closure-model simulation, is examined with the aid of direct numerical simulations of rotating turbulence with nonuniform helicity sustained by an external forcing. The numerical simulations show that the spatial distribution of the Reynolds stress is in agreement with the helicity-related term coupled with the angular velocity, and that a large-scale flow is generated in the direction of angular velocity. Such a large-scale flow is not induced in the case of homogeneous turbulent helicity. This result confirms the validity of the inhomogeneous helicity effect in large-scale flow generation and suggests that a vortex dynamo is possible even in incompressible turbulence where there is no baroclinicity effect.
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.
Distributed strain measurement of welded tubular joint with long gauge FBG
NASA Astrophysics Data System (ADS)
Murayama, H.; Kageyama, K.; Ohara, K.; Uzawa, K.; Kanai, M.; Igawa, H.
2008-04-01
Strain along a welded joint submitted to a load can fluctuate because of inhomogeneity in thickness or residual stress distributions and defects. Inversely, strain fluctuation may represent such inhomogeneities or defects. We applied the distributed strain sensing technique with a long gauge FBG to monitoring strain distributions along a welded tubular joint of a steel pipe. By using this sensing technique, we can measure a strain distribution at an arbitrary position along a FBG with the high spatial resolution less than 1 mm. In the tensile test of the steel pipe, we could successfully measure the strain distribution along the weld line of about 100 mm in length. We also observed the strain fluctuating sharply in some areas and acoustic emissions were simultaneously detected by the other sensors. In some areas where sharp fluctuations occurred, defects were observed by also computer tomography carried out after the tensile test. Applications for the sensing technique include health monitoring for other joint configurations, such as fastening and bonding.
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 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.
Nevirkovets, I.P.; Rudenko, E.M.
1985-05-01
The spatial distribution of the two-gap inhomogeneous state of superconducting tin films was investigated experimentally using a number of detectors at injection voltage V/sub i/approx. =2..delta../e. It was found that the initiation of the inhomogeneous state depended on how the current was fed into the generator. The spatial structure of the inhomogeneous state and the instability in the form of a negative voltage jump on the current-voltage characteristic of the generator, which leads to the inhomogeneous state, were found to be very sensitive to weak magnetic fields. The form of the current-voltage characteristic of low-resistance tunnel junctions for V/sub i/approx. =2..delta../e was very dependent on the dimensions of the junction and the transparency of the barrier. Instability was observed only for tunnel junctions whose dimensions exceeded the Josephson penetration depth of the magnetic field. The results are interpreted in terms of the presence in the junction of an inhomogeneous distribution of the constant component of the current, inherent in distributed Josephson junctions.
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.
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
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.
How Local and Average Particle Diffusivities of Inhomogeneous Fluids Depend on Microscopic Dynamics.
Bollinger, Jonathan A; Jain, Avni; Truskett, Thomas M
2015-07-23
Computer simulations and a stochastic Fokker-Planck equation based approach are used to compare the single-particle diffusion coefficients of equilibrium hard-sphere fluids exhibiting identical inhomogeneous static structure and governed by either Brownian (i.e., overdamped Langevin) or Newtonian microscopic dynamics. The physics of inhomogeneity is explored via the imposition of one-dimensional sinusoidal density profiles of different wavelengths and amplitudes. When imposed density variations are small in magnitude for distances on the scale of a particle diameter, bulk-like average correlations between local structure and mobility are observed. In contrast, when density variations are significant on that length scale, qualitatively different structure-mobility correlations emerge that are sensitive to the governing microscopic dynamics. Correspondingly, a previously proposed scaling between long-time diffusivities for bulk isotropic fluids of particles exhibiting Brownian versus Newtonian dynamics [Pond et al. Soft Matter 2011, 7, 9859-9862] cannot be generalized to describe the position-dependent behaviors of strongly inhomogeneous fluids. While average diffusivities in the inhomogeneous and homogeneous directions are coupled, their qualitative dependencies on inhomogeneity wavelength are sensitive to the details of the microscopic dynamics. Nonetheless, average diffusivities of the inhomogeneous fluids can be approximately predicted for either type of dynamics based on knowledge of bulk isotropic fluid behavior and how inhomogeneity modifies the distribution of available volume. Analogous predictions for average diffusivities of experimental, inhomogeneous colloidal dispersions (based on known bulk behavior) suggest that they will exhibit qualitatively different trends than those predicted by models governed by overdamped Langevin dynamics that do not account for hydrodynamic interactions. PMID:25350488
Reconstruction of the stiffness of an inhomogeneous elastic plate
NASA Astrophysics Data System (ADS)
Bogachev, I. V.; Vatul'yan, A. O.; Yavruan, O. V.
2016-05-01
The paper discusses the problem of reconstructing the inhomogeneous cylindrical, symmetric stiffness distribution of a round plate using information on the bias function for established oscillations, which is measured at a certain point. A solution is constructed to the direct problem using the Galerkin method and to the inverse problem of reconstructing the stiffness using an iterative approach based on the regularized linearization method. We present the results of calculation experiments on reconstructing different types of functions that show the efficiency of the proposed approach and make it possible to estimate changes in stiffness.
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
Structure-Function Discrepancy: Inhomogeneity and Delays in Synchronized Neural Networks
Ton, Robert; Deco, Gustavo; Daffertshofer, Andreas
2014-01-01
The discrepancy between structural and functional connectivity in neural systems forms the challenge in understanding general brain functioning. To pinpoint a mapping between structure and function, we investigated the effects of (in)homogeneity in coupling structure and delays on synchronization behavior in networks of oscillatory neural masses by deriving the phase dynamics of these generic networks. For homogeneous delays, the structural coupling matrix is largely preserved in the coupling between phases, resulting in clustered stationary phase distributions. Accordingly, we found only a small number of synchronized groups in the network. Distributed delays, by contrast, introduce inhomogeneity in the phase coupling so that clustered stationary phase distributions no longer exist. The effect of distributed delays mimicked that of structural inhomogeneity. Hence, we argue that phase (de-)synchronization patterns caused by inhomogeneous coupling cannot be distinguished from those caused by distributed delays, at least not by the naked eye. The here-derived analytical expression for the effective coupling between phases as a function of structural coupling constitutes a direct relationship between structural and functional connectivity. Structural connectivity constrains synchronizability that may be modified by the delay distribution. This explains why structural and functional connectivity bear much resemblance albeit not a one-to-one correspondence. We illustrate this in the context of resting-state activity, using the anatomical connectivity structure reported by Hagmann and others. PMID:25078715
Inhomogeneous light shift effects on atomic quantum state evolution in non-destructive measurements
NASA Astrophysics Data System (ADS)
Windpassinger, Patrick J.; Oblak, Daniel; Busk Hoff, Ulrich; Appel, Jürgen; Kjærgaard, Niels; Polzik, Eugene S.
2008-05-01
Various parameters of a trapped collection of cold and ultracold atoms can be determined non-destructively by measuring the phase shift of an off-resonant probe beam, caused by the state-dependent index of refraction of the atoms. The dispersive light-atom interaction, however, gives rise to a differential light shift (ac Stark shift) between the atomic states which, for a non-uniform probe intensity distribution, causes an inhomogeneous dephasing between the atoms. In this paper, we investigate the effects of this inhomogeneous light shift in non-destructive measurement schemes in cold caesium. We interpret our experimental data on dispersively probed Rabi oscillations and Ramsey fringes in terms of a simple light shift model which is shown to describe the observed behavior well. Furthermore, we show that by using spin echo techniques, the inhomogeneous phase shift distribution between the two clock levels can be reversed.
Topological defect dynamics in operando battery nanoparticles
NASA Astrophysics Data System (ADS)
Ulvestad, A.; Singer, A.; Clark, J. N.; Cho, H. M.; Kim, J. W.; Harder, R.; Maser, J.; Meng, Y. S.; Shpyrko, O. G.
2015-06-01
Topological defects can markedly alter nanomaterial properties. This presents opportunities for “defect engineering,” where desired functionalities are generated through defect manipulation. However, imaging defects in working devices with nanoscale resolution remains elusive. We report three-dimensional imaging of dislocation dynamics in individual battery cathode nanoparticles under operando conditions using Bragg coherent diffractive imaging. Dislocations are static at room temperature and mobile during charge transport. During the structural phase transformation, the lithium-rich phase nucleates near the dislocation and spreads inhomogeneously. The dislocation field is a local probe of elastic properties, and we find that a region of the material exhibits a negative Poisson’s ratio at high voltage. Operando dislocation imaging thus opens a powerful avenue for facilitating improvement and rational design of nanostructured materials.
Inhomogeneous mixmaster universes: Some exact solutions
Carmeli, M.; Charach, C.; Feinstein, A.
1983-10-15
Algorithms for generating new exact solutions of the Einstein-Klein-Gordon field equations, which describe inhomogeneous universes with S/sup 3/ topology of spatial sections, are developed. The known exact vacuum and still-fluid solutions with S/sup 3/ topology are used as an input. The methods developed are further applied to derive inhomogeneous generalizations of Bianchi type IX solutions and inhomogeneous S/sup 3/ Gowdy models with gravitational and scalar waves. It is shown that the new solutions, which are generalizations of the Bianchi type IX models, permit identification of the scalar field with the velocity potential of the stiff irrotational fluid. The latter result is further used to study the growth rate of density perturbations of the isotropic and anisotropic Bianchi type IX universes in a fully nonlinear relativistic regime. The role of anisotropy on the rate of growth of density perturbations is studied in detail.
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.
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. PMID:27140761
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.
Two Dimensional Inhomogeneous Magnetic Electron Drift Modes
Shaikh, Dastgeer; Eliasson, Bengt; Shukla, P. K.
2009-11-10
We present simulations of the magnetic electron drift vortex (MEDV) mode turbulence in a magnetoplasma in the presence of inhomogeneities in the plasma temperature and density, as well as in the external magnetic field. The study shows that the influence of the magnetic field in-homogeneity is to suppress streamer-like structures observed in previous simulation studies without background magnetic fields. The MEDV mode turbulence exhibits non-universal (non-Kolmogorov type) spectra for different sets of the plasma parameters. In the presence of an inhomogeneous magnetic field, the spectrum changes to a 7/3 power law, which is flatter than without magnetic field gradients. The relevance of this work to laboratory and cosmic plasmas is briefly mentioned.
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
NASA Astrophysics Data System (ADS)
Yamamoto, Akio; Miwa, Hiroshi; Wang, Wen Jun; Hashimoto, Akihiro
2006-01-01
This paper reports the in-depth and in-plane inhomogeneities in InN films. Samples of InN are grown on sapphire substrates without or with a buffer using the atmospheric-pressure MOVPE. For the in-depth inhomogeneity analysis, the conventional PL measurement using an excitation source with a different wavelength is made from both the front surface and the film/substrate interface sides of samples. The measurement reveals that samples grown for a long time without buffer contain a deteriorated layer, which shows a higher PL peak energy, near the film/substrate interface. Such a layer is never found on the surface side. The deterioration is markedly enhanced when the sample is annealed in an NH3 flow. Since the coexistence of TMI and NH3 (growth environment) suppresses the deterioration and the InN samples used in this experiment have an In-polarity, such a deterioration is hydrogen-related degradation on the N-face of InN film. In-plane inhomogeneity of InN grown with a different buffer is studied by analyzing PL and absorption data. A wider PL spectrum and a larger discrepancy between PL peak energy and absorption edge, those are observed for films grown without buffer, are well explained by taking account of a large in-plane inhomogeneity in the samples. The existence of the large in-plane inhomogeneity is confirmed by the near-field PL mapping obtained by the SNOM. The SNOM analysis also shows that, although the use of the buffer improves the apparent in-plane uniformity, such a film has a fine inhomogeneity due to small grains of the buffer.
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.
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.
Growing inhomogeneities in cosmological Goldstone modes
NASA Astrophysics Data System (ADS)
Benson, Katherine M.
1992-08-01
We examine the evolution of initial inhomogeneities in a Goldstone field in an expanding Friedmann-Robertson-Walker universe. We find subhorizon inhomogeneities grow, relative to the homogeneous state. This stems not from growing fluctuations - which simply redshift - but from rapid (ϱ ~ a-6) decay of the homogeneous state. We show how Goldstone modes escape assumptions - some inapplicable, some ill-founded - underpinning conventional analyses of cosmological fluctuations. Finally, we reconcile our analysis to standard cosmology, noting that the Goldstone evolution is essentially decoupled and dynamical. This material is based upon work supported by NSF grants PHY-87-14654 (while the author was at Harvard University) and PHY91-06210.
Cosmic Inhomogeneities and Averaged Cosmological Dynamics
NASA Astrophysics Data System (ADS)
Paranjape, Aseem; Singh, T. P.
2008-10-01
If general relativity (GR) describes the expansion of the Universe, the observed cosmic acceleration implies the existence of a “dark energy.” However, while the Universe is on average homogeneous on large scales, it is inhomogeneous on smaller scales. While GR governs the dynamics of the inhomogeneous Universe, the averaged homogeneous Universe obeys modified Einstein equations. Can such modifications alone explain the acceleration? For a simple generic model with realistic initial conditions, we show the answer to be “no.” Averaging effects negligibly influence the cosmological dynamics.
Filamentation of laser in an inhomogeneous plasma
Singh, Ranjeet; Tripathi, V. K.
2011-02-15
Filamentation of an intense short pulse laser in an inhomogeneous plasma is investigated when laser propagates along the direction of density gradient and nonlinearity arises due to the relativistic mass variation and ponderomotive force. The ion motion is neglected; however, the effect of dielectric swelling is included. The inhomogeneity in the density profile introduces dielectric swelling of the pump intensity enhancing the plasma permittivity and the growth rate of the instability. The perturbation in laser amplitude grows faster than exponential as the laser penetrates deeper into the denser plasma.
Canonical Hamiltonians for waves in inhomogeneous media
NASA Astrophysics Data System (ADS)
Gershgorin, Boris; Lvov, Yuri V.; Nazarenko, Sergey
2009-01-01
We obtain a canonical form of a quadratic Hamiltonian for linear waves in a weakly inhomogeneous medium. This is achieved by using the Wentzel-Kramers-Brillouin representation of wave packets. The canonical form of the Hamiltonian is obtained via the series of canonical Bogolyubov-type and near-identical transformations. Various examples of the application illustrating the main features of our approach are presented. The knowledge of the Hamiltonian structure for linear wave systems provides a basis for developing a theory of weakly nonlinear random waves in inhomogeneous media generalizing the theory of homogeneous wave turbulence.
Plasmons in inhomogeneously doped neutral and charged graphene nanodisks
Silveiro, Iván; Javier García de Abajo, F.
2014-03-31
We study plasmons in graphene nanodisks including the effect of inhomogeneity in the distribution of the doping charge. Specifically, we discuss the following two configurations: charged disks containing a fixed amount of additional carriers, which are self-consistently distributed along the surface to produce a uniform DC potential; and neutral disks exposed to a neighboring external point charge. A suitable finite-element method is elaborated to compute the charge density associated with the plasmons in the electrostatic limit. For charged disks, we find dipolar plasmons similar to those of uniformly doped graphene structures, in which the plasmon induced charge piles up near the edges. In contrast, in neutral disks placed near an external point charge, plasmons are strongly localized away from the edges. Surprisingly, a single external electron is enough to trap plasmons. The disks also display axially symmetric dark-plasmons, which can be excited through external illumination by coupling them to a neighboring metallic element. Our results have practical relevance for graphene nanophotonics under inhomogeneous doping conditions.
Azimuthal inhomogeneity in the MHD waveguide in the outer magnetosphere
NASA Astrophysics Data System (ADS)
Mazur, V. A.; Chuiko, D. A.
2015-06-01
Geomagnetic field and plasma inhomogeneities in the outer equatorial part of the magnetosphere create a channel with low Alfvén speeds which spans from the nose to the far flanks of the magnetosphere, in both the morning and the evening sectors. This channel plays the role of a waveguide for fast magnetosonic waves. The waveguide eigenmodes and corresponding Alfvén resonance (field line resonance) regions are directly related to geomagnetic pulsations Pc3 and Pc5. U-shaped model of the waveguide allows for full analytical investigation of waveguide eigenmodes. Quantities such as mode wave numbers, group velocities, and their energy density distribution are found as functions of coordinate along the waveguide. The linkage of the waveguide magnetosonic oscillation energy to the Alfvén waves in the vicinity of the field line resonance deeper inside the magnetosphere is investigated, and corresponding energy leakage coefficient is found. Thus, the influence of longitudinal (i.e., azimuthal) waveguide inhomogeneity on wave propagation is analytically investigated. Obtained results can be used for interpretation of the observed wave power distribution in the frequency bands of geomagnetic pulsations Pc3 and Pc5, as well as for explanation of their spectral properties in the outer magnetosphere.
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.
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
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.
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.
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…
Preskill, J. )
1992-11-15
I analyze the interplay of gauge and global symmetries in the theory of topological defects. In a two-dimensional model in which both gauge symmetries and {ital exact} global symmetries are spontaneously broken, stable vortices may fail to exist even though magnetic flux is topologically conserved. Following Vachaspati and Achucarro, I formulate the condition that must be satisfied by the pattern of symmetry breakdown for finite-energy configurations to exist in which the conserved magnetic flux is spread out instead of confined to a localized vortex. If this condition is met, vortices are always unstable at sufficiently weak gauge coupling. I also describe the properties of defects in models with an accidental'' symmetry that is partially broken by gauge-boson exchange. In some cases, the spontaneously broken accidental symmetry is not restored inside the core of the defect. Then the structure of the defect can be analyzed using an effective field theory; the details of the physics responsible for the spontaneous symmetry breakdown need not be considered. Examples include domain walls and vortices that are classically unstable, but are stabilized by loop corrections, and magnetic monopoles that have an unusual core structure. Finally, I examine the general theory of the electroweak strings'' that were recently discussed by Vachaspati. These arise only in models with gauge-boson mixing,'' and can always end on magnetic monopoles. Cosmological implications are briefly discussed.
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.
Exact sum rules for inhomogeneous drums
Amore, Paolo
2013-09-15
We derive general expressions for the sum rules of the eigenvalues of drums of arbitrary shape and arbitrary density, obeying different boundary conditions. The formulas that we present are a generalization of the analogous formulas for one dimensional inhomogeneous systems that we have obtained in a previous paper. We also discuss the extension of these formulas to higher dimensions. We show that in the special case of a density depending only on one variable the sum rules of any integer order can be expressed in terms of a single series. As an application of our result we derive exact sum rules for the homogeneous circular annulus with different boundary conditions, for a homogeneous circular sector and for a radially inhomogeneous circular annulus with Dirichlet boundary conditions. -- Highlights: •We derive an explicit expression for the sum rules of inhomogeneous drums. •We discuss the extension to higher dimensions. •We discuss the special case of an inhomogeneity only along one direction.
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 .
Spectral models of strongly inhomogeneous turbulence
NASA Astrophysics Data System (ADS)
Bragg, Andrew; Kurien, Susan; Clark, Timothy
2015-11-01
We compare results from a spectral model for inhomogeneous turbulence (Besnard et al., Theor. Comp. Fluid. Dyn., vol. 8, pp 1-35, 1996) with DNS data of a shear-free mixing layer (SFML) (Tordella et al., Phys. Rev. E, vol. 77, 016309, 2008). The SFML is used as a test case in which the efficacy of the model closure for the physical-space energy transport can be tested in a flow with strong 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 does not work so well. It may be argued that the discrepancy arises due to the local approximation to the intrinsically non-local pressure transport in physical-space, the effect of which would be particularly strong at short-times when the inhomogeneity of the SFML is strongest. Motivated by these results, we briefly discuss a new model that captures the non-local transport effects, for arbitrarily strong inhomogeneities of the flow.
Prisk, G K; Guy, H J; Elliott, A R; Paiva, M; West, J B
1995-02-01
We used multiple-breath N2 washouts (MBNW) to study the inhomogeneity 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 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 (P < 0.05) and significantly greater changes in the changes in slope of the N2 washouts (P < 0.001), 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. PMID:7759429
NASA Astrophysics Data System (ADS)
Uchiyama, Toshiro; Takeuchi, Shotaro; Kamada, Shohei; Arauchi, Takuji; Hashimoto, Yasuhiro; Yamane, Keisuke; Okada, Narihito; Imai, Yasuhiko; Kimura, Shigeru; Tadatomo, Kazuyuki; Sakai, Akira
2016-05-01
We have investigated the position dependence of crystalline quality and defect distribution in a semipolar (20\\bar{2}1) hydride vapor phase epitaxy (HVPE)-GaN film grown on a (22\\bar{4}3) patterned sapphire substrate (PSS). Position-dependent X-ray microdiffraction (XRMD) measurement clearly revealed the periodic fluctuation of the 20\\bar{2}1 lattice plane tilting in HVPE-GaN films. This correlated with the periodic distribution of (a + c)-type dislocations owing to the patterning pitch of the PSS as confirmed by transmission electron microscopy (TEM). In the three-dimensional reciprocal lattice space map, the diffuse streak exactly along the c-axis can be clearly detected, indicating the presence of basal plane stacking faults in HVPE-GaN films. Furthermore, we have quantitatively estimated the defect densities from the results of XRMD and TEM measurements. From the obtained results of XRMD and TEM measurements, the fluctuation of the lattice plane tilting and the defect distribution in (20\\bar{2}1) HVPE-GaN films grown on two types of metalorganic vapor phase epitaxy-GaN templates will be discussed in detail.
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.
A study of radiation propagation in a medium with quadratic inhomogeneity
Pikulev, A A
2001-09-30
The propagation of Hermitian beams in a medium with a distributed quadratic inhomogeneity is studied and is shown that any solution can be represented as a function of some particular solution. This is accomplished by establishing a one-to-one correspondence between optical fields in a homogeneous medium and in a medium with an arbitrary quadratic inhomogeneity. The stability of optical resonators is studied and the condition for their stability is found. Several solutions are found using the method developed. (physical foundations of quantum electronics)
Holographic measurements of inhomogeneous cloud mixing at the centimeter scale
NASA Astrophysics Data System (ADS)
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.
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.
Modeling inhomogeneous van der Waals fluids using an analytical direct correlation function
NASA Astrophysics Data System (ADS)
Tang, Yiping; Wu, Jianzhong
2004-07-01
Rosenfeld’s perturbative method [J. Chem. Phys. 98, 8126 (1993)] for constructing the Helmholtz energy functional of classical systems is applied to studying inhomogeneous Lennard-Jones fluids, in which the key input—the bulk direct correlation function—is obtained from the first-order mean-spherical approximation (FMSA) [J. Chem. Phys. 118, 4140 (2003)]. Preserving its high fidelity at the bulk limit, the FMSA shows stable and satisfactory performance for a variety of inhomogeneous Lennard-Jones fluids including those near hard walls, inside slit pores, and around colloidal particles. In addition, the inhomogeneous FMSA reproduces reliably the radial distribution function at its bulk limit. The FMSA is found, in particular, much better than the mean-field theory for fluids near hard surfaces. Unlike alternative non-mean-field approaches, the FMSA is computationally as efficient as the mean-field theory, free of any numerical determination of structure information, weight functions, or empirical parameters.
NASA Astrophysics Data System (ADS)
Ortiz, Dolores; Saiz, Jose M.; González, Francisco
2004-04-01
The presence of local inhomogeneities in corneal tissue after refractive surgery has an influence on visual performance. Here we focus on the corneal ablation associated with Lasik surgery and its effect on the modulation transfer function (MTF) that we obtained by modifying a personalized Kooijman model. Inhomogeneities induced by the ablation occur in the form of Gaussian-distributed refractive-index variations of a given correlation length. We show how variation of refractive-index deviation and correlation length (size) of the inhomogeneities allows us to obtain pairs of values that are able to achieve a MTF evolution similar to that observed for contrast sensitivity in the same patients. An estimate of the characteristics of the local effects is obtained.
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.
Scattering of shear waves by an elliptical cavity in a radially inhomogeneous isotropic medium
NASA Astrophysics Data System (ADS)
Hei, Baoping; Yang, Zailin; Chen, Zhigang
2016-03-01
Complex function and general conformal mapping methods are used to investigate the scattering of elastic shear waves by an elliptical cylindrical cavity in a radially inhomogeneous medium. The conformal mappings are introduced to solve scattering by an arbitrary cavity for the Helmholtz equation with variable coefficient through the transformed standard Helmholtz equation with a circular cavity. The medium density depends on the distance from the origin with a power-law variation and the shear elastic modulus is constant. The complex-value displacements and stresses of the inhomogeneous medium are explicitly obtained and the distributions of the dynamic stress for the case of an elliptical cavity are discussed. The accuracy of the present approach is verified by comparing the present solution results with the available published data. Numerical results demonstrate that the wave number, inhomogeneous parameters and different values of aspect ratio have significant influence on the dynamic stress concentration factors around the elliptical cavity.
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.
Chillara, Vamshi Krishna; Ren, Baiyang; Lissenden, Cliff J
2016-04-01
This article describes the use of the frequency domain finite element (FDFE) technique for guided wave mode selection in inhomogeneous waveguides. Problems with Rayleigh-Lamb and Shear-Horizontal mode excitation in isotropic homogeneous plates are first studied to demonstrate the application of the approach. Then, two specific cases of inhomogeneous waveguides are studied using FDFE. Finally, an example of guided wave mode selection for inspecting disbonds in composites is presented. Identification of sensitive and insensitive modes for defect inspection is demonstrated. As the discretization parameters affect the accuracy of the results obtained from FDFE, effect of spatial discretization and the length of the domain used for the spatial fast Fourier transform are studied. Some recommendations with regard to the choice of the above parameters are provided. PMID:26746160
Modeling Inhomogeneous DNA Replication Kinetics
Gauthier, Michel G.; Norio, Paolo; Bechhoefer, John
2012-01-01
In eukaryotic organisms, DNA replication is initiated at a series of chromosomal locations called origins, where replication forks are assembled proceeding bidirectionally to replicate the genome. The distribution and firing rate of these origins, in conjunction with the velocity at which forks progress, dictate the program of the replication process. Previous attempts at modeling DNA replication in eukaryotes have focused on cases where the firing rate and the velocity of replication forks are homogeneous, or uniform, across the genome. However, it is now known that there are large variations in origin activity along the genome and variations in fork velocities can also take place. Here, we generalize previous approaches to modeling replication, to allow for arbitrary spatial variation of initiation rates and fork velocities. We derive rate equations for left- and right-moving forks and for replication probability over time that can be solved numerically to obtain the mean-field replication program. This method accurately reproduces the results of DNA replication simulation. We also successfully adapted our approach to the inverse problem of fitting measurements of DNA replication performed on single DNA molecules. Since such measurements are performed on specified portion of the genome, the examined DNA molecules may be replicated by forks that originate either within the studied molecule or outside of it. This problem was solved by using an effective flux of incoming replication forks at the model boundaries to represent the origin activity outside the studied region. Using this approach, we show that reliable inferences can be made about the replication of specific portions of the genome even if the amount of data that can be obtained from single-molecule experiments is generally limited. PMID:22412853
Theory of Superfluorescence in Highly Inhomogeneous Quantum Systems
NASA Astrophysics Data System (ADS)
Ishikawa, Akira; Miyajima, Kensuke; Ashida, Masaaki; Itoh, Tadashi; Ishihara, Hajime
2016-03-01
Superfluorescence originates from quantum coherence between polarizations in a radiation field. In general, system homogeneity is essential for superfluorescence because inhomogeneity causes decoherence. However, superfluorescence has been recently realized using solid-state materials with large inhomogeneity, with regard to the application for a coherent-light source, etc. This study proposes theoretical criteria for classifying superfluorescence in highly inhomogeneous systems into two regimes on the basis of competition between the generation of coherence due to the strong light-matter coupling in solid-state materials and decoherence caused by the system inhomogeneity. These criteria supports controlling and designing the system inhomogeneity with limited available fabrication technologies.
Beginning inflation in an inhomogeneous universe
NASA Astrophysics Data System (ADS)
East, William; Kleban, Matthew; Linde, Andrei; Senatore, Leonardo
2016-03-01
The idea that a period of exponential expansion occurred early in the Universe's history was originally proposed in order to explain the large scale homogeneity and isotropy of the Universe. However, there remain open questions about the conditions under which inflation can eventually arise when homogeneity is not assumed to begin with it. I will describe an investigation, utilizing simulations in full general relativity, of the very inhomogeneous regime where initially the gradient energy of the scalar inflaton field dominates over the potential energy, including the strong-field regime where the wavelength of the inhomogeneities are comparable to the Hubble radius, and black holes form. The results show that inflation can eventually arise from a general class of such initial conditions, at least as long as the scalar field variations do not include values off the inflationary plateau. I will also comment on future directions for using the tools of numerical relativity to explore nonlinear and strong-field dynamics in cosmology.
Cyclotron resonance in an inhomogeneous magnetic field
Albert, J.M. )
1993-08-01
Relativistic test particles interacting with a small monochromatic electromagnetic wave are studied in the presence of an inhomogeneous background magnetic field. A resonance-averaged Hamiltonian is derived which retains the effects of passage through resonance. Two distinct regimes are found. In the strongly inhomogeneous case, the resonant phase angle at successive resonances is random, and multiple resonant interactions lead to a random walk in phase space. In the other, adiabatic limit, the phase angle is determined by the phase portrait of the Hamiltonian and leads to a systematic change in the appropriate canonical action (and therefore in the energy and pitch angle), so that the cumulative effect increases directly with the number of resonances.
Criterion for convection in an inhomogeneous star
NASA Technical Reports Server (NTRS)
Stothers, Richard B.; Chin, Chao-Wen
1992-01-01
To resolve the question of whether the Schwarzschild criterion or the Ledoux criterion should be used to test for convective instability in a star, a well-observed cluster of chemically inhomogeneous massive stars, in which the choice of the criterion for convection makes a crucial and easily observable difference, is required. NGC 330, a metal-poor cluster in the Small Magellanic Cloud, is ideal for this test. Its large evolved stellar population contains both blue and red supergiants, of which its many red supergiants should be absent if a gradient of mean molecular weight did not choke off rapid convective motions in the inhomogeneous region connecting the envelope and core. Thus the Ledoux criterion for convection is strongly indicated as being correct.
Temporal inhomogeneities in radiosonde temperature records
NASA Astrophysics Data System (ADS)
Gaffen, Dian J.
1994-02-01
Historical information on changes in radiosonde instruments and observing methods is combined with time series of upper-air temperature data to estimate the effects of (1) changes in sensors, (2) changes in solar radiation corrections to the data, and (3) changes in the length of the train between the balloon and the instrument package. These changes can induce discontinuities in the temperature records from several tenths to as high as several degrees Celsius. The discontinuities can be larger than the temperature trends of a few tenths of a degree per decade, computed by previous investigators from radiosonde observations. An assessment of the 63-station network used by Angell to monitor tropospheric and stratospheric temperature suggests that about 43% of those stations' records have inhomogeneities, most notably in the stratosphere. These findings suggest that some previously computed temperature trends, especially estimates of stratospheric cooling, may be influenced by data inhomogeneities.
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.
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
Declercq, Nico F; Leroy, Oswald
2011-08-01
Plane waves are solutions of the visco-elastic wave equation. Their wave vector can be real for homogeneous plane waves or complex for inhomogeneous and evanescent plane waves. Although interesting from a theoretical point of view, complex wave vectors normally only emerge naturally when propagation or scattering is studied of sound under the appearance of damping effects. Because of the particular behavior of inhomogeneous and evanescent waves and their estimated efficiency for surface wave generation, bounded beams, experimentally mimicking their infinite counterparts similar to (wide) Gaussian beams imitating infinite harmonic plane waves, are of special interest in this report. The study describes the behavior of bounded inhomogeneous and bounded evanescent waves in terms of amplitude and phase distribution as well as energy flow direction. The outcome is of importance to the applicability of bounded inhomogeneous ultrasonic waves for nondestructive testing. PMID:21453948
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. PMID:26891886
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.
Gaussian beam evolution in nonlinear inhomogeneous plasma
NASA Astrophysics Data System (ADS)
Berczynski, P.; Kravtsov, Yu. A.; Tikhonchuk, V.; Tikhonchuk
2014-04-01
The method of nonlinear complex geometrical optics (NCGO) is proposed in this paper for description of the evolution of a spatially narrow Gaussian beam (GB) in an inhomogeneous nonlinear plasma. NCGO method deals with first-order ordinary differential equations for the complex curvature of the wave front and for GB amplitude and for second-order ordinary differential equation for GB width. Thus, NCGO simplifies the description of GB diffraction and self-focusing effects as compared to the known methods of plasma physics and this way it can be assumed to be attractive and comprehensive approach in problems of plasma heating by electromagnetic waves. Moreover, we demonstrate in this paper some regularity for nonlinear inhomogeneous plasma in the framework of which central ray of a GB is not subjected to nonlinear refraction within NCGO method boundary applicability. On the contrary, the beam width, wave front curvature, and GB amplitude are modified by diffraction and self-focusing processes. General properties of the beam propagation are illustrated with results of numerical modeling for two particular cases: GB diffraction and self-focusing along curvilinear trajectory with torsion in axially symmetric plasma column and GB reflection from nonlinear inhomogeneous plasma layer. We prove in this paper that NCGO is new effective method of plasma physics, which can be applied for improvement of ray tracing techniques and plasma diagnostics.
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
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.
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.
Viscosity of confined inhomogeneous nonequilibrium fluids.
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. PMID:15549963
Inhomogeneous CDMFT and nonmagnetic impurities in graphene
NASA Astrophysics Data System (ADS)
Charlebois, M.; Sénéchal, D.; Gagnon, A.-M.; Tremblay, A.-M. S.
In cluster dynamical mean-field theory (CDMFT), we usually apply the self-consistency condition on an infinite super-lattice of identical clusters. However, in some problems a large unit cell is required, for instance in the presence of a periodically repeated impurity. Since the impurity solver (exact diagonalization) can only treat small clusters, we break the unit cell into multiple small clusters that can be solved individually. This new technique is called inhomogeneous CDMFT (1) and is analogous to inhomogeneous DMFT (2). In this presentation, we will explain both the CDMFT and inhomogeneous CDMFT self-consistency loops within a unified, simple picture. We then apply this technique to a nonmagnetic impurity in graphene and study the emerging magnetism. Our results take into account dynamical correlations; nevertheless they qualitatively agree with previous mean-field and density functional theory studies. (1) Charlebois, M. et al., Phys. Rev. B 91, 035132 (2015). (2) Snoek, M. et al., New J. Phys. 10, 093008 (2008). Supported by NSERC, CIFAR and the Tier I Canada Research Chair Program.
Voting and catalytic processes with inhomogeneities
NASA Astrophysics Data System (ADS)
Mobilia, Mauro; Georgiev, Ivan T.
2005-04-01
We consider the dynamics of the voter model and of the monomer-monomer catalytic process in the presence of many “competing” inhomogeneities and show, through exact calculations and numerical simulations, that their presence results in a nontrivial fluctuating steady state whose properties are studied and turn out to specifically depend on the dimensionality of the system, the strength of the inhomogeneities, and their separating distances. In fact, in arbitrary dimensions, we obtain an exact (yet formal) expression of the order parameters (magnetization and concentration of adsorbed particles) in the presence of an arbitrary number n of inhomogeneities (“zealots” in the voter language) and formal similarities with suitable electrostatic systems are pointed out. In the nontrivial cases n=1,2 , we explicitly compute the static and long-time properties of the order parameters and therefore capture the generic features of the systems. When n>2 , the problems are studied through numerical simulations. In one spatial dimension, we also compute the expressions of the stationary order parameters in the completely disordered case, where n is arbitrary large. Particular attention is paid to the spatial dependence of the stationary order parameters and formal connections with electrostatics.
Assessment of complex EMF exposure situations including inhomogeneous field distribution.
Jokela, Kari
2007-06-01
Assessment of exposure to time varying electric and magnetic fields is difficult when the fields are non-uniform or very localized. Restriction of the local spatial peak value below the reference level may be too restrictive. Additional problems arise when the fields are not sinusoidal. The objective of this review is to present practical measurement procedures for realistic and not too conservative exposure assessment for verification of compliance with the exposure guidelines of ICNIRP. In most exposure situations above 10 MHz the electric field (E) is more important than the magnetic field (B). At frequencies above 500 MHz the equivalent electric field power density averaged over the body is the most relevant indicator of exposure. Assessment of specific absorption rate (SAR) is not needed when the spatial peak value does not exceed by 6 dB the average value. Below 50 MHz down to 50 Hz, the electric field induces currents flowing along the limbs and torso. The current is roughly directly proportional to the electric field strength averaged over the body. A convenient way to restrict current concentration and hot spots in the neck, ankle and wrist, is to measure the current induced in the body. This is not possible for magnetic fields. Instead, for a non-uniform magnetic field below 100 kHz the average magnetic flux density over the whole body and head are valid exposure indicators to protect the central nervous system. The first alternative to analyze exposure to non-sinusoidal magnetic fields below 100 kHz is based on the spectral comparison of each component to the corresponding reference level. In the second alternative the waveform of B or dB/dt is filtered in the time domain with a simple filter, where the attenuation varies proportionally to the reference level as a function of frequency, and the filtered peak value is compared to the peak reference level derived from the ICNIRP reference levels. PMID:17495653
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.
Inhomogeneous field in cavities of zero index metamaterials
NASA Astrophysics Data System (ADS)
Fu, Yangyang; Xu, Yadong; Chen, Huangyang
2015-06-01
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.
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.
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.
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.
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
Zhou, Lian; Zhu, Shanan; He, Bin
2014-06-01
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 a 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 this 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
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.
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
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.
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.
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.
Inhomogeneous Elastic Response of Silica Glass
NASA Astrophysics Data System (ADS)
Léonforte, F.; Tanguy, A.; Wittmer, J. P.; Barrat, J.-L.
2006-08-01
Using large scale molecular dynamics simulations we investigate the properties of the nonaffine displacement field induced by macroscopic uniaxial deformation of amorphous silica, a strong glass according to Angell’s classification. We demonstrate the existence of a length scale ξ characterizing the correlations of this field (corresponding to a volume of about 1000 atoms), and compare its structure to the one observed in a standard fragile model glass. The “boson-peak” anomaly of the density of states can be traced back in both cases to elastic inhomogeneities on wavelengths smaller than ξ where classical continuum elasticity becomes simply unapplicable.
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.
Inhomogeneous and anisotropic Universe and apparent acceleration
NASA Astrophysics Data System (ADS)
Fanizza, G.; Tedesco, L.
2015-01-01
In this paper, we introduce a Lemaître-Tolman-Bondi (LTB) Bianchi type I (plane symmetric) model of the Universe. We study and solve Einstein field equations. We investigate the effects of such a model of the Universe; in particular, these results are important in understanding the effect of the combined presence of an inhomogeneous and anisotropic universe. The observational magnitude-redshift data deviated from the UNION 2 catalog have been analyzed in the framework of this LTB anisotropic universe, and the fit has been achieved without the inclusion of any dark energy.
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.
Complementary Variational Theorems for inhomogeneous superconductors
NASA Astrophysics Data System (ADS)
Choy, T. C.
1997-03-01
Complementary variational theorems are derived for an inhomogeneous London (local) superconductor in which both the magnetic permeability μ(r) and the London penetration length λ_L(r) vary randomly in space (T.C. Choy, Physical Review B (1997) (to appear)). An essential feature is the close coupling between magnetic and supercurrent polarisation effects, developed self-consistently in this work. Using these theorems and a suitable ansatz for the single particle polarisabilities, we obtained complementary bounds for a composite superconductor near Tc and T=0^circ K. Our results may be important for the empirical study of systems containing magnetic (normal) and superconducting mixtures, including the high Tc oxide superconductors.
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.
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
Honeycomb lattices with defects
NASA Astrophysics Data System (ADS)
Spencer, Meryl A.; Ziff, Robert M.
2016-04-01
In this paper, we introduce a variant of the honeycomb lattice in which we create defects by randomly exchanging adjacent bonds, producing a random tiling with a distribution of polygon edges. We study the percolation properties on these lattices as a function of the number of exchanged bonds using an alternative computational method. We find the site and bond percolation thresholds are consistent with other three-coordinated lattices with the same standard deviation in the degree distribution of the dual; here we can produce a continuum of lattices with a range of standard deviations in the distribution. These lattices should be useful for modeling other properties of random systems as well as percolation.
Herranz, G.; Copie, O.; Bouzehouane, K.; Fusil, S.; Jacquet, E.; Carretero, C.; Bibes, M.; Barthelemy, A.; Tafra, E.; Basletic, M.; Hamzic, A.; Fortuna, F.
2010-05-15
Using a combination of advanced characterization tools (positron annihilation spectroscopy, conductive-tip atomic force microscopy, and high-field magnetotransport), we have studied the extension, origin and properties of the high mobility electron gas (HMEG) generated by etching the SrTiO{sub 3} surfaces with Ar{sup +} ions. Contrary to previous assumptions, we show that this HMEG is not confined to nanometric thickness but extends to a few micrometer from the surface. We discuss this unanticipated large spatial extension in terms of the striking large diffusion of oxygen vacancy-related defects.
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.
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.
Topological defects from the multiverse
NASA Astrophysics Data System (ADS)
Zhang, Jun; Blanco-Pillado, Jose J.; Garriga, Jaume; Vilenkin, Alexander
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.
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.
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
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.
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
Nonlinear acoustics of micro-inhomogeneous media
NASA Astrophysics Data System (ADS)
Nazarov, Veniamin E.; Ostrovsky, Lev A.; Soustova, Irina A.; Sutin, Aleksandr M.
1988-01-01
Acoustic waves can interact in micro-inhomogeneous media much more intensively than in homogeneous media. This has been repeatedly observed in experiments with ground species, marine sediments, porous materials and metals. This paper considers two models of such media which seem to be applicable to the description of these results. One of them is based on the consideration of nonlinear sound scattering by separate spherical cavities in liquids and solids. The second model is based on the phenomenological stress-deformation relation in solids with microplasticity which often has hysteresis (heritage) properties associated with the micro-inhomogeneities. In metals, for example, it is caused by the movement of dislocations. Different nonlinear effects in such media (harmonic and combination frequency generation, nonlinear, variations of resonance frequency amplitude-dependent losses) are considered. Some results of experiments with metallic resonators supporting the theory developed here are also presented. These mechanisms may determine the nonlinear properties of real soils and rocks summarized in a table given in the paper.
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.
Reheating in the presence of inhomogeneous noise
NASA Astrophysics Data System (ADS)
Zanchin, V.; Maia, A., Jr.; Craig, W.; Brandenberger, R.
1999-07-01
Explosive particle production due to parametric resonance is a crucial feature of reheating in inflationary cosmology. Coherent oscillations of the inflaton field lead to a periodically varying mass in the evolution equation of matter and gravitational fluctuations and often induce a parametric resonance instability. In a previous paper [V. Zanchin et al., Phys. Rev. D 57, 4651 (1998)] it was shown that homogeneous (i.e. space-independent) noise leads to an increase of the generalized Floquet exponent for all modes, at least if the noise is temporally uncorrelated. Here we extend the results to the physically more realistic case of spatially inhomogeneous noise. We demonstrate-modulo some mathematical fine points which are addressed in a companion paper-that the Floquet exponent is a non-decreasing function of the amplitude of the noise. We provide numerical evidence for an even stronger statement, namely that in the presence of inhomogeneous noise, the Floquet exponent of each mode is larger than the maximal Floquet exponent of the system in the absence of noise.
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.
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.
NMR quantitation: influence of RF inhomogeneity
Mo, Huaping; Harwood, John; Raftery, Daniel
2016-01-01
The NMR peak integral is ideally linearly dependent on the sine of excitation angle (θ), which has provided unsurpassed flexibility in quantitative NMR by allowing the use of a signal of any concentration as the internal concentration reference. Controlling the excitation angle is particularly critical for solvent proton concentration referencing to minimize the negative impact of radiation damping, and to reduce the risk of receiver gain compression. In practice, due to the influence of RF inhomogeneity for any given probe, the observed peak integral is not exactly proportional to sin θ. To evaluate the impact quantitatively, we introduce a RF inhomogeneity factor I(θ) as a function of the nominal pulse excitation angle and propose a simple calibration procedure. Alternatively, I(θ) can be calculated from the probe’s RF profile, which can be readily obtained as a gradient image of an aqueous sample. Our results show that without consideration of I(θ), even for a probe with good RF homogeneity, up to 5% error can be introduced due to different excitation pulse angles used for the analyte and the reference. Hence, a simple calibration of I(θ) can eliminate such errors and allow an accurate description of the observed NMR signal’s dependence on the excitation angle in quantitative analysis. PMID:21919056
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.
Quasar Accretion Disks are Strongly Inhomogeneous
NASA Astrophysics Data System (ADS)
Dexter, Jason; Agol, Eric
2011-01-01
Active galactic nuclei have been observed to vary stochastically with 10%-20% rms amplitudes over a range of optical wavelengths where the emission arises in an accretion disk. Since the accretion disk is unlikely to vary coherently, local fluctuations may be significantly larger than the global rms variability. We investigate toy models of quasar accretion disks consisting of a number of regions, n, whose temperatures vary independently with an amplitude of σ T in dex. Models with large fluctuations (σ T = 0.35-0.50) in 102-103 independently fluctuating zones for every factor of two in radius can explain the observed discrepancy between thin accretion disk sizes inferred from microlensing events and optical luminosity while matching the observed optical variability. For the same range of σ T , inhomogeneous disk spectra provide excellent fits to the Hubble Space Telescope quasar composite without invoking global Compton scattering atmospheres to explain the high levels of observed UV emission. Simulated microlensing light curves for the Einstein cross from our time-varying toy models are well fit using a time-steady power-law temperature disk and produce magnification light curves that are consistent with current microlensing observations. Deviations due to the inhomogeneous, time-dependent disk structure should occur above the 1% level in the light curves, detectable in future microlensing observations with millimagnitude sensitivity.
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.
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
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.
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".
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.
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
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.
Ventricular Septal Defect (VSD)
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Neural tube defects are birth defects of the brain, spine, or spinal cord. They happen in the first month ... that she is pregnant. The two most common neural tube defects are spina bifida and anencephaly. In spina bifida, ...
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
Monte Carlo prediction of radiative heat transfer in inhomogeneous, anisotropic, nongray media
NASA Technical Reports Server (NTRS)
Farmer, Jeff T.; Howell, John R.
1994-01-01
A Monte Carlo solution technique has been formulated to predict the radiative heat transfer in three-dimensional, inhomogeneous participating media which exhibit spectrally dependent emission and absorption and anisotropic scattering. Details of the technique and selected numerical sensitivities are discussed. The technique was applied to a problem involving a medium composed of a gas mixture of carbon dioxide and nitrogen and suspended carbon particles. A homogeneous medium was modeled to examine the effect of total pressure and carbon-particle concentration on radiative heat transfer. Variation in total pressure, over the range studied, had minimal effect on the amount of heat radiated to the enclosure walls and on the radiative-flux distribution within the medium. Increases in the carbon particle concentration produced significantly higher heat fluxes at the boundaries and altered the radiative flux distribution. The technique was then applied to an inhomogeneous medium to examine effects of specific temperature and carbon particle concentration distributions on radiative heat transfer. For the inhomogeneous conditions examined, the largest radiative flux divergence occurs near the center of the medium and the regions near some enclosure walls act as energy sinks.
Electron transport and barrier inhomogeneities in palladium silicide Schottky diodes
NASA Astrophysics Data System (ADS)
Chand, S.; Kumar, J.
The current-voltage (I-V) characteristics of Schottky diodes, prepared by deposition of palladium film on to a n/n+ silicon wafer held at 573 K, are measured over a temperature range 37-307 K and analyzed in terms of thermionic emission-diffusion (TED) theory by incorporating the concept of barrier inhomogeneities through a Gaussian distribution function. The process adopted is shown to yield an ideal Schottky diode with a near constant barrier height of 0.734 V and ideality factor 1.05 in the temperature interval 215-307 K. Below 215 K, both the barrier height (φbo) and the ideality factor (η) exhibit abnormal temperature dependence and are explained by invoking two sets of Gaussian distributions of barrier heights at 84-215 K and 37-84 K. Further, it is demonstrated that the forward bias makes the Gaussian distribution dynamic so that the mean fluctuates (i.e., increases or decreases depending on whether its voltage coefficient is positive or negative) and the standard deviation decreases progressively, i.e., the barrier homogenizes temporarily. The changes occur in such a way that the apparent barrier height at any bias is always higher than at zero-bias. Finally, it is pointed out that the presence of single/multiple distributions can be ascertained and the values of respective parameters deduced from the φap vs. 1/T plot itself. Also, the inverse ideality factor versus inverse temperature plot provides bias coefficients of the mean barrier height and standard deviation of the distribution function.
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
Fluence inhomogeneities due to a ripple filter induced Moiré effect
NASA Astrophysics Data System (ADS)
Printz Ringbæk, Toke; Brons, Stephan; Naumann, Jakob; Ackermann, Benjamin; Horn, Julian; Latzel, Harald; Scheloske, Stefan; Galonska, Michael; Bassler, Niels; Zink, Klemens; Weber, Uli
2015-02-01
At particle therapy facilities with pencil beam scanning, the implementation of a ripple filter (RiFi) broadens the Bragg peak, so fewer energy steps from the accelerator are required for a homogeneous dose coverage of the planning target volume (PTV). However, sharply focusing the scanned pencil beams at the RiFi plane by ion optical settings can lead to a Moiré effect, causing fluence inhomogeneities at the isocenter. This has been experimentally proven at the Heidelberg Ionenstrahl-Therapiezentrum (HIT), Universitätsklinikum Heidelberg, Germany. 150 MeV u-1 carbon-12 ions are used for irradiation with a 3 mm thick RiFi. The beam is focused in front of and as close to the RiFi plane as possible. The pencil beam width is estimated to be 0.78 mm at a 93 mm distance from the RiFi. Radiographic films are used to obtain the fluence profile 30 mm in front of the isocenter, 930 mm from the RiFi. The Monte Carlo (MC) code SHIELD-HIT12A is used to determine the RiFi-induced inhomogeneities in the fluence distribution at the isocenter for a similar setup, pencil beam widths at the RiFi plane ranging from σ x\\text{RiFi}=0.56 to 1.2 mm and for scanning step sizes ranging from 1.5 to 3.7 mm. The beam application and monitoring system (BAMS) used at HIT is modelled and simulated. When the width of the pencil beams at the RiFi plane is much smaller than the scanning step size, the resulting inhomogeneous fluence distribution at the RiFi plane interfers with the inhomogeneous RiFi mass distribution and fluence inhomogeneity can be observed at the isocenter as large as an 8% deviation from the mean fluence. The inverse of the fluence ripple period at the isocenter is found to be the difference between the inverse of the RiFi period and the inverse of the scanning step size. We have been able to use MC simulations to reproduce the spacing of the ripple stripes seen in films irradiated at HIT. Our findings clearly indicate that pencil beams sharply focused near the RiFi plane
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.
Optical diffraction by inhomogeneous volume objects
NASA Astrophysics Data System (ADS)
Forte, Gustavo; Lencina, Alberto; Tebaldi, Myrian; Bolognini, Nestor
2008-08-01
Electromagnetic waves propagation research in volume media increases considerably in the last years. The study evolved from thick hologram gratings, Bragg and Raman-Nath diffraction regimes up to current research in photonics materials. Usually differential methods are employed to account for the light transmitted for volume media. In our proposal, we develop a simple and versatile integral method to calculate the diffracted field provided the media refractive index has low variations in a wavelength scale. In fact, starting from first principles, we obtain a modified version of the Fresnel propagator of the scalar diffraction theory. Our method is valid for some kind of magnetic, dielectric and absorbent inhomogeneous media. In particular, for TE (TM) fields, we can study media where the permittivity (permeability) gradient is perpendicular to the electric (magnetic) field and its permeability (permittivity) is constant. To validate the approach, we applied it to (in) homogeneous media having well known diffraction properties.
Optimal stochastic transport in inhomogeneous thermal environments
NASA Astrophysics Data System (ADS)
Bo, Stefano; Aurell, Erik; Eichhorn, Ralf; Celani, Antonio
2013-07-01
We consider the optimization of the average entropy production in inhomogeneous temperature environments within the framework of stochastic thermodynamics. For systems modeled by Langevin equations (e.g. a colloidal particle in a heat bath) it has been recently shown that a space-dependent temperature breaks the time reversal symmetry of the fast velocity degrees of freedom resulting in an anomalous contribution to the entropy production of the overdamped dynamics. We show that optimization of entropy production is determined by an auxiliary deterministic problem formally analogous to motion on a curved manifold in a potential. The “anomalous contribution” to entropy plays the role of the potential and the inverse of the diffusion tensor is the metric. We also find that entropy production is not minimized by adiabatically slow, quasi-static protocols but there is a finite optimal duration for the transport process. As an example we discuss the case of a linearly space-dependent diffusion coefficient.
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.
Trapping and reaction on inhomogeneous structures
NASA Astrophysics Data System (ADS)
Cassi, Davide
2011-05-01
We consider the problem of two chemical species, A and B, undergoing an annihilation process A + B → B, on generic discrete inhomogeneous structures, such as disordered solids, glasses, fractals, polymer networks and gels. Two particular cases are analysed: in the fist one A is immobile and B is diffusing (target decay process); in the second one A is diffusing and B is immobile (trapping process). The survival probability of A is analytically calculated in the limit of large times, showing that, while for the target decay it is related to the spectral dimension ? of the structure, for the trapping problem it depends, in general, on a different anomalous dimension, which we call the exploration dimension.
Deformed bubbles in inhomogeneous ultrasonic fields
NASA Astrophysics Data System (ADS)
Zaleski, Stéphane; Popinet, Stéphane
1998-11-01
We study numerically a bubble undergoing expansions and contractions under an ultrasonic acoustic field. The bubble deforms under the influence of intrinsic instabilities as well as inhomogeneities in the pressure field. Interface kinematics through connected marker chains, with cut-cell reconstructions are used to solve the Navier-Stokes equations in axisymmetric geometry. A series of embedded grids is used to follow large expansions and contractions. Test cases involve a bubble oscillating at a variable distance from a solid wall as well as a levitating bubble subject to a net force (the Bjerknes force). The numerical scheme is able to follow relatively small bubbles down to 3 μm, in the sonoluminescence regime. The Rayleigh-Taylor instability predicted in that regime is reproduced. Larger, millimeter size bubbles may also be followed. In that case the numerical results show a typical jet formation analogous to the experimental observations of Lauterborn. Preliminary observations of jet velocities are made and compared to experiment.
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.
Sensor array processing for random inhomogeneous media
NASA Astrophysics Data System (ADS)
Ringelstein, Joerg; Gershman, Alex B.; Boehme, Johann F.
1999-11-01
The performances of high-resolution array processing methods are known to degrade in random inhomogeneous media because the amplitude and phase of each wavefront tend to fluctuate and to loose their coherence between array sensors. As a result, in the presence of such a multiplicative noise, the conventional coherent wavefront model becomes inapplicable. Such a type of degradation may be especially strong for large aperture arrays. Below, we develop new high-resolution covariance matching (CM) techniques with an improved robustness against multiplicative noise and related coherence losses. Using a few unrestrictive physics-based assumptions on the environment, we show that reliable algorithms can be developed which take into account possible coherence losses. Computer simulation results and real sonar data processing results are presented. These results demonstrate drastic improvements achieved by our approach as compared with conventional high- resolution array processing techniques.
Inhomogeneous thermalization in strongly coupled field theories.
Balasubramanian, V; Bernamonti, A; de Boer, J; Craps, B; Franti, L; Galli, F; Keski-Vakkuri, E; Müller, B; Schäfer, A
2013-12-01
To describe theoretically the creation and evolution of the quark-gluon plasma, one typically employs three ingredients: a model for the initial state, nonhydrodynamic early time evolution, and hydrodynamics. In this Letter we study the nonhydrodynamic early time evolution using the AdS/CFT correspondence in the presence of inhomogeneities. We find that the AdS description of the early time evolution is well matched by free streaming. Near the end of the early time interval where our analytic computations are reliable, the stress tensor agrees with the second order hydrodynamic stress tensor computed from the local energy density and fluid velocity. Our techniques may also be useful for the study of far-from-equilibrium strongly coupled systems in other areas of physics. PMID:24476254
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.
Klumbies, H; Müller-Meskamp, L; Mönch, T; Schubert, S; Leo, K
2013-02-01
The reaction of calcium thin films with water - monitored optically or electrically - is widely used for evaluating ultrahigh barrier foils for the encapsulation of organic electronic devices. We studied the common optical and the electrical method and compared them with in situ atomic force microscope topography scans. All three methods were applied at the same sample in parallel in a typical test design containing a gas volume for water distribution next to the calcium layer of 60 and 1000 nm thickness, respectively. The common assumption for the interpretation of such measurement data is laterally homogeneous calcium consumption of the layer from top to bottom. In contrast, we observed a significant ratio of laterally inhomogeneous corrosion of the calcium on the micro-scale for both thicknesses. Some areas were strongly or completely corroded through the whole layer while others exhibited less or no corrosion. Furthermore, those corroded spots grew in lateral direction. As a consequence of lateral inhomogeneous calcium corrosion the electrical calcium measurement method underestimates the amount of calcium left; according to our results this does not affect the water vapor transmission rate (WVTR). Optical data evaluated by Lambert-Beer law underestimate the amount of calcium left as well and also underestimate the WVTR. If the data are evaluated, using a linear relationship between transmission and amount of calcium left, the both values are more precise. The scope of this study is to call attention to the existence of lateral inhomogeneity in calcium corrosion and its impact on the calcium permeation measurements. While more investigations would be needed to quantify the effect of this inhomogeneity on the electrical and optical method in general, the discussion sheds light on the way, calcium test data are influenced by lateral inhomogeneous calcium corrosion. Our observations highlight the need for careful interpretation of calcium test results, but also
Effects of ventilation inhomogeneity on DLcoSB-3EQ in normal subjects.
Cotton, D J; Prabhu, M B; Mink, J T; Graham, B L
1992-12-01
In patients with airflow obstruction, we found that ventilation inhomogeneity during vital capacity single-breath maneuvers was associated with decreases in the three-equation single-breath CO diffusing capacity of the lung (DLcoSB-3EQ) when breath-hold time (tBH) decreased. We postulated that this was due to a significant resistance to diffusive gas mixing within the gas phase of the lung. In this study, we hypothesized that this phenomenon might also occur in normal subjects if the breathing cycle were altered from traditional vital capacity maneuvers to those that increase ventilation inhomogeneity. In 10 normal subjects, we examined the tBH dependence of both DLcoSB-3EQ and the distribution of ventilation, measured by the mixing efficiency and the normalized phase III slope for helium. Preinspiratory lung volume (V0) was increased by keeping the maximum end-inspiratory lung volume (Vmax) constant or by increasing V0 and Vmax. When V0 increased while Vmax was kept constant, we found that the tBH-independent and the tBH-dependent components of ventilation inhomogeneity increased, but DLcoSB-3EQ was independent of V0 and tBH. Increasing V0 and Vmax did not change ventilation inhomogeneity at a tBH of 0 s, but the tBH-dependent component decreased. DLcoSB-3EQ, although independent of tBH, increased slightly with increases in Vmax. We conclude that in normal subjects increases in ventilation inhomogeneity with increases in V0 do not result in DLcoSB-3EQ becoming tBH dependent. PMID:1490979
Effects of nanoscale density inhomogeneities on shearing fluids
NASA Astrophysics Data System (ADS)
Dalton, Benjamin A.; Daivis, Peter J.; Hansen, J. S.; Todd, B. D.
2013-11-01
It is well known that density inhomogeneities at the solid-liquid interface can have a strong effect on the velocity profile of a nanoconfined fluid in planar Poiseuille flow. However, it is difficult to control the density inhomogeneities induced by solid walls, making this type of system unsuitable for a comprehensive study of the effect on density inhomogeneity on nanofluidic flow. In this paper, we employ an external force compatible with periodic boundary conditions to induce the density variation, which greatly simplifies the problem when compared to flow in nonperiodic nanoconfined systems. Using the sinusoidal transverse force method to produce shearing velocity profiles and the sinusoidal longitudinal force method to produce inhomogeneous density profiles, we are able to observe the interactions between the two property inhomogeneities at the level of individual Fourier components. This gives us a method for direct measurement of the coupling between the density and velocity fields and allows us to introduce various feedback control mechanisms which customize fluid behavior in individual Fourier components. We briefly discuss the role of temperature inhomogeneity and consider whether local thermal expansion due to nonuniform viscous heating is sufficient to account for shear-induced density inhomogeneities. We also consider the local Newtonian constitutive relation relating the shear stress to the velocity gradient and show that the local model breaks down for sufficiently large density inhomogeneities over atomic length scales.
Optical inhomogeneities in sol-gel derived ormosils and nanocomposites
Duarte, E.J.; Pope, E.J.A.
1995-12-31
Interferometric measurements are used to characterize and quantify optical inhomogeneities present in laser dye doped MPMMA, ORMOSILS, and silicate/PMMA nanocomposites. A brief history of the effect of optical inhomogeneities in high beam quality dye lasers is given and their importance to the solid-state dye laser program is discussed.
Elastic properties of inhomogeneous media with chaotic structure.
Novikov, V V; Wojciechowski, K W; Belov, D V; Privalko, V P
2001-03-01
The elastic properties of an inhomogeneous medium with chaotic structure were derived within the framework of a fractal model using the iterative averaging approach. The predicted values of a critical index for the bulk elastic modulus and of the Poisson ratio in the vicinity of a percolation threshold were in fair agreement with the available experimental data for inhomogeneous composites. PMID:11308722
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.
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
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.
Inhomogeneity of fluid flow in Stirling engine regenerators
Jones, J.D. )
1989-10-01
The literature relating to inhomogeneity of flow regenerators is briefly reviewed. It is noted that, in contrast to other applications of regenerators, relatively little attention has been paid to the consequences of flow inhomogeneity for thermal regeneration in Stirling cycle machines. The construction of regenerator capsules for a large stationary Stirling engine is described. A test rig is developed to measure the gas velocity profile across the face of the packed regenerator capsules under steady flow conditions. Measured flow profiles for a number of different matrix materials and construction techniques are presented, and it is noted that stacked-mesh regenerator matrices tend to display marked inhomogeneities of flow. The consequences of flow inhomogeneity for flow friction and regenerator effectiveness are analyzed theoretically, and approximate formulae deduced. One method for reducing flow inhomogeneity in stacked-screen matrice
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.
BATTERIES. Topological defect dynamics in operando battery nanoparticles.
Ulvestad, A; Singer, A; Clark, J N; Cho, H M; Kim, J W; Harder, R; Maser, J; Meng, Y S; Shpyrko, O G
2015-06-19
Topological defects can markedly alter nanomaterial properties. This presents opportunities for "defect engineering," where desired functionalities are generated through defect manipulation. However, imaging defects in working devices with nanoscale resolution remains elusive. We report three-dimensional imaging of dislocation dynamics in individual battery cathode nanoparticles under operando conditions using Bragg coherent diffractive imaging. Dislocations are static at room temperature and mobile during charge transport. During the structural phase transformation, the lithium-rich phase nucleates near the dislocation and spreads inhomogeneously. The dislocation field is a local probe of elastic properties, and we find that a region of the material exhibits a negative Poisson's ratio at high voltage. Operando dislocation imaging thus opens a powerful avenue for facilitating improvement and rational design of nanostructured materials. PMID:26089511
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.
NASA Astrophysics Data System (ADS)
Passeri, Alessandro; Mazzuca, Stefano; Del Bene, Veronica
2014-06-01
Clinical magnetic resonance spectroscopy imaging (MRSI) is a non-invasive functional technique, whose mathematical framework falls into the category of linear inverse problems. However, its use in medical diagnostics is hampered by two main problems, both linked to the Fourier-based technique usually implemented for spectra reconstruction: poor spatial resolution and severe blurring in the spatial localization of the reconstructed spectra. Moreover, the intrinsic ill-posedness of the MRSI problem might be worsened by (i) spatially dependent distortions of the static magnetic field (B0) distribution, as well as by (ii) inhomogeneity in the power deposition distribution of the radiofrequency magnetic field (B1). Among several alternative methods, slim (Spectral Localization by IMaging) and bslim (B0 compensated slim) are reconstruction algorithms in which a priori information concerning the spectroscopic target is introduced into the reconstruction kernel. Nonetheless, the influence of the B1 field, particularly when its operating wavelength is close to the size of the human organs being studied, continues to be disregarded. starslim (STAtic and Radiofrequency-compensated slim), an evolution of the slim and bslim methods, is therefore proposed, in which the transformation kernel also includes the B1 field inhomogeneity map, thus allowing almost complete 3D modelling of the MRSI problem. Moreover, an original method for the experimental determination of the B1 field inhomogeneity map specific to the target under evaluation is also included. The compensation capabilities of the proposed method have been tested and illustrated using synthetic raw data reproducing the human brain.
Cotton, D J; Prabhu, M B; Mink, J T; Graham, B L
1993-08-01
In normal seated subjects we increased single-breath ventilation inhomogeneity by changing both the preinspiratory lung volume and breath-hold time and examined the ensuing effects on two different techniques of measuring the diffusing capacity of the lung for carbon monoxide (DLCO). We measured the mean single-breath DLCO using the three-equation method (DLCOSB-3EQ) and also measured DLCO over discrete intervals during exhalation by the "intrabreath" method (DLCOexhaled). We assessed the distribution of ventilation using the normalized phase III slope for helium (SN). DLCOSB-3EQ was unaffected by preinspiratory lung volume and breath-hold time. DLCOexhaled increased with increasing preinspiratory lung volume and decreased with increasing breath-hold time. These changes correlated with the simultaneously observed changes in ventilation inhomogeneity as measured by SN (P < 0.01). We conclude that measurements of DLCOexhaled do not accurately reflect the mean DLCO. Intrabreath methods of measuring DLCO are based on the slope of the exhaled CO concentration curve, which is affected by both ventilation and diffusion inhomogeneities. Although DLCOexhaled may theoretically provide information about the distribution of CO uptake, the concomitant effects of ventilation nonuniformity on DLCOexhaled may mimic or mask the effects of diffusion nonuniformity. PMID:8226498
NASA Astrophysics Data System (ADS)
Burow, Daniel; Sergeeva, Kseniya; Calles, Simon; Schorb, Klaus; Börger, Alexander; Roth, Christina; Heitjans, Paul
2016-03-01
The aging of graphite anodes in prismatic lithium ion cells during a low temperature pulse charging regime was studied by electrical tests and post-mortem analysis. The capacity decrease and impedance increase mainly occurs in the beginning of cycling and lithium plating was identified as the major aging mechanism. The degradation and the local states of charge show an inhomogeneous distribution over the anode, which is confirmed from spatially resolved XRD studies and SEM combined with EDX performed on electrode cross sections. Comparing a charged cell with a discharged cell reveals that ca. 1/3 of the lithium is plated reversibly at the given SOH of 60%. It is proposed that high charge rates at low temperatures induce inhomogeneities of temperature and anode utilization resulting in inhomogeneous aging effects that accumulate over lifetime.
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
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)
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.
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.
NASA Astrophysics Data System (ADS)
Tokunaga, M.; Song, H.; Tokunaga, Y.; Tamegai, T.
2006-05-01
Using magneto-optical imaging technique, real-space distributions of magnetic fields are visualized in images of a polarized-light microscope. Application of this technique to crystals of (La1-z Prz )0.7Ca0.3MnO3 (z = 0.7) and Nd0.5Ca0.5Mn1-y Cry O3 (y = 0.03) revealed inhomogeneous magnetization and currents in the phase-separated states into ferromagnetic metal and antiferromagnetic insulator. Increase of the transport current switches this inhomogeneous current flow to homogeneous one concomitantly with abrupt increase in resistivity. Using magnetic field dependence of this switching phenomenon, operation fields for colossal magnetoresistance effects can be significantly reduced. Empirical relation between the magnitude of bias currents and transition fields is provided.
Modulation of thermoelectric power factor via radial dopant inhomogeneity in B-doped Si nanowires.
Zhuge, Fuwei; Yanagida, Takeshi; Fukata, Naoki; Uchida, Ken; Kanai, Masaki; Nagashima, Kazuki; Meng, Gang; He, Yong; Rahong, Sakon; Li, Xiaomin; Kawai, Tomoji
2014-10-01
We demonstrate a modulation of thermoelectric power factor via a radial dopant inhomogeneity in B-doped Si nanowires. These nanowires grown via vapor-liquid-solid (VLS) method were naturally composed of a heavily doped outer shell layer and a lightly doped inner core. The thermopower measurements for a single nanowire demonstrated that the power factor values were higher than those of homogeneously B-doped Si nanowires. The field effect measurements revealed the enhancement of hole mobility for these VLS grown B-doped Si nanowires due to the modulation doping effect. This mobility enhancement increases overall electrical conductivity of nanowires without decreasing the Seebeck coefficient value, resulting in the increase of thermoelectric power factor. In addition, we found that tailoring the surface dopant distribution by introducing surface δ-doping can further increase the power factor value. Thus, intentionally tailoring radial dopant inhomogeneity promises a way to modulate the thermoelectric power factor of semiconductor nanowires. PMID:25229842
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.
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
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.
Yatsenko, Yu P; Mashinsky, V M; Medvedkov, O I; Sazhin, O D; Dianov, Evgenii M; Khopin, V F; Vechkanov, N N; Gur'yanov, A N
2003-03-31
The effect of the inhomogeneous distribution of nitrogen impurity on the photosensitivity of germanosilicate fibres is studied. For this purpose, single-mode fibres with different alternations of the core layers sintered in nitrogen and oxygen atmospheres were specially prepared by the MCVD technique. Photoinduced variations in the quadratic nonlinear susceptibility and refractive index of these fibres were recorded. It is shown that the recording efficiency depends on the radial distribution of germanium oxygen-deficient centres, which can be controlled at the stage of sintering through a nonuniform doping by nitrogen over the cross-section. (fibre optics)
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.
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.
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.
Computation of transient electromagnetic waves in inhomogeneous media
NASA Astrophysics Data System (ADS)
Moghaddam, M.; Chew, W. C.; Anderson, B.; Yannakakis, E.; Liu, Q. H.
1991-02-01
A brief summary of the methods of solving transient EM wave problems in inhomogeneous media is given. The two distinct general techniques, the inverse Fourier transformation of time-harmonic solutions and the direct time-domain formulation, are illustrated by way of two examples. In the first, an efficient numerical mode-matching method to obtain the response of an EM source in a two-dimensional cylindrical inhomogeneity is described. In the second method, a finite-difference scheme is used to find the transient response of a point source in a two-dimensional inhomogeneity. Two different methods are proposed to treat the source-region singularity.
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.
Local texture of microstructural inhomogeneities in rolled microalloyed steel
NASA Astrophysics Data System (ADS)
Zolotorevsky, N.; Panpurin, S.; Kazakov, A.; Pakhomova, O.; Petrov, S.
2015-04-01
Specific inhomogeneities consisting of coarse-grained bainite are observed in the microstructure of low carbon microalloyed steels after hot rolling. Earlier a special etching method has been developed allowing to reveal that these inhomogeneities markedly affect a fracture toughness of steels. In the present work their crystal geometry was studied using EBSD technique, and orientations of former austenite grains were reconstructed. The austenite, from which the coarse-grained bainite regions have been produced, is shown to have orientations concentrated predominantly within the brass component of austenite rolling texture. The inhomogeneities of steel microstructure are promoted by orientation dependency of the deformation substructure of heavily deformed austenite grains.
Cauchy problems of pseudo-parabolic equations with inhomogeneous terms
NASA Astrophysics Data System (ADS)
Li, Zhongping; Du, Wanjuan
2015-12-01
This paper deals with Cauchy problems of pseudo-parabolic equations with inhomogeneous terms. The aim of the paper is to study the influence of the inhomogeneous term on the asymptotic behavior of solutions. We at first determine the critical Fujita exponent and then give the secondary critical exponent on the decay asymptotic behavior of an initial value at infinity. Furthermore, the precise estimate of life span for the blow-up solution is obtained. Our results show that the asymptotic behavior of solutions is seriously affected by the inhomogeneous term.
Pinning of flux lines by planar defects
NASA Astrophysics Data System (ADS)
Petković, Aleksandra; Emig, Thorsten; Nattermann, Thomas
2009-06-01
The influence of randomly distributed point impurities and planar defects on order and transport in type-II superconductors and related systems is studied. It is shown that the Bragg glass phase is unstable with respect to planar defects. Even a single weak defect plane oriented parallel to the magnetic field as well as to one of the main axes of the Abrikosov flux-line lattice is a relevant perturbation in the Bragg glass. A defect that is aligned with the magnetic field restores the flux density oscillations, which decay algebraically with the distance from the defect. The theory exhibits striking similarities to the physics of a Luttinger liquid with a frozen impurity. The exponent for the flux-line creep in the direction perpendicular to a relevant defect is derived. We find that the flux-line lattice exhibits in the presence of many randomly distributed parallel planar defects aligned to the magnetic field a glassy phase which we call planar glass. The planar glass is characterized by diverging shear and tilt moduli, a transverse Meissner effect, and resistance against shear deformations. We also obtain sample-to-sample fluctuations of the longitudinal magnetic susceptibility and an exponential decay of translational long-range order in the direction perpendicular to the defects. The flux creep perpendicular to the defects leads to a nonlinear resistivity ρ(J→0)˜exp[-(JD/J)3/2] . Strong planar defects enforce arrays of dislocations that are located at the defects with a Burgers vector parallel to the defects in order to relax shear strain.
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).
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.
Complex geometrical optics of nonlinear inhomogeneous fibres
NASA Astrophysics Data System (ADS)
Berczynski, Pawel
2011-03-01
This paper analyses the Gaussian beam (GB) evolution in nonlinear fibres with special attention given to the influence of the initial curvature of the wavefront and to the fibres' permittivity profile. The analysis is performed in the framework of paraxial complex geometrical optics (PCGO). This method reduces the problem of GB evolution in nonlinear and inhomogeneous media to the solution of ordinary differential equations, which can be easily solved either analytically or numerically. It is shown that the PCGO approach radically simplifies modelling of nonlinear phenomena in fibres as compared with standard methods of nonlinear optics such as the variational method approach and the method of moments. It is shown that the PCGO method readily supplies the solution of the nonlinear Schrödinger equation (NLS) for a self-focusing fibre with a focusing permittivity profile and provides a number of new results. The discussion on the interplay between the nonlinear (self-focusing and self-defocusing) and linear (focusing and defocusing) components of the total permittivity demonstrates the new possibilities to limit the collapse phenomenon in nonlinear fibres of Kerr type taking into account the effect of initial beam divergence.
Stochastic modeling of inhomogeneous ocean waves
NASA Astrophysics Data System (ADS)
Smit, P. B.; Janssen, T. T.; Herbers, T. H. C.
2015-12-01
Refraction of swell waves in coastal waters can result in fast-scale variations of wave statistics due to wave interference. These variations cannot be resolved by wave models based on the radiative transport equation. More advanced models based on quasi-coherent theory, a generalization of the radiative transfer equation, can be coupled or nested into larger-scale models to resolve such local inhomogeneous effects. However, source terms for quasi-coherent models to account for non-conservative and nonlinear effects are not available, which hampers their operational use. In the present work we revisit the derivation of quasi-coherent theory to consistently include a source term for dissipation associated with depth-induced wave breaking. We demonstrate how general source terms can be incorporated in this class of models and compare model simulations with the new dissipation term to laboratory observations of focusing and breaking waves over a submerged shoal. The results show that a consistent derivation of source terms is essential to accurately capture coherent effects in coastal areas. Specifically, our results show that if coherent effects are ignored in the dissipation term, interference effects are strongly exaggerated. With the development of source terms for quasi-coherent models they can be effectively nested inside or otherwise coupled to larger-scale wave models to efficiently improve operational predictive capability of wave models near the coast.
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.
Simulation of a spectral inhomogeneous broadening
NASA Astrophysics Data System (ADS)
Kozlov, V. V.; Rosanov, N. N.
2014-06-01
The standard approach that is used to simulate effects of inhomogeneous spectral broadening in a medium consisting of two- or multilevel systems is to calculate the microscopic polarization (the dipole moment of an individual system) as a function of the frequency detuning and further to average this quantity over detunings with corresponding weights. This just leads to the macroscopic polarization that appears in Maxwell's equations of electrodynamics of continuous media. Here, we study and develop an alternative method that has been recently proposed by N.V. Vysotina, N.N. Rozanov, and V.E. Semenov (Opt. Spectrosc. 106 (5), 713 (2009)) for calculation of the macroscopic polarization and that has been aimed at solving problems of computational quantum optics. In this approach, the frequency detuning is considered as a stochastic function of coordinates; in one-dimensional problems, of longitudinal coordinate z. At each step of evolution, the microscopic polarization is calculated for a randomly chosen fixed value of the detuning. Therefore, calculating the macroscopic polarization does not need an additional averaging over detunings; it is replaced by averaging over spatial coordinates, which is naturally performed when describing the radiation propagation through an ensemble of quantum systems. This radically reduces the amount of computations, especially in the context of the finite-difference time domain (FDTD) method.
Imaging the sensitivity inhomogeneities ofdiamond detectors
NASA Astrophysics Data System (ADS)
Barrett, R.; Tromson, D.; Hainaut, O.; Amosov, V. N.; Bergonzo, P.
2003-03-01
Diamond is a semiconducting material which can withstand high temperatures, a wide range of corrosive environments and exhibits high radiation hardness. This combination of properties makes it extremely attractive for use as photon and particle detectors. The ESRF ID21 SXM has been used to image the spatial variations of detector sensitivity over a range of both natural and Chemical Vapour Deposited (CVD) diamond devices. The measurements are performed by mapping the photon-induced current flow of the biased detectors. Evaluation of the sensitivity inhomogeneities are of dual interest; For detection applications involving relatively small beams it is important that the device response be as uniform as possible. Furthermore, from a fundamental aspect, the understanding of the origin of the sensitivity variations can be a route, for example in CVD materials, to modifying the growth and processing parameters in order to produce improved devices. This paper demonstrates an application of alternative detection modes in X-ray microscopy for a problem of technological interest. Moreover, it shows how the flexible control of the primary X-ray penetration depth by varying the probe energy permits an evaluation of the relative influence of the surface and bulk material.
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.
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.
Analysis of inhomogeneous Ge/SiC heterojunction diodes
NASA Astrophysics Data System (ADS)
Gammon, P. M.; Pérez-Tomás, A.; Shah, V. A.; Roberts, G. J.; Jennings, M. R.; Covington, J. A.; Mawby, P. A.
2009-11-01
In this article Schottky barrier diodes comprising of a n-n germanium-silicon carbide (Ge-SiC) heterojunction are electrically characterized. Circular transmission line measurements prove that the nickel front and back contacts are Ohmic, isolating the Ge/SiC heterojunction as the only contributor to the Schottky behavior. Current-voltage plots taken at varying temperature (IVT) reveal that the ideality factor (n ) and Schottky barrier height (SBH) (Φ) are temperature dependent and that incorrect values of the Richardson constant (A∗∗) are being produced, suggesting an inhomogeneous barrier. Techniques originally designed for metal-semiconductor SBH extraction are applied to the heterojunction results to extract values of Φ and A∗∗ that are independent of temperature. The experimental IVT data are replicated using the Tung model. It is proposed that small areas, or patches, making up only 3% of the total contact area will dominate the I-V results due to their low SBH of 1.033 eV. The experimental IVT data are also analyzed statistically using the extracted values of Φ to build up a Gaussian distribution of barrier heights, including the standard deviation and a mean SBH of 1.126 eV, which should be analogous to the SBH extracted from capacitance-voltage (C-V) measurements. Both techniques yield accurate values of A∗∗ for SiC. However, the C-V analysis did not correlate with the mean SBH as expected.
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. PMID:12269574
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
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.
Multiscale distribution of oxygen puddles in 1/8 doped YBa2Cu3O6.67
Ricci, Alessandro; Poccia, Nicola; Campi, Gaetano; Coneri, Francesco; Caporale, Alessandra Stella; Innocenti, Davide; Burghammer, Manfred; Zimmermann, Martin v.; Bianconi, Antonio
2013-01-01
Despite intensive research a physical explanation of high Tc superconductors remains elusive. One reason for this is that these materials have generally a very complex structure making useless theoretical models for a homogeneous system. Little is known on the control of the critical temperature by the space disposition of defects because of lack of suitable experimental probes. X-ray diffraction and neutron scattering experiments used to investigate y oxygen dopants in YBa2Cu3O6+y lack of spatial resolution. Here we report the spatial imaging of dopants distribution inhomogeneity in YBa2Cu3O6.67 using scanning nano X-ray diffraction. By changing the X-ray beam size from 1 micron to 300 nm of diameter, the lattice inhomogeneity increases. The ordered oxygen puddles size distribution vary between 6–8 nm using 1 × 1 μm2 beam, while it is between 5–12 nm with a fat tail using the 300 × 300 nm2 beam. The increased inhomogeneity at the nanoscale points toward a network of superconducting puddles made of ordered oxygen interstitials. PMID:23924946
Extreme ultraviolet multilayer defect analysis and geometry reconstruction
NASA Astrophysics Data System (ADS)
Xu, Dongbo; Evanschitzky, Peter; Erdmann, Andreas
2016-01-01
This paper proposes a method for the characterization of multilayer defects from extreme ultraviolet (EUV) projection images at different focus positions. The transport-of-intensity equation is applied to retrieve the phase distribution of the reflected light in the vicinity of the defect. The defect-induced intensity and phase modifications and their dependency from defect geometry parameters are analyzed by several selected optical properties of multilayer defect. To reconstruct the defect geometry parameters from the intensity and phase of a defect, a principal component analysis (PCA) is employed to parameterize the intensity and phase distributions into principal component coefficients. In order to construct the base functions of the PCA, a combination of a reference multilayer defect and appropriate pupil filters is introduced to obtain the designed sets of intensity and phase distributions. Finally, an artificial neural network is applied to correlate the principal component coefficients of the intensity and the phase of the defect with the defect geometry parameters and to reconstruct the unknown defect geometry parameters. The performance of the proposed approach is evaluated both for mask blank defects and for defects in the vicinity of an absorber pattern.
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.
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.
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). PMID:27155906
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).
Inhomogeneity-induced variance of cosmological parameters
NASA Astrophysics Data System (ADS)
Wiegand, A.; Schwarz, D. J.
2012-02-01
Context. Modern cosmology relies on the assumption of large-scale isotropy and homogeneity of the Universe. However, locally the Universe is inhomogeneous and anisotropic. This raises the question of how local measurements (at the ~102 Mpc scale) can be used to determine the global cosmological parameters (defined at the ~104 Mpc scale)? Aims: We connect the questions of cosmological backreaction, cosmic averaging and the estimation of cosmological parameters and show how they relate to the problem of cosmic variance. Methods: We used Buchert's averaging formalism and determined a set of locally averaged cosmological parameters in the context of the flat Λ cold dark matter model. We calculated their ensemble means (i.e. their global value) and variances (i.e. their cosmic variance). We applied our results to typical survey geometries and focused on the study of the effects of local fluctuations of the curvature parameter. Results: We show that in the context of standard cosmology at large scales (larger than the homogeneity scale and in the linear regime), the question of cosmological backreaction and averaging can be reformulated as the question of cosmic variance. The cosmic variance is found to be highest in the curvature parameter. We propose to use the observed variance of cosmological parameters to measure the growth factor. Conclusions: Cosmological backreaction and averaging are real effects that have been measured already for a long time, e.g. by the fluctuations of the matter density contrast averaged over spheres of a certain radius. Backreaction and averaging effects from scales in the linear regime, as considered in this work, are shown to be important for the precise measurement of cosmological parameters.
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
Effect of magnetic field inhomogeneity on ion cyclotron motion coherence at high magnetic field.
Vladimirov, Gleb; Kostyukevich, Yury; Hendrickson, Christopher L; Blakney, Greg T; Nikolaev, Eugene
2015-01-01
A three-dimensional code based on the particle-in-cell algorithm modified to account for the inhomogeneity of the magnetic field was applied to determine the effect of Z(1), Z(2), Z(3), Z(4), X, Y, ZX, ZY, XZ(2) YZ(2), XY and X(2)-Y(2) components of an orthogonal magnetic field expansion on ion motion during detection in an FT-ICR cell. Simulations were performed for magnetic field strengths of 4.7, 7, 14.5 and 21 Tesla, including experimentally determined magnetic field spatial distributions for existing 4.7 T and 14.5 T magnets. The effect of magnetic field inhomogeneity on ion cloud stabilization ("ion condensation") at high numbers of ions was investigated by direct simulations of individual ion trajectories. Z(1), Z(2), Z(3) and Z(4) components have the largest effect (especially Z(1)) on ion cloud stability. Higher magnetic field strength and lower m/z demand higher relative magnetic field homogeneity to maintain cloud coherence for a fixed time period. The dependence of mass resolving power upper limit on Z(1) inhomogeneity is evaluated for different magnetic fields and m/z. The results serve to set the homogeneity requirements for various orthogonal magnetic field components (shims) for future FT-ICR magnet design. PMID:26307725
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.
NASA Astrophysics Data System (ADS)
Schuengel, Edmund; Schulze, Julian; Mohr, Sebastian; Czarnetzki, Uwe
2014-10-01
For large area processing applications of capacitively coupled radio frequency (CCRF) discharges, the lateral uniformity of the plasma surface interaction is crucially important. The benefit of an increase in the plasma density and, therefore, in the overall deposition rate by driving the discharge at higher frequencies is accompanied with inhomogeneities caused by the presence of electromagnetic effects. Here, we propose a method based on the Electrical Asymmetry Effect (EAE) to prevent such inhomogeneities. Spatially resolved measurements of the ion flux onto the grounded electrode of a CCRF discharge operated in hydrogen show a standing wave pattern in a 81.36 MHz single-frequency discharge, strongly reducing the ion flux uniformity. However, applying a dual-frequency voltage waveform consisting of 40.68 MHz + 81.36 MHz, the lateral distribution of the ion flux can be controlled via the phase angle between the two applied harmonics. Using the EAE, a phase angle dependent DC self-bias develops in the geometrically symmetric discharge. Tuning the phase angle allows for the compensation of ion flux inhomogeneities due to the standing wave effect. Thus, a high and laterally uniform ion flux can be generated in electrically asymmetric high frequency plasmas. Funding by the German Federal Ministry for the Environment, Nature conservation, and Nuclear Safety (0325210B) is gratefully acknowledged.
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.
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.
Topological defect motifs in two-dimensional Coulomb clusters.
Radzvilavičius, A; Anisimovas, E
2011-09-28
We study the distribution of topological defects in two-dimensional Coulomb clusters with parabolic lateral confinement. The minima hopping algorithm based on molecular dynamics is used to efficiently locate the ground- and low-energy metastable states, and their structure is analysed by means of the Delaunay triangulation. The size, structure and distribution of geometry-induced lattice imperfections strongly depends on the system size and the energetic state. Besides isolated disclinations and dislocations, classification of defect motifs includes defect compounds-grain boundaries, rosette defects, vacancies and interstitial particles. Proliferation of defects in metastable configurations destroys the orientational order of the Wigner lattice. PMID:21891854
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... Coronary angiography (for patients over 35 years old) ECG Heart MRI Transesophageal echocardiography (TEE) Treatment ASD may ... of the complications can be prevented with early detection. Alternative Names Congenital heart defect - ASD; Birth defect ...
Metallurgy of Miura-ori: lattice theory for inhomogeneous deformations of origami tessellations
NASA Astrophysics Data System (ADS)
Evans, Arthur; Silverberg, Jesse; McLeod, Lauren; Cohen, Itai; Santangelo, Christian
2014-03-01
In nature, as well as in art, one often encounters thin materials that have been deformed by their environment or their creator into complex folded states; examples include the folds of the endoplasmic reticulum, the villi in the intestinal tract, and tessellated patterns in the ancient Japanese art of origami. One (engineering) advantage of creating a folded structure is that the geometric constraints associated with creasing imbues the construction with exotic mechanical properties, such as generating a material with a negative Poisson's ratio. Materials exhibiting novel behavior of this type, arising from the special properties of the unit cell, are generally classified as metamaterials. In this talk I consider a mechanical metamaterial known as Miura-ori, an origami tessellation pattern that displays soft modes and crystallographic defects not accounted for by a purely geometric theory of an infinitely thin material. I will discuss a method for deriving how inhomogeneous deformations arise from bending within Miura-ori, and show that this leads to a natural coherence length over which the inhomogeneity decays. Additionally, I will show how the modular nature of origami unit cells lends additional richness to the mechanical properties associated with deformation.
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)
Zhao, Jun; Zeng, Hui; Wei, Jianwei; Li, Biao; Xu, Dahai
2014-01-01
Using the first principles calculations associated with nonequilibrium Green's function, we have studied the electronic structures and quantum transport properties of defective armchair graphene nanoribbon (AGNR) in the presence of divacancy defects. The triple pentagon-triple heptagon (555-777) defect in the defective AGNR is energetically more favorable than the pentagon-octagon-pentagon (5-8-5) defect. Our calculated results reveal that both 5-8-5-like defect and 555-777-like defect in AGNR could improve the electron transport. It is anticipated that defective AGNRs can exhibit large range variations in transport behaviors, which are strongly dependent on the distributions of the divacancy defect.
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.
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)
Kijamnajsuk, P.; Pelzl, J.; Chirtoc, M.; Horny, N.; Schäfer, D.; Eisenmenger-Sittner, C.
2012-11-01
In this study, the heat transport in copper-carbon flat model systems was studied by frequency-dependent photothermal radiometry (PTR). The samples consist of Cu films of about 1 μm thickness deposited by magnetron sputtering on vitreous carbon (Sigradur). Particular interest was devoted to the influence of interface defects on the interfacial thermal conductance (or resistance) of the CuC systems. The PTR data were analyzed in the frame of a heat diffusion equation for one- and three-dimensional heat transport. By comparing PTR signals from as-prepared and from heat-treated samples, the lateral inhomogeneities of the interfacial thermal conductance could be quantified. The measured phase differences were analyzed in the scope of a model where a small part of the surface area has a different interfacial thermal conductance than the major part of the surface.
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Analysis of defect luminescence in Ga-doped ZnO nanoparticles.
Zhu, Wenliang; Kitamura, Shoichiro; Boffelli, Marco; Marin, Elia; Gaspera, Enrico Della; Sturaro, Marco; Martucci, Alessandro; Pezzotti, Giuseppe
2016-04-14
We applied cathodoluminescence (CL) spectroscopy to evaluate the defect-induced luminescence within ZnO and Ga-doped ZnO (GZO) nanoparticles. The observed emissions from defect sites present in the GZO lattice exhibited a strong dependence on both dopant content and synthesis methods. The strong and broad defect-induced emissions and inhomogeneous population of intrinsic defects in nano-sized ZnO particles could effectively be suppressed by Ga doping, although large dopant amounts caused the generation of negatively-charged defects, VZn and Oi, with a subsequent increase of the luminescence. Upon deconvolution of the retrieved CL spectra into individual sub-bands, the physical origin of all the sub-bands could be clarified, and related to sample composition and synthesis protocol. This study lays the foundation of quantitative CL evaluation of defects to assess the quality of GZO optoelectronic devices. PMID:26996752
Plasma waves in the inhomogeneous auroral ionosphere
NASA Astrophysics Data System (ADS)
Kintner, Paul
1999-11-01
Detailed observations of plasma waves in the auroral ionosphere during the past decade have revealed the existence of modes which depend on inhomogeneities the order of or somewhat larger than the ion gyroradius. The auroral ionosphere is the most strongly driven region of space which is conveniently accessible to space probes. The region is filled with currents, electric fields, electron beams and transversely accelerated ions. During the past decade improved instrumentation has permitted investigation of the ionospheric plasma properties down to spatial scales including the ion gyroradius. These investigations have revealed at least two novel wave modes not previously anticipated. The first wave mode is associated with cylindrical density cavities aligned along the geomagnetic field. The cavities act like resonant structures near the lower hybrid frequency and admit two classes of waves near the lower hybrid frequency. Below the lower hybrid frequency the modes are trapped and rotate in a left-hand sense. Above the lower hybrid frequency waves the modes are not trapped but rotate in a right-hand sense. The symmetry in rotation is broken by the Hall current and the sense of rotation has been confirmed with sounding rocket interferometers. The cavity wave fields also accelerate ions transversely which maintain and expand the cavity dimensions. The second wave mode is less well understood and has the phenomenological name of broad band ELF (BBELF) electric fields. The bandwidth of this mode covers the ion cyclotron frequencies (O+ and H+) and it is also associated with transversely accelerated ions but not with ionospheric density structuring. Instead these modes are associated with electron flow in field-aligned currents although the flows are sub-critical for either the ion acoustic or electrostatic ion cyclotron modes. Furthermore the frequency spectrum shows no structure at the ion cyclotron frequencies. Limited evidence suggests that these modes are shear
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.
Defects in silicon plastically deformed at room temperature
NASA Astrophysics Data System (ADS)
Leipner, H. S.; Wang, Z.; Gu, H.; Mikhnovich, V. V., Jr.; Bondarenko, V.; Krause-Rehberg, R.; Demenet, J.-L.; Rabier, J.
2004-07-01
The article [1] describes specific features of positron trapping in silicon plastically deformed at room temperature. The results are related to the dislocation core structure and the inhomogeneous deformation. The picture shows the probability density function of a positron localized in a vacancy in silicon. The calculation was performed with the superimposed-atom model. The degree of localization and consequently the defect-related positron lifetime vary for different open-volume defects, such as vacancies, voids, and dislocations.The first author, Hartmut S. Leipner, is CEO of the Center of Materials Science of the University Halle-Wittenberg. His research activities are focused on the characterization of extended defects in semiconductors.
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. PMID:14651897
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.
Numerical scheme for a spatially inhomogeneous matrix-valued quantum Boltzmann equation
NASA Astrophysics Data System (ADS)
Lu, Jianfeng; Mendl, Christian B.
2015-06-01
We develop an efficient algorithm for a spatially inhomogeneous matrix-valued quantum Boltzmann equation derived from the Hubbard model. The distribution functions are 2 × 2 matrix-valued to accommodate the spin degree of freedom, and the scalar quantum Boltzmann equation is recovered as a special case when all matrices are proportional to the identity. We use Fourier discretization and fast Fourier transform to efficiently evaluate the collision kernel with spectral accuracy, and numerically investigate periodic, Dirichlet and Maxwell boundary conditions. Model simulations quantify the convergence to local and global thermal equilibrium.
NASA Astrophysics Data System (ADS)
Shaw, Justin M.; Nembach, Hans T.; Silva, T. J.
2010-11-01
We report on the effect roughness has on the magnetic properties of Co/Ni multilayers with perpendicular anisotropy. We can systematically vary the surface roughness and grain size by the variation in the Cu seed layer thickness. The roughness has a significant effect on the lateral anisotropy variation across the material, which was studied through the size dependence of the switching field and switching field distribution in nanostructures. Ferromagnetic resonance measurements show a large dependence of the linewidth on the topography. However, only the inhomogeneous linewidth broadening varied significantly with roughness with little to no effect on the intrinsic damping parameter of α =0.015-0.018.
NASA Technical Reports Server (NTRS)
Baumeister, K. J.
1983-01-01
A time-dependent finite difference formulation to the inhomogeneous wave equation is derived for plane wave propagation with harmonic noise sources. The difference equation and boundary conditions are developed along with the techniques to simulate the Dirac delta function associated with a concentrated noise source. Example calculations are presented for the Green's function and distributed noise sources. For the example considered, the desired Fourier transformed acoustic pressures are determined from the transient pressures by use of a ramping function and an integration technique, both of which eliminates the nonharmonic pressure associated with the initial transient.
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.
Defect production and recombination during low-energy ion processing
Kellerman, B.K.; Floro, J.A.; Chason, E.; Brice, D.K.; Picraux, S.T.; White, J.M.
1994-10-01
Low-energy ion processing produces damaged, microroughened semiconductor surfaces due to the production of point defects. The authors present a study of point defect production and annealing on the Ge(001)-2x1 surface during low-energy inert ion bombardment as a function of ion energy, ion mass and substrate temperature. Ion-induced surface point defect production was quantified experimentally in real time using in situ Reflection High Energy Electron Diffraction. The observed surface defect yield decreased abruptly around room temperature as the substrate temperature was increased from 175 K to 475 K. The authors have developed Monte Carlo simulations of defect diffusion to model defect recombination both in the bulk and on the surface. Bulk defect production statistics generated by a binary collision simulator, TRIMRC, were coupled with our bulk diffusion simulator to predict the number of ion-induced surface defects. A comparison between the experimental results and the simulation predictions indicated that defects produced in the bulk may represent a significant contribution to the observed surface defect yield and suggested that TRIMRC may overestimate the depth distribution of the defects. The simulations further indicated that the abrupt drop in the experimental yield with increasing substrate temperature does not arise from bulk defect recombination. The Monte Carlo simulations of surface diffusion (applicable to any crystalline surface) support a defect annealing mechanism (at low ion fluxes) that involves surface recombination of defects generated within a single cascade.
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.
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
Inhomogeneous quasistationary state of dense fluids of inelastic hard spheres.
Fouxon, Itzhak
2014-05-01
We study closed dense collections of freely cooling hard spheres that collide inelastically with constant coefficient of normal restitution. We find inhomogeneous states (ISs) where the density profile is spatially nonuniform but constant in time. The states are exact solutions of nonlinear partial differential equations that describe the coupled distributions of density and temperature valid when inelastic losses of energy per collision are small. The derivation is performed without modeling the equations' coefficients that are unknown in the dense limit (such as the equation of state) using only their scaling form specific for hard spheres. Thus the IS is the exact state of this dense many-body system. It captures a fundamental property of inelastic collections of particles: the possibility of preserving nonuniform temperature via the interplay of inelastic cooling and heat conduction that generalizes previous results. We perform numerical simulations to demonstrate that arbitrary initial state evolves to the IS in the limit of long times where the container has the geometry of the channel. The evolution is like a gas-liquid transition. The liquid condenses in a vanishing part of the total volume but takes most of the mass of the system. However, the gaseous phase, which mass grows only logarithmically with the system size, is relevant because its fast particles carry most of the energy of the system. Remarkably, the system self-organizes to dissipate no energy: The inelastic decay of energy is a power law [1+t/t(c)](-2), where t(c) diverges in the thermodynamic limit. This is reinforced by observing that for supercritical systems the IS coincide in most of the space with the steady states of granular systems heated at one of the walls. We discuss the relation of our results to the recently proposed finite-time singularity in other container's geometries. PMID:25353790
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
Microwave radiative transfer through horizontally inhomogeneous precipitating clouds
NASA Technical Reports Server (NTRS)
Roberti, Laura; Haferman, Jeff; Kummerow, Christian
1994-01-01
Recent advances in cloud microphysical models have led to realistic three-dimensional distributions of cloud constituents. Radiative transfer schemes can make use of this detailed knowledge in order to study the effects of horizontal as well as vertical inhomogeneities within clouds. This study looks specifically at the differences between three-dimensional radiative transfer results and those obtained by plane parallel, independent pixel approximations in the microwave spectrum. A three-dimensional discrete ordinates method as well as a backward Monte Carlo method are used to calculate realistic radiances emerging from the cloud. Analyses between these models and independent pixel approximations reveal that plane parallel approximations introduce two distinct types of errors. The first error is physical in nature and is related to the fact that plane parallel approximations do not allow energy to leak out of dense areas into surrouding areas. In general, it was found that these errors are quite small for emission-dominated frequencies (37 GHz and lower) and that physical errors are highly pronounced only at scattering frequencies (85 GHz) where large deviations and biases up to 8 K averaged over the entire cloud were found. The second error is more geometric in nature and is related to the fact that plane parallel approximations cannot accommodate physical boundaries in the horizontal dimension for off-nadir viewing angles. The geometric errors were comparable in magnitude for all frequencies. Their magnitude, however, depends on a number of factors including the scheme used to deal with the edge, the nature of the surface, and the viewing angle.
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.
Evolution of inhomogeneous condensates: Self-consistent variational approach
Boyanovsky, D.; Cooper, F.; de Vega, H.J.; Sodano, P.
1998-07-01
We establish a self-consistent variational framework that allows us to study numerically the non-equilibrium evolution of non-perturbative inhomogeneous field configurations including quantum back reaction effects. After discussing the practical merits and disadvantages of different approaches we provide a closed set of local and renormalizable update equations that determine the dynamical evolution of inhomogeneous condensates and can be implemented numerically. These incorporate self-consistently the back reaction of quantum fluctuations and particle production. This program requires the solution of a self-consistent inhomogeneous problem to provide initial Cauchy data for the inhomogeneous condensates and Green`s functions. We provide a simple solvable ansatz for such an initial value problem for the sine-Gordon and {phi}{sup 4} quantum field theories in one spatial dimension. We compare exact known results of the sine-Gordon model to this simple ansatz. We also study the linear sigma model in the large N limit in three spatial dimensions as a microscopic model for pion production in ultrarelativistic collisions. We provide a solvable self-consistent ansatz for the initial value problem with cylindrical symmetry. For this case we also obtain a closed set of local and renormalized update equations that can be numerically implemented. A novel phenomenon of spinodal instabilities and pion production arises as a result of a Klein paradox for large amplitude inhomogeneous condensate configurations. {copyright} {ital 1998} {ital The American Physical Society}
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.
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.
Barrier height inhomogeneity and its impact on (Al,In,Ga)N Schottky diodes
NASA Astrophysics Data System (ADS)
Laurent, Matthew A.; Gupta, Geetak; Suntrup, Donald J.; DenBaars, Steven P.; Mishra, Umesh K.
2016-02-01
III-N materials, especially ternary and quaternary alloys, are profoundly affected by barrier height inhomogeneity as evidenced by great variability in reported barrier height and Richardson constant values for Schottky diode samples involving epilayers with identical material composition. Research into AlInGaN-based devices is gaining traction due to its usefulness for strain engineering, polarization engineering, and vertical device design. Thus it is important to characterize the Schottky barrier height between AlInGaN and technologically relevant metals like nickel. It is proposed that alloy composition fluctuations inherent to low-temperature III-N alloys result in a Schottky barrier height inhomogeneity, and that the Schottky barrier height follows a Gaussian distribution. Current vs voltage data as a function of temperature was measured for three AlInGaN samples of varying composition. Utilizing a model tailored to thermionic emission over a Gaussian distribution of barriers, both the average barrier height and the standard deviation in the distribution were extracted from experimental data via multiple linear regression. Average barrier height was found to correlate with the AlInGaN band gap, while the standard deviation in barrier height increased with aluminum and indium concentration on the group-III sublattice.
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
Application of Principal Component Analysis to EUV multilayer defect printing
NASA Astrophysics Data System (ADS)
Xu, Dongbo; Evanschitzky, Peter; Erdmann, Andreas
2015-09-01
This paper proposes a new method for the characterization of multilayer defects on EUV masks. To reconstruct the defect geometry parameters from the intensity and phase of a defect, the Principal Component Analysis (PCA) is employed to parametrize the intensity and phase distributions into principal component coefficients. In order to construct the base functions of PCA, a combination of a reference multilayer defect and appropriate pupil filters is introduced to obtain the designed sets of intensity and phase distributions. Finally, an Artificial Neural Network (ANN) is applied to correlate the principal component coefficients of the intensity and the phase of the defect with the defect geometry parameters and to reconstruct the unknown defect geometry parameters.
NASA Astrophysics Data System (ADS)
Rudenko, Konstantin V.; Fadeev, A. V.; Orlikovsky, Alexander A.; Valiev, K. A.
2004-05-01
Lateral distribution of particles density in the plasma across the wafer surface is critical for plasma processing steps in IC manufacturing and should be optimized at the stage of process design. Optical emission tomography of the plasma is promising technique for this goal. Presented investigation is carried out to develop the algorithms of tomographic reconstruction of 2D-distribution plasma species density from its characteristic optical emission data. The geometry of the tomographic data acquisition was chosen to be compatible with the commercial types of plasma reactors. Advanced accuracy of reconstruction has been achieved by including the classes of the space profiles of inhomogeneities based on the discharge physics into reconstruction algorithm. The tests have been performed with the kinds of inhomogeneities, which is most probable in plasma reactors with HDP sources.
Gaussian beam diffraction in inhomogeneous and logarithmically saturable nonlinear media
NASA Astrophysics Data System (ADS)
Berczynski, Pawel
2012-08-01
The method of paraxial complex geometrical optics (PCGO) is presented, which describes Gaussian beam (GB) diffraction and self-focusing in smoothly inhomogeneous and nonlinear saturable media of cylindrical symmetry. PCGO reduces the problem of Gaussian beam diffraction in nonlinear and inhomogeneous media to the system of the first order ordinary differential equations for the complex curvature of the wave front and for GB amplitude, which can be readily solved both analytically and numerically. As a result, PCGO radically simplifies the description of Gaussian beam diffraction in inhomogeneous and nonlinear media as compared to the numerical and analytical methods of nonlinear optics. The power of PCGO method is presented on the example of Gaussian beam evolution in logarithmically saturable medium with either focusing and defocusing refractive profile. Besides, the influence of initial curvature of the wave front on GB evolution in nonlinear saturable medium is discussed in this paper.
Trapping of interacting propelled colloidal particles in inhomogeneous media.
Magiera, Martin P; Brendel, Lothar
2015-07-01
A trapping mechanism for propelled colloidal particles based on an inhomogeneous drive is presented and studied by means of computer simulations. In experiments this method can be realized using photophoretic Janus particles driven by a light source, which is partially blocked by a shading mask. This leads to an accumulation of particles in the passive part. An equation for an accumulation parameter is derived using the effective inhomogeneous diffusion constant generated by the inhomogeneous drive. The impact of particle interaction on the trapping mechanism is studied, as well as the interplay between passivity-induced trapping and the emergent self-clustering of systems containing a high density of active particles. The combination of both effects makes the clusters more controllable for applications. PMID:26274159
Trapping of interacting propelled colloidal particles in inhomogeneous media
NASA Astrophysics Data System (ADS)
Magiera, Martin P.; Brendel, Lothar
2015-07-01
A trapping mechanism for propelled colloidal particles based on an inhomogeneous drive is presented and studied by means of computer simulations. In experiments this method can be realized using photophoretic Janus particles driven by a light source, which is partially blocked by a shading mask. This leads to an accumulation of particles in the passive part. An equation for an accumulation parameter is derived using the effective inhomogeneous diffusion constant generated by the inhomogeneous drive. The impact of particle interaction on the trapping mechanism is studied, as well as the interplay between passivity-induced trapping and the emergent self-clustering of systems containing a high density of active particles. The combination of both effects makes the clusters more controllable for applications.
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.
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.
A tetrahedron-based inhomogeneous Monte Carlo optical simulator
Shen, H; Wang, G
2010-01-01
Optical imaging has been widely applied in preclinical and clinical applications. Fifteen years ago, an efficient Monte Carlo program ‘MCML’ was developed for use with multi-layered turbid media and has gained popularity in the field of biophotonics. Currently, there is an increasingly pressing need for simulating tools more powerful than MCML in order to study light propagation phenomena in complex inhomogeneous objects, such as the mouse. Here we report a tetrahedron-based inhomogeneous Monte Carlo optical simulator (TIM-OS) to address this issue. By modeling an object as a tetrahedron-based inhomogeneous finite-element mesh, TIM-OS can determine the photon– triangle interaction recursively and rapidly. In numerical simulation, we have demonstrated the correctness and efficiency of TIM-OS. PMID:20090182
Stokes-vector evolution in a weakly anisotropic inhomogeneous medium.
Kravtsov, Yu A; Bieg, B; Bliokh, K Yu
2007-10-01
The equation for evolution of the four-component Stokes vector in weakly anisotropic and smoothly inhomogeneous media is derived on the basis of a quasi-isotropic approximation of the geometrical optics method, which provides the consequent asymptotic solution of Maxwell's equations. Our equation generalizes previous results obtained for the normal propagation of electromagnetic waves in stratified media. It is valid for curvilinear rays with torsion and is capable of describing normal mode conversion in inhomogeneous media. Remarkably, evolution of the four-component Stokes vector is described by the Bargmann-Michel-Telegdi equation for relativistic spin precession, whereas the equation for the three-component Stokes vector resembles the Landau-Lifshitz equation describing spin precession in ferromagnetic systems. The general theory is applied for analysis of polarization evolution in a magnetized plasma. We also emphasize fundamental features of the non-Abelian polarization evolution in anisotropic inhomogeneous media and illustrate them by simple examples. PMID:17912336
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)
Iwayama, H.; Sugishima, A.; Nagaya, K.; Yao, M.; Fukuzawa, H.; Motomura, K.; Liu, X.-J.; Yamada, A.; Wang, C.; Ueda, K.; Saito, N.; Nagasono, M.; Tono, K.; Yabashi, M.; Ishikawa, T.; Ohashi, H.; Kimura, H.; Togashi, T.
2010-08-01
The emission of highly charged ions from Xe clusters exposed to intense extreme ultraviolet laser pulses (λ ~ 52 nm) from the free electron laser in Japan was investigated using ion momentum spectroscopy. With increasing average cluster size, we observed multiply charged ions Xez + up to z = 3. From kinetic energy distributions, we found that multiply charged ions were generated near the cluster surface. Our results suggest that charges are inhomogeneously redistributed in the cluster to lower the total energy stored in the clusters.
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.
Structural defects in crystalline silicon
NASA Technical Reports Server (NTRS)
Sirtl, E.
1985-01-01
The basic photovoltaic properties of a given crystalline silicon specimen seem to be governed by density and nature of two to three dimensional lattice defects. These are mainly generated by primary growth conditions as grain boundaries of more or less intrinsic character or second phase precipitates from supersaturated solutions of carbon or oxygen. Considerably high values of both solubility and diffusivity in connection with their abundance in common refractory material systems account for the predominance of the two particular elements. Unsaturated dislocations of different types very often can be seen as a consequence of the existence of more dimensional defects as described initially. The final performance of a solar cell is dependent of the concentration and distribution of recombination active centers in the different regions of this device. Typical representatives are fast diffusing transition metals in form of either single atoms or simple complexes. Their avoidance, annihilation, or removal is of great concern in different fields of electronic materials development.
Reconstruction of spatially inhomogeneous dielectric tensors through optical tomography.
Hammer, Hanno; Lionheart, William R B
2005-02-01
A method to reconstruct weakly anisotropic inhomogeneous dielectric tensors inside a transparent medium is proposed. The mathematical theory of integral geometry is cast into a workable framework that allows the full determination of dielectric tensor fields by scalar Radon inversions of the polarization transformation data obtained from six planar tomographic scanning cycles. Furthermore, a careful derivation of the usual equations of integrated photoelasticity in terms of heuristic length scales of the material inhomogeneity and anisotropy is provided, resulting in a self-contained account about the reconstruction of arbitrary three-dimensional, weakly anisotropic dielectric tensor fields. PMID:15717553
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
Unusual thermopower of inhomogeneous graphene grown by chemical vapor deposition
NASA Astrophysics Data System (ADS)
Nam, Youngwoo; Sun, Jie; Lindvall, Niclas; Jae Yang, Seung; Rae Park, Chong; Woo Park, Yung; Yurgens, August
2014-01-01
We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone.
A model of the emergent Universe in inhomogeneous spacetime
NASA Astrophysics Data System (ADS)
Bhattacharya, Subhra; Chakraborty, S.
2016-02-01
The scenario of an emergent Universe is constructed in the background of an inhomogeneous spacetime model with an asymptotically (at spatial infinity) FRW spacetime. The cosmic substratum consists of two non-interacting components, namely (a) homogeneous and isotropic fluid that is dissipative in nature and (b) an inhomogeneous and anisotropic barotropic fluid. In the non-equilibrium thermodynamic prescription (second order deviations), the particle creation mechanism is considered the cause for the dissipative phenomena. It is found that for a constant value of the particle creation rate parameter there exists a scenario of an emergent Universe.
Dendritic signal transmission induced by intracellular charge inhomogeneities
NASA Astrophysics Data System (ADS)
Lazarevich, Ivan A.; Kazantsev, Victor B.
2013-12-01
Signal propagation in neuronal dendrites represents the basis for interneuron communication and information processing in the brain. Here we take into account charge inhomogeneities arising in the vicinity of ion channels in cytoplasm and obtain a modified cable equation. We show that charge inhomogeneities acting on a millisecond time scale can lead to the appearance of propagating waves with wavelengths of hundreds of micrometers. They correspond to a certain frequency band predicting the appearance of resonant properties in brain neuron signaling. We also show that membrane potential in spiny dendrites obeys the modified cable equation suggesting a crucial role of the spines in dendritic subthreshold resonance.
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.
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.
Unusual thermopower of inhomogeneous graphene grown by chemical vapor deposition
Nam, Youngwoo; Sun, Jie; Lindvall, Niclas; Yurgens, August; Jae Yang, Seung; Rae Park, Chong; Woo Park, Yung
2014-01-13
We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone.
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
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.
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.
Probing large scale homogeneity and periodicity in the LRG distribution using Shannon entropy
NASA Astrophysics Data System (ADS)
Pandey, Biswajit; Sarkar, Suman
2016-05-01
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 analyze the data by carrying out measurements in overlapping spheres and find that it suppresses inhomogeneities by a factor of 5 to 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 analyze 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.
NASA Astrophysics Data System (ADS)
Pan, Lijun; Shen, Zigang; Jia, Yu; Dai, Xianqi
2012-07-01
The interaction and coupling between the electrical, mechanical properties and formation energy for SW defective (10,0) carbon nanotube is studied in density functional theory. The investigated configurations include the axial and circumferential orientations for single defect as well as four distribution types for double ones. The more stable defective configurations, namely, SW-I configurations for single SW defective carbon nanotube and II-II-(2) and I-I ones for double SW defective tubes are related to high symmetry distribution of the defects. Moreover, we found that the σ*-π* hybridization induced by curvature effect causes the semiconductor to metal transition for double axial SW defects case. Young's modulus reduction of SW defective carbon nanotube with respect to defect-free one is less than 8%. The energy bands and Young's moduli of double SW defective tubes are mostly affected by the defect distribution and concentration but insensitive to the circumferential distance between the double defects.
NASA Astrophysics Data System (ADS)
Endo, M.; Cuma, M.; Zhdanov, M. S.
2009-12-01
In geophysical applications, it is difficult to describe an earth structure using a horizontally layered background conductivity model, which is required for efficient implementation of the conventional integral equation (IE) approach. As a result, a large domain of interest with anomalous conductivity distribution needs to be discretized, which complicates the computations. Contrary to conventional IE, finite-difference (FD), or finite-element (FE) techniques, the new multiple-domain (MD) IE method allows us to consider multiple inhomogeneous domains, where the conductivity distribution is different from that of the background, and to use independent discretizations for different domains. This reduces dramatically the computational resources required for large-scale modeling. In addition, using this method, we can analyze the response of each domain separately without an inappropriate use of the superposition principle for EM field calculations. The numerical modeling results demonstrate that the MD IE method can be effectively used not only for studying the EM fields in complex geoelectrical models with multiple inhomogeneous domains, but also for evaluating the ability of an EM survey to detect complex geoelectrical targets.
NASA Astrophysics Data System (ADS)
Chow, James C. L.
2013-05-01
This study investigated the variations of the dose and dose distribution in a small-animal irradiation due to the photon beam energy and presence of inhomogeneity. Based on the same mouse computed tomography image set, three Monte Carlo phantoms namely, inhomogeneous, homogeneous and bone-tissue phantoms were used in this study. These phantoms were generated by overriding the relative electron density of no voxel (inhomogeneous), all voxel (homogeneous) and the bone voxel (bone-tissue) to one. 360° photon arcs with beam energies of 50-1250 kV were used in mouse irradiations. Doses in the above phantoms were calculated using the EGSnrc-based DOSXYZnrc code through the DOSCTP. It was found that the dose conformity increased with the increase of the photon beam energy from the kV to MV range. For the inhomogeneous mouse phantom, increasing the photon beam energy from 50 kV to 1250 kV increased about 21 times the dose deposited at the isocenter. For the bone dose enhancement, the mean dose was 1.4 times higher when the bone inhomogeneity was not neglected using the 50 kV photon beams in the mouse irradiation. Bone dose enhancement affecting the mean dose in the mouse irradiation can be found in the photon beams with energy range of 50-200 kV, and the dose enhancement decreases with an increase of the beam energy. Moreover, the MV photon beam has a higher dose at the isocenter, and a better dose conformity compared to the kV beam.
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.
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.
Improvement of Thermoelectric Cooling with Inhomogeneous Thermal Conductivity
NASA Astrophysics Data System (ADS)
Zhou, Jun; Lu, Tingyu; Li, Baowen; CenterPhononics and Thermal Energy Science Team
2014-03-01
Thermal rectifier with inhomogeneous thermal conductivity has been theoretically proposed [ Li, Wang, and Casati, Phys. Rev. Lett. 93, 184301 (2004); Segal and Nitzan, Phys. Rev. Lett. 94, 034301 (2005); Terraneo, Peyrard, and Casati, Phys. Rev. Lett. 88, 094302 (2002)] and been experimentally observed in carbon and boron-nitride nanotubes which are mass-loaded externally and inhomogeneously with heavy molecules [Chang et al., Science 314, 1121 (2006)]. We theoretically investigate the thermal rectification effect on the thermoelectric cooling process with linearly changed spatial dependent thermal conductivity. We find that the dissipation of Joule heat generated in such thermoelectric devices could be inhomogeneous that is very different from the convention thermoelectric devices. Such inhomogeneity of heat dissipation could enhance the heat absorption at the cold end in cooling and therefore enhance the cooling power. The energy conversion efficiency can also be modified with a redefined thermoelectric figure-of-merit ZT. Our finding is believed to be useful for high performance of thermoelectric devices in the future.
Fluorescence of pyrene in inhomogeneous media containing silver nanoparticles
NASA Astrophysics Data System (ADS)
Romanovskaya, G. I.
2014-05-01
Pyrene fluorescence in inhomogeneous media based on ionic detergents containing silver nanoparticles with different morphologies is investigated. An increase in pyrene monomer emissions in the spectral range of 400-500 nm is observed, due to the resonance between electronic transitions in pyrene molecules in that region and the plasmonic oscillations of silver nanoparticles.
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.