Gaussian beam diffraction in weakly anisotropic inhomogeneous media
Energy Technology Data Exchange (ETDEWEB)
Kravtsov, Yu.A., E-mail: kravtsov@am.szczecin.p [Institute of Physics, Maritime University of Szczecin, Szczecin 70-500 (Poland); Space Research Institute, Russian Academy of Science, Moscow 117 997 (Russian Federation); Berczynski, P., E-mail: pawel.berczynski@ps.p [Institute of Physics, West Pomeranian University of Technology, Szczecin 70-310 (Poland); Bieg, B., E-mail: b.bieg@am.szczecin.p [Institute of Physics, Maritime University of Szczecin, Szczecin 70-500 (Poland)
2009-08-10
Combination of quasi-isotropic approximation (QIA) of geometric optics with paraxial complex geometric optics (PCGO) is suggested, which allows describing both diffraction and polarization evolution of Gaussian electromagnetic beams in weakly anisotropic inhomogeneous media. Combination QIA/PCGO reduces Maxwell equations to the system of the ordinary differential equations of the first order and radically simplifies solution of various problems, related to microwave plasma diagnostics, including plasma polarimetry, interferometry and refractometry in thermonuclear reactors. Efficiency of the method is demonstrated by the example of electromagnetic beam diffraction in a linear layer of magnetized plasma with parameters, modeling tokamak plasma in the project ITER.
Multiple scattering of ultrasound in weakly inhomogeneous media: application to human soft tissues
Aubry, Alexandre
2010-01-01
Waves scattered by a weakly inhomogeneous random medium contain a predominant single scattering contribution as well as a multiple scattering contribution which is usually neglected, especially for imaging purposes. We propose a method, based on random matrix theory, in order to separate the single and multiple scattering contributions. The experimental set up uses an array of programmable sources/receivers placed in front of the medium. The impulse responses between every couple of transducers are measured and form a matrix. Single-scattering contributions are shown to exhibit a deterministic coherence along the antidiagonals of the array response matrix, whatever the distribution of inhomogeneities. This property is taken advantage of to discriminate single from multiple-scattered waves. This allows one to evaluate the absorption losses and the scattering losses separately, by comparing the multiple scattering intensity with a radiative transfer model. Moreover, the relative contribution of multiple scatter...
Gerritsen, S.
2007-01-01
In this thesis we study wave propagation in inhomogeneous media. Examples of the classical (massless) waves we consider are acoustic waves (sound) and electromagnetic waves (light, for example). Interaction with inhomogeneities embedded in a reference medium alter the propagation direction, velocity
Gerritsen, S.
2007-01-01
In this thesis we study wave propagation in inhomogeneous media. Examples of the classical (massless) waves we consider are acoustic waves (sound) and electromagnetic waves (light, for example). Interaction with inhomogeneities embedded in a reference medium alter the propagation direction, velocity
Antennas in inhomogeneous media
Galejs, Janis; Fock, V A; Wait, J R
2013-01-01
Antennas in Inhomogeneous Media details the methods of analyzing antennas in such inhomogeneous media. The title covers the complex geometrical configurations along with its variational formulations. The coverage of the text includes various conditions the antennas are subjected to, such as antennas in the interface between two media; antennas in compressible isotropic plasma; and linear antennas in a magnetoionic medium. The selection also covers insulated loops in lossy media; slot antennas with a stratified dielectric or isotropic plasma layers; and cavity-backed slot antennas. The book wil
Measurements of weak localization of graphene in inhomogeneous magnetic fields
DEFF Research Database (Denmark)
Lindvall, N.; Shivayogimath, Abhay; Yurgens, A.
2015-01-01
Weak localization in graphene is studied in inhomogeneous magnetic fields. To generate the inhomogeneous field, a thin film of type-II superconducting niobium is put in close proximity to graphene. A deviation from the ordinary quadratic weak localization behavior is observed at low fields. We...
Traveltime approximations for inhomogeneous HTI media
Alkhalifah, Tariq Ali
2011-01-01
Traveltimes information is convenient for parameter estimation especially if the medium is described by an anisotropic set of parameters. This is especially true if we could relate traveltimes analytically to these medium parameters, which is generally hard to do in inhomogeneous media. As a result, I develop traveltimes approximations for horizontaly transversely isotropic (HTI) media as simplified and even linear functions of the anisotropic parameters. This is accomplished by perturbing the solution of the HTI eikonal equation with respect to η and the azimuthal symmetry direction (usually used to describe the fracture direction) from a generally inhomogeneous elliptically anisotropic background medium. The resulting approximations can provide accurate analytical description of the traveltime in a homogenous background compared to other published moveout equations out there. These equations will allow us to readily extend the inhomogenous background elliptical anisotropic model to an HTI with a variable, but smoothly varying, η and horizontal symmetry direction values. © 2011 Society of Exploration Geophysicists.
On electromagnetic field problems in inhomogeneous media
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.
Cherenkov radiation threshold in random inhomogeneous media
Grichine, V M
2009-01-01
Cherenkov radiation in media with random inhomogeneities like aerogel or Earth atmosphere is discussed. The spectral-angular distribution of Cherenkov photons emitted by relativistic charged particle and averaged over the dielectric permittivity fluctuations shows angular broadening similarly to the case of media with the photon absorption. The broadening results in the smoothing of Cherenkov threshold, and therefore media with strong photon scattering have more extended dependence of Cherenkov light output on the particle speed. It can be potentially used for the particle identification
Theory of Thomson scattering in inhomogeneous media
Kozlowski, P M; 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 partic- ularly 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 even lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous ...
Theory of Thomson scattering in inhomogeneous media
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.
Wave beam propagation in a weakly inhomogeneous isotropic medium: paraxial approximation and beyond
Energy Technology Data Exchange (ETDEWEB)
Bornatici, M [INFM, Physics Department ' A. Volta' , University of Pavia, I-27100 Pavia (Italy); Maj, O [INFM, Physics Department, University of Milan, I-20133 Milan (Italy)
2003-05-01
The various methods put forward for the description of paraxial wave beams propagating in weakly inhomogeneous media are shown to be equivalent to each other. This issue is discussed in terms of a comparative analysis with respect to the complex eikonal-based solution relevant to the propagation of a Gaussian wave beam in a lens-like isotropic medium (such a solution being readily extendible to the propagation in a plasma slab). The accuracy of the paraxial solution thus considered is assessed numerically in comparison with the corresponding exact solution of the Helmholtz equation.
Broadband dielectric spectroscopy of inhomogeneous and composite weak conductors
Petzelt, J.; Nuzhnyy, D.
2016-08-01
In this paper, we discuss broadband dielectric spectroscopy from mHz up to the infrared range mainly for materials with inhomogeneous weak conductivity, including conductor-dielectric nanocomposites. Our discussion is based on the effective medium approximation (EMA) and experiments modeled by this approach are reviewed. We discuss core-shell composites modeled by coated-spheres (Hashin-Shtrikman model) and normal composites with a possible percolation of the conductor component resulting in sharp or smeared percolation threshold of the DC conductivity and diverging static permittivity in the former case. The sharp percolation threshold is modeled by the Bruggeman EMA or by general EMA with arbitrary percolation threshold and arbitrary critical exponents of the DC conductivity and static permittivity. For the case of smeared percolation threshold in the case of complex topologies, we use the Lichtenecker model allowing for partial percolation of both the components. Finally, numerous papers reporting negative permittivity in weakly conducting materials are criticized and concluded to be due to spurious effects.
Soliton structure dynamics in inhomogeneous media
Guerrero, L E; González, J A
1998-01-01
We show that soliton interaction with finite-width inhomogeneities can activate a great number of soliton internal modes. We obtain the exact stationary soliton solution in the presence of inhomogeneities and solve exactly the stability problem. We present a Karhunen-Loeve analysis of the soliton structure dynamics as a time-dependent force pumps energy into the traslational mode of the kink. We show the importance of the internal modes of the soliton as they can generate shape chaos for the soliton as well as cases in which the first shape mode leads the dynamics.
On the accuracy of wave equations for inhomogeneous media
Xiang, Zhihai
2014-01-01
Homogeneous media is a very ideal assumption to establishing wave equations. Compared to the interested wave length, most materials in reality are inhomogeneous. To investigate the accuracy of electromagnetic, acoustic and elastic wave equations for inhomogeneous media, this paper checks their form-invariance in global Cartesian coordinate system by transforming them from arbitrary spatial geometries, in which they must be form-invariant according to the definition of tensor. In this way, it shows that form-invariant or not is an intrinsic property of wave equations, which is independent with the relation between field variables before and after coordinate transformation. With this approach, one can prove that Maxwell equations and acoustic equations are locally accurate to describe the wave propagation in inhomogeneous media, but Navier equations are not. In addition, new elastodynamic equations can be naturally obtained as the local versions of Willis equations, which are verified by some numerical simulati...
Geometrical approach to light in inhomogeneous media
Piwnicki, P
2002-01-01
Electromagnetism in an inhomogeneous dielectric medium at rest is described using the methods of differential geometry. In contrast to a general relativistic approach the electromagnetic fields are discussed in three-dimensional space only. The introduction of an appropriately chosen three-dimensional metric leads to a significant simplification of the description of light propagation in an inhomogeneous medium: light rays become geodesics of the metric and the field vectors are parallel transported along the rays. The new metric is connected to the usual flat space metric diag[1,1,1] via a conformal transformation leading to new, effective values of the medium parameters leading to an effective constant value of the index of refraction n=1. The corresponding index of refraction is thus constant and so is the effective velocity of light. Space becomes effectively empty but curved. All deviations from straight line propagation are now due to curvature. The approach is finally used for a discussion of the Riema...
Electromagnetic field representation in inhomogeneous anisotropic media
Mohsen, A.
1973-01-01
Some of the basic developments in the theory of electromagnetic field representation in terms of Hertz vectors are reviewed. A solution for the field in an inhomogeneous anisotropic medium is given in terms of the two Hertz vectors. Conditions for presentation of the field in terms of uncoupled transverse electric and transverse magnetic modes, in a general orthogonal coordinate system, are derived when the permeability and permittivity tensors have only diagonal components. These conditions are compared with some known special cases.
Quantum electrodynamics of inhomogeneous anisotropic media
Energy Technology Data Exchange (ETDEWEB)
Lopez, Adrian E.R.; Lombardo, Fernando C. [Ciudad Universitaria, Departamento de Fisica Juan Jose Giambiagi, Buenos Aires (Argentina); IFIBA CONICET-UBA, Facultad de Ciencias Exactas y Naturales, Buenos Aires (Argentina)
2015-02-01
In this work we calculate the closed time path generating functional for the electromagnetic (EM) field interacting with inhomogeneous anisotropic matter. For this purpose, we first find a general expression for the electromagnetic field's influence action from the interaction of the field with a composite environment consisting in the quantum polarization degrees of freedom in each point of space, at arbitrary temperatures, connected to thermal baths. Then we evaluate the generating functional for the gauge field, in the temporal gauge, by implementing the Faddeev-Popov procedure. Finally, through the point-splitting technique, we calculate closed expressions for the energy, the Poynting vector, and the Maxwell tensor in terms of the Hadamard propagator. We show that all the quantities have contributions from the field's initial conditions and also from the matter degrees of freedom. Throughout the whole work we discuss how the gauge invariance must be treated in the formalism when the EM-field is interacting with inhomogeneous anisotropic matter. We study the electrodynamics in the temporal gauge, obtaining the EM-field's equation and a residual condition. Finally we analyze the case of the EM-field in bulk material and also discuss several general implications of our results in relation with the Casimir physics in a non-equilibrium scenario. (orig.)
Spherically symmetric inhomogeneous bianisotropic media: Wave propagation and light scattering
DEFF Research Database (Denmark)
Novitsky, Andrey; Shalin, Alexander S.; Lavrinenko, Andrei
2017-01-01
We develop a technique for finding closed-form expressions for electromagnetic fields in radially inhomogeneous bianisotropic media, both the solutions of the Maxwell equations and material tensors being defined by the set of auxiliary two-dimensional matrices. The approach is applied to determine...... the scattering cross-sections by spherical particles, the fields inside which correspond to the Airy-exponential waves....
Quantum electrodynamics of inhomogeneous anisotropic media
Lopez, Adrian E Rubio
2014-01-01
In this work we calculate the closed time path (CTP) generating functional for the electromagnetic (EM) field interacting with inhomogeneous anisotropic matter. For this purpose, we first find a general expression for the electromagnetic field's influence action from the interaction of the field with a composite environment consisting in the quantum polarization degrees of freedom in each point of space, at arbitrary temperatures, connected to thermal baths. Then, we evaluate the generating functional for the gauge field, in the temporal gauge, by implementing the Faddeev-Popov procedure. Finally, through the point-splitting technique, we calculate closed expressions for the energy, the Poynting vector and the Maxwell tensor in terms of the Hadamard propagator. We show that all the quantities have contributions from the field's initial conditions and also from the matter degrees of freedom. Throughout the whole work we discuss and give insights about how the gauge invariance must be treated in the formalism w...
Non-Abelian evolution of electromagnetic waves in a weakly anisotropic inhomogeneous medium
Bliokh, K. Yu.; Frolov, D. Yu.; Kravtsov, Yu. A.
2007-05-01
A theory of electromagnetic wave propagation in a weakly anisotropic smoothly inhomogeneous medium is developed, based on the quantum-mechanical diagonalization procedure applied to Maxwell equations. The equations of motion for the translational (ray) and intrinsic (polarization) degrees of freedom are derived ab initio. The ray equations take into account the optical Magnus effect (spin Hall effect of photons) as well as trajectory variations owing to the medium anisotropy. Polarization evolution is described by the precession equation for the Stokes vector. In the generic case, the evolution of wave turns out to be non-Abelian: it is accompanied by mutual conversion of the normal modes and periodic oscillations of the ray trajectories analogous to electron zitterbewegung. The general theory is applied to examples of wave evolution in media with circular and linear birefringence.
Modification of light transmission channels by inhomogeneous absorption in random media
Liew, Seng Fatt
2015-01-01
Optical absorption is omnipresent and very often distributed non-uniformly in space. We present a numerical study on the effects of inhomogeneous absorption on transmission eigenchannels of light in highly scattering media. In the weak absorption regime, the spatial profile of a transmission channel remains very similar to that without absorption, and the effect of inhomogeneous absorption can be stronger or weaker than homogeneous absorption depending on the spatial overlap of the localized absorbing region with the field intensity maximum of the channel. In the strong absorption regime, the high transmission channels redirect the energy flows to circumvent the absorbing regions to minimize loss. The attenuation of high transmission channels by inhomogeneous absorption is lower than that by homogeneous absorption, regardless of the location of the absorbing region. The statistical distribution of transmission eigenvalues in the former becomes broader than that in the latter, due to a longer tail at high tran...
Demi, L; van Dongen, K W A; Verweij, M D
2011-03-01
Experimental data reveals that attenuation is an important phenomenon in medical ultrasound. Attenuation is particularly important for medical applications based on nonlinear acoustics, since higher harmonics experience higher attenuation than the fundamental. Here, a method is presented to accurately solve the wave equation for nonlinear acoustic media with spatially inhomogeneous attenuation. Losses are modeled by a spatially dependent compliance relaxation function, which is included in the Westervelt equation. Introduction of absorption in the form of a causal relaxation function automatically results in the appearance of dispersion. The appearance of inhomogeneities implies the presence of a spatially inhomogeneous contrast source in the presented full-wave method leading to inclusion of forward and backward scattering. The contrast source problem is solved iteratively using a Neumann scheme, similar to the iterative nonlinear contrast source (INCS) method. The presented method is directionally independent and capable of dealing with weakly to moderately nonlinear, large scale, three-dimensional wave fields occurring in diagnostic ultrasound. Convergence of the method has been investigated and results for homogeneous, lossy, linear media show full agreement with the exact results. Moreover, the performance of the method is demonstrated through simulations involving steered and unsteered beams in nonlinear media with spatially homogeneous and inhomogeneous attenuation.
Some stationary weak solutions to inhomogeneous Landau-Lifshitz equations in three dimensions
Institute of Scientific and Technical Information of China (English)
FANG Dao-yuan; LI Tai-long; XUE Ru-ying
2007-01-01
In this paper, we describe several stationary conditions on weak solutions to the inhomogeneous Landau-Lifshitz equation, which ensure the partial regularity. For certain class of proper stationary weak solutions, a compactness result of the solutions, a finite Hausdorff measure result of the t-slice energy concentration sets and an asymptotic limit result of the Radon measures are proved. We also present a subtle rectifiability result for the energy concentration set of certain sequence of strong stationary weak solutions.
Traveltime approximations for transversely isotropic media with an inhomogeneous background
Alkhalifah, Tariq
2011-05-01
A transversely isotropic (TI) model with a tilted symmetry axis is regarded as one of the most effective approximations to the Earth subsurface, especially for imaging purposes. However, we commonly utilize this model by setting the axis of symmetry normal to the reflector. This assumption may be accurate in many places, but deviations from this assumption will cause errors in the wavefield description. Using perturbation theory and Taylor\\'s series, I expand the solutions of the eikonal equation for 2D TI media with respect to the independent parameter θ, the angle the tilt of the axis of symmetry makes with the vertical, in a generally inhomogeneous TI background with a vertical axis of symmetry. I do an additional expansion in terms of the independent (anellipticity) parameter in a generally inhomogeneous elliptically anisotropic background medium. These new TI traveltime solutions are given by expansions in and θ with coefficients extracted from solving linear first-order partial differential equations. Pade approximations are used to enhance the accuracy of the representation by predicting the behavior of the higher-order terms of the expansion. A simplification of the expansion for homogenous media provides nonhyperbolic moveout descriptions of the traveltime for TI models that are more accurate than other recently derived approximations. In addition, for 3D media, I develop traveltime approximations using Taylor\\'s series type of expansions in the azimuth of the axis of symmetry. The coefficients of all these expansions can also provide us with the medium sensitivity gradients (Jacobian) for nonlinear tomographic-based inversion for the tilt in the symmetry axis. © 2011 Society of Exploration Geophysicists.
The perceived transmittance of inhomogeneous surfaces and media.
Anderson, Barton L; Singh, Manish; Meng, Jeanette
2006-06-01
A series of experiments was performed to determine how the visual system computes the transmittance of inhomogeneous surfaces and media. Previous work (Anderson, B. L. (1999) Stereoscopic surface perception. Neuron, 26, 919-928; Anderson, B. L. (2003) The role of occlusion in the perception of depth, lightness, and opacity. Psychological Review, 110, 762-784) has suggested that the visual system employs a transmittance anchoring principle in determining when transparency is perceived. This principle states that the visual system interprets the highest contrast region along contours and surfaces as a region in plain view and uses this anchor as a reference point for transparency computations. In particular, recent work has shown that the transmittance of homogeneous transparent surfaces is well described by a ratio of contrasts model (Singh, M., & Anderson, B. L. (2002). Toward a perceptual theory of transparency. Psychological Review, 109, 492-519). In this model, the transmittance of a transparent surface is determined by the contrast of a transparent image region normalized by the contrast of the region in plain view. Here, a series of experiments is reported that assesses this model for inhomogeneous transparent surfaces that vary in both space and time. The results of these experiments reveal that transmittance anchoring has both a spatial and temporal component, and that the perceived transmittance of transparent surfaces is well described by a ratio of perceived contrasts model.
Institute of Scientific and Technical Information of China (English)
LU Ming-Zhu; LIU Xue-Jin; SHI Yu; KANG Yan-Ni; GUAN Yu-Bo; WAN Ming-Xi
2012-01-01
We concentrate on the nondissipative mechanism induced shear wave in inhomogenous tissue.The shear wave equation of radiation force in inhomogeneous media is solved numerically with a finite-difference time-domain method.A rarely studied nondissipative mechanism of shear displacement due to a smooth medium inhomogeneity is evaluated.It is noted that unlike the dissipative effect,the nondissipative action on a localized inhomogeneity with its hardness parameter changing smoothly along the beam axis,compresses or stretches the focus area.The shear waves in nondissipative inhomogeneous media remain the property of sharp turn with 100％ peak positive displacement and 64％ peak negative displacement.This action is useful in discerning the water-like lesion.%We concentrate on the nondissipative mechanism induced shear wave in inhomogenous tissue. The shear wave equation of radiation force in inhomogeneous media is solved numerically with a finite-difference time-domain method. A rarely studied nondissipative mechanism of shear displacement due to a smooth medium inhomogeneity is evaluated. It is noted that unlike the dissipative effect, the nondissipative action on a localized inhomogeneity with its hardness parameter changing smoothly along the beam axis, compresses or stretches the focus area. The shear waves in nondissipative inhomogeneous media remain the property of sharp turn with 100% peak positive displacement and 64% peak negative displacement. This action is useful in discerning the water-like lesion.
Waheed, Umair bin
2013-09-01
On several simple models of isotropic and anisotropic media, we have studied the accuracy of the two-point paraxial traveltime formula designed for the approximate calculation of the traveltime between points S\\' and R\\' located in the vicinity of points S and R on a reference ray. The reference ray may be situated in a 3D inhomogeneous isotropic or anisotropic medium with or without smooth curved interfaces. The twopoint paraxial traveltime formula has the form of the Taylor expansion of the two-point traveltime with respect to spatial Cartesian coordinates up to quadratic terms at points S and R on the reference ray. The constant term and the coefficients of the linear and quadratic terms are determined from quantities obtained from ray tracing and linear dynamic ray tracing along the reference ray. The use of linear dynamic ray tracing allows the evaluation of the quadratic terms in arbitrarily inhomogeneous media and, as shown by examples, it extends the region of accurate results around the reference ray between S and R (and even outside this interval) obtained with the linear terms only. Although the formula may be used for very general 3D models, we concentrated on simple 2D models of smoothly inhomogeneous isotropic and anisotropic (~8% and ~20% anisotropy) media only. On tests, in which we estimated twopoint traveltimes between a shifted source and a system of shifted receivers, we found that the formula may yield more accurate results than the numerical solution of an eikonal-based differential equation. The tests also indicated that the accuracy of the formula depends primarily on the length and the curvature of the reference ray and only weakly depends on anisotropy. The greater is the curvature of the reference ray, the narrower its vicinity, in which the formula yields accurate results.
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Polarimetric scattering from inhomogeneous random media of non-spherical scatterers under a pulse incidence is studied. The time-dependent Mueller matrix solution of vector radiative transfer for layering random media is derived. Co-polarized and cross-polarized bistatic and back-scattering are numerically simulated. The shape and intensity of polarized echoes well depict the inhomogeneous fraction profile of random scatterers. Its functional dependence upon the fraction profile, layering thickness, and other parameters are discussed. This technique is applicable to reconstruction of inhomogeneous fraction profile and inversion of the media thickness.
Laser Beam Propagation Through Inhomogeneous Media with Shock-Like Profiles: Modeling and Computing
Adamovsky, Grigory; Ida, Nathan
1997-01-01
Wave propagation in inhomogeneous media has been studied for such diverse applications as propagation of radiowaves in atmosphere, light propagation through thin films and in inhomogeneous waveguides, flow visualization, and others. In recent years an increased interest has been developed in wave propagation through shocks in supersonic flows. Results of experiments conducted in the past few years has shown such interesting phenomena as a laser beam splitting and spreading. The paper describes a model constructed to propagate a laser beam through shock-like inhomogeneous media. Numerical techniques are presented to compute the beam through such media. The results of computation are presented, discussed, and compared with experimental data.
Behaviour of light transmission channels in random media with inhomogeneous disorder
Xu, Yuchen; ZHANG Hao; Lin, Yujun; Zhu, Heyuan
2016-01-01
We present a numerical study on the light transport properties and statistics of transmission channels in random media with inhomogeneous disorder. For the case of longitudinal inhomogeneity of disorder we find that the statistics of the transmission channels is independent of the inhomogeneity and the system can be equivalent to a counterpart with homogeneous disorder strength, both of which have the same statistical distribution of the transmission channels. However, for the case of transve...
Study of inhomogeneities in turbid media: experimental and numerical results
Carbone, N. A.; di Rocco, Héctor O.; Iriarte, Daniela I.; Pomarico, Juan A.; Ranea-Sandoval, Héctor F.; Pardini, Pamela; Waks-Serra, M. Victoria
2011-08-01
Near Infrared diffuse transmission of light through tissue is a tool for noninvasive imaging for diagnostic purposes. Most of the research has been focused over breast cancer imaging; however, major efforts have been done in cerebral tomography and topography imaging, as well as small animal organs imaging systems. In this work, we investigate the transmitted light profiles when scattering and absorbing cylindrical inhomogeneities are submerged at different depths inside slabs of turbid media. We analyze the transilluminance profiles when the phantom is scanned using both, CW and time resolved detection. The study of the spatial profiles obtained with CW light, shows an apparently contradictory effect when the absorption coefficient of the inclusion is higher than that of the bulk. In this case, the intensity profiles displays a peak of higher intensity where the inclusion is located, as it would be expected for a less absorbing inclusion. The experiments were compared and analyzed with a theoretical model for cylindrical inclusions and Monte Carlo simulations implemented in a Graphic Processing Unit (GPU).
Compressive Structured Light for Recovering Inhomogeneous Participating Media.
Gu, Jinwei; Nayar, Shree K; Grinspun, Eitan; Belhumeur, Peter N; Ramamoorthi, Ravi
2013-03-01
We propose a new method named compressive structured light for recovering inhomogeneous participating media. Whereas conventional structured light methods emit coded light patterns onto the surface of an opaque object to establish correspondence for triangulation, compressive structured light projects patterns into a volume of participating medium to produce images which are integral measurements of the volume density along the line of sight. For a typical participating medium encountered in the real world, the integral nature of the acquired images enables the use of compressive sensing techniques that can recover the entire volume density from only a few measurements. This makes the acquisition process more efficient and enables reconstruction of dynamic volumetric phenomena. Moreover, our method requires the projection of multiplexed coded illumination, which has the added advantage of increasing the signal-to-noise ratio of the acquisition. Finally, we propose an iterative algorithm to correct for the attenuation of the participating medium during the reconstruction process. We show the effectiveness of our method with simulations as well as experiments on the volumetric recovery of multiple translucent layers, 3D point clouds etched in glass, and the dynamic process of milk drops dissolving in water.
Kim, Seulong
2016-01-01
Bi-isotropic media, which include isotropic chiral media and Tellegen media as special cases, are the most general form of linear isotropic media where the electric displacement and the magnetic induction are related to both the electric field and the magnetic intensity. In inhomogeneous bi-isotropic media, electromagnetic waves of two different polarizations are coupled to each other. In this paper, we develop a generalized version of the invariant imbedding method for the study of wave propagation in arbitrarily-inhomogeneous stratified bi-isotropic media, which can be used to solve the coupled wave propagation problem accurately and efficiently. We verify the validity and usefulness of the method by applying it to several examples, including the wave propagation in a uniform chiral slab, the surface wave excitation in a bilayer system made of a layer of Tellegen medium and a metal layer, and the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations in inhomogeneous Telle...
Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field
Ratushnaya, Valeria
2016-12-17
We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.
Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field
Ratushnaya, Valeria; Samtaney, Ravi
2016-12-01
We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.
An Inverse Electromagnetic Scattering Method for One-Dimensional Inhomogeneous Media
Institute of Scientific and Technical Information of China (English)
LIN Zhi-Wei; XU Xin; ZHANG Xiao-Juan; FANG Guang-You
2011-01-01
A frequency-domain inversion scheme for reconstructing the permittivity profile of one-dimensional inhomogeneous media is proposed. The generalized reflection coefficients and the generalized transmission coefficients of the inhomogeneous media are used as the input data of the inverse model. A Newton-like iterative algorithm known as the generalized pulse-spectrum technique with the Tikhonov regularization is applied to solve the inverse problem. Novel boundary conditions are proposed for the inverse problem and therefore the permittivity at the boundary of the inhomogeneous media is not required as prior knowledge. The choice of frequency points of the frequency-domain method is also investigated. Numerical examples are carried out to validate the inversion technique. Good agreements between the reconstructed profiles and the true profiles are shown.
Dispersion properties of helical waves in radially inhomogeneous elastic media.
Syresin, D E; Zharnikov, T V; Tyutekin, V V
2012-06-01
In this paper, a method describing dispersion curve calculation for waves propagating in radially layered, inhomogeneous isotropic elastic waveguides is developed. Particular emphasis is placed on the helical waves with noninteger azimuthal wavenumbers, which can be potentially applied in such fields as nondestructive evaluation, acoustic tomography, etc., stipulating their practical importance. To solve the problem under consideration, the matrix Riccati equation is formulated for an impedance matrix. The use of the latter yields a simple form of the dispersion equation. Numerical computation of dispersion curves can encounter difficulties, which are due to potential singularities of the impedance matrix and the necessity to separate roots of the dispersion equation. These difficulties are overcome by employing the Cayley transform and invoking the parametric continuation method. The method developed by the authors is demonstrated by calculating dispersion diagrams in support of helical waves for several models of practical interest. Such computations for an inhomogeneous layer and its approximation by a set of homogeneous layers using a transfer matrix and Riccati equation methods revealed higher computational accuracy of the latter. Dispersion curves calculated for layers with different types of inhomogeneity demonstrated significant discrepancies at low frequencies.
Institute of Scientific and Technical Information of China (English)
GUO Fei
2007-01-01
In this paper we study the mixed initial-boundary value problem for inhomogeneous quasilinear hyperbolic systems in the domain D={(t,x)| t≥O,x≥O}.Under the assumption that the source term satisfies the matching condition,a sufficient condition to guarantee the existence and uniqueness of global weakly discontinuous solution is given.
Behaviour of light transmission channels in random media with inhomogeneous disorder
Xu, Yuchen; Lin, Yujun; Zhu, Heyuan
2016-01-01
We present a numerical study on the light transport properties and statistics of transmission channels in random media with inhomogeneous disorder. For the case of longitudinal inhomogeneity of disorder we find that the statistics of the transmission channels is independent of the inhomogeneity and the system can be equivalent to a counterpart with homogeneous disorder strength, both of which have the same statistical distribution of the transmission channels. However, for the case of transverse inhomogeneity of disorder, such equivalence does not exist, moreover, the transmission eigenvalues are pushed to the two ends of the distribution and the distribution of the total transmission is broadened since the spatial structure gives rise to larger and smaller transmitted incident channels.
General polarized ray-tracing method for inhomogeneous uniaxially anisotropic media
Sluijter, M.; De Boer, D.K.G.; Braat, J.J.M.
2008-01-01
Uniaxial optical anisotropy in the geometrical-optics approach is a classical problem, and most of the theory has been known for at least fifty years. Although the subject appears frequently in the literature, wave propagation through inhomogeneous anisotropic media is rarely addressed. The rapid ad
The Real-Space Renormalization Group Applied to Diffusion in Inhomogeneous Media
Kawasaki, Mitsuhiro
2002-01-01
The real-space renormalization group technique is introduced to evaluate the effective diffusion constant for diffusion in inhomogeneous media, which has been obtained by singular perturbation methods. Our method is formulated on a discretized real space and hence it can be easily combined with numerical studies for partial differential equations.
Diffusive Limits of the Master Equation in Inhomogeneous Media
Sattin, F; Salasnich, L
2015-01-01
In inhomogeneous environments several expressions for the flux of a diffusing quantity may apply--from Fick-Fourier's to Fokker-Planck's--depending upon the system studied. The integro-differential Master Equation (ME) provides a fairly generic framework for describing the dynamics of arbitrary systems driven by stochastic rules. Diffusive dynamics does arise as long-wavelength limit of the ME. However, while it is straightforward to obtain a diffusion equation with Fokker-Planck flux, its Fick-Fourier counterpart has never been worked out from the ME. In this work we show under which hypothesis the Fick's flux can actually be recovered from the ME. Analytical considerations are supported by explicit computer models.
Theory of Radio Propagation in Inhomogeneous Media (The Eikonal Method)
Bianchi, S; Settimi, A
2010-01-01
The Istituto Nazionale di Geofisica e Vulcanologia has been involved since its foundation in the forecast of the conditions in which a radio link that makes use of propagation by means of ionospheric wave takes place. In the last times it gained interest also the precise forecast of the trajectory covered by a radio wave propagating into the atmosphere, specifically into the ionosphere, which can be considered, at first approximation, as an inhomogeneous medium, defined by a refraction index slowly varying in time. This work describes the theoretical bases to study a trajectory; they substantially make use of the methods of the geometrical optics. Such theoretical bases find applications in numerical methods to calculate the trajectories, as quoted in references [Bianchi, 2009].
Ignatchenko, V. A.; Polukhin, D. S.; Tsikalov, D. S.
2017-10-01
A new self-consistent approximation proposed earlier, is compared with various existing approximations, as well as with a numerical simulation of solutions of the wave equation for a medium with one-dimensional inhomogeneities. The Green's function, found using the new approach, is the closest to the result obtained by the numerical simulation. The results of the work show that the new approach has undoubted advantages in the study of stochastic problems in media with longwave inhomogeneities. The new self-consistent approximation in some cases has advantages over a numerical method: a more rapid process of calculation and the possibility of consideration of three-dimensional problems.
Diffraction traveltime approximation for TI media with an inhomogeneous background
Waheed, Umair bin
2013-09-01
Diffractions in seismic data contain valuable information that can help improve our modeling capability for better imaging of the subsurface. They are especially useful for anisotropic media because they inherently possess a wide range of dips necessary to resolve the angular dependence of velocity. We develop a scheme for diffraction traveltime computations based on perturbation of the anellipticity anisotropy parameter for transversely isotropic media with tilted axis of symmetry (TTI). The expansion, therefore, uses an elliptically anisotropic medium with tilt as the background model. This formulation has advantages on two fronts: first, it alleviates the computational complexity associated with solving the TTI eikonal equation, and second, it provides a mechanism to scan for the best-fitting anellipticity parameter η without the need for repetitive modeling of traveltimes, because the traveltime coefficients of the expansion are independent of the perturbed parameter η. The accuracy of such an expansion is further enhanced by the use of Shanks transform. We established the effectiveness of the proposed formulation with tests on a homogeneous TTI model and complex media such as the Marmousi and BP models.
Nonlinear surface waves in soft, weakly compressible elastic media.
Zabolotskaya, Evgenia A; Ilinskii, Yurii A; Hamilton, Mark F
2007-04-01
Nonlinear surface waves in soft, weakly compressible elastic media are investigated theoretically, with a focus on propagation in tissue-like media. The model is obtained as a limiting case of the theory developed by Zabolotskaya [J. Acoust. Soc. Am. 91, 2569-2575 (1992)] for nonlinear surface waves in arbitrary isotropic elastic media, and it is consistent with the results obtained by Fu and Devenish [Q. J. Mech. Appl. Math. 49, 65-80 (1996)] for incompressible isotropic elastic media. In particular, the quadratic nonlinearity is found to be independent of the third-order elastic constants of the medium, and it is inversely proportional to the shear modulus. The Gol'dberg number characterizing the degree of waveform distortion due to quadratic nonlinearity is proportional to the square root of the shear modulus and inversely proportional to the shear viscosity. Simulations are presented for propagation in tissue-like media.
Masmoudi, Nabil
2014-01-01
We present an approximate, but efficient and sufficiently accurate P-wave ray tracing and dynamic ray tracing procedure for 3D inhomogeneous, weakly orthorhombic media with varying orientation of symmetry planes. In contrast to commonly used approaches, the orthorhombic symmetry is preserved at any point of the model. The model is described by six weak-anisotropy parameters and three Euler angles, which may vary arbitrarily, but smoothly, throughout the model. We use the procedure for the calculation of rays and corresponding two-point traveltimes in a VSP experiment in a part of the BP benchmark model generalized to orthorhombic symmetry.
NUMERICAL METHODS FOR MAXWELL'S EQUATIONS IN INHOMOGENEOUS MEDIA WITH MATERIAL INTERFACES
Institute of Scientific and Technical Information of China (English)
Wei Cai
2004-01-01
In this paper, we will present some recent results on developing numerical methods for solving Maxwell's equations in inhomogeneous media with material interfaces. First,we will present a second order upwinding embedded boundary method - a Cartesian grid based finite difference method with special upwinding treatment near the material interfaces. Second, we will present a high order discontinuous spectral element with Dubinar orthogonal polynomials on triangles. Numerical results on electromagnetic scattering and photonic waveguide will be included.
A convergent Born series for solving the inhomogeneous Helmholtz equation in arbitrarily large media
Osnabrugge, Gerwin; Vellekoop, Ivo M
2016-01-01
We present a fast method for numerically solving the inhomogeneous Helmholtz equation. Our iterative method is based on the Born series, which we modified to achieve convergence for scattering media of arbitrary size and scattering strength. Compared to pseudospectral time-domain simulations, our modified Born approach is two orders of magnitude faster and nine orders of magnitude more accurate in benchmark tests in 1-dimensional and 2-dimensional systems.
A convergent Born series for solving the inhomogeneous Helmholtz equation in arbitrarily large media
Osnabrugge, Gerwin; Leedumrongwatthanakun, Saroch; Vellekoop, Ivo M.
2016-10-01
We present a fast method for numerically solving the inhomogeneous Helmholtz equation. Our iterative method is based on the Born series, which we modified to achieve convergence for scattering media of arbitrary size and scattering strength. Compared to pseudospectral time-domain simulations, our modified Born approach is two orders of magnitude faster and nine orders of magnitude more accurate in benchmark tests in 1, 2, and 3-dimensional systems.
Energy Technology Data Exchange (ETDEWEB)
Matsushima, J.; Rokugawa, S.; Kato, Y. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering; Yokota, T.; Miyazaki, T. [Geological Survey of Japan, Tsukuba (Japan); Ichie, Y. [The University of Tokyo, Tokyo (Japan)
1996-10-01
Data processing techniques have been investigated for clarifying structures and physical properties of geothermal reservoirs in the deep underground by seismic exploration using multiple wells. They include the initial motion time-distance tomography, amplitude tomography, diffracted wave tomography, and structure imaging using reflected wave or scattered wave. When applying these data processing methods to observed records, weak and minor signals essentially required are canceled due to averaging the analytical fields. In this study, influence of inhomogeneous media on the wavefield was evaluated. Data were analyzed considering frequency by using wavelet transform by which time-frequency can be easily analyzed. From the time-frequency analysis using wavelet transform, it was illustrated that high frequency scattered waves, generated by scatterer like cracks or by irregularity on the reflection surface, arrive behind direct P-wave and direct S-wave. 5 refs., 8 figs.
Alkhalifah, Tariq Ali
2012-04-30
Traveltime information is crucial for parameter estimation, especially if the medium is described by a set of anisotropy parameters. We can efficiently estimate these parameters if we are able to relate them analytically to traveltimes, which is generally hard to do in inhomogeneous media. I develop traveltime approximations for transversely isotropic media with a horizontal symmetry axis (HTI) as simplified and even linear functions of the anisotropy parameters. This is accomplished by perturbing the solution of the HTI eikonal equation with respect to the anellipticity parameter, η and the azimuth of the symmetry axis (typically associated with the fracture direction) from a generally inhomogeneous, elliptically anisotropic background medium. Such a perturbation is convenient since the elliptically anisotropic information might be obtained from well velocities in HTI media. Thus, we scan for only η and the symmetry-axis azimuth. The resulting approximations can provide a reasonably accurate analytical description of the traveltime in a homogenous background compared to other published moveout equations. They also help extend the inhomogenous background isotropic or elliptically anisotropic models to an HTI one with a smoothly variable η and symmetry-axis azimuth. © 2012 European Association of Geoscientists & Engineers.
Solitary waves of α-helix propagation in media with arbitrary inhomogeneities
Mvogo, Alain; Ben-Bolie, Germain Hubert; Kofané, Timoléon Crépin
2013-05-01
We study the dynamics of solitary waves in α-helical proteins going beyond the standard nearest-neighbour interaction by taking into account influence long-range dipole-dipole interactions of the Kac-Baker type. By means of the coherent state representation of operators, the model Hamiltonian is transformed into a pair of classical lattice equations, which is further reduced to a sole nonlinear Schrödinger (NLS) equation using the continuum approximation of which the dispersive coefficient depends on the long-range interactions (LRI) parameter. It comes out from our results that the bright-like solitons, solitary waves which govern the energy transfer in α-helix, are deeply influenced by the LRI. At the end, we transform the NLS equation for more currently-important inhomogeneous NLS models in media with inhomogeneities. Application of this transformation to two example models is illustrated and soliton-like solutions are also graphically discussed.
Kaur, Paramjit; Wasan, Ajay
2015-01-01
We present a theoretical model, using density matrix approach, to study the effect of weak as well as strong probe field on the optical properties of an inhomogeneously broadened multilevel V-system of the $^{87}$Rb D2 line. We consider the case of stationary as well as moving atoms and perform thermal averaging at room temperature. The presence of multiple excited states results in asymmetric absorption and dispersion profiles. In the weak probe regime, we observe the partial transparency window due to the constructive interference occurs between transition pathways at the line center. In a room temperature vapour, we obtain an increased linewidth of the transparency window and steep positive dispersion. For a strong probe regime, the transparency window with normal dispersion switches to enhanced absorption with anomalous dispersion at the line center. Here, we show how the electromagnetically induced transparency (EIT) depends on the polarizations of the applied fields. We also discuss the transient behavi...
The variety of stable vortical solitons in Ginzburg-Landau media with radially inhomogeneous losses
Skarka, V; Leblond, H; Malomed, B A; Mihalache, D
2010-01-01
Using a combination of the variation approximation (VA) and direct simulations, we consider the light transmission in nonlinearly amplified bulk media, taking into account the localization of the gain, i.e., the linear loss shaped as a parabolic function of the transverse radius, with a minimum at the center. The balance of the transverse diffraction, self-focusing, gain, and the inhomogeneous loss provide for the hitherto elusive stabilization of vortex solitons in a large zone of the parameter space. Adjacent to it, stability domains are found for several novel kinds of localized vortices, including spinning elliptically shaped ones, eccentric elliptic vortices which feature double rotation, spinning crescents, and breathing vortices.
The Quasi-Static Electromagnetic Approximation for Weakly Conducting Media
Heubrandtner, T
2002-01-01
In a conducting dielectric charge and electric field decay with a time constant tau_R = \\varepsilon/\\sigma. In a weakly conducting medium, as e.g. glass or melamine-phenolic laminate in use in RPC's, this time is about 10^{-3} s; so it is long as compared to the time the charge cloud needs to move through the gap and to the time the signal needs to propagate through a dielectric to the electrode. A quasi-static theory to deal with transient phenomena in weakly conducting media has been developed in Haus and Melcher (1989), Fano, Chu and Adler (1963); it simplifies the analysis considerably since it requires only the solution of a scalar diffusion-type equations in place of the time-dependent Maxwell equations. This little known theory is applied to treat the generation of signals in simple models for chambers with such materials.
Channeling of Branched Flow in Weakly Scattering Anisotropic Media
Degueldre, Henri; Metzger, Jakob J.; Schultheis, Erik; Fleischmann, Ragnar
2017-01-01
When waves propagate through weakly scattering but correlated, disordered environments they are randomly focused into pronounced branchlike structures, a phenomenon referred to as branched flow, which has been studied in a wide range of isotropic random media. In many natural environments, however, the fluctuations of the random medium typically show pronounced anisotropies. A prominent example is the focusing of tsunami waves by the anisotropic structure of the ocean floor topography. We study the influence of anisotropy on such natural focusing events and find a strong and nonintuitive dependence on the propagation angle which we explain by semiclassical theory.
Effects of diffusion in magnetically inhomogeneous media on rotating frame spin-lattice relaxation
Spear, John T.; Gore, John C.
2014-12-01
In an aqueous medium containing magnetic inhomogeneities, diffusion amongst the intrinsic susceptibility gradients contributes to the relaxation rate R1ρ of water protons to a degree that depends on the magnitude of the local field variations ΔBz, the geometry of the perturbers inducing these fields, and the rate of diffusion of water, D. This contribution can be reduced by using stronger locking fields, leading to a dispersion in R1ρ that can be analyzed to derive quantitative characteristics of the material. A theoretical expression was recently derived to describe these effects for the case of sinusoidal local field variations of a well-defined spatial frequency q. To evaluate the degree to which this dispersion may be extended to more realistic field patterns, finite difference Bloch-McConnell simulations were performed with a variety of three-dimensional structures to reveal how simple geometries affect the dispersion of spin-locking measurements. Dispersions were fit to the recently derived expression to obtain an estimate of the correlation time of the field variations experienced by the spins, and from this the mean squared gradient and an effective spatial frequency were obtained to describe the fields. This effective spatial frequency was shown to vary directly with the second moment of the spatial frequency power spectrum of the ΔBz field, which is a measure of the average spatial dimension of the field variations. These results suggest the theory may be more generally applied to more complex media to derive useful descriptors of the nature of field inhomogeneities. The simulation results also confirm that such diffusion effects disperse over a range of locking fields of lower amplitude than typical chemical exchange effects, and should be detectable in a variety of magnetically inhomogeneous media including regions of dense microvasculature within biological tissues.
Khmelnytskaya, Kira V.; Kravchenko, Vladislav V.; Torba, Sergii M.
2016-05-01
The time-dependent Maxwell system describing electromagnetic wave propagation in inhomogeneous isotropic media in the one-dimensional case reduces to a Vekua-type equation for bicomplex-valued functions of a hyperbolic variable, see Kravchenko and Ramirez [Adv. Appl. Cliord Algebr. 21(3), 547-559 (2011)]. Using this relation, we solve the problem of the transmission through an inhomogeneous layer of a normally incident electromagnetic time-dependent plane wave. The solution is written in terms of a pair of Darboux-associated transmutation operators [Kravchenko, V. V. and Torba, S. M., J. Phys. A: Math. Theor. 45, 075201 (2012)], and combined with the recent results on their construction [Kravchenko, V. V. and Torba, S. M., Complex Anal. Oper. Theory 9, 379-429 (2015); Kravchenko, V. V. and Torba, S. M., J. Comput. Appl. Math. 275, 1-26 (2015)] can be used for efficient computation of the transmitted modulated signals. We develop the corresponding numerical method and illustrate its performance with examples.
Berrocal, Edouard; Meglinski, Igor; Jermy, Mark
2005-11-01
Modern optical diagnostics for quantitative characterization of polydisperse sprays and other aerosols which contain a wide range of droplet size encounter difficulties in the dense regions due to the multiple scattering of laser radiation with the surrounding droplets. The accuracy and efficiency of optical measurements can only be improved if the radiative transfer within such polydisperse turbid media is understood. A novel Monte Carlo code has been developed for modeling of optical radiation propagation in inhomogeneous polydisperse scattering media with typical drop size ranging from 2 μm to 200 μm in diameter. We show how strong variations of both particle size distribution and particle concentration within a 3D scattering medium can be taken into account via the Monte Carlo approach. A new approximation which reduces ~20 times the computational memory space required to determine the phase function is described. The approximation is verified by considering four log-normal drop size distributions. It is found valid for particle sizes in the range of 10-200 μm with increasing errors, due to additional photons scattered at large angles, as the number of particles below than 10 μm increases. The technique is applied to the simulation of typical planar Mie imaging of a hollow cone spray. Simulated and experimental images are compared and shown to agree well. The code has application in developing and testing new optical diagnostics for complex scattering media such as dense sprays.
Varieties of stable vortical solitons in Ginzburg-Landau media with radially inhomogeneous losses.
Skarka, V; Aleksić, N B; Leblond, H; Malomed, B A; Mihalache, D
2010-11-19
Using a combination of the variation approximation and direct simulations, we consider the model of the light transmission in nonlinearly amplified bulk media, taking into account the localization of the gain, i.e., the linear loss shaped as a parabolic function of the transverse radius, with a minimum at the center. The balance of the transverse diffraction, self-focusing, gain, and the inhomogeneous loss provides for the hitherto elusive stabilization of vortex solitons, in a large zone of the parameter space. Adjacent to it, stability domains are found for several novel kinds of localized vortices, including spinning elliptically shaped ones, eccentric elliptic vortices which feature double rotation, spinning crescents, and breathing vortices.
A systematic approach for quantifying wave propagation in vertically inhomogeneous media
Foster, Douglas J.; Lane, F. D.; Zhao, Zeyu
2017-08-01
We examine wave propagation in transversely homogeneous media characterized by variations of properties with respect to depth. Our intent is to provide analytic formulae that quantify scattering effects from fine scale inhomogeneities typically observed on seismic field data. We employ a Born scattering series approach that systematically includes higher order phenomena (transmission losses, mode conversions and multiples). Although, the Born series is inexact, it provides useful approximations. Analytic examples show how various terms of the Born series include higher order scattering effects. We also document the inexact nature of the approximation. Numerical examples illustrate the magnitude of scattering induced time delays and attenuation. A generalized (complex) reflection coefficient is introduced to describe backscattered energy from a discrete interval instead of an isolated interface. The main goal of this paper is to quantify thin-bed scattering in order to provide a more complete representation of seismic reflections in realistic geological settings. It is our hope that this insight will lead to useful applications.
Huang, Chao; Nie, Liming; Wang, Lihong V; Anastasio, Mark A
2013-01-01
Existing approaches to image reconstruction in photoacoustic computed tomography (PACT) with acoustically heterogeneous media are limited to weakly varying media, are computationally burdensome, and/or cannot effectively mitigate the effects of measurement data incompleteness and noise. In this work, we develop and investigate a discrete imaging model for PACT that is based on the exact photoacoustic (PA) wave equation and facilitates the circumvention of these limitations. A key contribution of the work is the establishment of a procedure to implement a matched forward and backprojection operator pair associated with the discrete imaging model, which permits application of a wide-range of modern image reconstruction algorithms that can mitigate the effects of data incompleteness and noise. The forward and backprojection operators are based on the k-space pseudospectral method for computing numerical solutions to the PA wave equation in the time domain. The developed reconstruction methodology is investigated...
Zhao, J. M.; Tan, J. Y.; Liu, L. H.
2013-01-01
A new second order form of radiative transfer equation (named MSORTE) is proposed, which overcomes the singularity problem of a previously proposed second order radiative transfer equation [J.E. Morel, B.T. Adams, T. Noh, J.M. McGhee, T.M. Evans, T.J. Urbatsch, Spatial discretizations for self-adjoint forms of the radiative transfer equations, J. Comput. Phys. 214 (1) (2006) 12-40 (where it was termed SAAI), J.M. Zhao, L.H. Liu, Second order radiative transfer equation and its properties of numerical solution using finite element method, Numer. Heat Transfer B 51 (2007) 391-409] in dealing with inhomogeneous media where some locations have very small/zero extinction coefficient. The MSORTE contains a naturally introduced diffusion (or second order) term which provides better numerical property than the classic first order radiative transfer equation (RTE). The stability and convergence characteristics of the MSORTE discretized by central difference scheme is analyzed theoretically, and the better numerical stability of the second order form radiative transfer equations than the RTE when discretized by the central difference type method is proved. A collocation meshless method is developed based on the MSORTE to solve radiative transfer in inhomogeneous media. Several critical test cases are taken to verify the performance of the presented method. The collocation meshless method based on the MSORTE is demonstrated to be capable of stably and accurately solve radiative transfer in strongly inhomogeneous media, media with void region and even with discontinuous extinction coefficient.
Scattering of homogeneous and inhomogeneous seismic waves in low-loss viscoelastic media
Moradi, Shahpoor; Innanen, Kristopher A.
2015-09-01
Motivated by the need to derive and characterize increasingly sophisticated seismic data analysis and inversion methods incorporating wave dissipation, we consider the problem of scattering of homogeneous and inhomogeneous waves from perturbations in five viscoelastic parameters (density, P- and S-wave velocities, and P- and S-wave quality factors), as formulated in the context of the Born approximation. Within this approximation the total wave field is the superposition of an incident plane wave and a scattered wave, the latter being a spherical wave weighted by a function of solid angle called the scattering potential. In elastic media the scattering potential is real, but if dissipation is included through a viscoelastic model, the potential becomes complex and thus impacts the amplitude and phase of the outgoing wave. The isotropic-elastic scattering framework of Stolt and Weglein, extended to admit viscoelastic media, exposes these amplitude and phase phenomena to study, and in particular allows certain well-known layered-medium viscoelastic results due to Borcherdt to be re-considered in an arbitrary heterogeneous Earth. The main theoretical challenge in doing this involves the choice of coordinate system over which to evaluate and analyse the waves, which in the viscoelastic case must be based on complex vector analysis. We present a candidate system within which several of Borcherdt's key results carry over; for instance, we show that elliptically polarized P and SI waves cannot be scattered into linearly polarized SII waves. Furthermore, the elastic formulation is straightforwardly recovered in the limit as P- and S-wave quality factors tend to infinity.
De Ryck, L; Lauriks, W; Leclaire, P; Groby, J P; Wirgin, A; Depollier, C
2008-09-01
The present paper deals with the inverse scattering problem involving macroscopically inhomogeneous rigid frame porous media. It consists of the recovery, from acoustic measurements, of the profiles of spatially varying material parameters by means of an optimization approach. The resolution is based on the modeling of acoustic wave propagation in macroscopically inhomogeneous rigid frame porous materials, which was recently derived from the generalized Biot's theory. In practice, the inverse problem is solved by minimizing an objective function defined in the least-square sense by the comparison of the calculated reflection (and transmission) coefficient(s) with the measured or synthetic one(s), affected or not by additive Gaussian noise. From an initial guess, the profiles of the x-dependent material parameters are reconstructed iteratively with the help of a standard conjugate gradient method. The convergence rate of the latter and the accuracy of the reconstructions are improved by the availability of an analytical gradient.
Acoustic Localization in Weakly Compressible Elastic Media Permeated with Air Bubbles
Institute of Scientific and Technical Information of China (English)
LIANG Bin; ZHU Zhe-Min; CHENG Jian-Chun
2006-01-01
@@ The propagation of longitudinal acoustic waves in weakly compressible elastic media permeated with air bubbles is investigated on the basis of the radial pulsation equation of a single bubble. The multiple scattering of waves in such media is rigorously described by using a self-consistent approach.
Lee, Chung Il; Yoon, Sei-Chul; Suh, Tae Suk; Hong, Seung-Woo; Min, Kyung Joo; Lee, Sang Deok; Chung, Su Mi; Jung, Jae-Yong
2014-01-01
The percentage depth dose distributions in inhomogeneous phantoms with lung and bone equivalent media are studied. For lung equivalent media a Balsa wood is used, and for a soft bone equivalent media a compound material with epoxy resin, hardener and calcium carbonate is used. Polystyrene slabs put together with these materials are used as an inhomogeneous phantom. Dose measurements are performed with Gafchromic EBT film by using photon beams from 6MV CyberKnife at the Seoul Uridul Hospital. The cone sizes of the photon beams are varied from 5, 10 to 30 mm. As a simulation tool GEANT4 Monte Carlo code v9.4.p02 is used. When the Balsa wood is inserted in the phantom, the dose measured with EBT film is found to be significantly different from the dose without the EBT film in and beyond the Balsa wood region, particularly for small field sizes. On the other hand, when the soft bone equivalent material is inserted in the phantom, discrepancy between the dose measured with EBT film and the dose without EBT film ca...
Identifying Weak Ties from Publicly Available Social Media Data in an Event
DEFF Research Database (Denmark)
Prakash Gupta, Jayesh; Menon, Karan; Kärkkäinen, Hannu
2016-01-01
or potential weak ties using publicly available social media data in the context of an event. Our case study environment is community managers' online discussions in social media in connection to the yearly-organized Community Manager Appreciation Day (CMAD 2016) event in Finland. We were able to identify...... potential weak ties using the conversation based structural holes, making use of social network analysis methods (like clustering) and content analysis in the context of events. We add to the understanding of and useful data sources for the Strength of weak ties theory originated from Granovetter...
Stolk, C.C.
2004-01-01
A one-way wave equation is an evolution equation in one of the space directions that describes (approximately) a wave field. The exact wave field is approximated in a high frequency, microlocal sense. Here we derive the pseudodifferential one-way wave equation for an inhomogeneous acoustic medium us
Mechano-chemical effects in weakly charged porous media.
Zholkovskij, Emiliy K; Yaroshchuk, Andriy E; Koval'chuk, Volodymyr I; Bondarenko, Mykola P
2015-08-01
The paper is concerned with mechano-chemical effects, namely, osmosis and pressure-driven separation of ions that can be observed when a charged porous medium is placed between two electrolyte solutions. The study is focused on porous systems with low equilibrium interfacial potentials (about 30 mV or lower). At such low potentials, osmosis and pressure-driven separation of ions noticeably manifest themselves provided that the ions in the electrolyte solutions have different diffusion coefficients. The analysis is conducted by combining the irreversible thermodynamic approach and the linearized (in terms of the normalized equilibrium interfacial potential) version of the Standard Electrokinetic Model. Osmosis and the pressure-driven separation of ions are considered for an arbitrary mixed electrolyte solution and various porous space geometries. It is shown that the effects under consideration are proportional to a geometrical factor which, for all the considered geometries of porous space, can be expressed as a function of porosity and the Λ- parameter of porous medium normalized by the Debye length. For all the studied geometries, this function turns out to be weakly dependent on both the porosity and the geometry type. The latter allows for a rough evaluation of the geometrical factor from experimental data on electric conductivity and hydraulic permeability without previous knowledge of the porous space geometry. The obtained results are used to illustrate how the composition of electrolyte solution affects the mechano-chemical effects. For various examples of electrolyte solution compositions, the obtained results are capable of describing positive, negative and anomalous osmosis, positive and negative rejection of binary electrolytes, and pressure-driven separation of binary electrolyte mixtures.
Indian Academy of Sciences (India)
Johannes Breur; Sitabhra Sinha
2005-04-01
Formation of feedback loops of excitation waves (reentrant circuit) around non-conducting ventricular scar tissue is a common cause of cardiac arrhythmias, such as ventricular tachycardia, often leading to death. This is typically treated by rapid stimulation from an implantable device (ICD). However, the mechanisms of reentry termination success and, more importantly, failure, are poorly understood. To study such mechanisms, we simulated pacing termination of reentry in a model of cardiac tissue having significant restitution and dispersion properties. Our results show that rapid pacing dynamically generates conduction inhomogeneities in the reentrant circuit, leading to successful pacing termination of tachycardia. The study suggests that more effective pacing algorithms can be designed by taking into account the role of such dynamical inhomogeneities.
Effective photons in weakly absorptive dielectric media and the Beer-Lambert-Bouguer law
Judge, A C; Bhat, N A R; Sipe, J E; Steel, M J; de Sterke, C Martijn
2013-01-01
We derive effective photon modes that facilitate an intuitive and convenient picture of photon dynamics in a structured Kramers-Kronig dielectric in the limit of weak absorption. Each mode is associated with an effective line-width which determines the temporal decay rate of the photon. These results are then applied to obtain an expression for the Beer-Lambert-Bouguer law absorption coefficient for unidirectional propagation in structured media consisting of dispersive, weakly absorptive dielectric materials.
Inversion assuming weak scattering
DEFF Research Database (Denmark)
Xenaki, Angeliki; Gerstoft, Peter; Mosegaard, Klaus
2013-01-01
The study of weak scattering from inhomogeneous media or interface roughness has long been of interest in sonar applications. In an acoustic backscattering model of a stationary field of volume inhomogeneities, a stochastic description of the field is more useful than a deterministic description...... due to the complex nature of the field. A method based on linear inversion is employed to infer information about the statistical properties of the scattering field from the obtained cross-spectral matrix. A synthetic example based on an active high-frequency sonar demonstrates that the proposed...
Fahrenberger, Florian
2013-01-01
The local approach to computing electrostatic interactions proposed by Maggs and adapted by Pasichnyk for molecular dynamics simulations is extended to situations where the dielectric background medium is inhomogeneous. We furthermore correct a problem of the original algorithm related to the correct treatment of the global dipole moment, provide an error estimate for the accuracy of the algorithm, and suggest a different form of the treatment of the self-energy problem. Our implementation is highly scalable on many cores, and we have validated and compared its performance against theoretical predictions and simulation data obtained by other algorithmic approaches.
Directory of Open Access Journals (Sweden)
N. N. Romanova
1998-01-01
Full Text Available The dynamics of weakly nonlinear wave trains in unstable media is studied. This dynamics is investigated in the framework of a broad class of dynamical systems having a Hamiltonian structure. Two different types of instability are considered. The first one is the instability in a weakly supercritical media. The simplest example of instability of this type is the Kelvin-Helmholtz instability. The second one is the instability due to a weak linear coupling of modes of different nature. The simplest example of a geophysical system where the instability of this and only of this type takes place is the three-layer model of a stratified shear flow with a continuous velocity profile. For both types of instability we obtain nonlinear evolution equations describing the dynamics of wave trains having an unstable spectral interval of wavenumbers. The transformation to appropriate canonical variables turns out to be different for each case, and equations we obtained are different for the two types of instability we considered. Also obtained are evolution equations governing the dynamics of wave trains in weakly subcritical media and in media where modes are coupled in a stable way. Presented results do not depend on a specific physical nature of a medium and refer to a broad class of dynamical systems having the Hamiltonian structure of a special form.
Scatter and Blurring Compensation in Inhomogeneous Media Using a Postprocessing Method
Directory of Open Access Journals (Sweden)
Yan Yan
2008-01-01
Full Text Available An efficient postprocessing method to compensate for the scattering and blurring effects in inhomogeneous medium in SPECT is proposed. A two-dimensional point spread function (2D-PSF was estimated in the image domain to model the combination of these two physical effects. This 2D-PSF in the inhomogeneous medium is fitted with an asymmetric Gaussian function based on Monte Carlo simulation results. An efficient further blurring and deconvolution method was used to restore images from the spatially variant 2D-PSF kernel. The compensation is performed using a computer-simulated NCAT phantom and a flanged Jaszczak experimental phantom. The preliminary results demonstrate an improvement in image quality and quantity accuracy with increased image contrast (25% increase compared to uncompensated image and decreased error (40% decrease compared to uncompensated image. This method also offers an alternative to compensate for scatter and blurring in a more time efficient manner compared to the popular iterative methods. The execution time for this efficient postprocessing method is only a few minutes, which is within the clinically acceptable range.
Steering far-field spin-dependent splitting of light by inhomogeneous anisotropic media
Ling, Xiaohui; Luo, Hailu; Wen, Shuangchun
2012-01-01
An inhomogeneous anisotropic medium with specific structure geometry can apply tunable spin-dependent geometrical phase to the light passing through the medium, and thus can be used to steer the spin-dependent splitting (SDS) of light. In this paper, we exemplify this inference by the $q$-plate, an inhomogeneous anisotropic medium. It is demonstrated that when a linearly polarized light beam normally passes through a $q$-plate, $k$-space SDS first occurs, and then the real-space SDS in the far-field focal plane of a converging lens is distinguishable. Interestingly, the SDS, described by the normalized Stokes parameter $S_3$, shows a multi-lobe and rotatable splitting pattern with rotational symmetry. Further, by tailoring the structure geometry of $q$-plate or/and incident polarization angle of light, the lobe number and the rotation angle both are tunable. Our result suggests that the $q$-plate can serve as potential devices for manipulating the photon spin states and enable applications such as in nano-opt...
Resonant absorption and amplification of circularly-polarized waves in inhomogeneous chiral media
Kim, Seulong
2016-01-01
It has been found that in the media where the dielectric permittivity $\\epsilon$ or the magnetic permeability $\\mu$ is near zero and in transition metamaterials where $\\epsilon$ or $\\mu$ changes from positive to negative values, there occur a strong absorption or amplification of the electromagnetic wave energy in the presence of an infinitesimally small damping or gain and a strong enhancement of the electromagnetic fields. We attribute these phenomena to the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations and its inverse process. In this paper, we study analogous phenomena occurring in chiral media theoretically using the invariant imbedding method. In uniform isotropic chiral media, right-circularly-polarized and left-circularly-polarized waves are the eigenmodes of propagation with different effective refractive indices $n_+$ and $n_-$, whereas in the chiral media with a nonuniform impedance variation, they are no longer the eigenmodes and are coupled to each othe...
Jisha, Chandroth P.; Alberucci, Alessandro; Marrucci, Lorenzo; Assanto, Gaetano
2017-02-01
We discuss the propagation of an electromagnetic field in an inhomogeneously anisotropic material where the optic axis is rotated in the transverse plane but is invariant along the propagation direction. In such a configuration, the evolution of an electromagnetic wave packet is governed by the Pancharatnam-Berry phase (PBP), which is responsible for the appearance of an effective photonic potential. In a recent paper [ACS Photon. 3, 2249 (2016), 10.1021/acsphotonics.6b00700] we demonstrated that the effective potential supports transverse confinement. Here we find the profile of the quasimodes and show that the photonic potential arises from the Kapitza effect of light. The theoretical results are confirmed by numerical simulations, accounting for the medium birefringence. Finally, we analyze in detail a configuration able to support nonleaky guided modes.
Convective instability in inhomogeneous media: impulse response in the subcritical cylinder wake
Marais, Catherine; Barkley, Dwight; Wesfreid, José Eduardo
2010-01-01
We study experimentally the impulse response of a cylinder wake below the critical Reynolds number of the B\\'enard-von K\\'arm\\'an instability. In this subcritical regime, a localized inhomogeneous region of convective instability exists which causes initial perturbations to be transiently amplified. The aim of this work is to quantify the evolution resulting from this convective instability using two-dimensional particle image velocimetry in a hydrodynamic tunnel experiment. The velocity fields allow us to describe the evolution of wave packets in terms of two control parameters: the Reynolds number and the magnitude of the imposed perturbation. The temporal evolution of energy exhibits a transient algebraic growth at short times followed by an exponential decay.
Jisha, Chandroth Pannian; Marrucci, Lorenzo; Assanto, Gaetano
2016-01-01
We discuss the propagation of an electromagnetic field in a inhomogeneously rotated anisotropic material. Rotation is taken invariant along the propagation direction, the latter corresponding to the rotation axis as well. In such a configuration, electromagnetic evolution is dictated by the Pancharatnam-Berry phase (PBP), responsible for the appearance of an effective photonic potential. In the accompanying paper [A. Alberucci et al., "Electromagnetic confinement via spin-orbit interaction in anisotropic dielectrics"] we demonstrate that the effective potential support transverse confinement of light. Here we find the profile of the quasi-modes and we show that the photonic potential arises from the Kapitza effect. Theoretical results are confirmed by numerical simulations, with particular attention to the dependence on the medium birefringence. Finally, we investigate a configuration capable to support non-leaky guided modes.
Berrocal, Edouard; Meglinski, I. V.; Jermy, Mark C.
2005-01-01
Modern optical diagnostics for quantitative characterization of polydisperse sprays and other aerosols which contain a wide range of droplet size encounter difficulties in the dense regions due to the multiple scattering of laser radiation with the surrounding droplets. The accuracy and efficiency of optical measurements can only be improved if the radiative transfer within such polydisperse turbid media is understood. A novel Monte Carlo code has been developed for modeling...
Coherent beam control through inhomogeneous media in multi-photon microscopy
Paudel, Hari Prasad
Multi-photon fluorescence microscopy has become a primary tool for high-resolution deep tissue imaging because of its sensitivity to ballistic excitation photons in comparison to scattered excitation photons. The imaging depth of multi-photon microscopes in tissue imaging is limited primarily by background fluorescence that is generated by scattered light due to the random fluctuations in refractive index inside the media, and by reduced intensity in the ballistic focal volume due to aberrations within the tissue and at its interface. We built two multi-photon adaptive optics (AO) correction systems, one for combating scattering and aberration problems, and another for compensating interface aberrations. For scattering correction a MEMS segmented deformable mirror (SDM) was inserted at a plane conjugate to the objective back-pupil plane. The SDM can pre-compensate for light scattering by coherent combination of the scattered light to make an apparent focus even at a depths where negligible ballistic light remains (i.e. ballistic limit). This problem was approached by investigating the spatial and temporal focusing characteristics of a broad-band light source through strongly scattering media. A new model was developed for coherent focus enhancement through or inside the strongly media based on the initial speckle contrast. A layer of fluorescent beads under a mouse skull was imaged using an iterative coherent beam control method in the prototype two-photon microscope to demonstrate the technique. We also adapted an AO correction system to an existing in three-photon microscope in a collaborator lab at Cornell University. In the second AO correction approach a continuous deformable mirror (CDM) is placed at a plane conjugate to the plane of an interface aberration. We demonstrated that this "Conjugate AO" technique yields a large field-of-view (FOV) advantage in comparison to Pupil AO. Further, we showed that the extended FOV in conjugate AO is maintained over a
Radiative transfer in plane-parallel inhomogeneous media and solar ponds
Energy Technology Data Exchange (ETDEWEB)
Cengel, Y.A.
1984-01-01
The use of Galerkin method is generalized to handle the radiation problems of participating plane-parallel media involving isotropic or anisotropic scattering, space dependent albedo, and Fresnel reflections. The method provides a simple, straightforward approach for solving such radiation problems efficiently with a high degree of accuracy. In this method, the integral form of the equation of radiation transfer is transformed into a set of algebraic equations for the determination of the expansion coefficients associated with the representation of the incident radiation in a power series in the space variable. A step-by-step approach is applied for the development of this method, starting with the relatively simple isotropic scattering constant property problems and generalizing it to the more involved problems of anisotropic scattering and variable properties. In the last section, the radiation problem of solar ponds is analyzed and the solar energy absorption rates are determined.
Goto, Shin-itiro; Walton, Timothy J
2010-01-01
This is paper I of a series of two papers, offering a self-contained analysis of the role of electromagnetic stress-energy-momentum tensors in the classical description of continuous polarizable perfectly insulating media. While acknowledging the primary role played by the total stress-energy-momentum tensor on spacetime, we argue that it is meaningful and useful in the context of covariant constitutive theory to assign preferred status to particular parts of this total tensor, when defined with respect to a particular splitting. The notion of a force density that arises from the divergence of these tensors is strictly defined relative to some inertial property of the medium. Consistency with the laws of Newtonian continuum mechanics demands that the total force density on any element of a medium be proportional to the local linear acceleration field of that element in an inertial frame and must also arise as part of the divergence of the total stress-energy-momentum tensor. In this paper we explore how elect...
Acoustic localization in weakly compressible elastic media containing random air bubbles.
Liang, Bin; Cheng, Jian-chun
2007-01-01
We study theoretically the propagation of longitudinal wave in weakly compressible elastic media containing random air bubbles by using a self-consistent method. By inspecting the scattering cross section of an individual bubble and estimating the mean free paths of the elastic wave propagating in the bubbly weakly compressible media, the mode conversion is numerically proved negligible as the longitudinal wave is scattered by the bubbles. On the basis of the bubble dynamic equation, the wave propagation is solved rigorously with the multiple scattering effects incorporated. In a range of frequency slightly above the bubble resonance frequency, the acoustic localization in such a class of media is theoretically identified with even a very small volume fraction of bubbles. We present a method by analyzing the spatial correlation of wave field to identify the phenomenon of localization, which turns out to be effective. The sensibility of the features of localization to the structure parameters is numerically investigated. The spatial distribution of acoustic energy is also studied and the results show that the waves are trapped within a spatial domain adjacent to the source when localization occurs.
Wang, Dong; Ming, Fei; Huang, Ai-Jun; Sun, Wen-Yang; Ye, Liu
2017-09-01
The uncertainty principle configures a low bound to the measuring precision for a pair of non-commuting observables, and hence is considerably nontrivial to quantum precision measurement in the field of quantum information theory. In this letter, we consider the entropic uncertainty relation (EUR) in the context of quantum memory in a two-qubit isotropic Heisenberg spin chain. Specifically, we explore the dynamics of EUR in a practical scenario, where two associated nodes of a one-dimensional XXX-spin chain, under an inhomogeneous magnetic field, are connected to a thermal entanglement. We show that the temperature and magnetic field effect can lead to the inflation of the measuring uncertainty, stemming from the reduction of systematic quantum correlation. Notably, we reveal that, firstly, the uncertainty is not fully dependent on the observed quantum correlation of the system; secondly, the dynamical behaviors of the measuring uncertainty are relatively distinct with respect to ferromagnetism and antiferromagnetism chains. Meanwhile, we deduce that the measuring uncertainty is dramatically correlated with the mixedness of the system, implying that smaller mixedness tends to reduce the uncertainty. Furthermore, we propose an effective strategy to control the uncertainty of interest by means of quantum weak measurement reversal. Therefore, our work may shed light on the dynamics of the measuring uncertainty in the Heisenberg spin chain, and thus be important to quantum precision measurement in various solid-state systems.
Finite-element method for calculation of the effective permittivity of random inhomogeneous media
Myroshnychenko, Viktor; Brosseau, Christian
2005-01-01
The challenge of designing new solid-state materials from calculations performed with the help of computers applied to models of spatial randomness has attracted an increasing amount of interest in recent years. In particular, dispersions of particles in a host matrix are scientifically and technologically important for a variety of reasons. Herein, we report our development of an efficient computer code to calculate the effective (bulk) permittivity of two-phase disordered composite media consisting of hard circular disks made of a lossless dielectric (permittivity ɛ2 ) randomly placed in a plane made of a lossless homogeneous dielectric (permittivity ɛ1 ) at different surface fractions. Specifically, the method is based on (i) a finite-element description of composites in which both the host and the randomly distributed inclusions are isotropic phases, and (ii) an ordinary Monte Carlo sampling. Periodic boundary conditions are employed throughout the simulation and various numbers of disks have been considered in the calculations. From this systematic study, we show how the number of Monte Carlo steps needed to achieve equilibrated distributions of disks increases monotonically with the surface fraction. Furthermore, a detailed study is made of the dependence of the results on a minimum separation distance between disks. Numerical examples are presented to connect the macroscopic property such as the effective permittivity to microstructural characteristics such as the mean coordination number and radial distribution function. In addition, several approximate effective medium theories, exact bounds, exact results for two-dimensional regular arrays, and the exact dilute limit are used to test and validate the finite-element algorithm. Numerical results indicate that the fourth-order bounds provide an excellent estimate of the effective permittivity for a wide range of surface fractions, in accordance with the fact that the bounds become progressively narrower as
2D spectral element modeling of GPR wave propagation in inhomogeneous media
Zarei, Sajad; Oskooi, Behrooz; Amini, Navid; Dalkhani, Amin Rahimi
2016-10-01
We present a spectral element method, for simulation of ground-penetrating radar (GPR) in two dimensions. The technique is based upon a weak formulation of the equations of Maxwell and combines the flexibility of the elemental-based methods with the accuracy of the spectral based methods. The wave field on the elements is discretized using high-degree Lagrange interpolation and integration over an element is accomplished based upon the Gauss-Lobatto-Legendre integration rule. As a result, the mass matrix and the damping matrix are always diagonal, which drastically reduces the computational cost. We first develop the formulation of 2D spectral element method (SEM) in the time-domain based on Maxwell's equations. The presented formulation is with matrix notation that simplifies the implementation of the relations in computer programs, especially in MATLAB application. We discuss the differences between spectral element method and finite-element method in the time-domain. Also, we show that the SEM numerical dispersion is much lower than FEM. To absorb waves at the edges of the modeling domain, we implement first order Clayton and Engquist absorbing boundary conditions (CE-ABC) introduced in numerical finite-difference modeling of seismic wave propagation. We used the SEM to simulate a complex model to show its abilities and limitations. As well as, one distinct advantage of SEM is that we can easily define our model features in nodal points, because the integration points and the interpolation points are similar that makes it very flexible in simulation of complex models.
Park, Daniel J; Backman, Vadim
2016-01-01
Reflection statistics have not been well studied for optical random media whose mean refractive indices do not match with the refractive indices of their surrounding media. Here, we theoretically study how this refractive index mismatch between a one dimensional (1D) optical sample and its surrounding medium affects the reflection statistics in the weak disorder limit, when the fluctuation part of the refractive index (dn) is much smaller than the mismatch as well as the mean refractive index of the sample (dn ). In the theoretical derivation, we perform a detailed calculation that results in the analytical forms of mean and standard deviation (STD) of the reflectance in terms of disorder parameters (dn and lc) in an index mismatched backscattering system. Particularly, the orders of disorder parameters in STD of the reflectance for index mismatched systems is shown to be lower ( ( lc )^1/2 ) than that of the matched systems ( lc). By comparing STDs of the reflection coefficient of index matched and mismatche...
Michałowski, Tadeusz; Pilarski, Bogusław; Asuero, Agustin G; Dobkowska, Agnieszka; Wybraniec, Sławomir
2011-10-30
The isohydricity (pH constancy) principle is referred to the pair of solutions: weak acid (HL, C(0)mol/L) and strong acid (HB, C mol/L) when mixed e.g., according to titrimetric mode. Such a case takes place if the relation C(0)=C+C(2) × 10(pK(1)) is valid, where pK(1)=-log K(1), K(1) - dissociation constant for a weak monoprotic acid HL. This principle, outlined and formulated in earlier paper (Michałowski et al., Talanta 82 (2010) 1965), is the basis for a sensitive method of pK(1) determination, confirmed for a series of weak acids in presence of basal electrolytes or in water+organic solvent (dimethyl sulphoxide, methanol, isopropanol) media. The results of titrations were elaborated according to principles of regression analysis, with use of least squares method. A new criterion for precision of the results obtained according to this method is formulated. The pK(1) values obtained are comparable with ones found in literature.
Self-averaging and weak ergodicity breaking of diffusion in heterogeneous media
Russian, Anna; Dentz, Marco; Gouze, Philippe
2017-08-01
Diffusion in natural and engineered media is quantified in terms of stochastic models for the heterogeneity-induced fluctuations of particle motion. However, fundamental properties such as ergodicity and self-averaging and their dependence on the disorder distribution are often not known. Here, we investigate these questions for diffusion in quenched disordered media characterized by spatially varying retardation properties, which account for particle retention due to physical or chemical interactions with the medium. We link self-averaging and ergodicity to the disorder sampling efficiency Rn, which quantifies the number of disorder realizations a noise ensemble may sample in a single disorder realization. Diffusion for disorder scenarios characterized by a finite mean transition time is ergodic and self-averaging for any dimension. The strength of the sample to sample fluctuations decreases with increasing spatial dimension. For an infinite mean transition time, particle motion is weakly ergodicity breaking in any dimension because single particles cannot sample the heterogeneity spectrum in finite time. However, even though the noise ensemble is not representative of the single-particle time statistics, subdiffusive motion in q ≥2 dimensions is self-averaging, which means that the noise ensemble in a single realization samples a representative part of the heterogeneity spectrum.
Ryu, Seungoh; Johnson, David L.
2009-03-01
We consider the diffusion-relaxation dynamics in porous media with partially absorbing boundary conditions. Spectral analysis of Helmholtz equation for the uniform boundary condition has been widely used as a probe of geometry of the medium. The NMR relaxation of the fluid magnetization, for example, is used for a variety of media such as rocks, cement, bones, and cheese. While direct relationship between their geometry and the spectrum forms the basis for such applications, little attention has been paid to the spatial variation of the boundary condition. We report on the way the geometry and such inhomogeneity become intertwined and affect the spectrum. It is often impossible to gauge how severe such interference is in the biological or geophysical experiments. We develop a perturbative theory and numerical techniques and test for cases for which exact solution is obtained.
Ryu, Seungoh
2009-08-01
We consider aspects of the population dynamics, inside a bound domain, of diffusing agents carrying an attribute which is stochastically destroyed upon contact with the boundary. The normal mode analysis of the relevant Helmholtz equation under the partially absorbing, but uniform, boundary condition provides a starting framework in understanding detailed evolution dynamics of the attribute in the time domain. In particular, the boundary-localized depletion has been widely employed in practical applications that depend on geometry of various porous media such as rocks, cement, bones, and cheese. While direct relationship between the pore geometry and the diffusion-relaxation spectrum forms the basis for such applications and has been extensively studied, relatively less attention has been paid to the spatial variation in the boundary condition. In this work, we focus on the way the pore geometry and the inhomogeneous depletion strength of the boundary become intertwined and thus obscure the direct relationship between the spectrum and the geometry. It is often impossible to gauge experimentally the degree to which such interference occurs. We fill this gap by perturbatively incorporating classes of spatially varying boundary conditions and derive their consequences that are observable through numerical simulations or controlled experiments on glass bead packs and artificially fabricated porous media. We identify features of the spectrum that are most sensitive to the inhomogeneity, apply the method to the spherical pore with a simple hemispherical binary distribution of the depletion strength, and obtain bounds for the induced change in the slowest relaxation mode.
Pierce, Allan D.
1989-01-01
Transient sound propagation in an inhomogeneous moving medium is considered. For circumstances in which the medium is slowly varying over distances of a wavelength but possibly varying substantially over the propagation distance, a derivation is given of a new wave equation, which implicitly allows for diffraction and scattering and which also is consistent with earlier geometrical acoustics formulations. This wave equation is used as a starting point to derive a version of the Helmholtz-Kirchhoff integral relation that applies to inhomogeneous moving medium. It is suggested that a good approximation to the Green's function that appears in this relation is that derived from geometrical acoustics, the approximation becoming progressively better the shorter the distance between surfaces in the computation. It should also be at least as good as conventional ray acoustics, but can account for diffraction effects, such as at caustics.
Optimal Acoustic Attenuation of Weakly Compressible Media Permeated with Air Bubbles
Institute of Scientific and Technical Information of China (English)
LIANG Bin; CHENG Jian-Chun
2007-01-01
Based on fuzzy logic (FL) and genetic algorithm (GA), we present an optimization method to obtain the optimal acoustic attenuation of a longitudinal acoustic wave propagating in a weakly compressible medium permeated with air bubbles. In the optimization, the parameters of the size distribution of bubbles in the medium are optimized for providing uniformly high acoustic attenuation in the frequency band of interest. Compared with other traditional optimization methods, the unique advantage of the present method is that it can locate the global optimum quickly and effectively in need of knowing the mathematical model precisely. As illustrated by a numerical simulation, the method is effective and essential in enhancing the acoustic attenuation of such a medium in an optimal manner. The bubbly medium with optimized structural parameters can effectively attenuate longitudinal waves at intermediate frequencies with an acoustic attenuation approximating a constant value of 10(dB/cm). Such bubbly media with optimal acoustic attenuations may be applied to design acoustic absorbent by controlling broader attenuation band and higher efficiency.
Rumyantseva, O. D.; Shurup, A. S.
2017-01-01
The paper considers the derivation of the wave equation and Helmholtz equation for solving the tomographic problem of reconstruction combined scalar-vector inhomogeneities describing perturbations of the sound velocity and absorption, the vector field of flows, and perturbations of the density of the medium. Restrictive conditions under which the obtained equations are meaningful are analyzed. Results of numerical simulation of the two-dimensional functional-analytical Novikov-Agaltsov algorithm for reconstructing the flow velocity using the the obtained Helmholtz equation are presented.
Karabash, Illya M
2011-01-01
The paper is devoted to optimization of quasi-normal eigenvalues of a spectral problem associated with a 1-D wave equation in an inhomogeneous medium. The wave equation is equipped with a radiation boundary condition, and so the set of quasi-normal eigenvalues lies in $\\C_+$. The problem is to design for a given $\\alpha \\in \\R$ the structure of the inhomogeneous medium such that it generates a quasi-normal eigenvalue on the line $\\alpha + \\i \\R$ with a minimal possible imaginary part. We consider the problem for three admissible families of structures. Two of these families have a natural mechanical interpretation as classes of Krein strings with total mass and static moment constraints. For these two classes we find optimal quasi-normal eigenvalues explicitly. The third class of admissible structures is connected with the problem of optimal design for photonic crystals. For this class, the paper gives a wider statement of the optimization problem, proves existence of optimal structures, and study their prope...
2010-01-08
and A. S. Fokas, Complex Variables: Introduction and Applications. NY, USA: Cam- ridge University Press, 1997. 47. K. A. Michalski and J. R. Mosig...G. Alexopoulos, “Real Axis Integration of Sommerfeld Inetgrals,” Jour. Math. Phys., vol. 24, no. 3, pp. 527-533, March 1983. 57. K. A. Michalski ...Methods for Electromagnetic and Elastic Waves. USA: Morgan & Claypool, 2009. A2. K. A. Michalski and J. R. Mosig, “Multilayered Media Green’s Functions
Controlling Spiral Dynamics in Excitable Media by a Weakly Localized Pacing
Institute of Scientific and Technical Information of China (English)
LI Bing-Wei; SUN Li-Li; CHEN Bin; YING He-Ping
2007-01-01
@@ Spiral dynamics controlled by a weakly localized pacing around the spiral tip is investigated. Numerical simulations show two distinct characteristics when the pacing is applied with the weak amplitude for suitable frequencies:for a rigidly rotating spiral, a transition from rigid rotation to meandering motion is observed, and for unstable spiral waves, spiral breakup can be prevented. Successfully preventing spiral breakup is relevant to the modulation of the tip trajectory induced by a localized pacing.
Kartashova, Elena
2013-01-01
In this Letter we study the form of the energy spectrum of Riemann waves in weakly nonlinear non-dispersive media. For quadratic and cubic nonlinearity we demonstrate that the deformation of an Riemann wave over time yields an exponential energy spectrum which turns into power law asymptotic with the slope being approximately -8/3 at the last stage of evolution before breaking. We argue, that this is the universal asymptotic behaviour of Riemann waves in any nonlinear non-dispersive medium at the point of breaking. The results reported in this Letter can be used in various non-dispersive media, e.g. magneto-hydro dynamics, physical oceanography, nonlinear acoustics.
Global existence of weak solution to the heat and moisture transport system in fibrous porous media
Li, Buyang; Wang, Yi
2009-01-01
This paper is concerned with theoretical analysis of a heat and moisture transfer model arising from textile industries, which is described by a degenerate and strongly coupled parabolic system. We prove the global (in time) existence of weak solution by constructing an approximate solution with some standard smoothing. The proof is based on the physcial nature of gas convection, in which the heat (energy) flux in convection is determined by the mass (vapor) flux in convection.
Pradhan, Prabhakar; Sahay, Peeyush; Almabadi, Huda M.
2016-01-01
Considering the complex reflection amplitude R=|R|exp(i{\\theta}) of a light wave, real delay time {\\tau}_r (i.e., sojourn or Wigner delay time), which is the energy derivative of the real phase ({\\tau}_r =d{\\theta}/cdk), and complex delay time {\\tau}_i , which is the energy derivative of the reflection coefficient ({\\tau}_i=d{\\theta}_i/cdk, |R|=r^1/2=exp(-{\\theta}_i)), have the same statistical form and a mirror image with a shift in time in weak disorder and short length regime. Real delay t...
Social features of online networks: the strength of weak ties in online social media
Grabowicz, Przemyslaw A; Moro, Esteban; Pujol, Josep; Eguiluz, Victor M
2011-01-01
An increasing fraction of today social interactions occurs using online social media as communication channels. Recent worldwide events, such as the revolts in Middle East or the recent social movements in Spain, reflect their capacity to boost people coordination. Online networks display, in general, a rich internal structure where users can choose among different types and intensity of interactions. Despite of this and their growing popularity, there are still open questions regarding the social value of online relations. For example, the existence of users with thousands or millions of online friends sheds doubts on the relevance of these connections. In this work, we focus on Twitter, one of the most popular online social networks, and find that the network formed by the basic type of relations is organized in groups. The activity of the users in the network is related to the landscape determined by such groups. Twitter's distinction between different types o interactions allows us to establish a parallel...
Institute of Scientific and Technical Information of China (English)
GUO Lei; NIE GuoHua
2008-01-01
This paper presents an analytical solution for the elastic fields induced by non-elastic eigenstrains in a plane elliptical inhomogeneity embedded in the orthotropic matrix under tension at infinity and inclined at any angle. The conformal transformation and complex function method for the snisotropic elastic material were used to determine the strain energies in the inhomogeneity and matrix, which were expressed by four undetermined coefficients characterizing the equilibrium boundary of the inhomogeneity due to the acting eigenstrains and external load. The use of the principle of the minimum potential energy led to analytical expres-sions for these coefficients and thus generated a closed-form solution for the elas-tic strain/stress fields. The resulting stress field in the inhomogeneity was exam-ined and verified by checking the continuity conditions for the normal and shear stresses on the interior boundary of the matrix.
Institute of Scientific and Technical Information of China (English)
2008-01-01
This paper presents an analytical solution for the elastic fields induced by non-elastic eigenstrains in a plane elliptical inhomogeneity embedded in the orthotropic matrix under tension at infinity and inclined at any angle. The conformal transformation and complex function method for the anisotropic elastic material were used to determine the strain energies in the inhomogeneity and matrix, which were expressed by four undetermined coefficients characterizing the equilibrium boundary of the inhomogeneity due to the acting eigenstrains and external load. The use of the principle of the minimum potential energy led to analytical expres-sions for these coefficients and thus generated a closed-form solution for the elas-tic strain/stress fields. The resulting stress field in the inhomogeneity was exam-ined and verified by checking the continuity conditions for the normal and shear stresses on the interior boundary of the matrix.
MHD Jets in inhomogeneous media
Directory of Open Access Journals (Sweden)
S. O´Sullivan
2002-01-01
Full Text Available Presentamos simulaciones de la propagaci on de jets moleculares no-adiab aticos en un medio ambiente inhomog eneo. Los jets tienen condiciones descritos por un modelo de jet MHD en el cual la forma de las l neas magn eticas se prescribe cerca de la fuente. Per les de densidad ambiental fueron elegidos para representar la zona de transici on entre las regiones exteriores de una nube molecular y el medio interestelar. Escalamos las tasas de enfriamiento at omico y molecular a niveles apropriados para resolver todas las escalas espaciales apropriadas. Con la inclusi on de variabilidad de la fuente, las simulaciones reproducen varias caracter sticas observacionales de jets moleculares, entre ellas las cavidades moleculares. Adicionalmente, encontramos similitudes entre teor a y observaci on para la fracci on de ionizaci on a lo largo del jet. Encontramos que la extensi on lateral de las super cies de trabajo internas son sensibles al medio ambiente. Tambi en presentamos resultados preliminares para un m etodo de calcular mapas de emisi on en l neas usando solamente variables fundamentales de estado que parecen reproducir la emisi on lamentosa de Balmer en frentes de choque.
Inhomogeneous anisotropic cosmology
Energy Technology Data Exchange (ETDEWEB)
Kleban, Matthew [Center for Cosmology and Particle Physics, New York University,4 Washington Place, New York, NY 10003 (United States); Senatore, Leonardo [Stanford Institute for Theoretical Physics and Department of Physics, Stanford University,382 Via Pueblo Mall, Stanford, CA 94306 (United States); Kavli Institute for Particle Astrophysics and Cosmology, Stanford University and SLAC,2575 Sand Hill Road, M/S 29, Menlo Park, CA 94025 (United States)
2016-10-12
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with “flat” (including toroidal) and “open” (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are “flat” or “open”. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with “flat” or “open” topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Inhomogeneous anisotropic cosmology
Kleban, Matthew; Senatore, Leonardo
2016-10-01
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with ``flat'' (including toroidal) and ``open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are ``flat'' or ``open''. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with ``flat'' or ``open'' topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Inhomogeneous Big Bang Cosmology
Wagh, S M
2002-01-01
In this letter, we outline an inhomogeneous model of the Big Bang cosmology. For the inhomogeneous spacetime used here, the universe originates in the infinite past as the one dominated by vacuum energy and ends in the infinite future as the one consisting of "hot and relativistic" matter. The spatial distribution of matter in the considered inhomogeneous spacetime is {\\em arbitrary}. Hence, observed structures can arise in this cosmology from suitable "initial" density contrast. Different problems of the standard model of Big Bang cosmology are also resolved in the present inhomogeneous model. This inhomogeneous model of the Big Bang Cosmology predicts "hot death" for the universe.
Escher, Joachim; Matioc, Bogdan-Vasile
2011-01-01
We prove global existence of nonnegative weak solutions to a degenerate parabolic system which models the interaction of two thin fluid films in a porous medium. Furthermore, we show that these weak solutions converge at an exponential rate towards flat equilibria.
Moving inhomogeneous envelopes of stars
Oskinova, Lidia M; Hamann, Wolf-Rainer
2016-01-01
Massive stars are extremely luminous and drive strong winds, blowing a large part of their matter into the galactic environment before they finally explode as a supernova. Quantitative knowledge of massive star feedback is required to understand our Universe as we see it. Traditionally, massive stars have been studied under the assumption that their winds are homogeneous and stationary, largely relying on the Sobolev approximation. However, observations with the newest instruments, together with progress in model calculations, ultimately dictate a cardinal change of this paradigm: stellar winds are highly inhomogeneous. Hence, we are now advancing to a new stage in our understanding of stellar winds. Using the foundations laid by V.V. Sobolev and his school, we now update and further develop the stellar spectral analysis techniques. New sophisticated 3-D models of radiation transfer in inhomogeneous expanding media elucidate the physics of stellar winds and improve classical empiric mass-loss rate diagnostics...
Full-wave solution of short impulses in inhomogeneous plasma
Indian Academy of Sciences (India)
Orsolya E Ferencz
2005-02-01
In this paper the problem of real impulse propagation in arbitrarily inhomogeneous media will be presented on a fundamentally new, general, theoretical way. The general problem of wave propagation of monochromatic signals in inhomogeneous media was enlightened in [1]. The earlier theoretical models for spatial inhomogeneities have some errors regarding the structure of the resultant signal originated from backward and forward propagating parts. The application of the method of inhomogeneous basic modes (MIBM) and the complete full-wave solution of arbitrarily shaped non-monochromatic plane waves in plasmas made it possible to obtain a better description of the problem, on a fully analytical way, directly from Maxwell's equations. The model investigated in this paper is inhomogeneous of arbitrary order (while the wave pattern can exist), anisotropic (magnetized), linear, cold plasma, in which the gradient of the one-dimensional spatial inhomogeneity is parallel to the direction of propagation.
Lai, H. M.; Chan, S. W.
2002-05-01
Applying Artmann's formula to a light beam in the TM state of wave polarization, we show analytically the existence of a large and negative Goos-Hanchen shift near the angle of the Brewster dip on reflection from a weakly absorbing semi-infinite medium. The shift is opposite that in the case of total internal reflection, and it can be an order of magnitude larger than a wavelength if the absorption of the reflecting medium is sufficiently weak. Examples are given, and the detectibility of the shift is discussed.
Lai, H M; Chan, S W
2002-05-01
Applying Artmann's formula to a light beam in the TM state of wave polarization, we show analytically the existence of a large and negative Goos-Hänchen shift near the angle of the Brewster dip on reflection from a weakly absorbing semi-infinite medium. The shift is opposite that in the case of total internal reflection, and it can be an order of magnitude larger than a wavelength if the absorption of the reflecting medium is sufficiently weak. Examples are given, and the detectibility of the shift is discussed.
No hair theorem for inhomogeneous cosmologies
Energy Technology Data Exchange (ETDEWEB)
Jensen, L.G.; Stein-Schabes, J.A.
1986-03-01
We show that under very general conditions any inhomogeneous cosmological model with a positive cosmological constant, that can be described in a synchronous reference system will tend asymptotically in time towards the de Sitter solution. This is shown to be relevant in the context of inflationary models as it makes inflation very weakly dependent on initial conditions. 8 refs.
Spectroscopic properties of inhomogeneously broadened spin ensembles in a cavity
DEFF Research Database (Denmark)
Kurucz, Zoltan; Wesenberg, Janus; Mølmer, Klaus
2011-01-01
The enhanced collective coupling to weak quantum fields may turn atomic or spin ensembles into an important component in quantum information processing architectures. Inhomogeneous broadening can, however, significantly reduce the coupling and the lifetime of the collective excitation...
Anand, Akash; Pandey, Ambuj; Rathish Kumar, B. V.; Paul, Jagabandhu
2016-04-01
This text proposes a fast, rapidly convergent Nyström method for the solution of the Lippmann-Schwinger integral equation that mathematically models the scattering of time-harmonic acoustic waves by inhomogeneous obstacles, while allowing the material properties to jump across the interface. The method works with overlapping coordinate charts as a description of the given scatterer. In particular, it employs "partitions of unity" to simplify the implementation of high-order quadratures along with suitable changes of parametric variables to analytically resolve the singularities present in the integral operator to achieve desired accuracies in approximations. To deal with the discontinuous material interface in a high-order manner, a specialized quadrature is used in the boundary region. The approach further utilizes an FFT based strategy that uses equivalent source approximations to accelerate the evaluation of large number of interactions that arise in the approximation of the volumetric integral operator and thus achieves a reduced computational complexity of O (Nlog N) for an N-point discretization. A detailed discussion on the solution methodology along with a variety of numerical experiments to exemplify its performance are presented in this paper.
Institute of Scientific and Technical Information of China (English)
LI Zhong-Hua; LI Yuan; DOU Ya-Fang; GAO Jiang-Rui; ZHANG Jun-Xiang
2012-01-01
The output amplitude noises of one squeezed probe light which is at resonance throughout different optical depths media in strong- and weak-coupling-Seld regimes are investigated theoretically. By comparing the output quantum noises for different Rabi frequencies of coupling field and also for different optical depths, it is found that the optimal squeezing preservation of the probe light occurs in an optically thin medium with strong-coupling-field, where we can obtain the output squeezing ciose to the input one at nonzero detection frequency.%The output amplitude noises of one squeezed probe light which is at resonance throughout different optical depths media in strong- and weak-coupling-field regimes are investigated theoretically.By comparing the output quantum noises for different Rabi frequencies of coupling field and also for different optical depths,it is found that the optimal squeezing preservation of the probe light occurs in an optically thin medium with strong-coupling-field,where we can obtain the output squeezing close to the input one at nonzero detection frequency.
Malkov, M A
1996-01-01
The asymptotic travelling wave solution of the KdV-Burgers equation driven by the long scale periodic driver is constructed. The solution represents a shock-train in which the quasi-periodic sequence of dispersive shocks or soliton chains is interspersed by smoothly varying regions. It is shown that the periodic solution which has the spatial driver period undergoes period doublings as the governing parameter changes. Two types of chaotic behavior are considered. The first type is a weak chaos, where only a small chaotic deviation from the periodic solution occurs. The second type corresponds to the developed chaos where the solution ``ignores'' the driver period and represents a random sequence of uncorrelated shocks. In the case of weak chaos the shock coordinate being repeatedly mapped over the driver period moves on a chaotic attractor, while in the case of developed chaos it moves on a repellor. Both solutions depend on a parameter indicating the reference shock position in the shock-train. The structure...
Energy Technology Data Exchange (ETDEWEB)
Nishizawa, O.; Sato, T. [Geological Survey of Japan, Tsukuba (Japan); Lei, X. [Dia Consultants Company, Tokyo (Japan)
1996-05-01
In the study of seismic wave propagation, a model experimenting technique has been developed using a laser Doppler velocimeter (LDV) as the sensor. This technique, not dependent on conventional piezoelectric devices, only irradiates the specimen with laser to measure the velocity amplitude on the target surface, eliminating the need for close contact between the specimen and sensor. In the experiment, elastic penetration waves with their noise levels approximately 0.05mm/s were observed upon application of vibration of 10{sup 6}-10{sup 5}Hz. The specimen was stainless steel or rock, and waveforms caught by the LDV and piezoelectric device were compared. As the result, it was found that the LDV is a powerful tool for effectively explaining elastic wave propagation in inhomogeneous media. The piezoelectric device fails to reproduce accurately the waves to follow the initial one while the LDV detect the velocity amplitude on the specimen surface in a wide frequency range encouraging the discussion over the quantification of observed waveforms. 10 refs., 7 figs.
Inhomogeneous electromagnetic gravitational collapse
Energy Technology Data Exchange (ETDEWEB)
Stein-Schabes, J.A.
1985-04-15
The collapse of an inhomogeneous dust cloud in the presence of an electromagnetic field is investigated in detail. The possibility of a naked singularity arising is studied using some known solutions for a spherical charged inhomogeneous dust cloud. It is found that locally naked singularities may develop when the arbitrary functions in the solution are chosen in a special way, but that a global naked singularity will not form. Also the role of the electromagnetic pressure is discussed.
Inhomogeneous Polyakov loop induced by inhomogeneous chiral condensates
Directory of Open Access Journals (Sweden)
Tomoya Hayata
2015-05-01
Full Text Available 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.
Inhomogeneous Polyakov loop induced by inhomogeneous chiral condensates
Energy Technology Data Exchange (ETDEWEB)
Hayata, Tomoya, E-mail: hayata@riken.jp [Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Theoretical Research Division, Nishina Center, RIKEN, Wako, Saitama 351-0198 (Japan); Yamamoto, Arata [Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Theoretical Research Division, Nishina Center, RIKEN, Wako, Saitama 351-0198 (Japan)
2015-05-11
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.
Haspot, Boris
2016-06-01
We consider the compressible Navier-Stokes equations for viscous and barotropic fluids with density dependent viscosity. The aim is to investigate mathematical properties of solutions of the Navier-Stokes equations using solutions of the pressureless Navier-Stokes equations, that we call quasi solutions. This regime corresponds to the limit of highly compressible flows. In this paper we are interested in proving the announced result in Haspot (Proceedings of the 14th international conference on hyperbolic problems held in Padova, pp 667-674, 2014) concerning the existence of global weak solution for the quasi-solutions, we also observe that for some choice of initial data (irrotationnal) the quasi solutions verify the porous media, the heat equation or the fast diffusion equations in function of the structure of the viscosity coefficients. In particular it implies that it exists classical quasi-solutions in the sense that they are {C^{∞}} on {(0,T)× {R}N} for any {T > 0}. Finally we show the convergence of the global weak solution of compressible Navier-Stokes equations to the quasi solutions in the case of a vanishing pressure limit process. In particular for highly compressible equations the speed of propagation of the density is quasi finite when the viscosity corresponds to {μ(ρ)=ρ^{α}} with {α > 1}. Furthermore the density is not far from converging asymptotically in time to the Barrenblatt solution of mass the initial density {ρ0}.
Synchronized Firing in Coupled Inhomogeneous Excitable Neurons
Institute of Scientific and Technical Information of China (English)
ZHENG Zhi-Gang; WANG Fu-Zhong
2002-01-01
We study the firing synchronization behavior of the inhomogeneous excitable media. Phase synchronizationof neuron firings is observed with increasing the coupling, while the phases of neurons are different (out-of-phase synchronization). We found the synchronization of bursts can be greatly enhanced by applying an external forcing (in-phasesynchronization). The external forcing can be either a periodic or just homogeneous thermal noise. The mechanismresponsible for this enhancement is discussed.PACS numbers: 05.45.-a, 87.10.+e
Wakes in inhomogeneous plasmas
Kompaneets, Roman; Nosenko, Vladimir; Morfill, Gregor E
2014-01-01
The Debye shielding of a charge immersed in a flowing plasma is an old classic problem in plasma physics. 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 non-oscillatory and weaker.
Crisp, D J; W Moran; Pollington, A. D.
2012-01-01
We show that the inhomogenous approximation spectrum, associated to an irrational number \\alpha\\ always has a Hall's Ray; that is, there is an \\epsilon>0 such that [0,\\epsilon) is a subset of the spectrum. In the case when \\alpha\\ has unbounded partial quotients we show that the spectrum is just a ray.
Chemical inhomogeneities and pulsation
Turcotte, S
2001-01-01
Major improvements in models of chemically peculiar stars have been achieved in the past few years. With these new models it has been possible to test quantitatively some of the processes involved in the formation of abundance anomalies and their effect on stellar structure. The models of metallic A (Am) stars have shown that a much deeper mixing has to be present to account for observed abundance anomalies. This has implications on their variability, which these models also reproduce qualitatively. These models also have implications for other chemically inhomogeneous stars such as HgMn B stars which are not known to be variable and lambda Bootis stars which can be. The study of the variability of chemically inhomogeneous stars can provide unique information on the dynamic processes occurring in many types of stars in addition to modeling of the evolution of their surface composition.
SAINI, CHITRA; ,
2015-01-01
The advent of social media has led to Luxury brands increasingly turning to social media sites to build brand value. Understanding the discussions that happen on social media is therefore a key for the marketing managers of luxury brands. There are two prominent methodologies which have been used widely in the literature to study consumer conversations on social media, these two methodologies are Text Mining and Netnography. In this study I will compare and contrast both these methodologies t...
Moffat, J W
2016-01-01
An alternative to the postulate of dark energy required to explain the accelerated expansion of the universe is to adopt an inhomogeneous cosmological model to explain the supernovae data without dark energy. We adopt a void cosmology model, based on the inhomogeneous Lema\\^{i}tre-Tolman-Bondi solution of Einstein's field equations. The model can resolve observational anomalies in the $\\Lambda CDM$ model, such as the discrepancy between the locally measured value of the Hubble constant, $H_0=73.24\\pm 1.74\\,{\\rm km}\\,{\\rm s}^{-1}\\,{\\rm Mpc}^{-1}$, and the $H_0=66.93\\pm 0.62\\,{\\rm km}\\,{\\rm s}^{-1}\\,{\\rm Mpc}^{-1}$ determined by the Planck satellite data and the $\\Lambda CDM$ model, and the lithium $^{7}{\\rm Li}$ problem, which is a $5\\sigma$ mismatch between the theoretical prediction for the $^{7}{\\rm Li}$ from big bang nucleosynthesis and the value that we observe locally today at $z=0$. The void model can also resolve the tension between the number of massive clusters derived from the Sunyaev-Zel'dovich eff...
Indian Academy of Sciences (India)
K D Patil; S H Ghate; R V Saraykar
2001-04-01
We consider a collapsing spherically symmetric inhomogeneous dust cloud in higher dimensional space-time. We show that the central singularity of collapse can be a strong curvature or a weak curvature naked singularity depending on the initial density distribution.
Green's function for a prestressed thermoelastic half-space with an inhomogeneous coating
Belyankova, T. I.; Kalinchuk, V. V.
2016-09-01
A mathematical model is developed for an inhomogeneous thermoelastic prestressed half-space consisting of a stack of homogeneous or functionally graded layers rigidly attached to a homogeneous base. Each component of the inhomogeneous medium is subjected to initial mechanical stresses and temperature. Successive linearization of the constitutive relations of the nonlinear mechanics of a thermoelastic medium is performed using the theory of superposition of small deformations on finite deformations with the inhomogeneity of the medium taken into account. Integral formulas are derived to explore dynamic processes in inhomogeneous prestressed thermoelastic media.
Inhomogeneous Thermal Quenches
Sohrabi, Kiyoumars A
2015-01-01
We describe holographic thermal quenches that are inhomogeneous in space. The main characteristic of the quench is to take the system far from its equilibrium configuration. Except special extreme cases, the problem has no analytic solution. Using the numerical holography methods, we study different observables that measure thermalization such as the time evolution of the horizon, two-point Wightman function and entanglement entropy (EE). Having an extra nontrivial spacial direction, allows us to study this peculiar generalization since we categorize the problem based on whether we do the measurements along this special direction or perpendicular to it. Exciting new features appear that are absent in the common computations in the literature, the appearance of negative EE valleys surrounding the positive EE hills and abrupt quenches that occupy the whole space at their universal limit are some of the results of this paper. We have tried to provide physical explanations wherever possible. The physical picture ...
Effective wavefield extrapolation in anisotropic media: Accounting for resolvable anisotropy
Alkhalifah, Tariq Ali
2014-04-30
Spectral methods provide artefact-free and generally dispersion-free wavefield extrapolation in anisotropic media. Their apparent weakness is in accessing the medium-inhomogeneity information in an efficient manner. This is usually handled through a velocity-weighted summation (interpolation) of representative constant-velocity extrapolated wavefields, with the number of these extrapolations controlled by the effective rank of the original mixed-domain operator or, more specifically, by the complexity of the velocity model. Conversely, with pseudo-spectral methods, because only the space derivatives are handled in the wavenumber domain, we obtain relatively efficient access to the inhomogeneity in isotropic media, but we often resort to weak approximations to handle the anisotropy efficiently. Utilizing perturbation theory, I isolate the contribution of anisotropy to the wavefield extrapolation process. This allows us to factorize as much of the inhomogeneity in the anisotropic parameters as possible out of the spectral implementation, yielding effectively a pseudo-spectral formulation. This is particularly true if the inhomogeneity of the dimensionless anisotropic parameters are mild compared with the velocity (i.e., factorized anisotropic media). I improve on the accuracy by using the Shanks transformation to incorporate a denominator in the expansion that predicts the higher-order omitted terms; thus, we deal with fewer terms for a high level of accuracy. In fact, when we use this new separation-based implementation, the anisotropy correction to the extrapolation can be applied separately as a residual operation, which provides a tool for anisotropic parameter sensitivity analysis. The accuracy of the approximation is high, as demonstrated in a complex tilted transversely isotropic model. © 2014 European Association of Geoscientists & Engineers.
Weak Convergence and Weak Convergence
Directory of Open Access Journals (Sweden)
Narita Keiko
2015-09-01
Full Text Available In this article, we deal with weak convergence on sequences in real normed spaces, and weak* convergence on sequences in dual spaces of real normed spaces. In the first section, we proved some topological properties of dual spaces of real normed spaces. We used these theorems for proofs of Section 3. In Section 2, we defined weak convergence and weak* convergence, and proved some properties. By RNS_Real Mizar functor, real normed spaces as real number spaces already defined in the article [18], we regarded sequences of real numbers as sequences of RNS_Real. So we proved the last theorem in this section using the theorem (8 from [25]. In Section 3, we defined weak sequential compactness of real normed spaces. We showed some lemmas for the proof and proved the theorem of weak sequential compactness of reflexive real Banach spaces. We referred to [36], [23], [24] and [3] in the formalization.
Nonlinear acoustic waves in micro-inhomogeneous solids
Nazarov, Veniamin
2014-01-01
Nonlinear Acoustic Waves in Micro-inhomogeneous Solids covers the broad and dynamic branch of nonlinear acoustics, presenting a wide variety of different phenomena from both experimental and theoretical perspectives. The introductory chapters, written in the style of graduate-level textbook, present a review of the main achievements of classic nonlinear acoustics of homogeneous media. This enables readers to gain insight into nonlinear wave processes in homogeneous and micro-inhomogeneous solids and compare it within the framework of the book. The subsequent eight chapters covering: Physical m
Simple inhomogeneous cosmological (toy) models
I., Eddy G Chirinos; Zimdahl, Winfried
2016-01-01
Based on the Lema\\^itre-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 provides a better description of the observations than a local void. Future redshift-drift measurements are discussed as a promising tool to discriminate between inhomogeneous configurations and the $\\Lambda$CDM model.
Supramolecular polymers in inhomogeneous systems
Zweistra, H.J.A.
2007-01-01
This thesis describes theoretical results of supramolecular polymers in inhomogeneous systems. Supramolecular polymers are linear assemblies of which the monomers are joined by reversible bonds. Many types of supramolecular polymers have been synthesized in recent years. Moreover, there are numerous
Modelling Inhomogeneity in the Universe
Hellaby, Charles
2009-01-01
An overview of some recent developments in inhomogeneous models is presented. As the volume and precision of cosmological data improves, it will become more and more essential to understand the non-linear behaviour of the Einstein field equations. This requires the study of exact inhomogeneous solutions, including their density distributions, their evolution, their geometry, and their causal structure. Observations are strongly affected by the detailed geometry and evolution of a model, and therefore interpretation of observations depends on understanding them. It is generally assumed the universe is homogeneous if averaged over large enough scales, but to actually prove this is so, will require the assumption to be relaxed, and a rigorous inhomogeneous approach to be applied. Though the \\LT metric has long been used for models of spherical inhomogeneities, there have been a number of new results, including a variety of methods for creating models with specific properties, and their application to cosmic stru...
Inclusions and inhomogeneities under stress
CSIR Research Space (South Africa)
Nabarro, FRN
1996-02-01
Full Text Available Some general theorems, new and old, concerning the behaviour of elastic inclusions and inhomogeneities in bodies without or with external stress, are assembled. The principal new result is that arbitrary external tractions cannot influence the shape...
The Noncommutative Inhomogeneous Hopf Algebra
Lagraa, M
1997-01-01
From the bicovariant first order differential calculus over inhomogeneous Hopf algebra B we construct the set of right-invariant Maurer Cartan one-forms considered as a right-invariant basis of a bicovariant B-bimodule over which we develope the Woronowicz'general theory differential calculus on quantum groups. In this context, we derive the inhomogeneous commutation rules and investigate the properties of their different terms.
The Noncommutative Inhomogeneous Hopf Algebra
1997-01-01
From the bicovariant first order differential calculus on inhomogeneous Hopf algebra ${\\cal B}$ we construct the set of right-invariant Maurer-Cartan one-forms considered as a right-invariant basis of a bicovariant ${\\cal B}$-bimodule over which we develop the Woronowicz's general theory of differential calculus on quantum groups. In this formalism, we introduce suitable functionals on ${\\cal B}$ which control the inhomogeneous commutation rules. In particular we find that the homogeneous par...
Without the weak force, the sun wouldn't shine. The weak force causes beta decay, a form of radioactivity that triggers nuclear fusion in the heart of the sun. The weak force is unlike other forces: it is characterised by disintegration. In beta decay, a down quark transforms into an up quark and an electron is emitted. Some materials are more radioactive than others because the delicate balance between the strong force and the weak force varies depending on the number of particles in the atomic nucleus. We live in the midst of a natural radioactive background that varies from region to region. For example, in Cornwall where there is a lot of granite, levels of background radiation are much higher than in the Geneva region. Text for the interactive: Move the Geiger counter to find out which samples are radioactive - you may be surprised. It is the weak force that is responsible for the Beta radioactivity here. The electrons emitted do not cross the plastic cover. Why do you think there is some detected radioa...
Quantizing polaritons in inhomogeneous dissipative systems
Drezet, Aurélien
2017-02-01
In this article we provide a general analysis of canonical quantization for polaritons in dispersive and dissipative electromagnetic inhomogeneous media. We compare several approaches based either on the Huttner-Barnett model [B. Huttner and S. M. Barnett, Phys. Rev. A 46, 4306 (1992), 10.1103/PhysRevA.46.4306] or the Green function, Langevin-noise method [T. Gruner and D.-G. Welsch, Phys. Rev. A 53, 1818 (1996), 10.1103/PhysRevA.53.1818] which includes only material oscillators as fundamental variables. We show that in order to preserve unitarity, causality, and time symmetry, one must necessarily include with an equal footing both electromagnetic modes and material fluctuations in the evolution equations. This becomes particularly relevant for all nanophotonics and plasmonics problems involving spatially localized antennas or devices.
Effective inhomogeneous inflation: curvature inhomogeneities of the Einstein vacuum
Energy Technology Data Exchange (ETDEWEB)
Buchert, Thomas [Universite Lyon 1, Centre de Recherche Astrophysique de Lyon, 9 Avenue Charles Andre, F-69230 Saint-Genis-Laval (France); Obadia, Nathaniel, E-mail: buchert@obs.univ-lyon1.fr, E-mail: nathaniel.obadia@ens-lyon.fr [Ecole Normale Superieure de Lyon, Centre de Recherche Astrophysique de Lyon, 46 Allee d' Italie, F-69364 Lyon Cedex 07 (France)
2011-08-21
We consider spatially averaged inhomogeneous universe models and argue that, already in the absence of sources, an effective scalar field arises through foliating and spatially averaging inhomogeneous geometrical curvature invariants of the Einstein vacuum. This scalar field (the 'morphon') acts as an inflaton, if we prescribe a potential of some generic form. We show that, for any initially negative average spatial curvature, the morphon is driven through an inflationary phase and leads-on average-to a spatially flat, homogeneous and isotropic universe model, providing initial conditions for pre-heating and, by the same mechanism, a possibly natural self-exit. (fast track communication)
Manifestations of Magnetic Field Inhomogeneities
Indian Academy of Sciences (India)
Lawrence Rudnick
2011-12-01
Both observations and simulations reveal large inhomogeneities in magnetic field distributions in diffuse plasmas. Incorporating these inhomogeneities into various calculations can significantly change the inferred physical conditions. In extragalactic sources, e.g., these can compromise analyses of spectral ageing, which I will illustrate with some current work on cluster relics. I also briefly re-examine the old issue of how inhomogeneous fields affect particle lifetimes; perhaps not surprisingly, the next generation of radio telescopes are unlikely to find many sources that can extend their lifetimes from putting relativistic electrons into a low-field ‘freezer’. Finally, I preview some new EVLA results on the complex relic in Abell 2256, with implications for the interspersing of its relativistic and thermal plasmas.
Comments on inhomogeneous anisotropic cosmology
Kaya, Ali
2016-01-01
Recently a new no-global-recollapse argument is given for some inhomogeneous and anisotropic cosmologies that utilizes surface deformation by the mean curvature flow. In this note we point out a few important issues about the proposed deformations and in particular indicate that in the presence of large spatial variations the mean curvature flow may deform an initially spacelike surface to a surface with null or timelike portions. The time evolution of the spatial scalar curvature that prevents recollapse is determined in normal coordinates, which shows the impact of inhomogeneities explicitly. Our analysis also indicates a possible caveat in numerical solutions that give rise to inflation.
Remarks on inhomogeneous anisotropic cosmology
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 INITIAL-BOUNDARY VALUE PROBLEM FOR GINZBURG-LANDAU EQUATIONS
Institute of Scientific and Technical Information of China (English)
杨灵娥; 郭柏灵; 徐海祥
2004-01-01
Some integral identities of smooth solution of inhomogeneous initial boundary value problem of Ginzburg-Landau equations were deduced, by which a priori estimates of the square norm on boundary of normal derivative and the square norm of partial derivatives were obtained. Then the existence of global weak solution of inhomogeneous initial-boundary value problem of Ginzburg-Landau equations was proved by the method of approximation technique and a priori estimates and making limit.
Acceleration of near-field scattering from an inhomogeneous spherical shell
Indian Academy of Sciences (India)
M D Sharma
2005-08-01
The three dimensional scattering of near-field, from a point source, is studied for acceleration in the time domain. The perturbation method is applied to define the acceleration for the first order scattering from a weak inhomogeneity in a homogeneous surrounding. A body force, arising from the interaction between the primary waves and the inhomogeneity, acts as the source generating the scattered motion. The acceleration of scattered waves is related to the velocity and density fluctuations of the inhomogeneity. No restrictions are placed on the inhomogeneity size or locations of the source and receiver. Decoupling of scattered motion enables the identification of different phases. Integral expressions are derived for the scattering acceleration due to the incidence of near-field wave (from an impulsive point force) at a radially inhomogeneous volume element. These integrals are solved further for scattering from an inhomogeneous spherical shell. The accelerations for back scattering are obtained as a special case. These accelerations are simple analytically solvable expressions in closed form. Only spherical asymmetry of wave velocity inhomogeneity can affect the scattered acceleration. Scattered acceleration is affected by the gradient of wave velocity inhomogeneity. The back scattering of near-field from a spherical shell, is independent of radial inhomogeneity of wave velocity. Inhomogeneity with smoothly perturbed wave velocity does not back-scatter any acceleration. Accelerations are computed numerically for scattering from a part of inhomogeneous spherical shell. Hypothetical models are considered to study the effects of the distances of spherical shell from source, receiver, its thickness and its position relative to the direction of impulsive force.
Inhomogeneous microstructural growth by irradiation
DEFF Research Database (Denmark)
Krishan, K.; Singh, Bachu Narain; Leffers, Torben
1985-01-01
In the present paper we discuss the development of heterogeneous microstructure for uniform irradiation conditions. It is shown that microstructural inhomogeneities on a scale of 0.1 μm can develop purely from kinematic considerations because of the basic structure of the rate equations used to d...
Numerical micromagnetism of strong inhomogeneities
Energy Technology Data Exchange (ETDEWEB)
Andreas, Christian [Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich GmbH, D-52428 Jülich (Germany); Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504, Strasbourg (France); Gliga, Sebastian [Laboratory for Micro- and Nanotechnology, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Laboratory for Mesoscopic Systems, Department of Materials, ETH Zurich, 8093 Zurich (Switzerland); Hertel, Riccardo, E-mail: hertel@ipcms.unistra.fr [Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504, Strasbourg (France)
2014-08-01
The size of micromagnetic structures, such as domain walls or vortices, is comparable to the exchange length of the ferromagnet. Both, the exchange length of the stray field l{sub s} and the magnetocrystalline exchange length l{sub k}, are material-dependent quantities that usually lie in the nanometer range. This emphasizes the theoretical challenges associated with the mesoscopic nature of micromagnetism: the magnetic structures are much larger than the atomic lattice constant, but at the same time much smaller than the sample size. In computer simulations, the smallest exchange length serves as an estimate for the largest cell size admissible to prevent appreciable discretization errors. This general rule is not valid in special situations where the magnetization becomes particularly inhomogeneous. When such strongly inhomogeneous structures develop, micromagnetic simulations inevitably contain systematic and numerical errors. It is suggested to combine micromagnetic theory with a Heisenberg model to resolve such problems. We analyze cases where strongly inhomogeneous structures pose limits to standard micromagnetic simulations, arising from fundamental aspects as well as from numerical drawbacks. - Highlights: • We discuss the impact of strong inhomogeneities on micromagnetic simulations. • Analysis of fundamental and numerical errors in micromagnetic point singularities. • Numerical and methodological errors in exchange energy terms are quantified. • Suggestion to combine atomistic Heisenberg models with micromagnetism in such cases.
Selleri, Franco
2015-01-01
Weak Relativity is an equivalent theory to Special Relativity according to Reichenbach’s definition, where the parameter epsilon equals to 0. It formulates a Neo-Lorentzian approach by replacing the Lorentz transformations with a new set named “Inertial Transformations”, thus explaining the Sagnac effect, the twin paradox and the trip from the future to the past in an easy and elegant way. The cosmic microwave background is suggested as a possible privileged reference system. Most importantly, being a theory based on experimental proofs, rather than mutual consensus, it offers a physical description of reality independent of the human observation.
Inhomogeneous Markov point processes by transformation
DEFF Research Database (Denmark)
Jensen, Eva B. Vedel; Nielsen, Linda Stougaard
2000-01-01
We construct parametrized models for point processes, allowing for both inhomogeneity and interaction. The inhomogeneity is obtained by applying parametrized transformations to homogeneous Markov point processes. An interesting model class, which can be constructed by this transformation approach......, is that of exponential inhomogeneous Markov point processes. Statistical inference For such processes is discussed in some detail....
Quasiadiabatic modes from viscous inhomogeneities
Giovannini, Massimo
2016-01-01
The viscous inhomogeneities of a relativistic plasma determine a further class of entropic modes whose amplitude must be sufficiently small since curvature perturbations are observed to be predominantly adiabatic and Gaussian over large scales. When the viscous coefficients only depend on the energy density of the fluid the corresponding curvature fluctuations are shown to be almost adiabatic. After addressing the problem in a gauge-invariant perturbative expansion, the same analysis is repeated at a non-perturbative level by investigating the nonlinear curvature inhomogeneities induced by the spatial variation of the viscous coefficients. It is demonstrated that the quasiadiabatic modes are suppressed in comparison with a bona fide adiabatic solution. Because of its anomalously large tensor to scalar ratio the quasiadiabatic mode cannot be a substitute for the conventional adiabatic paradigm so that, ultimately, the present findings seems to exclude the possibility of a successful accelerated dynamics solely...
Reionization of an Inhomogeneous Universe
Umemura, M; Susa, H
2001-01-01
Full radiative transfer in 3D space has been solved to pursue the reionization history in an inhomogeneous universe. It has been shown that the reionization of an inhomogeneous universe is not a prompt event, but a fairly slow process. Also, QSO absorption line systems are simulated with using the results of radiative transfer calculations. Ly$\\alpha$ continuum depression implies that the metagalactic UV intensity decreases rapidly with $z$ at $z>5$, and the reionization must have taken place between $z=6$ and 10. Finally, it is stressed that H$\\alpha$ forest is a more powerful tool to probe the reionization history and the density fluctuations in the universe at $z>5$.
Inhomogeneous and interacting vacuum energy
De-Santiago, Josue; Wang, Yuting
2012-01-01
Vacuum energy is a simple model for dark energy driving an accelerated expansion of the universe. If the vacuum energy is inhomogeneous in spacetime then it must be interacting. We present the general equations for a spacetime-dependent vacuum energy in cosmology, including inhomogeneous perturbations. We show how any dark energy cosmology can be described by an interacting vacuum+matter. Different models for the interaction can lead to different behaviour (e.g., sound speed for dark energy perturbations) and hence could be distinguished by cosmological observations. As an example we present the cosmic microwave microwave background anisotropies and the matter power spectrum for two different versions of a generalised Chaplygin gas cosmology.
Inhomogeneous Cosmology with Numerical Relativity
Macpherson, Hayley J; Price, Daniel J
2016-01-01
We perform three-dimensional numerical relativity simulations of homogeneous and inhomogeneous expanding spacetimes, with a view towards quantifying non-linear effects from cosmological inhomogeneities. We demonstrate fourth-order convergence with errors less than one part in 10^6 in evolving a flat, dust Friedmann-Lemaitre-Roberston-Walker (FLRW) spacetime using the Einstein Toolkit within the Cactus framework. We also demonstrate agreement to within one part in 10^3 between the numerical relativity solution and the linear solution for density, velocity and metric perturbations in the Hubble flow over a factor of ~350 change in scale factor (redshift). We simulate the growth of linear perturbations into the non-linear regime, where effects such as gravitational slip and tensor perturbations appear. We therefore show that numerical relativity is a viable tool for investigating nonlinear effects in cosmology.
Inhomogeneous recombinations during cosmic reionization
Sobacchi, Emanuele; Mesinger, Andrei
2014-01-01
By depleting the ionizing photon budget available to expand cosmic HII 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 sub-grid prescription for tracking inhomogeneous recombinations in the intergalactic medium. Building on previous work parameterizing photo-heating feedb...
Quasiadiabatic modes from viscous inhomogeneities
Giovannini, Massimo
2016-01-01
The viscous inhomogeneities of a relativistic plasma determine a further class of entropic modes whose amplitude must be sufficiently small since curvature perturbations are observed to be predominantly adiabatic and Gaussian over large scales. When the viscous coefficients only depend on the energy density of the fluid the corresponding curvature fluctuations are shown to be almost adiabatic. After addressing the problem in a gauge-invariant perturbative expansion, the same analysis is repea...
Al Kaissi, Ali; Ryabykh, Sergey; Ochirova, Polina; Kenis, Vladimir; Hofstätter, Jochen G.; Grill, Franz; Ganger, Rudolf; Kircher, Susanne Gerit
2017-01-01
Marked ligamentous hyperlaxity and muscle weakness/wasting associated with awkward gait are the main deficits confused with the diagnosis of myopathy. Seven children (6 boys and 1 girl with an average age of 8 years) were referred to our department because of diverse forms of skeletal abnormalities. No definitive diagnosis was made, and all underwent a series of sophisticated investigations in other institutes in favor of myopathy. We applied our methodology through the clinical and radiographic phenotypes followed by targeted genotypic confirmation. Three children (2 boys and 1 girl) were compatible with the diagnosis of progressive pseudorheumatoid chondrodysplasia. The genetic mutation was correlated with the WISP 3 gene actively expressed by articular chondrocytes and located on chromosome 6. Klinefelter syndrome was the diagnosis in 2 boys. Karyotyping confirmed 47,XXY (aneuploidy of Klinefelter syndrome). And 2 boys were finally diagnosed with Morquio syndrome (MPS type IV A) as both showed missense mutations in the N-acetylgalactosamine-sulfate sulfatase gene. Misdiagnosis can lead to the initiation of a long list of sophisticated investigations. PMID:28210640
Energy Technology Data Exchange (ETDEWEB)
Jin Yaqiu [Center for Wave Scattering and Remote Sensing, Fudan University, Shanghai 200433 (China)]. E-mail: yqjin@fundan.ac.cn; Liang Zichang [Center for Wave Scattering and Remote Sensing, Fudan University, Shanghai 200433 (China)
2005-05-15
To solve the 3D-VRT equation for the model of spatially inhomogeneous scatter media, the finite enclosure of the scatter media is geometrically divided, in both vertical z and transversal (x,y) directions, to form very thin multi-boxes. The zeroth order emission, first-order Mueller matrix of each thin box and an iterative approach of high-order radiative transfer are applied to derive high-order scattering and emission of whole inhomogeneous scatter media. Numerical results of polarized brightness temperature at microwave frequency and under different radiometer resolutions from inhomogeneous scatter model such as vegetation canopy and alien target beneath canopy are simulated and discussed.
Cui, Liang; Zhao, Ningbo
2012-01-01
The photonic crystal fiber (PCF) is one of the excellent media for generating photon pairs via spontaneous four wave mixing. Here we study how the inhomogeneity of PCFs affect the spectral properties of photon pairs from both the theoretical and experimental aspects. The theoretical model shows that the photon pairs born in different place of the inhomogeneous PCF are coherently superposed, and a modulation in the broadened spectrum of phase matching function will appear, which prevents the realization of spectral factorable photon pairs. In particular, the inhomogeneity induced modulation can be examined by measuring the spectrum of individual signal or idler field when the asymmetric group velocity matching is approximately fulfilled. Our experiments are performed by tailoring the spectrum of pulsed pump to satisfy the specified phase matching condition. The observed spectra of individual signal photons, which are produced from different segments of the 1.9 m inhomogeneous PCF, agree with the theoretical pr...
Inhomogeneous interface laser mirror coatings.
Ledger, A M
1979-09-01
Methods of improving the durability of thin-film laser mirror coatings for 10.6 microm using thorium fluoride, zinc selenide, and zinc sulfide materials have been investigated. The largest improvement in film durability was obtained by using inhomogeneous interface fabrication for all the dielectric-dielectric interfaces and by incorporating cerium fluoride protective overcoating material into the film design. Experimental results are given for enhanced reflectors, polarization-selective coatings, and buried-grating aperture-sharing coatings designed for high-power laser applications.
Institute of Scientific and Technical Information of China (English)
2007-01-01
In this paper, we consider the Cauchy problem with initial data given on a semi-bounded axis for inhomogeneous quasilinear hyperbolic systems. Under the assumption that the rightmost (resp. leftmost) eigenvalue is weakly linearly degenerate and the inhomogeneous term satisfies the corresponding matching condition, we obtain the global existence and uniqueness of C1 solution with small and decaying initial data.
Generation of auroral kilometric radiation in inhomogeneous magnetospheric plasma
Burinskaya, T. M.; Shevelev, M. M.
2017-01-01
The generation of auroral kilometric radiation in a narrow 3D plasma cavity, in which a weakly relativistic electron flow is propagated along the magnetic field against a low-density cold background plasma, is studied. The time dynamics of the propagation and intensification of waves are analyzed using geometric optics equations. The waves have different wave vector components and start from the cavity center at an altitude of about the Earth's radius at plasma parameters typical for the auroral zone at this altitude. It is shown that the global inhomogeneity of the Earth's magnetic field is of key importance in shaping the auroral kilometric radiation spectra.
Sensitivity of resistive and Hall measurements to local inhomogeneities
DEFF Research Database (Denmark)
Koon, Daniel W.; Wang, Fei; Petersen, Dirch Hjorth
2014-01-01
We derive exact, analytic expressions for the sensitivity of sheet resistance and Hall sheet resistance measurements to local inhomogeneities for the cases of nonzero magnetic fields, strong perturbations, and perturbations over a finite area, extending our earlier results on weak perturbations. We...... simulations on both a linear four-point probe array on a large circular disc and a van der Pauw square geometry. Furthermore, the results also agree well with Náhlík et al. published experimental results for physical holes in a circular copper foil disc....
Quasiadiabatic modes from viscous inhomogeneities
Giovannini, Massimo
2016-04-01
The viscous inhomogeneities of a relativistic plasma determine a further class of entropic modes whose amplitude must be sufficiently small since curvature perturbations are observed to be predominantly adiabatic and Gaussian over large scales. When the viscous coefficients only depend on the energy density of the fluid the corresponding curvature fluctuations are shown to be almost adiabatic. After addressing the problem in a gauge-invariant perturbative expansion, the same analysis is repeated at a nonperturbative level by investigating the nonlinear curvature inhomogeneities induced by the spatial variation of the viscous coefficients. It is demonstrated that the quasiadiabatic modes are suppressed in comparison with a bona fide adiabatic solution. Because of its anomalously large tensor to scalar ratio the quasiadiabatic mode cannot be a substitute for the conventional adiabatic paradigm so that, ultimately, the present findings seems to exclude the possibility of a successful accelerated dynamics solely based on relativistic viscous fluids. If the dominant adiabatic mode is not affected by the viscosity of the background a sufficiently small fraction of entropic fluctuations of viscous origin cannot be a priori ruled out.
3DHZETRN: Inhomogeneous Geometry Issues
Wilson, John W.; Slaba, Tony C.; Badavi, Francis F.
2017-01-01
Historical methods for assessing radiation exposure inside complicated geometries for space applications were limited by computational constraints and lack of knowledge associated with nuclear processes occurring over a broad range of particles and energies. Various methods were developed and utilized to simplify geometric representations and enable coupling with simplified but efficient particle transport codes. Recent transport code development efforts, leading to 3DHZETRN, now enable such approximate methods to be carefully assessed to determine if past exposure analyses and validation efforts based on those approximate methods need to be revisited. In this work, historical methods of representing inhomogeneous spacecraft geometry for radiation protection analysis are first reviewed. Two inhomogeneous geometry cases, previously studied with 3DHZETRN and Monte Carlo codes, are considered with various levels of geometric approximation. Fluence, dose, and dose equivalent values are computed in all cases and compared. It is found that although these historical geometry approximations can induce large errors in neutron fluences up to 100 MeV, errors on dose and dose equivalent are modest (<10%) for the cases studied here.
Institute of Scientific and Technical Information of China (English)
金亚秋; 陈扉; 常梅
2003-01-01
The time-dependent Mueller matrix solution of vector radiative transfer for inhomogeneous random media of non-spherical scatterers is presented. Co-polarized and cross-polarized bistatic scatterings for a polarized pulse incidence are numerically simulated. Numerical results well demonstrate volumetric and surface scattering mechanism and depict the inhomogeneous fraction profile of random scatterers. The peak tails in polarized echoes due to wave reflections from the underlying surface can be identified. Its co-polarized peaks in the specular direction are applied to simultaneous retrievals of the underlying surface roughness and moisture in the presence of inhomogeneous vegetation canopy.
MR image intensity inhomogeneity correction
(Vişan Pungǎ, Mirela; Moldovanu, Simona; Moraru, Luminita
2015-01-01
MR technology is one of the best and most reliable ways of studying the brain. Its main drawback is the so-called intensity inhomogeneity or bias field which impairs the visual inspection and the medical proceedings for diagnosis and strongly affects the quantitative image analysis. Noise is yet another artifact in medical images. In order to accurately and effectively restore the original signal, reference is hereof made to filtering, bias correction and quantitative analysis of correction. In this report, two denoising algorithms are used; (i) Basis rotation fields of experts (BRFoE) and (ii) Anisotropic Diffusion (when Gaussian noise, the Perona-Malik and Tukey's biweight functions and the standard deviation of the noise of the input image are considered).
Quantifying uncertainty from material inhomogeneity.
Energy Technology Data Exchange (ETDEWEB)
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
Weak Galois and Weak Cocleft Coextensions
Institute of Scientific and Technical Information of China (English)
J.N. Alonso (A)lvarez; J.M. Fernández Vilaboa; R. González Rodríguez; A.B. Rodríguez Raposo
2007-01-01
For a weak entwining structure (A, C,ψ) living in a braided monoidal category with equalizers and coequalizers, we formulate the notion of weak A-Galois coextension with normal basis and we show that these Galois coextensions are equivalent to the weak A-cocleft coextensions introduced by the authors.
Real-time imaging through strongly scattering media: seeing through turbid media, instantly.
Sudarsanam, Sriram; Mathew, James; Panigrahi, Swapnesh; Fade, Julien; Alouini, Mehdi; Ramachandran, Hema
2016-01-01
Numerous everyday situations like navigation, medical imaging and rescue operations require viewing through optically inhomogeneous media. This is a challenging task as photons propagate predominantly diffusively (rather than ballistically) due to random multiple scattering off the inhomogenieties. Real-time imaging with ballistic light under continuous-wave illumination is even more challenging due to the extremely weak signal, necessitating voluminous data-processing. Here we report imaging through strongly scattering media in real-time and at rates several times the critical flicker frequency of the eye, so that motion is perceived as continuous. Two factors contributed to the speedup of more than three orders of magnitude over conventional techniques - the use of a simplified algorithm enabling processing of data on the fly, and the utilisation of task and data parallelization capabilities of typical desktop computers. The extreme simplicity of the technique, and its implementation with present day low-cost technology promises its utility in a variety of devices in maritime, aerospace, rail and road transport, in medical imaging and defence. It is of equal interest to the common man and adventure sportsperson like hikers, divers, mountaineers, who frequently encounter situations requiring realtime imaging through obscuring media. As a specific example, navigation under poor visibility is examined.
Real-time imaging through strongly scattering media: seeing through turbid media, instantly
Sudarsanam, Sriram; Mathew, James; Panigrahi, Swapnesh; Fade, Julien; Alouini, Mehdi; Ramachandran, Hema
2016-04-01
Numerous everyday situations like navigation, medical imaging and rescue operations require viewing through optically inhomogeneous media. This is a challenging task as photons propagate predominantly diffusively (rather than ballistically) due to random multiple scattering off the inhomogenieties. Real-time imaging with ballistic light under continuous-wave illumination is even more challenging due to the extremely weak signal, necessitating voluminous data-processing. Here we report imaging through strongly scattering media in real-time and at rates several times the critical flicker frequency of the eye, so that motion is perceived as continuous. Two factors contributed to the speedup of more than three orders of magnitude over conventional techniques - the use of a simplified algorithm enabling processing of data on the fly, and the utilisation of task and data parallelization capabilities of typical desktop computers. The extreme simplicity of the technique, and its implementation with present day low-cost technology promises its utility in a variety of devices in maritime, aerospace, rail and road transport, in medical imaging and defence. It is of equal interest to the common man and adventure sportsperson like hikers, divers, mountaineers, who frequently encounter situations requiring realtime imaging through obscuring media. As a specific example, navigation under poor visibility is examined.
Acoustic Scattering by Near-Surface Inhomogeneities in Porous Media
1990-02-21
then applying the in- verse Hankel transform gives equations that have been obtained by Rudnick [66], and Briquet et al [67], and alternative forms have...The propagation of an acoustic wave along a boundary. Journal of the Acoustical Society of America, 19:348-356, 1947. 131 1I t [67] M. Briquet and P
Ray-optics analysis of inhomogeneous optically anisotropic media
Sluijter, M.
2010-01-01
When the optical behavior of light in a medium depends on the direction in which light is traveling, the medium is called optically anisotropic. Light is an electromagnetic wave and in this thesis, we discuss the electromagnetic theory on optical anisotropy. We do this with the assumption that the w
A class of amplitude modulating and invisible inhomogeneous media
Vial, Benjamin; Horsley, Simon A R; Philbin, Thomas G; Hao, Yang
2016-01-01
We propose a general method to arbitrarily manipulate the amplitude of an electromagnetic wave propagating in a two-dimensional medium, without introducing any scattering. This leads to a whole class of isotropic spatially varying permittivity and permeability profiles that are invisible while shaping the field magnitude. In addition, we propose a metamaterial structure working in the infrared that demonstrates deep sub-wavelength control of the electric field amplitude and strong reduction of the scattering. This work offers an alternative strategy to achieve invisibility with isotropic materials and paves the way for tailoring the propagation of light at the nanoscale.
Refractive index determination in axially symmetric oprtically inhomogeneous media
Ionescu-Pallas, Nicholas; Vlad, Valentin I.; Bociort, Florian
The focussing method from transversally light, put forward by Dietrich Marcuse in view of determining the refractive index profile (RIP) in optical fibers and fiber performs, is revised. A more rigorous derivation of the Marcuse formula is given, establishing the conditions of its validity and a simplified version is initially proposed, able to avoid the systematic errors in the processing of light intensity data.
Bayesian-based localization in inhomogeneous transmission media
DEFF Research Database (Denmark)
Nadimi, E. S.; Blanes-Vidal, V.; Johansen, P. M.
2013-01-01
with heterogeneous transmission medium as a function of the given RSS measurements and the characteristics of the heterogeneous medium. The results of this study show that the localization mean square error (MSE) of the Bayesian-based method outperformed all other existing localization approaches. © 2013 ACM....
Ray-optics analysis of inhomogeneous biaxially anisotropic media
Sluijter, M.; De Boer, D.K.G.; Urbach, H.P.
2009-01-01
Firm evidence of the biaxial nematic phase in liquid crystals, not induced by a magnetic or electric field, has been established only recently. The discovery of these biaxially anisotropic liquid crystals has opened up new areas of both fundamental and applied research. The advances in biaxial
Ray-optics analysis of inhomogeneous optically anisotropic media
Sluijter, M.
2010-01-01
When the optical behavior of light in a medium depends on the direction in which light is traveling, the medium is called optically anisotropic. Light is an electromagnetic wave and in this thesis, we discuss the electromagnetic theory on optical anisotropy. We do this with the assumption that the w
Hydrodynamic limit of symmetric exclusion processes in inhomogeneous media
Faggionato, A
2010-01-01
In \\cite{J} M. Jara has presented a method, reducing the proof of the hydrodynamic limit of symmetric exclusion processes to an homogenization problem, as unified approach to recent works on the field as \\cite{N}, \\cite{F1}, \\cite{F2} and \\cite{FJL}. Although not stated in \\cite{J}, the reduction of the hydrodynamic limit to an homogenization problem was already obtained (in a different way) in \\cite{N}, \\cite{F1}. This alternative and very simple relation between the two problems goes back to an idea of K.\\ Nagy \\cite{N}, is stated in \\cite{F1}[Section B] for exclusion processes on $\\bbZ^d$ and, as stressed in \\cite{F2}, is completely general. The above relation has been applied to \\cite{N}, \\cite{F1}, \\cite{F2} and \\cite{FJL} and could be applied to other symmetric exclusion processes, mentioned in \\cite{J}. In this short note we briefly recall this unified approach in a complete general setting. Finally, we recall how the homogenization problem has been solved in the above previous works.
Locating where Transient Signals Travel in Inhomogeneous Media
Spiesberger, J L
2005-01-01
Locating where transient signals travel between a source and receiver requires a final step that is needed after using a theory of diffraction such as the integral theorem of Helmholtz and Kirchhoff. Introduced here, the final step accounts for interference between adjacent apertures on a phase screen by adaptively adjusting their phase and amplitude, yielding a hierarchy of energy contributions to any desired window of signal travel time at the receiver. The method allows one to check errors in ray theory at finite wavelengths. Acoustic propagation at long distance in the oceanic waveguide (50-100 Hz, 0.05 s resolution) has significant deviations from ray theory. The boundary condition of zero pressure at the surface of the ocean appears to cause sound to travel in a nearly horizontal trajectory for a much greater distance near the surface than predicted by rays. The first Fresnel zone is an inappropriate scale to characterize where transient sounds travel near a ray path as assumed by a standard scattering ...
Features of vibrations of structural inhomogeneous solid media
Karimbaev, Telman; Baishagirov, Khairulla; Nurgaliyeva, Saltanat
2017-09-01
Homogeneous or quasi-homogeneous classic models of deformation are generally used at a mathematical de-scription of deformation composite materials (CM). These theories, however, are limited within initial conditions and do not cover the most important properties of CM: heterogeneity of inertia and elasticity of components, their interaction when deforming, etc. Among the models that complement the classical theories, it is possible to allocate the so-called theory of mixture where CM is considered as two (or more) interacting homogeneous continuum. Therefore, the model increase of motion freedom degrees of the particles of such heterogeneous medium allows each component of CM to show their inertial properties. This leads to the identification of such exclusive features as "bifurcation of fre-quencies", i.e., to description of motion on each form of normal modes at two different frequencies. In the research this phenomenon was investigated by the analysis of biquadratic equation obtained at solving the proper value problem of heterogeneous medium, and was verified by testing the normal mode of frequencies of blades made of CM. In the particular case there was received a simple calculation formula for determination of bar technical frequencies from CM on the basis of the characteristic equation of natural vibrations. In this case the numerical results for the lower forms of the vibration normal mode coincide with the experimental data for homogeneous medium. The characteristic equation contains the introduced physical parameters of the two-component theory; therefore, it describes the other forms of vibration. However, in this case the freedom of structural fluctuations of CM each component is limited to their coupling and interaction, providing continuity and shared the compound materials.
Ray-optics analysis of inhomogeneous optically anisotropic media
Sluijter, M.
2010-01-01
When the optical behavior of light in a medium depends on the direction in which light is traveling, the medium is called optically anisotropic. Light is an electromagnetic wave and in this thesis, we discuss the electromagnetic theory on optical anisotropy. We do this with the assumption that the
Inhomogenous loop quantum cosmology with matter
Blas, Daniel Martín-de; Marugán, Guillermo A Mena; 10.1088/1742-6596/360/1/012032
2013-01-01
The linearly polarized Gowdy $T^3$ model with a massless scalar field with the same symmetries as the metric is quantized by applying a hybrid approach. The homogeneous geometry degrees of freedom are loop quantized, fact which leads to the resolution of the cosmological singularity, while a Fock quantization is employed for both matter and gravitational inhomogeneities. Owing to the inclusion of the massless scalar field this system allows us to modelize flat Friedmann-Robertson-Walker cosmologies filled with inhomogeneities propagating in one direction. It provides a perfect scenario to study the quantum back-reaction between the inhomogeneities and the polymeric homogeneous and isotropic background.
Inflation in spherically symmetric inhomogeneous models
Energy Technology Data Exchange (ETDEWEB)
Stein-Schabes, J.A.
1986-11-01
Exact analytical solutions of Einstein's equations are found for a spherically symmetric inhomogeneous metric in the presence of a massless scalar field with a flat potential. The process of isotropization and homogenization is studied in detail. It is found that the time dependence of the metric becomes de Sitter for large times. Two cases are studied. The first deals with a homogeneous scalar field, while the second with a spherically symmetric inhomogeneous scalar field. In the former case the metric is of the Robertson-Walker form, while the latter is intrinsically inhomogeneous. 16 refs.
Holographic confinement in inhomogeneous backgrounds
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.
Enhancing light transmission through a random medium with inhomogeneous scattering and loss
Sarma, Raktim; Cao, Hui
2016-01-01
We enhanced the total transmission of light through a disordered waveguide with spatially inhomogeneous scattering and loss by shaping the incident wavefront of a laser beam. Using an on-chip tapered lead, we were able to access all input modes in the waveguide with a spatial light modulator. The adaptive wavefront shaping resulted in selective coupling of input light to high transmission channels, which bypassed the regions of higher scattering and loss in the waveguide. The spatial inhomogeneity of scattering and loss led to redirecting of energy flux to optical paths with less scattering and loss to maximize total energy transported through the system. This work demonstrated the power of wavefront shaping in coherent control of light transport in inhomogeneous scattering media, which are common in real applications.
Inhomogeneous Universe Models with Varying Cosmological Term
Chimento, L P; Chimento, Luis P.; Pavon, Diego
1998-01-01
The evolution of a class of inhomogeneous spherically symmetric universe models possessing a varying cosmological term and a material fluid, with an adiabatic index either constant or not, is studied.
Inhomogenous quantum codes (Ⅰ):additive case
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
In this paper,the quantum error-correcting codes are generalized to the inhomogenous quantumstate space Cq1 Cq2 ··· Cqn,where qi(1 i n) are arbitrary positive integers.By attaching an abelian group Ai of order qi to the space Cqi(1 i n),we present the stabilizer construction of such inhomogenous quantum codes,called additive quantum codes,in term of the character theory of the abelian group A = A1⊕A2⊕···⊕An.As usual case,such construction opens a way to get inhomogenous quantum codes from the classical mixed linear codes.We also present Singleton bound for inhomogenous additive quantum codes and show several quantum codes to meet such bound by using classical mixed algebraic-geometric codes.
Analysis of defect-related inhomogeneous electroluminescence in InGaN/GaN QW LEDs
Ren, C. X.; Rouet-Leduc, B.; Griffiths, J. T.; Bohacek, E.; Wallace, M. J.; Edwards, P. R.; Hopkins, M. A.; Allsopp, D. W. E.; Kappers, M. J.; Martin, R. W.; Oliver, R. A.
2016-11-01
The inhomogeneous electroluminescence (EL) of InGaN/GaN quantum well light emitting diode structures was investigated in this study. Electroluminescence hyperspectral images showed that inhomogeneities in the form of bright spots exhibited spectrally blue-shifted and broadened emission. Scanning electron microscopy combined with cathodoluminescence (SEM-CL) was used to identify hexagonal pits at the centre of approximately 20% of these features. Scanning transmission electron microscopy imaging with energy dispersive X-ray spectroscopy (STEM-EDX) indicated there may be p-doped AlGaN within the active region caused by the presence of the pit. Weak beam dark-field TEM (WBDF-TEM) revealed the presence of bundles of dislocations associated with the pit, suggesting the surface features which cause the inhomogeneous EL may occur at coalescence boundaries, supported by trends in the number of features observed across the wafer.
Neutron depolarization imaging of the hydrostatic pressure dependence of inhomogeneous ferromagnets
Schulz, M.; Neubauer, A.; Böni, P.; Pfleiderer, C.
2016-05-01
The investigation of fragile and potentially inhomogeneous forms of ferromagnetic order under extreme conditions, such as low temperatures and high pressures, is of central interest for areas such as geophysics, correlated electron systems, as well as the optimization of materials synthesis for applications where particular material properties are required. We report neutron depolarization imaging measurements on the weak ferromagnet Ni3Al under pressures up to 10 kbar using a Cu:Be clamp cell. Using a polychromatic neutron beam with wavelengths λ ≥ 4 Å in combination with 3He neutron spin filter cells as polarizer and analyzer, we were able to track differences of the pressure response in inhomogeneous samples by virtue of high resolution neutron depolarization imaging. This provides spatially resolved and non-destructive access to the pressure dependence of the magnetic properties of inhomogeneous ferromagnetic materials.
Exactly solvable one-dimensional inhomogeneous models
Energy Technology Data Exchange (ETDEWEB)
Derrida, B.; France, M.M.; Peyriere, J.
1986-11-01
The authors present a simple way of constructing one-dimensional inhomogeneous models (random or quasiperiodic) which can be solved exactly. They treat the example of an Ising chain in a varying magnetic field, but their procedure can easily be extended to other one-dimensional inhomogeneous models. For all the models they can construct, the free energy and its derivatives with respect to temperature can be computed exactly at one particular temperature.
Inhomogeneous Einstein-Rosen string cosmology
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.
Inhomogeneous Fragmentation of the Rolling Tachyon
Felder, Gary N; Kofman, Lev
2004-01-01
Dirac-Born-Infeld type effective actions reproduce many aspects of string theory classical tachyon dynamics of unstable Dp-branes. The inhomogeneous tachyon field rolling from the top of its potential forms topological defects of lower codimensions. In between them, as we show, the tachyon energy density fragments into a p-dimensional web-like high density network evolving with time. We present an analytic asymptotic series solution of the non-linear equations for the inhomogeneous tachyon an...
Real-time quadrature lock-in discrimination imaging through scattering media
Sudarsanam, Sriram; Panigrahi, Swapnesh; Fade, Julien; Alouini, Mehdi; Ramachandran, Hema
2015-01-01
Numerous everyday situations like navigation, medical imaging and rescue operations require viewing through optically inhomogeneous media. This is a challenging task as photons, instead of traversing ballistically, propagate predominantly diffusively due to random multiple scattering off the inhomogenieties. Imaging {\\it in real-time} with ballistic light under continuous-wave illumination is even more challenging due to the extremely weak signal, necessitating voluminous data-processing. In this paper, we report imaging through strongly scattering media in real-time and at rates several times the critical flicker frequency of the eye, so that motion is perceived as continuous. Two factors contributed to the speedup of {\\it more than three orders of magnitude} over conventional techniques - the use of a simplified algorithm enabling processing of data on the fly, and the utilisation of task and data parallelization capabilities of typical desktop computers. The extreme simplicity and low cost promises great u...
Institute of Scientific and Technical Information of China (English)
Yong Hua LI; Hai Bin KAN; Bing Jun YU
2004-01-01
In this paper, a special kind of partial algebras called projective partial groupoids is defined.It is proved that the inverse image of all projections of a fundamental weak regular *-semigroup under the homomorphism induced by the maximum idempotent-separating congruence of a weak regular *-semigroup has a projective partial groupoid structure. Moreover, a weak regular *-product which connects a fundamental weak regular *-semigroup with corresponding projective partial groupoid is defined and characterized. It is finally proved that every weak regular *-product is in fact a weak regular *-semigroup and any weak regular *-semigroup is constructed in this way.
Masmoudi, Nabil
2014-05-01
Traveltimes are conventionally evaluated by solving the zero-order approximation of the Wentzel, Kramers and Brillouin (WKB) expansion of the wave equation. This high frequency approximation is good enough for most imaging applications and provides us with a traveltime equation called the eikonal equation. The eikonal equation is a non-linear partial differential equation which can be solved by any of the familiar numerical methods. Among the most popular of these methods is the method of characteristics which yields the ray tracing equations and the finite difference approaches. In the first part of the Master Thesis, we use the ray tracing method to solve the eikonal equation to get P-waves traveltimes for orthorhombic models with arbitrary orientation of symmetry planes. We start with a ray tracing procedure specified in curvilinear coordinate system valid for anisotropy of arbitrary symmetry. The coordinate system is constructed so that the coordinate lines are perpendicular to the symmetry planes of an orthorohombic medium. Advantages of this approach are the conservation of orthorhombic symmetry throughout the model and reduction of the number of parameters specifying the model. We combine this procedure with first-order ray tracing and dynamic ray tracing equations for P waves propagating in smooth, inhomogeneous, weakly anisotropic media. The first-order ray tracing and dynamic ray tracing equations are derived from the exact ones by replacing the exact P-wave eigenvalue of the Christoffel matrix by its first-order approximation. In the second part of the Master Thesis, we compute traveltimes using the fast marching method and we develop an approach to estimate the anisotropy parameters. The idea is to relate them analytically to traveltimes which is challenging in inhomogeneous media. Using perturbation theory, we develop traveltime approximations for transversely isotropic media with horizontal symmetry axis (HTI) as explicit functions of the
The weak measurement process and the weak value of spin for metastable helium 23S1
Monachello, Vincenzo; Barker, Peter; Flack, Robert; Hiley, Basil
2016-05-01
An experiment is being designed and constructed in order to measure the weak value of spin for an atomic system. The principle of the ``weak measurement'' process was first proposed by Aharonov, Albert and Vaidman, and describes a scenario in which a system is weakly coupled to a pointer between well-defined pre- and post-selected states. This experiment will utilise a pulsed supersonic beam of spin-1 metastable Helium (He*) atoms in the 23S1 state. The spin of the pre-selected He* atoms will be weakly coupled to its centre-of-mass. During its flight, the atomic beam will be prepared in a desired quantum state and travel through two inhomogeneous magnets (weak and strong) which both comprise the ``weak measurement'' process. The deviation of the post-selected ms = + 1 state as measured using a micro-channel plate, phosphor screen and CCD camera setup will allow for the determination of the weak value of spin. This poster will report on the methods used and the experimental realisation.
Spatial structure of a collisionally inhomogeneous Bose-Einstein condensate
Energy Technology Data Exchange (ETDEWEB)
Li, Fei, E-mail: wiself@gmail.com [Hunan First Normal University, Department of Education Science (China); Zhang, Dongxia; Rong, Shiguang; Xu, Ying [Hunan University of Science and Technology, Department of Physics (China)
2013-11-15
The spatial structure of a collisionally inhomogeneous Bose-Einstein condensate (BEC) in an optical lattice is studied. A spatially dependent current with an explicit analytic expression is found in the case with a spatially dependent BEC phase. The oscillating amplitude of the current can be adjusted by a Feshbach resonance, and the intensity of the current depends heavily on the initial and boundary conditions. Increasing the oscillating amplitude of the current can force the system to pass from a single-periodic spatial structure into a very complex state. But in the case with a constant phase, the spatially dependent current disappears and the Melnikov chaotic criterion is obtained via a perturbative analysis in the presence of a weak optical lattice potential. Numerical simulations show that a strong optical lattice potential can lead BEC atoms to a state with a chaotic spatial distribution via a quasiperiodic route.
A note on generalized hydrodynamics: inhomogeneous fields and other concepts
Doyon, Benjamin
2016-01-01
Generalized hydrodynamics (GHD) was proposed recently as a formulation of hydrodynamics for integrable systems, taking into account infinitely-many conservation laws. In this note we further develop the theory in various directions. By extending GHD to all commuting flows of the integrable model, we provide a full description of how to take into account weakly varying force fields, temperature fields and other inhomogeneous external fields within GHD. We expect this can be used, for instance, to characterize the non-equilibrium dynamics of one-dimensional Bose gases in trap potentials. We also show that the GGE equations of state, and thus GHD, emerge uniformly in free particle models under the condition that the space-time variation scale of hydrodynamic observables grows unboundedly with time. We further show how the equations of state at the core of GHD follow from the continuity relation for entropy, and we show how to recover Euler-like equations and discuss possible viscosity terms.
Sensitivity of resistive and Hall measurements to local inhomogeneities
Koon, Daniel W.; Wang, Fei; Hjorth Petersen, Dirch; Hansen, Ole
2013-10-01
We derive exact, analytic expressions for the sensitivity of resistive and Hall measurements to local inhomogeneities in a specimen's material properties in the combined linear limit of a weak perturbation over an infinitesimal area in a small magnetic field. We apply these expressions both to four-point probe measurements on an infinite plane and to symmetric, circular van der Pauw discs, obtaining functions consistent with published results. These new expressions speed up calculation of the sensitivity for a specimen of arbitrary shape to little more than the solution of two Laplace equation boundary-value problems of the order of N3 calculations, rather than N2 problems of total order N5, and in a few cases produces an analytic expression for the sensitivity. These functions provide an intuitive, visual explanation of how, for example, measurements can predict the wrong carrier type in n-type ZnO.
An Inhomogeneous Quasilinear Hyperbolic System.
1980-11-01
bounded variation and v0(x) has a positive bound, Lemma 2.1 • 1 and h < that 1 +a V r(.,t) + V s(.,t) < Q for t < T (2.7) +G +W K2M 24K1T K2 where Q...that u 0(x) are bounded functions with bounded variation , v 0(x) has a positive lower bound. U(u,v,x,t), V(u,v,x,t) are smooth functions satisfying...t) to denote the weak solution of (0.1) and (0.2). Theorem 4.1. Suppose that u0 (x), v0 (x) are bounded functions with bounded variation and do not
Network theory for inhomogeneous thermoelectrics
Angst, Sebastian; Wolf, Dietrich E.
2016-04-01
The Onsager-de Groot-Callen transport theory, implemented as a network model, is used to simulate the transient Harman method, which is widely used experimentally to determine all thermoelectric transport coefficients in a single measurement setup. It is shown that this method systematically overestimates the Seebeck coefficient for samples composed of two different materials. As a consequence, the figure of merit is also overestimated, if the thermal coupling of the measurement setup to the environment is weak. For a mixture of metal and semiconductor particles near metal percolation the figure of merit obtained by the Harman method is more than 100% too large. For a correct interpretation of the experimental data, information on composition and microstructure of the sample are indispensable.
1987-12-01
location of the inhomogeneities and their geometry. Secondly we use this repr""’ntatien formula to prove a Lipschitz c,,t ,,¢us dcpcoidence estimate...A. Pericak-Spector, S. J. Spector, Nonuniqueness for a Hyperbolic System: Cavitation in Nonlinear Elastodynamics 306 E. G. Kalnins, W. Miller, Jr., q...Saturated Porous Media: Lipschitz Continuity of the Interface 336 B. J. Lucier, Regularity Through Approximation for Scalar Conservation Laws 337 B
Cofinitely weak supplemented modules
Alizade, Rafail; Büyükaşık, Engin
2003-01-01
We prove that a module M is cofinitely weak supplemented or briefly cws (i.e., every submodule N of M with M/N finitely generated, has a weak supplement) if and only if every maximal submodule has a weak supplement. If M is a cws-module then every M-generated module is a cws-module. Every module is cws if and only if the ring is semilocal. We study also modules, whose finitely generated submodules have weak supplements.
DEFF Research Database (Denmark)
Fatnassi, Chemseddine; Boucenna, Rachid; Zaidi, Habib
2017-01-01
and at the paranasal sinuses, however, this assumption is often broken. Herein, we explored a novel model that considers both linear and stochastic dependences of the phase evolution with echo time in the presence of weak and strong macroscopic field inhomogeneities. We tested the performance of the model at large...
Institute of Scientific and Technical Information of China (English)
丁夏畦; 罗佩珠
2004-01-01
In this paper the authors introduce some new ideas on generalized numbers and generalized weak functions. They prove that the product of any two weak functions is a generalized weak function. So in particular they solve the problem of the multiplication of two generalized functions.
Beginning inflation in an inhomogeneous universe
Energy Technology Data Exchange (ETDEWEB)
East, William E. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Kleban, Matthew [Center for Cosmology and Particle Physics, New York University, New York, New York 10003 (United States); Linde, Andrei [SITP and Department of Physics, Stanford University,Stanford, California 94305 (United States); Senatore, Leonardo [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); SITP and Department of Physics, Stanford University,Stanford, California 94305 (United States)
2016-09-06
Using numerical solutions of the full Einstein field equations coupled to a scalar inflaton field in 3+1 dimensions, we study the conditions under which a universe that is initially expanding, highly inhomogeneous and dominated by gradient energy can transition to an inflationary period. If the initial scalar field variations are contained within a sufficiently flat region of the inflaton potential, and the universe is spatially flat or open on average, inflation will occur following the dilution of the gradient and kinetic energy due to expansion. This is the case even when the scale of the inhomogeneities is comparable to 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.
Solitons and Weakly Nonlinear Waves in Plasmas
DEFF Research Database (Denmark)
Pécseli, Hans
1985-01-01
Theoretical descriptions of solitons and weakly nonlinear waves propagating in plasma media are reviewed, with particular attention to the Korteweg-de Vries (KDV) equation and the Nonlinear Schrödinger equation (NLS). The modifications of these basic equations due to the effects of resonant...
Cosmological perturbations from an inhomogeneous phase transition
Energy Technology Data Exchange (ETDEWEB)
Matsuda, Tomohiro, E-mail: matsuda@sit.ac.j [Laboratory of Physics, Saitama Institute of Technology, Fusaiji, Okabe-machi, Saitama 369-0293 (Japan)
2009-07-21
A mechanism for generating metric perturbations in inflationary models is considered. Long-wavelength inhomogeneities of light scalar fields in a decoupled sector may give rise to superhorizon fluctuations of couplings and masses in the low-energy effective action. Cosmological phase transitions may then occur that are not simultaneous in space, but occur with time lags in different Hubble patches that arise from the long-wavelength inhomogeneities. Here an interesting model in which cosmological perturbations may be created at the electroweak phase transition is considered. The results show that phase transitions may be a generic source of non-Gaussianity.
Spectral Distortion in a Radially Inhomogeneous Cosmology
Caldwell, R R
2013-01-01
The spectral distortion of the cosmic microwave background blackbody spectrum in a radially inhomogeneous spacetime, designed to exactly reproduce a LambdaCDM expansion history along the past light cone, is shown to exceed the upper bound established by COBE-FIRAS by a factor of approximately 3000. This simple observational test helps uncover a slew of pathological features that lie hidden inside the past light cone, including a radially contracting phase at decoupling and, if followed to its logical extreme, a naked singularity at the radially inhomogeneous Big Bang.
Cosmic inhomogeneities and averaged cosmological dynamics.
Paranjape, Aseem; Singh, T P
2008-10-31
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.
Spectral distortion in a radially inhomogeneous cosmology
Caldwell, R. R.; Maksimova, N. A.
2013-11-01
The spectral distortion of the cosmic microwave background blackbody spectrum in a radially inhomogeneous space-time, designed to exactly reproduce a ΛCDM expansion history along the past light cone, is shown to exceed the upper bound established by COBE-FIRAS by a factor of approximately 3700. This simple observational test helps uncover a slew of pathological features that lie hidden inside the past light cone, including a radially contracting phase at decoupling and, if followed to its logical extreme, a naked singularity at the radially inhomogeneous big bang.
Effective permittivity of finite inhomogeneous objects
Raghunathan, S.B.; Budko, N.V.
2010-01-01
A generalization of the S-parameter retrieval method for finite three-dimensional inhomogeneous objects under arbitrary illumination and observation conditions is presented. The effective permittivity of such objects may be rigorously defined as a solution of a nonlinear inverse scattering problem.
On non-singular inhomogeneous cosmological models
Fernández-Jambrina, L
2009-01-01
In this talk we would like to review recent results on non-singular cosmological models. It has been recently shown that among stiff perfect fluid inhomogeneous spacetimes the absence of singularities is more common than it was expected in the literature. We would like to generalize these results and apply them to other matter sources.
Imaging of material inhomogeneities with flexural waves
Hörchens, L.
2010-01-01
The detection of inhomogeneities in plates or plate-like structures constitutes a major problem in the field of non-destructive testing. For a few decades, classical techniques based on X-ray radiography have - as far as possible - been complemented and replaced by the usage of vibrations or acousti
Multifractal Analysis of Inhomogeneous Bernoulli Products
Batakis, Athanasios; Testud, Benoît
2011-03-01
We are interested to the multifractal analysis of inhomogeneous Bernoulli products which are also known as coin tossing measures. We give conditions ensuring the validity of the multifractal formalism for such measures. On another hand, we show that these measures can have a dense set of phase transitions.
Waves and vibrations in inhomogeneous structures
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard
Denne afhandling omhandler bølger og vibrationer i inhomogene strukturer med speciel fokus på undersøgelse af båndgabsfænomenet og optimering af båndgabsstrukturer. Afhandlingen består af 21 artikler, hvoraf 17 er publiceret i internationale tidsskrifter og 4 er publiceret i konferenceproceedings...
Lie Algebra of Noncommutative Inhomogeneous Hopf Algebra
Lagraa, M
1997-01-01
We construct the vector space dual to the space of right-invariant differential forms construct from a first order differential calculus on inhomogeneous quantum group. We show that this vector space is equipped with a structure of a Hopf algebra which closes on a noncommutative Lie algebra satisfying a Jacobi identity.
Inhomogeneous generalization of some Bianchi models
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.
Metric inhomogeneous Diophantine approximation in positive characteristic
DEFF Research Database (Denmark)
Kristensen, S.
We obtain asymptotic formulae for the number of solutions to systems of inhomogeneous linear Diophantine inequalities over the field of formal Laurent series with coefficients from a finite fields, which are valid for almost every such system. Here 'almost every' is with respect to Haar measure...
Field quantization in inhomogeneous absorptive dielectrics
Suttorp, L.G.; Wubs, Martijn
2004-01-01
The quantization of the electromagnetic field in a three-dimensional inhomogeneous dielectric medium with losses is carried out in the framework of a damped-polariton model with an arbitrary spatial dependence of its parameters. The equations of motion for the canonical variables are solved explicit
Magnetic properties in the inhomogeneous chiral phase
Yoshiike, Ryo; Tatsumi, Toshitaka
2016-01-01
We investigate the magnetic properties of quark matter in the inhomogeneous chiral phase, where both scalar and pseudoscalar condensates spatially modulate. The energy spectrum of the lowest Landau level becomes asymmetric about zero in the external magnetic field, and gives rise to the remarkably magnetic properties: quark matter has a spontaneous magnetization, while the magnetic susceptibility does not diverge on the critical point.
Wideband Flat Radomes Using Inhomogeneous Planar Layers
Directory of Open Access Journals (Sweden)
Mohammad Khalaj-Amirhosseini
2008-01-01
Full Text Available Inhomogeneous planar layers (IPLs are optimally designed as flat radomes in a desired frequency range. First, the electric permittivity function of the IPL is expanded in a truncated Fourier series. Then, the optimum values of the coefficients of the series are obtained through an optimization approach. The performance of the proposed structure is verified using some examples.
Institute of Scientific and Technical Information of China (English)
谢永珍; 朱彩婕
2016-01-01
From the perspective of the disclosure of internal control material weakness ,regarding media supervision as the moderators ,we found that the governance of the board can promote the remediation of the internal control material weakness .The setting for audit committee has a positive impact on the remediation of the internal control material weakness ,otherwise the ratio of no salary directors , the meetings and the professional traits of audit committee and media supervision are negatively correlated with it . Media supervision plays the significantly moderating role in this influence process .Our research significance is that ,including media supervision ,it is necessary to set the more audit committee , have audit committee meetings and more non‐financial experts , reform the director’s compensation and to decrease the ratio of the no‐salary directors in order to remediate the internal control material weakness .%从内部控制重大缺陷披露后的视角，以媒体监督为调节变量，对董事会治理与内部控制缺陷修复关系的验证发现：董事会治理对内部控制缺陷修复具有显著的影响，审计委员会设置、审计意见与内部控制重大缺陷修复显著正相关；未领取薪酬董事比例、审计委员会会议次数、审计委员会专业性、媒体监督与内部控制重大缺陷修复负相关；媒体监督在审计委员会设置、会议次数、高管激励对公司内部控制重大缺陷修复中调节作用显著。对其研究的启发意义在于：为了有效修复内部控制的重大缺陷，在适度发挥媒体监督的作用下，上市公司应健全审计委员会、提高会议效率、发挥非财务专长专家的治理作用、改善董事薪酬制度等途径强化对内部控制缺陷的修复。
The Amplification in FEL with Inhomogeneous Magnetic Field
Oganesyan, K B
2016-01-01
The gain in a plane wiggler with inhomogeneous magnetic field is calculated.. It is shown, that the account of inhomogenity of the magnetic field leads to appearance of additional peaks in the amplification
Parametrization of turbulent fluxes over inhomogeneous landscapes
Panin, G. N.; Bernhofer, Ch.
2008-12-01
Reasons for the nonclosure of the heat balance in the atmospheric boundary layers over natural land surfaces are analyzed. Results of measuring the heat-balance components over different land surfaces are used. The Cabauw (Netherlands) data (obtained throughout 1996 over a grass surface with intermittent shrubs and single trees) and the data from the Anchor station in Germany (measured over coniferous forest in 2000-2001) are analyzed. In all, the analysis involves about fifty thousand independent values of the heat-balance components measured in the experiments, which should be indicative of the reliability of the results obtained in the paper. The data have shown that the heat balance is not closed and the imbalance is 50-250 W/m2. The sum of the latent and sensible heat fluxes λ E + H = STF is found to be systematically smaller than the difference between the net radiation and the heat flux into the ground R n - G. It is shown that the main cause of a systematic heat imbalance in the atmospheric boundary layers over inhomogeneous land surfaces is that the methods of surface-flux measurement and estimation are based on the theory that requires the hypothesis of stationarity and horizontal homogeneity. Direct data analysis has shown that the heat imbalance increases with landscape inhomogeneity. In the paper, a parametrization of the heat imbalance is carried out and the coefficient k f ( z {0/ ef }/ L ef ) is introduced as a measure of inhomogeneity. For this, data from the experiments FIFE, KUREX, TARTEX, SADE, etc., are also used. Empirical formulas are presented to refine the results of direct measurements and calculations of surface fluxes over natural (inhomogeneous) land surfaces from profile and standard (using bulk parametrizations) data. These formulas can also be used to determine surface fluxes over inhomogeneous underlying land surfaces in order to take into account so-called subgrid-scale effects in constructing prediction models.
Directory of Open Access Journals (Sweden)
Rupamanjari Majumder
Full Text Available Cardiac arrhythmias, such as ventricular tachycardia (VT and ventricular fibrillation (VF, are among the leading causes of death in the industrialized world. These are associated with the formation of spiral and scroll waves of electrical activation in cardiac tissue; single spiral and scroll waves are believed to be associated with VT whereas their turbulent analogs are associated with VF. Thus, the study of these waves is an important biophysical problem. We present a systematic study of the combined effects of muscle-fiber rotation and inhomogeneities on scroll-wave dynamics in the TNNP (ten Tusscher Noble Noble Panfilov model for human cardiac tissue. In particular, we use the three-dimensional TNNP model with fiber rotation and consider both conduction and ionic inhomogeneities. We find that, in addition to displaying a sensitive dependence on the positions, sizes, and types of inhomogeneities, scroll-wave dynamics also depends delicately upon the degree of fiber rotation. We find that the tendency of scroll waves to anchor to cylindrical conduction inhomogeneities increases with the radius of the inhomogeneity. Furthermore, the filament of the scroll wave can exhibit drift or meandering, transmural bending, twisting, and break-up. If the scroll-wave filament exhibits weak meandering, then there is a fine balance between the anchoring of this wave at the inhomogeneity and a disruption of wave-pinning by fiber rotation. If this filament displays strong meandering, then again the anchoring is suppressed by fiber rotation; also, the scroll wave can be eliminated from most of the layers only to be regenerated by a seed wave. Ionic inhomogeneities can also lead to an anchoring of the scroll wave; scroll waves can now enter the region inside an ionic inhomogeneity and can display a coexistence of spatiotemporal chaos and quasi-periodic behavior in different parts of the simulation domain. We discuss the experimental implications of our study.
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
On Weakly Semicommutative Rings*
Institute of Scientific and Technical Information of China (English)
CHEN WEI-XING; CUI SHU-YING
2011-01-01
A ring R is said to be weakly scmicommutative if for any a, b ∈ R,ab = 0 implies aRb C_ Nil(R), where Nil(R) is the set of all nilpotcnt elements in R.In this note, we clarify the relationship between weakly semicommutative rings and NI-rings by proving that the notion of a weakly semicommutative ring is a proper generalization of NI-rings. We say that a ring R is weakly 2-primal if the set of nilpotent elements in R coincides with its Levitzki radical, and prove that if R is a weakly 2-primal ring which satisfies oα-condition for an endomorphism α of R (that is, ab = 0 （←→） aα(b) ＝ 0 where a, b ∈ R) then the skew polynomial ring R[π; αα]is a weakly 2-primal ring, and that if R is a ring and I is an ideal of R such that I and R/I are both weakly semicommutative then R is weakly semicommutative.Those extend the main results of Liang et al. 2007 (Taiwanese J. Math., 11(5)(2007),1359-1368) considerably. Moreover, several new results about weakly semicommutative rings and NI-rings are included.
Idiopathic isolated orbicularis weakness
MacVie, O P; Majid, M A; Husssin, H M; Ung, T; Manners, R M; Ormerod, I; Pawade, J; Harrad, R A
2012-01-01
Purpose Orbicularis weakness is commonly associated with seventh nerve palsy or neuromuscular and myopathic conditions such as myotonic dystrophy and myasethenia gravis. We report four cases of idiopathic isolated orbicularis weakness. Methods All four cases were female and the presenting symptoms of ocular irritation and epiphora had been present for over 7 years in three patients. All patients had lagophthalmos and three had ectropion. Three patients underwent full investigations which excluded known causes of orbicularis weakness. Two patients underwent oribularis oculi muscle biopsy and histological confirmation of orbicularis atrophy. Results All patients underwent surgery to specifically address the orbicularis weakness with satisfactory outcomes and alleviation of symptoms in all cases. Isolated orbicularis weakness may be a relatively common entity that is frequently overlooked. Conclusion Early recognition of this condition may lead to better management and prevent patients undergoing unnecessary surgical procedures. PMID:22322997
Vortex structure in a long Josephson junction with two inhomogeneities
Energy Technology Data Exchange (ETDEWEB)
Andreeva, O.Yu. [Tumen Thermal Networks OAO ' TRGK' , Tobolsk 626150 (Russian Federation); Boyadjiev, T.L. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Shukrinov, Yu.M. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation)], E-mail: shukrinv@theor.jinr.ru
2007-09-01
We study the vortex structure in the long Josephson junctions with one and two rectangular inhomogeneities in the barrier layer. In case of one inhomogeneity we demonstrate the existence of the asymmetric fluxon states. The disappearance of the mixed fluxon-antifluxon states is shown when the position of the inhomogeneity shifted to the end of the junction. In case of two inhomogeneities the change of the amplitude of Josephson current through the inhomogeneity in the end of the junction makes strong effect on the stability of the fluxon states and smoothes the maximums on the dependence 'critical current-magnetic field'.
Vortex structure in a long Josephson junction with two inhomogeneities
Andreeva, O. Yu.; Boyadjiev, T. L.; Shukrinov, Yu. M.
2007-09-01
We study the vortex structure in the long Josephson junctions with one and two rectangular inhomogeneities in the barrier layer. In case of one inhomogeneity we demonstrate the existence of the asymmetric fluxon states. The disappearance of the mixed fluxon-antifluxon states is shown when the position of the inhomogeneity shifted to the end of the junction. In case of two inhomogeneities the change of the amplitude of Josephson current through the inhomogeneity in the end of the junction makes strong effect on the stability of the fluxon states and smoothes the maximums on the dependence “critical current-magnetic field”.
How Forest Inhomogeneities Affect the Edge Flow
DEFF Research Database (Denmark)
Boudreault, Louis-Étienne; Dupont, Sylvain; Bechmann, Andreas
2016-01-01
is investigated using large-eddy simulation. The three-dimensional forest structure is prescribed in the model using high resolution helicopter-based lidar scans. After evaluating the simulation against wind measurements upwind and downwind of the forest leading edge, the flow dynamics are compared between......Most of our knowledge on forest-edge flows comes from numerical and wind-tunnel experiments where canopies are horizontally homogeneous. To investigate the impact of tree-scale heterogeneities (>1 m) on the edge-flow dynamics, the flow in an inhomogeneous forest edge on Falster island in Denmark...... the scanned forest and an equivalent homogeneous forest. The simulations reveal that forest inhomogeneities facilitate flow penetration into the canopy from the edge, inducing important dispersive fluxes in the edge region as a consequence of the flow spatial variability. Further downstream from the edge...
Localized standing waves in inhomogeneous Schrodinger equations
Marangell, R; Susanto, H
2010-01-01
A nonlinear Schrodinger equation arising from light propagation down an inhomogeneous medium is considered. The inhomogeneity is reflected through a non-uniform coefficient of the non-linear term in the equation. In particular, a combination of self-focusing and self-defocusing nonlinearity, with the self-defocusing region localized in a finite interval, is investigated. Using numerical computations, the extension of linear eigenmodes of the corresponding linearized system into nonlinear states is established, particularly nonlinear continuations of the fundamental state and the first excited state. The (in)stability of the states is also numerically calculated, from which it is obtained that symmetric nonlinear solutions become unstable beyond a critical threshold norm. Instability of the symmetric states is then investigated analytically through the application of a topological argument. Determination of instability of positive symmetric states is reduced to simple geometric properties of the composite phas...
Automatically generated code for relativistic inhomogeneous cosmologies
Bentivegna, Eloisa
2017-02-01
The applications of numerical relativity to cosmology are on the rise, contributing insight into such cosmological problems as structure formation, primordial phase transitions, gravitational-wave generation, and inflation. In this paper, I present the infrastructure for the computation of inhomogeneous dust cosmologies which was used recently to measure the effect of nonlinear inhomogeneity on the cosmic expansion rate. I illustrate the code's architecture, provide evidence for its correctness in a number of familiar cosmological settings, and evaluate its parallel performance for grids of up to several billion points. The code, which is available as free software, is based on the Einstein Toolkit infrastructure, and in particular leverages the automated code generation capabilities provided by its component Kranc.
Inhomogeneous Fragmentation of the Rolling Tachyon
Felder, G N; Felder, Gary N.; Kofman, Lev
2004-01-01
Dirac-Born-Infeld type effective actions reproduce many aspects of string theory classical tachyon dynamics of unstable Dp-branes. The inhomogeneous tachyon field rolling from the top of its potential forms topological defects of lower codimensions. In between them, as we show, the tachyon energy density fragments into a p-dimensional web-like high density network evolving with time. We present an analytic asymptotic series solution of the non-linear equations for the inhomogeneous tachyon and its stress energy. The generic solution for a tachyon field with a runaway potential in arbitrary dimensions is described by the free streaming of noninteracting massive particles whose initial velocities are defined by the gradients of the initial tachyon profile. Thus, relativistic particle mechanics is a dual picture of the tachyon field effective action. Implications of this picture for inflationary models with a decaying tachyon field are discussed.
Primordial inhomogeneities from massive defects during inflation
Firouzjahi, Hassan; Karami, Asieh; Rostami, Tahereh
2016-10-01
We consider the imprints of local massive defects, such as a black hole or a massive monopole, during inflation. The massive defect breaks the background homogeneity. We consider the limit that the physical Schwarzschild radius of the defect is much smaller than the inflationary Hubble radius so a perturbative analysis is allowed. The inhomogeneities induced in scalar and gravitational wave power spectrum are calculated. We obtain the amplitudes of dipole, quadrupole and octupole anisotropies in curvature perturbation power spectrum and identify the relative configuration of the defect to CMB sphere in which large observable dipole asymmetry can be generated. We observe a curious reflection symmetry in which the configuration where the defect is inside the CMB comoving sphere has the same inhomogeneous variance as its mirror configuration where the defect is outside the CMB sphere.
Primordial inhomogeneities from massive defects during inflation
Firouzjahi, Hassan; Rostami, Tahereh
2016-01-01
We consider the imprints of local massive defects, such as a black hole or a massive monopole, during inflation. The massive defect breaks the background homogeneity. We consider the limit that the physical Schwarzschild radius of the defect is much smaller than the inflationary Hubble radius so a perturbative analysis is allowed. The inhomogeneities induced in scalar and gravitational wave power spectrum are calculated. We obtain the amplitudes of dipole, quadrupole and octupole anisotropies in curvature perturbation power spectrum and identify the relative configuration of the defect to CMB sphere in which large observable dipole asymmetry can be generated. We observe a curious reflection symmetry in which the configuration where the defect is inside the CMB comoving sphere has the same inhomogeneous variance as its mirror configuration where the defect is outside the CMB sphere.
Strong Primordial Inhomogeneities and Galaxy Formation
Khlopov, M Ya; Sakharov, Alexander S
2002-01-01
The new element of theory of galaxy formation, strong primordial inhomogeneities, is shown to be a reflection of unstable large scale structures of topological defects, created in second order phase transitions in the inflationary Universe. In addition to {\\it archioles-like} large scale correlation of the primordial inhomogeneity of energy density of coherent scalar field oscillations, the same mechanism, based on the second order phase transitions on the inflational stage and the domain wall formation upon the end of inflation, leads to the formation of massive black hole clusters that can serve as nuclei for the future galaxies. The number of black holes with $M \\sim 100M_{\\odot}$ and above is comparable with the number of galaxies within the modern cosmological horizon. The primordial fractal structure of galaxies can find natural grounds in the framework of model we developed . The proposed approach offers the physical basis for new scenarios of galaxy formation in the Big Bang Universe.
Inhomogeneities from quantum collapse scheme without inflation
Directory of Open Access Journals (Sweden)
Gabriel R. Bengochea
2015-04-01
Full Text Available In this work, we consider the problem of the emergence of seeds of cosmic structure in the framework of the non-inflationary model proposed by Hollands and Wald. In particular, we consider a modification to that proposal designed to account for breaking the symmetries of the initial quantum state, leading to the generation of the primordial inhomogeneities. This new ingredient is described in terms of a spontaneous reduction of the wave function. We investigate under which conditions one can recover an essentially scale free spectrum of primordial inhomogeneities, and which are the dominant deviations that arise in the model as a consequence of the introduction of the collapse of the quantum state into that scenario.
Inhomogeneities from quantum collapse scheme without inflation
Energy Technology Data Exchange (ETDEWEB)
Bengochea, Gabriel R., E-mail: gabriel@iafe.uba.ar [Instituto de Astronomía y Física del Espacio (IAFE), UBA-CONICET, CC 67, Suc. 28, 1428 Buenos Aires (Argentina); Cañate, Pedro, E-mail: pedro.canate@nucleares.unam.mx [Instituto de Ciencias Nucleares, UNAM, México D.F. 04510, México (Mexico); Sudarsky, Daniel, E-mail: sudarsky@nucleares.unam.mx [Instituto de Ciencias Nucleares, UNAM, México D.F. 04510, México (Mexico)
2015-04-09
In this work, we consider the problem of the emergence of seeds of cosmic structure in the framework of the non-inflationary model proposed by Hollands and Wald. In particular, we consider a modification to that proposal designed to account for breaking the symmetries of the initial quantum state, leading to the generation of the primordial inhomogeneities. This new ingredient is described in terms of a spontaneous reduction of the wave function. We investigate under which conditions one can recover an essentially scale free spectrum of primordial inhomogeneities, and which are the dominant deviations that arise in the model as a consequence of the introduction of the collapse of the quantum state into that scenario.
Equilibrium figures of inhomogeneous synchronous binary asteroids
Descamps, P.
2010-06-01
The present paper deals with the application of the classical theory of equilibrium figures of two rotating liquid masses to the case where bodies exhibit a radially stratified internal density distribution so that they can be considered as inhomogeneous bodies. The derived ellipsoidal shape solutions are applied to five real systems of equal-sized synchronous asteroids. Furthermore, internal inhomogeneity puts strong constraints on the surface grain density. A satisfactory model fit is achieved with internal densities of asteroids steadily increasing outwards. In particular, from such an approach we derived grain densities of the considered systems in agreement with their mineralogical composition inferred from reflectance spectroscopy. According to this new approach, 4492 Debussy, presently of unknown spectral type, is predicted to appear as a C-type object with a grain density on the order of 2 g/cm 3.
Improving Thermoelectric Properties of Nanowires Through Inhomogeneity
González, J. Eduardo; Sánchez, Vicenta; Wang, Chumin
2017-05-01
Inhomogeneity in nanowires can be present in the cross-section and/or by breaking the translational symmetry along the nanowire. In particular, the quasiperiodicity introduces an unusual class of electronic and phononic transport with a singular continuous eigenvalue spectrum and critically localized wave functions. In this work, the thermoelectricity in periodic and quasiperiodically segmented nanobelts and nanowires is addressed within the Boltzmann formalism by using a real-space renormalization plus convolution method developed for the Kubo-Greenwood formula, in which tight-binding and Born models are, respectively, used for the calculation of electric and lattice thermal conductivities. For periodic nanowires, we observe a maximum of the thermoelectric figure-of-merit ( ZT) in the temperature space, as occurred in the carrier concentration space. This maximum ZT can be improved by introducing into nanowires periodically arranged segments and an inhomogeneous cross-section. Finally, the quasiperiodically segmented nanowires reveal an even larger ZT in comparison with the periodic ones.
Observational Aspects of an Inhomogeneous Cosmology
Saulder, Christoph; Zeilinger, Werner W
2012-01-01
One of the biggest mysteries in cosmology is Dark Energy, which is required to explain the accelerated expansion of the universe within the standard model. But maybe one can explain the observations without introducing new physics, by simply taking one step back and re-examining one of the basic concepts of cosmology, homogeneity. In standard cosmology, it is assumed that the universe is homogeneous, but this is not true at small scales (<200 Mpc). Since general relativity, which is the basis of modern cosmology, is a non-linear theory, one can expect some backreactions in the case of an inhomogeneous matter distribution. Estimates of the magnitude of these backreactions (feedback) range from insignificant to being perfectly able to explain the accelerated expansion of the universe. In the end, the only way to be sure is to test predictions of inhomogeneous cosmological theories, such as timescape cosmology, against observational data. If these theories provide a valid description of the universe, one expe...
Inference of magnetic fields in inhomogeneous prominences
Milic, Ivan; Atanackovic, Olga
2016-01-01
Most of the quantitative information about the magnetic field vector in solar prominences comes from the analysis of the Hanle effect acting on lines formed by scattering. As these lines can be of non-negligible optical thickness, it is of interest to study the line formation process further. We investigate the multidimensional effects on the interpretation of spectropolarimetric observations, particularly on the inference of the magnetic field vector. We do this by analyzing the differences between multidimensional models, which involve fully self-consistent radiative transfer computations in the presence of spatial inhomogeneities and velocity fields, and those which rely on simple one-dimensional geometry. We study the formation of a prototype line in ad hoc inhomogeneous, isothermal 2D prominence models. We solve the NLTE polarized line formation problem in the presence of a large-scale oriented magnetic field. The resulting polarized line profiles are then interpreted (i.e. inverted) assuming a simple 1D...
Inhomogeneous Monte Carlo simulations of dermoscopic spectroscopy
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.
Spatially discontinuous ionization phenomenon in inhomogeneous soil
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
By using X-ray film imaging technology,a phenomenon of discontinuous ionization was observed in the inhomogeneous soil around the grounding electrode on which a surge voltage was applied.A simplified two-phase solid-gas model was built to study the electric field distribution in the soil to explain the discontinuous ionization phenomenon.Analysis showed the differences of the dielectric properties,the shapes and sizes of soil particles can cause discontinuous ionization in the soil.
Programming of inhomogeneous resonant guided wave networks.
Feigenbaum, Eyal; Burgos, Stanley P; Atwater, Harry A
2010-12-06
Photonic functions are programmed by designing the interference of local waves in inhomogeneous resonant guided wave networks composed of power-splitting elements arranged at the nodes of a nonuniform waveguide network. Using a compact, yet comprehensive, scattering matrix representation of the network, the desired photonic function is designed by fitting structural parameters according to an optimization procedure. This design scheme is demonstrated for plasmonic dichroic and trichroic routers in the infrared frequency range.
Production of heavy elements in inhomogeneous cosmologies
Rauscher, Thomas; Applegate, James H.; Cowan, John J.; Thielemann, Friedrich-Karl; Wiescher, Michael
1994-07-01
Baryon density inhomogeneities during big bang nucleosynthesis can result from a variety of possible causes (e.g., quantum chromodynamic and electroweak phase transitions; cosmic strings). We present here the consequences of such inhomogeneities with special emphasis on the production of heavy elements in a parameter study, varying the global baryon-to-photon ratio eta (which is related to the baryon density and the Hubble constant via eta10 = 64.94 Omegab(H0/50)2 and the length scale of the density inhomogeneities. The production of heavy elements beyond Fe can only occur in neutron-rich environments; thus, we limit our study to neutron-rich zones, originating from neutron diffusion into low-density regions. In this first calculation including elements heavier than Si, we prove an earlier hypothesis that under such conditions r-process elements can be produced, strongly enhanced by the process of fission cycling. Primordial r-process abundances are, however, very sensitive to the choice of eta. Significant amounts, comparable to or larger than the (permitted) floor of heavy-element abundances found in low-metallicity stars at the onset of galactic evolution, can only be obtained for values in excess of eta10 = 133 (i.e., Omegab(h50)2 = 2.0; e.g., Omegab = 1, H0 = 71, or Omegab = 0.5, H0 = 100) and large length scales of inhomogeneities, which minimize the back-diffusion of neutrons into proton-rich regions. Recent investigations analyzing the primordial abundances of light elements seem to set tighter limits, eta10 less than 26 to 39 (Omega b)(h50)2 less than 0.4 to 0.6, from He-4 and apparently considerably lower values based on Li, Be, and B. Under such conditions the predicted abundances of heavy elements are a factor of 105 or more below presently observable limits.
Inversion identities for inhomogeneous face models
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.
Inversion identities for inhomogeneous face models
Directory of Open Access Journals (Sweden)
Holger Frahm
2014-10-01
Full Text Available 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.
Inversion identities for inhomogeneous face models
Energy Technology Data Exchange (ETDEWEB)
Frahm, Holger; Karaiskos, Nikos
2014-10-15
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.
Metric inhomogeneous Diophantine approximation in positive characteristic
DEFF Research Database (Denmark)
Kristensen, S.
We obtain asymptotic formulae for the number of solutions to systems of inhomogeneous linear Diophantine inequalities over the field of formal Laurent series with coefficients from a finite fields, which are valid for almost every such system. Here 'almost every' is with respect to Haar measure o......-infinity laws for Hausdorff measure in the spirit of Jarník's Theorem. The latter result depends on extending a recently developed slicing technique of Beresnevich and Velani to the present setup....
Redshift-distance relation in inhomogeneous cosmology
Scharf, Günter
2015-01-01
We continue to study a cosmological model with large-scale inhomogeneity. Working in the cosmic rest frame we determine null geodesics, redshift and area and luminosity distance. Combining the result with Hubble's law enables us to calculate the distance of the local group of galaxies from the origin where the Big Bang gas taken place. We obtain a surprisingly small value of about 2 million light years.
Metric inhomogeneous Diophantine approximation in positive characteristic
DEFF Research Database (Denmark)
Kristensen, Simon
2011-01-01
We obtain asymptotic formulae for the number of solutions to systems of inhomogeneous linear Diophantine inequalities over the field of formal Laurent series with coefficients from a finite fields, which are valid for almost every such system. Here `almost every' is with respect to Haar measure o......-infinity laws for Hausdorff measure in the spirit of Jarník's Theorem. The latter result depends on extending a recently developed slicing technique of Beresnevich and Velani to the present setup....
Cosmic Inhomogeneities and the Average Cosmological Dynamics
Paranjape, Aseem; Singh, T. P.
2008-01-01
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 \\emph{in}homogeneous Universe, the averaged \\emph{homogeneous} Universe obeys modified Einstein equations. Can such modifications alone explain the acceleration? For a simple generic model with realistic ini...
Collapse of Langmuir solitons in inhomogeneous plasmas
Chen, Y A; Nishida, Y; Cheng, C Z
2016-01-01
Propagation of Langmuir solitons in inhomogeneous plasmas is investigated numerically. Through numerical simulation solving Zakharov equations, the solitons are accelerated toward the low density side. As a consequence, isolated cavities moving at ion sound velocities are emitted. When the acceleration is further increased, solitons collapse and the cavities separate into two lumps released at ion sound velocities. The threshold is estimated by an analogy between the soliton and a particle overcoming the self-generated potential well.
On inhomogeneous straining in compressed sylvinite
Barannikova, S. A.; Nadezhkin, M. V.; Zuev, L. B.; Zhigalkin, V. M.
2010-06-01
Spatiotemporal distributions of local components of the distortion tensor of quasi-plastic materials—saliferous rocks (sylvinite)—have been studied under active compressive straining conditions using double-exposure speckle photography techniques. The strain localization patterns are presented and the features of macroscopic strain inhomogeneity are considered for inelastic behavior of the material. Results obtained for the slow wave processes in deformed saliferous rocks are compared to analogous data available for ionic crystals.
Temperature fluctuations in an inhomogeneous diffusive fluid
Haba, Z
2014-01-01
We discuss metric perturbations of the relativistic diffusion equation around the homogeneous Juttner equilibrium of massless particles in a homogeneous expanding universe. The metric perturbation describes matter distribution and the gravitational wave background in an inhomogeneous universe. We show that the lowest order perturbation can be treated as a variation of temperature. We derive a formula expressing temperature fluctuations in terms of the diffusion and tensor power spectrum. We discuss the multipole expansion of the fluctuations in the presence of diffusion.
2008-04-25
Lorentzian listed by Summers and Thorne .1 where nM, VM, 0M, and 0al in Eqs. (15) and (16) denote the values of these quantities at £=0. The function f^(v...first relate Z^M to Z* of Summers and Thorne ’ [see Eq. (60) of Ref. 9] and then use the series and asymptotic expansions of Z for half-integer values of...0 and its approximate solution for A2>0 is Re cot = \\Jc^s, (79) (80) B(kL,kn): 1 [(2K- 1)/(2K-3)][1 +(k1/kl)(V’e0/ile)] + kip 2’ (74) Both
Loop quantum cosmology: Anisotropies and inhomogeneities
Wilson-Ewing, Edward
In this dissertation we extend the improved dynamics of loop quantum cosmology from the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker space-times to cosmological models which allow anisotropies and inhomogeneities. Specifically, we consider the cases of the homogeneous but anisotropic Bianchi type I, II and IX models with a massless scalar field as well as the vacuum, inhomogeneous, linearly polarized Gowdy T3 model. For each case, we derive the Hamiltonian constraint operator and study its properties. In particular, we show how in all of these models the classical big bang and big crunch singularities are resolved due to quantum gravity effects. Since the Bianchi models play a key role in the Belinskii, Khalatnikov and Lifshitz conjecture regarding the nature of generic space-like singularities in general relativity, the quantum dynamics of the Bianchi cosmologies are likely to provide considerable intuition about the fate of such singularities in quantum gravity. In addition, the results obtained here provide an important step toward the full loop quantization of cosmological space-times that allow generic inhomogeneities; this would provide falsifiable predictions that could be compared to observations.
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.
A method for quantifying visual field inhomogeneities.
Anderson, Jennifer E; Leslie Cameron, E; Levine, Michael W
2014-12-01
It is well known that performance is not homogeneous across the visual field, even at isoeccentric locations. Several inhomogeneities in particular have been identified - a Horizontal-Vertical Anisotropy (HVA - better performance in the horizontal than in the vertical direction); a Vertical Asymmetry (VA - better performance in the lower than the upper visual field); and a Vertical Meridian Asymmetry (VMA - better performance below than above the point of fixation on the vertical meridian). Performance has also been reported to be particularly poor at the location directly above the point of fixation, i.e., the "North" (N) location and sometimes at the location directly below the point of fixation, i.e., the "South" (S) location. These phenomena are typically characterized by statistics that compare performance across the visual field to a homogeneous (circular) model. Here we propose an alternative method for assessing visual field inhomogeneities, which involves comparing performance to an elliptical model of the visual field. We maintain that this method provides a more robust analysis of visual field inhomogeneities because it does not overestimate the North and South effects.
Structural elucidation of inhomogeneous lignins from bamboo.
Wen, Jia-Long; Sun, Shao-Long; Xue, Bai-Liang; Sun, Run-Cang
2015-01-01
A better understanding of the inhomogeneous molecular structure of lignin from bamboo is a prerequisite for promoting the "biorefinery" technologies of the bamboo feedstock. A mild and successive method for fractionating native lignin from bamboo species was proposed in the present study. The molecular structure and structural inhomogeneity of the isolated lignin polymers were comprehensively investigated by elemental analysis, carbohydrate analysis, state-of-the-art NMR and analytical pyrolysis techniques (quantitative (13)C NMR, (13)C-DEPT 135 NMR, 2D-HSQC NMR, (31)P NMR, and pyrolysis-GC-MS). The results showed that the proposed method is effective for extracting lignin from bamboo. NMR results showed that syringyl (S) was the predominant unit in bamboo lignin over guaiacyl (G) and p-hydroxyphenyl (H) units. In addition, the lignin was associated with p-coumarates and ferulates via ester and ether bonds, respectively. Moreover, various substructures, such as β-O-4, β-β, β-5, β-1, and α,β-diaryl ether linkages, were identified and quantified by NMR techniques. Based on the results obtained, a proposed schematic diagram of structural heterogeneity of the lignin polymers extracted from the bamboo is presented. In short, well-defined inhomogeneous structures of native lignin from bamboo will facilitate further applications of bamboo in current biorefineries.
Rotational inhomogeneities from pre-big bang?
Giovannini, Massimo
2005-01-01
The evolution of the rotational inhomogeneities is investigated in the specific framework of four-dimensional pre-big bang models. While minimal (dilaton-driven) scenarios do not lead to rotational fluctuations, in the case of non-minimal (string-driven) models, fluid sources are present in the pre-big bang phase. The rotational modes of the geometry, coupled to the divergenceless part of the velocity field, can then be amplified depending upon the value of the barotropic index of the perfect fluids. In the light of a possible production of rotational inhomogeneities, solutions describing the coupled evolution of the dilaton field and of the fluid sources are scrutinized in both the string and Einstein frames. In semi-realistic scenarios, where the curvature divergences are regularized by means of a non-local dilaton potential, the rotational inhomogeneities are amplified during the pre-big bang phase but they decay later on. Similar analyses can also be performed when a contraction occurs directly in the str...
Inference of magnetic fields in inhomogeneous prominences
Milić, I.; Faurobert, M.; Atanacković, O.
2017-01-01
Context. Most of the quantitative information about the magnetic field vector in solar prominences comes from the analysis of the Hanle effect acting on lines formed by scattering. As these lines can be of non-negligible optical thickness, it is of interest to study the line formation process further. Aims: We investigate the multidimensional effects on the interpretation of spectropolarimetric observations, particularly on the inference of the magnetic field vector. We do this by analyzing the differences between multidimensional models, which involve fully self-consistent radiative transfer computations in the presence of spatial inhomogeneities and velocity fields, and those which rely on simple one-dimensional geometry. Methods: We study the formation of a prototype line in ad hoc inhomogeneous, isothermal 2D prominence models. We solve the NLTE polarized line formation problem in the presence of a large-scale oriented magnetic field. The resulting polarized line profiles are then interpreted (i.e. inverted) assuming a simple 1D slab model. Results: We find that differences between input and the inferred magnetic field vector are non-negligible. Namely, we almost universally find that the inferred field is weaker and more horizontal than the input field. Conclusions: Spatial inhomogeneities and radiative transfer have a strong effect on scattering line polarization in the optically thick lines. In real-life situations, ignoring these effects could lead to a serious misinterpretation of spectropolarimetric observations of chromospheric objects such as prominences.
From Suitable Weak Solutions to Entropy Viscosity
Guermond, Jean-Luc
2010-12-16
This paper focuses on the notion of suitable weak solutions for the three-dimensional incompressible Navier-Stokes equations and discusses the relevance of this notion to Computational Fluid Dynamics. The purpose of the paper is twofold (i) to recall basic mathematical properties of the three-dimensional incompressible Navier-Stokes equations and to show how they might relate to LES (ii) to introduce an entropy viscosity technique based on the notion of suitable weak solution and to illustrate numerically this concept. © 2010 Springer Science+Business Media, LLC.
Multi-Parameter Estimation for Orthorhombic Media
Masmoudi, Nabil
2015-08-19
Building reliable anisotropy models is crucial in seismic modeling, imaging and full waveform inversion. However, estimating anisotropy parameters is often hampered by the trade off between inhomogeneity and anisotropy. For instance, one way to estimate the anisotropy parameters is to relate them analytically to traveltimes, which is challenging in inhomogeneous media. Using perturbation theory, we develop travel-time approximations for orthorhombic media as explicit functions of the anellipticity parameters η1, η2 and a parameter Δγ in inhomogeneous background media. Specifically, our expansion assumes inhomogeneous ellipsoidal anisotropic background model, which can be obtained from well information and stacking velocity analysis. This approach has two main advantages: in one hand, it provides a computationally efficient tool to solve the orthorhombic eikonal equation, on the other hand, it provides a mechanism to scan for the best fitting anisotropy parameters without the need for repetitive modeling of traveltimes, because the coefficients of the traveltime expansion are independent of the perturbed parameters. Furthermore, the coefficients of the traveltime expansion provide insights on the sensitivity of the traveltime with respect to the perturbed parameters. We show the accuracy of the traveltime approximations as well as an approach for multi-parameter scanning in orthorhombic media.
Energy Technology Data Exchange (ETDEWEB)
Gabriel, P. [Colorado State Univ., Fort Collins, CO (United States)
1995-09-01
The use of cloud fraction as a means of incorporating horizontal cloud inhomogeneity in radiative transfer calculations is widespread in the atmospheric science community. This research attempts to bypass the use of cloud fraction in radiative transfer modeling for two-dimensional media. Gabriel describes two approximation techniques useful in calculating the domain averaged bulk radiative properties such as albedo, flux divergence and mean radiance that dispense with the need to use cloud fraction as a specifier of cloud inhomogeneity. The results suggest that the variability of the medium can largely be accounted for through the pseudo-source term, offering hope of parameterizing the equation of transfer in terms of the statistical properties of the medium. 1 fig.
Energy Technology Data Exchange (ETDEWEB)
Borovsky, J.E.
1987-02-01
The propagation of ultralow-frequency (ulf) electromagnetic signals (Alfven and magnetosonic waves) in collisional, inhomogeneous, magnetized plasmas is analyzed by numerical simulation. The problem is formulated from a Maxwell-equation orbit-theory approach rather than from a magnetohydrodynamic point of view, and the problem is numerically treated in a fully time-dependent manner. Boundary-value-problem behavior is distinguished from initial-value-problem behavior. The propagation of two-dimensional small-amplitude electromagnetic disturbances in plasmas with spatially dependent densities and in plasmas with spatially dependent conductivities is numerically simulated, and when possible, the simulations are compared with theory. Changes in the plasma density lead to changes in the signal speed and to reflections; collisions lead to changes in the signal speed, to reflections, and to attenuations. Theoretical descriptions based upon discontinuities in the media are generally incorrect in predicting the amplitudes of signals reflected from plasma inhomogeneities. 19 refs., 16 figs.
Weak decays. [Lectures, phenomenology
Energy Technology Data Exchange (ETDEWEB)
Wojcicki, S.
1978-11-01
Lectures are given on weak decays from a phenomenological point of view, emphasizing new results and ideas and the relation of recent results to the new standard theoretical model. The general framework within which the weak decay is viewed and relevant fundamental questions, weak decays of noncharmed hadrons, decays of muons and the tau, and the decays of charmed particles are covered. Limitation is made to the discussion of those topics that either have received recent experimental attention or are relevant to the new physics. (JFP) 178 references
Weakly asymptotically hyperbolic manifolds
Allen, Paul T; Lee, John M; Allen, Iva Stavrov
2015-01-01
We introduce a class of "weakly asymptotically hyperbolic" geometries whose sectional curvatures tend to $-1$ and are $C^0$, but are not necessarily $C^1$, conformally compact. We subsequently investigate the rate at which curvature invariants decay at infinity, identifying a conformally invariant tensor which serves as an obstruction to "higher order decay" of the Riemann curvature operator. Finally, we establish Fredholm results for geometric elliptic operators, extending the work of Rafe Mazzeo and John M. Lee to this setting. As an application, we show that any weakly asymptotically hyperbolic metric is conformally related to a weakly asymptotically hyperbolic metric of constant negative curvature.
Hosoya, Akio
2010-01-01
We develop a formal theory of the weak values with emphasis on the consistency conditions and a probabilistic interpretation in the counter-factual processes. We present the condition for the choice of the post-selected state to give a negative weak value of a given projection operator and strange values of an observable in general. The general framework is applied to Hardy's paradox and the spin $1/2$ system to explicitly address the issues of counter-factuality and strange weak values. The counter-factual arguments which characterize the paradox specifies the pre-selected state and a complete set of the post-selected states clarifies how the strange weak values emerge.
Judge, A C; Sipe, J E; de Sterke, C M
2012-01-01
We present a canonical quantization of macroscopic electrodynamics. The results apply to inhomogeneous media with a broad class of linear magneto-electric responses which are consistent with the Kramers-Kronig and Onsager relations. Through its ability to accommodate strong dispersion and loss, our theory provides a rigorous foundation for the study of quantum optical processes in structures incorporating metamaterials, provided these may be modeled as magneto-electric media. Previous canonical treatments of dielectric and magneto-dielectric media have expressed the electromagnetic field operators in either a Green function or mode expansion representation. Here we present our results in the mode expansion picture with a view to applications in guided wave and cavity quantum optics.
Energy Technology Data Exchange (ETDEWEB)
Mensch, Th.
2000-01-12
The seismic anisotropy causes in the Earth are known. The anisotropy characterization can provide valuable informations on the structure, lithology or eventual deformation processes in geological media. The orthorhombic symmetry allows a more complete description and representation of the anisotropy than the transversely isotropy symmetry usually assumed. Moreover this symmetry is potentially common in sedimentary basins, and particularly in fractured reservoir. In anisotropic media of arbitrary symmetry (triclinic), there is no simple analytic expressions on the phase slowness surface. The weak anisotropy assumption, often reasonable in geological media, makes perturbation techniques relevant. An approximate first order analytical expression of the qP-wave slowness surface is obtained. Using an adequate parameterization, the forward problem is solved by the ray theory. The Hamiltonian formulation introduces by a simple way ray equations in anisotropic media. The rays, travel time and its Fruchet derivatives expressions, valid to first order, are given for orthorhombic inhomogeneous media. Perturbation method applied to the ray theory allows the development of fast ray tracing in these media. Synthetic examples illustrate the accuracy and efficiency of the proposed approach. A tomographic method is developed. The travel time are inverted by minimizing, in term of least-square, the misfit between the observed and calculated travel times. The solution is approached iteratively by using a singular value decomposition algorithm. The inversion stability is assured by introducing a priori constraints. Synthetics examples show the need of an acquisition geometry well conceived to take account of anisotropy. (author)
Joyal, André
2009-01-01
We define weak units in a semi-monoidal 2-category $\\CC$ as cancellable pseudo-idempotents: they are pairs $(I,\\alpha)$ where $I$ is an object such that tensoring with $I$ from either side constitutes a biequivalence of $\\CC$, and $\\alpha: I \\tensor I \\to I$ is an equivalence in $\\CC$. We show that this notion of weak unit has coherence built in: Theorem A: $\\alpha$ has a canonical associator 2-cell, which automatically satisfies the pentagon equation. Theorem B: every morphism of weak units is automatically compatible with those associators. Theorem C: the 2-category of weak units is contractible if non-empty. Finally we show (Theorem E) that the notion of weak unit is equivalent to the notion obtained from the definition of tricategory: $\\alpha$ alone induces the whole family of left and right maps (indexed by the objects), as well as the whole family of Kelly 2-cells (one for each pair of objects), satisfying the relevant coherence axioms.
Effects from inhomogeneities in the chiral transition
Taketani, B G; Taketani, Bruno G.; Fraga, Eduardo S.
2006-01-01
We consider an approximation procedure to evaluate the finite-temperature one-loop fermionic density in the presence of a chiral background field which systematically incorporates effects from inhomogeneities in the chiral field through a derivative expansion. We apply the method to the case of a simple low-energy effective chiral model which is commonly used in the study of the chiral phase transition, the linear sigma-model coupled to quarks. The modifications in the effective potential and their consequences for the bubble nucleation process are discussed.
Albedo and transmittance of inhomogeneous stratus clouds
Energy Technology Data Exchange (ETDEWEB)
Zuev, V.E.; Kasyanov, E.I.; Titov, G.A. [Institute of Atmospheric Optics, Tomsk (Russian Federation)] [and others
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.
Measurement of Density Inhomogeneity for Glass Pendulum
Institute of Scientific and Technical Information of China (English)
LIU Lin-Xia; LIU Qi; SHAO Cheng-Gang; ZHANG Ya-Ting; LUO Jun; Vadim Milyukov
2008-01-01
@@ The density inhomogeneity of a glass pendulum is determined by an optical interference method.The relative variations of the densities over a volume with sizes of 5 × 5 × 5mm3 are (0.64±0.97) × 10-5 and (0.99 ± 0.92) ×10-5 for the K9 glass and silica glass pendulum, respectively.These variations of densities contributing to the relative uncertainties of the Newtonian gravitational constant G are 0.20 ppm and 0.21 ppm in our experiment on measurement of G.
Heat transport in coupled inhomogeneous chains
Institute of Scientific and Technical Information of China (English)
Hu Tao; Bai Meng; Hu Ke; Tang Yi
2011-01-01
We first investigate the heat transport in a network model consisting of two coupled dimerized chains. Results indicate that the thermal resistance of each chain increases with the decrease of the mass ratio γ of the two types of atoms. Then, we find, when a light impurity or a heavy one is added in the two coupled homogeneous chains and coupled with a particle of another chain, the interface thermal resistances Rlint andRγint present different dependences on the mass ratio γ'. Finally, a persistent circulation of energy current is observed in coupled inhomogeneous chains with two pairs of interchain coupling.
CMB radiation in an inhomogeneous spherical space
Aurich, R; Lustig, S
2011-01-01
We analyse the CMB radiation in spherical 3-spaces with non-trivial topology. The focus is put on an inhomogeneous space which possesses observer dependent CMB properties. The suppression of the CMB anisotropies on large angular scales is analysed with respect to the position of the CMB observer. The equivalence of a lens space with a Platonic cubic space is shown and used for the harmonic analysis. We give the transformation of the CMB multipole radiation amplitude as a function of the position of the observer. General sum rules are obtained in terms of the squares of the expansion coefficients for invariant polynomials on the 3-sphere.
Observable Deviations from Homogeneity in an Inhomogeneous Universe
Giblin, John T; Starkman, Glenn D
2016-01-01
How does inhomogeneity affect our interpretation of cosmological observations? It has long been wondered to what extent the observable properties of an inhomogeneous universe differ from those of a corresponding Friedman-Lemaitre-Robertson-Walker (FLRW) model, and how the inhomogeneities affect that correspondence. Here, we use numerical relativity to study the behavior of light beams traversing an inhomogeneous universe and construct the resulting Hubble diagrams. The universe that emerges exhibits an average FLRW behavior, but inhomogeneous structures contribute to deviations in observables across the observer's sky. We also investigate the relationship between angular diameter distance and the angular extent of a source, finding deviations that grow with source redshift. These departures from FLRW are important path-dependent effects with implications for using real observables in an inhomogeneous universe such as our own.
DEFF Research Database (Denmark)
Amber, Van der Graaf; Otjes, Simon; Rasmussen, Anne
2016-01-01
Social media have the potential to offset existing inequalities in representation among interest groups and act as a ‘weapon of the weak’ by providing a technological infrastructure that allows even groups with limited resources to create content and interact across the globe. We expand on the sp......Social media have the potential to offset existing inequalities in representation among interest groups and act as a ‘weapon of the weak’ by providing a technological infrastructure that allows even groups with limited resources to create content and interact across the globe. We expand...
Entanglement in Anisotropic Heisenberg XYZ Chain with Inhomogeneous Magnetic Field
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The thermal entanglement of a two-qubit anisotropic Heisenberg XYZ chain under an inhomogeneous magnetic field b is studied. It is shown that when inhomogeneity is increased to a certain value, the entanglement can exhibit a larger revival than that of less values of b. The property is both true for zero temperature and a finite temperature. The results also show that the entanglement and threshold temperature can be increased by increasing inhomogeneous external magnetic field.
Moody's Correlated Binomial Default Distributions for Inhomogeneous Portfolios
Mori, S.; Kitsukawa, K.; Hisakado, M.
2006-01-01
This paper generalizes Moody's correlated binomial default distribution for homogeneous (exchangeable) credit portfolio, which is introduced by Witt, to the case of inhomogeneous portfolios. As inhomogeneous portfolios, we consider two cases. In the first case, we treat a portfolio whose assets have uniform default correlation and non-uniform default probabilities. We obtain the default probability distribution and study the effect of the inhomogeneity on it. The second case corresponds to a ...
Multi-parameters scanning in HTI media
Masmoudi, Nabil
2014-08-05
Building credible anisotropy models is crucial in imaging. One way to estimate anisotropy parameters is to relate them analytically to traveltime, which is challenging in inhomogeneous media. Using perturbation theory, we develop traveltime approximations for transversely isotropic media with horizontal symmetry axis (HTI) as explicit functions of the anellipticity parameter η and the symmetry axis azimuth ϕ in inhomogeneous background media. Specifically, our expansion assumes an inhomogeneous elliptically anisotropic background medium, which may be obtained from well information and stacking velocity analysis in HTI media. This formulation has advantages on two fronts: on one hand, it alleviates the computational complexity associated with solving the HTI eikonal equation, and on the other hand, it provides a mechanism to scan for the best fitting parameters η and ϕ without the need for repetitive modeling of traveltimes, because the traveltime coefficients of the expansion are independent of the perturbed parameters η and ϕ. The accuracy of our expansion is further enhanced by the use of shanks transform. We show the effectiveness of our scheme with tests on a 3D model and we propose an approach for multi-parameters scanning in TI media.
Transverse flow induced by inhomogeneous magnetic fields in the Bjorken expansion
Pu, Shi
2016-01-01
We investigate the magnetohydrodynamics in the presence of an external magnetic field following the power-law decay in proper time and having spatial inhomogeneity characterized by a Gaussian distribution in one of transverse coordinates under the Bjorken expansion. The leading-order solution is obtained in the weak-field approximation, where both energy density and fluid velocity are modified. It is found that the spatial gradient of the magnetic field results in transverse flow, where the flow direction depends on the decay exponents of the magnetic field. We suggest that such a magnetic-field-induced effect might influence anisotropic flow in heavy ion collisions.
Determinantal formulae for the Casimir operators of inhomogeneous Lie algebras
Energy Technology Data Exchange (ETDEWEB)
Campoamor-Stursberg, Rutwig [Dpto. Geometria y Topologia, Fac CC Matematicas, Universidad Complutense de Madrid, Plaza de Ciencias, 3, E-28040 Madrid (Spain)
2006-03-10
Contractions of Lie algebras are combined with the classical matrix method of Gel'fand to obtain matrix formulae for the Casimir operators of inhomogeneous Lie algebras. The method is presented for the inhomogeneous pseudo-unitary Lie algebras Iu(p,q). This procedure is extended to contractions of Iu(p,q) isomorphic to an extension by a derivation of the inhomogeneous special pseudo-unitary Lie algebras Isu(p-1,q), providing an additional analytical method to obtain their invariants. Further, matrix formulae for the invariants of other inhomogeneous Lie algebras are presented.
Inhomogeneous Superconductivity in Condensed Matter and QCD
Casalbuoni, Roberto; Casalbuoni, Roberto; Nardulli, Giuseppe
2004-01-01
Inhomogeneous superconductivity arises when the species participating in the pairing phenomenon have different Fermi surfaces with a large enough separation. In these conditions it could be more favorable for each of the pairing fermions to stay close to its Fermi surface and, differently from the usual BCS state, for the Cooper pair to have a non zero total momentum. For this reason in this state the gap varies in space, the ground state is inhomogeneous and a crystalline structure might be formed. This situation was considered for the first time by Fulde, Ferrell, Larkin and Ovchinnikov, and the corresponding state is called LOFF. The spontaneous breaking of the space symmetries in the vacuum state is a characteristic feature of this phase and is associated to the presence of long wave-length excitations of zero mass. The situation described here is of interest both in solid state and in elementary particle physics, in particular in Quantum Chromo-Dynamics at high density and small temperature. In this revi...
Inhomogeneous chemical enrichment in the Galactic Halo
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.
Model of non-stationary, inhomogeneous turbulence
Bragg, Andrew D.; Kurien, Susan; Clark, Timothy T.
2017-02-01
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.
WEAK CONVERGENCE OF SOME SERIES
Institute of Scientific and Technical Information of China (English)
2000-01-01
This paper continues the study of [1] on weak functions.The weak convergence theory is investigated in complex analysis,Fourier transform and Mellin transform.A Mobius inverse formula of weak functions is obtained.
DEFF Research Database (Denmark)
Kohlenbach, Ulrich Wilhelm
2002-01-01
We show that the so-called weak Markov's principle (WMP) which states that every pseudo-positive real number is positive is underivable in E-HA + AC. Since allows one to formalize (atl eastl arge parts of) Bishop's constructive mathematics, this makes it unlikely that WMP can be proved within the...
On closed weak supplemented modules
Institute of Scientific and Technical Information of China (English)
ZENG Qing-yi; SHI Mei-hua
2006-01-01
A module M is called closed weak supplemented if for any closed submodule N of M, there is a submodule K of M such that M=K+N and K(c)N＜＜M. Any direct summand of closed weak supplemented module is also closed weak supplemented.Any nonsingular image of closed weak supplemented module is closed weak supplemented. Nonsingular V-rings in which all nonsingular modules are closed weak supplemented are characterized in Section 4.
Majhi, S.; Pal, P. C.; Kumar, S.
2017-01-01
This study investigates the reflection and transmission of plane SH-waves in two semi-infinite anisotropic magnetoelastic media. The lower half-space is considered as initially stressed and inhomogeneous. The density of lower half-space is taken exponentially varying with depth. The solutions for half-spaces are obtained analytically. The expressions for reflection and transmission coefficient are obtained in the closed form subject to continuity conditions at the interfaces of anisotropic magnetoelastic half-spaces and the Snell's law. It is found that these coefficients depend on the initial stress, inhomogeneity parameter, the magnetoelastic coupling parameter, and the angle at which wave crosses the magnetic field of the half-spaces. Numerical computations are performed for these coefficients for a specific model of two different anisotropic magnetoelastic half-spaces. The numerical results are illustrated by the graph of reflection and transmission coefficient versus the angle of incidence. In general, as the initial stress increases the reflection and transmission coefficient increases, the affect is more prominent for more than 10 GPa. Inhomogeneity in the density of the material also increases the reflection and transmission coefficient. The anisotropic magnetoelastic parameter and the angle at which the wave crosses the magnetic field for both the half-spaces have a quite significant effect on the reflection and transmission coefficient.
Majhi, S.; Pal, P. C.; Kumar, S.
2016-06-01
This study investigates the reflection and transmission of plane SH-waves in two semi-infinite anisotropic magnetoelastic media. The lower half-space is considered as initially stressed and inhomogeneous. The density of lower half-space is taken exponentially varying with depth. The solutions for half-spaces are obtained analytically. The expressions for reflection and transmission coefficient are obtained in the closed form subject to continuity conditions at the interfaces of anisotropic magnetoelastic half-spaces and the Snell's law. It is found that these coefficients depend on the initial stress, inhomogeneity parameter, the magnetoelastic coupling parameter, and the angle at which wave crosses the magnetic field of the half-spaces. Numerical computations are performed for these coefficients for a specific model of two different anisotropic magnetoelastic half-spaces. The numerical results are illustrated by the graph of reflection and transmission coefficient versus the angle of incidence. In general, as the initial stress increases the reflection and transmission coefficient increases, the affect is more prominent for more than 10 GPa. Inhomogeneity in the density of the material also increases the reflection and transmission coefficient. The anisotropic magnetoelastic parameter and the angle at which the wave crosses the magnetic field for both the half-spaces have a quite significant effect on the reflection and transmission coefficient.
Daga, Bijoy; Mondal, Souvik; Chandra, Anjan Kumar; Banerjee, Tirthankar; Basu, Abhik
2017-01-01
We study the totally asymmetric exclusion process (TASEP) on a nonuniform one-dimensional ring consisting of two segments having unequal hopping rates, or defects. We allow weak particle nonconservation via Langmuir kinetics (LK), which are parametrized by generic unequal attachment and detachment rates. For an extended defect, in the thermodynamic limit the system generically displays inhomogeneous density profiles in the steady state—the faster segment is either in a phase with spatially varying density having no density discontinuity, or a phase with a discontinuous density changes. Nonequilibrium phase transitions between the above phases are controlled by the inhomogeneity and LK. The slower segment displays only macroscopically uniform bulk density profiles in the steady states, reminiscent of the maximal current phase of TASEP but with a bulk density generally different from half. With a point defect, there are spatially uniform low- and high-density phases as well, in addition to the inhomogeneous density profiles observed for an extended defect. In all the cases, it is argued that the mean particle density in the steady state is controlled only by the ratio of the LK attachment and detachment rates.
Ising Critical Behavior of Inhomogeneous Curie-Weiss Models and Annealed Random Graphs
Dommers, Sander; Giardinà, Cristian; Giberti, Claudio; van der Hofstad, Remco; Prioriello, Maria Luisa
2016-11-01
We study the critical behavior for inhomogeneous versions of the Curie-Weiss model, where the coupling constant {J_{ij}(β)} for the edge {ij} on the complete graph is given by {J_{ij}(β)=β w_iw_j/( {sum_{kin[N]}w_k})}. We call the product form of these couplings the rank-1 inhomogeneous Curie-Weiss model. This model also arises [with inverse temperature {β} replaced by {sinh(β)} ] from the annealed Ising model on the generalized random graph. We assume that the vertex weights {(w_i)_{iin[N]}} are regular, in the sense that their empirical distribution converges and the second moment converges as well. We identify the critical temperatures and exponents for these models, as well as a non-classical limit theorem for the total spin at the critical point. These depend sensitively on the number of finite moments of the weight distribution. When the fourth moment of the weight distribution converges, then the critical behavior is the same as on the (homogeneous) Curie-Weiss model, so that the inhomogeneity is weak. When the fourth moment of the weights converges to infinity, and the weights satisfy an asymptotic power law with exponent {τ} with {τin(3,5)}, then the critical exponents depend sensitively on {τ}. In addition, at criticality, the total spin {S_N} satisfies that {S_N/N^{(τ-2)/(τ-1)}} converges in law to some limiting random variable whose distribution we explicitly characterize.
Small scales formation via Alfven wave propagation in compressible nonuniform media
Malara, F.; Primavera, L.; Veltri, P.
1995-01-01
In weakly dissipative media governed by the magnetohydrodynamics (MHD) equations, any efficient mechanism of energy dissipation requires the formation of small scales. The possibility to produce small scales has been studied by Malara et al. in the case of MHD disturbances propagating in an incompressible and inhomogeneous medium, for a strictly 2D geometry. We extend the work of Malara et al. to include both compressibility and the third component for vector quantities. Using numerical simulations we show that, when an Alfven wave propagates in a compressible nonuniform medium, the two dynamical effects responsible for the small scales formation in the incompressible case are still at work: energy pinching and phase-mixing. Moreover, the interaction between the initial Alfven wave and the inhomogeneity gives rise to the formation of compressible perturbations (fast and slow waves or a static entropy wave). Some of these compressive fluctuations are subject to the steepening of the wave front and become shock waves, which are extremely efficient in dissipating their energy, their dissipation being independent of the Reynolds number. A rough estimate of the typical times which the various dynamical processes take to produce small scales and then to dissipate the energy show that these times are consistent with those required to dissipate inside the solar corona the energy of Alfven waves of photospheric origin.
Tests of Cosmological Inhomogeneity Using WMAP
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
Kosevich, Yuriy A; Gann, Vladimir V
2013-06-19
We study the localization of magnon states in finite defect-free Heisenberg spin-1/2 ferromagnetic chains placed in an inhomogeneous magnetic field with a constant spatial gradient. Continuous transformation from the extended magnon states to the localized Wannier-Zeeman states in a finite spin chain placed in an inhomogeneous field is described both analytically and numerically. We describe for the first time the non-monotonic dependence of the energy levels of magnons, both long and short wavelength, on the magnetic field gradient, which is a consequence of magnon localization in a finite spin chain. We show that, in contrast to the destruction of the magnon band and the establishment of the Wannier-Stark ladder in a vanishingly small field gradient in an infinite chain, the localization of magnon states at the chain ends preserves the memory of the magnon band. Essentially, the localization at the lower- or higher-field chain end resembles the localization of the positive- or negative-effective-mass band quasiparticles. We also show how the beat dynamics of coherent superposition of extended spin waves in a finite chain in a homogeneous or weakly inhomogeneous field transforms into magnon Bloch oscillations of the superposition of localized Wannier-Zeeman states in a strongly inhomogeneous field. We provide a semiclassical description of the magnon Bloch oscillations and show that the correspondence between the quantum and semiclassical descriptions is most accurate for Bloch oscillations of the magnon coherent states, which are built from a coherent superposition of a large number of the nearest-neighbour Wannier-Zeeman states.
Weak Polarized Electron Scattering
Erler, Jens; Mantry, Sonny; Souder, Paul A
2014-01-01
Scattering polarized electrons provides an important probe of the weak interactions. Precisely measuring the parity-violating left-right cross section asymmetry is the goal of a number of experiments recently completed or in progress. The experiments are challenging, since A_{LR} is small, typically between 10^(-4) and 10^(-8). By carefully choosing appropriate targets and kinematics, various pieces of the weak Lagrangian can be isolated, providing a search for physics beyond the Standard Model. For other choices, unique features of the strong interaction are studied, including the radius of the neutron density in heavy nuclei, charge symmetry violation, and higher twist terms. This article reviews the theory behind the experiments, as well as the general techniques used in the experimental program.
Energy Technology Data Exchange (ETDEWEB)
Suzuki, M.
1988-04-01
Dynamical mechanism of composite W and Z is studied in a 1/N field theory model with four-fermion interactions in which global weak SU(2) symmetry is broken explicitly by electromagnetic interaction. Issues involved in such a model are discussed in detail. Deviation from gauge coupling due to compositeness and higher order loop corrections are examined to show that this class of models are consistent not only theoretically but also experimentally.
Inhomogeneous waves in lossy metamaterials and negative refraction
Fedorov, Vladimir Yu
2013-01-01
We study the formation of inhomogeneous waves at the interface of a lossy metamaterial. We show that negative refraction can be interpreted as the formation of an inhomogeneous wave with the obtuse angle between equiamplitude and equiphase planes. Additionally we show that the refractive index and attenuation coefficient of a lossy metamaterial depend on an incident angle even if this metamaterial is isotropic.
Collapse arresting in an inhomogeneous quintic nonlinear Schrodinger model
DEFF Research Database (Denmark)
Gaididei, Yuri Borisovich; Schjødt-Eriksen, Jens; Christiansen, Peter Leth
1999-01-01
Collapse of (1 + 1)-dimensional beams in the inhomogeneous one-dimensional quintic nonlinear Schrodinger equation is analyzed both numerically and analytically. It is shown that in the vicinity of a narrow attractive inhomogeneity, the collapse of beams in which the homogeneous medium would blow up...
MRI intensity inhomogeneity correction by combining intensity and spatial information
Energy Technology Data Exchange (ETDEWEB)
Vovk, Uros; Pernus, Franjo; Likar, Bostjan [Faculty of Electrical Engineering, University of Ljubljana, Trzaska 25, 1000 Ljubljana (Slovenia)
2004-09-07
We propose a novel fully automated method for retrospective correction of intensity inhomogeneity, which is an undesired phenomenon in many automatic image analysis tasks, especially if quantitative analysis is the final goal. Besides most commonly used intensity features, additional spatial image features are incorporated to improve inhomogeneity correction and to make it more dynamic, so that local intensity variations can be corrected more efficiently. The proposed method is a four-step iterative procedure in which a non-parametric inhomogeneity correction is conducted. First, the probability distribution of image intensities and corresponding second derivatives is obtained. Second, intensity correction forces, condensing the probability distribution along the intensity feature, are computed for each voxel. Third, the inhomogeneity correction field is estimated by regularization of all voxel forces, and fourth, the corresponding partial inhomogeneity correction is performed. The degree of inhomogeneity correction dynamics is determined by the size of regularization kernel. The method was qualitatively and quantitatively evaluated on simulated and real MR brain images. The obtained results show that the proposed method does not corrupt inhomogeneity-free images and successfully corrects intensity inhomogeneity artefacts even if these are more dynamic.
Direct optical imaging of structural inhomogeneities in crystalline materials.
Grigorev, A M
2016-05-10
A method for optical imaging of structural inhomogeneities in crystalline materials is proposed, based on the differences in the optical properties of the structural inhomogeneity and the homogeneous material near the fundamental absorption edge of the crystalline material. The method can be used to detect defects in both semiconductors and insulators.
Dielectric Fluid in Inhomogeneous Pulsed Electric Field
Shneider, M N
2013-01-01
We consider the dynamics of a compressible fluid under the influence of electrostrictive ponderomotive forces in strong inhomogeneous nonstationary electric fields. It is shown that if the fronts of the voltage rise at a sharp, needle-like electrode are rather steep (less than or about nanoseconds), and the region of negative pressure arises, which can reach values at which the fluid loses its continuity with the formation of cavitation ruptures. If the voltage on the electrode is not large enough or the front is flatter, the cavitation in the liquid does not occur. However, a sudden shutdown of the field results in a reverse flow of liquid from the electrode, which leads to appearance of negative pressure, and, possibly, cavitation.
Casimir Torque in Inhomogeneous Dielectric Plates
Long, William
2013-01-01
In this work, we consider a torque caused by the well known quantum mechanical Casimir effect arising from quantized field fluctuations between plates with inhomogeneous, sharply discontinuous, dielectric properties. While the Casimir effect is a relatively well understood phenomenon, systems resulting in lateral or rotational forces are far less developed; to our knowledge, a theoretical study of discontinuous dielectric variants of such systems has not been attempted. We utilize a Proximity Force Approximation in conjunction with the Lifshitz dielectric formula to perform theoretical analyses of resultant torques in systems with bisected and quadrisected dielectric regions. We also develop a high precision Monte Carlo type numerical integrator to approximate our derived expressions. Our calculations of an energy density linear with the alignment angle result in a constant torque and have implications in NEMS (nano electromechanical systems) and MEMS (micro electromechanical systems), including a postulated ...
Creating Statistically Anisotropic and Inhomogeneous Perturbations
Armendariz-Picon, C
2007-01-01
In almost all structure formation models, primordial perturbations are created within a homogeneous and isotropic universe, like the one we observe. Because their ensemble averages inherit the symmetries of the spacetime in which they are seeded, cosmological perturbations then happen to be statistically isotropic and homogeneous. Certain anomalies in the cosmic microwave background on the other hand suggest that perturbations do not satisfy these statistical properties, thereby challenging perhaps our understanding of structure formation. In this article we relax this tension. We show that if the universe contains an appropriate triad of scalar fields with spatially constant but non-zero gradients, it is possible to generate statistically anisotropic and inhomogeneous primordial perturbations, even though the energy momentum tensor of the triad itself is invariant under translations and rotations.
Origin of Inhomogeneity in Glass Melts
DEFF Research Database (Denmark)
Jensen, Martin; Keding, Ralf; Yue, Yuanzheng
The homogeneity of a glass plays a crucial role in many applications as the inhomogeneities can provide local changes in mechanical properties, optical properties, and thermal expansion coefficient. Homogeneity is not a single property of the glass, instead, it consists of several factors...... such as bubbles, striae, trace element concentration, undissolved species, and crystallised species. As it is not possible to address all the factors in a single study, this work focuses on one of the major factors: chemical striae. Up to now, the quantification of chemical striae in glasses, particularly......, in less transparent glasses, has been a challenge due to the lack of an applicable method. In this study, we have established a simple and accurate method for quantifying the extent of the striae, which is based on the scanning and picture processing through the Fourier transformation. By performing...
CMB anisotropies from primordial inhomogeneous magnetic fields
Lewis, A
2004-01-01
Primordial inhomogeneous magnetic fields of the right strength can leave a signature on the CMB temperature anisotropy and polarization. Potentially observable contributions to polarization B-modes are generated by vorticity and gravitational waves sourced by the magnetic anisotropic stress. We compute the corresponding CMB transfer functions in detail including the effect of neutrinos. The shear rapidly causes the neutrino anisotropic stress to cancel the stress from the magnetic field, suppressing the production of gravitational waves and vorticity on super-horizon scales after neutrino decoupling. A significant large scale signal from tensor modes can only be produced before neutrino decoupling, and the actual amplitude is somewhat uncertain. Plausible values suggest primordial nearly scale invariant fields of ~ 10^(-10)G today may be observable from their large scale tensor anisotropy. They can be distinguished from primordial gravitational waves by their non-Gaussianity. Vector mode vorticity sources B-m...
The past attractor in inhomogeneous cosmology
Uggla, C; Wainwright, J; Ellis, G F R; Uggla, Claes; Elst, Henk van; Wainwright, John; Ellis, George F R
2003-01-01
We present a general framework for analyzing spatially inhomogeneous cosmological dynamics. It employs Hubble-normalized scale-invariant variables which are defined within the orthonormal frame formalism, and leads to the formulation of Einstein's field equations with a perfect fluid matter source as an autonomous system of evolution equations and constraints. This framework incorporates spatially homogeneous dynamics in a natural way as a special case, thereby placing earlier work on spatially homogeneous cosmology in a broader context, and allows us to draw on experience gained in that field using dynamical systems methods. One of our goals is to provide a precise formulation of the approach to the spacelike initial singularity in cosmological models, described heuristically by Belinski\\v{\\i}, Khalatnikov and Lifshitz. Specifically, we construct an invariant set which we conjecture forms the local past attractor for the evolution equations. We anticipate that this new formulation will provide the basis for ...
Inhomogeneous All-Dielectric Magnetic Metamaterials
Sun, Jingbo; Zhou, Ji; Kudyshev, Zhaxylyk; Litchinitser, Natalia M
2015-01-01
Anomalous field enhancement accompanied by resonant absorption phenomenon was originally discussed in the context of plasma physics and in applications related to radio-communications between the ground and spacecraft returning to Earth. Indeed, there is a critical period of time when all communications are lost due to the reflection/absorption of electromagnetic waves by the sheath of plasma created by a high speed vehicle re-entering the atmosphere. While detailed experimental studies of these phenomena in space are challenging, the emergence of electromagnetic metamaterials enables researchers exceptional flexibility to study them in the laboratory environment. Here, we experimentally demonstrated the localized field enhancement of the electromagnetic wave obliquely incident on a Mie-resonance-based inhomogeneous metamaterials with magnetic permeability gradually changing from positive to negative values.
Measurable inhomogeneities in stock trading volume flow
Cortines, A. A. G.; Riera, R.; Anteneodo, C.
2008-08-01
We investigate the statistics of volumes of shares traded in stock markets. We show that the stochastic process of trading volumes can be understood on the basis of a mixed Poisson process at the microscopic time level. The beta distribution of the second kind (also known as q-gamma distribution), that has been proposed to describe empirical volume histograms, naturally results from our analysis. In particular, the shape of the distribution at small volumes is governed by the degree of granularity in the trading process, while the exponent controlling the tail is a measure of the inhomogeneities in market activity. Furthermore, the present case furnishes empirical evidence of how power law probability distributions can arise as a consequence of a fluctuating intrinsic parameter.
Supernova Feedback in an Inhomogeneous Interstellar Medium
Martizzi, Davide; Quataert, Eliot
2014-01-01
Supernova (SN) feedback is one of the key processes shaping the interstellar medium (ISM) of galaxies. SNe contribute to (and in some cases may dominate) driving turbulence in the ISM and accelerating galactic winds. Modern cosmological simulations have sufficient resolution to capture the main structures in the ISM of galaxies, but are typically still not capable of explicitly resolving all of the small-scale stellar feedback processes, including the expansion of supernova remnants (SNRs). We perform a series of controlled three-dimensional hydrodynamic (adaptive mesh refinement, AMR) simulations of single SNRs expanding in an inhomogeneous density field with statistics motivated by those of the turbulent ISM. We use these to quantify the momentum and thermal energy injection from SNe as a function of spatial scale and the density, metallicity, and structure of the ambient medium. Using these results, we develop an analytic sub-resolution model for SN feedback for use in galaxy formation simulations. We then...
Monodromy of Inhomogeneous Picard-Fuchs Equations
Jefferson, Robert A
2013-01-01
We study low-degree curves on one-parameter Calabi-Yau hypersurfaces, and their contribution to the space-time superpotential in a superstring compactification with D-branes. We identify all lines that are invariant under at least one permutation of the homogeneous variables, and calculate the inhomogeneous Picard-Fuchs equation. The irrational large volume expansions satisfy the recently discovered algebraic integrality. The bulk of our work is a careful study of the topological integrality of monodromy under navigation around the complex structure moduli space. This is a powerful method to recover the single undetermined integration constant that is itself also of arithmetic significance. The examples feature a variety of residue fields, both abelian and non-abelian extensions of the rationals, thereby providing a glimpse of the arithmetic D-brane landscape.
Inhomogeneous reheating scenario with DBI fields
Li, Sheng
2010-08-01
We discuss a new mechanism which can be responsible for the origin of the primordial perturbation in inflationary models, the inhomogeneous DBI reheating scenario. Light DBI fields fluctuate during inflation, and finally create the density perturbations through modulation of the inflation decay rate. In this note, we investigate the curvature perturbation and its non-Gaussianity from this new mechanism. Presenting generalized expressions for them, we show that the curvature perturbation not only depends on the particular process of decay but is also dependent on the sound speed cs from the DBI action. More interestingly we find that the non-Gaussianity parameter fNL is independent of cs. As an application we exemplify some decay processes which give a viable and detectable non-Gaussianity. Finally we find a possible connection between our model and the DBI-Curvaton mechanism.
Inhomogeneity of the $\\Lambda$LTB models
Sundell, Peter
2016-01-01
The Lema\\'itre-Toman-Bondi (LTB) models have reported to suffer from incompatibility with cosmological observations and fine-tuning of the observer's location. Further analysis of these issues indicates that they could be resolved by models that are compatible with the supernova Ia data, but less inhomogeneous than those that have been presented in the literature so far. We study if such models exist by employing the degrees of freedom of the LTB models in a novel manner. We discovered two scenarios which may meet the expectations, but extensive numerical and analytical investigation showed them inviable. We extended our studies to the $\\Lambda$LTB models, which generalizes the LTB models by including a non-zero cosmological constant $\\Lambda$ in Einsteins equations. This adds an additional degree of freedom for the earlier scenarios and introduces a new scenario capable of meeting the expectations. However, extensive numerical and analytical investigation reveals that inclusion of $\\Lambda$ does not enhance ...
Inhomogeneous thermal conductivity enhances thermoelectric cooling
Directory of Open Access Journals (Sweden)
Tingyu Lu
2014-12-01
Full Text Available 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.
Origin of Inhomogeneity in Glass Melts
DEFF Research Database (Denmark)
Jensen, Martin; Keding, Ralf; Yue, Yuanzheng
The homogeneity of a glass plays a crucial role in many applications as the inhomogeneities can provide local changes in mechanical properties, optical properties, and thermal expansion coefficient. Homogeneity is not a single property of the glass, instead, it consists of several factors...... such as bubbles, striae, trace element concentration, undissolved species, and crystallised species. As it is not possible to address all the factors in a single study, this work focuses on one of the major factors: chemical striae. Up to now, the quantification of chemical striae in glasses, particularly......, in less transparent glasses, has been a challenge due to the lack of an applicable method. In this study, we have established a simple and accurate method for quantifying the extent of the striae, which is based on the scanning and picture processing through the Fourier transformation. By performing...
The thermoelectric properties of inhomogeneous holographic lattices
Donos, Aristomenis
2014-01-01
We consider inhomogeneous, periodic, holographic lattices of D=4 Einstein-Maxwell theory. We show that the DC thermoelectric conductivity matrix can be expressed analytically in terms of the horizon data of the corresponding black hole solution. We numerically construct such black hole solutions for lattices consisting of one, two and ten wave-numbers. We numerically determine the AC electric conductivity which reveals Drude physics as well as resonances associated with sound modes. No evidence for an intermediate frequency scaling regime is found. All of the monochromatic lattice black holes that we have constructed exhibit scaling behaviour at low temperatures which is consistent with the appearance of $AdS_2\\times\\mathbb{R}^2$ in the far IR at T=0.
Inhomogeneous Reheating Scenario with DBI fields
Li, Sheng
2010-01-01
We discuss a new mechanism which can be responsible for the origin of the primordial perturbation in inflationary models, the inhomogeneous DBI reheating scenario. Light DBI fields fluctuate during inflation, and finally create the density perturbations through modulation of the inflation decay rate. In this note, we investigate the curvature perturbation and its non-Gaussianity from this new mechanism. Presenting generalized expressions for them, we show that the curvature perturbation not only depends on the particular process of decay but is also dependent on the sound speed $c_s$ from the DBI action. More interestingly we find that the non-Gaussianity parameter $f_{NL}$ is independent of $c_s$. As an application we exemplify some decay processes which give a viable and detectable non-Gaussianity. Finally we find a possible connection between our model and the DBI-Curvaton mechanism.
Resistance switching in oxides with inhomogeneous conductivity
Institute of Scientific and Technical Information of China (English)
Shang Da-Shan; Sun Ji-Rong; Shen Bao-Gen; Wuttig Matthias
2013-01-01
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.
Problem of time in slightly inhomogeneous cosmology
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.
Effects of nanoscale density inhomogeneities on shearing fluids
DEFF Research Database (Denmark)
Ben, Dalton,; Peter, Daivis,; Hansen, Jesper Schmidt
2013-01-01
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...... 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...
DEFF Research Database (Denmark)
Haagerup, Uffe; Knudby, Søren
2015-01-01
The weak Haagerup property for locally compact groups and the weak Haagerup constant were recently introduced by the second author [27]. The weak Haagerup property is weaker than both weak amenability introduced by Cowling and the first author [9] and the Haagerup property introduced by Connes [6......] and Choda [5]. In this paper, it is shown that a connected simple Lie group G has the weak Haagerup property if and only if the real rank of G is zero or one. Hence for connected simple Lie groups the weak Haagerup property coincides with weak amenability. Moreover, it turns out that for connected simple...... Lie groups the weak Haagerup constant coincides with the weak amenability constant, although this is not true for locally compact groups in general. It is also shown that the semidirect product R2 × SL(2,R) does not have the weak Haagerup property....
Optical response of strongly absorbing inhomogeneous materials: Application to paper degradation
Missori, M.; Pulci, O.; Teodonio, L.; Violante, C.; Kupchak, I.; Bagniuk, J.; Łojewska, J.; Conte, A. Mosca
2014-02-01
In this paper, we present a new noninvasive and nondestructive approach to recover scattering and absorption coefficients from reflectance measurements of highly absorbing and optically inhomogeneous media. Our approach is based on the Yang and Miklavcic theoretical model of light propagation through turbid media, which is a generalization of the Kubelka-Munk theory, extended to accommodate optically thick samples. We show its applications to paper, a material primarily composed of a web of fibers of cellulose, whose optical properties are strongly governed by light scattering effects. Samples studied were ancient and industrial paper sheets, aged in different conditions and highly absorbing in the ultraviolet region. The recovered experimental absorptions of cellulose fibers have been compared to theoretical ab initio quantum-mechanical computational simulations carried out within time-dependent density functional theory. In this way, for each sample, we evaluate the absolute concentration of different kinds of oxidized groups formed upon aging and acting as chromophores causing paper discoloration. We found that the relative concentration of different chromophores in cellulose fibers depends on the aging temperature endured by samples. This clearly indicates that the oxidation of cellulose follows temperature-dependent reaction pathways. Our approach has a wide range of applications for cellulose-based materials, like paper, textiles, and other manufactured products of great industrial and cultural interest, and can potentially be extended to other strongly absorbing inhomogeneous materials.
Weak martingale Hardy spaces and weak atomic decompositions
Institute of Scientific and Technical Information of China (English)
HOU; Youliang; REN; Yanbo
2006-01-01
In this paper we define some weak martingale Hardy spaces and three kinds of weak atoms. They are the counterparts of martingale Hardy spaces and atoms in the classical martingale Hp-theory. And then three atomic decomposition theorems for martingales in weak martingale Hardy spaces are proved. With the help of the weak atomic decompositions of martingale, a sufficient condition for a sublinear operator defined on the weak martingale Hardy spaces to be bounded is given. Using the sufficient condition, we obtain a series of martingale inequalities with respect to the weak Lp-norm, the inequalities of weak (p ,p)-type and some continuous imbedding relationships between various weak martingale Hardy spaces. These inequalities are the weak versions of the basic inequalities in the classical martingale Hp-theory.
Institute of Scientific and Technical Information of China (English)
郭乃川; 王尚旭; 董春晖; 郭锐
2012-01-01
That seismic wave propagation is itself affected by small scale inhomogeneities of geologic bodies is an important issue of interpreting geophysical images and receives much attention in recent years. In this work, first of all, a statistical representation is used to describe small-scale inhomogeneities in seismological studies and a new way to build random media in which the preferred orientation of the small-scale inhomogeneities is expanded is proposed. Then, the importance of dealing with the errors is stated. And the long-wavelength theory of seismic wave propagating in horizontal layered media is discussed and its significance is pointed out. Next, based on ID random layered media, the long-wavelength theory is studied by the local anisotropy factors' curves, and the influences of fluctuations in density and Poisson's ratio on the curves' pattern are analyzed. Finally, the characteristics of seismographic records of the ID and 2D random media are studied especially when the long-wavelength theory can not be satisfied. For comparative analysis, we also compute the theoretical traveltimes of the equivalent media which is got by the long-wavelength theory when the ID random layered media has different averaging lengths (The predicted traveltimes are got under the hypothesis that the anisotropy is weak) , and then give some conclusions with guidance meanings.%地球物理成像解释的一个重要问题是,地震波传播时其本身受到地质体中小尺度非均匀性的影响,对该问题的研究具有重要的意义且备受关注.据此,本文首先从统计意义上的表示形式来描述小尺度非均匀性,给出一种拓展了小尺度非均匀性择优取向的随机介质建模新方法,重点阐述了建模过程中对误差处理的重要性.其次讨论了地震波在水平层状介质中传播时的长波长理论,并指出对该理论的适用条件进行研究的重要意义.且还基于ID随机层状介质,从局部各向异性因子曲
Erler, Jens
2013-01-01
This is a review of electroweak precision physics with particular emphasis on low-energy precision measurements in the neutral current sector of the electroweak theory and includes future experimental prospects and the theoretical challenges one faces to interpret these observables. Within the minimal Standard Model they serve as determinations of the weak mixing angle which are competitive with and complementary to those obtained near the Z-resonance. In the context of new physics beyond the Standard Model these measurements are crucial to discriminate between models and to reduce the allowed parameter space within a given model. We illustrate this for the minimal supersymmetric Standard Model with or without R-parity.
Measurement of weak radioactivity
Theodorsson , P
1996-01-01
This book is intended for scientists engaged in the measurement of weak alpha, beta, and gamma active samples; in health physics, environmental control, nuclear geophysics, tracer work, radiocarbon dating etc. It describes the underlying principles of radiation measurement and the detectors used. It also covers the sources of background, analyzes their effect on the detector and discusses economic ways to reduce the background. The most important types of low-level counting systems and the measurement of some of the more important radioisotopes are described here. In cases where more than one type can be used, the selection of the most suitable system is shown.
Weakly broken galileon symmetry
Energy Technology Data Exchange (ETDEWEB)
Pirtskhalava, David [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy); Santoni, Luca; Trincherini, Enrico [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy); INFN, Sezione di Pisa, Piazza dei Cavalieri 7, 56126 Pisa (Italy); Vernizzi, Filippo [Institut de Physique Théorique, Université Paris Saclay, CEA, CNRS, Gif-sur-Yvette cédex, F-91191 (France)
2015-09-01
Effective theories of a scalar ϕ invariant under the internal galileon symmetryϕ→ϕ+b{sub μ}x{sup μ} have been extensively studied due to their special theoretical and phenomenological properties. In this paper, we introduce the notion of weakly broken galileon invariance, which characterizes the unique class of couplings of such theories to gravity that maximally retain their defining symmetry. The curved-space remnant of the galileon’s quantum properties allows to construct (quasi) de Sitter backgrounds largely insensitive to loop corrections. We exploit this fact to build novel cosmological models with interesting phenomenology, relevant for both inflation and late-time acceleration of the universe.
Steward, David R.
2016-11-01
Recharge from surface to groundwater is an important component of the hydrological cycle, yet its rate is difficult to quantify. Percolation through two-dimensional circular inhomogeneities in the vadose zone is studied where one soil type is embedded within a uniform background, and nonlinear interface conditions in the quasilinear formulation are solved using Newton's method with the Analytic Element Method. This numerical laboratory identifies detectable variations in pathline and pressure head distributions that manifest due to a shift in recharge rate through in a heterogeneous media. Pathlines either diverge about or converge through coarser and finer grained materials with inverse patterns forming across lower and upper elevations; however, pathline geometry is not significantly altered by recharge. Analysis of pressure head in lower regions near groundwater identifies a new phenomenon: its distribution is not significantly impacted by an inhomogeneity soil type, nor by its placement nor by recharge rate. Another revelation is that pressure head for coarser grained inhomogeneities in upper regions is completely controlled by geometry and conductivity contrasts; a shift in recharge generates a difference Δp that becomes an additive constant with the same value throughout this region. In contrast, shifts in recharge for finer grained inhomogeneities reveal patterns with abrupt variations across their interfaces. Consequently, measurements aimed at detecting shifts in recharge in a heterogeneous vadose zone by deciphering the corresponding patterns of change in pressure head should focus on finer grained inclusions well above a groundwater table.
Scanning anisotropy parameters in complex media
Alkhalifah, Tariq Ali
2011-03-21
Parameter estimation in an inhomogeneous anisotropic medium offers many challenges; chief among them is the trade-off between inhomogeneity and anisotropy. It is especially hard to estimate the anisotropy anellipticity parameter η in complex media. Using perturbation theory and Taylor’s series, I have expanded the solutions of the anisotropic eikonal equation for transversely isotropic (TI) media with a vertical symmetry axis (VTI) in terms of the independent parameter η from a generally inhomogeneous elliptically anisotropic medium background. This new VTI traveltime solution is based on a set of precomputed perturbations extracted from solving linear partial differential equations. The traveltimes obtained from these equations serve as the coefficients of a Taylor-type expansion of the total traveltime in terms of η. Shanks transform is used to predict the transient behavior of the expansion and improve its accuracy using fewer terms. A homogeneous medium simplification of the expansion provides classical nonhyperbolic moveout descriptions of the traveltime that are more accurate than other recently derived approximations. In addition, this formulation provides a tool to scan for anisotropic parameters in a generally inhomogeneous medium background. A Marmousi test demonstrates the accuracy of this approximation. For a tilted axis of symmetry, the equations are still applicable with a slightly more complicated framework because the vertical velocity and δ are not readily available from the data.
Shock Wave Dynamics in Weakly Ionized Plasmas
Johnson, Joseph A., III
1999-01-01
An investigation of the dynamics of shock waves in weakly ionized argon plasmas has been performed using a pressure ruptured shock tube. The velocity of the shock is observed to increase when the shock traverses the plasma. The observed increases cannot be accounted for by thermal effects alone. Possible mechanisms that could explain the anomalous behavior include a vibrational/translational relaxation in the nonequilibrium plasma, electron diffusion across the shock front resulting from high electron mobility, and the propagation of ion-acoustic waves generated at the shock front. Using a turbulence model based on reduced kinetic theory, analysis of the observed results suggest a role for turbulence in anomalous shock dynamics in weakly ionized media and plasma-induced hypersonic drag reduction.
Alberico, W M
2004-01-01
The focus of these Lectures is on the weak decay modes of hypernuclei, with special attention to Lambda-hypernuclei. The subject involves many fields of modern theoretical and experimental physics, from nuclear structure to the fundamental constituents of matter and their interactions. The various weak decay modes of Lambda-hypernuclei are described: the mesonic mode and the non-mesonic ones. The latter are the dominant decay channels of medium--heavy hypernuclei, where, on the contrary, the mesonic decay is disfavoured by Pauli blocking effect on the outgoing nucleon. In particular, one can distinguish between one-body and two-body induced decays. Theoretical models employed to evaluate the (partial and total) decay widths of hypernuclei are illustrated, and their results compared with existing experimental data. Open problems and recent achievements are extensively discussed, in particular the determination of the ratio Gamma_n/Gamma_p, possible tests of the Delta I=1/2 rule in non-mesonic decays and the pu...
Jolley, Sarah E; Bunnell, Aaron E; Hough, Catherine L
2016-11-01
Survivorship after critical illness is an increasingly important health-care concern as ICU use continues to increase while ICU mortality is decreasing. Survivors of critical illness experience marked disability and impairments in physical and cognitive function that persist for years after their initial ICU stay. Newfound impairment is associated with increased health-care costs and use, reductions in health-related quality of life, and prolonged unemployment. Weakness, critical illness neuropathy and/or myopathy, and muscle atrophy are common in patients who are critically ill, with up to 80% of patients admitted to the ICU developing some form of neuromuscular dysfunction. ICU-acquired weakness (ICUAW) is associated with longer durations of mechanical ventilation and hospitalization, along with greater functional impairment for survivors. Although there is increasing recognition of ICUAW as a clinical entity, significant knowledge gaps exist concerning identifying patients at high risk for its development and understanding its role in long-term outcomes after critical illness. This review addresses the epidemiologic and pathophysiologic aspects of ICUAW; highlights the diagnostic challenges associated with its diagnosis in patients who are critically ill; and proposes, to our knowledge, a novel strategy for identifying ICUAW. Copyright © 2016 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.
Strasburger, Victor C
2010-11-01
The American Academy of Pediatrics recognizes that exposure to mass media (eg, television, movies, video and computer games, the Internet, music lyrics and videos, newspapers, magazines, books, advertising) presents health risks for children and adolescents but can provide benefits as well. Media education has the potential to reduce the harmful effects of media and accentuate the positive effects. By understanding and supporting media education, pediatricians can play an important role in reducing harmful effects of media on children and adolescents.
Effect of Tissue Inhomogeneity on Nonlinear Propagation of Focused Ultrasound
Institute of Scientific and Technical Information of China (English)
LIU Zhen-Bo; FAN Ting-Bo; GUO Xia-Sheng; ZHANG Dong
2010-01-01
@@ We study the influence of tissue inhomogeneity on the focused ultrasound based on the phase screen model and the acoustic nonlinear equation.The inhomogeneous tissue is considered as a combination of a homogeneous medium and a phase aberration screen.Six polyethylene(PE)plates with various correlation lengths and standard deviations are made to mimic the inhomogeneity induced by the human body abdominal.Results indicate that the correlation length affects the side lobe structure of the beam pattern; while the standard deviation is associated with the focusing capability.This study provides a theoretical and experimental basis for the development of a precise treatment plan for high intensity focused ultrasound.
Evolution of Vacuum Bubbles Embeded in Inhomogeneous Spacetimes
Pannia, F A Teppa
2016-01-01
As a first step in the analysis of the influence of inhomogeneities in the evolution of an inflating region, we study the propagation of bubbles of new vacuum in a radially inhomogeneous background filled with dust or radiation, and including a cosmological constant. For comparison, we also analyse the cases with homogeneous dust and radiation backgrounds. We show that the evolution of the bubble in the radiation environments is always slower than in the dust cases, both for homogeneous and inhomogeneous ambients, and leads to appreciable differences in the evolution of the proper radius of the bubble.
Resonance linewidth and inhomogeneous broadening in a metamaterial array
Jenkins, Stewart D
2012-01-01
We examine the effect of inhomogeneous broadening on the collective response of a planar metamaterial consisting of asymmetric split ring resonators. We show that such a response leads to a transmission resonance that can persist when the broadening of individual meta-atom resonance frequencies is roughly one half the frequency characterizing the split ring asymmetry. We also find that larger degrees of inhomogeneous broadening can drastically alter the cooperative response, destroying this resonance. The reduced effect of cooperative response due to inhomogeneous broadening may find applications in producing metamaterial samples that more closely mimic homogeneous magneto-dielectric medium with well-defined susceptibility and permittivity.
Entanglement in Ising Chain with Inhomogeneous Magnetic Field
Institute of Scientific and Technical Information of China (English)
Cenk Akyüz; Ekrem Aydmer
2008-01-01
We have numerically calculated the thermal entanglement of a two-qubit system at low temperatures in a isotropic Ising chain under an inhomogeneous magnetic field.It is shown that in the homogeneous magnetic field,the twoqubit system has entangled states.It is concluded that the presence of the inhomogeneity in the magnetic field plays an effective role on the entangled states.Finally,it is suggested that the inhomogeneity in the magnetic field can be used to create two separated entangled formations in a two-qubit system.
Jeans instability of an inhomogeneous streaming dusty plasma
Indian Academy of Sciences (India)
B P Pandey; B Van Der Holst; J Vranješ; S Poedts
2003-07-01
The dynamics of a self-gravitating unmagnetized, inhomogeneous, streaming dusty plasma is studied in the present work. The presence of the shear ﬂow causes the coupling between gravitational and electrostatic forces. In the absence of self-gravity, the ﬂuctuations in the plasma may grow at the expense of the density inhomogeneity and for certain wavelengths, such an unstable mode may dominate the usual streaming instability. However, in the presence of self-gravity, the plasma inhomogeneity causes an overlap between Jeans and streaming modes and collapse of the grain will continue at all wavelengths.
First artificial periodic inhomogeneity experiments at HAARP
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.
Optimality of Spatially Inhomogeneous Search Strategies.
Schwarz, Karsten; Schröder, Yannick; Qu, Bin; Hoth, Markus; Rieger, Heiko
2016-08-05
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.
Inhomogeneous field theory inside the arctic circle
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.
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 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.
Kaplan, L
1998-01-01
We examine the consequences of classical ergodicity for the localization properties of individual quantum eigenstates in the classical limit. We note that the well known Schnirelman result is a weaker form of quantum ergodicity than the one implied by random matrix theory. This suggests the possibility of systems with non-gaussian random eigenstates which are nonetheless ergodic in the sense of Schnirelman and lead to ergodic transport in the classical limit. These we call "weakly quantum ergodic.'' Indeed for a class of "slow ergodic" classical systems, it is found that each eigenstate becomes localized to an ever decreasing fraction of the available state space, in the semiclassical limit. Nevertheless, each eigenstate in this limit covers phase space evenly on any classical scale, and long-time transport properties betwen individual quantum states remain ergodic due to the diffractive effects which dominate quantum phase space exploration.
The formation of composite chaotic multiattractors containing inhomogeneities
Prokopenko, V. G.
2017-08-01
Two methods for introducing inhomogeneities into composite chaotic multiattractors have been proposed. The first method makes it possible to change the mutual arrangement of multiattractor elements. The second method allows one to preset differences between chaotic attractors forming a multiattractor.
Capacity analysis of inhomogeneous hybrid wireless networks using directional antennas
Institute of Scientific and Technical Information of China (English)
WU Feng; ZHU Jiang; TIAN Yi-long; ZOU Jian-bin
2016-01-01
Most of studies on network capacity are based on the assumption that all the nodes are uniformly distributed, which means that the networks are characterized by homogeneity. However, many realistic networks exhibit inhomogeneity due to natural and man-made reasons. In this work, the capacity of inhomogeneous hybrid networks with directional antennas for the first time is studied. By setting different node distribution probabilities, the whole network can be devided into dense cells and sparse cells. On this basis, an inhomogeneous hybrid network model is proposed. The network can exhibit significant inhomogeneity due to the coexistence of two types of cells. Then, we derive the network capacity and maximize the capacity under different channel allocation schemes. Finally, how the network parameters influence the network capacity is analyzed. It is found that if there are plenty of base stations, the per-node throughput can achieve constant order, and if the beamwidth of directional antenna is small enough, the network capacity can scale.
An oscillation criterion for inhomogeneous Stieltjes integro-differential equations
Directory of Open Access Journals (Sweden)
M. A. El-Sayed
1994-01-01
Full Text Available The aim of the paper is to give an oscillation theorem for inhomogeneous Stieltjes integro-differential equation of the form p(tx′+∫atx(sdσ=f(t. The paper generalizes the author's work [2].
The Absorption Characteristics of Inhomogeneous Double-Clad Fibers
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
The absorption characteristics of radially inhomogeneous double-clad fiber (DCF) are investigated firstly with the method of caustic radius, combined with the method of WKBJ. The results are significant for double-clad optical fiber lasers and amplifiers.
Perfect fluids coupled to inhomogeneities in the late Universe
Zhuk, Alexander
2016-01-01
We consider the Universe at the late stage of its evolution and deep inside the cell of uniformity. At such scales, the Universe is highly inhomogeneous and is filled with inhomogeneities in the form of galaxies and the groups of galaxies. We also suggest that the Universe is filled with a perfect fluid, and its fluctuations have peculiar velocities of the same (non-relativistic) order of magnitude as for the inhomogeneities. In this sense, the inhomogeneities (e.g. galaxies) and fluctuations of perfect fluids are coupled with each other. We clarify some important points of this approach and present a brief review of previous studies (e.g. CPL model and Chaplygin gas). We demonstrate that considered perfect fluids which satisfy our approach are really coupled to galaxies concentrating around them. The averaged (over the whole Universe) value of their fluctuations is equal to zero.
Kim, Kihong; Phung, D K; Rotermund, F; Lim, H
2008-01-21
We develop a generalized version of the invariant imbedding method, which allows us to solve the electromagnetic wave equations in arbitrarily inhomogeneous stratified media where both the dielectric permittivity and magnetic permeability depend on the strengths of the electric and magnetic fields, in a numerically accurate and efficient manner. We apply our method to a uniform nonlinear slab and find that in the presence of strong external radiation, an initially uniform medium of positive refractive index can spontaneously change into a highly inhomogeneous medium where regions of positive or negative refractive index as well as metallic regions appear. We also study the wave transmission properties of periodic nonlinear media and the influence of nonlinearity on the mode conversion phenomena in inhomogeneous plasmas. We argue that our theory is very useful in the study of the optical properties of a variety of nonlinear media including nonlinear negative index media fabricated using wires and split-ring resonators.
Breakdown of an Inhomogeneous Scale- Free Network Under Intentional Attack
Institute of Scientific and Technical Information of China (English)
LIN Guo-Ji; CHENG Xiang; OU-YANG Qi
2003-01-01
Using a recently introduced network model with node and connection diversity, we study the breakdown of different scale-free networks under intentional attacks. Our simulation results show that inhomogeneous networks are more sensitive to intentional attack than the homogeneous ones and that the centralization of the networks is an important variable, reflecting the characteristics of the network under intentional attack. Using a recently introduced method we can theoretically develop the critical point of the inhomogeneous networks.
Asymptotic properties of the inhomogeneous Lotka-Von Foerster system.
Inaba, H
1988-01-01
"In this paper, we investigate an extension of the multistate stable population model, which makes allowances for migration. The model is formulated as an inhomogeneous system of first order partial differential equations with integral boundary conditions. First, we construct its classical solution. Next, we reformulate the system as an abstract inhomogeneous Cauchy problem on a Banach space, and give its mild solution by using the population semigroup. Our main purpose is to investigate the asymptotic behavior of the mild solution." (SUMMARY IN FRE)
Media Pedagogy: Media Education, Media Socialisation and Educational Media
Directory of Open Access Journals (Sweden)
Lars Qvortrup
2007-07-01
Full Text Available The aim of this paper is to examine the relationship between education and media. These two concepts can be combined in three ways: one can think of media education, i.e. education in the subject of mass media. One can think of media socialisation, i.e. education within the context of a media society in which pupils and students are experienced media users. Finally, one can think of educational media, i.e. media used for educational purposes.After having specified these three subject areas, the paper focuses on the third subject: Media used for educational purposes. According to the paper teaching can be defined as a specialised form of communication, and the basic point of the paper is that all communication is mediated. One cannot talk about such a thing as “non-mediated” communication. Also talking or touching implies media: Language or body language.Consequently, the introduction of new, digital media for teaching does not imply to make teaching more artificial or non-authentic. The introduction of new, digital media for teaching implies that other and older educational media are re-mediated.
Minimum weight design of inhomogeneous rotating discs
Energy Technology Data Exchange (ETDEWEB)
Jahed, Hamid [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of); Farshi, Behrooz [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of)]. E-mail: farshi@iust.ac.ir; Bidabadi, Jalal [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16844 (Iran, Islamic Republic of)
2005-01-01
There are numerous applications for gas turbine discs in the aerospace industry such as in turbojet engines. These discs normally work under high temperatures while subjected to high angular velocities. Minimizing the weight of such items in aerospace applications results in benefits such as low dead weights and lower costs. High speed of rotation causes large centrifugal forces in a disc and simultaneous application of high temperatures reduces disc material strength. Thus, the latter effects tend to increase deformations of the disc under the applied loads. In order to obtain a reliable disc analysis and arrive at the corresponding correct stress distribution, solutions should consider changes in material properties due to the temperature field throughout the disc. To achieve this goal, an inhomogeneous disc model with variable thickness is considered. Using the variable material properties method, stresses are obtained for the disc under rotation and a steady temperature field. In this paper this is done by modelling the rotating disc as a series of rings of different but constant properties. The optimum disc profile is arrived at by sequentially proportioning the thicknesses of each ring to satisfy the stress requirements. This method vis-a-vis a mathematical programming procedure for optimization shows several advantages. Firstly, it is simple iterative proportioning in each design cycle not requiring involved mathematical operations. Secondly, due to its simplicity it alleviates the necessity of certain simplifications that are common in so-called rigorous mathematical procedures. The results obtained, compared to those published in the literature show agreement and superiority. A further advantage of the proposed method is the independence of the end results from the initially assumed point in the iterative design routine, unlike most methods published so far.
Can we remove the systematic error due to isotropic inhomogeneities?
Negishi, Hiroyuki; Nakao, Ken-ichi
2017-01-01
Usually, we assume that there is no inhomogeneity isotropic in terms of our location in our Universe. This assumption has not been observationally confirmed yet in sufficient accuracy, and we need to consider the possibility that there are non-negligible large-scale isotropic inhomogeneities in our Universe. The existence of large-scale isotropic inhomogeneities affects the determination of cosmological parameters. In particular, from only the distance-redshift relation, we cannot distinguish the inhomogeneous isotropic universe model from the homogeneous isotropic one, because of the ambiguity in the cosmological parameters. In this paper, in order to avoid such ambiguity, we consider three observables—the distance-redshift relation, the fluctuation spectrum of the cosmic microwave background radiation, and the scale of the baryon acoustic oscillation—and compare these observables in two universe models. One is the inhomogeneous isotropic universe model with the cosmological constant, and the other is the homogeneous isotropic universe model with dark energy other than the cosmological constant. We show that these two universe models cannot predict the same observational data of all three observables but the same ones of only two of three, as long as the perturbations are adiabatic. In principle, we can distinguish the inhomogeneous isotropic universe from the homogeneous isotropic one through the appropriate three observables, if the perturbations are adiabatic.
Media Komunitas dan Media Literacy
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Pawito .
2013-12-01
Full Text Available Abstract:This essay deals with community media in relation to media literacy. After a short discussion on a number of community media characters is made the essay goes further with somewhat detail theoretical presumptions of the roles of media community with respect primarily to the development as Amartya Sen mentioned about. The author suggests that community media may play some significant roles in the development including (a disseminating information (from varieties of perspective, (b facilitating public discussion, (c helping to reach solutions of problems, (d encouraging participations, and (e encouraging the development of media literacy. Regarding the last point the author remarks that media community may have a dual-roles i.e facilitating communityâ€™s member in media participation and facilitating communityâ€™s member in media education.
Solvolyses of Benzoyl Chlorides in Weakly Nucleophilic Media
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Haldon Carl Harris
2011-07-01
Full Text Available Rate constants and activations parameters are reported for solvolyses of p-Z-substituted benzoyl chlorides (1, Z = OMe, Me, H, and Cl in 97% w/w hexafluoroisopropanol-water (97H. Additional kinetic data are reported for solvolyses in acetic and formic acids. Plots of log k vs. σp in 97H are consistent with previous research showing that a cationic reaction channel is dominant, even for solvolyses of 1, Z = NO2. A benzoyl cation intermediate was trapped by Friedel-Crafts reaction with 1,3,5-trimethoxybenzene in hexafluoroisopropanol. The results are explained by an SN2-SN1 spectrum of mechanisms with variations in nucleophilic solvent assistance. Ab initio calculations of heterolytic bond dissociation energies of various chloro- and fluoro-substituted and other benzoyl chlorides are correlated with log k for solvolyses.
Dosen, K
2010-01-01
An operad (this paper deals with non-symmetric operads) may be conceived as a partial algebra with a family of insertion operations, Gerstenhaber's circle-i products, which satisfy two kinds of associativity, one of them involving commutativity. A Cat-operad is an operad enriched over the category Cat of small categories, as a 2-category with small hom-categories is a category enriched over Cat. The notion of weak Cat-operad is to the notion of Cat-operad what the notion of bicategory is to the notion of 2-category. The equations of operads like associativity of insertions are replaced by isomorphisms in a category. The goal of this paper is to formulate conditions concerning these isomorphisms that ensure coherence, in the sense that all diagrams of canonical arrows commute. This is the sense in which the notions of monoidal category and bicategory are coherent. The coherence proof in the paper is much simplified by indexing the insertion operations in a context-independent way, and not in the usual manner. ...
Electromagnetic beam propagation in nonlinear media
Institute of Scientific and Technical Information of China (English)
V.V.Semak; M.N.Shneider
2015-01-01
We deduce a complete wave propagation equation that includes inhomogeneity of the dielectric constant and present this propagation equation in compact vector form. Although similar equations are known in narrow fields such as radio wave propagation in the ionosphere and electromagnetic and acoustic wave propagation in stratified media, we develop here a novel approach of using such equations in the modeling of laser beam propagation in nonlinear media. Our approach satisfies the correspondence principle since in the limit of zero-length wavelength it reduces from physical to geometrical optics.
Energy Technology Data Exchange (ETDEWEB)
Liu Yuwen; Zhang Qianfan [Hubei Electrochemical Power Sources Key Laboratory, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University, Wuhan 430072 (China); Chen Shengli, E-mail: slchen@whu.edu.c [Hubei Electrochemical Power Sources Key Laboratory, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University, Wuhan 430072 (China)
2010-11-30
The effect of the supporting electrolyte concentration on the interfacial profiles and voltammetric responses of nanometer-sized disk electrodes have been investigated theoretically by combining the Poisson-Nernst-Planck (PNP) theory and Butler-Volmer (BV) equation. The PNP-theory is used to treat the nonlinear couplings of electric field, concentration field and dielectric field at electrochemical interface without the electroneutrality assumption that has been long adopted in various voltammetric theories for macro/microelectrodes. The BV equation is modified by using the Frumkin correction to account for the effect of the diffuse double layer potential on interfacial electron-transfer (ET) rate and by including a distance-dependent ET probability in the expression of rate constant to describe the radial heterogeneity of the ET rate constant at nanometer-sized disk electrodes. The computed voltammetric responses for disk electrodes larger than 200 nm in radii in the absence of the excess of the supporting electrolyte using the present theoretical scheme show reasonable agreements with the predications of the conventional microelectrode voltammetric theory which uses the combined Nernst-Planck equation and electroneutrality equation to describe the mixed electromigration-diffusion mass transport without including the possible effects of the diffuse double layer (Amatore et al. ). For electrodes smaller than 200 nm, however, the voltammetric responses predicated by the present theory exhibit significant deviation from the microelectrode theory. It is shown that the deviations are mainly resulted from the overlap between the diffuse double layer and the concentration depletion layer (CDL) at nanoscale electrochemical interfaces in weakly supported media, which will result in the invalidation of the electroneutrality condition in CDL, and from the radial inhomogeneity of ET probability at nanometer-sized disk electrodes.
Strasburger, V C
1999-01-01
For decades, media violence has been viewed as largely a Western problem. New studies indicate that Indian children have increasing access to the media and that media violence will subject them to the same problems as Western children: imitation, desensitization, fear, and inappropriate attitudes about violence and aggression. Solutions exist but will have to be implemented within the next decade to protect Indian children and adolescents from the harmful effects of media violence.
Weak Total Resolvability In Graphs
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Casel Katrin
2016-02-01
Full Text Available A vertex v ∈ V (G is said to distinguish two vertices x, y ∈ V (G of a graph G if the distance from v to x is di erent from the distance from v to y. A set W ⊆ V (G is a total resolving set for a graph G if for every pair of vertices x, y ∈ V (G, there exists some vertex w ∈ W − {x, y} which distinguishes x and y, while W is a weak total resolving set if for every x ∈ V (G−W and y ∈ W, there exists some w ∈ W −{y} which distinguishes x and y. A weak total resolving set of minimum cardinality is called a weak total metric basis of G and its cardinality the weak total metric dimension of G. Our main contributions are the following ones: (a Graphs with small and large weak total metric bases are characterised. (b We explore the (tight relation to independent 2-domination. (c We introduce a new graph parameter, called weak total adjacency dimension and present results that are analogous to those presented for weak total dimension. (d For trees, we derive a characterisation of the weak total (adjacency metric dimension. Also, exact figures for our parameters are presented for (generalised fans and wheels. (e We show that for Cartesian product graphs, the weak total (adjacency metric dimension is usually pretty small. (f The weak total (adjacency dimension is studied for lexicographic products of graphs.
McMC-based AVAZ direct inversion for fracture weaknesses
Pan, Xinpeng; Zhang, Guangzhi; Chen, Huaizhen; Yin, Xingyao
2017-03-01
Considering that wide-azimuth seismic data contains abundant azimuthal amplitude information about the fractured reservoir with obvious characteristics of amplitude variation with incident angle and azimuth (AVAZ), azimuthal seismic data can be used for the inversion of anisotropic parameters in fractured reservoir. Fractured reservoir with a single set of vertically aligned fractures embedded in a purely isotropic background medium may be considered as a long-wavelength effective transversely isotropic medium with a horizontal symmetry axis (HTI). The normal and tangential fracture weaknesses are two key parameters to the evaluation of fracture properties in HTI media, thus the inversion of fracture weaknesses may be used for characterizing the anisotropy in fractured reservoir. The elastic properties of background isotropic media without fractures, however, do not cause azimuthal changes in AVAZ data compared to the fracture anisotropic properties, therefore simultaneous inversion for the background elastic parameters and fracture anisotropic parameters may be not stable. Thus we propose a method of azimuth-difference-based AVAZ direct inversion for fracture weaknesses. First, we extract the fracture symmetry axis azimuth based on the least square ellipse fitting (LSEF) method to obtain a linear AVAZ approximation. Then we build a fractured anisotropic rock-physics model for the estimation of anisotropic well-log information, building the initial background low-frequency trend of fracture weaknesses. Finally, an AVAZ direct inversion method of normal and tangential fracture weaknesses is proposed with the nonlinear Markov chain Monte Carlo (McMC) strategy. So we can eliminate the influence of isotropic background elastic properties on the fracture weakness properties and obtain the normal and tangential fracture weaknesses more stably. Tests on both 2D over-thrust model and real data demonstrate that the normal and tangential fracture weaknesses may be estimated
Directory of Open Access Journals (Sweden)
Zhou Gang
2016-01-01
Full Text Available Modern colleges are faced with the dual pressures of university reform and international competition, how to overcome difficulties, to play the role of modern English teaching in colleges and colleges to enhance the core competitiveness of colleges, colleges and colleges modern English teaching problems to be solved. Based on the current situation of modern colleges in the premise of the Modern media platform fully demonstrated the characteristics and viability of the Modern media English teaching, the necessity of modern English teaching of college Modern media. Discusses the Modern media targeting English teaching and important role is in the English teaching to guide the development of modern colleges modern media.
SECTIONING METHOD APPLICATION AT ELLIPSOMETRY OF INHOMOGENEOUS REFLECTION SYSTEMS
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A. N. Gorlyak
2014-05-01
Full Text Available The paper deals with investigation of application peculiarities of ellipsometry methods and UF spectrophotometry at mechanical and chemical processing of optical engineering surface elements made of quartz glass. Ellipsometer LEF–3M–1, spectrophotometer SF–26 and interferometer MII–4 are used as experiment tools; they obtain widely known technical characteristics. Polarization characteristics of reflected light beam were measured by ellipsometry method; spectrophotometry method was used for measuring radiation transmission factor in UF spectrum area; by interference method surface layer thickness at quartz glass etching was measured. A method for HF–sectioning of inhomogeneous surface layer of polished quartz glass is developed based on ellipsometry equation for reflection system «inhomogeneous layer – inhomogeneous padding». The method makes it possible to carry out the measuring and analysis of optical characteristics for inhomogeneous layers system on inhomogeneous padding and to reconstruct optical profile of surface layers at quartz glass chemical processing. For definition of refractive index change along the layer depth, approximation of experimental values for polarization characteristics of homogeneous layers system is used. Inhomogeneous surface layer of polished quartz glass consists of an area (with thickness up to 20 nm and layer refractive index less than refractive index for quartz glass and an area (with thickness up to 0,1 μm and layer refractive index larger than refractive index for quartz glass. Ellipsometry and photometry methods are used for definition of technological conditions and optical characteristics of inhomogeneous layers at quartz glass chemical processing for optical elements with minimum radiation losses in UF spectrum area.
Numerical Simulation for sonic boom propagation through an Inhomogeneous atmosphere with winds
Yamamoto, Masafumi; Hashimoto, Atsushi; Takahashi, Takashi; Kamakura, Tomoo; Sakai, Takeharu
2012-09-01
Noise annoyance due to sonic boom is one of the serious problems for development of next-generation supersonic transport. To decrease this sonic boom noise, the design and analysis techniques are developed at Japan Aerospace eXploration Agency (JAXA). To predict the sonic boom on the ground accurately, we have developed a numerical code (Xnoise) using the augmented Burgers equation combined with the ray tracing. In this method, effects of nonlinearity, geometrical spreading, inhomogeneity of atmosphere, thermoviscous attenuation, molecular vibration relaxation and winds are taken into account. This method gives an estimation of the rise times of ground signatures without resorting to the weak shock theory and area balancing techniques. The nonlinear term is evaluated by the finite difference scheme in this method. In ray-path calculation, an explicit updating methodology is adopted. The augmented Burgers equation is numerically solved by using the operator split method entirely in the time domain. As for the effects of nonlinearity, geometrical spreading, and atmospheric inhomogeneity, the result obtained with the augmented Burgers equation agrees well with that obtained with the waveform parameter method (Thomas' method). For the effects of absorption and dispersion, the calculation based on the augmented Burgers equation is verified by comparing with a detailed one-dimensional CFD analysis. Moreover, we show calculations which account the effect of winds on the propagation of a sonic boom. The validation of model is a future work.
Gravitational lensing in an exact locally inhomogeneous cosmology
Attard, Allen
2005-11-01
A Recursive Swiss-Cheese (RSC) cosmological model is an exact solution to Einstein's general relativistic field equations allowing for dramatic local density inhomogeneities while maintaining global homogeneity and isotropy. It is constructed by replacing spherical regions of an FRW background with higher density cores placed at the centre of a Schwarzschild vacuum, with each core itself potentially being given the same treatment and the process repeated to generate a range of multifractal structures. Code was developed to tightly pack spheres into spaces of constant curvature in an efficient manner, and was used to develop libraries of packings with positive, negative, and zero curvature. Various projections are used to illustrate their structure, and means of measuring its dimensionality are discussed. A method by which these packings can be used as building blocks of an RSC model, along with a way of selecting parameters to define the model, is described, and a coordinate system allowing a relativistically consistent means of synchronizing its various components is developed. Formulations of the optical scalar equations for the expansion and shear rates of a beam are considered, and a set suitable for numerical integration selected. The forms of the null geodesic beam trajectories in each region of the model are computed, and a parallel propagated shadow plane basis that can be consistently followed between the various model sections is established. This allowed the development of code using a fourth order, variable step size Runge-Kutta integration routine to compute the gravitational lensing effect within an RSC model by tracking the amplification and distortion of a series of beams that are propagated through it. The output generated allows the redshift evolution of these quantities to be plotted for each beam, and enables maps to be made of the "observed sky". The amplification signature produced by a single lens in the model is examined, and the form shown
Weak compactness of biharmonic maps
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Shenzhou Zheng
2012-10-01
Full Text Available This article shows that if a sequence of weak solutions of a perturbed biharmonic map satisfies $Phi_ko 0$ in $(W^{2,2}^*$ and $u_kightharpoonup u$ weakly in $W^{2,2}$, then $u$ is a biharmonic map. In particular, we show that the space of biharmonic maps is sequentially compact under the weak-$W^{2,2}$ topology.
Variational Approach to Scattering by Inhomogeneous Layers Ab ove Rough Surfaces
Institute of Scientific and Technical Information of China (English)
Luan Tian; Ma Fu-ming
2014-01-01
In this paper, we study, via variational methods, the problem of scattering of time harmonic acoustic waves by unbounded inhomogeneous layers above a sound soft rough surface. We first propose a variational formulation and exploit it as a theoretical tool to prove the well-posedness of this problem when the media is non-absorbing for arbitrary wave number and obtain an estimate about the solution, which exhibit explicitly dependence of bound on the wave number and on the geometry of the domain. Then, based on the non-absorbing results, we show that the variational problem remains uniquely solvable when the layer is absorbing by means of a priori estimate of the solution. Finally, we consider the finite element approximation of the problem and give an error estimate.
Gopalakrishnan, Srinivasan; Roy Mahapatra, Debiprosad
2008-01-01
The use of composites and Functionally Graded Materials (FGMs) in structural applications has increased. FGMs allow the user to design materials for a specified functionality and have many uses in structural engineering. However, the behaviour of these structures under high-impact loading is not well understood. This book is the first to apply the Spectral Finite Element Method (SFEM) to inhomogeneous and anisotropic structures in a unified and systematic manner. It focuses on some of the problems with this media which were previously thought unmanageable. Types of SFEM for regular and damaged 1-D and 2-D waveguides, solution techniques, methods of detecting the presence of damages and their locations, and methods for controlling the wave propagation responses are discussed. Tables, figures and graphs support the theory and case studies are included. This book is of value to senior undergraduates and postgraduates studying in this field, and researchers and practicing engineers in structural integrity.
Institute of Scientific and Technical Information of China (English)
WANG Gang; WU Shao-Quan; HOU Bang-Pin
2005-01-01
@@ In order to study the capability of amplifying the input optical signal of certain materials, we investigate the Helmholtz equation which describes a system of inhomogeneous media. After exploring its SU(1,1) algebraic structure, we obtain the exact solutions of this Helmholtz equation by means of the algebraic dynamical method.Based on the exact solutions, we analyse the capability of optical amplifiers, which is an important issue in modern optical communication. We take the wave number ko(z) and the expansion coefficient k2(z) to be the trigonometric functions, exponential functions and power functions of variable z, respectively. It is found that the material following the exponential functions is the best one for optical amplifiers.
Observations of 't Hooft's sublattices and Dirac's monopole by inhomogeneous phases of solitons
Afzal, Muhammad Imran; Lee, Yong Tak
2016-01-01
Here, we experimentally generated photonic graphene by resonance of inhomogeneously strained one dimensional lattices of triangular solitons. Where mildly twisted solitons are considered as north and south monopoles, while strongly twisted solitons are considered as defect north monopoles. Weak bounding is observed between the opposite monopoles. Strong bounding occurred between the monopoles with same polarity. Where a defect north monopole is transformed into a flux-like tube. Which generated an optical analogue of the torus sublattice. Bogomolny's vortice-like symmetry is remained intact in all these observations. Dirac's north monopole along with the string is also observed. The results presented in this paper were also described in terms of supersymmetry and quantum phase transitions, and reported in ref[20].
Waves in vertically inhomogeneous dissipative atmosphere
Dmitrienko, I S
2015-01-01
A method of construction of solution for acoustic-gravity waves (AGW) above a wave source, taking dissipation throughout the atmosphere into account (Dissipative Solution above Source, DSAS), is proposed. The method is to combine three solutions for three parts of the atmosphere: an analytical solution for the upper isothermal part and numerical solutions for the real non-isothermal dissipative atmosphere in the middle part and for the real non-isothermal small dissipation atmosphere in the lower one. In this paper the method has been carried out for the atmosphere with thermal conductivity but without viscosity. The heights of strong dissipation and the total absorption index in the regions of weak and average dissipation are found. For internal gravity waves the results of test calculations for an isothermal atmosphere and calculations for a real non-isothermal atmosphere are shown in graphical form. An algorithm and appropriate code to calculate DSAS, taking dissipation due to finite thermal conductivity i...
Inhomogeneity in microstructure and mechanical properties during twist extrusion
Energy Technology Data Exchange (ETDEWEB)
Noor, Sh. Vakili [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Eivani, A.R., E-mail: aeivani@iust.ac.ir [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Jafarian, H.R. [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Mirzaei, M. [Material Engineering Group, Islamic Azad University, Kermanshah (Iran, Islamic Republic of)
2016-01-15
In the present paper, the effect of twist extrusion (TE) on the variations of hardness and tensile properties in commercial pure copper is investigated. It is found that hardness, yield and ultimate tensile strength of the alloy increased by increasing distance from the center of the sample after one pass TE. Similar consequences are observed when the second pass of deformation is considered. This is attributed to inhomogeneity of deformation and the higher strain imposed on the material at the peripheral regions. It should be noted that the inhomogeneity is increased at the second pass when route A of deformation is utilized and reduces by utilization of route D. This has as a well-established effect on the development of microstructure throughout the cross section of the samples. In fact, it is found that the microstructure at the peripheral regions is more significantly deformed leading to higher dislocation density and extensive subgrain formation. In addition, it is found that at the second pass using route A, inhomogeneity of deformation and microstructure increases. However, less inhomogeneity is observed when route D is utilized which is in line with the hardness and tensile test results. In the end, it is concluded that depending on the aim of the SPD process, if more homogeneous deformation and microstructure is required, route D is recommended and route A should be utilized in case if maximum inhomogeneity is desirable.
[Systemic lupus erythematosus and weakness].
Vinagre, Filipe; Santos, Maria José; da Silva, José Canas
2006-01-01
We report a case of a 13-year old young girl, with Juvenile Systemic Lupus Erythematosus and recent onset of muscle weakness. Investigations lead to the diagnosis of Myasthenia Gravis. The most important causes of muscle weakness in lupus patients are discussed.
A study of low-dimensional inhomogeneous systems
Energy Technology Data Exchange (ETDEWEB)
Arredondo Leon, Yesenia
2009-01-15
While the properties of homogeneous one-dimensional systems, even with disorder, are relatively well-understood, very little is known about the properties of strongly interacting inhomogeneous systems. Their high-energy physics is determined by the underlying chemistry which, in the atomic scale, introduces Coulomb correlations and local potentials. On the other hand, at large length scales, the physics has to be described by the Tomonaga-Luttinger liquid (TLL) model. In order to establish a connection between the low-energy TLL and the quasi-one-dimensional systems synthesized in the laboratory, we investigate the density-density correlation function in inhomogeneous one-dimensional systems in the asymptotic region. To investigate homogeneous as well as inhomogeneous systems, we use the density-matrix renormalization group (DMRG) method. We present results for ground state properties, such as the density-density correlation function and the parameter K{sub c}, which characterizes its decay at large distances. (orig.)
Double-electron ionization driven by inhomogeneous fields
Chacón, A; Cucchietti, F; Suárez, N; Pérez-Hernández, J A; Ciappina, M F; Landsman, A S; Lewenstein, M
2016-01-01
Electron-electron correlation effects play an instrumental role in our understanding of sequential (SDI) and non-sequential double ionization (NSDI) mechanisms. Here, we present a theoretical study of NSDI driven by plasmonic-enhanced spatial inhomogeneous fields. By numerically solving the time-dependent Schr\\"odinger equation for a linear reduced model of He and a double-electron time-evolution probability analysis, we provide evidence for the enhancement effects in NSDI showing that the double ionization yield at lower laser peak intensities is increased due to the inhomogeneity of the laser field. Furthermore, our quantum mechanical model, as well as classical trajectory Monte Carlo simulations, show that inhomogeneous fields are a useful tool for splitting the binary and recoil processes in the rescattering scenario.
Flux and polarization signals of spatially inhomogeneous gaseous exoplanets
Karalidi, T; Guirado, D
2013-01-01
We present numerically calculated, disk--integrated, spectropolarimetric signals of starlight that is reflected by vertically and horizontally inhomogeneous gaseous exoplanets. We include various spatial features that are present on Solar System's gaseous planets: belts and zones, cyclonic spots, and polar hazes, to test whether such features leave traces in the disk--integrated flux and polarization signals. Broadband flux and polarization signals of starlight that is reflected by gaseous exoplanets are calculated using an efficient, adding--doubling radiative transfer code, that fully includes single and multiple scattering and polarization. The planetary model atmospheres are vertically inhomogeneous and can be horizontally inhomogeneous, and contain gas molecules and/or cloud and/or aerosol particles.
Inhomogeneous stationary and oscillatory regimes in coupled chaotic oscillators.
Liu, Weiqing; Volkov, Evgeny; Xiao, Jinghua; Zou, Wei; Zhan, Meng; Yang, Junzhong
2012-09-01
The dynamics of linearly coupled identical Lorenz and Pikovsky-Rabinovich oscillators are explored numerically and theoretically. We concentrate on the study of inhomogeneous stable steady states ("oscillation death (OD)" phenomenon) and accompanying periodic and chaotic regimes that emerge at an appropriate choice of the coupling matrix. The parameters, for which OD occurs, are determined by stability analysis of the chosen steady state. Three model-specific types of transitions to and from OD are observed: (1) a sharp transition to OD from a nonsymmetric chaotic attractor containing random intervals of synchronous chaos; (2) transition to OD from the symmetry-breaking chaotic regime created by negative coupling; (3) supercritical bifurcation of OD into inhomogeneous limit cycles and further evolution of the system to inhomogeneous chaotic regimes that coexist with complete synchronous chaos. These results may fill a gap in the understanding of the mechanism of OD in coupled chaotic systems.
Phonon-plasmon interaction in magnetized inhomogeneous semiconductor quantum plasmas
Ghosh, S.; Muley, Apurva
2016-12-01
The phonon-plasmon interaction in a magnetized inhomogeneous semiconductor quantum plasma is reported using a quantum hydrodynamic model. A quantum modified dispersion relation is employed, which leads to an evolution expression for the gain coefficient of the acoustic wave. In the present study, quantum effects and inhomogeneity are taken into account through non-dimensional quantum parameter-H and scale length of density variation parameter-L, respectively. The effects of these parameters, as well as propagation distance z, angular frequency ω, and orientation of magnetic field θ, on gain characteristics of the acoustic wave are investigated. These investigations are made for linearly and quadratically varying density structures in the presence and the absence of the magnetic field. The results infer that the magnetic field and linearly or quadratically varying density structures would play a decisive role in deciding the gain characteristics of the acoustic wave in the inhomogeneous semiconductor quantum plasma.
Solutions of the chemical kinetic equations for initially inhomogeneous mixtures.
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.
Inclusion of matter in inhomogeneous loop quantum cosmology
Blas, Daniel Martín-de; Marugán, Guillermo A Mena; 10.1063/1.4734461
2013-01-01
We study the hybrid quantization of the linearly polarized Gowdy $T^3$ model with a massless scalar field with the same symmetries as the metric. For simplicity, we quantize its restriction to the model with local rotational symmetry. Using this hybrid approach, the homogeneous degrees of freedom of the geometry are quantized \\`a la loop, leading to the resolution of the cosmological singularity. A Fock quantization is employed both for the matter and the gravitational inhomogeneities. Owing to the inclusion of the massless scalar field this system allows us to modelize flat Friedmann-Robertson-Walker cosmologies filled with inhomogeneities propagating in one direction, providing a perfect scenario to study the quantum back-reaction of the inhomogeneities on the polymeric homogeneous and isotropic background.
Control of inhomogeneous atomic ensembles of hyperfine qudits
Mischuck, Brian E; Deutsch, Ivan H
2011-01-01
We study the ability to control d-dimensional quantum systems (qudits) encoded in the hyperfine spin of alkali-metal atoms through the application of radio- and microwave-frequency magnetic fields in the presence of inhomogeneities in amplitude and detuning. Such a capability is essential to the design of robust pulses that mitigate the effects of experimental uncertainty and also for application to tomographic addressing of particular members of an extended ensemble. We study the problem of preparing an arbitrary state in the Hilbert space from an initial fiducial state. We prove that inhomogeneous control of qudit ensembles is possible based on a semi-analytic protocol that synthesizes the target through a sequence of alternating rf and microwave-driven SU(2) rotations in overlapping irreducible subspaces. Several examples of robust control are studied, and the semi-analytic protocol is compared to a brute force, full numerical search. For small inhomogeneities, < 1%, both approaches achieve average fide...
Symmetry Analysis of Thermoelectric Energy Converters with Inhomogeneous Legs
Korzhuev, M. A.
2010-09-01
Symmetry analysis has been applied to thermoelectric energy converters [thermoelectric generators (TEG), coolers (TEC), and heaters (TEH)] with inhomogeneous legs. The features of the crystallographic symmetry of thermoelectric materials and the symmetry of legs, thermocouples, and modules are studied. The effect of symmetry on the figure of merit Z of thermoelectric energy converters is considered. A general rule for proper placement of legs in thermoelectric converters is developed. A modified tetratomic classification for thermoelectric energy converters with inhomogeneous legs (TEGa, TEGb, TEC, and TEH) is proposed. An increase in Z for thermoelectric energy converters with inhomogeneous legs is due to the bulk thermoelectric effect. An increase in Z gives the reduction of irreversible processes in the modules (Joule heating and thermal conductivity), accompanying breaking of the symmetry of the legs. It is found that violations of the symmetry requirements can lead to significant energy losses in converters.
A method for longitudinal relaxation time measurement in inhomogeneous fields
Chen, Hao; Cai, Shuhui; Chen, Zhong
2017-08-01
The spin-lattice relaxation time (T1) plays a crucial role in the study of spin dynamics, signal optimization and data quantification. However, the measurement of chemical shift-specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic fields or intrinsic magnetic susceptibility heterogeneity in samples. In this study, we present a new protocol to determine chemical shift-specific T1 constants in inhomogeneous fields. Based on intermolecular double-quantum coherences, the new method can resolve overlapped peaks in inhomogeneous fields. The measurement results are in consistent with the measurements in homogeneous fields using the conventional method. Since spatial encoding technique is involved, the experimental time for the new method is very close to that for the conventional method. With the aid of T1 knowledge, some concealed information can be exploited by T1 weighting experiments.
Dynamics of Weak, Bifurcated and Strong Hydrogen Bonds in Lithium Nitrate Trihydrate
Energy Technology Data Exchange (ETDEWEB)
Werhahn, Jasper C.; Pandelov, S.; Xantheas, Sotiris S.; Iglev, H.
2011-07-07
The properties of three distinct types of hydrogen bonds, namely a weak, a bifurcated and a strong one, all present in/the LiNO3 (HDO)(D2O)2 hydrate lattice unit cell are studied using steady-state and time-resolved spectroscopy. The lifetimes of the OH stretching vibrations for the three individual bonds are 2.2 ps (weak), 1.7 ps (bifurcated), and 1.2 ps (strong), respectively. For the first time the properties of bifurcated H bonds can thus be unambiguously directly compared to those of weak and strong H bonds in the same system. The values of their OH stretching vibration lifetime, anharmonicity, red shift and bond strength lie between those for the strong and weak H bonds. The experimentally observed inhomogeneous broadening of their spectral signature is attributed to the coupling with a low frequency intermolecular wagging vibration/
DEFF Research Database (Denmark)
Kabel, Lars
2016-01-01
News and other kinds of journalistic stories, 16-17 hours a day, all year round, on all platforms, also the moderated social media. The key research thesis behind this article is that the continuous and speedy stream of news stories and media content now is becoming the centre of the production...... processes and the value creation in converged multimedia newsrooms. The article identify new methods and discuss editorial challenges in handling media flow....
Institute of Scientific and Technical Information of China (English)
叶全荣
2006-01-01
@@ Every day,we are all influenced by the mass media.Although some critics of the media claim that these means of communication are used mainly to control our thinking and get us to buy products that we don't need,the media also contribute to keeping people informed.In other words,while dangers do exist,the benefits of the media far outweigh(超过)the disadvantages.Most of the messages brought to viewers,listeners,and readers are designed either to inform or to entertain,and neither of these goals can be considered dangerous or harmful.
Protest: Critical Lessons of Using Digital Media for Social Change
LaRiviere, Kristin; Snider, Jeanette; Stromberg, Alison; O'Meara, KerryAnn
2012-01-01
In this article, the authors consider the strengths and weaknesses of digital media in the organization of student activism, and how educators can better assist and advise student activists using digital media to create improved learning opportunities. To gain a perspective on the relative strengths and challenges of online media in regard to…
Protest: Critical Lessons of Using Digital Media for Social Change
LaRiviere, Kristin; Snider, Jeanette; Stromberg, Alison; O'Meara, KerryAnn
2012-01-01
In this article, the authors consider the strengths and weaknesses of digital media in the organization of student activism, and how educators can better assist and advise student activists using digital media to create improved learning opportunities. To gain a perspective on the relative strengths and challenges of online media in regard to…
Inhomogeneous Reionization and the Polarization of the Cosmic Microwave Background.
Weller
1999-12-10
In a universe with inhomogeneous reionization, the ionized patches create a second-order signal in the cosmic microwave background polarization anisotropy. This signal originates in the coupling of the free-electron fluctuation to the quadruple moment of the temperature anisotropy. We examine the contribution from a simple inhomogeneous reionization model and find that the signal from such a process is below the detectable limits of the Planck Surveyor mission. However, the signal is above the fundamental uncertainty limit from cosmic variance, so that a future detection with a high-accuracy experiment on subarcminute scales is possible.
Nonlinear Waves in an Inhomogeneous Fluid Filled Elastic Tube
Institute of Scientific and Technical Information of China (English)
DUAN Wen-Shan
2004-01-01
In a thin-walled, homogeneous, straight, long, circular, and incompressible fluid filled elastic tube, small but finite long wavelength nonlinear waves can be describe by a KdV (Korteweg de Vries) equation, while the carrier wave modulations are described by a nonlinear Schrodinger equation (NLSE). However if the elastic tube is slowly inhomogeneous, then it is found, in this paper, that the carrier wave modulations are described by an NLSE-like equation. There are soliton-like solutions for them, but the stability and instability regions for this soliton-like waves will change,depending on what kind of inhomogeneity the tube has.
A novel method for evaluating tissue inhomogeneity in elastography
Institute of Scientific and Technical Information of China (English)
BAI Peirui; WAN Mingxi; WANG Supin; ZHANG Dachun; DANG Jun
2006-01-01
Based on the detection of differential Rényi information (DRI) of segmented pre- and post-compression radio-frequency (RF) echo signals, a novel method for evaluating tissue inhomogeneity in elastography prior to the cross-correlation operation is proposed.In vitro experiments were carried out to corroborate the performance of the DRI method. Experimental results illustrate that valuable insights into local tissue inhomogeneity can be obtained through analyzing the DRI curves of the echo segments, which can provide information to aid the study of strain estimation algorithm in elastography.
Baryon inhomogeneities in a charged quark gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Ray, Avijeet [Indian Institute of Technology Roorkee, Uttarakhand, 247667 (India); Sanyal, Soma, E-mail: sossp@uohyd.ernet.in [School of Physics, University of Hyderabad, Gachibowli, Hyderabad, 500046 (India)
2013-10-07
We study the generation of baryon inhomogeneities in regions of the quark gluon plasma which have a charge imbalance. We find that the overdensity in the baryon lumps for positively charged particles is different from the overdensity due to the negatively charged particles. Since quarks are charged particles, the probability of forming neutrons or protons in the lumps would thus be changed. The probability of forming hadrons having quarks of the same charges would be enhanced. This might have interesting consequences for the inhomogeneous nucleosynthesis calculations.
Transdimensional imaging of random velocity inhomogeneities in Nankai subduction zone
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
Possible effect of subsurface inhomogeneities on the lunar microwave spectrum
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.
Inhomogeneous helicity effect in the solar angular-momentum transport
Yokoi, Nobumitsu
2017-04-01
Coupled with mean absolute vorticity Ω∗ (rotation and mean relative vorticity), inhomogeneous turbulent helicity is expected to contribute to the generation of global flow structure against the linear and angular momentum mixing due to turbulent or eddy viscosity. This inhomogeneous helicity effect was originally derived in Yokoi & Yoshizawa (1993) [1], and recently has been validated by direct numerical simulations (DNSs) of rotating helical turbulence [2]. Turbulence effect enters the mean-vorticity equation through the turbulent vortexmotive force ⟨u'×ω'⟩ [u': velocity fluctuation, ω'(= ∇× u'): vorticity fluctuation], which is the vorticity counterpart of the electromotive force ⟨u'× b'⟩ (b': magnetic fluctuation) in the mean magnetic-field induction. The mean velocity induction δU is proportional to the vortexmotive force. According to the theoretical result [1,2], it is expressed as δU = -νT∇×Ω∗-ηT(∇2H)Ω∗, where ηT is the transport coefficient, H = ⟨u'ṡω'⟩ the turbulent helicity, and Ω∗ the mean absolute vorticity. The first term corresponds to the enhanced diffusion due to turbulent viscosity νT. The second term expresses the large-scale flow generation due to inhomogeneous helicity. Since helicity is self-generated in rotating stratified turbulence [3], an inhomogeneous helicity distribution is expected to exist in the solar convection zone. A rising flow with expansion near the surface of the Sun generates a strongly negative helicity there [4]. This spatial distribution of helicity would lead to a positive Laplacian of turbulent helicity (∇2H > 0) in the subsurface layer of the Sun. In the combination with the large-scale vorticity associated with the meridional circulation, the inhomogeneous helicity effect works for accelerating the mean velocity in the azimuthal direction. The relevance of this inhomogeneous helicity effect in the solar convection zone is discussed further. References [1] Yokoi, N. and
Energy Density Inhomogeneities with Polynomial $f(R)$ Cosmology
Sharif, M
2015-01-01
In this paper, we study the effects of polynomial $f(R)$ model on the stability of homogeneous energy density in self-gravitating spherical stellar object. For this purpose, we construct couple of evolution equations which relate the Weyl tensor with matter parameters. We explore different factors responsible for density inhomogeneities with non-dissipative dust, isotropic as well as anisotropic fluids and dissipative dust cloud. We find that shear, pressure, dissipative parameters and $f(R)$ terms affect the existence of inhomogeneous energy density.
Dose inhomogeneities at various levels of biological organization
Energy Technology Data Exchange (ETDEWEB)
Bond, V.P.
1988-01-01
Dose inhomogeneities in both tumor and normal tissue, inherent to the application of boron neutron capture therapy (BNCT), can be the result not only of ununiform distribution of /sup 10/B at various levels of biological organization, but also of the distribution of the thermal neutrons and of the energy depositions from more energetic neutrons and other radiations comprising the externally-applied beams. The severity of the problems resulting from such inhomogeneities, and approaches to evaluating them, are illustrated by three examples, at the macro, micro and intermediate levels.
A Model of Emergent Universe in Inhomogeneous Space-Time
Bhattacharya, Subhra
2016-01-01
A scenario of an emergent universe is constructed in the background of an inhomogeneous space-time model which is asymptotically (at spatial infinity) FRW space-time. The cosmic substratum consists of non-interacting two components, namely {\\bf a)} homogeneous and isotropic fluid but dissipative in nature and {\\bf b)} an inhomogeneous and anisotropic barotropic fluid. In non-equilibrium thermodynamic prescription (second order deviations), particle creation mechanism is considered the cause for the dissipative phenomena. It is found that for constant value of the particle creation rate parameter there exists a scenario of emergent universe.
Optical coherent control in semiconductors: Fringe contrast and inhomogeneous broadening
DEFF Research Database (Denmark)
Østergaard, John Erland; Vadim, Lyssenko; Hvam, Jørn Märcher
2001-01-01
Optical coherent control experiments in semiconductors reveal how inhomogeneous broadening must be taken into account in contrast to previous coherent control experiments in atomic and molecular systems. With spectral resolution elf the coherent control signal, the optical phases involved...... is observed in the four-wave mixing spectra as a function of phase-delay representing coherent control in the spectral domain. The spectral phase change of this modulation provides a spectroscopic tool to analyze contributions of inhomogeneous broadening to electronic resonances in semiconductor structures....
DEFF Research Database (Denmark)
Kabel, Lars
2016-01-01
News and other kinds of journalistic stories, 16-17 hours a day, all year round, on all platforms, also the moderated social media. The key research thesis behind this article is that the continuous and speedy stream of news stories and media content now is becoming the centre of the production...
Peterson, Erin
2010-01-01
While institutions do not often have a hook as compelling as an eagerly awaited movie, great content is critical for media relations success--and coupling it with the right distribution channel can ensure the story finds the right audience. Even better, retooling it for several media platforms can extend the life and reach of a story. The changes…
DEFF Research Database (Denmark)
Linde, Per; Messeter, Jörn
for the Media places project, give some brief insights into the themes of setting up temporary digital streams of media and mobile games. Considering the work-in-progress character of the research and the smaller format of text, no real in-depth analysis will be carried out. The goal is rather to position...
Peterson, Erin
2010-01-01
While institutions do not often have a hook as compelling as an eagerly awaited movie, great content is critical for media relations success--and coupling it with the right distribution channel can ensure the story finds the right audience. Even better, retooling it for several media platforms can extend the life and reach of a story. The changes…
Chalmers, Matthew
2008-01-01
He is the media-friendly face of particle physics, appearing on countless TV and radio shows in the run-up to the opening of CERN's Large Hadron Collider. Matthew Chalmers discovers how Brian Cox finds the time to be both a physicist and a media personality. (2 pages)
Nucleation in the chiral transition with an inhomogeneous background
Taketani, B G; Taketani, Bruno G.; Fraga, Eduardo S.
2007-01-01
We consider an approximation procedure to evaluate the finite-temperature one-loop fermionic density in the presence of a chiral background field which systematically incorporates effects from inhomogeneities in the chiral field through a derivative expansion. Modifications in the effective potential and their consequences for the bubble nucleation process are discussed.
Inhomogeneous generalizations of Bianchi type VIh models with perfect fluid
Roy, S. R.; Prasad, A.
1991-07-01
Inhomogeneous universes admitting an Abelian G2 of isometry and filled with perfect fluid have been derived. These contain as special cases exact homogeneous universes of Bianchi type VIh. Many of these universes asymptotically tend to homogeneous Bianchi VIh universes. The models have been discussed for their physical and kinematical behaviors.
Tracking inhomogeneity in high-capacity lithium iron phosphate batteries
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.
Ventilation inhomogeneity in children with primary ciliary dyskinesia
DEFF Research Database (Denmark)
Green, Kent; Buchvald, Frederik F; Marthin, June Kehlet
2012-01-01
The lung clearance index (LCI) derived from the multiple breath inert gas washout (MBW) test reflects global ventilation distribution inhomogeneity. It is more sensitive than forced expiratory volume in 1 s (FEV(1)) for detecting abnormal airway function and correlates closely with structural lun...
Stress engineering and the applications of inhomogeneously polarized optical fields
Institute of Scientific and Technical Information of China (English)
Thomas G. BROWN; Amber M. BECKLEY
2013-01-01
Spatial inhomogeneities in the polarization of a light field can show fascinating effects in focusing, propagation, illumination, and imaging. This paper provides examples of these effects and describes how deterministic stress on the periphery of an optical element can be used in fundamental studies of beam propagation, as well as applications such as polarimetry.
ON FINITE ELEMENT METHODS FOR INHOMOGENEOUS DIELECTRIC WAVEGUIDES
Institute of Scientific and Technical Information of China (English)
Zhiming Chen; Jian-hua Yuan
2004-01-01
We investigate the problem of computing electromagnetic guided waves in a closed,inhomogeneous, pillared three-dimensional waveguide at a given frequency. The problem is formulated as a generalized eigenvalue problem. By modifying the sesquilinear form associated with the eigenvalue problem, we provide a new convergence analysis for the finite element approximations. Numerical results are reported to illustrate the performance of the method.
Multiwavelength erbium-doped fiber laser exploiting intracavity polarization inhomogeneity
Institute of Scientific and Technical Information of China (English)
孙军强; 丘军林; 黄德修
2000-01-01
Simultaneous multiwavelength lasing is demonstrated exploiting intracavity polarization in-homogeneity in an erbium-doped fiber laser. Experiments indicate that polarization hole burning can be enhanced by the changes of optical MQW waveguide bias current and the polarization states in the laser cavity. Ten wavelengths with 0.9 nm spacing are generated at room temperature.
Scattering of acoustic waves by macroscopically inhomogeneous poroelastic tubes.
Groby, J-P; Dazel, O; Depollier, C; Ogam, E; Kelders, L
2012-07-01
Wave propagation in macroscopically inhomogeneous porous materials has received much attention in recent years. For planar configurations, the wave equation, derived from the alternative formulation of Biot's theory of 1962, was reduced and solved recently: first in the case of rigid frame inhomogeneous porous materials and then in the case of inhomogeneous poroelastic materials in the framework of Biot's theory. This paper focuses on the solution of the full wave equation in cylindrical coordinates for poroelastic tubes in which the acoustic and elastic properties of the poroelastic tube vary in the radial direction. The reflection coefficient is obtained numerically using the state vector (or the so-called Stroh) formalism and Peano series. This coefficient can then be used to straightforwardly calculate the scattered field. To validate the method of resolution, results obtained by the present method are compared to those calculated by the classical transfer matrix method in the case of a two-layer poroelastic tube. As an example, a long bone excited in the sagittal plane is considered. Finally, a discussion is given of ultrasonic time domain scattered field for various inhomogeneity profiles, which could lead to the prospect of long bone characterization.
Higher dimensional inhomogeneous dust collapse and cosmic censorship
Ghosh, S G
2001-01-01
We investigate the occurrence and nature of a naked singularity in the gravitational collapse of an inhomogeneous dust cloud described by higher dimensional Tolman-Bondi space-times. The naked singularities are found to be gravitationally strong in the sense of Tipler. Higher dimensions seem to favour black holes rather than naked singularities.
Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields
DEFF Research Database (Denmark)
Karlsen, Jonas Tobias; Augustsson, Per; Bruus, Henrik
2016-01-01
We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems...
An algorithm of computing inhomogeneous differential equations for definite integrals
Nakayama, Hiromasa; Nishiyama, Kenta
2010-01-01
We give an algorithm to compute inhomogeneous differential equations for definite integrals with parameters. The algorithm is based on the integration algorithm for $D$-modules by Oaku. Main tool in the algorithm is the Gr\\"obner basis method in the ring of differential operators.
Non-parametric Bayesian inference for inhomogeneous Markov point processes
DEFF Research Database (Denmark)
Berthelsen, Kasper Klitgaard; Møller, Jesper
With reference to a specific data set, we consider how to perform a flexible non-parametric Bayesian analysis of an inhomogeneous point pattern modelled by a Markov point process, with a location dependent first order term and pairwise interaction only. A priori we assume that the first order term...
Multiwavelength erbium-doped fiber laser exploiting intracavity polarization inhomogeneity
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Simultaneous multiwavelength lasing is demonstrated exploiting intracavity polarization inhomogeneity in an erbium-doped fiber laser. Experiments indicate that polarization hole burning can be enhanced by the changes of optical MQW waveguide bias current and the polarization states in the laser cavity. Ten wavelengths with 0.9 nm spacing are generated at room temperature.
Inhomogeneous magnetic field in AdS/CFT superconductor
Wen, Wen-Yu
2008-01-01
We study the holographically dual description of superconductor in (2+1)-dimensions in the presence of inhomogeneous magnetic field and observe that there exists type I and type II superconductor. A new feature of type changing is observed for type I superconductor near critical temperature.
A time inhomogeneous Cox-Ingersoll-Ross diffusion with jumps
Hoepfner, Reinhard
2009-01-01
We consider a time inhomogeneous Cox-Ingersoll-Ross diffusion with positive jumps. We exploit a branching property to prove existence of a unique strong solution under a restrictive condition on the jump measure. We give Laplace transforms for the transition probabilities, with an interpretation in terms of limits of mixtures over Gamma laws.
Rate-optimal Bayesian intensity smoothing for inhomogeneous Poisson processes
E. Belitser; P. Serra; H. van Zanten
2015-01-01
We apply nonparametric Bayesian methods to study the problem of estimating the intensity function of an inhomogeneous Poisson process. To motivate our results we start by analyzing count data coming from a call center which we model as a Poisson process. This analysis is carried out using a certain
Material inhomogeneities and their evolution a geometric approach
Epstein, Marcelo
2007-01-01
Presents a unified treatment of the inhomogeneity theory using some of the tools of modern differential geometry. This book deals with the geometrical description of uniform bodies and their homogeneity conditions. It also develops a theory of material evolution and discusses its relevance in various applied contexts.
Coherent excitonic nonlinearity versus inhomogeneous broadening in single quantum wells
DEFF Research Database (Denmark)
Langbein, Wolfgang Werner; Borri, Paola; Hvam, Jørn Märcher;
1998-01-01
The coherent response of excitons in semiconductor nanostructures, as measured in four wave mixing (FWM) experiments, depends strongly on the inhomogeneous broadening of the exciton transition. We investigate GaAs-AlGaAs single quantum wells (SQW) of 4 nm to 25 nm well width. Two main mechanisms...
Multiple solutions for inhomogeneous nonlinear elliptic problems arising in astrophyiscs
Directory of Open Access Journals (Sweden)
Marco Calahorrano
2004-04-01
Full Text Available Using variational methods we prove the existence and multiplicity of solutions for some nonlinear inhomogeneous elliptic problems on a bounded domain in $mathbb{R}^n$, with $ngeq 2$ and a smooth boundary, and when the domain is $mathbb{R}_+^n$
Matrix algorithms for solving (in)homogeneous bound state equations.
Blank, M; Krassnigg, A
2011-07-01
In the functional approach to quantum chromodynamics, the properties of hadronic bound states are accessible via covariant integral equations, e.g. the Bethe-Salpeter equation for mesons. In particular, one has to deal with linear, homogeneous integral equations which, in sophisticated model setups, use numerical representations of the solutions of other integral equations as part of their input. Analogously, inhomogeneous equations can be constructed to obtain off-shell information in addition to bound-state masses and other properties obtained from the covariant analogue to a wave function of the bound state. These can be solved very efficiently using well-known matrix algorithms for eigenvalues (in the homogeneous case) and the solution of linear systems (in the inhomogeneous case). We demonstrate this by solving the homogeneous and inhomogeneous Bethe-Salpeter equations and find, e.g. that for the calculation of the mass spectrum it is as efficient or even advantageous to use the inhomogeneous equation as compared to the homogeneous. This is valuable insight, in particular for the study of baryons in a three-quark setup and more involved systems.
Phase Diagram of Inhomogeneous Percolation with a Defect Plane
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.
Ekman Spiral in Horizontally Inhomogeneous Ocean with Varying Eddy Viscosity
2015-01-01
1 Ekman Spiral in Horizontally Inhomogeneous Ocean with Varying Eddy Viscosity...Oceanography Naval Postgraduate School, Monterey, California, USA Manuscript Click here to download Manuscript: Ekman -chu-pageoph-rev.docx 1...currently valid OMB control number. 1. REPORT DATE 2015 2. REPORT TYPE 3. DATES COVERED 00-00-2015 to 00-00-2015 4. TITLE AND SUBTITLE Ekman Spiral
One-dimensional diffusion model in an Inhomogeneous region
CSIR Research Space (South Africa)
Fedotov, I
2006-01-01
Full Text Available A one-dimensional model is developed to describe atomic diffusion in a graphite tube atomizer for electrothermal atomic adsorption spectrometry. The underlying idea of the model is the solution of an inhomogeneous one-dimensional diffusion equation...
Spatial Inhomogeneity of Kinetic and Magnetic Dissipations in Thermal Convection
Hotta, H.
2017-08-01
We investigate the inhomogeneity of kinetic and magnetic dissipations in thermal convection using high-resolution calculations. In statistically steady turbulence, the injected and dissipated energies are balanced. This means that a large amount of energy is continuously converted into internal energy via dissipation. As in thermal convection, downflows are colder than upflows and the inhomogeneity of the dissipation potentially changes the convection structure. Our investigation of the inhomogeneity of the dissipation shows the following. (1) More dissipation is seen around the bottom of the calculation domain, and this tendency is promoted with the magnetic field. (2) The dissipation in the downflow is much larger than that in the upflow. The dissipation in the downflow is more than 80% of the total at maximum. This tendency is also promoted with the magnetic field. (3) Although 2D probability density functions of the kinetic and magnetic dissipations versus the vertical velocity are similar, the kinetic and magnetic dissipations are not well correlated. Our result suggests that the spatial inhomogeneity of the dissipation is significant and should be considered when modeling a small-scale strong magnetic field generated with an efficient small-scale dynamo for low-resolution calculations.
Control of inhomogeneous atomic ensembles of hyperfine qudits
DEFF Research Database (Denmark)
Mischuck, Brian Edward; Merkel, Seth T.; Deutsch, Ivan H.
2012-01-01
We study the ability to control d-dimensional quantum systems (qudits) encoded in the hyperfine spin of alkali-metal atoms through the application of radio- and microwave-frequency magnetic fields in the presence of inhomogeneities in amplitude and detuning. Such a capability is essential...
An inhomogeneous wave equation and non-linear Diophantine approximation
DEFF Research Database (Denmark)
Beresnevich, V.; Dodson, M. M.; Kristensen, S.;
2008-01-01
A non-linear Diophantine condition involving perfect squares and arising from an inhomogeneous wave equation on the torus guarantees the existence of a smooth solution. The exceptional set associated with the failure of the Diophantine condition and hence of the existence of a smooth solution...... is studied. Both the Lebesgue and Hausdorff measures of this set are obtained....
An inhomogeneous Lax representation for the Hirota equation
Fioravanti, Davide
2016-01-01
Motivated by recent work on quantum integrable models without U(1) symmetry, we show that the sl(2) Hirota equation admits a Lax representation with inhomogeneous terms. The compatibility of the auxiliary linear problem leads to a new consistent family of Hirota-like equations.
Apparent horizons in Clifton-Mota-Barrow inhomogeneous universe
Vitagliano, Vincenzo; Sotiriou, Thomas P; Liberati, Stefano
2013-01-01
We analyze the apparent horizon dynamics in the inhomogeneous Clifton-Mota-Barrow solution of Brans-Dicke theory. This solution models a central matter configuration embedded in a cosmological background. In certain regions of the parameter space we find solutions exhibiting dynamical creation or merging of two horizons.
Inhomogeneous Absorption of Laser Radiation : Trigger of LIPSS Formation
Skolski, J. Z. P.; Romer, G. R. B. E.; Obona, J. V.; Ocelik, V.; in 't Veld, A. J. Huis; De Hosson, J. Th. M.
2013-01-01
The finite-difference time-domain method is used to study the inhomogeneous absorption of linearly polarized laser radiation below a rough surface. The results are analyzed in the frequency domain. It is shown that laser-induced periodic surface structures, with a periodicity larger than the laser w
Electron-Bernstein Waves in Inhomogeneous Magnetic Fields
DEFF Research Database (Denmark)
Armstrong, R. J.; Frederiksen, Å.; Pécseli, Hans
1984-01-01
The propagation of small amplitude electron-Bernstein waves in different inhomogeneous magnetic field geometries is investigated experimentally. Wave propagation towards both cut-offs and resonances are considered. The experimental results are supported by a numerical ray-tracing analysis. Spatial...... enhancements of the wave amplitude are interpreted as a result of caustic formation....
A formulation for dissolution in inhomogeneous temperature field
Fukagawa, Hiroki
2014-01-01
We propose equations governing the dissolution in inhomogeneous temperature field in terms of the variational principle. The derived equations clarify that the interface energy between solute and solvent has a significant effect on the process of the dissolution. The interface energy restrains the dissolution, and the moving interface involves the heat of dissolution.
Precision Metrology Using Weak Measurements
Zhang, Lijian; Datta, Animesh; Walmsley, Ian A.
2015-05-01
Weak values and measurements have been proposed as a means to achieve dramatic enhancements in metrology based on the greatly increased range of possible measurement outcomes. Unfortunately, the very large values of measurement outcomes occur with highly suppressed probabilities. This raises three vital questions in weak-measurement-based metrology. Namely, (Q1) Does postselection enhance the measurement precision? (Q2) Does weak measurement offer better precision than strong measurement? (Q3) Is it possible to beat the standard quantum limit or to achieve the Heisenberg limit with weak measurement using only classical resources? We analyze these questions for two prototypical, and generic, measurement protocols and show that while the answers to the first two questions are negative for both protocols, the answer to the last is affirmative for measurements with phase-space interactions, and negative for configuration space interactions. Our results, particularly the ability of weak measurements to perform at par with strong measurements in some cases, are instructive for the design of weak-measurement-based protocols for quantum metrology.
Precision metrology using weak measurements.
Zhang, Lijian; Datta, Animesh; Walmsley, Ian A
2015-05-29
Weak values and measurements have been proposed as a means to achieve dramatic enhancements in metrology based on the greatly increased range of possible measurement outcomes. Unfortunately, the very large values of measurement outcomes occur with highly suppressed probabilities. This raises three vital questions in weak-measurement-based metrology. Namely, (Q1) Does postselection enhance the measurement precision? (Q2) Does weak measurement offer better precision than strong measurement? (Q3) Is it possible to beat the standard quantum limit or to achieve the Heisenberg limit with weak measurement using only classical resources? We analyze these questions for two prototypical, and generic, measurement protocols and show that while the answers to the first two questions are negative for both protocols, the answer to the last is affirmative for measurements with phase-space interactions, and negative for configuration space interactions. Our results, particularly the ability of weak measurements to perform at par with strong measurements in some cases, are instructive for the design of weak-measurement-based protocols for quantum metrology.
Acute muscular weakness in children
Directory of Open Access Journals (Sweden)
Ricardo Pablo Javier Erazo Torricelli
Full Text Available ABSTRACT Acute muscle weakness in children is a pediatric emergency. During the diagnostic approach, it is crucial to obtain a detailed case history, including: onset of weakness, history of associated febrile states, ingestion of toxic substances/toxins, immunizations, and family history. Neurological examination must be meticulous as well. In this review, we describe the most common diseases related to acute muscle weakness, grouped into the site of origin (from the upper motor neuron to the motor unit. Early detection of hyperCKemia may lead to a myositis diagnosis, and hypokalemia points to the diagnosis of periodic paralysis. Ophthalmoparesis, ptosis and bulbar signs are suggestive of myasthenia gravis or botulism. Distal weakness and hyporeflexia are clinical features of Guillain-Barré syndrome, the most frequent cause of acute muscle weakness. If all studies are normal, a psychogenic cause should be considered. Finding the etiology of acute muscle weakness is essential to execute treatment in a timely manner, improving the prognosis of affected children.
Kennedy, K.D.; Vries, E.T. de; Koorevaar, P.
1998-01-01
This paper presents results obtained from two different Dynamic Channel Allocation (DCA) algorithms, namely the Timid and Persistent Polite Aggressive (PPA) algorithms, simulated under both static homogeneous and dynamic inhomogeneous traffic. The dynamic inhomogeneous traffic is modelled upon real
Analyses of Inhomogeneities in Radiosonde Temperature and Humidity Time Series.
Zhai, Panmao; Eskridge, Robert E.
1996-04-01
Twice daily radiosonde data from selected stations in the United States (period 1948 to 1990) and China (period 1958 to 1990) were sorted into time series. These stations have one sounding taken in darkness and the other in sunlight. The analysis shows that the 0000 and 1200 UTC time series are highly correlated. Therefore, the Easterling and Peterson technique was tested on the 0000 and 1200 time series to detect inhomogeneities and to estimate the size of the biases. Discontinuities were detected using the difference series created from the 0000 and 1200 UTC time series. To establish that the detected bias was significant, a t test was performed to confirm that the change occurs in the daytime series but not in the nighttime series.Both U.S. and Chinese radiosonde temperature and humidity data include inhomogeneities caused by changes in radiosonde sensors and observation times. The U.S. humidity data have inhomogeneities that were caused by instrument changes and the censoring of data. The practice of reporting relative humidity as 19% when it is lower than 20% or the temperature is below 40°C is called censoring. This combination of procedural and instrument changes makes the detection of biases and adjustment of the data very difficult. In the Chinese temperatures, them are inhomogeneities related to a change in the radiation correction procedure.Test results demonstrate that a modified Easterling and Peterson method is suitable for use in detecting and adjusting time series radiosonde data.Accurate stations histories are very desirable. Stations histories can confirm that detected inhomogeneities are related to instrument or procedural changes. Adjustments can then he made to the data with some confidence.
Astrocyte signaling in the presence of spatial inhomogeneities
Stamatakis, Michail; Mantzaris, Nikos V.
2007-09-01
Astrocytes, a special type of glial cells, were considered to have just a supporting role in information processing in the brain. However, several recent studies have shown that they can be chemically stimulated by various neurotransmitters, such as ATP, and can generate Ca2+ and ATP waves, which can propagate over many cell lengths before being blocked. Although pathological conditions, such as spreading depression and epilepsy, have been linked to abnormal wave propagation in astrocytic cellular networks, a quantitative understanding of the underlying characteristics is still lacking. Astrocytic cellular networks are inhomogeneous, in the sense that the domain they occupy contains passive regions or gaps, which are unable to support wave propagation. Thus, this work focuses on understanding the complex interplay between single-cell signal transduction, domain inhomogeneity, and the characteristics of wave propagation and blocking in astrocytic cellular networks. The single-cell signal transduction model that was employed accounts for ATP-mediated IP3 production, the subsequent Ca2+ release from the ER, and ATP release into the extracellular space. The model is excitable and thus an infinite range of wave propagation is observed if the domain of propagation is homogeneous. This is not always the case for inhomogeneous domains. To model wave propagation in inhomogeneous astrocytic networks, a reaction-diffusion framework was developed and one-gap as well as multiple-gap cases were simulated using an efficient finite-element algorithm. The minimum gap length that blocks the wave was computed as a function of excitability levels and geometric characteristics of the inhomogeneous network, such as the length of the active regions (cells). Complex transient patterns, such as wave reflection, wave trapping, and generation of echo waves, were also predicted by the model, and their relationship to the geometric characteristics of the network was evaluated. Therefore, the
Cantor, J
2000-08-01
Research on the effects of media violence is not well understood by the general public. Despite this fact, there is an overwhelming consensus in the scientific literature about the unhealthy effects of media violence. Meta-analyses show that media-violence viewing consistently is associated with higher levels of antisocial behavior, ranging from the trivial (imitative violence directed against toys) to the serious (criminal violence), with many consequential outcomes in between (acceptance of violence as a solution to problems, increased feelings of hostility, and the apparent delivery of painful stimulation to another person). Desensitization is another well-documented effect of viewing violence, which is observable in reduced arousal and emotional disturbance while witnessing violence, the reduced tendency to intervene in a fight, and less sympathy for the victims of violence. Although there is evidence that youth who are already violent are more likely to seek out violent entertainment, there is strong evidence that the relationship between violence viewing and antisocial behavior is bidirectional. There is growing evidence that media violence also engenders intense fear in children which often lasts days, months, and even years. The media's potential role in solutions to these problems is only beginning to be explored, in investigations examining the uses and effects of movie ratings, television ratings, and the V-chip, and the effects of media literacy programs and public education efforts. Future research should explore important individual differences in responses to media violence and effective ways to intervene in the negative effects.
Weak Lensing On the Celestial Sphere
Stebbins, Albert
1996-01-01
This paper details a description of the pattern of galaxy image distortion over the entire sky caused by the gravitational lensing which is the result of large scale inhomogeneities in our universe. We present a tensor spherical harmonic formalism to describe this pattern, giving many useful formulae. This is applied to density inhomogeneities, where we compute the angular power spectrum of the shear pattern, as well as the noise properties due to finite galaxy sampling and cosmic variance. W...
Turbulence generation by a shock wave interacting with a random density inhomogeneity field
Huete Ruiz de Lira, C.
2010-12-01
When a planar shock wave interacts with a random pattern of pre-shock density non-uniformities, it generates an anisotropic turbulent velocity/vorticity field. This turbulence plays an important role in the early stages of the mixing process in a compressed fluid. This situation emerges naturally in a shock interaction with weakly inhomogeneous deuterium-wicked foam targets in inertial confinement fusion and with density clumps/clouds in astrophysics. We present an exact small-amplitude linear theory describing such an interaction. It is based on the exact theory of time and space evolution of the perturbed quantities behind a corrugated shock front for a single-mode pre-shock non-uniformity. Appropriate mode averaging in two dimensions results in closed analytical expressions for the turbulent kinetic energy, degree of anisotropy of velocity and vorticity fields in the shocked fluid, shock amplification of the density non-uniformity and sonic energy flux radiated downstream. These explicit formulae are further simplified in the important asymptotic limits of weak/strong shocks and highly compressible fluids. A comparison with the related problem of a shock interacting with a pre-shock isotropic vorticity field is also presented.
Energy Technology Data Exchange (ETDEWEB)
Song, P.; Vasyliūnas, V. M., E-mail: paul_song@uml.edu [Space Science Laboratory and Department of Physics, University of Massachusetts Lowell, Lowell, MA 01854 (United States)
2014-12-01
The solar chromosphere is heated by damped Alfvén waves propagating upward from the photosphere at a rate that depends on magnetic field strength, producing enhanced heating at low altitudes in the extended weak-field regions (where the additional heating accounts for the radiative losses) between the boundaries of the chromospheric network as well as enhanced heating per particle at higher altitudes in strong magnetic field regions of the network. The resulting inhomogeneous radiation and temperature distribution produces bulk flows, which in turn affect the configuration of the magnetic field. The basic flow pattern is circulation on the spatial scale of a supergranule, with upward flow in the strong-field region; this is a mirror image in the upper chromosphere of photospheric/subphotospheric convection widely associated with the formation of the strong network field. There are significant differences between the neutral and the ionized components of the weakly ionized medium: neutral flow streamlines can form closed cells, whereas plasma is largely constrained to flow along the magnetic field. Stresses associated with this differential flow may explain why the canopy/funnel structures of the network magnetic field have a greater horizontal extent and are relatively more homogeneous at high altitudes than is expected from simple current-free models.
Ground-state Properties of Inhomogeneous Graphene Sheets
Polini, Marco
2009-03-01
When inter-valley scattering is weak and gauge fields due to e.g. ripples are neglected, doped and gated graphene sheets can be described using an envelope-function Hamiltonian with a new sublattice pseudospin degree-of freedom, an ultrarelativistic massless-Dirac free-fermion term, a pseudospin scalar disorder potential, and a non-relativistic instantaneous Coulombic interaction term. There is considerable evidence from experiment that this simplified description of a honeycomb lattice of Carbon atoms is usually a valid starting point for theories of those observables that depend solely on the electronic properties of π-electrons near the graphene Dirac point [1]. Although the use of this model simplifies the physics considerably it still leaves us with a many-body problem without translational invariance, which we do not know how to solve. In this talk we present a Kohn-Sham-Dirac density-functional-theory (DFT) scheme for graphene sheets that treats slowly-varying inhomogeneous scalar external potentials and electron-electron interactions on an equal footing [2]. The theory is able to account for the unusual property that the exchange-correlation contribution to chemical potential increases with carrier density in graphene [3,4]. Consequences of this property, and advantages and disadvantages of using the DFT approach to describe it, are discussed. The approach is illustrated by solving the Kohn-Sham-Dirac equations self-consistently for a model random potential describing charged point-like impurities located close to the graphene plane. The influence of electron-electron interactions on these non-linear screening calculations is discussed at length, in the light of recent experiments [5,6] reporting evidence for the presence of electron-hole puddles in nearly-neutral graphene sheets. [4pt] [1] A.K. Geim and K.S. Novoselov, Nature Mater. 6, 183 (2007); A.K. Geim and A.H. MacDonald, Phys. Today 60, 35 (2007); A.H. Castro Neto, F. Guinea, N.M.R. Peres, K
... stroke After injury to a nerve During a flare-up of multiple sclerosis (MS) You may feel ... Duchenne) Myotonic dystrophy POISONING Botulism Poisoning ( insecticides , nerve gas) Shellfish poisoning OTHER Not enough healthy red blood ...
Azimuthal Seismic Amplitude Difference Inversion for Fracture Weakness
Chen, Huaizhen; Zhang, Guangzhi; Ji, Yuxin; Yin, Xingyao
2016-08-01
Fracture weakness prediction is an important task in fractured reservoir analysis. We propose a new method to use seismic amplitude differences between azimuths to estimate the normal and tangential fracture weaknesses under the assumption that the anisotropic perturbation of the reflection coefficient is mainly induced by fractures. We first derive an expression of the reflection coefficient in terms of the normal and tangential fracture weaknesses for the case of an interface separating two fractured media. Then we use the linear fitting method to get the relationship between the two fracture weaknesses, and change the variables to precondition the inversion problem. The Bayesian framework, under the hypothesis of a Cauchy distribution prior information and a Gaussian distribution likelihood function, is employed to construct the objective function, and an initial low-frequency constraint is introduced to the objective function to make the inversion more stable. The conjugate gradient algorithm is adopted to solve the inverse problem. Tests on both synthetic and real data demonstrate that the normal and tangential fracture weaknesses can be estimated reasonably in the case of seismic data containing a moderate noise, and our inversion approach appears to be a stable method for predicting the fracture weaknesses.
From Augmentation Media to Meme Media.
Tanaka, Yuzuru
Computers as meta media are now evolving from augmentation media vehicles to meme media vehicles. While an augmentation media system provides a seamlessly integrated environment of various tools and documents, meme media system provides further functions to edit and distribute tools and documents. Documents and tools on meme media can easily…
Community Media: Muting the Democratic Media Discourse?
Carpentier, N.; Lie, R.; Servaes, J.
2003-01-01
Focuses on the concept of community media. Components that construct the identity of community media; Multi-theoretical approaches for analysis of community media; Definition of community media based on the concept of alternative media; Link between community media and civil society; Problems faced
African Journals Online (AJOL)
to managers of Essential Medicines programmes. ... media (AOM) in children as an example of such a condition, in order Lo explore these challenges more closely. ... pain, fever or deafness) and the ... at 15 and 30 minutes after each morning.
Willis, E; Strasburger, V C
1998-04-01
American media are the most violent in the world, and American society is now paying a high price in terms of real life violence. Research has confirmed that mass media violence contributes to aggressive behavior, fear, and desensitization of violence. Television, movies, music videos, computer/video games are pervasive media and represent important influences on children and adolescents. Portraying rewards and punishments and showing the consequences of violence are probably the two most essential contextual factors for viewers as they interpret the meaning of what they are viewing on television. Public health efforts have emphasized public education, media literacy campaign for children and parents, and an increased use of technology to prevent access to certain harmful medial materials.
Pels, D.
2008-01-01
The present article compendiously presents the interlinked and abruptly developing processes of media democracy and political matters’ personalization. The writer expressly opts for these processes which can radically rejuvenate communication and trust among citizens and politicians and therefore
Peripheral facial weakness (Bell's palsy).
Basić-Kes, Vanja; Dobrota, Vesna Dermanović; Cesarik, Marijan; Matovina, Lucija Zadro; Madzar, Zrinko; Zavoreo, Iris; Demarin, Vida
2013-06-01
Peripheral facial weakness is a facial nerve damage that results in muscle weakness on one side of the face. It may be idiopathic (Bell's palsy) or may have a detectable cause. Almost 80% of peripheral facial weakness cases are primary and the rest of them are secondary. The most frequent causes of secondary peripheral facial weakness are systemic viral infections, trauma, surgery, diabetes, local infections, tumor, immune disorders, drugs, degenerative diseases of the central nervous system, etc. The diagnosis relies upon the presence of typical signs and symptoms, blood chemistry tests, cerebrospinal fluid investigations, nerve conduction studies and neuroimaging methods (cerebral MRI, x-ray of the skull and mastoid). Treatment of secondary peripheral facial weakness is based on therapy for the underlying disorder, unlike the treatment of Bell's palsy that is controversial due to the lack of large, randomized, controlled, prospective studies. There are some indications that steroids or antiviral agents are beneficial but there are also studies that show no beneficial effect. Additional treatments include eye protection, physiotherapy, acupuncture, botulinum toxin, or surgery. Bell's palsy has a benign prognosis with complete recovery in about 80% of patients, 15% experience some mode of permanent nerve damage and severe consequences remain in 5% of patients.
Sendhil Mullainathan; Andrei Shleifer
2002-01-01
There are two different types of media bias. One bias, which we refer to as ideology, reflects a news outlet's desire to affect reader opinions in a particular direction. The second bias, which we refer to as spin, reflects the outlet's attempt to simply create a memorable story. We examine competition among media outlets in the presence of these biases. Whereas competition can eliminate the effect of ideological bias, it actually exaggerates the incentive to spin stories.
2013-01-01
Anlässlich der 10. Wissenschaftlichen Tagung „Soziale Medien“ am 27. und 28. Juni 2013 im Statistischen Bundesamt in Wiesbaden und in Fortsetzung des 2010 erschienenen Recherche Spezial Web 2.0 – Alle machen mit! werden in dieser Ausgabe in sechs Kapiteln Nachweise zu Veröffentlichungen und Forschungsprojekte der letzten drei Jahre zusammengestellt, die sich mit der Rolle von Social Media in verschiedenen Nutzungskontexten befassen. Social-Media-Dienste sind mittlerweile fester Bestandtei...
Weakly nonlinear electrophoresis of a highly charged colloidal particle
Schnitzer, Ory; Zeyde, Roman; Yavneh, Irad; Yariv, Ehud
2013-05-01
At large zeta potentials, surface conduction becomes appreciable in thin-double-layer electrokinetic transport. In the linear weak-field regime, where this effect is quantified by the Dukhin number, it is manifested in non-Smoluchowski electrophoretic mobilities. In this paper we go beyond linear response, employing the recently derived macroscale model of Schnitzer and Yariv ["Macroscale description of electrokinetic flows at large zeta potentials: Nonlinear surface conduction," Phys. Rev. E 86, 021503 (2012), 10.1103/PhysRevE.86.021503] as the infrastructure for a weakly nonlinear analysis of spherical-particle electrophoresis. A straightforward perturbation in the field strength is frustrated by the failure to satisfy the far-field conditions, representing a non-uniformity of the weak-field approximation at large distances away from the particle, where salt advection becomes comparable to diffusion. This is remedied using inner-outer asymptotic expansions in the spirit of Acrivos and Taylor ["Heat and mass transfer from single spheres in Stokes flow," Phys. Fluids 5, 387 (1962), 10.1063/1.1706630], with the inner region representing the particle neighborhood and the outer region corresponding to distances scaling inversely with the field magnitude. This singular scheme furnishes an asymptotic correction to the electrophoretic velocity, proportional to the applied field cubed, which embodies a host of nonlinear mechanisms unfamiliar from linear electrokinetic theories. These include the effect of induced zeta-potential inhomogeneity, animated by concentration polarization, on electro-osmosis and diffuso-osmosis; bulk advection of salt; nonuniform bulk conductivity; Coulomb body forces acting on bulk volumetric charge; and the nonzero electrostatic force exerted upon the otherwise screened particle-layer system. A numerical solution of the macroscale model validates our weakly nonlinear analysis.
Warping the Weak Gravity Conjecture
Directory of Open Access Journals (Sweden)
Karta Kooner
2016-08-01
Full Text Available The Weak Gravity Conjecture, if valid, rules out simple models of Natural Inflation by restricting their axion decay constant to be sub-Planckian. We revisit stringy attempts to realise Natural Inflation, with a single open string axionic inflaton from a probe D-brane in a warped throat. We show that warped geometries can allow the requisite super-Planckian axion decay constant to be achieved, within the supergravity approximation and consistently with the Weak Gravity Conjecture. Preliminary estimates of the brane backreaction suggest that the probe approximation may be under control. However, there is a tension between large axion decay constant and high string scale, where the requisite high string scale is difficult to achieve in all attempts to realise large field inflation using perturbative string theory. We comment on the Generalized Weak Gravity Conjecture in the light of our results.
Interpolation for weak Orlicz spaces with condition
Institute of Scientific and Technical Information of China (English)
JIAO Yong; PENG LiHua; LIU PeiDe
2008-01-01
An interpolation theorem for weak Orlicz spaces generalized by N-functions satisfying M△ condition is given.It is proved to be true for weak Orlicz martingale spaces by weak atomic decomposition of weak Hardy martingale spaces.And applying the interpolation theorem,we obtain some embedding relationships among weak Orlicz martingale spaces.
Electromagnetism in nonleptonic weak interactions
Energy Technology Data Exchange (ETDEWEB)
Ecker, G. E-mail: ecker@doppler.thp.univie.ac.at; Isidori, G.; Mueller, G.; Neufeld, H.; Pich, A
2000-12-18
We construct a low-energy effective field theory that permits the complete treatment of isospin-breaking effects in nonleptonic weak interactions to next-to-leading order. To this end, we enlarge the chiral Lagrangian describing strong and {delta}S=1 weak interactions by including electromagnetic terms with the photon as additional dynamical degree of freedom. The complete and minimal list of local terms at next-to-leading order is given. We perform the one-loop renormalization at the level of the generating functional and specialize to K{yields}{pi}{pi} decays.
Cosmology and the weak interaction
Energy Technology Data Exchange (ETDEWEB)
Schramm, D.N. (Fermi National Accelerator Lab., Batavia, IL (USA)):(Chicago Univ., IL (USA))
1989-12-01
The weak interaction plays a critical role in modern Big Bang cosmology. This review will emphasize two of its most publicized cosmological connections: Big Bang nucleosynthesis and Dark Matter. The first of these is connected to the cosmological prediction of Neutrino Flavours, N{sub {nu}} {approximately} 3 which is now being confirmed at SLC and LEP. The second is interrelated to the whole problem of galaxy and structure formation in the universe. This review will demonstrate the role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure. 87 refs., 3 figs., 5 tabs.
Weak disorder in Fibonacci sequences
Energy Technology Data Exchange (ETDEWEB)
Ben-Naim, E [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Krapivsky, P L [Department of Physics and Center for Molecular Cybernetics, Boston University, Boston, MA 02215 (United States)
2006-05-19
We study how weak disorder affects the growth of the Fibonacci series. We introduce a family of stochastic sequences that grow by the normal Fibonacci recursion with probability 1 - {epsilon}, but follow a different recursion rule with a small probability {epsilon}. We focus on the weak disorder limit and obtain the Lyapunov exponent that characterizes the typical growth of the sequence elements, using perturbation theory. The limiting distribution for the ratio of consecutive sequence elements is obtained as well. A number of variations to the basic Fibonacci recursion including shift, doubling and copying are considered. (letter to the editor)
Surface Plasmon States in Inhomogeneous Media at Critical and Subcritical Metal Concentrations
Directory of Open Access Journals (Sweden)
Katyayani Seal
2012-01-01
Full Text Available Semicontinuous metal-dielectric films are composed of a wide range of metal clusters of various geometries—sizes as well as structures. This ensures that at any given wavelength of incident radiation, clusters exist in the film that will respond resonantly, akin to resonating nanoantennas, resulting in the broad optical response (absorption that is a characteristic of semicontinuous films. The physics of the surface plasmon states that are supported by such systems is complex and can involve both localized and propagating plasmons. This chapter describes near-field experimental and numerical studies of the surface plasmon states in semicontinuous films at critical and subcritical metal concentrations and evaluates the local field intensity statistics to discuss the interplay between various eigenmodes.
A class of invisible inhomogeneous media and the control of electromagnetic waves
Vial, B.; Liu, Y.; Horsley, S. A. R.; Philbin, T. G.; Hao, Y.
2016-12-01
We propose a general method to arbitrarily manipulate an electromagnetic wave propagating in a two-dimensional medium, without introducing any scattering. This leads to a whole class of isotropic spatially varying permittivity and permeability profiles that are invisible while shaping the field magnitude and/or phase. In addition, we propose a metamaterial structure working in the infrared that demonstrates deep subwavelength control of the electric field amplitude and strong reduction of the scattering. This work offers an alternative strategy to achieve invisibility with isotropic materials and paves the way for tailoring the propagation of light at the nanoscale.
Stochastic interference of fluorescence radiation in random media with large inhomogeneities
Zimnyakov, D. A.; Asharchuk, I. A.; Yuvchenko, S. A.; Sviridov, A. P.
2017-03-01
Stochastic interference of fluorescence light outgoing from a dye-doped coarse-grained random medium, which was pumped by the continuous-wave laser radiation, was experimentally studied. It was found that the contrast of random interference patterns highly correlates with the wavelength-dependent fluorescence intensity and reaches its minimum in the vicinity of the cusp of emission spectrum. The decay in the contrast of spectrally selected speckle patterns was interpreted in terms of the pathlength distribution broadening for fluorescence radiation propagating in the medium. This broadening is presumably caused by the wavelength-dependent negative absorption of the medium.
Institute of Scientific and Technical Information of China (English)
Xia Ji; Wei Cai; Pingwen Zhang
2008-01-01
In this paper, we analyze the transmission and reflection properties of a high order discontinuous Galerkin method for dispersive Maxwell's equations, originally proposed by Lu et al. [J. Comput. Phys. 200 (2004), pp. 549-580]. We study the reflection and transmission properties of the numerical method for up to second-order polynomial elements for one-and two-dimensional Maxwell's equations with rectangular meshes. High order accuracy has been shown for reflection and transmission coefficients near material interfaces.
Twisted toroidal vortex-solitons in inhomogeneous media with repulsive nonlinearity
Kartashov, Y V; Shnir, Y; Torner, L
2014-01-01
Toroidal modes in the form of so-called Hopfions, with two independent winding numbers, a hidden one (twist, s), which characterizes a circular vortex thread embedded into a three-dimensional soliton, and the vorticity around the vertical axis m, appear in many fields, including the field theory, ferromagnetics, and semi- and superconductors. Such topological states are normally generated in multi-component systems, or as trapped quasi-linear modes in toroidal potentials. We uncover that stable solitons with this structure can be created, without any linear potential, in the single-component setting with the strength of repulsive nonlinearity growing fast enough from the center to the periphery, for both steep and smooth modulation profiles. Toroidal modes with s=1 and vorticity m=0,1,2 are produced. They are stable for m1. An approximate analytical solution is obtained for the twisted ring with s=1, m=0. Under the application of an external torque, it rotates like a solid ring. The setting can be implemented...
Du, Yijun; Segall, Paul; Gao, Huajian
1994-07-01
Quasi-static elastic dislocations in a homogeneous elastic half-space are commonly used to model earthquake faulting processes. Recent studies of the 1989 Kalapana, Hawaii, and Loma Prieta, California, earthquakes suggest that spatial variations in elastic properties are necessary to reconcile geodetic and seismic results. In this paper, we use a moduli perturbation approach to investigate the effect of lateral and vertical variations in elastic properties on the elastic fields produced by dislocations. The method is simple, efficient, and in some cases leads to closed form solutions. The zero-order solution is simply the solution for a homogeneous body. The first-order correction for elastic heterogeneity is given by a volume integral involving the spatial variations in moduli, the displacements due to a dislocation in a homogeneous half-space, and the half-space Green's function. The same representation can be also used to obtain higher-order solutions. If there are only piecewise constant variations in shear modulus, the volume integral can be reduced to a surface integral (or line integral in two-dimensions). Comparisons with the analytical solutions for a screw dislocation in a layered medium suggest that the perturbation solutions are valid for nearly an order of magnitude variation in modulus. It is shown that a simple two-dimensional model with both vertical and lateral variations in the elastic properties may explain a large part of the discrepancy between seismic and geodetically inferred fault depths for the 1989 Kalapana, Hawaii, earthquake.
A scheme comparison of Autler-Townes based slow light in inhomogeneously broadened quantum dot media
DEFF Research Database (Denmark)
Hansen, Per Lunnemann; Mørk, Jesper
2010-01-01
configurations. Qualitative differences of the V scheme compared to the Ξ and Λ schemes are found, which show that features of (ATS) are only revealed in the V scheme. The underlying physical mechanisms causing this discrepancy are analyzed and discussed. Finally we compare field propagation calculations...
Real-time quantum field theory at finite temperature in an inhomogeneous media
Bibilashvili, T M
1995-01-01
The method of the real time perturbative calculations of nonequilibrium averages is generalised to the case of varying chemical potential. Calculations are performed in the frame of Zubarev's nonequilibrium density matrix approach. In this approach perturbations of temperature and other thermodynamical parameters are taken into account explicitly including nonlinear terms. It differs from the Schwinger-Keldysh approach through the choice of more general initial conditions for the density matrix.
Large-scale flow generation by inhomogeneous helicity
Yokoi, Nobumitsu
2015-01-01
The effect of kinetic helicity (velocity--vorticity correlation) on turbulent momentum transport is investigated. The turbulent kinetic helicity (pseudoscalar) enters into the Reynolds stress (mirrorsymmetric 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 non-uniform 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 hom...
A dynamical system approach to inhomogeneous dust solutions
Sussman, Roberto A
2007-01-01
We examine numerically and qualitatively the Lema\\^\\i tre--Tolman--Bondi (LTB) inhomogeneous dust solutions as a 3--dimensional dynamical system characterized by six critical points. One of the coordinates of the phase space is an average density parameter, $$, which behaves as the ordinary $\\Omega$ in Friedman-Lema\\^\\i tre--Robertson--Walker (FLRW) dust spacetimes. The other two coordinates, a shear parameter and a density contrast function, convey the effects of inhomogeneity. As long as shell crossing singularities are absent, this phase space is bounded or it can be trivially compactified. This space contains several invariant subspaces which define relevant particular cases, such as: ``parabolic'' evolution, FLRW dust and the Schwarzschild--Kruskal vacuum limit. We examine in detail the phase space evolution of several dust configurations: a low density void formation scenario, high density re--collapsing universes with open, closed and wormhole topologies, a structure formation scenario with a black hol...
An automatically generated code for relativistic inhomogeneous cosmologies
Bentivegna, Eloisa
2016-01-01
The applications of numerical relativity to cosmology are on the rise, contributing insight into such cosmological problems as structure formation, primordial phase transitions, gravitational-wave generation, and inflation. In this paper, I present the infrastructure for the computation of inhomogeneous dust cosmologies which was used recently to measure the effect of nonlinear inhomogeneity on the cosmic expansion rate. I illustrate the code's architecture, provide evidence for its correctness in a number of familiar cosmological settings, and evaluate its parallel performance for grids of up to several billion points. The code, which is available as free software, is based on the Einstein Toolkit infrastructure, and in particular leverages the automated-code-generation capabilities provided by its component Kranc.
TRANSMISSION AND ABSORPTION OF MICROWAVES BY AN INHOMOGENEOUS SPHERE PLASMA
Institute of Scientific and Technical Information of China (English)
SONG Falun; CAO Jinxiang; WANG Ge
2004-01-01
The numerical calculation of the transmission and absorption of microwaves at an arbitrarily incident angle to the inhomogeneous spherically symmetric plasma is presented.The nonuniform sphere is modeled by a series of concentric spherical shells, and the electron density is constant in each shell. The overall density profile follows any given distribution function. By using the geometrical optics approximation and considering the propagation coefficient is complex, as well as the attenuation and phase coefficients are vectors, the detailed evaluation shows that the transmission and absorption of microwaves in the inhomogeneous spherically symmetric plasma depend on the electron and neutral particle collision frequency, central density, incident angle of the microwaves and density distribution profiles.
Effect of inhomogeneities on high precision measurements of cosmological distances
Peel, Austin; Ishak, Mustapha
2014-01-01
We study exact relativistic effects of inhomogeneities on distance measures, focusing on the distance modulus, in a Swiss-cheese model of the universe with $\\Lambda$CDM background dynamics, and where the `holes' are non-symmetric 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. Unlike Swiss-cheese model studies with spherically symmetric holes, we find a net shift in the distance modulus $\\mu$ to distant sources even when we average over many lines of sight with randomized hole orientations and impact parameters. The light also need not propagate strictly through underdense regions to result in an overall bias, which is an accumulated effect associated with the evolution of the anisotropic holes. We find the average shift $\\langle\\Delta\\mu\\rangle$ relative to a pure $\\Lambda$CDM model to increase with redshift...
Generation of indirect combustion noise by compositional inhomogeneities
Magri, Luca; O'Brien, Jeff; Ihme, Matthias
2016-11-01
The generation of indirect combustion noise in nozzles and turbine stages is commonly attributed to temperature inhomogeneities and vorticity fluctuations. Here, compositional inhomogeneities in a multi-component gas mixture are shown to produce indirect noise both theoretically and numerically. The chemical potential function is introduced as an additional acoustic source mechanism. The contribution of the compositional noise is compared to the entropy noise and direct noise by considering subsonic, supersonic and shocked nozzles downstream of the combustor exit. It is shown that the compositional noise is dependent on the local mixture composition and can exceed entropy noise for fuel-lean conditions and supersonic/shocked nozzle flows. This suggests that compositional indirect combustion noise may require consideration with the implementation of advanced combustion concepts in gas turbines, including low-emissions combustors, high-power-density engine cores, or compact burners.
Spin diffusion from an inhomogeneous quench in an integrable system
Ljubotina, Marko; Žnidarič, Marko; Prosen, Tomaž
2017-07-01
Generalized hydrodynamics predicts universal ballistic transport in integrable lattice systems when prepared in generic inhomogeneous initial states. However, the ballistic contribution to transport can vanish in systems with additional discrete symmetries. Here we perform large scale numerical simulations of spin dynamics in the anisotropic Heisenberg XXZ spin 1/2 chain starting from an inhomogeneous mixed initial state which is symmetric with respect to a combination of spin reversal and spatial reflection. In the isotropic and easy-axis regimes we find non-ballistic spin transport which we analyse in detail in terms of scaling exponents of the transported magnetization and scaling profiles of the spin density. While in the easy-axis regime we find accurate evidence of normal diffusion, the spin transport in the isotropic case is clearly super-diffusive, with the scaling exponent very close to 2/3, but with universal scaling dynamics which obeys the diffusion equation in nonlinearly scaled time.
Determination of critical exponents of inhomogeneous Gd films
Energy Technology Data Exchange (ETDEWEB)
Rosales-Rivera, A., E-mail: arosalesr@unal.edu.co [Laboratorio de Magnetismo y Materiales Avanzados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia, Sede Manizales, Manizales (Colombia); Salazar, N.A. [Laboratorio de Magnetismo y Materiales Avanzados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia, Sede Manizales, Manizales (Colombia); Hovorka, O.; Idigoras, O.; Berger, A. [CIC nanoGUNE Consolider, Tolosa Hiribidea 76, E-20018 Donostia-San Sebastian (Spain)
2012-08-15
The role of inhomogeneity on the critical behavior is studied for non-epitaxial Gd films. For this purpose, the film inhomogeneity was varied experimentally by annealing otherwise identical samples at different temperatures T{sub AN}=200, 400, and 500 Degree-Sign C. Vibrating sample magnetometry (VSM) was used for magnetization M vs. T measurements at different external fields H. A method based upon the linear superposition of different sample parts having different Curie temperatures T{sub C} was used to extract the critical exponents and the intrinsic distribution of Curie temperatures. We found that this method allows extracting reliable values of the critical exponents for all annealing temperatures, which enabled us to study the effects of disorder onto the universality class of Gd films.
Enhancement of photoacoustic detection of inhomogeneities in polymers
Grondona, P; Iriarte, D I; Pomarico, J A; Ranea-Sandoval, Héctor F; Bilmes, G M
2013-01-01
We report a series of experiments on laser pulsed photoacoustic excitationin turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon(R) samples in different situations and we show the limitations of the method.
Two-step estimation for inhomogeneous spatial point processes
DEFF Research Database (Denmark)
Waagepetersen, Rasmus; Guan, Yongtao
2009-01-01
The paper is concerned with parameter estimation for inhomogeneous spatial point processes with a regression model for the intensity function and tractable second-order properties (K-function). Regression parameters are estimated by using a Poisson likelihood score estimating function and in the ......The paper is concerned with parameter estimation for inhomogeneous spatial point processes with a regression model for the intensity function and tractable second-order properties (K-function). Regression parameters are estimated by using a Poisson likelihood score estimating function...... and in the second step minimum contrast estimation is applied for the residual clustering parameters. Asymptotic normality of parameter estimates is established under certain mixing conditions and we exemplify how the results may be applied in ecological studies of rainforests....
Twisted inhomogeneous Diophantine approximation and badly approximable sets
Harrap, Stephen
2010-01-01
For any real pair i, j geq 0 with i+j=1 let Bad(i, j) denote the set of (i, j)-badly approximable pairs. That is, Bad(i, j) consists of irrational vectors x:=(x_1, x_2) in R^2 for which there exists a positive constant c(x) such that max {||qx_1||^(-i), ||qx_2||^(-j)} > c(x)/q for all q in N. Building on a result of Kurzweil, a new characterization of the set Bad(i, j) in terms of `well-approximable' vectors in the area of `twisted' inhomogeneous Diophantine approximation is established. In addition, it is shown that Bad^x(i, j), the `twisted' inhomogeneous analogue of Bad(i, j), has full Hausdorff dimension 2 when x is chosen from the set Bad(i, j).
Stability analysis for bad cavity lasers with inhomogeneously broadened gain
Kazakov, Georgy A
2016-01-01
Bad cavity lasers are experiencing renewed interest in the context of active optical frequency standards, due to their enhanced robustness against fluctuations of the laser cavity. The gain medium would consist of narrow-linewidth atoms, either trapped inside the cavity or intersecting the cavity mode dynamically. A finite velocity distribution, atomic interactions, or interactions of realistic multilevel atoms with external field leads to an inhomogeneous broadening of the atomic gain profile. This can bring the bad cavity laser to operate in unstable regimes characterized by complex temporal patterns of the field amplitude. We present a new and efficient method for the stability analysis of bad cavity lasers with inhomogeneously broadened gain. We apply this method to identify the steady-state solutions for the metrology-relevant case of spin-1/2 atoms interacting with an external magnetic field.
Potential generated by a massive inhomogeneous straight segment
Institute of Scientific and Technical Information of China (English)
Nour-Eddine Najid; El Haj Elourabi; Mohamed Zegoumou
2011-01-01
The discoveries of binary asteroids have opened an important new field of research concerning the calculation of potential generated by irregular bodies. Some of them have an elongated shape. A simple model to describe the motion of a test parficle in that kind of potential requires consideration of a finite homogeneous straight segment. We construct 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 closed analytical form of the potential generated by this inhomogeneous massive segment. The study of the dynamical behavior is fulfilled by the use of Lagrangian formulation, which allows us to calculate some two and three dimensional orbits.
Geometric spin Hall effect of light with inhomogeneous polarization
Ling, Xiaohui; Zhou, Xinxing; Yi, Xunong
2017-01-01
The spin Hall effect of light originates from spin-orbit interaction of light, which manifests two types of geometric phases. In this paper, we report the observation of a geometric spin Hall effect by generating a light beam with inhomogeneous polarization distribution. Unlike the previously reported geometric spin Hall effect observed in a tilted beam-detector system, which is believed to result from an effective spin-redirection Berry geometric phase, the geometric spin Hall effect demonstrated here is attributed to an effective, spatially varying Pancharatnam-Berry geometric phase generated by the inhomogeneous polarization geometry. Our further experiments show that the geometric spin Hall effect can be tuned by tailoring the polarization geometry of light, demonstrating the spin states of photons can be steered with a great flexibility.
Glauber theory and the quantum coherence of curvature inhomogeneities
Giovannini, Massimo
2016-01-01
The curvature inhomogeneities are systematically scrutinized in the framework of the Glauber approach. The amplified quantum fluctuations of the scalar and tensor modes of the geometry are shown to be first-order coherent while the interference of the corresponding intensities is larger than in the case of Bose-Einstein correlations. After showing that the degree of second-order coherence does not suffice to characterize unambiguously the curvature inhomogeneities, we argue that direct analyses of the degrees of third and fourth-order coherence are necessary to discriminate between different correlated states and to infer more reliably the statistical properties of the large-scale fluctuations. We speculate that the moments of the multiplicity distributions of the relic phonons might be observationally accessible thanks to new generations of instruments able to count the single photons of the Cosmic Microwave Background in the THz region.
Acoustic Wavefront Manipulation: Impedance Inhomogeneity and Extraordinary Reflection
Zhao, Jiajun; Chen, Zhining; Li, Baowen
2013-01-01
Optical wavefront can be manipulated by interfering elementary beams with phase inhomogeneity. Therefore a surface allowing huge, abrupt and position-variant phase change would enable all possibilities of wavefront engineering. However, one may not have the luxury of efficient abrupt-phase-changing materials in acoustics. This motivates us to establish a counterpart mechanism for acoustics, in order to empower the wide spectrum of novel acoustic applications. Remarkably, the proposed impedance-governed generalized Snell's law (IGSL) of reflection is distinguished from that in optics. Via the manipulation of inhomogeneous acoustic impedance, extraordinary reflection can be tailored for unprecedented wavefront manipulation while ordinary reflection can be surprisingly switched on or off. Our results may power the acoustic-wave manipulation and engineering. We demonstrate novel acoustic applications by planar surfaces designed with IGSL.