Design of three-dimensional nonimaging concentrators with inhomogeneous media

Science.gov (United States)

Minano, J. C.

1986-09-01

A three-dimensional nonimaging concentrator is an optical system that transforms a given four-parametric manifold of rays reaching a surface (entry aperture) into another four-parametric manifold of rays reaching the receiver. A procedure of design of such concentrators is developed. In general, the concentrators use mirrors and inhomogeneous media (i.e., gradient-index media). The concentrator has the maximum concentration allowed by the theorem of conservation of phase-space volume. This is the first known concentrator with such properties. The Welford-Winston edge-ray principle in three-dimensional geometry is proven under several assumptions. The linear compound parabolic concentrator is derived as a particular case of the procedure of design.

Scattering characteristics of electromagnetic waves in time and space inhomogeneous weakly ionized dusty plasma sheath

Science.gov (United States)

Guo, Li-xin; Chen, Wei; Li, Jiang-ting; Ren, Yi; Liu, Song-hua

2018-05-01

The dielectric coefficient of a weakly ionised dusty plasma is used to establish a three-dimensional time and space inhomogeneous dusty plasma sheath. The effects of scattering on electromagnetic (EM) waves in this dusty plasma sheath are investigated using the auxiliary differential equation finite-difference time-domain method. Backward radar cross-sectional values of various parameters, including the dust particle radius, charging frequency of dust particles, dust particle concentration, effective collision frequency, rate of the electron density variation with time, angle of EM wave incidence, and plasma frequency, are analysed within the time and space inhomogeneous plasma sheath. The results show the noticeable effects of dusty plasma parameters on EM waves.

Influence of inhomogeneous coercivities on media noise in granular perpendicular media investigated by using magnetic force microscopy

International Nuclear Information System (INIS)

Bai, J.; Takahoshi, H.; Ito, H.; Rheem, Y.W.; Saito, H.; Ishio, S.

2004-01-01

We investigated the influence of the inhomogeneous coercivities on the media noise in a CoPtCr-SiO 2 granular perpendicular magnetic recording medium via ex situ and in situ magnetic force microscopy (MFM) techniques. The ex situ MFM analyses exhibited that transition zigzags contributed to strong magnetic clusters in noise images, and thus resulted in dominant component of the media noise. According to the in situ MFM measurements, it was suggested that an amount of magnetic grains inside a microscopic area reversed like one magnetic ''particle because of strong inter-grain exchange coupling, and that these microscopic areas showed their local magnetic switching behaviors. A mathematic transformation was used to obtain approximately the magnetization distribution in recording layer. And the individual microscopic areas inside recorded bits were compared quasi-quantitatively with those leading large transition zigzags in magnetization switching behaviors. It was indicated that the inhomogeneous coercivities is one of crucial reasons of the medium noise in the perpendicular magnetic recording

Massively parallel simulator of optical coherence tomography of inhomogeneous turbid media.

Science.gov (United States)

Malektaji, Siavash; Lima, Ivan T; Escobar I, Mauricio R; Sherif, Sherif S

2017-10-01

An accurate and practical simulator for Optical Coherence Tomography (OCT) could be an important tool to study the underlying physical phenomena in OCT such as multiple light scattering. Recently, many researchers have investigated simulation of OCT of turbid media, e.g., tissue, using Monte Carlo methods. The main drawback of these earlier simulators is the long computational time required to produce accurate results. We developed a massively parallel simulator of OCT of inhomogeneous turbid media that obtains both Class I diffusive reflectivity, due to ballistic and quasi-ballistic scattered photons, and Class II diffusive reflectivity due to multiply scattered photons. This Monte Carlo-based simulator is implemented on graphic processing units (GPUs), using the Compute Unified Device Architecture (CUDA) platform and programming model, to exploit the parallel nature of propagation of photons in tissue. It models an arbitrary shaped sample medium as a tetrahedron-based mesh and uses an advanced importance sampling scheme. This new simulator speeds up simulations of OCT of inhomogeneous turbid media by about two orders of magnitude. To demonstrate this result, we have compared the computation times of our new parallel simulator and its serial counterpart using two samples of inhomogeneous turbid media. We have shown that our parallel implementation reduced simulation time of OCT of the first sample medium from 407 min to 92 min by using a single GPU card, to 12 min by using 8 GPU cards and to 7 min by using 16 GPU cards. For the second sample medium, the OCT simulation time was reduced from 209 h to 35.6 h by using a single GPU card, and to 4.65 h by using 8 GPU cards, and to only 2 h by using 16 GPU cards. Therefore our new parallel simulator is considerably more practical to use than its central processing unit (CPU)-based counterpart. Our new parallel OCT simulator could be a practical tool to study the different physical phenomena underlying OCT

Interactions between butterfly-shaped pulses in the inhomogeneous media

International Nuclear Information System (INIS)

Liu, Wen-Jun; Huang, Long-Gang; Pan, Nan; Lei, Ming

2014-01-01

Pulse interactions affect pulse qualities during the propagation. Interactions between butterfly-shaped pulses are investigated to improve pulse qualities in the inhomogeneous media. In order to describe the interactions between butterfly-shaped pulses, analytic two-soliton solutions are derived. Based on those solutions, influences of corresponding parameters on pulse interactions are discussed. Methods to control the pulse interactions are suggested. - Highlights: • Interactions between butterfly-shaped pulses are investigated. • Methods to control the pulse interactions are suggested. • Analytic two-soliton solutions for butterfly-shaped pulses are derived

Interactions between butterfly-shaped pulses in the inhomogeneous media

Energy Technology Data Exchange (ETDEWEB)

Liu, Wen-Jun [State Key Laboratory of Information Photonics and Optical Communications, School of Science, P. O. Box 91, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Huang, Long-Gang; Pan, Nan [State Key Laboratory of Information Photonics and Optical Communications, School of Science, P. O. Box 91, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Lei, Ming, E-mail: mlei@bupt.edu.cn [State Key Laboratory of Information Photonics and Optical Communications, School of Science, P. O. Box 91, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

2014-10-15

Pulse interactions affect pulse qualities during the propagation. Interactions between butterfly-shaped pulses are investigated to improve pulse qualities in the inhomogeneous media. In order to describe the interactions between butterfly-shaped pulses, analytic two-soliton solutions are derived. Based on those solutions, influences of corresponding parameters on pulse interactions are discussed. Methods to control the pulse interactions are suggested. - Highlights: • Interactions between butterfly-shaped pulses are investigated. • Methods to control the pulse interactions are suggested. • Analytic two-soliton solutions for butterfly-shaped pulses are derived.

Percolation for a model of statistically inhomogeneous random media

International Nuclear Information System (INIS)

Quintanilla, J.; Torquato, S.

1999-01-01

We study clustering and percolation phenomena for a model of statistically inhomogeneous two-phase random media, including functionally graded materials. This model consists of inhomogeneous fully penetrable (Poisson distributed) disks and can be constructed for any specified variation of volume fraction. We quantify the transition zone in the model, defined by the frontier of the cluster of disks which are connected to the disk-covered portion of the model, by defining the coastline function and correlation functions for the coastline. We find that the behavior of these functions becomes largely independent of the specific choice of grade in volume fraction as the separation of length scales becomes large. We also show that the correlation function behaves in a manner similar to that of fractal Brownian motion. Finally, we study fractal characteristics of the frontier itself and compare to similar properties for two-dimensional percolation on a lattice. In particular, we show that the average location of the frontier appears to be related to the percolation threshold for homogeneous fully penetrable disks. copyright 1999 American Institute of Physics

Traveltime approximations for transversely isotropic media with an inhomogeneous background

KAUST Repository

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.

Traveltime approximations for transversely isotropic media with an inhomogeneous background

KAUST Repository

Alkhalifah, Tariq

2011-01-01

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.

Parametrically induced low-frequency waves in weakly inhomogeneous magnetized plasmas

International Nuclear Information System (INIS)

Pesic, S.

1981-01-01

The linear dispersion relation governing the parametric interaction of a lower hybrid pump wave with a weakly-inhomogeneous current carrying hot plasma confined by a helical magnetic field is derived and solved numerically. The stability boundaries are delineated over a wide range in the k-space. The frequency and growth rate of decay instabilities are calculated for plasma parameters relevant to lower hybrid plasma heating experiments. The parametric excitation of drift waves and ion cyclotron current instabilities is discussed. In the low-density plasma region low minimum thresholds and high growth rates are obtained for the pump decay into ion cyclotron and nonresonant quasimodes. The spatial amplification of hot ion Bernstein waves and nonresonant quasimodes dominate in the plasma core (ω 0 /ωsub(LH) < 2). The presented theoretical results are in qualitative agreement with current LH plasma heating experiments. (author)

Wavefield analysis in inhomogeneous media by wavelet transform; Wavelet henkan ni yoru fukinshitsu baitai no hadoba kaiseki

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.

High-order FDTD methods for transverse electromagnetic systems in dispersive inhomogeneous media.

Science.gov (United States)

Zhao, Shan

2011-08-15

This Letter introduces a novel finite-difference time-domain (FDTD) formulation for solving transverse electromagnetic systems in dispersive media. Based on the auxiliary differential equation approach, the Debye dispersion model is coupled with Maxwell's equations to derive a supplementary ordinary differential equation for describing the regularity changes in electromagnetic fields at the dispersive interface. The resulting time-dependent jump conditions are rigorously enforced in the FDTD discretization by means of the matched interface and boundary scheme. High-order convergences are numerically achieved for the first time in the literature in the FDTD simulations of dispersive inhomogeneous media. © 2011 Optical Society of America

Dynamics of weakly inhomogeneous oscillator populations: perturbation theory on top of Watanabe-Strogatz integrability

Science.gov (United States)

Vlasov, Vladimir; Rosenblum, Michael; Pikovsky, Arkady

2016-08-01

As has been shown by Watanabe and Strogatz (WS) (1993 Phys. Rev. Lett. 70 2391), a population of identical phase oscillators, sine-coupled to a common field, is a partially integrable system: for any ensemble size its dynamics reduce to equations for three collective variables. Here we develop a perturbation approach for weakly nonidentical ensembles. We calculate corrections to the WS dynamics for two types of perturbations: those due to a distribution of natural frequencies and of forcing terms, and those due to small white noise. We demonstrate that in both cases, the complex mean field for which the dynamical equations are written is close to the Kuramoto order parameter, up to the leading order in the perturbation. This supports the validity of the dynamical reduction suggested by Ott and Antonsen (2008 Chaos 18 037113) for weakly inhomogeneous populations.

Dynamics of weakly inhomogeneous oscillator populations: perturbation theory on top of Watanabe–Strogatz integrability

International Nuclear Information System (INIS)

Vlasov, Vladimir; Rosenblum, Michael; Pikovsky, Arkady

2016-01-01

As has been shown by Watanabe and Strogatz (WS) (1993 Phys. Rev. Lett. 70 2391), a population of identical phase oscillators, sine-coupled to a common field, is a partially integrable system: for any ensemble size its dynamics reduce to equations for three collective variables. Here we develop a perturbation approach for weakly nonidentical ensembles. We calculate corrections to the WS dynamics for two types of perturbations: those due to a distribution of natural frequencies and of forcing terms, and those due to small white noise. We demonstrate that in both cases, the complex mean field for which the dynamical equations are written is close to the Kuramoto order parameter, up to the leading order in the perturbation. This supports the validity of the dynamical reduction suggested by Ott and Antonsen (2008 Chaos 18 037113) for weakly inhomogeneous populations. (letter)

Light-sheet generation in inhomogeneous media using self-reconstructing beams and the STED-principle.

Science.gov (United States)

Gohn-Kreuz, Cristian; Rohrbach, Alexander

2016-03-21

Self-reconstruction of Bessel beams in inhomogeneous media is beneficial in light-sheet based microscopy. Although the beam's ring system enables propagation stability, the resulting image contrast is reduced. Here, we show that by a combination of two self-reconstructing beams with different orbital angular momenta it is possible to inhibit fluorescence from the ring system by using stimulated emission depletion (STED) even in strongly scattering media. Our theoretical study shows that the remaining fluorescence γ depends non-linearly on the beams' relative radial and orbital angular momenta. For various scattering media we demonstrate that γ remains remarkably stable over long beam propagation distances.

EPR dosimetry of radiotherapy photon beams in inhomogeneous media using alanine films

Energy Technology Data Exchange (ETDEWEB)

Oesteraas, Bjoern Helge [Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Montebello, N-0310 Oslo (Norway); Hole, Eli Olaug [Department of Physics, University of Oslo, PO Box 1048 Blindern, N-0316 Oslo (Norway); Olsen, Dag Rune [Department of Radiation Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, N-0310 Oslo (Norway); Malinen, Eirik [Department of Radiation Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, N-0310 Oslo (Norway)

2006-12-21

In the current work, EPR (electron paramagnetic resonance) dosimetry using alanine films (134 {mu}m thick) was utilized for dose measurements in inhomogeneous phantoms irradiated with radiotherapy photon beams. The main phantom material was PMMA, while either Styrofoam or aluminium was introduced as an inhomogeneity. The phantoms were irradiated to a maximum dose of about 30 Gy with 6 or 15 MV photons. The performance of the alanine film dosimeters was investigated and compared to results from ion chamber dosimetry, Monte Carlo simulations and radiotherapy treatment planning calculations. It was found that the alanine film dosimeters had a linear dose response above approximately 5 Gy, while a background signal obscured the response at lower dose levels. For doses between 5 and 60 Gy, the standard deviation of single alanine film dose estimates was about 2%. The alanine film dose estimates yielded results comparable to those from the Monte Carlo simulations and the ion chamber measurements, with absolute differences between estimates in the order of 1-15%. The treatment planning calculations exhibited limited applicability. The current work shows that alanine film dosimetry is a method suitable for estimating radiotherapeutical doses and for dose measurements in inhomogeneous media.

EPR dosimetry of radiotherapy photon beams in inhomogeneous media using alanine films

International Nuclear Information System (INIS)

Oesteraas, Bjoern Helge; Hole, Eli Olaug; Olsen, Dag Rune; Malinen, Eirik

2006-01-01

In the current work, EPR (electron paramagnetic resonance) dosimetry using alanine films (134 μm thick) was utilized for dose measurements in inhomogeneous phantoms irradiated with radiotherapy photon beams. The main phantom material was PMMA, while either Styrofoam or aluminium was introduced as an inhomogeneity. The phantoms were irradiated to a maximum dose of about 30 Gy with 6 or 15 MV photons. The performance of the alanine film dosimeters was investigated and compared to results from ion chamber dosimetry, Monte Carlo simulations and radiotherapy treatment planning calculations. It was found that the alanine film dosimeters had a linear dose response above approximately 5 Gy, while a background signal obscured the response at lower dose levels. For doses between 5 and 60 Gy, the standard deviation of single alanine film dose estimates was about 2%. The alanine film dose estimates yielded results comparable to those from the Monte Carlo simulations and the ion chamber measurements, with absolute differences between estimates in the order of 1-15%. The treatment planning calculations exhibited limited applicability. The current work shows that alanine film dosimetry is a method suitable for estimating radiotherapeutical doses and for dose measurements in inhomogeneous media

Modulated electromagnetic fields in inhomogeneous media, hyperbolic pseudoanalytic functions, and transmutations

Energy Technology Data Exchange (ETDEWEB)

Khmelnytskaya, Kira V., E-mail: khmel@uaq.edu.mx [Faculty of Engineering, Autonomous University of Queretaro, Cerro de las Campanas s/n, col. Las Campanas Querétaro, Qro. CP 76010 (Mexico); Kravchenko, Vladislav V., E-mail: vkravchenko@math.cinvestav.edu.mx; Torba, Sergii M., E-mail: storba@math.cinvestav.edu.mx [Department of Mathematics, CINVESTAV del IPN, Unidad Querétaro, Libramiento Norponiente # 2000 Fracc. Real de Juriquilla Querétaro, Qro., CP 76230 (Mexico)

2016-05-15

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.

Account of an optical beam spreading caused by turbulence for the problem of partially coherent wavefield propagation through inhomogeneous absorbing media

Science.gov (United States)

Dudorov, Vadim V.; Kolosov, Valerii V.

2003-04-01

The propagation problem for partially coherent wave fields in inhomogeneous media is considered in this work. The influence of refraction, inhomogeneity of gain medium properties and refraction parameter fluctuations on target characteristics of radiation are taken into consideration. Such problems arise in the study of laser propagation on atmosphere paths, under investigation of directional radiation pattern forming for lasers which gain media is characterized by strong fluctuation of dielectric constant and for lasers which resonator have an atmosphere area. The ray-tracing technique allows us to make effective algorithms for modeling of a partially coherent wave field propagation through inhomogeneous random media is presented for case when the influecne of an optical wave refraction, the influence of the inhomogeiety of radiaitn amplification or absorption, and also the influence of fluctuations of a refraction parameter on target radiation parameters are basic. Novelty of the technique consists in the account of the additional refraction caused by inhomogeneity of gain, and also in the method of an account of turbulent distortions of a beam with any initial coherence allowing to execute construction of effective numerical algorithms. The technique based on the solution of the equation for coherence function of the second order.

A second order radiative transfer equation and its solution by meshless method with application to strongly inhomogeneous media

Energy Technology Data Exchange (ETDEWEB)

Zhao, J.M., E-mail: jmzhao@hit.edu.cn [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, People' s Republic of China (China); Tan, J.Y., E-mail: tanjy@hit.edu.cn [School of Auto Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai 264209, People' s Republic of China (China); Liu, L.H., E-mail: lhliu@hit.edu.cn [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, People' s Republic of China (China); School of Auto Engineering, Harbin Institute of Technology at Weihai, 2 West Wenhua Road, Weihai 264209, People' s Republic of China (China)

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.

Full-wave solution of short impulses in inhomogeneous plasma

Indian Academy of Sciences (India)

... in arbitrarily inhomogeneous media will be presented on a fundamentally new, ... The general problem of wave propagation of monochromatic signals in inhomogeneous media was enlightened in [1]. ... Pramana – Journal of Physics | News.

Role of spiral wave pinning in inhomogeneous active media in the termination of atrial fibrillation by electrical cardioversion.

Science.gov (United States)

Kuklik, Pawel; Wong, Christopher X; Brooks, Anthony G; Zebrowski, Jan Jacek; Sanders, Prashanthan

2010-03-01

Atrial fibrillation is the most common type of arrhythmia to affect humans. One of the treatment modalities for atrial fibrillation is an electrical cardioversion. Electrical cardioversion can result in one of three outcomes: an immediate termination of arrhythmic activity, a delayed termination or unsuccessful termination. The mechanism of delayed termination is unknown. Here we present a model of an atrial fibrillation as a coexistence of several spiral waves pinned to the inhomogeneities in active media. We show that in inhomogeneous system delayed termination can be explained as the unpinning of a spiral wave from inhomogeneities and its termination after collision with the edge of the system. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

Investigation of Condensed Media in Weak Fields by the Method of Nuclear Magnetic Resonance

Science.gov (United States)

Davydov, V. V.; Myazin, N. S.; Dudkin, V. I.; Velichko, E. N.

2018-05-01

A compact design of a rapid-response nuclear magnetic spectrometer for investigation of condensed media in weak fields is reported. As a result of investigation of different condensed media, special features of recording a nuclear magnetic resonance (NMR) signal in a weak magnetic field from a small volume of the medium under study are established. For the first time the NMR absorption spectra of condensed media in a weak field are collected. Based on the results of experimental studies, the potential of using a compact NMR-spectrometer for condensed media monitoring in a rapid response mode is determined.

Shock waves in weakly compressed granular media.

Science.gov (United States)

van den Wildenberg, Siet; van Loo, Rogier; van Hecke, Martin

2013-11-22

We experimentally probe nonlinear wave propagation in weakly compressed granular media and observe a crossover from quasilinear sound waves at low impact to shock waves at high impact. We show that this crossover impact grows with the confining pressure P0, whereas the shock wave speed is independent of P0-two hallmarks of granular shocks predicted recently. The shocks exhibit surprising power law attenuation, which we model with a logarithmic law implying that shock dissipation is weak and qualitatively different from other granular dissipation mechanisms. We show that elastic and potential energy balance in the leading part of the shocks.

Time-averaged and time-dependent energy-related quantities of harmonic waves in inhomogeneous viscoelastic anisotropic media

Czech Academy of Sciences Publication Activity Database

Červený, V.; Pšenčík, Ivan

2007-01-01

Roč. 170, č. 3 (2007), s. 1253-1261 ISSN 0956-540X R&D Projects: GA ČR GA205/05/2182 Institutional research plan: CEZ:AV0Z30120515 Keywords : inhomogeneous media * seismic anisotropy * seismic waves Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.112, year: 2007

Radio-Wave Tomography of Inhomogeneities in Biological Media with Multi-Frequency Sounding in the Range 2-8 GHZ

Directory of Open Access Journals (Sweden)

Shipilov Sergey

2018-01-01

Full Text Available In this paper, a method for detecting and mapping inhomogeneities in biological tissues using the radio-wave tomosynthesis method is presented. The proposed method of radio-wave tomosynthesis allows us to calculate the three-dimensional distribution of the permittivity of the space under study and, thereby, to detect tissue inhomogeneities and to determine their location and size. Due to their harmlessness for humans, these methods are suitable for dynamic observation of changes in the size of formation, in contrast to x-ray methods, for which regular doses of ionizing radiation are contraindicated. Therefore, the development of non-invasive methods for the search for inhomogeneities in biological media based on radio-wave sounding, which makes it possible to identify pathological formations, is now very relevant.

Electrostatic field in inhomogeneous dielectric media. I. Indirect boundary element method

International Nuclear Information System (INIS)

Goel, N.S.; Gang, F.; Ko, Z.

1995-01-01

A computationally fast method is presented for calculating electrostatic field in arbitrary inhomogeneous dielectric media with open boundary condition. The method involves dividing the whole space into cubical cells and then finding effective dielectric parameters for interfacial cells consisting of several dielectrics. The electrostatic problem is then solved using either the indirect boundary element method described in this paper or the so-called volume element method described in the companion paper. Both methods are tested for accuracy by comparing the numerically calculated electrostatic fields against those analytically obtained for a dielectric sphere and dielectric ellipsoid in a uniform field and for a dielectric sphere in a point charge field

Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field

KAUST Repository

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

KAUST Repository

Ratushnaya, Valeria; Samtaney, Ravi

2016-01-01

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.

Non-reciprocality of waves in inhomogeneous gyrotropic media and multi layer systems with gyrotropic layers

International Nuclear Information System (INIS)

Gevorgyan, A.A.

2002-01-01

There has been considered the dispersion of electromagnetic waves in natural gyrotropic, inhomogeneous media. There has been discovered a new mechanism of waves non-reciprocality conditioned by simultaneous presence of one of the media gradients and natural gyrotropy. The non- reciprocality of waves in multilayer systems with gydrotropic layers has been investigated. It was considered a simple multilayer system glass (1)- cholesteric liquid crystal- glass(2) and demonstrated that non-reciprocality of waves in multilayer system offers good challenges for establishing simple systems with greater reciprocality. It has been shown that the multilayer systems with cholesteric liquid crystal layer can be used as optic diodes

Full-wave solution of short impulses in inhomogeneous plasma

International Nuclear Information System (INIS)

Ferencz, Orsolya E.

2005-01-01

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. 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. (author)

Penetration of an ordinary wave into a weakly inhomogeneous magnetoplasma at oblique incidence

International Nuclear Information System (INIS)

Preinhaelter, J.

1973-12-01

The propagation was studied of high-frequency electromagnetic waves in a plane-stratified weakly inhomogeneous plasma. The density gradient was assumed to be perpendicular to the external magnetic field and the wave vector was not considered to be generally parallel to the plane given by the two former vectors. The analysis shows that an ordinary wave may penetrate the plasma resonance region if the orientation of the vacuum wave vector is appropriately chosen. Analytical expressions for the reflexion and transmission coefficients were obtained and their dependence on the direction cosines of the wave vector of the incident wave was studied. It is also briefly shown that after the transmission through plasma resonance the ordinary wave was transformed into an extraordinary wave and the latter was reflected back to the region of hybrid resonance. In this region the extraordinary wave was fully transformed into the Bernstein modes. (author)

Effective wavefield extrapolation in anisotropic media: Accounting for resolvable anisotropy

KAUST Repository

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.

Effective wavefield extrapolation in anisotropic media: Accounting for resolvable anisotropy

KAUST Repository

Alkhalifah, Tariq Ali

2014-01-01

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.

Non-geometrical optics investigation of mode conversion in weakly relativistic inhomogeneous plasmas

International Nuclear Information System (INIS)

Imre, K.

1985-06-01

Electron cyclotron resonance heating of plasmas by waves incident to the fundamental and second harmonic layer is investigated. When the wave propagation is nearly perpendicular to the equilibrium field in a weakly inhomogeneous plasma the standard geometrical optics breaks down and the relativistic corrections become significant at the resonance layer. Unlike the previous studies of this problem, the governing equations are derived from the linearized relativistic Vlasov equation coupled with Maxwell's equations, rather than using the uniform field dispersion relation to construct equations by replacing the refractive index by some spatial differential operations. We employ a boundary layer analysis at the resonance region and match the inner and outer solutions in the usual manner. We obtain not only the full wave solution of the problem, but also the set of physical parameters and their ranges in which the analysis is valid. Although we obtain analytic results for the asymptotic solutions, our analysis usually requires a numerical procedure when the relativistic and/or nonzero parallel refractive index are included

Instabilities in inhomogeneous plasma

International Nuclear Information System (INIS)

Mikhailovsky, A.B.

1983-01-01

The plasma inhomogeneity across the magnetic field causes a wide class of instabilities which are called instabilities of an inhomogeneous plasma or gradient instabilities. The instabilities that can be studied in the approximation of a magnetic field with parallel straight field lines are treated first, followed by a discussion of the influence of shear on these instabilities. The instabilities of a weakly inhomogeneous plasma with the Maxwellian velocity distribution of particles caused by the density and temperature gradients are often called drift instabilities, and the corresponding types of perturbations are the drift waves. An elementary theory of drift instabilities is presented, based on the simplest equations of motion of particles in the field of low-frequency and long-wavelength perturbations. Following that is a more complete theory of inhomogeneous collisionless plasma instabilities which uses the permittivity tensor and, in the case of electrostatic perturbations, the scalar of permittivity. The results are used to study the instabilities of a strongly inhomogeneous plasma. The instabilities of a plasma in crossed fields are discussed and the electromagnetic instabilities of plasma with finite and high pressure are described. (Auth.)

Transformation instability of oscillations in inhomogeneous beam-plasma system

International Nuclear Information System (INIS)

Kitsenko, A.B.

1985-01-01

Wave transformation is studied in a plasma system which was weak-inhomogeneous along beam velocity, in absence of external magnetic field. For the case of small density beam formulae are obtained which have set a coupling between the charge density beam wave amplitudes and the Langmuir wave on both sides of transformation point. It is shown that in collisionless plasma the wave production is a cause of the absorption of the charge density beam waves. Transformation mechanism of the absolute instability in the weak-inhomogeneous beam-plasma system is revealed

Measurements of weak localization of graphene in inhomogeneous magnetic fields

DEFF Research Database (Denmark)

Lindvall, N.; Shivayogimath, Abhay; Yurgens, A.

2015-01-01

attribute this to the inhomogeneous field caused by vortices in the superconductor. The deviation, which depends on the carrier concentration in graphene, can be tuned by the gate voltage. In addition, collective vortex motion, known as vortex avalanches, is observed through magnetoresistance measurements...

Nonlinear interaction of waves in an inhomogeneous plasma

International Nuclear Information System (INIS)

Istomin, Ya.N.

1988-01-01

Nonlinear wave processes in a weakly inhomogeneous plasma are considered. A quasilinear equation is derived which takes into account the effect of the waves on resonance particles, provided that the inhomogeneity appreciably affects the nature of the resonance interaction. Three-wave interaction is investigated under the same conditions. As an example, the nonlinear interaction in a relativistic plasma moving along a strong curvilinear magnetic field is considered

Microstructural evolution in inhomogeneous elastic media

International Nuclear Information System (INIS)

Jou, H.J.; Leo, P.H.; Lowengrub, J.S.

1997-01-01

We simulate the diffusional evolution of microstructures produced by solid state diffusional transformations in elastically stressed binary alloys in two dimensions. The microstructure consists of arbitrarily shaped precipitates embedded coherently in an infinite matrix. The precipitate and matrix are taken to be elastically isotropic, although they may have different elastic constants (elastically inhomogeneous). Both far-field applied strains and mismatch strains between the phases are considered. The diffusion and elastic fields are calculated using the boundary integral method, together with a small scale preconditioner to remove ill-conditioning. The precipitate-matrix interfaces are tracked using a nonstiff time updating method. The numerical method is spectrally accurate and efficient. Simulations of a single precipitate indicate that precipitate shapes depend strongly on the mass flux into the system as well as on the elastic fields. Growing shapes (positive mass flux) are dendritic while equilibrium shapes (zero mass flux) are squarish. Simulations of multiparticle systems show complicated interactions between precipitate morphology and the overall development of microstructure (i.e., precipitate alignment, translation, merging, and coarsening). In both single and multiple particle simulations, the details of the microstructural evolution depend strongly o the elastic inhomogeneity, misfit strain, and applied fields. 57 refs., 24 figs

Nonequilibrium statistical Zubarev's operator and Green's functions for an inhomogeneous electron gas

Directory of Open Access Journals (Sweden)

P.Kostrobii

2006-01-01

Full Text Available Nonequilibrium properties of an inhomogeneous electron gas are studied using the method of the nonequilibrium statistical operator by D.N. Zubarev. Generalized transport equations for the mean values of inhomogeneous operators of the electron number density, momentum density, and total energy density for weakly and strongly nonequilibrium states are obtained. We derive a chain of equations for the Green's functions, which connects commutative time-dependent Green's functions "density-density", "momentum-momentum", "enthalpy-enthalpy" with reduced Green's functions of the generalized transport coefficients and with Green's functions for higher order memory kernels in the case of a weakly nonequilibrium spatially inhomogeneous electron gas.

A new scheme for solving inhomogeneous Boltzmann equation for electrons in weakly ionised gases

International Nuclear Information System (INIS)

Mahmoud, M.O.M.; Yousfi, M.

1995-01-01

In the case of weakly ionized gases, the numerical treatment of non-hydrodynamic regime involving spatial variation of distribution function due to boundaries (walls, electrodes, electron source, etc hor-ellipsis) by using direct Boltzmann equation always constitute a challenge if the main collisional processes occurring in non thermal plasmas are to be considered (elastic, inelastic and super-elastic collisions, Penning ionisation, Coulomb interactions, etc hor-ellipsis). In the non-thermal discharge modelling, the inhomogeneous electron Boltzmann equation is needed in order to be coupled for example to a fluid model to take into account the electron non-hydrodynamic effects. This is for example the case of filamentary discharge, in which the space charge electric field due to streamer propagation has a very sharp spatial profile thus leading to important space non-hydrodynamic effects. It is also the case of the cathodic zone of glow discharge where electric field has a rapid spatial decrease until the negative glow. In the present work, a new numerical scheme is proposed to solve the inhomogeneous Boltzmann equation for electrons in the framework of two-term approximation (TTA) taking into account elastic and inelastic processes. Such a method has the usual drawbacks associated with the TTA i.e. not an accurate enough at high E/N values or in presence of high inelastic processes. But the accuracy of this method is considered sufficient because in a next step it is destinated to be coupled to fluid model for charged particles and a chemical kinetic model where the accuracy is of the same order of magnitude or worse. However there are numerous advantages of this method concerning time computing, treatment of non-linear collision processes (Coulomb, Penning, etc hor-ellipsis)

Hamiltonian approach to the derivation of evolution equations for wave trains in weakly unstable media

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.

Inhomogeneous Pre-Big Bang String Cosmology

OpenAIRE

Veneziano, Gabriele

1997-01-01

An inhomogeneous version of pre--Big Bang cosmology emerges, within string theory, from quite generic initial conditions, provided they lie deeply inside the weak-coupling, low-curvature regime. Large-scale homogeneity, flatness, and isotropy appear naturally as late-time outcomes of such an evolution.

Strong mobility in weakly disordered systems

Energy Technology Data Exchange (ETDEWEB)

Ben-naim, Eli [Los Alamos National Laboratory; Krapivsky, Pavel [BOSTON UNIV

2009-01-01

We study transport of interacting particles in weakly disordered media. Our one-dimensional system includes (i) disorder, the hopping rate governing the movement of a particle between two neighboring lattice sites is inhomogeneous, and (ii) hard core interaction, the maximum occupancy at each site is one particle. We find that over a substantial regime, the root-mean-square displacement of a particle s grows superdiffusively with time t, {sigma}{approx}({epsilon}t){sup 2/3}, where {epsilon} is the disorder strength. Without disorder the particle displacement is subdiffusive, {sigma} {approx}t{sup 1/4}, and therefore disorder strongly enhances particle mobility. We explain this effect using scaling arguments, and verify the theoretical predictions through numerical simulations. Also, the simulations show that regardless of disorder strength, disorder leads to stronger mobility over an intermediate time regime.

Weak bases and formation of a less soluble lauryl sulfate salt/complex in sodium lauryl sulfate (SLS) containing media.

Science.gov (United States)

Bhattachar, Shobha N; Risley, Donald S; Werawatganone, Pornpen; Aburub, Aktham

2011-06-30

This work reports on the solubility of two weakly basic model compounds in media containing sodium lauryl sulfate (SLS). Results clearly show that the presence of SLS in the media (e.g. simulated gastric fluid or dissolution media) can result in an underestimation of solubility of some weak bases. We systematically study this phenomenon and provide evidence (chromatography and pXRD) for the first time that the decrease in solubility is likely due to formation of a less soluble salt/complex between the protonated form of the weak base and lauryl sulfate anion. Copyright © 2011 Elsevier B.V. All rights reserved.

Dissipative Vortex Solitons in Defocusing Media with Spatially Inhomogeneous Nonlinear Absorption

Science.gov (United States)

Lai, Xian-Jing; Cai, Xiao-Ou; Zhang, Jie-Fang

2018-02-01

In this paper, by solving a complex nonlinear Schrödinger equation, radially symmetric dissipative vortex solitons are obtained analytically and are tested numerically. We find that spatially inhomogeneous nonlinear absorption gives rise to the stability of dissipative vortex solitons in self-defocusing nonlinear medium in the presence of constant linear gain. Numerical simulation reveals the interaction effect among linear gain and nonlinear loss in the azimuthal modulation instabilities of these vortices suppression. Apart from the uniform linear gain indeed affects the stability of vortex in this media, another noticeable feature of current setup is that the steep spatial modulation of the nonlinear absorption can suppress sidelobes effectively and support stable vortex solitons in situations with uniform linear gain. Under appropriate conditions, the vortex solitons can propagate stably and feature no symmetry breaking, although the beams exhibit radical compression and amplification as they propagate. Supported by the National Natural Science Foundation of China under Grant No. 11705164 and the Zhejiang Provincial Natural Science Foundation of China under Grant No. LQ16A040003

'Perfectly disordered' medium as a model for the description of micro-inhomogeneous mixtures

International Nuclear Information System (INIS)

Levin, V M; Markov, M G; Alvarez-Tostado, J M

2004-01-01

The correct description of the macroscopic (overall) physical properties of micro-inhomogeneous (composite) materials by micro-mechanics methods (the self-consistent schemes, for example) requires information about the microstructure and texture of such materials. Often, such information (of shapes inhomogeneities and peculiarities of their spatial distribution) is not available. In this paper, we suggest a method of calculation of the characteristics of micro-inhomogeneous materials that could be applied to a wide class of isotropic materials. This method assumes the absence of a closed order in the material microstructure (a 'perfectly disordered' (PD) medium). We used the PD approximation to predict the effective thermo- and poroelastic, electric and thermal properties of micro-inhomogeneous media. The expressions for the effective characteristics obtained by this method are always inside of the Hashin-Shtrikman universal bounds. For a two-phase material with fluid component, the effective bulk module satisfies Gassmann's relation for fluid-filled porous media and generalizes such a relation to inhomogeneous thermoelastic and poroelastic media. A comparison of the theoretical results with available experimental data shows a satisfactory coincidence even in the case of high contrast of the component properties. The simplicity of the numerical realization of the method makes it attractive for applications in the absence of detailed information about the material's microstructure

A neutron depolarization study of magnetic inhomogeneities in weak-link superconductors. Issledovanie magnitnykh neodnorodnostej v sverkhprovodnikakh so slabymi svyazyami metodom depolyarizatsii nejtronov

Energy Technology Data Exchange (ETDEWEB)

Zhuchenko, N K; Yagud, R Z [AN SSSR, Leningrad (Russian Federation). Inst. Yadernoj Fiziki

1993-09-01

Neutron depolarization measurements in the mixed state of both high-T[sub c] and low-T[sub c] weak-link superconductors have been carried out. Samples of YBCO, BSCCO, SnMo[sub 6]S[sub 8] and 0.5 Nb-0.5 Ti of different magnetic prehistory were analyzed at temperatures T 4.2 K under applied magnetic fields II <= 16.5 kOe. We ascribe the appearance of magnetic inhomogeneities and their hysteresis behaviour to the interaction between dipole magnetic fields (diamagnetic and paramagnetic ones) and applied magnetic fields.

Nonlinear acoustic waves in micro-inhomogeneous solids

CERN Document Server

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

Quantum entanglement in inhomogeneous 1D systems

Science.gov (United States)

Ramírez, Giovanni

2018-04-01

The entanglement entropy of the ground state of a quantum lattice model with local interactions usually satisfies an area law. However, in 1D systems some violations may appear in inhomogeneous systems or in random systems. In our inhomogeneous system, the inhomogeneity parameter, h, allows us to tune different regimes where a volumetric violation of the area law appears. We apply the strong disorder renormalization group to describe the maximally entangled state of the system in a strong inhomogeneity regime. Moreover, in a weak inhomogeneity regime, we use a continuum approximation to describe the state as a thermo-field double in a conformal field theory with an effective temperature which is proportional to the inhomogeneity parameter of the system. The latter description also shows that the universal scaling features of this model are captured by a massless Dirac fermion in a curved space-time with constant negative curvature R = h2, providing another example of the relation between quantum entanglement and space-time geometry. The results we discuss here were already published before, but here we present a more didactic exposure of basic concepts of the rainbow system for the students attending the Latin American School of Physics "Marcos Moshinsky" 2017.

Restoration of longitudinal laser tomography target image from inhomogeneous medium degradation under common conditions.

Science.gov (United States)

Yi, WenJun; Wang, Ping; Fu, MeiCheng; Tan, JiChun; Zhu, Jubo; Li, XiuJian

2017-07-10

In order to overcome the shortages of the target image restoration method for longitudinal laser tomography using self-calibration, a more general restoration method through backscattering medium images associated with prior parameters is developed for common conditions. The system parameters are extracted from pre-calibration, and the LIDAR ratio is estimated according to the medium types. Assisted by these prior parameters, the degradation caused by inhomogeneous turbid media can be established with the backscattering medium images, which can further be used for removal of the interferences of turbid media. The results of simulations and experiments demonstrate that the proposed image restoration method can effectively eliminate the inhomogeneous interferences of turbid media and achieve exactly the reflectivity distribution of targets behind inhomogeneous turbid media. Furthermore, the restoration method can work beyond the limitation of the previous method that only works well under the conditions of localized turbid attenuations and some types of targets with fairly uniform reflectivity distributions.

The Quasi-Static Electromagnetic Approximation for Weakly Conducting Media

CERN Document Server

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.

Solitons of an envelope in an inhomogeneous medium

International Nuclear Information System (INIS)

Churilov, S.M.

1982-01-01

Solutions of the Schroedinger nonlinear equation (SNE) used for the description of evolution of a wave packet envelope has been investigated in inhomogeneous and nonstationary media. It is shown that the SNE solution possessing two important properties exists. Firstly, the wave packet remains localized when propagating in an inhomogeneous medium. Secondly, the soliton width and amplitude are determined only with local characteristics of medium and don't depend on the prehistory. Problem of limits of obtained result applicability has been considered

Examples of backreaction of small-scale inhomogeneities in cosmology

Science.gov (United States)

Green, Stephen R.; Wald, Robert M.

2013-06-01

In previous work, we introduced a new framework to treat large-scale backreaction effects due to small-scale inhomogeneities in general relativity. We considered one-parameter families of spacetimes for which such backreaction effects can occur, and we proved that, provided the weak energy condition on matter is satisfied, the leading effect of small-scale inhomogeneities on large-scale dynamics is to produce a traceless effective stress-energy tensor that itself satisfies the weak energy condition. In this work, we illustrate the nature of our framework by providing two explicit examples of one-parameter families with backreaction. The first, based on previous work of Berger, is a family of polarized vacuum Gowdy spacetimes on a torus, which satisfies all of the assumptions of our framework. As the parameter approaches its limiting value, the metric uniformly approaches a smooth background metric, but spacetime derivatives of the deviation of the metric from the background metric do not converge uniformly to zero. The limiting metric has nontrivial backreaction from the small-scale inhomogeneities, with an effective stress energy that is traceless and satisfies the weak energy condition, in accord with our theorems. Our second one-parameter family consists of metrics which have a uniform Friedmann-Lemaître-Robertson-Walker limit. This family satisfies all of our assumptions with the exception of the weak energy condition for matter. In this case, the limiting metric has an effective stress-energy tensor which is not traceless. We emphasize the importance of imposing energy conditions on matter in studies of backreaction.

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. ...... 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.......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...

No hair theorem for inhomogeneous cosmologies

International Nuclear Information System (INIS)

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

Noninvasive detection of inhomogeneities in turbid media with time-resolved log-slope analysis

International Nuclear Information System (INIS)

Wan, S.K.; Guo Zhixiong; Kumar, Sunil; Aber, Janice; Garetz, B.A.

2004-01-01

Detecting foreign objects embedded in turbid media using noninvasive optical tomography techniques is of great importance in many practical applications, such as in biomedical imaging and diagnosis, safety inspection on aircrafts and submarines, and LIDAR techniques. In this paper we develop a novel optical tomography approach based on slope analysis of time-resolved back-scattered signals collected at the medium boundaries where the light source is an ultrafast, short-pulse laser. As the optical field induced by the laser-pulse propagates, the detected temporal signals are influenced by the optical properties of the medium traversed. The detected temporal signatures therefore contain information that can indicate the presence of an inhomogeneity as well as its size and location relative to the laser source and detection systems. The log-slope analysis of the time-resolved back-scattered intensity is shown to be an effective method for extracting the information contained in the signal. The technique is validated by experimental results and by Monte Carlo simulations

Effective photons in weakly absorptive dielectric media and the Beer–Lambert–Bouguer law

International Nuclear Information System (INIS)

Judge, A C; Brownless, J S; Martijn de Sterke, C; Bhat, N A R; Sipe, J E; Steel, M J

2014-01-01

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 a mode field distribution that includes the effects of both material and structural dispersion, and an effective line-width that 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

NONLINEAR EVOLUTION OF BEAM-PLASMA INSTABILITY IN INHOMOGENEOUS MEDIUM

International Nuclear Information System (INIS)

Ziebell, L. F.; Pavan, J.; Yoon, P. H.; Gaelzer, R.

2011-01-01

The problem of electron-beam propagation in inhomogeneous solar wind is intimately related to the solar type II and/or type III radio bursts. Many scientists have addressed this issue in the past by means of quasi-linear theory, but in order to fully characterize the nonlinear dynamics, one must employ weak-turbulence theory. Available numerical solutions of the weak-turbulence theory either rely on only one nonlinear process (either decay or scattering), or when both nonlinear terms are included, the inhomogeneity effect is generally ignored. The present paper reports the full solution of weak-turbulence theory that includes both decay and scattering processes, and also incorporating the effects of density gradient. It is found that the quasi-linear effect sufficiently accounts for the primary Langmuir waves, but to properly characterize the back-scattered Langmuir wave, which is important for eventual radiation generation, it is found that both nonlinear decay and scattering processes make comparable contributions. Such a finding may be important in the quantitative analysis of the plasma emission process with application to solar type II and/or type III radio bursts.

The Prediction of Wave Competitions in Inhomogeneous Brusselator Systems

International Nuclear Information System (INIS)

Cui Xiao-Hua; Dong Yun-Xia; Huang Xiao-Qing; Li Ning

2015-01-01

The competition of waves has remained a hot topic in physics over the past few decades, especially the area of pattern control. Because of improved understanding of various dynamic behaviors, many practical applications have sprung up recently. The prediction of wave competitions is also very important and quite useful in these fields. This paper considers the behaviors of wave competitions in simple, inhomogeneous media which is modeled by Brusselator equations. We present a simple rule to judge the results of wave competitions utilizing the dispersion relation curves and the waves coming from different wave sources. Moreover, this rule can also be used to predict the results of wave propagation. It provides methods of obtaining the desired waves with given frequencies in inhomogeneous media. All our results are concluded and verified by computer simulations. (paper)

Weak universality in inhomogeneous Ising quantum chains

International Nuclear Information System (INIS)

Karevski, Dragi

2006-01-01

The Ising quantum chain with arbitrary coupling distribution {λ i } leading to an anisotropic scaling is considered. The smallest gap of the chain is connected to the surface magnetization by the relation Λ 1 = m s ({λ i })m s ({λ -1 i }). For some aperiodic distribution {λ i }, a weak universality of the critical behaviour is found. (letter to the editor)

Diazotisation of Weakly Basic Aromatic and Heterocyclic Amines in Strongly Acid Media

Science.gov (United States)

Godovikova, Tamara I.; Rakitin, Oleg A.; Khmel'nitskii, Lenor I.

1983-05-01

The review is devoted to the diazotisation of weakly basic aromatic amines. The methods of synthesis of diazonium salts based on these amines by non-traditional methods are examined. Data on the mechanism of the diazotisation reaction in strongly acid media are surveyed. Reactions of diazonium salts leading to the synthesis of new compounds are presented. The bibliography includes 75 references.

Scattering of electromagnetic wave by the layer with one-dimensional random inhomogeneities

Science.gov (United States)

Kogan, Lev; Zaboronkova, Tatiana; Grigoriev, Gennadii., IV.

oscillating function versus the average fluctuations length if the standard of fluctuations of inhomogeneities length is greater then the wave length. When the standard of fluctuations of medium inhomogeneities extension is smaller then the wave length, the av-erage intensity value weakly depends from the average fluctuations extension. The obtained results may be used for analysis of the electromagnetic wave propagation into the media with the fluctuating parameters caused by such factors as leafs of trees, cumulus, internal gravity waves with a chaotic phase and etc. Acknowledgment: This work was supported by the Russian Foundation for Basic Research (projects 08-02-97026 and 09-05-00450).

Unified formulation for inhomogeneity-driven instabilities in the lower-hybrid range

International Nuclear Information System (INIS)

Silveira, O.J.G.; Ziebell, L.F.; Gaelzer, R.; Yoon, Peter H.

2002-01-01

A local dispersion relation that describes inhomogeneity-driven instabilities in the lower-hybrid range is derived following a procedure that correctly describes energy exchange between waves and particles in inhomogeneous media, correcting some inherent ambiguities associated with the standard formalism found in the literature. Numerical solutions of this improved dispersion relation show that it constitutes a unified formulation for the instabilities in the lower-hybrid range, describing the so-called modified two-stream instability, excited by the ion cross-field drift, including the ion Weibel instability, and also describing the lower-hybrid drift instability, which is due to inhomogeneity effects on the electron population

Scattering and emission from inhomogeneous vegetation canopy and alien target beneath by using three-dimensional vector radiative transfer (3D-VRT) equation

International Nuclear Information System (INIS)

Jin Yaqiu; Liang Zichang

2005-01-01

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

Large linear magnetoresistivity in strongly inhomogeneous planar and layered systems

International Nuclear Information System (INIS)

Bulgadaev, S.A.; Kusmartsev, F.V.

2005-01-01

Explicit expressions for magnetoresistance R of planar and layered strongly inhomogeneous two-phase systems are obtained, using exact dual transformation, connecting effective conductivities of in-plane isotropic two-phase systems with and without magnetic field. These expressions allow to describe the magnetoresistance of various inhomogeneous media at arbitrary concentrations x and magnetic fields H. All expressions show large linear magnetoresistance effect with different dependencies on the phase concentrations. The corresponding plots of the x- and H-dependencies of R(x,H) are represented for various values, respectively, of magnetic field and concentrations at some values of inhomogeneity parameter. The obtained results show a remarkable similarity with the existing experimental data on linear magnetoresistance in silver chalcogenides Ag 2+δ Se. A possible physical explanation of this similarity is proposed. It is shown that the random, stripe type, structures of inhomogeneities are the most suitable for a fabrication of magnetic sensors and a storage of information at room temperatures

Multi-Parameter Estimation for Orthorhombic Media

KAUST Repository

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.

Multi-Parameter Estimation for Orthorhombic Media

KAUST Repository

Masmoudi, Nabil; Alkhalifah, Tariq Ali

2015-01-01

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.

Multi-parameters scanning in HTI media

KAUST Repository

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.

Multi-parameters scanning in HTI media

KAUST Repository

Masmoudi, Nabil; Alkhalifah, Tariq Ali

2014-01-01

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.

A study of the dosimetry of small field photon beams used in intensity modulated radiation therapy in inhomogeneous media: Monte Carlo simulations, and algorithm comparisons and corrections

International Nuclear Information System (INIS)

Jones, Andrew Osler

2004-01-01

There is an increasing interest in the use of inhomogeneity corrections for lung, air, and bone in radiotherapy treatment planning. Traditionally, corrections based on physical density have been used. Modern algorithms use the electron density derived from CT images. Small fields are used in both conformal radiotherapy and IMRT, however, their beam characteristics in inhomogeneous media have not been extensively studied. This work compares traditional and modern treatment planning algorithms to Monte Carlo simulations in and near low-density inhomogeneities. Field sizes ranging from 0.5 cm to 5 cm in diameter are projected onto a phantom containing inhomogeneities and depth dose curves are compared. Comparisons of the Dose Perturbation Factors (DPF) are presented as functions of density and field size. Dose Correction Factors (DCF), which scale the algorithms to the Monte Carlo data, are compared for each algorithm. Physical scaling algorithms such as Batho and Equivalent Pathlength (EPL) predict an increase in dose for small fields passing through lung tissue, where Monte Carlo simulations show a sharp dose drop. The physical model-based collapsed cone convolution (CCC) algorithm correctly predicts the dose drop, but does not accurately predict the magnitude. Because the model-based algorithms do not correctly account for the change in backscatter, the dose drop predicted by CCC occurs farther downstream compared to that predicted by the Monte Carlo simulations. Beyond the tissue inhomogeneity all of the algorithms studied predict dose distributions in close agreement with Monte Carlo simulations. Dose-volume relationships are important in understanding the effects of radiation to the lung. The dose within the lung is affected by a complex function of beam energy, lung tissue density, and field size. Dose algorithms vary in their abilities to correctly predict the dose to the lung tissue. A thorough analysis of the effects of density, and field size on dose to the

Inhomogeneous ensembles of radical pairs in chemical compasses

Science.gov (United States)

Procopio, Maria; Ritz, Thorsten

2016-11-01

The biophysical basis for the ability of animals to detect the geomagnetic field and to use it for finding directions remains a mystery of sensory biology. One much debated hypothesis suggests that an ensemble of specialized light-induced radical pair reactions can provide the primary signal for a magnetic compass sensor. The question arises what features of such a radical pair ensemble could be optimized by evolution so as to improve the detection of the direction of weak magnetic fields. Here, we focus on the overlooked aspect of the noise arising from inhomogeneity of copies of biomolecules in a realistic biological environment. Such inhomogeneity leads to variations of the radical pair parameters, thereby deteriorating the signal arising from an ensemble and providing a source of noise. We investigate the effect of variations in hyperfine interactions between different copies of simple radical pairs on the directional response of a compass system. We find that the choice of radical pair parameters greatly influences how strongly the directional response of an ensemble is affected by inhomogeneity.

Modulated magnetic structure of an inhomogeneous stressed single crystal FeBO3

International Nuclear Information System (INIS)

Sharipiv, M.Z.; Dzhuraev, D.R.; Sokolov, B.Yu.; Kurbanov, M.

2010-01-01

With the help of low-symmetry mechanical stresses, we induced an additional spatially inhomogeneous anisotropy in the basal plane of a single crystal FeBO 3 . By the magnetooptical method, we study the effect of an inhomogeneous magnetic anisotropy on the magnetic state of this easy-plane weak ferromagnetic. It is established that, at the magnetization of inhomogeneously stressed FeBO 3 in the basal plane near some separated direction, the crystal transits from the homogeneous state into a spatially modulated magnetic state. The latter can be represented in the form of a static spin wave, in which a local vector of ferromagnetism oscillates near the direction of the mean magnetization of a crystal, by remaining in the basal plane.

Non collinear magnetic phase of the inhomogeneously stressed FeBO3 monocrystals

International Nuclear Information System (INIS)

Sharipov, M.Z.

2011-01-01

With the help of low-symmetry mechanical stresses, an additional spatially inhomogeneous anisotropy in the basal plane of a single crystal FeBO 3 has been induced. By the magnetooptical method, an effect of the inhomogeneous magnetic anisotropy on the magnetic state of this easy-plane weak ferromagnetic has been investigated. It is established that at the magnetization of inhomogeneously stressed FeBO 3 in the basal plane near the separated direction, the crystal turns from the homogeneous state into a spatially modulated magnetic state. The latter can be represented in the form of a static spin wave, in which a local vector of ferromagnetism oscillates near the direction of the mean magnetization of a crystal, remaining in the basal plane. (authors)

Laser dynamics in transversely inhomogeneous plasma and its relevance to wakefield acceleration

Science.gov (United States)

Pathak, V. B.; Vieira, J.; Silva, L. O.; Nam, Chang Hee

2018-05-01

We present full set of coupled equations describing the weakly relativistic dynamics of a laser in a plasma with transverse inhomogeneity. We apply variational principle approach to obtain these coupled equations governing laser spot-size, transverse wavenumber, curvature, transverse centroid, etc. We observe that such plasma inhomogeneity can lead to stronger self-focusing. We further discuss the guiding conditions of laser in parabolic plasma channels. With the help of multi-dimensional particle in cell simulations the study is extended to the blowout regime of laser wakefield acceleration to show laser as well as self-injected electron bunch steering in plasma to generate unconventional particle trajectories. Our simulation results demonstrate that such transverse inhomogeneities due to asymmetric self focusing lead to asymmetric bubble excitation, thus inducing off-axis self-injection.

Discretization-dependent model for weakly connected excitable media

Science.gov (United States)

Arroyo, Pedro André; Alonso, Sergio; Weber dos Santos, Rodrigo

2018-03-01

Pattern formation has been widely observed in extended chemical and biological processes. Although the biochemical systems are highly heterogeneous, homogenized continuum approaches formed by partial differential equations have been employed frequently. Such approaches are usually justified by the difference of scales between the heterogeneities and the characteristic spatial size of the patterns. Under different conditions, for example, under weak coupling, discrete models are more adequate. However, discrete models may be less manageable, for instance, in terms of numerical implementation and mesh generation, than the associated continuum models. Here we study a model to approach discreteness which permits the computer implementation on general unstructured meshes. The model is cast as a partial differential equation but with a parameter that depends not only on heterogeneities sizes, as in the case of quasicontinuum models, but also on the discretization mesh. Therefore, we refer to it as a discretization-dependent model. We validate the approach in a generic excitable media that simulates three different phenomena: the propagation of action membrane potential in cardiac tissue, in myelinated axons of neurons, and concentration waves in chemical microemulsions.

Intermittency for stochastic partial differential equations driven by strongly inhomogeneous space-time white noises

Science.gov (United States)

Xie, Bin

2018-01-01

In this paper, the main topic is to investigate the intermittent property of the one-dimensional stochastic heat equation driven by an inhomogeneous Brownian sheet, which is a noise deduced from the study of the catalytic super-Brownian motion. Under some proper conditions on the catalytic measure of the inhomogeneous Brownian sheet, we show that the solution is weakly full intermittent based on the estimates of moments of the solution. In particular, it is proved that the second moment of the solution grows at the exponential rate. The novelty is that the catalytic measure relative to the inhomogeneous noise is not required to be absolutely continuous with respect to the Lebesgue measure on R.

A new mathematical formulation of the line-by-line method in case of weak line overlapping

Science.gov (United States)

Ishov, Alexander G.; Krymova, Natalie V.

1994-01-01

A rigorous mathematical proof is presented for multiline representation on the equivalent width of a molecular band which consists in the general case of n overlapping spectral lines. The multiline representation includes a principal term and terms of minor significance. The principal term is the equivalent width of the molecular band consisting of the same n nonoverlapping spectral lines. The terms of minor significance take into consideration the overlapping of two, three and more spectral lines. They are small in case of the weak overlapping of spectral lines in the molecular band. The multiline representation can be easily generalized for optically inhomogeneous gas media and holds true for combinations of molecular bands. If the band lines overlap weakly the standard formulation of line-by-line method becomes too labor-consuming. In this case the multiline representation permits line-by-line calculations to be performed more effectively. Other useful properties of the multiline representation are pointed out.

Effect of Inhomogeneity on s-wave Superconductivity in the Attractive Hubbard Model

Energy Technology Data Exchange (ETDEWEB)

Aryanpour, K. A. [University of California, Davis; Dagotto, Elbio R [ORNL; Mayr, Matthias [Max-Planck-Institut fur Feskorperforschung, Stuttgart, Germany; Paiva, T. [Universidade Federal do Rio de Janeiro, Brazil; Pickett, W. E. [University of California, Davis; Scalettar, Richard T [ORNL

2006-01-01

Inhomogeneous s-wave superconductivity is studied in the two-dimensional, square lattice attractive Hubbard Hamiltonian using the Bogoliubov-de Gennes BdG mean field approximation. We find that at weak coupling, and for densities mainly below half-filling, an inhomogeneous interaction in which the on-site interaction Ui takes on two values, Ui=0, 2U results in a larger zero temperature pairing amplitude, and that the superconducting Tc can also be significantly increased, relative to a uniform system with Ui=U on all sites. These effects are observed for stripe, checkerboard, and even random patterns of the attractive centers, suggesting that the pattern of inhomogeneity is unimportant. Monte Carlo calculations which reintroduce some of the fluctuations neglected within the BdG approach see the same effect, both for the attractive Hubbard model and a Hamiltonian with d-wave pairing symmetry.

Inhomogeneous anisotropic cosmology

International Nuclear Information System (INIS)

Kleban, Matthew; Senatore, Leonardo

2016-01-01

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.

High Frequency Asymptotic Methods for Traveltimes and Anisotropy Parameter Estimation in Azimuthally Varying Media

KAUST Repository

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

Nonspecular reflection of light at an inhomogeneous interface between two media and in a nanostructured layer with a quasi-zero refractive index

International Nuclear Information System (INIS)

Gadomsky, O. N.; Gadomskaya, I. V.

2015-01-01

We have derived formulas for the amplitudes of light reflection and refraction at an inhomogeneous interface between two media and in a nanostructured layer with a quasi-zero refractive index. These formulas are applied to explain the experimental spectra of nonspecular light reflection using a nanostructured (PMMA + Ag) layer with silver nanoparticles on a silicon surface as an example. We show that a surface wave is formed in the nanostructured layer at various angles of light incidence and the layer with a quasi-zero refractive index is an antireflection coating that provides uniform 5% silicon antireflection in the wavelength range from 450 to 1000 nm

Fractal behaviour of flow of an inhomogeneous fluid over a smooth inclined surface

International Nuclear Information System (INIS)

Rouhani, S.; Maleki Jirsarani, N.; Ghane Motlagh, B.; Baradaran, S.; Shokrian, E.

2001-01-01

We have observed and analyzed fractal patterns made by the flow of an inhomogeneous fluid (a suspension) over an inclined smooth surface. We observed that if the angle of inclination is above a threshold (10 d eg C - 12 d eg C), the length of fractal clusters become infinity. We measured a fractal dimension of df=1.40 ± 0.05. This falls within the same general class of patterns of flow of water over an inhomogeneous surface. This observation is consistent with the results of theoretical modes for nonlinear fluid flow in random media

A steady weak solution of the equations of motion of a viscous incompressible fluid through porous media in a domain with a non-compact boundary

Czech Academy of Sciences Publication Activity Database

Akyildiz, F.T.; Neustupa, Jiří; Siginer, D.

2012-01-01

Roč. 119, č. 1 (2012), s. 23-42 ISSN 0167-8019 R&D Projects: GA AV ČR IAA100190905 Institutional research plan: CEZ:AV0Z10190503 Keywords : flows in porous media * steady-state problems * inhomogeneous boundary data Subject RIV: BA - General Mathematics Impact factor: 0.985, year: 2012 http://www.springerlink.com/content/t8n71p67w2282t96/

The propagation property of ion-acoustic soliton in an inhomogeneous plasma

International Nuclear Information System (INIS)

Zhu Jiazhen; Wang Gengguo.

1990-01-01

The propagation property of ion-acoustic soliton in a weakly inhomogeneous plamsa caused by ionization is studied. Finite ion temperature and ion-neutral collisions are considered the self consistent stationary distribution N(x), v(x) and the corresponding soliton solution are obtained, numerical results of soliton amplitude, speed and width dependent on position are given, which are reasonable and consistent with experiments

Correlation characteristics of optical coherence tomography images of turbid media with statistically inhomogeneous optical parameters

International Nuclear Information System (INIS)

Dolin, Lev S.; Sergeeva, Ekaterina A.; Turchin, Ilya V.

2012-01-01

Noisy structure of optical coherence tomography (OCT) images of turbid medium contains information about spatial variations of its optical parameters. We propose analytical model of statistical characteristics of OCT signal fluctuations from turbid medium with spatially inhomogeneous coefficients of absorption and backscattering. Analytically predicted correlation characteristics of OCT signal from spatially inhomogeneous medium are in good agreement with the results of correlation analysis of OCT images of different biological tissues. The proposed model can be efficiently applied for quantitative evaluation of statistical properties of absorption and backscattering fluctuations basing on correlation characteristics of OCT images.

Phase function of a spherical particle when scattering an inhomogeneous electromagnetic plane wave

DEFF Research Database (Denmark)

Frisvad, Jeppe Revall

2018-01-01

of the complex hypergeometric function 2F1 for every term of a series expansion. In this work, I develop a simpler solution based on associated Legendre functions with argument zero. It is similar to the solution for homogeneous plane waves but with new explicit expressions for the angular dependency of the far......In absorbing media, electromagnetic plane waves are most often inhomogeneous. Existing solutions for the scattering of an inhomogeneous plane wave by a spherical particle provide no explicit expressions for the scattering components. In addition, current analytical solutions require evaluation......-field scattering components, that is, the phase function. I include recurrence formulae for practical evaluation and provide numerical examples to evaluate how well the new expressions match previous work in some limiting cases. The predicted difference in the scattering phase function due to inhomogeneity...

Nonlinear and diffraction effects in propagation of N-waves in randomly inhomogeneous moving media.

Science.gov (United States)

Averiyanov, Mikhail; Blanc-Benon, Philippe; Cleveland, Robin O; Khokhlova, Vera

2011-04-01

Finite amplitude acoustic wave propagation through atmospheric turbulence is modeled using a Khokhlov-Zabolotskaya-Kuznetsov (KZK)-type equation. The equation accounts for the combined effects of nonlinearity, diffraction, absorption, and vectorial inhomogeneities of the medium. A numerical algorithm is developed which uses a shock capturing scheme to reduce the number of temporal grid points. The inhomogeneous medium is modeled using random Fourier modes technique. Propagation of N-waves through the medium produces regions of focusing and defocusing that is consistent with geometrical ray theory. However, differences up to ten wavelengths are observed in the locations of fist foci. Nonlinear effects are shown to enhance local focusing, increase the maximum peak pressure (up to 60%), and decrease the shock rise time (about 30 times). Although the peak pressure increases and the rise time decreases in focal regions, statistical analysis across the entire wavefront at a distance 120 wavelengths from the source indicates that turbulence: decreases the mean time-of-flight by 15% of a pulse duration, decreases the mean peak pressure by 6%, and increases the mean rise time by almost 100%. The peak pressure and the arrival time are primarily governed by large scale inhomogeneities, while the rise time is also sensitive to small scales.

Radiance intensity enhanced by thin inhomogeneous lossy films

International Nuclear Information System (INIS)

Ben-Abdallah, Philippe; Ni Bo

2004-01-01

Basically, the classical radiative transfer theory assumes that the coherent component of the radiation field is equal to zero and heuristic considerations about energy conservation are used in the phenomenological derivation of the RTE. Here a self-consistent theory is presented to investigate radiative transport in the presence of diffraction processes within thin inhomogeneous films. The problem of linear optics about the transport of scalar radiation within film is solved, a new definition of the radiance is introduced in agreement with earlier definitions and a corresponding radiative transfer equation is derived. The influence of spatial variations of the bulk properties on the propagating mode is described in detail. It is analytically predicted that, unlike homogeneous media, an inhomogeneous film can enhance the radiance intensity in spite of the diffraction and the local extinction. From a practical point of view, the results of this work should be useful to perform the optimal design for many thermoelectric devices such as the new generations of photovoltaiec cells

Physical model of optical inhomogeneities of water

Science.gov (United States)

Shybanov, E. B.

2017-11-01

The paper is devoted to theoretical aspects of the light scattering of water that does not contain suspended particles. To be consistent with current physical point of view the water as far as any liquid is regarded as a complex unstable nonergodic media. It was proposed that at fixed time the water as a condensed medium had global inhomogeneities similar to linear and planar defects in a solid. Anticipated own global inhomogeneities of water have been approximated by the system randomly distributed spherical clusters filling the entire water bulk. An analytical expression for the single scattered light has been derived. The formula simultaneously describes both the high anisotropy of light scattering and the high degree of polarization which one close to those for molecular scattering. It is shown that at general angles there is a qualitative coincidence with the two-component Kopelevich's model for the light scattering by marine particles. On the contrary towards to forwards angles the spectral law becomes much more prominent i.e. it corresponds to results for model of optically soft particles.

Fluctuations and transport in an inhomogeneous plasma

International Nuclear Information System (INIS)

Nevins, W.M.; Chen, L.

1979-11-01

A formalism is developed for calculating the equilibrium fluctuation level in an inhomogeneous plasma. This formalism is applied to the collisionless drift wave in a sheared magnetic field. The fluctuation level is found to be anomalously large due to both the presence of weakly damped normal modes and convective amplification. As the magnetic shear is reduced, the steady-state fluctuation spectrum is found to increase both in coherence and in amplitude. The transport associated with this mode is evaluated. The diffusion coefficient is found to scale as D is proportional to B 2 /nT/sup 1/2/

A Systematic Approach to Higher-Order Parabolic Propagation in a Weakly Range-Dependent Duct

National Research Council Canada - National Science Library

Gragg, Robert F

2005-01-01

Energy-conserving transformations are exploited to split a monochromatic field in a weakly inhomogeneous waveguide into a pair of components that undergo uncoupled parabolic propagation in opposite...

Influence of welded boundaries in anelastic media on energy flow, and characteristics of P, S-I, and S-II waves: Observational evidence for inhomogeneous body waves in low-loss solids

Science.gov (United States)

Borcherdt, Roger D.; Glassmoyer, Gary; Wennerberg, Leif

1986-10-01

A general computer code, developed to calculate anelastic reflection-refraction coefficients, energy flow, and the physical characteristics for general P, S-I, and S-II waves, quantitatively describes physical characteristics for wave fields in anelastic media that do not exist in elastic media. Consideration of wave fields incident on boundaries between anelastic media shows that scattered wave fields experience reductions in phase and energy speeds, increases in maximum attenuation and Q-1, and directions of maximum energy flow distinct from phase propagation. Each of these changes in physical characteristics are shown to vary with angle of incidence. Finite relaxation times for anelastic media result in energy flow due to interaction of superimposed radiation fields and contribute to energy flow across anelastic boundaries for all angles of incidence. Agreement of theoretical and numerical results with laboratory measurements argues for the validity of the theoretical and numerical formulations incorporating inhomogeneous wave fields. The agreement attests to the applicability of the model and helps confirm the existence of inhomogeneous body waves and their associated set of distinct physical characteristics in the earth. The existence of such body waves in layered, low-loss anelastic solids implies the need to reformulate some seismological models of the earth. The exact anelastic formulation for a liquid-solid interface with no low-loss approximations predicts the existence of a range of angles of incidence or an anelastic Rayleigh window, through which significant amounts of energy are transmitted across the boundary. The window accounts for the discrepancy apparent between measured reflection data presented in early textbooks and predictions based on classical elasticity theory. Characteristics of the anelastic Rayleigh window are expected to be evident in certain sets of wide-angle, ocean-bottom reflection data and to be useful in estimating Q-1 for some

On Electron Hole Evolution in Inhomogeneous Plasmas

Science.gov (United States)

Kuzichev, I.; Vasko, I.; Agapitov, O. V.; Mozer, F.; Artemyev, A.

2017-12-01

Electron holes (EHs) are the stationary localized non-linear structures in phase space existing due to an electron population trapped within EH electrostatic potential. EHs were found to be a common phenomenon in the Earth's magnetosphere. Such structures were observed in reconnecting current sheets, injection fronts in the outer radiation belt, and in many other situations. EHs usually propagate along magnetic field lines with velocities about electron thermal velocity, are localized on the scale of about 4-10 Debye lengths, and have the field amplitude up to hundreds of mV/m. Generation of these structures, evolution, and their role in relaxation of instabilities and energy dissipation, particle energization, supporting large-scale potential drops is under active investigation. In this report, we present the results of 1.5D gyrokinetic Vlasov-Maxwell simulations of the EH evolution in plasmas with inhomogeneous magnetic field and inhomogeneous density. Our calculations show that the inhomogeneity has a critical effect on the EH dynamics. EHs propagating into stronger (weaker) magnetic field are decelerated (accelerated) with deceleration (acceleration) rate dependent on the magnetic field gradient. During the deceleration of EH, the potential drop (weak double layer) along EH is generated. Such a potential drop might be experimentally observable even for single EH in the reconnecting current sheets. The same holds for the propagation in the plasma with inhomogeneous density. For some parameters of the system, the deceleration results in the turning of the hole. The interesting feature of this process is that the turning point depends only on the EH parameters, being independent of the average inhomogeneity scale. Our calculations also demonstrate the significant difference between "quasi-particle" concept and real evolution of the hole. Indeed, the EH is accelerated (decelerated) faster than it follows from a quasi-particle energy conservation law. It indicates

The two-qubit quantum Rabi model: inhomogeneous coupling

International Nuclear Information System (INIS)

Mao, Lijun; Huai, Sainan; Zhang, Yunbo

2015-01-01

We revisit the analytic solution of the two-qubit quantum Rabi model with inhomogeneous coupling and transition frequencies using a displaced oscillator basis. This approach enables us to apply the same truncation rules and techniques adopted in the Rabi model to the two qubits system. The derived analytical spectra match perfectly with the numerical solutions in the parameter regime where the qubits’ transition frequencies are far off-resonance with the field frequency and the interaction strengths reach the ultrastrong coupling regime. We further explore the dynamical behavior of the two qubits as well as the evolution of entanglement. The analytical methods provide unexpectedly accurate results in describing the dynamics of the two qubits in the present experimentally accessible coupling regime. The time evolutions of the probability for the qubits show that the collapse-revival phenomena emerge, survive and finally disappear when one coupling strength increases from weak to strong coupling regimes and the other coupling strength is well into the ultrastrong coupling regime. The inhomogeneous coupling system exhibits new dynamics, which are different from the homogeneous coupling case. (paper)

Bivariational calculations for radiation transfer in an inhomogeneous participating media

International Nuclear Information System (INIS)

El Wakil, S.A.; Machali, H.M.; Haggag, M.H.; Attia, M.T.

1986-07-01

Equations for radiation transfer are obtained for dispersive media with space dependent albedo. Bivariational bound principle is used to calculate the reflection and transmission coefficients for such media. Numerical results are given and compared. (author)

Comments on the dispersion equation of a turbulent plasma - an inhomogeneous, magnetoactive case

International Nuclear Information System (INIS)

Ag, A.

1978-03-01

A weakly turbulent, magnetoactive plasma is considered in an inhomogeneous case with anisotropic temperature distribution. The dispersion relation is established following a method developed by Tsytovich and Nekrasov. The correction coefficients are calculated in the three principal scaling modes: (1) the turbulent frequencies predominate, (2) the cyclotronic velocities of the macroinstabilities predominate, (3) the turbulent frequencies are lower. (D.P.)

Dose distributions in thorax inhomogeneity for fast neutron beam from NIRS cyclotron

International Nuclear Information System (INIS)

Kutsutani-Nakamura, Yuzuru; Furukawa, Shigeo; Iinuma, T.A.; Kawashima, Katsuhiro; Hoshino, Kazuo; Hiraoka, Takeshi; Maruyama, Takashi; Sakashita, Kunio; Tsunemoto, Hiroshi

1990-01-01

The power law tissue-air ratio (TAR) method developed by Batho appears to be practical use for inhomogeneity corrections to the dose calculated in a layered media for photon beam therapy. The validity was examined in applying the modified power law TAR and the isodose shift methods to the dose calculation in thorax tissue inhomogeneity containing the boundary region for fast neutron beam. The neutron beam is produced by bombarding a thick beryllium target with 30 MeV deuterons. Lung phantom was made of granulated tissue equivalent plastic, which resulted in density of 0.30 and 0.60 g/cm 3 . Depth dose distributions for neutron beam were measured in thorax phantom by an air-filled cylindrical ionization chamber with TE plastic wall. The power law TAR method considering TAR of zero depth at boundary was compared with the measured data and a good result was obtained that the calculated dose was within ±3 % against the measured. But the isodose shift method is not so good for dose calculation in thorax tissue inhomogeneity using fast neutron beam. (author)

Scanning anisotropy parameters in complex media

KAUST Repository

Alkhalifah, Tariq Ali

2011-01-01

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.

Scanning anisotropy parameters in complex media

KAUST Repository

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.

Propagation of electromagnetic waves in stratified media with nonlinearity in both dielectric and magnetic responses.

Science.gov (United States)

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.

Cluster Tails for Critical Power-Law Inhomogeneous Random Graphs

Science.gov (United States)

van der Hofstad, Remco; Kliem, Sandra; van Leeuwaarden, Johan S. H.

2018-04-01

Recently, the scaling limit of cluster sizes for critical inhomogeneous random graphs of rank-1 type having finite variance but infinite third moment degrees was obtained in Bhamidi et al. (Ann Probab 40:2299-2361, 2012). It was proved that when the degrees obey a power law with exponent τ \\in (3,4), the sequence of clusters ordered in decreasing size and multiplied through by n^{-(τ -2)/(τ -1)} converges as n→ ∞ to a sequence of decreasing non-degenerate random variables. Here, we study the tails of the limit of the rescaled largest cluster, i.e., the probability that the scaling limit of the largest cluster takes a large value u, as a function of u. This extends a related result of Pittel (J Combin Theory Ser B 82(2):237-269, 2001) for the Erdős-Rényi random graph to the setting of rank-1 inhomogeneous random graphs with infinite third moment degrees. We make use of delicate large deviations and weak convergence arguments.

Transformation optics, isotropic chiral media and non-Riemannian geometry

International Nuclear Information System (INIS)

Horsley, S A R

2011-01-01

The geometrical interpretation of electromagnetism in transparent media (transformation optics) is extended to include chiral media that are isotropic but inhomogeneous. It was found that such media may be described through introducing the non-Riemannian geometrical property of torsion into the Maxwell equations, and it is shown how such an interpretation may be applied to the design of optical devices.

Multilayer bimetallic media as protection method of radioactive radiation

International Nuclear Information System (INIS)

Borts, B.V.; Tkachenko, V.I.; Tkachenko, I.V.

2010-01-01

Multilayer bimetallic media as means of protection of the earth's space vehicle from radioactive space radiation is described in the proposed paper. Evaluation of radiation losses of electron energy in inhomogeneous media is carried out; these media may be formed by layers of materials with different dielectric constants or they may be simulated by dielectric permittivity varying in space by harmonic law. It is shown that in such media the radiation losses of electron are proportional to the square of parameter of inhomogeneity, that is the losses are low. In the case when in periodic laminar medium with sharp boundaries the conditions of parametric union of self-waves of medium are satisfied, the losses of electron are proportional to the inhomogeneity parameter to first power and are comparable with losses that are caused by elementary events of scattering. The mean length of radiation losses of electron with energy 2(6) MeV in multilayer bimetallic medium tungsten-aluminum with period L ∼ 0,3 ·10 -6 cm is comparable with mean path of electron in such medium. The characteristic angles of radiation have the discrete character and are directed from 0 to 180 degree C. The power of losses increases with the radiation angle increase and is maximal for characteristic angles approaching 90 degree C.

Bayesian Markov Chain Monte Carlo inversion for weak anisotropy parameters and fracture weaknesses using azimuthal elastic impedance

Science.gov (United States)

Chen, Huaizhen; Pan, Xinpeng; Ji, Yuxin; Zhang, Guangzhi

2017-08-01

A system of aligned vertical fractures and fine horizontal shale layers combine to form equivalent orthorhombic media. Weak anisotropy parameters and fracture weaknesses play an important role in the description of orthorhombic anisotropy (OA). We propose a novel approach of utilizing seismic reflection amplitudes to estimate weak anisotropy parameters and fracture weaknesses from observed seismic data, based on azimuthal elastic impedance (EI). We first propose perturbation in stiffness matrix in terms of weak anisotropy parameters and fracture weaknesses, and using the perturbation and scattering function, we derive PP-wave reflection coefficient and azimuthal EI for the case of an interface separating two OA media. Then we demonstrate an approach to first use a model constrained damped least-squares algorithm to estimate azimuthal EI from partially incidence-phase-angle-stack seismic reflection data at different azimuths, and then extract weak anisotropy parameters and fracture weaknesses from the estimated azimuthal EI using a Bayesian Markov Chain Monte Carlo inversion method. In addition, a new procedure to construct rock physics effective model is presented to estimate weak anisotropy parameters and fracture weaknesses from well log interpretation results (minerals and their volumes, porosity, saturation, fracture density, etc.). Tests on synthetic and real data indicate that unknown parameters including elastic properties (P- and S-wave impedances and density), weak anisotropy parameters and fracture weaknesses can be estimated stably in the case of seismic data containing a moderate noise, and our approach can make a reasonable estimation of anisotropy in a fractured shale reservoir.

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 describe such evolution. Two aspects of the growth of such inhomogeneities are discussed. Firstly, it is shown that a local variation in the sink densities of the various microstructural defects will tend to enhance the inhomogeneity rather than remove it. Secondly, such inhomogeneities will lead to point...... defect fluxes that result in a spatial growth of the inhomogeneous region, which will be stopped only when the microstructural density around this region becomes large. The results have important implications in the formation of denuded zones and void formation in metals....

Phase function of a spherical particle when scattering an inhomogeneous electromagnetic plane wave.

Science.gov (United States)

Frisvad, Jeppe Revall

2018-04-01

In absorbing media, electromagnetic plane waves are most often inhomogeneous. Existing solutions for the scattering of an inhomogeneous plane wave by a spherical particle provide no explicit expressions for the scattering components. In addition, current analytical solutions require evaluation of the complex hypergeometric function F 1 2 for every term of a series expansion. In this work, I develop a simpler solution based on associated Legendre functions with argument zero. It is similar to the solution for homogeneous plane waves but with new explicit expressions for the angular dependency of the far-field scattering components, that is, the phase function. I include recurrence formulas for practical evaluation and provide numerical examples to evaluate how well the new expressions match previous work in some limiting cases. The predicted difference in the scattering phase function due to inhomogeneity is not negligible for light entering an absorbing medium at an oblique angle. The presented theory could thus be useful for predicting scattering behavior in dye-based random lasing and in solar cell absorption enhancement.

Green function as an integral superposition of Gaussian beams in inhomogeneous anisotropic layered structures in Cartesian coordinates

Czech Academy of Sciences Publication Activity Database

Červený, V.; Pšenčík, Ivan

2016-01-01

Roč. 26 (2016), s. 131-153 ISSN 2336-3827 R&D Projects: GA ČR(CZ) GA16-05237S Institutional support: RVO:67985530 Keywords : elastodynamic Green function * inhomogeneous anisotropic media * integral superposition of Gaussian beams Subject RIV: DC - Siesmology, Volcanology, Earth Structure

Influence of inhomogeneities in scintillating fibre electromagnetic calorimeter on its energy resolution

International Nuclear Information System (INIS)

Stavina, P.; Tokar, S.; Budagov, Yu.A.; Chirikov-Zorin, I.; Pantea, D.

1998-01-01

The specific aspects related to the discrete structure of the scintillating fibre electromagnetic calorimeter are investigated by means of Monte-Carlo simulation. It is shown that the structure inhomogeneity leads to an additional contribution to the systematic term in the energy resolution parametrization formula which weakly depends on energy and to the distortion of the Gaussian form of response distribution. The investigation was carried out for small tilt angles and for the absorber-to-fibre ratio 4:1

The point ground electrode in vicinity of the semi-spherical inhomogenity

Directory of Open Access Journals (Sweden)

Cvetković Nenad N.

2005-01-01

Full Text Available Characterization of the point ground electrode placed in the surroundings or inside of the semi-spherical earth inhomogenity and fed by low frequency (LF current using isolated earthling conductor, is presented in this paper. The ground impedance (resistance and reactance and potential distribution on the ground surface are determined. Image theory for two-layer semi conducting media, as well as for the one point electrode placed nearby or inside of the spherical body is used during the analysis.

AN FDTD ALGORITHM WITH PERFECTLY MATCHED LAYERS FOR CONDUCTIVE MEDIA. (R825225)

Science.gov (United States)

We extend Berenger's perfectly matched layers (PML) to conductive media. A finite-difference-time-domain (FDTD) algorithm with PML as an absorbing boundary condition is developed for solutions of Maxwell's equations in inhomogeneous, conductive media. For a perfectly matched laye...

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

We propose a method to achieve significant optical signal delays exploiting the effect of Autler–Townes splitting (ATS) in an inhomogeneously broadened quantum dot medium. The absorption and slowdown effects are compared for three schemes i.e., Ξ, V, and Λ, corresponding to different excitation c...

Casimir stress in an inhomogeneous medium

International Nuclear Information System (INIS)

Philbin, T.G.; Xiong, C.; Leonhardt, U.

2010-01-01

The Casimir effect in an inhomogeneous dielectric is investigated using Lifshitz's theory of electromagnetic vacuum energy. A permittivity function that depends continuously on one Cartesian coordinate is chosen, bounded on each side by homogeneous dielectrics. The result for the Casimir stress is infinite everywhere inside the inhomogeneous region, a divergence that does not occur for piece-wise homogeneous dielectrics with planar boundaries. A Casimir force per unit volume can be extracted from the infinite stress but it diverges on the boundaries between the inhomogeneous medium and the homogeneous dielectrics. An alternative regularization of the vacuum stress is considered that removes the contribution of the inhomogeneity over small distances, where macroscopic electromagnetism is invalid. The alternative regularization yields a finite Casimir stress inside the inhomogeneous region, but the stress and force per unit volume diverge on the boundaries with the homogeneous dielectrics. The case of inhomogeneous dielectrics with planar boundaries thus falls outside the current understanding of the Casimir effect.

Microcavity polariton linewidths in the weak-disorder regime

DEFF Research Database (Denmark)

Borri, Paola; Langbein, Wolfgang Werner; Woggon, U.

2000-01-01

Polariton linewidths have been measured in a series of high-quality microcavities with different excitonic inhomogeneous broadening in the weak-disorder regime. We show experimentally that the influence of the disorder on the polariton linewidths is canceled when the polariton energies are far in...... in the tail of the excitonic absorption. The measured linewidths are quantitatively compared with an estimation using the measured excitonic absorption spectrum of the bare quantum wells, and good agreement is found....

Scroll-wave dynamics in human cardiac tissue: lessons from a mathematical model with inhomogeneities and fiber architecture.

Directory of Open Access Journals (Sweden)

Rupamanjari Majumder

2011-04-01

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.

Nearly incompressible fluids: Hydrodynamics and large scale inhomogeneity

International Nuclear Information System (INIS)

Hunana, P.; Zank, G. P.; Shaikh, D.

2006-01-01

A system of hydrodynamic equations in the presence of large-scale inhomogeneities for a high plasma beta solar wind is derived. The theory is derived under the assumption of low turbulent Mach number and is developed for the flows where the usual incompressible description is not satisfactory and a full compressible treatment is too complex for any analytical studies. When the effects of compressibility are incorporated only weakly, a new description, referred to as 'nearly incompressible hydrodynamics', is obtained. The nearly incompressible theory, was originally applied to homogeneous flows. However, large-scale gradients in density, pressure, temperature, etc., are typical in the solar wind and it was unclear how inhomogeneities would affect the usual incompressible and nearly incompressible descriptions. In the homogeneous case, the lowest order expansion of the fully compressible equations leads to the usual incompressible equations, followed at higher orders by the nearly incompressible equations, as introduced by Zank and Matthaeus. With this work we show that the inclusion of large-scale inhomogeneities (in this case time-independent and radially symmetric background solar wind) modifies the leading-order incompressible description of solar wind flow. We find, for example, that the divergence of velocity fluctuations is nonsolenoidal and that density fluctuations can be described to leading order as a passive scalar. Locally (for small lengthscales), this system of equations converges to the usual incompressible equations and we therefore use the term 'locally incompressible' to describe the equations. This term should be distinguished from the term 'nearly incompressible', which is reserved for higher-order corrections. Furthermore, we find that density fluctuations scale with Mach number linearly, in contrast to the original homogeneous nearly incompressible theory, in which density fluctuations scale with the square of Mach number. Inhomogeneous nearly

Inhomogeneous dusty Universes and their deceleration

CERN Document Server

Giovannini, Massimo

2006-01-01

Exact results stemming directly from Einstein equations imply that inhomogeneous Universes endowed with vanishing pressure density can only decelerate, unless the energy density of the Universe becomes negative. Recent proposals seem to argue that inhomogeneous (but isotropic) space-times, filled only with incoherent matter,may turn into accelerated Universes for sufficiently late times. To scrutinize these scenarios, fully inhomogeneous Einstein equations are discussed in the synchronous system. In a dust-dominated Universe, the inhomogeneous generalization of the deceleration parameter is always positive semi-definite implying that no acceleration takes place.

Analysis of a quantum memory for photons based on controlled reversible inhomogeneous broadening

International Nuclear Information System (INIS)

Sangouard, Nicolas; Simon, Christoph; Afzelius, Mikael; Gisin, Nicolas

2007-01-01

We present a detailed analysis of a quantum memory for photons based on controlled and reversible inhomogeneous broadening. The explicit solution of the equations of motion is obtained in the weak excitation regime, making it possible to gain insight into the dependence of the memory efficiency on the optical depth, and on the width and shape of the atomic spectral distributions. We also study a simplified memory protocol which does not require any optical control fields

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....

A unidirectional acoustic cloak for multilayered background media with homogeneous metamaterials

Science.gov (United States)

Zhu, Jian; Chen, Tianning; Liang, Qingxuan; Wang, Xiaopeng; Xiong, Jie; Jiang, Ping

2015-08-01

The acoustic cloak, which can make an object hard to detect acoustically in a homogeneous background, has attracted great attention from researchers in recent years. The inhomogeneous background media were considered in this paper. The relative constitutive parameters were derived for acoustic cloaks working in multilayered media. And a unidirectional acoustic cloak for layered background media was proposed, designed and implemented successfully in a wide frequency range. In water and NaCl aqueous solution, the acoustic cloak was designed and realized with homogeneous metamaterials which were composed of steel and porous materials. The effective parameters of the unit cells of the cloak were determined by using the effective medium theory. Numerical results demonstrated excellent cloaking performance and showed that such a device could be physically realized with natural materials which will greatly promote the real applications of an invisibility cloak in inhomogeneous backgrounds.

Diffraction traveltime approximation for TI media with an inhomogeneous background

KAUST Repository

Waheed, Umair bin; Alkhalifah, Tariq Ali; Stovas, A.

2013-01-01

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.

Diffraction traveltime approximation for TI media with an inhomogeneous background

KAUST Repository

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.

Particle creation in inhomogeneous spacetimes

International Nuclear Information System (INIS)

Frieman, J.A.

1989-01-01

We study the creation of particles by inhomogeneous perturbations of spatially flat Friedmann-Robertson-Walker cosmologies. For massless scalar fields, the pair-creation probability can be expressed in terms of geometric quantities (curvature invariants). The results suggest that inhomogeneities on scales up to the particle horizon will be damped out near the Planck time. Perturbations on scales larger than the horizon are explicitly shown to yield no created pairs. The results generalize to inhomogeneous spacetimes several earlier studies of pair creation in homogeneous anisotropic cosmologies

Influence of inhomogeneities in scintillating fibre electromagnetic calorimeter on its energy resolution

Energy Technology Data Exchange (ETDEWEB)

Stavina, P; Tokar, S [Department of Nuclear Physics, Comenius University, Bratislava (Slovak Republic); Budagov, Yu A [Joint Institute for Nuclear Research, Dubna (Russian Federation); Chirikov-Zorin, I; Pantea, D [Institute of Atomic Physics, Bucharest (Romania)

1998-12-01

The specific aspects related to the discrete structure of the scintillating fibre electromagnetic calorimeter are investigated by means of Monte-Carlo simulation. It is shown that the structure inhomogeneity leads to an additional contribution to the systematic term in the energy resolution parametrization formula which weakly depends on energy and to the distortion of the Gaussian form of response distribution. The investigation was carried out for small tilt angles and for the absorber-to-fibre ratio 4:1 10 refs., 7 refs., 2 tabs.

Influence of microscopic inhomogeneity on macroscopic transport current of Ag/Bi2223 tapes

International Nuclear Information System (INIS)

Ogawa, Kazuhiro; Osamura, Kozo

2004-01-01

In Ag/Bi2223 tapes, inhomogeneities such as spatially distributed weak links or non-superconducting oxides are inevitably introduced because of the complicated manufacturing process and thermodynamic instability. In order to clarify the effect of the difference in such microscopic inhomogeneites on the macroscopic current transport properties, we carried out a numerical analysis. By changing volume fraction (V f ) of the Bi2223 phase and the shape of local distribution of critical current at each weak link, it is revealed that I-V characteristics are largely affected by the breadth of local distributions with different dependence on V f of Bi2223 and calculated results can be analyzed by Weibull distribution function with some parameters including the information of two-dimensional distribution

Effect of finite ion-temperature on ion-acoustic solitary waves in an inhomogeneous plasma

International Nuclear Information System (INIS)

Shivamoggi, B.K.

1981-01-01

The propagation of weakly nonlinear ion-acoustic waves in an inhomogeneous plasma is studied taking into account the effect of finite ion temperature. It is found that, whereas both the amplitude and the velocity of propagation decrease as the ion-acoustic solitary wave propagates into regions of higher density, the effect of a finite ion temperature is to reduce the amplitude but enhance the velocity of propagation of the solitary wave. (author)

Entropic uncertainty for spin-1/2 XXX chains in the presence of inhomogeneous magnetic fields and its steering via weak measurement reversals

Science.gov (United States)

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.

Deflection of slow light by magneto-optically controlled atomic media

International Nuclear Information System (INIS)

Zhou, D. L.; Wang, R. Q.; Zhou, Lan; Yi, S.; Sun, C. P.

2007-01-01

We present a semiclassical theory for light deflection by a coherent Λ-type three-level atomic medium in an inhomogeneous magnetic field or an inhomogeneous control laser. When the atomic energy levels (or the Rabi coupling by the control laser) are position-dependent due to the Zeeman effect caused by the inhomogeneous magnetic field (or due to inhomogeneity of the control field profile), the spatial dependence of the refraction index of the atomic medium will result in an observable deflection of slow signal light when the electromagnetically induced transparency cancels medium absorption. Our theoretical approach based on Fermat's principle in geometrical optics not only provides a consistent explanation for the most recent experiment in a straightforward way, but also predicts the two-photon detuning dependent behaviors and larger deflection angles by three orders of magnitude for the slow signal light deflection by the atomic media in an inhomogeneous off-resonant control laser field

Inverse random source scattering for the Helmholtz equation in inhomogeneous media

Science.gov (United States)

Li, Ming; Chen, Chuchu; Li, Peijun

2018-01-01

This paper is concerned with an inverse random source scattering problem in an inhomogeneous background medium. The wave propagation is modeled by the stochastic Helmholtz equation with the source driven by additive white noise. The goal is to reconstruct the statistical properties of the random source such as the mean and variance from the boundary measurement of the radiated random wave field at multiple frequencies. Both the direct and inverse problems are considered. We show that the direct problem has a unique mild solution by a constructive proof. For the inverse problem, we derive Fredholm integral equations, which connect the boundary measurement of the radiated wave field with the unknown source function. A regularized block Kaczmarz method is developed to solve the ill-posed integral equations. Numerical experiments are included to demonstrate the effectiveness of the proposed method.

A unidirectional acoustic cloak for multilayered background media with homogeneous metamaterials

International Nuclear Information System (INIS)

Zhu, Jian; Chen, Tianning; Liang, Qingxuan; Wang, Xiaopeng; Xiong, Jie; Jiang, Ping

2015-01-01

The acoustic cloak, which can make an object hard to detect acoustically in a homogeneous background, has attracted great attention from researchers in recent years. The inhomogeneous background media were considered in this paper. The relative constitutive parameters were derived for acoustic cloaks working in multilayered media. And a unidirectional acoustic cloak for layered background media was proposed, designed and implemented successfully in a wide frequency range. In water and NaCl aqueous solution, the acoustic cloak was designed and realized with homogeneous metamaterials which were composed of steel and porous materials. The effective parameters of the unit cells of the cloak were determined by using the effective medium theory. Numerical results demonstrated excellent cloaking performance and showed that such a device could be physically realized with natural materials which will greatly promote the real applications of an invisibility cloak in inhomogeneous backgrounds. (paper)

Perturbed soliton excitations in inhomogeneous DNA

International Nuclear Information System (INIS)

Daniel, M.; Vasumathi, V.

2005-05-01

We study nonlinear dynamics of inhomogeneous DNA double helical chain under dynamic plane-base rotator model by considering angular rotation of bases in a plane normal to the helical axis. The DNA dynamics in this case is found to be governed by a perturbed sine-Gordon equation when taking into account the interstrand hydrogen bonding energy and intrastrand inhomogeneous stacking energy and making an analogy with the Heisenberg model of the Hamiltonian for an inhomogeneous anisotropic spin ladder with ferromagnetic legs and antiferromagentic rung coupling. In the homogeneous limit the dynamics is governed by the kink-antikink soliton of the sine-Gordon equation which represents the formation of open state configuration in DNA double helix. The effect of inhomogeneity in stacking energy in the form of localized and periodic variations on the formation of open states in DNA is studied under perturbation. The perturbed soliton is obtained using a multiple scale soliton perturbation theory by solving the associated linear eigen value problem and constructing the complete set of eigen functions. The inhomogeneity in stacking energy is found to modulate the width and speed of the soliton depending on the nature of inhomogeneity. Also it introduces fluctuations in the form of train of pulses or periodic oscillation in the open state configuration (author)

Dynamic and static correlation functions in the inhomogeneous Hartree-Fock-state approach with random-phase-approximation fluctuations

International Nuclear Information System (INIS)

Lorenzana, J.; Grynberg, M.D.; Yu, L.; Yonemitsu, K.; Bishop, A.R.

1992-11-01

The ground state energy, and static and dynamic correlation functions are investigated in the inhomogeneous Hartree-Fock (HF) plus random phase approximation (RPA) approach applied to a one-dimensional spinless fermion model showing self-trapped doping states at the mean field level. Results are compared with homogeneous HF and exact diagonalization. RPA fluctuations added to the generally inhomogeneous HF ground state allows the computation of dynamical correlation functions that compare well with exact diagonalization results. The RPA correction to the ground state energy agrees well with the exact results at strong and weak coupling limits. We also compare it with a related quasi-boson approach. The instability towards self-trapped behaviour is signaled by a RPA mode with frequency approaching zero. (author). 21 refs, 10 figs

Simple inhomogeneous cosmological (toy) models

International Nuclear Information System (INIS)

Isidro, Eddy G. Chirinos; Zimdahl, Winfried; Vargas, Cristofher Zuñiga

2016-01-01

Based on the Lemaître-Tolman-Bondi (LTB) metric we consider two flat inhomogeneous big-bang models. We aim at clarifying, as far as possible analytically, basic features of the dynamics of the simplest inhomogeneous models and to point out the potential usefulness of exact inhomogeneous solutions as generalizations of the homogeneous configurations of the cosmological standard model. We discuss explicitly partial successes but also potential pitfalls of these simplest models. Although primarily seen as toy models, the relevant free parameters are fixed by best-fit values using the Joint Light-curve Analysis (JLA)-sample data. On the basis of a likelihood analysis we find that a local hump with an extension of almost 2 Gpc provides a better description of the observations than a local void for which we obtain a best-fit scale of about 30 Mpc. Future redshift-drift measurements are discussed as a promising tool to discriminate between inhomogeneous configurations and the ΛCDM model.

Turbulence of Weak Gravitational Waves in the Early Universe.

Science.gov (United States)

Galtier, Sébastien; Nazarenko, Sergey V

2017-12-01

We study the statistical properties of an ensemble of weak gravitational waves interacting nonlinearly in a flat space-time. We show that the resonant three-wave interactions are absent and develop a theory for four-wave interactions in the reduced case of a 2.5+1 diagonal metric tensor. In this limit, where only plus-polarized gravitational waves are present, we derive the interaction Hamiltonian and consider the asymptotic regime of weak gravitational wave turbulence. Both direct and inverse cascades are found for the energy and the wave action, respectively, and the corresponding wave spectra are derived. The inverse cascade is characterized by a finite-time propagation of the metric excitations-a process similar to an explosive nonequilibrium Bose-Einstein condensation, which provides an efficient mechanism to ironing out small-scale inhomogeneities. The direct cascade leads to an accumulation of the radiation energy in the system. These processes might be important for understanding the early Universe where a background of weak nonlinear gravitational waves is expected.

Multicolour Observations, Inhomogeneity & Evolution

OpenAIRE

Hellaby, Charles

2000-01-01

We propose a method of testing source evolution theories that is independent of the effects of inhomogeneity, and thus complementary to other studies of evolution. It is suitable for large scale sky surveys, and the new generation of large telescopes. In an earlier paper it was shown that basic cosmological observations - luminosity versus redshift, area distance versus redshift and number counts versus redshift - cannot separate the effects of cosmic inhomogeneity, cosmic evolution and sourc...

Large-scale brightness inhomogeneities in the solar atmosphere

International Nuclear Information System (INIS)

Mitchell, W.E. Jr.

1982-01-01

The intensity residuals are analyzed from a series of solar limb-darkening measurements in the wavelength range 5656 to 2997 A. The lengths of residual strings of the same sign exceed expectation by several orders of magnitude. The power spectrum fo the residuals shows a weak excess around 6000 km. For further study the 34000 limb-darkening residuals are subdivided into 5100 bright and faint cells. The frequency distribution of cell sizes peaks around 4500 km and increases from center to limb, the faint cells showing the greater center-limb effect. The cells are also studied as to contrast. A synoptic view indicates that only 12% of the cells are identifiable after a half hour. Phenomena that may combine to produce the observed wide spectrum of brightness inhomogeneities are briefly discussed. (orig.)

Nonstationary interference and scattering from random media

International Nuclear Information System (INIS)

Nazikian, R.

1991-12-01

For the small angle scattering of coherent plane waves from inhomogeneous random media, the three dimensional mean square distribution of random fluctuations may be recovered from the interferometric detection of the nonstationary modulational structure of the scattered field. Modulational properties of coherent waves scattered from random media are related to nonlocal correlations in the double sideband structure of the Fourier transform of the scattering potential. Such correlations may be expressed in terms of a suitability generalized spectral coherence function for analytic fields

OBSERVABLE DEVIATIONS FROM HOMOGENEITY IN AN INHOMOGENEOUS UNIVERSE

Energy Technology Data Exchange (ETDEWEB)

Giblin, John T. Jr. [Department of Physics, Kenyon College, 201 N College Road Gambier, OH 43022 (United States); Mertens, James B.; Starkman, Glenn D. [CERCA/ISO, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106 (United States)

2016-12-20

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 Friedmann–Lemaître–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.

OBSERVABLE DEVIATIONS FROM HOMOGENEITY IN AN INHOMOGENEOUS UNIVERSE

International Nuclear Information System (INIS)

Giblin, John T. Jr.; Mertens, James B.; 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 Friedmann–Lemaître–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.

Traveltime approximations and parameter estimation for orthorhombic media

KAUST Repository

Masmoudi, Nabil

2016-05-30

Building anisotropy models is necessary for seismic modeling and imaging. However, anisotropy estimation is challenging due to the trade-off between inhomogeneity and anisotropy. Luckily, we can estimate the anisotropy parameters Building anisotropy models is necessary for seismic modeling and imaging. However, anisotropy estimation is challenging due to the trade-off between inhomogeneity and anisotropy. Luckily, we can estimate the anisotropy parameters if we relate them analytically to traveltimes. Using perturbation theory, we have developed traveltime approximations for orthorhombic media as explicit functions of the anellipticity parameters η1, η2, and Δχ in inhomogeneous background media. The parameter Δχ is related to Tsvankin-Thomsen notation and ensures easier computation of traveltimes in the background model. Specifically, our expansion assumes an inhomogeneous ellipsoidal anisotropic background model, which can be obtained from well information and stacking velocity analysis. We have used the Shanks transform to enhance the accuracy of the formulas. A homogeneous medium simplification of the traveltime expansion provided a nonhyperbolic moveout description of the traveltime that was more accurate than other derived approximations. Moreover, the formulation provides a computationally efficient tool to solve the eikonal equation of an orthorhombic medium, without any constraints on the background model complexity. Although, the expansion is based on the factorized representation of the perturbation parameters, smooth variations of these parameters (represented as effective values) provides reasonable results. Thus, this formulation provides a mechanism to estimate the three effective parameters η1, η2, and Δχ. We have derived Dix-type formulas for orthorhombic medium to convert the effective parameters to their interval values.

Inhomogeneous wire explosion in water

International Nuclear Information System (INIS)

Hwangbo, C.K.; Kong, H.J.; Lee, S.S.

1980-01-01

Inhomogeneous processes are observed in underwater copper wire explosion induced by a condensed capacitor discharge. The wire used is 0.1 mm in diameter and 10 mm long, and the capacitor of 2 μF is charged to 5 KV. A N 2 laser is used for the diagnostic of spatial extension of exploding copper vapour. The photographs obtained in this experiment show unambiguously the inhomogeneous explosion along the exploding wire. The quenching of plasma by the surrounding water inhibits the expansion of the vapour. It is believed the observed inhomogeneous explosion along the wire is located and localized around Goronkin's striae, which was first reported by Goronkin and discussed by Froengel as a pre-breakdown phenomenon. (author)

Dynamics of inhomogeneous chiral condensates

Science.gov (United States)

Carlomagno, Juan Pablo; Krein, Gastão; Kroff, Daniel; Peixoto, Thiago

2018-01-01

We study the dynamics of the formation of inhomogeneous chirally broken phases in the final stages of a heavy-ion collision, with particular interest on the time scales involved in the formation process. The study is conducted within the framework of a Ginzburg-Landau time evolution, driven by a free energy functional motivated by the Nambu-Jona-Lasinio model. Expansion of the medium is modeled by one-dimensional Bjorken flow and its effect on the formation of inhomogeneous condensates is investigated. We also use a free energy functional from a nonlocal Nambu-Jona-Lasinio model which predicts metastable phases that lead to long-lived inhomogeneous condensates before reaching an equilibrium phase with homogeneous condensates.

The impact of reduced gastric acid secretion on dissolution of salts of weak bases in the fasted upper gastrointestinal lumen: Data in biorelevant media and in human aspirates.

Science.gov (United States)

Litou, Chara; Vertzoni, Maria; Xu, Wei; Kesisoglou, Filippos; Reppas, Christos

2017-06-01

To propose media for simulating the intragastric environment under reduced gastric acid secretion in the fasted state at three levels of simulation of the gastric environment and evaluate their usefulness in evaluating the intragastric dissolution of salts of weak bases. To evaluate the importance of bicarbonate buffer in biorelevant in vitro dissolution testing when using Level II biorelevant media simulating the environment in the fasted upper small intestine, regardless of gastric acid secretions. Media for simulating the hypochlorhydric and achlorhydric conditions in stomach were proposed using phosphates, maleates and bicarbonates buffers. The impact of bicarbonates in Level II biorelevant media simulating the environment in upper small intestine was evaluated so that pH and bulk buffer capacity were maintained. Dissolution data were collected using two model compounds, pioglitazone hydrochloride and semifumarate cocrystal of Compound B, and the mini-paddle dissolution apparatus in biorelevant media and in human aspirates. Simulated gastric fluids proposed in this study were in line with pH, buffer capacity, pepsin content, total bile salt/lecithin content and osmolality of the fasted stomach under partial and under complete inhibition of gastric acid secretion. Fluids simulating the conditions under partial inhibition of acid secretion were useful in simulating concentrations of both model compounds in gastric aspirates. Bicarbonates in Level III biorelevant gastric media and in Level II biorelevant media simulating the composition in the upper intestinal lumen did not improve simulation of concentrations in human aspirates. Level III biorelevant media for simulating the intragastric environment under hypochlorhydric conditions were proposed and their usefulness in the evaluation of concentrations of two model salts of weak bases in gastric aspirates was shown. Level II biorelevant media for simulating the environment in upper intestinal lumen led to

Nonlinear waves and weak turbulence

CERN Document Server

Zakharov, V E

1997-01-01

This book is a collection of papers on dynamical and statistical theory of nonlinear wave propagation in dispersive conservative media. Emphasis is on waves on the surface of an ideal fluid and on Rossby waves in the atmosphere. Although the book deals mainly with weakly nonlinear waves, it is more than simply a description of standard perturbation techniques. The goal is to show that the theory of weakly interacting waves is naturally related to such areas of mathematics as Diophantine equations, differential geometry of waves, Poincaré normal forms, and the inverse scattering method.

Inhomogeneous condensates in dilute nuclear matter and BCS-BEC crossovers

International Nuclear Information System (INIS)

Stein, Martin; Sedrakian, Armen; Huang, Xu-Guang; Clark, John W; Röpke, Gerd

2014-01-01

We report on recent progress in understanding pairing phenomena in low-density nuclear matter at small and moderate isospin asymmetry. A rich phase diagram has been found comprising various superfluid phases that include a homogeneous and phase-separated BEC phase of deuterons at low density and a homogeneous BCS phase, an inhomogeneous LOFF phase, and a phase-separated BCS phase at higher densities. The transition from the BEC phases to the BCS phases is characterized in terms of the evolution, from strong to weak coupling, of the condensate wavefunction and the second moment of its density distribution in r-space. We briefly discuss approaches to higher-order clustering in low-density nuclear matter.

Big Bounce and inhomogeneities

International Nuclear Information System (INIS)

Brizuela, David; Mena Marugan, Guillermo A; Pawlowski, Tomasz

2010-01-01

The dynamics of an inhomogeneous universe is studied with the methods of loop quantum cosmology, via a so-called hybrid quantization, as an example of the quantization of vacuum cosmological spacetimes containing gravitational waves (Gowdy spacetimes). The analysis of this model with an infinite number of degrees of freedom, performed at the effective level, shows that (i) the initial Big Bang singularity is replaced (as in the case of homogeneous cosmological models) by a Big Bounce, joining deterministically two large universes, (ii) the universe size at the bounce is at least of the same order of magnitude as that of the background homogeneous universe and (iii) for each gravitational wave mode, the difference in amplitude at very early and very late times has a vanishing statistical average when the bounce dynamics is strongly dominated by the inhomogeneities, whereas this average is positive when the dynamics is in a near-vacuum regime, so that statistically the inhomogeneities are amplified. (fast track communication)

Spectrum of harmonic emission by inhomogeneous plasma in intense electromagnetic wave

International Nuclear Information System (INIS)

Kovalev, V.F.; Pustovalov, V.V.

1989-01-01

The spectrum and angular distribution of the harmonics of arbitrary index emitted by a cold, inhomogeneous electron plasma subjected to a p-polarized electromagnetic wave have been studied analytically. The results are shown in graphical form. The intensity of the wave was varied over a wide range. At energy flux densities of the electromagnetic wave at which the inverse effect of the higher harmonics on the lower harmonics becomes appreciable, it becomes possible to observe a decay of the absolute value of the complex amplitude of a harmonic with increasing harmonic index in vacuum which is substantially slower than that predicted by the theory for a weak nonlinearity

Large scale inhomogeneities and the cosmological principle

International Nuclear Information System (INIS)

Lukacs, B.; Meszaros, A.

1984-12-01

The compatibility of cosmologic principles and possible large scale inhomogeneities of the Universe is discussed. It seems that the strongest symmetry principle which is still compatible with reasonable inhomogeneities, is a full conformal symmetry in the 3-space defined by the cosmological velocity field, but even in such a case, the standard model is isolated from the inhomogeneous ones when the whole evolution is considered. (author)

Millimeter wave propagation modeling of inhomogeneous rain media for satellite communications systems

Science.gov (United States)

Persinger, R. R.; Stutzman, W. L.

1978-01-01

A theoretical propagation model that represents the scattering properties of an inhomogeneous rain often found on a satellite communications link is presented. The model includes the scattering effects of an arbitrary distribution of particle type (rain or ice), particle shape, particle size, and particle orientation within a given rain cell. An associated rain propagation prediction program predicts attenuation, isolation and phase shift as a function of ground rain rate. A frequency independent synthetic storm algorithm is presented that models nonuniform rain rates present on a satellite link. Antenna effects are included along with a discussion of rain reciprocity. The model is verified using the latest available multiple frequency data from the CTS and COMSTAR satellites. The data covers a wide range of frequencies, elevation angles, and ground site locations.

Parametric instabilities in inhomogeneous plasma

International Nuclear Information System (INIS)

Nicholson, D.R.

1975-01-01

The nonlinear coupling of three waves in a plasma is considered. One of the waves is assumed large and constant; its amplitude is the parameter of the parametric instability. The spatial-temporal evolution of the other two waves is treated theoretically, in one dimension, by analytic methods and by direct numerical integration of the basic equations. Various monotonic forms of inhomogeneity are considered; agreement with previous work is found and new results are established. Nonmonotonic inhomogeneities are considered, in the form of turbulence and, as a model problem, in the form of a simple sinusoidal modulation. Relatively small amounts of nonmonotonic inhomogeneity, in the presence of a linear density gradient, are found to destabilize the well-known convective saturation, absolute growth occurring instead. (U.S.)

Consideration of inhomogeneities in irradiation planning. Pt. 1

International Nuclear Information System (INIS)

Zwicker, H.; Felix, R.

1976-01-01

In radiation therapy, the focal doses during irradiation of a tumor are based on the values for water, since water has almost the same absorption coefficient as muscular tissue, even for different kinds and energies of radiation. But calculation of the tumor dose will become inaccurate if inhomogeneities in the ray path are not considered such as fat, bones, plaster, metal plates, Kuentscher nails, endoprotheses. These materials, having a density sigma different from water, represent inhomogeneities relative to water with regard to the absorption of high-energy radiation. The experiments yielded the following results: All measurements revealed that the change in the course of the depth dose curve caused by inhomogeneities in water depends essentially on the density sigma and on the thickness d of the inhomogeneity. If the density sigma of the inhomogeneity exceeds one, a shift of the depth dose curve in water results in the direction of the surface; if the density sigma is smaller than one, the depth dose curve will move towards greater depth because of the inhomogeneity. With Co-60 gamma radiation, the shift of the depth dose curve in water due to an inhomogeneity occurs almost parallel. A correlation obtained empirically allows a calculation of th extent of the shift the depth dose is subject to for different inhomogeneities. (orig./ORU) [de

Effective Ohm's law for magnetized plasmas with anisotropic inhomogeneities

International Nuclear Information System (INIS)

Shamma, S.E.; Martinez-Sanchez, M.; Louis, J.F.

1978-01-01

Reduction formulae for the effective, or macroscopic, Ohm's law parameters are derived for inhomogeneous plasmas with anisotropic conductivity fluctuations having two general types of geometry: (a) elongated or shortened in the direction of the magnetic field and (b) two-dimensional, with the direction of constant properties lying in the plane perpendicular to the magnetic field. In each case, two approaches are used: (a) a small perturbation method and (b) an approximate method where each region in the plasma is considered separately, and consistency conditions are used to relate the results corresponding to each separate region to the effective properties of the whole plasma. Both methods are found to agree well when the fluctuations are weak, but differences appear at high fluctuation levels and, for nonuniformities very elongated along B, when the Hall parameter β is high. Comparison with available exact solutions valid at high β and strong fluctuation levels indicates that the self-consistency method gives accurate results even in these cases. The results of these analyses are used to evaluate the performance reduction in magnetohydrodynamic channels with plasma nonuniformities of several geometries, including axial streamers, perfectly isotropic fluctuations, and fluctuations elongated along B; the power density is reduced most strongly when β and the rms of the fluctuations are high, and also when the inhomogeneities are stretched along the magnetic field

Properties of weak contrast PP reflection/transmission coefficients for weakly anisotropic elastic media

Czech Academy of Sciences Publication Activity Database

Pšenčík, Ivan; Martins, J. L.

2001-01-01

Roč. 45, č. 2 (2001), s. 176-199 ISSN 0039-3169. [ICTCA'99. Trieste, 10.05.1999-14.05.1999] Institutional research plan: CEZ:AV0Z3012916 Keywords : elastic media * anisotropy * seismic reflection Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.680, year: 2001

Inhomogeneous initial data and small-field inflation

Science.gov (United States)

Marsh, M. C. David; Barrow, John D.; Ganguly, Chandrima

2018-05-01

We consider the robustness of small-field inflation in the presence of scalar field inhomogeneities. Previous numerical work has shown that if the scalar potential is flat only over a narrow interval, such as in commonly considered inflection-point models, even small-amplitude inhomogeneities present at the would-be onset of inflation at τ = τi can disrupt the accelerated expansion. In this paper, we parametrise and evolve the inhomogeneities from an earlier time τIC at which the initial data were imprinted, and show that for a broad range of inflationary and pre-inflationary models, inflection-point inflation withstands initial inhomogeneities. We consider three classes of perturbative pre-inflationary solutions (corresponding to energetic domination by the scalar field kinetic term, a relativistic fluid, and isotropic negative curvature), and two classes of exact solutions to Einstein's equations with large inhomogeneities (corresponding to a stiff fluid with cylindrical symmetry, and anisotropic negative curvature). We derive a stability condition that depends on the Hubble scales H(τi) and H(τIC), and a few properties of the pre-inflationary cosmology. For initial data imprinted at the Planck scale, the absence of an inhomogeneous initial data problem for inflection-point inflation leads to a novel, lower limit on the tensor-to-scalar ratio.

The effect of inhomogeneity of microstructure on ducility in superplasticity

International Nuclear Information System (INIS)

Manonukul, A.; Dunne, F.P.E.

1996-01-01

Finite element cell models have been developed to represent inhomogeneous grain size fields that occur in commercial Ti-6Al-4V. The models are used to investigate the influence of microstructure on superplastic stress-strain behaviour, inhomogeneity of deformation, and on ductility in superplastic deformation. It is shown that increasing the level of initial microstructural inhomogeneity leads to increasing flow stress for given strain, and that the microstructural inhomogeneity leads to inhomogeneous deformation. As superplasticity proceeds, the level of microstructural inhomogeneity diminishes, but the inhomogeneity itself is preserved during the deformation. It is shown that the inhomogeneity of microstructure leads to strain localisation which increases in severity with deformation until material necking and failure occur. Increasing the initial microstructural inhomogeneity is shown to lead to a decrease in ductility, but the effect diminishes for grain size ranges in excess of 30 μm. An empirical relationship is presented that relates the ductility to the initial grain size range through a power law. (orig.)

Magnon localization and Bloch oscillations in finite Heisenberg spin chains in an inhomogeneous magnetic field.

Science.gov (United States)

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.

Magnon localization and Bloch oscillations in finite Heisenberg spin chains in an inhomogeneous magnetic field

International Nuclear Information System (INIS)

Kosevich, Yuriy A; Gann, Vladimir V

2013-01-01

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. (paper)

Retrieving the elastodynamic Green's function of an arbitrary inhomogeneous medium by cross correlation

International Nuclear Information System (INIS)

Wapenaar, Kees

2004-01-01

A correlation-type reciprocity theorem is used to show that the elastodynamic Green's function of any inhomogeneous medium (random or deterministic) can be retrieved from the cross correlation of two recordings of a wave field at different receiver locations at the free surface. Unlike in other derivations, which apply to diffuse wave fields in random media or irregular finite bodies, no assumptions are made about the diffusivity of the wave field. In a second version, it is assumed that the wave field is diffuse due to many uncorrelated sources inside the medium

Impact of Uncertainty on the Porous Media Description in the Subsurface Transport Analysis

Science.gov (United States)

Darvini, G.; Salandin, P.

2008-12-01

In the modelling of flow and transport phenomena in naturally heterogeneous media, the spatial variability of hydraulic properties, typically the hydraulic conductivity, is generally described by use of a variogram of constant sill and spatial correlation. While some analyses reported in the literature discuss of spatial inhomogeneity related to a trend in the mean hydraulic conductivity, the effect in the flow and transport due to an inexact definition of spatial statistical properties of media as far as we know had never taken into account. The relevance of this topic is manifest, and it is related to the uncertainty in the definition of spatial moments of hydraulic log-conductivity from an (usually) little number of data, as well as to the modelling of flow and transport processes by the Monte Carlo technique, whose numerical fields have poor ergodic properties and are not strictly statistically homogeneous. In this work we investigate the effects related to mean log-conductivity (logK) field behaviours different from the constant one due to different sources of inhomogeneity as: i) a deterministic trend; ii) a deterministic sinusoidal pattern and iii) a random behaviour deriving from the hierarchical sedimentary architecture of porous formations and iv) conditioning procedure on available measurements of the hydraulic conductivity. These mean log-conductivity behaviours are superimposed to a correlated weakly fluctuating logK field. The time evolution of the spatial moments of the plume driven by a statistically inhomogeneous steady state random velocity field is analyzed in a 2-D finite domain by taking into account different sizes of injection area. The problem is approached by both a classical Monte Carlo procedure and SFEM (stochastic finite element method). By the latter the moments are achieved by space-time integration of the velocity field covariance structure derived according to the first- order Taylor series expansion. Two different goals are

Drift vortices in continuous media

International Nuclear Information System (INIS)

Chernousenko, V.M.; Chernenko, I.V.; Chernyshenko, S.V.

1989-01-01

The work is devoted to investigation into the problems of large-scale cortex drift and generation in continuous media based on the solution of notably non-linear differential equations. Using the capability of the modern computer technique it is possible to consider a series of cases with regard to medium viscosity and its inhomogeneity and with regard to three-dimensional vortex nature. Based on the solutions obtained the large-scale steady-state vortex generation processes are considered. The results can be used when studying non-linear phenomena in plasma and processes of substance and energy transfer in non-equilibrium media. 16 refs.; 5 figs

Acoustic Streaming and Its Suppression in Inhomogeneous Fluids.

Science.gov (United States)

Karlsen, Jonas T; Qiu, Wei; Augustsson, Per; Bruus, Henrik

2018-02-02

We present a theoretical and experimental study of boundary-driven acoustic streaming in an inhomogeneous fluid with variations in density and compressibility. In a homogeneous fluid this streaming results from dissipation in the boundary layers (Rayleigh streaming). We show that in an inhomogeneous fluid, an additional nondissipative force density acts on the fluid to stabilize particular inhomogeneity configurations, which markedly alters and even suppresses the streaming flows. Our theoretical and numerical analysis of the phenomenon is supported by ultrasound experiments performed with inhomogeneous aqueous iodixanol solutions in a glass-silicon microchip.

Metrical theorems on systems of small inhomogeneous linear forms

DEFF Research Database (Denmark)

Hussain, Mumtaz; Kristensen, Simon

In this paper we establish complete Khintchine-Groshev and Schmidt type theorems for inhomogeneous small linear forms in the so-called doubly metric case, in which the inhomogeneous parameter is not fixed.......In this paper we establish complete Khintchine-Groshev and Schmidt type theorems for inhomogeneous small linear forms in the so-called doubly metric case, in which the inhomogeneous parameter is not fixed....

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...

First-order P-wave ray synthetic seismograms in inhomogeneous, weakly anisotropic, layered media

Czech Academy of Sciences Publication Activity Database

Pšenčík, Ivan; Farra, V.

2014-01-01

Roč. 198, č. 1 (2014), s. 298-307 ISSN 0956-540X R&D Projects: GA ČR(CZ) GAP210/11/0117 Institutional support: RVO:67985530 Keywords : body waves * seismic anisotropy * wave propagation Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.724, year: 2013

Acoustic probing of elastic behavior and damage in weakly cemented granular media

Science.gov (United States)

Langlois, V.; Jia, X.

2014-02-01

We investigate the elastic behavior and damage of weakly cemented granular media under external load with ultrasound. The cementation controlled experiments are performed by freezing the capillary liquid at the bead contact in a dense glass or polymeric [poly(methyl methacrylate)] bead pack wet by tetradecane of volume fraction ϕ = 0.1%-4%. When the pendular rings are solidified, an abrupt increase by a factor of 2 in the compressional wave velocity is observed. We interpret the data in terms of effective medium models in which the contact stiffnesses are derived by either a bonded contact model [P. J. Digby, J. Appl. Mech. 48, 803 (1981), 10.1115/1.3157738] or a cemented contact model [J. Dvorkin, A. Nur, and H. Yin, Mech. Mater. 18, 351 (1994), 10.1016/0167-6636(94)90044-2]. The former fails to quantitatively account for the results with a soft cement relative to the grain, whereas the latter considering the mechanical properties of the cement does apply. Moreover, we monitor the irreversible behavior of the cemented granular packs under moderate uniaxial loading (cemented materials is accompanied by a compressional wave velocity decrease up to 60%, likely due to the fractures induced at the grain-cement interfaces.

Inhomogenous loop quantum cosmology with matter

International Nuclear Information System (INIS)

Martín-de Bias, D; Mena Marugán, G A; Martín-Benito, M

2012-01-01

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.

Estimating functions for inhomogeneous Cox processes

DEFF Research Database (Denmark)

Waagepetersen, Rasmus

2006-01-01

Estimation methods are reviewed for inhomogeneous Cox processes with tractable first and second order properties. We illustrate the various suggestions by means of data examples.......Estimation methods are reviewed for inhomogeneous Cox processes with tractable first and second order properties. We illustrate the various suggestions by means of data examples....

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

The concept of weak ties was introduced by Granovetter through the seminal paper titled "Strength of weak ties". Since then the role of weak ties in general and their specific role as occupying the structural hole has been explored in many different fields. In this study, we identify actual or po...

Propagation of strong electromagnetic beams in inhomogeneous plasmas

Energy Technology Data Exchange (ETDEWEB)

Ferrari, A; Massaglia, S [Consiglio Nazionale delle Ricerche, Turin (Italy). Lab. di Cosmo-Geofisica; Turin Univ. (Italy). Ist. di Fisica Generale)

1980-09-01

We study some simple aspects of nonlinear propagation of relativistically strong electromagnetic beams in inhomogeneous plasmas, especially in connection with effects of beam self-trapping in extended extragalactic radio sources. The two effects of (i) long scale longitudinal and radial inhomogeneities inherent to the plasma and (ii) radial inhomogeneities produced by the ponderomotive force of the beam itself are investigated.

Dynamics of an inhomogeneous anisotropic antiferromagnetic spin chain

International Nuclear Information System (INIS)

Daniel, M.; Amuda, R.

1994-11-01

We investigate the nonlinear spin excitations in the two sublattice model of a one dimensional classical continuum Heisenberg inhomogeneous antiferromagnetic spin chain. The dynamics of the inhomogeneous chain reduces to that of its homogeneous counterpart when the inhomogeneity assumes a particular form. Apart from the usual twists and pulses, we obtain some planar configurations representing the nonlinear dynamics of spins. (author). 12 refs

Filamentation and light bullet formation dynamics in solid-state dielectric media with weak, moderate and strong anomalous group velocity dispersion

International Nuclear Information System (INIS)

Gražulevičiūtė, I; Garejev, N; Majus, D; Tamošauskas, G; A Dubietis; Jukna, V

2016-01-01

We present a series of measurements, which characterize filamentation dynamics of intense ultrashort laser pulses in the space–time domain, as captured by means of three-dimensional imaging technique in sapphire and fused silica, in the wavelength range of 1.45–2.25 μm, accessing the regimes of weak, moderate and strong anomalous group velocity dispersion (GVD). In the regime of weak anomalous GVD (at 1.45 μm), pulse splitting into two sub-pulses producing a pair of light bullets with spectrally shifted carrier frequencies in both nonlinear media is observed. In contrast, in the regimes of moderate (at 1.8 μm) and strong (at 2.25 μm) anomalous GVD we observe notably different transient dynamics, which however lead to the formation of a single self-compressed quasistationary light bullet with an universal spatiotemporal shape comprised of an extended ring-shaped periphery and a localized intense core that carries the self-compressed pulse. (paper)

Filamentation and light bullet formation dynamics in solid-state dielectric media with weak, moderate and strong anomalous group velocity dispersion

Science.gov (United States)

Gražulevičiūtė, I.; Garejev, N.; Majus, D.; Jukna, V.; Tamošauskas, G.; Dubietis, A.

2016-02-01

We present a series of measurements, which characterize filamentation dynamics of intense ultrashort laser pulses in the space-time domain, as captured by means of three-dimensional imaging technique in sapphire and fused silica, in the wavelength range of 1.45-2.25 μm, accessing the regimes of weak, moderate and strong anomalous group velocity dispersion (GVD). In the regime of weak anomalous GVD (at 1.45 μm), pulse splitting into two sub-pulses producing a pair of light bullets with spectrally shifted carrier frequencies in both nonlinear media is observed. In contrast, in the regimes of moderate (at 1.8 μm) and strong (at 2.25 μm) anomalous GVD we observe notably different transient dynamics, which however lead to the formation of a single self-compressed quasistationary light bullet with an universal spatiotemporal shape comprised of an extended ring-shaped periphery and a localized intense core that carries the self-compressed pulse.

Large sample neutron activation analysis of a reference inhomogeneous sample

International Nuclear Information System (INIS)

Vasilopoulou, T.; Athens National Technical University, Athens; Tzika, F.; Stamatelatos, I.E.; Koster-Ammerlaan, M.J.J.

2011-01-01

A benchmark experiment was performed for Neutron Activation Analysis (NAA) of a large inhomogeneous sample. The reference sample was developed in-house and consisted of SiO 2 matrix and an Al-Zn alloy 'inhomogeneity' body. Monte Carlo simulations were employed to derive appropriate correction factors for neutron self-shielding during irradiation as well as self-attenuation of gamma rays and sample geometry during counting. The large sample neutron activation analysis (LSNAA) results were compared against reference values and the trueness of the technique was evaluated. An agreement within ±10% was observed between LSNAA and reference elemental mass values, for all matrix and inhomogeneity elements except Samarium, provided that the inhomogeneity body was fully simulated. However, in cases that the inhomogeneity was treated as not known, the results showed a reasonable agreement for most matrix elements, while large discrepancies were observed for the inhomogeneity elements. This study provided a quantification of the uncertainties associated with inhomogeneity in large sample analysis and contributed to the identification of the needs for future development of LSNAA facilities for analysis of inhomogeneous samples. (author)

Cyclotron spectra from inhomogeneous accretion columns. II. Polarization

International Nuclear Information System (INIS)

Wu, K.; Chanmugam, G.

1989-01-01

Circularly and linearly polarized radiation from inhomogeneous cyclotron emission regions with uniform magnetic field and temperature but different electron density profiles are studied. Calculations show that the inhomogeneous models generally produce larger polarization for low harmonics and smaller polarization for high harmonics compared to the homogeneous models. Polarization light curves for different inhomogeneous models with a wide variety of parameters are presented, providing handy theoretical results to compare with observations. The observed polarization light curves of ST LMi, EF Eri, and BL Hydri are fitted using an inhomogeneous model for the first time, and good fits are obtained, supporting the hypothesis that the cyclotron emission regions of AM Her systems have a complicated structure. 37 refs

Integrability Aspects and Soliton Solutions for a System Describing Ultrashort Pulse Propagation in an Inhomogeneous Multi-Component Medium

International Nuclear Information System (INIS)

Guo Rui; Tian Bo; Lue Xing; Zhang Haiqiang; Xu Tao

2010-01-01

For the propagation of the ultrashort pulses in an inhomogeneous multi-component nonlinear medium, a system of coupled equations is analytically studied in this paper. Painleve analysis shows that this system admits the Painleve property under some constraints. By means of the Ablowitz-Kaup-Newell-Segur procedure, the Lax pair of this system is derived, and the Darboux transformation (DT) is constructed with the help of the obtained Lax pair. With symbolic computation, the soliton solutions are obtained by virtue of the DT algorithm. Figures are plotted to illustrate the dynamical features of the soliton solutions. Characteristics of the solitons propagating in an inhomogeneous multi-component nonlinear medium are discussed: (i) Propagation of one soliton and two-peak soliton; (ii) Elastic interactions of the parabolic two solitons; (iii) Overlap phenomenon between two solitons; (iv) Collision of two head-on solitons and two head-on two-peak solitons; (v) Two different types of interactions of the three solitons; (vi) Decomposition phenomenon of one soliton into two solitons. The results might be useful in the study on the ultrashort-pulse propagation in the inhomogeneous multi-component nonlinear media. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

MRI intensity inhomogeneity correction by combining intensity and spatial information

International Nuclear Information System (INIS)

Vovk, Uros; Pernus, Franjo; Likar, Bostjan

2004-01-01

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

Inhomogeneous ordered states and translational nature of the gauge group in the Landau continuum theory: II. Applications of the general theory

International Nuclear Information System (INIS)

Braginsky, A. Ya.

2007-01-01

A group theory approach to description of phase transitions to an inhomogeneous ordered state, proposed in the preceding paper, is applied to two problems. First, a theory of the state of a liquid-crystalline smectic type-A phase under the action of uniaxial pressure is developed. Second, a model of strengthening in quasicrystals is constructed. According to the proposed approach, the so-called elastic dislocations always appear during the phase transitions in an inhomogeneous deformed state in addition to static dislocations, which are caused by peculiarities of the crystal growth or by other features in the prehistory of a sample. The density of static dislocations weakly depends on the external factors, whereas the density of elastic dislocations depends on the state. An analogy between the proposed theory of the inhomogeneous ordered state and the quantum-field theory of interaction between material fields is considered. On this basis, the phenomenological Ginzburg-Landau equation for the superconducting state is derived using the principle of locality of the transformation properties of the superconducting order parameter with respect to temporal translations

Symbolic computation and solitons of the nonlinear Schroedinger equation in inhomogeneous optical fiber media

International Nuclear Information System (INIS)

Li Biao; Chen Yong

2007-01-01

In this paper, the inhomogeneous nonlinear Schroedinger equation with the loss/gain and the frequency chirping is investigated. With the help of symbolic computation, three families of exact analytical solutions are presented by employing the extended projective Riccati equation method. From our results, many previous known results of nonlinear Schroedinger equation obtained by some authors can be recovered by means of some suitable selections of the arbitrary functions and arbitrary constants. Of optical and physical interests, soliton propagation and soliton interaction are discussed and simulated by computer, which include snake-soliton propagation and snake-solitons interaction, boomerang-like soliton propagation and boomerang-like solitons interaction, dispersion managed (DM) bright (dark) soliton propagation and DM solitons interaction

From Suitable Weak Solutions to Entropy Viscosity

KAUST Repository

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.

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...

WKB solution 4×4 for electromagnetic waves in a planar magnetically anisotropic inhomogeneous layer

Science.gov (United States)

Moiseeva, Natalya Michailovna; Moiseev, Anton Vladimirovich

2018-04-01

In the paper, an oblique incidence of a plane electromagnetic wave on a planar magnetically anisotropic inhomogeneous layer is considered. We consider the case when all the components of the magnetic permeability tensor are non zero and vary with distance from the interface of media. The WKB method gives a matrix 4 × 4 solution for the projections of the electromagnetic wave fields during its propagation. The dependence of the cross-polarized components on the orientation of the anisotropic medium relative to the plane of incidence of the medium is analyzed.

Acoustic Streaming and Its Suppression in Inhomogeneous Fluids

DEFF Research Database (Denmark)

Karlsen, Jonas Tobias; Qiu, Wei; Augustsson, Per

2018-01-01

We present a theoretical and experimental study of boundary-driven acoustic streaming in an inhomogeneous fluid with variations in density and compressibility. In a homogeneous fluid this streaming results from dissipation in the boundary layers (Rayleigh streaming). We show...... that in an inhomogeneous fluid, an additional nondissipative force density acts on the fluid to stabilize particular inhomogeneity configurations, which markedly alters and even suppresses the streaming flows. Our theoretical and numerical analysis of the phenomenon is supported by ultrasound experiments performed...

The dynamics of short envelope solitons in media with controlled dispersion

International Nuclear Information System (INIS)

Aseeva, N.V.; Gromov, E.M.; Tyutin, V.V.

2007-01-01

The dynamics of short envelope solitons in media with controlled dispersion is investigated in the framework of the third-order nonlinear Schroedinger equation. Evolution of the solitons amplitude is analyzed in the adiabatic approximation. The existence of short envelope solitons independent from linear dispersion inhomogeneity is shown

Sensitivity of resistive and Hall measurements to local inhomogeneities

DEFF Research Database (Denmark)

Koon, Daniel W.; Wang, Fei; Petersen, Dirch Hjorth

2013-01-01

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....

Coherent beam control through inhomogeneous media in multi-photon microscopy

Science.gov (United States)

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

Inhomogeneous inflation: The initial-value problem

International Nuclear Information System (INIS)

Laguna, P.; Kurki-Suonio, H.; Matzner, R.A.

1991-01-01

We present a spatially three-dimensional study for solving the initial-value problem in general relativity for inhomogeneous cosmologies. We use York's conformal approach to solve the constraint equations of Einstein's field equations for scalar field sources and find the initial data which will be used in the evolution. This work constitutes the first stage in the development of a code to analyze the effects of matter and spacetime inhomogeneities on inflation

Ehrenfest force in inhomogeneous magnetic field

International Nuclear Information System (INIS)

Sisakyan, A.N.; Shevchenko, O.Yu.; Samojlov, V.N.

2000-01-01

The Ehrenfest force in an inhomogeneous magnetic field is calculated. It is shown that there exist such (very rare) topologically nontrivial physical situations when the Gauss theorem in its classic formulation fails and, as a consequence, apart from the usual Lorentz force an additional, purely imaginary force acts on the charged particle. This force arises only in inhomogeneous magnetic fields of special configurations, has a purely quantum origin, and disappears in the classical limit

Nuclear signals in magnetically ordered media

International Nuclear Information System (INIS)

Ignatchenko, V.A.; Tsifrinovich, V.I.

1993-01-01

The book contains a review of theoretical and experimental investigations in the field of nuclear magnetism in magnetically ordered media. The semiclassical theory of nuclear spins motion is developed that takes into consideration three main features of magnetically ordered media: Suhl-Nakamura interaction, quadrupole interaction and microscopic inhomogeneity of nuclear frequencies. The detailed classification of nuclear spin echo signals is given for standard conditions of experiments, when the Suhl-Nakamura interaction is small in comparison with the NMR line width. The extremal states of the electron - nuclear magnetic system are described in detail: the coexistence of NMR and FMR, nuclear ferromagnetism and NMR at fast remagnetization of a ferromagnet. 157 refs., 20 figs

Polarimetric imaging of turbid inhomogeneous slab media based on backscattering using a pencil beam for illumination: Monte Carlo simulation

Science.gov (United States)

Otsuki, Soichi

2018-04-01

Polarimetric imaging of absorbing, strongly scattering, or birefringent inclusions is investigated in a negligibly absorbing, moderately scattering, and isotropic slab medium. It was proved that the reduced effective scattering Mueller matrix is exactly calculated from experimental or simulated raw matrices even if the medium is anisotropic and/or heterogeneous, or the outgoing light beam exits obliquely to the normal of the slab surface. The calculation also gives a reasonable approximation of the reduced matrix using a light beam with a finite diameter for illumination. The reduced matrix was calculated using a Monte Carlo simulation and was factorized in two dimensions by the Lu-Chipman polar decomposition. The intensity of backscattered light shows clear and modestly clear differences for absorbing and strongly scattering inclusions, respectively, whereas it shows no difference for birefringent inclusions. Conversely, some polarization parameters, for example, the selective depolarization coefficients exhibit only a slight difference for the absorbing inclusions, whereas they showed clear difference for the strongly scattering or birefringent inclusions. Moreover, these quantities become larger with increasing the difference in the optical properties of the inclusions relative to the surrounding medium. However, it is difficult to recognize inclusions that buried at the depth deeper than 3 mm under the surface. Thus, the present technique can detect the approximate shape and size of these inclusions, and considering the depth where inclusions lie, estimate their optical properties. This study reveals the possibility of the polarization-sensitive imaging of turbid inhomogeneous media using a pencil beam for illumination.

Light Manipulation in Inhomogeneous Liquid Flow and Its Application in Biochemical Sensing

Directory of Open Access Journals (Sweden)

Yunfeng Zuo

2018-04-01

Full Text Available Light manipulation has always been the fundamental subject in the field of optics since centuries ago. Traditional optical devices are usually designed using glasses and other materials, such as semiconductors and metals. Optofluidics is the combination of microfluidics and optics, which brings a host of new advantages to conventional solid systems. The capabilities of light manipulation and biochemical sensing are inherent alongside the emergence of optofluidics. This new research area promotes advancements in optics, biology, and chemistry. The development of fast, accurate, low-cost, and small-sized biochemical micro-sensors is an urgent demand for real-time monitoring. However, the fluid flow in the on-chip sensor is usually non-uniformed, which is a new and emerging challenge for the accuracy of optical detection. It is significant to reveal the principle of light propagation in an inhomogeneous liquid flow and the interaction between biochemical samples and light in flowing liquids. In this review, we summarize the current state of optofluidic lab-on-a-chip techniques from the perspective of light modulation by the unique dynamic properties of fluid in heterogeneous media, such as diffusion, heat transfer, and centrifugation etc. Furthermore, this review introduces several novel photonic phenomena in an inhomogeneous liquid flow and demonstrates their application in biochemical sensing.

Evolution of vacuum bubbles embedded in inhomogeneous spacetimes

Energy Technology Data Exchange (ETDEWEB)

Pannia, Florencia Anabella Teppa [Grupo de Astrofísica, Relatividad y Cosmología, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n B1900FWA, La Plata (Argentina); Bergliaffa, Santiago Esteban Perez, E-mail: fteppa@fcaglp.unlp.edu.ar, E-mail: sepbergliaffa@gmail.com [Departamento de Física Teórica, Instituto de Física, Universidade do Estado de Rio de Janeiro, CEP 20550-013, Rio de Janeiro, Brazil. (Brazil)

2017-03-01

We study the propagation of bubbles of new vacuum in a radially inhomogeneous background filled with dust or radiation, and including a cosmological constant, as a first step in the analysis of the influence of inhomogeneities in the evolution of an inflating region. We also compare the cases with dust and radiation backgrounds and show that the evolution of the bubble in radiation environments is notably different from that in the corresponding dust cases, both for homogeneous and inhomogeneous ambients, leading to appreciable differences in the evolution of the proper radius of the bubble.

Overcoming limits to near-field radiative heat transfer in uniform planar media through multilayer optimization.

Science.gov (United States)

Jin, Weiliang; Messina, Riccardo; Rodriguez, Alejandro W

2017-06-26

Radiative heat transfer between uniform plates is bounded by the narrow range and limited contribution of surface waves. Using a combination of analytical calculations and numerical gradient-based optimization, we show that such a limitation can be overcome in complicated multilayer geometries, allowing the scattering and coupling rates of slab resonances to be altered over a broad range of evanescent wavevectors. We conclude that while the radiative flux between two inhomogeneous slabs can only be weakly enhanced, the flux between a dipolar particle and an inhomogeneous slab-proportional to the local density of states-can be orders of magnitude larger, albeit at the expense of increased frequency selectivity. A brief discussion of hyperbolic metamaterials shows that they provide far less enhancement than optimized inhomogeneous slabs.

Inhomogeneity of the grain size of aircraft engine turbine polycrystalline blades

Directory of Open Access Journals (Sweden)

J. Chmiela

2011-10-01

Full Text Available The determination of the behaviour of inhomogeneous materials with a complex microstructure requires taking into account the inhomogeneity of the grain size, as it is the basis for the process of designing and modelling effective behaviours. Therefore, the functional description of the inhomogeneity is becoming an important issue. The paper presents an analytical approach to the grain size inhomogeneity, based on the derivative of a logarithmic-logistic function. The solution applied enabled an effective evaluation of the inhomogeneity of two macrostructures of aircraft engine turbine blades, characterized by a high degree of diversity in the grain size. For the investigated single-modal and bimodal grain size distributions on a perpendicular projection and for grains with a non-planar surface, we identified the parameters that describe the degree of inhomogeneity of the constituents of weight distributions and we also derived a formula describing the overall degree of inhomogeneity of bimodal distributions. The solution presented in the paper is of a general nature and it can be used to describe the degree of inhomogeneity of multi-modal distributions. All the calculations were performed using the Mathematica® package.

Effect of the single-scattering phase function on light transmission through disordered media with large inhomogeneities

International Nuclear Information System (INIS)

Marinyuk, V V; Sheberstov, S V

2017-01-01

We calculate the total transmission coefficient (transmittance) of a disordered medium with large (compared to the light wavelength) inhomogeneities. To model highly forward scattering in the medium we take advantage of the Gegenbauer kernel phase function. In a subdiffusion thickness range, the transmittance is shown to be sensitive to the specific form of the single-scattering phase function. The effect reveals itself at grazing angles of incidence and originates from small-angle multiple scattering of light. Our results are in a good agreement with numerical solutions to the radiative transfer equation. (paper)

The dynamics of spiral tip adjacent to inhomogeneity in cardiac tissue

Science.gov (United States)

Zhang, Juan; Tang, Jun; Ma, Jun; Luo, Jin Ming; Yang, Xian Qing

2018-02-01

Rotating spiral waves in cardiac tissue are implicated in life threatening cardiac arrhythmias. Experimental and theoretical evidences suggest the inhomogeneities in cardiac tissue play a significant role in the dynamics of spiral waves. Based on a modified 2D cardiac tissue model, the interaction of inhomogeneity on the nearby rigidly rotating spiral wave is numerically studied. The adjacent area of the inhomogeneity is divided to two areas, when the initial rotating center of the spiral tip is located in the two areas, the spiral tip will be attracted and anchor on the inhomogeneity finally, or be repulsed away. The width of the area is significantly dependent on the intensity and size of the inhomogeneity. Our numerical study sheds some light on the mechanism of the interaction of inhomogeneity on the spiral wave in cardiac tissue.

Parametric interaction of waves in the plasma with random large-scale inhomogeneities

International Nuclear Information System (INIS)

Abramovich, B.S.; Tamojkin, V.V.

1980-01-01

Parametric processes of the decay and fusion of three waves in a weakly turbulent plasma with random inhomogeneities, the size of which is too big as compared with wave-lengths are considered. Under the diffusive approximation applicability closed equations are obtained, which determine the behaviour of all the intensity moments of parametrically bound waves. It is shown that under the conditions when the characteristic length of the multiple scattering is considerably less than the nonlinear interaction, length the effective increment of average intensity increase and its moments at dissociation processes is too small as compared with the homogeneous plasma case. At fusion processes the same increment (decrement) determines the distance at which all intensity moments are in the saturation regime

Transport processes in macroscopically disordered media from mean field theory to percolation

CERN Document Server

Snarskii, Andrei A; Sevryukov, Vladimir A; Morozovskiy, Alexander; Malinsky, Joseph

2016-01-01

This book reflects on recent advances in the understanding of percolation systems to present a wide range of transport phenomena in inhomogeneous disordered systems. Further developments in the theory of macroscopically inhomogeneous media are also addressed. These developments include galvano-electric, thermoelectric, elastic properties, 1/f noise and higher current momenta, Anderson localization, and harmonic generation in composites in the vicinity of the percolation threshold. The book describes how one can find effective characteristics, such as conductivity, dielectric permittivity, magnetic permeability, with knowledge of the distribution of different components constituting an inhomogeneous medium. Considered are a wide range of recent studies dedicated to the elucidation of physical properties of macroscopically disordered systems. Aimed at researchers and advanced students, it contains a straightforward set of useful tools which will allow the reader to derive the basic physical properties of compli...

Kinematics of the quasi-p wave in anisotropic media. Application to tomography; Cinematique de l'onde quasi p en milieux anisotropes. Application a la tomographie

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)

SECTIONING METHOD APPLICATION AT ELLIPSOMETRY OF INHOMOGENEOUS REFLECTION SYSTEMS

Directory of Open Access Journals (Sweden)

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.

Rotational inhomogeneities from pre-big bang?

International Nuclear Information System (INIS)

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 string frame metric

Rotational inhomogeneities from pre-big bang?

Energy Technology Data Exchange (ETDEWEB)

Giovannini, Massimo [Department of Physics, Theory Division, CERN, 1211 Geneva 23 (Switzerland)

2005-01-21

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 string frame metric.

MICROWAVE INTERACTIONS WITH INHOMOGENEOUS PARTIALLY IONIZED PLASMA

Energy Technology Data Exchange (ETDEWEB)

Kritz, A. H.

1962-11-15

Microwave interactions with inhomogeneous plasmas are often studied by employing a simplified electromagnetic approach, i.e., by representing the effects of the plasma by an effective dielectric coefficient. The problems and approximations associated with this procedure are discussed. The equation describing the microwave field in an inhomogeneous partially ionized plasma is derived, and the method that is applied to obtain the reflected, transmitted, and absorbed intensities in inhomogeneous plasmas is presented. The interactions of microwaves with plasmas having Gaussian electron density profiles are considered. The variation of collision frequency with position is usually neglected. In general, the assumption of constant collision frequency is not justified; e.g., for a highly ionized plasma, the electron density profile determines, in part, the profile of the electron-ion collision frequency. The effect of the variation of the collision frequency profile on the interaction of microwaves with inhomogeneous plasmas is studied in order to obtain an estimate of the degree of error that may result when constant collision frequency is assumed instead of a more realistic collision frequency profile. It is shown that the degree of error is of particular importance when microwave analysis is used as a plasma diagnostic. (auth)

Investigation of local optical inhomogeneities in flashlamp photolysis lasers

Energy Technology Data Exchange (ETDEWEB)

Alekhin, B V; Borovkov, V V; Lazhintsev, B V; Nor-Arenian, V A; Sukhanov, L V; Ustinenko, V A

1979-09-01

Local changes in the refractive index which occur in the active medium under flashlamp-excited photolysis laser action are examined experimentally. Under conditions of the inverse population storage and suppression of the laser action by a strong quencher, local inhomogeneities have been absent. It is shown that the stimulated emission is inhomogeneous over the active medium and features regular character with the radiation density modulation within 20-30 percent and with typical size of inhomogeneities of not greater than 0.5 mm. On the basis of experimental results and estimation, a conclusion is drawn that the local optical inhomogeneities are caused by gasdynamic displacements of the gas due to different heat evolutions in the regions of the radiation density maximum and minimum.

Bistable soliton states and switching in doubly inhomogeneously ...

Indian Academy of Sciences (India)

Dec. 2001 physics pp. 969–979. Bistable soliton states and switching in doubly inhomogeneously doped fiber couplers. AJIT KUMAR. Department of Physics, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, India. Abstract. Switching between the bistable soliton states in a doubly and inhomogeneously doped.

An effective dead oil model for two-phase flow in inhomogeneous porous media

International Nuclear Information System (INIS)

Bourgeat, A.

1988-01-01

The authors are investigating displacement process of incompressible two phase flow miscible or immiscible in heterogeneous porous media, including capillary and gravity effects. The authors' aim is to derive rigorously a Global or Effective Model which then allow, in Numerical Simulations, to disconnect the numerical mesh size from the heterogeneities size inside the reservoir itself. The reservoir is assumed to be made of uniformly (or non uniformly) periodically repeated cells. Each cell being made with different types of porous media. Then, calling ε the ratio of the cell size to the Reservoir size, we get equations depending on the parameter ε because the Porosity and Permeabilities, say Phi/sup ε/ and Κ/sup ε/ are themselves rapidly oscillating. From these ε-parametrized equations the authors derive simpler ''Effective Equations'' no more dependant on ε, called ''Homongenized Equations by the mathematical technique of Homogenization. In these new equations, which are describing Global Displacement process throughout a Globally Equivallent homogenous media where now //Phi and Κ are no more depending on the space variable or ε

Mass media influence spreading in social networks with community structure

Science.gov (United States)

Candia, Julián; Mazzitello, Karina I.

2008-07-01

We study an extension of Axelrod's model for social influence, in which cultural drift is represented as random perturbations, while mass media are introduced by means of an external field. In this scenario, we investigate how the modular structure of social networks affects the propagation of mass media messages across a society. The community structure of social networks is represented by coupled random networks, in which two random graphs are connected by intercommunity links. Considering inhomogeneous mass media fields, we study the conditions for successful message spreading and find a novel phase diagram in the multidimensional parameter space. These findings show that social modularity effects are of paramount importance for designing successful, cost-effective advertising campaigns.

Attraction and repulsion of spiral waves by inhomogeneity of conduction anisotropy--a model of spiral wave interaction with electrical remodeling of heart tissue.

Science.gov (United States)

Kuklik, Pawel; Sanders, Prashanthan; Szumowski, Lukasz; Żebrowski, Jan J

2013-01-01

Various forms of heart disease are associated with remodeling of the heart muscle, which results in a perturbation of cell-to-cell electrical coupling. These perturbations may alter the trajectory of spiral wave drift in the heart muscle. We investigate the effect of spatially extended inhomogeneity of transverse cell coupling on the spiral wave trajectory using a simple active media model. The spiral wave was either attracted or repelled from the center of inhomogeneity as a function of cell excitability and gradient of the cell coupling. High levels of excitability resulted in an attraction of the wave to the center of inhomogeneity, whereas low levels resulted in an escape and termination of the spiral wave. The spiral wave drift velocity was related to the gradient of the coupling and the initial position of the wave. In a diseased heart, a region of altered transverse coupling corresponds with local gap junction remodeling that may be responsible for stabilization-destabilization of spiral waves and hence reflect potentially important targets in the treatment of heart arrhythmias.

Diffusion in inhomogeneous polymer membranes

Science.gov (United States)

Kasargod, Sameer S.; Adib, Farhad; Neogi, P.

1995-10-01

The dual mode sorption solubility isotherms assume, and in instances Zimm-Lundberg analysis of the solubilities show, that glassy polymers are heterogeneous and that the distribution of the solute in the polymer is also inhomogeneous. Under some conditions, the heterogeneities cannot be represented as holes. A mathematical model describing diffusion in inhomogeneous polymer membranes is presented using Cahn and Hilliard's gradient theory. The fractional mass uptake is found to be proportional to the fourth root of time rather than the square root, predicted by Fickian diffusion. This type of diffusion is classified as pseudo-Fickian. The model is compared with one experimental result available. A negative value of the persistence factor is obtained and the results are interpreted.

Axi-symmetric analysis of vertically inhomogeneous elastic multilayered systems

CSIR Research Space (South Africa)

Maina, JW

2009-06-01

Full Text Available primary resilient responses are investigated by way of worked examples of hypothetical three-layer system, which was analyzed by considering homogenous and inhomogeneous material properties in each of the three layers. Effect of a inhomogeneity parameter...

Effects of Shear Fracture on In-depth Profile Modification of Weak Gels

Institute of Scientific and Technical Information of China (English)

Li Xianjie; Song Xinwang; Yue Xiang'an; Hou Jirui; Fang Lichun; Zhang Huazhen

2007-01-01

Two sand packs were filled with fine glass beads and quartz sand respectively. The characteristics of crosslinked polymer flowing through the sand packs as well as the influence of shear fracture of porous media on the in-depth profile modification of the weak gel generated from the crosslinked polymer were investigated. The results indicated that under the dynamic condition crosslinking reaction happened in both sand packs,and the weak gels in these two cases became small gel particles after water flooding. The differences were:the dynamic gelation time in the quartz sand pack was longer than that in the glass bead pack. Residual resistance factor (FRR) caused by the weak gel in the quartz sand pack was smaller than that in the glass bead pack. The weak gel became gel particles after being scoured by subsequent flood water. A weak gel with uniform apparent viscosity and sealing characteristics was generated in every part of the glass bead pack,which could not only move deeply into the sand pack but also seal the high capacity channels again when it reached the deep part. The weak gel performed in-depth profile modification in the glass bead pack,while in the quartz sand pack,the weak gel was concentrated with 100 cm from the entrance of the sand pack. When propelled by the subsequent flood water,the weak gel could move towards the deep part of the sand pack but then became tiny gel particles and could not effectively seal the high capacity channels there. The in-depth profile modification of the weak gel was very weak in the quartz sand pack. It was the shear fracture of porous media that mainly affected the properties and weakened the in-depth profile modification of the weak gel.

On the penetration of solar wind inhomogeneities into the magnetosphere

International Nuclear Information System (INIS)

Maksimov, V.P.; Senatorov, V.N.

1980-01-01

Laboratory experiments were used as a basis to study the process of interaction between solar wind inhomogeneities and the Earth's magnetosphere. The given inhomogeneity represents a lump of plasma characterized by an increased concentration of particles (nsub(e) approximately 20-30 cm -3 ), a discrete form (characteristic dimensions of the lump are inferior to the magnetosphere diameter) and the velocity v approximately 350 km/s. It is shown that there is the possibility of penetration of solar wind inhomogeneities inside the Earth's magnetosphere because of the appearance in the inhomogeneity of an electric field of transverse polarization. The said process is a possible mechanism of the formation of the magnetopshere entrance layer

Self-consistent field model for strong electrostatic correlations and inhomogeneous dielectric media.

Science.gov (United States)

Ma, Manman; Xu, Zhenli

2014-12-28

Electrostatic correlations and variable permittivity of electrolytes are essential for exploring many chemical and physical properties of interfaces in aqueous solutions. We propose a continuum electrostatic model for the treatment of these effects in the framework of the self-consistent field theory. The model incorporates a space- or field-dependent dielectric permittivity and an excluded ion-size effect for the correlation energy. This results in a self-energy modified Poisson-Nernst-Planck or Poisson-Boltzmann equation together with state equations for the self energy and the dielectric function. We show that the ionic size is of significant importance in predicting a finite self energy for an ion in an inhomogeneous medium. Asymptotic approximation is proposed for the solution of a generalized Debye-Hückel equation, which has been shown to capture the ionic correlation and dielectric self energy. Through simulating ionic distribution surrounding a macroion, the modified self-consistent field model is shown to agree with particle-based Monte Carlo simulations. Numerical results for symmetric and asymmetric electrolytes demonstrate that the model is able to predict the charge inversion at high correlation regime in the presence of multivalent interfacial ions which is beyond the mean-field theory and also show strong effect to double layer structure due to the space- or field-dependent dielectric permittivity.

Self-consistent field model for strong electrostatic correlations and inhomogeneous dielectric media

Energy Technology Data Exchange (ETDEWEB)

Ma, Manman, E-mail: mmm@sjtu.edu.cn; Xu, Zhenli, E-mail: xuzl@sjtu.edu.cn [Department of Mathematics, Institute of Natural Sciences, and MoE Key Laboratory of Scientific and Engineering Computing, Shanghai Jiao Tong University, Shanghai 200240 (China)

2014-12-28

Electrostatic correlations and variable permittivity of electrolytes are essential for exploring many chemical and physical properties of interfaces in aqueous solutions. We propose a continuum electrostatic model for the treatment of these effects in the framework of the self-consistent field theory. The model incorporates a space- or field-dependent dielectric permittivity and an excluded ion-size effect for the correlation energy. This results in a self-energy modified Poisson-Nernst-Planck or Poisson-Boltzmann equation together with state equations for the self energy and the dielectric function. We show that the ionic size is of significant importance in predicting a finite self energy for an ion in an inhomogeneous medium. Asymptotic approximation is proposed for the solution of a generalized Debye-Hückel equation, which has been shown to capture the ionic correlation and dielectric self energy. Through simulating ionic distribution surrounding a macroion, the modified self-consistent field model is shown to agree with particle-based Monte Carlo simulations. Numerical results for symmetric and asymmetric electrolytes demonstrate that the model is able to predict the charge inversion at high correlation regime in the presence of multivalent interfacial ions which is beyond the mean-field theory and also show strong effect to double layer structure due to the space- or field-dependent dielectric permittivity.

Assessment of inhomogeneous ELF magnetic field exposures

International Nuclear Information System (INIS)

Leitgeb, N.; Cech, R.; Schroettner, J.

2008-01-01

In daily life as well as at workplaces, exposures to inhomogeneous magnetic fields become very frequent. This makes easily applicable compliance assessment methods increasingly important. Reference levels have been defined linking basic restrictions to levels of homogeneous fields at worst-case exposure conditions. If reference levels are met, compliance with basic restrictions can be assumed. If not, further investigations could still prove compliance. Because of the lower induction efficiency, inhomogeneous magnetic fields such as from electric appliances could be allowed exceeding reference levels. To easily assess inhomogeneous magnetic fields, a quick and flexible multi-step assessment procedure is proposed. On the basis of simulations with numerical, anatomical human models reference factors were calculated elevating reference levels to link hot-spot values measured at source surfaces to basic limits and allowing accounting for different source distance, size, orientation and position. Compliance rules are proposed minimising assessment efforts. (authors)

A study of low-dimensional inhomogeneous systems

International Nuclear Information System (INIS)

Arredondo Leon, Yesenia

2009-01-01

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 c , which characterizes its decay at large distances. (orig.)

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.)

Scattering of a spherical pulse from a small inhomogeneity ...

Indian Academy of Sciences (India)

R. Narasimhan (Krishtel eMaging Solutions)

Perturbations in elastic constants and density distinguish a volume inhomogeneity from its homoge- neous surroundings. The equation of motion for the first order scattering is studied in the perturbed medium. The scattered waves are generated by the interaction between the primary waves and the inhomogeneity.

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...

Thermal quantum discord of spins in an inhomogeneous magnetic field

International Nuclear Information System (INIS)

Guo Jinliang; Mi Yingjuan; Zhang Jian; Song Heshan

2011-01-01

In contrast with the thermal entanglement, we study the quantum discord and classical correlation in a two-qubit Heisenberg XXZ model with an inhomogeneous magnetic field. It is shown that the effects of the external magnetic fields, including the uniform and inhomogeneous magnetic fields, on the thermal entanglement, quantum discord and classical correlation behave differently in various aspects, which depend on system temperature and model type. We can tune the inhomogeneous magnetic field to enhance the entanglement or classical correlation and meanwhile decrease the quantum discord. In addition, taking into account the inhomogeneous magnetic field, the sudden change in the behaviour of quantum discord still survives, which can detect the critical points of quantum phase transitions at finite temperature, but not for a uniform magnetic field.

Inhomogeneous superconductors

International Nuclear Information System (INIS)

Tinkham, M.

1978-01-01

The coherence length xi and penetration depth lambda set the characteristic length scales in superconductors, typically 100 to 5,000 A. A lattice of flux lines, each carrying a single quantum, can penetrate type II superconductors, i.e., those for which kappa identical with lambda/xi > 1/√2. Inhomogeneities on the scale of the flux lattice spacing are required to pin the lattice to prevent dissipative flux motion. Recent work using voids as pinning centers has demonstrated this principle, but practical materials rely on cold-work, inclusions of second phases, etc., to provide the inhomogeneity. For stability against thermal fluctuations, the superconductor should have the form of many filaments of diameter 10 to 100 μm imbedded in a highly conductive normal metal matrix. Such wire is made by drawing down billets of copper containing rods of the superconductor. An alternative approach is the metallurgical one of Tsuei, which leads to thousands of superconducting filamentary segments in a copper matrix. The superconducting proximity effect causes the whole material to superconduct at low current densities. At high current densities, the range of the proximity effect is reduced so that the effective superconducting volume fraction falls below the percolation threshold, and a finite resistance arises from the copper matrix. But, because of the extremely elongated filaments, this resistance is orders of magnitude lower than that of the normal wire, and low enough to permit the possibility of technical applications

Effect of Inhomogeneity correction for lung volume model in TPS

International Nuclear Information System (INIS)

Chung, Se Young; Lee, Sang Rok; Kim, Young Bum; Kwon, Young Ho

2004-01-01

The phantom that includes high density materials such as steel was custom-made to fix lung and bone in order to evaluation inhomogeneity correction at the time of conducting radiation therapy to treat lung cancer. Using this, values resulting from the inhomogeneous correction algorithm are compared on the 2 and 3 dimensional radiation therapy planning systems. Moreover, change in dose calculation was evaluated according to inhomogeneous by comparing with the actual measurement. As for the image acquisition, inhomogeneous correction phantom(Pig's vertebra, steel(8.21 g/cm 3 ), cork(0.23 g/cm 3 )) that was custom-made and the CT(Volume zoom, Siemens, Germany) were used. As for the radiation therapy planning system, Marks Plan(2D) and XiO(CMS, USA, 3D) were used. To compare with the measurement value, linear accelerator(CL/1800, Varian, USA) and ion chamber were used. Image, obtained from the CT was used to obtain point dose and dose distribution from the region of interest (ROI) while on the radiation therapy planning device. After measurement was conducted under the same conditions, value on the treatment planning device and measured value were subjected to comparison and analysis. And difference between the resulting for the evaluation on the use (or non-use) of inhomogeneity correction algorithm, and diverse inhomogeneity correction algorithm that is included in the radiation therapy planning device was compared as well. As result of comparing the results of measurement value on the region of interest within the inhomogeneity correction phantom and the value that resulted from the homogeneous and inhomogeneous correction, gained from the therapy planning device, margin of error of the measurement value and inhomogeneous correction value at the location 1 of the lung showed 0.8% on 2D and 0.5% on 3D. Margin of error of the measurement value and inhomogeneous correction value at the location 1 of the steel showed 12% on 2D and 5% on 3D, however, it is possible to

Critical-temperature inhomogeneities and resistivity rounding in copper oxide superconductors

International Nuclear Information System (INIS)

Maza, J.; Vidal, F.

1991-01-01

By using effective-medium approaches, we obtain the onset of the electrical-resistivity rounding, above the normal-superconducting transition, associated with inhomogeneities of the mean-field critical temperature T c0 at scales larger than the superconducting correlation length. These results are compared with available data in single-crystal and single-phase (to within 4%) polycrystalline YBa 2 Cu 3 O 7-δ samples. This comparison shows that the measured resistivity rounding cannot be explained by these types of local T c0 inhomogeneities. Complementarily, our calculations allow us to check some proposals on T c0 inhomogeneities associated with local sample strains or oxygen-content variations. The interplay between T c0 inhomogeneities and superconducting order-parameter fluctuations (SCOPF) leads to the conclusion that in the mean-field-like region (MFR) above the superconducting transition, the T c0 inhomogeneity contribution to the measured resistivity rounding in high-quality (single-phase) cuprate oxide superconductors is negligible. In contrast, our analysis confirms that in the MFR these effects may be explained quantitatively on the grounds of the Lawrence-Doniach theory for SCOPF

Impact of cosmic inhomogeneities on SNe observations

Science.gov (United States)

Kainulainen, Kimmo; Marra, Valerio

2010-06-01

We study the impact of cosmic inhomogeneities on the interpretation of SNe observations. We build an inhomogeneous universe model that can confront supernova data and yet is reasonably well compatible with the Copernican Principle. Our model combines a relatively small local void, that gives apparent acceleration at low redshifts, with a meatball model that gives sizeable lensing (dimming) at high redshifts. Together these two elements, which focus on different effects of voids on the data, allow the model to mimic the concordance model.

Inhomogeneous Markov Models for Describing Driving Patterns

DEFF Research Database (Denmark)

Iversen, Emil Banning; Møller, Jan K.; Morales, Juan Miguel

2017-01-01

. Specifically, an inhomogeneous Markov model that captures the diurnal variation in the use of a vehicle is presented. The model is defined by the time-varying probabilities of starting and ending a trip, and is justified due to the uncertainty associated with the use of the vehicle. The model is fitted to data...... collected from the actual utilization of a vehicle. Inhomogeneous Markov models imply a large number of parameters. The number of parameters in the proposed model is reduced using B-splines....

Inhomogeneous Markov Models for Describing Driving Patterns

DEFF Research Database (Denmark)

Iversen, Jan Emil Banning; Møller, Jan Kloppenborg; Morales González, Juan Miguel

. Specically, an inhomogeneous Markov model that captures the diurnal variation in the use of a vehicle is presented. The model is dened by the time-varying probabilities of starting and ending a trip and is justied due to the uncertainty associated with the use of the vehicle. The model is tted to data...... collected from the actual utilization of a vehicle. Inhomogeneous Markov models imply a large number of parameters. The number of parameters in the proposed model is reduced using B-splines....

A new approach to the existence of weak solutions of the steady Navier-Stokes system with inhomogeneous boundary data in domains with noncompact boundaries

Czech Academy of Sciences Publication Activity Database

Neustupa, Jiří

2010-01-01

Roč. 198, č. 1 (2010), 331-348 ISSN 0003-9527 R&D Projects: GA ČR GA201/08/0012 Institutional research plan: CEZ:AV0Z10190503 Keywords : Navier-Stokes equations * inhomogeneous boundary data Subject RIV: BA - General Mathematics Impact factor: 2.277, year: 2010 http://link.springer.com/article/10.1007%2Fs00205-010-0297-7

A computational study of syngas auto-ignition characteristics at high-pressure and low-temperature conditions with thermal inhomogeneities

KAUST Repository

Pal, Pinaki

2015-07-30

A computational study was conducted to investigate the characteristics of auto-ignition in a syngas mixture at high-pressure and low-temperature conditions in the presence of thermal inhomogeneities. Highly resolved one-dimensional numerical simulations incorporating detailed chemistry and transport were performed. The temperature inhomogeneities were represented by a global sinusoidal temperature profile and a local Gaussian temperature spike (hot spot). Reaction front speed and front Damköhler number analyses were employed to characterise the propagating ignition front. In the presence of a global temperature gradient, the ignition behaviour shifted from spontaneous propagation (strong) to deflagrative (weak), as the initial mean temperature of the reactant mixture was lowered. A predictive Zel\\'dovich–Sankaran criterion to determine the transition from strong to weak ignition was validated for different parametric sets. At sufficiently low temperatures, the strong ignition regime was recovered due to faster passive scalar dissipation of the imposed thermal fluctuations relative to the reaction timescale, which was quantified by the mixing Damköhler number. In the presence of local hot spots, only deflagrative fronts were observed. However, the fraction of the reactant mixture consumed by the propagating front was found to increase as the initial mean temperature was lowered, thereby leading to more enhanced compression-heating of the end-gas. Passive scalar mixing was not found to be important for the hot spot cases considered. The parametric study confirmed that the relative magnitude of the Sankaran number translates accurately to the quantitative strength of the deflagration front in the overall ignition advancement. © 2015 Taylor & Francis

A computational study of syngas auto-ignition characteristics at high-pressure and low-temperature conditions with thermal inhomogeneities

Science.gov (United States)

Pal, Pinaki; Mansfield, Andrew B.; Arias, Paul G.; Wooldridge, Margaret S.; Im, Hong G.

2015-09-01

A computational study was conducted to investigate the characteristics of auto-ignition in a syngas mixture at high-pressure and low-temperature conditions in the presence of thermal inhomogeneities. Highly resolved one-dimensional numerical simulations incorporating detailed chemistry and transport were performed. The temperature inhomogeneities were represented by a global sinusoidal temperature profile and a local Gaussian temperature spike (hot spot). Reaction front speed and front Damköhler number analyses were employed to characterise the propagating ignition front. In the presence of a global temperature gradient, the ignition behaviour shifted from spontaneous propagation (strong) to deflagrative (weak), as the initial mean temperature of the reactant mixture was lowered. A predictive Zel'dovich-Sankaran criterion to determine the transition from strong to weak ignition was validated for different parametric sets. At sufficiently low temperatures, the strong ignition regime was recovered due to faster passive scalar dissipation of the imposed thermal fluctuations relative to the reaction timescale, which was quantified by the mixing Damköhler number. In the presence of local hot spots, only deflagrative fronts were observed. However, the fraction of the reactant mixture consumed by the propagating front was found to increase as the initial mean temperature was lowered, thereby leading to more enhanced compression-heating of the end-gas. Passive scalar mixing was not found to be important for the hot spot cases considered. The parametric study confirmed that the relative magnitude of the Sankaran number translates accurately to the quantitative strength of the deflagration front in the overall ignition advancement.

Inhomogeneity of epidemic spreading with entropy-based infected clusters.

Science.gov (United States)

Wen-Jie, Zhou; Xing-Yuan, Wang

2013-12-01

Considering the difference in the sizes of the infected clusters in the dynamic complex networks, the normalized entropy based on infected clusters (δ*) is proposed to characterize the inhomogeneity of epidemic spreading. δ* gives information on the variability of the infected clusters in the system. We investigate the variation in the inhomogeneity of the distribution of the epidemic with the absolute velocity v of moving agent, the infection density ρ, and the interaction radius r. By comparing δ* in the dynamic networks with δH* in homogeneous mode, the simulation experiments show that the inhomogeneity of epidemic spreading becomes smaller with the increase of v, ρ, r.

Dependence of inhomogeneous vibrational linewidth broadening on attractive forces from local liquid number densities

International Nuclear Information System (INIS)

George, S.M.; Harris, C.B.

1982-01-01

The dependence of inhomogeneous vibrational linewidth broadening on attractive forces form slowly varying local liquid number densities is examined. The recently developed Schweizer--Chandler theory of vibrational dephasing is used to compute absolute inhomogeneous broadening linewidths. The computed linewidths are compared to measured inhomogeneous broadening linewidths determined using picosecond vibrational dephasing experiments. There is a similarity between correlations of the Schweizer--Chandler and George--Auweter--Harris predicted inhomogeneous broadening linewidths and the measured inhomogeneous broadening linewidths. For the methyl stretches under investigation, this correspondence suggests that the width of the number density distribution in the liquid determines the relative inhomogeneous broadening magnitudes

Elastic fracture in driven media

International Nuclear Information System (INIS)

Lung Chiwei; Wang Shenggang; Long Qiyi

1999-08-01

Fracture as one of the mechanical properties of materials is structurally dependent. Defects, defect assemblies, grain boundaries and sub-boundaries materials, modify the local stress intensity factors intensively. Brittle fracture prefers to confine to the grain boundary where the specific surface energy is lower than that in the grain. Again, transgranular cracking may occur on the crystal cleavage plane or planes where the local toughness is lowered by dislocation interaction and motion. This paper shows the complexity of the fractal dimension or roughness index of fractured surfaces in materials with metallographic structures or in inhomogeneous media. (author)

General multimode polarization splitter design in uniaxial media

Science.gov (United States)

Teixeira, Poliane A.; Silva, Daniely G.; Gabrielli, Lucas H.; Spadoti, Danilo H.; Junqueira, Mateus A. F. C.

2018-03-01

Quasiconformal transformation optics is used to design two-dimensional polarization beam splitters. The resulting media present inhomogeneous uniaxial permittivity and nonmagnetic response. The compact devices are theoretically designed and investigated for symmetrical and asymmetrical geometries, with footprint of 64 and 110 μm2, respectively. The polarization splitter performance is evaluated for the fundamental mode and third mode, exhibiting an insertion loss closer to 0 dB and extinction ratio above 40 dB over a broad wavelength range.

Random field assessment of nanoscopic inhomogeneity of bone

OpenAIRE

Dong, X. Neil; Luo, Qing; Sparkman, Daniel M.; Millwater, Harry R.; Wang, Xiaodu

2010-01-01

Bone quality is significantly correlated with the inhomogeneous distribution of material and ultrastructural properties (e.g., modulus and mineralization) of the tissue. Current techniques for quantifying inhomogeneity consist of descriptive statistics such as mean, standard deviation and coefficient of variation. However, these parameters do not describe the spatial variations of bone properties. The objective of this study was to develop a novel statistical method to characterize and quanti...

Observable relations in an inhomogeneous self-similar cosmology

International Nuclear Information System (INIS)

Wesson, P.S.

1979-01-01

An exact self-similar solution is taken in general relativity as a model for an inhomogeneous cosmology. The self-similarity property means (conceptually) that the model is scale-free and (mathematically) that its essential parameters are functions of only one dimensionless variable zeta (equivalentct/R, where R and t are distance and time coordinates and c is the velocity of light). It begins inhomogeneous (zeta=0 or t=0), and tends to a homogeneous Einstein--de Sitter type state as zeta (or t) →infinity. Such a model can be used (a) for evaluating the observational effects of a clumpy universe; (b) for studying astrophysical processes such as galaxy formation and the growth and decay of inhomogeneities in initially clumpy cosmologies; and (c) as a relativistic basis for cosmological models with extended clustering of the de Vaucouleurs and Peebles types. The model has two adjustable parameters, namely, the observer's coordinate zeta 0 and a constant α/sub s/ that fixes the effect of the inhomogeneity. Expressions are obtained for the redshift, Hubble parameter, deceleration parameter, magnitude-redshift relation, and (number density of objects) --redshift relation. Expected anisotropies in the 3 K microwave background are also examined. There is no conflict with observation if zeta 0 /α/sub s/> or approx. =10, and four tests of the model are suggested that can be used to further determine the acceptability of inhomogeneous cosmologies of this type. The ratio α/sub s//zeta 0 on presently available data is α/sub s//zeta 0 < or approx. =10% and this, loosely speaking, means that the universe at the present epoch is globally homogeneous to within about 10%

QCD under extreme conditions. Inhomogeneous condensation

Energy Technology Data Exchange (ETDEWEB)

Heinz, Achim

2014-10-15

Almost 40 years after the first publication on the phase diagram of quantum chromodynamics (QCD) big progress has been made but many questions are still open. This work covers several aspects of low-energy QCD and introduces advanced methods to calculate selected parts of the QCD phase diagram. Spontaneous chiral symmetry breaking as well as its restoration is a major aspect of QCD. Two effective models, the Nambu-Jona-Lasinio (NJL) model and the linear σ-model, are widely used to describe the QCD chiral phase transition. We study the large-N{sub c} behavior of the critical temperature T{sub c} for chiral symmetry restoration in the framework of both models. While in the NJL model T{sub c} is independent of N{sub c} (and in agreement with the expected QCD scaling), the scaling behavior in the linear σ-model reads T{sub c} ∝ N{sup 1/2}{sub c}. However, this mismatch can be corrected: phenomenologically motivated temperature-dependent parameters or the extension with the Polyakov-loop renders the scaling in the linear σ-model compatible with the QCD scaling. The requirement that the chiral condensate which is the order parameter of the chiral symmetry is constant in space is too restrictive. Recent studies on inhomogeneous chiral condensation in cold, dense quark matter suggest a rich crystalline structure. These studies feature models with quark degrees of freedom. In this thesis we investigate the formation of the chiral density wave (CDW) in the framework of the so-called extended linear sigma model (eLSM) at high densities and zero temperature. The eLSM is a modern development of the linear σ-model which contains scalar, pseudoscalar, vector, as well as axial-vector mesons, and in addition, a light tetraquark state. The nucleon and its chiral partner are introduced as parity doublets in the mirror assignment. The model describes successfully the vacuum phenomenology and nuclear matter ground-state properties. As a result we find that an inhomogeneous phase

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 inhomogeneous Suslov problem

Energy Technology Data Exchange (ETDEWEB)

García-Naranjo, Luis C., E-mail: luis@mym.iimas.unam.mx [Departamento de Matemáticas y Mecánica, IIMAS-UNAM, Apdo Postal 20-726, Mexico City 01000 (Mexico); Maciejewski, Andrzej J., E-mail: andrzej.j.maciejewski@gmail.com [J. Kepler Institute of Astronomy, University of Zielona Góra, Licealna 9, 65-417 Zielona Góra (Poland); Marrero, Juan C., E-mail: jcmarrero@ull.edu.es [ULL-CSIC, Geometría Diferencial y Mecánica Geométrica, Departamento de Matemática Fundamental, Facultad de Matemáticas, Universidad de la Laguna, La Laguna, Tenerife, Canary Islands (Spain); Przybylska, Maria, E-mail: M.Przybylska@if.uz.zgora.pl [Institute of Physics, University of Zielona Góra, Licealna 9, 65-417 Zielona Góra (Poland)

2014-06-27

We consider the Suslov problem of nonholonomic rigid body motion with inhomogeneous constraints. We show that if the direction along which the Suslov constraint is enforced is perpendicular to a principal axis of inertia of the body, then the reduced equations are integrable and, in the generic case, possess a smooth invariant measure. Interestingly, in this generic case, the first integral that permits integration is transcendental and the density of the invariant measure depends on the angular velocities. We also study the Painlevé property of the solutions. - Highlights: • We consider the Suslov problem of nonholonomic rigid body motion with inhomogeneous constraints. • We study the problem in detail for a particular choice of the parameters that has a clear physical interpretation. • We show that the equations of motion possess an invariant measure whose density depends on the velocity variables. • We show that the reduced system is integrable due to the existence of a transcendental first integral. • We study the Painlevé property of the solutions.

Two-step estimation procedures for inhomogeneous shot-noise Cox processes

DEFF Research Database (Denmark)

Prokesová, Michaela; Dvorák, Jirí; Jensen, Eva B. Vedel

In the present paper we develop several two-step estimation procedures for inhomogeneous shot-noise Cox processes. The intensity function is parametrized by the inhomogeneity parameters while the pair-correlation function is parametrized by the interaction parameters. The suggested procedures...

A nonquasiclassical description of inhomogeneous superconductors

International Nuclear Information System (INIS)

Zaikin, A.D.; Panyukov, S.V.

1988-01-01

Exact microscopic equations are derived that make it possible to describe inhomogeneous superconductors when the quasi-classical approach is not suitable. These equations are simpler than the Gorkov equations. The authors generalize the derived equations for describing the nonequilibrium states of inhomogeneous superconductors. It is demonstrated that the derived equations (including the case of a nonequilibrium quasi particle distribution function) may be written in the form of linear differential equations for the simultaneous wave function μ, ν. The quasi-classical limit of such equations is examined. Effective boundary conditions are derived for the μ, ν functions that allow description of superconductors with a sharp change in parameters within the scope of the quasi-classical approach

Does sexy media promote teen sex? A meta-analytic and methodological review

DEFF Research Database (Denmark)

Ferguson, Chris; Nielsen, Rune Kristian Lundedal; Markey, Patrick

2016-01-01

Parents and policy makers are often concerned that sexy media (media depicting or discussing sexual encounters) may promote sexual behavior in young viewers. There has been some debate among scholars regarding whether such media promote sexual behaviors. It remains unclear to what extent sexy media...... is a risk factor for increased sexual behavior among youth. The current study employed a meta-analysis of 22 correlational and longitudinal studies of sexy media effects on teen sexual behavior (n = 22,172). Moderator analyses examined methodological and science culture issues such as citation bias. Results...... indicated the presence only of very weak effects. General media use did not correlate with sexual behaviors (r = 0.005), and sexy media use correlated only weakly with sexual behaviors (r = 0.082) once other factors had been controlled. Higher effects were seen for studies with citation bias, and lower...

Inhomogeneities and the Modeling of Radio Supernovae

Energy Technology Data Exchange (ETDEWEB)

Björnsson, C.-I.; Keshavarzi, S. T., E-mail: bjornsson@astro.su.se [Department of Astronomy, AlbaNova University Center, Stockholm University, SE–106 91 Stockholm (Sweden)

2017-05-20

Observations of radio supernovae (SNe) often exhibit characteristics not readily accounted for by a homogeneous, spherically symmetric synchrotron model; e.g., flat-topped spectra/light curves. It is shown that many of these deviations from the standard model can be attributed to an inhomogeneous source structure. When inhomogeneities are present, the deduced radius of the source and, hence, the shock velocity, is sensitive to the details of the modeling. As the inhomogeneities are likely to result from the same mechanism that amplify the magnetic field, a comparison between observations and the detailed numerical simulations now under way may prove mutually beneficial. It is argued that the radio emission in Type Ib/c SNe has a small volume filling factor and comes from a narrow region associated with the forward shock, while the radio emission region in SN 1993J (Type IIb) is determined by the extent of the Rayleigh–Taylor instability emanating from the contact discontinuity. Attention is also drawn to the similarities between radio SNe and the structural properties of SN remnants.

Numerical study on general dispersion relation of anisotropic and weakly relativistic plasma

International Nuclear Information System (INIS)

Ke Fujiu; Chen Yanping

1987-01-01

The key problem in heating and instability studies in plasma physics is to obtain dispersive equation and its solution. This paper presents the general dispersive equation and corresponding procedure for electromagnetic wave which nearly poloidally impinges on anisotropic, weakly relativistic Maxwellian plasma with inhomogeneous density in nonuniform magnetic field (such as plasma in TOKAMAK). The double index function F ij , significant in plasma physics, was expanded as single index function F 1 , and then the values were calculated by means of dispersive function. It was also pointed out that the severe error would be involved in the calculation of F ij from recurrence relation of F 11

Distinguishing different types of inhomogeneity in Neyman-Scott point processes

Czech Academy of Sciences Publication Activity Database

Mrkvička, Tomáš

2014-01-01

Roč. 16, č. 2 (2014), s. 385-395 ISSN 1387-5841 Institutional support: RVO:60077344 Keywords : clustering * growing clusters * inhomogeneous cluster centers * inhomogeneous point process * location dependent scaling * Neyman-Scott point process Subject RIV: BA - General Mathematics Impact factor: 0.913, year: 2014

Collapse arresting in an inhomogeneous two-dimensional nonlinear Schrodinger model

DEFF Research Database (Denmark)

Schjødt-Eriksen, Jens; Gaididei, Yuri Borisovich; Christiansen, Peter Leth

2001-01-01

Collapse of (2 + 1)-dimensional beams in the inhomogeneous two-dimensional cubic nonlinear Schrodinger equation is analyzed numerically and analytically. It is shown that in the vicinity of a narrow attractive inhomogeneity, the collapse of beams that in a homogeneous medium would collapse may...

Shock Wave Dynamics in Weakly Ionized Plasmas

Science.gov (United States)

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.

Quasiadiabatic modes from viscous inhomogeneities

CERN Document Server

Giovannini, Massimo

2016-04-20

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...

Effect of corneal inhomogeneity on the mechanical behavior of the eye

Science.gov (United States)

Stein, A. A.; Moiseeva, I. N.

2018-05-01

The effect of spatial inhomogeneity of the effective cornea stiffness distribution on the mechanical properties of the eye is investigated on the basis of the two-component model of the eyeball, in which the cornea is represented by a momentless deformable, linearly elastic surface and the scleral region by an elastic element that responds to changes in intraocular pressure by changes in volume. The approach used makes it possible to consider within the same model both the natural corneal inhomogeneity and mechanical consequences of local cornea weakening owing to surgical procedures. The dependences on changes in intraocular pressure of parameters that characterize deformation properties of both the cornea (apex displacement) and the eyeball as a whole (change in intraocular volume) are obtained. For moderate inhomogeneity they differ from the same dependences for the homogenous cornea with effective stiffness equal to the average value for the corresponding inhomogeneous distribution only slightly. However, if the effective stiffness amplitude is very high, corneal inhomogeneity discernibly affects the integral response of the cornea and the eyeball as a whole to changes in pressure. The effect of inhomogeneity on the data of tonometry also mainly depends on the average effective corneal stiffness. The difference between the tonometric and true pressures increases with surgical cornea weakening in the apical region for both Schiøtz and Maklakoff tonometers.

The inhomogeneous MUSIG model for the simulation of polydispersed flows

International Nuclear Information System (INIS)

Krepper, Eckhard; Lucas, Dirk; Frank, Thomas; Prasser, Horst-Michael; Zwart, Phil J.

2008-01-01

A generalized inhomogeneous multiple size group (MUSIG) model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into the CFD code CFX. The model enables the subdivision of the dispersed phase into a number of size groups regarding the mass balance as well as regarding the momentum balance. In this work, the special case of polydispersed bubbly flow is considered. By simulating such flows, the mass exchanged between bubble size classes by bubble coalescence and bubble fragmentation, as well as the momentum transfer between the bubbles and the surrounding liquid due to bubble size dependent interfacial forces have to be considered. Particularly the lift force has been proven to play an important role in establishing a certain bubble size distribution dependent flow regime. In a previous study [Krepper, E., Lucas, D., Prasser, H.-M., 2005. On the modeling of bubbly flow in vertical pipes. Nucl. Eng. Des. 235, 597-611] the application of such effects were considered and justified and a general outline of such a model concept was given. In this paper the model and its validation for several vertical pipe flow situations is presented. The experimental data were obtained from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The wire-mesh technology measuring local gas volume fractions, bubble size distributions and velocities of gas and liquid phases were employed. The inhomogeneous MUSIG model approach was shown as capable of describing bubbly flows with higher gas content. Particularly the separation phenomenon of small and large bubbles is well described. This separation has been proven as a key phenomenon in the establishment of the corresponding flow regime. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble fragmentation, which must be further investigated

Inflation and inhomogeneities: a hybrid quantization

International Nuclear Information System (INIS)

Olmedo, J; Fernández-Méndez, M; Mena Marugán, G A

2012-01-01

We provide a complete quantization of a homogeneous and isotropic spacetime with positive spatial curvature coupled to a massive scalar field in the framework of Loop Quantum Cosmology. The physical Hilbert space is constructed out of the space of initial data on the minimum volume section. By means of a perturbative treatment we introduce inhomogeneities and thereafter we adopt a hybrid quantum approach, in which these inhomogeneous degrees of freedom are described by a standard Fock quantization. For the considered case of compact spatial topology, the requirements of: i) invariance of the vacuum state under the spatial isometries, and ii) unitary implementation of the quantum dynamics, pick up a privileged set of canonical fields and a unique Fock representation (up to unitary equivalence).

Nonlinear electrostatic ion cyclotron waves in an rf-plugged inhomogeneous plasma slab

International Nuclear Information System (INIS)

Ikemura, Tsutomu.

1977-01-01

A theory based on the fluid and perturbation theories is developed to analytically study a nonlinear electrostatic ion cyclotron wave excited in an rf-plugged inhomogeneous plasma slab by applying a pair of external potentials phi sub(ext)(x,z) = +-PHI 0 cos ω 0 t.exp(-z 2 /2h 2 ) at its boundaries x = +-L. Here, B 0 is applied along the z-axis. The potential forms of the fundamental and the nonlinear second harmonic are found as functions of x, z and t provided the field-free densities vary as exp(-x 2 /2d 2 )(d 2 /h 2 0 ) created by the fundamental potential can approximately be regarded as a dipole field, provided that /1-μ/ 0 2 -ω sub(cl)sup(2))m sub(i)d 2 /(γ sub(i)T sub(i)+Z γ sub(e)T sub(e)). Under the stricter condition μ asymptotically equals 1, a dipole-like electric field can also be excited in the entire region for the case of high density and weak nonlinearity. It is shown that the assumption ω 0 -1 √ γ sub(e)T sub(e)/m sub(e) can lead to the Boltzmann relation for the electron fluid even in inhomogeneous plasmas. Moreover, the density depletion delta N sub(i) obtained here contains a new considerable term proportional to /phi/ 2 , in addition to the usual term proportional to -/delta phi/delta x/ 2 which originates from the ponderomotive force. (auth.)

Influence of magnetic-field inhomogeneity on nonlinear magneto-optical resonances

International Nuclear Information System (INIS)

Pustelny, S.; Jackson Kimball, D. F.; Rochester, S. M.; Yashchuk, V. V.; Budker, D.

2006-01-01

In this work, a sensitivity of the rate of relaxation of ground-state atomic coherences to magnetic-field inhomogeneities is studied. Such coherences give rise to many interesting phenomena in light-atom interactions, and their lifetimes are a limiting factor for achieving better sensitivity, resolution, or contrast in many applications. For atoms contained in a vapor cell, some of the coherence-relaxation mechanisms are related to magnetic-field inhomogeneities. We present a simple model describing relaxation due to such inhomogeneities in a buffer-gas-free antirelaxation-coated cell. A relation is given between relaxation rate and magnetic-field inhomogeneities including the dependence on cell size and atomic species. Experimental results, which confirm predictions of the model, are presented. Different regimes, in which the relaxation rate is equally sensitive to the gradients in any direction and in which it is insensitive to gradients transverse to the bias magnetic field, are predicted and demonstrated experimentally

Radio frequency conductivity of plasma in inhomogeneous magnetic field

International Nuclear Information System (INIS)

Itoh, Sanae; Nishikawa, Kyoji; Fukuyama, Atsushi; Itoh, Kimitaka.

1985-01-01

Nonlocal conductivity tensor is obtained to study the kinetic effects on propagation and absorption of radio frequency (rf) waves in dispersive plasmas. Generalized linear propagator in the presence of the inhomogeneity of magnetic field strength along the field line is calculated. The influence of the inhomogeneity to the rf wave-energy deposition is found to be appreciable. Application to toroidal plasmas is shown. (author)

Density gradient instabilities in a neutron inhomogeneous guiding-centre plasma

International Nuclear Information System (INIS)

Shoucri, M.M.; Gagne, R.R.J.

1977-01-01

The guiding-centre equations for a plasma of cold ions and thermal electrons admit neutral and non-neutral inhomogeneous equilibrium solutions, and the linear stability of these solutions has been recently investigated numerically by Shoucri and Knorr (1975). With arbitrary density profiles, numerical techniques appear to be the only practical way to study the linear stability of the inhomogeneous equilibrium solutions for the guiding centre plasma. However, analytical methods can be applied to some simple types of density profiles. The purpose of the present note is to present some analytical results on the linear instabilities of an inhomogeneous neutral guiding centre plasma. (U.K.)

Inhomogeneous neutrino degeneracy and big bang nucleosynthesis

International Nuclear Information System (INIS)

Whitmire, Scott E.; Scherrer, Robert J.

2000-01-01

We examine big bang nucleosynthesis (BBN) in the case of inhomogeneous neutrino degeneracy, in the limit where the fluctuations are sufficiently small on large length scales that the present-day element abundances are homogeneous. We consider two representative cases: degeneracy of the electron neutrino alone and equal chemical potentials for all three neutrinos. We use a linear programming method to constrain an arbitrary distribution of the chemical potentials. For the current set of (highly restrictive) limits on the primordial element abundances, homogeneous neutrino degeneracy barely changes the allowed range of the baryon-to-photon ratio η. Inhomogeneous degeneracy allows for little change in the lower bound on η, but the upper bound in this case can be as large as η=1.1x10 -8 (only ν e degeneracy) or η=1.0x10 -9 (equal degeneracies for all three neutrinos). For the case of inhomogeneous neutrino degeneracy, we show that there is no BBN upper bound on the neutrino energy density, which is bounded in this case only by limits from structure formation and the cosmic microwave background. (c) 2000 The American Physical Society

Protest: Critical Lessons of Using Digital Media for Social Change

Science.gov (United States)

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…

Cosmic acceleration driven by mirage inhomogeneities

Energy Technology Data Exchange (ETDEWEB)

Galfard, Christophe [DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce road, Cambridge CB3 0WA (United Kingdom); Germani, Cristiano [DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce road, Cambridge CB3 0WA (United Kingdom); Kehagias, Alex [Physics Division, National Technical University of Athens, 15780 Zografou Campus, Athens (Greece)

2006-03-21

A cosmological model based on an inhomogeneous D3-brane moving in an AdS{sub 5} x S{sub 5} bulk is introduced. Although there are no special points in the bulk, the brane universe has a centre and is isotropic around it. The model has an accelerating expansion and its effective cosmological constant is inversely proportional to the distance from the centre, giving a possible geometrical origin for the smallness of a present-day cosmological constant. Besides, if our model is considered as an alternative of early-time acceleration, it is shown that the early stage accelerating phase ends in a dust-dominated FRW homogeneous universe. Mirage-driven acceleration thus provides a dark matter component for the brane universe final state. We finally show that the model fulfils the current constraints on inhomogeneities.

Nonlocality and optics of inhomogeneous systems : The role of quantum induction

NARCIS (Netherlands)

Wijers, C.M.J.; de Boeij, P.L.

2002-01-01

Nonlocal interactions play a prominent role in the optics of inhomogeneous systems. Classical discrete dipole descriptions take into account only electro-magnetic nonlocality. This is insufficient to describe correctly the inhomogeneous optical response (e.g., reflectance anisotropy) for covalently

Transfer equations for spectral densities of inhomogeneous MHD turbulence

International Nuclear Information System (INIS)

Tu, C.-Y.; Marsch, E.

1990-01-01

On the basis of the dynamic equations governing the evolution of magnetohydrodynamic fluctuations expressed in terms of Elsaesser variables and of their correlation functions derived by Marsch and Tu, a new set of equations is presented describing the evolutions of the energy spectrum e ± and of the residual energy spectra e R and e S of MHD turbulence in an inhomogeneous magnetofluid. The nonlinearities associated with triple correlations in these equations are analysed in detail and evaluated approximately. The resulting energy-transfer functions across wavenumber space are discussed. For e ± they are shown to be approximately energy-conserving if the gradients of the flow speed and density are weak. New cascading functions are heuristically determined by an appropriate dimensional analysis and plausible physical arguments, following the standard phenomenology of fluid turbulence. However, for e R the triple correlations do not correspond to an 'energy' conserving process, but also represent a nonlinear source term for e R . If this source term can be neglected, the spectrum equations are found to be closed. The problem of dealing with the nonlinear source terms remains to be solved in future investigations. (author)

Corrections to the apparent value of the cosmological constant due to local inhomogeneities

International Nuclear Information System (INIS)

Romano, Antonio Enea; Chen, Pisin

2011-01-01

Supernovae observations strongly support the presence of a cosmological constant, but its value, which we will call apparent, is normally determined assuming that the Universe can be accurately described by a homogeneous model. Even in the presence of a cosmological constant we cannot exclude nevertheless the presence of a small local inhomogeneity which could affect the apparent value of the cosmological constant. Neglecting the presence of the inhomogeneity can in fact introduce a systematic misinterpretation of cosmological data, leading to the distinction between an apparent and true value of the cosmological constant. We establish the theoretical framework to calculate the corrections to the apparent value of the cosmological constant by modeling the local inhomogeneity with a ΛLTB solution. Our assumption to be at the center of a spherically symmetric inhomogeneous matter distribution correspond to effectively calculate the monopole contribution of the large scale inhomogeneities surrounding us, which we expect to be the dominant one, because of other observations supporting a high level of isotropy of the Universe around us. By performing a local Taylor expansion we analyze the number of independent degrees of freedom which determine the local shape of the inhomogeneity, and consider the issue of central smoothness, showing how the same correction can correspond to different inhomogeneity profiles. Contrary to previous attempts to fit data using large void models our approach is quite general. The correction to the apparent value of the cosmological constant is in fact present for local inhomogeneities of any size, and should always be taken appropriately into account both theoretically and observationally

Inhomogeneous chiral symmetry breaking in isospin-asymmetric strong-interaction matter

Energy Technology Data Exchange (ETDEWEB)

Nowakowski, Daniel

2017-07-01

In this thesis we investigate the effects of an isospin asymmetry on inhomogeneous chiral symmetry breaking phases, which are characterized by spatially modulated quarkantiquark condensates. In order to determine the relevance of such phases for the phase diagram of strong-interaction matter, a two-flavor Nambu-Jona-Lasinio model is used to study the properties of the ground state of the system. Confirming the presence of inhomogeneous chiral symmetry breaking in isospin-asymmetric matter for a simple Chiral Density Wave, we generalize the modulation of the quark-antiquark pairs to more complicated shapes and study the effects of different degrees of flavor-mixing on the inhomogeneous phase at non-zero isospin asymmetry. Then, we investigate the occurrence of crystalline chiral symmetry breaking phases in charge-neutral matter, from which we determine the influence of crystalline phases on a quark star by calculating mass-radius sequences. Finally, our model is extended through color-superconducting phases and we study the interplay of these phases with inhomogeneous chiral-symmetry breaking at non-vanishing isospin asymmetry, before we discuss our findings.

Dose inhomogeneities at various levels of biological organization

International Nuclear Information System (INIS)

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 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

Spectral properties of waves in superlattices with 2D and 3D inhomogeneities

International Nuclear Information System (INIS)

Ignatchenko, V. A.; Tsikalov, D. S.

2011-01-01

We investigate the dynamic susceptibility and one-dimensional density of states in an initially sinusoidal superlattice containing simultaneously 2D phase inhomogeneities simulating correlated rough-nesses of superlattice interfaces and 3D amplitude inhomogeneities of the superlattice layer materials. The analytic expression for the averaged Green’s function of the sinusoidal superlattice with two phase inhomogeneities is derived in the Bourret approximation. It is shown that the effect of increasing asymmetry in the peak heights of dynamic susceptibility at the Brillouin zone boundary of the superlattice, which was discovered earlier [15] upon an increase in root-mean-square (rms) fluctuations, also takes place upon an increase in the correlation wavenumber of inhomogeneities. However, the peaks in this case also become closer, and the width and depth of the gap in the density of states decrease thereby. It is shown that the enhancement of rms fluctuations of 3D amplitude inhomogeneities in a superlattice containing 2D phase inhomogeneities suppresses the effect of dynamic susceptibility asymmetry and leads to a slight broadening of the gap in the density of states and a decrease in its depth. Targeted experiments aimed at detecting the effects studied here would facilitate the development of radio-spectroscopic and optical methods for identifying the presence of inhomogeneities of various dimensions in multilayer magnetic and optical structures.

Off-center observers versus supernovae in inhomogeneous pressure universes

OpenAIRE

Balcerzak, Adam; Dabrowski, Mariusz P.; Denkiewicz, Tomasz

2013-01-01

Exact luminosity distance and apparent magnitude formulas are applied to Union2 557 supernovae sample in order to constrain possible position of an observer outside of the center of symmetry in spherically symmetric inhomogeneous pressure Stephani universes which are complementary to inhomogeneous density Lema\\^itre-Tolman-Bondi (LTB) void models. Two specific models are investigated. The first which allows a barotropic equation of state at the center of symmetry with no scale factor function...

Does Sexy Media Promote Teen Sex? A Meta-Analytic and Methodological Review.

Science.gov (United States)

Ferguson, Christopher J; Nielsen, Rune K L; Markey, Patrick M

2017-06-01

Parents and policy makers are often concerned that sexy media (media depicting or discussing sexual encounters) may promote sexual behavior in young viewers. There has been some debate among scholars regarding whether such media promote sexual behaviors. It remains unclear to what extent sexy media is a risk factor for increased sexual behavior among youth. The current study employed a meta-analysis of 22 correlational and longitudinal studies of sexy media effects on teen sexual behavior (n = 22,172). Moderator analyses examined methodological and science culture issues such as citation bias. Results indicated the presence only of very weak effects. General media use did not correlate with sexual behaviors (r = 0.005), and sexy media use correlated only weakly with sexual behaviors (r = 0.082) once other factors had been controlled. Higher effects were seen for studies with citation bias, and lower effects when family environment is controlled. The impact of media on teen sexuality was minimal with effect sizes near to zero.

Process Modeling With Inhomogeneous Thin Films

Science.gov (United States)

Machorro, R.; Macleod, H. A.; Jacobson, M. R.

1986-12-01

Designers of optical multilayer coatings commonly assume that the individual layers will be ideally homogeneous and isotropic. In practice, it is very difficult to control the conditions involved in the complex evaporation process sufficiently to produce such ideal films. Clearly, changes in process parameters, such as evaporation rate, chamber pressure, and substrate temperature, affect the microstructure of the growing film, frequently producing inhomogeneity in structure or composition. In many cases, these effects are interdependent, further complicating the situation. However, this process can be simulated on powerful, interactive, and accessible microcomputers. In this work, we present such a model and apply it to estimate the influence of an inhomogeneous layer on multilayer performance. Presently, the program simulates film growth, thermal expansion and contraction, and thickness monitoring procedures, and includes the effects of uncertainty in these parameters or noise. Although the model is being developed to cover very general cases, we restrict the present discussion to isotropic and nondispersive quarterwave layers to understand the particular effects of inhomogeneity. We studied several coating designs and related results and tolerances to variations in evaporation conditions. The model is composed of several modular subprograms, is written in Fortran, and is executed on an IBM-PC with 640 K of memory. The results can be presented in graphic form on a monochrome monitor. We are currently installing and implementing color capability to improve the clarity of the multidimensional output.

Propagation of acoustic waves in a one-dimensional macroscopically inhomogeneous poroelastic material.

Science.gov (United States)

Gautier, G; Kelders, L; Groby, J P; Dazel, O; De Ryck, L; Leclaire, P

2011-09-01

Wave propagation in macroscopically inhomogeneous porous materials has received much attention in recent years. The wave equation, derived from the alternative formulation of Biot's theory of 1962, was reduced and solved recently in the case of rigid frame inhomogeneous porous materials. This paper focuses on the solution of the full wave equation in which the acoustic and the elastic properties of the poroelastic material vary in one-dimension. The reflection coefficient of a one-dimensional macroscopically inhomogeneous porous material on a rigid backing 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 at both normal and oblique incidence and to experimental measurements at normal incidence for a known two-layers porous material, considered as a single inhomogeneous layer. Finally, discussion about the absorption coefficient for various inhomogeneity profiles gives further perspectives. © 2011 Acoustical Society of America

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.

Large Scale Cosmological Anomalies and Inhomogeneous Dark Energy

Directory of Open Access Journals (Sweden)

Leandros Perivolaropoulos

2014-01-01

Full Text Available A wide range of large scale observations hint towards possible modifications on the standard cosmological model which is based on a homogeneous and isotropic universe with a small cosmological constant and matter. These observations, also known as “cosmic anomalies” include unexpected Cosmic Microwave Background perturbations on large angular scales, large dipolar peculiar velocity flows of galaxies (“bulk flows”, the measurement of inhomogenous values of the fine structure constant on cosmological scales (“alpha dipole” and other effects. The presence of the observational anomalies could either be a large statistical fluctuation in the context of ΛCDM or it could indicate a non-trivial departure from the cosmological principle on Hubble scales. Such a departure is very much constrained by cosmological observations for matter. For dark energy however there are no significant observational constraints for Hubble scale inhomogeneities. In this brief review I discuss some of the theoretical models that can naturally lead to inhomogeneous dark energy, their observational constraints and their potential to explain the large scale cosmic anomalies.

Electron-positron pair production in inhomogeneous electromagnetic fields

International Nuclear Information System (INIS)

Kohlfürst, C.

2015-01-01

The process of electron-positron pair production is investigated within the phase-space Wigner formalism. The similarities between atomic ionization and pair production for homogeneous, but time-dependent linearly polarized electric fields are examined mainly in the regime of multiphoton absorption (field-dependent threshold, above-threshold pair production). Characteristic signatures in the particle spectra are identified (effective mass, channel closing). The non-monotonic dependence of the particle yield on the carrier frequency is discussed as well. The investigations are then extended to spatially inhomogeneous electric fields. New effects arising due to the spatial dependence of the effective mass are discussed in terms of a semi-classical interpretation. An increase in the normalized particle yield is found for various field configurations.Pair production in inhomogeneous electric and magnetic fields is also studied. The influence of a time-dependent spatially inhomogeneous magnetic field on the momentum spectrum and the particle yield is investigated. The Lorentz invariants are identified to be crucial in order to understand pair production by strong electric fields in the presence of strong magnetic fields. (author) [de

Quantification of inhomogeneities in malignancy grading of non-Hodgkin lymphoma with MR imaging

International Nuclear Information System (INIS)

Rehn, S.; Sperber, G.O.; Nyman, R.; Glimelius, B.; Hagberg, H.; Hemmingsson, A.

1993-01-01

In a previous study of 50 patients with non-Hodgkin lymphoma (NHL) it was shown that the inhomogeneous appearance of a tumor at MR imaging strongly indicated a high malignancy grade. In this study of 33 patients with NHL, the administration of an i.v. contrast medium, Gadolinium-DTPA, improved the subjective detectability of the inhomogeneities. A method of quantifying the degree of inhomogeneity in the tumors (inhomogeneity index, IH-index) was developed and tested. The mean value of IH-index in the T2-weighted image before contrast medium administration, and of the T1-weighted image after contrast medium administration, as well as the IH-index value in the T2-weighted image before contrast medium administration alone, was able to discriminate well between low- and high-grade NHL. This method of quantifiying the degree of inhomogeneity in tumors improved sensitivity in detecting high-grade NHL. (orig.)

Estimating functions for inhomogeneous spatial point processes with incomplete covariate data

DEFF Research Database (Denmark)

Waagepetersen, Rasmus

and this leads to parameter estimation error which is difficult to quantify. In this paper we introduce a Monte Carlo version of the estimating function used in "spatstat" for fitting inhomogeneous Poisson processes and certain inhomogeneous cluster processes. For this modified estimating function it is feasible...

Estimating functions for inhomogeneous spatial point processes with incomplete covariate data

DEFF Research Database (Denmark)

Waagepetersen, Rasmus

2008-01-01

and this leads to parameter estimation error which is difficult to quantify. In this paper, we introduce a Monte Carlo version of the estimating function used in spatstat for fitting inhomogeneous Poisson processes and certain inhomogeneous cluster processes. For this modified estimating function, it is feasible...

Love waves in a structure with an inhomogeneous layer

International Nuclear Information System (INIS)

Ghazaryan, K.B.; Piliposyan, D.G.

2011-01-01

The problem of the propagation of Love type waves in a structure consisting of a finite inhomogeneous layer sandwiched between two isotropic homogeneous half spaces is investigated. Two types of inhomogeneity are considered. It is shown that in one case the amplitude of vibrations in the middle layer is a sinusoidal function of distance from the plane of symmetry, but that in the other case it may be non-sinusoidal for certain values of the parameters of the problem

Solutions of the chemical kinetic equations for initially inhomogeneous mixtures.

Science.gov (United States)

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.

Effective permittivity of finite inhomogeneous objects

NARCIS (Netherlands)

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.

Impact of inhomogeneity on SH-type wave propagation in an initially stressed composite structure

Science.gov (United States)

Saha, S.; Chattopadhyay, A.; Singh, A. K.

2018-02-01

The present analysis has been made on the influence of distinct form of inhomogeneity in a composite structure comprised of double superficial layers lying over a half-space, on the phase velocity of SH-type wave propagating through it. Propagation of SH-type wave in the said structure has been examined in four distinct cases of inhomogeneity viz. when inhomogeneity in double superficial layer is due to exponential variation in density only (Case I); when inhomogeneity in double superficial layers is due to exponential variation in rigidity only (Case II); when inhomogeneity in double superficial layer is due to exponential variation in rigidity, density and initial stress (Case III) and when inhomogeneity in double superficial layer is due to linear variation in rigidity, density and initial stress (Case IV). Closed-form expression of dispersion relation has been accomplished for all four aforementioned cases through extensive application of Debye asymptotic analysis. Deduced dispersion relations for all the cases are found in well-agreement to the classical Love-wave equation. Numerical computation has been carried out to graphically demonstrate the effect of inhomogeneity parameters, initial stress parameters as well as width ratio associated with double superficial layers in the composite structure for each of the four aforesaid cases on dispersion curve. Meticulous examination of distinct cases of inhomogeneity and initial stress in context of considered problem has been carried out with detailed analysis in a comparative approach.

Brownian motion probe for water-ethanol inhomogeneous mixtures

Science.gov (United States)

Furukawa, Kazuki; Judai, Ken

2017-12-01

Brownian motion provides information regarding the microscopic geometry and motion of molecules, insofar as it occurs as a result of molecular collisions with a colloid particle. We found that the mobility of polystyrene beads from the Brownian motion in a water-ethanol mixture is larger than that predicted from the liquid shear viscosity. This indicates that mixing water and ethanol is inhomogeneous in micron-sized probe beads. The discrepancy between the mobility of Brownian motion and liquid mobility can be explained by the way the rotation of the beads in an inhomogeneous viscous solvent converts the translational movement.

Phase synchronization in inhomogeneous globally coupled map lattices

International Nuclear Information System (INIS)

Ho Mingchung; Hung Yaochen; Jiang, I-M.

2004-01-01

The study of inhomogeneous-coupled chaotic systems has attracted a lot of attention recently. With simple definition of phase, we present the phase-locking behavior in ensembles of globally coupled non-identical maps. The inhomogeneous globally coupled maps consist of logistic map and tent map simultaneously. Average phase synchronization ratios, which are used to characterize the phase coherent phenomena, depend on different coupling coefficients and chaotic parameters. By using interdependence, the relationship between a single unit and the mean field is illustrated. Moreover, we take the effect of external noise and parameter mismatch into consideration and present the results by numerical simulation

Spatial Inhomogeneity of Kinetic and Magnetic Dissipations in Thermal Convection

Energy Technology Data Exchange (ETDEWEB)

Hotta, H. [Department of Physics, Graduate School of Science, Chiba university, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522 (Japan)

2017-08-20

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.

Chemical inhomogeneity populations in various zircaloy claddings and their association with SCC and corrosion resistance

International Nuclear Information System (INIS)

Tasooji, A.; Miller, A.K.; Cheung, T.Y.; Brooks, M.; Santucci, J.

1987-01-01

A technique has been developed that permits detection and characterization of sparsely distributed chemical inhomogeneities in Zircaloy. These inhomogeneities have previously been observed at the origins of iodine stress-corrosion cracks but are not detectable by, for example, simple scanning electron microscopy (SEM) examination. The technique uses radioactive iodine to ''label'' the chemical inhomogeneities, autoradiography to detect their locations, and SEM and energy-dispersive X-ray analysis (EDAX) to further characterize them. Large areas of surface have been surveyed and statistically meaningful populations of chemical inhomogeneities measured for five different lots of Zircaloy cladding. Inner surfaces and cladding cross-sectional surfaces have been studied. There are clear differences in chemical inhomogeneity size distribution and composition between the various claddings. For three of the claddings characterized in this work, the previously measured stress-corrosion cracking (SCC) threshold stresses correlate well (inversely) with the new data on their average chemical inhomogeneity sizes. Of special interest is the fact that the most SCC-resistant cladding contains far fewer iron-bearing inhomogeneities than the other claddings

Quasilinear diffusion in inhomogeneous plasmas

International Nuclear Information System (INIS)

Hooley, D.L.

1975-05-01

The problem of inhomogeneous diffusion in a plasma is considered with emphasis on its possible application to relativistic electron beams. A one-dimensional model with a background electrostatic field is used to illustrate the basic approach, which is then extended to a two-dimensional plasma with a background magnetic field. Only preliminary results are available. (U.S.)

High-speed imaging of inhomogeneous ignition in a shock tube

Science.gov (United States)

Tulgestke, A. M.; Johnson, S. E.; Davidson, D. F.; Hanson, R. K.

2018-05-01

Homogeneous and inhomogeneous ignition of real and surrogate fuels were imaged in two Stanford shock tubes, revealing the influence of small particle fragmentation. n-Heptane, iso-octane, and Jet A were studied, each mixed in an oxidizer containing 21% oxygen and ignited at low temperatures (900-1000 K), low pressures (1-2 atm), with an equivalence ratio of 0.5. Visible images (350-1050 nm) were captured through the shock tube endwall using a high-speed camera. Particles were found to arrive near the endwalls of the shock tubes approximately 5 ms after reflection of the incident shock wave. Reflected shock wave experiments using diaphragm materials of Lexan and steel were investigated. Particles collected from the shock tubes after each experiment were found to match the material of the diaphragm burst during the experiment. Following each experiment, the shock tubes were cleaned by scrubbing with cotton cloths soaked with acetone. Particles were observed to fragment after arrival near the endwall, often leading to inhomogeneous ignition of the fuel. Distinctly more particles were observed during experiments using steel diaphragms. In experiments exhibiting inhomogeneous ignition, flames were observed to grow radially until all the fuel within the cross section of the shock tube had been consumed. The influence of diluent gas (argon or helium) was also investigated. The use of He diluent gas was found to suppress the number of particles capable of causing inhomogeneous flames. The use of He thus allowed time history studies of ignition to extend past the test times that would have been limited by inhomogeneous ignition.

Attosecond extreme ultraviolet generation in cluster by using spatially inhomogeneous field

Energy Technology Data Exchange (ETDEWEB)

Feng, Liqiang, E-mail: lqfeng-lngy@126.com [College of Science, Liaoning University of Technology, Jinzhou, 121000 (China); State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics Chinese Academy of Sciences, Dalian 116023 (China); Liu, Hang [School of Chemical and Environmental Engineering, Liaoning University of Technology, Jinzhou 121000 (China)

2015-01-15

A promising method to generate the attosecond extreme ultraviolet (XUV) sources has been theoretically investigated emerging from the two-dimensional Ar{sup +} cluster driven by the spatially inhomogeneous field. The results show that with the introduction of the Ar{sup +} cluster model, not only the harmonic cutoffs are enhanced, but also the harmonic yields are reinforced. Furthermore, by properly moderating the inhomogeneity as well as the laser parameters of the inhomogeneous field, the harmonic cutoff can be further extended. As a result, three almost linearly polarized XUV pulses with durations of 40 as, 42 as, and 45 as can be obtained.

Critical behavior in inhomogeneous random graphs

NARCIS (Netherlands)

Hofstad, van der R.W.

2009-01-01

We study the critical behavior of inhomogeneous random graphs where edges are present independently but with unequal edge occupation probabilities. We show that the critical behavior depends sensitively on the properties of the asymptotic degrees. Indeed, when the proportion of vertices with degree

Aspek Ekonomi, Politik, Dan Kultural Media Massa

OpenAIRE

Inayah, Sitti Syahar

2015-01-01

The phenomenon of mass media relates to economic, political, and cultural aspects. Implication of each aspect can be explained theoretically through several models and theories. Some of them are issues and themes in mass communication theory, available paradigms and approaches – including their methodological implications, models and theories supplemented with brief description of each theory, and strengths and weaknesses of each paradigm and approachwithin mass media research.

A systematic study of head tissue inhomogeneity and anisotropy on EEG forward problem computing

International Nuclear Information System (INIS)

Bashar, M.R.; Li, Y.; Wen, P.

2010-01-01

Full text: In this study, we propose a stochastic method to analyze the effects of inhomogeneous anisotropic tissue conductivity on electroencephalogram (EEG) in forward computation. We apply this method to an inhomogeneous and anisotropic spherical human head model. We apply stochastic finite element method based on Legendre polynomials, Karhunen-Loeve expansion and stochastic Galerkin methods. We apply Volume and Wang's constraints to restrict the anisotropic conductivities for both the white matter (WM) and the skull tissue compartments. The EEGs resulting from deterministic and stochastic FEMs are compared using statistical measurement techniques. Based on these comparisons, we find that EEGs generated by incorporating WM and skull inhomogeneous anisotropic tissue properties individually result in an average of 56.5 and 57.5% relative errors, respectively. Incorporating these tissue properties for both layers together generate 43.5% average relative error. Inhomogeneous scalp tissue causes 27% average relative error and a full inhomogeneous anisotropic model brings in an average of 45.5% relative error. The study results demonstrate that the effects of inhomogeneous anisotropic tissue conductivity are significant on EEG.

Azimuthal Seismic Amplitude Variation with Offset and Azimuth Inversion in Weakly Anisotropic Media with Orthorhombic Symmetry

Science.gov (United States)

Pan, Xinpeng; Zhang, Guangzhi; Yin, Xingyao

2018-01-01

Seismic amplitude variation with offset and azimuth (AVOaz) inversion is well known as a popular and pragmatic tool utilized to estimate fracture parameters. A single set of vertical fractures aligned along a preferred horizontal direction embedded in a horizontally layered medium can be considered as an effective long-wavelength orthorhombic medium. Estimation of Thomsen's weak-anisotropy (WA) parameters and fracture weaknesses plays an important role in characterizing the orthorhombic anisotropy in a weakly anisotropic medium. Our goal is to demonstrate an orthorhombic anisotropic AVOaz inversion approach to describe the orthorhombic anisotropy utilizing the observable wide-azimuth seismic reflection data in a fractured reservoir with the assumption of orthorhombic symmetry. Combining Thomsen's WA theory and linear-slip model, we first derive a perturbation in stiffness matrix of a weakly anisotropic medium with orthorhombic symmetry under the assumption of small WA parameters and fracture weaknesses. Using the perturbation matrix and scattering function, we then derive an expression for linearized PP-wave reflection coefficient in terms of P- and S-wave moduli, density, Thomsen's WA parameters, and fracture weaknesses in such an orthorhombic medium, which avoids the complicated nonlinear relationship between the orthorhombic anisotropy and azimuthal seismic reflection data. Incorporating azimuthal seismic data and Bayesian inversion theory, the maximum a posteriori solutions of Thomsen's WA parameters and fracture weaknesses in a weakly anisotropic medium with orthorhombic symmetry are reasonably estimated with the constraints of Cauchy a priori probability distribution and smooth initial models of model parameters to enhance the inversion resolution and the nonlinear iteratively reweighted least squares strategy. The synthetic examples containing a moderate noise demonstrate the feasibility of the derived orthorhombic anisotropic AVOaz inversion method, and the

Time-dependent inhomogeneous jet models for BL Lac objects

Science.gov (United States)

Marlowe, A. T.; Urry, C. M.; George, I. M.

1992-05-01

Relativistic beaming can explain many of the observed properties of BL Lac objects (e.g., rapid variability, high polarization, etc.). In particular, the broadband radio through X-ray spectra are well modeled by synchrotron-self Compton emission from an inhomogeneous relativistic jet. We have done a uniform analysis on several BL Lac objects using a simple but plausible inhomogeneous jet model. For all objects, we found that the assumed power-law distribution of the magnetic field and the electron density can be adjusted to match the observed BL Lac spectrum. While such models are typically unconstrained, consideration of spectral variability strongly restricts the allowed parameters, although to date the sampling has generally been too sparse to constrain the current models effectively. We investigate the time evolution of the inhomogeneous jet model for a simple perturbation propagating along the jet. The implications of this time evolution model and its relevance to observed data are discussed.

Evaluation of planning dose accuracy in case of radiation treatment on inhomogeneous organ structure

Energy Technology Data Exchange (ETDEWEB)

Kim, Chan Yong; Lee, Jae Hee; Kwak, Yong Kook; Ha, Min Yong [Dept. of Radiation Oncology, Seoul National University Hospital, Seoul (Korea, Republic of)

2013-09-15

We are to find out the difference of calculated dose of treatment planning system (TPS) and measured dose in case of inhomogeneous organ structure. Inhomogeneous phantom is made with solid water phantom and cork plate. CT image of inhomogeneous phantom is acquired. Treatment plan is made with TPS (Pinnacle3 9.2. Royal Philips Electronics, Netherlands) and calculated dose of point of interest is acquired. Treatment plan was delivered in the inhomogeneous phantom by ARTISTE (Siemens AG, Germany) measured dose of each point of interest is obtained with Gafchromic EBT2 film (International Specialty Products, US) in the gap between solid water phantom or cork plate. To simulate lung cancer radiation treatment, artificial tumor target of paraffin is inserted in the cork volume of inhomogeneous phantom. Calculated dose and measured dose are acquired as above. In case of inhomogeneous phantom experiment, dose difference of calculated dose and measured dose is about -8.5% at solid water phantom-cork gap and about -7% lower in measured dose at cork-solid water phantom gap. In case of inhomogeneous phantom inserted paraffin target experiment, dose difference is about 5% lower in measured dose at cork-paraffin gap. There is no significant difference at same material gap in both experiments. Radiation dose at the gap between two organs with different electron density is significantly lower than calculated dose with TPS. Therefore, we must be aware of dose calculation error in TPS and great care is suggested in case of radiation treatment planning on inhomogeneous organ structure.

Evaluation of planning dose accuracy in case of radiation treatment on inhomogeneous organ structure

International Nuclear Information System (INIS)

Kim, Chan Yong; Lee, Jae Hee; Kwak, Yong Kook; Ha, Min Yong

2013-01-01

We are to find out the difference of calculated dose of treatment planning system (TPS) and measured dose in case of inhomogeneous organ structure. Inhomogeneous phantom is made with solid water phantom and cork plate. CT image of inhomogeneous phantom is acquired. Treatment plan is made with TPS (Pinnacle3 9.2. Royal Philips Electronics, Netherlands) and calculated dose of point of interest is acquired. Treatment plan was delivered in the inhomogeneous phantom by ARTISTE (Siemens AG, Germany) measured dose of each point of interest is obtained with Gafchromic EBT2 film (International Specialty Products, US) in the gap between solid water phantom or cork plate. To simulate lung cancer radiation treatment, artificial tumor target of paraffin is inserted in the cork volume of inhomogeneous phantom. Calculated dose and measured dose are acquired as above. In case of inhomogeneous phantom experiment, dose difference of calculated dose and measured dose is about -8.5% at solid water phantom-cork gap and about -7% lower in measured dose at cork-solid water phantom gap. In case of inhomogeneous phantom inserted paraffin target experiment, dose difference is about 5% lower in measured dose at cork-paraffin gap. There is no significant difference at same material gap in both experiments. Radiation dose at the gap between two organs with different electron density is significantly lower than calculated dose with TPS. Therefore, we must be aware of dose calculation error in TPS and great care is suggested in case of radiation treatment planning on inhomogeneous organ structure

Learning from Weak and Noisy Labels for Semantic Segmentation

KAUST Repository

Lu, Zhiwu

2016-04-08

A weakly supervised semantic segmentation (WSSS) method aims to learn a segmentation model from weak (image-level) as opposed to strong (pixel-level) labels. By avoiding the tedious pixel-level annotation process, it can exploit the unlimited supply of user-tagged images from media-sharing sites such as Flickr for large scale applications. However, these ‘free’ tags/labels are often noisy and few existing works address the problem of learning with both weak and noisy labels. In this work, we cast the WSSS problem into a label noise reduction problem. Specifically, after segmenting each image into a set of superpixels, the weak and potentially noisy image-level labels are propagated to the superpixel level resulting in highly noisy labels; the key to semantic segmentation is thus to identify and correct the superpixel noisy labels. To this end, a novel L1-optimisation based sparse learning model is formulated to directly and explicitly detect noisy labels. To solve the L1-optimisation problem, we further develop an efficient learning algorithm by introducing an intermediate labelling variable. Extensive experiments on three benchmark datasets show that our method yields state-of-the-art results given noise-free labels, whilst significantly outperforming the existing methods when the weak labels are also noisy.

Learning from Weak and Noisy Labels for Semantic Segmentation

KAUST Repository

Lu, Zhiwu; Fu, Zhenyong; Xiang, Tao; Han, Peng; Wang, Liwei; Gao, Xin

2016-01-01

A weakly supervised semantic segmentation (WSSS) method aims to learn a segmentation model from weak (image-level) as opposed to strong (pixel-level) labels. By avoiding the tedious pixel-level annotation process, it can exploit the unlimited supply of user-tagged images from media-sharing sites such as Flickr for large scale applications. However, these ‘free’ tags/labels are often noisy and few existing works address the problem of learning with both weak and noisy labels. In this work, we cast the WSSS problem into a label noise reduction problem. Specifically, after segmenting each image into a set of superpixels, the weak and potentially noisy image-level labels are propagated to the superpixel level resulting in highly noisy labels; the key to semantic segmentation is thus to identify and correct the superpixel noisy labels. To this end, a novel L1-optimisation based sparse learning model is formulated to directly and explicitly detect noisy labels. To solve the L1-optimisation problem, we further develop an efficient learning algorithm by introducing an intermediate labelling variable. Extensive experiments on three benchmark datasets show that our method yields state-of-the-art results given noise-free labels, whilst significantly outperforming the existing methods when the weak labels are also noisy.

Seismic wave propagation in non-homogeneous elastic media by boundary elements

CERN Document Server

Manolis, George D; Rangelov, Tsviatko V; Wuttke, Frank

2017-01-01

This book focuses on the mathematical potential and computational efficiency of the Boundary Element Method (BEM) for modeling seismic wave propagation in either continuous or discrete inhomogeneous elastic/viscoelastic, isotropic/anisotropic media containing multiple cavities, cracks, inclusions and surface topography. BEM models may take into account the entire seismic wave path from the seismic source through the geological deposits all the way up to the local site under consideration. The general presentation of the theoretical basis of elastodynamics for inhomogeneous and heterogeneous continua in the first part is followed by the analytical derivation of fundamental solutions and Green's functions for the governing field equations by the usage of Fourier and Radon transforms. The numerical implementation of the BEM is for antiplane in the second part as well as for plane strain boundary value problems in the third part. Verification studies and parametric analysis appear throughout the book, as do both ...

Detection of Buried Inhomogeneous Elliptic Cylinders by a Memetic Algorithm

OpenAIRE

Caorsi, Salvatore; Massa, Andrea; Pastorino, Matteo; Raffetto, Mirco; Randazzo, Andrea

2003-01-01

The application of a global optimization procedure to the detection of buried inhomogeneities is studied in the present paper. The object inhomogeneities are schematized as multilayer infinite dielectric cylinders with elliptic cross sections. An efficient recursive analytical procedure is used for the forward scattering computation. A functional is constructed in which the field is expressed in series solution of Mathieu functions. Starting by the input scattered data, the iterative minimiza...

The phase transition to an inhomogeneous condensate state

International Nuclear Information System (INIS)

Voskresensky, D.N.

1984-01-01

The Lagrangian (free energy) of the model with a complex scalar order parameter in which the phase transition to an inhomogeneous condensate state exists is constructed in the coordinate representation. In the case of condensation of charged particles (for example paired electrons) interaction with the electromagnetic field is included. The excitation spectrum in the presence of the condensate is found. The oscillations are strongly anisotropic. It is shown that superfluidity is absent for an uncharged system but that the charged one has the property of superconductivity. The important role of thermal fluctuations is demonstrated. They drastically change the behaviour of the condensate system. The condensation in a finite system is considered. A study is carried out for the behaviour of an inhomogeneous condensate in magnetic field. It is shown that the inhomogeneous condensate is a type II superconductor with Ginzburg-Landau parameter kappa >> 1, but that the structure of the mixed state of the system is unusual - consisting of plane layers of the normal phase, when Hsub(c1)< H< H'sub(c2). The distribution of condensate in the strong magnetic field H'sub(c2)< H< Hsub(c2) is also studied. (Auth.)

Peeling stress analysis for an inhomogeneous high-Tc superconductor with a discontinuous interface at the substrate

International Nuclear Information System (INIS)

Gao Zhiwen; Lee, Kang Yong; Zhou Youhe

2011-01-01

Research highlights: → The thermal stress generated in the inhomogeneous HTS is larger on a SiTiO 3 substrate than on a MgO substrate. → The maximum thermal stresses, i.e., the peeling stresses, occur near the bottom corner of the inhomogeneous HTS and may induce fracture behavior at the bi-material interface. → The inhomogeneous HTS cools at a slower pace than the homogeneous HTS from the room temperature to the operating temperature. → The magnitude of the peeling stress for a homogeneous HTS is larger than that for an inhomogeneous HTS. - Abstract: This paper presents an analysis of a superconductor-substrate system to calculate the peeling stress of a high temperature superconductor (HTS) when the temperature decreases from ambient to operating conditions (cryogenic temperatures). Firstly, the values for the material properties of the inhomogeneous high temperature superconductor (HTS) were obtained by fitting a second order polynomial to the experimental data. It is assumed that the material properties of the inhomogeneous HTS vary with varying height coordinate and temperature. Then, through the proposed graded finite element method, the coupled thermo-mechanical equations were solved numerically. The numerical results show that the thermal stress generated in the inhomogeneous HTS is larger on a SiTiO 3 substrate than on a MgO substrate. The maximum thermal stresses, i.e., the peeling stresses, occur near the bottom corner of the inhomogeneous HTS and may induce fracture behavior at the bi-material interface. The inhomogeneous HTS cools at a slower pace than the homogeneous HTS from the room temperature to the operating temperature. It is also shown that the magnitude of the peeling stress for a homogeneous HTS is larger than that for an inhomogeneous HTS. It is intended that the model presented here be useful to researchers who are interested in the mechanical properties of an inhomogeneous HTS.

Electron Beam interaction with an inhomogeneous

Energy Technology Data Exchange (ETDEWEB)

Zaki, N G; El-Shorbagy, Kh H [Plasma physics and Nuclear Fusion Dept. Nuclear Research Centre Atomic Energy Authority, Cairo, (Egypt)

1997-12-31

The linear and nonlinear interaction of an electron beam with an inhomogeneous semi bounded warm plasma is investigated. The amount of energy absorbed by the plasma is obtained. The formation of waves at double frequency at the inlet of the beam into the plasma is also considered.

Electron dynamics in inhomogeneous magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Nogaret, Alain, E-mail: A.R.Nogaret@bath.ac.u [Department of Physics, University of Bath, Bath BA2 7AY (United Kingdom)

2010-06-30

This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done on electron localization in random magnetic fields, the experimental methods for fabricating magnetic potentials are presented. Drift-diffusion phenomena are then described, which include commensurability oscillations, magnetic channelling, resistance resonance effects and magnetic dots. We then review quantum phenomena in magnetic potentials including magnetic quantum wires, magnetic minibands in superlattices, rectification by snake states, quantum tunnelling and Klein tunnelling. The third part is devoted to spintronics in inhomogeneous magnetic fields. This covers spin filtering by magnetic field gradients and circular magnetic fields, electrically induced spin resonance, spin resonance fluorescence and coherent spin manipulation. (topical review)

Optical Modeling of Sea Salt Aerosols: The Effects of Nonsphericity and Inhomogeneity

Science.gov (United States)

Bi, Lei; Lin, Wushao; Wang, Zheng; Tang, Xiaoyun; Zhang, Xiaoyu; Yi, Bingqi

2018-01-01

The nonsphericity and inhomogeneity of marine aerosols (sea salts) have not been addressed in pertinent radiative transfer calculations and remote sensing studies. This study investigates the optical properties of nonspherical and inhomogeneous sea salts using invariant imbedding T-matrix simulations. Dry sea salt aerosols are modeled based on superellipsoidal geometries with a prescribed aspect ratio and roundness parameter. Wet sea salt particles are modeled as coated superellipsoids, as spherical particles with a superellipsoidal core, and as homogeneous spheres depending on the level of relative humidity. Aspect ratio and roundness parameters are found to be critical to interpreting the linear depolarization ratios (LDRs) of NaCl crystals from laboratory measurements. The optimal morphology parameters of NaCl necessary to reproduce the measurements are found to be consistent with data gleaned from an electron micrograph. The LDRs of wet sea salts are computed based on inhomogeneous models and compared with the measured data from ground-based LiDAR. The dependence of the LDR on relative humidity is explicitly considered. The increase in the LDR with relative humidity at the initial phase of deliquescence is attributed to both the size increase and the inhomogeneity effect. For large humidity values, the LDR substantially decreases because the overall particle shape becomes more spherical and the inhomogeneity effect in a particle on the LDR is suppressed for submicron sea salts. However, the effect of inhomogeneity on optical properties is pronounced for coarse-mode sea salts. These findings have important implications for atmospheric radiative transfer and remote sensing involving sea salt aerosols.

Equilibrium and stability in strongly inhomogeneous plasmas

International Nuclear Information System (INIS)

Mynick, H.E.

1978-10-01

The equilibrium of strongly inhomogeneous, collisionless, slab plasmas, is studied using a generalized version of a formalism previously developed, which permits the generation of self-consistent equilibria, for plasmas with arbitrary magnetic shear, and variation of magnetic field strength. A systematic procedure is developed for deriving the form of the guiding-center Hamiltonian K, for finite eta, in an axisymmetric geometry. In the process of obtaining K, an expression for the first adiabatic invariant (the gyroaction) is obtained, which generalizes the usual expression 1/2 mv/sub perpendicular/ 2 /Ω/sub c/ (Ω/sub c/ = eB/mc), to finite eta and magnetic shear. A formalism is developed for the study of the stability of strongly-inhomogeneous, magnetized slab plasmas; it is then applied to the ion-drift-cyclotron instability

How Forest Inhomogeneities Affect the Edge Flow

DEFF Research Database (Denmark)

Boudreault, Louis-Étienne; Dupont, Sylvain; Bechmann, Andreas

2016-01-01

Most of our knowledge on forest-edge flows comes from numerical and wind-tunnel experiments where canopies are horizontally homogeneous. To investigate the impact of tree-scale heterogeneities (>1 m) on the edge-flow dynamics, the flow in an inhomogeneous forest edge on Falster island in Denmark...... is investigated using large-eddy simulation. The three-dimensional forest structure is prescribed in the model using high resolution helicopter-based lidar scans. After evaluating the simulation against wind measurements upwind and downwind of the forest leading edge, the flow dynamics are compared between...... the scanned forest and an equivalent homogeneous forest. The simulations reveal that forest inhomogeneities facilitate flow penetration into the canopy from the edge, inducing important dispersive fluxes in the edge region as a consequence of the flow spatial variability. Further downstream from the edge...

Primordial inhomogeneities from massive defects during inflation

Energy Technology Data Exchange (ETDEWEB)

Firouzjahi, Hassan; Karami, Asieh; Rostami, Tahereh, E-mail: firouz@ipm.ir, E-mail: karami@ipm.ir, E-mail: t.rostami@ipm.ir [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)

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.

Line broadening interference for high-resolution nuclear magnetic resonance spectra under inhomogeneous magnetic fields

International Nuclear Information System (INIS)

Wei, Zhiliang; Yang, Jian; Lin, Yanqin; Chen, Zhong; Chen, Youhe

2015-01-01

Nuclear magnetic resonance spectroscopy serves as an important tool for analyzing chemicals and biological metabolites. However, its performance is subject to the magnetic-field homogeneity. Under inhomogeneous fields, peaks are broadened to overlap each other, introducing difficulties for assignments. Here, we propose a method termed as line broadening interference (LBI) to provide high-resolution information under inhomogeneous magnetic fields by employing certain gradients in the indirect dimension to interfere the magnetic-field inhomogeneity. The conventional spectral-line broadening is thus interfered to be non-diagonal, avoiding the overlapping among adjacent resonances. Furthermore, an inhomogeneity correction algorithm is developed based on pattern recognition to recover the high-resolution information from LBI spectra. Theoretical deductions are performed to offer systematic and detailed analyses on the proposed method. Moreover, experiments are conducted to prove the feasibility of the proposed method for yielding high-resolution spectra in inhomogeneous magnetic fields

Forces and energy dissipation in inhomogeneous non-equilibrium superconductors

International Nuclear Information System (INIS)

Poluehktov, Yu.M.; Slezov, V.V.

1987-01-01

The phenomenological theory of volume forces and dissipation processes in inhomogeneous non-equilibrium superconductors near temperature transition from the normal to superconducting state is constructed. The approach is based on application of dynamic equations of superconductivity formulated on the basis of the Lagrangian formalism. These equations are generalized the Ginzburg-Landau theory in the nonstationary non-equilibrium case for ''foul'' superconductors. The value estimations of volume forces arising in inhomogeneities during relaxation of an order parameter and when the electrical field is penetrated into the superconductor, are given

Annealing effect on Schottky barrier inhomogeneity of graphene/n-type Si Schottky diodes

International Nuclear Information System (INIS)

Lin, Yow-Jon; Lin, Jian-Huang

2014-01-01

Highlights: • The current–voltage characteristics of graphene/n-type Si devices were measured. • The ideality factor increases with the decrease measurement temperatures. • Such behavior is attributed to Schottky barrier inhomogeneities. • Both Schottky barrier inhomogeneity and the T 0 effect are affected by annealing. • Stoichiometry of SiO x has a noticeable effect on the inhomogeneous barriers. - Abstract: The current–voltage characteristics of graphene/n-type Si (n-Si) Schottky diodes with and without annealing were measured in the temperature range of −120 to 30 °C and analyzed on the basis of thermionic emission theory. It is found that the barrier height decreases and the ideality factor increases with the decrease measurement temperatures. Such behavior is attributed to Schottky barrier inhomogeneities. It is shown that both the barrier height and the ideality factor can be tuned by changing the annealing temperature. Through the analysis, it can be suspected that a SiO x layer at the graphene/n-Si interfaces influences the electronic conduction through the device and stoichiometry of SiO x is affected by annealing treatment. In addition, both Schottky barrier inhomogeneity and the T 0 effect are affected by annealing treatment, implying that stoichiometry of SiO x has a noticeable effect on the inhomogeneous barriers of graphene/n-Si Schottky diodes

Experimental analysis on stress wave in inhomogeneous multi-layered structures

International Nuclear Information System (INIS)

Cho, Yun Ho; Ham, Hyo Sick

1998-01-01

The guided wave propagation in inhomogeneous multi-layered structures is experimentally explored based on theoretical dispersion curves. It turns out that proper selection of incident angle and frequency is critical for guided wave generation in multi-layered structures. Theoretical dispersion curves greatly depend on adhesive zone thickness, layer thickness and material properties. It was possible to determine the adhesive zone thickness of an inhomogeneous multi-layered structure by monitoring experimentally the change of dispersion curves.

Critical behavior in inhomogeneous random graphs

NARCIS (Netherlands)

Hofstad, van der R.W.

2013-01-01

We study the critical behavior of inhomogeneous random graphs in the so-called rank-1 case, where edges are present independently but with unequal edge occupation probabilities. The edge occupation probabilities are moderated by vertex weights, and are such that the degree of vertex i is close in

Reconstructing weak values without weak measurements

International Nuclear Information System (INIS)

Johansen, Lars M.

2007-01-01

I propose a scheme for reconstructing the weak value of an observable without the need for weak measurements. The post-selection in weak measurements is replaced by an initial projector measurement. The observable can be measured using any form of interaction, including projective measurements. The reconstruction is effected by measuring the change in the expectation value of the observable due to the projector measurement. The weak value may take nonclassical values if the projector measurement disturbs the expectation value of the observable

Organic random lasers in the weak-scattering regime

CERN Document Server

Polson, R C; 10.1103/PhysRevB.71.045205

2005-01-01

We used the ensemble-averaged power Fourier transform (PFT) of random laser emission spectra over the illuminated area to study random lasers with coherent feedback in four different disordered organic gain media in the weak scattering regime, where the light mean free path, l* is much larger than the emission wavelength. The disordered gain media include a pi -conjugated polymer film, an opal photonic crystal infiltrated with a laser dye (rhodamine 6G; R6G) having optical gain in the visible spectral range, a suspension of titania balls in R6G solution, and biological tissues such as chicken breast infiltrated with R6G. We show the existence of universality among the random resonators in each gain medium that we tested, in which at the same excitation intensity a dominant random cavity is excited in different parts of the sample. We show a second universality when scaling the average PFT of the four different media by l*; we found that the dominant cavity in each disordered gain medium scales with l *. The e...

Three-dimensional distribution of random velocity inhomogeneities at the Nankai trough seismogenic zone

Science.gov (United States)

Takahashi, T.; Obana, K.; Yamamoto, Y.; Nakanishi, A.; Kaiho, Y.; Kodaira, S.; Kaneda, Y.

2012-12-01

The Nankai trough in southwestern Japan is a convergent margin where the Philippine sea plate is subducted beneath the Eurasian plate. There are major faults segments of huge earthquakes that are called Tokai, Tonankai and Nankai earthquakes. According to the earthquake occurrence history over the past hundreds years, we must expect various rupture patters such as simultaneous or nearly continuous ruptures of plural fault segments. Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted seismic surveys at Nankai trough in order to clarify mutual relations between seismic structures and fault segments, as a part of "Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes" funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. This study evaluated the spatial distribution of random velocity inhomogeneities from Hyuga-nada to Kii-channel by using velocity seismograms of small and moderate sized earthquakes. Random velocity inhomogeneities are estimated by the peak delay time analysis of S-wave envelopes (e.g., Takahashi et al. 2009). Peak delay time is defined as the time lag from the S-wave onset to its maximal amplitude arrival. This quantity mainly reflects the accumulated multiple forward scattering effect due to random inhomogeneities, and is quite insensitive to the inelastic attenuation. Peak delay times are measured from the rms envelopes of horizontal components at 4-8Hz, 8-16Hz and 16-32Hz. This study used the velocity seismograms that are recorded by 495 ocean bottom seismographs and 378 onshore seismic stations. Onshore stations are composed of the F-net and Hi-net stations that are maintained by National Research Institute for Earth Science and Disaster Prevention (NIED) of Japan. It is assumed that the random inhomogeneities are represented by the von Karman type PSDF. Preliminary result of inversion analysis shows that spectral gradient of PSDF (i.e., scale dependence of

Polymers undergoing inhomogeneous adsorption: exact results and Monte Carlo simulations

Energy Technology Data Exchange (ETDEWEB)

Iliev, G K [Department of Mathematics, University of Melbourne, Parkville, Victoria (Australia); Orlandini, E [Dipartimento di Fisica, CNISM, Universita di Padova, Via Marzolo 8, 35131 Padova (Italy); Whittington, S G, E-mail: giliev@yorku.ca [Department of Chemistry, University of Toronto, Toronto (Canada)

2011-10-07

We consider several types of inhomogeneous polymer adsorption. In each case, the inhomogeneity is regular and resides in the surface, in the polymer or in both. We consider two different polymer models: a directed walk model that can be solved exactly and a self-avoiding walk model which we investigate using Monte Carlo methods. In each case, we compute the phase diagram. We compare and contrast the phase diagrams and give qualitative arguments about their forms. (paper)

Torsional surface waves in an inhomogeneous layer over a gravitating anisotropic porous half-space

International Nuclear Information System (INIS)

Gupta, Shishir; Pramanik, Abhijit

2015-01-01

The present work aims to deal with the propagation of torsional surface wave in an inhomogeneous layer over a gravitating anisotropic porous half space. The inhomogeneous layer exhibits the inhomogeneity of quadratic type. In order to show the effect of gravity the equation for the velocity of torsional wave has been obtained. It is also observed that for a layer over a homogeneous half space without gravity, the torsional surface wave does not propagate. An attempt is also made to assess the possible propagation of torsional surface waves in that medium in the absence of the upper layer. The effects of inhomogeneity factors and porosity on the phase velocity are depicted by means of graphs. (paper)

INHOMOGENEOUS NEARLY INCOMPRESSIBLE DESCRIPTION OF MAGNETOHYDRODYNAMIC TURBULENCE

International Nuclear Information System (INIS)

Hunana, P.; Zank, G. P.

2010-01-01

The nearly incompressible theory of magnetohydrodynamics (MHD) is formulated in the presence of a static large-scale inhomogeneous background. The theory is an inhomogeneous generalization of the homogeneous nearly incompressible MHD description of Zank and Matthaeus and a polytropic equation of state is assumed. The theory is primarily developed to describe solar wind turbulence where the assumption of a composition of two-dimensional (2D) and slab turbulence with the dominance of the 2D component has been used for some time. It was however unclear, if in the presence of a large-scale inhomogeneous background, the dominant component will also be mainly 2D and we consider three distinct MHD regimes for the plasma beta β > 1. For regimes appropriate to the solar wind (β 2 s δp is not valid for the leading-order O(M) density fluctuations, and therefore in observational studies, the density fluctuations should not be analyzed through the pressure fluctuations. The pseudosound relation is valid only for higher order O(M 2 ) density fluctuations, and then only for short-length scales and fast timescales. The spectrum of the leading-order density fluctuations should be modeled as k -5/3 in the inertial range, followed by a Bessel function solution K ν (k), where for stationary turbulence ν = 1, in the viscous-convective and diffusion range. Other implications for solar wind turbulence with an emphasis on the evolution of density fluctuations are also discussed.

Computed tomography imaging parameters for inhomogeneity correction in radiation treatment planning

Directory of Open Access Journals (Sweden)

Indra J Das

2016-01-01

Full Text Available Modern treatment planning systems provide accurate dosimetry in heterogeneous media (such as a patient' body with the help of tissue characterization based on computed tomography (CT number. However, CT number depends on the type of scanner, tube voltage, field of view (FOV, reconstruction algorithm including artifact reduction and processing filters. The impact of these parameters on CT to electron density (ED conversion had been subject of investigation for treatment planning in various clinical situations. This is usually performed with a tissue characterization phantom with various density plugs acquired with different tube voltages (kilovoltage peak, FOV reconstruction and different scanners to generate CT number to ED tables. This article provides an overview of inhomogeneity correction in the context of CT scanning and a new evaluation tool, difference volume dose-volume histogram (DVH, dV-DVH. It has been concluded that scanner and CT parameters are important for tissue characterizations, but changes in ED are minimal and only pronounced for higher density materials. For lungs, changes in CT number are minimal among scanners and CT parameters. Dosimetric differences for lung and prostate cases are usually insignificant (<2% in three-dimensional conformal radiation therapy and < 5% for intensity-modulated radiation therapy (IMRT with CT parameters. It could be concluded that CT number variability is dependent on acquisition parameters, but its dosimetric impact is pronounced only in high-density media and possibly in IMRT. In view of such small dosimetric changes in low-density medium, the acquisition of additional CT data for financially difficult clinics and countries may not be warranted.

Radio wave propagation in the inhomogeneous magnetic field of the solar corona

International Nuclear Information System (INIS)

Zheleznyakov, V.V.; Zlotnik, E.Ya.

1977-01-01

Various types of linear coupling between ordinary and extra-ordinary waves in the coronal plasma with the inhomogeneous magnetic field and the effect of this phenomenon upon the polarization characteristics of solar radio emission are considered. A qualitative analysis of the wave equation indicates that in a rarefied plasma the coupling effects can be displayed in a sufficiently weak magnetic field or at the angles between the magnetic field and the direction of wave propagation close enough to zero or π/2. The wave coupling parameter are found for these three cases. The radio wave propagation through the region with a quasi-transverse magnetic field and through the neutral current sheet is discussed more in detail. A qualitative picture of coupling in such a layer is supported by a numerical solution of the ''quasi-isotropic approximation'' equations. The role of the coupling effects in formation of polarization characteristics of different components of solar radio emission has been investigated. For cm wave range, the polarization is essentially dependent on the conditions in the region of the transverse magnetic field

Modeling of the anode of a liquid-feed DMFC: Inhomogeneous compression effects and two-phase transport phenomena

Science.gov (United States)

García-Salaberri, Pablo A.; Vera, Marcos; Iglesias, Immaculada

2014-01-01

An isothermal two-phase 2D/1D across-the-channel model for the anode of a liquid-feed Direct Methanol Fuel Cell (DMFC) is presented. The model takes into account the effects of the inhomogeneous assembly compression of the Gas Diffusion Layer (GDL), including the spatial variations of porosity, diffusivity, permeability, capillary pressure, and electrical conductivity. The effective anisotropic properties of the GDL are evaluated from empirical data reported in the literature corresponding to Toray carbon paper TGP-H series. Multiphase transport is modeled according to the classical theory of porous media (two-fluid model), considering the effect of non-equilibrium evaporation and condensation of methanol and water. The numerical results evidence that the hydrophobic Leverett J-function approach is physically inconsistent to describe capillary transport in the anode of a DMFC when assembly compression effects are considered. In contrast, more realistic results are obtained when GDL-specific capillary pressure curves reflecting the mixed-wettability characteristics of GDLs are taken into account. The gas coverage factor at the GDL/channel interface also exhibits a strong influence on the gas-void fraction distribution in the GDL, which in turn depends on the relative importance between the capillary resistance induced by the inhomogeneous compression, Rc(∝ ∂pc / ∂ ε) , and the capillary diffusivity, Dbarc(∝ ∂pc / ∂ s) .

Plasma waves in an inhomogeneous cylindrical plasma

International Nuclear Information System (INIS)

Pesic, S.S.

1976-01-01

The complete dispersion equation governing small amplitude plasma waves propagating in an inhomogeneous cylindrical plasma confined by a helical magnetic field is solved numerically. The efficiency of the wave energy thermalization in the lower hybrid frequency range is studied

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. Spatia...

Baryon inhomogeneity from the cosmic quark-hadron phase transition

International Nuclear Information System (INIS)

Kurki-Suonio, H.

1991-01-01

We discuss the generation of inhomogeneity in the baryon-number density during the cosmic quark-hadron phase transition. We use a simple model with thin-wall phase boundaries and ideal-gas equations of state. The nucleation of the phase transition introduces a new distance scale into the universe which will be the scale of the generated inhomogeneity. We review the estimate of this scale. During the transition baryon number is likely to collect onto a layer at the phase boundary. These layers may in the end be deposited as small regions of very high baryon density. 21 refs., 1 fig

Inhomogeneities in a Friedmann universe

International Nuclear Information System (INIS)

Tauber, G.E.

1987-08-01

One of the outstanding problems in cosmology is the growth of inhomogeneities, which are characterized by an anisotropic pressure and density distribution. Following a method developed by McVittie (1967, 1968) it has been possible to find time-dependent spherically symmetric solutions of Einstein's field equations containing an arbitrary pressure and density distribution which connect smoothly to a Friedmann universe for any desired equation of state. (author). 5 refs

Terpaan Media Massa dan Turbulensi Budaya Lokal

Directory of Open Access Journals (Sweden)

Dominikus Tulasi

2012-04-01

Full Text Available The attack of mass media in digital era now is an inevitability of the advanced information communication technology. The development of media relation in the current time also shows a higher scientific human existence. And, the side effect of those advances is the ultimate culture turbulence across developing countries. The sophisticated information communication technology at the present time has been victimizing young generation particularly in under developed countries. The power of media is a matter of fact which showing the domination influence of advance nations. In the other hand, the local culture of the victimized countries though still exists, but ultimately is the overwhelmed market of the media goal itself. The hegemony of media influence is the objective of advanced countries to dominate all aspect of weak countries including Indonesia. The global dominanace of advance country like American media is often resented overseas. 

Granule fraction inhomogeneity of calcium carbonate/sorbitol in roller compacted granules

DEFF Research Database (Denmark)

Bacher, Charlotte; Olsen, P.M.; Bertelsen, P.

2008-01-01

The granule fraction inhomogeneity of roller compacted granules was examined on mixtures of three different morphologic forms of calcium carbonate and three particle sizes of sorbitol. The granule fraction inhomogeneity was determined by the distribution of the calcium carbonate in each of the 10...... size fractions between 0 and 2000 µm and by calculating the demixing potential. Significant inhomogeneous occurrence of calcium carbonate in the size fractions was demonstrated, depending mostly on the particles sizes of sorbitol but also on the morphological forms of calcium carbonate......, the ability of the powder to agglomerate in the roller compactor was demonstrated to be related to the ability of the powder to be compacted into a tablet, thus the most compactable calcium carbonate and the smallest sized sorbitol improved the homogeneity by decreasing the demixing potential....

Electric field computation and measurements in the electroporation of inhomogeneous samples

Science.gov (United States)

Bernardis, Alessia; Bullo, Marco; Campana, Luca Giovanni; Di Barba, Paolo; Dughiero, Fabrizio; Forzan, Michele; Mognaschi, Maria Evelina; Sgarbossa, Paolo; Sieni, Elisabetta

2017-12-01

In clinical treatments of a class of tumors, e.g. skin tumors, the drug uptake of tumor tissue is helped by means of a pulsed electric field, which permeabilizes the cell membranes. This technique, which is called electroporation, exploits the conductivity of the tissues: however, the tumor tissue could be characterized by inhomogeneous areas, eventually causing a non-uniform distribution of current. In this paper, the authors propose a field model to predict the effect of tissue inhomogeneity, which can affect the current density distribution. In particular, finite-element simulations, considering non-linear conductivity against field relationship, are developed. Measurements on a set of samples subject to controlled inhomogeneity make it possible to assess the numerical model in view of identifying the equivalent resistance between pairs of electrodes.

Effective constants for wave propagation through partially saturated porous media

International Nuclear Information System (INIS)

Berryman, J.G.; Thigpen, L.

1985-01-01

The multipole scattering coefficients for elastic wave scattering from a spherical inhomogeneity in a fluid-saturated porous medium have been calculated. These coefficients may be used to obtain estimates of the effective macroscopic constants for long-wavelength propagation of elastic waves through partially saturated media. If the volume average of the single scattering from spherical bubbles of gas and liquid is required to vanish, the resulting equations determine the effective bulk modulus, density, and viscosity of the multiphase fluid filling the pores. The formula for the effective viscosity during compressional wave excitation is apparently new

A theoretical description of inhomogeneous turbulence

International Nuclear Information System (INIS)

Turner, L.

2000-01-01

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). In this LDRD, we have developed a highly compact and descriptive formalism that allows us to broach the theoretically formidable morass of inhomogeneous turbulence. Our formalism has two novel aspects: (a) an adaptation of helicity basis functions to represent an arbitrary incompressible channel flow and (b) the invocation of a hypothesis of random phase. A result of this compact formalism is that the mathematical description of inhomogeneous turbulence looks much like that of homogeneous turbulence--at the moment, the most rigorously explored terrain in turbulence research. As a result, we can explore the effect of boundaries on such important quantities as the gradients of mean flow, mean pressure, triple-velocity correlations and pressure velocity correlations, all of which vanish under the conventional, but artificial, assumption that the turbulence is statistically spatially uniform. Under suitable conditions, we have predicted that a mean flow gradient can develop even when none is initially present

Sulfur passivation of semi-insulating GaAs: Transition from Coulomb blockade to weak localization regime

Energy Technology Data Exchange (ETDEWEB)

Bagraev, N. T., E-mail: Bagraev@mail.ioffe.ru [Ioffe Institute (Russian Federation); Chaikina, E. I. [Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Division de Fisica Aplicada (Mexico); Danilovskii, E. Yu.; Gets, D. S.; Klyachkin, L. E.; L’vova, T. V.; Malyarenko, A. M. [Ioffe Institute (Russian Federation)

2016-04-15

The sulfur passivation of the semi-insulating GaAs bulk (SI GaAs) grown in an excess phase of arsenic is used to observe the transition from the Coulomb blockade to the weak localization regime at room temperature. The I–V characteristics of the SI GaAs device reveal nonlinear behavior that appears to be evidence of the Coulomb blockade process as well as the Coulomb oscillations. The sulfur passivation of the SI GaAs device surface results in enormous transformation of the I–V characteristics that demonstrate the strong increase of the resistance and Coulomb blockade regime is replaced by the electron tunneling processes. The results obtained are analyzed within frameworks of disordering SI GaAs surface that is caused by inhomogeneous distribution of the donor and acceptor anti-site defects which affects the conditions of quantum- mechanical tunneling. Weak localization processes caused by the preservation of the Fermi level pinning are demonstrated by measuring the negative magnetoresistance in weak magnetic fields at room temperature. Finally, the studies of the magnetoresistance at higher magnetic fields reveal the h/2e Aharonov–Altshuler–Spivak oscillations with the complicated behavior due to possible statistical mismatch of the interference paths in the presence of different microdefects.

Gluon Bremsstrahlung in Weakly-Coupled Plasmas

International Nuclear Information System (INIS)

Arnold, Peter

2009-01-01

I report on some theoretical progress concerning the calculation of gluon bremsstrahlung for very high energy particles crossing a weakly-coupled quark-gluon plasma. (i) I advertise that two of the several formalisms used to study this problem, the BDMPS-Zakharov formalism and the AMY formalism (the latter used only for infinite, uniform media), can be made equivalent when appropriately formulated. (ii) A standard technique to simplify calculations is to expand in inverse powers of logarithms ln(E/T). I give an example where such expansions are found to work well for ω/T≥10 where ω is the bremsstrahlung gluon energy. (iii) Finally, I report on perturbative calculations of q.

EFFECT OF HORIZONTALLY INHOMOGENEOUS HEATING ON FLOW AND MAGNETIC FIELD IN THE CHROMOSPHERE OF THE SUN

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.

EFFECT OF HORIZONTALLY INHOMOGENEOUS HEATING ON FLOW AND MAGNETIC FIELD IN THE CHROMOSPHERE OF THE SUN

International Nuclear Information System (INIS)

Song, P.; Vasyliūnas, V. M.

2014-01-01

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

Limits to the primordial helium abundance in the baryon-inhomogeneous big bang

Science.gov (United States)

Mathews, G. J.; Schramm, D. N.; Meyer, B. S.

1993-01-01

The parameter space for baryon inhomogeneous big bang models is explored with the goal of determining the minimum helium abundance obtainable in such models while still satisfying the other light-element constraints. We find that the constraint of (D + He-3)/H less than 10 exp -4 restricts the primordial helium mass fraction from baryon-inhomogeneous big bang models to be greater than 0.231 even for a scenario which optimizes the effects of the inhomogeneities and destroys the excess lithium production. Thus, this modification to the standard big bang as well as the standard homogeneous big bang model itself would be falsifiable by observation if the primordial He-4 abundance were observed to be less than 0.231. Furthermore, a present upper limit to the observed helium mass fraction of Y(obs)(p) less than 0.24 implies that the maximum baryon-to-photon ratio allowable in the inhomogeneous models corresponds to eta less than 2.3 x 10 exp -9 (omega(b) h-squared less than 0.088) even if all conditions are optimized.

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.

Determination of critical exponents of inhomogeneous Gd films

International Nuclear Information System (INIS)

Rosales-Rivera, A.; Salazar, N.A.; Hovorka, O.; Idigoras, O.; Berger, A.

2012-01-01

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 AN =200, 400, and 500 °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 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.

On dislocation inhomogeneity of electroerosion crater zone in molybdenum single crystals

International Nuclear Information System (INIS)

Larikov, L.N.; Dubovitskaya, N.V.; Zakharov, S.M.

1979-01-01

Methods of diffraction electron microscopy, X-ray analysis and microhardness measurements have been applied to study the inhomogeneity of dislocation structure of the electroerosion crater zone in molybdenum single crystals. Microhardness inhomogeneous distribution in this zone is established, conditioned by changes in dislocation structure as a result of the development of thermally activated processes of the plastic deformation and dynamic recovery. Dislocationless channels are detected in predeformed crystals

Global thermodynamics of confined inhomogeneous dilute gases: A semi-classical approach

Science.gov (United States)

Poveda-Cuevas, F. J.; Reyes-Ayala, I.; Seman, J. A.; Romero-Rochín, V.

2018-04-01

In this work we present our contribution to the Latin American School of Physics "Marcos Moshinsky" 2017 on Quantum Correlations which was held in Mexico City during the summer of 2017. We review the efforts that have been done to construct a global thermodynamic description of ultracold dilute gases confined in inhomogeneous potentials. This is difficult because the presence of this non-uniform trap makes the pressure of the gas to be a spatially dependent variable and its volume an ambiguously defined quantity. In this paper we introduce new global thermodynamic variables, equivalent to pressure and volume, and propose a realistic model of the equation of state of the system. This model is based on a mean-field approach which asymptotically reaches the Thomas-Fermi limit for a weakly interacting Bose gas. We put special emphasis to the transition between the normal and superfluid phases by studying the behavior of the isothermal compressibility across the transition. We reveal how the potential modifies the critical properties of the transition by determining the critical exponents associated to the divergences not of the susceptibilities but of their derivatives.

On the radio source scintillations caused by plasma inhomogeneities behind a shock wave

International Nuclear Information System (INIS)

Pimenov, S.F.

1984-01-01

The turbulence in the interplanetary and interstellar medium is shown to become anisotropic and statistically inhomogeneous after a shock wave passing. Scintillation intensity spectra of radio sources are estimated. The possibilities to derive the inhomogeneity spectra and source brightness distribution from scintillation changes are discussed

The voltammetric responses of nanometer-sized electrodes in weakly supported electrolyte: A theoretical study

International Nuclear Information System (INIS)

Liu Yuwen; Zhang Qianfan; Chen Shengli

2010-01-01

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.

The voltammetric responses of nanometer-sized electrodes in weakly supported electrolyte: A theoretical study

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.

Percolation, statistical topography, and transport in random media

International Nuclear Information System (INIS)

Isichenko, M.B.

1992-01-01

A review of classical percolation theory is presented, with an emphasis on novel applications to statistical topography, turbulent diffusion, and heterogeneous media. Statistical topography involves the geometrical properties of the isosets (contour lines or surfaces) of a random potential ψ(x). For rapidly decaying correlations of ψ, the isopotentials fall into the same universality class as the perimeters of percolation clusters. The topography of long-range correlated potentials involves many length scales and is associated either with the correlated percolation problem or with Mandelbrot's fractional Brownian reliefs. In all cases, the concept of fractal dimension is particularly fruitful in characterizing the geometry of random fields. The physical applications of statistical topography include diffusion in random velocity fields, heat and particle transport in turbulent plasmas, quantum Hall effect, magnetoresistance in inhomogeneous conductors with the classical Hall effect, and many others where random isopotentials are relevant. A geometrical approach to studying transport in random media, which captures essential qualitative features of the described phenomena, is advocated

Photon storage in ¿-type optically dense atomic media. IV. Optimal control using gradient ascent

DEFF Research Database (Denmark)

Gorshkov, Alexey V.; Calarco, Tomasso; Lukin, Mikhail D.

2008-01-01

We use the numerical gradient ascent method from optimal control theory to extend efficient photon storage in -type media to previouslyinaccessible regimes and to provide simple intuitive explanations for our optimization techniques. In particular, by using gradient ascent to shape classical....... We also demonstrate that the often discussed connection between time reversal andoptimality in photon storage follows naturally from gradient ascent. Finally, we discuss the optimization of controlled reversible inhomogeneous broadening....

Random field assessment of nanoscopic inhomogeneity of bone.

Science.gov (United States)

Dong, X Neil; Luo, Qing; Sparkman, Daniel M; Millwater, Harry R; Wang, Xiaodu

2010-12-01

Bone quality is significantly correlated with the inhomogeneous distribution of material and ultrastructural properties (e.g., modulus and mineralization) of the tissue. Current techniques for quantifying inhomogeneity consist of descriptive statistics such as mean, standard deviation and coefficient of variation. However, these parameters do not describe the spatial variations of bone properties. The objective of this study was to develop a novel statistical method to characterize and quantitatively describe the spatial variation of bone properties at ultrastructural levels. To do so, a random field defined by an exponential covariance function was used to represent the spatial uncertainty of elastic modulus by delineating the correlation of the modulus at different locations in bone lamellae. The correlation length, a characteristic parameter of the covariance function, was employed to estimate the fluctuation of the elastic modulus in the random field. Using this approach, two distribution maps of the elastic modulus within bone lamellae were generated using simulation and compared with those obtained experimentally by a combination of atomic force microscopy and nanoindentation techniques. The simulation-generated maps of elastic modulus were in close agreement with the experimental ones, thus validating the random field approach in defining the inhomogeneity of elastic modulus in lamellae of bone. Indeed, generation of such random fields will facilitate multi-scale modeling of bone in more pragmatic details. Copyright © 2010 Elsevier Inc. All rights reserved.

The influence of inhomogeneities on the dose distribution of fast electrons in radiotherapy

International Nuclear Information System (INIS)

Windemuth, M.

1985-01-01

Simple models are used to make a principal comparison between measured fast-electron dose distributions behind tissue inhomogeneities and those calculated by means of an irradiation planning system. The different organs were represented by water (for muscle), by cork (for the lungs) and by graphite (for bone). Corresponding to their density, inhomogeneities result, in principle, in a dose shift to a greater or smaller body depth which is correctly considered by the irradiation planning system. However, electron scattering transversal to beam direction will occur behind inhomogeneity edges which, in general, are not covered by the irradiation planning system, but which result in dose distributions deviating strongly from those expected as due to the shift. This is the reason for the limited accuracy of irradiation planning systems in complicated inhomogeneity distribution. The thesis demonstrates those cases which justify irradiation planning and those cases where they are not a reliable basis for irradiation. (orig./HP) [de

Reflection of oblique electron thermal modes in an inhomogeneous plasma

International Nuclear Information System (INIS)

Ohnuma, T.; Watanabe, T.; Sanuki, H.

1980-04-01

In an inhomogeneous magnetoplasma, reflection of an oblique electron thermal mode radiated from a local source is investigated experimentally and theoretically near the electron plasma frequency layer. The experimental observation of reflection in the lower plasma density region than the f sub(p)-layer is found to be in qualitative accord with the theoretical reflection, which is obtained from a kinetic theory in an inhomogeneous magnetoplasma. The reflection of the thermal mode is also compared with that of an electromagnetic mode at the f sub(p)-layer. (author)

Estimation of geometrically undistorted B0 inhomogeneity maps

International Nuclear Information System (INIS)

Matakos, A; Balter, J; Cao, Y

2014-01-01

Geometric accuracy of MRI is one of the main concerns for its use as a sole image modality in precision radiation therapy (RT) planning. In a state-of-the-art scanner, system level geometric distortions are within acceptable levels for precision RT. However, subject-induced B 0 inhomogeneity may vary substantially, especially in air-tissue interfaces. Recent studies have shown distortion levels of more than 2 mm near the sinus and ear canal are possible due to subject-induced field inhomogeneity. These distortions can be corrected with the use of accurate B 0 inhomogeneity field maps. Most existing methods estimate these field maps from dual gradient-echo (GRE) images acquired at two different echo-times under the assumption that the GRE images are practically undistorted. However distortion that may exist in the GRE images can result in estimated field maps that are distorted in both geometry and intensity, leading to inaccurate correction of clinical images. This work proposes a method for estimating undistorted field maps from GRE acquisitions using an iterative joint estimation technique. The proposed method yields geometrically corrected GRE images and undistorted field maps that can also be used for the correction of images acquired by other sequences. The proposed method is validated through simulation, phantom experiments and applied to patient data. Our simulation results show that our method reduces the root-mean-squared error of the estimated field map from the ground truth by ten-fold compared to the distorted field map. Both the geometric distortion and the intensity corruption (artifact) in the images caused by the B 0 field inhomogeneity are corrected almost completely. Our phantom experiment showed improvement in the geometric correction of approximately 1 mm at an air-water interface using the undistorted field map compared to using a distorted field map. The proposed method for undistorted field map estimation can lead to improved geometric

Estimation of geometrically undistorted B0 inhomogeneity maps

Science.gov (United States)

Matakos, A.; Balter, J.; Cao, Y.

2014-09-01

Geometric accuracy of MRI is one of the main concerns for its use as a sole image modality in precision radiation therapy (RT) planning. In a state-of-the-art scanner, system level geometric distortions are within acceptable levels for precision RT. However, subject-induced B0 inhomogeneity may vary substantially, especially in air-tissue interfaces. Recent studies have shown distortion levels of more than 2 mm near the sinus and ear canal are possible due to subject-induced field inhomogeneity. These distortions can be corrected with the use of accurate B0 inhomogeneity field maps. Most existing methods estimate these field maps from dual gradient-echo (GRE) images acquired at two different echo-times under the assumption that the GRE images are practically undistorted. However distortion that may exist in the GRE images can result in estimated field maps that are distorted in both geometry and intensity, leading to inaccurate correction of clinical images. This work proposes a method for estimating undistorted field maps from GRE acquisitions using an iterative joint estimation technique. The proposed method yields geometrically corrected GRE images and undistorted field maps that can also be used for the correction of images acquired by other sequences. The proposed method is validated through simulation, phantom experiments and applied to patient data. Our simulation results show that our method reduces the root-mean-squared error of the estimated field map from the ground truth by ten-fold compared to the distorted field map. Both the geometric distortion and the intensity corruption (artifact) in the images caused by the B0 field inhomogeneity are corrected almost completely. Our phantom experiment showed improvement in the geometric correction of approximately 1 mm at an air-water interface using the undistorted field map compared to using a distorted field map. The proposed method for undistorted field map estimation can lead to improved geometric

Spectral finite element method wave propagation, diagnostics and control in anisotropic and inhomogeneous structures

CERN Document Server

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.

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...... 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 semianalytic 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 semianalytic protocol...

Effect of base-pair inhomogeneities on charge transport along the DNA molecule, mediated by twist and radial polarons

International Nuclear Information System (INIS)

Palmero, F; Archilla, J F R; Hennig, D; Romero, F R

2004-01-01

Some recent results for a three-dimensional, semi-classical, tight-binding model for DNA show that there are two types of polarons, namely radial and twist polarons, which can transport charge along the DNA molecule. However, the existence of two types of base pairs in real DNA makes it crucial to find out if charge transport also exists in DNA chains with different base pairs. In this paper, we address this problem in its simple case, a homogeneous chain except for a single different base pair, which we call a base-pair inhomogeneity, and its effect on charge transport. Radial polarons experience either reflection or trapping. However, twist polarons are good candidates for charge transport along real DNA. This transport is also very robust with respect to weak parametric and diagonal disorder

Stabilization of the dissipation-free current transport in inhomogeneous MgB2 thin films

International Nuclear Information System (INIS)

Treiber, S.; Stahl, C.; Schütz, G.; Soltan, S.; Albrecht, J.

2014-01-01

Highlights: • We investigate transport properties of inhomogeneous MgB 2 films. • An inhomogeneous microstructure stabilizes supercurrents. • Vortex pinning forces and energies have been analyzed experimentally. • In inhomogeneous films the increase of the pinning energy is responsible for stable supercurrents. - Abstract: In type-II superconductors at T = 0 the critical current density is determined by the pinning of flux lines. Considering an arbitrarily shaped energy landscape the pinning force at each pinning site is given by the derivative of the flux line energy with respect to the considered direction. At finite temperatures, in addition, thermal activation can lead to a depinning of flux lines. The governing property in this case is the depth of the corresponding pinning potential, i.e. the pinning energy. We show a detailed analysis of both pinning forces and pinning energies of MgB 2 films with inhomogeneous microstructure. We show that a pronounced increase of the pinning energy is responsible for the significantly enhanced stability of the dissipation-free current transport in thin inhomogeneous MgB 2 films. This is found even if the corresponding pinning forces are small

Propagation of dispersion-nonlinearity-managed solitons in an inhomogeneous erbium-doped fiber system

International Nuclear Information System (INIS)

Mahalingam, A; Porsezian, K; Mani Rajan, M S; Uthayakumar, A

2009-01-01

In this paper, a generalized nonlinear Schroedinger-Maxwell-Bloch model with variable dispersion and nonlinearity management functions, which describes the propagation of optical pulses in an inhomogeneous erbium-doped fiber system under certain restrictive conditions, is under investigation. We derive the Lax pair with a variable spectral parameter and the exact soliton solution is generated from the Baecklund transformation. It is observed that stable solitons are possible only under a very restrictive condition for the spectral parameter and other inhomogeneous functions. For various forms of the inhomogeneous dispersion, nonlinearity and gain/loss functions, construction of different types of solitary waves like classical solitons, breathers, etc is discussed

Integrability and soliton solutions for an inhomogeneous generalized fourth-order nonlinear Schrödinger equation describing the inhomogeneous alpha helical proteins and Heisenberg ferromagnetic spin chains

International Nuclear Information System (INIS)

Wang, Pan; Tian, Bo; Jiang, Yan; Wang, Yu-Feng

2013-01-01

For describing the dynamics of alpha helical proteins with internal molecular excitations, nonlinear couplings between lattice vibrations and molecular excitations, and spin excitations in one-dimensional isotropic biquadratic Heisenberg ferromagnetic spin with the octupole–dipole interactions, we consider an inhomogeneous generalized fourth-order nonlinear Schrödinger equation. Based on the Ablowitz–Kaup–Newell–Segur system, infinitely many conservation laws for the equation are derived. Through the auxiliary function, bilinear forms and N-soliton solutions for the equation are obtained. Interactions of solitons are discussed by means of the asymptotic analysis. Effects of linear inhomogeneity on the interactions of solitons are also investigated graphically and analytically. Since the inhomogeneous coefficient of the equation h=α x+β, the soliton takes on the parabolic profile during the evolution. Soliton velocity is related to the parameter α, distance scale coefficient and biquadratic exchange coefficient, but has no relation with the parameter β. Soliton amplitude and width are only related to α. Soliton position is related to β

On distortions of TPC coordinates: inhomogeneities of electric and magnetic field

CERN Document Server

Dydak, F

2003-01-01

After a general discussion of electron drift in a gas volume with electric and magnetic fields, distortions in the r and r phi coordinates arising from inhomogeneities of the electric and magnetic fields in the HARP TPC are calculated. Inhomogeneities of the electric field arise from i) positive ions released by cosmic rays, ii) positive ions released by interaction secondaries, iii) positive ions released by beam muons, iv) positive ions released from beam particles downstream of the inner field cage, and v) a high voltage misalignment between the outer and inner field cages. Also, distortions arising from the inhomogeneity of the magnetic field are calculated. These effects resolve the controversy on unphysical numbers of 'wrong-charge' TPC tracks. The bad news are that effects are too big to be neglected. The good news are that, with enough sweat and tears, they can be adequately corrected.

Ordering dynamics of self-propelled particles in an inhomogeneous medium

Science.gov (United States)

Das, Rakesh; Mishra, Shradha; Puri, Sanjay

2018-02-01

Ordering dynamics of self-propelled particles in an inhomogeneous medium in two dimensions is studied. We write coarse-grained hydrodynamic equations of motion for density and polarisation fields in the presence of an external random disorder field, which is quenched in time. The strength of inhomogeneity is tuned from zero disorder (clean system) to large disorder. In the clean system, the polarisation field grows algebraically as LP ∼ t0.5 . The density field does not show clean power-law growth; however, it follows Lρ ∼ t0.8 approximately. In the inhomogeneous system, we find a disorder-dependent growth. For both the density and the polarisation, growth slows down with increasing strength of disorder. The polarisation shows a disorder-dependent power-law growth LP(t,Δ) ∼ t1/\\bar zP(Δ) for intermediate times. At late times, there is a crossover to logarithmic growth LP(t,Δ) ∼ (\\ln t)1/\\varphi , where φ is a disorder-independent exponent. Two-point correlation functions for the polarisation show dynamical scaling, but the density does not.

Spatial inhomogeneity in spectra and exciton dynamics in porphyrin ...

Indian Academy of Sciences (India)

inhomogeneity. This is elucidated by time-resolved confocal microscopy. ... dynamics of such supramolecular aggregates. Weisman ... protein scaffold and faithfully represents a biomimetic reminiscent .... increased intermolecular interactions.

Effect of layerwise structural inhomogeneity on stress- corrosion cracking of steel tubes

Science.gov (United States)

Perlovich, Yu A.; Krymskaya, O. A.; Isaenkova, M. G.; Morozov, N. S.; Fesenko, V. A.; Ryakhovskikh, I. V.; Esiev, T. S.

2016-04-01

Based on X-ray texture and structure analysis data of the material of main gas pipelines it was shown that the layerwise inhomogeneity of tubes is formed during their manufacturing. The degree of this inhomogeneity affects on the tendency of tubes to stress- corrosion cracking under exploitation. Samples of tubes were cut out from gas pipelines located under various operating conditions. Herewith the study was conducted both for sections with detected stress-corrosion defects and without them. Distributions along tube wall thickness for lattice parameters and half-width of X-ray lines were constructed. Crystallographic texture analysis of external and internal tube layers was also carried out. Obtained data testifies about considerable layerwise inhomogeneity of all samples. Despite the different nature of the texture inhomogeneity of gas pipeline tubes, the more inhomogeneous distribution of texture or structure features causes the increasing of resistance to stress- corrosion. The observed effect can be explained by saturation with interstitial impurities of the surface layer of the hot-rolled sheet and obtained therefrom tube. This results in rising of lattice parameters in the external layer of tube as compared to those in underlying metal. Thus, internal layers have a compressive effect on external layers in the rolling plane that prevents cracks opening at the tube surface. Moreover, the high mutual misorientation of grains within external and internal layers of tube results in the necessity to change the moving crack plane, so that the crack growth can be inhibited when reaching the layer with a modified texture.

Effects of dipole magnet inhomogeneities on the beam ellipsoid

International Nuclear Information System (INIS)

Tsoupas, N.; Colman, J.; Levine, M.; McKenzie-Wilson, R.; Ward, T.; Grand, P.

1986-01-01

The RAYTRACE computer code has been modified to accept magnetic fields measured in the median plane of a dipole magnet. This modification allows one to study the effects of a non-ideal dipole magnet on the beam ellipsoid (as defined by the TRANSPORT code manual). The effects on the beam ellipsoid are due to: field inhomogeneities in the interior region of the dipole, and discrepancies from design conditions of the magnetic field values in the fringe field region. The results of the RAYTRACE code calculations based on experimentally measured fields will be compared with the results derived using both an ideal (no inhomogeneities) dipole with SCOFF boundaries and an ideal dipole with perfect (according to design) fringe fields

Thermal domains in inhomogeneous current-carrying superconductors. Current-voltage characteriscs and dynamics of domain formation after current jumps

International Nuclear Information System (INIS)

Bezuglyj, A.I.; Shklovskij, V.A.

1984-01-01

The static and dynamic behavior of thermal domains in inhomogeneous superconducting films, where the inhomogeneity behaves like a portion of the film with a reduced critical current, have been studied theoretically within the framework of the phenomenological approach, using the heat balance equation and the dependence of the superconductor critical current on temperature. Depending on the size of the inhomogeneity (local or extended) and on the relative values of parameters of the homogeneous and inhomogeneous regions, different types of current-voltage characteristics are obtained. The nonstationary problem of thermal domain formation near the inhomogeneity after a current jump has been solved, and the domain boundary (kink) dynamics at a distance from the inhomogeneity has been analyzed. A combination of the results allows one to describe the whole process of normal phase formation and its spread throughout the superconducting film

Excitation of magnetic inhomogeneities in three-layer ferromagnetic structure with different parameters of the magnetic anisotropy and exchange

Energy Technology Data Exchange (ETDEWEB)

Ekomasov, E.G., E-mail: EkomasovEG@gmail.com [Bashkir State University, 32, Validy Str., Ufa, 450076 (Russian Federation); Murtazin, R.R. [Bashkir State University, 32, Validy Str., Ufa, 450076 (Russian Federation); Nazarov, V.N. [Institute of Molecule and Crystal Physics Ufa Research Centre of Russian Academy of Sciences, Prospekt Oktyabrya 151, Ufa, 450075 (Russian Federation)

2015-07-01

The generation and evolution of magnetic inhomogeneities, emerging in a thin flat layer with the parameters of the magnetic anisotropy and exchange interaction, with the parameters different from other two thick layers of the three-layer ferromagnetic structure, were investigated. The parameters ranges that determine the possibility of their existence were found. The possibility of the external magnetic field influence on the structure and dynamic properties of localized magnetic inhomogeneities was shown. - Highlights: • The generation of magnetic inhomogeneities in the three-layer ferromagnetic. • The influence of an external field on the parameters of magnetic inhomogeneities. • Numerical study of the structure and dynamics of magnetic inhomogeneities.

Relationship between the Amplitude and Phase of a Signal Scattered by a Point-Like Acoustic Inhomogeneity

Science.gov (United States)

Burov, V. A.; Morozov, S. A.

2001-11-01

Wave scattering by a point-like inhomogeneity, i.e., a strong inhomogeneity with infinitesimal dimensions, is described. This type of inhomogeneity model is used in investigating the point-spread functions of different algorithms and systems. Two approaches are used to derive the rigorous relationship between the amplitude and phase of a signal scattered by a point-like acoustic inhomogeneity. The first approach is based on a Marchenko-type equation. The second approach uses the scattering by a scatterer whose size decreases simultaneously with an increase in its contrast. It is shown that the retarded and advanced waves are scattered differently despite the relationship between the phases of the corresponding scattered waves.

Inhomogeneous vortex tangles in counterflow superfluid turbulence: flow in convergent channels

Directory of Open Access Journals (Sweden)

Saluto Lidia

2016-06-01

Full Text Available We investigate the evolution equation for the average vortex length per unit volume L of superfluid turbulence in inhomogeneous flows. Inhomogeneities in line density L andincounterflowvelocity V may contribute to vortex diffusion, vortex formation and vortex destruction. We explore two different families of contributions: those arising from asecondorder expansionofthe Vinenequationitself, andthose whichare notrelated to the original Vinen equation but must be stated by adding to it second-order terms obtained from dimensional analysis or other physical arguments.

Cliques in dense inhomogenous random graphs

Czech Academy of Sciences Publication Activity Database

Doležal, Martin; Hladký, Jan; Máthé, A.

2017-01-01

Roč. 51, č. 2 (2017), s. 275-314 ISSN 1042-9832 R&D Projects: GA ČR GA16-07378S EU Projects: European Commission(XE) 628974 - PAECIDM Institutional support: RVO:67985840 Keywords : inhomogeneous random graphs * clique number Subject RIV: BA - General Mathematics OBOR OECD: Pure mathematics Impact factor: 1.243, year: 2016 http://onlinelibrary.wiley.com/doi/10.1002/ rsa .20715/abstract

Cliques in dense inhomogenous random graphs

Czech Academy of Sciences Publication Activity Database

Doležal, Martin; Hladký, Jan; Máthé, A.

2017-01-01

Roč. 51, č. 2 (2017), s. 275-314 ISSN 1042-9832 R&D Projects: GA ČR GA16-07378S EU Projects: European Commission(XE) 628974 - PAECIDM Institutional support: RVO:67985840 Keywords : inhomogeneous random graphs * clique number Subject RIV: BA - General Mathematics OBOR OECD: Pure mathematics Impact factor: 1.243, year: 2016 http://onlinelibrary.wiley.com/doi/10.1002/rsa.20715/abstract

Measurements of the electron dose distribution near inhomogeneities using a plastic scintillation detector

International Nuclear Information System (INIS)

Wells, C.M.M.; Mackie, T.R.; Podgorsak, M.B.; Holmes, M.A.; Papanikolaou, N.; Reckwerdt, P.J.; Cygler, J.; Rogers, D.W.O.; Bielajew, A.F.; Schmidt, D.G.

1994-01-01

Accurate measurement of the electron dose distribution near an inhomogeneity is difficult with traditional dosimeters which themselves perturb the electron field. The authors tested the performance of a new high resolution, water-equivalent plastic scintillation detector which has ideal properties for this application. A plastic scintillation detector with a 1 mm diameter, 3 mm long cylindrical sensitive volume was used to measure the dose distributions behind standard benchmark inhomogeneities in water phantoms. The plastic scintillator material is more water equivalent than polystyrene in terms of its mass collision stopping power and mass scattering power. Measurements were performed for beams of electrons having initial energies of 6 and 18 MeV at depths from 0.2-4.2 cm behind the inhomogeneities. The detector reveals hot and cold spots behind heterogeneities at resolutions equivalent to typical film digitizer spot sizes. Plots of the dose distributions behind air, aluminum, lead, and formulations for cortical and inner bone-equivalent materials are presented. The plastic scintillation detector is suited for measuring the electron dose distribution near an inhomogeneity. 14 refs., 9 figs

Moessbauer spectroscopy of locally inhomogeneous systems

International Nuclear Information System (INIS)

Rusakov, V. S.; Kadyrzhanov, K. K.

2004-01-01

Substances with characteristic local inhomogeneities - with different from position to position neighborhood and properties of like atoms - gain recently increased scientific attention and wide practical application. We would call a system locally inhomogeneous if atoms in the system are in non-equivalent atomic locations and reveal different properties. Such systems are, first of all, variable composition phases, amorphous, multi-phase, admixture, defect and other systems. LIS are most convenient model objects for studies of structure, charge, and spin atomic states, interatomic interactions, relations between matter properties and its local characteristics as well as for studies of diffusion kinetics, phase formation, crystallization and atomic ordering; all that explains considerable scientific interest in such LIS. Such systems find their practical application due to wide spectrum of useful, and sometimes unique, properties that can be controlled varying character and degree of local inhomogeneity. Moessbauer spectroscopy is one of the most effective methods for investigation of LIS. Local character of obtained information combined with information on cooperative phenomena makes it possible to run investigations impossible for other methods. Moessbauer spectroscopy may provide with abundant information on peculiarities of macro- and microscopic state of matter including that for materials without regular structure. At the same time, analysis, processing and interpretation of Moessbauer spectra for LIS (that are sets of a large amount of partial spectra) face considerable difficulties. Development of computer technique is accompanied with development of mathematical methods used for obtaining physical information from experimental data. The methods make it possible to improve considerably, with some available a priori information, effectiveness of the research. Utilization of up-to-date mathematical methods in Moessbauer spectroscopy requires not only adaptation

Artificial blood-flow controlling effects of inhomogeneity of twisted magnetic fields

Science.gov (United States)

Nakagawa, Hidenori; Ohuchi, Mikio

2017-06-01

We developed a blood-flow controlling system using magnetic therapy for some types of nervous diseases. In our research, we utilized overlapped extremely low frequency (ELF) fields for the most effective blood-flow for the system. Results showed the possibility that the inhomogeneous region obtained by overlapping the fields at 50 Hz, namely, a desirably twisted field revealed a significant difference in induced electromotive forces at the insertion points of electrodes. In addition, ELF exposures with a high inhomogeneity of the twisted field at 50 Hz out of phase were more effective in generating an induced electromotive difference by approximately 31%, as contrasted with the difference generated by the exposure in phase. We expect that the increase of the inhomogeneity of the twisted field around a blood vessel can produce the most effective electromotive difference in the blood, and also moderately affect the excitable cells relating to the autonomic nervous system for an outstanding blood-flow control in vivo.

TPC track distortions: correction maps for magnetic and static electric inhomogeneities

CERN Document Server

Dydak, F; Nefedov, Y

2003-01-01

Inhomogeneities of the magnetic and electric fields in the active TPC volume lead to displacements of cluster coordinates, and therefore to track distortions. In case of good data taking conditions, the largest effects are expected from the inhomogeneity of the solenoidal magnetic field, and from a distortion of the electric field arising from a high voltage misalignment between the outer and inner field cages. Both effects are stable over the entire HARP data taking. The displacements are large compared to the azimuthal coordinate resolution but can be corrected with sufficient precision, except at small TPC radius. The high voltage misalignment between the outer and inner field cages is identified as the likely primary cause of sagitta distortions of TPC tracks. The position and the length of the target plays an important role. Based on a detailed modelling of the magnetic and static electric field inhomogeneities, precise correction maps for both effects have been calculated. Predictions from the correctio...

Waveguide effect under 'antiguiding' conditions in graded anisotropic media.

Science.gov (United States)

Kozlov, A V; Mozhaev, V G; Zyryanova, A V

2010-02-24

A new wave confinement effect is predicted in graded crystals with a concave slowness surface under conditions of growth of the phase velocity with decreasing distance from the waveguide axis. This finding overturns the common notion about the guiding and 'antiguiding' profiles of wave velocity in inhomogeneous media. The waveguide effect found is elucidated by means of ray analysis and particular exact wave solutions. The exact solution obtained for localized flexural waves in thin plates of graded cubic and tetragonal crystals confirms the predicted effect. Since this solution is substantially different with respect to the existence conditions from all others yet reported, and it cannot be deduced from the previously known results, the predicted waves can be classified as a new type of waveguide mode in graded anisotropic media. Although the concrete calculations are given in the article for acoustic waves, its general predictions are expected to be valid for waves of various natures, including spin, plasma, and optical waves.

Waveguide effect under 'antiguiding' conditions in graded anisotropic media

International Nuclear Information System (INIS)

Kozlov, A V; Mozhaev, V G; Zyryanova, A V

2010-01-01

A new wave confinement effect is predicted in graded crystals with a concave slowness surface under conditions of growth of the phase velocity with decreasing distance from the waveguide axis. This finding overturns the common notion about the guiding and 'antiguiding' profiles of wave velocity in inhomogeneous media. The waveguide effect found is elucidated by means of ray analysis and particular exact wave solutions. The exact solution obtained for localized flexural waves in thin plates of graded cubic and tetragonal crystals confirms the predicted effect. Since this solution is substantially different with respect to the existence conditions from all others yet reported, and it cannot be deduced from the previously known results, the predicted waves can be classified as a new type of waveguide mode in graded anisotropic media. Although the concrete calculations are given in the article for acoustic waves, its general predictions are expected to be valid for waves of various natures, including spin, plasma, and optical waves.

Relation of wave energy and momentum with the plasma dispersion relation in an inhomogeneous plasma

International Nuclear Information System (INIS)

Berk, H.L.; Pfirsch, D.

1988-01-01

The expressions for wave energy and angular momentum commonly used in homogeneous and near-homogeneous media is generalized to inhomogeneous media governed by a nonlocal conductivity tensor. The expression for wave energy applies to linear excitations in an arbitrary three-dimensional equilibrium, while the expression for angular momentum applies to linear excitations of azimuthally symmetric equilibria. The wave energy E-script/sub wave/ is interpreted as the energy transferred from linear external sources to the plasma if there is no dissipation. With dissipation, such a simple interpretation is lacking as energy is also thermally absorbed. However, for azimuthally symmetric equilibria, the expression for the wave energy in a frame rotating with a frequency ω can be unambiguously separated from thermal energy. This expression is given by E-script/sub wave/ -ωL/sub wave/ l, where L/sub wave/ is the wave angular momentum defined in the text and l the azimuthal wavenumber and it is closely related to the real part of a dispersion relation for marginal stability. The imaginary part of the dispersion is closely related to the energy input into a system. Another useful quantity discussed is the impedance form, which can be used for three-dimensional equilibrium without an ignorable coordinate and the expression is closely related to the wave impedance used in antenna theory. Applications to stability theory are also discussed

Inhomogeneous ozone doping and heat induced defects in graphene studied by infrared near-field microscopy

Science.gov (United States)

Wang, Wenjie; Zhang, Jiawei; Deng, Haiming; Liu, Megnkun; Xu, Du

With the potential use of surface plasmon such as transfer data many orders faster than traditional wires, it has been very popular in research. The fact is that the wavelength of of plasmon is much shorter than the one of free space radiation. The UV ozone doping level can be fine controlled in room temperature creating selected plasmon circuit. We study inhomogeneous graphene plasmonics in ozone doped graphene using scattering-type scanning near-field infrared microscopy and spectroscopy. The single layer and bilayer graphene are doped with different dosage of ozone under UV exposure, which lead to surface inhomogeneity and inhomogeneous graphene plasmon polarition excitation under tip. After annealing the ozone doped graphene in air, the inhomogeneous doping induced plasmons disappear, together with the occurrence of local defects after high temperature annealing.

Inhomogeneous target-dose distributions: a dimension more for optimization?

International Nuclear Information System (INIS)

Gersem, Werner R.T. de; Derycke, Sylvie; Colle, Christophe O.; Wagter, Carlos de; Neve, Wilfried J. de

1999-01-01

Purpose: To evaluate if the use of inhomogeneous target-dose distributions, obtained by 3D conformal radiotherapy plans with or without beam intensity modulation, offers the possibility to decrease indices of toxicity to normal tissues and/or increase indices of tumor control stage III non-small cell lung cancer (NSCLC). Methods and Materials: Ten patients with stage III NSCLC were planned using a conventional 3D technique and a technique involving noncoplanar beam intensity modulation (BIM). Two planning target volumes (PTVs) were defined: PTV1 included macroscopic tumor volume and PTV2 included macroscopic and microscopic tumor volume. Virtual simulation defined the beam shapes and incidences as well as the wedge orientations (3D) and segment outlines (BIM). Weights of wedged beams, unwedged beams, and segments were determined by optimization using an objective function with a biological and a physical component. The biological component included tumor control probability (TCP) for PTV1 (TCP1), PTV2 (TCP2), and normal tissue complication probability (NTCP) for lung, spinal cord, and heart. The physical component included the maximum and minimum dose as well as the standard deviation of the dose at PTV1. The most inhomogeneous target-dose distributions were obtained by using only the biological component of the objective function (biological optimization). By enabling the physical component in addition to the biological component, PTV1 inhomogeneity was reduced (biophysical optimization). As indices for toxicity to normal tissues, NTCP-values as well as maximum doses or dose levels to relevant fractions of the organ's volume were used. As indices for tumor control, TCP-values as well as minimum doses to the PTVs were used. Results: When optimization was performed with the biophysical as compared to the biological objective function, the PTV1 inhomogeneity decreased from 13 (8-23)% to 4 (2-9)% for the 3D-(p = 0.00009) and from 44 (33-56)% to 20 (9-34)% for the BIM

Inhomogeneous compact extra dimensions

Energy Technology Data Exchange (ETDEWEB)

Bronnikov, K.A. [Center of Gravity and Fundamental Metrology, VNIIMS, 46 Ozyornaya st., Moscow 119361 (Russian Federation); Budaev, R.I.; Grobov, A.V.; Dmitriev, A.E.; Rubin, Sergey G., E-mail: kb20@yandex.ru, E-mail: buday48@mail.ru, E-mail: alexey.grobov@gmail.com, E-mail: alexdintras@mail.ru, E-mail: sergeirubin@list.ru [National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409 Moscow (Russian Federation)

2017-10-01

We show that an inhomogeneous compact extra space possesses two necessary features— their existence does not contradict the observable value of the cosmological constant Λ{sub 4} in pure f ( R ) theory, and the extra dimensions are stable relative to the 'radion mode' of perturbations, the only mode considered. For a two-dimensional extra space, both analytical and numerical solutions for the metric are found, able to provide a zero or arbitrarily small Λ{sub 4}. A no-go theorem has also been proved, that maximally symmetric compact extra spaces are inconsistent with 4D Minkowski space in the framework of pure f ( R ) gravity.

Head-on collision between positron acoustic waves in homogeneous and inhomogeneous plasmas

Science.gov (United States)

Alam, M. S.; Hafez, M. G.; Talukder, M. R.; Ali, M. Hossain

2018-05-01

The head-on collision between positron acoustic solitary waves (PASWs) as well as the production of rogue waves (RWs) in homogeneous and PASWs in inhomogeneous unmagnetized plasma systems are investigated deriving the nonlinear evolution equations. The plasmas are composed of immobile positive ions, mobile cold and hot positrons, and hot electrons, where the hot positrons and hot electrons are assumed to follow the Kappa distributions. The evolution equations are derived using the appropriate coordinate transformation and the reductive perturbation technique. The effects of concentrations, kappa parameters of hot electrons and positrons, and temperature ratios on the characteristics of PASWs and RWs are examined. It is found that the kappa parameters and temperature ratios significantly modify phase shifts after head-on collisions and RWs in homogeneous as well as PASWs in inhomogeneous plasmas. The amplitudes of the PASWs in inhomogeneous plasmas are diminished with increasing kappa parameters, concentration and temperature ratios. Further, the amplitudes of RWs are reduced with increasing charged particles concentration, while it enhances with increasing kappa- and temperature parameters. Besides, the compressive and rarefactive solitons are produced at critical densities from KdV equation for hot and cold positrons, while the compressive solitons are only produced from mKdV equation for both in homogeneous and inhomogeneous plasmas.

Numerical modeling of Gaussian beam propagation and diffraction in inhomogeneous media based on the complex eikonal equation

Science.gov (United States)

Huang, Xingguo; Sun, Hui

2018-05-01

Gaussian beam is an important complex geometrical optical technology for modeling seismic wave propagation and diffraction in the subsurface with complex geological structure. Current methods for Gaussian beam modeling rely on the dynamic ray tracing and the evanescent wave tracking. However, the dynamic ray tracing method is based on the paraxial ray approximation and the evanescent wave tracking method cannot describe strongly evanescent fields. This leads to inaccuracy of the computed wave fields in the region with a strong inhomogeneous medium. To address this problem, we compute Gaussian beam wave fields using the complex phase by directly solving the complex eikonal equation. In this method, the fast marching method, which is widely used for phase calculation, is combined with Gauss-Newton optimization algorithm to obtain the complex phase at the regular grid points. The main theoretical challenge in combination of this method with Gaussian beam modeling is to address the irregular boundary near the curved central ray. To cope with this challenge, we present the non-uniform finite difference operator and a modified fast marching method. The numerical results confirm the proposed approach.

Friction, slip and structural inhomogeneity of the buried interface

International Nuclear Information System (INIS)

Dong, Y; Wu, J; Martini, A; Li, Q

2011-01-01

An atomistic model of metallic contacts using realistic interatomic potentials is used to study the connection between friction, slip and the structure of the buried interface. Incommensurability induced by misalignment and lattice mismatch is modeled with contact sizes that are large enough to observe superstructures formed by the relative orientations of the surfaces. The periodicity of the superstructures is quantitatively related to inhomogeneous shear stress distributions in the contact area, and a reduced order model is used to clarify the connection between friction and structural inhomogeneity. Finally, the movement of atoms is evaluated before, during and after slip in both aligned and misaligned contacts to understand how the interfacial structure affects the mechanisms of slip and the corresponding frictional behavior

Fluence inhomogeneities due to a ripple filter induced Moiré effect.

Science.gov (United States)

Ringbæk, Toke Printz; Brons, Stephan; Naumann, Jakob; Ackermann, Benjamin; Horn, Julian; Latzel, Harald; Scheloske, Stefan; Galonska, Michael; Bassler, Niels; Zink, Klemens; Weber, Uli

2015-02-07

At particle therapy facilities with pencil beam scanning, the implementation of a ripple filter (RiFi) broadens the Bragg peak, so fewer energy steps from the accelerator are required for a homogeneous dose coverage of the planning target volume (PTV). However, sharply focusing the scanned pencil beams at the RiFi plane by ion optical settings can lead to a Moiré effect, causing fluence inhomogeneities at the isocenter. This has been experimentally proven at the Heidelberg Ionenstrahl-Therapiezentrum (HIT), Universitätsklinikum Heidelberg, Germany. 150 MeV u(-1) carbon-12 ions are used for irradiation with a 3 mm thick RiFi. The beam is focused in front of and as close to the RiFi plane as possible. The pencil beam width is estimated to be 0.78 mm at a 93 mm distance from the RiFi. Radiographic films are used to obtain the fluence profile 30 mm in front of the isocenter, 930 mm from the RiFi. The Monte Carlo (MC) code SHIELD-HIT12A is used to determine the RiFi-induced inhomogeneities in the fluence distribution at the isocenter for a similar setup, pencil beam widths at the RiFi plane ranging from σχ(RiFi to 1.2 mm and for scanning step sizes ranging from 1.5 to 3.7 mm. The beam application and monitoring system (BAMS) used at HIT is modelled and simulated. When the width of the pencil beams at the RiFi plane is much smaller than the scanning step size, the resulting inhomogeneous fluence distribution at the RiFi plane interfers with the inhomogeneous RiFi mass distribution and fluence inhomogeneity can be observed at the isocenter as large as an 8% deviation from the mean fluence. The inverse of the fluence ripple period at the isocenter is found to be the difference between the inverse of the RiFi period and the inverse of the scanning step size. We have been able to use MC simulations to reproduce the spacing of the ripple stripes seen in films irradiated at HIT. Our findings clearly indicate that pencil beams sharply focused near the RiFi plane result in

Radiation transport in statistically inhomogeneous rocks

International Nuclear Information System (INIS)

Lukhminskij, B.E.

1975-01-01

A study has been made of radiation transfer in statistically inhomogeneous rocks. Account has been taken of the statistical character of rock composition through randomization of density. Formulas are summarized for sigma-distribution, homogeneous density, the Simpson and Cauchy distributions. Consideration is given to the statistics of mean square ranges in a medium, simulated by the jump Markov random function. A quantitative criterion of rock heterogeneity is proposed

Spectroscopy and Raman imaging of inhomogeneous materials

International Nuclear Information System (INIS)

Maslova, Olga

2014-01-01

This thesis is aimed at developing methodologies in Raman spectroscopy and imaging. After reviewing the statistical instruments which allow treating giant amount of data (multivariate analysis and classification), the study is applied to two families of well-known materials which are used as models for testing the limits of the implemented developments. The first family is a series of carbon materials pyrolyzed at various temperatures and exhibiting inhomogeneities at a nm scale which is suitable for Raman-X-ray diffraction combination. Another results concern the polishing effect on carbon structure. Since it is found to induce Raman artifacts leading to the overestimation of the local structural disorder, a method based on the use of the G band width is therefore proposed in order to evaluate the crystallite size in both unpolished and polished nano-graphites. The second class of materials presents inhomogeneities at higher (micrometric) scales by the example of uranium dioxide ceramics. Being well adapted in terms of spatial scale, Raman imaging is thus used for probing their surfaces. Data processing is implemented via an approach combining the multivariate (principal component) analysis and the classical fitting procedure with Lorentzian profiles. The interpretation of results is supported via electron backscattering diffraction (EBSD) analysis which enables us to distinguish the orientation effects of ceramic grains from other underlying contributions. The last ones are mainly localized at the grain boundaries, that is testified by the appearance of a specific Raman mode. Their origin seems to be caused by stoichiometric oxygen variations or impurities, as well as strain inhomogeneities. The perspectives of this work include both the implementation of other mathematical methods and in-depth analysis of UO 2 structure damaged by irradiation (anisotropic effects, role of grain boundaries). (author) [fr

Network-derived inhomogeneity in monthly rainfall analyses over western Tasmania

International Nuclear Information System (INIS)

Fawcett, Robert; Trewin, Blair; Barnes-Keoghan, Ian

2010-01-01

Monthly rainfall in the wetter western half of Tasmania was relatively poorly observed in the early to middle parts of the 20th century, and this causes a marked inhomogeneity in the operational gridded monthly rainfall analyses generated by the Australian Bureau of Meteorology up until the end of 2009. These monthly rainfall analyses were generated for the period 1900 to 2009 in two forms; a national analysis at 0.25 0 latitude-longitude resolution, and a southeastern Australia regional analysis at 0.1 0 resolution. For any given month, they used all the monthly data from the standard Bureau rainfall gauge network available in the Australian Data Archive for Meteorology. Since this network has changed markedly since Federation (1901), there is obvious scope for network-derived inhomogeneities in the analyses. In this study, we show that the topography-resolving techniques of the new Australian Water Availability Project analyses, adopted as the official operational analyses from the start of 2010, substantially diminish those inhomogeneities, while using largely the same observation network. One result is an improved characterisation of recent rainfall declines across Tasmania. The new analyses are available at two resolutions, 0.25 0 and 0.05 0 .

Inhomogeneous Spin Diffusion in Traps with Cold Atoms

DEFF Research Database (Denmark)

Heiselberg, Henning

2012-01-01

increases. The inhomogeneity and the smaller nite trap size signicantly reduce the spin diusion rate at low temperatures. The resulting spin diusion rates and spin drag at longer time scales are compatible with measurements at low to high temperatures for resonant attractive interactions...

Heating and acceleration of solar wind ions by turbulent wave spectrum in inhomogeneous expanding plasma

Energy Technology Data Exchange (ETDEWEB)

Ofman, Leon, E-mail: Leon.Ofman@nasa.gov [Department of Physics, The Catholic University of America, Washington, DC (United States); NASA Goddard Space Flight Center, Greenbelt, MD (United States); Visiting, Department of Geosciences, Tel Aviv University, Tel Aviv (Israel); Ozak, Nataly [Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven (Belgium); Viñas, Adolfo F. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)

2016-03-25

Near the Sun (< 10R{sub s}) the acceleration, heating, and propagation of the solar wind are likely affected by the background inhomogeneities of the magnetized plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects of background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super-Alfvénic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.

Parallel application of plasma equilibrium fitting based on inhomogeneous platforms

International Nuclear Information System (INIS)

Liao Min; Zhang Jinhua; Chen Liaoyuan; Li Yongge; Pan Wei; Pan Li

2008-01-01

An online analysis and online display platform EFIT, which is based on the equilibrium-fitting mode, is inducted in this paper. This application can realize large data transportation between inhomogeneous platforms by designing a communication mechanism using sockets. It spends approximately one minute to complete the equilibrium fitting reconstruction by using a finite state machine to describe the management node and several node computers of cluster system to fulfill the parallel computation, this satisfies the online display during the discharge interval. An effective communication model between inhomogeneous platforms is provided, which could transport the computing results from Linux platform to Windows platform for online analysis and display. (authors)

Inhomogeneous Relaxation of a Molecular Layer on an Insulator due to Compressive Stress

Science.gov (United States)

Bocquet, F.; Nony, L.; Mannsfeld, S. C. B.; Oison, V.; Pawlak, R.; Porte, L.; Loppacher, Ch.

2012-05-01

We discuss the inhomogeneous stress relaxation of a monolayer of hexahydroxytriphenylene (HHTP) which adopts the rare line-on-line (LOL) coincidence on KCl(001) and forms moiré patterns. The fact that the hexagonal HHTP layer is uniaxially compressed along the LOL makes this system an ideal candidate to discuss the influence of inhomogeneous stress relaxation. Our work is a combination of noncontact atomic force microscopy experiments, density functional theory and potential energy calculations, and a thorough interpretation by means of the Frenkel-Kontorova model. We show that the assumption of a homogeneous molecular layer is not valid for this organic-inorganic heteroepitaxial system since the best calculated energy configuration correlates with the experimental data only if inhomogeneous relaxations of the layer are taken into account.

Multi-layer composite mechanical modeling for the inhomogeneous biofilm mechanical behavior.

Science.gov (United States)

Wang, Xiaoling; Han, Jingshi; Li, Kui; Wang, Guoqing; Hao, Mudong

2016-08-01

Experiments showed that bacterial biofilms are heterogeneous, for example, the density, the diffusion coefficient, and mechanical properties of the biofilm are different along the biofilm thickness. In this paper, we establish a multi-layer composite model to describe the biofilm mechanical inhomogeneity based on unified multiple-component cellular automaton (UMCCA) model. By using our model, we develop finite element simulation procedure for biofilm tension experiment. The failure limit and biofilm extension displacement obtained from our model agree well with experimental measurements. This method provides an alternative theory to study the mechanical inhomogeneity in biological materials.

pH-Dependent Solubility and Dissolution Behavior of Carvedilol--Case Example of a Weakly Basic BCS Class II Drug.

Science.gov (United States)

Hamed, Rania; Awadallah, Areeg; Sunoqrot, Suhair; Tarawneh, Ola; Nazzal, Sami; AlBaraghthi, Tamadur; Al Sayyad, Jihan; Abbas, Aiman

2016-04-01

The objective of this study was to investigate the pH-dependent solubility and dissolution of weakly basic Biopharmaceutical Classification Systems (BCS) class II drugs, characterized by low solubility and high permeability, using carvedilol, a weak base with a pK a value of 7.8, as a model drug. A series of solubility and in vitro dissolution studies was carried out using media that simulate the gastric and intestinal fluids and cover the physiological pH range of the GI from 1.2 to 7.8. The effect of ionic strength, buffer capacity, and buffer species of the dissolution media on the solubility and dissolution behavior of carvedilol was also investigated. The study revealed that carvedilol exhibited a typical weak base pH-dependent solubility profile with a high solubility at low pH (545.1-2591.4 μg/mL within the pH range 1.2-5.0) and low solubility at high pH (5.8-51.9 μg/mL within the pH range 6.5-7.8). The dissolution behavior of carvedilol was consistent with the solubility results, where carvedilol release was complete (95.8-98.2% released within 60 min) in media simulating the gastric fluid (pH 1.2-5.0) and relatively low (15.9-86.2% released within 240 min) in media simulating the intestinal fluid (pH 6.5-7.8). It was found that the buffer species of the dissolution media may influence the solubility and consequently the percentage of carvedilol released by forming carvedilol salts of varying solubilities. Carvedilol solubility and dissolution decreased with increasing ionic strength, while lowering the buffer capacity resulted in a decrease in carvedilol solubility and dissolution rate.

Determination of the three-dimensional structure for weakly aligned biomolecules by NMR spectroscopy

International Nuclear Information System (INIS)

Shahkhatuni, Astghik A; Shahkhatuni, Aleksan G

2002-01-01

The key achievements and the potential of NMR spectroscopy for weakly aligned biomolecules are considered. Due to weak alignment, it becomes possible to determine a number of NMR parameters dependent on the orientation of biomolecules, which are averaged to zero in usual isotropic media. The addition of new orientational constraints to standard procedures of 3D structure determination markedly increases the achievable accuracy. The possibility of structure determination for biomolecules using only orientation-dependent parameters without invoking other NMR data is discussed. The methods of orientation, experimental techniques, and calculation methods are systematised. The main results obtained and the prospects of using NMR spectroscopy of weakly aligned systems to study different classes of biomolecules and to solve various problems of molecular biology are analysed. Examples of biomolecules whose structures have been determined using orientation-dependent parameters are given. The bibliography includes 508 references.

Magnetostatic modes in ferromagnetic samples with inhomogeneous internal fields

Science.gov (United States)

Arias, Rodrigo

2015-03-01

Magnetostatic modes in ferromagnetic samples are very well characterized and understood in samples with uniform internal magnetic fields. More recently interest has shifted to the study of magnetization modes in ferromagnetic samples with inhomogeneous internal fields. The present work shows that under the magnetostatic approximation and for samples of arbitrary shape and/or arbitrary inhomogeneous internal magnetic fields the modes can be classified as elliptic or hyperbolic, and their associated frequency spectrum can be delimited. This results from the analysis of the character of the second order partial differential equation for the magnetostatic potential under these general conditions. In general, a sample with an inhomogeneous internal field and at a given frequency, may have regions of elliptic and hyperbolic character separated by a boundary. In the elliptic regions the magnetostatic modes have a smooth monotonic character (generally decaying form the surfaces (a ``tunneling'' behavior)) and in hyperbolic regions an oscillatory wave-like character. A simple local criterion distinguishes hyperbolic from elliptic regions: the sign of a susceptibility parameter. This study shows that one may control to some extent magnetostatic modes via external fields or geometry. R.E.A. acknowledges Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia under Project No. FB 0807 (Chile), Grant No. ICM P10-061-F by Fondo de Innovacion para la Competitividad-MINECON, and Proyecto Fondecyt 1130192.

Weak measurements and quantum weak values for NOON states

Science.gov (United States)

Rosales-Zárate, L.; Opanchuk, B.; Reid, M. D.

2018-03-01

Quantum weak values arise when the mean outcome of a weak measurement made on certain preselected and postselected quantum systems goes beyond the eigenvalue range for a quantum observable. Here, we propose how to determine quantum weak values for superpositions of states with a macroscopically or mesoscopically distinct mode number, that might be realized as two-mode Bose-Einstein condensate or photonic NOON states. Specifically, we give a model for a weak measurement of the Schwinger spin of a two-mode NOON state, for arbitrary N . The weak measurement arises from a nondestructive measurement of the two-mode occupation number difference, which for atomic NOON states might be realized via phase contrast imaging and the ac Stark effect using an optical meter prepared in a coherent state. The meter-system coupling results in an entangled cat-state. By subsequently evolving the system under the action of a nonlinear Josephson Hamiltonian, we show how postselection leads to quantum weak values, for arbitrary N . Since the weak measurement can be shown to be minimally invasive, the weak values provide a useful strategy for a Leggett-Garg test of N -scopic realism.

Inhomogeneous Big Bang Nucleosynthesis Revisited

OpenAIRE

Lara, J. F.; Kajino, T.; Mathews, G. J.

2006-01-01

We reanalyze the allowed parameters for inhomogeneous big bang nucleosynthesis in light of the WMAP constraints on the baryon-to-photon ratio and a recent measurement which has set the neutron lifetime to be 878.5 +/- 0.7 +/- 0.3 seconds. For a set baryon-to-photon ratio the new lifetime reduces the mass fraction of He4 by 0.0015 but does not significantly change the abundances of other isotopes. This enlarges the region of concordance between He4 and deuterium in the parameter space of the b...

Catheter visualisation in MR tomography: first animal experimental experiences with field inhomogeneity catheters

International Nuclear Information System (INIS)

Adam, G.; Glowinski, A.; Neuerburg, J.; Buecker, A.; Vaals, J.J. van; Hurtak, W.; Guenther, R.W.

1997-01-01

Purpose: To assess the feasibility of a new developed field inhomogeneity catheter for interventional MR imaging in vivo. Materials and methods: Three different prototypes of a field inhomogeneity catheter were investigated in 6 pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guide wire on an interventional MR system (Philips Gyroscan NT combined with a C-arm fluoroscopy unit [Philips BV 212[). Catheters were placed in veins and arteries. The catheter position was controlled by a fast gradient echo sequence (Turbo Field Echo [TEF[). Results: Catheters were introduced over a guide wire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualised in the inferior vena cava and the aorta by the fast gradient echo technique on MR in all cases. Although aortic branches were successfully cannulated, the catheters were not displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. Conclusion: MR guided visualisation of a field inhomogeneity catheter is a simple concept which can be realised on each MR scanner and may allow intravascular MR guided interventions in future. (orig.) [de

Inhomogeneous strain induced by fast neutron irradiation in NaKSO4 crystals

International Nuclear Information System (INIS)

Kandil, S.H.; Kassem, M.E.; El-Khatib, A.; El-Gamal, M.A.; El-Wahidy, E.F.

1987-01-01

The paper reports the effect of fast neutron irradiation on the thermal properties of NaKSO 4 crystals in the temperature range 400-475 K. Results are presented for the thermal expansion, tensile strain and specific heat of NaKSO 4 , as a function of neutron irradiation dose. All these results revealed an inhomogeneous strain induced by the radiation. It is suggested that this induced inhomogeneous strain could be used to detect neutron exposure doses. (UK)

Effect of natural aging on quench-induced inhomogeneity of microstructure and hardness in high strength 7055 aluminum alloy

International Nuclear Information System (INIS)

Liu, Shengdan; Li, Chengbo; Han, Suqi; Deng, Yunlai; Zhang, Xinming

2015-01-01

Highlights: • The quench-induced hardness inhomogeneity in 7055 Al alloy decreases by natural aging. • The reason is discussed based on natural aging effect on microstructural inhomogeneity. • Natural aging decreases the difference of hardening precipitates due to slow quenching. • GPII zones appear in the rapidly-quenched sample after natural aging for 17,280 h. - Abstract: The effect of natural aging on quench-induced inhomogeneity of microstructure and hardness in high strength 7055 aluminum alloy was investigated by means of end quenching technique, transmission electron microscopy and differential scanning calorimetry thermal analysis. The hardness inhomogeneity in the end-quenched specimens after artificial aging decreases with the increase of natural aging time prior to artificial aging. The quench-induced differences in the amount and size of η′ phase are large in the end-quenched specimen after artificial aging at 120 °C for 24 h, leading to high hardness inhomogeneity. Natural aging for a long time results in a larger amount of stable GPI zones in the slowly-quenched sample, and thus decreases such differences in the end-quenched specimens after subsequent artificial aging, leading to lower hardness inhomogeneity. The hardness inhomogeneity can be reduced from 14% to be 4% by natural aging for 17,280 h prior to artificial aging

Multiple scattering of elliptically polarized light in two-dimensional medium with large inhomogeneities

Energy Technology Data Exchange (ETDEWEB)

Gorodnichev, E. E., E-mail: gorodn@theor.mephi.ru [National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) (Russian Federation)

2016-12-15

For elliptically polarized light incident on a two-dimensional medium with large inhomogeneities, the Stokes parameters of scattered waves are calculated. Multiple scattering is assumed to be sharply anisotropic. The degree of polarization of scattered radiation is shown to be a nonmonotonic function of depth when the incident wave is circularly polarized or its polarization vector is not parallel to the symmetry axis of the inhomogeneities.

Karlin–McGregor-like formula in a simple time-inhomogeneous birth–death process

International Nuclear Information System (INIS)

Ohkubo, Jun

2014-01-01

Algebraic discussions are developed to derive transition probabilities for a simple time-inhomogeneous birth–death process. Algebraic probability theory and Lie algebraic treatments make it easy to treat the time-inhomogeneous cases. As a result, an expression based on the Charlier polynomials is obtained, which can be considered as an extension of a famous Karlin–McGregor representation for a time-homogeneous birth–death process. (paper)

Real-space observation of a right-rotating inhomogeneous cycloidal spin spiral by spin-polarized scanning tunneling microscopy in a triple axes vector magnet.

Science.gov (United States)

Meckler, S; Mikuszeit, N; Pressler, A; Vedmedenko, E Y; Pietzsch, O; Wiesendanger, R

2009-10-09

Using spin-polarized scanning tunneling microscopy performed in a triple axes vector magnet, we show that the magnetic structure of the Fe double layer on W(110) is an inhomogeneous right-rotating cycloidal spin spiral. The magnitude of the Dzyaloshinskii-Moriya vector is extracted from the experimental data using micromagnetic calculations. The result is confirmed by comparison of the measured saturation field along the easy axis to the respective value as obtained from Monte Carlo simulations. We find that the Dzyaloshinskii-Moriya interaction is too weak to destabilize the single domain state. However, it can define the sense of rotation and the cycloidal spiral type once the single domain state is destabilized by dipolar interaction.

Inhomogeneities in dusty universe — a possible alternative to dark energy?

International Nuclear Information System (INIS)

Chatterjee, S.

2011-01-01

There have been of late renewed debates on the role of inhomogeneities to explain the observed late acceleration of the universe. We have looked into the problem analytically with the help of the well known spherically symmetric but inhomogeneous Lemaitre-Tolman-Bondi(LTB) model generalised to higher dimensions. It is observed that in contrast to the claim made by Kolb et al. the presence of inhomogeneities as well as extra dimensions can not reverse the signature of the deceleration parameter if the matter field obeys the energy conditions. The well known Raychaudhuri equation also points to the same result. Without solving the field equations explicitly it can, however, be shown that although the total deceleration is positive everywhere nevertheless it does not exclude the possibility of having radial acceleration, even in the pure dust universe, if the angular scale factor is decelerating fast enough and vice versa. Moreover it is found that introduction of extra dimensions can not reverse the scenario. To the contrary it actually helps the decelerating process

Method for remote diagnostics of the internal structure of layered media

International Nuclear Information System (INIS)

Lychagov, V V; Kal'yanov, A L; Ryabukho, V P; Lyakin, D V

2008-01-01

The method of autocorrelation low coherence interferometry is proposed for diagnostics of inhomogeneities and the internal structure of layered technical and biological samples. In this method the low coherence optical field reflected from the layered sample is analysed by using a Michelson interferometer. Because the object is outside the interferometer, the distance between the interferometer and the object under study is not limited and thus the object can move during the measurements. Theoretical substantiation of the autocorrelation method for media with discrete and continuous optical structure modifications is presented. (special issue devoted to application of laser technologies in biophotonics and biomedical studies)

Modeling groundwater flow to elliptical lakes and through multi-aquifer elliptical inhomogeneities

Science.gov (United States)

Bakker, Mark

2004-05-01

Two new analytic element solutions are presented for steady flow problems with elliptical boundaries. The first solution concerns groundwater flow to shallow elliptical lakes with leaky lake beds in a single-aquifer. The second solution concerns groundwater flow through elliptical cylinder inhomogeneities in a multi-aquifer system. Both the transmissivity of each aquifer and the resistance of each leaky layer may differ between the inside and the outside of an inhomogeneity. The elliptical inhomogeneity may be bounded on top by a shallow elliptical lake with a leaky lake bed. Analytic element solutions are obtained for both problems through separation of variables of the Laplace and modified-Helmholtz differential equations in elliptical coordinates. The resulting equations for the discharge potential consist of infinite sums of products of exponentials, trigonometric functions, and modified-Mathieu functions. The series are truncated but still fulfill the differential equation exactly; boundary conditions are met approximately, but up to machine accuracy provided enough terms are used. The head and flow may be computed analytically at any point in the aquifer. Examples are given of uniform flow through an elliptical lake, a well pumping near two elliptical lakes, and uniform flow through three elliptical inhomogeneities in a multi-aquifer system. Mathieu functions may be applied in a similar fashion to solve other groundwater flow problems in semi-confined aquifers and leaky aquifer systems with elliptical internal or external boundaries.

Cellular-automation fluids: A model for flow in porous media

International Nuclear Information System (INIS)

Rothman, D.H.

1987-01-01

Because the intrinsic inhomogeneity of porous media makes the application of proper boundary conditions difficult, fluid flow through microgeometric models has typically been achieved with idealized arrays of geometrically simple pores, throats, and cracks. The author proposes here an attractive alternative, capable of freely and accurately modeling fluid flow in grossly irregular geometries. This new method numerically solves the Navier-Stokes equations using the cellular-automation fluid model introduced by Frisch, Hasslacher, and Pomeau. The cellular-automation fluid is extraordinarily simple - particles of unit mass traveling with unit velocity reside on a triangular lattice and obey elementary collisions rules - but capable of modeling much of the rich complexity of real fluid flow. The author shows how cellular-automation fluids are applied to the study of porous media. In particular, he discusses issues of scale on the cellular-automation lattice and present the results of 2-D simulations, including numerical estimation of permeability and verification of Darcy's law

Exploring entropic uncertainty relation in the Heisenberg XX model with inhomogeneous magnetic field

Science.gov (United States)

Huang, Ai-Jun; Wang, Dong; Wang, Jia-Ming; Shi, Jia-Dong; Sun, Wen-Yang; Ye, Liu

2017-08-01

In this work, we investigate the quantum-memory-assisted entropic uncertainty relation in a two-qubit Heisenberg XX model with inhomogeneous magnetic field. It has been found that larger coupling strength J between the two spin-chain qubits can effectively reduce the entropic uncertainty. Besides, we observe the mechanics of how the inhomogeneous field influences the uncertainty, and find out that when the inhomogeneous field parameter b1. Intriguingly, the entropic uncertainty can shrink to zero when the coupling coefficients are relatively large, while the entropic uncertainty only reduces to 1 with the increase of the homogeneous magnetic field. Additionally, we observe the purity of the state and Bell non-locality and obtain that the entropic uncertainty is anticorrelated with both the purity and Bell non-locality of the evolution state.

Regular Bulk Solutions in Brane-Worlds with Inhomogeneous Dust and Generalized Dark Radiation

International Nuclear Information System (INIS)

Rocha, Roldão da; Kuerten, A. M.; Herrera-Aguilar, A.

2015-01-01

From the dynamics of a brane-world with matter fields present in the bulk, the bulk metric and the black string solution near the brane are generalized, when both the dynamics of inhomogeneous dust/generalized dark radiation on the brane-world and inhomogeneous dark radiation in the bulk as well are considered as exact dynamical collapse solutions. Based on the analysis on the inhomogeneous static exterior of a collapsing sphere of homogeneous dark radiation on the brane, the associated black string warped horizon is studied, as well as the 5D bulk metric near the brane. Moreover, the black string and the bulk are shown to be more regular upon time evolution, for suitable values for the dark radiation parameter in the model, by analyzing the soft physical singularities

Material inhomogeneities and their evolution a geometric approach

CERN Document Server

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.

Big bang nucleosynthesis with Gaussian inhomogeneous neutrino degeneracy

International Nuclear Information System (INIS)

Stirling, Spencer D.; Scherrer, Robert J.

2002-01-01

We consider the effect of inhomogeneous neutrino degeneracy on big bang nucleosynthesis for the case where the distribution of neutrino chemical potentials is given by a Gaussian. The chemical potential fluctuations are taken to be isocurvature, so that only inhomogeneities in the electron chemical potential are relevant. Then the final element abundances are a function only of the baryon-photon ratio η, the effective number of additional neutrinos ΔN ν , the mean electron neutrino degeneracy parameter ξ-bar, and the rms fluctuation of the degeneracy parameter, σ ξ . We find that for fixed η, ΔN ν , and ξ-bar, the abundances of 4 He, D, and 7 Li are, in general, increasing functions of σ ξ . Hence, the effect of adding a Gaussian distribution for the electron neutrino degeneracy parameter is to decrease the allowed range for η. We show that this result can be generalized to a wide variety of distributions for ξ

Trace element evidence for a laterally inhomogeneous moon

International Nuclear Information System (INIS)

Jovanovic, S.; Reed, G.W. Jr.

1978-01-01

A number of trace element interrelations support the concept of a laterally inhomogeneous moon based orginally in Cl/sub r//P 2 O 5 ratios. The correspondence between Cl/sub r//P 2 O 5 and Rb/Sr ratios in basalts are of special interest since the isotopic evolution of the latter pair of elements relates to the earliest history of the moon. This implies the times when the Cl/sub r//P 2 O 5 relations were established. The early magma ocean is conjectured to have been made up of nonintermixing seas resulting either from large convection cells or large body accretion. These mutually exclusive regions could be lunar geological provinces. It is proposed that the diversity of basalts from the Apollo 17 site is related to the lateral inhomogeneity of the moon. Ca/Na ratios in basalts show a trend which parallels that of Ru/Os and in a corresponding fashion may serve as a depth indicator. 4 figures, 4 tables, 12 references

The Optimal Inhomogeneity for Superconductivity: Finite Size Studies

Energy Technology Data Exchange (ETDEWEB)

Tsai, W-F.

2010-04-06

We report the results of exact diagonalization studies of Hubbard models on a 4 x 4 square lattice with periodic boundary conditions and various degrees and patterns of inhomogeneity, which are represented by inequivalent hopping integrals t and t{prime}. We focus primarily on two patterns, the checkerboard and the striped cases, for a large range of values of the on-site repulsion U and doped hole concentration, x. We present evidence that superconductivity is strongest for U of order the bandwidth, and intermediate inhomogeneity, 0 < t{prime} < t. The maximum value of the 'pair-binding energy' we have found with purely repulsive interactions is {Delta}{sub pb} = 0.32t for the checkerboard Hubbard model with U = 8t and t{prime} = 0.5t. Moreover, for near optimal values, our results are insensitive to changes in boundary conditions, suggesting that the correlation length is sufficiently short that finite size effects are already unimportant.

Dynamics of spiral waves in a cardiac electromechanical model with a local electrical inhomogeneity

International Nuclear Information System (INIS)

Mesin, Luca

2012-01-01

Highlights: ► I study spirals in a model of electromechanical coupling in a cardiac tissue. ► The model is anisotropic and includes an electrical heterogeneity. ► Mechanical deformation is described under the active strain hypothesis. ► Joint effect of inhomogeneity and deformation influences spiral dynamics. ► Conductivity of stretch activated current is the parameter most affecting spirals. - Abstract: Joint effect of electrical heterogeneity (e.g. induced by ischemia) and mechanical deformation is investigated for an anisotropic, quasi–incompressible model of cardiac electromechanical coupling (EMC) using the active strain approach and periodic boundary conditions. Three local inhomogeneities with different geometry are simulated. Under a specific stimulation protocol, the heterogeneities are able to induce spirals. The interplay between the dimension of the electrical inhomogeneity, the EMC and the mechano-electrical feedback provided by the stretch activated current (SAC) determines the dynamics of the spiral waves of excitation, which could extinguish (in the case of low SAC), or be stable (with the tip rotating inside the inhomogeneity), or drift and be annihilated (in the case of high SAC).

The effect of dust charge inhomogeneity on low-frequency modes in a strongly coupled plasma

International Nuclear Information System (INIS)

Farid, T.; Mamun, A.A.; Shukla, P.K.

2000-01-01

An analysis of low-frequency modes accounting for dust grain charge fluctuation and equilibrium grain charge inhomogeneity in a strongly coupled dusty plasma is presented. The existence of an extremely low frequency mode, which is due to the inhomogeneity in the equilibrium dust grain charge, is reported. Besides, the equilibrium dust grain charge inhomogeneity makes the dust-acoustic mode unstable. The strong correlations in the dust fluid significantly drive a new mode as well as the existing dust-acoustic mode. The applications of these results to recent experimental and to some space and astrophysical situations are discussed

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.

Toroidal inhomogeneity of the vertical field in a tokamak apparatus

International Nuclear Information System (INIS)

Sometani, Taro; Takashima, Hidekazu

1977-01-01

An experiment with a model device has been made on the toroidal inhomogeneity of the vertical field in a Tokamak with an iron core. The D.C. vertical field is increased near the yokes of the iron core, while the gross plasma image field (consisting of the components due to the plasma current, the primary current, and its image) is reduced there. These two vertical fields, when superposed, exert force on the plasma as a less inhomogeneous external vertical field. The vertical field can be homogenized satisfactorily by using a compensation winding wound at a proper position on the iron core even if the shielding plates, which are mounted on some Tokamaks, are dispensed with. (auth.)

Heating and Acceleration of Solar Wind Ions by Turbulent Wave Spectrum in Inhomogeneous Expanding Plasma

Science.gov (United States)

Ofman, Leon; Ozak, Nataly; Vinas, Adolfo F.

2016-01-01

Near the Sun (plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects of background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super- Alfvenic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.

Diffusion MRI: Mitigation of Magnetic Field Inhomogeneities

Czech Academy of Sciences Publication Activity Database

Marcon, P.; Bartušek, Karel; Dokoupil, Zdeněk; Gescheidtová, E.

2012-01-01

Roč. 12, č. 5 (2012), s. 205-212 ISSN 1335-8871 R&D Projects: GA MŠk ED0017/01/01; GA ČR GAP102/11/0318; GA ČR GAP102/12/1104 Institutional support: RVO:68081731 Keywords : correction * diffusion * inhomogeneity * eddy currents * magnetic resonance Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.233, year: 2012

Optical inhomogeneity developing in flashlamp photolysis lasers

Energy Technology Data Exchange (ETDEWEB)

Alekhin, B V; Borovkov, V V; Brodskii, A Ya; Lazhintsev, B V; Nor-Arevian, V A; Sukhanov, L V

1980-07-01

The paper discusses the dynamics of optical inhomogenity developing in the active medium of a high-power flashlamp-pumped photolysis laser in inverse population storage, fast inversion suppression, and free-running lasing regimes. A chemical component of the refractive index was found in a C3F7I photolysis experiment, along with the anomalous growth of a gas refractive index.

Amplification of Frequency-Modulated Similariton Pulses in Length-Inhomogeneous Active Fibers

Directory of Open Access Journals (Sweden)

I. O. Zolotovskii

2012-01-01

Full Text Available The possibility of an effective gain of the self-similar frequency-modulated (FM wave packets is studied in the length-inhomogeneous active fibers. The dynamics of parabolic pulses with the constant chirp has been considered. The optimal profile for the change of the group-velocity dispersion corresponding to the optimal similariton pulse amplification has been obtained. It is shown that the use of FM pulses in the active (gain and length-inhomogeneous optical fibers with the normal group-velocity dispersion can provide subpicosecond optical pulse amplification up to the energies higher than 1 nJ.

Physical mechanism of parametric instabilities near the lower-hybrid frequency in inhomogeneous plasma

International Nuclear Information System (INIS)

Porkolab, M.

1974-10-01

The dispersion relation for parametric instabilities near the lower-hybrid frequency is obtained from model fluid equations. The following instabilities are discussed: for rf pump frequencies ω 0 greater than or equal to 3ω/sub LH/, ω/sub pe/ approximately equal to Ω/sub e/, resonant decay into ion sound (ion cyclotron) modes (previously predicted) is found. In the regime of 1 less than or equal to ω 0 /ω/sub LH/ less than or equal to 3, ω/sub pe/ approximately equal to Ω/sub e/, decay into ion quasi-modes is found. In strong magnetic fields decay into quasi-modes is also found for 3 less than or equal to ω 0 /ω/sub LH/. This mechanism is similar to nonlinear Landau damping in weak turbulence theory. In addition, decay into the purely growing mode and fluid-quasi modes may also occur. The results are compared with recent calculations from the Vlasov equation. The effects of plasma-inhomogeneities are considered, including effective thresholds due to density gradients and finite pump extent. The implications of these results to rf heating of tokamaks near the lower-hybrid frequency are discussed. (auth)

Effect of active medium inhomogeneity on lasing characteristics of InAs/InP quantum-dash lasers

KAUST Repository

Khan, Mohammed Zahed Mustafa

2010-01-01

The authors report on the effect of quantum-dash (Qdash) inhomogeneity on the characteristics of InAs/InP Qdash laser utilizing a single state rate equation model. The inhomogeneity is assumed to follow the Gaussian approximation. From our observation, an increased in Qdash inhomogeneity results in increasing of threshold current density and redshifting of the peak lasing wavelength. The lasing linewidth of the Qdash lasers has also found to increase under large injection current, attaining a full width at half maximum (FWHM) of ~ 17 nm.

Polarized optical scattering by inhomogeneities and surface roughness in an anisotropic thin film.

Science.gov (United States)

Germer, Thomas A; Sharma, Katelynn A; Brown, Thomas G; Oliver, James B

2017-11-01

We extend the theory of Kassam et al. [J. Opt. Soc. Am. A12, 2009 (1995)JOAOD60740-323210.1364/JOSAA.12.002009] for scattering by oblique columnar structure thin films to include the induced form birefringence and the propagation of radiation in those films. We generalize the 4×4 matrix theory of Berreman [J. Opt. Soc. Am.62, 502 (1972)JOSAAH0030-394110.1364/JOSA.62.000502] to include arbitrary sources in the layer, which are necessary to determine the Green function for the inhomogeneous wave equation. We further extend first-order vector perturbation theory for scattering by roughness in the smooth surface limit, when the layer is anisotropic. Scattering by an inhomogeneous medium is approximated by a distorted Born approximation, where effective medium theory is used to determine the effective properties of the medium, and strong fluctuation theory is used to determine the inhomogeneous sources. In this manner, we develop a model for scattering by inhomogeneous films, with anisotropic correlation functions. The results are compared with Mueller matrix bidirectional scattering distribution function measurements for a glancing-angle deposition (GLAD) film. While the results are applied to the GLAD film example, the development of the theory is general enough that it can guide simulations for scattering in other anisotropic thin films.

ION HEATING IN INHOMOGENEOUS EXPANDING SOLAR WIND PLASMA: THE ROLE OF PARALLEL AND OBLIQUE ION-CYCLOTRON WAVES

International Nuclear Information System (INIS)

Ozak, N.; Ofman, L.; Viñas, A.-F.

2015-01-01

Remote sensing observations of coronal holes show that heavy ions are hotter than protons and their temperature is anisotropic. In-situ observations of fast solar wind streams provide direct evidence for turbulent Alfvén wave spectrum, left-hand polarized ion-cyclotron waves, and He ++ - proton drift in the solar wind plasma, which can produce temperature anisotropies by resonant absorption and perpendicular heating of the ions. Furthermore, the solar wind is expected to be inhomogeneous on decreasing scales approaching the Sun. We study the heating of solar wind ions in inhomogeneous plasma with a 2.5D hybrid code. We include the expansion of the solar wind in an inhomogeneous plasma background, combined with the effects of a turbulent wave spectrum of Alfvénic fluctuations and initial ion-proton drifts. We study the influence of these effects on the perpendicular ion heating and cooling and on the spectrum of the magnetic fluctuations in the inhomogeneous background wind. We find that inhomogeneities in the plasma lead to enhanced heating compared to the homogenous solar wind, and the generation of significant power of oblique waves in the solar wind plasma. The cooling effect due to the expansion is not significant for super-Alfvénic drifts, and is diminished further when we include an inhomogeneous background density. We reproduce the ion temperature anisotropy seen in observations and previous models, which is present regardless of the perpendicular cooling due to solar wind expansion. We conclude that small scale inhomogeneities in the inner heliosphere can significantly affect resonant wave ion heating

Turbulent structure of stably stratified inhomogeneous flow

Science.gov (United States)

Iida, Oaki

2018-04-01

Effects of buoyancy force stabilizing disturbances are investigated on the inhomogeneous flow where disturbances are dispersed from the turbulent to non-turbulent field in the direction perpendicular to the gravity force. Attaching the fringe region, where disturbances are excited by the artificial body force, a Fourier spectral method is used for the inhomogeneous flow stirred at one side of the cuboid computational box. As a result, it is found that the turbulent kinetic energy is dispersed as layered structures elongated in the streamwise direction through the vibrating motion. A close look at the layered structures shows that they are flanked by colder fluids at the top and hotter fluids at the bottom, and hence vertically compressed and horizontally expanded by the buoyancy related to the countergradient heat flux, though they are punctuated by the vertical expansion of fluids at the forefront of the layered structures, which is related to the downgradient heat flux, indicating that the layered structures are gravity currents. However, the phase between temperature fluctuations and vertical velocity is shifted by π/2 rad, indicating that temperature fluctuations are generated by the propagation of internal gravity waves.

Glauber theory and the quantum coherence of curvature inhomogeneities

CERN Document Server

Giovannini, Massimo

2017-01-12

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.

Spatial inhomogeneity in Schottky barrier height at graphene/MoS2 Schottky junctions

Science.gov (United States)

Tomer, D.; Rajput, S.; Li, L.

2017-04-01

Transport properties of graphene semiconductor Schottky junctions strongly depend on interfacial inhomogeneities due to the inherent formation of ripples and ridges. Here, chemical vapor deposited graphene is transferred onto multilayer MoS2 to fabricate Schottky junctions. These junctions exhibit rectifying current-voltage behavior with the zero bias Schottky barrier height increases and ideality factor decreases with increasing temperature between 210 and 300 K. Such behavior is attributed to the inhomogeneous interface that arises from graphene ripples and ridges, as revealed by atomic force and scanning tunneling microscopy imaging. Assuming a Gaussian distribution of the barrier height, a mean value of 0.96  ±  0.14 eV is obtained. These findings indicate a direct correlation between temperature dependent Schottky barrier height and spatial inhomogeneity in graphene/2D semiconductor Schottky junctions.

Spatial inhomogeneity in Schottky barrier height at graphene/MoS2 Schottky junctions

International Nuclear Information System (INIS)

Tomer, D; Rajput, S; Li, L

2017-01-01

Transport properties of graphene semiconductor Schottky junctions strongly depend on interfacial inhomogeneities due to the inherent formation of ripples and ridges. Here, chemical vapor deposited graphene is transferred onto multilayer MoS 2 to fabricate Schottky junctions. These junctions exhibit rectifying current–voltage behavior with the zero bias Schottky barrier height increases and ideality factor decreases with increasing temperature between 210 and 300 K. Such behavior is attributed to the inhomogeneous interface that arises from graphene ripples and ridges, as revealed by atomic force and scanning tunneling microscopy imaging. Assuming a Gaussian distribution of the barrier height, a mean value of 0.96  ±  0.14 eV is obtained. These findings indicate a direct correlation between temperature dependent Schottky barrier height and spatial inhomogeneity in graphene/2D semiconductor Schottky junctions. (paper)

Accretion from an inhomogeneous medium

International Nuclear Information System (INIS)

Livio, M.; Soker, N.; Koo, M. de; Savonije, G.J.

1986-01-01

The problem of accretion by a compact object from an inhomogeneous medium is studied in the general γnot=1 case. The mass accretion rate is found to decrease with increasing γ. The rate of accretion of angular momentum is found to be significantly lower than the rate at which angular momentum is deposited into the Bondi-Hoyle, symmetrical, accretion cylinder. The consequences of the results are studied for the cases of neutron stars accreting from the winds of early-type companions and white dwarfs and main-sequence stars accreting from winds of cool giants. (author)

geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff

Energy Technology Data Exchange (ETDEWEB)

Light, Max Eugene [Los Alamos National Laboratory

2017-04-13

This report outlines the theory underlying electromagnetic (EM) wave propagation in an unmagnetized, inhomogeneous plasma. The inhomogeneity is given by a spatially nonuniform plasma electron density n_e(r), which will modify the wave propagation in the direction of the gradient rn_e(r).

Flux and polarization signals of spatially inhomogeneous gaseous exoplanets

NARCIS (Netherlands)

Karalidi, T.; Stam, D.M.; Guirado, D.

2013-01-01

Aims. 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

Effects of inhomogeneity on the Shukla-Nambu-Salimullah potential in a magnetized plasma

International Nuclear Information System (INIS)

Salimullah, M.; Shah, H.A.; Murtaza, G.; Nitta, H.; Tessarotto, M.

2007-01-01

Detailed properties of the electrostatic Shukla-Nambu-Salimullah potential in an inhomogeneous magnetoplasma in the presence of ion streaming due to diamagnetic drift as in a laboratory discharge plasma have been examined analytically. The potential becomes a sensitive function of the external static magnetic field, the scalelength of inhomogeneity, and the diamagnetic ion streaming velocity. For a decreasing ion density gradient, there is a limit of existence of this static modified shielding potential

Effect of active medium inhomogeneity on lasing characteristics of InAs/InP quantum-dash lasers

KAUST Repository

Khan, Mohammed Zahed Mustafa; Ng, Tien Khee; Ooi, Boon S.; Schwingenschlö gl, Udo

2010-01-01

The authors report on the effect of quantum-dash (Qdash) inhomogeneity on the characteristics of InAs/InP Qdash laser utilizing a single state rate equation model. The inhomogeneity is assumed to follow the Gaussian approximation. From our

Magnetic response of localized spins coupled to itinerant electrons in an inhomogeneous crystal field

International Nuclear Information System (INIS)

Iannarella, L.; Guimaraes, A.P.; Silva, X.A. da.

1990-01-01

The magnetic behavior at T = O K of a system consisting of conduction electrons coupled to localized electrons, the latter submitted to an inhomogeneous crystal field distribution, is studied. The study implies that the inhomogeneity of the crystal field attenuates the quenching effects. The model is interesting to the study of disordered rare-earth intermetallic compounds. (A.C.A.S.) [pt

Studies of small-scale plasma inhomogeneities in the cusp ionosphere using sounding rocket data

Science.gov (United States)

Chernyshov, Alexander A.; Spicher, Andres; Ilyasov, Askar A.; Miloch, Wojciech J.; Clausen, Lasse B. N.; Saito, Yoshifumi; Jin, Yaqi; Moen, Jøran I.

2018-04-01

Microprocesses associated with plasma inhomogeneities are studied on the basis of data from the Investigation of Cusp Irregularities (ICI-3) sounding rocket. The ICI-3 rocket is devoted to investigating a reverse flow event in the cusp F region ionosphere. By numerical stability analysis, it is demonstrated that inhomogeneous-energy-density-driven (IEDD) instability can be a mechanism for the excitation of small-scale plasma inhomogeneities. The Local Intermittency Measure (LIM) method also applied the rocket data to analyze irregular structures of the electric field during rocket flight in the cusp. A qualitative agreement between high values of the growth rates of the IEDD instability and the regions with enhanced LIM is observed. This suggests that IEDD instability is connected to turbulent non-Gaussian processes.

Fuel effects on the stability of turbulent flames with compositionally inhomogeneous inlets

KAUST Repository

Guiberti, T. F.

2016-10-11

This paper reports an analysis of the influence of fuels on the stabilization of turbulent piloted jet flames with inhomogeneous inlets. The burner is identical to that used earlier by the Sydney Group and employs two concentric tubes within the pilot stream. The inner tube, carrying fuel, can be recessed, leading to a varying degree of inhomogeneity in mixing with the outer air stream. Three fuels are tested: dimethyl ether (DME), liquefied petroleum gas (LPG), and compressed natural gas (CNG). It is found that improvement in flame stability at the optimal compositional inhomogeneity is highest for CNG and lowest for DME. Three possible reasons for this different enhancement in stability are investigated: mixing patterns, pilot effects, and fuel chemistry. Numerical simulations realized in the injection tube highlight similarities and differences in the mixing patterns for all three fuels and demonstrate that mixing cannot explain the different stability gains. Changing the heat release rates from the pilot affects the three fuels in similar ways and this also implies that the pilot stream is unlikely to be responsible for the observed differences. Fuel reactivity is identified as a key factor in enhancing stability at some optimal compositional inhomogeneity. This is confirmed by inference from joint images of PLIF-OH and PLIF-CHO, collected at a repetition rate of 10kHz in turbulent flames of DME, and from one-dimensional calculations of laminar flames using detailed chemistry for DME, CNG, and LPG.

Genomic mid-range inhomogeneity correlates with an abundance of RNA secondary structures

Directory of Open Access Journals (Sweden)

Song Jun

2008-06-01

Full Text Available Abstract Background Genomes possess different levels of non-randomness, in particular, an inhomogeneity in their nucleotide composition. Inhomogeneity is manifest from the short-range where neighboring nucleotides influence the choice of base at a site, to the long-range, commonly known as isochores, where a particular base composition can span millions of nucleotides. A separate genomic issue that has yet to be thoroughly elucidated is the role that RNA secondary structure (SS plays in gene expression. Results We present novel data and approaches that show that a mid-range inhomogeneity (~30 to 1000 nt not only exists in mammalian genomes but is also significantly associated with strong RNA SS. A whole-genome bioinformatics investigation of local SS in a set of 11,315 non-redundant human pre-mRNA sequences has been carried out. Four distinct components of these molecules (5'-UTRs, exons, introns and 3'-UTRs were considered separately, since they differ in overall nucleotide composition, sequence motifs and periodicities. For each pre-mRNA component, the abundance of strong local SS ( Conclusion We demonstrate that the excess of strong local SS in pre-mRNAs is linked to the little explored phenomenon of genomic mid-range inhomogeneity (MRI. MRI is an interdependence between nucleotide choice and base composition over a distance of 20–1000 nt. Additionally, we have created a public computational resource to support further study of genomic MRI.

Controlling Charged Particles with Inhomogeneous Electrostatic Fields

Science.gov (United States)

Herrero, Federico A. (Inventor)

2016-01-01

An energy analyzer for a charged-particle spectrometer may include a top deflection plate and a bottom deflection plate. The top and bottom deflection plates may be non-symmetric and configured to generate an inhomogeneous electrostatic field when a voltage is applied to one of the top or bottom deflection plates. In some instances, the top and bottom deflection plates may be L-shaped deflection plates.

A Research Program on the Asymptotic Description of Electromagnetic Pulse Propagation in Spatially Inhomogeneous, Temporally Dispersive, Attenuative Media

National Research Council Canada - National Science Library

Oughstun, Kurt E; Cartwright, Natalie A

2007-01-01

.... Indeed, previous studies of ultrawideband electromagnetic pulse propagation through dispersive, nonconducting media has shown the existence of a so-called Brillouin precursor whose peak amplitude...

Sharing and Discussing News in Private Social Media Groups

DEFF Research Database (Denmark)

Swart, Joëlle; Peters, Chris; Broersma, Marcel

2018-01-01

to their membership in a particular (1) location-based (2) work-related or (3) leisure-oriented community. It finds that communication within social media communities whose members consider their ties as weak generally tended to be more news-centred. Even more significant was perceived control over privacy......Social media platforms are an increasingly dominant medium through which people encounter news in everyday life. Yet while we know more-and-more about frequency of use and sharing, content preferences and network configurations around news use on social media, the social experiences associated...... with such practices remain relatively unexplored. This paper addresses this gap to consider if and how news facilitates conversations in everyday contexts where social media play a communicative role. It investigates how people engage with current affairs collectively in different social formations...

Inhomogeneous MUSIG Model - a population balance approach for polydispersed bubbly flows

International Nuclear Information System (INIS)

Frank, T.; Zwart, P.J.; Shi, J.; Krepper, E.; Lucas, D.; Rohde, U.

2005-01-01

Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, with one phase being a continuous liquid and the other phase consisting of gas or vapour of the liquid phase. In the range of low to intermediate volume fraction of the gaseous phase the multiphase flow under consideration is a bubbly or slug flow, where the disperse phase is characterized by an evolving bubble size distribution due to bubble breakup and coalescence processes. The paper presents a generalized inhomogeneous Multiple Size Group (MUSIG) Model. Within this model the disperse gaseous phase is divided into N inhomogeneous velocity groups (phases) and each of these groups is subdivided into M bubble size classes. Bubble breakup and coalescence processes between all bubble size classes are taken into account by appropriate models. The derived inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility at the Research Center Rossendorf (FZR). Comparisons of gas volume fraction and velocity profiles with TOPFLOW-074 test case data are provided, showing the applicability and accuracy of the model for polydispersed bubbly flow in large diameter vertical pipe flow. (author)

Jeans instability of an inhomogeneous streaming dusty plasma

Indian Academy of Sciences (India)

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 ...

Shock dynamics in layered periodic media

KAUST Repository

Ketcheson, David I.

2012-01-01

Solutions of constant-coeffcient nonlinear hyperbolic PDEs generically develop shocks, even if the initial data is smooth. Solutions of hyperbolic PDEs with variable coeffcients can behave very differently. We investigate formation and stability of shock waves in a one-dimensional periodic layered medium by a computational study of time-reversibility and entropy evolution. We find that periodic layered media tend to inhibit shock formation. For small initial conditions and large impedance variation, no shock formation is detected even after times much greater than the time of shock formation in a homogeneous medium. Furthermore, weak shocks are observed to be dynamically unstable in the sense that they do not lead to significant long-term entropy decay. We propose a characteristic condition for admissibility of shocks in heterogeneous media that generalizes the classical Lax entropy condition and accurately predicts the formation or absence of shocks in these media.

Waveguide effect under 'antiguiding' conditions in graded anisotropic media

Energy Technology Data Exchange (ETDEWEB)

Kozlov, A V; Mozhaev, V G; Zyryanova, A V, E-mail: av_kozlov@inbox.r, E-mail: vgmozhaev@mail.r, E-mail: annazyr@mail.r [Faculty of Physics, Moscow State University, Moscow, 119991 GSP-1 (Russian Federation)

2010-02-24

A new wave confinement effect is predicted in graded crystals with a concave slowness surface under conditions of growth of the phase velocity with decreasing distance from the waveguide axis. This finding overturns the common notion about the guiding and 'antiguiding' profiles of wave velocity in inhomogeneous media. The waveguide effect found is elucidated by means of ray analysis and particular exact wave solutions. The exact solution obtained for localized flexural waves in thin plates of graded cubic and tetragonal crystals confirms the predicted effect. Since this solution is substantially different with respect to the existence conditions from all others yet reported, and it cannot be deduced from the previously known results, the predicted waves can be classified as a new type of waveguide mode in graded anisotropic media. Although the concrete calculations are given in the article for acoustic waves, its general predictions are expected to be valid for waves of various natures, including spin, plasma, and optical waves.

Inhomogeneous strain induced by fast neutron irradiation in NaKSO/sub 4/ crystals

Energy Technology Data Exchange (ETDEWEB)

Kandil, S.H.; Kassem, M.E.; El-Khatib, A.; El-Gamal, M.A.; El-Wahidy, E.F.

1987-11-01

The paper reports the effect of fast neutron irradiation on the thermal properties of NaKSO/sub 4/ crystals in the temperature range 400-475 K. Results are presented for the thermal expansion, tensile strain and specific heat of NaKSO/sub 4/, as a function of neutron irradiation dose. All these results revealed an inhomogeneous strain induced by the radiation. It is suggested that this induced inhomogeneous strain could be used to detect neutron exposure doses.

Investigation of small-scale optical inhomogeneities in an electroionization CO/sub 2/-laser

Energy Technology Data Exchange (ETDEWEB)

Borovkov, V V; Kornilov, V G; Lazhintsev, B V; Nor-arevian, V A; Sukhanov, L V

1987-08-01

A technique for the interferometer investigation of optical inhomogeneities in an electroionization CO/sub 2/-laser in the free-oscillation regime is developed which involves active-medium sounding that is coaxial with the laser resonator. Experimental results are presented on small-scale optical inhomogeneities for a pulsed electroionization laser pumped by a nonself-sustained discharge in a CO/sub 2/:N/sub 2/:He = 1:3:6 mixture at a total pressure of 1 atm. 11 references.

Lie Symmetry Analysis of the Inhomogeneous Toda Lattice Equation via Semi-Discrete Exterior Calculus

International Nuclear Information System (INIS)

Liu Jiang; Wang Deng-Shan; Yin Yan-Bin

2017-01-01

In this work, the Lie point symmetries of the inhomogeneous Toda lattice equation are obtained by semi-discrete exterior calculus, which is a semi-discrete version of Harrison and Estabrook’s geometric approach. A four-dimensional Lie algebra and its one-, two- and three-dimensional subalgebras are given. Two similarity reductions of the inhomogeneous Toda lattice equation are obtained by using the symmetry vectors. (paper)

Energy transfer rates in inhomogeneous van der Waals clusters

International Nuclear Information System (INIS)

Desfrancois, C.; Schermann, J.P.

1991-01-01

The internal energy exchange inside an inhomogeneous van der Waals cluster are investigated by means of molecular dynamic calculations. The very long time scales for relaxation of the high frequency degrees of freedom are examined within the framework of Nekhoroshev's theorem. (orig.)

EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources

Energy Technology Data Exchange (ETDEWEB)

Abdalla, Hassan; Böttcher, Markus [Centre for Space Research, North-West University, Potchefstroom 2520 (South Africa)

2017-02-01

The unexpectedly hard very-high-energy (VHE; E > 100 GeV) γ -ray spectra of a few distant blazars have been interpreted as evidence of a reduction of the γγ opacity of the universe due to the interaction of VHE γ -rays with the extragalactic background light (EBL) compared to the expectation from current knowledge of the density and cosmological evolution of the EBL. One of the suggested solutions to this problem involves the inhomogeneity of the EBL. In this paper, we study the effects of such inhomogeneity on the energy density of the EBL (which then also becomes anisotropic) and the resulting γγ opacity. Specifically, we investigate the effects of cosmic voids along the line of sight to a distant blazar. We find that the effect of such voids on the γγ opacity, for any realistic void size, is only of the order of ≲1% and much smaller than expected from a simple linear scaling of the γγ opacity with the line-of-sight galaxy underdensity due to a cosmic void.

Spatially inhomogeneous acceleration of electrons in solar flares

Science.gov (United States)

Stackhouse, Duncan J.; Kontar, Eduard P.

2018-04-01

The imaging spectroscopy capabilities of the Reuven Ramaty high energy solar spectroscopic imager (RHESSI) enable the examination of the accelerated electron distribution throughout a solar flare region. In particular, it has been revealed that the energisation of these particles takes place over a region of finite size, sometimes resolved by RHESSI observations. In this paper, we present, for the first time, a spatially distributed acceleration model and investigate the role of inhomogeneous acceleration on the observed X-ray emission properties. We have modelled transport explicitly examining scatter-free and diffusive transport within the acceleration region and compare with the analytic leaky-box solution. The results show the importance of including this spatial variation when modelling electron acceleration in solar flares. The presence of an inhomogeneous, extended acceleration region produces a spectral index that is, in most cases, different from the simple leaky-box prediction. In particular, it results in a generally softer spectral index than predicted by the leaky-box solution, for both scatter-free and diffusive transport, and thus should be taken into account when modelling stochastic acceleration in solar flares.

Non-Linear Instabilities in an Inhomogeneous Plasma

International Nuclear Information System (INIS)

Coppi, B.; Laval, G.; Pellat, R.; Khiet, Tu

1969-01-01

The low-frequency drift modes of a low-pressure isothermal inhomogeneous plasma can be stabilized if the shear of the magnetic field lines exceeds a critical value given by the expression r/L s = (1/2 √2) (a/r), where L s is the shear length, r the characteristic length of density variation, and a the ion Larmor radius. The authors first show that, even if r/L s [fr

Constitutive model of friction stir weld with consideration of its inhomogeneous mechanical properties

Science.gov (United States)

Zhang, Ling; Min, Junying; Wang, Bin; Lin, Jianping; Li, Fangfang; Liu, Jing

2016-03-01

In practical engineering, finite element(FE) modeling for weld seam is commonly simplified by neglecting its inhomogeneous mechanical properties. This will cause a significant loss in accuracy of FE forming analysis, in particular, for friction stir welded(FSW) blanks due to the large width and good formability of its weld seam. The inhomogeneous mechanical properties across weld seam need to be well characterized for an accurate FE analysis. Based on a similar AA5182 FSW blank, the metallographic observation and micro-Vickers hardness analysis upon the weld cross-section are performed to identify the interfaces of different sub-zones, i.e., heat affected zone(HAZ), thermal-mechanically affected zone(TMAZ) and weld nugget(WN). Based on the rule of mixture and hardness distribution, a constitutive model is established for each sub-zone to characterize the inhomogeneous mechanical properties across the weld seam. Uniaxial tensile tests of the AA5182 FSW blank are performed with the aid of digital image correlation(DIC) techniques. Experimental local stress-strain curves are obtained for different weld sub-zones. The experimental results show good agreement with those derived from the constitutive models, which demonstrates the feasibility and accuracy of these models. The proposed research gives an accurate characterization of inhomogeneous mechanical properties across the weld seam produced by FSW, which provides solutions for improving the FE simulation accuracy of FSW sheet forming.

Utilizing pulsed laser deposition lateral inhomogeneity as a tool in combinatorial material science.

Science.gov (United States)

Keller, David A; Ginsburg, Adam; Barad, Hannah-Noa; Shimanovich, Klimentiy; Bouhadana, Yaniv; Rosh-Hodesh, Eli; Takeuchi, Ichiro; Aviv, Hagit; Tischler, Yaakov R; Anderson, Assaf Y; Zaban, Arie

2015-04-13

Pulsed laser deposition (PLD) is widely used in combinatorial material science, as it enables rapid fabrication of different composite materials. Nevertheless, this method was usually limited to small substrates, since PLD deposition on large substrate areas results in severe lateral inhomogeneity. A few technical solutions for this problem have been suggested, including the use of different designs of masks, which were meant to prevent inhomogeneity in the thickness, density, and oxidation state of a layer, while only the composition is allowed to be changed. In this study, a possible way to take advantage of the large scale deposition inhomogeneity is demonstrated, choosing an iron oxide PLD-deposited library with continuous compositional spread (CCS) as a model system. An Fe₂O₃-Nb₂O₅ library was fabricated using PLD, without any mask between the targets and the substrate. The library was measured using high-throughput scanners for electrical, structural, and optical properties. A decrease in electrical resistivity that is several orders of magnitude lower than pure α-Fe₂O₃ was achieved at ∼20% Nb-O (measured at 47 and 267 °C) but only at points that are distanced from the center of the PLD plasma plume. Using hierarchical clustering analysis, we show that the PLD inhomogeneity can be used as an additional degree of freedom, helping, in this case, to achieve iron oxide with much lower resistivity.

LANGMUIR WAVE DECAY IN INHOMOGENEOUS SOLAR WIND PLASMAS: SIMULATION RESULTS

Energy Technology Data Exchange (ETDEWEB)

Krafft, C. [Laboratoire de Physique des Plasmas, Ecole Polytechnique, F-91128 Palaiseau Cedex (France); Volokitin, A. S. [IZMIRAN, Troitsk, 142190, Moscow (Russian Federation); Krasnoselskikh, V. V., E-mail: catherine.krafft@u-psud.fr [Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, 3A Av. de la Recherche Scientifique, F-45071 Orléans Cedex 2 (France)

2015-08-20

Langmuir turbulence excited by electron flows in solar wind plasmas is studied on the basis of numerical simulations. In particular, nonlinear wave decay processes involving ion-sound (IS) waves are considered in order to understand their dependence on external long-wavelength plasma density fluctuations. In the presence of inhomogeneities, it is shown that the decay processes are localized in space and, due to the differences between the group velocities of Langmuir and IS waves, their duration is limited so that a full nonlinear saturation cannot be achieved. The reflection and the scattering of Langmuir wave packets on the ambient and randomly varying density fluctuations lead to crucial effects impacting the development of the IS wave spectrum. Notably, beatings between forward propagating Langmuir waves and reflected ones result in the parametric generation of waves of noticeable amplitudes and in the amplification of IS waves. These processes, repeated at different space locations, form a series of cascades of wave energy transfer, similar to those studied in the frame of weak turbulence theory. The dynamics of such a cascading mechanism and its influence on the acceleration of the most energetic part of the electron beam are studied. Finally, the role of the decay processes in the shaping of the profiles of the Langmuir wave packets is discussed, and the waveforms calculated are compared with those observed recently on board the spacecraft Solar TErrestrial RElations Observatory and WIND.

Spectral Analysis of Quantum-Dash Lasers: Effect of Inhomogeneous Broadening of the Active-Gain Region

KAUST Repository

Khan, Mohammed Zahed Mustafa

2012-05-01

The effect of the active region inhomogeneity on the spectral characteristics of InAs/InP quantum-dash (Qdash) lasers is examined theoretically by solving the coupled set of carrier-photon rate equations. The inhomogeneity due to dash size or composition fluctuation is included in the model by considering dispersive energy states and characterized by a Gaussian envelope. In addition, the technique incorporates multilongitudinal photon modes and homogeneous broadening of the optical gain. The results predict a red shift in the central lasing wavelength of Qdash lasers on increasing the inhomogeneous broadening either explicitly or implicitly, which supports various experimental observations. The threshold current density and the lasing bandwidth are also found to increase. © 2012 IEEE.

Spectral Analysis of Quantum-Dash Lasers: Effect of Inhomogeneous Broadening of the Active-Gain Region

KAUST Repository

Khan, Mohammed Zahed Mustafa; Ng, Tien Khee; Ooi, Boon S.; Schwingenschlö gl, Udo

2012-01-01

The effect of the active region inhomogeneity on the spectral characteristics of InAs/InP quantum-dash (Qdash) lasers is examined theoretically by solving the coupled set of carrier-photon rate equations. The inhomogeneity due to dash size or composition fluctuation is included in the model by considering dispersive energy states and characterized by a Gaussian envelope. In addition, the technique incorporates multilongitudinal photon modes and homogeneous broadening of the optical gain. The results predict a red shift in the central lasing wavelength of Qdash lasers on increasing the inhomogeneous broadening either explicitly or implicitly, which supports various experimental observations. The threshold current density and the lasing bandwidth are also found to increase. © 2012 IEEE.

Measurements of ultrasonic waves by means of laser Doppler velocimeter and an experimental study of elastic wave propagation in inhomogeneous media; Laser doppler sokudokei ni yoru choonpa keisoku to ganseki wo mochiita fukinshitsu baishitsu no hado denpa model jikken

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.

Rate-optimal Bayesian intensity smoothing for inhomogeneous Poisson processes

NARCIS (Netherlands)

Belitser, E.; Andrade Serra, De P.J.; Zanten, van J.H.

2013-01-01

We apply nonparametric Bayesian methods to study the problem of estimating the intensity function of an inhomogeneous Poisson process. We exhibit a prior on intensities which both leads to a computationally feasible method and enjoys desirable theoretical optimality properties. The prior we use is

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...

Magnetic Resonance Imaging of Surgical Implants Made from Weak Magnetic Materials

Science.gov (United States)

Gogola, D.; Krafčík, A.; Štrbák, O.; Frollo, I.

2013-08-01

Materials with high magnetic susceptibility cause local inhomogeneities in the main field of the magnetic resonance (MR) tomograph. These inhomogeneities lead to loss of phase coherence, and thus to a rapid loss of signal in the image. In our research we investigated inhomogeneous field of magnetic implants such as magnetic fibers, designed for inner suture during surgery. The magnetic field inhomogeneities were studied at low magnetic planar phantom, which was made from four thin strips of magnetic tape, arranged grid-wise. We optimized the properties of imaging sequences with the aim to find the best setup for magnetic fiber visualization. These fibers can be potentially exploited in surgery for internal stitches. Stitches can be visualized by the magnetic resonance imaging (MRI) method after surgery. This study shows that the imaging of magnetic implants is possible by using the low field MRI systems, without the use of complicated post processing techniques (e.g., IDEAL).

Let the Weakest Link Go! Empirical Explorations on the Relative Importance of Weak and Strong Ties on Social Networking Sites

OpenAIRE

Nicole C. Krämer; Leonie Rösner; Sabrina C. Eimler; Stephan Winter; German Neubaum

2014-01-01

Theoretical approaches as well as empirical results in the area of social capital accumulation on social networking sites suggest that weak ties/bridging versus strong ties/bonding social capital should be distinguished and that while bonding social capital is connected to emotional support, bridging social capital entails the provision of information. Additionally, recent studies imply the notion that weak ties/bridging social capital are gaining increasing importance in today’s social media...

Weak interactions

International Nuclear Information System (INIS)

Ogava, S.; Savada, S.; Nakagava, M.

1983-01-01

The problem of the use of weak interaction laws to study models of elementary particles is discussed. The most typical examples of weak interaction is beta-decay of nucleons and muons. Beta-interaction is presented by quark currents in the form of universal interaction of the V-A type. Universality of weak interactions is well confirmed using as examples e- and μ-channels of pion decay. Hypothesis on partial preservation of axial current is applicable to the analysis of processes with pion participation. In the framework of the model with four flavours lepton decays of hadrons are considered. Weak interaction without lepton participation are also considered. Properties of neutral currents are described briefly

Electromagnetic Characterization of Inhomogeneous Media

Science.gov (United States)

2012-03-22

Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements...found in the laboratory data, fun is the code that contains the theatrical formulation of S11, and beta0 is the initial constitutive parameter estimate...collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources

Weakly clopen functions

International Nuclear Information System (INIS)

Son, Mi Jung; Park, Jin Han; Lim, Ki Moon

2007-01-01

We introduce a new class of functions called weakly clopen function which includes the class of almost clopen functions due to Ekici [Ekici E. Generalization of perfectly continuous, regular set-connected and clopen functions. Acta Math Hungar 2005;107:193-206] and is included in the class of weakly continuous functions due to Levine [Levine N. A decomposition of continuity in topological spaces. Am Math Mon 1961;68:44-6]. Some characterizations and several properties concerning weakly clopenness are obtained. Furthermore, relationships among weak clopenness, almost clopenness, clopenness and weak continuity are investigated

Second-order analysis of structured inhomogeneous spatio-temporal point processes

DEFF Research Database (Denmark)

Møller, Jesper; Ghorbani, Mohammad

Statistical methodology for spatio-temporal point processes is in its infancy. We consider second-order analysis based on pair correlation functions and K-functions for first general inhomogeneous spatio-temporal point processes and second inhomogeneous spatio-temporal Cox processes. Assuming...... spatio-temporal separability of the intensity function, we clarify different meanings of second-order spatio-temporal separability. One is second-order spatio-temporal independence and relates e.g. to log-Gaussian Cox processes with an additive covariance structure of the underlying spatio......-temporal Gaussian process. Another concerns shot-noise Cox processes with a separable spatio-temporal covariance density. We propose diagnostic procedures for checking hypotheses of second-order spatio-temporal separability, which we apply on simulated and real data (the UK 2001 epidemic foot and mouth disease data)....

Feminism as a media product: the Beyoncé paradox

Directory of Open Access Journals (Sweden)

Lola Fernández Hernández

2017-12-01

Full Text Available Since 2014, an increasing number of celebrities has manifested itself publicly as feminist, a phenomenon that has coincided in time with the emergence of a new space for the discussion about women issues in traditional media and social media netwotks. Taking as paradigmatic the case of Beyoncé, this text explores the intersection between mainstream culture, mass media and feminism, contextualized in the logics of advanced capitalism, neo-liberalism and its patriarchal rearmament and the celebritization of the media space in which they coincide. Its objective will be to expose, through the academic and media reactions to Beyonce’s feminism, the strengths and weaknesses of the so-called postfeminism, and to propose that its utility as a subversive tool could be considered not in relation to the public that receives and reworks it, but in terms of its ability to mobilize and produce mutations in both journalistic and academic practice.

Green function formalism for nonlinear acoustic waves in layered media

International Nuclear Information System (INIS)

Lobo, A.; Tsoy, E.; De Sterke, C.M.

2000-01-01

Full text: The applications of acoustic waves in identifying defects in adhesive bonds between metallic plates have received little attention at high intensities where the media respond nonlinearly. However, the effects of reduced bond strength are more distinct in the nonlinear response of the structure. Here we assume a weak nonlinearity acting as a small perturbation, thereby reducing the problem to a linear one. This enables us to develop a specialized Green function formalism for calculating acoustic fields in layered media

Robustness of inflation to inhomogeneous initial conditions

Energy Technology Data Exchange (ETDEWEB)

Clough, Katy; Lim, Eugene A. [Theoretical Particle Physics and Cosmology Group, Physics Department, Kings College London, Strand, London WC2R 2LS (United Kingdom); DiNunno, Brandon S.; Fischler, Willy; Flauger, Raphael; Paban, Sonia, E-mail: katy.clough@kcl.ac.uk, E-mail: eugene.a.lim@gmail.com, E-mail: bsd86@physics.utexas.edu, E-mail: fischler@physics.utexas.edu, E-mail: flauger@physics.utexas.edu, E-mail: paban@physics.utexas.edu [Department of Physics, The University of Texas at Austin, Austin, TX, 78712 (United States)

2017-09-01

We consider the effects of inhomogeneous initial conditions in both the scalar field profile and the extrinsic curvature on different inflationary models. In particular, we compare the robustness of small field inflation to that of large field inflation, using numerical simulations with Einstein gravity in 3+1 dimensions. We find that small field inflation can fail in the presence of subdominant gradient energies, suggesting that it is much less robust to inhomogeneities than large field inflation, which withstands dominant gradient energies. However, we also show that small field inflation can be successful even if some regions of spacetime start out in the region of the potential that does not support inflation. In the large field case, we confirm previous results that inflation is robust if the inflaton occupies the inflationary part of the potential. Furthermore, we show that increasing initial scalar gradients will not form sufficiently massive inflation-ending black holes if the initial hypersurface is approximately flat. Finally, we consider the large field case with a varying extrinsic curvature K , such that some regions are initially collapsing. We find that this may again lead to local black holes, but overall the spacetime remains inflationary if the spacetime is open, which confirms previous theoretical studies.

Subspace-based optimization method for inverse scattering problems with an inhomogeneous background medium

International Nuclear Information System (INIS)

Chen, Xudong

2010-01-01

This paper proposes a version of the subspace-based optimization method to solve the inverse scattering problem with an inhomogeneous background medium where the known inhomogeneities are bounded in a finite domain. Although the background Green's function at each discrete point in the computational domain is not directly available in an inhomogeneous background scenario, the paper uses the finite element method to simultaneously obtain the Green's function at all discrete points. The essence of the subspace-based optimization method is that part of the contrast source is determined from the spectrum analysis without using any optimization, whereas the orthogonally complementary part is determined by solving a lower dimension optimization problem. This feature significantly speeds up the convergence of the algorithm and at the same time makes it robust against noise. Numerical simulations illustrate the efficacy of the proposed algorithm. The algorithm presented in this paper finds wide applications in nondestructive evaluation, such as through-wall imaging

Mobile devices and weak ties: a study of vision impairments and workplace access in Bangalore.

Science.gov (United States)

Pal, Joyojeet; Lakshmanan, Meera

2015-07-01

To explore ways in which social and economic interactions are changed by access to mobile telephony. This is a mixed-methods study of mobile phone use among 52 urban professionals with vision impairments in Bangalore, India. Interviews and survey results indicated that mobile devices, specifically those with adaptive technology software, play a vital role as multi-purpose devices that enable people with disabilities to navigate economically and socially in an environment where accessibility remains a significant challenge. We found that mobile devices play a central role in enabling and sustaining weak ties, but also that these weak ties have important gender-specific implications. We found that women have less access to weak ties than men, which impacts women's access to assistive technology (AT). This has potential implications for women's sense of safety and independence, both of which are strongly related to AT access. Implications for Rehabilitation Adaptive technologies increase individuals' ability to keep in contact with casual connections or weak ties through phone calls or social media. Men tend to have stronger access to weak ties than women in India due to cultural impediments to independent access to public spaces. Weak ties are an important source of assistive technology (AT) due to the high rate of resale of used AT, typically through informal networks.

Integrability and soliton in a classical one dimensional site dependent biquadratic Heisenberg spin chain and the effect of nonlinear inhomogeneity

International Nuclear Information System (INIS)

Kavitha, L.; Daniel, M.

2002-07-01

The integrability of one dimensional classical continuum inhomogeneous biquadratic Heisenberg spin chain and the effect of nonlinear inhomogeneity on the soliton of an underlying completely integrable spin model are studied. The dynamics of the spin system is expressed in terms of a higher order generalized nonlinear Schroedinger equation through a differential geometric approach which becomes integrable for a particular choice of the biquadratic exchange interaction and for linear inhomogeneity. The effect of nonlinear inhomogeneity on the spin soliton is studied by carrying out a multiple scale perturbation analysis. (author)

Calculation of Prestressed Pressure Vessel Taking into Account the Concrete Temperature Inhomogeneity

Science.gov (United States)

Andreev, Vladimir

2018-03-01

The paper deals with the problem of determining the stress state of the pressure vessel (PV) with considering the concrete temperature inhomogeneity. Such structures are widely used in heat power engineering, for example, in nuclear power engineering. The structures of such buildings are quite complex and a comprehensive analysis of the stress state in them can be carried out either by numerical or experimental methods. However, a number of fundamental questions can be solved on the basis of simplified models, in particular, studies of the effect on the stressed state of the inhomogeneity caused by the temperature field.

Aspects of second-order analysis of structured inhomogeneous spatio-temporal processes

DEFF Research Database (Denmark)

Møller, Jesper; Ghorbani, Mohammad

2012-01-01

Statistical methodology for spatio-temporal point processes is in its infancy. We consider second-order analysis based on pair correlation functions and K-functions for general inhomogeneous spatio-temporal point processes and for inhomogeneous spatio-temporal Cox processes. Assuming spatio......-temporal separability of the intensity function, we clarify different meanings of second-order spatio-temporal separability. One is second-order spatio-temporal independence and relates to log-Gaussian Cox processes with an additive covariance structure of the underlying spatio-temporal Gaussian process. Another...... concerns shot-noise Cox processes with a separable spatio-temporal covariance density. We propose diagnostic procedures for checking hypotheses of second-order spatio-temporal separability, which we apply on simulated and real data....

GENERAL P, TYPE-I S, AND TYPE-II S WAVES IN ANELASTIC SOLIDS; INHOMOGENEOUS WAVE FIELDS IN LOW-LOSS SOLIDS.

Science.gov (United States)

Borcherdt, Roger D.; Wennerberg, Leif

1985-01-01

The physical characteristics for general plane-wave radiation fields in an arbitrary linear viscoelastic solid are derived. Expressions for the characteristics of inhomogeneous wave fields, derived in terms of those for homogeneous fields, are utilized to specify the characteristics and a set of reference curves for general P and S wave fields in arbitrary viscoelastic solids as a function of wave inhomogeneity and intrinsic material absorption. The expressions show that an increase in inhomogeneity of the wave fields cause the velocity to decrease, the fractional-energy loss (Q** minus **1) to increase, the deviation of maximum energy flow with respect to phase propagation to increase, and the elliptical particle motions for P and type-I S waves to approach circularity. Q** minus **1 for inhomogeneous type-I S waves is shown to be greater than that for type-II S waves, with the deviation first increasing then decreasing with inhomogeneity. The mean energy densities (kinetic, potential, and total), the mean rate of energy dissipation, the mean energy flux, and Q** minus **1 for inhomogeneous waves are shown to be greater than corresponding characteristics for homogeneous waves, with the deviations increasing as the inhomogeneity is increased for waves of fixed maximum displacement amplitude.

Acoustic invisibility cloaks of arbitrary shapes for complex background media

Science.gov (United States)

Zhu, Jian; Chen, Tianning; Liang, Qingxuan; Wang, Xiaopeng; Xiong, Jie; Jiang, Ping

2016-04-01

We report on the theoretical investigation of the acoustic cloaks working in complex background media in this paper. The constitutive parameters of arbitrary-shape cloaks are derived based on the transformation acoustic theory and coordinate transformation technique. The detailed analysis of boundaries conditions and potential applications of the cloaks are also presented in our work. To overcome the difficulty of achieving the materials with ideal parameters in nature, concentric alternating layered isotropic materials is adopted to approximate the required properties of the cloak. Theoretical design and excellent invisibility are demonstrated by numerical simulations. The inhomogeneous medium and arbitrary-shape acoustic cloaks grow closer to real application and may be a new hot spot in future.

Field distribution of a source and energy absorption in an inhomogeneous magneto-active plasma

International Nuclear Information System (INIS)

Galushko, N.P.; Erokhin, N.S.; Moiseev, S.S.

1975-01-01

In the present paper the distribution of source fields in in a magnetoactive plasma is studied from the standpoint of the possibility of an effective SHF heating of an inhomogeneous plasma in both high (ωapproximatelyωsub(pe) and low (ωapproximatelyωsub(pi) frequency ranges, where ωsub(pe) and ωsub(pi) are the electron and ion plasma frequencies. The localization of the HF energy absorption regions in cold and hot plasma and the effect of plasma inhomogeneity and source dimensions on the absorption efficiency are investigated. The linear wave transformation in an inhomogeneous hot plasma is taken into consideration. Attention is paid to the difference between the region localization for collisional and non-collisional absorption. It has been shown that the HF energy dissipation in plasma particle collisions is localized in the region of thin jets going from the source; the radiation field has a sharp peak in this region. At the same time, non-collisional HF energy dissipation is spread over the plasma volume as a result of Cherenkov and cyclotron wave attenuation. The essential contribution to the source field from resonances due to standing wave excitation in an inhomogeneous plasma shell near the source is pointed out

Weak value controversy

Science.gov (United States)

Vaidman, L.

2017-10-01

Recent controversy regarding the meaning and usefulness of weak values is reviewed. It is argued that in spite of recent statistical arguments by Ferrie and Combes, experiments with anomalous weak values provide useful amplification techniques for precision measurements of small effects in many realistic situations. The statistical nature of weak values is questioned. Although measuring weak values requires an ensemble, it is argued that the weak value, similarly to an eigenvalue, is a property of a single pre- and post-selected quantum system. This article is part of the themed issue `Second quantum revolution: foundational questions'.

Stable dissipative optical vortex clusters by inhomogeneous effective diffusion.

Science.gov (United States)

Li, Huishan; Lai, Shiquan; Qui, Yunli; Zhu, Xing; Xie, Jianing; Mihalache, Dumitru; He, Yingji

2017-10-30

We numerically show the generation of robust vortex clusters embedded in a two-dimensional beam propagating in a dissipative medium described by the generic cubic-quintic complex Ginzburg-Landau equation with an inhomogeneous effective diffusion term, which is asymmetrical in the two transverse directions and periodically modulated in the longitudinal direction. We show the generation of stable optical vortex clusters for different values of the winding number (topological charge) of the input optical beam. We have found that the number of individual vortex solitons that form the robust vortex cluster is equal to the winding number of the input beam. We have obtained the relationships between the amplitudes and oscillation periods of the inhomogeneous effective diffusion and the cubic gain and diffusion (viscosity) parameters, which depict the regions of existence and stability of vortex clusters. The obtained results offer a method to form robust vortex clusters embedded in two-dimensional optical beams, and we envisage potential applications in the area of structured light.

Parametric trapping of electromagnetic waves in an inhomogeneous plasma

International Nuclear Information System (INIS)

Silin, V.P.; Starodub, A.N.

1977-01-01

Considered is parametric instability in an inhomogeneous plasma at which a pumping wave is transformed to an electromagnetic wave and aperiodically in-time-growing disturbances. It is shown that after achievement of some boundary pumping value by electric field intensity an absolute parametric instability evolution becomes possible. In-time growing plasma disturbances are localized near electric field extremums of a pumping wave. Such localization areas are small as compared to characteristic size of pumping inhomogeneity in a plasma. The secondary electromagnetic waves stay within the localization areas and, therefore, are not scattered by a plasma. As following from this it has been established, that due to parametric instability electromagnetic radiation trapping by a plasma occurs. Such a trapping is considerably connected with a spatial structure of a pumping field and it cannot arise within the field of a running wave in the theoretical model considered. However parametric trapping turns out to be possible even with very small reflection coefficients

Relativistic acceleration of captured particles by a longitudinal wave in a slightly inhomogeneous plasma

International Nuclear Information System (INIS)

Erokhin, N.S.; Zol'nikova, N.N.; Mikhajlovskaya, L.A.

1991-01-01

Relativistic acceleration of charged particles, captured by a longitudinal wave in a slightly inhomogeneous plasma without an external magnetic field is considered numerically and analytically. It is shown that with the growth of the plasma inhomogeneity parameter the maximum energy of accelerated captured particles exponentially increases. Attention is paid to the possibility of 'eternal' confinement and, respectively, unlimited acceleration of captured particles by an undamped longitudinal wave in a plasma without a magnetic field

Anomalous transient behavior from an inhomogeneous initial optical vortex density

CSIR Research Space (South Africa)

Roux, FS

2011-04-01

Full Text Available . However, the decay curves contain oscillatory features that are counterintuitive: for a short while, the inhomogeneity actually increases. The author provides numerical simulations and analytic calculations to study the appearance of the anomalous features...

Rate-optimal Bayesian intensity smoothing for inhomogeneous Poisson processes

NARCIS (Netherlands)

Belitser, E.N.; Serra, P.; van Zanten, H.

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

Weak Acid Ionization Constants and the Determination of Weak Acid-Weak Base Reaction Equilibrium Constants in the General Chemistry Laboratory

Science.gov (United States)

Nyasulu, Frazier; McMills, Lauren; Barlag, Rebecca

2013-01-01

A laboratory to determine the equilibrium constants of weak acid negative weak base reactions is described. The equilibrium constants of component reactions when multiplied together equal the numerical value of the equilibrium constant of the summative reaction. The component reactions are weak acid ionization reactions, weak base hydrolysis…

Common features of a vortex structure in long exponentially shaped Josephson junctions and Josephson junctions with inhomogeneities

International Nuclear Information System (INIS)

Boyadjiev, T.L.; Semerdjieva, E.G.; Shukrinov, Yu.M.

2007-01-01

We study the vortex structure in three different models of the long Josephson junction: the exponentially shaped Josephson junction and the Josephson junctions with the resistor and the shunt inhomogeneities in the barrier layer. For these three models the critical curves 'critical current-magnetic field' are numerically constructed. We develop the idea of the equivalence of the exponentially shaped Josephson junction and the rectangular junction with the distributed inhomogeneity and demonstrate that at some parameters of the shunt and the resistor inhomogeneities in the ends of the junction the corresponding critical curves are very close to the exponentially shaped one

The Problem of Weak Governments and Weak Societies in Eastern Europe

Directory of Open Access Journals (Sweden)

Marko Grdešić

2008-01-01

Full Text Available This paper argues that, for Eastern Europe, the simultaneous presence of weak governments and weak societies is a crucial obstacle which must be faced by analysts and reformers. The understanding of other normatively significant processes will be deficient without a consciousness-raising deliberation on this problem and its implications. This paper seeks to articulate the “relational” approach to state and society. In addition, the paper lays out a typology of possible patterns of relationship between state and society, dependent on whether the state is weak or strong and whether society is weak or strong. Comparative data are presented in order to provide an empirical support for the theses. Finally, the paper outlines two reform approaches which could enable breaking the vicious circle emerging in the context of weak governments and weak societies.

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

in the interplay between the homogeneous and inhomogeneous broadenings are measured. Based on these experiments, a coherent control model describing the optical fringe contrast using different detection schemes, such as photoluminescence or four-wave mixing, is established. Significant spectral modulation...

Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields

DEFF Research Database (Denmark)

Karlsen, Jonas Tobias; Augustsson, Per; Bruus, Henrik

2016-01-01

, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip....