Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Lossy Source Coding via Spatially Coupled LDGM Ensembles  [PDF]
Vahid Aref,Nicolas Macris,Rudiger Urbanke,Marc Vuffray
Mathematics , 2012,
Abstract: We study a new encoding scheme for lossy source compression based on spatially coupled low-density generator-matrix codes. We develop a belief-propagation guided-decimation algorithm, and show that this algorithm allows to approach the optimal distortion of spatially coupled ensembles. Moreover, using the survey propagation formalism, we also observe that the optimal distortions of the spatially coupled and individual code ensembles are the same. Since regular low-density generator-matrix codes are known to achieve the Shannon rate-distortion bound under optimal encoding as the degrees grow, our results suggest that spatial coupling can be used to reach the rate-distortion bound, under a {\it low complexity} belief-propagation guided-decimation algorithm. This problem is analogous to the MAX-XORSAT problem in computer science.
The scattering of $f$- and $p$-modes from ensembles of thin magnetic flux tubes - An analytical approach  [PDF]
Chris S. Hanson,Paul S. Cally
Physics , 2014, DOI: 10.1088/0004-637X/791/2/129
Abstract: Motivated by the observational results of Braun (1995), we extend the model of Hanson & Cally (2014) to address the effect of multiple scattering of f and p-modes by an ensemble of thin vertical magnetic flux tubes in the surface layers of the Sun. As in observational Hankel analysis we measure the scatter and phase shift from an incident cylindrical wave in a coordinate system roughly centred in the core of the ensemble. It is demonstrated that, although thin flux tubes are unable to interact with high order fluting modes individually, they can indirectly absorb energy from these waves through the scatters of kink and sausage components. It is also shown how the distribution of absorption and phase shift across the azimuthal order m depends strongly on the tube position, as well as on the individual tube characteristics. This is the first analytical study into an ensembles multiple scattering regime, that is embedded within a strati?ed atmosphere.
The detection of upwardly propagating waves channelling energy from the chromosphere to the low corona  [PDF]
N. Freij,E. M. Scullion,C. J. Nelson,S. Mumford,S. Wedemeyer,R. Erdélyi
Physics , 2014, DOI: 10.1088/0004-637X/791/1/61
Abstract: There have been ubiquitous observations of wave-like motions in the solar atmosphere for decades. Recent improvements to space- and ground-based observatories have allowed the focus to shift to smaller magnetic structures on the solar surface. In this paper, high-resolution ground-based data taken using the Swedish 1 m Solar Telescope is combined with co-spatial and co-temporal data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) satellite to analyze running penumbral waves (RPWs). RPWs have always been thought to be radial wave propagation that occurs within sunspots. Recent research has suggested that they are in fact upwardly propagating field-aligned waves (UPWs). Here, RPWs within a solar pore are observed for the first time and are interpreted as UPWs due to the lack of a penumbra that is required to support RPWs. These UPWs are also observed co-spatially and co-temporally within several SDO/AIA elemental lines that sample the transition region and low corona. The observed UPWs are traveling at a horizontal velocity of around 17 +- 0.5 km s-1 and a minimum vertical velocity of 42 +- 21 km s-1. The estimated energy of the waves is around 150 W m-2, which is on the lower bound required to heat the quiet-Sun corona. This is a new, yet unconsidered source of wave energy within the solar chromosphere and low corona.
Un aspect nouveau de la prospection sismique en appliquant la théorie des sous-ensembles flous Improvement of Seismic Prospecting by Using Fuzzy Subsets Theory  [cached]
Bois P.
Oil & Gas Science and Technology , 2006, DOI: 10.2516/ogst:1989010
Abstract: Durant les dix dernières années, la théorie des sous-ensembles flous a connu un intérêt croissant grace aux travaux de Zadeh [1]. Cette théorie a vu son champ d'application s'étendre à différentes branches des mathématiques pures et appliquées en particulier à la topologie, à la théorie des graphes, des automates et à la reconnaissance des formes. Son but est d'analyser l'imprécision qui se glisse partout dans le comportement humain et dans la connaissance humaine. Cet article donne deux applications de la théorie des sous-ensembles flous à la prospection sismique. La première concerne l'interprétation d'une section sismique qui consiste à tracer une carte du sous-sol montrant la position des différents horizons sismiques situés au dessous de la surface du sol. Le problème qui se pose au sismicien est de trouver la structure géologique correspondante dans un plan vertical à la surface du sol. La seconde est la détermination de la nature des réservoirs contenant des hydrocarbures. On utilisera une méthode s'appuyant sur la reconnaissance des formes avec apprentissage préalable. Cette méthode consiste à comparer la nature d'un réservoir qui a été foré à celle d'un réservoir inconnu. Le réservoir connu joue le r le du moniteur dans le processus d'apprentissage. Pour ce faire, un algorithme est con u utilisant la méthode de Burg appliquée à des portions de traces sismiques représentatives des deux réservoirs. Enfin, une analyse floue des données représentant ces deux réservoirs sert de critère pour décider s'ils sont de nature identique ou différente. During the past decade, interest in fuzzy subsets theory has led to the development of a well-organized theory developed by Zadeh [1]. This theory has grown up, exploring and developing various branches of pure and applied mathematics, including topology, graph theory, mapping, automata and pattern recognition. Basically, the theory of fuzzy subsets aims at an accomodation with the pervasive imprecision of human thinking and cognition. One way in which imprecision can be analyzed is through understanding of the organized structure of human knowledge. This paper is concerned with two applications of fuzzy subsets theory to seismic prospecting. The first application is seismic interpretation from a seismic section, which is a chart showing the position of different seismic horizons situated under the surface of theground. This problem consists of finding out the corresponding geological structure of a vertical plane on the surface of the ground. The second application is determination of the nature of reservoirs
Seismic performance of variable cross-sectional concrete filled steel tubular laced columns with flat lacing tubes

- , 2018, DOI: 10.11835/j.issn.1000-582X.2018.01.003
Abstract: 应用OpenSEES通用程序建立变截面平缀管式钢管混凝土格构柱有限元模型,试件的分析结果与拟静力试验结果吻合良好。以柱肢坡度为计算参数,对四肢变截面平缀管式钢管混凝土格构柱开展抗震性能研究,探讨了构件的耗能能力、骨架曲线、结构延性、刚度退化等方面的受力性能和规律,并与等截面钢管混凝土格构柱进行对比研究。在此基础上进一步分析了轴压比、试件高度(长细比)、平缀管竖向间距、柱肢含钢率、支主管管径比、钢材屈服强度、混凝土强度等参数对变截面平缀管式钢管混凝土格构柱抗震性能的影响,为钢管混凝土计算理论的进一步完善和变截面钢管混凝土格构式桥墩的工程应用提供参考。
A finite element analysis model of variable cross-sectional concrete-filled steel tubular(CFST)laced column with flat lacing tubes is built with universal program of OpenSEES, and the calculating results of specimen obtained by OpenSEES agree well with the quasi-static test results.The seismic performance of four-element variable cross-sectional CFST laced columns with flat lacing tubes is researched with calculation parameter of column slope, including the rules on energy dissipation capacity, skeleton curve, structure ductility, and stiffness degradation of elements, and these calculation results are compared with the research results of uniform cross-sectional CFST laced columns. And the influence of axial compression ratio, column height (slenderness ratio), vertical spacing of flat lacing tubes, steel ratio of longitudinal element, diameter ratio of lacing tubes to longitudinal tubes, yield strength of steel, concrete strength and other structural parameters on seismic performance of variable cross-sectional CFST laced columns with flat lacing tubes are investigated. It's hoped that the results can provide reference for the improvement of CFST calcalation theory and engineering application of variable cross-sectional CFST laced column piers
Statistical Mechanical Approach to Error Exponents of Lossy Data Compression  [PDF]
Tadaaki Hosaka,Yoshiyuki Kabashima
Physics , 2003,
Abstract: We present herein a scheme by which to accurately evaluate the error exponents of a lossy data compression problem, which characterize average probabilities over a code ensemble of compression failure and success above or below a critical compression rate, respectively, utilizing the replica method (RM). Although the existing method used in information theory (IT) is, in practice, limited to ensembles of randomly constructed codes, the proposed RM-based approach can be applied to a wider class of ensembles. This approach reproduces the optimal expressions of the error exponents achieved by the random code ensembles, which are known in IT. In addition, the proposed framework is used to show that codes composed of non-monotonic perceptrons of a specific type can provide the optimal exponents in most cases, which is supported by numerical experiments.
Numerical simulations of multiple scattering of the $f-$mode by flux tubes  [PDF]
T. Felipe,A. D. Crouch,A. C. Birch
Physics , 2013, DOI: 10.1088/0004-637X/775/1/74
Abstract: We use numerial simulations to study the absorption and phase shift of surface-gravity waves caused by groups of magnetic flux tubes. The dependence of the scattering coefficients with the distance between the tubes and their positions is analyzed for several cases with two or three flux tubes embedded in a quiet Sun atmosphere. The results are compared with those obtained neglecting completely or partially multiple scattering effects. We show that multiple scattering has a significant impact on the absorption measurements and tends to reduce the phase shift. We also consider more general cases of ensembles of randomly distributed flux tubes, and we have evaluated the effects on the scattering measurements of changing the number of tubes included in the bundle and the average distance between flux tubes. We find that for the longest wavelength incoming waves multiple scattering enhances the absorption, and its efficiency increases with the number of flux tubes and the reduction of the distance between them.
Strategies for Estimating Quantum Lossy Channels  [PDF]
Xian-Ting Liang
Physics , 2002,
Abstract: Due to the anisotropy of quantum lossy channels one must choose optimal bases of input states for best estimating them. In this paper, we obtain that the equal probability Schr\"{o}dinger cat states are optimal for estimating a single lossy channel and they are also the optimal bases of input states for estimating composite lossy channels. On the other hand, by using the symmetric logarithmic derivative (SLD) Fisher information of output states exported from the lossy channels we obtain that if we take the equal probability Schr\"{o}dinger cat states as the bases of input states the maximally entangled inputs are not optimal, however if the bases of the input states are not the equal probability Schr\"{o}dinger cat states the maximally entangled input states may be optimal for the estimating composite lossy channel.
Wave Damping Observed in Upwardly Propagating Sausage-mode Oscillations contained within a Magnetic Pore  [PDF]
S. D. T. Grant,D. B. Jess,M. G. Moreels,R. J. Morton,D. J. Christian,I. Giagkiozis,G. Verth,V. Fedun,P. H. Keys,T. Van Doorsselaere,R. Erdelyi
Physics , 2015, DOI: 10.1088/004-637X/806/1/132
Abstract: We present observational evidence of compressible magnetohydrodynamic wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four wavelength bands using the Dunn Solar Telescope. Employing Fourier and wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations. The intensity and area fluctuations exhibit a range of periods from 181-412s, with an average period ~290s, consistent with the global p-mode spectrum. Intensity and area oscillations present in adjacent bandpasses were found to be out-of-phase with one another, displaying phase angles of 6.12 degrees, 5.82 degrees and 15.97 degrees between 4170 Angstrom continuum - G-band, G-band - Na I D1 and Na I D1 - Ca II K heights, respectively, reiterating the presence of upwardly-propagating sausage-mode waves. A phase relationship of ~0 degrees between same-bandpass emission and area perturbations of the pore best categorises the waves as belonging to the `slow' regime of a dispersion diagram. Theoretical calculations reveal that the waves are surface modes, with initial photospheric energies in excess of 35000 W/m^2. The wave energetics indicate a substantial decrease in energy with atmospheric height, confirming that magnetic pores are able to transport waves that exhibit appreciable energy damping, which may release considerable energy into the local chromospheric plasma.
Modeling lossy propagation of non-classical light  [PDF]
Ulvi Yurtsever
Physics , 2009,
Abstract: The lossy propagation law (generalization of Lambert-Beer's law for classical radiation loss) for non-classical, dual-mode entangled states is derived from first principles, using an infinite-series of beam splitters to model continuous photon loss. This model is general enough to accommodate stray-photon noise along the propagation, as well as amplitude attenuation. An explicit analytical expression for the density matrix as a function of propagation distance is obtained for completely general input states with bounded photon number in each mode. The result is analyzed numerically for various examples of input states. For N00N state input, the loss of coherence and entanglement is super exponential as predicted by a number of previous studies. However, for generic input states, where the coefficients are generated randomly, the decay of coherence is very different; in fact no worse than the classical Beer-Lambert law. More surprisingly, there is a plateu at a mid-range interval in propagation distance where the loss is in fact sub-classical, following which it resumes the classical rate. The qualitative behavior of the decay of entanglement for two-mode propagation is also analyzed numerically for ensembles of random states using the behavior of negativity as a function of propagation distance.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.