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Discrete Structure (discrete + structure)
Selected AbstractsLesion studies targeting food-anticipatory activityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2009Alec J. Davidson Abstract Behavior ablation remains a powerful, if not cutting-edge, approach for localization of function within the nervous system. The initial discovery of the suprachiasmatic nuclei as the site of the mammalian light-entrainable circadian pacemaker is owed to this approach. Food-anticipatory activity (FAA), an output of a putative feeding-entrainable circadian pacemaker, is a behavior that has been surprisingly resilient to elimination by surgical lesion. Here we review this literature, with particular attention paid to recent studies aimed at defining the role of the dorsomedial hypothalamus in the generation of FAA. This literature is fraught with examples of inconsistent results among lesion studies, which in some cases can be accounted for by varied endpoint measures. The site of the feeding-entrainable circadian pacemaker, if it resides in a discrete structure at all, remains unknown. [source] Semi-analytical far field model for three-dimensional finite-element analysisINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2004James P. Doherty Abstract A challenging computational problem arises when a discrete structure (e.g. foundation) interacts with an unbounded medium (e.g. deep soil deposit), particularly if general loading conditions and non-linear material behaviour is assumed. In this paper, a novel method for dealing with such a problem is formulated by combining conventional three-dimensional finite-elements with the recently developed scaled boundary finite-element method. The scaled boundary finite-element method is a semi-analytical technique based on finite-elements that obtains a symmetric stiffness matrix with respect to degrees of freedom on a discretized boundary. The method is particularly well suited to modelling unbounded domains as analytical solutions are found in a radial co-ordinate direction, but, unlike the boundary-element method, no complex fundamental solution is required. A technique for coupling the stiffness matrix of bounded three-dimensional finite-element domain with the stiffness matrix of the unbounded scaled boundary finite-element domain, which uses a Fourier series to model the variation of displacement in the circumferential direction of the cylindrical co-ordinate system, is described. The accuracy and computational efficiency of the new formulation is demonstrated through the linear elastic analysis of rigid circular and square footings. Copyright © 2004 John Wiley & Sons, Ltd. [source] A discrete tomography algorithm for improving the quality of three-dimensional X-ray diffraction grain mapsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2006A. Alpers A discrete tomography algorithm is presented for the reconstruction of grain maps based on X-ray diffraction data. This is the first algorithm for this task, inherently exploiting the discrete structure of grain maps. Gibbs potentials serve to characterize the statistics of the local morphology of the grain boundaries. A Monte Carlo based algorithm is applied as a restoration method for improving the quality of grain maps produced by a classical (non-discrete) tomography algorithm (ART). The quality of the restored maps is demonstrated and quantified by simulation studies. The robustness of the algorithm with respect to the choice of Gibbs potentials is investigated. [source] Control of electron transport through a quantum wire by side-attached nanowiresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2004P. A. Orellana Abstract A system of arrays of nanowires side-coupled to a quantum wire is studied. Transport through the quantum wire is investigated by using a noninteracting-electron Anderson tunneling Hamiltonian. An analytical expression of the conductance at zero temperature is given, showing a band with alternating forbidden and allowed minibands due to the discrete structure of the nanowires. The conductance is found to exhibit a forbidden miniband in the center of the band for an odd number of sites in the nanowires, while shows an allowed band for an even number. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Semiclassical quantum gravity: statistics of combinatorial Riemannian geometriesANNALEN DER PHYSIK, Issue 8 2005L. Bombelli Abstract This paper is a contribution to the development of a framework, to be used in the context of semiclassical canonical quantum gravity, in which to frame questions about the correspondence between discrete spacetime structures at "quantum scales" and continuum, classical geometries at large scales. Such a correspondence can be meaningfully established when one has a "semiclassical" state in the underlying quantum gravity theory, and the uncertainties in the correspondence arise both from quantum fluctuations in this state and from the kinematical procedure of matching a smooth geometry to a discrete one. We focus on the latter type of uncertainty, and suggest the use of statistical geometry as a way to quantify it. With a cell complex as an example of discrete structure, we discuss how to construct quantities that define a smooth geometry, and how to estimate the associated uncertainties. We also comment briefly on how to combine our results with uncertainties in the underlying quantum state, and on their use when considering phenomenological aspects of quantum gravity. [source] Insensitivity to glutamate neurotoxicity mediated by NMDA receptors in association with delayed mitochondrial membrane potential disruption in cultured rat cortical neuronsJOURNAL OF NEUROCHEMISTRY, Issue 5 2008Yuki Kambe Abstract We have attempted to elucidate mechanisms underlying differential vulnerability to glutamate (Glu) using cultured neurons prepared from discrete structures of embryonic rat brains. Brief exposure to Glu led to a significant decrease in the mitochondrial activity in hippocampal neurons cultured for 9 or 12 days at 10 ,M to 1 mM with an apoptosis-like profile, without markedly affecting that in cortical neurons. Brief exposure to Glu also increased lactate dehydrogenase release along with a marked decrease in the number of cells immunoreactive for a neuronal marker protein in hippocampal, but not cortical, neurons. Similar insensitivity was seen to the cytotoxicity by NMDA, but not to that by tunicamycin, 2,4-dinitrophenol, hydrogen peroxide or A23187, in cortical neurons. However, NMDA was more efficient in increasing intracellular free Ca2+ levels in cortical neurons than in hippocampal neurons. Antagonists for neuroprotective metabotropic Glu receptors failed to significantly affect the insensitivity to Glu, while NMDA was more effective in disrupting mitochondrial membrane potentials in hippocampal than cortical neurons. These results suggest that cortical neurons would be insensitive to the apoptotic neurotoxicity mediated by NMDA receptors through a mechanism related to mitochondrial membrane potentials, rather than intracellular free Ca2+ levels, in the rat brain. [source] Probing small scale structure in the atmosphere of V471 TauriASTRONOMISCHE NACHRICHTEN, Issue 3 2004F. M. Walter Abstract The white dwarf in the eclipsing binary system V471 Tau is viewed through the atmosphere of the active K star prior to ingress and after egress. In the far UV the surface brightness of the hot white dwarf far outshines the K star emission. We can use this to probe the structure of the extended K star atmosphere along one line of sight, in absorption, on spatial scales of the radius of the white dwarf (10,000 km). The time series of HST/STIS spectra which show a hot (>250,000 K) extended (>1 K star radius) atmosphere around the K star. We see discrete structures in the velocity-resolved spectra, on spatial scales of less than 100,000 km. The mean velocity is that expected of gas in co-rotation with the K star, but the discrete velocity structures have excursions of up to 70 km/s from the mean. The mean temperature seems to increase with height above the K star photosphere. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||