124,839 research outputs found
Photorefractive Solitons and Their Underlying Nonlocal Physics
No full textOur aim is to provide an account of the recent progress in the physical understanding of the phenomenon, including the origin of quasi-steady-state solitons and round two-dimensional (2D) solitons, which is something beyond to providing an extensive review of photorefractive soliton phenomenology, as can be found in a number of review articles (Crosignani et al., 1998;DelRe, Crosignani, and Di Porto, 2001; DelRe et al., 2006; Krolikowski, Luther-Davies, and Denz, 2003)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Cholesterol metabolism in primary biliary cirrhosis during simvastatin and UDCA administration
No full textLittle is known about the effects of cholesterol-lowering agents in hypercholesterolemic patients with primary biliary cirrhosis (PBC). The aim of this study was to compare the changes induced by simvastatin and ursodeoxycholic acid (UDCA) on cholesterol metabolism in patients with PBC and preserved liver function. Six patients with PBC were administered simvastatin (40 mg/day) for 30 days and, after a washout period of 30 days, ursodeoxycholic acid (600 mg/day) for 30 days. Serum levels of lathosterol, campesterol, 7 alpha-hydroxycholesterol, and 27-hydroxycholesterol were measured by gas chromatography-mass spectrometry. During simvastatin administration, reduction of cholesterol levels (34% in 30 days) was paralleled by the decrease of lathosterol (55%), whereas concentrations of campesterol and of the two hydroxysterols were not substantially modified. During ursodeoxycholic acid administration, a trend toward a decrease of serum cholesterol concentrations was observed after only one year of treatment, and these changes were paralleled by the decrease of campesterol serum levels. Both simvastatin and UDCA were well tolerated, and a reduction of serum liver enzyme levels occurred with the latter. Simvastatin proved to be safe and effective in reducing serum cholesterol levels in patients with PBC by an inhibitory effect on cholesterol synthesis occurring within 24 h. --Del Puppo, M., M. Galli Kienle, A. Crosignani, M. L. Petroni, B. Amati, M. Zuin, and M. Podda. Cholesterol metabolism in primary biliary cirrhosis during simvastatin and UDCA administration. J. Lipid Res. 2001. 42: 437--441
HAMILTONIAN DESCRIPTION OF NONLINEAR PROPAGATION IN OPTICAL FIBERS
No full textNonlinear propagation in single-mode and multimode fibers in the presence of the optical Kerr effect is described in terms of a number of parameters (four for each propagating mode) which can be interpreted as conjugate variables of a suitable Hamiltonian system. The formal simplicity of this approach, which admittedly furnishes a limited description of nonlinear propagation because of the finiteness of the number of variables employed, is, however, very useful for gaining a straightforward physical insight into the problem. The solution of the pertinent equations, either analytical or numerical, presents a much less formidable task than the solution of the set of nonlinear equations fully describing propagation. © 1988 The American Physical Society
The adiabatic piston and the second law of thermodynamics
No full textAip Conference Proceedings 643 (1), 267-272 (American Institute of Physics, November 2002
Intrinsic irreversibility of Markovian chains
No full textWe show that for a large class of stationary Markov processes the total variation distance between the final equilibrium distribution and that at a given time is a strongly monotonic vanishing function. We illustrate this for basic paradigmatic processes and discuss how, for systems susceptible to a canonical description, this can be interpreted as a statistical arrow of time that exists besides the standard decrease of free energy
Novel optical phenomena in near-critical photorefractive crystals: diffusion-driven diffraction and spontaneous self-trapping
No full textWe investigate nonlinear optical diffraction in a photorefractive paraelectric, heated slightly above the ferroelectric phase transition. Theoretically, the basic photorefractive band-transport model leads to an anisotropic, nonlinear and nonlocal propagation equation that remarkably allows for explicit analytical solutions, in the form of anisotropic diffraction and noncircular solitons without characteristic length scale. Experiments qualitatively support predictions, but suggest that spontaneous crystal response is present. Actual spontaneous domain formation is experimentally seen to lead to optical self-trapping in both one and two transverse spatial dimensions
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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