2,725 research outputs found
Looks Can Be Deceiving—A Comparison of Initial Public Offering Procedures Under Japanese and U.S. Securities Laws
In order to examine the divergent administration of statutes that are by their terms similar, the initial public offering procedures that a non-sovereign domestic issuer follows in the US and Japan are described
Vasopressin
Antidiuretic hormone liberated the vertebrates from their aqueous environment, and permitted them to establish themselves on dry land. The combination of sensitive volume and osmoreceptors, a pituitary secretory apparatus which can vary its output from virtually zero to high levels in a short space of time, and receptor cells functioning in the countercurrent system of the renal medulla, has resulted in a water conservation system of great efficiency. The hormone rapidly alters the luminal membrane of receptor cells in the collecting tubule and collecting duct, increasing the permeability of these structures to water.1 The permeability of the collecting duct to urea and sodium is also increased.This review will be centered on the sequence of events that follows the attachment of vasopressin to its receptors in the distal nephron. This has become an area of intense activity since the discovery by Sutherland and his colleagues of the central role of cyclic AMP in the action of hormones [2]. The review will cover in brief much of the ground covered by the extensive review of Handler and OrlofT [3], emphasizing recent additions to the literature. It is regrettable that the important advances in our understanding of the synthesis and release of antidiuretic hormone cannot be included; the reader is referred to recent symposia and reviews in this area [4–6], as well as in the comparative physiology of water regulation [7] and the countercurrent system [8]
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Determination of biomembrane bending moduli in fully atomistic simulations.
The bilayer bending modulus (Kc) is one of the most important physical constants characterizing lipid membranes, but precisely measuring it is a challenge, both experimentally and computationally. Experimental measurements on chemically identical bilayers often differ depending upon the techniques employed, and robust simulation results have previously been limited to coarse-grained models (at varying levels of resolution). This Communication demonstrates the extraction of Kc from fully atomistic molecular dynamics simulations for three different single-component lipid bilayers (DPPC, DOPC, and DOPE). The results agree quantitatively with experiments that measure thermal shape fluctuations in giant unilamellar vesicles. Lipid tilt, twist, and compression moduli are also reported
Regulatory activity revealed by dynamic correlations in gene expression noise
Gene regulatory interactions are context dependent, active in some cellular states but not in others. Stochastic fluctuations, or 'noise', in gene expression propagate through active, but not inactive, regulatory links^(1,2). Thus, correlations in gene expression noise could provide a noninvasive means to probe the activity states of regulatory links. However, global, 'extrinsic', noise sources generate correlations even without direct regulatory links. Here we show that single-cell time-lapse microscopy, by revealing time lags due to regulation, can discriminate between active regulatory connections and extrinsic noise. We demonstrate this principle mathematically, using stochastic modeling, and experimentally, using simple synthetic gene circuits. We then use this approach to analyze dynamic noise correlations in the galactose metabolism genes of Escherichia coli. We find that the CRP-GalS-GalE feed-forward loop is inactive in standard conditions but can become active in a GalR mutant. These results show how noise can help analyze the context dependence of regulatory interactions in endogenous gene circuits
Staircase polygons: moments of diagonal lengths and column heights
We consider staircase polygons, counted by perimeter and sums of k-th powers
of their diagonal lengths, k being a positive integer. We derive limit
distributions for these parameters in the limit of large perimeter and compare
the results to Monte-Carlo simulations of self-avoiding polygons. We also
analyse staircase polygons, counted by width and sums of powers of their column
heights, and we apply our methods to related models of directed walks.Comment: 24 pages, 7 figures; to appear in proceedings of Counting Complexity:
An International Workshop On Statistical Mechanics And Combinatorics, 10-15
July 2005, Queensland, Australi
Pure point diffraction and cut and project schemes for measures: The smooth case
We present cut and project formalism based on measures and continuous weight
functions of sufficiently fast decay. The emerging measures are strongly almost
periodic. The corresponding dynamical systems are compact groups and
homomorphic images of the underlying torus. In particular, they are strictly
ergodic with pure point spectrum and continuous eigenfunctions. Their
diffraction can be calculated explicitly. Our results cover and extend
corresponding earlier results on dense Dirac combs and continuous weight
functions with compact support. They also mark a clear difference in terms of
factor maps between the case of continuous and non-continuous weight functions.Comment: 30 page
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