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Metformin, dimethylbiguanide, is an agent that has been widely used in the treatment of non-insulin-dependent diabetes mellitus. Its mechanism of action is not dependent on the stimulation of insulin secretion, unlike the sulfonylureas. It is clear that metformin reduces fasting endogenous glucose production rates, which are elevated in non-insulin-dependent diabetes mellitus. Some studies have proposed that metformin reduces endogenous glucose production primarily by reducing gluconeogenesis, whereas others have proposed that gluconeogenesis is not affected. The authors review the literature regarding the effects of metformin on hepatic carbohydrate metabolism.
This paper gives several basic results on dynamic nonlinear networks from a geometric point of view. One of the main advantages of a geometric approach is that it is coordinate-free, i.e., results obtained by a geometric method do not depend on the particular choices of a tree, a loop matrix, state variables, etc. Therefore, the method is suitable for studying intrinsic properties of networks. It is shown that transversality of resistor constitutive relations and Kirchhoff space is a sufficient condition for the configuration space to be a submanifold. Main result of the paper states that a network is locally solvable, i.e., the dynamics of a network is well defined in the sense of Definition 3, if and only if, capacitor charges and inductor fluxes serve as a local coordinate system for the configuration space. In other words, if all the variables in a network are determined as functions of capacitor charges and inductor fluxes, at least locally, then the dynamics is well defined. Conversely, if the dynamics is well defined, then all the variables in a network are determined as functions of capacitor charges and inductor fluxes. Because of its coordinate-free property, the main result also says that if the dynamics is well defined in terms of some coordinate system, then it must be well defined in terms of capacitor charges and inductor fluxes. Conversely, if the dynamics is not well-defined in terms of capacitor charges and inductor fluxes, then there is no choice of variables in terms of which the dynamics is well defined in the sense of Definition 3. This shows that capacitor charges and inductor fluxes are the fundamental quantities in describing the dynamics of networks. Perturbation results are given which guarantee transversality and local solvability. Finally, several other perturbation results are given which guarantee eventual strict passivity of dynamic nonlinear networks. They explain why the voltage and current waveforms of almost every network of practical importance are eventually uniformly bounded.
Our reactive metals-based civilization is possible only because of the formation of thin oxide (passive) films on surfaces that effectively separate the reactive metals from the corrosive environments. Previously, the conditions under which passivity occurred were defined in terms of equilibrium potential-pH relationships in the form of Pourbaix diagrams, which delineated regions of stability, passivity, and immunity. However, recent work has demonstrated that a passive film is never at equilibrium, but instead exists in the meta- stable state, if it exists at all. Thus, the limits of stability must be defined in terms of kinetic factors and not in terms of equilibrium principles. This has been done in the present study by phase space analysis of the rate law for film growth afforded by the Point Defect Model to yield Kinetic Stability Diagrams, which are proposed as kinetic alternatives to the equilibrium thermodynamic Pourbaix diagrams.
Abstract The applicability of AC Impedance Spectroscopy (ACIS) for detecting corrosion on rebar in concrete is explored theoretically. Corroding rebar is simulated as a one-dimensional electrical transmission line of twenty one-meter segments embedded in a uniform concrete matrix, with the corrosion being restricted to one segment. The simulations indicate that corrosion can only be detected at very low frequencies (<1mHz), but that the impedance and the peak voltage monitored at the concrete surface may be used to locate the site of the corrosive attack.
Abstract Detailed derivations of the Legendre-Hadamard necessary conditions for energy-minimizing states of fiber-reinforced three-dimensional solids and two-dimensional shells are presented. The underlying conceptual framework is Cosserat elasticity theory in which the Cosserat rotation field controls the orientation of the embedded fibers. This is partially coupled to the continuum deformation gradient by the requirement that the fibers convect as material curves with respect to the matrix material in which they are embedded. The conditions obtained combine the effects of deformation and rotation and subsume previously obtained decoupled inequalities involving these effects separately.
Abstract The asymmetric alkylation of acyclic ketones is a longstanding challenge in organic synthesis. Reported herein are diastereoselective and enantioselective allylic substitutions with acyclic α‐alkoxy ketones catalyzed by a metallacyclic iridium complex to form products with contiguous stereogenic centers derived from the nucleophile and electrophile. These reactions occur between allyl methyl carbonates and unstabilized copper(I) enolates generated in situ from acyclic α‐alkoxy ketones. The resulting products can be readily converted into enantioenriched tertiary alcohols and tetrahydrofuran derivatives without erosion of enantiomeric purity.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTrimethylsilyl derivatives of bis(cyclopentadienyl)zirconium and -hafnium. Crystal structure of (.eta.5-C5H5)2Zr(SiMe3)(S2CNEt2)T. Don TilleyCite this: Organometallics 1985, 4, 8, 1452–1457Publication Date (Print):August 1, 1985Publication History Published online1 May 2002Published inissue 1 August 1985https://doi.org/10.1021/om00127a025Request reuse permissionsArticle Views333Altmetric-Citations70LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (775 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
Blunted growth hormone (GH) release in response to stimulation by a secretagogue has been widely reported in both children and adults with anxiety and depressive disorders. Blunted GH responsiveness appears to be a stable characteristic of an individual, suggesting that it may be useful as a biological marker that would allow early recognition of these disease processes. Another potential biological marker for anxiety disorders is the temperamental construct of behavioral inhibition. Children identified as being behaviorally inhibited early in life are more likely than less inhibited children to suffer from anxiety disorders later in life (Biederman et al. 1993; Hirshfeld et al. 1992). If blunted GH responsiveness to pharmacological challenge and behavioral inhibition are markers of anxiety and depressive disorders, then it would follow that they would coexist in a subset of individuals. However, such prospective studies in clinically normal young children are difficult to perform. Therefore, in this study, we examined GH responsiveness and temperament in a group of 38 young rhesus monkeys (ages 3-6 months). Monkeys received an intravenous dose of 10 microg/kg of growth hormone-releasing hormone (GHRH) and 5 microg/kg of clonidine, combined, to assess GH response to stimulation. Behavioral reactivity in a fearful situation was assessed using the Human Intruder Test developed by Kalin et al. (1991). This test measures response to a potentially threatening stimulus (a human stranger making direct eye contact). Results showed a population distribution of GH response to GHRH and clonidine ranging from 120 ng/mL/90 minutes to 3,000 ng/mL/90 minutes. There was no difference in GH response in males versus females or any significant effect of age on GH response. There was a significant correlation between GH responsiveness and the time spent reacting to the intruder in the Human Intruder Test. Monkeys with lower GH responsiveness reacted less to the intruder (p < 0.01). Additionally, when monkeys were classified based on their reactivity in the Human Intruder Test, behaviorally nonreactive monkeys had significantly lower GH responsiveness than behaviorally reactive monkeys (p < 0.005). These data provide evidence that there are inherent differences in GH responsiveness to stimulation in young rhesus monkeys and that low GH responsiveness is linked to low behavioral reactivity, which may be a form of behavioral inhibition. Further studies will be necessary to determine if the characteristics of low GH responsiveness and low behavioral reactivity predict an increased propensity to develop anxious or depressive behaviors over the course of the life span.
