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Search Results: 1 - 10 of 239105 matches for " David G. Edwards "
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Peripheral Vascular Dysfunction in Chronic Kidney Disease
Christopher R. Martens,David G. Edwards
Cardiology Research and Practice , 2011, DOI: 10.4061/2011/267257
Abstract: There is an increased prevalence of cardiovascular disease- (CVD-) related mortality in patients with chronic kidney disease (CKD). Endothelial dysfunction is a primary event in the development of atherosclerosis and hypertension and likely contributes to the elevated cardiovascular risk in CKD. Endothelial dysfunction has been shown to occur in the peripheral vasculature of patients with both severe and moderate CKD. Mechanisms include oxidative stress, L-arginine deficiency, and elevated plasma levels of ADMA. Interventions designed to restore vascular function in patients with CKD have shown mixed results. Evidence from cell culture studies suggest that the accumulation of uremic toxins inhibits L-arginine transport and reduces nitric oxide production. The results of these studies suggest that endothelial dysfunction may become less reversible with advancing kidney disease. The purpose of this paper is to present the current literature pertaining to potential mechanisms of peripheral vascular dysfunction in chronic kidney disease and to identify possible targets for treatment. 1. Introduction Chronic kidney disease (CKD) is a major public health concern affecting nearly 20 million people in the United States alone [1]. Patients with CKD are at greater risk of cardiovascular disease- (CVD-) related morbidity and mortality than individuals without CKD with similar cardiovascular risk factors and tend to die before reaching end-stage renal disease (ESRD) [2–5]. Treatments aimed solely at reducing traditional cardiovascular risk factors do not improve cardiovascular function in patients with late-stage CKD [6]. Therefore, traditional CVD risk factors alone cannot explain the high incidence of CVD in CKD. Endothelial dysfunction is a precursor to the development of atherosclerosis [7, 8] and has been shown to be associated with increased cardiovascular risk in patients with left ventricular dysfunction and congestive heart failure [9–11]. The combination of traditional risk factors in CKD is not enough to explain the high incidence of CVD and endothelial dysfunction has been suggested to play a role in the increased CV risk in CKD [12, 13]. In support of this, a longitudinal study of patients with end-stage renal disease (ESRD) found all cause mortality to be independently associated with impaired endothelial function [14]. The majority of studies of endothelial function in renal disease have focused on ESRD and patients receiving dialysis; however, little is known about endothelial function in earlier stages of CKD. Guidelines from the Kidney Disease
Radiative Transitions in Charmonium from Lattice QCD
Jozef J. Dudek,Robert G. Edwards,David G. Richards
Physics , 2006, DOI: 10.1103/PhysRevD.73.074507
Abstract: Radiative transitions between charmonium states offer an insight into the internal structure of heavy-quark bound states within QCD. We compute, for the first time within lattice QCD, the transition form-factors of various multipolarities between the lightest few charmonium states. In addition, we compute the experimentally unobservable, but physically interesting vector form-factors of the $\eta_c, J/\psi$ and $\chi_{c0}$. To this end we apply an ambitious combination of lattice techniques, computing three-point functions with heavy domain wall fermions on an anisotropic lattice within the quenched approximation. With an anisotropy $\xi=3$ at $a_s \sim 0.1 \mathrm{fm}$ we find a reasonable gross spectrum and a hyperfine splitting $\sim 90 \mathrm{MeV}$, which compares favourably with other improved actions. In general, after extrapolation of lattice data at non-zero $Q^2$ to the photopoint, our results agree within errors with all well measured experimental values. Furthermore, results are compared with the expectations of simple quark models where we find that many features are in agreement; beyond this we propose the possibility of constraining such models using our extracted values of physically unobservable quantities such as the $J/\psi$ quadrupole moment. We conclude that our methods are successful and propose to apply them to the problem of radiative transitions involving hybrid mesons, with the eventual goal of predicting hybrid meson photoproduction rates at the GlueX experiment.
High-Dimensional Graphical Model Search with the gRapHD R Package
Gabriel C. G. Abreu,Rodrigo Labouriau,David Edwards
Journal of Statistical Software , 2010,
Abstract: This paper presents the R package gRapHD for efficient selection of high-dimensional undirected graphical models. The package provides tools for selecting trees, forests, and decomposable models minimizing information criteria such as AIC or BIC, and for displaying the independence graphs of the models. It has also some useful tools for analysing graphical structures. It supports the use of discrete, continuous, or both types of variables.
High-dimensional Graphical Model Search with gRapHD R Package
Gabriel C. G. de Abreu,Rodrigo Labouriau,David Edwards
Statistics , 2009,
Abstract: This paper presents the R package gRapHD for efficient selection of high-dimensional undirected graphical models. The package provides tools for selecting trees, forests and decomposable models minimizing information criteria such as AIC or BIC, and for displaying the independence graphs of the models. It has also some useful tools for analysing graphical structures. It supports the use of discrete, continuous, or both types of variables simultaneously.
Unconscious Influences on Discourses About Consciousness: Ideology, State-Specific Science and Unformulated Experience
David Edwards
Indo-Pacific Journal of Phenomenology , 2005,
Abstract: Discussions about consciousness are complicated by the fact that participants do not share a common underlying “ordinary” consciousness. Everyday experience is founded on what Teasdale calls implicational cognition, much of which is not verbally formulated. An unacknowledged aspect of debate is individuals’ attempts to negotiate the expression of their unformulated experience. This is further complicated by the way in which a discourse, based on particular ontological assumptions, exercises an ideological control which limits what underlying aspects of experience can be formulated at all. Tart’s concept of state specific sciences provides a framework within which the role of unformulated experience can be acknowledged and taken into account. Unless this is done, debates will be vitiated by participants engaging in ideological struggles and talking at cross-purposes. Indo-Pacific Journal of Phenomenology, Volume 5, Edition 1 April 2005
Mythic and theoretic aspects of the concept of ‘the unconscious’ in popular and psychological discourse
David Edwards
Indo-Pacific Journal of Phenomenology , 2003,
Abstract:
Toward the excited meson spectrum of dynamical QCD
Jozef J. Dudek,Robert G. Edwards,Michael J. Peardon,David G. Richards,Christopher E. Thomas
Physics , 2010, DOI: 10.1103/PhysRevD.82.034508
Abstract: We present a detailed description of the extraction of the highly excited isovector meson spectrum on dynamical anisotropic lattices using a new quark-field construction algorithm and a large variational basis of operators. With careful operator construction, the combination of these techniques is used to identify the continuum spin of extracted states reliably, overcoming the reduced rotational symmetry of the cubic lattice. Excited states, states with exotic quantum numbers (0+-, 1-+ and 2+-) and states of high spin are resolved, including, for the first time in a lattice QCD calculation, spin-four states. The determinations of the spectrum of isovector mesons and kaons are performed on dynamical lattices with two volumes and with pion masses down to ~ 400 MeV, with statistical precision typically at or below 1% even for highly excited states.
Lattice Calculations of Nucleon Electromagnetic Form Factors at Large Momentum Transfer
Huey-Wen Lin,Saul D. Cohen,Robert G. Edwards,Kostas Orginos,David G. Richards
Physics , 2010,
Abstract: In this work, we report a novel technique in lattice QCD for studying the high momentum-transfer region of nucleon form factors. These calculations could give important theoretical input to experiments, such as those of JLab's 12-GeV program and studies of nucleon deformation. There is an extensive history of form-factor calculations on the lattice, primarily with ground states for both the initial and final state. However, determining form factors at large momentum transfer ($Q^2$) has been difficult due to large statistical and systematic errors in this regime. We study the nucleon form factors using three pion masses with both quenched and 2+1-flavor anisotropic lattice configurations with $Q^2$ as large as $6 GeV^2$. These form factors are further processed to obtain transverse charge and magnetization densities across 2-dimensional impact-parameter space. Our approach can be applied to isotropic lattices and lattices with smaller lattice spacing to calculate even larger-$Q^2$ form factors.
First Lattice Study of the $N$-$P_{11}(1440)$ Transition Form Factors
Huey-Wen Lin,Saul D. Cohen,Robert G. Edwards,David G. Richards
Physics , 2008, DOI: 10.1103/PhysRevD.78.114508
Abstract: Experiments at Jefferson Laboratory, MIT-Bates, LEGS, Mainz, Bonn, GRAAL, and Spring-8 offer new opportunities to understand in detail how nucleon resonance ($N^*$) properties emerge from the nonperturbative aspects of QCD. Preliminary data from CLAS collaboration, which cover a large range of photon virtuality $Q^2$ show interesting behavior with respect to $Q^2$ dependence: in the region $Q^2 \le 1.5 {GeV}^2$, both the transverse amplitude, $A_{1/2}(Q^2)$, and the longitudinal amplitude, $S_{1/2}(Q^2)$, decrease rapidly. In this work, we attempt to use first-principles lattice QCD (for the first time) to provide a model-independent study of the Roper-nucleon transition form factor.
Challenges in Hadronic Form Factor Calculations
Huey-Wen Lin,Saul D. Cohen,Robert G. Edwards,Kostas Orginos,David G. Richards
Physics , 2008,
Abstract: There is an extensive history of form factor calculations on the lattice, primarily with ground states for both initial and final states. However, there have never been any radially excited transition form factor calculations. Furthermore, the lattice faces difficulty in extracting signal from noise at large transfer momenta ($Q^2$). These measurements could give important theoretical input to experiments, such as those of JLab's 12 GeV program and studies of deformation of the nucleon. In this work, I will present a simple technique to resolve both of these difficulties and present results from anisotropic configurations showing improved signals for excited-state quantities. It should also be possible to apply this technique to isotropic lattices for calculating large-$Q^2$ form factors.
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