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Search Results: 1 - 10 of 90437 matches for " PHILIP W; "
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High order explicit Runge-Kutta pairs for ephemerides of the Solar System and the Moon
Philip W. Sharp
Advances in Decision Sciences , 2000, DOI: 10.1155/s1173912600000146
Abstract: Numerically integrated ephemerides of the Solar System and the Moon require very accurate integrations of systems of second order ordinary differential equations. We present a new family of 8-9 explicit Runge-Kutta pairs and assess the performance of two new 8-9 pairs on the equations used to create the ephemeris DE102. Part of this work is the introduction of these equations as a test problem for integrators of initial value ordinary differential equations.
Models of the human metabolic network: aiming to reconcile metabolomics and genomics
Philip W Kuchel
Genome Medicine , 2010, DOI: 10.1186/gm167
Abstract: There are approximately ten times as many expressed genes (proteins) as there are different metabolites in most cells. Biochemical analysis of cells has been the art of the possible; you know about what you can detect. In the past, assays have largely focused on small organic (bio)molecules analyzed by colorimetry or spectrophotometry. The genome projects have revealed a completely different data set from that of classical metabolic biochemistry, and a totally different perspective on metabolism. Two different perspectives, as neatly presented by Gerrard et al. [1], are presented in Figure 1; note how the genome draws attention to the proteins, many of which are enzymes, but many of which are not. So, measuring the concentrations of metabolites as we do in clinical biochemistry only indirectly reports on which of the enzymes, control proteins, or structural proteins are at fault in a case of chemical poisoning, drug side-effects, or in an inborn error of metabolism.Figure 2 reminds us that there are at least 5,000 different enzymes, with as many metabolites in pathways that interconvert molecules in well-ordered sequences of reactions in an 'average' human cell. Figure 3 emphasizes that any one metabolite (denoted γ in this case) can modulate reactions from within its own pathway, across pathways, and even alters expression of genes and translation of messenger RNA into protein. An enzyme can also serve to modulate the activity of another enzyme, and affect its level of expression. Cations, including H+, and extraneous compounds such as xenobiotics (H in Figure 3), also exert effects on enzymes and metabolites that potentially affect fluxes through multiple pathways.A modern and emerging form of advanced diagnostic strategy in chemical pathology is metabolomics, also called metabonomics [2]. There is a semantic and operational difference between these 'omics'. The former is the study of an extensive collection of metabolites present in a cell or tissue under a parti
Verbal autopsy and global mortality statistics: if not now, then when?
Philip W Setel
Population Health Metrics , 2011, DOI: 10.1186/1478-7954-9-20
Abstract: In 2000, the state of knowledge on verbal autopsy (VA, a term that covers the design and application of postmortem caregiver interviews, procedures for assigning one or more probable causes of death, and the aggregation and tabulation of population-level mortality statistics based on this data source) centered on a small group of demographers and epidemiologists, many of whom ran intervention trials in various demographic surveillance sites. Almost the entire community of scholarship was on a first-name basis; we could easily gather in a medium-sized conference room, and any of our students or colleagues could become an expert on the VA literature with a week or two of focused reading. Throughout this period, those who remained dedicated to maximizing the potential of VA made steady progress. Yet throughout, a deep and sometimes reflexive scepticism remained that VA could ever really deliver the goods as a reliable measurement tool. The persistent shortcomings in cause of death data, and reluctance to widely embrace VA outside of demographic surveillance sites, have forced the global health community to make do with sources of limited coverage and dubious quality and consistency, applying increasingly complex statistical analyses to "correct" for all manner of bias and nonsampling error.The papers in this issue of Population Health Metrics go far in addressing central questions about how much VA can contribute to our measurement of health and health impact. How close to truth can VA ever get? How good is "good enough" for decision-making? Is our putative "gold standard" of medically certified deaths all that robust to begin with - in industrialized or lower-income countries? Can we make the production of VA data better, faster, and cheaper? What alternatives to demographic surveillance systems exist to permit the collection of mortality data from large, representative population samples? Can VA detect disease outbreaks, the population effects of antiretroviral thera
Resistance to malaria in humans: the impact of strong, recent selection
Hedrick Philip W
Malaria Journal , 2012, DOI: 10.1186/1475-2875-11-349
Abstract: Malaria is one of the leading causes of death worldwide and has been suggested as the most potent type of selection in humans in recent millennia. As a result, genes involved in malaria resistance are excellent examples of recent, strong selection. In 1949, Haldane initially suggested that infectious disease could be a strong selective force in human populations. Evidence for the strong selective effect of malaria resistance includes the high frequency of a number of detrimental genetic diseases caused by the pleiotropic effects of these malaria resistance variants, many of which are “loss of function” mutants. Evidence that this selection is recent comes from the genetic dating of the age of a number of these malaria resistant alleles to less than 5,000 years before the present, generally much more recent than other human genetic variants. An approach to estimate selection coefficients from contemporary case–control data is presented. In the situations described here, selection is much greater than 1%, significantly higher than generally observed for other human genetic variation. With these selection coefficients, predictions are generated about the joint change of alleles S and C at the β-globin locus, and for α-thalassaemia haplotypes and S, variants that are unlinked but exhibit epistasis. Population genetics can be used to determine the amount and pattern of selection in the past and predict selection in the future for other malaria resistance variants as they are discovered.
Diets of Cape clawless otters at two South African coastal localities
W. Emmerson,S. Philip
African Zoology , 2011,
Abstract: The diet of the Cape clawless otterAonyx capensis was investigated at the Dwessa Nature Reserve and Mkambati Nature Reserve on the Wild Coast, Eastern Cape Province, South Africa. Their diet was more varied at Mkambati (15 prey species) than Dwessa (7 species). In terms of percentage relative frequency of occurrence, the spiny lobster Panulirus homarus was found to be the most common prey item at both Mkambati (37.93%) and at Dwessa (35.21%), followed by fish (31.03% and 36.62%, respectively), crab (22.41% and 19.72%) and molluscs (3.11% and 4.23%). No significant differences were found in spraint dry masses between sites (15.10 g vs 17.95 g) or between masses of the diet categories for the two regions, but, when converted to ‘fresh’ mass, mean spraint mass was significantly lower at Mkambati than Dwessa (108.08 g and 135.73 g, respectively). When diet categories were compared using ANOVA, only fish were found to be significantly different when expressed as fresh mass. Spiny lobster mandibles collected from spraints were used to estimate otter prey size preferences by comparing with wild-caught lobster dimensions (ANCOVA, paired t -tests, correlation and regression). Otters
Physics of the Pseudogap II: Dynamics, Incompressibility, and Fermi Arcs as Motional Narrowing
Philip W Anderson
Physics , 2007,
Abstract: A further discussion of the vortex fluid in the cuprate high Tc superconductors is presented. The crucial property of incompressibility towards the addition of net vorticity, leading to the marked nonlinearity of the response functions, is justified from first principles. We also discuss the Fermi Arc phenomenon of Campuzano as a consequence of the time-fluctuating phase in the vortex fluid.
Bose Fluids Above Tc: Incompressible Vortex Fluids and "Supersolidity"
Philip W Anderson
Physics , 2007, DOI: 10.1103/PhysRevLett.100.215301
Abstract: This paper emphasizes that non-linear rotational or diamagnetic susceptibility is characteristic of Bose fluids above their superfluid Tcs, and for sufficiently slow rotation or weak B-fields amounts to an incompressible response to vorticity. The cause is a missing term in the conventionally accepted model Hamiltonian for quantized vortices in the Bose fluid. The resulting susceptibility can account for recent observations of Chan et al on solid He, and Ong et al on cuprate superconductors.
A Gross-Pitaevskii Treatment for Supersolid He
Philip W Anderson
Physics , 2008, DOI: 10.1126/science.1169456
Abstract: The observations of non-linear rotational susceptibility (NCRI) in samples of solid He below 1-200 mK temperatures are conjectured to be describable in terms of a rarified Gross-Pitaevskii superfluid of vacancies (or, more generally, incommensuracies) with a transition temperature of about 50 mK, whose density is locally enhanced by crystal imperfections. We argue that the observations can be much affected by this density enhancement. We argue also that it is likely that the ground state of every pure Bose solid is supersolid.
Present status of the theory of high Tc cuprates
Philip W anderson
Physics , 2005, DOI: 10.1063/1.2199427
Abstract: The Gutzwiller-projected mean field theory, also called Plain Vanilla or RMFT, is explained and its successes and possible extensions in describing the phenomenology of the cuprate superconductors are discussed. Throughout we emphasize that while this is a Hartree-Fock-BCS based theory, it embodies fundamental differences from conventional perturbative many-body theory which may be characterized by calling it a theory of the doped Mott insulator.
Simple Explanation of Fermi Arcs in Cuprate Pseudogaps: a Motional Narrowing Phenomenon
Philip W Anderson
Physics , 2008,
Abstract: ARPES measurements on underdoped cuprates above the superconducting transition temperature exhibit the unique phenomenon of Fermi arcs, gapless arcs of Fermi surface around the nodal points of the superconducting gap, which terminate before reaching the antinodes. We show that this phenomenon is easily explained (including its temperature dependence and observed hole-electron asymmetry) as the natural consequence of a time-fluctuating d-wave gap.
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