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Search Results: 1 - 10 of 32733 matches for " Derek Thomas "
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Successive coefficients of convex functions
Derek Thomas
Mathematics , 2015,
Abstract: It is shown that for $f$ analytic and convex in $z\in D=\{z:|z|<1\}$ and given by $f(z)=z+\sum_{n=2}^{\infty}a_{n}z^{n}$, the difference of coefficients $||a_{3}|-|a_{2}||\le 25/48$ and $||a_{4}|-|a_{3}||\le 25/48$ . Both inequalities are sharp.
Nearly Perfect Fluidity: From Cold Atomic Gases to Hot Quark Gluon Plasmas
Thomas Schaefer,Derek Teaney
Physics , 2009, DOI: 10.1088/0034-4885/72/12/126001
Abstract: Shear viscosity is a measure of the amount of dissipation in a simple fluid. In kinetic theory shear viscosity is related to the rate of momentum transport by quasi-particles, and the uncertainty relation suggests that the ratio of shear viscosity eta to entropy density s in units of hbar/k_B is bounded by a constant. Here, hbar is Planck's constant and k_B is Boltzmann's constant. A specific bound has been proposed on the basis of string theory where, for a large class of theories, one can show that eta/s is greater or equal to hbar/(4 pi k_B). We will refer to a fluid that saturates the string theory bound as a perfect fluid. In this review we summarize theoretical and experimental information on the properties of the three main classes of quantum fluids that are known to have values of eta/s that are smaller than hbar/k_B. These fluids are strongly coupled Bose fluids, in particular liquid helium, strongly correlated ultracold Fermi gases, and the quark gluon plasma. We discuss the main theoretical approaches to transport properties of these fluids: kinetic theory, numerical simulations based on linear response theory, and holographic dualities. We also summarize the experimental situation, in particular with regard to the observation of hydrodynamic behavior in ultracold Fermi gases and the quark gluon plasma.
Unquenching the Rho Meson
Derek B. Leinweber,Thomas D. Cohen
Physics , 1993, DOI: 10.1103/PhysRevD.49.3512
Abstract: Two-pion induced self-energy contributions to the $\rho$-meson mass are examined in relation to the quenched approximation of QCD, where the physics associated with two-pion intermediate states has been excluded from vector-isovector correlation functions. Corrections to quenched QCD calculations of the $\rho$-meson mass are estimated to be small at the order of a few percent of the $\rho$-meson mass. The two-pion contributions display nonanalytic behavior as a function of the pion mass as the two-pion cut is encountered. The implications of this nonanalytic behavior in extrapolations of full QCD calculations are also discussed. We note that for full QCD, the error made in making a linear extrapolation of the $\rho$ mass, neglecting nonanalytic behavior, increases as one approaches the two-pion cut.
Chiral Corrections to Lattice Calculations of Charge Radii
Derek B. Leinweber,Thomas D. Cohen
Physics , 1992, DOI: 10.1103/PhysRevD.47.2147
Abstract: Logarithmic divergences in pion and proton charge radii associated with chiral loops are investigated to assess systematic uncertainties in current lattice determinations of charge radii. The chiral corrections offer a possible solution to the long standing problem of why present lattice calculations yield proton and pion radii which are similar in size.
The Pion Cloud in Quenched QCD
Thomas D. Cohen,Derek B. Leinweber
Physics , 1992,
Abstract: Diagrammatic methods and Large $N_c$ QCD are used to argue that the nucleon as calculated in quenched QCD contains physics which can be ascribed to the pion cloud of the nucleon. In particular, it is argued that the physics corresponding to one-pion loops in chiral perturbation theory are included in the quenched approximation.
A Lattice QCD Analysis of the Strangeness Magnetic Moment of the Nucleon
Derek B. Leinweber,Anthony W. Thomas
Physics , 1999, DOI: 10.1103/PhysRevD.62.074505
Abstract: The outcome of the SAMPLE Experiment suggests that the strange-quark contribution to the nucleon magnetic moment, G_M^s(0), may be greater than zero. This result is very difficult to reconcile with expectations based on the successful baryon magnetic-moment phenomenology of the constituent quark model. We show that careful consideration of chiral symmetry reveals some rather unexpected properties of QCD. In particular, it is found that the valence u-quark contribution to the magnetic moment of the neutron can differ by more than 50% from its contribution to the Xi^0 magnetic moment. This hitherto unforeseen result leads to the value G_M^s(0) = -0.16 +/- 0.18 with a systematic error, arising from the relatively large strange quark mass used in existing lattice calculations, that would tend to shift G_M^s(0) towards small positive values.
Seroprevalence of Bovine Parainfluenza Virus Type 3 (bPI-3V) in Ruminants from Grenada  [PDF]
Keshaw Tiwari, Christine Cornish, Brittany Gamble, Derek Thomas, Ravindra Nath Sharma
Open Journal of Veterinary Medicine (OJVM) , 2016, DOI: 10.4236/ojvm.2016.62004
Abstract: Respiratory viral infections are known for serious economic losses in ruminants. Bovine parain-fluenza 3 virus (bPI-3V) a member of Respirovirus genus in association with other respiratory viruses causes respiratory disease complex in ruminants. The aim of this study was to estimate the seroprevalence of bPI-3V in non vaccinated cattle, sheep and goats from Grenada. Sera were collected randomly from 60 sheep, 60 goats and 60 cattle from all six parishes of Grenada. Sera were tested for antibodies to bPI-3V using an indirect Enzyme Linked Immunosorbant Assay (ELISA) kit. Antibodies to bPI-3V were detected in 13.4% (Confidence Level (CL): 95%; Confidence Interval (CI): 4.76% to 22.02%) in cattle; 16.7% (CL: 95%; CI: 7.26% to 26.14%) in sheep and 11.7% (CL: 95%; CI: 3.57% to 19.83%) in goats. There was statistically no significant difference in prevalence (p > 0.05) of antibodies to bPI-3V in cattle, sheep and goats in Grenada. This is the first report on seroprevalence of bPI-3V in ruminants in Grenada, West Indies.
Seroprevalence of Bluetongue Virus Antibody in Ruminants from Grenada  [PDF]
Ravindra Nath Sharma, Sureni Beckford, Keshaw Tiwari, Elodie Vinet, Derek Thomas, Claude de Allie, Alfred Chikweto
Open Journal of Veterinary Medicine (OJVM) , 2016, DOI: 10.4236/ojvm.2016.66013
Abstract: The aim of the present study was to estimate the seroprevalence of antibodies to bluetongue virus (BTV) among domestic ruminants of Grenada. Sera samples from cattle (133), goat (314) and sheep (481) were tested using competitive Enzyme-linked immunosorbent assay (c-ELISA). Of the total of 928 samples tested, the overall BTV seroprevalence was 78.4% (95% confidence interval (CI ± 2.65). The seropositivity of ovine, caprine and bovine was found to be 71.7% (95% CI, 67.67% to 75.73%), 80.2% (95% CI, 75.79% to 84.61%) and 98.5% (95% CI, 96.43% to 100.57%), respectively. There was statistical significance in the seroprevalence of BTV among bovine, caprine and ovine (p < 0.05). It is evident from this study that blue tongue virus is endemic in Grenada.
Circling the Blood in the Water: The Difficulties in Endangered Species Protections for the Great White Shark  [PDF]
Derek Julio
Natural Resources (NR) , 2014, DOI: 10.4236/nr.2014.511058
The purpose of legislation like the Endangered Species Act is to provide a means to conserve the ecosystems of endangered and threatened species, but not all species that may appear to need conservation are granted protection. An estimated 100 million sharks are killed each year largely due to exploitation, yet few shark species are ever granted protection under state or federal endangered species acts. The Northeastern Pacific population of the Great White Shark is no exception. Despite the numerous threats facing the white shark, NOAA denied a petition to list it as an endangered or threatened species under the federal Endangered Species Act. In light of the pending California decision to list the white shark under its state endangered species act, this paper considers whether or not such extreme protections are necessary. This paper first discusses the threats facing the white shark, the listing processes of both the federal and the California endangered species acts, and NOAA’s 12-month negative finding. Finally, this paper concludes that endangered species protections are not warranted in the case of the Northeastern Pacific white shark because of prior government intervention and conservation efforts already in place.
Pre-Exposure to Moving Form Enhances Static Form Sensitivity
Thomas S. A. Wallis,Mark A. Williams,Derek H. Arnold
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0008324
Abstract: Motion-defined form can seem to persist briefly after motion ceases, before seeming to gradually disappear into the background. Here we investigate if this subjective persistence reflects a signal capable of improving objective measures of sensitivity to static form.
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