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Search Results: 1 - 10 of 53967 matches for " David Richards "
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Nucleon Structure from Lattice QCD
David Richards
Physics , 2007, DOI: 10.1007/978-3-540-85144-8_8
Abstract: Recent advances in lattice field theory, in computer technology and in chiral perturbation theory have enabled lattice QCD to emerge as a powerful quantitative tool in understanding hadron structure. I describe recent progress in the computation of the nucleon form factors and moments of parton distribution functions, before proceeding to describe lattice studies of the Generalized Parton Distributions (GPDs). In particular, I show how lattice studies of GPDs contribute to building a three-dimensional picture of the proton. I conclude by describing the prospects for studying the structure of resonances from lattice QCD.
Calculation of f_B and the ``Isgur-Wise Function'' using a non-perturbatively improved fermion action
UKQCD Collaboration,David Richards
Physics , 1998, DOI: 10.1016/S0920-5632(99)85080-4
Abstract: We present a calculation of f_B and of the form factors for the semi-leptonic decay B -> D l nu in the quenched approximation to QCD. Results are generated on lattices at beta = 6.2, using an O(a)-improved fermion action, with the clover coefficient determined non-perturbatively.
Spatial Regulation of Exocytic Site and Vesicle Mobilization by the Actin Cytoskeleton
Jie Wang, David A. Richards
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0029162
Abstract: Numerous studies indicate a role for the actin cytoskeleton in secretion. Here, we have used evanescent wave and widefield fluorescence microscopy to study the involvement of the actin cytoskeleton in secretion from PC12 cells. Secretion was assayed as loss of ANF-EmGFP in widefield mode. Under control conditions, depolarization induced secretion showed two phases: an initial rapid rate of loss of vesicular cargo (tau = 1.4 s), followed by a slower, sustained drop in fluorescence (tau = 34.1 s). Pretreatment with Latrunculin A changed the kinetics to a single exponential, slightly faster than the fast component of control cells (1.2 s). Evanescent wave microscopy allowed us to examine this at the level of individual events, and revealed equivalent changes in the rates of vesicular arrival at the plasma membrane immediately following and during the sustained phase of release. Co-transfection of mCherry labeled β-actin and ANF-EmGFP demonstrated that sites of exocytosis had an inverse relationship with sites of actin enrichment. Disruption of visualized actin at the membrane resulted in the loss of specificity of exocytic site.
Normal Total WBC and Operative Delay in Appendicitis
Guss, David A,Richards, Christopher
Western Journal of Emergency Medicine : Integrating Emergency Care with Population Health , 2000,
Mass splittings and matrix elements of mesons and baryons containing a single heavy quark
UKQCD Collaboration,presented by David Richards
Physics , 1995, DOI: 10.1016/0920-5632(96)00098-9
Abstract: We present a study in the quenched approximation of the $B$ parameter $B_B$ and the decay constant $f_B$ using heavy-quark propagators implemented in the static approximation, and light-quark propagators computed using an $O(a)$-improved fermion action. We find a value of $\Bbstat$ close unity, and discuss the systematic errors entering into the calculation. $\fbstat$ is extracted using a variational fitting technique in order to obtain a reliable estimate of the ground state. In the second part of the talk, we describe an exploratory study of baryons containing a single heavy quark, computed using the $O(a)$-improved fermion action. We obtain masses generally in good agreement with experiment in both the charm and beauty sectors. We also report preliminary results for the form factor $G_1$ in the semi-leptonic $\Lambda_b \rightarrow \Lambda_c$ transition.
Charmed Meson Spectroscopy and Matrix Elements with an O(a)-Improved Clover Fermion Action
UKQCD Collaboration,presented by David Richards
Physics , 1992,
Abstract: We present preliminary results for the spectrum and decay matrix elements for heavy-light and heavy-heavy mesons, obtained on the 64-node Meiko Computing Surface at the University of Edinburgh. Quark propagators are computed with an O(a)-improved fermion action on 24^3x48 lattices at beta = 6.2, using three values of the quark mass up to around the strange quark mass, and four values of the quark mass in the region of the charm quark mass. We compare results for the hyperfine splitting in charmonium with those obtained using the conventional Wilson fermion action and find that the splitting is 1.83(15) times larger with the improved action. Our measurements of f_B indicate non-scaling corrections of the order of 20% to the Heavy Quark Effective Theory expectation. A comparison is made with results obtained on 16^3x48 lattices at beta = 6.0.
A Mathematical Modelling Approach for Systems Where the Servers Are Almost Always Busy
Christina Pagel,David A. Richards,Martin Utley
Computational and Mathematical Methods in Medicine , 2012, DOI: 10.1155/2012/290360
Abstract: The design and implementation of new configurations of mental health services to meet local needs is a challenging problem. In the UK, services for common mental health disorders such as anxiety and depression are an example of a system running near or at capacity, in that it is extremely rare for the queue size for any given mode of treatment to fall to zero. In this paper we describe a mathematical model that can be applied in such circumstances. The model provides a simple way of estimating the mean and variance of the number of patients that would be treated within a given period of time given a particular configuration of services as defined by the number of appointments allocated to different modes of treatment and the referral patterns to and between different modes of treatment. The model has been used by service planners to explore the impact of different options on throughput, clinical outcomes, queue sizes, and waiting times. We also discuss the potential for using the model in conjunction with optimisation techniques to inform service design and its applicability to other contexts.
Decay constants of the pion and its excitations on the lattice
Ekaterina V. Mastropas,David G. Richards
Physics , 2014, DOI: 10.1103/PhysRevD.90.014511
Abstract: We present a calculation using lattice QCD of the ratios of decay constants of the excited states of the pion, to that of the pion ground state, at three values of the pion mass between 400 and 700 MeV, using an anisotropic clover fermion action with three flavors of quarks. We find that the decay constant of the first excitation, and more notably of the second, is suppressed with respect to that of the ground-state pion, but that the suppression shows little dependence on the quark mass. The strong suppression of the decay constant of the second excited state is consistent with its interpretation as a predominantly hybrid state.
Lattice study of the leptonic decay constant of the pion and its excitations
Ekaterina V. Mastropas,David G. Richards
Physics , 2013,
Abstract: We present a calculation of the decay constant of the pion, and its lowest-lying three excitations, at three values of the pion mass between around 400 and 700 MeV, using anisotropic clover lattices. We use the variational method to determine an optimal interpolating operator for each of the states. We find that the decay constant of the first excitation, and more notably of the second, is suppressed with respect to that of the ground-state pion, but that the suppression shows little dependence on the quark mass.
Radiative Transitions in Charmonium
Jozef Dudek,Robert Edwards,David Richards
Physics , 2005,
Abstract: The form factors for the radiative transitions between charmonium mesons are investigated. We employ an anisotropic lattice using a Wilson gauge action, and domain-wall fermion action. We extrapolate the form factors to $Q^2 = 0$, corresponding to a real photon, using quark-model-inspired functions. Finally, comparison is made with photocouplings extracted from the measured radiative widths, where known. Our preliminary results find photocouplings commensurate with these experimentally extracted values.
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