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Search Results: 1 - 10 of 400011 matches for " K. J. Sharkey "
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The flavour singlet mesons in QCD
UKQCD Collaboration,C. McNeile,C. Michael,K. J. Sharkey
Physics , 2001, DOI: 10.1103/PhysRevD.65.014508
Abstract: We study the flavour singlet mesons from first principles using lattice QCD. We explore the splitting between flavour singlet and non-singlet for vector and axial mesons as well as the more commonly studied cases of the scalar and pseudoscalar mesons.
Is the up-quark massless?
UKQCD Collaboration,A. C. Irving,C. McNeile,C. Michael,K. J. Sharkey,H. Wittig
Physics , 2001, DOI: 10.1016/S0370-2693(01)01062-0
Abstract: We report on determinations of the low-energy constants alpha5 and alpha8 in the effective chiral Lagrangian at O(p^4), using lattice simulations with N_f=2 flavours of dynamical quarks. Precise knowledge of these constants is required to test the hypothesis whether or not the up-quark is massless. Our results are obtained by studying the quark mass dependence of suitably defined ratios of pseudoscalar meson masses and matrix elements. Although comparisons with an earlier study in the quenched approximation reveal small qualitative differences in the quark mass behaviour, numerical estimates for alpha5 and alpha8 show only a weak dependence on the number of dynamical quark flavours. Our results disfavour the possibility of a massless up-quark, provided that the quark mass dependence in the physical three-flavour case is not fundamentally different from the two-flavour case studied here.
The Influence of Therapeutic Radiation on the Patterns of Bone Marrow in Ovary-Intact and Ovariectomized Mice
Susanta K. Hui, Leslie Sharkey, Louis S. Kidder, Yan Zhang, Greg Fairchild, Kayti Coghill, Cory J. Xian, Douglas Yee
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0042668
Abstract: Background The functional components of bone marrow (i.e., the hematopoietic and stromal populations) and the adjacent bone have traditionally been evaluated incompletely as distinct entities rather than the integrated system. We perturbed this system in vivo using a medically relevant radiation model in the presence or absence of ovarian function to understand integrated tissue interaction. Methodology/Principal Findings Ovary-intact and ovariectomized mice underwent either no radiation or single fractional 16 Gy radiation to the caudal skeleton (I±R, OVX±R). Marrow fat, hematopoietic cellularity, and cancellous bone volume fraction (BV/TV %) were assessed. Ovariectomy alone did not significantly reduce marrow cellularity in non-irradiated mice (OVX?R vs. I?R, p = 0.8445) after 30 days; however it impaired the hematopoietic recovery of marrow following radiation exposure (OVX+R vs. I+R, p = 0.0092). The combination of radiation and OVX dramatically increases marrow fat compared to either factor alone (p = 0.0062). The synergistic effect was also apparent in the reduction of hematopoietic marrow cellularity (p = 0.0661); however it was absent in BV/TV% changes (p = 0.2520). The expected inverse relationship between marrow adiposity vs. hematopoietic cellularity and bone volume was observed. Interestingly compared with OVX mice, intact mice demonstrated double the reduction in hematopoietic cellularity and a tenfold greater degree of bone loss for a given unit of expansion in marrow fat. Conclusions/Significance Ovariectomy prior to delivery of a clinically-relevant focal radiation exposure in mice, exacerbated post-radiation adipose accumulation in the marrow space but blunted bone loss and hematopoietic suppression. In the normally coupled homeostatic relationship between the bone and marrow domains, OVX appears to alter feedback mechanisms. Confirmation of this non-linear phenomenon (presumably due to differential radiosensitivity) and demonstration of the mechanism of action is needed to provide strategies to diminish the effect of radiation on exposed tissues.
Lattice calculation of $1/p^2$ corrections to $α_s$ and of $Λ_{\rm {QCD}}$ in the $\widetilde{MOM}$ scheme
Ph. Boucaud,G. Burgio,F. Di Renzo,J. P. Leroy,J. Micheli,C. Parrinello,O. Pène,C. Pittori,J. Rodríguez-Quintero,C. Roiesnel,K. Sharkey
Physics , 2000, DOI: 10.1088/1126-6708/2000/04/006
Abstract: We report on very strong evidence of the occurrence of power terms in $\as(p)$, the QCD running coupling constant in the $\widetilde{MOM}$ scheme, by analyzing non-perturbative measurements from the lattice three-gluon vertex between 2.0 and 10.0 GeV at zero flavor. While putting forward the caveat that this definition of the coupling is a gauge dependent one, the general relevance of such an occurrence is discussed. We fit $\Lambda_{\bar{\rm MS}}^{(n_f=0)}= 237 \pm 3 ^{+ 0}_{-10}$ MeV in perfect agreement with the result obtained by the ALPHA group with a totally different method. The power correction to $\as(p)$ is fitted to $(0.63\pm 0.03 ^{+ 0.0}_{- 0.13}) {\rm GeV}^2/p^2$.
Three agonist antibodies in combination with high-dose IL-2 eradicate orthotopic kidney cancer in mice
Jennifer A Westwood, Phillip K Darcy, Preethi Guru, Janelle Sharkey, Hollie J Pegram, Sally M Amos, Mark J Smyth, Michael H Kershaw
Journal of Translational Medicine , 2010, DOI: 10.1186/1479-5876-8-42
Abstract: To determine the relative response of orthotopic tumors, we inoculated Renca into the kidney followed by treatment with Tri-mAb.We found that orthotopic tumors responded much less to treatment (~13% survival), but a significant improvement in survival was achieved through the addition of IL-2 to the treatment regimen (55% survival). All three agonist antibodies and high dose IL-2, 100,000 IU for up to six doses, were required. CD8+ T cells were also required for optimal anti-tumor responses. Coadministration of IL-2 led to enhanced T cell activity as demonstrated by an increased frequency of IFN-gamma-producing T cells in tumor-draining lymph nodes, which may have contributed to the observed improvement of therapy against kidney tumors.Responses of subcutaneous tumors to immunotherapy do not necessarily reflect how orthotopic tumors respond. The use of combination immunotherapy stimulating multiple facets of immunity and including cytokine support for T cells can induce effective anti-tumor responses against orthotopic and metastatic tumors.Immunotherapies involving combinations of various immunomodulating agents are demonstrating considerable promise for the treatment of cancer. In particular, the use of agents that together stimulate multiple immune components can mediate regression of established tumors. Important steps to achieve robust anti-tumor immunity include tumor antigen release, optimal antigen presentation to specific T cells and costimulation of T cells resulting in optimal activation and expansion of tumor-specific T cells.Monoclonal antibodies (mAb) targeting death receptors expressed on a range of transformed cells [1] can mediate apoptosis of a proportion of tumor cells leading to induction of tumor-specific T cells and inhibition of tumor growth in preclinical mouse models[2]. An agonistic antibody targeting CD40 expressed on antigen presenting cells has been demonstrated to lead to activation of APCs and the generation of CTL and eradication of l
Local Barriers and Solutions to Improve Care-Seeking for Childhood Pneumonia, Diarrhoea and Malaria in Kenya, Nigeria and Niger: A Qualitative Study
K. Juliet A. Bedford, Alyssa B. Sharkey
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0100038
Abstract: We present qualitative research findings on care-seeking and treatment uptake for pneumonia, diarrhoea and malaria among children under 5 in Kenya, Nigeria and Niger. The study aimed to determine the barriers caregivers face in accessing treatment for these conditions; to identify local solutions that facilitate more timely access to treatment; and to present these findings as a platform from which to develop context-specific strategies to improve care-seeking for childhood illness. Kenya, Nigeria and Niger are three high burden countries with low rates of related treatment coverage, particularly in underserved areas. Data were collected in Homa Bay County in Nyanza Province, Kenya; in Kebbi and Cross River States, Nigeria; and in the Maradi and Tillabéri regions of Niger. Primary caregivers of children under 5 who did not regularly engage with health services or present their child at a health facility during illness episodes were purposively selected for interview. Data underwent rigorous thematic analysis. We organise the identified barriers and related solutions by theme: financial barriers; distance/location of health facilities; socio-cultural barriers and gender dynamics; knowledge and information barriers; and health facility deterrents. The relative importance of each differed by locality. Participant suggested solutions ranged from community-level actions to facility-level and more policy-oriented actions, plus actions to change underlying problems such as social perceptions and practices and gender dynamics. We discuss the feasibility and implications of these suggested solutions. Given the high burden of childhood morbidity and mortality due to pneumonia, diarrhoea and malaria in Kenya, Nigeria and Niger, this study provides important insights relating to demand-side barriers and locally proposed solutions. Significant advancements are possible when communities participate in both problem identification and resolution, and are engaged as important partners in improving child health and survival.
An Exact Relationship Between Invasion Probability and Endemic Prevalence for Markovian SIS Dynamics on Networks
Robert R. Wilkinson, Kieran J. Sharkey
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0069028
Abstract: Understanding models which represent the invasion of network-based systems by infectious agents can give important insights into many real-world situations, including the prevention and control of infectious diseases and computer viruses. Here we consider Markovian susceptible-infectious-susceptible (SIS) dynamics on finite strongly connected networks, applicable to several sexually transmitted diseases and computer viruses. In this context, a theoretical definition of endemic prevalence is easily obtained via the quasi-stationary distribution (QSD). By representing the model as a percolation process and utilising the property of duality, we also provide a theoretical definition of invasion probability. We then show that, for undirected networks, the probability of invasion from any given individual is equal to the (probabilistic) endemic prevalence, following successful invasion, at the individual (we also provide a relationship for the directed case). The total (fractional) endemic prevalence in the population is thus equal to the average invasion probability (across all individuals). Consequently, for such systems, the regions or individuals already supporting a high level of infection are likely to be the source of a successful invasion by another infectious agent. This could be used to inform targeted interventions when there is a threat from an emerging infectious disease.
Complete hierarchies of SIR models on arbitrary networks with exact and approximate moment closure
Kieran J Sharkey,Robert R Wilkinson
Quantitative Biology , 2015, DOI: 10.1016/j.mbs.2015.03.008
Abstract: We first generalise ideas discussed by Kiss et al. (2015) to prove a theorem for generating exact closures (here expressing joint probabilities in terms of their constituent marginal probabilities) for susceptible-infectious-removed (SIR) dynamics on arbitrary graphs (networks). For Poisson transmission and removal processes, this enables us to obtain a systematic reduction in the number of differential equations needed for an exact `moment closure' representation of the underlying stochastic model. We define `transmission blocks' as a possible extension of the block concept in graph theory and show that the order at which the exact moment closure representation is curtailed is the size of the largest transmission block. More generally, approximate closures of the hierarchy of moment equations for these dynamics are typically defined for the first and second order yielding mean-field and pairwise models respectively. It is frequently implied that, in principle, closed models can be written down at arbitrary order if only we had the time and patience to do this. However, for epidemic dynamics on networks, these higher-order models have not been defined explicitly. Here we unambiguously define hierarchies of approximate closed models that can utilise subsystem states of any order, and show how well-known models are special cases of these hierarchies.
Message passing and moment closure for susceptible-infected-recovered epidemics on finite networks
Robert R. Wilkinson,Kieran J. Sharkey
Quantitative Biology , 2013, DOI: 10.1103/PhysRevE.89.022808
Abstract: The message passing approach of Karrer and Newman [Phys. Rev. E 82, 016101 (2010)] is an exact and practicable representation of susceptible-infected-recovered dynamics on finite trees. Here we show that, assuming Poisson contact processes, a pair-based moment closure representation [Sharkey, J. Math. Biol. 57, 311 (2008)] can be derived from their equations. We extend the applicability of both representations and discuss their relative merits. On arbitrary time-independent networks, as was shown for the message passing formalism, the pair-based moment closure equations also provide a rigorous lower bound on the expected number of susceptibles at all times.
Effects of non-perturbatively improved dynamical fermions in QCD at fixed lattice spacing
UKQCD Collaboration,C. R. Allton,S. P. Booth,K. C. Bowler,J. Garden,A. Hart,D. Hepburn,A. C. Irving,B. Joo,R. D. Kenway,C. M. Maynard,C. McNeile,C. Michael,S. M. Pickles,J. C. Sexton,K. J. Sharkey,Z. Sroczynski,M. Talevi,M. Teper,H. Wittig
Physics , 2001, DOI: 10.1103/PhysRevD.65.054502
Abstract: We present results for the static inter-quark potential, lightest glueballs, light hadron spectrum and topological susceptibility using a non-perturbatively improved action on a $16^3\times 32$ lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units ($\sim 1.7$ fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavours of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied ($M_{PS}/M_{V}\ge0.58$). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities.
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