433 research outputs found
Hybrid Monte Carlo Without Pseudofermions
We introduce a dynamical fermion algorithm which is based on the hybrid Monte
Carlo (HMC) algorithm, but without pseudofermions. The molecular dynamics steps
in HMC are retained except the derivatives with respect to the gauge fields are
calculated with the noise. The determinant ratios are estimated with the
Pa\`{d}e - method. Finally, we use the Kennedy-Kuti linear accept/reject
method for the Monte Carlo step which is shown to respect detailed balance. We
comment on the comparison of this algorithm with the pseudofermion algorithm.Comment: 4 pages, Latex, 3 ps figures. Talk presente at Lattice '9
A Noisy Monte Carlo Algorithm
We propose a Monte Carlo algorithm to promote Kennedy and Kuti's linear
accept/reject algorithm which accommodates unbiased stochastic estimates of the
probability to an exact one. This is achieved by adopting the Metropolis
accept/reject steps for both the dynamical and noise configurations. We test it
on the five state model and obtain desirable results even for the case with
large noise. We also discuss its application to lattice QCD with stochastically
estimated fermion determinants.Comment: 10 pages, 1 tabl
Finite Density Algorithm in Lattice QCD -- a Canonical Ensemble Approach
I will review the finite density algorithm for lattice QCD based on finite
chemical potential and summarize the associated difficulties. I will propose a
canonical ensemble approach which projects out the finite baryon number sector
from the fermion determinant. For this algorithm to work, it requires an
efficient method for calculating the fermion determinant and a Monte Carlo
algorithm which accommodates unbiased estimate of the probability. I shall
report on the progress made along this direction with the Pad\'{e} - Z
estimator of the determinant and its implementation in the newly developed
Noisy Monte Carlo algorithm.Comment: Invited talk at Nankai Symposium on Mathematical Physics, Tianjin,
Oct. 2001, 18 pages, 3 figures; expanded and references adde
Renovascular adaptive changes in chronic hypoxic polycythemia
Renovascular adaptive changes in chronic hypoxic polycythemia.BackgroundChronic hypoxia in rats produces polycythemia, and the plasma fraction falls, reducing renal plasma flow (RPF) relative to renal blood flow (RBF). Polycythemia also causes increased blood viscosity, which tends to reduce RBF and renal oxygen delivery. We studied how renal regulation of electrolyte balance and renal tissue oxygenation (which is crucial for erythropoietin regulation) are maintained in rats during hypoxic exposure.MethodsRats of two strains with differing polycythemic responses, with surgically implanted catheters in the urinary bladder, femoral artery, and left renal and right external jugular veins, were exposed to a simulated high altitude (0.5 atm) for 0, 1, 3, 14, and 30days, after which RPF (para-aminohippurate clearance), glomerular filtration rate (GFR, polyfructosan clearance), hematocrit and blood gases were measured, and RBF, renal vascular resistance and hindrance (resistance/viscosity), renal oxygen delivery, and renal oxygen consumption were calculated.ResultsDuring chronic hypoxia RBF increased, but RPF decreased because of the polycythemia. GFR remained normal because the filtration fraction (FF) increased. Renal vascular resistance decreased, and renal vascular hindrance decreased more markedly. Renal oxygen delivery and consumption both increased.ConclusionsDuring chronic hypoxia GFR homeostasis apparently took precedence over RBF autoregulation. The large decrease in renal vascular hindrance suggested that renal vascular remodeling contributes to GFR regulation. The reduced hindrance also prevented a vicious cycle of increasing polycythemia and blood viscosity, decreasing RBF, and increasing renal hypoxia and erythropoietin release
Recent atmospheric neutrino results from Soudan 2
An updated measurement of the atmospheric nu_mu/nu_e ratio-of-ratios,
0.68+-0.11+-0.06, has been obtained using a 4.6-kty exposure of the Soudan-2
iron tracking calorimeter. The L/E distributions have been analyzed for effects
of nu_mu -> nu_x oscillations, and an allowed region in the Delta m^2 vs. sin^2
2 theta plane has been determined.Comment: 3 pages, 4 figures; presented at TAUP99, the 6th Int. Workshop on
Topics in Astroparticle and Underground Physics, Sept. 6-10, 1999, College de
France, Paris, Franc
Analysis of Control Measures for Vector-borne Diseases Using a Multistage Vector Model with Multi-Host Sub-populations
We propose and analyze an epidemiological model for vector borne diseases
that integrates a multi-stage vector population and several host
sub-populations which may be characterized by a variety of compartmental model
types: subpopulations all include Susceptible and Infected compartments, but
may or may not include Exposed and/or Recovered compartments. The model was
originally designed to evaluate the effectiveness of various prophylactic
measures in malaria-endemic areas, but can be applied as well to other
vector-borne diseases. This model is expressed as a system of several
differential equations, where the number of equations depends on the particular
assumptions of the model. We compute the basic reproduction number , and show that if , the disease free equilibrium
(DFE) is globally asymptotically stable (GAS) on the nonnegative orthant. If
, the system admits a unique endemic equilibrium (EE) that is
GAS. We analyze the sensitivity of and the EE to different system
parameters, and based on this analysis we discuss the relative effectiveness of
different control measures.Comment: 42 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1808.0757
Численное моделирование данных высокочастотного индукционного каротажа в процессе бурения наклонно-горизонтальных скважин
Mixing of scalar glueballs and flavour-singlet scalar mesons
We discuss in detail the extraction of hadronic mixing strengths from lattice
studies. We apply this to the mixing of a scalar glueball and a scalar meson in
the quenched approximation. We also measure correlations appropriate for
flavour-singlet scalar mesons using dynamical quark configurations from UKQCD.
This enables us to compare the results from the quenched study of the mixing
with the direct determination of the mixed spectrum. Improved methods of
evaluating the disconnected quark diagrams are also presented.Comment: 23 pages, 5 postscript figure
Speeding up finite step-size updating of full QCD on the lattice
We propose various improvements of finite step-size updating for full QCD on
the lattice that might turn finite step-size updating into a viable alternative
to the hybrid Monte Carlo algorithm. These improvements are noise reduction of
the noisy estimator of the fermion determinant, unbiased inclusion of the
hopping parameter expansion and a multi-level Metropolis scheme. First
numerical tests are performed for the 2 dimensional Schwinger model with two
flavours of Wilson fermions and for QCD two flavours of Wilson fermions and
Schr"odinger functional boundary conditions.Comment: 22 pages, 1 figur
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