657 research outputs found
On the speed of convergence to stationarity of the Erlang loss system
We consider the Erlang loss system, characterized by servers, Poisson arrivals and exponential service times, and allow the arrival rate to be a function of We discuss representations and bounds for the rate of convergence to stationarity of the number of customers in the system, and display some bounds for the total variation distance between the time-dependent and stationary distributions. We also pay attention to time-dependent rates
Derivation of exact master equation with stochastic description: Dissipative harmonic oscillator
A systematic procedure for deriving the master equation of a dissipative
system is reported in the framework of stochastic description. For the
Caldeira-Leggett model of the harmonic-oscillator bath, a detailed and
elementary derivation of the bath-induced stochastic field is presented. The
dynamics of the system is thereby fully described by a stochastic differential
equation and the desired master equation would be acquired with statistical
averaging. It is shown that the existence of a closed-form master equation
depends on the specificity of the system as well as the feature of the
dissipation characterized by the spectral density function. For a dissipative
harmonic oscillator it is observed that the correlation between the stochastic
field due to the bath and the system can be decoupled and the master equation
naturally comes out. Such an equation possesses the Lindblad form in which time
dependent coefficients are determined by a set of integral equations. It is
proved that the obtained master equation is equivalent to the well-known
Hu-Paz-Zhang equation based on the path integral technique. The procedure is
also used to obtain the master equation of a dissipative harmonic oscillator in
time-dependent fields.Comment: 24page
Modeling and Analysis of Effective Ways for Improving the Reliability of Second-hand Products Sold with Warranty
Often, customers are uncertain about the performance and durability of the used/second-hand products. The warranties play an important role in reassuring the buyer. Offering the warranty implies that the dealer incurs additional costs to service any claims made by the customers. Reducing warranty costs is an issue of great interest to dealers. One way of improving the reliability and reducing the warranty servicing cost for second-hand items is through actions such as overhaul and upgrade which are carried out by the dealer or a third party. Improving actions allow the dealer to offer better warranty terms and to sell the item at a higher price. This paper deals with two effective approaches (virtual age approach and screening test approach) to decide on the reliability improvement strategies for second-hand products sold under various warranty policies (failure-free, rebate warranty, and a combination of free replacement and lump sum). A numerical example illustrates that from a dealer’s point of view, it is beneficial to carry out an improvement action only if the reduction in the warranty servicing cost is greater than the extra cost incurred due to this improvement action
Quadrupole Anisotropy in Dihadron Azimuthal Correlations in Central Au Collisions at =200 GeV
The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC)
reports measurements of azimuthal dihadron correlations near midrapidity in
Au collisions at =200 GeV. These measurements
complement recent analyses by experiments at the Large Hadron Collider (LHC)
involving central Pb collisions at =5.02 TeV, which
have indicated strong anisotropic long-range correlations in angular
distributions of hadron pairs. The origin of these anisotropies is currently
unknown. Various competing explanations include parton saturation and
hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies
in Au collisions compared to those seen in Pb collisions at the
LHC. The larger extracted values in Au collisions at RHIC are
consistent with expectations from hydrodynamic calculations owing to the larger
expected initial-state eccentricity compared with that from Pb
collisions. When both are divided by an estimate of the initial-state
eccentricity the scaled anisotropies follow a common trend with multiplicity
that may extend to heavy ion data at RHIC and the LHC, where the anisotropies
are widely thought to arise from hydrodynamic flow.Comment: 375 authors, 7 pages, 5 figures. Published in Phys. Rev. Lett. v2 has
minor changes to text and figures in response to PRL referee suggestions.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
J/psi suppression at forward rapidity in Au+Au collisions at sqrt(s_NN)=39 and 62.4 GeV
We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and
62.4 GeV Au+Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields
are presented as a function of both collision centrality and transverse
momentum. Nuclear modifications are obtained for central relative to peripheral
Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative
to scaled p+p cross sections obtained from other measurements (R_AA). The
observed suppression patterns at 39 and 62.4 GeV are quite similar to those
previously measured at 200 GeV. This similar suppression presents a challenge
to theoretical models that contain various competing mechanisms with different
energy dependencies, some of which cause suppression and others enhancement.Comment: 365 authors, 10 pages, 11 figures, 4 tables. Submitted to Phys. Rev.
C. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Cross section for production via dielectrons in dAu collisions at GeV
We report a measurement of pairs from semileptonic heavy-flavor
decays in Au collisions at GeV. Exploring the mass
and transverse-momentum dependence of the yield, the bottom decay contribution
can be isolated from charm, and quantified by comparison to {\sc pythia} and
{\sc mc@nlo} simulations. The resulting -production cross section is
~mb, which is equivalent to a nucleon-nucleon cross section of
b.Comment: 375 authors, 16 pages, 8 figures, 7 tables, 2008 data. Submitted to
Phys. Rev. C Plain text data tables for the points plotted in figures for
this and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Observation of direct-photon collective flow in sqrt(s_NN)=200 GeV Au+Au collisions
The second Fourier component v_2 of the azimuthal anisotropy with respect to
the reaction plane was measured for direct photons at midrapidity and
transverse momentum (p_T) of 1--13 GeV/c in Au+Au collisions at sqr(s_NN)=200
GeV. Previous measurements of this quantity for hadrons with p_T < 6 GeV/c
indicate that the medium behaves like a nearly perfect fluid, while for p_T > 6
GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence
for parton energy loss. In this measurement with the PHENIX detector at the
Relativistic Heavy Ion Collider we find that for p_T > 4 GeV/c the anisotropy
for direct photons is consistent with zero, as expected if the dominant source
of direct photons is initial hard scattering. However, in the p_T < 4 GeV/c
region dominated by thermal photons, we find a substantial direct photon v_2
comparable to that of hadrons, whereas model calculations for thermal photons
in this kinematic region significantly underpredict the observed v_2.Comment: 384 authors, 6 pages, 3 figures, and 1 table. Submitted to Phys. Rev.
Lett. v2 has minor changes to match the submission version. Plain text data
tables for the points plotted in the figures are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/info/data/ppg126_data.htm
Centrality categorization for R_{p(d)+A} in high-energy collisions
High-energy proton- and deuteron-nucleus collisions provide an excellent tool
for studying a wide array of physics effects, including modifications of parton
distribution functions in nuclei, gluon saturation, and color neutralization
and hadronization in a nuclear environment, among others. All of these effects
are expected to have a significant dependence on the size of the nuclear target
and the impact parameter of the collision, also known as the collision
centrality. In this article, we detail a method for determining centrality
classes in p(d)+A collisions via cuts on the multiplicity at backward rapidity
(i.e., the nucleus-going direction) and for determining systematic
uncertainties in this procedure. For d+Au collisions at sqrt(s_NN) = 200 GeV we
find that the connection to geometry is confirmed by measuring the fraction of
events in which a neutron from the deuteron does not interact with the nucleus.
As an application, we consider the nuclear modification factors R_{p(d)+A}, for
which there is a potential bias in the measured centrality dependent yields due
to auto-correlations between the process of interest and the backward rapidity
multiplicity. We determine the bias correction factor within this framework.
This method is further tested using the HIJING Monte Carlo generator. We find
that for d+Au collisions at sqrt(s_NN)=200 GeV, these bias corrections are
small and vary by less than 5% (10%) up to p_T = 10 (20) GeV. In contrast, for
p+Pb collisions at sqrt(s_NN) = 5.02 TeV we find these bias factors are an
order of magnitude larger and strongly p_T dependent, likely due to the larger
effect of multi-parton interactions.Comment: 375 authors, 18 pages, 16 figures, 4 tables. Submitted to Phys. Rev.
C. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
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