94,733 research outputs found
Expectations for the Difference Between Local and Global Measurements of the Hubble Constant
There are irreducible differences between the Hubble constant measured
locally and the global value. They are due to density perturbations and finite
sample volume (cosmic variance) and finite number of objects in the sample
(sampling variance). We quantify these differences for a suite of
COBE-normalized CDM models that are consistent with the observed large-scale
structure. For small samples of objects that only extend out to 10,000 km/sec,
the variance can approach 4%. For the largest samples of Type Ia supernovae
(SNeIa), which include about 40 objects and extend out to almost 40,000 km/sec,
the variance is 1-2% and is dominated by sampling variance. Sampling and cosmic
variance may be an important consideration in comparing local determinations of
the Hubble constant with precision determinations of the global value that will
be made from high-resolution maps of CBR anisotropy.Comment: 10 pages, Latex, 2 figures, version accepted for Ap.
Implementation of a single femtosecond optical frequency comb for rovibrational cooling
We show that a single femtosecond optical frequency comb may be used to
induce two-photon transitions between molecular vibrational levels to form
ultracold molecules, e.g., KRb. The phase across an individual pulse in the
pulse train is sinusoidally modulated with a carefully chosen modulation
amplitude and frequency. Piecewise adiabatic population transfer is fulfilled
to the final state by each pulse in the applied pulse train providing a
controlled population accumulation in the final state. Detuning the pulse train
carrier and modulation frequency from one-photon resonances changes the time
scale of molecular dynamics but leads to the same complete population transfer
to the ultracold state. A standard optical frequency comb with no modulation is
shown to induce similar dynamics leading to rovibrational cooling.Comment: 14 pages, 7 figure
Charge Transfer Fluctuations as a QGP Signal
In this study, we analyze the recently proposed charge transfer fluctuations
within a finite pseudo-rapidity space. As the charge transfer fluctuation is a
measure of the local charge correlation length, it is capable of detecting
inhomogeneity in the hot and dense matter created by heavy ion collisions. We
predict that going from peripheral to central collisions, the charge transfer
fluctuations at midrapidity should decrease substantially while the charge
transfer fluctuations at the edges of the observation window should decrease by
a small amount. These are consequences of having a strongly inhomogeneous
matter where the QGP component is concentrated around midrapidity. We also show
how to constrain the values of the charge correlations lengths in both the
hadronic phase and the QGP phase using the charge transfer fluctuations.
Current manuscript is based on the preprints hep-ph/0503085 (to appear in
Physical Review C) and nucl-th/0506025.Comment: To appear in the proceedings of 18th International Conference on
Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2005 (QM 2005),
Budapest, Hungary, 4-9 Aug 200
Dynamics over Signed Networks
A signed network is a network with each link associated with a positive or
negative sign. Models for nodes interacting over such signed networks, where
two different types of interactions take place along the positive and negative
links, respectively, arise from various biological, social, political, and
economic systems. As modifications to the conventional DeGroot dynamics for
positive links, two basic types of negative interactions along negative links,
namely the opposing rule and the repelling rule, have been proposed and studied
in the literature. This paper reviews a few fundamental convergence results for
such dynamics over deterministic or random signed networks under a unified
algebraic-graphical method. We show that a systematic tool of studying node
state evolution over signed networks can be obtained utilizing generalized
Perron-Frobenius theory, graph theory, and elementary algebraic recursions.Comment: In press, SIAM Revie
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