2,182 research outputs found
From Young and Hot to Old and Cold: Comparing White Dwarf Cooling Theory to Main Sequence Stellar Evolution in Open Clusters
I explore the current ability of both white dwarf cooling theory and main
sequence stellar evolution theory to accurately determine stellar population
ages by comparing ages derived using both techniques for open clusters ranging
from 0.1 to 4 Gyr. I find good agreement between white dwarf and main sequence
evolutionary ages over the entire age range currently available for study. I
also find that directly comparing main sequence turn-off ages to white dwarf
ages is only weakly sensitive to realistic levels of errors in cluster
distance, metallicity, and reddening. Additional detailed comparisons between
white dwarf and main sequence ages have tremendous potential to refine and
calibrate both of these important clocks, and I present new simulations of
promising open cluster targets. The most demanding requirement for these white
dwarf studies are very deep (V > 25-28) cluster observations made necessary by
the faintness of the oldest white dwarfs.Comment: 25 pages, incl. 10 figures, ApJ accepted for April, 200
Radiative corrections to the lattice gluon action for highly improved staggered quarks (HISQ) and the effect of such corrections on the static potential
We perform a perturbative calculation of the influence of dynamical HISQ
fermions on the perturbative improvement of the gluonic action in the same way
as we have previously done for asqtad fermions. We find the fermionic
contributions to the radiative corrections in the Luescher-Weisz gauge action
to be somewhat larger for HISQ fermions than for asqtad. Using one-loop
perturbation theory as a test, we estimate that omission of the fermion-induced
radiative corrections in dynamical asqtad simulations will give a measurable
effect. The one-loop result gives a systematic shift of about -0.6% in (r_1/a)
on the coarsest asqtad improved staggered ensembles. This is the correct sign
and magnitude to explain the scaling violations seen in Phi_B on dynamical
lattice ensembles.Comment: 10 pages, 5 figures. Minor corrections suggested by refere
Modelling diffusional transport in the interphase cell nucleus
In this paper a lattice model for diffusional transport of particles in the
interphase cell nucleus is proposed. Dense networks of chromatin fibers are
created by three different methods: randomly distributed, non-interconnected
obstacles, a random walk chain model, and a self avoiding random walk chain
model with persistence length. By comparing a discrete and a continuous version
of the random walk chain model, we demonstrate that lattice discretization does
not alter particle diffusion. The influence of the 3D geometry of the fiber
network on the particle diffusion is investigated in detail, while varying
occupation volume, chain length, persistence length and walker size. It is
shown that adjacency of the monomers, the excluded volume effect incorporated
in the self avoiding random walk model, and, to a lesser extent, the
persistence length, affect particle diffusion. It is demonstrated how the
introduction of the effective chain occupancy, which is a convolution of the
geometric chain volume with the walker size, eliminates the conformational
effects of the network on the diffusion, i.e., when plotting the diffusion
coefficient as a function of the effective chain volume, the data fall onto a
master curve.Comment: 9 pages, 8 figure
Unquenching effects on the coefficients of the L\"uscher-Weisz action
The effects of unquenching on the perturbative improvement coefficients in
the Symanzik action are computed within the framework of L\"uscher-Weisz
on-shell improvement. We find that the effects of quark loops are surprisingly
large, and their omission may well explain the scaling violations observed in
some unquenched studies.Comment: 7 pages, 5 figures, uses revtex4; version to appear in Phys.Rev.
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