2,883 research outputs found
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Sauromalus hispidus
Number of Pages: 4Integrative BiologyGeological Science
Quantitative estimates of discrete harmonic measures
A theorem of Bourgain states that the harmonic measure for a domain in
is supported on a set of Hausdorff dimension strictly less than
\cite{Bourgain}. We apply Bourgain's method to the discrete case, i.e., to the
distribution of the first entrance point of a random walk into a subset of , . By refining the argument, we prove that for all \b>0 there
exists \rho (d,\b)N(d,\b), any , and any | \{y\in\Z^d\colon \nu_{A,x}(y)
\geq n^{-\b} \}| \leq n^{\rho(d,\b)}, where denotes the
probability that is the first entrance point of the simple random walk
starting at into . Furthermore, must converge to as \b \to
\infty.Comment: 16 pages, 2 figures. Part (B) of the theorem is ne
Recommended from our members
Sauromalus varius
Number of Pages: 4Integrative BiologyGeological Science
A Spatial Heterodyne Spectrometer for Laboratory Astrophysics; First Interferogram
A Spatial Heterodyne Spectrometer with broad spectral coverage across the VUV - UV region and with a high (> 500,000 ) spectral resolving power is being built for laboratory measurements of spectroscopic data including emission branching fractions, improved level energies, and hyperfine/isotopic parameters
Families of Vicious Walkers
We consider a generalisation of the vicious walker problem in which N random
walkers in R^d are grouped into p families. Using field-theoretic
renormalisation group methods we calculate the asymptotic behaviour of the
probability that no pairs of walkers from different families have met up to
time t. For d>2, this is constant, but for d<2 it decays as a power t^(-alpha),
which we compute to O(epsilon^2) in an expansion in epsilon=2-d. The second
order term depends on the ratios of the diffusivities of the different
families. In two dimensions, we find a logarithmic decay (ln t)^(-alpha'), and
compute alpha' exactly.Comment: 20 pages, 5 figures. v.2: minor additions and correction
s-Processing in the Galactic Disk. I. Super-Solar Abundances of Y, Zr, La, Ce in Young Open Clusters
In a recent study, based on homogeneous barium abundance measurements in open
clusters, a trend of increasing [Ba/Fe] ratios for decreasing cluster age was
reported. We present here further abundance determinations, relative to four
other elements hav- ing important s-process contributions, with the aim of
investigating whether the growth found for [Ba/Fe] is or not indicative of a
general property, shared also by the other heavy elements formed by slow
neutron captures. In particular, we derived abundances for yttrium, zirconium,
lanthanum and cerium, using equivalent widths measurements and the MOOG code.
Our sample includes 19 open clusters of different ages, for which the spectra
were obtained at the ESO VLT telescope, using the UVES spectrometer. The growth
previously suggested for Ba is confirmed for all the elements analyzed in our
study. This fact implies significant changes in our views of the Galactic
chemical evolution for elements beyond iron. Our results necessarily require
that very low-mass AGB stars (M < 1.5M\odot) produce larger amounts of
s-process elements (hence acti- vate the 13 C-neutron source more effectively)
than previously expected. Their role in producing neutron-rich elements in the
Galactic disk has been so far underestimated and their evolution and
neutron-capture nucleosynthesis should now be reconsidered.Comment: ApJ accepte
The Hitting Times with Taboo for a Random Walk on an Integer Lattice
For a symmetric, homogeneous and irreducible random walk on d-dimensional
integer lattice Z^d, having zero mean and a finite variance of jumps, we study
the passage times (with possible infinite values) determined by the starting
point x, the hitting state y and the taboo state z. We find the probability
that these passages times are finite and analyze the tails of their cumulative
distribution functions. In particular, it turns out that for the random walk on
Z^d, except for a simple (nearest neighbor) random walk on Z, the order of the
tail decrease is specified by dimension d only. In contrast, for a simple
random walk on Z, the asymptotic properties of hitting times with taboo
essentially depend on the mutual location of the points x, y and z. These
problems originated in our recent study of branching random walk on Z^d with a
single source of branching
A Model Ground State of Polyampholytes
The ground state of randomly charged polyampholytes is conjectured to have a
structure similar to a necklace, made of weakly charged parts of the chain,
compacting into globules, connected by highly charged stretched `strings'. We
suggest a specific structure, within the necklace model, where all the neutral
parts of the chain compact into globules: The longest neutral segment compacts
into a globule; in the remaining part of the chain, the longest neutral segment
(the 2nd longest neutral segment) compacts into a globule, then the 3rd, and so
on. We investigate the size distributions of the longest neutral segments in
random charge sequences, using analytical and Monte Carlo methods. We show that
the length of the n-th longest neutral segment in a sequence of N monomers is
proportional to N/(n^2), while the mean number of neutral segments increases as
sqrt(N). The polyampholyte in the ground state within our model is found to
have an average linear size proportional to sqrt(N), and an average surface
area proportional to N^(2/3).Comment: 8 two-column pages. 5 eps figures. RevTex. Submitted to Phys. Rev.
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