4,454 research outputs found
Neutral Gas Distributions and Kinematics of Five Blue Compact Dwarf Galaxies
We present the results of high spatial resolution HI observations of five
intrinsically compact dwarf galaxies which are currently experiencing a strong
burst of star formation. The HI maps indicate that these systems have a complex
and clumpy interstellar medium. Unlike typical dwarf irregular galaxies, these
Blue Compact Dwarf (BCD) galaxies exhibit strong central concentrations in
their neutral gas distributions which may provide a clue to the origin of their
strong star-burst activity. Furthermore, while all of the systems do appear to
be rotating, based on observed velocity gradients, the kinematics are complex.
All systems have non-ordered kinematic structure at some level; some of the
extended gas is not necessarily kinematically connected to the main system.
The observed gas distributions and kinematics place constraints on
evolutionary scenarios for BCDs. Evolutionary links between BCDs, dwarf
irregulars, and dwarf ellipticals have been postulated to explain their high
star formation rates and low luminosity, low metallicity nature. The BCDs
appear to have higher central mass concentrations in both gas and stellar
content than the dwarf irregulars, indicating that evolutionary scenarios
connecting these two classes will require mass redistribution. In addition, the
fact that BCDs are rotationally supported systems indicates that BCDs are
unlikely to evolve into dwarf ellipticals without substantial loss of angular
momentum. Thus, while such evolutionary scenarios may still be possible with
the aid of mergers or tidal interactions, the isolated nature of BCDs suggests
that the majority of BCDs will not fade to become objects similar to the
present day dwarf ellipticals.Comment: 19 pages, 15 figures. To appear in A
Stochastic modeling of soil salinity
A minimalist stochastic model of primary soil salinity is proposed, in which the rate of soil salinization is determined by the balance between dry and wet salt deposition and the intermittent leaching events caused by rainfall events. The long term probability density functions of salt mass and concentration are found by reducing the coupled soil moisture and salt mass balance equation to a single stochastic differential equation driven by multiplicative Poisson noise. The novel analytical solutions provide insight on the interplay of the main soil, plant and climate parameters responsible for long-term soil salinization. In particular, they show the existence of two distinct regimes, one where the mean salt mass remains nearly constant (or decreases) with increasing rainfall frequency, and another where mean salt content increases markedly with increasing rainfall frequency. As a result, relatively small reductions of rainfall in drier climates may entail dramatic shifts in long-term soil salinization trends, with significant consequences e.g. for climate change impacts on rain-fed agricultur
Electromagnetic Structure of Light Baryons in Lattice QCD
A method in which electromagnetic properties of hadrons are studied by direct
simulation of dynamical photon effects is applied to the extraction of the
isomultiplet structure of the octet baryons. Using 187 configurations at
with Wilson action, and up and down quark masses determined from
the meson spectrum, the nucleon splitting is found to be MeV; the hyperon splittings are found to be
, ,
MeV. Estimated systematic corrections arising
from finite volume and the quenched approximation are included in these
results.Comment: Talk presented at LATTICE96(phenomenology
Renormalizing Rectangles and Other Topics in Random Matrix Theory
We consider random Hermitian matrices made of complex or real
rectangular blocks, where the blocks are drawn from various ensembles. These
matrices have pairs of opposite real nonvanishing eigenvalues, as well as
zero eigenvalues (for .) These zero eigenvalues are ``kinematical"
in the sense that they are independent of randomness. We study the eigenvalue
distribution of these matrices to leading order in the large limit, in
which the ``rectangularity" is held fixed. We apply a variety of
methods in our study. We study Gaussian ensembles by a simple diagrammatic
method, by the Dyson gas approach, and by a generalization of the Kazakov
method. These methods make use of the invariance of such ensembles under the
action of symmetry groups. The more complicated Wigner ensemble, which does not
enjoy such symmetry properties, is studied by large renormalization
techniques. In addition to the kinematical -function spike in the
eigenvalue density which corresponds to zero eigenvalues, we find for both
types of ensembles that if is held fixed as , the
non-zero eigenvalues give rise to two separated lobes that are located
symmetrically with respect to the origin. This separation arises because the
non-zero eigenvalues are repelled macroscopically from the origin. Finally, we
study the oscillatory behavior of the eigenvalue distribution near the
endpoints of the lobes, a behavior governed by Airy functions. As the lobes come closer, and the Airy oscillatory behavior near the endpoints
that are close to zero breaks down. We interpret this breakdown as a signal
that drives a cross over to the oscillation governed by Bessel
functions near the origin for matrices made of square blocks.Comment: LateX, 34 pages, 3 ps figure
Phase transitions in spinor quantum gravity on a lattice
We construct a well-defined lattice-regularized quantum theory formulated in
terms of fundamental fermion and gauge fields, the same type of degrees of
freedom as in the Standard Model. The theory is explicitly invariant under
local Lorentz transformations and, in the continuum limit, under
diffeomorphisms. It is suitable for describing large nonperturbative and
fast-varying fluctuations of metrics. Although the quantum curved space turns
out to be on the average flat and smooth owing to the non-compressibility of
the fundamental fermions, the low-energy Einstein limit is not automatic: one
needs to ensure that composite metrics fluctuations propagate to long distances
as compared to the lattice spacing. One way to guarantee this is to stay at a
phase transition.
We develop a lattice mean field method and find that the theory typically has
several phases in the space of the dimensionless coupling constants, separated
by the second order phase transition surface. For example, there is a phase
with a spontaneous breaking of chiral symmetry. The effective low-energy
Lagrangian for the ensuing Goldstone field is explicitly
diffeomorphism-invariant. We expect that the Einstein gravitation is achieved
at the phase transition. A bonus is that the cosmological constant is probably
automatically zero.Comment: 37 pages, 12 figures Discussion of dimensions and of the
Berezinsky--Kosterlitz--Thouless phase adde
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