7,345 research outputs found
Fermion Number Conservation Isn't Fermion Conservation
A nonperturbative regularization of the Standard Model may have a
superficially undesirable exact global U(1) symmetry corresponding to exact
fermion number conservation. We argue that such a formulation can still have
the desired physics of fermion nonconservation, i.e. fermion particle creation
and annihilation by sphaleron transitions. We illustrate our reasoning in
massless axial QED in 1+1 dimensions.Comment: 3 pages to appear in the proceedings of Lattice '93, Dallas, Texas,
12-16 October 1993, comes as a single uuencoded postscript file (LaTeX source
available from the authors), ITFA 93-3
Ruppeiner theory of black hole thermodynamics
The Ruppeiner metric as determined by the Hessian of the Gibbs surface
provides a geometric description of thermodynamic systems in equilibrium. An
interesting example is a black hole in equilibrium with its own Hawking
radiation. In this article, we present results from the Ruppeiner study of
various black hole families from different gravity theories e.g. 2D dilaton
gravity, BTZ, general relativity and higher-dimensional Einstein-Maxwell
gravity.Comment: 10 pages, 1 figure. Talk given by N Pidokrajt at ERE2006 in Palma de
Mallorca, Spai
The fragmentation of expanding shells III: Oligarchic accretion and the mass spectrum of fragments
We use SPH simulations to investigate the gravitational fragmentation of
expanding shells through the linear and non--linear regimes. The results are
analysed using spherical harmonic decomposition to capture the initiation of
structure during the linear regime; the potential-based method of Smith et al.
(2009) to follow the development of clumps in the mildly non-linear regime; and
sink particles to capture the properties of the final bound objects during the
highly non-linear regime. In the early, mildly non--linear phase of
fragmentation, we find that the clump mass function still agrees quite well
with the mass function predicted by the analytic model. However, the sink mass
function is quite different, in the sense of being skewed towards high-mass
objects. This is because, once the growth of a condensation becomes non-linear,
it tends to be growing non-competitively from its own essentially separate
reservoir; we call this Oligarchic Accretion.Comment: 14 pages, accepted for publication in MNRA
Computer Model for Simulating Almond Moth (Lepidoptera: Pyralidae) Population Dynamics
We developed a computer model for simulating the population dynamics of the almond moth, Cadra cautella (Walker). The model incorporates previously published life history data for the almond moth developing on stored peanuts, Arachis hypogaea L., including stage-specific immature developmental time and survival and adult longevity and fecundity. The model was modified so that it also could be used to simulate almond moth population dynamics on stored, dried citrus pulp and stored corn (Zea mays L.). We tested the validity of the model by using 4 previously published data sets. The model was useful for interpreting population dynamics observed in the previously published studies and will be useful for optimizing management strategies for the almond moth
Taxic Revisions
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72423/1/j.1096-0031.2001.tb00112.x.pd
Fixational Eye Movements in the Earliest Stage of Metazoan Evolution
All known photoreceptor cells adapt to constant light stimuli, fading the retinal image when exposed to an immobile visual scene. Counter strategies are therefore necessary to prevent blindness, and in mammals this is accomplished by fixational eye movements. Cubomedusae occupy a key position for understanding the evolution of complex visual systems and their eyes are assumedly subject to the same adaptive problems as the vertebrate eye, but lack motor control of their visual system. The morphology of the visual system of cubomedusae ensures a constant orientation of the eyes and a clear division of the visual field, but thereby also a constant retinal image when exposed to stationary visual scenes. Here we show that bell contractions used for swimming in the medusae refresh the retinal image in the upper lens eye of Tripedalia cystophora. This strongly suggests that strategies comparable to fixational eye movements have evolved at the earliest metazoan stage to compensate for the intrinsic property of the photoreceptors. Since the timing and amplitude of the rhopalial movements concur with the spatial and temporal resolution of the eye it circumvents the need for post processing in the central nervous system to remove image blur
The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results
We present an overview and first results of the Stratospheric Observatory For
Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the
FORCAST instrument to image massive protostars from
--. These wavelengths trace thermal emission from
warm dust, which in Core Accretion models mainly emerges from the inner regions
of protostellar outflow cavities. Dust in dense core envelopes also imprints
characteristic extinction patterns at these wavelengths, causing intensity
peaks to shift along the outflow axis and profiles to become more symmetric at
longer wavelengths. We present observational results for the first eight
protostars in the survey, i.e., multiwavelength images, including some
ancillary ground-based MIR observations and archival {\it{Spitzer}} and
{\it{Herschel}} data. These images generally show extended MIR/FIR emission
along directions consistent with those of known outflows and with shorter
wavelength peak flux positions displaced from the protostar along the
blueshifted, near-facing sides, thus confirming qualitative predictions of Core
Accretion models. We then compile spectral energy distributions and use these
to derive protostellar properties by fitting theoretical radiative transfer
models. Zhang and Tan models, based on the Turbulent Core Model of McKee and
Tan, imply the sources have protostellar masses --50
accreting at -- inside cores of
initial masses --500 embedded in clumps with mass surface
densities --3. Fitting Robitaille
et al. models typically leads to slightly higher protostellar masses, but with
disk accretion rates smaller. We discuss reasons for these
differences and overall implications of these first survey results for massive
star formation theories.Comment: Accepted to ApJ, 32 page
The SOFIA Massive (SOMA) Star Formation Survey. II. High Luminosity Protostars
We present multi-wavelength images observed with SOFIA-FORCAST from 10
to 40 m of seven high luminosity massive protostars, as part of the SOFIA
Massive (SOMA) Star Formation Survey. Source morphologies at these wavelengths
appear to be influenced by outflow cavities and extinction from dense gas
surrounding the protostars. Using these images, we build spectral energy
distributions (SEDs) of the protostars, also including archival data from
Spitzer, Herschel and other facilities. Radiative transfer (RT) models of Zhang
& Tan (2018), based on Turbulent Core Accretion theory, are then fit to the
SEDs to estimate key properties of the protostars. Considering the best five
models fit to each source, the protostars have masses accreting at rates of inside cores of initial masses embedded in clumps with mass surface densities and span a luminosity range of . Compared with the first eight protostars in Paper I, the sources
analyzed here are more luminous, and thus likely to be more massive protostars.
They are often in a clustered environment or have a companion protostar
relatively nearby. From the range of parameter space of the models, we do not
see any evidence that needs to be high to form these massive
stars. For most sources the RT models provide reasonable fits to the SEDs,
though the cold clump material often influences the long wavelength fitting.
However, for sources in very clustered environments, the model SEDs may not be
such a good description of the data, indicating potential limitations of the
models for these regions.Comment: 30 pages, 19 figures, Accepted for publication in Ap
- …