1,819 research outputs found
A nonequilibrium renormalization group approach to turbulent reheating
We use nonequilibrium renormalization group (RG) techniques to analyze the
thermalization process in quantum field theory, and by extension reheating
after inflation. Even if at a high scale the theory is described by a
non-dissipative theory, the RG running induces nontrivial
noise and dissipation. For long wavelength, slowly varying field
configurations, the noise and dissipation are white and ohmic, respectively.
The theory will then tend to thermalize to an effective temperature given by
the fluctuation-dissipation theorem.Comment: 8 pages, 2 figures; to appear in J. Phys. A; more detailed account of
the calculation of the noise and dissipation kernel
Estudos da patogenicidade do circovirus suĂno tipo 2 (PCV2) em suĂnos e do papel do macho suĂno na disseminação viral dentro do plantel.
Projeto/Plano de Ação: 03.03.230.01
On the He II Emission In Eta Carinae and the Origin of Its Spectroscopic Events
We describe and analyze Hubble Space Telescope (HST) observations of
transient emission near 4680 {\AA} in Eta Car, reported earlier by Steiner &
Damineli (2004). If, as seems probable, this is He II 4687, then it is
a unique clue to Eta Car's 5.5-year cycle. According to our analysis, several
aspects of this feature support a mass-ejection model of the observed
spectroscopic events, and not an eclipse model. The He II emission appeared in
early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and
then abruptly disappeared. It did not appear in any other HST spectra before or
after the event. The peak brightness was larger than previously reported, and
is difficult to explain even if one allows for an uncertainty factor of order
3. The stellar wind must provide a temporary larger-than-normal energy supply,
and we describe a special form of radiative amplification that may also be
needed. These characteristics are consistent with a class of mass-ejection or
wind-disturbance scenarios, which have implications for the physical structure
and stability of Eta Car.Comment: 47 pages (including all appendices, tabs, & figs), 9 figures, 3
tables; submitted to Astrophysical Journal (2005 March 29), accepted for
publication in Ap
The Binarity of Eta Carinae and its Similarity to Related Astrophysical Objects
I examine some aspects of the interaction between the massive star Eta
Carinae and its companion, in particular during the eclipse-like event, known
as the spectroscopic event or the shell event. The spectroscopic event is
thought to occur when near periastron passages the stellar companion induces
much higher mass loss rate from the primary star, and/or enters into a much
denser environment around the primary star. I find that enhanced mass loss rate
during periastron passages, if it occurs, might explain the high eccentricity
of the system. However, there is not yet a good model to explain the presumed
enhanced mass loss rate during periastron passages. In the region where the
winds from the two stars collide, a dense slow flow is formed, such that large
dust grains may be formed. Unlike the case during the 19th century Great
Eruption, the companion does not accrete mass during most of its orbital
motion. However, near periastron passages short accretion episodes may occur,
which may lead to pulsed ejection of two jets by the companion. The companion
may ionize a non-negligible region in its surrounding, resembling the situation
in symbiotic systems. I discuss the relation of some of these processes to
other astrophysical objects, by that incorporating Eta Car to a large class of
astrophysical bipolar nebulae.Comment: Updated version. ApJ, in pres
Palaeomagnetic analysis on Late Bronze Age Pottery from Santorini: New data from the Akrotiri excavation and estimation of the deposition temperatures of the Minoan pyroclastic products
Endemic fish calling: Acoustics and reproductive behaviour of the Neretva dwarf goby Orsinigobius croaticus
The Neretva dwarf goby Orsinigobius croaticus (Gobiiformes, Gobionellidae) is an endemic
fish native to the freshwaters of the Adriatic Basin in Croatia and Bosnia and
Herzegovina, a Mediterranean Biodiversity Hotspot. Due to its limited distribution
range, specific karst habitat and endangered status, laboratory studies on reproductive
biology are scarce but crucial. Herein, we investigated the sound production and
acoustic behaviour of the endangered O. croaticus during reproductive intersexual
laboratory encounters, utilising an interdisciplinary approach. We also performed dissections
and micro-computed tomography (ÎĽCT) scanning of the pectoral girdle to
explore its potential involvement in sound production. Finally, comparative acoustic
analysis was conducted on sounds produced by previously recorded soniferous sand
gobies to investigate whether acoustic features are species-specific. The endemic
O. croaticus is a soniferous species. Males of this species emit pulsatile sounds composed
of a variable number of short (~15 ms) consecutive pulses when interacting with
females, usually during the pre-spawning phase in the nest, but also during courtship
outside the nest. Pulsatile sounds were low-frequency and short pulse trains (~140 Hz,
<1000 ms). Male visual behaviour rate was higher when co-occurring with sounds
and females entered the male's nest significantly more frequently when sounds were
present. Characteristic body movements accompanied male sound production, such
as head thrust and fin spreading. Furthermore, ÎĽCT scans and dissections suggest that
O. croaticus shares certain anatomical similarities of the pectoral girdle (i.e. osseous
elements and arrangement of levator pectoralis muscles) to previously studied sand
gobies that could be involved in sound production. Multivariate comparisons, using
sounds produced by eight soniferous European sand gobies, effectively distinguished
soniferous (and sympatric) species based on their acoustic properties. However, the
discrimination success decreased when temperature-dependent features (sound
duration and pulse repetition rate) were excluded from the analysis. Therefore, we
suggest both spectral and temporal features are important for the acoustic differentiation
of sand gobies
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