1,445 research outputs found
Dynamics of Circumstellar Disks II: Heating and Cooling
We present a series of 2-d () hydrodynamic simulations of marginally
self gravitating disks around protostars using an SPH code. We implement simple
dynamical heating and we cool each location as a black body, using a
photosphere temperature obtained from the local vertical structure. We
synthesize SEDs from our simulations and compare them to fiducial SEDs derived
from observed systems. These simulations produce less distinct spiral structure
than isothermally evolved systems, especially in the inner third of the disk.
Pattern are similar further from the star but do not collapse into condensed
objects. The photosphere temperature is well fit to a power law in radius with
index , which is very steep. Far from the star, internal heating
( work and shocks) are not responsible for generating a large fraction of
the thermal energy contained in the disk matter. Gravitational torques
responsible for such shocks cannot transport mass and angular momentum
efficiently in the outer disk. Within 5--10 AU of the star, rapid break
up and reformation of spiral structure causes shocks, which provide sufficient
dissipation to power a larger fraction of the near IR energy output. The
spatial and size distribution of grains can have marked consequences on the
observed near IR SED and can lead to increased emission and variability on
year time scales. When grains are vaporized they do not reform
into a size distribution similar to that from which most opacity calculations
are based. With rapid grain reformation into the original size distribution,
the disk does not emit near infrared photons. With a plausible modification to
the opacity, it contributes much more.Comment: Accepted by ApJ, 60pg incl 24 figure
Shining new light on mammalian diving physiology using wearable near-infrared spectroscopy
Investigation of marine mammal dive-by-dive blood distribution and oxygenation has been limited by a lack of non-invasive technology for use in freely diving animals. Here, we developed a non-invasive near-infrared spectroscopy (NIRS) device to measure relative changes in blood volume and haemoglobin oxygenation continuously in the blubber and brain of voluntarily diving harbour seals. Our results show that seals routinely exhibit preparatory peripheral vasoconstriction accompanied by increased cerebral blood volume approximately 15 s before submersion. These anticipatory adjustments confirm that blood redistribution in seals is under some degree of cognitive control that precedes the mammalian dive response. Seals also routinely increase cerebral oxygenation at a consistent time during each dive, despite a lack of access to ambient air. We suggest that this frequent and reproducible reoxygenation pattern, without access to ambient air, is underpinned by previously unrecognised changes in cerebral drainage. The ability to track blood volume and oxygenation in different tissues using NIRS will facilitate a more accurate understanding of physiological plasticity in diving animals in an increasingly disturbed and exploited environment
Equine Arteritis Virus Subgenomic RNA Transcription: UV Inactivation and Translation Inhibition Studies
AbstractThe expression of the genetic information of equine arteritis virus (EAV), an arterivirus, involves the synthesis of six subgenomic (sg) mRNAs. These are 5′ and 3′ coterminal since they are composed of a leader and a body sequence, which are identical to the 5′ and 3′ ends of the genome, respectively. Previously, it has been suggested thatcis-splicing of a genome-length precursor RNA is involved in their synthesis. This was reevaluated in a comparative analysis of the sg RNA synthesis of EAV, the coronavirus mouse hepatitis virus (MHV), and the alphavirus Sindbis virus. UV transcription mapping showed that the majority of the EAV sg RNAs made at later stages of infection is not derived from a genome-length precursor. However, complete independence of sg RNA synthesis from that of genomic RNA was never observed during the course of infection. The possibility that this resulted from UV irradiation-induced effects on the synthesis of the viral replicase was investigated by inhibiting translation using cycloheximide. For EAV, ongoing protein synthesis was found to be more important for the synthesis of sg RNA than for that of genomic RNA. In general, MHV transcription was extremely sensitive to translation inhibition, whereas EAV genomic RNA synthesis became independent ofde novoprotein synthesis late in infection
Equipos de respuesta rápida de vigilancia epidemiológica: Mitigación de la pandemia de coronavirus en Perú, 2020: Rapid response teams for epidemiological surveillance: Mitigation of the coronavirus pandemic in Peru, 2020
On January 30, 2020, with more than 9,700 confirmed cases in China, the World Health Organization declared the coronavirus outbreak to be a public health emergency of international concern. At the end of January, the National Center for Epidemiology, Prevention and Control of Diseases (CDC-Peru) of the Ministry of Health prepared the “National Plan of Preparation and Response to the Introduction of the coronavirus 2019-nCoV”, where one of the strategic components was strengthen the epidemiological response through mitigation actions that allow early identification of cases, diagnosis, follow-up of contacts and identification of people with risk conditions.El 30 de enero de 2020, con más de 9,700 casos confirmados en China, la Organización Mundial de la Saluddeclaró que el brote de coronavirus era una emergencia de salud pública de importancia internacional. A fines de enero el Centro Nacional de Epidemiologia, Prevención y Control de Enfermedades (CDC-Perú)del Ministerio de Salud elaboró el “Plan Nacional de Preparación y Respuesta frente a la Introduccióndel coronavirus 2019-nCoV”, donde uno de los componentes estratégicos fue fortalecer la respuestaepidemiológica a través de acciones de mitigación que permitan la identificación temprana de casos,diagnóstico, seguimiento de contactos e identificación de personas con condiciones de riesgo
The Operator Product Expansion for Wilson Loops and Surfaces in the Large N Limit
The operator product expansion for ``small'' Wilson loops in {\cal N}=4, d=4
SYM is studied. The OPE coefficients are calculated in the large N and g_{YM}^2
N limit by exploiting the AdS/CFT correspondence. We also consider Wilson
surfaces in the (0,2), d=6 superconformal theory. In this case, we find that
the UV divergent terms include a term proportional to the rigid string action.Comment: 22 pages LaTeX2e, using utarticle.cls (included) and AMS-LaTeX macro
What Can the Accretion Induced Collapse of White Dwarfs Really Explain?
The accretion induced collapse (AIC) of a white dwarf into a neutron star has
been invoked to explain gamma-ray bursts, Type Ia supernovae, and a number of
problematic neutron star populations and specific binary systems. The ejecta
from this collapse has also been claimed as a source of r-process
nucleosynthesis. So far, most AIC studies have focussed on determining the
event rates from binary evolution models and less attention has been directed
toward understanding the collapse itself. However, the collapse of a white
dwarf into a neutron star is followed by the ejection of rare neutron-rich
isotopes. The observed abundance of these chemical elements may set a more
reliable limit on the rate at which AICs have taken place over the history of
the galaxy.
In this paper, we present a thorough study of the collapse of a massive white
dwarf in 1- and 2-dimensions and determine the amount and composition of the
ejected material. We discuss the importance of the input physics (equation of
state, neutrino transport, rotation) in determining these quantities. These
simulations affirm that AICs are too baryon rich to produce gamm-ray bursts and
do not eject enough nickel to explain Type Ia supernovae (with the possible
exception of a small subclass of extremely low-luminosity Type Ias). Although
nucleosynthesis constraints limit the number of neutron stars formed via AICs
to <0.1% of the total galactic neutron star population, AICs remain a viable
scenario for forming systems of neutron stars which are difficult to explain
with Type II core-collapse supernovae.Comment: Latex File, aaspp4 style, 18 pages total (5 figures), accepted by Ap
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