1,048 research outputs found
Accretion Disks Phase Transitions: 2-D or not 2-D?
We argue that the proper way to treat thin-thick accretion-disk transitions
should take into account the 2-D nature of the problem. We illustrate the
physical inconsistency of the 1-D vertically integrated approach by discussing
a particular example of the convective transport of energy.Comment: 4 pages, 2 figure
Self-Organized Criticality in Compact Plasmas
Compact plasmas, that exist near black-hole candidates and in gamma ray burst
sources, commonly exhibit self-organized non-linear behavior. A model that
simulates the non-linear behavior of compact radiative plasmas is constructed
directly from the observed luminosity and variability. The simulation shows
that such plasmas self organize, and that the degree of non-linearity as well
as the slope of the power density spectrum increase with compactness. The
simulation is based on a cellular automaton table that includes the properties
of the hot (relativistic) plasmas, and the magnitude of the energy
perturbations. The plasmas cool or heat up, depending on whether they release
more or less than the energy of a single perturbation. The energy release
depends on the plasmas densities and temperatures, and the perturbations
energy. Strong perturbations may cool the previously heated plasma through
shocks and/or pair creation.
New observations of some active galactic nuclei and gamma ray bursters are
consistent with the simulationComment: 9 pages, 5 figures, AASTeX, Submitted to ApJ
Boomerang returns unexpectedly
Experimental study of the anisotropy in the cosmic microwave background (CMB)
is gathering momentum. The eagerly awaited Boomerang results have lived up to
expectations. They provide convincing evidence in favor of the standard
paradigm: the Universe is close to flat and with primordial fluctuations which
are redolent of inflation. Further scrutiny reveals something even more
exciting however -- two hints that there may be some unforeseen physical
effects. Firstly the primary acoustic peak appears at slightly larger scales
than expected. Although this may be explicable through a combination of mundane
effects, we suggest it is also prudent to consider the possibility that the
Universe might be marginally closed. The other hint is provided by a second
peak which appears less prominent than expected. This may indicate one of a
number of possibilities, including increased damping length or tilted initial
conditions, but also breaking of coherence or features in the initial power
spectrum. Further data should test whether the current concordance model needs
only to be tweaked, or to be enhanced in some fundamental way.Comment: 11 pages, 3 figures, final version accepted by Ap
Energy Injection in GRB Afterglow Models
We extend the standard fireball model, widely used to interpret gamma-ray
burst (GRB) afterglow light curves, to include energy injections, and apply the
model to the afterglow light curves of GRB 990510, GRB 000301C and GRB 010222.
We show that discrete energy injections can cause temporal variations in the
optical light curves and present fits to the light curves of GRB 000301C as an
example. A continuous injection may be required to interpret other bursts such
as GRB 010222. The extended model accounts reasonably well for the observations
in all bands ranging from X-rays to radio wavelengths. In some cases, the radio
light curves indicate that additional model ingredients may be needed.Comment: Accepted for publication in the Astrophysical Journa
Multiple melt plumes observed at the Breioamerkurjokull ice face in the upper waters of Jokulsarlon lagoon, Iceland
Breioamerkurjokull flows from the Vatnajokull ice cap and calves into the Jokulsarlon proglacial lagoon. The lagoon is connected to the North Atlantic Ocean through a 6 m deep narrow channel. Four hydrographic surveys in spring 2012, and a 2011 4-month long temperature and salinity time series of lagoon inflow show that the lake has significantly changed since 1976. Warm saline ocean water enters each tidal cycle and descends below the maximum sampled depths. The lagoon has a surface layer of ice melt, freshwater and Atlantic derived water. Beneath 10 m depth an advective/diffusive balance is responsible for determining the temperature and salinity of the lagoon waters down to ~90 m. To maintain the observed hydrographic structure, we calculate an upwelling of deep water of ~0.2 m dâ1. A survey within 30 m of Breioamerkurjokull showed that the warmest and most saline waters sampled within the lagoon below 10 m depth were adjacent to the glacier face, along with multiple interleaved warm and cold layers. A heat and salt balance model shows that submarine melting along the ice face generates multiple meltwater plumes that are mixed and diluted within 200 m of the ice face
Gravity and elevation changes caused by magma movement beneath the Krafla Caldera, Northeast Iceland
Prior to the present activity of the Krafla volcano, which started in 1975, levelling and gravity surveys had been carried out in the area. The network has since been extended, and measurements are carried out about every second month. The measurements reveal a quasi-periodic behaviour of the tectonic activity, characterized by slow inflation of the caldera for several weeks or months at a rate of 6â10 mm/d, interrupted by sudden subsidence events lasting for one or a few days. Elevation changes within the caldera are described by a deflation-inflation swelling with its apex near the center of the caldera. Calculations. using a model of a spherical chamber with varying pressure at 3 km depth, show good agreement with the measured elevation values. Comparison of gravity and levelling data, using a Bouguer type relationship, suggests that inflation and deflation of the floor of the caldera is caused entirely by in- and outflow of magma. Some discrepancies between the levelling and gravity data immediately after subsidence events can be explained by additional mass flow of groundwater.
ARK: https://n2t.net/ark:/88439/y037843
Permalink: https://geophysicsjournal.com/article/99
 
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