1,091 research outputs found
A supersymmetric model for triggering Supernova Ia in isolated white dwarfs
We propose a model for supernovae Ia explosions based on a phase transition
to a supersymmetric state which becomes the active trigger for the deflagration
starting the explosion in an isolated sub-Chandrasekhar white dwarf star. With
two free parameters we fit the rate and several properties of type Ia
supernovae and address the gap in the supermassive black hole mass
distribution. One parameter is a critical density fit to about
g/cc while the other has the units of a space time volume and is found to be of
order Gyr where is the earth radius. The model involves
a phase transition to an exact supersymmetry in a small core of a dense star.Comment: 20 pages, 5 figures, expanded version to be published in Physical
Review
Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies
Revised (B-V)_0-Mg_2 data for 402 elliptical galaxies are given to test
reddening predictions which can also tell us both what the intrinsic errors are
in this relationship among gE galaxy stellar populations, as well as details of
nearby structure in the interstellar medium (ISM) of our Galaxy and of the
intrinsic errors in reddening predictions. Using least-squares fits, the
explicit 1-sigma errors in the Burstein-Heiles (BH) and the Schlegel et al.
(IR) predicted reddenings are calculated, as well as the 1-sigma observational
error in the (B-V)_0-Mg_2 for gE galaxies. It is found that, in directions with
E(B-V)<0.100 mag (where most of these galaxies lie), 1-sigma errors in the IR
reddening predictions are 0.006 to 0.009 in E(B-V) mag, those for BH reddening
prediction are 0.011 mag, and the 1-sigma agreement between the two reddening
predictions is 0.007 mag. IR predictions have an accuracy of 0.010-0.011 mag in
directions with E(B-V)>= 0.100 mag, significantly better than those of the BH
predictions (0.024-0.025). Gas-to-dust variations that vary by a factor of 3,
both high and low, exist along many lines-of-sight in our Galaxy. The approx
0.02 higher reddening zero point in E(B-V) previously determined by Schlegel et
al. is confirmed, primarily at the Galactic poles. Despite this, both methods
also predict many directions with E(B-V)<0.015 mag. Independent evidence of
reddening at the North Galactic pole is reviewed, with the conclusion that
there still exists directions at the NGP that have E(B-V)<<0.01. Two lines of
evidence suggest that IR reddenings are overpredicted in directions with high
gas-to-dust ratios. As high gas-to-dust directions in the ISM also include the
Galactic poles, this overprediction is the likely cause of the E(B-V) = 0.02
mag larger IR reddening zero point.Comment: 5 figure
A comparative study of satellite and ground-based phenology
Long time series of ground-based plant phenology, as well as more than two decades of satellite-derived phenological metrics, are currently available to assess the impacts of climate variability and trends on terrestrial vegetation. Traditional plant phenology provides very accurate information on individual plant species, but with limited spatial coverage. Satellite phenology allows monitoring of terrestrial vegetation on a global scale and provides an integrative view at the landscape level. Linking the strengths of both methodologies has high potential value for climate impact studies. We compared a multispecies index from ground-observed spring phases with two types (maximum slope and threshold approach) of satellite-derived start-of-season (SOS) metrics. We focus on Switzerland from 1982 to 2001 and show that temporal and spatial variability of the multispecies index correspond well with the satellite-derived metrics. All phenological metrics correlate with temperature anomalies as expected. The slope approach proved to deviate strongly from the temporal development of the ground observations as well as from the threshold-defined SOS satellite measure. The slope spring indicator is considered to indicate a different stage in vegetation development and is therefore less suited as a SOS parameter for comparative studies in relation to ground-observed phenology. Satellite-derived metrics are, however, very susceptible to snow cover, and it is suggested that this snow cover should be better accounted for by the use of newer satellite sensor
9286 Stars: An Agglomeration of Stellar Polarization Catalogs
This is a revision. The revisions are minor. The new version of the catalog
should be used in preference to the old. The most serious error in the older
version was that was incorrect, being sometimes far too large,
for Reiz and Franco entries; the correct values are all zero for that
reference.
We present an agglomeration of stellar polarization catalogs with results for
9286 stars. We have endeavored to eliminate errors, provide accurate
(arcsecond) positions, sensibly weight multiple observations of the same star,
and provide reasonable distances. This catalog is included as an ASCII file
(catalog.txt) in the source of this submission.Comment: The most serious error in the older version was that
was incorrect, being sometimes far too large, for Reiz and Franco entries;
the correct values are all zero for that reference. 11 pages, no figures.
Accepted for Astronomical Journal. Catalog also available as an ASCII file by
anonymous FTP from ftp://vermi.berkeley.edu/pub/polcat/p14.ou
Spherical collapse of supermassive stars: neutrino emission and gamma-ray bursts
We present the results of numerical simulations of the spherically symmetric
gravitational collapse of supermassive stars (SMS). The collapse is studied
using a general relativistic hydrodynamics code. The coupled system of Einstein
and fluid equations is solved employing observer time coordinates, by foliating
the spacetime by means of outgoing null hypersurfaces. The code contains an
equation of state which includes effects due to radiation, electrons and
baryons, and detailed microphysics to account for electron-positron pairs. In
addition energy losses by thermal neutrino emission are included. We are able
to follow the collapse of SMS from the onset of instability up to the point of
black hole formation. Several SMS with masses in the range are simulated. In all models an apparent horizon
forms initially, enclosing the innermost 25% of the stellar mass. From the
computed neutrino luminosities, estimates of the energy deposition by
-annihilation are obtained. Only a small fraction of this energy
is deposited near the surface of the star, where, as proposed recently by
Fuller & Shi (1998), it could cause the ultrarelativistic flow believed to be
responsible for -ray bursts. Our simulations show that for collapsing
SMS with masses larger than the energy deposition is
at least two orders of magnitude too small to explain the energetics of
observed long-duration bursts at cosmological redshifts. In addition, in the
absence of rotational effects the energy is deposited in a region containing
most of the stellar mass. Therefore relativistic ejection of matter is
impossible.Comment: 13 pages, 11 figures, submitted to A&
A Fully Tunable Single-Walled Carbon Nanotube Diode
We demonstrate a fully tunable diode structure utilizing a fully suspended
single-walled carbon nanotube (SWNT). The diode's turn-on voltage under forward
bias can be continuously tuned up to 4.3 V by controlling gate voltages, which
is ~6 times the nanotube bandgap energy. Furthermore, the same device design
can be configured into a backward diode by tuning the band-to-band tunneling
current with gate voltages. A nanotube backward diode is demonstrated for the
first time with nonlinearity exceeding the ideal diode. These results suggest
that a tunable nanotube diode can be a unique building block for developing
next generation programmable nanoelectronic logic and integrated circuits.Comment: 14 pages, 4 figure
Quantum kinetic description of Coulomb effects in one-dimensional nano-transistors
In this article, we combine the modified electrostatics of a one-dimensional
transistor structure with a quantum kinetic formulation of Coulomb interaction
and nonequilibrium transport. A multi-configurational self-consistent Green's
function approach is presented, accounting for fluctuating electron numbers. On
this basis we provide a theory for the simulation of electronic transport and
quantum charging effects in nano-transistors, such as gated carbon nanotube and
whisker devices and one-dimensional CMOS transistors. Single-electron charging
effects arise naturally as a consequence of the Coulomb repulsion within the
channel
ОПАЛЬНИЙ ГОЛОВА ОБЛВИКОНКОМУ Г.Г. ДЕМЕНТЬЄВ
У статті висвітлюється життя та діяльність в органах міського самоврядування першого секретаря Дніпропетровського обкому КП(б)У та голови виконкому обласної ради депутатів трудящих, учасника Великої Вітчизняної війни 1941-1945 рр Г.Г.ДементьєваThis article introduces G.G.Dementyevs life and activities in local governmental organs. G.G.Dementyev was the first Secretari of Dniepropetrovsk Regional Executive Committee of the Communist Party ( bolchevyks) of Ukraine, participant in the Great Patriotic War ( from 1941-1945 )
- …