34,596 research outputs found
Thermal reactor
A thermal reactor apparatus and method of pyrolyticaly decomposing silane gas into liquid silicon product and hydrogen by-product gas is disclosed. The thermal reactor has a reaction chamber which is heated well above the decomposition temperature of silane. An injector probe introduces the silane gas tangentially into the reaction chamber to form a first, outer, forwardly moving vortex containing the liquid silicon product and a second, inner, rewardly moving vortex containing the by-product hydrogen gas. The liquid silicon in the first outer vortex deposits onto the interior walls of the reaction chamber to form an equilibrium skull layer which flows to the forward or bottom end of the reaction chamber where it is removed. The by-product hydrogen gas in the second inner vortex is removed from the top or rear of the reaction chamber by a vortex finder. The injector probe which introduces the silane gas into the reaction chamber is continually cooled by a cooling jacket
Intermittency and Lifetime of the 625 Hz QPO in the 2004 Hyperflare from the Magnetar SGR 1806-20 as evidence for magnetic coupling between the crust and the core
Quasi-periodic oscillations (QPOs) detected in the 2004 giant flare from SGR
1806-20 are often interpreted as global magneto-elastic oscillations of the
neutron star. There is, however, a large discrepancy between theoretical
models, which predict that the highest frequency oscillations should die out
rapidly, and the observations, which suggested that the highest-frequency
signals persisted for ~100s in X-ray data from two different spacecraft. This
discrepancy is particularly important for the high-frequency QPO at ~625 Hz.
However, previous analyses did not systematically test whether the signal could
also be there in much shorter data segments, more consistent with the
theoretical predictions. Here, we test for the presence of the high-frequency
QPO at 625 Hz in data from both the Rossi X-ray Timing Explorer (RXTE) and the
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) systematically both in
individual rotational cycles of the neutron star, as well as averaged over
multiple successive rotational cycles at the same phase. We find that the QPO
in the RXTE data is consistent with being only present in a single cycle, for a
short duration of ~0.5s, whereas the RHESSI data are as consistent with a
short-lived signal that appears and disappears as with a long-lived QPO. Taken
together, this data provides evidence for strong magnetic interaction between
the crust and the core.Comment: Accepted for publication in ApJ. The data and simulations are
available at
http://figshare.com/articles/SGR_1806_20_Giant_Flare_Data_and_Simulations/1126082
, the code can be downloaded from
https://github.com/dhuppenkothen/giantflare-paper , some documentation is
under
http://nbviewer.ipython.org/github/dhuppenkothen/giantflare-paper/blob/master/documents/giantflare-analysis.ipyn
Inverse spectral results for Schr\"odinger operators on the unit interval with potentials in L^P spaces
We consider the Schr\"odinger operator on with potential in . We
prove that two potentials already known on () and having
their difference in are equal if the number of their common eigenvalues
is sufficiently large. The result here is to write down explicitly this number
in terms of (and ) showing the role of
Nucleation of Spontaneous Vortices in Trapped Fermi Gases Undergoing a BCS-BEC Crossover
We study the spontaneous formation of vortices during the superfluid
condensation in a trapped fermionic gas subjected to a rapid thermal quench via
evaporative cooling. Our work is based on the numerical solution of the time
dependent crossover Ginzburg-Landau equation coupled to the heat diffusion
equation. We quantify the evolution of condensate density and vortex length as
a function of a crossover phase parameter from BCS to BEC. The more interesting
phenomena occur somewhat nearer to the BEC regime and should be experimentally
observable; during the propagation of the cold front, the increase in
condensate density leads to the formation of supercurrents towards the center
of the condensate as well as possible condensate volume oscillations.Comment: 5 pages, 3 figure
A 6-INCH SUBSONIC HIGH-TEMPERATURE ARC TUNNEL FOR STRUCTURES AND MATERIAL TESTS
Subsonic high temperature arc heated wind tunnel tests for structural material
Coulomb Glasses: A Comparison Between Mean Field and Monte Carlo Results
Recently a local mean field theory for both eqilibrium and transport
properties of the Coulomb glass was proposed [A. Amir et al., Phys. Rev. B 77,
165207 (2008); 80, 245214 (2009)]. We compare the predictions of this theory to
the results of dynamic Monte Carlo simulations. In a thermal equilibrium state
we compare the density of states and the occupation probabilities. We also
study the transition rates between different states and find that the mean
field rates underestimate a certain class of important transitions. We propose
modified rates to be used in the mean field approach which take into account
correlations at the minimal level in the sense that transitions are only to
take place from an occupied to an empty site. We show that this modification
accounts for most of the difference between the mean field and Monte Carlo
rates. The linear response conductance is shown to exhibit the Efros-Shklovskii
behaviour in both the mean field and Monte Carlo approaches, but the mean field
method strongly underestimates the current at low temperatures. When using the
modified rates better agreement is achieved
Flame Propagation on the Surfaces of Rapidly Rotating Neutron Stars during Type I X-ray Bursts
We present the first vertically resolved hydrodynamic simulations of a
laterally propagating, deflagrating flame in the thin helium ocean of a
rotating accreting neutron star. We use a new hydrodynamics solver tailored to
deal with the large discrepancy in horizontal and vertical length scales
typical of neutron star oceans, and which filters out sound waves that would
otherwise limit our timesteps. We find that the flame moves horizontally with
velocities of order cm s, crossing the ocean in few seconds,
broadly consistent with the rise times of Type I X-ray bursts. We address the
open question of what drives flame propagation, and find that heat is
transported from burning to unburnt fuel by a combination of top-to-bottom
conduction and mixing driven by a baroclinic instability. The speed of the
flame propagation is therefore a sensitive function of the ocean conductivity
and spin: we explore this dependence for an astrophysically relevant range of
parameters and find that in general flame propagation is faster for slower
rotation and higher conductivity.Comment: Accepted for publication by MNRA
Rotational effects in thermonuclear Type I Bursts: equatorial crossing and directionality of flame spreading
In a previous study on thermonuclear (type I) nursts on accreting neutron
stars we addressed and demonstrated the importance of the effects of rotation,
through the Coriolis force, on the propagation of the burning flame. However,
that study only analysed cases of longitudinal propagation, where the Coriolis
force coefficient was constant. In this paper, we study the
effects of rotation on propagation in the meridional (latitudinal) direction,
where the Coriolis force changes from its maximum at the poles to zero at the
equator. We find that the zero Coriolis force at the equator, while affecting
the structure of the flame, does not prevent its propagation from one
hemisphere to another. We also observe structural differences between the flame
propagating towards the equator and that propagating towards the pole, the
second being faster. In the light of the recent discovery of the low spin
frequency of burster IGR~J17480-2446 rotating at 11 Hz (for which Coriolis
effects should be negligible) we also extend our simulations to slow rotation.Comment: Accepted for publication by MNRA
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