46,924 research outputs found
The Impact of Type Ia Supernova Ejecta on Binary Companions
We present adaptive mesh refinement (AMR) hydrodynamical simulations of the
interaction between Type Ia supernovae and their companion stars within the
context of the single-degenerate model. Results for 3D red-giant companions
without binary evolution agree with previous 2D results by Marietta et al. We
also consider evolved helium-star companions in 2D. For a range of helium-star
masses and initial binary separations, we examine the mass unbound by the
interaction and the kick velocity delivered to the companion star. We find that
unbound mass versus separation obeys a power law with index between -3.1 and
-4.0, consistent with previous results for hydrogen-rich companions. Kick
velocity also obeys a power-law relationship with binary separation, but the
slope differs from those found for hydrogen-rich companions. Assuming accretion
via Roche-lobe overflow, we find that the unbound helium mass is consistent
with observational limits. Ablation (shock heating) appears to be more
important in removing gas from helium-star companions than from hydrogen-rich
ones, though stripping (momentum transfer) dominates in both cases.Comment: 6 pages, 2 figures, to appear in the proceedings of the conference
"Binary Star Evolution: Mass Loss, Accretion, and Mergers" at Mykonos,
Greece, June 22-25, 201
Constructing the cultural repertoire in a natural disaster: The role of social media in the Thailand flood of 2011
In 2011, Thailand witnessed its worst flooding catastrophe in half a century. In this study, we explored social media as a new and promising weapon to address the physical and morale challenges caused by the natural disaster. A case study was conducted in the context of crisis response, whichinvestigated the use of social media to contribute to the collective cultural repertoire during the natural disaster. By investigating two paths toward the cultural repertoire construction considering different social groups, this study also identified the roles of social media as an information market and an information threshold in the crisis response
Optimal Dynamical Decoupling Sequence for Ohmic Spectrum
We investigate the optimal dynamical decoupling sequence for a qubit coupled
to an ohmic environment. By analytically computing the derivatives of the
decoherence function, the optimal pulse locations are found to satisfy a set of
nonlinear equations which can be easily solved. These equations incorporates
the environment information such as high-energy (UV) cutoff frequency \omega_c,
giving a complete description of the decoupling process. The solutions explain
previous experimental and theoretical results of locally optimized dynamical
decoupling (LODD) sequence in high-frequency dominated environment, which were
obtained by purely numerical computation and experimental feedback. As shown in
numerical comparison, these solutions outperform the Uhrig dynamical decoupling
(UDD) sequence by one or more orders of magnitude in the ohmic case.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions
We have developed a method for the reproducible fabrication of
superconducting scanning tunneling microscope (STM) tips. We use these tips to
form superconductor/insulator/superconductor tunnel junctions with the STM tip
as one of the electrodes. We show that such junctions exhibit fluctuation
dominated Josephson effects, and describe how the Josephson product IcRn can be
inferred from the junctions' tunneling characteristics in this regime. This is
first demonstrated for tunneling into Pb films, and then applied in studies of
single crystals of NbSe2. We find that in NbSe2, IcRn is lower than expected,
which could be attributed to the interplay between superconductivity and the
coexisting charge density wave in this material.Comment: 3 pages, 2 figures. Presented at the New3SC-4 meeting, San Diego,
Jan. 16-21 200
A New Young Diagrammatic Method For Kronecker Products of O(n) and Sp(2m)
A new simple Young diagrammatic method for Kronecker products of O(n) and
Sp(2m) is proposed based on representation theory of Brauer algebras. A general
procedure for the decomposition of tensor products of representations for O(n)
and Sp(2m) is outlined, which is similar to that for U(n) known as the
Littlewood rules together with trace contractions from a Brauer algebra and
some modification rules given by King.Comment: Latex, 11 pages, no figure
Piezoelectric mechanism of orientation of stripe structures in two-dimensional electron systems
A piezoelectric mechanism of orientation of stripes in two-dimensional
quantum Hall systems in GaAs heterostructures is considered. The anisotropy of
the elastic moduli and the boundary of the sample are taken into account. It is
found that in the average the stripes line up with the [110] axis. In double
layer systems the wave vector of the stripe structure rotates from the [110] to
[100] axis if the period of density modulation becomes large than the
interlayer distance. From the experimental point of view it means that in
double layer systems anisotropic part of resistivity changes its sign under
variation of the external magnetic field.Comment: 8 page
Josephson scanning tunneling microscopy
We propose a set of scanning tunneling microscopy experiments in which the
surface of superconductor is scanned by a superconducting tip. Potential
capabilities of such experimental setup are discussed. Most important
anticipated results of such an experiment include the position-resolved
measurement of the superconducting order parameter and the possibility to
determine the nature of the secondary component of the order parameter at the
surface. The theoretical description based on the tunneling Hamiltonian
formalism is presented.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Swift UVOT Grism Observations of Nearby Type Ia Supernovae - I. Observations and Data Reduction
Ultraviolet (UV) observations of Type Ia supernovae (SNe Ia) are useful tools
for understanding progenitor systems and explosion physics. In particular, UV
spectra of SNe Ia, which probe the outermost layers, are strongly affected by
the progenitor metallicity. In this work, we present 120 Neil Gehrels Swift
Observatory UV spectra of 39 nearby SNe Ia. This sample is the largest UV
(lambda < 2900 A) spectroscopic sample of SNe Ia to date, doubling the number
of UV spectra and tripling the number of SNe with UV spectra. The sample spans
nearly the full range of SN Ia light-curve shapes (delta m(B) ~ 0.6-1.8 mag).
The fast turnaround of Swift allows us to obtain UV spectra at very early
times, with 13 out of 39 SNe having their first spectra observed >~ 1 week
before peak brightness and the earliest epoch being 16.5 days before peak
brightness. The slitless design of the Swift UV grism complicates the data
reduction, which requires separating SN light from underlying host-galaxy light
and occasional overlapping stellar light. We present a new data-reduction
procedure to mitigate these issues, producing spectra that are significantly
improved over those of standard methods. For a subset of the spectra we have
nearly simultaneous Hubble Space Telescope UV spectra; the Swift spectra are
consistent with these comparison data.Comment: Accepted for publication in MNRA
Current Path Properties of the Transport Anisotropy at Filling Factor 9/2
To establish the presence and orientation of the proposed striped phase in
ultra-high mobility 2D electron systems at filling factor 9/2, current path
transport properties are determined by varying the separation and allignment of
current and voltage contacts. Contacts alligned orthogonal to the proposed
intrinsic striped phase produce voltages consistent with current spreading
along the stripes; current driven along the proposed stripe direction results
in voltages consistent with channeling along the stripes. Direct comparison is
made to current spreading/channeling properties of artificially induced 1D
charge modulated systems, which indicates the 9/2 direction.Comment: 10 pages, 4 figure
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