10,380 research outputs found
The Gravitational Wave Signature of Core-Collapse Supernovae
We review the ensemble of anticipated gravitational-wave (GW) emission
processes in stellar core collapse and postbounce core-collapse supernova
evolution. We discuss recent progress in the modeling of these processes and
summarize most recent GW signal estimates. In addition, we present new results
on the GW emission from postbounce convective overturn and protoneutron star
g-mode pulsations based on axisymmetric radiation-hydrodynamic calculations.
Galactic core-collapse supernovae are very rare events, but within 3-5 Mpc from
Earth, the rate jumps to 1 in ~2 years. Using the set of currently available
theoretical gravitational waveforms, we compute upper-limit optimal
signal-to-noise ratios based on current and advanced LIGO/GEO600/VIRGO noise
curves for the recent SN 2008bk which exploded at ~3.9 Mpc. While initial LIGOs
cannot detect GWs emitted by core-collapse events at such a distance, we find
that advanced LIGO-class detectors could put significant upper limits on the GW
emission strength for such events. We study the potential occurrence of the
various GW emission processes in particular supernova explosion scenarios and
argue that the GW signatures of neutrino-driven, magneto-rotational, and
acoustically-driven core-collapse SNe may be mutually exclusive. We suggest
that even initial LIGOs could distinguish these explosion mechanisms based on
the detection (or non-detection) of GWs from a galactic core-collapse
supernova.Comment: Topical Review, accepted for publication in CQG. 51 pages, 13
figures, a version of the article with high-resolution figures is available
from http://stellarcollapse.org/papers/Ott_SN_GW_review2008.pdf. Update:
Added section on core collapse simulations and the treatment of general
relativit
Space shuttle lift-off dynamic model
Previously developed dynamic models for the calculation of lift-off dynamic response of the space shuttle vehicle can handle only response of the vehicle with eight holddown arms attached or with all holddown arms detached. The new model developed in the referenced report takes into account the transition period between holddown and lift-off by giving the model the ability to vary holddown point separation as a function of vehicle flexible body and rigid body motion. This report documents a study made to verify the new model's capability to simulate vehicle response at lift-off. To do this, a finite element model of the skirt is made and coupled to the free-free modes of the vehicle and cantilevered modes calculated and compared with the previously developed model. Results indicate that the new model will be able to predict accurate vehicle loads
Long-term impacts of tropical storms and earthquakes on human population growth in Haiti and the Dominican Republic
Since the 18th century, Haiti and the Dominican Republic have experienced similar natural forces, including earthquakes and tropical storms. These countries are two of the most prone of all Latin American and Caribbean countries to natural hazards events, while Haiti seems to be more vulnerable to natural forces. This article discusses to what extent geohazards have shaped both nation's demographic developments. The data show that neither atmospheric nor seismic forces that directly hit the territory of Haiti have significantly affected the country's population growth rates and spatial population densities. Conversely, since the 1950s more people were exposed to atmospheric hazards, in particular, in regions which historically experienced higher storm frequencies
Canonical Interacting Quantum Fields on Two-Dimensional De Sitter Space
We present the model on de Sitter space in the
canonical formulation. We discuss the role of the Noether theorem and we
provide explicit expressions for the energy-stress tensor of the interacting
model.Comment: minor correction
Two algebraic properties of thermal quantum field theories
We establish the Schlieder and the Borchers property for thermal field
theories. In addition, we provide some information on the commutation and
localization properties of projection operators.Comment: plain tex, 14 page
Pore formation in fluctuating membranes
We study the nucleation of a single pore in a fluctuating lipid membrane,
specifically taking into account the membrane fluctuations, as well as the
shape fluctuations of the pore. For large enough pores, the nucleation free
energy is well-described by shifts in the effective membrane surface tension
and the pore line tension. Using our framework, we derive the stability
criteria for the various pore formation regimes. In addition to the well-known
large-tension regime from the classical nucleation theory of pores, we also
find a low-tension regime in which the effective line and surface tensions can
change sign from their bare values. The latter scenario takes place at
sufficiently high temperatures, where the opening of a stable pore of finite
size is entropically favorable.Comment: 9 pages, 3 figure
The Progenitor Dependence of the Preexplosion Neutrino Emission in Core-Collapse Supernovae
We perform spherically-symmetric general-relativistic simulations of core
collapse and the postbounce preexplosion phase in 32 presupernova stellar
models of solar metallicity with zero-age-main-sequence masses of 12 M_{sun} to
120 M_{sun}. Using energy-dependent three-species neutrino transport in the
two-moment approximation with an analytic closure, we show that the emitted
neutrino luminosities and spectra follow very systematic trends that are
correlated with the compactness (~M/R) of the progenitor star's inner regions
via the accretion rate in the preexplosion phase. We find that these
qualitative trends depend only weakly on the nuclear equation of state, but
quantitative observational statements will require independent constraints on
the equation of state and the rotation rate of the core as well as a more
complete understanding of neutrino oscillations. We investigate the simulated
response of water Cherenkov detectors to the electron antineutrino fluxes from
our models and find that the large statistics of a galactic core collapse event
may allow robust conclusions on the inner structure of the progenitor star.Comment: 16 emulateapj pages, 10 figures, 1 table. matches published versio
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