18,808 research outputs found
Black hole formation in core-collapse supernovae and time-of-flight measurements of the neutrino masses
In large stars that have exhausted their nuclear fuel, the stellar core collapses to a hot and dense proto-neutron star that cools by the radiation of neutrinos and antineutrinos of all flavors. Depending on its final mass, this may become either a neutron star or a black hole. Black hole formation may be triggered by mass accretion or a change in the high-density equation of state. We consider the possibility that black hole formation happens when the flux of neutrinos is still measurably high. If this occurs, then the neutrino signal from the supernova will be terminated abruptly (the transition takes ≲0.5 ms). The properties and duration of the signal before the cutoff are important measures of both the physics and astrophysics of the cooling proto-neutron star. For the event rates expected in present and proposed detectors, the cutoff will generally appear sharp, thus allowing model-independent time-of-flight mass tests for the neutrinos after the cutoff. If black hole formation occurs relatively early, within a few (∼1) seconds after core collapse, then the expected luminosities are of order LBH=1052 erg/s per flavor. In this case, the neutrino mass sensitivity can be extraordinary. For a supernova at a distance D=10 kpc, SuperKamiokande can detect a ν̅e mass down to 1.8 eV by comparing the arrival times of the high-energy and low-energy neutrinos in ν̅e+p→e++n. This test will also measure the cutoff time, and will thus allow a mass test of νμ and ντ relative to ν̅e. Assuming that νμ and ντ are nearly degenerate, as suggested by the atmospheric neutrino results, masses down to about 6 eV can be probed with a proposed lead detector of mass MD=4 kton (OMNIS). Remarkably, the neutrino mass sensitivity scales as (D/LBHMD)1/2. Therefore, direct sensitivity to all three neutrino masses in the interesting few-eV range is realistically possible; there are no other known techniques that have this capability
Post Big Bang Processing of the Primordial Elements
We explore the Gnedin-Ostriker suggestion that a post-Big-Bang
photodissociation process may modify the primordial abundances of the light
elements. We consider several specific models and discuss the general features
that are necessary (but not necessarily sufficient) to make the model work. We
find that with any significant processing, the final D and He abundances,
which are independent of their initial standard big bang nucleosynthesis (SBBN)
values, rise quickly to a level several orders of magnitude above the
observationally inferred primordial values. Solutions for specific models show
that the only initial abundances that can be photoprocessed into agreement with
observations are those that undergo virtually no processing and are already in
agreement with observation. Thus it is unlikely that this model can work for
any non-trivial case unless an artificial density and/or photon distribution is
invoked.Comment: 12 page Latex file (AASTEX style). Tarred, gzipped, and uuencoded
postscript files of seven figures. Also available (with ps file of paper) at
ftp://www-physics.mps.ohio-state.edu/pub/nucex/phot
Parametric down-conversion from a wave-equations approach: geometry and absolute brightness
Using the approach of coupled wave equations, we consider spontaneous
parametric down-conversion (SPDC) in the narrow-band regime and its
relationship to classical nonlinear processes such as sum-frequency generation.
We find simple expressions in terms of mode overlap integrals for the absolute
pair production rate into single spatial modes, and simple relationships
between the efficiencies of the classical and quantum processes. The results,
obtained with Green function techniques, are not specific to any geometry or
nonlinear crystal. The theory is applied to both degenerate and non-degenerate
SPDC. We also find a time-domain expression for the correlation function
between filtered signal and idler fields.Comment: 10 pages, no figure
Advances in serpentine geoecology: A retrospective
(In absence of a text abstract the first paragraph of the paper is provided.)
Serpentine habitats have long provided model settings for geoecological research (reviewed in Alexander et al. 2007, Brady et al. 2005, Brooks 1987, Kazakou et al. 2008, Kruckeberg 1984, Proctor and Woodell 1975, Raja-karuna et al 2009). Serpentine loosely refers to a broad group of minerals associated with the weathering of ultramafi c (high iron and magnesium-rich) rocks found along continental margins and orogenic belts. Soils associated with such rocks often differ from more widespread soils, being less fertile and having high concentrations of some heavy metals. The unique geochem-istry of serpentine soils generates habitats worldwide that are biologically unique, providing model settings for research on how geology and soils can shape the biotic world around us
Nonlinear switching and solitons in PT-symmetric photonic systems
One of the challenges of the modern photonics is to develop all-optical
devices enabling increased speed and energy efficiency for transmitting and
processing information on an optical chip. It is believed that the recently
suggested Parity-Time (PT) symmetric photonic systems with alternating regions
of gain and loss can bring novel functionalities. In such systems, losses are
as important as gain and, depending on the structural parameters, gain
compensates losses. Generally, PT systems demonstrate nontrivial
non-conservative wave interactions and phase transitions, which can be employed
for signal filtering and switching, opening new prospects for active control of
light. In this review, we discuss a broad range of problems involving nonlinear
PT-symmetric photonic systems with an intensity-dependent refractive index.
Nonlinearity in such PT symmetric systems provides a basis for many effects
such as the formation of localized modes, nonlinearly-induced PT-symmetry
breaking, and all-optical switching. Nonlinear PT-symmetric systems can serve
as powerful building blocks for the development of novel photonic devices
targeting an active light control.Comment: 33 pages, 33 figure
The effect of composition on the mechanism of stress-corrosion cracking of titanium alloys in nitrogen tetroxide, and aqueous and hot- salt environments Annual summary report, 1 May 1967 - 30 Apr. 1968
Stress corrosion data for titanium alloys in aqueous, hot salt, and nitrogen dioxide environment
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