8,780 research outputs found
Nuclear radiation problems, unmanned thermionic reactor ion propulsion spacecraft
A nuclear thermionic reactor as the electric power source for an electric propulsion spacecraft introduces a nuclear radiation environment that affects the spacecraft configuration, the use and location of electrical insulators and the science experiments. The spacecraft is conceptually configured to minimize the nuclear shield weight by: (1) a large length to diameter spacecraft; (2) eliminating piping penetrations through the shield; and (3) using the mercury propellant as gamma shield. Since the alumina material is damaged by the high nuclear radiation environment in the reactor it is desirable to locate the alumina insulator outside the reflector or develop a more radiation resistant insulator
Development of a polysilicon process based on chemical vapor deposition (phase 1)
A dichlorosilane-based reductive chemical vapor deposition (CVD) process demonstrated is capable of producing, at low cost, high quality polycrystalline silicon. Testing of decomposition reactor heat shields to insure that the shield provides adequate personnel protection assuming a worst case explosion was completed. Minor modifications to a production reactor heat shield provided adequate heat shield integrity. Construction of the redesigned PDU (Process Development Unit) to accommodate all safety related information proceeded on schedule. Structural steel work was completed as is the piping and instrumentation design work. Major pieces of process equipment were received and positioned in the support structure and all transfer piping and conduits to the PDU were installed. Construction was completed on a feed system for supplying DCS to an intermediate sized reactor. The feed system was successfully interfaced with a reactor equipped with a modified heat shield. Reactor checkout was completed
On some singularities of the correlation functions that determine neutrino opacities
Certain perturbation graphs in the calculation of the effects of the medium
on neutrino scattering in supernova matter have a nonintegrable singularity in
a physical region. A number of papers have addressed the apparent pathology
through an ansatz that invokes higher order (rescattering) effects. Taking the
Gamow-Teller terms as an example, we display an expression for the spin-spin
correlation function that determines the cross-sections. It is clear from the
form that there are no pathologies in the order by order perturbation
expansion. Explicit formulae are given for a simple case, leading to an answer
that is very different from one given by other authors.Comment: 8 page
Elevated temperature fatigue of TZC MOLYBDENUM alloy under high frequency and high vacuum conditions
Elevated temperature fatigue of TZC molybdenum alloy determined in high frequency and high vacuum test
A Self-Consistent Approach to Neutral-Current Processes in Supernova Cores
The problem of neutral-current processes (neutrino scattering, pair emission,
pair absorption, axion emission, \etc) in a nuclear medium can be separated
into an expression representing the phase space of the weakly interacting
probe, and a set of dynamic structure functions of the medium. For a
non-relativistic medium we reduce the description to two structure functions
S_A(\o) and S_V(\o) of the energy transfer, representing the axial-vector
and vector interactions. is well determined by the single-nucleon
approximation while may be dominated by multiply interacting nucleons.
Unless the shape of S_A(\o) changes dramatically at high densities,
scattering processes always dominate over pair processes for neutrino transport
or the emission of right-handed states. Because the emission of right-handed
neutrinos and axions is controlled by the same medium response functions, a
consistent constraint on their properties from consideration of supernova
cooling should use the same structure functions for both neutrino transport and
exotic cooling mechanisms.Comment: 33 pages, Te
Stabilization of premixed combustors
In order to attain a sufficiently good insight into the fluid mechanical processes taking place in combustors operating on premixed, prevaporized, and preheated gases, an experimental facility was developed where the flow field is tractable both experimentally and analytically. The configuration adopted for the initial stage of the study is based on the use of a step to stabilized the combustion zone. The primary purpose of the experimental apparatus is to provide a facility for studying the effects of the elementary fluid mechanical processes on the stability of a model combustion system in order to further the understanding of the intrinsic mechanism of nonsteady phenomena, rather than to provide criteria for unstable operation of combustors, as expressed by overall performance parameters, such as the blowout and flashback limits
Evolution of Protoneutron Stars
We study the thermal and chemical evolution during the Kelvin-Helmholtz phase
of the birth of a neutron star, employing neutrino opacities that are
consistently calculated with the underlying equation of state (EOS).
Expressions for the diffusion coefficients appropriate for general relativistic
neutrino transport in the equilibrium diffusion approximation are derived. The
diffusion coefficients are evaluated using a field-theoretical finite
temperature EOS that includes the possible presence of hyperons. The variation
of the diffusion coefficients is studied as a function of EOS and compositional
parameters. We present results from numerical simulations of protoneutron star
cooling for internal stellar properties as well as emitted neutrino energies
and luminosities. We discuss the influence of the initial stellar model, the
total mass, the underlying EOS, and the addition of hyperons on the evolution
of the protoneutron star and upon the expected signal in terrestrial detectors.Comment: 67 pages, 25 figure
Spin susceptibility of neutron matter at zero temperature
The Auxiliary Field Diffusion Monte Carlo method is applied to compute the
spin susceptibility and the compressibility of neutron matter at zero
temperature. Results are given for realistic interactions which include both a
two-body potential of the Argonne type and the Urbana IX three-body potential.
Simulations have been carried out for about 60 neutrons. We find an overall
reduction of the spin susceptibilty by about a factor 3 with respect to the
Pauli susceptibility for a wide range of densities. Results for the
compressibility of neutron matter are also presented and compared with other
available estimates obtained for semirealistic nucleon-nucleon interactions by
using other techniques
State permutations from manipulation of near level-crossings
We discuss some systematic methods for implementing state manipulations in
systems formally similar to chains of a few spins with nearest-neighbor
interactions, arranged such that there are strong and weak scales of coupling
links. States are permuted by means of bias potentials applied to a few
selected sites. This generic structure is then related to an atoms-in-a-cavity
model that has been proposed in the literature as a way of achieving a
decoherence free subspace. A new method using adiabatically varying laser
detuning to implement a CNOT gate in this model is proposed.Comment: 6 pages, 5 figures. Substantial revision and extension of the
introduction and the atoms-in-a-cavity section
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