8,289 research outputs found
Science aspects of 1980 ballistic missions to comet Encke, using Mariner and Pioneer spacecraft
Science aspects of a 1980 spacecraft reconnaissance of Comet Encke are considered. The mission discussed is a ballistic flyby (more exactly, a fly-through) of P/Encke, using either a spin stabilized spacecraft, without despin of instruments, or a 3-axis stabilized spacecraft
Scientific possibilities of a solar electric powered rendezvous with comet Encke
The minimum scientific spacecraft instrumentation is considered that is likely to result in as complete an understanding of the composition, structure, and activity of a cometary nucleus as is possible without landing on it. The payload will also give useful results on secondary goals of a better understanding of physical processes in the inner and outer coma. Studies of composition, by means of an actual landing on the surface, details of the internal structure of the nucleus, and sample return were considered beyond the scope of this mission
Experimentally elevated testosterone in male dark-eyed juncos suppresses cell-mediated immune function of social mates and offspring
Stability and electronic structure of the complex KPtCl structure-type hydrides
The stability and bonding of the ternary complex KPtCl structure
hydrides is discussed using first principles density functional calculations.
The cohesion is dominated by ionic contributions, but ligand field effects are
important, and are responsible for the 18-electron rule. Similarities to oxides
are discussed in terms of the electronic structure. However, phonon
calculations for SrRuH also show differences, particularly in the
polarizability of the RuH octahedra. Nevertheless, the yet to be made
compounds PbRuH and BeFeH are possible ferroelectrics. The
electronic structure and magnetic properties of the decomposition product,
FeBe are reported. Implications of the results for H storage are discussed
Preliminary Reconnaissance Water Quality Survey of the Buffalo National River
In accordance with Contract No. CX 700030105, dated 12 February 1973, the University of Arkansas , Water Resources Resear ch Center is submitting a Preliminary Reconnaissance Water Quality Survey of the Buffalo National River. The Water Resources Research Center of Arkansas has supplied the necessary personnel and facil ities to perform a preliminary reconnaissance survey of the Buffalo National River of Arkansas with special emphasis placed on the establishment of both permanent and temporary benchmarks for water quality sampling. Preliminary water quality samples have been collected to make those chemical, physical, and biological analyses as defined by Mr . Roland H. Wauer and other Park Service personnel on 3 May 1973
4D, N = 1 Supersymmetry Genomics (I)
Presented in this paper the nature of the supersymmetrical representation
theory behind 4D, N = 1 theories, as described by component fields, is
investigated using the tools of Adinkras and Garden Algebras. A survey of
familiar matter multiplets using these techniques reveals they are described by
two fundamental valise Adinkras that are given the names of the cis-Valise
(c-V) and the trans-Valise (t-V). A conjecture is made that all off-shell 4D, N
= 1 component descriptions of supermultiplets are associated with two integers
- the numbers of c-V and t-V Adinkras that occur in the representation.Comment: 53 pages, 19 figures, Report-II of SSTPRS 2008 Added another chapter
for clarificatio
Semiclassical charged black holes with a quantized massive scalar field
Semiclassical perturbations to the Reissner-Nordstrom metric caused by the
presence of a quantized massive scalar field with arbitrary curvature coupling
are found to first order in \epsilon = \hbar/M^2. The DeWitt-Schwinger
approximation is used to determine the vacuum stress-energy tensor of the
massive scalar field. When the semiclassical perturbation are taken into
account, we find extreme black holes will have a charge-to-mass ratio that
exceeds unity, as measured at infinity. The effects of the perturbations on the
black hole temperature (surface gravity) are studied in detail, with particular
emphasis on near extreme ``bare'' states that might become precisely zero
temperature ``dressed'' semiclassical black hole states. We find that for
minimally or conformally coupled scalar fields there are no zero temperature
solutions among the perturbed black holes.Comment: 19 pages; 1 figure; ReVTe
Energy-Momentum Tensor of Field Fluctuations in Massive Chaotic Inflation
We study the renormalized energy-momentum tensor (EMT) of the inflaton
fluctuations in rigid space-times during the slow-rollover regime for chaotic
inflation with a mass term. We use dimensional regularization with adiabatic
subtraction and introduce a novel analytic approximation for the inflaton
fluctuations which is valid during the slow-rollover regime. Using this
approximation we find a scale invariant spectrum for the inflaton fluctuations
in a rigid space-time, and we confirm this result by numerical methods. The
resulting renormalized EMT is covariantly conserved and agrees with the
Allen-Folacci result in the de Sitter limit, when the expansion is exactly
linearly exponential in time. We analytically show that the EMT tensor of the
inflaton fluctuations grows initially in time, but saturates to the value H^2
H(0)^2, where H is the Hubble parameter and H(0) is its value when inflation
has started. This result also implies that the quantum production of light
scalar fields (with mass smaller or equal to the inflaton mass) in this model
of chaotic inflation depends on the duration of inflation and is larger than
the usual result extrapolated from the de Sitter result.Comment: revtex style, 24 pages, 6 eps figures Numerical checks added and
moduli section improve
Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity
We study the effects of magnetic fields on the evolution of differentially
rotating neutron stars, which can form in stellar core collapse or binary
neutron star coalescence. Magnetic braking and the magnetorotational
instability (MRI) both redistribute angular momentum; the outcome of the
evolution depends on the star's mass and spin. Simulations are carried out in
axisymmetry using our recently developed codes which integrate the coupled
Einstein-Maxwell-MHD equations. For initial data, we consider three categories
of differentially rotating, equilibrium configurations, which we label normal,
hypermassive and ultraspinning. Hypermassive stars have rest masses exceeding
the mass limit for uniform rotation. Ultraspinning stars are not hypermassive,
but have angular momentum exceeding the maximum for uniform rotation at the
same rest mass. We show that a normal star will evolve to a uniformly rotating
equilibrium configuration. An ultraspinning star evolves to an equilibrium
state consisting of a nearly uniformly rotating central core, surrounded by a
differentially rotating torus with constant angular velocity along magnetic
field lines, so that differential rotation ceases to wind the magnetic field.
In addition, the final state is stable against the MRI, although it has
differential rotation. For a hypermassive neutron star, the MHD-driven angular
momentum transport leads to catastrophic collapse of the core. The resulting
rotating black hole is surrounded by a hot, massive, magnetized torus
undergoing quasistationary accretion, and a magnetic field collimated along the
spin axis--a promising candidate for the central engine of a short gamma-ray
burst. (Abridged)Comment: 27 pages, 30 figure
Synthesis of the elements in stars: forty years of progress
Forty years ago Burbidge, Burbidge, Fowler, and Hoyle combined what we would now call fragmentary evidence from nuclear physics, stellar evolution and the abundances of elements and isotopes in the solar system as well as a few stars into a synthesis of remarkable ingenuity. Their review provided a foundation for forty years of research in all of the aspects of low energy nuclear experiments and theory, stellar modeling over a wide range of mass and composition, and abundance studies of many hundreds of stars, many of which have shown distinct evidence of the processes suggested by B2FH. In this review we summarize progress in each of these fields with emphasis on the most recent developments
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