35,421 research outputs found
A Linear Approximation for the Excitation Energies of single and double analog states in the f_{7/2} shell
We find that the excitation energies of single analog states for odd-even
nuclei in the f shell with J=j=7/2 and the J=0 double
analog states in the even-even nuclei are well described by the formulas
and ,respectively,
where is usually the ground state isospin. It is remarkable
to note that the parameter X accounts for the departures from the symmetry
energy based predictions.Comment: 8 pages and no figure
Development and application of the GIM code for the Cyber 203 computer
The GIM computer code for fluid dynamics research was developed. Enhancement of the computer code, implicit algorithm development, turbulence model implementation, chemistry model development, interactive input module coding and wing/body flowfield computation are described. The GIM quasi-parabolic code development was completed, and the code used to compute a number of example cases. Turbulence models, algebraic and differential equations, were added to the basic viscous code. An equilibrium reacting chemistry model and implicit finite difference scheme were also added. Development was completed on the interactive module for generating the input data for GIM. Solutions for inviscid hypersonic flow over a wing/body configuration are also presented
Development of the general interpolants method for the CYBER 200 series of supercomputers
The General Interpolants Method (GIM) is a 3-D, time-dependent, hybrid procedure for generating numerical analogs of the conservation laws. This study is directed toward the development and application of the GIM computer code for fluid dynamic research applications as implemented for the Cyber 200 series of supercomputers. An elliptic and quasi-parabolic version of the GIM code are discussed. Turbulence models, algebraic and differential equations, were added to the basic viscous code. An equilibrium reacting chemistry model and an implicit finite difference scheme are also included
A Planck-like problem for quantum charged black holes
Motivated by the parallelism existing between the puzzles of classical
physics at the beginning of the XXth century and the current paradoxes in the
search of a quantum theory of gravity, we give, in analogy with Planck's black
body radiation problem, a solution for the exact Hawking flux of evaporating
Reissner-Nordstrom black holes. Our results show that when back-reaction
effects are fully taken into account the standard picture of black hole
evaporation is significantly altered, thus implying a possible resolution of
the information loss problem.Comment: 6 pages, LaTeX file, Awarded Fifth Prize in the Gravity Research
Foundation Essay Competition for 200
The star-formation history of the universe - an infrared perspective
A simple and versatile parameterized approach to the star formation history
allows a quantitative investigation of the constraints from far infrared and
submillimetre counts and background intensity measurements.
The models include four spectral components: infrared cirrus (emission from
interstellar dust), an M82-like starburst, an Arp220-like starburst and an AGN
dust torus. The 60 m luminosity function is determined for each chosen
rate of evolution using the PSCz redshift data for 15000 galaxies. The
proportions of each spectral type as a function of 60 m luminosity are
chosen for consistency with IRAS and SCUBA colour-luminosity relations, and
with the fraction of AGN as a function of luminosity found in 12 m
samples. The luminosity function for each component at any wavelength can then
be calculated from the assumed spectral energy distributions. With assumptions
about the optical seds corresponding to each component and, for the AGN
component, the optical and near infrared counts can be accurately modelled.
A good fit to the observed counts at 0.44, 2.2, 15, 60, 90, 175 and 850
m can be found with pure luminosity evolution in all 3 cosmological models
investigated: = 1, = 0.3 ( = 0), and
= 0.3, = 0.7.
All 3 models also give an acceptable fit to the integrated background
spectrum. Selected predictions of the models, for example redshift
distributions for each component at selected wavelengths and fluxes, are shown.
The total mass-density of stars generated is consistent with that observed,
in all 3 cosmological models.Comment: 20 pages, 25 figures. Accepted for publication in ApJ. Full details
of models can be found at http://astro.ic.ac.uk/~mrr/countmodel
Shell-model test of the rotational-model relation between static quadrupole moments Q(2^+_1), B(E2)'s, and orbital M1 transitions
In this work, we examine critically the relation between orbital magnetic
dipole (scissors mode) strength and quadrupole deformation properties. Assuming
a simple K=0 ground state band in an even-even nucleus, the quantities Q(2^+_1)
(i.e., the static quadrupole moment) and B(E2)_{0_1 \to 2_1} both are described
by a single parameter--the intrinsic quadrupole moment Q_0. In the shell model,
we can operationally define Q_0(Static) and Q_0(BE2) and see if they are the
same. Following a brief excursion to the sd shell, we perform calculations in
the fp shell. The nuclei we consider ({44,46,48}Ti and {48,50}Cr) are far from
being perfect rotors, but we find that the calculated ratio
Q_0(Static)/Q_0(BE2) is in many cases surprisingly close to one. We also
discuss the collectivity of orbital magnetic dipole transitions. We find that
the large orbital B(M1) strength in {44}Ti relative to {46}Ti and {48}Ti cannot
be explained by simple deformation arguments.Comment: 12 pages, RevTeX4. Sections II (Quadrupole properties in the
sd-shell) and V (Random interaction studies) added. Minor changes throughout
the text and 48Cr added to present Table IV, as well as results for the
lowest 100 state
Graviton-Graviton Scattering, Bel-Robinson and Energy (Pseudo)-Tensors
Motivated by recent work involving the graviton-graviton tree scattering
amplitude, and its twin descriptions as the square of the Bel-Robinson tensor,
B_{\m\n\a\b}, and as the "current-current interaction" square of
gravitational energy pseudo-tensors t_{\a\b},we find an exact tensor-square
root equality B_{\mn\a\b} = \pa^2_\mn t_{\a\b}, for a combination of Einstein
and Landau-Lifschitz t_\ab, in Riemann normal coordinates. In the process, we
relate, on-shell, the usual superpotential basis for classifying pseudo-tensors
with one spanned by polynomials in the curvature.Comment: 7 page
Review of some classical gravitational superenergy tensors using computational techniques
We use computational algorithms recently developed by us to study completely
four index divergence free quadratic in Riemann tensor polynomials in GR. Some
results are new and some other reproduce and/or correct known ones. The
algorithms are part of a Mathematica package called Tools of Tensor Calculus
(TTC)[web address: http://baldufa.upc.es/ttc
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