457 research outputs found
Numerical implications of stabilization by the use of integrals
Liapunov or energy restraint methods for dynamic stabilization in two body motion perturbation problems are considered. Results of computerized orbital stabilization estimates show that the application of energy restraint prevents the occurrence of consistent timing errors in the stepwise integration of equations of motion for a nearly circular orbit
LAMMR world data base documentation support and demonstrations
The primary purpose of the World Surface Map is to provide the LAMMR subsystem with world surface type classifications that are used to set up LAMMR LEVEL II process control. This data base will be accessed solely by the LAMMR subsystem. The SCATT and ALT subsystems will access the data base indirectly through the T sub b (Brightness Temperature) Data Bank, where the surface types were updated from a priori to current classification, and where the surface types were organized on an orbital subtrack basis. The single most important factor in the design of the World Surface Maps is the ease of access to the information while the complexity of generating these maps is of lesser importance because their generation is a one-time, off-line process. The World Surface Map provides storage of information with a resolution of 7 km necessary to set flags concerning the earth's features with a different set of maps for each month of the year
Context sensitive formulations of antenna pattern correction and side lobe compensation for NOSS/LAMMR real time processing
Large antenna multi-channel microwave radiometer (LAMMR) software specifications were written for LAMMR ground processing. There is a need to determine more computationally-efficient antenna temperature correction methods in compensating side lobe contributions especially near continents, islands and weather fronts. One of the major conclusions was that the antenna pattern corrections (APC) processes did not accomplish the implied goals of compensating for the antenna side lobe influences on brightness temperature. A-priori knowledge of land/water locations was shown to be needed and had to be incorporated in a context sensitive APC process if the artifacts caused by land presence is to be avoided. The high temperatures in land regions can severely bias the lower ocean response
An information adaptive system study report and development plan
The purpose of the information adaptive system (IAS) study was to determine how some selected Earth resource applications may be processed onboard a spacecraft and to provide a detailed preliminary IAS design for these applications. Detailed investigations of a number of applications were conducted with regard to IAS and three were selected for further analysis. Areas of future research and development include algorithmic specifications, system design specifications, and IAS recommended time lines
Active-Sterile neutrino oscillations and BBN+CMBR constraints
We show how active-sterile neutrino oscillations in the early Universe can
play an interesting role in explaining the current observations of CMBR
anisotropies and light element abundances. We describe different possible
phenomenological scenarios in the interpretation of present data and how
active-sterile neutrino oscillations can provide a viable theoretical
framework.Comment: Some changes, to appear in Phys. Rev.
Molecular hydrogen adsorbed on benzene: insights from a quantum Monte Carlo study
We present a quantum Monte Carlo study of the hydrogen-benzene system where
binding is very weak. We demonstrate that the binding is well described at both
variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC) levels by a
Jastrow correlated single determinant geminal wave function with an optimized
compact basis set that includes diffuse orbitals. Agreement between VMC and
fixed-node DMC binding energies is found to be within 0.18 mHa, suggesting the
calculations are well-converged with respect to the basis. Essentially the same
binding is also found in independent DMC calculations using a different trial
wave function of a more conventional Slater-Jastrow form, supporting our
conclusion that the binding energy is accurate and includes all effects of
correlation. We compare with empirical models and previous calculations, and we
discuss the physical mechanisms of the interaction, the role of diffuse basis
functions, and the charge redistribution in the bond.Comment: 12 pages, 4 figure
Molecular dynamics study of melting of a bcc metal-vanadium II : thermodynamic melting
We present molecular dynamics simulations of the thermodynamic melting
transition of a bcc metal, vanadium using the Finnis-Sinclair potential. We
studied the structural, transport and energetic properties of slabs made of 27
atomic layers with a free surface. We investigated premelting phenomena at the
low-index surfaces of vanadium; V(111), V(001), and V(011), finding that as the
temperature increases, the V(111) surface disorders first, then the V(100)
surface, while the V(110) surface remains stable up to the melting temperature.
Also, as the temperature increases, the disorder spreads from the surface layer
into the bulk, establishing a thin quasiliquid film in the surface region. We
conclude that the hierarchy of premelting phenomena is inversely proportional
to the surface atomic density, being most pronounced for the V(111) surface
which has the lowest surface density
Update on neutrino mixing in the early Universe
From the current cosmological observations of CMB and nuclear abundances we
show, with an analytic procedure, that the total effective number of extra
neutrino species . We also describe the possible
signatures of non standard effects that could be revealed in future CMB
observations. This cosmological information is then applied to neutrino mixing
models. Taking into account the recent results from the SNO and SuperKamiokande
experiments, disfavouring pure active to sterile neutrino oscillations, we show
that all 4 neutrino mixing models, both of 2+2 and 3+1 type, lead to a full
thermalization of the sterile neutrino flavor. Moreover such a sterile neutrino
production excludes the possibility of an electron neutrino asymmetry
generation and we conclude that , in
disagreement with the cosmological bound. This result is valid under the
assumption that the initial neutrino asymmetries are small. We suggest the
existence of a second sterile neutrino flavor, with mixing properties such to
generate a large electron neutrino asymmetry, as a possible way out.Comment: 29 pages, 3 figures; to appear on Phys.Rev.D; added discussion (at
page 19) and references; typos correcte
The Effect of Bound Dineutrons upon BBN
We have examined the effects of a bound dineutron, n2, upon big bang
nucleosynthesis (BBN) as a function of its binding energy B_n2. We find a
weakly bound dineutron has little impact but as B_n2 increases its presence
begins to alter the flow of free nucleons to helium-4. Due to this disruption,
and in the absence of changes to other binding energies or fundamental
constants, BBN sets a reliable upper limit of B_n2 <~ 2.5 MeV in order to
maintain the agreement with the observations of the primordial helium-4 mass
fraction and D/H abundance
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