48,626 research outputs found
Complete relativistic equation of state for neutron stars
We construct the equation of state (EOS) in a wide density range for neutron
stars using the relativistic mean field theory. The properties of neutron star
matter with both uniform and non-uniform distributions are studied
consistently. The inclusion of hyperons considerably softens the EOS at high
densities. The Thomas-Fermi approximation is used to describe the non-uniform
matter, which is composed of a lattice of heavy nuclei. The phase transition
from uniform matter to non-uniform matter occurs around ,
and the free neutrons drip out of nuclei at about $2.4 \times 10^{-4}\
\rm{fm^{-3}}$. We apply the resulting EOS to investigate the neutron star
properties such as maximum mass and composition of neutron stars.Comment: 23 pages, REVTeX, 9 ps figures, to appear in Phys. Rev.
Data acquisition and path selection decision making for an autonomous roving vehicle
Problems related to the guidance of an autonomous rover for unmanned planetary exploration were investigated. Topics included in these studies were: simulation on an interactive graphics computer system of the Rapid Estimation Technique for detection of discrete obstacles; incorporation of a simultaneous Bayesian estimate of states and inputs in the Rapid Estimation Scheme; development of methods for estimating actual laser rangefinder errors and their application to date provided by Jet Propulsion Laboratory; and modification of a path selection system simulation computer code for evaluation of a hazard detection system based on laser rangefinder data
Spin-bias driven magnetization reversal and nondestructive detection in a single molecular magnet
The magnetization reversal in a single molecular magnet (SMM) weakly coupled
to an electrode with spin-dependent splitting of chemical potentials (spin
bias) is theoretically investigated by means of the rate equation. A
microscopic mechanism for the reversal is demonstrated by the avalanche
dynamics at the reversal point. The magnetization as a function of the spin
bias shows hysteresis loops tunable by the gate voltage and varying with
temperature. The nondestructive measurement to the orientation of giant spin in
SMM is presented by measuring the fully polarized electric current in the
response to a small spin bias. For Mnac molecule, its small transverse
anisotropy only slightly violates the results above. The situation when there
is an angle between the easy axis of the SMM and the spin quantization
direction of the electrode is also studied.Comment: 17 pages, 12 figure
Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration
Problems related to an unmanned exploration of the planet Mars by means of an autonomous roving planetary vehicle are investigated. These problems include: design, construction and evaluation of the vehicle itself and its control and operating systems. More specifically, vehicle configuration, dynamics, control, propulsion, hazard detection systems, terrain sensing and modelling, obstacle detection concepts, path selection, decision-making systems, and chemical analyses of samples are studied. Emphasis is placed on development of a vehicle capable of gathering specimens and data for an Augmented Viking Mission or to provide the basis for a Sample Return Mission
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