9,078 research outputs found
Differences between stellar and laboratory reaction cross sections
Nuclear reactions proceed differently in stellar plasmas than in the
laboratory due to the thermal effects in the plasma. On one hand, a target
nucleus is bombarded by projectiles distributed in energy with a distribution
defined by the plasma temperature. The most relevant energies are low by
nuclear physics standards and thus require an improved description of
low-energy properties, such as optical potentials, required for the calculation
of reaction cross sections. Recent studies of low-energy cross sections suggest
the necessity of a modification of the proton optical potential. On the other
hand, target nuclei are in thermal equilibrium with the plasma and this
modifies their reaction cross sections. It is generally expected that this
modification is larger for endothermic reactions. We show that there are many
exceptions to this rule.Comment: 4 pages, Proceedings of Nuclear Physics in Astrophysics 4, Frascati,
Italy; to appear in J. Phys. Conf. Serie
Guidance methods for low-thrust space vehicles Cumulative progress report, 1 Jan. 1969 - 31 Jan. 1970
Guidance and control schemes for optimal low-thrust Earth-Mars transfer mission
Electrostatic Analyzer for 1.5-Mev Protons
A system for analyzing the ion beam of an electrostatic generator is described. A weak magnetic field separates protons from heavier components and a 90° electrostatic deflection gives the required energy resolution. With the analyzer controlling the generator voltage, a proton beam of one microampere with an energy spread of the order of 300 volts in one million is obtained
First order control for low-thrust interplanetary vehicles
First order control for low thrust interplanetary vehicles based on calculus of variations and Weierstrass E-functio
Simple models for the shuttle remote manipulator system
The investigation is aimed at establishing a series of simple models which can be used to study the forces and moments which occur due to the reaction control system (RCS) jet plume firings during a deployment or retrieval of an IUS type payload. The models considered in this investigation are primarily planar in nature. In this study primary attention is given to the roles the payload play in determining the overall moments on the remote manipulator system arm
Variability Flagging in the Wide-field Infrared Survey Explorer Preliminary Data Release
The Wide-field Infrared Survey Explorer Preliminary Data Release Source Catalog contains over 257 million objects. We describe the method used to flag variable source candidates in the Catalog. Using a method based on the chi-square of single-exposure flux measurements, we generated a variability flag for each object, and have identified almost 460,000 candidate sources that exhibit significant flux variability with greater than ~7σ confidence. We discuss the flagging method in detail and describe its benefits and limitations. We also present results from the flagging method, including example light curves of several types of variable sources including Algol-type eclipsing binaries, RR Lyr, W UMa, and a blazar candidate
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