91,940 research outputs found
The Gentlest Ascent Dynamics
Dynamical systems that describe the escape from the basins of attraction of
stable invariant sets are presented and analyzed. It is shown that the stable
fixed points of such dynamical systems are the index-1 saddle points.
Generalizations to high index saddle points are discussed. Both gradient and
non-gradient systems are considered. Preliminary results on the nature of the
dynamical behavior are presented
Arc-cathode interaction study
Insufficient electrode life and uncertainties in that life are major problems hampering the development in many plasma application areas which make use of plasma torches, arc heaters, and arc jet thrusters. In spite of a considerable amount of work published dealing with arc-cathode phenomena, our present understanding is still incomplete because different physical phenomena dominate for different combinations of experimental parameters. The objective of our present research project is to gain a better understanding of the behavior of arc-cathode surface interaction over a wide range of parameters, and furthermore to develop guidelines for better thermal design of the electrode and the selection of materials. This report will present the research results and progress obtained on the arc-cathode interaction studies at the University of Minnesota. It includes results which have been obtained under programs other than the NASA funded program. Some of the results have been submitted in an informal interim progress report, and all of the results have been presented in a seminar during a visit to the NASA Lewis Research Center on October 16, 1992
Conditions for Nondistortion Interrogation of Quantum System
Under some physical considerations, we present a universal formulation to
study the possibility of localizing a quantum object in a given region without
disturbing its unknown internal state. When the interaction between the object
and probe wave function takes place only once, we prove the necessary and
sufficient condition that the object's presence can be detected in an initial
state preserving way. Meanwhile, a conditioned optimal interrogation
probability is obtained.Comment: 5 pages, Revtex, 1 figures, Presentation improved, corollary 1 added.
To appear in Europhysics Letter
Spin-3/2 baryons from an anisotropic lattice QCD action
The mass spectrum of baryons in the spin-3/2 sector is computed in quenched
lattice QCD using a tadpole-improved anisotropic action. Both isospin 1/2 and
3/2 (the traditional decuplet) are considered, as well as members that contain
strange quarks. States with positive and negative parities are isolated by
parity projection, while states with spin-3/2 and spin-1/2 are separated by
spin projection. The extent to which spin projection is needed is examined. The
issue of optimal interpolating field is also investigated. The results are
discussed in relation to previous calculations and experiment.Comment: modified version to appear in Phys Rev
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