25,595 research outputs found
A covariant gauge-invariant three-dimensional description of relativistic bound-states
A formalism is presented which allows covariant three-dimensional bound-state
equations to be derived systematically from four-dimensional ones without the
use of delta-functions. The amplitude for the interaction of a bound state
described by these equations with an electromagnetic probe is constructed. This
amplitude is shown to be gauge invariant if the formalism is truncated at the
same coupling-constant order in both the interaction kernel of the integral
equation and the electromagnetic current operator.Comment: 17 pages, RevTeX, uses BoxedEPS.te
Surgery description of colored knots
The pair (K,r) consisting of a knot K and a surjective map r from the knot
group onto a dihedral group is said to be a p-colored knot. D. Moskovich
conjectured that for any odd prime p there are exactly p equivalence classes of
p-colored knots up to surgery along unknots in the kernel of the coloring. We
show that there are at most 2p equivalence classes. This is a vast improvement
upon the previous results by Moskovich for p=3, and 5, with no upper bound
given in general. T. Cochran, A. Gerges, and K. Orr, in "Dehn surgery
equivalence relations of 3-manifolds", define invariants of the surgery
equivalence class of a closed 3-manifold M in the context of bordisms. By
taking M to be 0-framed surgery of the 3-sphere along K we may define
Moskovich's colored untying invariant in the same way as the Cochran-Gerges-Orr
invariants. This bordism definition of the colored untying invariant will be
then used to establish the upper bound.Comment: 41 pages, 23 figures (Version 3) Minor revisions and typos fixed.
Proofs of Propositions 4.1 and 4.8 revise
Possible application of remote-sensing techniques and satellite communications for earthquake studies
Passive and active remote sensing techniques used with satellite communication for earthquake studie
NOSS/ALDCS analysis and system requirements definition
The results of system analyses and implementation studies of an advanced location and data collection system (ALDCS) , proposed for inclusion on the National Oceanic Satellite System (NOSS) spacecraft are reported. The system applies Doppler processing and radiofrequency interferometer position location technqiues both alone and in combination. Aspects analyzed include: the constraints imposed by random access to the system by platforms, the RF link parameters, geometric concepts of position and velocity estimation by the two techniques considered, and the effects of electrical measurement errors, spacecraft attitude errors, and geometric parameters on estimation accuracy. Hardware techniques and trade-offs for interferometric phase measurement, ambiguity resolution and calibration are considered. A combined Doppler-interferometer ALDCS intended to fulfill the NOSS data validation and oceanic research support mission is also described
Analysis of Meteorological Satellite location and data collection system concepts
A satellite system that employs a spaceborne RF interferometer to determine the location and velocity of data collection platforms attached to meteorological balloons is proposed. This meteorological advanced location and data collection system (MALDCS) is intended to fly aboard a low polar orbiting satellite. The flight instrument configuration includes antennas supported on long deployable booms. The platform location and velocity estimation errors introduced by the dynamic and thermal behavior of the antenna booms and the effects of the presence of the booms on the performance of the spacecraft's attitude control system, and the control system design considerations critical to stable operations are examined. The physical parameters of the Astromast type of deployable boom were used in the dynamic and thermal boom analysis, and the TIROS N system was assumed for the attitude control analysis. Velocity estimation error versus boom length was determined. There was an optimum, minimum error, antenna separation distance. A description of the proposed MALDCS system and a discussion of ambiguity resolution are included
The GPRIME approach to finite element modeling
GPRIME, an interactive modeling system, runs on the CDC 6000 computers and the DEC VAX 11/780 minicomputer. This system includes three components: (1) GPRIME, a user friendly geometric language and a processor to translate that language into geometric entities, (2) GGEN, an interactive data generator for 2-D models; and (3) SOLIDGEN, a 3-D solid modeling program. Each component has a computer user interface of an extensive command set. All of these programs make use of a comprehensive B-spline mathematics subroutine library, which can be used for a wide variety of interpolation problems and other geometric calculations. Many other user aids, such as automatic saving of the geometric and finite element data bases and hidden line removal, are available. This interactive finite element modeling capability can produce a complete finite element model, producing an output file of grid and element data
Do the electromagnetic fields generated by mobile-phone base-stations have short-term effects on health? A response to commentaries
An \emph{ab initio} method for locating characteristic potential energy minima of liquids
It is possible in principle to probe the many--atom potential surface using
density functional theory (DFT). This will allow us to apply DFT to the
Hamiltonian formulation of atomic motion in monatomic liquids [\textit{Phys.
Rev. E} {\bf 56}, 4179 (1997)]. For a monatomic system, analysis of the
potential surface is facilitated by the random and symmetric classification of
potential energy valleys. Since the random valleys are numerically dominant and
uniform in their macroscopic potential properties, only a few quenches are
necessary to establish these properties. Here we describe an efficient
technique for doing this. Quenches are done from easily generated "stochastic"
configurations, in which the nuclei are distributed uniformly within a
constraint limiting the closeness of approach. For metallic Na with atomic pair
potential interactions, it is shown that quenches from stochastic
configurations and quenches from equilibrium liquid Molecular Dynamics (MD)
configurations produce statistically identical distributions of the structural
potential energy. Again for metallic Na, it is shown that DFT quenches from
stochastic configurations provide the parameters which calibrate the
Hamiltonian. A statistical mechanical analysis shows how the underlying
potential properties can be extracted from the distributions found in quenches
from stochastic configurations
Mercury in the environment
Problems in assessing mercury concentrations in environmental materials are discussed. Data for situations involving air, water, rocks, soils, sediments, sludges, fossil fuels, plants, animals, foods, and man are drawn together and briefly evaluated. Details are provided regarding the toxicity of mercury along with tentative standards and guidelines for mercury in air, drinking water, and food
- …