242,309 research outputs found
Properties of perturbative multi-particle amplitudes in and theories
Threshold amplitudes are considered for multi-particle production in
and theories. It is found that the disappearance of tree-level
threshold amplitudes of on-shell particles producing a large number of
particles occurs in theory only for and . The one-loop
correction to the threshold amplitude for a highly virtual scalar particle
decaying into particles in an model is derived.Comment: 7 pages, LaTex, TPI-MINN-92/60-
Kolmogorov-Burgers Model for Star Forming Turbulence
The process of star formation in interstellar molecular clouds is believed to
be controlled by driven supersonic magnetohydrodynamic turbulence. We suggest
that in the inertial range such turbulence obeys the Kolmogorov law, while in
the dissipative range it behaves as Burgers turbulence developing shock
singularities. On the base of the She-Leveque analytical model we then predict
the velocity power spectrum in the inertial range to be E_k ~ k^{-1.74}. This
result reproduces the observational Larson law, ~ l^{0.74...0.76},
[Larson, MNRAS 194 (1981) 809] and agrees well with recent numerical findings
by Padoan and Nordlund [astro-ph/0011465]. The application of the model to more
general dissipative structures, with higher fractal dimensionality, leads to
better agreement with recent observational results.Comment: revised, new material added, 8 page
Atlas and zoogeography of common fishes in the Bering Sea and northeastern Pacific
The geographic and depth frequency distribution of 124 common demersal fish species in the northeastern Pacific were plotted from data on me at the Northwest and Alaska Fisheries Center (NWAFC), National Marine Fisheries Service. The data included catch records of fishes and invertebrates from 24,881 samples taken from the Chukchi Sea, throughout the Bering Sea, Aleutian Basin, Aleutian
Archipelago, and the Gulf of Alaska, and from southeastern Alaska south to southern California. Samples were collected by a number of agencies and institutions over a 30-year period (1953-83), but were primarily from NWAFC demersal
trawls. The distributions of all species with 100 or more occurrences in the data set were plotted by computer.
Distributions plotted from these data were then compared with geographic and depth-range limits given in the literature. These data provide new range extensions
(geographic, depth, or both) for 114 species. Questionable extensions are noted, the depth ranges determined for 95% of occurrences, and depths of most frequent occurrence are recorded.
Ranges of the species were classified zoogeographically, according to life zone, and with regard to the depth zone of greatest occurrence. Because most species examined have broad geographic ranges, they do not provide the best information for testing the validity of proposed zoogeographic province boundaries. Because of the location of greatest sampling effort and methods used in sampling,
most fIShes examined were eastern boreal Pacific, sublittoral-bathyal (outer shelf) species. (PDF file contains 158 pages.
The metabolism of ingested peroxides Final report, 1 May 1970 - 30 Apr. 1971
Determination of growth patterns in rats fed on balanced diets differing by the presence of either oxidized or unoxidized fa
Study made of pneumatic high pressure piping materials /10,000 psi/
Evaluations of five types of steel for use in high pressure pneumatic piping systems include tests for impact strength, tensile and yield strengths, elongation and reduction in area, field weldability, and cost. One type, AISI 4615, was selected as most advantageous for extensive use in future flight vehicles
Active joints for microrobot limbs
The authors propose an electrostatic actuator for active joints. The active joint consists of two plates, one of which is a bilayer and bent by the bimorph effect. The plates are clamped to each other at one edge. A voltage between the plates leads to a very large field at the clamp where the plates are in intimate contact, thereby producing a force large enough to pull the bent bimorph cantilever beam to the other plate. The design uses an actuator in which large electrical forces acting over a short distance are used to produce large deflections. An appealing application of this actuation principle is seen in active joints for robot arms, e.g. by attaching members to the actuator and by combining two or more active joints and members to form micro robot arms, legs and grippers
Sound separation probe
Probe separates sound waves from turbulent flow pressure fluctuations in ducted airstreams by using principle that sound waves and turbulent flow pressure perturbations travel at different velocities
Low cost uniform heat source
Electrically powered heat source was developed for ground simulation of isotope heat-source assembly in Brayton power system. Heat source, which operates on ordinary 110 vac power, consists of tungsten filament heating element wound onto a spirally grooved boron nitride core and inserted in a hollowed-out graphite hexahedron
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