18,775 research outputs found
Development of a flash, bang, and smoke simulation of a shell burst
A large number of experiments (cue test firings) were performed in the definition of the cue concepts and packaging configurations. A total of 344 of these experiments were recorded with instrumentation photography to allow a quantitative analysis of the smoke cloud to be made as a function of time. These analyses were predominantly made using a short test site. Supplementary long range visibility tests were conducted to insure the required 3 kilometer visibility of the smoke signature
Bacterial infections of certain lower vertebrates: with particular reference to "furunculosis of the salmonidae"
The summary and conclusions referable to the
study of Furunculosis are given - Page 53.Bacterial infection of certain lower vertebrates
may be produced by specific organisms which
have been found only in association with cert:ain conditions of disease, e.g., Bacillus
sonicida, Furunculosis among the Salmonidae.Organisms naturally saprophytic may, under certain conditions, become pathogenic. These
organisms comprise some types frequently found
in water, such as, Bacillus fluorescens and
certain Gram-negative, non- sporing, non-chromogenic bacilli.A vibrio, with general biological characters
similar to those of vibrios which have been
described in water and in diseases of fish,
was isolated from heart blood of a salmon.
This organism proved highly pathogenic for
trout.Bacterial disease of fish and frogs usually takes
the form of a general infection. Focal
lesions may or may not be found. In Furunculosis, infection may be both focal and
general.Bacterial disease of these cold-blooded animals
frequently appears in epizootic form, e.g.,
"Red -leg" of frogs; Furunculosis of the
Salmonidae.
Occurrence of such epizootics requires further
study,Secondary infections, including ante-mortem infection, are of common occurrence among fish
and frogs, when the resistance of the animals
has been lowered by primary infection or injury.
Other adverse conditions probably also predispose to such infections. This requires
further investigation.Little or no tissue reaction against invading
bacteria has been observed in frogs or fish,
analogous to such reaction in mammalian animals.A certain degree of phagocytic activity is displayed in some cases of bacterial infection
of frogs and fish.Sources and modes of infection of lower vertebrates generally, require further study
An 8-cm ion thruster characterization
The performance of the Ion Auxiliary Propulsion System (IAPS) thruster was increased to thrust T = 32 mN, specific impulse I sub sp = 4062 s, and thrust-to-power ratio T/P = 33 mN/kW. This performance was obtained by increasing the discharge power, accelerating voltage, propellant flow rate, and chamber magnetic field. Adding a plenum and main vaporizer for propellant distribution was the only major change required in the thruster. The modified thruster characterization is presented. A cathode magnet assembly did not improve performance. A simplified power processing unit was designed and evaluated. This unit decreased the parts count of the IAPS power processing unit by a factor of ten
What can GLAST say about the origin of cosmic rays in other galaxies ?
Gamma rays in the band from 20 MeV to 300 GeV, used in combination with data
from radio and X-ray bands, provide a powerful tool for studying the origin of
cosmic rays in our sister galaxies Andromeda and the Magellanic Clouds.
Gamma-ray Large Area Space Telescope (GLAST) will spatially resolve these
galaxies and measure the spectrum and intensity of diffuse gamma radiation from
the collisions of cosmic rays with gas and dust in them. Observations of
Andromeda will give an external perspective on a spiral galaxy like the Milky
Way. Observations of the Magellanic Clouds will permit a study of cosmic rays
in dwarf irregular galaxies, where the confinement is certainly different and
the massive star formation rate is much greater.Comment: 4 pages including 6 figures; to appear in Proc. ACE-2000 Symp. "The
Acceleration and Transport of Energetic Particles Observed in the
Heliosphere" (Jan. 5-8, 2000, Indian Wells, CA), AIP Conf. Proc. More details
can be found at the LHEA GLAST page at
http://lhea-glast.gsfc.nasa.gov/pub/science/index.htm
Meson-exchange Currents and Quasielastic Neutrino Cross Sections
We illustrate and discuss the role of meson-exchange currents in quasielastic
neutrino-nucleus scattering induced by charged currents, comparing the results
with the recent MiniBooNE data for differential and integrated cross sections.Comment: 9 pages, 8 figures; Proceedings of the 30th International Workshop on
Nuclear Theory IWNT30, Rila Mountains, Bulgaria, June 27 - July 2, 201
Superscaling of non-quasielastic electron-nucleus scattering
The present study is focused on the superscaling behavior of electron-nucleus
cross sections in the region lying above the quasielastic peak, especially the
region dominated by electroexcitation of the Delta. Non-quasielastic cross
sections are obtained from all available high-quality data for Carbon 12 by
subtracting effective quasielastic cross sections based on the superscaling
hypothesis. These residuals are then compared with results obtained within a
scaling-based extension of the relativistic Fermi gas model, including an
investigation of violations of scaling of the first kind in the region above
the quasielastic peak. A way potentially to isolate effects related to
meson-exchange currents by subtracting both impulsive quasielastic and
impulsive inelastic contributions from the experimental cross sections is also
presented.Comment: RevTeX, 34 pages including 11 figure
Non-Gaussian Radio-Wave Scattering in the Interstellar Medium
It was recently suggested by Boldyrev & Gwinn that the characteristics of
radio scintillations from distant pulsars are best understood if the
interstellar electron-density fluctuations that cause the time broadening of
the radio pulses obey non-Gaussian statistics. In this picture the density
fluctuations are inferred to be strong on very small scales (). We argue that such density structures could correspond to the ionized
boundaries of molecular regions (clouds) and demonstrate that the power-law
distribution of scattering angles that is required to match the observations
arises naturally from the expected intersections of our line of sight with
randomly distributed, thin, approximately spherical ionized shells of this
type. We show that the observed change in the time-broadening behavior for
pulsar dispersion measures is consistent
with the expected effect of the general ISM turbulence, which should dominate
the scattering for nearby pulsars. We also point out that if the clouds are
ionized by nearby stars, then their boundaries may become turbulent on account
of an ionization front instability. This turbulence could be an alternative
cause of the inferred density structures. An additional effect that might
contribute to the strength of the small-scale fluctuations in this case is the
expected flattening of the turbulent density spectrum when the eddy sizes
approach the proton gyroscale.Comment: 15 pages, 3 figures, accepted to Ap
Anomalous Radio-Wave Scattering from Interstellar Plasma Structures
This paper considers scattering screens that have arbitrary spatial
variations of scattering strength transverse to the line of sight, including
screens that are spatially well confined, such as disks and filaments. We
calculate the scattered image of a point source and the observed pulse shape of
a scattered impulse. The consequences of screen confinement include: (1) Source
image shapes that are determined by the physical extent of the screen rather
than by the shapes of much-smaller diffracting microirregularities. These
include image elongations and orientations that are frequency dependent. (2)
Variation with frequency of angular broadening that is much weaker than the
trademark \nu^{-2} scaling law (for a cold, unmagnetized plasma), including
frequency-independent cases; and (3) Similar departure of the pulse broadening
time from the usually expected \nu^{-4} scaling law. We briefly discuss
applications that include scattering of pulses from the Crab pulsar by
filaments in the Crab Nebula; image asymmetries from Galactic scattering of the
sources Cyg X-3, Sgr A*, and NGC 6334B; and scattering of background active
galactic nuclei by intervening galaxies. We also address the consequences for
inferences about the shape of the wavenumber spectrum of electron density
irregularities, which depend on scaling laws for the image size and the pulse
broadening. Future low-frequency (< 100 MHz) array observations will also be
strongly affected by the Galactic structure of scattering material. Our
formalism is derived in the context of radio scattering by plasma density
fluctuations. It is also applicable to optical, UV and X-ray scattering by
grains in the interstellar medium.Comment: 21 pages, LaTeX2e with AASTeX-4.0, 6 PostScript figures, accepted by
ApJ, revised version has minor changes to respond to referee comments and
suggestion
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