42,783 research outputs found
Vacuum forming of thermoplastic sheet results in low-cost investment casting patterns
Vacuum forming of a sheet of thermoplastic material around a mandrel conforming to the shape of the finished object provides a pattern for an investment mold. The thickness of the metal part is determined by the thickness of the plastic pattern
Dynamics and Structure of Three-Dimensional Poloidally Magnetized Supermagnetosonic Jets
A set of 3D MHD simulations of magnetized jets has been performed. The jets
contain an equipartition primarily poloidal magnetic field and the effect of
jet density on jet dynamics and structure is evaluated. The jet is precessed at
the origin to excite Kelvin-Helmholtz unstable helical modes. We extensively
compare the structure in these simulations with linear stability theory. The
jet that is dense with respect to the external medium develops a high speed
core surrounded by a less dense sheath consisting of slower moving jet fluid.
These simulations suggest that extended extragalactic jets propagate to such
large distances because they are surrounded by a lobe or cocoon whose density
is less than the jet density. (Abridged abstract.)Comment: 30 pages, AASTeX, to appear in ApJ, much better versions of Figures
2-5 are available at http://crux.astr.ua.edu/~rosen/hcr/hcr.htm
Aircraft electromagnetic compatibility
Illustrated are aircraft architecture, electromagnetic interference environments, electromagnetic compatibility protection techniques, program specifications, tasks, and verification and validation procedures. The environment of 400 Hz power, electrical transients, and radio frequency fields are portrayed and related to thresholds of avionics electronics. Five layers of protection for avionics are defined. Recognition is given to some present day electromagnetic compatibility weaknesses and issues which serve to reemphasize the importance of EMC verification of equipment and parts, and their ultimate EMC validation on the aircraft. Proven standards of grounding, bonding, shielding, wiring, and packaging are laid out to help provide a foundation for a comprehensive approach to successful future aircraft design and an understanding of cost effective EMC in an aircraft setting
Assessment of risk to Boeing commerical transport aircraft from carbon fibers
The possible effects of free carbon fibers on aircraft avionic equipment operation, removal costs, and safety were investigated. Possible carbon fiber flow paths, flow rates, and transfer functions into the Boeing 707, 727, 737, 747 aircraft and potentially vulnerable equipment were identified. Probabilities of equipment removal and probabilities of aircraft exposure to carbon fiber were derived
Low Frequency VLA Observations of Abell 754: Evidence for a Cluster Radio Halo and Possible Radio Relics
We present 74 MHz and 330 MHz VLA observations of Abell 754. Diffuse,
halo-like emission is detected from the center of the cluster at both
frequencies. At 330 MHz the resolution of 90'' distinguishes this extended
emission from previously known point sources. In addition to the halo and at a
much lower level, outlying steep-spectrum emission regions straddle the cluster
center and are seen only at 74 MHz. The location, morphology and spectrum of
this emission are all highly suggestive of at least one, and possibly two
cluster radio relics. Easily obtained higher resolution, higher sensitivity VLA
observations at both frequencies are required to confirm the extended nature of
the halo-like emission and the 74 MHz relic detections. However, since there is
prior evidence that this cluster is or has recently been in the process of a
major merger event, the possible discovery of relics in this system is of great
interest in light of recent observational and theoretical evidence in favor of
a merger-relic connection. We discuss the possible role the merger shock waves,
which are seen in the X-ray emission, may have played in the formation of the
halo and radio relics in A754.Comment: 15 pages including 4 figures. Accepted for publication by Ap
Control Plane Compression
We develop an algorithm capable of compressing large networks into a smaller
ones with similar control plane behavior: For every stable routing solution in
the large, original network, there exists a corresponding solution in the
compressed network, and vice versa. Our compression algorithm preserves a wide
variety of network properties including reachability, loop freedom, and path
length. Consequently, operators may speed up network analysis, based on
simulation, emulation, or verification, by analyzing only the compressed
network. Our approach is based on a new theory of control plane equivalence. We
implement these ideas in a tool called Bonsai and apply it to real and
synthetic networks. Bonsai can shrink real networks by over a factor of 5 and
speed up analysis by several orders of magnitude.Comment: Extended version of the paper appearing in ACM SIGCOMM 201
The relation between accretion rates and the initial mass function in hydrodynamical simulations of star formation
We analyse a hydrodynamical simulation of star formation. Sink particles in
the simulations which represent stars show episodic growth, which is presumably
accretion from a core that can be regularly replenished in response to the
fluctuating conditions in the local environment. The accretion rates follow
, as expected from accretion in a gas-dominated
potential, but with substantial variations over-laid on this. The growth times
follow an exponential distribution which is tapered at long times due to the
finite length of the simulation. The initial collapse masses have an
approximately lognormal distribution with already an onset of a power-law at
large masses. The sink particle mass function can be reproduced with a
non-linear stochastic process, with fluctuating accretion rates , a distribution of seed masses and a distribution of growth times. All
three factors contribute equally to the form of the final sink mass function.
We find that the upper power law tail of the IMF is unrelated to Bondi-Hoyle
accretion.Comment: 13 pages, 13 figures, MNRAS accepte
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Dietary manipulation of broiler breeder growth through the feeding of conjugated linoleic acid
Swath Mapping on the Continental Shelf and Slope: The Eel River Basin, Northern California
First Paragraph
The STRATAFORM program sponsored by the Office of Naval Research (Nittrouer and Kravitz, 1996, this issue) seeks to understand how sedimentary processes lead to the formation of the stratigraphic sequences on continental margins. A central challenge facing this effort is to understand the transport of sediments in shore-parallel as well as shore-perpendicular directions• Multidimensionality is necessary to describe, for example, the accumulation of sediments from river inputs, the distribution of gullies and canyons on the slope, the meandering of channels, and the structure of slumps and slides
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