505 research outputs found
Diffusive Versus Free-Streaming Cosmic Ray Transport in Molecular Clouds
Understanding the cosmic ray (CR) ionization rate is crucial in order to
simulate the dynamics of, and interpret the chemical species observed in
molecular clouds. Calculating the CR ionization rate requires both accurate
knowledge of the spectrum of MeV to GeV protons at the edge of the cloud as
well as a model for the propagation of CRs into molecular clouds. Some models
for the propagation of CRs in molecular clouds assume the CRs to stream freely
along magnetic field lines, while in others they propagate diffusively due to
resonant scattering off of magnetic disturbances excited by MHD turbulence
present in the medium. We discuss the conditions under which CR diffusion can
operate in a molecular cloud, calculate the local CR spectrum and ionization
rate in both a free-streaming and diffusive propagation model, and highlight
the different results from the two models. We also apply these two models to
the propagation through the ISM to obtain the spectrum seen by Voyager 1, and
show that such a spectrum favors a diffusive propagation model.Comment: Submitted to Ap
Causes of Cracking of Ignition Cable
The experiments described here show that the cracking at sharp bends, observed in the insulation of internal combustion engine high tension ignition wires after service, is due to a chemical attack upon the rubber by the ozone produced by the electric discharge that takes place at the surface of the cable. This cracking does not occur if the insulating material is not under tension, or if the cable is surrounded by some medium other than air. But it does occur even if the insulation is not subjected to electric stress, provided that the atmosphere near the cable contains ozone. The extent of this cracking varies greatly with the insulating material used. The cracking can be materially reduced by using braided cable and by avoiding sharp bends
Non-linear spin to charge conversion in mesoscopic structures
Motivated by recent experiments [Vera-Marun et al., arXiv:1109.5969], we
formulate a non-linear theory of spin transport in quantum coherent conductors.
We show how a mesoscopic constriction with energy-dependent transmission can
convert a spin current injected by a spin accumulation into an electric signal,
relying neither on magnetic nor exchange fields. When the transmission through
the constriction is spin-independent, the spin-charge coupling is non-linear,
with an electric signal that is quadratic in the accumulation. We estimate that
gated mesoscopic constrictions have a sensitivity that allows to detect
accumulations much smaller than a percent of the Fermi energy.Comment: 4 pages, 3 figure
Magnetic bipolar transistor
A magnetic bipolar transistor is a bipolar junction transistor with one or
more magnetic regions, and/or with an externally injected nonequilibrium
(source) spin. It is shown that electrical spin injection through the
transistor is possible in the forward active regime. It is predicted that the
current amplification of the transistor can be tuned by spin.Comment: 4 pages, 2 figure
The effect of electrode temperature on the sparking voltage of short spark gaps
This report presents the results of an investigation to determine what effect the temperature of spark plug electrodes might have on the voltage at which a spark occurred. A spark gap was set up so that one electrode could be heated to temperatures up to 700 degrees C., while the other electrode and the air in the gap were maintained at room temperature. The sparking voltages were measured both with direct voltage and with voltage impulse from ignition coil. It was found that the sparking voltage of the gap decreased materially with increase of temperature. This change was more marked when the hot electrode was of negative polarity. The phenomena observed can be explained by the ionic theory of gaseous conduction, and serve to account for certain hitherto unexplained actions in the operation of internal combustion engines. These results indicate that the ignition spark will pass more readily when the spark-plug design is such as to make the electrodes run hot. This possible gain is, however, very closely limited by the danger of producing preignition. These experiments also show that sparking is somewhat easier when the hot electrode (which is almost always the central electrode) is negative than when the polarity is reversed
The sparking voltage of spark plugs
This report has been prepared in order to collect and correlate into convenient and useful form the available data on this subject. The importance of the subject lies in the fact that it forms the common meeting ground for studies of the performance of spark generators and spark plugs on the one hand and of the internal combustion engines on the other hand. While much of the data presented was obtained from various earlier publications, numerous places were found where necessary data were lacking, and these have been provided by experiments in gasoline engines at the Bureau of Standards
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