128,579 research outputs found
Solidification studies of monotectic systems
Described is an attempt to determine critical wetting temperatures in monotectic systems and to investigate the wetting phase on container walls and the phase preferential wetting of a monotectic solid
Pulse Profiles, Spectra and Polarization Characteristics of Non-Thermal Emissions from the Crab-Like Pulsars
We discuss non-thermal emission mechanism of the Crab-like pulsars with both
a two-dimensional electrodynamical study and a three-dimensional model. We
investigate the emission process in the outer gap accelerator. In the
two-dimensional electrodynamical study, we solve the Poisson equation of the
accelerating electric field in the outer gap and the equation of motion of the
primary particles with the synchrotron and the curvature radiation process and
the pair-creation process. We show a solved gap structure which produces a
consistent gamma-ray spectrum with EGRET observation. Based on the
two-dimensional model, we conduct a three-dimensional emission model to
calculate the synchrotron and the inverse-Compton processes of the secondary
pairs produced outside the outer gap. We calculate the pulse profiles, the
phase-resolved spectra and the polarization characteristics in optical to
-ray bands to compare the observation of the Crab pulsar and PSR
B0540-69. For the Crab pulsar, we find that the outer gap geometry extending
from near the stellar surface to near the light cylinder produces a complex
morphology change of the pulse profiles as a function of the photon energy.
This predicted morphology change is quite similar with that of the
observations. The calculated phase-resolved spectra are consistent with the
data through optical to the -ray bands. We demonstrate that the
1020 % of the polarization degree in the optical emissions from the Crab
pulsar and the Vela pulsar are explained by the synchrotron emissions with the
particle gyration motion.Comment: 39 pages, 11 figures, Accepted for publication in Ap
Low work function silicon collector for thermionic converters
To improve the efficiency of present thermionic converters, single crystal silicon was investigated as a low work function collector material. The experiments were conducted in a test vehicle which resembled an actual thermionic converter. Work function as low as 1.0eV was obtained with an n-type silicon. The stabilities of the activated surfaces at elevated temperatures were tested by raising the collector temperature up to 829 K. By increasing the Cs arrival rate, it was possible to restore the originally activated low work function of the surface at elevated surface temperatures. These results, plotted in the form of Rasor-Warner curve, show a behavior similar to that of metal electrode except that the minimum work function was much lower with silicon than with metals
Silicon crystal as a low work function collector
A test vehicle with a low work function collector which can be incorporated in a thermionic converter was constructed from standard vacuum components including an ultrahigh vacuum ion pump. The collector assembly was fabricated by diffusion bonding a (100) oriented silicon single crystal to a molybdenum block. The silicon surface was treated with cesium and oxygen to produce an NEA-type condition and the results were tested by photoemission and work function measurements. An n-type silicon collector was successfully activated to a work function of 1.0 eV, which was verified by photoemission spectral yield measurements. The stability test of an activated surface at elevated temperatures was conducted in the range from room temperature to 619 K, which was slightly lower than the designed collector temperature of 700 K. The work function measurements clearly demonstrated that the behavior of cesium replenishment on the activated Si surface was similar in nature to that of a metallic surface; that is, the loss of cesium by thermal desorption could be compensated by maintaining an adequate vapor pressure of cesium
- …