4,833 research outputs found
Development of a 1000V, 200A, low-loss, fast-switching, gate-assisted turn-off thyristor
Feasibility was demonstrated for a thyristor that blocks 1000V forward and reverse, conducts 200A, and turns on in little more than 2 microsec with only 2A of gate drive. Its features include a turn-off time of 3 microsec achieved with 2A of gate assist current of a few microseconds duration and an energy dissipation of only 12 mJ per pulse for a 20 microsec half sine wave, 200A pulse. Extensive theoretical and experimental study of the electrical behavior of thyristors having a fast turn-off time have significantly improved the understanding of the physics of turning thyristor off. Thyristors of two new designs were fabricated and evaluated. The high speed and low power were achieved by a combination of gate amplification, cathode shunting, and gate-assisted turn-off. Two techniques for making this combination practical are described
Soft X-ray Emission from the Spiral Galaxy NGC 1313
The nearby barred spiral galaxy NGC 1313 has been observed with the PSPC
instr- ument on board the ROSAT X-ray satellite. Ten individual sources are
found. Three sources (X-1, X-2 and X-3 [SN~1978K]) are very bright (~10^40
erg/s) and are unusual in that analogous objects do not exist in our Galaxy. We
present an X-ray image of NGC~1313 and \xray spectra for the three bright
sources. The emission from the nuclear region (R ~< 2 kpc) is dominated by
source X-1, which is located ~1 kpc north of the photometric (and dynamical)
center of NGC~1313. Optical, far-infrared and radio images do not indicate the
presence of an active galactic nucleus at that position; however, the compact
nature of the \xray source (X-1) suggests that it is an accretion-powered
object with central mass M >~ 10^3 Msun. Additional emission (L_X ~ 10^39
erg/s) in the nuclear region extends out to ~2.6 kpc and roughly follows the
spiral arms. This emission is from 4 sources with luminosity of several x 10^38
erg/s, two of which are consistent with emission from population I sources
(e.g., supernova remnants, and hot interstellar gas which has been heated by
supernova remnants). The other two sources could be emission from population II
sources (e.g., low-mass \xray binaries). The bright sources X-2 and SN~1978K
are positioned in the southern disk of NGC~1313. X-2 is variable and has no
optical counterpart brighter than 20.8 mag (V-band). It is likely that it is an
accretion-powered object in NGC~1313. The type-II supernova SN~1978K (Ryder
\etal 1993) has become extra- ordinarily luminous in X-rays 13 years
after optical maximum.Comment: to appear in 10 Jun 1995 ApJ, 30 pgs uuencoded compressed postscript,
25 pgs of figures available upon request from colbert, whole preprint
available upon request from Sandy Shrader ([email protected]),
hopefully fixed unknown problem with postscript fil
Development of a 1000V, 200A, low-loss, fast-switching, gate-assisted turn-off thyristor
The results of a program to develop a fast high power thyristor that can operate in switching circuits at frequencies of 10 to 20 kHz with very low power loss are given. Feasibility was demonstrated for a thyristor that blocks 1000V forward and reverse, conducts 200A, turns on in little more than 2 more microseconds with only 2A of gate drive, turns off in 3 microseconds with 2A of gate assist current and has an energy dissipation of only 12 mJ per pulse for a 20 microsecond half sine wave 200A pulse. Data were generated that clearly showed the tradeoffs that can be made between the turn off time and forward drop. The understanding of this relationship is necessary in the selection of deliverable thyristors with turn off times up to 7 microseconds to give improved efficiency in a series resonant dc to dc inverter application
New spectral classification technique for X-ray sources: quantile analysis
We present a new technique called "quantile analysis" to classify spectral
properties of X-ray sources with limited statistics. The quantile analysis is
superior to the conventional approaches such as X-ray hardness ratio or X-ray
color analysis to study relatively faint sources or to investigate a certain
phase or state of a source in detail, where poor statistics does not allow
spectral fitting using a model. Instead of working with predetermined energy
bands, we determine the energy values that divide the detected photons into
predetermined fractions of the total counts such as median (50%), tercile (33%
& 67%), and quartile (25% & 75%). We use these quantiles as an indicator of the
X-ray hardness or color of the source. We show that the median is an improved
substitute for the conventional X-ray hardness ratio. The median and other
quantiles form a phase space, similar to the conventional X-ray color-color
diagrams. The quantile-based phase space is more evenly sensitive over various
spectral shapes than the conventional color-color diagrams, and it is naturally
arranged to properly represent the statistical similarity of various spectral
shapes. We demonstrate the new technique in the 0.3-8 keV energy range using
Chandra ACIS-S detector response function and a typical aperture photometry
involving background subtraction. The technique can be applied in any energy
band, provided the energy distribution of photons can be obtained.Comment: 11 pages, 9 figures, accepted for publication in Ap
Effect of electron heating on self-induced transparency in relativistic intensity laser-plasma interaction
The effective increase of the critical density associated with the
interaction of relativistically intense laser pulses with overcritical plasmas,
known as self-induced transparency, is revisited for the case of circular
polarization. A comparison of particle-in-cell simulations to the predictions
of a relativistic cold-fluid model for the transparency threshold demonstrates
that kinetic effects, such as electron heating, can lead to a substantial
increase of the effective critical density compared to cold-fluid theory. These
results are interpreted by a study of separatrices in the single-electron phase
space corresponding to dynamics in the stationary fields predicted by the
cold-fluid model. It is shown that perturbations due to electron heating
exceeding a certain finite threshold can force electrons to escape into the
vacuum, leading to laser pulse propagation. The modification of the
transparency threshold is linked to the temporal pulse profile, through its
effect on electron heating.Comment: 13 pages, 12 figures; fixed some typos and improved discussion of
review materia
Study of failure modes of multilevel large scale integrated circuits
Evaluation tests for electrical properties of oxide silicon interfaces in multilevel microcircuit
Design, development, fabrication, and delivery of improved MOS transistors Final report, 21 May 1965 - 21 May 1966
Instability, high threshold voltage, and gamma radiation in MOS transistor
Metal-oxide-silicon technology. A literature review
Literature review on metal oxide silicon semiconductor technolog
Study of Failure Modes of Multilevel Large Scale Integrated Circuits Interim Report, 15 Apr. - 14 Oct. 1968
Failure modes of large multilevel silicon microcircuit array
Design, development, fabrication, and delivery of improved MOS transistors Second quarterly progress report, 22 Aug. - 21 Nov. 1965
Causes of instability, high threshold voltage, and gamma radiation sensitivity of metal-oxide silicon transistor
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