11,254 research outputs found
Statistical Uncertainties in Temperature Diagnostics for Hot Coronal Plasma Using the ASCA SIS
Statistical uncertainties in determining the temperatures of hot (0.5 keV to
10 keV) coronal plasmas are investigated. The statistical precision of various
spectral temperature diagnostics is established by analyzing synthetic ASCA
Solid-state Imaging Spectrometer (SIS) CCD spectra. The diagnostics considered
are the ratio of hydrogen-like to helium-like line complexes of
elements, line-free portions of the continuum, and the entire spectrum. While
fits to the entire spectrum yield the highest statistical precision, it is
argued that fits to the line-free continuum are less susceptible to atomic data
uncertainties but lead to a modest increase in statistical uncertainty over
full spectral fits. Temperatures deduced from line ratios can have similar
accuracy but only over a narrow range of temperatures. Convenient estimates of
statistical accuracies for the various temperature diagnostics are provided
which may be used in planning ASCA SIS observations.Comment: postscript file of 8 pages+3 figures; 4 files tarred, compressed and
uuencoded. To appear in the Astrophysical Journal Letters; contents copyright
1994 American Astronomical Societ
Performance of high resistivity n+pp+ silicon solar cells under 1 MeV electron irradiation
High resistivity (1250 and 84 ohm-cm) n(+)pp(+) silicon solar cells were irradiated and their performance evaluated as a function of fluence. The greatest degradation in power occurred for the higher resistivity cell. The data were analyzed under open circuit conditions, and the components of V sub oc determined as a function of fluence. It was found that the voltage contributions from the front and back junctions decreased while the base component (V sub B) increased with fluence. The anomalous behavior of V sub B was attributed to an increase in the base minority carrier gradient with fluence. An argument that the increased power degradation in the 1250 ohm-cm cells was attributable to an increased voltage drop in the base is presented. Diffusion lengths calculated under high injection conditions were significantly greater than those determined under low injection. This was attributed to a saturation of recombination centers under high injection conditions
The optimal polarizations for achieving maximum contrast in radar images
There is considerable interest in determining the optimal polarizations that maximize contrast between two scattering classes in polarimetric radar images. A systematic approach is presented for obtaining the optimal polarimetric matched filter, i.e., that filter which produces maximum contrast between two scattering classes. The maximization procedure involves solving an eigenvalue problem where the eigenvector corresponding to the maximum contrast ratio is an optimal polarimetric matched filter. To exhibit the physical significance of this filter, it is transformed into its associated transmitting and receiving polarization states, written in terms of horizontal and vertical vector components. For the special case where the transmitting polarization is fixed, the receiving polarization which maximizes the contrast ratio is also obtained. Polarimetric filtering is then applies to synthetic aperture radar images obtained from the Jet Propulsion Laboratory. It is shown, both numerically and through the use of radar imagery, that maximum image contrast can be realized when data is processed with the optimal polarimeter matched filter
Cataphoresis in rotating electric fields
A new method of making cataphoresis measurements on colloid particles has been developed and tested. The method makes use of a rotating electric field which causes the particles to move in circles. In this way it is easily possible to test the effect of variable speed of the particle on the distribution of the diffuse electric double layer surrounding it. The results obtained indicate that this effect is negligible. Furthermore, it has been discovered that the mobility of the small particles (below 10^-4 cm in diameter) fluctuates widely and this is made very evident to the eye by the fluctuations in the circular paths of the particles. The fluctuations are quite violent with particles as small as 10^-6 cm in diameter. Considerable study of these variations has been made as well as an attempt to explain them qualitatively
A double junction model of irradiated silicon pixel sensors for LHC
In this paper we discuss the measurement of charge collection in irradiated
silicon pixel sensors and the comparison with a detailed simulation. The
simulation implements a model of radiation damage by including two defect
levels with opposite charge states and trapping of charge carriers. The
modeling proves that a doubly peaked electric field generated by the two defect
levels is necessary to describe the data and excludes a description based on
acceptor defects uniformly distributed across the sensor bulk. In addition, the
dependence of trap concentrations upon fluence is established by comparing the
measured and simulated profiles at several fluences and bias voltages.Comment: Talk presented at the 10th European Symposium on Semiconductor
Detectors, June 12-16 2005, Wildbad Kreuth, Germany. 9 pages, 4 figure
Driver vs. manager perceptions of commonly used safety practices in commercial motor vehicle operations
This research investigated the perceptions of Commercial Motor Vehicle Operators and Safety Professionals regarding 35 commonly implemented practices used to improve operating safety. Several differences were found in how drivers of different backgrounds rated various practices, and between the drivers and safety managers. These differences were found to be persistent even when combined with measures of safety performance and experience. Managers tended to overvalue (relative to drivers) practices related to hiring, while drivers tended to overvalue (relative to managers) practices related to company support and reward systems. Motor Carriers, insurers, and regulators could consider areas of agreement with respect to high value practices as actionable for increased investment of resources. At the same time, resources allocated toward areas of low perceived value could be reduced
Investigating 16O with the 15N(p,{\alpha})12C reaction
The 16O nucleus was investigated through the 15N(p,{\alpha})12C reaction at
excitation energies from Ex = 12 231 to 15 700 keV using proton beams from a 5
MeV Van de Graaff accelerator at beam energies of Ep = 331 to 3800 keV. Alpha
decay from resonant states in 16O was strongly observed for ten known excited
states in this region. The candidate 4-alpha cluster state at Ex = 15.1 MeV was
investigated particularly intensely in order to understand its particle decay
channels.Comment: Submitted for Proceedings of Fourth International Workshop on State
of the Art in Nuclear Cluster Physics (SOTANCP4), held from May 13 - 18, 2018
in Galveston, TX, US
Radiation damage in lithium-counterdoped n/p silicon solar cells
Lithium counterdoped n+/p silicon solar cells were irradiated with 1 MV electrons and their post irradiation performance and low temperature annealing properties were compared to that of the 0.35 ohm cm control cells. Cells fabricated from float zone and Czochralski grown silicon were investigated. It was found that the float zone cells exhibited superior radiation resistance compared to the control cells, while no improvement was noted for the Czochralski grown cells. Room temperature and 60 C annealing studies were conducted. The annealing was found to be a combination of first and second order kinetics for short times. It was suggested that the principal annealing mechanism was migration of lithium to a radiation induced defect with subsequent neutralization of the defect by combination with lithium. The effects of base lithium gradient were investigated. It was found that cells with negative base lithium gradients exhibited poor radiation resistance and performance compared to those with positive or no lithium gradients; the latter being preferred for overall performance and radiation resistance
Safety attitudes and behavioral intentions of municipal waste disposal drivers
The Theory of Planned Behavior was used to study factors useful for predicting Behavioral Intentions to commit unsafe acts while driving for commercial drivers working for municipal waste management operations centers. The Theory of Planned Behavior was found to be moderately effective in predicting behavioral intentions, particularly through the constructs of Attitude and Perceived Control. Driver perceptions of safety climate, self-assessed personal safety performance, risk aversion, and attitudes toward behavioral factors associated with engaging in risky behaviors while operating motor vehicles were studied. Risk aversion and driver perception of their own safety performance were also useful predictors of intention
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