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The analysis and modeling of microburst electron precipitation using pitch-angle diffusion theory /Datta, Suvro, January 1995 (has links)
Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (p. [91]-93).
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The effect of misfit on morphology and kinetics of plate shaped precipitatesSagoe-Crentsil, Kwesi Kurentsir January 1988 (has links)
Lattice misfit and its effect on the morphology, interfacial structure and kinetics of plate shaped precipitates are investigated in this study. The 7-Ag₂Al phase in the Al-Ag system was used as the reference system and its misfit was controlled by ternary additions of Mg and Cu. The addition of 0.S1 at% Mg was found to increase the misfit from 0.8% for the binary to 1.11%. Cu additions on the other hand, reduced the misfit by 0.38% for Cu concentrations up to 0.51 at%. Electron probe microanalysis showed that the Mg atoms preferentially partition to the 7 phase whereas Cu atoms partition equally between the precipitate and matrix phases.
Direct transmission election rnicroscope observations were made on the interface structure in both the equilibrated state and during precipitate dissolution. The interface structure in the ternary Mg alloy consisted of a hexagonal network of partial dislocations which essentially remained the same before and during dissolution. A single array of a/2<110> dislocations was observed in the binary and ternary Cu systems prior to dissolution. This unit array transformed to a stable hexagonal network structure having the equilibrium spacing at the onset of dissolution and remained throughout the period of dissolution.
The thinning and shortening kinetics of the precipitate plates were at least five times slower than the rates for volume diffusion control in all three systems. This interfacial inhibition has further been confirmed by the consistent fall below equilibrium values of the interface concentration as determined from electron probe microanalysis. This suggests the operation of a ledge migration mechanism. A mechanism of acquiring ledge/dislocations at the interface is used as a basis to correlate the
observed kinetics with misfit and ledge migration at the precipitate-matrix interphase. The
mechanism involves co-ordinated motion of sets of dislocations in the network which rids the surface of the highest steps thereby accomplishing dissolution. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate
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An investigation into pulsating aurora /Williams, John Denis. January 2002 (has links)
Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 102-108).
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Duskside relativistic electron precipitation /Lorentzen, Kirsten. January 1999 (has links)
Thesis (Ph. D.)--University of Washington, 1999. / Includes bibliographical references (p. [135]-143).
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Electron precipitation and ionospheric disturbanceTorr, Marsha R January 1966 (has links)
From Introduction: The minimum in the scalar magnitude of the geographic total field, which lies off the coast of Brazil, allows the mirror points of trapped particles to dip low into the atmosphere over the South Atlantic Ocean, resulting in two regions of maximum intensity of preciptated particles in that region, one from the inner belt and one from the outer. High charged particle fluxes have been observed at low altitudes over these regions by satellites Sputnik 5 and 6 (Ginsburg et al, 1961) and Discoverer 31 (Seward and Kornblum, 1963) amongst others. The more southerly of these two regions acts as a sink for electrons from the outer radiation belt and will be referred to in what follows as the Southern Radiation Anomaly. Gladhill and van Rooyen (1963) predicted that the energy deposited in the upper atmosphere by these charged particles would be sufficient to give rise to enhanced geophysical effects such as auroral emission, X-rays and ionization and heating of the upper atmosphere in this region. Although some of these effects have been correlated with precipitated electrons, no definite relation had until now been established between ionospheric effects and precipitated particles. The aim of this thesis was to investigate such a relationship and the results were extremely successful. It will be shown conclusively in what follows, that the precipitation of electrons can account for the ionospheric disturbances defined by a disturbance criterion at all stations around L=4. Part I describes the exploration of the radiation belts and the magnetosphere with rockets and satellites. The resulting theoretical models based on the observations are discussed. A brief review is given of the work that has been done to date to derive equations for the loss and replenishment of particles in the belts. Because of the complexity of these and the number of doubtful factors involved, a simple model of injection of electrons into the outer belt is devised, giving average values of trapped and precipitated electron fluxes at any point around L=4. In Part II, this model is employed together with the disturbance criterion of Gledhill and Torr (1965) to examine the relationship between ionospheric disturbances and electron fluxes. Also the energy range of the precipitated particles is examined.
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Effects of precipitating electrons in the ionosphereHaschick, Aubrey D January 1974 (has links)
As early as 1896, around the time of the discovery of the electron by J.J. Thompson, Birkeland was led to propose that aurorae were caused by fast moving electrons or similarly charged particles emitted by the sun and 'sucked in towards' the auroral zones by the geomagnetic field. He later supported this idea by firing electrons at a dipole field surrounding a sphere covered with a fluorescent coating. Extensive ground based observations of auroral features eventually led, in 1950, to the initial direct evidence of the fact that auroral emissions are due to energetic charged particles, consisting partly of protons, entering the earth's atmosphere (Meinel, 1951). However, it was only in 1952 and 1953 that the first measurements of what was later interpreted as bremsstrahlung X- rays from precipitating electrons were made at auroral latitudes. (Meredith et aI, 1955) During the IGY, 1957 - 1958, a number of rockets were fired through and near, visible aurorae and large fluxes of low energy electrons were detected ... Intro., p. 1.
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Ionospheric influence on the global characteristics of electron precipitation during auroral substorms /Chua, Damien Han. January 2002 (has links)
Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 108-119).
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Kinetic processes in the plasma sheet observed during auroral activity /Fillingim, Matthew Owen. January 2002 (has links)
Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 133-141).
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The origin of narrow band cyclotron wave emissions called chorus /Skoug, Ruth Marie, January 1995 (has links)
Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [117]-127).
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A study of wave induced electron precipitation at low and middle latitudes.Friedel, Reiner Hans-Walter. January 1991 (has links)
Wave induced electron precipitation (WIEP) can modify the ionosphere above
a sub-ionospherically propagating VLF signal in such a way as to perturb the
amplitude and phase of the signal: The "Trimpi Event".
In this thesis trimpi events are used in a study of WIEP events and in the responsible
mechanism: The gyroresonant interaction. Trimpi activity at middle latitudes
(SANAE, Antarctica, L = 4.02) and low latitudes (Durban, RSA , L = 1.69) together with the corresponding theory for the gyroresonant interaction is examined
and compared.
A newly developed computerised system for the detection and analysis of trimpi
events has been developed in Durban. This system has been used to analyse
tape data recorded at SANAE. Trimpi events were found on various transmitter
paths to SANAE and a complete study of 1982 data has led to the establishment
of trimpi characteristics as seen at SANAE: an absence of positive events
and causative whistlers, a preference for short duration events (t < 25s), the occurrence
of some very large events (up to 90% signal attenuation) , two minima
in occurrence near 0015 and 0400 h Local Time, low occurrence and occurrence
rate of events and evidence that interactions with non-ducted whistlers are of
importance.
The computerised sytem was then extended to collect data at Durban simultaneously
from up to 20 transmitters worldwide. Examination of data from this survey
showed very low occurrence rates of trimpis but yielded some daytime events
for which the effectiveness of the gyroresonance interaction, which successfully
explains the trimpi event at middle and low latitudes, had to be questioned.
Thus a fully relativisic test particle simulation of the gyroresonant interaction
was used to examine the effectiveness of gyroresonance at low L for producing
trimpi events. This simulation was run for a wide range of interaction parameters
and yielded the following constraints for effective pitch angle scattering (and hence
precipitation) of electrons at low L: wave intensities in excess of 150 nT, wave
frequencies in excess of 10 kHz and background electron densities at least one
order of magnitude higher than normal.
First data from the OMSKI project, a sophisticated VLF receiver operated at
Durban as part of an international project, shows further evidence of low-latitude
trirmpi activity. A survey of one month's continuous data is presented.
In face of the evidence that trimpi events that occur at low L have the same
signature as those at middle L but that the standard gyroresonance interaction is
insufficient to cause them, alternate scenarios that could enhance the interaction
were sought. In particular distortions in the ambient magnetic field (eg. PC-5
pulsations) were modelled using a new dipole-like background field model. This
simulation showed that distortions which tend to reduce magnetic field curvature
along field lines can significantly enhance the gyroresonant conditions and hence
the interaction. A new set of conditions for effective gyroresonance at low L is
thus established and contrasted with the more lenient conditions at middle L.
A study of "frequency tracking" as a means to prolong resonance showed that
natural whistlers do not posess the required frequency /time characteristics for this
mechanism, and that artificial waves in a narrow range around the equatorial
resonance frequency would ~ well suited for this purpose.
An overview of the status of worldwide Trimpi detection networks together with
the S.P.R.I. 's role in this regard is presented. / Thesis (Ph.D.)-University of Natal, Durban, 1991.
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