The work presented in this thesis concerns the oxidation of N-amino compounds and the interception of the reactive intermediates, the postulated amino-nitrenes. The Introduction has been divided into three parts concerning (1) the synthesis of aziridines from nitrenes and olefins (2) nitrogen inversion as studied by N.M.R. spectroscopy (3) synthetic approaches to 2H-azirines. The preparation of one new N-amino compound, N-aminophthalimidine is reported and the oxidations of that compound and of N-aminophthalimide, N-aminonaphthalimide, 3-aminobenzoxazolin-2(3H)-one and N-aminocarbazole are reported. The oxidation of the N-amino compounds alone leads to a variety of products, a major one frequently being the deaminated compound. The mechanism of oxidative deamination is discussed and an intermediate in the reaction, a tetrazane, has been isolated. Oxidations in the presence of olefins and sulphoxides generally give aziridines and sulphoximines. The N.M.R. spectra of most aziridines studied showed the presence of invertomers at room temperature. The implications of slow nitrogen inversion as a tool for conformational analysis are discussed. Several chloro- and bromo-substituted aziridines were found to undergo a facile thermal rearrangement with ring opening to give hydrazones. Sulphoximines and certain aziridines substituted in the 2-position with an unsaturated group were shown to produce the amino-nitrenes upon photolysis. When N-aminophthalimide was oxidised in the presence of acetylenes, 2H-azirines and not 1H-azirines were isolated. The mechanism of this novel rearrangement is discussed, and other attempted syntheses of the 1H-azirine system are reported.

This work is concerned with the development of imaging detectors and was undertaken as part of a laboratory investigation into requirements for future experiments by the X-ray astronomy group of this university in its programme of study of solar and non-solar X-ray emission. Much of the work is concerned with the establishment of the operating characteristics of a new detector, the channel multiplier array, and its use as an imaging device. As a result of the investigations, new methods of one and two dimensional image dissection have been developed giving a spatial resolution comparable to that of photographic film. Together with recent advances in X-ray Imaging optics, these methods are of considerable interest in the rapidly expanding field of X-ray astronomy. In addition to work on channel arrays, a brief account is given of a spectroheliograph which is operating successfully on the 5th Orbiting Solar Observatory and which has been designed by Leicester University and University College, London.

This thesis reports several advances in x-ray crystal spectroscopic techniques for the diagnosis of high-temperature magnetically confined plasmas. Two complementary spectrometers have been developed, and have been demonstrated in a wide range of experiments on the Culham Laboratory DITE and COMPASS tokamaks, and on the Joint European JET tokamak. A Bragg rotor' spectrometer uses a combination of crystals and multilayers to give complete coverage of the spectrum between 1 A and 100 A. Developments were made to extend the coverage from 25 A to 100 A, using multilayer mirrors and organic crystals. The success of the instrument depends largely on the development of a high-rate ( 107 count/s) gas proportional counter system, capable of covering the energy range from 100 eV to 10 keV. A Johann spectrometer uses a novel four-pillar jig to bend' crystals to typically 1 m radius. A large-area cooled x-ray CCD array is used in the focus, resulting in a compact high-resolution instrument. This allows line profile and ratio measurements with a time resolution of ~1 ms. Observations using the Bragg rotor spectrometer include impurity monitoring under various plasma and limiter configurations. Temperature and density sensitive line ratios were measured under known plasma conditions and compared with theory, adding confidence to their use for less well diagnosed plasmas such as those observed in astrophysics. A major application has been the study of a switch (controlled by the refuelling rate) between long and short impurity confinement times in the DITE tokamak. Trace impurities were injected by laser ablation, and their subsequent temporal and spatial behavour studied spectroscopically. Weak lines, due to radiative recombination into excited states of H- and He-like ions, were observed in the outer plasma. The radial profiles of these "radiative recombination lines" were governed by a balance between transport and, recombination, and allowed the effective diffusion coefficient to be measured locally. It was shown that the transport changes occurred in the outer half of the plasma, and that conditions in the core were unchanged. The suitability of Bragg spectroscopy for a reactor-relevant plasma was demonstrated during the JET preliminary tritium experiment (PTE). A double- reflection instrument was used, with a tritium-compatible radiation-shielded beamline. Based on this operational experience, a soft x-ray spectroscopy system for a next-step device such as ITER is proposed.

No description available.

In this thesis we examine the evolution of emission line clouds via hydrodynamic modelling using a Godunov-type code which incorporates a simple radiative heating- cooling function. The results of this are used as the input to a photoionisation calculation from which we obtain emission line ratios and profiles. This allows comparison to observation. In the narrow line region we examine the "catapult model" which suggests that line broadening is a result of clouds falling under the influence of gravity into a nuclear supersonic wind. Larger clouds continue to fall in, whereas smaller clouds have their direction reversed and are ejected. We model the evolution of one of the smaller clouds and find that contrary to the "catapult model" the cloud is destroyed on the order of a sound-crossing time without any significant deceleration, and thus cannot reproduce observed line profiles. If the clouds are inflowing under the influence of gravity, this suggests that we turn our attention to the acceleration region, independent of any destruction process. We find that the thermostatic effect of radiative cooling stabilises the cloud against mass loss. We argue that non- adiabatic clouds may survive of the order ~ 100 sound-crossing times. This is what we require if the narrow line region consists of ~ 104 clouds. In the broad line region we examine the "energy budget problem". The possibility that shock-heating may provide an additional source of energy input to this region is investigated. The results suggest that the high ionisation lines may be enhanced by this process.

In this thesis I describe a number of projects arising from the ROSAT mission, inspired by a desire to understand better the activity of late-type stars from studies of their coronal EUV and X-ray emission. A brief introduction summarises some of the most important work on cool star coronas. The second chapter describes the mechanisms by which X-rays are produced in coronal plasmas. I also discuss the ROSAT mission, its instrumentation and applicability for observing cool stars. In Chapter 3 I describe the discovery of one of the brightest sources in the EUV sky, the hot white dwarf companion to HD 33959C. I discuss the importance of such binaries for the determination of more accurate measurements of mass, radius and distance than is possible for isolated white dwarfs. Chapter 4 is a WFC survey of all known late-type stars within 25 parsecs of the Sun. I construct and discuss the first ever EUV luminosity functions for such a sample and show that stars in interacting binaries are more active than single stars. In Chapters 5 and 6 I present a deep PSPC survey of the Hyades, comprising 11 overlapping pointings. In Chapter 5 I derive the Hyades dK and dM X-ray luminosity functions down to Lx ~ 5 x 1027 erg s-1. In Chapter 6 I investigate the X-ray spectra of the more luminous Hyads, both non-parametrically using hardness ratios, and parametrically using simple one-temperature and two-temperature fits to the data. Flares were observed in VB 50 and VA 334; both stars show increases in temperature and emission measure during the flaring episodes. In Chapter 7 I summarise my conclusions and discuss projects which arise from the work presented in this thesis. Finally I describe some of the impacts that we may expect to see from three future missions, JET-X, AXAF and XMM.

The growth mode and the electronic and magnetic properties of nanoscale Mn structures, in the form of islanded films and deposited mesoscopic clusters, have been investigated using synchrotron radiation. The Volmer-Weber growth of Mn films was studied by modelling the surface reflectivity in the extreme ultraviolet region (6-36 nm). The island growth at 423 K showed a change in growth mode as a function of coverage. Spin Polarised Photoelectron Diffraction (SPPED) from thick Mn revealed that the short range magnetic order (SRMO) is lost at a temperature of 505 K, 5.3 times the bulk Neel Temperature. Results for an islanded film, where the average island size was 6 nm, showed surprisingly that SRMO breaks down at the bulk Mn Neel temperature, with the interpretation that a complete loss of magnetic order is induced down to atomic length scales in the mesoscopic system. Core level and valence band photoemission from islanded Mn films have shown modified lineshapes in comparison to the bulk. The peak asymmetry of the 3p core level increases with decreasing particle size indicating a perturbation of the collective electron response upon the production of a core hole. The valence band and 3p core level photoemission also showed marked changes in lineshape as the temperature was increased through the bulk Mn Neel temperature. Mesoscopic Mn clusters have been deposited in-situ with the use of a high temperature gas aggregation source. Both unfiltered and size-selected 2.5 nm clusters have been investigated. Photoemission from exposed clusters showed significant changes in the Mn 3s core level line shape with respect to the bulk, interpreted as an enhanced atomic magnetic moment. Unfiltered Mn clusters were also embedded in a V matrix revealing a satellite structure in the 3s photoemission from V suggesting that the Mn clusters magnetically polarise surrounding V atoms.

At auroral latitudes, large electric fields drive the F-region plasma of the ionosphere through the thermosphere, heating the ion population through frictional contact with the neutral gas. Ion frictional heating, which can double the unperturbed ion temperature, is an important manifestation of both magnetosphere-ionosphere and ionosphere-thermosphere interaction and provides a significant contribution to the energy budget of the ionosphere and neutral atmosphere at high-latitudes. Perhaps the single most powerful technique for ground based remote sensing of the ionosphere is incoherent scatter. The EISCAT radar facility, located in northern Scandinavia, employs this technique to investigate the highly dynamic nature of the high-latitude ionosphere. This thesis documents a study of ion frictional heating in the high-latitude ionosphere, principally employing common programme observations by the tristatic EISCAT UHF system. In excess of 3200 hours of EISCAT observations, taken during a six year period, were employed to study, on a statistical basis, ion frictional heating in the high-latitude F-region. The diurnal distribution of frictional heating was established and its dependence on such factors as geomagnetic activity and solar cycle was investigated; the distributions were interpreted with reference to corresponding distributions of enhanced ion velocity. A prolonged and intense interval of ion frictional heating was observed by EISCAT postnoon on 04/03/1992: this interval was modelled, using the Sheffield University plasmasphere and ionosphere model, and the model results compared with the observations. This study highlights the importance of ionospheric effects in determining neutral dynamics, particularly on the dayside. Furthermore, during this interval, the altitude dependence of the effect of enhanced electric fields on the velocity and temperature of the ion population was studied and, moreover, employed to provide first-order estimates of the normalised ion-neutral collision frequency and the neutral wind at E-region altitudes.

A variety of primary inclusions are present within apatite crystals extracted from East African and Swedish ijolites and carbonatites. They provide unique, albeit rather minute, geochemical samples of the crystallising fluids which were present during the growth of apatite. These inclusions contain varying amounts of solid material and by using the E.M. P., together with a combination of optical and microchemical tests the major chemistry of the various solid components has been established. In the ijolitic rocks from the Usaki complex of Western Kenya multisolid, carbonate-rich melt inclusions, which consist of alkali-rich carbonates, sulphates, and halides are present. The composition of the Ca-Na-K Carbonates within these inclusions is extremely similar to that recorded for the major carbonate phases from the natrocarbonatite lavas of Oldoinyo Lengai. Silicate glass inclusions are also present in some samples and these consist of two chemically contrasting types, one of which is Na-rich and undersaturated while the other is K-rich and oversaturated. These two glasses appear to show an immiscible relationship. Alkali-rich aqueous inclusions containing nahcolite (NaHCO3) together with solid inclusions composed of single crystals of calcite are also present within the ijolitic apatites of the Usaki complex. Apatite crystals which occur within late-stage patches of calcite in Alno ijolite pegmatites from Sweden do not contain melt inclusions but are dominated by concentrated aqueous saline types. Individual inclusions often contain up to 6o% of solids which include nahcolite, kalicine (KHCO3), alkali chlorides, alkali sulphates and opaque specks. These inclusions formed at lower temperatures (=450°C-) than the melt inclusions of the Usaki ijolites (= 680 - 950°C). Solid inclusions which contain calcite, pyrrhotite biotite and magnetite have also been recognised. Aqueous-rich inclusions are dominant in the apatites of the Tororo carbonatite of Eastern Uganda but a variety of solid inclusions are also present. The following types have been recognized: calcite, shortite, pyrrhotite and magnetite. It is concluded that these apatites were formed directly from an aqueous-rich alkaline solution at temperatures in the region of 400°C. The majority of inclusions studied contain minor amounts of opaque material and in both ijolitic and carbonatitic apatites pyrrhotite and magnetite have been recognised.

A theoretical model which permits the computation of average surface temperature trends over the whole life-time of any terrestrial planet is described. The evolution of the atmosphere is considered in detail, and the changes in the physical parameters which affect the surface temperature are discussed. The variables of particular importance are the planetary albedo, the flux factor (a parameter previously considered constant), the infrared absorption spectrum of the atmosphere, the surface infrared emissivity and the probable evolutionary changes in the solar luminosity. Each of these parameters is discussed in detail and the possible feedback mechanisms which may link them to the evolution of the planetary atmosphere/surface system are considered. The computational techniques utilized in the development of the numerical model are described. The errors are discussed and the model is found to be widely applicable and to produce smoothed temperature tracks which agree well with present-day data for both the Earth and Mars. Numerical methods are used to extend laboratory parameterizations for the variation of absorption with absorber amount and partial pressure for two gases: carbon dioxide and water vapour. Trace constituents and the effect of broadening: by neutral gases are discussed. The resulting temperature curves exhibit a number of interesting features. In particular, a number of the model planets considered are found to exhibit remarkably stable surface temperatures as their atmospheres evolve. This stability results, in part, from the compensatory nature of the evolution of some of the planetary parameters. The rate and mode of degassing is found to be particularly important for Mars and may also be important for Venus. The temperature curve for the Earth remains above the freezing point of water throughout the life-time of the planet, and thus the predicted results agree well with geological data. Shorter-term fluctuations leading to glaciations, etc., are also discussed.