The region of the ionosphere situated above the E layer peak and below the F layer is difficult to investigate using conventional ground based techniques, consequently our knowledge of this region is limited. An attempt has been made in this study to construct representative electron density distributions from a consideration of the fine structure observed on ionospheric sounding records and of the variation of the absorption and virtual height of a fixed frequency during the growth of the ionosphere below 200 km following the sunrise. Special reference was made to the results obtained for frequencies reflected near the E layer peak and the validity of this analysis in this region of high deviative absorption and group retardation is discussed. Attention is drawn to the large variation in published values of the collisional frequency above 120 km and an attempt has been made to construct a suitable height variation of this parameter for use in the calculation of absorption. Routine ionospheric soundings were made hourly over an extended period and augmented with continuous soundings on a number of selected days between February and June 1969. Also on 42 days during this period, measurements of absorption and virtual height were carried out on a fixed frequency for several hours following the sunrise. The variations of absorption with time and virtual height with time and frequency were computed from the electron density profiles obtained from 3 independent sources (a) Theoretical post sunrise profiles constructed by Bourne, Setty and Smith. (b) Monotonic profiles computed from Leicester Ionograms (c) Profiles observed by a Thomson Scatter technique at R.R.E. Malvern. The results of these calculations are compared directly with the experimental observations and computations of the variation of absorption with frequency are also discussed. From a synoptic study of the cusp features observed on ionospheric soundings it is found that complex cusp structure around f E is a regular phenomenon at Leicester occurring throughout the day but showing some decrease in occurrence frequency towards noon. The development of this structure can be represented by an expression of the form fcusp = A cosn x where different cusp features take differing values of the constant A. The comparisons made in this study indicate that the polynomial reduction technique produces monotonic electron density profiles which satisfactorily represent conditions when only the virtual height is considered but are not capable of producing calculated absorption values to the same degree of accuracy. The virtual height and absorption values computed from the Thomson Scatter profiles are in good agreement with experimental observations of these parameters at Leicester. These profiles are therefore considered to accurately represent the structure of the electron density distribution. The existence of the small undulations, as evident in these profiles, is shown to account for the multi-cusp phenomenon and various observations concerning the variability and extent of such structures are described. In addition, these comparisons have indicated some inadequacy in the growth theory employed in the derivation of the Bourne, Setty and Smith profiles. As a result of comparing the variation with frequency of both the virtual height and absorption it has been shown experimentally and supported theoretically that indicating that absorption especially in the deviative region may be a more sensitive parameter to profile fine structure. It is anticipated therefore that sweep frequency absorption sounding may indicate more clearly short term perturbations in the electron density profile.

The effects of volatile anaesthetic agents on three aspects of presynaptic acetylcholine (ACh) metabolism were investigated in vitro. Choline uptake and choline acetyltransferase (ChAT) activity were studied using rat cortical synaptosomes and ACh release was investigated employing rat cortical slices. The effect of volatile anaesthetic agents on neurotransmitter systems and the importance of ACh as a central neurotransmitter involved in the regulation of the conscious state is discussed. The evidence suggesting that central ACh function may be altered by anaesthesia is reviewed. Total choline uptake was inhibited non-competitively by all three volatile anaesthetic agents studied and the IC50 was 1.38 % for halothane, which is close to the ED50 for unconsciousness (minimum alveolar concentration, MAC). If present in vivo this may contribute to the process of anaesthesia. The Michaelis constant (Km) of ChAT was reduced significantly by enflurane but was unaffected by halothane and isoflurane. If present in vivo, an enflurane-induced reduction in Km of ChAT could lead to facilitation of ACh synthesis and contribute to the convulsant properties of enflurane, ACh release was measured using a modified chemiluminescent assay. ACh release was inhibited by halothane with an IC50 of 0.38 %, approximately one third of MAC. This is the most potent anaesthetic effect on neurotransmitter release reported in vitro to date. The results of this study demonstrate the in vitro sensitivity of presynaptic cholinergic metabolism to clinically relevant doses of anaesthetic agents and suggests that the cholinergic system may be a target for their action.

The thesis seeks to consider the extent to which the financial sector of a developing economy can increase economic growth and development. Following the description of the general characteristics of Kuwait's economy in chapter two, the literature on the relationship between finance and economic growth is discussed in chapter three. The implications of this research for the Kuwaiti situation were made explicit. An analysis of the structure and performance of the Kuwait financial system was undertaken in chapters four to seven. The evolution of financial and monetary policy in Kuwait before and after the establishment of the Central Bank is discussed. The activities and operations of commercial banks, specialised credit and non-bank institutions and the role of the Islamic bank are also discussed. This analysis sought to consider whether the operations of the financial system have been consistent with the country's development strategy. An econometric model was then constructed in chapter eight in order to investigate the behaviour of the monetary sector in Kuwait. Of particular importance here was the operation of Euro-dollar markets on such behaviour. The thesis contends that international interest rates have a direct effect upon Kuwaiti financial institutions, which, in turn, influence domestic liquidity and economic growth. A negative and highly significant relationship between the Euro-dollar interest rate variable (ur) and the public demand for money (M2) was found. Ur seems insignificant in affecting demand for narrow money (Ml). The ur variable was also found to be negative and highly significant in affecting the behaviour of time and saving deposits. It is argued that the C.B.K. has been unsuccessful in achieving an effective monetary policy capable of directly influencing financial and economic growth. The C.B.K. has been unable to influence the differential between international and domestic interest rates. The role played by commercial banking has also been under-developed. Greater attention to the development of the agricultural and manufacturing sectors, as well as to financial markets in Kuwait, needs to be undertaken. The financial system must play a more vital role in the country's overall development. These recommendations imply a reduction in the overall dependency on the oil sector in Kuwait.

This thesis describes principally ROSAT and HST observations of magnetic (or proposed magnetic) cataclysmic variables. Chapter 2 details a ROSAT observation of the polar EK UMa. The orbital light curve reveals a single bright phase. During this bright phase deep dips in the flux are seen, consistent with accretion stream occultation. The soft X-ray spectrum has an unusually high temperature of 50 KTBB 62 eV. No hard X-ray flux is detected. Chapter 3 details ROSAT observations of proposed intermediate polars SW UMa and 1H0709-360. The previously reported X-ray/optical periodicities in SW UMa were not detected. Spectral analysis indicates a two-temperature model is appropriate. The weak signal from 1H0709-360 precludes a detailed spectral analysis. 1H0709-360 has dropped in flux by ~ 2 orders of magnitude since its detection. The intermediate polar classification of these two systems remains unconfirmed. Chapter 4 describes ROSAT and contemporaneous optical and HST observations of the intermediate polar AE Aqr. During this observation X-ray flares were detected for the first time. The white dwarf spin modulated count rate increased only slightly with increased intensity. AE Aqr has an unusually soft spectrum which is only fit by a two temperature optically thin plasma emission model. Chapters 5 and 6 detail ROSAT, HST, EUVE and complementary optical observations of the polar QS Tel. The soft X-ray/EUV data showed a bright-faint morphology. The EUVE observations, ~ 1 year later, revealed a change in morphology, indicating that both poles were active. A deep narrow dip is observed in both the ROSAT and EUVE observations. The HST (FOS) observation had a mean spectrum of an underlying continuum with strong emission lines superposed. Orbital modulation was present in both. A narrow dip is observed in the continuum fold which is consistent with the dip observed by ROSAT and EUVE.

Extrapolated range values for homogeneous electron beams derived from an electrostatic generator, over the energy range 0.25 - 0.75 MeV, have been measured in aluminium, and four other metals, covering the range of atomic number 4-79, by two methods. Current collection range values in aluminium appear significantly lower than values obtained with other detectors, such as geiger counters and ionisation chambers with good geometry, but the extrapolation of ionisation-in-depth curves in aluminium yields range values in good agreement with accepted figures. Universal transmission curves and extrapolated range-energy curves for Be, Al, Cu, Ag and Au by current collection, and universal curves for Al and Ag from ionisation-in-depth curves are presented. The former curves are taken in carefully standardised geometrical conditions, the effect of suppressing low energy secondary emission and of varying collector geometry on range values having been assessed. The previous work on extrapolated range values in metals is reviewed, and the region of applicability of the extrapolation procedure appears to be greater with current collection methods than had been assumed in previous work with other detectors. Comparison of ionisation-in-depth curves with theoretical energy dissipation distributions for equivalent plane geometries has been made, and good agreement found. By comparing the data obtained with other results in equivalent geometrical conditions, an attempt has been made to assess an inferred slight dependence of range values upon the nature of the detector.

The extension of conventional monochromating techniques into the ultra soft x-ray region has been discussed. The use of large spacing pseudo crystals has been considered with particular reference to multilayer soap crystals. In an attempt to produce these crystals with the best possible x-ray reflection characteristics a detailed analysis of the building process and the associated parameters has been carried out. A specially constructed plane crystal spectrometer was used to obtain new extensive absolute reflectivity data for these optimised crystals. The results show that the crystals have an unusual structure exhibiting considerable imperfection. New reflectivity data for potassium acid phthalate (K.A.P.) crystals has also been obtained. Proportional counter detection was used throughout this work and in this connection proportional counter resolution has been studied in some detail. The importance of anode wire uniformity has been investigated in more detail than previously reported. By using a very smooth anode wire better resolution measurements have been obtained, in the 0.2-10 k.e.v. photon energy region, than reported in any previously published data.

Chapter 1 represents a review on the synthesis and structure of 1-substituted 2,2,3,4,4-pentamethylphosphetans. In Chapter 2 the stereochemistry and mechanism of base-catalysed phosphetanium salt hydrolysis are envisaged and shown to depend upon the reaction conditions, in particular the pH of the medium. The results are interpreted in terms of the intermediacy of TBP structural phosphoranes, and the most significant role of the BPR as a viable mechanism for intramolecular isomerization of such intermediates, in determining the products distribution, is discussed. The possibility of a pre-decomposition equilibrium between diastereomeric salts via pseudorotation is considered and shown to occur, specifically, in very dilute alkaline media. A change in the reaction rate-limiting step from a slow isomerization process to a phosphorane decomposition is postulated to account for variation in product composition on varying the conditions. The alkaline hydrolysis of r-1-substituted acetylenic 2,2,3-trans-4,4-pentamethylphosphetanium bromides proceeds, in contrast to the generally reported retention as the stereochemically preferred pathway for phosphetans, with complete inversion of configuration. Base-catalysed ring expansions of a number of salts are shown to proceed, stereospecifically, to give only one observable product oxide. This is attributed to a very short-lived intermediate phosphorane. In the end a qualitative scale of the relative apicophilicities of the studied groups, is observed. In Chapter 3, an attempt to synthesise the 1:2 adducts of 1-substituted acetylenic-2,2,3,4,4-pentamethylphosphetan with HFA resulted in formation of other products for which a probable mechanism and structures, based on spectroscopic and elemental analysis data are discussed and suggested for each product. A variety of phosphoranes containing phosphetan rings was synthesised. A kinetic study of the rate of reaction of 2-ethoxy-1,3,2-dioxaphospholan with benzil showed the reaction to follow a bimolecular step-wise mechanism. Relative apicophilicities of a number of groups attached to the phosphorus atom in phosphetan adducts were determined by monitoring the high energy isomerization pathways, accessible to these adducts, in which the five-membered rings span diequatorial positions, using 1H n.m.r, spectroscopy techniques. The values so determined are rationalised in terms of substituent electronegativities and the extent of a probable ?-electron interaction with the phosphorus d-orbitals.

Low frequency (LF: 30-300 KHz) radio waves can be employed for communications purposes and as a means of probing the earth's lower ionosphere. In this thesis theoretical and experimental techniques are employed to investigate the propagation characteristics of LF waves in the spherical earth - ionosphere duct, with particular emphasis on high latitude conditions. The "wave-hop" theory of LF propagation, in conjunction with previously measured electron density and collision frequency profiles of the ionospheric D region, is used in a study of the behaviour of LF radio links under realistic operating conditions. The choice of frequency and receiver height is shown to have a critical effect on the received signal strengths during day - and night-time conditions. The influence of the geomagnetic field, ground conductivity, and ionospheric parameters on the occurence of regions of low signal strength are also assessed. The results of a series of airborne experiments are presented. Interference effects arising at a discontinuity in ground conductivity are demonstrated. Propagation data obtained at VLF and LF are interpreted in terms of D region models; the LF data are found to be considerably more sensitive to D region parameters than those obtained at VLF. Profiles providing a best fit for daytime conditions are derived; their accuracy and resolution and their photochemical implications are discussed. LF data are also employed to select a best fit nighttime electron density profile from a set of published profiles. An overall assessment of the theoretical and experimental aspects of this study concludes that an acceptable degree of consistency has been obtained.

A new curved crystal Xray spectrometer, with a spot focus Xray source and proportional counter detector, has been constructed and its design is described. The results of a preliminary investigation into the variation of the intensity received at the detector, with movement of the source, are discussed. A study of the Mv absorption line of ytterbium has been made and the Miv and Mv absorption edges of ytterbium, lutecium and hafnium together with the Miii edge of ytterbium are reported for the first time. The discrepancy between the observed positions of the Miv and Mv edges and those calculated from data on the L spectra of these elements is discussed. A comparison has been made between the absorption of ytterbium in the pure metal and in compound, and the absence of the Mv absorption line for the metal clearly indicated. The Miv and Mv edges of the metal have been found to occur at energies some 14 ev lower than those of ytterbium fluoride (or oxide) and the cause of this shift is indicated. To facilitate the preparation of pure metal foils an evaporation chamber attached to the spectrometer tank has been designed and constructed. By this means the foils could be prepared and transfered into the Xray beam without exposure to air. The measurement of the Miv and Mv edges of tantalum (oxide) is described and a suggestion made to account for the difference between their previously reported positions.

The aim of this work was to investigate the luminescent mechanism in pure CdS single crystals and to attempt to obtain unambiguous evidence in favour of one of the two models proposed in the literature (the Schon-Klasens or the Lambe-Klick model). Experiments have been carried out on undoped specimens obtained from three different sources and an attempt has been made to correlate transport, electrical, optical and luminescent properties measured on the same specimens. The results of electron transport measurements, based on drift mobility techniques, on a number of specimens indicated that the drifting electrons interact predominately with either a shallow centre lying at about 0.03ev or with a deeper level at 0.l6ev below the conduction band. Moderate heat treatment (360C) led to a progressive reduction in the density of the 0.16ev centres and also quenched the emission. The other properties studied were (a) the free electron density as a function of temperature and excitation intensity, (b) the temperature and excitation intensity dependence of the luminescence (c) its spectral distribution, and (d) the optical quenching spectrum. From the results of these experiments it is concluded that: (i) the 0,16ev centres are not directly connected with the luminescent transition and a model based on the Lambe-Klick transition appears unlikely, and (ii) a class II centre (Sp > Sn) lies between 0.13 and 0.15ev above the valence band, which accounts for the supralinearity observed in the electron density as a function of excitation intensity, and also explains the temperature dependence of n. The results of the electrical measurements have been fitted to a three centre model of a photoconductor. The free carrier densities and occupation of the centres have been calculated by computer as a function of temperature and excitation intensity for various sets of parameters characterising the centres. On the basis of this model the dependence of luminescence on the temperature and excitation intensity has been predicted. A comparison between the computed and experimental curves indicates that only a model in which the radiative recombination is associated with a trapped hole (in a class II centre) and a free electron (Schon-Klasens model) can predict the experimental results correctly. It appears likely that the luminescent centre is a class II centre. The reduction in the density of 0.16ev centres below the conduction band and the loss of emission appear to be two effects which are not directly associated. It is tentatively suggested that the centre seen in transport measurements is a cadmium interstitial and that the loss of edge emission by heat treatment in a vacuum, is probably due to the creation of cadmium vacancies at the surface. A reduction in the density of luminescent sites is not essential to explain the effect which is observed.