No description available.

No description available.

No description available.

No description available.

No description available.

A major problem experienced in HF data communications is that of multipath interference. Interference between the components, of a transmitted signal, arriving at the receiver over different propagation paths can produce serious errors in data transmission. A pulse sounding technique has been developed to resolve the interfering modes in the time domain. This signal consists of a O.7ms pulse of radio wave energy sent within a 2Oms break in transmission, repeated every 9Oms. The sounding signal is generated by a small computer which keys the radio transmitter. After reflection in the ionosphere the signal was received and digitised. A second computer then analyses the digital record to discover the amplitude and time of arrival of any sounding pulses present. The results are then compared with predictions to identify the active modes. Pulse sounding experiments were undertaken over four paths of lengths from 4 to 2156km. E,Es,F,2F,3F and auroral propagation paths were successfully recognised. This information could be used to advise on the likelihood of interference fading or more positively to control an elevation steerable antenna to adaptively cancel out this unwanted effect. To investigate the relationship between ionospheric conditions and the error rate in data communications a pseudo random test data message was transmitted with the pulse sounding. Measurements in the error rate in the message were conducted over the 578km path from Elgin to Leicester. It proved possible to establish an approximate correlation between the recorded data errors and the ionospheric conditions derived from the pulse sounding. This allows error rates to be estimated from the sounding results.

Electron spin resonance has been used to study the solvation and aggregate formation of silver species in various systems. Studies of silver centres formed in frozen mixtures of both protic and aprotic solvents, after gamma-irradiation at 77 K in a 60Co [special character omitted]source, have been made in an attempt to establish a link between the different types of solvation found in various solvent systems. These studies have also led to the identification of a series of organo-silver adducts. Studies have also been made using a range of nitrogen containing solvents where the detection of 14N super-hyperfine coupling to silver has provided information concerning the arrangement of solvent molecules around the central metal ion. Following this mixed solvent work, the effect of mixed silver salt systems, comprising AgC104 +AgN03 and + Ag2S04 in methyl cyanide, has been studied in order to probe the competition which exists between different anions and solvent molecules as they attempt to coordinate to the silver ion. A section describing the study of various copper (I) and copper (II) salts in methyl cyanide has been included in a study of a series of gold(I) compounds of clinical interest and gold(III) compounds of photographic interest. This has enabled a comparison of certain analogous Cu, Ag and Au species to be made. Complexes of silver with a range of organic olefins have been prepared and studied by e.s.r. after gamma-irradiation, including complexes with cyclohexene, toluene, benzene and but-2-ene. A range of photographic emulsion systems containing sensitising and electron trapping agents have been exposed to blue light and gamma-irradiation, the effects of which have been recorded by e.s.r. Finally, a variable temperature u.v. spectrophotometric method, designed to study samples which have been X-irradiated at 77 K, is described. Included in this section are initial experiments aimed at detecting silver centres and aggregates formed on irradiation, at low temperatures.

A detailed programme of methods for calculating and measuring crystal Bragg reflection characteristics is presented. The characterisation of an analyser involves determination of, as a function of wavelength, the Bragg dispersion function (defined in Chapter 2) and Rc, wc, Pc the integral, width and peak respectively of P lambda(theta) the crystal line spread function (or diffraction profile). Calculations are based on the Prins perfect lattice, Darwin zero-extinction and zero-absorption models,outlines of which are given. Measurement methods for determining the Bragg dispersion function and P lambda(theta) of an analyser are described. A comparison of various 1- and 2-reflection techniques used to measure RC(lambda) is made and from this it is clear that the chosen 2-reflection methods,with the inclusion of appropriate polarisation corrections,provide an efficient means of measuring this characteristic. Likewise a comparison is made of 1-, 2- and 3-reflection techniques previously used to determine P lambda(theta) and a new technique is introduced. This latter involves perturbing the calculated Prins function so that a fit between the self-convolution of the perturbed function and the (1,-1) rocking curve is obtained. Only perturbations which model the effects of known lattice defects are allowed. Within the limits discussed the perturbed function describes the true P lambda(theta). Emphasis is placed upon instrument alignment, and measurement conditions required,in all measurement techniques used. A description of the Leicester 2-crystal spectrometer and its alignment is included,together with measurement procedures. The above methods are applied in full characterisations of the analysers PET (002), EDdT (020) and ADP (101). Also included are calculated results for SHA (110) which allow interpretation of previous studies made by measurement alone. The thesis concludes with two brief reports of crystal calibration studies for the satellite UK5 and for American Science and Engineering. These reports illustrate the application of the methods used in this study to other research work.

Several aspects of X-ray position location in an imaging multiwire proportional chamber (MWPC) are examined in this work. Experimental confirmation is obtained of existing theoretical predictions which take into account the presence of avalanche angular localisation. An attempt is made to exploit the effects of the latter by means of a position-encoding RC transmission line, revealing that the variations in signal risetime caused by angular localisation are detrimental to linear operation of the line. Other results indicate that successful exploitation by different means is possible. A brief study of electron diffusion effects in MWPC's is made, giving some agreement with predictions, but also exposing an effect which degrades resolution and improves linearity in one sensing direction only (that perpendicular to the anode wires). This effect has yet to be explained. The series capacitance line is examined in the context of MWPC operation, and is found to offer superior spatial resolution (though slightly inferior linearity) to that obtainable with an RC line. The concept of the graded-density (GD) cathode is introduced, and an experimental study shows that the device can be fully competitive as the encoding cathode of a MWPC. Once again, the spatial resolution is superior to that obtained with an RC line, although some small local readout non-linearity mars the present performance. Finally, the cascading of two such electrodes to form a single "subdivided" GD cathode is studied. In this case the cathode behaves similarly to a series capacitance line, and the facility for partially compensating for the resultant nonlinearity, by adjustment of the density gradings, is demonstrated.

No description available.