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This thesis addresses itself to the solution of a number of problems which arise in the development of Radio Frequency filters, particularly those involving coupled transmission lines as resonant elements. The text is divided into a number of sections dealing with individual topics. After a brief description of Darlington filter design principles, there is an account of the pivotal role of quarter wave sections and their vital part in the realisation of high frequency filters. This is followed by the development of new material relating to equivalent circuits of physical lines in terms of quarter wave sections, and its application to improvements in the design of wide-band filters. There follows an account of a new procedure for calculating the dimensions of comb-line and inter-digital filters. This section includes a new proposal for the inversion of Getsinger's procedure to permit the calculation of rectangular rod dimensions and spacings from given electrical data. There is also an algorithm for use with round rods which circumvents the tedious manual interpolation procedure devised by Cristal. There follows an investigation of and a proposed solution to a long-known but unexplained discrepancy existing between the calculated and measured pass-band width of the class of comb-line filters. With the new procedure the discrepancy reported previously to be of the order of 10% is eliminated. Finally, experimental evidence is adduced to verify the algorithms outlined in the preceding chapters.

In the course of four initial studies a new stereotype measure is developed which captures ingroup serving generalisations. The new implicit ratio technique draws on experiences gained from using existing instruments to assess stereotyping. It combines the probabilistic approach of diagnostic ratios (McCauley & Stitt, 1978) with elements introduced by Esses et al. (1993), using perceiver-generated idiosyncratic stereotypic material which is qualified for meaning. The implicit ratio assesses individual levels of generalisation. The trait frequency processing involved in generalisation was found to be consistently biased in favour of the ingroup. Trait frequency bias tends to be spontaneous, automatic and largely independent of specific content or context. Since mere categorization into arbitrary groups already elicits trait frequency bias, four further studies examine perceivers' level of control over trait frequency processing. Changing attributional perspective towards the ingroup as a whole accentuated bias, whereas heightened accountability and direct instructions to suppress stereotyping reduced it. However, significant inhibition of bias as result of suppression instructions were restricted to within subjects designs. After these instructions are relaxed trait frequency bias recovers in strength. The differential effect of category primes on content valence and trait frequency bias suggests a direct effect of manipulations, merely mediated by content dilution. Differences between semantic suppression and inhibition of trait frequency bias are discussed. The discussion extends to the usefulness of the implicit ratio as an experimental tool and to wider implications of the trait frequency bias approach to stereotype measurement

Atrial fibrillation (AF), is characterised by rapid, irregular atrial stimulation, which leads to reduced contraction, resulting in a negative force-frequency-relationship (FFR). It is thought that rapid stimulation frequencies, which are synonymous with AF, disturb excitation-contraction-coupling (ECC). Ageing increases both the prevalence and economic impact of AF progressively. Although mechanisms underlying AF have been investigated in human and animal models, the cellular electrophysiology, and molecular changes that render the atria in aged individuals more susceptible to AF, still remain poorly understood. To our knowledge, there are no data investigating the effects of rapid stimulation frequencies on the Ca2+ handling within atrial myocytes, of a larger mammal, which are able to maintain AF, and is physiologically relevant to the human. To investigate this, sheep atrial myocytes were isolated, via enzymatic digestion. Measurements of intracellular Ca2+ ([Ca2+]i) were obtained via analysis of fluorescence (Fluo 5F am). Electrophysiological experiments were performed via the perforated-patch clamp technique, under voltage-clamp stimulation, to assess measurements of [Ca2+]i and trans-sarcolemmal currents. All voltage clamp experiments were performed at 37°C. Analysis of CaMKII inhibition, on Ca2+ wave frequency, was performed in non-stimulated atrial myocytes, at room temperature. Increased stimulation frequency (from 1Hz – 5Hz) had a significant impact on Ca2+ handling and trans-sarcolemmal currents within the atria. A reduction in Ca2+ transient amplitude was observed with increased rate. This was achieved despite increases in SR Ca2+ content, which were due to increased SERCA activity. The reduction in Ca2+ transient amplitude was attributed to reduced L-type Ca2+ current (ICa-L). Ageing augmented the rise in diastolic [Ca2+]i which was observed with rate, but with no further impac on Ca2+ transient amplitude. The rate dependent increase in SR Ca2+ content was augmented with age, and was presumed to be as a result of a reduction in ICa-L.By sensitising the ryanodine receptor (RyR), with low-dose caffeine (500 μmol.l-1), the fractional release of the first Ca2+ transient upon application was exacerbated by an increase in rate. This rapidly decayed to control levels at all stimulation frequencies. This data suggests that increases in RYR sensitivity lead to a greater Ca2+ release from the SR, for a given trigger. By ceasing stimulation there was potentiation of the first Ca2+ transient, post-rest, in comparison to pre-rest at 1Hz. This was augmented by increased rate. As ICa-L was unaltered between pre- and post-rest, within each frequency, it was assumed that the increased SR Ca2+ content with rate, coupled with continued SR Ca2+ uptake during the rest period, enhanced the fractional SR Ca2+ release for a given trigger, thus potentiating the amplitude of the Ca2+ transient. However, this requires further investigation. Other data found that CaMKII inhibition (via KN93) had no effect on Ca2+ wave frequency in control, or heart failure (HF), non-stimulated sheep atrial myocytes, which suggests either CaMKII is not up-regulated in the HF model used, or the concentration of KN93 used was insufficient. Further investigation is required in this area. The alterations in the mechanisms that modulate SR Ca2+ release and uptake are affected by alterations in stimulation frequency, which alter key modulators of contractile force.

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A synchronization scheme enabling the use of OFDM/FM in a pure ALOHA environment over a mobile radio channel is proposed, implemented, and tested. The synchronization scheme encodes synchronization information in parallel with data in the same manner in which data is encoded in the OFDM/FM frame. The encoded synchronization information is in the form of tones, centered in reserved frequency sub-channels of the OFDM signal. The receiver uses a correlation detector, implemented in the frequency domain, to accurately acquire synchronization on a packet by packet basis. Experimental results indicate that BER performance with synchronization is achieved to within 1.5 dB of the performance achievable with ideal synchronization. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis describes a new method of obtaining suitable equal-ripple rational functions for use in the synthesis of networks. It has two principal advantages over other methods used for this purpose. Firstly, it is capable of finding the best approximation to a given magnitude function, phase function or both simultaneously. The error of approximation may be weighted as desired at any frequency in the range of approximation. Secondly, it is easily adapted for use on anautomatic computer. This enables quick comparison of the approximations produced by using rational functions of different orders of complexity. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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The subject of this master’s thesis is „Frequency method for investigation discreet regulation systems“. It’s primary conversant of constructing frequency characteristics for discreet systems. The works has a two parts. The firs part indicates provides theoretical information and the basic relations needed to clarify construction of frequency characteristics continuous and discrete systems too. The second part includes main job description given by the headman of this thesis. It’s consisting of constructing catalogue of the frequency discrete characteristics for discrete systems and creation program for calculation and construction of this systems.