This thesis describes the theoretical adjustment of the tuning of multicavity klystron amplifiers for prescribed frequency response. The method used is an iterative process developed at Stanford University in 1952. The purpose of the investigation was to test the applicability of the iterative method to the design of microwave amplifiers. The rational function representation of klystron amplifier response is described and it is shown that for physical realizability the zeros of transmission must be dependent on the poles of transmission. An iterative numerical method is developed for simultaneously fulfilling the prescribed response conditions and the physical realizability condition. Illustrative numerical designs of four- and five cavity klystron amplifier tuning are given which verify the method. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A multistable composite volt-ampere characteristic can be realized using a number of tunnel diodes. A maximum of 2ⁿ stable states can be obtained using n suitably chosen tunnel diodes connected in series. The main purpose of this study is to investigate the static and dynamic characteristics of such a circuit. Preliminary work deals with the switching behaviour of a single tunnel diode and the dependence of the switching time on the figure of merit and the current overdrive. This work serves as a background to the study of the multistate circuit. The study of the static characteristics of the composite device determines the conditions necessary for the generation of the required number of stable states. Additional conditions necessary to ensure proper operation are derived from the study of dynamic characteristics of a two tunnel diode multistate circuit. The dynamic conditions derived involve the tunnel diode capacitances and their ratio. The temperature dependence of the circuit is also investigated. Experimental results are presented showing an operating speed of 12.5 ns for a four state circuit using available tunnel diodes. The versatility of the composite characteristic obtained, and the inherent high speed of the tunnel diodes combine to make the multistate device useful in high-speed digital applications such as: binary addition, analog-to-digital conversion .and counting. These applications are discussed briefly. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The theory of the magnetic amplifier and other carrier amplifiers is put on a general mixer basis. The amplifiers are compared from this common basis and paths of further development indicated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Vortex stabilized argon arcs are of interest as sources of high intensity light. Previous workers in the field have found that the heat transported to the wall of the arc vessel greatly exceeded that predicted by theory. Two modifications to the theory have been proposed to account for the observed values of heat transport. This thesis describes a specialized arc vessel which has been constructed to allow the measurement of the axial profile of heat transported to the wall. The axial profile of radiation produced by the arc has also been measured. These experiments elucidate the mechanisms responsible for the large values of heat transported to the wall. In this work a 225 A d.c. arc was used. It was stabilized by an argon vortex at a pressure of 5.5 atm. It is found that the electrode regions of the arc contribute significantly to the total heat transported to the wall. Midway between the electrodes however, the profile is found to be quite flat. The experiments also indicate that some heat is transported upstream from the arc, and it has been shown that this is due to a reverse axial flow core in the gas vortex. The measured profile of radiation produced by the arc is found to be very uniform in the arc column. In the region midway between the electrodes the dependence of the radiation and heat transported to the wall on the gas flow rate in the vortex were examined. The measured radiation is found to be 30-35% less than predicted by theory. It is shown that this may be due to the axial transport of energy in the arc. The scaling of the amount of heat transported to the wall is found to be in good agreement with the predictions of a model for the arc which includes turbulent heat transport by using a mixing length model. The d.c. power supply used in this work produces a waveform with considerable ripple. Time dependent measurements were therefore made of the radiation produced by the arc and the electrical power input to the arc column. These results are compared with a time dependent theory of the arc column. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Yes / The application of vacuum venting for the removal of air from mould cavity has been introduced in injection moulding with the intent to enhance micro/nano features replication and definition. The technique is adopted to remove air pockets trapped in the micro-features, which are out of reach for conventional venting technologies and can create considerable resistance to the melt filling flow. Nonetheless, several studies have revealed a negative effect on replication that could possibly arise from the application of vacuum venting. Although the incomplete filling of micro-scale features has often been attributed to poor venting, the limited research examining the application of vacuum venting has produced mixed results. In this work, the effect of air evacuation was experimentally investigated, monitoring mould and polymer temperature evolution during the micro injection moulding process by means of a high speed infrared camera and a sapphire window, which forms part of the mould wall. The results show that air evacuation removes a mould surface heating effect caused by rapid compression of the air ahead of the flow front and subsequent conduction of that heat into the mould surface. Hence, with the increase of the surface-to-volume ratio in micro-cavities, air evacuation has a detrimental effect on the cavity filling with polymers that are sensitive to changes of the mould temperature.

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Fine coal constitutes a relatively small portion of a product stream in a coal cleaning plant. However, its processing cost is approximately three times higher than the cost of processing coarse coal. Therefore, many coal companies chose to discard the fines to refuse ponds, causing a loss of profit and creating environmental concerns. This problem can be solved by developing more efficient fine coal dewatering processes, since bulk of the cost associated with processing fine coal is due to dewatering. For this reason, Virginia Tech has developed new chemicals that can increase the efficiency of mechanically dewatering coal fines. To determine the performance of the novel reagents on fine coal dewatering, laboratory vacuum filtration and centrifugation tests were conducted. The utilization of the novel dewatering aids in the dewatering systems decreased the final moisture contents of the filter cakes to sufficiently low values. There was approximately 50% reduction in the cake moisture of many coal samples with the usage of the novel dewatering aids. The tests were performed on various coal samples from different coal preparation plants. This gave the advantage of testing the novel dewatering aids at many different conditions since each sample had its own characteristics. The vacuum filtration tests were extensively used to compare the efficiency of each novel reagent in dewatering. The best performing dewatering aids were determined and they were further utilized to analyze the effects of operational variables, such as; drying cycle time, cake thickness, vacuum pressure level and slurry temperature on dewatering. A statistical analysis was also performed to observe the effect of each factor quantitatively. The analyses were very useful in terms of determining the synergistic effects of these factors in dewatering of fine coal. The centrifuge tests were conducted to examine the efficiency of the novel reagents in a different dewatering application. The experimental results showed a significant improvement in centrifuge dewatering with the usage of proper coal sample. The moisture contents of fairly thick cakes decreased down to 5-10%. This outcome was very satisfactory since most of the dewatering aids commonly used in the coal industry were observed to increase the final cake moisture in centrifuge dewatering instead of decreasing it. Finally, surface chemistry analyses were performed on the coal samples and slurries to analyze the changes in the chemistry of the dewatering system in the presence of the novel dewatering aids. It was observed that there was a favorable improvement in the system chemistry, which was helpful in terms of decreasing the cake moisture content. These observations were also consistent with the results of the dewatering tests. The combined effect of the novel additives in decreasing the surface tension of the slurry and increasing the contact angle of the coal surface at the same time was concluded to be the reason for their significant performance as dewatering aids. / Master of Science