Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Cressler, John; Committee Member: Citrin, David; Committee Member: Shen, Shyh-Chiang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.Sc.(Electrical Engineering))--University of Pretoria, 2003. / Summaries in Afrikaans and English. Includes bibliographical references.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2017. / Food and water fuel and sustain life on earth. Since ancient times, their sourcing and preservation have been very important issues to humanity. In modern times, experimentation is a major step in analysing how cold storage problems in the medical and food science technology fields can be addressed. For investigating spoilage of new products and/or growth of pathogens in such cases, it is necessary to do experiments at different low temperatures for prolonged periods and check the effects. While this can be undertaken in a conventional two chambers fridge, it takes a long time to investigate a whole range of feasible storage temperatures. This dissertation describes work intended to treble the samples in such investigations and, therefore, significantly reduce the times. Six well- insulated chambers were constructed from plastic and wood and set at different temperatures. An ordinary deep freezer was used as the main heat sink for the chambers. Experiments were done with different methods to get the best result for the cold air flow into the chambers over period of eight months. The chambers temperatures were set between 0 and 15°C. It was finally established that a properly-designed six-chamber system could successfully be added to an ordinary freezer to provide different medium-to-high refrigeration temperatures without the use of a multi-pressure refrigeration cycle.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Electrical Engineering))--University of Pretoria, 2003. / Electrical, Electronic and Computer Engineering / unrestricted

Surpassing the fundamental limits that govern all electromagnetic structures, such as reciprocity and the delay-bandwidth-size limit, will have a transformative impact on all applications based on electromagnetic circuits and systems. For instance, violating principles of reciprocity enables non-reciprocal components such as isolators and circulators, which find application in full-duplex wireless radios, radar, biomedical imaging, and quantum computing systems. Overcoming the delay-bandwidth-size limit enables ultra-broadband yet extremely-compact devices whose size is not fundamentally related to the wavelength at the operating frequency. The focus of this dissertation is on using time-variance as a new toolbox to overcome these fundamental limits and re-imagine circuit and system design. Traditional non-reciprocal components are realized using ferrite materials that loose their reciprocity under the application of external magnetic bias. However, the sheer volume, cost and weight of these magnet based non-reciprocal components coupled with their inability to be fabricated in conventional semiconductor processes, have limited their application to bulky and large-scale systems. Other approaches such as active-biased and non-linearity based non-reciprocity are compatible with semiconductor processes, however, they suffer from other poor linearity and noise performance. In this dissertation, using passive transistor switch as the modulating element, we have proposed the concept of spatio-temporal conductivity modulation and have demonstrated a gamut of non-reciprocal devices ranging from gyrators to isolators and circulators. Through novel circuit topologies, for the first time, we have demonstrated on-chip circulators with multi-watt input power handling, operation at high millimeter-wave frequencies, and tailor made circulators for emerging technologies such as simultaneous-transmit-and-receive MRI and quantum computing. Delay-bandwidth-size trade-off is another fundamental electromagnetic limit, that constrains the delay imparted by a medium or a device within a fixed footprint to be inversely proportional to the signal bandwidth. It is this limit that governs the size of any microwave passive devices to be inversely proportional to its operating frequency. As a part of this dissertation, through intelligent clocking of switched capacitor networks we overcame the delay-bandwidth-size limit, thus resulting in infinitesimal, yet broadband microwave devices. Here we proposed a new paradigm in wave propagation where the properties such as the propagation delay and characteristic impedance does not depend on the constituent elements/materials of the medium, but rather heavily rely on the user-defined modulation scheme, thereby opening huge opportunities for realizing highly-reconfigurable passives. Leveraging these concepts, we demonstrated wide range of reciprocal an non-reciprocal devices including ultra-compact delay elements, highly-reconfigurable microwave passives, ultra-wideband circulators with infinitesimal form-factors and dispersion-free chip scale floquet topological insulators. Application of these devices have also been evaluated in real-world systems through our demonstrations of wideband, full-duplex receivers leveraging switched capacitors based true-time-delay interference cancelers and floquet topological insulator based antenna interfaces for full-duplex phased-arrays and ultra-wideband beamformers. Furthermore, to cater the growing RF and microwave needs of future, large-scale quantum computing systems, we demonstrated a low-cryogenic, wideband circulator based on time modulation of superconducting devices. This superconducting circulator is expected to operate alongside the superconducting qubits, inside a dilution refrigerator at 10mK-100mK, thus enabling a tightly integrated quantum system. We also presented the design and implementation of a cryogenic-CMOS clock driver chip that will generate the clocks required by the superconducting circulator. Finally, we also demonstrated the design and implementation of a low-noise, low power consumption, 6GHz - 8GHz cryogenic downconversion receiver at 4K for cryogenic qubit readout.

During World War II, with the armed forces waging war on several fronts and with the development of high altitude aircraft, the necessity for a great deal of low temperature testing was brought about. The production testing of various instruments and appliances, such as radios, cameras, clocks, and meters, which would be subjected to low temperatures in arctic climates or at high altitudes, was found necessary. This subject had been given very little consideration prior to the war. When it became necessary to test equipment at a low temperature, it was normally transported to a cold climate and there the tests were conducted. With the increased demand for low temperature testing, the expense and time delay encountered in such movements became prohibitive. During and since the war many low temperature test chambers have been built. The design problems encountered, such as load determination, defrosting, lubrication, refrigerant selection, proper staging, and control selection, have been similar, but the solutions have been different. Moore, Gellalles, and Young state: "Experience has shown that research requirements change so quickly and so radically that the original design specification cannot be much more than a hopeful guess.”(22) Mr. Coy W. Brown states: "Any systems requiring evaporating refrigerant temperatures below -40° F. should be attempted only by engineers experienced in this presently special field."(5) Since definite data on equipment for low temperature test rooms seems to be limited, it is believed that from a design of such a machine much valuable information can be gained. Two low temperature testing rooms have been constructed in the Mechanical Engineering Laboratory at The Virginia Polytechnic Institute. One will operate at temperatures down to 0° F. and the other will operate at temperatures down to -40° F. In addition to being used for low temperature research, it is anticipated that the refrigerating equipment for these rooms will be used by students taking Mechanical Laboratory in routine experiments. The object of this thesis is to design suitable refrigeration equipment for the two rooms. The design will include specifications, bill of material and equipment, detail and assembly drawings, and operating instructions. Available data on the design, control, and operation of low temperature refrigerating equipment will be assembled and correlated. This information, with interpretation thereof, will be used in solving a practical engineering problem which is, at the present, in a special field. / Master of Science

A cryogenic thermoelectric generator is proposed to increase the efficiency of a vehicle propulsion system that uses liquid nitrogen as its fuel. The proposed design captures some of the heat required for vaporizing or initial heating of the liquid nitrogen to produce electricity. The thermoelectric generator uses pressurized liquid nitrogen as its cold reservoir and ambient air as the high-temperature reservoir to generate power. This study concentrated on the selection of thermoelectric materials whose properties would result in the highest efficiency over the operating temperature range and on estimating the initial size of the generator. The preliminary selection of materials is based upon their figure of merit at the operating temperatures. The results of this preliminary design investigation of the cryogenic thermoelectric generator indicate that sufficient additional energy can be used to increase overall efficiency of the thermodynamic cycle of a vehicle propulsion system.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Vita. / Includes bibliographical references. / Ph.D.

The evidence supporting the presence of Dark Matter in the universe ranges over many length scales: from the rotational curves within galaxies that cannot be explained only by the dust and other visible component to the anisotropies in the cosmological microwave background that sets the most precise quantification for the DM content in the universe at 26.8% of the energy density. One of the candidates for DM with the most theoretical support is a family of particles that appear in extensions of the Standard Model of Particles. These new particles, known as Weakly Interacting Massive Particles (WIMPs), provide a natural solution to the missing mass in the universe that interact only via weak interaction and whose origin dates back from the very early universe. The XENON Dark Matter search experiments aim to the direct detection of WIMPs via scattering off xenon nuclei. Following the success of the first prototype, XENON10, the XENON100 detector has been, up to late 2013, the most sensitive DM detector setting an upper bound limit on the spin-independent WIMP-nucleon cross-section of 2. × 10 −45 cm 2 and the spin-dependent equivalent of 3.5 × 10 −44 cm 2 . The detector consists of a dual-phase xenon Time Projection Chamber (TPC) with an inner target of 62 kg, located at the un- derground facility at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. XENON100 is still in operation, currently testing new calibration sources of potential use for the next generation XENON1T experiment, under commissioning in Hall B of LNGS, aims to im- prove the XENON100 sensitivity by two orders of magnitude by increasing the xenon target mass in the detector to the tonne scale and by reducing the intrinsic background rate and consequently, increase the expected number of WIMP events per year. The scale-up of a liquid xenon TPC imposes many technical challenges that needed to be addressed prior to the realization of the XENON1T phase of the project. The focus of my thesis work has been the research and development of Dark Matter detectors operated with a xenon mass at the tonne scale. In particular, the topic of purification of a large amount of Xe gas to reduce the concentration of electronegative impurities to levels below afew parts per billion in a reasonable amount of time has been a driver in my work with the XENON1T Demonstrator facility at the Columbia Nevis laboratories. Two complementary approaches were followed in order to address this problem: i) a study of the performance of XENON100 concerning the electron lifetime (eLT) among other parameters that depend on the purity and ii) the construction of a full-size Xe TPC prototype to test multiple technologies with the goal of an optimized XENON1T TPC, with several tonnes of Xe. In addition to my work on the XENON1T Demonstrator, I have also contributed to the operation and analysis of data from XENON100. In particular, I developed a cut based on the information theory concept of entropy to reduce the electronic noise in the data. A detailed description of the motivation and implementation of the entropy cut is presented in Chapter 3. The experience gained from the successful performance of XENON100 and the information from variety of measurements with the XENON1T Demonstrator have influenced the design of XENON1T and will impact other next-generation Dark Matter detectors using LXe in a TPC. More specifically, the design of the XENON1T cryogenic system which is at the heart of the experiment, has been guided by this experience. The testing of the system was performed at Nevis where the various components were assembled and leak checked before being shipped to LNGS. The XENON1T detector’s cryostat and its cryogenics system, designed by the Columbia University XENON group were installed underground in the Hall B of the LNGS laboratory in Summer/Fall 2014. Their commissioning represent a major milestone in the realization of XENON1T. The last chapter of the thesis summarizes the status of XENON1T, with particular focus on the design of the cryogenic, purification and cryostat system influenced by the R & D with the Demonstrator.

The purpose of this study was to determine whether deep-cryogenic freezing produces a change in the timbre or playing characteristics of brass trumpets. The experimental procedure consisted of two parts: quantitative analysis and qualitative analysis. For qualitative analysis a panel of four professional trumpet players evaluated five trumpets: four were frozen and re-evaluated, and one served as the experimental control. Analysis of the harmonic spectra of tones from each instrument provided quantitative data. Since previous studies requiring the analysis of musical instrument tones have suffered from a high degree of variation among tones played by human performers, I constructed a mechanical device that could play tones on the test instruments with greater consistency than is possible with live performers.The changes observed in the qualitative and quantitative analyses are very small, and possibly contradictory. The test panel rated all of the instruments higher after they had been frozen, and any actual improvement in the playing characteristics is suspect because the control instrument received the second highest improvement of the five instruments in the study. In the quantitative analysis, I observed some slight changes in the amplitudes of some of the harmonics in the spectral graphs, but I also observed slight variations in some of the harmonics of the control instrument. Inconsistencies in the performance of the electronic equipment used in the study could account for some of the variation. The instrument that showed the most statistically significant improvements was rated significantly higher in intonation after cryogenic processing, but I was unable to measure any frequency changes in the tones the mechanical embouchure played on the test instruments.Although one may not actually be able to measure differences reported in the qualitative analysis, it is not possible to rule out any acoustical change from cryogenic freezing. In fact, in the quantitative measurements, three of the instruments showed changes greater (some positive and some negative) than the "experimental error" seen in the control instrument's measurements. Additionally, one member of the test panel is convinced that cryogenic freezing has improved his instrument significantly, but the other three trumpeters are ambivalent. / School of Music