No description available.

No description available.

Microwave and water blanching of carrots and sweet potatoes were evaluated with respect to peroxidase inactivation, texture degradation and color changes for obtaining stable frozen stored products. Carrot slices and french fry style sweet potatoes were blanched in a 700 W domestic microwave oven as well as in boiling water for different treatment times. Blanched and unblanched samples were packaged in retort pouches and frozen stored at $-$20$ sp circ$C, and evaluated for peroxidase activity, texture and color before and after blanching, and after 3.5 and/or 7 months frozen storage. Kinetics of peroxidase activity and texture softening due to blanching was described by semi-logarithmic models. All frozen products, except unblanched samples, were of good quality at the end of 7 months storage. Small quality differences were detected in the blanched frozen samples during storage; samples blanched for intermediate times were superior. / Temperature distribution profiles were determined for model foods consisting of a starch gel with different concentrations of protein and fat, as well as commercial frozen and refrigerated prepared foods. Microwave heating of model foods showed considerable nonuniformity in temperature distribution and alarmingly low center temperatures. Prolonged lower power heating or holding after microwave heating did not always elevate center temperatures to safe levels. Addition of protein to the starch gel reduced temperature uniformity and heating rate, while added fat resulted in an opposite trend. / For the commercial foods, center temperatures reached after heating according to manufacturer's instructions were below 70$ sp circ$C indicating some safety concerns. However, longer heating time at lower power levels improved the temperature uniformity as well as the quality and appearance of these foods.

No description available.

This thesis studies the role of antennas in the achievable resolution and accuracy from nearfield microwave tomography (MWT). Near-field MWT is an emerging imaging modality in which the object being imaged is successively irradiated by several antennas, located close to the object, in the microwave frequency range. The scattered fields emanating from the object are then processed to form quantitative images from the dielectric properties of the object. This thesis starts with proposing a mathematical framework to study the achievable resolution from MWT. Within this framework, the effect of the near-field distribution of the utilized antennas on the achievable image resolution will be studied. Specifically, it will be shown that the use a focused near-field distribution to irradiate the object can enhance the achievable resolution. Within the same framework, the effects of the frequency of operation, multiple frequencies of operation, signal-to-noise ratio of the measured data, and the number of antenna elements on the achievable resolution and accuracy will be studied. After establishing the importance of the antenna’s incident field distribution, this thesis continues with investigating two different methods to achieve a focused near-field distribution. The first method, which attempts to synthesize focused beams from existing omnidirectional antenna elements, will be shown to be not successful using the method employed in this thesis. The second method is based on modifying an existing antenna element so as to make its near-field distribution more focused. Through different experiments and simulations, it will be shown that the second method can make the near-field distribution of the antenna more focused while maintaining multiple frequencies of operation for the antenna, and keeping its physical size reasonably small.

No description available.

Effects of microwave drying on the mechanical and optical properties of handsheets made from kraft and chemi-thermomechanical pulps were studied experimentally. The quality of paper dried in a microwave field of 2450 MHz is compared with that of paper dried by conventional method under standard conditions. Key physical properties measured include burst index, density, tear index, breaking length, zero-span tensile strength, double fold, STFI compressibility and optical properties include brightness, opacity and scattering coefficient. All properties were found to be either enhanced or at the same level as those obtained under standard conditions. Furthermore, it is suggested that microwave drying could replace the conventional drying method in the standard testing of pulp and paper samples for quality control purposes.

129 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1972) from the Dept. of Physics, University of Adelaide

Thesis (M.S.)--Ohio University, November, 1988. / Title from PDF t.p.

Thesis (M.Sc.) -- University of Adelaide, Dept. of Physics, 1973.