Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 322-329).

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2 pp. / Revised version of 1999 title by Meer and Misner / Food irradiation is the treatment of food by a certain type of intense energy known as ionizing radiation. This involves exposing bulk or packaged food to carefully controlled amounts of energy. Food does not come in contact with radioactive material. The publication discusses the technology of food irradiation including; the energy source, effect on foods, identifying treated foods, environmental concerns and approved uses in the U.S.

Ce travail concerne l’étude des effets de la lumière sur les propriétés optiques, électro-optiques et diélectriques d’un cristal liquide pur de la famille azobenzène. Ces études ont été réalisées, en fonction de la température et de l’intensité de la lumière UV, en phase smectique C hélicoïdale (SmC*) qui est photo-ferroélectrique. Les études optiques ont montré que les modifications observées, sous irradiation UV, sont dues à la photo-isomérisation des molécules azobenzène. Le passage de la forme Trans à la forme Cis se traduit par des changements des propriétés physico-chimiques du composé et une diminution de la température de transition haute température SmC*-TGBA. Les études électro-optiques révèlent une forte diminution de la polarisation spontanée Ps et une baisse modérée de l’angle d’inclinaison q. La spectroscopie diélectrique montre que l’amplitude du mode de Goldstone augmente et sa fréquence de relaxation diminue sous irradiation lumineuse. L’exploitation des résultats montre que les évolutions photo-induites des amplitudes et fréquences de relaxation du mode Goldstone sont étroitement liées aux variations de Ps, de µ, de la viscosité rotationnelle °G et de la constante élastique de flexion K3. Dans la seconde partie de ce travail, nous avons quantifié les populations des deux isomères ainsi que les paramètres caractéristiques de leur dynamique sous irradiation à l’aide d’un modèle théorique. D’autre part nous avons montré que les variations des propriétés optiques, électro-optiques et diélectriques sont étroitement liées à la profondeur de pénétration de la lumière incidente dans la cellule. Ces comportements obéissent à une loi de type Beer-Lambert-Bouguer. / This work concerns the study of the light effects on the optical, electro-optical and dielectric properties of a pure azobenzene liquid crystal. These studies were carried out, according to temperature and the UV light intensity, in the helicoidal SmC phase which is photo-ferroelectric.The optical studies show that the observed modifications, under UV irradiation, are due to the photo-isomerization of the azobenzene molecules. The transformation from the Trans to Cis form results in changes of the physico-chemical properties and a reduction of the SmC*-TGBA transition temperature Tc.The electro-optical studies reveal a strong decrease of the spontaneous polarization Ps and a moderate one of the tilt angle q. The dielectric spectroscopy studies show that the amplitude of the Goldstone mode increases and the relaxation frequency decreases under irradiation.We show that these variations of the dielectric strength and relaxation frequencies, under UV illumination, are related, at the same time, of the variations of Ps, q , rotational viscosity g G and elastic constant K3. Using a theoretical model, we determine in the second part of this work the populations of the Trans and Cis isomers as well as the characteristic dynamic parameters under irradiation. Finally we show that the variations of the optical, electro-optical and dielectric properties are closely related to the light penetration depth in the cell. Finally we show that the variations of the optical, electro-optical and dielectric properties are closely related to the light penetration depth in the cell. These behaviors obey to a Beer-Lambert law.

The main goal of this research was to determine the feasibility of using electron beam irradiation as an alternative disinfestation technology while preserving the overall quality of mangoes, and to verify its suitability for the preservation shelf life of blueberries. Physicochemical and sensory characteristics of the fruits were evaluated. Mangoes were irradiated at 1.0, 1.5 and 3.1 kGy using a 10MeV (10 kW) linear accelerator (LINAC) with double beam fixture. Samples were stored at 12ºC and 62.7% RH for 21 days. Blueberries packed in plastic clamshell containers were irradiated at 1.1, 1.6 and 3.2 kGy doses using the same linear accelerator with a single beam. The shelf life of the berries stored at 5ºC and 70.4% RH was evaluated for 14 days. The firmness of mangoes irradiated at 1.5 and 3.1 kGy significantly (p > 0.05) decreased during storage. There was a reduction of total sugars (8.1% and 14.1%) in samples irradiated at 1.0 kGy and 1.5 kGy, respectively. All irradiated mangoes had significantly lower (50- 70 %) ascorbic acid content throughout storage. The phenolic compounds increased in samples irradiated at 1.5 kGy (27.4%) and 3.1 kGy) (18.3%). Sensory evaluation of the fruits irradiated with 3.1 kGy showed significantly less acceptability for overall quality, color, texture and aroma. Irradiation of blueberries at 1.1 kGy had no significant (p > 0.05) effect on the fruits' physicochemical characteristics with the exception of ascorbic acid which decreased by 17% after 14 days. A significant decrease in texture (firmness) of irradiated berries was observed during storage time. Total sugars decreased in all irradiated fruits while total phenolics and tannins increased (10 -20%). Sensory attributes of samples irradiated with 1.1 kGy and 1.6 kGy were found acceptable by the panelists. The high dose-treated fruits were considered unacceptable. The results from this research suggest that a 1.5 kGy is the best treatment to maintain the quality attributes of mangoes and increase the shelf life by three days. The electron beam irradiation of packed blueberries at doses of 1.1 and 1.6 kGy ensures and enhances the quality and the shelf life of blueberries up to 14 days.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M.S. in Physics)--Vanderbilt University. / Typescript. Bibliography: l. 83-84.

Thesis (Ph. D.)--University of Wisconsin--Masison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

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