Polymer Light-Emitting Electrochemical Cells (PLECs) are solid state devices based on the in situ electrochemical doping of the luminescent polymer and the formation of a p-n junction where light is emitted upon the application of a bias current or voltage. PLECs answer the drawbacks of polymer light-emitting diodes as they do not require an ultra-thin active layer nor are they reliant on low work function cathode materials that are air unstable. However, because of the dynamic nature of the doping, they suffer from slow response times and poor stability over time. Frozen-junction PLECs offer a solution to these drawbacks, yet they are impractical due to their sub-ambient operation temperature requirement. Our work presented henceforth aims to achieve room temperature frozen-junction PLECS. In order to do that we removed the ion solvating/transporting polymer from the active layer, resulting in a luminescent polymer combined solely with a salt sandwiched between an ITO electrode and an aluminum electrode. The resulting device was not expected to operate like a PLEC due to the absence of an ion-solvating and ion-transporting medium. However, we discovered that the polymer/salt devices could be activated by applying a large voltage bias, resulting in much higher current and luminance. More important, the activated state is quasi static. Devices based on the well-known orange-emitting polymer MEH-PPV displayed a luminance storage half-life of 150 hours when activated by forward bias (ITO biased positively with respect to the aluminum) and 200 hours when activated by reverse bias. More remarkable yet, devices based on a green co-polymer displayed no notable decay in current density or luminance even after being stored for 1200 hours at room temperature! PL imaging under UV excitation demonstrates the presence of doping. These devices are described herein along with an explanation of their operating mechanisms. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-11-29 17:40:19.152

LD2668 .T4 1949 W49 / Master of Science

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Freezing is one of the important technologies for preservation of foods. In this project, using surimi as a food model, thermophysical properties of frozen foods were evaluated and the freezing process was simulated using a finite element package. To measure temperature-dependent thermal conductivity, a line-source probe system was used. Effects of test conditions and sample history were investigated. Thermal conductivity of Alaska pollock (Theragra chalcogramma) surimi having 0, 4, 6, 8, and 12% cryoprotectant levels was measured in the range of -40 to 30 ° C. Other thermal properties were analyzed using differential scanning calorimetry (DSC) at the same cryoprotectant concentrations and in the same temperature range. Each dynamically corrected DSC thermogram was used to determine initial freezing point, unfreezable water (bound water), apparent specific heat, enthalpy and unfrozen water weight fraction. When water content of the sample is controlled, thermophysical properties of surimi have a relatively weak dependence upon cryoprotectant level in the unfrozen and fully frozen (-40° C) ranges. However, the initial freezing point and the properties just below this point were significantly affected. From measured data, the Schwartzberg thermal property models for frozen foods were investigated. The models agreed well with experimental data. However, possibility for further improvement is demonstrated by using DSC analysis. This research additionally demonstrated the great potential of DSC for measuring and modeling frozen food thermal properties. Using the derived property models, a commercial PC-based finite element package was used to simulate the process of freezing a food block in a plate freezer. The capability of the program to handle temperature-dependent thermal properties and time-dependent boundary conditions enabled a simulation which accounted for measured changes in thermal properties, ambient temperatures and overall heat transfer coefficient. Predicted temperature history agreed well with measured data. Sensitivities of important model parameters, which were varied within their experimental error range, were also investigated using a factorial experimental design method. The result showed that in decreasing order of influencing freezing time prediction, attention should be given to apparent specific heat, block thickness, overall heat transfer coefficient, ambient temperature, thermal conductivity, and density. / Graduation date: 1991

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

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This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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Although periglacial research in the high Drakensberg and Lesotho mountains has received growing interest amongst southern African geomorphologists, little detailed, quantitative information was available prior to this study. In an attempt to help overcome this deficit, a quantitative assessment on cryogenic landforms and processes operative in the high Drakensberg was undertaken. Morphological and sedimentological assessments of sorted patterned ground, non-sorted steps, thufur, blockstreams, stone-banked lobes, debris deposits and turf exfoliation landforms were undertaken. In addition, geomorphic process assessments in the field included the measurement of turf retreat at turf exfoliation sites, the determination of frost-heave mechanisms within wetlands and sediment mobilization along the Mashai Stream. Ground temperatures were recorded for thufur from 1993 to 1996. The environmental implications of some of the findings are discussed. Seasonal frost-induced sorted patterned ground emerges annually within a few weeks, demonstrating the effect of regular, diurnal freeze-thaw cycles during the winter months. It is found that the present climate is not conducive to maintaining or preserving miniature periglacial landforms below 3200m a.s.l. during the summer months. Large relict sorted circles, stone-banked lobes and blockstreams are the most conspicuous periglacial landforms in the high Drakensberg and are products of at least seasonally-frozen ground. It is suggested that debris deposits found within high Drakensberg cutbacks are possible indicators for marginal niche and cirque glaciation during the Late Pleistocene. It is demonstrated that in climatically marginal periglacial regions, the microtopographically controlled freezing processes may be of paramount importance in maintaining and modifying the cryogenic landforms that occur. Pronounced temperature differentials are found during the winter months, when thufur are frozen for several weeks and depressions remain predominantly unfrozen. It is suggested that such contemporary temperature differentials induce thermodynamic forces and ultimately ground heave at sites in the high Drakensberg. The pronounced seasonal weather patterns in the high Drakensberg have promoted a cycle of geomorphic process events that operate synergistically and initiate particular erosion landforms. However, cryogenic activity during the colder period is overwhelmed by water induced erosion processes during the summer months in the high Drakensberg. It is concluded that the high Drakensberg is currently a marginal periglacial region, but that periglacial conditions prevailed during both the Pleistocene and some Late Holocene Neoglacial events. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1997.