Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [80]-83).

Thesis (M.A.)--Carleton University, 1988. / Also available in electronic format on the Internet.

Thesis (M.S.)--University of Wisconsin--Madison, 1960. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 62).

Prediction of needle ice events requires an understanding of energy and water transfer between the atmosphere and the soil. A project in southwestern British Columbia was conducted during 1961-1968 for the purposes of (1) constructing a general model of needle ice growth, (2) characterizing the processes which combine to produce ice needle events, and (3) explaining the variations in ice needle morphology. The problem was approached by (1) comparing environmental conditions on event and non-event nights, (2) identifying the heat sinks which produce surface cooling and fusion, (3) determining the range of the variability in soil water and heat flow properties produced by changing soil water content, (4) statistically analyzing the event, non-event record, and (5) determining the time dependence of the components of the energy-water transfer system during needle ice growth. Statistical and physical analysis demonstrated the overriding control of the thermal and evaporative heat sinks in needle ice growth and indicated that the equivalent radiant temperature of the night sky must drop below -15°C before a needle ice event is probable. Further, it was demonstrated that after ice crystals form at the surface the magnitude of the surface heat sink (equilibrium surface temperature) and the soil water content control the depth of the normally frozen soil cap above the needles and the spatial homogeneity of needle growth. The statistical study of the event record produced a simple dew point-cloud cover empirical model for event prediction and a listing of favorable-unfavorable conditions for needle ice growth. A general model for needle ice growth was developed indicating the relationship between surface equilibrium temperature and soil water tension on the growth and the spatial temporal homogeneity of needle growth. Contributions to general micrometeorology were made by demonstrating the utility of combined measurement of surface temperature soil water tension and soil heave in the analysis of soil structural evolution during diurnal freeze-thaw cycles. Specifically, the anomalous positive "bump" which frequently occurs in nocturnal surface temperature curves was shown to be coincident with a thermally driven flux of warm subsoil water toward the surface and a sudden increase in soil water tension was demonstrated to occur at the time when heave (ice segregation) began. Finally specific problems which appear both tractable and rewarding were formulated for future investigators. / Arts, Faculty of / Geography, Department of / Graduate

No description available.

Freeze-injury at the plasma membrane level has been identified as being crucial for the survival of living matter. Since plasma membranes consist of several micro domains that make the structure rather complex, this study attempted to use simple model membranes to investigate the changes of phospholipid bilayers at sub-zero temperatures. Egg yolk L-α-phosphatidylcholine (EPC) and 1, 2-dipalmitoyl-rac-glycero-3-phosphocholine (DPPC) that mimic plasma membranes in their unique ways were used to prepare large unilamellar vesicles (LUV), which were the model membranes of this study. At cooling rates of 0.5 and 10�C/min, LUV were freeze-concentrated in the unfrozen matrix as a result of the advancing extraliposomal ice front and the decreasing phase volume of the unfrozen matrix, both of which led to membrane lesion. At the slow cooling rate of 0.5�C/min, an additional freezing stress imposed by the osmotic gradient across the bilayers, due to the increase of solute concentration in the unfrozen matrix, promoted leakage of LUV. The gel-liquid crystal phase transition temperature of phospholipids played an important role in determining if the LUV could withstand freezing stress when the LUV were held at a defined sub-zero temperature for a given period of holding time. EPC LUV were more leaky than DPPC LUV when they were held at the high sub-zero temperatures and their leakage increased with increasing holding time. The leakiness of EPC LUV could be related to the fluid and deformable nature of the EPC above its phase transition temperature. In contrast, DPPC LUV with a higher gel-liquid crystal phase transition temperature compared to EPC may become increasingly fragile at lower sub-zero temperatures, which led to the increase of leakage when the DPPC LUV were held at the lower sub-zero temperatures. These results indicated that the determination of the fatty acid profile of the plasma membranes was essential to aid in developing the most suitable holding temperature and time during the cryopreservation of biological specimens. Adding to the integrity of LUV that depended on the gel-liquid crystal phase transition temperature of phospholipids, intraliposomal ice formation also depended on the phase transition temperature of phospholipids. Intraliposomal ice formation was only observed for DPPC LUV but not for EPC LUV. In addition to the extraliposomal ice formation, other physical changes such as the eutectic crystallization of sodium chloride (NaCl) and ice mixture on the stability of LUV were also investigated. The eutectic crystallization of NaCl/ice mixture was governed by the intra- and extraliposomal distribution of NaCl and was more likely to occur at the physiological NaCl concentrations compared to lower NaCl concentrations. The eutectic crystallization of NaCl/ice mixture further increased the leakage of LUV. The understanding of the freezing behaviour and the mechanisms of freeze-injury of LUV allowed the use of the current model membranes for further investigations of the cryoprotective actions of cryoprotective agents (CPA). Partial phase diagrams of sugar-salt-water, dimethyl sulfoxide (DMSO)-salt-water and ethylene glycol (EG)-salt-water systems that resembled extraliposomal solute compositions were constructed and the phase volume of ice and unfrozen matrix was estimated from the freezing curves. Ice reduction was the major mechanism by which the non-permeable and permeable CPA protected the LUV from freeze-injury. Other cryoprotective mechanisms of the non-permeable and permeable CPA through the dilution and spacing out of the LUV in the unfrozen matrix as well as the suppression of the eutectic crystallization of NaCl/ice mixture were not ruled out. Non-permeable CPA were more effective in preventing leakage of DPPC than EPC LUV. Unlike the non-permeable CPA, permeable CPA were more effective for EPC than DPPC LUV that had been subjected to freezing and thawing processes. At room temperature, however, DMSO and EG were detrimental to the stability of DPPC LUV. The choice of CPA is strictly dependent on the type of phospholipids that varied in their acyl chain length and phase transition temperature. In summary, this study provides insights of the freeze-injury of LUV and the cryoprotective mechanisms of the non-permeable and permeable CPA which are beneficial to the field of cryopreservation that often depends on empirical trial and error methods. By integrating a comprehensive molecular-based understanding, an optimal cryopreservation procedure could be designed.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 122-138).

No description available.

Freeze-injury at the plasma membrane level has been identified as being crucial for the survival of living matter. Since plasma membranes consist of several micro domains that make the structure rather complex, this study attempted to use simple model membranes to investigate the changes of phospholipid bilayers at sub-zero temperatures. Egg yolk L-α-phosphatidylcholine (EPC) and 1, 2-dipalmitoyl-rac-glycero-3-phosphocholine (DPPC) that mimic plasma membranes in their unique ways were used to prepare large unilamellar vesicles (LUV), which were the model membranes of this study. At cooling rates of 0.5 and 10�C/min, LUV were freeze-concentrated in the unfrozen matrix as a result of the advancing extraliposomal ice front and the decreasing phase volume of the unfrozen matrix, both of which led to membrane lesion. At the slow cooling rate of 0.5�C/min, an additional freezing stress imposed by the osmotic gradient across the bilayers, due to the increase of solute concentration in the unfrozen matrix, promoted leakage of LUV. The gel-liquid crystal phase transition temperature of phospholipids played an important role in determining if the LUV could withstand freezing stress when the LUV were held at a defined sub-zero temperature for a given period of holding time. EPC LUV were more leaky than DPPC LUV when they were held at the high sub-zero temperatures and their leakage increased with increasing holding time. The leakiness of EPC LUV could be related to the fluid and deformable nature of the EPC above its phase transition temperature. In contrast, DPPC LUV with a higher gel-liquid crystal phase transition temperature compared to EPC may become increasingly fragile at lower sub-zero temperatures, which led to the increase of leakage when the DPPC LUV were held at the lower sub-zero temperatures. These results indicated that the determination of the fatty acid profile of the plasma membranes was essential to aid in developing the most suitable holding temperature and time during the cryopreservation of biological specimens. Adding to the integrity of LUV that depended on the gel-liquid crystal phase transition temperature of phospholipids, intraliposomal ice formation also depended on the phase transition temperature of phospholipids. Intraliposomal ice formation was only observed for DPPC LUV but not for EPC LUV. In addition to the extraliposomal ice formation, other physical changes such as the eutectic crystallization of sodium chloride (NaCl) and ice mixture on the stability of LUV were also investigated. The eutectic crystallization of NaCl/ice mixture was governed by the intra- and extraliposomal distribution of NaCl and was more likely to occur at the physiological NaCl concentrations compared to lower NaCl concentrations. The eutectic crystallization of NaCl/ice mixture further increased the leakage of LUV. The understanding of the freezing behaviour and the mechanisms of freeze-injury of LUV allowed the use of the current model membranes for further investigations of the cryoprotective actions of cryoprotective agents (CPA). Partial phase diagrams of sugar-salt-water, dimethyl sulfoxide (DMSO)-salt-water and ethylene glycol (EG)-salt-water systems that resembled extraliposomal solute compositions were constructed and the phase volume of ice and unfrozen matrix was estimated from the freezing curves. Ice reduction was the major mechanism by which the non-permeable and permeable CPA protected the LUV from freeze-injury. Other cryoprotective mechanisms of the non-permeable and permeable CPA through the dilution and spacing out of the LUV in the unfrozen matrix as well as the suppression of the eutectic crystallization of NaCl/ice mixture were not ruled out. Non-permeable CPA were more effective in preventing leakage of DPPC than EPC LUV. Unlike the non-permeable CPA, permeable CPA were more effective for EPC than DPPC LUV that had been subjected to freezing and thawing processes. At room temperature, however, DMSO and EG were detrimental to the stability of DPPC LUV. The choice of CPA is strictly dependent on the type of phospholipids that varied in their acyl chain length and phase transition temperature. In summary, this study provides insights of the freeze-injury of LUV and the cryoprotective mechanisms of the non-permeable and permeable CPA which are beneficial to the field of cryopreservation that often depends on empirical trial and error methods. By integrating a comprehensive molecular-based understanding, an optimal cryopreservation procedure could be designed.

Univ., Diss.--Bremen, 2007.