Nucleation of ice crystals in the atmosphere often occurs through heterogeneous freezing processes facilitated by an atmospheric aerosol that acts as the ice nuclei (IN). Depending on ambient conditions and aerosol composition, heterogeneous nucleation will occur through one of several mechanisms including the contact and immersion freezing mechanisms. Through a series of contact freezing experiments, we have characterized the ability of aerosols composed of volcanic ash, soot, and peat soil, to act as ice nuclei (IN) as a function of temperature. The immersion freezing ability of the ash particles has also been measured. In these studies, an optical microscope apparatus equipped with a cooling stage and a digital camera was used to observe the freezing events. For each experiment, a particular IN was placed in contact with the surface, or immersed in the bulk, of an ultra pure water droplet. The droplet was then subjected to freezing-melting cycles resulting in 25 independent measurements of the freezing temperature of the droplet. In the volcanic ash experiments, we observed contact freezing at warmer temperatures than immersion freezing. As contact freezing IN, the peat was the most effective with an average contact freezing temperature of -10.5 �C, followed by volcanic ash (-11.2 �C), and then soot (-25.6 �C). In addition, we have used classical nucleation theory to identify the contact parameters and nucleation rates for the compositions explored.

Call number: LD2668 .T4 1935 W32

No description available.

The freezing of model atmospheric aerosols – specifically, model cirrus cloud particles – was investigated through laboratory studies of supercooled water aerosols. Water droplets with radii of 1 – 2.7 µm were exposed to well-defined temperature profiles ranging from 240 – 230 K in a cryogenic flow tube apparatus, and observed using infrared extinction spectroscopy. A computational characterization procedure, based on theories of light scattering, was used to determine the size and phase composition of aerosols from extinction spectra. The procedure showed large ice fractions at uncharacteristically warm temperatures, which was attributed to the formation of ordered, “ice-like” clusters of molecules in supercooled water. Temperature-dependent complex indices of refraction were determined from the supercooled water extinction spectra, and showed changes reflecting this ordered formation. Taking the “ice-like” character of clusters into account, the homogeneous nucleation point for micrometre-sized water aerosols was determined to be 236.2 K. A microphysical model was developed to determine temperature-dependent, volume- and surface-based homogeneous nucleation rates from experimental freezing data. The model results indicated that surface nucleation was the dominant process for our range of experimental conditions. This was supported by separate studies of smaller, 0.63 and 0.75 µm radius aerosols, with larger surface-to-volume ratios. An optical microscopy apparatus was placed in the cryogenic flow tube to allow real-time imaging of particles in freezing experiments. The imaging studies demonstrated the utility of the microscopy apparatus for the observation and classification of ice crystal habits. Ray tracing and image processing algorithms were used to analyze particle geometry and size. The latter was used to validate the size retrievals from the aerosol characterization procedure. Additional studies probed the changes in the optical properties of crystalline ammonium sulfate, (NH₄)₂SO₄, due to the paraelectric-to-ferroelectric transition at 223 K. Temperature- dependent refractive indices were determined from crystalline (NH₄)₂SO₄ extinction spectra. Only small changes in these values were observed down to 223 K, below which significant changes were observed, due to the changes in lattice structure accompanying the ferroelectric transition.

The freezing of model atmospheric aerosols – specifically, model cirrus cloud particles – was investigated through laboratory studies of supercooled water aerosols. Water droplets with radii of 1 – 2.7 µm were exposed to well-defined temperature profiles ranging from 240 – 230 K in a cryogenic flow tube apparatus, and observed using infrared extinction spectroscopy. A computational characterization procedure, based on theories of light scattering, was used to determine the size and phase composition of aerosols from extinction spectra. The procedure showed large ice fractions at uncharacteristically warm temperatures, which was attributed to the formation of ordered, “ice-like” clusters of molecules in supercooled water. Temperature-dependent complex indices of refraction were determined from the supercooled water extinction spectra, and showed changes reflecting this ordered formation. Taking the “ice-like” character of clusters into account, the homogeneous nucleation point for micrometre-sized water aerosols was determined to be 236.2 K. A microphysical model was developed to determine temperature-dependent, volume- and surface-based homogeneous nucleation rates from experimental freezing data. The model results indicated that surface nucleation was the dominant process for our range of experimental conditions. This was supported by separate studies of smaller, 0.63 and 0.75 µm radius aerosols, with larger surface-to-volume ratios. An optical microscopy apparatus was placed in the cryogenic flow tube to allow real-time imaging of particles in freezing experiments. The imaging studies demonstrated the utility of the microscopy apparatus for the observation and classification of ice crystal habits. Ray tracing and image processing algorithms were used to analyze particle geometry and size. The latter was used to validate the size retrievals from the aerosol characterization procedure. Additional studies probed the changes in the optical properties of crystalline ammonium sulfate, (NH₄)₂SO₄, due to the paraelectric-to-ferroelectric transition at 223 K. Temperature- dependent refractive indices were determined from crystalline (NH₄)₂SO₄ extinction spectra. Only small changes in these values were observed down to 223 K, below which significant changes were observed, due to the changes in lattice structure accompanying the ferroelectric transition.

In this report, electrostatic force microscopy (EFM), zeta-potential analyzer, circular dichroism Spectrophotometer and Fourier transform infrared spectroscopy are used to study the electrostatic property of surface on insulin fibril. EFM provides a simultaneous probe of topography and electrostatic property with highly local resolution in nanometer-scale. To understand the correlation between charge distribution on fibril surface and structure transformation, we controlled the incubation time and salt concentration. The results show that the surface charge increases with incubation time, and with the salt concentration increased, the pitch is found to decrease, variation of charge distribution are increased. In addition, we also have evaluated influence of amino acid sequence on growth rate of fibril associated with bovine, porcine and human insulin by atomic force microscopy and circular dichroism Spectrophotometer. The experimental results show that the number of hydrophilic groups on the peptide sequence will affect the speed of fibril generated, and the location of hydrophilic groups on the peptide sequence will affect the stability of the fibril under the frozen environment.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1954. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 125-132).

Made available in DSpace on 2014-06-11T19:29:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-08-05Bitstream added on 2014-06-13T20:19:12Z : No. of bitstreams: 1 velloso_nm_dr_botfmvz.pdf: 1133143 bytes, checksum: 56ab5aea54c24909c943421f3d719a7f (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho teve por objetivo avaliar o efeito da congelação e do meio sobre as características físicas e químicas do sêmen de 10 reprodutores suínos durante o inverno e o verão. No protocolo utilizado para a congelação seminal, 2 diluentes de congelação foram testados em combinação com 2 diluentes de transporte e refrigeração. Os resultados encontrados demonstraram que os parâmetros de integridade de membranas, morfologia e cinética espermática nos momentos que antecederam a congelação não foram influenciados, de forma geral, pela estação do ano. Apesar do número de células espermáticas totais e o volume do ejaculado terem sido superiores no inverno em relação ao verão, a motilidade progressiva pós-descongelação foi melhor no verão do que no inverno na maior parte dos meios de congelação avaliados. A metodologia de congelação aplicada e os diluentes utilizados mostraram índices de viabilidade espermática do sêmen descongelado sem precedentes e superiores aos encontrados na literatura, independentemente do diluente ou da estação do ano avaliada. Em relação ao perfil químico seminal, apenas os níveis de sódio no sêmen e de cálcio no plasma seminal foram mais elevados durante o verão, devido ao menor volume seminal produzido neste período. As temperaturas e umidades foram evidentemente superiores durante o verão e as concentrações de metabólitos fecais de corticosterona mais elevadas nesta mesma estação, porém estes índices não ocasionaram alterações consistentes na viabilidade do sêmen descongelado dos cachaços. Desta forma, os resultados do presente trabalho indicam que os animais encontram-se adaptados ao ambiente, não apresentando alterações marcantes de suas características seminais de acordo com as condições climáticas / This study aimed to evaluate the effect of freezing and environment on physical and chemical characteristics of the semen of 10 breeding pigs during the winter and summer. In the protocol used for the freezing of semen, 2 freezing extenders were tested in combination with 2 diluents for transport and refrigeration. The results show that the parameters of membrane integrity, sperm morphology and kinetics in the moments preceding the freezing were not affected, in general, by the season. Although the number of sperm cells and the total volume of the ejaculate were higher in winter compared to summer, the post-thaw motility was better in summer than in winter in most media tested for freezing. The freezing methodology and the extenders applied showed indices of viability of the thawed sperm unprecedented and higher than those found in the literature, regardless of the diluents or the season assessed. Regarding the chemical seminal profile, only the levels of sodium and calcium in semen in the seminal plasma were higher during the summer due to lower volume seminal produced in this period. Temperatures and humidities were clearly higher during the summer and the concentrations of fecal corticosterone metabolites higher in the same season, but these rates did not cause consistent changes in the viability of frozen-thawed semen of boars. Thus, the present results indicate that the animals are adapted to the environment, showing no marked changes in their semen characteristics according to the season

Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Jack D. Fry / 'Meyer' zoysiagrass (Zoysia japonica Steud.) has been the predominant cultivar used in the transition zone since its release in 1952, primarily because of its excellent freezing tolerance. Six hundred and nineteen zoysiagrass progeny were evaluated over 3 years, and 31 were identified from which one or more cultivars may be released with a finer texture and/or faster establishment and recovery rate compared to Meyer, but with comparable freezing tolerance. DALZ 0102 (Z. japonica), a selection tested in the 2002 National Turfgrass Evaluation Program (NTEP) Zoysiagrass Study has exhibited a faster establishment and recovery rate than Meyer; however, a lower percentage of living rhizomes and nodes was observed in DALZ 0102 compared to Meyer at temperatures [less than or equal to]-15 C in a controlled freezing chamber experiment. Physiological contributors to freezing tolerance, including lipid and fatty acid composition, and endogenous abscisic acid (ABA) levels, were monitored in 'Cavalier' [Z. matrella (L.) Merrill] (cold sensitive, LT[subscript50] = -9.6 C) and Meyer (cold tolerant, LT[subscript50] = -16.2 C) rhizomes during cold acclimation over two years. The most abundant lipids in Zoysia rhizomes were digalactosyl diacylglycerol (DGDG), monogalactosyl diacylglycerol (MGDG), phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidic acid (PA). It has been suggested that DGDG and PC adopt bilayer structure; whereas MGDG, PE and PA have higher tendency to form a nonbilayer, hexagonal II (HII) phase, which compromises bilayer structure and cell function. Greater fluctuations in PC, PA, and the ratio of PC to (PE + PA) were observed in Zoysia rhizomes during cold acclimation compared to the galactolipids (DGDG and MGDG). Changes in PC and PA levels and the ratio of PC to (PE + PA) were more gradual in Meyer than in Cavalier in one year of the two-year study. There was no clear relationship between double bond indices (DBI) and LT[subscript50] in Cavalier and Meyer; thus, DBI might not be a good indicator of freezing tolerance. Abscisic acid (ABA) levels were higher in Meyer than in Cavalier on all sampling dates and were significantly correlated with LT[subscript50] (r = -0.65, P = 0.01).

The nature of ice-sheet damage to overwintering forage plants was studied in a controlled environment at non-injurious freezing temperatures. The soil atmosphere was analyzed in a gas-chromatograph and the plants were assessed for injury by histological examination and recovery rates in the greenhouse. Under experimental ice-covers carbon dioxide accumulated in the soil in some instances to as high as 10% while oxygen was depleted to less than 4% of the atmosphere. Plants rooted in such soils were killed after 7 weeks of ice-cover. When the soil under the ice-sheet was flushed with carbon dioxide the plants were killed after periods as short as 21 days. In both cases injury appeared to be physiological rather than mechanical. Furthermore, carbon dioxide accumulation rather than oxygen depletion was responsible for the injury since the plants were able to withstand periods of 3 weeks in a nitrogen-saturated soil. A freeze-thaw-freeze cycle, with moderate freezing temperatures and associated with an ice-sheet, did not appear to be damaging to alfalfa. Continuous ice-covers resulted in a greater accumulation of carbon dioxide and consequently more injury suffered by the plants than where the cover was temporarily broken by a thaw. High soil-moisture conditions which are usually associated with ice-sheets did not result in an increased hydration level in the tissue and consequently did not make the plants more susceptible to cold injury. A technique was developed to determine the ability of plants to withstand ice-encasement. Several varieties and species that were tested exhibited no clear-cut correlation between resistance to ice encasement and frost hardiness. / Land and Food Systems, Faculty of / Graduate