L'étude concerne la prise en glace d'une paroi thermiquement contrôlée placée au sein d'une conduite dans laquelle se développe un écoulement turbulent d'air humide. L'ensemble des essais expérimentaux a été réalisé à partir du banc d'essai HUMIDE, soufflerie dédiée conçue au laboratoire et modifiée afin de suivre au cours du temps l'augmentation de masse de glace. Une analyse paramétrique de l'influence du taux d'humidité et de la vitesse de l'écoulement sur le dépôt de glace a été réalisée et, à partir de la mesure du flux global, il a été possible d'estimer les flux convectifs en présence de la glace. Les résultats soulignent clairement que les flux convectifs sont plus ou moins accentués en fonction de l'humidité.Une tentative de modélisation du mélange air - vapeur d'eau/glace, a été développée en partout de la théorie de nucléation et les différentes confrontations soulignent la très forte sensibilité des résultats vis-à-vis des conditions aux limites et de la modélisation. Au-delà de géométries simples comme la plaque, une géométrie caractéristique d'un échangeur a également été simulée notamment pour caractériser de manière qualitative les mécanismes de prise en glace de tels systèmes. / The study concerns the de-sublimation of a thermally controlled flat plate placedwithin a wind tunnel in which develops a turbulent moist air flow. A parametric analysis of the influence of humidity and the velocity of the flow on the ke formation was carried out and, from the measurement of global heat flux, it is possible to estimate the convective heat transfer with the presence of ice. The results show that the convective fluxes are more or less accentuated depending on the humidity. A solver to modeling of air - vapor/ice, was developed base on the theory of nucleation heterogeneous. Beyond simple geometry such as a flat plate, a characteristic geometry of a heat ex.changer was also simulated in particular to qualitatively characterize the ice formation mechanisms of such systems.

The needle chlorenchyma of Pinus contorta Dougl. ex Loud spp. Lat? - folia (Engelm. ex Wats) was fixed on site in the sub-alpine forests of the southern interior plateau of British Columbia, in order to conduct comparative observations by light and electron microscopy on the chloren-chymal cytology in summer and winter. Material fixed in the growing season (summer) demonstrated a chlorenchymal ultrastructure similar to that of other mature higher plant chlorenchymal tissues. Material fixed in mid winter (usually at below freezing tempertures) revealed extensive changes in the structural and positional aspects of most cytoplasmic components. Some of the most dramatic changes in the chlorenchyma cytoplasm in the winter state are as follows: chloroplasts became irregularly shaped and clumped together usually in certain specific areas of the cell; close associations form between the outer membranes of adjacent chloroplasts, these areas may lead to the apparent fusion of some chloroplasts. The cytoplasm became massively vacuolated, particularly in areas removed from the nucleus or the chloroplast clumps. The extent of this vacuolation can be deduced from the use of the adjective "foamy" to describe the extent and degree of these vacuolated cytoplasmic areas. Associated with the cytoplasmic winter vacuoles were highly osmiophilic bodies. A distinct seasonal cycle of cytoplasmic oil reserves was also noted. The reaction of the winter chlorenchymal cytoplasm to extentive manipulation in fixative osmotic potential was remarkably conservative. This observation allows inferences to be made about the permeability characteristics of winter cytoplasmic membranes. In order to verify the observed winter changes, chemical fixation studies were supplemented by observations on material collected, transported, stored, sectioned and observed by light microscopy in the frozen and unthawed, stained or fixed state. This work was conducted with specially designed transport devices and a cryomicrotome and cryomicros-cope. Observations were also conducted in summer and winter on the chlorenchyma of Pinus albicaulis Engelm and Tsuga mertensiana (Bong.) Corr. collected near timberline at the Whistler mountain ski resort ninety miles north of Vancouver. Observations from the cryomicroscopy of Pinus contorta needles indicate that the seasonal changes are not artifacts of chemical fixation procedures. Observations on the needles of the two conifer species collected at Whistler mountain indicate that the detailed seasonal observations on Pinus contorta may also apply to the needle chlorenchyma of other conifer species. A possible spring transitional stage between the winter and summer ultrastructural appearance of Pinus contorta chlorenchyma is discussed. Related experiments were conducted to indicate what effects the needle age of field trees had on winter-summer comparisons, and what effect drought stress and artificial hardening and freezing had on chlorenchymal ultrastructure. The drought and hardening-freezing experiments were conducted on laboratory grown trees in controlled environment chambers. No clear relationship between frost hardiness and drought stress was established. Experiments on the artificial inducement of frost hardiness in seedling trees were not considered successful. / Science, Faculty of / Botany, Department of / Graduate

This diploma thesis deals with creation of reduction core problem mainly in fired roofing tiles. With those is the emphasis on the impermeability and frost resistance. Black reduction core is reducing frost resistance but depends on firing temperature. At 1060 °C the reduction in frost resistance is not as unfavorable as at 900 °C. This thesis includes overview of research conducted on reduction core topic. There is enough literature focusing on frost resistance, experimental part is focused mainly on the impact of reduction core on impermeability and compares two types of production mixtures used in Czech Republic (calcium-containing type from Hranice and non-calcium type from Stod). It includes comparison of mixtures with fluidized fly ash and dust from grinding masonry elements. It opens discussion if those mixtures can be used for reduction core elimination.

The greatest weather enemy in all fruit destruction is the late spring frost which moves across the country under the high pressure areas that are occasionally seen on the weather maps, and kills the fruit buds.

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