Techmer, Kirsten S.

[["dc.bibliographiccitation.firstpage","459"],["dc.bibliographiccitation.issue","1-2"],["dc.bibliographiccitation.journal","Canadian Journal of Physics"],["dc.bibliographiccitation.lastpage","468"],["dc.bibliographiccitation.volume","81"],["dc.contributor.author","Legagneux, L."],["dc.contributor.author","Lauzier, T."],["dc.contributor.author","Domine, F."],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Heinrich, Steffen"],["dc.contributor.author","Techmer, Kirsten S."],["dc.date.accessioned","2018-11-07T10:42:07Z"],["dc.date.available","2018-11-07T10:42:07Z"],["dc.date.issued","2003"],["dc.description.abstract","The quantification of the specific surface area (SSA) of snow crystals and of its variation during metamorphism are essential to understand and model the exchange of reactive gases between the snowpack and the atmosphere. Therefore, the decay rate of SSA of five fresh snow samples was studied in the laboratory at -4, -10, and -15degreesC under isothermal conditions in closed systems. The time-evolution of the snow SSA can in all cases be very well described by an empirical law of the form, SSA = - A log(t + Deltat) + B, where A, B, and Deltat are adjustable parameters. B seems to be closely related to the initial SSA of the snow, and A describes the SSA decay rate. Our preliminary findings at -15degreesC suggest that a linear relationship exists between A and B, so that it may be possible to predict the decay rate of snow SSA from its initial value. For the first time, images obtained from scanning electron microscopy show that crystal rounding of snow is the main process taking place during isothermal metamorphism. New grain boundaries also form. More surprising, however, was the formation of new basal, prismatic, and pyramidal crystal faces, sometimes with very sharp angles, especially at -15degreesC. The growth of facets with sharp angles is not fully explained by current theories of snow metamorphism and has not been observed before."],["dc.identifier.doi","10.1139/P03-025"],["dc.identifier.isi","000183264100056"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46710"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Canadian Science Publishing, Nrc Research Press"],["dc.relation.issn","1208-6045"],["dc.relation.issn","0008-4204"],["dc.title","Rate of decay of specific surface area of snow during isothermal experiments and morphological changes studied by scanning electron microscopy"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","33"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Microscopy Research and Technique"],["dc.bibliographiccitation.lastpage","48"],["dc.bibliographiccitation.volume","62"],["dc.contributor.author","Domine, F."],["dc.contributor.author","Lauzier, T."],["dc.contributor.author","Cabanes, A."],["dc.contributor.author","Legagneux, L."],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Techmer, Kirsten S."],["dc.contributor.author","Heinrich, Steffen"],["dc.date.accessioned","2018-11-07T10:36:40Z"],["dc.date.available","2018-11-07T10:36:40Z"],["dc.date.issued","2003"],["dc.description.abstract","Current theories of snow metamorphism indicate that sublimating snow crystals have rounded shapes, while growing crystals have shapes that depend on growth rates. At slow growth rates, crystals are rounded. At moderate rates, they have flat faces with rounded edges. At fast growth rates, crystals have flat faces with sharp edges, and they have hollow faces at very fast growth rates. The main growth/sublimation mechanism is thought to be by the homogeneous nucleation of new layers at or near crystal edges. It was also suggested that the equilibrium shape of snow crystals would be temperature dependent: rounded above - 10.5degreesC, and faceted below. To test these paradigms, we have performed SEM investigations of snow samples having undergone metamorphism under natural conditions, and of snow samples subjected to isothermal metamorphism at -4degrees and -15degreesC in the laboratory. In general, current theories predicting crystal shapes as a function of growth rates, and of whether crystals are growing or sublimating, are verified. However, the transition in equilibrium shapes from rounded to faceted at - 10.5degreesC is not observed in our isothermal experiments that reveal a predominance of rounded shapes after more than a month of metamorphism at - 4 and -15degreesC. Some small crystals with flat faces that also have sharp angles at - 15degreesC, are observed in our isothermal experiments. These faces are newly formed, and contradict current theory. Several hypotheses are proposed to explain their occurrence. One is that they are due to sublimation at emerging dislocations. (C) 2003 Wky-Liss. Inc."],["dc.identifier.doi","10.1002/jemt.10384"],["dc.identifier.isi","000184886300004"],["dc.identifier.pmid","12938116"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/45381"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-liss"],["dc.relation.issn","1059-910X"],["dc.title","Snow metamorphism as revealed by scanning electron microscopy"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","62"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Environmental Chemistry"],["dc.bibliographiccitation.lastpage","73"],["dc.bibliographiccitation.volume","8"],["dc.contributor.author","Ariya, P. A."],["dc.contributor.author","Domine, F."],["dc.contributor.author","Kos, G."],["dc.contributor.author","Amyot, M."],["dc.contributor.author","Cote, V."],["dc.contributor.author","Vali, H."],["dc.contributor.author","Lauzier, T."],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Techmer, Kirsten S."],["dc.contributor.author","Heinrich, Steffen"],["dc.contributor.author","Mortazavi, R."],["dc.date.accessioned","2018-11-07T09:01:08Z"],["dc.date.available","2018-11-07T09:01:08Z"],["dc.date.issued","2011"],["dc.description.abstract","Field and laboratory studies of organic compounds in snow (12 species; concentrations <= 17 mu g L(-1)) were conducted and microorganisms in snow and aerosols at urban and Arctic sites were investigated (snow: total bacteria count <= 40000 colony forming units per millilitre (CFU mL(-1)), fungi <= 400 CFU mL(-1); air: bacteria <= 2.2 x 10(7) CFU m(-3), fungi <= 84 CFU m(-3)). Bio-organic material is transferred between snow and air and influence on snow-air exchange processes is demonstrated. Volatile organic compounds in snow are released into the air upon melting. In vitro photochemistry indicated an increase of <= 60 mu g L(-1) for 1,3- and 1,4-dimethylbenzenes. Bacillus cereus was identified and observed in snow and air with ice-nucleating being P. syringae absent. As a result snow photobiochemical reactions should be considered in describing organic matter air-snow exchanges, and the investigation of climate change."],["dc.description.sponsorship","NSERC; FQRNT; CFI"],["dc.identifier.doi","10.1071/EN10056"],["dc.identifier.isi","000287764800008"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/24342"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Csiro Publishing"],["dc.relation.issn","1448-2517"],["dc.title","Snow - a photobiochemical exchange platform for volatile and semi-volatile organic compounds with the atmosphere"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","2929"],["dc.bibliographiccitation.issue","18"],["dc.bibliographiccitation.journal","Geophysical Research Letters"],["dc.bibliographiccitation.lastpage","2932"],["dc.bibliographiccitation.volume","27"],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Klapproth, A."],["dc.contributor.author","Gotthardt, F."],["dc.contributor.author","Techmer, Kirsten S."],["dc.contributor.author","Heinrich, Steffen"],["dc.date.accessioned","2018-11-07T10:09:55Z"],["dc.date.available","2018-11-07T10:09:55Z"],["dc.date.issued","2000"],["dc.description.abstract","We present results of experimental studies on the formation of gas hydrates (clathrates) at conditions of geophysical interest. Clathrate hydrates formed by a reaction of gas at ice Ih surfaces are always found to be mesoporous to macroporous with pores sizes between 100 to 400 nm and pore volumes of approximately 25-40% for CH4, Ar and Nz hydrate, and smaller pores of 20 to 100 nm with a porosity of approximately 10-20% for CO2 hydrate. The three-dimensional sponge-like microstructure occurs in single crystalline grains of typically a few mu m size and was observed by field-emission scanning electron microscopy. It forms over a wide range of p-T conditions below the ice Ih melting. The porous microstructure is stable for at least several months, even close to the clathrate decomposition, and is proposed to be formed by local differences in the energy balance between hydrate formation and ice decompositon. The results presented are considered of potential major importance for the understanding of the behaviour of natural gas hydrates found e.g. in polar ice sheets and permafrost regions, and also in some celestial bodies."],["dc.identifier.doi","10.1029/2000GL006112"],["dc.identifier.isi","000089390400027"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/39748"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Geophysical Union"],["dc.relation.issn","0094-8276"],["dc.title","The formation of meso- and macroporous gas hydrates"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]