Résumé: L’Institut pour l'étude de la neige et des avalanches en Suisse (SLF) a développé SNOWPACK, un modèle thermodynamique multi-couches de neige permettant de simuler les propriétés géophysiques du manteau neigeux (densité, température, taille de grain, teneur en eau, etc.) à partir desquelles un indice de stabilité est calculé. Il a été démontré qu’un ajustement de la microstructure serait nécessaire pour une implantation au Canada. L'objectif principal de la présente étude est de permettre au modèle SNOWPACK de modéliser de manière plus réaliste la taille de grain de neige et ainsi obtenir une prédiction plus précise de la stabilité du manteau neigeux à l’aide de l’indice basé sur la taille de grain, le Structural Stability Index (SSI). Pour ce faire, l’erreur modélisée (biais) par le modèle a été analysée à l’aide de données précises sur le terrain de la taille de grain à l’aide de l’instrument IRIS (InfraRed Integrated Sphere). Les données ont été recueillies durant l’hiver 2014 à deux sites différents au Canada : parc National des Glaciers, en Colombie-Britannique ainsi qu’au parc National de Jasper. Le site de Fidelity était généralement soumis à un métamorphisme à l'équilibre tandis que celui de Jasper à un métamorphisme cinétique plus prononcé. Sur chacun des sites, la stratigraphie des profils de densités ainsi des profils de taille de grain (IRIS) ont été complétés. Les profils de Fidelity ont été complétés avec des mesures de micropénétromètre (SMP). L’analyse des profils de densité a démontré une bonne concordance avec les densités modélisées (R[indice supérieur 2]=0.76) et donc la résistance simulée pour le SSI a été jugée adéquate. Les couches d’instabilités prédites par SNOWPACK ont été identifiées à l’aide de la variation de la résistance dans les mesures de SMP. L’analyse de la taille de grain optique a révélé une surestimation systématique du modèle ce qui est en accord avec la littérature. L’erreur de taille de grain optique dans un environnement à l’équilibre était assez constante tandis que l’erreur en milieux cinétique était plus variable. Finalement, une approche orientée sur le type de climat représenterait le meilleur moyen pour effectuer une correction de la taille de grain pour une évaluation de la stabilité au Canada. / Abstract : The snow thermodynamic multi-layer model SNOWPACK was developed in order to address the risk of avalanches by simulating the vertical geophysical and thermophysical properties of snow. Risk and stability assessments are based on the simulation of the vertical variability of snow microstructure (grain size, sphericity, dendricity and bond size), as well as snow cohesion parameters. Previous research has shown a systematic error in the grain size simulations (equivalent optical grain size) over several areas in northern Canada. In order to quantify the simulated errors in snow grain size and associated uncertainties in stability, snow specific surface area (SSA), was measured using a laser-based system measuring snow albedo through an integrating sphere (InfraRed Integrating Sphere, IRIS) at 1310 nm. Optical grain size was retrieved from the IRIS SSA measurements in order to validate the optical equivalent grain radius from simulated SNOWPACK outputs. Measurements occurred during a field campaign conducted during the 2013-2014 winter season in the Canadian Rockies. The two study plots selected are located at Glacier National Park, BC and Jasper National Park, AB. Profiles of density and stratigraphic analysis were completed as well as grain size (IRIS) profiles, combine with snow micropenetrometer (SMP) measurements. Density analysis showed good agreement for the simulated values (R[superscript 2]=0.76) and thus the simulated resistance for the SSI was assumed of reasonable precision. Snow instabilities predicted by SNOWPACK were observed by SMP resistance variation. The optical grain size analysis showed systematic overestimation of the modeled values, in agreement with the current literature. Error in SSA evolution in a rounding environment was mostly constant whereas error in conditions driven by temperature gradient was variable. Finally, it is suggested that a climate-oriented parametrization of the microstructure could represent an improvement for stability assessment in Canada given the variability and size of avalanche terrain.

Avalanches pose a significant natural hazard in many parts of the world. Worldwide the hazard is being managed in a number of new and traditional methods. In New Zealand, the Milford Road, Fiordland, has a significant avalanche problem which has been managed by the Transit New Zealand Milford Road Avalanche Programme since 1984. This avalanche programme has generated a database of all avalanche occurrences and associated meteorological parameters for the time period 1985 to 2002. Elsewhere around the world, similar and more extensive data sets have been used to examine a wide variety of aspects in relation to the snow cover, avalanching and avalanche hazard. The availability of the Milford Road database has provided the opportunity use new and traditional approaches to examine many aspects of avalanching including; the trends in and relationships with the snow and avalanche regime, evaluation of the avalanche hazard, statistical forecasting of avalanches and the visualisation of avalanche occurrence information in a GIS. Statistical and graphical examination of the inter-annual variation in the snow and avalanche regime revealed relationships between the snow depth, avalanche occurrences and atmospheric circulation similar to those found elsewhere around the world, but not previously examined in New Zealand. Furthermore, the analysis resulted in strong correlations despite using a database significantly shorter than those used elsewhere. Atmospheric circulation types that bring strong winds and precipitation were found to be highly significantly correlated with avalanche occurrences and snow depth. Avalanche occurrences were more highly correlated with atmospheric circulation than snow depth was, reflecting the strong maritime avalanche climate. Risk evaluation was undertaken using two approaches, the avalanche hazard index (AHI) and the probability of death to individuals (PDI) method. The present avalanche risk was compared to a theoretically uncontrolled avalanche regime, using 2002 traffic volumes for AHI and PDI. The AHI analysis highlighted the reduction in the AHI resulting from the control programme, and the significantly lower AHI when compared to Rogers Pass, B.C., Canada. The PDI analysis using equations modified to allow for a range of consequences indicated that the Milford Road is similar in risk to roads in Switzerland, but is far more accessible, with fewer closed days. A new equation for PDI, which accounted for waiting traffic was derived, and suggested that the calculated risk was high and unacceptable compared to standards applied to other hazards. Statistical forecasting using classification tree analysis has been successfully applied to avalanche forecasting in other climatic settings. This study has applied an extension to this technique through 10-fold cross validation to permit classification of an avalanche day in this direct action maritime climate. Using varying misclassification costs two classification trees were generated. The tree that used only wind speed and wind speed and precipitation combined in a temperature sensitive wind drift parameter obtained an overall accuracy of 78%, with correct prediction for an avalanche day at 86%. These predictor variables are considered to be the fundamental controls on avalanche forecasting in this climate, and coincide with important variables inferred from the atmospheric circulation analysis. Following the investigation of various methods for the creation of a high resolution digital elevation model (DEM), a GIS was used for the visualisation and examination of avalanche occurrences. Similar to other studies, qualitative and quantitative analysis of the spatial distribution in terms of aspect of avalanche occurrences was undertaken using the GIS. Colour coding of occurrences highlighted the influence of two storm directions, while an excess ratio showed the clear influence of aspect on avalanche occurrences in relation to two dominant storm directions, avalanche size and avalanche paths. Furthermore, the GIS has many applications for operational forecasting, teaching and the maintenance of institutional memory for the avalanche programme.

We present a preliminary design for a neutron detection system that is compact, lightweight, and low power consuming, utilizing the CubeSat platform making it suitable for space-based applications. This is made possible using the scintillating crystal lithium indium diselenide ((LiInSe2)-Li-6), the first crystal to include Li-6 in the crystalline structure, and a silicon avalanche photodiode. The schematics of this instrument are presented as well as the response of the instrument to initial testing under alpha radiation. A principal aim of this work is to demonstrate the feasibility of such a neutron detection system within a CubeSat platform. The entire end-to-end system presented here is 10 x 10 x 15 cm(3), weighs 670 g, and requires 5 V direct current at 3 W. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains viii, 80 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 47-51).

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Shen, Shyh-Chiang; Committee Member: Doolittle, William A.; Committee Member: Dupuis, Russell Dean. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The quaternary material system In[subscript x]Ga[subscript 1-x]As[subscript y]P[subscript 1-y] is an important material system for optoelectronic devices, specifically covering optimum fiber optic wavelengths. Among the limitations of using this material system concerning photodetector performance is generation of carriers due to material defects and impurities. This dissertation reports on the growth optimization of InGaAs using molecular-beam epitaxy for low-dark-current avalanche photodiodes through the study of the effects of the growth conditions on dark current. An optimum growth temperature of 545°C and arsenic beam equivalent pressure of 2x10⁻⁵ Torr was found for producing the lowest dark current density. Avalanche photodiodes were implemented with a dark current density 80 mA/cm² at 90% of the breakdown voltage.

No description available.

Avalanches pose a significant natural hazard in many parts of the world. Worldwide the hazard is being managed in a number of new and traditional methods. In New Zealand, the Milford Road, Fiordland, has a significant avalanche problem which has been managed by the Transit New Zealand Milford Road Avalanche Programme since 1984. This avalanche programme has generated a database of all avalanche occurrences and associated meteorological parameters for the time period 1985 to 2002. Elsewhere around the world, similar and more extensive data sets have been used to examine a wide variety of aspects in relation to the snow cover, avalanching and avalanche hazard. The availability of the Milford Road database has provided the opportunity use new and traditional approaches to examine many aspects of avalanching including; the trends in and relationships with the snow and avalanche regime, evaluation of the avalanche hazard, statistical forecasting of avalanches and the visualisation of avalanche occurrence information in a GIS. Statistical and graphical examination of the inter-annual variation in the snow and avalanche regime revealed relationships between the snow depth, avalanche occurrences and atmospheric circulation similar to those found elsewhere around the world, but not previously examined in New Zealand. Furthermore, the analysis resulted in strong correlations despite using a database significantly shorter than those used elsewhere. Atmospheric circulation types that bring strong winds and precipitation were found to be highly significantly correlated with avalanche occurrences and snow depth. Avalanche occurrences were more highly correlated with atmospheric circulation than snow depth was, reflecting the strong maritime avalanche climate. Risk evaluation was undertaken using two approaches, the avalanche hazard index (AHI) and the probability of death to individuals (PDI) method. The present avalanche risk was compared to a theoretically uncontrolled avalanche regime, using 2002 traffic volumes for AHI and PDI. The AHI analysis highlighted the reduction in the AHI resulting from the control programme, and the significantly lower AHI when compared to Rogers Pass, B.C., Canada. The PDI analysis using equations modified to allow for a range of consequences indicated that the Milford Road is similar in risk to roads in Switzerland, but is far more accessible, with fewer closed days. A new equation for PDI, which accounted for waiting traffic was derived, and suggested that the calculated risk was high and unacceptable compared to standards applied to other hazards. Statistical forecasting using classification tree analysis has been successfully applied to avalanche forecasting in other climatic settings. This study has applied an extension to this technique through 10-fold cross validation to permit classification of an avalanche day in this direct action maritime climate. Using varying misclassification costs two classification trees were generated. The tree that used only wind speed and wind speed and precipitation combined in a temperature sensitive wind drift parameter obtained an overall accuracy of 78%, with correct prediction for an avalanche day at 86%. These predictor variables are considered to be the fundamental controls on avalanche forecasting in this climate, and coincide with important variables inferred from the atmospheric circulation analysis. Following the investigation of various methods for the creation of a high resolution digital elevation model (DEM), a GIS was used for the visualisation and examination of avalanche occurrences. Similar to other studies, qualitative and quantitative analysis of the spatial distribution in terms of aspect of avalanche occurrences was undertaken using the GIS. Colour coding of occurrences highlighted the influence of two storm directions, while an excess ratio showed the clear influence of aspect on avalanche occurrences in relation to two dominant storm directions, avalanche size and avalanche paths. Furthermore, the GIS has many applications for operational forecasting, teaching and the maintenance of institutional memory for the avalanche programme.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 170-178).