Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Afin d’adresser la problématique liée aux limitations des interconnections métalliques en termes de débits notamment, la photonique Si s’est imposée comme une technologie de choix. Un des composants de base des circuits photonique Si est le photodétecteur : Il permet de convertir un signal optique en signal électrique. Les photodétecteurs à base de Ge sur Si ont montré leur potentiel et offrent la meilleure alternative aux photodétecteurs III-V, pour une intégration dans les circuits photoniques Si.Dans ce contexte, les photodiodes à base de Ge su Si ont été étudiées. L’optimisation des photodiodes p-i-n a permis l’obtention de résultats à l’état de l’art. Une nouvelle approche utilisant une double hétéro-jonction latérale Si/Ge/Si a été proposée afin d’augmenter la responsivité mais aussi afin de proposer une meilleure solution d’intégration, avec les modulateurs Si notamment. Pour augmenter encore la sensibilité des récepteurs, l’utilisation de photodiodes à avalanche est cependant nécessaire. La structure SACM (Separate Absorption Charge Multiplication), combinant le faible bruit de multiplication du Si et l’absorption du Ge aux longueurs d’onde télécom, a d’abord été étudiée. Des modèles ont été développées afin d’optimiser le fonctionnement, et ces photodiodes ont été fabriquées et caractérisées. Les résultats obtenus sur des photodiodes éclairées par la surface (produit Gain-Bande passante de 560GHz à seulement -11V) sont très encourageant pour une intégration avec un guide d’onde. D’autre part, les photodiodes p-i-n en Ge sur Si, ont été étudiées en avalanche. La faible largeur de la zone intrinsèque a permis de diminuer le bruit de multiplication par effet « dead space », et le fonctionnement à 10Gbits/s pour un gain de 20 et une puissance optique de seulement -26dBm, pour une tension de -7V, sans utilisation d’amplificateur (TIA), a pu être démontré. Ces développements ouvrent ainsi la voie vers des récepteurs rapides, à faible consommation électrique et grande sensibilité. / To address the issue related to the limitations of metallic interconnects especially in terms of bitrate, Si photonics has become the technology of choice. One of the basic components of photonic circuits is the photodetector: It allows to convert an optical signal into an electrical signal. Photodetectors based on Ge on Si have shown their potential and offer the best alternative to III-V photodetectors, for integration into Si photonic circuits. In this context, the Ge on Si photodiodes have been studied. The optimization of pin photodiodes enabled the achievement of state of the art results. A new approach using a double lateral Si/Ge/Si heterojunction was proposed to increase the responsivity but also to provide a better integration solution, especially with Si modulators. To further increase the sensitivity of the receivers, the use of avalanche photodiodes, is however necessary. SACM (Separate Absorption Charge Multiplication) structure, combining Si low multiplication noise and Ge absorption at telecom wavelengths was first studied. Models have been developed to optimize the devices, and the photodiodes have been fabricated and characterized. The results obtained on the surface illuminated photodiodes (Gain-bandwidth product of 560GHz only -11V) are very encouraging for waveguide integration. On the other hand, Ge on Si pin photodiodes have been studied in avalanche. The small width of the intrinsic region contributed to the multiplication noise reduction thanks to "dead space" effect, and operation at 10Gbps for a gain of 20 and an optical power of -26dBm at only-7V, without using amplifier (TIA), have been demonstrated. These developments open the way to fast, low power consumption and high sensitivity receivers.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Not available

Snow avalanches a natural phenomenon typical for snowy winter mountains consist of snow and sometimes of other material (debris, rocks, truncated trees and soil). On first sight they seem to be harmless mass of snow sliding down on a slope. But not they can be disastrous. Despite the snow avalanches event lasts for couple of seconds, they can take human lives, and destroy infrastructure. Until they occur in far and remote places they are not concern. The avalanche run- out has been always an issue. How far avalanches can travel? Is there avalanche activity out there? How large is the avalanche hazard on certain places? Will the avalanche airbag will influence the probability of not being critically buried by an avalanche. These are the question the thesis attempt to solve with the use of GIS, remote sensing and statistical analysis. The aim of the thesis was to find reasonable answers to these questions. The effectiveness of avalanche airbags was first tested by pilot study when the artificial avalanche was triggered and motion of the dummies with different types was recorded. Additional estimation of impact forces, speed and final position of dummies was investigated and modelled (publication 6). The mechanism behind the avalanche airbags - inverse segregation was proofed to work in field test, but how is...

Major advances in fiber optic transmissions have brought about a need for highly sensitive photodetectors. In order to detect this type of transmission, the photodetector must be able to detect one of the two low loss windows of the fiber optics transmission. The photodetector must also be characterized by a high gain and fast speed of response without generating excessive noise power. This report compares different types of high speed phodetectors with emphasis on the merits of using an avalanche photodiode. The report studies the avalanche multiplication and the signal-to-noise power ratio in the ternary InGaAs. The effects of the absorption coefficient, the depletion width, and the impurity concentration are studied. Finally, an optimization of the signal-to-noise power ratio is achieved by selecting the proper impurity concentration profile at suitable values of absorption coefficient and epitaxial width.

This study aimed to combine avalanche statistics with climate change models in orderto assess how a change in precipitation patterns, snow depth and snow density canimpact the avalanche danger in Jämtland, Sweden. Existing climate model reportsfrom SMHI and the Swedish county administration offices were used, and avalanchestatistics were compiled using data from SEPA from 2017 to 2020.It was found that days with moderate avalanche danger are most common (56 %) andthat a lot of days the danger is considerable (33%). The most common avalancheproblem is wind-drifted snow. The results show that wind velocity of 8 m/s isconnected to considerable danger in over 80 % of cases and for 10 m/s even 90 %. Dailyprecipitation of 3 mm or more is also connected to considerable danger on 81% of days;independently of wind. Towards the end of the 21st century, precipitation in Jämtland in winter and spring isexpected to increase by up to 50 % whereas snow depth is likely to decrease so muchthat many places will not reach 100 cm anymore (under the conservative RCP8.5scenario). While the snow depth comes with shortened winter seasons, increasedprecipitation is shown to increase the danger level. It is therefore likely that theavalanche forecasting period will be shortened but intensified in terms of danger.In conclusion, this study confirms again that avalanches are difficult to predict, andthat climate change will not make this easier. This makes it essential to keep updatingthe avalanche information that is available not just in Sweden but across the globe.However, the results are inconclusive due to the shortage of data and due to thecomplex combinations of factors that can impact avalanche danger. Further researchis required. / <p>2021-07-02</p>

The thesis deal with possibility of localization of avalanche victims. Main focus is for RF avalanche beacons. The major objects of this thesis are design and construction of this device. A large part of thesis describes design of avalanche beacon and particular steps of realization. The design take into account the compatibility with commercial beacons. The paramters of designed device are verified by testing and measurement.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper was prepared as part of the team design competition for a graduate level course given at the University of Canterbury, in Christchurch, New Zealand. It presents a high level design of a snow avalanche telemetry system. The goal of the system is to provide data to better assess avalanche risk, and to assist in designing more effective protection measures in avalanche prone areas. The primary conditions monitored are air pressure, snow density, snow depth, snow temperature, wind velocity, wind direction, and ambient air temperature. All critical aspects of the telemetering system have been specified, including the sensors, transmitter/receiver, and telemetry frame design. Aspects of the system packaging and the link budget which are unique to the alpine environment are discussed.