This thesis is devoted in two associated topics: a unique laser facility for researches of gaseous detectors; the investigations of Resistive Plate Chamber (RPC) detectors and the measurement of gas parameters in a realistic condition of timing RPC. A pulsed UV laser test facility has been assembled in HZDR. The focus of pico-second laser pulses is placed in a specific position in a gaseous detector sample to produce laser plasma, where free electrons are generated in ionizations with well defined number, micro-meter spatial accuracy in a volume of micro-meter scale. It provides a method, independent from accelerators, to make investigations with gaseous detectors in a laboratory. Samples of RPC detectors are designed and assembled for experiments with the laser test facility. Methods are developed to acquire the waveforms of electron avalanches for different drift lengths and to obtain the key gas parameters: the effective Townsend coefficient and the electron drift velocity. We have succeeded in the direct measurement of gas parameters at the field strength of timing RPC under atmospheric pressure for the first time in experimental conditions. The research has obtained different achievements. The laser test facility is proven to be qualified for the measurement of gas parameters, and has a potential to contribute to the eco-gas research for future RPC. The possible measurement range of electric field of gas parameter at atmospheric pressure is extended by a factor of two, from the range of trigger RPC to timing RPC. The results of experiments have revealed some fundamental mechanisms, which will extend the understanding of RPC performance and electron avalanche process.

La photodétection est un sujet de recherche très actif encore de nos jours et l’industrie, particulièrement de la physique des hautes énergies et de l’imagerie médicale, est en quête de détecteurs avec une plus grande sensibilité, de meilleures résolutions temporelles et une plus grande densité d’intégration. Pour ces raisons, les photodiodes avalanche à photon unique (Single photon avalanche diode, ou SPAD) suscitent beaucoup d’intérêt depuis quelques années pour ses performances en temps et sa grande photosensibilité. Les SPAD sont des photodiodes avalanche opérées au-dessus de la tension de claquage et un photoporteur atteignant la région de multiplication peut à lui seul déclencher une avalanche soutenue de porteurs et entraîner le claquage de la jonction. Un circuit détecte le courant divergent et l’étouffe en abaissant la polarisation de la jonction sous la tension de claquage. Le circuit recharge ensuite la jonction en réappliquant la tension initiale permettant la détection d’un nouveau photon. Dans le but d’augmenter le nombre de photons simultanés détectables, les SPAD s’intègrent en matrice. Cependant, dans le cas où une matrice de SPAD et leurs circuits d’étouffement s’intègrent sur le même substrat, la surface photosensible devient limitée par l’espace qu’occupent les circuits d’étouffement. Dans le but d’augmenter leur région photosensible, les matrices de SPAD peuvent s’intégrer en trois dimensions (3D) avec leurs circuits d’étouffement. Ce projet porte sur le développement de matrices de SPAD en technologie CMOS HV 0,8 µm de Teledyne DALSA dédiées à une intégration 3D avec leurs circuits d’étouffement actifs. Les résultats de caractérisation montrent que les SPAD atteignent une résolution temporelle de 27 ps largeur à mi hauteur (LMH), possèdent un taux de comptage en obscurité (DCR, ou Dark Count Rate) de 3 s[indice supérieur -1]µm[indice supérieur -2] et ont une probabilité de photodétection (PDP) de 49 %. De plus, une méthode d’isolation utilisant un puits p a été développée. Les SPAD conçus avec cette méthode ont un facteur de remplissage pouvant atteindre 54 % et une probabilité de diaphonie de 6,6 % à une tension excédentaire à la tension de claquage (V[indice inférieur E]) de 4 V.

A wide variety of group III-Nitride-based photonic and electronic devices have opened a new era in the field of semiconductor research in the past ten years. The direct and large bandgap nature, intrinsic high carrier mobility, and the capability of forming heterostructures allow them to dominate photonic and electronic device market such as light emitters, photodiodes, or high-speed/high-power electronic devices. Avalanche photodiodes (APDs) based on group III-Nitrides materials are of interest due to potential capabilities for low dark current densities, high sensitivities and high optical gains in the ultraviolet (UV) spectral region. Wide-bandgap GaN-based APDs are excellent candidates for short-wavelength photodetectors because they have the capability for cut-off wavelengths in the UV spectral region (λ < 290 nm). These intrinsically solar-blind UV APDs will not require filters to operate in the solar-blind spectral regime of λ < 290 nm. For the growth of GaN-based heteroepitaxial layers on lattice-mismatched substrates, a high density of defects is usually introduced during the growth; thereby, causing a device failure by premature microplasma, which has been a major issue for GaN-based APDs. The extensive research on epitaxial growth and optimization of Al_x Ga _1-x N (0 ≤ x ≤ 1) grown on low dislocation density native bulk III-N substrates have brought UV APDs into realization. GaN and AlGaN UV <i> p-i-n </i> APDs demonstrated first and record-high true avalanche gain of > 10,000 and 50, respectively. The large stable optical gains are attributed to the improved crystalline quality of epitaxial layers grown on low dislocation density bulk substrates. GaN <i>p-i-n </i> rectifiers have brought much research interest due to its superior physical properties. The AIN-free full-vertical GaN<i> p-i-n </i> rectifiers on<i> n </i>- type 6H-SiC substrates by employing a conducting AIGaN:Si buffer layer provides the advantages of the reduction of sidewall damage from plasma etching and lower forward resistance due to the reduction of current crowding at the bottom<i> n </i> -type layer. The AlGaN:Si nucleation layer was proven to provide excellent electrical properties while also acting as a good buffer role for subsequent GaN growth. The reverse breakdown voltage for a relatively thin 2.5 μm-thick<i> i </i>-region was found to be over -400V.

Glacial floods and mass movements of ice, rock or debris are a significant hazard in many populated mountainous regions, often with devastating impacts upon human settlements and infrastructure. In response to atmospheric warming, glacial retreat and permafrost thaw are expected to alter high mountain geomorphic processes, and related instabilities. In the Aoraki/Mount Cook region of New Zealand's Southern Alps, a first investigation of geomorphic hazards associated with glacial change is undertaken and is based primarily on the use of remote sensing and Geographic Information Systems (GIS) for mapping, modelling, and analysing related processes and terrain. Following a comprehensive review of available techniques, remote sensing methods involving the use Advanced Spaceborne Thermal Emission and Radiometer (ASTER) imagery were applied to map glacial ice, lakes and debris accumulations in the Aoraki/Mount Cook region. Glacial lakes were mapped from two separate classification techniques using visible near infrared wavelengths, capturing highly turbid and clearer water bodies. Large volume (10⁶– 10⁸ m³) proglacial lakes have developed rapidly over recent decades, with an overall 20 % increase in lake area recorded between 2002 and 2006, increasing the potential for large mass movement impacts and flooding from displaced water. Where significant long-term glacial recession has occurred, steep moraines have been exposed, and large talus slopes occupy formerly glaciated slopes at higher elevations. At the regional-scale, these potential source areas for debris instabilities were distinguished from surrounding bedrock slopes based on image texture variance. For debris and ice covered slopes, potentially unstable situations were classified using critical slope thresholds established from international studies. GIS-based flow routing was used to explore possible intersections between zones of human use and mass movement or flood events, assuming worst-case, probable maximum runout distances. Where glacial lakes are dammed by steep moraine or outwash gravel, primarily in cirque basins east of the Main Divide, modelled debris flows initiated by potential flood events did not reach any infrastructure. Other potential peri- and para-glacial debris flows from steep moraines or talus slopes can reach main roads and buildings. The direct hazard from ice avalanches is restricted to backcountry huts and walking tracks, but impacts into large glacial lakes are possible, and could produce a far reaching hazard, with modelled clear water flood-waves capable of reaching village infrastructure and main roads both east and west of the Main Divide. A numerical modelling approach for simulating large bedrock failures has been introduced, and offers potential with which to examine possible lake impacts and related scenarios. Over 500 bedrock slope failures were analysed within a GIS inventory, revealing distinct patterns in geological and topographic distribution. Rock avalanches have occurred most frequently from greywacke slopes about and east of the Main Divide, particularly from slopes steeper than 50°, and appear the only large-magnitude failure mechanism above 2500 m. In the schist terrain west of the Main Divide, and at lower elevations, other failure types predominate. The prehistoric distribution of all failure types suggests a preference for slopes facing west to northwest, and is likely to be strongly influenced by earthquake generated failures. Over the past 100 years, seismicity has not been a factor, and the most failures have been as rock avalanches from slopes facing east to southeast, particularly evident from the glaciated, and potentially permafrost affected hangingwall of the Main Divide Fault Zone. An initial estimate of permafrost distribution based on topo-climatic relationships and calibrated locally using mean annual air temperature suggested permafrost may extend down to elevations of 3000 m on sunny slopes, and as low as 2200 m on shaded slopes near the Main Divide. A network of 15 near-surface rock temperature sensors was installed on steep rock walls, revealing marginal permafrost conditions (approaching 0 °C) extending over a much larger elevation range, occurring even where air temperature is likely to remain positive, owing to extreme topographic shading. From 19 rock failures observed over the past 100 years, 13 detachment zones were located on slopes characterized by marginal permafrost conditions, including a sequence of 4 failures that occurred during summer 2007/08, in which modelled bedrock temperatures near the base of the detachments were in the range of 1.4 to +2.5 °C. Ongoing monitoring of glacial and permafrost conditions in the Aoraki/Mount Cook region is encouraged, with more than 45 km2 of extremely steep slopes (>50°) currently ice covered or above modelled permafrost elevation limits. Approaches towards modelling and analysing glacial hazards in this region are considered to be most applicable within other remote mountain regions, where seismicity and steep topography combine with possible destabilizing influences of glacial recession and permafrost degradation.

This thesis describes the fabrication and characterization of GaN homojunction visible-blind ultraviolet (UV) p-i-n avalanche photodiodes (APDs) grown by metalorganic chemical vapor deposition (MOCVD) on free-standing bulk GaN substrates. The objective of this research is to develop GaN UV p-i-n APDs with high linear-mode avalanche gains and the Geiger-mode operation for single photon detection. Low noise, high responsivity, and high detectivity are also required for fabricated APDs used as photodiodes in the photovoltaic mode (zero bias) and the photoconductive mode (low reverse bias). High material defect density and immature fabrication technology have hampered the development of III-nitride APDs in the past. In this thesis, sidewall leakage reduction methods have been developed to achieve significant improvement in dark current density, noise performance, and photo detection performance. A record linear-mode avalanche gain > 10⁵ for GaN APDs was demonstrated at λ = 360 nm. The first Geiger-mode deep UV (DUV) APD using front-illuminated homojunction p-i-n diode structure on a free-standing bulk GaN substrate was also measured with single photo detection efficiency (SPDE) of 1.0 % and dark count probability (DCP) of 0.03 at 265 nm. The performance of fabricated homojunction GaN p-i-n photodiodes was also evaluated in the photoconductive mode as well as the photovoltaic mode. For an 80-µm-diameter device biased at - 20 V (in the photoconductive mode) the dark current density is lower than 40 pA/cm² which is the lowest value achieved for any III-nitride photodiode so far. Its responsivity is 0.140 A/W at 360 nm with an ultraviolet-visible rejection ratio of 8×10³. The room-temperature noise equivalent power is 4.27×10 ⁻¹⁷ W-Hz-[superscript 0.5] and the detectivity D* is 1.66×10¹⁴ cm-Hz[superscript 0.5]-W ⁻¹ at - 20 V. The minimum detectable optical power is as low as 100 fW. They are among the best values reported for reverse-biased GaN p-i-n photodiodes to date.

Glacial floods and mass movements of ice, rock or debris are a significant hazard in many populated mountainous regions, often with devastating impacts upon human settlements and infrastructure. In response to atmospheric warming, glacial retreat and permafrost thaw are expected to alter high mountain geomorphic processes, and related instabilities. In the Aoraki/Mount Cook region of New Zealand's Southern Alps, a first investigation of geomorphic hazards associated with glacial change is undertaken and is based primarily on the use of remote sensing and Geographic Information Systems (GIS) for mapping, modelling, and analysing related processes and terrain. Following a comprehensive review of available techniques, remote sensing methods involving the use Advanced Spaceborne Thermal Emission and Radiometer (ASTER) imagery were applied to map glacial ice, lakes and debris accumulations in the Aoraki/Mount Cook region. Glacial lakes were mapped from two separate classification techniques using visible near infrared wavelengths, capturing highly turbid and clearer water bodies. Large volume (10⁶– 10⁸ m³) proglacial lakes have developed rapidly over recent decades, with an overall 20 % increase in lake area recorded between 2002 and 2006, increasing the potential for large mass movement impacts and flooding from displaced water. Where significant long-term glacial recession has occurred, steep moraines have been exposed, and large talus slopes occupy formerly glaciated slopes at higher elevations. At the regional-scale, these potential source areas for debris instabilities were distinguished from surrounding bedrock slopes based on image texture variance. For debris and ice covered slopes, potentially unstable situations were classified using critical slope thresholds established from international studies. GIS-based flow routing was used to explore possible intersections between zones of human use and mass movement or flood events, assuming worst-case, probable maximum runout distances. Where glacial lakes are dammed by steep moraine or outwash gravel, primarily in cirque basins east of the Main Divide, modelled debris flows initiated by potential flood events did not reach any infrastructure. Other potential peri- and para-glacial debris flows from steep moraines or talus slopes can reach main roads and buildings. The direct hazard from ice avalanches is restricted to backcountry huts and walking tracks, but impacts into large glacial lakes are possible, and could produce a far reaching hazard, with modelled clear water flood-waves capable of reaching village infrastructure and main roads both east and west of the Main Divide. A numerical modelling approach for simulating large bedrock failures has been introduced, and offers potential with which to examine possible lake impacts and related scenarios. Over 500 bedrock slope failures were analysed within a GIS inventory, revealing distinct patterns in geological and topographic distribution. Rock avalanches have occurred most frequently from greywacke slopes about and east of the Main Divide, particularly from slopes steeper than 50°, and appear the only large-magnitude failure mechanism above 2500 m. In the schist terrain west of the Main Divide, and at lower elevations, other failure types predominate. The prehistoric distribution of all failure types suggests a preference for slopes facing west to northwest, and is likely to be strongly influenced by earthquake generated failures. Over the past 100 years, seismicity has not been a factor, and the most failures have been as rock avalanches from slopes facing east to southeast, particularly evident from the glaciated, and potentially permafrost affected hangingwall of the Main Divide Fault Zone. An initial estimate of permafrost distribution based on topo-climatic relationships and calibrated locally using mean annual air temperature suggested permafrost may extend down to elevations of 3000 m on sunny slopes, and as low as 2200 m on shaded slopes near the Main Divide. A network of 15 near-surface rock temperature sensors was installed on steep rock walls, revealing marginal permafrost conditions (approaching 0 °C) extending over a much larger elevation range, occurring even where air temperature is likely to remain positive, owing to extreme topographic shading. From 19 rock failures observed over the past 100 years, 13 detachment zones were located on slopes characterized by marginal permafrost conditions, including a sequence of 4 failures that occurred during summer 2007/08, in which modelled bedrock temperatures near the base of the detachments were in the range of 1.4 to +2.5 °C. Ongoing monitoring of glacial and permafrost conditions in the Aoraki/Mount Cook region is encouraged, with more than 45 km2 of extremely steep slopes (>50°) currently ice covered or above modelled permafrost elevation limits. Approaches towards modelling and analysing glacial hazards in this region are considered to be most applicable within other remote mountain regions, where seismicity and steep topography combine with possible destabilizing influences of glacial recession and permafrost degradation.

Les propriétés mécaniques d’un tricot diffèrent drastiquement de celles du fil dont il est constitué. Par exemple, une étoffe tricotée d’un fil inextensible présente une étonnante propension à la déformabilité. À l’instar des systèmes mécaniques où la géométrie joue un rôle prépondérant, tels les origamis, la réponse mécanique d’un tricot va être déterminée par le chemin imposé au fil. Lors du tricotage, le fil est contraint de se courber et de former des points de croisement suivant un motif répétitif, figeant de cette manière sa topologie. Les trois ingrédients sur lesquels repose la réponse mécanique d’un tricot sont l’élasticité du fil, sa topologie et le frottement aux contacts. Une sélection des nombreux phénomènes qui émergent du couplage entre ces ingrédients fait l’objet de cette thèse. Premièrement, l’intérêt a été porté sur l’élasticité du tricot. En se basant sur une expérience de traction d’un tricot-modèle, une théorie, qui vise à décrire cette réponse mécanique, a été construite en tenant compte de la conservation de la topologie, l’énergie de flexion et l’inextensibilité du fil. Dans un second temps, l’accent est mis sur les fluctuations de la réponse mécanique. Ces fluctuations ont pour origine la friction du fil qui empêche sa répartition dans la maille jusqu’à ce qu’un contact glisse brusquement, déclenchant alors une succession de glissements. La mesure de la réponse en force et du champ de déformations montrent que ces évènements suivent une dynamique d’avalanches. Enfin, l’action de la topologie et de la métrique du tricot sur sa forme tridimensionnelle, ainsi que la transition de configuration spontanée de la structure d’un tricot, ont été examinés. / Knits mechanical properties are fundamentally different from those of its constitutive yarn. For instance, a fabric knitted with an inextensible yarn demonstrates a surprising inclination for deformability. Like mechanical systems where geometry plays a preponderant role, such as origami, the mechanical response of knitted fabrics is governed by the pattern imposed on the yarn. In the process of knitting, the yarn is constrained to bend and to cross itself following a periodic pattern, anchoring its topology. The three factors which determine the mechanical response of a knit are the elasticity of the yarn, its topology, and friction between crossing strands. This thesis explores several phenomena that arise from the interplay of these factors. First, we focused on the elasticity of a knit. Working from experimental data, we developed a theory to decipher the mechanical response of model knits under traction, taking into account the unaltered topology, bending energy, and inextensibility of the yarn. Next, we explored fluctuations in the mechanical response of a knit. Those fluctuations originate from yarn-yarn friction, preventing free yarn redistribution in the stitch until a contact slides and triggers propagative slips. Measures of the force response and deformation fields reveal that those events follow an avalanching dynamic, including a power law distribution of their size. Finally, the impact of topology and metric on knit three-dimensional shapes, along with spontaneous configuration transitions in a knit structure, are studied.

No description available.

The theme of this thesis is the Avalanche prevention course for High Schools. Thesis includes both theoretical and experimental part. The theoretical part mainly includes a description of various items used in the avalanche prevention courses. It also contains various methodological procedures, rules, strategy and analysis, which are used for such courses. The research part includes the avalanche prevention course for secondary schools proposal itself under the given conditions and next specifics. In partial steps thesis is mainly focused on proposed content, time allocation, methodical layout, capacity of the course and equipment needed for the implementation of the course.

The occurrence of avalanche paths is usually frequent in alpine environment, but it is also present in mid-mountains such as the High Sudetes. The submitted master thesis is focused on avalanche paths in the Eastern High Sudetes. The morphometric analysis of 8 paths was accomplished to determine their characteristics and comparison with statistical verification. The dendrogeomorphological analysis and further geomorphological mapping was performed in 2 selected paths (Sněžná kotlina and Králický Sněžník) to cover their avalanche activity frequency and to find relationship between their activity and morphology. The results of this study show that there is a strong difference between two groups of avalanche paths in the Eastern High Sudetes. The Sněžná kotlina and The Králický Sněžník avalanche paths are longer and narrower than the other paths. They also have higher elevation difference. The comparison of these two paths performed by dendrogeomorphology indicates higher avalanche activity frequency in the Sněžná kotlina path, which was strengthened after strong avalanche event in 2004. It is assumed that the Sněžná kotlina path contains advanced avalanche landform, which is a long gully, probably also affected by debris- flows in the past. On the other hand the Králický Sněžník path is rather less...