Determination of Hf, Sc and Y in geological samples together with the rare-earth elements

A method is described for the determination of Hf, Sc and Y simultaneously with the REE in geological materials. An earlier method for REE separation from major elements was studied with the aim to apply it also to the determination of Hf, Sc and Y. Sample decomposition was carried out by melting with LiBO2. The method involves separation and concentration stages, using the cation-exchange resin DOWEX AG 50W-X8. Matrix elements were eluted with 2 mol/1 HCl, whereas 6 mol/1 HNO3 with oxalic acid and 8 mol/1 HNO3 were used to elute the elements to be determined. Some of the matrix elements could not be completely removed. This effect as well as the recovery rates of the determined elements were investigated. The measurements were performed by ICP-AES. Spectral interferences were also teste

Laparoscopic management of appendicitis and symptomatic cholelithiasis during pregnancy

Background: Laparoscopic surgery during pregnancy is a challenging procedure that most surgeons are reluctant to perform. The objective of this study was to evaluate whether laparoscopic appendectomy and cholecystectomy is safe in pregnant women. The management of these situations remains controversial. We report a single center study describing the successful management of 16 patients during pregnancy. Methods: More than 3,356 laparoscopic procedures were performed in our institutions between May 1990 and June 2005. Sixteen of these patients were operated on in the second and third trimester between 22 and 32weeks of estimated gestational age. We performed 11 laparoscopic appendectomies and 5 laparoscopic cholecystectomies. We also reviewed the management and operative technique used in these patients. Results: In this study, the laparoscopic appendectomy or cholecystectomy was performed successfully in all patients. Three patients were in their second trimester, weeks22, 23, and 25, and 13 were in the third trimester, weeks27 (three patients), 28 (five patients), 31 (three patients), and 32 (two patients). No maternal or fetal morbidity occurred. Open laparoscopy was performed safely in all patients and all patients delivered healthy babies. Conclusion: From our experience laparoscopic management of appendicitis and biliary colic during pregnancy is safe, however the second trimester is preferable for laparoscopic cholecystectomy. Pregnancy is not a contraindication to the laparoscopic approach to appendicitis or symptomatic cholelithiasis. We believe that laparoscopic operations, when performed by experienced surgeons, are safe and even preferable for the mother and the fetu

Permafrost is warming at a global scale

Permafrost warming has the potential to amplify global climate change, because when frozen sediments thaw it unlocks soil organic carbon. Yet to date, no globally consistent assessment of permafrost temperature change has been compiled. Here we use a global data set of permafrost temperature time series from the Global Terrestrial Network for Permafrost to evaluate temperature change across permafrost regions for the period since the International Polar Year (2007-2009). During the reference decade between 2007 and 2016, ground temperature near the depth of zero annual amplitude in the continuous permafrost zone increased by 0.39 ± 0.15 °C. Over the same period, discontinuous permafrost warmed by 0.20 ± 0.10 °C. Permafrost in mountains warmed by 0.19 ± 0.05 °C and in Antarctica by 0.37 ± 0.10 °C. Globally, permafrost temperature increased by 0.29 ± 0.12 °C. The observed trend follows the Arctic amplification of air temperature increase in the Northern Hemisphere. In the discontinuous zone, however, ground warming occurred due to increased snow thickness while air temperature remained statistically unchanged

Laparoscopic management of appendicitis and symptomatic cholelithiasis during pregnancy

BACKGROUND: Laparoscopic surgery during pregnancy is a challenging procedure that most surgeons are reluctant to perform. The objective of this study was to evaluate whether laparoscopic appendectomy and cholecystectomy is safe in pregnant women. The management of these situations remains controversial. We report a single center study describing the successful management of 16 patients during pregnancy. METHODS: More than 3,356 laparoscopic procedures were performed in our institutions between May 1990 and June 2005. Sixteen of these patients were operated on in the second and third trimester between 22 and 32 weeks of estimated gestational age. We performed 11 laparoscopic appendectomies and 5 laparoscopic cholecystectomies. We also reviewed the management and operative technique used in these patients. RESULTS: In this study, the laparoscopic appendectomy or cholecystectomy was performed successfully in all patients. Three patients were in their second trimester, weeks 22, 23, and 25, and 13 were in the third trimester, weeks 27 (three patients), 28 (five patients), 31 (three patients), and 32 (two patients). No maternal or fetal morbidity occurred. Open laparoscopy was performed safely in all patients and all patients delivered healthy babies. CONCLUSION: From our experience laparoscopic management of appendicitis and biliary colic during pregnancy is safe, however the second trimester is preferable for laparoscopic cholecystectomy. Pregnancy is not a contraindication to the laparoscopic approach to appendicitis or symptomatic cholelithiasis. We believe that laparoscopic operations, when performed by experienced surgeons, are safe and even preferable for the mother and the fetu

Contribution à l'étude du pergélisol de montagne en zone marginale

L’objectif principal de cette thèse est l’identification de processus régulant la présence et l’évolution du pergélisol dans les zones marginales de son domaine d’existence, c’est-à-dire là où sa présence est fortement discontinue, sporadique, voire incertaine. Cette thématique n’a que peu été étudiée jusqu’à ce jour. Cependant, comme les interrogations portant sur les effets du réchauffement climatique sur l’environnement alpin se multiplient, la compréhension des processus dictant l’évolution de la température du sol dans une situation de pergélisol marginal revêt une importance primordiale. En effet, ce type de pergélisol devrait a priori être le premier à subir une disparition complète. Une vingtaine de sites localisés principalement dans la partie occidentale des Alpes Suisses, mais aussi dans les Préalpes, le Jura et les Pyrénées, ont été investigués essentiellement par le biais de mesures de température du sol (instantanées ou continues) et de résistivité électrique. Des données météorologiques et nivologiques ont également été relevées en permanence sur plusieurs sites entre 1998 et 2003. Quatre types de terrain ont été analysés, à savoir : - des éboulis de basse altitude où il s’avère que le sol peut demeurer gelé en permanence à une altitude aussi basse que 1200 m.s.m. et où la température moyenne annuelle de l’air est supérieure à +5°C; - des éboulis de haute altitude (2200-3000 m.s.m.) situés à proximité de la limite inférieure du pergélisol discontinu, là où la présence de pergélisol n’est le plus souvent restreinte qu’à quelques portions du versant; - des glaciers rocheux inactifs/fossiles où des corps de pergélisol pourraient avoir été préservés depuis plusieurs milliers d’années; - des marges proglaciaires historiques (Petit Age Glaciaire) de petits glaciers ayant souvent recouvert tout ou partie de glaciers rocheux préexistants et où la répartition spatiale actuelle du pergélisol est encore marquée par le profond remaniement thermique et mécanique causé par l’avancée glaciaire. Les résultats obtenus soutiennent l’hypothèse formulée au début du travail, à savoir qu’il faut considérer la répartition spatiale du pergélisol dans un environnement alpin comme étant la superposition de deux modes dont les mécanismes de fonctionnement thermique diffèrent: un mode que l’on peut qualifier de typique, résultant d’un bilan d’énergie dont les composantes sont essentiellement des flux de chaleur (conductifs et convectifs) verticaux, et un mode atypique, influencé en grande partie par une composante advective du bilan d’énergie. Au moins deux processus générant ou ayant généré une répartition atypique du pergélisol dans des dépôt sédimentaires meubles ont pu être mis en évidence : les effets de l’avancée glaciaire historique du Petit Age Glaciaire et la circulation d’air interne, de type «effet de cheminée» ou «tube à vent». Ces processus peuvent affecter ou avoir affecté à peu près n’importe quelle accumulation de matériaux et il y a lieu d’en tenir compte en vue d’une estimation fiable des effets du réchauffement climatique sur l’évolution et la répartition spatiale du pergélisol. Dans les marges proglaciaires historiques, la présence de pergélisol est souvent limitée au pourtour du champ proglaciaire. Des corps de matériaux gelés ont pu être déplacés (formation de moraines de poussée) et d’importants déséquilibres, autant thermiques que géométriques, ont été provoqués par l’avancée glaciaire. Dans ces terrains fortement perturbés, les effets de l’évolution du climat s’additionnent à des rééquilibrages thermiques en cours et peuvent contribuer à accélérer le réchauffement du pergélisol déplacé (?) dans certains secteurs marginaux du champ proglaciaire. Une circulation d’air qui s’inverse et s’intensifie en fonction du gradient de température entre l’intérieur d’une accumulation de débris rocheux et l’air extérieur a pu être démontrée dans tous les éboulis de basse et moyenne altitude qui ont été observés. Cette ventilation interne est cruciale pour permettre la présence de pergélisol dans ces éboulis; elle peut en effet conduire selon les cas à une anomalie thermique annuelle du sol de 3 à 7°C par rapport à la température moyenne annuelle de l’air dans la partie basse de l’éboulis. Le fonctionnement de la phase de ventilation ascendante hivernale, provoquant un refroidissement très marqué de la moitié inférieure d’un éboulis, n’est pas significativement entravée par un épais couvert neigeux continu. Il est possible qu’une telle circulation d’air contribue également à déterminer la répartition spatiale du pergélisol dans des éboulis de haute altitude et à préserver des corps gelés dans des glaciers rocheux inactifs/fossiles. Les mesures de température du sol à disposition ont en tout cas montré l’existence, certes atténuée, de la phase hivernale ascendante du système de ventilation. Une partie de cette thèse est consacrée à des questions d’ordre méthodologique concernant la pertinence et l’apport des techniques de mesure mises en oeuvre. Une interprétation basée sur une approche qualitative des mesures effectuées et non pas seulement purement quantitative a été privilégiée. Ainsi par exemple, l’analyse détaillée de l’aspect de la courbe d’un sondage électrique vertical permet de mettre en évidence une possible hétérogénéité et renseigne tout autant sur la nature du terrain que les résistivités mesurées dans l’absolu. Une typologie de courbes caractéristiques a par ailleurs été dressée dans le cadre de la prospection des marges proglaciaires. En ce qui concerne les mesures de température du sol, les mesures BTS (température à la base de la couche de neige hivernale) ont par exemple été utilisées de préférence en vue de l’identification de particularités du régime thermique du sol plutôt que pour la prospection même du pergélisol. Par ailleurs, une typologie du comportement thermique annuel du sol a pu être défi- nie pour décrire le fonctionnement du système de ventilation d’un éboulis de basse altitude. L’importance de la répétition de mesures dans le temps (monitoring) a également été soulignée. En effet, de nombreux résultats originaux proposés découlent de mesures répétées occasionnellement ou acquises en continu durant plusieurs années. Au contraire d’une simple prospection, le monitoring ne donne pas seulement une image figée de la situation investiguée, mais également évolutive, ce qui en permet une meilleure appréciation.The main objective of this thesis is the identification of mechanisms controlling the occurrence and the evolution of mountain permafrost in peripheral areas, i.e. where the presence of permafrost is strongly discontinuous, isolated, or even uncertain. This area has not been greatly studied so far. As investigations relating to the effects of climate warming on the alpine environment multiply, the comprehension of the mechanisms controlling the thermal regime of the ground in a situation of marginal permafrost takes on particular significance. Indeed, this type of permafrost should be a priori the first to completely disappear. About twenty sites mainly located in the western part of the Swiss Alps, but also in the Prealps, Jura and Pyrenees, were primarily investigated by means of electrical resistivity and ground temperature (instantaneous or continuous) measurements. Weather and snow data were also permanently recorded on several sites between 1998 and 2003. Four types of terrain were analysed, namely : - scree slopes at low elevation where permafrost can occur as low as 1200 m a.s.l. (above sea level) while the mean annual air temperature is higher than +5°C; - talus slopes at high elevation (2200-3000 m a.s.l.) located near the lower limit of the discontinuous alpine permafrost belt, where the occurrence of permafrost is generally restricted to some portions of a slope; - inactive/relict rock glaciers where materials can be preserved in a frozen state since several thousands of years ago; - historical (Little Ice Age) forefield of small glaciers having often covered whole or part of pre-existing rock glaciers and where the current spatial distribution of permafrost is still marked by strong thermal and mechanical disruption caused by the glacier advance. The results obtained support the assumption formed at the beginning of the work, namely that it is necessary to consider the spatial distribution of permafrost in an alpine environment as being the superposition of two modes in which the thermal mechanisms differ: a typical mode resulting from an energy balance whose components are primarily vertical (conductive and convective) heat fluxes, and an atypical mode mainly influenced by an advective component of the energy balance. At least two processes generating or having generated an atypical distribution of permafrost in non-consolidated sedimentary deposits can be highlighted: the effects of the Little Ice Age glacier advance and an internal circulation of air («chimney effect» or «wind tube»). One or the other of these processes may affect or have affected the permafrost conditions in any accumulation of materials and it is necessary to take this into account for a reliable estimate of the effects of the climate warming on the evolution and the spatial distribution of permafrost. In the historical glacier forefields, the occurrence of permafrost is often limited to the margins of the former proglacial field. Frozen materials can be moved (formation of push-moraines) and significant imbalances, as much thermal as geometrical, can be caused by the glacier advance. In these strongly disturbed terrains, the effects of climate evolution are added to thermal adjustments in progress and can contribute to accelerate the warming of permafrost which was moved (?) in certain marginal sectors of the proglacial field. An air circulation which reverses and intensifies according to the contrast in temperature between the air in the interior of the blocky accumulation and the surrounding air could be shown in all the talus slopes of low and medium elevation that were analysed. The internal ventilation mechanism is crucial to allow the occurrence of permafrost in these talus slopes; in the lower part of a slope, it can indeed lead, depending on cases, to a thermal annual anomaly of the ground reaching 3 to 7°C compared to the mean annual temperature of the outside air. The winter ascending ventilation phase, causing a very strong cooling of the lower half of a slope, is not significantly blocked by a thick continuous snow cover. It is possible that such a circulation of air also contributes to determine the spatial distribution of permafrost in talus slopes at high elevation and to preserve materials in a permanent frozen state in inactive or fossil rock glaciers. Indeed, the available ground temperature measurements showed in any case the existence, certainly attenuated, of the ascending winter phase of the ventilation system. Part of this thesis is devoted to methodological questions concerning the relevance and the contribution of the used measurement techniques. An interpretation based on a qualitative and not purely quantitative approach of the obtained data is preferenced. Thus, for example, the detailed analysis of the aspect of the curve of a vertical electrical sounding allow us to highlight a possible heterogeneity of the ground composition and informs as much about the nature of the ground as the resistivities measured alone. A typology of characteristic curves was in addition drawn up within the framework of glacier fore- field investigation. Concerning the measurements of ground temperature, BTS (Bottom Temperature of the winter Snow cover) measurements, for example, were used in preference for the identification of characteristics of the ground thermal regime rather than for the prospecting itself of permafrost. In addition, a typology of the annual thermal regime of the ground was defined to describe the effects and the specificities of the ventilation system in a low elevation talus slope. The importance of repeating measurements in time (monitoring) is also underlined. Indeed, many original results suggested herein arise from measurements that were occasionally repeated or acquired in an uninterrupted way during several years. Unlike a simple prospection, monitoring does not only give a fixed image of the investigated situation, but also an evolutionary insight, which allows a better appreciation of it