Notch signaling in the pigmented epithelium of the anterior eye segment promotes ciliary body development at the expense of iris formation.

The ciliary body and iris are pigmented epithelial structures in the anterior eye segment that function to maintain correct intra-ocular pressure and regulate exposure of the internal eye structures to light, respectively. The cellular and molecular factors that mediate the development of the ciliary body and iris from the ocular pigmented epithelium remain to be fully elucidated. Here, we have investigated the role of Notch signaling during the development of the anterior pigmented epithelium by using genetic loss- and gain-of-function approaches. Loss of canonical Notch signaling results in normal iris development but absence of the ciliary body. This causes progressive hypotony and over time leads to phthisis bulbi, a condition characterized by shrinkage of the eye and loss of structure/function. Conversely, Notch gain-of-function results in aniridia and profound ciliary body hyperplasia, which causes ocular hypertension and glaucoma-like disease. Collectively, these data indicate that Notch signaling promotes ciliary body development at the expense of iris formation and reveals novel animal models of human ocular pathologies.

The Tertiary structural and thermal evolution of the central Alps - Compressional and extensional structures in an orogenic belt

The Western Alpine Are has been created during the Cretaceous and the Tertiary orogenies. The interference patterns of the Tertiary structures suggest their formation during continental collision of the European and the Adriatic Plates, with an accompanying anticlockwise rotation of the Adriatic indenter. Extensional structures are mainly related to ductile deformation by simple shear. These structures developed at a deep tectonic level, in granitic crustal rocks, at depths in excess of 10 km. In the early Palaeogene period of the Tertiary Orogeny, the main Tertiary nappe emplacement resulted from a NW-thrusting of the Austroalpine, Penninic and Helvetic nappes. Heating of the deep zone of the Upper Cretaceous and Tertiary nappe stack by geothermal heat flow is responsible for the Tertiary regional metamorphism, reaching amphibolite-facies conditions in the Lepontine Gneiss Dome (geothermal gradient 25 degrees C/ km). The Tertiary thrusting occurred mainly during prograde metamorphic conditions with creation of a penetrative NW-SE-oriented stretching lineation, X(1) (finite extension), parallel to the direction of simple shear. Earliest cooling after the culmination of the Tertiary metamorphism, some 38 Ma ago, is recorded by the cooling curves of the Monte Rosa and Mischabel nappes to the west and the Suretta Nappe to the east of the Lepontine Gneiss Dome. The onset of dextral transpression, with a strong extension parallel to the mountain belt, and the oldest S-vergent `'backfolding'' took place some 35 to 30 Ma ago during retrograde amphibolite-facies conditions and before the intrusion of the Oligocene dikes north of the Periadriatic Line. The main updoming of the Lepontine Gneiss Dome started some 32-30 Ma ago with the intrusion of the Bergell tonalites and granodiorites, concomitant with S-vergent backfolding and backthrusting and dextral strike-slip movements along the Tonale and Canavese Lines (Argand's Insubric phase). Subsequently, the center of main updoming migrated slowly to the west, reaching the Simplon region some 20 Ma ago. This was contemporaneous with the westward migration of the Adriatic indenter. Between 20 Ma and the present, the Western Aar Massif-Toce culmination was the center of strong uplift. The youngest S-vergent backfolds, the Glishorn anticline and the Berisal syncline fold the 12 Ma Rb/Sr biotite isochron and are cut by the 11 Ma old Rhone-Simplon Line. The discrete Rhone-Simplon Line represents a late retrograde manifestation in the preexisting ductile Simplon Shear Zone. This fault zone is still active today. The Oligocene-Neogene dextral transpression and extension in the Simplon area were concurrent with thrusting to the northwest of the Helvetic nappes, the Prealpes (35-15 Ma) and with the Jura thin-skinned thrust (11-3 Ma). It was also contemporaneous with thrusting to the south of the Bergamasc (> 35-5 Ma) and Milan thrusts (16-5 Ma).

Anachronistic facies from a drowned Lower Triassic carbonate platform: Lower member of the Alwa Formation (Ba'id Exotic), Oman Mountains

- The lower member of the Alwa Formation (Lower Olenekian), found within the Ba'id Exotic in the Oman Mountains (Sultanate of Oman), consists of ammonoid-bearing, pelagic limestones that were deposited on an isolated, drowned carbonate platform on the Neotethyan Gondwana margin. The strata contain a variety of unusual carbonate textures and features, including thrombolites, Frutexites-bearing microbialites that contain synsedimentary cements, matrix-free breccias surrounded by isopachous calcite cement, and fissures and cavities filled with large botryoidal cements. Thrombolites are found throughout the study interval, and occur as 0.5-1.0 m thick lenses or beds that contain laterally laterally-linked stromatactis cavities. The Frutexites-bearing microbialites occur less frequently, and also form lenses or beds, up to 30 cm thick; the microbialites may be laminated, and often developed on hardgrounds. In addition, the Frutexites-bearing microbialites also contain synsedimentary calcite cement crusts and botryoids (typically <1 cm thick) that harbour layers or pockets of what appear to be bacterial sheaths and coccoids, and are indicative of biologically mediated precipitation of the cement bodies. Slumping following lithification led to fracturing of the limestone and the precipitation of large, botryoidal aragonite cements in fissures that cut across the primary fabric. Environmental conditions, specifically palaeoxygenation and the degree of calcium carbonate supersaturation, likely controlled whether the thrombolites (high level of calcium carbonate supersaturation associated with vertical mixing of water masses and dysoxic conditions) or Frutexites-bearing microbialites (low level of calcium carbonate supersaturation associated with anoxic conditions and deposition below a stable chemocline) formed. The results of this study point to continued environmental stress in the region during the Early Triassic that likely contributed to the uneven recovery from the Permian-Triassic mass extinction.

Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter

this study presents a review of published geological data, combined with original observations on the tectonics of the simplon massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute angle by the Miocene, epi- to anchizonal, dextral centovalli strike-slip fault. the structures of the simplon massif result from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for this zone of oblique continental collision. the following main Alpine tectonic phases and structures may be distinguished: 1. NW-directed nappe emplacement, starting in the Early Eocene (similar to 50 Ma); 2. W, SW and S- verging transverse folds; 3. transpressional movements on the dextral simplon ductile shear zone since similar to 32 Ma; 4. formation of the Bergell - Vanzone backfolds and of the southern steep belt during the Oligocene, emplacement of the mantle derived 31 - 29 Ma Bergell and Biella granodiorites and porphyritic andesites as well as intrusions of 29-25 Ma crustal aplites and pegmatites; 5. formation of the dextral discrete Rhone-Simplon line and the centovalli line during the Miocene, accompanied by the pull-apart development of the Lepontine gneiss dome - Dent blanche (Valpelline) depression. It is suggested that movements of shortening in fan shaped NW, W and sW directions accompanied the more regular NW- to WNW-directed displacement of the Adriatic indenter during continental collision.

cAMP-dependent chloride secretion mediates tubule enlargement and cyst formation by cultured mammalian collecting duct cells.

Polycystic kidney diseases result from disruption of the genetically defined program that controls the size and geometry of renal tubules. Cysts which frequently arise from the collecting duct (CD) result from cell proliferation and fluid secretion. From mCCD(cl1) cells, a differentiated mouse CD cell line, we isolated a clonal subpopulation (mCCD-N21) that retains morphogenetic capacity. When grown in three-dimensional gels, mCCD-N21 cells formed highly organized tubular structures consisting of a palisade of polarized epithelial cells surrounding a cylindrical lumen. Subsequent addition of cAMP-elevating agents (forskolin or cholera toxin) or of membrane-permeable cAMP analogs (CPT-cAMP) resulted in rapid and progressive dilatation of existing tubules, leading to the formation of cystlike structures. When grown on filters, mCCD-N21 cells exhibited a high transepithelial resistance as well as aldosterone- and/or vasopressin-induced amiloride-sensitive and -insensitive current. The latter was in part inhibited by Na(+)-K(+)-2Cl(-) cotransporter (bumetanide) and chloride channel (NPPB) inhibitors. Real-time PCR analysis confirmed the expression of NKCC1, the ubiquitous Na(+)-K(+)-2Cl(-) cotransporter and cystic fibrosis transmembrane regulator (CFTR) in mCCD-N21 cells. Tubule enlargement and cyst formation were prevented by inhibitors of Na(+)-K(+)-2Cl(-) cotransporters (bumetanide or ethacrynic acid) or CFTR (NPPB or CFTR inhibitor-172). These results further support the notion that cAMP signaling plays a key role in renal cyst formation, at least in part by promoting chloride-driven fluid secretion. This new in vitro model of tubule-to-cyst conversion affords a unique opportunity for investigating the molecular mechanisms that govern the architecture of epithelial tubes, as well as for dissecting the pathophysiological processes underlying cystic kidney diseases.

Tertiary Himalayan structures and metamorphism in the Kulu Valley (Mandi-Khoksar transect of the Western Himalaya) - Shikar-Beh-nappe and crystalline nappe

The Crystalline Nappe of the High Himalayan Crystalline has been examined along the Kulu Valley and its vicinity (Mandi-Khoksar transect). This nappe was believed to have undergone deformation related only to its transport towards the SW essentially during the `'Main Central Thrust event''. New data has led to the conclusion that during the Himalayan orogeny, two distinctive phases, related to two opposite transport directions, characterize the evolution of this part of the chain, before the creation of the late NE-vergent backfolding. The first phase corresponds to an early NE-vergent folding and thrusting, creating the Tandi Syncline and the NE-oriented Shikar Beh Nappe stack, with a displacement amplitude of about 50 km. Two schistosities, together with a strong stretching lineation are developed at a deep tectonic level under amphibolite facies conditions (kyanite-staurolite-garnet-two mica schists). At a higher tectonic level and in the southern part of the section (Tandy Syncline and southern Kulu Valley between Kulu and Mandi) one or two schistosities are developed in the greenschist facies grade rocks (garnet-biotite and biotite schists). These structures and the associated Barrovian type metamorphism are all related to the NE-verging Shikar Beh Nappe. The creation of the NE-verging Shikar Beh Nappe may be explained by the reactivation of a SW dipping listric normal fault of the N Indian flexural passive margin, during the early stages of the Himalayan orogeny. In the second phase, the still hot metamorphic rocks of the Shikar Beh Nappe were folded and thrust towards the SW (mainly along the MBT and the MCT with a displacement in excess of 100 km) onto the cold, low-grade metamorphic rocks of the Larji-Kulu-Rampur Window or, near Mandi, on the non-metamorphic sandstones of the Ganges Molasse (Siwaliks). Sense of shear criteria and a strong NE-SW stretching-lineation indicate that the Crystalline Nappe has been overthrusted towards the SW. Thermometry on synkinematically crystallised garnet-biotite and garnet-hornblende pairs reveals the lower amphibolite facies temperature conditions related to the Crystalline Nappe formation. From the muscovite and biotite Rb-Sr cooling ages, the Shikar Beh Nappe emplacement occurred before 32 Ma and the southwestward thrusting of the Crystalline Nappe began before 21 Ma. Our model involving two opposite directions of thrusting goes against the conventional idea of only one main SW-oriented transport direction in the High Himalayan Crystalline Nappes.

The meiosis-specific recombinase hDmc1 forms ring structures and interacts with hRad51.

Eukaryotic cells encode two homologs of Escherichia coli RecA protein, Rad51 and Dmc1, which are required for meiotic recombination. Rad51, like E.coli RecA, forms helical nucleoprotein filaments that promote joint molecule and heteroduplex DNA formation. Electron microscopy reveals that the human meiosis-specific recombinase Dmc1 forms ring structures that bind single-stranded (ss) and double-stranded (ds) DNA. The protein binds preferentially to ssDNA tails and gaps in duplex DNA. hDmc1-ssDNA complexes exhibit an irregular, often compacted structure, and promote strand-transfer reactions with homologous duplex DNA. hDmc1 binds duplex DNA with reduced affinity to form nucleoprotein complexes. In contrast to helical RecA/Rad51 filaments, however, Dmc1 filaments are composed of a linear array of stacked protein rings. Consistent with the requirement for two recombinases in meiotic recombination, hDmc1 interacts directly with hRad51.

Flow structures at an idealized bifurcation : a numerical experiment

River bifurcations are key nodes within braided river systems controlling the flow and sediment partitioning and therefore the dynamics of the river braiding process. Recent research has shown that certain geometrical configurations induce instabilities that lead to downstream mid-channel bar formation and the formation of bifurcations. However, we currently have a poor understanding of the flow division process within bifurcations and the flow dynamics in the downstream bifurcates, both of which are needed to understand bifurcation stability. This paper presents results of a numerical sensitivity experiment undertaken using computational fluid dynamics (CFD) with the purpose of understanding the flow dynamics of a series of idealized bifurcations. A geometric sensitivity analysis is undertaken for a range of channel slopes (0.005 to 0.03), bifurcation angles (22 degrees to 42 degrees) and a restricted set of inflow conditions based upon simulating flow through meander bends with different curvature on the flow field dynamics through the bifurcation. The results demonstrate that the overall slope of the bifurcation affects the velocity of flow through the bifurcation and when slope asymmetry is introduced, the flow structures in the bifurcation are modified. In terms of bifurcation evolution the most important observation appears to be that once slope asymmetry is greater than 0.2 the flow within the steep bifurcate shows potential instability and the potential for alternate channel bar formation. Bifurcation angle also defines the flow structures within the bifurcation with an increase in bifurcation angle increasing the flow velocity down both bifurcates. However, redistributive effects of secondary circulation caused by upstream curvature can very easily counter the effects of local bifurcation characteristics. Copyright (C) 2011 John Wiley & Sons, Ltd.

Apprentissage automatique de la morphologie : le cas des structures racine-schème

RÉSUMÉ Cette thèse porte sur le développement de méthodes algorithmiques pour découvrir automatiquement la structure morphologique des mots d'un corpus. On considère en particulier le cas des langues s'approchant du type introflexionnel, comme l'arabe ou l'hébreu. La tradition linguistique décrit la morphologie de ces langues en termes d'unités discontinues : les racines consonantiques et les schèmes vocaliques. Ce genre de structure constitue un défi pour les systèmes actuels d'apprentissage automatique, qui opèrent généralement avec des unités continues. La stratégie adoptée ici consiste à traiter le problème comme une séquence de deux sous-problèmes. Le premier est d'ordre phonologique : il s'agit de diviser les symboles (phonèmes, lettres) du corpus en deux groupes correspondant autant que possible aux consonnes et voyelles phonétiques. Le second est de nature morphologique et repose sur les résultats du premier : il s'agit d'établir l'inventaire des racines et schèmes du corpus et de déterminer leurs règles de combinaison. On examine la portée et les limites d'une approche basée sur deux hypothèses : (i) la distinction entre consonnes et voyelles peut être inférée sur la base de leur tendance à alterner dans la chaîne parlée; (ii) les racines et les schèmes peuvent être identifiés respectivement aux séquences de consonnes et voyelles découvertes précédemment. L'algorithme proposé utilise une méthode purement distributionnelle pour partitionner les symboles du corpus. Puis il applique des principes analogiques pour identifier un ensemble de candidats sérieux au titre de racine ou de schème, et pour élargir progressivement cet ensemble. Cette extension est soumise à une procédure d'évaluation basée sur le principe de la longueur de description minimale, dans- l'esprit de LINGUISTICA (Goldsmith, 2001). L'algorithme est implémenté sous la forme d'un programme informatique nommé ARABICA, et évalué sur un corpus de noms arabes, du point de vue de sa capacité à décrire le système du pluriel. Cette étude montre que des structures linguistiques complexes peuvent être découvertes en ne faisant qu'un minimum d'hypothèses a priori sur les phénomènes considérés. Elle illustre la synergie possible entre des mécanismes d'apprentissage portant sur des niveaux de description linguistique distincts, et cherche à déterminer quand et pourquoi cette coopération échoue. Elle conclut que la tension entre l'universalité de la distinction consonnes-voyelles et la spécificité de la structuration racine-schème est cruciale pour expliquer les forces et les faiblesses d'une telle approche. ABSTRACT This dissertation is concerned with the development of algorithmic methods for the unsupervised learning of natural language morphology, using a symbolically transcribed wordlist. It focuses on the case of languages approaching the introflectional type, such as Arabic or Hebrew. The morphology of such languages is traditionally described in terms of discontinuous units: consonantal roots and vocalic patterns. Inferring this kind of structure is a challenging task for current unsupervised learning systems, which generally operate with continuous units. In this study, the problem of learning root-and-pattern morphology is divided into a phonological and a morphological subproblem. The phonological component of the analysis seeks to partition the symbols of a corpus (phonemes, letters) into two subsets that correspond well with the phonetic definition of consonants and vowels; building around this result, the morphological component attempts to establish the list of roots and patterns in the corpus, and to infer the rules that govern their combinations. We assess the extent to which this can be done on the basis of two hypotheses: (i) the distinction between consonants and vowels can be learned by observing their tendency to alternate in speech; (ii) roots and patterns can be identified as sequences of the previously discovered consonants and vowels respectively. The proposed algorithm uses a purely distributional method for partitioning symbols. Then it applies analogical principles to identify a preliminary set of reliable roots and patterns, and gradually enlarge it. This extension process is guided by an evaluation procedure based on the minimum description length principle, in line with the approach to morphological learning embodied in LINGUISTICA (Goldsmith, 2001). The algorithm is implemented as a computer program named ARABICA; it is evaluated with regard to its ability to account for the system of plural formation in a corpus of Arabic nouns. This thesis shows that complex linguistic structures can be discovered without recourse to a rich set of a priori hypotheses about the phenomena under consideration. It illustrates the possible synergy between learning mechanisms operating at distinct levels of linguistic description, and attempts to determine where and why such a cooperation fails. It concludes that the tension between the universality of the consonant-vowel distinction and the specificity of root-and-pattern structure is crucial for understanding the advantages and weaknesses of this approach.

Edar/Eda interactions regulate enamel knot formation in tooth morphogenesis.

tabby and downless mutant mice have apparently identical defects in teeth, hair and sweat glands. Recently, genes responsible for these spontaneous mutations have been identified. downless (Dl) encodes Edar, a novel member of the tumour necrosis factor (TNF) receptor family, containing the characteristic extracellular cysteine rich fold, a single transmembrane region and a death homology domain close to the C terminus. tabby (Ta) encodes ectodysplasin-A (Eda) a type II membrane protein of the TNF ligand family containing an internal collagen-like domain. As predicted by the similarity in adult mutant phenotype and the structure of the proteins, we demonstrate that Eda and Edar specifically interact in vitro. We have compared the expression pattern of Dl and Ta in mouse development, taking the tooth as our model system, and find that they are not expressed in adjacent cells as would have been expected. Teeth develop by a well recorded series of epithelial-mesenchymal interactions, similar to those in hair follicle and sweat gland development, the structures found to be defective in tabby and downless mice. We have analysed the downless mutant teeth in detail, and have traced the defect in cusp morphology back to initial defects in the structure of the tooth enamel knot at E13. Significantly, the defect is distinct from that of the tabby mutant. In the tabby mutant, there is a recognisable but small enamel knot, whereas in the downless mutant the knot is absent, but enamel knot cells are organised into a different shape, the enamel rope, showing altered expression of signalling factors (Shh, Fgf4, Bmp4 and Wnt10b). By adding a soluble form of Edar to tooth germs, we were able to mimic the tabby enamel knot phenotype, demonstrating the involvement of endogenous Eda in tooth development. We could not, however, reproduce the downless phenotype, suggesting the existence of yet another ligand or receptor, or of ligand-independent activation mechanisms for Edar. Changes in the structure of the enamel knot signalling centre in downless tooth germs provide functional data directly linking the enamel knot with tooth cusp morphogenesis. We also show that the Lef1 pathway, thought to be involved in these mutants, functions independently in a parallel pathway.

Qui utilise les crèches en Suisse ? : logiques sociales du recours aux structures d'accueil collectif pour la petite enfance

Depuis quelque temps, de plus en plus de spécialistes de la politique sociale préconisent une stratégie d'investissement social dans laquelle les crèches joueraient un rôle majeur. Cette stratégie vise à prévenir les exclusions sociales par la promotion de l'égalité des chances et de l'accès à l'emploi en vue d'un allègement des dépenses de protection sociale passive. Outre qu'elles permettent aux familles d'avoir deux revenus, les crèches ont en effet l'avantage de réduire les écarts au niveau des compétences cognitives et linguistiques entre les enfants venant de différents milieux sociaux. Mais le succès d'une telle stratégie présuppose que certains publics cibles recourent effectivement aux crèches, à savoir les ménages disposant d'un faible revenu ou/et de niveau de formation, ainsi que les familles issues de l'immigration. Or, des analyses statistiques sur la base de l'Enquête suisse sur la population active (ESPA) de 2008 montrent que, pour les familles en Suisse, les chances d'utiliser une crèche augmentent avec le niveau de formation des parents. Concernant plus particulièrement le niveau de formation des mères, ce phénomène n'est d'ailleurs que partiellement conditionné par le taux d'activité supérieur de celles ayant accompli une formation de degré tertiaire. En outre, certaines populations d'immigrés dont l'intégration dans la société suisse est réputée difficile sont peu disposées à recourir aux crèches. Les immigrés de première génération de quasiment toutes les origines fortement représentées en Suisse ont en revanche plus de chances que les parents d'origine suisse de faire appel au service d'une crèche à raison d'au moins 4 jours/semaine, ce qui peut influer négativement sur le comportement de l'enfant. Ce dernier résultat semble paradoxal mais montre qu'une migration rend plus difficile l'organisation d'une garde informelle comme solution complémentaire à la crèche. En synthèse, la présente étude attire l'attention sur le fait que les atouts pédagogiques et socialisants des crèches reviennent avant tout aux enfants de parents d'origine suisse ou venant de pays culturellement proches et ayant un niveau de formation supérieur. Telle que conçue actuellement, l'offre de crèches en Suisse ne semble guère opérer comme un instrument efficace de l'investissement social. Immer mehr Experten der Sozialpolitik empfehlen eine ,,Strategie der sozialen Investitionen", die den Kindertagesstätten (bzw. Kinderkrippen) eine wichtige Rolle zuschreibt. Ziel dieser Strategie ist es, durch Förderung von Chancengleichheit und Arbeitsmarktpartizipation sozialen Ausgrenzungen vorzubeugen, um Einsparungen im Bereich der passiven Sozialleistungen zu ermöglichen. Krippen haben einerseits den Vorteil, dass sie es den Familien ermöglichen, zwei Einkommen zu erzielen. Andererseits tragen sie zur Minderung von kognitiven und sprachlichen Fähigkeitsunterschieden zwischen Vorschulkindern aus verschiedenen sozialen Milieus bei. Der Erfolg dieser Strategie setzt jedoch voraus, dass gewisse Zielgruppen tatsächlich Krippen nutzen, nämlich bezüglich Einkommen und/oder Bildung benachteiligte Haushalte sowie Familien mit Migrationshintergrund. Die vorliegenden statistischen Analysen aufgrund der SAKE-Daten von 2008 (Schweizerische Arbeitskräfteerhebung) ergeben jedoch für die Schweiz, dass die Wahrscheinlichkeit, eine Krippe zu nutzen, mit dem Bildungsniveau der Eltern steigt. Was das Bildungsniveau der Mütter im Besonderen anbelangt, ist dieses Phänomen nur teilweise bedingt durch den tendenziell höheren Beschäftigungsgrad der besser Ausgebildeten. Zudem haben einige Migrantengruppen, deren Integration in die Schweizer Gesellschaft als besonders schwierig betrachtet wird, eine bedeutend tiefere Benützungswahrscheinlichkeit als Eltern Schweizer Herkunft. Für fast alle in der Schweiz stark vertretenen Migranten erster Generation ist dennoch das statistische Risiko grösser, die Krippe während mindestens 4 Tagen/Woche zu nutzen, was einen negativen Einfluss auf das Verhalten des Kindes haben kann. Dieses scheinbar paradoxe Ergebnis ist darauf zurückzuführen, dass ein Migrationshintergrund das Organisieren von krippenergänzenden Betreuungslösungen informeller Art meist erschwert. Gesamthaft zeigt die vorliegende Studie auf, dass die positiven pädagogischen und sozialisierenden Effekte der Krippen in erster Linie Kindern zugutekommen, deren Eltern eine höhere Ausbildung haben, Schweizer Herkunft sind oder aus einem kulturell nahestehenden Land kommen. So wie es gegenwärtig eingerichtet ist, scheint das Krippenangebot in der Schweiz kaum als effizientes Instrument sozialer Investitionen zu wirken.

Response to the comments on "The formation of Pangea" by D.A. Ruban

The Variscan structures of the Caucasus region are still quite difficult to decipher, they certainly deserved some in depth investigations in the future. Thus, it is right to question any paleogeographic models proposed in that area, as made by D.A. Ruban. We present here the arguments that we used to decide on the distribution of the terranes in that region. The Transcaucasus massif is regarded as pertaining to the Galatian super-terrane, whereas, the Great Caucasus terrane belongs to the Hanseatic ribbon terrane. The latter was a part of Hunia, detached from Laurussia in the Devonian.

Volcanic debris avalanche deposits of the upper Maronne valley (Cantal Volcano, France): evidence for contrasted formation and transport mechanisms

The deposits of two volcanic debris avalanches (VDA I and II) that occur in the upper Maronne valley, northwest sector of Cantal Volcano, France, were studied to establish their mechanisms of formation, transport and deposition. These two volcanic debris avalanches that clearly differ with regard to their structures, textures and extensions, exemplify the wide spectrum of events associated with large-scale sector collapse. VDA I is voluminous (similar to1 km(3) in the upper Maronne valley) and widespread. The deposits comprise two distinct facies: the block facies that forms the intermediate and upper part of the unit and the mixed facies that crops out essentially at the base of the unit. The block facies consists of more or less brecciated lava, block-and-ash-flow breccia and pumice-flow tuff megablocks set in breccias resulting from block disaggregation. Mixing and differential movements are almost absent in this part of the VDA. The mixed facies consists of breccias rich in fine particles that originate from block disagregation, as well as being picked up from the substratum during movement. Mixing and differential movements are predominant in this zone. Analysis of fractures on lava megablocks suggests that shear stress during the initial sliding is the principal cause of fracture. These data strongly indicate that VDA I is purely gravitational and argue for a model in which the initial sliding mass transforms into a flow due to differential in situ fragmentation caused by the shear stress. VDA II is restricted to low-topography areas. Its volume, in the studied area, is about 0.3 km(3). The deposits consist of brecciated, rounded blocks and megablocks set in a fine-grained matrix composed essentially of volcanic glass. This unit is stratified, with a massive layer that contains all the megablocks at the base and in the intermediate part, and in the upper part a normally graded layer that contains only blocks <1 m in size. The different lithologies present are totally mixed. These observations suggest that VDA II may be of the Bezymianny-type and that it underwent a flow transformation from a turbulent to a stratified flow consisting of a basal hyperconcentrated laminar body overlain by a dilute layer. (C) 2000 Elsevier Science B.V. All rights reserved.

L'hôpital psychiatrique: un lieu pour la formation à la psychothérapie des troubles psychotiques

Dans le contexte de prises en charge psychiatriques hospitalières complexes pour des patients souffrant de troubles psychotiques, le risque est grand que le traitement se limite à l'identification de symptômes, à la définition d'un diagnostic et à l'instauration d'un traitement médicamenteux. La prise en compte des aspects psychologiques de la crise qui conduit à l'hospitalisation et son intégration dans le contexte de l'histoire de vie du patient sont pourtant d'une importance fondamentale pour l'évolution et le succès du traitement. Dans cet article, nous rendons compte d'une démarche de réflexion, conduite dans une unité hospitalière universitaire spécialisée dans le traitement des troubles du spectre de la schizophrénie, visant à identifier les moyens qui permettraient de renforcer la place de l'approche psychologique des troubles psychotiques en milieu hospitalier et de rendre cette approche accessible aux médecins psychiatres en formation dans de telles structures.