791 research outputs found
Floras from red beds of the Permian Basin of Lodève (Southern France)
Las plantas fĂłsiles de las capas rojas de la cuenca de Lodève son generalmente escasas y su estado de conservaciĂłn es relativamente pobre comparada a la flora del âAutuniense grisâ. De acuerdo con los trabajos previos de Doubinger y tras una reevaluaciĂłn de las colecciones disponibles gracias a nuevos datos, son propuestas unas listas de las floras de las âcapas rojasâ de la âzona de transiciĂłnâ de la FormaciĂłn de Rabejac y, por primera vez, de la FormaciĂłn de Salagou. Callipteris cf. uralensis y Supaia representan dos taxones significativos; el primero aparece en las capas rojas mientras que Supaia solamente es conocido en la FormaciĂłn de Rabejac. Este gĂŠnero, previamente considerado endĂŠmico de Arizona, ha sido citado como presente en Rusia, EspaĂąa y China, ademĂĄs de la cuenca de Lodève, en la que su presencia podrĂa indicar una edad Artinskiana tardĂa a Kunguriana para esta secciĂłn basal de lo que se conocĂa como âgrupo Saxonianoâ. TambiĂŠn es interesante el hecho de que algunas conĂferas de Rabejac y de la FormaciĂłn de Salagou, mĂĄs reciente, muestran conos y/o hojas suculentas, similares a los de algunas conĂferas TriĂĄsicas, lo que con toda certeza representa un cambio importante en la flora como respuesta a un clima progresivamente mĂĄs seco. Debido a las condiciones desfavorables de fosilizaciĂłn y teniendo en cuenta la importancia de la actividad animal en los ecosistemas de playa de la FormaciĂłn de Salagou, estas plantas poco frecuentes son interpretadas como los restos de una vegetaciĂłn originalmente mucho mĂĄs diversificada, posiblemente dominada por conĂferas arborescentes
The Permian-Triassic boundary and Early Triassic sedimentation in Western European basins: an overview
At the scale of the peri-Tethyan basins of western Europe, the âBuntsandsteinâ continental lithostratigraphic units are frequently attributed to the âPermian-Triassicâ because, in most cases, the lack of any âScythianâ (i.e. Early Triassic) biochronological evidence makes it very difficult to attribute the basal beds of the cycle to the Permian or to the Triassic. A careful recognition of unconformities and sedimentary indications of clearly arid climate provide powerful tools for correlation within non-marine successions that are devoid of any biostratigraphic markers, at least on the scale of the West European Plate. From a review of the âBuntsandsteinâ series of several basins we can characterize the Permian-Triassic boundary and the beginning of Triassic sedimentation at the scale of Western Europe. We clearly show that, except for the Central Germanic Basin, an unconformity can be observed between the Permian and the Triassic. Apart from the Germanic Basin, there is a total lack of typically âScythianâ fossils in the rest of West European basins, and the oldest biochronological markers yielded by these units are palynomorphs allowing to assign an Anisian age generally to the upper part of the âBuntsandsteinâ, but also its lowermost in a few cases. In the peri-Tethyan basins of western Europe, the Permian-Triassic boundary corresponds to an unconformity overlain by conglomerates containing ventifacts (followed by fluvial sandstones, sometimes rich in paleosols and sometimes totally devoid), which are attributed mainly to the lower Olenekian, i.e. Smithian. Alternatively, the succession passes up directly into fluvial sandstones containing the first paleosols, and then plant debris and palynomorphs attributed to the Anisian. In this way, the lack of typically Early Triassic fossils in most of the peri-Tethyan basins, at the scale of the west European Plate, can be explained by a true stratigraphic hiatus in the earliest Triassic (i.e. Induan) and by arid conditions unfavourable for the development of flora and fauna and their preservation during the Olenekian.En las cuencas peritĂŠthicas de Europa occidental, la unidad litoestratigrĂĄfi ca continental âBuntsandsteinâ es frecuentemente atribuida al âPĂŠrmico-TriĂĄsicoâ, porque, en la mayorĂa de los casos, la falta de elementos biocronolĂłgicos âscythiensesâ complica la atribuciĂłn de los niveles basales al PĂŠrmico o al TriĂĄsico. Un cuidadoso examen de las discordancias, y el uso de indicadores sedimentarios de climas claramente ĂĄridos constituyen herramientas fundamentales para la correlaciĂłn de estas unidades no marinas, desprovistas de cualquier marcador bioestratigrĂĄfi co, al menos en el Oeste de la Placa Europea. La revisiĂłn de las series âBuntsandsteinâ de varias cuencas nos ha permitido caracterizar el lĂmite PĂŠrmico-TriĂĄsico y el comienzo de la sedimentaciĂłn durante el TriĂĄsico inferior en el oeste de Europa, demostrando claramente que, excepto en la Cuenca GermĂĄnica Central, se puede observar una discordancia entre las series pĂŠrmicas y triĂĄsicas. Excepto en esta Cuenca GermĂĄnica, existe una falta total de fĂłsiles tĂpicamente âscythiensesâ, y los elementos bioestratigrĂĄfi cos mĂĄs antiguos encontrados son conjuntos de palinomorfos que permiten asignar a los niveles superiores de las series âBuntsandsteinâ una edad Anisiense, en algunos cortes los niveles inferiores. En las cuencas peritĂŠthicas de Europa occidental, el lĂmite PĂŠrmico-TriĂĄsico se corresponde con una discordancia que se recubre por conglomerados con ventifactos (seguidos por areniscas fl uviales, a veces ricas en paleosuelos y a veces totalmente desprovistas de ellos), atribuidos principalmente al Olenekiense inferior (Smithiense), o directamente areniscas fluviales donde aparecen los primeros paleosuelos, asĂ como restos de plantas y palinomorfos, atribuidos al Anisiense. De esta forma en el Oeste de la Placa Europea, la falta de fĂłsiles caracterĂsticos del TriĂĄsico Inferior, en la mayorĂa de las cuencas perithĂŠticas, puede explicarse por un importante hiato estratigrĂĄfi co durante el TriĂĄsico Inferior (Induense) y por unas condiciones ĂĄridas, desfavorables para la vida y la preservaciĂłn de fĂłsiles durante el Olenekiense
Middle Permian Ostracods from Tak Fa Limestone, Phetchabun Province, Central Thailand
This paper presents the first Permian ostracod fauna discovered in Thailand. The ostracods are recovered from the Tak Fa Limestone (Middle Permian) in Phetchabun province, central Thailand. The ostracods belong to eight genera and 15 species. Four species are newly described: Sargentina phetchabunensis nov. sp., Geffenina bungsamphanensis nov. sp., Reviya subsompongensis nov. sp. and Bairdia takfaensis nov. sp. The ostracod assemblages characterize a shallow marine, near shore environment at the time of deposition. Except for one species, which shows palaeobiogeographical links between Central Thailand and South China, all the other species are endemic
MĂŠthode d'ĂŠvaluation de l'action de conseil en irrigation IRRIPARC en rĂŠgions Nord-Pas-de-Calais et Picardie
Parmi les nombreuses actions de conseil en irrigation dÊveloppÊes en France, trop peu d'entre elles sont ÊvaluÊes pour apprÊcier leur impact sur les pratiques d'irrigation et les bÊnÊfices pour la ressource. Dans cet article, nous proposons une mÊthode d'Êvaluation de l'une d'entre elles, sur l'Êtude d'un cas concret : l'action IRRIPARC. Dans les rÊgions Nord-Pas-de-Calais et Picardie, des fiches de rÊglages de canons enrouleurs ont ÊtÊ diffusÊes aux agriculteurs, pour limiter les effets du vent sur l'uniformitÊ de la rÊpartition de l'eau d'irrigation. La mÊthode d'Êvaluation proposÊe repose sur l'Êtude de trois critères : l'efficacitÊ, la pertinence et la cohÊrence de l'action. La collecte des donnÊes se fait par enquêtes quantitatives et qualitatives auprès de diffÊrents acteurs : les agriculteurs, public cible de l'action, et les partenaires impliquÊs dans l'action IRRIPARC. L'analyse dÊbouche sur des perspectives d'Êvolution et fournit des recommandations pour l'action. / Several technical support actions in irrigation have been carried out in France. However, very few have been evaluated to determine their actual impact on irrigation practices and their water saving benefits. In this paper, an assessment method of a technical support action is presented on a concrete case: the IRRIPARC action. The action was carried in the Nord Pas-de-Calais region of France. It aims at providing to farmers technical forms to help them to set their irrigation guns according to the wind speed in order to improve water distribution uniformity. The method depends on three criteria based on the effectiveness, the relevance and the consistency of the action. The data have been collected through quantitative and qualitative enquiries to different stakeholders: farmers to which the action was intended, and other partners which were involved in the action. The analysis results in evolution perspective of IRRIPARC action
Coil conversion to β-strand induced by dimerisation
Most molecular processes in living organisms rely on proteinâprotein interactions, many of which are mediated by β-sheet interfaces; this study investigates the formation of β-sheet interfaces through the conversion of coils into β-strands. Following an exhaustive search in the Protein Data Bank, the corresponding structural dimorphic fragments were extracted, characterised and analysed. Their short strand lengths and specific amino acid profiles indicate that dimorphic β-strand interfaces are likely to be less stable than standard ones and could even convert to coil interfaces if their environment changes. Moreover, the construction of a simple classifier able to discriminate between the sequences of dimorphic and standard β-strand interfaces suggests that the nature of those dimorphic sequences could be predicted, providing a novel means of identifying proteins capable of forming dimers
Long and short paths in uniform random recursive dags
In a uniform random recursive k-dag, there is a root, 0, and each node in
turn, from 1 to n, chooses k uniform random parents from among the nodes of
smaller index. If S_n is the shortest path distance from node n to the root,
then we determine the constant \sigma such that S_n/log(n) tends to \sigma in
probability as n tends to infinity. We also show that max_{1 \le i \le n}
S_i/log(n) tends to \sigma in probability.Comment: 16 page
New data on the Silurian-Devonian paleontology and biostratigraphy of Bolivia
P. 269-314In order to precisely establish the bio- and chronostratigraphic position of several levels of the SilurianâDevonian succession
of Bolivia, with respect to the International Time Scale, additional Silurian and Devonian localities belonging to
the Eastern Cordillera and the Interandean Zone areas have been recently revised and sampled, both for macrofossils and
palynomorphs. Specifically, the localities are ĂuĂąumayani, and Muruhuta from the late Silurianâearly Devonian time
interval. Correlations with other fossiliferous localities are discussed, namely Huacallani and Rumicorral.S
Dynamic Carboniferous tropical forests: new views of plant function and potential for physiological forcing of climate
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138385/1/nph14700_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138385/2/nph14700.pd
Immune Boosting Explains Regime-Shifts in Prevaccine-Era Pertussis Dynamics
Understanding the biological mechanisms underlying episodic outbreaks of infectious diseases is one of mathematical epidemiologyâs major goals. Historic records are an invaluable source of information in this enterprise. Pertussis (whooping cough) is a re-emerging infection whose intermittent bouts of large multiannual epidemics interspersed between periods of smaller-amplitude cycles remain an enigma. It has been suggested that recent increases in pertussis incidence and shifts in the age-distribution of cases may be due to diminished natural immune boosting. Here we show that a model that incorporates this mechanism can account for a unique set of pre-vaccine-era data from Copenhagen. Under this model, immune boosting induces transient bursts of large amplitude outbreaks. In the face of mass vaccination, the boosting model predicts larger and more frequent outbreaks than do models with permanent or passively-waning immunity. Our results emphasize the importance of understanding the mechanisms responsible for maintaining immune memory fo
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
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