Search results for "NCT"
showing 10 items of 16712 documents
Prediction of Soil Formation as a Function of Age Using the Percolation Theory Approach
2018
Recent modeling and comparison with field results showed that soil formation by chemical weathering, either from bedrock or unconsolidated material, is limited largely by solute transport. Chemical weathering rates are proportional to solute velocities. Nonreactive solute transport described by non-Gaussian transport theory appears compatible with soil formation rates. This change in understanding opens new possibilities for predicting soil production and depth across orders of magnitude of time scales. Percolation theory for modeling the evolution of soil depth and production was applied to new and published data for alpine and Mediterranean soils. The first goal was to check whether the e…
New Pre-Main Sequence Candidates in the Taurus-Auriga Star Forming Region
2007
Aims. We have studied the X-ray source population of the Taurus Molecular Cloud (TMC) to search for new members of the Taurus-Auriga star forming region. Methods. Candidate members have been selected among the X-ray sources detected in 24 fields of the XMM-Newton Extended Survey of the Taurus Molecular Cloud, having an IR counterpart in the 2MASS catalog, based on color-magnitude and color-color diagrams. Their X-ray spectral properties have been compared with those of known members and other X-ray sources in the same fields but without a NIR counterpart. A search for flare-like variability in the time series of all new candidates and the analysis of the X-ray spectra of the brightest candi…
The XMM-Newton Optical Monitor survey of the Taurus molecular cloud
2007
The Optical Monitor (OM) on-board XMM-Newton obtained optical/ultraviolet data for the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST), simultaneously with the X-ray detectors. With the XEST OM data, we aim to study the optical and ultraviolet properties of TMC members, and to do correlative studies between the X-ray and OM light curves. In particular, we aim to determine whether accretion plays a significant role in the optical/ultraviolet and X-ray emissions. The Neupert effect in stellar flares is also investigated. Coordinates, average count rates and magnitudes were extracted from OM images, together with light curves with low time resolution (a few kiloseconds). For a …
Cuevas rituales ibéricas en el territorio de Kelin (ss. V-III a.C.).
2018
La Meseta de Requena-Utiel, en el interior de la provincia de Valencia, constituyó en época ibérica el territorio de la ciudad de Kelin. Entre otros aspectos, dicho territorio destacó por presentar una elevada concentración de cuevas con materiales ibéricos, de las cuales claramente cinco son resultado de prácticas rituales en su interior. Estas cuevas rituales fueron espacios estrechamente ligados al proceso de territorialización acaecido en la zona entre los siglos V y III a.C. En el presente artículo planteamos una revisión de sus características, ajuares y cronologías, integrándolas en todo momento en el paisaje y entorno inmediato. The Requena-Utiel plateau, in the interior of the Prov…
History of the reindeer (Rangifer tarandus) in the eastern Baltic region and its implications for the origin and immigration routes of the recent nor…
2006
A total of 45 subfossil reindeer (Rangifer tarandus) antlers and bones - artefacts excluded - have been found over the years in the Baltic countries of Estonia, Latvia and Lithuania. The relatively high number of specimens suggests a stable residence of the species in the eastern Baltic region. For the first time, 12 of these finds were radiocarbon-dated. The ages of the samples range between 12085 and 9970 C-14 yr BP (14180-11280 cal. yr BP), and cover the Lateglacial and early Holocene, a time period during which climatic conditions shifted from periglacial to temperate. The dates suggest a rapid colonization of the area during the deglaciation period and a local extinction around the Ple…
Dental microwear texture analysis on extant and extinct sharks : Ante- or post-mortem tooth wear?
2020
Sharks are apex-predators that play an important role in past and present aquatic food webs. However, their diet - especially in extinct species - is often not well constrained. Dental microwear texture analysis (DMTA) has been successfully applied to reconstruct diet and feeding behaviours of different aquatic and terrestrial vertebrates. However, unlike in mammals, food-to-tooth contact in sharks is rather limited because only larger prey is manipulated before swallowing. Together with a fast tooth replacement rate, this reduces wear on individual teeth. Here, we present an explorative study of dental microwear texture on extant and extinct sharks to test whether ante-mortem wear is relat…
The biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods (Late Devonian)
2007
International audience; The earliest diversification of tetrapods is dated as Late Devonian based on 10 localities worldwide that have yielded bone remains. At least 18 different species are known from these localities. Their ages span the "middle"-late Frasnian to latest Famennian time interval, with three localities in the Frasnian, one at the F/F transition (though this one is not securely dated) and six in the Famennian. These localities encompass a wide variety of environments, from true marine conditions of the nearshore neritic province, to fluvial or lacustrine conditions. However, it does not seem possible to characterize a freshwater assemblage in the Upper Old Red Sandstone based…
Transient metazoan reefs in the aftermath of the end-Permian mass extinction
2011
5 pages; International audience; Recovery from the devastating Permian-Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch1,2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are considered the hallmark of the Early Triassic4-7. Here we use field and microscopic investigations to document Early Triassic bioaccumulations and reefs f…
In the aftermath of the end-Permian extinction: the microbialite refuge?
2013
7 pages; International audience; We present the first study of micro-crustaceans (ostracods) associated with microbial crusts in the aftermath of the most devastating extinction, the end-Permian extinction (EPE). These post-extinction microbialites dominated shallow shelf marine environments and were traditionally considered as devoid of any associated fauna. We present a micro-palaeontological analysis of a large record from microbial and non-microbial settings following the EPE. This dataset documents the proliferation of ostracods strictly associated with microbialites. Based on the diet of extant ostracods and uniformitarianism, we propose that the abundant microbes in the mats served a…
Permian-Triassic extinctions and rediversifications.
2015
Ammonoids were a major component of Permian marine faunas, but were on the verge of extinction during the Permian-Triassic crisis ~ 252 myr ago. Despite the severity of this extinction, their recovery was explosive in less than 1.5 myr. By Smithian time, they had already reached levels of taxonomic richness much higher than those of the Permian. The causes for the rapid Early Triassic diversification and proliferation of these organisms still remain elusive, but the evolution of their spatio-temporal diversity and disparity patterns closely correlates with the numerous environmental changes recorded during this time interval.