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Search Results: 1 - 10 of 148191 matches for " Christophe Béclin "
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MicroRNAs in brain development and function: a matter of flexibility and stability
Philipp Follert,Harold Cremer,Christophe Béclin
Frontiers in Molecular Neuroscience , 2014, DOI: 10.3389/fnmol.2014.00005
Abstract: Fine-tuning of gene expression is a fundamental requirement for development and function of cells and organs. This requirement is particularly obvious in the nervous system where originally common stem cell populations generate thousands of different neuronal and glial cell types in a temporally and quantitatively perfectly orchestrated manner. Moreover, after their generation, young neurons have to connect with pre-determined target neurons through the establishment of functional synapses, either in their immediate environment or at distance. Lastly, brain function depends not only on static circuitries, but on plastic changes at the synaptic level allowing both, learning and memory. It appears evident that these processes necessitate flexibility and stability at the same time. These two contrasting features can only be achieved by complex molecular networks, superposed levels of control and tight interactions between regulatory mechanisms. Interactions between microRNAs and their target mRNAs fulfill these requirements. Here we review recent literature dealing with the involvement of microRNAs in multiple aspects of brain development and connectivity.
Recent Investigations into Ancient Maya Domestic and Ritual Activities at Pook's Hill, Belize
Christophe G. B. Helmke
Papers from the Institute of Archaeology , 2006, DOI: 10.5334/pia.271
Infrared and Raman Spectroscopic Study of Carbon-Cobalt Composites
André Tembre,Jacques Hénocque,Martial Clin
International Journal of Spectroscopy , 2011, DOI: 10.1155/2011/186471
Abstract: Analysis of carbon-cobalt thin films using infrared spectroscopy has shown existence of carbon-cobalt stretching mode and great porosity. The Raman spectroscopy and high-resolution transmission electron microscopy have been used in order to investigate the microstructure of the films. These films exhibit complex Raman spectra suggesting the presence of amorphous and crystallized phases. The different fractions of phases and the correlation between the atomic bond structures and the Raman features depend on the cobalt content. 1. Introduction In the last years, nanocrystalline magnetic materials made of metallic nanoclusters dispersed in an amorphous matrix have attracted considerable interest owing to their magnetic properties and promising applications as memory units for high-density storage and fundamental research [1, 2]. Hayashi et al. [3] have reported the fabrication and characterization of magnetic thin films of h.c.p cobalt nanocrystals of around 8 nm size encapsulated in graphite-like carbon cages. Due to their ferromagnetic nature, the cobalt grains have great potential for ultra-high-density magnetic recording media. The incorporation in the carbon network of various metallic atoms, like Ti, Zr, Ta, Cr, Mo, W, Fe, Co, and Ni, is a good alternative to improve the tribological [4–7], electric [8–10], and magnetic [11–15] properties of carbon films for various applications as solid lubricant films, microelectrodes, or magnetic films. It has been reported that insertion of metallic atoms in amorphous carbon matrix changes the fraction of Csp3-coordinated carbon sites [16] Various techniques have been used to fabricate metallic nanoclusters dispersed in an amorphous matrix; we can mention filtered cathodic vacuum arc [17, 18], pulsed laser deposition [19], cosputtering [10, 20], and dual beam evaporation system [5]. Among these different methods, cathodic arc deposition is widely used [21, 22]; this technique is characterized by high degree of ionization and great ion kinetic energy and deposition rate. Cathodic arc processes produce unwanted macroparticles in the mm range which are removed from the plasma by a magnetic filter; on the contrary, anodic arc do not suffer from macroparticles contamination, which was the main motivation of using this deposition technique in the present study. Recently, it has been reported that incorporation of iodine in amorphous carbon [23, 24] and boron in diamond [25] leads to a metal-insulator transition at low temperature. Cobalt-doped carbon thin films at 0.3% cobalt content, deposited by a pulsed anodic
Immediate correction required to expect a long-term effectiveness of a brace treatment: a biomechanical insight
Clin Julien,Aubin Carl-Eric,Labelle Hubert,Parent Stefan
Scoliosis , 2010, DOI: 10.1186/1748-7161-5-s1-o63
Hydrophobic pulses predict transmembrane helix irregularities and channel transmembrane units
Damien Paulet, Mireille Claustres, Christophe Béroud
BMC Bioinformatics , 2011, DOI: 10.1186/1471-2105-12-135
Abstract: We describe here how to extract new information from the analysis of hydrophobicity variations or hydrophobic pulses (HPulses) in the sequence of integral membrane proteins using the Hydrophobic Pulse Predictor, a new tool we developed for this purpose. To analyze the primary sequence of 70 integral membrane proteins we defined two levels of analysis: G1-HPulses for sliding windows of n = 2 to 6 and G2-HPulses for sliding windows of n = 12 to 16.The G2-HPulse analysis of 541 transmembrane helices allowed the definition of the new concept of transmembrane unit (TMU) that groups together transmembrane helices and segments with potential adjacent structures. In addition, the G1-HPulse analysis identified helix irregularities that corresponded to kinks, partial helices or unannotated structural events. These irregularities could represent key dynamic elements that are alternatively activated depending on the channel status as illustrated by the crystal structures of the lactose permease in different conformations.Our results open a new way in the understanding of transmembrane secondary structures: hydrophobicity through hydrophobic pulses strongly impacts on such embedded structures and is not confined to define the transmembrane status of amino acids.Integral membrane proteins (IMP) are involved in many aspects of cell physiology such as, for instance, transport of ions and solutes, cell-to-cell signaling and cell recognition. IMPs can be divided in two classes according to the characteristics (α-helix bundles or β-barrels) of their 3D structure. Helix-bundle IMPs are found in all cellular membranes, while β-barrel IMPs are only located in the outer membrane of Gram-negative bacteria, mitochondria and chloroplasts. In this paper, we will focus only on helix-bundle IMPs, as they are almost ubiquitous and represent about 25% of all open reading frames in genomes [1]. Despite their number and importance, high-resolution structures of IMPs represent only about 1% of the P
Liberalization reform, ‘neo-centralism’ and black market: The political diseconomy of Lake Nasser fishery development
Christophe Béné,Bastien Bandi,Fanny Durville
Water Alternatives , 2008,
Abstract: Despite its relatively modest importance, and the current difficulties faced by the government in implementing liberalization in the rest of the country, the Egyptian governement decided to embark on a reform of the Lake Nasser fishery in the early 2000s. The objective of this article is to analyse the evolution of this reform from a political economy perspective. The paper looks retrospectively at the general context of the reform, describes the different institutional and economic changes that have resulted from its realization, identifies how the distribution of power between the different actors has altered the course of its implementation, and finally assesses the outcomes of the reform. The analysis shows that, while some major institutional changes have taken place, those changes have had little to do with a 'liberalization' as conventionally understood in neo-classical literature. Instead, the new status quo turns out to be one where the central government and its different parastatal agencies have managed to maintain their existing advantages. The failure to reform more thoroughly the system also led fishers and fish traders to engage in a large-scale black market activity in which a substantial amount of fish is smuggled through unofficial trade channels.
Politiques de Tests Partiels \& Systèmes de Sécurité
Florent Brissaud,Anne Barros,Christophe Bérenguer
Mathematics , 2010,
Abstract: A set of general formulas is proposed for the probability of failure on demand (PFD) assessment of MooN architecture (i.e. k-out-of-n) systems subject to partial and full tests. Partial tests (e.g. visual inspections, imperfect testing) may detect only some failures, whereas owing to a full test, the system is restored to an as good as new condition. Following the proposed approach and according to an example, performance estimations of the system and test policies are presented, by using the feedback from partial and full tests. An optimization of the partial test distribution is also proposed, which allows reducing the average probability of system failure on demand (PFDavg).
Probability of Failure of Safety-Critical Systems Subject to Partial Tests
Florent Brissaud,Anne Barros,Christophe Bérenguer
Mathematics , 2010,
Abstract: A set of general formulas is proposed for the probability of failure on demand (PFD) assessment of MooN architecture (i.e. k-out-of-n) systems subject to proof tests. The proof tests can be partial or full. The partial tests (e.g. visual inspections, partial stroke testing) are able to detect only some system failures and leave the others latent, whereas the full tests refer to overhauls which restore the system to an as good as new condition. Partial tests may occur at different time instants (periodic or not), up to the full test. The system performances which are investigated are the system availability according to time, the PFD average in each partial test time interval, and the total PFD average calculated on the full test time interval. Following the given expressions, parameter estimations are proposed to assess the system failure rates and the partial test effectiveness according to feedback data from previous test policies. Subsequently, an optimization of the partial test strategy is presented. In the 2oo6 system given as example, an improvement of about 10% of the total PFD average has been obtained, just by a better (non-periodic) distribution of the same number of partial tests, in the full test time interval.
On the stability of some controlled Markov chains and its applications to stochastic approximation with Markovian dynamic
Christophe Andrieu,Vladislav B. Tadi?,Matti Vihola
Statistics , 2012, DOI: 10.1214/13-AAP953
Abstract: We develop a practical approach to establish the stability, that is, the recurrence in a given set, of a large class of controlled Markov chains. These processes arise in various areas of applied science and encompass important numerical methods. We show in particular how individual Lyapunov functions and associated drift conditions for the parametrized family of Markov transition probabilities and the parameter update can be combined to form Lyapunov functions for the joint process, leading to the proof of the desired stability property. Of particular interest is the fact that the approach applies even in situations where the two components of the process present a time-scale separation, which is a crucial feature of practical situations. We then move on to show how such a recurrence property can be used in the context of stochastic approximation in order to prove the convergence of the parameter sequence, including in the situation where the so-called stepsize is adaptively tuned. We finally show that the results apply to various algorithms of interest in computational statistics and cognate areas.
How to Value GDP-Linked Collar Bonds? An Introductory Perspective  [PDF]
Christophe Schinckus
Theoretical Economics Letters (TEL) , 2013, DOI: 10.4236/tel.2013.33024

This short paper proposed a pricing method for GDP-linked collar bonds based on the classical discounted pricing model and the assumption that the GDP can be described with a geometric Brownian motion. The estimation of parameters was not discussed because it is not central in our numerical exercise.

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