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Search Results: 1 - 10 of 3878 matches for " Etienne Klein "
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What does the “arrow of time” stand for?  [PDF]
Etienne Klein
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.23033
Abstract: One hundred and thirty years after the work of Ludwig Boltzmann on the interpretation of the irreversibility of physical phenomena, and one century after Einstein's formulation of Special Relativity, we are still not sure what we mean when we talk of “time” or “arrow of time”. We shall try to show that one source of this difficulty is our tendency to confuse, at least verbally, time and becoming, i.e. the course of time and the arrow of time, two concepts that the formalisms of modern physics are careful to distinguish. The course of time is represented by a time line that leads us to define time as the producer of duration. It is customary to place on this time line a small arrow that, ironically, must not be confused with the “arrow of time”. This small arrow is only there to indicate that the course of time is oriented, has a well-defined direction, even if this direction is arbitrary. The arrow of time, on the other hand, indicates the possibility for physical systems to experience, over the course of time, changes or transforma-tions that prevent them from returning to their initial state forever. Contrary to what the ex-pression “arrow of time” suggests, it is there-fore not a property of time itself but a property of certain physical phenomena whose dynamic is irreversible. By its very definition, the arrow of time presupposes the existence of a well- established course of time within which – in addition – certain phenomena have their own temporal orientation. We think that it is worth-while to emphasize the difference between sev-eral issues traditionally subsumed under the label “the problem of the direction of time”. If the expressions “course of time”, “direction of time” and “arrow of time” were better defined, systematically distinguished from one another and always used in their strictest sense, the debate about time, irreversibility and becoming in physics would become clearer.
Mixing of propagules from discrete sources at long distance: comparing a dispersal tail to an exponential
Etienne K Klein, Claire Lavigne, Pierre-Henri Gouyon
BMC Ecology , 2006, DOI: 10.1186/1472-6785-6-3
Abstract: We show that a fat-tailed kernel leads asymptotically to a diverse propagule pool containing a balanced mixing of the propagules from the two sources, whereas a thin-tailed kernel results in all propagules originating from the closest source. We further show that these results hold for biologically relevant distances under certain circumstances, and in particular if the number of propagules is large enough, as would be the case for pollen or seeds.To understand the impact of long-distance dispersal on the structure and dynamics of a metapopulation, it might be less important to precisely estimate an average dispersal distance than to determine if the tail of the dispersal kernel is fatter or thinner than that of an exponential function. Depending solely on this characteristic, a metapopulation will behave similarly to an island model with a diverse immigrant pool or to a stepping-stone model with migrants from closest populations. Our results further help to understand why thin-tailed dispersal kernels lead to a colonization wave of constant speed, whereas fat-tailed dispersal kernels lead to a wave of increasing speed. Our results also suggest that the diversity of the pollen cloud of a mother plant should increase with increasing isolation for fat-tailed kernels, whereas it should decrease for thin-tailed kernels.In plant species, the patterns of gene flow by way of seed and pollen dispersal determines the demographic behaviour of populations, the spatial distribution of neutral and selected genetic diversities, and their evolution. Long-distance dispersal (LDD) is an important characteristic of dispersal events affecting population ecology, species distribution, evolution, and conservation [1-4]. It can be quantified by the proportion of the dispersers present farther than a specified threshold or by a distance beyond which only a small fraction of dispersers are found, e.g. 1% [4]. An alternative formulation of LDD concerns the shape of the tail of the dispersal
Dependence of the superconducting transition temperature on the doping level in single crystalline diamond films
Etienne Bustarret,Jozef Kacmarcik,Christophe Marcenat,Etienne Gheeraert,Catherine Cytermann,Jacques Marcus,Thierry Klein
Physics , 2004, DOI: 10.1103/PhysRevLett.93.237005
Abstract: Homoepitaxial diamond layers doped with boron in the 10^20-10^21 /cm3 range are shown to be type II superconductors with sharp transitions (~0.2K) at temperatures increasing from 0 to 2.1 K with boron contents. The critical concentration for the onset of superconductivity is about 5-7 10^20 /cm3, close to the metal-insulator transition. The H-T phase diagram has been obtained from transport and a.c. susceptibility measurements down to 300mK. These results bring new quantitative constraints on the theoretical models proposed for superconductivity in diamond.
An Analysis of the Determinants of Arbitrage Spread  [PDF]
Etienne Redor
Theoretical Economics Letters (TEL) , 2019, DOI: 10.4236/tel.2019.93034
Abstract: This study examines the determinants of arbitrage spread of S&P 500 firms between 2004 and 2014. We find that bid hostility, the relative size of the target compared to the potential bidder and the acquisition premium paid by the bidding firm are associated with greater arbitrage spread while the proportion of cash in the offer and target termination fees are associated with smaller arbitrage spread.
Security & Privacy Implications in the Placement of Biometric-Based ID Card for Rwanda Universities  [PDF]
Eugen Harinda, Etienne Ntagwirumugara
Journal of Information Security (JIS) , 2015, DOI: 10.4236/jis.2015.62010
Abstract: Biometric authentication systems are believed to be effective compared to traditional authentication systems. The introduction of biometrics into smart cards is said to result into biometric-based smart ID card with enhanced security. This paper discusses the biometric-based smart ID card with a particular emphasis on security and privacy implications in Rwanda universities environment. It highlights the security and implementation issues. The analysis shows that despite the necessity to implement biometric technology, absence of legal and regulatory requirements becomes a challenge to implementation of the proposed biometric solution. The paper is intended to engage a broad audience from Rwanda universities planning to introduce the biometric-based smart ID cards to verify students and staff for authentication purpose.
Assortative mating and differential male mating success in an ash hybrid zone population
Pierre R Gérard, Etienne K Klein, Frédéric Austerlitz, Juan F Fernández-Manjarrés, Nathalie Frascaria-Lacoste
BMC Evolutionary Biology , 2006, DOI: 10.1186/1471-2148-6-96
Abstract: We detected a very high pollen immigration rate and a fat-tailed dispersal kernel, counter-balanced by slight phenological assortative mating and short-distance pollen dispersal. Early intermediate flowering hybrids, which had the highest male mating success, showed optimal sex allocation and increased selfing rates. We detected asymmetry of gene flow, with early flowering trees participating more as pollen donors than late flowering trees.This study provides striking evidence that long-distance gene flow alone is not sufficient to counter-act the effects of assortative mating and selfing. Phenological assortative mating and short-distance dispersal can create temporal and spatial structuring that appears to maintain this hybrid population. The asymmetry of gene flow, with higher fertility and increased selfing, can potentially confer a selective advantage to early flowering hybrids in the zone. In the event of climate change, hybridization may provide a means for F. angustifolia to further extend its range at the expense of F. excelsior.Hybrid zones, where lineages differentiable by one or more heritable traits meet and intercross, provide unique opportunities for studying the nature and dynamics of barriers to gene exchange. The evolution of these barriers can have many different outcomes, including divergence of populations leading to speciation, collapse of differentiated populations, hybrid speciation or invasion. The structure and evolution of hybrid zones depend mainly on the relative importance of dispersal, local adaptation and the fitness of hybrids [1,2], influencing the strength of reproductive isolation. For example, with relatively high dispersal between adjacent populations, gene exchange between species is prevented only if local adaptation is sufficiently strong to eliminate hybrids. Temporal isolation is a particular ecological isolation process that can result from divergent adaptations and cause assortative mating by itself. It involves differenc
Bee Venom and Its Component Apamin as Neuroprotective Agents in a Parkinson Disease Mouse Model
Daniel Alvarez-Fischer, Carmen Noelker, Franca Vulinovi?, Anne Grünewald, Caroline Chevarin, Christine Klein, Wolfgang H. Oertel, Etienne C. Hirsch, Patrick P. Michel, Andreas Hartmann
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0061700
Abstract: Bee venom has recently been suggested to possess beneficial effects in the treatment of Parkinson disease (PD). For instance, it has been observed that bilateral acupoint stimulation of lower hind limbs with bee venom was protective in the acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyri?dine(MPTP) mouse model of PD. In particular, a specific component of bee venom, apamin, has previously been shown to have protective effects on dopaminergic neurons in vitro. However, no information regarding a potential protective action of apamin in animal models of PD is available to date. The specific goals of the present study were to (i) establish that the protective effect of bee venom for dopaminergic neurons is not restricted to acupoint stimulation, but can also be observed using a more conventional mode of administration and to (ii) demonstrate that apamin can mimic the protective effects of a bee venom treatment on dopaminergic neurons. Using the chronic mouse model of MPTP/probenecid, we show that bee venom provides sustained protection in an animal model that mimics the chronic degenerative process of PD. Apamin, however, reproduced these protective effects only partially, suggesting that other components of bee venom enhance the protective action of the peptide.
Further Advantages of a Unique Author Identification Number
Etienne Joly
PLOS Medicine , 2006, DOI: 10.1371/journal.pmed.0030368
Abstract:
Marker assisted selection for the improvement of two antagonistic traits under mixed inheritance
Etienne Verrier
Genetics Selection Evolution , 2001, DOI: 10.1186/1297-9686-33-1-17
Abstract: (To access the full article, please see PDF)
The existence of species rests on a metastable equilibrium between inbreeding and outbreeding. An essay on the close relationship between speciation, inbreeding and recessive mutations
Etienne Joly
Biology Direct , 2011, DOI: 10.1186/1745-6150-6-62
Abstract: I do, however, contend that, if so much speciation occurs, the most likely explanation is that there must be conditions where reproductive barriers can be directly selected for. In other words, situations where it is advantageous for individuals to reproduce preferentially within a small group and reduce their breeding with the rest of the ancestral population. This leads me to propose a model whereby new species arise not by populations splitting into separate branches, but by small inbreeding groups "budding" from an ancestral stock. This would be driven by several advantages of inbreeding, and mainly by advantageous recessive phenotypes, which could only be retained in the context of inbreeding. Reproductive barriers would thus not arise as secondary consequences of divergent evolution in populations isolated from one another, but under the direct selective pressure of ancestral stocks. Many documented cases of speciation in natural populations appear to fit the model proposed, with more speciation occurring in populations with high inbreeding coefficients, and many recessive characters identified as central to the phenomenon of speciation, with these recessive mutations expected to be surrounded by patterns of limited genomic diversity.Whilst adaptive evolution would correspond to gains of function that would, most of the time, be dominant, this type of speciation by budding would thus be driven by mutations resulting in the advantageous loss of certain functions since recessive mutations very often correspond to the inactivation of a gene. A very important further advantage of inbreeding is that it reduces the accumulation of recessive mutations in genomes. A consequence of the model proposed is that the existence of species would correspond to a metastable equilibrium between inbreeding and outbreeding, with excessive inbreeding promoting speciation, and excessive outbreeding resulting in irreversible accumulation of recessive mutations that could ultimately o
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