The evolution of sperm morphometry in pheasants

Postcopulatory sexual selection is thought to be a potent evolutionary force driving the diversification of sperm shape and function across species. In birds, insemination and fertilisation are separated in time and sperm storage increases the duration of sperm female interaction and hence the opportunity for sperm competition and cryptic female choice. We performed a comparative study of 24 pheasant species (Phasianidae, Galliformes) to establish the relative importance of sperm competition and the duration of sperm storage for the evolution of sperm morphometry (i.e. size of different sperm traits). We found that sperm size traits were negatively associated with the duration of sperm storage but were independent of the risk of sperm competition estimated from relative testis mass. Our study emphasises the importance of female reproductive biology for the evolution of sperm morphometry particularly in sperm storing taxa

On the origin of variable structures in the winds of hot luminous stars

Examination of the temporal variability properties of several strong optical recombination lines in a large sample of Galactic Wolf-Rayet (WR) stars reveals possible trends, especially in the more homogeneous WC than the diverse WN subtypes, of increasing wind variability with cooler subtypes. This could imply that a serious contender for the driver of the variations is stochastic, magnetic subsurface convection associated with the 170 kK partial-ionization zone of iron, which should occupy a deeper and larger zone of greater mass in cooler WR subtypes. This empirical evidence suggests that the heretofore proposed ubiquitous driver of wind variability, radiative instabilities, may not be the only mechanism playing a role in the stochastic multiple small-scaled structures seen in the winds of hot luminous stars. In addition to small-scale stochastic behaviour, subsurface convection guided by a global magnetic field with localized emerging loops may also be at the origin of the large-scale corotating interaction regions as seen frequently in O stars and occasionally in the winds of their descendant WR stars.Comment: 8 pages, 2 figures and 2 tables. Monthly Notices of the Royal Astronomical Society 201

Directed transport in a classical lattice with a high-frequency driving

We analyze the dynamics of a classical particle in a spatially periodic potential under the influence of a periodic in time uniform force. It was shown in [S.Flach, O.Yevtushenko, Y. Zolotaryuk, Phys. Rev. Lett. 84, 2358 (2000)] that despite zero average force, directed transport is possible in the system. Asymptotic description of this phenomenon for the case of slow driving was developed in [X. Leoncini, A. Neishtadt, A. Vasiliev, Phys. Rev. E 79, 026213 (2009)]. Here we consider the case of fast driving using canonical perturbation theory. An asymptotic formula is derived for the average drift velocity as a function of the system parameters and the driving law. We show that directed transport arises in an effective Hamiltonian that does not possess chaotic dynamics, thereby clarifying the relation between chaos and transport in the system. Sufficient conditions for transport are derived.Comment: 5 page

Single File Diffusion of particles with long ranged interactions: damping and finite size effects

We study the Single File Diffusion (SFD) of a cyclic chain of particles that cannot cross each other, in a thermal bath, with long ranged interactions, and arbitrary damping. We present simulations that exhibit new behaviors specifically associated to systems of small number of particles and to small damping. In order to understand those results, we present an original analysis based on the decomposition of the particles motion in the normal modes of the chain. Our model explains all dynamic regimes observed in our simulations, and provides convincing estimates of the crossover times between those regimes.Comment: 30 pages, 9 figure

Les différentes approches méthodologiques de reconstitution des paléo-inondations : une revue de la littérature

Les deux dernières décennies en recherche scientifique se caractérisent par la multiplication des travaux concernant le réchauffement planétaire et les conséquences appréhendées de ce phénomène dans les divers milieux du globe. Ces travaux de recherche touchent différents champs disciplinaires dont la géomorphologie, l'hydrologie, l'écologie et bien d'autres. Dans le contexte des changements climatiques, on voit apparaître un intérêt grandissant pour l'étude des inondations anciennes ou des paléo-inondations. On tente de reconstituer la chronologie des inondations du passé notamment en regard des changements climatiques anciens ou subactuels (derniers siècles). Devant l'émergence de nombreux travaux dans ce domaine de la paléohydrologie, il nous est apparu intéressant d'examiner à travers une revue de la littérature scientifique les différentes approches méthodologiques utilisées dans l'étude des paléo-inondations. On s'attarde à décrire les principales méthodes et techniques employées dans la reconstitution des anciennes inondations, en particulier pour les environnements fluviaux (rivières, fleuves). On passe en revue les différents indicateurs biophysiques utilisés, notamment l'analyse des séquences stratigraphiques et sédimentaires, l'analyse des macrorestes, les méthodes de datation radiocarbone (14 C) et les techniques comme la thermoluminescence optique (TLO) et la dendrochronologie. Aussi, on présente les principaux modèles mathématiques utilisés dans la reconstitution des paléo-inondations, lesquels servent notamment à évaluer les variations niveaux/débits et la fréquence des inondations anciennes.The last two decades of scientific research have been characterized by an increase in the number of studies on global warming and its impact on the earth's various environments (e.g., terrestrial and aquatic ecosystems, river systems). The research concerns different fields such as geomorphology, ecology, hydrology and many others. In the context of climatic change, there is growing interest in the study of past floods or paleofloods. Researchers are attempting to reconstruct the chronology of past floods, especially with respect to past or subrecent (past centuries) climatic changes. The work involves using different methodological approaches borrowed from various disciplines including geology, geomorphology and ecology. The reconstruction of ancient hydrological events such as paleofloods in fact requires that different methods and techniques be combined in order to retrace the chronology of events as precisely as possible using different biological and physical indicators. The earliest research in this field was conducted in the United States, more specifically in the southern and southwestern parts of the country, which are regions characterized by an arid and semi-arid climate. Over the last few years, however, there have been an increasing number of studies from various parts of the world. Much of this research is based on previous work but with new elements of interpretation, which are mainly related to the many fluvial environments and climatic patterns associated with floods.A wide variety of indicators are used in the chronological reconstruction of ancient fluvial environments, whether in humid, sub-humid or desert regions. These indicators involve analyzing stratigraphic sequences and sedimentary deposits, organic matter and macrofossil deposits, as well as using radiocarbon dating (14 C), thermoluminescence (TL), and even dendrochronology. Some research uses statistical and mathematical models to evaluate river flow rates, which are transposed and adapted to ancient flood events. In fact, most of the work pertaining to the reconstruction of the frequency and magnitude of ancient floods uses several methods and techniques to obtain the long-term chronology of flood events in relation to the specific conditions (e.g. climate, geomorphology) of a region or study area.Many studies have analyzed slackwater deposits to reconstruct the paleoflood history of rivers (ELY and BAKER, 1985 ; JONES et al., 2001 ; KOCHEL and BAKER, 1982 ; WOHL et al., 1994). These kinds of deposits are mainly composed of fine-grained sediments (silt and fine sand) from river banks that were deposited during "large floods in areas of reduced flow velocity caused by ponding, eddying, or back-flooding up tributaries" (ELY and BAKER, 1985, p. 104). These deposits were found in different fluvial environments and for many researchers serve as adequate physical and geomorphologic indicators in the reconstruction of relic floods. Also, in many studies researchers used both slackwater deposits (SWD) and paleostage indicators (PSI) for the reconstruction of ancient floods. In addition to slackwater sediments, flood debris and silt lines (paleostage indicators) are often well-preserved along the river terraces (BAKER,1987; OSTENAA et al., 2002; WOHL et al., 1994) and facilitate the reconstruction of ancient flood events. The main problem in reconstructing paleofloods essentially lies in finding layers of organic matter in the sedimentary sequences, which makes it difficult to date the flood events using radiocarbon methods (14C). In arid or semi-arid environments, these organic layers are often rare because the prevalent climatic conditions do not favor the formation of a thick vegetation cover. However, this problem is not limited to these environments but also characterizes humid regions (YANG et al., 2000). The frequent absence of such organic matter layers in sediments is either due to an overly short vegetation cover formation period between phases of flooding or the erosion of such layers through the action of different natural phenomena (e.g. streaming, gliding, bioturbation, fluvial erosion). Other methods through which flood events can be dated include dendrochronology and thermoluminescence (TL). This last method can be used to obtain relatively precise dating of archaeological artefacts but at present is not very reliable for dating mineralogical samples (e.g. quartz or feldspath grains). The various problems involved in dating ancient floods make us aware of the importance of using as many physical and biological field indicators as possible in order to reconstruct the chronology of flood events as precisely as possible

Tissue-specific regulation of cyclin E transcription during Drosophila melanogaster embryogenesis

Cyclin E is an essential regulator of S phase entry. We have previously shown that transcriptional regulation of the gene that encodes Drosophila cyclin E, DmcycE, plays an important role in the control of the G(1) to S phase transition during development. We report here the first comprehensive analysis of the transcriptional regulation of a G(1 )phase cell cycle regulatory gene during embryogenesis. Analysis of deficiencies, a genomic transformant and reporter gene constructs revealed that DmcycE transcription is controlled by a large and complex cis-regulatory region containing tissue- and stage-specific components. Separate regulatory elements for transcription in epidermal cells during cell cycles 14-16, central nervous system cells and peripheral nervous system cells were found. An additional cis-regulatory element drives transcription in thoracic epidermal cells that undergo a 17th cell cycle when other epidermal cells have arrested in G(1 )phase prior to terminal differentiation. The complexity of DmcycE transcriptional regulation argues against a model in which DmcycE transcription is regulated simply and solely by G(1) to S phase transcription regulators such as RB, E2F and DP. Rather, our study demonstrates that tissue-specific transcriptional regulatory mechanisms are important components of the control of cyclin E transcription and thus of cell proliferation in metazoans.Lynn Jones, Helena Richardson and Robert Sain

A homomorphism between link and XXZ modules over the periodic Temperley-Lieb algebra

We study finite loop models on a lattice wrapped around a cylinder. A section of the cylinder has N sites. We use a family of link modules over the periodic Temperley-Lieb algebra EPTL_N(\beta, \alpha) introduced by Martin and Saleur, and Graham and Lehrer. These are labeled by the numbers of sites N and of defects d, and extend the standard modules of the original Temperley-Lieb algebra. Beside the defining parameters \beta=u^2+u^{-2} with u=e^{i\lambda/2} (weight of contractible loops) and \alpha (weight of non-contractible loops), this family also depends on a twist parameter v that keeps track of how the defects wind around the cylinder. The transfer matrix T_N(\lambda, \nu) depends on the anisotropy \nu and the spectral parameter \lambda that fixes the model. (The thermodynamic limit of T_N is believed to describe a conformal field theory of central charge c=1-6\lambda^2/(\pi(\lambda-\pi)).) The family of periodic XXZ Hamiltonians is extended to depend on this new parameter v and the relationship between this family and the loop models is established. The Gram determinant for the natural bilinear form on these link modules is shown to factorize in terms of an intertwiner i_N^d between these link representations and the eigenspaces of S^z of the XXZ models. This map is shown to be an isomorphism for generic values of u and v and the critical curves in the plane of these parameters for which i_N^d fails to be an isomorphism are given.Comment: Replacement of "The Gram matrix as a connection between periodic loop models and XXZ Hamiltonians", 31 page