Surface rearrangement at complex adsorbate-substrate interfaces

On the basis of the information theory approach we propose a novel statistical scheme for analyzing the evolution of coupled adsorbate-substrate systems, in which the substrate undergoes the adsorbate-induced transformations. A relation between the substrate morphology and the adsorbate thermodynamic state is established. This allows one to estimate the surface structure in terms of incomplete experimental information and the one concerning the adsorbate thermodynamic response to the structural modifications.Comment: 5 pages, 3 figure

2PI effective action for gauge theories: Renormalization

We discuss the application of two-particle-irreducible (2PI) functional techniques to gauge theories, focusing on the issue of non-perturbative renormalization. In particular, we show how to renormalize the photon and fermion propagators of QED obtained from a systematic loop expansion of the 2PI effective action. At any finite order, this implies introducing new counterterms as compared to the usual ones in perturbation theory. We show that these new counterterms are consistent with the 2PI Ward identities and are systematically of higher order than the approximation order, which guarantees the convergence of the approximation scheme. Our analysis can be applied to any theory with linearly realized gauge symmetry. This is for instance the case of QCD quantized in the background field gauge.Comment: 21 pages, 8 figures. Uses JHEP3.cl

Tight-binding electronic structure of high Tc superconductors

New superconducting oxides have important crystallographic similarities. They are bulk perovskites or structure derived compounds such as the K 2NiF4 one, with an alternating nature : the oxygen atoms nearest-neighbours are metallic atoms and vice-versa. We show that this structural property has important consequences on the electronic structure. We first present a general formalism allowing us to describe in a simple way the electronic structure as soon as one has an alternating lattice. In a second part, we illustrate this method for different oxides related with the high T c superconductors. Lastly, we show the results we obtain with the alternating lattice method in the two-band model of the CuO2 plane which is characteristic of the copper-based new superconductors.Les nouveaux oxydes supraconducteurs ont des similarités importantes au niveau de leur structure cristallographique. Ce sont des perovskites, ou des composés de structure dérivée qui ont en commun une nature alternée : les premiers voisins des atomes d'oxygène sont des atomes métalliques et réciproquement. Nous montrons que cette particularité structurale a des conséquences très importantes sur la structure électronique. Dans ce but, nous présentons d'abord un formalisme général permettant de décrire simplement la structure électronique proche du niveau de Fermi, dès que l'on a un réseau alterné. Dans la seconde partie, nous illustrons la méthode pour différents oxydes en lien avec les supraconducteurs à haute température critique à base de cuivre ou de bismuth. Enfin, nous montrons les résultats obtenus par la méthode du réseau alterné pour le modèle à deux bandes du plan CuO2, entité de base des nouveaux supraconducteurs à base de cuivre

Could thioredoxin h be involved in early response to gravitropic stimulation of poplar stems?

The perception of gravity is essential for plant development. Trees constantly develop specialized woody tissues, termed « reaction wood » to correct inclined branch and stem growth in order to adopt an optimal position. Despite the economical impact of reaction wood occurrence and itsimportance from a developmental point of view, the perception and response to the gravitational stimulus have not been extensively studied in woody species in which primary and secondary growth occur. Using complementary approaches (proteomics, qRT-PCR, immunolocalization), we have compared straight polar stems to stems that were inclined at 35° from the vertical axis for periods of time varying from 10 min to 6 hours depending on the experiments. The proteomics approach revealed that thirty six percent of the identified proteins that were differentially expressed after gravistimulation were established as potential Thioredoxin targets. qRT-PCR indicated an early induction of Thioredoxin h expression following gravistimulation. In situ immunolocalization indicated that Thioredoxin h protein co-localized with the amyloplasts located in the endodermalcells which may be specialized in gravity perception. These investigations suggest the involvement of Thioredoxin h in the first events of signal transduction in inclined poplar stems, leading to reaction wood formation

Sequential design of computer experiments for the estimation of a probability of failure

This paper deals with the problem of estimating the volume of the excursion set of a function $f:\mathbb{R}^d \to \mathbb{R}$ above a given threshold, under a probability measure on $\mathbb{R}^d$ that is assumed to be known. In the industrial world, this corresponds to the problem of estimating a probability of failure of a system. When only an expensive-to-simulate model of the system is available, the budget for simulations is usually severely limited and therefore classical Monte Carlo methods ought to be avoided. One of the main contributions of this article is to derive SUR (stepwise uncertainty reduction) strategies from a Bayesian-theoretic formulation of the problem of estimating a probability of failure. These sequential strategies use a Gaussian process model of $f$ and aim at performing evaluations of $f$ as efficiently as possible to infer the value of the probability of failure. We compare these strategies to other strategies also based on a Gaussian process model for estimating a probability of failure.Comment: This is an author-generated postprint version. The published version is available at http://www.springerlink.co

Prevalence and Associations, by Age Group, of IPV Among AGYW in Rural South Africa

The prevalence of intimate partner violence (IPV) is alarmingly high among South African adolescent girls and young women (AGYW). Limited data exist exploring how IPV prevalence and its risk factors differ by age. Study data were from the baseline visit of HPTN 068, a randomized controlled trial (RCT) conducted from 2011 to 2015 in Mpumalanga, South Africa. A cohort of 2,533 AGYW, aged 13 years to 20 years, answered survey questions on demographics and behaviors, including their experiences of physical and sexual violence ever and in the past 12 months. We calculated the prevalence of IPV and related risk factors, as well as prevalence ratios with 95% confidence intervals, stratified by age. Nearly one quarter (19.5%, 95% CI = [18.0, 21.2]) of AGYW experienced any IPV ever (physical or sexual) by a partner. The prevalence of any IPV ever among AGYW aged 13 years to 14 years, 15 years to 16 years, and 17 years to 20 years was 10.8%, 17.7%, and 32.1%, respectively. Key variables significantly associated with any IPV ever across all age groups included borrowing money from someone outside the home in the past 12 months, ever having had vaginal sex, ever having had anal sex, and consuming any alcohol. Few statistically significant associations were unique to specific age groups. The history of IPV among the youngest AGYW is a critical finding and should be a focus of prevention efforts

Thermodynamics of the Stockmayer fluid in an applied field

The thermodynamic properties of the Stockmayer fluid in an applied field are studied using theory and computer simulation. Theoretical expressions for the second and third virial coefficients are obtained in terms of the dipolar coupling constant (, measuring the strength of dipolar interactions as compared to thermal energy) and dipole-field interaction energy (α, being proportional to the applied field strength). These expressions are tested against numerical results obtained by Mayer sampling calculations. The expression for the second virial coefficient contains terms up to λ4, and is found to be accurate over realistic ranges of dipole moment and temperature, and over the entire range of the applied field strength (from zero to infinity). The corresponding expression for the third virial coefficient is truncated at λ3, and is not very accurate: higher order terms are very difficult to calculate. The virial coefficients are incorporated in to a thermodynamic theory based on a logarithmic representation of the Helmholtz free energy. This theory is designed to retain the input virial coefficients, and account for some higher order terms in the sense of a resummation. The compressibility factor is obtained from the theory and compared to results from molecular dynamics simulations with a typical value λ = 1. Despite the mathematical approximations of the virial coefficients, the theory captures the effects of the applied field very well. Finally, the vapour-liquid critical parameters are determined from the theory, and compared to published simulation results; the agreement between the theory and simulations is good. © 2015 Taylor & Francis

Twenty years online! A brief history of palaeontologia electronica

This issue marks the 20th anniversary of Palaeontologia Electronica (PE). From modest beginnings as a series of discussions on the PaleoNet listserver in 1996, it has become a well-recognised venue for publication and dissemination of research, techniques, and resources in palaeontology. The journal has many “firsts” to its credit, from the first species named on the internet, the first scientific journal with a plain-language abstract, and the first PDF “reprints” in palaeontology. Over 20 years PE also tried many new approaches that weren’t subsequently adopted by the broader scientific community, such as audio abstracts and animated journal covers. This anniversary issue gives us an opportunity to look back at the beginnings of the journal, its initial aims and aspirations, and to chronicle its evolution. It is as much a reflection of the changing nature of PE as it is a reminder of the larger scale changes that have taken place in the world of palaeontology, the internet, and our community over the past two decades

Random Convex Hulls and Extreme Value Statistics

In this paper we study the statistical properties of convex hulls of $N$ random points in a plane chosen according to a given distribution. The points may be chosen independently or they may be correlated. After a non-exhaustive survey of the somewhat sporadic literature and diverse methods used in the random convex hull problem, we present a unifying approach, based on the notion of support function of a closed curve and the associated Cauchy's formulae, that allows us to compute exactly the mean perimeter and the mean area enclosed by the convex polygon both in case of independent as well as correlated points. Our method demonstrates a beautiful link between the random convex hull problem and the subject of extreme value statistics. As an example of correlated points, we study here in detail the case when the points represent the vertices of $n$ independent random walks. In the continuum time limit this reduces to $n$ independent planar Brownian trajectories for which we compute exactly, for all $n$, the mean perimeter and the mean area of their global convex hull. Our results have relevant applications in ecology in estimating the home range of a herd of animals. Some of these results were announced recently in a short communication [Phys. Rev. Lett. {\bf 103}, 140602 (2009)].Comment: 61 pages (pedagogical review); invited contribution to the special issue of J. Stat. Phys. celebrating the 50 years of Yeshiba/Rutgers meeting

Patterns of ash (Fraxinus excelsior L.) colonization in mountain grasslands: the importance of management practices

International audienceWoody colonization of grasslands is often associated with changes in abiotic or biotic conditions or a combination of both. Widely used as fodder and litter in the past traditional agro-pastoral system, ash (Fraxinus excelsior L.) has now become a colonizing species of mountain grasslands in the French Pyrenees. Its present distribution is dependent on past human activities and it is locally controlled by propagule pressure and abiotic conditions. However, even when all favourable conditions are met, all the potentially colonizable grasslands are not invaded. We hypothesize that management practices should play a crucial role in the control of ash colonization. From empirical field surveys we have compared the botanical composition of a set of grasslands (present and former) differing in management practices and level of ash colonization. We have displayed a kind of successional gradient positively linked to both ash cover and height but not to the age of trees. We have tested the relationships between ash presence in grassland and management types i.e. cutting and/or grazing, management intensity and some grassland communities' features i.e. total and local specific richness and species heterogeneity. Mixed use (cutting and grazing) is negatively linked to ash presence in grassland whereas grazing alone positively. Mixed use and high grazing intensity are directly preventing ash seedlings establishment, when low grazing intensity is allowing ash seedlings establishment indirectly through herbaceous vegetation neglected by livestock. Our results show the existence of a limit between grasslands with and without established ashes corresponding to a threshold in the intensity of use. Under this threshold, when ash is established, the colonization process seems to become irreversible. Ash possesses the ability of compensatory growth and therefore under a high grazing intensity develops a subterranean vegetative reproduction. However the question remains at which stage of seedling development and grazing intensity these strategies could occur