Smoothening Transition of a Two-Dimensional Pressurized Polymer Ring

We revisit the problem of a two-dimensional polymer ring subject to an inflating pressure differential. The ring is modeled as a freely jointed closed chain of N monomers. Using a Flory argument, mean-field calculation and Monte Carlo simulations, we show that at a critical pressure, $p_c \sim N^{-1}$, the ring undergoes a second-order phase transition from a crumpled, random-walk state, where its mean area scales as $\sim N$, to a smooth state with $\sim N^2$. The transition belongs to the mean-field universality class. At the critical point a new state of polymer statistics is found, in which $\sim N^{3/2}$. For $p>>p_c$ we use a transfer-matrix calculation to derive exact expressions for the properties of the smooth state.Comment: 9 pages, 8 figure

Knots in Charged Polymers

The interplay of topological constraints and Coulomb interactions in static and dynamic properties of charged polymers is investigated by numerical simulations and scaling arguments. In the absence of screening, the long-range interaction localizes irreducible topological constraints into tight molecular knots, while composite constraints are factored and separated. Even when the forces are screened, tight knots may survive as local (or even global) equilibria, as long as the overall rigidity of the polymer is dominated by the Coulomb interactions. As entanglements involving tight knots are not easy to eliminate, their presence greatly influences the relaxation times of the system. In particular, we find that tight knots in open polymers are removed by diffusion along the chain, rather than by opening up. The knot diffusion coefficient actually decreases with its charge density, and for highly charged polymers the knot's position appears frozen.Comment: Revtex4, 9 pages, 9 eps figure

New Insight into the Colonization Processes of Common Voles: Inferences from Molecular and Fossil Evidence

Elucidating the colonization processes associated with Quaternary climatic cycles is important in order to understand the distribution of biodiversity and the evolutionary potential of temperate plant and animal species. In Europe, general evolutionary scenarios have been defined from genetic evidence. Recently, these scenarios have been challenged with genetic as well as fossil data. The origins of the modern distributions of most temperate plant and animal species could predate the Last Glacial Maximum. The glacial survival of such populations may have occurred in either southern (Mediterranean regions) and/or northern (Carpathians) refugia. Here, a phylogeographic analysis of a widespread European small mammal (Microtus arvalis) is conducted with a multidisciplinary approach. Genetic, fossil and ecological traits are used to assess the evolutionary history of this vole. Regardless of whether the European distribution of the five previously identified evolutionary lineages is corroborated, this combined analysis brings to light several colonization processes of M. arvalis. The species' dispersal was relatively gradual with glacial survival in small favourable habitats in Western Europe (from Germany to Spain) while in the rest of Europe, because of periglacial conditions, dispersal was less regular with bottleneck events followed by postglacial expansions. Our study demonstrates that the evolutionary history of European temperate small mammals is indeed much more complex than previously suggested. Species can experience heterogeneous evolutionary histories over their geographic range. Multidisciplinary approaches should therefore be preferentially chosen in prospective studies, the better to understand the impact of climatic change on past and present biodiversity

Hydrological variability and chemical weathering in the Southern Alps based on diatoms and their isotopic composition (O and Si)

International audienceLa gestion des ressources de haute montagne du pourtour méditerranéen est d’une importance majeure pour les sociétés aussi bien pour l’approvisionnement en eau que la gestion des risques environnementaux. Les changements climatiques actuels montrent un réchauffement plus rapide en haute altitude et dans la région méditerranéenne que la moyenne globale (+2°C par rapport aux niveaux préindustriels).Le projet Hydro-ALPS a pour but de fournir de nouveaux enregistrements paléoclimatiques continus afin d’aider à la réalisation de modèles climatiques régionaux intégrant des échelles de temps longs. Les interactions étroites entre les activités humaines, l’évolution du climat et l’occurrence d’événements extrêmes, comme l’événement climatique à 4200 cal BP (Cartier et al. 2019), seront également approfondies. Pour cela, les sédiments lacustres de deux lacs, situés à la même altitude (2200 m a.s.l.) dans le massif du Mercantour, mais entourés d’un couvert végétal différent (pâturages versus végétation plus boisée) vont être étudiés de façon pluridisciplinaire (sédimentologie, géochimie, palynologie). L’accent sera mis sur l’utilisation des diatomées, organismes microscopiques siliceux abondants dans ces lacs. L’étude de leurs assemblages et composition isotopique (O et Si) permettra de reconstituer les variations du bilan hydrique et de l’érosion chimique des sols et du socle cristallin.Ce poster présente les objectifs du projet Hydro-ALPS ainsi que les résultats d’une première mission de carottage (septembre 2022) au lac Petit (Valdeblore, France) qui a permis d’obtenir une séquence sédimentaire de 7 m de long avec sections de recouvrement. Les sédiments sont de type « diatomite » sur une majorité de l’enregistrement et la sédimentation caractéristique à l’échelle régionale sur les 30 premiers cm - i.e. sédiments fins bleutés ponctués de lamines noires - permet de penser que la séquence remonte à la fin de la déglaciation. Le cadre chronologique des différentes unités lithologiques sera déterminé par des analyses 14C sur des macrorestes d’origine terrestre. In fine, ces enregistrements paléoclimatiques à haute résolution pourront être comparés à des évolutions/perturbations majeures documentées dans les sociétés du pourtour méditerranéen

SJAELLAND (Dinamarca) (Isla). Mapas generales (1777). 1:240000

Comprende además pequeñas zonas de las islas que las rodeanEscalas gráficas de 3 millas danesas de 12000 varas cada una [= 9,3 cm] y 3 millas geográficas de 15 al grado [= 9,1 cm]. Coordenadas referidas al meridiano de Copenhague (O 2°00'--E 0°28'/N 56°09'--N 54°52'). Recuadro geográfico de 5' en 5'. Orientado con lis en rosa de dieciséis vientosOrografía a trazosTabla de signos convencionales para indicar núcleos de distinta categoría, caminos, etc.Título, autor, fecha y escalas enmarcados en cartela de forma arquitectónica coronada con escudo y decorado con paisaje y tabla de signos en otra decorada con motivos vegetalesForma parte de la Colección Mendoz

Multiproxy analyses of Lake Allos reveal synchronicity and divergence in geosystem dynamics during the Lateglacial/Holocene in the Alps

Palaeoenvironmental reconstructions of ecosystem responses to external forcing are generally limited by the difficulty of understanding the geosystem as a whole, because of the complex interactions between ecological compartments. Therefore, identifying which geosystem compartments or proxies co-vary is a prerequisite in unravelling the propagation of disturbances (e.g. climatic or anthropogenic) from one compartment to another. A multiproxy study of a continuous 13,500-year sedimentary profile cored in Lake Allos (European Alps, 2200 m a.s.l) was carried out on the basis of high-resolution sedimentological, geochemical, and botanical analyses, as well as determination of aquatic biotic proxies (diatoms, ostracods). These multiproxy datasets are rare at these high altitudes. Major changes occurred in the course of the palaeoenvironmental history of this alpine watershed at 12,000, 8600, 7200 and 3000 cal. BP. During the Holocene, two main transitions were recorded in all the ecological compartments (8600 and 3000 cal. BP), but the period 4500-3000 cal. BP stands out because of major changes that concerned only the lacustrine ecosystem. The frequent switches in lake level might correspond to the 4.2 ka climatic event. Proximity of this alpine lake to climatically-sensitive thresholds (ice-cover, thermal stratification, hydrological balance) may have amplified climatic signals in the lake ecosystem. This study illustrates the difficulties inherent to the use of common intra-Holocene stratigraphical limits, given that ecological compartments are likely to have different responses to forcing factors depending on the characteristics of the watershed and its capacity to accommodate disturbances