Growth in systems of vesicles and membranes

We present a theoretical study for the intermediate stages of the growth of membranes and vesicles in supersaturated solutions of amphiphilic molecules. The problem presents important differences with the growth of droplets in the classical theory of Lifshitz-Slyozov-Wagner, because the aggregates are extensive only in two dimensions, but still grow in a three dimensional bath. The balance between curvature and edge energy favours the nucleation of small planar membranes, but as they grow beyond a critical size they close themselves to form vesicles. We obtain a system of coupled equations describing the growth of planar membranes and vesicles, which is solved numerically for different initial conditions. Finally, the range of parameters relevant in experimental situations is discussed.Comment: 13 pages and 5 postscript figures. To appear in Phys. Rev

Taxonomic Revision and Morphometric Analysis of Selected Anthurium (Araceae) Species From Bolivia and Peru

The genus Anthurium (Araceae) consists of around 1,200 species distributed in the Neotropics, particularly in Central and South America. The montane forests in the eastern flank of the Andes, ranging from northern Ecuador to central Bolivia; hereafter, the East Andes Gradient region, are particularly rich in terms of species diversity, and include an understudied group of Anthurium species endemic to the region. Within this group of species, some taxa are difficult to distinguish from each other mainly due to the lack of identification keys, incomplete species descriptions and unknown synonyms. In this study, a combination of traditional taxonomic techniques and linear morphometric was used to better delimit species within the East Andes Gradient region. A total of 135 morphological characters, including leaf, reproductive, qualitative and quantitative characters were measured for more than 100 herbarium specimens from the Missouri Botanical Garden herbarium. This revision of Anthurium species occurring in the East Andes Gradient region includes a total of 24 species and 1 subspecies. Standardized descriptions, photographs and distribution maps are presented for each taxa. Additionally, summary descriptions of each section considered in this study are also included. Considerations regarding similar species and how to distinguish them are provided to avoid confusion while identifying herbarium specimens from the region. Identification keys to all species and all sections included in this revision are also provided

Lattice density-functional theory of surface melting: the effect of a square-gradient correction

I use the method of classical density-functional theory in the weighted-density approximation of Tarazona to investigate the phase diagram and the interface structure of a two-dimensional lattice-gas model with three phases -- vapour, liquid, and triangular solid. While a straightforward mean-field treatment of the interparticle attraction is unable to give a stable liquid phase, the correct phase diagram is obtained when including a suitably chosen square-gradient term in the system grand potential. Taken this theory for granted, I further examine the structure of the solid-vapour interface as the triple point is approached from low temperature. Surprisingly, a novel phase (rather than the liquid) is found to grow at the interface, exhibiting an unusually long modulation along the interface normal. The conventional surface-melting behaviour is recovered only by artificially restricting the symmetries being available to the density field.Comment: 16 pages, 6 figure

Free energies, vacancy concentrations and density distribution anisotropies in hard--sphere crystals: A combined density functional and simulation study

We perform a comparative study of the free energies and the density distributions in hard sphere crystals using Monte Carlo simulations and density functional theory (employing Fundamental Measure functionals). Using a recently introduced technique (Schilling and Schmid, J. Chem. Phys 131, 231102 (2009)) we obtain crystal free energies to a high precision. The free energies from Fundamental Measure theory are in good agreement with the simulation results and demonstrate the applicability of these functionals to the treatment of other problems involving crystallization. The agreement between FMT and simulations on the level of the free energies is also reflected in the density distributions around single lattice sites. Overall, the peak widths and anisotropy signs for different lattice directions agree, however, it is found that Fundamental Measure theory gives slightly narrower peaks with more anisotropy than seen in the simulations. Among the three types of Fundamental Measure functionals studied, only the White Bear II functional (Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)) exhibits sensible results for the equilibrium vacancy concentration and a physical behavior of the chemical potential in crystals constrained by a fixed vacancy concentration.Comment: 17 pages, submitted to Phys. Rev.

Capillary wave spectrum at adsorbed liquid films

Capillary wave fluctuations at the edges of liquid wetting layers are analyzed in Monte Carlo simulations of a Lennard-Jones fluid adsorbed on a planar wall substrate. The analysis is based on the Fourier modes of the liquid surface, constructed via the intrinsic sampling method. For films thinner than four molecular layers we can quantify the damping of the capillary waves due to the wall potential. Our results are presented in the theoretical framework of the effective surface Hamiltonians, to establish a quantitative link between the molecular structure and the mesoscopic descriptions used for renormalization-group analysis. We observe the predicted exponential decay of the wall damping, with the correlation length of the liquid bulk. However, associated with the molecular layering of the density profiles, we observe a strong oscillatory dependence with respect to the mean film thickness, not included in any theoretical prediction. We discuss the possibility of finite-size effects in this respect. Three different definitions of the intrinsic surface at molecular level are tested, to show that the square gradient terms of the Hamiltonian are robust, while the surface bending (or nonlocal) terms are tied to each specific definitionWe acknowledge the support of the Spanish Minister of Science and Innovation (Grant No. FIS2010-22047-C05) and the Comunidad Autónoma de Madrid under program MODELICO (Grant No. S2009/ESP-1691

Thickness and fluctuations of free and adsorbed liquid films

Effective mesoscopic Hamiltonians with the thickness of the adsorbed liquid films as a collective variable have been widely used in the study of adsorbed systems. In the present work, we show that the intrinsic surface of a liquid-vapor interface provides a very accurate way to evaluate the instantaneous film thickness in computer simulations. This film thickness follows with quantitative accuracy the predictions of simple model Hamiltonians, even for films as thin as one monolayer, and the effective interfacial potential has the simplest exponential form with a surprising accuracy, from a single monolayer to very thick films. For both the free liquid slabs and the adsorbed films and despite of the low vapor density, we have found that the fluctuations associated with the evaporation of particles to the vapor and their condensation in the liquid layer give an important contribution to the probability distributions of the liquid film thickness in our canonical (NVT) simulationsWe acknowledge the support of the Spanish Minister of Science and Innovation (Grant No. FIS2010-22047-C05) and the Comunidad Autonoma de Madrid under program MODELICO (Grant No. S2009/ESP-1691

Human Relationships with Domestic and Other Animals: One Health, One Welfare, One Biology

Excessive human population growth, uncontrolled use of natural resources, including deforestation, mining, wasteful systems, biodiversity reduction by agriculture, and damaging climate change affect the existence of all animals, including humans. This discussion is now urgent and people are rethinking their links with the animals we use for clothing, food, work, companionship, entertainment, and research. The concepts of one health, one welfare, and one biology are discussed as a background to driving global change. Nothing should be exploited without considering the ethics of the action and the consequences. This review concerns domesticated animals, including those used for human consumption of meat, eggs, and milk; horses kept for work; and dogs kept for company. Animal welfare includes health, emotional state, and comfort while moving and resting, and is affected by possibilities to show behavior and relationships with others of the same species or with humans. We show some examples of the relations between humans and domesticated animals in the environmental context, including zoonotic diseases, and consider the consequences and the new paradigms resulting from current awareness

Thin films of van der Waals fluid: From interface interactions to wetting transitions

We present a theoretical study of wetting phenomena and interactions between liquid-vapor interfaces based on the density functional theory. The focus is mostly on the impact of long-range van der Waals interactions both within the fluid and between the fluid and substrate. For the latter, we consider two models-hard wall and soft wall approximations-differing by the role of steric effects and leading to a qualitatively different character of phase transitions. We compute numerically the disjoining and conjoining potentials (which are important dynamically for spreading, spinodal dewetting, and coarsening in thin films, as well as resolution of interfacial singularities), and loci of intermediate and complete wetting transitions as functions of the Hamaker constant and temperature. We find that taking into account short-range interactions is essential for the description of wetting transitions in the soft wall limit. We derive an analytical form of the disjoining potential and analyze it in the context of the complete, frustrated and partial wetting.Comment: 13 pages, 12 figure

Eigen model as a quantum spin chain: exact dynamics

We map Eigen model of biological evolution [Naturwissenschaften {\bf 58}, 465 (1971)] into a one-dimensional quantum spin model with non-Hermitean Hamiltonian. Based on such a connection, we derive exact relaxation periods for the Eigen model to approach static energy landscape from various initial conditions. We also study a simple case of dynamic fitness function.Comment: 10 pages. Physical Revew E vol. 69, in press (2004

Production and turnover of organic matter in three southern European Fagus sylvatica L. Stands

17 pages, 5 figures, 7 tables.[EN] Above-ground biomass, litterfall and litter accumulation and decomposition at the soil surface were studied within three Mediterranean beech forests from Italy, France and Spain in order to better understand the recycling of elements associated with the turnover organic matter Above-ground tree biomass amounted to 131.9 Mg ha'^ at Etna (Italy), 134.2 Mg ha'' at Sierra de la Demanda (Spain) and 223.9 Mg ha'' at Mont Lozère (France). The highest amount of total litterfall was observed at Sierra de la Demanda (4.7 Mg ha-' year'), followed by the Mont Lozère (4.4 Mg ha' year' ) and Etna (3.9 Mg ha' year'). Total organic matter accumulated on the soil surface in the three beech forests amounted to 25.8 Mg ha'' at Mont Lozère, 14.4 Mg ha'' at Sierra de la Demanda and 12.6 Mg ha'' at Etna. The relative proportions of leaf litter versus total litter were nearly the same in the Etna and Sierra de la Demanda forests (72 - 70%), and close to these values for Mont Lozère (65%). All the studied Mediterranean Fagus sylvatica stands appeared very similar concerning the organic matter distribution and fluxes, even if local climate and soil differences can be noticed.[FR] Les biomasses aériennes, les retombées de litières, leur accumulation à la surface du sol et leur décomposition, ont été étudiées dans trois hêtraies méditerranéennes d'Italie, de France et d'Espagne, pour mieux connaître la restitution au sol des bioéléments par l'intermédiaire de la matière organique. Les biomasses aériennes s'élevaient respectivement à 131.9 Mg ha-1 dans la hêtraie de l'Etna (Italie), 134.2 Mg ha-1 dans celle de Sierra de la Demanda (Espagne) et à 223.9 Mg ha-1 au Mont Lozère (France). Les retombées de litière les plus fortes sont observées dans la hêtraie de la Sierra de la Demanda (4.7 Mg ha-1 an-1), suivie de celles du Mont Lozère (4.4 Mg ha-1 an-1) et de l'Etna (3.9 Mg ha-1 an-1). L'ensemble de la matière organique accumulée à la surface du sol des trois hêtraies était de 25.8 Mg ha-1 au Mont Lozère, 14.4 Mg ha-1 à Sierra de la Demanda et 12.6 Mg ha-1 dans l'Etna. Les proportions respectives de la fraction feuilles par rapport à la litière totale étaient proches dans les stations de l'Etna et de la Sierra de la Demanda (72 - 70%) et voisines de celle du Mont Lozère (65%). Toutes les forêts de Fagus sylvatica dans le climat Méditerranéen sont très similaires par rapport à la distribution et aux flux, malgré que les conditions de climat et de sol soient différentes.[ES] Se han estudiado la biomasa aérea, la caída, acumulación y descomposición de la hojarasca en tres ecosistemas forestales de hayedo en Italia, Francia y España en orden a conocer mejor el reciclado de elementos- biógenos asociados al reciclaje de materia orgánica. La biomasa aérea estimada es de 131.0 Mg ha-1 en Etna (Italia), 134.2 Mg ha-1 en la Sierra de la Demanda (España) y 223.9 Mg ha-1 en Mont Lozère (Francia). La mayor cantidad de caída de hojarasca se ha observado en la Sierra de la Demanda (4.7 Mg ha-1 año-1) seguida de Mont Lozère (4.4 Mg ha-1 año-1). La materia orgánica acumulada en la superficie del suelo en los tres ecosistemas forestales estudiados fue de 25.8 Mg ha-1 en Mont Lozère, 14.4 Mg ha-1 en la Sierra de la Demanda y 12.6 Mg ha-1 en Etna. El porcentaje relativo de las hojas con relación a la hojarasca total fue similar en las parcelas de Etna y Sierra de la Demanda (72-70%) y algo más bajo en Mont Lozère (65%). Los bosques de Fagus sylvatica estudiados reflejaron valores similares respecto a la distribución y flujos de materia orgánica, aunque se han evidenciado diferencias en cuanto a condiciones locales de clima y suelo.This project has been financed by C. E. and I. N. I. A. We thank the facilities given to us by the Environmental Service of J. C. L. in Burgos, Montpellier and Catania and in the same way to the ground staff who have collaborated in it.Peer reviewe