Simple relationship between the virial-route hypernetted-chain and the compressibility-route Percus--Yevick values of the fourth virial coefficient

As is well known, approximate integral equations for liquids, such as the hypernetted chain (HNC) and Percus--Yevick (PY) theories, are in general thermodynamically inconsistent in the sense that the macroscopic properties obtained from the spatial correlation functions depend on the route followed. In particular, the values of the fourth virial coefficient $B_4$ predicted by the HNC and PY approximations via the virial route differ from those obtained via the compressibility route. Despite this, it is shown in this paper that the value of $B_4$ obtained from the virial route in the HNC theory is exactly three halves the value obtained from the compressibility route in the PY theory, irrespective of the interaction potential (whether isotropic or not), the number of components, and the dimensionality of the system. This simple relationship is confirmed in one-component systems by analytical results for the one-dimensional penetrable-square-well model and the three-dimensional penetrable-sphere model, as well as by numerical results for the one-dimensional Lennard--Jones model, the one-dimensional Gaussian core model, and the three-dimensional square-well model.Comment: 8 pages; 4 figures; v2: slight change of title; proof extended to multicomponent fluid

Pump-and-probe optical transmission phase shift as a quantitative probe of the Bogoliubov dispersion relation in a nonlinear channel waveguide

We theoretically investigate the dispersion relation of small-amplitude optical waves superimposing upon a beam of polarized monochromatic light propagating along a single-mode channel waveguide characterized by an instantaneous and spatially local Kerr nonlinearity. These small luminous fluctuations propagate along the waveguide as Bogoliubov elementary excitations on top of a one-dimensional dilute Bose quantum fluid evolve in time. They consequently display a strongly renormalized dispersion law, of Bogoliubov type. Analytical and numerical results are found in both the absence and the presence of one- and two-photon losses. Silicon and silicon-nitride waveguides are used as examples. We finally propose an experiment to measure this Bogoliubov dispersion relation, based on a stimulated four-wave mixing and interference spectroscopy techniques.Comment: 17 pages, 7 figure

Information theory of quantum systems with some hydrogenic applications

The information-theoretic representation of quantum systems, which complements the familiar energy description of the density-functional and wave-function-based theories, is here discussed. According to it, the internal disorder of the quantum-mechanical non-relativistic systems can be quantified by various single (Fisher information, Shannon entropy) and composite (e.g. Cramer-Rao, LMC shape and Fisher-Shannon complexity) functionals of the Schr\"odinger probability density. First, we examine these concepts and its application to quantum systems with central potentials. Then, we calculate these measures for hydrogenic systems, emphasizing their predictive power for various physical phenomena. Finally, some recent open problems are pointed out.Comment: 9 pages, 3 figure

Intensification of Pastoralism as a Driver of Degradation in the Algerian Steppe

Land degradation linked to pastoralism use has been a worldwide concern for decades. A biological approach has often been use to understand such phenomena, usually disregarding economic and social factors. Radical transformations of pastoralism at the Algerian steppe constitute a good case study to provide an integrated understanding and to better orient development in other pastoralist areas across the world. Different actions by the public sector since the 1960s, as well as the land legislation adopted and the strong agricultural subventions during 2000-2010, have favored a massive conversion of land and resource management. This translates into conversion of many pastures into crops and overuse of the remaining ones. In order to understand the consequences of such changes into natural resources (pasture, water and soil), 236 field surveys were conducted (quantitative as well as qualitative) between 2006 and 2017. They were accompanied by phytoecological samplings to estimate impact on vegetation recovery, biomass and pastoralist production. While nomadic pastoralism practicing north-south transhumance and based on sheep and goats has declined, other more sedentary types of pastoralism (based on sheep, goats or cattle) combined with intensive crops have emerged. Family-related or paid herders live on tents during herd mobility, and live in a fix household the rest of the year. Grass represents just one third of the total livestock intake and barley crops, previously found only in valleys, are today mechanized and expanded into fragile rangeland soils. Vulnerability to climate variability and cereal price fluctuations in the international market is consequently higher. The higher cereal consumption increases fiber demand in animals, devastating plant cover and triggering land degradation. Specific mechanisms should be envisioned to prevent severe environmental impacts associated with pastoralism intensification. This lesson should be applied to other development interventions currently envisioned by different stakeholders who propose increase of animal feeds

Sobre la presencia de Vicia dasycarpa Ten. en el centro peninsular

Peer reviewe

Colorectal Cancer Chemoprevention: Is This the Future of Colorectal Cancer Prevention?

Colorectal cancer (CRC) is presently one of the most common causes of cancer-related death in our setting and affects a great number of people each year. Screening strategies are commonly used but they do not seem enough to avoid CRC development or prevent completely its mortality. Because of this fact other prevention strategies have gained interest in recent years. Chemoprevention seems to be an attractive option in this setting and several drugs have been studied in this field. This review is focused on salicylates, nonsteroidal anti-inflammatory drugs (NSAIDs) and cycloxygenase-2 inhibitors (COXIBs), whose mechanism of action could be directly related to colon cancer chemoprevention