Effects of immersed moonlets in the ring arc particles of Saturn

Ring arcs are the result of particles in corotation resonances with nearby satellites. Arcs are present in Saturn and Neptune systems, in Saturn they are also associated with small satellites immersed on them. The satellite Aegaeon is immersed in the G~ring arc, and the satellites Anthe and Methone are embedded in arcs named after them. Since most of the population of the arcs is formed by $\mu$m-sized particles the dissipative effects, such as the plasma drag and the solar radiation force, decrease the lifetime of the arcs. We analysed the effects of the immersed satellites on these arcs by computing the mass production rate and the perturbation caused by them in the arc particles. By comparing the lifetime of the particles and the mass production rate we concluded that Aegaeon, Anthe and Methone did not act as sources for their arcs. We took a step further by analysing a hypothetical scenario formed by an immersed moonlet of different sizes. As a result we found that regardless the size of the hypothetical moonlet (from about 0.10 km to 4.0 km) these moonlets will not act as a source. These arcs are temporary structures and they will disappear in a very short period of time

Properties of Flexible Functional Forms for Modeling Bilateral Export Supply and Import Demand in Multi-Country Agri-Food Models

This paper illustrates the opportunities of incorporating more advanced functional forms into multi-country trade policy models. It suggests the use of flexible forms such as the Symmetric Generalized McFadden Function (SGMF) or the Normalized Quadratic-Quadratic Expenditure System (NQQES). Particularly if issues namely trade in differentiated products, preferential trade and effects of standards and traceability on bilateral trade are considered the NQQES offers attractive properties since it allows estimating variety specific expenditure elasticities which might compensate for example increased certification costs. A second aim of the paper refers to the critique on the handling of model parameters in calibrated policy models. In general, employed elasticities violate the theoretical conditions. We describe the calibration procedure developed to obtain model parameters consistent with economic theory.bilateral trade modelling, flexible functions, calibration, International Relations/Trade, Research Methods/ Statistical Methods, B41, C61, F13, Q18, Q17,

EU Food Safety Standards, Traceability and Other Regulations: A Growing Trade Barrier to Developing Countries' Exports?

Food Consumption/Nutrition/Food Safety, International Relations/Trade,

A rapid change in virulence gene expression during the transition from the intestinal lumen into tissue promotes systemic dissemination of Salmonella.

Bacterial pathogens causing systemic disease commonly evolve from organisms associated with localized infections but differ from their close relatives in their ability to overcome mucosal barriers by mechanisms that remain incompletely understood. Here we investigated whether acquisition of a regulatory gene, tviA, contributed to the ability of Salmonella enterica serotype Typhi to disseminate from the intestine to systemic sites of infection during typhoid fever. To study the consequences of acquiring a new regulator by horizontal gene transfer, tviA was introduced into the chromosome of S. enterica serotype Typhimurium, a closely related pathogen causing a localized gastrointestinal infection in immunocompetent individuals. TviA repressed expression of flagellin, a pathogen associated molecular pattern (PAMP), when bacteria were grown at osmotic conditions encountered in tissue, but not at higher osmolarity present in the intestinal lumen. TviA-mediated flagellin repression enabled bacteria to evade sentinel functions of human model epithelia and resulted in increased bacterial dissemination to the spleen in a chicken model. Collectively, our data point to PAMP repression as a novel pathogenic mechanism to overcome the mucosal barrier through innate immune evasion