34,910 research outputs found
Spherically symmetric solutions of a boundary value problem for monopoles
In this paper we study spherically symmetric monopoles, which are critical
points for the Yang-Mills-Higgs functional over a disk in 3 dimensions, with
prescribed degree and covariant constant at the boundary. This is a
3-dimensional gauge-theory generalization of the Ginzburg-Landau model in 2
dimensions.Comment: 15 pages, 2 figures, LaTe
Can Solar System observations tell us something about the cosmological constant?
In this note we show that the latest determinations of the residual Mercury's
perihelion advance, obtained by accounting for almost all known Newtonian and
post-Newtonian orbital effects, yields only very broad constraints on the
cosmological constant. Indeed, from \delta\dot\omega=-0.0036 + - 0.0050
arcseconds per century one gets -2 10^-34 km^-2 < Lambda < 4 10^-35 km^-2. The
currently accepted value for Lambda, obtained from many independent
cosmological and large-scale measurements, amounts to almost 10^-46 km^-2.Comment: Latex2e, 4 pages, 2 table, no figures, 11 references. Table 2 added,
typos in the units of Lambda correcte
Is HIV short-sighted? Insights from a multistrain nested model
An important component of pathogen evolution at the population level is evolution within hosts. Unless evolution within hosts is very slow compared to the duration of infection, the composition of pathogen genotypes within a host is likely to change during the course of an infection, thus altering the composition of genotypes available for transmission as infection progresses. We develop a nested modeling approach that allows us to follow the evolution of pathogens at the epidemiological level by explicitly considering within-host evolutionary dynamics of multiple competing strains and the timing of transmission. We use the framework to investigate the impact of short-sighted within-host evolution on the evolution of virulence of human immunodeficiency virus (HIV), and find that the topology of the within-host adaptive landscape determines how virulence evolves at the epidemiological level. If viral reproduction rates increase significantly during the course of infection, the viral population will evolve a high level of virulence even though this will reduce the transmission potential of the virus. However, if reproduction rates increase more modestly, as data suggest, our model predicts that HIV virulence will be only marginally higher than the level that maximizes the transmission potential of the virus
The Motivational Profile of Organic Food Consumers: a Survey of Specialized Stores Customers in Italy
Organic food demand is becoming increasingly important throughout the world. Despite this relevance, however, not many attempts have been carried out to profile this food market segment. This paper aims to investigate on motivations that drive consumers towards purchasing organic foods in Italy. Through a survey carried out in some organic specialized stores sited in Sardinia, we explored organic consumer behaviour with specific emphasis on understanding consumer reasons to buy organic products. A Multiple Correspondence Analysis has obtained four consumers’ motivational profiles and several findings. Furthermore, a Logit regression allowed us to evaluate the relationships between individual motivations and some socio-demographic characteristics of organic consumers. Some marketing and policy implications arise from the obtained results
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