Directed cycles and related structures in random graphs: II--Dynamic properties

We study directed random graphs (random graphs whose edges are directed) as they evolve in discrete time by the addition of nodes and edges. For two distinct evolution strategies, one that forces the graph to a condition of near acyclicity at all times and another that allows the appearance of nontrivial directed cycles, we provide analytic and simulation results related to the distributions of degrees. Within the latter strategy, in particular, we investigate the appearance and behavior of the strong components that were our subject in the first part of this study.Comment: submitted to Physica

Early appraisal of the fixation probability in directed networks

In evolutionary dynamics, the probability that a mutation spreads through the whole population, having arisen in a single individual, is known as the fixation probability. In general, it is not possible to find the fixation probability analytically given the mutant's fitness and the topological constraints that govern the spread of the mutation, so one resorts to simulations instead. Depending on the topology in use, a great number of evolutionary steps may be needed in each of the simulation events, particularly in those that end with the population containing mutants only. We introduce two techniques to accelerate the determination of the fixation probability. The first one skips all evolutionary steps in which the number of mutants does not change and thereby reduces the number of steps per simulation event considerably. This technique is computationally advantageous for some of the so-called layered networks. The second technique, which is not restricted to layered networks, consists of aborting any simulation event in which the number of mutants has grown beyond a certain threshold value, and counting that event as having led to a total spread of the mutation. For large populations, and regardless of the network's topology, we demonstrate, both analytically and by means of simulations, that using a threshold of about 100 mutants leads to an estimate of the fixation probability that deviates in no significant way from that obtained from the full-fledged simulations. We have observed speedups of two orders of magnitude for layered networks with 10000 nodes

Comer fuera de casa en Brasil hoy

This article aims to explore the meanings and practices of eating out in Brazilian daily life. Since the mid-1980s, this practice has been spreading and diversifying in Brazil. Based on a series of three qualitative/quantitative surveys carried out between 2005 and 2015 in major Brazilian urban centres, we identified a clear distinction between eating out at weekdays and at weekends. At weekdays, by association with work, commitments and studies, this practice is perceived as both an obligation and an expense. At weekends, however, its association with leisure, family and friends makes it a pleasant investment and a cultural product. In this context, the meanings of eating at home versus eating out change, as well as the sense of the meals, selection of restaurants, sociability patterns and even the ethos of eating.Este artículo tiene como objetivo explorar los significados y las prácticas del ‘comer fuera de casa’ en la vida diaria brasileña. Desde mediados de la década de 1980, esta práctica se ha extendido y diversificado en Brasil. Sobre la base de una serie de tres encuestas cualitativas/cuantitativas, llevadas a cabo entre 2005 y 2015 en los principales centros urbanos de Brasil, identificamos una clara distinción entre comer afuera los días de semana y los fines de semana. En los días de la semana, por asociación con el trabajo, los compromisos y los estudios, esta práctica se percibe como una obligación y un gasto. Los fines de semana, sin embargo, su asociación con el ocio, la familia y los amigos la convierte en una inversión agradable y un producto cultural. En este contexto, los significados de comer en casa versus comer afuera cambian, así como el sentido de las comidas, la selección de restaurantes, los patrones de sociabilidad e incluso el ethos de la comida

Crack Cocaine Use and its Relationship with Violence and Hiv

OBJECTIVES: To evaluate crack cocaine use practices, risk behaviors associated with HIV infection among drug users, and their involvement with violence. INTRODUCTION: HIV infections are frequent among drug users due to risky sexual behavior. It is generally accepted that crack cocaine use is related to increased levels of violence. Several reports point to an increase in violence from those involved in drug trafficking. Although HIV infections and risky sexual behavior among drug users have been quite well studied, there are few studies that evaluate violence as it relates to drugs, particularly crack. METHODS: A total of 350 drug users attending drug abuse treatment clinics in São Paulo, Brazil were interviewed about their risky behaviors. Each patient had a serological HIV test done. RESULTS: HIV prevalence was 6.6% (4.0 to 10.2). Violence was reported by 97% (94.7 to 99.1) of the subjects (including cases without personal involvement). Acts of violence such as verbal arguments, physical fights, threats, death threats, theft, and drug trafficking were significantly higher among crack users. A decrease in frequency of sexual intercourse was observed among users of injected drugs, though prostitution was observed as a means of obtaining drugs. A high number of crack cocaine users had a history of previous imprisonment, many for drug-related infractions. DISCUSSION: The data presented are in accordance with other reports in the literature, and they show a correlation between drug use, imprisonment, violence, and drug trafficking. CONCLUSION: A high HIV prevalence and associated risky sexual behaviors were observed among crack cocaine users. The society and the authorities that deal with violence related to crack users and drug trafficking should be aware of these problems