Estimating Self-Sustainability in Peer-to-Peer Swarming Systems

Peer-to-peer swarming is one of the \emph{de facto} solutions for distributed content dissemination in today's Internet. By leveraging resources provided by clients, swarming systems reduce the load on and costs to publishers. However, there is a limit to how much cost savings can be gained from swarming; for example, for unpopular content peers will always depend on the publisher in order to complete their downloads. In this paper, we investigate this dependence. For this purpose, we propose a new metric, namely \emph{swarm self-sustainability}. A swarm is referred to as self-sustaining if all its blocks are collectively held by peers; the self-sustainability of a swarm is the fraction of time in which the swarm is self-sustaining. We pose the following question: how does the self-sustainability of a swarm vary as a function of content popularity, the service capacity of the users, and the size of the file? We present a model to answer the posed question. We then propose efficient solution methods to compute self-sustainability. The accuracy of our estimates is validated against simulation. Finally, we also provide closed-form expressions for the fraction of time that a given number of blocks is collectively held by peers.Comment: 27 pages, 5 figure

Ultrasonic pulse technique for evaluation of mechanical damage in processed coffee beans.

The knowledge of the physical characteristics of the coffee bean allows the transition from the conventional storage model in bags to the silo storage, and as an indirect measure of the improvement and conservation of the quality of the stored grain. The elastic modulus allows comparisons on the strength of material. The variations of this occur due to its chemical composition, microstructures and material defects, being able to be used as indicator of the physical integrity of the grain. The ultrasonic pulse technique is an alternative to obtain the elastic modulus in a simple and non-destructive way. In this context, it was proposed the development of a non-destructive methodology that will perform the quality evaluation by determining the elastic modulus of the coffee beans. For this purpose, a reference silo was constructed, reproducing the storage conditions, and the elastic modulus values were determined. The values obtained by the Stress Wave Timer apparatus are between 2.54 and 4.23 MPa, with a maximum load of 8.32 kN, and a calculated vertical pressure of 1,526 kPa. To evaluate the impact of the storage conditions and the loads applied during the non-destructive test, laboratory tests applied in seeds were performed, and the tetrazolium test was the only one able to differentiate the samples. It was concluded that Stress Wave Timer was able to determine the elastic modulus values for the coffee bean mass and could be used as an indicative of the quality.Título em português: Técnica de pulso ultrassônico para avaliação de danos mecânicos em grãos de café beneficiados

Controle biológico da broca-da-cana-de-açúcar.

bitstream/item/44196/1/broca-cana.pd

Atividade de endo-ß-manase em sementes de café colhidas em diferentes estádios fenológicos.

Sementes de café apresentam germinação lenta e desuniforme, dificultando consideravelmente a formação das mudas. Nestas sementes a germinação é limitada pelo endosperma, e para que ocorra a emergência da radícula, o amolecimento do endosperma é desempenhado por várias enzimas, principalmente, a endo-?-mananase. O presente trabalho foi realizado com o objetivo de avaliar a atividade da enzima endo-?-mannase em sementes de café (Coffea arabica L.) colhidas em diferentes estádios fenológicos e submetidas à secagem. As sementes foram avaliadas nos estádios de desenvolvimento verde, verde cana, cereja, passa e seco, após três tratamentos de secagem: sem secagem, sementes avaliadas imediatamente após a colheita e antes que os frutos perdessem água; secagem convencional, em que os frutos foram colocados em camada única dentro de bandejas plásticas e deixados em ambiente de laboratório, até que atingissem a umidade desejada; secagem em ambiente controlado, realizada em estufa de circulação forçada de ar, regulada à temperatura constante de 35ºC. Realizou-se a eletroforese da enzima endo-?-mananase em gel de agarose. Concluiu-se que Há diferenças na atividade da enzima endo-?-mananase em sementes colhidas nos diferentes estádios fenológicos; a secagem não afeta a atividade da enzima endo-?-mananase em sementes colhidas nos estádios verde, verde cana e cereja; e ocorre maior atividade da enzima endo-?-mananase em sementes colhidas no estádio seco e submetidas à secagem lenta, convencional