3,801 research outputs found
A group membership algorithm with a practical specification
Presents a solvable specification and gives an algorithm for the group membership problem in asynchronous systems with crash failures. Our specification requires processes to maintain a consistent history in their sequences of views. This allows processes to order failures and recoveries in time and simplifies the programming of high level applications. Previous work has proven that the group membership problem cannot be solved in asynchronous systems with crash failures. We circumvent this impossibility result building a weaker, yet nontrivial specification. We show that our solution is an improvement upon previous attempts to solve this problem using a weaker specification. We also relate our solution to other methods and give a classification of progress properties that can be achieved under different models
Self-organized Segregation on the Grid
We consider an agent-based model in which two types of agents interact
locally over a graph and have a common intolerance threshold for
changing their types with exponentially distributed waiting times. The model is
equivalent to an unperturbed Schelling model of self-organized segregation, an
Asynchronous Cellular Automata (ACA) with extended Moore neighborhoods, or a
zero-temperature Ising model with Glauber dynamics, and has applications in the
analysis of social and biological networks, and spin glasses systems. Some
rigorous results were recently obtained in the theoretical computer science
literature, and this work provides several extensions. We enlarge the
intolerance interval leading to the formation of large segregated regions of
agents of a single type from the known size to size . Namely, we show that for (and by symmetry
), the expected size of the largest segregated region
containing an arbitrary agent is exponential in the size of the neighborhood.
We further extend the interval leading to large segregated regions to size
considering "almost segregated" regions, namely regions where
the ratio of the number of agents of one type and the number of agents of the
other type vanishes quickly as the size of the neighborhood grows. In this
case, we show that for (and by symmetry for ) the expected size of the largest almost segregated region
containing an arbitrary agent is exponential in the size of the neighborhood.
The exponential bounds that we provide also imply that complete segregation,
where agents of a single type cover the whole grid, does not occur with high
probability for and the range of tolerance considered
Screening of point charges in Si quantum dots
The screening of point charges in hydrogenated Si quantum dots ranging in
diameter from 10 A to 26 A has been studied using first-principles
density-functional methods. We find that the main contribution to the screening
function originates from the electrostatic field set up by the polarization
charges at the surface of the nanocrystals. This contribution is well described
by a classical electrostatics model of dielectric screening
Evaluation of social capital promotion in rural development programmes: a methodological approach
The academic literature makes evident that the main immaterial contribution of the LEADER approach (LA) consists in the promotion of social capital in rural areas. Therefore the insertion of LA in the framework of Rural Development Programmes (RDPs) should be considered as a powerful opportunity to promote rural development initiatives by means of a bottom-up methodology, much more focused on social relationships among local actors. These aspects open new opportunities also in terms of evaluations of RDPs and of LA, in the context of the already established Common Monitoring and Evaluation Framework (CMEF). The objective of this paper is to present a methodology for the definition of the Relative Index of Social Capital Promotion (RISCP) to be used in the ongoing evaluation of RDPs. The RISCP doesn’t represent an impact indicator, but it measures the potential social capital that could be promoted by means of the logic of intervention of selected measures of the RDPs.social capital, rural development programmes, evaluation, index, Agricultural and Food Policy, Z0,
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