Siting Multiple Observers for Maximum Coverage: An Accurate Approach

The selection of the minimal number of observers that ensures the maximum visual coverage over an area represented by a digital elevation model (DEM) have great interest in many elds, e.g., telecommunications, environment planning, among others. However, this problem is complex and intractable when the number of points of the DEM is relatively high. This complexity is due to three issues: 1) the di culty in determining the visibility of the terrain from one point, 2) the need to know the visibility at all points of the terrain and 3) the combinatorial complexity of the selection of observers. The recent progress in total-viewshed maps computation not only provides an e cient solu- tion to the rst two problems, but also opens other ways to new solutions that were unthinkable previously. This paper presents a new type of cartography, called the masked total viewshed map, and provides optimal solutions for both sequential and simultaneous observers location.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

16 Cards to Get Into Computer Organization

This paper presents a novel educative activity for teaching computer architecture fundamentals. This activity is actually a game that uses 16 cards and involves about twenty active participant students. Executing this activity in the fi rst class of the course allows the studentin only 45 minutes to acquire the fundamental concepts of computer organization. The results of the surveys that evaluate the proposed activity together with the grades obtained by the students at the end of course corroborate the importance of the proposed game in the assimilation of more complex concepts in computer architecture.Universidad de Granada: Departamento de Arquitectura y Tecnología de Computadores; Vicerrectorado para la Garantía de la Calidad

Gamma Ray Bursts with peculiar temporal asymmetry

Based on the study of temporal asymmetry of 631 gamma ray bursts from the BATSE 3B catalog by Link and Epstein [Ap J 466, 764 (1996)], we identify the population of bursts whose rising times are longer than their decays, thus showing atypical profiles. We analyse their sky distribution, morphology, time-space clustering and other average properties and compare them with those associated with the bulk of the bursts. We show how most of the peculiar bursts analysed are consistent with recent fireball models, but a fraction of bursts ($\sim 4$% of the total sample) appear to be inconsistent.Comment: mn style (included in the submission), 4 figures that must be printed separately. Submitted to Monthly Notices of RA

Diffusion in a class of exactly solvable non-harmonic potentials. Intrinsic effects induced by non-linearities

This paper deals with the problem of a particle that diffuses in a potential with a reflecting barrier and has a point of stable equilibrium and a point of unstable equilibrium. Based on the exact solutions obtained earlier for the Fokker-Planck equation of a class of these models, we analyze the behavior of the probability density, the mean path and the onset time which determines the transition from unimodal to bimodal probability densities. The study is made over different initial positions, two of them very close to the unstable point, which permits a clear comparison among the subsequent evolutions, and the observation of some intrinsic effects induced by non-linearities

Intersection of crisis loci in a driven nonlinearly damped oscillator

We report on a phenomenon observed in a driven nonlinearly damped oscillator when two control parameters, the frequency of the external excitation and the nonlinear damping coefficient, are varied simultaneously. An interior crisis locus and a boundary crisis locus, corresponding to two different chaotic attractors, intersect in a point of the parameter space. There exists an interchange in the type of crisis that each attractor suffers after crossing the intersection point

Spiral waves solutions in reaction-diffusion equations with symmetries. Analysis through specific models

Symmetries of nonlinear reaction-diffusion equations determine the existence of regular rotating spiral waves. They are only a consequence of kinetics processes and molecular diffusion. We prove the existence of these waves as invariant solutions of reaction-diffusion models with appropiate Lie point symmetries