Utility-based reputation model for VO in GRIDs

In this paper we extend the existing utility-based reputation model for VOs in Grids by incorporating a statistical model of user behaviour (SMUB) that was previously developed for computer networks and distributed systems, and different functions to address threats scenarios in the area of trust and reputation management. These modifications include: assigning initial reputation to a new entity in VO, capturing alliance between consumer and resource, time decay function, and score function.В данной статье предложена модификация существующей модели репутаций для виртуальных организаций в Grid-системах, которая основана на оценке функции полезности. Модификация модели состоит в добавлении статистической модели поведения пользователя, которая ранее была разработана для компьютерных сетей и распределенных систем, а также компонентов, которые позволяют противостоять угрозам в области управления доверием и репутацией. К числу этих компонентов относятся: механизм присвоения начальной репутации для новых субъектов виртуальной организации; учет взаимосвязей между пользователями и ресурсами; функция учета времени; а также классификация предоставляемых сервисов в Grid-системе

Skeleton as a probe of the cosmic web: the 2D case

We discuss the skeleton as a probe of the filamentary structures of a 2D random field. It can be defined for a smooth field as the ensemble of pairs of field lines departing from saddle points, initially aligned with the major axis of local curvature and connecting them to local maxima. This definition is thus non local and makes analytical predictions difficult, so we propose a local approximation: the local skeleton is given by the set of points where the gradient is aligned with the local curvature major axis and where the second component of the local curvature is negative. We perform a statistical analysis of the length of the total local skeleton, chosen for simplicity as the set of all points of space where the gradient is either parallel or orthogonal to the main curvature axis. In all our numerical experiments, which include Gaussian and various non Gaussian realizations such as \chi^2 fields and Zel'dovich maps, the differential length is found within a normalization factor to be very close to the probability distribution function of the smoothed field. This is in fact explicitly demonstrated in the Gaussian case. This result might be discouraging for using the skeleton as a probe of non Gausiannity, but our analyses assume that the total length of the skeleton is a free, adjustable parameter. This total length could in fact be used to constrain cosmological models, in CMB maps but also in 3D galaxy catalogs, where it estimates the total length of filaments in the Universe. Making the link with other works, we also show how the skeleton can be used to study the dynamics of large scale structure.Comment: 15 pages, 11 figures, submitted to MNRA

Transport of the repulsive Bose-Einstein condensate in a double-well trap: interaction impact and relation to Josephson effect

Two aspects of the transport of the repulsive Bose-Einstein condensate (BEC) in a double-well trap are inspected: impact of the interatomic interaction and analogy to the Josephson effect. The analysis employs a numerical solution of 3D time-dependent Gross-Pitaevskii equation for a total order parameter covering all the trap. The population transfer is driven by a time-dependent shift of a barrier separating the left and right wells. Sharp and soft profiles of the barrier velocity are tested. Evolution of the relevant characteristics, involving phase differences and currents, is inspected. It is shown that the repulsive interaction substantially supports the transfer making it possible i) in a wide velocity interval and ii) three orders of magnitude faster than in the ideal BEC. The transport can be approximately treated as the d.c. Josephson effect. A dual origin of the critical barrier velocity (break of adiabatic following and d.c.-a.c. transition) is discussed. Following the calculations, robustness of the transport (d.c.) crucially depends on the interaction and barrier velocity profile. Only soft profiles which minimize undesirable dipole oscillations are acceptable.Comment: 10 pages, 8 figures, accepted by Laser Physis. arXiv admin note: text overlap with arXiv:1312.2750 The replaced version has a few corrections and additional reference

Gravity effects on thick brane formation from scalar field dynamics

The formation of a thick brane in five-dimen\-sional space-time is investigated when warp geometries of $AdS_5$ type are induced by scalar matter dynamics and triggered by a thin-brane defect. The scalar matter is taken to consist of two fields with $O(2)$ symmetric self interaction and with manifest $O(2)$ symmetry breaking by terms quadratic in fields. One of them serves as a thick brane formation mode around a kink background and another one is of a Higgs-field type which may develop a classical background as well. Scalar matter interacts with gravity in the minimal form and gravity effects on (quasi)localized scalar fluctuations are calculated with usage of gauge invariant variables suitable for perturbation expansion. The calculations are performed in the vicinity of the critical point of spontaneous breaking of the combined parity symmetry where a non-trivial v.e.v. of the Higgs-type scalar field is generated. The nonperturbative discontinuous gravitational effects in the mass spectrum of light localized scalar states are studied in the presence of a thin-brane defect. The thin brane with negative tension happens to be the most curious case when the singular barriers form a potential well with two infinitely tall walls and the discrete spectrum of localized states arises completely isolated from the bulk.Comment: 15 pages, minor corrections, two-column EPJ-C styl

Rotationally-invariant mapping of scalar and orientational metrics of neuronal microstructure with diffusion MRI

We develop a general analytical and numerical framework for estimating intra- and extra-neurite water fractions and diffusion coefficients, as well as neurite orientational dispersion, in each imaging voxel. By employing a set of rotational invariants and their expansion in the powers of diffusion weighting, we analytically uncover the nontrivial topology of the parameter estimation landscape, showing that multiple branches of parameters describe the measurement almost equally well, with only one of them corresponding to the biophysical reality. A comprehensive acquisition shows that the branch choice varies across the brain. Our framework reveals hidden degeneracies in MRI parameter estimation for neuronal tissue, provides microstructural and orientational maps in the whole brain without constraints or priors, and connects modern biophysical modeling with clinical MRI.Comment: 25 pages, 12 figures, elsarticle two-colum