Information driven evaluation of data hiding algorithms

Abstract. Privacy is one of the most important properties an information system must satisfy. A relatively new trend shows that classical access control techniques are not sufficient to guarantee privacy when datamining techniques are used. Privacy Preserving Data Mining (PPDM) algorithms have been recently introduced with the aim of modifying the database in such a way to prevent the discovery of sensible information. Due to the large amount of possible techniques that can be used to achieve this goal, it is necessary to provide some standard evaluation metrics to determine the best algorithms for a specific application or context. Currently, however, there is no common set of parameters that can be used for this purpose. This paper explores the problem of PPDM algorithm evaluation, starting from the key goal of preserving of data quality. To achieve such goal, we propose a formal definition of data quality specifically tailored for use in the context of PPDM algorithms, a set of evaluation parameters and an evaluation algorithm. The resulting evaluation core process is then presented as a part of a more general three step evaluation framework, taking also into account other aspects of the algorithm evaluation such as efficiency, scalability and level of privacy.

A shooting algorithm for problems with singular arcs

In this article we propose a shooting algorithm for a class of optimal control problems for which all control variables appear linearly. The shooting system has, in the general case, more equations than unknowns and the Gauss-Newton method is used to compute a zero of the shooting function. This shooting algorithm is locally quadratically convergent if the derivative of the shooting function is one-to-one at the solution. The main result of this paper is to show that the latter holds whenever a sufficient condition for weak optimality is satisfied. We note that this condition is very close to a second order necessary condition. For the case when the shooting system can be reduced to one having the same number of unknowns and equations (square system) we prove that the mentioned sufficient condition guarantees the stability of the optimal solution under small perturbations and the invertibility of the Jacobian matrix of the shooting function associated to the perturbed problem. We present numerical tests that validate our method.Comment: No. RR-7763 (2011); Journal of Optimization, Theory and Applications, published as 'Online first', January 201

Magnetic and magnetoelastic properties of the UGa2 intermetallic compound

Dans l'état ferromagnétique (Tc = 125 K) on a observé une distorsion orthorhombique de la maille du réseau cristallin hexagonal due à la grande magnétostriction (λγ.2 = - 4 × 10-3 à 4,2 K) et aussi à la grande anisotropie magnétocristalline (K = - 2 x × 107 erg/g à 4,2 K). Le moment magnétique de U diffère de celui de l'ion libre qui a une valence différente, probablement à cause de la délocalisation des électrons 5f.In the ferromagnetic state of the UGa2 (Tc = 125 K) the rhombic distortions of the hexagonal lattice due to the great mgnetostriction (λγ.2 = - 4 × at 4.2 K) as well as the large magnetocrystalline anisotropy (K = - 2 × 107 erg/g at 4.2 K) were founded. The magnetic moment per U-atom (µU = 2. 71 µB) is different from one for a free ion of different valency, that may be caused by partial delocalization of the 5f-electrons

U4+ FORM FACTOR IN UGa2

UGa2 cristallise dans la structure hexagonale de type AlB2 et une forte distorsion orthorhombique est observée dans l'état ferromagnétique (Tc = 125 K) due à une magnétostriction gigantesque. Nous avons effectué une étude par neutrons polarisés à 4,2 K dans un champ magnétique de 46,2 kOe, appliqué parallèlement à l'axe de facile aimantation [MATH]. Nous avons mesuré les intensités intégrées afin d'affiner les facteurs de structure nucléaires dans la structure distordue. La projection de la densité magnétique sur un plan (100) met en évidence une forte densité sur les sites d'uranium presque sphérique, l'absence de densité sur les sites de gallium et une faible polarisation positive entre les atomes. Le facteur de forme de l'uranium déduit a été analysé afin de déterminer l'état fondamental. Nous pensons que les atomes d'uranium sont dans l'état de valence U4+. Le facteur de forme observé correspond à une délocalisation des électrons 5f plus grande que celle calculée dans l'approximation du couplage de Russell-Saunders. Un premier calcul, utilisant l'approximation dipolaire dans le cadre du couplage intermédiaire, associée à la contribution d'une polarisation positive, a pu rendre compte de la variation observée du facteur de forme de l'uranium.UGa2 crystallizes in the hexagonal AlB2 type structure and a large orthorhombic distortion is observed in the ferromagnetic state (Tc = 125 K) due to a giant magnetostriction. A polarized neutron study has been performed at 4.2 K in a magnetic field of 46.2 kOe, applied parallel to the easy magnetization axis [MATH]. Integrated intensities have been measured for the refinement of the nuclear structure factors in the distorted structure. The projection of the magnetic density on the (100) plane evidences a large and almost spherical density on U sites, no density on the Ga sites, and a slight positive polarization between the atoms. The deduced U form factor has been analyzed in order to determine the magnetic ground state. We think that the uranium atoms are in the 4+ state. The observed form factor corresponds to a larger delocalization of the 5f electrons than that calculated in the Russell- Saunders coupling approximation. A first calculation using the dipole approximation in the intermediate coupling framework, associated with the contribution of a positive polarization can account for the observed variation of the U form factor

Space weather and space anomalies

A large database of anomalies, registered by 220 satellites in different orbits over the period 1971–1994 has been compiled. For the first time, data from 49 Russian Kosmos satellites have been included in a statistical analysis. The database also contains a large set of daily and hourly space weather parameters. A series of statistical analyses made it possible to quantify, for different satellite orbits, space weather conditions on the days characterized by anomaly occurrences. In particular, very intense fluxes (>1000 pfu at energy >10MeV) of solar protons are linked to anomalies registered by satellites in high-altitude (>15 000 km), near-polar (inclination >55_) orbits typical for navigation satellites, such as those used in the GPS network, NAVSTAR, etc. (the rate of anomalies increases by a factor ~20), and to a much smaller extent to anomalies in geostationary orbits, (they increase by a factor ~4). Direct and indirect connections between anomaly occurrence and geomagnetic perturbations are also discussed

Different space weather effects in anomalies of the high and low orbital satellites

Preliminary results of the EU INTAS Project 00810, which aims to improve the methods of safeguarding satellites in the Earth's magnetosphere from the negative effects of the space environment, are presented. Anomaly data from the ‘‘Kosmos’’ series satellites in the period 1971–1999 are combined in one database, together with similar information on other spacecraft. This database contains, beyond the anomaly information, various characteristics of the space weather: geomagnetic activity indices (Ap, AE and Dst), fluxes and fluences of electrons and protons at different energies, high energy cosmic ray variations and other solar, interplanetary and solar wind data. A comparative analysis of the distribution of each of these parameters relative to satellite anomalies was carried out for the total number of anomalies (about 6000 events), and separately for high (~5000 events) and low (about 800 events) altitude orbit satellites. No relation was found between low and high altitude satellite anomalies. Daily numbers of satellite anomalies, averaged by a superposed epoch method around sudden storm commencements and proton event onsets for high (>1500 km) and low (<1500 km) altitude orbits revealed a big difference in a behavior. Satellites were divided on several groups according to the orbital characteristics (altitude and inclination). The relation of satellite anomalies to the environmental parameters was found to be different for various orbits that should be taken into account under developing of the anomaly frequency models. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved

Magnetization, magnetic susceptibility and ESR in Tb3Ga5O12

We report on the measurement of the magnetic susceptibility and of ESR transitions in the garnet substance Tb3Ga5O12 (TGG). The results are compared with a calculation in the framework of crystal field theory for the orthorhombic surroundings of the six inequivalent Tb ions of TGG. We also present a calculation of the magnetization for the three main crystal directions