Fuzzy directional enlacement landscapes

International audienceSpatial relations between objects represented in images are of high importance in various application domains related to pattern recognition and computer vision. By definition, most relations are vague, ambiguous and difficult to formalize precisely by humans. The issue of describing complex spatial configurations, where objects can be imbri-cated in each other, is addressed in this article. A novel spatial relation, called enlacement, is presented and designed using a directional fuzzy landscape approach. We propose a generic fuzzy model that allows to visualize and evaluate complex enlacement configurations between crisp objects, with directional granularity. The interest and the behavior of this approach is highlighted on several characteristic examples

Comparison of VLBI, TV and traveling clock techniques for time transfer

A three part experiment was conducted to develop and compare time transfer techniques. The experiment consisted of (1) a very long baseline interferometer (VLBI), (2) a high precision portable clock time transfer system between the two sites, and (3) a television time transfer. A comparison of the VLBI and traveling clock shows each technique can perform satisfactorily at the five nsec level. There was a systematic offset of 59 nsec between the two methods, which we attributed to a difference in epochs between VLBI formatter and station clock. The VLBI method had an internal random error of one nsec at the three sigma level for a two day period. Thus, the Mark II system performed well, and VLBI shows promise of being an accurate method of time transfer. The TV system, which had technical problems during the experiment, transferred time with a random error of about 50 nsec

The notion of histogram of forces : a new way to represent the relative position of 2D-objects

The assessment of the directional spatial relations (such as "to the right of", "to the south of" . . .) between 2D-objects relies generally on the computation of a histogram of angles, which is supposed to provide a reasonably good representation o f the relative position of an object with regard to another . In this paper, we introduce the notion of histogram of forces . It generalize s and supersedes the one of histogram of angles . The objects are handled as longitudinal sections (1D-entities) . It is thus possibl e to benefit in full by the power of integral calculus and to ensure a rapid processing of raster data as well as of vector data unde r explicit consideration of both angular and metric information .L'évaluation des relations spatiales directionnelles (telles que « à droite de », « au sud de » ...) entre objets 2D repose généralement sur la constitution d'un histogramme d'angles. Un tel histogramme est supposé constituer une bonne représentation de la position relative d'un objet par rapport à un autre. Dans cet article, nous introduisons la notion d'histogramme de forces. Elle généralise et supplante celle d'histogramme d'angles. La manipulation des objets (entités de dimension 2) est ramenée à celle de leurs sections longitudinales (entités de dimension 1), non pas à celle de points. Il est ainsi possible de bénéficier de la puissance du calcul intégral et d'assurer un traitement incomparablement plus rapide aussi bien de données rasters que vecteurs, tout en tenant compte explicitement aussi bien de l'information angulaire que de l'information métrique

Describing topological relationships in words: Refinements.

Abstract-In earlier work, we introduced a method for generating linguistic descriptions of the topological relationships between two-dimensional objects. The input to the system is a pair of rasterized objects and the output is a set of propositions about their spatial relationships expressed in natural language. The method relies on finding one or two Allen relations that best describe the relationships along a direction of major object interaction. In this paper, we address some of the issues related to the use of Allen relations for describing two-dimensional object configurations, and we propose two extensions in order to solve problems encountered in the original algorithm. Global subsethood-based information is used to suppress counterintuitive descriptions and an ancillary method for generating alternative descriptions is introduced

Gravitational wave detection using pulsars: status of the Parkes Pulsar Timing Array project

The first direct detection of gravitational waves may be made through observations of pulsars. The principal aim of pulsar timing array projects being carried out worldwide is to detect ultra-low frequency gravitational waves (f ~ 10^-9 to 10^-8 Hz). Such waves are expected to be caused by coalescing supermassive binary black holes in the cores of merged galaxies. It is also possible that a detectable signal could have been produced in the inflationary era or by cosmic strings. In this paper we review the current status of the Parkes Pulsar Timing Array project (the only such project in the Southern hemisphere) and compare the pulsar timing technique with other forms of gravitational-wave detection such as ground- and space-based interferometer systems.Comment: Accepted for publication in PAS

Status Update of the Parkes Pulsar Timing Array

The Parkes Pulsar Timing Array project aims to make a direct detection of a gravitational-wave background through timing of millisecond pulsars. In this article, the main requirements for that endeavour are described and recent and ongoing progress is outlined. We demonstrate that the timing properties of millisecond pulsars are adequate and that technological progress is timely to expect a successful detection of gravitational waves within a decade, or alternatively to rule out all current predictions for gravitational wave backgrounds formed by supermassive black-hole mergers.Comment: 10 pages, 3 figures, Amaldi 8 conference proceedings, accepted by Classical & Quantum Gravit

Key Rotation for Authenticated Encryption

A common requirement in practice is to periodically rotate the keys used to encrypt stored data. Systems used by Amazon and Google do so using a hybrid encryption technique which is eminently practical but has questionable security in the face of key compromises and does not provide full key rotation. Meanwhile, symmetric updatable encryption schemes (introduced by Boneh et al. CRYPTO 2013) support full key rotation without performing decryption: ciphertexts created under one key can be rotated to ciphertexts created under a different key with the help of a re-encryption token. By design, the tokens do not leak information about keys or plaintexts and so can be given to storage providers without compromising security. But the prior work of Boneh et al. addresses relatively weak confidentiality goals and does not consider integrity at all. Moreover, as we show, a subtle issue with their concrete scheme obviates a security proof even for confidentiality against passive attacks. This paper presents a systematic study of updatable Authenticated Encryption (AE). We provide a set of security notions that strengthen those in prior work. These notions enable us to tease out real-world security requirements of different strengths and build schemes that satisfy them efficiently. We show that the hybrid approach currently used in industry achieves relatively weak forms of confidentiality and integrity, but can be modified at low cost to meet our stronger confidentiality and integrity goals. This leads to a practical scheme that has negligible overhead beyond conventional AE. We then introduce re-encryption indistinguishability, a security notion that formally captures the idea of fully refreshing keys upon rotation. We show how to repair the scheme of Boneh et al., attaining our stronger confidentiality notion. We also show how to extend the scheme to provide integrity, and we prove that it meets our re- encryption indistinguishability notion. Finally, we discuss how to instantiate our scheme efficiently using off-the-shelf cryptographic components (AE, hashing, elliptic curves). We report on the performance of a prototype implementation, showing that fully secure key rotations can be performed at a throughput of approximately 116 kB/s

Timing stability of millisecond pulsars and prospects for gravitational-wave detection

Analysis of high-precision timing observations of an array of approx. 20 millisecond pulsars (a so-called "timing array") may ultimately result in the detection of a stochastic gravitational-wave background. The feasibility of such a detection and the required duration of this type of experiment are determined by the achievable rms of the timing residuals and the timing stability of the pulsars involved. We present results of the first long-term, high-precision timing campaign on a large sample of millisecond pulsars used in gravitational-wave detection projects. We show that the timing residuals of most pulsars in our sample do not contain significant low-frequency noise that could limit the use of these pulsars for decade-long gravitational-wave detection efforts. For our most precisely timed pulsars, intrinsic instabilities of the pulsars or the observing system are shown to contribute to timing irregularities on a five-year timescale below the 100 ns level. Based on those results, realistic sensitivity curves for planned and ongoing timing array efforts are determined. We conclude that prospects for detection of a gravitational-wave background through pulsar timing array efforts within five years to a decade are good.Comment: 21 pages, 5 figures, submitted to MNRA

A precise mass measurement of the intermediate-mass binary pulsar PSR J1802-2124

PSR J1802-2124 is a 12.6-ms pulsar in a 16.8-hour binary orbit with a relatively massive white dwarf (WD) companion. These properties make it a member of the intermediate-mass class of binary pulsar (IMBP) systems. We have been timing this pulsar since its discovery in 2002. Concentrated observations at the Green Bank Telescope, augmented with data from the Parkes and Nancay observatories, have allowed us to determine the general relativistic Shapiro delay. This has yielded pulsar and white dwarf mass measurements of 1.24(11) and 0.78(4) solar masses (68% confidence), respectively. The low mass of the pulsar, the high mass of the WD companion, the short orbital period, and the pulsar spin period may be explained by the system having gone through a common-envelope phase in its evolution. We argue that selection effects may contribute to the relatively small number of known IMBPs.Comment: 9 pages, 4 figures, 3 tables, accepted for publication in the Astrophysical Journa