2,149 research outputs found
A fast distance between histograms
Iberoamerican Congress on Pattern Recognition (CIARP), 2005, Havana (Cuba)In this paper we present a new method for comparing histograms. Its main advantage is that it takes less time than previous methods. The present distances between histograms are defined on a structure called signature, which is a lossless representation of histograms. Moreover, the type of the elements of the sets that the histograms represent are ordinal, nominal and modulo. We show that the computational cost of these distances is O(z′) for the ordinal and nominal types and O(z′2) for the modulo one, where z′ is the number of non-empty bins of the histograms. In the literature, the computational cost of the algorithms presented depends on the number of bins in the histograms. In most applications, the histograms are sparse, so considering only the non-empty bins dramatically reduces the time needed for comparison. The distances we present in this paper are experimentally validated on image retrieval and the positioning of mobile robots through image recognition.Peer Reviewe
EsPRESSo: Efficient Privacy-Preserving Evaluation of Sample Set Similarity
Electronic information is increasingly often shared among entities without
complete mutual trust. To address related security and privacy issues, a few
cryptographic techniques have emerged that support privacy-preserving
information sharing and retrieval. One interesting open problem in this context
involves two parties that need to assess the similarity of their datasets, but
are reluctant to disclose their actual content. This paper presents an
efficient and provably-secure construction supporting the privacy-preserving
evaluation of sample set similarity, where similarity is measured as the
Jaccard index. We present two protocols: the first securely computes the
(Jaccard) similarity of two sets, and the second approximates it, using MinHash
techniques, with lower complexities. We show that our novel protocols are
attractive in many compelling applications, including document/multimedia
similarity, biometric authentication, and genetic tests. In the process, we
demonstrate that our constructions are appreciably more efficient than prior
work.Comment: A preliminary version of this paper was published in the Proceedings
of the 7th ESORICS International Workshop on Digital Privacy Management (DPM
2012). This is the full version, appearing in the Journal of Computer
Securit
Ultrashort intense-field optical vortices produced with laser-etched mirrors
We introduce a simple and practical method to create ultrashort intense
optical vortices for applications involving high-intensity lasers. Our method
utilizes femtosecond laser pulses to laser-etch grating lines into
laser-quality gold mirrors. These grating lines holographically encode an
optical vortex. We derive mathematical equations for each individual grating
line to be etched, for any desired (integer) topological charge. We investigate
the smoothness of the etched grooves. We show that they are smooth enough to
produce optical vortices with an intensity that is only a few percent lower
than in the ideal case. We demonstrate that the etched gratings can be used in
a folded version of our 2f-2f setup [Mariyenko et al., Opt. Express 19, 7599
(2005)] to compensate angular dispersion. Lastly, we show that the etched
gratings withstand intensities of up to 10^12 W/cm2.Comment: 14 pages, 12 figures, submitted to Optics Expres
Measurement of the Current-Phase Relation in Josephson Junctions Rhombi Chains
We present low temperature transport measurements in one dimensional
Josephson junctions rhombi chains. We have measured the current phase relation
of a chain of 8 rhombi. The junctions are either in the classical phase regime
with the Josephson energy much larger than the charging energy, , or in the quantum phase regime where . In the
strong Josephson coupling regime () we observe a
sawtooth-like supercurrent as a function of the phase difference over the
chain. The period of the supercurrent oscillations changes abruptly from one
flux quantum to half the flux quantum as the rhombi are
tuned in the vicinity of full frustration. The main observed features can be
understood from the complex energy ground state of the chain. For
we do observe a dramatic suppression and rounding of the
switching current dependence which we found to be consistent with the model
developed by Matveev et al.(Phys. Rev. Lett. {\bf 89}, 096802(2002)) for long
Josephson junctions chains.Comment: to appear in Phys. Rev.
Unexpected series of regular frequency spacing of delta Scuti stars in the non-asymptotic regime -- I. The methodology
A sequence search method was developed to search regular frequency spacing in
delta Scuti stars by visual inspection and algorithmic search. We searched for
sequences of quasi-equally spaced frequencies, containing at least four members
per sequence, in 90 delta Scuti stars observed by CoRoT. We found an
unexpectedly large number of independent series of regular frequency spacing in
77 delta Scuti stars (from 1 to 8 sequences) in the non-asymptotic regime. We
introduce the sequence search method presenting the sequences and echelle
diagram of CoRoT 102675756 and the structure of the algorithmic search. Four
sequences (echelle ridges) were found in the 5-21 d^{-1} region, where the
pairs of the sequences are shifted (between 0.5-0.59 d^{-1}) by twice the value
of the estimated rotational splitting frequency (0.269 d^{-1}). The general
conclusions for the whole sample are also presented in this paper. The
statistics of the spacings derived by the sequence search method, by FT and
that of the shifts are also compared. In many stars, more than one almost
equally valid spacing appeared. The model frequencies of FG Vir and their
rotationally split components were used to reveal a possible explanation that
one spacing is the large separation, while the other is a sum of the large
separation and the rotational frequency. In CoRoT 102675756, the two spacings
(2.249 and 1.977 d^{-1}) agree better with the sum of a possible 1.710 d^{-1}
large separation and two or one times, respectively, the value of the
rotational frequency.Comment: 12 pages, 10 figures, accepted for publication in Ap
Rotationally invariant 3D shape contexts using asymmetry patterns
This paper presents an approach to resolve the azimuth ambiguity of 3D Shape Contexts (3DSC) based on asymmetry patterns. We show that it is possible to provide rotational invariance to 3DSC at the expense of a marginal increase in computational load, outperforming previous algorithms dealing with the azimuth ambiguity. We build on a recently presented measure of approximate rotational symmetry in 2D defined as the overlapping area between a shape and rotated versions of itself to extract asymmetry patterns from a 3DSC in a variety of ways, depending on the spatial relationships that need to be highlighted or disabled. Thus, we define Asymmetry Patterns Shape Contexts (APSC) from a subset of the possible spatial relations present in the spherical grid of 3DSC; hence they can be thought of as a family of descriptors that depend on the subset that is selected. This provides great flexibility to derive different descriptors. We show that choosing the appropriate spatial patterns can considerably reduce the errors obtained with 3DSC when targeting specific types of points
Kicked Burgers Turbulence
Burgers turbulence subject to a force ,
where the 's are ``kicking times'' and the ``impulses'' have
arbitrary space dependence, combines features of the purely decaying and the
continuously forced cases. With large-scale forcing this ``kicked'' Burgers
turbulence presents many of the regimes proposed by E, Khanin, Mazel and Sinai
(1997) for the case of random white-in-time forcing. It is also amenable to
efficient numerical simulations in the inviscid limit, using a modification of
the Fast Legendre Transform method developed for decaying Burgers turbulence by
Noullez and Vergassola (1994). For the kicked case, concepts such as
``minimizers'' and ``main shock'', which play crucial roles in recent
developments for forced Burgers turbulence, become elementary since everything
can be constructed from simple two-dimensional area-preserving Euler--Lagrange
maps.
One key result is for the case of identical deterministic kicks which are
periodic and analytic in space and are applied periodically in time: the
probability densities of large negative velocity gradients and of
(not-too-large) negative velocity increments follow the power law with -7/2
exponent proposed by E {\it et al}. (1997) in the inviscid limit, whose
existence is still controversial in the case of white-in-time forcing. (More in
the full-length abstract at the beginning of the paper.)Comment: LATEX 30 pages, 11 figures, J. Fluid Mech, in pres
Finite-size scaling at infinite-order phase transitions
For systems with infinite-order phase transitions, in which an order
parameter smoothly becomes nonzero, a new observable for finite-size scaling
analysis is suggested. By construction this new observable has the favourable
property of diverging at the critical point. Focussing on the example of the
F-model we compare the analysis of this observable with that of another
observable, which is also derived from the order parameter but does not
diverge, as well as that of the associated susceptibility. We discuss the
difficulties that arise in the finite-size scaling analysis of such systems. In
particular we show that one may reach incorrect conclusions from large-system
size extrapolations of observables that are not known to diverge at the
critical point. Our work suggests that one should base finite-size scaling
analyses for infinite-order phase transitions only on observables that are
guaranteed to diverge.Comment: 7 pages, 5 figures, 1 table; v2: publication details adde
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