19,410 research outputs found
Systematic methods for the computation of the directional fields and singular points of fingerprints
The first subject of the paper is the estimation of a high resolution directional field of fingerprints. Traditional methods are discussed and a method, based on principal component analysis, is proposed. The method not only computes the direction in any pixel location, but its coherence as well. It is proven that this method provides exactly the same results as the "averaged square-gradient method" that is known from literature. Undoubtedly, the existence of a completely different equivalent solution increases the insight into the problem's nature. The second subject of the paper is singular point detection. A very efficient algorithm is proposed that extracts singular points from the high-resolution directional field. The algorithm is based on the Poincare index and provides a consistent binary decision that is not based on postprocessing steps like applying a threshold on a continuous resemblance measure for singular points. Furthermore, a method is presented to estimate the orientation of the extracted singular points. The accuracy of the methods is illustrated by experiments on a live-scanned fingerprint databas
Fingerprint of Galactic Loop I on polarized microwave foregrounds
Context: Currently, detection of the primordial gravitational waves by the
B-mode of Cosmic Microwave Background (CMB) is primarily limited by our
knowledge of the polarized microwave foreground emissions. Thus improvements of
the foreground analysis are necessary. As revealed
in~\cite{2018arXiv180410382L}, the E-mode and B-mode of the polarized
foreground have noticeable different properties, both in morphology and
frequency spectrum, suggesting that they arise from different physical
processes, and need to be studied separately.
Aims: I will study the polarized emission from Galactic loops, especially
Loop I, and mainly focus on the following issues: Does it contribute
predominantly to the E-mode or B-mode? In which frequency bands and in which
sky regions can it be identified?
Methods: Based on a well known result about the magnetic field alignment in
supernova explosions, a theoretical expectation is established that the loop
polarizations should be predominantly E-mode. In particular, the expected
polarization angles of Loop I are compared with those from the real microwave
band data of WMAP and Planck.
Results and conclusions: The comparison between model and data shows
remarkable consistency between data and expectation at all bands and for a
large area of the sky. This result suggests that the polarized emission of
Galactic Loop I is a major polarized component in all microwave bands from 23
to 353 GHz, and a considerable part of the polarized foreground is likely
originated from a local bubble associated with Loop I, instead of the far more
distant Galactic emission. The result also provides a possible way to explain
the reported E-to-B excess~\citep{2016A&A...586A.133P} by contribution of the
loops. Finally, this work may also provide the first geometrical evidence that
the Earth was hit by a supernova explosion.Comment: Updated using the Planck 2018 data, and the main conclusion is now
even better supporte
How Unique is Your .onion? An Analysis of the Fingerprintability of Tor Onion Services
Recent studies have shown that Tor onion (hidden) service websites are
particularly vulnerable to website fingerprinting attacks due to their limited
number and sensitive nature. In this work we present a multi-level feature
analysis of onion site fingerprintability, considering three state-of-the-art
website fingerprinting methods and 482 Tor onion services, making this the
largest analysis of this kind completed on onion services to date.
Prior studies typically report average performance results for a given
website fingerprinting method or countermeasure. We investigate which sites are
more or less vulnerable to fingerprinting and which features make them so. We
find that there is a high variability in the rate at which sites are classified
(and misclassified) by these attacks, implying that average performance figures
may not be informative of the risks that website fingerprinting attacks pose to
particular sites.
We analyze the features exploited by the different website fingerprinting
methods and discuss what makes onion service sites more or less easily
identifiable, both in terms of their traffic traces as well as their webpage
design. We study misclassifications to understand how onion service sites can
be redesigned to be less vulnerable to website fingerprinting attacks. Our
results also inform the design of website fingerprinting countermeasures and
their evaluation considering disparate impact across sites.Comment: Accepted by ACM CCS 201
Evaluating indoor positioning systems in a shopping mall : the lessons learned from the IPIN 2018 competition
The Indoor Positioning and Indoor Navigation (IPIN) conference holds an annual competition in which indoor localization systems from different research groups worldwide are evaluated empirically. The objective of this competition is to establish a systematic evaluation methodology with rigorous metrics both for real-time (on-site) and post-processing (off-site) situations, in a realistic environment unfamiliar to the prototype developers. For the IPIN 2018 conference, this competition was held on September 22nd, 2018, in Atlantis, a large shopping mall in Nantes (France). Four competition tracks (two on-site and two off-site) were designed. They consisted of several 1 km routes traversing several floors of the mall. Along these paths, 180 points were topographically surveyed with a 10 cm accuracy, to serve as ground truth landmarks, combining theodolite measurements, differential global navigation satellite system (GNSS) and 3D scanner systems. 34 teams effectively competed. The accuracy score corresponds to the third quartile (75th percentile) of an error metric that combines the horizontal positioning error and the floor detection. The best results for the on-site tracks showed an accuracy score of 11.70 m (Track 1) and 5.50 m (Track 2), while the best results for the off-site tracks showed an accuracy score of 0.90 m (Track 3) and 1.30 m (Track 4). These results showed that it is possible to obtain high accuracy indoor positioning solutions in large, realistic environments using wearable light-weight sensors without deploying any beacon. This paper describes the organization work of the tracks, analyzes the methodology used to quantify the results, reviews the lessons learned from the competition and discusses its future
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