34,111 research outputs found
On the Measurement of Privacy as an Attacker's Estimation Error
A wide variety of privacy metrics have been proposed in the literature to
evaluate the level of protection offered by privacy enhancing-technologies.
Most of these metrics are specific to concrete systems and adversarial models,
and are difficult to generalize or translate to other contexts. Furthermore, a
better understanding of the relationships between the different privacy metrics
is needed to enable more grounded and systematic approach to measuring privacy,
as well as to assist systems designers in selecting the most appropriate metric
for a given application.
In this work we propose a theoretical framework for privacy-preserving
systems, endowed with a general definition of privacy in terms of the
estimation error incurred by an attacker who aims to disclose the private
information that the system is designed to conceal. We show that our framework
permits interpreting and comparing a number of well-known metrics under a
common perspective. The arguments behind these interpretations are based on
fundamental results related to the theories of information, probability and
Bayes decision.Comment: This paper has 18 pages and 17 figure
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Time-dependent stochastic shortest path(s) algorithms for a scheduled transportation network
Following on from our work concerning travellersâ preferences in public transportation networks (Wu and Hartley, 2004), we introduce the concept of stochasticity to our algorithms. Stochasticity greatly increases the complexity of the route finding problem, so greater algorithmic efficiency becomes imperative. Public transportation networks (buses, trains) have two important features: edges can only be traversed at certain points in time and the weights of these edges change in a day and have an uncertainty associated with them. These features determine that a public transportation network is a stochastic and time-dependent network. Finding multiple shortest paths in a both stochastic and time-dependent network is currently regarded as the most difficult task in the route finding problems (Loui, 1983). This paper discusses the use of k-shortest-paths (KSP) algorithms to find optimal route(s) through a network in which the edge weights are defined by probability distributions. A comprehensive review of shortest path(s) algorithms with probabilistic graphs was conducted
Calibration and Sensitivity Analysis of a Stereo Vision-Based Driver Assistance System
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CN Morphology Studies of Comet 103P/Hartley 2
We report on narrowband CN imaging of Comet 103P/Hartley 2 obtained at Lowell
Observatory on 39 nights from 2010 July until 2011 January. We observed two
features, one generally to the north and the other generally to the south. The
CN morphology varied during the apparition: no morphology was seen in July; in
August and September the northern feature dominated and appeared as a mostly
face-on spiral; in October, November, and December the northern and southern
features were roughly equal in brightness and looked like more side-on
corkscrews; in January the southern feature was dominant but the morphology was
indistinct due to very low signal. The morphology changed smoothly during each
night and similar morphology was seen from night to night. However, the
morphology did not exactly repeat each rotation cycle, suggesting that there is
a small non-principal axis rotation. Based on the repetition of the morphology,
we find evidence that the fundamental rotation period was increasing: 16.7 hr
from August 13-17, 17.2 hr from September 10-13, 18.2 hr from October 12-19,
and 18.7 hr from October 31-November 7. We conducted Monte Carlo jet modeling
to constrain the pole orientation and locations of the active regions based on
the observed morphology. Our preliminary, self-consistent pole solution has an
obliquity of 10 deg relative to the comet's orbital plane (i.e., it is centered
near RA = 257 deg and Dec=+67 deg with an uncertainty around this position of
about 15 deg) and has two mid-latitude sources, one in each hemisphere.Comment: Accepted by The Astronomical Journal; 23 pages of text, 2 tables, 8
figure
Bound and Conquer: Improving Triangulation by Enforcing Consistency
We study the accuracy of triangulation in multi-camera systems with respect
to the number of cameras. We show that, under certain conditions, the optimal
achievable reconstruction error decays quadratically as more cameras are added
to the system. Furthermore, we analyse the error decay-rate of major
state-of-the-art algorithms with respect to the number of cameras. To this end,
we introduce the notion of consistency for triangulation, and show that
consistent reconstruction algorithms achieve the optimal quadratic decay, which
is asymptotically faster than some other methods. Finally, we present
simulations results supporting our findings. Our simulations have been
implemented in MATLAB and the resulting code is available in the supplementary
material.Comment: 8 pages, 4 figures, Submitted to IEEE Transactions on Pattern
Analysis and Machine Intelligenc
A Distribution of Large Particles in the Coma of Comet 103P/Hartley 2
The coma of comet 103P/Hartley 2 has a significant population of large
particles observed as point sources in images taken by the Deep Impact
spacecraft. We measure their spatial and flux distributions, and attempt to
constrain their composition. The flux distribution of these particles implies a
very steep size distribution with power-law slopes ranging from -6.6 to -4.7.
The radii of the particles extend up to 20 cm, and perhaps up to 2 m, but their
exact sizes depend on their unknown light scattering properties. We consider
two cases: bright icy material, and dark dusty material. The icy case better
describes the particles if water sublimation from the particles causes a
significant rocket force, which we propose as the best method to account for
the observed spatial distribution. Solar radiation is a plausible alternative,
but only if the particles are very low density aggregates. If we treat the
particles as mini-nuclei, we estimate they account for <16-80% of the comet's
total water production rate (within 20.6 km). Dark dusty particles, however,
are not favored based on mass arguments. The water production rate from bright
icy particles is constrained with an upper limit of 0.1 to 0.5% of the total
water production rate of the comet. If indeed icy with a high albedo, these
particles do not appear to account for the comet's large water production rate.
production rate.
Erratum: We have corrected the radii and masses of the large particles of
comet 103P/Hartley 2 and present revised conclusions in the attached erratum.Comment: Original article: 46 pages, 17 figures, 5 tables, published in
Icarus. Erratum: 5 pages, 1 table, accepted for publication in Icaru
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