1,928 research outputs found
On the Unicity of Smartphone Applications
Prior works have shown that the list of apps installed by a user reveal a lot
about user interests and behavior. These works rely on the semantics of the
installed apps and show that various user traits could be learnt automatically
using off-the-shelf machine-learning techniques. In this work, we focus on the
re-identifiability issue and thoroughly study the unicity of smartphone apps on
a dataset containing 54,893 Android users collected over a period of 7 months.
Our study finds that any 4 apps installed by a user are enough (more than 95%
times) for the re-identification of the user in our dataset. As the complete
list of installed apps is unique for 99% of the users in our dataset, it can be
easily used to track/profile the users by a service such as Twitter that has
access to the whole list of installed apps of users. As our analyzed dataset is
small as compared to the total population of Android users, we also study how
unicity would vary with larger datasets. This work emphasizes the need of
better privacy guards against collection, use and release of the list of
installed apps.Comment: 10 pages, 9 Figures, Appeared at ACM CCS Workshop on Privacy in
Electronic Society (WPES) 201
Morphological instabilities of a thin film on a Penrose lattice: a Monte Carlo study
We computed by a Monte Carlo method the thermal relaxation of a
polycrystalline thin film deposited on a Penrose lattice. The thin film was
modelled by a 2 dimensional array of elementary domains, which have each a
given height. During the Monte Carlo process, the height of each of these
elementary domains is allowed to change as well as their crystallographic
orientation. After equilibrium is reached at a given numerical temperature, all
elementary domains have changed their orientation into the same one and small
islands appear, preferentially on the domains of the Penrose lattice located in
the center of heptagons. This method is a new numerical approach to study the
influence of the substrate and its defects on the islanding process of
polycrystalline films.Comment: 9 pages,5 figure
One Dimensional Nonequilibrium Kinetic Ising Models with Branching Annihilating Random Walk
Nonequilibrium kinetic Ising models evolving under the competing effect of
spin flips at zero temperature and nearest neighbour spin exchanges at
are investigated numerically from the point of view of a phase
transition. Branching annihilating random walk of the ferromagnetic domain
boundaries determines the steady state of the system for a range of parameters
of the model. Critical exponents obtained by simulation are found to agree,
within error, with those in Grassberger's cellular automata.Comment: 10 pages, Latex, figures upon request, SZFKI 05/9
Monte Carlo approach of the islanding of polycrystalline thin films
We computed by a Monte Carlo method derived from the Solid on Solid model,
the evolution of a polycrystalline thin film deposited on a substrate during
thermal treatment. Two types of substrates have been studied: a single
crystalline substrate with no defects and a single crystalline substrate with
defects. We obtain islands which are either flat (i.e. with a height which does
not overcome a given value) or grow in height like narrow towers. A good
agreement was found regarding the morphology of numerical nanoislands at
equilibrium, deduced from our model, and experimental nanoislands resulting
from the fragmentation of YSZ thin films after thermal treatment.Comment: 20 pages, 7 figure
Wang-Landau sampling for quantum systems: algorithms to overcome tunneling problems and calculate the free energy
We present a generalization of the classical Wang-Landau algorithm [Phys.
Rev. Lett. 86, 2050 (2001)] to quantum systems. The algorithm proceeds by
stochastically evaluating the coefficients of a high temperature series
expansion or a finite temperature perturbation expansion to arbitrary order.
Similar to their classical counterpart, the algorithms are efficient at thermal
and quantum phase transitions, greatly reducing the tunneling problem at first
order phase transitions, and allow the direct calculation of the free energy
and entropy.Comment: Added a plot showing the efficiency at first order phase transition
Parallelization of Markov chain generation and its application to the multicanonical method
We develop a simple algorithm to parallelize generation processes of Markov
chains. In this algorithm, multiple Markov chains are generated in parallel and
jointed together to make a longer Markov chain. The joints between the
constituent Markov chains are processed using the detailed balance. We apply
the parallelization algorithm to multicanonical calculations of the
two-dimensional Ising model and demonstrate accurate estimation of
multicanonical weights.Comment: 15 pages, 5 figures, uses elsart.cl
Magnetization reversal times in the 2D Ising model
We present a theoretical framework which is generally applicable to the study
of time scales of activated processes in systems with Brownian type dynamics.
This framework is applied to a prototype system: magnetization reversal times
in the 2D Ising model. Direct simulation results for the magnetization reversal
times, spanning more than five orders of magnitude, are compared with
theoretical predictions; the two agree in most cases within 20%.Comment: 9 pages, 8 figure
Configurational entropy of Wigner crystals
We present a theoretical study of classical Wigner crystals in two- and
three-dimensional isotropic parabolic traps aiming at understanding and
quantifying the configurational uncertainty due to the presence of multiple
stable configurations. Strongly interacting systems of classical charged
particles confined in traps are known to form regular structures. The number of
distinct arrangements grows very rapidly with the number of particles, many of
these arrangements have quite low occurrence probabilities and often the
lowest-energy structure is not the most probable one. We perform numerical
simulations on systems containing up to 100 particles interacting through
Coulomb and Yukawa forces, and show that the total number of metastable
configurations is not a well defined and representative quantity. Instead, we
propose to rely on the configurational entropy as a robust and objective
measure of uncertainty. The configurational entropy can be understood as the
logarithm of the effective number of states; it is insensitive to the presence
of overlooked low-probability states and can be reliably determined even within
a limited time of a simulation or an experiment.Comment: 12 pages, 8 figures. This is an author-created, un-copyedited version
of an article accepted for publication in J. Phys.: Condens. Matter. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The definitive
publisher-authenticated version is available online at
10.1088/0953-8984/23/7/075302.
Data clustering and noise undressing for correlation matrices
We discuss a new approach to data clustering. We find that maximum likelihood
leads naturally to an Hamiltonian of Potts variables which depends on the
correlation matrix and whose low temperature behavior describes the correlation
structure of the data. For random, uncorrelated data sets no correlation
structure emerges. On the other hand for data sets with a built-in cluster
structure, the method is able to detect and recover efficiently that structure.
Finally we apply the method to financial time series, where the low temperature
behavior reveals a non trivial clustering.Comment: 8 pages, 5 figures, completely rewritten and enlarged version of
cond-mat/0003241. Submitted to Phys. Rev.
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