10,128 research outputs found
Cryptanalyzing a discrete-time chaos synchronization secure communication system
This paper describes the security weakness of a recently proposed secure
communication method based on discrete-time chaos synchronization. We show that
the security is compromised even without precise knowledge of the chaotic
system used. We also make many suggestions to improve its security in future
versions.Comment: 11 pages, 3 figures, latex forma
Breaking a secure communication scheme based on the phase synchronization of chaotic systems
A security analysis of a recently proposed secure communication scheme based
on the phase synchronization of chaotic systems is presented. It is shown that
the system parameters directly determine the ciphertext waveform, hence it can
be readily broken by parameter estimation of the ciphertext signal.Comment: 4 pages, 6 figure
Breaking parameter modulated chaotic secure communication system
This paper describes the security weakness of a recently proposed secure
communication method based on parameter modulation of a chaotic system and
adaptive observer-based synchronization scheme. We show that the security is
compromised even without precise knowledge of the chaotic system used.Comment: 8 pages, 3 figures, latex forma
Nonparametric Bayesian Mixed-effect Model: a Sparse Gaussian Process Approach
Multi-task learning models using Gaussian processes (GP) have been developed
and successfully applied in various applications. The main difficulty with this
approach is the computational cost of inference using the union of examples
from all tasks. Therefore sparse solutions, that avoid using the entire data
directly and instead use a set of informative "representatives" are desirable.
The paper investigates this problem for the grouped mixed-effect GP model where
each individual response is given by a fixed-effect, taken from one of a set of
unknown groups, plus a random individual effect function that captures
variations among individuals. Such models have been widely used in previous
work but no sparse solutions have been developed. The paper presents the first
sparse solution for such problems, showing how the sparse approximation can be
obtained by maximizing a variational lower bound on the marginal likelihood,
generalizing ideas from single-task Gaussian processes to handle the
mixed-effect model as well as grouping. Experiments using artificial and real
data validate the approach showing that it can recover the performance of
inference with the full sample, that it outperforms baseline methods, and that
it outperforms state of the art sparse solutions for other multi-task GP
formulations.Comment: Preliminary version appeared in ECML201
Breaking projective chaos synchronization secure communication using filtering and generalized synchronization
This paper describes the security weaknesses of a recently proposed secure
communication method based on chaotic masking using projective synchronization
of two chaotic systems. We show that the system is insecure and how to break it
in two different ways, by high-pass filtering and by generalized
synchronization.Comment: 14 pages, 6 figures, latex forma
Rudiments of Holography
An elementary introduction to Maldacena's AdS/CFT correspondence is given,
with some emphasis in the Fefferman-Graham construction. This is based on
lectures given by one of us (E.A.) at the Universidad Autonoma de Madrid.Comment: 60 pages, additional misprints corrected, references adde
Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy
Stripe domains are studied in perpendicular magnetic anisotropy films
nanostructured with a periodic thickness modulation that induces the lateral
modulation of both stripe periods and inplane magnetization. The resulting
system is the 2D equivalent of a strained superlattice with properties
controlled by interfacial misfit strain within the magnetic stripe structure
and shape anisotropy. This allows us to observe, experimentally for the first
time, the continuous structural transformation of a grain boundary in this 2D
magnetic crystal in the whole angular range. The magnetization reversal process
can be tailored through the effect of misfit strain due to the coupling between
disclinations in the magnetic stripe pattern and domain walls in the in-plane
magnetization configuration
Asymptomatic Carotid Stenosis and Cognitive Improvement using Transcervical Stenting with Protective Flow Reversal Technique
ObjectivesThe relationship between carotid artery stenosis and cognitive function in individuals without a history of stroke is not clear. The possible pathomechanisms of cognitive impairment include silent embolization and hypoperfusion. In this study the aim was to assess cognitive changes after transcervical carotid artery stenting with proximal cerebral protection by flow reversal in patients with asymptomatic carotid stenosis, a novel technique that has been proved to decrease the number intraoperative emboli.Methods25 consecutive patients were assessed, of which 22 were men (88%) mean age of 74 years with severe asymptomatic carotid stenosis who underwent revascularization by carotid artery stenting (CAS) with flow reversal. Patients were evaluated 1 day before and 6 months after the procedure using a standardized neuropsychological battery. Test scores were adjusted according to age, sex, education level and were standardized (0–100). The mean of all the cognitive function scores yielded the global cognitive score (GCS).ResultsThere were no neurological complications during the procedure or during hospitalization in any patient. No deaths or cardiac complications occurred in any patient. The pre-procedure neuropsychological study showed cognitive impairment in: information processing speed in 15 patients (62.5%), visuospatial function in 14 (56.0%), memory in 18 (72.0%), executive functions in 14 (56.0%), language in three (12.0%), attention in 10 (40.0%), and global cognitive performance in eight (32.0%). Comparison of these scores with those obtained 6-month post-procedure showed significant improvement in GCS in all patients (p = .002), with a particularly marked gain in information processing speed (p = .018). Although significant improvement was not found for the remaining cognitive functions assessed, some gain was documented, and there was no deterioration.ConclusionsRevascularization by transcervical CAS with flow reversal for cerebral protection results in improved neurocognitive performance in asymptomatic elderly patients with severe carotid artery stenosis
Factorization method for difference equations of hypergeometric type on nonuniform lattices
We study the factorization of the hypergeometric-type difference equation of
Nikiforov and Uvarov on nonuniform lattices. An explicit form of the raising
and lowering operators is derived and some relevant examples are given.Comment: 21 page
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