2,619 research outputs found
Secret Sharing for Cloud Data Security
Cloud computing helps reduce costs, increase business agility and deploy
solutions with a high return on investment for many types of applications.
However, data security is of premium importance to many users and often
restrains their adoption of cloud technologies. Various approaches, i.e., data
encryption, anonymization, replication and verification, help enforce different
facets of data security. Secret sharing is a particularly interesting
cryptographic technique. Its most advanced variants indeed simultaneously
enforce data privacy, availability and integrity, while allowing computation on
encrypted data. The aim of this paper is thus to wholly survey secret sharing
schemes with respect to data security, data access and costs in the
pay-as-you-go paradigm
Coherence in monoidal track categories
We introduce homotopical methods based on rewriting on higher-dimensional
categories to prove coherence results in categories with an algebraic
structure. We express the coherence problem for (symmetric) monoidal categories
as an asphericity problem for a track category and we use rewriting methods on
polygraphs to solve it. The setting is extended to more general coherence
problems, seen as 3-dimensional word problems in a track category, including
the case of braided monoidal categories.Comment: 32 page
WLC22-4: Efficient request mechanism usage in IEEE 802.16
IEEE 802.16 protocols for metropolitan broadband wireless access systems have been standardized recently. According to the standard, a subscriber station can deliver bandwidth request messages to a base station by numerous methods. This paper provides both the simulation and analytical models for the investigation of specified random access method, which is compared with centralized polling and station- grouping mechanisms. Based on the assumptions of Bernoulli request arrival process and ideal channel conditions, the mean delay of a request transmission is evaluated for varying number of transmission opportunities and different arrival rates
Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: III. X-ray spectral modelling
Following the Swift X-ray observations of the 2006 outburst of the recurrent
nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from
which the forward shock velocities were used to estimate the ejecta mass and
velocity. In order to further constrain our model parameters, here we present
synthetic X-ray spectra from our hydrodynamical calculations which we compare
to the Swift data. An extensive set of simulations was carried out to find a
model which best fits the spectra up to 100 days after outburst. We find a good
fit at high energies but require additional absorption to match the low energy
emission. We estimate the ejecta mass to be in the range (2-5) x 10^{-7} solar
masses and the ejection velocity to be greater than 6000 km/s (and probably
closer to 10,000 km/s). We also find that estimates of shock velocity derived
from gas temperatures via standard model fits to the X-ray spectra are much
lower than the true shock velocities.Comment: 13 pages, 5 figures, Accepted for publication in Ap
CO observations of symbiotic stellar systems
We have performed mm-wave observations with the IRAM 30m telescope of the
12CO J=2-1 and J=1-0, 13CO J=2-1 and J=1-0, and SiO J=5-4 transitions in the
symbiotic stars R Aqr, CH Cyg, and HM Sge. The data were analyzed by means of a
simple analytical description of the general properties of molecular emission
from the inner shells around the cool star. Numerical calculations of the
expected line profiles, taking into account the level population and radiative
transfer under such conditions, were also performed. Weak emission of 12CO
J=2-1 and J=1-0 was detected in R Aqr and CH Cyg; a good line profile of 12CO
J=2-1 in R Aqr was obtained. The intensities and profile shapes of the detected
lines are compatible with emission coming from a very small shell around the
Mira-type star, with a radius comparable to or slightly smaller than the
distance to the hot dwarf companion, 10 - 2 10 cm. We argue that
other possible explanations are improbable. This region probably shows
properties similar to those characteristic of the inner shells around standard
AGB stars: outwards expansion at about 5 - 25 km/s, with a significant
acceleration of the gas, temperatures decreasing with radius between about 1000
and 500 K, and densities ~ 10 - 3 10 cm. Our model calculations
are able to explain the asymmetric line shape observed in 12CO J=2-1 from R
Aqr, in which the relatively weaker red part of the profile would result from
selfabsorption by the outer layers (in the presence of a velocity increase and
a temperature decrease with radius). The mass-loss rates are somewhat larger
than in standard AGB stars, as often happens for symbiotic systems. In R Aqr,
we find that the total mass of the CO emitting region is ~ 2 - 3 10 Mo,
corresponding to M' ~ 5 10 - 10 Mo/yr, and compatible with
results obtained from dust emission. Taking into account other existing data on
molecular emission, we suggest that the small extent of the molecule-rich gas
in symbiotic systems is mainly due to molecule photodissociation by the
radiation of the hot dwarf star.Comment: 11 pages, 4 figure
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The pendulum swings back to scoliosis screening: screening policies for early detection and treatment of idiopathic scoliosis - current concepts and recommendations
This editorial article initiates the school scoliosis screening thematic series of the Scoliosis journal. The various issues on screening policies are discussed; clinical and practical recommendations of setting up school screening programs are also described
Ability of eight multi-joint models to compensate for soft tissue artefacts using global optimisation - An in vivo study of knee kinematics during squats
International Symposium on 3D Analysis of Human Movement (3D-AHM), LAUSANNE, SUISSE, 14-/07/2014 - 17/07/2014Soft tissue artefacts (STA) distort marker-based knee kinematics. Global optimization (GO) compensates for STA, but it lacks of direct validation on subjects. This study evaluates the performance of eight multi-joint models used in GO. Ten subjects were recruited: five healthy and five osteoarthritis subjects. Each subject performed dynamic squats recorded with a motion capture system (KneeKG?), and a quasi-static squat recorded with a low-dose upright biplanar radiographic imaging system (EOS®). The eight multi-joint models were evaluated by comparing dynamic knee kinematics optimized with GO to quasi-static knee kinematics measured by EOS®. The mean RMSE values ranged from 1.5-11.4° for rotations and 1.4-6.2 mm for translations. Some models were able to compensate for STA along one axe of movement but not along another. None of these models seemed optimal for STA compensation along all axes of movement. Future studies should investigate new models based on subject-specific joint geometry
DRLViz: Understanding Decisions and Memory in Deep Reinforcement Learning
We present DRLViz, a visual analytics interface to interpret the internal
memory of an agent (e.g. a robot) trained using deep reinforcement learning.
This memory is composed of large temporal vectors updated when the agent moves
in an environment and is not trivial to understand due to the number of
dimensions, dependencies to past vectors, spatial/temporal correlations, and
co-correlation between dimensions. It is often referred to as a black box as
only inputs (images) and outputs (actions) are intelligible for humans. Using
DRLViz, experts are assisted to interpret decisions using memory reduction
interactions, and to investigate the role of parts of the memory when errors
have been made (e.g. wrong direction). We report on DRLViz applied in the
context of video games simulators (ViZDoom) for a navigation scenario with item
gathering tasks. We also report on experts evaluation using DRLViz, and
applicability of DRLViz to other scenarios and navigation problems beyond
simulation games, as well as its contribution to black box models
interpretability and explainability in the field of visual analytics
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