648 research outputs found
Evidence of a new low field cross-over in the vortex critical velocity of type-II superconducting thin films
We measure current-voltage characteristics as function of magnetic field and
temperature in Nb strips of different thickness and width. The instability
voltage of the flux flow state related to the vortex critical velocity v* is
studied and compared with the Larkin-Ovchinnikov theory. Beside the usual
power-law dependence v* ~ B^-1/2, in the low field range a new cross-over
field, Bcr1, is observed below which v* decreases by further lowering the
external magnetic field B. We ascribe this unexpected cross-over to vortex
channeling due to a fan-like penetration of the applied magnetic field as
confirmed by magneto-optic imaging. The observation of Bcr1 becomes a direct
evidence of a general feature in type-II superconducting films at low fields,
that is a channel-like vortex motion induced by the inhomogeneous magnetic
state caused by the relatively strong pinning
A new apparatus for deep patterning of beam sensitive targets by means of high-energy ion beam
The paper reports on a high precision equipment designed to modify over
3-dimensions (3D) by means of high-energy gold ions the local properties of
thin and thick films. A target-moving system aimed at creating patterns across
the volume is driven by an x-y writing protocol that allows one to modify beam
sensitive samples over micrometer-size regions of whatever shape. The apparatus
has a mechanical resolution of 15 nm. The issue of the local fluence
measurement has been particularly addressed. The setup has been checked by
means of different geometries patterned on beam sensitive sheets as well as on
superconducting materials. In the last case the 3D modification consists of
amorphous nanostructures. The nanostructures create zones with different
dissipative properties with respect to the virgin regions. The main analysis
method consists of magneto-optical imaging that provides local information on
the electrodynamics of the modified zones. Features typical of non-linear
current flow hint at which pattern geometry is more functional to applications
in the framework of nanostructures across superconducting films.Comment: 7 page
Trust-Based Mechanisms for Robust and Efficient Task Allocation in the Presence of Execution Uncertainty
Vickrey-Clarke-Groves (VCG) mechanisms are often used to allocate tasks to selfish and rational agents. VCG mechanisms are incentive-compatible, direct mechanisms that are efficient (i.e. maximise social utility) and individually rational (i.e. agents prefer to join rather than opt out). However, an important assumption of these mechanisms is that the agents will always successfully complete their allocated tasks. Clearly, this assumption is unrealistic in many real-world applications where agents can, and often do, fail in their endeavours. Moreover, whether an agent is deemed to have failed may be perceived differently by different agents. Such subjective perceptions about an agent’s probability of succeeding at a given task are often captured and reasoned about using the notion of trust. Given this background, in this paper, we investigate the design of novel mechanisms that take into account the trust between agents when allocating tasks. Specifically, we develop a new class of mechanisms, called trust-based mechanisms, that can take into account multiple subjective measures of the probability of an agent succeeding at a given task and produce allocations that maximise social utility, whilst ensuring that no agent obtains a negative utility. We then show that such mechanisms pose a challenging new combinatorial optimisation problem (that is NP-complete), devise a novel representation for solving the problem, and develop an effective integer programming solution (that can solve instances with about 2×105 possible allocations in 40 seconds).
Velocity Dispersions and X-Ray Temperatures of Galaxy Clusters
Using a large and well-controlled sample of clusters of galaxies, we
investigate the relation between cluster velocity dispersions and X-ray
temperatures of intra-cluster gas. In order to obtain a reliable estimate of
the total velocity dispersion of a cluster, independent of the level of
anisotropies in galaxy orbits, we analyze the integrated velocity dispersion
profiles over increasing distances from the cluster centers. Distortions in the
velocity fields, the effect of close clusters, the presence of substructures,
and the presence of a population of (spiral) galaxies not in virial equilibrium
with the cluster potential are taken into account. Using our final sample of 37
clusters, for which a reliable estimate of the velocity dispersion could be
obtained, we derive a relation between the velocity dispersions and the X-ray
temperatures, with a scatter reduced by more than 30 % with respect to previous
works. A chi square fit to the temperature-velocity dispersion relation does
not exclude the hypothesis that the ratio between galaxy and gas energy density
(the so-called spectral beta) is a constant for all clusters. In particular,
the value of beta=1, corresponding to energy equipartition, is acceptable.Comment: 13 pages, uuencoded gzipped postscript file, fig.1 available upon
request, to appear in ApJ on 20th December 1995, corrected misprint in table
Giant dispersion of critical currents in superconductor with fractal clusters of a normal phase
The influence of fractal clusters of a normal phase on the dynamics of a
magnetic flux trapped in a percolative superconductor is considered. The
critical current distribution and the current-voltage characteristics of
fractal superconducting structures in the resistive state are obtained for an
arbitrary fractal dimension of the cluster boundaries. The range of fractal
dimensions, where the dispersion of critical currents becomes infinite, is
found. It is revealed that the fractality of clusters depresses of the electric
field caused by the magnetic flux motion thus increasing the critical current
value. It is expected that the maximum current-carrying capability of a
superconductor can be achieved in the region of giant dispersion of critical
currents.Comment: 7 pages with 3 figure
Industrial experiences with resource management under software randomization in ARINC653 avionics environments
Injecting randomization in different layers of the computing platform has been shown beneficial for security, resilience to software bugs and timing analysis. In this paper, with focus on the latter, we show our experience regarding memory and timing resource management when software randomization techniques are applied to one of the most stringent industrial environments, ARINC653-based avionics. We describe the challenges in this task, we propose a set of solutions and present the results obtained for two commercial avionics applications, executed on COTS hardware and RTOS.The work leading to these results has been funded by the European Community’s Seventh Framework Programme (FP7/2007-2013) un-
der the PROXIMA Project (grant agreement 611085). Moreover, it has been partially supported by the Spanish Ministry of Science and Innovation under grant TIN2015-65316-P and the HiPEAC Network of Excellence.Peer ReviewedPostprint (published version
The Effect of Cromolyn Sodium and Nedocromil Sodium Administered by A pressurized Aerosol with A spacer Device on Exercise-Induced Asthma in Children
To compare the effectiveness of cromolyn sodium (CS)
(10 mg) and nedocromil sodium (NS) (4 mg) administered
by a metered dose inhaler (MDI) with a spacer
device in preventing exercise-induced asthma (EIA), eight
asthmatic children with EIA were studied in a
randomized double-blind, cross-over, placebo-controlled
study, CS and NS provided significant, comparable protection
from EIA and both were better than placebo. We
conclude that CS and NS administered by a pressurized
aerosol with a spacer device provide equal protection
against EIA in children
Trust-based mechanisms for robust and efficient task allocation in the presence of execution uncertainty
Vickrey-Clarke-Groves (VCG) mechanisms are often used to allocate tasks to selfish and rational agents. VCG mechanisms are incentive-compatible, direct mechanisms that are efficient (i.e. maximise social utility) and individually rational (i.e. agents prefer to join rather than opt out). However, an important assumption of these mechanisms is that the agents will always successfully complete their allocated tasks. Clearly, this assumption is unrealistic in many real-world applications where agents can, and often do, fail in their endeavours. Moreover, whether an agent is deemed to have failed may be perceived differently by different agents. Such subjective perceptions about an agent’s probability of succeeding at a given task are often captured and reasoned about using the notion of trust. Given this background, in this paper, we investigate the design of novel mechanisms that take into account the trust between agents when allocating tasks. Specifically, we develop a new class of mechanisms, called trust-based mechanisms, that can take into account multiple subjective measures of the probability of an agent succeeding at a given task and produce allocations that maximise social utility, whilst ensuring that no agent obtains a negative utility. We then show that such mechanisms pose a challenging new combinatorial optimisation problem (that is NP-complete), devise a novel representation for solving the problem, and develop an effective integer programming solution (that can solve instances with about 2×105 possible allocations in 40 seconds)
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