9,138 research outputs found
Laser beam cutting and welding of coronary stents
Coronary stents are thin-walled and mesh-structured
metallic implants, which are made generally by laser beam
cutting of high-precision tubes of 90-120 micrometer
thickness. The tube material can be 316L stainless steel or
L605 type cobalt-chromium alloy. The paper present how
laser settings influence geometry and surface quality of the
kerf and residual stresses, which play very important role in
the precision of stent strut homogeneity.
Hungarian Tentaur stent was developed 15 years ago. This
coil stent made of 145 micrometers thick stainless steel wire
contains 9-25 joints produced by electric resistance
projection welding. Developments were bringing out for
increasing flexibility of Tentaur stent, and a new design and
a new tech-nology was elaborated, which’s based on laser
beam mi-crowelding. TentaFlex stent also is constructed
from austenitic stainless steel wire, but it does not contain
any wire-crossing joint, because stent struts are configured
from sinusoidal helix. Stent contains only two welded joints
at its ends. Laser welding experiences of these joints are
presented in the paper. A Trumpf PowerWeld Nd:YAG laser
work station was used for welding, and after optimization of
laser settings joints can’t produces from only one side of the
coiled stent
The Two Phases of Galaxy Formation
Cosmological simulations of galaxy formation appear to show a two-phase
character with a rapid early phase at z>2 during which in-situ stars are formed
within the galaxy from infalling cold gas followed by an extended phase since
z<3 during which ex-situ stars are primarily accreted. In the latter phase
massive systems grow considerably in mass and radius by accretion of smaller
satellite stellar systems formed at quite early times (z>3) outside of the
virial radius of the forming central galaxy. These tentative conclusions are
obtained from high resolution re-simulations of 39 individual galaxies in a
full cosmological context with present-day virial halo masses ranging from 7e11
M_sun h^-1 < M_vir < 2.7e13 M_sun h^-1 and central galaxy masses between 4.5e10
M_sun h^-1 < M_* < 3.6e11 M_sun h^-1. The simulations include the effects of a
uniform UV background, radiative cooling, star formation and energetic feedback
from SNII. The importance of stellar accretion increases with galaxy mass and
towards lower redshift. In our simulations lower mass galaxies (M_* > 1.7e11 M_sun h^-1) assembly is dominated by accretion and
merging with about 80 per cent of the stars added by the present-day. In
general the simulated galaxies approximately double their mass since z=1. For
massive systems this mass growth is not accompanied by significant star
formation. The majority of the in-situ created stars is formed at z>2,
primarily out of cold gas flows. We recover the observational result of
archaeological downsizing, where the most massive galaxies harbor the oldest
stars. We find that this is not in contradiction with hierarchical structure
formation. Most stars in the massive galaxies are formed early on in smaller
structures, the galaxies themselves are assembled late.Comment: 13 pages, 13 figures, accepted for publication in Ap
Non-collaborative Attackers and How and Where to Defend Flawed Security Protocols (Extended Version)
Security protocols are often found to be flawed after their deployment. We
present an approach that aims at the neutralization or mitigation of the
attacks to flawed protocols: it avoids the complete dismissal of the interested
protocol and allows honest agents to continue to use it until a corrected
version is released. Our approach is based on the knowledge of the network
topology, which we model as a graph, and on the consequent possibility of
creating an interference to an ongoing attack of a Dolev-Yao attacker, by means
of non-collaboration actuated by ad-hoc benign attackers that play the role of
network guardians. Such guardians, positioned in strategical points of the
network, have the task of monitoring the messages in transit and discovering at
runtime, through particular types of inference, whether an attack is ongoing,
interrupting the run of the protocol in the positive case. We study not only
how but also where we can attempt to defend flawed security protocols: we
investigate the different network topologies that make security protocol
defense feasible and illustrate our approach by means of concrete examples.Comment: 29 page
Service Security and Privacy as a Socio-Technical Problem: Literature review, analysis methodology and challenge domains
Published online September 2015 accepted: 15 September 2014Published online September 2015 accepted: 15 September 2014The security and privacy of the data that users transmit, more or less deliberately, to modern services is an open problem. It is not solely limited to the actual Internet traversal, a sub-problem vastly tackled by consolidated research in security protocol design and analysis. By contrast, it entails much broader dimensions pertaining to how users approach technology and understand the risks for the data they enter. For example, users may express cautious or distracted personas depending on the service and the point in time; further, pre-established paths of practice may lead them to neglect the intrusive privacy policy offered by a service, or the outdated protections adopted by another. The approach that sees the service security and privacy problem as a socio-technical one needs consolidation. With this motivation, the article makes a threefold contribution. It reviews the existing literature on service security and privacy, especially from the socio-technical standpoint. Further, it outlines a general research methodology aimed at layering the problem appropriately, at suggesting how to position existing findings, and ultimately at indicating where a transdisciplinary task force may fit in. The article concludes with the description of the three challenge domains of services whose security and privacy we deem open socio-technical problems, not only due to their inherent facets but also to their huge number of users
Cost Benefit Analysis of Labor Allocation and Training Schemes
Discrepancies in local labor markets occur as unsatisfactory matching of skill within the same region as well as redundant supply and unsatiated demand among regions. Some of this discrepancy could -- in principle -- be removed by letting supply in one region meet demand in another. A reallocation policy of this kind poses a few questions of prominent concern: 1. Can economic disvalue arising from imperfection of labor markets at a regional level be mathematically assessed? 2. Is it possible to define a regional measure of inefficiency on both sides -- demand and supply -- of the labor market? 3. How should vacancies be distributed over skill and space to alleviate inefficiency? These questions are investigated in this paper and a short-run solution is obtained via the primal-dual linear programming formulation of the problem
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