39,044 research outputs found
Bi-Directional Safety Analysis for Product-Line, Multi-Agent Systems
Abstract. Safety-critical systems composed of highly similar, semi-autonomous agents are being developed in several application domains. An example of such multi-agent systems is a fleet, or “constellation ” of satellites. In constellations of satellites, each satellite is commonly treated as a distinct autonomous agent that must cooperate to achieve higher-level constellation goals. In previous work, we have shown that modeling a constellation of satellites or spacecraft as a product line of agents (where the agents have many shared commonalities and a few key differences) enables reuse of software analysis and design assets. We have also previously developed efficient safety analysis techniques for product lines. We now propose the use of Bi-Directional Safety Analysis (BDSA) to aid in system certification. We extend BDSA to product lines of multi-agent systems and show how the analysis artifacts thus produced contribute to the software’s safety case for certification purposes. The product-line approach lets us reuse portions of the safety analysis for multiple agents, significantly reducing the burden of certification. We motivate and illustrate this work through a specific application, a product-line, multi-agent satellite constellation
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Design, characterization, and fabrication of solar-retroreflective cool-wall materials
Raising urban albedo increases the fraction of incident sunlight returned to outer space, cooling cities and their buildings. We evaluated the angular distribution of solar radiation incident on exterior walls in 17 U S. climates to develop performance parameters for solar-retroreflective walls, then applied first-principle physics and ray-tracing simulations to explore designs. Our analysis indicates that retroreflective walls must function at large incidence angles to reflect a substantial portion of summer sunlight, and that this will be difficult to attain with materials that rely on total internal reflection. Gonio-spectrophotometer measurements of the solar spectral bi-directional reflectivity of a bicycle reflector showed little to no retroreflection at large incidence angles. Visual comparisons of retroreflection to specular first-surface reflection for four different retroreflective safety films using violet and green lasers suggest their retroreflection to be no greater than 0.09 at incidence angles up to 45°, and no greater than 0.30 at incidence angles of up to 70°. Attempts to produce a two-surface retroreflector with orthogonal mirror grooves by cutting and polishing an aluminum block indicate that residual surface roughness impedes retroreflection. Ongoing efforts focus on forming orthogonal surfaces with aluminized Mylar film, a material with very high specular reflectance across the solar spectrum. We investigated (1) folding or stamping a free film; (2) adhering the film to a pre-shaped substrate; or (3) attaching the film to a flat ductile substrate, then shaping. The latter two methods were more successful but yielded imperfect right angles
Motorway Tidal Flow Lane Control
A traffic control case of particular importance occurs when inbound and outbound traffic on a motorway stretch is unbalanced throughout the day. This scenario may benefit of a lane management strategy called tidal flow (or reversible) lane control, in which case the direction of a contraflow buffer lane is reversed according to the needs of each direction. This paper proposes a simple and practical real-time strategy for efficient motorway tidal flow lane control. A switching policy based on the fundamental diagram, that requires only aggregated measurements of density (or occupancy), is adopted. A kinematic wave theory-based traffic flow analysis shows that the proposed strategy provides a Pareto-optimal solution. Simulation studies of the A38(M) Aston Expressway (Birmingham, UK), are used to demonstrate its operation. The results confirm an increase of motorway throughput and a smooth operation of the strategy
Artificial restoration of the linkage between laminin and dystroglycan ameliorates the disease progression of MDC1A muscular dystrophy at all stages
Laminin-α2 deficient congenital muscular dystrophy, classified as MDC1A, is a severe
progressive muscle-wasting disease that leads to death in early childhood. MDC1A is caused by
mutations in lama2, the gene encoding the laminin-α2 chain being part of laminin-2, the main
laminin isoform present in the extracellular matrix of muscles and peripheral nerves. Via selfpolymerization,
laminin-2 forms the primary laminin scaffold and binds with high affinity to α-
dystroglycan on the cell surface, providing a connection to the cytoskeleton via the
transmembranous protein β-dystroglycan. Deficiency in laminin-α2 leads to absence of laminin-2
and to upregulation of laminin-8, a laminin isoform that cannot self-polymerize and does not bind
to α-dystroglycan. Therefore, in laminin α2-deficient muscle the chain of proteins linking the
intracellular contractile apparatus via the plasma membrane to the extracellular matrix is
interrupted. Consequently, muscle fibers loose their stability and degenerate what finally leads to
a progressive muscle wasting.
In previous studies, we have shown that a miniaturized form of the extracellular matrix protein
agrin, which is not related to the disease-causing lama2 gene and was designed to contain highaffinity
binding sites for the laminins and for α-dystroglycan, was sufficient to markedly improve
muscle function and overall health in the dyW-/- mouse model of MDC1A. In a follow-up study we
provided additional evidence that mini-agrin, both increases the tolerance to mechanical load but
also improves the regeneration capacity of the dystrophic muscle.
We now report on our progress towards further testing the use of this approach for the treatment
of MDC1A. To test whether mini-agrin application after onset of the disease would still ameliorate
the dystrophic symptoms, we have established the inducible tetracycline-regulated “tet-off”
expression system in dyW-/- mice to temporally control mini-agrin expression in skeletal muscles.
We show that mini-agrin slows down the progression of the dystrophy when applied at birth or in
advanced stages of the disease. However, the extent of the amelioration depends on the
dystrophic condition of the muscle at the time of mini-agrin application. Thus, the earlier miniagrin
is applied, the higher is the profit of its beneficial properties.
In addition to gene therapeutical approaches, the increase of endogenous agrin expression levels
in skeletal muscles by pharmacologically active compounds would be a safe and promising
strategy for the treatment of MDC1A. To evaluate the potential and pave the way to further
expand on the development of such a treatment, we determined whether full-length agrin
ameliorates the dystrophic phenotype to a comparable extent as it was observed by application of
mini-agrin. We provide evidence that constitutive overexpression of chick full-length agrin in dyW-/-
muscle ameliorates the dystrophic phenotype, although not as pronounced as mini-agrin does.
In conclusion, our results are conceptual proof that linkage of laminin to the muscle fiber
membrane is a means to treat MDC1A at any stage of the disease. Our findings definitely
encourage to further expanding on this therapeutic concept, especially in combination with
treatment using functionally different approaches. Moreover, these experiments set the basis for
further developing clinically feasible and relevant application methods such as gene therapy4
and/or the screening of small molecules able to upregulate production of agrin in muscle
Multi-objective Compositions for Collision-Free Connectivity Maintenance in Teams of Mobile Robots
Compositional barrier functions are proposed in this paper to systematically
compose multiple objectives for teams of mobile robots. The objectives are
first encoded as barrier functions, and then composed using AND and OR logical
operators. The advantage of this approach is that compositional barrier
functions can provably guarantee the simultaneous satisfaction of all composed
objectives. The compositional barrier functions are applied to the example of
ensuring collision avoidance and static/dynamical graph connectivity of teams
of mobile robots. The resulting composite safety and connectivity barrier
certificates are verified experimentally on a team of four mobile robots.Comment: To appear in 55th IEEE Conference on Decision and Control, December
12-14, 2016, Las Vegas, NV, US
Open TURNS: An industrial software for uncertainty quantification in simulation
The needs to assess robust performances for complex systems and to answer
tighter regulatory processes (security, safety, environmental control, and
health impacts, etc.) have led to the emergence of a new industrial simulation
challenge: to take uncertainties into account when dealing with complex
numerical simulation frameworks. Therefore, a generic methodology has emerged
from the joint effort of several industrial companies and academic
institutions. EDF R&D, Airbus Group and Phimeca Engineering started a
collaboration at the beginning of 2005, joined by IMACS in 2014, for the
development of an Open Source software platform dedicated to uncertainty
propagation by probabilistic methods, named OpenTURNS for Open source Treatment
of Uncertainty, Risk 'N Statistics. OpenTURNS addresses the specific industrial
challenges attached to uncertainties, which are transparency, genericity,
modularity and multi-accessibility. This paper focuses on OpenTURNS and
presents its main features: openTURNS is an open source software under the LGPL
license, that presents itself as a C++ library and a Python TUI, and which
works under Linux and Windows environment. All the methodological tools are
described in the different sections of this paper: uncertainty quantification,
uncertainty propagation, sensitivity analysis and metamodeling. A section also
explains the generic wrappers way to link openTURNS to any external code. The
paper illustrates as much as possible the methodological tools on an
educational example that simulates the height of a river and compares it to the
height of a dyke that protects industrial facilities. At last, it gives an
overview of the main developments planned for the next few years
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