21,935 research outputs found
A General Upper Bound on the Size of Constant-Weight Conflict-Avoiding Codes
Conflict-avoiding codes are used in the multiple-access collision channel
without feedback. The number of codewords in a conflict-avoiding code is the
number of potential users that can be supported in the system. In this paper, a
new upper bound on the size of conflict-avoiding codes is proved. This upper
bound is general in the sense that it is applicable to all code lengths and all
Hamming weights. Several existing constructions for conflict-avoiding codes,
which are known to be optimal for Hamming weights equal to four and five, are
shown to be optimal for all Hamming weights in general.Comment: 10 pages, 1 figur
Code Design Principles for Ultra-Reliable Random Access with Preassigned Patterns
We study medium access control layer random access under the assumption that the receiver can perform successive interference cancellation, without feedback. During recent years, a number of protocols with impressive error performance have been suggested for this channel model. However, the random nature of these protocols causes an error floor which limits their usability when targeting ultra-reliable communications. In very recent works by Paolini et al. and Boyd et. al., it was shown that if each user employs predetermined combinatorial access patterns, this error floor disappears. In this paper, we develop code design criteria for deterministic random access protocols in the ultra-reliability region, and build codes based on these principles. The suggested design methods are supported by simulations.Peer reviewe
Information and communication on the designation and management of Natura2000 sites. Main Report 3: Towards Integrated Management
Following the selection of Special Protection Areas (SPA) and Sites of Community Importance (SCI) according to the Birds and the Habitats Directives, most European Member States are now in process of formally designating SPAs and SCIs as Special Areas of Conservation (SAC) or Natura2000 sites. These protected areas collectively form the European Union’s Natura2000 network. Member States are also selecting and implementing adequate management approaches and instruments to maintain and restore the favourable conservation status of protected species and habitat types and to prevent damage to the integrity of the sites. Both actions follow Articles 6.1 and 6.2 of the Habitats Directive.
To help the Member States, the European Commission wishes to improve the knowledge and exchange of information and good practice both on the designation process of SPAs and SACs and on the establishment of conservation measures and instruments for these areas. Furthermore, the Commission wants to stress the importance of the sites and their management by involving a wider group of stakeholders in the development of so-called integrated management, in accordance with Article 2 of the Habitats Directive.
The project ‘PREPARATORY ACTIONS- Lot 2: Information and communication on the designation and management of sites’ (tender ENV.B.2/SER/2007/0076) is intended to help the Commission to achieve these objectives. In this report we will elaborate on the concept of integrated management as an option for managing the sites. In the first part the meaning of integrated management will be explored. In a second part we give some examples of management approaches that we think illustrate best the concept of integrated management and its potential to achieve the Natura2000 goals
Safe driving in a green world : a review of driver performance benchmarks and technologies to support ‘smart’ driving
Road transport is a significant source of both safety and environmental concerns. With climate change and fuel prices increasingly prominent on social and political agendas, many drivers are turning their thoughts to fuel efficient or ‘green’ (i.e., environmentally friendly) driving practices. Many vehicle manufacturers are satisfying this demand by offering green driving feedback or advice tools. However, there is a legitimate concern regarding the effects of such devices on road safety – both from the point of view of change in driving styles, as well as potential distraction caused by the in-vehicle feedback. In this paper, we appraise the benchmarks for safe and green driving, concluding that whilst they largely overlap, there are some specific circumstances in which the goals are in conflict. We go on to review current and emerging in-vehicle information systems which purport to affect safe and/or green driving, and discuss some fundamental ergonomics principles for the design of such devices. The results of the review are being used in the Foot-LITE project, aimed at developing a system to encourage ‘smart’ – that is safe and green – driving
Tackling Exascale Software Challenges in Molecular Dynamics Simulations with GROMACS
GROMACS is a widely used package for biomolecular simulation, and over the
last two decades it has evolved from small-scale efficiency to advanced
heterogeneous acceleration and multi-level parallelism targeting some of the
largest supercomputers in the world. Here, we describe some of the ways we have
been able to realize this through the use of parallelization on all levels,
combined with a constant focus on absolute performance. Release 4.6 of GROMACS
uses SIMD acceleration on a wide range of architectures, GPU offloading
acceleration, and both OpenMP and MPI parallelism within and between nodes,
respectively. The recent work on acceleration made it necessary to revisit the
fundamental algorithms of molecular simulation, including the concept of
neighborsearching, and we discuss the present and future challenges we see for
exascale simulation - in particular a very fine-grained task parallelism. We
also discuss the software management, code peer review and continuous
integration testing required for a project of this complexity.Comment: EASC 2014 conference proceedin
A new generation 99 line Matlab code for compliance Topology Optimization and its extension to 3D
Compact and efficient Matlab implementations of compliance Topology
Optimization (TO) for 2D and 3D continua are given, consisting of 99 and 125
lines respectively. On discretizations ranging from to
elements, the 2D version, named top99neo, shows speedups from
2.55 to 5.5 times compared to the well-known top88 code (Andreassen-etal 2011).
The 3D version, named top3D125, is the most compact and efficient Matlab
implementation for 3D TO to date, showing a speedup of 1.9 times compared to
the code of Amir-etal 2014, on a discretization with elements.
For both codes, improvements are due to much more efficient procedures for the
assembly and implementation of filters and shortcuts in the design update step.
The use of an acceleration strategy, yielding major cuts in the overall
computational time, is also discussed, stressing its easy integration within
the basic codes.Comment: 17 pages, 8 Figures, 4 Table
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