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Search Results: 1 - 10 of 570 matches for " Veronika Rehn-Sonigo "
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Optimal Replica Placement in Tree Networks with QoS and Bandwidth Constraints and the Closest Allocation Policy
Veronika Rehn-Sonigo
Computer Science , 2007,
Abstract: This paper deals with the replica placement problem on fully homogeneous tree networks known as the Replica Placement optimization problem. The client requests are known beforehand, while the number and location of the servers are to be determined. We investigate the latter problem using the Closest access policy when adding QoS and bandwidth constraints. We propose an optimal algorithm in two passes using dynamic programming.
Resource Allocation for Multiple Concurrent In-Network Stream-Processing Applications
Anne Benoit,Henri Casanova,Veronika Rehn-Sonigo,Yves Robert
Computer Science , 2009,
Abstract: This paper investigates the operator mapping problem for in-network stream-processing applications. In-network stream-processing amounts to applying one or more trees of operators in steady-state, to multiple data objects that are continuously updated at different locations in the network. The goal is to compute some final data at some desired rate. Different operator trees may share common subtrees. Therefore, it may be possible to reuse some intermediate results in different application trees. The first contribution of this work is to provide complexity results for different instances of the basic problem, as well as integer linear program formulations of various problem instances. The second second contribution is the design of several polynomial-time heuristics. One of the primary objectives of these heuristics is to reuse intermediate results shared by multiple applications. Our quantitative comparisons of these heuristics in simulation demonstrates the importance of choosing appropriate processors for operator mapping. It also allow us to identify a heuristic that achieves good results in practice.
Resource Allocation Strategies for In-Network Stream Processing
Anne Benoit,Henri Casanova,Veronika Rehn-Sonigo,Yves Robert
Computer Science , 2008,
Abstract: In this paper we consider the operator mapping problem for in-network stream processing applications. In-network stream processing consists in applying a tree of operators in steady-state to multiple data objects that are continually updated at various locations on a network. Examples of in-network stream processing include the processing of data in a sensor network, or of continuous queries on distributed relational databases. We study the operator mapping problem in a ``constructive'' scenario, i.e., a scenario in which one builds a platform dedicated to the application buy purchasing processing servers with various costs and capabilities. The objective is to minimize the cost of the platform while ensuring that the application achieves a minimum steady-state throughput. The first contribution of this paper is the formalization of a set of relevant operator-placement problems as linear programs, and a proof that even simple versions of the problem are NP-complete. Our second contribution is the design of several polynomial time heuristics, which are evaluated via extensive simulations and compared to theoretical bounds for optimal solutions.
Bi-criteria Pipeline Mappings for Parallel Image Processing
Anne Benoit,Harald Kosch,Veronika Rehn-Sonigo,Yves Robert
Computer Science , 2008,
Abstract: Mapping workflow applications onto parallel platforms is a challenging problem, even for simple application patterns such as pipeline graphs. Several antagonistic criteria should be optimized, such as throughput and latency (or a combination). Typical applications include digital image processing, where images are processed in steady-state mode. In this paper, we study the mapping of a particular image processing application, the JPEG encoding. Mapping pipelined JPEG encoding onto parallel platforms is useful for instance for encoding Motion JPEG images. As the bi-criteria mapping problem is NP-complete, we concentrate on the evaluation and performance of polynomial heuristics.
Multi-criteria scheduling of pipeline workflows
Anne Benoit,Veronika Rehn-Sonigo,Yves Robert
Computer Science , 2007,
Abstract: Mapping workflow applications onto parallel platforms is a challenging problem, even for simple application patterns such as pipeline graphs. Several antagonist criteria should be optimized, such as throughput and latency (or a combination). In this paper, we study the complexity of the bi-criteria mapping problem for pipeline graphs on communication homogeneous platforms. In particular, we assess the complexity of the well-known chains-to-chains problem for different-speed processors, which turns out to be NP-hard. We provide several efficient polynomial bi-criteria heuristics, and their relative performance is evaluated through extensive simulations.
Optimizing Latency and Reliability of Pipeline Workflow Applications
Anne Benoit,Veronika Rehn-Sonigo,Yves Robert
Computer Science , 2007,
Abstract: Mapping applications onto heterogeneous platforms is a difficult challenge, even for simple application patterns such as pipeline graphs. The problem is even more complex when processors are subject to failure during the execution of the application. In this paper, we study the complexity of a bi-criteria mapping which aims at optimizing the latency (i.e., the response time) and the reliability (i.e., the probability that the computation will be successful) of the application. Latency is minimized by using faster processors, while reliability is increased by replicating computations on a set of processors. However, replication increases latency (additional communications, slower processors). The application fails to be executed only if all the processors fail during execution. While simple polynomial algorithms can be found for fully homogeneous platforms, the problem becomes NP-hard when tackling heterogeneous platforms. This is yet another illustration of the additional complexity added by heterogeneity.
Strategies for Replica Placement in Tree Networks
Yves Robert,Anne Benoit,Veronika Rehn
Computer Science , 2006,
Abstract: In this paper, we discuss and compare several policies to place replicas in tree networks, subject to server capacity and QoS constraints. The client requests are known beforehand, while the number and location of the servers are to be determined. The standard approach in the literature is to enforce that all requests of a client be served by the closest server in the tree. We introduce and study two new policies. In the first policy, all requests from a given client are still processed by the same server, but this server can be located anywhere in the path from the client to the root. In the second policy, the requests of a given client can be processed by multiple servers. One major contribution of this paper is to assess the impact of these new policies on the total replication cost. Another important goal is to assess the impact of server heterogeneity, both from a theoretical and a practical perspective. In this paper, we establish several new complexity results, and provide several efficient polynomial heuristics for NP-complete instances of the problem. These heuristics are compared to an absolute lower bound provided by the formulation of the problem in terms of the solution of an integer linear program.
Scheduling and data redistribution strategies on star platforms
Loris Marchal,Veronika Rehn,Yves Robert,Frédéric Vivien
Computer Science , 2006,
Abstract: In this work we are interested in the problem of scheduling and redistributing data on master-slave platforms. We consider the case were the workers possess initial loads, some of which having to be redistributed in order to balance their completion times. We examine two different scenarios. The first model assumes that the data consists of independent and identical tasks. We prove the NP-completeness in the strong sense for the general case, and we present two optimal algorithms for special platform types. Furthermore we propose three heuristics for the general case. Simulations consolidate the theoretical results. The second data model is based on Divisible Load Theory. This problem can be solved in polynomial time by a combination of linear programming and simple analytical manipulations.
Semi-infinite TASEP with a Complex Boundary Mechanism
Nicky Sonigo
Mathematics , 2009, DOI: 10.1007/s10955-009-9823-0
Abstract: We consider a totally asymmetric exclusion process on the positive half-line. When particles enter in the system according to a Poisson source, Liggett has computed all the limit distributions when the initial distribution has an asymptotic density. In this paper we consider systems for which particles enter at the boundary according to a complex mechanism depending on the current configuration in a finite neighborhood of the origin. For this kind of models, we prove a strong law of large numbers for the number of particles entered in the system at a given time. Our main tool is a new representation of the model as a multi-type particle system with infinitely many particle types.
Improving adjustments for older age in pre-hospital assessment and care
Rehn Marius
Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine , 2013, DOI: 10.1186/1757-7241-21-4
Abstract: Population estimates projects a significant increase in the geriatric population making elderly trauma patients more common. The geriatric trauma patients experience higher incidence of pre-existing medical conditions, impaired age-dependent physiologic reserve, use potent drugs and suffer from trauma system related shortcomings that influence outcomes. To improve adjustments for older age in pre-hospital assessment and care, several initiatives should be implemented. Decision-makers should make system revisions and introduce advanced point-of-care initiatives to improve outcome after trauma for the elderly.
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