Peter Kropf

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Papers by Peter Kropf

Proceedings of the 2013 Summer Computer Simulation Conference

Proceedings of the 2011 15th International Conference on Computer Supported Cooperative Work in Design (CSCWD)

Summer computer simulation conference

Computer Methods in Applied Mechanics and Engineering, 1982

2013 Doctoral Workshop on Distributed Systems

The Doctoral Workshop on Distributed Systems was held at Les Plans-sur-Bex, Switzerland, from Jun... more The Doctoral Workshop on Distributed Systems was held at Les Plans-sur-Bex, Switzerland, from June 26-28, 2013. Ph.D. students from the Universities of Neuchâtel and Bern as well as the University of Applied Sciences of Fribourg presented their current research work and discussed recent research results. This technical report includes the extended abstracts of the talks given during the workshop.

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Proceedings of the 2012 IEEE 16th International Conference on Computer Supported Cooperative Work in Design (CSCWD)

Towards the integration of physically-based hydrological modelling, data assimilation and cloud computing for real-time management of water resources

Integrating hydrological modelling, data assimilation and cloud computing for real-time management of water resources

Environmental Modelling and Software, Jul 1, 2017

Online data acquisition, data assimilation and integrated hydrological modelling have become more... more Online data acquisition, data assimilation and integrated hydrological modelling have become more and more important in hydrological science. In this study, we explore cloud computing for integrating field data acquisition and stochastic, physically-based hydrological modelling in a data assimilation and optimisation framework as a service to water resources management. For this purpose, we developed an ensemble Kalman filter-based data assimilation system for the fully-coupled, physically-based hydrological model HydroGeoSphere, which is able to run in a cloud computing environment. A synthetic data assimilation experiment based on the widely used tilted V-catchment problem showed that the computational overhead for the application of the data assimilation platform in a cloud computing environment is minimal, which makes it well-suited for practical water management problems. Advantages of the cloud-based implementation comprise the independence from computational infrastructure and the straightforward integration of cloud-based observation databases with the modelling and data assimilation platform.

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Quantitative Intramuscular Myoelectric Activity of Lumbar Portions of Psoas and the Abdominal Wall during Cycling

Journal of Applied Biomechanics, Nov 1, 1998

The purpose of this study was to quantify activation using intramuscular EMG from lumbar psoas an... more The purpose of this study was to quantify activation using intramuscular EMG from lumbar psoas and the three layers of the abdominal wall during several styles of cycling: normal posture (slightly flexed), upright posture, racing in flexed posture, standing up from the saddle, and standing during maximal sprint effort. Lumbar erector spinae and rectus femoris were also monitored with surface electrodes. Results demonstrated that the activity patterns were influenced by the style of cycling. Furthermore, psoas activity peaked at 14% of MVC (or less) during the upstroke phase of normal cycling but became much more active at TDC during flexed cycling (approximately 30% MVC) and approached 60% of MVC during sprinting. Generally, the abdominal wall was activated to relatively low but continual levels except during standing and sprinting. Erector spinae activity was very low at less than 5% MVC throughout the cycle until standing or sprinting styles were adopted. These normalized and scaled data on deep muscle activity during ergometer cycling provide insight into the functioning of these muscles; this information can be used to prescribe rehabilitation and training programs and can help biomechanists understand muscle activity associated with cycling.

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Collaborative Ranking and Profiling: Exploiting the Wisdom of Crowds in Tailored Web Search

Springer eBooks, 2010

Popular search engines essentially rely on information about the structure of the graph of linked... more Popular search engines essentially rely on information about the structure of the graph of linked elements to find the most relevant results for a given query. While this approach is satisfactory for popular interest domains or when the user expectations follow the main trend, it is very sensitive to the case of ambiguous queries, where queries can have answers over several different domains. Elements pertaining to an implicitly targeted interest domain with low popularity are usually ranked lower than expected by the user. This is a consequence of the poor usage of user-centric information in search engines. Leveraging semantic information can help avoid such situations by proposing complementary results that are carefully tailored to match user interests. This paper proposes a collaborative search companion system, CoFeed, that collects user search queries and accesses feedback to build user-and document-centric profiling information. Over time, the system constructs ranked collections of elements that maintain the required information diversity and enhance the user search experience by presenting additional results tailored to the user interest space. This collaborative search companion requires a supporting architecture adapted to large user populations generating high request loads. To that end, it integrates mechanisms for ensuring scalability and load balancing of the service under varying loads and user interest distributions. Experiments with a deployed prototype highlight the efficiency of the system by analyzing improvement in search relevance, computational cost, scalability and load balance. This work is partially funded by the Hasler fundation and SNF project 102819.

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Efficient Broadcasting Algorithm in Harary-like Networks

In this paper, we analyze the properties of Harary graphs and some derivatives with respect to th... more In this paper, we analyze the properties of Harary graphs and some derivatives with respect to the achievable performance of communication within network structures based on these graphs. In particular we defined Cordal-Haray graphs on n nodes which can be constructed for any even n for any odd degree between 3 and 2[log n] – 1. We also present a simple algorithm for fast message broadcasting in this network. Our analysis show that when nodes of a Cordal-Harary Graph have logarithmic degree then the broadcasting time will be as small as [log n] which is the minimum possible value for a network on n nodes. All this properties show that Cordal-Harary is a very good network architecture for parallel processing.

Applying big data paradigms to a large scale scientific workflow: Lessons learned and future directions

Future Generation Computer Systems, Sep 1, 2020

The increasing amounts of data related to the execution of scientific workflows has raised awaren... more The increasing amounts of data related to the execution of scientific workflows has raised awareness of their shift towards parallel data-intensive problems. In this paper, we deliver our experience combining the traditional high-performance computing and grid-based approaches with Big Data analytics paradigms, in the context of scientific ensemble workflows. Our goal was to assess and discuss the suitability of such data-oriented mechanisms for production-ready workflows, especially in terms of scalability. We focused on two key elements in the Big Data ecosystem: the data-centric programming model, and the underlying infrastructure that integrates storage and computation in each node. We experimented with a representative MPI-based iterative workflow from the hydrology domain, EnKF-HGS, which we re-implemented using the Spark data analysis framework. We conducted experiments on a local cluster, a private cloud running OpenNebula, and the Amazon Elastic Compute Cloud (AmazonEC2). The results we obtained were analysed to synthesize the lessons we learned from this experience, while discussing promising directions for further research.

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Two-level communication protocol for a Web operating system (WOS/sup TM/)

Proceedings. 24th EUROMICRO Conference (Cat. No.98EX204), Nov 27, 2002

The WorldWide Web consists not only of informational, but also computational resources. However, ... more The WorldWide Web consists not only of informational, but also computational resources. However, these resources, especially computational ones are underutilized. One characteristic of the Web is its ever changing structure; for instance, nodes are dynamically added and removed. This makes it difficult, if not impossible, to draw a complete and accurate picture of available resources. We consider the Web as a versioned system: resources, services and protocols are versioned. This paper presents a two-level protocol within this framework. The first protocol, the WOS Request Protocol (WOSRP), allows to select an appropriate version of a server. The second protocol, the WOS Protocol (WOSP), allows for locating and using these distributed (informational and computational) resources. We show how the latter protocol provides an efficient fault-tolerant resource search mechanism.

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Proceedings of the Third International Workshop on Distributed Communities on the Web

A Method to Optimize Ship Maneuvers for the Coordination of Hardkill and Softkill Weapons within a Frigate

The coordination of anti-air warfare hardkill and softkill weapon systems is an important aspect ... more The coordination of anti-air warfare hardkill and softkill weapon systems is an important aspect of command and control for a Frigate. Since the effectiveness of a particular weapon varies depending on the orientation of the Frigate with respect to the threats faced, a key element of the coordination process is to maneuver the Frigate to most effectively use all the weapons available. This paper shows that the environment surrounding the Frigate can be divided into six fundamental sectors for weapon engagement. The method to determine the general effectiveness of each sector for the threats faced is shown. A naïve Bayes method that determines the optimal positioning of the Frigate to most effectively use the hardkill and softkill weapons is presented. Also discussed are the different types of planners that were investigated for planning engagements for the hardkill and softkill weapon systems. Preliminary results comparing and rating these planners are shown, both with and without the recommended maneuvers.

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Revised Papers from the 4th International Workshop on Distributed Communities on the Web

A Roadmap for Research in Sustainable Ultrascale Systems

The roadmap document has been discussed during plenary sessions of various NESUS meetings. We tha... more

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Applications for ultrascale computing

Supercomputing Frontiers and Innovations, 2015

Studies of real complex physical and engineering problems represented by multiscale and multiphys... more Studies of real complex physical and engineering problems represented by multiscale and multiphysics computer simulations have an increasing demand for computing power. The demand is driven by the increasing scales and complexity of the scientific problems investigated or the time constraints. Ultrascale computing systems could offer the computing power required to solve these problems. Future ultrascale systems will be large-scale complex computing systems combining technologies from high performance computing, distributed systems, big data, and cloud computing. The challenge of developing and programming complex algorithms that can efficiently perform on such systems is twofold. Firstly, the complex computer simulations have to be either developed from scratch, or redesigned in order to yield high performance, while retaining correct functional behaviour. Secondly, ultrascale computing systems impose a number of non-functional cross-cutting concerns, such as fault tolerance or energy consumption, which can significantly impact the deployment of applications on large complex computing systems. This article discusses the state-of-the-art of programming for current and future large-scale computing systems with an emphasis on complex applications. We derive a number of requirements regarding programming and execution support by studying several computationally demanding applications that the authors are currently developing and discuss their potential and necessary upgrades for ultrascale execution on ultrascale facilities.

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Numerical algorithms for estimating least squares problems

Acknowledgments First, I would like to thank my Ph.D. supervisor and friend Prof. Erricos John Ko... more Acknowledgments First, I would like to thank my Ph.D. supervisor and friend Prof. Erricos John Kon- toghiorghes for his guidance, help and support during these years of Ph.D. study. He introduced me to the world of research and taught me to express my ideas and the results I obtained from the research in a scientific manner. I am also grateful

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BALLS: A structured peer-to-peer system with integrated load balancing

Annales Des Télécommunications, Dec 1, 2006

Simulation is an efficient way to evaluate new peer-to-peer models. It requires two implicit prop... more Simulation is an efficient way to evaluate new peer-to-peer models. It requires two implicit properties: large scale and high dynamicity. In the context of our work that proposes a peer-to-peer structure based on partitioning a de Bruijn graph and its load balancing algorithms, we developed a simulator for evaluation purposes. This paper introduces a threelayer architecture of the simulator. This architecture allows to support simulations in two modes: centralized (where all peers are simulated on one physical machine) and decentralized (where the peers run on separate machines communicating through the underlying network).

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P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks

Advancing Conceptual and Algorithmic Applications

The most important characteristics of mobile ad-hoc networks (MANETs) such as broadcast and multi... more The most important characteristics of mobile ad-hoc networks (MANETs) such as broadcast and multihop communication, limited resources (particularly energy) and physical proximity are often ignored in solutions being proposed for information lookup and distribution. Thus, many lookup approaches rely on unstructured algorithms using flooding techniques, while content distribution mechanisms frequently generate inefficient multicast trees without considering the presence of nodes that are involved only as relays and are not interested in the distributed content. In this chapter, the authors present a multicast algorithm designed to build efficient multicast trees in MANETs that strive to limit the number of relay nodes and transmissions required. This distribution infrastructure relies on a lightweight distributed hash table (DHT) specifically adapted to MANETs, and exploits the physical proximity of nodes and broadcast communication. The algorithmic efficiency and scalability are eval...

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