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Kæfisvefn veldur hjarta- og æðasjúkdómum - segir doktorsnemi í líffræöi
(2009) Arnardóttir, Erna Sif; Verkfræðideild
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Distributed and high-performance multimedia : Introduction
(2007) Kosh, Harald; Amsaleg, Laurent; Pauwels, Eric; Jónsson, Björn Þór; Department of Computer Science
Verk
Performance and overhead of semantic cache management
(2006) Jónsson, Björn Þór; Arinbjarnar, María; Þórsson, Bjarnsteinn; Franklin, Michael J.; Srivastava, Divesh; Department of Computer Science
The emergence of query-based online data services and e-commerce applications has prompted much recent research on data caching. This article studies semantic caching, a caching architecture for such applications, that caches the results of selection queries. The primary contribution of this article is to revisit the performance and overhead of semantic caching using a modern database server and modern hardware. Initially, the performance study focuses on simple workloads and demonstrates several benefits of semantic caching, including low overhead, insensitivity to the physical layout of the database, reduced network traffic, and the ability to answer some queries without contacting the server. With moderately complex workloads, careful coding of remainder queries is required to maintain efficient query processing at the server. Using very complex workloads, we demonstrate that semantic caching works well in a range of applications, especially in network-constrained environments.
Verk
The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves
(2005-10-28) Song, Y. Tony; Ji, Chen; Fu, L. L.; Zlotnicki, Victor; Shum, C. K.; Yi, Yuchan; Hjorleifsdottir, Vala; Department of Engineering
The 26 December 2004 Indian Ocean tsunami was the first earthquake tsunami of its magnitude to occur since the advent of both digital seismometry and satellite radar altimetry. Both have independently recorded the event from different physical aspects. The seismic data has then been used to estimate the earthquake fault parameters, and a three-dimensional ocean-general-circulation-model (OGCM) coupled with the fault information has been used to simulate the satellite-observed tsunami waves. Here we show that these two datasets consistently provide the tsunami source using independent methodologies of seismic waveform inversion and ocean modeling. Cross-examining the two independent results confirms that the slip function is the most important condition controlling the tsunami strength, while the geometry and the rupture velocity of the tectonic plane determine the spatial patterns of the tsunami.
Verk
A clean slate 4D approach to network control and management
(2005-10) Greenberg, Albert; Hjalmtysson, Gisli; Maltz, David A.; Myers, Andy; Rexford, Jennifer; Xie, Geoffrey; Yan, Hong; Zhan, Jibin; Zhang, Hui; Department of Computer Science
Today's data networks are surprisingly fragile and difficult to manage. We argue that the root of these problems lies in the complexity of the control and management planes - the software and protocols coordinating network elements - and particularly the way the decision logic and the distributed-systems issues are inexorably intertwined. We advocate a complete refactoring of the functionality and propose three key principles - network-level objectives, network-wide views, and direct control - that we believe should underlie a new architecture. Following these principles, we identify an extreme design point that we call "4D," after the architecture's four planes: decision, dissemination, discovery, and data. The 4D architecture completely separates an AS's decision logic from pro-tocols that govern the interaction among network elements. The AS-level objectives are specified in the decision plane, and en-forced through direct configuration of the state that drives how the data plane forwards packets. In the 4D architecture, the routers and switches simply forward packets at the behest of the decision plane, and collect measurement data to aid the decision plane in controlling the network. Although 4D would involve substantial changes to today's control and management planes, the format of data packets does not need to change; this eases the deployment path for the 4D architecture, while still enabling substantial innovation in network control and management. We hope that exploring an extreme design point will help focus the attention of the research and industrial communities on this crucially important and intellectually challenging area.

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