| 1. |
- Foerster, Klaus Tycho, et al.
(författare)
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Analyzing the Communication Clusters in Datacenters
- 2023
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Ingår i: ACM Web Conference 2023. - : Association for Computing Machinery (ACM). ; , s. 3022-3032
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Konferensbidrag (refereegranskat)abstract
- Datacenter networks have become a critical infrastructure of our digital society and over the last years, great efforts have been made to better understand the communication patterns inside datacenters. In particular, existing empirical studies showed that datacenter traffic typically features much temporal and spatial structure, and that at any given time, some communication pairs interact much more frequently than others. This paper generalizes this study to communication groups and analyzes how clustered the datacenter traffic is, and how stable these clusters are over time. To this end, we propose a methodology which revolves around a biclustering approach, allowing us to identify groups of racks and servers which communicate frequently over the network. In particular, we consider communication patterns occurring in three different Facebook datacenters: a Web cluster consisting of web servers serving web traffic, a Database cluster which mainly consists of MySQL servers, and a Hadoop cluster. Interestingly, we find that in all three clusters, small groups of racks and servers can produce a large fraction of the network traffic, and we can determine these groups even when considering short snapshots of network traffic. We also show empirically that these clusters are fairly stable across time. Our insights on the size and stability of communication clusters hence uncover an interesting potential for resource optimizations in datacenter infrastructures.
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| 2. |
- Foerster, Klaus-Tycho, et al.
(författare)
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TI-MFA : Keep Calm and Reroute Segments Fast
- 2018
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Ingår i: IEEE INFOCOM 2018 - IEEE CONFERENCE ON COMPUTER COMMUNICATIONS WORKSHOPS (INFOCOM WKSHPS). - : IEEE. - 9781538659793 ; , s. 415-420
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Konferensbidrag (refereegranskat)abstract
- Segment Routing (SR) promises to provide scalable and fine-grained traffic engineering. However, little is known today on how to implement resilient routing in SR, i.e., routes which tolerate one or even multiple failures. This paper initiates the theoretical study of static fast failover mechanisms which do not depend on reconvergence and hence support a very fast reaction to failures. We introduce formal models and identify fundamental tradeoffs on what can and cannot be achieved in terms of static resilient routing. In particular, we identify an inherent price in terms of performance if routing paths need to be resilient, even in the absence of failures. Our main contribution is a first algorithm which is resilient even to multiple failures and which comes with provable resiliency and performance guarantees. We complement our formal analysis with simulations on real topologies, which show the benefits of our approach over existing algorithms.
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| 3. |
- Heijl, Anders, et al.
(författare)
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Nordic research in ophthalmology.
- 2005
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Ingår i: Acta ophthalmologica Scandinavica. - : Wiley. - 1395-3907 .- 1600-0420. ; 83:3, s. 278-88
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Nordic ophthalmologists and vision scientists are active in many fields of eye research. This is most evident at the biannual Nordic Congress of Ophthalmology, most recently held in Malmö in June 2004. The authors here review some of the research in vision and ophthalmology presented at this meeting or published recently by Nordic scientists. This paper does not represent a comprehensive review of all Nordic research in the field, but attempts to give an overview of some of the activities underway in eye research in this part of the world.
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| 4. |
- Mattsson, Niklas, et al.
(författare)
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Prevalence of the apolipoprotein E epsilon 4 allele in amyloid beta positive subjects across the spectrum of Alzheimers disease
- 2018
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Ingår i: Alzheimer's & Dementia. - : ELSEVIER SCIENCE INC. - 1552-5260 .- 1552-5279. ; 14:7, s. 913-924
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Apolipoprotein E (APOE) epsilon 4 is the major genetic risk factor for Alzheimers disease (AD), but its prevalence is unclear because earlier studies did not require biomarker evidence of amyloid beta(A beta) pathology. Methods: We included 3451 A beta+ subjects (853 AD-type dementia, 1810 mild cognitive impairment, and 788 cognitively normal). Generalized estimating equation models were used to assess APOE epsilon 4 prevalence in relation to age, sex, education, and geographical location. Results: The APOE epsilon 4 prevalence was 66% in AD-type dementia, 64% in mild cognitive impairment, and 51% in cognitively normal, and it decreased with advancing age in A beta+ cognitively normal and A beta+ mild cognitive impairment (P amp;lt;.05) but not in A beta+ AD dementia (P =.66). The prevalence was highest in Northern Europe but did not vary by sex or education. Discussion: The APOE E4 prevalence in AD was higher than that in previous studies, which did not require presence of A beta pathology. Furthermore, our results highlight disease heterogeneity related to age and geographical location. (C) 2018 the Alzheimers Association. Published by Elsevier Inc. All rights reserved.
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| 5. |
- Rominger, Axel, et al.
(författare)
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Validation of the Octamouse for Simultaneous 18F-Fallypride Small-Animal PET Recordings from 8 Mice
- 2010
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Ingår i: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 1535-5667 .- 2159-662X. ; 51:10, s. 1576-1583
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Tidskriftsartikel (refereegranskat)abstract
- Data collection in preclinical small-animal PET studies has been hindered by the small number of recordings typically obtained for a single radiosynthesis. Therefore, we tested procedures for obtaining 8 simultaneous small-animal PET recordings from the brains of 8 mice using an acrylic anesthesia distributor (the Octamouse), with the dopamine D-2/3 ligand F-18-fallypride serving as a test substance for brain receptor imaging. Methods: The effect of scatter correction on the small-animal PET recordings was first evaluated in phantom studies in which sources of different radioactivity concentration were placed within the chambers of the Octamouse. Next, potential effects of mass on the F-18-fallypride binding potential (BPND) in the striatum were tested in groups of mice receiving F-18-fallypride at 2 different specific activities (140 and 50 GBq/mu mol), with and without scatter correction. Finally, the relationship between BPND and injected dose of F-18-fallypride (3.5-17 MBq/mouse) was tested. Results: Scatter correction improved the contrast between sources and air space within the Octamouse phantom. The magnitude of F-18-fallypride BPND in mouse striatum was invariant across the tested range of specific activities, and scatter correction increased BPND by a mean of 6%; covariances of the inter-and intraoperator variability of BPND were 10%. There was a positive correlation between radiochemical dose and BPND with (R-2 = 0.53) and without (R-2 = 0.63) scatter correction, which was driven by increasing area under the percentage injected dose curve in the striatum. Conclusion: The quantitation of emission sources placed within the Octamouse is linear over a wide range of source activities. In the striatum of living mice, the magnitude of F-18-fallypride BPND was highly reproducible between operators and was constant over a 3-fold range of specific activities, indicating a lack of significant occupancy. Scatter correction improved quantitation but did not entirely correct for the dependence of BPND on injected dose, which was deemed to arise because of effects propagating from detector dead time when the total radiochemical dose in the field of view exceeded 50 MBq. Given this consideration, we were still able to quantify F-18-fallypride BPND in 16 mice from a single radiosynthesis, an economy that should be generalizable to brain studies of diverse radioligands.
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