| 1. |
- Anoushirvani, B., et al.
(författare)
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Gamma-ray bursts from primordial quark objects in space
- 1997
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Ingår i: Proceedings of the Joint Meeting of the Networks 'The Fundamental Structure of Matter' and 'Tests of the Electroweak Symmetry Breaking', Ouranoupolis, Greece, May 1997.
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Konferensbidrag (refereegranskat)abstract
- We investigate the possibility that gamma-ray bursts originate in a concentric spherical shell with a given average redshift and find that this is indeed compatible with the data from the third BATSE (3B) catalog. It is also shown that there is enough freedom in the choice of unknown burst properties to allow even for extremely large distances to the majority of bursts. Therefore, we speculate about an early, and very energetic, origin of bursts, and suggest that they come from phase transitions in massive objects of pure quark matter, left over from the Big Bang.
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| 2. |
- Anselmino, Mauro, et al.
(författare)
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Diquarks
- 1993
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Ingår i: Reviews of Modern Physics. - 0034-6861 .- 1539-0756. ; 65:4, s. 1199-1233
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Tidskriftsartikel (refereegranskat)abstract
- It is becoming increasingly clear that the concept of a diquark (a two-quark system) is important for understanding hadron structure and high-energy particle reactions. According to our present knowledge of quantum chromodynamics (QCD), diquark correlations arise in part from spin-dependent interactions between two quarks, from quark radial or orbital excitations, and from quark mass differences. Diquark substructures affect the static properties of baryons and the mechanisms of baryon decay. Diquarks also play a role in hadron production in hadron-initiated reactions, deep-inelastic lepton scattering by hadrons, and in e+e- reactions. Diquarks are important in the formation and properties of baryonium and mesonlike semistable states. Many spin effects observed in high-energy exclusive reactions pose severe problems for the pure quark picture of baryons and might be explained by the introduction of diquarks as hadronic constituents. There is considerable controversy, not about the existence of diquarks in hadrons, but about their properties and their effects. In this work a broad selection of the main ideas about diquarks is reviewed.
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| 3. |
- Bergfeldt, Erik, et al.
(författare)
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A Performance Study of Bandwidth Measurement Tools over Mobile Connections
- 2009
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Ingår i: 2009 IEEE 69th Vehicular Technology Conference Spring. - : IEEE. - 9781424425174 ; , s. 2978-2982
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Konferensbidrag (refereegranskat)abstract
- The knowledge of the present available bandwidth on a network path is essential in numerous contexts, such as network management and streaming applications. A network path nowadays often contains at least one wireless link. This is obviously true for mobile users having a wireless connection to the Internet through a laptop or mobile terminal. The existing tools for measuring end-to-end available bandwidth are developed and optimized for paths with only guided media links. Since the characteristics for wired links and radio links differ in many aspects, such as fluctuations in capacity and stability, the network tools need to be evaluated also for network paths containing wireless links. In this investigation we have performed experiments over a high-speed downlink UMTS channel. This makes the present paper unique in the sense that it evaluates and analyzes the applicability of available-bandwidth measurement tools over a radio interface in a wide-area mobile communication network. For the experiments, a commercial mobile network has been used. The measurements show that it is feasible to achieve reliable estimates under certain circumstances. However, some cases pose challenges which motivate further studies.
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| 4. |
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| 5. |
- Bergfeldt, Erik, et al.
(författare)
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Real-time bandwidth measurements over mobile connections
- 2011
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Ingår i: European transactions on telecommunications. - : John Wiley and Sons. - 1124-318X .- 2161-3915. ; 22:6, s. 255-267
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Tidskriftsartikel (refereegranskat)abstract
- The first study that investigates the characteristics of received probe packets and the reliability of bandwidth estimates when actively measuring the available bandwidth over radio interfaces in mobile communication networks is presented. Knowledge of available bandwidth is very useful in various contexts, e. g. in network management and adaptive streaming applications. Bandwidth measuring tools have so far primarily been designed for and evaluated in wired networks. However, such tools should also be examined in wireless networks since the use of, e. g., mobile broadband is rapidly increasing. The properties of wired and wireless links differ substantially, which affect the performance of the tools. We have made active-probing experiments over a high-speed downlink shared channel, which is used for High-Speed Downlink Packet Access (HSDPA) in the mobile communication technology UMTS, and over a forward traffic channel in CDMA2000 1xEV-DO. Both experiments were performed over commercial networks. They show that one cannot always expect uniform per-packet processing over the radio channel in mobile networks, which is expected by many probing tools. This reduces the reliability of the available-bandwidth estimates, however we suggest how this can be handled. Finally, the mobile-network measurements are compared to experiments performed in an IEEE 802.11 wireless LAN, where the radio channel does not create the same packet-processing behaviour. We also discuss the possibility of using the probe traffic for the purpose of identifying the communication technology at the bottleneck of the network path, assumed this is a wireless broadband link, by mapping specifications of standardised communication technologies to observed probe-traffic characteristics.
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| 6. |
- Ekelin, Svante, et al.
(författare)
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Baryons from diquarks in e+e- annihilation
- 1983
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Ingår i: Physical Review D. Particles and fields. - 0556-2821 .- 1089-4918. ; 28:1, s. 257-259
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We find experimental support for the view that diquarks appear only as spin-0 objects. When their production rate in the color field of a quark from e+e- annihilation is described by the appropriate Schwinger formula for scalars, it turns out that they must be substantially lighter than earlier believed in order to explain the baryon yield.
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| 7. |
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| 8. |
- Ekelin, Svante, et al.
(författare)
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Hadron pT correlations in quark jets
- 1986
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 56:22, s. 2428-2428
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Tidskriftsartikel (refereegranskat)
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| 9. |
- Ekelin, Svante, et al.
(författare)
-
Indications of hard diquarks in e+e- annihilation
- 1984
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 30:11, s. 2310-2315
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Tidskriftsartikel (refereegranskat)abstract
- It is suggested that very small spin-0 diquarks are directly produced in e+e- annihilation and then fragment into leading baryons and other hadrons. The most influential diquark is the charmed diquark (uc), due to its high charge. It gives a sizable contribution to the hadronic R factor and to the two-jet angular distribution in the energy region W=4-8 GeV. At these energies, a careful study of Λ production would provide the best additional test of the model.
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| 10. |
- Ekelin, Svante, et al.
(författare)
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Large-pT protons from constituent diquark scattering
- 1984
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 149:6, s. 509-513
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Tidskriftsartikel (refereegranskat)abstract
- Recent data from the CERN ISR on the fractional proton yield in pp collisions are explained within the Stockholm diquark model. Describing the proton as a u(ud)0 system, the observed high magnitude and fall-off pT, θ and √s of the proton yield are natural consequences of constituent diquark elastic scattering. The pT and θ dependence favour a value of around 10 GeV2/c2 for the size parameter in the diquark form factor, corresponding to a diquark rms radius of around 0.2 fm. This is consistent with earlier results of the model applied to deep inelastic lepton-nucleon scattering and e+e- annihilation
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| 11. |
- Ekelin, Svante, et al.
(författare)
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Real-Time Measurement of End-to-End Available Bandwidth using Kalman Filtering
- 2006
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Ingår i: 10th IEEE/IFIP Network Operations and Management Symposium, 2006. NOMS 2006.. - Piscataway, New Jersey, USA : IEEE Computer Society. - 1424401429 - 9781424401420 ; , s. 73-84
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Konferensbidrag (refereegranskat)abstract
- This paper presents a new method, BART (bandwidth available in real-time), for estimating the end-to-end available bandwidth over a network path. It estimates bandwidth quasi-continuously, in real-time. The method has also been implemented as a tool. It relies on self-induced congestion, and repeatedly samples the available bandwidth of the network path with sequences of probe packet pairs, sent at randomized rates. BART requires little computation in each iteration, is lightweight with respect to memory requirements, and adds only a small amount of probe traffic. The BART method uses Kalman filtering, which enables real-time estimation (a.k.a. tracking). It maintains a current estimate, which is incrementally improved with each new measurement of the inter-packet time separations in a sequence of probe packet pairs. The measurement model has a strong non-linearity, and would not at first sight be considered suitable for Kalman filtering, but we show how this non-linearity can be handled. BART may be tuned according to the specific needs of the measurement application, such as agility vs. stability of the estimate. We have tested an implementation of BART in a physical test network with carefully controlled cross traffic, with good accuracy and agreement. Test measurements have also been performed over the Internet. We compare the performance of BART with that of pathChirp, a state-of-the-art tool for measuring end-to-end available bandwidth in real-time
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| 12. |
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| 13. |
- Ekelin, Svante, et al.
(författare)
-
Real-time measurement of end-to-end available bandwidth using Kalman filtering
- 2006. - 1
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a new method, BART (Bandwidth Available in Real-Time), for estimating the end-to-end available bandwidth over a network path. It estimates bandwidth quasi-continuously, in real-time. The method has also been implemented as a tool. It relies on self-induced congestion, and probes the network path with trains of probe packets, sent at randomized rates. BART requires little computation in each iteration, is light-weight with respect to memory requirements, and adds only a small amount of probe traffic. The BART method is based on Kalman filtering, which enables real-time estimation (a.k.a. tracking) with optimum performance under general conditions. It maintains a current estimate, which is incrementally improved with each new measurement of the inter-packet time separations in a probe packet train. The measurement model has a strong non-linearity, and would not at first sight be considered suitable for Kalman filtering, but we show how this non-linearity can be handled. BART may be tuned according to the specific needs of the measurement application, such as agility vs. stability of the estimate, and the desired time-scale on which to track traffic fluctuations. We have tested BART in a physical test network with carefully controlled cross traffic, with good accuracy and agreement. Test measurements have also been performed over the Internet. We compare the performance of BART with that of pathChirp, a state-of-the-art tool for measuring end-to-end available bandwidth in real-time.
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| 14. |
- Ekelin, Svante, et al.
(författare)
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The Failure of 'The Failure of Poisson Modeling' for Internet Bandwidth Measurements
- 2005. - 1
-
Konferensbidrag (refereegranskat)abstract
- There is a classic paper, which claims that many parameters of network traffic are best modeled by stochastic distributions with infinite variance. We believe that although this paper is correct, it has commonly been overinterpreted. It is true that some distributions have infinite variance, but not all. There are important cases where distributions of traffic parameters have finite variance. As an example, we show that the end-to-end available bandwidth must have finite variance, outline a method for measuring it, and present some experimental data.
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| 15. |
- Enström, Daniel, et al.
(författare)
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A Quark matter dominated universe
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a new scenario for the development of the Universe after the Big Bang, built on the conjecture that a vast majority of the primordial quark matter did not undergo a phase transition to normal nuclear matter, but rather split up into massive quark objects that remained stable. Hence, such primordial quark matter would make up the so-called dark matter. We discuss, mostly in qualitative terms, the consequences for galaxy formation, the origin of normal matter, the occurrence of massive black-holes in galactic centres and the cosmic gamma-ray bursts.
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| 16. |
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| 17. |
- Fredriksson, Sverker, et al.
(författare)
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A potential diquark in the proton
- 1997
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Ingår i: Zeitschrift für Physik C Particles and Fields. - : Springer Science and Business Media LLC. - 0170-9739 .- 1431-5858. ; 75:1, s. 107-111
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Tidskriftsartikel (refereegranskat)abstract
- A non-relativistic, QCD-based, potential quark model for the proton and the neutron inevitably predicts a spin-0 diquark structure with an rms radius of the order of 0.35rfm or smaller. We prove this by solving the (S wave) hamiltonian by De Rújula et al. with variational methods. It is essential to include all quark interactions and to use realistic test wave-functions. The protondelta mass difference, the magnetic moments and the nucleon charge radii can be reproduced only with wave functions that contain a mixture of quark-diquark and three-quark states. Approaches with just a quark-diquark component give incorrect magnetic moments, while those without diquarks lead to a too low proton-delta mass difference.
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| 18. |
- Fredriksson, Sverker, et al.
(författare)
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Is dark matter made up of massive quark objects?
- 1999
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Ingår i: Dark matter in astrophysics and particle physics 1998. - Bristol : IOP Publishing Ltd. - 0750306343 ; , s. 651-658
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Konferensbidrag (refereegranskat)abstract
- We suggest that dark matter is made up of massive quark objects that have survived from the Big Bang, representing the ground state of "baryonic'' matter. Hence, there was no overall phase transition of the original quark matter, but only a split-up into smaller objects. We speculate that normal hadronic matter comes about through enforced phase transitions when such objects merge or collide, which also gives rise to the cosmic gamma-ray bursts.
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| 19. |
- Fredriksson, Sverker, et al.
(författare)
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New ideas on the proton-neutron differences in deep inelastic structure functions
- 1985
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 162:4-6, s. 373-378
-
Tidskriftsartikel (refereegranskat)abstract
- It is shown how future data from deep inelastic scattering of charged leptons on protons and neutrons can be used to discriminate between the two main possible scale-breaking QCD effects - perturbative gluon processes and non-perturbative diquark formation. Current data from the Stanford Linear Accelerator Center and from CERN on the structure function combinations Fp2-Fn2, Fn2/Fp2 and σL/σT are in line with both the Stockholm diquark model and perturbative QCD, considering the low statistics as well as the possibility of a substantial normalisation error between the two data sets. This calls for a new high-statistics experiment on a deuterium target before any definite conclusions can be made.
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| 20. |
- Hartikainen, Erik, 1977-, et al.
(författare)
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Adjustment of the BART Kalman Filter to Improve Real-Time Estimation of End-to-End Available Bandwidth
- 2005
-
Ingår i: Proceedings of SNCNW 2005. - Sweden : SNCNW. ; , s. 56-
-
Konferensbidrag (refereegranskat)abstract
- This paper concerns simulation results using the network simulator ns-2 to validate the end-to-end available bandwidth estimation ability of the real-time measurement tool BART (Bandwidth Available in Real-Time). In addition to an active probing scheme, this method applies Kalman filtering in order to produce available bandwidth estimates. Simulation results show that clever use of an adjustable filter parameter yields great possibilities of achieving highly accurate estimates, even in the presence of harsh circumstances.
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| 21. |
- Hartikainen, Erik, 1977-, et al.
(författare)
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Change Detection and Estimation for Network-Measurement Applications
- 2007
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Ingår i: Proceedings of the 2nd ACM workshop on Performance monitoring and measurement of heterogeneous wireless and wired networks. - New York, NY, USA : ACM Digital Library. - 9781595938053 ; , s. 1-10
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a method for improving filter-based network-state estimation by adding detection and estimation of sudden changes in the system state. This can be of benefit in various contexts, e.g. in network management and adaptive streaming applications. In particular, it is shown that the performance of available-bandwidth estimation can be significantly enhanced by employing change detection in conjunction with a filter-based estimator. The use of filtering makes it feasible to track the communication network state and to estimate selected properties in real-time. In addition, filter-based methods may be combined with change detection in order to overcome the trade-off regarding stable estimation versus speed of adaptation to change. We discuss filtering and change detection in general, and present the novel approach of combining the filter-based available-bandwidth estimator BART with the Generalized Likelihood Ratio (GLR) change-detection test, which estimates both the time and magnitude of changes.
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| 22. |
- Hartikainen, Erik, 1977-, et al.
(författare)
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Enhanced network-state estimation using change detection
- 2006
-
Ingår i: Proceedings - Conference on Local Computer Networks, LCN. - Piscataway, New Jersey, USA : IEEE Computer Society. - 1424404185 - 9781424404186 - 1424404193 ; , s. 683-693
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Konferensbidrag (refereegranskat)abstract
- This paper presents the concept of change detection for filter-based network-state estimation. This could be useful in various contexts; two examples are network management and adaptive applications. In particular, it is shown that the performance of availablebandwidth estimation can be significantly enhanced by employing a change-detection technique in conjunction with a filter-based estimator. By using filter-based approaches, it is possible to track the state of communication systems, and to estimate network properties in real-time. A virtue of filter-based methods is the ability to enhance the estimation performance by combining them with change detection. This makes it feasible to overcome the tradeoffs regarding speed of adaptation to changes versus stable estimation. We discuss filtering and change detection in general, and illustrate the power of this combination with the filter-based available-bandwidth estimator BART enhanced by the light-weight change-detection test CUSUM.
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| 23. |
- Hartikainen, Erik, 1977-, et al.
(författare)
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Tuning the Temporal Characteristics of a Kalman-Filter Method for End-to-End Bandwidth Estimation
- 2006
-
Ingår i: 4th IEEE/IFIP Workshop on End-to-End Monitoring Techniques and Services, 2006. - Piscataway, New Jersey, USA : IEEE Press. - 1424401453 ; , s. 58-65
-
Konferensbidrag (refereegranskat)abstract
- In this paper we present a way of tuning the temporal characteristics of a new available-bandwidth estimation method, BART. The estimation engine in this method is Kalman-filter based. A current estimate of the available bandwidth is maintained, and for each new sequence of probe packet pairs an updated estimate is produced. The main input parameters needed by the Kalman filter are the variance of the measurement noise and the covariance of the process noise. The former is measured by the method, whereas the latter is not in general attainable by analytical or empirical investigation. Instead, it is reasonable to treat this as a tunable parameter. We discuss how the temporal characteristics of the tracking of end-to-end available bandwidth may be tuned.
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