| 1. |
- Özyagci, Ali, 1982-, et al.
(författare)
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Distributed multichannel random access networks with selfish users
- 2010
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Ingår i: Proceedings of the Fifth International Conference on Cognitive Radio Oriented Wireless Networks Communications (CROWNCOM), 2010. - 9781424458851 ; , s. 5577687-
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Konferensbidrag (refereegranskat)abstract
- Dynamic spectrum access (DSA) schemes allow the users to share spectrum resources by taking advantage of the variations in spectrum demand over time and space. Carrying out dynamic spectrum allocation centrally, however, can be a complex task. For this reason, distributed schemes in which users can access the available channels independently may be preferable to centralized DSA schemes. Cognitive radio systems, which enable user terminals to sense their environment and form their action accordingly, are particularly well-suited for distributed systems. On the other hand, the freedom in distributed schemes gives the users the option to act selfishly, which has decisive effects on system performance. In this paper we consider a distributed multichannel wireless random access system where users selfishly access the channels in the system. We analyze the behavior of the selfish users by modeling the system as a non-cooperative game and we identify all stable operating points (Nash equilibria) of this game. We then compare the performance of this system with a number of cooperative distributed DSA schemes in terms of user utilities. Our results show that the performance of the selfish multichannel random access system can be comparable to cooperative schemes.
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| 2. |
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| 3. |
- Özeren, Hüsamettin Deniz, et al.
(författare)
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Role of Hydrogen Bonding in Wheat Gluten Protein Systems Plasticized with Glycerol and Water
- 2021
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 232, s. 124149-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Many biopolymers are stiff and brittle and require plasticizers. To optimize the choice and amount of plasticizer, the mechanisms behind plasticization need to be understood. For polar biopolymers, such as polysaccharides and proteins, plasticization depends to a large extent on the hydrogen bond network. In this study, glycerol-plasticized protein systems based on wheat gluten were investigated, in combination with the effects of water. The methodology was based on a combination of mechanical tests and molecular dynamics simulations (MD). The simulations accurately predicted the glycerol content where the experimental depression in glass transition temperature (Tg) occurred (between 20 and 30 wt.% plasticizer). They also predicted the strong water-induced depression in Tg. Detailed analysis revealed that in the dry system, the main effect of glycerol was to break protein-protein hydrogen bonds. In the moist system, glycerol was partly outcompeted by water in forming hydrogen bonds with the protein, making the glycerol plasticizer less effective than in dry conditions. These results show that MD can successfully predict the plasticizer concentration at which the onset of efficient plasticization occurs. MD can therefore be an important tool for understanding plasticizer mechanisms, even in a complex system, on a level of detail that is impossible with experiments.
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| 4. |
- Adler, Niclas, et al.
(författare)
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- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Özdogan, Özgecan, 1992-
(författare)
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Analysis of Cellular and Cell-Free Massive MIMO with Rician Fading
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The data traffic in cellular networks has grown at an exponential pace for decades. This trend will most probably continue in the future, driven by new innovative applications. One of the key enablers of future cellular networks is the massive MIMO technology. A massive MIMO base station is equipped with a massive number (e.g., a hundred) of individually steerable antennas, which can be effectively used to serve tens of user equipments simultaneously on the same time-frequency resource. It can provide a notable enhancement of both spectral efficiency and energy efficiency in comparison with conventional MIMO.In the literature, the achievable spectral efficiencies of massive MIMO systems with a practical number of antennas have been rigorously characterized and optimized when the channels are subject to either spatially uncorrelated or correlated Rayleigh fading. Typically, in massive MIMO research, i.i.d. Rayleigh fading or less frequently free-space line-of-sight (LoS) channel models are assumed since they simplify the analysis. Massive MIMO technology is able to support both rich scattering and LoS scenarios. However, practical channels can consist of a combination of an LoS path and a correlated small-scale fading component caused by a finite number of scattering clusters that can be modeled by spatially correlated Rician fading. In the first part of this thesis, we consider a multi-cell scenario with spatially correlated Rician fading channels and derive closed-form achievable spectral efficiency expressions for different signal processing techniques.Alternatively, a massive number of antennas can be spread over a large geographical area and this concept is called cell-free massive MIMO. In the canonical form of cell-free massive MIMO, the access points cooperate via a fronthaul network to spatially multiplex the users on the same time-frequency resource using network MIMO methods that only require locally obtained channel state information. Cellfree massive MIMO is a densely deployed system. Hence, the probability of having an LoS path between some access points and the users is quite high. In the second part of this thesis, we consider a practical scenario where the channels between the access points and the users are modeled with Rician fading.
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| 6. |
- Kokk, Gary, 1963, et al.
(författare)
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- 2009
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Ingår i: 20th “Scandinavian Academy of Management”. 19-21 August, 2009. Turku, Finland..
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Konferensbidrag (refereegranskat)
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| 7. |
- Aad, G., et al.
(författare)
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- 2015
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Tidskriftsartikel (refereegranskat)
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| 8. |
- Rodriguez-Rojas, F., et al.
(författare)
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Oxidation behaviour of pressureless liquid-phase-sintered α-SiC with additions of 5Al2O3 + 3RE2O3 (RE = La, Nd, Y, Er, Tm, or Yb)
- 2010
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 30:15, s. 3209-3217
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation behaviour of pressureless liquid-phase-sintered (PLPS) α-SiC was investigated as a function of the sintering additives of 5Al2O3 + 3RE2O3 (RE = La, Nd, Y, Er, Tm, or Yb) by thermogravimetry experiments in oxygen at 1075–1400 °C for up to 22 h. It was found that the oxidation is in all cases passive and protective, with kinetics governed by the arctan-rate law. This is because the PLPS SiC ceramics develop oxide scales having no cracks or open porosity and accordingly prevent the parent material from direct contact with oxygen. In addition, these oxide scales crystallize gradually during the exposure to the oxidizing atmosphere with the attendant reduction in the amorphous cross-section available for oxygen diffusion. It was also found that the rate-limiting mechanism of the oxidation is outward diffusion of RE3+ cations from the intergranular phase into the oxide scale, and that the activation energy of the oxidation increases with increasing size of the RE3+ cation. It was also observed that the oxidation of PLPS SiC increases with increasing size of the RE3+ cation, an effect that is especially marked for cation sizes above 0.9 Å because the oxidation rate becomes several orders of magnitude faster. This trend is attributable to the oxide scales being more crystalline, and containing crystals that are more refractory and amorphous residual phases that are more viscous as the size of the RE3+ cation decreases. Finally, implications for the design of PLPS SiC ceramics with superior oxidation resistance are discussed.
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| 9. |
- Juhlin, Greger
(författare)
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Development and Application of Laser Diagnostics for Studies of Phenomena Related to IC Engine Combustion
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Various laser diagnostic techniques have been developed and demonstrated for engine, or engine-related measurements. The experimental work is presented in Chapter 3 and in Papers I-VII. In Chapter 3, imaging of soot in a running compression-ignition (CI) is described. Four different approaches were applied with the aim of investigating the applicability of these approaches in a running engine. In Paper I, Planar Laser-Induced Fluorescence (PLIF) was applied in a running spark ignition (SI) engine for measurements of the fuel concentration and homogeneity in the vicinity of the spark gap prior to ignition. The aim was to find out how the fuel distribution influences the cycle-to-cycle variations of the engine. In Paper II, PLIF of water was applied in a running engine to investigate the influence of residual gases in the vicinity of the spark gap prior to ignition. In Paper III is reported a basic investigation of the potential of PLIF for the study of water as a marker for residual gas in engines. Special care was taken in studying the effects of a focused laser beam in combination with a two-photon transition which arises in the excitation of water at 248 nm. In Paper IV is described how a combination of PLIF and spontaneous Raman scattering can be used for simultaneous imaging of vapour and liquid phase water. In Paper V, the application of PLIF to investigate the emissions of hydrocarbons in the exhaust of small two-stroke engines is described. Cycle-resolved, 2D measurements were conducted in order to find out when, during the stroke, the hydrocarbons are emitted. Cycle-resolved spectral measurements gave information on the species emitted at different crank angle positions. In Paper VI is demonstrated how phosphor thermometry can be applied to measure the temperature of a falling water droplet. Finally, in Paper VII, phosphor thermometry was applied to perform two-dimensional surface temperature measurements in a running optically accessible engine.
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| 10. |
- Ravinet, Mark, 1986, et al.
(författare)
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Unique mitochondrial DNA lineages in Irish stickleback populations: cryptic refugium or rapid recolonization?
- 2014
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 4:12, s. 2488-2504
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Tidskriftsartikel (refereegranskat)abstract
- Repeated recolonization of freshwater environments following Pleistocene glaciations has played a major role in the evolution and adaptation of anadromous taxa. Located at the western fringe of Europe, Ireland and Britain were likely recolonized rapidly by anadromous fishes from the North Atlantic following the last glacial maximum (LGM). While the presence of unique mitochondrial haplotypes in Ireland suggests that a cryptic northern refugium may have played a role in recolonization, no explicit test of this hypothesis has been conducted. The three-spined stickleback is native and ubiquitous to aquatic ecosystems throughout Ireland, making it an excellent model species with which to examine the biogeographical history of anadromous fishes in the region. We used mitochondrial and microsatellite markers to examine the presence of divergent evolutionary lineages and to assess broad-scale patterns of geographical clustering among postglacially isolated populations. Our results confirm that Ireland is a region of secondary contact for divergent mitochondrial lineages and that endemic haplotypes occur in populations in Central and Southern Ireland. To test whether a putative Irish lineage arose from a cryptic Irish refugium, we used approximate Bayesian computation (ABC). However, we found no support for this hypothesis. Instead, the Irish lineage likely diverged from the European lineage as a result of postglacial isolation of freshwater populations by rising sea levels. These findings emphasize the need to rigorously test biogeographical hypothesis and contribute further evidence that postglacial processes may have shaped genetic diversity in temperate fauna.
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