| 1. |
- Adler, Niclas, et al.
(författare)
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- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
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| 7. |
- Özdogan, Özgecan, et al.
(författare)
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Massive MIMO With Spatially Correlated Rician Fading Channels
- 2019
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 67:5, s. 3234-3250
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers multi-cell massive multiple-input multiple-output systems, where the channels are spatially correlated Rician fading. The channel model is composed of a deterministic line-of-sight path and a stochastic non-line-of-sight component describing a practical spatially correlated multipath environment. We derive the statistical properties of the minimum mean squared error (MMSE), element-wise MMSE, and least-square channel estimates for this model. Using these estimates for maximum ratio combining and precoding, rigorous closed-form uplink (UL) and downlink (DL) achievable spectral efficiency (SE) expressions are derived and analyzed. The asymptotic SE behavior, when using the different channel estimators, are also analyzed. The numerical results show that the SE is higher when using the MMSE estimator than that of the other estimators, and the performance gap increases with the number of antennas.
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| 8. |
- Özbek, Nurgül, et al.
(författare)
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Markets for Promoting Innovation in Health Care? : A Market Practice Study of Public Procurement of Innovation (PPI)
- 2023
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Ingår i: Novation : Critical Studies of Innovation. - : Curitiba PR: Universidade Federal do Paraná Setor de Ciências Sociais Aplicadas. - 2562-7147. ; , s. 86-114
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This article critically analyzes public procurement of innovation (PPI) as an instance of using markets or market-like aspects as a means to resolve public concerns. It reports findings from a case of procuring radiation therapy equipment for a university hospital in Stockholm, Sweden. By extending a line of literature built on economic sociology as well as science and technology studies (STS), the study elaborates on public actors' efforts in framing markets to promote innovation. The case illustrates how the participating actors constructed the notion of innovativeness to be introduced into health care as means of addressing various public concerns. It also reveals the intended—and unintended— consequences of PPI as manifested in various actors' claims on the value of PPI realized in practice. The study suggests that it is extremely difficult to frame a market for the realization of innovation via procurement as a policy instrument because we cannot predict the ultimate impacts of devices and practices employed in such initiatives. By formulating a practice-based critique of PPI, our study invites important questions about the potentiality of such instruments for governing innovation without delimiting their consequences to the successor failure dichotomy as prescribed in predefined tools and strategies.
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| 9. |
- Öztas, Ahmet M., et al.
(författare)
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Spacetime curvature is important for cosmology constrained with supernova emissions
- 2008
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Ingår i: International journal of theoretical physics. - : Springer Science and Business Media LLC. - 0020-7748 .- 1572-9575. ; 47:9, s. 2464-2478
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Tidskriftsartikel (refereegranskat)abstract
- We investigate universe expansion models as functions of emission frequency ratio decline rather than redshift z, using the latest on-line, self-consistent data from 192 supernovae. We present results for simpler and some current models of cosmology, including those with dark energy (standard model) and a recent model correcting for the effect of a small time-dependent, emission frequency increase with lookback. This new model, with a gentle lookback decline of the Planck constant, and the standard model fit the data with similar confidence according to Bayesian Information Criteria. The standard model tends towards solutions high in matter density while remaining flat, but models without dark energy tend towards dilute universes with significant spacetime and curvature and a smaller Hubble constant. We conclude the normalized spacetime parameter, Ω k , should not be ignored and it includes the combined contributions of huge spacetime magnitude and curvature.
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| 10. |
- Edvardsson, Bo, et al.
(författare)
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- 2008
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Konferensbidrag (refereegranskat)
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