| 1. |
- Mahata, Kaushik, 1973-
(författare)
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Estimation Using Low Rank Signal Models
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Designing estimators based on low rank signal models is a common practice in signal processing. Some of these estimators are designed to use a single low rank snapshot vector, while others employ multiple snapshots. This dissertation deals with both these cases in different contexts. Separable nonlinear least squares is a popular tool to extract parameter estimates from a single snapshot vector. Asymptotic statistical properties of the separable non-linear least squares estimates are explored in the first part of the thesis. The assumptions imposed on the noise process and the data model are general. Therefore, the results are useful in a wide range of applications. Sufficient conditions are established for consistency, asymptotic normality and statistical efficiency of the estimates. An expression for the asymptotic covariance matrix is derived and it is shown that the estimates are circular. The analysis is extended also to the constrained separable nonlinear least squares problems. Nonparametric estimation of the material functions from wave propagation experiments is the topic of the second part. This is a typical application where a single snapshot vector is employed. Numerical and statistical properties of the least squares algorithm are explored in this context. Boundary conditions in the experiments are used to achieve superior estimation performance. Subsequently, a subspace based estimation algorithm is proposed. The subspace algorithm is not only computationally efficient, but is also equivalent to the least squares method in accuracy. Estimation of the frequencies of multiple real valued sine waves is the topic in the third part, where multiple snapshots are employed. A new low rank signal model is introduced. Subsequently, an ESPRIT like method named R-Esprit and a weighted subspace fitting approach are developed based on the proposed model. When compared to ESPRIT, R-Esprit is not only computationally more economical but is also equivalent in performance. The weighted subspace fitting approach shows significant improvement in the resolution threshold. It is also robust to additive noise.
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| 2. |
- Viberg, Olga, 1982-
(författare)
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Design and use of mobile technology in distance language education : Matching learning practices with technologies-in-practice
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on the adaptation of formal education to people’s technology- use patterns, theirtechnology-in-practice, where the ubiquitous use of mobile technologies is central. The research question is: How can language learning practices occuring in informal learning environments be effectively integrated with formal education through the use of mobile technology? The study investigates the technical, pedagogical, social and cultural challenges involved in a design science approach.The thesis consists of four studies. The first study systematises MALL (mobile-assisted language learning) research. The second investigates Swedish and Chinese students’ attitudes towards the use of mobile technology in education. The third examines students’ use of technology in an online language course, with a specific focus on their learning practices in informal learning contexts and their understanding of how this use guides their learning. Based on the findings, a specifically designed MALL application was built and used in two courses. Study four analyses the app use in terms of students’ perceived level of self-regulation and structuration.The studies show that technology itself plays a very important role in reshaping peoples’ attitudes and that new learning methods are coconstructed in a sociotechnical system. Technology’s influence on student practices is equally strong across borders. Students’ established technologies-in-practice guide the ways they approach learning. Hence, designing effective online distance education involves three interrelated elements: technology, information, and social arrangements. This thesis contributes to mobile learning research by offering empirically and theoretically grounded insights that shift the focus from technology design to design of information systems.
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| 3. |
- Drevin, Jennifer, et al.
(författare)
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Patients' views on using human embryonic stem cells to treat Parkinson's disease : an interview study
- 2022
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Ingår i: BMC Medical Ethics. - : Springer Nature. - 1472-6939 .- 1472-6939. ; 23
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Tidskriftsartikel (refereegranskat)abstract
- Background: Human embryonic stem cells (hESC) as a source for the development of advanced therapy medicinal products are considered for treatment of Parkinson's disease (PD). Research has shown promising results and opened an avenue of great importance for patients who currently lack a disease modifying therapy. The use of hESC has given rise to moral concerns and been the focus of often heated debates on the moral status of human embryos. Approval for marketing is still pending.Objective: To Investigate the perspectives and concerns of patients with PD, patients being the directly concerned stakeholders in the ethical discussion.Methods: Qualitative semi-structured interviews related to this new therapy in seventeen patients from two Swedish cities.Results: The participants expressed various interests related to the use of human embryos for development of medicinal therapies; however, overall, they were positive towards the use of hESC for treatment of PD. It was deemed important that the donating woman or couple made the choice to donate embryos voluntarily. Furthermore, there were concerns that the industry does not always prioritise the patient over profit; thus, transparency was seen as important.
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| 4. |
- Hagberg-Persson, Barbro, 1950-
(författare)
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Barns mångfaldiga språkresurser i mötet med skolan
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation investigates language proficiency in children aged 6–8 in their contact with school – both from an oral and written language perspective. The study is predicated on the current situation in Sweden, where school classes today have a more heterogeneous composition than ever before. This means that the focus of this study is not just on the age and sex of the children but also on their different language backgrounds. The aim of the dissertation is to map out the development of the oral and written proficiency of both monolingual and bilingual children at the beginning of school, individually and in groups. This study belongs in essence to the field of research known as qualitative school ethnography. Material for the study was gathered during a single school year in a school located in a mid-sized Swedish town. To examine the children’s language proficiency, three different analytical instruments were combined to produce more reliable results. The results show that the children’s Swedish proficiency varies in a similar way across the group of informants regardless of language background. With respect to the bilingual children’s proficiency in their mother tongue/first language, the results show that only one child had command in a language other than Swedish that was sufficient for his age. The study confirms that a monolingual norm prevails in the school that the study was carried out in, which means that it is no different than other Swedish schools for which previous studies mapped out language relations. The results also show that the children’s different language backgrounds do not affect the interaction pattern during small group activities; however, the age and sex of the children do. The results further show that the choice of small group activities and the formation of heterogeneous small groups allow the children the opportunity to solve tasks in which they can support each other and benefit from each other’s different competencies.
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| 5. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
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Quantized Uplink Massive MIMO Systems with Linear Receivers
- 2020
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Ingår i: IEEE International Conference on Communications. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728150895 ; 2020-June
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Konferensbidrag (refereegranskat)abstract
- This paper considers the uplink of a single-cell multi-user massive multiple-input multiple-output (MIMO) system. Each receiver antenna of the base station is assumed to be equipped with a pair of analog-to-digital converters (ADCs) to quantize the real and imaginary part of the received signal. We propose a novel Bussgang-based weighted zero-forcing (B-WZF) receiver, which distinguishes the clipping and granular distortion. Numerical results demonstrate that for sufficiently high SNR and users that do not experience deep large-scale fading, the B-WZF brings significant performance gain over existing linear receivers in the literature, when the training sequence length is higher than the number of users. © 2020 IEEE.
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| 6. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
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Reconstruction of Clipped Signals in Quantized Uplink Massive MIMO Systems
- 2020
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers Inc.. - 0090-6778 .- 1558-0857. ; 68:5, s. 2891-2905
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the uplink of a single-cell multiuser massive multiple-input multiple-output system. Each receiver antenna of the base station (BS) is assumed to be equipped with a pair of analog-to-digital converters to quantize the real and imaginary part of the received signal. We propose a novel clipping-aware receiver (CA-MMSE), which performs minimum mean square error (MMSE) reconstruction only on the clipped received samples, while the granular samples are left unchanged after the quantization. On this basis, we present an iterative algorithm to implement the CA-MMSE receiver and derive a sufficient condition for its geometrical convergence to a fixed point. We show that as long as the number of BS antennas or the quantization resolution is sufficiently high, then, the performance of the CA-MMSE is as good as the optimal MMSE receiver which reconstructs all quantized received symbols. Additionally, we propose a novel Bussgang-based weighted zero-forcing (B-WZF) receiver which distinguishes the clipping and granular distortion and it is shown that as long as the received training symbols per antenna are correlated, the CA-MMSE brings significant improvements compared to conventional receivers in the literature while for users that do not experience deep large-scale fading the simpler B-WZF is near to the CA-MMSE for sufficiently high signal-to-noise ratio and quantization resolution. © 1972-2012 IEEE.
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| 7. |
- Pesavento, Marius, et al.
(författare)
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Three More Decades in Array Signal Processing Research : An optimization and structure exploitation perspective
- 2023
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Ingår i: IEEE signal processing magazine (Print). - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-5888 .- 1558-0792. ; 40:4, s. 92-106
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Tidskriftsartikel (refereegranskat)abstract
- The signal processing community is currently witnessing the emergence of sensor array processing and direction-of-arrival (DoA) estimation in various modern applications, such as automotive radar, mobile user and millimeter wave indoor localization, and drone surveillance, as well as in new paradigms, such as joint sensing and communication in future wireless systems. This trend is further enhanced by technology leaps and the availability of powerful and affordable multiantenna hardware platforms. © 1991-2012 IEEE.
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| 8. |
- Schenck, David, et al.
(författare)
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Full covariance fitting DOA estimation using partial relaxation framework
- 2019
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Ingår i: European Signal Processing Conference. - : European Signal Processing Conference, EUSIPCO. - 9789082797039
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Konferensbidrag (refereegranskat)abstract
- The so-called Partial Relaxation approach has recently been proposed to solve the Direction-of-Arrival estimation problem. In this paper, we extend the previous work by applying Covariance Fitting with a data model that includes the noise covariance. Instead of applying a single source approximation to multi-source estimation criteria, which is the case for MUSIC, the conventional beamformer, or the Capon beamformer, the Partial Relaxation approach accounts for the existence of multiple sources using a non-parametric modification of the signal model. In the Partial Relaxation framework, the structure of the desired direction is kept, whereas the sensor array manifold corresponding to the remaining signals is relaxed [1], [2]. This procedure allows to compute a closed-form solution for the relaxed signal part and to come up with a simple spectral search with a significantly reduced computational complexity. Unlike in the existing Partial Relaxed Covariance Fitting approach, in this paper we utilize more prior-knowledge on the structure of the covariance matrix by also considering the noise covariance. Simulation results show that, the proposed method outperforms the existing Partial Relaxed Covariance Fitting method, especially in difficult conditions with small sample size and low Signal-to-Noise Ratio. Its threshold performance is close to that of Deterministic Maximum Likelihood, but at significantly lower cost. © 2019 IEEE
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| 9. |
- Schölin Bywall, Karin, et al.
(författare)
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Patients accept therapy using embryonic stem cells for Parkinson's disease : a discrete choice experiment
- 2023
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Ingår i: BMC Medical Ethics. - : BioMed Central (BMC). - 1472-6939 .- 1472-6939. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: New disease-modifying ways to treat Parkinson's disease (PD) may soon become a reality with intracerebral transplantation of cell products produced from human embryonic stem cells (hESCs). The aim of this study was to assess what factors influence preferences of patients with PD regarding stem-cell based therapies to treat PD in the future.Methods: Patients with PD were invited to complete a web-based discrete choice experiment to assess the importance of the following attributes: (i) type of treatment, (ii) aim of treatment, (iii) available knowledge of the different types of treatments, (iv) effect on symptoms, and (v) risk for severe side effects. Latent class conditional logistic regression models were used to determine preference estimates and heterogeneity in respondents' preferences.Results: A substantial difference in respondents' preferences was observed in three latent preference patterns (classes). "Effect on symptoms" was the most important attribute in class 1, closely followed by "type of treatment," with medications as preferred to other treatment alternatives. Effect on symptoms was also the most important attribute in class 2, with treatment with hESCs preferred over other treatment alternatives. Likewise for class 3, that mainly focused on "type of treatment" in the decision-making. Respondents' class membership was influenced by their experience in treatment, side effects, and advanced treatment therapy as well as religious beliefs.Conclusions: Most of the respondents would accept a treatment with products emanating from hESCs, regardless of views on the moral status of embryos. Preferences of patients with PD may provide guidance in clinical decision-making regarding treatments deriving from stem cells.
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| 10. |
- Trinh-Hoang, Minh, et al.
(författare)
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CramÉr-rao Bound for DOA Estimators under the Partial Relaxation Framework
- 2019
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Ingår i: 2019 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP). - : IEEE. - 9781479981311 ; , s. 4469-4473
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Konferensbidrag (refereegranskat)abstract
- In this paper, the Cramer-Rao Bound for the Direction-of-Arrival parameter under the partial relaxation framework is derived. We introduce a non-redundant parameterization of the signal model corresponding to the partial relaxation framework, in which the array structure in part of the steering matrix is neglected while the rank of the relaxed steering matrix is maintained. We prove that the stochastic Cramer-Rao Bound for the Direction-of-Arrival parameter under the partial relaxation signal model is lower-bounded by that of the conventional stochastic Cramer-Rao Bound. Furthermore, we prove that the partial relaxation estimator for the Weighted Subspace Fitting criterion asymptotically achieves the conventional Cramer-Rao Bound in the case of uncorrelated source signals.
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