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Sökning: WFRF:(Johansson C)

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41.
  • Özkahraman, Özer, 1992- (författare)
  • Multi-Agent Mission Planning and Execution for Small Autonomous Underwater Vehicles
  • 2023
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Our planet is mostly covered in water, most of it still unexplored.In order to understand our environment better, oceanographers have been mapping and monitoring these waters using ship-mounted sensors and wired vehicles with limited range compared to the vastness of the oceans.The limited range and dependence on manned support vehicles has kept missions expensive and infrequent.To solve this problem, the sensors need to become independent of support vehicles, they need to venture into completely unexplored, unmapped regions of the seas by themselves and safely return with the data.This is where autonomous underwater vehicles (AUVs) have started to make a difference.In this thesis we investigate how multiple small AUVs can be utilized to efficiently and accurately sense very large volumes of water.Water absorbs electromagnetic radiation, meaning satellite-based global positioning systems (we will use GPS to refer to any such system), wide-angle cameras and radio communications are infeasible.These constraints ultimately result in uncertain localization of  the vehicles.Furthermore, the vehicles are under constant disturbances from the water currents, fish and bio-fouling, which result in the dynamics of the vehicles being uncertain or even changing during the mission.In the first part of this thesis, we focus on the large-scale sensing problem under localization uncertainties by examining the caging and coverage problems.In the coverage problem, each AUV is uncertain about its exact position while tasked with sensing a stationary area.We show that we can still guarantee complete coverage and formulate the efficiency characteristics of different approaches.Furthermore, we show that when the vehicles are equipped with sensors and low-bandwidth communication methods, we can increase the effective range of a team of AUVs considerably by utilizing loop-closures over shared pose-graphs. In the caging problem, the localization uncertainty is focused on the entity that is being caged, its location is unknown but bounded.We show that through a combination of algorithms, the caging problem can be solved and a solution can be guaranteed, while simultaneously producing a list of specifications for the mission.In the second part, we focus on the individuals of the team and what they need to do in order for the team of AUVs to succeed.First, we identify that when there is a team of cooperative vehicles working together, conflicting goals rise.Each vehicle needs to pick between satisfying its own constraints and the constraints that come from being in a team. We propose a solution to this problem through a combination of Control Barrier Function (CBF) and Behavior Trees (BT).Secondly, we examine the possibility that a vehicle might undergo physical changes, like a broken thruster, that result in the vehicle being unable to complete the entire mission.Even in such a scenario, if the broken vehicle can still move to contact a normal one, the rest of the team can compensate through re-planning and the overall mission can still be completed.To do so, the broken vehicle must compensate for the change until a rendezvous.We propose a data-driven pipeline that can detect and plan around such a physical change within some bounds.
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42.
  • Özkan, Emre, et al. (författare)
  • Non-Parametric Bayesian Measurement Noise Density Estimation in Non-Linear Filtering
  • 2011
  • Ingår i: Acoustics, Speech and Signal Processing (ICASSP), 2011. - : IEEE. - 9781457705380 - 9781457705373 ; , s. 5924-5927
  • Konferensbidrag (refereegranskat)abstract
    • In this study, we investigate online Bayesian estimation of the measurement noise density of a given state space model using particle filters and Dirichlet process mixtures. Dirichlet processes are widely used in statistics for nonparametric density estimation. In the proposed method, the unknown noise is modeled as a Gaussian mixture with unknown number of components. The joint estimation of the state and the noise density is done via particle filters. Furthermore, the number of components and the noise statistics are allowed to vary in time. An extension of the method for the estimation of time varying noise characteristics is also introduced.
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44.
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45.
  • Öztekin, Buket (författare)
  • Typical and atypical language development in Turkish-Swedish bilingual children aged 4–7
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis investigates the vocabulary and narrative macrostructure skills of 102 typically-developing (TD) 4- to 7-year-old Turkish-Swedish bilingual children (cross-sectional), the development of these skills over time from age 4 to 6 in a subgroup of 10 children (longitudinal), and six Turkish-Swedish children with a language impairment (LI) diagnosis (clinical). The children’s health, family and language backgrounds, their language use and input patterns are explored through parental questionnaires, family interviews, and interviews with teachers and speech-language pathologists. In both Turkish and Swedish, comprehension and production are assessed with comparable materials: Cross-Linguistic Lexical Tasks (CLT; Haman et al., 2015), and Multilingual Assessment Instrument for Narratives (MAIN; Gagarina et al., 2012). For vocabulary (CLT), age development, language differences (Turkish vs. Swedish), differences between comprehension and production, and effects of language use and input are explored. For narrative macrostructure (MAIN), age development, language differences and task differences (Cat/Dog vs. Baby Birds/Baby Goats) are analyzed. LI children’s scores are compared with TD children, with additional focus on the LI children’s communicative, linguistic and social behavior. In both vocabulary comprehension and production, the youngest TD groups performed better in Turkish than in Swedish, but by age 6, Turkish and Swedish vocabulary scores matched due to rapid improvement in Swedish. Factors related to vocabulary scores were: daily language input, parents’ language use with each other and with the child, and child’s language with the sibling(s). For narratives, comprehension was ahead of production. There was no difference between Turkish and Swedish MAIN comprehension, but for both languages a task effect was found (higher scores on Cat/Dog than Baby Birds/Baby Goats). Narrative production scores were generally low for both languages, but increased more with age in Swedish than in Turkish. The longitudinal study largely confirmed the patterns found in the cross-sectional data.The majority of the LI children performed far below their TD peers in both their languages. Some LI children performed very low in only one language, despite extensive and long-term exposure to that language. In contrast, TD children with very low scores in one language usually had very limited exposure to that language. LI children were also reported to have difficulties with word learning, pragmatics, and attention, and a family history with language problems. It is suggested that bilingual children with potential language impairment should be assessed holistically in both their languages and extensive information about their family backgrounds and language input characteristics be collected. 
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46.
  • Öztokatli, Hande, 1985-, et al. (författare)
  • Retinoic acid receptor and CNGA2 channel signaling are part of a regulatory feedback loop controlling axonal convergence and survival of olfactory sensory neurons
  • 2012
  • Ingår i: The FASEB Journal. - : Federation of American Society of Experimental Biology (FASEB). - 0892-6638 .- 1530-6860. ; 26:2, s. 617-627
  • Tidskriftsartikel (refereegranskat)abstract
    • Little is known about the identities and functions of extracellular signaling molecules that work in concert with neuronal activity to regulate refinement and maintenance of the mouse olfactory sensory map. We show that expression of a dominant negative retinoic acid receptor (RAR) in olfactory sensory neurons (OSNs) increased the number of glomeruli that incorrectly contained OSN axons expressing different odorant receptors. This phenotype became apparent postnatally, coincided with increased cell death, and was preceded by increased Neuropilin-1 and reduced Kirrel-2 expressions. Kirrel-2-mediated cell adhesion influences odorant receptor-specific axonal convergence and is regulated by odorant receptor signaling via the olfactory cyclic nucleotide-gated (CNG) ion channel. Accordingly, we found that inhibited RAR function correlated with reduced CNG channel expression. Naris occlusion experiments and analysis of CNG channel-deficient mice further indicated that RAR-regulated CNG channel levels influenced the intrinsic neuronal activity required for cell survival in the absence of odor stimulation. Finally, we showed that CNG channel activity regulated expression of the retinoic acid-degrading enzyme Cyp26B1. Combined, these results identify a novel homeostatic feedback mechanism involving retinoic acid metabolism and CNG channel activity, which influences glomerular homogeneity and maintenance of precisely connected OSNs.
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47.
  • Öztürk, Ahmet Erdi, et al. (författare)
  • Diyanet as a Turkish Foreign Policy Tool: Evidence from the Netherlands and Bulgaria
  • 2018
  • Ingår i: Politics and Religion. - : CAMBRIDGE UNIV PRESS. - 1755-0483 .- 1755-0491. ; 11:3, s. 624-648
  • Tidskriftsartikel (refereegranskat)abstract
    • How does Turkeys Presidency of Religious Affairs (Diyanet) act as an instrument of foreign policy (FP)? What are the factors that allow such an instrumentalization of Islam in Turkish FP? In addressing these questions, this paper uses semi-structured expert interviews from Bulgaria and the Netherlands. Although both countries host a sizeable Muslim minority, these populations differ in their characteristics and historical ties with Turkey. Comparing Diyanets role in the Netherlands with its recent Turkish-Muslim diaspora, and in Bulgaria with its centuries-old Muslim minority allows us to reveal variation in the practical engagement strategies that Diyanet adopts in different country contexts. Thus, this paper advances two main claims; first, Diyanet serves as a primary FP tool of Turkey in countries with a significant Turkish-Muslim minority. Secondly, this instrumentalization destabilizes secularization projects both at home and abroad.
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48.
  • Öztürk, İbrahim, et al. (författare)
  • Preferred level of vehicle automation : How technology adoption, knowledge, and personality affect automation preference in Türkiye and Sweden
  • 2024
  • Ingår i: Cogent Psychology. - : Taylor & Francis. - 2331-1908. ; 11:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The acceptance of automated vehicles and advanced vehicle technologies by users is subject to different human factors variables. Personality, technology adoption, and prior previous knowledge about the systems have been significant determinants of people’s attitudes toward new technologies across different settings. The present study examined the effects of technology adoption, knowledge of vehicle automation, and personality on the preferred level of vehicle automation in Türkiye and Sweden. The study was conducted with 297 drivers from Türkiye (age: M = 22.47, SD = 2.83) and 332 drivers from Sweden (age: M = 30.06, SD = 10.48). Participants completed a questionnaire regarding technology adoption, knowledge and preference of vehicle automation, and the Basic Personality Traits Inventory (BPTI). The findings indicated that high technology adoption was associated with preferring higher levels of automation. Furthermore, drivers from Türkiye, in comparison to drivers from Sweden, and drivers with previous knowledge of high or full automation, compared to those who have not heard of these systems in the two countries, expressed a preference toward higher levels of automation. High extraversion and openness to change were associated with high technology adoption, leading to preferring vehicles with higher levels of automation.
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49.
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50.
  • Özyagci, Ali, 1982-, et al. (författare)
  • Selfish multi-channel random access in heterogeneous channels
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • We analyze the behavior of selfish users in a multichannel random access system in which the propagation characteristics of the available channels in the system exhibit different statistics. We formulate the behavior of the selfish users as a Bayesian game and identify the transmission strategies at the Nash equilibria. Following this, we propose a simple iterative algorithm to obtain the transmission probabilities of the selfish uses at the Nash equilibria and investigate the convergence properties of this algorithm. Using the transmission probabilities of the selfish users at the Nash equilibria, we analyze the performance of the MRA system with selfish users in terms of sum and per-user utilities and compare this system with its cooperative and scheduling system counterparts. We find that selfish behavior results in significant performance loss compared to scheduling and cooperative systems, which increases as the system load increases.
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