| 1. |
- Aad, G., et al.
(författare)
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- 2011
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swepub:Mat__t (refereegranskat)
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| 2. |
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| 3. |
- Özkahraman, Özer, 1992-, et al.
(författare)
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Efficient Navigation Aware Seabed Coverage using AUVs
- 2021
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Ingår i: Proceedings of 2021 IEEE International Conference on Safety, Security, and Rescue Robotics (SSRR), October 25-27 2021, New York, USA..
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Konferensbidrag (refereegranskat)abstract
- Area coverage and robot navigation are two important research fields within robotics. However, their intersection has received limited attention. In coverage problems, perfect navigation is often assumed, and in robot navigation, the focus is often to minimize the localization error while traveling a given trajectory.The need for integration of the two becomes clear in environments with very sparse features or landmarks, for example when an Autonomous Underwater Vehicle (AUV) is to search the seafloor for dangerous objects, such as mines.The potential consequences of missing a mine due to navigation errors can be catastrophic.If the localization error is large, a trajectory that was designed to guarantee complete coverage might have missed significant parts of the area. Thus, the coverage trajectory must be planned with the navigation performance in mind, applying a combination of using large enough planned overlaps of sensor footprints to account for the position uncertainty, and reducing this uncertainty by re-visiting the known sparse landmarks.In this paper we compute trajectories that guarantee coverage for a given area under assumptions on worst case localization error growth.We further more compute upper bounds for how large areas can be covered using common coverage patterns and a single landmark, which leads to bounds on how sparse the landmarks can be in the regions to be covered.
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| 4. |
- Özkirimli, Umut
(författare)
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Speed. I am Speed
- 2018
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Ingår i: Ahval.
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 5. |
- Öztekin, Buket
(författare)
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Typical and atypical language development in Turkish-Swedish bilingual children aged 4–7
- 2019
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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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| 6. |
- Özkan, Emre, et al.
(författare)
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Recursive Maximum Likelihood Identification of Jump Markov Nonlinear Systems
- 2015
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 63:3, s. 754-765
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Tidskriftsartikel (refereegranskat)abstract
- We present an online method for joint state and parameter estimation in jump Markov non-linear systems (JMNLS). State inference is enabled via the use of particle filters which makes the method applicable to a wide range of non-linear models. To exploit the inherent structure of JMNLS, we design a Rao-Blackwellized particle filter (RBPF) where the discrete mode is marginalized out analytically. This results in an efficient implementation of the algorithm and reduces the estimation error variance. The proposed RBPF is then used to compute, recursively in time, smoothed estimates of complete data sufficient statistics. Together with the online expectation maximization algorithm, this enables recursive identification of unknown model parameters including the transition probability matrix. The method is also applicable to online identification of jump Markov linear systems(JMLS). The performance of the method is illustrated in simulations and on a localization problem in wireless networks using real data.
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| 7. |
- 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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| 8. |
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| 9. |
- Özkan, Emre, et al.
(författare)
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Non-Parametric Bayesian Measurement Noise Density Estimation in Non-Linear Filtering
- 2011
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Ingår i: Acoustics, Speech and Signal Processing (ICASSP), 2011. - : IEEE. - 9781457705380 - 9781457705373 ; , s. 5924-5927
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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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| 10. |
- Öztaş, Ahmet M., et al.
(författare)
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Re-evaluation of Ωk of the normalised Friedmann-Lemaître-Robertson-Walker model : Implications for Hubble constant determinations
- 2021
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Ingår i: New Astronomy. - : Elsevier. - 1384-1076 .- 1384-1092. ; 88
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Tidskriftsartikel (refereegranskat)abstract
- The description of spacetime is an fundamental problem of cosmology. We explain why the current assignments of spacetime geometries for Ωk of the Friedmann-Lemaître-Robertson-Walker (FLRW) model are probably incorrect and suggest more useful descriptions. We show that Ωk represents not only curvature but the influence of matter density on the extent of spacetime between massive objects. Recent analyses of supernovae type Ia (SNe Ia) and HII/GEHR data with the FLRW model present the best fits with a small value for Ωm and a large Ωk. These results are consistent with our Universe exhibiting sparse matter density and quasi-Euclidean geometry and the small Ωm value agrees with Big Bang nucleosynthesis calculations. We suggest the geometry of our current Universe is better described by a value for Ωk≈1 rather than 0. As an example we extend the FLRW model towards the Big Bang and discover a simple explanation of how matter creation developed into the currently geometrically flat Universe with sparse, homogeneous, isotropic matter and energy distributions. Assigning Ωk≈1 to describe quasi-Euclidean spacetime geometry is also useful for estimating H0 and should help resolve the “tension” surrounding current estimates by different investigators.
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