| 1. |
- Bishop, Adrian N., et al.
(author)
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Optimal Range-Difference-Based Localization Considering Geometrical Constraints
- 2008
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In: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 33:3, s. 289-301
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Journal article (peer-reviewed)abstract
- This paper proposes a new type of algorithm aimed at finding the traditional maximum-likelihood (TML) estimate of the position of a target given time-difference-of-arrival (TDOA) information, contaminated by noise. The novelty lies in the fact that a performance index, akin to but not identical with that in maximum likelihood (ML), is a minimized subject to a number of constraints, which flow from geometric constraints inherent in the underlying problem. The minimization is in a higher dimensional space than for TML, and has the advantage that the algorithm can be very straightforwardly and systematically initialized. Simulation evidence shows that failure to converge to a solution of the localization problem near the true value is less likely to occur with this new algorithm than with TML. This makes it attractive to use in adverse geometric situations.
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| 4. |
- Basiri, Meysam, et al.
(author)
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Distributed Control of Triangular Sensor Formations with Angle-Only Constraints
- 2009
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In: 2009 INTERNATIONAL CONFERENCE ON INTELLIGENT SENSORS, SENSOR NETWORKS AND INFORMATION PROCESSING (ISSNIP 2009). - NEW YORK : IEEE. - 9781424435173 ; , s. 121-126
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Conference paper (peer-reviewed)abstract
- This paper considers the coupled formation control of three mobile agents moving in the plane. Each agent has only local inter-agent bearing knowledge and is required to maintain a specified angular separation relative to its neighbors. The problem considered in this paper differs from similar problems in the literature since no inter-agent distance measurements are employed and the desired formation is specified entirely by the internal triangle angles. Each agent's control law is distributed and based only on its locally measured bearings. A convergence result is established which guarantees global convergence of the formation to the desired formation shape.
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| 5. |
- Bishop, Adrian N., et al.
(author)
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A Stochastically Stable Solution to the Problem of Robocentric Mapping
- 2009
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In: ICRA. - 9781424427888 ; , s. 1540-1547
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Conference paper (peer-reviewed)abstract
- This paper provides a novel solution for robo-centric mapping using an autonomous mobile robot. The robot dynamic model is the standard unicycle model and the robot is assumed to measure both the range and relative bearing to the landmarks. The algorithm introduced in this paper relies on a coordinate transformation and an extended Kalman filter like algorithm. The coordinate transformation considered in this paper has not been previously considered for robocentric mapping applications. Moreover, we provide a rigorous stochastic stability analysis of the filter employed and we examine the conditions under which the mean-square estimation error converges to a steady-state value.
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| 6. |
- Bishop, Adrian N., et al.
(author)
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An Optimality Analysis of Sensor-Target Geometries for Signal Strength Based Localization
- 2009
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In: 2009 INTERNATIONAL CONFERENCE ON INTELLIGENT SENSORS, SENSOR NETWORKS AND INFORMATION PROCESSING (ISSNIP 2009). - NEW YORK : IEEE. - 9781424435173 ; , s. 127-132
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Conference paper (peer-reviewed)abstract
- In this paper we characterize the bounds on localization accuracy in signal strength based localization. In particular, we provide a novel and rigorous analysis of the relative receiver-transmitter geometry and the effect of this geometry on the potential localization performance. We show that uniformly spacing sensors around the target is not optimal if the sensor-target ranges are not identical and is not necessary in any case. Indeed, we show that in general the optimal sensor-target geometry for signal strength based localization is not unique.
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| 7. |
- Boberg, Anders, et al.
(author)
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Robocentric Mapping and Localization in Modified Spherical Coordinates with Bearing Measurements
- 2009
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In: 2009 INTERNATIONAL CONFERENCE ON INTELLIGENT SENSORS, SENSOR NETWORKS AND INFORMATION PROCESSING (ISSNIP 2009). - NEW YORK : IEEE. - 9781424435173 ; , s. 139-144
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Conference paper (peer-reviewed)abstract
- In this paper, a new approach to robotic mapping is presented that uses modified spherical coordinates in a robot-centered reference frame and a bearing-only measurement model. The algorithm provided in this paper permits robust delay-free state initialization and is computationally more efficient than the current standard in bearing-only (delay-free initialized) simultaneous localization and mapping (SLAM). Importantly, we provide a detailed nonlinear observability analysis which shows the system is generally observable. We also analyze the error convergence of the filter using stochastic stability analysis. We provide an explicit bound on the asymptotic mean state estimation error. A comparison of the performance of this filter is also made against a standard world-centric SLAM algorithm in a simulated environment.
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| 8. |
- Boyle, P, et al.
(author)
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Need for global action for cancer control
- 2008
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In: Annals of oncology : official journal of the European Society for Medical Oncology. - : Elsevier BV. - 1569-8041. ; 19:9, s. 1519-1521
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Journal article (other academic/artistic)
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| 11. |
- Green, Dido, et al.
(author)
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Is questionnaire-based screening part of the solution to waiting lists for children with developmental coordination disorder?
- 2005
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In: British Journal of Occupational Therapy. - : Sage Publications. - 0308-0226 .- 1477-6006. ; 68:1, s. 2-10
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Journal article (peer-reviewed)abstract
- This study was undertaken to determine whether questionnaire-based screening could be part of the solution to a long waiting list of referrals for occupational therapy assessment by identifying the requirement for clinical assessments. The performance of two questionnaires - the Developmental Coordination Disorder Questionnaire (DCDQ) completed by parents and the Checklist of the Movement Assessment Battery for Children (C-ABC) completed by teachers - was compared with a more traditional clinical assessment for the identification of DCD in children already referred to occupational therapy. It was found that the parent report was quite reliable in the identification of DCD if no other developmental problem was present. However, there was little benefit to using the teacher report to screen children. Several confounding variables, including an unequal proportion of children with DCD in the sample and the inclusion of children who were younger than the age range of the DCDQ, may have influenced how well the questionnaires performed. Although questionnaires cannot replace a full clinical assessment, the results showed that there may be some value in including the parent report in the identification of DCD.
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| 12. |
- Hughes, R. N., et al.
(author)
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Paradoxical polyembryony? Embryonic cloning in an ancient order of marine bryozoans
- 2005
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In: Biology Letters. - 1744-9561. ; 1:2, s. 178-180
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Journal article (peer-reviewed)abstract
- Prolific polyembryony is reported in few major taxa, but its occurrence has generated theoretical debate on potential conflict between sexual and asexual reproduction. It is, therefore, important to genetically confirm a widely cited inference, based on microscopy, that polyembryony characterizes marine bryozoans of the order Cyclostomata. Microsatellite genotyping of brooded embryos and maternal colonies conclusively demonstrated polyembryony, while genetic variation among broods within colonies indicated outcrossing via water-borne sperm, in the rocky-shore species Crisia denticulata. The characteristically voluminous brood chamber of cyclostomes is judged to be an adaptation linked to larval cloning and hence an indicator of polyembryony. We speculate that although the almost universal occurrence of polyembryony among crown-group Cyclostomata is probably attributable to phylogenetic constraint, adaptive consequences are likely to be significant.
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| 13. |
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| 14. |
- Pemberton, A. J., et al.
(author)
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Microscale genetic differentiation in a sessile invertebrate with cloned larvae: investigating the role of polyembryony
- 2007
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In: Marine Biology. - 0025-3162. ; 153:1, s. 71-82
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Journal article (peer-reviewed)abstract
- Microscale genetic differentiation of sessile organisms can arise from restricted dispersal of sexual propagules, leading to isolation by distance, or from localised cloning. Cyclostome bryozoans offer a possible combination of both: the localised transfer of spermatozoa between mates with limited dispersal of the resulting larvae, in association with the splitting of each sexually produced embryo into many clonal copies (polyembryony). We spatially sampled 157 colonies of Crisia denticulata from subtidal rock overhangs from one shore in Devon, England at a geographic scale of ca. 0.05 to 130 m plus a further 21 colonies from Pembrokeshire, Wales as an outgroup. Analysis of molecular variance (AMOVA) revealed that the majority (67%) of genetic variation was distributed among individuals within single rock overhangs, with only 16% of variation among different overhangs within each shore and 17% of variation between the ingroup and outgroup shores. Despite local genetic variation, pairwise genetic similarity analysed by spatial autocorrelation was greatest at the smallest inter-individual distance we tested (5 cm) and remained significant and positive across generally within-overhang comparisons (< 4 m). Spatial autocorrelation and AMOVA analyses both indicated that patches of C. denticulata located on different rock overhangs tended to be genetically distinct, with the switch from positive to negative autocorrelation, which is often considered to be the distance within which individuals reproduce with their close relatives or the radius of a patch, occurring at the 4-8 m distance class. Rerunning analyses with twenty data sets that only included one individual of each multilocus genotype (n = 97) or the single data set that contained just the unique genotypes (n = 67) revealed that the presence of repeat genotypes had an impact on genetic structuring (PhiPT values were reduced when shared genotypes were removed from the dataset) but that it was not great and only statistically evident at distances between individuals of 1-2 m. Comparisons to a further 20 randomisations of the data set that were performed irrespective of genotype (n = 97) suggested that this conclusion is not an artefact of reduced sample size. A resampling procedure using kinship coefficients, implemented by the software package GENCLONE gave broadly similar results but the greater statistical power allowed small but significant impacts of repeat genotypes on genetic structure to be also detected at 0.125-0.5 and 4-16 m. Although we predict that a proportion of the repeat multilocus genotypes are shared by chance, such generally within-overhang distances may represent a common distance of cloned larval dispersal. These results suggests that closely situated potential mates include a significant proportion of the available genetic diversity within a population, making it unlikely that, as previously hypothesised, the potential disadvantage of producing clonal broods through polyembryony is offset by genetic uniformity within the mating neighbourhood. We also report an error in the published primer note of Craig et al. (Mol Ecol Notes 1:281-282, 2001): loci Cd5 and Cd6 appear to be the same microsatellite.
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| 15. |
- Pronobis, Andrzej, et al.
(author)
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A Framework for Robust Cognitive Spatial Mapping
- 2009
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In: 2009 International Conference on Advanced Robotics, ICAR 2009. - : IEEE. - 9781424448555 ; , s. 686-693
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Conference paper (peer-reviewed)abstract
- Spatial knowledge constitutes a fundamental component of the knowledge base of a cognitive, mobile agent. This paper introduces a rigorously defined framework for building a cognitive spatial map that permits high level reasoning about space along with robust navigation and localization. Our framework builds on the concepts of places and scenes expressed in terms of arbitrary, possibly complex features as well as local spatial relations. The resulting map is topological and discrete, robocentric and specific to the agent's perception. We analyze spatial mapping design mechanics in order to obtain rules for how to define the map components and attempt to prove that if certain design rules are obeyed then certain map properties are guaranteed to be realized. The idea of this paper is to take a step back from existing algorithms and literature and see how a rigorous formal treatment can lead the way towards a powerful spatial representation for localization and navigation. We illustrate the power of our analysis and motivate our cognitive mapping characteristics with some illustrative examples.
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