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Task allocation in networks of satellites with Keplerian dynamics
No full textThe management of distributed satellite systems requires the coordination of a large number of heterogeneous spacecraft. Task allocation in such a system is complicated by limited communication and individual satellite dynamics. Previous work has shown that task allocation using a market-based mechanism can provide scalable and efficient management of static networks; in this paper we extend this work to determine the impact of dynamic topologies. We develop a Keplerian mobility model to describe the topology of the communication network over time. This movement model is then used in simulation to show that the task allocation mechanism does not show a significant decrease in effectiveness from the static case, reflecting the suitability of distributed market-based control to the highly dynamic environment
Task allocation in dynamic networks of satellites
No full textThe management of distributed satellite systems requires the coordination of a large number of heterogeneous spacecraft. Task allocation in such a system is complicated by limited communication and individual satellite dynamics. Previous work has shown that task allocation using a market-based mechanism can provide scalable and efficient management of static networks; in this paper we extend this work to determine the impact of dynamic topologies. We develop a Keplerian mobility model to describe the topology of the communication network over time. This movement model is then used in simulation to show that the task allocation mechanism does not show a significant decrease in effectiveness from the static case, reflecting the suitability distributed market-based control to the highly dynamic environment
Van der Horst gebundeld
No full textRecensie van Joop van der Horst, Met het oog op morgen : opstellen over taal, taalverandering en standaardtaal. - Leuven : Universitaire Pers, 201
Dendrophyllia boschmai van der Horst 1926
No full textDendrophyllia boschmai van der Horst, 1926 Dendrophyllia japonica van der Horst, 1922: 51, pl. 7, fig. 6 (junior primary homonym of D. japonica Rehberg, 1892). Dendrophyllia boschmai van der Horst, 1926: 44.– Cairns, 1994: 91 (synonymy, remarks); 1998: 409 (WA). New records. None. Types. The holotype is deposited at ZMA (Coel. 5451). Type Locality: “ Japan ”, depth unknown.Published as part of Cairns, S. D., 2004, The Azooxanthellate Scleractinia (Coelenterata: Anthozoa) of Australia, pp. 259-329 in Records of the Australian Museum 56 on page 31
Distributed and Centralized Task Allocation: When and Where to Use Them
No full textSelf-organisation is frequently advocated as the solution for managing large, dynamic systems. Distributed algorithms are implicitly designed for infinitely large problems, while small systems are regarded as being controllable using traditional, centralised approaches. Many real-world systems, however, do not fit conveniently into these "small" or "large" categories, resulting in a range of cases where the optimal solution is ambiguous. This difficulty is exacerbated by enthusiasts of either approach constructing problems that suit their preferred control architecture. We address this ambiguity by building an abstract model of task allocation in a community of specialised agents. We are inspired by the problem of work distribution in distributed satellite systems, but the model is also relevant to the resource allocation problems in distributed robotics, autonomic computing and wireless sensor networks. We compare the behaviour of a self-organising, market-based task allocation strategy to a classical approach that uses a central controller with global knowledge. The objective is not to prove one mechanism inherently superior to the other; instead we are interested in the regions of problem space where each of them dominates. Simulation is used to explore the trade-off between energy consumption and robustness in a system of intermediate size, with fixed communication costs and varying rates of component failure. We identify boundaries between regions in the parameter space where one or the other architecture will be favoured. This allows us to derive guidelines for system designers, thus contributing to the development of a disciplined approach to controlling distributed systems using self-organising mechanisms
Faster Fréchet Distance Approximation Through Truncated Smoothing
Get PDFThe Fréchet distance is a popular distance measure for curves. Computing the Fréchet distance between two polygonal curves of n vertices takes roughly quadratic time, and conditional lower bounds suggest that even approximating to within a factor 3 cannot be done in strongly-subquadratic time, even in one dimension. The current best approximation algorithms present trade-offs between approximation quality and running time. Recently, van der Horst et al. (SODA, 2023) presented an O((n²/α) log³ n) time α-approximate algorithm for curves in arbitrary dimensions, for any α ∈ [1, n]. Our main contribution is an approximation algorithm for curves in one dimension, with a significantly faster running time of O(n log³ n + (n²/α³) log²n log log n). Additionally, we give an algorithm for curves in arbitrary dimensions that improves upon the state-of-the-art running time by a logarithmic factor, to O((n²/α) log² n). Both of our algorithms rely on a linear-time simplification procedure that in one dimension reduces the complexity of the reachable free space to O(n²/α) without making sacrifices in the asymptotic approximation factor
Rhizopsammia nuda van der Horst 1926
No full textRhizopsammia nuda van der Horst, 1926 Rhizopsammia nuda van der Horst, 1926: 50–51, pl. 2, figs. 10– 12.–Cairns & Zibrowius, 1997: 189–190 (synonymy, description). New record. NORTHERN TERRITORY: WTDSHW P2-7 (Stokes Hill Wharf, Darwin Harbour), 5.5 m, 2 corallites, NTM. Types. Four of the five syntypes are deposited at ZMA and BM (Cairns & Zibrowius, 1997). Type Locality: Singapore, South China Sea, depth unknown.Published as part of Cairns, S. D., 2004, The Azooxanthellate Scleractinia (Coelenterata: Anthozoa) of Australia, pp. 259-329 in Records of the Australian Museum 56 on page 31
Van Der Horst, Mrs Griet Hekker, [No Service Number]
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/422830Surname: VAN DER HORST. Given Name(s) or Initials: MRS GRIET HEKKER. Military Service Number or Last Known Location: [No Registration Number]. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 50815.249345
Item: [2016.0049.55091] "Van Der Horst, Mrs Griet Hekker, [No Service Number]
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