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Kurucz A.,King's College London | Wolter F.,University of Liverpool | Zakharyaschev M.,Birkbeck College London
Advances in Modal Logic 2006 | Year: 2010

ℰℒ is a tractable description logic serving as the logical underpinning of large-scale ontologies. We launch a systematic investigation of the boundary between tractable and intractable reasoning in ℰℒ under relational constraints. For example, we show that there are (modulo equivalence) exactly 3 universal constraints on a transitive and reexive relation under which reasoning is tractable: being a singleton set, an equivalence relation, or the empty constraint. We prove a number of results of this type and discuss a spectrum of open problems including generalisations to the algebraic semantics for ℰℒ (semi-lattices with monotone operators).

Kontchakov R.,Birkbeck College London | Lutz C.,University of Bremen | Toman D.,University of Waterloo | Wolter F.,University of Liverpool | Zakharyaschev M.,Birkbeck College London
IJCAI International Joint Conference on Artificial Intelligence | Year: 2011

The use of ontologies for accessing data is one of the most exciting new applications of description logics in databases and other information systems. A realistic way of realising sufficiently scalable ontology-based data access in practice is by reduction to querying relational databases. In this paper, we describe the combined approach, which incorporates the information given by the ontology into the data and employs query rewriting to eliminate spurious answers. We illustrate this approach for ontologies given in the DL-Lite family of description logics and briefly discuss the results obtained for the EL family.

Clift P.D.,Louisiana State University | Clift P.D.,CAS South China Sea Institute of Oceanology | Carter A.,Birkbeck College London | Nicholson U.,Royal Dutch Shell | Masago H.,Japan Agency for Marine - Earth Science and Technology
Tectonics | Year: 2013

The Nankai accretionary complex is the most recent addition to the accretionary complexes of southwest Japan and has preserved a record of sediment flux to the trench during its construction. In this study, we use U-Pb zircon and fission track analysis of both zircons and apatites from sediments taken from the forearc and trench of the Nankai Trough, as well as rivers from southwest Japan to examine the exhumation history of the margin since the Middle Miocene. Modern rivers show a flux dominated by erosion of the Mesozoic-Eocene Shimanto and Sanbagawa accretionary complexes. Only the Fuji River, draining the collision zone between the Izu and Honshu arcs, is unique in showing much faster exhumation. Sediment from the Izu-Honshu collision is not found 350-500 km along the margin offshore Kyushu indicating limited along-strike sediment transport. Sediment deposited since 2 Ma on the midtrench slope offshore the Muroto Peninsula of Shikoku (ODP Site 1176) and on the lower slope trenchward of the Kumano Basin (IODP Sites C0006E and C00007E) shares the dominant source in the Shimanto and Sanbagawa complexes seen in the modern rivers. Prior to 5 Ma, additional sediment was being sourced from further north in more slowly exhumed terrains, ∼350 km from the trench axis. Around 9.4 Ma, U-Pb zircon ages of ∼1800 Ma indicate enhanced erosion from the North China Craton, exposed in northern Honshu. In the middle Miocene, at ∼15.4 Ma, the sediment was being derived from a much wider area including the Yangtze Craton (U-Pb ages ∼800 Ma). We suggest that this enhanced catchment may have reflected the influence of the Yangtze River in supplying into the Shikoku Basin prior to rifting of the Okinawa Trough at 10 Ma and migration of the Palau-Kyushu Ridge to form a barrier to transport. The restriction of Nankai Trough provenance to Mesozoic source partly reflects continued uplift of the Shimanto and Sanbagawa complexes since the Middle Miocene. ©2013. American Geophysical Union. All Rights Reserved.

Kontchakov R.,Birkbeck College London | Nenov Y.,University of Manchester | Pratt-Hartmann I.,University of Manchester | Zakharyaschev M.,Birkbeck College London
IJCAI International Joint Conference on Artificial Intelligence | Year: 2011

We investigate (quantifier-free) spatial constraint languages with equality, contact and connectedness predicates, as well as Boolean operations on regions, interpreted over low-dimensional Euclidean spaces. We show that the complexity of reasoning varies dramatically depending on the dimension of the space and on the type of regions considered. For example, the logic with the interior-connectedness predicate (and without contact) is undecidable over polygons or regular closed sets in ℝ2, EXPTIME-complete over polyhedra in ℝ3, and NP-complete over regular closed sets in ℝ3.

Pedersen R.B.,University of Bergen | Searle M.P.,University of Oxford | Carter A.,Birkbeck College London | Bandopadhyay P.C.,Geological Survey of India
Journal of the Geological Society | Year: 2010

The Andaman ophiolites form the basement of the Andaman Islands, which is a part of the outer forearc that links the Indo-Burma accretionary complex to the north with the Java-Sumatra trench-arc system to the SE. Upper mantle harzburgite and dunite are overlain by a cumulate peridotite-gabbro complex, highlevel intrusive rocks and a tholeiitic volcanic series. The upper crust in the South Andaman ophiolite shows also a prominent andesite-dacite volcanic suite, suggesting arc volcanism built onto ocean crust. U-Pb zircon dating of a trondhjemitic rock from Chiriya Tapu in South Andaman Island using laser ablation inductively coupled mass spectrometry reveals an age of crustal formation of 95 ± 2 Ma. The trondhjemites have geochemistry comparable with that of plagiogranites associated with ophiolite complexes, and Nd values around +7 further confirm that they are derived from depleted mantle melts. Basaltic pillow lava and basaltic dykes that cut the trondhjemites have mid-ocean ridge basalt-like trace-element geochemistry. The new data show that the Andaman volcanic arc was built on Cenomanian ophiolite-oceanic crust and that subduction was initiated at this time along Tethys, at least from Cyprus through Oman to the Andaman Islands. © 2010 Geological Society of London.

Kontchakov R.,Birkbeck College London | Wolter F.,University of Liverpool | Zakharyaschev M.,Birkbeck College London
Artificial Intelligence | Year: 2010

We develop a formal framework for comparing different versions of ontologies, and apply it to ontologies formulated in terms of DL-Lite, a family of 'lightweight' description logics designed for data-intensive applications. The main feature of our approach is that we take into account the vocabulary (=signature) with respect to which one wants to compare ontologies. Five variants of difference and inseparability relations between ontologies are introduced and their respective applications for ontology development and maintenance discussed. These variants are obtained by generalising the notion of conservative extension from mathematical logic and by distinguishing between differences that can be observed among concept inclusions, answers to queries over ABoxes, by taking into account additional context ontologies, and by considering a model-theoretic, language-independent notion of difference. We compare these variants, study their meta-properties, determine the computational complexity of the corresponding reasoning tasks, and present decision algorithms. Moreover, we show that checking inseparability can be automated by means of encoding into QBF satisfiability and using off-the-shelf general purpose QBF solvers. Inseparability relations between ontologies are then used to develop a formal framework for (minimal) module extraction. We demonstrate that different types of minimal modules induced by these inseparability relations can be automatically extracted from real-world medium-size DL-Lite ontologies by composing the known tractable syntactic locality-based module extraction algorithm with our non-tractable extraction algorithms and using the multi-engine QBF solver aqme. Finally, we explore the relationship between uniform interpolation (or forgetting) and inseparability. © 2010 Elsevier B.V. All rights reserved.

Crawford I.A.,Birkbeck College London
Astronomy and Geophysics | Year: 2012

Ian Crawford explains why human space exploration will tell us more about the solar system than robotic exploration alone. © 2012 Royal Astronomical Society.

Crawford I.A.,Birkbeck College London
JBIS - Journal of the British Interplanetary Society | Year: 2016

In this paper we outline the range of probes and scientific instruments that will be required for an Icarus-style interstellar mission to fulfill its scientific objectives of exploring a nearby star, its attendant planetary system, and the intervening interstellar medium. Based on this preliminary analysis, we estimate that the minimum total Icarus scientific payload mass will be in the region of 100 tonnes. Of this, approximately 10 tonnes would be allocated for cruise-phase science instruments (not all of which would necessarily need to be decelerated at the target system), and about 35 tonnes would be contributed by the intra-system science payload itself (i.e. the dry mass of the stellar and planetary probes and their instruments). The remaining ∼55 tonnes is allocated for the sub-probe intra-system propulsion requirements (crudely estimated from current Solar System missions; detailed modelling of sub-probe propulsion systems will be needed to refine this figure). However, the overall mass contributed by the science payload to the total that must be decelerated from the interstellar cruise velocity will be significantly more than 100 tonnes, as allowance must be made for the payload structural and infrastructural elements required to support, deploy, and communicate with the science probes and instruments. Based on the earlier Daedalus study, we estimate another factor of two to allow for these components. Pending the outcome of more detailed studies, it therefore appears that an overall science-related payload mass of ∼200 tonnes will be required. This paper is a submission of the Project Icarus Study Group.

Crawford I.A.,Birkbeck College London
JBIS - Journal of the British Interplanetary Society | Year: 2014

Interstellar exploration will advance human knowledge and culture in multiple ways. Scientifically, it will advance our understanding of the interstellar medium, stellar astrophysics, planetary science and astrobiology. In addition, significant societal and cultural benefits will result from a programme of interstellar exploration and colonisation. Most important will be the cultural stimuli resulting from expanding the horizons of human experience, and increased opportunities for the spread and diversification of life and culture through the Galaxy. Ultimately, a programme of interstellar exploration may be the only way for human (and post-human) societies to avoid the intellectual stagnation predicted for the 'end of history'.

Crawford I.A.,Birkbeck College London
JBIS - Journal of the British Interplanetary Society | Year: 2010

In this paper we outline the considerations required in order to select a target star system for the Icarus interstellar mission. It is considered that the maximum likely range for the Icarus vehicle will be 15 light-years, and a list is provided of all known stars within this distance range. As the scientific objectives of Icarus are weighted towards planetary science and astrobiology, a final choice of target star(s) cannot be made until we have a clearer understanding of the prevalence of planetary systems within 15 light-years of the Sun, and we summarise what is currently known regarding planetary systems within this volume. We stress that by the time an interstellar mission such as Icarus is actually undertaken, astronomical observations from the solar system will have provided this information. Finally, given the high proportion of multiple star systems within 15 lightyears (including the closest of all stars to the Sun in the a Centauri system), we stress that a flexible mission architecture, able to visit stars and accompanying planets within multiple systems, is desirable. This paper is a submission of the Project Icarus Study Group.

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