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Institution

University of British Columbia

EducationVancouver, British Columbia, Canada
About: University of British Columbia is a education organization based out in Vancouver, British Columbia, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 89939 authors who have published 209679 publications receiving 9226862 citations. The organization is also known as: UBC & The University of British Columbia.


Papers
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Journal ArticleDOI
TL;DR: An algorithm for computing the set of reachable states of a continuous dynamic game based on a proof that the reachable set is the zero sublevel set of the viscosity solution of a particular time-dependent Hamilton-Jacobi-Isaacs partial differential equation.
Abstract: We describe and implement an algorithm for computing the set of reachable states of a continuous dynamic game. The algorithm is based on a proof that the reachable set is the zero sublevel set of the viscosity solution of a particular time-dependent Hamilton-Jacobi-Isaacs partial differential equation. While alternative techniques for computing the reachable set have been proposed, the differential game formulation allows treatment of nonlinear systems with inputs and uncertain parameters. Because the time-dependent equation's solution is continuous and defined throughout the state space, methods from the level set literature can be used to generate more accurate approximations than are possible for formulations with potentially discontinuous solutions. A numerical implementation of our formulation is described and has been released on the web. Its correctness is verified through a two vehicle, three dimensional collision avoidance example for which an analytic solution is available.

1,107 citations

Book ChapterDOI
01 Oct 1987
TL;DR: This paper shows that closed world evaluation of an arbitrary query may be reduced to open world evaluated of so-called atomic queries, and shows that the closed world assumption can lead to inconsistencies, but for Horn data bases no such inconsistencies can arise.
Abstract: Deductive question-answering system generally evaluate queries under one of two possible assumptions which we in this paper refer to as the open and closed world assumptions. The open world assumption corresponds to the usual first order approach to query evaluation: Given a data base DB and a query Q, the only answers to Q are those which obtain from proofs of Q given DB as hypotheses. Under the closed world assumption, certain answers are admitted as a result of failure to find a proof. More specifically, if no proof of a positive ground literal exists, then the negation of that literal is assumed true. In this paper, we show that closed world evaluation of an arbitrary query may be reduced to open world evaluation of so-called atomic queries. We then show that the closed world assumption can lead to inconsistencies, but for Horn data bases no such inconsistencies can arise. Presented at the Workshop on Logic and Data Bases, Toulouse, France, November 16-18, 1977.

1,106 citations

Journal ArticleDOI
TL;DR: The Lambeth Conventions are guidelines intended to be of practical value in the investigation of arrhythmias induced by ischaemia, infarction, and reperfusion and are encouraged to adopt in the hope that this will improve uniformity and interlaboratory comparisons.
Abstract: The Lambeth Conventions are guidelines intended to be of practical value in the investigation of arrhythmias induced by ischaemia, infarction, and reperfusion. They cover the design and execution of experiments and the definition, classification, quantification, and analysis of arrhythmias. Investigators are encouraged to adopt the conventions in the hope that this will improve uniformity and interlaboratory comparisons.

1,105 citations

Journal ArticleDOI
TL;DR: The first rigorous example of an isotropic model in such a phase is presented in this paper, where the Hamiltonian has an exactSO(3) symmetry and is translationally invariant, but the model has a unique ground state and exponential decay of the correlation functions in the ground state.
Abstract: Haldane predicted that the isotropic quantum Heisenberg spin chain is in a “massive” phase if the spin is integral. The first rigorous example of an isotropic model in such a phase is presented. The Hamiltonian has an exactSO(3) symmetry and is translationally invariant, but we prove the model has a unique ground state, a gap in the spectrum of the Hamiltonian immediately above the ground state and exponential decay of the correlation functions in the ground state. Models in two and higher dimension which are expected to have the same properties are also presented. For these models we construct an exact ground state, and for some of them we prove that the two-point function decays exponentially in this ground state. In all these models exact ground states are constructed by using valence bonds.

1,105 citations

Journal ArticleDOI
04 Nov 2004-Nature
TL;DR: This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s, and salps appear to have increased in the southern part of their range.
Abstract: Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are major grazers in the Southern Ocean, and krill support commercial fisheries. Their density distributions have been described in the period 1926-51, while recent localized studies suggest short-term changes. To examine spatial and temporal changes over larger scales, we have combined all available scientific net sampling data from 1926 to 2003. This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s. Spatially, within their habitat, summer krill density correlates positively with chlorophyll concentrations. Temporally, within the southwest Atlantic, summer krill densities correlate positively with sea-ice extent the previous winter. Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean. Krill need the summer phytoplankton blooms of this sector, where winters of extensive sea ice mean plentiful winter food from ice algae, promoting larval recruitment and replenishing the stock. Salps, by contrast, occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill. As krill densities decreased last century, salps appear to have increased in the southern part of their range. These changes have had profound effects within the Southern Ocean food web.

1,103 citations


Authors

Showing all 90682 results

NameH-indexPapersCitations
Gordon H. Guyatt2311620228631
John C. Morris1831441168413
Douglas Scott1781111185229
John R. Yates1771036129029
Deborah J. Cook173907148928
Richard A. Gibbs172889249708
Evan E. Eichler170567150409
James F. Sallis169825144836
Michael Snyder169840130225
Jiawei Han1681233143427
Michael Kramer1671713127224
Bruce L. Miller1631153115975
Peter A. R. Ade1621387138051
Marc W. Kirschner162457102145
Kaj Blennow1601845116237
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20241
2023307
20221,209
202113,228
202012,052
201910,934