Publications
88 results found
Peters O, Christensen K, Neelin JD, 2011, Rainfall and Dragon Kings, European Physical Journal. Special Topics
Frette V, Kleppe G, Christensen K, 2011, Analysis of ship maneuvering data from simulators, 11th Granada Seminar on Computational and Statistical Physics, Publisher: AMER INST PHYSICS, Pages: 276-276, ISSN: 0094-243X
Espinosa A, Cardoso PP, Arcaute E, et al., 2011, Complexity approaches to self-organisation: a case study from an Irish eco-village, KYBERNETES, Vol: 40, Pages: 536-558, ISSN: 0368-492X
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- Citations: 13
Richardson TO, Robinson EJH, Christensen K, et al., 2010, Record dynamics in ants, PLOS One, Vol: 5, ISSN: 1932-6203
The success of social animals (including ourselves) can be attributed to efficiencies that arise from a division of labour. Many animal societies have a communal nest which certain individuals must leave to perform external tasks, for example foraging or patrolling. Staying at home to care for young or leaving to find food is one of the most fundamental divisions of labour. It is also often a choice between safety and danger. Here we explore the regulation of departures from ant nests. We consider the extreme situation in which no one returns and show experimentally that exiting decisions seem to be governed by fluctuating record signals and ant-ant interactions. A record signal is a new ‘high water mark’ in the history of a system. An ant exiting the nest only when the record signal reaches a level it has never perceived before could be a very effective mechanism to postpone, until the last possible moment, a potentially fatal decision. We also show that record dynamics may be involved in first exits by individually tagged ants even when their nest mates are allowed to re-enter the nest. So record dynamics may play a role in allocating individuals to tasks, both in emergencies and in everyday life. The dynamics of several complex but purely physical systems are also based on record signals but this is the first time they have been experimentally shown in a biological system.
Arcaute E, Christensen K, Sendova-Franks AB, et al., 2009, Division of labour in ant colonies in terms of attractive fields, Ecological Complexity, Vol: 6, Pages: 396-402
Pancaldi V, King PR, Christensen K, 2009, Hierarchical coarse-graining transform, Phys Rev E, Vol: 79
Pancaldi V, King PR, Christenen K, 2008, Wavelet-based upscaling of advection equations, Physica A: Statistical Mechanics and its Applications, Vol: 387, Pages: 4760-4770
Christensen K, Farid N, Pruessner G, et al., 2008, On the scaling of probability density functions with apparent power-law exponent less than unity, Eur. Phys. J. B, Vol: 62, Pages: 331-336
Pancaldi V, Christensen K, King P, 2007, Two-phase flow up-scaling using Haar wavelets, Vth IMA conference on modelling permeable rocks
Pancaldi V, Christensen K, King PR, 2007, Upscaling of the saturation equation, 69th European Association of Geoscientists and Engineers Conference and Exhibition 2007: Securing The Future. Incorporating SPE EUROPEC 2007, Vol: 1, Pages: 224-228
Given the high level of detail present in numerical models, fluid dynamic simulations of subsurface flow in porous media are very intensive in computational time. Moreover, to account for the inherent uncertainty in the information available, many realizations of the same model should be constructed to extract statistical data. For this purpose, less detailed coarse scale models are often constructed, starting from the fine scale ones but with a reduced number of grid cells. Each grid cell is now bigger in physical terms and must contain information relative to the entire portion of rock contained in it. The challenge in this process is to find equivalent properties for the important variables in the system, ensuring that the original knowledge about the geological reservoir is preserved as much as possible. Upscaling is the procedure with which these coarse scale effective properties are obtained. We present an upscaling method for the saturation equation governing advcction of a passive tracer in a porous medium. The upscaling rule is such that the saturation on the coarse scale closely matches the averaged fine scale saturation. Results are presented in one-dimensional systems and compared to analytical solutions.
Welinder P, Pruessner G, Christensen K, 2007, Multiscaling in the sequence of areas enclosed by coalescing random walkers, New J. Phys., Vol: 9, Pages: 149-166
Pancaldi V, Christensen K, King P, 2007, Permeability up-scaling using Haar wavelets, Transport in Porous Media, Vol: 67, Pages: 395-412
Peters O, Christensen K, 2006, Rain viewed as relaxational events, JOURNAL OF HYDROLOGY, Vol: 328, Pages: 46-55, ISSN: 0022-1694
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- Citations: 35
Pancaldi V, Christensen K, King P, 2006, Upscaling using Haar wavelets, Computational methods in water resources XVI
Corral A, Christensen K, 2006, Comment on "Earthquakes descaled: On waiting time distributions and scaling laws", PHYSICAL REVIEW LETTERS, Vol: 96, ISSN: 0031-9007
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- Citations: 35
Farid N, Christensen K, 2006, Evolving networks through deletion and duplication, New J. Phys., Vol: 8, Pages: 212-229
Stapleton M, Christensen K, 2006, One-dimensional directed sandpile models and the area under a Brownian curve, J. Phys. A, Vol: 39, Pages: 9107-9126
Stapleton M, Christensen K, 2005, Universality class of one-dimensional directed sandpile models, PHYSICAL REVIEW E, Vol: 72, ISSN: 1539-3755
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- Citations: 3
Kamp C, Christensen K, 2005, Spectral analysis of protein-protein interactions in <i>Drosophila melanogaster</i> -: art. no. 041911, PHYSICAL REVIEW E, Vol: 71, ISSN: 1539-3755
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- Citations: 21
Christensen K, Moloney NR, 2005, Complexity and criticality, London, Publisher: Imperial College Press, ISBN: 9781860945175
Christensen K, Moloney NR, Peters O, et al., 2004, Avalanche behavior in an absorbing state Oslo model, PHYSICAL REVIEW E, Vol: 70, ISSN: 1539-3755
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- Citations: 12
Alstrom P, Bohr T, Christensen K, et al., 2004, Complexity and criticality - In memory of Per Bak (1947-2002), PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, Vol: 340, Pages: V-VIII, ISSN: 0378-4371
Christensen K, 2004, On self-organised criticality in one dimension, PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, Vol: 340, Pages: 527-534, ISSN: 0378-4371
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- Citations: 9
Stapleton M, Dingler M, Christensen K, 2004, Sensitivity to initial conditions in self-organised critical systems, Journal of Statistical Physics, Vol: 117, Pages: 891-900, ISSN: 0022-4715
di Collobiano SA, Christensen K, Jensen HJ, 2003, The tangled nature model as an evolving quasi-species model, JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, Vol: 36, Pages: 883-891, ISSN: 0305-4470
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- Citations: 38
Peters O, Christensen K, 2003, Micro rain radar measurements reveal evidence of self-organised criticality in precipitation processes, Leiden, 6th International Symposium on Tropospheric Profiling, Leipzig, Germany, 14 - 20 September 2003, Publisher: Institute of Tropical Medicine Rotterdam - Leiden, Pages: 312-314
Watkins NW, Chapman SC, Rowlands G, et al., 2002, Comment on "universal fluctuations in correlated systems" [1] (multiple letters), Physical Review Letters, Vol: 89, Pages: 2089011-2089021, ISSN: 0031-9007
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- Citations: 19
Bramwell ST, Christensen K, Fortin JY, et al., 2002, Comment on "Universal fluctuations in correlated systems" -: Reply -: art. no. 208902, PHYSICAL REVIEW LETTERS, Vol: 89, ISSN: 0031-9007
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- Citations: 16
Peters O, Christensen K, 2002, Rain: Relaxations in the sky, PHYSICAL REVIEW E, Vol: 66, ISSN: 1539-3755
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- Citations: 75
Hall M, Christensen K, di Collobiano SA, et al., 2002, Time-dependent extinction rate and species abundance in a tangled-nature model of biological evolution, PHYSICAL REVIEW E, Vol: 66, ISSN: 2470-0045
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- Citations: 73
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