| 1. |
- Alhassid, Y, et al.
(författare)
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Fano interference and cross-section fluctuations in molecular photodissociation
- 2006
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Ingår i: Physical Review A. - 1050-2947. ; 73
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Tidskriftsartikel (refereegranskat)abstract
- We derive an expression for the total photodissociation cross section of a molecule incorporating both direct and indirect processes that proceed through excited resonances, and show that it exhibits generalized Beutler-Fano line shapes. Assuming that the closed system can be modeled by random-matrix theory, we derive the statistical properties of the photodissociation cross section and find that they are significantly affected by the direct processes. In the limit of isolated resonances, we find that direct processes suppress the correlation hole of the cross-section autocorrelation function and lead to a maximum in the cross-section distribution.
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| 2. |
- Andersson, Björn, et al.
(författare)
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Advective collisions
- 2007
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 80
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Arvedson, Erik, et al.
(författare)
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Staggered ladder spectra.
- 2006
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Ingår i: Physical review letters. - 0031-9007. ; 96:3
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Tidskriftsartikel (refereegranskat)abstract
- We exactly solve a Fokker-Planck equation by determining its eigenvalues and eigenfunctions: we construct nonlinear second-order differential operators which act as raising and lowering operators, generating ladder spectra for the odd- and even-parity states. The ladders are staggered: the odd-even separation differs from even-odd. The Fokker-Planck equation corresponds, in the limit of weak damping, to a generalized Ornstein-Uhlenbeck process where the random force depends upon position as well as time. The process describes damped stochastic acceleration, and exhibits anomalous diffusion at short times and a stationary non-Maxwellian momentum distribution.
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| 4. |
- Bezuglyy, V., et al.
(författare)
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Generalised Ornstein-Uhlenbeck processes
- 2006
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Ingår i: Journal of Mathematical Physics. - : AIP Publishing. - 0022-2488 .- 1089-7658. ; 47
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Tidskriftsartikel (refereegranskat)abstract
- We solve a physically significant extension of a classic problem in the theory of diffusion, namely the Ornstein-Uhlenbeck process [Ornstein and Uhlenbeck, Phys. Rev. 36, 823 (1930)]. Our generalized Ornstein-Uhlenbeck systems include a force which depends upon the position of the particle, as well as upon time. They exhibit anomalous diffusion at short times, and non-Maxwellian velocity distributions in equilibrium. Two approaches are used. Some statistics are obtained from a closed-form expression for the propagator of the Fokker-Planck equation for the case where the particle is initially at rest. In the general case we use spectral decomposition of a Fokker-Planck equation, employing nonlinear creation and annihilation operators to generate the spectrum which consists of two staggered ladders.
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| 5. |
- Duncan, Kevin, et al.
(författare)
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Clustering by mixing flows.
- 2005
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Ingår i: Physical review letters. - 0031-9007. ; 95:24
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the Lyapunov exponents for particles suspended in a random three-dimensional flow, concentrating on the limit where the viscous damping rate is small compared to the inverse correlation time. In this limit Lyapunov exponents are obtained as a power series in epsilon, a dimensionless measure of the particle inertia. Although the perturbation generates an asymptotic series, we obtain accurate results from a Padé-Borel summation. Our results prove that particles suspended in an incompressible random mixing flow can show pronounced clustering when the Stokes number is large and we characterize two distinct clustering effects which occur in that limit.
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| 6. |
- Eriksson, Anders, 1975, et al.
(författare)
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An accurate model for genetic hitchhiking
- 2008
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Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 178:1, s. 439-451
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Tidskriftsartikel (refereegranskat)abstract
- We suggest a simple deterministic approximation for the growth of the favored-allele frequency during a selective sweep. Using this approximation we introduce an accurate model for genetic hitchhiking. Only when Ns < 10 (N is the population size and s denotes the selection coefficient) are discrepancies between our approximation and direct numerical simulations of a Moran model notable. Our model describes the gene genealogies of a contiguous segment of neutral loci close to the selected one, and it does not assume that the selective sweep happens instantaneously. This enables us to compute SNP distributions on the neutral segment without bias.
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| 7. |
- Eriksson, Anders, 1975, et al.
(författare)
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On the effect of fluctuating recombination rates on the decorrelation of gene histories in the human genome.
- 2005
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Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 169:2, s. 1175-8
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Tidskriftsartikel (refereegranskat)abstract
- We show how to incorporate fluctuations of the recombination rate along the chromosome into standard gene-genealogical models for the decorrelation of gene histories. This enables us to determine how small-scale fluctuations (Poissonian hot-spot model) and large-scale variations (Kong et al. 2002) of the recombination rate influence this decorrelation. We find that the empirically determined large-scale variations of the recombination rate give rise to a significantly slower decay of correlations compared to the standard, unstructured gene-genealogical model assuming constant recombination rate. A model with long-range recombination-rate variations and with demographic structure (divergent population) is found to be consistent with the empirically observed slow decorrelation of gene histories. Conversely, we show that small-scale recombination-rate fluctuations do not alter the large-scale decorrelation of gene histories.
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| 8. |
- Eriksson, Anders, 1975, et al.
(författare)
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Sequential Markov coalescent algorithms for population models with demographic structure.
- 2009
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Ingår i: Theoretical population biology. - : Elsevier BV. - 1096-0325 .- 0040-5809. ; 76:2, s. 84-91
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Tidskriftsartikel (refereegranskat)abstract
- We analyse sequential Markov coalescent algorithms for populations with demographic structure: for a bottleneck model, a population-divergence model, and for a two-island model with migration. The sequential Markov coalescent method is an approximation to the coalescent suggested by McVean and Cardin, and by Marjoram and Wall. Within this algorithm we compute, for two individuals randomly sampled from the population, the correlation between times to the most recent common ancestor and the linkage probability corresponding to two different loci with recombination rate R between them. These quantities characterise the linkage between the two loci in question. We find that the sequential Markov coalescent method approximates the coalescent well in general in models with demographic structure. An exception is the case where individuals are sampled from populations separated by reduced gene flow. In this situation, the correlations may be significantly underestimated. We explain why this is the case.
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