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Sökning: LAR1:gu > Tidskriftsartikel > Chalmers tekniska högskola > Jagers Peter 1941

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21.
  • Jagers, Peter, 1941 (författare)
  • Opinionsmätningar tar över
  • 2009
  • Ingår i: Dagens Nyheter. ; 2009-04-07
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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22.
  • Jagers, Peter, 1941, et al. (författare)
  • Politiken hotar matematiken
  • 2009
  • Ingår i: Svenska Dagbladet. ; 2009-09-02
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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23.
  • Jagers, Peter, 1941, et al. (författare)
  • Population-size-dependent, age-structured branching processes linger around their carrying capacity
  • 2011
  • Ingår i: Journal of Applied Probability. - 0021-9002. ; 48A, s. 249-260
  • Tidskriftsartikel (refereegranskat)abstract
    • Dependence of individual reproduction upon the size of the whole population is studied in a general branching process context. The particular feature under scrutiny is that of reproduction changing from supercritical in small populations to subcritical in large ones. The transition occurs when population size passes a critical threshold, known in ecology as the carrying capacity. We show that populations either die out directly, never coming close to the carrying capacity, or else they grow quickly towards the latter, subsequently lingering around it for a time that is expected to be exponentially long in terms of a carrying capacity tending to infinity.
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24.
  • Jagers, Peter, 1941, et al. (författare)
  • Populations in environments with a soft carrying capacity are eventually extinct
  • 2020
  • Ingår i: Journal of Mathematical Biology. - : Springer Science and Business Media LLC. - 0303-6812 .- 1432-1416. ; 81:3, s. 845 -851
  • Tidskriftsartikel (refereegranskat)abstract
    • Consider a population whose size changes stepwise by its members reproducing or dying (disappearing), but is otherwise quite general. Denote the initial (non-random) size by Z(0) and the size of the nth change by C-n, n = 1, 2, .... Population sizes hence develop successively as Z(1) = Z(0) + C-1, Z(2) = Z(1)+ C-2 and so on, indefinitely or until there are no further size changes, due to extinction. Extinction is thus assumed final, so that Z(n) = 0 implies that Z(n+1) = 0, without there being any other finite absorbing class of population sizes. We make no assumptions about the time durations between the successive changes. In the real world, or more specific models, those may be of varying length, depending upon individual life span distributions and their interdependencies, the age-distribution at hand and intervening circumstances. We could consider toy models of Galton-Watson type generation counting or of the birth-and-death type, with one individual acting per change, until extinction, or the most general multitype CMJ branching processes with, say, population size dependence of reproduction. Changes may have quite varying distributions. The basic assumption is that there is a carrying capacity, i.e. a non-negative number K such that the conditional expectation of the change, given the complete past history, is non-positive whenever the population exceeds the carrying capacity. Further, to avoid unnecessary technicalities, we assume that the change C-n equals -1 (one individual dying) with a conditional (given the past) probability uniformly bounded away from 0. It is a simple and not very restrictive way to avoid parity phenomena, it is related to irreducibility in Markov settings. The straightforward, but in contents and implications far-reaching, consequence is that all such populations must die out. Mathematically, it follows by a supermartingale convergence property and positive probability of reaching the absorbing extinction state.
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25.
  • Jagers, Peter, 1941, et al. (författare)
  • Random variation and concentration effects in PCR
  • 2003
  • Ingår i: J. Theoret. Biol. 224, 299-304 (2003). - 0022-5193 .- 1095-8541. ; 224, s. 299-304
  • Tidskriftsartikel (refereegranskat)abstract
    • Even though the efficiency of the PCR reaction decreases, analyses are made in terms of Galton-Watson processes, or simple deterministic models with constant replication probability (efficiency).Recently Schnell and Mendoza have suggested that the form of the efficiency can be derived from enzyme kinetics. This results in the sequence of molecules numbers forming a stochastic process with the properties of a branching process with population size dependence, which is supercritical, but has a mean reproductionnumber that approaches one. Such processes display ultimate linear growth, after an initial exponential phase, as is the case in PCR. It is also shown that the resulting stochastic process for a large Michaelis Menten constant behaves like the deterministic sequence x_n arising by iterations of the function f(x) = x+x/(1+x).
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26.
  • Jagers, Peter, 1941, et al. (författare)
  • Stochastic fixed points for the maximum
  • 2004
  • Ingår i: Trends in Mathematics} Birkh\"auser Verlag, Basel (2004).
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider stochastic fixed point equations X=sup_iT_iX_i (in distribution) in Xfor known $T=(T_1,T_2,... The rvs T,X_i,i = 1, 2, .. are independent and X_i distributed as X. We present a systematic approach in order to find solutions using the monotonicity of the corresponding operator. These equations come up in the natural setting of weighted trees with finite or countable many branches. Examples are in branching processes and the analysis of algorithms (for parallel computing).
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27.
  • Jagers, Peter, 1941, et al. (författare)
  • Stochasticity in the adaptive dynamics of evolution: the bare bones
  • 2011
  • Ingår i: Journal of Biological Dynamics. - : Informa UK Limited. - 1751-3758 .- 1751-3766. ; 5:2, s. 147-162
  • Tidskriftsartikel (refereegranskat)abstract
    • First a population model with one single type of individuals is considered. Individuals reproduce asexually by splitting into two, with a population size dependent probability. Population extinction, growth and persistence are studied. Subsequently results are extended to such a population with two competing morphs.Results are applied to a simple model, where morphs arise through mutation. The movement in trait space of a monomorphic population and its possible branching into polymorphism are discussed. This is a first report.It purports to display the basic conceptual structure of a simple exact probabilistic formulation of adaptive dynamics.
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29.
  • Jagers, Peter, 1941, et al. (författare)
  • The mixing advantage is less than 2
  • 2009
  • Ingår i: Extremes. - : Springer Science and Business Media LLC. - 1386-1999 .- 1572-915X. ; 12:1, s. 19-31
  • Tidskriftsartikel (refereegranskat)abstract
    • Corresponding to n independent non-negative random variables X_1,...,X_n , are values M_1,...,M_n , where each M_i is the expected value of the maximum of n independent copies of X_i. We obtain an upper bound for the expected value of the maximum of X_1,...,X_n in terms of M_1,...,M_n . This inequality is sharp in the sense that the random variables can be chosen so that the bound is approached arbitrarily closely. We also present related comparison results.
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  • Resultat 21-30 av 38

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