The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform

Kevin S Mckelvey - One of the best experts on this subject based on the ideXlab platform.

  • Power Law Behaviour and parametric models for the size distribution of forest fires
    Ecological Modelling, 2002
    Co-Authors: William J Reed, Kevin S Mckelvey
    Abstract:

    Abstract This paper examines the distribution of areas burned in forest fires. Empirical size distributions, derived from extensive fire records, for six regions in North America are presented. While they show some commonalities, it appears that a simple Power-Law distribution of sizes, as has been suggested by some authors, is too simple to describe the distributions over their full range. A stochastic model for the spread and extinguishment of fires is used to examine conditions for Power-Law Behaviour and deviations from it. The concept of the extinguishment growth rate ratio (EGRR) is developed. A null model with constant EGRR leads to a Power-Law distribution, but this does not appear to hold empirically for the data sets examined. Some alternative parametric forms for the size distribution are presented, with a four-parameter ‘competing hazards’ model providing the overall best fit.

Mark Gerstein - One of the best experts on this subject based on the ideXlab platform.

  • the dominance of the population by a selected few Power Law Behaviour applies to a wide variety of genomic properties
    Genome Biology, 2002
    Co-Authors: Nicholas M Luscombe, Jiang Qian, Zhaolei Zhang, Ted Johnson, Mark Gerstein
    Abstract:

    Background The sequencing of genomes provides us with an inventory of the 'molecular parts' in nature, such as protein families and folds, and their functions in living organisms. Through the analysis of such inventories, it has been shown that different genomes have very different usage of parts; for example, the common folds in the worm are very different from those in Escherichia coli.

  • protein family and fold occurrence in genomes Power Law Behaviour and evolutionary model
    Journal of Molecular Biology, 2001
    Co-Authors: Jiang Qian, Nicholas M Luscombe, Mark Gerstein
    Abstract:

    Global surveys of genomes measure the usage of essential molecular parts, defined here as protein families, superfamilies or folds, in different organisms. Based on surveys of the first 20 completely sequenced gen- omes, we observe that the occurrence of these parts follows a Power-Law distribution. That is, the number of distinct parts (F) with a given geno- mic occurrence (V) decays as Fa aVb , with a few parts occurring many times and most occurring infrequently. For a given organism, the distri- butions of families, superfamilies and folds are nearly identical, and this is reflected in the size of the decay exponent b. Moreover, the exponent varies between different organisms, with those of smaller genomes dis- playing a steeper decay (i.e. larger b). Clearly, the Power Law indicates a preference to duplicate genes that encode for molecular parts which are already common. Here, we present a minimal, but biologically meaning- ful model that accurately describes the observed Power Law. Although the model performs equally well for all three protein classes, we focus on the occurrence of folds in preference to families and superfamilies. This is because folds are comparatively insensitive to the effects of point mutations that can cause a family member to diverge beyond detectable similarity. In the model, genomes evolve through two basic operations: (i) duplication of existing genes; (ii) net flow of new genes. The flow term is closely related to the exponent b and can accommodate consider- able gene loss; however, we demonstrate that the observed data is repro- duced best with a net inflow, i.e. with more gene gain than loss. Moreover, we show that prokaryotes have much higher rates of gene acquisition than eukaryotes, probably reflecting lateral transfer. A further natural outcome from our model is an estimation of the fold composition of the initial genome, which potentially relates to the common ancestor for modern organisms. Supplementary material pertaining to this work is available from www.partslist.org/PowerLaw. # 2001 Academic Press

William J Reed - One of the best experts on this subject based on the ideXlab platform.

  • The Pareto Law of incomes—an explanation and an extension
    Physica A-statistical Mechanics and Its Applications, 2003
    Co-Authors: William J Reed
    Abstract:

    A stochastic model for the generation of observed income distributions is used to provide an explanation for the Pareto Law of incomes. Analysis of the model also yields a prediction of Paretian (Power Law) Behaviour in the lower tail of the distribution and this is shown to occur in a number of empirical distributions. A tractable four-parameter distribution is derived, and shown to fit extremely well to a number of different empirical income distributions.

  • Power Law Behaviour and parametric models for the size distribution of forest fires
    Ecological Modelling, 2002
    Co-Authors: William J Reed, Kevin S Mckelvey
    Abstract:

    Abstract This paper examines the distribution of areas burned in forest fires. Empirical size distributions, derived from extensive fire records, for six regions in North America are presented. While they show some commonalities, it appears that a simple Power-Law distribution of sizes, as has been suggested by some authors, is too simple to describe the distributions over their full range. A stochastic model for the spread and extinguishment of fires is used to examine conditions for Power-Law Behaviour and deviations from it. The concept of the extinguishment growth rate ratio (EGRR) is developed. A null model with constant EGRR leads to a Power-Law distribution, but this does not appear to hold empirically for the data sets examined. Some alternative parametric forms for the size distribution are presented, with a four-parameter ‘competing hazards’ model providing the overall best fit.

  • The Pareto, Zipf and other Power Laws
    Economics Letters, 2001
    Co-Authors: William J Reed
    Abstract:

    Abstract Many empirical size distributions in economics and elsewhere exhibit Power-Law Behaviour in the upper tail. This article contains a simple explanation for this. It also predicts lower-tail Power-Law Behaviour, which is verified empirically for income and city-size data.

S.k. Tripathi - One of the best experts on this subject based on the ideXlab platform.

  • effect of heating rate on the glass transition temperature in se79te15in6 xpbx bulk alloys using Power Law Behaviour
    SOLID STATE PHYSICS: Proceedings of the 58th DAE Solid State Physics Symposium 2013, 2014
    Co-Authors: Balbir Singh Patial, Nagesh Thakur, S.k. Tripathi
    Abstract:

    In the present study, the effect of heating rate on the glass transition temperature (Tg) in quaternary Se79Te15In6-xPbx (x = 0.5, 1, 2 and 4) chalcogenide bulk alloys using differential scanning calorimetry (DSC) experiment under non-isothermal conditions has been reported and discussed. The heating rate dependence of Tg has been investigated theoretically using Power-Law Behaviour. An excellent agreement of Tg has been observed between experimental values obtained from DSC scans and theoretical values using Power-Law Behaviour.

  • Heating rate dependence of the glass transition temperature in Se85–xTe15Inx amorphous alloys
    2013
    Co-Authors: Balbir Singh Patial, Nagesh Thakur, S.k. Tripathi
    Abstract:

    In the present paper, heating rate dependence of glass transition temperature (Tg) of Se85-xTe15Inx (x = 0, 2, 6, 10 and 15) chalcogenide alloys under non-isothermal conditions using differential scanning calorimetry (DSC) technique has been reported and discussed. The glass transition temperature is found to increase with the increase in heating rate. The heating rate dependence of Tg has been investigated theoretically using Power Law Behaviour. An excellent agreement of Tg has been observed between experimental values obtained from DSC scans and theoretical values using Power Law Behaviour.

A Hunt - One of the best experts on this subject based on the ideXlab platform.

  • transport in ionic conducting glasses ii scaling relations and approximate Power Law Behaviour
    Journal of Physics: Condensed Matter, 1992
    Co-Authors: A Hunt
    Abstract:

    For pt.I see ibid., vol.3, p.7831 (1991). A recent theory of transport in ionic conducting glasses treats dielectric relaxation in a pair approximation at high frequencies, an augmented pair approximation at intermediate frequencies, and a cluster theory at low frequencies (below the alpha -peak in the imaginary part of the dielectric constant, epsilon 2( omega )). The results were shown to reproduce the general features of the relaxation. Here the analysis of the results is continued, expressions for the approximate Power of the high-frequency conductivity (the exponent s in sigma ( omega ) alpha omega s) are derived and the degree of the universality of the Barton-Nakajima-Namikawa relation is discussed in view of the non-universality of the Power s.