53 research outputs found
Multiplier phenomenology in random multiplicative cascade processes
We demonstrate that the correlations observed in conditioned multiplier
distributions of the energy dissipation in fully developed turbulence can be
understood as an unavoidable artefact of the observation procedure. Taking the
latter into account, all reported properties of both unconditioned and
conditioned multiplier distributions can be reproduced by cascade models with
uncorrelated random weights if their bivariate splitting function is non-energy
conserving. For the alpha-model we show that the simulated multiplier
distributions converge to a limiting form, which is very close to the
experimentally observed one. If random translations of the observation window
are accounted for, also the subtle effects found in conditioned multiplier
distributions are precisely reproduced.Comment: 4 pages, 3 figure
Analytic multivariate generating function for random multiplicative cascade processes
We have found an analytic expression for the multivariate generating function
governing all n-point statistics of random multiplicative cascade processes.
The variable appropriate for this generating function is the logarithm of the
energy density, ln epsilon, rather than epsilon itself. All cumulant statistics
become sums over derivatives of ``branching generating functions'' which are
Laplace transforms of the splitting functions and completely determine the
cascade process. We show that the branching generating function is a
generalization of the multifractal mass exponents. Two simple models from fully
developed turbulence illustrate the new formalism.Comment: REVTeX, 4 pages, 2 PostScript figs, submitted to PR
Spatial correlations of singularity strengths in multifractal branching processes
The n-point statistics of singularity strength variables for multiplicative
branching processes is calculated from an analytic expression of the
corresponding multivariate generating function. The key ingredient is a
branching generating function which can be understood as a natural
generalisation of the multifractal mass exponents. Various random
multiplicative cascade processes pertaining to fully developed turbulence are
discussed.Comment: REVTeX, 18 pages, 5 PS figs, submitted to PR
Criticality and Superfluidity in liquid He-4 under Nonequilibrium Conditions
We review a striking array of recent experiments, and their theoretical
interpretations, on the superfluid transition in He in the presence of a
heat flux, . We define and evaluate a new set of critical point exponents.
The statics and dynamics of the superfluid-normal interface are discussed, with
special attention to the role of gravity. If is in the same direction as
gravity, a self-organized state can arise, in which the entire sample has a
uniform reduced temperature, on either the normal or superfluid side of the
transition. Finally, we review recent theory and experiment regarding the heat
capacity at constant . The excitement that surrounds this field arises from
the fact that advanced thermometry and the future availability of a
microgravity experimental platform aboard the International Space Station will
soon open to experimental exploration decades of reduced temperature that were
previously inaccessible.Comment: 16 pages, 9 figures, plus harvard.sty style file for references
Accepted for publication in Colloquia section of Reviews of Modern Physic
Genetic variability of the neogregarine apicystis bombi, an etiological agent of an emergent bumblebee disease
The worldwide spread of diseases is considered a major threat to biodiversity and a possible driver of the decline of pollinator populations, particularly when novel species or strains of parasites emerge. Previous studies have suggested that populations of introduced European honeybee (Apis mellifera) and bumblebee species (Bombus terrestris and Bombus ruderatus) in Argentina share the neogregarine parasite Apicystis bombi with the native bumblebee (Bombus dahlbomii). In this study we investigated whether A. bombi is acting as an emergent parasite in the non-native populations. Specifically, we asked whether A. bombi, recently identified in Argentina, was introduced by European, non-native bees. Using ITS1 and ITS2 to assess the parasite's intraspecific genetic variation in bees from Argentina and Europe, we found a largely unstructured parasite population, with only 15% of the genetic variation being explained by geographic location. The most abundant haplotype in Argentina (found in all 9 specimens of non-native species) was identical to the most abundant haplotype in Europe (found in 6 out of 8 specimens). Similarly, there was no evidence of structuring by host species, with this factor explaining only 17% of the genetic variation. Interestingly, parasites in native Bombus ephippiatus from Mexico were genetically distant from the Argentine and European samples, suggesting that sufficient variability does exist in the ITS region to identify continent-level genetic structure in the parasite. Thus, the data suggest that A. bombi from Argentina and Europe share a common, relatively recent origin. Although our data did not provide information on the direction of transfer, the absence of genetic structure across space and host species suggests that A. bombi may be acting as an emergent infectious disease across bee taxa and continents
Wavelets and Some Applications in Physics
The basic ideas of the wavelet transformation are sketched. Some applications in (statistical) physics are indicated
Wavelet-Correlations In Hierarchical Cascade Processes -- The Question Of Scaling And Clustering In Complex Reactions
Introduction Relativistic heavy-ion collisions represent very complex reactions. A theoretician imagines these reactions to occur in various steps. An experimentalist, on the other hand, only measures the hundreds or thousands of particles which come out as the final state of the reaction. Here, a simple question comes to our minds: Given only the outcome, is it possible to analyse and reconstruct the underlying evolution process? Surely an extensive statistical analysis would be necessary for such a demanding enterprise and this means correlation functions to all orders. With conventional representations of the correlation functions this will not work in practice as we have to cope with an enormous amount of redundant information. New techniques have to be employed, which discard redundancy and concentrate on the really important information. Such new compression and analysing techniques can be borrowed from signal analysis. Over the past ten years it has been the wa
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