144 research outputs found

    Genetic Correlations in Mutation Processes

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    We study the role of phylogenetic trees on correlations in mutation processes. Generally, correlations decay exponentially with the generation number. We find that two distinct regimes of behavior exist. For mutation rates smaller than a critical rate, the underlying tree morphology is almost irrelevant, while mutation rates higher than this critical rate lead to strong tree-dependent correlations. We show analytically that identical critical behavior underlies all multiple point correlations. This behavior generally characterizes branching processes undergoing mutation.Comment: revtex, 8 pages, 2 fig

    A hybrid neuro--wavelet predictor for QoS control and stability

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    For distributed systems to properly react to peaks of requests, their adaptation activities would benefit from the estimation of the amount of requests. This paper proposes a solution to produce a short-term forecast based on data characterising user behaviour of online services. We use \emph{wavelet analysis}, providing compression and denoising on the observed time series of the amount of past user requests; and a \emph{recurrent neural network} trained with observed data and designed so as to provide well-timed estimations of future requests. The said ensemble has the ability to predict the amount of future user requests with a root mean squared error below 0.06\%. Thanks to prediction, advance resource provision can be performed for the duration of a request peak and for just the right amount of resources, hence avoiding over-provisioning and associated costs. Moreover, reliable provision lets users enjoy a level of availability of services unaffected by load variations

    Domain Growth, Wetting and Scaling in Porous Media

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    The lattice Boltzmann (LB) method is used to study the kinetics of domain growth of a binary fluid in a number of geometries modeling porous media. Unlike the traditional methods which solve the Cahn-Hilliard equation, the LB method correctly simulates fluid properties, phase segregation, interface dynamics and wetting. Our results, based on lattice sizes of up to 4096×40964096\times 4096, do not show evidence to indicate the breakdown of late stage dynamical scaling, and suggest that confinement of the fluid is the key to the slow kinetics observed. Randomness of the pore structure appears unnecessary.Comment: 13 pages, latex, submitted to PR

    Interaction of Hawking radiation with static sources in deSitter and Schwarzschild-deSitter spacetimes

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    We study and look for similarities between the response rates RdS(a0,Λ)R^{\rm dS}(a_0, \Lambda) and RSdS(a0,Λ,M)R^{\rm SdS}(a_0, \Lambda, M) of a static scalar source with constant proper acceleration a0a_0 interacting with a massless, conformally coupled Klein-Gordon field in (i) deSitter spacetime, in the Euclidean vacuum, which describes a thermal flux of radiation emanating from the deSitter cosmological horizon, and in (ii) Schwarzschild-deSitter spacetime, in the Gibbons-Hawking vacuum, which describes thermal fluxes of radiation emanating from both the hole and the cosmological horizons, respectively, where Λ\Lambda is the cosmological constant and MM is the black hole mass. After performing the field quantization in each of the above spacetimes, we obtain the response rates at the tree level in terms of an infinite sum of zero-energy field modes possessing all possible angular momentum quantum numbers. In the case of deSitter spacetime, this formula is worked out and a closed, analytical form is obtained. In the case of Schwarzschild-deSitter spacetime such a closed formula could not be obtained, and a numerical analysis is performed. We conclude, in particular, that RdS(a0,Λ)R^{\rm dS}(a_0, \Lambda) and RSdS(a0,Λ,M)R^{\rm SdS}(a_0, \Lambda, M) do not coincide in general, but tend to each other when Λ0\Lambda \to 0 or a0a_0 \to \infty. Our results are also contrasted and shown to agree (in the proper limits) with related ones in the literature.Comment: ReVTeX4 file, 9 pages, 5 figure

    Particle production and classical condensates in de Sitter space

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    The cosmological particle production in a k=0k=0 expanding de Sitter universe with a Hubble parameter H0H_0 is considered for various values of mass or conformal coupling of a free, scalar field. One finds that, for a minimally coupled field with mass 0m2<9H02/40 \leq m^2 < 9 H_0^2/4 (except for m2=2H02m^2= 2H_0^2), the one-mode occupation number grows to unity soon after the physical wavelength of the mode becomes larger than the Hubble radius, and afterwards diverges as n(t)O(1)(λphys(t)/H01)2νn(t) \sim O(1)(\lambda_{phys}(t)/H_0^{-1})^{2\nu}, where ν[9/4m2/H02]1/2\nu \equiv [9/4 - m^2/H_0^2]^{1/2}. However, for a field with m2>9H02/4m^2 > 9H_0^2/4, the occupation number of a mode outside the Hubble radius is rapidly oscillating and bounded and does not exceed unity. These results, readily generalized for cases of a nonminimal coupling, provide a clear argument that the long-wavelength vacuum fluctuations of low-mass fields in an inflationary universe do show classical behavior, while those of heavy fields do not. The interaction or self-interaction does not appear necessary for the emergence of classical features, which are entirely due to the rapid expansion of the de Sitter background and the upside-down nature of quantum oscillators for modes outside the Hubble radius.Comment: Revtex + 5 postscript figures. Accepted for Phys Rev D15. Revision of Aug 1996 preprint limited to the inclusion and discussion of references suggested by the referee
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