602,070 research outputs found
The origin of biological macromolecules on the earth. The hypothesis of inorganic template
Studies about the origin of life are reviewed. The nonrandom organization of organelles is discussed from a structural and functional point of view. After postulating that the origin of biomacromolecules was not a random event, the paper develops the hypothesis that polypeptides and polynucleotides were formed on an inorganic template. Only information-containing structures can pass natural selection and develop through evolution
Quantification and prediction of extreme events in a one-dimensional nonlinear dispersive wave model
The aim of this work is the quantification and prediction of rare events
characterized by extreme intensity in nonlinear waves with broad spectra. We
consider a one-dimensional non- linear model with deep-water waves dispersion
relation, the Majda-McLaughlin-Tabak (MMT) model, in a dynamical regime that is
characterized by broadband spectrum and strong non- linear energy transfers
during the development of intermittent events with finite-lifetime. To
understand the energy transfers that occur during the development of an extreme
event we perform a spatially localized analysis of the energy distribution
along different wavenumbers by means of the Gabor transform. A stochastic
analysis of the Gabor coefficients reveals i) the low-dimensionality of the
intermittent structures, ii) the interplay between non-Gaussian statis- tical
properties and nonlinear energy transfers between modes, as well as iii) the
critical scales (or critical Gabor coefficients) where a critical amount of
energy can trigger the formation of an extreme event. We analyze the unstable
character of these special localized modes directly through the system equation
and show that these intermittent events are due to the interplay of the system
nonlinearity, the wave dispersion, and the wave dissipation which mimics wave
breaking. These localized instabilities are triggered by random localizations
of energy in space, created by the dispersive propagation of low-amplitude
waves with random phase. Based on these properties, we design low-dimensional
functionals of these Gabor coefficients that allow for the prediction of the
extreme event well before the nonlinear interactions begin to occur.Comment: 21 pages, 14 figure
Gamma-based clustering via ordered means with application to gene-expression analysis
Discrete mixture models provide a well-known basis for effective clustering
algorithms, although technical challenges have limited their scope. In the
context of gene-expression data analysis, a model is presented that mixes over
a finite catalog of structures, each one representing equality and inequality
constraints among latent expected values. Computations depend on the
probability that independent gamma-distributed variables attain each of their
possible orderings. Each ordering event is equivalent to an event in
independent negative-binomial random variables, and this finding guides a
dynamic-programming calculation. The structuring of mixture-model components
according to constraints among latent means leads to strict concavity of the
mixture log likelihood. In addition to its beneficial numerical properties, the
clustering method shows promising results in an empirical study.Comment: Published in at http://dx.doi.org/10.1214/10-AOS805 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Accelerated rogue waves generated by soliton fusion at the advanced stage of supercontinuum formation in photonic crystal fibers
Soliton fusion is a fascinating and delicate phenomenon that manifests itself
in optical fibers in case of interaction between co-propagating solitons with
small temporal and wavelengths separation. We show that the mechanism of
acceleration of trailing soliton by dispersive waves radiated from the
preceding one provides necessary conditions for soliton fusion at the advanced
stage of supercontinuum generation in photonic crystal fibers. As a result of
fusion large intensity robust light structures arise and propagate over
significant distances. In presence of small random noise the delicate condition
for the effective fusion between solitons can easily be broken, making the
fusion induced giant waves a rare statistical event. Thus oblong-shaped giant
accelerated waves become excellent candidates for optical rogue waves.Comment: Optics Letters Journal. In pres
Random combinatorial structures: the convergent case
This paper studies the distribution of the component spectrum of combinatorial structures such as uniform random forests, in which the classical generating function for the numbers of (irreducible) elements of the different sizes converges at the radius of convergence; here, this property is expressed in terms of the expectations of independent random variables Zj, j ≥ 1, whose joint distribution, conditional on the event that Σnj=1 jZj = n, gives the distribution of the component spectrum for a random structure of size n. For a large class of such structures, we show that the component spectrum is asymptotically composed of Zj components of small sizes j, j ≥ 1, with the remaining part, of size close to n, being made up of a single, giant component
Grasping asymmetric information in market impacts
The price impact for a single trade is estimated by the immediate response on
an event time scale, i.e., the immediate change of midpoint prices before and
after a trade. We work out the price impacts across a correlated financial
market. We quantify the asymmetries of the distributions and of the market
structures of cross-impacts, and find that the impacts across the market are
asymmetric and non-random. Using spectral statistics and Shannon entropy, we
visualize the asymmetric information in price impacts. Also, we introduce an
entropy of impacts to estimate the randomness between stocks. We show that the
useful information is encoded in the impacts corresponding to small entropy.
The stocks with large number of trades are more likely to impact others, while
the less traded stocks have higher probability to be impacted by others
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