2,155 research outputs found
Precise tail asymptotics of fixed points of the smoothing transform with general weights
We consider solutions of the stochastic equation ,
where is a fixed constant, are independent, identically distributed
random variables and are independent copies of , which are independent
both from 's and . The hypotheses ensuring existence of solutions are
well known. Moreover under a number of assumptions the main being
and , the
limit exists. In the present
paper, we prove positivity of .Comment: Published at http://dx.doi.org/10.3150/13-BEJ576 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Large deviations for solutions to stochastic recurrence equations under Kesten's condition
In this paper we prove large deviations results for partial sums constructed
from the solution to a stochastic recurrence equation. We assume Kesten's
condition [Acta Math. 131 (1973) 207-248] under which the solution of the
stochastic recurrence equation has a marginal distribution with power law
tails, while the noise sequence of the equations can have light tails. The
results of the paper are analogs to those obtained by A. V. Nagaev [Theory
Probab. Appl. 14 (1969) 51-64; 193-208] and S. V. Nagaev [Ann. Probab. 7 (1979)
745-789] in the case of partial sums of i.i.d. random variables. In the latter
case, the large deviation probabilities of the partial sums are essentially
determined by the largest step size of the partial sum. For the solution to a
stochastic recurrence equation, the magnitude of the large deviation
probabilities is again given by the tail of the maximum summand, but the exact
asymptotic tail behavior is also influenced by clusters of extreme values, due
to dependencies in the sequence. We apply the large deviation results to study
the asymptotic behavior of the ruin probabilities in the model.Comment: Published in at http://dx.doi.org/10.1214/12-AOP782 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Characterization of a caleosin expressed during olive (Olea europaea L.) pollen ontogeny
<p>Abstract</p> <p>Background</p> <p>The olive tree is an oil-storing species, with pollen being the second most active site in storage lipid biosynthesis. Caleosins are proteins involved in storage lipid mobilization during seed germination. Despite the existence of different lipidic structures in the anther, there are no data regarding the presence of caleosins in this organ to date. The purpose of the present work was to characterize a caleosin expressed in the olive anther over different key stages of pollen ontogeny, as a first approach to unravel its biological function in reproduction.</p> <p>Results</p> <p>A 30 kDa caleosin was identified in the anther tissues by Western blot analysis. Using fluorescence and transmission electron microscopic immunolocalization methods, the protein was first localized in the tapetal cells at the free microspore stage. Caleosins were released to the anther locule and further deposited onto the sculptures of the pollen exine. As anthers developed, tapetal cells showed the presence of structures constituted by caleosin-containing lipid droplets closely packed and enclosed by ER-derived cisternae and vesicles. After tapetal cells lost their integrity, the caleosin-containing remnants of the tapetum filled the cavities of the mature pollen exine, forming the pollen coat. In developing microspores, this caleosin was initially detected on the exine sculptures. During pollen maturation, caleosin levels progressively increased in the vegetative cell, concurrently with the number of oil bodies. The olive pollen caleosin was able to bind calcium <it>in vitro</it>. Moreover, PEGylation experiments supported the structural conformation model suggested for caleosins from seed oil bodies.</p> <p>Conclusions</p> <p>In the olive anther, a caleosin is expressed in both the tapetal and germ line cells, with its synthesis independently regulated. The pollen oil body-associated caleosin is synthesized by the vegetative cell, whereas the protein located on the pollen exine and its coating has a sporophytic origin. The biological significance of the caleosin in the reproductive process in species possessing lipid-storing pollen might depend on its subcellular emplacement. The pollen inner caleosin may be involved in OB biogenesis during pollen maturation. The protein located on the outside might rather play a function in pollen-stigma interaction during pollen hydration and germination.</p
Maximizing the hyperpolarizability of one-dimensional systems
Previous studies have used numerical methods to optimize the
hyperpolarizability of a one-dimensional quantum system. These studies were
used to suggest properties of one-dimensional organic molecules, such as the
degree of modulation of conjugation, that could potentially be adjusted to
improve the nonlinear-optical response. However, there were no conditions set
on the optimized potential energy function to ensure that the resulting
energies were consistent with what is observed in real molecules. Furthermore,
the system was placed into a one-dimensional box with infinite walls, forcing
the wavefunctions to vanish at the ends of the molecule. In the present work,
the walls are separated by a distance much larger than the molecule's length;
and, the variations of the potential energy function are restricted to levels
that are more typical of a real molecule. In addition to being a more
physically-reasonable model, our present approach better approximates the bound
states and approximates the continuum states - which are usually ignored. We
find that the same universal properties continue to be important for optimizing
the nonlinear-optical response, though the details of the wavefunctions differ
from previous result.Comment: 10 pages, 5 figure
Generalized Berreman's model of the elastic surface free energy of a nematic liquid crystal on a sawtoothed substrate
In this paper we present a generalization of Berreman's model for the elastic
contribution to the surface free-energy density of a nematic liquid crystal in
presence of a sawtooth substrate which favours homeotropic anchoring, as a
function of the wavenumber of the surface structure , the tilt angle
and the surface anchoring strength . In addition to the previously
reported non-analytic contribution proportional to , due to the
nucleation of disclination lines at the wedge bottoms and apexes of the
substrate, the next-to-leading contribution is proportional to for a given
substrate roughness, in agreement with Berreman's predictions. We characterise
this term, finding that it has two contributions: the deviations of the nematic
director field with respect to the corresponding to the isolated disclination
lines, and their associated core free energies. Comparison with the results
obtained from the Landau-de Gennes model shows that our model is quite accurate
in the limit , when strong anchoring conditions are effectively achieved.Comment: 13 pages, 9 figures; revised version submitted to Phys. Rev.
Monocular, Real-Time Surface Reconstruction using Dynamic Level of Detail
We present a scalable, real-time capable method for robust surface reconstruction that explicitly handles multiple scales. As a monocular camera browses a scene, our algorithm processes images as they arrive and incrementally builds a detailed surface model. While most of the existing reconstruction approaches rely on volumetric or point-cloud representations of the environment, we perform depth-map and colour fusion directly into a multi-resolution triangular mesh that can be adaptively tessellated using the concept of Dynamic Level of Detail. Our method relies on least-squares optimisation, which enables a probabilistically sound and principled formulation of the fusion algorithm. We demonstrate that our method is capable of obtaining high quality, close-up reconstruction, as well as capturing overall scene geometry, while being memory and computationally efficient
Modelling Heat Transfer of Carbon Nanotubes
Modelling heat transfer of carbon nanotubes is important for the thermal
management of nanotube-based composites and nanoelectronic device. By using a
finite element method for three-dimensional anisotropic heat transfer, we have
simulated the heat conduction and temperature variations of a single nanotube,
a nanotube array and a part of nanotube-based composite surface with heat
generation. The thermal conductivity used is obtained from the upscaled value
from the molecular simulations or experiments. Simulations show that nanotube
arrays have unique cooling characteristics due to its anisotropic thermal
conductivity.Comment: 10 pages, 4 figure
Large deviation estimates for exceedance times of perpetuity sequences and their dual processes
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