2,362 research outputs found
Productivity estimated as in vivo chlorophyll a fluorescence and biochemical composition in Chlorella fusca (Chlorophyta) grown in outdoor thin-layer cascades
The photosynthetic performance by using in vivo chlorophyll a florescence, biomass composition and productivity of three cultures of Chlorella fusca (Chlorophyta) grown in thin-layer cascades (TLCs) in different locations and time of the year were evaluated. Biomass productivity was higher in 120 m-1 S/V TLC (3.65 g L-1 d-1) compared at 27 m-1 S/V TLC (0.08-0.15 g L-1 d-1). Online monitoring of in vivo chlorophyll fluorescence provided data with high temporal resolution. The simultaneous measure of the PAR irradiance and the effective quantum yield together to the determination of absorption coefficient allowed the determination of daily Electron transport rate (ETR), what led to the estimation of biomass productivity by using conversion factors of mol photons per oxygen produced and relation between carbon assimilated and oxygen produced. The relation between estimated productivity and measured productivity estimated as g l-1 d-1 was 0.90 with R2=0.94. Final biochemical composition was similar in summer culture independent of the S/V of the TLC i.e 30-37% DW lipids, 30-34 % DW proteins and 16-19% DW starch. Lower accumulation was found in autumn cultures, ~23, 28% and 13% DW for lipid and starch content, respectively. The S/V ratio of the system was a key factor to obtain high biomass and storage product productivity. This strain was able to grow outdoors in TLC, exhibiting very high productivity according to the optimal photosynthetic performance and accumulating high lipid and protein content. It is shown as first time a good estimation of algal biomass productivity by using daily integrated values of electron transport rate (ETR) converted to estimated biomass productivity.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Sieve-based confidence intervals and bands for L\'{e}vy densities
The estimation of the L\'{e}vy density, the infinite-dimensional parameter
controlling the jump dynamics of a L\'{e}vy process, is considered here under a
discrete-sampling scheme. In this setting, the jumps are latent variables, the
statistical properties of which can be assessed when the frequency and time
horizon of observations increase to infinity at suitable rates. Nonparametric
estimators for the L\'{e}vy density based on Grenander's method of sieves was
proposed in Figueroa-L\'{o}pez [IMS Lecture Notes 57 (2009) 117--146]. In this
paper, central limit theorems for these sieve estimators, both pointwise and
uniform on an interval away from the origin, are obtained, leading to pointwise
confidence intervals and bands for the L\'{e}vy density. In the pointwise case,
our estimators converge to the L\'{e}vy density at a rate that is arbitrarily
close to the rate of the minimax risk of estimation on smooth L\'{e}vy
densities. In the case of uniform bands and discrete regular sampling, our
results are consistent with the case of density estimation, achieving a rate of
order arbitrarily close to , where is the
number of observations. The convergence rates are valid, provided that is
smooth enough and that the time horizon and the dimension of the sieve
are appropriately chosen in terms of .Comment: Published in at http://dx.doi.org/10.3150/10-BEJ286 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Existence of minimal and maximal solutions to first--order differential equations with state--dependent deviated arguments
We prove some new results on existence of solutions to first--order ordinary
differential equations with deviating arguments. Delay differential equations
are included in our general framework, which even allows deviations to depend
on the unknown solutions. Our existence results lean on new definitions of
lower and upper solutions introduced in this paper, and we show with an example
that similar results with the classical definitions are false. We also
introduce an example showing that the problems considered need not have the
least (or the greatest) solution between given lower and upper solutions, but
we can prove that they do have minimal and maximal solutions in the usual
set--theoretic sense. Sufficient conditions for the existence of lower and
upper solutions, with some examples of application, are provided too
Small-time asymptotics of stopped L\'evy bridges and simulation schemes with controlled bias
We characterize the small-time asymptotic behavior of the exit probability of
a L\'evy process out of a two-sided interval and of the law of its overshoot,
conditionally on the terminal value of the process. The asymptotic expansions
are given in the form of a first-order term and a precise computable error
bound. As an important application of these formulas, we develop a novel
adaptive discretization scheme for the Monte Carlo computation of functionals
of killed L\'evy processes with controlled bias. The considered functionals
appear in several domains of mathematical finance (e.g., structural credit risk
models, pricing of barrier options, and contingent convertible bonds) as well
as in natural sciences. The proposed algorithm works by adding discretization
points sampled from the L\'evy bridge density to the skeleton of the process
until the overall error for a given trajectory becomes smaller than the maximum
tolerance given by the user.Comment: Published in at http://dx.doi.org/10.3150/13-BEJ517 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
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