40,746 research outputs found
Analysis of marketing systems on traditional bananas and plantains in Peru
Poster presented at Tropentag 2011 - Development on the Margin. Bonn (Germany), 3-7 Oct 2011
Vector-valued Littlewood-Paley-Stein theory for semigroups
We develop a generalized Littlewood-Paley theory for semigroups acting on
-spaces of functions with values in uniformly convex or smooth Banach
spaces. We characterize, in the vector-valued setting, the validity of the
one-sided inequalities concerning the generalized Littlewood-Paley-Stein
-function associated with a subordinated Poisson symmetric diffusion
semigroup by the martingale cotype and type properties of the underlying Banach
space. We show that in the case of the usual Poisson semigroup and the Poisson
semigroup subordinated to the Ornstein-Uhlenbeck semigroup on ,
this general theory becomes more satisfactory (and easier to be handled) in
virtue of the theory of vector-valued Calder\'on-Zygmund singular integral
operators.Comment: To appear in Adv. Mat
Prediction of jet engine parameters for control design using genetic programming
The simulation of a jet engine behavior is widely used in many different aspects of the engine development and maintenance. Achieving high quality jet engine control systems requires the iterative use of these simulations to virtually test the performance of the engine avoiding any possible damage on the real engine. Jet engine simulations involve the use of mathematical models which are complex and may not always be available. This paper introduces an approach based on Genetic Programming (GP) to model different parameters of a small engine for control design such as the Exhaust Gas Temperature (EGT). The GP approach has no knowledge of the characteristics of the engine. Instead, the model is found by the evolution of models based on past measurements of parameters such as the pump voltage. Once the model is obtained, it is used to predict the behaviour of the jet engine one step ahead. The proposed approach is successfully applied for the simulation of a Behotec j66 jet engine and the results are presented
Supernova neutrinos and nucleosynthesis
Observations of metal-poor stars indicate that at least two different
nucleosynthesis sites contribute to the production of r-process elements. One
site is responsible for the production of light r-process elements Z<~50 while
the other produces the heavy r-process elements. We have analyzed recent
observations of metal-poor stars selecting only stars that are enriched in
light r-process elements and poor in heavy r-process elements. We find a strong
correlation between the observed abundances of the N=50 elements (Sr, Y and Zr)
and Fe. It suggest that neutrino-driven winds from core-collapse supernova are
the main site for the production of these elements. We explore this possibility
by performing nucleosynthesis calculations based on long term Boltzmann
neutrino transport simulations. They are based on an Equation of State that
reproduces recent constrains on the nuclear symmetry energy. We predict that
the early ejecta is neutron-rich with Ye ~ 0.48, it becomes proton rich around
4 s and reaches Ye = 0.586 at 9 s when our simulation stops. The
nucleosynthesis in this model produces elements between Zn and Mo, including
92Mo. The elemental abundances are consistent with the observations of the
metal-poor star HD 12263. For the elements between Ge and Mo, we produce mainly
the neutron-deficient isotopes. This prediction can be confirmed by
observations of isotopic abundances in metal-poor stars. No elements heavier
than Mo (Z=42) and no heavy r-process elements are produced in our
calculations.Comment: 18 pages, 5 figures, submitted to J. Phys. G: Nucl. Part. Phys.
(Focus issue "Nucleosynthesis and the role of neutrinos", ed. Baha Balantekin
and Cristina Volpe
Effects of heat release on triple flames
Heat release effects on laminar flame propagation in partially premixed flows are studied. Data for analysis are obtained from direct numerical simulations of a laminar mixing layer with a uniformly approaching velocity field. The structure that evolves under such conditions is a triple flame, which consists of two premixed wings and a trailing diffusion flame. Heat release increases the flame speed over that of the corresponding planar premixed flame. In agreement with previous analytical work, reductions in the mixture fraction gradient also increase the flame speed. The effects of heat release and mixture fraction gradients on flame speed are not independent, however; heat release modifies the effective mixture fraction gradient in front of the flame. For very small mixture fraction gradients, scaling laws that determine the flame speed in terms of the density change are presented. © 1995 American Institute of Physics
Non-degenerate solutions of universal Whitham hierarchy
The notion of non-degenerate solutions for the dispersionless Toda hierarchy
is generalized to the universal Whitham hierarchy of genus zero with
marked points. These solutions are characterized by a Riemann-Hilbert problem
(generalized string equations) with respect to two-dimensional canonical
transformations, and may be thought of as a kind of general solutions of the
hierarchy. The Riemann-Hilbert problem contains arbitrary functions
, , which play the role of generating functions of
two-dimensional canonical transformations. The solution of the Riemann-Hilbert
problem is described by period maps on the space of -tuples
of conformal maps from disks of the
Riemann sphere and their complements to the Riemann sphere. The period maps are
defined by an infinite number of contour integrals that generalize the notion
of harmonic moments. The -function (free energy) of these solutions is also
shown to have a contour integral representation.Comment: latex2e, using amsmath, amssym and amsthm packages, 32 pages, no
figur
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