24,780 research outputs found
Amostragem de solo em plantio direto para aplicação em agricultura de precisão.
O objetivo deste estudo seria a comparação das diversas técnicas estatísticas disponíveis, visando o estudo da amostragem de solo para plantio direto. Com a formação de bases de dados digitais e melhores métodos para coleção de dados e análise geoestatfstica, estudos mais detalhados podem ser realizados sobre a variação dos solos e suas conseqüências.bitstream/item/76078/1/CNPTIA-PESQ.AND.-1-99.pd
Decoherence, pointer engineering and quantum state protection
We present a proposal for protecting states against decoherence, based on the
engineering of pointer states. We apply this procedure to the vibrational
motion of a trapped ion, and show how to protect qubits, squeezed states,
approximate phase eigenstates and superpositions of coherent states.Comment: 1 figur
Damped and sub-damped Lyman-α absorbers in z > 4 QSOs
We present the results of a survey of damped (DLA, log N(H I) > 20.3) and sub-damped Lyman-α systems (19.5 2.55 along the lines-of-sight to 77 quasars with emission redshifts in the range 4 19.5 were detected of which 40 systems are damped Lyman-α systems for an absorption length of ΔX = 378. About half of the lines of sight of this homogeneous survey have never been investigated for DLAs. We study the evolution with redshift of the cosmological density of the neutral gas and find, consistent with previous studies at similar resolution, that Ω_(DLA,HI) decreases at z > 3.5. The overall cosmological evolution of Ω_(HI) shows a peak around this redshift. The H I column density distribution for log N(H I) ≥ 20.3 is fitted, consistent with previous surveys, with a single power-law of index α ~ −1.8 ± 0.25. This power-law overpredicts data at the high-end and a second, much steeper, power-law (or a gamma function) is needed. There is a flattening of the function at lower H I column densities with an index of α ~ −1.4 for the column density range log N(H I) = 19.5−21. The fraction of H I mass in sub-DLAs is of the order of 30%. The H I column density distribution does not evolve strongly from z ~ 2.5 to z ~ 4.5
Distribution of epicenters in the Olami-Feder-Christensen model
We show that the well established Olami-Feder-Christensen (OFC) model for the
dynamics of earthquakes is able to reproduce a new striking property of real
earthquake data. Recently, it has been pointed out by Abe and Suzuki that the
epicenters of earthquakes could be connected in order to generate a graph, with
properties of a scale-free network of the Barabasi-Albert type. However, only
the non conservative version of the Olami-Feder-Christensen model is able to
reproduce this behavior. The conservative version, instead, behaves like a
random graph. Besides indicating the robustness of the model to describe
earthquake dynamics, those findings reinforce that conservative and non
conservative versions of the OFC model are qualitatively different. Also, we
propose a completely new dynamical mechanism that, even without an explicit
rule of preferential attachment, generates a free scale network. The
preferential attachment is in this case a ``by-product'' of the long term
correlations associated with the self-organized critical state. The detailed
study of the properties of this network can reveal new aspects of the dynamics
of the OFC model, contributing to the understanding of self-organized
criticality in non conserving models.Comment: 7 pages, 7 figure
Non-linear Poisson-Boltzmann Theory for Swollen Clays
The non-linear Poisson-Boltzmann equation for a circular, uniformly charged
platelet, confined together with co- and counter-ions to a cylindrical cell, is
solved semi-analytically by transforming it into an integral equation and
solving the latter iteratively. This method proves efficient, robust, and can
be readily generalized to other problems based on cell models, treated within
non-linear Poisson-like theory. The solution to the PB equation is computed
over a wide range of physical conditions, and the resulting osmotic equation of
state is shown to be in fair agreement with recent experimental data for
Laponite clay suspensions, in the concentrated gel phase.Comment: 13 pages, 4 postscript figure
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