Controle de plantas daninhas em pomares de cajueiro.

bitstream/CNPAT/7813/1/ctec_10.pd

Multimode Hong-Ou-Mandel interference

We consider multimode two-photon interference at a beam splitter by photons created by spontaneous parametric down-conversion. The resulting interference pattern is shown to depend upon the transverse spatial symmetry of the pump beam. In an experiment, we employ the first-order Hermite-Gaussian modes in order to show that, by manipulating the pump beam, one can control the resulting two-photon interference behavior. We expect these results to play an important role in the engineering of quantum states of light for use in quantum information processing and quantum imaging.Comment: 4 pages, 6 figures, submitted to PR

Mean-field calculation of critical parameters and log-periodic characterization of an aperiodic-modulated model

We employ a mean-field approximation to study the Ising model with aperiodic modulation of its interactions in one spatial direction. Two different values for the exchange constant, $J_A$ and $J_B$, are present, according to the Fibonacci sequence. We calculated the pseudo-critical temperatures for finite systems and extrapolate them to the thermodynamic limit. We explicitly obtain the exponents $\beta$, $\delta$, and $\gamma$ and, from the usual scaling relations for anisotropic models at the upper critical dimension (assumed to be 4 for the model we treat), we calculate $\alpha$, $\nu$, $\nu_{//}$, $\eta$, and $\eta_{//}$. Within the framework of a renormalization-group approach, the Fibonacci sequence is a marginal one and we obtain exponents which depend on the ratio $r \equiv J_B/J_A$, as expected. But the scaling relation $\gamma = \beta (\delta -1)$ is obeyed for all values of $r$ we studied. We characterize some thermodynamic functions as log-periodic functions of their arguments, as expected for aperiodic-modulated models, and obtain precise values for the exponents from this characterization.Comment: 17 pages, including 9 figures, to appear in Phys. Rev.

Fracture and fatigue strength of grouted macadams

Grouted macadams form a class of material which provides significant advantages in comparison to both concrete and conventional asphalt, having both rut resistance and a degree of flexibility. This paper presents a series of laboratory tests on several grouted macadam mixtures, for stiffness, fatigue and low temperature fracture. The variables explored include binder grade and content, aggregate size and gradation, and grout strength. Although the material is found to perform fundamentally as an asphalt, there are several significant differences in the form of fatigue behavior found compared to that usually expected from an asphalt. In particular the effect of varying binder content is found to be markedly different. The results are discussed in terms of optimizing mixture design in order to obtain the most desirable combination of properties (stiffness, fatigue strength, low temperature fracture resistance). Discussion is also presented regarding the possible role of grouted macadams as base or binder courses within highway pavements, and the conclusion is drawn that they are likely to provide an economical solution in many circumstances owing to their superior mechanical properties

The Oberbeck-Boussinesq problem modified by a thermo-absorption term

We consider the Oberbeck-Boussinesq problem with an extra coupling, establishing a suitable relation between the velocity and the temperature. Our model involves a system of equations given by the transient Navier-Stokes equations modified by introducing the thermo-absorption term. The model involves also the transient temperature equation with nonlinear diffusion. For the obtained problem, we prove the existence of weak solutions for any N >= 2 and its uniqueness if N = 2. Then, considering a low range of temperature, but upper than the phase changing one, we study several properties related with vanishing in time of the velocity component of the weak solutions. First, assuming the buoyancy forces field extinct after a finite time, we prove the velocity component will extinct in a later finite time, provided the thermo-absorption term is sublinear. In this case, considering a suitable buoyancy forces field which vanishes at some instant of time, we prove the velocity component extinct at the same instant. We prove also that for non-zero buoyancy forces, but decaying at a power time rate, the velocity component decay at analogous power time rates, provided the thermo-absorption term is superlinear. At last, we prove that for a general non-zero bounded buoyancy force, the velocity component exponentially decay in time whether the thermo-absorption term is sub or superlinear. (C) 2011 Elsevier Inc. All rights reserved.FEDER; FCTinfo:eu-repo/semantics/publishedVersio

Of Protein Size and Genomes

An approach for approximately calculating the number of genes in a genome is presented, which takes into account the average protein length expected for the species. A number of virus, bacterial and eukaryotic genomes are scrutinized. Genome figures are presented, which support the average protein size of a species as a criterion for assessing life complexity. The human gene distribution in the 23 chromosomes is investigated emphasizing the genomic rate, the mean 'exon' length, and the mean 'exons per gene'. It is shown that storing all genes of a single human definitely requires less than 12 MB.Comment: 6 pages, 1 figure, 5 table