189 research outputs found
Avaliação de acessos de alfafa na região sudeste do Brasil.
O trabalho foi desenvolvido em São Carlos, SP, região Central do Estado de São Paulo. Foram avaliados 92 acessos de alfafa quanto a produção de forragem, por meio de um delineamento experimental de blocos ao acaso, com duas repetições. Em 14 cortes de produção, ocorreram diferenças significativas para a produção de matéria seca, com destaque para LEN 4, P30, Crioula, Barbara SP INTA e P5715, com produção média acima de 1800 Kg de matéria seca/ha/corte
Three-Wave Modulational Stability and Dark Solitons in a Quadratic Nonlinear Waveguide with Grating
We consider continuous-wave (CW) states and dark solitons (DSs) in a system
of two fundamental-frequency (FF) and one second-harmonic (SH) waves in a
planar waveguide with the quadratic nonlinearity, the FF components being
linearly coupled by resonant reflections on the Bragg grating. We demonstrate
that, in contrast with the usual situation in quadratic spatial-domain models,
CW states with the phase shift between the FF and SH components are
modulationally stable in a broad parameter region in this system, provided that
the CW wavenumber does not belong to the system's spectral gap. Stationary
fundamental DSs are found numerically, and are also constructed by means of a
specially devised analytical approximation. Bound states of two and three DSs
are found too. The fundamental DSs and two-solitons bound states are stable in
all the cases when the CW background is stable, which is shown by dint of
calculation of the corresponding eigenvalues, and verified in direct
simulations. Tilted DSs are found too. They attain a maximum contrast at a
finite value of the tilt, that does not depend on the phase mismatch. At a
maximum value of the tilt, which grows with the mismatch, the DS merges into
the CW background. Interactions between the tilted solitons are shown to be
completely elastic.Comment: 10 pages, 12 figures; Journal of Optics A, in pres
Spatiotemporally Localized Multidimensional Solitons in Self-Induced Transparency Media
"Light bullets" are multi-dimensional solitons which are localized in both
space and time. We show that such solitons exist in two- and three-dimensional
self-induced-transparency media and that they are fully stable. Our approximate
analytical calculation, backed and verified by direct numerical simulations,
yields the multi-dimensional generalization of the one-dimensional Sine-Gordon
soliton.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Spatiotemporally localized solitons in resonantly absorbing Bragg reflectors
We predict the existence of spatiotemporal solitons (``light bullets'') in
two-dimensional self-induced transparency media embedded in a Bragg grating.
The "bullets" are found in an approximate analytical form, their stability
being confirmed by direct simulations. These findings suggest new possibilities
for signal transmission control and self-trapping of light.Comment: RevTex, 3 pages, 2 figures, to be published in PR
Angular Dependences of Third Harmonic Generation from Microdroplets
We present experimental and theoretical results for the angular dependence of
third harmonic generation (THG) of water droplets in the micrometer range (size
parameter ). The THG signal in - and -polarization obtained
with ultrashort laser pulses is compared with a recently developed nonlinear
extension of classical Mie theory including multipoles of order .
Both theory and experiment yield over a wide range of size parameters
remarkably stable intensity maxima close to the forward and backward direction
at ``magic angles''. In contrast to linear Mie scattering, both are of
comparable intensity.Comment: 4 pages, RevTeX, 3 figures available on request from
[email protected], submitted to PR
UNCLES: Method for the identification of genes differentially consistently co-expressed in a specific subset of datasets
Background: Collective analysis of the increasingly emerging gene expression datasets are required. The recently proposed binarisation of consensus partition matrices (Bi-CoPaM) method can combine clustering results from multiple datasets to identify the subsets of genes which are consistently co-expressed in all of the provided datasets in a tuneable manner. However, results validation and parameter setting are issues that complicate the design of such methods. Moreover, although it is a common practice to test methods by application to synthetic datasets, the mathematical models used to synthesise such datasets are usually based on approximations which may not always be sufficiently representative of real datasets. Results: Here, we propose an unsupervised method for the unification of clustering results from multiple datasets using external specifications (UNCLES). This method has the ability to identify the subsets of genes consistently co-expressed in a subset of datasets while being poorly co-expressed in another subset of datasets, and to identify the subsets of genes consistently co-expressed in all given datasets. We also propose the M-N scatter plots validation technique and adopt it to set the parameters of UNCLES, such as the number of clusters, automatically. Additionally, we propose an approach for the synthesis of gene expression datasets using real data profiles in a way which combines the ground-truth-knowledge of synthetic data and the realistic expression values of real data, and therefore overcomes the problem of faithfulness of synthetic expression data modelling. By application to those datasets, we validate UNCLES while comparing it with other conventional clustering methods, and of particular relevance, biclustering methods. We further validate UNCLES by application to a set of 14 real genome-wide yeast datasets as it produces focused clusters that conform well to known biological facts. Furthermore, in-silico-based hypotheses regarding the function of a few previously unknown genes in those focused clusters are drawn. Conclusions: The UNCLES method, the M-N scatter plots technique, and the expression data synthesis approach will have wide application for the comprehensive analysis of genomic and other sources of multiple complex biological datasets. Moreover, the derived in-silico-based biological hypotheses represent subjects for future functional studies.The National Institute for Health Research (NIHR) under its Programme Grants for Applied Research
Programme (Grant Reference Number RP-PG-0310-1004)
Stable spinning optical solitons in three dimensions
We introduce spatiotemporal spinning solitons (vortex tori) of the
three-dimensional nonlinear Schrodinger equation with focusing cubic and
defocusing quintic nonlinearities. The first ever found completely stable
spatiotemporal vortex solitons are demonstrated. A general conclusion is that
stable spinning solitons are possible as a result of competition between
focusing and defocusing nonlinearities.Comment: 4 pages, 6 figures, accepted to Phys. Rev. Let
Higher-order nonlinear modes and bifurcation phenomena due to degenerate parametric four-wave mixing
We demonstrate that weak parametric interaction of a fundamental beam with
its third harmonic field in Kerr media gives rise to a rich variety of families
of non-fundamental (multi-humped) solitary waves. Making a comprehensive
comparison between bifurcation phenomena for these families in bulk media and
planar waveguides, we discover two novel types of soliton bifurcations and
other interesting findings. The later includes (i) multi-humped solitary waves
without even or odd symmetry and (ii) multi-humped solitary waves with large
separation between their humps which, however, may not be viewed as bound
states of several distinct one-humped solitons.Comment: 9 pages, 17 figures, submitted to Phys. Rev.
Theory of multidimensional parametric band-gap simultons
Multidimensional spatiotemporal parametric simultons (simultaneous solitary waves) are possible in a nonlinear chi((2)) medium with a Bragg grating structure, where large effective dispersion occurs near two resonant band gaps for the carrier and second-harmonic field, respectively. The enhanced dispersion allows much reduced interaction lengths, as compared to bulk medium parametric simultons. The nonlinear parametric band-gap medium permits higher-dimensional stationary waves to form. In addition, solitons can occur with lower input powers than conventional nonlinear Schrodinger equation gap solitons. In this paper, the equations for electromagnetic propagation in a grating structure with a parametric nonlinearity are derived from Maxwell's equation using a coupled mode Hamiltonian analysis in one, two, and three spatial dimensions. Simultaneous solitary wave solutions are proved to exist by reducing the equations to the coupled equations describing a nonlinear parametric waveguide, using the effective-mass approximation (EMA). Exact one-dimensional numerical solutions in agreement with the EMA solutions are also given. Direct numerical simulations show that the solutions have similar types of stability properties to the bulk case, providing the carrier waves are tuned to the two Bragg resonances, and the pulses have a width in frequency space less than the band gap. In summary, these equations describe a physically accessible localized nonlinear wave that is stable in up to 3 + 1 dimensions. Possible applications include photonic logic and switching devices. [S1063-651X(98)06109-1]
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