RESUMOAs comunidades infestantes de sistemas agrícolas são dinâmicas e respondem às mudanças nas práticas agronômicas. Este estudo tem por objetivo avaliar os efeitos dos programas de controle com herbicidas implantados em pós-emergência por produtores em plantações comerciais de arroz e em comunidades infestantes. As avaliações foram realizadas em 96 lotes comerciais localizados nas regiões do Centro, Meseta e Norte do departamento de Tolima. Foi demarcado 1 ha em cada lote, onde foram feitas avaliações com um quadrado inventário de 0.2 x 0.2 m, lançado aleatoriamente 5 vezes. As amostras foram colhidas antes da primeira aplicação em pós-emergência, após a primeira aplicação em pós-emergência, após a segunda aplicação em pós-emergência, e logo após a finalização das aplicações em pós-emergência. As variáveis avaliadas incluíram densidade e cobertura das plantas daninhas e das culturas. Foi calculado o Índice de Valor de Importância (IVI) de cada espécie, e o programa de controle foi analisado quanto à diminuição no número de indivíduos para as mais de 15 espécies encontradas. Antes das aplicações, foram encontrados valores mais elevados de densidade. A primeira e segunda aplicações em pós-emergência reduziram a densidade média em 41% e 12%, respectivamente, em todo o departamento. Entre a primeira e a quarta avaliação, a densidade das plantas daninhas e culturas sofreu uma redução, no departamento inteiro, de 51.7% e 39%, respectivamente. Foi constatado que a variável densidade de plantas daninhas exerceu maior influência nas populações após a implantação dos programas de controle com herbicidas.

ABSTRACTThe weed communities of agricultural systems are dynamic and respond to changes in agronomic practices. This study aimed to evaluate the effect of post-emergence herbicide control programs made by farmers on weed communities and commercial lots of rice. The evaluations were carried out in 96 commercial lots located in the Centro, Meseta and Norte zones of the department of Tolima. In each lot, 1 ha was marked off, in which the evaluations were carried out by randomly throwing a 0.2 x 0.2 m sampling-square 5 times. Samples were taken before the first post-emergence application, after the first post-emergence application, after the second post-emergence application, and once the post-emergence applications were finished. The evaluated variables included density and cover of the weeds and the crops. The IVI of each species was calculated and the control program was analyzed in terms of decreases in the number of individuals for the 15 more encountered species. Before the applications, higher density values were found. The first and second post-emergence applications reduced the average density by 41% and 12%, respectively, throughout the department. Between the first and fourth evaluations, the density of the weeds and crops decreased throughout the department by 51.7% and 39%, respectively. The weed density variable proved to be the most influential in the populations after the herbicide programs were carried out.

With simultaneous phase and absorption gratings, we calculated the contribution of the absorption grating to the total diffraction efficiency in thick samples (around 0.5 cm) of iron doped lithium niobate with an applied electric field between 0 and -400 kV/cm in reflection geometry. We started by solving numerically the set of partial, non-linear, material rate differential equations. Then, we used these solutions to find numerical solutions in a self-consistent way to the beam coupling equations in two-wave mixing along sample thickness. For the given set of values of physical parameters of lithium niobate, we found that the presence of the absorption grating has a weak influence on the diffraction efficiency. It diminishes the total value of the diffraction efficiency in a small amount of around only 1%.

Con rejillas simultáneas de fase y de absorción, calculamos la contribución de la rejilla de absorción a la eficiencia total de difracción en muestras gruesas (aproximadamente 0.5 cm) de niobato de litio dopado con hierro. Consideramos la geometría de reflexión, con campos aplicados entre 0 y -400 kV/cm. Primero resolvimos numéricamente el sistema de ecuaciones diferenciales parciales, no lineales del material. Estas soluciones fueron utilizadas luego para calcular el intercambio de energía en la mezcla de dos ondas. Resolvimos numéricamente las ecuaciones del acoplamiento de los haces a lo largo del grosor de la muestra. Para el valor usado del dopaje de hierro, encontramos que la contribución de la rejilla de absorción es menos de 1% del valor total de la eficiencia de difracción.

We studied growth mechanisms in semiconducting Ga1 - xIn xAs ySb1 - y films grown by liquid phase epitaxy on (100) GaSb:Te (10(17) cm- 3) substrates at 600 ºC solution-substrate temperature. Atomic Force Microscopy (AFM) images of these films show step-like corrugations, undulations, grooves, and terraces. The terraces are a few nm in height and hundreds of nanometers in length. Epitaxial Ga1 - xIn xAs ySb1 - y films grow lattice-matched to the (100) GaSb substrates. These narrow-gap quaternary Ga1 - xIn xAs ySb1 - y compounds are suitable materials for heterostructure devices operating in the infrared wavelength range. The estimated x and y values are in the GaSb-rich zone. The step-like corrugations (bunching steps) are formed by different mechanisms, such as pinning effect probably due to impurities on the substrate surface.

A dynamic scaling and kinetic roughening study was done on digitized atomic force microscope (AFM) images of Pb(Zr0.52,Ti0.48)O3 (PZT) thin films. The films were grown on Si(001) and Nb - SrTiO3(001) (STNO) substrates via rf-sputtering technique at high oxygen pressures at substrate temperatures of 600 ºC by varying the deposition time and keeping other growth parameters fixed. By using a specific self-designed algorithm, we can extract from digitized 512-pixel resolution AFM-images, quantitative values of roughness parameters, i.e., interface width (sigma(l)), lateral correlation length (xi||) and, roughness exponent (alpha). Herein, we report on the sputter-time deposition dependence of the parameters describing roughness for both kinds of substrates. We report alpha-values for different time depositions (between 15 and 60 minutes) close to 0.55 for Si substrates and 0.63 for Nb - SrTiO3 substrates, indicating that the surface becomes more correlated in STNO substrates. The alpha-values are associated to the Lai-Das-Sarma-Villain model.