Bioactivity, persistence and mobility of picloram in Selangor and Serdang soil series

The effects of environmental factors on bioactivity, persistence and mobility of picloram were studied in the laboratory and greenhouse using long beans (Vigna sinensis Endl. ex Hassk), as a bioassay species. Two soils were used, namely Selangor series (silty clay loam soil) and Serdang series (silty clay soil). The bioactivity of picloram (Tordon®) was inversely correlated with the organic matter content of the soil and increased with increasing herbicide concentrations. The half-life ofpicloram decreased from 33.1 to 24.1 days as soil temperature increased from 25°C to 35°C in the Selangor series, and from 28.1 to 17.7 days in the Serdang series soil. The degradation rate of picloram also increased with increasing moisture level in both soil series. However, picloram persisted longa in Selangor series soil than in Serdang series. Downward mobility through the soil profile was inversely related to the organic maller content of the soil. The quantity and frequency of simulated rain directly influenced the extent of leaching of the herbicide. Downward movement of picloram was greater in Serdang series which contains less organic matter but high sand than Selangor series longest available vessel

Modulational instability of perturbative nonlinear Schrödinger equation with higher order dispersion

Modulation instability conditions for the generation of femtosecond pulses represented by perturbative nonlinear Schrödinger equation with higher order dispersion and nonlinear effects is investigated. It is observed that modulation instability occurs even in the normal dispersion regime due to the presence of fourth order dispersion

Cnoidal and solitary wave solutions of the coupled higher order nonlinear Schrödinger equation in nonlinear optics

By using coupled amplitude-phase formulation, we construct the quartic anharmonic oscillator equation from the coupled higher order nonlinear Schrödinger equation. For arbitrary physical parameter values, we discuss the construction of new cnoidal wave solutions and the exact solutions of both bright (GVD < 0) and dark (GVD < 0) solitary waves. In addition, we investigate the pairs of dark-dark and bright-bright solitary waves

Modulational instability in resonant optical fiber with higher-order dispersion effect

International audienceThe modulational instability (MI) of an electromagnetic wave in a resonant optical fiber with a two-level system is investigated. In the normal dispersion regime, we find the occurrence of nonconventional MI sidebands which are induced by the two-level resonant atoms. We also observe that the MI gain spectra are suppressed by the higher-order dispersion effect in the anomalous dispersion regime

Generation of self-induced-transparency gap solitons by modulational instability in uniformly doped fiber Bragg gratings

We consider the continuous-wave (cw) propagation through a fiber Bragg grating that is uniformly doped with two-level resonant atoms. Wave propagation is governed by a system of nonlinear coupled-mode Maxwell-Bloch (NLCM-MB) equations. We identify modulational instability (MI) conditions required for the generation of ultrashort pulses in both anomalous and normal dispersion regimes. From a detailed linear stability analysis, we find that the atomic detuning frequency has a strong influence on the MI. That is, the atomic detuning frequency induces nonconventional MI sidebands at the photonic band gap (PBG) edges and near the PBG edges. Especially in the normal dispersion regime, MI occurs without any threshold condition, which is in contrast with that of conventional fiber Bragg gratings. We also perform a numerical analysis to solve the NLCM-MB equations. The numerical results of the prediction of both the optimum modulation wave number and the optimum gain agree well with that of the linear stability analysis. Another main result of the present work is the prediction of the existence of both bright and dark self-induced transparency gap solitons at the PBG edges

Modulational instability of optical beams in photorefractive media due to two-wave or parametric four-wave mixing effects

Modulational instability in a photorefractive medium is studied in the presence of two-wave mixing. We then propose and derive a model for forward four-wave mixing in the photorefractive medium and investigate the modulational instability induced by four-wave mixing effects. By using the standard linear stability analysis the instability gain is obtained. In both cases, the geometry is such that the effect of self-phase-modulation self-focusing is suppressed and only the holographic focusing nonlinearity is acting

Modulational instability and generation of self-induced transparency solitons in resonant optical fibers

International audienceWe consider continuous-wave propagation through a fiber doped with two-level resonant atoms, which is described by a system of nonlinear Schrodinger-Maxwell-Bloch (NLS-MB) equations. We identify the modulational instability (MI) conditions required for the generation of ultrashort pulses, in cases of both anomalous and normal GVD (group-velocity dispersion). It is shown that the self-induced transparency (SIT) induces non-conventional MI sidebands. The main result is a prediction of the existence of both bright and dark SIT solitons in the anomalous and normal GVD regimes

Modulational instability with higher-order dispersion and walk-off in Kerr media with cross-phase modulation

We investigate the cross-phase-modulation-induced modulational instability (MI) of two co-propagating optical beams in the system of relaxing Kerr nonlinearity with the effect of higher-order dispersion (HOD) and walk-off effect. We identify and discuss the salient features of relaxation of nonlinear responses and HOD using suitable theoretical model. First, we analyzed the impact of HOD and walk-off on the MI spectrum and found both analytically and numerically that the MI exhibits alternate characteristics like the evolution of different spectral bands in addition to the conventional MI bands. The walk-off effects in the virtue of HOD not only consist of the conventional group velocity mismatch (GVM) but also the difference in third-order dispersion (TOD) of the two beams, and thereby significantly modify the dynamical behavior of the MI. We also consider the combined effect of relaxation of nonlinear response and the HOD effects, and we observe that any finite value of delay leads to the evolution of two unstable modes and thereby extends the range of unstable frequency; HOD on the other hand along with the walk-off effect brings other characteristic spectral bands. A detailed discussion about the various combinations of parameters and the relative competence of one over the other on the MI spectrum is presented. Thus the evolution of MI from cross-phase modulation in the system of relaxing Kerr nonlinearity is emphasized in detail and the influence of HOD and the walk-off effect are highlighted

Modulational instability in optical fibers with arbitrary higher-order dispersion and delayed Raman response

International audienceWe analyse modulational instability (MI) of electromagnetic waves in a large variety of optical fibers having different refractive-index profiles. For the normal-, anomalous-, and zero-dispersion regimes of the wave propagation, we show that whenever the second-order dispersion competes with higher-order dispersion (HOD), propagation of plane waves leads to a rich variety of dynamical behaviors. Most of the richness comes from the existence of critical behaviors, which include situations in which the HOD suppresses MI in the anomalous dispersion regime, and other situations in which the HOD acts in the opposite way by inducing non-conventional MI processes in the normal- and anomalous-dispersion regimes. We show that non-conventional MI sidebands are more prone to Raman-induced degradations than ordinary MI sidebands can be