An innovative approach to reduce chemicals in mite control

The efficacy of an innovative technique using acaricide treated nets was recently demonstrated to control phytophagous mites on vegetables. The net impregnated with the acaricide dicofol was efficient against the broad mite Polyphagotarsonemus latus (Banks) and spider mites (Tetranychus spp.) when used temporarily (once every three nights) covering eggplant. The technique was evaluated with chlorpyriphos ethyl impregnating nets in southern Benin. Results showed that the populations of Tetranychus urticae, and T. ludeni in the first trials and the invasive specie T. evansi in a last trial were significantly controlled by this technique. Very few mites were observed on plants covered with the acaricide treated net compared with very high densities on leaves in the unprotected control plots. This new concept of mite control using an acaricide-treated net temporarily covering vegetable crop appears to be an efficient tool which is easy to use by small-scale farmers. With this technique the pesticide remains on the material reducing the risk of plant contamination and environmental pollution. Thus the same treatment can be applied many times reducing chemicals for controlling mites. In greenhouses, particularly where populations of mites can increase rapidly on vegetables or ornamental flowers acaricide-treated nets could be used to control outbreaks just before the prompt release of useful insects as is permitted by absence of pesticide residues on plants with this innovative technique. In Sub-Saharian countries where mite outbreaks are observed mainly in the dry season the application of acaricide treated net poses a very low risk of pesticide workout by rain reducing the risk of pesticide residues on plants and their negative impact on useful insects. (Résumé d'auteur

Guaranteeing Failsafe Operation of Extended-Scene Shack-Hartmann Wavefront Sensor Algorithm

A Shack-Hartmann sensor (SHS) is an optical instrument consisting of a lenslet array and a camera. It is widely used for wavefront sensing in optical testing and astronomical adaptive optics. The camera is placed at the focal point of the lenslet array and points at a star or any other point source. The image captured is an array of spot images. When the wavefront error at the lenslet array changes, the position of each spot measurably shifts from its original position. Determining the shifts of the spot images from their reference points shows the extent of the wavefront error. An adaptive cross-correlation (ACC) algorithm has been developed to use scenes as well as point sources for wavefront error detection. Qualifying an extended scene image is often not an easy task due to changing conditions in scene content, illumination level, background, Poisson noise, read-out noise, dark current, sampling format, and field of view. The proposed new technique based on ACC algorithm analyzes the effects of these conditions on the performance of the ACC algorithm and determines the viability of an extended scene image. If it is viable, then it can be used for error correction; if it is not, the image fails and will not be further processed. By potentially testing for a wide variety of conditions, the algorithm s accuracy can be virtually guaranteed. In a typical application, the ACC algorithm finds image shifts of more than 500 Shack-Hartmann camera sub-images relative to a reference sub -image or cell when performing one wavefront sensing iteration. In the proposed new technique, a pair of test and reference cells is selected from the same frame, preferably from two well-separated locations. The test cell is shifted by an integer number of pixels, say, for example, from m= -5 to 5 along the x-direction by choosing a different area on the same sub-image, and the shifts are estimated using the ACC algorithm. The same is done in the y-direction. If the resulting shift estimate errors are less than a pre-determined threshold (e.g., 0.03 pixel), the image is accepted. Otherwise, it is rejected

Method for Pre-Conditioning a Measured Surface Height Map for Model Validation

This software allows one to up-sample or down-sample a measured surface map for model validation, not only without introducing any re-sampling errors, but also eliminating the existing measurement noise and measurement errors. Because the re-sampling of a surface map is accomplished based on the analytical expressions of Zernike-polynomials and a power spectral density model, such re-sampling does not introduce any aliasing and interpolation errors as is done by the conventional interpolation and FFT-based (fast-Fourier-transform-based) spatial-filtering method. Also, this new method automatically eliminates the measurement noise and other measurement errors such as artificial discontinuity. The developmental cycle of an optical system, such as a space telescope, includes, but is not limited to, the following two steps: (1) deriving requirements or specs on the optical quality of individual optics before they are fabricated through optical modeling and simulations, and (2) validating the optical model using the measured surface height maps after all optics are fabricated. There are a number of computational issues related to model validation, one of which is the "pre-conditioning" or pre-processing of the measured surface maps before using them in a model validation software tool. This software addresses the following issues: (1) up- or down-sampling a measured surface map to match it with the gridded data format of a model validation tool, and (2) eliminating the surface measurement noise or measurement errors such that the resulted surface height map is continuous or smoothly-varying. So far, the preferred method used for re-sampling a surface map is two-dimensional interpolation. The main problem of this method is that the same pixel can take different values when the method of interpolation is changed among the different methods such as the "nearest," "linear," "cubic," and "spline" fitting in Matlab. The conventional, FFT-based spatial filtering method used to eliminate the surface measurement noise or measurement errors can also suffer from aliasing effects. During re-sampling of a surface map, this software preserves the low spatial-frequency characteristic of a given surface map through the use of Zernike-polynomial fit coefficients, and maintains mid- and high-spatial-frequency characteristics of the given surface map by the use of a PSD model derived from the two-dimensional PSD data of the mid- and high-spatial-frequency components of the original surface map. Because this new method creates the new surface map in the desired sampling format from analytical expressions only, it does not encounter any aliasing effects and does not cause any discontinuity in the resultant surface map

Techniques for Down-Sampling a Measured Surface Height Map for Model Validation

This software allows one to down-sample a measured surface map for model validation, not only without introducing any re-sampling errors, but also eliminating the existing measurement noise and measurement errors. The software tool of the current two new techniques can be used in all optical model validation processes involving large space optical surface

Optimal Occulter Design for Finding Extrasolar Planets

One proposed method for finding terrestrial planets around nearby stars is to use two spacecraft--a telescope and a specially shaped occulter that is specifically designed to prevent all but a tiny fraction of the starlight from diffracting into the telescope. As the cost and observing cadence for such a mission will be driven largely by the separation between the two spacecraft, it is critically important to design an occulter that can meet the observing goals while flying as close to the telescope as possible. In this paper, we explore this tradeoff between separation and occulter diameter. More specifically, we present a method for designing the shape of the outer edge of an occulter that is as small as possible and gives a shadow that is deep enough and large enough for a 4m telescope to survey the habitable zones of many stars for Earth-like planets. In particular, we show that in order for a 4m telescope to detect in broadband visible light a planet 0.06 arcseconds from a star shining $10^{10}$ times brighter than the planet requires a specially-shaped occulter 50m in diameter positioned about $72,000$ km in front of the telescope.Comment: 14 pages, 4 figures, 15 subfigure

Fast linearized coronagraph optimizer (FALCO) I: a software toolbox for rapid coronagraphic design and wavefront correction

The Fast Linearized Coronagraph Optimizer (FALCO) is an open-source toolbox of routines for coronagraphic focal plane wavefront correction. The goal of FALCO is to provide a free, modular framework for the simulation or testbed operation of several common types of coronagraphs. FALCO includes routines for pair-wise probing estimation of the complex electric field and Electric Field Conjugation (EFC) control, and we ask the community to contribute other wavefront correction algorithms. FALCO utilizes and builds upon PROPER, an established optical propagation library. The key innovation in FALCO is the rapid computation of the linearized response matrix for each deformable mirror (DM), which facilitates re-linearization after each control step for faster DM-integrated coronagraph design and wavefront correction experiments. FALCO is freely available as source code in MATLAB at github.com/ajeldorado/falco-matlab and will be available later this year in Python 3 at github.com/ajeldorado/falco-python

Fast linearized coronagraph optimizer (FALCO) III: optimization of key coronagraph design parameters

Deformable mirrors (DMs) are increasingly becoming part of nominal coronagraph designs, such as the hybrid Lyot coronagraph, in addition to their role counteracting optical aberrations. Previous studies have investigated the effects of the inter-DM Fresnel number on achievable contrast, throughput, and tip/tilt sensitivity for apodized coronagraphs augmented with DMs to suppress diffraction from struts and segment gaps. In this paper, we build upon that previous work by directly suppressing tip/tilt sensitivity with the controller, both for coronagraphs with and without apodizers. We also explore the effects of other important design parameters such as actuator density and tip/tilt controller weighting on performance. These comprehensive coronagraph design studies are enabled by the Fast Linearized Coronagraph Optimizer (FALCO) software toolbox, which provides rapid re-calculation of the DM response matrix for a variety of coronagraphs

A sustainable method for small-scale farmers to protect cabbage crops in african urban areas

Screen tunnels over vegetables, used only at night, are well adapted for pest management in tropical urban areas because they are "easy to use" they improve the quality of production and reduce unsustainable insecticide practices of small-scale farmers. This technique was focused on cabbage crops for three years in Cotonou, Benin. Trials were performed in research station and in urban areas with local farmers. In this study, the biological efficacy, environmental impact, and economic factors of this technique were compared with the usual practices of small-scale farmers. The following results have been confirmed: 1) A tunnel screen used only at night physically protects cabbage against the Diamondback moth, #Plutella xylostella#, and the borer, #Hellula undalis#; 2) The screen is not efficient against the armyworm, #Spodoptera littoralis#, which lays eggs on the screen; 3) The screen impregnated with deltamethrin is effective in protecting cabbages against the aphid, #Lipaphis erysimi#; 4) The yield and quality of cabbage obtained using this technique can double the profits of the farmer; 5) The environmental benefit is due to a reduction of insecticide sprays and so pesticide residues in vegetables and the soil. The cost of chemicals typically used by farmers is, on average, US$45/100 m² for one crop cycle. This is nearly double the cost of the tunnel screen materials, which are available in local markets for about US$24/100 m² for one crop cycle (due to the fact that this material can be used for 10 crop cycles). The investment in material, a major constraint for small-scale farmers, can be done progressively plot by plot. (Texte intégral

Fast Linearized Coronagraph Optimizer (FALCO) IV. Coronagraph design survey for obstructed and segmented apertures

Coronagraph instruments on future space telescopes will enable the direct detection and characterization of Earth-like exoplanets around Sun-like stars for the first time. The quest for the optimal optical coronagraph designs has made rapid progress in recent years thanks to the Segmented Coronagraph Design and Analysis (SCDA) initiative led by the Exoplanet Exploration Program at NASA's Jet Propulsion Laboratory. As a result, several types of high-performance designs have emerged that make use of dual deformable mirrors to (1) correct for optical aberrations and (2) suppress diffracted starlight from obstructions and discontinuities in the telescope pupil. However, the algorithms used to compute the optimal deformable mirror surface tend to be computationally intensive, prohibiting large scale design surveys. Here, we utilize the Fast Linearized Coronagraph Optimizer (FALCO), a tool that allows for rapid optimization of deformable mirror shapes, to explore trade-offs in coronagraph designs for obstructed and segmented space telescopes. We compare designs for representative shaped pupil Lyot and vortex coronagraphs, two of the most promising concepts for the LUVOIR space mission concept. We analyze the optical performance of each design, including their throughput and ability to passively suppress light from partially resolved stars in the presence of low-order aberrations. Our main result is that deformable mirror based apodization can suffciently suppress diffraction from support struts and inter-segment gaps whose widths are on the order of ~0.1% of the primary mirror diameter to detect Earth-sized planets within a few tens of milliarcseconds from the star

Anomalous Momentum States, Non-Specular Reflections, and Negative Refraction of Phase-Locked, Second Harmonic Pulses

We simulate and discuss novel spatio-temporal propagation effects that relate specifically to pulsed, phase-mismatched second harmonic generation in a negative index material having finite length. Using a generic Drude model for the dielectric permittivity and magnetic permeability, the fundamental and second harmonic frequencies are tuned so that the respective indices of refraction are negative for the pump and positive for the second harmonic signal. A phase-locking mechanism causes part of the second harmonic signal generated at the entry surface to become trapped and dragged along by the pump and to refract negatively, even though the index of refraction at the second harmonic frequency is positive. These circumstances culminate in the creation of an anomalous state consisting of a forward-moving second harmonic wave packet that has negative wave vector and momentum density, which in turn leads to non-specular reflections at intervening material interfaces. The forward-generated second harmonic signal trapped under the pump pulse propagates forward, but has all the attributes of a reflected pulse, similar to its twin counterpart generated at the surface and freely propagating backward away from the interface. This describes a new state of negative refraction, associated with nonlinear frequency conversion and parametric processes, whereby a beam generated at the interface can refract negatively even though the index of refraction at that wavelength is positive