Two-region model for positive and negative plasma sheaths and its application to Hall thruster metallic anodes.

An asymptotic presheath/sheath model for positive and negative sheaths in front of a conducting electrode, with a continuous parametric transition at the no-sheath case, is presented. Key aspects of the model are as follows: full hydrodynamics of both species in the presheath; a kinetic formulation with a truncated distribution function for the repelled species within the sheath; and the fulfillment of the marginal Bohm condition at the sheath edge, in order to match the two formulations of the repelled species. The sheath regime depends on the ratios of particle fluxes and sound speeds between the two species. The presheath model includes the effect of a magnetic field parallel to the wall on electrons. An asymptotic, parametric study of the anode presheath is carried out in terms of the local ion-to-electron flux ratio and Hall parameter. The drift-diffusive model of magnetized electrons fails in a parametric region that includes parts of the negative sheath regime. In the case of the Hall parameter vanishing near the electrode and a weakly collisional plasma, a quasisonic, quasineutral plateau forms next to the sheath edge

Reflectance measurements of cotton leaf senescence altered by mepiquat chloride

Spectrophotometric reflectance measurements were made on plant-attached leaves to evaluate growth chamber-grown cotton leaf (Gossypium hirsutum L.) senescence (chlorophyll degradation as criterion) that was delayed by mepiquat chloride (1,1-dimethylpiperidinium chloride) rates of 0, 10, 40, 70, and 100 g a.i./ha. Mepiquat chloride (MC increased both chlorophyll and leaf water contents as compared with that of untreated leaves. Reflectance was inversely and linearly correlated (r = -0.873**) with eater content at the 1.65 micrometer wavelength and was inversely correlated (r = -0.812**) with chlorophyll concentration at the 0.55 micrometer wavelength but best fit a quadratic equation. Either wavelength measurement might be useful to remotely detect cotton leaf senescence or fields of MC-treated cotton plants

Leaf reflectance-nitrogen-chlorophyll relations among three south Texas woody rangeland plant species

Annual variations in the nitrogen-chlorophyll leaf reflectance of hackberry, honey mesquite and live oak in south Texas, were compared. In spring, leaf reflectance at the 0.55 m wavelength and nitrogen (N) concentration was high but leaf chlorophyll (chl) concentrations were low. In summer, leaf reflectance and N-concentration were low but lead chl concentrations were high. Linear correlations for both spring and summer of leaf reflectance with N and chl concentration or deviations from linear regression were not statistically significant

Comparison of LANDSAT-2 and field spectrometer reflectance signatures of south Texas rangeland plant communities

The accuracy was assessed for an atmospheric correction method that depends on clear water bodies to infer solar and atmospheric parameters for radiative transfer equations by measuring the reflectance signature of four prominent south Texas rangeland plants with the LANDSAT satellite multispectral scanner (MSS) and a ground based spectroradiometer. The rangeland plant reflectances produced by the two sensors were correlated with no significant deviation of the slope from unity or of the intercept from zero. These results indicated that the atmospheric correction produced LANDSAT MSS estimates of rangeland plant reflectances that are as accurate as the ground based spectroradiometer

Comunicación colectiva y desarrollo socioeconómico: cambio social, información y libertad

With regard to the socio-economic development process undertaken by a large number of countries in the so-called Third World and in connection with the central role played by collective communications within modern society, the authors of this article state -and try to answer- the following questions: 1) -What is the role of collective communications with regard to the modernization process? 2) -Is the former at the same time one of the motors and one of the indicators of the latter? 3) -Is freedom of information and of expression one of the sacrifices which have to be made in order to attain the desired objective? To answer these questions, the authors start off by defining the frame of reference of their work which is made up of an adequate notion of what constitutes both terms, collective communications and socio-economic development. Afterwards, they investigate the nexus existing between these two realities. For this task, they bear in mind the latest basic bibliography on the subject, put out by such classic researchers as LERNER, SCHRAMM, ROSTOW, PYE, MERRILL, DE SOLA POOL, FREY, etc. In this sense, and following SCHRAMM aboye all, they point out systematically the uses and the conditions for effectiveness of the means of collective communications in societies which initiate the difficult and long development process. The authors then put forth the problems of freedom and responsibility with regard to development, taking as their starting point for this investigation the freedom and responsibilities of the media themselves. To solve adequately the relations which exist between these two realities, the co-ordination of which holds obvious ethical implications, is not an easy task, and constitutes as the authors point out one of the main challenges facing those nations which hope to attain social and economical development

Increase of cold tolerance in cotton plant (Gossypium hirsutum L.) by mepiquat chloride

Three mepiquat chloride (MC) concentrations - 40, 70, and 100 g a.i./ha - were used to spray cotton (Gossypium hirsutum L., cultival McNair 220) plants to determine whether or not MC would increase their cold tolerance. Seven to ten days after the spray, the plants were exposed to three different cold treatments. No important difference in cold damage was noticed between the control and the MC-treated plants when they were exposed repeatedly to 4.5 C. No plants died when exposed to 0.5 C for 12 h; however, 90% of the 1st and 2nd leaves of the control plants were damaged. This was three times more damage than those leaves of plants treated with 70 and 100 g a.i./ha MC concentrations; 60% f the control and 10-20% of the MC-treated plants died when the plants were subjected to a cold hardening process with 15.5 C day (12 h) and 1.7 C night (12 h) for 10 days, and then, held at -2.2 C for 24 hours. The electrolyte leakage and reflectance measurement data showed that the cell membranes of the MC-treated plants sustained much less damage than those of the control. Freezing injury was easily assessed by reflectance measurements at the 1.65 micrometer wavelength

Nonlinear Meissner effect in a high-temperature superconductor: Local versus nonlocal electrodynamics

Measured intermodulation distortion (IMD) power at 1.5 GHz in a series of YBa[subscript 2]Y[subscript 3]O[subscript 7−δ] stripline resonators of varying strip widths is compared to the predictions of two qualitatively distinct theories of the nonlinear Meissner effect. The stripline resonators are patterned from a single wafer to ensure uniformity of the material properties. According to the first theory [T. Dahm and D. J. Scalapino, Phys. Rev. B 60, 13125 (1999)], the IMD power is dominated by contributions from the strip edges, while according to the second theory [D. Agassi and D. E. Oates, Phys. Rev. B 72, 014538 (2005)] it is dominated by contributions from the body of the strip. The parameter-free comparison of the measured data with the theoretical predictions clearly favors the latter theory. We conclude that the nonlinear component of the penetration depth must be treated with nonlocal electrodynamics. The origins of this outcome are discussed briefly in the framework of a Green’s-function approach

Application of Design of Experiments (DOE) on the Processing of Rapid Prototyped Samples

The purpose of this experiment was to improve the Fused Deposition Modeling Process by examining the tensile strength of samples fabricated in a Stratasys FDM 1650 Machine utilizing the methods of Design of Experiments. A two-level, four-factor, full factorial experiment was conducted. The selected factors were temperature, air gap, slice thickness, and raster orientation. A regression equation determined the level each factor should be set in order to optimize the FDM machine settings. It was found that single factors - small air gap, small layer thickness and low raster orientation, as well as the interaction between high temperature and small layer thickness yielded the greatest effect the response.Mechanical Engineerin

An Overview of Aircraft Remote Sensing in Integrated Pest Management

English: This paper presents four exemplary applications of aerial photography and videography, global positioning system (GPS), and geographic information system (GIS) technologies for detecting, monitoring, and mapping insect infestations in agriculture, forestry, and rangeland areas. Applications demonstrated include detecting and mapping: (1) citrus blackfly (Aleurocanthus woglumi Ashby) infestations in citrus orchards; (2) silverleaf whitefly (Bemisia argentifolii Bellows and Perring) infestations in cotton; (3) harvester ant (Pogonomyrmex barbatus F. Smith) infestations on rangelands; and (4) western pine beetle (Dendroctonus brevicomis LeConte) infestations in a forested area. The integration of a GPS with the video imagery permitted latitude and longitude coordinates of insect infestations to be recorded on each image. The GPS coordinates were entered into a GIS to map insect infestations on a regional scale. The integration of remote sensing, GPS, and GIS provide valuable tools that can enable resource managers to develop maps showing the distribution of insect infestations over large areas. The digital imagery can serve as a permanent geographically located image data base for monitoring future contraction or spread of insect infestations over time. Spanish: En este artículo se presentan cuatro ejemplos de las aplicaciones de las tecnologías de fotografía y videografía aéreas, el sistema de posición global (GPS), y del sistema de información geográfica (GIS) para la detección, monitoreo, y mapeo de infestaciones de insectos en áreas agrícolas, forestales y en pastizales. Las aplicaciones demonstradas incluyeron la detección y el mapeo de (1) infestaciones por la mosca negra de los cítricos (Aleurocanthus woglumi Ashby) en huertas de cítricos; (2) mosquita blanca (Bemisia argentifolii Bellows and Perring) en algodón; (3) hormiga cosechadora (Pogonomyrex barbatus F. Smith) en pastizales; y (4) escarabajo del pino del oeste (Dendroctonus brevicomis Le Conte) en una área forestal. La integración del sistema de GPS con las imágenes de video permitió registrar las coordenadas de longitud y latitud en cada imagen. Las coordenadas de cada imagen se incorporaron en un mapa de GIS para crear un mapa de las infestaciones de insectos a una escala regional. La integración de un sistema de detección a distancia, GPS, and GIS brinda herramientas valiosas para permitir a los supervisores de recursos desarrollar mapas que muestren la distribución de infestaciones de insectos en áreas extensas. El sistema de imágenes digital puede servir como una base permanente de datos localizados geográficamente para el monitoreo de futuras concentraciones o dispersiones de plagas de insectos a lo largo del tiempo