Performance measurement in farmer-managed irrigation systems: Proceedings of an International Workshop of the Farmer-Managed Irrigation Systems Network, Mendoza, Argentina, 12-15 November 1991

Farmer managed irrigation systems / Performance evaluation / Performance indexes / Irrigation management / Case studies / Water distribution / Social aspects / Water users' associations / Tube wells / Indonesia / Pakistan / Bolivia / Israel / Mexico / Peru / Venezuela / Andean Region / Philippines / Nepal / Sri Lanka / India / Egypt / Portugal / Tanzania / Argentina / China / Bangladesh

Influencia de la altura del cultivo en la evapotranspiración relativa de la alfalfa

Report herein are be results of an experiment rneasuring tbe influence of crop heigh t on the relative evapotranspiration of alfalfa field. Experiments were conducted at the Instituto de Suelos y Riego Experimental Farm, Facultad de Ciencias Agrarias, Mendoza, Argentina. Three different treatments of crop height were evaluated : treatment A, complete plant height development (before cutting); treatment B, half height plant development; treatment C, small-plant height (after cutting). Total evapotranspiration of the cyele and rate of evapotranspiration were higher in B than in treatment C. Average evapotranspiration values were : 4, 4.90 mm per day ; B, 3.86 mm per day ; and C, 3.17 mm per day. The evapotranspiration evaporation ratios in each treatment were: A, 1.06; B, 0.83; e, o.867. The reported experiments show that even in a perennial crop like alfalfa, which completely covers the soil, a considerable difierence in the relative evapotranspiration value is obtained. From the period after cuttiug to the period of full leaf and complete plant height development the crop coefficient is rising. This variation of crop coefficients shold be kept in mind in applying formulas to estimate the evapotranspiration rate of an alfalfa crop for specific periods between cuttings.Se analiza en le presente trabajo, la influencia de la altura del cultivo en la evapotranspiración relativa de la alfalfa. Las experiencias se realizaron en el campo experimental del Instituto de Suelos y Riego, Facultad de Ciencias Agrarias, Mendoza, con tres variantes de altura del cultivo: tratamiento A pleno desarrollo; tratamiento B media altura; tratamiento C a ras del suelo. La evapotranspiración total del ciclo y la velocidad de evapotranspiración, resultó mayor en el tratamiento A. que en el B y en el B que en el C, con los siguientes valores medios: tratamiento A, 4,90 mm/ día; tratamiento B, 3,68 mm/día; tratamiento C, 3,17 mm/ día. La evapotranspiración con respecto a la evaporación de una superficie libre de agua tanque standard tipo A resultó: tratamiento A, 1,06; tratamiento B, 0,835, tratamiento C, 0,687. La expereincia señala claramente que, aún en un cultivo permanente que cubre íntegramente el terreno, tal como ocurre con la alfalfa, se observa una apreciable diferencia en el valor del coeficiente de cultivo, desde el período de siega a pleno desarrollo. Ello señala que, dicha variación debe ser tenida en cuenta al estimar la evapotranspirac10n de la alfalfa, para períodos específicos y de corta duración comprendidos entre una y otra siegaFil: Grassi, Carlos J.. Universidad Nacional de Cuyo. Facultad de Ciencias AgrariasFil: Chambouleyron, Jorge Luis. Universidad Nacional de Cuyo. Facultad de Ciencias Agraria

Order parameter model for unstable multilane traffic flow

We discuss a phenomenological approach to the description of unstable vehicle motion on multilane highways that explains in a simple way the observed sequence of the phase transitions "free flow -> synchronized motion -> jam" as well as the hysteresis in the transition "free flow synchronized motion". We introduce a new variable called order parameter that accounts for possible correlations in the vehicle motion at different lanes. So, it is principally due to the "many-body" effects in the car interaction, which enables us to regard it as an additional independent state variable of traffic flow. Basing on the latest experimental data (cond-mat/9905216) we assume that these correlations are due to a small group of "fast" drivers. Taking into account the general properties of the driver behavior we write the governing equation for the order parameter. In this context we analyze the instability of homogeneous traffic flow manifesting itself in both of the mentioned above phase transitions where, in addition, the transition "synchronized motion -> jam" also exhibits a similar hysteresis. Besides, the jam is characterized by the vehicle flows at different lanes being independent of one another. We specify a certain simplified model in order to study the general features of the car cluster self-formation under the phase transition "free flow synchronized motion". In particular, we show that the main local parameters of the developed cluster are determined by the state characteristics of vehicle motion only.Comment: REVTeX 3.1, 10 pages with 10 PostScript figure

Average mass of seeds encountered by foraging dabbling ducks in Western Europe

Many dabbling ducks Anas spp. are largely granivorous, consuming a variety of seeds chiefly from aquatic plants. To assess the relative value and carrying capacity of wetlands for dabbling ducks, species-specific information about seed mass is needed, but it is still largely missing or scattered in the literature. By combining weights of seeds collected in the field with a literature review, we provide a reference table for seed mass of 200 western European plant taxa frequently encountered by foraging dabbling ducks. Seeds collected in the field were sampled in microhabitats and at depths at which ducks were observed to forage, and study sites represent wintering, staging as well as breeding areas within a flyway in western Europe. When combined with calorimetric data, the present reference table will aid managers and scientists in assessing the importance of seed food resources at different sites and during different parts of the annual cycle.</p

Theoretical study of the insulating oxides and nitrides: SiO2, GeO2, Al2O3, Si3N4, and Ge3N4

An extensive theoretical study is performed for wide bandgap crystalline oxides and nitrides, namely, SiO_{2}, GeO_{2}, Al_{2}O_{3}, Si_{3}N_{4}, and Ge_{3}N_{4}. Their important polymorphs are considered which are for SiO_{2}: $\alpha$-quartz, $\alpha$- and $\beta$-cristobalite and stishovite, for GeO_{2}: $\alpha$-quartz, and rutile, for Al_{2}O_{3}: $\alpha$-phase, for Si_{3}N_{4} and Ge_{3}N_{4}: $\alpha$- and $\beta$-phases. This work constitutes a comprehensive account of both electronic structure and the elastic properties of these important insulating oxides and nitrides obtained with high accuracy based on density functional theory within the local density approximation. Two different norm-conserving \textit{ab initio} pseudopotentials have been tested which agree in all respects with the only exception arising for the elastic properties of rutile GeO_{2}. The agreement with experimental values, when available, are seen to be highly satisfactory. The uniformity and the well convergence of this approach enables an unbiased assessment of important physical parameters within each material and among different insulating oxide and nitrides. The computed static electric susceptibilities are observed to display a strong correlation with their mass densities. There is a marked discrepancy between the considered oxides and nitrides with the latter having sudden increase of density of states away from the respective band edges. This is expected to give rise to excessive carrier scattering which can practically preclude bulk impact ionization process in Si_{3}N_{4} and Ge_{3}N_{4}.Comment: Published version, 10 pages, 8 figure