Little is known about optimum design of gas pycnometers, so that they can determine the volume of solid particles with the greatest accuracy. The purpose of this study was to investigate the optimum design of the ‘variable-volume’ gas pycnometer, because its ease of handling makes it a good candidate for widespread use. The law of propagation of uncertainty was used to derive a theoretical formula that relates the pycnometer's accuracy to the main sources of random uncertainty (gas-pressure measurements, pycnometer temperature, sample-chamber and piston-chamber volumes). The consequences of this formula in terms of optimizing the geometry and working conditions of the pycnometer are discussed. It was found that some gas pycnometers described in the literature may not have been used under the best conditions. As for the ‘constant-volume’ gas pycnometer, which was considered in a previous study, it seems possible to use commercially available components for constructing a variable-volume gas pycnometer that can determine the volume of solid particles with a relative standard uncertainty smaller than 0.25%. However, an accurately calibrated pressure transducer is required for the variable-volume gas pycnometer (instead, the only requirement for the constant-volume gas pycnometer is that the transducer's response varies linearly with pressure).
Gas pycnometry is based on Boyle-Mariotte's law. There are three kinds of gas pycnometers reported in literature: "constant-volume", "variable-volume" and "comparative". These instruments are widely used to determine the volume-and thus the density-of granular, porous or soluble compounds (e.g., rocks, soil particles, pigments, ceramic, drugs, seeds). However, many users do not know the optimum use conditions of their gas pycnometer. This work provides a synthesis of recent studies about the optimum design of the gas pycnometers. It seems possible to use commercially available components for constructing gas pycnometers that can determine the volume of solid particles with a relative standard uncertainty smaller than 0.25%. Compared against other gas pycnometers, the constant-volume pycnometer presents several practical advantages.
En un cauce natural o artificial es usual la presencia de vegetación en el fondo y en la pared. Los efectos que produce la presencia de ésta es una alteración en el campo de flujo. La magnitud de las alteraciones en el campo del flujo depende de la extensión, altura, densidad y flexibilidad de la vegetación. Para analizar a detalle las estructuras turbulentas, en este trabajo se realizó un estudio experimental en laboratorio en un canal de sección rectangular con un tramo de vegetación sumergida, flexible y artificial. La región de medición se ubicó aguas arriba de la zona de vegetación hasta el final de esta misma, además se determinó la asimetría que puede inducir la presencia de la pared del canal. Las mediciones se realizaron con equipo de velocimetría acústica de efecto Doppler (ADV). Los resultados obtenidos identifican el desarrollo de la capa de mezcla a partir de los patrones de velocidad media y los esfuerzos de Reynolds. En el caso de los perfiles de velocidad media sobre la capa de vegetación fue posible identificar un punto de inflexión donde se identificaron inestabilidades tipo Kelvin-Helmholtz. Con el fin de analizar los procesos en la capa de mezcla se propone un modelo fenomenológico basado en el análisis de la curvatura de las velocidades promediadas. Además, se determinó la aportación en el transporte de momento de las estructuras turbulentas con un análisis de cuadrantes con las velocidades fluctuantes.
En un distrito de riego, la red de distribución del agua es un punto esencial en el manejo y la entrega de agua a los usuarios. En el diseño de un nuevo distrito de riego se establece la forma de manejo, y se aplican 2022, Instituto Mexicano de Tecnología del Agua Open Access bajo la licencia CC BY-NC-SA 4.0 (https://creativecommons.org/licenses/by-ncsa/4.0/) 90
On the market there are several LED lamps that were not designed to produce lettuce, however, they can be purchased at a low cost. In Mexico there is a lack of research on its use in small-scale vertical farms and hydroponic established in urban agriculture. The objective of this work was to measure the response of three commercial lamps with LED lights on the growth and morphogenesis of sangria lettuce grown in a low-cost home vertical farm. The sangria lettuce was subjected to three light intensities with different spectra and photoperiod after 30 days of growth the plant height, leaf length, leaf width, number of leaves and fresh weight were measured, and a one-way analysis of variance (ANOVA) and Duncan's multiple comparison method was used through an algorithm designed in Python. According to the results, the highest fresh weight is made for a light intensity of 5700 lux. In the 2100 lux treatment, the highest height of the plant is performed and it was the treatment with the highest energy consumption. The production of lettuce at home is technically feasible, however, in addition to the light intensity, it is necessary to evaluate the quality (wavelengths) from the agronomic point of view.
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