Evaluación de niveles de daño, causados por el barrenador de la caña de azúcar (Diatraea spp.) y su parasitismo natural durante Julio-Diciembre de 1995 en el Ingenio Benjamin Zeledon, Rivas

El presente estudio se realizó en el ingenio Benjamín Zeledón con el objetivo de determinar los niveles de daño causados por Diatraea spp. y la incidencia del parasitismo natural para su control durante el periodo julio-diciembre de 1995. Evaluándose los parámetros: infestación, intensidad de infestación e índice de infestación, así como los niveles del parasitismo natural de Diatraea spp. en diversas variedades de caña en una área que representa el 16.30% del área total productiva del Ingenio. Determinándose una infestación promedio de 5.35%, una intensidad de infestación promedio de 14.39% y un índice de infestación promedio de 0.85, el cual es considerado internacionalmente como bajo. La variedades L 68-40, J 60-5, L 68-90 y la mezcla de diversas variedades fueron las más afectadas por Diatraea spp. Determinándose en estas variedades índices de infestación superiores al promedio general (0.85)y que corresponden a 1.26, 1.14, 1.13 y 1.09 respectivamente. Sin embargo, SP 70-4790, MEX. 53-4-73 y MEX. 68-P-23 fueron las variedades menos afectadas con 0.51, 0.23 y 0.24 de índice de infestación respectivamente. Por otro lado, se determinó un bajo nivel de parasitismo natural que se concentró sólo en el trimestre julio-septiembre con 19, 21 y 251% de parasitismo natural a partir de 58,19 y 4 larvas colectadas durante estos meses respectivamente. Identificándose a los parasitoides larvales: Billaea claripalpis Wulp, Cotesia flavipes Camerón y Apanteles diatraeae Muesebeck. Aunque no se pudo determinar la incidencia de los parasitoides ovifagos se determinó la presencia de Telenomus sp. y una especie de la familia Trichogrammatidae en los campos muestreados.

Analysis of Temperature and Pressure Changes in Liquefied Natural Gas (LNG) Cryogenic Tanks

Liquefied natural gas (LNG) is being developed as a transportation fuel for heavy vehicles such as trucks and transit buses, to lessen the dependency on oil and to reduce greenhouse gas emissions. The LNG stations are properly designed to prevent the venting of natural gas (NG) from LNG tanks, which can cause evaporative greenhouse gas emissions and result in fluctuations of fuel flow and changes of fuel composition. Boil-off is caused by the heat added into the LNG fuel during the storage and fueling. Heat can leak into the LNG fuel through the shell of tank during the storage and through hoses and dispensers during the fueling. Gas from tanks onboard vehicles, when returned to LNG tanks, can add additional heat into the LNG fuel. A thermodynamic and heat transfer model has been developed to analyze different mechanisms of heat leak into the LNG fuel. The evolving of properties and compositions of LNG fuel inside LNG tanks is simulated. The effect of a number of buses fueled each day on the possible total fuel loss rate has been analyzed. It is found that by increasing the number of buses, fueled each day, the total fuel loss rate can be reduced significantly. It is proposed that an electric generator be used to consume the boil-off gas or a liquefier be used to re-liquefy the boiloff gas to reduce the tank pressure and eliminate fuel losses. These approaches can prevent boil-off of natural gas emissions, and reduce the costs of LNG as transportation fuel.

Transient natural ventilation of a space with localised heating

The natural ventilation of a well-mixed, pre-heated room with a point source of heating, and openings at the base and roof is investigated. The transient draining associated with the room being warmer than the exterior combined with the convective ow produced by the point source of heat leads to a fascinating series of transient ow regimes as the system evolves to the two-layer steady-state regime described by Linden, Lane-Ser_ and Smeed [1]. As the room begins to ventilate, a turbulent plume rises from the point source of heat to the ceiling, and typically forms a deepening layer of hot air. However, with a weak heat source, then at some point the ascending plume will intrude beneath the layer of original uid. Otherwise, the ascending plume always reaches the top of the room as the system evolves to a steady state. We develop a simpli_ed model of the transient evolution and test this with some new laboratory experiments. We conclude with a discussion of the implications of our results for real buildings.

Refractive index and thickness analysis of natural silicon dioxide film growing on silicon with variable-angle spectroscopic ellipsometry

The refractive index and thickness of SiO2 thin films naturally grown on Si substrates were determined simultaneously within the wavelength range of 220-1100 nm with variable-angle spectroscopic ellipsometry. Different angles of incidence and wavelength ranges were chosen to enhance the analysis sensitivity for more accurate results. Several optical models describing the practical SiO2-Si system were investigated, and best results were obtained with the optical model, including an interface layer between SiO2 and Si, which proved the existence of the interface layer in this work as described in other publications.

A comparison of winter pre-heating requirements for natural displacement and natural mixing ventilation

In winter, natural ventilation can be achieved either through mixing ventilation or upward displacement ventilation (P.F. Linden, The fluid mechanics of natural ventilation, Annual Review of Fluid Mechanics 31 (1999) pp. 201-238). We show there is a significant energy saving possible by using mixing ventilation, in the case that the internal heat gains are significant, and illustrate these savings using an idealized model, which predicts that with internal heat gains of order 0.1 kW per person, mixing ventilation uses of a fraction of order 0.2-0.4 of the heat load of displacement ventilation assuming a well-insulated building. We then describe a strategy for such mixing natural ventilation in an atrium style building in which the rooms surrounding the atrium are able to vent directly to the exterior and also through the atrium to the exterior. The results are motivated by the desire to reduce the energy burden in large public buildings such as hospitals, schools or office buildings centred on atria. We illustrate a strategy for the natural mixing ventilation in order that the rooms surrounding the atrium receive both pre-heated but also sufficiently fresh air, while the central atrium zone remains warm. We test the principles with some laboratory experiments in which a model air chamber is ventilated using both mixing and displacement ventilation, and compare the energy loads in each case. We conclude with a discussion of the potential applications of the approach within the context of open plan atria type office buildings.

The influence of stacks on flow patterns and stratification associated with natural ventilation

We investigate the steady state natural ventilation of an enclosed space in which vent A, located at height hA above the floor, is connected to a vertical stack with a termination at height H, while the second vent, B, at height hB above the floor, connects directly to the exterior. We first examine the flow regimes which develop with a distributed source of heating at the base of the space. If hBhB>hA, then two different flow regimes may develop. Either (i) there is inflow through vent B and outflow through vent A, or (ii) the flow reverses, with inflow down the stack into vent A and outflow through vent B. With inflow through vent A, the internal temperature and ventilation rate depend on the relative height of the two vents, A and B, while with inflow through vent B, they depend on the height of vent B relative to the height of the termination of the stack H. With a point source of heating, a similar transition occurs, with a unique flow regime when vent B is lower than vent A, and two possible regimes with vent B higher than vent A. In general, with a point source of buoyancy, each steady state is characterised by a two-layer density stratification. Depending on the relative heights of the two vents, in the case of outflow through vent A connected to the stack, the interface between these layers may lie above, at the same level as or below vent A, leading to discharge of either pure upper layer, a mixture of upper and lower layer, or pure lower layer fluid. In the case of inflow through vent A connected to the stack, the interface always lies below the outflow vent B. Also, in this case, if the inflow vent A lies above the interface, then the lower layer becomes of intermediate density between the upper layer and the external fluid, whereas if the interface lies above the inflow vent A, then the lower layer is composed purely of external fluid. We develop expressions to predict the transitions between these flow regimes, in terms of the heights and areas of the two vents and the stack, and we successfully test these with new laboratory experiments. We conclude with a discussion of the implications of our results for real buildings.

Transient Natural Ventilation of a Room with a Distributed Heat Source

We report on an experimental and theoretical study of the transient flows which develop as a naturally ventilated room adjusts from one temperature to another. We focus on a room heated from below by a uniform heat source, with both high- and low-level ventilation openings. Depending on the initial temperature of the room relative to (i) the final equilibrium temperature and (ii) the exterior temperature, three different modes of ventilation may develop. First, if the room temperature lies between the exterior and the equilibrium temperature, the interior remains well-mixed and gradually heats up to the equilibrium temperature. Secondly, if the room is initially warmer than the equilibrium temperature, then a thermal stratification develops in which the upper layer of originally hot air is displaced upwards by a lower layer of relatively cool inflowing air. At the interface, some mixing occurs owing to the effects of penetrative convection. Thirdly, if the room is initially cooler than the exterior, then on opening the vents, the original air is displaced downwards and a layer of ambient air deepens from above. As this lower layer drains, it is eventually heated to the ambient temperature, and is then able to mix into the overlying layer of external air, and the room becomes well-mixed. For each case, we present new laboratory experiments and compare these with some new quantitative models of the transient flows. We conclude by considering the implications of our work for natural ventilation of large auditoria.

Energy efficiency with natural ventilation: a case study

Application of laboratory analogue modelling of air flow in a naturally ventilated shopping mall is reviewed in this paper. A detailed study of the ventilation was undertaken to establish the principles and to explore how natural ventilation might interact with a localised mechanical ventilation system designed to enhance the cooling of a high density food court area. The case study is used to show how the combination of laboratory modelling and simplified mathematical modelling enables one to rapidly identify the various flow regimes which can occur, to quantify the resultant flows and mean temperatures and to thereby develop appropriate ventilation strategies for the different external conditions which occur through the year.

Efecto de las frecuencias de pastoreo sobre un pastizal natural con presencia de Lotus tenuis en el partido de Olavarría, provincia de Buenos Aires

Resumen: La Pampa deprimida bonaerense está considerada la zona de cría más importante del país; el 85% de su superficie está cubierta por pastizales naturales, siendo éstos la principal fuente de alimento para la ganadería local. La productividad del pastizal natural, puede ser mejorada aplicando tecnología de procesos, al utilizar pastoreos en forma rotacional, en lugar del usual pastoreo continuo. El objetivo del presente trabajo, es evaluar el efecto en la producción bruta de materia seca del pastizal natural en un ambiente de un bajo dulce, en donde Lolium multiflorum y Lotus tenuis constituyen especies indicadoras, y cuya frecuencia en el tapiz vegetal es alta. Este ensayo se realizó en el establecimiento “El Fortín” ubicado en la Estación Pourtalé (Partido de Olavarría), durante un año, desde Mayo del 2014 hasta Mayo del 2015. Se utilizó un diseño experimental de bloques completamentes aleatorizados (DCBA), con dos tratamientos: frecuencia de 45 días y frecuencia de 90 días. Aleatorizados en tres bloques que corresponden al número de parcelas existentes dentro del potrero. Se realizaron en total 11 muestreos midiendo la producción de materia seca, siendo esta la variable en estudio. El análisis estadístico se realizó mediante un análisis de varianza, utilizando como software el programa Infostat. Los resultados sobre la producción en promedio, sostienen que existen diferencias significativas entre ambos tratamientos: de 45 días y de 90 días. La materia seca acumulada y anualizada, fue de 3306,7kg.MS ha-1 para el tratamiento de 45 días y de 3190,0 kg.MS ha-1 para el tratamiento de 90 días, entre pastoreos sucesivos. Mientras que la producción promedio acumulada entre cortes para cada tratamiento fue de 472,4kg.MS ha-1 para el tratamiento de 45 días y de 797,5 kg.MS ha-1 para el tratamiento de 90 días.

Natural convection in metal foams with open cells

This paper presents a combined experimental and numerical study on natural convection in open-celled metal foams. The effective thermal conductivities of steel alloy (FeCrAlY) samples with different relative densities and cell sizes are measured with the guarded-hot-plate method. To examine the natural convection effect, the measurements are conducted under both vacuum and ambient conditions for a range of temperatures. The experimental results show that natural convection is very significant, accounting for up to 50% of the effective foam conductivity obtained at ambient pressure. This has been attributed to the high porosity (ε > 0.9) and inter-connected open cells of the metal foams studied. Morphological parameters characterizing open-celled FeCrAlY foams are subsequently identified and their cross-relationships are built. The non-equilibrium two-equation energy transfer model is employed, and selected calculations show that the non-equilibrium effect between the solid foam skeleton and air is significant. The study indicates that the combined parameter, i.e., the porous medium Rayleigh number, is no longer appropriate to correlate natural convection by itself when the Darcy number is sufficiently large as in the case of natural convection in open-celled metal foams. Good agreement between model predictions and experimental measurements is obtained. © 2005 Elsevier Ltd. All rights reserved.

Respuesta a la fertilización fosforada en campo natural con presencia de Lotus tenuis en el partido de Olavarría, Cuenca del Salado, provincia de Buenos Aires

Resumen: La pampa deprimida bonaerense (región denominada Cuenca del Salado) es considerada la zona de cría más importante del país y su principal recurso forrajero son los pastizales naturales. Allí se encuentra Lotus tenuis como especie herbácea naturalizada y muy valorada por su aporte a la oferta forrajera de los sistemas ganaderos de la región. En condiciones de campos naturales en bajos dulces (con horizonte superficial de pH cercano a la neutralidad) el agregado de fósforo mediante la fertilización incrementaría la presencia de leguminosas, mejorando la receptividad y calidad de los forrajes y por ende, la producción de carne. El objetivo del presente trabajo fue evaluar la respuesta del pastizal natural, medida como producción de materia seca, utilizando distintas dosis de fertilización fosforada (NPK 5-40-0). Se realizó un ensayo en un establecimiento ubicado en las cercanías de la ciudad de Olavarría, en el paraje rural Pourtalé, Provincia de Buenos Aires, utilizando un diseño de bloques al azar con tres repeticiones. Los tratamientos fueron 0, 50 y 120 kg.ha-1 realizándose cinco muestreos luego de la fertilización en el transcurso de un año, en los cuales se determinó la producción de materia seca como estimación de la disponibilidad forrajera. La producción acumulada promedio para el tratamiento con 0kg.ha-1 fue de 2793kgMS.ha-1, con 50kg.ha-1 fue de 5159 kgMS.ha-1 y con 120kg.ha-1 fue de 7206 kgMS.ha-1. Para analizar estadísticamente los resultados, se realizó un análisis de varianza mediante un software estadístico (Infostat), donde se pudo observar diferencias significativas entre el testigo y el tratamiento con 120kg ha-1 (p-valor<0,05).

Actitud natural y actitud fenomenológica

Resumen: La fenomenología de Husserl toma como punto de partida el problema del conocimiento con el fin de reformular la idea de una filosofía como ciencia estricta que aspira en última instancia a establecer una vida éticamente buena sobre bases racionales. Tiene que enfrentarse para ello con las cuestiones del comienzo de la filosofía y de su método. Ambas exigen tener en cuenta la distinción entre la actitud natural y la actitud propiamente filosófica porque la epojé que abre el camino a la reducción fenomenológica requiere advertir, tematizar y suspender la validez de la actitud natural. En la primera sección del artículo se deslindan los rasgos esenciales de las actitudes y se distinguen tipos generales de actitudes. A continuación se muestra, en la segunda sección, a la actitud natural como el fondo o suelo de todas las actitudes especiales y se delinean sus caracteres más sobresalientes. En la tercera sección, por último, se contrasta esta actitud natural básica con la actitud fenomenológica en conexión con el modo como Descartes comprende las cuestiones del comienzo y del método. Con ello se retorna al planteo de la filosofía como conocimiento en vistas a una renovación ética de la vida espiritual a fin de precisar por qué el paso de la actitud natural a la actitud fenomenológica es la condición necesaria para poder abandonar la instalación ingenua sobre el suelo incuestionado del mundo.