Approximation of the critical buckling factor for composite panels

This article is concerned with the approximation of the critical buckling factor for thin composite plates. A new method to improve the approximation of this critical factor is applied based on its behavior with respect to lamination parameters and loading conditions. This method allows accurate approximation of the critical buckling factor for non-orthotropic laminates under complex combined loadings (including shear loading). The influence of the stacking sequence and loading conditions is extensively studied as well as properties of the critical buckling factor behavior (e.g concavity over tensor D or out-of-plane lamination parameters). Moreover, the critical buckling factor is numerically shown to be piecewise linear for orthotropic laminates under combined loading whenever shear remains low and it is also shown to be piecewise continuous in the general case. Based on the numerically observed behavior, a new scheme for the approximation is applied that separates each buckling mode and builds linear, polynomial or rational regressions for each mode. Results of this approach and applications to structural optimization are presented

He II λ4686 in η Carinae: Collapse of the wind-wind collision region during periastron passage

The periodic spectroscopic events in η Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of η Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II λ4686 emission line (L 310 L) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II λ4686 light curves. After a short-lived minimum, He II λ4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the "surface" of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind.Facultad de Ciencias Astronómicas y Geofísica

He II λ4686 in η Carinae: Collapse of the wind-wind collision region during periastron passage

The periodic spectroscopic events in η Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of η Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II λ4686 emission line (L 310 L) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II λ4686 light curves. After a short-lived minimum, He II λ4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the "surface" of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind.Facultad de Ciencias Astronómicas y Geofísica

He II λ4686 in η Carinae: Collapse of the wind-wind collision region during periastron passage

The periodic spectroscopic events in η Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of η Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II λ4686 emission line (L 310 L) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II λ4686 light curves. After a short-lived minimum, He II λ4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the "surface" of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind.Facultad de Ciencias Astronómicas y Geofísica

Organic and inorganic fertilization effects on DTPA-extractable Fe, Cu, Mn and Zn, and their concentration in the edible portion of crops

The application of organic composts to soil may affect the availability of micronutrients and their concentration in plants. The present field research study compared soil micronutrient extractability after 5 years of organic fertilization v. conventional inorganic fertilization. Iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) were extracted from soil using diethylene triamine pentaacetic acid (DTPA) and the data obtained were compared with the concentration of these micronutrients in the edible portion of the crop. The study was carried out on a loam soil classified as a Xerofluvent. The soil was fertilized with composted plant residues or with conventional inorganic fertilizer and all treatments were replicated four times in a randomized complete block design. In all cases a crop rotational system was applied. The use of organic fertilization resulted in a higher extractability for all the elements studied; however, the micronutrient content in the edible part of the crops was variable depending on the plant species and element. Crop yields depended on the type of crop rather than the type of soil fertilization. The present study showed that the use of plant compost and the elimination of synthetic fertilizers result in an increase of Fe, Cu, Mn and Zn extractability compared to soil treated with inorganic fertilization, which should provide long-term fertility benefits.Peer Reviewe

Biochemical properties of two different textured soils (loam and clay) after the addition of two different composts during conversion to organic farming

[EN]: The conversion to organic farming of two soils, a loam (Xerofluvent) under irrigation and a clay (Chromic Haploxerept) under dryland management, was studied through analysis of their biochemical properties. Soil biological status was evaluated by measuring microbial biomass carbon and the ratio of enzymatic activity to microbial biomass. Results were compared to those after application of inorganic fertilizer. At the end of the study, in both soil types the organic treatments had increased the organic matter and nitrogen content compared with the inorganic treatment. Total organic carbon (TOC) values in the clay were higher than in the loam. This could be related to a lower mineralization rate of soil organic matter under dry land management and/or with a protection effect, by the clay on the organic fraction. However, absolute ratios of some enzymatic activities (dehydrogenase, protease and alkaline phosphatase) by microbial biomass carbon in the clay were lower than in the loam indicating a lower rate of enzyme production by microbial biomass in the clay. In the clay soil there was a great increase in TOC, total N, microbial biomass and enzymatic activity, in all treatments, in the last crop cycle. This was mainly related to a previous legume crop. Generally organic management improved biomass and enzymatic activity in both soils. In the future further studies are required to confirm the positive long-term effect of organic fertilization on biochemical properties which maintain or improve soil quality. [ES]: En este trabajo se aborda el estudio de la reconversión a la agricultura ecológica en dos suelos de diferente textura y régimen hídrico, un suelo franco (Xerofluvent) en regadío y un suelo arcilloso (Chromic Haploxerept) en secano. Se compara el manejo ecológico del suelo con respecto a un manejo convencional, desde el punto de vista biológico. Se eva- luó el estado biológico del suelo a través del carbono de la biomasa microbiana y el cociente entre las actividades enzi- máticas por biomasa microbiana. Se observó un incremento en el contenido de materia orgánica y nitrógeno en los sue- los fertilizados orgánicamente de ambos experimentos de reconversión. No obstante, los valores más altos de los contenidos de carbono orgánico total se encontraron en el suelo arcilloso. Estos resultados pueden estar relacionados con la menor tasa de mineralización debido a baja humedad de este suelo y/o al mayor contenido en arcilla que tiene un efecto pro- tector en la fracción orgánica. Las razones de las actividades enzimáticas (deshidrogenasa, proteasa y fosfatasa alcali- na) por biomasa microbiana en el suelo arcilloso fueron más bajas que en el suelo franco, reflejando una menor síntesis de enzimas por los microorganismos en el suelo arcilloso. En el último ciclo de cultivo del experimento de reconversión en secano se observó un importante incremento del contenido en carbono orgánico total, nitrógeno total, biomasa mi- crobiana y actividades enzimáticas, lo cual se atribuye al cultivo anterior (una leguminosa). Por lo tanto, serían necesa- rios estudios a más largo plazo para confirmar una mejora de las propiedades bioquímicas bajo manejo orgánico.The European Commission, the Spanish Ministry of Science and Technology and the Government of Andalusia for financial support of projects FEDER AGL00-0493-C02-02 and P.I.A 13.01.1, which allowed this work to be conducted.Peer Reviewe

Effect of transition from conventional to organic farming on biological properties of an irrigated loam soil

Comunicación presentada a la citada conferencia, celebrada del 28 noviembre-1 diciembre, 2007, Sevilla, España.Peer reviewe