Role of the oxygen plasma during in situ growth of YBa2Cu3O6+x thin films by pulsed laser deposition

The incorporation of oxygen into YBa2Cu3O6+x (YBaCuO) thin films during in situ growth by pulsed laser deposition (PLD) has been investigated as a function of the ablation conditions. A quenching technique has been used immediately after termination of growth to avoid any oxygen in or out-diffusion during the cooling down step. It is shown that superconducting YBaCuO thin films can be formed without any post-oxygenation procedure, contrary to what is expected from the (Image, T) thermodynamic diagram. Moreover, it is found that there is an optimal target-substrate distance, D, for each O2 deposition pressure, Image, that leads to the higher critical temperature (i.e., higher oxygenation) as well as to the best structural and morphological properties of quenched films. The results are discussed considering the formation of reactive oxygen in the laser-induced plasma during film growth

Enhancing the Main Characteristics of Active Methodologies: A Case with Micro Flip Teaching and Teamwork

All active methodologies have common objectives and processes. Their mission is to ensure that students participate actively in the learning process, cooperating with other students, reflecting, making decisions and creating knowledge. For this purpose, groups that work in a timely manner to carry out an activity or in a more stable way through work teams are usually formed. In both cases, active learning takes place within the groups. This work proposes fostering an active inter-team learning; that is, forming a meta-team where active learning takes place. The aim is checking if students who follow an active methodology, have the active habit; that is, if the work teams share knowledge among themselves and use it to improve their own knowledge. The proposed model contains a virtual layer that all teams can access, making possible the cooperation, the creation of new knowledge, reflection and decision making. This model is applicable to any active methodology and the proposed model has been applied to the Micro Flip Teaching methodology. This quasi experimental research methodology, based on quantitative and qualitative assessment, shows how the work teams, in an Engineering context, in this case, use this virtual layer and how that use impacts the academic performance of their members. Another conclusion of this work is that feedback must be included in active methodologies

A theoretical analysis of Ballistic Electron Emission Microscopy: k-space distributions and spectroscopy

We analyze BEEM experiments. At low temperatures and low voltages, near the threshold value of the Schottky barrier, the BEEM current is dominated by the elastic component. Elastic scattering by the lattice results in the formation of focused beams and narrow lines in real space. To obtain the current injected in the semiconductor, we compute the current distribution in reciprocal space and, assuming energy and $k_{\parallel}$ conservation. Our results show an important focalization of the injected electron beam and explain the similarity between BEEM currents for Au/Si(111) and Au/Si(100).Comment: 17 pages, 5 figures (postscript), Latex, APS, http://www.icmm.csic.es/Pandres/pedro.htm. Appl. Surf. Sci. (in press

Análisis de la problemática de los impactos fruto-fruto en las líneas de manipulación.

Se han realizado diferentes ensayos con el objetivo de analizar la problemática de los impactos manzana-manzana en las líneas de manipulación de fruta. Para ello se ha utilizado una línea experimental de manipulación de frutas en la que se han evaluado las características de estos impactos en función de diferentes factores: características del producto, flujo de producto en línea y características de los puntos de transferencia entre elementos de la línea. Una vez conocida la problemática de los impactos fruto-fruto, se ha desarrollado un elemento decelerador accionado para minimizar dichos impactos en una transferencia en 90° entre dos cintas transportadoras. El elemento decelerador ha sido evaluado comparando su eficacia con otros sistemas. En los diferentes ensayos se han utilizado frutos electrónicos IS 100 y manzanas "Golden"

Characterization of a 90° Transfer Point in a Fruit Packing Line.

Characteristics of the impacts suffered by the fruit on a transfer point of an experimental fruit packing line were analysed. The transfer is made up by two transporting belts at different heights forming an angle of 90°. These transfer points are very common in fruit packing lines, in which fruits receive two impacts: the first onto the belt base and the second into the lateral plate. Different tests were earned out to study the effect of transfer height, velocity, belt structure and padding on tire acceleration values recorded by an instrumental sphere (IS 100). Results showed that transfer height and belt structure affect mainly impact values on the belt base, and padding affects mainly impact values registered in lateral impact. The effect of belt velocity in both impacts is less important when compared to the rest of the variables. Additionally, two powered transfer decelerators were tested at the same point with the aim of decreasing impacts suffered by the fruit. Comparing impacts registered using these decelerators to those analysed in the first part of the study without decelerators a high reduction of the impact values was observed

Comparison of Four Natural Ventilation Systems in a Mediterranean Greenhouse

Ventilation is one of the most important tools for controlling the greenhouse climate, influencing the environmental conditions such as temperature, humidity and carbon dioxide concentration, which affect the development and production of the crop. Natural ventilation is the result of the action of two natural forces, wind and thermal buoyancy. The main objectives of this study were to: 1). compare the behaviour of internal air parameters such as air temperature and humidity in a greenhouse with different management of natural ventilation and 2). calibrate and validate a climatic model. The study was based on experiments carried out in a greenhouse located at the ETSIA-Universidad Politecnica de Madrid, with floor area of 132 m2. The greenhouse was equipped with roof and side vents along the entire length. Four different systems (S) were studied, both roof and side openings (S1, A1=21.3 m2) and only roof openings (S2, A2=12.3 m2; S3, A3=7.9 m2 and S4, A4=4.4 m2). External and internal climatic parameters, such as air temperature, relative humidity, solar radiation and wind speed were measured and recorded using a data logger. All the data were recorded during several days for the different systems. Data of internal air temperature and water vapour pressure difference were analysed and compared between the different systems. In this study, ventilation rates were calculated using a model based on wind and buoyancy forces, assuming that total ventilation is due to the combined effect of both natural forces. Ventilation rates were then related to internal air conditions. Temperature differences between inside and outside varied within a range of 3.3 ºC (S1) and 10.6 ºC (S4), presenting an inverse proportionality to the ventilation area. The vapour pressure difference presented the highest value (0.111 kPa) for S2 and the lowest (0.011 kPa) for S3. A climatic model, based on energy and mass balances, allowing the prediction of internal air temperature and relative humidity, was calibrated and validated for the different ventilation systems. Partial data were used to calibrate the model and another set of data from different periods was used for model validation. Measured and predicted data were comparatively close

Application of low-cost sensors for the development of a methodology to design front-end loaders for tractors

Tractor front-end loaders are an essential part of the equipment used on farms. At present, there are an important number of small- and medium-sized companies involved in the manufacturing of this equipment. These companies rely heavily on experience for innovative designs, as in the vast majority of cases they lack access to adequate methodology for the optimal design of new front-end loaders. The study conducted has developed a methodology to design tractor front-end loaders with a view of obtaining their accurate design during the bucket loading process. The methodology comprises two phases: the first phase involves a numerical analysis of the structural behaviour of the front-end loader components by means of the Finite Element Method; the second phase, the experimental phase, makes use of low-cost sensors, in particular, strain gauges, to analyse existing strains at selected points in the front-end loader structure. The experimental results obtained by means of low-cost sensors fitted onto the front-end loader allow analysing the existing strains at the points measured, as well as validate the numerical model developed. This methodology is validated by applying it to a commercial front-end loader, more specifically to model 430E2 of the company Maquinaria Agrícola El León S.A (Spain)

Centennial-scale vegetation and North Atlantic Oscillation changes during the Late Holocene in the southern Iberia

High-reso CE to lution pollen analysis, charcoal, non-pollen palynomorphs and magnetic susceptibility have been analyzed in the sediment record of a peat bog in Sierra Nevada in southern Iberia. The study of these proxies provided the reconstruction of vegetation, climate, fire and human activity of the last ∼4500 cal yr BP. A progressive trend towards aridification during the late Holocene is observed in this record. This trend is interrupted by millennial- and centennial-scale variability of relatively more humid and arid periods. Arid conditions are recorded between ∼4000 and 3100 cal yr BP, being characterized by a decline in arboreal pollen and with a spike in magnetic susceptibility. This is followed by a relatively humid period from ∼3100 to 1600 cal yr BP, coinciding partially with the Iberian-Roman Humid Period, and is indicated by the increase of Pinus and the decrease in xerophytic taxa. The last 1500 cal yr BP are characterized by several centennial-scale climatic oscillations. Generally arid conditions from ∼450 to 1300 CE, depicted by a decrease in Pinus and an increase in Artemisia, comprise the Dark Ages and the Medieval Climate Anomaly. Since ∼ 1300 to 1850 CE pronounced oscillations occur between relatively humid and arid conditions. Four periods depicted by relatively higher Pinus coinciding with the beginning and end of the Little Ice Age are interrupted by three arid events characterized by an increase in Artemisia. These alternating arid and humid shifts could be explained by centennial-scale changes in the North Atlantic Oscillation and solar activity