Experimental study for the determination of the turbulence onset in natural convection on inclined plates

In June, 8th, 2009 the balloon-borne solar telescope SUNRISE was launched from the Swedish Space Corporation balloon facility Esrange. A telescope with a mirror of 1 m in diameter ob-served the Sun during six days until the mission was terminated in Canada. The design process of SUNRISE and of any optical telescope requires the analysis of the effect of surrounding air on the quality of images. The turbulence encountered in the local telescope environment de-grades its optical performance. This phenomenon called `seeing' consists of optical aberrations produced by density non-homogeneities in the air along the optical path. The refraction index of air changes due to thermal non-uniformities so that the wavefront incident on the mirror is randomly distorted, and therefore, images are altered. When telescope mirrors are heated, as it happens in solar telescopes, and therefore they are at a temperature different from the environment's, natural convection occurs. It is then crucial to know whether the flow in front of the mirror is laminar or turbulent. After reviewing the literature, it was found that the scattering of results about the onset of the transition gives only rough orders of magnitude of the values of the critical Grashof numbers. Aiming to obtain more information about it, the problem of determination of the turbulence onset in natural convection on heated inclined plates in air environment was experimentally revisited. The transition has been determined from hot wire velocity measurements. The onset of turbulence has been considered to take place where velocity perturbations start to grow. Experiments have shown that the onset depends not only on the Grashof number, but also on other parameters as the temperature difference between the heated plate and the surrounding air. A correlation between dimensionless Grashof and Reynolds numbers has been obtained, fitting extraordinarily well the experimental data. The results are obtained in terms of non-dimensional numbers, this way they apply to any air pressure and therefore to any floating altitud

Effective Educational Practices and Students' Well-being: The Mediating Role of Students' Self-efficacy

Effective educational practices aim to promote students’ academic achievement; however, they also have an impact on students’ well-being which is a growing topic of interest in educational research. In a sample of 2242 students (5th to 10th grades) nested in 104 classrooms from Spanish schools, we have tested the mediating role of students’ self-efficacy on the relationship between effective educational practices and both students’ well-being and academic performance. Analyses were run at student and class levels, by performing a multilevel mediation structural equation model with cross-sectional data. Results supported a partial mediation model at the individual level, in which effective educational practices had a direct and indirect effect on students’ well-being, and indirect effect on academic performance in math and language through self-efficacy. At the group level, results support a full mediation model of the effect of effective educational practices in class well-being and in class math performance (but not in language), mediated by the group mean of self-efficacy. These findings suggest the importance of educational practices in increasing self-efficacy beliefs on their students, as a source to increase students’ well-being and academic performance

Matrix form of the Bayes theorem and diagnostic tests

In order to solve certain problems in calculating probabilities, such as Markov chains or conditional specification of discrete distributions, the use of matrix and vector treatment of conditioned probabilities and of vectors of marginal probabilities is common. Following these ideas, the present study obtains matrix forms of some elementary results of probability theory, such as the total probability and Bayes theorems. These results and methodology are applied to the matrix study of results of diagnostic tests, allowing an immediate generalization to tests with more than two results. In addition,we propose safety and validity measures of a test based on matrix rules, which in some cases are related to the well-known Youden index

A proposal for the content of the chapter "poverty measures" in a master's subject in economy and development

The objective of this work is teaching. We ask ourselves, what should students be taught about statistical measures of poverty? In a master's course, Measures of Inequality and Poverty, given at the University of Seville, Spain, a chapter dedicated to Measures of Poverty is included. In this work we want to provide this chapter with content. We include the different conceptions of this phenomenon together with the most commonly used measures or indicators. Objective and subjective poverty (with the measures of Kaptein or Leiden), absolute and relative, one-dimensional or multidimensional, are ideas that are shelled in the development of this work. We also include a set of possible axioms or properties required for a good indicator of poverty

Determination of Soluble Sugars in Arabidopsis thaliana Leaves by Anion Exchange Chromatography

Determination of soluble sugars is basic for the study of carbon metabolism in plants. Soluble sugar quantitation can be achieved by enzymatic methods implying different coupled reactions. Here we describe a simple method that allows rapid determination of the most abundant soluble sugars (glucose, fructose and sucrose) in Arabidopsis leaves by anion exchange chromatography. We have applied this method to study the levels of soluble sugars during the photoperiodic transition to flowering (Ortiz-Marchena et al., 2014).España, MINECO projects CSD2007-00057, BIO2008-02292, and BIO2011-28847-C02-00España, Junta de Andalucía P06-CVI-01450 and P08-AGR-0358

Rockets and feathers behaviour in the Spanish gasoline and diesel market: New evidence

In this paper we analyse the potential asymmetric response of retail prices for gasoline and diesel-fuel to changes in oil prices for the Spanish economy and its relation with the so-called ‘rockets and feathers’ behaviour. We show that the assumption made by previous studies, which use as the key explanatory variable the sign –positive or negativeof the change in international oil prices, is inadequate for the Spanish case and the magnitude of the change in international oil prices is also relevant. For small changes in international oil prices there is neither price asymmetry nor rockets and feathers behavior in the retail markets. However, price asymmetries in line with rockets and feathers behavior in retail gasoline and gasoil markets are present when these changes exceed a certain threshold. Following Martín-Moreno et al. (2018) we first apply an Auto-regressive Error Correction Model and endogenously estimate the threshold triggering the rockets and feathers behaviour. A time-varying nature for the dynamic response of retail prices to oil price shocks is revealed when we estimate the TAR-ECM model using rolling windows. Hence, in a second stage, we use a Markov-switching estimation of the model to test the robustness of the results given its suitability to changing environments. This study could have relevant policy implications for the Spanish gasoline and gasoil retail markets due to the ongoing debate on the existence of a rockets and feathers behavior in gasoline and gasoil retail markets between the Spanish regulatory body and the oil companies.Ministerio de Economía y Competitividad | Ref. ECO2015-67305-PMinisterio de Economía y Competitividad | Ref. ECO2015-68367-RXunta de Galicia | Ref. GRC2014/02

Evidence about asymmetric price transmission in the main European fuel markets: from TAR-ECM to Markov-switching approach

This paper presents new evidence on the existence of asymmetries in the transmission of shocks in oil prices in the main European fuel markets and their relation to the so-called rockets and feathers effect. Our approach differs from the existing literature in two ways: (1) the data used: we use forward prices rather than spot prices because fuel leaders use forward contracts to buy crude oil. (2) The methodological approach is different. We adopt a more sophisticated econometric model, the Markov-switching model, and use it to contrast the robustness of the results obtained with the TAR-ECM methodology with an endogenous threshold (nonzero threshold). In general, the results show evidence of an asymmetric response of gasoline and diesel prices to changes in the price of crude oil, both in the short-run and with respect to the adjustment towards long-run equilibrium. These price asymmetries fall in line with the “rockets and feathers” hypothesis.Ministerio de Economía y Competitividad | Ref. ECO2015-67305-PBanco de España | Ref. PR71/15-20229Ministerio de Economía y Competitividad | Ref. ECO2015-68367-RXunta de Galicia | Ref. GRC2014/02

On the onset of turbulence in natural convection on inclined plates

The problem of determination of the turbulence onset in natural convection on heated inclined plates in an air environment has been experimentally revisited. The transition has been detected by using hot wire velocity measurements. The onset of turbulence has been considered to take place where velocity fluctuations (measured through turbulence intensity) start to grow. Experiments have shown that the onset depends not only on the Grashof number defined in terms of the temperature difference between the heated plate and the surrounding air. A correlation between dimensionless Grashof and Reynolds numbers has been obtained, fitting quite well the experimental data

Galloping instabilities of Z-shaped shading louvers

Modern design of civil constructions such as office blocks, airport terminal buildings, factories, etc. incorporates more and more environmental considerations that lead to, amongst other elements, the use of glazed façades with shading devices to optimize energy consumption. These shading devices, normally slats or louvers, are very flexible structures exposed to the action of wind, and therefore aeroelastic effects such as galloping must be taken into account in their design. A typical cross-section for such elements is a Z-shaped profile made out of a central web and two side wings. The results of a parametric analysis based on static wind tunnel tests and performed on different Z-shaped louvers to determine translational galloping instability regions are presented in this paper

Experimental determination of the onset of turbulence on inclined plates using hot wire velocity measurements

The problem of determination of the turbulence onset in natural convection on heated inclined plates in an air environment has been experimentally revisited. The transition has been detected by using hot wire velocity measurements. The onset of turbulence has been considered to take place where velocity fluctuations (measured through turbulence intensity) start to grow. Experiments have shown that the distance to the plate edge where the onset begins depends both on the plate inclination angle and the plate temperature, and thus on the Grashof number defined in terms of the temperature difference between the heated plate and the surrounding air. An experimental setup to measure the above mentioned distance has been developed. In this paper, such an apparatus is presented, as well as the experimental procedure and some experimental results