Convergence to Weighted Fractional Brownian Sheets

We define weighted fractional Brownian sheets, which are a class of Gaussian random fields with four parameters that include fractional Brownian sheets as special cases, and we give some of their properties. We show that for certain values of the parameters the weighted fractional Brownian sheets are obtained as limits in law of occupation time fluctuations of a stochastic particle model. In contrast with some known approximations of fractional Brownian sheets which use a kernel in a Volterra type integral representation of fractional Brownian motion with respect to ordinary Brownian motion, our approximation does not make use of a kernel

Multivariate Statistical Analysis of Phyllite Samples Based on Chemical (XRF) and Mineralogical Data by XRD

It is presented the results obtained of a multivariate statistical analysis concerning the chemical and phase composition, as a characterization purpose, carried out with 52 rock phyllite samples selected from the provinces of Almería and Granada (SE Spain). Chemical analysis was performed by X-ray fluorescence (XRF). Crystalline phase analysis was performed by X-ray powder diffraction (XRD) and the mineralogical composition was then deduced. Quantification of weight loss (100° and 1000°C) was carried out by thermal analysis. The aims of this investigation were to analyze and compare the chemical and mineralogical composition of all these samples and to find similarities and differences between them to allow a classification. Several correlations between results of the characterization techniques have been also investigated. All the data have been processed using the multivariate statistical analysis method. The XRF macroelements (10) and microelements (39) data generate one macrogroup with two new subgroups (1 and 2), and an isolated sample. In subgroup 1 of macroelements, a positive correlation was found between XRF results and geographic location characterized by lower MgO content, which is associated to its geological origins. When multivariate statistical analysis is applied to results obtained by XRD, two groups appear: the first one with a sample with zero percentage of iron oxide and the second one with the rest of the samples, which is classified in two groups. A correlation is observed between the alkaline content (XRF) and illite (XRD), CaO and MgO with dolomite and indirectly between the weight loss after heating at 1000°C and the contents of phase minerals that lose structural water (illite + chlorite) or carbon dioxide (dolomite). The present investigation has interest and implications for geochemistry and analytical chemistry concerning earth rocks and silicate raw material

Correlation between chemical and mineralogical characteristics and permeability of phyllite clays using multivariate statistical analysis

Phyllite clays are applied as a layer on a surface to be waterproofed and subsequently compacted. For this purpose, phyllite clays deposits can be grouped by their chemical and mineralogical characteristics, and these characteristics can be connected with their properties, mainly permeability, in order to select those deposits with the lowest permeability values. Several deposits of phyllite clays in the provinces of Almería and Granada (SE Spain) have been studied. The results of applying a multivariate statistical analysis (MVA) to the chemical data analysed from 52 samples determined by XRF, mineralogical analysis by XRD and permeability are reported. Permeability, a characteristic physical property of phyllite clays, was calculated using the results for experimental nitrogen gas adsorption and nitrogen adsorption-desorption permeability dependence. According to the results, permeability values differentiated two groups, i.e. group 1 and group 2, with two subgroups in the latter. The influence of chemical as well as mineralogical characteristics on the permeability values of this set of phyllite clays was demonstrated using a multiple linear regression model. Two regression equations were deduced to describe the relationship between adsorption and desorption permeability values, which support this correlation. This was an indication of the statistical significance of each chemical and mineralogical variable, as it was added to the model. The statistical tests of the residuals suggested that there was no serious autocorrelation in the residuals.Peer ReviewedPostprint (author's final draft

Unveiling the Meaning of Social Justice in Colombia

English Abstract: Through the presentation of the history of social justice in global constitutional discourse, this article aims to demonstrate that, although in Colombia there is not a constitutionalized purpose or principle of social justice, as in other countries, the modern notion of distributive justice, also called social justice today, is implicit in the Constitution of 1991 because it enshrined as mandatory rules the three main elements of its meaning at the time of its promulgation: the principle of social rule of law, the principle of human dignity and the right to a material equality. Thus, in Colombia social justice must not be understood in the Aristotelian sense of distributive justice but in accordance with these three elements, and can only be achieved if they are fulfilled. Spanish Abstract: Mediante la presentación de la historia de la justicia social en el discurso constitucional global, este artículo pretende demostrar que, a pesar de no existir en Colombia, como en otros países, un valor o principio constitucional de justicia social, la noción moderna de justicia distributiva, también llamada hoy justicia social, se encuentra implícita en la Constitución de 1991 porque esta consagró como normas obligatorias los tres elementos principales de su significado en el tiempo en el que fue promulgada: el principio de Estado Social de Derecho, el principio de dignidad humana y el derecho a una igualdad material. Así pues, la justicia social debe entenderse en Colombia a partir de esos tres elementos, no según el sentido aristotélico de justicia distributiva, y sólo puede ser alcanzada si ellos se cumplen

Academic procrastination in non-traditional college students

Introducción. La procrastinación es la acción de retrasar la realización de tareas necesarias, hasta el extremo de generar malestar y perjuicios a los individuos que la protagonizan. La presencia de alumnado no tradicional en las universidades se ha incrementado notablemente en las últimas décadas. Este tipo de estudiantes encuentra dificultades en sus estudios, las cua- les podrían propiciar una mayor incidencia de las conductas procrastinadoras. Para compro- barlo, comparamos los niveles de procrastinación y motivos para procrastinar entre estudian- tes tradicionales y no tradicionales. Método. Utilizamos una muestra de 479 estudiantes colombianos. Los niveles de procrasti- nación y motivos para procrastinar fueron medidos a partir de la Procrastination Assessment Scale – Students (PASS). En el análisis de datos se utilizaron estadísticos descriptivos, análisis factorial exploratorio, prueba t para muestras independientes y d de Cohen. Resultados. Los estudiantes no tradicionales han presentado niveles de procrastinación supe- riores (t=4,412; p<0,001; d=0,459), aunque los motivos para procrastinar no difieren de los aportados por estudiantes tradicionales. El carácter de estudiante no tradicional ha resultado ser una variable relevante en la explicación de la procrastinación académica. Discusión y conclusiones. A partir de estos resultados, se deriva la conveniencia de ofrecer una orientación académica al alumnado no tradicional, con el fin de tratar la procrastinación y reducir así posibles riesgos de bajo rendimiento o abandono en este colectivo estudiantil.Introduction. Procrastination is the act of delaying necessary tasks until the extreme of ex- periencing discomfort and negative consequences to the individuals. The presence of nontra- ditional students at universities is a phenomenon which has increased remarkably over the last decades. This type of university students finds some difficulties during their grade. This could result in a higher prevalence of procrastination behaviors among nontraditional students at university. To test this, our work compares procrastination levels and reasons to procrastinate among traditional and nontraditional students Method. A sample of 479 Colombian college students was used. Procrastination and the rea- sons to procrastinate are measured by the Procrastination Assessment Scale - Students (PASS). The data analysis is based on descriptive statistics, exploratory factorial analysis, t test for independent samples and Coohen’s d. Results. Nontraditional students show higher procrastination levels (t=4,412; p<0,001; d=0,459), although their reasons to procrastinate are similar to those of traditional students. The nontraditional student condition is a demographic variable relevant for explaining aca- demic procrastination. Discussion and Conclusion. These results suggest the convenience of offering academic counselling and guidance to nontraditional students, in order to attend procrastination and reducing that way low achievement or dropout risks

Three-dimensional decomposition of galaxies with bulge and long bar

Some observations indicate that the Milky Way has two inner components, a bulge and a long bar, which present a misalignment of about 20 degrees that is against the predictions of some theoretical models that are based on numerical simulations. In this paper, we wish to determine whether this misalignment between the bar and the bulge can be observed in barred galaxies other than the Milky Way. For that, each galaxy of our sample was decomposed based on its Ks-band 2MASS image by fitting and modelling in a three-dimensional (3D) space the following components: a disc, a bar, and a bulge. The chi-square goodness-of-fit estimation allowed retrieving the best-fit angle values for the bar and the bulge to detect any misalignment. From the 3D decomposition of six barred galaxies, we have detected at least three galaxies (NGC 2217, NGC 3992, and NGC 4593) that present a significant misalignment between the bar and the bulge of more than 20 degrees.Comment: 8 pages, 1 figure. Accepted for publication in A&A. Corrected typo