Spectrophotometric and electrochemical studies of the interaction of cryptand 222 with DDQ and I2 in ethanol solution

Spectrophotometric and electrochemical studies concerning the interaction of cryptand 222 with DDQ and I2 have been performed in ethanol solution. In the case of DDQ, the results are indicative of the formation of C222+ and DDQ- through an equilibrium reaction. The results of I2 indicate the formation of I2-ethanol complex and I3- in the absence of C222. In the presence of C222, the formation of C222I+ and I3- through a non-equilibrium reaction is confirmed. The equilibrium constant of the redox reaction between DDQ and C222 has been calculated from the absorbance mole ratio data, using the nonlinear least square program “KINFIT”. The electrochemical reversibility of I-/I2 couple and irreversibility of DDQ/DDQ- is indicated by amperometry. The behavior of DDQ and I2 has been compared. A comparison with aprotic solvents has also been made.KEY WORDS: Spectrophotometry, Electrochemistry, Cryptand 222, DDQ, I2Bull. Chem. Soc. Ethiop. 2006, 20(2), 183-192

MODELLING THEORY OF MIND, DIVERGENT THINKING AND MATHEMATICAL PROBLEM POSING OF FIRST GRADERS

Objetivo: A colocação de problemas tem uma importância central na disciplina de matemática e na natureza do pensamento matemático. O objetivo deste estudo foi investigar as relações explicativas e preditivas entre as variáveis da teoria da mente, pensamento divergente e problema que se apresentam nos alunos da primeira série do ensino fundamental, utilizando a abordagem de modelagem de equações estruturais. Método: Os sujeitos são 345 alunos (176 meninas e 169 meninos) da primeira série da escola primária de Zahedan, usando o modelo de amostragem disponível. Eles viviam e eram educados nas áreas urbanas médias da cidade. Os alunos responderam à teoria da mente, pensamento divergente e problemas matemáticos que colocam testes. A modelagem de equações estruturais foi utilizada para analisar os dados coletados no instrumento de pesquisa. Resultados: A análise dos dados revelou um impacto significativo (P <0,05) da variável de pensamento divergente no resultado das habilidades de colocação de problemas. Curiosamente, um impacto indireto da variável teoria da mente, via pensamento divergente, sobre a variável que coloca o problema foi observado neste estudo. Essas descobertas demonstraram claramente os impactos positivos dos componentes do pensamento e da teoria da mente divergentes sobre o problema matemático. Implicações para pesquisa e prática: continua a ser necessário explorar ainda mais o papel da mente noproblema que coloca a capacidade em relação à educação matemática.Propósito: La presentación de problemas tiene una importancia central en la disciplina de las matemáticas y en la naturaleza del pensamiento matemático. El propósito de este estudio fue investigar las relaciones explicativas y predictivas entre las variables de la teoría de la mente, el pensamiento divergente y la presentación de problemas en los estudiantes de primer grado de la escuela primaria, utilizando el enfoque de modelado de ecuaciones estructurales. Método: Los sujetos son 345 estudiantes (176 niñas y 169 niños) de los alumnos de primer grado de la escuela primaria de Zahedan, utilizando el modelo de muestreo disponible. Vivieron y fueron educados en las áreas urbanas promedio de la ciudad. Los estudiantes respondieron a la teoría de la mente, el pensamiento divergente y las pruebas de planteamiento de problemas matemáticos. El modelado de ecuaciones estructurales se utilizó para analizar los datos recopilados en el instrumento de encuesta.Resultados: El análisis de datos reveló un impacto significativo (P <0.05) de la variable de pensamientoen el resultado de las habilidades para plantear problemas. Curiosamente, en este estudio se observó un impacto indirecto de la variable de la teoría de la mente a través del pensamiento divergente sobre la variable de planteamiento del problema. Estos hallazgos demostraron claramente los impactos positivos de los componentes del pensamiento divergente y la teoría de la mente sobre el problema matemático que plantea. Implicaciones para la investigación y la práctica: sigue siendo necesario explorar más a fondo el papel de la mente en la capacidad de plantear problemas con respecto a la educación matemática.Purpose: Problem posing has a central importance in the discipline of mathematics and in the nature of mathematical thinking. The purpose of this study was to investigate the explanatory and predictive relationships among the variables of the theory of mind, divergent thinking, and problem posing in the first grade students of elementary school, using structural equation modeling approach. Method: The subjects are 345 students (176 girls and 169 boys) of the first graders of elementary school of Zahedan, using available sampling model. They lived and were educated in the average, urban areasof the city. Students responded to the theory of mind, divergent thinking, and mathematical problem posing tests. Structural Equation Modeling was used to analyze the data gathered survey instrument. Findings: The data analysis revealed a significant (P<0.05) impact of divergent thinking variable on the outcome of problem posing skills. Interestingly, an indirect impact of theory of mind variable via divergent thinking on the problem posing variable were observed in this study. These findings clearly demonstrated the positive impacts of the components of divergent thinking and theory of mind on the mathematical problem posing. Implications for Research and Practice: remains necessary to further explore the role of mind on the problem posing ability with regard to mathematical education

Monitoring of the Physical and Chemical Properties of a Gasoline Engine Oil during Its Usage

Physicochemical properties of a mineral-based gasoline engine oil have been monitored at 0, 500, 1000, 2000, 3500, 6000, 8500, and 11500 kilometer of operation. Tracing has been performed by inductively coupled plasma and some other techniques. At each series of measurements, the concentrations of twenty four elements as well as physical properties such as: viscosity at 40 and 100°C; viscosity index; flash point; pour point; specific gravity; color; total acid and base numbers; water content have been determined. The results are indicative of the decreasing trend in concentration of additive elements and increasing in concentration for wear elements. Different trends have been observed for various physical properties. The possible reasons for variations in physical and chemical properties have been discussed

<b>Spectrophotometric and electrochemical studies of the interaction of cryptand 222 with DDQ and I₂ in ethanol solution</b>

Spectrophotometric and electrochemical studies concerning the interaction of cryptand 222 with DDQ and I₂ have been performed in ethanol solution. In the case of DDQ, the results are indicative of the formation of C222^¬+ and DDQ^- through an equilibrium reaction. The results of I₂ indicate the formation of I₂-ethanol complex and I₃<sup>-</sub> in the absence of C222. In the presence of C222, the formation of C222I^¬+ and I₃<sup>-</sub> through a non-equilibrium reaction is confirmed. The equilibrium constant of the redox reaction between DDQ and C222 has been calculated from the absorbance mole ratio data, using the nonlinear least square program “KINFIT”. The electrochemical reversibility of I^-/I₂ couple and irreversibility of DDQ/DDQ^- is indicated by amperometry. The behavior of DDQ and I₂ has been compared. A comparison with aprotic solvents has also been made

Prediction of viscosity index and pour point in ester lubricants using quantitative structure-property relationship (QSPR)

Since ancient times, lubricants have been applied in different fields of technology and, from the very beginning, there has been a wide interest on improving some of their physical-chemical properties. The turning point in the development of lubricants came in the twentieth century, when modern synthetic ester base fluids were realized. In fact, with respect to “natural” lubricants (fats and mineral oils), they can be modified in order to optimize some specific technological properties; in particular, it is desirable that they present high viscosity index and a low pour point. Nevertheless, it is not always straightforward to accustom these parameters, and different theoretical studies have been pursued on this regard. Above all, valid tools to investigate these type of problems are the Quantitative Structure-Properties/Activity relationship studies (QSPA/QSPR). Starting from this considerations, the aim of the present paper is to investigate, by means of QSPR models, whether it can be possible to individuate or design ester base lubricants with some peculiar technological specificities. In particular, a QSPR analysis has been conducted in order to predict viscosity index and pour point on 41 ester lubricants by means of partial least squares combined with Leardi's genetic algorithms. The present study has provided satisfying results from the prediction point of view, and it has led to interesting conclusions from the interpretation viewpoint. In fact, it has highlighted that, the viscosity index and, to a lesser extent, the pour point, are highly correlated to the geometry, the molecular connectivity and the spatial autocorrelation of the investigated substances. © 2018 Elsevier B.V

Educatio siglo XXI : revista de la Facultad de Educación

Incluye apéndiceTítulo también en inglésResumen y palabras clave también en español y francésResumen basado en el de la publicaciónSe presenta el diseño y desarrollo de un instrumento para medir la comprensión del concepto de derivada, dentro del cálculo matemático y su comprensión instrumental y relacional, por estudiantes universitarios. Usando una técnica de muestreo intencional, se seleccionaron 162 estudiantes varones y mujeres, estudiantes de primer año de pregrado de ingeniería y ciencias básicas de la Universidad de Teherán. Todos los seleccionados habían pasado el curso de cálculo 1. Después de las investigaciones realizadas a través del análisis factorial exploratorio, basándose en el cuestionario de comprensión matemática de Yoong (1984), se desarrolla y valida un instrumento con 50 items, al que se agregan 7 preguntas sobre el concepto de definición de derivada al final del cuestionario, dado que no había herramientas disponibles para medir la comprensión relacional e instrumental de la derivada, resultando un total de 57 ítems. Se puede inferir que la comprensión instrumental puede ser la base para el aprendizaje. La comprensión relacional debe incluir el conocimiento de las principales ideas en el concepto de derivada, es decir, la tasa de variación, la pendiente de la recta tangente y el límite, y las relaciones entre ellos.ES

<b>Thermodynamic study of charge-transfer complex of iodine with HT18C6 in chloroform solution</b>

A spectrophotometric study concerning the interaction between HT18C6 as n-donor and I₂ as &sigma;-acceptor has been performed in chloroform solution at different temperatures. The results are indicative of the formation 1:1 complex through equilibrium reaction. The stability constant of the complex at 7, 13, 19 and 25 ^oC is obtained by the computer-fitting of absorbance-mole ratio data in MATLAB software. The ΔH^o and ΔS^o values are obtained by the Vant Hoff method. The obtained data show that the complex is enthalpy stabilized and entropy destabilized. The entropy destabilitization is attributed to the decrease of the entropy of the free donor upon complexation. Comparison of the data from this work with those of previous works done on 18C6-I₂ and HA18C6-I₂ is indicative of different stability, stoichiometry and products. The possible reasons for such differences are discussed