Study of the temperature distribution in Si nanowires under microscopic laser beam excitation

The use of laser beams as excitation sources for the characterization of semiconductor nanowires (NWs) is largely extended. Raman spectroscopy and photoluminescence (PL) are currently applied to the study of NWs. However, NWs are systems with poor thermal conductivity and poor heat dissipation, which result in unintentional heating under the excitation with a focused laser beam with microscopic size, as those usually used in microRaman and microPL experiments. On the other hand, the NWs have subwavelength diameter, which changes the optical absorption with respect to the absorption in bulk materials. Furthermore, the NW diameter is smaller than the laser beam spot, which means that the optical power absorbed by the NW depends on its position inside the laser beam spot. A detailed analysis of the interaction between a microscopic focused laser beam and semiconductor NWs is necessary for the understanding of the experiments involving laser beam excitation of NWs. We present in this work a numerical analysis of the thermal transport in Si NWs, where the heat source is the laser energy locally absorbed by the NW. This analysis takes account of the optical absorption, the thermal conductivity, the dimensions, diameter and length of the NWs, and the immersion medium. Both free standing and heat-sunk NWs are considered. Also, the temperature distribution in ensembles of NWs is discussed. This analysis intends to constitute a tool for the understanding of the thermal phenomena induced by laser beams in semiconductor NWs

An advanced Gibbs-Duhem integration method: Theory and applications

The conventional Gibbs-Duhem integration method is very convenient for the prediction of phase equilibria of both pure components and mixtures. However, it turns out to be inefficient. The method requires a number of lengthy simulations to predict the state conditions at which phase coexistence occurs. This number is not known from the outset of the numerical integration process. Furthermore, the molecular configurations generated during the simulations are merely used to predict the coexistence condition and not the liquid- and vapor-phase densities and mole fractions at coexistence. In this publication, an advanced Gibbs-Duhem integration method is presented that overcomes above-mentioned disadvantage and inefficiency. The advanced method is a combination of Gibbs-Duhem integration and multiple-histogram reweighting. Application of multiple-histogram reweighting enables the substitution of the unknown number of simulations by a fixed and predetermined number. The advanced method has a retroactive nature; a current simulation improves the predictions of previously computed coexistence points as well. The advanced Gibbs-Duhem integration method has been applied for the prediction of vapor-liquid equilibria of a number of binary mixtures. The method turned out to be very convenient, much faster than the conventional method, and provided smooth simulation results. As the employed force fields perfectly predict pure-component vapor-liquid equilibria, the binary simulations were very well suitable for testing the performance of different sets of combining rules. Employing Lorentz-Hudson-McCoubrey combining rules for interactions between unlike molecules, as opposed to Lorentz-Berthelot combining rules for all interactions, considerably improved the agreement between experimental and simulated data.Physical Chemistry and Molecular ThermodynamicsApplied Science

Durkheim, Vygotsky e o currículo do futuro Durkheim, Vigotsky and the curriculum

Este artigo reporta-se às bases epistemológicas do currículo do futuro. Inicia examinando os debates em curso sobre o impacto das mudanças curriculares na economia global. A parte principal do texto refere-se à explicação e comparação de duas teorias sociais do conhecimento - a de Emile Durkheim e a do psicólogo russo Lev Vygotsky, focalizando particularmente a questão das origens do conhecimento e a relação entre o conhecimento cotidiano e o conhecimento teórico. O autor argumenta que a abordagem genético-histórica adotada por Vygotsky precisa ser combinada com a ênfase durkheimiana na realidade social do conhecimento. Finalmente, conclui com algumas observações acerca das implicações da comparação para a teoria de currículo contemporânea.<br>This article is concerned with the epistemological basics of the curriculum of the future. It begins by examining current debates on the impact on the curriculum of changes in the global economy. The major part of the paper is concerned with an explication and comparison of two social theories of knowledge - those of Emile Durkheim and the Russian psychologist Lev Vygotsky, with a particular focus on the concern with the origins of knowledge and the relationship between everyday and theoretical knowledge. It argues that the genetic/historical approach adopted by Vygotsky needs to be combined with Durkheim's focus on the social reality of knowledge itself. It concludes with some observations on the implications of the comparison for contemporary curriculum theory

Treatment of wastewater containing polyacrylamide using three dimensional electrodes

A method using three-dimensional electrode is applied to treat wastewater in oil fields, which contains polyacrylamide (PAM), for analogue. A best condition for electrolysis (I = 1.0 A, t=90 min, c=0.1%, m=980 g, =5 mm, d=5.0 cm) has been determined, under which the COD removal efficiency reached 96.0%, COD containing in wastewater reduced to 64.3 mg/L from 1 622.9 mg/L, the figure before treatment. Three categories of PAM-containing wastewater in production practice have been treated with the COD removal ratios being 87.5%, 82.4% and 84.7% respectively. Presence of H2O2 and •OH are detected by means of Ti(IV)-5-Br-PADAP technique and colorimetry respectively. The concentration is positively proportional to the COD removal ratio and increases in accordance with increment of time of electrolysis and current