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

A RECORD OF CALIDRIS-SUBMINUTA FROM KENYA

Volume: 89Start Page: 121End Page: 12

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