1.55-mu m InGaAs/InGaAlAs MQW vertical-cavity surface-emitting lasers with InGaAlAs/InP distributed Bragg reflectors

High-performance InGaAs/InGaAlAs multiple-quantum-well vertical-cavity surface-emitting lasers (VCSELs) with lnGaAlAs/InP distributed Bragg reflectors are proposed for operation at the wavelength of 1.55 mum. The lasers have good heat diffusion characteristic, large index contrast in DBRs, and weak temperature sensitivity. They could be fabricated either by metal-organic chemical vapor deposition (MOCVD) or by molecular beam epitaxy (MBE) growth. The laser light-current characteristics indicate that a suitable reflectivity of the DBR on the light output side in a laser makes its output power increase greatly and its lasing threshold current reduce significantly, and that a small VCSEL could output the power around its maximum for the output mirror at the reflectivity varying in a broader range than a large VCSEL does. (C) 2004 Elsevier Ltd. All rights reserved.

Varieties generated by modular lattices of width four

A variety (equational class) of lattices is said to be finitely based if there exists a finite set of identities defining the variety. Let M^∞_n denote the lattice variety generated by all modular lattices of width not exceeding n. M^∞₁ and M^∞₂ are both the class of all distributive lattices and consequently finitely based. B. Jónsson has shown that M^∞₃ is also finitely based. On the other hand, K. Baker has shown that M^∞_n is not finitely based for 5 ≤ n ˂ ω. This thesis settles the finite basis problem for M^∞₄. M^∞₄ is shown to be finitely based by proving the stronger result that there exist ten varieties which properly contain M^∞₄ and such that any variety which properly contains M^∞₄ contains one of these ten varieties.

The methods developed also yield a characterization of sub-directly irreducible width four modular lattices. From this characterization further results are derived. It is shown that the free M^∞₄ lattice with n generators is finite. A variety with exactly k covers is exhibited for all k ≥ 15. It is further shown that there are 2^Ӄo sub- varieties of M^∞₄.

Rare-earth-doped silica microchip laser fabricated by sintering nanoporous glass

We report a new method for fabricating rare-earth-doped silica glasses for laser materials obtained by sintering nanoporous silica glasses impregnated with rare-earth-doped ions. The fabricated materials have no residual pores and show good optical and mechanical properties. Good performance from a Nd3+-doped silica microchip laser operating at 1.064 mum is successfully demonstrated, suggesting that the fabricated silica glasses have potential for use as active materials for high-power solid-state lasers. (C) 2005 Optical Society of America.

Entre mapas e moças do tempo: informação e entretenimento na meteorologia do Jornal Nacional e do Rural Notícias

Este trabalho é um estudo sobre a mistura que se estabelece entre informação meteorológica e entretenimento nos quadros da previsão do tempo de dois telejornais nacionais das Organizações Globo: Jornal Nacional JN (canal aberto Rede Globo) e Rural Notícias RN (canal fechado Canal Rural). A recepção dos programas sobre o tempo é analisada a partir de entrevistas abertas, com 40 espectadores de ambos os noticiários, habitantes da cidade e do campo. Também por meio de entrevistas, são avaliadas as representações da produção, privilegiando as denominadas moças do tempo, Flávia Freire (JN) e Lilian Lima (RN). Auxiliam na identificação do entretenimento, nos espaços da meteorologia, a observação do surgimento do consumidor moderno, a extensão do consumo ao lazer, o divertimento pela televisão, o tempo como assunto para conversa, as representações do corpo na cultura brasileira e traços da educação na transmissão meteorológica no Telejornalismo do país. Assim, são analisados os formatos dos quadros do tempo, suas funções aparentes, formatações, imagem corporal construída de suas apresentadoras e o público-alvo de cada telejornal. Esses principais pontos são relacionados com o pensamento de autores que estudam comunicação, tempo, hedonismo, utilitarismo, consumo, representações sociais, corpo, educação e pedagogia. A previsão da meteorologia aparece com várias funções, sendo dominantes a ênfase no cotidiano, em ambos os jornais; o foco no lazer, sobretudo no Jornal Nacional; e o destaque para o vínculo com a produção rural em sentido amplo, no caso do Rural Notícias.