Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited at 1540 nm

Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited by CW laser radiation at 1540 nm and under cryogenic temperatures is reported. Intense upconversion emission signals around 530, 550 and 660 nm corresponding to the H-2(11/2), S-4(3/2), and F-4(9/2) transitions to the I-4(15/2) ground state were generated and studied as a function of the laser intensity and temperature. The upconversion excitation mechanism of the Er3+ ions emitting energy levels was accomplished via stepwise multiphoton absorption. The green upconversion luminescence exhibited a fivefold intensity enhancement when the temperature of the sample was varied in the range between 5 and 300 K. A maximum green upconversion intensity was attained around 120 K and a steady decreasing behavior for higher temperatures up to 300 K was observed. A model based upon conventional rate equations was used to model the observed temperature evolution of the upconversion luminescence. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Le progrès technique chez Joan Robinson : un essai de systématisation et de formalisation

This paper deals with Joan Robinson's contributions to the issue of technical progress and her attempts of treating this subject in accordance to the Keynesian theory of employment and income distribution, mainly in the long run. This paper aims to review this aspect of her work and to establish a systematisation and a formalisation of her approach. At the same time the paper exposes the problems she faced - and did not always solve. Looking through her main contributions, the paper concludes that she used different criteria for the classification of innovations and that they depended on the specific situations described by the models in which she used the classification.

Technical Progress in Joan Robinson's View: An attempt at systematisation and formalisation

This paper deals with Joan Robinson's contributions to the issue of technical progress and her attempts at treating this subject in accordance with the Keynesian theory of employment and income distribution, mainly in the long run. The paper aims to review this aspect of her work and to establish a systematisation and a formalisation of her approach. At the same time, the paper exposes the problems she faced - but did not always solve. Looking through her main contributions, the paper concludes that she used different criteria for the classification of innovations and that they depended on the specific situations described by the models in which she used the classification.

O universo imaginário dos holandeses no Brasil seiscentista: um estudo da narrativa do viajante Joan Nieuhof

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Mil años de ciencia ficción hermética latinoamericana [1492-2500]: En tres episodios: Borges, la conspiración; Sor Juana y Antônio Vieira, íntimos herejes; Bizarros profetas ciberculturales

Pós-graduação em Letras - IBILCE

Influence of a Z+(1540) resonance on K+N scattering

The impact of a (I=0, JP=1/2+)Z+(1540) resonance with a width of 5 MeV or more on the K+N(I=0) elastic cross section and on the P01 phase shift is examined within the KN meson-exchange model of the Jülich group. It is shown that the rather strong enhancement of the cross section caused by the presence of a Z + with the above properties is not compatible with the existing empirical information on KN scattering. Only a much narrower Z+ state could be reconciled with the existing data - or, alternatively, the Z + state must lie at an energy much closer to the KN threshold.