1,720,990 research outputs found
2 micron lasers with fuoride crystals: researcher and development
No full textIn the present work we present a review of the 2 micron laser based on fluoride crystals. We will provide a brief description of the theoretical aspects of rare earth ions embedded in insulating crystals, with particular attention to the advantages in using fluoride single crystals and the growth technique. The core article is represented by an overall survey of the laser and spectroscopic properties: Sections 4 and 6 will present the spectroscopic properties of the Tm, Ho and Tm, respectively, explained in the frame of the rate equation formalism and we will report a summary of the literature results. Finally Sections 5 and 7 will describe the state-of-the-art for the two systems
LiGdF(4):Tm(3+): spectroscopy and diode-pumped laser experiments
No full textA novel LiGdF(4) crystal doped with Thulium ions has been grown using the Czochralski technique. Three samples with doping concentrations of 0.3 at.%, 8 at.%, and 12 at.% have been extensively spectroscopically analyzed. We also performed room-temperature preliminary laser experiments, pumping the samples with a laser diode at 792 nm obtaining 53% as maximum slope efficiency with a maximum output power of 205 mW and a minimum lasing threshold of 22 mW. The laser emission spectrum in free running condition typically spans between 1990 and 2018 nm
Solution for cross- and angle-ply laminated Kirchhoff nano plates in bending using strain gradient theory
No full textThe static analysis of Kirchhoff nano plates subjected to uniformly (UDL) and sinusoidally (SSL) distributed load is computed. The strain gradient nonlocal theory has been employed in order to involve the size effects of nanostructures in classical continuum theory. The governing equation of motion of Kirchhoff in weak form are applied to nano plates, involving second-order strain gradient nonlocal theory. Thus, the obtained partial differential equations have an increased order of derivation respect to the classical theory, from the fourth to the sixth. The displacements are carried out following the Navier procedure for simply supported boundary conditions. Isotropic and antisymmetric orthotropic laminates, both cross- and angle-ply are studied, for different layouts involving different material properties. Dimensionless outcomes in terms of transverse displacements, and normal and shear stresses, are given to changing aspect ratio and non local ratio, also making a comparison with the classical theory
Analytical solution of cross- and angle-ply nano plates with strain gradient theory for linear vibrations and buckling
Full text linkVibrations and buckling of Kirchhoff nano plates are investigated using second-order strain gradi- ent theory. The Navier displacement field has been considered for two different sets of boundary conditions and stacking sequences. Different geometries and material properties for isotropic, orthotropic cross- and angle-ply laminates are considered, and numerical simulations are discussed in terms of plate aspect ratio and non local ratio. A comparison with the classical analytical solu- tion is provided whenever possible for buckling loads and fundamental frequencies.Vibrations and buckling of Kirchhoff nano plates are investigated using second-order strain gradient theory. The Navier displacement field has been considered for two different sets of boundary conditions and stacking sequences. Different geometries and material properties for isotropic, orthotropic cross- and angle-ply laminates are considered, and numerical simulations are discussed in terms of plate aspect ratio and non local ratio. A comparison with the classical analytical solution is provided whenever possible for buckling loads and fundamental frequencies
Microscopic treatment of upconversion in Nd3+-doped samples
No full textWe deal with the analysis of fluorescence decay of metastable manifolds of rare-earth ions in the presence of upconversion processes, with attention focused on Nd3+-doped crystals. In the literature this phenomenon is usually studied by means of rate equations or microscopic treatment. Here we show that only the second approach is correct in our experimental conditions, i.e., when the population dynamics is fast in comparison with the typical migration time tau(0), and tau(0) is considerably longer than the radiative lifetime. We studied the population dynamics after pulsed-laser excitation of some Nd3+-doped crystals, namely, Bay(2)F(8):Nd3+ at 3.75%, LiYF4:Nd3+ at 1.05%, and KLa(MoO4)(2):Nd3+ at 5.3%. We observed that the rate-equation formalism cannot reproduce the experimental data, therefore we used a microscopic treatment that gave much better results. From this analysis, after reaching the saturation regime, we were able to determine the donor-acceptor transfer constant Cd. for the samples under investigation in an unconventional way. (C) 2003 Optical Society of America
Comparative analysis of the 2 micron emission in Tm3+:BaY2F8 and Tm3+:KYF4: Spectroscopy and laser experiment
No full textIn the present work we report the growth, spectroscopy and laser results of Tm:BaY2F8 (8% and 12% doping density) and Tm:KYF 4 (10% doping density). A comparison of the laser emission in the 2 micron region is presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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