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131.
132.
MARTI´NEZ C. Encinas-Sanz F. Serna J. MEJI´AS P. M. MARTI´NEZ-HERRERO R. 《Optical and Quantum Electronics》1997,29(9):923-931
A simple analytical model is proposed to describe the transversal spatial structure of a tridimensional rotationally symmetric
pulsed beam. The spatial behaviour of the pulse amplitude is shown to be linked to its (measurable) second- and higher-order
intensity moments, namely, beam width, quality parameter and kurtosis. As an illustrative experimental example, this model
has been applied to high-quality TEA CO2 laser pulses.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
133.
F. M. Couto M. S. Sthel M. P. P. Castro M. G. da Silva M. V. Rocha J. R. Tavares C. F. M. Veiga H. Vargas 《Applied physics. B, Lasers and optics》2014,117(3):897-903
In order to investigate the generation of greenhouse gases in sugarcane ethanol production chain, a comparative study of N2O emission in artificially fertilized soils and soils free from fertilizers was carried out. Photoacoustic spectroscopy using quantum cascade laser with an emission ranging from 7.71 to 7.88 µm and differential photoacoustic cell were applied to detect nitrous oxide (N2O), an important greenhouse gas emitted from soils cultivated with sugar cane. Owing to calibrate the experimental setup, an initial N2O concentration was diluted with pure nitrogen and detection limit of 50 ppbv was achieved. The proposed methodology was selective and sensitive enough to detect N2O from no fertilized and artificially fertilized soils. The measured N2O concentration ranged from ppmv to ppbv. 相似文献
134.
The blue colour in ancient soda-lime glasses has been attributed to the presence of copper and/or cobalt but the origin of different shades is not yet fully interpreted. As a contribution to this question, a non-destructive X-ray absorption study at [
Cu]K-edge was undertaken on the blue (turquoise) layer from a “Nueva Cadiz” type tubular glass bead dated pre-XVII century where copper is the unique colouring agent. Minerals configuring two distinct blue tonalities due to Cu (2+) in similar square coordination were selected as basic model compounds: azurite, which is a classical navy-blue pigment used in ancient wall paintings over plaster, and chalcanthite, displaying exactly the same turquoise-blue tonality of tubular glass beads manufactured since the Egyptian Antiquity. Theoretical modelling of the XAFS spectra was undertaken using the FEFF code. The IFEFFIT software package was used for fitting the calculated spectra to experimental data. EXAFS results are discussed in view of the crystal structures of copper minerals chosen to model the speciation state and structural situation of that element prevailing in the turquoise-blue archaeological glass. Special attention is focused on the difficulties in theoretical modelling [
Cu]K-XANES spectra of ancient glasses with different colourings. PACS 61.43.Fs; 61.46.+w; 41.60.Ap; 61.10.Ht. 相似文献
135.
H. Beirão da Veiga 《Journal of Mathematical Analysis and Applications》2009,352(1):271-292
In the beginning of the 1990s we devoted a sequence of papers to perturbation theory, singular limits and well-posedness problems. In particular, the strong well-posedness of the initial-boundary value problem for the compressible Euler equations was demonstrate for the first time. Our method also allowed singular limit results in the strong norm, even under assumptions weaker than the current ones in the literature (where the strong norm is not reached). It is worth noting that, until now, the above method and results have not been substantially improved. Hence an introduction to it still looks timely. Actually, in a forthcoming paper, by returning to this method, we improve (in a very substantial way) some important results recently appeared in the literature. 相似文献
136.
A local a posteriori error indicator for the well known Morley element for the Kirchhoff plate bending problem is presented.
The error indicator is proven to be both reliable and efficient. The technique applied is general and it is shown to have
also other applications. 相似文献
137.
138.
A. Veiga C. M. Grunfeld G. A. Pasquevich P. Mendoza Zélis N. Martínez F. H. Sánchez 《Hyperfine Interactions》2014,224(1-3):73-81
Long term gamma spectroscopy experiments involving single-channel analyzer equipment depend upon thermal stability of the detector and its associated high-voltage supply. Assuming constant discrimination levels, a drift in the detector gain impacts the output rate, producing an effect on the output spectrum. In some cases (e.g. single-energy resonant absorption experiments) data of interest can be completely lost. We present a digital self-adapting discrimination strategy that tracks emission line shifts using statistical measurements on a predefined region-of-interest of the spectrum. It is developed in the form of a synthesizable module that can be intercalated in the digital processing chain. It requires a moderate to small amount of digital resources and can be easily activated and deactivated. 相似文献
139.
A family of plate elements introduced by Falk and Tu [25] is considered. A new stability and a-priori error analysis is given.
In addition, an a-posteriori error estimate is proved. The analysis is confirmed by numerical benchmark computations.
AMS subject classification (2000) 65F20 相似文献
140.
Ana C.F. Ribeiro Cecilia I.A.V. Santos Victor M.M. Lobo Ana M.T.D.P.V. Cabral Francisco J.B. Veiga Miguel A. Esteso 《The Journal of chemical thermodynamics》2009,41(12):1324-1328
Ternary mutual diffusion coefficients measured by Taylor dispersion method (D11, D22, D12, and D21) are reported for aqueous solutions of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) + caffeine at T = 298.15 K at carrier concentrations from (0.000 to 0.010) mol · dm−3, for each solute, respectively. These diffusion coefficients have been measured having in mind a better understanding of the structure of these systems and thermodynamic behaviour of caffeine and 2-hydroxypropyl-β-cyclodextrin in solution. For example, from these data it will be possible to estimate some parameters, such as the fraction of associated species HP-β-CD (X1) and caffeine (X2) in this complex, the monomer and dimer fractions, and , respectively, and the limiting diffusion coefficients of the HP-β-CD, , of the dimers caffeine entities, , and of those complexes (1:1), . 相似文献