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881.
A.Y. Zasetsky B. Cosic I.A. Grishin R.G. Pancescu A.F. Khalizov J.J. Sloan 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,107(2):294-305
We report several results that validate the accuracy of a retrieval method for the determination of a number of aerosol particle properties from their mid infrared (600-6000 cm−1) extinction spectra. These properties include the number density, chemical composition, phase, size distribution, and to some extent, shape. The approach is based on information obtained in laboratory studies of micron-sized particles using the aerosol flow tube (AFT) technique. We report here experiments in which our method is used to measure a variety of aerosols including SiO2 micro-spheres as well as solid NaCl, (NH4)2SO4, ice and liquid water particles. The uncertainties in the retrieved aerosol properties associated with the particle shapes (spheres, spheroids, cylinders, hexagonal and rectangular prisms) as well as the effect of variations in the spectral range were evaluated. To assess the accuracy of the retrieved size distributions and particle shapes, the properties calculated from infrared spectra were compared with corresponding properties determined using alternative methods. We used scanning electron microscopy (SEM) for solid (NH4)2SO4 and NaCl aerosols and direct particle imaging with an optical microscope assembly for liquid water aerosols. On the basis of the validation results, we discuss the boundaries of applicability of the most popular spectral model, single scattering by spherical, homogeneous aerosol particles. 相似文献
882.
Dunxi Yu Minghou Xu Hong Yao Jiancai Sui Xiaowei Liu Yun Yu Qian Cao 《Proceedings of the Combustion Institute》2007,31(2):1921-1928
The chemical composition of particles generated during pulverized coal combustion is the consequence of their formation processes. This work aims to use the size resolved elemental composition of coal-derived particles to identify their formation modes. A size-classified bituminous coal is burnt in a laboratory drop tube furnace at 1150, 1250, and 1350 °C, respectively. The elemental composition of the size-segregated particles from coal combustion is analyzed and the total mass fraction size distributions of Si and Al are obtained. Three particle formation modes are observed in these distribution profiles. The coarse mode has the highest value of the total mass fraction of Si and Al while the ultrafine mode has the lowest one. The total mass fraction of Si and Al in these two modes is nearly independent of particle size. It is believed that the coarse mode is formed by the mineral coalescence mechanism and the ultrafine mode by the vaporization–condensation mechanism. The difference in the total mass fraction of Si and Al between the central mode and the other two indicates that the central mode is formed by different mechanisms. Based on the observation that the total mass fraction of Si and Al in this mode increases with increasing particle size, heterogeneous condensation of vaporized species on existing fine residual ash particles is proposed to account for the formation of these particles. The study of the elemental composition of the three modes represented in five categories verifies the proposed formation mechanisms for them to some extent. 相似文献
883.
The one-dimensional totally asymmetric simple exclusion process (TASEP) is considered. We study the time evolution property
of a tagged particle in the TASEP with the step initial condition. Calculated is the multi-time joint distribution function
of its position. Using the relation of the dynamics of the TASEP to the Schur process, we show that the function is represented
as the Fredholm determinant. We also study the scaling limit. The universality of the largest eigenvalue in the random matrix
theory is realized in the limit. When the hopping rates of all particles are the same, it is found that the joint distribution
function converges to that of the Airy process after the time at which the particle begins to move. On the other hand, when
there are several particles with small hopping rate in front of a tagged particle, the limiting process changes at a certain
time from the Airy process to the process of the largest eigenvalue in the Hermitian multi-matrix model with external sources. 相似文献
884.
The intracavity photon density and the initial population-inversion density in the diode-pumped passively Q-switched lasers are assumed to be Gaussian spatial distributions. The space-dependent rate equations are solved numerically. The key parameters of an optimally coupled passively Q-switched laser under Gaussian approximation are determined, and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter and the optimal normalized saturable absorber parameter that maximize the peak power, and the corresponding normalized energy, normalized peak power, and normalized pulse width. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the saturable absorber, and the resonator. In addition, the importance including the space variation is also shown. The optimal calculations for a diode-pumped passively Nd:YVO4 laser are presented to demonstrate the use of the curves and the related formulas. 相似文献
885.
886.
An analysis is made on the absorption distribution within a cylindrical active medium lamp pumped by means of fused silica light-guides. The performances of the proposed pump cavities are analysed through a non-sequential 3D ray-trace program and are compared to those of three reflective chambers: an elliptical cavity, a close-coupled cavity and a diffusive close-wrap cavity. Two light-guides cavities with eight and nine guides, respectively, were built and tested. High coupling efficiency and a reasonable uniform absorption distribution were registered. An overall laser efficiency of 1% was measured. The proposed cavities have permitted the tailoring of the absorption distribution within the laser rod. 相似文献
887.
Eric Jourdanneau Tony Gabard Frdric Chaussard Robert Saint-Loup Hubert Berger Elena Bertseva Frdric Grisch 《Journal of Molecular Spectroscopy》2007,246(2):167-179
CARS laboratory experiments were done in the 2905–2925 cm−1 range, in the vicinity of the ν1 band of the methane molecule, for pressures ranging from 1 to 50 bar, and temperatures up to 1100 K. These experiments were carried out in order to retrieve the pressure evolution of the CH4 spectrum, as well as to confirm its temperature dependance. After a brief recall on the theory used to compute pressure broadening coefficients and relaxation rates, we consider the ν3 and ν4 infrared bands of methane for benchmark calculations purposes. Next, we present recent experimental CARS spectra and calculated ones. Lastly, we discuss flame experiments as well as comparisons of temperature retrieval using N2 and CH4 as probe molecules. 相似文献
888.
The goal in this work is to investigate the effectiveness of time-frequency representations for analysing dispersive waves by comparing the performance of three different methods. In particular, the smoothed pseudo-Wigner distribution, the continuous wavelet transform and the Hilbert-Huang transform are compared and evaluated in terms of their ability to analyse dispersive elastic waves. The waves under consideration are transient flexural ones generated by an impact in a beam. In view of the results of the comparative study, the advantages and shortcomings of each method are presented and discussed. 相似文献
889.
The CO2-broadened water coefficients (half-widths, line shifts, and temperature dependence of the widths) are predicted using a fully complex Robert-Bonamy formulation for the 937 allowed and forbidden perpendicular type transitions of (000)-(000) between 200 and 900 cm−1 in order to facilitate atmospheric remote sensing of Mars and Venus. In addition, empirical Lorentz line widths and pressure-induced frequency-shifts of CO2-broadened H216O are obtained at room temperature for 257 perpendicular transitions of the (010)-(000) fundamental. For this, calibrated spectra recorded at 0.0054 cm−1 resolution are measured assuming Voigt line shapes. For transitions between 1287 and 1988 cm−1 with rotational quanta up to J = 13 and Ka = 6, the widths vary from 0.045 to 0.212 cm−1 atm−1 at 300 K; the pressure-shifts are quite large and range from −0.0386 to +0.0436 cm−1 atm−1. For the (010)-(000) band, the RMS and mean observed and calculated differences for CO2-broadened H2O half-widths are 12% and −1.9%, respectively, while the RMS and mean ratios of the observed and calculated pressure-induced shift coefficients are 1.6 and 0.79, respectively. For pairs of transitions involving Ka = 0 and 1, such as 20 2 ← 31 3 and 31 3 ← 20 2, both the calculated and observed pressure induced shifts in positions are opposite in sign and often similar in magnitude. The data are too limited to characterize vibrational dependencies of the widths, however. 相似文献
890.
《Journal of computational and graphical statistics》2013,22(2):281-294
By introducing auxiliary variables, the traditional Markov chain Monte Carlo method can be improved in certain cases by implementing a “slice sampler.” In the current literature, this sampling technique is used to sample from multivariate distributions with both single and multiple auxiliary variables. When the latter is employed, it generally updates one component at a time. In this article, we propose two variations of a new multivariate normal slice sampling method that uses multiple auxiliary variables to perform multivariate updating. These methods are flexible enough to allow for truncation to a rectangular region and/or exclusion of any n-dimensional hyper-quadrant. We present results of our methods and existing state-of-the-art slice samplers by comparing efficiency and accuracy. We find that we can generate approximately iid samples at a rate that is more efficient than other methods that update all dimensions at once. Supplemental materials are available online. 相似文献