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1.
Shufeng Zuo 《Applied Surface Science》2006,253(5):2508-2514
Al-pillared clays supported rare earths (RE/Al-PILC) are prepared and used as supports of palladium catalysts for deep oxidation of low concentrations of benzene (130-160 ppm). The supports and catalysts are characterized by X-ray powder diffraction (XRD), FT-IR, BET, transmission electron microscopy (TEM) and temperature-programmed reduction (H2-TPR). The results show that Al-pillaring results in a strong increase in the basal spacing (d0 0 1) from about 1.2 to 1.8 nm, and an increase in the BET surface area from 63.6 (±3.2) to 238.8 (±11.9) m2/g. Activity tests of deep oxidation of low concentration benzene show catalysts supported on Al-PILC and RE/Al-PILC are obviously more active than that on raw clay. Pd/6% Ce/Al-PILC, in particular, can catalyze the complete oxidation of low concentration benzene at a temperature as low as about 290 °C. 相似文献
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A fully quantum mechanical approach to the calculation and normalization of the Franck–Condon factors for diatomic species is described. The treatment is based on the fundamental demand of completeness of the energy eigenfunctions, which results in the rigorous sum rule for the Franck–Condon overlap integrals. The importance of this general rule has been discussed and thoroughly illustrated in the case of diatomic xenon molecules. Exactly solvable reference potentials for this system have been constructed and a complete basis of the actual energy eigenstates (including both bound and scattering states) has been created. Several direct spectroscopic applications to xenon excimers are presented, and their good agreement with relevant experimental data demonstrated. In particular, a kinetic model is proposed to explain the observed oscillatory structures in the fluorescence spectra of Xe2* [Chem. Phys. Lett. 117 (1985) 301] related to their classical left turning points. The same model gives a uniform explanation to the well-known first and second emission continua of rare gases. 相似文献
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Uptake of trace elements into fish otoliths is governed by several factors such as life histories and environment in addition to stock and species differences. In an attempt to elucidate the elemental signatures of rare earth elements (REEs) in otoliths, a solid phase extraction (SPE) protocol was used in combination with electrothermal vaporization (ETV) as a sample introduction procedure for the determinations by inductively coupled plasma quadrupole mass spectrometry (ICP-MS). Effects of various parameters, such as carrier gas flow rate, atomization temperature and chemical modification, were examined for optimization of the conditions by ETV-ICP-MS. Atomization was achieved at 2800 °C. Lower temperatures (i.e. 2600 °C) resulted in severe memory problems due to incomplete atomization. Palladium was used as a chemical modifier. It was found that an increase in Pd concentration up to 0.5 μg in the injection volume (70 μl) led up to four-fold enhancement in the integrated signals. This phenomenon is attributed to the carrier effect of Pd rather than the stabilization since no significant losses were observed for high temperature drying around 700 °C even in the absence of Pd. Preconcentration was performed on-line at pH 5 by using a mini-column of Toyopearl AF-Chelate 650M chelating resin, which also eliminated the calcium matrix of otolith solutions. After preconcentration of 6.4 ml of solution, the concentrate was collected in 0.65 ml of 0.5% (v/v) HNO3 in autosampler cups, and then analyzed by ETV-ICP-MS. The method was validated with the analysis of a fish otolith certified reference material (CRM) of emperor snapper, and then applied to samples. Results obtained from otoliths of fish captured in the same habitat indicated that otolith rare earth element concentrations are more dependent on environmental conditions of the habitat than on species differences. 相似文献
7.
将稀土配合物Eu(asprin)_3phen掺杂到导电聚合物PVK中,制成结构分别为ITO/PVK:RE配合物/LiF/AI(1),ITO/PVK:RE配合物/PBD/LiF/AI(2)的电致发光(EL)器件。发现二者的电致发光谱存在着较大的差别:在器件(1)中,来自Eu~(3 )的位于594nm(~5D_0→~7F_1)和614nm(~5D_0→~7F_2)处的发光强度大致相当,而在器件(2)中,EL主要来自Eu~(3 )位于614nm的发光,594nm处的发光很弱,与薄膜状态下的光致发光谱(PL)一致。并针对此现象进行了初步讨论。 相似文献
8.
Keka Chakraborty S K Paranjpe V Siruguri O D Jayakumar S K Kulshreshtha 《Pramana》1997,48(6):1115-1122
Neutron diffraction and M?ssbauer measurements have been carried out on the cubic Laves phase intermetallic TbMnFe. The magnetic
moment on the transition metal atom is found to be low, 0.2μ
B, at room temperature. This moment is temperature independent down to 10 K. Magnetic moment on the rare earth atom varies
from 2.5μ
B at 296 K to 7.27μ
B at 10 K. M?ssbauer spectra recorded at 298 K and 78 K have magnetic character but there is a large distribution of hyperfine
field values. Both these features arise due to magnetic frustration created in the sample due to the competing ferro and antiferromagnetic
interactions between the transition metal atoms. 相似文献
9.
S. Juneja 《Queueing Systems》2007,57(2-3):115-127
Efficient estimation of tail probabilities involving heavy tailed random variables is amongst the most challenging problems
in Monte-Carlo simulation. In the last few years, applied probabilists have achieved considerable success in developing efficient
algorithms for some such simple but fundamental tail probabilities. Usually, unbiased importance sampling estimators of such
tail probabilities are developed and it is proved that these estimators are asymptotically efficient or even possess the desirable
bounded relative error property. In this paper, as an illustration, we consider a simple tail probability involving geometric
sums of heavy tailed random variables. This is useful in estimating the probability of large delays in M/G/1 queues. In this setting we develop an unbiased estimator whose relative error decreases to zero asymptotically. The key
idea is to decompose the probability of interest into a known dominant component and an unknown small component. Simulation
then focuses on estimating the latter ‘residual’ probability. Here we show that the existing conditioning methods or importance
sampling methods are not effective in estimating the residual probability while an appropriate combination of the two estimates
it with bounded relative error. As a further illustration of the proposed ideas, we apply them to develop an estimator for
the probability of large delays in stochastic activity networks that has an asymptotically zero relative error.
相似文献
10.
M. Aglietta B. Alessandro P. Antonioli F. Arneodo L. Bergamasco A. Campos Fauth C. Castagnoli A. Castellina C. Cattadori A. Chiavassa et al. 《Il Nuovo Cimento C》1992,15(4):441-446
Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower
array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement
the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y−1 (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E
0
)≈E
0
−2.5
, the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10−5erg cm−2. 相似文献