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31.
综述了几种气相色谱固定相包括聚硅氧烷、液晶、冠醚、环糊精、离子液体及纤维填充固定相,在分离多环芳香烃(PAHs)、多环芳香化合物(PACs)及多氯联苯(PCBs)等环境污染物中的应用进展,展望了此类固定相的应用前景(引用文献64篇)。 相似文献
32.
Diego Richard Emiliano L. Muñoz Leonardo A. Errico Mario Rentería 《Physica B: Condensed Matter》2012,407(16):3134-3136
In this work we present an ab initio study of Ta-doped Sc2O3 semiconductor. Calculations were performed at dilute Ta impurities located at both cationic sites of the host structure, using the Augmented Plane Wave plus Local Orbitals (APW+lo) method. The structural atomic relaxations and the electric-field gradients (EFG) were studied for different charge states of the cell in order to simulate different ionization states of the double-donor Ta impurity. From the results for the EFG tensor at Ta impurity sites and the comparison with experimental results obtained using the Time-Differential γ–γ Perturbed-Angular-Correlations technique we could determined the structural distortions induced by the Ta impurity and the electronic structure of the doped-semiconductor. 相似文献
33.
We present an ab initio study of diluted Cd impurities localized at both cation sites of the semiconductor Sc2O3. The electric-field-gradient (EFG) tensor at Cd impurities located at both cationic sites of the host structure was determined from the calculation of the electronic structure of the doped system. Calculations were performed with the full-potential augmented-plane wave plus local orbitals (APW+lo) method within the framework of the density functional theory. We studied the atomic structural relaxations and the perturbation of the electronic charge density induced by the impurities in the host system in a fully self-consistent way. We showed that the Cd impurity introduces an increase of 8% in the nearest oxygen neighbors bond-lengths, changing the EFG sign for probes located at the asymmetric cation site. The APW+lo predictions for the charged state of the Cd impurity were compared with EFG results existent in the literature, coming from time-differential γ–γ perturbed-angular-correlations experiments performed on 111Cd-implanted Sc2O3 powder samples. From the excellent agreement between theory and experiment, we can strongly suggest that the Cd acceptor impurities are ionized at room temperature. Finally, we showed that simple calculations like those performed within the point-charge model with antishielding factors do not correctly describe the problem of a Cd impurity in Sc2O3. 相似文献
34.
Theg-factors of the 265 and 280 keV levels have been measured to be 0.61±0·16 and 0·30±0·05 respectively. The PAC technique was
used for the measurements. In addition, the half-life of the 280 keV level has been remeasured to beT
1/2=0·32±0·02 ns using γ-γ delayed coincidences. Electromagnetic properties of the various levels calculated on the core-particle
coupling model agree with the experimental results. The results are compared with other existing theoretical calculations. 相似文献
35.
Egbert R. Nieuwenhuis Aurélie Favrot Li Kang Matthew O. Zacate Gary S. Collins 《Hyperfine Interactions》2004,158(1-4):305-308
Nuclear quadrupole interactions of 111Cd probes in In2La and CeIn2 were measured using perturbed angular correlation of gamma rays (PAC). Near room temperature, a single non-axially symmetric
quadrupole interaction was observed in each compound, with ω
0 = eQV
zz
/ℏ = 78.8(2) Mrad/s and η = 0.312(1) for In2La at 11°C and ω
0 = 80(1) Mrad/s and η = 0.29(2) for CeIn2 at 34°C. The observed non-axial symmetry is consistent with the reported CeCu2 structure of the phases. The non-axially symmetric interactions were replaced completely by axially symmetric interactions
(η = 0) at 524°C, with ω
0 = 101.0(1) Mrad/s in In2La and ω
0 = 96.9(4) Mrad/s in CeIn2. The change in symmetry is attributed to a polymorphic phase transformation. Based on symmetry information from the quadrupole
interaction and on chemical arguments, it is proposed that high-temperature phases of In2La and CeIn2 both have the AlB2 (C32) structure. 相似文献
36.
过程分析化学的提出与进展 总被引:2,自引:0,他引:2
文中对过程分析化学(PAC)的应用进行了全面评述,主要包括PAC的一般概念、特征、五个阶段和各种应用技术以及发展前景。 相似文献
37.
Investigation of dynamic processing on aluminum floc aggregation:Cyclic shearing recovery and effect of sulfate ion 总被引:1,自引:0,他引:1
The floc formation and re-aggregation potential and the effects of sulfate on coagulation by AlCl3, polyaluminum chloride (PAC), and Al13 species using a photometric dispersion analyzer (PDA) are in- vestigated. It is found that the recovery level from shearing is the highest for the Al13 species. This is likely a result of increased collision efficiency due to more effective charge neutralization. The ex- perimental results show that sulfate has a significant effect on coagulation and promoting aggregation of hydrolyzed species for the Al13 species. It results in significant improvement of the coagulation effi- ciency through an electrostatic patch effect. The results further indicate that zeta potential of the parti- cle suspension is not the only indicator for the coagulant efficiency when precipitate formation sig- nificantly improves coagulation. 相似文献
38.
K.W. Pi W.Q. Gong M. Wang Z.Q. Huang 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,330(2-3):103-107
A novel effective method for preparing polyaluminum chloride (PAC) with high content of Al13 polymer through conventional electrolysis coupled with rare earth Nd-Fe-B magnetic field was introduced. The content of Al13 polymer in PAC synthesized by this method was highly influenced by the electrobath voltage (E), the magnetic flux density (B), the current density (i) and the distance between the two adjacent electrodes (dadj). A total aluminum concentration (AlT) in the PAC solution of 0.8 mol l−1 was obtained when the E, B and i was 2.2 V, 0.4 T and 3.2 A dm−2, respectively. The optimum dadj and circulating flow (Qf) were 20 mm and 23.7 l h−1. With accelerated mass transfer rate by external magnetic field and high Qf, this process had the advantages of forming more Al(OH)4− as the precursor of Al13 polymer and inhibiting the concentration polarization more obviously than conventional electrolysis process. Under the optimum conditions, the amount of Al13 polymer in PAC accounted for 82.3% of the AlT (AlT = 0.8 M, basicity = 2.2), which was higher than that of PAC prepared by other methods. 相似文献
39.
R.E. Alonso A.R. López García M.A. de la Rubia J. De Frutos 《Physica B: Condensed Matter》2012,407(13):2610-2616
In this work, the hyperfine quadrupole interaction at Ta-doped PbTi1−xHfxO3 polycrystalline samples is studied for the first time. Powders with x=0.25, 0.50 and 0.75 were prepared and characterized by X-ray diffraction analysis. Perturbed Angular Correlation (PAC) analyses were done as a function of temperature, using low concentration 181Ta nuclei as probes. In the ferroelectric and paraelectric phases of these compounds two sites were occupied by the probes. For each site the quadrupole frequency, asymmetry and relative distribution width parameters were obtained as a function of temperature above and below the Curie temperature (TC). One of these sites was assigned to the regular Ti–Hf site, while the other one was assigned to some kind of defect. The behavior of the hyperfine parameters as a function of temperature was analyzed in terms of a recent published phase diagram and the presence of disorder below and above TC. For the three compositions measured, the obtained hyperfine parameters present discontinuities which correspond to the ferroelectric–paraelectric phase transition. In both phases it was found broad frequency distributed interactions. The disorder in the electronic distribution would be responsible for the broad line width of the hyperfine interaction. 相似文献
40.
J. P. Araújo J. G. Correia V. S. Amaral P. B. Tavares F. Lencart-Silva A. A. C. S. Lourenço J. B. Sousa J. M. Vieira J. C. Soares 《Hyperfine Interactions》2001,133(1-4):89-94
Although Cd and Ca ions have the same valence and cation size, their incorporation into vacancy-doped La manganites induce different properties. While the incorporation of Ca leads to high Tc up to 250 K and induces a metallic-like behaviour, the incorporation of Cd severely reduces Tc and promotes insulator-like behaviour. In this work, the Cd hyperfine fields have been measured with the Perturbed Angular Correlations (PAC) technique after implantation and annealing of 111m
Cd in La–Cd–MnO3 samples. The PAC results are compared with measurements of the resistivity and magnetization performed on the same samples. The mixed La and Mn site Cd occupancy is suggested as a possibility to explain the properties of the La–Cd–MnO3 system. 相似文献