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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.
Xianwen Zhang Ming Jiang Mingyang Zhu Kailin Liu Chunming Zhao 《Entropy (Basel, Switzerland)》2022,24(8)
Although long polar codes with successive cancellation decoding can asymptotically achieve channel capacity, the performance of short blocklength polar codes is far from optimal. Recently, Arıkan proposed employing a convolutional pre-transformation before the polarization network, called polarization-adjusted convolutional (PAC) codes. In this paper, we focus on improving the performance of short PAC codes concatenated with a cyclic redundancy check (CRC) outer code, CRC-PAC codes, since error detection capability is essential in practical applications, such as the polar coding scheme for the control channel. We propose an enhanced adaptive belief propagation (ABP) decoding algorithm with the assistance of CRC bits for PAC codes. We also derive joint parity-check matrices of CRC-PAC codes suitable for iterative BP decoding. The proposed CRC-aided ABP (CA-ABP) decoding can effectively improve error performance when partial CRC bits are used in the decoding. Meanwhile, the error detection ability can still be guaranteed by the remaining CRC bits and adaptive decoding parameters. Moreover, compared with the conventional CRC-aided list (CA-List) decoding, our proposed scheme can significantly reduce computational complexity, to achieve a better trade-off between the performance and complexity for short PAC codes. 相似文献
35.
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
36.
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
37.
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
38.
Let be a finite set of rational primes. We denote the maximal Galois extension of in which all totally decompose by . We also denote the fixed field in of elements in the absolute Galois group of by . We denote the ring of integers of a given algebraic extension of by . We also denote the set of all valuations of (resp., which lie over ) by (resp., ). If , then denotes the ring of integers of a Henselization of with respect to . We prove that for almost all , the field satisfies the following local global principle: Let be an affine absolutely irreducible variety defined over . Suppose that for each and for each . Then . We also prove two approximation theorems for .
39.
Summary Semipreparative HPLC utilizing a polar bonded phase was applied to the isolation of polycyclic aromatic compounds (PAC) from complex samples using a backflush technique. Aminopropyl- and cyanopropyl-modified silica was tested. Aminopropyl-modified silica was found to be superior in achieving rapid, selective and non discriminating isolation of PAC. This was compared with the most commonly used isolation methods, dimethylsulfoxide (DMSO), dimethylformamide (DMF) and nitromethane liquid-liquid extractions, and silica and SephadexLH-20 open column chromatography. Strong discrimination of alkylated PAC and polycyclic aromatic nitrogen heterocyclics (PANH) was found for the liquid-liquid extractions and the LH-20 column chromatography. These comparisions were made using both standard compounds and a sample of used crankcase oil, indicating the necessity of using a real sample for evaluation of extraction methods. Recoveries of 42 PACs are reported. 相似文献
40.
P. Bonville 《Hyperfine Interactions》2001,134(1):5-12
The usefulness of local hyperfine techniques in the investigation of the physical properties of Kondo lattices is illustrated through three examples. First, we show how Mössbauer spectroscopy on 170Yb down to very low temperature (0.025 K) provides evidence for the existence of an incommensurate modulated magnetic structure close to T=0 in YbPtAl; a modulated structure at T=0 is in principle forbidden for Kramers ions, but it is made possible in YbPtAl due to the presence of the Kondo coupling. Second, we present a μSR study of the Kondo insulator YbB12, and we evidence the persistence of fluctuations of very small correlated Yb moments close to T=0. Third, we report on a study by Perturbed Angular Correlation spectroscopy on the isotope 172Yb of the Kondo lattice Yb2Co3Ga9, which is characterised by a high Kondo temperature (T 0?260 K). Our aim was to compare, on a large temperature range, the thermal variations of the 4f quadrupole moment and of the magnetic susceptibility, to check whether the scaling property predicted by theory could be observed. 相似文献