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31.
Four compounds in the system (Li, Na)VO3 were synthesized and their structures refined in the space group . Site population analysis showed that their compositions are (Na0.5Li0.5)VO3, (Na0.62Li0.38)VO3, (Na0.71Li0.29)VO3 and (Na0.84Li0.16)VO3. All have the structure of LiVO3 and α-NaVO3 which are related to the silicate pyroxenes. Structural data of eight compounds in the system (K, Na, Li)VO3 were compiled, and correlations were established by multiple regression analyses between the effective ionic radii rM1 and rM2 of the alkali metal ions and various structural parameters. The size of the M2 site and the relative displacement of the (VO3)∞ chains are found to depend primarily on rM2 only. The size of the M1 site and the amount of chain rotation are affected by both rM1 and rM2. Changes in lattice parameters are related to the chain movements. The anomalous chain configuration of LiVO3 is also discussed. 相似文献
32.
Poon KW Liu W Chan PK Yang Q Chan TW Mak TC Ng DK 《The Journal of organic chemistry》2001,66(5):1553-1559
Up to eight redox-active ferrocenyl units have been incorporated, through the unsaturated ethynyl linkers, on the periphery of a series of cyclic tetrapyrrole derivatives including zinc(II) phthalocyanine and 2,3-naphthalocyanine, and nickel(II) meso-diphenylporphyrin. The synthesis of the former two macrocycles 4 and 7 involves the Sonogashira coupling reaction of ferrocenylethyne with 4,5-dichlorophthalonitrile (1) or 6,7-dibromonaphthalonitrile (5), respectively, followed by a base-promoted cyclization. The meso-bis(ferrocenylethynyl)porphyrin 11 has been prepared from the dibromo analogue 10 also by a palladium-catalyzed coupling reaction. These novel macrocyclic compounds have been spectroscopically and electrochemically characterized. As revealed by cyclic voltammetry, the ferrocenyl moieties appear to be electrochemically independent in these complexes and there is no significant electronic coupling among the iron(II) centers. 相似文献
33.
The elastic vibrations of spherical nanoparticles have been widely studied by Raman scattering. However, there exist more than one set of selection rules for Raman scattering from these vibrations. For instance, Kanehisa has stated that only torsional modes with angular momentum l = 2 are Raman-active, while Tanaka et al. proposed that spheroidal modes of even l and torsional modes of odd l are Raman-active. These contradict selection rules of Duval which states that only spheroidal modes of l = 0 or 2 are Raman-active. Our present calculations based on a macroscopic model show that all torsional modes have vanishing intensity in the Raman spectrum. 相似文献
34.
A novel chiral stationary phase (CSP) was prepared by immobilizing mono(6A-N-allylamino-6A-deoxy)-perphenylcarbamoylated beta-cyclodextrin onto the surface of silica gel via hydrosilylation. The chromatographic properties of this column were tested with a wide range of structurally diverse racemic compounds and drugs under reverse phases. Separation mechanisms involved are also discussed. 相似文献
35.
A GC-MS protocol for profiling spirits, based on 19 acids and phenolic compounds, has been proposed and evaluated. The method combined a simple preconcentration procedure based on solid-phase (anion-exchange) disk extraction, and in-vial elution and silylation of the analytes. The derivatized extract was directly injected into the GC-MS system. These analytes were: C6, C8, C10, C12 acids, pyruvic acid, 2-furoic acid, succinic acid, fumaric acid, glutaric acid, lactic acid, glycolic acid, malic acid, tartaric acid, citric acid, vanillin, syringaldehyde, coniferaldehyde, vanillic acid and gallic acid. The profiles of six different spirits were found reproducible from day-to-day with <20% RSD for measurements of most of the analytes at different concentrations. Recoveries of individual analytes appear to be affected by the level of tannins in the spirits, and they varied from sample to sample. The method of standard addition was used to quantify age-related analytes. Good linearity of response with correlation coefficients in the range of 0.992-0.999 was obtained. The results of the study indicate that for spirits of the same brand but of different ages, the amounts of these analytes appear to increase with the ageing period. 相似文献
36.
Guang‐Fei Liu Lin‐Lin Li Yong Zhang Jian‐Ping Lang Seik Weng Ng 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(1):m1-m3
The title compound, [Cu(ClO4)2(C4H9N3O2)2][Cu(C4H9N3O2)2(CH4O)2](ClO4)2·2CH3OH, comprises two independent CuII species lying on different inversion sites. In the Cu complexes, a distorted octahedral geometry arises (from basic square‐planar N4 coordination) from the weak coordination of two perchlorate ions (as Cu—O) in one species and two methanol molecules in the other (also as Cu—O). Interactions between the O atoms of the perchlorate anions or methanol groups and the imide or amine NH groups afford an extensive intermolecular hydrogen‐bonding network. 相似文献
37.
Balest R Cho K Ford WT Lohner M Park H Rankin P Smith JG Alexander JP Bebek C Berger BE Berkelman K Bloom K Browder TE Cassel DG Cho HA Coffman DM Crowcroft DS Dickson M Drell PS Dumas DJ Ehrlich R Elia R Gaidarev P Garcia-Sciveres M Gittelman B Gray SW Hartill DL Heltsley BK Henderson S Jones CD Jones SL Kandaswamy J Katayama N Kim PC Kreinick DL Lee T Liu Y Ludwig GS Masui J Mevissen J Mistry NB Ng CR Nordberg E Patterson JR Peterson D Riley D Soffer A Avery P Freyberger A Lingel K Prescott C 《Physical review letters》1995,75(21):3809-3813
38.
Least squares estimations have been used extensively in many applications, e.g. system identification and signal prediction. When the stochastic process is stationary, the least squares estimators can be found by solving a Toeplitz or near-Toeplitz matrix system depending on the knowledge of the data statistics. In this paper, we employ the preconditioned conjugate gradient method with circulant preconditioners to solve such systems. Our proposed circulant preconditioners are derived from the spectral property of the given stationary process. In the case where the spectral density functions() of the process is known, we prove that ifs() is a positive continuous function, then the spectrum of the preconditioned system will be clustered around 1 and the method converges superlinearly. However, if the statistics of the process is unknown, then we prove that with probability 1, the spectrum of the preconditioned system is still clustered around 1 provided that large data samples are taken. For finite impulse response (FIR) system identification problems, our numerical results show that annth order least squares estimator can usually be obtained inO(n logn) operations whenO(n) data samples are used. Finally, we remark that our algorithm can be modified to suit the applications of recursive least squares computations with the proper use of sliding window method arising in signal processing applications.Research supported in part by HKRGC grant no. 221600070, ONR contract no. N00014-90-J-1695 and DOE grant no. DE-FG03-87ER25037. 相似文献
39.
40.
Acosta D Athanas M Masek G Paar H Bean A Gronberg J Kutschke R Menary S Morrison RJ Nakanishi S Nelson HN Nelson TK Richman JD Ryd A Tajima H Schmidt D Sperka D Witherell MS Procario M Yang S Balest R Cho K Daoudi M Ford WT Johnson DR Lingel K Lohner M Rankin P Smith JG Alexander JP Bebek C Berkelman K Besson D Browder TE Cassel DG Cho HA Coffman DM Drell PS Ehrlich R Galik RS Garcia-Sciveres M Geiser B Gittelman B Gray SW Hartill DL Heltsley BK Jones CD Jones SL Kandaswamy J Katayama N Kim PC 《Physical review D: Particles and fields》1994,49(11):5690-5700