The structure of an M-type lead hexaferrite (magnetoplumbite) crystal is studied via the diffraction of synchrotron radiation. The crystal model contains two iron ions positions with dynamic disorder. The dynamics of the crystal lattice in the temperature range of 80 to 775 K is studied by Raman scattering. Particular attention is given to the discussing the nature of the local disorder of iron ions in the trigonal bipyramidal environment of oxygen ions. 相似文献
Comprehensive NMR investigation of low-frequency spin dynamics of LiCu2O2 (LCO) and NaCu2O2 (NCO) low-dimensional helical magnets in the paramagnetic state has been carried out for the first time. Temperature dependences of the spin–lattice relaxation rate and anisotropy on various LCO/NCO nuclei have been determined at various orientations of single crystals in an external magnetic field. The spatial asymmetry of spin fluctuations in LCO multiferroic has been discovered. The quantitative analysis of the anisotropy of spin–lattice relaxation in LCO/NCO has allowed estimating the contributions of individual neighboring Cu2+ ions to the transferred hyperfine field on Li+(Na+) ions. 相似文献
The structure of Ni1 ? xCoxCr2O4 solid solutions has been investigated by synchrotron X-ray powder diffraction in the temperature range of 90–350 K for compositions x = 0, 0.005, 0.01, 0.015, 0.02, 0.1, 0.5, and 0.8, and their structures have been refined using the Rietveld analysis. The T-x phase diagram for solid solutions in the studied range of temperatures and concentrations has been constructed based on the obtained data. The revealed structural phase transitions have been explained from the viewpoint of the crystal field theory and the Jahn-Teller cooperative effect. Distortions of polyhedra, which are the cause of the structural phase transition, have been evaluated. The applicability of the Landau phenomenological theory and the possibility of using the magnitude of spontaneous strains as the order parameter have been discussed. 相似文献
We consider the possibility of designing a plasma trap with a magnetic system formed by super-conducting rings and coils levitating in the field of a fixed coaxial coil carrying constant current. An analytic dependence of the potential energy of such a system with one or two levitating superconducting rings having trapped preset magnetic fluxes on their coordinates in the uniform gravitational field is obtained in the thin ring approximation. Calculations performed in the Mathcad system show that equilibrium states of such a system exist for certain values of parameters. Levitating states of a single superconducting ring and two superconducting rings in the field of the coil with constant current are observed experimentally in positions corresponding to calculated values. 相似文献
In this study, the extraction of lipophilic wood extractives from dissolving pulp samples using ionic liquid–liquid extraction and a two phase hollow fibre supported liquid membrane was investigated. Ionic liquids are capable of dissolving a range of organic and polymeric compounds and are biodegradable, with a negligible vapour pressure. Pulp samples were dissolved in a suitable amount of molten 1-butyl-3-methylimidazolium chloride to give 5 % cellulose solution. Pure cellulose was regenerated by adding water and filtered off. The ionic liquid-aqueous filtrate was first extracted for lipophilic extractives using liquid–liquid extraction. Then, a two phase hollow fibre supported liquid membrane extraction of lipophilic extractives was performed to extract the derivatized compounds prior to analysis by gas chromatography mass spectrometry. The operational parameters of this sample preparation approach were optimised using sterols and fatty acid methyl esters. The variation of enrichment factors and extraction efficiency with respect to liquid membrane, extraction time, stirring speed and sample pH were observed and used to get the optimal parameters. The approach was used in the analysis of oxygen bleached dissolving pulp samples in which main compounds identified were fatty acids, sterols, fatty alcohols, steroid hydrocarbons and ketones. These compounds were similar to those obtained using molecular solvent extraction method, which indicated the absence of chemical reaction between extractives and ionic liquid used.
Samples of 3 matrices (air, superficial dust and subsurface soil) from an aged PCB-containing landfill were extracted and
the extracts refined for bioassay. Acetone:hexane extraction was modestly selected for non-planar compounds. Coplanar PCBs
and PCDFs were enriched about 2-fold in the subsequent benzene:methylene chloride extracts of the soil. Extract refinement
with Florisil slurry and alumina column chromatography did not appreciably change the composition of the extracts. CB 28 (2,4,4′-triCB)
dominated in all extracts. The congener composition of soil and air were surprisingly similar, being enriched in tri- and
tetraCBs while dust retained higher proportions of congeners with 4 and 5 chlorines. It is postulated that anaerobic dechlorination
in the moist subsurface soil depleted the higher chlorinated congeners; more volatile congeners escaped into the atmosphere
while moderately chlorinated congeners were trapped in the superficial dust and debris. The refined extracts represent distinct
compositions of environmental PCB mixtures suitable for bioassay.
Received: 21 November 1995 / Revised: 9 April 1996 / Accepted: 14 April 1996 相似文献
The structures of lithiated and sodiated glutamine, both with and without a water molecule, are investigated using experiment and theory. Loss of water from these complexes and from lithiated and sodiated complexes of asparagine methyl ester, asparagine ethyl ester, and glutamine methyl ester is probed with blackbody infrared radiative dissociation experiments performed over a wide temperature range. Threshold dissociation energies, E(o), for loss of a water molecule from these complexes are obtained from master equation modeling of these data. The values of E(o) are 63 +/- 1 and 53 +/- 1 kJ/mol for the lithiated and sodiated glutamine complexes, respectively. These values are similar to those for the nonzwitterionic model complexes and are in excellent agreement with calculated values. In contrast, water binding to the zwitterionic form is calculated to be significantly higher. These results indicate that glutamine in these lithiated and sodiated complexes with a water molecule are nonzwitterionic. Complexes with the asparagine side chain have slightly higher E(o) values than those with the glutamine side chain, a result consistent with more effective solvation of the metal ion due to the slightly longer side chain of glutamine. Calculations indicate that lithiated and sodiated glutamine are nonzwitterionic, with the metal ion interacting with the amine nitrogen and carbonyl oxygen from the amino acid backbone and the amide oxygen of the side chain. Addition of a water molecule does not affect the lowest-energy structure of lithiated glutamine, whereas, for sodiated glutamine, the lowest-energy zwitterionic and nonzwitterionic structures are essentially isoenergetic. 相似文献