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131.
Lehtinen KE Backman U Jokiniemi JK Kulmala M 《Journal of colloid and interface science》2004,274(2):526-530
Silver nanoparticles were prepared in a tubular flow reactor using an evaporation-condensation technique. The size distribution of the particles was measured using standard aerosol instruments and electron microscopy. A comparison with results obtained by a discrete population balance model with molecule-by-molecule resolution suggest that the particles probably nucleate kinetically through a dimerization process instead of a thermodynamic pathway over a free energy barrier, as is typically described by classical nucleation theory. Furthermore, the kinetic rate of dimerization seems to be accompanied by a correction term, associated with the requirement of energy and momentum conservation in molecule-molecule collisions. This energy conservation requires the presence of three-body collisions at the very initial step of particle formation. 相似文献
132.
A few remarks on the simulation and use of crystal field energy level schemes of the rare earth ions
The usefulness of the simulation of the energy level schemes of the trivalent rare earth (R3+) ions in the prediction of the properties of the rare earth compounds is demonstrated for a few selected cases emphasizing the connection between different spectroscopic and magnetic properties of the R3+ ions. The importance of the calculated energy level schemes in the UV-VUV range in interpreting complicated spectra and designing new phosphors by energy transfer and quantum cutting is described. In the absence of direct measurements, the calculated energy level values can be very useful. The possibilities to interpret the magnetic properties of the R3+ (and R2+) ions are described by using the wave functions of the energy levels obtained from the energy level simulations. As a fine example, it is shown how the amount of an Eu2+ impurity can be obtained from the calculation of the paramagnetic susceptibility as a function of temperature. The problems involved in the simulation of the 7FJ crystal field energy level scheme of the Eu3+ ion are highlighted by using a comparison between the extensive literature data and calculated level schemes. 相似文献
133.
Jorma HölsäManu Lahtinen Mika Lastusaari Jussi ValkonenJussi Viljanen 《Journal of solid state chemistry》2002,165(1):48-55
The crystal structures of the tetragonal rare earth (RE) oxychlorides, REOCl (RE=La-Nd, Sm-Ho, and Y) were studied by X-ray powder diffraction measurements, Rietveld analyses, and bond valence calculations. The tetragonal structure (space group P4/nmm, No. 129, Z=2) is stable for all but Er-Lu oxychlorides, which possess a hexagonal structure. The tetragonal structure consists of alternating layers of (REO)nn+ complex cations and Xn− anions, where the rare earth is coordinated to four oxygens and four plus one chlorines in a monocapped tetragonal antiprism arrangement. The Rietveld analyses yielded a coherent series of structural parameters. Preferred orientation and microabsorption effects were found significant. The evolution of interatomic distances and bond angles indicated that the reason for the preferred structure changing from tetragonal to hexagonal is the strain in the chlorine layer. The bond valence parameter B for the RE-O bonds had to be recalculated due to the covalent nature of the (REO)nn+ unit. The results obtained with the new parameter confirmed the strains in the chlorine layer to be the cause for the phase transition. 相似文献
134.
Rhodiola rosea L. (Golden Root) has been used for a long time as an adaptogen in Chinese traditional medicine and is reported to have many pharmacological properties. A liquid chromatographic (LC) method with mass spectrometric (MS) detection based on selected ion monitoring (SIM) was developed for determining salidroside, sachaliside 1, rosin, 4-methoxycinnamyl-O-beta-glucopyranoside, rosarin, rosavin, cinnamyl-(6'-O-beta-xylopyranosyl)-O-beta-glucopyranoside, 4-methoxy-cinnamyl-(6'-O-alpha-arabinopyranosyl)-O-beta-glucopyranoside, rosiridin and benzyl-O-beta-glucopyranoside from the callus and plant extracts in one chromatographic run. Good linearity over the range 0.5-500 ng ml(-1) for salidroside, 2-2000 ng ml(-1) for rosavin and 2-500 ng ml(-1) for benzyl-O-beta-glucopyranoside was observed. The intra-assay accuracy and precision within quantitation ranges varied between -10.0 and +13.2% and between 0.7 and 9.0%, respectively. Optimization of the ionization process was performed with electrospray and atmospheric pressure chemical ionization techniques using four different additive compositions for eluents in the LC/MS scan mode, using both positive and negative ion modes. The best ionization sensitivity for the compounds studied was obtained with electrospray ionization when using pure water without any additives as the aqueous phase. 相似文献
135.
Iko Hyppänen Jorma Hölsä Jouko Kankare Mika Lastusaari Marja Malkamäki Laura Pihlgren 《Journal of luminescence》2009,129(12):1739-1743
The effect of the defects due to the charge compensation obtained with the yttrium co-doping to the ZrO2:Yb3+,Er3+ up-converting phosphors was studied. The materials were prepared with the combustion method. The materials purity was analyzed with the FT-IR spectroscopy. The crystal structure was studied with the X-ray powder diffraction and the crystallite sizes were estimated with the Scherrer formula. Up-conversion luminescence was excited at room temperature with an IR-laser at 970 nm. The up-conversion luminescence spectra showed red (650-685 nm) and green emission (520-560 nm) due to the 4F9/2→4I15/2 and (2H11/2,4S3/2)→4I15/2 transitions of Er3+, respectively. Persistent up-conversion luminescence was observed both in the Yb3+,Er3+ and Y3+,Yb3+,Er3+ doped materials. 相似文献
136.
Let A be an n × n matrix with real eigenvalues λ1 ? … ? λn, and let 1 ? k < l ? n. Bounds involving trA and trA2 are introduced for λk/λl, (λk ? λl)/(λk + λl), and {kλk + (n ? l + 1)λl}2/{kλ2k + (n ? l + 1)λ2l}. Also included are conditions for λl >; 0 and for λk + λl > 0. 相似文献
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140.
We construct topological geon quotients of two families of Einstein-Yang-Mills black holes. For Künzle??s static, spherically symmetric SU(n) black holes with n?>?2, a geon quotient exists but generically requires promoting charge conjugation into a gauge symmetry. For Kleihaus and Kunz??s static, axially symmetric SU(2) black holes a geon quotient exists without gauging charge conjugation, and the parity of the gauge field winding number determines whether the geon gauge bundle is trivial. The geon??s gauge bundle structure is expected to have an imprint in the Hawking-Unruh effect for quantum fields that couple to the background gauge field. 相似文献