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排序方式: 共有152条查询结果,搜索用时 31 毫秒
31.
Teresa Kowalik-Jankowska Henryk Kozlowski Karol Kociolek Miroslaw T. Leplawy Giovanni Micera 《Transition Metal Chemistry》1995,20(1):23-25
Summary Potentiometric and spectroscopic measurements were used to characterize the binding ability of -hydroxy-methylserine (Hms) with copper(II) and oxovanadium(IV) ions. The ligand was found to be generally a more efficient chelating agent than serine. Both of the deprotonated hydroxyl groups of Hms can be involved in coordination to vanadyl ions, whereas copper(II) binds in the same way as with serine. 相似文献
32.
Heats of formation (ΔHf) and proton affinities (PA) of 2-, 3-, and 4-monosubstituted pyridines in the gas phase are calculated using the AM1 and PM3 semiempirical methods. The following substitutents are considered: NO2, CN, CF3, CHO, F, Cl, COCH3, H, CH3, OCH3, SCH3, NH2, and N(CH3)2. The results are compared with the experimental data. Both methods reproduce the ΔHf with comparble accuracy; the rms deviations are 4.1 (AM1) and 4.5 kcal/mol (PM3) for the free bases and 9.5 (AM1) and 9.7 kcal/mol (PM3) for their conjugated acids. The PA are systematically underestimated by both methods, but AM1 appears to be clearly better than PM3 for reproducing the experimental values. The rms deviations for AM1 and PM3 are 5.1 and 9.6 kcal/mol, respectively. This is due to a cancellation of systematic errors in the calculated ΔHf in the AM1 case and to a summation of the errors in the PM3 case. Both methods correctly reproduce conformations of the molecules under consideration. 相似文献
33.
Miroslaw Dworniczak 《Reaction Kinetics and Catalysis Letters》2003,78(1):65-72
Reaction of chloranilic acid with N-methylpiperidine in acetonitrile has been studied. The product of the reaction is an unusually stable anion radical of quinone.
The presence of radicals has been confirmed by EPR measurements. Stability constant, extinction coefficients and thermodynamic
reaction parameters are reported. Mechanism of the reaction is proposed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
34.
The pyrolysis of samples containing copper, lead, iron, sulphur compounds and organic carbon is applied to separate mercury prior to its determination by a.a.s. Amalgamation on gold collectors followed by thermal desorption, or trapping in an absorption solution followed by reduction/aeration were used depending on the mercury content in the materials. Appropriate additives to the samples and filters are used to ensure complete release of mercury and removal of interfering pyrolysis products. 相似文献
35.
We propose a class of nonlinear integro-differential equations that at the mesoscopic level models the competition between a tumor and the immune system. The model describes the evolution of a distribution function of the microscopic parameter referred to as activity of cells. The idea is somehow similar to the Enskog theory in kinetic theory. By averaging with respect to the parameter, the mesoscopic class of models reduces to the general class of macroscopic models introduced by A. d’Onofrio that may assess the effect of delays in stimulation of the immune system by tumor cells. The existence and uniqueness theory is developed. 相似文献
36.
The main objective of this article is to present the authors' view of and results on non-linear lateral stability of rail vehicles in a curved track. Three elements are exploited in order to secure this objective. Firstly, physical genesis of the problem is discussed, and its similarity to straight track analysis is emphasised. Results of the theories of self-exciting vibrations and bifurcation are the key elements here. Secondly, the method suitable for analysis in a curved track is presented. New necessary elements, extending the better established methods for straight track are clearly mentioned and described. The methodology of building original stability maps, being the basis for the analysis and valid for whole range of curve radii and straight track is represented. Thirdly, a sample of the analysis is shown in order to give the idea how the method can be utilised. The case study refers to the influence of wheel/rail profiles on the stability in circularly curved track and straight track as well. Two different pairs of wheel/rail profiles are used and the corresponding results compared. The main contributions of the article are: a discussion of the physical nature of phenomena related to the stability in a curved tracks, and the method (procedure) established for the reasons of the analysis. Another and more general contribution is our say in the hot polemics on the advisability of stability analysis in curves and the advantages of the non-linear critical speed over the linear one. 相似文献
37.
Hai‐Qiao Wang Mirza Mačković Andres Osvet Ivan Litzov Elena Epelbaum Alfons Stiegelschmitt Miroslaw Batentschuk Erdmann Spiecker Christoph J. Brabec 《Particle & Particle Systems Characterization》2015,32(3):340-346
A new upconversion nanocrystal phase Yb2Mo4O15:Er is developed by using a facile aqueous‐precipitation procedure combined with thermal annealing. Nanocrystals of Yb2Mo4O15 are exclusively synthesized, with particle sizes ranging from 1 to 20 nm. The optical properties are characterized and a high upconversion quantum yield is determined to be ≈1.3% at room temperature, under excitation of ≈500 mW cm?2 IR (975 nm). To the best of our knowledge, this is the first work concerning the synthesis of nanocrystalline Yb2Mo4O15 and the characterization of its upconversion properties, which possesses the potential to be utilized in bio‐probing and thin‐film optoelectronic device applications. 相似文献
38.
In this work we demonstrate the properties of spatial solitary waves in chiral nematic liquid crystals with an external electric field. Such self-trapped beams, called nematicons, were created due to the optical reorientation nonlinearity for a light power of a few tens of milliwatts. We show that the direction of propagation of such nematicons can be changed by applying an external electric field. Additionally, this effect can be modified by changing the input polarization of the light beam. The experimental results were obtained in four independent guiding layers created by a chiral nematic structure. 相似文献
39.
We prove the existence of C0 semigroups related to some birth-and-death type infinite systems of ODEs with possibly unbounded coefficients, in the scale
of spaces lp,
For some particular cases we also provide a characterization of the spectra of their generators. For the proof of the generation
theorem in the case p > 1 we extend the Chernoff perturbation result ([9]) on relatively bounded perturbations of generators.
The results presented here have been used in [5] and they play important role for analysing chaoticity of dynamical systems
considered there. As a by-product of our approach we obtain a result related to the classical Shubin theorem [20]. We show
that this theorem, saying that for a class of bounded infinite matrices the spectrum of the corresponding maximal operator
in lp is independent on
cannot be extended to unbounded matrices. 相似文献
40.
Contributions to the Chemistry of Transition Metal Alkyl Compounds. XIII. the Reaction of Vanadium Isopropyl Ester with Dimethyl Zinc. — On the Formation of CH3VO(i-OC3H7)2 Dimethyl zinc reacts with ortho vanadium acid triisopropyl ester forming methyl zinc isopropoxide (CH3Zn-i-OC3H7)n and methyl vanadium oxide diisopropoxide CH3VO(i-OC3H7)2. The new σ-organovanadium compound was isolated and thoroughly characterized. 相似文献