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排序方式: 共有127条查询结果,搜索用时 15 毫秒
1.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献
2.
C. von Borczyskowski F. Cichos J. Martin J. Schuster A. Issac J. Brabandt 《The European physical journal. Special topics》2007,144(1):13-25
Optical spectroscopy in combination with wide field or confocal optical
microscopy enables the investigation of single quantum objects such as
organic molecules, II/VI semiconductor quantum dots and silicon nanocrystals.
They all have fluctuations of luminescence intensities on time scales longer
than μs in common. A comparison reveals that despite the large differences
of the nature of the respective quantum objects, the intensity fluctuations
are related to a slow ionisation process followed
by a trapping of the photoejected charge in the non-conducing environment.
Detailed aspects of the dynamics are controlled by the dielectric properties
of the matrix. 相似文献
3.
Rodolphe Clérac Dieter Fenske Ibrahim Issac Alexander Rothenberger 《Journal of Cluster Science》2004,15(2):189-198
Two Fe–Ta containing sulfido complexes were prepared by the reaction of the metal halide salts with bis-trimethylsilylsulfide in the presence of PMe3. The complexes demonstrate that coordination chemistry with iron sulfides can give access to a range of heterometallic complexes. In [Cl(Me3P)Ta(
2-S)2(
3-S)Fe(PMe3)2]2 the two [Cl(Me3P)Ta] units are arranged around one central Fe2(
2-S)2 unit. In [(Me3P)4(MeCN)2FeII]2+[(Me3P)2TaIVFeII
3(
3-S)4Br4]2– a [TaFe3S4]2+ cuboidal arrangement was observed. The complex salt forms a polymeric structure in the solid-state with weak H-bonds between the ions. The [(Me3P)2TaIVFeII
3(
3-S)4Br4]2– ion was characterised by magnetic measurements showing strong antiferromagnetic interactions between the metal centres. 相似文献
4.
Caussé E Issac C Malatray P Bayle C Valdiguié P Salvayre R Couderc F 《Journal of chromatography. A》2000,895(1-2):173-178
In recent papers, we presented a new analytical method for thiol quantification in serum. It is based on the use of capillary electrophoresis and laser-induced fluorescence to analyze thiol 6-iodoacetamidofluoresceine (IAF) derivatives. Quantitative results of homocysteine, glutathione, cysteine-glycin, and cysteine were shown (Clin. Chem. 45 (1999) 412). A comprehensive comparison of the quantitation of homocysteine in serum, using high-performance liquid chromatography/conventional fluorescence detection and fluorescence polarization immunoassay was also used (E. Caussé et al., Electrophoresis 21 (2000) 2074). Sample preparation prior to derivatization with IAF had never been investigated. In this work we present the results of quantitation of thiols in serum and plasma with three different anticoagulants widely used: ethylenediaminetetraacetic acid (EDTA), heparin, and sodium citrate. We show that serum and EDTA plasma gave the same results. Then serum protein precipitations by acetonitrile, acetone, sulfosalicylic acid, perchloric acid and trichloracetic acid, prior to derivatization by IAF, were also investigated. Their influence on the concentrations of the thiols were determined. Sulfosalicylic acid and acetonitrile precipitations are well adapted, whereas acetone cannot be used. 相似文献
5.
Self-replicating peptide systems hold great promise for a wide range of technological applications, as well as to address fundamental questions pertaining to the molecular origins of life. The development of self-replicating compounds capable of high efficiency, however, has remained elusive. Here we disclose a successful strategy whereby modulation of coiled-coil stability results in remarkable catalytic efficiency for self-replication. By shortening the peptide to the minimum length necessary for coiled-coil formation a highly efficient self-replicating system was obtained due to very low background reaction rates, bringing the efficiency close to naturally occurring enzymes. 相似文献
6.
Isaac B. Bersuker Natalia N. Gorinchoi Victor Z. Polinger 《Theoretical chemistry accounts》1984,66(3-4):161-172
The vibronic origin of dynamic instability of molecular systems considered earlier, is here given a more complete and rigorous treatment. It is shown that the nonvibronic contribution to the curvature of the adiabatic potential arising due to nuclear displacements under fixed electronic density distribution, is always positive, and hence the only reason for dynamic instability is the pseudo Jahn-Teller effect. For some examples of special interest (planar equilateral NH3, planar square CH4 and linear H
3
+
) the molecular excited states, responsible for the instability of the ground state, are revealed by means of ab initio calculations. 相似文献
7.
I. B. Bersuker S. Bahceci J. E. Boggs R. S. Pearlman 《SAR and QSAR in environmental research》2013,24(2-3):157-173
Abstract A novel method of pharmacophore identification and activity prediction in structure-activity (structure-property) relationships is worked out as an essential extension and improvement of previous publications. In this method each conformation of the molecular systems in the training set of the SAR problem is presented by both electronic structure and geometry parameters arranged in a matrix form. Multiple comparisons of these matrices for the active and inactive compounds allows one to separate a smaller number of matrix elements that are common for all the active compounds and are not present in the same arrangement in the inactive ones. This submatrix of activity represents the pharmacophore (Pha). By introducing the Anti-Pharmacophore Shielding (APS) defined as molecular groups and competing charges outside the Pha that hinder the proper docking of the Pha with the bioreceptor, the procedure of Pha identification is essentially reduced to the treatment of a smaller number of simplest in structure most active and inactive compounds. A simple empirical scheme is suggested to estimate the APS numerically, while the contributions of different conformations of the same compound are taken into account by means of Boltzmann distribution. This enables us to make approximate quantitative predictions of activities. In application to rice blast activity we reached an approximately 100% (within experimental error) prediction probability of the activity qualitatively (yes, no), and with r 2 = 70% quantitatively. 相似文献
8.
We predict, by means of ab initio calculations, stable electron and hole polaron states in perfect monoclinic HfO2. Hole polarons are localized on oxygen atoms in the two oxygen sublattices. An electron polaron is localized on hafnium atoms. Small barriers for polaron hopping suggest relatively high mobility of trapped charges. The one-electron energy levels in the gap, optical transition energies and ESR g-tensor components are calculated. 相似文献
9.
10.
Achamma Kurian C V Bindhu S S Harilal Riju C Issac V P N Nampoori C P G Vallabhan 《Pramana》1994,43(5):401-406
A simple method based on laser beam deflection to study the variation of diffusion coefficient with concentration in a solution
is presented. When a properly fanned out laser beam is passed through a rectangular cell filled with solution having concentration
gradient, the emergent beam traces out a curved pattern on a screen. By taking measurements on the pattern at different concentrations,
the variation of diffusion coefficient with concentration can be determined. 相似文献