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81.
A family of linear copolymers, characterized by the presence along the polymer chain of variable amounts of two atomic groups of different mesogenic potentiality, has been studied by differential scanning calorimetry and X-ray diffraction methods. The range of composition that allows enantiotropic mesophasic behaviour is defined for four homologous sets of copolymers. The experimental phase diagram gives, by extrapolation, indications about the potential mesophasic properties of that extreme composition (corresponding to a homopolymer) that shows no direct mesophasic properties.  相似文献   
82.
Abstract 2-Methyl-1,4-naphtoquinone (vitamin K3) quenches the phosphorescence from enzyme-generated triplet acetone. Concomitantly the vitamin undergoes a photochemical-like alteration as the result of transfer of the electronic energy ( k ET– 1 ± 105 M-1). This transfer appears to be of the long-range type.  相似文献   
83.
84.
The present paper describes the one-pot procedure for the formation of self-assembled thin films of two silanes on the model oxidized silicon wafer, SiO2/Si. SiO2/Si is a model system for other surfaces, such as glass, quartz, aerosol, and silica gel. MALDI-TOF MS with and without a matrix, XPS, and AFM have confirmed the formation of self-assembled thin films of both 3-imidazolylpropyltrimethoxysilane (3-IPTS) and 4-(N-propyltriethoxysilane-imino)pyridine (4-PTSIP) on the SiO2/Si surface after 30 min. Longer adsorption times lead to the deposition of nonreacted 3-IPTS precursors and the formation of agglomerates on the 3-IPTS monolayer. The formation of 4-PTSIP self-assembled layers on SiO2/Si is also demonstrated. The present results for the flat SiO2/Si surface can lead to a better understanding of the formation of a stationary phase for affinity chromatography as well as transition-metal-supported catalysts on silica and their relationship with surface roughness and ordering. The 3-IPTS and 4-PTSIP modified SiO2/Si wafers can also be envisaged as possible built-on-silicon thin-layer chromatography (TLC) extraction devices for metal determination or N-heterocycle analytes, such as histidine and histamine, with "on-spot" MALDI-TOF MS detection.  相似文献   
85.
86.
We study partially hyperbolic attractors ofC 2 diffeomorphisms on a compact manifold. For a robust (non-empty interior) class of such diffeomorphisms, we construct Sinai-Ruelle-Bowen measures, for which we prove exponential decay of correlations and the central limit theorem, in the space of Hölder continuous functions. The techniques we develop (backward inducing, redundancy elimination algorithm) should be useful in the study of the stochastic properties of much more general non-uniformly hyperbolic systems.  相似文献   
87.
The reaction between diaminomaleonitrile (DAMN) and aldehydes and the resulting monoimines are well known. Since the standard reaction conditions involve the use of toxic solvents (typically methanol), we have sought to apply green chemistry principles to this reaction by either using water as the solvent without any catalysts or employing "solvent-free" conditions. The monoimines derived from DAMN are of interest as precursors for obtaining different heterocyclic systems and linear polymers. The methodologies used have significant advantages with regards to cost and environmental considerations.  相似文献   
88.
In this contribution we present the analysis of the third harmonic susceptibility data of the new superconductor NdFeAs1−0.14F0.14. ‘Cole-Cole’ polar plots respect to the magnetic frequency of the exciting field are presented and discussed. Data show that NdFeAs1−0.14F0.14 exhibit a ‘bulk pinning’ with a 3D flux dynamic character. A comparison of the responses of high Tc materials and an evaluation of theoretical critical states is also presented.  相似文献   
89.
The hydrated shell of both Fe2+ and Fe3+ aqueous solutions are investigated by using the molecular dynamics (MD) and X-ray absorption structure (XAS) methods. The MD simulations show that the first hydrated shells of both Fe2+ and Fe3+ are characterized by a regular octahedron with an Fe-O distance of 2.08 for Fe2+ and 1.96 for Fe3+, and rule out the occurrence of a Jahn-Teller distortion in the hydrated shell of an Fe2+ aqueous solution. The corresponding X-ray absorption near edge fine structure (XANES) calculation successfully reproduces all features in the XANES spectra in Fe2+ and Fe3+ aqueous solution. A feature that is located at energy 1 eV higher than the white line (WL) in an Fe3+ aqueous solution may be assigned to the contribution of the charge transfer.  相似文献   
90.
A new semi‐empirical electrotopological index, ISET, for quantitative structure–retention relationships (QSRR) models was developed based on the refinement of the previously published semi‐empirical topological index, IET. We demonstrate that the values of Ci fragments that were firstly attributed from the experimental chromatographic retention and theoretical deductions have an excellent relationship with the net atomic charge of the carbon atoms. Thus, the values attributed to the vertices in the hydrogen‐suppressed graph of carbon atoms (Ci) are calculated from the correlation of the net atomic charge in each carbon atom, which is obtained from quantum chemical semi‐empirical calculations, and the Ci fragments for primary, secondary, tertiary and quaternary carbon atoms (1.0, 0.9, 0.8 and 0.7, respectively) obtained from the experimental values. This shows that IET encoded this quantum physical reality and that it is possible to calculate a new ISET (the semi‐empirical electrotopological index) through the net atomic charge values obtained from a Mulliken population analysis using the semi‐empirical AM1 method and their correlation with the values attributed to the different types of carbon atoms. This demonstrates that the ISET encodes information on the charge distribution of the solute on which dispersive and electrostatic interactions between the solute (alkanes and alkenes) and the stationary phase strongly depend. Thus, this new method can be considered as an initial step towards forthcoming QSRR/QSAR studies. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
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