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71.
The electron charge distribution in a strongly twisted push-pull ethylene [PPE, 3-(1,3-diisopropyl-2-imidazolidinylidene)-2,4-pentanedione] has been determined by low temperature (T = 21 K) single-crystal X-ray diffraction analysis. The derived electronic properties are consistent with a zwitterionic molecule, as indicated by a charge transfer of 0.82(16) e from the push to the pull moieties and a charge polarization of 0.29(7) e on the olefinic bond. A dipole moment of 12(3) D has been determined, which compares well with ab initio theoretical results in terms of both modulus and orientation. The second moments, which have also been obtained with good precision, characterize PPE as a highly quadrupolar molecule. The special electronic features of the molecule confer particular topological properties to the electron density distribution, as evidenced by comparison with "standard" organic molecules. The crystallographic asymmetric unit of the present system includes one water molecule, which is hydrogen bonded to PPE. Its topological properties have also been investigated, together with an analysis of the hydrogen bonds involved. 相似文献
72.
Schlesinger PH Djedovic NK Ferdani R Pajewska J Pajewski R Gokel GW 《Chemical communications (Cambridge, England)》2003,(3):308-309
Two membrane-anchored heptapeptides have been prepared and their pore-formation behavior in phospholipid bilayer membranes has been found to differ profoundly as a result only of alkyl chain length. 相似文献
73.
Liliana Caristia Giuseppe Nicotra Corrado Bongiorno Nicola Costa Sebastiano Ravesi Salvo Coffa Riccardo De Bastiani Maria Grazia Grimaldi Corrado Spinella 《Microelectronics Reliability》2007,47(4-5):777
This work reports the study concerning the influence of the preparation conditions on the structure of silicon rich oxide (SRO) deposited by PECVD method by which the structural properties of the film are strictly related. In particular we investigated the role of reactant gases N2O and SiH4 on the total Si concentration, Si excess concentration, Si clustered concentration and size of nanoclusters formed by high annealing temperature. We payed particular attention on the role of the hydrogen and nitrogen during the Si agglomeration.The presence of hydrogen atoms on the as-deposited specimen, confirmed by the Si–H bonds peak on the FTIR analysis, has been directly correlated to the silicon excess concentration in the layer. The silicon, oxygen and nitrogen atomic density has been calculated from RBS analysis. These information were coupled to the ones obtained using methodology based on electron energy loss spectroscopy combined with energy filtered images, which allowed us to quantify the clustered silicon concentration in annealed sub-stoichiometric silicon oxide layers (SiOx). We have verified that the nitrogen dissolved in the layer inhibits the Si excess clustering so that the efficiency of silicon agglomeration process decreases as the nitrogen content increases. 相似文献
74.
Riccardo LeardiRandy J. Pell 《Analytica chimica acta》2002,461(2):189-200
Variable selection using a genetic algorithm is combined with partial least squares (PLS) for the prediction of additive concentrations in polymer films using Fourier transform-infrared (FT-IR) spectral data. An approach using an iterative application of the genetic algorithm is proposed. This approach allows for all variables to be considered and at the same time minimizes the risk of overfitting. We demonstrate that the variables selected by the genetic algorithm are consistent with expert knowledge. This very exciting result is a convincing application that the algorithm can select correct variables in an automated fashion. 相似文献
75.
Riccardo Ricceri Alessandro Abbotto Antonio Facchetti Daniela Grando Gabriella Gabrielli Giorgio A. Pagani 《Colloids and surfaces. A, Physicochemical and engineering aspects》1999,150(1-3):289-296
We report on Langmuir-Blodgett (LB) films characterization of 4-[5-dicyanomethanido)thien-2-y1]-N-(n-hexadecyl)pyridinium (C16H33-PDCNT), and 1-(N-(n-hexadecy]-4-pyridinio)-2-[5-(dicyanomethanido)thien-2-yl]ethene (C16H33-PDCNTE); LB films of the pure compounds and of the mixtures of the two compounds were prepared at 291 K: UV-vis investigation revealed the presence of photobleachable absorption bands, the ones at about 530 nm and 640 nm were due to charge transfer transitions of the monomer of C16H33-PDCNT and C16H33-PDCNTE, respectively; the sharp, photobleachable ones shifted to shorter wavelengths were due to H-aggregates of the two compounds. By changing the molar ratios of the two compounds in the mixtures and in other cases by annealing the LB films, the absorption maxima of the sharp, photobleachable bands due to H-aggregates could be tuned in the range 415–467 nm. These LB films are thus very promising in view of optical data storage applications. 相似文献
76.
77.
We generalize some identities and q-identities previously known for the symmetric group to Coxeter groups of type B and D. The extended results include theorems of Foata and Schützenberger, Gessel, and Roselle on various distributions of statistics, like inversion number, major index, and descent number. In order to show our results we provide explicit characterizations of the systems of minimal coset representatives of Coxeter groups of type B and D. 相似文献
78.
Riccardo Narizzano Fulvia Risso Gloria VenturelliCarla Devia Eugenio CarliniStefano Maggiolo 《Journal of chromatography. A》2009,1216(39):6762-6766
Two methods for the analysis of dimethyl fumarate (DMF) on silica gel, leather and other similar products are presented. The methods are based on solvent extraction or head space solid phase microextraction coupled with gas-chromatography–mass spectrometry. The methods are developed in order to satisfy the mandatory requirements of the European Community and with the aim to have easy and reliable methods to provide rapid responses. 相似文献
79.
80.
We introduce and analyze the characteristic foliation induced by a contact structure on a branched surface, in particular
a branched standard spine of a 3-manifold. We extend to (fairly general) singular foliations of branched surfaces the local
existence and uniqueness results which hold for genuine surfaces. Moreover we show that global uniqueness holds when restricting
to tight structures. We establish branched versions of the elimination lemma. We prove a smooth version of the Gillman-Rolfsen
PL-embedding theorem, deducing that branched spines can be used to construct contact structures in a given homotopy class
of plane fields.
Entrata in Redazione il 6 novembre 1998. 相似文献