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排序方式: 共有199条查询结果,搜索用时 31 毫秒
61.
62.
Wieslaw Strek 《Molecular physics》2013,111(6):2005-2015
A quantum mechanical theory of the solvent effect on radiationless transitions is developed within the framework of a dynamic coupling model. This model allows us to describe the solvent effect on any mechanism of intramolecular radiationless transition, in polar as well as non-polar solvents. 相似文献
63.
Effects of the method of identification of the diffusion coefficient on accuracy of modeling bound water transfer in wood 总被引:2,自引:0,他引:2
An alternative approach to determining the bound water diffusion coefficient is proposed. It comprises a method for solving
the inverse diffusion problem, an improved algorithm for the bound-constrained optimization as well as an alternative submodel
for the diffusion coefficient’s dependency on the bound water content. Identification of the diffusion coefficient for Scots
pine wood (Pinus sylvestris L.) using the proposed inverse approach is presented. The accuracy of predicting the diffusion process with the use of the
coefficient values determined by traditional sorption methods as well as by the inverse modeling approach is quantified. The
similarity approach is used and the local and global relative errors are calculated. The results show that the inverse method
provides valuable data on the bound water diffusion coefficient as well as on the boundary condition. The results of the identification
can significantly improve the accuracy of mass transfer modeling as studied for drying processes in wood. 相似文献
64.
An observation of negative refraction in the naturally obtained composition of graphene and barium ferrite is reported. The capacitance and inductance measurements revealed the electric and magnetic resonances accompanied with the negative values of permittivity and permeability in the overlapped frequency range. According to the “left‐handed” media approach such a material is characterized by negative refraction. The derived values of the real part of refractive index are negative at the frequencies above 500 MHz.
65.
Abstract The liquid crystalline properties of 1-(alkylamino)-3-[(4″-hexyl-trans-cyclohexyl-4′-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the SA phase in both ligands and complexes, whereas long chains promote SC and crystal H phases for the ligands or SA and SC phases for the complexes. A partly bilayer smectic Ad phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data. 相似文献
66.
Allyl ethers are widely used for the “temporary” protection of hydroxy groups in carbohydrates. The allyl group is conveniently removed by isomerization and subsequent cleavage of the labile prop-1-enyl group.2 The rearrangement of allyl ethers to prop-1-enyl ethers is readily achieved by treatment with potassium t-butoxide in dimethyl sulfoxide, using tris(tripheny1phosphine)rhodium chloride, palladium on activated charcoal and by an ene reaction with diethylazodicarboxylate. acidic conditions, ozonolysis followed by alkaline hydrolysis, reaction with alkaline permanganate solution, or treatment with mercuric chloride in the presence of mercuric oxide. The isomerization of allyl ethers to prop-1-enyl ethers can also be carried out in the presence of palladium on carbon or complex bis(benzonitrile)palladium(11) chloride. Bruce and Roshan-Ali' showed that derivatives of allyl phenyl ether are smoothly cleaved by this complex. This has made it possible to remove the protecting group in a one-pot operation. We have now investigated the effect of palladium catalysts on the isomerization and cleavage of the allyl group in carbohydrate derivatives. 相似文献
67.
Marek Chmielewski Izabela Fokt Jacek Grodner Grzegorz Grynkiewicz Wieslaw Szeja 《Journal of carbohydrate chemistry》2013,32(5):735-741
Abstract Benzylated glycals, unlike their acylated congeners which easily undergo allylic rearrangement, are frequently employed as reactive enol ether type substrates in a variety of electrophilic addition reactions.1–4 Although these compounds are considered to be readily available substrates, reported procedures for their syntheses involve some steps of limited efficiency, chromatographic separations or costly reagents,5–7 and experimental requirements not amenable for large scale preparations. In view of the recent applications of benzylated glycals to syntheses of O-glycosides,1,2 C-glycosyl compounds,3 and β-lactams,4 we have undertaken a study aimed at efficient one step benzylation procedures applicable to pyranoid 1-enitols as well as to their acylated derivatives. This goal was eventually achieved by employing a catalytic phase transfer alkylation system with 相似文献
68.
Terhalle B Desyatnikov AS Neshev DN Krolikowski W Denz C Kivshar YS 《Physical review letters》2011,106(8):083902
We reveal a direct link between two fundamental wave phenomena in periodic media, Pendell?sung oscillations and resonant coupling between spectral bands. We experimentally measure the power transfer between laser beams associated with the high-symmetry points in periodic and biased hexagonal photonic lattices. As a result, we demonstrate that Pendell?sung oscillations dominate the dynamics of resonant interband transitions on a short propagation scale. 相似文献
69.
Profiles analysis of proanthocyanidins in the argun nut (Medemia argun—an ancient Egyptian palm) by LC–ESI–MS/MS 下载免费PDF全文
Arafa I. Hamed Abdulla S. Al‐Ayed Jaroslaw Moldoch Sonia Piacente Wieslaw Oleszek Anna Stochmal 《Journal of mass spectrometry : JMS》2014,49(4):306-315
Medemia argun is an ancient palm rich in proanthocyanidins (PACs). These polyphenolic compounds are widely distributed in plants and are an integral part of the human diet. A sensitive high‐performance liquid chromatography and electrospray ionization mass spectrometry (HPLC–ESI–MS) method in the negative ion mode for sequencing these ubiquitous and highly beneficial antioxidants is described in order to profile different PACs in M. argun nuts. The analytical protocol based on tandem mass spectrometry was used to sequence dimers, trimers, tetramers and pentamers with different A‐type, B‐type and A/B‐type linkages. Diagnostic ions resulting from heterocyclic ring fission and retro‐Diels–Alder reaction of flavan‐3‐ol provided information on the hydroxylation pattern and the type of interflavan bond. The sequences were discovered through ions derived from quinone methide cleavage of the interflavan bond. The identification of PACs linkages through LC–MSn eliminates a number of tedious separation steps. The method was successfully applied to give a view of PAC profile in M. argun nuts. M. argun nuts contained 636.88 mg/g PACs (as equivalent of (þ)‐catechin). The data obtained in our research show that M. argun is a rich source of hydrolyzable PACs. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
70.
Wieslaw Gessner Arnold Brossi Judith L. Flippen-anderson Clifford George 《合成通讯》2013,43(12):1371-1377
The unsubstituted ketospirolactam 1 afforded on alkyla-tion the two C(9)-butylated ketolactams 2 and 3, with 3 being the more stabile epimer, and the C(9)-dibutylated ketolactam 4. Structure of alcohol 5 obtained from 3 was secured by X-ray analysis. 相似文献