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排序方式: 共有132条查询结果,搜索用时 31 毫秒
1.
The reaction of 3-acylsubstituted 2H-1-benzo-pyran-2-ones 1, 5 and 11a-c with acid anhydrides in the presence of potassium fluoride (KF)/molecular sieves 4A gives the 4-(2-oxoalkyl)-2-oxochromans 2, 6 and 12a-c as the main products. Also the 3-carboxylic acid derivatives, such as esters and N,N-dialkylamides, of 2H-1-benzopyran-2-one (11d-g) react with isobutyric acid anhydride in the presence of KF/molecular sieves 4A to give the corresponding 2-oxochroman-4-acetic acid derivatives. 相似文献
2.
RaymondH.Chan Chung-waHo MilaNikolova 《计算数学(英文版)》2004,22(2):168-177
Recently, two-phase schemes for removing salt-and-pepper and random-valued impulse noise are proposed in [6, 7]. The first phase uses decision-based median filters to locate those pixels which are likely to be corrupted by noise (noise candidates). In the second phase, these noise candidates are restored using a detail-preserving regularization method which allows edges and noise-free pixels to be preserved. As shown in [18], this phase is equivalent to solving a one-dimensional nonlinear equation for each noise candidate.One can solve these equations by using Newton‘s method. However, because of the edgepreserving term, the domain of convergence of Newton‘s method will be very narrow. In this paper, we determine the initial guesses for these equations such that Newton‘s method will always converge. 相似文献
3.
P.S. Ramanujam C. Dam-Hansen R.H. Berg S. Hvilsted L. Nikolova 《Optics and Lasers in Engineering》2006,44(9):912
In this article, we describe fabrication of polarisation holographic optical elements in azobenzene polyesters. Both liquid crystalline and amorphous side-chain polyesters have been utilised. Diffractive optical elements such as lenses and gratings that are sensitive to the polarisation of the incident light have been fabricated with polarisation holography. Computer-generated optical elements and patterns have also been written with a single polarised laser beam. Recording of polarisation defects enabling easy visualisation is also shown to be feasible in azobenzene polyesters. 相似文献
4.
We show that the (p, p') Clarkson's inequality holds in the Edmunds-Triebel logarithmic spaces Aq(logA)b,q A_{\theta}({\log}A)_{b,q} and in the Zygmund spaces Lp(logL)b(W) L_p({\log}L)_b(\Omega) , for
b ? \mathbbR b \in \mathbb{R} and for suitable 1 £ p £ 2 1 \leq p \leq 2 . As a consequence of these results we also obtain some new information about the types and the cotypes of these spaces. 相似文献
5.
F. Grunewald B. Kunyavskii D. Nikolova E. Plotkin 《Journal of Mathematical Sciences》2003,116(1):2972-2981
We study two-variable Engel-like relations and identities characterizing finite-dimensional solvable Lie algebras and, conjecturally, finite solvable groups and introduce some invariants of finite groups associated with such relations. Bibliography: 29 titles. 相似文献
6.
The absorption edge shift and the spectra of the dichroism in suspension layers of As2S3 dispersed in gelatin induced by a linearly polarized laser light are measured. The results are compared to the photoinduced changes in evaporated As2S3 layers. 相似文献
7.
We investigate the influence of the type of light polarization (linear or circular) on the efficiency of non-linear optical
processes in photoanisotropic materials. A theoretical model of photoprocesses in materials in which optical non-linearity
is related to absorbing centres with intrinsic linear anisotropy is constructed. Theoretical calculations show that the photostationary
concentration of the photoproducts (and the mean values of the non-linear changes in optical constants) in these materials
is higher if the exciting light is circularly polarized. Experimental results on non-linear processes in samples of fluorescein
incorporated in orthoboric acid and in azodye/polymer layers are in good agreement with the theory.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
8.
Foam bilayers from individual and mixed phosphatidylcholines are experimentally studied at different temperatures. Occurrence of a chain-melting phase transition in the foam bilayers is detected by two independent parameters—the critical concentrationC
c
for formation of foam bilayer and the foam bilayer thickness. The data forC
c
are discussed on the basis of the hole-nucleation theory, which applies the Ising model to foam bilayers and uses the mean-field approximation for interpretation of their stability. This allows the determination of the binding energy of a phospholipid molecule in gel and liquid-crystalline foam bilayers. New possibilities to relate the microscopic and macroscopic characteristics of foam bilayers are demonstrated. 相似文献
9.
B. B. Koleva R. D. Nikolova S. Zareva T. Kolev A. G. Bojilova H. Mayer-Figge W. S. Sheldrick 《Structural chemistry》2008,19(6):975-982
IR-spectroscopic characterization of the coumarin-3-phosphonic acid and 1,2-benzoxaphosphorine-3-carboxylic acid ethyl esters has been carried out by means of linear-polarized IR (IR-LD) spectroscopy of oriented colloid suspensions in a nematic host. Quantum chemical DFT calculations at the B3LYP level of theory and 6-311++G** basis set were performed. The electronic structure and vibrational properties of both compounds are discussed. The spectroscopic data for 2-benzoxaphosphorine-3-carboxylic acid ethyl ester are in accordance with the crystal structure determined by single crystal X-ray diffraction. The compound C13H15O5P crystallizes in the noncentrosymmetric space group P212121, and its structure consists of a 3D network formed by short contacts of the type P=O···HC(Ar) with distances of 3.420 and 2.467 Å. The geometry of the PO3C fragment exhibits a pseudo T d symmetry. 相似文献
10.
Polarization reflection holographic gratings in azobenzene-containing gelatine films 总被引:1,自引:0,他引:1
We have written polarization reflection holograms in an azobenzene-containing material. Two waves with circular polarization were used to record the gratings; the light resulting from their overlap induces chirality in the samples. The holographic reflection of the polarization gratings has the properties of Bragg reflection in cholesteric liquid crystals. 相似文献