All-optical control of the phase-matching condition in four-wave mixing (FWM) processes is demonstrated using the Brillouin slow-light effect in optical fibers. A counterpropagating stimulated Brillouin scattering (SBS) pump has been used to control the phase velocity of the FWM pump in a wavelength conversion scheme. Both experimental results and theoretical simulations show an SBS-controlled 20 dB difference on the wavelength conversion efficiency. 相似文献
2,6-Dimethylnaphthalene (2,6-DMN) is one of the crucial intermediates for the synthesis of polybutylenenaphthalate and polyethylene naphthalate (PEN). The complex synthesis procedure and the high cost of 2,6-DMN production significantly reduce the commercialisation of PEN even though PEN demonstrates superior properties compared with polyethylene terephthalate. 2,6-DMN can be produced by methylation of 2-methylnaphthalene (2-MN) and/or naphthalene, disproportionation of 2-MN, and/or isomerisation of dimethylnaphthalenes (DMNs). In this study, synthesis of 2,6-triad DMN isomers consisting of 2,6-DMN, 1,6-DMN, and 1,5-DMN have been investigated with the disproportionation of 2-MN over unmodified and Zr-modified mesoporous MCM-41 zeolite catalysts. In contrast to other DMN isomers, both 1,5-DMN and 1,6-DMN can be effectively isomerised to be profitable 2,6-DMN. The disproportionation of 2-MN experiments were carried out in a catalytic fixed-bed reactor in the presence of 1 g of catalyst at a temperature range of 350–500 °C and weight hourly space velocity between 1 to 3 h?1. The results demonstrated that mesoporous MCM-41 zeolite catalyst has a selective pore shape for 2,6-triad DMN isomers, which may allow a decrease in the production cost of 2,6-DMN. Additionally, 2,6-DMN was successfully synthesised by the disproportionation of 2-MN over MCM-41 zeolite catalyst. Furthermore, both the conversion of 2-MN and the selectivity of 2,6-DMN were considerably enhanced by the Zr impregnation on MCM-41. 相似文献
An efficient procedure for the directed reductive amination of beta-hydroxy-ketones (3) for the stereoselective preparation of 1,3-syn-amino alcohols (6) is reported. The operationally simple protocol uses Ti(iOPr)4 for coordination of the intermediate imino alcohol (5) and PMHS as the reducing agent. The method was expanded to an asymmetric aldol reductive amination sequence to allow a highly convergent synthesis of the hydroxy-amine core of the HIV-protease inhibitors ritonavir and lopinavir. [reaction: see text]. 相似文献
We have calculated the effects of the intense laser field on the total optical absorption coefficient (the linear and third-order nonlinear) for transition between two lower-lying electronic levels in the asymmetric parabolic \({\text{GaAs/ Ga}}_{{ 1 {\text{ - x}}}} {\text{Al}}_{\text{x}} {\text{As}}\) quantum well. Total absorption coefficient (linear and nonlinear absorption coefficient) for the transitions between any two electronic states was calculated by using density matrix formalism and the perturbation expansion method. Our results show that the effects of intense laser field and the well dimensions on the optical transitions are more pronounced. If well center is changed to be \({\text{L}}_{\text{c}} < 0 \, ({\text{L}}_{\text{c}} > 0)\), effective well width decreases (increases) and thus we can obtain the red or blue shift in the peak position of the absorption coefficient by changing the intensities of the non-resonant intense laser field as well as dimensions of the well. 相似文献
Two chemiluminescent compounds containing 2,5-di(thien-2-yl)pyrrole and pyridazine units, namely 5,7-di(thiophen-2-yl)-2,3-dihydro-1H-pyrrolo[3,4-d]pyridazine-1,4(6H)-dione (5) and 6-phenyl-5,7-di(thiophen-2-yl)-2,3-dihydro-1H-pyrrolo[3,4-d]pyridazine-1,4(6H)-dione (6), were successfully synthesized and electrochemically polymerized. The compounds have chemiluminescent properties and glow in the presence of hydrogen peroxide in basic medium. The intensity of the glow can be increased dramatically by using Fe3+ ions, hemin (1.0 ppm) or blood samples (1.0 ppm) as catalyst. The compounds 5 and 6 have one well-defined irreversible oxidation peak at 1.08 V and 1.33 V vs Ag/AgCl, respectively. Electrochemical polymerization of both 5 and 6 were carried out successfully by repeating potential scanning in the presence of BF3. Et2O in an electrolyte solution of 0.1 M LiClO4 dissolved in acetonitrile. The electronic band gaps (Eg) of the polymers P5 and P6 were found to be 2.02 eV and 2.16 eV, respectively. On the other hand, the corresponding polymers are electroactive and exhibited electrochromic features.
The diamagnetic susceptibility of a hydrogenic donor placed in Si, Ge and GaAs quantum wells with infinite confinement potential which have different effective mass anisotropy parameters (γ=m⊥/m∥) has been investigated as a function of the well sizes. The binding energies of the donor have also been computed using a trial wave function with two parameters in the framework of the effective mass approximation. It has been observed that the diamagnetic susceptibility of the donor in the anisotropic materials converges rapidly to the bulk limit as the well size increases. 相似文献
In this study, we have investigated theoretically the effects of the electric field and doping concentration on the optical transitions in a modulation-doped GaAs-AlGaAs quantum well for different well widths. The binding energies of the donor have also been computed using a trial wave function with two parameters in the framework of an effective-mass approximation. The electronic structure of a modulation-doped quantum well under the electric field is determined by solving the Schrödinger and Poisson equations self-consistently in the effective-mass approximation. The results obtained show that inter-sub-band transitions and the energy levels in the modulation-doped quantum well can be significantly modified and controlled by the well width and donor concentration. The sensitivity to the well widths of the absorption coefficient can be used in various optical semiconductor devices’ applications. 相似文献
A novel bridged binuclear Cu(II) complex with mixed ligands, di-μ-(2-aminopyridine(N,N′))-bis[(2,6-pyridinedicarboxylate)aquacopper(II)] tetrahydrate, formulated as [Cu(μ-ap)(dipic)(H2O)]2·4H2O (1) (dipic = 2,6-pyridinedicarboxylate, ap = 2-aminopyridine), has been synthesized and characterized by elemental, spectral (IR and UV–Vis.), thermal analysis, magnetic measurements and single crystal X-ray diffraction analysis. The central Cu(II) ion resides on a centre of symmetry in a distorted square-pyramid coordination environment comprising of two N atoms, one from dipic and one from the ap ring, two carboxylate O atoms from dipic, and one O atom from water. Intermolecular N–HO and O–HO hydrogen bonds and π–π stacking interactions seem to be effective in the stabilization of the crystal structure. The free ligands and the complex were also evaluated for their antimicrobial and radical scavenging activities (DPPH = 1,1-diphenyl-2-picrylhydrazyl hydrate) using in vitro microdilution methods. Antimicrobial screening of the free ligands and their complex showed that the free ligands and the complex possess antifungal activity against Candida sp. 相似文献
In this study, we present an approach based on neural networks, as an alternative to the ordinary least squares method, to describe the relation between the dependent and independent variables. It has been suggested to construct a model to describe the relation between dependent and independent variables as an alternative to the ordinary least squares method. A new model, which contains the month and number of payments, is proposed based on real data to determine total claim amounts in insurance as an alternative to the model suggested by Rousseeuw et al. (1984) [Rousseeuw, P., Daniels, B., Leroy, A., 1984. Applying robust regression to insurance. Insurance: Math. Econom. 3, 67–72] in view of an insurer. 相似文献