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161.
S.M. Islam Anupam Singha Roy Paramita Mondal Kazi Tuhina Manir Mobarak John Mondal 《Tetrahedron letters》2012,53(2):127-131
A new polymer-anchored Cu(II) complex has been synthesized and characterized. The catalytic performance of the complex has been tested for the oxidation of sulfides and in oxidative bromination reaction with hydrogen peroxide as the oxidant. Sulfides have been selectively oxidized to the corresponding sulfoxides in excellent yields and in the presence of KBr as the bromine source, organic substrates have been selectively converted to mono bromo substituted compounds using polymer-anchored Cu(II) catalyst. This catalyst showed excellent catalytic activity, high selectivity, and recyclability. The polymer-anchored Cu(II) catalyst could be easily recovered by filtration and reused more than five times without appreciable loss of its initial activity. 相似文献
162.
Giovanni Ferrara Tienan Jin Md. Akhtaruzzaman Ashraful Islam Liyuan Han Hua Jiang Yoshinori Yamamoto 《Tetrahedron letters》2012,53(15):1946-1950
A facile, efficient, and general synthetic method for iodo-substituted benzo[b]naphtho[2,1-d]thiophenes has been developed via a cascade cyclization of thioanisole-substituted aryldiynes using iodine. A new donor–π linker–acceptor (D–π–A) organic dye, G1, with the benzo[b]naphtho[2,1-d]thiophene moiety as an electron donor has been synthesized, and the performance of dye-sensitized solar cell based on G1 has been investigated. 相似文献
163.
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165.
We present a highly nonlinear non-circular core photonic crystal fiber (HNL-NCPCF) with all normal group velocity dispersion (GVD) to design a supercontinuum (SC) light source for optical coherence tomography (OCT) system. Nonlinear coefficient is increased as large as 66 W?1 km?1 at by reducing the effective mode area and core is made non-circular to increase birefringence by putting the square lattice of air-holes inside the silica host. About 85 nm 10 dB spectral bandwidths for 2.5 ps input optical pulse and 140 nm 10 dB spectral bandwidths for 1.0 ps input optical pulse have been observed using the same fiber length of 200 m and input optical power of 15 W. Coherent lengths of the generated supercontinuum light sources are found for 2.5 ps input optical pulse and for 1.0 ps input optical pulse. Therefore, the highest longitudinal resolution for dental OCT at is found about for tooth enamel. 相似文献
166.
Molla Rafiquel Islam Elianne Dahan Sundar Saimani Pudupadi R. Sundararajan 《European Polymer Journal》2012,48(9):1538-1554
Self-assembly of amphiphilic molecules ranging from simple surfactants to block copolymers in a solvent depends on one part of the molecule (one block in block copolymers) being soluble, and the other not. The aggregation of the insoluble segment in the block-selective solvent leads to the self assembly. In this paper, we describe a system of amphiphilic rod–coil and coil–rod–coil molecules, which do not show self assembly in block-selective non-aqueous solvents. We prepared rod–coil molecules based on hydrophilic propylene oxide/ethylene oxide copolymer (PO–EO copolymer) (Jeffamine®) as the flexible segment and photo-conducting large aromatic perylenediimide (PTCDI) as the rod. PO–EO copolymer was attached either to one side of PTCDI (MJ–PTCDI) or both sides (DJ–PTCDI). The former can be considered an inverse macromolecular surfactant, since the tail is hydrophilic and the head is hydrophobic. The DJ–PTCDI is a pseudo Gemini surfactant. Because of the presence of the chromophore, UV–Vis and fluorescent spectra could be used to study the self assembly of these amphiphilic rod coil polymers in solution. PTCDI forms π-interaction mediated aggregates in aqueous solution and these are H-stacked in MJ–PTCDI and J-stacked in DJ–PTCDI. Variable temperature UV and NMR spectra show that the assembly is stable over a large temperature range in water. The aggregates are also stable up to a pH of 12. However, when a non-aqueous solvent is used, no aggregation occurs. This is attributed to the “solvation” of the π-system of the PTCDI. With the addition of water, such solvation seems to be interrupted and aggregation occurs when water becomes a major component. We find that the mole percentage of the aggregates in acetone/water mixtures increases almost linearly with the concentration of water, providing a route to control the extent of aggregation of the chromophores. Due to the long, waxy PO–EO copolymer, MJ–PTCDI and DJ–PTCDI do not show liquid crystalline behavior or nanorod morphology, which were seen with short side chains. The optical microscopy of the bulk material shows aggregated crystals of PTCDI in the waxy matrix, showing that even in the presence of PO–EO copolymer, the molecular assembly of PTCDI takes place in the bulk. Secondary assembly was seen, in that upon ageing of the aqueous solutions, the drop cast films show that the spherical aggregates one-dimensionally coalesced into long fibers. Although UV–Vis spectra indicated no aggregation in non-aqueous solvents, drop-cast films of these solutions show needle-like aggregates and Lego-like assemblies. 相似文献
167.
Nanofibers of the composite of pullulan (PULL), poly(vinyl alcohol) (PVA), and montmorillonite clay (MMT) were prepared using electrospinning method in aqueous solutions. Pullulan is an interesting natural polymer for many of its merits and good properties. Because of biocompatibility and non-toxicity of PVA, it could be used in numerous fields. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were done to characterize the PULL/PVA/MMT nanofibers morphology and properties. XRD patterns and FTIR data demonstrated that there were good interactions between PULL and PVA caused by possibly hydrogen bonds. Moreover, XRD data and TEM images indicated that intercalated and exfoliated MMT nanoplatelets can be obtained within the PULL/PVA/MMT nanofibers depending on the PULL/PVA blend ratios. Furthermore, the thermal stability and mechanical property (tensile strength) of PULL/PVA/MMT nanofibers could be enhanced more by exfoliated MMT nanoplatelets than intercalated structures of that nanoplatelets. 相似文献
168.
The development of the thermo-viscous fingering instability of miscible displacements in homogeneous porous media is examined. In this first part of the study dealing with stability analysis, the basic equations and the parameters governing the problem in a rectilinear geometry are developed. An exponential dependence of viscosity on temperature and concentration is represented by two parameters, thermal mobility ratio β T and a solutal mobility ratio β C , respectively. Other parameters involved are the Lewis number Le and a thermal-lag coefficient λ. The governing equations are linearized and solved to obtain instability characteristics using either a quasi-steady-state approximation (QSSA) or initial value calculations (IVC). Exact analytical solutions are also obtained for very weakly diffusing systems. Using the QSSA approach, it was found that an increase in thermal mobility ratio β T is seen to enhance the instability for fixed β C , Le and λ. For fixed β C and β T , a decrease in the thermal-lag coefficient and/or an increase in the Lewis number always decrease the instability. Moreover, strong thermal diffusion at large Le as well as enhanced redistribution of heat between the solid and fluid phases at small λ is seen to alleviate the destabilizing effects of positive β T . Consequently, the instability gets strictly dominated by the solutal front. The linear stability analysis using IVC approach leads to conclusions similar to the QSSA approach except for the case of large Le and unity λ flow where the instability is seen to get even less pronounced than in the case of a reference isothermal flow of the same β C , but β T = 0. At practically, small value of λ, however, the instability ultimately approaches that due to β C only. 相似文献
169.
Raman scattering (RS), photoluminescence (PL) and energy dispersive X‐ray (EDX) experiments have been carried out to investigate residual strain and hence to understand breakage issue in bulk Inx Ga1–x As crystal grown by multi component zone melting (MCZM) method. It is found from a comparison that there is a large discrepancy among the RS, PL and EDX results due to the strain induced by compositional variation in the crystal. The strain induced changes in TOGaAs and PL peak positions are found to be 4.04 cm–1 and 0.097 eV, respectively, for the variation of composition from 0.06 to 0.29 from the seed‐end to the tail‐end of the crystal. By assuming a simple one‐dimensional strain distribution, the strain value corresponding to 4.04 cm–1/ 0.097 eV can be obtained of the order of 10–2, which is large enough for understanding the breakage issue in the crystal investigated here. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
170.
Experimental studies on flow visualization and heat transfer measurements of finned surface in a narrow duct were carried
out to understand the flow behavior and its effect on heat transfer. In this experiment, short rectangular fins were attached
to a surface (endwall) with having inclination angle of 20° and exposed to air flow. Several flow visualization results reveal
that horse shoe vortex was formed just at the front of the fin whereas the main longitudinal vortex was formed by the side
top edge of the fin. Some important features of the vortex structure, size and flow reattachment positions were noticed from
the smoke flow visualization. Detailed heat transfer distributions were discussed from the thermal image. Nusselt number shows
that the finned surface achieved average heat transfer enhancement at a factor of four times than that of without fins. 相似文献