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排序方式: 共有156条查询结果,搜索用时 15 毫秒
21.
A class of photoelastically insensitive materials consisting of a blend of rigid and flexible polyesters is described. The mechanical and optical response of these polymers is viscoelastic in character. For a wide range of the compositions, the birefringence changes from positive to negative under constant load or constant displacement. The influence of composition, time under load, and principal stress difference on the birefringence is studied. Isochromatic-fringe development in a diametrally loaded disk shows that a major region of the stressed body becomes optically insensitive after a reasonable period of time under load and remains insensitive for a time sufficiently large for associated photoelastic operations. A typical operating-time band is presented during which the optical response of a model characterized by the fringe order per unit thickness is reasonably small. It appears that this class of photoelastically insensitive materials can be employed to produce composite models with glass-fiber reinforcements. Compared to other zero-birefringent polymers, the present material has the advantage of easier processing (casting and curing), improved adhesion to glass fibers and closer matching of the refractive index with that of glass. 相似文献
22.
Cover Picture: A new topological insulator built from quasi one‐dimensional atomic ribbons (Phys. Status Solidi RRL 2/2015) 下载免费PDF全文
23.
M. Parthibavarman S. Sathishkumar S. Prabhakaran M. Jayashree R. BoopathiRaja 《Journal of the Iranian Chemical Society》2018,15(12):2789-2801
The paper investigates the structural, optical and photocatalytic activity of large surface area single crystalline copper (Cu) doped SnO2 nanorods (NRs) synthesized by a novel one-step microwave irradiation method. Powder X-ray diffraction (XRD) analysis confirms that both pure and Cu doped SnO2 are tetragonal rutile type structure (space group P42/mnm) formed during the microwave process within 10 min without any post annealing treatment. Transmission electron microscopy (TEM) reveals that the as synthesized Cu doped SnO2 samples exhibited rod-like shape and the length was less than 80 nm and diameter was about few nanometers. Typical selected-area electron diffraction (SAED) pattern indicates that, the growth direction of Cu–SnO2 nanorod is along [110] direction. The variety of phonon interaction in the pure and Cu doped SnO2 is observed by Raman spectroscopy. Electron paramagnetic resonance and X-ray photoelectron spectroscopy (XPS) confirms that the presence of copper and tin as Cu2+ and Sn4+ in state, respectively. The photocatalytic activity was monitored via the degradation of methylene blue (MB) and Rhodamine B (RhB) dyes and the Cu–SnO2 showed better photocatalytic activity than that of pure SnO2. This could be attributed to the effective electron–hole separation by surface modification. 相似文献
24.
Viswanathan R Smith CR Prabhakaran EN Johnston JN 《The Journal of organic chemistry》2008,73(8):3040-3046
5-exo-trig Cyclization of an aryl radical to the nitrogen of an azomethine is used as the key annulating step in a modular preparation of 2,3-cis- and trans-disubstituted indolines. The precursors are readily prepared by phase-transfer-catalyzed Michael addition of a glycine Schiff base to a variety of acceptors. When the more reactive alkylidene malonate Michael acceptors are implemented, a one-pot three-component coupling is possible. The net result is a convergent [3 + 2] coupling strategy for the construction of highly functionalized indolines, a substructure occurring in numerous biologically active natural products. 相似文献
25.
Ruthenium acts as a good catalyst for the racemization reaction of secondary alcohols and amines. Ruthenium-catalyzed racemization is coupled with enzymatic kinetic resolution to prepare chiral compounds in 100% theoretical yield. Ten ruthenium complexes (1–10) act as a good catalyst the for racemization reaction and are also compatible with DKR process. Two other ruthenium complexes [RuCl2(PPh3)3] and [Cp*RuCl(COD)] are active for racemization reaction but their successful compatibility with DKR has not yet been reported. Ru/γ-Al2O3 and Ru–HAP are the heterogeneous catalysts used for the racemization reaction. They have also not been employed for DKR process. Polymer supported ruthenium is employed as a reusable racemization catalyst for aerobic DKR of alcohols. 相似文献
26.
Prabhakaran R Kalaivani P Poornima P Dallemer F Paramaguru G Vijaya Padma V Renganathan R Huang R Natarajan K 《Dalton transactions (Cambridge, England : 2003)》2012,41(31):9323-9336
One pot synthesis of three structurally different Ni(II) thiosemicarbazone complexes 1, 2 and 3 were obtained from the reaction between [NiCl(2)(PPh(3))(2)], 1,2-bis(diphenylphosphino)ethane, and [H(2)-(Sal-tsc)]. The obtained products were characterized by various spectral and analytical techniques. From the X-ray crystallographic analysis, an unexpected N-arylation on the coordinated salicylaldehydethiosemicarbazone was found in complex 2. The comparative biological evolutions such as DNA/protein binding, antioxidant, cytotoxicity (MTT, LDH, and NO) and cellular uptake studies have been examined for [Ni(Sal-tsc)(PPh(3))] (1) and [(Ni(Sal-tsc))(2)(μ-dppe)] (3). When comparing the cytotoxicity of the complexes, 1 exhibited higher activity than 2 and 3 and by comparing with standard cis-platin, both of them were found to exhibit better activity under identical conditions. 相似文献
27.
V Azzarito P Prabhakaran AI Bartlett NS Murphy MJ Hardie CA Kilner TA Edwards SL Warriner AJ Wilson 《Organic & biomolecular chemistry》2012,10(32):6469-6472
The design and synthesis of a new 2-O-alklyated benzamide α-helix mimetic is described. Comparison with regioisomeric 3-O-alkylated benzamides permits a preliminary evaluation of the role that mimetic curvature has in determining molecular recognition properties. 相似文献
28.
Thermal and Spectroscopic Studies on the Decomposition of Some Aminoguanidine Nitrates 总被引:1,自引:0,他引:1
S. R. Naidu K. V. Prabhakaran N. M. Bhide E. M. Kurian 《Journal of Thermal Analysis and Calorimetry》2000,61(3):861-871
Diaminoguanidine nitrate (DAGN) and triaminoguanidine nitrate (TAGN),potential energetic materials in emerging propulsion
technology with high mass impetus at low isochoric flame temperature have been studied as regards kinetics and mechanism of
thermal decomposition using thermogravimetry (TG), differential thermal analysis (DTA),infrared spectroscopy (IR) and hot
stage microscopy. Kinetics of thermolysis has been followed by isothermal TG and IR. For the initial stage of thermolysis
of DAGN the best linearity with a correlation coefficient of 0.9976 was obtained for the Avrami-Erofe'evequation, n=2, by isothermal TG. The activation energy was found to be 130 kJ mol–1 and logA=11.4. The initial stage of thermolysis of TAGN also obeyed the Avrami-Erofe'ev equation, n=2, with a correlation coefficient of 0.9975by isothermal TG and the kinetic parameters are E=160.0 kJ mol–1 and logA=16.0. High temperature IR spectra showed exquisite preferential loss in intensity of the NH2, NH, N–N stretching and CNN bending. Spectroscopic and other results favour deamination reaction involving the rupture of
the N–N bond as the primary step in the thermal decomposition.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
29.
Force-constant softening due to impurities in Si and Ge has been estimated, using the band model of sievers and Takeno, to be between 10–15%. The molecular model yields a value of about 20% for the same effect. 相似文献
30.
Synthesis of small cyclic peptides via reverse turn induced ring closing metathesis of tripeptides 总被引:1,自引:0,他引:1
A reverse turn induced (gamma/beta-turn) cyclization of tripeptides 1 can be performed in a ring closing metathesis reaction with Grubbs' catalyst to the corresponding cyclic peptides 2. These cyclic peptides may be useful probes as a conformationally constrained mimic of the bioactive conformation of structurally related HIV protease inhibitors. 相似文献