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排序方式: 共有93条查询结果,搜索用时 31 毫秒
1.
Venkataraman Ganesh Perali Ramu Sridhar Srinivasan Chandrasekaran 《Israel journal of chemistry》2016,56(6-7):417-430
In this account, we elaborate our group's contribution towards understanding the chemistry of carbohydrate-derived donor-acceptor (DA) cyclopropanes. Our work was mainly focused on the ring opening of these versatile chiral synthons under the influence of Lewis acid promoters like electrophilic halogen species, TMSOTf, BF3.OEt2, etc. We studied various modes of ring opening on these DA cyclopropanes, envisaging the access to intriguing molecular architectures. These modes of reaction of the DA cyclopropanes can be controlled by strategically introducing an electron-withdrawing group (EWG) onto the cyclopropane ring, which could direct the ring cleavage by polarizing the cyclopropane C−C bond. Our studies also revealed that the ring opening is sluggish in the absence of an EWG. Using this concept, we demonstrated the synthesis of various biologically interesting molecular skeletons, viz., glycoamino acids (GAA), GAA nucleotides, α-levoglucosan amino acid, and septano-oligosaccharides, with high selectivity. We also applied our understanding to the first stereoselective synthesis of (S)-(−)-longianone and confirmed its absolute configuration. Apart from the inherently activated DA cyclopropanes, we introduced the in situ generation of DA cyclopropanes, starting from vinylcyclopropanes (VCPs). The ring-opening and ring-expansion chemistry of these easily accessible synthons was studied. The chemistry developed for carbohydrate-fused cyclopropanes was also applied for carbohydrate-derived spiro-cyclopropanes. The Lewis-acid-mediated ring opening of spiro-DA-cyclopropanes enabled easy access to fused furopyrans and spirolactones. 相似文献
2.
Reddy C.C. Ramu T.S. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2007,14(6):1509-1515
The paper deals with some important aspects of steady state thermal stability in the insulation of HVDC cables. The resistively graded electric field distribution and the temperature distribution, under steady state, in dc cables, are interrelated. The dc conductivity is known to be a function of stress as well as of temperature. Reasonably convincing theories of electric stress and temperature distribution are now available in the literature. Until recently, the thermal runaway was believed, primarily, to be a consequence of an inordinate run away in the sheath temperature due to dynamic interaction with the ambient. While this premise is partly true, there are other overriding factors controlling the stability. This paper presents a detailed investigation on this aspect and it is shown that the multi-factor dependent dc conductivity alone causes the thermal instability, boundary conditions at sheath having a marginal role. 相似文献
3.
This paper proposes a two-stage feedforward neural network (FFNN) based approach for modeling fundamental frequency (F0) values of a sequence of syllables. In this study, (i) linguistic constraints represented by positional, contextual and phonological features, (ii) production constraints represented by articulatory features and (iii) linguistic relevance tilt parameters are proposed for predicting intonation patterns. In the first stage, tilt parameters are predicted using linguistic and production constraints. In the second stage, F0 values of the syllables are predicted using the tilt parameters predicted from the first stage, and basic linguistic and production constraints. The prediction performance of the neural network models is evaluated using objective measures such as average prediction error (μ), standard deviation (σ) and linear correlation coefficient (γX,Y). The prediction accuracy of the proposed two-stage FFNN model is compared with other statistical models such as Classification and Regression Tree (CART) and Linear Regression (LR) models. The prediction accuracy of the intonation models is also analyzed by conducting listening tests to evaluate the quality of synthesized speech obtained after incorporation of intonation models into the baseline system. From the evaluation, it is observed that prediction accuracy is better for two-stage FFNN models, compared to the other models. 相似文献
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7.
S. Anantha Ramu 《International Journal of Mechanical Sciences》1974,16(7):473-477
A method is presented to obtain stresses and displacements in rotating disks by taking into account the effect of out-of-plane restraint conditions at the hub. The stresses and displacements are obtained in a non-dimensional form, presented in the form of graphs and compared with the generalized plane stress solution. 相似文献
8.
The self-similar solutions for converging spherical and cylindrical strong shock waves in a non-ideal gas satisfying the equation of state of the Mie-Gruneisen type are investigated. The equations governing the flow, which are highly non-linear hyperbolic partial differential equations, are first reduced to a Poincaré-type ordinary differential equation with suitable approximation. Such an approximation helps in obtaining the self-similar solutions and the similarity exponent numerically by phase-plane analysis. 相似文献
9.
G Ramu 《Canadian Metallurgical Quarterly》1981,50(4):226-232
10.
Murugesan Rajesh Ramu Manikandan Seungil Park Byung Chul Kim Won-Je Cho Kook Hyun Yu C. Justin Raj 《国际能源研究杂志》2020,44(11):8591-8605
Activated carbon, from biomass (pinecone), was synthesized by conventional pyrolysis/chemical activation process and utilized for the fabrication of supercapacitor electrodes. The pinecone-activated carbon synthesized with 1:4 ratio of KOH (PAC4) showed an increase in surface area and pore density with a considerable amount of oxygen functionalities on the surface. Moreover, PAC4, as supercapacitor electrode, exhibited excellent electrochemical performances with specific capacitance value ∼185 Fg−1 in 1 M H2SO4, which is higher than that of nonactivated pinecone carbon and 1:2 ratio KOH-based activated carbon (PAC2) (∼144 Fg−1). The systematic studies were performed to design various forms of devices (symmetric and asymmetric) to investigate the effect of device architecture and operating voltage on the performance and stability of the supercapacitors. The symmetric supercapacitor, designed utilizing PAC4 in H2SO4 electrolyte, exhibited a maximum device-specific capacitance of 43 Fg−1 with comparable specific energy/power and excellent stability (∼96% after 10 000 cycles). Moreover, a symmetric supercapacitor was specially designed using PAC4, as a positive electrode, and PAC2, as a negative electrode, under their electrolytic ion affinity, and which operates in aqueous Na2SO4 electrolyte for a wide cell voltage (1.8 V) and showed excellent supercapacitance performances. Also, a device was assembled with poly(3,4-ethylene dioxythiophene) (PEDOT) nanostructure, as positive electrode, and PAC4, as a negative electrode, to evaluate the feasibility of designing a hybrid supercapacitor, using polymeric nanostructure, as an electrode material along with biomass-activated carbon electrode. 相似文献