Nimal Rajapakse

Nonlocal Continuum Modeling and Molecular Dynamics Simulation of Torsional Vibration of Carbon Nanotubes

This paper investigates the size effects in the dynamic torsional response of single-walled carbon nanotubes (SWCNTs) by developing a modified nonlocal continuum shell model. The purpose is to facilitate the design of devices based on CNT torsion by providing a simple, accurate, and efficient continuum model that can predict the frequency of torsional vibrations and the propagation speed of torsional waves. To this end, dispersion relations of torsional waves are obtained from the proposed nonlocal model and compared to classical models. It is seen that the classical and nonlocal models predict nondispersive and dispersive behavior, respectively. Molecular dynamics simulations of torsional vibrations of (6, 6) and (10, 10) SWCNTs are also performed, the results of which are compared with the classical and nonlocal models and used to extract consistent values of the nonlocal elasticity constant. The superiority and accuracy of the nonlocal elasticity model in predicting the size-dependent dynamic torsional response of SWCNTs are demonstrated.

Catalytic O2-oxidation of thioethers to sulfoxides using ruthenium(VI) dioxo porphyrin species

Ruthenium(VI) dioxo porphyrin species in benzene act as stoichiometric oxygen-atom transfer reagents toward alkyl thioethers to give the sulfoxide; the systems become catalytic in the presence of dioxygen at room temperature, but turn-overs are limited by formation of substitution-inert bis(S-bonded sulfoxide) complexes.

Selective Oxidations Catalyzed By Dioxo(Porphyrinato)Ruthenium(VI) Species

The complexes trans -Ru(porp) (O) 2 , where porp = the dianion of 5,10,15,20-tetramesitylporphyrin (TMP) or 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin (OCP), are readily formed in benzene by treatment of the Ru(II) bis(acetonitrile) precursors with O 2 or air. Such dioxo species in solution utilize both oxygen atoms for oxygenation of thioethers to sulfoxides, phenol to hydroquinone, and (as noted by other groups) olefins to epoxides; 2-propanol is also dehydrogenated to give acetone. Catalytic O 2 -oxygenation has been demonstrated for the thioether and olefinic substrates. In summary, dioxo(porphyrinato)ruthenium(VI) species are capable of transferring O-atoms to, or abstracting H-atoms from, several diverse types of substrates; as O 2 is the O-atom source, the systems represent a major advance in O 2 -oxidation chemistry and offer an excellent opportunity for detailed mechanistic insight into oxidations of biological and industrial importance. The scene is comparable to that of catalytic hydrogenation in the early 1960s, when many transition metal hydrides were being synthesized using H 2 , and their catalytic properties were being discovered (ref. 43).

A coupled analytical model for hydrostatic response of 1-3 piezocomposites

This study presents a fully coupled analysis of a unit cell of a 1-3 piezocomposite under hydrostatic loading. The governing equations for coupled axisymmetric electroelastic field of a transversely isotropic piezoelectric medium and a transversely isotropic elastic medium are used. A reduced form of the analytical general solutions expressed in terms of series of modified Bessel functions of the first and second kind are used. The solution of the boundary-value problem corresponding to a unit cell is presented. The effective properties of a 1-3 piezocomposite are obtained for different fiber volume fractions, polymer and piezoceramic properties, and fiber aspect ratios. Comparisons with previously reported simplified and uncoupled models are made.

Bis(alkoxy)ruthenium(IV) porphyrin complexes and aerobic oxidation of alcohols

The complex trans-RuVI(tmp)(O)2(tmp = dianion of 5,10,15,20-tetramesitylporphyrin) oxidizes alcohols via bis(alkoxy) species, of which the bis(isopropoxy) complex has been characterized crystallographically.

Modeling of the Cyclic Behavior of Shape Memory Alloys during Localized Unstable Mechanical Response

Experiments have shown that the localization of transformation in NiTi shape memory alloys (SMAs) is an important factor in determining their mechanical response during cyclic loading. A one-dimensional constitutive model for the cyclic behavior of SMAs is presented that takes into account the localization of transformation and transformation-induced plasticity. An internal variable is introduced that characterizes the amount of temperature-dependent cyclic change. The results of simulations at two different temperatures are also presented.