Fullerene as radical inhibitor in polymerization of acrylonitrile initiated by arsonium ylide

Kinetics of polymerization of acrylonitrile (AN) in presence of fullerene (C₆₀) has been studied using p-acetyl benzylidine triphenyl arsonium ylide as initiator in dioxane at 60 ± 0.1°C under the blanket of nitrogen. The rate of polymerization (R _p ) at low concentration of fullerene may be represented as R _p ?? [Ylide]^0.5[AN]^1.0 [Full]^?0.6, indicating inhibition effect of fullerene on the polymerization. The energy of activation for the polymerization was found to be 71.5 ± 0.5 kJ mol^?1. Fourier transform infrared spectroscopic analysis (FTIR) confirmed the insertion of fullerene in to the final polymer. The mechanism for the polymerization has also been proposed.     

A stable two-coordinate acyclic silylene

Simple two-coordinate acyclic silylenes, SiR(2), have hitherto been identified only as transient intermediates or thermally labile species. By making use of the strong σ-donor properties and high steric loading of the B(NDippCH)(2) substituent (Dipp = 2,6-(i)Pr(2)C(6)H(3)), an isolable monomeric species, Si{B(NDippCH)(2)}{N(SiMe(3))Dipp}, can be synthesized which is stable in the solid state up to 130 °C. This silylene species undergoes facile oxidative addition reactions with dihydrogen (at sub-ambient temperatures) and with alkyl C-H bonds, consistent with a low singlet-triplet gap (103.9 kJ mol(-1)), thus demonstrating fundamental modes of reactivity more characteristic of transition metal systems.     

Dual Q-switched laser outputs from a single lasing medium using an intracavity MEMS micromirror array

An intracavity array of individually controlled microelectromechanical system scanning micromirrors was used to actively Q-switch a single side-pumped Nd:YAG gain medium. Two equal power independent laser outputs were simultaneously obtained by separate actuation of two adjacent micromirrors with a combined average output power of 125?mW. Pulse durations of 28?ns FWHM at 8.7?kHz repetition frequency and 34?ns FWHM at 7.9?kHz repetition frequency were observed for the two output beams with beam quality factors M² of 1.2 and 1.1 and peak powers of 253?W and 232?W, respectively.     

Quantum dynamics of h(2)(+) in intense laser fields on time-dependent potential energy surfaces

We have exploited the fully time-dependent Born-Oppenheimer approximation to develop time-dependent potential energy surfaces for the lowest two states of H(2)(+) in the presence of intense, time-varying, few-cycle laser fields of 2-8 fs duration. Quantum dynamics are explored on these field-dressed, time-dependent potentials. Our results show that the potential well in the lowest-energy state of H(2)(+) (i) collapses as the laser pulse reaches its peak amplitude and (ii) regains its form on the trailing edge of the pulse, and (iii) the trapped nuclear wavepacket has a higher probability of leaking out from the well in the case of longer laser pulses. The carrier envelope phase is found to have negligible effect on the nuclear dynamics.     

Investigation of folding patterns in homo-oligomers of (R)-β2,2-amino acids with carbohydrate side chain

The study describes the synthesis of new β^2,2-peptides made from geminally disubstituted β^2,2-amino acid and their folding propensities. The (R)-C-linked carbo-β^2,2-amino acid [(R)-β^2,2-Caa] was prepared from d-glucose and converted into the homo-oligomeric di-, tetra-, and hexapeptides. The conformational studies were carried out using NMR (in CDCl₃), CD, IR, and MD calculations. These β^2,2-peptides were interestingly stabilized by five-membered (mr) inter-residue H-bonds NH(i)?O(i-1) (furanoside) and a 6-mr intra-residue H-bond between amide proton (NH(i)) and the oxygen of –OMe(i) at the C3 carbon of the carbohydrate side chain. These results amply demonstrate that the ‘epimerization’ at the spiro carbon center has an effect on the conformational behavior of these peptides. Finding of these, H-bonding patterns, which are not so common to stabilize the folds in this class of β^2,2-Caa derived peptides would further facilitate augmentation in the domain of foldamer.     

Direct determination of tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate by HPLC and GC methods

The high performance liquid chromatography and gas chromatography methods were investigated for their applicability in determining micro-level concentrations of tri-n-butyl phosphate (TBP). A high performance liquid chromatograph (HPLC) equipped with refractive index detector was used in determining TBP up to 2 ppm concentration level in the aqueous nitric acid solutions. The gas chromatography incorporated with Thermionic Detector (NPD) and Flame Photometric Detector (FPD) were examined for their potential in analyzing TBP in organic phase up to sub-ppm level. The results indicated that HPLC-RI technique is well suited for direct analysis of aqueous phase. For organic phase analysis, gas chromatographic methods with the TID and FPD were suitable but performance of detectors deteriorated often due to fouling.     

Systems theoretic questions in coding theory

A central theme of current research in coding theory are low density parity-check (LDPC) codes and more generally codes defined via graphs. There exist various decoding algorithms which work in a decentralized manner and which can be viewed as discrete dynamical systems. In this talk, we explain these algorithms from a systems theoretic point of view. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)