Definite paths and upper bounds on regular regions of velocity phase space

Hamilton's principle states that the path integral of the Langrangian is stationary with respect to variations of a classical path. It does not distinguish between a local minimum, a local maximum or a saddle point in path space. A simple algorithm is devised which provides strict and useful upper bounds on the region of velocity phase space occupied by paths that are either local maxima or local minima. The technique is illustrated graphically for the standard map. It is found that the bounds provide accurate numerical upper estimates for the region of velocity phase space filled by the rotational KAM surfaces at arbitrarily chosen values of the perturbation parameter.     

N- and P-channel transport behavior in thin film transistors based on tricyanovinyl-capped oligothiophenes

We report the structural and electrical characterization of thin films of organic semiconductor molecules consisting of an oligothiophene core capped with electron-withdrawing tricyanovinyl (TCV) groups. X-ray diffraction and atomic force microscopy of evaporated films of three different TCV-capped oligothiophenes showed that the films were highly crystalline. Electrical transport was measured in thin film transistors employing silver source and drain contacts and channel probes to correct for contact resistance. Three compounds exhibited n-channel (electron) conduction consistent with cyclic voltametry data that indicated they undergo facile reduction. Maximum electron mobilities were 0.02 cm2/V.s with an on/off current ratio of 10(6). A fourth end-capped molecule, TCV-6T-TCV, which had six thiophene rings, exhibited both p- and n-channel transport. Overall, these results confirm that substitution of oligothiophene cores with electron-withdrawing groups is a useful strategy to achieve electron-transporting materials.     

Effect of solvents on carbon-13 spin-lattice relaxation in 1-phenyladamantane

Rotational diffusion of 1-phenyladamantane was studied by means of carbon-13 spin-lattice relaxation. Seven different solvents were used. Rotational correlation times showed a linear dependence on solvent viscosity, except for chloroform and 1,1,2,2-tetrachloroethane which retarded motion of the phenyl moiety through specific interactions.     

Direct Radiometric Measurement of Vapor-Liquid Equilibria: Hydrogen Sulfide-Diethanolamine

Direct radiometric measurements of the vapor concentration of H₂S in equilibrium with aqueous diethanolamine absorbing solution were made using ³⁵S-labeled H₂S. A thin-window Geiger-Müller tube viewed the gas phase only, while the absorbing solution was held in another part of the reaction flask. The equilibrium data were measured at H₂S partial pressures below 0.01 mm Hg; the agreement with published results obtained by chemical analysis was good. The radiometric results were obtained very rapidly; a test run with seven data points took about two hours to complete. The results were applied to processes for reducing H₂S concentrations in petroleum refinery fuel gases needed to meet tightening air pollution requirements.     

A note on some piecewise-linear difference equations with Mersenne-type periodic solutions

This paper studies solutions of some piecewise-linear difference equations. In two particular cases, a descent argument is used to show that all solutions are periodic with either prime period 3(2 ^k  ? 1) or 6(2 ^k  ? 1) for some k ≥ 1. The existence of solutions with such periods is also considered.     

Bounded matrix groups

The principal result is that if G is any irreducible subgroup of GL(n, C) (C the complex field) such that |tr(7^)| is uniformly bounded for all A in G and some fixed n × n nonzero matrix T, then G is equivalent to a unitary group. Similar results are proved for certain associated representations of G.     

Further Thoughts on Turbulent Flow in a Pipe

Nikuradse’s 1932 paper on turbulent flow in a smooth pipe contains a wealth of information on flow resistance (friction factor) and profiles of velocity and eddy viscosity. The goal here is to study this information in detail with the objective of applying it to other turbulent-flow situations. In particular, reverse engineering supports a value of n = 2 for the exponent on the volumetric dissipation in the decay term of the equation of the dissipation theorem. Of equal importance, integration of Nikuradse’s profiles of eddy viscosity does not lead to his formula for the universal resistance law; instead the presence of the viscous sublayer has an overt effect on the result even though we had thought that such a region influenced only the form of mass transfer at high values of the Schmidt number. A formula is proposed for the decay of dissipation for turbulent flow in smooth pipes.

     

Microchip micellar electrokinetic chromatography separation of alkaloids with UV-absorbance spectral detection

A microchip device is demonstrated for the electrophoretic separation and UV-absorbance spectral detection of four toxic alkaloids: colchicine, aconitine, strychnine, and nicotine. A fused-silica (quartz) microchip containing a simple cross geometry is utilized to perform the separations, and a miniature, fiber-optic CCD spectrometer is coupled to the microchip for detection. Sensitive UV-absorbance detection is achieved via the application of online preconcentration techniques in combination with the quartz microchip substrate which contains an etched bubble-cell for increased pathlength. The miniature CCD spectrometer is configured to detect light between 190 and 645 nm and LabView programming written in-house enables absorbance spectra as well as separations to be monitored from 210 to 400 nm. Consequently, the configuration of this microchip device facilitates qualitative and quantitative separations via simultaneous spatial and spectral resolution of solutes. UV-absorbance limits of quantification for colchicine, 20 microM (8 mg/L); strychnine, 50 microM (17 mg/L); aconitine, 50 microM (32 mg/L); and nicotine, 100 microM (16 mg/L) are demonstrated on the microchip. With the exception of aconitine, these concentrations are > or =20-times more sensitive than lethal dose monitoring requirements. Finally, this device is demonstrated to successfully detect each toxin in water, skim milk, and apple juice samples spiked at sublethal dose concentrations after a simple, SPE procedure.