Thermal degradation of polyacrylonitrile in the temperature range 280–450°c.

This paper presents a study of the thermal degradation of polyacrylonitrile of 13,000 to 43,000 number-average molecular weight in vacuum over the temperature range 280–450°C. Sixteen products of the decomposition were identified by chromatographic and infrared analytical techniques. The five major products, i.e., cyanogen, hydrogen cyanide, acrylonitrile, acetonitrile, and vinylacetonitrile, were monitored at intervals during the decomposition using gas chromatography. Activation energies of 15 and 23 kcal./mole were calculated from initial rates of formation of HCN and cyanogen, respectively. The overall activation energy of the polymer degradation was found to be 3.6 kcal./mole. The residue of the decomposition in the temperature region 280–450°C. was suggested by infrared absorption measurements and elemental analysis to be a polymer of the structure The rate of production of vinylacetonitrile was found to be proportional to the production of the residual black poly-1,4,4-trihydronaphthyridine. A new photothermal degradation cell is also presented.     

Indirect fluorescence detection of simple sugars via high-pH electrophoresis in poly(dimethylsiloxane) microfluidic chips

This article describes the successful electrophoretic separation of simple carbohydrates in a polymeric microfluidic chip. The device fabricated in poly(dimethylsiloxane) (PDMS) is found to be stable in high-pH solutions. This allows sugars to be separated electrophoretically at pH values at or above their pK(a) using indirect fluorescence detection. Signal-to-noise values greater than 10:1 were obtained using a mercury arc lamp excitation source and a fluorescein-containing mobile phase for the detection of sugars at concentrations as low as 5 mM. The results obtained compare favorably with published results for the same system using a traditional fused-silica capillary. Analysis of the data revealed a significant experimental sensitivity of the migration times measured in these PDMS devices, an aging effect that leads to considerable systematic drift over the course of a series of replicate measurements. These experiments highlighted the importance of the surface chemistry of PDMS, especially as it pertains to its ability to support stable electroosmotic flow within the separation device. Channel priming at high pH provides a necessary, but by itself insufficient, means by which this instability can be minimized.     

Radiative improvement of the lattice nonrelativistic QCD action using the background field method and application to the hyperfine splitting of quarkonium states

We present the first application of the background field method to nonrelativistic QCD (NRQCD) on the lattice in order to determine the one-loop radiative corrections to the coefficients of the NRQCD action in a manifestly gauge-covariant manner. The coefficients of the σ·B term in the NRQCD action and the four-fermion spin-spin interaction are computed at the one-loop level; the resulting shift of the hyperfine splitting of bottomonium is found to bring the lattice predictions in line with experiment.     

A new class of high birefringence smectic C liquid crystals. 3,3'-Difluorodiphenyldiacetylenes

Ferroelectric smectic C* liquid crystals have been shown to exhibit high speed, multistate electro-optic switching, particularly when incorporated into the surface stabilized ferroelectric liquid crystal (SSFLC) light valve. Certain applications utilizing IR modulation, waveguide, and fibre-optic devices can benefit from a birefringence higher than the value of Δn = 0·15 seen in typical FLC materials. By incorporating the highly conjugated diacetylene moiety into an FLC core, an increase in birefringence to greater than Δn = 0·3 is achieved. Fluorination of the core induces a strong preference for the tilted smectic C phase as compared to the unfluorinated materials which typically show the nematic phase. The effect of different tail substitutions is examined in the 3,3'-difluorodiphenyldiacetylene system.     

Effect of age and food intake on dietary carbon turnover recorded in sheep wool

We present the results of a series of controlled feeding experiments with sheep, designed to investigate the effects of age and level of food intake on the kinetics of incorporation of the dietary carbon signal into wool. Four different groups of three sheep each, ranging in age from 6 to 78 months, were fed a C(3) diet and switched to a C(4) diet for up to 250 days. Different quantities of the same C(4) diet were provided to each group, in order to achieve different growth rates (high, low, and no growth). Wool was repeatedly shorn from each animal and processed for delta(13)C analyses. Results show that newly grown wool does not start recording the isotope composition of the new diet immediately after the diet-switch. The time-lag varies according to the age of the animal, from 6 +/- 1 days in lambs to up to 15 +/- 4 days in the older ewes. Wool from fast-growing lambs approached equilibrium faster than that from slow-growing lambs and young ewes, with old ewes being the slowest. However, 3 weeks after the diet-switch, the differences in wool delta(13)C values between the four different groups of animals were relatively small and represented less than 15% of the isotopic difference between the two diets. These results suggest that a single equation can be used to reconstruct previous diets for animals of different age, provided that the diet is similar and all individuals are in positive protein balance.     

Transport in time-dependent dynamical systems: finite-time coherent sets

We study the transport properties of nonautonomous chaotic dynamical systems over a finite-time duration. We are particularly interested in those regions that remain coherent and relatively nondispersive over finite periods of time, despite the chaotic nature of the system. We develop a novel probabilistic methodology based upon transfer operators that automatically detect maximally coherent sets. The approach is very simple to implement, requiring only singular vector computations of a matrix of transitions induced by the dynamics. We illustrate our new methodology on an idealized stratospheric flow and in two and three-dimensional analyses of European Centre for Medium Range Weather Forecasting (ECMWF) reanalysis data.     

Photochemistry of poly(tert-butyl acrylate). Effect of ester spatial conformation on the cycloelimination process

A preferred geometric isomer was found to exist for the Norrish type II photocycloelimination of isobutene from poly(tert–butyl acrylate). A detailed analysis of infrared spectroscopic and kinetic data under thin film conditions is consistent with the mechanism: i.e., a photoinduced rotational equilibrium is established between the cis and trans ester spatial conformations, with isobutene elimination occurring from the cis form. In the glassy state of the polymer, an activation energy of 3.0 kcal./mole was obtained for the elimination step. Energy transfer experiments with naphthalene, benzophenone, and oxygen resulted in a significant decrease in the isobutene yield. This indicates that reaction occurs at least in part from a triplet state of the carbonyl group in the polymer.     

Alteration of the carbon and nitrogen stable isotope composition of beef by substitution of grass silage with maize silage

This study investigated the effect of substituting grass silage (C3 photosynthetic plant product) with maize silage (C4 photosynthetic plant product) on the natural abundance carbon (delta13C) and nitrogen (delta15N) stable isotope composition of bovine muscle tissue. Forty-five continental crossbred heifers were assigned to one of three diets consisting of 3 kg of a barley-based concentrate plus grass silage, maize silage or an equal mixture (dry matter basis) of grass silage and maize silage, fed ad libitum, for 167 days. Substitution resulted in less negative delta13C values (P<0.001) in lipid-free muscle and in lipid, and also a lower delta15N (P<0.001) in lipid-free muscle. Feeding of maize silage was clearly reflected in the delta13C of muscle, with each 10% difference in the dietary C4 carbon intake resulting in a 0.9 to 1.0 per thousand shift of delta13C in lipid-free muscle and a 1.0 to 1.2 per thousand in lipid. Minimum detectable mean differences (95% confidence, power 0.80, n=15) in this experiment were about 0.5 per thousand and 1.0 per thousand for delta13C of lipid-free muscle and lipid, respectively, and about 0.5 per thousand for delta15N of lipid-free muscle. The power analysis presented here is useful for estimating minimum isotopic differences that can be detected between any two groups of beef samples with a given number of replicates. It is concluded that carbon stable isotope ratio analysis of meat can be used to quantify C3/C4 dietary constituents in beef production.