Concentration measurements in a self-excited jet

The near field of helium-air jets exhausting into an air environment has been experimentally investigated using an aspiration probe and flow visualization. Jets with varying density ratios and Reynolds numbers were studied. Pure helium jets with density ratios of 0.14 were found to display a self-excited behavior characterized by intense mixing. The centerline concentration decay was found to be substantially increased for the self-excited jet. Flow visualization revealed the expulsion of side jets from the potential core region of low density jets. Radial profiles of concentration provide additional evidence that side-jets produce vigorous mixing.     

Hyperfine interactions,including Bhf[FrFe], studied in the decay chain of225Ra by alpha and gamma anisotropy measurements

A low temperature nuclear orientation experiment has been performed on the 14.8d²²⁵Ra activity. Gamma anistotropy [²²¹Fr (4.8m) and²¹³Bi (45.6m)] and alpha anisotropy [²²⁵Ac (10.0d),²²¹Fr,²¹⁷At (32.3ms) and²⁰⁹Po (4.2μs)] measurements has been carried out and values for the hyperfine field of²²⁵Ac and²²¹Fr in iron and the magnetic moment of²¹³Bi are reported.     

Solid phase synthesis of 5-aminopyrazoles and derivatives

The development of a novel solid phase synthesis of some 5-aminopyrazoles and derivatives is described. Reaction of hydrazines with solid supported β-keto-nitrile (1) affords 5-aminopyrazoles (2) the amino group of which is readily acylated or sulphonylated. Generation of the solid supported β-keto-nitrile (1) is non trivial and represents a key step in the overall synthesis.     

Sensitivity to envelope coherence

Measurements are reported on the ability of observers to discriminate whether the envelope of two amplitude-modulated sinusoids are in phase or out of phase. Spacing between the two carriers was either 2/3 or 4/3 octave, and the depth of modulation was varied to determine threshold. Discrimination performance improved as the level of the carriers increases up to about 60 dB SPL. The frequency locus of the two carriers (geometric mean of the two frequencies), which varied from 500 to 8000 Hz in different experiments, had little effect on discrimination accuracy. Discrimination performance was relatively constant for modulation rates below 100 Hz and deteriorates for higher modulation rates. These results are compared with data obtained from comodulation masking release experiments.     

Solvatochromic effects on the photoinduced charge-transfer states in donor-acceptor substituted polydioctylfluorenes

Polymer morphology affects quantum efficiency. The influence of polymer morphology on the emission from charge transfer states within donor-acceptor (D-A) polydioctylfluorene derivatives is investigated. Two D-A copolymers, comprising one- and two-electron-donating triphenylamines substituted into the electron-accepting dioctylfluorene repeat unit were studied. Time-resolved emission spectra (with a resolution of 330 fs) in both liquid and glass phase isolate nuclear relaxation to the large-amplitude motion of the triphenylamine moiety about the single bond, analogous to the twisted intramolecular charge-transfer (TICT) model. The charge separation in the polymers' emitting states is therefore increased, suggesting a potential approach to enhance quantum efficiency in devices otherwise limited by exciton recombination.