Chain morphologies in semicrystalline polyfluorene: evidence from Raman scattering

The beta phase in di-octyl substituted polyfluorene (PF8) exhibits a surprising level of conformational order at nanometer length scales compared to other phases. We present Raman scattering studies of PF8 as a function of thermal cycling, which establishes a connection between the conformational isomers and the side and main chain morphology. Density-functional calculations of the vibrational spectra of single chain oligomers in conjunction with the experimental results demonstrate the incompatibility of the beta phase with the overall alpha crystalline phase in PF8.     

Pulsradiolyse von Gasen: Optisches Spektrum und Reaktionen von N+4 (oder N+3? bei Atmosph?rendruck

Ohne Zusammenfassung     

Thermal insulating behavior in crystals at high frequencies

When solving heat-conduction problems with periodic temperature perturbations, the thermal conductivity is assumed to remain frequency independent. We, however, show by using the molecular dynamics technique and the fluctuation-dissipation theorem a decrease of the effective thermal conductivity of 2 orders of magnitude when the excitation frequency approaches or exceeds the reverse of the phonon mean relaxation time. Most of the dielectric and semiconductor materials have to be considered as strongly insulating in those conditions. The comparison between molecular-dynamics simulations performed in Si crystals and theoretical predictions reveals a clear agreement.     

Stability conditions for systems of linear nonautonomous delay differential equations

Systems of linear nonautonomous delay differential equations are considered which are of the form y′_i(t) = ∑_{k = 1}ⁿ ∝₀^T b_ik(t, s) y_k(t − s) dη_ik(s) − c_i(t) y_i(t), where I = 1,…, n. Sufficient conditions are derived for both the asymptotic stability and the instability of the zero solution. The main result is found by a monotone technique using elementary methods only. Moreover, additional criteria are obtained by using the method of Lyapunov functionals.     

Solid phase extraction GC/ECD method for the analysis of organochlorine pesticides in wildlife plasma

A gas chromatographic method for the analysis of nine organo-chlorine pesticides in wildlife plasma is described. Reversed-phase solid phase extraction is utilized to extract the organochlorine pesticides from plasma. This is followed by a normal phase solid phase extraction clean-up as the pesticides are recovered by elution with hexane:ethyl ether (1:1) and quantified by gas chromatogra-phy/electron capture detection. Method limits of detection range from 7.0–25 μg/L. The mean recovery for all pesticides is 81%.