Some Methods for Estimation in a Negative-Binomial Model

To clarify the advantage of using the quasilikelihood method, lack of robustness of the maximum likelihood method was demonstrated for the negative-binomial model. Efficiency calculations of the method of moments and the pseudolikelihood method in the estimation of extra-Poisson parameters in a negative-binomial model were carried out. Especially when the overdispersion parameter is small, both methods are relatively highly efficient and the pseudolikelihood estimate is more efficient than the method of moments estimate. Two examples of the quasilikelihood analyses of count data with overdispersion are given. The bootstrap method also is applied to the data to illustrate the advantage of the method of moments or pseudolikelihood method in the estimation of the standard errors of the mean parameter estimates under the negative-binomial model.     

Time-resolved fluorescence studies on the formation and decomposition of the aromatic hydrocarbon-aliphatic amine exciplex in solution

Fluorescence rise and decay processes were measured and rate parameters were determined for the pyrene-tri-n-butylamine and pyrene-N,N-diethylaniline exciplex system in various solvents. An additional activation energy over that for the diffusional motion appears necessary for both exciplex formation and the deactivating quenching processes in the case of the pyrene-tri-n-butylamine system. The rate-determining step for these processes is electron transfer in the encounter collision leading to the nonrelaxed electron transfer state.     

Influence of superimposed steady shear flow on the dynamic properties of polyethylene melts

Experiments in which an oscillatory shear flow is superimposed on a steady state shear flow were performed on polyethylene melts by the use of a cone and plate type rheogoniometer. The phase difference between oscillatory shear stress and shear strain increases in all cases and for all frequencies with the increase of the superimposed shear rate. Between ω₀, the frequency at which the phase difference is π/2 and the steady shear rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}, as found by Booij for polymer solution, the relation ω₀ = 1/2 \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma$\end{document}. holds also for polyethylene melts. The significance of this relation is discussed briefly from the viewpoint that the entanglement density decreases with the increase of the imposed shear rate.     

Mössbauer spectra at 77 K of products formed during transformation of iron(II) hydroxide containing zinc(II) ion to Zn-bearing ferrite in aqueous suspension by air oxidation

At pH 7.0, lower crystalline iron (II) hydroxide, “green rust II” (the Fe^II:Fe^III mol ratios and the electron diffraction measurements do not indicate the tendency for Zn²⁺ ion to be incorporated in place of the Fe²⁺ ion) and Zn-bearing ferrite are formed from aqueous iron (II) hydroxide suspensions containing the zinc (II) ion at a Zn: Fe_tot. mol ratio of 1.00:2.00. At pH 9.0 and 10.0, higher and lower crystalline iron (II) hydroxides and Zn-bearing ferrite are formed. The ratios of higher to lower crystalline iron (II) hydroxide are approximately constant during oxidation at pH 9.0. The oxidation reactions are divided into two classes according to the Zn: Fe_tot. mol ratios. At pH 7.0, lower crystalline iron (II) hydroxide is formed at the early stages of oxidation and dissolved iron (II) species are formed during the oxidation at a Zn:Fe_tot. mol ratio of 0.20:2.80. Iron (II) hydroxide is formed during oxidation and dissolved iron (II) species are formed at an early stage of the oxidation at Zn:Fe_tot. mol ratios of 0.60:2.40 and higher. At pH 9.0 and 10.0, both higher and lower crystalline iron (II) hydroxides are formed at Zn: Fe_tot. mol ratios of 0.60:2.40 and higher, and 1.00:2.00, respectively. However, at a Zn:Fe_tot. mol ratio of 0.20:2.80, iron (II) hydroxide with a large quadrupole splitting value and dissolved iron (II) species with large isomer shifts and quadrupole splitting values are formed before and during oxidation at pH 7.0, and the formation of Zn-bearing ferrite is depressed (-FeO(OH) is formed) at pH 10.0.     

Synthesis,crystal structures and magnetic properties of Co particles encapsulated in carbon nanocapsules

Carbon-coated cobalt particles were produced by arc-evaporation of a Co-packed graphite rod in a modified fullerene generator. Cobalt particles grown were in an fcc phase, with a trace amount of hcp-Co. The particles were nominally spherical in shape, and typically 10–100 nm in diameter. Thickness and structure of outer carbon layers could be controlled by varying the relative area of a Co-packed hole drilled in the graphite rod. Saturation magnetization (M _s) and the coercive force (H _c) was measured between room temperature and 800°C for powder samples: Temperature dependence of the measured M _s was consistent with that for fcc-Co. The highest value of M _s of 160 emu/g at room temperature, nearly the same value for bulk fcc-Co, was obtained for Co particles covered with thin carbon layers. H _c varied from 600 Oe to 300 Oe, depending on the size of Co particles.