Degradation of ZnS:Cu,Al,Au phosphor powder in different gas mixtures

The ZnS:Cu,Al,Au (P22G) phosphor powder was bombarded by an electron beam in an O₂ ambient, Ar ambient and other mixture of gases. These gases consisted of mixtures of O₂ and CO_x, and O₂, CO_x and Ar gas. Auger electron spectroscopy (AES) was used to monitor changes in the surface composition of the P22G phosphor during electron bombardment. When the P22G phosphor powder was exposed to the electron beam in a water-rich O₂ ambient, a chemically limited ZnO layer was formed on the surface. The electron beam degradation of the P22G phosphor powder was also performed in a dry O₂ ambient and a layer of ZnSO₄ was formed on the surface. The ZnSO₄ formation decayed exponentially with time and it is postulated that this was due to the diffusion of the charge reactants through the ZnSO₄ film to the reaction interfaces. The P22G phosphor exposed to the electron beam in an Ar ambient and to the other gas mixtures degraded at a lower rate than in the case of the O₂ ambient. This suggests that Ar and CO_x may suppress the degradation of the P22G phosphor powder.     

Photoluminescence of liquid-crystal azo derivatives in nanopores

Optics and Spectroscopy - The fluorescence of the nematic liquid crystal n-butyl-n′-methoxyazoxybenzene (BMAOB) in the form of a layer and in porous glasses with pores of different diameter...     

Viscoelastic properties of nanostructured natural rubber/polystyrene interpenetrating polymer networks

The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (T_g's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the T_g values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003     

Bounds and Inequalities for the Perron Root of a Nonnegative Matrix

In this paper, bounds and inequalities for the Perron root of a nonnegative matrix, extending and complementing the classical theorems of Frobenius and Ostrowski in terms of (deleted) row and column sums, are presented. All the results are derived by using the same approach, based on the monotonicity property of the Perron root. Bibliography: 12 titles.     

Preface

Journal of Statistical Physics -     

Appearance of anomalous phase in <Superscript>4</Superscript>He crystal in the presence of small <Superscript>3</Superscript>He impurity

The kinetics of formation of an anomalous phase from a solution with a small ³He impurity was studied in the temperature range 0.2–0.7 K up to a supersaturation of ～30 mbar. The phase diagram was determined for normal and anomalous growths. It is found that, in the presence of impurities, the formation of a fast-growing state is retarded. This experimental fact indicates that the dissipative processes in fluids have an appreciable effect on the phase formation kinetics. The retardation is, possibly, caused by the direct interaction of an impurity with the crystal surface.