Raman scattering in low wavenumber region as a new probe to structural properties of microcrystalline silicon

The structural properties of microcrystalline silicon (μc-Si) are studied by Raman scattering. It is found that the intensity of each Raman band closely correlates with the absorption coefficient in the interband region and that the Raman band at ca. 150 cm^?1 is a sensitive probe to randomness of Si-Si bonding structure in μc-Si.     

Mode of oxidations of organosulfur compounds: Example of nucleophilic oxygenations of thiolsulfinates

Two types of oxygenative oxidations (Nucleophilic and Electrophilic Oxidations) of sulfur atom are proposed and a typical mode of nucleophilic oxidation is shown with a few unsymmetrical thiolsulfinates.     

The chemical form and acute toxicity of arsenic compounds in marine organisms

A method for the separation and identification of inorganic and methylated arsenic compounds in marine organisms was constructed by using a hydride generation/cold trap/gas chromatography mass spectrometry (HG/CT/GC MS) measurement system. The chemical form of arsenic compounds in marine organisms was examined by the HG/CT/GC MS system after alkaline digestion. It was observed that trimethylarsenic compounds were distributed mainly in the water-soluble fraction of muscle of carnivorous gastropods, crustaceans and fish. Also, dimethylated arsenic compounds were distributed in the water-soluble fraction of Phaeophyceae. It is thought that most of the trimethylated arsenic is likely to be arsenobetaine since this compound released trimethylarsine by alkaline digestion and subsequent reduction with sodium borohydride. The major arsenic compound isolated from the water-soluble fraction in the muscle and liver of sharks was identified as arsenobetaine from IR, FAB Ms data, NMR spectra and TLC behaviour. The acute toxicity of arsenobetaine was studied in male mice. The LD₅₀ value was higher than 10 g kg⁻¹. This compound was found in urine in the non-metabolized form. No particular toxic symptoms were observed following administration. These results suggest that arsenobetaine has low toxicity and is not metabolized in mice. The LD₅₀ values of other minor arsenicals in marine organisms, trimethylarsine oxide, arsenocholine and tetramethylarsonium salt, were also examined in mice.     

Relative stability of η-cyclopentadienyl(olefin)ruthenium cations: The first estimation of the nature of the Ru-olefin bond

Relative stability in coordination of substituted styrene derivatives to [Ru(η-C₅H₅)(dtpe)]⁺ (dtpe = 1,2-bis(di-p-tolylphosphino)-ethane) was determined by NMR spectroscopy to reveal unusually weak substituent dependency of the stability.     

High field magnetization of Y2Co7 and YCo3 hydrides

The magnetization curves for the Y₂Co₇H_x and the YCo₃H_x systems have been measured at 4.2 K in the pulsed high magnetic fields up to 280 kOe. The metamagnetic transition is observed in the β and the γ hydrides except for Y₂Co₇H₃ and YCo₃H₁, which is interpreted in terms of the itinerant electron metamagnetism.     

Remarkable Change in Fluorescence Emission of Poly(diphenylacetylene) Film via in situ Desilylation Reaction: Correlation with Variations in Microporous Structure,Chain Conformation,and Lamellar Layer Distance

Fluorescence (FL) emission properties, microporous structures, energy‐minimized chain conformations, and lamellar layer structures of the silicon‐containing poly(diphenylacetylene) derivative of p‐PTMSDPA before and after desilylation were investigated. The nitrogen‐adsorption isotherms of p‐PTMSDPA film before and after desilylation were typical of type I, indicating microporous structures. The BET surface area and pore volume of the p‐PTMSDPA film were significantly reduced after the desilylation reaction, simultaneously, its FL emission intensity remarkably decreased. The theoretical calculation on both model compounds of p‐PTMSDPA and its desilylated polymer, PDPA, showed a remarkable difference in chain conformation: The side phenyl rings of p‐PTMSDPA are discontinuously arranged in a zig‐zag pattern, while the PDPA is continuously coiled in a helical manner. The lamellar layer distance (LLD) in the p‐PTMSDPA film significantly decreased after the desilylation reaction.

     

Global dynamics of a class of SEIRS epidemic models in a periodic environment

In this paper, we study a class of periodic SEIRS epidemic models and it is shown that the global dynamics is determined by the basic reproduction number R₀ which is defined through the spectral radius of a linear integral operator. If R₀<1, then the disease free periodic solution is globally asymptotically stable and if R₀>1, then the disease persists. Our results really improve the results in [T. Zhang, Z. Teng, On a nonautonomous SEIRS model in epidemiology Bull. Math. Biol. 69 (8) (2007) 2537-2559] for the periodic case. Moreover, from our results, we see that the eradication policy on the basis of the basic reproduction number of the time-averaged system may overestimate the infectious risk of the periodic disease. Numerical simulations which support our theoretical analysis are also given.