Effect of polymerization catalysts on the microstructure of P(LLA-co-εCL)

The copolymerization of L ,L -lactide and ε-caprolactone was carried out using antimony trioxide and stannous octoate as catalysts. The effect of polymerization catalysts on the physical and the chemical microstructures of this copolymer was investigated by ¹³C NMR and DSC analysis. Antimony trioxide causes more random sequence distribution within the copolymer chain due to its higher transesterification characteristic than stannous octoate. The copolymer samples made with the antimony trioxide catalyst seem to have more amorphous phase structure, than those prepared using stannous octoate which are semicrystalline for the entire compositional range due to blocky copolymer sequences. © 1994 John Wiley & Sons, Inc.     

Finger Replacement Method for Rake Receivers in the Soft Handover Region

We propose and analyze a new finger replacement technique that is applicable for RAKE receivers in the soft handover (SHO) region. More specifically, the receiver uses in the SHO region by default the strongest paths from the serving base station (BS) and only when the combined signal-to-noise ratio falls below a certain pre-determined threshold, the receiver uses more resolvable paths from the target BS to improve the performance. Instead of changing the configuration for all fingers, the receiver just compares the sum of the weakest paths out of the currently connected paths from the serving BS with the sum of the strongest paths from the target BS and selects the better group. Using accurate statistical analysis, we investigate in this letter the tradeoff between error performance, average number of required path comparisons, and SHO overhead offered by this newly proposed scheme.     

Elucidation of the structure of a highly efficient blue emitting lithium boron 2-(2-hydroxyphenyl) benzoxazole

We have studied the new blue electroluminescent material (compound 1) synthesized from the reaction of 2-(2-hydroxyphenyl)benzoxazole with LiBH₄ according to Tao's procedure [J. Am. Chem. Soc. 121 (1999) 9447; Appl. Phys. Lett. 75 (1999) 1665] Compound 1 showed the UV and the PL peak at 366 and 432 nm, respectively. The manufactured device (ITO/compound 1(600 Å)/Al) showed the EL peak at 412 nm. However, the structure of compound 1 was not fully identified as examined by experiment. In order to disclose the structure of compound 1, we proposed several possible compounds and calculated each compound, using the following methods. Hartree–Fock with the 3-21G(d) basis set was used for energy calculation and geometry optimizations of those compounds. Excitation energies were obtained from time-dependent density functional theory (TD-DFT) using the B3LYP functional with the 3-21G(d) basis set. As a result, [(box)(boxH)Li]₂ was found to be one of the possible compounds which had the most stable geometry structure. Its optical properties showed remarkably good agreement with the characterization data of compound 1. In addition, the structure of [(box)(boxH)Li]₂ was also compared well with that of LiBq₄ which was reported by the groups of Tao and was argumentatively asserted by Radu and coworkers [J. Am. Chem. Soc. 125 (2003) 880].     

The limiting spectral distribution function of large dimensional random matrices of sample covariance type

Results on the analytic behavior of the limiting spectral distribution of matrices of sample covariance type, studied in Marcěnko and Pastur [2], are derived. Using the Stieltjes transform, it is shown that the limiting distrbution has a continuous derivative away from zero, the derivative being analytic whenever it is positive, and the behavior of it resembles the behavior of a square root function near the boundary of its support.     

Estimation of system reliability for redundant stress-strength model

The reliability and an estimate for it are derived for series-parallel and parallel-series stress-strength model under assumption that all components are subjected to a common stress. We also obtain the asymptotic normal distribution of the estimate.     

Government—Media—Audiences: Private Sector Participation in Public Service Broadcasting: The Case of Kenya

Commercial advertising and religious broadcasts are allowed in order to raise revenues, but at the same time the public broadcasting organization must ensure that the stability of the state is not threatened by alternative voices.     

Ionization spectroscopy of a DNA base: vacuum-ultraviolet mass-analyzed threshold ionization spectroscopy of jet-cooled thymine

The high-resolution ionization spectroscopy of DNA bases is reported for the first time. Vacuum-UV mass-analyzed threshold ionization (VUV-MATI) spectrum of jet-cooled thymine provides not only the most precise ionization potential but also its vibrational structure in the ground cationic state.