Improved Stability Characteristics Research Articles

Characterization of H-Y and Cr-Y Zeolite Catalysts during the Oxidative Destruction of CFC11 and CFC12

The long term stability-deactivation characteristics of two Y zeolite catalysts, namely H-Y and cation exchanged Cr-Y, were studied during the oxidative destruction of CFC11 and CFC12 feeds. Experiments were carried out at 300°C and 5000 h−1 space velocity. Properties of the catalysts including activity, selectivity, surface area, acidity, composition, and crystallinity were determined as a function of reaction time. Comparison of these properties with time indicated a significantly higher degree of deactivation for the H-Y catalyst than for the Cr-Y catalyst. The most probable reasons for the improved stability characteristics of the Cr-Y catalyst were the greater stability of the zeolite matrix due to multivalency of the exchanged Cr cation, and also the Deacon reaction characteristic of Cr3+, which converted HCl produced during the destruction of CFCs into Cl2, thereby restoring the zeolite acid sites.

High-performance and highly stable 03-nm-full-width-at-half-maximum interference optical filters

Fabrication of very-narrow-bandpass optical tunable filters [(0.3 nm full width at half-maximum) (FWHM)] is reported. To improve the film densities, the O(2) ion-assisted deposition-method is used in the fabrication. In the succession of high- and low-refractive-index layers, the commonly used TiO(2) material is replaced by Ta(2)O(5), which suits the ion-assisted fabrication technique. The relative thicknesses of the filter multilayer structure of 1/2/1 are modified to 0.998/2.007/0.998, which reduces the shift difference in the central wavelengths with regard to the p and s polarizations when the filter is tilted. These improvements enabled fabrication of 0.3-nm-FWHM optical tunable filters with improved stability characteristics.

Magnet cooling economics

The recommendation to use superfluid helium II in superconducting magnet design has become more prevalent in recent years. Advanced fusion reactor studies such as the Mirror Advanced Reactor Study recently completed by the Lawrence Livermore National Laboratory (LLNL) have based superconducting magnet design on the use of He II because of reduced magnet volume, improved stability characteristics, or increased superconductor critical current at fields above 9 Tesla. This paper reports the results of a study to determine the capital costs ($/watt) and the operating costs (watts/watt) of refrigeration systems in the 1.8K to 300K temperature range. The cost data is applied to a 1.8K magnet that is subject to neutronic heating wherein the magnet case is insulated from the winding so that the case can be cooled at a higher temperature (less costly) than the winding. The life cycle cost (capital plus operating) is reported as a function of coil temperature and insulation thickness. In some cases there is an optimum, least-cost thickness. In addition, the basic data can be used to evaluate the impact of neutron shielding effectiveness trades on the combined shield, magnet, cryorefrigerator, and operating life cycle cost.

Fifth and sixth order PECE algorithms based on g-splines with improved stability characteristics

In this note fifth and sixth order PECE algorithms are presented. The corrector formulae are derived by using natural g-splines. The resulting PECE algorithms which use the Schoen predictor have larger regions of absolute stability and smaller truncation errors than the Krogh and Schoen algorithms of corresponding order.

Predictor-Corrector Methods of High Order With Improved Stability Characteristics

Some new predictors are presented for use with the Adams-Moulton correctors of orders 4 through 8. The resulting algorithms have better stability characteristics than the usual ones which employ the Adams Bashforth predictors and at the same time require no additional storage. The regions of absolute and relative stability for the methods mentioned above and for the iterated Adams-Moulton correctors are given. Results obtained using the various methods are compared.