Characterization of novolac resins based on p-tert-butylphenol by PMR spectroscopy

The direct silylation of tert-butylphenol formaldehyde resins with N,O-bis(trimethylsily)acetamide (BSA) has allowed a more complete analysis of these resins to be made with proton magnetic resonance (PMR) spectrometry. A quantitative determination of mixtures of the monomer, dimer, trimer, and tetramer may be carried out at 100 MHz.     

Spectroscopic diagnostics of temperature-controlled trench etching of silicon

Ernission from the plasma species CCl, CN, CO, N₂, and Si was monitored during trench etching of silicon with a CHCl,₃/ N, chemistry. The temperature of the backside of the wafer was recorded simultaneously. The emission response to experimentally induced perturbations of the plasma was found to be particularly informative. One such perturbation was a sudden change of the wafer temperature through control of the He pressure under the wafer. The other perturbation involved a drastic change of the N₂, flow rate. Our results confirm the mechanism of control of the trench profile through the temperature-dependent rate of deposition of polymers on the sidewalls during etch. Further, N₂, which certainly plays a crucial role in this chemistry, may engage in a surface reaction producing CN radicals; our data are consistent with this surface reaction. Finally, an algorithm was constructed for real-time monitoring of the selectivity of .silicon to the oxide mask; selectivity is shown to be very sensitive to the presence of N₂.     

Experimental results for multichannel feedforward ANC with noninvasive system identification

This paper presents experimental validation of a class of algorithms designed to enable active noise control (ANC) to function in environments when transfer functions change significantly over time. The experimental results presented are for broadband, local quieting in a diffuse field using a multichannel ANC system. The reverberant enclosure is an ordinary room, measuring approximately 1.4 x 2.4 x 2.4 m3 and containing a seated occupant, with six microphones defining the quiet zone near the occupant's ears. The control system uses a single reference signal and two error channels to drive four secondary sources. Using an ideal reference sensor, reduction in sound pressure level is obtained at the quiet-zone microphones averaged over the frequency range 50 to 1000 Hz with an occupant seated in the room. Two main results are presented: first for an adaptive cancelling algorithm that uses static system models, and second for the same algorithm joined with a noninvasive real-time system identification algorithm. In the first case better than 23 dB of performance is obtained if the occupant remains still through calibration and testing. In the second case, approximately 18 dB is obtained at the error microphones regardless of the motion of the occupant.     

Ethylene polymerization reactions with Ziegler–Natta catalysts. I. Ethylene polymerization kinetics and kinetic mechanism

Kinetics of ethylene homopolymerization reactions and ethylene/1-hexene copolymerization reactions using a supported Ziegler–Natta catalyst was carried out over a broad range of reaction conditions. The kinetic data were analyzed using a concept of multicenter catalysis with different centers that respond differently to changes in reaction parameters. The catalyst contains five types of active centers that differ in the molecular weights of material they produce and in their copolymerization ability. In ethylene homopolymerization reactions, each active center has a high reaction order with respect to ethylene concentration, close to the second order. In ethylene/α-olefin copolymerization reactions, the centers that have poor copolymerization ability retain this high reaction order, whereas the centers that have good copolymerization ability change the reaction order to the first order. Hydrogen depresses activity of each type of center in the homopolymerization reactions in a reversible manner; however, the centers that copolymerize ethylene and α-olefins well are not depressed if an α-olefin is present in the reaction medium. Introduction of an α-olefin significantly increases activity of those centers, which are effective in copolymerizing it with ethylene but does not affect the centers that copolymerize ethylene and α-olefins poorly. To explain these kinetic features, a new reaction scheme is proposed. It is based on a hypothesis that the Ti—C₂H₅ bond in active centers has low reactivity due to the equilibrium formation of a Ti—C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4255–4272, 1999     

Spectroscopic diagnostics of temperature-controlled trench etching of silicon

Emission from the plasma species CCI, CN, CO, N₂, and Si teas monitored during trench etching of silicon with a CHCl₃/ N, chernistrv. The temperature of the backside of the wafer was recorded simultaneously. The emission response to experimentally induced perturbations of the plasma was found to be particularly informative. One such perturbation teas a sudden change of the wafer temperature through control of the He pressure under the wafer. The other perturbation involved a drastic change of the N₂ flow rate. Our results confirm the mechanism of control of the trench profile through the temperature-dependent rate of deposition of polymers on the sidewalls during etch. Further, N₂, which certainly plays a crucial role in this chemistry, may engage in a surlàce reaction producing CN radicals; our data are consistent with this surlàce reaction. Finally, an algorithm tvas constructed for real-time monitoring of the selectivity of .silicon to the oxide mask; selectivity is shown to be very sensitive to the presence of N₂.     

Partitioning the complement of a simplex in PG(e,qd+1) into copies of PG(d,q)

In some projective spaces the complement of a simplex can be partitioned into disjoint copies of a higher or lower dimensional projective space of a different order. More precisely, let d and e be positive integers with e 2. We exhibit an embedding of PG(d,q) in PG(e,q^d+1) and show that the complement of a simplex in PG(e,q^d+1) may be partitioned into disjoint copies of embedded PG(d,q)'s, Each embedded PG(d,q) spans PG(e,q^d+1) whenever d e. These results are also true for PG(d,F) and PG(e,K) for infinite fields for which deg_F K=d+1 and the field extension is normal, separable, and cyclic.This research was supported in part by Grant Number A8027, Natural Sciences and Engineering Research Council of Canada.     

AlR2Cl/MgR2 combinations as universal cocatalysts for Ziegler–Natta,metallocene, and post‐metallocene catalysts

Combinations of dialkylaluminum chlorides and dialkylmagnesium compounds, when used at molar [AlR₂Cl]:[MgR₂] ratios ≥ 2, act as universal cocatalysts for all three presently known types of alkene polymerization catalysts—Ziegler–Natta, metallocene, and post‐metallocene. When these cocatalysts are used with supported Ti‐based Ziegler–Natta catalysts, they produce catalyst systems which are 1.5–2 times more active than the systems utilizing AlR₃ compounds as cocatalysts. Combinations of AlR₂Cl/MgR₂ cocatalysts and various metallocene complexes produce single‐center catalyst systems similar to those formed in the presence of MAO. The same cocatalysts activate numerous post‐metallocene Ti complexes containing bidentate ligands of a different nature and produce multicenter systems of very high activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3271–3285, 2009     

Elations and homologies in collineation groups of finite projective planes

Let G be a collineation group of a finite projective plane. The action of G on the centers and axes of non-identity elations and homologies is discussed. There are several results on the possible numbers of orbits of centers, axes, and center-axis pairs of homologies and elations of a particular order. Several results on the generation of homologies or elations by other homologies or elations reveal additional information on the structures formed by the centers and axes. Some sets of sufficient conditions for the centers and axes to form Desarguesian subplanes are given.     

Application of an acoustic noise removal method to aircraft-based atmospheric temperature measurements

An acoustic noise removal method is used to reject engine acoustical disturbances from aircraft-based atmospheric temperature measurements. Removal of engine noise from atmospheric temperature measurements allows a larger wave number range to be fit while quantifying the magnitude of atmospheric temperature turbulence. The larger wave number range was found to result in a more statistically certain spectral slope estimate, with up to a 50% reduction in the standard deviation of measured spectral slopes. The noise removal technique was found to break down under conditions of weak atmospheric temperature turbulence where the engine acoustical disturbance can be several orders of magnitude larger than atmospheric temperature turbulence.