Choosing a Spin-Lock Transmitter Position Which Minimizes HOHAHA Distortions of ROESY Spectra. Observation of a Correlation-Time Dependence of Frequency Offset

A technique for reliably selecting a transmitter position for rotating-frame NOE experiments which minimize scalar coupling artifacts is described. The technique makes use of the COSY spectrum of the molecule in question. The method is illustrated by application to thiostrepton, an antibiotic of molecular weight 1665. For an individual compound, the range of transmitter settings over which HOHAHA distortions are observed is found to depend on the molecular correlation time of the compound under study. The origin of this effect is discussed in terms of rotating-frame relaxation during the spin-lock period.     

Dissipative solitons in active Bragg gratings

Motionless and moving bright dissipative solitons in an optical fiber with a Bragg grating and non-linear amplification and absorption are found numerically and studied. These solitons form a one-parameter family whose parameter—the soliton velocity—can continuously change in a certain range. The presence of saturation of the nonlinearity is necessary for stability of such solitons. Neglect of saturation of the cubic-in-field polarization of the medium results in the instability of the possible localized structures.     

Unconstrained geometry complexes: Ethylene/α‐olefin copolymerizations with a tetramethyldisilyl‐bridged Cp‐amido titanium complex

A new disilyl‐bridged complex, [(N‐tert‐butylamido)(3‐indenyl)tetramethyldisilyl]titanium dichloride ( 3 ), was synthesized and activated with methylaluminoxane (MAO) for propylene homopolymerization and ethylene/propylene and ethylene/1‐hexene copolymerizations. A polypropylene with a slight isotactic enrichment was obtained. The number of regioerrors present in the polypropylene was somewhat smaller than that found in most polypropylenes made from monosilyl‐bridged [(N‐tert‐butylamido)(3‐indenyl)dimethylsilyl]titanium dichloride. The regioerrors detected in the copolymers obtained from 3 /MAO were on the order of the amounts observed in polymers made with the monosilyl‐bridged constrained geometry catalysts. Ethylene copolymers of propylene and 1‐hexene had random sequence distributions and showed significant comonomer incorporation. Because of the presence of regioerrors, a modified method for determining the monomer composition and sequence distribution was developed from the direct measurement of the monomer content from the number of methylene and methine carbons per polymer chain, regardless of propylene inversion. An estimate of the error in the copolymerization reactivity ratio determination for regioirregular ethylene/α‐olefin copolymers was obtained by the calculation of the reactivity ratios from monomer dyad sequences, with consideration given to the contribution of major regioirregular sequences. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3840–3851, 2005     

Extensions of zip rings

A ring R is called right zip provided that if the right annihilator r_R(X) of a subset X of R is zero, r_R(Y)=0 for a finite subset Y⊆X. Faith [5] raised the following questions: When does R being a right zip ring imply R[x] being right zip?; Characterize a ring R such that Mat_n(R) is right zip; When does R being a right zip ring imply R[G] being right zip when G is a finite group? In this note, we continue the study of the extensions of noncommutative zip rings based on Faith's questions.     

Suppression of particle generation in a plasma process using a sine-wave modulated rf plasma

Sine-wave modulated rf plasma has been used to control particle generation and growth in a plasma-enhanced chemical vapor deposition of silicon dioxide thin films using TEOS/O₂. The density and the size of particles generated in the plasma are greatly reduced when the plasma is modulated with sine-wave modulation at low modulation frequency (<1000 Hz). In addition, particle contamination on the films is significantly reduced also for nanoparticles, and the film growth rates at the range of modulation frequencies where particle generation are greatly reduced do not decrease appreciably. Compared to its counterpart pulse-wave modulation plasma, the sine-wave modulation plasma has demonstrated a better performance in terms of reduction of particle generation and film contamination, and of film growth rate. Thus, the sine-wave modulation plasma has shown as a promising method to be applied in the production of thin film with a high deposition rate and a low particle contamination.     

Bayesian analysis of constant elasticity of variance models

This paper focuses on the estimation of some models in finance and in particular, in interest rates. We analyse discretized versions of the constant elasticity of variance (CEV) models where the normal law showing up in the usual discretization of the diffusion part is replaced by a range of heavy‐tailed distributions. A further extension of the model is to allow the elasticity of variance to be a parameter itself. This generalized model allows great flexibility in modelling and simplifies the model implementation considerably using the scale mixtures representation. The mixing parameters provide a means to identify possible outliers and protect inference by down‐weighting the distorting effects of these outliers. For parameter estimation, Bayesian approach is adopted and implemented using the software WinBUGS (Bayesian inference using Gibbs sampler). Results from a real data analysis show that an exponential power distribution with a random shape parameter, which is highly leptokurtic compared with the normal distribution, forms the best CEV model for the data. Copyright © 2006 John Wiley & Sons, Ltd.     

A Three-Day Workweek Multiple-Shift Scheduling Model

Compressed workweeks have gained acceptance in many 7-days-a-week operations. This paper provides a multiple-shift workforce scheduling model and a simple algorithm for the 3-day workweek. The model presented here is of practical relevance and the algorithm is intuitive and simple enough to be implemented by hand. A scheduler planning to switch to a 3-day workweek but not certain how to schedule off-days and shifts, may find this paper helpful.     

Melting behavior of lamellae of isotactic polypropylene studied using hot-stage atomic force microscopy

The α- and β-form lamellae of isotactic polypropylene were developed at different temperatures. The melting behaviors of the lamellae were observed in real time at elevated temperatures using a hot-stage atomic force microscopy. The melting behavior of the α-form lamellae was determined by the lamellar defects. For the α-form lamellae developed at different undercoolings, the larger the undercoolings, the relatively higher amount of defect in the lamellae was observed. The lamellae with defects were melted into lamellar segments, and recrystallization took place during the heating process. The β-form lamellae had lower thermal stability, and they melted firstly and separately from that of α-form.