Electron spin emission spectra from pairs of radicals

Electron spin emission from both radicals of a pair has been observed. It is demonstrated that it is possible to explain the polarization by the radical pair mechanism if nuclear relaxation is fast enough. The extent of ST_?1 mixing induced by an anisotropic g-factor is deduced.     

Generation of elastic stress waves at a corner junction of square rods

Fourier techniques are used to predict the transmitted and reflected waves at an L-joint in rods of square cross-section. The expressions for both longitudinal and flexural wave components are derived for a variable angle of connection for the rods. These components are evaluated for a 90° angle of connection and an arbitrary longitudinal input pulse. The predicted waves are compared with experimental results at a number of locations away from the joint for an input pulse with wavelengths which are large compared with the cross-sectional dimensions of the rods. Good agreement is obtained for all waves. For the flexural wave this agreement is shown to improve with distance from the joint. This confirms the adequacy of elementary and Timoshenko beam theory to describe the longitudinal and flexural wave motions respectively. The results demonstrate the applicability of Fourier techniques to the solution of stress wave propagation in rods.     

Performance evaluation of scheduling control of queueing networks: Fluid model heuristics

Motivated by dynamic scheduling control for queueing networks, Chen and Yao [8] developed a systematic method to generate dynamic scheduling control policies for a fluid network, a simple and highly aggregated model that approximates the queueing network. This study addresses the question of how good these fluid policies are as heuristic scheduling policies for queueing networks. Using simulation on some examples these heuristic policies are compared with traditional simple scheduling rules. The results show that the heuristic policies perform at least comparably to classical priority rules, regardless of the assumptions made about the traffic intensities and the arrival and service time distributions. However, they are certainly not always the best and, even when they are, the improvement is seldom dramatic. The comparative advantage of these policies may lie in their application to nonstationary situations such as might occur with unreliable machines or nonstationary demand patterns.     

Analysis of anomalous X-ray diffraction effects of isotactic polystyrene gels and its implications for chain conformation and isomeric homogeneity

Oriented gels, obtained by high supercoolings of isotactic polystyrene solutions, exhibit unexpected “fiber-type” x-ray diffraction patterns. In particular a pronounced meridional reflection at a spacing of 0.51 nm, together with its successive orders, requires an extended, or nearly extended, chain conformation which appears irreconcilable with the stereochemistry of isotactic polystyrene. Furthermore, the value of 0.51 nm correlates directly with the axial projected repeat expected for two styrene monomer units. Two possible stereosequences merit atention: syndiotactic and syncephalic (head-to-head, tail-to-tail). In addition to the 0.51 nm meridional reflection, layer lines are observed with spacing 3.06 nm (6 × 0.51) which equate with 24 carbon–carbon bonds in the backbone. Cylindrically averaged Fourier transform calculations for the various models are compared with the observed x-ray results and the best fit is obtained for a 24/11 helix of isolactic polystyrene with the syncephalic stereosequence. This conclusion, however, clashes with the ¹³CNMR evidence which indicates that the polymer is essentially isotactic. The implications of these novel results in relation to gel crystallization are discussed.     

A Case Study on the Use of Intervention Analysis Applied to Traffic Accidents

This paper discusses the identification of the effects of outside interventions on a time series, using Intervention Analysis. Its aim is to act as a guide to other analyses and to enhance the literature on the important new technique of Intervention Analysis. A case is presented which concerns the effects of the lowering of the speed limit on traffic accidents.     

Infrared multiple photon dissociation spectra of proton- and sodium ion-bound glycine dimers in the N-H and O-H stretching region

The proton- and the sodium ion-bound glycine homodimers are studied by a combination of infrared multiple photon dissociation (IRMPD) spectroscopy in the N-H and O-H stretching region and electronic structure calculations. For the proton-bound glycine dimer, in the region above 3100 cm (-1), the present spectrum agrees well with one recorded previously. The present work also reveals a weak, broad absorption spanning the region from 2650 to 3300 cm (-1). This feature is assigned to the strongly hydrogen-bonded and anharmonic N-H and O-H stretching modes. As well, the shared proton stretch is observed at 2440 cm (-1). The IRMPD spectra for the proton-bound glycine dimer confirms that the lowest energy structure is an ion-dipole complex between N-protonated glycine and the carboxyl group of the second glycine. This spectrum also helps to eliminate the existence of any of the higher-energy structures considered. The IRMPD spectrum for the sodium ion-bound dimer is a much simpler spectrum consisting of three bands assigned to the O-H stretch and the asymmetric and symmetric NH 2 stretching modes. The positions of these bands are very similar to those observed for the proton-bound glycine dimer. Numerous structures were considered and the experimental spectrum agrees with the B3LYP/6-31+G(d,p) predicted spectrum for the lowest energy structure, two bidentate glycine molecules bound to Na (+). Though some of the structures cannot be completely ruled out by comparing the experimental and theoretical spectra, they are energetically disfavored by at least 20 kJ mol (-1).