Preparation of 5-hydroxy-1-alkenyboronates from 1-alkynylboronates, Cp2ZrCl2/2EtMgBr, and aldehydes

1-Alkynylboronates form five-membered zirconacycles with Cp(2)ZrCl(2)/2-EtMgBr as indicated by deuterium labeling. The zirconacycles add aldehydes to form seven-membered zirconacycles. Hydrolysis of the latter provides 5-hydroxy-1-alkenylboronates in fair to good isolated yields. Both aliphatic and aromatic aldehydes undergo insertion.     

Cartan-decomposition subgroups of

For and , we give explicit, practical conditions that determine whether or not a closed, connected subgroup of has the property that there exists a compact subset of with . To do this, we fix a Cartan decomposition of , and then carry out an approximate calculation of for each closed, connected subgroup of .

     

Transition to turbulence in particulate pipe flow

We investigate experimentally the influence of suspended particles on the transition to turbulence. The particles are monodisperse and neutrally buoyant with the liquid. The role of the particles on the transition depends upon both the pipe to particle diameter ratios and the concentration. For large pipe-to-particle diameter ratios the transition is delayed while it is lowered for small ratios. A scaling is proposed to collapse the departure from the critical Reynolds number for pure fluid as a function of concentration into a single master curve.     

Formation of electrically active clusterized neural networks

Ordinarily, in vitro neurons self-organize into homogeneous networks of single neurons linked by dendrites and axons. We show that under special conditions they can also self-organize into neuronal clusters, which are linked by bundles of axons. Multielectrode array measurement reveals that the clusterized networks are also electrically active and exhibit synchronized bursting events similar to those observed in the homogeneous networks. From time-lapse recording, we deduced the features required for the neuronal clusterized versus homogeneous self-organization and developed a simple model for testing their validity.     

Variable-temperature microcrystal X-ray diffraction studies of negative thermal expansion in the pure silica zeolite IFR

Variable-temperature single-crystal X-ray diffraction using a synchrotron X-ray source has allowed the mechanism of negative thermal expansion in the pure silica zeolite IFR to be studied in greater detail than was previously possible over the temperature range 30-557 K. The results have allowed the changes in average atomic position with temperature to be measured and the structural features that are important in negative thermal expansion to be identified. The structure of zeolite IFR can be split into two regions: columns of fused rings that expand with temperature and the intercolumn regions, which tend to contract on heating. These competing changes combine to produce a material that contracts parallel to the crystallographic a and b axes and expands in the c-direction. Correlations between zeolite structure and thermal expansivity are also reported.     

The role of magnesium in the susceptibility of soldiers to noise-induced hearing loss

A number of studies have demonstrated that magnesium, administered prophylactically, can reduce the amount of hearing loss resulting from noise exposure. This study explored the possible role of naturally occurring body magnesium concentration in susceptibility of soldiers to noise-induced hearing loss. Participants were 68 adult males who had received extensive noise exposure over several years as a result of training with weapon systems. Each participant provided a pure-tone audiogram, blood sample, and noise-exposure history. A variety of pure-tone indices was correlated with serum magnesium levels as determined by atomic absorption spectroscopy. No significant correlations were observed between any audiometric index and body magnesium. The results of this study, therefore, do not support the hypothesis that there is a strong association between naturally occurring body magnesium and susceptibility to noise-induced hearing loss.     

An investigation of the bromination of 1,4-dihydropyridine rings

Conditions for bromination at the C3 and C5 positions of a 1,4-dihydropyridine (DHP) were investigated. The effect of base concentration, base type, reaction temperature, and solvent were examined. DHP derivatives with ester and amide moieties were synthesized and brominated. The bromine atoms can be replaced by other substituents, utilizing Suzuki cross coupling.