The variation of trace element concentrations in single human head hairs

The concentrations of nine trace elements in segments of individual human head hairs have been determined by neutron activation analysis. Concentration variations have been studied along individual hairs, among hairs plucked from various locations on the scalp, among hairs in different phases of the growth cycle, and before and after hair cleaning. Recent atomic absorption analysis data indicate strong concentration fluctuations in successive single hair segments of 2 to 5 mm in length. The results are discussed in a forensic context. Work supported by the National Research Council of Canada under Grant No. A2510, by the Canada Council through a bursary to D. Maes, by a grant from the President's Research Grant Fund of Simon Fraser University, and under a contract with the Department of the Solicitor-General of Canada through the Royal Canadian Mounted Police.     

Einwirkung der Oberfl?chenspannung auf die Kapillarviskosimetrie bei biologischen Materialien

Ohne Zusammenfassung     

Raman spectroscopy of calcium aluminate glasses and crystals

Solar furnace melting and fast-quench techniques have been used to prepare calcium aluminate glasses from 75 mol% CaO to 82 mol% Al₂O₃, which have been studied by Raman spectroscopy. The CaAl₂O₄ glass spectrum may be interpreted in terms of a fully-polymerized network of tetrahedral aluminate units, which is depolymerized on addition of CaO component analogous to binary silicate systems. The spectra of glasses with higher alumina content than CaAl₂O₄ may not be simply interpreted and a structural model is proposed which would be consistent with the glass spectra and with observed crystal structures along the CaAl₂O₄Al₂O₃ join. This model suggests formation of highly condensed aluminate tetrahedral on initial addition of alumina, with the appearance of aluminate polyhedra of higher average coordination at higher alumina content. Similar high coordination polyhedral are also suggested for a limited composition range along the CaOCaAl₂O₄ join. These interpretations are compared with the results of a previous study in the SiO₂Al₂O₃ glass system.     

Spatio-temporal dynamics of the NO + NH3 reaction on polycrystalline platinum

Spontaneous reaction rate oscillations and spatio-temporal patterns have been observed by mass spectrometry and photoemission electron microscopy (PEEM) during the reduction of NO by NH₃ on polycrystalline platinum at 1 × 10⁻⁴ Torr and temperatures from 460-520 K. The appearance of both oscillations and patterns was found to be strongly dependent on the gas phase composition and the temperature. In addition, the overall dynamics of the catalyst were found to be dominated by the nonlinear behavior of Pt(1 0 0) type grains, while other types of grains did not participate. In contrast to previous studies, a large number of complex multimodal oscillations were observed, particularly as the coupling between the surface and the gas phase was increased. The appearance of these complex oscillations demonstrates the importance of gas phase coupling to understanding catalytic reactions, even in high vacuum systems.     

Structure, bonding, and phase relations in Bi2Sn2O7 and Bi2Ti2O7 pyrochlores: new insights from high pressure and high temperature studies

One of the key points of interest in pyrochlore materials containing bismuth derives from the dielectric properties of some such materials that are linked to the displacements of the bismuth atoms from the ideal site. This study uses high pressure to probe the variations in, and causes of, these displacements. Under compression Bi(2)Ti(2)O(7) does not undergo any phase changes, but Bi(2)Sn(2)O(7) undergoes a similar series of changes to those observed during heating. The trigonal β-Bi(2)Sn(2)O(7) structure is solved from high temperature powder neutron diffraction data and hence the sequence of phases observed in Bi(2)Sn(2)O(7) is discussed for the first time. The variation in Bi displacements can be considered in terms of the frustration of the tetrahedral lattice that accommodates them. It can also be inferred that the main driver for Bi displacement is a deficiency in the bond valence sum of bismuth.