[en] Multivariate statistical analysis identified the heavy metal accumulation layers of sediment profiles and showed the various sources of metals in the estuary. - The concentrations and chemical partitioning of heavy metals in the sediment cores of the Pearl River Estuary were studied. Based on Pearson correlation coefficients and principal component analysis results, Al was selected as the concentration normalizer for Pb, while Fe was used as the normalizing element for Co, Cu, Ni and Zn. In each profile, sections with metal concentrations exceeding the upper 95% prediction interval of the linear regression model were regarded as metal enrichment layers. The heavy metal accumulation mainly occurred at sites in the western shallow water areas and east channel, which reflected the hydraulic conditions and influence from riparian anthropogenic activities. Heavy metals in the enrichment sections were evaluated by a sequential extraction method for possible chemical forms in sediments. Since the residual, Fe/Mn oxides and organic/sulfide fractions were dominant geochemical phases in the enriched sections, the bioavailability of heavy metals in sediments was generally low. The ²⁰⁶Pb/²⁰⁷Pb ratios in the metal-enriched sediment sections also revealed the influence of anthropogenic sources. The spatial distribution of cumulative heavy metals in the sediments suggested that the Zn and Cu mainly originated from point sources, while the Pb probably came from non-point sources in the estuary

[en] The crystal structure of the high-T/sub c/ superconductor Ba₂YCu₃O/sub 7+//sub x/ at 124 and 71 K was refined by Rietveld analysis of neutron diffraction data. We found that at 124 and 71 K the structure is of the same space group Pmmm, but when the temperature is decreased and passes the critical temperature T/sub c/, 0.12 of the oxygen population on the one 1e site transfers to the 1b site. This remarkable change in the structure can be related to its superconductivity

[en] The crystal structure of the high-T/sub c/ superconductor Ba₂YCu₃O/sub x/ at 750 ⁰C was elucidated using Rietveld analysis of neutron powder diffraction data. We find that the phase is tetragonal at this temperature, with space group P4/mmm, and lattice constants a = 3.8823 A and c = 11.826 A. This is an oxygen deficient triperovskite, in which Ba and Y ions are ordered along the c axes in Ba-Y-Ba-Ba sequence. The occupation factors of the oxygen sites 4i, 2g, 2f are 0.97, 1.00, 0.33, respectively. The total number of the oxygen atoms per unit cell is 6.54

[en] A new technique utilizing a high-power-density pulsed ion beam for modification of material surfaces is presented. The power density of the pulsed ion beam ranges between 10⁴ and 10⁷ w cm^-2, the kinetic energy is 1 to 5 KeV, the deposition energy is of the order of 1 to 10 J cm^-2 and the pulsed duration is about 60 μsec. The post-treatment samples were analysed using Auger electron spectroscopy, scanning electron microscopy, X-ray diffractometry, and Vicker's microhardness tester. It is found that the concentration of the injected particles has a Gaussian distribution. The thermal zone induced by the fast heating-cooling process forms a white-bright layer, indicating that there are new carbides and nitrides produced in the surface layer, which increases the microhardness of the surface. (author)

[en] The generalized phonon density of states for the high-T_c superconductor YBa₂Cu₃O_7.1 with high Meissner effect (50%) and for its retreated sample with low Meissner effect (15%) at T=300 K and T=86 K respectively was measured by using inelastic neutron scattering method. The density of states of the superconductor YBa₂Cu₃O_7.1 at temperatures of both 300 K and 86 K shows a similar energy spectrum below 95 meV. However, above this energy there are evident softening of modes at 86 K. In addition, a large decrease of 92 meV peak in the density of states for a sample with lower Meissner effect was observed, this effect is supposed to be a result of an increase of vacancies on O₄ site

[en] Two kinds of coating techniques, including magnetron sputtering deposition and electroless plating, were used to deposit Ni films onto cenosphere particles. An ultrasonic vibrating generator was equipped on a conventional magnetron sputtering apparatus to prevent the substrates from accumulating. The X-ray diffraction analysis, field emission scanning electron microscope and atomic force microscope were used to characterize the performance of the deposited Ni films. The surface morphology was quite smooth and the films were well compacted for the coatings fabricated by magnetron sputter deposition, whereas large roughness and poor compactness were found in the electroless coated Ni films. Nevertheless, the deposition rate coated by electroless plating was found to be faster than that coated by magnetron sputtering. In addition, Ni films coated on cenosphere particles by electroless plating appeared to have a greater high specific surface area than that coated by magnetron sputtering. (author)

[en] This paper reports both the tetragonal and orthorhombic phases for YBa₂(Cu_1-xFe_x)₃O_y(x = 0.07, 0.10, and 0.12) formed an investigated. It was found that the phase structure not only depends on the concentration (x) of Fe, but also depends on the synthesis process of the sample. Basically the superconductivity of the Fe doped samples is still associated with the orthorhombic phase