Occurrence of butyltin compounds in marine sediments and bivalves from three harbour areas (Saigon,Da Nang and Hai Phong) in Vietnam

A survey of organotin compounds comprising tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) in sediment and clam (Meretrix meretrix) was undertaken in Vietnam in 2003. Samples were collected from dry docks and cargo harbours in Ho Chi Minh (south), Da Nang (centre) and Hai Phong (north) cities. Measurable amounts of TBT, DBT and MBT were found in all samples. The total concentration of the butyltin compounds (ΣBTs) in sediment from shipyards and vessel repair yards (Nam Trieu, Song Cam, Lach Tray and Ba Son) were always higher than those measured in cargo ports (Hai Phong, Da Nang, and Sai Gon). The highest ΣBTs concentration (as tin: 122 ng g^?1 dry wt) was found in the sediment from Song Cam station, where seven shipyards are located. The lowest concentrations of ΣBTs occurred in sediments from the Da Nang and Hai Phong cargo ports (as tin: 21–22 ng g^?1 dry wt). This implies that the major source of BTs in the marine environment in Vietnam is from the shipbuilding activities. The ratio of TBT to Σ(MBT + DBT) in sediment was 0.67 ± 0.03 for all the sampling sites, indicating the recent use of TBT in Vietnam. For the clam (M. meretrix), the concentration of ΣBTs (as tin) varied in the range 11.2–60.1 ng g^?1 wet wt. There was a good correlation (R² = 0.85) between total organic matter‐normalized ΣBTs in sediment and hexane‐extractable organic matter‐normalized ΣBTs in clam soft tissue. The mean biota–sediment accumulation factors (organic carbon/lipid) for MBT, DBT and TBT in clam's soft tissue were found to be 1.83 ± 0.66, 1.44 ± 0.23 and 1.16 ± 0.47 respectively, indicating that sediment‐bound BTs might be an important source of contamination for the clam. Copyright © 2005 John Wiley & Sons, Ltd.     

Preparative Synthesis of Vinyl Diamondoids

We describe a convenient four-step preparation of 1- vinyl adamantane, 1- vinyl diamantane, and 4,9-divinyl diamantane from the respective diamondoid acetic acids in 50–80% isolated yields involving esterification, reduction, and hydrobromination/dehydrobromination.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

An approximate explicit constitutive relation for non-flowing granular materials

An approximate stress-strain relation is derived for a granular material composed of spherical elastic granules in contact. The material is assumed to be statistically homogeneous so that the effective stress tensor can be obtained by a volume average. The resulting stress-strain relation is markedly non-linear and begins with the term $\text{∥ε∥}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, where ε is the classical infinitesimal strain tensor. Some simple deformation fields are worked out.     

The flow past a sphere in a cylindrical tube: effects of intertia,shear-thinning and elasticity

Numerical solutions are presented for the flow past a sphere placed at the centreline of a cylindrical tube for Reynolds numbers ranging from 0 to 150, using a boundary element method. Fluids are modelled by a variety of constitutive equations including the Newtonian, the Carreau and the Phan-Thien-Tanner models. The influence of inertia, shear-thinning and fluid elasticity on the flow field, drag and the pressure drop force-drag ratio is examined. Some results are compared with available experimental data.     

Using oscillatory squeezing flow to measure the viscoelastic properties of dental composite resin cements during curing

We have investigated the rheological changes in two particulate-filled dental composite resin cements during the curing process using a Micro-Fourier Rheometer (MFR). In the MFR, the sample was sandwiched between two parallel plates, and pseudorandom small amplitude squeezing was applied by oscillating the upper plate over a range of frequencies. Fourier transforms of the displacement signal and the resulting time dependent force signal enabled the rapid determination of the dynamic properties G′ and G′′ over the frequency range 2π–200π rad/s . This technique permitted us to follow changes in the rheological properties of the resin cements through the setting period. A typical result was that G′ increased from 2×10³ Pa to 2×10⁵ Pa after about 120 s, and that G′′ changed from 4×10³ Pa to 4×10⁴ Pa over the same period at frequency 40π rad/s. We also found that the dental composite resin cements show linear viscoelastic behaviour over a range of strain amplitudes before curing, but the response becomes distinctly non-linear at the later stages of curing for strain amplitudes γ>0.067%.     

A Short Review of the Separation of Iridium and Rhodium from Hydrochloric Acid Solutions by Solvent Extraction

Iridium and rhodium are among the platinum group metals. The properties, production processes, and aqueous chemistry of both metals are reviewed. The separation of Ir(IV) and Rh(III) from hydrochloric acid solution is dependent on the characteristics of the solvent extraction systems. In most of the extraction conditions, Ir(IV) is selectively extracted over Rh(III) by either amines or neutral extractants. Rh(I) can be selectively extracted over Ir(III) by neutral extractants after Rh(III) is reduced in the presence of a reducing agent. The separation of these two metals using cationic extractants has also been reported. Although selective extraction of one metal over the other is possible, more efficient solvent extraction systems need to be developed.     

Transverse standing waves in a cylindrical duct with noise sources distributed along two generating lines

Tests were carried out to detect the transverse standing waves in a cylindrical duct with 24 noise sources regularly distributed along two generating lines. Pressure mappings were done and it was found that phase and force optimization of the noise sources would increase the pressure levels at cut-off frequencies. A splitter baffle installed along a pressure nodal plane would destroy the resonance.