Distribution of heavy metal concentrations in surface sediments in Dubai Creeks, United Arab Emirates

Dubai is developing rapidly and many developmental activities are concentrated around its Creek. The present study reports the lateral distribution of heavy metals and compares it with local historical record of heavy metal concentrations. For this purpose surface sediment samples were collected and analyzed for metal contents, total organic carbon content (TOC), mineralogy and grain size. The percentages of the different grain size fraction of the collected sediments were as follow 65% for sand size, 15% for silt size fraction, and the rest accounted for clay size fraction. The microscopic analyses indicate that the sediment composed mainly from carbonate and quartz with traces of rock fragments. Such mineral composition is not believed to be a potential source of heavy metal. The study found that the average recorded heavy metal concentrations in the collected sediment samples were 87, 96, 127, 38.5, and 279 ppm for Cr, Cu, Ni, Pb, and Zn, respectively. Those values were slightly higher than metal concentrations recoded in 2001 with 1.22 (Cr), 2.5 (Cu), 2.87 (Ni), 0.69 (Pb), and 2.1 (Zn) folds. However, in 2001 and 2003 the measured metal contents, along the creek, were lower than those of the average earth crust. Along the Creek most metals recorded the highest concentrations in the upper reach of the Creek. The distribution of the measured heavy metals was not affected significantly with the TOC values. The present study also documented obvious related point sources of pollution.     

Comparison of Spectral Matching Algorithms for Identifying Natural Salt Crusts

This paper presents a comparison between the capabilities of different spectral matching algorithms to indentify the spectra of samples from salt crusts obtained by a hand-operated spectroradiometer. The following algorithms have been used: absolute difference; squared difference; derivative difference; Euclidean vector distance; and correlation coefficient. As the investigations have shown, the results depend on the method used. For example, the correlation coefficient algorithm yielded the best results, next come the squared derivative, the Euclidean vector difference, and the absolute difference algorithms. It has been found that automated search of spectra of salt crusts does not permit exact identification of the unknown spectra of salts by means of the existing spectra libraries. Besides the quality of the algorithms and libraries used, the discrepancy between the results of matching is also due to the inherent factors related to the nature of the salt crusts, such as variations in the layering, moisture content, grain size, etc. However, in the case of large databases of the spectra of salts or minerals, the above algorithms can be useful for reducing the search to a small number of spectra of interest which should subsequently be interpreted in a conventional manner.     

Further developments in the modelling of a sequential chromatographic refiner unit

Summary A classical plate-type model developed to simulate the separation of binary mixtures by sequential semicontinuous chromatography is modified by the inclusion of a separate expression to account for the effects of solute concentration on the feed plate. The improved model is tested on three systems of different separation difficulty, for which experimental data are available. Comparison of experimental and simulated separations is achieved by consideration of the solute concentration profiles. In determining the success of the simulation, particular note is made of profile shape, feed point location and concentration levels. Best agreement between experimental and simulated profiles is shown to exist for high separation factor systems at low flowrates and low temperatures. Relatively poor agreement for difficult systems at higher flowrates is attributed to phase changes, column temperature effects and the influence of the anti-Langmuir shape of the absorption isotherm.     

Chemical and environmental implications of visible and near-infrared spectral features of salt crusts formed from different brines

This work describes a laboratory experiment intended to study the formation and spectral reflectance properties of stratified salt crusts that cause severe environmental degradations to soil and water resources in arid regions. Salt crusts were prepared by evaporating three types of saline solutions consisting of i) NaCl - Na2SO4, ii) Na2SO4 - MgSO4, and iii) NaCl - MgSO4 at an initial concentrations of 50 mmol L(-1). They were examined for evaporite mineralogy using X-ray diffraction, optical and reflected microscopes, and for spectral reflectance with a high-resolution spectroradiometer (GER 3700) in the visible and near-infrared regions (400-2500 nm). The study documented chemical and environmental implications of the spectral properties of salt formed from the studied saline-systems. The reported results can be used to understand remotely sensed signatures of salt crusts and their implications.     

Application of NMI-TfCl-mediated amide bond formation in the synthesis of biologically relevant oxadiazole derivatives employing less basic (hetero)aryl amines

Molecular Diversity - We herein report a modified methodology for the synthesis of some oxadiazoles linked to amides under mild conditions. The developed protocol using NMI-TfCl has been found to...     

Nanocrystalline formation and optical properties of germanium thin films prepared by physical vapor deposition

Amorphous and nanocrystalline germanium thin films were prepared on glass substrates by physical vapor deposition (PVD). The influence of thermal annealing on the characteristics of the Ge thin films has been investigated. X-ray diffraction (XRD) and SEM show amorphous structure of films deposited at room temperature. After thermal annealing, the crystallinity was improved when the annealing temperature increases. The Ge thin films annealed at different temperatures in air were nanocrystalline, having the face-centered cubic structure with preferred orientation along the 〈1 1 1〉 direction. The nanostructural parameters have been evaluated by using a single-order Voigt profile analysis. Moreover, the analysis of the optical transmission and reflection behavior was carried out. The values of direct and indirect band gap energies for amorphous and nanocrystalline phases are 0.86±0.02, 0.65±0.02 and 0.79±0.02, 0.61±0.02 eV, respectively. In addition, the complex optical functions for the wavelength range 600-2200 nm are reported. The refractive index of the nanocrystalline phase drops from 4.80±0.03 to 2.04±0.02, and amorphous phase changes from 5.18±0.03 to 2.42±0.02 for the whole wavelength range. The dielectric functions ε₁ and ε₂ of the deposited films were recorded as a function of wavelength within the range from 600 to 2200 nm.