Development of a coprecipitation system for the speciation/preconcentration of chromium in tap waters

A method for the speciation of chromium(III), chromium(VI) and determination of total chromium based on coprecipitation of chromium(III) with dysprosium hydroxide has been investigated and applied to tap water samples. Chromium(III) was quantitatively recovered by the presented method, while the recovery values for chromium(VI) was below 10%. The influences of analytical parameters including amount of dysprosium(III), pH, centrifugation speed and sample volume for the quantitative precipitation were examined. No interferic effects were observed from alkali, earth alkali and some transition metals for the analyte ions. The detection limits (k = 3, N = 15) were 0.65 μg/L for chromium(III) and 0.78 μg/L for chromium(VI). The validation of the presented method was checked by the analysis of certified reference materials.     

Analysis of interface states and series resistance of Ag/SiO2/n-Si MIS Schottky diode using current-voltage and impedance spectroscopy methods

The electrical characteristics and interface state density properties of Ag/SiO₂/n-Si metal-insulator-semiconductor diode have been analyzed by current-voltage and impedance spectroscopy techniques. The electronic parameters such as barrier height, ideality factor and average series resistance were determined and were found to be 0.62 eV, 1.91 and 975.8 Ω, respectively. The calculated ideality factor shows that Ag/SiO₂/n-Si structure obeys a metal-interfacial layer-semiconductor configuration rather than ideal Schottky barrier diode. The interface state density of the diode is of order of ∼10¹¹ eV⁻¹ cm⁻². The dielectrical relaxation mechanism of the diode is analyzed by Cole-Cole plots, indicating the presence of single relaxation mechanism. It is evaluated that the interfacial oxide layer modifies electrical parameters such as interface state density, series resistance and barrier height of Ag/SiO₂/n-Si diode.     

Temperature Dependence of Growth Mechanism for Nanoscale High T_c Superconductors

The growth mechanisms of high temperature Yttrium- and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi-2233, and then extended to another growth mechanism of Bi-2223 and the growth of yttrium-based high-temperature nanosuperconductors （nano-YBCO）. A time dependence of growth experiment was performed. In this experiment, the Bi-based superconductors grew within different sintering periods, and its three phases were determined by X-ray diffraction. And then, a time dependence of growth model was suggested to explain the experimental facts. With this model, governing equations were derived to quantitatively describe the growth and decomposition mechanisms during sintering period. The results calculated from the derived equations were well in agreement with the experimental data. We also suggested an alternative growth mechanism for the Bi-2223 phase, which was supported by an observation of transmission electron microscopy （TEM）. The nano-YBCO also grew, and their orthorhombic crystal structures were determined by the TEM. The superconducting properties of Bi-2223 were investigated by the measurements of ac magnetic susceptibility. It is expected that the derived equations will fit the alternative experimental growth mechanism of the Bi-2223 phase and the nano-YBCO growth mechanism, too.     

A comparative study of the emission of volatile organic compounds (VOCs) from different sulfur content crude oils

A new lab-made passive sampler method was employed to collect volatile organic compounds (VOCs) and volatile sulfur compounds (VSCs) which they were emitted from the spill of two different sulfur content crude oils. In this study, two different models have been used to represent of spill crude oil in two different areas, a laboratory and field model for spill crude oil on the surface area and pipeline leak respectively. The effective meteorological parameters such as rain, wind speed, and air temperature were controlled. The results show that the emitted VOCs were inversely proportional to the sulfur content crude oils.     

Theoretical and spectroscopic investigations on the structure and bonding in B-C-N thin films

In this study, we have synthesized boron, carbon, and nitrogen containing films using RF sputter deposition. We investigated the effects of deposition parameters on the chemical environment of boron, carbon, and nitrogen atoms inside the films. Techniques used for this purpose were grazing incidence reflectance-Fourier-transform infrared spectroscopy (GIR-FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). GIR-FTIR experiments on the B-C-N films deposited indicated presence of multiple features in the 600 to 1700 cm^− 1 range for the infrared (IR) spectra. Analysis of the IR spectra, XPS and the corresponding EELS data from the films has been done in a collective manner. The results from this study suggested even under nitrogen rich synthesis conditions carbon atoms in the B-C-N films prefer to be surrounded by other carbon atoms rather than boron and/or nitrogen. Furthermore, we have observed a similar behavior in the chemistry of B-C-N films deposited with increasing substrate bias conditions. In order to better understand these results, we have compared and evaluated the relative stability of various nearest-neighbor and structural configurations of carbon atoms in a single BN sheet using DFT calculations. These calculations also indicated that structures and configurations that increase the relative amount of C-C bonding with respect to B-C and/or C-N were energetically favorable than otherwise. As a conclusion, carbon tends to phase-segregate in to carbon clusters rather than displaying a homogeneous distribution for the films deposited in this study under the deposition conditions studied.     

The impact of applying natural clinoptilolite (zeolite) on the chemical,sensory and microbiological changes of vacuum packed sardine fillets

Different doses (1% and 5%) of natural zeolite were applied to determine quality changes in vacuum packaged sardine fillets during 19 days at 4 ± 1 °C. Zeolite had an effect to improve sensory quality of sardine especially for removing off‐odour. The acceptable shelf life of vacuum packaged sardine was 8 days for control and 12 days for groups treated with 1% and 5% zeolite. The zeolite application resulted in significant reduction in total volatile basic nitrogen values, except for group treated with 5% zeolite at 15 days. Although the effect of zeolite depended on dose and specific storage days, application of zeolite had no effect on free fatty acid analysis. The use of zeolite significantly reduced ammonia and biogenic amine accumulation, especially for histamine and tyramine. The result of the study showed that the efficacy of zeolite as natural antimicrobials was high and lower dose of zeolite has to be applied to get maximum preservation effect.     

Repair of post‐tensioned precast beam to column connections

Earthquakes can cause immense damage to precast structures, rendering them inhabitable. After the 1999 Marmara earthquake in Turkey, research by the Turkish Precast Union stated that 24.50% of the precast structures were damaged with some of this damage being observed in the beam‐to‐column connections of the structures. Since it is essential to provide those rendered homeless by the earthquake with safe habitable accommodation, repairing medium and slight levels of damage at the connection parts should be undertaken. In order to prove that a repaired connection was sufficiently strong, a precast beam‐to‐column post‐tensioned connection was tested in three phases. In phase one, middle level damage was observed at 6% drift at these connections. In phase two, 1.2, 2.4 and 4.8% drifts were applied three times to the test specimens. As a result of the extra loads applied, little damage was observed. In the last phase, the four connections tested in the first phase were repaired using epoxy resin and then retested. The results from the tests on the repaired precast and the reference undamaged specimens showed that the repaired specimens were sufficiently strong, thus proving that repair to damaged precast beam‐to‐column post‐tensioned connections can be undertaken. Copyright © 2010 John Wiley & Sons, Ltd.     

Monitoring and control of biogas desulphurization using oxidation reduction potential under denitrifiying conditions

BACKGROUND: Hydrogen sulphide (H₂S) present in biogas can be oxidized to elemental sulphur (S₀) or sulphate (SO₄^2?) using nitrate and nitrite. Both nitrate and nitrite are normally available in most wastewater treatment plants and could be used to oxidize H₂S depending on the molar loading ratio of wastewater and biogas. A control approach is required in order to minimize the fluctuations in inlet and outlet H₂S concentrations in biogas, and the oxidation potential of the wastewater used. RESULTS: A control scheme has been developed for biogas desulphurization using oxidation reduction potential under industrial conditions. The redox potential was maintained at about + 50 to + 100 mV in the activated sludge plant to monitor the performance of the nitrification process. The redox potential in the bioscrubber was related to sulphide removal from biogas. More than 90% of the hydrogen sulphide was removed from the biogas. CONCLUSION: The oxidation reduction potential can be used as a key parameter for monitoring and controlling biogas cleaning. Fluctuations of the inlet H₂S concentration in biogas can be compensated by manipulating the flowrates of wastewater used in order to achieve consistent and desired H₂S concentrations in treated biogas. Copyright © 2011 Society of Chemical Industry     

Solving two-machine assembly scheduling problems with inventory constraints

This paper considers a scheduling problem with component availability constraints in a supply chain consisting of two manufacturing facilities and a merge-in-transit facility. Three mixed-integer programming (MIP) models and a constraint programming (CP) model are compared in an extensive numerical study. Results show that when there are no components shared among the two manufacturers, the MIP model based on time-index variables is the best for proving optimality for problems with short processing times whereas the CP model tends to perform better than the others for problems with a large range of processing times. When shared components are added, the performance of all models deteriorates, with the time-indexed MIP providing the best results. By explicitly modelling the dependence of scheduling decisions on the availability of component parts, we contribute to the literature on the integration of inventory and scheduling decisions, which is necessary for solving realistic supply chain problems.