Constructing a new optical sensor for monitoring ammonia in water samples using bis(acetylacetoneethylendiamine)-tributylphosphin cobalt(III) tetraphenylborate complex-coated triacetylcellulose.

A new ammonia optical sensor was designed using bis(acetylacetoneethylendiamine)tributylphosphin cobalt(III) tetraphenylborate complex, coated on transparent triacetylcellulose film as membrane. The change in the absorbance of the optode at the maximum wavelength of 408 nm was related to ammonia concentration in aqueous samples. A buffer solution with a pH of 9 (sodium borate-HCl) was used. The optode was fully regenerated in pH 2. The linear dynamic range for determination of ammonia was 3.3 x 10(-4) to 6.9 x 10(-3) mol l(-1) with a detection limit of 5.0 x 10(-5) mol l(-1) and a response time range of 4 - 6 min. This membrane was successfully applied for determination of ammonia in drinking water.     

A rate-dependent algebraic stress model for turbulence

Based on the stress transport model, a rate-dependent algebraic expression for the Reynolds stress tensor is developed. It is shown that the new model includes the normal stress effects and exhibits viscoelastic behavior. Furthermore, it is compatible with recently developed improved models of turbulence. The model is also consistent with the limiting behavior of turbulence in the inertial sublayer and is capable of predicting secondary flows in noncircular ducts. The TEACH code is modified according to the requirements of the rate-dependent model and is used to predict turbulent flow fields in a channel and behind a backward-facing step. The predicted results are compared with the available experimental data and those obtained from the standard k-ε and algebraic stress models. It is shown that the predictions of the new model are in better agreements with the experimental data.     

Modification of the GV-MSA model in obtaining the activity and osmotic coefficients of aqueous electrolyte solutions

In this work a modified form of the Ghotbi–Vera Mean Spherical Approximation model (MGV-MSA) has been used to correlate the mean ionic activity coefficients (MIAC) for a number of symmetric and asymmetric aqueous electrolyte solutions at 25 °C. In the proposed model the hard sphere as well as the electrostatic contributions to the MIAC and the osmotic coefficient of the previously GV-MSA model has been modified. The results of the proposed model for the MIAC of the electrolyte solutions studied in this work are used to directly calculate the values of the osmotic coefficients without introducing any new adjustable parameter. In the MGV-MSA model the cation diameter as well as the relative permittivity of water depends on the electrolyte concentration. Having considered such dependency for both cation and relative permittivity for water in an electrolyte solution the modification of the GV-MSA has been made. It should be stated that in the MGV-MSA model the anion diameter in the solution similar to that in the GV-MSA model remains constant and independent of the electrolyte concentration. The results obtained from the proposed model have been favorably compared with those of the GV-MSA model. The results showed that the MGV-MSA model can more accurately correlate the MIAC of the single electrolyte solutions than those of the GV-MSA model. The same comparison has been observed in case of the osmotic coefficients for the electrolyte solutions studied in this work. It should be noted that in order to do an unequivocal comparison between the results obtained from the models used in this work the same minimization procedure and the same experimental data for the MIAC and the osmotic coefficients have been used. Also it should be mentioned that in the MGV-MSA model the conversion from the McMillan–Mayer (MM) framework to that of the Lewis–Randall (LR) has been performed. It has been concluded that such transformation can affect the results in particular at higher electrolyte concentrations.     

Adsorptive Stripping Voltammetric Determination of Ultra Trace of Zinc and Lead with Carbidopa as Complexing Agent in Food and Water Samples

In the present work, the cathodic stripping voltammetric methodology using a hanging mercury drop electrode was described for simultaneous determination of lead and zinc in different real samples. The method is based on adsorption of metal ions on mercury electrode using carbidopa as a suitable complexing agent. The potential was scanned to the negative direction and the differential pulse stripping voltammograms were recorded. Optimal conditions were found to be: accumulation time; 70 s, accumulation potential; 50 mV versus Ag/AgCl, scan rate; 40 mV s^?1, supporting electrolyte; 0.01 M ammonia buffer at pH 8.5, and concentration of carbidopa; 8.0 μM. The relationship between the peak current versus concentration was linear over the range of 0.1–210 and 0.2–170 nM for lead and zinc, respectively. The detection limits are 0.09 and 0.15 nM for lead and zinc ions respectively. The relative standard deviations at a concentration level of 70 nM of both metal ions are found 1.08 and 1.24% for lead and zinc ions respectively.     

New computer program to calculate the symmetry of molecules

In this paper we, present some MATLAB and GAP programs and use them to find the automorphism group of the Euclidean graph of the C₈₀ fullerence with connectivity and geometry of I _h symmetry point group. It is proved that this group has order 120 and is isomorphic to I _h ≊Z₂×A₅, where Z₂ is, a cyclic group of order 2 and A₅ is the alternating group on five symbols.     

Bioaccumulation and biosorption of stable strontium and <Superscript>90</Superscript>Sr by <Emphasis Type="Italic">Oscillatoria homogenea</Emphasis> cyanobacterium

The ability of living filamentous cells of the cyanobacterium Oscillatoria homogenea to separate stable strontium and ⁹⁰Sr from aqueous solution is demonstrated in this study. On a basis of filamentous cell biovolume, the removal were 43.78 nM·ml·(mm³)⁻¹ and 3129.48 mBq·ml·(mm³)⁻¹ after 240 hour incubation. The optimum pH for strontium uptake is 9±0.3. The increasing biovolume of the blue-green alga elevates sorption. In the liquid culture containing 21.2 mm³·ml⁻¹ filamentous cells and 1000 nM·ml⁻¹ initial strontium concentration, the maximum strontium removal was 455.34 nM·ml·(mm³)⁻¹. At 1200 Lux illumination, the maximum removal value was 58.62 nM·ml·(mm³)⁻¹, and at the initial strontium concentration of 6590 nM·ml⁻¹, 235.40 nM·ml·(mm³)⁻¹ removal was observed. The experimental data fitted to Langmuir isotherm and the model parameters and correlation coefficient (R ²) were q _max = 7.143 μg·(mm³)⁻¹, b = 0.003 and 0.99, respectively.     

Picosecond wavelength conversion using semiconductor optical amplifier integrated with microring resonator notch filter

Optical and Quantum Electronics - In this paper, we analyse the picosecond wavelength conversion using semiconductor optical amplifier (SOA) with a novel technique. For an accurate and precise...     

Functionalization of BN nanosheet with N2H4 may be feasible in the presence of Stone–Wales defect

Following recent experimental works, herein we investigated chemical functionalization of a BN graphene-like sheet with hydrazine (N₂H₄) molecule based on the density functional theory. We found that the functionalization of the pristine sheet is not possible; while the presence of some structural defects such as Stone–Wales is essential to make it feasible. Functionalization energy of the defected sheet is calculated to be in the range of ?6.1 to ?7.4 kcal/mol at B3LYP/6-31G (d) level. Based on the obtained results, the functionalized BN sheet is found to be more soluble in water in comparison with the pristine sheet which is in good agreement with previous experimental reports. Also, it was found that the electronic properties of the defected sheet are slightly changed upon the chemical functionalization.     

A Theoretical Study of OH and OCH3 Free Radical Adsorption on a Nanosized Tube of BC2N

By using density functional theory calculations, we have investigated the adsorption of OH and OCH₃ free radicals on a BC₂N nanotube based on the energetic, electronic and geometric properties. The adsorption of radicals on the top of a B atom is more favorable than that on the other sites and reaction energies have been calculated to be in the range of ?0.57 to ?1.48 eV for OH and ?0.27 to ?1.19 eV for OCH₃. It was found that the adsorption of radicals may facilitate the electron emission from the BC₂N nanotube surface by decreasing the work function due to the charge transfer which occurs between the tube and radicals. Also, HOMO/LUMO gap of the tube is significantly decreased, which may result in the increase of the electrical conductivity of the tube.