Effect of sodium montmorillonite nanoclay on the water absorbency and cationic dye removal of carrageenan-based nanocomposite superabsorbents

Nanocomposite superabsorbents were synthesized by simultaneously solution copolymerization of acrylamide (AAm) and sodium acrylate (Na-AA) in the presence of carrageenan biopolymer and sodium montmorillonite (Na-MMt) nanoclay. Potassium persulfate (KPS) and methylenebisacrylamide (MBA) were used as initiator and crosslinker, respectively. The structure and morphology of the nanocomposites were investigated using XRD, FTIR, scanning electron microscopy (SEM), and TEM techniques. The influence of nanoclay and carrageenan contents as well as monomer weight ratios on the degree of swelling of nanocomposites was studied. The optimum water absorbency was obtained at 10 wt% of clay, 10 wt% of carrageenan, and 1:1 of monomers weight ratio. The obtained nanocomposites were examined to remove of crystal violet (CV) cationic dye from water. The effect of carrageenan and clay content on the speed of dye adsorption revealed that while the rate of dye adsorption is enhanced by increasing the clay content up to 14 wt% of clay, it was decreased as the carrageenan increased in nanocomposite composition. The results showed that the pseudo-second-order adsorption kinetic was predominated for the adsorption of CV onto nanocomposites. The experimental equilibrated adsorption capacity of nanocomposites was analyzed using Freundlich and Langmuir isotherm models. The results corroborated that the experimental data fit the Freundlich isotherm the best.     

Evaluation of ground convergence and squeezing potential in the TBM driven Ghomroud tunnel project

One of the new components of water conveyance system in central Iran is the Ghomroud water conveyance tunnel that is being excavated by a double shield TBM. The 36 km long tunnel mainly passes through the metamorphic weak rocks of Jurassic age. Key geotechnical design issues for the tunnel, which has up to 650 m of overburden, include the potential for high ground pressure due to high in situ stress. In order to prevent the shield jamming in these weak rocks, it was necessary to evaluate the amount of ground pressure on the outer surface of TBM shield in the vicinity of the tunnel face. The stress and strain condition in the vicinity of the tunnel face has a 3D nature and it is not realistic to assume a two-dimensional stress state at the tunnel face area. In the convergence-confinement method, it is possible to simulate the tunnel face effect with an internal fictitious pressure that is imposed on the tunnel perimeter. In this study, based on the convergence-confinement method, a new method was introduced to calculate the tunnel face effect on ground pressure distribution around the tunnel face region. Then by using this method, critical areas with potential for shield jamming was predicted along the Ghomroud water conveyance tunnel. The obtained results by this method are in good agreement with the current TBM jamming situations along the Ghomroud tunnel.     

Multispectroscopic studies on the interaction of 2-tert-butylhydroquinone (TBHQ), a food additive,with bovine serum albumin

The interaction of 2-tert-butylhydroquinone (TBHQ) and bovine serum albumin (BSA) was investigated by spectrophotometry, spectrofluorimetry, circular dichroism (CD) and FT-IR techniques. The experimental results indicated that the quenching mechanism of BSA by TBHQ was a static procedure. Various binding parameters were evaluated. The negative value of ΔH, positive value of ΔS and the negative value of ΔG indicated that hydrophobic and hydrogen bonding interactions play major roles in the binding of TBHQ and BSA. Based on Forster’s theory of non-radiation energy transfer, the binding distance, r, between the donor (BSA) and acceptor (TBHQ) was evaluated. The results of CD, UV–vis and FT-IR spectroscopy showed that the binding of TBHQ to BSA induced conformational changes in BSA.     

Tin(II)-quercetin complex: Synthesis, spectral characterisation and antioxidant activity

The complex formation between quercetin (Q) and stannous chloride (SnCl₂·2H₂O) was studied using UV-visible, IR and ¹H NMR spectroscopic techniques. Spectroscopic data suggest that Q can chelate stannous cations through both 3-hydroxy-4-carbonyl and the 3′,4′-dihydroxyl (catechol) chelation sites. The antioxidant activity of the complex was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) diammonium salt and ferric reducing antioxidant power (FRAP) methods. It was shown that radical scavenging activity and ferric reducing potential of free Q was decreased after chelation of stannous cation.     

Reverse Link Performance of DS-CDMA Cellular Systems through Closed-Loop Power Control, Base Station Assignment, and Antenna Arrays in 2D Urban Environment

The interference reduction capability of antenna arrays, base station assignment, and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. In this paper, we propose smart step closed-loop power control (SSPC) algorithm and base station assignment method based on minimizing the transmitter power (BSA-MTP) technique for direct sequence-code division multiple access (DS-CDMA) receiver in a 2D urban environment. This receiver consists of conjugate gradient adaptive beamforming and matched filter in two stages using antenna arrays. In addition, we study an analytical approach for the evaluation of the impact of power control error (PCE) on the DS-CDMA cellular systems. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly improve the network bit error rate in comparison with conventional methods. Our proposed methods can also significantly save total transmit power and extend battery life in mobile units. In addition, we show that the convergence speed of the SSPC algorithm is faster than that of conventional algorithms. Finally, we discuss two parameters of PCE and channel propagation conditions (path-loss parameter and variance of shadowing) and their effects on the capacity of the system via some computer simulations.     

Potassium permanganate as an electron receiver in a microbial fuel cell

Microbial fuel cells with air as a cathode electron receiver are simple systems but they need expensive catalysts. In comparison to microbial fuel cells with oxygen as an electron receiver, microbial fuel cells with potassium permanganate produce higher voltage. In this study, electrical performance of a microbial fuel cells containing anaerobic sludge and potassium permanganate as an oxidizing agent was investigated. Glucose (1 g/l) was used as a carbon and energy source. The maximum power density and current density at the maximum power density were 93.13 mW/m² and 0.030 mA/cm² with respect to a potassium permanganate concentration of 400 µM. It is observed that the maximum power density increased to 114.00 mW/m² using an acid-heat treated carbon brush anode. Also, chemical oxygen demand removal was 51% when the microbial fuel cells was operated using 400 µM of potassium permanganate.     

Predictions of toughness and hardness by using chemical composition and tensile properties in microalloyed line pipe steels

Artificial neural networks with multilayer feed forward topology and back propagation algorithm containing two hidden layers are implemented to predict the effect of chemical composition and tensile properties on the both impact toughness and hardness of microalloyed API X70 line pipe steels. The chemical compositions in the forms of “carbon equivalent based on the International Institute of Welding equation (CE_IIW)”, “carbon equivalent based on the Ito-Bessyo equation (CE_Pcm)”, “the sum of niobium, vanadium and titanium concentrations (VTiNb)”, “the sum of niobium and vanadium concentrations (NbV)” and “the sum of chromium, molybdenum, nickel and copper concentrations (CrMoNiCu)”, as well as, tensile properties of “yield strength (YS)”, “ultimate tensile strength (UTS)” and “elongation (El)” are considered together as input parameters of networks while Vickers microhardness with 10 kgf applied load (HV10) and Charpy impact energy at ?10 °C (CVN ?10 °C) are assumed as the outputs of constructed models. For the purpose of constructing the models, 104 different measurements are performed and gathered data from examinations are randomly divided into training, testing and validating sets. Scatter plots and statistical criteria of “absolute fraction of variance (R²)”, and “mean relative error (MRE)” are used to evaluate the prediction performance and universality of the developed models. Based on analyses, the proposed models can be further used in practical applications and thermo-mechanical manufacturing processes of microalloyed steels.