Thermal decomposition behavior of γ‐irradiated poly(vinyl acetate)/poly(methyl methacrylate) miscible blends

Miscible polymer blends based on various ratios of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were prepared in film form by the solution casting technique using benzene as a common solvent. The thermal decomposition behavior of these blends and their individual homopolymers before and after γ‐irradiation at various doses (50–250 kGy) was investigated. The thermogravimetric analysis technique was utilized to determine the temperatures at which the maximum value of the rate of reaction (T_max) occurs and the kinetic parameters of the thermal decomposition. The rate of reaction curves of the individual homopolymers or their blends before or after γ‐ irradiation displayed similar trends in which the T_max corresponding to all polymers was found to exist in the same position but with different values. These findings and the visual observations of the blend solutions and the transparency of the films gave support to the complete miscibility of these blends. Three transitions were observed along the reaction rate versus temperature curves; the first was around 100–200°C with no defined T_max, which may arise from the evaporation of the solvent. The second T_max was in the 340–380°C range, which depended on the polymer blend and the γ‐irradiation condition. A third transition was seen in the rate of reaction curves only for pure PVAc and its blends with PMMA with ratios up to 50%, regardless of γ‐ irradiation. We concluded that γ‐irradiation improved the thermal stability of PVAc/PMMA blends, even though the PMMA polymer was degradable by γ irradiation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1773–1780, 2006     

Clustering MIT–BIH arrhythmias with Ant Colony Optimization using time domain and PCA compressed wavelet coefficients

In this paper, Ant Colony Optimization (ACO) based clustering analysis of ECG arrhythmias taken from the MIT–BIH Arrhythmia Database is proposed. Both time domain and discrete wavelet transform (DWT) based frequency domain features are used in the analysis. Since the number of wavelet coefficients are huge amount as compared to the time domain parameters, Principal Component Analysis (PCA) based compression is applied on them in order to decrease their number to the number of time domain features. Then, the reduced numbers of frequency parameters are combined with the time domain features, in order to get the total feature sets. Different types of feature sets are tried and the classification results are compared. These are: time domain feature set, frequency domain feature set and the mixture of them. A neural network algorithm is developed in parallel to verify and measure the ACO classifier's success. Moreover, linear discriminant analysis (LDA) is used to show the effect of clustering on the system's results. The method is tested with MIT–BIH database to classify normal beats and five different critical and having vital importance arrhythmia types. Chosen six classes are normal sinus rhythm, premature ventricular contraction (PVC), atrial premature contraction (APC), right bundle branch block (RBBB), ventricular fusion (F) and fusion (f). Comparison results indicate that the mixture feature set gave a better success for the classification.     

Template Synthesis of Iminodiacetic Acid Polysiloxane Immobilized Ligand Systems and their Metal Uptake Capacity

Porous solid polysiloxane ligand systems bearing an iminodiacetic acid chelating ligand of the general formula P-IDA (where P- represents [Si-O] _n polysiloxane network and IDA represent an organofunctional group) were achieved in two-step reaction. The first step includes a template synthesis of 3-iodopropylpolysiloxane (P-I) or 3-aminopropylpolysiloxane (P-MA) by hydrolytic polycondensation of TEOS and the corresponding silane agent in the presence of CTAB as a surfactant. The second step includes a modification of 3-iodopropylpolysiloxane with diethyliminodiacetate or 3-aminopropylpolysiloxane with ethylchloroacetate to produce IDA-functionalized polysiloxane ligand systems P-IDA-I & P-IDA-II respectively. It was found that the modified IDA-functionalized polysiloxane ligand systems exhibited higher capacities for uptake of the metal ions (Ni ²⁺, Cu ²⁺ and Pb ²⁺) than those prepared without surfactants.     

Developing a hybrid PSO–ANN model for estimating the ultimate bearing capacity of rock-socketed piles

Neural Computing and Applications - Rock-socketed piles are commonly used in foundations built in soft ground, and thus, their bearing capacity is a key issue of universal concern in research,...     

Radiation crosslinking and sorption properties of hydrogels based on 1‐vinyl‐2‐pyrrolidone,hydroxyethyl methacrylate,and their copolymers

This work has been concerned with the synthesis of the hydrogels of poly (vinyl pyrrolidone) (NVP), poly (hydroxy ethylmethacrylate) (HEMA), and their copolymer under the effect of gamma radiation in the presence of N,N‐methylenebisacryl‐amide (MBAm) as a crosslinking agent. The effect of the different factors that may affect the gelation and yield product, such as solvent composition and irradiation dose, was investigated. The formed hydrogels were characterized in terms of swelling in water and different organic solvents, X‐ray diffraction (XRD), and IR spectroscopic analysis. The sorption capability of these hydrogels towards some commercial basic and acid dyesstuffs was also studied. The results showed that a solvent mixture composed of equal contents of water and methanol is the most suitable to afford the minimum sol fraction and the highest yield product at a minimal irradiation dose of 10 kGy. It was observed that NVP hydrogel displayed the highest swelling in water, alcohols, and dimethyformamide of ～1300% and a lower tendency to swell in nonpolar solvents. The results showed that HEMA hydrogel has a high affinity to absorb basic dyes while NVP has a tendency for acid dyes. Also, the sorption of either the basic or acid dyes by the different hydrogels was found to greatly depend on the concentration of dye in solution and the mass of the used hydrogel. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3274–3280, 2004     

Characterization of gamma irradiated concentrated aqueous solutions of chitosan/sodium alginate blends and their drug uptake‐release characters

Blends films based on different ratios of concentrated aqueous solutions of chitosan (CS) and sodium alginate (AG) in the presence of 1% of glutaraldehyde, as a cross‐linking agent for chitosan, were prepared by solution casting and then exposed to gamma irradiation. The formed blends were characterized by IR spectroscopic analysis, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The uptake‐release properties of CS/AG blends, taking ketoprofen as an example for drug, were also investigated. DSC thermograms of CS/AG blends revealed good miscibility was sustained between CS and AG. The water uptake and gel content of CS/AG blends was found to decrease by increasing the ratio of AG in the initial solution. The IR spectra indicated the formation of cross‐linking and hydrogen bonding, while the TGA study showed that the CS/AG blends displayed higher thermal stability than pure CS polymer. Based on Fick's law, it was demonstrated that the main parameters affecting the release of ketoprofen drug from the CS/AG blend hydrogels were composition and pH. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Current-voltage behavior of AlGaAs/InGaAs pHEMT structures and the effect of optical illumination

Various pseudomorphic High Electron Mobility Transistor (pHEMT) structures of AlGaAs/InGaAs alloys have been observed their current-voltage behavior. The tungsten probes were used for a measurement the structures by ramping the voltage from −5 to 5 V and measure the electrical current. Measurement was carried out at room temperature and also under optical illumination. From the measurement, the electrical current was found to increase as the increase of Al content in the AlGaAs alloys layer in the pHEMT structure. This phenomenon was supported by the decrease of sheet resistance as obtained from Hall effect measurement. Under visible light illumination, the current-voltage behavior of pHEMT structure was observed to vary as the light power density was varied for 0, 25 and 55 μW/cm.     

Sargassum swartzii extracts ameliorate memory functions by neurochemical modulation in a rat model

Food Science and Biotechnology - Recently, considerable attention has been paid to drug exploration from natural sources for treating memory loss, a major manifestation of various neurodegenerative...     

Removal of Cr(VI) and As(V) from aqueous solutions by HDTMA-modified zeolite Y

The synthesized zeolite NaY from rice husk ash (RHA) and the commercial zeolite NaY both modified with surfactants in amounts equal to 50%, 100% and 200% of their external cation exchange capacity (ECEC) were used to remove chromate and arsenate anions from aqueous solutions. While the unmodified zeolite Y had little or no affinity for the Cr(VI) and As(V) anionic species, the surfactant-modified zeolite Y (SMZY) showed significant ability to remove of these anions from the aqueous solutions. The highest chromates and arsenates adsorption efficiency was observed from solutions of pH values 3 and 8, respectively because of the dominance of the univalent species of both anions. The adsorption equilibrium data were best fitted with the Langmuir isotherm model with the highest removal capacities observed for the SMZY initially prepared considering the hexadecyltrimethyl ammonium (HDTMA) amount equal to the 100% of the ECEC of zeolite Y. Synthesized SMZY remove Cr(VI) and As(V) more than the corresponding commercial one due to its lower silica to alumina ratio. Thus, the HDTMA-covered modified zeolite Y synthesized using RHA can be used to remove Cr(VI) and As(V) from water.