Synthesis and characterization of polyethylene glycol mediated silver nanoparticles by the green method

The roles of green chemistry in nanotechnology and nanoscience fields are very significant in the synthesis of diverse nanomaterials. Herein, we report a green chemistry method for synthesized colloidal silver nanoparticles (Ag NPs) in polymeric media. The colloidal Ag NPs were synthesized in an aqueous solution using silver nitrate, polyethylene glycol (PEG), and β-D-glucose as a silver precursor, stabilizer, and reducing agent, respectively. The properties of synthesized colloidal Ag NPs were studied at different reaction times. The ultraviolet-visible spectra were in excellent agreement with the obtained nanostructure studies performed by transmission electron microscopy (TEM) and their size distributions. The Ag NPs were characterized by utilizing X-ray diffraction (XRD), zeta potential measurements and Fourier transform infrared (FT-IR). The use of green chemistry reagents, such as glucose, provides green and economic features to this work.     

Preparation of synthesized sulfide polymer through phase-transfer catalyzed polycondensation of ethylene dibromide and sodium tetrasulfide: characterization,thermal and rheological properties

Sulfide polymers were obtained through the interfacial polymerization of sodium tetrasulfide and ethylene dibromide. The polymerization process was carried out under interfacial condition using two phase-transfer catalysts: methyl-tributyl ammonium bromide and methyl-tributyl ammonium chloride. The polymer characteristics were examined by attenuated total reflectance- fourier transform infrared spectroscopy, elemental analysis (CHNS/O) and X-ray diffraction methods. Thermal characteristics were investigated by differential scanning calorimetry and thermogravimetric analysis methods. The rheological behavior of the synthesized sulfide polymer during curing reaction, and isothermal time dependency of elastic storage modulus, G^′, at different temperatures and constant shear frequency was studied using a stress-controlled rheometer. Moreover, the solvent resistance of synthesized polymer was investigated through the swelling method.     

Effect of chemical substitution on the morphology and optical properties of Bi1−xCaxFeO3 films grown by pulsed-laser deposition

The morphological characteristics as well the optical properties of Ca-doped BiFeO₃ films grown by pulsed-laser deposition technique have been investigated. AFM images revealed that calcium has a radical effect on the surface features of BiFeO₃ films. By utilizing spectrophotometer, transmission behaviour of the films was investigated. Local IV characteristics of the films disclosed about three orders of magnitude enhancement concerning electrical conductivity through Ca doping. X-ray photoelectron spectroscopy results revealed that Ca can reduce the valence state of iron in the compound.     

Response of Triangular-Shaped Leaky Aquifers to Rainfall-Induced Groundwater Recharge: an Analytical Study

Different aspects of groundwater mound dynamics in triangular-shaped aquifers are investigated analytically under spatially uniform recharge of time-varying rate. The aquifer response is analyzed relying on 2-D linearized Boussinesq equation, subject to two different configurations of hydrogeological boundary conditions (constant-head streams and no-flow barrier). The aquifer is homogeneous, isotropic and rests over a horizontal, semipervious layer, through which vertical leakage can take place. Point-recharge formula (Green’s function) is first derived for the intended aquifer domain and then properly converted to accommodate the effect of rainfall-induced areal recharge. Components of groundwater budget are evaluated in terms of volumetric rates, taking into account the jointed effects of leakage, mound storage and outflow to adjacent streams. The resulting expressions are then proven to obey the expected mass balance in a rigorous mathematical fashion. Hypothetical examples illustrating main features of flow field are presented, with attention paid on groundwater equpotentials and streamlines. The computed mound profiles appear to agree well with numerical results from finite element method. Further, the most influential parameters affecting each component of groundwater budget are identified with the help of sensitivity analysis. Finally, the combined effects of a pumping well and rainfall-induced mound are discussed. The present solution may serve as a test case for verifying numerical schemes that are being developed for more comprehensive mound analysis.

     

Application of neural networks and State-space averaging to DC/DC PWM converters in sliding-mode operation

A novel output feedback neural controller is presented in This work for the implementation of sliding-mode control of dc/dc converters. The controller, which consists of a multilayer perceptron, has been trained in order to be robust for large variations of system parameters and state variables. Fast dynamic behavior is the other main advantage of the proposed controller, which allows realization of all beneficial features of the sliding-mode control technique. Other advantages of the controller are simplicity and low cost. Computer simulations have been carried out to investigate the effectiveness of the controller in voltage regulation for a relatively complex dc/dc converter topology of the Cuk converter. Simulation results confirm the excellent performance of the control system in response to large signal variations. In order to verify the simulation results, a controller prototype has been designed and built using analog components. The controller is applied to regulate the output voltage of the Cuk converter. Experimental results confirm the analytical and simulation achievements.     

Optical activity induced in Bi/sub 4/Ge/sub 3/O/sub 12/ waveguides by ion implantation

The authors report data for ion implanted Bi/sub 4/Ge/sub 3/O/sub 12/ in which the modified material becomes optically active. The optical rotary power, after implantation and annealing, increases from zero to some 90 degrees /mm. The effect is attributed to an ion beam induced relaxation to a modified BiGeO phase.<>     

A genetic algorithm for optimization problems with fuzzy relation constraints using max-product composition

We consider nonlinear optimization problems constrained by a system of fuzzy relation equations. The solution set of the fuzzy relation equations being nonconvex, in general, conventional nonlinear programming methods are not practical. Here, we propose a genetic algorithm with max-product composition to obtain a near optimal solution for convex or nonconvex solution set. Test problems are constructed to evaluate the performance of the proposed algorithm showing alternative solutions obtained by our proposed model.     

A photochemical method for controlling the size of CdS nanoparticles

The optical and electrical properties of semiconductor nanoparticles are strongly dependent on their size. A flexible control of the size of the nanoparticles is of interest for tuning their properties for different applications. Here we use a coupled method to control the size of CdS nanoparticles. The method involves the photochemical growth of CdS nanoparticles together with the use of a capping agent as an inhibiting factor. CdS nanoparticles were formed through a photoinduced reaction of CdSO(4) and Na(2)S(2)O(3) in an aqueous solution. Mercaptoethanol (C(2)H(6)OS) was used as the capping agent, and we investigated the effect of illumination time, illumination intensity and the concentration of capping agent on the nanoparticle size. Transmission electron microscopy (TEM) shows crystalline nanoparticles with relatively low dispersion. Optical absorption spectroscopy was mainly used to measure the band gap and size of the nanoparticles. Increasing the illumination time or illumination intensity increases the nanoparticle size, while higher capping agent concentration leads to smaller nanoparticle size. A band gap range of 2.75-3.4?eV was possible with our experimental conditions, corresponding to a 3.2-6.0?nm size range.     

A quick method to fabricate large glass micromodel networks

Microsystem Technologies - The study of multi-phase fluid flow in microfluidic devices provides an opportunity for researchers to characterize effective factors and mechanisms in microscale. The...