Preparation and characterization of nanocomposite hydrogels based on polyacrylamide for enhanced oil recovery applications

In the present work, attempts have been made to prepare nanocomposite type of hydrogels (NC gels) by crosslinking the polyacrylamide/montmorillonite (Na‐MMT) clay aqueous solutions with chromium (III). The X‐ray diffraction patterns of the NC gels exhibited a significant increase in d₀₀₁ spacing between the clay layers, indicating the formation of intercalated as well as exfoliated type of morphology. Exfoliation of the clay layers through out the gel network was found to be predominated, which evidences the high interaction between the polyacrylamide segments and montmorillonite layers. Gelation time as well as variation of viscoelastic parameters such as storage modulus (G′) of the gel network during gelation process at 75°C was studied and followed by rheomechanical spectroscopy (RMS). The NC gels prepared with lower crosslinker concentration showed higher strength and elastic modulus compared with the similar but unfilled polyacrylamide gel. This distinct characteristic of the NC gels yields a gel network structure with high resistance towards syneresis at high temperature in the presence of the oil reservoir formation water. The effects of the composition, such as clay content, crosslinker concentration, and also water salinity upon the gelation rate, gel strength as well as rate of syneresis have been investigated. To optimize the injectivity of the intercalated polyacrylamide solution before the onset of gelation with the gel strength of the final developed gel, sodium lactate was employed as retarder. This was found to be effective to balance these two characteristics of the NC gels, which are aimed to be used for water shut‐off and as profile modifier in enhanced oil recovery (EOR) process during water flooding process. The nanocomposite gels showed much more elasticity and extensibility at low crosslinker concentration compared with the similar but unfilled gel, which makes the NC gels suitable as an in‐depth profile modifier, and also as an oil displacing agent in the heterogeneous oil reservoir in chemical EOR. Effects of the clay content on the thermal stability of the gel network have also been investigated by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) has been performed upon the NC‐gel samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2096–2103, 2006     

Preparation and characterization of high efficiency ion‐exchange crosslinked acrylic fibers

Commercial acrylic fiber samples were first pretreated with hydrazine under various concentrations to give crosslinked structure. Then, the crosslinked fiber samples with different degree of crosslinking were treated with hydroxylamine hydrochloride to develop ion‐exchange fibers. These fibers contain amidoxime, amine, amide, and hydrazide groups simultaneously. The effects of reaction conditions on physical properties, thermal characteristics, surface morphology, ion adsorption quantity, and reusability were investigated. The results show that by increasing the reaction time, temperature, and concentration of hydroxylamine hydrochloride, the content of amidoxime groups in all samples were increased, but with noncrosslinked fibers noticeable drop in the mechanical properties were observed, while in crosslinked sample prepared under optimum conditions of reaction, good ion adsorption capacity with keeping mechanical properties was achieved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2202–2209, 2006     

Detection of stator winding faults in induction motors using three-phase current monitoring

The objective of this paper is to propose a new method for the detection of inter-turn short circuits in the stator windings of induction motors. In the previous reported methods, the supply voltage unbalance was the major difficulty, and this was solved mostly based on the sequence component impedance or current which are difficult to implement. Some other methods essentially are included in the offline methods. The proposed method is based on the motor current signature analysis and utilizes three phase current spectra to overcome the mentioned problem. Simulation results indicate that under healthy conditions, the rotor slot harmonics have the same magnitude in three phase currents, while under even 1 turn (0.3%) short circuit condition they differ from each other. Although the magnitude of these harmonics depends on the level of unbalanced voltage, they have the same magnitude in three phases in these conditions. Experiments performed under various load, fault, and supply voltage conditions validate the simulation results and demonstrate the effectiveness of the proposed technique. It is shown that the detection of resistive slight short circuits, without sensitivity to supply voltage unbalance is possible.     

Microwave Sensing of Moisture Content in Concrete Using Open-Ended Rectangular Waveguide

The existence of moisture in concrete is a major cause of damage to the concrete structure, so there is an increasing need for nondestructive detection and monitoring of moisture content in concrete. Microwave nondestructive testing (MNDT) techniques have advantages over other NDT methods (such as radiography, ultrasonic, and eddy current) regarding low cost, good penetration in nonmetallic materials, good resolution and requirement of only one face of material for testing. In this paper, microwave open-ended rectangular waveguide was used to measure the electromagnetic properties of Portland cement concrete (PCC) over a frequency range of 7.0 to 13.0 GHz. PCC specimens of six different water cement ratio (w/c) were prepared. PCC dielectric properties were evaluated at different moisture content ranges from saturated to oven dry. The results show reflection coefficients, dielectric constants and loss factors increase with increasing moisture content of PCC. At the same values of moisture content, the reflection coefficients, dielectric constants and loss factors of PCC increase with decreasing w/c ratio. The measured values of reflection coefficients, dielectric constants and loss factors can be used to determine the moisture content of PCC.     

Anisotropic characterization of particleboard by ultrasonic and static techniques

The anisotropic properties of particleboard (PB) are studied by ultrasonic and static techniques. Ultrasonic wave velocity and modulus of elasticity in bending (MOE) are determined at parallel and perpendicular to manufacturing direction and at the interval angles of 15° in clockwise and counter-clockwise directions. The experimental results are compared with the predicted values using empirical formulas such as the Hankinson and Jacoby equations. The results show that the ultrasonic wave velocity and MOE are the highest in the parallel direction in PB and the lowest values occurred in the perpendicular direction. The predicted ultrasonic wave velocity using the Hankinson and Jacoby equations are in close agreement with the measured value. The relationship among particles angle, ultrasonic wave velocities, and MOE could be successfully presented by cubic and quadratic regression equations as well.Translated from Defektoskopiya, Vol. 40, No. 9, 2004, pp. 42–50. Original Russian Text Copyright © 2004 by Kazemi Najafi, Abbasi Marasht, Ebrahimi.This article was submitted by the authors in English.     

Unconfined compressive strength of loose sandy soils grouted with zeolite and cement

Cement production requires a lot of energy and is also one of the most important sources of carbon dioxide emissions. Consequently, the replacement of part of the cement with a more environmentally friendly material, such as zeolite, is of great importance. The present research involves the conducting of a series of laboratory tests on loose sand specimens ($D_r\approx 30\%$) grouted with cementitious materials (cement and zeolite) to investigate the effect of different parameters, such as the size of the sand particles, the ratio of water to cementitious materials (W/CM) and the replacement of a certain percentage of the cement in the grout with zeolite (Z), on the unconfined compressive strength (UCS) of the grouted sand specimens. The results indicate that for all the grout W/CM and sand grain sizes, when Z is increased from zero zeolite (Z₀), the UCS initially increases. Then, after reaching an optimal amount (Z₃₀), it decreases. Moreover, increasing both the size of the sand particles and the W/CM of the grout is seen to reduce the UCS of the grouted specimens. The UCS of the grouted sand specimens increases with the equilibrium of SiO₂ and Al₂O₃ with CaO elements in the grouting suspension. Finally, equations with a high performance are proposed to predict the UCS of sands grouted with zeolite-cement using a multiple regression model (MRM) and a group method of data handling (GMDH)-type neural network.     

A new prediction model of electricity load based on hybrid forecast engine

In this paper, a new prediction model is introduced based on hybrid forecast engine and new feature selection. In this model, the load signal is filtered by feature selection to filter out the best candidates. Then, the proposed forecast engine is predicted the output of feature selection. In this model, the weights of proposed forecast engine are optimised by an intelligent algorithm to increase its accuracy. Effectiveness of the proposed method is applied over real-world engineering test case and compared with other different well-known methods. Obtained results proof the validity of the proposed method.     

Design and optimization of multi‐band Wilkinson power divider

In this paper, a general and easy procedure for designing the symmetrical Wilkinson power divider that achieves equal‐power split at N arbitrary frequencies is introduced. Each quarter‐wave branch in the conventional Wilkinson divider is replaced by N sections of transmission lines, and the isolation between the output ports is achieved by using N resistors. The design parameters are the characteristic impedances and lengths of the N transmission line sections, and the N isolation resistors. The even–odd modes of analysis are used to derive the design equations. Closed‐form expressions, which are suitable for CAD purposes, are derived for the dual‐band divider. For N ≥ 3, closed‐form expressions are not available, and therefore, the powerful particle swarm optimization method is used to obtain the design parameters. Examples of the dual‐, triple‐, and quad‐band dividers are presented to validate the proposed design procedure, and the results are compared, wherever possible, with published results using other methods. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Prediction of Thermodynamic Properties of Liquid Air

In this work, a simple equation of state (EoS) has been used to predict some thermodynamic properties of air as a pseudo-pure fluid; as a ternary mixture of nitrogen, oxygen, and argon; and as a binary mixture of nitrogen and oxygen at different temperatures and pressures. A comparison with literature tabulated values has been made. The agreement of calculated densities with corresponding tabulated values is good for which the average absolute deviations are better than 0.06% if we assume air as a pseudo-pure fluid, and 0.9% and 1.2% if we consider air as a ternary mixture and as a binary mixture, respectively. To show the ability of this equation of state to predict density, the calculated densities of air have been compared with those computed by other methods.     

Density functional calculations of response of single-walled armchair carbon nanotubes to axial tension

The response of single-walled armchair carbon nanotubes (SWACNTs) to axial tension was studied using density functional calculations. A new response causing an abrupt change in nanotube structure at specific strains was detected. Atom rearrangement results in a lower energy than expected. The geometry of armchair nanotube plays an important role in the observed response, with the effect of curvature being important. There is a meaningful relationship between rearrangement strain and nanotube diameter. Rearrangement can be explained using the Poisson effect, which increases with the lateral displacement and is inversely proportional to nanotube index number.