A continuum model for granular materials: Considering dilatancy and the Mohr-Coulomb criterion

Summary In this paper we will explore the consequences of the Mohr-Coulomb criterion on the constitutive equation proposed by Rajagopal and Massoudi [1]. This contunuum model which is based on the earlier works of Cowin [2] has also the ability to predict the dilatancy effect which is related to the normal stress effects. At the same time, if a proper representation is given to some of the material parameters, this model would also comply with the Mohr-Coulomb criterion. We also present, as a special case, an exact solution for the case of simple shear flows.     

Characteristics of optimization algorithms applied to the electrode design of a magnetohydrodynamic micromixer

To reduce the time needed for the analysis and diagnosis in a lab-on-a-chip, the sample and reagent inside a micromixer should be efficiently blended within a short time. In this paper, we propose an efficient mixing method based on the magnetohydrodynamic effect, which is driven by Lorentz force. In our development of the proposed mixing system, we optimize the dimensions of five electrodes located at the bottom of the batch-type micromixer in order to shorten the mixing time of the sample and reagent. The optimization algorithms are thus verified as useful tools, enabling a rapid mixing in the micromixer.     

Modeling viscosity of methane,nitrogen, and hydrocarbon gas mixtures at ultra-high pressures and temperatures using group method of data handling and gene expression programming techniques

Accurate gas viscosity determination is an important issue in the oil and gas industries. Experimental approaches for gas viscosity measurement are time-consuming, expensive and hardly possible at high pressures and high temperatures (HPHT). In this study, a number of correlations were developed to esti-mate gas viscosity by the use of group method of data handling (GMDH)-type neural network and gene expression programming (GEP) techniques using a large data set containing more than 3000 experimen-tal data points for methane, nitrogen, and hydrocarbon gas mixtures. It is worth mentioning that unlike many of viscosity correlations, the proposed ones in this study could compute gas viscosity at pressures ranging between 34 and 172 MPa and temperatures between 310 and 1300 K. Also, a comparison was performed between the results of these established models and the results of ten well-known models reported in the literature. Average absolute relative errors of GMDH models were obtained 4.23％, 0.64％, and 0.61％for hydrocarbon gas mixtures, methane, and nitrogen, respectively. In addition, graph-ical analyses indicate that the GMDH can predict gas viscosity with higher accuracy than GEP at HPHT conditions. Also, using leverage technique, valid, suspected and outlier data points were determined. Finally, trends of gas viscosity models at different conditions were evaluated.     

Determination of molecular weight and molecular radius of the polyamido carboxylic acid dendrimer using generation numbers

Using of a Molecular equation of a first dendrimer surface and its relation to dendrimer molecular radios, it is possible to suggest the number of generation. Whereas a relative molecular weight is affiliated to the number of molecule formed in structural cells and on the other hand, structural cells have definite and determined dimensions, so by a simple replacement, the dendrimer molecular weight was directly related to its generation number. Data analysis derived from specific equation was shown that the prediction of a dendrimer molecular weight may be applicable by a specific generation.Molecular weight of polyamido carboxylic acid dendrimer with specific number of generation could be theoretically estimated using the following eqs. (4) and (5).

y = log M_w

=2.0703 + 0.0844R_i (4)

=2.6339 + 0.4750G_n (5)

R_i and G_n are molecular radius and number of generation respectively.Such equations would result the molecular radius of the dendrimer. In this invented model there is no need to experiments and it can be key value to evaluate the experimental data.     

Novel carrageenan-based hydrogel nanocomposites containing laponite RD and their application to remove cationic dye

Novel hydrogel nanocomposites were synthesized by solution polymerization of acrylamide in the presence of carrageenan biopolymer and laponite RD clay. Laponite was used as an inorganic cross-linker. Ammonium persulfate was applied as an initiator. The structure and morphology of the nanocomposites were investigated using XRD, scanning electron microscopy, and transition electron microscopy techniques. The influence of both laponite nanoclay and the carrageenan content on the swelling degree of nanocomposites was studied and it was found that all nanocomposites containing carrageenan component have a high swelling degree compared to a nanocomposite without carrageenan. The obtained nanocomposites were examined to remove a cationic crystal violet (CV) dye from water. The effect of carrageenan and clay contents on the speed of dye adsorption revealed that while the rate of dye adsorption is enhanced by increasing the clay content, it was depressed as the carrageenan content increased in nanocomposite composition. The results showed that the pseudo-second-order adsorption kinetic was predominant in adsorption of CV onto nanocomposites. The experimental equilibrated adsorption capacity of nanocomposites was analyzed using Freundlich and Langmuir isotherm models. The results indicated that the experimental data fit the Langmuir isotherm best. Maximum adsorption capacity was obtained for carrageenan-free nanocomposite with 79.8?mg?g^?1 of adsorbed CV onto nanocomposite.     

Multi-walled carbon nanotube-filled polypropylene nanocomposites: high velocity impact response and mechanical properties

Polymer nanocomposites containing 0.75, 1.0 and 1.5 wt% of multi-walled carbon nanotubes (MWNTs) in a polypropylene (PP) matrix were studied in relation to their low and high velocity impact performances. PP nanocomposites reinforced MWNTs were prepared via melt compounding in an internal mixer followed by injection molding. Transmission electron microscopy analysis confirmed well dispersed 1?wt% MWNT in the polymer nanocomposites. The same analysis showed agglomeration and cluster formation in 1.5?wt% MWNT specimens. Results showed increase in Izod impact strength in nanocomposites containing 1?wt% MWNT, which attained the highest value (with 33.4?% increment). A single stage gas gun was used to carry out high velocity impact test in velocity range of 20?C150?m/s using hard steel hemispherical tip projectile of 11.34?g weight and 8.1?mm diameter. Results showed better ballistic limit velocity (the average of highest impact velocity causing perforation but unable to go through and lowest impact velocities with no residual velocity recording) and energy absorption for specimens, each containing 1?wt% MWNT, showing the highest value (with 100?% increment), compared with neat PP. Considerable increases were observed in tensile and flexural strengths and modulus for the MWNT-containing specimens as compared with neat PP.     

Experimental measurement and modeling of saturated reservoir oil viscosity

A novel mathematical-based approach is proposed to develop reliable models for prediction of saturated crude oil viscosity in a wide range of PVT properties. A new soft computing approach, namely least square support vector machine modeling optimized with coupled simulated annealing optimization technique, is proposed. Six models have been developed to predict saturated oil viscosity, which are designed in such a way that could predict saturated oil viscosity with every available PVT parameter. The constructed models are evaluated by carrying out extensive experimental saturated crude oil viscosity data from Iranian oil reservoirs, which were measured using a “Rolling Ball viscometer.” To evaluate the performance and accuracy of these models, statistical and graphical error analyses were used simultaneously. The obtained results demonstrated that the proposed models are more robust, reliable and efficient than existing techniques for prediction of saturated crude oil viscosity.     

Terror management and adults' attachment to their parents: The safe haven remains.

Six studies examined the role of young adults' parental attachment in terror management. Studies 1-3 revealed that activating thoughts of one's parent in response to mortality salience (MS) reduced death-thought accessibility and worldview defense and increased feelings of self-worth. Studies 4-5 demonstrated that MS led to greater ease of recalling positive maternal interactions and greater difficulty recalling negative interactions, and increased attraction to a stranger who was described as being similar to one's parent. If reliance on parents for terror management purposes reflects the operation of attachment mechanisms, then such effects should vary on the basis of an individual's attachment style. Study 6 demonstrated that, after MS, insecure individuals were more likely to rely on relationships with their parents, whereas secure individuals were more likely to rely on relationships with romantic partners. (PsycINFO Database Record (c) 2010 APA, all rights reserved)