Spacing characterization in Al–Cu alloys directionally solidified under transient growth conditions

We study spacing selection in directional solidification of Al–Cu alloys under transient growth conditions. New experimental results are presented which reveal that the mean dendritic spacing vs. solidification front speed exhibits plateau-like regions separated by regions of rapid change, consistent with previous experiments of Losert and co-workers. Quantitative phase-field simulations of directional solidification with dynamical growth conditions approximating those in the experiments confirm this behavior. The mechanism of this type of change in mean dendrite arm spacing is consistent with the notion that a driven periodically modulated interface must overcome an energy barrier before becoming unstable, in accord with a previous theory of Langer and co-workers.     

Patterns of authors’ information scattering: towards a causal explanation of information scattering from a scholarly information-seeking behavior perspective

This study primarily aims to reveal the worldwide patterns of authors’ information scattering through illustrating the possible differences among authors based on subject, country, geographic region, institution, economic and scientific level factors. Second, changes in patterns of information scattering during the past 21 years are checked. Finally, a hypothesis aimed at demonstrating a probable relationship among the three research domains including information scattering, scholarly information-seeking behavior and scholarly journal usage is presented. 176,943 authors, who have more than ten papers in WoS from 1990 to 2010 were examined. The findings revealed that patterns of information scattering have changed during the past 21 years, and the number of journals in the core and middle zones has almost doubled. It was also found that authors tend to use a small number of journals to retrieve the majority of their required information, while a small amount of their information needs come from a wide variety of journals. However, with regard to patterns of information scattering, some differences exist among authors based on factors including institutions, countries and subject fields. In addition, this study shows that information-scattering patterns might be affected by scholars’ information-seeking behaviors. A causal explanation of information scattering through scholarly information-seeking behavior has, without a doubt, the potential to provide practical solutions to better meet scholars’ information needs and requirements.     

The Interaction of Methylene Blue Dye with Calcium–Silicate–Hydrate

The interaction of methylene blue (MB) dye solution with various calcium–silicate–hydrate (C–S–H) preparations (C/S ratio=0.60–1.80) was investigated. Experiments were also performed by treating the C–S–H in lime-saturated water and distilled water. The effects of MB on the X-ray basal spacing and the degree of polymerization were determined using low-angle X-ray diffraction (XRD) and ²⁹Si MAS NMR spectroscopy. An interaction mechanism for C–S–H–MB using a "bridging" model for the C–S–H nanostructure is proposed. The model is consistent with the XRD and ²⁹Si MAS NMR results.     

Estimation of thermodiffusion coefficients in ternary associating mixtures

Following the non‐equilibrium thermodynamics formulation and taking into account the complexities in the structure of aqueous associating mixtures, expressions are proposed to estimate the thermodiffusion coefficients in ternary associating mixtures, such as water and alcohol mixtures. The model expressions are used to estimate the thermodiffusion coefficients in methanol–ethanol–water, dimethyl sulfoxide (DMSO)–ethanol–water and DMSO–t‐butanol–water mixtures at various concentrations. The perturbed‐chain statistical associating fluid theory (PC‐SAFT) equation of state is used to obtain the mixture properties, such as the derivatives of the chemical potentials needed to evaluate the thermodiffusion coefficient expressions. The results show that at certain concentrations of one component, variation of the concentration of the other two components can cause a sign change in the thermodiffusion coefficients. While the model cannot be evaluated due to the lack of any pertinent experimental data, the model predictions may be used to choose suitable mixture compositions in space experiments to be performed onboard the International Space Station (ISS) in near future. © 2011 Canadian Society for Chemical Engineering     

Estimation of mid‐distillates production rate in a low temperature Fischer–Tropsch process

BACKGROUND: The Fischer–Tropsch process is the most important path for converting natural gas to high quality liquid hydrocarbons. Low temperature Fischer–Tropsch synthesis in slurry bubble column reactors with cobalt‐based catalysts is used for mid‐distillates production. RESULTS: In this work the slurry bubble column reactor was simulated by applying the two‐bubble class mathematical model. In addition, the effect of operating parameters on synthesis gas conversion was studied. The distribution of products was also predicted from the simulation framework. CONCLUSIONS: The effect of synthesis gas inlet velocity on mid‐distillates production rate was studied in the present work. A maximum production rate for mid‐distillates of about 23 kg s^?1 was predicted from the simulation program. Copyright © 2011 Society of Chemical Industry     

Preparation of alginate and chitosan nanoparticles using a new reverse micellar system

Alginate and chitosan nanoparticles were prepared using a new reverse micelle system, composed of cetyltrimethylammonium bromide (CTAB) as a surfactant, isooctane as a solvent, and 1-hexananol as a co-solvent. The obtained nanoparticles were characterized by FTIR, DLS and TEM techniques. The main objective of this study was to investigate the effects of polymer concentration, water content, and volumetric ratio of co-solvent to solvent on the physical and morphological properties of the prepared nanoparticles. To evaluate the results, the design of experimental was initially carried out and then the obtained data were statistically analyzed using the Qualitek-4^? software. Results revealed that the size of the prepared alginate and chitosan nanoparticles varied in the range 220?C490 and 210?C1,050?nm, respectively. Furthermore, increasing either alginate or chitosan concentration increased the size of their nanoparticles. The results also showed that the size of nanoparticles was decreased with increasing the volumetric ratio of co-solvent/solvent. Finally, the size of alginate nanoparticles was increased by increasing the water content while it decreased the size of chitosan nanoparticles. Considering the statistical analysis of experiments, the polymer concentration is the major parameter affecting nanoparticles?? size. In contrast, water content has the smallest effect on the size of nanoparticles. However, the difference between the particle sizes of chitosan and alginate nanoparticles cab be attributed to the electrostatic repulsion between chitosan and CTAB.     

Selective storage and evolution of hydrogen on nafion/NaCl/graphene quantum dot mixed matrix using tensammetry as power electrochemical technique

Hydrogen storage/evolution behavior of nafion/NaCl/graphene quantum dot (GQD) mixed matrix as selective hydrogen capacitor (power source) was evaluated in detail through an electrochemical process at two independent potential ranges. For this purpose, a three-electrode system included Pt disk as counter electrode, Ag/AgCl as reference electrode and GQD-based mixed matrix-modified Pt disk as working electrode. For hydrogen storage, the deposition potential and time were evaluated to ?1.0 V (vs. Ag/AgCl) and 120 s, respectively under high basic solution generated using NaOH (1.0 M) solution, followed by evolution of hydrogen at +0.8 V (vs. Ag/AgCl) during formation of hydrogen bubbles. The main advantage of this system was the occurrence of hydrogen storage and evolution at two independent potential windows. Both mass transfer and adsorption processes were estimated for the tensammetric peak during the evolution step. The mechanism of hydrogen storage and evolution was obeyed from diffusion and tensammetry, respectively. According to Randles–Sevcik equation using 1.0 mM ${{\text{Fe}\left(\text{CN}\right)}_6}^{3?/4?}$, the active surface area of nafion/NaCl/GQD mixed matrix was ～1906 m²g^?1. Based on the CHN analyses, pressure-concentration temperature as well as hydrogen temperature-programmed desorption, the capacity of the synthesized GQDs for hydrogen storage and evolution was estimated to at least 10.1 and 8.6 wt%, respectively. The stability of the electrode was also estimated during 7000s by chronoamperometry during applying at least 40 cycles in the range from ?1.0 to +1.3 V with reproducible tensammetric peak current (relative standard deviation: 2.54%).     

Analytical and numerical fluid–structure interaction study of a microscale piezoelectric wind energy harvester

In this paper, an analytical approach and two numerical models have been developed to study an energy‐harvesting device for micropower generation. This device uses wind energy to oscillate a cantilevered beam attached to a piezoelectric layer for generating electric energy output. The analytical approach and the first numerical model consider the fluid–structure interaction phenomenon in the harvester performance. The equations governing beam oscillations and airflow have been coupled to a set of four differential equations in the analytical approach. This set of equations has been solved to determine the beam deflection and the air pressure variation with time. The numerical methods have been conducted by employing a commercial software. The results of the analytical method and the first numerical model have been compared in different working conditions, and their credibility has been discussed. In the second numerical model, the electromechanical performance of the piezoelectric material has also been incorporated in the harvester device analysis. This model has been verified against experimental data for the output voltage and power of the device available in the literature. Finally, the effect of different geometrical parameters has been studied on the harvester performance, and suggestions have been made to improve the harvester efficiency.     

Electromagnetic scattering from conductor-coated material bodies

A moment method solution is presented to compute electromagnetic scattering from material bodies. The bodies are supposed to be homogeneous, arbitrarily shaped and lossy; they can be coated with very thin perfect conductors in some parts. A formulation of the scattering problem is made in terms of the equivalent surface current densities for which mixed potentials are used. The equivalent currents are expanded in the space-domain by a triangular expansion function on the triangulated surfaces of the scatterer. The Galerkin procedure is carried out to test boundary integral equations and reduce the functional form of the equations to a partitioned matrix equation. The solution is applied to the scattering problem of a dielectric slab, a thin conductor coated by absorber material and a rectangular patch on a grounded dielectric slab. The computed backscattering radar cross-section and surface current densities of the structures are presented and some of the results are compared with experimental data.