Porous Superabsorbent Hydrogel Composites: Synthesis,Morphology and Swelling Rate

Summary: Novel porous hydrogel composites with very high swelling capacity and enhanced rate of water absorption were synthesized in aqueous media at room temperature under normal atmospheric conditions. The porosity was induced through either foaming conducted in the course of polymerization or non‐solvent dewatering of the as‐synthesized gels. Kaolin was incorporated as an inorganic component in the polymerization process. The foaming technique was used to form porosity using three systems of different porogens (porosity generators), i.e. sodium bicarbonate, acetone and their combination. The as‐synthesized gels were dried through oven drying and non‐solvent dewatering. Morphology and swelling rate of the superabsorbent hydrogel composites (SHCs) were studied versus either the porogen system or the drying method. It was found that the simultaneous polymerization‐foaming technique had great influence on the improvement of porosity, morphology of the porous structure and the rate of water absorption. It was also shown that the drying procedure had remarkable influence on preserving the preformed porosity. Methanol as a dewatering solvent produced SHCs with higher porosity and swelling rate in comparison with the porosity of the hydrogels dewatered in acetone. Our invented methodology including simultaneous polymerization and foam formation using dual‐porogen system and the subsequent methanol‐dewatering approach was found to be the most efficient, highly practical, and cost‐effective route for preparing improved superabsorbing hydrogel materials.

     

Negotiation decision functions for autonomous agents

We present a formal model of negotiation between autonomous agents. The purpose of the negotiation is to reach an agreement about the provision of a service by one agent for another. The model defines a range of strategies and tactics that agents can employ to generate initial offers, evaluate proposals and offer counter proposals. The model is based on computationally tractable assumptions, demonstrated in the domain of business process management and empirically evaluated.     

Scalable Feature Selection in High-Dimensional Data Based on GRASP

Feature selection in high-dimensional data is one of the active areas of research in pattern recognition. Most of the algorithms in this area try to select a subset of features in a way to maximize the accuracy of classification regardless of the number of selected features that affect classification time. In this article, a new method for feature selection algorithm in high-dimensional data is proposed that can control the trade-off between accuracy and classification time. This method is based on a greedy metaheuristic algorithm called greedy randomized adaptive search procedure (GRASP). It uses an extended version of a simulated annealing (SA) algorithm for local search. In this version of SA, new parameters are embedded that allow the algorithm to control the trade-off between accuracy and classification time. Experimental results show supremacy of the proposed method over previous versions of GRASP for feature selection. Also, they show how the trade-off between accuracy and classification time is controllable by the parameters introduced in the proposed method.     

Reduction of stilling basin length with tall end sill

Experiments were conducted to characterize forced hydraulic jumps in stilling basins for enforced cases due to tail water level or dam site arrangement and construction.The case with a single tall sill was simulated in a horizontal flume downstream of a sluice gate.Results of experiments are compared with the classical hydraulic jump, and significant effect of tall sill on dissipation of energy in shorter distance was confirmed.Furthermore, the generated jumps were classified based on the ratio of sill height to basin length, and a simple design criterion was proposed to estimate the basin length for a desired jump and particular inflow.     

A pixel-based regularization approach to inverse lithography

Inverse lithography attempts to synthesize the input mask which leads to the desired output wafer pattern by inverting the forward model from mask to wafer. In this article, we extend our earlier framework for image prewarping to solve the mask design problem for coherent, incoherent, and partially coherent imaging systems. We also discuss the synthesis of three variants of phase shift masks (PSM); namely, attenuated (or weak) PSM, 100% transmission PSM, and strong PSM with chrome. A new two-step optimization strategy is introduced to promote the generation and placement of assist bar features. The regularization framework is extended to guarantee that the estimated PSM have only two or three (allowable) transmission values, and the aerial-image penalty term is introduced to boost the aerial image contrast and keep the side-lobes under control. Our approach uses the pixel-based mask representation, a continuous function formulation, and gradient-based iterative optimization techniques to solve the inverse problem. The continuous function formulation allows analytic calculation of the gradient in O(MNlog (MN)) operations for an M × N pattern making it practically feasible. We also present some results for coherent and incoherent imaging systems with very low k₁ values to demonstrate the effectiveness of our approach.     

A first-principles study of calcium-decorated, boron-doped graphene for high capacity hydrogen storage

Hydrogen adsorption and storage on calcium-decorated, boron-doped graphene was explored using density functional theory simulations based on local density approximation and generalized gradient approximation methods. The clustering problem for calcium-decorated graphene was investigated and it was shown that individual calcium atoms are not stable on pure graphene, and formation of aggregates is favorable. Substitutional boron doping can eliminate the clustering problem for Ca atoms on graphene. Up to four hydrogen molecules can stably bind to a Ca atom on a graphene plane with substitutional doping of a single boron atom. The average binding energy of ∼0.4 eV/H₂ is in the range that permits H₂ recycling at ambient conditions. Two binding mechanisms contribute to the adsorption of H₂ molecules: polarization of the H₂ molecule under the electric field produced by the Ca–graphene dipole, and hybridization of the 3d orbitals of Ca with the σ orbitals of H₂. Double-sided Ca-decorated graphene doped with individual boron atoms of 12 at.% can theoretically reach a gravimetric capacity of 8.38 wt.% hydrogen.     

Multivariate Optimization and Adsorption Characterization of As(III) by Using Fraxinus Tree Leaves

This study introduces Fraxinus tree leaves as a new, efficient biosorbent of As(III). A suitable response surface was achieved by running a central composite design. Simultaneous optimization of both responses (R% and q) was carried out and 67% of the goal of desirability function was attained. The results obtained for simultaneous optimization are R = 70% and q = 80.6 mg g^?1 with 67% desirability in m = 600 mg L^?1 where s = 0.10 g and pH = 3.9. Langmuir and Freundlich isotherms model were applied in explaining the sorbent–sorbate equilibrium study, and maximum capacity uptake equals 99.97 mg g^?1 and K_L = 0.05 L mg^?1 has been obtained. Fourier Transfer Infra-Red (FT-IR) and kinetic results were considered to examine the functional groups involved and the adsorption mechanism.     

Electrode polarization impedance in weak NaCl aqueous solutions

In this paper, we characterize the polarization impedance behavior of several common metals in diluted NaCl solution operated at low current densities. The objective was to provide a useful reference for those wishing to calculate the electrode polarization impedance in diluted NaCl solutions. Serial equivalent resistance (R) and capacitance (C) for silver, aluminum, gold, platinum, and medical stainless-steel were measured as a function of frequency (10(-2)-10(3) Hz) and NaCl concentration (2.4-77.0 mmol/L). The ratio of electrode polarization impedance with respect to the bulk resistance was calculated and plotted against concentration for each metal. Such a ratio shows the effect of the electrode polarization contribution as a function of electrolyte concentration when the bulk resistance of the solution changes. All metals showed a decrease of serial resistance Rp and capacitance Cp as a function of frequency. The medical stainless-steel electrode showed largest impedance values at lower frequencies compared to the other electrodes, and was concentration independent at all frequencies. Aluminum had smallest polarization impedance at low frequencies. Pure gold and platinum behaved similar with the exception that the serial resistance for gold showed a lower value at higher frequencies.     

Effect of filler material on local and global behaviour of buckling‐restrained braces

The nonlinear response of buildings has attracted a tremendous amount of attention in recent years. Braces, as lateral force‐resisting elements of a structure, are designed to not only react in the elastic region, but also to exhibit nonlinear response beyond the elastic limit. However, buckling in compression drastically degrades the performance of braces under earthquake loading. Buckling restrained braces (BRBs) have been evolved into very effective systems for severe seismic applications. They prevent buckling in compression through the encasing of core steel into a steel tube and confining infill concrete. The effect of infill material is investigated in this research through the use of experimental tests. Filler material may be concrete, grout or mortar, as well as granular material such as compacted aggregate. Moreover, lightweight concrete or lean concrete may be utilized as filler to reduce the overall structural weight. Furthermore, the need for unbonding material may not arise when sand and gravel mixture is used. Nevertheless, the strength of the aggregate should be such that no buckling or strength deterioration is observed. Parametric studies on BRB characteristics are carried out in this research. Results of cyclic loading tests are then provided for individual cases to characterize the effect of response parameters of BRB assemblages. Copyright © 2009 John Wiley & Sons, Ltd.     

In vitro evaluation of biopolymer networks based on crosslinked cellulose with various diamines

In this study, we investigated some hydrogels based on natural, biodegradable, and biocompatible polysaccharides and cellulose, as sustained release carriers and evaluated their controlled drug release. The crosslinking of bromoacetylated cellulose with various aliphatic and aromatic diamines, such as ethylene diamine, hexamethylene diamine, and paraphenylene diamine, were carried out in N,N‐dimethylformamide in the presence of triethylamine as a base. On the other hand, the synthesized hydrogels were characterized with Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and CHN elemental analysis. Also, the equilibrium swelling behavior of the hydrogels in water was calculated, and this indicated their sustained expansion. The loading of ceftizoxime antibiotic was carried out on the prepared hydrogels, and the in vitro and drug‐release behaviors were investigated in three different media (HCl solution at pH 3 and bicarbonate buffer solutions at pH 6 and 8). Finally, the release profiles of ceftizoxime from the hydrogels and their loading capacities were determined by ultraviolet–visible absorption measurements at λ_max 295 nm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42568.