Molecular dynamics simulations of polyphosphazenes: poly[bis(chloro)phosphazene][NPCl2] n

Suitable parameter sets for the CHARMm force field were derived for the structural units in polychlorophosphazene [P=N, P N, P Cl] using the Dinur Hagler energy second derivative procedure based on quantum mechanical SCI calculations using the 6–31G^* basis set. To validate the reliability of the parameter set, structural results obtained with CHARMm for the adopted model compounds (OP₂NCl₅ and OP₃N₂Cl₅) were compared with those derived fromab initio quantum mechanics using the 6–31G^* basis set. Application of molecular dynamics (MD) simulations in combinatioin with the available X-ray diffraction data provided structural and conformational information on the polymer. The calculation made using the periodic boundary conditions (PBC) agree well with the polychlorophosphazene ordered in a monoclinic unit cell (a=5.98,b=12.99,c=4.92 A; β=111.7). This model was stabilized mainly by the image atoms contribution to the electrostatic energy term and had aquasi-planar conformation of the backbone chain (glide symmetry). The MD calculations also provided evidence that the difference between single and double PN bonds is less marked than that measured experimentally. This result is, however, in agreement with more recent and accurate X-ray studies on poly(methylphosphazene). Validation of the polymer model provided a complete picture, otherwise experimentally inaccessible, of the internal fluctuations of the polymeric chains.     

Synthesis and properties of novel amphiphilic sulfated ionomers by the ring‐opening reaction of an epoxidized styrene–butadiene–styrene triblock copolymer

A method for the synthesis of novel sulfated ionomer of styrene–butadiene–styrene triblock copolymer (SBS) was developed. SBS was first epoxidized by performic acid in the presence of a phase‐transfer catalyst; this was followed by a ring‐opening reaction with an aqueous solution of alkali salt of bisulfate. The optimum conditions for the ring‐opening reaction of the epoxidized SBS with an aqueous solution of KHSO₄ were studied. During the ring‐opening reaction, both phase‐transfer catalyst and ring‐opening catalyst were necessary to enhance the conversion of epoxy groups to ionic groups. The products were characterized with Fourier transform infrared spectrophotometry and transmission electron microscopy (TEM). After the potassium ions of the ionomer were substituted with lead ions, the lead sulfated ionomer exhibited dark spots under TEM. Some properties of the sulfated ionomer were studied. With increasing ionic groups or ionic potential of the cations, the water absorbency and emulsifying volume of the ionomer and the intrinsic viscosity of the ionomer solution increased, whereas the oil absorbency decreased. The sulfated ionomer possessed excellent emulsifying properties compared with the sulfonated SBS ionomer. The sodium sulfated ionomers in the presence of 10% zinc stearate showed better mechanical properties than the original SBS. When the ionomer was blended with crystalline polypropylene, a synergistic effect occurred with respect to the tensile strength. The ionomer behaved as a compatibilizer for blending equal amounts of SBS and oil‐resistant chlorohydrin rubber. In the presence of 3% ionomer, the blend exhibited much better mechanical properties and solvent resistance than the blend without the ionomer. SEM photographs indicated improved compatibility between the two components of the blend in the presence of the ionomer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Design and implementation of a general software library for using NSGA-II with SWAT for multi-objective model calibration

Calibrating watershed-scale hydrologic models remains a critical but challenging step in the modeling process. The Soil and Water Assessment Tool (SWAT) is one example of a widely used watershed-scale hydrologic model that requires calibration. The calibration algorithms currently available to SWAT modelers through freely available and open source software, however, are limited and do not include many multi-objective genetic algorithms (MOGAs). The Non-Dominated Sorting Genetic Algorithm II (NSGA-II) has been shown to be an effective and efficient MOGA calibration algorithm for a wide variety of applications including for SWAT model calibration. Therefore, the objective of this study was to create an open source software library for multi-objective calibration of SWAT models using NSGA-II. The design and implementation of the library are presented, followed by a demonstration of the library through a test case for the Upper Neuse Watershed in North Carolina, USA using six objective functions in the model calibration.     

SWITCHING MECHANISMS IN A GENERALIZED INFORMATION SYSTEM

Abstract

A generalized information system has recently been proposed     

Synthesis and evaluation of novel injectable and biodegradable polyglycolide‐based composites

Novel 3‐arm methacrylate‐endcapped biodegradable polyglycolide prepolymer was synthesized and characterized. Injectable and in situ curable composites formulated with the liquid prepolymer and bioabsorbable β‐tricalcium phosphate were prepared. The pastelike composites were cured at room temperature using a redox‐initiation system. The initial compressive strengths (CSs), curing time, exotherm, and degree of conversion of the cured composites were determined. The composites showed initial yield CS ranging from 20.1 to 92.3 MPa, modulus from 0.73 to 5.65GPa, ultimate strength from 119.9 to 310.5 MPa, and toughness from 630 to 3930 N mm. Increasing filler content increased yield strength and modulus but decreased ultimate strength and toughness. Diametral tensile strength test showed the same trend as did CS test. Increasing filler content also increased curing time but decreased exotherm and degree of conversion. During the course of degradation, all the materials showed a significant burst degradation behavior within 24 h, followed by a significant increase in strength between Day 1 and Day 3, and then continuous degradation until no strength was detected. The composites with higher filler content retained their strengths longer but those with lower filler contents lost their strengths in 45 or 60 days. The degradation rate is filler‐content dependent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2977–2984, 2007     

Friction and wear mechanisms in hip prosthesis: Comparison of joint materials behaviour in several lubricants

In this work, the most commonly used joint materials for substitution of hip joints, ultra high molecular weight polyethylene (UHMWPE) for the cup, and alumina, stainless steel or CoCrMo alloy for the head, were submitted to pin-on-disk tribological tests. The interfacial behaviour prosthetic material/lubricant was investigated through wettability measurements. Four lubricants were used: Hanks’ balanced salt solution (HBSS) and solutions of bovine serum albumin (BSA), of hyaluronic acid (HA) and of both components (BSA + HA) in HBSS. It was observed that the friction coefficient increased significantly with time, in a random way, when the lubricant did not contain albumin. The addition of HA induced a slight reduction in the initial value of the friction coefficient but did not affect qualitatively its behaviour for longer times. Observation of the worn metallic surfaces revealed parallel grooves typical of abrasive wear and also lumpy transfer film of UHMWPE, while the transfer of polymer to alumina was incipient. Wear was particularly intense on the steel surface where delamination and fatigue wear mechanisms were also found. In the presence of albumin, the friction coefficient remained constant and small for the metallic surfaces and increased in the case of alumina. The observation of the worn surfaces showed that the presence of albumin in the lubricant avoided the transfer of polymer for the metallic surfaces but not for the alumina surfaces. These results, together with the wettability measurements, strongly indicate that the presence of albumin in the lubricant avoids the adhesion and transfer of UHMWPE only for the least hydrophilic surfaces, which are the metallic ones.     

Integrated micro- and miniscale electromechanical systems with permanent-magnet servo-motors and VLSI drivers–controllers

The current trends in development and deployment of advanced micro- and miniscale electromechanical systems (MEMS) have facilitated the unified fundamental, applied, and experimental research activities in the analysis and design of state-of-the-art motion devices (rotational and translational electromechanical motion devices), integrated circuits (ICs), and controllers. The objectives of this paper are to design, develop, and compare different control algorithms for high-performance MEMS with permanent-magnet rotational servo-motors controlled by ICs (VLSI driver–controller is fabricated using CMOS technology). The problems to be solved are very challenging because a number of long-standing issues in design, hardware integration, control, nonlinear analysis, and robustness have to be solved. The major emphases of this paper are the analysis and design of robust servo-systems, as well as the comparison of the dynamic performance of closed-loop MEMS with different control algorithms. We synthesize, verify, and test proportional–integral, integral with state feedback extension, relay, and sliding mode controllers. It is illustrated that the sliding mode control laws drive the states and tracking error to the switching surface and maintain (keep) the states and tracking error within this nonlinear switching surface in spite of different references, disturbances, parameter variations, and uncertainties. That is, robust tracking, desired accuracy, and disturbance attenuation are achieved. We report the experimental setup which was built to perform the advanced studies of high-performance MEMS. The testbed was built to integrate permanent-magnet microscale servo-motor and ICs (driver–controller).     

Numerical Model of Polydispersed Silica Grain Dissolution in Glass Melting Furnaces

The objective of this paper is to report on a numerical methodology addressing the defect problem in glass-melting furnaces. Specifically, given a furnace, through use of the proposed models one can predict the individual grain dissolution behavior and global size distribution curves of the undissolved silica grains at every point in the glass melt and, of course, in the final glass. Through some illustrative results, the utility of the proposed models is illustrated.