Kinetic study of polyesterification: Unsaturated polyesters

Synthesis of unsaturated polyesters using adipic acid, ethylene glycol, and fumaric acid in the absence and presence of a foreign acid (phosphoric acid) as catalyst was carried out by a two-stage method under constant reaction temperatures of 160–180°C and at different ratios of diol to diacid. The experimental data fit the Chen–Wu rate equations for self-catalyzed and acid-catalyzed reactions. The reaction rate constants and activation energies for both systems were calculated. The rate constants of fumaric acid–ethylene glycol systems were found to be nearly constant and had negligible variations with increasing chain length of polymer. © 1995 John Wiley & Sons, Inc.     

A numerical study on the effect of static magnetic field on the hemodynamics of magnetic fluid in biological porous media

Journal of Thermal Analysis and Calorimetry - High interstitial fluid pressure in the tumor is among the most important barriers to drug delivery. The use of the static magnetic field is one of the...     

A low-cost optimization framework to solve muscle redundancy problem

Prediction of muscle activations based on optimization procedures mostly leads to a prohibitive computational effort. To overcome this problem, an optimization framework by reformulation of the so-called method of extended inverse dynamics (EID) was developed. A planar, seven-segment model with sixteen muscle groups was used to represent human neuromusculoskeletal dynamics. The muscle activations were estimated based on two methods: EID, which treats the system dynamics (compatibility between muscular and skeletal torques), as an equality constraint, and the proposed method, which employs unconstrained system dynamics of EID (USDEID). The proposed method is based on the idea that the EID equality constraint, which is difficult to satisfy, can be eliminated by reformulation of the governing equations and optimization variables, which not only relaxes the optimization problem and leads to less optimization parameters, but also guarantees the full compatibility of the system dynamics. The comparison of simulation results of optimal muscle activations against experimental data showed a reasonable agreement for both methods during half of a gait cycle. Optimization results showed that USDEID is not only more accurate than EID in terms of the compatibility between the skeletal and muscular system dynamics, but also approximately eight times faster for ten random initial values. USDEID may be used to predict muscle activations, when the computational cost becomes prohibitive.     

Application of Polymerization Kinetic Modeling in High‐Throughput Screening of Catalyst Systems for Productivity

In high‐throughput research, it is essential to use “right data” and “meaningful parameters” to reach reliable conclusions. The complexity and the large amount of data obtained from each set of experiments make the analysis of reaction data a nontrivial task. The important role of reaction kinetic modeling in the analysis of polymerization reaction data is discussed, and it is shown that the application of traditional methods for the determination of catalyst productivity can be misleading. Reaction kinetic modeling provides meaningful parameters for data analysis, gives complete information about the polymerization kinetic profile, and makes it possible to evaluate assumptions and hypotheses.

     

Two‐phase electromembrane extraction followed by gas chromatography‐mass spectrometry analysis

A two‐phase electromembrane extraction (EME) was developed and directly coupled with gas chromatography mass spectrometry (GC‐MS) analysis. The proposed method was successfully applied to the simultaneous determination of imipramine, desipramine, citalopram and sertraline. The model compounds were extracted from neutral aqueous sample solutions into the organic phase filled in the lumen of the hollow fiber. This method was accomplished with 1‐heptanol as organic phase, by means of 60 V applied voltage and with the extraction time of 15 min. Experiments reported recoveries in the range of 69–87% from 1.2 mL neutral sample solution. The compounds were quantified by GC‐MS instrument, with acceptable linearity ranging from 1 to 500 ng mL^?1 (R² in the range of 0.989 to 0.998), and repeatability (RSD) ranging between 7.5 and 11.5% (n = 5). The estimated detection limits (S/N ratio of 3:1) were less than 0.25 ng mL^?1. This novel approach based on two‐phase EME brought advantages such as simplicity, low‐costing, low detection limit and fast extraction with a total analysis time less than 25 min. These experimental findings were highly interesting and demonstrated the possibility of solving ionic species in the organic phase at the presence of electrical potential.     

Effect of cocatalyst on the chain microstructure of polyethylene made with CGC‐Ti/MAO/B(C6F5)3

This investigation studied the solution polymerization of ethylene in Isopar E in a semibatch reactor using CGC‐Ti as catalyst and methylalumoxane (MAO) and tris(pentaflourophenyl)borane [B(C₆F₅)₃] as cocatalysts. The effects of cocatalyst type and amount on the chain microstructure were investigated. ¹³C NMR and gel permeation chromatography were used to determine the long‐chain branching (LCB) content and molecular weight distribution (MWD), respectively, of the samples. It was observed that higher concentrations of MAO increased the LCB content and decreased the molecular weight of the polymer. On the other hand, increasing the amount of B(C₆F₅)₃ lowered the LCB content, increased the molecular weight, and broadened MWD significantly. We believe that this approach can be used as an efficient way to control the microstructure of polyolefins made with these catalytic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3055–3061, 2004     

Asymmetric three-link passive walker

Passive walkers are dynamically stable robots with a gait that resembles the human locomotion. These walkers can be studied to better understand the dynamic behavior of the human gait and design efficient active walkers and assistive devices. In this paper, we study the walking dynamics of a three-link passive walker with an asymmetrical structure where one leg has a knee while the other is knee-less. After finding a 2-periodic steady gait for the three-link walker with humanlike inertial parameters for both legs, the possibility of a gait with symmetrical step lengths is discussed where the half inter-leg angles at the beginning of every step are made equal by altering the physical parameters of the knee-less leg. We further study the gaits with symmetrical step lengths and show that by replacing one leg of a four-link symmetric walker with the knee-less leg of the three-link walker with the symmetrical half inter-leg angles, the dynamic behavior of the kneed leg remains unchanged. This approach can be adapted in the field of gait rehabilitation and prosthesis design to obtain a more symmetrical gait and preserve the motion of the healthy leg.

     

Electromembrane extraction of zwitterionic compounds as acid or base: Comparison of extraction behavior at acidic and basic pHs

This study has performed on electromembrane extraction (EME) of some zwitterionic compounds based on their acidic and basic properties. High performance liquid chromatography (HPLC) equipped with UV detection was used for determination of model compounds. Cetirizine (CTZ) and mesalazine (MS) were chosen as model compounds, and each of them was extracted from acidic (as a cation) and basic (as an anion) sample solutions, separately. 1-Octanol and 2-nitrophenyl octylether (NPOE) were used as the common supported liquid membrane (SLM) solvents. EME parameters, such as extraction time, extraction voltage and pH of donor and acceptor solutions were studied in details for cationic and anionic forms of each model compound and obtained results for two ionic forms (cationic and anionic) of each compound were compared together. Results showed that zwitterionic compounds could be extracted in both cationic and anionic forms. Moreover, it was found that the extraction of anionic form of each model compound could be done in low voltages when 1-octanol was used as the SLM solvent. Results showed that charge type was not highly effective on the extraction efficiency of model compounds whereas the position of charge within the molecule was the key parameter. In optimized conditions, enrichment factors (EF) of 27–60 that corresponded to recoveries ranging from 39 to 86% were achieved.     

Feedback control of temperature in specific geometry of porous media: application to hyperthermia

Journal of Thermal Analysis and Calorimetry - One of the methods of treating cancer is hyperthermia which is performed in several different ways. One of the recent treatment modalities is with...