Numerical Study on Heat Transfer Between Turbulent Flow and Porous Rectangular Cylinders with Uniform Injection or Suction

The heat transfer characteristics of the flow around rectangular cylinders having various aspect ratios with uniform injection or suction through the rear, top, bottom, and all surfaces have been studied numerically. The effects of injection or suction on heat transfer have been linked to the analysis via wall functions of the velocity and temperature sublayers. The computational code employed in the present study was verified with a typical benchmark problem of the flow around a square cylinder. The results show that the heat transfer between the main flow and rectangular cylinders is substantially influenced by injection or suction—that is, suction enhances the heat transfer, while injection through the rear surface provides some thermal protection.     

Effect of Ti amount on wear and corrosion properties of Ti-doped Al2O3 nanocomposite ceramic coated CP titanium implant material

Al₂O₃ and Ti-doped Al₂O₃ nanocomposite ceramic coatings were prepared by using a sol-gel dip-coating process. Corrosion and wear resistance of Al₂O₃ ceramic coatings in relation to Ti amount were carried out using pin-on-disk tribotester, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Surface characterizations before and after the corrosion and wear tests were investigated by the scanning electron microscope (SEM) and X-ray diffraction (XRD) and hardness analysis. The results of corrosion and wear tests exhibited that the corrosion and wear resistance of nanocomposite ceramic coatings became better than uncoated samples. Also, corrosion and wear resistance of nanocomposite ceramic coatings improved with Ti doping content increased.     

Hemocompatibility,cytotoxicity, and genotoxicity of poly(methylmethacrylate)/nanohydroxyapatite nanocomposites synthesized by melt blending method

The aim of this study was to show the hemocompatibility, cytotoxicity, and genotoxicity of nanocomposites that were synthesized with different molecular weights of poly(methyl methacrylate) (PMMA) and different concentrations of nanohydroxyapatite (nHAp). Different techniques to characterize the nanocomposites were used. The cytotoxicity and genotoxic effects of the polymers and nanocomposites on human lymphocytes were determined by acid phosphatase assay, viability test, and comet assay. Moreover, hemocompatibility test was performed. It was found that all of the PMMA/nHAp nanocomposites are highly hemocompatible and biocompatible, none of the nanocomposites showed a cytotoxic effect, and nHAp addition decreased the genotoxicity.     

Synthesis,Characterization, and In Vitro Bioactivity of Sol‐Gel‐Derived Zn,Mg, and Zn‐Mg Co‐Doped Bioactive Glasses

Bioactive glasses in the systems CaO‐SiO₂‐P₂O₅‐ZnO, CaO‐SiO₂‐P₂O₅‐MgO, and CaO‐SiO₂‐P₂O₅‐MgO‐ZnO were prepared and characterized. Bioactive glass powders were produced by the sol‐gel method. The prepared bioactive glass powders were immersed in a simulated body fluid (SBF) for periods of up to 28 days at 310 K to investigate the bioactivity of the produced samples. Inductively coupled plasma (ICP) and ultraviolet (UV) spectroscopic techniques were used to detect changes in the SBF composition. X‐Ray diffraction (XRD) was utilized to recognize and confirm the formation of a hydroxyapatite (HA) layer on the bioactive glass powders. Microstructural characterizations of the bioactive glass samples were investigated by scanning electron microscopy (SEM) techniques. Density, porosity, and surface area values of bioactive glass powders were also determined in order to characterize the textural properties of the samples. The results revealed the growth of an HA layer on the surface of the bioactive glass samples. MgO in the glass sample increases the rate of formation of an HA layer while ZnO in the glass slows it down.     

The investigation of the effect of thermal barrier coating on the performance of Stirling engine

The shuttle heat transfer is one of the reasons reducing the performance of Stirling engines. This study is concerned with the reduction in shuttle heat transfer by coating the displacer. The displacer of a gamma type Stirling engine was coated with a layer of yttria‐stabilized zirconia (YSZ), and the effect of the coating on the engine performance was evaluated by comparing speed‐power and speed‐torque characteristics of the engine with coated and uncoated displacers. Characteristics were obtained for 700, 800 and 900°C heater temperatures. At each stage of the heater temperature, the charge pressure ranged from 1 to 3.5 bars with 0.5 bar increments. At 900°C heater temperature and 3 bars charge pressure, the shaft power before coating was 34.9 W, after coating the power increased to 43.8 W, which corresponds to a 25% increment. The temperature applied to the engine did not cause any damage on the coating layer. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of conducting copolymers of thiophene-3-yl acetic acid cholesteryl ester with pyrrole

A new polythiophene containing a cholesteryl side chain in the -position was chemically polymerised in nitromethane/carbontetrachloride using FeCl₃ as the oxidizing agent. Polymerisation was also achieved by constant current electrolysis in dichloromethane. Subsequently, conducting copolymers of thiophene-3-yl acetic acid cholesteryl ester (CM), PCM1 (obtained from chemical polymerisation method) and PCM4 (obtained from constant current electrolysis) with pyrrole were synthesized using p-toluene sulfonic acid and sodium dodecyl sulfate as the supporting electrolytes via constant potential electrolyses. Characterizations of the samples were performed by CV, FTIR, NMR, DSC, TGA and SEM analyses. Electrical conductivities were measured by the four-probe technique.     

Analysis of the reaction mechanism and substrate specificity of haloalkane dehalogenases by sequential and structural comparisons

Haloalkane dehalogenases catalyse environmentally importantdehalogenation reactions. These microbial enzymes representobjects of interest for protein engineering studies, attemptingto improve their catalytic efficiency or broaden their substratespecificity towards environmental pollutants. This paper presentsthe results of a comparative study of haloalkane dehalogenasesoriginating from different organisms. Protein sequences andthe models of tertiary structures of haloalkane dehalogenaseswere compared to investigate the protein fold, reaction mechanismand substrate specificity of these enzymes. Haloalkane dehalogenasescontain the structural motifs of /ß-hydrolases and epoxidaseswithin their sequences. They contain a catalytic triad withtwo different topological arrangements. The presence of a structurallyconserved oxyanion hole suggests the two-step reaction mechanismpreviously described for haloalkane dehalogenase from Xanthobacterautotrophicus GJ10. The differences in substrate specificityof haloalkane dehalogenases originating from different speciesmight be related to the size and geometry of an active siteand its entrance and the efficiency of the transition stateand halide ion stabilization by active site residues. Structurallyconserved motifs identified within the sequences can be usedfor the design of specific primers for the experimental screeningof haloalkane dehalogenases. Those amino acids which were predictedto be functionally important represent possible targets forfuture site-directed mutagenesis experiments.     

Effect of growth rate and lamellar spacing on microhardness in the directionally solidified Pb-Cd, Sn-Zn and Bi-Cd eutectic alloys

Lead-cadmium, Zinc-tin and Bismuth-cadmium of (99.99%) high purity eutectic alloys were melted in a graphite crucible under vacuum atmosphere. These eutectic alloys were directionally solidified upward with a constant temperature gradient G and different growth rates V in the Bridgman type directional solidification furnace. The lamellar spacings and microhardness H _V were measured from both transverse section and longitudinal section of the specimen. The variations of H _V with respect to V and have been determined by using the linear regression analysis method. H _V values increase with the increasing values of V and decrease with the increasing values. The Hall-petch type relationships obtained in this work have been compared with the previous works.     

Doubly Iterative Equalization of Continuous-Phase Modulation

In this paper, a doubly iterative receiver is proposed for joint turbo equalization, demodulation, and decoding of coded binary continuous-phase modulation (CPM) in multipath fading channels. The proposed receiver consists of three soft-input soft-output (SISO) blocks: a front-end soft-information-aided minimum mean square error (MMSE) equalizer followed by a CPM demodulator and a back-end channel decoder. The MMSE equalizer, combined with an a priori soft-interference canceler (SIC) and an a posteriori probability mapper, forms a SISO processor suitable for iterative processing that considers discrete-time CPM symbols which belong to a finite alphabet. The SISO CPM demodulator and the SISO channel decoder are both implemented by the a posteriori probability algorithm. The proposed doubly iterative receiver has a central demodulator coupled with both the front-end equalizer and the back-end channel decoder. A few back-end demodulation/decoding iterations are performed for each equalization iteration so as to improve the a priori information for the equalizer. As presented in the extrinsic information transfer (EXIT) chart analysis and simulation results for different multipath fading channels, this provides not only faster convergence to low bit error rates, but also lower computational complexity.