Studies on sintering kinetics and correlation with the sinterability of 8Y zirconia ceramics based on the dilatometric shrinkage curves

Prediction of the dominant sintering mechanism and corresponding temperature regimes become important in arriving at the optimum sintering schedule of ceramics. The sintering kinetics of 8Y zirconia (8YSZ) submicron powders, with particle sizes ～205 nm, has been evaluated through, (i) constant rates of heating and (ii) master sintering curve (MSC) technique. Slip cast green 8YSZ compacts, close to 50% of the theoretical density, have been subjected to dilatometry, for recording the shrinkage behavior, at constant heating rates of 5, 10 and 20 °C/min. The kinetics of the corresponding sintering process has been evaluated by estimating and comparing the apparent activation energies (Q) from the constant heating rate technique, and MSC approach. The observed apparent activation energy (～350 kJ/mol) suggests grain-boundary diffusion to be the dominant mechanism in sintering of 8YSZ ceramics.     

Assessment of factors responsible for polymer electrolyte membrane fuel cell electrode performance by statistical analysis

The performance of the fuel cell electrode depends on many factors: types of materials and their properties, composition, process parameters and fuel cell operation conditions. In the present paper, cathode electrode performance in a PEM fuel cell as a function of Teflon concentration in the substrate materials and in micro-layer carbon, pore former in the micro-layer, amount of carbon used in the diffusion layer and Platinum & Nafion loading in the catalyst layer are studied. These six factors each at two levels are considered. A full factorial design would have required 2⁶, i.e., 64 experiments to be carried out. With the use of Taguchi method, L₁₂ designs, the number of experiments can be reduced to 12. The electrode current density values are taken as responses for the analysis. Statistical sensitivity analysis (ANOVA analysis) is used to compute the effects and the contributions of the various factors to the fuel cell electrode. Some graphic representations are employed in order to display the results of the statistical analysis made for different current values. The behavior of cathode PEM fuel cell electrode was studied using humidified hydrogen and compressed air. The present paper examines the six main factors and their levels responsible for altering the performance particularly when the fuel is operated under ambient pressure.     

Concentration-dependent growth and morphology of doped polyaniline nanowires

Polyaniline nanowires with entangled network structures were synthesised through an electropolymerisation route using a step galvanostatic method on titanium substrate. The morphology of the synthesised polyaniline was investigated by scanning electron microscopy and transmission electron microscopy. The dependence of morphology on the concentration and duration of synthesis has also been studied. Structural characterisation has been done by UV–VIS spectroscopy and Fourier transform infrared spectroscopy. The concentration of the monomer and the duration of synthesis affect the morphology as well as the amount of nanowires deposited.     

Analysis of Stress Control on 33-kV Non-ceramic Insulators Using Finite-element Method

In this article, analysis of electric field stress and electric potential distributions of a 33-kV composite insulator and factors that affect the electric field are discussed. Accordingly, the article is classified into two parts. In the first part, the designs of three different configurations of non-ceramic (composite) insulator based on their geometry modification in end fittings and water shed are discussed. The electrical performances are analyzed using electric field and electrical potential distribution. In the second part, a reduction of the electric field near the end fittings is done to control the electric field stress intended for long-term performance. For that, the grading material is placed between the core and housing materials by fitting the arcing horn near the end fittings. A 33-kV composite insulator is modeled in two dimensions by the finite-element method to investigate the electric field and electric potential distribution under normal and polluted conditions. The results reveal that an optimum installation of an arcing horn at the high-voltage end in the composite insulator with silicone rubber overlapping the edges of metal end fittings made a significant reduction in electric field stress on 33-kV non-ceramic insulators.     

Medium optimization and in vitro antioxidant activity of exopolysaccharide produced by Bacillus subtilis

The present study involves medium formulation using an agro waste, cane molasses, as the carbon substrate that was used instead of sucrose, to produce exopolysaccharide from Bacillus subtilis. Plackett Burman design was applied to evaluate twenty selected components, from which cane molasses, yeast extract, CaCl₂, NaCl were found to be significant for fermentation. To study the concentration of each component, response surface methodology experimental design was performed using central composite design. The response plots resulted in optimized conditions—Cane molasses-2.36%, Yeast extract-0.56%, NaCl–0.71%, CaCl₂ — 0.05%—which yielded 4.92 g/L at 48 h, at a temperature of 37 °C, initial pH 7 under still conditions. Antioxidant activity of EPS on DPPH resulted in a reducing capacity of 61.19%, at a concentration of 0.8mg/ml, greater than standard, Vitamin C. The biopolymer could thus be an ecofriendly product which can be subjected to various industrial and pharmaceutical applications.     

Electrochemical,SEM and XPS investigations on phosphoric acid treated surgical grade type 316L SS for biomedical applications

A simple surface pre-treatment method was attempted to establish a stable passive layer on the surface of surgical grade stainless steel (SS) of type 316L for biomedical applications. Surgical grade type 316L SS specimens were subjected to H₃PO₄ treatment for 1 h by completely immersing them in the acid solutions to develop a passive barrier film. The effect of various concentrations of phosphoric acid on the localized corrosion resistance behavior of type 316L SS was investigated through electrochemical techniques using cyclic polarization studies and electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy (XPS) was used to evaluate the nature and composition of the passive films. The surface morphology and relative elemental composition of the untreated and acid treated surfaces subjected to anodic polarization was studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) techniques, respectively. Compared with untreated (pristine) 316L SS, the 40% acid treated surface formed a stable passive layer that had superior corrosion resistance.     

Minimally invasive injectable short nanofibers of poly(glycerol sebacate) for cardiac tissue engineering

Myocardial tissue lacks the ability to appreciably regenerate itself following myocardial infarction (MI) which ultimately results in heart failure. Current therapies can only retard the progression of disease and hence tissue engineering strategies are required to facilitate the engineering of a suitable biomaterial to repair MI. The aim of this study was to investigate the in?vitro properties of an injectable biomaterial for the regeneration of infarcted myocardium. Fabrication of core/shell fibers was by co-axial electrospinning, with poly(glycerol sebacate) (PGS) as core material and poly-l-lactic acid (PLLA) as shell material. The PLLA was removed by treatment of the PGS/PLLA core/shell fibers with DCM:hexane (2:1) to obtain PGS short fibers. These PGS short fibers offer the advantage of providing a minimally invasive injectable technique for the regeneration of infarcted myocardium. The scaffolds were characterized by SEM, FTIR and contact angle and cell-scaffold interactions using cardiomyocytes. The results showed that the cardiac marker proteins actinin, troponin, myosin heavy chain and connexin 43 were expressed more on short PGS fibers compared to PLLA nanofibers. We hypothesized that the injection of cells along with short PGS fibers would increase cell transplant retention and survival within the infarct, compared to the standard cell injection system.     

Multi-capping agents in size confinement of ZnO nanostructured particles

In the present paper, we report a new approach to synthesize crystalline zinc oxide (ZnO) nanoparticles in the presence of multi-capping agents namely poly-vinylpyrrolidone (PVP) and citric acid (CA), with zinc acetate dihydrate and sodium hydroxide (NaOH as pellets) as a source material and their characteristic studies. The ZnO nanoparticles grown under this simple chemical process involve a heterogeneous chemical reaction in the presence of water as a solvent medium and reaction temperature of 100 °C for 48 h in a closed environment. The structural, optical and chemical features of ZnO nanoparticles were systematically studied by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and Ultra Violet–visible (UV–vis) absorption spectroscopy. The Williamson–Hall (W–H) plot was also performed to distinguish the effect of crystalline size-induced broadening and strain-induced broadening at Full Width Half Maximum (FWHM) of the XRD profile. The growth mechanism of ZnO nanoparticles and the effective capping mechanism shown by each capping agent are briefly discussed.     

Effect of black tea on histological and immunohistochemical changes in pancreatic tissues of normal and streptozotocin‐induced diabetic mice (Mus musculus)

The aim of the present study is to evaluate the effect of hot water extract of black tea in regenerating β cells in streptozotocin‐induced diabetic mice. Light microscopic examination of pancreatic sections of streptozotocin‐induced diabetic mice showed the acinar cells to be small, shrunken, and with deteriorated β cells. The dose of streptozotocin not only altered the function of β cells but also damaged the acinar region. The changes in acinar cells were coarsening of endoplasmic reticulation suggesting alteration in their secretory function. The control pancreatic tissue showed well‐defined granulated islets and dark β cells when stained with chrome hematoxylin and phloxine. Interestingly, pancreatic sections of diabetic mice fed with black‐tea extract showed regeneration of β cells and acinar region appeared normal with increased numbers of β cells. To understand the probable mechanism of action of black‐tea extract, we analyzed inducible nitric oxide synthase (iNOS) expression by immunohistochemistry and the results showed an increased iNOS levels in streptozotocin‐induced diabetic pancreas, and such high iNOS levels were inhibited in black‐tea extract treated mice. According to histological results obtained, it can be concluded that the black‐tea extract helps in regeneration of damaged pancreas and protects pancreatic β cells by its antioxidant action against nitrosative stress in streptozotocin‐induced diabetes. Microsc. Res. Tech., 2009. © 2009 Wiley‐Liss, Inc.     

Wing-body interference using a hybrid panel method

Summary The problem of determining the pressures acting on bodies in the region of wing-body interference in subsonic, inviscid flows is dealt with in detail in the current paper in the framework of a hybrid vortex lattice/first order panel method. Here the lift carryover and the wing-body interference effects are accounted for by the use of interpenetrating singularity panels. The non-lifting components are modeled by constant source panels and lifting elements by horse shoe vortices. Several alternative models have been programmed to study their effects on the pressure distribution in the wing-body interference region. The final procedure has been validated by comparing the pressures from experiments for several wing-body combinations.Notation AR Wing aspect ratio - b Wing span - B Body - C _p ,C _p Pressure coefficient,P-P /1/2 U ² - ,n Unit normal to panel; also direction of normal - r(p, q) Distance between two points in three dimensional space; especially between a point where a source is located and a point where the velocities are computed - U ,V _FS Free stream velocity - V _B Velocity due to body sources - V _D Velocity due to distributed vortices - V _T Velocity due to wing thickness sources - V _P Total velocity at pointP - V _c+ Velocity due to camber and incidence - W Wing - X _B Distance along length of body - Angle of attack - , Vortex strength - Air density - Azimuthal distribution of panels on fuselage - Non-dimensional spanwise station - Source density - Free stream conditions