Pressureless sintering of β-SiAlON ceramic compositions using fluorine and oxide additive system

SiAlONs are silicon aluminium oxynitride ceramic materials with a range of technically important applications, from cutting tools to specialised refractories and the properties of SiAlONs can be tailored for specific purposes. In this study, different β-SiAlON compositions were prepared using fluoride (MgF₂ as fluorine source plus Y₂O₃) and oxide (MgO plus Y₂O₃). These compositions were pressureless sintered under nitrogen atmosphere in the range of 1450–1750 °C for 0.5–2.5 h for comparison of densification behaviour and mechanical properties. Densities of samples were measured and analyses of result products were carried out using SEM and XRD. The F-doped sintered β-SiAlON ceramics showed better densities and less pore micrographs especially at lower temperatures compared with the fluorine free samples. Full densifications were achieved for β-SiAlON ceramics with fluoride addition at 1700 °C for 60 min. Consequently, fluorine addition to additive system has a good effect on mechanical properties and densification behaviour.     

Influence of pH on recombinant human growth hormone production by Pichia pastoris

BACKGROUND: Effect of pH on recombinant human growth hormone (rhGH) production by Pichia pastoris hGH‐Mut⁺ was investigated at pH = 4.2, 5.0, 5.5, and 6.0. RESULTS: The highest cell concentration was obtained at pH = 6.0 with 53 g L^?1, while the highest rhGH concentration was attained at pH = 5.0 as 0.27 g L^?1. Total protease secretion increased with increase in pH and with the cultivation time. Oxygen uptake rate increased with increasing pH up to pH = 6.0, having the maximum value, 37 mmol m^?3 s^?1, at pH = 5.5. K_La values were similar at all the conditions, having a maximum value of 0.14 s^?1 at pH = 5.0. Taking the final rhGH concentration into account, the most favourable pH was 5.0; where AOX1 expression level showed a similar trend to AOX activity profiles, having the highest value of 9.4 × 10¹⁰ copy mg^?1 CDW at t = 15 h; in parallel to AOX1 expression profile, hGH expression level increased until t = 15 h, with the highest value of 4.0 × 10¹⁰ copy mg^?1 CDW, where a sharp increase in rhGH concentration was obtained. The expression levels of pep4, prb1 and prc1 genes, responsible from the production of proteinase A, proteinase B and, carboxypeptidase Y, were parallel to each other. CONCLUSION: Since it was shown that pH is a crucial operating parameter in fermentation processes using P. pastoris, keeping pH constant at its determined optimum value, pH = 5.0, during the bioprocess is vital in terms of recombinant protein production. Copyright © 2010 Society of Chemical Industry     

A new implementation of common matrix approach using third-order tensors for face recognition

In the classical common matrix approach (CMA), the common matrix for each individual face class is obtained using basis matrices calculated by Gram–Schmidt orthogonalization of the class covariance matrix. This common matrix represents the common or invariant properties of a given face class. The CMA idea relies on the concept of basis matrices of a face class which span the, so called, difference subspace of that class. In this paper, an alternative method to obtain the basis matrices for CMA is proposed. The basis matrices are obtained using the higher order singular value decomposition (HOSVD) of a third-order tensor constructed with face images and these basis matrices are utilized in the construction of CMA. In order to exemplify the improvements in the recognition rates, face recognition experiments are carried out via the AR face database. The original face matrices, as well as 2DPCA-, 2DSVD-, and 2DFDA-based feature matrices are applied as the input matrices for the two different implementations of CMA in the experimental studies. The results indicate that the recognition rates obtained by the proposed method are slightly higher than those obtained using the basis matrices calculated by Gram–Schmidt orthogonalization.     

Active only integrator and differentiator with tunable time constants

In this paper new active only current-mode integrator and differentiator with electronically tunable time constants are described. They are composed of one operational amplifier (OA) and two operational transconductance amplifiers (OTAs), and are suitable for monolithic implementation either with CMOS or bipolar technologies. No realizability conditions are imposed for the proposed circuits and all of the active sensitivities are low. The performances of the circuits are demonstrated on the PSPICE platform.     

In situ evaluation of recommender systems: Framework and instrumentation

This paper deals with the evaluation of the recommendation functionality inside a connected consumer electronics product in prototype stage. This evaluation is supported by a framework to access and analyze data about product usage and user experience. The strengths of this framework lie in the collection of both objective data (i.e., “What is the user doing with the product?”) and subjective data (i.e., “How is the user experiencing the product?”), which are linked together and analyzed in a combined way. The analysis of objective data provides insights into how the system is actually used in the field. Combined with the subjective data, personal opinions and evaluative judgments on the product quality can be then related to actual user behavior. In order to collect these data in a most natural context, remote data collection allows for extensive user testing within habitual environments. We have applied our framework to the case of an interactive TV recommender system application to illustrate that the user experience of recommender systems can be evaluated in real-life usage scenarios.     

Comparison of performance and emissions of diesel fuel,rapeseed and soybean oil methyl esters injected at different pressures

Fuel properties of rapeseed oil and soybean oil methyl esters (e.g. density, cetane number and viscosity etc.) are similar to those of the diesel fuel. These methyl esters can be used as diesel engine fuel by mixing withy diesel fuel. In this study a comparison of diesel fuel, the rapeseed oil methyl ester and the soybean oil methyl ester was made from the engine performance and emissions point of view. The tests were carried out with a four-cylinder diesel engine for tree different injection pressures such as 250, 300 and 350 bar with each of these fuels. For the purpose of comparison, tests were also conducted at full load conditions with diesel fuel. As the result, the performance and emission values of rapeseed oil (R) and soybean oil (S) methyl esters were found to be nearly the same with those of diesel fuels (D) when injection pressure was increased to 300 bar.     

Failure Analysis of a Location Axle in Tracked Tractor

In this study, a failure analysis was performed on the location axle (brace axle) of a blade on a tracked tractor used in agricultural areas. The analysis included evaluation of the macrostructure of the damage and the microstructure of the material, as well as a chemical analysis of the material. A commercial finite element method software package was used to determine the behavior of the location axle under the defined boundary conditions. After all the examination steps were completed, the main reason for the damage was determined to be manufacture and material error despite the presence of fatigue tracks in the damaged area. In addition, a heat treatment was carried out with the specimens taken from the damaged area and microstructure was re-examined. The experimental and simulation evaluation results provide a technical basis for suggestions to prevent future damage to the location axle.     

On a multivariable extension of Jacobi matrix polynomials

The classical Jacobi matrix polynomials only for commutative matrices were first studied by Defez et al. [E. Defez, L. Jódar, A. Law. Jacobi matrix differential equation, polynomial solutions and their properties, Comput. Math. Appl. 48 (2004) 789–803]. The main aim of this paper is to construct a multivariable extension with the help of the classical Jacobi matrix polynomials (JMPs). Generating matrix functions and recurrence relations satisfied by these multivariable matrix polynomials are derived. Furthermore, general families of multilinear and multilateral generating matrix functions are obtained and their applications are presented.     

Preparation of nano-size ZrB2 powder by self-propagating high-temperature synthesis

Preparation of nano-size ZrB₂ powder by SHS has been investigated. Zr and B elemental powders were mixed with 10–50 wt.% NaCl, and prepared pellets were reacted under argon. Adiabatic temperatures were calculated by HSC software. Increasing NaCl content led to a continuous decrease in adiabatic temperatures and reaction wave velocity. Products were subjected to XRD, SEM and FESEM analyses. Average crystallite size of ZrB₂, which was 303 nm without NaCl, decreased to 32 nm with 40% NaCl addition. Distinct decrease in ZrB₂ particle size was also observed from SEM analyses. 30% NaCl addition was found to be optimum for ensuring a stable SHS reaction and providing the formation of nano-size ZrB₂ particles. It was revealed from particle size distribution measurements that ZrB₂ powder obtained by 30 wt.% NaCl addition contained particles mostly finer than 200 nm. A mechanism, similar to solution-precipitation was proposed for the particle size refining effect of NaCl.     

Functionalization of low molecular weight atactic polypropylene Part I. Spectroscopic studies

Summary Low molecular weight atactic polypropylene (APP) was functionalized with 4-allyl-2-methoxyphenol (eugenol), 4-allyl-1,2-dimethoxybenzene (DMAB), 4-propenylanisole(trans-anethole), cis-2,4,5-trimethoxypropenylbenzene (β-asarone) and 4-allyl-2,6-dimethoxyphenol (ADMP) in the presence of dicumyl peroxide (DCP) at 170°C. Amount of grafted eugenol, DMAB and anethole on APP and characterization of the products were carried by UV-VIS and FTIR spectroscopies respectively. The effects of the reaction time, concentrations of the functional compounds and DCP on the extent of grafting were examined. Received: 8 June 1999/Revised version: 31 August 1999/Accepted: 31 August 1999