Optimization of alkaline protease production from Shewanella oneidensis MR‐1 by response surface methodology

BACKGROUND: The proteases are among the most important groups of enzymes. Therefore, it is important to produce inexpensive and optimized media for large‐scale commercial production. In the present work, three different Shewanella species were screened on skim milk agar medium for their ability to produce alkaline protease. The effects of different culture conditions were optimized for alkaline protease production by S. oneidensis MR‐1 using a Box–Behnken design combined with response surface methodology (RSM). RESULTS: Highest yield (112.90 U mL^?1) of protease production was obtained at pH 9.0, a temperature of 30 °C, glucose (12.5 g L^?1), tryptone (12.5 g L^?1) and an incubation period of 36 h. A second‐order polynomial regression model was used for analysis of the experiment. The experimental values were in good agreement with predicted values, with correlation coefficient 0.9996. CONCLUSION: Carbon and nitrogen, pH, temperature and incubation period were chosen as the main factors to be used in an experimental design for optimization to produce low‐cost enzymes, potentially for use on an industrial scale. A 60% increase in enzyme activity was achieved in the optimized medium compared with the original medium. Copyright © 2008 Society of Chemical Industry     

Utility accrual real-time scheduling for multiprocessor embedded systems

We present the first Utility Accrual (or UA) real-time scheduling algorithm for multiprocessors, called the global Multiprocessor Utility Accrual scheduling algorithm (or gMUA). The algorithm considers an application model where real-time activities are subject to time/utility function time constraints, variable execution time demands, and resource overloads where the total activity utilization demand exceeds the total capacity of all processors. We consider the scheduling objective of (1) probabilistically satisfying lower bounds on each activity’s maximum utility, and (2) maximizing the system-wide, total accrued utility. We establish several properties of gMUA including optimal total utility (for a special case), conditions under which individual activity utility lower bounds are satisfied, a lower bound on system-wide total accrued utility, and bounded sensitivity for assurances to variations in execution time demand estimates. Finally, our simulation experiments validate our analytical results and confirm the algorithm’s effectiveness.     

Compatibility of ZrN and HfN with molten LiCl-KCl-NaCl-UCl3

The reaction kinetics of ZrN and HfN immersed in a quaternary salt of composition of 28.5% LiCl-36.3% KCl-29.4% NaCl-5.8% UCl₃ (in weight percent) were assessed. Coupons of ZrN and HfN were exposed to the quaternary salt at 525-900 °C for 4-485 h. The reaction kinetics of the salt-refractory interactions were assessed through physical and microstructural characterization including scanning electron microscopy, X-ray diffraction and mass spectrometry. The results indicated that ZrN and HfN lose weight under all conditions investigated. While multiple mechanisms were evident, it is proposed that dissolution and oxidation were the dominant reactions that influence the weight loss. For the overall reaction, negative apparent activation energy values of −46 and −28 kJ/mol were observed in ZrN and HfN, respectively. These seemingly anomalous activation energies were associated with the simultaneous occurrence of electrochemical dissolution and surface oxide formation.     

Grain Growth of Microtubes During Sintering in Semiconducting Ba3Ce3−xBixTi5Nb5O30 (x=0.5, 1.0, 2.0, and 3.0) Ceramics

Well grown microtubes of Ba₃Ce_{3− x} Bi _x Ti₅Nb₅O₃₀ ( x =0.5, 1.0, 2.0, and 3.0) have been observed in the sintered ceramics. The microtubes have octagonal shapes at the cylindrical ends, hollow cores with diameters of 2–3 μm, lengths over a few tens of micrometers and wall thickness of 0.5–1.0 μm. In morphology, the tubes are very straight and are apparently welded to each other on the sides. The tubular growth as well as increase of wall thickness is observed to be more with greater Bi content, but when Ce is fully substituted by Bi, the tubes have grown into solid rods without hollowness. The growth spirals at the ends of tubes as seen by scanning electron microscope indicate that growth takes place in the longitudinal direction of the tubes. Observation of growth spirals on grains of a sintered ceramic is unusual. In fact, such features are usually seen in liquid phase growth and, therefore, we propose here grain growth in partially fluid conditions. The phase identification by X-ray diffraction shows that the compound has a tetragonal tungsten bronze type structure. The resistivity measurements above room temperature indicate that these compounds are semiconductors and both resistivity and activation energy increase with Bi content.     

Relationships Between Solidification Parameters in A319 Aluminum Alloy

The design of high-performance materials depends on a comprehensive understanding of the alloy-specific relationships between solidification and properties. However, the inconsistent use of a particular solidification parameter for presenting materials characterization in the literature impedes inter-study comparability and the interpretation of findings. Therefore, there is a need for accurate expressions relating the solidification parameters for each alloy. In this study, A319 aluminum alloy castings were produced in a permanent mold with various preheating temperatures in order to control metal cooling. Analysis of the cooling curve for each casting enabled the identification of its liquidus, Al-Si eutectic, and solidus temperatures and times. These values led to the calculation of the primary solidification rate, total solidification rate, primary solidification time, and local solidification time for each casting, which were related to each other as well as to the average casting SDAS and material hardness. Expressions for each of their correlations have been presented with high coefficients of determination, which will aid in microstructural prediction and casting design.     

Effect of Melt Cleanliness on the Mechanical Properties and Microstructure on AZ91E Mg Alloy Castings

The current study examines various filter configurations, argon bubbling, and degasser addition to improve melt cleanliness of AZ91E permanent mold castings. The unfiltered castings had an average yield strength, ultimate tensile strength, and elongation of 93.3, 153.3 MPa, and 2.2% respectively. Using a fine mesh filter within the well of the mold, the ultimate tensile strength and elongation increased by 9 and 41%, respectively, compared to the unfiltered samples. A combination of a fine filter and argon bubbling resulted in an average increase in ultimate tensile strength and elongation of 29 and 123%, respectively, that matched the performance of the C₂Cl₆-based degassed castings with 95.8, 194.3, and 4.9% for yield strength, ultimate tensile strength, and elongation, respectively. The addition of the C₂Cl₆-based degasser released harmful vapors that can be avoided using the fine filter with argon bubbling. In all cases, the removal of MgO-based inclusions improved mechanical properties.     

Improvements in Mechanical Properties of 319 Al Alloy Engine Blocks Through Cost-Effective Solution Heat Treatment

The use of Al engine blocks has increased significantly to improve vehicle fuel efficiency. However, the gray cast iron cylinder liners cause the development of large tensile residual stress along the cylinder bores which necessitates the optimization of mechanical properties in this region to prevent premature engine failure. This study compared the microstructure of T4-treated Al billet castings of varying cooling rate to that of the cylinder region of T4-treated (current production schedule) Al engine blocks. The aim of this study was to develop a cost-effective small scale heat treatment optimization method for engine block production. Comparisons in microstructure between the engine block and the billet castings were carried out using optical and scanning electron microscopy. The results suggest that the microstructure and hardness at the top, middle, and bottom of the cylinder were similar to those of each representative billet casting, indicating that heat treatment resulted in successful replication of the engine block locations. In addition, tensile testing revealed that the YS and UTS increased slightly following T4 treatment for all billet castings, which was also observed at the middle of the engine block cylinder bridge. As such, this method can be an effective forerunner for future heat treatment optimization in Al engine block production.     

Microstructural,physico-chemical and mechanical characterisation of Sansevieria cylindrica fibres – An exploratory investigation

The microstructural, physical, chemical and mechanical properties of Sansevieria cylindrica fibres are described for the first time in this work. A microstructural analysis of S. cylindrica leaves showed the presence of structural fibres and arch fibres. Polarised light microscopy and scanning electron microscopy of these fibres revealed a hierarchical cell structure that consisted of a primary wall, a secondary wall, a fibre lumen and middle lamellae. The cross-sectional area and porosity fraction of the fibre were estimated to be approximately 0.0245 mm² and 37%, respectively. The fibre density and fineness were approximately 0.915 ± 0.005 g/cm³ and 9 Tex, respectively. An X-ray diffraction and Fourier transform infrared analysis of the fibres showed the presence of cellulose I_β with a crystallinity index of 60%. Tensile tests showed that the corrected Young’s modulus was approximately 7 GPa, the tensile strength was 658 MPa, and the total elongation was between 10% and 12%.     

Yttrium aluminum garnet powders by nitrate decomposition and nitrate–urea solution combustion reactions—a comparative study

Precursors for yttrium aluminum garnet (Y₃Al₅O₁₂—YAG) were synthesized by simple decomposition of concentrated aqueous solution of nitrates and combustion of concentrated aqueous solution of nitrates with urea on a heater. The precursor formed by the former reaction was granules of agglomerated powder while that from the latter reaction was a voluminous and porous sponge-like mass. Both precursors were ground to powders and subjected to detailed thermogravimetric–differential thermal analysis and X-ray diffraction studies. The precursor from the simple decomposition of nitrates exhibited a total loss in weight of about 18% in stages (25 to 300 °C and 300 to 600 °C) accompanied by endotherms—characterized as processes of dehydration of absorbed moisture and decomposition of residual nitrates, respectively. The as formed precursor and that heated to 820 °C were amorphous. Crystallization to YAG phase occurred from an amorphous oxide characterized by an exotherm above 820 °C with no loss of weight. The precursor from nitrate–urea combustion reaction was found to exhibit a weight loss of 2.5% accompanied by a shallow endotherm in the range of 25 to 300 °C—characterized as the process of dehydration of absorbed moisture. No further weight loss or heat effect was noticed, confirming it to be chemically pure YAG. This as formed precursor was found to be crystalline YAG. The difference in chemical composition of the precursors formed by these two reactions is attributed to the difference in the actual reaction temperatures during their formation—lower reaction temperature for the endothermic decomposition of nitrates and higher reaction temperature for the exothermic combustion associated with the formation of a bright flame. The morphology of the precursor powder formed by the former reaction exhibited only cracks while that of the precursor from the latter reaction exhibited pores and voids. The precursor from the former reaction was calcined at 1100 °C to form into chemically pure YAG. Zeta potential variation with pH for the aqueous suspensions of the crystalline YAG powders from both the reactions exhibited a maximum value in the range of 40 to 50 mV around a pH of 4, indicating stability of these dispersions towards coagulation at this pH. Particle size distribution of wet ground powders (slurries with 20%, v/v, solid at a pH of 4) showed that the powder from combustion reaction could be formed into a finer size than that from simple nitrate decomposition, indicating the agglomerates of combustion reaction were softer.