Fabrication and characterization of reaction-bonded silicon carbide with poly(methyl methacrylate) as pore-forming agent

Reaction-bonded silicon carbide (RBSC) ceramics were prepared by liquid silicon infiltration at 1600 °C using a carbon biscuit. The green body was made by slip casting a stabilized carbon powder slurry, followed by pyrolysis in a vacuum furnace at 1000 °C for 2 h; the density of the biscuit (ρ_b) was controlled using poly(methyl methacrylate) (PMMA) powder as pore former in mass proportion from 30% to 50% in 5 percentage point intervals. The particle size of the PMMA had significant effects on the microstructure, distribution of residual silicon, and the mechanical properties of the ceramic. For 40 mass% PMMA with d₅₀=1.17 μm and d₅₀=0.51 μm, ρ_b was 0.81 and 0.82 g/mL, with corresponding biscuit porosities of 51% and 50%, which gave peak values of both RBSC ceramic density of 3.07 and 3.10 g/mL, and flexural strength of 741 and 794 MPa, respectively. XRD analysis showed that the main phase was β-SiC, with a small quantity of α-SiC. Using PMMA with d₅₀=0.51 μm, a small quantity of residual Si was well dispersed with grain size <1 μm. “Black core” residual carbon in the RBSC was successfully avoided when ρ_b≤0.82 g/mL (mass proportion PMMA≥35%). PMMA as pore former favored the elimination of the detrimental black core and the preparation of dense RBSC with good mechanical properties.     

DESIGN OPTIMIZATION OF INDUCTION MOTORS WITH DIFFERENTIAL EVOLUTION ALGORITHMS WITH AN APPLICATION IN TEXTILE SPINNING

This article deals with the design optimization of a squirrel-cage three-phase induction motor, selected as the driving power of spinning machines in the textile industry, using three newly developed versions of differential evolution (DE) algorithms called modified DE versions (CMDE, GMDE, and LMDE). Efficiency, which decides the operating or running cost of the motor (industry), is considered as the objective function. First, the algorithms are applied to design a general purpose motor with seven variables and nine performance-related parameters with their nominal values as constraints. To make the machine feasible, practically acceptable to serve in textile industries, and less costly to operate, certain constraints are modified in accordance with the demands of the spinning application. Comparison of the optimum designs with the industrial (existing) motor reveals that the motor designed by the proposed algorithms consumes less power input.     

Porous Li-Na-K niobate bone-substitute ceramics: Microstructure and piezoelectric properties

Disc specimens of a porous ceramic, lithium sodium potassium niobate (Li_0.06Na_0.5K_0.44)NbO₃, were prepared using ammonium oxalate monohydrate or poly(methyl methacrylate) as pore-forming agent, and made piezoelectric using a modified polarizing method to preserve biocompatibility. Scanning electron microscopy showed a bicontinuous 3-3 structure of interconnected pores 150-250 µm in size. The piezoelectric constant (d₃₃) and electromechanical coupling coefficient (Kp) are discussed as a function of porosity and pore shape: d₃₃ fitted the theoretical expectation for shape factor K_s = 1, while Kp was approximately constant (~ 0.23) for porosity of 15-45 vol.%. 50 vol.% AOM gave the highest porosity (~ 45%) without decline of the value of Kp whilst maintaining mechanical integrity. Such materials show promise for use as a piezoelectric composite bone substitute.     

Preparation of hollow hydroxyapatite microspheres

The preparation of hollow hydroxyapatite (HA) microspheres as potential drug-delivery vehicles was investigated. A lithium-calcium-borate (10Li₂O-15CaO-75B₂O₃) (mol%) glass, made by fusing the components at 1100°C for 1 h, was ground to a powder and passed through a flame at ∼1400°C to spheroidize the particles. The resulting glass microspheres (106–125 μm in diameter) were reacted in 0.25 M K₂HPO₄ solution for 5 days at 37°C and pH 10–12, resulting in the formation of porous, hollow microspheres of a calcium phosphate (Ca-P) material with external diameters similar to those of the original glass particles. Heat treatment at 600°C for 4 h partially converted the Ca-P material to HA, as confirmed by X-ray diffraction, and also increased the strength of the hollow microspheres.     

Solution to industrial optimization problems through differential evolution variants

Optimization forms the core of several industrial problems and demands suitable methods of solution for determining the best possible solution. However, it is often observed that the classical optimization algorithms available in literature may not be applicable in real-life scenarios where the nature of the problems is quite complex. Under such circumstances, nature-inspired algorithms (NIA) can be beneficial because of their generic nature. This is shown in the present study by obtaining the optimal solution of two fundamental industrial problems, viz. optimizing and controlling the level of noise in an industry having multiple sources of noise; and optimizing the total production cost in a machining process through different NIA including two newly proposed differential evolution (DE) variants. Comparison is also done through classical methods. Both the problems are nonlinear in nature where the complexity increases by increasing the number of variables. The first problem taken is unconstrained in nature, while the second problem is constrained. A thorough comparison of all the methods is done through various performance measures and it is observed that the proposed DE variants form an attractive alternative for dealing with such problems.     

Combustion properties of some power station biomass fuels

In this study, the combustion properties of three of the UK’s commonly imported biomass fuels for co-firing, which are palm kernel expellers, shea residue, and waste from olive oil production are examined. The fuels were characterised and their thermal decomposition properties were studied by thermogravimetric analysis (TGA). Additionally the products from their devolatilisation were identified by gas chromatography-mass spectrometry (py-GC-MS) analysis of the evolved vapours and tars from high heating rate pyrolysis tests. Finally, chars from the fuels were prepared, analysed, and combustion studies were conducted by TGA-MS to determine the conversion of char-nitrogen to different nitrogen-containing species. In general, the main constituents of their ash fractions were K, Si, Ca and Mg, resulting in high alkali indices, which predict a large tendency to fouling. The pyrolysis and combustion kinetic parameters, estimated from TGA studies of these fuels and their chars, are much lower than those reported in the literature for lignocellulosic biomass. It is suspected that there is oil/fat evaporation processes overlapping with the decomposition of their lignocellulosic fractions, which significantly affects the apparent kinetics. The pyrolysis conditions used promoted depletion of nitrogen in the char, resulting in approximately 79-91% of the fuel-N being released with the volatiles. In combustion of the char, NO_x and N₂ are the major nitrogen compounds detected. Another primary product, HCN, was detected from the combustion of some of the fuel chars, as well as C₂N₂.     

Genetic algorithms in supply chain management: A critical analysis of the literature

Genetic algorithms (GAs) are perhaps the oldest and most frequently used search techniques for dealing with complex and intricate real-life problems that are otherwise difficult to solve by the traditional methods. The present article provides an extensive literature review of the application of GA on supply chain management (SCM). SCM consists of several intricate processes and each process is equally important for maintaining a successful supply chain. In this paper, eight processes (where each process has a set of sub-processes) as given by Council of SCM Professionals (CSCMF) are considered. The idea is to review the application of GA on these aspects and to provide the readers a detailed study in this area. The authors have considered more than 220 papers covering a span of nearly two decades for this study. The analysis is shown in detail with the help of graphs and tables. It is expected that such an extensive study will encourage and motivate the fellow researchers working in related area; to identify the gaps and to come up with innovative ideas.     

Dioxonaphthoimidazoliums are Potent and Selective Rogue Stem Cell Clearing Agents with SOX2‐Suppressing Properties

Pluripotent stem cells are uniquely positioned for regenerative medicine, but their clinical potential can only be realized if their tumorigenic tendencies are decoupled from their pluripotent properties. Deploying small molecules to remove remnant undifferentiated pluripotent cells, which would otherwise transform into teratomas and teratomacarcinomas, offers several advantages over non‐pharmacological methods. Dioxonapthoimidazolium YM155, a survivin suppressant, induced selective and potent cell death of undifferentiated stem cells. Herein, the structural requirements for stemotoxicity were investigated and found to be closely aligned with those essential for cytotoxicity in malignant cells. There was a critical reliance on the quinone and imidazolium moieties but a lesser dependence on ring substituents, which served mainly to fine‐tune activity. Several potent analogues were identified which, like YM155, suppressed survivin and decreased SOX2 in stem cells. The decrease in SOX2 would cause an imbalance in pluripotent factors that could potentially prompt cells to differentiate and hence decrease the risk of aberrant teratoma formation. As phosphorylation of the NF‐κB p50 subunit was also suppressed, the crosstalk between phospho‐p50, SOX2, and survivin could implicate a causal role for NF‐κB signaling in mediating the stem cell clearing properties of dioxonaphthoimidazoliums.     

Artificial salivas for in vitro studies of dental materials

In a preliminary study, levels of activity of enzymes involved in anaerobic glycerol catabolism by Enterobacter agglomerans grown in batch cultures regulated in a pH range of 6.5-8.0 were monitored. That study showed that activities of key enzymes of the downstream metabolism of glycerol--glyceradehyde-3-phosphate dehydrogenase (GAP-DH), lactate dehydrogenase and pyruvate formate lyase--were strongly dependent on the culture pH. To investigate the influence of pH on the physiology of the strain, E. agglomerans was grown anaerobically in a continuous culture supplied with glycerol as the sole carbon source and regulated at pH 8. A complete biochemical analysis was performed and was compared with that previously described for the continuous culture regulated at pH 7. A limitation of the glycolytic flux at the level of GAP-DH was demonstrated at high dilution rate, resulting in an overflow metabolism through the 1,3-propanediol formation pathway. Increasing the specific rate of glycerol consumption also resulted in enhanced lactate production due to limitation by the pyruvate decarboxylation step. Finally, changing the culture pH significantly modified the enzymatic profile of E. agglomerans, and it enabled the stability of the culture to be increased by preventing the accumulation in the fermentation broth of 3-hydroxypropionaldehyde, an inhibitory metabolite, when the glycerol supply was suddenly increased.