Processing of Bulk Alumina Ceramics Using Laser Engineered Net Shaping

Application of rapid prototyping (RP) in ceramics manufacturing is motivated by advances in engineering ceramics where attaining complex shapes using traditional processing is difficult. Laser Engineered Net Shaping (LENS^™), a commercial RP process, is used to fabricate dense, net-shaped structures of α-Al₂O₃. Shapes such as cylinder, cube, and gear have been fabricated successfully with 10–25 mm section sizes. As-processed structures show anisotropy in mechanical properties with a high compressive strength normal to the build direction and columnar grains along the build direction. Heat treatment did not alter strength and anisotropy, but increased the grain size from 6 to 200 μm and hardness from 1550 to 1700 Hv.     

Synthesis of Hydroxyapatite Nanopowders via Sucrose-Templated Sol–Gel Method

The present research describes synthesis of hydroxyapatite (HAp) nanopowders using a sol–gel route with calcium nitrate and ammonium hydrogen phosphate as calcium and phosphorous precursors, respectively. Sucrose is used as template material, and alumina is added as a dopant to study its effects on particle size and surface area. Synthesized powders are characterized using X-ray diffractometry, BET surface-area analysis, and transmission electron microscopy. Results show that alumina stabilizes the HAp crystalline phase. Average particle size of mesoporous HAp samples is between 30 and 50 nm with surface area of 51–60 m²/g.     

Nanocrystalline α-Al2O3 Using Sucrose

Nanocrystalline α-Al₂O₃ ceramic powders have been prepared from an aqueous solution of aluminum nitrate and sucrose. Soluble Al ion-sucrose solution forms the precursor material once it is completely dehydrated. Heat treatment of the dehydrated precursors at low temperature (600°C) results in the formation of porous single-phase α-Al₂O₃. The precursor and heat-treated powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and BET surface area analysis. The phase-pure nanocrystalline α-Al₂O₃ particles had an average specific surface area of >190 m²/g, with an average pore size between 18 and 25 nm.     

Applying modified NSGA-II for bi-objective supply chain problem

This paper minimizes the value of total cost and bullwhip effect in a supply chain. The objectives have been achieved through developing a new multi-objective formulation for minimizing the total cost and minimizing the bullwhip effect of a two-echelon serial supply chain. A new crossover algorithm for a fuzzy variable and a new mutation algorithm have also been proposed while applying Non-dominated Sorting Genetic Algorithm-II (NSGA-II) to the proposed problem. The formulated problem has been simulated by Matlab software and the results of the modified NSGA-II have been compared with those of original NSGA-II. It is found from the results that the modified NSGA-II algorithm performs better than the original NSGA-II algorithm since the minimum values for both total cost and the bullwhip effect are obtained in case of the modified NSGA-II. The formulated bi-objective problem is new to the research community. The minimization of bullwhip effect has never been considered in a multi-objective optimization before. Besides crossover operator applied to the fuzzy variable and the mutation operator are newly introduced operators.     

MAkE: Multiobjective algorithm for k-way equipartitioning of a point set

The classical problem of partitioning a given set of points, has applications in several areas such as facility location, scattered network, and in hierarchical design of VLSI circuits. While equipartitioning is traditionally associated with the single objective of minimum cutcost, the above application areas appear to demand more. In this paper, we introduce the problem of multiobjective k-way equipartitioning of a point set. Brief discussions on the above applications are followed by their generic formulation as a multiobjective k-way equipartitioning problem of a given point set. The non-commensurate multiobjective criteria addressed include (i) minimizing overall areas of the partitions, (ii) maximizing area of the individual partitions, (iii) minimizing the total compactness of the partitions, and (iv) minimizing the total geometric diversity of the obtained partitions. Since this optimization problem is computationally expensive in time and space, a technique based on genetic algorithm is proposed in order to obtain high quality results. Crossover and mutation operators specific to the k-way equipartitioning problem, have been designed and a new greedy operator named compaction is proposed to accelerate convergence. To illustrate the utility of the proposed formulation and the algorithm, a problem in VLSI layout design is considered. Results on synthetic data sets as well as those extracted from layouts of benchmark circuits demonstrate the effectiveness of the proposed multiobjective approach.     

Lovastatin release from polycaprolactone coated β-tricalcium phosphate: Effects of pH,concentration and drug–polymer interactions

The approach of local drug delivery from polymeric coating is currently getting significant attention for both soft and hard tissue engineering applications for sustained and controlled release. The chemistry of the polymer and the drug, and their interactions influence the release kinetics to a great extent. Here, we examine lovastatin release behaviour from polycaprolactone (PCL) coating on β-tricalcium phosphate (β-TCP). Lovastatin was incorporated into biodegradable water insoluble PCL coating. A burst and uncontrolled lovastatin release was observed from bare β-TCP, whereas controlled and sustained release was observed from PCL coating. A higher lovastatin release was observed pH 7.4 as compared to pH 5.0. Effect of PCL concentration on lovastatin release was opposite at pH 7.4 and 5.0. At pH 5.0 lovastatin release was decreased with increasing PCL concentration, whereas release was increased with increasing PCL concentration at pH 7.4. High Ca^2 + ion concentration due to high solubility of β-TCP and degradation of PCL coating were observed at pH 5.0 compared to no detectable Ca^2 + ion release and visible degradation of PCL coating at pH 7.4. The hydrophilic–hydrophobic and hydrophobic–hydrophobic interactions between lovastatin and PCL were found to be the key factors controlling the diffusion dominated release kinetics of lovastatin from PCL coating over dissolution and degradation processes. Understanding the lovastatin release chemistry from PCL will be beneficial for designing drug delivery devices from polymeric coating or scaffolds.     

Mechanical property and in vitro biocompatibility of brushite cement modified by polyethylene glycol

Brushite (dicalcium phosphate dihydrate, DCPD) cement, owing to its high solubility in physiological condition and ability to guide new bone formation, is widely used to treat bone defects. In the present study, we have evaluated the effects of poly ethylene glycol (PEG) addition on the setting time, compressive strength and in vitro biocompatibility of brushite cement. The brushite cements were prepared by mixing β-tricalcium phosphate [β-TCP, Ca₃(PO₄)₂] and monocalcium phosphate monohydrate [MCPM, Ca(H₂PO₄)₂ ? H₂O]. PEG was introduced at 2.0 and 5.0 wt% with the liquid. Introduction of PEG resulted in marginal increase in both initial and final setting time, however, significantly affected the compressive strength. Effects of PEG incorporation on in vitro biocompatibility of brushite cements were studied by using human fetal osteoblast cells (hFOB) cells. Field emission scanning electron microscope (FESEM) images and immunohistochemical analysis indicated that pure and PEG incorporated brushite cement facilitates cell adhesion, proliferation and differentiation. Fewer cells expressed vinculin protein with increased PEG content in the cement. Cell proliferation was found to decrease with increased PEG concentration while the cell differentiation increased with PEG content. Our results provide a better understanding of in vitro biocompatibility of PEG added brushite cements that can be used to customize the cement compositions based on application need.     

Modeling Arsenite Adsorption on Rusting Metallic Iron

Experimental data on As(III) adsorption by rusted zero valent iron (ZVI) could be modeled using a simple Langmuir isotherm model. However, the adsorption equilibrium was observed to shift with time, as continued rusting produced additional sites on the rusted ZVI surface for potential arsenic adsorption. A modified Langmuir isotherm model was formulated taking into consideration the temporal variation in the site concentration for potential arsenic adsorption on the rusted ZVI surface. This model simulated the long-term experimental data on As(III) adsorption quite well. The model was further refined by apportioning the arsenic adsorbed on the rusted ZVI surface into labile and irreversibly adsorbed fractions. Finally, the developed model was used to simulate the performance of an adsorption column. The simulation results indicate that an adsorption column of length 0.4 m and diameter 0.056 m, i.e., containing 0.001?m3 of rusted ZVI weighing 4.76 kg, and operated at an empty bed contact time of 12 min, can treat 2,375–2,525 L of water containing 100?μg?L?1 of As(III) such that the effluent As(III) concentration from the column is less than 10?μg?L?1.