Impact of precursor solution concentration to form superparamagnetic MgFe2O4 nanospheres by ultrasonic spray pyrolysis technique for magnetic thermotherapy

The superparamagnetic magnesium ferrite (MgFe₂O₄) dense nanospheres are synthesized by ultrasonic spray pyrolysis (USP) method from different concentrations of the initial precursor solution. The effect of precursor solution concentration on the particle’s size, morphology, and superparamagnetic behavior has been investigated. XRD results confirm that studied precursor concentration (0.06, 0.12 and 0.24 M) exhibited single phase cubic structure. The mean crystallites size (called as primary particles) of 0.06, 0.12 and 0.24 M samples are 9.6, 11.5, 11.0 nm, respectively but the entire nanosphere’s diameter (called as secondary particles) increases from 206 to 340 nm with increasing precursor concentration. TEM analysis also reveals that nanospheres consist of densely aggregated crystallites of spherical shape and smooth surface. The value of polydispersity index (PDI) shows narrower size distribution for lower concentration. Magnetic properties indicate the superparamagnetic nature for all samples. Herein, the appropriate induction heat generation rate with better morphology was obtained for 0.06 M concentration. Ion release in the aqueous solution of the composition (about 95% for Mg; 99% for Fe) indicating better stability has been confirmed by ICP-OES test. In this approach, as-synthesized nanospheres are suitable for using as a heating agent in magnetic thermotherapy application.     

A hybrid push/pull system in assemble-to-order manufacturing environment

A hybrid push/pull system of an assemble-to-order manufacturing environment is investigated in this paper. In this environment, raw material can be transformed into common semi-finished products at a point where next downstream operations are triggered by customer orders. The production of the earlier upstream stations is controlled by push-type production, while the production of the later downstream stations is controlled by pull-type production. The hybrid system often compromises the conflicting performance characteristics of the push and the pull environments. In the push type, high inventory cost is anticipated in the return of low delivery leadtime. On the contrary, in the pull type, high delivery leadtime is expected in the return of low inventory cost. The objective function for the presented hybrid model is to minimize the sum of inventory holding cost and delivery leadtime cost, which is the cost of the time period since customers have placed an order until it is fulfilled. The model is applied to solve the inventory and late delivery problems in an assemble-to-order manufacturer. A genetic algorithm (GA) is used. A discrete event simulation model is used to evaluate the objective function for each chromosome in the GA. The pure push and pull systems are also simulated in order to compare their performance with the hybrid system. Sensitivity analysis on the coefficient of variation (CV) of time between actual customer order arrivals and on various cost ratios of delivery leadtime and inventory are carried out. In most cases, the hybrid performs the best. Results show that the hybrid production system would save the company significantly compared to the pure push or pure pull production systems.     

Synthesis and characterization of proton exchange poly (phenylenebenzophenone)s membranes grafted with propane sulfonic acid on pendant phenyl groups

A series of poly(phenylenebenzophenone)s with sulfonic acid groups via long alkyl side chains, SPPBPs, were successfully prepared as proton exchange membranes for fuel cells. The new monomer, 1,4-dichloro-2,5 diphenylenemethoxybenzophenone (PMBP) was synthesized by the Friedel–Crafts reaction of tetrachloroterephthalate with anisole and copolymerized with 1,4-dichloro-2,5-diphenylenebenzophenone (PBP) to prepare poly(phenylenebenzophenone)s copolymers containing dimethoxy groups (sPPMBP). After converting the methoxy group to the reactive hydroxyl group, the resulting side-chain-type sulfonated copolymers (SPPBP) were obtained by a sulfopropylation reaction. These SPPBP series membranes showed high proton conductivity in the range of 98.4–162.1 mS/cm 80 °C under 90% hydrated conditions. SPPBP-40 (IEC = 2.45 meq./g) showed comparable higher proton conductivity (162.1 mS/cm) than Nafion 211 (130.2 mS/cm) in the 90% hydrated state. The membranes were studied by ¹H NMR spectroscopy, thermo-gravimetric analysis, ionic exchange capacity, water uptake, and proton conductivity. Also surface morphologies were assessed by atomic force microscope (AFM).     

Magnetic-field-induced phase separation via spinodal decomposition in epitaxial manganese ferrite thin films

In this study, we report about the occurrence of phase separation through spinodal decomposition (SD) in spinel manganese ferrite (Mn ferrite) thin films grown by Dynamic Aurora pulsed laser deposition. The driving force behind this SD in Mn ferrite films is considered to be an ion-impingement-enhanced diffusion that is induced by the application of magnetic field during film growth. The phase separation to Mn-rich and Fe-rich phases in Mn ferrite films is confirmed from the Bragg’s peak splitting and the appearance of the patterned checkerboard-like domain in the surface. In the cross-sectional microstructure analysis, the distribution of Mn and Fe-signals alternately changes along the lateral (x and y) directions, while it is almost homogeneous in the z-direction. The result suggests that columnar-type phase separation occurs by the up-hill diffusion only along the in-plane directions. The propagation of a quasi-sinusoidal compositional wave in the lateral directions is confirmed from spatially resolved chemical composition analysis, which strongly demonstrates the occurrence of phase separation via SD. It is also found that the composition of Mn-rich and Fe-rich phases in phase-separated Mn ferrite thin films deposited at higher growth temperature and in situ magnetic field does not depend on the corresponding average film composition.     

A mathematical model and heuristic procedure to schedule printed circuit packs on sequencers

This paper considers the NP-hard problem of scheduling printed circuit packs (PCPs) on sequencers to minimize the total number of changeovers of input tapes required to produce PCPs. A mathematical model for this problem is given. However, when the size of the problem increases, the model will not be computationally feasible. An effective and fast heuristic to solve this problem is presented. The heuristic has shown its effectiveness over two previous heuristics found in the literature. It has been tested on a problem with 45 PCPs, two sequencers, each with seven dispensing heads, and a total of 20 input tape types. Comparison results showed that the heuristic reduced the total number of changeovers by 34% and 23% over previous heuristics. In addition, the proposed heuristic provided balanced workload across available sequencers. To investigate the efficiency of our heuristic further, we tested it against data sets from the literature. The proposed heuristic performs reasonably well compared with the reported results. In printed circuit packs' environment, set-up reduction is a main concern. Set-up is composed of the time required to changeover input tapes on sequencers when switching from PCP type to another. The proposed heuristic is more effective in reducing the number of changeovers of input tapes than heuristics found in the literature. The same heuristic can be used to schedule jobs on CNC machines so that total amount of tool switching is minimized.     

Incidence of Staphylococcus aureus and associated risk factors in Nham,a Thai fermented pork product

Staphylococcus aureus is one of the most prevalent bacterial pathogens causing food-borne disease worldwide. Staphylococcal food poisoning is caused by ingestion of staphylococcal enterotoxins (SEs) pre-formed in the implicated food. In this study, the incidences of S. aureus and classical SEs (SEA-SEE) contamination in ‘Nham’, a traditional Thai fermented pork product, were determined. Among 155 Nham samples tested, as high as 39.35% of the samples were positive for S. aureus (2–3500 MPN/g), but none were positive for the SEs. The risk factors for S. aureus contamination were highly correlated with the manufacturer and the pH of the product. A predictive model determined the probability of the presence of S. aureus to be ≤0.24 at the pH ≤ 4.6. During the fermentation process, the number of S. aureus slightly increased in the first day and decreased afterward. S. aureus counts continued to decrease when Nham was stored refrigerated. The negative result for enterotoxins and low counts of S. aureus in Nham surveyed in this study, and reduction of the pathogen counts during fermentation and storage suggested that there is very low risk of staphylococcal food poisoning from consuming properly fermented Nham.     

Optimal batching in a wafer fabrication facility using a multiproduct G/G/c model with batch processing

Wafer fabrication, the first portion of semiconductor manufacturing, typically involves numerous batch-processing operations. These operations play an important role in determining how the system performs in terms of throughput, WIP and cycle time. In this paper, batch sizes that minimize the expected cycle time of batch-processing operations for a real-world semiconductor manufacturer are determined by a new approximated analytical model. This model, denoted by G / G ( bp ) , represents multiple products, multiple servers, batch-processing, incompatible products and unequal batch service size queues. Incompatible products mean that different products are not allowed to be in the same batch. Unequal batch service size means that batch service sizes depend upon products. Steady-state approximation formulas for cycle time and WIP of this queuing system are derived. These approximate performance measures are compared with those of discrete-event simulation. The results are reasonable and the approximation formulas much more computationally efficient than conducting the corresponding simulation studies. Finally, a batch-processing system with the goal of minimizing the total expected cycle times of items by determining the 'optimal' batch sizes is presented. Solutions are obtained using genetic algorithms.     

Controlled synthesis of dense MgFe2O4 nanospheres by ultrasonic spray pyrolysis technique: Effect of ethanol addition to precursor solvent

We present the results of controlled synthesis of spherical shape magnesium ferrite (MgFe₂O₄) dense nanoparticles by using ultrasonic spray pyrolysis (USP) method without any post-annealing processes. A new strategy was proposed to improve nano-crystallinity and observed morphology by ethanol (EtOH) addition in the initial precursor solution of MgFe₂O₄. Influence of EtOH, not only decrease the synthesized secondary particle size but also enhancing crystallization into MgFe₂O₄ single phase cubic structure. We observe that average nanosphere size decrease from 220 to 189?nm but increases of crystallite size from 9.6 to 19.2?nm with increasing the amount of EtOH from 0 to 20?vol%. Also, surface morphology revealed that nanospheres with some irregular shape and rough surface appear in case of EtOH additives. The magnetic properties are studied and different parameters viz. saturation magnetization, remanence, and coercivity have been correlated with crystallite size.