Conceptualizing manufacturing flexibility: An operational approach and a comparative evaluation

An operational approach to conceptualization and the measurement of manufacturing flexibility is presented. A critical review of selected measures from the literature is provided in the context of the operational approach. A flexibility measure is proposed. A formulation and the features of the proposed measure are discussed. An application of the measure is demonstrated through a hypothetical example. Using the same example, selected flexibility measures from the literature are evaluated. The performance of the measures and the proposed measure are compared.     

Open cell lead foams: processing, microstructure, and mechanical properties

Open cell lead foams with the porosities between 48 and 74 % were prepared by means of powder metallurgical and casting routes, using ammonium bicarbonate particles, silica beads, and sodium chloride salt particles as space holder. The resulting foam samples structure closely resembled open cell foam structure: each cell had few interconnections with neighboring cells. Small-sized lead (II) fluoride precipitates were microscopically observed in the interior of cells in the foam samples prepared using silica beads as space holder, resulting from the reaction between silica and hydrofluoric acid in the space holder dissolution step. The compression stress–strain curve of foam samples prepared by powder metallurgical route showed brittle deformation behavior following the initial elastic deformation region, while the foam samples prepared by casting route showed characteristic foam deformation behavior: cell edge crushing on the bent cell walls, and cell wall tearing. The collapse stresses, densification strains, and elastic moduli of the prepared foams were further fitted with scaling relations.     

Performance analysis of two stage combined heat pump system based on thermoeconomic optimization criterion

A thermoeconomic performance analysis based on a new kind of optimization criterion has been performed for a two stage endoreversible combined heat pump cycle model. The optimal performances and design parameters that maximize the objective function (heating load per unit total cost) are investigated. The optimal temperatures of the working fluids, the optimum performance coefficient, the optimum specific heating load and the optimal distribution of the heat exchanger areas are determined in terms of technical and economical parameters. The effects of the economical parameter on the global and optimal performances have been discussed.     

Free amino acids profile and quantities of 'sırt', 'bohca' and 'sekerpare' pastirma, dry cured meat products

BACKGROUND: Pastirma is a dry‐cured and semi‐fermented meat product, produced from whole beef or water buffalo muscles. Sixteen to twenty different types of pastirma can be produced from a carcass, and each pastirma type has a different name, shape and quality characteristics. The objective of this study was to determine the free amino acid (FAA) composition, pH and moisture values of ‘s?rt’, ‘bohca’ and ‘sekerpare’ pastirma. RESULTS: Significant differences were determined among the pastirma types in glutamic acid (P < 0.05), threonine (P < 0.05), arginine (P < 0.05), alanine (P < 0.01), methionine (P < 0.01), tryptophan (P < 0.05), proline (P < 0.01) and valine (P < 0.01). Threonine, methionine and valine were higher in s?rt pastirma than the others; glutamic acid, arginine and tryptophan were higher in sekerpare pastirma. The predominant FAA in the all pastirma samples was alanine, while the lowest was asparagine. The highest mean pH was in s?rt pastirma, and the lowest mean pH in bohca pastirma. There was no significant difference in mean moisture values among pastirma types. CONCLUSION: Significant differences were determined among pastirma types in some FAA. Analysis results indicated that quality and nutritional properties for different pastirma types are different. The most advantageous pastirma types in terms of FAA were bohca and s?rt, which contain the highest quantity of threonine, methionine and valine. Copyright © 2011 Society of Chemical Industry     

Simultaneous hydrogen gas formation and COD removal from cheese whey wastewater by electrohydrolysis

Cheese whey (CW) was subjected to DC voltages between 0.5 and 5 V for hydrogen gas production with simultaneous COD removal by electrohydrolysis of CW organics. Hydrogen gas formation and COD removal were investigated at different DC voltages using aluminum electrodes. The highest cumulative hydrogen production (5551 mL), hydrogen yield (1709 mL H₂ g⁻¹ COD), hydrogen gas formation rate (913 ml d⁻¹), and percent hydrogen (99%) in the gas phase were obtained with 5 V DC voltage within 158 h. Energy conversion efficiency reached the highest level (80.7%) at 3 V DC voltage with cumulative hydrogen production of 4808 mL and hydrogen yield of 1366 mL H₂ g⁻¹ COD. Hydrogen gas was mainly produced by electrohydrolysis of CW organics due to low H₂ gas production in water and CW control experiments. The highest COD removal (22%) was also obtained with 3 V DC voltage. Major COD removal mechanism was anaerobic degradation of carbohydrates producing volatile fatty acids (VFA) and CO₂. Hydrogen gas was produced by reaction of protons released from VFAs and electrons provided by DC current. Hydrogen gas production by electrohydrolysis of CW solution was proven to be an effective method with simultaneous COD removal.     

High-Strain-Rate Material Behavior and Adiabatic Material Instability in Impact of Micron-Scale Al-6061 Particles

Impact of spherical particles onto a flat sapphire surface was investigated in 50-950 m/s impact speed range experimentally and theoretically. Material parameters of the bilinear Johnson–Cook model were determined based on comparison of deformed particle shapes from experiment and simulation. Effects of high-strain-rate plastic flow, heat generation due to plasticity, material damage, interfacial friction and heat transfer were modeled. Four distinct regions were identified inside the particle by analyzing temporal variation of material flow. A relatively small volume of material near the impact zone becomes unstable due to plasticity-induced heating, accompanied by severe drop in the flow stress for impact velocity that exceeds ~?500 m/s. Outside of this region, flow stress is reduced due to temperature effects without the instability. Load carrying capacity of the material degrades and the material expands horizontally leading to jetting. The increase in overall plastic and frictional dissipation with impact velocity was found to be inherently lower than the increase in the kinetic energy at high speeds, leading to the instability. This work introduces a novel method to characterize HSR (10⁹ s^?1) material properties and also explains coupling between HSR material behavior and mechanics that lead to extreme deformation.     

New generation polymeric nanospheres for lysozyme adsorption

Novel hydrophobic nanospheres with an average size of 100 nm utilizing N‐methacryloyl‐(l)‐tryptophan methyl ester (MAT) as a hydrophobic monomer were prepared by surfactant free emulsion polymerization of 2‐hydroxyethyl methacrylate (HEMA) and MAT. MAT was synthesized using methacryloyl chloride and l‐tryptophan methyl ester. Specific surface area of the nonporous nanospheres was found to be 1914 m²/g. Poly(HEMA–MAT) nanospheres were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Average particle size, size distribution, and surface charge measurements were also performed. Elemental analysis of MAT for nitrogen was estimated as 1.95 mmol/g polymer. Then, poly(HEMA–MAT) nanospheres were used in the adsorption of lysozyme in batch system. Using an optimized adsorption protocol, a very high loading of 1075 mg lysozyme/g nanosphere was obtained. The adsorption phenomena appeared to follow a typical Langmuir isotherm. It was observed that enzyme could be repeatedly adsorbed and desorbed without significant loss in adsorption amount or enzyme activity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Evaluation of normal-appearing white matter with perfusion and diffusion MRI in patients with treated glioblastoma

Magnetic Resonance Materials in Physics, Biology and Medicine - We tried to reveal how the normal appearing white matter (NAWM) was affected in patients with glioblastoma treated with...