Maintenance-outsourcing contracts for a system with backup machines

In this paper, we consider a system with multiple components, each prone to failure, during which production is halted. Minimal repair is performed by an external contractor whenever a component breaks down. The contractor also conducts a general preventive maintenance (PM) for the whole system at pre-determined times. The contractor’s goal is to minimise maintenance-related costs; however, the system (made up of the contractor and the manufacturer, who gains revenue whenever the system is up) profit would be maximised if the revenue is also considered. Since these goals usually require different PM schedules, we propose a cost subsidisation scheme which coordinates the system. We then extend this basic model by considering the existence of a backup machine which will allow the system to continue running (albeit, generating a lower revenue) whenever a component fails. We show that the existence of such a machine reduces the profit difference between uncoordinated and coordinated systems.     

On the trade-offs between risk pooling and logistics costs in a multi-plant network with commonality

This paper examines the benefits and costs of two alternative manufacturing network configurations in the presence of component commonality. We evaluate the trade-off between the decreased logistics costs and loss of risk-pooling benefits in plant networks which spread component manufacturing over each plant (product network) as compared to those that consolidate component manufacturing in a single plant (process network). We examine for conditions that mean that a product network would be chosen instead of a process network and vice-versa. We find that the risk-pooling benefit obtained by consolidating common subassembly production is reduced when the cost of acquiring common component capacity is sufficiently high or low. A post-optimality sensitivity analysis for the process network provides insights into subtle substitution effects, which are a direct outcome of cost mix differentials and network structure and complementarity effects, which are induced by the considered sequential assembly system. Our results suggest that the impact of operational cost parameters on strategic decisions can often be non-intuitive. Overall, our analysis provides a link between strategic and operational decision-making in supply chain management, in the context of multi-plant configuration.     

Influence of rotational speed during centrifugal casting on sliding wear behaviour of the Al-2Si alloy

The microstructures and dry sliding wear behaviour of an Al-2Si alloy cast centrifugally are studied. Results indicate that at optimum speed the cast has a microstructure consisting of uniformly distributed α-Al grains and fine eutectic silicon grains. The cast exhibited better wear resistance compared to the same cast prepared at different rpms. This paper attempts to investigate the influence of the microstructural changes in the Al-2Si alloy by varying the rotational speed of the mould and its combined action on the dry sliding wear behaviour.     

Ultra-low power incremental delta-sigma ADC for energy harvesting sensor applications

This paper presents an ultra-low power incremental \({\varDelta {\Sigma }}\) ADC with flexible sampling frequency, accuracy, and operational duty-cycle. The flexibility and low leakage power enable efficient scaling of average power together with performance. This allows simultaneous optimization of the sensor system (1) for various multiplexed, both on-chip and off-chip sensor interfaces, and (2) for a wide range of available harvested energy. The architecture allows further flexibility as it can be used in regular continuous \({\varDelta {\Sigma }}\) mode as well, without trading off accuracy. The ADC was implemented in a 180 nm CMOS process, on the same ASIC with a temperature sensor, pressure sensor and energy harvesting functionalities. The ADC has a nominal power consumption of \(1.3\,\upmu\)W, SNDR of 68 dB and BW of 200 Hz, denoting a \(FOM_w =1.58\) pJ/conv.     

Solubilisation study of water‐insoluble dye in cationic single/dimeric surfactant micelles: effect of headgroup,non‐polar tail,and spacer chain in aqueous and salt solution

The solubilisation of hydrophobic azo dye Orange OT in aqueous/salt solution in several cationic surfactant micelles was studied using UV‐vis spectroscopy. An attempt was made to correlate dye solubilising strength with adsorption/micellar characteristics. In our experiments we determined the change in solubilisation of hydrophobic dye when added to an aqueous solution of oppositely charged quaternary‐salt‐based cationic surfactants (conventional and gemini) and remarked on the probable location of the solubilised dye in the surfactant micelle. Results highlight the onset of dye solubilisation around the critical micelle concentration of each surfactant, which is influenced by the non‐polar tail, spacer, and polar headgroup, while no dye could be solubilised at concentrations below the critical micelle concentration. Orange OT solubilised almost linearly with increase in surfactant concentration at and above the critical micelle concentration. The change in colour intensity of the dye (darker below the critical micelle concentration, lighter at and above the critical micelle concentration) could be attributed to dye–surfactant interactions. Further dye solubilisation was observed in the presence of salt.     

Highly exfoliated poly(ϵ‐caprolactone)/organomontmorillonite nanocomposites prepared by in situ polymerization

Ethylene–propylene–diene rubbers (EPDM) with 2-ethylidene-5-norbornene (ENB), dicyclopentadiene (DCPD), and 1,4-hexadiene (HD) as third monomers have been vulcanized with peroxide and with a conventional sulfur vulcanization recipe, and their devulcanization was subsequently investigated for recycling purposes. The behavior of these vulcanizates during pure thermal devulcanization depends on the EPDM third monomer and the crosslinker used. Peroxide vulcanizates of ENB-EPDM devulcanize only to a small extent and predominantly by random scission, whereas peroxide vulcanizates of HD-EPDM devulcanize by crosslink scission. In contrast, sulfur vulcanizates of ENB-EPDM, devulcanize mainly by crosslink scission. During devulcanization of sulfur-cured HD-EPDM, scission of both crosslinks and main chains occurs. Sulfur-cured DCPD-EPDM cannot be devulcanized but shows further crosslinking instead. In those cases, where purely thermal devulcanization is already effective to a certain extent, diphenyldisulfide as devulcanization agent increases the effectivity during thermochemical devulcanization. Hexadecylamine as an alternative devulcanization agent is effective for ENB-EPDM but does not contribute to thermochemical devulcanization of HD-EPDM. In summary, devulcanization proceeds by different mechanisms in ENB-EPDM, DCPD-EPDM, and HD-EPDM. Explanations are given in terms of the chemical structures of the third monomers, the corresponding crosslinks, and devulcanization agents. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of Refiner in ZA-12 Alloys During Centrifugal Casting Process

The behavior of the molten melt plays a predominant role in determining the quality cast product. In continuous casting, addition of refiner 1% (Al+Ti+B2) onto the molten metal increases its mechanical properties as a result of the nucleation within the process. In this article, the effect of refiners in the centrifugal casting process was studied. Eutectic ZA-12 alloys were taken for our experiment and cast at various rotational speeds (400 rpm, 600 rpm, and 800 rpm) with and without the addition of refiners. Rather than increase in the solidification rate as in continuous casting, these refiners diminish the solidification rate, which in turn forms an irregular-shaped cast tube. The microstructure and hardness for the entire cast specimen were discussed finally.     

Non-Newtonian power-law flow across a confined triangular bluff body in a channel

Wall effects on the flow of incompressible non-Newtonian power-law fluids across an equilateral triangular cylinder confined in a horizontal plane channel have been investigated for the range of conditions: Reynolds number, Re=1–40, power-law index, n=0.4–1.8 (covering shear-thinning, Newtonian and shear-thickening behaviors) and blockage ratio=0.125–0.5. Extensive numerical results on flow pattern, wake/recirculation length, individual and overall drag coefficients, variation of pressure coefficient on the surface of the triangular cylinder and so forth are reported to elucidate the combined effect of power-law index, blockage ratio and Reynolds number. The size of vortices decreases with an increase in the value of the blockage ratio and/or power-law index. For a fixed value of the Reynolds number, individual and overall drags decrease with decrease in power-law index and/or blockage ratio in steady confined flow regime. Simple correlations of wake length and drag are also obtained for the range of settings considered.