Optimisation of opportunistic maintenance of a multi-component system considering the effect of failures on quality and production schedule: A case study

For a manufacturing equipment, any unplanned breakdown during the production period results into a high production loss. To keep the manufacturing facilities in good condition, preventive maintenance is planned. However, because of limited time and availability of resources, not all the system components can be or need to be repaired/replaced during a planned opportunity. Hence, the unplanned breakdowns can also be considered as an opportunity to do the maintenance activities for other components to take the advantage of economic dependency in multi-component system. However, when the system is under maintenance, it is very conservative to take the decision of maintenance actions on the components because of limited available time and resources. For such situation, this paper consider an opportunistic maintenance model for a multi-component system to take maintenance decision with a constraint on available time and the system availability requirements. The maintenance decisions for each component involves one of the three actions namely, repair, replace or do nothing to achieve the target availability with minimum maintenance cost. The model also considers the effect of component failures on the quality of product being manufactured as well as the production schedule on the machine. The cost of rejections is considered in the total failure cost along with the maintenance and downtime costs. The production schedule delay factor is considered as a constraint for the maintenance decision to account for the effect on production schedule delay. The optimal solution for the model is obtained using three solution methodologies namely simulated annealing, genetic algorithm and sequence heuristics. Using a real-life example of high pressure die casting machine, the opportunistic maintenance approach is demonstrated and results are discussed.     

Preparation and characterization of crosslinked chitosan microspheres for the colonic delivery of 5-fluorouracil

In this work, we attempted to develop a simple and inexpensive colon specific pulsatile drug-delivery system using chitosan microspheres loaded with 5-fluorouracil (5-FU) using an enteric-coated soft gelatin capsule. Chemical crosslinking by glutaraldehyde and interactions between the polymer and the drug were determined by Fourier transform infrared spectral study. Scanning electron microscopy of the microspheres revealed spherical shapes with smooth surfaces. Differential scanning calorimetry studies confirmed the molecular dispersion of the drug in the polymer matrix. Three different formulations (i.e., F1, F2, and F3) were prepared by the variation of the amount of 5-FU. Encapsulation efficiencies of 5.5, 10.8, and 17.9% for drug loadings of 10, 20, and 50%, respectively, were obtained. In vitro release studies were conducted at pH 1.2 and pH 7.4 (to simulate actual gastrointestinal fluid and gastrointestinal tract conditions, respectively). The results indicate that chitosan microspheres released 5-FU in both acidic (60%) and basic pH (40%) conditions, whereas the capsule (filled with chitosan microspheres) showed only 8–10% release in acidic media and nearly 90% in basic media within 12 h. The newly designed pulsatile capsule device could be used for targeting 5-FU to the colon. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites

Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.     

Subcarrier allocation and bit loading algorithms for OFDMA-based wireless networks

Orthogonal Frequency Division Multiple Access (OFDMA) is an emerging multiple access technology. In this paper, we consider OFDMA in the context of fixed wireless networks. This paper addresses the problem of assigning subcarriers and bits to point-to-point wireless links in the presence of cochannel interference and Rayleigh fading. The objective is to minimize the total transmitted power over the entire network while satisfying the data rate requirement of each link. We formulate this problem as a constrained optimization problem and present centralized algorithms. The simulation results show that our approach results in an efficient assignment of subcarriers and transmitter power levels in terms of the energy required for transmitting each bit of information. However, centralized algorithms require knowledge of the entire network topology and channel characteristics of every link. In a practical scenario, that would not be the situation and there is a need for distributed rate allocation algorithms. To address this need, we also present a distributed algorithm for allocating subcarriers and bits in order to satisfy the rate requirements of the links.     

On stability analysis of systems featuring a multiplicative combination of nonlinear and linear time‐invariant feedback

We show that sufficient conditions for the finite‐gain stability of certain systems featuring a multiplicative combination of memoryless nonlinear feedback and linear time‐invariant feedback, as encountered in some systems' biology prototype applications, can be obtained by building on the Rantzer multipliers. These results are obtained by observing that for all finite energy signals x, the time‐truncated inner product 〈x, H(x)N(x)〉_T is positive for all T>0 if N belongs to a subclass of positive memoryless monotone nonlinearities and if, in addition, H is a Rantzer multiplier. Copyright © 2011 John Wiley & Sons, Ltd.     

Sulphonic acids doped poly(N-ethyl aniline): A material for humidity sensing application

Substituted polyaniline, poly(N-ethyl aniline) (PNEA), doped with camphor sulphonic acid (CSA) and p-toluene sulphonic acid (p-TSA), was synthesized by single-step chemical polymerization method using ammonium persulphate as an oxidizing agent. This is a single-step polymerization process to synthesize directly the conducting emeraldine salt phase of the polymer using CSA and p-toluene sulphonic acid as dopants. The synthesized polymers were characterized by UV–vis and FTIR spectroscopy, scanning electron microscopy, TGA/SDTA, DSC, and conductivity measurements. This single-step chemical synthesis method offers a polymer having very good physicochemical properties with good electrical conductivity. High temperature conductivity measurements show “thermal activated behavior.” The change in resistance with respect to % relative humidity (% RH) is observed, when pressed pellets of the polymer were exposed to the broad range of humidity (ranging between 20 and 100% RH). POLYM. ENG. SCI., 47:1621–1629, 2007. © 2007 Society of Plastics Engineers     

NH4Zr2V3O12 proton conductor

NH₄Zr₂V₃O₁₂, a new proton conductor, has been synthesized by flux, melt and hydrothermal methods. The crystals were subjected to X-ray diffraction, differential thermal analysis, infrared spectroscopy and impedance measurements.     

Synthesis and compressive behavior of Cr2GeC up to 48 GPa

M_n+1AX_n compounds have gathered huge momentum because of its exciting properties. In this paper we report the synthesis of ternary layered ceramic Cr₂GeC, a 211 M_n+1AX_n compound by hot-pressing. Scanning electron microscopy and X-ray diffraction have been employed to characterize the new synthesized phase. High-pressure compressibility of Cr₂GeC were measured using diamond anvil cell and synchrotron radiation at room temperature up to 48 GPa. No phase transformation was observed in the experimental pressure range. The bulk modulus of Cr₂GeC calculated using the Birch–Murnaghan equation of state is 169 ± 3 GPa, with K′ = 3.05 ± 0.15.