Bi-objective optimization research on integrated fixed time interval preventive maintenance and production for scheduling flexible job-shop problem

This paper investigates integrated flexible job shop problem (FJSP) with preventive maintenance (PM) activities under the multi-objective optimization approaches. Finding compromise solutions between the production objectives and maintenance ones is under consideration. In order to carry out the maintenance activities, reliability models are employed. This paper attempts to simultaneously optimize two objectives: the minimization of the makespan for the production part and the minimization of the system unavailability for the maintenance part. For doing it so, two decisions are taken at the same time: finding the appropriate assignment of n jobs on m machines in order to minimize the makespan and deciding when to execute the PM activities in order to minimize the system unavailability. Both the maintenance activity numbers and maintenance intervals are not fixed in advance. Four multi-objective optimization methods are compared to find the Pareto-optimal front in the flexible job-shop problem case. Promising the obtained results, a benchmark with a large number of test instances (more than 4800) and meticulous care is employed.     

A new approach for estimation of the rock mass deformation modulus: a rock engineering systems-based model

Bulletin of Engineering Geology and the Environment - The deformation modulus of a rock mass is one of the crucial parameters used in the design of surface and underground rock engineering...     

Ethanol purification using polyamide‐carbon nanotube composite membranes

This work presents synthesis and characterization of polyamide‐carbon nanotube (CNT) composite membranes for purification of ethanol. The solution‐casting method was applied for preparation of nanocomposite membranes. The nanocomposite membranes were characterized using scanning electron microscopy to ensure the fine dispersion of nanoparticles in polymer matrix. The effect of CNT loading on membrane performance was investigated. The separation performance of synthesized membranes was evaluated in separation of ethanol from ethanol/water mixture using pervaporation. Effect of feed temperature and feed concentration on separation of ethanol was investigated. The results showed that increasing temperature increases flux of ethanol through the membrane, but decreases separation factor. The results also confirmed that the best separation performance can be obtained at CNT loading of 0.5 wt%. Furthermore, a mathematical model was developed to simulate the separation process. The model was based on solving the continuity equation for ethanol in the feed side and membrane. The simulation results were compared with the experimental data and were in good agreement. POLYM. ENG. SCI., 54:961–968, 2014. © 2013 Society of Plastics Engineers     

De-alloying of 316 stainless steel in the presence of a mixture of metal-oxidizing bacteria

The corrosion behavior of 316 stainless steel was investigated in the presence of a mixture of metal-oxidizing bacteria isolated from marine environments. Ennoblement of stainless steel in the presence of these bacteria can lead to localized corrosion that confirmed by ESEM images. The corrosion rate of the metals also increased. EDS results showed that these bacteria caused the segregation of Si elements in the metal structure and promoted the depletion of Cr and Fe contents in the corrosion products. Thus, the de-alloying of stainless steel can occur in the presence of metal-oxidizing bacteria.     

Seismic response of steel braced frames with shape memory alloy braces

In this paper, the seismic performance of steel frames equipped with superelastic SMA braces was investigated. To do so, buildings with various stories and different bracing configurations including diagonal, split X, chevron (V and inverted V) bracings were considered. Nonlinear time history analyses of steel braced frames equipped with SMA subjected to three ground motion records have been performed using OpenSees software. To evaluate the possibility of adopting this innovative bracing system and its efficiency, the dynamic responses of frames with SMA braces were compared to the ones with buckling restrained braces. After comparing the results, one can conclude that using an SMA element is an effective way to improve the dynamic response of structures subjected to earthquake excitations. Implementing the SMA braces can lead to a reduction in residual roof displacement and peak inter-story drift compare to the buckling restrained braced frames.     

A glycerol–water-based nanofluid containing graphene oxide nanosheets

Nanofluids are simply the dispersion of nanometer-sized particles in different fluids. Graphene oxide nanosheets (GONs) were prepared by exfoliating the graphite oxide. The GONs were investigated using Fourier transform-infrared spectroscopy, Raman spectroscopy, XRD analysis, high-resolution emission electron microscopy, transmission electron microscopy, and UV–visible spectroscopy. GONs/glycerol–water-based nanofluid was prepared by the two-step method. The stability of the nanofluid was investigated with respect to time. Thermal and electrical conductivity of the prepared nanofluid was examined with different temperatures (25–45 °C) and weight fractions (0.02–0.1 wt%). The nanofluid is found to be stable for more than 5 months. The results showed an enhancement in thermal conductivity of about 4.5 % at 25 °C with a weight fraction of 0.02 %. The improvement was up to 11.7 % with a weight fraction of 0.1 wt% at 45 °C. The electrical conductivity was increased with increasing the weight fraction and temperature. The improvement in electrical conductivity was about 5890 % at 25 °C and 0.1 wt%.     

An analytic approach for CDMA output of feedforward power amplifier

In this paper, a novel method is introduced to predict the Code-Division Multiple-Access (CDMA) output spectrum of an RF power amplifier linearized with feedforward technique based on transfer function. In this method, an RF power amplifier is modeled mathematically by nonlinear complex envelope transfer function based on AM-AM and AM-PM distortion diagrams. Using this model, analytic expressions of CDMA output spectrum of power amplifier is calculated. Having mathematical model of RF power amplifier leads to derive analytic expressions for InterModulation (IM) products in feedforward amplifier. Based on these expressions, IM products are related to nonlinear complex envelope transfer function of feedforward amplifier. Then, CDMA output spectrum of feedforward linearization technique is predicted. The loops imbalances in feedforward technique are considered in analysis. Finally, the results of derived expressions in MATLAB software are compared with ADS simulations results and good agreements were achieved. Employing this method gives insight for feedforward analysis and loops imbalances effects in feedforward amplifier for CDMA applications.     

Planting a tree while envisioning the forest--The recursive relation between theory and research: Reply to Blustein (2003).

In his comments regarding D. M. Tokar, J. R. Withrow, R. J. Hall, and B. Moradi's (see record 2002-08430-002) article, "Psychological Separation, Attachment Security, Vocational Self-Concept Crystallization, and Career Indecision: A Structural Equation Analysis," D. L. Blustein (see record 2002-08430-003) offered several useful suggestions for future research in the area of relationship variables and career development and also raised several concerns about Tokar et al's rationale for and use of structural equation modeling in testing their models. In this reply, the authors note points of agreement with Blustein and respond to comments with which they disagree. (PsycINFO Database Record (c) 2010 APA, all rights reserved)