Sharif Digital Repository

Scheduling of the maintenance activities is considered, in which the duration of activities is uncertain, delivery date of the maintenance shutdown is predefined, and activities are multi-mode. The problem is a multi-mode time-constrained project scheduling problem (MTCPSP). The glycol regeneration unit in a gas refinery is as the case study. Based on the effect of equipment or sub-equipment on the system reliability, the importance value of equipment and sub-equipment within the system is determined, and these values are used in a heuristic algorithm as a priority rule for choosing activities in the schedule. Outcomes demonstrate the performance of the algorithm in early or on time delivery... 

The problem of this paper deals with the multi-mode project scheduling problem under uncertainty of activity duration where only the renewable resources are taken into account and a given deadline has to be met at the cost of recruiting additional resources. A heuristic algorithm is employed to solve this problem, and to maintain the robustness of the baseline schedule, the concept of critical chain project management (CCPM) is applied in which a new definition to resource buffer is considered. A simulation methodology is used to determine the size and location of resource buffers in the schedules in which three different buffer sizes and three different uncertainty levels are considered.... 

There are several critical measures in the project performance evaluation such as time, cost, and quality. In this paper, a new method for project performance evaluation is presented by combining the project Golden Triangle and the methods in decision science. At first, strategies and measures are introduced for the perspectives of the Balanced Scorecard (BSC) method according to their effect on time, cost, and quality. Next, the Analytic Hierarchy Process (AHP) method is used to weigh the measures by the judgments of experts after integrating AHP and BSC. Then, the weights of the five project phases - from the initiation to the closure - are calculated by the Technique for Order of... 

Transesterification reaction was performed in the presence of soybean oil, methanol, and Demineralized water plant sedimentation catalyst at 60°C for 8 h in this study. Central composite design method was used to study the effect of catalyst concentration and methanol to oil molar ratio on purity and yield of produced biodiesel. The results showed catalyst concentration of 9.08 wt% and methanol to oil molar ratio of 22.49 as the optimum condition in which the values of purity and yield of the produced biodiesel in the second-order models were 99.89% and 81.83%, respectively. Experiments are in good agreement with the mentioned values as corresponded values are 99.95% and 86.68%,... 

In this article, the extended finite element method is employed to solve problems, including weak and strong discontinuities. To this end, a level set framework is used to represent the discontinuities location, and the Heaviside and Branch function are included in the standard finite element method. The case of two arbitrary curved cracks is solved numerically and stress intensity factor (SIF) values at the crack tips are calculated based on the evaluation of the crack tip opening displacement. Afterwards, J-integral methodology is adopted to evaluate the SIFs for isotropic and anisotropic bi-material interface crack problems. Numerical results are verified with those presented in the... 

Moisture control of food products is of great importance in drying processes. Improving the dryer control system results in consistent production and reduction in energy consumption. In this paper, a state observer is used to estimate the moisture content and other state variables online. Estimated states are used in a control system including the regulator for disturbance rejection and robust controller for tracking objective. Since the bed dryer mechanism is a multivariable complex system associated with various uncertainties, a realistic uncertain model is considered. Moisture content and temperature of tea leaves (or other food products) are controlled at desired set points by... 

This paper introduces congestion relief management (CRM) as one of ancillary services in market structure for improving its operation. The CRM maintains the system operation within the security limits and defines the charge, receiving and paying in non-discriminatory methods which are based on how much of congestion is relieved and caused by each participant. The proposed method is based on congestion relief index (CRI) which can be used for selecting the offers. We compare two market-clearing procedures for CRM in terms of only supply side management and economical efficiency of demand side management to avoid transmission congestion in an optimum manner. We also use a zonal-based... 

If an ideal membrane for gas separation is to be obtained, the following three characteristics should be considered: the membrane should be as thin as possible, be mechanically robust, and have welldefined pore sizes. These features will maximize its solvent flux, preserve it from fracture, and guarantee its selectivity. Graphene is made up of a hexagonal honeycomb lattice of carbon atoms with sp2 hybridization state forming a one-atom-thick sheet of graphite. Following conversion of the honeycomb lattices into nanopores with a specific geometry and size, a nanoporous graphene membrane that offers high efficiency as a separation membrane because of the ultrafast molecular permeation rate as... 

This study introduces a novel Bayesian framework for online and real-time vibration control of beam type structures, which represent a comprehensive control system associated with input-state algorithms. Control design systems typically require knowledge of system states, which in structures are displacements and velocities at some degrees of freedom. Currently, full-field measurements of displacements and velocities in large structural systems are not feasible. Also, properties of the moving inertial loads as key parameters in control designs are assumed known; however, in practice, measuring their characteristics is a challenging issue. As a remedy, an observer is required to estimate... 

Using the unique pricing method of Tapsi, the second-largest ride-hailing company in Iran, we estimate the price elasticity of demand for Tapsi rides. Tapsi mechanically divides Tehran, the largest city of Iran, into 256 regions using a 16 × 16 matrix of straight lines, to implement surge pricing in response to excess regional demand or supply. Surge multiplier works for all ride requests within each region, independent of supply and demand in neighboring regions or rides characteristics. We exploit this sharp discontinuity in pricing by running a regression discontinuity to estimate the causal effect of the price change on the number of ride requests, i.e., price elasticity of demand. Using... 

Solar power is among the cleanest forms of renewable energy, and various methods have been proposed to increase its energy output. Among these proposals are control methods for the solar panel to maximize energy output. This paper presents the design of a dual-Axis solar tracking system to maximize the power output at different times of day and geographical locations. The system calculates the optimal solar tracking angles ahead of time using the astronomical and geometrical relationships. These pre-calculated angles are stored and used to position the panel every 30 minutes without the need for photocells. The system uses brush-less DC motors with PID controllers for precise tracking.... 

A heterogeneous nanocatalyst was prepared via covalent anchoring of dioxomolybdenum(VI) Schiff base complex on core-shell structured Fe3O4@SiO2. The properties and the nature of the surface-fixed complex have been identified by a series of characterization techniques such as SEM, EDX, XRD, TGA, FT-IR, and VSM. The synthesized hybrid material was an efficient nanocatalyst for selective oxidation of olefins to corresponding epoxides with t-BuOOH in high yields and selectivity. The catalyst could be conveniently recovered by applying an external magnetic field and reused several times without significant loss of efficiency. © 2016 Taylor and Francis  

The radical chlorination of polyethylene was carried out in perchloroethylene solvent using chlorine gas and ultraviolet photoradiation to investigate a reaction kinetics model. The recurrent structure of chloromethylene (-CHCl-) and methylene (-CH 2 -) groups and the percentage of substituted chlorine were determined using hydrogen-nuclear magnetic resonance (H-NMR) (500 MHz) spectra. A kinetics model has been proposed for this reaction in which the conversion of methylene (-CH 2 -) units to chloromethylene (-CHCl-) units was considered to be the main reaction step. The simplified version of the obtained kinetics model indicates that the reaction is first order with respect to the chlorine... 

A graph G is called an Mr(k)-graph if G has no k-list assignment to its vertices with exactly r vertex colorings. We characterize all A 3(2)-graphs. More precisely, it is shown that a connected graph G is an A3(2)-graph if and only if each block of G is a complete graph with at least three vertices  

Magnetite nanoparticles with a size distribution of 15-21 nm were synthesized and decorated onto surface of graphene oxide by ultrasound assisted precipitation. Size and size distribution of the obtained M-GO hybrid were appreciably finer than the hybrids prepared by stirring method. M-GO is a superparamagnetic material with saturation magnetization of 31 emu g-1. The Langevin equation was successfully applied for estimation of size of Fe3O4 nanoparticles in M-GO hybrid, with maximum error of 17.5%. The study put forward a formation mechanism for M-GO, based on instrumental analyses. Adsorption isotherms of Sr2+ and Co2+ ions, which were fitted by Langmuir monolayer... 

One of the important challenges in the auto industry is to reduce the mass of the vehicle while meeting structural performance requirements for Crashworthiness, Noise, Vibration and Harshness (NVH) etc. In this paper, a multidisciplinary optimization (MDO) of a car back-bonnet is investigated by using trie Response Surface Method (RSM). Firstly, a car body is fully surface modeled in CATIA and meshed in HYPERMESH software. Then, modal analysis of the finite element model is performed by NASTRAN software to find natural frequencies. Frequency map of that component is extracted and compared with a reference map to detect defects. Design of Experiments (DOE) methodologies is used for a... 

Implanted biomedical sensor networks provide a major application of sensor networks in the near future. Their high temperature due to wireless communication, might damage the surrounding tissues. This paper presents an efficient thermal-aware routing. Our proposed protocol states that when some nodes in the shortest path have a high temperature, ignores this path. The simulation results indicate the superiority of the proposed method compared to other thermal-aware routing protocols in terms of reducing temperature without a significant increase in packet delivery delay and power consumption of nodes. © 2009 IEEE  

One of the important challenges in the auto industry is to reduce the mass of the vehicle while meeting structural performance requirements for crashworthiness, noise, vibration and harshness, etc. In this paper, a multidisciplinary optimisation of a car back-bonnet is investigated by using the response surface method. A car body is fully surface modelled in CATIA and meshed in software. Then, modal analysis of the finite element model is performed by NASTRAN software to find natural frequencies. A frequency map of that component is extracted and compared with a reference map to detect defects. Design of experiments methodology is used for a screening of the design space and for the... 

Control problem in a biological system is the problem of finding an interventional policy for changing the state of the biological system from an undesirable state, e.g. disease, into a desirable healthy state. Boolean networks are utilized as a mathematical model for gene regulatory networks. This paper provides an algorithm to solve the control problem in Boolean networks. The proposed algorithm is implemented and applied on two biological systems: T-cell receptor network and Drosophila melanogaster network. Results show that the proposed algorithm works faster in solving the control problem over these networks, while having similar accuracy, in comparison to previous exact methods. Source... 

Haptic interfaces, a kinesthetic link between a virtual environment and a human operator play a pivotal role in the reproduction of realistic haptic force feedback of the virtual reality-based simulators. Since most of the practical control theories are model-based, the identification of the robot’s dynamics, for precise modeling of the system dynamics, is a process of high significance and usage. This research addresses dynamic characterization, performance issues, and structural stability, associated with a parallel haptic device interaction with an admittance type virtual environment. In this regard, considering the Lion identification scheme, we characterized the dynamics of a robot...