Sharif Digital Repository

The authors consider the Multi-Skilled Project Scheduling Problem (MSPSP) as a version of the Multi-mode Resource-Constrained Project Scheduling Problem (MRCPSP), which extends the well-known NP-hard Resource-Constrained Project Scheduling Problem (RCPSP). In the MSPSP, it is made up of activities, which require specific skills to be done. Moreover, resources are staff members who master fixed skill(s). Thus, each resource requirement of an activity corresponds to the number of persons doing the corresponding skill that must be assigned to the activity during its whole processing time. The authors focus on taking into account the setup times when performing work, depending on the appointment... 

This study presented a qualitative and quantitative project risk assessment using a hybrid PMBOK model developed under uncertainty conditions. Accordingly, an exploratory and applied research design was employed in this study. The research sample included 15 experienced staff working in main and related positions in Neyr Perse Company. After reviewing the literature and the Project Management Body of Knowledge (PMBOK), 32 risk factors were identified and their number reduced to 17 risks using the expert opinions via the fuzzy Delphi technique run through three stages. The results of the confirmatory factor analysis showed that all risks were confirmed by the members of the research sample.... 

In order to define a new temperature correction factor in this study, accurate experimental values were presented for permeability and diffusivity of carbon dioxide and methane in imidazolium-based room temperature ionic liquid: [bmim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) immobilized on an inorganic membrane support. Results were presented as a function of temperature and pressure for temperatures within 300-320K and pressures below 50kPa. According to the literature, experimental values of permeability and diffusivity for CH4 in [bmim][PF6] vs. temperature are reported for the first time in this study. Results obtained for CO2 permeability revealed good agreement with data... 

In this paper, we will combine the frequency hopping (FH) and the multi-carrier code division multiple access scheme (MC-CDMA) through an internal coding. The total bandwidth will be divided to a number of sub-bands with equal bandwidth. In each signalling interval, the output of a super orthogonal encoder selects one of the sub-bands for data transmission. Sub-carriers are modulated by a user specific PN sequence, and are transmitted over the selected sub-band similar to the MC-CDMA communications. We will derive the exact bit error rate of the MC-CDMA system and the new coded system. It will be shown by analysis and simulation that the proposed system performs much better than the MC-CDMA... 

The aim of this study was to develop an appropriate kinetic model for propane dehydrogenation (PDH) over an industrial Pt-Sn/γ-Al 2O 3 catalyst in the presence of small amounts of oxygenated compounds. Experimental data were obtained from a previous study where catalytic PDH was carried out in a laboratory scale reactor at atmospheric pressure in the temperature range of 575-620 °C in the presence of small amounts of water or methanol. The kinetics of the main dehydrogenation reaction was described and the effects of water and methanol on coke deposition and catalyst sintering were considered in a catalyst deactivation model to explain the observed optimum level in the amount of added... 

A reduction in catalyst's activity with time-on-stream and the formation of side products are two of the problems associated with catalytic propane dehydrogenation (PDH). Previous studies have indicated that the presence of small amounts of oxygenated additives such as water can reduce coke formation and enhance catalyst activity. The aim of the present work was to develop an appropriate kinetic model for PDH over a commercial Pt-Sn/γ-Al 2O3 catalyst in the presence of small amounts of water. Experimental data were obtained from a previous study where catalytic PDH was carried out in a bench scale reactor system at atmospheric pressure in the temperature range of 575-620°C in the presence of... 

Micro motion stages are one of the essential components in field of micro robotics and ultra fine positioning systems. This research presents the optimum design of a 3-DOF micro motion stage and its position control using FEM simulation. This stage to be studied uses a 3 RRR flexure hinge base compliant mechanism driven by three piezoelectric stack actuators to provide micro scale planar motion. First of all parametric modeling of the stage will be fulfilled in ANSYS environment utilizing a commercial piezostack and different types of flexure hinges. Hence the Jacobian matrix will be achieved for each case. The optimum selection of the hinge form will be achieved upon results of the previous... 

IT Governance provides a business focus to enable alignment between business and IT objectives at high level COBIT framework and focused on IT operational levels, ITIL standard. COBIT and ITIL are not mutually exclusive and can be combined to provide a powerful IT governance, control and best-practice framework in IT service management. So ITIL business-IT strategic alignment perspective could be improved using COBIT framework. Focusing on COBIT processes which support (primarily and secondarily) strategic alignment, in this paper, first, we map COBIT 4.1 to ITIL v3 to identify how ITIL cover COBIT control objectives. Furthermore, based on control objectives which are not completely... 

Quasi-periodic and chaotic behavior, along with the control of chaos for a Gyrostat satellite (GS), is investigated in this work. The quaternion-based dynamical model of the GS is first derived, and then the influences of the reaction wheels in the GS structure, under the gravity gradient perturbation that causes a route to chaos through quasi-periodicity mechanism, is investigated. For the suppression of chaos in the system, a chaos control system with the quaternion feedback is designed for the GS based on the extension of the Ott-Grebogi-Yorke (OGY) method using the linearization of the Poincaré map. In the extended OGY controller, the Poincaré map is estimated using the Least Square... 

The chaotic dynamics of roto-translatory motion of a triaxial Kelvin-type gyrostat satellite under gravity gradient perturbations is considered. The Hamiltonian approach is used for modelling of the coupled spin-orbit equations of motion. The complex Hamiltonian of the system is reduced via the extended Deprit canonical transformation using the Serret- Andoyer variables. Therefore, this reduction leads to the derivation of the perturbation form of the Hamiltonian that can be used in the Ricci curvature criterion based on the Riemannian manifold geometry for the analysis of chaos phenomenon. The results obtained from Ricci method as well as the values from the Lyapunov exponent demonstrate... 

This article presents a study on the capability of the time domain OMA method, NExT-ERA, to identify closely spaced structural dynamic modes. A survey in the literature reveals that few experimental studies have been conducted on the effectiveness of the NExT-ERA methodology in case of closely spaced modes specifically. In this paper we present the formulation for NExT-ERA. This formulation is then implemented in an algorithm and a code, developed in house to identify the modal parameters of different systems using their generated time history data. Some numerical models are firstly investigated to validate the code. Two different case studies involving a plate with closely spaced modes and... 

Micro motion stages are one of the essential components in field of micro robotics and ultra fine positioning systems. This research presents the optimum design of a 3-DOF micro motion stage and its position control using FEM simulation. This stage to be studied uses a 3 RRR flexure hinge base compliant mechanism driven by three piezoelectric stack actuators to provide micro scale planar motion. First of all parametric modeling of the stage will be fulfilled in ANSYS environment utilizing a commercial piezostack and different types of flexure hinges. Hence the Jacobian matrix will be achieved for each case. The optimum selection of the hinge form will be achieved upon results of the previous... 

Vivid banding pattern of the chromosome image is a crucial part for diagnosis in karyotype medical test. Furthermore, thriving computer aided segmentation and classification depend on the initial image quality. In this paper, we propose an adaptive and iterative histogram matching algorithm for chromosome contrast enhancement especially in banding patterns which is one of the most important information laid in chromosome image. Objective histogram, with which the initial image needs to be matched, is created based on processes on the initial image histogram. Calculation of statistical moments of image histogram and determination of parameters in each step of iteration based on these moments... 

Vivid banding patterns in medical images of chromosomes are a vital feature for karyotyping and chromosome classification. The chromosome image quality may be degraded by many phenomenon such as staining, sample defectness and imaging conditions. Thus, an image enhancement processing algorithm is needed before classification of chromosomes. In this paper, we propose an adaptive and iterative histogram matching (AIHM) algorithm for chromosome contrast enhancement especially in banding patterns. The reference histogram, with which the initial image needs to be matched, is created based on some processes on the initial image histogram. Usage of raw information in the histogram of initial image... 

The present study tries to use the methanol-silver nanofluid filled thermosyphon heat exchanger and compares the effectiveness as well as energy saving with pure methanol. Experimental results show that using methanol-silver nanofluid, leads to energy saving around 8.8-31.5% for cooling and 18-100% for reheating the supply air stream in an air conditioning system  

Most of the publications regarding the maxim covering location problem (MCLP) address the case where the decision is to be made for one period. In this paper, we deal with a rather untouched version of MCLP which is called dynamic MCLP (DMCLP). In order to solve this problem, a simulated annealing (SA) has been presented. The proposed solution algorithm is capable of solving problems with up to 2500 demand nodes and 200 potential facilities with a fair amount of exactness. Our experiments showed that the proposed approach finds solutions with errors less than one percent  

In the present study, alginate/cartilage extracellular matrix (ECM)-based injectable hydrogel was developed incorporated with silk fibroin nanofibers (SFN) for cartilage tissue engineering. The in situ forming hydrogels were composed of different ionic crosslinked alginate concentrations with 1% w/v enzymatically crosslinked phenolized cartilage ECM, resulting in an interpenetrating polymer network (IPN). The response surface methodology (RSM) approach was applied to optimize IPN hydrogel's mechanical properties by varying alginate and SFN concentrations. The results demonstrated that upon increasing the alginate concentration, the compression modulus improved. The SFN concentration was... 

Equal channel angular pressing is an outstanding method for imposing large plastic deformation to metallic materials without any decreasing in cross section area of as processed samples. In this paper, the effect of working temperature, ram speed and the number of passes on the formation of adiabatic shear bands in Al6061 during equal channel angular pressing was investigated. Billets of the alloy were processed up to four passes via route BC from room temperature to 200°C with two ram speeds using a die that imparts an effective strain of ∼1.1 per pass. The results have demonstrated that the onset of the adiabatic shear banding in this alloy strongly depends on the ram speed: more...