Loading...
Search for:
sheikh-sajadieh--mohsen
0.109 seconds
Total 617 records
Concurrent project scheduling and material planning: a genetic algorithm approach
, Article Scientia Iranica ; Volume 16, Issue 2 E , 2009 , Pages 91-99 ; 10263098 (ISSN) ; Shadrokh, S ; Hassanzadeh, F ; Sharif University of Technology
2009
Abstract
Scheduling projects incorporated with materials ordering results in a more realistic problem. This paper deals with the combined problem of project scheduling and material ordering. The purpose of this paper is to minimize the total cost of this problem by determining the optimal values of activity duration, activity finish time and the material ordering schedule subject to constraints. We employ a genetic algorithm approach to solve it. Elements of the algorithm, such as chromosome structure, unfitness function, crossover, mutation and local search operations are explained. The results of the experimentation are quite satisfactory
Optimizing shipment, ordering and pricing policies in a two-stage supply chain with price-sensitive demand
, Article Transportation Research Part E: Logistics and Transportation Review ; Volume 45, Issue 4 , 2009 , Pages 564-571 ; 13665545 (ISSN) ; Akbari Jokar, M. R ; Sharif University of Technology
Elsevier Ltd
2009
Abstract
In this paper we focus on a two-stage supply chain consisting of one vendor and one buyer. We develop an integrated production-inventory-marketing model to determine the relevant profit-maximizing decision variable values. The model proposed is based on the joint total profit of both the vendor and the buyer, and it finds out the optimal ordering, shipment and pricing policies. We are able to ascertain the optimal decision variable values employing an analytical solution procedure. The numerical evidence suggests that it is more beneficial for the buyer and the vendor to cooperate with each other when the demand is more price sensitive. © 2008 Elsevier Ltd. All rights reserved
An integrated vendor-buyer cooperative model under stochastic supply lead-time
, Article International Journal of Advanced Manufacturing Technology ; Volume 41, Issue 9-10 , 2009 , Pages 1043-1050 ; 02683768 (ISSN) ; Akbari Jokar, M. R ; Sharif University of Technology
2009
Abstract
This paper presents a single-vendor, single-buyer integrated inventory model. We relax the assumption of deterministic lead-time in the hitherto existing joint economic lot sizing (JELS) models and analyze the problem where the buyer lead-time is a stochastic variable. Moreover, we consider the situation in which shortage is allowed. The vendor produces the product in batches and periodically delivers final goods at a fixed lot size to the customer, who has a constant demand rate. The proposed model, based on the integrated expected total relevant costs of both buyer and vendor finds out optimal values of reorder point, order quantity, and number of shipments, using a solution procedure....
Developing a coordinated vendor-buyer model in two-stage supply chains with stochastic lead-times
, Article Computers and Operations Research ; Volume 36, Issue 8 , 2009 , Pages 2484-2489 ; 03050548 (ISSN) ; AkbariJokar, M. R ; Modarres, M ; Sharif University of Technology
2009
Abstract
This paper develops an approach to determine the optimal production and shipment policy for an integrated vendor-buyer problem. The vendor manufactures the product in batches at a finite rate and ships the output to the buyer. All shipments to the buyer are equal-sized batches. Despite previous papers in the literature, we assume that the supply lead-time between vendor and buyer is stochastic and shortage is also allowed. The objective is to minimize the expected total cost of both buyer and vendor. We derive the expected annual integrated total cost function and propose an analytic solution procedure to determine the optimal policy. To illustrate the significance of cost-reduction of the...
Developing a Joint Economic Lot Sizing (JELS) Model in Multi-Stage Supply Chains
, Ph.D. Dissertation Sharif University of Technology ; Akbari Jokar, Mohammad Reza (Supervisor)
Abstract
In this thesis, we develop seven integrated production-inventory models for two or three-stage supply chains under stochastic and/or dependent parameters. The problem is called Joint Economic Lot Sizing (JELS) and can be considered as the building block for wider supply chain systems. The first and the second researches deal with the problem in which the supply lead time between the vendor and the buyer is stochastic with uniform and exponential distribution, respectively. The numerical analyses shows that the cooperation between two partners is more critical in unpredictable purchasing environments in terms of stochastic lead-times. In the third research, we investigate four sourcing models...
Coordination in supply chain management
, Article Supply Chain Sustainability and Raw Material Management: Concepts and Processes ; 2011 , Pages 52-74 ; 9781613505045 (ISBN) ; Bolooriarabani, A ; Sharif University of Technology
2011
Abstract
The aim of this chapter is to review various perspectives on supply chain (SC) coordination issues and appreciate a range of coordination categories and mechanisms. The application of information technology in supply chain coordination (SCC) and the related cases are also studied in this chapter
Sole versus dual sourcing under order dependent lead times and prices
, Article Computers and Operations Research ; Volume 36, Issue 12 , 2009 , Pages 3272-3280 ; 03050548 (ISSN) ; Eshghi, K ; Sharif University of Technology
2009
Abstract
In this paper, we consider a dual-sourcing model with constant demand and stochastic lead times. Two suppliers may be different in terms of purchasing prices and lead-time parameters. The ordering takes place when the inventory level depletes to a reorder level, and the order is split among two suppliers. Unlike previous works in the order splitting literature, the supply lead time between vendor and buyer as well as unit purchasing prices is considered to be order quantity dependent. The proposed model finds out the optimal reorder point, order quantity and splitting proportion, using a solution procedure. Numerical results show that neglecting the relationship between ordering batch size...
A Survey on Searchable Symmetric Encryption Schemes
, M.Sc. Thesis Sharif University of Technology ; Khazaei, Shahram (Supervisor)
Abstract
Using “Searchable Encryption” enables us to encrypt the data, while preserving the possibility of running search queries. One of the most important applications of the mentioned is in Cloud Storage. As users do not trust the Cloud space, they are not inclined to store their data on the Could. The solution to this problem is of course, Cryptography. However, ordinary Cryptography methods, eliminate the data’s searchability. Hence, we need encryption schemes that code the data while retaining their searchability. So far, various schemes has been proposed that differ in their performance, security level, and usage. In this thesis, we aim to discuss and analyze these methods
Optimizing a joint economic lot sizing problem with price-sensitive demand
, Article Scientia Iranica ; Volume 16, Issue 2 E , 2009 , Pages 159-164 ; 10263098 (ISSN) ; Sheikh Sajadieh, M ; Sharif University of Technology
2009
Abstract
This paper considers the problem of a vendor-buyer integrated production-inventory model. The vendor manufactures the item at a finite rate and delivers the final goods at a lot-for-lot shipment policy to the buyer. We relax the assumption of uniform demand in the hitherto existing joint economic lot sizing models and analyze the problem where the end customer demand is price-sensitive. The relation between demand and price is considered to be linear. The model proposed, based on the integrated expected total relevant profits of both buyer and vendor, finds out the optimal values of order quantity and mark-up percentage, using an analytical approach. Some numerical examples are also used to...
Investigation into characteristics of Portevin-Le Chatelier effect of an Al-Mg Alloy
, Article Journal of Materials Engineering and Performance ; Volume 19, Issue 9 , 2010 , Pages 1264-1267 ; 10599495 (ISSN) ; Sharif University of Technology
2010
Abstract
In this study, the plastic instabilities associated with the Portevin-Le Chatelier (PLC) and their effects on the mechanical properties and the fracture surfaces have been investigated for AA 5083. Tensile tests were performed at various temperatures and strain rates in order to do so. Then, serrated and smooth yielding domains were determined in Ln ε̇-1/T diagram. The stress-strain curves related to the serrated domain show the values of flow stress decreases by increasing the strain rate at a constant temperature. In addition, the plot of critical strain versus imposed strain rate indicates an inverse manner at very low strain rates. It is confirmed that the type of PLC bands alters the...
Analyzing the supply chain using SCOR model in a steel producing company
, Article 40th International Conference on Computers and Industrial Engineering, 25 July 2010 through 28 July 2010 ; 2010 ; 9781424472956 (ISBN) ; Akbari, M. R ; Ssheikh Sajadieh, M ; Sharif University of Technology
2010
Abstract
Supply Chain Operations Reference (SCOR) model is developed and maintained by the Supply Chain Council (SCC). The model is a reference model which can be used to map, benchmark and improve the supply chain operations. SCOR model provides companies with a basic process modeling tool, an extensive benchmark database and defines a set of supply chain metrics. Mobarakeh Steel Company (located in Isfahan, Iran) initiated the project of studying and analyzing its supply chain performance based on the SCOR model. This paper explains the steps and the results of the project. Interviews with the managers and considering the documents on the four major subjects of planning, logistics, information flow...
An integrated vendor-buyer model with stock-dependent demand
, Article Transportation Research Part E: Logistics and Transportation Review ; Volume 46, Issue 6 , November , 2010 , Pages 963-974 ; 13665545 (ISSN) ; Thorstenson, A ; Akbari Jokar, M. R ; Sharif University of Technology
2010
Abstract
We develop an integrated vendor-buyer model for a two-stage supply chain. The vendor manufactures the product and delivers it in a number of equal-sized batches to the buyer. The items delivered are presented to the end customers in a display area. Demand is assumed to be positively dependent on the amount of items displayed. The objective is to maximize total supply chain profit. The numerical analysis shows that buyer-vendor coordination is more profitable in situations when demand is more stock dependent. It also shows that the effect of double marginalization provides a link between the non-coordinated and the coordinated case
Numerical investigation of the effects of porosity and tortuosity on soil permeability using coupled three-dimensional discrete-element method and lattice Boltzmann method
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 91, Issue 5 , May , 2015 ; 15393755 (ISSN) ; Pak, A ; Sharif University of Technology
American Physical Society
2015
Abstract
Permeability of porous materials is an important characteristic which is extensively used in various engineering disciplines. There are a number of issues that influence the permeability coefficient among which the porosity, size of particles, pore shape, tortuosity, and particle size distribution are of great importance. In this paper a C++ GPU code based on three-dimensional lattice Boltzmann method (LBM) has been developed and used for investigating the effects of the above mentioned factors on the permeability coefficient of granular materials. Multirelaxation time collision scheme of the LBM equations is used in the simulator, which is capable of modeling the exact position of the...
Estimation of flow stress behavior of AA5083 using artificial neural networks with regard to dynamic strain ageing effect
, Article Journal of Materials Processing Technology ; Volume 196, Issue 1-3 , 2008 , Pages 115-119 ; 09240136 (ISSN) ; Serajzadeh, S ; Sharif University of Technology
2008
Abstract
In this work, neural networks are used for estimation of flow stress of AA5083 with regard to dynamic strain ageing that occurs in certain deformation conditions and varies flow stress behavior of the metal being deformed. The input variables are selected to be strain rate, temperature and strain and the output value is the flow stress. In the first stage, the appearance and terminal of dynamic strain aging are determined with the aid of tensile testing at various temperatures and strain rates and subsequently for the serrated flow and the smooth yielding domains different neural networks are constructed based on the achieved results. While a feed-forward backpropagation algorithm is...
Multi-objective optimization of a multi-layer PTSA for LNG production
, Article Journal of Natural Gas Science and Engineering ; Volume 49 , 2018 , Pages 435-446 ; 18755100 (ISSN) ; Farhadi, F ; Sharif University of Technology
Elsevier B.V
2018
Abstract
In this work, a novel multi-layer pressure-temperature swing adsorption (PTSA) process was designed for efficient simultaneous water and mercaptans removal from natural gas (NG) to less than 0.1 ppmv and 3 ppmv in a mini liquefied NG unit. The proposed multi-layer PTSA consists of a three-layer fixed bed including activated alumina, molecular sieves 4A and 13X. To gain in-depth insights about the process, a descriptive model considering mass, energy and momentum balances, along with the kinetic and equilibrium equations was developed. After validating the model with the experimental and operational data from the literature, the total energy requirement and long-term operational requirements...
Extraction of effective constitutive parameters of artificial media using bloch modes
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 11 , 2019 , Pages 3226-3235 ; 07403224 (ISSN) ; Rejaei, B ; Sharif University of Technology
OSA - The Optical Society
2019
Abstract
The effective constitutive parameters of a three-dimensional periodic structure are calculated using its Bloch modes. These modes and their propagation constants are obtained from eigenvectors and eigenvalues of the generalized transfer matrix of a unit layer of the structure. Effective bulk permittivity and permeability tensors of the medium are obtained when two of the Bloch modes are dominant, i.e., propagate without significant decay inside the medium. The effect of the strongly decaying Bloch modes, which are excited at the interface with a conventional medium, are included by means of surface impedance matrices. The results are in excellent agreement with full-wave electromagnetic...
Extraction of effective constitutive parameters of artificial media using Bloch modes
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 11 , 2019 , Pages 3226-3235 ; 07403224 (ISSN) ; Rejaei, B ; Sharif University of Technology
OSA - The Optical Society
2019
Abstract
The effective constitutive parameters of a three-dimensional periodic structure are calculated using its Bloch modes. These modes and their propagation constants are obtained from eigenvectors and eigenvalues of the generalized transfer matrix of a unit layer of the structure. Effective bulk permittivity and permeability tensors of the medium are obtained when two of the Bloch modes are dominant, i.e., propagate without significant decay inside the medium. The effect of the strongly decaying Bloch modes, which are excited at the interface with a conventional medium, are included by means of surface impedance matrices. The results are in excellent agreement with full-wave electromagnetic...
Effect of organoclay loading and electron beam irradiation on the physico-mechanical properties of low-density polyethylene/ethylene-vinyl acetate blend
, Article Polymers for Advanced Technologies ; Volume 22, Issue 12 , 2011 , Pages 2352-2359 ; 10427147 (ISSN) ; Behradfar, A ; Sheikh, N ; Sharif University of Technology
2011
Abstract
The influence of electron beam (EB) irradiation and organoclay (OC) loading on the properties of low-density polyethylene (LDPE)/ethylene-vinyl acetate (EVA) blends was investigated. The samples were subjected to the EB irradiation with the dose values of 50 and 250kGy. X-ray diffraction (XRD), gel content, mechanical, thermal, and electrical properties were utilized to analyze the characteristics of the LDPE/EVA blends with and without OC at different irradiation dosages. Gel content analysis showed that the OC promotes considerably the insoluble part so that the LDPE/EVA blends filled with OC become fully crosslinked at 250kGy; possibly through the formation of further crosslinks between...
Rheological and mechanical characteristics of low density polyethylene/ethylene-vinyl acetate/organoclay nanocomposites
, Article Polymer Engineering and Science ; Volume 50, Issue 7 , March , 2010 , Pages 1315-1325 ; 00323888 (ISSN) ; Shojaei, A ; Sheikh, N ; Sharif University of Technology
2010
Abstract
Attempts were made to trace the effect of organoclay (OC) on the rheological and mechanical behaviors of the low density polyethylene (LDPE)/ethylene-vinyl acetate (EVA) blends. To do this effectively, in addition to LDPE/EVA/OC system, pure LDPE and LDPE/EVA blends were also examined as model systems. The rheological behavior was determined by the capillary rheometer. Morphological characterization was also carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and theoretical approach based on interfacial energies. Shear viscosity, tensile strength and elastic modulus of LDPE/EVA were found to decrease by increasing the EVA...
Adhesion modification of polyethylenes for metallization using radiation-induced grafting of vinyl monomers
, Article Surface and Coatings Technology ; Volume 201, Issue 16-17 , 2007 , Pages 7519-7529 ; 02578972 (ISSN) ; Fathi, R ; Sheikh, N ; Sharif University of Technology
2007
Abstract
The present paper demonstrates the performance of the radiation grafting technique as a chemically based surface pretreatment method to adhesion modification of polyethylene surfaces toward the metallic layer. Gamma irradiation over a dose range of 4-10 kGy is used for grafting of vinyl monomers including acrylamide (AAm) and 1-vinyl-2-pyrrolidone (NVP) onto the surface of three different polyethylenes including low density polyethylene (LDPE) and two kinds of high density polyethylenes, namely HDPE-1 and HDPE-2. The grafting yield is evaluated based on the weight increase of the samples. It is found that the grafting yield is dominated by the crystallinity of the polyethylene, so that lower...