LDPE/EVA/graphene nanocomposites with enhanced mechanical and gas permeability properties

, Article Polymers for Advanced Technologies ; Volume 26, Issue 9 , 2015 , Pages 1083-1090 ; 10427147 (ISSN) Tayebi, M ; Ramazani S. A ; Hamed Mosavian, M. T ; Tayyebi, A ; Sharif University of Technology

John Wiley and Sons Ltd 2015

Abstract

In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1-nm thickness and good transparency was synthesized using the well-known Hummers's method. Fourier transform infrared and X-ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are...

Differential Item Functioning (DIF)in Terms of Gender in a High Stakes Test

, M.Sc. Thesis Sharif University of Technology Tayebi, Alireza (Author) ; Salehi, Mohammad (Supervisor)

Abstract

Validation is an important enterprise especially when the test to be validated is a high-stakes one the results of which bring about life-changing implications for the candidates (Roever, 2001). Messick’s (1988) notion of construct irrelevant factors is pertinent in test validation. Demographic variables like gender, field of study and age can affect test results and interpretations. A fair test needs to be neutral when it comes to construct irrelevant factors such as gender. Differential Item Functioning is a way of making sure that the test does not favor one group of test takers over the others. The current study investigated differential item functioning (DIF) in terms of gender in the...

Developing Inventory Control Policies with No Ordering Costs in Two-Echelon Supply Chains

, Ph.D. Dissertation Sharif University of Technology Tayebi, Hamed (Author) ; Haji, Rasoul (Supervisor)

Abstract

This dissertation attempts to develop four inventory control models for two-echelon supply chains. For the all models, the retailers face Poisson demand and lost sales during a stockout. There is also a time-dependent holding cost and a cost per unit of lost sales. However, there is no (or negligible) cost associated with placing an order.
For the first model, we consider a two-echelon inventory system with one central warehouse and a number of retailers. The central warehouse applies (R, Q) policy and retailers apply base stock policy. In this model, we approximate the arrival process of the central warehouse and obtain the total cost of the system, as well as the optimal solution....

Proposing a Two-Stage Stochastic Model and a Heuristic Solution Method for a Green Supply Chain Location-Routing Problem with Stochastic Demand Considering Time Windows

, M.Sc. Thesis Sharif University of Technology Tayebi, Ali (Author) ; Rafiee, Majid (Supervisor)

Abstract

Location-routing problems are a class of well-known supply chain problems. the purpose of these problems are to locate depots, assign customers to the located depots, and to determine the routes in a way to minimize the costs of the supply chain.In the past two decades, with a rise in environmental problems including air pollution, green location-routing problems have been introduced and studied, problems in which environmental aspects such as air pollution have been considered.In this study, first, we model a two-stage stochastic green location routing problem; this problem includes a certain number of cities that each represent a customer. the locations of the cities are known and each...

An efficient tabu search algorithm for the single row facility location problem [electronic resource]

, Article European Journal Of Operational Research ; Vol. 205, No. 1, pp. 98-105 Samarghandi, H. (Hamed) ; Eshghi, Kourosh ; Sharif University of Technology

Abstract

The general goal of the facility layout problem is to arrange a given number of facilities to minimize the total cost associated with the known or projected interactions between them. One of the special classes of the facility layout problem is the Single Row Facility Layout Problem (SRFLP), which consists of finding an optimal linear placement of rectangular facilities with varying dimensions on a straight line. This paper first presents and proves a theorem to find the optimal solution of a special case of SRFLP. The results obtained by this theorem prove to be very useful in reducing the computational efforts when a new algorithm based on tabu search for the SRFLP is proposed in this...

Sensitivity analysis of matching pennies game [electronic resource]

, Article Mathematical and Computer Modelling ; Volume 51, Issues 5–6, March 2010, Pages 722–735 Yarmand, H. (Hamed) ; Eshghi, Kourosh ; Sharif University of Technology

Abstract

In this paper, we have discussed the results of sensitivity analysis in a payoff matrix of the Matching Pennies game. After representing the game as a LP model, the sensitivity analysis of the elements of the payoff matrix is presented. The game value and the optimal strategies for different values of parameters are determined and compared

Joint order (1, T) policy for a two-echelon, single-item, multi-retailer inventory system with Poisson demand

, Article Computers and Industrial Engineering ; Volume 119 , 2018 , Pages 353-359 ; 03608352 (ISSN) Tayebi, H ; Haji, R ; Ghalebsaz Jeddi, B ; Sharif University of Technology

Elsevier Ltd 2018

Abstract

This study considers a two-echelon inventory system with one central warehouse and a number of non-identical retailers with Poisson demands, constant lead times, and lost sales for a single item. The warehouse works as a cross-docking terminal with no inventory and coordinates shipments to retailers. We apply the Joint order (1, T) policy in such an inventory system. In the standard (1, T) policy, the warehouse sends one unit of the item to each retailer in a fixed cycle time, which is calculated by considering each retailer separately. In the joint order (1, T) policy, the warehouse decides to replenish one unit of the item for each retailer in a cycle time which is adjusted to be an...

The effect of additives on the properties of HAp-Al2O3nano-composite powders

, Article Journal of Ceramic Processing Research ; Volume 17, Issue 10 , 2016 , Pages 1033-1041 ; 12299162 (ISSN) Tayebi, S ; Mirjalili, F ; Samadi, H ; Nemati, A ; Sharif University of Technology

Hanyang University 2016

Abstract

Hydroxyapatite is the most important bio ceramic, due to its structure and chemical composition which is similar to bone. Since feeble fracture toughness, brittleness and low tensile strength have restricted their use, for overcoming this problem, they were often used as a secondary component. HAp-Al2O3 nano-composite powder combined the benefits of biocompatibility of HAp and high strength of Al2O3. When HAp-Al2O3 nano-composite powders were sintered at a higher temperature than 1100- 1200°C, HAp was decomposed and converted to the second phase of TCP, due to the formation of calcium aluminate increasing decomposition speed of HAp to TCP at higher degree than 1100-1200°C temperatures;...

Impact of magnetic field localization on the vortex generation in hybrid nanofluid flow

, Article Journal of Thermal Analysis and Calorimetry ; Volume 148, Issue 13 , 2023 , Pages 6283-6300 ; 13886150 (ISSN) Ali, K ; Ahmad, S ; Ahmad, S ; Tayebi, T ; Sharif University of Technology

Springer Science and Business Media B.V 2023

Abstract

The term "vortex" refers to a region in a fluid where the flow spin around an axis line, which could be flat or curved. Vortices can twist, stretch, move, and interact in several situations, once they are formed. The angular and linear momentum, along with some energy and mass, are all noticeable in a rotating vortex. Descriptions of vortices developed in various flows include smoke rings, dust devils, cyclones, and the wind surrounding a tropical tornado. The existence of vortices in the natural environment makes it important for researchers to explore them when and wherever they are encountered. Magnetic field effects include numerous technical applications such as: B. Extraction of...

Parametric study and computation of seismic performance factors of braced shear panels

, Article Scientia Iranica ; Volume 23, Issue 2 , 2016 , Pages 460-474 ; 10263098 (ISSN) Hamed, A ; Mofid, M ; Sharif University of Technology

Sharif University of Technology 2016

Abstract

By locating a steel shear panel on the intersection point of the X-braces, concentrically or eccentrically braced shear panel (CBFSP or EBFSP) is formed. In this paper, to perform parametric study, 1-story CBFSP and EBFSP models with span length greater or less than height are considered. Using linear static analyses, the effects of size and location of the shear panel on the lateral stiffness of the frame with respect to the moment resisting frame with the same member sections are investigated. Next, for 1- And 3-story models, maximum displacement, along with base shear, and the ratio between the dissipated energy and input energy are examined under 4 ground motion records. Behavior of the...

Assessment of Seismic Retrofit Policies for Buildings

, M.Sc. Thesis Sharif University of Technology Movahedi, Ali (Author) ; Kashani, Hamed (Supervisor)

Abstract

Occurrence of natural disasters such as earthquake could seriously damage most buildings especially those with insufficient resistance located in urban worn-out textures. In order to reduce unpleasant consequences of an earthquake, appropriate policies need to be considered to persuade the beneficiaries to follow retrofitting standards in the process of planning, designing, and construction of buildings. These policies shall be implemented through institutions in arbitrary or obligatory forms, by encouragement or penalty mechanisms. In order to consider these policies, first of all we need to identify the beneficiaries and their particulars. By studying and considering subjects discussed in...

Optimal-Robust Control of Drug Delivery in Cancer Chemotherapy

, M.Sc. Thesis Sharif University of Technology Hosseini, Fatemeh (Author) ; Moradi, Hamed (Supervisor)

Abstract

Chemotherapy is a proven and effective systematic approach to treat various types of cancers. Despite its advantages, chemotherapy would kill healthy as well as cancer cells. To overcome this problem, different controlling strategies are implemented. This study aims to provide a medicine drug delivery schedule for chemotherapy (by designing a proper controlling system) based on the verifiable mathematical models. First, the dynamic model is analysed and stability points are reviewed. The selected model has five state variables and two inputs. In this study, the focus is on dynamic model analysis and obtaining an effective and appropriate treatment pattern by designing a proper controller. To...

Real Options Analysis Framework for the Optimal Timing of Network Infrastructure Systems Retrofits

, M.Sc. Thesis Sharif University of Technology Roghani, Mehran (Author) ; Kashani, Hamed (Supervisor)

Abstract

Natural disasters can damage the infrastructure of society. Damages to the infrastructure components of society can disrupt their service delivery. Disruption in providing services to society's infrastructure can disrupt social and economic activities and impose various significant costs on society. The cost of repairing the damaged infrastructure and reducing the income of households are among the economic damages of accidents. The decline in the quality of life, as well as the death and injury of people due to the breakdown of the infrastructure or the disruption in their services, are among the social damages caused by accidents. In the same way, natural disasters are considered a...

Analysis of Seismic Vulnerability Reduction Policies of Residential Buildings Using a Multi-agent Evolutionary Game Model Based on Prospect Theory

, M.Sc. Thesis Sharif University of Technology Hosseini, Ahmad (Author) ; Kashani, Hamed (Supervisor)

Abstract

Due to the vulnerability of urban fabric and residential buildings to earthquakes and considering its destructive social and economic effects on society, the need to adopt appropriate policies to prevent and reduce vulnerability, has been increasingly considered by policy makers. Despite the laws, regulations, incentives and penalties that policymakers have envisioned to prevent unprincipled and unsafe construction, evidence shows that a significant number of new buildings being built in the country are not earthquake resistant and there are many violations in design, implementation and supervision that is done by the stakeholders. To solve this problem, research has been done on the...

Development of a Multi-functional Soil Column for Studying Bioremediation and Multiphase Flow

, M.Sc. Thesis Sharif University of Technology Samari, Peyman (Author) ; Sadeghi, Hamed (Supervisor)

Abstract

Soil and water pollution is one of the most common types of pollution in terrestrial and aquatic ecosystems. The development of mines and the oil and petrochemical industry on one hand and the non-compliance with environmental requirements on the other hand have caused large amounts of hydrocarbon pollutants and heavy metals to enter the environment in recent decades. Petroleum materials and heavy metals leak into the surrounding environment during drilling and extraction in oil sites and mines or during land and sea transportation, despite the measures taken to control their pollution. The conducted studies show that human industrial activities are the only cause of environmental pollution...

Developing Novel Algorithms to Simultaneous Power Regulation and Load Mitigation of Modern Variable Speed Wind Turbines

, Ph.D. Dissertation Sharif University of Technology Golnary, Farshad (Author) ; Moradi, Hamed (Supervisor)

Abstract

The power control of horizontal axis wind turbines can affect significantly the vibration loads and fatigue life of the tower and the blades. In this thesis, we are going to consider both the power control and vibration load mitigation of the tower fore-aft vibration. For this purpose, at first, we developed a fully coupled model of the NREL 5MW turbine. This model considers the full aeroelastic behavior of the blades and tower and is validated by experiment results, comparing the time history data with the FAST (Fatigue, Aerodynamics, Structures, and Turbulence ) code which is developed by NREL (National Renewable Energy Lab in the United States). In the next, to estimate EWV, a novel...

Laboratory Investigation of the Effects of Sodium Chloride Concentration on Soil Water Retention Curve and Volumetric behavior Using an Unsaturated Automatic Oedometer

, M.Sc. Thesis Sharif University of Technology Nasiri, Hamed (Author) ; Sadeghi, Hamed (Supervisor)

Abstract

Laboratory studies to investigate the effects of different saline concentrations (such as sodium chloride or calcium chloride) on the soil water retention behavior of clayey soils and their volumetric changes have received much attention recently. However, many previous studies have investigated these effects in only one path of the SWRC (wetting or drying path) and the effects of saline concentration on hydraulic hysteresis have not been considered. In addition, researchers have frequently studied these effects on SWRC on clay samples, and little research has been done on collapsible soils. Therefore, the most important purpose of this study is to investigate the effects of increasing...

Robust and Nonlinear Control of the Boiler-Turbine Unit Performance in a Coal Fired Ultra-Supercritical Once Through Boiler Power Plant in Order to Optimize the Uncertain Problem

, M.Sc. Thesis Sharif University of Technology Esmaeili, Mohammad (Author) ; Moradi, Hamed (Supervisor)

Abstract

Nowadays electricity power has a key role in developing various aspects of the world. The great importance of fossil fuel power plants come from their large contribution in electricity power generation. Among the different fossil fuel power generation technologies, supercritical power plants have great advantages. They are an advanced power generation technology with high plant efficiency, high coal utilization and low emission. Their complexity and existing many unavoidable uncertainty sources in their dynamic such as changes of ambient temperature, climate condition and wear of components make their control challenging. To overcome mentioned problems and achieving a good performance, a...

Numerical Modeling of Stability and Transport of Soluble Contaminants in Tailings Dams under Coupled Hydro-Chemical Processes (A Case Study of Sarcheshmeh Tailings Dam)

, M.Sc. Thesis Sharif University of Technology Anbarestani, Mona (Author) ; Sadeghi, Hamed (Supervisor)

Abstract

The instability and contamination leakage through tailings dams is one of the major problems of them. These dams are usually constructed through self-consolidation with minimum compaction effort, so special attention must be given to the stability of these structures. In addition, tailings dams contain considerable amounts of metals and chemically soluble contaminants resulting from mining processes in their reservoirs, making them more likely to leak contamination from the dam's foundation and body, causing pollution downstream. The infiltration of various chemical contaminants into the soil may alter its hydraulic and resistance properties. Laboratory studies have shown that pore solution...

Modelling and Electromechanical Control of Variable Speed wind Turbine in Order to Gain Maximum Wind Power

, M.Sc. Thesis Sharif University of Technology Golnary, Farshad (Author) ; Moradi, Hamed (Supervisor)

Abstract

In this research, the main purpose of the controller design is in the second region of operation of a wind turbine, which involves absorbing the maximum energy from the wind. WindPACT 1.5MW turbine has been investigated and the power coefficient of this turbine has been obtained using WT-PERF and FAST softwares. Simulations show that the results of both methods are well matched. Then, using ANFIS, a method for estimating the wind speed is derived from the data obtained by FAST. Inputs to the ANFIS system are the turbine aerodynamic power, rotor speed and blade pitch angle while the output of ANFIS system is the estimated wind speed. The maximum power coefficient of the wind turbine occurs...