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shafiei--yousef
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Experimental study on macro segregation behavior in short and wide range solidification of different aluminum alloys
, Article Materials Science and Technology Conference and Exhibition 2013, MS and T 2013 ; Volume 2 , 2013 , Pages 822-829 ; 9781629933092 (ISBN) ; Mohammad Salehi, E ; Hassan Nejad, H ; Shafiei Zadeh, S ; Sharif University of Technology
2013
Abstract
Data are presented on the solidification of aluminum alloys and their macro segregation behavior. Three alloys with different solidification ranges were prepared in two temperatures. Two types of molds were also prepared by sand and metallic materials. The solidification of Al alloys were studied and the effects of four parameters were determined, including cooling rate, casting temperature, degassing and nucleation effects on solidification and a comparison was conducted to Scheil model performance. Three types of aluminum alloys (Al-12.1%Si, Al-6.9%Si and Al-4.4% Cu) with short, medium and wide solidification ranges were studied and the results showed that degassing, nucleation, increasing...
A new model for the effect of grain size on the elastic modulus of nanocrystalline materials
, Article Materials Science- Poland ; Volume 27, Issue 1 , 2009 , Pages 279-285 ; 01371339 (ISSN) ; Sharif University of Technology
2009
Abstract
A new model is developed for the structure of nanocrystalline materials. Based on the developed model, a new approach for investigating the effect of grain size on the elastic moduli of nanocrystalline materials is introduced. The predictions of the model are strongly correlated with the experimental results reported in the existing literature
Adding backlash to the connection elements can improve the performance of a robotic exoskeleton
, Article Mechanism and Machine Theory ; Volume 152 , 2020 ; Behzadipour, S ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Kinematic mismatch between exoskeletons and human body results in excess internal forces/torques and hence discomfort as well as increase the power consumption. The connection stiffness has been shown to have potentials for minimizing the kinematic mismatch effects. However, realization of a desired stiffness in the connection element seems difficult if not impractical. In this work, adding controlled backlash to the exoskeleton-body connection is investigated as a possible solution for the kinematic mismatch challenge. A stiffness model which includes backlash parameters was formulated and identified experimentally using three male subjects on a typical lower extremity exoskeleton. A...
Optimisation of an integrated parallel distribution system by including network marketing
, Article International Journal of Logistics Systems and Management ; Volume 36, Issue 2 , 2020 , Pages 305-318 ; Modarres, M ; Sharif University of Technology
Inderscience Publishers
2020
Abstract
Network marketing is a business model that depends upon a network of distributors for growth, such as in multilevel marketing. A direct selling method features independent agents that make up a distribution network for goods and services. This paper provides a framework to study the network marketing by adopting the traditional channel. To motivate all distributers in network marketing as well as retailers, it is required to design a well-balanced distribution and pricing system. The allocated commission for distributers in different layers of network marketing is part of pricing system, which is vital. In this paper, we develop an approach to determine all elements of system, including...
The Concept of Truth in Husserl’s Phenomenology
, M.Sc. Thesis Sharif University of Technology ; Rashidian, Abdolkarim (Supervisor)
Abstract
Concept of Truth is the most fundamental concept in any intellectual activity. Knowledge systems are distinguished, above all, by their different viewpoint about truth and different criteria which they present for determining truth. Phenomenology, that its motto is returning to things as such, should introduce a definition of truth free from the presuppositions which lie in the definitions (implied or expressed ones) of it in most knowledge systems. In this project, we try to clarify concept of truth as correlation of transcendental act in philosophy of Husserl, and also study antecedents and consequents of this conception. In this project we investigate the place of the idea of “truth” in...
On Some Pancyclicity Properties of OTIS Network
, M.Sc. Thesis Sharif University of Technology ; Movaghar, Ali (Supervisor)
Abstract
A parallel computer system is composed of a collection of processors used to speed up running a program or performance of multiple programs. If we consider the processors as nodes and the channels between processors as edges, the constructed graph represents an interconnection networks. Network topology affects performance and energy consumption of interconnection network very much. Some parameters of topology quality are low node degree and diameter, high connectivity degree and bisection width and symmetry. Since some of these parameters are in contrast with others, a network with more parameter improvements, is more desirable. Finding cycles with specific length and particularly ...
Optimization of Coordinated Distribution System by Adopting the Network Marketing and Traditional Channel
, Ph.D. Dissertation Sharif University of Technology ; Modarres, Mohammad (Supervisor)
Abstract
Nowadays network marketing has promoted marketing, sale and customer relationship altogether. On the other hand, due to the growth of internet, network marketing has become a powerful and attractive channel that can be utilized alongside the other traditional channel. Pricing and network marketing structure influences on distribution system coordination and networker motivation in network marketing. This thesis provides a framework to study the integration of network marketing with retailers in a dual channel distribution system and provide the pattern for determining the different variables of distribution systems, including of product price in diverse channels, commission payment to...
Coordinated Scheduling in Public Transportation to Decrease Transfer Waiting Time Through Slight Changes in Headways
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Decreasing travel time is one of the main goals of passengers in urban areas for which transportation operators use various policies. Among these policies, expanding public transportation facilities is one of the urban planner major purposes. Considering the fact that making these facilities needs great investment, optimize use of the current facilities is valuable. Waiting time in transit station has influence on increasing passengers’ travel time and inconsistency, so coordination between different transit lines is necessary. In this thesis, creating coordination among different transit lines in a transit network by the use of integer programming is studied in the form of two models. In...
An Applied Model for Highway Alignment Optimization Using Particle Swarm Optimization Method
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
A basic highway design problem is to find the most economical alignment connecting two given end points based on topography, soil conditions, socioeconomic factors and environmental impacts, while satisfying a set of design and operational constraints. The cost function complexity and numerous limitations such as highway design criteria have made this problem a NP-hard one. In this study, a swarm based searching algorithm has been applied to a three dimensional highway alignment optimization model. The spatial data has been exploited from a GIS databases using a heuristic swift approach. In addition, the majority of cost items that depend on highway design have been extended in a practical...
Route Choice Estimation Using Cell Phone Data
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Knowing the trip information such as paths that travelers prefer to choose is useful for practice in developing certain transportation planning step. There are different methods such as using GPS and conducting survey for volunteer travelers in order to understand actual paths. Obviously, all of these methods have some deficiencies. This research suggests and examines a method for estimating travelers’ path by using cell phone data. The main advantage of using these kinds of data is enabling the process of collecting information without any active interference of the users. A big data set consisting of 300,000 cell phone users’ information in the city of Shiraz is studied to achieve this...
Determining Mode of Travel Using Cell Phone Data
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
There has been growing interest in exploiting cellular network data for transportation planning purposes in recent years. In this thesis, we utilize these data for determining mode of travel in the city of Shiraz, Iran. Cellular data records -including location updates in 5minute time intervals- of 300,000 users from the city of Shiraz has been collected for 40 hours in three consecutive days in a cooperation with the major telecommunications service provider of the country. Depending on the density of mobile BTS’s in different zones of the city, the user location can be located within an average of 200 meters. Considering data filtering and smoothing, data preparation and converting them to...
Estimating Activity Patterns Using Spatio-temporal Data of Cell phone Networks
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
The tendency towards using activity-based models to predict trip demand has increased dramatically over recent years, but these models have suffered insufficient data for calibration and the intrinsic problems of traditional methods imposes the need to search for better alternatives. This paper discusses ways to process the cellphone spatio-temporal data in a manner that makes it comprehensible for traffic interpretations and proposes methods on how to infer urban mobility and activity patterns from the aforementioned data. Movements of each subscriber is described by a sequence of stays and trips and each stay is labelled by an activity. The type of activities are estimated using features...
Estimation of Origin-Destination Trip Matrix Using Mobile Phone Network’s Spatiotemporal Dataset
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Knowledge about travel demand patterns is an important requirement for strategic planning and management of urban transportation networks. Use of theoretical trip distribution models such as growth, gravity or intervening opportunities, estimation with the help of questionnaire surveys and development of volume- based O-D estimation methods have been major fields of scientific efforts in recent years.Rapid changes in land use and transportation networks especially in developing countries has raised the importance level of knowledge about changes in travel demand.Traditional approaches are costly, time consuming and suffer from inaccuracies, so,...
Flight Rescheduling After Perturbation with Crew Constraints
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Airlines spend considerable time, effort and financial resources on planning. It is essential to create a competitive timetable and construct a fleet and a crew schedule that utilizes these resources to maximum. Unfortunately, it is all too common that an airline is faced with the necessity of reconstructing their schedule due to some unforeseen event such as an aircraft breakdown or unsuitable weather condition. Rescheduling flight in such conditions is inevitable. In this article, first, a mathematical model is presented to minimize the expense caused by aircraft breakdown, flight delay and airport closure with considering crew constraints. Cancellation, delay, aircraft swaps and replacing...
A Comprehensive Model for Aircraft Maintenance Routing
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
One of the fundamental constraints that should have been in mind in flight scheduling is aircraft maintenance scheduling. Based on the accepted rules, regulations and flight safety, in a given period of time or after definite number of flight hours each aircraft should be sent to maintenance site. This influences the flight schedule. This research provides a comprehensive model for the flight scheduling. Given the flight schedule, number of the flights and aircrafts, maintenance center's capacity and other parameters such as each check's time, allowable flight days and allowable flight hours this model could determine each season's flight schedule and solve the aircraft routing problem....
Estimation of Origin-Destination Trip Matrix Using Spatio-Temporal Data of Cell Phone Networks Collected based on the PLU method
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Origin-destination (OD) matrix is one of the most important sources of information used in planning and management of transportation networks. Estimation of a precise OD matrix is a fundamental component for enabling the administrative authorities to optimize the use of their transportation network. Traditionally, urban planners use direct approaches including household questionnaires to estimate OD matrices. These methods are time-consuming and costly. Strategies that are more recent like Bluetooth, Wi-Fi, and RFID scanners and detectors include deficient precision and the additional cost of accessories. Exploiting GPS technology in spite of its high locating accuracy, due to user...
Trip-Chain-Based Travel-Mode-Shares Driven Framework Using Mobile Data
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
The costly and time-consuming methods of traditional data collection through interviews or questionnaires have led researchers to use new methods, including mobile networks, to obtain the information they need. Information obtained from the mobile network has been widely used in recent studies due to features such as passive information generation, extensive coverage and low cost of data collection, and attempts have been made to use this information to model citizens activities and urban travel demand. However, extracting information such as travel patterns and mode share of transportation has been challenging given the nature of this type of data. This research pursues two goals separately...
Urban Mobility Pattern Estimation Using O-D Surveys and Mobile Phone Data: A Case Study of Shiraz City
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Activity bases models of travel demand considers travel demand as a derived demand to fulfill activities. Development of these models cause better understanding of the mechanism of travel through Integrity, interdependencies, higher temporal and spatial aggregation, and behavioral basis. Although these models requires of spatial and temporal data with high resolution of huge number of peoples. Gathering this data through surveys require great labor and time. Mobile phone data of cellular network have high spatial-temporal resolution used for billing purposes and can be used as a supplementary source of data to develop activity based models. This research uses mobility patterns called motifs...
The Impacts of Autonomous Vehicles on Parking Demand in Urban Areas
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Autonomous vehicles will have a major impact on parking demands in urban areas in the future. Compared to conventional vehicles that should park near the destination of the passengers, autonomous vehicles can drop off the travelers at their destinations and then drive to the parking spaces by themselves. However, choosing a parking space in a far zone from the destination could lead to more travel demand in the network. We investigate traffic network equilibrium for traveling and parking with autonomous vehicles under a fully automated traffic environment. We introduce a Bi-level model, considering parking choices in the upper level and route choices in the lower level. The upper-level...
A Model to Predict the Railway Track Deterioration and Provide a Decision-Support System for Maintenance by Life Cycle Cost
, M.Sc. Thesis Sharif University of Technology ; Shafahi, Yousef (Supervisor)
Abstract
Rail transport system plays an important role in the development of the economies of the countries. This system is worn out over time by operating and weather conditions and requires maintenance and repair. One of the objectives of maintenance operations is to maintain tracks in an acceptable level and prevent their excessive deviation from the optimal situation. This deviation is called geometric irregular deviation. If these irregularities go away, they can cause traffic accidents and derailment in addition to losing travel convenience. So avoiding the deviation of the tracks is a very important. Maintenance management systems in the past few decades have been considered by the experts in...