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α-Visibility
, Article Computational Geometry: Theory and Applications ; Vol. 47, issue. 3 PART A , April , 2014 , pp. 435-446 ; ISSN: 09257721 ; ISBN: 9783642311543 ; Maheshwari, A ; Nouri-Baygim, M ; Sack, J. R ; Zarrabi-Zadeh, H ; Sharif University of Technology
Abstract
We study a new class of visibility problems based on the notion of α-visibility. Given an angle α and a collection of line segments S in the plane, a segment t is said to be α-visible from a point p, if there exists an empty triangle with one vertex at p and the side opposite to p on t such that the angle at p is α. In this model of visibility, we study the classical variants of point visibility, weak and complete segment visibility, and the construction of the visibility graph. We also investigate the natural query versions of these problems, when α is either fixed or specified at query time
Touring a sequence of disjoint polygons: Complexity and extension
, Article Theoretical Computer Science ; Vol. 556, Issue. C , October , 2014 , pp. 45-54 ; ISSN: 03043975 ; Mozafari, A ; Zarei, A ; Sharif University of Technology
Abstract
In the Touring Polygons Problem (TPP) there is a start point s, a sequence of simple polygons P=(P1,. . .,Pk) and a target point t in the plane. The goal is to obtain a path of minimum possible length that starts from s, visits in order each of the polygons in P and ends at t. This problem was introduced by Dror, Efrat, Lubiw and Mitchell in STOC '03. They proposed a polynomial time algorithm for the problem when the polygons in P are convex and proved its NP-hardness for intersecting and non-convex polygons. They asked as an open problem whether TPP is NP-hard when the polygons are pairwise disjoint. In this paper, we prove that TPP is also NP-hard when the polygons are pairwise disjoint in...
A modified ant colony system for finding the expected shortest path in networks with variable arc lengths and probabilistic nodes
, Article Applied Soft Computing Journal ; Vol. 21, issue , August , 2014 , p. 491-500 ; Hassanzadeh, R ; Mahdavi, I ; Mahdavi-Amiri, N ; Sharif University of Technology
Abstract
The problem of finding the expected shortest path in stochastic networks, where the presence of each node is probabilistic and the arc lengths are random variables, have numerous applications, especially in communication networks. The problem being NP-hard we use an ant colony system (ACS) to propose a metaheuristic algorithm for finding the expected shortest path. A new local heuristic is formulated for the proposed algorithm to consider the probabilistic nodes. The arc lengths are randomly generated based on the arc length distribution functions. Examples are worked out to illustrate the applicability of the proposed approach
Robots’ cooperation for finding a target in streets
, Article 1st IFIP WG 1.8 International Conference on Topics in Theoretical Computer Science, 26 August 2015 through 28 August 2015 ; Volume 9541 , 2016 , Pages 30-43 ; 03029743 (ISSN) ; 9783319286778 (ISBN) ; Ghodsi, M ; Tabatabaei, A
Springer Verlag
Abstract
We study the problem of finding a target t from a start point s in street environments with the cooperation of two robots which have a minimal sensing capability; that is, robots do not know any information about the workspace including information on distances, edges, coordinates, angles etc. They just can detect the discontinuities in the visibility region of their location. The robots can detect target point t as soon as it enters their visibility region and have communication peripherals to send messages to each other. Our aim is to minimize the length of the path passed by the robots. We propose an online algorithm for robots such that they move in the workspace and find the target....
A thermal-aware shortest hop routing algorithm for in vivo biomedical sensor networks
, Article ITNG 2009 - 6th International Conference on Information Technology: New Generations, 27 April 2009 through 29 April 2009, Las Vegas, NV ; 2009 , Pages 1612-1613 ; 9780769535968 (ISBN) ; Jahed, M ; Ahourai, F ; Moradi, S ; Sharif University of Technology
Abstract
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
Weighted TINs Smplification and Design of Some Algorithms on it
, M.Sc. Thesis Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
Due to increasing quality of satellite images, volume of stored data significantly increased, so speed of statistical and computational processing decreased. For solving this problem, simplification
problem has been suggested. Surface simplification problem is a fundamental problem in computational geometry and it has many applications in other fields such as GIS, computer graphics, and image processing. Major goal of simplification problems is reducing stored information in any surface, Because it improves speed of processes. One of common types in this field is 3D terrain simplification while error of simplified surface be acceptable. Simplification is NP-Hard problem. In this project,...
problem has been suggested. Surface simplification problem is a fundamental problem in computational geometry and it has many applications in other fields such as GIS, computer graphics, and image processing. Major goal of simplification problems is reducing stored information in any surface, Because it improves speed of processes. One of common types in this field is 3D terrain simplification while error of simplified surface be acceptable. Simplification is NP-Hard problem. In this project,...
Airline Flight Schedule Planning with Network Optimization
,
M.Sc. Thesis
Sharif University of Technology
;
Malaek, Mohammad Bagher
(Supervisor)
Abstract
Airline scheduling is a dynamic process in nature such that it changes not only during one year period but also in smaller intervals due to the economic, political, religious, and social factors. Basically, airlines schedule planners through using mathematical models decide which flights are to be served in what periods of time and at what costs. This has to be done considering a set of constraints of different nature, from airspace and airport congestion up to climatic conditions or even crews working conditions. Such a complex problem requires different methods for an efficient solution. In this study by using network optimization method and applying different operational constraints on...
Computing the Shortest Path on Weighted Triangulated Irregular Networks by Multicore Algorithms
, M.Sc. Thesis Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
Shortest path computation is one the fundamental problems in computer science. Triangulated Irregular Networks (TINs) are used in computational geometry to represent terrians and geometric surfaces. One of the most efficient mothods to solve the shortest path problem on a TIN is reducing it to shortest path problem on a graph. This reduction from continuous space to discrete space results in approximate solutions, but acceptable in real applications. In real applications we still encounter a large graph and using the simple Dijkstra algorithm consumes a lot of times. Memory shortage is another issue. Parallel processing could be a solution in this case. Multicore industry caused a...
Evaluation of Performance of Emergency Relief Vehicles Responding to Traffic Accidents in Tehran
, M.Sc. Thesis Sharif University of Technology ; Nassiri, Habibollah (Supervisor)
Abstract
High number of traffic accidents in Iran and its rate which is well above the world's average is a major issue of concern. The results of recent researches show a direct relation between survival rate of traffic accidents' injuries and the Emergency Response Time (ERT). The main objective of this research is to analyze different aspects of ERT in Tehran, Iran and to compare these results with the International standards. This study intends to compare the selected routes by ambulance drivers with the shortest paths recommended by EMME/2. Results of analysis show that when the travel time between accident scene and the emergency dispatch center is less than 8 minutes, the possibility of...
Shortest Path to View a Point in General Polygons
, M.Sc. Thesis Sharif University of Technology ; Ghodsi, Mohammad (Supervisor) ; Abam, Mohammad Ali (Co-Advisor)
Abstract
We consider two variations of shortest paths problem inside a poly-gon. In the first variation, we want to find a shortest path from asource to view a destination inside a polygon with holes. We pro-pose two algorithms for this problem with the time complexity of O (hn log n) and O(n log n) in which the second one is optimal. In the second variation, we want to place a center policeman inside a sim-ple polygon so that the longer of the two shortest paths from two existing guards to the visibility polygon of the center policeman is minimized. We propose an algorithm for this problem with the time complexity of O(n 3)
Analysis and Evaluation of Routing Protocols Conformance Test
, M.Sc. Thesis Sharif University of Technology ; Jahangir, Amir Hossein (Supervisor)
Abstract
Nowadays, one of the problems of network designers and users is the correctness of network equipment functionality. Since routers play an important role in information transfer between various networks and communicate with each other through a routing protocol, any violation of such protocol can result in the network's failure or defective transfer of data. Thus, being assured of the conformance of the implemented protocol in a router with what has been defined in the protocol's standard is of great significance. To this end, before using or exposing a router, network equipment testers should run protocol conformance tests on it and insure its correct functionality. This brings up the...
Analysis and Evaluation of Router Security Based on a Routing Protocol
, M.Sc. Thesis Sharif University of Technology ; Jahangir, Amir Hossein (Supervisor)
Abstract
The importance of routers in information transfer among networks is critical. Thus, vulnerabilities and security deficiencies in routers and the related services like routing protocols can be destructive not only for some hosts, but also for the whole network. Hence, it is necessary that 1) vulnerabilities related to the routers and their services be evaluated and analyzed, and 2) the functional aspects of routers related to the vulnerabilities be formally modeled and analyzed. In this thesis, we present a method for the evaluation and the analysis of OSPF routing protocol from the security point of view. First, reported vulnerabilities on the OSPF are collected and evaluated by a...
Analysis and Verification of a Routing Protocol Conformance Test Program
, M.Sc. Thesis Sharif University of Technology ; Jahangir, Amir Hossein (Supervisor)
Abstract
Routers play a key role in transferring information between various Networks. It is very important to make sure about the compatibility of OSPF in a router with its standard description. In this regard, before presenting or applying a router and also evaluating its performance, it is necessary to carry out conformance test with the help of network equipment testers Tester designers extract test cases from protocol standard description through non-formal ways and exam them on network equipment.
In this thesis, a part of OSFP protocol has been modeled through colored Petri nets. In this regard, two sections of OSPF RFC have been model checked: neighbor state machine and data base...
In this thesis, a part of OSFP protocol has been modeled through colored Petri nets. In this regard, two sections of OSPF RFC have been model checked: neighbor state machine and data base...
Multi-objective Route Planning in a Multi-modal Network with Alternative Paths
, M.Sc. Thesis Sharif University of Technology ; Kourosh, Eshghi (Supervisor)
Abstract
In respect of increasing expanse public urban transport, road network complexity as well optimized route planning is necessary in transport network more than ever. Multi-modal network is a transport network which has various means of transportation modes. In that network the presentation a sequence transport mode is essential apart from determining the optimal route. Although choosing the shortest viable path has some limitation the user chooses that. In this paper a modal path planning in multi-modal network has been expressed which two objective functions in addition to minimize the number of change modes have been designed the first is cost and the second is time. Moreover, in this...
Electrical Vehicles' Traffic Assignment Considering Recharging Time as Function of Amount of Charge
, M.Sc. Thesis Sharif University of Technology ; Aashtiani, Hedayat (Supervisor)
Abstract
Nonstop growth of environmental concerns regarding ordinary vehicles detrimental effects have led to increasing use of Electrical Vehicles which require more researches in different fields of study. The main purpose of this study is solving the problem of Electrical Vehicles' traffic assignment considering recharging time as a function of amount of charge. Existing EVs have limited driving range, and these cars' drivers usually have to spend a considerable amount of time on recharging in order to complete a path. As a result, their corresponding optimum route choice differs from that of gasoline-based vehicles' drivers. In more detail, this study proposes an algorithm to solve the shortest...
Usage-based Nonlinear Pricing on Traffic Zones
, M.Sc. Thesis Sharif University of Technology ; Zokaei Ashtiani, Hedayat (Supervisor)
Abstract
Nowadays, the necessity of management tools for controlling the ever increasing congestions in transportation networks has been increased. Pricing is one of these tools for mitigating congestions in transportation networks. In this regard, different pricing models have been developed for transportation networks. By considering the advancement in technologies and possibility of recording the vehicles’ traveled distance in the tolling areas, the amount of toll each user pays could be a nonlinear function of the distance traveled inside tolling areas. As a result, the generalized travel cost of each path may not be link-wise additive; therefore, the resulting shortest path problem cannot be...
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...
Developing a Methodology for Evaluating the Vulnerability of Urban Transportation Networks after an Earthquake
, M.Sc. Thesis Sharif University of Technology ; Nassiri, Habibollah (Supervisor)
Abstract
Natural disasters, earthquakes in particular, claim many human lives and damage major lifelines such as transportation networks. Transportation networks play an important role in various stages of response to disasters, such as evacuation, search, rescue and reconstruction missions. Hence, special attention must be paid to transportation networks in any disaster management system. Hence, in order to reduce the impacts of earthquakes on denser cities and metropolitan areas, analysis of the resiliency and vulnerability of critical infrastructures such as transportation network, can be used as an effective strategy.The resiliency and vulnerability of transportation network have attract a lot...
A Survey on the Steiner Forest Problem
, M.Sc. Thesis Sharif University of Technology ; Foroughmand-Arabi, Mohammad Hadi (Supervisor)
Abstract
The Steiner forest problem is one of the most fundamental issues in network design that emerges in various contexts, such as the design of communication networks,transportation networks, VLSI circuits and phylogenetic network reconstruction. In this problem, we are given a connected weighted undirected graph and a special subset of vertices that are partitioned in pairs. The goal is to fnd a minimum-cost sub-graph in which each special vertex is connected to its mate. In this thesis we review a set of selected solutions for this problem and a few other related problems.For example, we study modeling and solving the s-t shortest path problem in order to gain insight into current Steiner...
A Survey on Min-cut On Planar Graphs
, M.Sc. Thesis Sharif University of Technology ; Foroughmand Arabi, Mohammad Hadi (Supervisor)
Abstract
In minimum cut problem we aim at finding a set of edges with minimum overall cost possible, such that removing them would separate two specific vertices, source and sink. This problem has been studied thoroughly, however the available algorithms were not proven to be time-wise optimal. Nowadays, planar graphs have attracted more attention because of their applications in cities and countries map. Moreover,their characteristics and properties, make some problems easier to solve in planar case. In this thesis, we will have a survey on algorithms for minimum cut on planar graphs. Our motivation to choose these algorithms is the balance between how easily they could be implemented and how fast...