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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 new efficient approach to search for all multi-state minimal cuts
, Article IEEE Transactions on Reliability ; Volume 63, Issue 1 , March , 2014 , Pages 154-166 ; Mahdavi Amiri, N ; Sharif University of Technology
Abstract
There are several exact or approximating approaches that apply {m d}-MinCuts (d-MCs) to compute multistate two-Terminal reliability. Searching for and determining d-MCs in a stochastic-flow network are important for computing system reliability. Here, by investigating the existing methods and using our new results, an efficient algorithm is proposed to find all the d-MCs. The complexity of the new algorithm illustrates its efficiency in comparison with other existing algorithms. Two examples are worked out to show how the algorithm determines all the d -MCs in a network flow with unreliable nodes, and in a network flow of moderate size. Moreover, using the d-MCs found by the algorithm, the...
Designing market-based control with a genetic algorithm
, Article Scientia Iranica ; Vol. 21, Issue. 6 , 2014 ; ISSN: 10263098 ; Amini, F ; Sharif University of Technology
Abstract
Semi-active devices are low-cost as well as small and by changing the properties of low-power intensive structures, the aims of control are accomplished. On the other hand, the limited control force which can be applied to the structure for each damper causes more dampers to be used in the structures compared to the larger and stronger control devices which are more costly. These dampers coupled with sensors and the structure themselves make a complex dynamic system which is best controlled by a decentralized method such as Market-Based Control (MBC). In MBC, the actuators and the supply energy are modeled as buyer and seller respectively in the market place. To define the demand function of...
Hub location problem considering an elastic demand
, Article CIE 2014 - 44th International Conference on Computers and Industrial Engineering and IMSS 2014 - 9th International Symposium on Intelligent Manufacturing and Service Systems, Joint International Symposium on "The Social Impacts of Developments in Information, Manufacturing and Service Systems" - Proceedings ; 2014 , pp. 581-588 ; Akbari Jokar, M. R ; Sharif University of Technology
Abstract
In most hub location problem in the literature, the demand is independent of the market share. However, especially about the services and products which are not essential, this assumption does not mirror the reality. Considering the elastic demand increases the complexity and solution of the problem. The elasticity of demand depends on the utility of available hub. For simplicity, we assume that the utility of hub nodes are additive. Utility of the nodes is based on the attraction of the facility on that node and also the decay function of distance. In this paper we propose a new model for hub location problem in an airline industry with elastic demand. In this problem, passengers use hubs...
Wisecode: Wise image segmentation based on community detection
, Article Imaging Science Journal ; Vol. 62, Issue 6 , 2014 , pp. 327-336 ; Online ISSN: 1743131X ; Mahdisoltani, F ; Beigy, H ; Sharif University of Technology
Abstract
Image segmentation is one of the fundamental problems in image processing and computer vision, since it is the first step in many image analysis systems. This paper presents a new perspective to image segmentation, namely, segmenting input images by applying efficient community detection algorithms common in social and complex networks. First, a common segmentation algorithm is used to fragment the image into small initial regions. A weighted network is then constructed. Each initial region is mapped to a vertex, and all these vertices are connected to each other. The similarity between two regions is calculated from colour information. This similarity is then used to assign weights to the...
A comparative study of energy/power consumption in parallel decimal multipliers
, Article Microelectronics Journal ; Vol. 45, Issue 6 , June , 2014 , pp. 775-780 ; Ejlali, A ; Gorgin, S ; Sharif University of Technology
Abstract
Decimal multiplication is a frequent operation with inherent complexity in implementation. Commercial and financial applications require working with decimal numbers while it has been shown that if we convert decimal number to binary ones, this will negatively influence the preciseness required for these applications. Existing research works on parallel decimal multipliers have mainly focused on latency and area as two major factors to be improved. However, energy/power consumption is another prominent issue in today's digital systems. While the energy consumption of parallel decimal multipliers has not been addressed in previous works, in this paper we present a comparative study of...
A novel force-based approach for designing armor blocks of high-crested breakwaters
, Article Scientia Iranica ; Vol. 21, issue. 3 , 2014 , pp. 534-547 ; ISSN: 10263098 ; Sarfaraz, M ; Sharif University of Technology
Abstract
Rubble-mound breakwaters are common marine structures that provide a safe area for human coastal activities. The stability of these structures against sea-waves requires their seaward slope to be protected by an armor layer consisting of natural rock or concrete units. To provide a safe breakwater, it is reasonable to establish a relation between the exerted wave loads and the stability of the armor units. However, up to now, the empirical design equations, derived from model tests, relate wave parameters to armor weight, and keeps the effect of wave loads in a black box. In this paper, a new approach, based on numerically-derived wave loads on the armor, is presented to evaluate the...
Linear index coding via graph homomorphism
, Article Proceedings - 2014 International Conference on Control, Decision and Information Technologies, CoDIT 2014 ; 2014 , pp. 158-163 ; ISBN: 9781479967735 ; Siavoshani, M. J ; Sharif University of Technology
Abstract
In [1], [2] it is shown that the minimum broadcast rate of a linear index code over a finite field Fq is equal to an algebraic invariant of the underlying digraph, called minrankq. In [3], it is proved that for F2 and any positive integer k, minrankq(G) ≤ k if and only if there exists a homomorphism from the complement of the graph G to the complement of a particular undirected graph family called 'graph family {Gk}'. As observed in [2], by combining these two results one can relate the linear index coding problem of undirected graphs to the graph homomorphism problem. In [4], a direct connection between linear index coding problem and graph homomorphism problem is introduced. In contrast to...
RGB-D scene segmentation with conditional random field
, Article 2014 6th Conference on Information and Knowledge Technology, IKT 2014 ; 2014 , pp. 134-139 ; ISBN: 9781479956609 ; Kasaei, S ; Sanaei, E ; Sharif University of Technology
Abstract
Segmentation of a scene to the part made is a challenging work. In this paper a graphical model is used for this task. The methods based on geometrical derivatives such as curvature and normal often haven't good result in segmentation of geometrically-complex architecture and lead to over-segmentation and even failure. Proposed method for segmentation contains two steps. At first region growing based on curvature, normal and color is used for growing region. This segmented cloud is used for unary potential in graphical model. Fully connected graph for Conditional Random Field with Gaussian kernel for pair wise potentials is used for correcting this segmentation. Gaussian kernels are based on...
Design of a robust model predictive controller with reduced computational complexity
, Article ISA Transactions ; Volume 53, Issue 6 , 1 November , 2014 , Pages 1754-1759 ; ISSN: 00190578 ; Haeri, M ; Sharif University of Technology
Abstract
The practicality of robust model predictive control of systems with model uncertainties depends on the time consumed for solving a defined optimization problem. This paper presents a method for the computational complexity reduction in a robust model predictive control. First a scaled state vector is defined such that the objective function contours in the defined optimization problem become vertical or horizontal ellipses or circles, and then the control input is determined at each sampling time as a state feedback that minimizes the infinite horizon objective function by solving some linear matrix inequalities. The simulation results show that the number of iterations to solve the problem...
A comparative study of different approaches for finding the upper boundary points in stochastic-flow networks
, Article International Journal of Enterprise Information Systems ; Volume 10, Issue 3 , 1 July , 2014 , Pages 13-20 ; ISSN: 15481115 ; Nasseri, S. H ; Forghani Elahabad, M ; Ebrahimnejad, A ; Sharif University of Technology
Abstract
An information system network (ISN) can be modeled as a stochastic-flow network (SFN). There are several algorithms to evaluate reliability of an SFN in terms of Minimal Cuts (MCs). The existing algorithms commonly first find all the upper boundary points (called d-MCs) in an SFN, and then determine the reliability of the network using some approaches such as inclusion-exclusion method, sum of disjoint products, etc. However, most of the algorithms have been compared via complexity results or through one or two benchmark networks. Thus, comparing those algorithms through random test problems can be desired. Here, the authors first state a simple improved algorithm. Then, by generating a...
Cube and dynamic cube attacks on SIMON32/64
, Article 2014 11th International ISC Conference on Information Security and Cryptology, ISCISC 2014 ; Sept , 2014 , pp. 98-103 ; ISBN: 9781479953837 ; Ahmadian, Z ; Salmasizadeh, M ; Aref, M. R ; Sharif University of Technology
Abstract
This paper presents cube and dynamic cube attacks on reduced-round lightweihgt block cipher SIMON32/64, proposed by U.S. National Security Agency in 2013. Cube attack is applied to 17 rounds out of 32 rounds of SIMON using a 13-round distinguisher and dynamic cube breaks 14 rounds out of 32 rounds using 10-round distinguishers. Both attacks recover the full 64-bit key of the cipher in a practical time complexity
Distributed user association and femtocell allocation in heterogeneous wireless networks
, Article IEEE Transactions on Communications ; Vol. 62, issue. 8 , 2014 , p. 3027-3043 ; Louie, R. H. Y ; Han, Z ; Vucetic, B ; Li, Y ; Sharif University of Technology
Abstract
Deployment of low-power low-cost small access points such as femtocell access points (FAPs) constitute an attractive solution for improving the existing macrocell access points' (MAPs) capacity, reliability, and coverage. However, FAP deployment faces challenging problems such as interference management and the lack of flexible frameworks for deploying the FAPs by the service providers (SPs). In this paper, we propose a novel solution that jointly associates the user equipment (UE) to the APs, and allocates the FAPs to the SPs such that the the total satisfaction of the UEs in an uplink OFDMA network is maximized. We model the competitive behaviors among the UEs, FAPs, and SPs as a dynamic...
A queuing approach for a tri-objective manufacturing problem with defects: A tuned Pareto-based genetic algorithm
, Article International Journal of Advanced Manufacturing Technology ; Vol. 73, issue. 9-12 , May , 2014 , p. 1373-1385 ; Niaki, S. T. A ; Maleki, L ; Sharif University of Technology
Abstract
In this research, a manufacturing facility with independent workstations to remanufacture nonconforming products is investigated. Each workstation is first modeled as an M/M/m queuing system with m being a decision variable. Then, a tri-objective integer nonlinear programming models is developed to formulate the problem. The first objective tries to minimize the waiting times of products, while the second one tries to maximize the minimum reliability of machines at the workstations. Since minimization of the waiting times results in using a large number of machines with higher idle times, the third objective is considered to minimize the mean idle time of the machines. The aim is to...
A four-phase algorithm to improve reliability in series-parallel systems with redundancy allocation
, Article Scientia Iranica ; Vol. 21, issue. 3 , 2014 , p. 1072-1082 ; Eshraghniaye Jahromi A ; Salmani, M. H ; Ghasemi, F ; Sharif University of Technology
Abstract
In general, reliability is the ability of a system to perform and maintain its functions in routine, as well as hostile or unexpected, circumstances. The Redundancy Allocation Problem (RAP) is a combinatorial problem which maximizes system reliability by discrete simultaneous selection from available components. The main purpose of this study is to develop an effective approach to solve RAP, expeditiously. In this study, the basic assumption is considering Erlang distribution density for component failure rates. Another assumption is that each subsystem can have one of cold-standby or active redundancy strategies. The RAP is a NP-Hard problem which cannot be solved in reasonable time using...
An approximation algorithm for computing the visibility region of a point on a terrain and visibility testing
, Article VISAPP 2014 - Proceedings of the 9th International Conference on Computer Vision Theory and Applications ; Vol. 3, issue , January , 2014 , p. 699-704 ; Ghodsi, M ; Gudukbay, U ; Golkari, M ; Sharif University of Technology
Abstract
Given a terrain and a query point p on or above it, we want to count the number of triangles of terrain that are visible from p. We present an approximation algorithm to solve this problem. We implement the algorithm and then we run it on the real data sets. The experimental results show that our approximation solution is very close to the real solution and compare to the other similar works, the running time of our algorithm is better than their algorithm. The analysis of time complexity of algorithm is also presented. Also, we consider visibility testing problem, where the goal is to test whether p and a given triangle of train are visible or not. We propose an algorithm for this problem...
A theoretical and experimental investigation of wastewater treatment for a polyethylene terephthalate production unit
, Article Chemical Engineering Transactions ; Vol. 39, issue. Special Issue , 2014 , p. 751-756 ; 22839216 ; Mohammadpour, A ; Khorasheh, F ; Sharif University of Technology
Abstract
In this research, mathematical modelling of an anaerobic hybrid bioreactor for effluent treatment of a Poly-Ethylene Terephthalate (PET) unit in a petrochemical complex was performed. The developed model included a combination of a biofilm model for describing the substrate kinetics; a fluidized bed model for determination of species profiles along the reactor length and a bioreactor model for particle distribution inside the reactor. The reactions performed in the bioreactor included; i) the polymers hydrolysis; ii) fermentation of the resulting monomers; iii) the volatile fatty acids fermentation to Acetate and Hydrogen and iv) the Methane formation as the final product. The reactor was...
Survey article: Simplicial complexes satisfying Serre's condition: A survey with some new results
, Article Journal of Commutative Algebra ; Vol. 6, issue. 4 , 2014 , p. 455-483 ; Seyed Fakhari, S. A ; Terai, N ; Yassemi, S ; Sharif University of Technology
Abstract
The problem of finding a characterization of Cohen-Macaulay simplicial complexes has been studied intensively by many authors. There are several attempts at this problem available for some special classes of simplicial complexes satisfying some technical conditions. This paper is a survey, with some new results, of some of these developments. The new results about simplicial complexes with Serre's condition are an analogue of the known results for Cohen-Macaulay simplicial complexes
A review of multiple description coding techniques for error-resilient video delivery
, Article Multimedia Systems ; Vol. 20, issue. 3 , 2014 , p. 283-309 ; Shirmohammadi, S ; Sadeghi, K. H ; Sharif University of Technology
Abstract
Multiple description coding (MDC) is one of the promising solutions for live video delivery over lossy networks. In this paper, we present a review of MDC techniques based on their application domain and we explain their functionality, with the objective of giving enough insight to designers to decide which MDC scheme is best suited for their specific application based on requirements such as standard compatibility, redundancy tunability, complexity, and extendibility to n-description coding. The focus is mainly on video sources but imagebased algorithms applicable to video are considered as well. We also cover the well-known and important problem of drift and solutions to avoid it
A water-oxidizing dinuclear iron complex as an efficient catalyst toward organic sulfide oxidation
, Article Journal of Coordination Chemistry ; Vol. 67, issue. 18 , Jul , 2014 , p. 3026-3032 ; Najafpour, M. M ; Zare, M ; Holynska, M ; Moghaddam, A. N ; Bagherzadeh, M ; Sharif University of Technology
Abstract
In this paper, we report that a known dinuclear Fe complex, [tpa(H2O)FeOFe(H2O)tpa](ClO4)4 (tpa: tris(2-pyridylmethyl)amine), is an efficient catalyst toward organic sulfide oxidation in the presence of urea-hydrogen peroxide