Sharif Digital Repository

The arrival of the mobile phone and its rapid and widespread growth may well be seen as one of the most significant developments in the fields of communication and information technology over the past two decades. The aim of this study is to compare two hybrid multi-criteria decision-making (MCDM) approaches to evaluate the mobile phone options with respect to user’s preferences. Firstly, we identify the most desirable features influencing the choice of a mobile phone. This is realised through a survey conducted among the target group, the experiences of the telecommunication sector experts and the studies in the literature. Secondly, two MCDM methods are used in the evaluation procedure.... 

Functional relationship between supplier and buyer in an open market place leads to investigate the role of both quantifiable and non-quantifiable parameters in coordination mechanism with the aim of achieving higher performance in supply chain activities. Here, we develop a supply chain model and a new agent to analyze and simulate the players' behavior in the network. A cooperative game theory framework is utilized between buyer and supplier in order to increase the supply chain performance. The study is supported by presenting SC Net Optimizer as a tool for implementing the proposed coordination mechanism and evaluates the performance of the chain by simulation using stochastic Petri nets... 

Let F be a field and M be a maximal subgroup of the multiplicative group F* = F {0} of index p. It is proved that if M is divisible, then Br(F)p ≠ 0 if and only if p = 2 and F is Euclidean. Furthermore, it is shown that in this case F* contains a divisible maximal subgroup if and only if F* is isomorphic to the multiplicative group of a real closed field. © 2009 Iranian Mathematical Society  

Let D be an infinite division algebra of finite dimension over its centre Z(D) = F, and n a positive integer. The structure of maximal subgroups of skew linear groups are investigated. In particular, assume N is a normal subgroup of GLn(D) and M is a maximal subgroup of N containing Z(N). It is shown that if M/Z(N) is finite, then N is central. © Inst. Math. CAS 2002  

Let D be a noncommutative division algebra of finite dimension over its centre F. Given a maximal subgroup M of GLn (D) with n ≥ 1, it is proved that either M contains a noncyclic free subgroup or there exists a finite family {Ki}1r of fields properly containing F with Ki* ⊂ M for all 1 ≤ i ≤ r such that M/A is finite if Char F = 0 and M/A is locally finite if Char F = p > 0, where A = K1* x ⋯ x Kr*. © 2004 Elsevier Inc. All rights reserved  

Let D be a division algebra of finite dimension over its center F. Given a noncommutative maximal subgroup M of D*:= GL1(D), it is proved that either M contains a noncyclic free subgroup or there exists a maximal subfield K of D which is Galois over F such that K* is normal in M and M/K*≅Gal(K/F). Using this result, it is shown in particular that if D is a noncrossed product division algebra, then M does not satisfy any group identity. © 2001 Academic Press  

We consider the design of an optimal natural-gas network. Our proposed network contains two echelons, Town Broad Stations (TBSs), and consumers (demand zones). Here, our aim is a two-stage cost minimization. We first determine locations of the TBS so that the location-allocation cost is minimized. Then, we show how to distribute the flow of gas among the TBS minimizing the flow cost by using Minimum Spanning Tree (MST). A case study in Mazandaran Gas Company in Iran is made to assess the validity and effectiveness of our proposed model  

In this paper, a novel hard-output detection algorithm for the complex multiple-input multiple-output (MIMO) detectors is proposed, which results in a significant throughput enhancement, a near-ML performance, and an SNR-independent fixed-throughput. Moreover, a high-throughput VLSI implementation is proposed, which is based on a novel method of the node generation and sorting scheme. The proposed design achieves the throughput of 10Gbps in a 0.13 μ CMOS process, which is the highest throughput reported in the literature for both the real and the complex domains. Synthesis results in 90nm CMOS also show that the proposed scheme can achieve the throughput of up to 15Gbps. Moreover, the FPGA... 

A novel detection algorithm with an efficient VLSI architecture featuring efficient operation over infinite complex lattices is proposed. The proposed design results in the highest throughput, the lowest latency, and the lowest energy compared to the complex-domain VLSI implementations to date. The main innovations are a novel complex-domain means of expanding/visiting the intermediate nodes of the search tree on demand, rather than exhaustively, as well as a new distributed sorting scheme to keep track of the best candidates at each search phase. Its support of unbounded infinite lattice decoding distinguishes the present method from previous K-Best strategies and also allows its complexity... 

Fast and high quality document clustering is a crucial task in organizing information, search engine results, enhancing web crawling, and information retrieval or filtering. Recent studies have shown that the most commonly used partition-based clustering algorithm, the K-means algorithm, is more suitable for large datasets. However, the K-means algorithm can generate a local optimal solution. In this paper we propose a novel Harmony K-means Algorithm (HKA) that deals with document clustering based on Harmony Search (HS) optimization method. It is proved by means of finite Markov chain theory that the HKA converges to the global optimum. To demonstrate the effectiveness and speed of HKA, we... 

In the last few years, there has been explosive growth in the application of Harmony Search (HS) in solving NP-complete problems in computer science. The success of the HS algorithm in finding relatively good solutions to these problems discriminates it as an affirmative alternative to other conventional optimization techniques. This chapter surveys the existing literature on the application of HS in combinatorial optimization problems. We begin by presenting HS based algorithms for solving problems such as Sudoku puzzle, music composition, orienteering problem, and vehicle routing. We then turn to solve a multicast routing problem with two constraints (i.e. bandwidth and delay constraints).... 

A novel ultra high-throughput detection algorithm with an efficient VLSI architecture for high-order MIMO detectors in the complex constellations is proposed. The main contributions include a new method for the node generation in complex-domain, pipelinable sorters, and a simple combinational circuit instead of the conventional multipliers, which makes the proposed architecture multiplication-free. The proposed design achieves an SNR-independent throughput of 13.3 Gbps at the clock frequency of 556 MHz in a 0.13 μm CMOS technology with a near ML performance. The implemented design consumes 90 pJ per detected bit with the initial latency of 0.3 μs. Also, the synthesis results in a 90 nm CMOS... 

The problem of estimating pulse repetition interval (PRI) of an interleaved pulse train which consist of several independent radar signals, is the main issue of signal processing in electronic support systems. PRI Transform algorithm is one of the well known and effective methods of PRI detection which is capable of detecting several close jittered signals and surpassing subharmonics, but have some drawbacks especially because of small PRI dynamic range and heavy computations. In this paper a modified PRI transform is introduced which manage wide range of PRIs simultaneously, and speed up the algorithm by significantly reducing the computations. Moreover an efficient threshold is set for... 

Let D be an F-central division algebra of index n. Here we present a criterion for the triviality of the group G(D) = D*/Nrd D/F(D*)D′ and thus generalizing various related results published recently. To be more precise, it is shown that G(D) = 1 if and only if SK 1(D) = 1 and F *2 = F *2n. Using this, we investigate the role of some particular subgroups of D* in the algebraic structure of D. In this direction, it is proved that a division algebra D of prime index is a symbol algebra if and only if D* contains a non-abelian nilpotent subgroup. More applications of this criterion including the computation of G(D) and the structure of maximal subgroups of D* are also investigated  

Given a divisible finite field extension K/F, the structure of Br(F), the Brauer group of F, is investigated. It is shown that, if F is indivisible, then Br(F) ≅ ℤ 2, which generalizes the Frobenius Theorem. As a consequence, when F is indivisible, the class of all finite dimensional non-commutative F-central division algebras D having radicable multiplicative groups D* is determined. In fact, it is proved that the following statements are equivalent: (1) D is radicable, (2) D contains a divisible subfield K/F, and (3) D is the ordinary quaternion division algebra and F(√-1) is divisible  

To construct an effective minimization algorithm for locally Lipschitz functions, we show how to compute a descent direction satisfying Armijo's condition. We present a finitely terminating algorithm to construct an approximating set for the Goldstein subdifferential leading to the desired descent direction. Using this direction, we propose a minimization algorithm for locally Lipschitz functions and prove its convergence. Finally, we implement our algorithm with matrix laboratory (MATLAB) codes and report our testing results. The comparative numerical results attest to the efficiency of the proposed algorithm  

We present an effective algorithm for minimization of locally nonconvex Lipschitz functions based on mollifier functions approximating the Clarke generalized gradient. To this aim, first we approximate the Clarke generalized gradient by mollifier subgradients. To construct this approximation, we use a set of averaged functions gradients. Then, we show that the convex hull of this set serves as a good approximation for the Clarke generalized gradient. Using this approximation of the Clarke generalized gradient, we establish an algorithm for minimization of locally Lipschitz functions. Based on mollifier subgradient approximation, we propose a dynamic algorithm for finding a direction...