Sharif Digital Repository

In this paper, we introduce a new class of sigature matrices for overloaded synchronous CDMA systems that have a very low complexity decoder. While overloaded systems are more efficient from the bandwidth point of view, the Maximum Likelihood (ML) implementation for decoding is impractical even for moderate dimensions. Simulation results show that the performance of the proposed decoder is very close to that of the ML decoder. Indeed, the proposed decoding scheme needs neither multiplication nor addition and requires only a few comparisons. Furthermore, the computational complexity and the probability of error vs. Signal to Noise Ratios (SNR) are derived analytically  

Flow mediated dilation (FMD) is a non-invasive method for endothelial function assessment providing an index extracted from ultrasonic B-mode images. Although utilized in the research community, the difficulty of its application and high cost of ultrasonic devices prevent it from being widely used in clinical settings. In this study we show that substituting the ultrasonic device with more easily handled and low cost photoplethysmography and electrocardiography is possible. We introduce new indices based on the photoplethysmogram (PPG) and electrocardiogram (ECG) and show that they are correlated with the ultrasound-based FMD Index. To this end, a conventional ultrasound FMD test was carried... 

We present an ontology based indexing method for unstructured P2P networks. We maintain limited size indexes at each node to identify number of documents accessible on each concept without loosing any indexing information. Out method supports complex queries, combined of conjunction and disjunction phrases. We simulate our search algorithm on an unstructured P2P network and show that our method significantly reduces the network traffic. © 2008 Springer-Verlag  

Internet technology has influenced the banking systems because of its capability to enhance performance of financial operations. A major concern of Internet banking systems is the customers’ perception of security and trust. This study presents an experimental investigation on important factors influencing trust in e-payments systems in Iran. A set of potentially determinant factors of trust is developed and organized in three major groups: technical and transaction procedures, access to security guidelines, and usability. The direct effect of the factors on perceived trust, along with their indirect effect through perceived security, is evaluated in an empirical study. The data are... 

Cost and time overruns have been a common characteristic of development projects in many countries. This paper presents a theory of cost and time overruns based on project cost structure. The cost of a development project consists of base cost and progress cost. Base cost keeps a project ready for physical progress. Progress cost creates real physical progress on the project. This cost structure has an important inherent dynamic characteristic with implications for the efficiency and effectiveness of project management. An imbalance between annual budget and ongoing projects results in an increasing inefficiency and ineffectiveness unrelated to the quality of management of individual... 

Efficient storage and handling of data stored in a peer-to-peer (P2P) network, proves vital for various applications such as query processing and data mining. This paper presents a distributed, scalable and robust layered overlay (L-overlay) to index and manage multidimensional data in a dynamic P2P network. The proposed method distinguishes between the data and peer layers, with efficient mapping between the two. The data is organized such that semantically similar data objects are accessed hastily. Grid and tree structures are proposed for the peer layer. As application examples of L-overlay in query processing and data mining, k-nearest neighbors query processing and distributed Naïve... 

Data classification in large scale systems, such as peer-to-peer networks, can be very communication-expensive and impractical due to the huge amount of available data and lack of central control. Frequent data updates pose even more difficulties when applying existing classification techniques in peer-to-peer networks. We propose a distributed, scalable and robust classification algorithm based on k-nearest neighbor estimation. Our algorithm is asynchronous, considers data updates and imposes low communication overhead. The proposed method uses a content based overlay structure to organize data and moderate the number of query messages propagated in the network. Simulation results show that... 

Effectiveness of Peer-to-Peer (P2P) systems highly depends on efficiency and scalability of their search algorithms. Moreover, managing trust is a key issue for wide acceptance of P2P computing. Surprisingly, the majority of the available trust systems ignore the underlying search algorithm and assume it is preexisting. We claim that combining search and trust systems yields significant performance gains in terms of network traffic and query success rate. In this paper, we propose a robust and efficient trust based search framework for unstructured P2P networks. Our framework maintains limited size routing indexes combining search and trust data to guide queries to most reputable nodes. By... 

The Endurance Time (ET) method is a dynamic analysis procedure using intensifying excitation. The ET excitation functions are generated so that structural performance can be assessed at different excitation levels in a single response history analysis. ET accelerograms, which have been generated so far, possess response spectra consistency; this means that the duration consistency has not been directly considered. Strong-motion duration can influence the response of structures which have stiffness or strength degrading characteristics. In this paper, several well-known strong-motion duration definitions are studied in the context of the ET method. Ground motions are scaled to spectral... 

Endurance Time (ET) method is a dynamic analysis procedure using intensifying accelerograms which can be used to assess the structural performance at different excitation levels. In generation process of current ET accelerograms, the compatibility between acceleration spectrum produced by the ET accelerograms and acceleration spectrum associated with the real ground motions is applied, whereas the duration consistency is not directly considered. It is generally accepted that the strong-motion duration can strongly influence the response of structures which have stiffness or strength degrading characteristics. In this study, the number of cycles that a structure should resist due to a ground...