Sharif Digital Repository

Different efforts have been done to address the problem of information overload on the Internet. Recommender systems aim at directing users through this information space, toward the resources that best meet their needs and interests by extracting knowledge from the previous users' interactions. In this paper, we propose an algorithm to solve the web page recommendation problem. In our algorithm, we use distributed learning automata to learn the behavior of previous users' and recommend pages to the current user based on learned pattern. Our experiments on real data set show that the proposed algorithm performs better than the other algorithms that we compared to and, at the same time, it is... 

Recently, Grid infrastructures have provided wide integrated use of resources. DotGrid intends to introduce required Grid services and toolkits that are implemented as a layer wrapped over the existing operating systems. Our DotGrid has been developed based on Microsoft .NET in Windows and MONO .NET in Linux and UNIX. Using DotGrid APls, Grid middlewares and applications can be implemented easily. We evaluated DotGrid capabilities by implementing some applications including a high throughput file transfer and solving a typical computational problem. ©2006 IEEE  

In an ac microgrid, a common frequency exists for coordinating active power sharing among droop-controlled sources. A common frequency is absent in a dc microgrid, leaving only the dc source voltages for coordinating active power sharing. That causes sharing error and poorer voltage regulation in dc microgrids, which in most cases, are solved by a secondary control layer reinforced by an extensive communication network. To avoid such an infrastructure and its accompanied complications, this paper proposes an alternative droop scheme for low-voltage dc microgrid with both primary power sharing and secondary voltage regulation merged. The main idea is to introduce a non-zero unifying frequency... 

In this paper, we introduce DiFF, a novel extension of the Fast Forward (FF) planning system. FF is a domain independent planner that employs a forward heuristic search. Its search strategy is an enforced form of hill climbing. In order to move to a more promising state, FF evaluates successor states without any particular order. In this paper, we introduce a new form of the enforced hill climbing, which we call directed enforced hill climbing, to enhance the efficiency of Fast Forward planning. This strategy evaluates successor states in the order recommended by an adaptive heuristic function. Our experimental results in several planning domains show a significant improvement in the... 

Call admission control schemes are crucially Important concepts ID researches on cellular mobile networks. One of them is the new thinning scheme. In this study we define a confidence interval for threshold and the numerical results show the performance of the scheme in defined interval. Also we discuss the sensitivity of the scheme (in sample-based sensitivity method) at different thresholds. The results show the better performance in confidence thresholds and sensitivity of scheme into variations of thresholds  

Vibration control is an essential problem in different structure. Smart material can make a structure smart, adaptive and self-controlling so they are effective in active vibration control. Piezoelectric elements can be used as sensors and actuators in flexible structures for sensing and actuating purposes. In this paper we use PZT elements as sensors and actuator to control the vibration of a cantilever beam. Also we study the effect of different types of controller on vibration. © 2009 IEEE  

One of the distributed solutions for scaling Web Search Engines (WSEs) may be peer-to-peer (P2P) structures. P2P structures are successfully being used in many systems with lower cost than ordinary distributed solutions. However, the fact that they can also be beneficial for large-scale WSEs is still a controversial subject. In this paper, we introduce challenges in using P2P structures to design a large-scale WSE. Considering different types of P2P systems, we introduce possible P2P models for this purpose. Using some quantitative evaluation, we compare these models from different aspects to find out which one is the best in order to construct a large-scale WSE. Our studies indicate that... 

Prevention of unauthorized access to services in mobile ad hoc networks is a more sophisticated problem than access control in other networks, due to interconnection facilities and lack of any fixed network infrastructure in such networks. Therefore regarding the nature of these networks, controlling access to services should be in a decentralized manner providing good performance and preserving network security. In this paper, we propose a decentralized Cooperation Enforcement Based Access Control (CEBAC) framework for mobile ad hoc networks. CEBAC comprises several groups of Service Authorizers, each issuing Credentials for access to a specific kind of services. The User Authorization for... 

Performance evaluation is an important engineering tool that provides valuable feedback on design choices in the implementation of multi-core systems such as parallel systems, multicomputers, and Systems-on-Chip (SoCs). The significant advantage of analytical models over simulation is that they can be used to obtain performance results for large systems under different configurations and working conditions which may not be feasible to study using simulation on conventional computers due to the excessive computation demands. We present Caspian, a novel analytic performance model, aimed to minimize prediction cost, while providing prediction accuracy. This is accomplished by using a G/G/1... 

A new meta-heuristic algorithm is proposed for constructing multicast trees in real-time multimedia applications such that satisfies two important Quality of Service (QoS) constraints. The QoS based multicast routing problem is a known NP-complete problem that depends on (1) bounded end-to-end delay and link bandwidth along the paths from the source to each destination, and (2) minimum cost of the multicast tree. We evaluate the performance and efficiency of the proposed method with a modified version of the BSMA algorithm which is the best known deterministic heuristic algorithm to delay-constrained multicast problem. Simulation results reveal that the proposed algorithm can achieve a... 

Robot navigation is a challenging problem in robotics, which involves determining of robot positioning relative to objects in the environment, and also the mobility of robot through obstacles without colliding into them. The former is known as localization, while the latter is called motion planning. This paper introduces a roadmap method for solving motion planning problem in a dynamic environment based on Generalized Voronoi Diagram (GVD). The efficiency of the proceeding work is verified by examining it in a sample home environment. © 2008 Springer-Verlag  

This paper studies the automatic noise recognition problem based on RBF and MLP neural networks classifiers using linear predictive and Mel-frequency cepstral coefficients (LPC and MFCC). We first briefly review the architecture of each network as automatic noise recognition (ANR) approach, then, compare them to each other and investigate factors and criteria that influence final recognition performance. The proposed networks are evaluated on 15 stationary and non-stationary types of noises with frame length of 20 ms in term of correct classification rate. The results demonstrate that the MLP network using LPCs is a precise ANR with accuracy rate of 99.9%, while the RBF network with MFCCs... 

Eligibility is one of the important security properties which must be satisfied in electronic voting systems. This property refers to legitimacy of voters and their right to vote only once. Due to insufficiency of an observational analysis to guarantee this property, formal methods are recently used to build trust on sensitive systems such as e-voting for all the involved parties. This paper reports our attempt to automatically check the eligibility property in electronic voting systems using the model checking approach. ThemCRL2 language and its toolset are also used to achieve such a checking. Two protocols, FOO92 and Lee&Kim, are modeled as case studies  

Authenticated key exchange protocols allow parties to establish a common session key which in turn is fundamental to building secure channels. Authenticated group key exchange protocols allow parties to interact with each other and establish a common group session key and avoid peer to peer key exchange; in other words they pave the way to build a broadcast channel. We construct an authenticated group key exchange protocol over UC framework which has the contributiveness property; i.e., the output is not biased by inputs of any party. Our protocol uses CRS model and discrete logarithm. Other protocols over UC framework either are defined over RO model [19] or benefit from a non-standard... 

With the advent of semantic technology, access control cannot be done in a safe way unless the access decision takes into account the semantic relationships between entities in a semantic-aware environment. SBAC model considers this issue in the decision making process. However, time plays a crucial role in new computing environments which is not supported in this model. In this paper we introduce temporal semantic based access control model (TSBAC), as an extension of SBAC model, which enhances the specification of user-defined authorization rules by constraining time interval and temporal expression over users' history of accesses. A formal semantics for temporal authorizations is provided... 

Modeling languages as programming languages need precise and unambiguous semantics to be used appropriately, the formal semantics is significant for designing CASE tools and model verification. Several approaches have been used throughout these years to describe the semantics of modeling languages, but in spite of programming languages, these semantics frameworks are not used in large scale for modeling languages. This paper reviews the history of developments on semantics frameworks for modeling languages. © 2009 IEEE  

With the advent of semantic technology, access control cannot be done in a safe way unless the access decision takes into account the semantic relationships among the entities in a semantic-aware environment. SBAC model considers this issue in its decision making process. However, time plays a crucial role in new computing environments which is not supported in the model. In this paper we introduce the Temporal Semantic Based Access Control model (TSBAC), as an extension of SBAC, which enhances the specification of user-defined authorization rules by constraining time interval and temporal expression over users' history of accesses. A formal semantics for temporal authorizations is provided... 

Apart from its security, an SIP (Session Initiation Protocol) authentication protocol shall be efficient; because in order to replace traditional telephony, VoIP services have to offer enough security and QoS compared to PSTN services. Recently, Srinivasan et al. proposed an efficient SIP authentication scheme. The low delay overhead introduced by their scheme, causes the total call setup time to be well within the acceptable limit recommended by ITU-T. Based on their work, this paper proposes an SIP authentication scheme. In both schemes, the end users are authenticated with the proxy server in their domain using the registrar server. Comparing with the Srinivasan et al.'s scheme, our... 

Much effort has been put in defining methods, techniques, and tools for software architecture reconstruction (SAR) Software Architecture Transformation (SAT), and Software Architecture-based Development, but much less attention has been paid to what lies at the heart of architecture-based development, software architectural styles. We argue that architecture-based software development could be much more productive if centered around the concept of software architecture styles, hence the need for style recovery in the process of software architecture reconstruction. The reason behind this is generally. Furthermore, with the coherence architectural styles can bring to the process of automated... 

The labels mathematician, engineer, and physicist have all been used in reference to Balthazar van der Pol. The van der Pol oscillator, which we study in this paper, is a model developed by him to describe the behavior of nonlinear vacuum tube circuits in the relatively early days of the development of electronics technology. Our study in this paper will be based entirely on numerical solutions. The rigorous foundations for the analysis (e.g., the proof that the equation has a limit cycle solution which is a global attractor) date back to the work of Lienard in 1928, with later more general analysis by Levinson and others