Sharif Digital Repository

Twitter as one of the most important microblogging online social networks has attracted more than 200 million users in recent years. Although there have been several attempts on characterizing the Twitter by using incomplete sampled data, they have not been very successful to estimate the characteristics of the whole network. In this paper, we characterize Twitter by sampling from its social graph and user behaviors through a random walk based sampling technique called Respondent-Driven Sampling (RDS). To the best of our knowledge, for the first time RDS method and its estimator are used in order to obtain uniform unbiased estimation of several key structural and behavioral properties of... 

In this paper, a new approach for online reactive path generation and control of multi-agent systems is proposed. This method is based on local optimization techniques used for solving the inverse kinematic problem of redundant manipulators. Convergence of the agents' velocities to the desired values in the null-space of the primary task is guaranteed by introducing a new control law. The efficacy of the proposed algorithm is demonstrated through simulation experiments. © 2006 IEEE  

In this study, two methods for solving economic dispatch problems, namely Hopfield neural network and X iteration method are compared. Three sample of power system with 3, 6 and 20 units have been considered. The time required for CPU, for solving economic dispatch of these two systems has been calculated. It has been shown that for on-line economic dispatch, Hopfield neural network is more efficient and the time required for convergence is considerably smaller compared to classical methods. © 2006 IEEE  

Fuzzy logic has proved to be a powerful tool to represent imprecise and irregular patterns. This paper presents a novel fuzzy approach for recognizing online Persian (Farsi) handwriting which is also useful for multi-writer environments. In this approach, the representation of handwriting parameters is accomplished by fuzzy linguistic modeling. The representative features are selected to describe the shape of tokens. Fuzzy linguistic terms provide robustness against handwriting variations. The purposed method was run on a database of Persian isolated handwritten characters and achieved a relatively high recognition rate. © 2005 IEEE  

Persian (Farsi) script is totally cursive and each character is written in several different forms depending on its former and later characters in the word. These complexities make automatic handwriting recognition of Persian a very hard problem and there are few contributions trying to work it out. This paper presents a novel practical approach to online recognition of Persian handwriting which is based on representation of inputs and patterns with very simple visual features and comparison of these simple terms. This recognition approach is tested over a set of Persian words and the results have been quite acceptable when the possible words where unknown and they were almost all correct in... 

Vehicle localization and environment mapping are the most essential parts of the robot navigation in unknown environments. Since the problem of localization in indoor environments is directly related to the problem of online map generation, in this paper a new and efficient algorithm for simultaneous localization and map generation is proposed and novel results for real environments are achieved. This new algorithm interprets and validates the raw sonar measurements in first step, and applies them to the environment map in the next step. There are various adjustable parameters which make the algorithm flexible for different sonar types. This algorithm is efficient and is robust to sonar... 

The study presented in this paper investigated online data loss in a substation automation system (SAS) under network faults or failures. Online data loss refers to the amount of data that become inaccessible when a failure occurs in the SAS. It is a mathematical index related to the network's topology and architecture, and the calculation of which requires knowledge of the physical characteristics of SAS elements. The elements that record data were identified, and then the online data lost due to failures in those elements were determined. Also, as a case study, a typical SAS was examined under various states of failure, and the online data loss occurring under each scenarios was calculated... 

Representing nonlinear systems by linear models along with structured or unstructured uncertainties and applying robust control strategies could reduce the computational complexity in comparison with implementing the nonlinear model predictive controllers. In this paper design of robust model predictive controllers which are based on special classes of nonlinear systems representations called Wiener and Hammerstein are presented. The proposed algorithms approximate the nonlinear systems by uncertain linear models and reduce online the computational demands in the control implementation. The advantages of the proposed approaches are illustrated by two examples  

Large scale decentralized communication systems have motivated a new trend towards online routing where routing decisions are performed based on a limited and localized knowledge of the network. Geometrical greedy routing has been among the simplest and most common online routing schemes. While a geometrical online routing scheme is expected to deliver each packet to the point in the network that is closest to the destination, geometrical greedy routing, when applied over generalized substrate graphs, does not guarantee such delivery as its forwarding decision might deliver packets to a localized minimum instead. This letter investigates the necessary and sufficient conditions of greedy... 

Energy harvesting has been developed as an effective technology for communication systems in order to extend their lifetime. In this paper, we consider a single-user energy harvesting wireless communication system, in which arrival data and harvested energy curves are modeled as continuous functions. Our first goal is to find an offline algorithm, which maximizes the amount of data, which is transmitted to the receiver node by a given deadline. If more than one scheme exists that transmits the maximum data, we choose the one with minimum utilized energy at the transmitter node. We find this optimal algorithm, by showing its properties. Next, we propose an online algorithm for this system and... 

Energy harvesting (EH) has been developed to extend the lifetimes of energy-limited communication systems. In this letter, we consider a single-user EH communication system, in which both of the arrival data and the harvested energy curves are modeled as general functions. Unlike most of the works in the field, we investigate the online algorithms which only acquire the causal information of the arrival data and the harvested energy processes. We study how well the optimal online algorithm works compared with the optimal offline algorithm, and thus our goal is to find the lower and upper bounds for the ratio of the completion time in the optimal online algorithm to the optimal offline... 

In this paper, the concept of coordination is introduced within the framework of two-level large-scale systems and a new approach based on Interaction Prediction Principle is presented. The proposed approach is formulated in an intelligent manner in such a way that it provides a new strategy that can be used to synthesize an on-line supervisory controller for the overall two-level large-scale systems, extendable to multi-level control systems. By using the new methodology which is based on using neural network for modeling each sub-system, typical gradient method for optimization of first-level sub-problems, and the gradient of the interaction prediction errors related to the predicted... 

This paper presents a novel approach for small signal stability assessment of a multi-machine system using only synchronized Phasor Measurement Units (PMUs) data. The proposed method does not need any information about the generators, network configuration or line impedances. By installing one PMU on each generator bus and using classical model for generator, all of the network and generators parameters needed for small signal stability analysis are estimated using the ambient data registered in the PMUs. Least square error estimation is used to obtain a reduced admittance matrix for the network in real-time. The estimated model is then used to evaluate the multi machine system dynamics in... 

For real-time embedded systems, energy consumption and reliability are two major design concerns. We consider the problem of minimizing the energy consumption of a set of periodic real-time applications when running on a multi-core system while satisfying given reliability targets. Multi-core platforms provide a good capability for task replication in order to achieve given reliability targets. However, careless task replication may lead to significant energy overhead. Therefore, to provide a given reliability level with a reduced energy overhead, the level of replication and also the voltage and frequency assigned to each task should be determined cautiously. The goal of this paper is to... 

One of the most important issues in modal estimation of power systems using PMUs data is the negative effect of outliers. Hence, in addition to the techniques of analyzing PMUs data, the necessity of implementing some kinds of approach to overcome these outliers is tangible. This paper aims to present different approaches to overcome outliers and also estimate the electromechanical modes of the system accurately when there is suspicion that the PMUs data may be contaminated by discordant measurements. Proposed approaches are generally categorized into two main classifications: the first category detects and modifies outliers in the pre-processing stage adaptively and then prepares the... 

In communications, the nodes with the ability of harvesting energy potentially can prolong the overall network lifetime. In this paper, we consider a single-user energy harvesting wireless communication system, in which arrival data and harvested energy curves are modeled as continuous functions. Our goal is to find an online algorithm for the throughput maximization problem, which only needs the causal information of the arrival processes. We propose a heuristic online algorithm which is efficient for both discrete and continuous models, even when the distributions of harvested energy and arrival data are unknown  

In recent years, Solid-State Drives (SSDs) have gained tremendous attention in computing and storage systems due to significant performance improvement over Hard Disk Drives (HDDs). The cost per capacity of SSDs, however, prevents them from entirely replacing HDDs in such systems. One approach to effectively take advantage of SSDs is to use them as a caching layer to store performance critical data blocks in order to reduce the number of accesses to HDD-based disk subsystem. Due to characteristics of Flash-based SSDs such as limited write endurance and long latency on write operations, employing caching algorithms at the Operating System (OS) level necessitates to take such characteristics... 

An online operator position prediction approach based on artificial neural network for teleoperation systems is proposed in this paper, which predicts future position of operator's hand based on current available data. The neural network gathers inputs for some time at the beginning of the operation, then is trained, and is finally exploited through the rest of the operation. Superiority of the proposed approach can be investigated from two aspects. Firstly, no limiting assumption is required in this approach in contrast with the proposed methods in the literature. Secondly, unknown operator intention can be dealt with in real time if it is not too sudden and unpredictable. Two different... 

Tackling the dark silicon problem in a heterogeneous multi-core system, the temperature constraints across the system should be addressed carefully by assigning a proper set of tasks to a pool of the heterogeneous cores during the run-time. When such a system is utilized in a reliable/realtime application, the reliability/timing constraints of the application should also be augmented to the temperature constraints and make the tasks mapping problem more and more complex. To solve the mapping problem in such a situation, we propose READY; an online reliability-and deadline-aware mapping and scheduling algorithm for heterogeneous multi-core systems. READY utilizes an adaptive power constraint... 

In modern multicore mixed-criticality (MC) systems, a rise in peak power consumption due to parallel execution of tasks with maximum frequency, specially in the overload situation, may lead to thermal issues, which may affect the reliability and timeliness of MC systems. Therefore, managing peak power consumption has become imperative in multicore MC systems. In this regard, we propose an online peak power and thermal management heuristic for multicore MC systems. This heuristic reduces the peak power consumption of the system as much as possible during runtime by exploiting dynamic slack and per-cluster dynamic voltage and frequency scaling (DVFS). Specifically, our approach examines...