Sharif Digital Repository

The main concern of steganography (image hiding) methods is to embed a secret image into a host image in such a way that the host should remain as similar as possible to its original version. In addition the host image should remain robust with respect to usual attacks. In this paper we present a method that tries to cover all above mentioned concerns. The secret and host images are divided into blocks of size 4 × 4. Each block in secret image is taken as a texture pattern for which the most similar block is found among the blocks of the host image. The embedding procedure is carried on by replacing these small blocks of the secret image with blocks in host image in such a way that least... 

Some of the most important classes of watermark detection methods in image watermarking are correlation based algorithms. In these methods usually a pseudorandom pattern is embedded in host image. Receiver can regenerate this pattern by having a key that is the seed of a random number generator. After that if the correlation between this pattern and the image that is assumed to have the watermark is higher than a predefined threshold, this means that the watermark exists and vise versa. In this paper we showed the advantage of using the Julian set patterns as a watermark, instead of commonly used pseudorandom noisy pattern. Julian set patterns can be regenerate in receiver with few... 

Optical character recognition of cursive scripts present a number of challenging problems in both segmentation and recognition processes and this attracts many researches in the field of machine learning. This paper presents a novel approach based on a combination of MLP and SVM to design a trainable OCR for Persian/Arabic cursive documents. The implementation results on a comprehensive database show a high degree of accuracy which meets the requirements of commercial use. © Springer-Verlag Berlin Heidelberg 2005  

Image-Adaptive watermarking systems exploit visual models to adapt the watermark to local properties of the host image. This leads to a watermark power enhancement, hence an improved resilience against different attacks, while keeping the mark imperceptible. Visual models consider different properties of the human visual system, such as frequency sensitivity, luminance sensitivity and contrast masking. Entropy masking is another human visual system's characteristic, which rarely has been addressed in visual models. In this paper we have utilized this masking effect to improve the robustness of Image-Adaptive watermarks while keeping their transparency. Experimental results show a significant... 

The ubiquity of broadband digital communications and mass storage in modern society has stimulated the widespread acceptance of digital media. However, easy access to royalty-free digital media has also resulted in a reduced perception in society of the intellectual value of digital media and has promoted unauthorised duplication practices. To detect and discourage the unauthorised duplication of media, researchers have investigated watermarking methods to embed ownership data into media. However, some authorities have expressed doubt over the efficacy of watermarking methods to protect digital media. The paper introduces a novel method to discourage unauthorised duplication of digital... 

This paper develops methodology and technique tor the design, analysis, and impie mentation of an adaptive generalized predictive controller (AGPC) for Active Queue Management in TCP Networks. The TCP/AQM dynamic is modeled experimentally as a second-order system with a time delay where its parameters are estimated using the standard gradient algorithm. Based on this model, an AGPC is designed to gain the set-point tracking and robustness. AGPC, as a queue-based control mechanism, responds quickly to traffic changes, thus allowing for high utilization and small loss. We illustrate our results using ns-2 simulations and demonstrate the practical impact of adaptive model reference control on... 

The performance of a new robust AQM strategy for dynamically varying TCP/AQM networks is proposed. Network variations include in both network topology and traffic variations. The developed AQM is designed based on Coefficient Diagram Method (CDM), which is a new indirect pole placement method that considers the speed, stability and robustness of the closed loop system in terms of time domain specifications. Simulation results show different features of the proposed method. ©2005 IEEE  

A novel robust image-adaptive digital watermarking algorithm using Multi-Resolution Singular value Decomposition (MR-SVD) is proposed in this paper. The proposed method strengthens the watermark based on the concept of entropy masking, while meeting the mark imperceptibility requirement. Experimental results show that the proposed method improves watermarking performance over watermarking methods in wavelet domain transform, in terms of both invisibility and robustness. © 2005 IEEE  

A novel output feedback neural controller is presented for the implementation of sliding mode control of DC/DC converters. The controller, which consists of a multilayer perceptron, has been trained so as to be robust for large variations of system parameters and state variables. Fast dynamic behavior is the other main advantage of the proposed controller, which allows realization of all the beneficial features of sliding mode control technique. Other advantages of the controller are simplicity and low cost. Computer simulations are carried out to investigate the effectiveness of the controller in voltage regulation for a relatively complex topology such as a Cuk converter. Simulation... 

This paper presents a robust decentralized proportional-integral (PI) control design as a solution of the load frequency control (LFC) in a multi-area power system. In the proposed methodology, the system robustness margin and transient performance are optimized simultaneously to achieve the optimum PI controller parameters. The Kharitonov's theorem is used to determine the robustness margin, i.e., the maximal uncertainty bounds under which the stable performance of the power system is guaranteed. The integral time square error (ITSE) is applied to quantify the transient performance of the LFC system. In order to tune the PI gains, the control objective function is optimized using the... 

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... 

Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

In this paper, a novel decentralized adaptive control scheme for multiagent formation control is proposed based on an integration of artificial potential functions with robust control techniques. Fully actuated mobile agents with partially unknown models are considered, where an adaptive fuzzy logic system is used to approximate the unknown system dynamics. The robust performance criterion is used to attenuate the adaptive fuzzy approximation error and external disturbances to a prescribed level. The advantages of the proposed controller can be listed as robustness to input nonlinearity, external disturbances, and model uncertainties, and applicability on a large diversity of autonomous... 

This paper presents a robust control scheme for an islanded microgrid in the presence of structured uncertainties. The microgrid consists of parallel connection of two Distributed Generation (DG) units and a passive load. The DG units are connected to the passive load by using the power electronics converters. The microgrid model is structurally uncertain due to the large perturbations in the load parameters. To deal with the uncertainties, a Linear Fractional Representation (LFR) of the parametrically uncertain system is obtained. To achieve robust performance, the μ-synthesis approach is applied to the derived LFR model to design a μ controller. The resultant controller is structurally... 

This technical note considers the fixed-order H∞ output feedback control design problem for linear time invariant (LTI)systems. The objective is to design a fixed-order controller with guaranteed stability and closed-loop H∞ performance. This problem is NP-hard due to the non-convex rank constraint which appears in the formulation. We propose an algorithm for non-iterative direct synthesis (NODS) of reduced order robust controllers. NODS entails initial computation of two positive-definite matrices via full-order convex LMI conditions. These are then utilized by appropriate eigenvalue decomposition to directly obtain a suboptimal convex formulation for the fixed-order controller  

Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

To achieve a cost-effective and reliable use of wind power generation, advanced control techniques are required. In this paper, the application of two control strategies for the improvement of wind turbine power output is investigated in the presence of model/environmental uncertainties. Rotational speed of the wind turbine and consequently its power output are controlled via manipulation of blades pitch angle (at a constant generator torque). First, the classical PID controller is designed based on root locus analysis while in the second scheme, an H∞-robust controller is designed via μ-synthesis based on DKiteration algorithm. Performance of the two controllers in tracking of the desired... 

Integrated guidance and control of an elastic flight vehicle based on constrained robust model predictive control is proposed. The design is based on a partial state feedback control law that minimizes a cost function within the framework of linear matrix inequalities. It is shown that the solution of the defined optimization problem stabilizes the nonlinear plant. Nonlinear kinematics and dynamics are taken into account, and internal stability of the closed-loop nonlinear system is guaranteed. The performance and effectiveness of the proposed integrated guidance and control against non-maneuvering and weaving targets are evaluated using computer simulations  

A decentralized servomechanism controller for islanded (autonomous) operation of radial connection of two distributed generation (DG) units is proposed in this paper. Each DG unit utilizes a voltage-sourced converter (VSC) for interface to its dedicated load. The DG units and the loads are to operate in the islanded mode of operation. Each DG unit regulates the voltage of its dedicated load in a decentralized manner. In this paper, it is first shown that the radial connection of two DG units in the islanded mode constitutes an interconnected composite system consisting of two subsystems. Moreover, the paper shows that the overall islanded system can be controlled by the local controllers,... 

A hot gas generator is a compact heat exchanger that produces high temperature or enthalpy gases. This paper presents two methods for controlling the system. The first one is an adaptive sliding mode controller that is a Lyapunov based method and proposed to confront the dynamic modeling deficiencies and system uncertainties. The second one is a linear adaptive controller that gives a new attractive ability to the system which can track a complicated requested path. Each of the presented controllers has some capabilities that may be preferred to other. In this paper, these methods are extensively compared by several transient inputs. On the other hand, since heat exchangers are typically...