Journal of Modeling and Simulation
Volume:46 Issue: 1, Spring 2014

Friction is a nonlinear phenomenon which has destructive effects on performance of control systems. To obviate these effects, friction compensation is an effectual solution. In this paper, an adaptive technique is proposed in order to eliminate limit cycles as one of the undesired behaviors due to presence of friction in control systems which happen frequently. The proposed approach works for nonlinear dynamic and static friction models and is applicable to a wide range of different mechanical systems. It is also applied to a simple inverted pendulum on a cart as a highly nonlinear under-actuated system. A nonlinear optimal controller based on the approximate solution of Hamilton-Jacobi-Bellman partial differential equation is designed to fulfill our control objectives and achieve preferable performance compared to those of the linear optimal controllers. It causes to have more accuracy in system's response and positioning in the presence of friction. Simulation result approve the effectiveness of both the presented technique and controller.

The problem of pole assignment, also known as an eigenvalue assignment, in linear discrete-time periodic systems in discs was solved by a novel method which employs elementary similarity operations. The former methods tried to assign the points inside the unit circle while preserving the stability of the discrete time periodic system. Nevertheless, now we can obtain the location of eigenvalues in the specified discs, randomly. An illustrative example with random system matrices is presented in order to show the effectiveness of the method.

One of the main features of High Throughput Computing systems is the availability of high power processing resources. Cloud Computing systems can offer these features through concepts like Pay-Per-Use and Quality of Service (QoS) over the Internet. Many applications in Cloud computing are represented by workflows. Quality of Service is one of the most important challenges in the context of scheduling scientific workflows. On the other hand, the remarkable growth of the multicore processor technology has led to the use of these processors by service providers as building blocks of their infrastructure. Therefore, scheduling scientific workflows on the Cloud requires especial attention to multicore processor infrastructure which adds more challenges to the problem. On the other hand, in addition to these challenges users’ QoS constraints like execution time and cost should be regarded. The main objective of this research is scheduling workflows on the Cloud, considering a multicore based infrastructure. A new algorithm is proposed which finds clusters of the workflow that can be executed in parallel while having large data communications. These kinds of clusters could be appropriate candidates to be executed on a multicore processor. In contrast, there are other clusters which should be executed in serial. This algorithm investigates whether serial execution of these clusters is possible or not. The experimental results show that the algorithm has a positive effect on execution time and cost of the workflow execution.

Advanced metering infrastructure (AMI) is a key part of the smart grid; thus, one of the most important concerns is to offer a secure mutual authentication. This study focuses on communication between a smart meter and a server on the utility side. Hence, a mutual authentication mechanism in AMI is presented based on the elliptic curve cryptography (ECC) and one time signature (OTS) consists of two phases: a key and signature generation phase as well as a signature verification phase. The next challenge, is securing communication messages. Accordingly, a message authentication mechanism based on ECC and OTS is proposed in this paper. Such protocols are designed based on resource constraint problem on the consumer side and security requirement satisfaction in AMI. Security of the protocol with BAN logic is proved and possibility of signature forgery via the mathematical principle of birthday paradox formula is represented. In the end, security of the protocol is scrutinized with informal methods and is simulated on Java. Simulation and analytical results show that proposed protocols are more secure and efficient than similar methods against most of the security attacks.

In the present work, a hybrid of Fourier transform and homotopy perturbation method is developed for solving the non-homogeneous partial differential equations with variable coefficients. The Fourier transform is employed with combination of homotopy perturbation method (HPM), the so called Fourier transform homotopy perturbation method (FTHPM) to solve the partial differential equations. The closed form solutions obtained from the series solution of recursive sequence forms are obtained. We show that the solutions to the non-homogeneous partial differential equations are valid for the entire range of problem domain. However the validity of the solutions using the previous semi-analytical methods in the entire range of problem domain fails to exist. This is the deficiency of the previous HPMs caused by unsatisfied boundary conditions that is overcome by the new method, the Fourier transform homotopy perturbation method. Moreover, it is shown that solutions approach very rapidly to the exact solutions of the partial differential equations. The effectiveness of the new method for three non-homogenous differential equations with variable coefficients is shown schematically. The very rapid approach to the exact solutions is also shown schematically.

Given a set of points in the plane and a constant, -center problem is to find two closed disks which each covers the whole, the diameter of the bigger one is minimized, and the distance of the two centers is at least. Constrained -center problem is the -center problem in which the centers are forced to lie on a given line. In this paper, we first introduce -center problem and its constrained version. Then, we present an algorithm for solving the -center problem. Finally, we propose a linear time algorithm for its constrained version.