Sharif Digital Repository

In order to be adapted to changes in user requirements and/or the environment, many software systems need to run continuously while they evolve. Most current approaches for such dynamic reconfiguration assume that the evolved system will behave as expected and thus will be reliable if the reconfiguration is consistent. This assumption may not correspond to reality because the delivered quality estimated previously could vary due to parameter changes at runtime. To ensure that the system acts correctly in the field after the reconfiguration, reliability of changes has to be checked at runtime. Existing approaches, however, are not applicable in highly available systems due to the possibility... 

In this article, we study the formation of nanomeniscus around a nanoneedle using molecular dynamics simulation approach. The results reveal three distinct phases in the time-evolution of meniscus before equilibrium according to the contact angle, meniscus height, and potential energy. In addition, we investigated the correlation between the nanoneedle diameter and nanomeniscus characteristics. The results have applications in various fields such as scanning probe microscopy and rheological measurements  

Forthcoming networked systems require mechanisms for on-the-fiy reconfiguration in their protocol stacks to be able to operate in different situations and networks. Since every protocol in a protocol stack has at least one peer protocol in another system, dynamic reconfiguration of a protocol raises the need for reconfiguration in the peer stack. For an assured dynamic (run-time) reconfiguration, executions of two peer protocols are stopped in a safe state, new protocols are initialized, and stacks switch to the new protocols at the same time. This paper proposes a software framework for dynamic reconfiguration of two communicating protocol stacks. A distributed algorithm is implemented in... 

In this paper, we introduce a general framework for coinfection as cooperative susceptible-infected-removed (SIR) dynamics. We first solve the SIR model analytically for two symmetric cooperative contagions [L. Chen, Europhys. Lett. 104, 50001 (2013)10.1209/0295-5075/104/50001] and then generalize and solve the model exactly in the symmetric scenarios for three and more cooperative contagions. We calculate the transition points and order parameters, i.e., the total number of infected hosts. We show that the behavior of the system does not change qualitatively with the inclusion of more diseases. We also show analytically that there is a saddle-node-like bifurcation for two cooperative SIR... 

Unmanned helicopters have gained great importance during recent years due to their special abilities such as hover flight, vertical take-off and landing, maneuverability and superior agility. The advances in electronic devices technologies lead to more powerful and lighter processors to be used in avionic systems which have attracted more attention to these UAVs. The first steps of utilizing an unmanned helicopter are dynamic modeling, control system design and performing model-in-the-loop (MIL) and hardware-in-the-loop (HIL) tests which are presented in this paper. In this research, MIL and HIL tests of an unmanned helicopter are done using novel Linux-based flight control system built on... 

Nonlinear dynamic model of a flying manipulator with two revolute joints and two highly flexible links is obtained using Hamilton's principle. Flying base of the manipulator is a rigid body. Stress is treated three dimensionally in the isotropic linearly-elastic links, but the in-plane and out-of-plane warpings of the links' cross-sections are neglected. Although the links' cross-sections undergo negligible elastic orientation, their models are more accurate than a nonlinear 3D Euler-Bernoulli beam. Tension, compression, twisting and spatial deflections of each link are coupled to each other by some nonlinear terms including two new ones. In the issue of flying flexible-link manipulators new... 

Chatter suppression is an important topic in any type of machining process. In this paper, orthogonal cutting process is modeled as a single degree of freedom dynamic system. A nonlinear delay differential equation is presented that models flank wear of the tool. Uncertainties in cutting velocity, tool wear size and parameters of the dynamic model are included in the model of cutting process. The force provided by a piezo-actuator is taken as the control input of the system. A sliding mode control scheme is used and an effective control law is derived which suppresses the chatter vibration. Results for two distinct cases of a sharp tool and a worn tool are presented and compared which shows... 

Brushless doubly fed induction machine has recently attracted attention in variable speed generators and motor drives. In order to have a high performance control, a precise dynamic model is required. This paper aims at introducing a model of brushless doubly fed induction machine taking core loss into account. The details of model derivation are outlined and the torque relation is expressed in the general reference frame. The model is then used for simulation of the dynamic performance of the machine. The error introduced by neglecting core loss effect is also shown  

In this work, a novel approach to model the dynamic behavior of the flash separation process (as a main building block of non-reacting stage-wise operations) based on Mamdani Fuzzy Inference Systems is proposed. This model surmounts the need to solve various types of mathematical equations governing the system and does not require thermodynamic properties which are either not available or computationally demanding. Hence it can be easily used in dynamic simulation of multi-phase flow in distributed systems. In the proposed approach the overall model is broken into several simple sub-models based on intuitive analysis of an expert. Moreover, a new fuzzy concept, named “Linguistic Composition... 

Removing space debris of various sizes, configurations, and properties from Earth’s orbits is one of the main missions of world space agencies. The existence of deactivated bodies within the path of other spacecraft increases the risk of collision. Althgough towing a satellite through a tether and taking it out of orbit may be a definite solution for space debris removal, most deactivated satellites have some fuel remaining in their fuel tank. This remaining liquid slosh within the tank directly affects satellite motion. To improve the mathematical modeling, the existence of unburned fuel is considered. More specifically, this research focuses on dynamic modeling and control of a selected...