Sharif Digital Repository

The trailing edge brakes are the conventional controller mechanisms for autonomous precision delivery parafoil systems. Asymetric braking creates differential drag on the left and right sides of canopy leading to generation of turn rate, whereas symmetric deflection changes the aangle of attack which in turn affects airspeed and limit the glide slope. In the current work , in addition to the conventional controller , the canopy is considered to have the ability of changing its longitudinal and lateral incidence angles. This can be achieved by changing the length of sidelong suspension lines.Unlike brakes, the lateral incidence angle creates heavily coupling in lateral dynamics.The results... 

In this research we examine the effects of internal corporate governance mechanisms on shareholder value of 247 firms that were accepted in Tehran Stock Exchange. The main focus is on ownership structure and board composition. Owners with different identities affect shareholder value both directly and to some extent indirectly (through affecting board composition). We measured firm value using 2 different measures: relative growth of share price and market to book value of the firm. Controlling for industry effects, considering different levels of competitiveness, we find that private owners affect firm value more positively than governments and so do institutional investors more than... 

Bone is one of the most important biomechanical organs in animal bodies which comprises of a dynamic tissue that can change its internal structure through remodeling process. A comprehensive understanding of this process is of great significance in prevention and cure of many bone diseases. Due to the special conditions of hard bone tissue, empirical studies on the details of bone processes is very costly and time consuming. Thus, mathematical models and in silico simulations are key to unraveling how bone homeostasis imbalance can lead to pathological conditions. Therefore, in the recent years, there has been an increasing interest in modeling bone remodeling process in cellular level. In... 

Structures that change shapes are often called morphing structures. Smart morphing composites refer to the morphing structures that can detect the change in conditions and, through a control mechanism, command the actuators to maintain the stability and/or perform a new task. The present report provides a framework on the eld of smart morphing composite structures. The emphasis on this work is on, particularly, multi-stable composite structures with capability to detect the new conditions and adapt themselves to properly respond to them. Due to cycling nature of applied load on morphing, these structures are vulnerable to failure due to fatigue. A failure control mechanism utilizing a... 

Wireless sensor network (WSN) multimedia applications impose new challenges in the design of algorithms and communication protocols for sensor networks. Indeed, wireless multimedia sensor networks (WMSNs) must provide relatively high throughput and low end-to-end delay and jitter while being energy-efficient. In view of these challenges, error control is an important mechanism which enables us to provide robust and high quality multimedia communication in WSNs. In this thesis, we first perform a comprehensive performance evaluation of different error control schemes for multimedia communication over WSNs. The results of our analysis show how wireless channel errors can affect the performance... 

Energy harvesters are used in today’s Wireless Sensor Networks (WSNs) to harvest the energy from the environment. One of the important advantages of the energy harvesting sensor networks over battery-operated sensor networks is that the use of the energy harvester prolongs the life time of the nodes, while a battery-operated node becomes useless once its energy runs out. Although an energy harvester can provide a supply source with a lifetime much greater than a battery, the amount of available energy for an energy harvesting system is a random variable and is not as predictable as the energy of a battery. This unpredictability may cause reliability problems. In order to solve the existing... 

Adaptation is a recurring phenomenon in biology by which biochemical systems can robustly- and in some cases completely- adapt their regulated outputs to en- vironmental disturbances and uncertainties. In nature, such a feature has been evolved in biological circuits through the construction of integral feedback control structures. Three types of biologically plausible controllers have been recently in- troduced which can ensure the existence of robust perfect adaptation for arbitrary plants. In this thesis, the main purpose is to have a comparison between them. To this end, we first find a stability criterion to relate the system’s stability with its internal parameters. We then calculate a...