Sharif Digital Repository

Network-on-Chips (NoCs) consume a significant portion of multiprocessors' total power. Dynamic Voltage Scaling (DVS) which can reduce both static and dynamic power consumption is widely applied to NoCs. However, prior DVS schemes usually impose significant performance overhead to NoCs as NoCs need to work with lower clock frequencies when the supply voltage is scaled down. In this chapter, we propose a novel DVS scheme for NoCs with no performance overhead. We reduce power consumption when there is few Virtual Channels (VCs) that have active allocation requests at each cycle compared to the total number of available VCs. To enable multiple latencies with different slack times, we propose a... 

During voluntary flexion/extension of the head-neck system, the cervical spine undergoes a stepwise motion from upper to lower regions with a specific pattern. The motion of each vertebra is composed of a translation and rotation with respect to lower vertebrae, which may be considered as an absolute rotation about an axis called instantaneous axis of rotation (IAR). The location of this axis is different between normal and degenerated spines. A biomechanical computer model of the head and cervical vertebrae, including eight separate rigid links and nine spinal muscles as actuating elements was developed to evaluate and compare inter-segmental force-moments and muscle forces in normal,... 

A mathematical model has been proposed for evaluation of velocity and temperature fields in hot forging operations for axisymmetric parts. The model can be applied to determine forging load, strain rate, strain and temperature distributions. In addition, the effects of temperature and strain rate on metal flow have been considered through simultaneous modelling of dynamic phase transformation within the deforming metal. Hot forging experiments have been carried out under different working conditions and the results have been compared with the predictions. A good agreement between the simulated and experimental results was found. © 2004 Elsevier Ltd. All rights reserved  

Direct yaw moment control (DYMC) is one of the most effective method that improves not only the directional stability of the vehicles but also their road handling and controllability to a great extent. In this method by developing a difference in the longitudinal force (often the braking force) on two sides of the vehicle, an external stabilizing yaw moment is applied to the vehicle. In this study, an optimal control law for DYMC is proposed. The control law is based on the yaw rate, the lateral velocity feedback, and the steering angle feedforward. Simulation results obtained indicate that considerable improvement in the vehicle dynamic behavior can be achieved when the optimal yaw moment... 

Three-axis rotary table is a flight motion simulator (FMS) used in the hardware in the loop (HWIL) simulation. Geometrical Modeling of 3-axis rotary tables is described and then three possible Geometrical layouts are driven. Kinematic and dynamic modelings of a 3-axis rotary table are developed in this paper. Denavit-Hartenberg (D-H) method, Recursive Newton-Euler (RNE) and Lagrange methods are used, respectively, in kinematic and dynamic modeling. A kinematic Error analysis is applied to determine the orientation and position accuracy of the table. Dynamic sensitivity analysis is also performed and the first-order sensitivity functions are derived corresponding several dynamic and control... 

Humanoid robots have recently been the subject of many new and interesting fields both in robotics research and industry. The wide variety of their applications in civic and hostile environments demand developing approperiate theoretical models for analysis. A dynamical model was developed to study the human jumping process, and the effect of factors like joint speeds and hand motion in jumping. An experiment was designed and setup to compare the theoretical model with experimental observations. Time histories of vertical force, mass center velocity and driving torques were also obtained. Using dynamical equations, the effect of joint speeds on the maximum values of these quantities is... 

This article investigates optimization of long-term operation of hydrothermal power systems consisting of cascaded reservoirs. Due to stochasticity of reservoir inflows, demand for energy, and unit forced outages, the uncertainty of this system is so significant that reliability of demand satisfaction becomes an indispensable component of the modelling process. On the other hand, existence of stochastic parameters, especially in the case of cascaded reservoirs, makes the problem very difficult to solve by applying existing optimization techniques. A hybrid genetic algorithm with dynamic tuning of its control parameters is developed that incorporates real number encoding and an analytical... 

In this paper, we apply the stochastic dynamic programming to find the dynamic shortest path from the source node to the sink node in stochastic dynamic networks, in which the arc lengths are independent random variables with exponential distributions. In each node there is an environmental variable, which evolves in accordance with a continuous time Markov process. The parameter of the exponential distribution of the transition time of each arc is also a function of the state of the environmental variable of its initiative node. Upon arriving at each node, we can move toward the sink node through the best outgoing arc or wait. At the beginning, it is assumed that upon arriving at each node,... 

Due to inherent potential of General Regression Neural Network(GRNN) to approximate nonlinear functions, it can be implemented as a nonlinear state-feedback controller. In this paper the methodology of direct collocation and nonlinear programming is utilized in combination with GRNN to determine the optimal control of dynamical systems. Application of this method to the design of an optimal controller for a chaotic flexible beam as a non-autonomous, nonlinear system is investigated. © 2002 The American Institute Aeronautics and Astronautics Inc. All rights reserved  

The individual and combined effect of shear deformation and rotary inertia on the columns was discussed. It was shown that the shear deformation effect always tends to reduce the buckling load. It was observed that rotary inertia for supported columns has no effect on the buckling load. The critical buckling load of perfect columns subjected to static axial loading was calculated using the Euler-Bernoulli theory  

This paper presents the kinematic and dynamic modeling of a two degrees of freedom manipulator attached to a vehicle with a two degrees of freedom suspension system. The vehicle is considered to move with a constant linear speed over an irregular ground-surface while the end-effector tracks a desired trajectory in a fixed reference frame. In addition, the effects of highly coupled dynamic interaction between the manipulator and vehicle (including the suspension system's effects) have been studied. Finally, simulation results for the end-effector's straight-line trajectory are presented to illustrate these effects  

In this study, the potential of using a polyacrylamide-silica nanocomposite (PAM-S) to control the filtration properties of bentonite water-based drilling muds under different salinity conditions was evaluated. Static filtration tests under low-pressure/low-temperature (LPLT) conditions accompanied by rheological measurements have been carried out to analyze the role of silica nanoparticles (NPs) and nanocomposites (NCs) in the base fluid properties. Moreover, high-pressure/high-temperature (HPHT) static filtration was also investigated to evaluate the thermal stability of PAM-S. Afterward, dynamic filtration has been conducted in a filtration cell equipped with an agitating system with a... 

Network-on-Chips (NoCs) consume a significant portion of multiprocessors' total power. Dynamic Voltage Scaling (DVS) which can reduce both static and dynamic power consumption is widely applied to NoCs. However, prior DVS schemes usually impose significant performance overhead to NoCs as NoCs need to work with lower clock frequencies when the supply voltage is scaled down. In this chapter, we propose a novel DVS scheme for NoCs with no performance overhead. We reduce power consumption when there is few Virtual Channels (VCs) that have active allocation requests at each cycle compared to the total number of available VCs. To enable multiple latencies with different slack times, we propose a... 

In most existing works on the flocking problem, results were obtained for the case where a double integrator dynamic is used to describe motion of agents and virtual leader. These results, however, may not be generalised to agents with general linear dynamic. In this study, it is shown that in the flocking of agents with a linear dynamic, the velocity convergence of agents does not generally lead to the position convergence of informed agents and the position convergence is possible only for a specified group of linear dynamics. In this study, a control protocol is proposed to flock agents with specified linear dynamics and guarantee the velocity convergence of all agents as well as average... 

I formulate a general finite element method (FEM) for self-gravitating stellar systems. I split the configuration space to finite elements, and express the potential and density functions over each element in terms of their nodal values and suitable interpolating functions. General expressions are then introduced for the Hamiltonian and phase-space distribution functions of the stars that visit a given element. Using the weighted residual form of Poisson's equation, I derive the Galerkin projection of the perturbed collisionless Boltzmann equation, and assemble the global evolutionary equations of nodal distribution functions. The FEM is highly adaptable to all kinds of potential and density... 

Dynamic modeling of piezo-driven compliant mechanisms is necessary to predict dynamic behavior of nanopositioning systems, and also to optimize their controlling methods. Dynamic tests on a real system or dynamic analyses on a FEM model is very time consuming when they must be carried out iteratively. According to previous works, obtaining static specifications of model is possible within a reasonable error margin. But all geometric dimensions and mass distribution details of the whole moving parts should be considered to calculate dynamic specifications of the model. In this paper, a functional method is described to obtain dynamic specifications of an planar compliant mechanism, by means... 

A fourth-order Hamiltonian describing the planar full two body problem is obtained, allowing for a mapping out of the geography of spin-spin-orbit resonances. The expansion of the mutual potential function up to the fourth-order results in the angles to come through one single harmonic and consequently the rotation of both bodies and mutual orbit are coupled. Having derived relative equilibria, stability analysis showed that the stability conditions are independent of physical and orbital characteristics. Simultaneously chaotic motion of bodies is investigated through the Chirikov diffusion utilizing geographic information of the complete resonances. The results show that simultaneous chaos... 

Login section is one of the most important parts of each system. This section is usually achieved through a username-password entering method. Since in these methods, user's security relays on how strong the password is, accordingly it is important how the password is provided. There are lots of different approaches in this regard which can be categorized in two main subgroups: Static and Dynamic passwords. Dynamic passwords are taking the lead in password generation context, since static password approaches suffer from some disadvantages like their vulnerability to easily get cracked, high possibility of oblivion and etc. In this paper, we introduce a novel dynamic password providing idea,... 

We use the weighted integral form of spherical Bessel functions and introduce a new analytical set of complete and biorthogonal potential-density basis functions. The potential and density functions of the new set have finite central values and they fall off, respectively, similar to r-(1+ l) and r-(4+ l) at large radii, where l is the latitudinal quantum number of spherical harmonics. The lowest order term associated with l = 0 is the perfect sphere of de Zeeuw. Our basis functions are intrinsically suitable for the modelling of three-dimensional, soft-centred stellar systems and they complement the basis sets of Clutton-Brock, Hernquist & Ostriker and Zhao. We test the performance of our... 

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...