Sharif Digital Repository

Enhancement of interaction between optical and mechanical fields is one of the main goals of cavity optomechanics as a newly founded physics context. If the coupling rate between these fields exceeds their decay rates from the cavity, then preparation of quantum entangled states between photons of the electromagnetic field and phonons of the mechanical field becomes feasible. Among different types of cavities, phoxonic crystal (PxC) cavities have attracted attention in recent years because they can confine optical and mechanical fields simultaneously. In this paper, we introduce four PxC slabs which exhibit simultaneous photonic and phononic bandgaps. All of these crystals have a triangular... 

Thermal stability of the topological color code in the presence of a thermal bath is studied. We study the Lindblad evolution of the observables in the weak-coupling limit of the Born-Markov approximation. The autocorrelation functions of the observables are used as a figure of merit for the thermal stability. We show that all of the observables autocorrelation functions decay exponentially in time. By finding a lower bound of the decay rate, which is a constant independent of the system size, we show that the topological color code is unstable against thermal fluctuations from the bath at finite temperature, even though it is stable at T=0 against local quantum perturbations  

In this research, the developing turbulent swirling flow in the entrance region of a pipe is investigated analytically by using the boundary layer integral method. The governing equations are integrated through the boundary layer and obtained differential equations are solved with forth-order Adams predictor-corrector method. The general tangential velocity is applied at the inlet region to consider both free and forced vortex velocity profiles. The comparison between present model and available experimental data demonstrates the capability of the model in predicting boundary layer parameters (e.g. boundary layer growth, shear rate and swirl intensity decay rate). Analytical results showed... 

In this paper a linear continuous theory for bending analysis of beams with an edge crack perpendicular to the neutral plane subject to bending has been developed. The model assumes that the displacement field is a superposition of the classical EulerBernoulli beam's displacement and of a displacement due to the crack. It is assumed that in bending the additional displacement due to crack decreases exponentially with distance from the crack tip. The strain and stress fields have been calculated using this displacement field and the bending equation has been obtained using equilibrium equations. Using a fracture mechanics approach the exponential decay rate has been calculated. There is a... 

In this paper, a model-based fuzzy controller for attitude stabilization of a Quadrotor is proposed. To achieve this purpose first a Takagi-Sugeno fuzzy model for Quadrotor which is obtained from dynamic model is presented. Parallel Distributed Compensation (PDC) technique is utilized to design a state feedback controller. The purpose of control is to stabilize the Quadrotor while taking into account performance specifications such as decay rate and constraint on the input. Both of these conditions can be represented in term of linear matrix inequalities (LMIs). By simultaneously solving these LMIs a stabilizing fuzzy controller that achieves desired speed of response and small control... 

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer assumptions and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order Adams predictor-corrector method. The free vortex and uniform velocity profiles are applied for the tangential and axial velocities at the inlet region, respectively. Due to the lack of experimental data for swirling flows in converging nozzles, the developed model is validated against the numerical simulations. The...