Scientia Iranica
Volume:16 Issue: 5, 2009

In this research، we investigated b quark decays by two di erent approaches; rstly، according to the structure of penguin decays، and secondly، based on an e ective Hamiltonian theory. Working with the standard model، the QCD penguin terms for various b and b decays are calculated. We also studied decay rates of the matter-antimatter of b quark decays. The gluonic penguin of b decays، b! qkg! qkqiqj، is studied through the Wilson coecients of the e ective Hamiltonian. We obtained the decay rates of the tree and penguin and magnetic dipole terms all together to compare them with the e ective Hamiltonian current-current and penguin operators. We described the e ective Hamiltonian theory and applied it to the calculation of current-current (Q1; 2)، QCD penguin (Q3;


; 6) and magnetic dipole (Q8) decay rates. Based on the e ective penguin model، the simple coecients، d1;


; d6; 8، are de ned according to the gluon penguin structure and used in the e ective Hamiltonian theory. In the other section of this research، the decay rates of processes like b! cdc (b! cdc)، b! csc (b! csc)، b! udu (b! udu) and b! usu (b! usu) are obtained based on the E ective Hamiltonian (EH) and E ective Penguin Model (EPM). Decay rates and branching ratios are very similar in all models، but in the E ective Hamiltonian Magnetic Dipole، the total decay rate is about 10% larger than the simple tree or E ective Hamiltonian. On the other hand، including the penguin induces matter-antimatter asymmetries. These are largest in the rate decays b! udu، the decay rate of which is about 7% smaller than the decay rate b! udu. Also، rate b! suu is larger than rate b! suu.

Using some agent variables, the general structure of the dynamic model of a spatial mobile robot with N long spatially exible links and N revolute joints has been exposed. It is composed of a set of 5N + 6 nonlinear coupled partial di erential motion equations under the in uence of the boundary conditions. Non-conservative forces/moments have been neglected. While being considered, the general structure of the dynamic model will not change, but a few exciting/damping terms will arise within the agent variables. The base of the robot is an unconstrained rigid body in space and the links as 3D Euler-Bernoulli beams undergo tension-compression, torsion and two spatial bendings while elastic orientation is considerable and the nonlinear part of the geometric Green-Lagrange strain is ignored. When the elastic orientation is neglected, the dynamic model of each link remains more accurate than that of a nonlinear 3D Euler-Bernoulli beam within which the elastic orientation is actually negligible. The obtained dynamic model is capable of creating the nonlinear 3D long Euler-Bernoulli beam and the fully-enhanced/enhanced/generalized nonlinear 3D Euler-Bernoulli beam theories, considering a ying or a xed support.

The purpose of this article is to describe the theoretical background to the Harmonic Balance approach; adopted and further developed for the analysis of general multi degree of freedom rotor bearing systems with nonlinear supports. System equations of motion are prepared for dynamic systems with any number of degrees of freedom. Nonlinear behaviour can be associated with any number of these freedoms. A computer program which uses the harmonic balance method to solve the system equations of motion is also written. These equations are partitioned into linear and nonlinear parts. The nonlinear sets of equations need to be solved prior to solving the linear sets of equations. Veri cation of the proposed method of solution is justi ed through two examples. The frequency response of a well known rotor bearing, the so called Jefcott rotor, is examined and tested against data reported by some other researchers. Also, the versatility of this method is tested by comparing the harmonic balance approach with the transient solution and some experimental measurements involving the nonlinear squeeze lm bearing supports, which have already been reported by this author. It is shown that by utilizing harmonic balance with appropriate condensation, it is possible to considerably reduce the number of simultaneous nonlinear equations inherent to such systems. The stability (linear) of the equilibrium solutions may be conveniently evaluated using the Floquet theory.

In this paper, a two dimensional numerical model for two phase ow is presented. For interface tracking, the FGVT-VOF (Fine Grid Volume Tracking-Volume Of Fluid) method is selected. For momentum advection, an improved approach is used. In this scheme, a volume tracking step is coupled with steps of computations for the advection of momentum. A Reynolds stress algebraic equation has been implemented in the algorithm of turbulent modeling. Standard test cases are used for the veri cation of interface tracking and hydrodynamic modeling in laminar and turbulent conditions. The test results show that this methodology can be used in di erent applications of two-phase ow modeling.

In this paper, an algorithm is proposed to improve the Maximum Load Carrying Capacity (MLCC) of exible robot manipulators. The maximum allowable load which can be achieved by a exible manipulator along a given trajectory is limited by the joints'' actuator capacity and the end e ector accuracy constraint. In an open-loop approach, the end e ector deviation from the prede ned path is signi cant and the accuracy constraint restrains the maximum payload before actuators go into saturation mode. By using a controller, the accuracy of tracking will improve. The actuator constraint is not a major concern and, therefore, the full power of the actuators, which leads to an increase in the Maximum Load Carrying Capacity, can be used. In this case, the controller can play an important role in improving the maximum payload, so a robust controller is designed. However, the control strategy requires measurement of the elastic variables'' velocity, which is not conveniently measurable. So, a nonlinear observer is designed to estimate these variables. A stability analysis of the proposed controller and state observer is performed on the basis of the Lyapunov Direct Method. In order to verify the e ectiveness of the presented method, simulation is done for a two link exible manipulator. The obtained maximum payload for open and closed-loop cases is compared, and the superiority of the method is illustrated.

This paper focuses on the biomechanical aspects of the human lower extremity loading condition during backpack load carrying. A biomechanical framework was generated with the aim of employing a block-oriented structure of Simulink integrated with the Virtual Reality Toolbox of MATLAB software to provide a simulation study of the musculoskeletal system in a virtual environment. In this case, a ten-degrees-of-freedom musculoskeletal model actuated with sixteen muscles in each leg was utilized to simulate movement in the sagittal plane. An inverse dynamics based optimization approach was employed to estimate the excitation level of the muscles. In addition, distributions of the mechanical power analysis for lower extremity muscles were carried out to enhance the understanding of human leg morphology and control mechanism to provide load support. Simulation results provide a biomechanical framework to identify the muscles and joints, which are critically subjected to musculoskeletal injuries during the activity under investigation. Analysis of the muscle activation patterns and their distribution of the mechanical powers revealed the important role of the plantar exors of the ankle and the extensors of the knee and hip joints in supporting the body during backpack load carrying.