Sharif Digital Repository

Problems regarding simulation of field emitter array (FEA) electron guns are discussed. A simple method is proposed to significantly reduce computational requirements such as computation power, system memory, and time of FEA electron gun simulation and modeling. The method can be applied to any numerical solver regardless of its meshing technique. In order to extract field emission parameter from any experimental cathode I-V curve, a partly numerical algorithm, which uses the presented truncation method at the heart of its solver, is proposed. The proposed method and algorithm are applied to a number of examples, including a double-gated FEA problem, and its effectiveness in terms of error... 

Needle insertion simulation and planning systems (SPSs) will play an important role in diminishing inappropriate insertions into soft tissues and resultant complications. Difficulties in SPS development are due in large part to the computational requirements of the extensive calculations in finite element (FE) models of tissue. For clinical feasibility, the computational speed of SPSs must be improved. At the same time, a realistic model of tissue properties that reflects large and velocity-dependent deformations must be employed. The purpose of this study is to address the aforementioned difficulties by presenting a cost-effective SPS platform for needle insertions into the liver. The study... 

A modular hierarchical structure is developed to describe human movement planning level. The modular feature of the proposed model enables it to generalize planning a task. The movements are planned based on decomposing a task into its corresponding subtasks (motion phases). There is a module responsible for one condition. The final plan is constructed using soft computing of the plans proposed by different modules. Each module estimates the kinematics of the joints at the end of each subtask; we call them kinematic estimator modules (KEMs). A timing module estimates the duration of motion and a gating module determines the responsibility of each KEM under different conditions. To evaluate...