Sharif Digital Repository

A two-dimensional seven link biped dynamic model was developed to investigate the mechanical characteristics of the normal and amputee locomotion during the complete gait cycle. The foot-ground contact was simulated using a five-point penetration contact model. The equations of motion were derived using Lagrange method. Optimization of the normal human walking model provided constant coefficients for the driving torque equations that could reasonably reproduce the normal kinematical pattern. The resulting torques were then applied to the intact joints of the amputee model with a prosthetic leg equipped with a kinematical driver controller for the ankle and either a hydraulic, elastic or... 

A new adaptive steganography method based on image contrast to improve the embedding capacity and imperceptibility of the stego images is presented. The method exploits the average difference between the gray level values of the pixels in 2x2 blocks of non-overlapping spatially and their mean gray level in order to select valid blocks for embedding. The method was tested on different gray scale images. Results show that our proposed approach provides larger embedding capacity, while being less detectable by steganalysis methods such as χ2 attack and machine learning steganalysis systems, as compared to some well-known adaptive and non-adaptive steganography algorithms  

Wind towers or wind catchers, as passive cooling systems, can provide natural ventilation in buildings located in hot, arid regions. These natural cooling systems can provide thermal comfort for the building inhabitants throughout the warm months. In this paper, a modular design of a wind tower is introduced. The design, called a modular wind tower with wetted surfaces, was investigated experimentally and analytically. To determine the performance of the wind tower, air temperature, relative humidity (RH) and air velocity were measured at different points. Measurements were carried out when the wind speed was zero. The experimental results were compared with the analytical ones. The results... 

A dynamic model of an above-knee prosthesis during the complete gait cycle was developed. The model was based on a two-dimensional multi-body mechanical system and included a hydraulic and an elastic controller for the knee and a kinematical driver controller for the prosthetic ankle. The equations of motion were driven using Lagrange method. Simulation of the foot contact was conducted using a two-point penetration contact model. The knee elastic and hydraulic controller units, the knee extension stop, and the kinematical driver controller of the ankle were represented by a spring and a dashpot, a nonlinear spring, and a torsional spring-damper within a standard prosthetic configuration....