Sharif Digital Repository

In this study, a dielectrophoresis field-flow fractionation device was analyzed using a numerical simulation method and the behaviors of a set of different cells were investigated. By reducing the alternating current frequency of the electrodes from the value used in the original setup configuration and increasing the number of exit channels, total discrimination in cell trajectories and subsequent separation of four cell types were achieved. Cells were differentiated based on their size and dielectric response that are represented in their real part of Clausius–Mossotti factor at different frequencies. A number of novel designs were also proposed based on the original setup configuration.... 

In this study, fabrication of a three-dimensional porous scaffold was performed using freeze gelation method. Recently, fabrication of scaffolds using polymer blends has become common for many tissue engineering applications due to their unique tunable properties. In this work, we fabricated alginate-gelatin porous hydrogels for wound healing application using a new method based on some modifications to the freeze-gelation method. Alginate and gelatin were mixed in three different ratios and the resulting solutions underwent freeze gelation to obtain 3D porous matrices. We analyzed the samples using different characterization tests. The scanning electron microscopy (SEM) results indicated... 

Roll control of the Autonomous Underwater Vehicles (AUVs) is a significant issue in the current field of research for many researchers in the subject of AUV control system designation. Especially at higher speeds, the roll angle generated by a single rotating propeller or other external disturbances can considerably influence the whole dynamics and therefore the operation of the vehicle. In this paper, the utilisation of a system of contra-rotating-propellers (CRP) to enhance the roll dynamics of an AUV is evaluated by developing a six-degrees-of-freedom (6DOF) dynamics and control systems’ simulator. The results show that: 1. The single propeller system can cause roll angle deflections... 

Roll control of the Autonomous Underwater Vehicles (AUVs) is a significant issue in the current field of research for many researchers in the subject of AUV control system designation. Especially at higher speeds, the roll angle generated by a single rotating propeller or other external disturbances can considerably influence the whole dynamics and therefore the operation of the vehicle. In this paper, the utilisation of a system of contra-rotating-propellers (CRP) to enhance the roll dynamics of an AUV is evaluated by developing a six-degrees-of-freedom (6DOF) dynamics and control systems’ simulator. The results show that: 1. The single propeller system can cause roll angle deflections... 

Microrobots design and manufacturing has been one of interesting fields in robotics in recent years. Various legged designs have been proposed in the literature. All designs rely on friction for locomotion. In this paper the dynamic model of a planar two-legged microrobot is presented using LuGre friction model. LuGre friction model is more realistic model, reducing uncertainties of the microrobot dynamic model, providing a better prediction for both design and control applications. The proposed microrobot is driven by a piezoelectric actuator mounted between centers of two legs. One of important issues in modeling of microrobots is to determine the friction force between robot and... 

Three-dimensional porous scaffolds are essential in tissue engineering applications. One of the most conventional methods to form porosity in scaffolds is freeze-drying, which is not energy efficient and cost effective. Therefore in this work, it was experimentally investigated whether gelatin, with its unique mechanical properties and cell binding applications, could be used as a comprising polymer of scaffolds with porous structure made by the freeze-gelation method. Chitosan, gelatin and chitosan/gelatin scaffolds were fabricated by the freeze-gelation method and their behaviors, determined by analysis of scanning electron microscopy images, Fourier transform infrared spectroscopy,... 

In synchros and resolvers, brushes, and slip-rings produce a lot of noise in the output signal. Compared to encoders, the application of such position sensors in precision control systems is restricted because of their low accuracy. In this paper, a novel scheme of a brushless synchro is introduced. In this scheme, the primary and secondary windings are mounted on the stator, and the stator magnetic flux passes a certain path in the rotor with inducing voltage in the secondary winding. In this paper, a software method based on simple look-up table is used to enhance accuracy and reliability of the output signal of the proposed synchro. The operation principle of the brushless synchro is... 

A series of samples with different compositions and parameters were welded together. The alloys were based on Ni-8Al-8Cr-l.5Mo-0.01B %wt composition with Zr additions of 1 and 3 %wt. Crack-free full-penetration welds of castable nickel aluminide alloy were performed using autogenous GTAW technique. It was found that Ni-Ni5Zr eutectic was associated with solidification cracks. Alloys were fully dendritic and also, weld metal consisted of columnar and axial dendrites beside the fusion line and in the middle, respectively. Optical and scanning electron microscopy (SEM) techniques were employed to characterize the composition as well as the weld structure. X-Ray diffraction was utilized to...