Sharif Digital Repository

Metal matrix composites (MMCs) reinforced with ceramic particulates have been attractive as high specific strength materials utilized in automobile and aerospace industries. In order to enhance refinement and dispersibility of the ceramic particulates, the synthesis process with in-situ reactions has been investigated. The in-situ synthesis can avoid complexity and harmfulness.processes of powder handling and produce fine inclusions in the matrix with rather lower costs than conventional fabrication methods. In this study, the Al-based composites with TiC, TiB2 and Al2O3 particulates have been prepared by the by mechanically activated self-propagating high-temperature synthesis (MASHS) on... 

Ground squeezing is defined as time-dependent shear displacement of rock mass that causes the decrease of the calculated excavation area of tunnels.Ground squeezing is one of the phenomenons that causes serious problems including the collapse of tunnels’ walls and TBM jamming during the construction of tunnels. Hence, the assessment of ground squeezing is an essential issue in tunneling. In this thesis, different ground squeezing potential prediction methods will be assessed. These methods consist of empirical, semi-emperical, analytical, and numerical methods. After assessing the ground squeezing potential, if it is evaluated high for a project, it will be required to consider the... 

In this research, for the first time in the literature of this field, indirect social pressure applied by text message campaign is used. The findings of this research can help the blood transfusion organization (IBTO) to send more optimal text messages. The advantage of indirect social pressure is lower cost while allowing for faster and wider use. Also, text message blood donation campaigns are more homogeneous than peer to peer pressure to motivate people to donate blood. For times when there is a severe shortage of blood resources, such campaigns can be very helpful. The method of causal identification in this research is the use of a randomized controlled trial. In this experiment,... 

This thesis aims to provide a method to obtain the radial dynamic properties of rolling element bearing, including stiffness and damping by experimental test methods. Methods such as modal test, vibration test, and static tests were known as experimental methods to obtain these properties, and in this research, all three of these methods were used to obtain these properties. After studying the theoretical relations governing the stiffness coefficients of the bearings, a test bed platform was designed and built to conduct the tests After the construction of this platform, the test design stage was reached done and different parameters changed during these tests several tests were it is noted... 

First atomistic simulation was used to study the deformation and fracture mechanisms of Ni-Si interfaces under tensile and shear loads dependent on the crystal structure of interface zone. Modified embedded atom method (MEAM) potential was utilized for molecular dynamics (MD) modeling. The simulation includes analysis of common neighbors, coordination number, least-square atomic local strain, and radial distribution function. The profound effect of interface crystallography on the tensile and shear deformation is shown. The highest tensile strength is obtained for interfaces with high plane density due to lowest atomic disorder while under shear loading planes with low density exhibit a high... 

The emerging field of compressed sensing deals with the techniques of combining the two blocks of sampling and compression into a single unit without compromising the performance. Clearly, this is not feasible for any general signal; however, if we restrict the signal to be sparse, it becomes possible. There are two main challenges in compressed sensing, namely the sampling process and the reconstruction methods. In this thesis, we will focus only on the deterministic sampling process as opposed to the random sampling. The sampling methods discussed in the literature are mainly linear, i.e., a matrix is used as the sampling operator. Here, we first consider linear sampling methods and...