Sharif Digital Repository

After school tutoring education is a concept that varies widely between countries. Evidence suggests that one of the factors explaining this difference is the existence of competitive tests. There is also evidence for Iran that, because of the existence of competitive test of the national entrance exam, a large percentage of Iranian families use after school tutoring to their children get a successful result in this exam. But the question is how much after school tutoring is effective? The answer to this question is important because if after school tutoring is effective, low-income families are expected to be unable to provide such training, and the national entrance exam will prevent... 

This study was conducted to investigate a theoretical and experimental two-dimensional model of a floating fish cage in regular waves and uniform current. Due to the inefficiency of computational fluid dynamics (CFD) in solving such problems, developing a simple model to predict the results is highly advantageous. In this study, a simple mass-spring model was developed to simulate the problem. After validating the results of this simple model through a series of model tests in a wave tank, it was further utilized to extract additional results. Experiments were conducted at six different wave heights and four current velocities. In all experiments, wave steepness was maintained at a ratio of... 

In this work, the effect of chemical composition on structural, mechanical, electrical and magnetic properties of nanocrystalline Finemet-type alloys with the composition of Fe73.5Si13.5B9Nb3Cu1 , Fe77Si11B9Nb2.4Cu0.6 and (〖Fe_0.5 Co_0.5)〗_77 Si_11 B_9 Nb_2.4 Cu_(0.6 )was investigated. The samples were prepared by vacuum arc melting of high purity constitution in order to obtain a nanocrystalline structure. The amorphous ribbons were then annealed under vacuum with the same conditions of temperatures and time to compare their properties. The structural and thermal properties of the samples were analyzed using various techniques such as X-ray Diffraction (XRD) and Differential Scanning... 

A numerical algorithm is proposed to design microstructure of a two-phase functionally graded material under dynamic loading. In order to direct energy propagation through the desired regions in the domain, we introduced a regularized Heaviside function, H(x), in our objective functional, namely the time-averaged sum of the elastic strain energy and the kinetic energy. Real-life systems are however, not undamped, but possess some kind of energy dissipation mechanism or damping. In order to apply modal analysis of undamped systems to damped systems, we use Rayleigh damping model in our formulations. To generate a well-posed topology optimization, we used homogenization via a solid isotropic... 

Due to its biodegradability, magnesium can be a good option for making degradable medical implants that disappear in the body over time and thus there would be no need for secondary surgery. However, high rate of corrosion of magnesium in the body environment and low formability at room temperature are the two main problems of magnesium, which lead to rapid destruction of the sample in a short time and serious problems. For these reasons, much research is currently being done to improve the corrosion behavior and mechanical properties of magnesium alloys through microstructure modification. In this regard, special attention has been paid to Mg-Li alloys as the lightest magnesium alloys. The... 

In the past decade, with the expansion of e-commerce, there has been an unprecedented growth in demand for online retailing. Due to this growth, fast, efficient, and flawless delivery of shipments to final customers has become especially important. On the other hand, the expansion of urbanization and the increase in urban traffic have also created obstacles to efficient delivery. These factors have introduced new challenges for logistics service provider companies. Several innovations have been proposed in recent years to address these problems. Delivery of goods to locations such as the trunk-in-car or shared delivery locations like lockers is one of the key innovations in solving logistics... 

Enzyme-powered motors self-propel through the catalysis of biofuels, which makes them excellent candidates for biomedical applications. However, fundamental issues such as their movement in biological fluids and understanding the mechanism of propulsion are important aspects that must be considered before application in biomedicine. Building active systems based on biocompatible materials that use non-toxic fuels to power their vehicles have always been challenging. In this study, self-propelled micromotors consist of titanium dioxide black spheres asymmetrically coated with a thin layer of gold. Cysteine was used to bind urease enzyme due to thiol binding. By biocatalytically converting...