Sharif Digital Repository

There is a class of small vertical take-off and landing flying vehicles that only have a dual coaxial engine on top and move based on the thrust vector control method. In this project in order to have better insight about the physical mechanism we are dealing with, a conceptual design of a prototype vehicle is first carried out. It is then followed by extraction of two and three dimensional dynamic models of the vehicle. By computer simulation and a simple dynamic analysis, the equations are verified and the movement of the aircraft is discussed for different flight phases  

Membrane bioreactors (MBRs) which are commonly understood as the combination of membrane filtration and biological treatment using activated sludge have several advantages, but membrane fouling reduces the membrane efficiency, permeability and lifetime. An alternative is replacing a moving bed biofilm reactor (MBBR) with the activated sludge system which may reduce the effect of membrane fouling. The sludge produced in MBBRs has poor settling characteristics, therefore, their efficiency is limited by the sedimentation tank performance and they require a larger settling surface. The combination of moving bed biofilm reactors and membrane bioreactors can compensate for the drawbacks of both of... 

In this text to find the answer of the question “ what is it to be physical” in a definition form or a scheme of the term physical, firstly we sought for a possible consensus among recent physicists and philosophers. But from their answers not only we did not find any clear consensus but also most of them confess that the term is ambiguous and unclear. In a general aspect, we can categorize the answers to two theoretical and realistic perspective. The theoretical perspective, beside circularity and Hempel’s triviality, seems not to present any criteria for being physical. In realistic perspective, it seems that there is no ontologic constraint for being physical, that is from “being... 

Rotor contact with a stationary element of a rotating machine and the subsequent rubbing at the contact area is a serious malfunction that may lead to the machine’s catastrophic failure. In the past decades, many studies have been done on the rubbing phenomena, its different regimes and its various consequences on the machine performance and safety. However, most of them have used a simple model to investigate the rubbing interaction between the rotor and the stator. This simple model consists of the Jeffcott rotor, as a model for the real rotors, and a rigid annular block surrounding the rotor, as a model for the real stators. The objective of this thesis is to build an algorithm to... 

Complex networks serve as generic models for many social, technological and biological systems that have been shown to share a number of common structural properties such as power-law degree distribution and small-worldness. These networks determine interactions and influence the spread of diseases, behaviours and ideas. Epidemics and failures like new behaviours ideas and innovations can spread throughout a network and prevent it from doing its functionalities. In this work, we investigate error and attack tolerance of epidemic spreading in complex networks. The main content of this thesis is arranged in three sections as follows: Firstly, the effect of random and systematic failures is... 

This thesis addresses the problem of dynamic security assessment in power sys-tems with an emphasis on its application in restructured power systems and issues arising in its applications. The new electric utility environment has an immedi-ate consequence of emphasis on reliability and secure operation of power systems. This requires faster and more precise methods to assess the dynamic aspect of se-curity. On the other hand, this issue is becoming challenging when the determined dispatch might not be accommodated due to violation of the limits.This thesis addresses the problem of dynamic security assessment in power sys-tems with an emphasis on its application in restructured power systems... 

Are the returns of the mineral companies in Tehran Stock Exchange affected by the changes in the commodity price at the Iran Mercantile Exchange? By implementing a Multi-Factor Model we will calculate the firms’ value elasticity to the commodity price changes. We try to explain the estimated elasticities on the basis of the firm’s fundamental variables using a discounted cash flow valuation model. An unbalanced panel data estimation is employed for this purpose. Afterwards, we will suggest a novel model on the ground of the assumption that the commodity prices and firm values follow the Geometric Brownian Motion. The result of the model is that the elasticity can be explained by commodity... 

The application of membranes for separate of particles in mainly microbial flacs , are fast growing in biological treatment systems. Membrane bioreactors are now considered as one of the major new processes in wastewater treatment. However , membranes are expensive and costly. This study is carried out to test an innovative , locally made filters for separation of flocs in an MBBR reactor. This innovative filter is replacing a traditional settling tank. This type of filters is made very cheaply and has important advantages in installing and operation. Experiments were carried out in a laboratory scale MBBR unit. A filter unit consisting of 3 innovative filter tubes were placed and the... 

Recommender systems are in the center of network science and are becoming increasingly important in individual business for providing efficient personalized services and products to users. The focus of previous research in the field of recommendation systems were on improving the accuracy of the system through designing more accurate recommendation lists. Recently, the community has been paying attention to diversity and novelty of recommendation list as key characteristics of modern recommender systems. In many cases, novelty and precision do not go in the same direction and the accuracy-novelty dilemma is one of the challenging problems in recommender systems, which needs efforts in... 

With the over-increasing growth of the information provided for the web users, from content providing systems and web stores to social networks, the exictence of recommender systems is strongly needed. Recommender systems personalize web for the users and help them with finding relevent information in the huge era of World Wide Web. Collaborative filtering methods are known as the most successful and vastly used recommendation systems. Although they generally outperform content-based algorithms, in cold-start situation and especially in the presence of the new items, they fail to predict ratings for the new items or make good recommendations. This problem is not negligible in the systems... 

Eutrophication and algae growth is one of the consequences of high concentration of nutrients in surface water bodies; therefore, both phosphorus and nitrogen existing in wastewater or at least one of them should be decreased to a standard amount before entering water to rivers. This can prevent eutrophication and detriment to the ecosystem of rivers. An investigation on both biological and chemical phosphorus and carbon removal in low loading rate influent ( below 100) has been carried out in this research. Investigated topics includes aerobic COD removal in IFAS reactor, comparison of biological nutrient removal to the combination of chemical and biological method, effect of the order of... 

Natural gas power plant installed in power system as rapid start unit. In the recent decades, with increasing in the number of gas generating units in the world, consideration of natural gas transmission network in optimal solution of security-constrained unit commitment (SCUC) become a non-negligible problem. The gas transmission grid constraints integrated into the scheduling of thermal units in the proposed model for minimizes power system operating cost. In a power plant transmission of natural gas to power plant is very important because congestion in natural gas pipeline increases. This model could consider natural gas storage tank in gas transmission network as decision variable.... 

In this thesis, we first explain how we can construct three-point amplitudes for both massive and massless particles by solely knowing the Lorentz invariance and spin or helicity of particles. Then, using BCFW recursion relation, we determine the tree-level amplitudes. To calculate the loop amplitude, we apply the unitarity of Smatrix.The unitarity relates the tree-level amplitudes to loop level. Finally, I discuss some exciting topics in this field, including color-kinematics duality, some relevant applications of contemporary S-matrix theory in effective field theories  

This study investigates the effect of commodity price shock, including oil and base metals prices, on Tehran exchange and industries stock returns. These industries have the largest market share in Tehran exchange and may heavily depend on global prices. Using weekly data from 1387 to 1396, Multifactor and VAR models are performed to analyze the variance decomposition and impulse response function of each industry to 1% price shock. In addition to global prices, some macroeconomic factors that are likely to affect stock returns are considered. The results show that commodities price shocks have dynamic and significant effects on stock returns  

With the rise of the concept of “Big Data”, both data volumes and data processing time increased, imposing the need for new methods of processing and computation of said data.Analytical and computational methods in Machine Learning are some of the most important applications of Big Data processing. There exist many methods of data analysis in the Machine Learning field, each requiring extensive processing on Big Data. One of the methods for working with Big Data is Distributed Systems. MapReduce is one of the most popular methods distributed computation by increasing the ease and speed of distributed processing of big data. But a number of bottlenecks have been discovered in MapReduce which... 

During years, supersymmetry has been a candidate for resolution of Higgs mass fine-tuning problem that is quadratic dependence of scalar mass radiative correction to UV-physics. So, supersymmetry phenomenology is of great importance. As accelerators have reached energy of 13 TeV in recent years and sparticles have not yet been observed, it is important to have a theory in hand, describing SUSY breaking dynamics with scale of SUSY breaking above the energies currently accessible to accelerators. As a result of mass-sum-rule constraint which holds in theories with spontaneous SUSY breaking at tree level and leads to light sparticles and even tachyonic directions, there are currently no... 

Although electronic banking service has been introduced in Iran for more than a decade، today half of the people who go to the physical bank branches are the ones can do their affairs via e-banking. The banks’ managers attribute the main reason for these unnecessary travels to insufficient trust towards e-banking systems. One of the important tools in this regard is mobile banking which is prevailing around the world، however it has not prevailed enough in Iran. This research has tried to investigate the cognitive and non-cognitive dimensions of trust to mobile banking. The data for this research has been collected from users of mobile bank service who have filled the online research... 

Massive MIMO is a key enabling technology in the fifth generation (5G) wireless communication systems. In this technology, the base station is equipped with a large number of antennas (e.g. 100-200) and communicates with a relatively smaller number of user terminals. The large number of antennas at the base station, on one hand, has enabled unprecedented improvements in data rate and energy-efficiency, while on the other hand has posed challenges on the practical deployment of this technology.One of these challenges, is the high computational complexity of the baseband processing algorithms, such as precoding, due to the large number of antennas. In this research, we propose a novel ZF...