Sharif Digital Repository

Multiphase flows in porous media hold significant importance in industrial processes and natural phenomena, being related to topics such as hydrocarbon recovery, groundwater flow, catalysts, and fuel cells. In recent decades, numerous experimental methods have been employed to study these issues, enabling the observation of dynamic interface behavior on a large scale, although accurately describing fluid flow details at the pore scale remains challenging. Laboratory studies using micromodels can predict the fingering patterns and their initial growth but do not provide useful information about the evolution and growth of fingering in later stages. Numerical simulators can complement... 

Because of severe weather events (such as floods and storms), transportation infrastructures are directly and indirectly damaged, which may cause many undesirable economic and social losses for people and cities. Among various severe events, flood is known as an important factor in the breakdown (closure of roads and bridges) of the components of the transportation network. Evaluating the performance of the city's road transport network against flood events leads to a better understanding of the network's condition and allows decision-makers to identify the weaknesses in the system and reduce potential damages as much as possible. In this research, with the aim of investigating the... 

During the last six decades, there were remarkable developments in the field of gas turbines. In the early 1950’s, the effciency of gas turbines was 20% and it is improved up to more than 40% for modern gas turbines. In addition, due to the implementation of the combined power cycles, the thermal effciency have been reached to 60%. According to the recent developments, further improvements in this field seem to be more costly and diffcult to obtain. Rotating detonation combustor (RDC) is a new generation of detonation combustors which has simpler design and several advantages compared to jet engine combustors, but it has its intrinsic problems which seem resolvable. Given that the RDC... 

A significant large amount of modern SOCs is occupied by SRAMs. Nowadays more than 70% of the Microprocessor area is occupied by SRAMs. The fast growth of battery-operated portable applications has compelled the SRAM designers to consider subthreshold operation as a viable choice to reduce the power consumption. In most such applications, the speed of the SRAM is not the challenging parameter therefore the thrust toward low power design influence the design choices in various parts of the SRAM architecture. With technology scaling to the nanometer, Bitline leakage current and offset voltage deteriorate SRAM reading performance since SRAM cell current is close to the Bitline leakage current.... 

After introducing “Prosopect Theory” by Kahneman and Tversky in 1979, it is mostly used as an alternative to expected utility theory in order to study human decision making under risky situatutions. Loss aversion has been considered as an important aspect of this theory. In this study, we review loss aversion and the effects of education and gender on it. Finally, we study the effect of repeating a gamble on its participants’ loss aversions. The results show that education and gender have direct effects on loss aversion and repeating a gamble can decrease loss aversion of participants.

 

Spam filtering is one of the large scale applications of machine learning. Much research has been carried out in the machine learning field with regards to spam filtering. Most of this work falls in the areas of batch learning or offline incremental learning. In batch learning, the learning process is carried out once on all the learning data. In applications such as spam filtering, in which the learning data is large in comparison to memory resources and data is generated in a stream, using incremental learning is required, in which the learning phase is repeated periodically. In each learning iteration of an offline incremental learning algorithm, a new set of data is learnt by the... 

The spherical ensemble is a well-studied determinantal process with a fixed number of points on the sphere. The points of this process correspond to the generalized eigenvalues of two appropriately chosen random matrices, mapped to the surface of the sphere by stereographic projection. This model can be considered as a spherical analogue for other random matrix models on the unit circle and complex plane such as the circular unitary ensemble or the Ginibre ensemble, and is one of the most natural constructions of a (statistically) rotation invariant point process with repelling property on the sphere. In this dissertation we study the spherical ensemble and its local repelling property by... 

With the development of science and industry increasingly need for seamless and high-strength rings, the attention of many researchers and industrialists paid on the ring rolling process. Then, Studying details of ring rolling process is very important. The most important issues in ring rolling process which are not sufficiently considered are: stress components distribution in ring, real amounts of friction coefficient, pressure distribution over the rollers, required power, required torque and force, and finally the minimum thickness of the ring during the process, all of these parameters have developed as analytical functions. In the present study, the minimum possible thickness of the... 

Investors are looking for profit making oppurtunities and using them to maximize their wealth. For investing in stock exchange, investors should be able to valuate the stock price rationally, so that he/she can define which stocks are trading below their intrinsic value. Stock price is the discount of future dividends of stock, but for discounting accurate rate is needed. Main goal of this study is presenting a way to calculate the proper discount rate or expected rate of return for investors. Method which has been studied in this thesis is “Fama & French five factor asset pricing model” which has been publish 2015 (Fama & French, 2015). The model concentrates on five factors to describe the... 

In this research, we consider a made-to-order production system which receives orders for a single product. The demand is stochastic and price-dependent. We also consider a sale index that links the demand of each period to the demands as well as to the quality of the previous periods. The variety of quality levels and its effect on the amount of orders make this revenue management complicated. Furthermore, the price of each product is related to its quality and sales index. Furthermore, reference price causes the model to be significantly more complicated. We model the problem within the framework of dynamic programming approach to maximize the discounted profit of the firm during a... 

In this study, the steps for designing an intelligent network for the Urban Air Mobility transportation system is proposed, and these steps are implemented for the city of Los Angeles as a case study, which is one of the busiest and most populous cities in the world.. Initially, the demand and its distribution in the study area is estimated; Then, according to the distribution of demand and existing infrastructure, the optimal location of stations are determined; afterwards, considering a well-designed electric vertical take-off and landing aircraft called Spricho the network is simulated, its performance and quality are examined and the optimal combination of the number of planes and the... 

Pipe freezing has become well established in industry as a method of short-termisolation in order to carry out maintenance or repairs. It is often necessary to repair system components without plant shutdown or drainage of system having many piping structures which may have hazardous or expensive fluid. Therefore, a series of tests has been arranged to investigate the ice plug formation in two standard pipes with different diameter size. The freeze zone on the pipe has been created by means of an aluminum jacket which liquid nitrogen flows in it. In the tests the freezing time, amount of liquid nitrogen usage andthe pressure tolerance of ice plug have been determined. Moreover, the numerical... 

In recent years, the area of research on micro flying robots has been developed due to the development in micro manufacturing technologies. Due to extra advantages of these flying robots, they are implemented in military and civilian missions such as identifying, espionage, aerial relays, traffic surveillance, rescue, aid, etc. Ability to fly in specified areas, without human injuries, low manufacturing and energy costs, easy and fast implementation, Easy Maintenance, etc, which are some advantages of these robots. We can control these robots manually by remote controllers (RC) or by Auto guidance systems. On the other hand, these robots are used in research laboratories for testing new... 

Range Profile (RP) is known as one of the most important tools for radar target recognition. The main problem with range profile for radar target recognition is its sensitivity to aspect angle. To overcome this problem, range profiles are assumed to have the same statistical characteristics in small frames of aspect angles or context dependent models such as HMM may be used. All methods presented, seems to have some shortcomings to offer a model based on physical circumstances of target maneuver. For example in such models, consecutive samples of RPs in an aspect frame are assumed to be statistically independent with the same distribution (IID). Here we propose dynamic system (DS) for... 

The present thesis aims at investigating the dynamic interaction of slosh and aeroelasticity in the fuel contained aero vehicles. The main approach in this research is to develop reduced order models for description of the coupled system. In this regard, boundary element method is used to develop slosh dynamic model. Axisymmetric boundary element method with non-symmetric boundary conditions is used to develop slosh dynamic model for axisymmetric containers. Zoning method is used to develop slosh dynamic model for the multi-baffled tanks and based on it, slosh equivalent mechanical model is developed for multi-baffled tanks. Finite element method along with modal technique is used to develop... 

There are numerous ways available to achieve low temperatures that cryocoolers might be among the most important of them. In the meantime, the pulse tube refrigerator has a special place due to its simple geometry and not be using any moving parts. This simple property make the pulse tube refrigerator one of the most popular methods to achieve low temperatures. Nowadays, a pulse tube refrigerator is used for cooling in the range of 4 to 123 Kelvin in two form of one-stage and two-stage and up to an approximate power of 1 KW. Today, due to the temperature and the amount of power required for cooling, as well as the time it takes to reach that temperature, this chiller is used in medical,... 

During the last few years, the study of urban environment structures is considered as a research field of interest in remote sensing. In satellite observations of the earth's surface, continuous imaging in terms of time and space has caused the remote sensing technique to be proposed as a useful and efficient tool for the analysis of urban areas. Obtaining quantitative spatial information from the urban environment in fields such as determining the height of buildings plays an essential role in urban planning, monitoring damage to buildings, establishing communication bases and digital cities. During the last two decades, the use of Tomosar approach in order to reconstruct the structures of... 

Gantry milling machines are one of the types of machine tools that have vast application in various industries. Considering requirements such as quality and roughness of work pieces which are becoming restricted day after day, it is necessary that various parts of this machine have sufficient functionality and precision so that it can fulfill the quality requirements; and production of these expensive machines be cost-effective. One of the most important parts of a gantry milling machines is its crossbeam that undergoes deflections when exposed to applied forces during work conditions and can have undesirable effect on work piece precision. Therefore, the goal of this research is to design... 

This research focuses on the topic of international portfolio diversification and its core attention is entitled to Middle East stock exchanges, as emergent markets. These markets are not analyzed yet as investment destinations for developed countries investors. Although all methodologies in this research are applied on ME markets data, but can be augmented and generalized for other markets. In this quest, we tried to investigate portfolio diversification opportunity for European (generally Frankfurt & Paris stock exchanges) or American investors with ME stock exchanges including Tehran, Istanbul, Saudi Arabia Tadawul, Abu Dhabi & Cairo stock exchanges, in order to reduce risk and increase...