Sharif Digital Repository

Presence of emergent vegetation can change the governing forces in flow through such systems and affects the turbulence structure and scalar transport. On the other hand, vertical variation of physical characteristics of stems, which is fairly observed in reality, leads to variation in frontal area and the called vertical density difference. In this study we experimentally investigate the effect of vertical density difference on both flow and vertical transport of mass. The results will be compared with theoretical predictions.
Using rigid emergent model of cylinders as stems with step density variation in depth I simmulate field conditions considering actual variation of frontal area.... 

In this work, the unsteady response of a laminar diffusion flame to harmonic mass fraction oscillations and also to flow velocity fluctuations is investigated. Flame-sheet assumption is utilized to model the laminar unsteady two-dimensional co-flow diffusion flame mathematically. The initial combustion of most combustion chambers is through diffusion mechanism. Therefore, developing analytical model of diffusion combustion is of great importance. The flow is assumed subsonic (incompressible), inviscid, and uniform. The convection-diffusion equation for conserved scalar variable with appropriate boundary conditions is solved. Considering stoichiometric mass fraction surface to be the flame... 

In the present study, the axisymmetric liquid gas/air diffusion flame in the presence of fuel concentration oscillations and velocity perturbations has been investigated experimentally. Several industrial combustions take a place by diffusion mechanism which necessitate scientists to make far better understanding of diffusion flames. In order to study diffusion flames, the instrument with two separated lines of fuel and air has been developed. Nitrogen is used for fuel dilution oscillatory with pulse of 1, 2, and 4 Hz frequencies. The pulse duration effects on flame structure are also studied. The flame shape has been captured by high speed camera and the results are processed by image... 

The tissue characteristics are important for all kinds of medical laser applications in order to understand the interaction mechanisms between light and tissue. Knowledge about light transport in tissue is essential for cancer treatment and cancer diagnostic techniques. By having the diffused reflectance of a tissue we can determine its optical characteristics. In this thesis we have solved the inverse process. That is, we compute the diffused reflectance of a turbid media with pre-determined optical parameters. This problem can be solved using two methods: Monte Carlo simulation and diffusion method. Since Monte Carlo simulation is computationally very expensive, it is not used in medical... 

Numerical analysis method improvement is a topic of interest among all engineering disciplines. Regarding the fact that our ability to predict the behavior of a physical system is often limited by our computational resources, the efficiency of the employed numerical method is an important factor in the degree of approximation used in modeling. One of the recent numerical methods is the Cell Method (CM), which is also known as the Direct Discrete Method (DDM). This method combines some features of a variety of methods, especially finite volume and finite element, and gains some insight from the graph theory used in network analysis. The result is a method in which the set of equations which... 

In this study, transient diffusion of drug into the intervertebral disc is considered. The amount of Diffused drug from the blood into the intervertebral disc of dog is measured and concentration of drug is calculated for each region of the intervertebral disc including nucleus pulpous, inner annulus fibroses and outer annulus fibroses. Using finite element method, it is shown that the amount of drug diffusion into the intervertebral disc is affected by some parameters such as the type of drug, dose if drug and endplate calcification. This research is done in two parts: In first part, diffusion of drug (sulphate) into the dog intervertebral disc is investigated to compare the obtained... 

Releasing radioactive materials in atmosphere and their damages on human health via emitting radioactivity, show the necessity of investigations on their behavior. To simulate behavior of radioactive materials in atmosphere, we use Gaussian plume model. Gaussian model as a mathematical tool can simulate diffusion of Gaseous matters. This model also can be employed for radioactive materials. Radioactive materials vanish by decaying and can be produced via decaying of their mothers! Therefore, later effect must be considered in the Gaussian model via a factor. Many factors like wind speed and weather conditions also are involved in diffusion of radioactive materials. By considering all of... 

The modern science of networks helps us to have a better understanding of complex systems. Networked systems can be found everywhere and many systems can be represented by a complex network. A networked structure consists of a number of nodes and links connecting to them. Networks’ ability in information propagation is one of their amazing features that have attracted lots of scholars to work on. It has potential applications in many fields ranging from marketing to biology, epidemiology and sociology. Information propagation studies how information such as computer viruses, contagion, rumor, or new product’s interest propagates over a network. Percolation theory and various epidemic models... 

In this essay, by putting in the framework of linear-quadratic optimal control (LQ),we study and solve the mean-variance portfolio selection problem. Two models will be studied in our work; in one we assume that the price process satisfies a diffusion stochastic differential equation, while in the second model, we assume it to satisfy a jump-diffusion stochastic differential equation. In both models, a formula for the efficient frontier is obtained. This essay is mainly obtained from the works of the following articles and books:
1)X.Y. Zhou and D. Li, Continuous-Time Mean-Variance Portfolio Selection:A Stochastic LQ Framework. Applied Mathematics and Optimization. 42(2000),... 

Opinion formation is one of the major topics in social networks analysis and mining. A number of methods have been introduced for describing and simulating this phenomenon. In this thesis, we proposed a novel optimization framework based on an opinion formation model that used the Deffuant’s model with some changes in neighbors’ selection policy. Its efficiency was compared with a number of benchmark optimization methods including genetic algorithms, differential evolution and particle swarm optimization.The proposed model demonstrated better performance than the others.In the proposed, each person changes his opinion based on one of his neighbors who has the best performance in terms of the... 

Nowadays, vegetations have an important role in protecting ecological systems. One of the impacts of vegetation in water system is pollution diffusion. The physical characteristics of plants, affect how vegetation influence the diffusion phenomenon. Plants’ flexibility may change the drag force and pollution diffusion. Also density variations of vegetation in depths have important affects on flow characteristics.
In this study we investigate experimentally the affects of flexible vegetations and their density changes in depths on vertical mass transport. Thus the current flume has modeled for crossing flow through the plants. To model the steep plants, inclined rigid cylinders have been... 

Magnetic resonance imaging is one of non-invasive methods to measure the hemodynamic and morphologic parameters of tissues, especially brain tissues. Hemodynamic parameters monitoring in brain tissue is of significant importance in many majors such as detection of tumor occurrence, brain abnormalities, and track of treatment procedures. Blood is a suspension, comprised of plasma, red blood cells, white blood cells, platelet, etc. Plasma is a Newtonian fluid which is composed of proteins and has a constant viscosity in body temperature. Rheological properties of blood are highly dependent on mechanical and rheological properties of its cells and this dependence is multiplied in narrow vessels... 

The diffusion process propagates information, viruses, ideas, innovations and new be-haviours over social networks. Adopting a new behaviour, which is mentioned as an in-fection, starts from a little group of people. Spreading it over more neighbors and friendscan result in an epidemic phenomenon over the network. As this infection propagates, aninformation cascade will be generated. The spread of information cascades over social net-works forms the diffusion networks. Although observing the infection time of a person ispossible, determining the source of infection is usually a difficult problem. Additionally, inmany applications we can not observe the underlying network which diffusion... 

Information cascade or affection in a broad social network is introduced as a dynamic epidemic phenomenon in the society. As people notify a new innovation, technology, or hobby, they try to share it with their friends, colleges or neighbors. Till now most of the cascade models are presented for unsigned network, in which all links have the same sign (such as friends and trusted networks). In these networks cascade is independent of the edge sign. But in reality signed networks are as common as simple networks. Thus, in this thesis, we study information cascade in networks with positive and negative edges. We link the cascade size to community structure of signed networks; communities are... 

Nowadays, Online Social Networks (OSNs) play an important role in the exchange of information among people. Some previous studies indicate that diffusion behavior and network structure are tightly related. Community structure is one of the most important features of OSNs. Access to the whole network topology is the necessary and prevalent requirement for most of community detection methods, so the limited access to full or partial topology can decrease their accuracy. Using traceable information over diffusion network is a solution to surmount this difficulty. In this work, we are concerned with the community detection by only using the diffusion information, while unlike the previous... 

The fundamental goal of communication networks is to transfer messages across the network between the nodes. Often, maximizing the information flow which is limited by connectivity of the network could be interesting. The concept of connectivity is divided into edge and vertex connectivity. If our focus were on the vertex-connectivity, connected dominating sets (CDS) could be a valuable tool. Obtaining (fractionally) vertex-disjoint connected dominating sets which are called fractional CDS packing presents a backbone to get an information flow matching the size of connectivity. In this thesis, we will present a distributed algorithm that is given a communication network with n nodes and... 

Recently, computer scientists and economists have defined many joint problems and cooperate widely in various areas. Importance of this interconnection is clear for everybody, now. New works have been conducted, nowadays, to use the daily - increasing web-based social networks in viral marketing for improving companies profits. The main problem which is proved to be NP-Complete in this context is about discovering k most influential nodes in a network. In this dissertation, we generalize the problem to a group-based version and we we use group-based advertising to achieve our main goal. A new algorithm called Group-Based Diffusion technique is proposed in this thesis for solving this problem... 

In the present study the production of ferrite-martensite dual-phase (DP) Steel was investigated during the bonding process by transient liquid phase method. The effect of martensite morphologies on mechanical properties of bonding zone were also studied. To make the bonding process and DP steel production heat treatment cycle simultaneously, the step in which the isothermal solidification completed, bonding process, was done simultaneously with austenitising of the steel. Homogenizing of the bond zone, was also done with DP steel making at the intercritical temperature. The St52 steel was utilized for producing DP steel and for bonding process, iron base interlayer with melting point of... 

This research studies a 3D channeled myocardium scaffold with computational fluid dynamics. It proposes a mathematical model to evaluate the impact of oxygen carriers and scaffold geometry on cell growth in a 3D cardiac construct. The modeling results show that using 5.4% perfluorocarbon oxygen carrier (PFC) has increased cardiac cells density 15% of the initial seeded cells comparing to pure culture medium without PFC supplementation. Effects of the scaffold geometry on cell density in the construct were examined by increasing channel numbers and changing the construct length. The results show that increasing channel numbers (by 50% decreasing channels diameter and wall to wall spacing) the... 

Phase change and deposition of solid particles in liquid flows are undesirable in industrial and natural processes and hazardous in some cases. Considering the intentions to petroleum exploration in deep waters such as Caspian Sea, the Gulf of Mexico and North Sea, precipitation and deposition of wax crystals in petroleum and gas pipelines is a real concern due to the fact that during production, oil is exposed to more intense temperature gradient (the dominant mechanism in wax deposition) and its heavier components change their phase to solid and deposit. Wax deposition in production lines starting at crude oil storage tanks is not accepted due to reduction in production rate and...