Sharif Digital Repository

In atmospheric studies, chemical transport models are formulated to simulate the spatial and temporal distribution of pollutant concentrations. However, the performance of these models is strongly dependent on the input parameters such as emissions. Inverse modeling is a widely used mathematical approach for estimating model parameters by minimizing the discrepancy between model output and observations. For air quality studies, inverse modeling is often used for emission inversion as emissions are associated with significant amount of uncertainties.This research aims to estimate optimal values for anthropogenic PM2.5 emission through a four-dimensional variational (4D-Var) inverse modeling... 

Complex systems involve a large number of degrees of freedom and consist of many components. Interactions of these components with each other, or with an external force, play a significant role in the collective behavior of the complex system.We come across complex systems in many different fields of study including neuroscience, climatology, studying stock markets, etc. The non-linearity of the interactions between their components is what they have in common. Interesting macro-scale properties can be observed in a complex system, as a result of the collective behavior of the system components. We usually focus on studying a group of components in a system, rather than a single component,... 

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... 

Knowledge of the properties of aerosols is of great importance in aerosol science. To gain a better understanding of particle properties, behaviors and dynamics, measurement capabilities are crucial and inevitable. The most critical steps in the aerosol size measurements based on electrical techniques are the processes of particle charging and neutralizing. Corona discharge is a paramount method among all aerosol charging methods because of highest concentration of produced ions, which is essential for the efficient particle charging, based on diffusion and field charging mechanisms. The only known method, which could be applied to provide required conditions for these two charging... 

Fracture reservoir modeling is an important subject since a lot of oil and gas resources around the world are preserved in them. One of the enhanced oil recovery methods in these reservoirs is gas injection and especially CO2 injection because of environmental issues. In one part of this research, a new diffusion mechanism called “double cross-phase diffusion” is introduced and applied to simulate the non-equilibrium gas injection process into fractured rocks. This new mechanism represents additional multicomponent gas diffusion into the crude oil through the water phase, existing in porous media as initial water saturation. Therefore, a lab-scale simulator, by implementing the generalized... 

People use social networks to share millions of stories every day, but these stories rarely become viral. Can we estimate the probability that a story becomes a u/rof cascade? If so, can we find a set of users that are more likely to trigger viral cascades? There are many factors influenced the message virality. In this thesis, we investigate the effect of graph structure, diffusion pattern as well as the message text on virality measure. Finally, the authors solve both source localization and inferring COVID-19 network via propsed methods.First, the authors investigate probability estimation and maximization of cascade virality. In this section, we develop an efficient viral cascade... 

In this study, at first the V2O5 spent catalysts were characterized. The aim was to identifying whether these catalyst may be regenerated. Then, for feasibility study of them, three methods were applied: washing, diffusion and milling the spent catalysts for their subsequent reproduction. A variety of techniques such as XRD, XRF, AAS, TPR and TPO were applied in order to identify factors contributing in vanadium pentoxide catalysts deactivation. The results showed that approximately all of pollutants caused their performance deterioration, while they still have some active phases. Then, the polluted catalysts were washed (their yield increased from 43% to 72.2%). In the underside of the... 

Cleanrooms have been widely used in many industries. The main goal in designing a clean space is to control the level of particles concentration. As a result, introduction, generation, and retention of airborne particles inside the environment need to be minimized. In this research, the effects of main parameters on the generation and deposition of particles through cleanrooms have been numerically investigated. At first, the role of geometric features of swirl diffusers on the induction effect and the resultant air mixing has been evaluated. Using parametric study approach, the diffuser geometry has been optimized and sensitivity of its optimum features to the airflow rate has been... 

In this research project, Ni electrodeposition process has been modeled by a 3D coupled continuum-kinetic Monte Carlo simulation. Kinetic Monte Carlo module processes surface reactions along the substrate using electrochemical equations for the relating events. Continuum model also determines concentration of the whole system according to a 3D interpretation of diffusion law in solutions. After running each module, exchange of data between two codes is done and boundary conditions are updated. In fact, the whole simulation time is divided by small time steps relating to time fastest reactions need to proceed. Present model will generate three outputs: current-time curve, surface morphology... 

Major parts of Iran's oil reservoirs are fractured carbonates, which need time to produce oil due to their much lower permeability than sandstone reservoirs. Molecular diffusion mechanism is an efficient mechanism in oil recovery from fractured reservoirs under gas injection conditions. The main subject of this work is to investigate the role of molecular diffusion mechanism in the non-equilibrium gas injection project and its role in increasing the oil recovery rate in two southern fractured reservoirs located in the west of Iran, taking into account the capillary pressure, as well as the change of interfacial tension closely miscible conditions is also investigated through simulation. The... 

In this thesis, we attempt to construct a model that can predict whether someone will retweet a tweet. For this purpose, we construct a machine learning model and we use Twitter’s network features as our model’s input. We collect about 1300 random tweets and their retweets to make retweet cascades. By collecting or calculating users’ features in each retweet cascade, we construct our desired input data for our model. We test both random forest and neural networks as our machine learning section of the model. Random forest is the most accurate of the two models, predicting retweet actions with an accuracy of 0.89. Additionally, we find out that two features of the network have the greatest... 

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... 

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 production of oil is challenging in the fractured reservoirs due to the large transmissibility contrast between matrix and fracture, and primary recovery is often low. The recovery efficiency depends on the relationship between the fracture and matrix permeability, and is strongly dependent on the wettability of the matrix, which reflects the imbibition potential of the reservoir. Among these parameters the multiphase fluid flow in gas invaded zone is the point of interest in this project. Gas injection in naturally fractured reservoirs maintains the reservoir pressure, and increases oil recovery primarily by gravity drainage and to a lesser extent by mass transfer between the flowing... 

gas injection method is one of the common methods of EOR, which has a long history. In gas injection, molecular entry gas mixing is the controlling factor of oil play. Therefore, the exact value of this coefficient becomes an important requirement for the simulation and modeling of oil reservoirs, which can only be determined by laboratory consumption methods. In this research, the pressure decay method is used as a common laboratory method to determine the penetration coefficient of methane, nitrogen and gas enriched with intermediate compounds in crude oil of one of Iran's oil reservoirs. In most of the available records in the investigation of the mentioned gas diffusion coefficient in... 

The aim of this study was to investigate the response of counter flow flames to acoustic excitations numerically. For this purpose, the one-dimensional and two-dimensional laminar counter flow flames are numerically simulated. Cantera is used to simulate the flame in one dimension. In order to consider the counter flow flame as one-dimensional, limiting assumptions are needed, and coding is also required to stimulate the flame acoustically. As a result, a two-dimensional field can be used to simulate a counter flow flame and its acoustic stimulation. This study used Ansys Fluent software to simulate a two-dimensional counterflow flame. Cold solutions without acoustic excitation are first... 

The purpose of this research is providing the preliminary study and designing, fabricating and installing diffuser vanes on the vaneless diffuser compressor to improve its overall performance. To meet the goal, the GT4082 turbocharger centrifugal compressor is chosen as the basis unit. The compressor is fully modeled, to predict the compressor performance curves. One dimensional and three dimensional models are provided, to simulate the compressor with vaneless diffuser as well as vaned diffuser. In one dimensional model, governing equations are continuity, energy, and state and also the empirical components losses coefficients of the compressor are used. In this method, fluid properties are... 

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... 

In this study, the performance of the Moss-Brooks semi-empirical model in estimating soot for six different diffusion flames with methane, ethylene, and kerosene fuels in laminar and turbulent regimes has been investigated. The results show that the model with the default constants in the laminar ethylene flame has relatively acceptable performance, but in the turbulent ethylene flame as well as the laminar and turbulent flames of methane, has a significant error. In this regard, inspired by past research and performing sensitivity analysis, the constants of oxidation and coagulation sub-models were reviewed and Improved. The results of soot volume fraction were evaluated for values of 0.015... 

Two phase flow through porous media is one of great interests which have been studied for decades in petroleum sciences and even other fields, e.g. hydrology and physics, to solve problems such as enhanced oil recovery, contaminated groundwater or CO2 sequestration projects. Flow in porous media typically predict by means of Darcy’ law which in two phase flow lead to equations such as Buckley-Leverett or Koval, but today it is well approved that compact prediction of flow pattern by these equations may be accompanied by enormous errors and it’s because flow in certain condition is fractal. In this work a new mechanistic model has been used for simulating of immiscible drainage process and...