Sharif Digital Repository

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... 

There are different approaches to the ideal closure of geodesic metric space with non-positive curvature in the sense of Busemann. We established relations between them with Andreev theorem. In this theorem we introduced a continuous surjection which coincides with identity mapping of Idx onto X. Due to we studied metric spaces, geodesics and their angles and also CATk domains. Then with asymptotic rays we introduced metric boundary and we produced compact metric space. Then we proved Andreev theorem with some theorems and lemmas. The Andreev theorem is correct for Alexandrov space. Finally we construct the counterexample showing that Busemann ideal closure can differ from the geodesic... 

Traditional methods for data classification only make use of the labeled data. However, in most of the applications, labeling the unlabeled data is expensive, time consuming and requires expert knowledge. To overcome these problems, Semi-supervised Learning (SSL) methods have become an area of recent research that aim to effectively addressing the problem of limited labeled data.One of the recently introduced SSL methods is the classification based on geometric structure of the data, namely the data manifold. In this approach unlabeled data is utilized to recover the underlying structure of the data. The common assumption is that despite of being represented in a high dimensional space, data... 

During the most recent years, investigating novel nanomaterials based on porous strucures has become an interesting field of research. Among these kinds of materials, mesoporous silica has extensive applications in catalysis, absorbants and biomedical engineering. By combining specific surface characteristics of mesoporous silica with magnetic properties of iron oxide nanoparticles, new nanocomposites owing unique properties, can be obtained. In the present research, magnetic mesoporous nanocomposite has been synthesized. Iron oxide nanoparticles were produced through reduction of water solution containing Fe2+/Fe3+ ions, followed by hydrothermal treatment of precipitan. Then, iron oxide... 

Given a snapshot of a network, link preditction methods try to infer future intractions be-tween its nodes. These methods may be used in either analyzing current state of the network or predicting future links of it. Link prediction techniques have many applications among which we can mention recommendation systems. These systems are implemented for com-mercial reasons or preventing user confusion in huge amount of information available.A new perspective toward link prediction is based on supervised random walk. In such methods, a random walker starts from a node in the network and randomly traverses to one of the current node’s neighbours with a probability proportional to the chosen link’s... 

In this work, we study spacelike surfaces in Minkowski space E3 1 foliated by pieces of circles that satisfy a linear Weingarten condition of type aH + bK=c, where a, b and c are constants and H and K denote the mean curvature and the Gauss curvature respectively. We show that such surfaces must be surfaces of revolution or surfaces with constant mean curvature H=0 or surfaces with constant Gauss curvature K=0  

Microbial electrolysis cell is a novel technology for hydrogen production. The biggest challenges for this new technology are low rate of hydrogen production and high investment cost.
In this research, catholite condition was investigated for increasing the rate of hydrogen production. Low price stainless steel was used as cathode electrod. The microbial electrolysis cell operated applying 1.3 v external voltage. Basic pH was found to be the best condition for maximum rate of hydrogen production, where the average rate of hydrogen production was 100.006 1.866 L/m3.d. However, the hydrogen production rate for the acidic and neutral cathodic condition, were 92.89 1.13 and 91.845 1.485... 

In this study in-situ Al/Al3Ti was fabricated by mechanical alloying, hot extrusion and subsequent heat treatment. First, initial pure powders of Al and Ti were mechanically alloyed with 5 weight percentages of Ti for 40 hours. The as-hot extruded samples containing 5 wt% of initial Ti particles, were exposed to heating at 600 oC for various time intervals up to 10 hours. Microstructure analysis by OM and SEM proved that in-situ Al3Ti phase was formed as a layer around Ti particles by solid reactive diffusion between Al and Ti particles. After 10 hours of heating, all the Ti particles were consumed and transformed to Al3Ti. Mechanical properties of samples were investigated by Brinell... 

In this project, tomato processing waste has been considered as a raw material for bio-refinery applications. Some products from tomato wastes that are usable, economical and environmentally friendly have chosen after lots of studying on researches in regards of producing valuable materials from tomato waste. I’ve used “Superpro designer” software for economical evaluation and determining the possibility of this practice for industrial applications. Beside the tomato paste factory, the process includes one unit of Lycopene production. In addition to Lycopene production, it is possible to produce fertilizer from residues and using them as livestock food or producing energy for the output... 

Proteins carry out most important roles in the organisms and they have a number of functions including structural, catalytically, regulatory and transportal, However for protein to have functional role they must be able to possess tridimensional structure. Several proteins due to various genetic and physico-chemical conditions have shown to alter their tridimensional structure leading to insoluble fibrilar structure. One of the properties of these insoluble fibrils is conformational change, converting to β-sheet rich structures; the entire process of converting soluble to proteins insoluble fibrils known as amyloid formation. The proteins amyloidosis have been seen as causative role in a... 

Event history analysis is a classic problem in stochastic process, that recently attracts the researchers' attention in complex networks. The goal is to model the time of events, like check in a restaurant check-in or post a message, given their history, and then control them. In this thesis we try to improve both aspects of the problem. In event modeling, we focus on two challenging cases. The first case removes the independence assumption in diffusion of cascades in social networks, and investigate the correlated cascades. We use a multidimensional Hawkes process with soft-max mark function, to model the competitive and cooperative cascades. We infer parameters of the problem using... 

One of the most popular methods in order to protect foods is to package using various materials. By this act, the shelf life of the packaged foods may range from a few days to more than a year. Multiple types of plastics are being used as materials for packaging food, including polyolefin, polyester, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide, and ethylene vinyl alcohol. Although more than 30 types of plastics have been used as packaging materials, polyolefin and polyesters are the most common. Biaxially Oriented Polypropylene (BOPP) is a polypropylene film that has been stretched in both the machine and cross directions. BOPP film has become one of the most popular... 

Human visual attention is a mapping that determines to what regions of an image human’s eyes focus more while perceiving it. Personalized visual attention is visual attention computed for a specific individual. The importance of visual attention lies in its wide range of applications in computer vision and cognitive science, such as neural encoding, image captioning, self-driving cars, video anomaly detection, image classification, and visual design. One of important aspects of visual attention is personalization, the ability to assign every individual their own, specialized attention map. In this project we aim to utilize EEG signals measured from people’s brain to predict their... 

Enzymes are proteins that carry out chemical reactions in the form of chemo, stereo, and regioselective under mild conditions. One of the characteristics of enzymes is that they perform a specific chemical reaction on a selective substrate and under specific environmental conditions. However, in recent years, a number of enzymes have been identified to display promiscous behavior. This promiscousity includes catalytic activity, variety of substrates, and environmental conditions. Promiscous activities of enzymes can be a good starting point for creating new and more favorable engineered pathways for the production of chemical and medicinal drugs. One of the aims of this project is to exploit... 

In this project, quantification of sulfide ion was investigated based on peroxidase enzyme inhibition. The fungal peroxidase was obtained from the liquid culture of Coprinus cinereus NBRC 30628. Two different biosensing systems were suggested for sulfide ion measurement: (1) An amperometric inhibition peroxidase biosensor proposed for determination of sulfide by in situ bulk polymerization of acrylamide for immobilization of peroxidase on screen-printed carbon electrode. Measurements were performed using phosphate buffer solution as a supporting electrolyte in the presence of hydroquinone as a mediator. Identification method was based on reduction of generation current, caused by hydrolysis... 

Development of new engineered materials for bone tissue engineering applications is rapidly growing. The most important characteristics of materials, which can be used for bone tissue engineering applications, are appropriate mechanical properties, degradation rate, swelling behavior, and bioactivity. The goal of the current investigation is to study the feasibility of incorporating a modified nano-biocomposite based on biodegradable thermoplastic starch for bone tissue engineering. Nano particles of ?-tricalcium phosphate and hydroxyapatite were incorporated for reinforcing the matrix as well as improving the bioactivity. A second biodegradable polymer, i.e. polycaprolactone, was used... 

Electrocoagulation is one of the new methods for water and wastewater treatment that is carried out by electrical current. This method is easily applicable to a variety of wastewater. it is highly efficient in organic matter removal and other toxic are and dangerous pollutants.
This study dealt with diesel and COD removal by Electrocoagulation method. Energy consumption, electricity consumption, and the amount of sludge produced by this method was evaluated. Experiments were conducted in a 2 L reactor, consisting aluminum and iron electrodes.The distance between anode and cathode was 5 cm. To evaluate the efficiency of electrocoagulation method, parameters including: pH, time,... 

Primary visual cortex plays a paramount role in processing visual information. Visual information after the primitive processing by LGN and Thalamus, will be sent to the primary visual cortex which is called V1 area. According to the fact that V1 neurons have the definitive sensitivity to the edge and contrast of visual stimuli so their behavior are very selective to the certain features, specially contrast, of visual stimuli. These neurons have different response behavior to contrast. In fact most of them have some nonlinear behavior to this feature. Normally we expect that response of them or spiking rate of them grow linearly by the contrast increases but in most many cases they have some... 

The accessibility of broadband Internet to home users has pushed video broadcasting applications up in the list of the most favorite IP-based applications. A Peer-to-Peer overlay network is an attractive foundation for video streaming as it can shift the burden of content distribution from the network routers and servers to the clients. However, live Peer-to-Peer media streaming systems face many challenges such as bandwidth heterogeneity, node churn, and selfish nodes. Although many tree based and mesh based streaming protocols have been proposed, each has its own drawbacks such as unreliability and unfairness in the tree based and long startup delay and complex scheduling in mesh based... 

Wireless sensor network (WSN) multimedia applications impose new challenges in the design of algorithms and communication protocols for sensor networks. Indeed, wireless multimedia sensor networks (WMSNs) must provide relatively high throughput and low end-to-end delay and jitter while being energy-efficient. In view of these challenges, error control is an important mechanism which enables us to provide robust and high quality multimedia communication in WSNs. In this thesis, we first perform a comprehensive performance evaluation of different error control schemes for multimedia communication over WSNs. The results of our analysis show how wireless channel errors can affect the performance...