Sharif Digital Repository

Biodiesel as an alternative fuel for fossil diesel has many benefits such as reducing regulated air pollutants emissions, reducing greenhouse gases emissions, being renewable, biodegradable and non-toxic. In this study, used frying oil was used as a low cost feedstock for biodiesel production by sodium silicate as an alkaline catalyst in transesterification reaction in order to optimize the conditions of biodiesel production. The factors studied were: reaction temperature, molar ratio of methanol to oil, catalyst amount and catalyst recovering. The optimum conditions of reaction obtained as follows: methanol to oil molar ratio of 7:1(mol⁄mol), catalyst amount of 3% w/w and reaction... 

Interactions in social networks consist of positive relations, such as friendship, trust, like, and negative relations, such as antagonism, distrust, dislike. “Signed networks” are utilized to model these networks. These networks are presented by “signed graphs” in which nodes are the people and relations are modeled by sign of edges. One of the challenging problem in signed networks is link sign prediction, i.e., specifying unknown edge sign along with evolution of the network given sign of some edges and further information about remainder of network. Two approaches are used to answer this problem. The first approach is proposing computing models for sign prediction. In this assertion we... 

In this study magnetite nanoparticles were synthesized by microemulsion and were coated with TiO2 by a precipitation technique. The synthesize process were done under fixed molar ratio of various constituents of microemulsion and molar ratio of water to oil. Results of X-ray diffraction spectroscopy (XRD) showed that the uncoated nanoparticles were consisted of magnetite as the major phase and no other detectable phases such as pure iron or hematite were found. Field emission scanning electron microscopy (FE-SEM) results showed that the synthesized nanoparticles small size and narrow particle size distribution. For TiO2 coating process the effect of TBOT concentration, water concentration,... 

Microbial fuel cell (MFC) has attracted a great attention in the recent years due to its advantage of simultaneous energy generation and pollution removal. However, utilization of MFC technologies a challenging issue because of the low energy output and high expenses. Generally, using ion exchange membrane in MFC contributes to a large proportion of the construction costs. Without using a membrane, oxygen intrudes to the anode chamber which will inhibit the anode reaction and decreases the coulombic efficiency. As a solution, using less expensive membranes can facilitate the commercialization of MFC technology.
In this study, soil cylinder and earthen plate were examined as low cost... 

A surfaceMin the Euclidean space is called a translation surfaceif it is given by the graph z(s,t)=f(s)+g(t), where f and gare smooth functions on some interval of R. These surfaces are called translation surfaces since its parameterization X(s,t)=(s,t,f(s)+g(t) ) can be written as the sum of two curves (translation), namely , X(s,t)=(s,0,f(s) )+(0,t,g(t) )
In this work , Minimal surfaces in Sol_3 and Nil_3have been studied,where Sol_3and Nil_3are two model geometry of the eight geometries of Thurston. We propose a similar problem in Sol_3 and Nil_3 changing the additive + in the Euclidean space by the group operation * of Sol_3 and Nil_3, such that we have X(s,t)=α(s)*β(t), where α... 

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...