Sharif Digital Repository

Today, social networks have provided an environment for disseminating all kinds of information and news among the people. One of the challenges of ex-panding social networks is reading and trusting fake news propagating against accurate information. Fake news is false information that the author intention-ally produces and publishes. Due to the destructive effects of spreading fake news, determining the trustworthiness of news is one of the critical issues in the so-cial, political, and economic fields. In this research, we worked on detecting fake news on social media using multimodal data. To solve the problem of fake news detection, we used the text and images of the information. Transfer... 

The precipitation hardenable 7075 Aluminum Alloy is one of the most important heat-treated aluminum alloys. The high strength of this alloy has led to its widespread use in the manufacture of various components in the automotive, aerospace, marine, defense and military industries. Although the production costs of this alloy sheet are high, but since the 7075 aluminum alloy has the capacity to be as strong as steels, by reducing the production process and thus reducing production costs, this alloy can be used more widely in various industries. Therefore, in this study, the mechanical properties of the 7075 aluminum sheet are improved by a new quenching method in the die (HFDQ), which is a... 

In medical science, preparing a high purity sample of certain kinds of cells plays an important role in studying the characteristics and functionality of cells, detecting in vitro harmful pathogens and helping to find ways of preventing and treating diseases that cause cellular disorders in the human body. The goal of this research is to improve the spiral microchannel with stair-like cross section in order to separate white blood cells from whole blood. First, the efficiency of this method was evaluated numerically, using a developed finite element model. Then, the desired microchannel mold was made using the micromiling method, and we fabricated the chip using soft lithography and pasting... 

Device to device communication (D2D) in cellular networks is seen as a promising thechnology to assist local communication services. It offers several gains including cellular traffic offloading gain and proximity gain of devices that allows high data rate, low power consumption, low delays and the reuse gain when cellular and D2D links are allowed to utilize same radio resources simultaneously. D2D communication is one of the key enabler for fifth generation (5G) networks. Major bottleneck in the operation of D2D communication is energy. The direct D2D communication can result in energy inefficiency as the battery powered devices are required to perform energy consuming tasks on their own... 

In this thesis, we have tried to study one of the most well known collective behavior phenomena known as the Wisdom of the crowd, from the perspective of statistical physics. In recent decades with the appearance of Social Networks and mass media, collective social phenomena have become a critical topic in the life of every human being. In the Wisdom of crowd phenomenon, the overall process is to ask the crowd’s opinion regarding a special topic and after aggregating the predicted values, the aggregated quantity is declared as the wisdom of the crowd. It has been observed that in some polls and elections, the result of the wisdom of crowd outperforms every individual of the group and in some... 

Hydroxyapatite is the most substantial inorganic component of bone tissue which displays great biocompability and bioactivity. Nevertheless, its mechanical properties is not appropriate for a bone substitiues. Therefore, it is used to improve the mechanical properties of polymer matrix composite scaffolds. In the present work chitosan as a polymeric matrix was employed to fabricate hydroxyapatite- chitosan biocomposite scaffolds. Sol-Gel method was employed to synthesize hydroxyapatite nano particles. Porous scaffolds were fabricated via freeze-drying by introducing two different cross linkers, Glutaraldehyde and Sodium Tripolyphosphate. Mechanical (compressive strength), biocampability and... 

One of the most dangerous phases of the flight is landing. Newly automatic landing is noticed. The vital element in an automatic landing system is navigation system. In this document, a PL/INS/DGPS auto landing system is introduced.In a PL based navigation system, accuracy is highly under the influence of relative geometry between PLs position and flight path. Therefore, it is necessary to locate PLs on the best position. An optimization is used to find PLs best configuration that increases the navigation performance. Tightly coupling of INS and GPS/PL is preferred, because some problems lead to GPS satellite signal unavailability  

Real-time applications play a significant role in the area of VANET, and are mainly required for these kinds of networks. On the other hand, when the number of messages received by vehicles increases in the network, then the applied computation load becomes extremely high and consequently, delay on the message authentication process significantly increases. This thesis, is presented with the aim of introducing a novel cooperative message authentication (CMA) scheme for VANET, the main purpose of which is alleviating the computation load on vehicles while verifying messages by using two-part identity-based signature. The scheme enables vehicles to verify only a limited number of the total... 

One of the main issues of business world is competition and competitiveness, and this cannot be happened unless one company absorb new ideas and innovations. Based on what scholars mentioned, companies should utilize users instead of professionals in order to create new innovations, and this is due to that users have better understanding of what users want. As a result, in the mobile platforms, platform owners need to know how to invoke users to create more innovative apps. In this research we were into finding important matters that increase number of innovation of users. We saw that lead-userness, toolkit support, work method autonomy, knowledge sharing, and modularity have an impact on... 

The goal of this thesis is to represent some application of algebraic topology specially homology and simplicial structures in data analysis and image processing. First the notion of topological persistence will be introduced and next for computing that several efficient algorithms will be proposed. Also complexity of the algorithms base on the topological spaces and by some algebraic topology tools. And it will be tried to test this theorical algorithms on real data and represent some application of topology in real data analysis. To do that, at the begining the tools of algebraic topology will be reviewed and the notions like singular complexes and singular homology and some related... 

Nowdays, the world’s need for energy from renewable sources is increasing due to the excessive use of non - renewable resources and the pollution of the environment. Energy converters are classified into three general types: electromagnetic, electrostatic, and piezoelectric, in which piezoelectric materials are used in converters that convert mechanical energy into electrical energy (and vice versa). In the last decade there has been extensive research into the use of these materials for self-charging of low consumption electrically-powered devices such as sensors. For this purpose, in this study, a new method for harvesting electrical energy from the sea using piezoelectric elements is... 

Credit risk is the possibility of a loss resulting from a borrower's failure to repay a loan or meet contractual obligations. All banks and financial institutions need to manage credit risk of their lending portfolios to maximize risk-adjusted rate of return and obey regulatory rules. The most commonly used method for determining credit risk is to calculate the maximum loss within the “Value at Risk” framework.Previous studies proposed different models for Credit VaR calculation like Vasicek Model and Credit Risk Plus Model. Furthermore, due to the high growth of computing power and easy access to information, the application of data-driven models such as Machine Learning has been increasing... 

Nowadays, many biological systems are modeled by bipartite networks. So, using network's concepts and techniques such as community detection may lead us to more accurate outcomes.In this thesis, we have presented an algorithm for detection of communities in a network of patients with Peripheral Nervous System (PNS) issues. The bipartite network of the patients is formed based on the dataset which is collected with cooperation of a Spinal Specialty Clinic. In our algorithm, called MRComSim, three different methods are used to project the bipartite graph to unipartite graph. Then the projected unipartite graph of each method is used for community detection. The output result of our algorithm... 

Research in the field of medical science goes back decades and significant progress has been made in understanding the behavior of organs and living tissues. Consequently, scientists need to work towards identifying how to mathematically model the mechanical behavior of these living organisms. If we consider any living entity, we can see that they are a product of atoms, molecules, cells, tissues, and/or organs. Differential geometry and continuum mechanics indicate that during the growth process these organisms are influenced by the phenomena of aging, remodeling and morphogenesis. The majority of research in this area, i.e. the study of these important phenomena in living tissues, has... 

The fabrication of potassium sodium niobate piezoceramic with oriented microstructure and study of its piezoelectric properties is one of the main objectives of the present study. For this purpose, first the raw materials were synthesized. solid state reaction and topochemical reaction were used for the synthesis of potassium sodium niobate and sodium niobate respectively. The X-ray diffraction results determined that the powder synthesized by the solid state method in the binary system KNbO3-NaNbO3 is closer to the morphotropic phase boundary compared to the powder synthesized in the ternary system Na2CO3-K2CO3-Nb2O5. Particles morphology also includes coarse cubic shape and small equiaxed... 

Nanomachines are molecules inspired by natural molecular machines and are able to move and transport at the nanoscale. Due to the advancement of nanotechnology, the need to move materials and energy on a small scale is necessary more than ever. Nanocars are artificial molecular machines with chassis, axles, and wheels designed for nanoscale transport at materials’ surfaces. Understanding the dependence of surface dynamics of nanocars on the substrate’s physico-chemical properties is critical to the design of the transport properties of such man-made nanoscale devices. Among the multitude of potential substrates for the nanotransporters, graphene exhibits intrinsic ripples on its surface,... 

Bulk metallic glasses (BMGs), in contrast to conventional crystalline materials, are defined as metals with an amorphous and disordered atomic-scale structure. Due to the absence of dislocations and grain boundaries, BMGs have considerably unique mechanical properties such as high strength and elastic strain, high wear resistance and desirable corrosion resistance. However, they generally suffer from poor plasticity caused by an inhomogeneous deformation which leads to catastrophic failure by localization of strain into narrow regions, known as shear bands. This factor has extremely restricted their application as advanced structural materials. Furthermore, the recently discovered phenomenon... 

An increase of wastewater treatment plants and wastewater treatments methods have increased the importance of selection of best wastewater treatment alternative. This selection should not be merely based on the quality of effluent, but the whole factors (economic, environmental, technical and social factor) should be considered. Different methods for the assessment of wastewater treatment plants is used. For example, life cycle assessment is used for the evaluation of environmental impacts or cost-benefit analysis are used for economic analysis. But, for selection of the most sustainable technology whole factors should be evaluated together. Multi-criteria decision-making methods can be... 

Heart disease is one of the major causes of death in all countries, especially developing countries. At the moment, using Image Processing methods as well as analysis of electrocardiographic signals, heart disease is diagnosed with the help of specialists. Applying artificial intelligence and machine learning methods, many studies attempted to provide models that are used to diagnose automatically the heart disease without the need for a specialist and only relying on the past data. But less is done on CTA images of the heart. Hence, in this thesis, a new method for image processing and a Multi Support Vector Machine (MSVM) classification for coronary artery disease detection based on CTA... 

In this thesis, we investigate the achievable secrecy rate in a relay channel where the source and the destination wish to keep the information confidential from an untrusted relay (potential eavesdropper). The relay has no energy supply, and harvests its required energy for relaying from its received signals. For radio-frequency (RF) Energy Harvesting (EH) at the relay,we adopt power splitting (PS) and time switching (TS) approach. We study the problem of achieving positive secrecy rates between the transmitter and the receiver while making use of an untrusted relay. Energy limitation at the relay makes the problem more interesting. Because,the relay must choose either to eavesdrop the...