Sharif Digital Repository

Optical metasurfaces are 2D structures of a repetitive arrangement of a number of nanoparticles that are artificially constructed and do not exist in nature. Important applications of optical metasurfaces are meta lenses, flexible solar cells and extremely small antennas. Fabricating surfaces with nanoparticles of proper geometry under light radiation along with elastic deformation, we can have optical metasurfaces with selective reflection or transparency in the visible spectrum. The aim of this project is modeling of an optical metasurface with elastic deformation leading to change of color and transparency. For this purpose, assuming vertical light radiation and linear polarization, we... 

Additive manufacturing (AM) has gained significant attention in recent years as a novel approach to fabricate three-dimensional parts. Its advantages, including high speed, low-cost production for small-scale batches, and greater design freedom, have made it a competitive alternative to traditional manufacturing methods. However, the application of AM for components subjected to fretting fatigue requires careful evaluation. Fretting fatigue is a major cause of failure in turbines, particularly at the contact interface between turbine blade roots and disk. In this study, the influence of AM and post-processing treatments on the fretting fatigue life of Ti-6Al-4V alloy was investigated. Five... 

Condensation is one of the main processes in environment and engineering systems, including thermal power plants, desalination systems and air conditioners. Thus, improvement of its performance can lead to decrease of energy consumption and the resulting air pollutions. Recently, using nanotechnology and new coating methods, there have been great researches on stable superhydrophobic surfaces and using theme as condensing surfaces which because of jumping droplet phenomena can increase condensation performance. Because of the great influence of wetting and structure properties of surfaces on condensation, in this study nucleation and growth of condensing droplets on smooth and structured... 

Today polyolefin definitely is one of the most applicable polymers in the world. One of these polymers is ultra-high molecular weight polyethylene. Being applicable in a number of high-tech industries such as military service, battery separators, and other areas, expands the usage of these polymers. Electrospinning is one of the molding methods in order to synthesize fiber polymers. Using this method, a great deal of polymer fibers have been prepared. It is worth noting that the device used for olefins should have temperature control and temperature increase ability. The electrospinning device with the temperature control has not been built in the country; therefore, this device has been... 

One of the most important problems in machine learning is investigating the performance of the learning algorithms, and especially deep neural networks, on adversarial examples, which are generated by imperceptibly perturbing input images, so that cause the model make a wrong prediction. Not only this line of research is important for making deep neural networks dependable, but also can help with understanding the fundamental limitations of deep neural networks, and the nature of their operation, which can in turn provide researchers with valuable insights into artificial intelligence. In this research work, we have tried to approach the topic with a mainly theoretical mindset. The method we... 

Existing face forgery detection methods mainly focus on certain features of images, such as features related to image noise, local textures or frequency statistics of images for forgery detection. This makes the extracted representations and the final decision depend on the data in the database and makes it difficult to detect forgery with unknown manipulation methods. Solving this challenge, which is called the generalization challenge in artificial intelligence literature, has become the main goal of researchers in this field. In this thesis, the focus is on extracting effective features for success in forgery detection and preventing the performance of the forgery detection network from... 

Processalgebras,acompositionalmethodofmodelingsystemsandtheirbehavioural features, have been a key instrument in the verification of systems and have strived to completely span a whole spectrum of verification solutions for diverse areas of applications. In this sense, modeling and analysis of the performance metrics in a Mobile Ad hoc Network (MANET) in contrast to other systems, face different challenges which demand different strategies. Hence, our goal here is to model and analyze the qualitative and quantitative aspects of MANETs within one especially designed compositional framework. To achieve this framework, we will first have a look at the different methods which aim to model MANETs... 

Application of composite patches in repair of damaged/aged aircraft structures is one of the most popular repairing methods in aerospace engineering and because of its advantages the use of this type of repair is increasing today. However, to use these patches in life extension of aged aircraft, the added weight to the structure should be strictly controlled. This could be best done if achieving the optimum and smart design by using optimization and structural health monitoring methods. These two concept about pre-designed of composite patch repair are investigated in this thesis. The simulation by Abaqus software and experimental results and tests will be used for this purpose. In first... 

Deployable structures have been used on small satellites since the beginning of such space programmes. Here, the design sequence for a special tensegrity structure, for use as supporting structure for deployable mesh-like antenna will be proposed. The design process is conducted to prevent structural elements from failure, and satisfy the minimum specified natural frequency. In this research, structural modeling is performed based on two external geometric parameters (overall height and diameter), and three internal geometric parameters (elements cross-section properties). The pre-stress in structural element is the last design parameter. Also, materials are pre-assigned. Internal forces of... 

In this research work, the concept of an unmanned aerial firefighting system with water thrusters has been studied. This system consists of a platform head, a waterhose and a ground pump. The concept is briefly to pump water through the hose and then fall it down on fire from the platform. This conceptual system may have many other applications. The other applications have also been addressed in the introduction section. This platform can be considered as an unmanned aerial vehicle whose lift and control forces is provided by water thrusters. The conceptual study has been carried out based on three subjects of preliminary sizing, system dynamic modeling and controller design for platform... 

In this thesis we construct a bounded translation of intuitionistic predicate logic into Basic predicate logic with restricted use of universal quantifier and without equality inspired by papers [1] and [2]  

In recent years, deep learning has experienced rapid and remarkable advancements, demonstrating exceptional performance in various applications such as computer vision, natural language processing, and autonomous vehicles. These models are continually evolving and expanding, yet they harbor inherent vulnerabilities that prevent complete trust in their reliability. One of the most critical issues is their susceptibility to adversarial attacks, where a clean image is subtly manipulated to create an adversarial example. Adversarial examples, generated by adding imperceptible perturbations to input data, can easily mislead deep learning models into making highly confident yet incorrect... 

In this study, an elastic-plastic analysis of fiber reinforced metal matrix composite structures loaded by uniaxial uniform tension in the direction perpendicular to the fiber is carried out by assuming elastic-plastic matrix with kinematic hardening. Representative volume element (RVE) is used for this analysis. The element consists of a combined square field composed of a solid circular cylinder fiber and matrix in plane strain condition. Elastic analysis is carried out using Airy stress function and Michell solution. Unknown coefficients of the Airy stress function are determined by satisfying boundary conditions as well as continuity conditions. The governing equation of plastic zone is... 

Wind energy technologies guarantee low pollution and operational costs. Using a DFIG and a fractionally rated power electronics converter gives variable speed operation with a low cost drive train. As energy policy organizations have allocated a considerable quota of wind energy generation to offshore wind farms, the absence of slip rings and brushes in the brushless DFIG (BDFIG) is an advantage for offshore wind turbines where maintenance is vital and expensive. With increasing wind power penetration in power systems, grid code requirements are an important consideration for the ride-through capability of wind farms through voltage dips, particularly for multi- MW wind turbine generators.... 

Concept drift is a common situation in data streams where distribution which data is generated from, changes over time due to various reasons like environmental changes. This phenomenon challenges classification process strongly. Recent studies on keeping a pool of classifiers each modeling one of the concepts, have achieved promising results. Storing used classifiers in a pool enables us to exploit prior knowledge of concepts in the future occurrence of them. Most of the methods presented so far, introduce a similarity measure between current and past concepts and select the closest stored concept as current one. These methods don’t consider possible relations and dependenies between...