Sharif Digital Repository

In this research, it has been trying to implement Virtual Structure method for formation flight of multiple spacecraft. In this method, a virtual solid frame with virtual center of mass is considered and agents are arranged in a formation with respect to the virtual center. In this work, a formation keeping control system is implemented in which a feedback from formation to virtual structure and vice versa is considered. The method is implemented firstly in a nongradient field and then developed into a circular orbit in order to investigate the in-orbital effects. An algorithm for collision avoidance, based on relative distances and relative velocities, was also developed. The algorithm was... 

When an object or its background changes, occlusion or shape change occurs, most of the existed methods fail to track the target. To tackle this problem, we want to use sparse representation that has a great power in classification and reconstruction. Sparsity is a typical and practical hypothesis in many spaces. If a signal isn’t sparse in a space, it can be transformed to another space that is sparse in it. Articles that are published on visual tracking using sparse representation show that this field has attracted a lot of interest in the recent years. Here we have proposed two new methods that have reasonable results. Moreover, while it is well known that sparse representation-based... 

To overcome challenges such as object appearance changes and environment illumination variations in tracking methods, online algorithms are suggested to be used instead of offline ones. Online algorithms update the model by the information acquired in the last processed frame. The main challenge of using online algorithms is the accumulation of small errors after several steps of updating of the model (drift) which disturbs the model and causes tracking failure. Using the object information in the first frame in each update can be considered as a solution. The proposed online semi-supervised boosting algorithms can overcome the drift problem at the expense of decreasing their capabilities in... 

Visual tracking is a classic problem, but is continuously an active area of research, in computer vision. Given a bounding box defining the object of interest (target) in the first frame of a video sequence, the goal of a general tracker is to determine the ob-ject’s bounding box in subsequent frames. Utilizing sparse representation, we propose a robust tracking algorithm to handle challenges such as illumination variation, pose change, and occlusion. Object appearance is modeled using a dictionary composed of target patch images contained in previous frames. In each frame, the target is found from a set of candidates via a likelihood measure that is proportional to the sum of the... 

Bag of words-based image classification systems have achieved state-of-the-art accuracies in the image classification task recently. These systems can be decomposed into four separate subsystems, each of which has its own objectives: Feature extraction, Feature learning and coding, Pooling, and classification. The effects of the feature learning stage, in which each extracted feature is represented as a linear combination of several visual words, can not be neglected in the success of the whole system. The importance of this part has attracted several researchers to develop different methods in order to alleviate the existing issues. Although several methods have been proposed so far, there... 

Vision-based localization and 3D orientation estimation of a moving camera, has been for long a vast research area including robot localization and mapping, virtual reality and structure from motion. By introduction of RGB-D cameras in 2010, many sparse methods which are based on key-point extraction and tracking, moved towards dense methods. Dense methods utilize the RGB-D depth and gray-scale values in the images and define the odometry estimation problem as an image registration optimization, without the need to make key-point correspondance in images. Although RGB-D cameras impose specific constraints such as limited depth, depth errors and medium resolution, dense methods have shown... 

A projectile was tested in a wind tunnel at various free sream Mach numbers and angles of attack. The tests were carried out at the transonic wind tunnel of the Imam Hussein University.The experiments were performed at subsonic and supersonic speeds and at different angles of attack. The aerodynamic behavior of the model was investigated using force and moment measurements. The results showed that in the range of measured angles of attack the separation did not occurr and variations of lift coefficient remained linear for all Mach numbers except for a free stream Mach number of 2.0. For this Mach number, the asymmetric bow shock makes a pressure difference between leeward and windward sides,... 

Nowadays TV broadcasting of soccer matches has attracted a lot of viewers. With advancement of technology, the broadcasting is also going under changes. One of these changes is using free-viewpoint video. In free-viewpoint video users can interactively choose any view to watch the match from. Generally free-viewpoint problem is defined as follows. We have sequential frames of a soccer match video from different views as input. We want to create sequential frames of the same video from a different view as output. There are several methods for solving this problem. We can classify these methods into to general approaches. Image-based and geometry-based. We will examine these approaches in... 

Data hiding in digital media has been widely investigated over the past decade because of covering different crucial applications. Amongst digital multimedia signals, video has been received a special attention and data hiding in video signals has reached a significant improvement in recent years. This thesis aims at introducing an information theoretic based analysis method for calculating the capacity of data hiding in video signals, as one of most challenging issues in this area. This analysis is expected to establish a reasonable basis for the design and analysis of data hiding algorithms. We study and investigate the data hiding problems that could be specific to video signals and its... 

The growing use of fossil fuels and their impacts on the environmental pollution, mostly originating from internal combustion engines, is one of the important issues in environmentally friendly energy management. One of the key solutions to improve engine performance and reduce exhaust emissions of internal combustion engines is direct injection of bio-fuels. In this regard, in the present study some new biofuels such as Bio-Norouzak, Modified Bio-Ethanol (MBE), and Modified Bio-Diesel (MBF) have been introduced and effects of different parameters on their sprays have been investigated experimentally and analytically. The literature survey shows there is not any comprehensive study on the... 

Tracking is one of the old and still not thoroughly solved problems in machine vision. Its importance lies on its many applications. These applications vary from security surveillance to examining the motion pattern of atomic particles. There is not a tracker which has acceptable results in all situations, yet. A tracker faces many difficulties such as change in illumination and occlusion. In past, tracking was done by using filters or optical flows. By use of the advances in machine learning and pattern recognition, many models have been proposed to accomplish tracking by using these new learning methods. In this dissertation, we proposed a new tracking method which utilizes sparse... 

Due to the recent advances in the learning of multimodal data, humans tend to use computer systems in order to solve more complex problems. One of them is Visual Question Answering (VQA), where the goal is finding the answer of a question asked about the visual contents of a given image. This is an interdisciplinary problem between the areas of Computer Vision, Natural Language Processing and Reasoning. Because of recent achievements of Deep Neural Networks in these areas, recent works used them to address the VQA task. In this thesis, three different methods have been proposed which adding each of them to existing solutions to the VQA problem can improve their results. First method tries to... 

Attention is a cognitive process in which the mind reacts to certain stimuli or stimuli of the environment while other environmental stimuli are ignored. Attention might be an overt or covert process. Overt attention is a process in which based on the purpose, we selectively choose an object or place among other objects and places to focus on and we are aware of it. However, the covert attention originates from hidden source, and we are not aware of it. In fact, the covert attention causes a clear and rapid movement of the eye toward the stimulus or space to be taken into consideration and the time when the movement of the eye it means overt attention has occurred. Visual attention is given... 

The growth of the knowledge of image processing and machine vision in recent years has led to many applications in various fields. One of the most important applications in machine vision is automotive navigation of vehicles and robots. The effective use of visual sensors to detect obstacles, routing, detecting the position of the robot, and mapping the environment is one of the most important goals in ground robotics. Few methods using sensors such as accelerometers, gyroscopes and global positioning systems, suffer from problems such as high costs, accumulative errors, dependencies on external systems, and the inability to be used in closed spaces. But with the use of the visual sensors,... 

The brain-computer interface is an advanced technology in human-machine interaction. The Speller system is a typical use of BCI, in which the target stimulation is detected by the induced signal in the brain. The most commonly speller system, the matrix Speller, has a major disadvantage, and it is Gaze-dependent. Research has proven that target-character selection in the matrix Speller is dependent on eye movement, or as referred to in technical terminology, it is gaze dependent. Therefore, the Speller matrix is not usable for users suffering from unimpaired oculomotor control. Many researchers attempted to overcome this issue, and their results led to two solutions; 1) changing the type of... 

Melanoma is a malignant skin cancer which is caused by cancerous growth of melanocytes. If not treated at its early development stages, melanoma is the deadliest form of cancer. The best way to cure melanoma is to treat it in its earliest stage of development. Since a melanoma leasion is similar to benign moles (regaring its shape and appearance) at its early stages of development, it is often mistaken for moles and left untreated. Therefore, automatic melanoma detection can increase the survival rate of patients by detecting melanoma in its early stages. In this thesis, a new method for automatic diagnosis of melanoma using segmented dermoscopic images is provided. Almost all related... 

In neural systems of living organism, moreover than differences in anatomic structure of cells, there is also differences in physiological functions of analogous cells.Specification and categorization of neurons based on physiological functions is one of objectives of neuroscience. Study of cognitive behaviors and systematic study of neural system, modeling and practical applications in neural prosthesis design are some of applications of categorizing neural cells. Neural signals can be studied by Spike rate of a single neuron activity or Local Field Potential (LFP) of a finite number of neurons. In previous studies neurons of first visual cortex are divided into two groups of simple and... 

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... 

Blindness is one of the destructive results of retinal diseases. Artificial retina is a device which can help blind people with AMD and RP diseases to restore their vision. Prevalent approaches to artificial retina use an external power supply and processor which the data and energy is transmitted to eye through an inductive link. Taking advantages of solar power, in this project we proposed a design which the required stimulation data and energy is produced internally so the patients don’t have to carry the processor and external power supply that is of major concern for them. This is the most important advantage of this device which doesn’t need any maintenance or battery either. In this... 

Aquatic plants play an important role in water environment. Increasing drag force, distorting the velocity and turbulence structures and other related parameters, are the results of the presences of plants. These changes affect the dispersion and mass transport in the aquatic areas. This thesis presents laboratory visualizations and measurements of wave motion, and passive solute surface dispersion (longitudinal and lateral) in arrays of cylinders, a model for emergent, rigid aquatic plants. In the range of (where is Keulegan–Carpenter number, is the maximum oscillatory velocity perpendicular to the cylinder axis, is the period of oscillation, and is the diameter of the cylinder), and (where...