Sharif Digital Repository

In this study, HSS and double angle braces subjected to cyclic loading in order to study the buckling and post buckling behavior have been investigated by Finite Element method. The results of FE analysis are fairly in good agreement with experiments. Analysis demonstrate that when local buckling occurs in middle span, subsequently, strain rises severely. Accordingly, this strain jumping causes early fracture in braces. Therefore, local buckling can be one of the primary reasons of fracture in braces. As a result, local buckling must be considered one of the primary limit state of Performance-Based design of steel braces. In addition, finding a way to predict local buckling can help us to... 

Reducing the size of transistors has dramatically increased the impacts of NBTI, HCI, and EM phenomena in comparison with decade ago. These phenomena are able to have influence on properties of different parts of a chip to make it changed gradually; including threshold voltage of a transistor and electrical conductivity of interconnections. These changes are known as the aging of a transistors that diminish the performance and reliability of a chip. A common reason that plays a significant role in all these phenomena is temperature. The temperature becomes more important when the power density increases per unit area due to decreased size of transistors, which is a trend in multi-core... 

In many papers, GDP is used as a measure of economic growth, which is shown to possess a nonlinear structure. The study focuses on the nonlinear Granger causality between liquidity, government spending, oil revenues and economic growth by markov-switching vector autoregressive and markov- switching Granger causality approach for the period of 1369-1397 for Iran. The empirical results from MSAI(2)-VAR(4) suggest that Oil revenues and government spending have a significant impact on economic growth in both regimes. Also, markov- switching Granger causality results are quite different from the traditional Granger causality results, that suggests the nonlinear Granger causality has more... 

To create applications for smart environments we can select from a huge variety of sensors that measure environmental parameters within the premises. Capacitive proximity sensors use weak electric fields to recognize conductive objects, such as the human body. They can be unobtrusively applied or even provide information when hidden from view which make these sensor more popular. Furthermore, these sensors are low cost, precise and low power. In this thesis, we study the construction and operation of capacitive sensors and the challenges of using them. Then we use them to produce smart devices. Smart flooring is used on the ground and it can be used to track people or fall detection. Smart... 

The use of protons and charged particles such as carbon in the treatment of cancerous tumors is one of the new methods of external radiation therapy. Proton therapy can achieve almost the same tumor dose coverage as traditional photon therapy with a greatly reduced dose to the normal organ. The radiation deviations caused by the magnetic field are an effective factor in reducing the dose of vital organs without sacrificing the dose coverage of tumors; Therefore, a new method of proton therapy, called magnetic field-modulated proton therapy, has been proposed, in which the Bragg peak positions of proton beams can be modulated under the cover of predesigned magnetic fields inside cancer... 

The use of microelectrode arrays in neural networks has offered a wonderful opportunity for evaluating numerous properties and interactions with excitable tissues such as the brain and spinal cord in the laboratory. In neural network applications, microelectrode arrays can be utilized to analyze nerve impulses or interact with neurons. They are either used to record neural data or to stimulate spinal cord nerves. Previous research has revealed that stimulating the spinal epidural region can help restore after spinal cord injuries (SCIs), which is the key to using them in the rehabilitation of living beings, including humans. According to the international campaign for the treatment of SCI... 

e study of the brain’s neural activity is an active research area in computational neuroscience aiming to provide insights about the functionality of the brain as well as dysfunctions that underlie disorders. Functional Magnetic Resonance Imaging (fMRI) plays an important role in brain studies by providing non-invasive records of neural activities during a specific task with location sensitivity. Recent advances in statistics and machine learning offer powerful tools for paern recognition and processing of fMRI data. In this thesis, we decode information recorded via fMRI from the visual cortex to reconstruct images presented to subjects. Current reconstruction methods face numerous... 

High-frequency oscillations of the frontal cortex are involved in functions of the brain that fuse processed data from different sensory modules or bind them with elements stored in the memory. These oscillations also provide inhibitory connections to neural circuits that perform lower-level processes. Deficit in the performance of these oscillations has been examined as a marker for Alzheimer’s disease (AD). Additionally, the neurodegenerative processes associated with AD, such as the deposition of amyloid-beta plaques, do not occur in a spatially homogeneous fashion and progress more prominently in the medial temporal lobe in the early stages of the disease. This region of the brain... 

In this study, at first the V2O5 spent catalysts were characterized. The aim was to identifying whether these catalyst may be regenerated. Then, for feasibility study of them, three methods were applied: washing, diffusion and milling the spent catalysts for their subsequent reproduction. A variety of techniques such as XRD, XRF, AAS, TPR and TPO were applied in order to identify factors contributing in vanadium pentoxide catalysts deactivation. The results showed that approximately all of pollutants caused their performance deterioration, while they still have some active phases. Then, the polluted catalysts were washed (their yield increased from 43% to 72.2%). In the underside of the... 

Silica nanoparticles is one of the most important mineral particles. In this study, Sodium silicate, Sulfuric acid and Sodium aluminate is used in order to synthesis of the modified Silica nanoparticles. The effects of temperature, reaction time and the molar ratio of regents were tested and optimized. Synthesized nanoparticles were characterized by use of XRD, FT-IR and SEM techniques. The results show that by controlling the reaction conditions, nanoparticles with an average size of 26.2 nm is obtained. The increase of temperature and reaction time alters the structure of the particles of amorphous state to a crystalline needles. The particle surface modification process was performed by... 

Human action recognition is one of the most attended topics in computer vision and robotics.One of the flavors of this problem relates to the situation in which the task of action recognition is carried out by data from several cameras. Different approaches have been proposed for combining information. Various reduction methods have been introduced to decrease the processing load. All of the methods in this particular field of study can be divided into two linear and non-linear methods. In the linear methods, we don’t pay attention to the non-linear structure of the data, and these kind of approaches are not reliable. Furthermore, combining different actions data is done before the dimension... 

Fabrication and characterization of different surface charged cellulose electrospun scaffolds including cellulose acetate, cellulose, carboxymethyl cellulose and quaternary ammonium cationic cellulose for biomedical applications have been reported in this research. We describe preparation of cellulosic nanofibers through the electrospinning following deacetylation cellulose acetate. Moreover, surface modification of electrospun cellulose nanofibers is carried out to obtain carboxymethyl cellulose and quaternized cellulose nanofibers, respectively. At last, the structural, morphological, mechanical, swelling, wettability and the cell culture properties of the scaffolds were analyzed and...