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bakhtiari--saman
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Critical Behavior of Neuronal Systems: an Information Theory Viewpoint
, M.Sc. Thesis Sharif University of Technology ; Moghimi, Saman (Supervisor)
Abstract
Experiments conducted in recent two decades indicated critical behavior in neural activity at different scales. Theoretically occurrences of these critical and power-law behavior can significantly facilitate brain activities correspondent to computation and memory tasks, but attaining the critical point essentially demands externally fine-tuning which has not been established yet. This fine-tuning often lies with placing system at transition point. Recent studies of group showed that a transition from synchronous to asynchronous phase could be achievable by a change in external parameters. At the very transition point, neuronal avalanches statistically demonstrate a power-law behavior which...
The effect of gap size on the microstructure and mechanical properties of the transient liquid phase bonded FSX-414 superalloy
, Article Materials and Design ; Volume 40 , September , 2012 , Pages 130-137 ; 02641275 (ISSN) ; Ekrami, A ; Sharif University of Technology
Elsevier
2012
Abstract
Optimization of transient liquid phase (TLP) bonding variables is essential to achieve a joint free from deleterious intermetallic constituents as well as with appropriate mechanical properties. In this research, TLP bonding of FSX-414 superalloy was performed using the MBF-80 interlayer. The effects of bonding time (1-30. min) and gap size (25-100 μm) were studied on the joint microstructure and its mechanical properties. Continuous centerline eutectic phases, characterized as nickel-rich and chromium-rich borides, were observed at the joints with incomplete isothermal solidification. The globular and acicular phases were seen at diffusion affected zone (DAZ). These phases could be...
Transient liquid phase bonding of FSX-414 superalloy at the standard heat treatment condition
, Article Materials Characterization ; Volume 66 , 2012 , Pages 38-45 ; 10445803 (ISSN) ; Ekrami, A ; Sharif University of Technology
2012
Abstract
The as-cast samples of FSX-414 Co-based superalloy were heat treated at the standard solution and aging heat treatment cycles. Specimens for joining were cut from the as-cast ingot. Transient liquid phase (TLP) bonding was carried out at the standard solution cycle, using MBF-30 interlayer. Also, bonded specimens were homogenized at the standard aging condition. The microstructure of the as-cast, heat treated and TLP bonded specimens were studied. These studies showed that the non-uniform distributed carbides of the as-cast specimen were replaced by uniform ones during the heat treatment. Eutectic M 23C 6 carbides were observed in all specimens. Due to the complete isothermal solidification,...
Microstructural changes of FSX-414 superalloy during TLP bonding
, Article Defect and Diffusion Forum ; Volume 312-315 , 2011 , Pages 399-404 ; 10120386 (ISSN) ; 9783037851173 (ISBN) ; Ekrami, A ; Sharif University of Technology
2011
Abstract
The as-cast FSX-414 Co-based superalloy samples were solution treated at 1150°C for 4h and then aged at 980°C for 4h. Specimens for joining were cut from the as-cast ingot and TLP bonding carried out at the same conditions as for the solution and solution+aging treatment, using MBF-30 interlayer. Microstructures were studied for as-cast, heat treated and TLP bonded specimens. These studies showed that the ununiform distributed carbides of MC type in the as-cast specimens replaced by M23C6 type carbides with uniform distribution in the heat treated microstructure. Due to complete isothermal solidification, no eutectic structure in the bond region were wasobserved, but some intermetallics in...
Microstructural study of a High Bainite Dual Phase (HBDP) steel austempered at different temperatures
, Article Defect and Diffusion Forum ; Volume 297-301 , 2010 , Pages 62-67 ; 10120386 (ISSN); 3908451809 (ISBN); 9783908451808 (ISBN) ; Ekrami, A ; Sharif University of Technology
Trans Tech Publications Ltd
2010
Abstract
4340 steel bars were austenitized at 850°C for 1 hour followed by heating at 700°C (ferrite and austenite region) for 90 min and quenching into a salt bath with different temperatures of 300, 350, 400 and 450°C. The steel bars were held for 1 hour at these temperatures before air cooling to room temperature. Various ferrite-bainite microstructures with 34% volume fraction of ferrite and different bainite morphologies were obtained. The results of SEM studies showed that by increasing the austempering temperature, the morphology of bainite varies from lower to upper bainite. According to the T-T-T diagram of the studied steel, the bainite transformation will not complete for the holding time...
The effect of bainite morphology on the mechanical properties of a high bainite dual phase (HBDP) steel
, Article Materials Science and Engineering A ; Volume 525, Issue 1-2 , 2009 , Pages 159-165 ; 09215093 (ISSN) ; Ekrami, A ; Sharif University of Technology
2009
Abstract
4340 steel bars were austenitized at 850 °C for 1 h followed by heating at 700 °C for 90 min and quenching into a salt bath at the temperature range of 300-450 °C for 1 h to obtain dual structures with 34 vol.% fraction ferrite and various bainite morphologies. SEM studies showed that by increasing the austempering temperature, bainite morphology varies from lower to upper bainite. Tensile, impact and hardness tests revealed that increasing the austempering temperature from 300 to 400 °C leads to a reduction in yield and ultimate tensile strength, hardness, uniform and total elongation and impact energy. But in dual phase steel produced by austempering at 450 °C, yield and tensile strength...
Consequences Analysis of Dust Explosions to Determine the Damage to Humans and Buildings
, M.Sc. Thesis Sharif University of Technology ; Rashtchian, Davood (Supervisor)
Abstract
Dust explosions are a serious hazard in many process industries and storage facilities. More than 70% of dusts processed in industry are combustible. This implies that majority of industrial plants that have dust processing equipment are susceptible to dust explosions. Dust explosions pose the most serious and widespread of explosion hazards in the process industry alongside vapour cloud explosions (VCE) and boiling liquid expanding vapour explosions (BLEVE). Dust explosions almost always lead to serious financial losses in terms of damage to facilities and down time. They also often cause serious injuries to personnel, and fatalities. In this project we presented a systematic algorithm in...
Service Platform Design in Tourism Field by Service Composition Approach
, M.Sc. Thesis Sharif University of Technology ; Hooshmand, Mahmoud (Supervisor)
Abstract
The tourism industry, as the world's largest industry, plays a significant role in the economic status of developing and developed countries, and has been among the fastest growing sectors in other industries in recent decades.The important role of the tourism industry in economic development has begun since the 19th century, but it has quickly traveled its course as a global industrial one.This rapid growth will enable us to exploit the potential of this industry with the growth of technology and knowledge.Designing a platform with the ability to link up the supply and demand among existing individuals as potential sources of resources to reduce the cost and facilitate tourism with a cheap...
Energy Harvesting from Stall Flutter of an Oscillating Airfoil with Upstream Cylinder
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor)
Abstract
In this study, energy harvesting from stall flutter phenomenon of a NACA 0012 airfoil with the generator in the presence of a fixed cylinder in its upstream has been done. The airfoil can freely rotate along its center axis. Also, a spiral spring is attached to one end of the shaft to adjust the system's stiffness. For a parametric study, airfoil's shaft is set either in 25, 33 or 50 percent of its chord length from the leading edge, initial angle of attack from 0 to 24 with steps of 2 degrees, airstream velocity of tunnel in its test section from 6 to 16 meters per second with a step of 2, and cylinder horizontal and vertical location as well as its diameter are changed. Final goal of this...
Sandpiles and Surface Growth
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
We study the Abelian Sandpile Model and its relation with surface growth. ese two models are related through their field theories and equations of motion. It has been shown that the different features of different sandpile models can be expressed in terms of the noise term in the surface growth equation. A mapping between the simplest sandpile model, the BTW model, and a surface growth has already been introduced. is surface growth has not been studied in details so far. In this thesis we study different features of this surface growth corresponding to the BTW model, continuous sandpile model and also massive abelian sandpile model. We also consider different boundary conditions
The Abelian Sand-pile Model (ASM) and Generalization to the Continuous State
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
The four-page article by Bak, Tang and Wiesenfeld in 1987 was a beginning to a new wave of physicists’ efforts to explain and describe the concept of complexity; a not-so-well-defined concept that resists against the reductionist tools and methods of physics. The Self-organized Criticality theory presented in that article via a simple model, known as sandpile model, was first of all an effort to explain the numerous occurrence of power law distribution in nature. SOC was introduced to tell us why so many natural phenomena like Earthquakes, landslides, forest fires, extinction and other seemingly non-related catastrophic events, more or less obey the scale-less power law distribution; A...
Transition from Abelian Sandpile Model to Manna Model
, M.Sc. Thesis Sharif University of Technology ; Moghimi-Araghi, Saman (Supervisor)
Abstract
In this research, we want to address the question of universality classes in BTW and Manna sandpile models. So far, number of works has been devoted to this issue but the the answer remained unsolved. We will try another approach to study this question by perturbing the original models. To this end, we introduce three models that have evolution rules between BTW model and Manna model. By simulating this models, we observe that in the presence of perturbation, the probability dis- tribution has two regimes of behaviour which are separated by a new characteristic scale. The regime of small avalanches is described by the exponent of BTW model and the regime of large avalanches by the exponent...
Generalized Growth Models
, M.Sc. Thesis Sharif University of Technology ; Moghimi-Araghi, Saman (Supervisor)
Abstract
Edwards-Wilkinson’s equation can be achieved from a Hamiltonian. When we have the Hamiltonian for the system, there are common approaches that makes it out of critical. In other words,the ”mass” should be added to the system. In this study we have tried to simulate and solve analytically these models that are involved mass term. We try to onstruct these mass terms in a way that have a minimum impact on the system and we study the quantities that characterize the out of critical behaviors
Percolation on Small World Networks
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
Percolation is a phenomenon that can be found in many physical problems. Additionally, as a statistical model, it has a very rich physics, since many fundamental concepts in the context of critical phenomena and complex systems-such as phase transition, scaling laws etc can be found in the model. Percolation phenomenon can be defined on different lattices. In this thesis we study percolation on small-world networks. In small-world networks, in addition to local bonds that connects the neighbouring sites, there exist some long-ranged bonds that connect cites far from each other. Social networks, some networks of internet or the gene networks are examples of such networks. Therefore, to study...
Chaos in Sandpile Models With and Without Bulk Dissipation
, M.Sc. Thesis Sharif University of Technology ; Moghimi-Araghi, Saman (Supervisor)
Abstract
A complte set of characteristic parameters of the sandpile models is still unknown. We have studied the existence of ”weak chaos” critical exponent in different sandpile models and we have shown that it is a characteristic exponent of deterministic models. We have shown that BTW and Zhang models do not belong to the same universality class (contrary to Zhang’s previous conjecture and contrary to Ben-Hur & Biham’s results.) Also we have shown that directed models, specificly Ramaswamy-Dhar’s directed model form a different universality class. ”Weak chaos” exponent in also studied in massive models and we have shown that by increase of dissipation, the exponent decreases rapidly to an...
Simulation of the Self-organized Critical Models on the
Human’s Brain Network
,
M.Sc. Thesis
Sharif University of Technology
;
Moghimi Araghi, Saman
(Supervisor)
Abstract
Self-organized critical phenomena are interesting phenomena which are ubiquitous in nature. Examples include mountain ranges , coastlines and also activities in the hu-man's brain. In these processes, without fine-tuning of any external parameter such as the temperature, the system exhibits critical behavior. In other words, the dynamics of the system, drives it towards an state in which long range correlations in space and scaling behaviors can be seen.The first successful model which could characterize such systems was BTW model, introduced by Bak , Tang and Wiesenfeld in 1987. This model, later named Abelian sandpile model, was very simple and because of this simplicity, a large amount of...
Fluctuations in the order of System Size in the Avalanche-Size Distribution of Sandpiles Model
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
Since the concept of Self-Organized Criticality was introduced in terms of BTW Sandpiles model, its major features have been known as broad power law distributions without any tuning parameters. In some selforganized critical systems like brain and neural networks, some evidences and experiments show a periodic or non-power law distribution of avalanches in addition to the power-law distributions of avalanches. In this thesis we try to observe the same phenomenon in the well-known SOC models, namely the BTW and Manna sandpile models. We have considered small lattice sizes with periodic boundary conditions and a small amount of dissipation. Within such conditions we observe a periodic-like...
Burridge-Knopoff Model with Nonuniform Parameters
, M.Sc. Thesis Sharif University of Technology ; Moghimi-Araghi, Saman (Supervisor)
Abstract
Power law behavior of earthquakes has been a matter of interest for many scientists. One on these power laws known as Gutenberg-Richter law describes the magnitude distribution of earthquakes. The Burridge-Knopoff model of faults, produces the same power law distribution of events as the Gutenberg-Richter law for earthquakes. Olami, Feder and Christensen in 1992, introduced a 2-D, continues sand pile model Known as OFC that displays self-organized-criticality. They claimed that this model is equivalent to Burridge-Knopoff model. It means that criticality is the origin of power law behavior of the Burridge-Knopoff model. Nevertheless, there are some evidence against criticality in the...
Mullins-Herring Equation with Lateral Growth
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
Surface growth have been one of the most interesting topics of research in non-equilibrium Statistical physics, due to their relevance in studying industrial growth processes. Many models such as Edwards-Wilkinson and KPZ have been proposed to study these systems where by incorporating renormalization group, numerical integration and computer simulations we can derive their critical exponents. In general, a thermal noise is implemented in these models, however, other types can be used as well. In particular for the case of Edwards-Wilkinson, it has been shown that a multiplicative noise changes the universality class of the model. In this thesis we want to investigate the effects of...
The Role of Simplified Models for Neurons in the Emergence of Collective Behaviors in Neuronal Populations
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
The brain, as a complex system with various components working in concert, plays a fundamental role in many cognitive processes and human perception of the surrounding environment. Perception, in many cases, can differ from reality due to evolutionary processes, natural selection, or even flaws in any of the parameters within this complex intelligent system. One of the observed phenomena in perception is the heightened visibility of edges, often depicted with Mach bands. To describe this phenomenon, primarily, rate models are used, especially in regions where a linear approximation is suitable for neuronal responses. However, the response of neuronal populations in a range of external...