Sharif Digital Repository

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 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... 

The theory of self-organized criticality is originally introduced by Bak, Tang and Wiesenfeld as a general mechanism that can explain the behaviour of complex systems which naturally organize themselves into a critical state. They defined the sandpile model as an example of slowly driven and dissipative complex system to explain the concept of self-organized criticality. From the definition of the model, extensive work has been done on this model. Thanks to the Abelian property of the model, many statistical results have been derived exactly. Other properties of the model such as critical exponents and dynamical behaviors have been also studied using the mapping with some statistical models... 

Schramm – Loewner Evolution (SLE) is a framework which helps to classify interfaces in critical models. At criticality two or more phases of the model are separated by an interface. In two dimensions this interface is a simple random curve, which can be addressed by SLE theory. This classification has crucial rule in our understanding of statistical models. In spite of our understanding of2 dimensional statistical models and 1+1dimensional quantum field theories, little workhas been done on these models out of criticality. In this thesis we focus on the Schramm-Loewner Evolutions and conformal field theoriesin vicinity of critical points. To this end we state the theories which the... 

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... 

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... 

Self-Organized Criticality (SOC) is observed in different systems in nature. Hights of mountains earthquakes and traffic are a few examples. In such systems, without tuning external parameters critical behavior is found. In other words the dynamics of the system takes it towards criticality, where the correlation length is very large and scaling laws are observed. Due to scale invariance, events of any size are found; for example in the case of earthquakes, one can find earthquakes with any sizes in the earth. Each event causes a cost and larger events cause much larger cost. Therefore it would be of great importance if one could somehow destroy criticality and as a result diminish large and...