Sharif Digital Repository

Kinetic roughening has attracted a lot of attention over the last few decades not only because of its practical importance for the growth of solid films, but olso as an example for a dynamical mechanism
that drives a system into a spatially and temporally scale invariant state. Most of the models of kinetic roughening studies so far can be described by the KPZ equation. In this project growth processes which
cannot be described by KPZ will be studied. The first nonequilibrium growth models including deposition and surface diffusion were intruduced independently by Wolf and villain. The Schramm-Loewner evolution (SLE_, where _ is the diffusivity) proposed recently is a very successful... 

In this study, an adaptive controller design for nonlinear fractional order systems in the strict-feedback form has been investigated. The system is subject to unknown dynamics, unmeasured state variables, quantized input and output, and input nonlinearity. A linear observer is used to solve the problem of unmeasured state variables. The fuzzy logic system is used to estimate the unknown functions, and instead of updating all the regressor weights, only the upper bound of their norms is updated, which significantly reduces the computational load. In the controller design, limitations due to the bandwidth of data transmission have been considered by applying quantizers in the input and output... 

In this thesis, in addition to reviewing the previous work done in the study of ideal access structures, we present the author's recent results in this field. As a first result, we introduce a new technique for reducing the size of the secret space in ideal homomorphic secret sharing schemes. The concept of decomposition of secret sharing schemes is formally introduced for the first time. In this regard, we show that ideal homomorphic and abelian secret sharing schemes are decomposable. We also examine the inherent group-characterizability of secret sharing schemes and show that an ideal secret sharing scheme is not necessarily inherently group-characterizable. Some weaker definitions of the... 

Due to the increase of computer networks and their application, the need for secure communication has become a very important concern. We introduce Cmail, a secure messaging system that works without any central party and in addition protects privacy of users. This system is on top of a cryptocurrency system such as Bitcoin. Bitcoin is cryptocurrency that works on the Internet. The suply of bitcoins and verification of transactions is done by Bitcoin miners, which are some typical client of Bitcoin system, in a decentralizd maner. In Cmail the miners have additional task, they should transfer messages of users and if needed, they hold it for a limited time. In order to increase incentive of... 

The commercially available finite element software, FLAC, was used to provide better understanding of the static and dynamic behavior of tieback and anchored walls. Many of the codes dealing with the design of these structures use empirical methods to estimate the amount of deformation under static conditions. Therefore, in terms of static behavior, this thesis mainly focuses on the deformation patterns of the wall and the retained soil. Mohr-Coulomb elasto-plastic constitutive model was used; however, in elastic part the nonlinear Duncan-Change was implemented. The efforts made for better representation of soil behavior resulted in the suggestion of a modification to Duncan-Chang’s... 

Usually in analysis of arch dams, applied seismic motions on dam-foundation interface are assumed to be uniform. This is while that recorded motions show non-uniform accelerations in dam-foundation interface. Analyzing of the dam under this non-uniform accelerations we can find the importance of this assumption in analysis of arch dams. Two earthquakes were excited “KAROON III” dam at 20.11.2007 and 21.11.2007. The respective motions were recorded by the array of accelerometers that has been installed on the dam. The recorded motions, indicated non-uniformity of excitations in accelerometers were installed near the dam-foundation interface. Therefore this data provided an opportunity to... 

Nowadays the combination of mechanical and electronic systems in small scales is gaining attention. Micro electro-mechanical systems are widely used in various industries such as car manufacturing and electronic chips. In these devices, the most important and useful mechanical structures are beams and plates. Therefore, investigating the mechanical properties of these structures in very small scales (micro and nano) is of great importance. Decreasing the size to these scales leads to the dependence of the behavior of these structures to size. Accordingly, some theories for prediction of these behaviors have been presented, one of which is the strain gradient theory. This theory is used in... 

Cardiovascular diseases are one of the leading causes of death in the world. Identifying the mechanical behavior of arteries and their growth and remodeling under applied loadings can help to better understand the progression of the disease and provide more effective clinical interventions. Therefore, many researchers in recent decades have turned their attention to modeling the process of stress-mediated growth and remodeling in soft tissues. Among the most important models proposed to study this process are the constrained mixture model proposed by Humphrey et al. and the volumetric growth model proposed by Hoger et al.. The constrained mixture model is based on the continuous turnover of... 

According to the growing population and the need to make optimal use of available resources, the discussion of planning and scheduling in healthcare will be useful. One of the most expensive and lucrative sections in a hospital, which always spends a large percentage of renewable and non-renewable resources, is the Operating rooms (ORs). These ORs are the most important part of the hospital in terms of health and financial issues. In these scheduling problems, in order to be able to model the real situation, we needed to consider the recovery section integrated with the ORs. Also, the duration of surgery and stay in the recovery rooms are considered stochastic. In this study, we solve the... 

Earth and rockfill dams are enormous three-dimensional structures constructed from earth and rockfill materials. They are mainly built for water supply, agricultural land irrigation, electricity generation, and flood control. Earthquake is one of the most significant natural hazards affecting the stability of these dams. Nowadays, with the development of computers and software, the seismic behavior of most dams are assessed by dynamic analysis. In a considerable part of technical literature, dynamic analysis of earth and rockfill dams have been performed by applying only the horizontal component of the earthquakes, and the effects of vertical component of the earthquakes have often been... 

Surgery theaters are one of the most important and expensive departments in hospitals. Since the operating theaters are connected with other departments, improving the efficiency in the operating theaters can affect other departments as well, so effective and efficient planning and scheduling of the operating theater It is necessary. In this research, we study and investigate the problem of planning and scheduling surgery theaters under the uncertainty of surgery duration, considering the open scheduling strategy and having the list of patients and limited resources after surgery. Let's say that the parameter of the duration of surgery is uncertain and we have little data about it. Some... 

In this research, a comprehensive examination on hot and cold deformation of Al-Mg6 alloy has been performed. In order to find out hot deformation behavior of Al-Mg6, hot compression tests at 350, 450, and 550 oC and at strain rates of 0.001, 0.1, and 1 s-1 have been carried out. After the correction of the curves due to friction and adiabatic heating effects, constitutive equation of this alloy has been derived. Corrected curves show the occurrence of dynamic recovery. A new method for developing strain dependent constitutive equation has been employed using normalized stress and strain curve. After normalization, the curves at all deformation conditions follow a similar behavior.Rolling of... 

The aim of this study was improvement of mechanical properties and grain refinem ent of aluminum 6061 alloy tubes by combining pre and post heat treatments with Tube Channel Pre ssing (TC P) as a new severe plastic deformation process. For this purpose , the effect of geometr i cal parameters of TCP on deformation behavior was studied at first. Then , the effect of pre and post heat treatments on mechanical properties improvement and micro structure was invest i gated. Finally, the effect of TCP process on mechanical properties improvement and grain refinement was considered. Results show that the mandrel design must follow die design in TCP. As an illustration ,... 

One of the extensively used, yet complex, structures in the industry is pre-twisted Micro/Nano beams. Studying their mechanical behavior helps to have a broader view of them. In this present study, explores and analyzes the behavior of a pre-twisted Micro/Nano beam with a quadrangular/rectangular cross-section using the strain gradient theory and modified couple stress theory. Using the calculus of variations and the Hamiltonian principle the elastodynamics governing partial differential equations of transverse deflection of the pre-twisted Micro/Nano beam with hinged-hinged boundary conditions are derived. Then the mechanical behavior of the pre-twisted Micro/Nano beam in static mode and... 

Severe plastic deformation (SPD) can refine microstructure of steel and increase its strain energy. Ultra-rapid annealing (URA) influences on the temperature and kinetics of recrystallization and transformation, and causes to improve the mechanical properties of steel. In this research, low-carbon steel with the average grain size of 80 μm was subjected to SPD using 2 passes of constrained groove pressing (CGP) method and its grains size is reduced to 30 μm. Ultra-rapid annealing with the reference heating rate of 200 oC/s was performed on SPDed steel up to subcritical and intercritical temperature ranges. Other heating rates of 75 oC/s to 1800 oC/s were performed for further examinations.... 

Selection of appropriate thermohydraulic tool for analyzing nuclear reactors is a trade of between accuracy and calculation run-time. Nuclear reactors analyses perform on two levels including system and sub-channel. In this regard or the system codes' one-dimensional approach is selected or the CFD codes for considering the three-dimensional and non-equilibrium phenomenon are employed. In this research a T-H tool for prediction of light-water cooled reactors core is developed. Although this code requires lower CPU and run-time in comparison with CFD codes, in contrast with system codes can report non-equilibrium and three-dimensional phenomenon. This code has a modular implementation based... 

Due to importance of micro electromechanical systems (MEMS), inability of the classical continuum theory to predict the mechanical behavior of micro-scale structures accurately, and vast applications of finite element method (FEM) in modeling of the MEMS, in this dissertation, the static and dynamic mechanical behavior of electrostatically actuated micro structures has been investigated using newly developed finite elements based on strain gradient continuum theory. The governing equations and boundary conditions have been developed for longitudinal and torsional behavior of microbars as well as flexural behavior of Euler-Bernoulli and Timoshenko microbeams based on strain gradient... 

In the present research, we have applied reverse non-equilibrium molecular dynamics (RNEMD) to investigate the thermal conductivity (λ) of carbon nanotube (CNT) bundles, CNT-polyamide (PA) nanocomposites, and nanoconfined PA in the vicinity of graphene layers. First, transversal heat transport in CNT bundles with and without intertube chemical bonds are examined. It is found that the transversal λ of samples with cross linkers can surprisingly increase ~9 times than that of neat CNT bundles (0.26 W m-1K-1). According to the simulation results, key parameters are overlapping vibrational density of state (DOS) profiles between the atoms forming the bridging units, cross linker in the direction...