Sharif Digital Repository

”Self-organized criticality” is a conceptual term that has helped us describe cer- tain critical behaviors in nature over the past approximately thirty years. In systems exhibiting this characteristic, critical behavior emerges without the need for external parameter adjustments. The necessary mechanism to observe such phenomena is for the critical point to be a dynamical attractor. Based on this, other phenomena have been proposed in which the critical point is not an attractor; instead, a stable cycle forms around it. This mechanism has led to the emergence of a new concept known as ”self- organized bistability.” The primary model proposed for such a phenomenon is based on a sandpile... 

Sponge Iron production is conducted in various methods that one of them is using coal as a reduction agent. Hoganas process is a different coal-based method that has not been investigated in details. Therefore, the heat transfer method in the system is one of the basic steps to a better recognition of this process (with special Hoganas charging). The present paper investigates the temperature distribution method in the Hoganas cylinder through a numerical model using finite elements. The effects of different parameters, namely preheating and porosity were studied on ceramic crucible made from silicon carbide and it was observed that the consumption energy decreases with the increase of... 

With the rapid growth of Internet popularity, web applications are growing in usage and complexity, and therefore, are attractive targets for attackers. Increasing number of services and amount of information stored in the Internet, stimulates attackers to focus on these kind of applications. On the other hand, security specialists are deploying different solutions to mitigate such threats. One of these solutions are Honeypot systems. In contrast with other security solutions, honeypots are not designed to defend against attackers directly. Honeypots, rather, are planned to gather data about what attackers do. This information can help security administrators to learn and understand... 

Obesity is a worldwide growing health challenge affecting ~30% of the world's population. Increased rate of disc degeneration and herniation, low back pain and surgery has been reported in obese individuals. Although obesity-related low back diseases have multifactorial etiology, presumably greater mechanical loads on the spine of heavier individuals during their daily activities may be considered as a risk factor. Likely larger trunk muscle sizes, disc sizes and thus passive stiffness in heavier individuals may however partly or fully offset the effect of their additional body weight on the spinal loads. In absence of in vivo approaches, the present study aims to construct subject-specific... 

Obesity is a worldwide growing health challenge affecting ~30% of the world's population. Increased rate of disc degeneration and herniation, low back pain and surgery has been reported in obese individuals. Although obesity-related low back diseases have multifactorial etiology, presumably greater mechanical loads on the spine of heavier individuals during their daily activities may be considered as a risk factor. Likely larger trunk muscle sizes, disc sizes and thus passive stiffness in heavier individuals may however partly or fully offset the effect of their additional body weight on the spinal loads. In absence of in vivo approaches, the present study aims to construct subject-specific... 

Due to adverse health problems with lumbar spine among professional drivers associated with exposure to whole body vibration (WBV), studying the effect of vibrations and parameters influencing WBV is of great importance. This study aims to simulate whole body vibration for a ground vehicle occupant and calculate loads that lumbar spine tolerate during harmonic sinusoidal vibrations. Moreover, this study determines the effect of lumbar spine angle, seat specifications (angles and materials), and vibration frequency on the results. To this end, a detailed viscoelastic lumbar spine (L1-S1) has been modeled using FE method which has been replaced with the simplified spine model in HYBRID III... 

Several geometrically-detailed passive finite element (FE) models of the lumbar spine have been developed and validated under in vitro loading conditions. As these models are devoid of muscles, they are either not used to simulate in vivo activities or muscle forces are modeled by a hypothetical compressive follower load (FL). A number of symmetric and asymmetric static tasks were first simulated using a validated musculoskeletal model of the thoracolumbar spine to predict trunk muscle forces. The predicted muscle forces along with the gravity loading were then applied to a passive FE model of the L4-L5 motion segment (developed and validated here) to estimate load sharing among the disc,... 

In this project we plan to propose a mechanism for controlling the profile of vertebra displacment and intera-discal pressure in in-vitro tests. Spineis the one of the most important members of the human musculoskeletal system. Health and stability of the spine help the people to moves on two legs. So any problems with this organ, causing movement problems and pain. For the treatment of spinal diseases, several methods such as surgery, insertion of implants and stabilizing were used. To ensure the accuracy of these methods, laboratory examination is essential. One of the ways to test these interventions, the implementation of in vitro tests on samples obtained from the bodies of the spine.... 

In the present study, the thermal behavior of human teeth during laser radiation has been discussed. The high laser power, as well as its low emission, can allow deviations from the Fourier heat transfer model. To overcome this problem, the non- Fourier heat transfer method, dual phase lagged (DPL), has been used. Wisdom considered in this study to evaluate the thermal behavior of tooth. Using the finite volume method, the DPL equations are solved and the thermal response of the teeth is obtained during laser irradiation. The effect of delay times, which are the parameters of the DPL model and depart from the Fourier model, is fully demonstrated on the temperature behavior of the tooth, and... 

Todays, thanks to the positive effects of electric vehicles, (against the vehicles which use patrol as their fuel), reduction of the Earth temperature and its climate change; the manufacturing, sale and use of electric vehicles experience a sharp increase. In addition to decreasing the air pollution, due to their abundant smart implications, they have been dramatically propagated. Massive use of these devices has raised the concern about the loss of the security which is indispensable part of the infrastructure. None of the past publications and works have taken the cyber-attack on the charging price rate and other data into account. In this thesis, charging methods of electric vehicles are... 

80% of people in all over the world, experience Low Back Pain (LBP) once in their lives. LBP leads to dysfunction of spine. About 25% of LBP relates to the intervertebral disks which in the critical cases, a Posterior Lumbar Surgery (PLS) on the one or more lumbar disks should be done. Due to the some procedure such as retracting, cutting or denervation of muscles, PLS can hurt trunk muscles and spine. Thus, investigation of LBP and postoperative complications of PLS can help us in recognition of causes of LBP and PLS complications and modification of PLS approaches. The objective of this research was investigation of effects of LBP and PLS on the biomechanical function of spine. Pattern of... 

Biomechanical models are indispensable tools in predictions of muscle forces and joint loads towards design of prevention and treatment programs. In most of these models intervertebral joints are modeled as hinge joints thus neglecting the existing translational degrees of freedom (DOFs). This simplification can alter the results of the model as changes in model kinematics affect the prediction of the joint and muscle forces. The current study aims to evaluate the likely effect of this simplification on the predictions of the musculoskeletal model of AnyBody Modeling System (AMS) for muscle forces and spinal loads. Clinical application of this study is in assessing the limitation of... 

Manual material handling (MMH) activities are identified as risk factors for occupational low back pain (LBP). Task-related variables including load and posture characteristics are required as input into these models and tools for estimation of trunk external moment. Biomechanical modeling studies that aim to mathematically estimate low back loads currently need an inevitable parallel time-consuming in vivo study in an equipped laboratory to measure trunk posture under physical activities. Inertial sensors as a portable, accurate, almost inexpensive, and small device could be very helpful in order to capture the kinematic data of movement in human activities. My master thesis aims to... 

Nowadays, we are witnesses of deaths caused by cancer in large statistical amounts. Vast number of investigations are conducted for anticancer drug evaluation on human and animal cells using traditional two-dimensional and three-dimensional culturing platforms. However, most of them are not successful due to the lack of in-vivo relevant microenvironment in these platforms. One of the best cancer in-vitro cultures is the tumor spheroid which is a spherical cellular aggregation. By culturing these tumor spheroids in a microfluidic chip, it is possible to mimic the in-vivo microenvironment elements such as nutrient and metabolite gradients. Here we present a microfluidic device fabricated using... 

Autism spectrum disorders (ASD) have been defined as developmental disorders characterized by abnormalities in social interaction, communication skills, and behavioral flexibility. Over the past decades, studies using various genetic, neurobiological, cognitive and behavioral approaches have sought a single explanation for the heterogeneous manifestations of ASD, but no consensus on the etiology of ASD has emerged. Further studies aim to clarify the mechanism of disease.
Functional Magnetic Resonance Imaging (fMRI) is a new way of imaging which evaluates activity of brain by measuring magnetic difference caused by oscillation in blood oxygen level. fMRI has been widely used in recent... 

Statistical studies indicate the fact that in Iran, like many other developing countries, a significant percentage of buildings are made of traditional materials and most of them are adobe buildings especially in rural areas. Furthermore, geological data indicates that Iran is located in alps-Himalayas seismic zone and exposed by destructive earthquakes and adobe buildings suffer the most damages comparing with other type of the structures. According to these explanations, this research deals with adobe buildings behavior and provides solutions for reinforcing them and improving the seismic response of these buildings. These studies include numerical modeling with finite elements methods by... 

Study of hydraulic characteristics of two-phase flow is one of the important issues in hydraulic engineering. Two-phase flows usually accur in hydraulic structures such as pressurized flow tunnels, culverts, sewer pipes, junctions, and similar conduits. Under certain conditions, air may also be introduced into pressurized intake systems, which may form large bubbles in portions of the pipe. The bubbles may, in turn, cause an unstable slug flow, or other flow patterns. Slug flow is one of the most probable patterns in these flows. Prediction of pressure in this situation is a complex subject which despite its great importance is rarely discussed. In this study, the results of a laboratory...