Sharif Digital Repository

The aim of this research is to analyze the failure and investigate crack growth in graphene using peridynamic theory. The presence of spatial partial derivatives in the equations of classical continuum mechanics has led to the fact that methods based on this theory are not valid in displacement discontinuities such as cracks. Peridynamic theory emerges as a nonlocal reformulation of mechanics, uniquely well-suited for modeling discontinuities and dynamic fractures in both continuous and discrete media. Its adaptability extends to various dimensions, encompassing phenomena at the nanoscale. In the present study, based on the ordinary state-based peridynamic theory, we investigated the... 

The present study investigates the vibrational behavior of a special type of nano-motor based on a thin cylindrical shell model and the nonlocal elasticity theory of Eringen. The presumed nano-motor is comprised of three single walled carbon nanotubes (CNT), where two of them are cantilevered and the third one is located in the middle. The CNT in the middle will suspend due to the Van-der-Waals forces generated from the interaction by the cantilevered CNT pair. Some proper chirality arrangements can conduct electricity and make the middle CNT rotate in extremely high speeds. In fact, the middle CNT rotates on a frictionless elastic foundation. In the present study, the nano-motor is modeled... 

Monitoring of activities of elderly and intelligent decisions about their living environment is a key challenge in smart environments. In the case of such challenges, correctness of system performance is highly dependent on how the model is designed. In the ambient intelligence (AMI) modeling, formal modeling is one of the best approaches because it supports certainty. In addition, time, location and mobility in AMI are crucial requirements, particularly in emergency treatment services. Ambient calculus is a formalism for describing mobility, process migration and message transfer, but it cannot express metric time duration. In this paper we propose an extension of ambient calculus with time... 

The distance measurement is the corner stone of the modern cosmology. They are measured via ”Doppler Effect”, accordingly the distances in cosmology are obtained in red-shift space. Despite the cosmological background expansion, the peculiar velocities due to the local density contrast distort these measurements. One of the main challenges in upcoming cosmological studies is to distinguish the peculiar velocity effect from the background expansion.Supernova Type Ia as standard candles can be think of a crucial observation to address the above problem. In this thesis, we study the effect of cosmological perturbations on distance-redshift relation of the SNIa. The corrective effects are from weak... 

There are many parameters which are utilized to obtain a more reasonable performance for structures under earthquake excitations in seismic provisions. It is well recognized that the main character to design of structures under seismic excitation is probabilistic rather than deterministic; therefore, it should be determined if the probability of structural damages is decreased when such parameters change in design of structures. In this thesis, fragility curves are developed in order to evaluate these parameters. Fragility curves are employed for various probability parameters. These diagrams are utilized to demonstrate when a coefficient or a number of parameters are used to improve... 

Deduplication is a data reduction technique, which eliminates redundant data by storing only a single copy of each file or block, along with a reference to the unique copy of data. Deduplication reduces the storage space and bandwidth requirements of data storage systems, and becomes more effective when applied across multiple users. All deduplication techniques use cryptographic algorithms to detect duplication instead of byte-by-byte comparison between input data and all previously stored data. In this manner, the data stream is divided into non-overlapping chunks of data. Then, the hash values of non-overlapping chunks create an exclusive criterion to identify duplicates. In this thesis,... 

With ever increasing amount of digital data, numerous efforts have been made in recent years towards improving reliability and availability of data storage systems. Previous studies have reported significant gap between estimated failure rates and observed failure rates in the field. This gap is mainly due to neglecting correlated failures in Redundant Array of Independent Disks (RAIDs). Proposing a model to consider correlated failures can significantly improve reliability models. In this thesis, we present a reliability model which considers correlated failures in RAID arrays. In the propose model, we use a correlation probability to take into account the correlation of failures between... 

Hoganas is a gas based process which is more than a hundred years old. In this research, studying parameters affecting the quality of sponge iron like temperature, time, particle size, type of reductant, type and dimension of crucible were discussed. Groups of particle size was 0-150,150-500,500-1000microns and temperature range was 900, 950, 1000, 1100, 1150°C. Time of tests was between 2 to 30 hours.at 1000 °C and 10 hours maximum metallization degree was 94.76.while at 1100 °C and 5hours better metallization degree was achieved. at 1000 °C and 5 h, particles with 500-1000micron size had better result than other groups.at higher temperature effect of particle size was gradually decreased... 

Removing nitrogen, as one the most surface and ground water contaminant is very important and in order to achieve this aim,nitrification and denitrification are effective and economical methods. In this work, moving bed biofilm reactor (MBBR) with initial denitrification structure, adapted from modified LUDZACK-ETTINGER (MLE) method used in order to industrial wastewater treatment with COD value in range of 900-2100 mg/lit and ammonium in range of 150-430 mg/lit in 3 hydrolic retention time of 18 , 12 and 8 hours.Aerobic reactor volume is 14.4 liter and anoxic reactor volume is 7.2 liter and reflux flow amount from aerobic reactor to anoxic reactor has considered being 3 times of anoxic... 

The air distribution is the main factor of contaminant transportation in cleanrooms. The experimental method is the most reliable one for investigation of flow field, which the difficulties associated with it, has limited not only the examination of the flow field in cleanrooms, but also the improvement of their qualities. Most of the experimental researches in indoor air quality concern conventional rooms and do not take into account specific supply-exhaust diffuser configurations, which are used in cleanrooms. Using small-scale models can reduce the complexity and the cost of measurements. In this research, the 3D velocity field of a small-scale cleanroom is measured in three different... 

Amorphous SiBNC ceramics have been developed as new high temperature materials. They show a high resistance against crystallization, high mechanical properties, low density, and high oxidation stability. Three synthesis methods have been developed for synthesis of SiBNC ceramics namely, Reactive magnetron sputtering, Mechanical alloying plus sintering, and polymer-derived ceramics. In this research among polymeric methods one pot synthesis due to high ceramic yield and high mechanical properties have been chosen. Two major methods for nanofiber preparation are Meltspinning and Electrospinng. It is notable that all of researches for SiBNC Nanofiber preparation has been conducted on... 

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... 

The study on new rheoforming technologies of semi-solid alloys has recently been one main subject interesting many researchers and industrials, and so many new methods about preparing semi-solid alloy slurry and rheoforming process have been suggested. Among more than 20 proposed methods, only MHD (Magneto Hydro Dynamics) and EMS (electromagnetic stirring) methods has been industrialized. In this research, the semi-solid slurry of A356 aluminum alloy was fabricated by electromagnetic stirrer under different conditions of stirring current, stirring time and pouring temperatures. Then the semi-solid slurry prepared in optimum conditions was injected into a step-die cavity by a drop device and...