Sharif Digital Repository

One of the main challenges in characterization and simulation of larg scale porous media is spatial heterogeneity and variability of porous media properties such as porosity, density, and lithology at different scales. These information can be achieved at different scale from coring, well logging or seismic data. Well logs are an efficient way to obtain rock and fluid properties of geological patterns specially water resources and hydrocarbon reservoirs. One of the characteristics of geophysical well logs is their complex behavior which seems to imply a multifractal nature.In this study we investigate multifractality and presence of long range correlations in petrophysical well log data such... 

Microrobots are the robots which manufactured or operated in micro dimentions. High accuracy, compatibility with harsh situations and caring or assembling in micro dimensions are the most important advantages of these robots. Manufacturing new microrobots with higher speed or increasing the velocity of existed microrobots is the discussion of these days.An A-shape microrobot designed and manufacturared before. The goal of this thesis is to model, identify the friction and observe the velocity of the A-shape microrobot. In low speeds both legs of microrobots are on the ground; it walks with the stick-slip motion principle. Increasing the velocity of the microrobot causes separation of one or... 

The market demand of super heavy crude oil is very low due to its determinative both physical and chemical properties. Unfortunately existing refineries in Iran are not capable to refine this kind of crude oil. Marketing issues besides great price difference with other crude oil types leads us to find economical solution for optimal use of this national possession. About 70 percent of super heavy crude oil produced from Soroush and Norouz oil fields is un-refineable materials and to refine this heavy crude oil to refinery products like gasoline or gas oil a refinery with RFCC ( Residual Fluid Catalitic Cracking) technology must be made. Super high Technology and very heavy capital cost... 

During the turning operation, the interaction of the metal cutting process and machine tool causes a dynamic instability called self-excited vibration or chatter. Limited productivity rate, decrease in tool life, poor surface quality and noisy workplace are some adverse effects of the chatter vibration. Chatter suppression in machining processes results in more material removal rate, high precision and surface quality. In this thesis, two control strategies are developed to suppress chatter vibration in turning process including a worn tool. A single degree of freedom model of the turning process including tool wear is briefly described. In the first stage, a sinusoidal spindle speed... 

A soft X-ray spectrometer based on Johann's method and an embedded curved crystal is designed and fabricated for Sharif University of Technology's Plasma Focus (SUT-PF) in this project. Focusing rays with the same wavelength at a point to increase the ray intensity is the reason of choosing the cylindrical curved crystal spectrometer since its performance is inspired to the Bragg's law.The optimal conditions for SUT-PF (pressure and voltage) is adjusted and examined by photodiode detector and the camera pinhole before spectroscopy experiments. The diameter of generated hot spots is measured as 80 microns in the optimal condition.The recorded spectral lines on the radiography film and the... 

The introduction of Minimally Invasive Surgery (MIS) has deeply influenced modern surgery. Despite all the advantages for the patient, this method produces some limitations for the surgeon. Limitations such as reducing degrees of freedom resulting in the loss of dexterity, depriving surgeons of the depth perception and sense of touch lead to human errors due to fatigue and intense mental activity. Overcoming these limitations is the reason for robots entering the operating rooms. In this research a robot-assisted surgery system including two 5-DOF robots is utilized. The goal of this research is to model and simulate this system and also to design a bilateral controller to provide haptic... 

Traditional assumptions about assessment and learning have been challenged in higher education. Alternative types of assessment have been introduced to align to the students’ learning aims. Although, the growing body of literature of alternative types of assessment such as peer-assessment and self-assessment shed light on the advantages and benefits of embedding assessment in classroom activities, there is not absolute agreement on the consistency and accuracy of these types of assessment. To this aim, this study attempted to investigate the reliability and validity of self-assessment and peer-assessment of Iranian EFL learners’ written and oral production. The data was obtained from 32... 

This research focuses on the dynamic analysis of an exoskeletal system to assist a paraplegic motion. Research in powered human exoskeletons began in the late 1960s, almost in parallel between the numbers of research groups for different applications. The main challenges for the recent work in exoskeletons were focused on the design and demonstration of an initial prototype. To this point, the reported advantages of the autonomous exoskeleton systems are largely anecdotal. Indeed, there is a marked lack of published quantitative performance results for exoskeleton devices that reportedly improve human locomotion. Considering this, there are many design challenges remained that may lead to... 

Keywords or keyphrases are of importance as the smallest unit of representing the meaning of a text. Automated Keyword Extraction (AKE), as one of the natural language processing tasks is used in various applications such as searching, indexing and information retrieval. Keywords of scientific articles are basically specified manually by their authors, whereas most of the information available on the internet lack such keywords. In this research, we endeavor to automatically extract keywords of a set of Persian paper abstracts using an unsupervised machine learning method. The method used is to extract a set of candidate phrases from the text, and to cluster the document words to find a set... 

Application of light metals such as Magnesium alloys due to proper mechanical behavior is increasing in industries such as automotive, electronics and so on. In this project, ingot of Mg-9Li-1Zn alloy with 10 mm thickness were produced by casting, then hot rolled at 300oC to reach 2mm thickness. Annealing at 350oC for 3 hours resulted homogenous properties in the final sheet.Study of monotonic and cyclic behavior of Mg-Li alloy by experiments and FE simulation was the goal of this project. Experimental monotonic and cyclic test were carried out in order to obtain the hysteresis loops and cyclic stress-strain curve. The Chaboche constant were extracted from the experimental test and used to... 

High efficiency and low-emission fuel cells have the capacity to replace fossil fuels for energy supply concerns. Solid oxide fuel cells operate in relatively high temperature and have power plant applications. Hence, they are acquainted to be coupled with cycle gas turbine to reduce the cost and increase the overall system efficiency. The control of these hybrid systems is so important. Due to the system nonlinearity and having more than one controlled variable, its control with classic methods would be difficult. The model based predictive control is used as an alternative to mitigate these difficulties. In addition to their high performance, their extension to the multivariate case would... 

With the progression of technology demands for novel method of heat cooling is increased so the old method of cooling such as heat removal by air stream with force convection and even single phase method was not sufficient for today’s industry need. Nowaday, spray cooling method which belongs to two phase cooling method is one of the most popular method. In this study two method of spray cooling: spray cooling with flow blurring nozzle and electrospray cooling were investigated. For both method, at first the physics of phenomena and morphology of spray is studied experimentally then the efficiency of heat removal in each method is evaluated by the assessment of variation of temperature and... 

Laser cladding is a processing technique of layer-by-layer material deposition which is widely used to repair important components. However, tensile residual stresses generated in this process may result in detrimental effects such as crack, undesirable deformation and reduced fatigue life. A thermo-mechanical finite element model is developed to accurately predict residual stresses of the multiple beads laser cladding process with incorporating the cyclic plasticity into the analysis by utilizing the nonlinear kinematic hardening behavior. FE results are presented for Inconel 718, a material for which the laser cladding process is widely used. The FE results are compared with those of... 

The objective of this study is to explore the relationship between the stock price volatility and dividend policy (dividend yield and dividend payout ratio) for the Iranian stock market. According to the studies of Baskin (1989) and Allen and Rachim (1996), the fixed effect and random effect regression models are applied in this research. The sample of data is composed of 200 public firms which are listed on the Tehran Stock Exchange (TSE) and paid dividends continuously from 2010 to 2020. The results indicate that the dividend policy has a significantly negative relationship with the stock price volatility. In addition, the Size of the company is negatively related to the stock price... 

Primary visual cortex plays a paramount role in processing visual information. Visual information after the primitive processing by LGN and Thalamus, will be sent to the primary visual cortex which is called V1 area. According to the fact that V1 neurons have the definitive sensitivity to the edge and contrast of visual stimuli so their behavior are very selective to the certain features, specially contrast, of visual stimuli. These neurons have different response behavior to contrast. In fact most of them have some nonlinear behavior to this feature. Normally we expect that response of them or spiking rate of them grow linearly by the contrast increases but in most many cases they have some... 

Epoxy resins are used for a wide number of application due to good stiffness, chemical resistant and dimensional stability. This is the reason of their use as matrix in composite material. The incorporation of a small amount of carbon nanotubes (CNTs) in epoxy increases mechanical properties if nanocomposite have strong interfacial interaction between epoxy and CNTs, fine dispersion of CNTs and high final aspect ratio CNTs. In Noncovalent functionalization by polymer surfactant, CNTs are dispersed in a solvent/surfactant solution by ultra-sonication and then added to epoxy. In this thesis a novel study of toughening and mechanical properties of epoxy/ rubber/ CNT nanocomposite is presented....