Sharif Digital Repository

One of the recent studies in the field of humanoid robots is to achieve a robot gait close to the human-like gait. Therefore, using the foot equipped with passive or active toe joint is developed in case of robots. The results of several studies show that the segmented foot with a toe joint has several advantages compared to the rigid foot in: walking speed, range of joint angle and ability to kneel and climb higher steps. Both passive and active toe joints of humanoid robots are developed. Advantages of the passive toe joint is obvious; in terms of design, it is more simple and light. Moreover, in normal gait, when the robot is equipped with passive toe joint, body inertial causes an... 

Long memory in assets return is important on the theoretical as well as the practical aspects and since it is a special form of nonlinear dynamics, in this study an ARFIMA model was used with the aim of considering the long memory in the return conditional average of automobile industry index. Then, due to the observation of ARCH effects, the simultaneous conditional average modeling and turbulences in the automotive industry index return using an ARFIMA-FIGARCH model was considered in the residuals of the best fitted model and results were that for modeling the returns and turbulences of automobile industry stocks which has a special long memory, FIGARCH will provide better and more... 

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... 

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... 

Formation of Cyclobutane Pyrimidine Dimer (CPD), one of the most abundant types of damages in DNA double helices, is caused by UV radiation and plays a major role in causing skin cancer. DNA photolyase is an efficient enzyme that repairs this UV-induced damaged DNA-base. Previous studies have shown that the enzyme flips the dimer out of the DNA double helix into its binding pocket.
In this project, several nanoseconds of molecular dynamics simulations was performed to investigate the process of base flipping energetically. These simulations are consist of equilibration of repaired and damaged double strands for 3 and 8 nanoseconds respectively. All these simulations ran over NVT... 

In this thesis, an extended nonlinear model of peripheral milling process (2D) is presented. For the first time, cutting forces are described through a complete third order polynomial function of the axial depth of cut. Also, cubic nonlinearity is considered for the structural stiffness as a function of tool tip displacement. To complete the model, process damping and tool wear effects are also considered. A set of experiments including modal tests to determine natural frequencies and structural damping ratios; and also cutting force measurements at different feed rates to determine nonlinear cutting force coefficients, are carried out. Also, measurement of critical axial depth of cut at... 

The main objective of this project is the deposition of photo-catalysts on cement and concrete blocks with an emphasis on commercialization. We started with an extensive study of common methods introduced in previous literature, and conclude with a number of suggestions for industrialization. First, slurry and sol-gel deposition of the photo-catalysts on blocks of type 2 commercial cement which is one of the most used materials in construction of buildings and waste-water treatment plants has been examined to reach a method of sample formation. Due to the simplicity of common methods and low quality of formed samples (less than 5 percent aging efficiency), the obtained experience was used to... 

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... 

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... 

Textile industry wastewaters are one of the important sources of environmental contamination because they produce large quantities of highly colored effluents. In recent years, use of advanced oxidation processes by producing highly active and reactive components such as hydroxyl radicals has been proposed. In this study, two oxygenated photocatalytic systems including UV/ZnO and UV/TiO2 were examined for degradation of C.I. reactive orange 16 dye as a typical organic pollutant in textile effluents. A thin gap annular photoreactor was designed and applied for the experiments. The photoreactor provided large surface area exposed to UV light, where in the solution layer renewal on the UV... 

Nowadays, in many of industrial processes, it’s necessary to measure acceleration of a moving object. Among the different type of accelerometers, the piezoelectric type are most useful and the most widely used. These sensors come in various configurations.
In the past, analytical and semi-empirical models have been used to design piezoelectric accelerometers. In these methods, based on some assumptions, the accelerometer nonlinear model is replaced with a linear model and the equivalent circuit model has been used to model accelerometer behavior. In these methods, the behavior of accelerometer become different from the expected one.
Recently, with the invention of efficient computing... 

Small animal SPECT imaging systems have a broad application in developing new diagnostic or therapeutic radiopharmaceutical and biomedical researches. The main goal of this imaging method is to determine distribution tendency and amount of radio pharmaceutics in body. In this study we have developed a reconstruction technique along with photon attenuation correction so as to obtain a high quality image and the finding a relationship between image matrix and absorbed radioisotope in tissues in order to quantify SPECT images with acceptable error range. In this research we have used MLEM method for image reconstruction and the obtained images were evaluated from quantitative and qualitative... 

Depletion of fossil fuels and their price increase, world is going to face critical energy challenges in the near future. Thereforefinding proper replacements for fossil fuels is inevitable. On the other hand, releasing of huge amount of wastewater into environment imposes serious nvironmental threats. Microalgae can be a potential alternative for biological wastewater treatment as well as fuel production. Microalgae grown in wastewater can eliminate remaining nitrogen and phosphorous. The gorwn biomass can be used for biofuel production afterward. Microalgae can also decrease the amount of greenhouse gas through the consumption of CO2 as energy sources. In this study, nutrient removal from... 

According to human needs and in line with the development of advanced technologies, different biomedical Engineering fields like hard tissue implants are growing rapidly. Despite significant biotechnology Developments in recent years, some problems to the recognition of implants related osseointegration phenomena persist. The deficient osseointegration and implant-associated infections are key issues for the long-term clinical success of titanium and titanium alloy implants, while development of multifunctional surfaces that can simultaneously overcome these problems remains highly challenging. Therefore, the ultimate goal of this paper was to improve bone cell attachment and simultaneously... 

Polycaprolactone (PCL) scaffolds and its composites containing bioactive glass particles (45S5) and TiO2 nanostructures with pre-defined and controlled external and internal architecture were prepared via an indirect three-dimensional (3D) printing process. The scaffolds had an interconnected structure with macro- (400-500 μm) and micro- (~25 μm) pores. Bioactivity, mechanical behavior and kinetics of tissue growth in 3D scaffolds were studied. The size effect of biogactive glass particles (6 μm, 250 nm, <100 nm) and morphology of titania nanostructures (spherical, tube, leaf-like, and flower-like particles) were elaborated. The biogactive glass particles with different sizes were prepared... 

Gas injection is a well-known enhanced recovery method which can improve recovery using two different displacement processes, miscible and immiscible. Typical non-hydrocarbon gases which have been utilized in these processes are carbon-dioxide and nitrogen. These gases are usually injected separately and have been rarely utilized together as a tertiary recovery process.
In this paper, we have focused on sequential carbon-dioxide and nitrogen gas injection as a novel EOR method. The periodic injections of carbon-dioxide and nitrogen have been repeated for six injection pore volumes. Sensitivity analysis of injection pressure, injection volume and injection rate have been also investigated... 

In recent years, carbon dioxide is used for enhanced oil recovery of heavy oil. Steam Huff and Puff is one of the enhanced oil recovery methods used for heavy oil. In this study liquid CO2 was used as an injecting fluid instead of steam. In this paper a series of experiments were performed to demonstrate the effect of carbon dioxide injection pressure on huff and puff process. The experimental data are used in lab scale model simulated with commercial simulator Eclipse 300 to investigate the effect of soaking time, injection pore volume and rate of injection on the heavy oil recovery. Result of experiments showed that huff and puff process under miscible pressure condition gives the most...