Sharif Digital Repository

Nowadays, continuum robots have found many applications in the field of medicine, especially in minimally invasive treatments, due to their relative advantages over rigid robots. These advantages include more degrees of freedom, the ability to manufacture on micro and nano scales, and so on. Following the widespread popularity of these robots in various surgeries, including brain, cardiovascular, pulmonary, etc., the importance of their precise steering and control within the human body has also been identified. One of the methods for achieving this precision is through the use of a magnetic field to actuate these robots. This approach not only ensures safety for the human body but also... 

In this thesis, the general form of descriptor linear systems with time-delay is studied. First, an approach is presented to analyze the stability of descriptor linear systems with commensurate time-delay. Through this approach, not only stable and unstable regions of the system can be determined, but also the number of unstable roots in each unstable region can be calculated. Additionally, a decomposition approach is proposed, which transforms the descriptor systems with time-delay to normal time-delay systems with a lower order. As a result, a large number of methods which are only available for normal systems with time-delay can be utilized for descriptor systems with time-delay. Also,... 

In this study, investigated the simulation flow over a double-delta wing. The flow field was simulated by three dimension grid and RANS flow equation by K-ω-SST model. In order to investigate effect of AOA and leading edge flap simulated variable AOA and leading edge flap angle. The results shows created two vortex in inside and outside the wing. The vortex burst at high AOA and the Lift decrease after vortex bursting. The using leading edge flap effect on the vortex power and postpone vortex bursting and increasing wing lift coefficient in the high AOA. Also the leading edge flap effect on the pitch moment coefficient and change the pitch moment coefficient curve slope. The other effects of... 

In this research, we investigate shape fitting problems in high dimensional streams and we provide lower bounds for the problems of minimum enclosing spherical shell and minimum enclosing cylindrical shell in streaming model. We will prove that no streaming algorithm can approximate these problems with constant factor with storage sub-exponential in dimension. More precisely, we will prove that every streaming algorithm that can solve these problems with storage sub-exponential in dimension, does not have an approximation factor better than√28 d1/3, where d is dimension of the input points. This is the first lower bound that has been proved for these two problems in high dimensional streams  

Machining in its general concept forms the major part of manufacturing processes regarding time and cost. Therefore any progress in machining techniques would be well beneficial. High speed machining is one of the recent concepts in machining technology which has attracted much attention and effort. But high speed spindles as the main part of high speed machines, have been notorious for their lack of reliability and sudden failure which originates mostly from thermal problems. In order to ensure reliable operation of spindles it is necessary to predict thermo-mechanical behavior of machine-tool spindles. The major sources of heat in a spindle are angular contact ball bearings (the most... 

The application of wet cooling towers is cooling the circulating water which in many processes extract the exess heat in the system. Any cooling tower involves different parts and one of these parts is packings. The effect of changing packing's charactorizations on the cooling tower's performance is significant and was studied in different researches. In this project the effect of packing roughness on the heat transfer, mass transfer and pressure drop in two arrays of packings and in different conditions of water flow rate, air flow rate and inlet water temperature was studied experimentally. For calculating and investigating the change of mass transfer coefitient, the Poppe model was ... 

The applications of Internet of Things technology are increasing day by day. In the Internet of Things, various devices are connected to each other with the help of the Internet and perform various operations automatically. Today, this technology has various applications in smart city, smart home, smart car, as well as military industries and industrial factories. One of the newest applications is its use in the field of health and hygiene, which is known as the Internet of Medical Things or Smart Health. With the emergence of new epidemic diseases, the importance of this application becomes more clear. Smart health helps the patient. without going to the hospital and doctor in person, to... 

Cardio Vascular Diseases (CVD) is currently the most important cause of mortality in the world. Coronary artery disease (CAD-with 3 major epicardial vessels) is one of the significant CVD. Coronary angiography remains the gold standard for identifying the presence and absence of stenosis due to CAD. It is performed by inserting a catheter into the coronary artery, directly injecting radiopaque contrast material there and recording radiographic images in different view of arteries. Images of this invasive way show severity and area of stenosis.
A sign of CAD is endothelial dysfunction (inner artery layer) in peripheral arteries like the brachial artery. Due to a significant correlation... 

Liquid crystals are the type of the matter which show different levels of symmetry and structural properties in between those of a crystalline solid and an isotropic liquid. They can form various phases such as uni- or bi-axial nematics that because of their applications in display technology, have been widely investigated. In this thesis, uniaxial and biaxial ellipsoid liquid crystals have been simulated by using molecular dynamics simulations using LAMMPS simulation software. By control of the density of the system in NVT ensemble, the phase transitions of the systems were investigated. In all the simulations, the mesogens interact with RE-squared coarse grained force field. By calculating... 

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... 

The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's... 

In this project, a processing algorithm is approached which is resistant against environmental and motion noises to find the pulse transmission time using two photoplethysmography signals. For this purpose, a new processing framework is checked and generalized for photoplethysmography signals. Already, this processing framework had impressive results. The considered processing method is obtained by offering a dynamic model for the signal and using it in a Kalman filter structure. For the photoplethysmography signals, with modeling every beat of signal to a Gaussian three or four sum form and with adding self-returned equations for model parameters, a nonlinear signal model is obtained. Then,... 

Fatigue crack growth can have harmful effects on the reliability rotary machine. While an early warning to crack, can be used to extend the life of these expensive machines and increase reliability.Structural Vibration Condition Monitoring as a primary fault detection method, achieved to a lot amazing result and for this reason studies vibration behavior of cracked rotational shaft is a big issue for engineers of dynamic machine.In this research, first check the fault detection methods based on structural vibration condition monitoring, mode shape methods were extracted. Then by modeling rotational shaft in computer and creation of crack on it, fault detection quality of these methods have... 

It is important to provide an appropriate and economically method with technical and engineering considerations to stabilize excavated underground spaces. The necessity of this, especially for the construction of underground metro stations located in the cities which faces many problems, is more evident. In this research, it has been tried to introduce an optimal method according to the type of area for the construction of the underground station. In order to obtain stress and strain condition in structural elements and surface deformations due to different stages of excavating, numerical modeling in FLAC3D has been used. By examining the parameters that affect the sustainability of this... 

In the present study, the effects of increasing the value of shale gas production, either due to increased production or price increases, have been studied on economic variables such as employment, wage, property value and the number of births. In this regard, the data for each of these variables was used at the county level in the United States of America between 2000 and 2011. In order to estimate the desired effects, counties are divided into two types of boom and non-boom counties. The findings indicate that increasing natural gas production will lead to more employment and wage growth in boom counties than non-boom counties. Also, during the period of increasing production, the value of... 

Co-movement between inflation and nominal interest in response to an interest rate shock, dubbed neo-fisherianism, has been the subject of contentious debate since the advent of non-inflationary ZLB environment. We design an economic model rich with banking features to understand the economic responses to permanent and long-term interest rate shocks. We find that responses to a permanent positive interest rate shock depend on the monetary authorities’ speculation of the new long-term inflation rate, with the most probable outcome being a permanent increase in inflation. Responses to a long-term positive interest rate shock depict an increase and then decrease in inflation. We also discover... 

In this study, we aim to learn representations from microscopic cell images that effectively capture the features of drugs affecting the cells, allowing us to identify effective drugs for treating a disease. We employ two parallel learning paths using predictive and generative models. Specifically, we have achieved a predictive model on the RxRx19a dataset that, unlike previous models, is interpretable, optimized, and robust to dras- tic changes in drug properties. Additionally, we have developed the first generative model on this dataset, which not only generates high-quality images but also discovers a meaningful latent space. This latent space divides the representation into relevant... 

According to the World Health Organization, about 35% of deaths worldwide are due to cardiovascular diseases, therefore the evaluation of vascular endothelial function has great prognostic and diagnostic value for cardiovascular diseases. The conventional noninvasive method for endothelial function evaluation is the measurement of flow-mediated dilation in brachial artery using ultrasound imaging (FMD-US). As the accuracy of FMD-US depends on the operator's skill and the resolution of the ultrasound images, this method has not been adopted. In this work, we propose to use a low cost, easily-accessible surrogate signal, the photoplethysmogram (PPG) to implement the FMD test. Whereas previous...