Sharif Digital Repository

The Fourth Industrial Revolution brought about a fundamental change in the system of management and production, especially in the field of industry, which was accompanied by the development of technology in the fields of artificial intelligence, robotics, nanotechnology and biotechnology. In line with these changes, the industry needs a new method to evaluate the reliability of operational equipment using artificial intelligence and intelligent systems, which aims to optimize the balance between a variety of repair methods with the possibility of timely replacement of parts. In this new method, the life of the parts is increased and the unplanned maintenance costs and labor are reduced. One... 

In practice, structures made of concrete are full of cracks. The strength of concrete is mainly determined by the tensile strength, which is about 10% of the compressive strength. As long as cracking in concrete is unavoidable, we have to try to minimize their detrimental effects. This objective can be achieved by resisting (or limiting) propagation of existing cracks. Because of this, reinforcement (mostly steel) is used to increase the carrying capacity of the material and to control the development of cracks. Concrete structures that fail, already shows a large number of large and small cracks before their maximum carrying capacity is reached. The failure of concrete can be characterized... 

In this thesis we review several arithmetical questions about the diophantine equation φ[x]=q where φ is a nondegenerate symmetric bilinear form on a finite dimensional vector space, φ[x] is the corresponding quadratic form and q is a nonzero element of the ground field. We obtain class number and mass formulae for the orthogonal group associated to φ in a number field utilizing the concept of quadratic forms, lattices and adelic language  

The purpose of this study is to investigate the effect of radiation pressure on accretion disks. The radiation density causes the separation of electrons from ions which leads to the creation of an internal electric dipole. In this study Radiation density is calculated using the Eddington limit. Afterwards radiation pressure is calculated with the use of collisions between photons and electrons in the plasma. Collisions are assumed to happen only between photons and electrons, due to the larger cross section of electrons compared to protons. The mentioned assumption causes the creation of an electric dipole and with it an internal electric field. The separation of the charges is assumed to... 

In this thesis, a coarse-grained multi-scale method for 2D crystallyn solids based-on finite element consepts has presented. In this method, both scales are atomic scale and similar to what we see in non-local QC method, the entire atomic structure will be intact. Accordingly, calculations of potential functions and forces in the domain will have the atomic accuracy. In the presented method to reduce the domain’s degrees of freedom, the classical finite-element meshing concept to mesh the elastic linear areas in the domain is used and the MD calculations will done on the mesh nodes. Therefore, degrees of freedom in the system will reduce and consequently, the computational cost will reduce.... 

Investigation about Hydraulic Fracturing phenomenon in fractured porous medium which was occurred by in-situ fracture pressure upon the crack wings, owes the fact that creating enormous damages. However, it might include advantages such as increasing the rate of crude oil production from deep and high pressure/ high temperature reservoirs. On account of the fact that, existence of cracks and natural discontinuities and heat sources such as boundary of geo thermal reservoirs in porous mediums it is undeniable fact. Also, cross sectioning hydraulic fracturing cracks with natural cracks it is an obvious impact. Actually, investigation and analyzing the break throw of HF crack with natural... 

The classification of biological sequences is an open issue for a variety of data sets, such as viral and metagenomics sequences. Therefore, many studies utilize neural network tools, as the well-known methods in this field, and focus on designing customized network structures. However, a few works focus on more effective factors, such as input encoding method or implementation technology, to address accuracy and efficiency issues in this area. Therefore, in this work, we propose an image-based encoding method, called as WalkIm, whose adoption, even in a simple neural network, provides competitive accuracy and superior efficiency, compared to the existing classification methods (e.g. VGDC,... 

An inseparable problem from human daily life is stress that causes problems such as heart disease and depression, so stress management and control is essential for the health of the individual and society. This thesis explores the possibility of stress detection using vital signs and machine learning algorithms. First, by examining the potential of unsupervised learning algorithms for stress detection, a general method is developed and the accuracy of the algorithm is evaluated with the ECG signals of a smart wristband made in Sharif University of Technology Biosen group as well as WESAD data set. The self-organizing map structure is created based on stress-related features and final result... 

Disorders of the lumbar spine are prevalent within the realm of musculoskeletal issues, emphasizing the importance of investigating contributing factors. This research focuses on assessing how flexible footwear influences the kinematics and dynamics of the vertebral column during drop vertical jump. The study involves mechanical tests on various footwear types, including simple, flexible and re entrant shoes with differing levels of rigidity. Bending tests were performed on simple and flexible shoes with hardness of 50 Asker C and flexible shoes with hardness of 40 Asker C. Additionally, compression tests were carried out on all soles at two different angles. The Bending tests revealed that,... 

Always, there has been a great interest toward electromagnetic wave propagation and new ways for simulation of the problem. Level set methods provide a powerful mathematical framework for propagating surfaces (in 3-D) or curves (in 2-D). The contours of the moving objects are viewed as the zero level sets of a function and propagated in a Eulerian point of view by means of a Hamilton–Jacobi partial differential equation expressing the conservation of the level sets under a given velocity field. Level set methods have been applied in a wide range of domains, such as physics, chemistry, fluid dynamics, combustion, image processing… In this thesis, we introduce a new numerical procedure for... 

Bearing capacity of foundations is one of the most controversial issues in foundation engineering. In this study regarding to the previous researches which has done by the other researchers the bearing capacity factors of a footing has calculatedusing finite element method. On the next step of this study some footings has modeled on different positions near slopes with different angles and bearing capacity of them has calculated, then some strip foundation has modeled and bearing capacity of them has calculated and compared with the values of the footings in this study and strip foundations of the other researches. Furthermore some foundations have modeled on the solpe and bearing capacity... 

Titanium dioxide (TiO2) is a transparent n-type semiconductor with wide band gap which makes it suitable for applications such as solar cells. TiO2 dye-sensitized solar cells (DSSCs) transform the visible light energy to the electrical energy by excitation of absorbed dye. In the present study, TiO2 nanowires and nanoparticles were synthesized by hydrothermal and sol-gel methods, respectively. The effect of TiO2 morphology on photovoltaic performance of the cells was studied by fabrication of single layer DSSCs containing pure nanowires, pure nanoparticles and mixture of nanowires and nanoparticles with various weight ratios. The results revealed that, DSSC made of 10 wt% nanowires and 90... 

Meshless Methods using kernel approximation like Reproducing Kernel Particle Method (RKPM) are methods for solving partial differential equations that require only nodal data and a description of the geometry without requiring element connectivity data and mesh producing. An innovative method of nonplanar material partitioning method (NMPM) with implementation of RKPM is employed to calculate the stress intensity factor (SIF) at the tip of an anticrack sited in an isotropic plate under a remote applied loading. Numerical examples in comparison with the exact closed form expressions show that accurate SIF for mode I can be obtained.

 

The critical strain energy release rate for the solder joint fracture was measured as a function of cooling rate, time above liquidus (TAL) and soldering temperature. The specimens were prepared at 4 different levels of cooling rate, 3 varying levels of TAL, and 3 soldering temperature levels. Then, experiments were designed using the Taguchi method. Fracture tests were performed under bending at a strain rates of 10-5 and 0.5 s-1 and mode I loading conditions. It was found that the effect of soldering temperature insignificant on the Jci, but the cooling rate and the TAL due to their many effects were also studied by their interaction effects. It was observed that at the cooling rate of... 

The development of intrinsic theories for area-minimization problems was motivated in the 1950 by the diffichlty to prove, existence for the Plateau problem for surfaces in Euclidean spaces of dimension higher than two. After the pioneering work of R. Caccioppoli and E. De Giorgi on set with finite perimeter, W. H. Fleming and H. Federer developed the theory of currents, which leads to existence results for the Plateau problem for oriented surfaces of any dimension and codimension. The aim of this paper is to develop an existence of the Federer-Fleming theory to spaces without a differentiable structure, and virtually to any complete metric space. The starting point of our research has been...