Sharif Digital Repository

Investigation of possible vibratory responses of dynamical systems around their stable equilibria is an essential step which must be taken before their both design and application. The attained results of such a study can largely help to prevent instability in closed-loop stabilized systems by avoiding excitation of the system in the neighborhood of its resonance. In this paper, nonlinear oscillations of a Rotary Inverted Pendulum (RIP) enjoying a full-state feedback controller is investigated. Lagrange’s equations are employed to derive an accurate 2-DoF mathematical model whose parameters are extracted by both measurement and 3D modeling of the real system components. The perturbative... 

Tipping points occur in diverse systems in various disciplines such as ecology, climate science, economy, sociology, and engineering. Critical thresholds in system parameters or state variables at which a tiny perturbation can lead to a qualitative change in the system exist in many subsystems in complex systems. These thresholds are called tipping points, and these subsystems are called tipping elements. Additionally, many systems with tipping points can be modeled as networks of coupled multistable subsystems. Domino-like tippings are called tipping cascades. Considering that these tipping cascades are primarily unprecedented, it is essential to study the dynamics and control of these... 

Considering the fact that human capital is a crucial element in explaining the differences in income per capita and economic growth among countries, this research focuses on the effect of initial endowments of individuals on the process of human capital accumulation. One of the most important questions one can ask in this regard is whether individuals that are born in households with a low level of endowments, cannot develop their level of human capital due to a lack in the ability to obtain the factors required for their educational attainment. To answer this question, and considering the limitations of obtaining educational data, we aim to answer this question using district-level data.... 

In this work, we try to develop a method for searching for an object which is known to us and also returning it back where the search was begun, through shortest possible path. The surrounding environment was assumed unknown and only a stereo camera and an IMU exist to work with. The proposed method was developed in Linux using GPU and with C++ language and also achieved 58 fps. Parallel programming was utilized in different parts of the algorithm and obstacle avoidance is guarranteed. The surrounding environment and obstacles are assumed changing over the time  

In this piece of work, a gravity model is suggested as Iranian non-fuel export model to OIC countries. The most important results out of this model are the acquired coefficients of two variables, namely “ECO membership” and “Economic and Trade Freedom of Importer”. At first, we expected that for importer, being a member of ECO would increase the amount of trade with iran. Surprisingly, this is not what we see in a model. In fact, as ECO has not achieved any tangible success in increasing trade between its members, eastern Asian Muslim countries has become an important trade partner for iranians. This result is compatible with other pieces of researches about ECO. “Economic and Trade Freedom... 

Today’s growing interest to the underwater explorations and navigations demands to design appropriate underwater communication methods and systems. However, radio frequencies which are widely being used in free space communications, can’t be a good candidate for underwater wireless communications, due to their sever attenuation in water. On the other hand, underwater acoustic communication has been widely studied and implemented in the past decades, inspired by suitable propagation of acoustic waves through the underwater medium. Nevertheless, acoustic communication systems have limited bandwidth, lower propagation speed and lower security than optical counterparts, which suggests underwater... 

Visible light communication (VLC) uses huge license-free spectral bandwidth of visible light for high-speed wireless communication. Since each VLC access point covers a small area, handovers of mobile users are inevitable. In order to deal with these handovers, developing fast and effective resource allocation algorithms is a challenge. this paper introduces the problem of mobility-aware optimization of resources in hybrid VLC and 5G radio access technologies networks using the T-step look-ahead policy and employing the notion of handover efficiency. It is shown that the handover efficiency can correlate the overall performance of the network with future actions based on the mobility of... 

In present research, a cohesive based finite element model has been introduced to estimate median crack depth during mechanical machining on optical glasses. Development of the machining numerical model has been initiated by investigating the indentation process. Experimental results of this step have been calibrated primary numerical model which has been used in the scratch process. Due to differences between the scratch mechanism and indentation one, mathematical bases fracture formulas and cohesive relations have been developed. After extracting primary result, using them in the scratch model and developing the primary model, ultimately numerical model has been evolved to an abstract... 

Hydrothermal supercritical method is one of the most suitable methods for metal oxide nano powder, ceramics and mineral catalyst synthesis. Metal oxides nanopowder in its pure or mixed form has wide potential application as chemical industrial catalyst, hot Superconductors, magnetic material, gas sensors and car catalyst convertors. One of the most important metal oxides aspects of application is uranium oxide as nuclear reactor fuel is used. In addition, UO2 is selective catalyst for converting methane to methanol process and Decomposition of organic Chlorine material. In Supercritical hydrothermal method done in high pressure reactor with critical to fluid, is new method for the... 

Lithium has 9 isotopes which two isotopes are stable and remaining isotopes are unstable and have half-life. Lithium stable isotopes include 6Li and 7Li that their abundance is 7.53% and 92.47% respectively. Importance of lighter lithium isotope appears for its small cross section against thermal neutron and producing fusion reactors fuel in nuclear industries. Thermal neutron absorption cross section for 6Li and 7Li are 950 barn and 37 mbarn respectively. Interesting of these isotopes in nuclear industry is due to the large difference in the absorption cross section.6Li compounds implied for tritium producing in coat of nuclear fusion reactor with DT fuel. Following tritium is used in... 

Speech enhancement in noisy environments improves the quality and intelligibility of speech and reduces communication fatigue. High performance speech enhancement models are based on Bayesian estimation models, requiring estimations of the parameters of the functions that describe the likelihood and the prior distributions of the signal and noise processes. Two Bayesian speech enhancement models which are used in this thesis are Bayesian-Kalman filter and Bayesian MAP estimation.In real time applications including VoIP, in addition to additive noise, packet loss or packet delays might also occur. In real time communications the receiver terminal replaces silence for the duration of lost... 

Knowledge sharing as one of the most important knowledge management processes has been discussed in this research. The purpose of this study is investigating relationship between the Nonaka’s conditions for organizational Knowledge Creation and strengthening interpersonal Knowledge Sharing in the “Oil Industries Engineering and Construction Co. (OIEC)”. A quantitative questionnaire based servey was used to collect the required data and Structural Equation Modeling (SEM) to test the questions. The findings suggest that the “project intention”, ”personal autonomy”, “autonomy of project team” and “requisite variety” have impact on “attitude toward knowledge sharing”, and there is no significant... 

Aphron drilling fluids or CGA fluids are the wellknown updated drilling fluids in recent years.this kind of drilling fluids can control the mud loss into the formation and thus reduce formation damage and drilling costs. its structure consists of two phase fluid (gas and liquid) that the aphrons are the micro bubbles with 10 to 100 micrometer diameter that have strong stability in liquid phase compared to foamy drilling fluids. Generally aphron drilling fluids are made of base drilling fluid and surfactants, for more stability, mixed surfactant-polymer additive is so beneficial. in the last two decades, the Lattice-Boltazmann method is introduced for computational fluid dynamic area and... 

In past decades, the measurement of partial discharges (PDs) in high voltage equipments, was appreciated as one of the most efficient methods for evaluation of the equipment insulation condition. Generators, transformers, cables and transmission lines are especially checked to detect the presence of any partial discharge.
In AC high voltage systems, the measurement method is well established and known. The Phase resolved method is used to determine the partial discharge signals. These methods have been used for many years and their success in differentiating the various sources of partial discharge have proven. Although phase resolved method works on AC; due to lack of frequency... 

Due to conspicuous increases in shopping and goods transportation in this unbridled world, a significant part of companies’ final interest and final cost are related to their distributions of goods. Meanwhile, because of practical constraints of service hours and service distances, logistics companies usually build multiple depots to serve a great number of dispersed customers. Hence, multi-depot vehicle routing problems (MDVRP) win more and more engineers’ and companies’ attention to thrift their cost by using optimization methods. Considering NP-hardness of MDVRP and the lack of optimal solution derived by heuristic and meta-heuristic approaches in the large scale problems, in this... 

Security for wireless communication networks has become a crucial issue because of the broadcast nature of wireless channels. On every cellular network Since it is possible for passive nodes to easily overhear the confidential information transmitted between transmitter and receiver, it is necessary to provide secure communication.When a cellular user wants to communicate with a node or base station on the cellular network, it expects that information will be transmitted and received without interference, with enough quality and without eavesdropping. On the other hand In practical scenarios, we know that cellular network nodes are not equipped with ideal equipment and some percent... 

Cancer is one of the most causes of mortality in the world. Leukemia is a type of cancer initiated by the rapid proliferation of blood cells including WBCs, RBCs, and Platelets, that classified into four general types of AML, ALL, CML, and CLL. The main treatment of leukemia is chemotherapy. Because of many problems that patients have with this treatment and not so good results of chemotherapy, we design a microfluidic chip that can perform personalized medicine treatment for leukemia patients.This microchip consists of two main parts, Concentration Gradient Generator (CGG), and cell culture. CGG system is a tree CGG with two inlets and four outlets, which makes a linear concentration of... 

In this thesis, we study the resilience of complex systems under structural perturbations. After a brief review of the resilience and its importance, we show that how one can map a system of N-coupled dynamical equations onto an effective one-dimensional dynamics. This procedure is based on a nearest neighbor averaging. The obtained map, helps us study the response of the system to the effective one-dimensional control parameter, instead of all parameters that are affecting the structure of the network. Next, we use this procedure and unveil the resilience pattern of second-order Kuramoto oscillators on complex networks. Moreover, we propose a control strategy for complex systems which is... 

Foil gas bearings are compliant surface, self-acting hydrodynamic bearings that use ambient gas as their working fluid. They do not require external pressurization and are typically constructed from several layers of sheet metal foils. In high-speed, high-temperature applications the GFB’s have the advantage of developing higher load capacities than with fixed geometry gas bearings. Since GFB’s have a complex structure consisting of a spring-like substructure with an overlying flexible surface, there exists a great variety of permutations on any given design. At current work presents a 1D model for GFB with couple solving Reynolds and Euler-Bernoulli beam equation. This mean top foil assume to...