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Plasmons at the LaAlO3/SrTiO3 interface and in the graphene- LaAlO3 / SrTiO3 double layer
, Article Physical Review B ; Volume 95, Issue 16 , 2017 ; 24699950 (ISSN) ; Asgari, R ; Sharif University of Technology
2017
Abstract
We study plasmon modes of the two-dimensional electron gas residing at the interface of band insulators LaAlO3 and SrTiO3 (LAO/STO) and the plasmon excitations of graphene-LAO/STO double layer as well. Considering the electron-electron interaction within random phase approximation, we calculate the plasmon dispersions of both systems numerically and in the long-wavelength limit analytical expressions for collective modes are found. One optical mode and two (three) acoustic modes are predicted for the LAO/STO (graphene-LAO/STO) system where only the uppermost acoustic mode of both systems can emerge above the electron-hole continuum depending on the characteristics of each system. In the case...
Electron mobility of a two-dimensional electron gas at the interface of SrTiO3 and LaAlO3
, Article Physical Review B - Condensed Matter and Materials Physics ; Volume 93, Issue 23 , 2016 ; 10980121 (ISSN) ; Asgari, R ; Langari, A ; Sharif University of Technology
American Physical Society
2016
Abstract
We calculate the mobility of a two-dimensional electron gas residing at the interface of LaAlO3/SrTiO3 following a three band Boltzmann approach at low temperature, where a carrier-charged impurity scattering process is assumed to be dominant. We explain the anisotropic characteristic of the dielectric function, which is a consequence of elliptical bands close to Fermi surface. The screening effect, which weakens the long-range Coulomb interaction of the electron-impurity, is considered within the random phase approximation. Working at carrier densities high enough to neglect the spin-orbit induced splitting of the bands, we find that the mobility varies inversely with the cubic power of the...
Magnetotransport of a two-dimensional electron gas with anisotropic Rashba interaction at the LaAlO3/SrTiO3 interface
, Article Physical Review B ; Volume 98, Issue 15 , 2018 ; 24699950 (ISSN) ; Asgari, R ; Langari, A ; Sharif University of Technology
American Physical Society
2018
Abstract
We investigate the magnetotransport properties of a two-dimensional electron gas with anisotropic k-cubic Rashba interaction at the LaAlO3/SrTiO3 interface. The Landau levels and density of states of the system as well as the magnetotransport coefficients are evaluated. A somehow anomalous beating pattern in low magnetic field regime is found in both the density profile and magnetoresistivity. We discuss the impact of electron density, Landau level broadening, and Rashba spin-orbit constant on the appearance of the beatings in low magnetic fields and find that at low electron concentrations and not very strong spin-orbit interactions the beatings smooth out. On the other hand, as the...
Thermal Analysis of Regenerative Cooling in Liquid Rocket Engines
, M.Sc. Thesis Sharif University of Technology ; Kebriaei, Azadeh (Supervisor)
Abstract
In this thesis to simulate the behavior of liquid engine Thrust chamber of hot gas from a quasi one dimensional code used when the effects of the heat transfer and friction in those terma. As well as during the regenerative channel is simulated by considering the equation’s of continuity, momentum and energy for one dimensional, effects of increase temperature, pressure drop, change the density of coolant flow resulting from the warming which is visible along the way to increase the accuracy of calculation of the thermal flux output of the engine, use a suitable model for unclear boiling in consideration of heat transfer coefficient used coolant flow it has been. As well as coupling of heat...
Prediction of Droplet size and Velocity Distribution by using Maximum Entropy Method
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)Experimental Investigation on Interaction of Three Converging Jets
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
In this thesis the instability regimes of the liquid sheet resulted from interactions of three converging jets is investigated. To this end, the shadowgraphy method is used. All the experiments have been done under the atmospheric pressure by using water as the jet fluid. The injectors are orifice ones.In our study, the effects of changing the jet velocities and changing the three jets’ structure (planar and non-planar) in having different liquid sheet shapes are investigated.Although so many researches have been done on interactions of two converging jets until now, there is almost not any researches about interactions of three converging jets. Considering this, this thesis topic is novel,...
Synthesis of Antibacterial Hydroxyapatite/Titania-Silver Coating on Titanium Substrate Using Sol-Gel Method
, M.Sc. Thesis Sharif University of Technology ; Afshar, Abdollah (Supervisor)
Abstract
With the increase in the average age of the world's population, osteoporosis is a worldwide incidence. This disease, along with natural disasters, are important factors in the occurrence of fractures in various bones of the body. One of the methods for solving this problem and replacing with broken body bones is the use of metal implants with hydroxyapatite-based coatings. One of the common problems with using implants in the body is the infection in the adjacent parts of the implant. To overcome this problem, several studies have been carried out on the use of hydroxyapatite coatings with metal ions or antibacterial oxide compounds. In the present study, the influence of factors such as the...
Experimental Investigation on Breakup Pattern of two Liquid Impinging Jets
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
Liquid atomization have broad range of usage in different industries. Colliding two jets is one method for atomization of different kind of fluids especially high viscose and viscoelastic fluids. Here, we experimentally investigated the effect of skewness and velocity differential of two Newtonian viscose colliding jets on formation of a special oscillating liquid sheet pattern with periodic fragmentation called “fishbone”. For this work, four liquid sheet regimes; triple chain, double chain, close rim, and open rim which fishbone pattern could be observed were produced and Skewness and jets velocity differential were applied to them. A synced CCD camera and stroboscope illumination source...
Interferometric Laser Imaging for Droplet Sizing (ILIDS)in Sparse Sprays
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
In the present work we first introduced ILIDS and review the theory of interferometry and light scattering from droplets. Bases on ILIDS method, droplets are irradiated by monochrome sheet laser, where the superposition of reflected and first-order refracted beams form a parallel fringe pattern at out of focus plane on the imaging sensor in the forward-scatter region. This pattern can be related to the droplet size by using simple geometrical optics. For the present work, an image processing algorithm is utilized to capture weak and noisy images of droplets to reduce the lost data in the sizing procedure. Since ILIDS method is applied for small and dilute spray, it is suitable for...
Particle Shadow Velocimetry in Premixed Flames
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
The velocity of the hot outflow gas in laminar premixed flame is one of the important properties of combustion, along with other properties such as temperature and flame components. In fact, laminar flame velocity has been employed in a multitude number of concepts ranging from engine design to achieving flame properties under turbulent conditions. In this research, a cylindrical Bunsen burner and appropriate TIO2 particles were used. Particles with diameters between 10-23 microns were used and the exit diameter of burner considered 14 mm. In this study, the equivalence ratio with a value between 0.9-1.2 are fed with LPG fuel to create a laminar premixed flame. As a result of the present...
Experimental Study of Spray Pattern of Two Impinging Jets of Non-Newtonian Gel Fluid Containing Aluminum Nanoparticles
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
In most of the studies conducted on the physics of the outflow from impinging jet injectors, Newtonian fluids have been used for their research and experiments. These studies have investigated the effect of factors such as geometrical parameters of the injector and physical properties of the fluid on different regimes resulting from the impact of the jet stream; Unfortunately, very few studies have been conducted on how to form spray and atomization in gel non-Newtonian fluids containing nanoparticles to investigate the above factors when using impinging jet injectors. Furthermore, although the addition of nanoparticles has advantages for better combustion, there are still problems in...
Implementation of Pressure Sensitive Paint (PSP)Method for Pressure Distribution Measurement
, M.Sc. Thesis Sharif University of Technology ; Kebriaei, Azadeh (Supervisor)
Abstract
Quantitative measurement of pressure on surfaces in wind tunnels and flight tests is essential to understand the aerodynamic performance of flying vehicles. Pressure data are also essential for validation and verification of computational fluid dynamics codes. One of the relatively new methods of measuring pressure distribution on aerodynamic surfaces is the method of pressure sensitive paint (PSP). The PSP method is an optical technique that can measure the pressure distribution on the surface without using common pressure sensors or transducers, with greater spatial resolution and lower cost. This method has a unique ability for non-contact (non-interfering) measurements. In this method,...
Experimental Study of Liquid Sheet Breakup in Cross Flow
, Ph.D. Dissertation Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
Injecting liquid fuel into the cross flow of air provides high penetration of the liquid, rapid mixing with air, and increased efficiency. This method has widespread applications in the propulsion systems of gas turbines, scramjets, turbine blade cooling, and fuel injection for engine afterburners. One of the design strategies for future aircraft engines is to reduce pollutants using fuel spray into the cross flow instead of direct jet fuel injection and using renewable energy sources. The applications of cross flows include injecting fluid through rotating pressure injectors in exhaust flows, injecting fluid through pressure-rotating injectors in radial injectors, and using slinger...
Implementation of Local Chemiluminescence Method on Flame
, M.Sc. Thesis Sharif University of Technology ; Kebriaei, Azadeh (Supervisor)
Abstract
In the present work, the local Chemiluminescence method has been implemented on a laminar premixed propane-air flame. The goal of this work is to achieve a system capable of measuring the intensity of Chemiluminescent radiations of CH* and OH* radicals locally and with high spatial and temporal accuracy. For this purpose, a setup has been designed and developed. In order to achieve high spatial accuracy for local measurements, a Cassegrain lens has been designed and built, which has the ability to collect light from a cylindrical control volume with a cross-sectional diameter of 58 μm and a depth of 3.4 mm. An optical system for dividing and filtering light based on wavelength has also been...
Investigation of Flow Formed by two Impinging Jets
, M.Sc. Thesis Sharif University of Technology ; Kebriaei, Azadeh (Supervisor)
Abstract
Due to importance of designing geometry and working condition of injector it is necessary that by testing cold flow, we gain better understanding of atomization characteristics and in particular initial atomization close to injector which defines the spray characteristics. Up to today experimental measurements in the high density zone close to injector has been difficult to to optical limitations and also analytical solutions of atomization process is limited due to complexity and highly nonlinear equations. Numerical solutions are also under development and researchers have recently done researches and simulations. In this field the modeling of liquid sheet collapse has challenged numerical...
Transport and Many-Body Studies at the LAO/STO Interface
, Ph.D. Dissertation Sharif University of Technology ; Asgari, Reza (Supervisor) ; Langari, Abdollah (Supervisor)
Abstract
In this thesis, we investigate some transport and many body properties of the 2DEG at the interface of LaAlO3=SrTiO3. First, following Boltzmann approach,we calculate conductivity and mobility of the system. We find that the mobility varies inversely with the cubic power of the carrier density ( / n3 2D) in good agreement with the experimental results. Taking in to account the variations of the dielectric constant of SrTiO3 with carrier density together with the variable impurity density are remarkably important in order to explain the abrupt decrease of the mobility with increasing the density in this system. We find that although the multiband nature of the system and interband...
An intelligent approach for improved predictive control of spray drying process
, Article INES 2010 - 14th International Conference on Intelligent Engineering Systems, Proceedings, 5 May 2010 through 7 May 2010, Las Palmas of Gran Canaria ; 2010 , Pages 127-136 ; 9781424476527 (ISBN) ; Neshat, N ; Saberi, M ; Sharif University of Technology
2010
Abstract
A flexible meta modelling approach is presented to predictive control of a drying process using Adaptive Neuro-Fuzzy Inference System (ANFIS), Artificial Neural Network (ANN) and Partial Least Squares (PLS) analysis. In the proposed approach, the PLS analysis is used to pre-process actual data and to provide the necessary background to apply ANN and ANFIS approaches. A reasonable section of this study is assigned to the modelling with aim at predicting the granule particle size and executing by ANFIS and ANN. ANN hold the promise of being capable of producing non-linear models, being able to work under noise conditions and being fault tolerant to the loss of neurons or connections. Also, the...
Integration of simulation and fuzzy multi-attribute decision making for modelling and assessment of fuzzy parameters
, Article International Journal of Industrial and Systems Engineering ; Volume 6, Issue 4 , 2010 , Pages 483-502 ; 17485037 (ISSN) ; Seifoory, M ; Abbasi, M ; Sharif University of Technology
2010
Abstract
This article introduces a methodology to integrate fuzzy multiattribute decision making (FMADM) and fuzzy simulation. According to this method, a fuzzy simulation method is applied to study the effect of different alternative on system's performance and decision criteria taking into account fuzzy inputs. Using a fuzzy analytical hierarchy process (FAHP) and the results of fuzzy simulation, a FMADM is conducted to select the best alternative. This article introduces how to incorporate fuzzy set theory with discrete-event simulation in order to model uncertain activity duration in simulating a realworld system, especially when insufficient or no sample data are available. A case study is...
Develoment of Droplet Velocimetry Method Using Shadowgrapy
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
Injection of liquid fuel in the cross-flowing air provides a means of higher penetration, rapid mixing of liquid fuel and air, and is encountered in many engineering applications. Air-breathing propulsion systems (e.g. gas turbine combustors, ramjets, and scramjets), liquid rocket engines,cooling sprays for turbine blades, and injection of fuel in the afterburners are examples of such applications. The identification of microscopic characteristics is one of the basic methods of atomizer examination, which has not been taken into account due to inadequate experimental equipment. In the present study, droplet mono-frame velocimetry and size distribution of secondary atomization in a pressure...
Experimental Investigation on Flame Chemiluminescence Emissions
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
The Chemiluminescence method is considered as one of the most widely optical methods that used for identifying combustion systems. In this study, the OH^* and CH^* Chemiluminescence signals were measured with the use of PMT detector and other optical equipments for a bunsen burner. Also the effect of equivalence ratio and flow rate on these signals have been investigated. The results show that with increasing flow rate, OH^* and CH^* signals increase linearly. By changing the equivalence ratio, both signals were maximized near stoichiometric condition (OH^* in lean side and CH^* in the rich side). Therefore, both OH^* and CH^* are considered as indicators of released heat rate. It was also...