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Creation of twisted terahertz waves carrying orbital angular momentum via a plasma vortex
, Article Journal of Physics D: Applied Physics ; Volume 49, Issue 29 , 2016 ; 00223727 (ISSN) ; Rooholamininejad, H ; Bahrampour, A ; Sharif University of Technology
Institute of Physics Publishing
2016
Abstract
In this paper a new method for generating twisted terahertz radiation is proposed. The generation of twisted terahertz radiation in a plasma vortex, where the plasma density profile has helical structure, is investigated. The method is described on the basis of angular momentum exchange between plasma vortex and laser beam. The interaction of the vortex plasma and photons causes the laser angular momentum to change. Twisted terahertz radiation is produced at the beat frequency of laser and electron plasma waves. In this process, for Gaussian laser modes, the angular momentum of terahertz wave derives from the plasma vortex, while for the Laguerre-Gaussian it originates in the difference in...
Nonlinear interaction of intense hypergeometric Gaussian subfamily laser beams in plasma
, Article Optics and Laser Technology ; Volume 81 , 2016 , Pages 40-45 ; 00303992 (ISSN) ; Vaziri, M. (Khamedi) ; Rooholamininejad, H ; Bahrampour, A. R ; Sharif University of Technology
Elsevier Ltd
Abstract
Propagation of Hypergeometric-Gaussian laser beam in a nonlinear plasma medium is investigated by considering the Source Dependent Expansion method. A subfamily of Hypergeometric-Gaussian beams with a non-negative, even and integer radial index, can be expressed as the linear superposition of finite number of Laguerre-Gaussian functions. Propagation of Hypergeometric-Gaussian beams in a nonlinear plasma medium depends on the value of radial index. The bright rings' number of these beams is changed during the propagation in plasma medium. The effect of beam vortex charge number l and initial (input) beam intensity on the self-focusing of Hypergeometric-Gaussian beams is explored. Also, by...
Investigation of optimum condition in oxygen gas-assisted laser cutting
, Article Optics and Laser Technology ; Volume 41, Issue 4 , 2009 , Pages 454-460 ; 00303992 (ISSN) ; Bahar, M ; Sharif University of Technology
2009
Abstract
Laser cutting characteristics including power level and cutting gas pressure are investigated in order to obtain an optimum kerf width. The kerf width is investigated for a laser power range of 50-170 W and a gas pressure of 1-6 bar for steel and mild steel materials. Variation of sample thickness, material type, gas pressure and laser power on the average cut width and slot quality are investigated. Optimum conditions for the steel and mild steel materials with a thickness range of 1-2 mm are obtained. The optimum condition for the steel cutting results in a minimum average kerf width of 0.2 mm at a laser power of 67 W, cutting rate of 7.1 mm/s and an oxygen pressure of 4 bar. A similar...
Simulation of Rapid Formation of Multicellular Spheroids in Double-emulsion Droplets with Controllable Microenvironment
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Sadrhosseini, Hani (Supervisor)
Abstract
This study is aimed at simulation of double emulsion formation in a microfluidic double flow focusing device which consists of two cross-junctions connected serially. The water in oil (w/o) emulsions are produced in the first junction. In the second junction, water in oil emulsions are encapsulated by an outer aqueous phase to generate water in oil in water (w/o/w) double emulsions. Water in oil emulsions are formed in hydrophobic channels and water in oil in water double emulsions are formed in hydrophilic channels. A three phase numerical model, based on the VOF-CSF method, is developed for simulating the process of double emulsion formation. An adaptive mesh refinement technique is...
An Investigation of Nonlinear Ultrasound Propagation in Soft-tissues and Transferred Energy
, M.Sc. Thesis Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor)
Abstract
In clinical applications of high intensity focused ultrasound, high amplitude acoustic waves are used to heat and ablate tumors and kidney stones. The high amplitude of ultrasonic waves leads to nonlinear effects within the acoustic filed. Heating stems from the acoustic power absorbed by tissues. The more the acoustic power is absorbed, the more the tissue temperature increases. On the other hand, more absorption means less penetration. Since the wave frequency is one of the important factors in power absorption, a compromise should be reached between the transferred energy and desired penetration depth. In this thesis, first, a problem with common HIFU-therapy conditions is simulated;...
Feasibility Study of Deposition by SUT-PF
, M.Sc. Thesis Sharif University of Technology ; Vosoughi, Naser (Supervisor)
Abstract
Sharif University of Technology Plasma Focus (SUT-PF) is a Mather Type DPF device which has a 39 μF capacitor bank with 14 KV charging ability at its ultimate limit corresponding to 7 KJ stored energy. In the first step of this experiment, a test has been done at three distances 5, 7, 10 cm from anode tip with the different number of shots 20, 30, and 40 at 0 constant angles.In the following, a test is done at 5 and 10 degrees with 40 shots, and PF chamber has been filled up with nitrogen gas. Various tests have carried out for survey of this experiment, the result of which are as follow:The X-ray diffraction (XRD) analysis are used in order to reveal if the Nickel or Nickel nitride have...
Simulation of Ultrasound Waves Propagation in Soft Tissue in Cancer Treating by HIFU
, M.Sc. Thesis Sharif University of Technology ; Ahmadiyan, Mohammad Taghi (Supervisor) ; Firoozbakhsh, Keikhosrow (Supervisor)
Abstract
Nowadays cancer has become one of the main and prevailing worldwide challenges in medical field, and many attempts have been made for treatment of this disease. The common methods for cancer treatment, have had significant side effects and even resulted death. The method of “High Intensity Focused Ultrasound” (HIFU) as a non-invasive method, has been welcomed by engineers and doctors and is using in some tumor based cancers. For predicting the level of temperature increasing in tissue, it’s necessary to model the ultrasound waves propagates from HIFU source precisely. The main object of this thesis is modeling and simulation of the behavior of ultrasound wave propagation and investigating...
Analysis of Appearance of Bone Barrier in HIFU Treatment Method
, M.Sc. Thesis Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor) ; Firoozbakhsh, Keykhosrow (Supervisor)
Abstract
Currently, the HIFU (High Intensity Focused Ultrasound) therapy method is known as one of the most advanced surgical techniques in tumor ablation therapy. Simulation of the HIFU therapy in the case of appearance of bon barrier is essential in HIFU planning to improve the usefulness and efficiency of treatment in brain tumor cases. In this work, linear, thermoviscous equations are applied for simulation of phase correction array and steering method, after analysis of performance, these methods are used in a 3D human brain and skull model to estimate thermal ablation in case of using these methods. Results indicate that the maximum focal pressure of 1.42 and 1.65 MPa can be achieved for...
Propagation Modeling of High Intensity Focused Ultrasound Wave through Multi Layer Tissue along with Experimental Validation
, Ph.D. Dissertation Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor)
Abstract
One of the main problems in human health, both in advanced societies and in growing societies, is a variety of cancers, one of which is brain tumor. One of the non-invasive methods of treating tumors is the use of ultrasound.HIFU (High Intensity Focused Ultrasound) therapy method is known as one of the most advanced surgical techniques in tumor ablation therapy. HIFU are produced and concentrated by powerful transducers. The two main mechanisms in HIFU are mechanical and thermal mechanisms, and the effects of these two mechanisms appear as thermal effects and cavitation. The fundamental mechanism in the HIFU is to absorb ultrasonic waves and to convert them into heat.The purpose of this...
Simulation of Microcapsule Formation for Cell Encapsulation Application
, M.Sc. Thesis Sharif University of Technology ; Saeedi, Mohammad Saeed (Supervisor) ; Kazemzadeh Hanani, Siamak (Co-Advisor)
Abstract
Co-culture of different cells is necessary for cancer spheroid formation in preclinical drug tests. It is possible to produce thousands of micro-droplets containing different cells, i.e. microcapsules, in a short time, using droplet microfluidics. However the homogeneity of the cell numbers in the droplets has remained as an unsolved problem.Despite the large amount of experimental efforts to reduce the number of undesirable microcapsules, no one tried to utilize the ease of computer aided simulation for investigating different parameters. In this study, we develop a novel method for capturing cell encapsulation using CFD simulations. The effect of the cell suspension inhomogeneity and...
Investigation of Energetic Electrons Behavior in Ultrafast High Power Laser-Matter Interaction
, Ph.D. Dissertation Sharif University of Technology ; Sadighi-Bonabi, Rasoul (Supervisor)
Abstract
Resent advances in ultra-intense short-pulse lasers and their numerous applications stimulated the research activities in important fields such as generation of high-energy electron and ion beams, monoenergetic electron beam, monoenergetic ion beam, X-ray emission, terahertz radiation, high harmonic and attosecond pulses generation. In all above mentioned applications the relativistic electrons behavior especially the electron density distribution and the velocity of electrons play an important role.
Investigating the behavior of relativistic electrons which are generated in the interaction of high power femtosecond lasers with plasma and their related applications is the main purpose...
Investigating the behavior of relativistic electrons which are generated in the interaction of high power femtosecond lasers with plasma and their related applications is the main purpose...
Numerical Modeling of Treatment of Liver Tissue Cancer by Using High Intensity Focused Ultrasound (Hifu)
, Ph.D. Dissertation Sharif University of Technology ; Firoozabadi, Bahar (Supervisor)
Abstract
In recent years, the incidence rate of liver cancer has increased sharply and nowadays liver cancer is known as the second leading cause of cancer death in the world. Surgical resection is usually used to treat malignant hepatic tumors. However, in some cases, surgical resection is not possible because of some reasons, such as tumor size and location. In these cases, other minimally invasive ablation methods such as radio-frequency ablation, microwave ablation, and high intensity focused ultrasound (HIFU) can be used. HIFU has some advantages such as noninvasiveness, high penetration depth, and low cost in comparison to the other ablation techniques such as radiofrequency ablation. In HIFU...
Focusing Wave Beyond the Diffraction Limitin Hyperthermia Application
, M.Sc. Thesis Sharif University of Technology ; Shishegar, Amir Ahmad (Supervisor)
Abstract
In this research, diffraction limit is introduced as the major challenge in wave focusing. Common wave focusing techniques have been reviewed and classified into two categories: far-field and near-field techniques. Through examples that illustrate its major inherent and practical challenges, super-oscillation has been presented as a specific idea of focusing waves using remote sources. By introducing subwavelength inhomogeneities in the region of interest, we have demonstrated sub-diffraction wave focusing in a near-field approach. Using the multipole method, the effect of injecting sub-wavelength cylindrical particles on focusing electromagnetic waves has been studied. Since when there are...
Numerical Investigation of Droplet Generation in a Microfluidic Flow-Focusing Junction Aiming High-Throughput Droplet Generation
, M.Sc. Thesis Sharif University of Technology ; Taghipoor, Mojtaba (Supervisor) ; Hosseini, Vahid (Supervisor)
Abstract
Droplet microfluidic platform generates monodisperse droplets in a desired size through immiscible multiphase flows inside microchannels. Droplets are individual reactor and can be used for bio(chemical) analyses. Also, for materials fabrication, droplet microfluidics offers a versatile platform for generation of nano- or micro-sized particles and microcapsules that are widely used in drug delivery. In addition to the monodispersity, high-throughput generation is also necessary in many applications. Therefore, droplets must be formed in stable regimes (dripping and squeezing) in the highest possible frequency. In this study, the flow-focusing geometry, which is the most common geometry in...
Production of drug Loaded Microgels Using Microfluidic
, M.Sc. Thesis Sharif University of Technology ; Saadatmand, Maryam (Supervisor) ; Eskandari, Mahnaz (Supervisor)
Abstract
Microfluidic systems have the ability to produce microgels with uniform size distribution and spherical shape due to the laminar flow and better control of the flow rates. Spherical microgels with same size can be used as high-potential carriers for drug release. An important challenge in the production of these drug-carrying microgels is the simultaneous process of drug loading into microgels and their production. The overall goal of this project was to produce drug-carrying microgels with uniform size distribution that show controlled drug release. To achieve this goal, various factors such as the type of polymer, the type of drug, the volume ratio of the polymer and the drug and the...
Numerical Study of Enhancement of Inflection Point Focusing for Blood Cell Separation
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Sadrhosseini, Hani (Co-Supervisor)
Abstract
Today, the determination and therapy of numerous illnesses, including malignant growth, relies upon the information and assessment of platelets, so blood testing and cell examination is fundamental to survey the movement of disease. The lab on a chip innovation is utilized as an extremely productive device in cell studies. The lab on a chip is used as a foundation and a substrate for making a legitimate stream for cell processes in medication. This innovation is a gadget or framework with millimeters or centimeters aspects like a chip, and it performs research facility handling on a micron-scale. In spite of the fact that it has a few impediments, it has so many values; for example, it...
Production of Liquid Metal Micro-droplets and Electrical Control of their Size and Rate of Formation
, M.Sc. Thesis Sharif University of Technology ; Kebriaee, Azadeh (Supervisor)
Abstract
The use of liquid metal droplets due to their high electrical and thermal conductivity are used in various industries today. One of the methods of producing these micro-droplets is the flow focusing method, which is widely used to produce integrated and monodispersed droplets. Liquid metals have high surface tension and these micro-droplets are formed only if there is sufficient shear force between the liquid metal and a continuous fluid phase. In the past, they used several different methods such as pressure fluctuations and changes in continuous phase flow rate to control the shear force and produced polymer, gas, etc. micro-droplets.In this research, use the electric potential to control...
An experimental review on microbubble generation to be used in echo-particle image velocimetry method to determine the pipe flow velocity
, Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 135, Issue 3 , Feb , 2013 , Paper No: FE-12-1217 ; 00982202 (ISSN) ; Shafii, M. B ; Shirani, S ; Sharif University of Technology
2013
Abstract
Microbubbles are broadly used as ultrasound contrast agents. In this paper we use a low-cost flow focusing microchannel fabrication method for preparing microbubble contrast agents by using some surface active agents and a viscosity enhancing material to obtain appropriate microbubbles with desired lifetime and stability for any in vitro infusion for velocity measurement. All the five parameters that govern the bubble size extract and some efforts are done to achieve the smallest bubbles by adding suitable surfactant concentrations. By using these microbubbles for the echo-particle image velocimetry method, we experimentally determine the velocity field of steady state and pulsatile pipe...
Importance of KPI in BI system, case study: Iranian industries
, Article ITNG2010 - 7th International Conference on Information Technology: New Generations, 12 April 2010 through 14 April 2010 ; April , 2010 , Pages 1245-1246 ; 9780769539843 (ISBN) ; Premier Hall for Advancing Science and Engineering, Inc. (PHASE) ; Sharif University of Technology
2010
Abstract
In today's competitive world, having an effective business intelligent (BI) system for monitoring and evaluation of industrial and product oriented organizations is vital. A perfect BI must help managers not only to speed up his decision making process; but also to increase quality of their decision. But how? One of the main specifications of an effective BI system is providing managers by correct format of information and at the correct time. Critical Success Factors (CSFs) are a kind of significant factors that must be considered in attaining an organization's goal; and key performance indicators (KPIs) are a type of quantitative and measurable CSF; and one character of an effective BI is...
Improved two-dimensional millimeter-wave imaging for concealed weapon detection through partial fourier sampling
, Article Journal of Infrared, Millimeter, and Terahertz Waves ; Volume 37, Issue 3 , 2016 , Pages 267-280 ; 18666892 (ISSN) ; Mokhtari Koushyar, F ; Seyed Talebi, S. M. J ; Kavehvash, Z ; Shabany, M ; Sharif University of Technology
Springer New York LLC
Abstract
Active millimeter-wave imaging based on synthetic aperture focusing offers certain unique and practical advantages in nondestructive testing applications. Traditionally, the imaging for this purpose is performed through a long procedure of raster scanning with a single antenna across a two-dimensional grid, leading to a slow, bulky, and expensive scanning platform. In this paper, an improved bistatic structure based on radial compressive sensing is proposed, where one fixed transmitter antenna and a linear array of receiving antennas are used. The main contributions of this paper are (a) reducing the scanning time, (b) improving the output quality, and (c) designing an inexpensive setup....