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    Hydrophilicity and AFM Based Surface Statistical Analysis of SiO2/TiO2/Glass Bilayer

    , M.Sc. Thesis Sharif University of Technology Daryaei, Ebrahim (Author) ; Moshfegh, Alireza (Supervisor) ; Jafari, Golamreza (Supervisor)
    Abstract
    Titanium dioxide (TiO2) is important because of wide applications such as self cleaning surfaces and using in photoelectrochemical cells .Recent researches have shown that addition of silicon dioxide into TiO2 increases hydrophilicity of SiO2-TiO2 and improves surface properties. Until now a little research has been done on the double layer TiO2/SiO2 system; therefore, this system is suitable for studying. In general this thesis consists of theoretical and experimental parts .In the experimental part, multilayer systems of SiO2/TiO2/Glass have been selected (thickness of SiO2 is 20 nm) and surface morphology and hydrophilicity have been investigated by Atomic Force Microscopy (AFM) and... 

    Control of Locomotion in a Two-Leg Robot with Uncertain Frictional Effects

    , M.Sc. Thesis Sharif University of Technology Khodabakhsh, Mohammad (Author) ; Vosoughi, Golamreza (Supervisor)
    Abstract
    Microrobots design and manufacturing has been one of interesting fields in robotics in recent decades. They have been designed in various types so far. In this paper a two-leg microrobot is simulated and controlled by using LuGre friction model.
    The proposed microrobot is driven by a piezoelectric actuator mounted between centers of two legs. The piezoelectric is actuated by a frequency near the natural frequency of the robot. The nonlinear dynamical equations of the system are obtained considering LuGre friction model. To control the system, the equations of motion are linearized using feedback linearization method. Then a stabilizing control law is designed and the robot model is... 

    Improving the Performance of the Fast Downward Planning System

    , M.Sc. Thesis Sharif University of Technology Sadraei, Reza (Author) ; Ghasem Sani, Golamreza (Supervisor)
    Abstract
    The so-called “Fast Downward” is a successful heuristic planner. This planner extracts informative data structures during planning. A number of efforts have been made to detect some constraints for guiding search toward the goal, in the hope to speed up the planning process. These constraints usually result in a number of sub-goals and determining their proper ordering. These sub-goals are called landmarks, which must be true at some point in every valid solution plan. Landmarks can be used to decompose a given planning task into several smaller sub-tasks. In this dissertation a new method is proposed to extracts landmark and recognizes their ordering based on fast downward basic data... 

    Bias of a Value-at-Risk Estimator

    , M.Sc. Thesis Sharif University of Technology Hasanzade, Mehrnoosh (Author) ; Keshavarz Hadad, Golamreza (Supervisor)
    Abstract
    The recent researches show that Value at Risk estimations are biased and is calculated conservatively. Bao and Olah (2004) proved that the bias of an ARCH(1) model for VaR can be formulated in to two parts: bias due to return Misspecification ( ) and bias due to estimation error ( ). Using a GARCH(1,1) and quasi maximum likelihood estimation method, this research intends to find an analytical framework for the two source of biases. We generate returns from Normal and t-student distributions, then estimate the GARCH(1,1) under Normal and t-student assumptions. Our findings reveal that equals to zero for the Normal likelihood function, but . Also, and are not zero for the t-student... 

    Dynamic Analysis of Electrostatical Scratch Drive Micromotors

    , M.Sc. Thesis Sharif University of Technology Abtahi, Mansour (Author) ; Vossoughi, Golamreza (Supervisor) ; Meghdari, Ali (Supervisor)
    Abstract
    In this thesis, the dynamic analysis of the scratch drive micromotor will be investigated. Scratch drive micromotor consists of a rotational arrangement of the scratch drive actuators (SDAs). SDAs that are actuated by using electrostatic force are used in a wide range of applications in microelectromechanical systems (MEMS) due to their unique advantages such as large output force, long travel distance and high-precision step size. However implementing a physical model to describe the movement of the SDA is chalanging and little researches have been performed to model and analyse the SDAs, in porpuse of predicting the behavior of the SDA before final design and manufacturing. By reviewing... 

    Modeling of Biological Cells with Applications to the Design of a Nano-Micro Gripper Used in Cell Manipulation

    , M.Sc. Thesis Sharif University of Technology Abbasi, Ali Asghar (Author) ; Ahmadian, Mohammad Taghi (Supervisor) ; Vossoughi, Golamreza (Supervisor)
    Abstract
    Grasping and manipulation of biological cells have an extensive applications in genetics ,cell proliferation ,cell injection and etc. In robotic manipulation ,it is often assumed that the objects being handled are rigid and only small deformations occurred during manipulation. this does not apply for the case of biological cells. biological cells are highly deformable structures, and their material properties are not well quantified. Therefore strategies for characterizing and manipulating of such deformable objects needs to develop. Different experimental techniques have recently been used and devised to study biological cells. On the one hand, although this experimental techniques have... 

    Design and Fabrication of a Device for Positioning Magnetic Micro Robot

    , M.Sc. Thesis Sharif University of Technology Agha Seyed Mirzabozorg, Amir Hossein (Author) ; Nejat, Hossein (Supervisor) ; Vossoughi, Golamreza (Supervisor)
    Abstract
    At the moment, one of the most important challenges that human beings are struggling with is the dominance of micro and nano dimensions. Considering the potential of microorganisms, and in particular magnetic microscopes, it is believed that using this technology, humans would be able to meet most of their needs. Studies have shown that it is possible to control the position of a magnetic microrobots, through the production of magnetic fields, with sufficient accuracy. Since magnetic fields are biocompatible, magnetic microrobots can also be used in biotechnology and medical applications.In this dissertation, a positioning device was designed and constructed with the ability to position the... 

    Gapless chiral excitons in thin films of topological insulators

    , Article EPL ; Vol. 107, issue. 2 , 2014 ; ISSN: 02955075 Jafari, S. A ; Sharif University of Technology
    2014
    Abstract
    In a nanoscopic thin film of a strong topological insulator (TI) the Coulomb interaction in the channel that exchanges the two electrons with the same chirality in two different planes of the slab takes advantage of the minus sign resulting from such "exchange" and gives rise to a bound state between the positive-energy states in one surface and the negative-energy states in the opposite surface. Therefore particle and hole pairs in the undoped Dirac cone of the TI thin film form an inter-surface spin-singlet state that lies below the continuum of free particle-hole pairs. This mode is similar to the excitons of semiconductors, albeit formed between the electron and hole pairs from two... 

    Collective excitations and the nature of Mott transition in undoped gapped graphene

    , Article Journal of Physics Condensed Matter ; Volume 24, Issue 30 , 2012 ; 09538984 (ISSN) Jafari, S. A ; Sharif University of Technology
    2012
    Abstract
    The particle-hole continuum (PHC) for massive Dirac fermions provides an unprecedented opportunity for the formation of two collective split-off states, one in the singlet and the other in the triplet (spin-1) channel, when the short-range interactions are added to the undoped system. Both states are close in energy and are separated from the continuum of free particle-hole excitations by an energy scale of the order of the gap parameter Δ. They both disperse linearly with two different velocities, reminiscent of spin-charge separation in Luttinger liquids. When the strength of Hubbard interactions is stronger than a critical value, the velocity of singlet excitation, which we interpret as a... 

    Nonlinear optical response in gapped graphene

    , Article Journal of Physics Condensed Matter ; Volume 24, Issue 20 , 2012 ; 09538984 (ISSN) Jafari, S. A ; Sharif University of Technology
    2012
    Abstract
    We present a formulation for the nonlinear optical response in gapped graphene, where the low-energy single-particle spectrum is modeled by massive Dirac theory. As a representative example of the formulation presented here, we obtain a closed form formula for the third harmonic generation in gapped graphene. It turns out that the covariant form of the low-energy theory gives rise to peculiar logarithmic singularities in the nonlinear optical spectra. The universal functional dependence of the response function on dimensionless quantities indicates that the optical nonlinearity can be largely enhanced by tuning the gap to smaller values  

    Exact phase boundaries and topological phase transitions of the XYZ spin chain

    , Article Physical Review E ; Volume 96, Issue 1 , 2017 ; 24700045 (ISSN) Jafari, S. A ; Sharif University of Technology
    2017
    Abstract
    Within the block spin renormalization group, we give a very simple derivation of the exact phase boundaries of the XYZ spin chain. First, we identify the Ising order along ◯ or ŷ as attractive renormalization group fixed points of the Kitaev chain. Then, in a global phase space composed of the anisotropy λ of the XY interaction and the coupling Δ of the Δσzσz interaction, we find that the above fixed points remain attractive in the two-dimesional parameter space. We therefore classify the gapped phases of the XYZ spin chain as: (1) either attracted to the Ising limit of the Kitaev-chain, which in turn is characterized by winding number ±1, depending on whether the Ising order parameter is... 

    Electric field assisted amplification of magnetic fields in tilted Dirac cone systems

    , Article Physical Review B ; Volume 100, Issue 4 , 2019 ; 24699950 (ISSN) Jafari, S. A ; Sharif University of Technology
    American Physical Society  2019
    Abstract
    We show that the continuum limit of the tilted Dirac cone in materials such as 8-Pmmn borophene and layered organic conductor α-(BEDT-TTF)2I3 corresponds to deformation of the Minkowski space-time of Dirac materials. From its Killing vectors we construct an emergent tilted-Lorentz (t-Lorentz) symmetry group for such systems. As an example of the t-Lorentz transformations we obtain the exact solution of the Landau bands for a crossed configuration of electric and magnetic fields. For any given tilt parameter 0≤ζ<1, if the ratio χ=vFBz/Ey of the crossed magnetic and electric fields satisfies χ≥1+ζ, one can always find appropriate t-boosts in both valleys labeled by τ=±1 in such a way that the... 

    Tilted-Lorentz symmetry

    , Article Iranian Journal of Physics Research ; Volume 19, Issue 4 , Winter , 2020 , Pages 831-834 Jafari, S. A ; Sharif University of Technology
    Isfahan University of Technology  2020
    Abstract
    Dirac cone can be tilted in condensed matter setting. As a result of tilt, the Lorentz symmetry is reduced to what we call tilted-Lorentz symmetry. In this paper, we derive the tilted-Lorentz transformations that leave a world with tilted Dirac cone invariant. © 2020, Isfahan University of Technology. All rights reserved  

    Mitigating DDoS Using BOTNET Analysis with Flow Anomaly Detection

    , M.Sc. Thesis Sharif University of Technology Baradaran Jafari, Navid (Author) ; Jafari, Mahdi (Supervisor) ; Endicott-Popovsky, Barbara (Co-Advisor)
    Abstract
    Internet is the largest multi-purpose, self-reliant, complex and distributed computer network across the globe. The nodes of this network are placed in every place like homes, offices, military camps, schools and all other locations by utilizing many different communication protocols, media and capacities. Furthermore, by rapid technology development, there are many newly born applications utilizing internet in new ways such as Internet of Things systems. The explosive growth of technology causing accelerated addition of new nodes to the internet, and any new single node may have several new unpatched vulnerabilities. This is a serious issue for managing this vast chaotic configuration and... 

    Analysis and simulation of ring resonator silicon electro-optic modulators based on PN junction in reverse bias

    , Article Optical Engineering ; Vol. 53, issue. 12 , 2014 ; ISSN: 00913286 Jafari, O ; Akbari, M ; Sharif University of Technology
    2014
    Abstract
    The theory of silicon optical modulators of ring resonators based on PN diode in reverse bias is primarily discussed. It secondarily provides a full-featured simulator to investigate the behavior of such modulators. Wave equation for ring structure will be solved by using the conformal transformation method and the matrix method as it was used to analyze bent planar optical waveguides. Power coupling between ring and straight waveguides will be calculated by coupled theory of nonparallel waveguides based on experimental results. The time response demonstrates the capability of this device to operate correctly at up to 10 Gbs-1 bitrate, and the frequency spectrum analysis of device shows a >... 

    Neural network-based brain tissue segmentation in MR images using extracted features from intraframe coding in H.264

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 9 December 2011 through 10 December 2011, Singapore ; Volume 8349 , December , 2012 ; 0277786X (ISSN) ; 9780819490254 (ISBN) Jafari, M ; Kasaei, S ; Sharif University of Technology
    2012
    Abstract
    Automatic brain tissue segmentation is a crucial task in diagnosis and treatment of medical images. This paper presents a new algorithm to segment different brain tissues, such as white matter (WM), gray matter (GM), cerebral spinal fluid (CSF), background (BKG), and tumor tissues. The proposed technique uses the modified intraframe coding yielded from H.264/(AVC), for feature extraction. Extracted features are then imposed to an artificial back propagation neural network (BPN) classifier to assign each block to its appropriate class. Since the newest coding standard, H.264/AVC, has the highest compression ratio, it decreases the dimension of extracted features and thus yields to a more... 

    Automatic brain tissue detection in MRI images using seeded region growing segmentation and neural network classification

    , Article Australian Journal of Basic and Applied Sciences ; Volume 5, Issue 8 , 2011 , Pages 1066-1079 ; 19918178 (ISSN) Jafari, M ; Kasaei, S ; Sharif University of Technology
    2011
    Abstract
    This paper presents a neural network-based method for automatic classification of magnetic resonance images (MRI) of brain under three categories of normal, lesion benign, and malignant. The proposed technique consists of six subsequent stages; namely, preprocessing, seeded region growing segmentation, connected component labeling (CCL), feature extraction, feature Dimension Reduction, and classification. In the preprocessing stage, the enhancement and restoration techniques are used to provide a more appropriate image for the subsequent automated stages. In the second stage, the seeded region growing segmentation is used for partitioning the image into meaningful regions. In the third... 

    Microstructure generation of severely deformed materials using Voronoi diagram in Laguerre geometry: Full algorithm

    , Article Computational Materials Science ; Volume 50, Issue 9 , July , 2011 , Pages 2698-2705 ; 09270256 (ISSN) Jafari, R ; Kazeminezhad, M ; Sharif University of Technology
    2011
    Abstract
    A new Voronoi diagram in Laguerre geometry based on closed-pack non-overlapping circles was proposed. This diagram was used to simulate microstructure of severely deformed materials at different applied strains. Grains size and their fractions were introduced by controlling the size and distribution of nuclei. Edge number distribution and neighboring cells edge number along with area distribution of the simulated Voronoi cells were determined. The edge number distribution was observed to fit gamma distribution more accurately. However, due to high inhomogeneity in the microstructure of the deformed samples at low strains, edge number distribution could not be matched by any distribution... 

    Three-qubits ground state and thermal entanglement of anisotropic Heisenberg (XXZ) and Ising models with Dzyaloshinskii-Moriya interaction

    , Article International Journal of Quantum Information ; Volume 9, Issue 4 , 2011 , Pages 1057-1079 ; 02197499 (ISSN) Jafari, R ; Langari, A ; Sharif University of Technology
    2011
    Abstract
    We have studied the symmetric and non-symmetric pairwise ground state and thermal entanglement in three-qubits system. We have considered the anisotropic Heisenberg (XXZ) model in the presence of DzyaloshinskiiMoriya (DM) interaction in addition to the Ising model in a magnetic field with DM interaction. We have found that the increment of DM interaction and magnetic field can enhance and reduce the entanglement of the system. We have shown that the non-symmetric pairwise state has higher value concurrence and critical temperature (above which the entanglement vanishes) than the symmetric pairwise one. For the negative anisotropy, the non-symmetric entanglement is a monotonic function of DM... 

    Fibre position effects on the operation of opto-pair fibre displacement sensors

    , Article Optics and Laser Technology ; Volume 43, Issue 4 , 2011 , Pages 814-819 ; 00303992 (ISSN) Jafari, R ; Golnabi, H ; Sharif University of Technology
    2011
    Abstract
    In this article, two optical-fibre probes used in displacement measurements are reported. In one arrangement, two optical fibres with protective buffer jackets are placed together, while in the second arrangement, the protective buffer jackets are removed and the two fibres are placed with the claddings in contact, with a concomitant smaller centrecentre distance. As the core and cladding diameters are the same in both probes, the effect of the centrecentre distance on double-fibre designs can be investigated. The reflected output powers are recorded for the probes as a function of the axial distance from a reflective surface. A theoretical model is also implemented, which considers the...