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Jafarian, Mohammad Javad,Nazarzadeh, Jalal The Korean Institute of Power Electronics 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.5
In this paper, a new development in the time optimal control theory in sliding mode control systems for multi-quadrant buck converters with a variable load is presented. In general, the closed-loop time optimal control system is applied to multi-quadrant buck converters for output regulation, so that an optimal switching surface is obtained. Moreover, an adjusted optimal sliding mode controller is suggested which adjusts the controller parameters to give an optimal switching surface. In addition, a description of the transient response of the closed-loop system is proposed and used to damp any output or input disturbances in minimum time. Numerical simulations and experimental results are employed to demonstrate that the output regulation time and transient performances of dc/dc converters using the proposed technique are improved effectively when compared to the classical sliding mode control method.
Jafarian, H.R.,Anijdan, S.H. Mousavi,Eivani, A.R.,Park, N. Elsevier 2017 Materials science & engineering. properties, micro Vol.703 No.-
<P><B>Abstract</B></P> <P>The evolution of microstructure together with mechanical properties change of Fe-28.5Ni steel, used in design of marine and nuclear related products, processed by different deformation amount during ARB process was elaborated by Electron Backscattered Diffraction (EBSD) method. EBSD results showed that the initial structure of the material contained retained austenite as the main phase besides martensite phase. Martensite phase was diminished after successive ARB cycles due to reduction of martensite start (M<SUB>s</SUB>) temperature. EBSD microstructural results exhibited that a stabilized nano structure was attained by 6-cycle or 8-cycle of the ARB process with the latter having slightly higher grain size due to the grain growth effect of dynamic restoration mechanism resulting from extreme deformation. Tensile test data on different cycles of ARB processed specimens showed that yield and ultimate tensile strengths were substantially increased after the first cycle of the ARB coinciding with the substantial amount of dislocations in the form of low angle grain boundaries (LAGB). Strengths increased in the successive cycles, though in a much slower pace. Ultra-fine grains were formed instead after high cycles of ARB process. Although such increase in strength generally came at the expense of ductility, the material after 8-cycle had still substantial ductility.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fe-28.5Ni contained two phases of retained austenite and martensite. </LI> <LI> Martensite phase is reduced and austenite stabilized during ARB process. </LI> <LI> A nano grain size structure is developed after severe plastic deformation. </LI> <LI> Extreme deformation slightly increases the grain size by dynamic restoration process. </LI> <LI> Substantial amount of ductility was achieved in SPD due to austenite stabilization. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
F. Jafarian,M. Taghipour,H. Amirabadi 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.5
Our goal is to propose a useful and effective method to determine optimal machining parameters in order to minimize surface roughness,resultant cutting forces and maximize tool life in the turning process. At first, three separate neural networks were used to estimate outputs of the process by varying input machining parameters. Then, these networks were used as optimization objective functions. Moreover, the proposed algorithm, namely, GA and PSO were utilized to optimize each of the outputs, while the other outputs would also be kept in the suitable range. The obtained results showed that by using trained neural networks with genetic algorithms as optimization objective functions, a powerful model would be obtained with high accuracy to analyze the effect of each parameter on the output(s)and optimally estimate machining conditions to reach minimum machining outputs.
Buckling analysis of embedded concrete columns armed with carbon nanotubes
Ali Jafarian Arani,Reza Kolahchi 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.17 No.5
As concrete is most usable material in construction industry it’s been required to improve its quality. Nowadays, nanotechnology offers the possibility of great advances in construction. For the first time, the nonlinear buckling of straight concrete columns armed with single-walled carbon nanotubes (SWCNTs) resting on foundation is investigated in the present study. The column is modelled with Euler-Bernoulli and Timoshenko beam theories. The characteristics of the equivalent composite being determined using mixture rule. The foundation around the column is simulated with spring and shear layer. Employing nonlinear strains-displacements, energy methods and Hamilton's principal, the governing equations are derived. Differential quadrature method (DQM) is used in order to obtain the buckling load of structure. The influences of volume percent of SWCNTs, geometrical parameters, elastic foundation and boundary conditions on the buckling of column are investigated. Numerical results indicate that reinforcing the concrete column with SWCNTs, the structure becomes stiffer and the buckling load increases with respect to concrete column armed with steel.
Analysis of a Triangular-shaped Plasmonic Metal-Insulator-Metal Bragg Grating Waveguide
Behnaz Jafarian,Najmeh Nozhat,Nosrat Granpayeh 한국광학회 2011 Current Optics and Photonics Vol.15 No.2
A novel triangular-shaped plasmonic metal-insulator-metal (MIM) Bragg grating waveguide is introduced,whose band-gap is narrower than that of the conventional step type and wider than that of the sawtoothshaped one. Moreover apodized triangular-shaped MIM Bragg grating structures are proposed in order to reduce the side lobes of the transmission spectrum, because the Bragg reflector with a sawtooth profile has a smoother transmission spectrum than that of a triangular-shaped one. The performance of the proposed structures is simulated by using the finite difference time domain method.
Mohammad Javad Jafarian,Jalal Nazarzadeh 전력전자학회 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.5
In this paper, a new development in the time optimal control theory in sliding mode control systems for multi-quadrant buck converters with a variable load is presented. In general, the closed-loop time optimal control system is applied to multi-quadrant buck converters for output regulation, so that an optimal switching surface is obtained. Moreover, an adjusted optimal sliding mode controller is suggested which adjusts the controller parameters to give an optimal switching surface. In addition, a description of the transient response of the closed-loop system is proposed and used to damp any output or input disturbances in minimum time. Numerical simulations and experimental results are employed to demonstrate that the output regulation time and transient performances of dc/dc converters using the proposed technique are improved effectively when compared to the classical sliding mode control method.
Rahimi, Hossein,Jafarian, Amirhossein,Samadi, Alireza,Meamar, Bahram,Rahmani, Shaghayegh Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.1
Background: Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkins lymphoma (NHL), accounting for approximately 25% of NHL cases. The aim of this study was to evaluate the association between the BCL6 and MUM1 gene expression and patient prognosis and stage. Materials and Methods: After ethical approval, in a cross-sectional study, tissue samples of 80 patients with diffuse large B-cell lymphoma were analyzed for BCL6 and MUM1 gene expression. Immunohistochemical staining was performed with division into categories of 0-5%, 5-25%, 26-50%, 51-75% and more than 75%. Other clinical and histological information such as lymph node involvement, T-stage, B symptoms and patient outcome were also recorded. Data were analyzed with SPSS version 16 and a P-value less than 0.05 was considered significant. Results: The patient mean age was $46.9{\pm}10.5$ years ($47.6{\pm}10.7$ and $46.1{\pm}9.6$ for males and females, respectively). A significant association was seen between lymphoma stage and BCL6 (p=0.045) but not MUM1 expression (p=0.09). However, the latter was associated with mortality (p=0.006) as was also the BCL6 level (p=0.006). Conclusions: : Overexpression of MUM1 and BCL6 is associated with poor prognosis in patients with diffuse large B-cell lymphoma.
A Kinetic Investigation of Ethanol Oxidation on a Nickel Oxyhydroxide Electrode
Danaee, I.,Jafarian, M.,Sharafi, M.,Gobal, F. The Korean Electrochemical Society 2012 Journal of electrochemical science and technology Vol.3 No.1
Nickel modified NiOOH electrodes were used for the electrocatalytic oxidation of ethanol in alkaline solutions where the methods of cyclic voltammetry (CV) and chronoamperometry (CA) were employed. In CV studies, in the presence of ethanol, an increase in the current for the oxidation of nickel hydroxide is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of ethanol is being catalysed through mediated electron transfer across the nickel hydroxide layer comprising of nickel ions of various valence states. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of ethanol was found to be $1{\times}10^7cm^2s^{-1}$.
An Upper Bound for the Probability of Generating a Finite Nilpotent Group
Halimeh Madadi,Seyyed Majid Jafarian Amir,Hojjat Rostami 경북대학교 자연과학대학 수학과 2023 Kyungpook mathematical journal Vol.63 No.2
Let G be a finite group and let ν(G) be the probability that two randomly selected elements of G produce a nilpotent group. In this article we show that for every positive integer n > 0, there is a finite group G such that ν(G) =1/n We also classify all groups G with ν(G) = 1/2 Further, we prove that if G is a solvable nonnilpotent group of even order, then ν(G) ≤p+3/4p , where p is the smallest odd prime divisor of |G|, and that equality exists if and only if G/Z∞(G) is isomorphic to the dihedral group of order 2p where Z∞(G) is the hypercenter of G. Finally we find an upper bound for ν(G) in terms of |G| where G ranges over all groups of odd square-free order.