A note on periodic solutions of matrix riccati differential equations

, Article Applied Mathematics E - Notes ; Volume 21 , 2021 , Pages 179-186 ; 16072510 (ISSN) Goodarzi, Z ; Mokhtarzadeh, M. R ; Pournaki, M. R ; Razani, A ; Sharif University of Technology

Tsing Hua University 2021

Abstract

In this note, we show that under certain assumptions the matrix Riccati differential equation X′ = A(t)X + XB(t)X + C(t) with periodic coeffi cients admits at least one periodic solution. Also, we give an illustrative example in order to indicate the validity of the assumptions and the novelty of our result. © 2021, Tsing Hua University. All rights reserved

An existence-uniqueness theorem for a class of boundary value problems

, Article Fixed Point Theory ; Volume 13, Issue 2 , 2012 , Pages 589-592 ; 15835022 (ISSN) Mokhtarzadeh, M. R ; Pournaki, M. R ; Razani, A ; Sharif University of Technology

2012

Abstract

In this paper the solutions of a two-endpoint boundary value problem is studied and under suitable assumptions the existence and uniqueness of a solution is proved. As a consequence, a condition to guarantee the existence of at least one periodic solution for a class of Liénard equations is presented

A note on periodic solutions of Riccati equations

, Article Nonlinear Dynamics ; Volume 62, Issue 1-2 , 2010 , Pages 119-125 ; 0924090X (ISSN) Mokhtarzadeh, M. R ; Pournaki, M. R ; Razani, A ; Sharif University of Technology

2010

Abstract

In this note, we show that under certain assumptions the scalar Riccati differential equation x′=a(t)x+b(t)x 2+c(t) with periodic coefficients admits at least one periodic solution. Also, we give two illustrative examples in order to indicate the validity of the assumptions

Extending protection selectivity in low voltage DC microgrids using compensation gain and artificial line inductance

, Article Electric Power Systems Research ; Volume 188 , 2020 Shamsoddini, M ; Vahidi, B ; Razani, R ; Nafisi, H ; Sharif University of Technology

Elsevier Ltd 2020

Abstract

Vulnerability of power electronic converters in DC microgrids in case of fault occurrence in DC cables necessitates using a fast fault detection and isolation scheme. In this paper, a modified, fast and selective protection scheme has been presented, which provides the required tripping of low voltage DC (LVDC) microgrids. This protection scheme has been developed based on the natural characteristics of the fault current, in which the first and second derivatives of the fault current have been employed to define thresholds for discriminating between faulted and non-faulted situations. To enhance fault detection capability of the protection scheme, definition of thresholds have been improved...

Modification in Topology and Control Method for Improving Performance of Modular Multilevel Converter in 2N+1 and N+1 Modulation

, M.Sc. Thesis Sharif University of Technology Razani, Ramin (Author) ; Parniani, Mostafa (Supervisor)

Abstract

In Modular Multilevel converter, it is necessary to attain different objectives simultaneously. One of the most effective control methods which can cope with this kind of systems is the Model Predictive Control (MPC). This method predicts the values of control objectives based on different feasible states and determines the optimal one using cost functions. The number of feasible states can increase when the number of switches increases in the converter. This makes the MPC unable to be applied in the MMCs with hundereds of submodules (SMs) in each arm because of its heavy computational burden. In this thesis, a modified model predictive control is proposed to reduce the computational burden....

Application of double-cell arrangement in planar laser-induced fluorescence experiments

, Article Review of Scientific Instruments ; Volume 76, Issue 8 , 2005 , Pages 1-5 ; 00346748 (ISSN) Golnabi, H ; Ahmadi, H ; Razani, M ; Sharif University of Technology

2005

Abstract

This paper describes a double-cell method, which offers some advantages in image capturing and analysis of the planar laser-induced fluorescence (PLIF) experiments. Double static-cell and circulating-static designs are tested and the fluorescence results are reported. The static-static design offers some advantages when comparing the fluorescence signals for two different dyes, the effect of additives, and of oxidation, whereas the circulating-static design provides an effective method to study the thermal contributions of the measured signal, the photostability of a particular dye, the effect of adding agents, and the quenching effects on a dye under study. In this experiment Rhodamine-WT...

An enhanced hybrid modular multilevel converter for improved performance

, Article IEEE Transactions on Power Electronics ; 2018 ; 08858993 (ISSN) Razani, R ; Ravanji, M. H ; Parniani, M ; Sharif University of Technology

Institute of Electrical and Electronics Engineers Inc 2018

Abstract

This paper proposes an enhanced hybrid modular multilevel converter (MMC), which utilizes a combination of halfbridge submodules (HBSM) and at least one full-bridge submodule (FBSM). In the proposed structure, FBSMs work with half of the HBSMs nominal voltage in each arm. Due to the presence of FBSMs, HBSMs switching frequency drops significantly, which reduces the converter power loss compared to half-bridge based MMCs. Furthermore, because of redundant FBSMs, (2N+1)-modulation can be employed to generate the output voltage without increasing the circulating current, thus the converter performance is improved notably. Besides, with the redundant FBSMs the converter can continue its...

A modified indirect model predictive control for modular multilevel converters

, Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 1366-1371 ; 9781509059638 (ISBN) Razani, R ; Ravanji, M. H ; Parniani, M ; Sharif University of Technology

2017

Abstract

Modular multilevel converter (MMC) is among the promising topologies used in high-voltage/power purposes, especially for high-voltage direct-current (HVDC) transmission systems. In this paper, a modified model predictive control (MPC) strategy for an MMC-HVDC system is presented. In the proposed MPC strategy, output current, circulating current and capacitors voltage are controlled separately. In order to reduce the computational burden of the controller, the output current is controlled directly without any optimization. For suppression of the circulating current, capacitors voltage variations are employed to settle the converter arms voltages to their reference values. In addition, the...

Enhanced hybrid modular multilevel converter with improved reliability and performance characteristics

, Article IEEE Transactions on Power Electronics ; Volume 34, Issue 4 , 2019 , Pages 3139-3149 ; 08858993 (ISSN) Razani, R ; Ravanji, M. H ; Parniani, M ; Sharif University of Technology

Institute of Electrical and Electronics Engineers Inc 2019

Abstract

This paper proposes an enhanced hybrid modular multilevel converter (MMC), which utilizes a combination of half-bridge submodules (HBSM) and at least one full-bridge submodule (FBSM). In the proposed structure, FBSMs work with half of the HBSMs nominal voltage in each arm. Due to the presence of FBSMs, HBSMs switching frequency drops significantly, which reduces the converter power loss compared to half-bridge based MMCs. Furthermore, because of redundant FBSMs, (2N + 1)-modulation can be employed to generate the output voltage without increasing the circulating current, thus, the converter performance is improved notably. Besides, with the redundant FBSMs, the converter can continue its...

Effect of Surface Treatment on Bioactivity of Ti-6Al-4V Alloy

, M.Sc. Thesis Sharif University of Technology Omidi Razani, Abbas Ali (Author) ; Asgari, Sirous (Supervisor)

Abstract

In this research Ti-6Al-4V samples were surface treated with acid, alkali and sandblasting treatment. Alkali treatment parameter was the NaOH concentration. The results of roughness measurement demonstrate that increase in NaOH Concentration results in rougher surface. Sandblasting produces rough surfaces in the scale of 1 to 10 micrometers. Acid treatment reduces initial roughness and the resultant roughness is in the under micrometer scale. After surface treatment, samples were soaked in simulated body fluid for invitro assessment. Results of this analysis indicate that sample with sandblasting+chemical treatment has the best invitro bioactivity. Chemical+sandblasting treated sample shows...

Design and operation of an evanescent optical fiber sensor

, Article Optics and Lasers in Engineering ; Volume 45, Issue 1 , 2007 , Pages 12-18 ; 01438166 (ISSN) Golnabi, H ; Bahar, M ; Razani, M ; Abrishami, M ; Asadpour, A ; Sharif University of Technology

2007

Abstract

Design and operation of an optical fiber sensor based on the intensity modulation is reported in this article. Two distinct mechanisms are considered for the optical power loss and the sensor operation is explained in terms of these effects. The dominant loss mechanism is found to be the evanescent loss and based on this phenomenon the optical fiber sensor is designed. Performance of this sensor is tested as a liquid level sensor for water and the experimental results are reported. The dry and wet signals for this probe are measured for a series of measurements and important factors concerning the design and operation of sensor are described. The precision of measured values, reproducibility...

Effect of material properties on the mechanical performance of nitinol esophageal stent: finite element analysis [electronic resource]

, Article Materials Science Forum ; Volumes 773 - 774, 2014, 9-17 Nematzadeh, F. (Fardin) ; Sadrnezhaad, K ; Kokabi, H. A ; Razani, M ; Mohagheghi, A. H ; Sharif University of Technology

Abstract

Stent placement has been a main approach to treat gastrointestinal diseases during past decade. Nitinol superelastic stents have been considered as a solution to such difficulties as restenosis after implantation, low twisting ability, inadequate radial mechanical strength and inappropriate dynamic behaviors associated with the ducts. In this paper, effects of Af temperatures on mechanical performance of z-shaped Nitinol wire stent under crimping test for clinical applications are investigated by finite element simulation. Having 60% crimping and high radial resistive strength, favorable superelastic behaviors are attained at Af temperature of 22°C. The performance of the stent is seen to be...

Friction stir welding parameters optimization of heterogeneous tailored welded blank sheets of aluminium alloys 6061 and 5083 using response surface methodology

, Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Volume 226, Issue 12 , 2012 , Pages 2013-2022 ; 09544054 (ISSN) Ghaffarpour, M ; Dariani, B. M ; Hossein Kokabi, A ; Razani, N. A ; Sharif University of Technology

2012

Abstract

Today, tailored welded blank sheets have found various applications in automotive, aeronautic and many other industrial fields. One of the most efficient methods for production of tailored welded blank sheets is application of the friction stir welding process. In the present article, the effect of friction stir welding parameters on the microstructure and mechanical properties of heterogeneous tailored welded blank sheets made from aluminium alloys of types 5083-H12 and 6061-T6 with the similar thickness of 1.5 mm is studied. The considered parameters are rotational speed of the tool, linear speed of the tool, pin diameter and shoulder diameter. In order to come by a tailored welded blank...

Network vulnerability analysis through vulnerability take-grant model (VTG)

, Article 7th International Conference on Information and Communications Security, ICICS 2005, Beijing, 10 December 2005 through 13 December 2005 ; Volume 3783 LNCS , 2005 , Pages 256-268 ; 03029743 (ISSN); 3540309349 (ISBN); 9783540309345 (ISBN) Shahriari, H. R ; Sadoddin, R ; Jalili, R ; Zakeri, R ; Omidian, A. R ; Sharif University of Technology

2005

Abstract

Modeling and analysis of information system vulnerabilities helps us to predict possible attacks to networks using the network configuration and vulnerabilities information. As a fact, exploiting most of vulnerabilities result in access rights alteration. In this paper, we propose a new vulnerability analysis method based on the Take-Grant protection model. We extend the initial Take-Grant model to address the notion of vulnerabilities and introduce the vulnerabilities rewriting rules to specify how the protection state of the system can be changed by exploiting vulnerabilities. Our analysis is based on a bounded polynomial algorithm, which generates the closure of the Take-Grant graph...

Sequence dependence of the binding energy in chaperone-driven polymer translocation through a nanopore

, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 83, Issue 1 , January , 2011 ; 15393755 (ISSN) Abdolvahab, R. H ; Ejtehadi, M. R ; Metzler, R ; Sharif University of Technology

2011

Abstract

We study the translocation of stiff polymers through a nanopore, driven by the chemical-potential gradient exerted by binding proteins (chaperones) on the trans side of the pore. Bound chaperones prevent backsliding through the pore and, therefore, partially rectify the polymer passage. We show that the sequence of chain monomers with different binding affinity for the chaperones significantly affects the translocation dynamics. In particular, we investigate the effect of the nearest-neighbor adjacency probability of the two monomer types. Depending on the magnitude of the involved binding energies, the translocation speed may either increase or decrease with the adjacency probability. We...

First passage time distribution of chaperone driven polymer translocation through a nanopore: Homopolymer and heteropolymer cases

, Article Journal of Chemical Physics ; Volume 135, Issue 24 , 2011 ; 00219606 (ISSN) Abdolvahab, R. H ; Metzler, R ; Ejtehadi, M. R ; Sharif University of Technology

2011

Abstract

Combining the advection-diffusion equation approach with Monte Carlo simulations we study chaperone driven polymer translocation of a stiff polymer through a nanopore. We demonstrate that the probability density function of first passage times across the pore depends solely on the Péclet number, a dimensionless parameter comparing drift strength and diffusivity. Moreover it is shown that the characteristic exponent in the power-law dependence of the translocation time on the chain length, a function of the chaperone-polymer binding energy, the chaperone concentration, and the chain length, is also effectively determined by the Péclet number. We investigate the effect of the chaperone size on...

Reply: Abedpour, asgari, and tabar

, Article Physical Review Letters ; Volume 106, Issue 20 , 2011 ; 00319007 (ISSN) Abedpour, N ; Asgari, R ; Tabar, M. R. R ; Sharif University of Technology

2011

Irreversibility in response to forces acting on graphene sheets

, Article Physical Review Letters ; Volume 104, Issue 19 , May , 2010 ; 00319007 (ISSN) Abedpour, N ; Asgari, R ; Tabar, M. R. R ; Sharif University of Technology

2010

Abstract

The amount of rippling in graphene sheets is related to the interactions with the substrate or with the suspending structure. Here, we report on an irreversibility in the response to forces that act on suspended graphene sheets. This may explain why one always observes a ripple structure on suspended graphene. We show that a compression-relaxation mechanism produces static ripples on graphene sheets and determine a peculiar temperature Tc, such that for T

Analysis of design goals of cryptography algorithms based on different components

, Article Indonesian Journal of Electrical Engineering and Computer Science ; Volume 23, Issue 1 , 2021 , Pages 540-548 ; 25024752 (ISSN) Molk, A.M.N.G ; Aref, M. R ; Khorshiddoust, R. R ; Sharif University of Technology

Institute of Advanced Engineering and Science 2021

Abstract

Cryptography algorithms are a fundamental part of a cryptographic system that is designed and implemented to increase information security. They are the center of attention of experts in the information technology domains. Although the cryptography algorithms are implemented to attain the goals such as confidentially, integrity, and authenticity of designing, but other matters that must be noticed by designers include speed, resource consumption, reliability, flexibility, usage type, and so on. For the useful allocation of hardware, software, and human resources, it is important to identify the role of each of the factors influencing the design of cryptographic algorithms to invest in the...

Conservation of statistical results under the reduction of pair-contact interactions to solvation interactions

, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 72, Issue 6 , 2005 ; 15393755 (ISSN) Radja, N.H ; Farzami, R. R ; Ejtehadi, M. R ; Sharif University of Technology

2005

Abstract

We show that the hydrophobicity of sequences is the leading term in Miyazawa-Jernigan interactions. Being the source of additive (solvation) terms in pair-contact interactions, they were used to reduce the energy parameters while resulting in a clear vector manipulation of energy. The reduced (additive) potential performs considerably successful in predicting the statistical properties of arbitrary structures. The evaluated designabilities of the structures by both models are highly correlated. Suggesting geometrically nondegenerate vectors (structures) as proteinlike structures, the additive model is a powerful tool for protein design. Moreover, a crossing point in the log-linear diagram of...