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The Effect of Pressure on the Coexistence of Superconductivity and Magnetism in RuSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2O10-δ
, Ph.D. Dissertation Sharif University of Technology ; Akhavan, Mohammad (Supervisor)
Abstract
The coexistence of long-range magnetic order and superconductivity in the ruthenocuprate families, Ru1212 and Ru1222 has been studied both theoretically and experimentally. Historically these two different phases are incompatible with each other and in the most previous research reported on the coexistence of these phases, there have been observed separated magnetic and superconducting phases. However in the ruthenocuprate families, there is a single phase with both magnetic and superconducting phase which coexist with each other. It has been determined that superconductivity arises in CuO2 planes, and magnetic orders occur in RuO2. From experimental point of view, we have investigated the...
First Principles Studies of Mechanical, Physical, and Electronic Properties of a-Si - also, Diffusion of a Self-interstitial Atom in an Ultra-thin fcc Film Via Lattice Statics
, Ph.D. Dissertation Sharif University of Technology ; Mohammadi Shodja, Hossein (Supervisor)
Abstract
By employing first principles density functional theory-based (DFT) molecular dynamics (MD), the influences of dangling and floating bonds as well as distorted tetrahedral bonds are studied on the mechanical, physical, and electronic properties of amorphous Si (a-Si). For further examination of the effects of these geometrical defects, two distinct amorphous samples, namely as-quenched and annealed are generated and examined. To verify the validity of the representative cells, the obtained radial distribution function, pair correlation function, and cohesive energy are compared with those corresponding results presented in the literature. Moreover, the surface energy is calculated at final...
Wardrop's first principle: Extension for capacitated networks
, Article Scientia Iranica ; Volume 28, Issue 1 , 2021 , Pages 175-191 ; 10263098 (ISSN) ; Poorzahedy, H ; Nourinejad, M ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
In transportation literature, User Equilibrium (UE) has been widely studied since early 1950's, many studies of which define equilibrium flow of traffic for uncapacitated networks based on Wardrop's first principle, implying also a Nash Equilibrium (NE). Although, in general, the two equilibria (UE and NE) are not explicitly the same, they are shown to be equivalent under special conditions for uncapacitated UE, when volume delay functions are separable, continuous, non-decreasing and non-negative. A good deal of research is devoted to explain UE in capacitated networks based on Wardrop's first principle and the concept of generalized costs. However, UE for capacitated networks, even under...
Near-room-temperature spin caloritronics in a magnetized and defective zigzag MoS2 nanoribbon
, Article Journal of Computational Electronics ; Volume 19, Issue 1 , 2020 , Pages 137-146 ; Fathipour, M ; Faez, R ; Darvish, G ; Sharif University of Technology
Springer
2020
Abstract
Using a tight-binding approach and first-principles calculations combined with the nonequilibrium Green’s function method, the thermal spin transport in a zigzag molybdenum disulfide (MoS 2) nanoribbon in the proximity of a ferromagnetic insulator that induces a local exchange magnetic field in the center of the nanoribbon is investigated. It is found that a pure spin current and perfect spin Seebeck effect with zero charge current can be generated by applying a thermal gradient and local exchange magnetic field without a bias voltage near room temperature. Furthermore, it is shown that this nanoscale device can act as a spin Seebeck diode for the control of thermal and spin information in...
Enhanced ORR catalytic activity of rare earth-doped Gd oxide ions in a CoFe2O4 cathode for low-temperature solid oxide fuel cells (LT-SOFCs)
, Article Ceramics International ; Volume 48, Issue 19 , 2022 , Pages 28142-28153 ; 02728842 (ISSN) ; Akbar, M ; Yousaf Shah, M. A. K ; Noor, A ; Lu, Y ; Akhtar, M. N ; Mushtaq, N ; Hu, E ; Yan, S ; Zhu, B ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
The search for cathode materials with fast oxygen reduction reaction (ORR) catalytic activities and high ionic conductivity is the key obstacle to SOFCs commercialization and its operation at low temperatures. In order to search for a cathode with enhanced catalytic functionality, herein we report a single-phase CoFe2O4 (CFO) and CoGd0.2Fe1.80O4 (CGFO), which can be employed as an active cathode to improve electrocatalytic ORR functionalities at low temperature. It is found that CGFO having enriched oxygen vacancies exhibits the least polarization resistance (RP) of 0.42 Ωcm2 compared to the pure CFO which shows polarization resistance of 0.56 Ω cm2 under H2/air conditions. Furthermore,...
Tunable magneto-optical and interfacial defects of Nd and Cr-doped bismuth ferrite nanoparticles for microwave absorber applications
, Article Journal of Colloid and Interface Science ; Volume 608 , 2022 , Pages 1868-1881 ; 00219797 (ISSN) ; Lu, Y ; Hu, E ; Wang, B ; Niaz Akhtar, M ; Noor, A ; Akbar, M ; Yousaf Shah, M. A. K ; Wang, F ; Zhu, B ; Sharif University of Technology
Academic Press Inc
2022
Abstract
Tunable microwave absorption characteristics are highly desirable for industrial applications such as antenna, absorber, and biomedical diagnostics. Here, we report BiNdxCrxFe1-2xO3 (x = 0, 0.05, 0.10, 0.15) nanoparticles (NPs) with electromagnetic matching, which exhibit tunable magneto-optical and feasible microwave absorption characteristics for microwave absorber applications. The experimental results and theoretical calculations demonstrate the original bismuth ferrite (BFO) crystal structure, while Nd and Cr injection in the BFO structure may cause to minimize dielectric losses and enhance magnetization by producing interfacial defects in the spinel structure. Nd and Cr co-doping plays...
First-principles study on lattice instabilities and structural phase transitions in Ba doped La2 CuO4
,
Article
Physica C: Superconductivity and its Applications
;
Volume 517
,
October
,
2015
,
Pages 20-25
;
09214534 (ISSN)
; Akhavan, M
; Draxl, C
;
Sharif University of Technology
Elsevier
2015
Abstract
We present linear-response density-functional theory calculations for the high-Tc superconductor La2- x Bax CuO4 to study the doping dependence of phonon dispersion. Using the virtual crystal approximation, the doping range up to x = 0.20 is investigated. We find unstable phonon modes that soften around high-symmetry points of the Brillouin zone. These branches are analyzed as a function of doping and pressure. The structural distortions related to these phonons are in accordance with the observed phase transitions from the high-temperature tetragonal (HTT) phase to the low-temperature orthorhombic (LTO) and the low-temperature tetragonal...
Optimal-time quadcopter descent trajectories avoiding the vortex ring and autorotation states
, Article Mechatronics ; Volume 68 , 2020 ; Antunes, D ; Nejat Pishkenari, H ; Alasty, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
It is well-known that helicopters descending fast may enter the so-called Vortex Ring State (VRS), a region in the velocity space where the blade's lift differs significantly from regular regions and high amplitude fluctuations are often present. These fluctuations may lead to instability and, therefore, this region is avoided, typically by increasing the horizontal speed. This paper researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel experiments. Moreover, we propose that the so-called Windmill-Brake State (WBS) or autorotation region should also be avoided for...
Simulation of vacancy diffusion in a silver nanocluster
, Article Chemical Physics Letters ; Volume 498, Issue 4-6 , 2010 , Pages 312-316 ; 00092614 (ISSN) ; Negreiros, F. R ; Parsafar, G ; Fortunelli, A ; Sharif University of Technology
Abstract
The formation and diffusion of a vacancy in a silver nanocluster are studied via a combination of first-principles and statistical mechanics simulations. A 38-atom truncated-octahedral (TO) arrangement and its homologue with 37 Ag atoms and one vacancy are considered, and density-functional calculations are performed to derive the energies of the local minima and the energy barriers connecting them. These data are then used as an input for a study of the system dynamics via a kinetic Monte Carlo algorithm, evaluating site occupancies, diffusion coefficient and equilibration time. It is found that vacancy formation and diffusion represents a viable path for atom-atom exchange in these...
Mechanism of photocatalytic reduction of CO2 by Ag3PO4(111)/g-C3N4 nanocomposite: a first-principles study
, Article Journal of Physical Chemistry C ; Volume 123, Issue 36 , 2019 , Pages 22191-22201 ; 19327447 (ISSN) ; Moshfegh, A. Z ; De Leeuw, N. H ; Sharif University of Technology
American Chemical Society
2019
Abstract
Density functional theory (DFT) calculations have been performed to investigate the electronic structure and photocatalytic activity of a hybrid Ag3PO4(111)/g-C3N4 structure. Due to Ag(d) and O(p) states forming the upper part of the valence band and C(p), N(p), and Ag(s) the lower part of the conduction band, the band gap of the hybrid material is reduced from 2.75 eV for Ag3PO4(111) and 3.13 eV for monolayer of g-C3N4 to about 2.52 eV, enhancing the photocatalytic activity of the Ag3PO4(111) surface and g-C3N4 sheet in the visible region. We have also investigated possible reaction pathways for photocatalytic CO2 reduction on the Ag3PO4(111)/g-C3N4 nanocomposite to determine the most...
Gap tuning and effective electron correlation energy in amorphous silicon: A first principles density functional theory-based molecular dynamics study
, Article Computational Materials Science ; Volume 102 , May , 2015 , Pages 110-118 ; 09270256 (ISSN) ; Shodja, H. M ; Esfarjani, K ; Sharif University of Technology
Elsevier
2015
Abstract
First principles density functional theory (DFT)-based molecular dynamics (MD) is used to study some physical and electronic properties of amorphous silicon (a-Si) samples, as-quenched and annealed containing dangling and floating bonds (pertinent to the threefold- and fivefold-coordinated defects, respectively) as well as distorted tetrahedral bonds. Surprisingly, except for the work of Pantelides (1986) who gave a rough estimate for the effective electron correlation energy, Ueff of a floating bond on the fivefold-coordinated Si, to date, there are no theoretical studies in the literature for the calculation of Ueff pertinent to this type of defect. In this work, Ueff for each type of...
Self-Powered humidity sensors based on sns2nanosheets
, Article ACS Applied Nano Materials ; Volume 5, Issue 11 , 2022 , Pages 17123-17132 ; 25740970 (ISSN) ; Rafiefard, N ; Barzegar, M ; Fardindoost, S ; Irajizad, A ; Mohammadpour, R ; Sharif University of Technology
American Chemical Society
2022
Abstract
With the advent of the Internet of Things (IoT), the development of self-powered sensors has received much attention. Introducing triboelectric nanogenerators (TENGs) as a power source that converts mechanical movement into electrical signals has been admired recently. Moreover, the monitoring of humidity has become enormously essential in several technological contexts from environment monitoring to biomedical applications, thus joining these two subjects provides a huge benefit in achieving self-powered humidity sensors. Here, in this research, facile, low-priced and self-powered humidity sensors are fabricated utilizing transition-metal dichalcogenides (TMD) nanosheets. Semi-vertical SnS2...
Elastic moduli tensors, ideal strength, and morphology of stanene based on an enhanced continuum model and first principles
, Article Mechanics of Materials ; Volume 110 , 2017 , Pages 1-15 ; 01676636 (ISSN) ; Ojaghnezhad, F ; Etehadieh, A ; Tabatabaei, M ; Sharif University of Technology
Elsevier B.V
2017
Abstract
The present work aims to provide an accurate description of the tensile behavior of the planar as well as low-buckled stanene and to capture their ideal strength in armchair (AC)- and zigzag (ZZ)-directions. For an accurate description of anisotropic response of such hyperelastic materials as stanene, consideration of a highly nonlinear constitutive model in which up to the fourth power of strains is incorporated is inevitable. By utilizing first principles calculations based on density functional theory (DFT), the second, third, fourth, and fifth order elastic moduli tensors corresponding to both planar and low-buckled states are obtained. Moreover, the morphology of the free-standing...
First-principle electronic structure calculation of BaFe2-x Cox As2 (X = 0,1, 2) superconductor
,
Article
Journal of Superconductivity and Novel Magnetism
;
Volume 28, Issue 8
,
August
,
2015
,
Pages 2249-2254
;
15571939 (ISSN)
; Khosroabadi, H
; Akhavan, M
;
Sharif University of Technology
Springer New York LLC
2015
Abstract
The equilibrium crystal structure and electronic structure of BaFe2-x Cox As2 (x = 0,1, 2) superconductor have been investigated by using the pseudopotential Quantum Espresso code based on the ab initio density functional theory in the generalized gradient approximation. The equilibrium crystal structure for x = 1.0 has been determined by considering five different Fe/Co configurations. This study shows that the spin calculation is essential to obtain the experimental values at x = 0.0. The total and partial density of states, band structure, and Fermi surfaces of the three compounds has been calculated. Density of states calculation indicates the important...
Manipulation of structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet through vacancy defects: First-principles numerical simulations based on density-functional-theory along with tight-binding approximation
, Article Materials Research Express ; Volume 6, Issue 8 , 2019 ; 20531591 (ISSN) ; Irfan, M ; Iqbal, A ; Shahid, F. A ; Junaid Amjad, R ; Usman, A ; Mahmood, H ; Latif, H ; Imran, M ; Akhtar Ehsan, S ; Akhtar, M. N ; Akbar, N ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
Using the first-principles procedure of density-functional-theory within tight-binding approximation and nonequilibrium Green's function formalism, this paper reports on the impact of vacancy defects on the structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet. After the introduction of vacancy defects in graphene atomic sheet passivated with hydrogen atoms, apart from increase in band gap, a suppression is noted in the intensity of transmission channels and density of states arising from the long array deformations of the graphene sheet and a corresponding shift of the Fermi level. This in turn decreases the conductance of the defected graphene atomic...
First-principles study on ZnV2O6 and Zn2V2O7: two new photoanode candidates for photoelectrochemical water oxidation
, Article Ceramics International ; Volume 44, Issue 6 , 2018 , Pages 6607-6613 ; 02728842 (ISSN) ; Sabbagh Alvani, A. A ; Naseri, N ; Du, S ; Rosei, F ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
We used first principles calculations based on density functional theory with generalized gradient approximation to investigate and compare the structural, electronic and optical properties of two photoanode materials, ZnV2O6 and Zn2V2O7, for use in photocatalytic water splitting. After geometry optimization, the calculated structural parameters evince a satisfactory agreement with the reported experimental results indicating that the used method and conditions are suitable. The electronic structures demonstrate that both photocatalysts possess favorable band gaps (2.31 and 2.52 eV) and appropriate band edge positions for oxygen evolution reaction under solar radiation. The relatively light...
Molecular dynamics study of two dimensional silicon dioxides with in-plane negative poisson's ratio
, Article Computational Materials Science ; Volume 153 , 2018 , Pages 258-267 ; 09270256 (ISSN) ; Tavakoli, R ; Jafary Zadeh, M ; Sharif University of Technology
Abstract
In the present work, the mechanical properties, in particular, the Poisson's ratio of four two-dimensional silica structures, called here α,β,γ and δ are studied by means of molecular dynamics simulations. The α structure has been synthesized experimentally and the others have been reported as the most stable low-energy structures that reveal in-plane negative Poisson's ratio based on the first principles calculations. Among these structures, β-silica exhibits the largest in-plane negative Poisson's ratio which is 2–4 times higher than penta-graphene. Our results illustrate that the classical molecular dynamics simulation reproduces results in agreement with those of the first principles...
Synthesis, first-principle simulation, and application of three-dimensional ceria nanoparticles/graphene nanocomposite for non-enzymatic hydrogen peroxide detection
, Article Journal of the Electrochemical Society ; Volume 166, Issue 5 , 2019 , Pages H3167-H3174 ; 00134651 (ISSN) ; Hatamie, A ; Berahman, M ; Simchi, M ; Angizi, S ; Rahmati, R ; Kennedy, J ; Simchi, A ; Sharif University of Technology
Electrochemical Society Inc
2019
Abstract
Owing to the exceptional properties of graphene and the crucial role of substrate on the performance of electrochemical biosensors, several graphene-based hybrid structures have recently emerged, yielding improved selectivity and sensitivity. To date, most of the reported biosensors utilize solution-driven graphene flakes with drawbacks of low conductivity (due to high inter-junction contact resistant) and structural fragility. Herein, we present a conductive three-dimensional CeO2 semiconductor nanoparticles/graphene nanocomposite, as a platform for sensitive detection of hydrogen peroxide, an important molecule in fundamental biological processes. The 3D conductive graphene architecture is...
Synthesis, first-principle simulation, and application of three-dimensional ceria nanoparticles/graphene nanocomposite for non-enzymatic hydrogen peroxide detection
, Article Journal of the Electrochemical Society ; Volume 166, Issue 5 , 2019 , Pages H3167-H3174 ; 00134651 (ISSN) ; Hatamie, A ; Berahman, M ; Simchi, M ; Angizi, S ; Rahmati, R ; Kennedy, J ; Simchi, A ; Sharif University of Technology
Electrochemical Society Inc
2019
Abstract
Owing to the exceptional properties of graphene and the crucial role of substrate on the performance of electrochemical biosensors, several graphene-based hybrid structures have recently emerged, yielding improved selectivity and sensitivity. To date, most of the reported biosensors utilize solution-driven graphene flakes with drawbacks of low conductivity (due to high inter-junction contact resistant) and structural fragility. Herein, we present a conductive three-dimensional CeO2 semiconductor nanoparticles/graphene nanocomposite, as a platform for sensitive detection of hydrogen peroxide, an important molecule in fundamental biological processes. The 3D conductive graphene architecture is...
A fuzzy traffic assignment algorithm based on driver perceived travel time of network links
, Article Scientia Iranica ; Volume 18, Issue 2 A , 2011 , Pages 190-197 ; 10263098 (ISSN) ; Shafahi, Y ; Seyedabrishami, S. E ; Sharif University of Technology
2011
Abstract
Traffic assignment is a step of travel demand estimation. Given a trip origin-destination demand matrix, this step determines traffic flow in each link, according to assumptions based on the behavior of drivers. Conventional assignment algorithms, which are mostly based on the Wardrop first principle of user equilibrium, assume that all drivers choose the shortest path to the destination, based on the same travel time computed by travel time functions. However, in reality, driver perception of travel time varies for a specific route. This paper presents a traffic assignment algorithm which assumes that driver perception of travel time affects route choices. Fuzzy set theory is used to define...