Loading...
Search for:
gadolinium
0.011 seconds
Total 39 records
The conduction mechanism in Gd1-x-zCexCazBa2Cu3O7-δ
, Article Superconductor Science and Technology ; Volume 21, Issue 9 , 4 July , 2008 ; 09532048 (ISSN) ; Mofakham, S ; Akhavan, M ; Sharif University of Technology
2008
Abstract
We have investigated the substitution of Ce and divalent Ca with a radius similar to Gd in Gd1-x-zCexCazBa 2Cu3O7-δ. We have prepared Gd 1-x-zCexCazBa2Cu3O 7-δ compounds with different concentrations of Ce and Ca by the standard solid-state reaction technique. X-ray diffraction (XRD) experiments are performed and the results are refined by the Rietveld method. XRD analysis shows a predominantly single-phase perovskite structure with orthorhombic Pmmm symmetry. In Gd1-x-zCexCazBa2Cu 3O7-δ compounds, induced suppression of T c due to Ce doping is compensated by hole doping with increasing Ca substitution for Gd. With the increase of Ca content, Tc increases up to an optimum value; thereafter...
Pr at Gd or Ba site in GdBa2Cu3O7: Appearance of superconductivity
, Article Physical Review B - Condensed Matter and Materials Physics ; Volume 68, Issue 10 , 2003 ; 10980121 (ISSN) ; Akhavan, M ; Sharif University of Technology
2003
Abstract
Gd(Ba2-xPrx)Cu3O7+δ single phase polycrystalline samples with 0.0 < − x < − 1.0 were investigated for their structural and electronic properties. Due to the solubility limit, the 123 structure forms in the 0.0 < − x < −0.50 range; for x > −0.6, a decomposition of the perovskite-type phases occurs. For x=0.2, there is an orthorhombic-tetragonal phase transition, concurrent with a metal-insulator transition, which is evident in the normal state resistivity. For xc=0.35, the superconductor-insulator transition occurs. An unusual hump has been observed on the resistivity vs temperature curve of the samples for particular values of Pr doping. Based on the Rietveld refinement of the x-ray...
Rapid microwave-assisted synthesis of PVP-coated ultrasmall gadolinium oxide nanoparticles for magnetic resonance imaging
, Article Chemical Physics ; Volume 453-454 , May , 2015 , Pages 35-41 ; 03010104 (ISSN) ; Madaah Hosseini, H. R ; Khodaei, A ; Montazerabadi, A. R ; Irajirad, R ; Oghabian, M. A ; Delavari,H. H ; Sharif University of Technology
Elsevier
2015
Abstract
Synthesis of polyvinyl pyrrolidone (PVP) coated ultrasmall Gd2 O3 nanoparticles (NPs) with enhanced T1 -weighted signal intensity and r2 /r1 ratio close to unity is performed by a microwave-assisted polyol process. PVP coated Gd2 O3 NPs with spherical shape and uniform size of 2.5 ± 0.5 nm have been synthesized below 5 min and structure and morphology confirmed by HRTEM, XRD and FTIR. The longitudinal (r1 ) and transversal relaxation (r2 ) of Gd2 O3 NPs is measured by a 3 T MRI scanner. The results showed considerable increasing of relaxivity for Gd2 O3 NPs in...
Comparing the physical properties of Pr/Gd and Pr/Ce substitutions in Ru(Gd 1.5Ce 0.5)Sr 2Cu 2O 10-δ
, Article European Physical Journal B ; Volume 63, Issue 4 , 2008 , Pages 461-467 ; 14346028 (ISSN) ; Nikseresht, N ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
2008
Abstract
We have compared the electrical and magnetic properties of Ru(Gd 1.5-x Pr x )Ce 0.5Sr 2Cu 2O 10-δ (Pr/Gd samples) with x = 0.0, 0.01, 0.03, 0.033, 0.035, 0.04, 0.05, 0.06, 0.1 and RuGd 1.5(Ce 0.5-x Pr x ) Sr 2 Cu 2O 10-δ (Pr/Ce samples) with x = 0.0, 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2 prepared by the standard solid-state reaction technique. We obtained the XRD patterns for different samples with various x. The lattice parameters versus x for different substitutions have been obtained from Rietveld analysis. To determine how the magnetic and superconducting properties of these layered cuprate systems can be affected by Pr substitution, the resistivity, and magnetoresistivity, with H ext...
Gadolinium triflate immobilized on magnetic nanocomposites as recyclable Lewis acid catalyst for acetylation of phenols
, Article Nanoscience and Nanotechnology Letters ; Vol. 6, issue. 4 , 2014 , p. 309-313 ; Kim, A ; Shokouhimehr, M ; Sharif University of Technology
Abstract
The acetylation of phenols with acetic anhydride proceeded in excellent yields when it was catalyzed by gadolinium triflate immobilized on magnetically recyclable nanocomposites. This heterogeneous catalyst provided high catalytic activity with low loading level (1 mol%), because the Lewis acid catalyst was grafted on the surface of the nanocomposites. The catalysts were also easily recovered from the reaction mixture using a magnet and reused for six consecutive cycles
Role of Pr doping in Gd1113
, Article Physica Status Solidi C: Conferences ; Volume 1, Issue 7 , 2004 , Pages 1855-1858 ; 16101634 (ISSN) ; Khosroabadi, H ; Akhavan, M ; Sharif University of Technology
2004
Abstract
Tetragonal Gd1-xPrxBaSrCu3O 7-δ polycrystalline samples (0 ≤ x ≤ 0.9) have been prepared by the standard solid-state reaction and characterized by XRD. A hump on the ρ(T) curve have been observed at about 80 K for large values of x. The normal state resistivity have been investigated with two and three dimensional variable range hopping (2&3D-VRH) and Coulomb gap (CG). For low concentration of Pr, 2D-VRH is the dominant mechanism, but with the increase of x, 3D-VRH is dominant. The magnetoresistance measurements of the samples have been analysed by the Ambegakor and Halperin (AH) phase slip model. The field dependences of the pinning energy and critical current density have been studied for...
High temperature superconductors as a two-dimensional electron gas
, Article Physica Status Solidi C: Conferences ; Volume 1, Issue 7 , 2004 , Pages 1828-1831 ; 16101634 (ISSN) ; Akhavan, M ; Sharif University of Technology
2004
Abstract
Based on transport and magnetic measurements on Gd(Ba2-xPr x)Cu3O7+δ, and some other properties of high temperature superconductors (HTSC), we have extracted similarities between superconductors, two-dimensional electron gas (2D-EG) i.e., MOSFETs. These are based on properties such as superconductor-insulator transition in superconductors and metal-insulator transition (MIT) in 2D-EG with doping and magnetic field, localization in transport conduction, quantum unit of resistance at MIT, larger change in resistivity from critical doping to the insulating side in comparison with change from critical doping to the metallic side, and strongly electron-electron coupling. These similarities could...
Synthesis and Surface Modification of Gadolinium Oxide Nanoparticles (Gd2O3) for MRI Contrast Agent
, M.Sc. Thesis Sharif University of Technology ; Madaah Hosseini, Hamid Reza (Supervisor)
Abstract
In recent years, much attention has been paid to the development of biofunctionalized nanoparticles with special magnetic properties for using in clinical imaging. Targeted magnetic materials with high MRI signal intensity can be used in tissue imaging and molecular and cellular detection as valuable tools. The aim of this study has been to synthesize the nanocomposite including the functional gadolinium oxide (Gd2O3) nanoaprticles for MRI contrast agent. Synthesis and in-situ surface modification of ultrasmall Gd2O3 nanoparticles (2.5nm) with PVP was performed by a microwave modified polyol in 5 min. The structure and size of synthesized nanoparticles were studied using X-ray diffraction...
Hall effect and sign reversal in Gd(Ba2-xNdx)Cu3O7+δ
, Article Journal of Magnetism and Magnetic Materials ; Volume 320, Issue 13 , 2008 , Pages 1884-1888 ; 03048853 (ISSN) ; Taheri, M ; Akhavan, M ; Sharif University of Technology
2008
Abstract
We have investigated the Hall measurement of Gd(Ba2-xNdx)Cu3O7+δ with x=0, 0.05, 0.1, 0.15, and 0.2 in a magnetic field of 0-1 T. The nominal samples has been prepared by the conventional solid-state reaction technique. The iodometric titration experiment was carried out for samples. The Rietveld analysis of the X-ray diffraction patterns indicates that samples are mainly single phase. The normal state Hall coefficient behaves as 1/T in all samples. All samples with nominal compositions show single sign reversal with variation of magnetic field and temperature. The Hall resistivity of the samples with x=0 and 0.1 close to the superconducting transition temperature changes its sign with...
Synthesis parameters and their effects on the resistivity anomaly in GdPr1113 ceramic
, Article Journal of Superconductivity and Novel Magnetism ; Volume 20, Issue 4 , 2007 , Pages 279-283 ; 15571939 (ISSN) ; Akhavan, M ; Sharif University of Technology
2007
Abstract
Tetragonal Gd 1-x Pr x BaSrCu 3O 7-δ (GdPr1113) polycrystalline high-temperature superconducting ceramic samples have been synthesized by the standard solid-state reaction process with different calcination and sintering temperatures and characterized by XRD and SEM. The optimum synthesis temperatures for obtaining single phase varied with Pr doping. Higher temperatures were necessary to obtain single phase for x ≥ 0.3. It was found that higher synthesis temperatures improved the electrical characteristics of these materials. The effects of different calcination and sintering temperatures on the anomalous hump in the ρ(T) curves observed at about 80 K is investigated. The percentage of the...
Phonon frequency calculations of GdBCO and PrBCO
, Article 4th International Conference on Magnetic and Superconducting Materials, MSM'05, Agadir, 5 September 2006 through 8 September 2006 ; Volume 3, Issue 9 , 2006 , Pages 3162-3165 ; 18626351 (ISSN) ; Khasroabadi, H ; Akhavan, M ; Sharif University of Technology
2006
Abstract
Ab initio frozen-phonon calculations have been performed for k = 0 A g Raman modes of superconducting GdBa2Cu3O 7 and insulating PrBa2Cu3O7. We have used the generalized gradient approximation full-potential linear augmented plane-wave method in our calculations by Wien2k code. Results have been compared with other computational and experimental data for similar systems. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA
Conduction mechanism and magnetoresistance in Gd1-xPr xBaCaCu3O7-δ
, Article European Physical Journal B ; Volume 47, Issue 1 , 2005 , Pages 47-53 ; 14346028 (ISSN) ; Akhavan, M ; Sharif University of Technology
2005
Abstract
Tetragonal Gd1-xPrxBaCaCu3O 7-δ (0≤x≤1) polycrystalline samples have been prepared by the standard solid-state reaction, and characterized by XRD and SEM. Rietveld analysis on X-ray diffraction pattern shows site mixing between rare earth (R) and Ca. Contrary to Gd1-xPrxBa2Cu 3O7-δ, a hump on the ρ(T) curve is observed at about 80 K. The normal state resistivity has been analyzed by the two and three dimensional variable range hopping (2&3D-VRH) and Coulomb gap. For low concentration of Pr (x<0.5-0.6, corresponding to the metal-insulator transition), 2D-VRH is the dominant mechanism, but with the increase of x, the 3D-VRH is dominant. Substitution of Ba by Ca highly increases the...
Modified Gadonanotubes as a promising novel MRI contrasting agent
, Article DARU, Journal of Pharmaceutical Sciences ; Volume 21, Issue 1 , 2013 ; 15608115 (ISSN) ; Atyabi, F ; Shanehsazzadeh, S ; Sobhani, Z ; Adeli, M ; Dinarvand, R ; Sharif University of Technology
2013
Abstract
Background and purpose of the study. Carbon nanotubes (CNTs) are emerging drug and imaging carrier systems which show significant versatility. One of the extraordinary characteristics of CNTs as Magnetic Resonance Imaging (MRI) contrasting agent is the extremely large proton relaxivities when loaded with gadolinium ion (Gdn 3+) clusters. Methods. In this study equated Gdn 3+ clusters were loaded in the sidewall defects of oxidized multiwalled (MW) CNTs. The amount of loaded gadolinium ion into the MWCNTs was quantified by inductively coupled plasma (ICP) method. To improve water solubility and biocompatibility of the system, the complexes were functionalized using diamine-terminated...
Scar Segmentation in CMR Images without Using Contrast Agent
, M.Sc. Thesis Sharif University of Technology ; Rohban, Mohammad Hossein (Supervisor) ; Houshmand, Golnaz (Co-Supervisor)
Abstract
Correct diagnosis of myocardial scar has always been a major challenge due to the low resolution of cardiac magnetic resonance imaging. The use of a gadolinium-based contrast agent that reveals a scar is the solution proposed in medical science. However, there are limitations to the use of contrast agents in some patients. In recent years, studies based on deep learning techniques have been presented, trying to identify myocardial infarction with the help of images without using contrast agent. This type of diagnosis can be done with the help of different movements of healthy and damaged tissue. Due to the lack of datasets suitable for this application, in this study, real dataset were...
Synthesis and Characterization of Metal-Organic Frameworks (Gadolinium Base) Carrying Quercetin Drug to Evaluate Memory Impairment in White Rats
, M.Sc. Thesis Sharif University of Technology ; Shamloo, Amir (Supervisor) ; Shojaei, Akbar (Supervisor) ; Sharifzadeh, Mohammad (Supervisor)
Abstract
One of the diseases of the central nervous system that are included in the neurodegenerative disorders and its impressive expansion among the people of the world and Iran is an alarming to us, is Alzheimer's disease. Since the cause of the disease has not yet been precisely determined, there is no definite cure for this disease yet. However, an important indicator in the disease is its early diagnosis so that the disease can be controlled and prevented from progressing in the early stages and before the degeneration of neurons. The big challenge that is observed in the diagnosis and effectiveness of drugs in this disease and any type of central nervous system disorder is the existence of the...
A two-level undercut-profile substrate for chemical-solution-based filamentary coated conductors
, Article IEEE Transactions on Applied Superconductivity ; Volume 26, Issue 3 , 2016 ; 10518223 (ISSN) ; Lundeman, J. H ; Hansen, J. B ; Mishin, O. V ; Zhao, Y ; Mohajeri, R ; Grivel, J. C ; Sharif University of Technology
Abstract
A recently developed two-level undercut-profile substrate (2LUPS), containing two levels of plateaus connected by a curved wall with an undercut profile, enables self-forming filaments in a coated conductor during physical line-of-sight deposition of buffer and superconducting layers. In the present study, the 2LUPS concept is applied to a commercial cube-textured Ni-5at.%W tape, and the surface of the 2LUPS coated with two Gd2Zr2O7 buffer layers using chemical solution deposition is examined. Except for narrow regions near the edge of upper plateaus, the plateaus are found to be covered by strongly textured Gd2Zr2O7 buffer layers after dip coating and sintering
Enhanced Activity of Pr6O11 and CuO Infiltrated Ce0.9Gd0.1O2 Based Composite Oxygen Electrodes
, Article Journal of the Electrochemical Society ; Volume 167, Issue 2 , January , 2020 ; Faghihi Sani, M. A ; Tong, X ; Chen, M ; Hendriksen, P. V ; Sharif University of Technology
Institute of Physics Publishing
2020
Abstract
Operation of solid oxide fuel/electrolysis cells (SOFC/SOEC) at high temperatures (T > 850 °C) is accompanied by degradation phenomena, which severely affect the operational lifetime of the cell. Degradation processes are expected to occur slower at low temperatures. However, significant reduction in electrocatalytic activity of the oxygen electrode, is one of the major challenges in decreasing the operating temperature down to 500 °C-650 °C. Recently, Pr6O11 infiltrated Ce0.9Gd0.1O2 (CGO) based electrodes have been proposed to realize high electrochemical performance at intermediate temperature. In this study, Pr-oxide has been infiltrated into a well performing sub-micro...
Ag Raman modes of RBCO (R = Gd, Pr) by density functional theory approach
, Article European Physical Journal B ; Volume 51, Issue 2 , 2006 , Pages 161-165 ; 14346028 (ISSN) ; Tavana, A ; Akhavan, M ; Sharif University of Technology
2006
Abstract
Ab initio total energy calculations have been performed for superconducting GdBa2Cu3O7 and insulating PrBa 2Cu3O7 using the full-potential linear augmented plane-wave method in the local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated unit cell volume and lattice parameters with the experimental data indicates the improvement of these parameters in the GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about 6% smaller and 1.25% larger than the experimental data, respectively for both systems. Thus frozen phonon calculations have been performed to determine the eigenvalues and eigenvectors of the k=0 Ag modes of...
Superconductor-insulator transition in composite granular (1 - n)Gd123-nPr123 and (1 - m)Gd123-mPrBa123
, Article Journal of Superconductivity and Novel Magnetism ; Volume 18, Issue 2 , 2005 , Pages 269-276 ; 15571939 (ISSN) ; Akhavan, M ; Sharif University of Technology
2005
Abstract
Granular composite samples of GdBa2Cu3O 7-δ (Gd123), PrBa2Cu3O 7-δ (Pr123), and Pr0.5Ba0.5Ba 2Cu3O7-δ (PrBa123) have been prepared by the solid state reaction technique. The characterization of samples has been done by SEM and XRD measurements. We have investigated the effect of Pr123 and PrBa123 insulating grains on the superconductor-insulator transition and the normal state resistivity of the (1 - n)Gd123-nPr123 and (1 - m)Gd123-mPrBa123 systems. The dominant diffusion of Pr ions onto the neighboring Gd123 grains in (1 - n)Gd123-nPr123 causes high rate of suppression of superconductivity similar to the chemical-doped GdPr123 system. For (1 - m)Gd123-mPrBal23 system, the suppression rate...
Effect of Sr/Ba substitution in Gd1-xPrxBaSrCu 3O7-δ
, Article Physica C: Superconductivity and its Applications ; Volume 423, Issue 3-4 , 2005 , Pages 163-174 ; 09214534 (ISSN) ; Akhavan, M ; Sharif University of Technology
2005
Abstract
Tetragonal Gd1-xPrxBaSrCu3O 7-δ (0 ≤ x ≤ 1) polycrystalline samples have been prepared by the standard solid-state reaction, and characterized by XRD and SEM. Resistance measurements and XRD patterns show site mixing between rare earth R and Sr is less than R and Ca. Contrary to Gd1-xPrxBa 2Cu3O7-δ, a hump on the ρ(T) curve is observed at about 80 K. Based on the resistivity measurements, the effect of Pr substitution in the 1113 structure, in comparison with the 123 structure, on the increase of pseudogap temperature is investigated. The normal state resistivity has been analyzed by the two and three dimensional variable range hopping (2D-VRH and 3D-VRH) and Coulomb gap. For the low...