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#### The effect of different rare earth elements content on microstructure, mechanical and wear behavior of Mg-Al-Zn alloy

, Article Materials Science and Engineering A ; Volume 527, Issue 7-8 , 2010 , Pages 2027-2035 ; 09215093 (ISSN) ; Masoudi, A ; Khomamizadeh, F ; Sharif University of Technology
2010

Abstract

The effect of Rare earths addition to AZ91 magnesium alloy and its influence on the microstructure and mechanical properties was investigated in this study. Addition of cerium rich misch metal to AZ91 alloy resulted in formation of needle shape particles, which had a very high thermal stability, providing superior mechanical properties compared to AZ91 magnesium alloy. As a result, the grain boundaries were less susceptible for grain boundary sliding at high temperatures. The steady state creep rates were specified and for the AZ91 alloy and the results indicate a mixed mode of creep behavior, with some grain boundary effects contributing to the overall behavior. However for the RE added...

#### Dry sliding wear behavior of SiCP/QE22 magnesium alloy matrix composites

, Article Materials Science and Engineering A ; Volume 435-436 , 2006 , Pages 653-657 ; 09215093 (ISSN) ; Masoudi, A ; Purazrang, K ; Sharif University of Technology
2006

Abstract

In present work, an attempt has been made to investigate the wear behavior of particle reinforced composites based on one of the proper magnesium alloys. The SiCP/QE22 composites and QE22 unreinforced specimens were produced via the powder metallurgy route. The volume fractions of SiC particles with three different shapes, i.e. sharp, blocky and round, were selected in the range of 10-25 vol.%. The dry sliding tests were conducted on unreinforced matrix and SiCP/QE22 composites using pin-on-disk apparatus, according to ASTM G99-95a standard. The applied loads were selected as 3, 5 and 20 N. The tests were carried out under sliding speeds of 0.5 and 1.2 m/s. In all tests, the sliding...

#### Investigation on the characteristics of micro- and nano-structured W-15 wt.%Cu composites prepared by powder metallurgy route

, Article International Journal of Refractory Metals and Hard Materials ; Volume 30, Issue 1 , 2012 , Pages 145-151 ; 02634368 (ISSN) ; Masoudi, A ; Safabinesh, H ; Takestani, M ; Sharif University of Technology
2012

Abstract

The properties of W-15 wt.%Cu composites were investigated by preparing two distinct composites of micrometer and nanoscale structures. Micrometer composite was produced by mixing elemental W and Cu powders and nanometer one was synthesized through a mechanochemical reaction between WO3 and CuO powders. Subsequent compaction and sintering process was performed to ensure maximum possible densification at 1000-1200 °C temperatures. Finally, the behavior of produced samples including relative density, hardness, compressive strength, electrical conductivity, coefficient of thermal expansion (CTE) and room temperature corrosion resistance were examined. Among the composites, nano-structured...

#### Avrami behavior of magnetite nanoparticles formation in co-precipitation process

, Article Journal of Mining and Metallurgy, Section B: Metallurgy ; Volume 47, Issue 2 , 2011 , Pages 211-218 ; 14505339 (ISSN) ; Hosseini, H. M. R ; Masoudi, A ; Sharif University of Technology
Abstract

In this work, magnetite nanoparticles (mean particle size about 20 nm) were synthesized via coprecipitation method. In order to investigate the kinetics of nanoparticle formation, variation in the amount of reactants within the process was measured using pH-meter and atomic absorption spectroscopy (AAS) instruments. Results show that nanoparticle formation behavior can be described by Avrami equations. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed to study the chemical and morphological characterization of nanoparticles. Some simplifying assumptions were employed for estimating the nucleation and growth rate of magnetite nanoparticles

#### Kinetics of magnetite nanoparticles formation in a one step low temperature hydrothermal process

, Article Ceramics International ; Volume 39, Issue 5 , July , 2013 , Pages 4999-5005 ; 02728842 (ISSN) ; Masoudi, A ; Madaah Hosseini, H. R ; Gu, N ; Sharif University of Technology
2013

Abstract

In the present study, a one step hydrothermal process was employed to synthesize magnetite nanoparticles using oleic acid as surfactant agent at 140 °C. Effects of reaction time and alkalinity were studied on particles size and morphology. By changing these parameters, some monodisperse spherical nanoparticles with mean particle size between 2.71 and 13.88 nm were synthesized and characterized via TEM, XRD, VSM, TGA and FT-IR techniques. Assuming the Avrami behavior of particles formation, a kinetics equation was proposed for the transformation rate at 140 °C. Using some simplifying assumptions, nucleation and growth rates were calculated for the hydrothermal formation of magnetite...

#### Level crossing analysis of Burgers equation in 1 + 1 dimensions

, Article Journal of Physics A: Mathematical and General ; Volume 39, Issue 15 , 2006 , Pages 3903-3909 ; 03054470 (ISSN) ; Bahraminasab, A ; Rezazadeh, H ; Masoudi, A. A ; Sharif University of Technology
2006

Abstract

We investigate the average frequency of positive slope ν +α, crossing the velocity field in the Burgers equation. The level crossing analysis in the inviscid limit and the total number of positive crossings of the velocity field before the creation of singularities are given. The main goal of this paper is to show that this quantity, ν+α, is a good measure for the fluctuations of velocity fields in the Burgers turbulence. © 2006 IOP Publishing Ltd

#### Singularity time scale of the kardar-parisi-zhang equation in 2+1 dimensions

, Article Journal of Statistical Physics ; Volume 112, Issue 3-4 , 2003 , Pages 437-456 ; 00224715 (ISSN) ; Masoudi, A. A ; Reza Rahimi Tabar, M ; Sharif University of Technology
2003

Abstract

A master equation for the Kardar-Parisi-Zhang (KPZ) equation in 2+1 dimensions is developed. In the fully nonlinear regime we determine the finite time scale of the singularity formation in terms of the characteristics of forcing. The exact probability density function of the one point height field is obtained correspondingly

#### Evaluating the effect of ultrasmall superparamagnetic iron oxide nanoparticles for a long-term magnetic cell labeling

, Article Journal of Medical Physics ; Volume 38, Issue 1 , 2013 , Pages 34-40 ; 09716203 (ISSN) ; Oghabian, M. A ; Allen, B. J ; Amanlou, M ; Masoudi, A ; Daha, F. J ; Sharif University of Technology
2013

Abstract

In order to evaluate the long-term viability, the iron content stability, and the labeling efficiency of mammalian cells using magnetic cell labeling; dextran-coated ultrasmall superparamagnetic iron oxide (USPIOs) nanoparticles with plain surfaces having a hydrodynamic size of 25 nm were used for this study. Tests were carried out in four groups each containing 5 flasks of 5.5 × 10 6 AD-293 embryonic kidney cells. The cell lines were incubated for 24 h using four different iron concentrations with and without protamine sulfate (Pro), washed with phosphate-buffered saline (PBS) and centrifuged three times to remove the unbounded USPIOs. Cell viability was also verified using USPIOs. There...

#### Taylor's frozen-flow hypothesis in Burgers turbulence

, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 77, Issue 6 , 2008 ; 15393755 (ISSN) ; Niry, M. D ; Davoudi, J ; Rahimi Tabar, M. R ; Masoudi, A. A ; Sreenivasan, K. R ; Sharif University of Technology
2008

Abstract

By detailed analytical treatment of the shock dynamics in the Burgers turbulence with large scale forcing we calculate the velocity structure functions between pairs of points displaced both in time and space. Our analytical treatment verifies the so-called Taylor's frozen-flow hypothesis without relying on any closure and under very general assumptions. We discuss the limitation of the hypothesis and show that it is valid up to time scales smaller than the correlation time scale of temporal velocity correlation function. We support the analytical calculation by performing numerical simulation of the periodically kicked Burgers equation. © 2008 The American Physical Society

#### Stochastic φ4-theory in the strong coupling limit

, Article Nuclear Physics B ; Volume 761, Issue 3 , 2007 , Pages 93-108 ; 05503213 (ISSN) ; Niry, M. D ; Bahraminasab, A ; Masoudi, A. A ; Davoudi, J ; Sahimi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
2007

Abstract

The stochastic φ4-theory in d dimensions dynamically develops domain wall structures within which the order parameter is not continuous. We develop a statistical theory for the φ4-theory driven with a random forcing which is white in time and Gaussian-correlated in space. A master equation is derived for the probability density function (PDF) of the order parameter, when the forcing correlation length is much smaller than the system size, but much larger than the typical width of the domain walls. Moreover, exact expressions for the one-point PDF and all the moments 〈 φn 〉 are given. We then investigate the intermittency issue in the strong coupling limit, and derive the tail of the PDF of...

#### Exact analysis of level-crossing statistics for (d+1)-dimensional fluctuating surfaces

, Article Journal of Statistical Physics ; Volume 124, Issue 6 , 2006 , Pages 1471-1490 ; 00224715 (ISSN) ; Movahed, M. S ; Nasiri, S. D ; Masoudi, A. A ; Sahimi, M ; Sharif University of Technology
2006

Abstract

We carry out an exact analysis of the average frequency ν+ αxi in the direction x i of positiveslope crossing of a given level α such that, h(x, t) h = α, of growing surfaces in spatial dimension d. Here, h(x, t) is the surface height at time t, and h is its mean value. We analyze the problem when the surface growth dynamics is governed by the Kardar-Parisi-Zhang (KPZ) equation without surface tension, in the time regime prior to appearance of cusp singularities (sharp valleys), as well as in the random deposition (RD) model. The total number N + of such level-crossings with positive slope in all the directions is then shown to scale with time as t d/2 for both the KPZ equation and the RD...

#### Zero tension Kardar-Parisi-Zhang equation in (d + 1)-dimensions

, Article Journal of Statistical Physics ; Volume 116, Issue 5-6 , 2004 , Pages 1521-1544 ; 00224715 (ISSN) ; Tabei, S. M. A ; Masoudi, A. A ; Shahbazi, F ; Rahimi Tabar, M. R ; Sharif University of Technology
2004

Abstract

The joint probability distribution function (PDF) of the height and its gradients is derived for a zero tension d + 1-dimensional Kardar-Parisi-Zliang (KPZ) equation. It is proved that the height's PDF of zero tension KPZ equation shows lack of positivity after a finite time tc. The properties of zero tension KPZ equation and its differences with the case that it possess an infinitesimal surface tension is discussed. Also potential relation between the time scale tc and the singularity time scale tc,v→0 of the KPZ equation with an infinitesimal surface tension is investigated. © 2004 Springer Science+Business Media, Inc

#### Intermittency of height fluctuations in stationary state of the Kardar-Parisi-Zhang equation with infinitesimal surface tension in 1+1 dimensions

, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 70, Issue 3 1 , 2004 , Pages 031101-1-0311011-3 ; 15393755 (ISSN) ; Bahraminasab, A ; Masoudi, A. A ; Mousavi, S. S ; Tabar, M. R. R ; Sharif University of Technology
2004

Abstract

Intermittency of height fluctuations in stationary state of the Kardar-Parisi-Zhang (KPZ) equation with infinitesimal surface tension in 1+1 dimensions was discussed. Stochastic differential equations were used for the study. It was found that the probability density function [in 1+1] is independent of the coefficient of the linear term. When the random force with smooth spatial correlation was considered, the problem changed to a more complicated one

#### Intermittency of height fluctuations in stationary state of the Kardar-Parisi-Zhang equationwith infinitesimal surface tension in [Formula presented] dimensions

, Article Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics ; Volume 70, Issue 3 , 2004 , Pages 13- ; 1063651X (ISSN) ; Bahraminasab, A ; Masoudi, A. A ; Mousavi, S. S ; Reza Rahimi Tabar, M ; Sharif University of Technology
2004

Abstract

The Kardar-Parisi-Zhang (KPZ) equation with infinitesimal surface tension, dynamically develops sharply connected valley structures within which the height derivative is not continuous. We discuss the intermittency issue in the problem of stationary state forced KPZ equation in [Formula presented] dimensions. It is proved that the moments of height increments [Formula presented] behave as [Formula presented] with [Formula presented] for length scales [Formula presented]. The length scale [Formula presented] is the characteristic length of the forcing term. We have checked the analytical results by direct numerical simulation. © 2004 The American Physical Society

#### Three-dimensional forced Burgers turbulence supplemented with a continuity equation

, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 63, Issue 5 II , 2001 , Pages 563081-5630813 ; 15393755 (ISSN) ; Masoudi, A. A ; Rahimi Tabar, M. R ; Rastegar, A. R ; Shahbazi, F ; Sharif University of Technology
2001

Abstract

The turbulent limit of three dimensional Burger equation was studied. An adjusting parameter emerged through the calculations, based on mean field analysis, that was the scaling exponent of conditional density-density correlations. Two kinds of solutions were also shown for velocity-increment probability density function (PDF)

#### Ultrasonic-assisted synthesis of magnetite based MRI contrast agent using cysteine as the biocapping coating

, Article Materials Chemistry and Physics ; Volume 131, Issue 1-2 , 2011 , Pages 170-177 ; 02540584 (ISSN) ; Malek, M ; Hosseini, H. R. M ; Shokrgozar, M. A ; Oghabian, M. A ; Masoudi, A ; Gu, N ; Zhang, Y ; Sharif University of Technology
2011

Abstract

Magnetite nanoparticles (mean particle size ranging from 10 to 20 nm) were prepared by a biomoleculeassisted solution-phase approach under ultrasonic irradiation. Cysteine was used as the capping agent in the solution. The results show that cysteine could be an efficient biocapping agent in producing Fe3O4 nanoparticles. The crystal structure and magnetic properties of the nanoparticles were characterized by XRD and VSM techniques, respectively. FT-IR was used to investigate the presence of cysteine on the nanoparticles surface. The influence of pH value of the solution on the size distribution and hydrodynamic size of nanoparticles were studied by TEM and DLS methods, respectively. The MTT...