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A simple model for the size and shape dependent Curie temperature of freestanding Ni and Fe nanoparticles based on the average coordination number and atomic cohesive energy
, Article Chemical Physics ; Volume 383, Issue 1-3 , 2011 , Pages 1-5 ; 03010104 (ISSN) ; Madaah Hosseini, H ; Simchi, A ; Sharif University of Technology
Abstract
To study the effect of size and shape of metallic nanoparticle on their Curie temperature, an analytical model is proposed. The core average coordination number (CAC) and surface average coordination number (SAC) of freestanding nanoparticles are considered in the model. Clusters of icosahedral (IC) and body centred cubic (BCC) structure without any vacancies and defects are modelled. A critical Curie temperature is introduced for metallic clusters with a diameter of 2-3 nm. This critical diameter is related to clusters which the ratio of surface atoms to total atoms is about 50%. The "shape effect" is shown to be important at sizes less than 20 nm. The obtained results are supported by...
Loop-erased random walk on a percolation cluster: Crossover from Euclidean to fractal geometry
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Vol. 89, Issue. 6 , 2014 ; ISSN: 15393755 ; Rouhani, S ; Sharif University of Technology
Abstract
We study loop-erased random walk (LERW) on the percolation cluster, with occupation probability p≥pc, in two and three dimensions. We find that the fractal dimensions of LERWp are close to normal LERW in a Euclidean lattice, for all p>pc. However, our results reveal that LERW on critical incipient percolation clusters is fractal with df=1.217±0.002 for d=2 and 1.43±0.02 for d=3, independent of the coordination number of the lattice. These values are consistent with the known values for optimal path exponents in strongly disordered media. We investigate how the behavior of the LERWp crosses over from Euclidean to fractal geometry by gradually decreasing the value of the parameter p from 1 to...
Estimation of 3-D pore network coordination number of rocks from watershed segmentation of a single 2-D image
, Article Advances in Water Resources ; Volume 94 , 2016 , Pages 264-277 ; 03091708 (ISSN) ; Ayatollahi, S ; Kharrat, R ; Dashti, N ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this study, we have utilized 3-D micro-tomography images of real and synthetic rocks to introduce two mathematical correlations which estimate the distribution parameters of 3-D coordination number using a single 2-D cross-sectional image. By applying a watershed segmentation algorithm, it is found that the distribution of 3-D coordination number is acceptably predictable by statistical analysis of the network extracted from 2-D images. In this study, we have utilized 25 volumetric images of rocks in order to propose two mathematical formulas. These formulas aim to approximate the average and standard deviation of coordination number in 3-D pore networks. Then, the formulas are applied...
The effect of steepness of soft-core square-well potential model on some fluid properties
, Article Molecular Physics ; Volume 106, Issue 1 , 2008 , Pages 103-112 ; 00268976 (ISSN) ; Parsafar, G. A ; Sharif University of Technology
2008
Abstract
The effect of repulsive steepness of the soft-core square well (SCSW) potential model on the second virial coefficient, critical behaviour (two- phase region and the position of critical point), and coordination number are investigated. The soft-core thermodynamic perturbation theory (TPT) presented by Weeks-Chandler-Anderson (WCA) recently developed by Ben-Amotz and Stell (BAS) has been used for the reference system, and the Barker-Henderson TPT for the perturbed system. The Barker-Henderson macroscopic compressibility approximation has been used for all order perturbation terms in which the second-order one is improved by assuming that the molecules in every two neighbouring shells are...
Estimation of carbonates permeability using pore network parameters extracted from thin section images and comparison with experimental data
, Article Journal of Natural Gas Science and Engineering ; Volume 42 , 2017 , Pages 85-98 ; 18755100 (ISSN) ; Assadi, A ; Kharrat, R ; Dashti, N ; Ayatollahi, S ; Sharif University of Technology
Elsevier B.V
2017
Abstract
Petrography and image analysis have been widely used to identify and quantify porous characteristics in carbonate reservoirs. This paper uses the thin section images of 200 carbonate rock samples to predict the absolute permeability using intelligent and empirical methods. For each thin section, several pore network parameters are extracted from thin section images of rocks including the average pore size, average throat size, average throat length and average 2-D coordination number of pore network. A neural-based model successfully predicts the permeability of samples using pore network parameters as the inputs. Second neural network is applied for predicting absolute permeability...
Design and Synthesis of Ni-Zn Magnetic Nanoparticles for Hyperthermia Treatment
, Ph.D. Dissertation Sharif University of Technology ; Madaah Hosseini, Hamid Reza (Supervisor) ; Simchi, Abdolreza (Supervisor)
Abstract
Hyperthermia (also called thermal therapy or thermotherapy) is defined as a type of cancer treatment in which body tissue is exposed to high temperatures, to damage and kill cancer cells, or to make cancer cells more sensitive to the effects of radiation and certain anticancer drugs. The temperature increase required by hyperthermia can be achieved via different heat sources, such as electromagnetic radiation waves (radiofrequency or microwave, ultrasound waves and electrical current. These techniques have shown good results, however, the major problem with present conventional methods is reaching homogenous heat distribution and therapeutic temperatures in the deep region of the tumor to be...
Multi-scale modeling of edge effect on band gap offset in polygonal cross-section Silicon nanowires
, Article Computational Materials Science ; Volume 79 , 2013 , Pages 262-275 ; 09270256 (ISSN) ; Dormohammadi, H ; Aramoon, A ; Sharif University of Technology
2013
Abstract
The band gap offset is an effect of coordination numbers (CNs) of atom reduction at the edge of transversal cross-section of Silicon nanowires (SiNWs). In this paper, a hierarchical multi-scale technique is developed to model the edge effect on the band gap shift of SiNWs since the geometric effect is dominant in the energy gap due to the appearance of strain in the self-equilibrium state. The multi-scale model is performed based on the molecular dynamics approach and finite element method for the micro- (atomistic) and macro-scale levels, respectively. The Cauchy-Born (CB) hypothesis is used to relate the atomic positions to the continuum field through the deformation gradient. Finally, the...
Melting enthalpy and entropy of freestanding metallic nanoparticles based on cohesive energy and average coordination number
, Article Journal of Physical Chemistry C ; Volume 115, Issue 35 , August , 2011 , Pages 17310-17313 ; 19327447 (ISSN) ; Delavari H., H ; Madaah Hosseini, H. R ; Sharif University of Technology
2011
Abstract
An analytical model is proposed to study the effect of particle size on melting enthalpy and entropy of metallic nanoparticles (NPs). The Mott's and Regel's equations for melting entropy in the combination of core average coordination number (CAC) and surface average coordination number (SAC) of freestanding NPs are considered. Clusters of icosahedral (IC), body centered cubic (BCC), and body centered tetragonal (BCT) structure without any vacancies and defects are modeled. Using the variable coordination number made this model to be in good agreement with experimental and molecular dynamic (MD) results of different crystal structures. The model predicts melting entropy and enthalpy of...
An automated simple algorithm for realistic pore network extraction from micro-tomography images
, Article Journal of Petroleum Science and Engineering ; Vol. 123, issue , 2014 , pp. 164-171 ; ISSN: 09204105 ; Jamshidi, S ; Salehi, S
Abstract
Using 3-D scanned data to analyze and extract pore network plays a vital role in investigation of porous media's characteristics. In this paper, a new simple method is developed to detect pores and throats for analyzing the connectivity and permeability of the network. This automated method utilizes some of the common and well-known image processing functions which are widely accessible by researchers and this has led to an easy algorithm implementation. In this method, after polishing and quality control of images, using city-block distance function and watershed segmentation algorithm, pores and throats are detected and 3-D network is produced. This method can also be applied on 2-D images...
Effects of crystal orientation on the tensile and shear deformation of nickel-silicon interfaces: A molecular dynamics simulation
, Article Materials Science and Engineering A ; Volume 543 , 2012 , Pages 217-223 ; 09215093 (ISSN) ; Simchi, A ; Kokabi, A. H ; Sharif University of Technology
2012
Abstract
Atomistic simulation was used to study the deformation and fracture mechanisms of Ni-Si interfaces under tensile and shear loads dependent on the crystal structure of interface zone. Modified embedded atom method (MEAM) potential was utilized for molecular dynamics (MD) modeling. The simulation includes analysis of common neighbors, coordination number, least-square atomic local strain, and radial distribution function. The profound effect of interface crystallography on the tensile and shear deformation is shown. The highest tensile strength is obtained for interfaces with high plane density due to lowest atomic disorder while under shear loading planes with low density exhibit a high local...
Effects of particle size, shape and crystal structure on the formation energy of Schottky vacancies in free-standing metal nanoparticles: A model study
, Article Physica B: Condensed Matter ; Volume 406, Issue 20 , October , 2011 , Pages 3777-3780 ; 09214526 (ISSN) ; Madaah Hosseini, H. R ; Simchi, A ; Sharif University of Technology
2011
Abstract
A simplified model based on cohesive energy is proposed to estimate the formation energy of Schottky vacancies (VFE) in free-standing metal nanoparticles with BCC and FCC crystal structures. To study the effect of particle size and shape, the surface energy, elastic contraction and average coordination number of particles at the surface and core was considered. It is shown that the energy of vacancy formation in FCC nanoparticles increases with decreasing the size while the effect of particle shape (sphere, cubic and icosahedral) is marginal. In spite of this behavior, BCC nanoparticles exhibit a critical particle size at around 25 Å, at which a minimum VFE is attained. Additionally, the...
Pore network modeling of nanoporous ceramic membrane for hydrogen separation
, Article Separation Science and Technology ; Volume 45, Issue 14 , Sep , 2010 , Pages 2028-2038 ; 01496395 (ISSN) ; Farhadi, F ; Sharif University of Technology
2010
Abstract
Pore network modeling of porous media has this advantage that can consider the pore structure incorporating any desired details, but it has not been studied sufficiently. In addition, most studies are limited to mathematical modeling only which need validation. In the present study, this approach was applied to hydrogen separation from syngas by nanoporous ceramic membrane to predict the membrane permeance theoretically based on its pore structure. Gas transport through nanoporous membrane was modeled with the aim of a 2D network model. A dusty gas model was used for gas transport in the individual pores. Model validation showed that the model predictions are in good agreement with the...
Topological color codes and two-body quantum lattice Hamiltonians
, Article New Journal of Physics ; Volume 12 , 2010 ; 13672630 (ISSN) ; Bombin, H ; Martin Delgado, M. A
2010
Abstract
Topological color codes are among the stabilizer codes with remarkable properties from the quantum information perspective. In this paper, we construct a lattice, the so-called ruby lattice, with coordination number 4 governed by a two-body Hamiltonian. In a particular regime of coupling constants, in a strong coupling limit, degenerate perturbation theory implies that the low-energy spectrum of the model can be described by a many-body effective Hamiltonian, which encodes the color code as its ground state subspace. Ground state subspace corresponds to a vortex-free sector. The gauge symmetry Z2 ×Z2 of the color code could already be realized by identifying three distinct plaquette...
Investigating the effect of co-solvents on heavy oil recovery in different pore geometries using five-spot micromodels
, Article 15th European Symposium on Improved Oil Recovery 2009, 27 April 2009 through 29 April 2009, Paris ; 2009 , Pages 669-682 ; 9781622768912 (ISBN) ; Kharrat, R ; Ghazanfari, M. H ; Vossoughi, S ; Sharif University of Technology
Abstract
The main issue in heavy oils enhanced recovery methods is to reduce their viscosity in order to get a better mobility. This is commonly obtained by blending the oil with light hydrocarbons. Co-solvents are good candidates to improve the hydrocarbon recovery efficiency especially in miscible processes. However, the effect of co-solvents on miscible flooding of heavy oil reservoirs at different pore geometries is not well understood. In this work different one-quarter five-spot network patterns along with those generated from reservoir rocks' thin sections were etches on glass surfaces. The models that had been initially saturated with the heavy crude oil were used to perform a series of...
Evolution of pore-scale morphology of oil shale during pyrolysis: a quantitative analysis
, Article Transport in Porous Media ; Volume 119, Issue 1 , 2017 , Pages 143-162 ; 01693913 (ISSN) ; Baychev, T. G ; Ayatollahi, S ; Jivkov, A. P ; Sharif University of Technology
Abstract
Changes of morphological parameters of oil shale under thermal conditions are investigated. Analyses are based on 26 micro-computed tomography (micro-CT) images of Green River immature shale rock available under creative commons license. Several image processing and characterization algorithms are applied to sequential high-resolution micro-CT images of oil shale samples undergoing pyrolysis. Pore-scale morphology is extracted and quantified, providing results for pore size, throat size, grain size, specific surface, coordination number, and fracture aperture. The results demonstrate critical increases of porosity, coordination number and fracture aperture in the temperature range from 390...
A new insight into pore body filling mechanism during waterflooding in a glass micro-model
, Article Chemical Engineering Research and Design ; Volume 151 , 2019 , Pages 100-107 ; 02638762 (ISSN) ; Sadatshojaie, A ; Mohebbi, A ; Riazi, M ; Sharif University of Technology
Institution of Chemical Engineers
2019
Abstract
By displacing oil in porous media with other fluid, different mechanisms of fluid displacing occur. The importance of understanding the trapping mechanisms like pore body filling is irrefutable. Pore body filling mechanism with a coordination number of four has different events like I0, I1, I2 and I3. Previous studies showed that the event of I0 occurs when the pore is only filled by a compressible non-wetting phase, but this study showed that this event could also occur by an incompressible non-wetting phase. Trapping mechanisms can be examined in a glass micro-model. In this research, a glass micro-model with three different patterns was used. Results showed that at two spots of the...
A rigorous algebraic-analytical method for pore network extraction from micro-tomography images
, Article Journal of Hydrology ; Volume 590 , 2020 ; Masihi, M ; Azadi Tabar, M ; Sharif University of Technology
Elsevier B.V
2020
Abstract
Static and dynamic properties of porous media are highly dependent on its internal geometry. CT scan images are generally used to characterize porous media geometry. Direct simulation of fluid flow on CT scan images is possible but considerably time-consuming. In this study, a new method was developed for extracting a simplified representation known as “pore network model” by utilizing a rigorous algebraic-analytical method. By using a moving frame in the 3D matrix of the CT scan image and stepwise identifying-removing of image components, running time for a 4003 voxels sample in a typical computer system decreased to less than 350 s. The identification of throats was based on a new...
Genetic algorithm-based pore network extraction from micro-computed tomography images
, Article Chemical Engineering Science ; Volume 92 , 2013 , Pages 157-166 ; 00092509 (ISSN) ; Jamshidi, S ; Iglauer, S ; Boozarjomehry, R ; Sharif University of Technology
2013
Abstract
A genetic-based pore network extraction method from micro-computed tomography (micro-CT) images is proposed in this paper. Several variables such as the number, radius and location of pores, the coordination number, as well as the radius and length of the throats are used herein as the optimization parameters. Two approaches to generate the pore network structure are presented. Unlike previous algorithms, the presented approaches are directly based on minimizing the error between the extracted network and the real porous medium. This leads to the generation of more accurate results while reducing required computational memories. Two different objective functions are used in building the...
Effect of a monomeric sequence on the structure of hydrated Nafion in the sandwich model and solvent dynamics in nano-channels: A molecular dynamic study
, Article Molecular Physics ; Volume 108, Issue 24 , 2010 , Pages 3393-3404 ; 00268976 (ISSN) ; Akbarzadeh, H ; Taherkhani, F ; Parsafar, G ; Sharif University of Technology
2010
Abstract
Molecular dynamics simulations are performed to obtain insight into the structural properties of hydrated Nafion using the sandwich model of the polymer membrane. It is shown that a larger distance between the sulfonate groups of a chain leads to the polymer forming a better inverted micelles structure. Water- and hydronium-polymer interfaces are investigated. Comparing our results with others indicates that, from the perspective of distance, the formation of shells of water and hydronium ions is independent of the model and monomer type, but depends on both if the coordination number is considered. The behaviour of water molecules and hydronium ions is also studied dynamically. Our survey...