Search for: fractal-dimension
Total 36 records
Article Electrochimica Acta ; Volume 53, Issue 13 , 2008 , Pages 4528-4536 ; 00134686 (ISSN) ; Gobal, F ; Danaee, I ; Biabani, R ; Mahjani, M. G ; Sharif University of Technology
The electrochemical behavior of a tin electrode in citric acid solutions of different concentrations was studied by electrochemical techniques. The E/I curves showed that the anodic behavior of tin exhibits active/passive transition. Passivation is due to the formation of Sn(OH)4 and/or SnO2 film on the electrode surface. Addition of NaCl to citric acid solution, enhances the active dissolution of tin and tends to breakdown the passivity at a certain breakdown potential. Cyclic voltammetry and galvanostatic measurements allow the pitting potential (Epit) and the repassivation potential (Erp) to be determined. Potentiostatic measurements showed that the overall anodic processes can be...
Effect of the shear loading direction on shear behavior of rock and finding new empirical method for determining JRC by fractal dimension, Article Annual Conference of the Canadian Society for Civil Engineering 2007: Where the Road Ends, Ingenuity Begins, Yellowknife, NT, 6 June 2007 through 9 June 2007 ; Volume 1 , 2007 , Pages 259-267 ; Sadaghiani, M. H ; Askari, M ; Khosravi, M ; Sharif University of Technology
Effect of different conditions on shear behaviour of rock has been investigated by various researchers. As known, in larger scale the continuity of the rock material is interrupted by separated planes such as bedding planes, faults, shear zones, closure and the behaviour converts to be inelastic and anisotropic. Generally, discontinuities appear repeatedly in more than one preferential direction, creating a three dimensional structure, reducing its stiffness and shear strength as mechanical effects and increasing its transport velocity associated with discontinuity flow as hydraulic effects. They also make rock behavior more complex and different compared to the behavior of soil. According...
M.Sc. Thesis Sharif University of Technology ; Foroughmand Arabi, Mohamad Hadi ; Alishahi, Kasra
Cancer can be defined as a stochastic phenomenon. Thus, the tumor growth can be defined as a stochastic process. A Cancer tumor can be analyzed by its geometric shape. Furthermore, computing fractal dimension of shapes is a useful technique to analyze chaosity and complexity of shapes. This approach can be used to compare results from laboratory with simulated results of a mathematical model. A stochastic model of tumor growth will be presented. And some geometrical properties will be analyzed through computer simulation of the model
The fractal study of Cu-Ni layer accumulation during electrodeposition under diffusion-controlled condition, Article Materials Research Bulletin ; Volume 42, Issue 9 , 2007 , Pages 1769-1776 ; 00255408 (ISSN) ; Dolati, A ; Sharif University of Technology
The fractal study of thin layer films has been concerned by numerous studies, but it is a novel idea to use this method for interpretation of layer formation during electrocrystallization, simultaneously. In present study, Scharifker's equations were derived for instantaneous and progressive nucleation and 3D growth of hemispherical centers under diffusion-controlled condition to calculate in situ change of fractal dimension of surface. It was assumed that the layer could be formed completely when fractal dimension of surface inclined to 2. Moreover, the fractal analysis of AFM images has confirmed the presumed model. © 2006 Elsevier Ltd. All rights reserved
Experimental Analysis of Immiscible Displacements of Heavy Oil in Heterogeneous Porous Media under Ultrasonic Effect, M.Sc. Thesis Sharif University of Technology ; Ghotbi, Siroos ; Ghazanfari, Mohammad Hossein
In the recent years, there has been an increasing attention toward usage of ultrasonic for enhanced oil recovery practices. But, thorough knowledge of active mechanisms and spreading and characterization of developed fingers during this practice is not available. From the other hand, due to limited amount of light oil fields, more attentions towards recovery from heavy oils is the need of the hour. Documents show that the big issues during the enhanced oil recovery from heavy crudes are high density of reservoir oil as well as poor development of fingers during injection due to high mobility ratios. In this study, results of ultrasound effect on the heavy oil recovery and its effect on the...
Ph.D. Dissertation Sharif University of Technology ; Nayebi, Mohammad Mehdi
Accurate modeling of clutter and detection of low observable targets within clutter are the major problems in radar signal processing applications. Recently, fractal geometry is applied to the analysis of high range resolution radar sea clutters. The intrinsic difference in the fractal dimension between sea clutter and the echoes from targets is extracted and used to detect targets. The box-counting method is widely used to estimate fractal dimension but it has some drawbacks never or rarely considered in literature. We explain the drawbacks and propose a new fractal dimension based detector to increase detection performance in comparison with traditional detectors. Both statistically...
Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Vol. 89, Issue. 6 , 2014 ; ISSN: 15393755 ; Rouhani, S ; Sharif University of Technology
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...
Monitoring and characterizing the finger patterns developed by miscible displacement in fractured heavy oil systems, Article Industrial and Engineering Chemistry Research ; Volume 52, Issue 31 , July , 2013 , Pages 10853-10863 ; 08885885 (ISSN) ; Majidi, S. M. J ; Ghazanfari, M. H ; Sharif University of Technology
This work concerns experimentally quantifying finger behavior during miscible displacements in fractured porous media. A series of miscible tests were performed on five-spot fractured micromodels which were initially saturated with heavy crude oil, and the developed finger patterns were quantified using an image analysis technique. The results revealed that the numbers of macro fingers formed is well correlated with the square root of dimensionless time, while the rate of finger initiation is independent of fracture characteristics. The level of bypassed oil linearly decreases with dimensionless distance traveled by front precisely. The transient fractal dimension behavior experiences a...
Permutation entropy and detrend fluctuation analysis for the natural complexity of cardiac heart interbeat signals, Article Physica A: Statistical Mechanics and its Applications ; Volume 392, Issue 14 , 2013 , Pages 3106-3112 ; 03784371 (ISSN) ; Rahmani, M ; Taherkhani, F ; Akbarzadeh, H ; Abroshan, H ; Sharif University of Technology
We compute fractal dimension and permutation entropy for healthy and people who have experienced heart failure. Our result shows that permutation entropy is a suitable approach as well as detrend fluctuation analysis (DFA). The result of DFA shows that the fractal dimensions for healthy and heart failure are different as well as the permutation entropy result. The fluctuation value for permutation entropy for an individual who has experienced heart failure is bigger than for a healthy person. There is some specific change in the interbeat signal of a person who has experienced heart failure, but there is not previous trend for a healthy person
Article Chaos, Solitons and Fractals ; Volume 103 , 2017 , Pages 294-306 ; 09600779 (ISSN) ; Nasrabadi, A. M ; Shamsollahi, M. B ; Sharif University of Technology
This paper presents a methodology to extract a number of quantifier features to characterize volumetric behavior of trajectories in phase space. These features quantify expanding and contracting behaviors and complexity that can be used in nonlinear and chaotic signals classification or clustering problems. One of the features is directly extracted from the distance matrix and seven features are extracted from a matrix that is subsequently obtained from the distance matrix. To illustrate the proposed quantifiers, Mackey–Glass time series and Lorenz system were employed and feature evaluation was performed. It is shown that the proposed quantifier features are robust to different...
Scaling of clusters and winding-angle statistics of isoheight lines in two-dimensional Kardar-Parisi-Zhang surfaces, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 79, Issue 3 , 2009 ; 15393755 (ISSN) ; Rouhani, S ; Sharif University of Technology
We investigate the statistics of isoheight lines of (2+1) -dimensional Kardar-Parisi-Zhang model at different level sets around the mean height in the saturation regime. We find that the exponent describing the distribution of the height-cluster size behaves differently for level cuts above and below the mean height, while the fractal dimensions of the height-clusters and their perimeters remain unchanged. The statistics of the winding angle confirms the previous observation that these contour lines are in the same universality class as self-avoiding random walks. © 2009 The American Physical Society
Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 79, Issue 3 , Volume 79, Issue 3 , 2009 ; 15393755 (ISSN) ; Moghimi-Araghi, S ; Dashti-Naserabadi, H ; Rouhani, S ; Sharif University of Technology
Appreciation of stochastic Loewner evolution (SLEκ), as a powerful tool to check for conformal invariant properties of geometrical features of critical systems has been rising. In this paper we use this method to check conformal invariance in sandpile models. Avalanche frontiers in Abelian sandpile model are numerically shown to be conformally invariant and can be described by SLE with diffusivity κ=2. This value is the same as value obtained for loop-erased random walks. The fractal dimension and Schramm's formula for left passage probability also suggest the same result. We also check the same properties for Zhang's sandpile model. © 2009 The American Physical Society
Article Physica A: Statistical Mechanics and its Applications ; Volume 356, Issue 2-4 , 2005 , Pages 609-627 ; 03784371 (ISSN) ; Jafari, G. R ; Sharif University of Technology
We report an empirical study of Tehran price index (TEPIX). To analyze our data we use various methods like as, rescaled range analysis (R/S), modified rescaled range analysis (Lo's method), detrended fluctuation analysis (DFA) and generalized Hurst exponents analysis. Based on numerical results, the scaling range of TEPIX returns is specified, long-memory effect or long-range correlation property in this market is investigated, fractal dimension of probability space of TEPIX returns is derived and finally the stage of development in Tehran stock exchange is determined. © 2005 Elsevier B.V. All rights reserved
Effect of miscible nitrogen injection on instability, particle size distribution, and fractal structure of asphaltene aggregates, Article Journal of Dispersion Science and Technology ; Volume 33, Issue 5 , 2012 , Pages 763-770 ; 01932691 (ISSN) ; Dabir, B ; Rashtchian, D ; Mahmoudi, B ; Sharif University of Technology
Precipitation, aggregation, and breakup of asphaltene particles are studied under natural depletion and nitrogen injection processes by means of high pressure filtration and a photographic procedure coupled with image analysis. Filtration results show that nitrogen destabilizes asphaltenes extremely, and the problem is more severe for heavier crude samples. Bimodal histograms of particle size distribution show two agglomeration mechanisms: cluster aggregation dominant around bubble point pressure and diffusion limited far away. The fractal structure of aggregates is also altered by gas injection; it is observed that the flocculent masses grow in size and become more compact and organized...
Article Applied Surface Science ; Volume 353 , 2015 , Pages 1143-1149 ; 01694332 (ISSN) ; Ranjbar, M ; Rouhani, S ; Sharif University of Technology
We use field emission scanning electron microscope (FE-SEM) to investigate the growth of palladium colloids over the surface of thin films of WO
3/glass. The film is prepared by Pulsed Laser Deposition (PLD) at different temperatures. A PdCl 2 (aq) droplet is injected on the surface and in the presence of steam hydrogen the droplet is dried through a reduction reaction process. Two distinct aggregation regimes of palladium colloids are observed over the substrates. We argue that the change in aggregation dynamics emerges when the measured water drop Contact Angel (CA) for the WO 3/glass thin films passes a certain threshold value, namely CA ≈ 46°, where a...
Article Construction and Building Materials ; Vol. 55 , 2014 , pp. 202-211 ; ISSN: 09500618 ; Kazemi, M. T ; Vaseghi Amiri, J ; Nikbin, I. M ; Rabbanifar, S ; Rahmani, E ; Sharif University of Technology
This paper presents and discusses the effect of maximum size of coarse aggregate on fracture characteristics and brittleness of self-compacting concrete (SCC). Based on an experimental program, a series of three point bending tests were carried out on 86 notched beams, as recommended by RILEM. For all mixes, the parameters were analyzed by the work-of-fracture method (WFM) and by the size effect method (SEM) and consequently a correlation between these methods was obtained which is used to calibrate cracking numerical models. Test results showed that with increase of size of coarse aggregate, (a): fracture energies of GF in WFM and Gf in SEM increase which may be explained by the change in...
Article Construction and Building Materials ; Volume 52 , 15 February , 2014 , Pages 137-145 ; ISSN: 09500618 ; Beygi, M. H. A ; Kazemi, M. T ; Vaseghi Amiri, J ; Rahmani, E ; Rabbanifar, S ; Eslami, M ; Sharif University of Technology
This paper presents the effect of volume of coarse aggregate on fracture characteristics of self- compacting concrete (SCC). Based on an experimental programme, a series of three point bending tests were carried out on 58 notched beams. SCC was prepared with coarse aggregate in varying percentages of 30%, 40%, 50% and 60% (as the percentage of the total aggregate volume). For all mixes, the fracture parameters were analyzed by the work-of- fracture method (WFM) and by the size effect method (SEM) to obtain a suitable correlation between these methods which is used to calibrate fracture numerical models. The results showed that with decrease of volume of coarse aggregate from 60% to 30% in...
Article Journal of Digital Imaging ; Vol. 27, issue. 5 , 2014 , pp. 661-669 ; ISSN: 08971889 ; AhmadiNoubari, H ; Fatemizadeh, E ; Khalili, M ; Sharif University of Technology
In this paper, we present an efficient fractal method for detection and diagnosis of mass lesion in mammogram which is one of the abnormalities in mammographic images. We used 110 images that were carefully selected by a radiologist, and their abnormalities were also confirmed by biopsy. These images included circumscribed benign, ill-defined, and spiculated malignant masses. Firstly, we discriminated lesions automatically using new fractal dimensions. The results which were examined by different types of breast density showed that the proposed method was able to yield quite satisfactory detection results. Secondly, noting that contours of masses playing the most important role in diagnosis...
Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; 2010 , Volume 82, Issue 6 ; 15393755 (ISSN) ; Rajabpour, M. A ; Sharif University of Technology
In complex systems with fractal properties the scale invariance has an important rule to classify different statistical properties. In two dimensions the Loewner equation can classify all the fractal curves. Using the Weierstrass-Mandelbrot (WM) function as the drift of the Loewner equation we introduce a large class of fractal curves with discrete scale invariance (DSI). We show that the fractal dimension of the curves can be extracted from the diffusion coefficient of the trend of the variance of the WM function. We argue that, up to the fractal dimension calculations, all the WM functions follow the behavior of the corresponding Brownian motion. Our study opens a way to classify all the...
An investigation of the surface morphology of nanostructured nickel thin films prepared by electrodeposition, Article International Journal of Surface Science and Engineering ; Volume 10, Issue 5 , 2016 , Pages 444-455 ; 1749785X (ISSN) ; Dolati, A ; Sharif University of Technology
Inderscience Enterprises Ltd
Nickel nanostructure thin films were electrodeposited on copper plates to investigate the fractal study. Scharifker's equations were derived for instantaneous and progressive nucleation and 3D growth of hemispherical centres under diffusion-controlled condition to calculate in situ change of fractal dimension of surface. It was assumed that the layer could be formed completely when fractal dimension of surface inclined to 2. Moreover, the fractal analysis of atomic force microscopy (AFM) images has confirmed the presumed model. Also, the power values of power spectral density (PSD) of the AFM images were determined using fast Fourier transform (FFT) algorithms. The PSD plots are approximated...