Sharif Digital Repository

Application of nanoparticles for wettability alteration offers a practical approach to resolve some surface-related problems encountered in the nowadays technological process. Examples are underground/subsurface engineering implications, including the enhanced oil recovery from the oil-wet carbonate reservoirs. However, the common wettability evaluating techniques such as contact angle and flotation cannot be representative of the dynamic phenomena occurring at the pore scale and hence are unable to give accurate information about the process. Therefore, in the present work, the electrokinetic evaluations are utilized to explore the wettability alteration of initially oil-wet carbonate rock... 

Tungsten Inert Gas (TIG) process and titanium cored wires filled with micro size TiC particles were employed to produce surface composite coatings on commercial pure Ti substrate for wear resistance improvement. Wire drawing process was utilized to produce several cored wires from titanium strips and titanium carbide powders. Subsequently, these cored wires were melted and coated on commercial pure Ti using TIG process. This procedure was repeated at different current intensities and welding travel speeds. Composite coating tracks were found to be affected by TIG heat input. The microstructural studies using optical and scanning electron microscopy supported by X-ray diffraction showed that... 

Analyzing contact stress in rails and wheels are very important in mechanical and railway engineering. In this paper, new formulations of the contact stress are presented for two rolling bodies by exponential and power law forms semi-analytically. Innovative elastic wheel-rail contact models and FE Modeling are proposed. The present model assumes the collection of rail and wheel as elastic deformable bodies and needs numerical and novel analytical solutions. Results of this work are close to the Hertz Stress, previous published work and FEM results, in which good agreements are found among the results. So, we can rely on this method and their results. With this approach, suitable results... 

In this article we study the effects of emotion on brain activity through nonlinear processing of EEG. EEG was recorded from 19 sites (10-20systems) in different states of brain activity; induced by emotionally valance music stimulus and also during no-task resting states. Then, we compared the EEG complexity of the rest condition with each emotional states. After that we determined the locations in which correlation dimension was changed in different states through one-way ANOVA test. In this study four excerpts of music from both Iranian traditional music and Western classical music, two negative valance and two positive valance pieces, were selected according to the results of... 

Wettability alteration of rock surfaces toward gas wetting have been recognized as a practical approach for maximizing the production from the gas condensate reservoirs. Most of the reported work in this area applied the so called sessile drop contact angle measurement technique to examine the change in wetting state of a surface. However, the size-dependent wetting behavior of drop which could affect the exact determination of wettability and wettability changes was not well discussed in the previous studies. Therefore, in this work, the size dependency of contact angle for four different liquid-solid-gas systems; i.e., water-calcite-air, water-treated calcite-air (nanofluid treated... 

Dynamic contact angle measurement; as a standard method for surface wettability analysis, is usually conducted through the analysis of sessile drops formed following the low rate injection of fluid from beneath through a drilled hole via an injection needle. However, understanding/characterizing the changes of drop contact angle from the point where the flat solid surface begins is not well discussed yet. Moreover, during the evaluation of size-dependent behavior of contact angle of millimeter-scale drops, the effect of the drilled hole is ignored. In this regard, in the current study, the experimental and thermodynamic characterizations of the sessile drop advancing contact angle... 

Recently, application of silica nanoparticles (SNP) for enhancing oil recovery during water flooding has been much attended. However, understanding how rock and nanoparticles (NP) interacts through adsorption onto the carbonate reservoir rocks is not well discussed. In this work, adsorption behavior of SNP onto the calcite had been characterized, through kinetic, equilibrium, thermodynamics and electrokinetic studies as well as interaction energy analysis by DLVO theory. Also, field emission scanning electron microscopy (FESEM) was utilized to visualize the adsorption process. It had been found that kinetic behavior of SNP-calcite system followed the pseudo-second order model. Equilibrium... 

Oil recovery from carbonate reservoirs can be enhanced by altering the wettability from oil-wet toward water-wet state. Recently, silica nanoparticle (SNP) suspensions are considered as an attractive wettability alteration agent in enhanced oil recovery applications. However, their performance along with the underlying mechanism for wettability alteration in carbonate rocks is not well discussed. In this work, the ability of SNP suspensions, in the presence/absence of salt, to alter the wettability of oil-wet calcite substrates to a water-wet condition was investigated. In the first step, to ensure that the properties of nanofluids have not been changed during the tests, stability analysis... 

In this paper, a generalized intelligent water drops algorithm (IWD) for solving robot path planning problem is proposed. The authors want to reduce the time of reaching the optimal solution as much as possible. To do this, some new heuristic operators and a multi section graph model of environment is introduced. The authors divide graph to equal sections and compare behaviour of the solutions (paths) in each section with behaviour of them in other sections. This comparison uses a fuzzy inference system. Base on this comparison, a fuzzy number is assigned to each part of solutions. This fuzzy number determines the worth of a solution in a section. Less worth solutions need more improvement.... 

In this work, application of silica nanoparticles for wettability alteration of initially oil-wet calcite was investigated through analysis of surface forces and DLVO theory. Doing so, the wettability and zeta potential of calcite surfaces were measured through the sessile drop method and an in-house experimental setup, respectively. Primary evaluation indicated that incorporating DLVO terms in the Frumkin-Derjaguin model was not sufficient to describe the wettability in an oil-wet calcite/nanofluid system. Sensitivity analysis showed that calculating the double-layer interaction using constant potential-constant potential boundaries along with structural hydrophobic forces (non-DLVO... 

Methods of human semen assessment are quite wide ranging. In this paper, we use background subtraction methods in order to detect progressive sperms whose quality of movement strongly influence fertility. Robust Principal Component Analysis (RPCA) is a powerful algorithm which has been used recently for background subtraction purposes. Sperm tracking problem can also be defined as a background subtraction problem. In RPCA algorithm, data is represented by a low rank plus sparse matrix. In our approach, the foreground data is recovered through such matrix decomposition. We compare the RPCA approach with four other background subtraction methods in order to check accuracy of algorithm as a... 

Wettability alteration analysis form gas-repellent to gas-wet with the aid of chemical agents has been subjected of numerous studies. However, fundamental understanding of the effect of surface tension of liquid on repellency strength, the change in the intermolecular forces due to the adsorption of nanoparticles onto the rock surfaces, and exposure of treated rock in brine are not well discussed in the available literature. In this study, X-ray diffraction, Atomic Force Microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were applied to characterize the treated and fresh samples. Dynamic and static contact angle measurements were then combined with six methods... 

Recently, super gas wet and gas wet surfaces have been extensively attended in petroleum industry, as supported by the increasing number of publications in the last decade related to wettability alteration in gas condensate reservoirs. In many cases, contact angle measurement has been employed to assess the wettability alteration. Even though contact angle measurement seems to be a straightforward approach, there exist many misuses of this technique and consequently misinterpretation of the corresponding results. In this regard, a critical inspection of the most recent updated concepts and the intervening parameters in the contact angle based wettability evaluation of liquid-solid-gas... 

Recently, super gas wet and gas wet surfaces have been extensively attended in petroleum industry, as supported by the increasing number of publications in the last decade related to wettability alteration in gas condensate reservoirs. In many cases, contact angle measurement has been employed to assess the wettability alteration. Even though contact angle measurement seems to be a straightforward approach, there exist many misuses of this technique and consequently misinterpretation of the corresponding results. In this regard, a critical inspection of the most recent updated concepts and the intervening parameters in the contact angle based wettability evaluation of liquid-solid-gas... 

The objective of this paper is to present some novel insights for solving a second stage creep problem in metal matrix composites. First, a new analytical approach is developed for obtaining some unknowns in second stage creep of short fiber composites under an applied axial load. The unknowns are the radial, circumferential, axial, shear and equivalent stresses, which are determined by approximation of creep constitutive equations and using proper assumed displacement rates. A nonlinear differential equation is solved employing suitable and correct approximate assumptions. Then, the difference of the stress components utilizing creep constitutive equations and assumed displacement rates is... 

A new mathematical insight based on logarithmic, polynomial mapping functions (MF), and dimensionless parameter (DP) models is presented for determination of some unknowns in the steady state creep stage of short fiber composites subjected to axial loading. These unknowns are displacement rate in outer surface of the unit cell, shear and equivalent stresses at interface and outer surface of the unit cell, and average axial stress in fiber. Dimensionless parameter technique is presented for determination of displacement rate and equivalent stress in outer surface of the unit cell. However, the polynomial mapping function is presented for determination of average axial stress in fiber. Most... 

A new analytical formulation is presented to study the steady-state creep in short fiber composites using complex variable method. In this new approach, both the fiber and matrix creep at low stresses and temperatures. To analyze the crept fiber, a plane stress model was used. Important novelties of the present analytical method are determination of displacement rates with proper boundary conditions in the crept fibers and also using the complex variable method in creep analyzing. It is noteworthy that the method can be useful to study the creep behavior in polymeric matrix composites due to their high capability of creep. Moreover, another significant application of the present method is to... 

Finite element analysis of creeping short fiber composites is carried out in the second stage creep with application in microelectronic and optoelectronic/photonic devices. Prediction of the creep behavior is very significant for designing the optoelectronic and photonic composites with optical fibers. Study on the creep behavior is necessary for failure, fracture, fatigue, and creep resistance of the optoelectronic/photonic composites. The creep behavior of the short fiber composites is estimated by FEM. Study on the creep behavior is necessary for defect analysis and creep resistance of the short fiber composites. In this research work, prediction of the creep behavior of the short fiber... 

FEM study is carried out for predicting the behavior of the short fiber composites in the steady state creep with application in optoelectronic and photonic devices. The study on the creep behavior is necessary in order for failure, fracture, fatigue, and creep resistance of the short fiber composites. In this article, the creep behavior of the short fiber composite is predicted under tensile axial loading by the numerical method. One of the significant applications of the work is in the short fiber composite designing and optimizing. Also, the available experimental results [10] are used for the FEM simulation