Showing 12 results for Afrasiab
Volume 2, Issue 1 (6-2013)
Abstract
Cell concentrations and growth rate of Dunaliella salina Teodoresco in light intensities e. g. 50 and 150 µmol. photons.m-2.s-1 and temperatures 25 ± 0.5 and 31 ± 0.5 oC (Mean ± SD) were studied. The algae was isolated from the Urumieh Lake and cultured in various treatments (n=12). Algae cells were counted regularly using Thoma counting chamber in 3 replicates on daily basis. The curve of changes in population was plotted. The specific growth rate (SGR; d-1) was calculated and compared within treatments by means of two ways ANOVA Analysis. The highest cell concentration (Mean ± SD) 4.8 ± 0.6 × 10 6 cell.ml-1 was observed in light intensity of 150 µmol. photons.m-2.s-1 and temperature 25 ± 0.5 oC. The minimum cell concentration (2.8 ± 0.3 × 10 6 cell.ml-1) was observed in light intensity of 50 µmol. photons.m-2.s-1 and temperature 31 ± 0.5 oC. Specific growth rate showed significant differences in various treatments (P
Volume 8, Issue 1 (6-2018)
Abstract
One of the methods to create loyalty among customers is presenting a value through customer clubs which is beyond the intrinsic value of the product or service. In order to achieve this aim, a new perspective of customer club’s basics that is based on findings business model is needed. As a result, the purpose of this study is to explore customer club Hafez Insurance business model as the first private insurance in free zones of Iran, with an emphasis on"innovation"and" customers block ".In this research, we try to find out the answer of questions such as customers segmentation in the insurance industry, Identifying distribution channels, the type of services and products that offered in the club correspond to the target of customers and the type of value which is created for customers to increase loyalty. From the data collection method standpoint, current study is a qualitative research and was conducted through in-depth interviews and semi-structured focus group. This focus group meeting is consist of 12 experts of Hafez Insurance Company that have been selected based on purposefully sampling method. Finally, by analyzing the findings from focus group research and using the Atlas.ti software, basics of "innovation" and " customers blocks are explained. The content of qualitative data suggests that components of customers block include three themes of customers segmentation, distribution channels and communication with customers, 11 sub-components and 40 items. Components of innovation include the proposed theme for value, eight sub-components and 29 items.
Volume 13, Issue 4 (Winter 2024)
Abstract
Aims: Tehran, as the capital of Islamic Iran, has a strong and valuable history in the modern period. The formation of new Tehran in less than three centuries ago and its dramatic changes in one and half century have created many problems for it. The most important identified challenge is the need to review Tehran's contemporary heritage, to materialize Islamic Iranian urban identity.
Methods: The research has a qualitative approach, which is known as "meta-analysis". The research technique is the analysis of documents through which the research examines the subject literature and upstream documents. Relying on "complete research" and "theoretical saturation" has given special validity to the research results.
Findings: The results of the research refer to ten concepts that are possible to recognize the modern identity of the city of Tehran, and redesign the Iranian Islamic identity of the city of Tehran through them. Things like 1- street, 2- urban open space, 3- religious places, 4- city geometry, 5- urban neighborhoods, 6- intermediate space, 7- cultural space in the city, 8- residence, 9- urban squares and 10- Education and educational spaces.
Conclusion: The results of the research emphasize the importance of "urban identification", "popularization" and "intelligence" as the three pillars of Iranian Islamic identity in the field of tasks and missions of Tehran City Beautification Organization; The issue that is needed to realize the vision of "Tehran; The metropolis is the model of the Islamic world" and its various dimensions are necessary and necessary.
Afrasiab Raisi, Mehdi Davoudian,
Volume 14, Issue 5 (8-2014)
Abstract
In this paper, the natural convection of water-Al2O3 nanofluid in a square enclosure exposed to a magnetic field is numerically investigated. The enclosure is bounded by two isothermal vertical walls at different temperaturesof Th and Tc.The two horizontals walls of the enclosure are thermally insulated. A vertical plate (membrane separator) with a negligible thickness and a variable height is located in the middle of the chamber. Discretization of the governing equations are achived through a finit method and are solved using the SIMPLE algorithm. Based on the results of the numerical solution, the effects of the relevant parameters such as the dimensionless height of the membrane separator, Rayleigh number, the solid volume fraction and the Hartmann number on the flow field and the heat transfer rate are investigated. The results show that the heat transfer rate decreases with an increase of the dimensionless height of the membrane separator and an increase of the Hartmann number. The heat transfer rate, however, increases as the Rayleigh number increases. Depending on the Rayleigh number, the thermal performance of the enclosure is either improved or deteriorated as the solid volume fraction is increased.
Behzad Ghasemi, Abbas Kasaeipoor, Afrasiab Raisi,
Volume 14, Issue 12 (3-2015)
Abstract
In this paper, the result of a numerical study on the natural convection in an inclined T shap cavity filled with Water-Cu nanofluid with the presence of a constant magnetic field was investigated. A heat source embedded on the bottom wall of enclosure, the upper wall is cold and the other walls are adiabatic. Discretization of the governing equations are achieved through a finite volume method and solved with SIMPLE algorithm. The Hartmann number has been varied from 0 to 80 and the cavity has been twisted under the angles between 0 to 90 degrees. The findings of study show that the effect magnetic field on the average Nusselt number is higher in high Reyleigh number. In Ra=105, the increase in nanofluid, to the Hartman number 20, contributes to decrease of the average number and in the Hartman number 40 and more, causes the average Nusselt number to increase. In Ra=106 , the increase in nanofluid, to the Hartman number 20, contributes to increase of the average number and in the Hartman number 40 and more, causes the average Nusselt number to decrease. The results also indicate that, the maximum heat transfer, in Ra=105 and Ra=106 accurse at 67.5° angle. the minimum heat transfer, in Ra=105 and Ra=106 accurse at 0° and 22.5° angle respectively.
Afrasiab Raisi,
Volume 15, Issue 11 (1-2016)
Abstract
In this study, the natural convection heat transfer is numerically examined in a square enclosure filled with a non-Newtonia power-law fluid. Two fixed temperature baffles are mounted on the left wall of the enclosure. The left wall of the enclosure and the baffles installed on it, are at a constant temperature of T_h and the right wall of the enclosure is at a constant temperature of T_c, while its horizontal walls are thermally insulated. The governing equations for the power-law fluid flow are solved with the numerical finite difference method based on the control volume formulation and SIMPLE algorithm. The study investigates the effects of relevant parameters such as the Rayleigh number (〖10〗^3≤Ra≤〖10〗^6), the power-law index (0.8≤n≤1.4), the baffles length (0≤B≤0.5) and the baffles distance from each other (0.1≤D≤0.8) on flow and temperature fields and the rate of heat transfer. The results show that an increase in Rayleigh number, particularly when n
Saeed Khodaygan, Amir Ghasemali, Hamed Afrasiab,
Volume 15, Issue 13 (Special Issue 2016)
Abstract
Mehdi Kazemiyan, Hamed Afrasiab, Mohammad Hadi Pashaei,
Volume 16, Issue 2 (4-2016)
Abstract
Recent observations have shown that artery stenosis occurs as multiple-stenosis in 70% of patients with atherosclerosis plaques. Accordingly, the frequent occurrence of double-stenosis in blood arteries has inspired this paper to investigate and compare the plaque rupture risk in different arrangements of common plaque shapes in a double-stenosis. The plaque von-Mises stress in plaque fibrous cap is calculated by finite element modeling of the fluid-structure interaction (FSI) between the blood flow, artery and plaque components. Arbitrary Lagrangian-Eulerian approach is employed for FSI simulations and a benchmark problem dealing with wave propagation in a fluid-filled elastic tube is used for model verification. Transient velocity and pressure conditions of actual pulsatile blood flow through coronary artery are prescribed. The blood is assumed to be a Newtonian fluid and hyper-elastic material model is employed for describing nonlinear behavior of the human tissue composed of the arterial wall, lipid core and fibrous cap. It was observed that the arrangement composed of two diffused plaques is subjected to the maximum von-Mises stress, while the arrangement of ascending-descending plaques experiences the minimum von-Mises stress. The effect of different parameters such as the stenosis degree, the space length between the plaques, and the plaque length is studied and discussed.
Hamed Afrasiab, Bahereh Kordrostami,
Volume 16, Issue 5 (7-2016)
Abstract
Stenting is considered to be the favoured tool for therapy of coronary stenosis disease. However, despite the many advantages of this treatment strategy, its outcome may be undermined by the restenosis occurrence in the stent deployment site. Observations have shown that stent deployment in the artery alters the hemodynamic parameters such as wall shear stress and vortices size and prepares the conditions for in-stent restenosis development. Considering this fact, in this paper, the effect of some geometrical parameters such as the shape and the size of the stent strut on the wall shear stress distribution and vortices size is investigated. Furthermore, employment of a stent with partial flexible strut is suggested to decrease the restenosis risk, and the effect of the flexible part stiffness is explored. For this purpose, the interaction between the blood flow and the flexible part is simulated by arbitrary Lagrangian-Eulerian approach in the framework of the finite element method. The results indicate that in stents with circular strut, the partial flexibility of the cross-section can be effective in reducing the restenosis risk by lowering the maximum value of the wall shear stress and considerably decreasing the vortices size. On the other hand, in stents with rectangular struts, it not only does not decrease the shear stress maximum value but also significantly increases the vortices size and may lead to increase of the restenosis risk.
Majid Tahmasebi, Behzad Ghasemi, Afrasiab Raisi,
Volume 16, Issue 9 (11-2016)
Abstract
Abstract melting of Cyclohexane-Cu nano-material in a porous square cavity is studied numerically in this paper. At first initial temperature of the cavity is Ti that is equal to melting temperature of nano-material,Tm ,. The horizontal walls are adiabatic. Suddenly the left wall's temperature has changed to Th>Tm . The effective parameters in this case are and which appear in the nondimensionalized equations. Nondimensionalized governing equations are obtained based on the Darcy model; a control volume approach is used for solving these equations. The effect of the variation of mentioned parameters are investigated on the heat transfer rate, fluid flow, isotherms and melting time of nano-PCM. The results show that changing of any parameters will be effective on increase or decrease of heat transfer rate and melting process time. For example variation of has high effect on melt fraction in cavity with time. The results show that melting of PCM is prolonged when nano-particles are added. the increases of the Ra increases the natural convection heat transfer and therefore increases the melting rate, and deforms the melting line.
Soroush Omiddezyani, Ramazan-Ali Jafari-Talookolaei, Maryam Abedi, Hamed Afrasiab,
Volume 17, Issue 2 (3-2017)
Abstract
In this study, the hydrostatic vibration analysis of an isotropic rectangular microplate in partial contact with a bounded fluid is studied. Modified couple stress theory based on the Kirchhoff plate assumptions are used to mathematically model the problem. The extended Hamilton’s principle is employed to drive the governing differential equation of motion and the corresponding boundary conditions. The transverse displacement of the microplate is approximated by a set of admissible functions which must satisfy the geometric boundary conditions. The fluid is assumed to be incompressible, inviscid and irrotational and the fluid velocity potential is obtained using the boundary and compatibility conditions. Natural frequencies of the microplate are calculated using the Rayleigh-Ritz method. To validate the present results, the natural frequencies of an isotropic macroplate in contact with fluid are compared with the available data in the literature and very good agreements are observed. Finally using the numerical data, the effect of different parameters such as thickness to length scale parameter, aspect ratio, length to thickness ratio and boundary conditions on the natural frequencies of the microplate are discussed in detail. We have observed that the difference between the natural frequencies predicted using the classical theory and the one evaluated by the modified couple stress theory is significant when thickness of the microplate is small, but diminishes as thickness increases.
M. Gholami, A. Hassani, H. Afrasiab, M. Kazemiyan,
Volume 19, Issue 12 (December 2019)
Abstract
Biodegradable polymers have widespread usages in the biomedical field, such as stents, sutures, scaffolds, and implants. Due to the importance of behavior of these materials exposed to environmental effects, whether in nature or the human body, extensive researches have been carried out in the last decade that most of them are experimental results and very few are theoretical results. These researches have mainly been performed for specific loading and temperature conditions and so on. For this purpose, in addition to validating the theoretical and empirical relationships derived through the experimental results, the effects of more complex conditions can be considered using the finite element method and numerical solution. In this paper, an analytical relationship extraction method has been presented, as well as the abilities and weaknesses of biodegradable polymers have been investigated by presenting the experimental results of biodegradable polymers. A numerical and finite element analysis is also provided to analyze the behavior of biodegradable polymers. The theoretical analysis and numerical simulation of biodegradable polymers have been carried out using the neo-Hookean hyperelastic model. First, the relationship of stress, versus the stretch has been derived using the strain energy of neo-Hookean material. Next, by assuming a degradation parameter, changes in the properties of the material exposed to environmental effects, according to the time in Abaqus Umat subroutine have been applied to the model. Finally, the accuracy of the simulation has been studied by a comparison between the experimental results and theoretical analyses with numerical solutions.