Showing 45 results for Wto
Volume 7, Issue 4 (9-2018)
Abstract
Beauveria bassiana (Balsamo) is one of the promising microbial control agents for the management of Oryzaephilus surinamensis (L.) Death rate, lethal time and survival expectancy were calculated for an infected population of O. surinamensis at 15, 20, 25, 30 and 35 °C. Results showed that the mean death rate under above mentioned temperatures was 0.89, 1.15, 1.40, 1.21, and 1.11 larvae/day, respectively. The values were 0.99, 1.38, 1.47, 1.18 and 1.16 insects/day for adults respectively. LT50s, at the same temperatures, were 7.11, 7.04, 4.82, 6.07 and 6.89 days for larvae and 7.03, 6.31, 4.83, 5.58, and 6.55 for adults, respectively. Survival curves for both larval and adult populations were more similar at 25, 30 and 35 °C compared to 15 and 20 °C. The survival rates in infected populations were low during 3rd and 4th days post inoculation and decreased with a sharp slope toward the end of the experiments under different temperatures. In every case, survival curves were of the 2nd type in which the mortality decreases in a steady linear form.
Volume 10, Issue 1 (4-2006)
Abstract
WTO as one of the 118th elements of third wave paradigm and also strategic shift from traditional management to brand management in global automotive industry, are regarded as the most important strategic challenges for local new established automotive companies particularly Iranian automotive companies. This article represents findings of a study which has examined growth models and learning barriers in Iranian automotive companies. This research has examined first, competition issues regarding Iran Khodro Company (as a pilot to apply results of research) by means of SD modeling in comparison with other internal competitors. And then simulates Iran automotive industry sector in a real competitive environment with presence of other foreign competitors by applying two scenarios. These two scenarios express that what are the growth enablers and impediments for Iran Khodro (in micro term) and Iranian automotive industry section (in macro term), whether or not the infrastructures of joining Iran to bilateral or multilateral WTO negotiates are strengthened. Finally, complementary policies for survival of Iranian automotive companies in a completely competitive situation is examined and addressed and necessary suggestions for their survival are presented.
Volume 10, Issue 2 (7-2019)
Abstract
Aims: The study of the behavior of active suspended fluid introduced a new topic for a wide range of applications such as reactors, microfluidic pumps, cultivating surfaces and antibacterial surfaces. The motility of bacterial suspension has generated a shear force (Hydrodynamic interaction) across the cells, which has an effect on the fluid viscosity. In this study, shear rheometer was used to evaluate the viscosity behavior of Escherichia coli (E. coli) in a water/polymer environment as a function of bacteria concentration and shear rate.
Materials and Methods: In the experimental study, the activity of E. coli was evaluated by choosing the constant concentration (0.01g/ml) and molecular weight of polyvinylpyrrolidone (360KDa). Also, the surface tensions of E. coli, Acetobacter xylinum, and S. aureus solutions were calculated using Wilhelmy test.
Findings: Activity of E. coli suspension results the lower viscosity comparing with the bacteria-free solution. The relative viscosities of the solutions were analyzed in a wide range of shear rates and bacterial concentrations. At a low shear rate up to1S-1, the relative viscosity was found to be less than a unit value (Less than water). Also, due to the collective motility break up to smaller parts at high shear rates, the viscosity increased. The critical volume fraction was defined in determined bacterial concentration (0.8v/v) to analyze the collective movement of bacteria. The interfacial tension was reduced by bacteria presence of three different stain types that confirmed the effect of bacteria activity on the flow behavior.
Conclusion: The activity of E. coli bacteria makes it easy for fluid to flow at low shear rates. The viscosity reduction of active particle has a potential to demonstrate a variety of novel applications when a reduced energy level is needed.
Volume 10, Issue 3 (10-2006)
Abstract
Government procurement constitutes an important part of the economic activities of the Country. To combat corruption, to create equal opportunities for all suppliers of goods and services, to obtain goods and services with good quality and price and to achieve transparency in government procurement, the new Tender Act was approved by the Expediency Council in early 2005. This legislation is particularly significant for replacing tens of various regulations which were applicable in different government bodies. In this article, the principles and objectives of the Tender Act are first discussed. Then, the standards and safeguards mentioned in this act are compared with the Agreement on Government Procurement of the World Trade Organization in order to assess to what extent the generally acceptable international standards in respect of government procurement have been respected in this Tender Act.
Mohammad Ali Kafaei, Neda Miri,
Volume 11, Issue 3 (10-2011)
Abstract
Armington elasticity measures the degree of responsiveness of relative demand of an imported good to its domestically produced one, to relative home produced-imported price ratio of that good. In fact, it shows the competitiveness (or its substitutability) of domestically produced goods with respect to the imported ones. These elasticities were estimated for 23 selected goods (because of data deficiencies) at 2, 3 and 4 digits of ISIC classification and found them (for 19 goods) positive and statistically significant.
Volume 13, Issue 5 (8-2013)
Abstract
Exoskeleton is a machine composed of a wearable anthropomorphic structure which noticeably magnifies user's might via its actuators. In this research, dynamic modeling and control system design for a lower limb type of this robot were done. In the literature at most a 1 DOF part of the robot is modeled and controlled which doesn't give a good insight on how all of the robot parts are controlled simultaneously. First, a suitable structure was chosen similar to that of UC Berkeley's BLEEX project. Then dynamic equations were derived in sagittal plane using the Newton-Euler method. By an experiment using Xsens system, gate kinematics data were measured and the inverse dynamics was simulated both in SimMechanics and on the model in MATLAB that proved accuracy of the derived model. Impedance control was investigated and some corrective remarks were included in that algorithm. Using this method the robot was controlled. It stabilized the system and the robot followed user's movement exactly. While a load of 50 kilograms was carried, mostly moments of less than 1 (Nm) were applied at each interface among man and robot.
Volume 13, Issue 7 (10-2013)
Abstract
Accurate estimation of the pressure losses for non-Newtonian drilling fluids inside annulus is quite important to determine pump rates and select mud pump systems during wellbore drilling operation. The aim of this study is to simulate non-Newtonian (power law and Herschel-Bulkly) foam flow in underbalanced drilling condition through wellbore annulus using finite volume method. The effect of various operational parameters on pressure loss such as fluid rheology, foam fluid velocity, foam quality, drillpipe rotation and wellbore eccentricity, have been considered. Simulation results were compared with the previously published experimental data. The agreement was close with a relative error less than 5%. The results of numerical method are closer to experimental data for Herschel Bulkly model for foam fluid. Also, the results of numerical method, showed that pressure drop increases with increasing the foam fluid velocity and quality and it decreases with increasing eccentricity, but drillpipe rotation don’t have noticeable effect on pressure drop.
Volume 13, Issue 14 (3-2014)
Abstract
The incompressible Newtonian and non-Newtonian fluid flow in a tube with disk insert is studied numerically using finite volume and boundary fitted coordinate method. The non-Newtonian fluid is time independent purely viscous that is simulated by the power law model. The effects of power law index, thickness, aspect ratio, Prandtl number and the distance between insert tubes on heat transfer, pressure drop and overall enhancement ratio (OER) are investigated for the Reynolds numbers 500, 1000 and 1500. The results show that the effect of power law index on pressure drop and overall enhancement ratio is more than the other parameters.
Volume 14, Issue 6 (9-2014)
Abstract
In this paper, numerical solution of non-Newtonian fluid flow through a channel with a cavity is studied. Carreau-Yasuda non-Newtonian model which represent dependence of stress on shear rate well is used and the effect of n index of model on attribute of flow is considered. Governing equations are discretized using finite difference method on staggered mesh and the form of allocating flow parameters on staggered mesh is based on marker and cell method. For dependence between continuity and momentum equations, artificial compressibility method is used. Numerical results express that with decrease of n index, the developing length is increased and the velocity in center of channel and pressure drop of flow are decreased.
Volume 14, Issue 8 (11-2014)
Abstract
In this paper, the immersed boundary-lattice Boltzmann method has been employed to simulate non-Newtonian flow around curve boundaries. The pressure base lattice Boltzmann equations have been used to solve the Eulerian domain to estimate proper pressure gradient in the Poiseuille flow. In addition Immersed boundary method (IBM) utilizes a discrete set of force density is also used to represent the effect of boundary on flow domain. In addition to simulate the real physical dominate problem and study the right effects of non-Newtonian fluid properties, scaling parameters have been introduced to notice the relationship between physical and lattice variables. At First, the capability of present method is examined for simulating the power-law fluid flow around a confined circular cylinder and the results show good agreement with previous study. In the following, the power-law fluid flow around elliptical cylinder in a channel is investigated for three aspect ratios eta=1,1.5,2 and for 5
Volume 14, Issue 10 (1-2015)
Abstract
In the present study the problem of a two-layered model for an unsteady and pulsatile flow of blood through a stenosed artery is numerically simulated. The model consists of a core layer of suspension of erythrocytes and a peripheral plasma layer. The core is assumed to be represented using a micropolar fluid and the plasma layer using a Newtonian fluid. The artery is considered to be elastic and the geometry of the stenosis is taken as time-dependent, however a comparison has been made with the rigid ones. The shape of the stenosis in the arterial lumen is chosen to be axially non-symmetric but radially symmetric in order to improve resemblance to the in-vivo situations. By applying a suitable coordinate transformation, the stenosed artery turns into a rectangular and rigid artery. The Navier-Stokes equations of motion of the blood flow, subjected to a pulsatile pressure gradient are solved numerically using the finite difference scheme. Dynamical characteristics of the blood flow such as the velocity profile, the volumetric flow rate and the resistance to flow are obtained and the effects of the wall motion and the severity of the stenosis on these flow characteristics are discussed. The results are found to be in good agreement with the available analytical results.
Volume 14, Issue 13 (3-2015)
Abstract
In this paper, steady creeping motion of non-Newtonian falling drop through a viscous fluid is investigated analytically. Here, the Upper Convected Maxwell model (UCM) is used for drop phase and Newtonian model is considered for external fluid. The perturbation technique is used to solve both exterior and interior flows and Deborah number that indicated the elastic effect is considered as the perturbation parameter. The present solution is derived up to second order of perturbation parameter so the present solution has a suitable accuracy for drops that made from dilute polymeric solutions. We found that the Newtonian drop has a spherical shape during the creeping motion but the non-Newtonian drop loses this shape and takes an oblate form. By increasing the elastic effect, a dimple at the rear end of the drop is created and developed. Here, it is shown that the present results have more agreement with experimental data than the previous analytical studies. The origin of drop deformation is also considered and it is proofed that the elastic property of drop phase creates a concentrated normal stress at the rear end of the drop that causes the dimple shape in this region.
Volume 14, Issue 13 (3-2015)
Abstract
This paper aims at obtaining the dynamic models of twoconstraint-over parallel mechanisms (PM) with 3-DOF (degree of freedom) and 4-DOF, the Tripteron and the Quadrupteron. The reasoning used in this paper is based on a judicious concept in detaching the whole mechanism into several subsystems and consecutive synergies between kinematic analysis, Lagrangian and Newtonian approaches. In this regard, the mechanisms are made equivalent to some subsystems and the equations of kinematic constraints are derived for all subsystems. Afterwards upon resorting to Lagrangian approach and blending it with the latter kinematic relations, the dynamic model of each leg in task space is obtained. The dynamic model of the end- effector is written in virtue of Newton-Euler’s approach where yields to three differential equations. Finally, the problem leads to a system of 12 equations for the Tripteron and 16 equations for the Quadrupteron, which do not need usaul simplifications in such problems. For the sake of comparison, the results are put into contrast by the one obtained with a dynamic analyzer software. The results obtained by both approaches are coherent which affirms the correctness of the proposed algorithm.
Volume 15, Issue 1 (3-2015)
Abstract
The echoes obtained from ultrasonic testing of materials contain valuable information about the geometry and grain structure of the test specimen. These echoes can be modeled by Gaussian pulses in a model-based estimation process. For precise modeling of an echo, the parameters of the Gaussian pulse should be estimated as accurately as possible. There are a number of algorithms that can be used for this purpose. In this study, three different algorithms are used: Gauss-Newton (GN), particle swarm optimization (PSO), and genetic algorithm (GA). The pros and cons of each of these three algorithms are reviewed and by combining them, the benefits of each algorithm are used while its shortcomings are avoided. For signals containing multiple echoes, the minimum description length (MDL) principle is used to estimate the numbers of required Gaussian echoes followed by space alternating generalized expectation maximization (SAGE) technique to translate it to separate echoes and to estimate the parameters of each echo. The performance of the proposed algorithms for simulated and experimental signals with overlapping and non-overlapping echoes is evaluated and shows to be quite effective.
Volume 15, Issue 1 (3-2015)
Abstract
This Study presents a numerical investigation of the hydro-thermal behavior of a Non-Newtonian ferrofluid (non-Newtonian base fluid and 4% Vol. Fe3O4) in a rectangular vertical duct in the presence of different magnetic fields, using two-phase mixture model, power-law model, and control volume technique. Considering the electrical conductivity of the base fluid, in addition to the ferrohydrodynamics principles, the magnetohydrodynamics principles have also been taken into account. To study the effects of non-Newtonian base fluid using power-law model, assuming the same flow consistency index with viscosity of Newtonian fluid, two different power law indexes (i.e., n=0.8 and 0.6), have been investigated and the results have been compared with that of Newtonian ones (i.e., n=1). Three cases for magnetic field have been considered to study mixed convection of the ferrofluid: non-uniform axial field, uniform transverse field and another case when both fields are applied simultaneously. The results indicate that the overall influence of magnetic fields on Nusselt number and friction factor is similar to the Newtonian case, although, by decreasing the power law index, the effect of axial field on velocity profile, Nusselt number and friction factor become more significant. Moreover, the results indicate that electrical conductivity has a significant effect on the behavior of ferrofluid and cannot be neglected and also negative gradient axial field and uniform transverse field act similarly and enhance both the Nusselt number and the friction factor, while positive gradient axial field decreases them.
Volume 15, Issue 4 (6-2015)
Abstract
One of the challenging problems of tribology is cam and follower elastohydrodynamic lubrication due to the simultaneous effect of various lubrication mechanisms. These mechanisms are transient, squeeze film, elastic deformation of contacting surfaces and variation of lubricant properties with pressure. In this paper, besides studying the mentioned factors, the effect of using a non-Newtonian lubricant such as grease is numerically investigated. The lubrication governing equations and Oswald’s grease behavior equation have been discretized using finite difference technique. The system of equation has been solved via Multi-Grid method which is an advanced iterative method in solving system of partial differential equations. The results are showed for Newtonian oil comparing to grease for different cam rotational speed. Also different grease behaviors are investigated. The results are verified by a comparison to the results obtained using the famous Newton-Raphson method. Finding shows that the minimum lubricant thickness as well as the maximum pressures is lower when using grease compared to the case that a Newtonian lubricant is used. In the case of Newtonian lubricant, increasing the speed results in an increase in the lubricant film thickness but it is shown that the speed does not affect the lubricant thickness in the case of non-Newtonian lubricant.
Volume 15, Issue 5 (7-2015)
Abstract
Compliance mismatch is one of the reasons of the coronary artery bypass graft (CABG) failure. The purpose of this study is to investigate the effect of compliance mismatch on the End to Side bypass graft. In order to model non Newtonian behavior of the blood flow, the Carreau–Yasuda model was employed and the graft and artery wall was assumed to be isotropic and modeled as a linearly elastic. In this study also the effects of blood rheology and wall distensibility on the wall shear stress distribution and velocity profile were investigated. The results of the simulation show that the maximum deformation occurs in the critical position of graft-artery junction and compliance mismatch cause smaller wall deformation in comparison to the cases in which the materials of the graft and artery are the same which leads to a higher intramural shear stress in graft-artery junction. The anastomotic wall deforms in a way that always tends to separate the graft and artery. Wall shear stress distribution on the bed centerline and the toe of the bypass graft indicates that the differences between the homologous and non-homologous material case are visible only when the internal pressure is lower than the external one. In the distal location of the artery after the toe of the anastomotic, the values of wall shear stress in the homologous material case are lower than the non-homologous material one.
Volume 15, Issue 5 (7-2015)
Abstract
Non-Newtonian fluid flows experience turbulent regime in some industrial applications. Several approaches have been proposed for numerical simulation of turbulent flows that each one has specific features. RANS turbulence models have reasonable computational costs, while include several sources of uncertainties affecting simulation results. In addition, developed RANS models for non-Newtonian fluids are modified versions of available models for Newtonian fluids, therefore, they cannot provide reliable estimation for viscoplastic stress term. On the contrary, DNS delivers accurate results but with high computational costs. Consequently, use of DNS data for estimation of uncertainty in RANS models can provide better decision making for engineers based on RANS results. In the present study, a turbulence model based on for power-law non-Newtonian fluid is developed and employed for simulation of flow in a pipe. Then, an efficient method is proposed for quantification of available model-form uncertainty. Moreover, it is assumed that uncertainties originating from various sources are combined together in calculation of Reynolds stress as well as viscoplastic stress. Deviation of the stresses, computed using RANS turbulence model, from DNS data are modeled through Gaussian Random Field. Thereafter, Karhunen-Loeve expansion is employed for uncertainty propagation in simulation process. Finally, the effects of these uncertainties on RANS results are shown in velocity field demonstrating the fact that the presented approach is accurate enough for statistical modeling of model-form uncertainty in RANS turbulence models.
Volume 15, Issue 6 (8-2015)
Abstract
This article is devoted to the derivation of formulation and isogeometric solution of nonlinear nearly incompressible elastic problems, known as nearly incompressible hyperelasticity. After problem definition, the governing equations are linearized for employing the Newton-Raphson iteration method. Then, the problem is discretized by using concepts of isogeometric analysis method and its solution algorithm is devised. To demonstrate the performance of the proposed approach, the obtained results are compared with finite elements. Due to large deformations in this kind of problems, the finite element method requires a relatively large number of elements, as well as the need for remeshings in some problems, that results in a large system of equations with a high computational cost. In the isogeometric analysis method, using B-Spline and NURBS (Non-Uniform Rational B-Spline) basis functions provides us with a good flexibility in modeling of geometry without any need for further remeshings. The examples studied in this article indicate that by using the isogeometric approach good quality results are obtained with a smaller system of equations and less computational cost. Also, influence of different volumetric functions for the nearly incompressible materials are investigated.
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
