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Abstact- There exist many methods of adding damping to a vibrating structure; however, very few can function without ever coming into contact with the structure. One such method is eddy current damping. This magnetic damping scheme functions through the eddy currents that are generated in a nonmagnetic conductive material when it is subjected to a time changing magnetic field. in this research work a variable eddy current damper is applied for controlling the vibrations of a cantilever beam. An displacement sensor is attached to the setup for measuring the feedback response for controlling system. A PID control algorithm is developed for the controlling system as the eddy current damper is a non-contacting system. Using this system, experiments are performed on a cantilever beam showing the system can effectively suppress each of the first three modes of vibration by upwards of 10 dB, demonstrating the actuator has an increased bandwidth over previously used eddy current methods. Keywors: Eddy Currents, Magnetic Dampers, FFT

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Tax evasion linked to imports is a cause for forming informal economy. Tax evasion decreases government revenue and makes restrictions in implementing economic policies. This paper investigates relationship between the tariff rate and tax evasion at the six- digit HS level on trade data of Iran and its twelve major trading partners during 2003 to 2008.  According to Bhagwati method, Tax evasion is defined as the discrepancy between the value of imports, reported by Iran, and the value of exports to Iran, reported by its trading partners. The results from estimated tax evasion models show that there is positive and significant relationship between the trading discrepancies or tax evasion and tariff rates among 27917 products. The elasticity of tax evasion with respect to tariff rates is 0.67, i.e. each one-percentage-point increase in the tariff rates raises tax evasion by 0.67 percent in case of total products. Additionally, the elasticity of tax evasion with respect to tariff rates is 0.8 for goods having tariff rates above average. In this case, tax evasion is more likely. The positive impact of tariff rate on tax evasion is not verified for goods having tariff rates lower than average.

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 The frequency bandwidth of microstrip patch antennas can be increased using both of U-slot and proximity feeding. Although some design rules have been already explained for the probe-fed U-slot antenna the proximity coupling causes to consider a lot of parameters for design procedure; consequently, to deal with all of them seems confusing. In this paper after investigating the effect of various parameters on the multiple resonant frequencies of the antenna and recognizing the most effective factors, some guidelines to design a proximity coupled U-slot microstrip antenna are proposed. In addition, an antenna element with 16% impedance bandwidth is designed at center frequency of 16.7GHz, and its broadband impedance and radiation characteristics are vastly considered. Also, 1×2 and 2×2 arrays of the antenna element are designed to use as subarrays for designing large arrays. The measurement results of return loss and radiation pattern, show good agreement with simulation results.

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Alfalfa crops were surveyed for the incidence of alfalfa mosaic virus (AMV), cucumber mosaic virus (CMV), peanut stunt virus (PSV), bean leaf roll virus (BLRV), bean yellow mosaic virus (BYMV) and bean common mosaic virus (BCMV) in the major growing areas in the southeast and central regions of Iran. Samples were collected between May 2009 and March 2011 and analyzed for viral infection initially by enzyme-linked immunosorbent assay (ELISA) followed by RT-PCR using capsid protein gene specific primers. In total, 634 symptomatic leaf samples were collected in four southeastern and central provinces of Iran representing 20 regions. Our results revealed a high incidence of AMV over a wide geographical area. AMV and BLRV were identified in most regions, whereas BYMV was found only in Yazd Province. PSV was detected in three regions, but not in Sistan- Balouchestan and Hormozgan Provinces. The highest incidence of viral infection amongst the surveyed provinces was recorded in Kerman (66.8%), followed by Yazd (39%), Sistan and Balouchestan (20.8 %), and Hormozgan (4.5%). AMV, BLRV, PSV and BYMV were present in 23.3%, 12%, 0.70% and 0.28% of the samples, respectively. CMV and BCMV were not detected in any surveyed region. Multiple virus infections were recorded in 42 samples. This is the first report on the detected occurrence of BLRV, PSV and BYMV in alfalfa in the southeast and central regions of Iran.

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In this paper a new model is developed to describe the response of Magneto-rheological fluids (MRF) in transient state. The models which are developed so far, cover the steady-state flow, or address the transient state, with step-wise input electrical current and constant shear rate. In this paper, a new model for transient state of MRF is developed in which the input electrical current is an exponential function in different values of shear rate. Due to the magnetic inertia caused by the inductance of the coil, the real magnetic flux density could not be step-wise. Hence, compare with the other models, this model is in well agreement with reality. To verify the presented model and study the fluid properties as input parameters, an experimental coupling is designed and fabricated. The coupling applies magnetic field perpendicular to shear direction, and measures the shear stress as a function of time. The results of the proposed model show acceptable agreement with experimental observations. According to experimental and theoretical results, the presented model is applied to a controllable torque coupling and acceptable results were obtained.

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The purpose of this paper is obtaining an optimal arrangement of permanent magnets in a non-contact eddy current damper in order to achieve the maximum damping coefficient (c) among dampers with the same dimension. Magnetic theory and eddy current equations have been employed and solved by finite element numerical method. The dominant damping parameters and the optimum ratio of the ferrite core and the permanent magnet for the specific dimension have been achieved. A damper with the dimensions obtained from design is manufactured in order to verify the result of simulations. A setup also is designed and manufactured to verify the damping coefficient. The damping coefficient of simulation and experimental setup is 69.50 and 68.37 respectively which shows a close correlation between simulation and experiment results. The damping coefficient of the designed damper has been increased by 22.5% compared with a same dimension damper. Furthermore, frequency response is obtained by MATLAB software and a decrease of vibration amplitude in eddy current damper has been investigated. The result showed 20 dB reduction in the peak amplitude of frequency response in the designed damper.

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Since private sector investment is dependent on people deposits with banks, the amount of deposits affects national investment and product. The various factors influence private deposits with banks. This paper investigates the relationship between rent-seeking opportunities and bank deposits using the Auto Regressive Distributed Lag Model (ARDL) in Iranian economy during 1971-2010. The results show that the exchange rate premium and interest rate premium affect quantity of deposits with banks in the short-run with coefficients of orders -0.1486 and -0.3468, respectively.  Moreover, the long-run equilibrium relationship indicates that the elasticity of deposits relative to rent-seeking opportunities in exchange and money markets are -0.0166 and -0.0389, respectively. These findings show that rent-seeking indicators have significant and negative effects on private deposits with banks. In fact, rent-seekingopportunities stimulate individuals to shift away their deposits from formal money market towards informal markets in order to make more profits.  

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One of the main difficulties in employing fully coupled algorithms for solving Navier-Stokes equations is the high computation cost of coefficient matrix determination and solving the linear equation system. Therefore, the number of required iterations and computational costs may be reduced by increasing the convergence rate. This article deals with the formulation and testing of an improved fully coupled algorithm based on physical influence scheme (PIS) for the solution of incompressible fluid flow on cell-centred grid. The discretisation of improved algorithm is investigated and fully clarified, by comparing the methodology with two similar schemes. For a better insight, two benchmark problems are solved. The first problem is a steady lid-driven cavity with different Reynolds numbers between 100 and 10000. The second problem is steady flow over a backward facing step for the specified Reynolds number of 800. The history of residuals for present and previous methods are compared, in order to demonstrate the performance of the new discretization scheme. It is worth mentioning, the presented method is based on nine cells discretization. Therefore, the computational costs and memory usage of the proposed method are almost the same as previous ones. The results indicate that, the improved method converges in fewer iterations in comparison with prior methods. The new scheme can be utilized for development of the computational fluid dynamics solvers based on cell-centred grid arrangement.

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Dry-joint masonry structures are one of the oldest building techniques from ancient and historical masonry buildings. This method used in building of historical structures that are highly vulnerable today. Also in many masonry structures, mortar strength is affected strongly by duration of time and corrosion, so the structure behavior is more likely dependent on the dry-joint characteristics. To assess the existing damages of masonry walls, non-destructive dynamic-based methods are attractive tools as they are able to capture the global structural behavior. In micro-modeling method of this paper, masonry walls are represented by Distinct Element Method (DEM) as assemblies of units consist of block and mortar, which represent an idealization of their discontinuous nature governing their nonlinear mechanical behavior. Due to the heterogeneity and the complexity of the interface’s behavior between blocks and mortar, DEM seems to be the best-adapted to model this kind of structures, in particular for reproducing complex nonlinear post-elastic behavior. At the first step, micro-modeling strategy is used for masonry walls by DEM, and particularly post-elastic behavior is verified with valid experimental data. However, DEM does not directly obtain natural frequencies and mode shapes of the wall via a classic vibrational analysis. Therefore, the second objective of this study is to propose a technique to indirectly identify dynamic characteristics of masonry walls using DEM. The aim of the part is to check the capability of dynamic identification procedures, in the extraction of the dynamic characteristics of the masonry wall in the used DEM software. For this purpose, the dynamic behavior at low vibration levels of an existing masonry building subjected to forced hammer impact test, was investigated. By transforming data collected from dynamic response of the wall, from the time domain to the frequency domain, using Fast Fourier Transform (FFT), we can find natural frequencies from Fourier amplitude spectrum. The proposed technique is then validated by comparison with the results of modal analysis which was carried out using Finite Element Method (FEM). The dynamic characteristics of walls (i.e., natural frequencies and mode shapes) may change when different levels of damage are induced in the wall. The proper knowledge of these variations is a key issue in order to study the seismic demand and seismic performance of structures. Aiming at finding adequate correspondence between dynamic behavior and internal crack growth, several numerical simulations are performed, progressive damage is induced in the wall, and sequential structural frequency identification analysis is then performed at each damage stage. In this paper, frequency and drift are selected as dynamic behavior and crack growth indices, respectively. Quantifying the relative frequency drop shows, despite the shape does not vary significantly with increasing damage, there is a relation between frequency drop and damage variations, based on analyzed data. These properties are firstly modified in the elastic range, and then is developed in the inelastic range with increasing damages. It is also observed that while the failure mode of the wall is diagonal cracking, the in-plain vibration mode shapes are much affected by initiation of crack. On the other hand, modal properties of out-of-plane mode shapes undergoes fewer effects by the diagonal crack.

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In the present work, numerical simulation of steady, compressible and supersonic airflow in a magneto-hydrodynamic (MHD) generator has been studied. This flow considered to be ideal with low magnetic Reynolds number. A two-dimensional channel with four-pair electrodes and with various geometries and boundary conditions were utilized as a MHD Faraday generator model. The computational model consists of the Navier-Stokes equations coupled with electromagnetic source terms, Maxwell's equations and Ohm's law. Implicit based on density solver is used to solve the Navier-Stokes and the electric potential method is used to solve the Poisson's equation. First, the boundary conditions of constant temperature and constant heat flux were compared. Due to the less Joule heating and generation of higher electrical power, constant heat flux boundary condition was selected to continue working.

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The aim of this study was to investigate the properties of polyethylene antimicrobial film containing niacin and limonene microcapsules in cheese process packaging. In this study microcapsules containing nisin (0.5, 1, 1.5, 2 and 2.5) and limonene (5, 7, 10, 14, 21 and 28 µg / mg) were prepared by gelation method. . After optimization, niacin and limonene microcapsules were used in polyethylene film based film formulation. After packaging cheese cheese in the film containing optimized microcapsules containing concentrations (1, 1.5 and 2 µg / mg nisin and 5, 7 and 10 µg / mg limonene), total microbial populations, mold and Yeast, Staphylococcus coagulase positive, Escherichia coli were examined on the first days of production, 20th, 40th, and 60th storage.
The results were analyzed by two-way ANOVA and Duncan tests at the significant level of 0.05. During 60 days of storage, total microbial indices, mildew and yeast, Staphylococcus coagulas positive and Escherichia coli significantly decreased (p≤0.05).
 The results showed that treatment with Nisin containing 2 IU / mg concentration and limonene with concentration of 10 µg / mg resulted in higher quality of processed cheese during storage period and were selected as optimal treatment.
 

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Ice slurry is called a mixture of fine ice particles with a fluid carrier such as water. The phase change ability of this mixture attracts the strong attention in the areas of thermal storage and refrigerant cooling of the secondary cycle. In this research, flow of ice slurry in horizontal tubes during the phase change is numerically investigated using FLUENT software. The two-phase nature of ice slurry mixture is studied using the Euler-Euler two-phase model based on kinetic theory of granular flows. The effect of ice particles phase change on heat and mass transfer between phases are investigated, the obtained results show that the local heat transfer coefficient for the use of the icy slurry mixture is increased 12% compare to the pure water. It is also determined by examining heat and mass transfer rate along tube, that the heat transfer coefficient for the pipe lengths larger than 10-15 times pipe diameter, remains constant. The variation of mean mass transfer is maximum at distance of 10-15 times of pipe diameter. The maximum value is 2-5 times larger than mean mass transfer in the pipe outlet. At the 20% end of the pipe, the decreasing trend of mass transfer accelerates.

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In this research, the Asphaltene particles deposition is modeled using species transport equations. It is assumed that the deposition phenomenon consists of two steps: transport of Asphaltene particles toward the wall and attachment of them to the wall. Due to the small size of Asphaltene particles, their motion is simulated using species transport equation. Transport of Asphaltene particles is modeled by turbulent and Brownian diffusion and attachment mechanism is modeled employing first order chemical reaction. Effects of surface temperature and velocity is considered in the model. Finally the effects of velocity, surface temperature and Asphaltene concentration is investigated and compared with experimental data. The simulation results are agreed well with experimental data and the maximum error of is about 20 percentage. Also in addition of deposition rate, transport and attachment rate are investigated. The results indicate that Asphaltene attachment is more important than transport of Asphaltene, so accurate modelling of attachment has significant effect on prediction of Asphaltene deposition rate.

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Aluminum alloys have become widespread in the various industries due to the characteristic of high strength-to-density ratio. These alloys do not have a suitable formability at ambient temperature so they formed at high temperatures. The main hot forming methods used for aluminum alloys include deep drawing and gas forming. Both of these methods have their own advantages and disadvantages. In this study, a combined process involving deep drawing and gas forming has been used. In this process, the first step is to create a pre-formed deep drawing and in the second stage, the final piece is produced by gas forming process. The purpose of this study is to optimize the levels of the main process parameters for the shaping of cubic parts of aluminum sheet 5083 sheet. These parameters include the temperature and blank-holder force of deep drawing stage and the temperature and gas pressure at the gas forming stage. The best levels of process parameters were selected using the Taguchi experimental design method. The results show that the temperature at 350 ° C and the blank-holder force of 1000 N for deep drawing, as well as the temperature of 485 ° C and the gas pressure of 0.6 MPa for the gas forming stage, can be achieved with the least degree of thinning in the specimen. The maximum thinning achieved is 22%.

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In recent years, pneumatic method of stigma separation has been considered by some researchers. In this regard, computer simulation of the process is necessary as well as determination of the engineering properties of the various flower parts. According to preliminary observations, the number of flower components, their characteristics, and the simulation of the separation process, all depend on the flower cutting location. In this study, cutting of flower was done in two modes. In the first mode, the flower was cut from the top of the receptacle and divided into three parts including petals (2), stamens (3) and a three-branch stigma. In the second mode, the cutting accomplished from the bottom of the receptacle and the flower divided into two parts including flower without stigma, and a three-branch stigma. Variations in weight, density and terminal velocity of different flower components were studied as a function of moisture content. According to the results of this study and in contrast to most of the published papers, vertical wind tunnels are not suitable for pneumatic separation of saffron stigma. In order to provide required information for computer simulation, the flower components were considered as spherical particles, and then their aerodynamic diameters were calculated using the proposed flowchart. The results showed that the difference in aerodynamic diameter values in the two-section cutting mode reach to significant amount of 70%. Results of present study also indicate that the appropriate stigma separator mechanism should have singular feeding system and ability to provide turbulent air flow. Preliminary results obtained from computer simulations are hopeful in the case of using dual internal tunnels equipped with rotational flow.

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The main disadvantage of natural draft dry cooling towers is the influence of atmospheric conditions as ambient temperature and wind speed on the thermal performance. Wind disrupts the natural flow of air inside the tower creating vortices at the back and inside the tower that disrupts the air flow structure. When the wind blows, increasing the velocity of inlet air through the front louvers causes the air to pass through the behind louvers rather than outlet opening. The negative effect of this phenomenon reduces the cooling performance and consequently reduces the turbine production power in power plants. A good solution to this problem is to adjust the Louvers angle correctly. Therefore, in the present study, the thermal performance of the dry cooling tower was evaluated under the conditions of opening and closing the front louvers and changing their angle. In this regard, a natural draft dry cooling tower unit with the dimensions of the cooling tower located in combined cycle power plant was simulated in 3D using fluent software and the numerical results with the experimental data have been validated. The Realizable k-ε turbulent model is used to model the turbulent flow and the performance of the tower has been studied in three modes, including no wind, with the wind and the fully open louvers and with the wind and the semi-open louvers. According to the results, by partially removing the louvers to 60°, the heat transfer can be increased to 16% and the mass flow rate to 15%.
 

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