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In recent years, synchronous with the development and diversification of bread production, have expanded various processing methods, as well as the co processes (additives). One of the traditional products that have been welcomed by consumers for many years in eastern Asia due to the simplicity of raw materials and ease of using is roti bread. Therefore, in the present study, has been investigated the use of baking methods, such as hot-electric plates and rotary oven and compare them with the traditional method and so on is evaluated using of guar, carboxymethyl cellulose (CMC) and Carrageenan hydrocolloids (each one 0.5%) in roti bread formulation in a completely randomized double factorial arrangement test (P≤0.05). The results of this study clearly showed that application of hot-electric plates for baking along with addition of both CMC and guar gum in the formulation, had effect on the moisture content and crust L* value and in this regard the effect of CMC gum was higher than guar gum. Also, based on the results, it was found that the sample produced by the hot-electric plates containing CMC gum had the least firmness of the texture during 2 and 72 hours after baking, as well as one week after baking (P≤0.05). Finally, tasting the samples, the panelists introduced the samples produced with hot-electric plates containing CMC gum and samples produced with hot-electric plates containing guar gum as the best samples.
 

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Objective: microRNAs (miRNAs) are noncoding RNAs that function as key regulators of diverse biological activities such as cellular metabolism, cell proliferation and cell cycle regulation. Recent studies have indicated the high potential of these small molecules to control stem cell differentiation into desired cells. The aim of present study is to investigate the possible effect of let-7f on expression of hepatic nuclear factor 4 alpha (HNF4a) and some hepatic specific factors such as albumin (ALB), alpha fetoprotein (AFP), cytokeratin18 (CK18) and cytokeratin19 (CK19) in human adipose tissue derived stem cells (hADSCs). Methods: ADSCs were isolated from human adipose tissue using collagenase type I and were transduced by recombinant lentiviruses that contained human inhibitor let-7f and Scramble (negative control). Afterward, the expressions of HNF4a, ALB, AFP, CK18 and CK19 were evaluated by Real-time PCR at different time points. Results: Transduction efficiency of lentiviral vectors into ADSCs was more than 80% as judged by the expression of the GFP reporter gene. Real-time PCR analysis revealed that inhibition of let-7f in hADSCs resulted in significant up regulation of hepatic specific genes compared with the negative control. The expression level of HNF4a also increased in experimental cells at day 14, which supported the suppression of HNF4a expression by let-7f. Conclusion: The results of this study identified let-7f as a negative regulator of HNF4a expression in hADSCs and increased the expression of hepatocyte specific factors through silencing of let-7f. Therefore, suppression of let-7f could be a considerable tool for hepatic differentiation of hADSCs.

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Motion and deformation of the drop falling in an immiscible fluid has become a benchmark problem in fluid mechanics and has a wide range of application in petroleum, medicine processing, metals extraction, power plant and heat exchanger. In this paper, an exact analytical solution of a falling viscous drop at low Reynolds number is investigated. Analytical solution for both internal and external flows is obtained using the perturbation method. The Reynolds numbers and capillary are considered as the perturbation parameters. Drop’s shape remains spherical for sufficient small ones. The falling drop’s shape at Newtonian phase, deforms from its spherical shape as its volume increases. Inertial forces, surface tension, normal components stresses have the most influence on the falling drop’s shape. Drop’s deformation is due to the forces at the interfaces acting between two fluids. By volume increase of the falling drop, normal components stresses overcome to the surface tension and cause a dimple at the bottom drops in addition to the inertial force enhancement. For small non-dimensional parameters (Reynolds number and capillary) drop’s deformation is exactly similar to a sphere and then by increase in Reynolds number and capillary, the drop’s shape alters and cause a dimple at the bottom drops. Analytical solution show suitable agreement in terminal velocity and drop shape estimation with experimental results.

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Space grids are highly modular structures assembled from components that are almost exclusively factory fabricated. The components therefore, are usually produced with high dimensional accuracy, with a high quality of surface finish and they are generally easily transportable, requiring little further work except assembly on site. Because of their modular nature, space grids may be extended without difficulty and even taken down and reassembled elsewhere. One of the most popular types of connectors that are widely used in the construction of double layer grids is the MERO system. The Mero KK space truss system, the first commercially available, is still considered to be one of the most elegant solutions for the construction of space grid structures. The elegance and simplicity of the Mero system means that it is not only used in buildings but also for shop displays and exhibition stands using lightweight materials. Circular tube members are connected to cast ‘ball’ joints at the nodes by a single concealed bolt for each tube. A double layer grid is combination of prefabricated tetrahedral, octahedral or skeleton pyramids or inverted pyramids having triangular, square or hexagonal basis with top and bottom members normally not lying in the same vertical plane. The connector is an extremely important part of a grid design. The type of connector depends primarily on the connecting technique, whether it is bolting, welding, or applying special mechanical connectors. It is also affected by the shape of the members. This system is multidirectional system allowing up to fourteen tubular members together at various angles. The system consists of tubular elements that are connected together by means of a MERO connector. The ball is located at the intersection of the longitudinal axes of tubular elements. The longitudinal axis of tabular element and all the constituent parts of its end connectors are along together. This axis is referred to as axis of member. The MERO system had only one type of standard joint, a sphere with 18 threaded holes and machined bearing surfaces at angles of 45, 60 and 90° to each other. A model of MERO connector is presented in this paper for double layer grid structure. The internal forces in the members of double layer grid are found using SAP software. These forces are applied as pressures on the MERO connector. The deflection and rotation patterns of the connector are studied under different loading conditions using the ABAQUS software. The forces to be applied on the connector are calculated using of displacementg control.
In order to take into account the connector effects in structural analysis, their behavior under combined load should be predicted. In double-layer grids that are an important family of space structures, the main internal forces are axial forces. In the present study, to determine the force-displacement relationship of MERO jointing system, some tensile, compressive and bending simulation tests were carried out on a connector of this type using 3D finite element method. The obtained force-displacement and moment- rotation relationship were used under different load. The results of the finite element simulation with experimental results have a good match. It was also found that in both compressive and tensile loading, the ball came to the plastic stage. Compressive axial force increases the flexural stiffness of the connection and with increasing compressive force decreases the elastic bending moment.

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Machining processes are the most important method to production in the industry. In these processes, the friction in tool-chip surface during the machining is one of the affecting factors on surface quality of work piece. The generated heat by friction, augment the tool wear mechanism and increase the wear rate of cutting edge which leads to reduction the surface quality. The high talent of aluminum to built-up edge formation during machining has the undesirable effect on the surface quality. In the present study in order to improvement the cooling-lubrication conditions in machining of 6061 aluminum alloy, a new cutting tool with creating micro-grooves on its rake face was developed to achieve the improving of cutting fluid transfer to machining zone and reducing the friction between tool-chip surface. Two types of micro-grooves have been created by laser machining process. Specimens by changing the machining parameters and types of the applying of cutting fluid to machining zone were machined. The experimental results obtained from surface roughness survey and prepared images of work piece surface by scanning electron microscope (SEM) and optical microscope showed that by creating the micro-grooves, the delivery conditions of cutting fluid to machining zone has improved and its effect to reduction of surface roughness is clearly visible. By comparison the results of two micro-grooves showed that direction of grooves is the most important parameters in its design, so that the perpendicular texture is not only improves the surface quality but also increase the surface roughness compared to non-texture tool.

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In this paper, steady motion of non-Newtonian falling drop through a Newtonian fluid at low Reynolds number is investigated analytically. Here, the Upper Convected Maxwell model (UCM) is used for drop phase and Newtonian model is considered for external fluid. During the past few decades, studies relating to non-Newtonian instabilities especially those involving free surfaces are amongst the most striking. These types of studies can be used to optimize design processes in, for example, the petroleum and medicine related processes, metal extraction, and paint and power-plant related fields. Analytical solution is obtained using the perturbation method. Reynolds and Deborah numbers are used to linearize the equations governing the problem in analytical method. Deborah number indicates the elastic effect of drop. The drag force increases by the growth of the elastic effect of non-Newtonian Drop’s. The non-Newtonian drop loses its shape and exchanges to an oblate form. Increment in Deborah number enhances the dimple at the bottom of the drop and results in an increment in its drag force and as a consequence its terminal velocity decreases. A hole is created at the rear of the drop due to the presence of inertia force and focus of normal component of stress at the rear of the drop. The novelty of this study is to consider the convection (non-linear) term of the momentum equations which was neglected in the previous studies due to the creeping flow.

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Resistant starch type III as a dietary fiber is included in the prebiotic composition. It can be used to enrich low-calorie, gluten-free diets for celiac patients. The aim of this study was to investigate the possibility of improving the quantitative and qualitative properties of gluten free rice cake via replacement rice flour by resistant starch type III at levels of 0, 5, 10, 15, 20, 25 and 30%. Physicochemical, textural and sensory properties of the product were evaluated in a completely randomized design (P˂0.05). The results showed that replacing the rice flour by resistant starch in the gluten free rice cake formulation reduced the specific gravity of batter and increased the moisture content of the final product. Also, by replacing rice flour by resistant starch up to 20%, the height, specific volume and porosity of the final product increased and then decreased. On the other hand, the sample containing 20% resistant starch had the lowest firmness at 2h, 3 and 7 days after production. In addition, the results showed that 25 and 30% replacements of the resistant starch in gluten-free rice cake formulation by rice flour, the L* value of the crust and crumb increased and the a* and b* were reduced. Finally, the panelists by evaluating the sensory properties such as shape, color, texture firmness and softness, taste and overall acceptance the sample containing 80% rice flour and 20% resistant starch type III introduced as the best sample. Therefore, according to the results of the physicochemical and sensory evaluation, replacement of 20% rice flour by resistant starch type III in gluten free cake formulation can produce a lower calorie product suitable for celiac patient.

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In this study, three levels of flour extraction rate (80, 88 and 96 %) and amylase and xylanase (50ppm) were used in barbari bread. The moisture, specific volume, porosity, firmness (2, 24 and 72 hours after baking), crust color and sensory properties of breads were evaluated. The result showed, the moisture and a^* value were increased and firmness (during 72 hours) and L^* value were decreased by increasing flour extraction rate. The sample containing 80% extraction rate and amylase and xylanase had the highest specific volume and porosity. Amylase and xylanase had the positive effect on texture, specific volume, porosity and sensory properties of bread. The flour extraction rate and enzymes didn’t have significant effect (P<0.05) on b^* value of samples. Finally, the evaluation of sensory properties showed the samples containing 80 and 88 % extraction rate and enzymes had the highest overall acceptability.  
 

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Due to high ability of built-up edge formation during aluminum machining, this study aim to reducing adhesive wear and increasing surface integrity of 5052 aluminum alloy workpiece has been focused on creating different surface texture on tungsten carbide cutting tool. For this purpose, four types of micro-grooves such as parallel and perpendicular to cutting edge and also pit and cross mode have been created on rake face by laser machining process. In addition to the types of texture, three methods of cooling-lubrication condition include: dry machining, flood mode without pressure and flood mode with high-pressure along with various holder and cutting inserts (with chip-breaker and without chip-breaker) as well as three levels of cutting speed (fixed feed rate and depth of cut) were considered as process variables. The experimental results obtained from surface roughness survey of the machined parts along with prepared images of optical microscopy from the workpiece surface showed that the presence of parallel micro-grooves significantly improves the cooling-lubrication conditions of the tool-chip surface and its effect on numerical reduction of surface roughness value and reduction of density of defective regions on the workpiece surface is visible. The prepared images by scanning electron microscope (SEM) of the tool rake face showed that the presence of chip-breaker did not significantly effect on reduction of adhesion wear in the machining of aluminum alloy but micro-texture can be largely improved the adhesion wear area compared to non-textured tool (with chip-breaker or without chip-breaker).

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The production of composite breads, in addition to reducing dependence on wheat, will improve the nutritional value of the final product and diversify the consumer food basket. So, the aim of this study was investigation of the effect of replacing wheat flour by millet flour at levels of 10, 20 and 30% in formulation at the presence of different ratios of guar-xanthan gums (0.3-0.1, 0.6-0.15 and 0.9-0.2%) on dough rheological properties and physicochemical and sensorial characteristics of semi volume Barbari bread in completely randomized factorial design (p˂0.05). The results of farinograph test showed that the amount of water absorption, dough development time, stability time and value of the dough valorimeter decreased by increasing the amount of millet flour in the formulation and increased by increasing amount of gum and xanthan gum. Also, the results indicated the moisture content and specific volume by increasing the amount of millet flour and addition gums, were decreased and increased respectively. Although the amount of water activity and texture firmness (2 h and 3 days after baking) were increased, while by increasing the amount of gums, these qualitative parameters were decreased. The results of evaluation crust color showed the L* and a* values were decreased and the a* value was increased by addition millet flour. On the other hand by adding different levels of gums the L* and a* values were increased and had no significant effect on b* value. In the sensory evaluation, the sample containing 10% millet flour, 0.9% of guar and 0.2% xanthan was introduced as the best sample by panelists.

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Improving the quality of bread and bakery products by modifying the formulation and production process is one of the most important ways to increase the level of public health in society. In this regard, steamed bread is free of harmful compounds such as acrylamides due to different baking processes, including foods. Therefore, the aim of this study was to investigate the effect of adding glycerol at levels of 0, 0.5 and 1% and using one-stage and two-stage fermentation methods on physicochemical and sensory properties of composite steamed bread (wheat-rye) in a completely randomized design with factorial arrangement in order to produce suitable bread taste for the Iranian consumer and improve the shelf life of the final product. Based on the results, it was found that by increasing the glycerol and using the two-stage fermentation method, the moisture content of the final product and firmness (during 2 and 72 hours after baking) increased and decreased respectively. In addition, the use of two-stage fermentation method improved the porosity and specific volume of the final product. However, glycerol had no effect on these parameters of bread. On the other hand, the amount of L* value increased with increasing glycerol and using two-stage fermentation method, while the amount of a* and b* values remained constant. In the sensory evaluation section, the taste judges gave the highest score to the sample containing 11% glycerol and prepared by two-stage fermentation process. Therefore, by localizing the technical knowledge of producing steamed bread, bread with better nutritional value can be contracted in peoplechr('39')s food basket.

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Improving the distribution of income is one of the main goals of governments in economic policy, regardless of the orientation of different systems. The purpose of this study is to investigate the distributive effects of monetary policy on income distribution in urban and rural areas of Iran. In this regard, the values of macroeconomic variables during the period of 1959-2014 and the household budget data over the period of 1997-2014 were used. The monetary policy was considered in three scenarios, including the increase in facilities granted to the private sector, the decrease in the reserve requirement ratio and decrease in the excess reserves ratio. The results showed that expansionary monetary policy improves the distribution of income in the short run, but in the long run it worsens the distribution of income due to its inflationary effect. An increase in facilities granted in the short term reduces the Gini coefficient in urban and rural areas, and whole country. However, it increases the Gini coefficients in all three sections in the long run. Reducing the reserve requirement ratio in the short run reduces Gini coefficients, but it does not change the whole Gini coefficient in the long run, but it increases the Gini coefficients in urban and rural areas. The effect of reducing excess reserves ratio is similar to that of reducing reserve requirement ratio.

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The aim of this study was to enrich and improve nutritional and technological properties of sponge cake. Wheat flour was replaced with okra flour at levels of 0, 15 and 30%, and okra gum was used at levels of 0, 2.5 and 5% to improve texture and sensory sensory properties of the final product. The results showed that replacing wheat flour with okra flour and increasing its consumption level led to an increase in ash (from 0.54 to 1.35%), protein (from 7.56 to 93.9%) and antioxidant activity (from 79 4.5 to 49.2%) of samples. Okra flour and gum, especially at 30 and 5% level, were effective in moisture of the cakes during the baking and shelf life. The lowest moisture loss was observed in the sample containing 5% okra gum (without okra flour) and moisture of this sample decreased from 21.7% to 18.5% during two weeks. The highest specific volume (5.2 cm3 / g), porosity (31.8) and texture softness during 2 hours and one and two weeks after baking ( 1.4, 4.9 and 7.1 N) were showed in samle containing 15 % okara flour and 2.5 % okara gum. Also, in the sensory evaluation, the highest score of sensory properties and finally overall acceptance were showed in to the sample containing 15% okra flour and 2.5% okra gum and 30% okra flour without the presence of okra gum.
 

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Resistant starches are classified in the category of indigestible starches and are introduced as a prebiotic product, which has lower calories and is cheaper compared to other dietary fibers. Therefore, the purpose of this research is to use type III resistant starch produced by thermal method at levels of 0, 5, 10, 15, 20, 25 and 30% in a completely random design as a substitute for wheat flour in biscuit, doughnut and cookie formulation. The results showed that by replacing wheat flour with resistant starch in the formulation more than 20%, the moisture content and water activity of the final product increased and decreased respectively. The specific volume and porosity of the doughnut were stable up to the level of 15% of resistant starch and then decreased. Also, the sample containing 15% resistant starch had the lowest amount of firmness in all the products. On the other hand, with the replacement of resistant starch in the formulation of the examined products on levels of 15% and above, the amount of L* value increased and the a* and b* values were decreased. The panelists also introduced the sample containing 15% resistant starch as the best sample. Therefore, it can be said that by replacing 15% of wheat flour with resistant starch, in addition to maintaining the physicochemical, textural and sensory characteristics of the final product, it is possible to enrich these snacks and the consumer can benefit from the benefits of using prebiotic products.
 

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In the present research work, the potential probiotic properties of Lactococcus lactis KMCM3 and Lactobacillus helveticus KMCH1 isolated from raw camel milk and traditional fermented camel milk (Chal), respectively, were studied. The probiotic properties of isolates that were investigated included the hemolysis, antibiotic resistance, antibacterial features, resistance to low pH and bile salts, survival under simulated GastroIntestinal Tract (GIT) conditions, adhesion ability to hydrocarbon, and their auto-aggregation and co-aggregation rates. None of isolates exhibited hemolytic activity. They were susceptible against tetracycline, penicillin, ampicillin, chloramphenicol, erythromycin and vancomycin. Lac. lactis KMCM3 and L. helveticus KMCH1 retained their viability at pH 3.0 (8.68 and 8.6 log cfu mL^-1, respectively), 0.3% w/v bile salts (8.23 and 8.58 log cfu mL^-1, respectively) and under simulated GIT conditions (8.31 and 8.46 log cfu mL^-1, respectively). Both of these isolates inhibited the growth of E. coli, S. aureus, L. monocytogenes, B. cereus and S. enterica subsp. enterica serovar Typhimurium with MIC values of 6.25 to 25 mg mL^-1. In addition, They exhibited an ability to adhere to hydrocarbon (xylene), and possessed a high auto-aggregation and co-aggregation rate (more than 40%).
 

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A significant number of engineering structures around the world are exposed to fire on a daily basis. The most important effect of fire on the structure is elevated temperatures, which may reach more than 1000 degrees Celsius and cause not only thermal stresses and deformations but also diminished mechanical properties of materials comprising the structure. Fire-related collapses have been observed in numerous structural fires. However, many reinforced concrete structures exposed to fire do not demonstrate notable apparent damage and survive despite having experienced elevated temperatures before the fire is put out. Estimating the residual strength of such structures is of critical importance when deciding whether such structures can be safely used after fire. Moreover, in many industrial applications, there is a need to concrete that can withstand repeated long-term cycles of elevated temperatures without diminished mechanical properties. The objective of this paper is to investigate the effects of silica fume and fly ash as two widely used supplementary cementitious materials on the residual strength of concrete exposed to elevated temperatures and evaluate while such materials can be of benefit in improving the strength retention in case of heat exposure. Using 19 mix designs, a series of 570 concrete cylinders was fabricated using different water to cement ratios (0.35, 0.5, and 0.65), silica fume replacement ratios (0, 10, and 15 percent), and fly ash replacement ratios (0, 10, 20, and 30 percent). The specimens were cured in water for 56 days, after which they were placed in a rate-controlled large-scale electrical furnace, and their residual compressive and tensile strengths were measured before heat, and after heat exposure for 2-, 12-, and 24-hour heating cycles with temperatures reaching 200, 400, and 600 degrees Celsius. To eliminate the risk of explosive spalling, all specimens were preheated at a temperature of 100 degrees for 24 hours before the main heating cycle. Results showed that the compressive and tensile strengths did not reduce noticeably after exposure to 200 degrees but demonstrated a significant drop after exposure to 400- and 600-degree cycles. In many cases, the residual compressive and tensile strengths of specimens were found to be smaller than those predicted in previous studies. The square root equation widely used in the literature was found to provide a reasonable lower-bound estimate of the residual splitting tensile strength of concrete from the residual compressive strength; however, a linear trend was identified to provide a more accurate estimate for the results of this study. Moreover, due to less scatter, the splitting tensile strength was found to be a better indicator of heat damage in the structure than the compressive strength. The use of silica fume did not result in a meaningful trend in the residual compressive strength but reduced the residual tensile strength of specimens. Fly ash, on the other hand, could increase the residual compressive strength of the specimens but reduces the residual tensile strength. The results suggest that generally, and with few exceptions, these two supplementary cementitious materials are not recommendable choices for improving the strength retention of concrete in case of heat exposure.

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Introduction:
All economists believe that the most important goals of economic policy are achieving full employment, price stabilization and economic growth in the society. On the other hand, rendering the formation of the exchange rate to the market mechanism and increasing it disproportionately with the purchasing power of the rial has a negative effect on production and employment and causes an increase in prices and a decrease in the value of the national currency, which again provides the ground for the next increase in the exchange rate. For this purpose, in most societies, especially in developing countries, currency policies are used to achieve the mentioned goals. Changes in exchange rates affect economic performance in different ways. In this study, we will examine the effect of exchange rate changes on the performance of important macroeconomic variables, namely production, employment and the general level of prices. Taking into account the effects of sanctions against the country, the model considers the mechanism and channel of its effect on the foreign sector of the economy, while creating an index with monthly frequency for it, and its effect has been calculated directly on all macroeconomic variables of the foreign sector of the model.

Methodology:
During the last two decades, tremendous developments have taken place in the field of modeling time series variables and predicting the future values of economic variables, one of which is to specify and estimate equations where the variables involved in that equation, unlike usual, have different frequencies. Mixed-data sampling (MIDAS) has been specified and estimated with the help of time series data over the period 1959-2017. Mixed data sampling regressions are now commonly used to deal with time series data sampled at different frequencies.
A MIDAS regression is a direct forecasting tool which can relate future low-frequency data with current and lagged high-frequency indicators, and yield different forecasting models for each forecast horizon. It can flexibly deal with data sampled at different frequencies and provide a direct forecast of the low-frequency variable. It incorporates each individual high-frequency data in the regression, which solves the problems of losing potentially useful information and including mis-specification.

Results and Discussion:
The presented macro econometric model is developed in the framework of the aggregate supply-aggregate demand model. Total demand is made up of household consumption expenditures, investment expenditures separately from private and government, government current expenditures and net exports. The production function forms the supply side of the economy according to the utilization rate of the production capacity. The modeling of the two parts of supply and demand has been done in a completely consistent manner, so that after the estimation of the model, it is possible to solve and simulate the model to examine the effect of economic policies and predict macro variables. According to the results of the model, in relation to the policy of devaluation of the national currency in the Iranian economy, the increase in the exchange rate in the face of sanctions, in addition to reducing production, paves the way for employment and inflationary pressures. Indeed, The incorrect approach of increasing the exchange rate has not only limited economic growth due to the increase in production costs, but has also caused the impoverishment of the oppressed and the unfair distribution of income in the society.

Conclusion:
Because the model under study has better explanatory power than other time series models due to more complete information, it is expected that it will be possible to evaluate exchange rate policies more accurately. The model has sections on production, consumption and investment expenditures, foreign trade, government, employment, money and prices. In addition, according to the very good results obtained from the dynamic simulation of the model, the model can be a good representative of the mechanism of the Iranian economy. Finally, the results of the evaluation of foreign exchange policies in the context of sanctions can be reviewed.

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Arch bridges have been commonly used in high-seismicity regions of the world, as a result of which notable damage has been documented in several arch bridges during past earthquakes. Certain aspects of seismic behavior of arch bridges are different from those in typical slab-on-girder bridges, including the significance of axial loads, sizable differences between in-plane and out-of-plane stiffness, and the use of piers with different heights. However, limited previous studies have addressed the seismic behavior of concrete arch bridges. In the present study, the effects of earthquake incidence angle and asynchronous support excitation on reinforced concrete arch bridges are investigated. Nonlinear 3-D models of four existing reinforced concrete deck-type arch bridges in Iran were developed. The bridges had arch spans of 23, 35, 45 and 50 meters and were subjected to nonlinear time history analyses using seven acceleration records. The incidence angle was changed in 15 degrees increment between 0 and 90 degrees. Moreover, the effect of asynchronous support excitation was investigated by means of introducing a time delay between excitation input for different supports. The relative displacement (drift) of the piers, the curvature ductility demands within the piers, the curvature ductility demand at different locations of the arch, and the displacement of the deck at the abutments (unseating) were used as damage indicators. The results showed that unseating of the bridge deck from abutments and pier drifts were the most and the least sensitive damage parameter to the change in incidence angle, respectively. The axial force at the end points of the arch was found to change significantly during earthquake, with a maximum of 40 percent in case of 90-degree incidence angle. The effect of asynchronous support excitations was relatively small, with a maximum increase of 10 percent in damage indicators and 5 percent in the axial forces and bending moments.   
 

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High stiffness to weight ratio, ease and speed of handling, as well as having favorable architectural appearance cause that, double layer grids with ball joint system are widely used to cover large spans. A double-layer grid has a complex behavior due to a large number of elements and a particular type of joints; hence, structural identification of this type of structure is an important issue, which refers to the determination of natural frequencies, mode shapes, and damping ratios. These results are necessary to complete the structural health monitoring, finite element model updating and damage detection. Due to the limitations of input-output methods, modal parameters of civil engineering structures such as bridges, dams, tall buildings, and double layer grids are determined mainly by output-only modal identification. In output-only methods, the vibration parameters are determined based on the information acquired only from the structure’s output. In this work, physical model of a ball jointed double-layer grid with dimensions of 2.8 m at 2.8 m, which is supported on four steel pipes in four corners was made in the laboratory. The grid consists of 32 members connected together with 13 balls, each having ten threaded holes at different angles. each member consists of a middle pipe and connecting parts including conical piece, sleeve and high strength bolt at both ends of the pipe. The middle pipe has the nominal length, diameter and thickness of 120 cm, 7.64 cm and 0.35 cm, respectively. The horizontal center to center distance of adjacent balls in each layer of the grid is 1.414 m and the total height of the structure includes the column length (1.3 m) and the distance between the top and bottom layers (1 m), which is equal to 2.3 m in total. The approximate weight of the structure is 3532 N. All the members and the balls used in the grid are identical. After all the members of the grid have been assembled, the bolt at each joint is tightened in a series of steps by twisting the corresponding sleeve. Exciting the grid, its acceleration response was measured. The modal parameters were obtained using four output-only modal identification techniques; namely enhanced frequency decomposition (EFDD), curve-fit frequency domain decomposition (CFDD), data-driven stochastic subspace identification (SSI-DD) and covariance-driven stochastic subspace identification (SSI-Cov). Two types of excitations were used in output-only modal tests, namely direct and indirect excitations. Since the modal parameters obtained via input-output modal analysis have less uncertainty compared to the output-only modal analysis techniques, an input-output modal test was also performed and the results are considered as reference values. It deduced that parameters identified in the direct excitation, were more accurate compared to indirect excitation. The results showed that the natural frequencies and mode shapes of the double-layer grid were estimated with a high accuracy via the four methods. The greatest relative difference between the natural frequencies belonged to the second mode and equaled 2.07%. The dispersion of estimated damping was much higher compared to natural frequencies and mode shapes. The results indicated that identified damping in the direct excitation was lower than indirect one. Among the 4 methods, SSI-Cov had the least error in damping estimation of the double-layer grid. The values of estimated modal damping ratios were relatively low (fraction of 1%). The mean relative error of the identified parameters showed that the time-domain methods estimated the damping ratios with less error; While the frequency-domain methods identified natural frequencies and mode shapes with higher accuracy.