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Showing 10 results for Growth Model
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Volume 4, Issue 2 (9-2015)
Volume 4, Issue 2 (9-2015)
Abstract
Key words: growth model, routine metabolism, rainbow trout , digestibility
A Numerical Investigation on the Appropriate Corner Radii of Beam Web Opening in Steel Moment Frames
Volume 15, Issue 3 (9-2015)
Abstract
Web openings may be provided in structural floor beams for different purposes. The corner radii of web openings can have a significant effect on stress and strain concentrations around the opening. AISC's design guide for steel and composite beams with web openings states that web openings are not recommended for members subjected to significant high cycle-low stress or low cycle-high stress fatigue loading even if a rational corner radii is provided for web openings. This is because, at the time the specification was written, there were only limited references available to the committee which indicates the need for further studies in this field. In this paper, effect of opening corner radii on cyclic behavior of steel moment connections with Reduced Web Beam Section (RWBS) is investigated using finite element analysis. For this purpose, a T-shaped moment connection (without web opening) which has been tested under cyclic loading by another author is used as the reference model. To see effect of opening corner radii, the reference model is considered with square and rectangular web openings of different corner radii. Fracture initiation in models is simulated using Cyclic Void Growth Model (CVGM) which is based on micro-void growth and coalescence. According to this model, fracture under cyclic loading is predicted to occur when the void size exceeds the critical value. Based on the results, for both square and rectangular openings the maximum equivalent plastic strain and fracture index at the opening corners will decrease as the opening corner radii increase. For openings with small corner radii the fracture index at corners will be very high. This is in accordance with recommendation of ASCE 23-97 which indicates that these configurations should not be used in real practice. However, it should be noticed that in the case of rectangular opening the damage index at the corners may be greater than unity even if ASCE 23-97 limitations are met. This means that if it is intended to achieve high rotation capacity at RWBS connections, ASCE 23-97 requirement about minimum corner radii may be non-conservative. As another result, as the opening corner radii increase local buckling around the web opening occurs at higher rotations. In addition to the local effects, the choice of opening corner radii can also affect the global behavior of RWBS connections. In the case of rectangular perforation, as the opening corner radii increase the load carrying and rotation capacity of connection increase too. This is because in these models, the weakening area prevents welds from failure and fracture occurs in the opening corners. As a result, as the opening corner radii increase the fracture index at opening corners decreases and hence the connection can undergo higher rotation capacities. This is not true for square perforation where fracture occurs at connection welds and the connection rotation capacity makes no change as the opening corner radii increase. As a general recommendation it can be said that web openings with the largest corner radii (elongated circular holes) is the best case for perforated steel connections.
Volume 16, Issue 1 (1-2014)
Abstract
The objectives of this study were to identify a suitable mathematical model for describing the growth curve of Baluchi sheep based on monthly records of live weight from birth to yearling; and to evaluate the efficacies of nonlinear mixed effect model (NLMM) and the nonlinear fixed effect model (NLM) methodologies. Growth models were fitted to a total of 16,650 weight–age data belonging to 2071 lambs. Five nonlinear growth functions of von Bertalanffy, Gompertz, Brody, Logistic, and Richards and two linear polynomial functions were applied. The growth models were compared by using the Akaike’s information criterion (AIC) and residual mean square (MSE). Among all nonlinear fixed effect models, the Brody function had the smallest AIC and MSE values, indicating the best fit for both sexes. The Brody fixed effect model compared with NLMM including one random effect of asymptotic mature weight. The model evaluation criteria indicated that the Brody mixed effect model fitted the data better than the corresponding fixed effect model. It can be concluded that, among the linear models, the polynomial of the third order and, among nonlinear models, Brody mixed model were found to best fit the Baluchi sheep growth data.
Volume 17, Issue 1 (4-2017)
Abstract
Using Ramsey – Cass – Koopmans optimal growth model and specifying government’ tax behavior, this study analyzes the effect of tax policies on steady-state and optimal dynamic path of consumption, capital stock and output for Iran and a group of East Asian countries. In this regard, after specifying consumption and capital stock dynamic behaviors, a model is calibrated and simulated for the selected economies by using annul data during 1980 -2010. Based on the simulation results for Iran, and compared to East Asian region, reductions in tax rates have no significant effects on steady- state and optimal dynamic path of capital stock, consumption and per capita output. Hence, tax policies are not effective in stimulating the real sector of the Iranian economy. The results also show that reductions in rates of income tax, capital gain tax and profit tax have positive and significant effects on the long-run steady-state path of consumption, capital stock and output, especially in less developed East Asian countries. The simulation results show that reduction in consumption tax rate, in particular across the highly developed East Asian countries, has positive and significant effect on steady-state of consumption; however, it has no effect on capital stock and output.
Volume 18, Issue 2 (7-2018)
Abstract
The exchange rate overshooting, which results from the monetary disruptions, has negative impact on production and investment in the main economic activities and de-stabilizes the whole economy because of their input-output linkages. Therefore, identifying the causes of economic instability can help to adopt appropriate policies and to create economic stability in the country. The main question is to what extent the exchange rate can cause instability in the economy. To answer this question, first, the exchange rate overshooting was calculated using the Hodrick- Prescott filtering method during 1989-2012. Then, it was introduced into the model by specifying the generalized Solow production function, and finally, the production function was estimated for the main activities of the economy using the panel data technique. The results show that the impact of the exchange rate overshooting on the major economic activities is negative.
Volume 19, Issue 78 (12-2022)
Abstract
Teaching literature to international students can be challenging. The teaching of literature has remained traditional. Studies reveal that most of the language lecturers and teachers teach literature based on their personal experience. This study attempts to provide answer to this question “what is the most efficient model for the instruction of Persian literature to non-Iranian Persian language learners?” In this investigation, after reviewing the relevant literature, the researcher developed and piloted a questionnaire. The questionnaire was randomly distributed among 52 Persian language teachers and experts to probe their perceptions concerning the most productive model for teaching Persian literature. The data analysis showed that the participants considered the integrated approach, personal growth, cultural, and linguistic models as the first, second, third, and forth models, respectively, appropriate in the teaching of both Persian poetry and prose despite with statistically significant difference. The results further indicated that the teachers did not show significant difference concerning the application of models in teaching Persian poetry and prose. The findings of this investigation might be used to upgrade the quality of teaching Persian literature to non-Iranian Persian language learners. The results could be promising in the design and development of useful educational materials in the teaching of Persian literature.
Volume 20, Issue 5 (11-2020)
Abstract
Following Northridge earthquake, wide spread brittle cracking had been observed in steel moment connection, and this, was in contrast with the philosophy of designing steel moment frames which accounts for dissipating energy by forming plastic hinges at beams. This situation led to the development of improved connections to make them less prone to brittle fracture. However, studies have shown that these new connections, typically known as post-Northridge connections, can still have the tendency to fracture but in a ductile manner when subjected to ultra low cycle fatigue loading. Ultra low cycle fatigue loading consists of limited cycles of loading with large amplitude which induce strains that are several times greater than yielding. Searching the literature, varied methods have been proposed to predict cracking in ductile steel for both monotonic and cyclic loading.
In this research, a micro mechanical model called cyclic void growth model has been applied to predict the instance and location of cracking in the steel structure. For the purpose of predicting the low cycle fatigue failure, finger shaped steel moment type connections with top and bottom cover plates which their experimental data were available, used as a benchmark study. A micro mechanical model is integrated into the ABAQUS finite element program in order to simulate crack initiations in the cover plate welded beam to column connection. For this purpose, a Fortran code is linked with the ABAQUS software for simulating the crack and specifically to predict when and where the crack initiates. By understanding the crack initiation and the location of this crack, a trend line for low cycle fatigue under various constant drift angels are put together. The trend line provides a number of cycles for the crack to initiate by applying the specific drift angle. Therefore, a finite element model of a cover plate welded moment connection was developed and was used in order to simulate cracking in the connection model. Thus, each crack location and the number of cycles to initiate the crack were detected. Utilizing cyclic void micro mechanical model of growth analysis, which is a technique to predict fracture in a ductile material, different cover plate connections were modeled in the steel moment frame, and then their critical points to trigger the crack were identified. Finally, for the finger shaped cover plate moment connection, considering different loading curves data and in order to present the low cycle fatigue life prediction, displacement versus the number of half cycles diagram is produced.
Finite element results demonstrated acceptable agreement with the experimental data. Furthermore, the low cycle fatigue life of connections under loading with constant amplitude is estimated, and S-N curves are proposed. These curves can be applicable for engineering purposes, such as performance based design. Also it is demonstrated that the finger plate joint revealed a good performance against soft cracking in low cycle fatigue compared to a number of previously tested joints. The results of the S-N curve for a constant displacement loading averaged 73% of the lifetime of the initial cracking. Sensitivity analysis with 20% tolerance on the intrinsic parameters of the micro mechanical model showed a maximum change of 15% in the responses.
Volume 22, Issue 6 (11-2020)
Abstract
Four nonlinear models including Logistic, Gompertz-Laird, Richards, and von Bertalanffy were compared to achieve the best prediction of growth parameters describing the growth curve in a crossbred chicken population. Growth data (weekly body weights of chicken from birth to 84 days of age) were collected on 303 birds (174 females and 129 males) of F2 cross of the Arian line broiler chicken (Line B) and Urmia native chicken. Some statistical criteria such as Akaike Information Criterion (AIC), Corrected Akaike Information Criterion for small sample sizes (AICc), and Bayesian Information Criterion (BIC) were used to find the best model. The results showed that the estimated values of the initial weight (W0) and final Weight (Wf) in male were significantly (P< 0.01) higher than the female birds in all models. The average estimated initial weight calculated by Gompertz-Laird (0.038 kg) was closer to the average observed initial weight (0.044 kg). Regardless of sex of the birds, the calculated age (ti) and Weight (Wi) at the inflection point were relatively the same in Gompertz-Laird, Richards and von Bertalanffy models, indicating that the growth patterns described by these models are similar. Meanwhile, the different ti and Wi values between the sexes in the four models revealed the different growth pattern in males and females. The goodness of fit indices (R2 and adjusted R2) were higher than 0.97 in all models, indicating that these models could appropriately be fitted on the growth data. However, based on the AIC, AICc, and BIC criteria, Gompertz-Laird model showed better performance, therefore, it was chosen as the best model to analyze the growth pattern in crossbred of .
Volume 23, Issue 1 (5-2019)
Abstract
Urban physical growth is affected by different parameters including environmental, neighborhood and socio-economic factors; however, socio-economic variables are often ignored due to the lack of socio-economic information, especially in developing countries, when the urban physical growth analysis and modeling is the aim. Accordingly, there is not many studies conducted to develop GIS-based socio-economic layers to be used along with common data, such as slope, distance to the roads and so on, in urban physical growth modeling. Therefore, this study aims to introduce an efficient method to generate GIS-based socio-economic layers to be exploited along with the information layers extracted from Landsat images and field-collected data for physical growth modeling of Karaj city. After generating the required information layers, random forest feature selection method was applied to select the most important variables. Then, the performance of the three modeling methods including multiple logistic regression, and two artificial neural networks, multi-layer perceptron (MLP) and self-organizing map (SOM) were compared using the selected attributes to model the urban physical growth from 2000 to 2010. The results indicated that SOM with overall accuracy of 84.5%, kappa coefficient of 68.9%, ROC of 90.7%, FOM of 43.98% and PCM of 84.5% performed better than the other methods for modelling of urban physical growth. Moreover, the proposed socio-economic attributes combined with the remote sensing-based data were able to improve the performance of the urban physical growth prediction. Finally, cellular automata was applied to predict the Karaj physical growth in 2017 and 2027.
Volume 24, Issue 4 (12-2024)
Abstract
Aim and Introduction
The world has suffered severe environmental degradation in the last two decades. The effects of ecological deviations and environmental destruction are alarming and cause concern for stakeholders and environmentalists. These problems have led to environmental disasters such as extreme weather changes and rising sea levels. For this reason, countries are trying to address environmental crises and economic growth at the same time. Basically, it is believed that the destruction of ecosystems in many countries is the result of human actions, including rapid industrialization, population growth, expansion of economic activities, urbanization, and widespread consumption of fossil fuels. Undoubtedly, one of the main factors of climate change and environmental degradation is the emission of carbon dioxide (CO2) caused by economic activities. The relationship between carbon dioxide emissions and economic growth has attracted the attention of researchers and policymakers to reduce carbon dioxide emissions without affecting economic growth. Achieving this goal may be difficult, but studies have included various factors in the growth-carbon dioxide relationship, such as different energy sources, technological innovations, population, financial development, urbanization, and trade openness. In addition to the factors mentioned above, there is a need to assess other relevant factors such as human capital for effective policy development. Despite the extensive role of human capital in promoting energy efficiency and economic growth, by skilled workers in the production process and the preference of educated households to use home appliances with high energy efficiency, few researchers have included this factor in the existing literature. Education is considered as one of the most important human capital investments and plays a vital role in the process of economic growth. Education, at the micro level, affects the future income flow of people, and at the macro level, it is thought that a workforce with better education increases the stock of human capital in the economy. Increased human capital in turn can have positive externalities, such as lower crime or improved health outcomes, which are socially desirable and likely to have positive effects on productivity. In fact, it is the existence of such positive externalities that provides economic justification for governments to support education. It is believed that public spending on education and health will lead to improvement of human capital, reduction of poverty, economic growth and development, and reduction of pollution.
Theoretical studies emphasize different mechanisms through which education affects economic growth. (1) Education increases the human capital of the labor force, thereby increasing labor productivity and shifting growth toward a higher equilibrium level of output. (2) In endogenous growth theories, education increases the economy's capacity to innovate new technologies, products, and processes, thereby promoting growth.
In the environmental field, improving human capital can reduce the use of fossil fuel in the production process. The motive of this research is to understand the effect of public education expenditure shocks on economic growth and environmental quality in Iran.
Methodology
To achieve the goal of the research, a dynamic stochastic general equilibrium (DSGE) model and Bayesian approach have been used. In this regard, observable variables, gross domestic product, private consumption, investment, government expenditure and the gross growth rate of money have been used in the period of 2004 to 2021.
Findings
The results indicate that an increase in public education expenses by one standard deviation increases the marginal efficiency of private education expenses. Because private and public education expenses complement each other and entered the model in the form of a Cobb-Douglas function. Therefore, education hours, investment in education and subsequently, human capital increased. The increase in human capital led to an increase in production, economic growth and a decrease in inflation. The decrease in inflation led to an increase in the real wages of the workforce and finally the desire of the household to increase the supply of labor. Consumption increased in response to an increase in real wages. Also, the behavior of investment is very similar to the behavior of consumption and production, but its changes are more intense than other expenses. Therefore, it can be said that the shock of public education expenses has affected the performance of the economy like an expansionary impulse and has improved the economic conditions. In the environmental sector, with the increase in human capital, economic growth has been improved and this has led to an increase in air pollution and a decrease in environmental quality.
Discussion and Conclusion
In justifying these results, we can point to the weak institutional quality in Iran, that despite the huge amount of human capital investment, there is no necessary effectiveness in the environmental sector, and this is a confirmation that Iran is in the early stages of economic development. As a policy recommendation, in addition to paying attention to education and its role in the development of human capital as a long-term investment, improving the quality of institutions should be considered
The world has suffered severe environmental degradation in the last two decades. The effects of ecological deviations and environmental destruction are alarming and cause concern for stakeholders and environmentalists. These problems have led to environmental disasters such as extreme weather changes and rising sea levels. For this reason, countries are trying to address environmental crises and economic growth at the same time. Basically, it is believed that the destruction of ecosystems in many countries is the result of human actions, including rapid industrialization, population growth, expansion of economic activities, urbanization, and widespread consumption of fossil fuels. Undoubtedly, one of the main factors of climate change and environmental degradation is the emission of carbon dioxide (CO2) caused by economic activities. The relationship between carbon dioxide emissions and economic growth has attracted the attention of researchers and policymakers to reduce carbon dioxide emissions without affecting economic growth. Achieving this goal may be difficult, but studies have included various factors in the growth-carbon dioxide relationship, such as different energy sources, technological innovations, population, financial development, urbanization, and trade openness. In addition to the factors mentioned above, there is a need to assess other relevant factors such as human capital for effective policy development. Despite the extensive role of human capital in promoting energy efficiency and economic growth, by skilled workers in the production process and the preference of educated households to use home appliances with high energy efficiency, few researchers have included this factor in the existing literature. Education is considered as one of the most important human capital investments and plays a vital role in the process of economic growth. Education, at the micro level, affects the future income flow of people, and at the macro level, it is thought that a workforce with better education increases the stock of human capital in the economy. Increased human capital in turn can have positive externalities, such as lower crime or improved health outcomes, which are socially desirable and likely to have positive effects on productivity. In fact, it is the existence of such positive externalities that provides economic justification for governments to support education. It is believed that public spending on education and health will lead to improvement of human capital, reduction of poverty, economic growth and development, and reduction of pollution.
Theoretical studies emphasize different mechanisms through which education affects economic growth. (1) Education increases the human capital of the labor force, thereby increasing labor productivity and shifting growth toward a higher equilibrium level of output. (2) In endogenous growth theories, education increases the economy's capacity to innovate new technologies, products, and processes, thereby promoting growth.
In the environmental field, improving human capital can reduce the use of fossil fuel in the production process. The motive of this research is to understand the effect of public education expenditure shocks on economic growth and environmental quality in Iran.
Methodology
To achieve the goal of the research, a dynamic stochastic general equilibrium (DSGE) model and Bayesian approach have been used. In this regard, observable variables, gross domestic product, private consumption, investment, government expenditure and the gross growth rate of money have been used in the period of 2004 to 2021.
Findings
The results indicate that an increase in public education expenses by one standard deviation increases the marginal efficiency of private education expenses. Because private and public education expenses complement each other and entered the model in the form of a Cobb-Douglas function. Therefore, education hours, investment in education and subsequently, human capital increased. The increase in human capital led to an increase in production, economic growth and a decrease in inflation. The decrease in inflation led to an increase in the real wages of the workforce and finally the desire of the household to increase the supply of labor. Consumption increased in response to an increase in real wages. Also, the behavior of investment is very similar to the behavior of consumption and production, but its changes are more intense than other expenses. Therefore, it can be said that the shock of public education expenses has affected the performance of the economy like an expansionary impulse and has improved the economic conditions. In the environmental sector, with the increase in human capital, economic growth has been improved and this has led to an increase in air pollution and a decrease in environmental quality.
Discussion and Conclusion
In justifying these results, we can point to the weak institutional quality in Iran, that despite the huge amount of human capital investment, there is no necessary effectiveness in the environmental sector, and this is a confirmation that Iran is in the early stages of economic development. As a policy recommendation, in addition to paying attention to education and its role in the development of human capital as a long-term investment, improving the quality of institutions should be considered
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