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In the  Bacillusamyloliquefaciens α-amylase (BAA), the loop (residues from 177-185; region І) is the constructive part of the cage responsible for attachment to calcium. It has two more amino acid residues than the α-amylase from Bacillus licheniformis (BLA). Arg176 in this region makes an ionic interaction with Glu126 from region ІІ (residues 118-131) but this interaction is lost in BLA due to substitution of R176Q and E126V. It is the common feature of α-amylases that calcium ion is required for their thermal stability. The present work quantitatively estimates the effect of ionic interaction on the overall stability of the enzyme. To clarify the functional and structural significance of corresponding salt bridge, first an automated homology model of the mutant enzyme (∆E126) was built by the Swiss-Model Protein Modeling Server.  Bacillus amyloliquefaciens α-amylase (3BH4.pdb) was used as the template and examined by GETAREA and WHAT IF programs, then Glu126 was deleted (∆E126) by site-directed mutagenesis and the thermostability was examined for the wild-type and mutant enzymes. Modeling results showed that deletion of salt bridge affected on the hydrophobic and hydrophilic residues orientation of two discussed regions (Ι, ΙΙ). The mutant enzyme also exhibited lower thermostability relative to the wild-type enzyme. Thus, it may be suggested that salt bridge could affect on accessible surface area of the discussed regions, decrease water diffusion,  prevent diffusion of cations and improve the thermostability of the whole protein.

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Aims: Modernization theory today, as one of the newest theories, suggests the application of contemporary architecture in the process of action in valuable cultural and historical contexts. The most challenging issue among these is to identify the differences and similarities of this theory with other competing opinions and analyze its strengths and weaknesses. The main goal of the research is to reread the theory of contemporization for adding quality to the old textures through the experience of creating value for the heritage of contemporary architecture.

Methods: The current research strategy is logical reasoning strategy. It is a descriptive-analytical research method that uses the tactic of comparative comparison to advance the research process. The theoretical framework of the research is a combination of the master architecture theory and the theory of contemporization. Hence, the research analyzes and rereads the strengths and weaknesses of the theory of contemporization by comparing competing theories.

Findings: The analysis of research findings in two fields including the field of formal system (physical-structural system) and content system (1- economic, 2- social system and 3- environmental system) shows that the theory of contemporization can be better than the theory competitors such as reconstruction, renovation, improvement and regeneration; In the category of quality, it acts as a part of historical and cultural contexts and increases the quality of life of the residents.

Conclusion: The results of the research show that the theory of contemporization by emphasizing the design approaches and values of contemporary architecture increases the quality of historical and cultural contexts; Along with simultaneous emphasis on formal system and content system.

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which have lost their main functions, and their abandonment and lack of proper use causes them to be destroyed more and more. Nowadays, historical buildings can no longer be used as in the past and by changing the use of historical buildings, they are saved from certain death, and the concept of contemporizing all these achievements is in mind.

Methods: In this study, the time range is related to the traditional houses located in the neighborhoods of Tehran in the period from 1941 to 1966., most of the houses are related to the central core of Tehran and the surrounding and neighborhood streets of Elginab, Waliasr, Karim Khan Zand, etc. The techniques used in the applied method of this research in order to modernize modern historical monuments are preparing and completing the questionnaire, using the interpretive structural modeling (ISM) approach and linear regression technique.

Findings: Among the 42 indicators studied in the five physical-structural, perceptual, functional, socio-economic and natural-environmental dimensions, the indicators of preserving old residents, improving the quality of housing, using special colors, easy access on foot, etc. are completely inappropriate conditions in terms of the principles of modernization They play a role in the historical monuments of Tehran metropolis.

Conclusion: The four indicators of neighborhood authenticity and sense of belonging, the use of a special form, the presence of necessary activities and the recognizability of spaces have the highest and best quality compared to other studied indicators from the point of view of the theory of contemporization, and they have medium-high conditions in terms of the points obtained.

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This paper aims to analyze the importance of balance sheet channel of credit approach in monetary transmission mechanism in Iran during 1989:2-2014:1. This analysis is based on a structural vector auto-regression (SVAR) model with ten variables including asset prices and the other seven-variable model excluding asset prices. These models are comparable with each other while assessing the importance of balance sheet channel. The comparison of SVAR model containing asset prices such as housing price, gold coin price, stock price and exchange rate with SVAR model excluding asset prices implies that adding asset prices to the model increases the effects of monetary policy shocks, through liquidity shocks, on output fluctuations. The findings confirms the importance of the balance sheet channel in monetary transmission mechanism. Therefore, monetary authorities should take precautions in implementing tight monetary policy due to its probable recession effect.

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In this paper, ferrofluid flow in a closed cooling loop without any mechanical pump has been simulated. The flow of the ferrofluid in the closed loop is resulted from applying a non-uniform magnetic field and the thermo-magnetic effect of the ferrofluids. The ferrofluid consist water and different volume fractions of iron oxide nanoparticles with nanoparticle diameter of 13nm. The two phase mixture model and the control volume technique have been used in the present study. The applied non-uniform magnetic field is resulted from an electromagnetic solenoid and the steady and also the transient modeling of the flow in the cooling loop from start point (stagnant ferrofluid in loop) have been carried out. The obtained results show that by applying magnetic field and also by taking advantage of temperature dependent property of the magnetic susceptibility, a flow of ferrofluid is created in the loop and by increasing the heat input (heater power) in the loop, the flow rate in the loop is increased. Moreover, the results show that by having a cold source (for rejection of produced heat) with higher constant temperature, the flow rate in the loop increases. Furthermore, the flow rate in the cooling loop is increased as the volume fraction of the nanoparticles in the base fluid increases. The mentioned cooling loop can be used in the electronic cooling systems.

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This study is an attempt to identify the persistent obstacles in improving labor productivity path and to give insight to policymakers into the food and beverage industry and related industries about the geographic concentration of industry, educational distribution of employees, and their relationships with labor productivity. For this purpose, a panel data model is applied for explaining labor productivity in the food and beverage industry over the period 2000- 2014. In addition, motivational indices (wage per worker), per capita capital stock and physical capital management index (the number of private and public firms) are used as explanatory variables. The results suggest that improvement in labor productivity in food and beverage industry sub-sectors requires reducing educational dispersion of the labor force by employing high-educated workers, increasing geographical concentration, improving incentive system by determining appropriate wage, and enhancing management through reducing state ownership of industrial firms.

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Macroeconomic policy makers and planners always use different tools to achieve economic goals. Credit control is one of these tools. The boom and recession of the financial sector of the economy are called the credit cycle, and of the real sector is called the business cycle. Credit as a complementary input for capital, intermediate goods, and primitive materials can be effective in improving business cycles. This study, by employing Structural Vector Auto Regressive (SVAR) model and using the annual data of Iran during 1973 to 2016, investigates the relationship between credit cycles and business cycles in Iranian economy. The results show that credit cycle has positive effect on business cycle, but business cycle has negative effect on credit cycle. Credit cycle fluctuations have the largest share in explaining the business cycle fluctuations, but business cycle ranks the fourth in explaining the credit cycle fluctuations following own variable, inflation rate and consumption shocks. The investigation of the co-movement between the credit cycle and the business cycle also show that the effect of the credit cycle on the business cycle is revealed from the second period and there is 24 years of co-movement between these cycles. Also, the persistence of the co-movement between these cycles in expansion - improvement phases has causes severe financial crises in the Iranian economy in the long run.

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Introduction:
Technological innovation is one of the key indicators for economic growth and productivity. Recent studies show that R&D investment causes technological change. However, this relationship is not always obvious and seems to vary according to the level of economic development. A large number of studies on developed countries confirm the positive relationship between research and development, innovation and productivity. However, in developing countries, this relationship is not always clear. In this regard, in order to allocate an important share of national income to research and development, developing economies need to achieve a high and sustainable economic growth rate or create an economic development policy based on new innovation. This paper investigates the threshold effect of medium-high technology exports on total factor productivity in 50 developing and developed countries over the period 2007-2020.

Methodology:
For analyzing data, panel smooth transition regression (PSTR) model is used, which was presented and expanded by Gonzalez et al. (2005) and Colletaz & Hurlin (2006) and is very suitable for heterogeneous panel data. Thus, Medium-High Technology Exports index is chosen as the transition variable. Following the study of Hammar and Bellarebi (2021), the general model shows the relationship between the logarithm of total factor productivity, the logarithm of advanced and medium exports (transition variable), the logarithm of trade openness, and the logarithm of research and development expenditures.

Results and Discussion:
The results show a nonlinear relationship between the variables under study. Based on the necessary test results, considering only one transition function with a threshold value and two regimes is sufficient for nonlinear estimation of the model. Also, the logarithm of the value of the transition variable threshold is estimated about 3.0816 and the slope parameter is estimated about 6.4226. Research and development (R&D) expenditures and trade have negative significant effects on total factor productivity in the first regime on total factor productivity that this effect by crossing the threshold (Medium-High Technology Exports) effect for the variable of R&D expenditures becomes positive and insignificant. This result is consistent with the study of Sepherdoost and Afshari (2016). In addition, the results show that the influence of trade on total factor productivity is negative and significant, but its influence is lower than before, in the second regime. This result is consistent with the study of Lotfalipour et al. (2015)

Conclusion:
Considering the role of high and medium technology exports in the relationship between research and development expenditures and total factor productivity, it can be said that developing countries in the initial stages of growth can increase their productivity by increasing the export of high technology industries, to a level of specific development, despite the very high importance of research and development in the development of high-tech industries. Only a very small part of the country's resources is spent on research and development, and the weakness of the workforce has reduced the utilization of this small amount of domestic research and development investment. So, the low contribution of research and development expenses indicates that companies do not have much desire for innovative efforts and the creation of new technology transfer capacity as a stimulus for the quantitative and qualitative growth of industrial products. This action has caused them to not provide new products and services and reduce their competitiveness in domestic and foreign markets.
The most important policy recommendation is that the governments of developing countries should develop high and medium technology exports witch through their positive effects such as productivity growth, reduction of production costs, improvement of financial development and growth of innovation and technology, it is possible to achieve favorable economic growth and to improve the productivity of all factors. Also, the development of exports with advanced and medium technology and knowledge-based production will initially attract educated and specialized unemployed people, and with the improvement of management practices, the productivity of production factors and the level of technology will increase and lead to product innovation. Therefore, considering the importance of exporting with advanced and medium technology and knowledge-based production, it is suggested that the universities move towards the third generation university, in which case the chain of knowledge to technology will be completed in the university and the university will support the industries by developing the latest technologies. It is also suggested that in order to improve their competitiveness in the international arena and to advance their development goals, developing countries allocate a greater share of their income resources to research and development and create incentives for researchers in various economic sectors, especially in industries with technological capabilities, and move more towards the knowledge-based economy and the implementation of research policies based on innovation.