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Showing 50 results for Abedin
Volume 17, Issue 4 (6-2017)
Abstract
Analysis of air bubbles entrainment in liquid slug body is one of the most important and complicated phenomena during slug flow regime. In the present attempt, a method is proposed for slug modeling to consider the air bubble entrainment into slug liquid body. The effect of consequencies and their impact on slug behaviour to predict more accurate correlations for slug parameters are estimated and calculated. This method considers a two-fluid single pressure model, combined with population balance model for equal bubble diameter series and solves using volume of fluid. In this regard based on slug and hydraulic jump similarity, a correlation for air bubble entrainment rate and its mechanism selected. This correlation developed in the form of a user defined function code and coupled with other models in FLUENT solver to calculate slug flow. Finally the result of this numerical modeling is validated with the result of other numerical and experimental results where exist in the related literature. The result is consist of the slug flow profile, entrained air bubble profile and their diameter distribution, vortex at slug front, pressure distribution during slugging, slug mixture velocity, turbullent model parameters and etc.
Volume 17, Issue 4 (6-2017)
Abstract
Slug flow is one the most complicated flow regime in industrial process that is seen for wide range of fluid flow. However, there are always some differences between experimental and numerical results obtained for slug flow. Proceeding the perivious attempt on the selection of the best turbulent model for numerical simulation, the slug flow is simulated numerically in two dimension by applying implicit VOF method and k-ε RNG turbulent model. To extract the slug flow parameters accurately FLUENT solver is used. The differences of the obtained results with and without turbulent model during slugging is also presented. To overcome this complicated flow behavior, a new user defined function code is developed. This UDF computes and predict slug parameters from FLUENT solver result without increasing the computational cost. The important slug parametrs are presented which are: liquid slug body velocity, liquid film velocity, slug front and tail velocity, slug center position and length, slug front and tail positions, pressure difference across slug, wall shear stress, slug mixture velocity, slug initiation time and position from the duct inlet. These parameters are analyzed and discused in details after that they had been validated
Volume 18, Issue 6 (11-2016)
Abstract
Worldwide distribution of the Date Palm Hopper (DPH), Ommatissus lybicus de Bergevin along with intensive regional chemical and cultural practices to control this pest provide a basis for development of high genetic divergence. This genetic divergence can result in demographically distinct populations. In this study, the demographic parameters of three genetically diverged Iranian populations of DPH (Bam, Jiroft, and Tezerj) were determined on two date palm cultivars (Berhi and Khunizi). The age-stage, two-sex life table theory was used to unveil biological differences among these populations. All experiments were carried out in a laboratory at 27±2˚C, 65±5% RH, and a photoperiod of 14:10 (L: D) hour. The results revealed significant differences in life history traits and growth parameters of different populations. The shortest development time was observed in the Bam population (75.86 and 85.03 days on Berhi and Khunizi, respectively). The highest values of the intrinsic rate of increase (r) and finite rate of increase (λ) were detected in Bam population (0.0377 and 1.0433 per day on Berhi as well as 0.0284 and 1.0288 per day on Khunizi, respectively). Based on these results, we can consider Bam as an aggressive population with higher infestation rate compared with the other populations due to its higher r and λ values as well as shorter mean generation time on both host cultivars. The significant differences in life history traits and variation in population growth parameters may suggest the presence of cryptic species among these populations. It can stem from the high genetic divergence among DPH populations which may be orchestrated by mismanagement of the pest.
Developing Combined Regional Drought Index and Presenting Return Period Curves Using Copula Function
Volume 19, Issue 5 (12-2019)
Abstract
Drought is an integral part of natural hazards. It usually occurs gradually and without any warning. Moreover, this phenomenon is usually created over time and does not disappear quickly Recently, some factors such as climate variability and the impact of climate change have influenced drought frequency and intensity in many parts of the world. Various definitions have been provided for drought but in general the lack of water resources in a specific period in a geographical area is considered as drought which implies this phenomenon as a regional hazard. IRAN is located in an arid and semi-arid region in which it experiences drought frequently. There are different types of drought such as meteorological, hydrological, agricultural and social-economic. These types are differentiated based on the factor which is rainfall, river flows, soil moisture, and social-economic consequences. There are many indices proposed for measuring drought severity; among them Standardized Precipitation Index (SPI), Palmer Drought Severity Index (PDSI) and Surface Water Supply Index (SWSI) could be mentioned. Each of these indices has its own pros and cons and is suitable for a particular type of drought. Therefore knowing the types of drought can provide a better understanding of shortages and their characteristics. Various factors are utilized for measuring these indices including precipitation, reservoir storage, discharge, temperature and potential evapotranspiration. In this study the three main aforementioned indices were first calculated for Aharchay watershed, located in East Azerbaijan province. Next based on combining these three indices with another two important parameters, groundwater level and solar radiation, a combined drought index is developed and calculated for the studied region. Considering the fact that the aforementioned parameters and indices have different level of importance in combined index, different weights based on expert opinions are assigned to the parameters considering how critical each parameter is in the overall drought analysis. This combined index demonstrated various climatic, hydrological and agricultural aspect of the region. In the next step, bivariate analysis of the two variables, intensity and duration, is carried out using copula. This is done by first checking the dependency between intensity and duration using Pearson, Spearman, and Kendall correlation coefficients. Second, various copula functions were fitted such as Gaussian, T, Clayton and Gumbel functions. Third, based on the Ordinary Least Square (OLS) and Kolmogorov–Smirnov (K-S) tests, the best copula functions were used. Lastly, based on the chosen copula the joint probability distributions were obtained. Two cases named “OR” and “AND” were defined for joint probability of the two variables and different return period curves is drawn. The results showed that the most severe drought in this watershed occurred in June 2004. Moreover, by assessing correlation coefficient between the considered indices it is shown that analysis of the drought in a region based solely on one index would neglect other imperative aspects in drought determination which necessitates a more integrated indicator. Furthermore, in bivariate analysis, return periods of “AND” cases were more than “OR” case. The results of this study could be utilized in preparedness and monitoring drought.
Volume 20, Issue 6 (June 2020)
Abstract
In this study, the effect of using of aluminum oxide and silicon oxide nanoparticles simultaneously into dielectric has been investigated in the process of electrical discharge machining of titanium alloy Ti-6Al-4V. After analyzing the parameters affecting the process of the electrical discharge machining using nanoparticles, intensity of the current, concentration, pulse on time, and particle composition were considered as input parameters. The effect of each parameters has been investigated on three levels; the material removal rate (MRR), the tool wear rate (TWR) and the surface roughness (SR) of the work piece. With respect to the development of the industry in the use of environmentally friendly dielectrics, deionized water was used as the dielectric fluid. Also, Design Expert software has been employed for the design of the experiments, analysis of the results and optimization of the parameters. The results showed that the best surface morphology is obtained by machining with the addition of nanoparticles in the relative composition of 50%. In this percentage of the composition, the surface roughness has the least value of the crack and the recast layer. In addition, the maximum value of the MRR and minimum value of TWR can be achieved in 12A of current intensity, 100µs of pulse on time and 75% of relative composition.
Volume 21, Issue 2 (9-2017)
Abstract
Many theorists of management emphasize on In-role and Extra-role performance in order to enhance effectiveness. Different studies have been done to improve the In-role and Extra-role performance of employees which include perception of social responsibility and job attitudes. The aim of this study is to evaluate perception of social responsibility effects with In-role and Extra-role performance considering job attitudes as a mediator variable. The population of the survey includes 1,640 managers and staff of Tejarat Bank. Data gathered through questionnaires and a sample of 314 randomly collected, and were analyzed using structural equation modeling. The validity of research questions confirmed using confirmatory factor analysis and reliability was approved by Cronbach's Alpha. According to The results of structural equation modeling, all hypotheses except one was proven. Also it showed that the job attitudes as a mediator in the relationship between the perception of social responsibility and employee performance has meaningful and significant effect.
Volume 21, Issue 2 (Summer 2018)
Abstract
Aims: Growth factor (GFs) delivery with the certain concentration and release kinetic is one of the main challenges in tissue engineering. The aim of this study was the preparation and characterization of smart poly (N-isopropylacrylamide) nanoparticles containing vascular endothelial growth factor for induction of angiogenesis in human bone marrow-derived mesenchymal stem cells.
Materials and Methods: In this exprimental study, two different formulations of temperature-sensitive Poly (N-isopropylacrylamide) (PNIPAM) nanoparticles (NPs) were synthesized by free radical polymerization technique. Nanoprecipitation and diffusion methods were used to load the vascular endothelial growth factor (VEGF) in PNIPAM NPs. The effects of released VEGF on the differentiation of human bone marrow stem cells (hBMSCs) into endothelial cells in angiogenic, osteogenic, and 50% angiogenic-osteogenic culture medium were investigated, using flow cytometry and light microscope. Statistical analysis was performed, using the GraphPad Prism 6 software.
Findings: The nanoprecipitation process caused polymer degradation due to using the organic N, N-Dimethylacetamide solvent. The cumulative VEGF released after 72hours for 70%. A total of 10ng/ml VEGF released from PNIPAM nanoparticles, in 2D culture with cell density of 3×104 hBMSCs, after 7 days, leading to the endothelial differentiation, capillary-like tube formation, and expression of 20% vWF as angiogenic marker.
Conclusion: The PNIPAM NPs have the potential to load and release the angiogenic GFs for induction of angiogenesis in hBMSCs and in osteogenic medium.
Materials and Methods: In this exprimental study, two different formulations of temperature-sensitive Poly (N-isopropylacrylamide) (PNIPAM) nanoparticles (NPs) were synthesized by free radical polymerization technique. Nanoprecipitation and diffusion methods were used to load the vascular endothelial growth factor (VEGF) in PNIPAM NPs. The effects of released VEGF on the differentiation of human bone marrow stem cells (hBMSCs) into endothelial cells in angiogenic, osteogenic, and 50% angiogenic-osteogenic culture medium were investigated, using flow cytometry and light microscope. Statistical analysis was performed, using the GraphPad Prism 6 software.
Findings: The nanoprecipitation process caused polymer degradation due to using the organic N, N-Dimethylacetamide solvent. The cumulative VEGF released after 72hours for 70%. A total of 10ng/ml VEGF released from PNIPAM nanoparticles, in 2D culture with cell density of 3×104 hBMSCs, after 7 days, leading to the endothelial differentiation, capillary-like tube formation, and expression of 20% vWF as angiogenic marker.
Conclusion: The PNIPAM NPs have the potential to load and release the angiogenic GFs for induction of angiogenesis in hBMSCs and in osteogenic medium.
Volume 21, Issue 3 (Fall 2017)
Abstract
Volume 21, Issue 4 (April 2021)
Abstract
Delamination is one of the most common modes of damage in laminated composites that can reduce stiffness and load-bearing capacity of the composite structure, which highlights the importance of studying of this phenomenon. For this purpose, in this study, the effect of the interface fiber angles on the mode II fracture toughness of plain woven laminated composites has been investigated. The end notch flexure specimens (ENF) with 24 layers which have 0//0, 0//30 and 30//-30 interface angles manufactured using hand lay-up method and experimental tests conducted on them in accordance with ASTM standard under load II mode loading. Experimental results show that the interface fiber angle has a significant effect on initiation and propagation of delamination toughness the initial and propagation fracture toughness, so that the load bearing capacity of the specimens with the non-zero interface fiber angle was the highest value. Moreover, the initiation and propagation value of fracture toughness for specimens with 0//0 interface fiber angle was less than the corresponding values for other samples with non-zero interface angles. In addition, the fracture process zone (FPZ) length was approximately the same for all samples. Taken images of fracture surfaces using scanning electron microscopy (SEM) show that in addition to the separation of fibers from the resin at delamination, other damage mechanisms Including fiber breakage and highly deformed matrix play a key role in increasing of the fracture toughness of the sample with 0//30 and 30//-30 interface fiber angle.
Volume 22, Issue 2 (February 2022)
Abstract
In the present study, the effect of natural microfibers (cork particles) on the mode I fracture toughness of plain-woven laminated composites has been investigated. For this purpose, double cantilever beam (DCB) specimens manufactured using hand lay-up method with stacking sequence of [0]28. To investigate the effect of cork particles on fracture toughness, samples with two different weight percentages (1% by weight and 3% by weight) were manufactured and the experimental results were compared with one obtained from sample with pure epoxy resin. Experimental results show that as the amount of cork particles increases, the onset of crack growth requires more energy. The amount of improvement in initiation fracture toughness for the DCB sample with 1% and 3% cork weigh has been increased by 67.15% and 71.96%, respectively which is due to the role of the cork in the resin rich area near the crack tip that arrested the delamination growth. Unlike the initiation fracture toughness, the propagation value is reduced by adding cork particles to the resin. During delamination growth, due to the agglomeration of micro fiber at delamination interface and role of stress concentration of these particles, hence, micro-cork fibers have not been able to increase the propagation fracture toughness and in some cases have slightly reduced the propagation fracture toughness of the delamination. Also, in order to investigate the mechanisms of damage, the fracture surfaces of the samples were scanned using scanning electron microscopy.
Volume 22, Issue 2 (February 2022)
Abstract
Incremental sheet forming is a flexible forming technology in which the sheet metal is gradually formed by the movement of tools in specified path. Due to the progressively localized deformation of the sheet and concentration of the forces on contact area of tool and sheet metal, the formability of the sheet increases compared with other common forming methods. In this study, numerical simulation of the incremental forming of AA3105-St12 two-layer sheet has been performed to calculate forming force and final thicknesses of the layers. The validity of the simulation results is evaluated by comparing them with those obtained from experiments. Numerical models for estimating the vertical force applied on the tool and the final thicknesses of the layers in terms of the process variables have been obtained using artificial neural network. Multi-objective optimization has been conducted to achieve the minimum force and the minimum thickness reduction of layers using obtained numerical models based on genetic algorithm method. Optimum thickness of the two-layer sheet and the thickness ratio the layers in different states of contact of the aluminum or the steel layers with the forming tool have been determined.
Volume 22, Issue 2 (summer 2022 2022)
Abstract
In this study, a new composite index, called the SWI (Sustainable Welfare Index) is proposed to assess "sustainable welfare". This index consists of significant social, economic, and environmental variables in flow and monetary forms, and can be directly compared to the GDP. Despite the paucity of statistical data, an attempt has been made to make a relative assessment of sustainable welfare in the Iranian economy during the years 2004 to 2018. According to the comparison of calculated SWI with GDP, it has been shown that the two indicators have similar movements and higher correlations in the period under study. In addition, despite the availability of economic growth during the period, society has been below a sustainable welfare level. In this study, the threshold effect of three SWI sub-indices on the total index was assessed using the smooth transition regression (STR) Model. As a result, the sub-index "Social Expenditure" through changes in "welfare losses due to income inequality" is of threshold effect on SWI.
Volume 22, Issue 4 (Winter 2019)
Abstract
Introduction
Water is a limited natural resource but essential for human survival. Among the water resources, groundwater is considered valuable for a variety of human activities. In the watershed Bajestan plain, the exploitation of drinking water is mostly done by wells especially due to the depth of water level. The purpose of this study is to unfold the qualitative parameter of ground drinking water in the Bajestan Plain based on Standard Classifications by Schoeller and prepare drinking water quality maps and then adjust the groundwater quality in terms of parameters affecting the quality of drinking water. Also determining the most appropriate points based on locally available information is another attempt of the study.
Methodology
In the present study, the measured parameters related to the Bajestan plain were obtained from the regional water company of Khorasan Razavi and the initial classification was carried out on them. Accordingly, 76 wells and the groundwater quality data were selected with a relatively complete statistic during the 2004-2011 periods. In order to evaluate the quality of drinking water, the parameters of sulfate, sodium, chloride, TDS and TH were extracted from the wells. Finally, qualitative changes to groundwater were investigated based on a 4-year period and appropriate points were noted down. In the next stage, the quality changes to drinking water were investigated in two 4-year periods and finally suitable drinking water areas were determined based on the passive defense technique and TDS.
Results and Discussion
The results showed that the best interpolation method for water quality parameters was the Statistical Estimator (IDW). In the Bajestan plain, 26.5% of the region was in inappropriate class, 66% had an unpleasant quality and only 7% of the region had a moderate drinking quality located in the mountain range of the study area. At the end, suitable places for drinking were determined. In other words, these are water harvesting sites for agriculture but suggested that those wells be sealed and be used in case of drinking water emergencies.
Conclusion
The extent of these classes indicates the low water quality in the region. As geological maps indicate, some places adjacent to the Cretaceous limestone, have moderate water quality while the plain area has inadequate quality water. Further, in the area adjacent to Playa, there is completely unpleasant quality of drinking water. According to reports from the Water Authority, drinking water provided to the region is mountainous and medium in quality. Also, the results of the qualitative timeliness of these resources indicate that the quality of groundwater resources is increasing with parameters reduction and hence; based on the amount of TDS allowed for drinking water, agricultural wells should be sealed and protected in some areas in order to be used in emergency.
Volume 23, Issue 3 (autumn 2023)
Abstract
Aim and Introduction
The growth of the digital currency market in the past years has attracted a lot of attention, and due to advantages such as transparency and new capabilities of the block chain, it is expected to continue its continuous growth in the future. The popularity of digital currencies such as Bitcoin and block chain-based currencies has created challenges and opportunities for the energy sector. Considering that electricity in most parts of the world are often produced using fossil fuels and non-renewable energies, the harmful environmental effects of digital currency mining are significant. Therefore, dealing with digital currency mining and considering related environmental costs can reveal the hidden costs of mining and provide a comprehensive and complete analysis in the field of digital currency. In this research, an attempt has been made to investigate and predict the trend of Bitcoin mining and related carbon dioxide emissions and environmental effects by using the method of system dynamics and design of the Bitcoin mining system from the time of the issuance of Bitcoin until 2034.
The results showed that Bitcoin mining will lead to the emergence and release of pollution in the world and its highest level during the peak of hash (300 billion GH) will be about 400 million kilograms of CO2 per day and until the next halving, Bitcoin mining will be profitable and after that the amount of extraction and consequently the level of its pollution will decrease.
Methodology
System dynamics is a method for modeling systems using accumulation, state and flow variables, which was introduced and developed in the 1960s by Forster (1961).
This method became very famous in the 1970s due to the publication of the book "Limits to Growth". This book used the system dynamics model to analyze the absurdity of the idea of unlimited growth, and today the most comprehensive source for the system dynamics model is the book "Business Dynamics" by Sterman (2000).
System dynamics can model the technical and social aspects of complex systems created by the adoption of Bitcoin and other cryptocurrencies. Therefore, due to its ability to explain emergent systemic phenomena in terms of interactions between agents related to human behavior and the (technical) framework of the system, it is a complete method to study the economic dynamics of this new form of money.
By using the system dynamics modeling technique (Forster, 1961; Sterman, 2000), the evolution of the network hash rate can be explained to a large extent. Assuming the existence of an efficient market, it can be analyzed that the miners will continue to mine Bitcoin to a certain extent that their expected profit from mining (which is netted from the cost of mining electricity) is realized. In other words, miners behave rationally, which is a basic concept for analyzing and predicting the future behavior of the hash rate of the network.
Results and Discussion
In this study, it was shown that the Bitcoin mining process can be modeled as a dynamic system using the dynamic systems method. Modeling begins with the hypothesis of efficient markets in Bitcoin mining. In the designed model it was shown how the Bitcoin mining system can be explained with a negative feedback loop that reduces the mining profit to zero with a time delay. By simulating this model for the next three halving periods, approximately in February 2024, digital currency mining will reach the point of maximum pollution production, and in other words, until the next halving, Bitcoin mining will be profitable, and after that, the amount of mining and, consequently, its pollution level will decrease. This model shows that the methods and tools of system dynamics can be effective for modeling Bitcoin and can be proposed for other existing or new cryptocurrencies as well as to explain the behavior of complex social systems created by the application of block chain technology.
Conclusion
The results showed that Bitcoin mining will lead to the emergence and release of pollution in the world, and its highest level will be around 400 million kilograms of CO2 per day during the peak of hash (300 billion Gigahash). Bitcoin mining, like any other profitable activity, when its profitability increases, it will be more welcome for exploitation and earning, therefore, according to its function and benefits, its pollution is predictable and unavoidable, but the main issue for decision makers and policy makers in this field is to compare the amount of hidden and obvious costs of digital currency mining with its benefits, and another point is to compare these costs to other similar activities.
The growth of the digital currency market in the past years has attracted a lot of attention, and due to advantages such as transparency and new capabilities of the block chain, it is expected to continue its continuous growth in the future. The popularity of digital currencies such as Bitcoin and block chain-based currencies has created challenges and opportunities for the energy sector. Considering that electricity in most parts of the world are often produced using fossil fuels and non-renewable energies, the harmful environmental effects of digital currency mining are significant. Therefore, dealing with digital currency mining and considering related environmental costs can reveal the hidden costs of mining and provide a comprehensive and complete analysis in the field of digital currency. In this research, an attempt has been made to investigate and predict the trend of Bitcoin mining and related carbon dioxide emissions and environmental effects by using the method of system dynamics and design of the Bitcoin mining system from the time of the issuance of Bitcoin until 2034.
The results showed that Bitcoin mining will lead to the emergence and release of pollution in the world and its highest level during the peak of hash (300 billion GH) will be about 400 million kilograms of CO2 per day and until the next halving, Bitcoin mining will be profitable and after that the amount of extraction and consequently the level of its pollution will decrease.
Methodology
System dynamics is a method for modeling systems using accumulation, state and flow variables, which was introduced and developed in the 1960s by Forster (1961).
This method became very famous in the 1970s due to the publication of the book "Limits to Growth". This book used the system dynamics model to analyze the absurdity of the idea of unlimited growth, and today the most comprehensive source for the system dynamics model is the book "Business Dynamics" by Sterman (2000).
System dynamics can model the technical and social aspects of complex systems created by the adoption of Bitcoin and other cryptocurrencies. Therefore, due to its ability to explain emergent systemic phenomena in terms of interactions between agents related to human behavior and the (technical) framework of the system, it is a complete method to study the economic dynamics of this new form of money.
By using the system dynamics modeling technique (Forster, 1961; Sterman, 2000), the evolution of the network hash rate can be explained to a large extent. Assuming the existence of an efficient market, it can be analyzed that the miners will continue to mine Bitcoin to a certain extent that their expected profit from mining (which is netted from the cost of mining electricity) is realized. In other words, miners behave rationally, which is a basic concept for analyzing and predicting the future behavior of the hash rate of the network.
Results and Discussion
In this study, it was shown that the Bitcoin mining process can be modeled as a dynamic system using the dynamic systems method. Modeling begins with the hypothesis of efficient markets in Bitcoin mining. In the designed model it was shown how the Bitcoin mining system can be explained with a negative feedback loop that reduces the mining profit to zero with a time delay. By simulating this model for the next three halving periods, approximately in February 2024, digital currency mining will reach the point of maximum pollution production, and in other words, until the next halving, Bitcoin mining will be profitable, and after that, the amount of mining and, consequently, its pollution level will decrease. This model shows that the methods and tools of system dynamics can be effective for modeling Bitcoin and can be proposed for other existing or new cryptocurrencies as well as to explain the behavior of complex social systems created by the application of block chain technology.
Conclusion
The results showed that Bitcoin mining will lead to the emergence and release of pollution in the world, and its highest level will be around 400 million kilograms of CO2 per day during the peak of hash (300 billion Gigahash). Bitcoin mining, like any other profitable activity, when its profitability increases, it will be more welcome for exploitation and earning, therefore, according to its function and benefits, its pollution is predictable and unavoidable, but the main issue for decision makers and policy makers in this field is to compare the amount of hidden and obvious costs of digital currency mining with its benefits, and another point is to compare these costs to other similar activities.
Volume 23, Issue 8 (August 2023)
Abstract
In this article, the numerical and experimental investigation of the effect of ultrasonic waves on the heat transfer rate with an increase of the wave amplitude is discussed. Numerical modeling determines the possibility of the investigation of the ultrasonic wave’s effects on fluid flow distribution and heat transfer. For this purpose, a cylindrical tank is considered inside which a spiral heater is placed at a fixed height in the water. In addition, ultrasonic transducers are considered as circular plates under the bottom of the tank. In order to simulate, the ANSYS Fluent software is used and the modeling is accomplished in two stages before and after ultrasonic excitation. To validate the numerical results, they are compared with those of the experiments. For this purpose, an experimental setup is prepared witch consists two coaxial cylinders, a spiral heater kept at a certain height in the water, and five transducers attached to the bottom of the tank. Both experimental and numerical results show that the convection heat transfer coefficient increases with the use of ultrasonic waves with a discrepancy of nearly 4% between the results. By increasing the heat transfer coefficient, the heater surface temperature decreases. The discrepancy between the measured and calculated temperature is about 5%. The velocity and temperature distributions obtained from the numerical results show that using ultrasonic waves enhance the fluid flow mixing which in turn increases the convection heat transfer. The higher the amplitude of the ultrasonic wave, the higher the heat transfer coefficient will result.
Volume 24, Issue 1 (spring 2024)
Abstract
Introduction
Currently, 87 countries – representing more than 90% of global GDP – are considering central bank digital currency (CBDC). It is therefore crucial that central banks understand the implications of CBDCs for financial stability and monetary policy. CBDCs should not harm the country's economy. In particular, they should not become a source of financial disruption that could disrupt the transmission of monetary policy. Recently, the details of the Central Bank's digital currency, which is called "Digital Rial" in Iran, have been published by the Central Bank of Iran. This study seeks to examine the changes in the country's monetary policies with the introduction of the Digital Rial by the Central Bank using the system dynamics method. The results of this study show that with the issue of the Digital Rial, the increasing coefficient of money decreases and reduces the money supply, and because the Digital Rial has the same nature as banknotes and coins, it can reduce the power of banks in creating liquidity. As a result, the central bank can use Digital Rial as contractionary monetary policy tool to control inflation in the country.
Methodology:
In order to provide a working solution for the research problem and to understand the importance of the topic, this study tries to use the system dynamics method to present a dynamic model of the relationship between digital currencies and its effect on monetary policies in Iran's economy. System dynamics is a method for modeling systems using accumulation, state and flow variables, which was developed in the 1960s by Professor Jay Forrester at MIT University. This model became very famous in the 70s thanks to the publication of the book "Limits to Growth". This book used the system dynamics model to analyze the absurdity of the idea of unlimited growth. Today, the most comprehensive source for the system dynamics model is the book "Business Dynamics" by Professor John Sterman (2000, MIT University). System dynamics can model the technical and social aspects of complex systems created by the adoption of Bitcoin and other cryptocurrencies. The idea of interaction between factors related to human behavior and the (technical) framework of the system is a perfect way to study the economic dynamics of this new form of money.
Results and Discussion:
The results showed that with the issue of Digital Rial, the increasing coefficient of money decreases and money supply decreases, and because the Digital Rial has the same nature as banknotes and coins, it can reduce the power of banks to create liquidity. On the other hand, the estimates of this research showed that the effect of the ratio of banknotes and coins on the increasing coefficient was not significant, and also the increasing coefficient had less effect on the money supply in pre-2013 period, which can be attributed to the effect of the increasing effect of the money supply. Most of the banks know that in increasing the country's liquidity, the use and expansion of the Digital Rial as a contractionary monetary policy tool will be effective in the current economic conditions. Also, this effect can be more effective with the increase in the use of electronic payments and new banking methods, because in addition to facilitating exchanges and reducing money printing costs, the use of Digital Rials also has the advantages of current electronic payments, with the difference that this part of deposits is not under the control of banks and is kept in electronic wallets, so they will not have the power to create liquidity. Therefore, the effectiveness of this money depends on the choice of the central bank to deposit electronic wallets in commercial banks, as well as the volume of this money issue.
Conclusion:
Considering the effect of Digital Rial on monetary contraction, it is suggested to design effective incentives in the design of Digital Rial, because the expansion of the use of this currency can be effective in controlling inflation. Among these incentives, we can mention fixed fees and lower taxes in transactions compared to other means of payments or increasing the limit of convertible money. Also, the requirement to purchase certain goods only through Digital Rial and to designate special shopping centers that only pay with Digital Rial (similar to China's policies on the use of Chinese Yuan by people) can also be other incentives to use Digital Rial. Also, due to the facilitation and acceleration of exchanges, the expansion of the Digital Rial can be effective in controlling the money supply besides the advantages of electronic payment methods.
Currently, 87 countries – representing more than 90% of global GDP – are considering central bank digital currency (CBDC). It is therefore crucial that central banks understand the implications of CBDCs for financial stability and monetary policy. CBDCs should not harm the country's economy. In particular, they should not become a source of financial disruption that could disrupt the transmission of monetary policy. Recently, the details of the Central Bank's digital currency, which is called "Digital Rial" in Iran, have been published by the Central Bank of Iran. This study seeks to examine the changes in the country's monetary policies with the introduction of the Digital Rial by the Central Bank using the system dynamics method. The results of this study show that with the issue of the Digital Rial, the increasing coefficient of money decreases and reduces the money supply, and because the Digital Rial has the same nature as banknotes and coins, it can reduce the power of banks in creating liquidity. As a result, the central bank can use Digital Rial as contractionary monetary policy tool to control inflation in the country.
Methodology:
In order to provide a working solution for the research problem and to understand the importance of the topic, this study tries to use the system dynamics method to present a dynamic model of the relationship between digital currencies and its effect on monetary policies in Iran's economy. System dynamics is a method for modeling systems using accumulation, state and flow variables, which was developed in the 1960s by Professor Jay Forrester at MIT University. This model became very famous in the 70s thanks to the publication of the book "Limits to Growth". This book used the system dynamics model to analyze the absurdity of the idea of unlimited growth. Today, the most comprehensive source for the system dynamics model is the book "Business Dynamics" by Professor John Sterman (2000, MIT University). System dynamics can model the technical and social aspects of complex systems created by the adoption of Bitcoin and other cryptocurrencies. The idea of interaction between factors related to human behavior and the (technical) framework of the system is a perfect way to study the economic dynamics of this new form of money.
Results and Discussion:
The results showed that with the issue of Digital Rial, the increasing coefficient of money decreases and money supply decreases, and because the Digital Rial has the same nature as banknotes and coins, it can reduce the power of banks to create liquidity. On the other hand, the estimates of this research showed that the effect of the ratio of banknotes and coins on the increasing coefficient was not significant, and also the increasing coefficient had less effect on the money supply in pre-2013 period, which can be attributed to the effect of the increasing effect of the money supply. Most of the banks know that in increasing the country's liquidity, the use and expansion of the Digital Rial as a contractionary monetary policy tool will be effective in the current economic conditions. Also, this effect can be more effective with the increase in the use of electronic payments and new banking methods, because in addition to facilitating exchanges and reducing money printing costs, the use of Digital Rials also has the advantages of current electronic payments, with the difference that this part of deposits is not under the control of banks and is kept in electronic wallets, so they will not have the power to create liquidity. Therefore, the effectiveness of this money depends on the choice of the central bank to deposit electronic wallets in commercial banks, as well as the volume of this money issue.
Conclusion:
Considering the effect of Digital Rial on monetary contraction, it is suggested to design effective incentives in the design of Digital Rial, because the expansion of the use of this currency can be effective in controlling inflation. Among these incentives, we can mention fixed fees and lower taxes in transactions compared to other means of payments or increasing the limit of convertible money. Also, the requirement to purchase certain goods only through Digital Rial and to designate special shopping centers that only pay with Digital Rial (similar to China's policies on the use of Chinese Yuan by people) can also be other incentives to use Digital Rial. Also, due to the facilitation and acceleration of exchanges, the expansion of the Digital Rial can be effective in controlling the money supply besides the advantages of electronic payment methods.
Volume 24, Issue 4 (April 2024)
Abstract
New surgical technologies are continuously being developed to enhance control during operations and mitigate injuries resulting from surgical procedures. One such advancement is the ultrasonic laparoscopic surgical tool known as the ultrasonic scalpel, which is designed to minimize surgery-related injuries when used alongside conventional tools. Establishing optimal input parameters for this ultrasonic instrument not only enhances operational reliability but also decreases the risk of resultant injuries. Ongoing research investigates the impact of varying power and duration of ultrasonic vibrations, along with the equivalent energy input into the blood vessel during surgery, on tissue mechanical characteristics and thermal effects. This study assesses the ability of sheep carotid artery tissues to withstand blood pressure within the vessel and examines thermal damage through pressure testing and optical imaging. Findings indicate that maintaining constant time at specific power yields maximum pressure tolerance at optimal power levels. However, varying the time at specific power settings produces different effects. For instance, the highest blood pressure resistance, at 1100 mmHg, was observed at 44 Watt of power over a 10 second duration at 10 newton. Furthermore, results demonstrate that increased energy input correlates with heightened thermal damage to surrounding tissues during the operation.
Volume 24, Issue 10 (October 2024)
Abstract
In recent years, paper-based microfluidic devices have attracted significant attention. However, the inability to precisely control multiple fluids simultaneously has remained a major challenge for paper-based microfluidic chips. Here, inspired by electrical circuits, a transistor component has been designed and fabricated for operation in paper-based microfluidic chips. This component, upon receiving an electrical command, regulates the flow of fluid within a paper-based microfluidic channel. The primary advantage of this transistor lies in its bi-stable operation (capability to open and close the channel) despite its simple structure. Its operation is based on the controlled movement of wax, driven by the heat generated from the electrical current applied to the transistor's gate, within the cross-section of the paper. To characterize this transistor, the parameters affecting its operation were analyzed. Experimental results indicated that in a channel with length of 25 mm, with widths of 2 mm and 3 mm, and hydrophobic section lengths of 2 mm and 3 mm, a fluid volume of 30 to 40 microliters could be controlled by applying a gate electrical current of about 1300 milliamperes for less than 35 seconds. Additionally, as a practical demonstration of this transistor's functionality, a sensor circuit was designed and fabricated to detect acidic and basic environments. The proposed transistor, by enhancing fluid controllability in microfluidic chips, plays a key role in advancing this technology. Paper-based microfluidic chips equipped with the transistor presented in this study hold promising potential for applications in medical diagnostics, performing complex multi-step tests, biosensors and chemical sensors
Volume 25, Issue 1 (Spriing 2025)
Abstract
Aim and Introduction
Carbon tax is one of the most important policy tools in the field of energy, which is applied to the consumption, production or distribution of fossil energy, including oil products, coal, natural gas, etc. The purpose of carbon tax is to reduce economic and environmental effects caused by pollution by including environmental costs in the price of goods and services. This policy tool can bring positive economic and environmental consequences through changes in consumer and producer behavior. The purpose of this study is to investigate the effects of carbon tax on energy-intensive and non-energy-intensive industries in different regions of the world.
Methodology
Since a CGE model can describe the interactions between different factors in macroeconomic systems and examine the effects of a policy at the global level, therefore, a dynamic multi-regional CGE model has been used to better understand the policy effects.
Results and Discussion
The results show that the carbon tax in all scenarios leads to an increase in the price of goods with high energy intensity in all regions, and the price of goods with low energy intensity decreases, except in the group of developed and high-income countries. Production in the energy-intensive and non-energy-intensive sectors is facing an average decrease. Imports in the energy-intensive sector, except for the group of countries with higher-than-average income, will decrease for other groups, and in the non-energy-intensive sector as well.
Conclusion
To investigate the effect of carbon tax on the industries of different countries, first the countries of the world were grouped into 5 regions based on the criteria of the World Bank and then 5 policy scenarios based on the report of the International Energy Agency were implemented in each region. For modeling, a dynamic calculable general equilibrium model was used in order to achieve more accurate results, and then important industrial consequences were obtained by solving the model. From the results of this research and the studies that have been carried out so far, it can be seen that what is decisive in the consequences of the implementation of the carbon tax is the region and the country implementing the policy.
Based on this, the policy makers, considering the national and regional conditions and being aware of the possible effects of the policy, can include assumptions in the design and implementation of the policy in order to achieve efficient and appropriate conditions in the implementation of the carbon tax by reducing the negative effects. Based on the results of the research, it was observed that due to the differences in the regions, the macroeconomic effects in the industry will be different for different regions of the world. Therefore, one of the important points in the effort to bring the emission of greenhouse gases to zero is to pay attention to the differences in industries in different countries and the coordinated actions of the governments with each other for technical and financial support in order to accelerate the transformation of clean energy and reach the commitment goal. Since energy consumption is mainly related to production activities, especially production from energy-intensive industries, reducing greenhouse gas emissions from industry takes more time than some economic sectors. For this purpose, governments should present regular and specific programs to attract investments in the long term so that they can guide industries in the direction of deploying the most efficient technologies. The governments that implement carbon tax policies can also use the collected tax revenues to strengthen energy innovation. Therefore, industries that use unclean energy sources as production inputs, by upgrading production technologies, in addition to reducing production costs, can specialize in producing clean products
Carbon tax is one of the most important policy tools in the field of energy, which is applied to the consumption, production or distribution of fossil energy, including oil products, coal, natural gas, etc. The purpose of carbon tax is to reduce economic and environmental effects caused by pollution by including environmental costs in the price of goods and services. This policy tool can bring positive economic and environmental consequences through changes in consumer and producer behavior. The purpose of this study is to investigate the effects of carbon tax on energy-intensive and non-energy-intensive industries in different regions of the world.
Methodology
Since a CGE model can describe the interactions between different factors in macroeconomic systems and examine the effects of a policy at the global level, therefore, a dynamic multi-regional CGE model has been used to better understand the policy effects.
Results and Discussion
The results show that the carbon tax in all scenarios leads to an increase in the price of goods with high energy intensity in all regions, and the price of goods with low energy intensity decreases, except in the group of developed and high-income countries. Production in the energy-intensive and non-energy-intensive sectors is facing an average decrease. Imports in the energy-intensive sector, except for the group of countries with higher-than-average income, will decrease for other groups, and in the non-energy-intensive sector as well.
Conclusion
To investigate the effect of carbon tax on the industries of different countries, first the countries of the world were grouped into 5 regions based on the criteria of the World Bank and then 5 policy scenarios based on the report of the International Energy Agency were implemented in each region. For modeling, a dynamic calculable general equilibrium model was used in order to achieve more accurate results, and then important industrial consequences were obtained by solving the model. From the results of this research and the studies that have been carried out so far, it can be seen that what is decisive in the consequences of the implementation of the carbon tax is the region and the country implementing the policy.
Based on this, the policy makers, considering the national and regional conditions and being aware of the possible effects of the policy, can include assumptions in the design and implementation of the policy in order to achieve efficient and appropriate conditions in the implementation of the carbon tax by reducing the negative effects. Based on the results of the research, it was observed that due to the differences in the regions, the macroeconomic effects in the industry will be different for different regions of the world. Therefore, one of the important points in the effort to bring the emission of greenhouse gases to zero is to pay attention to the differences in industries in different countries and the coordinated actions of the governments with each other for technical and financial support in order to accelerate the transformation of clean energy and reach the commitment goal. Since energy consumption is mainly related to production activities, especially production from energy-intensive industries, reducing greenhouse gas emissions from industry takes more time than some economic sectors. For this purpose, governments should present regular and specific programs to attract investments in the long term so that they can guide industries in the direction of deploying the most efficient technologies. The governments that implement carbon tax policies can also use the collected tax revenues to strengthen energy innovation. Therefore, industries that use unclean energy sources as production inputs, by upgrading production technologies, in addition to reducing production costs, can specialize in producing clean products
Volume 28, Issue 3 (autumn 2024)
Abstract
The expansion of the elderly demographic alongside the intricacies of their urban requirements underscores the imperative to reassess urban planning paradigms. The 15-minute city framework, regarded as a progressive model for sustainable advancement, seeks to facilitate equitable and prompt access to urban resources, particularly for marginalized populations such as the elderly. This investigation concentrates on the historical urban landscape of Urmia to explore the viability of this model in enhancing the quality of life for the elderly demographic. The research examines the existing conditions of accessibility for the elderly to vital services, including healthcare facilities, retail establishments, recreational areas, and public transit systems.
The methodological framework is predicated on spatial analyses employing Geographic Information System (GIS) software to assess the accessibility radius and the spatial distribution of services, in conjunction with modeling the interrelationships between accessibility metrics and service quality utilizing Smart Partial Least Squares (PLS) software. The overarching objective of this investigation is to evaluate the practicality and prerequisites for the adoption of the 15-minute city paradigm in Urmia, with a particular focus on enhancing access to vital services and amenities for the senior population.
The research findings elucidate that the augmentation of infrastructure quality, the proliferation of services in proximity to residential areas, and the assurance of equitable allocation of urban facilities can markedly enhance accessibility for the elderly, thereby promoting their autonomy and social engagement. The data imply that the adoption of the 15-minute city model has the potential to ameliorate the quality of life for senior citizens in Urmia while simultaneously addressing urban disparities and advancing social equity, thus contributing to the principles of sustainable development. This investigation emphasizes the imperative for an inclusive planning framework that is specifically attuned to the requirements of the elderly, and it advocates for priorities such as the establishment of accessible public transit systems, the enhancement of pedestrian thoroughfares, the creation of communal spaces for social interaction, and the elevation of the quality of urban services.
The methodological framework is predicated on spatial analyses employing Geographic Information System (GIS) software to assess the accessibility radius and the spatial distribution of services, in conjunction with modeling the interrelationships between accessibility metrics and service quality utilizing Smart Partial Least Squares (PLS) software. The overarching objective of this investigation is to evaluate the practicality and prerequisites for the adoption of the 15-minute city paradigm in Urmia, with a particular focus on enhancing access to vital services and amenities for the senior population.
The research findings elucidate that the augmentation of infrastructure quality, the proliferation of services in proximity to residential areas, and the assurance of equitable allocation of urban facilities can markedly enhance accessibility for the elderly, thereby promoting their autonomy and social engagement. The data imply that the adoption of the 15-minute city model has the potential to ameliorate the quality of life for senior citizens in Urmia while simultaneously addressing urban disparities and advancing social equity, thus contributing to the principles of sustainable development. This investigation emphasizes the imperative for an inclusive planning framework that is specifically attuned to the requirements of the elderly, and it advocates for priorities such as the establishment of accessible public transit systems, the enhancement of pedestrian thoroughfares, the creation of communal spaces for social interaction, and the elevation of the quality of urban services.