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This paper deals with the dynamic economic and emission dispatch during a day as an important challenge in engineering. On the other hand, renewable energy provides an undeniable contribution to the energy supply. Therefore, to create an efficient model, the probability wind energy models have been proposed. In principle, this problem has several limitations and to bring it to reality, practical and nonlinear constraints such as power balance, ramp rate, prohibited zone, non-smooth cost function, and production constraints have been considered. Since these functions i.e. emission, cost, and wind models are conflicting in nature, to solve this problem, a multi-objective virus colony search algorithm (VCS) based on Pareto theory has been proposed. To improve the performance of the virus colony search algorithm, the chaos theory has been employed that eliminates the weakness of the standard algorithm, ie the speed of convergence and increased number of iterations of the algorithm to achieve the optimal solution. Chaos theory refers to the nature of complex systems with unpredictable behavior. Using the stochastic properties of chaos system, Chaos theory can improve the quality of population distribution in search space and enhance algorithm convergence function. The fuzzy decision function is also used to select the best solution from the set of solutions. The proposed model and method are applied to different systems and in some cases are compared with other methods in the articles. The results show an improvement in the performance of the proposed algorithm. The results also show that the presence of renewable resources has reduced production costs and thus increased network security. [ABSTRACT FROM AUTHOR]

Human ankle-foot gait is the result of a complex interaction between nerves and muscles. A significant number of prosthetic ankles-foots (passive, semi-active, active) have been designed to restore an identical function of a real limb. Excluding passive and semi-active prosthesis, that cannot generate any positive work, one of the biggest challenges in creating these prostheses is providing the needed power and energy during movement. Supplying this power and energy, requires a high-torque and high-power actuator having high weight, thereby causing a dramatic increase in the weight and size of the resulted prosthesis. In this paper, a combination of an active actuator (an electrical motor) and a passive stimulus (a spring) is utilized, which can decrease the needed power and energy. This design does not only support walking mode, but also provides running mode up to 2.5m/s. Accordingly, the first stage of this article includes mechanical modeling of the ankle and evaluation of efficiency and power consumption in all presented models. Then, a combination of spring and series actuator is selected as the best and optimal combination, which is different from the previous structures. In this structure, power and energy consumption are dramatically reduced up to 58% and 26% in walking mode and 64% and 57% in running mode. Consequently, a lighter motor and battery can supply the required power, so the prosthesis’s weight is decreased. Thus, in order to optimize power and energy consumption, it is necessary to determine the optimal spring stiffness based on design priorities (maximum power reduction). In the last step, the most suitable segments are developed for receiving the best performance, and then the designed prosthetic ankle is built. The results of simulations and experimental tests show that the produced prosthesis has all the desired performance, and it uses less energy and power while its user is moving. [ABSTRACT FROM AUTHOR]

Recently, due to environmental issues and lack of fossil resources, the widespread use of renewable resources has been considered. The use of renewable resources in the power systems leads to decentralized generation and due to the changing nature of such resources, many fluctuations have been added to the network. DC microgrids, as a small power grid, make it easy to use and control such resources in the distribution network. Excessive penetration of power electronic based renewable sources has reduced the inertia and damping making the system more sensitive to disturbances and reducing the system stability margin. This paper uses a DC microgrid structure connected to an AC network equipped with a virtual synchronous machine to manage automatically the power of the DC microgrid and AC networks and analyzing the role of virtual inertia in small signal stability. In order to verify the proposed method, the network has been studied for different operating conditions and inertias. In this method, with the use of the voltage source converter response and proper design dual droop control of the voltage, frequency and active output controllers, the necessary support for adjusting the system frequency are provided to withstand disturbances leading to enhancing stability for different conditions. [ABSTRACT FROM AUTHOR]

Due to the increasing load growth and expansion and significant changes in structure of electricity distribution networks, the issues related to the optimization of these networks face many challenges. Optimal placement and capacity of Distribution substations and their feeder networks are among the important issues of optimization of distribution networks from technical and economic viewpoints. In this paper, considering two important factors including loss reduction and improvement of reliability in distribution networks, a new multi-objective function was presented for optimal placement of location and capacity of Distribution substations based on their service area. The proposed objective function includes all construction and operation costs of equipment, loss costs, and reliability index (Energy Not Supplied). The Artificial Bee Colony (ABC) algorithm was applied to optimize the proposed objective function with the purpose of determining the optimal placement and capacity of substations of two sample distribution networks. A comparison of results obtained from optimization of the proposed objective function by the Artificial Bee Colony (ABC) algorithm with results of other algorithms in two sample networks indicates the efficiency and effectiveness of the proposed algorithm and objective function. [ABSTRACT FROM AUTHOR]

In this paper, the efficiency of PEM fuel cell system by using ejector for returning the additional fuel in the fuel supply circuit and comparison with conventional systems with compressor in fuel supply circuit, are studied. For this purpose a semi-analytical developed model for calculating the amount of efficiency increment, as well as the amount of power saving as a result of employing ejector in the fuel cell return line is provided by extending the previous models. In this developed model the important stack design parameters and ejector design parameters are correlated by presenting a new dimensionless parameter. The results for a typical fuel cell show that the amount of efficiency increment at different values of current density is different and there is a maximum point for it. The amount of power saving as a result of employing ejector compared with fuel cell power is considerable and will increase with increasing the current density. These results indicate that the ejector for those applications that require high power (for instance the transport applications) is more efficient. [ABSTRACT FROM AUTHOR]

Considering the increasing rate of electrical energy usage, this energy has become one of the most important resources for human life. So all countries are seeking access to reliable and planned energy resource. Regarding the non-renewability of fossil fuel resources, especially oil and gas, the issue of replacing these types of energy with renewable energy has been considered for decades. Saving and optimal use of electrical energy in important applications such as residential and commercial buildings is critical. One of the most important factors for planning power consumption and optimizing it is accurate forecasting for next hours' power consumption of residential and commercial buildings. In this paper, first, the data sets of several residential buildings are analyzed using parallel wavelet converters. Then, using an optimal estimator model of the convolutional neural network, the short-term load of the building is estimated. The obtained results show that the proposed method has improved the prediction error about 70, 69 and 73 percent for ARIMA, SVR, and LSTM methods, respectively. [ABSTRACT FROM AUTHOR]

Introduction: In addition to the main and announced goals of the US government for attacking Afghanistan, including: the destruction of the Taliban and Al-Qaeda Network, advancing the process of democratization and nation-state building, strengthening the governmental and political structure, creating stability and security, there were other goals on the agenda, the most important of which was access to important mineral resources and energy transfer routes from Central Asia to South Asia, preventing Russia from regaining power and controlling China and Iran. It is obvious that the achievement of the above-mentioned goals by the United States required the existence of a grand strategy in the foreign policy of this country regarding the issue of Afghanistan. Meanwhile, a review of the actions and approaches announced and implemented by the American government during the three terms of the presidency of George Bush, Barack Obama and Donald Trump, clearly confirms this issue. Adopting different and sometimes conflicting approaches and strategies, Bush's "Anti-Terrorism and "Counterinsurgency Strategies", Obama, and Trump's "Zero Base Strategy" is at least three distinct strategies of the US government in this era, which ultimately ended in the withdrawal of the US military forces from Afghanistan after 20 years of presence in this country. Research Question: The main question of the article is what are the evidence for the change in the approach of the US foreign policy towards Afghanistan in the three mentioned periods? And what is the relationship between Afghanistan's internal developments and this change of approach? Research Hypothesis: The change in the US foreign policy approach towards Afghanistan has been affected by the internal developments of this country caused by the resistance of armed groups, especially the Taliban, against US policies and the failure of the announced and implemented programs of this country during the presidency of Bush, Obama and Trump. Methodology and Theoretical Framework: Since the first question of the article seeks to provide evidence of the change in the strategy of the United States regarding Afghanistan in the three terms of the presidency, by adapting the methodology of a comparative study at the descriptive level, the most important features that support the change in these three periods should be mentioned. Next, by focusing on the second question, we will investigate the relationship between two variables: the change in the US approach with the internal developments of this country from a descriptive and inferential point of view and analyzing the logic governing this change of approach, focusing on one of the causes mentioned in the systemic theory of James Rosena Results and Discussion: The findings show that the US diplomatic system did not follow the same approach in Afghanistan during the two terms of Bush's presidency and unlike the 2002 strategy, which sought a combination of ideological and strategic goals from its presence in Afghanistan, in the 2006 strategy, the security aspect of these goals was dominant got more priority. In the Obama administration, the revival of the US global influence and the destruction of terrorist groups required a transition from a counterterrorism strategy to a counter-insurgency. In the Obama administration, the restoration of the US global influence and the destruction of terrorist groups required a transition from anti-terrorism strategy to counter-insurgency. From this point of view, both the weakening of Bush's anti-terrorism strategy and the clarification of Obama's counter-insurgency strategy clearly indicate the role of Afghan internal groups in the failure of America's policies and successive changes in strategy. Conclusion: Apart from the ups and downs of the US relations with Afghan government officials, there are three other reasons: the rise of Al-Qaeda and the Taliban during the time of the US presence, the emergence of many internal problems in Afghanistan and the disgust of a large part of the Afghan people with the US government due to its inability to reduce insecurity. There are three reasons all of which confirm the prominent role of internal developments, especially the confrontation of groups such as the Taliban with the US policies. This means that even armed local groups with minimal facilities, if they stand up, can force them to make continuous changes in their strategy in addition to the failure of the policies of the great and superior powers. It is not possible simply by relying on the established approaches of power in the paradigm of realism. [ABSTRACT FROM AUTHOR]

Over the past few decades, China has concentrated on numerous resources, especially new power resources, to complete its all-aspects power. This research investigates the different reason for China’s increasing participation in international institutions as well as creating new economic and financial institutions. Findings show that China has taken a non-aggressive and peaceful approach to participating in international institutions and in some cases creates regional and international institutions (such as Shanghai Cooperation Organization, BRICS, and the Asian Infrastructure Investment Bank) in order to change and strengthen its international position, and to change global security and economic arrangements. This approach, which stems from the dominance of the pragmatic approach in Chinese foreign policy, includes three stages of refusal, participation, and institutionalization in the international arena. The method of this research is a descriptive-analytical method. [ABSTRACT FROM AUTHOR]