Efficiency Of Subsystem Research Articles

Air supply subsystem efficiency optimization for fuel cell power system with layered control method

Efficient and stable operation is critical for the large-scale commercialization of the proton exchange membrane fuel cell power system. The effective control and optimization of the operating conditions, such as oxygen excess ratio and cathode pressure of the air supply system, is a solution to improve the overall system efficiency. This work proposes a novel layered control method to achieve rapid and stable control of the operating conditions. The control structure in this paper consists of the optimization and control layers. A two-dimensional objective optimization function for the optimization layer is established to characterize the system efficiency based on theoretical analysis and experimental testing on the fuel cell power generation process and air supply system power consumption pattern. Then, a modified salp swarm algorithm with adaptive inertia weight is proposed to quickly and accurately obtain the optimal operating conditions for the maximum efficiency under different load current densities. Meanwhile, the local optimal solutions are avoided by introducing mutation operations. For the control layer, a third-order state space equation is developed to accurately describe the operating characteristics of the air supply system according to its operating principles. A feedback linearization-based sliding mode controller is designed to achieve rapid and stable control of the optimal working conditions outputted from the optimization layer. Finally, the fuel cell system was tested in the lab and verified on the fuel cell city buses. The results show that the system's operating efficiency is improved by 0.6 %–2.6 % at different current densities, and the hydrogen consumption of all three city buses is reduced by more than 5 %. The optimization effect was enhanced significantly. Therefore, the layered control method is effective in solving the optimization and control problems of the fuel cell power system.

Novel design and performance analysis of a selectively filtered nanofluid spectrum semi-trough solar concentrated photovoltaic/thermal system

ABSTRACT In this paper, the main novelty is the proposal and performance analysis of a novel selectively filtered nanofluid spectrum semi-trough solar concentrated photovoltaic-thermal (SPVT) system. Experimental preparation and optical tests of Ag-CoSO4/water nanofluid are conducted. The selected nanofluid for the SPVT system has an average absorptance of 53.5% and an average transmittance of 46.5% in 250.0 ~ 2500.0 nm. The optical analysis results show that the optical efficiency of the SPVT system is 94.3% under the optical filtering condition. When the solar tracking error increases to 0.3°, the optical efficiency of the SPVT system can still be kept at 84.8%. This means that the SPVT system has relatively good adaptability on solar tracking error. The operation performance analysis results indicate that under the optical filtering condition, the electric power and photo-electric efficiency of the PV subsystem are 392.1 W and 30.9%, and the thermal efficiency of the SPVT system is 40.7%. Effects of four factors on the thermal performance of the SPVT system are evaluated, which are the inlet nanofluid flow velocity and temperature, environmental temperature and convection heat transfer coefficient between the nanofluid flow channel and air. The results show that the thermal performance of the SPVT system can be improved by properly increasing the inlet nanofluid flow velocity and environmental temperature or by reducing the inlet nanofluid temperature and convection heat transfer coefficient between the nanofluid flow channel and air. When the inlet nanofluid flow velocity increases from 0.002 m/s to 0.004 m/s, the thermal efficiency of the SPVT system increases from 40.9% to 50.7%, and with the inlet nanofluid temperature increased from 6.0°C to 14.0°C, the thermal efficiency decreases from 48.6% to 45.6%. The results of this paper can provide certain reference for research and development works of solar PVT systems in the future.

System dynamics-multiple the objective optimization model for the coordinated development of urban economy-energy-carbon system

The deepening conflict between human societal progress and efforts to combat climate change necessitates immediate coordination among the Economy-Energy-Carbon (EEC) management. The study applies IPCC accounting methods to compute the historical carbon emissions in the Chengdu-Chongqing economic circle from 2005 to 2021. It assesses the developmental efficiency of various subsystems in the EEC system by employing the rank-sum ratio. Taking a typical city in the region (Chongqing) as a case study, this study integrates System Dynamics (SD) with NSGAIII to develop an EEC multi-objective optimization model. It utilizes the VIKOR model to select the optimal solution. Based on this, the analysis explores the coupled and coordinated state of the EEC system from 2022 to 2030 under the optimal solution mode. Research findings indicate that: (1) The overall carbon emissions exhibit a slight increase, where carbon sources surpass the carbon sink created by land use. (2) Compared to results from other preference-based scenarios, in the scenario where subsystem efficiencies are all optimal, the minimum cumulative carbon emissions amount to 1520.52 million tons, with the economy maintaining a favorable status. Moreover, the overall coupling coordination of the EEC is in a relatively favorable state, and it tends to improve annually. (3) To attain the coordinated development of the EEC system by 2030, the energy structure of the representative city must decrease coal consumption by 26.17%, maintain the construction land ratio below 3.7%, and guarantee forest coverage exceeds 57.77%. This study, utilizing complex system simulations and optimization analyses across various scenarios, offers pertinent recommendations for attaining urban low-carbon development while upholding societal advancement.

Can Green Finance Be a Regulator of “Water–Energy–Food” Synergy? Evidence from the Yangtze River Delta

The synergistic relationship between water, energy, and food faces increasing challenges. Green finance as a policy tool promotes high-quality and efficient development of water, energy, and food subsystems. However, whether it can improve the synergistic relationship of “water–energy–food” (WEF) still needs to be studied. Using the panel data of 38 prefecture-level cities in the Yangtze River Delta (YRD) from 2013 to 2021, and network DEA and panel regression models, we study the impact of green finance on the level of synergy of “water–energy–food”. The results of the study show that green finance can promote the synergy level of “water–energy–food” in the Yangtze River Delta city cluster, which was first inhibited and then promoted from 2013 to 2021. The impacts of green finance on the efficiency of the three subsystems are also characterized by a “U” shape. However, linear impacts show differences, with green finance improving the efficiency of the water subsystem but not the energy and food subsystems. The implementation of China’s national strategies empowers green finance. The digital strategy, the “dual carbon” strategy, and the new urbanization strategy have increased the effectiveness of green finance in contributing to the level of water–energy–food synergy. Regional heterogeneity analysis shows that the promotion effect of green finance mainly exists in non-resource-based cities, non-main grain-producing areas, and non-cities along the South-to-North water diversion route and large cities. Finally, this paper puts forward relevant policy recommendations.

Performance analysis of a compressed air energy storage incorporated with a biomass power generation system

Compressed air energy storage technology is recognized as a promising method to consume renewable energy on a large scale and establish the safe and stable operation of the power grid. To improve the energy efficiency and economic performance of the compressed air energy storage system, this study proposes a design for integrating a compressed air energy storage system with a biomass power generation system. In the energy storage process, the feedwater from the biomass power generation system is used to cool the compressed air in the compressed air energy storage system. In the energy release process, the flue gas from the biomass power generation system is used to heat the compressed air. Besides, the compressed air from the compressed air energy storage system first works in the expander and then goes to the biomass power generation system for combustion. Based on the system simulation, the proposed system is assessed from the energy, exergy, economy, and environment perspectives. The results show that the round-trip efficiency and the energy storage density of the compressed air energy storage subsystem are 84.90 % and 15.91 MJ/m3, respectively. The exergy efficiency of the compressed air energy storage subsystem is 80.46 %, with the highest exergy loss in the throttle valves. The total investment of the compressed air energy storage subsystem is 256.45 k$, and the dynamic payback period and the net present value are 4.20 years and 340.48 k$. Besides, the proposed system’s CO2 emission is 258 kg/GWh. This study provides a new option for enhancing the performance of compressed air energy storage through the system integration.

Model predictive control for optimal dispatch of chillers and thermal energy storage tank in airports

Cost of energy consumption is one of the biggest operational cost for airports, and it is increasing from time to time as airports expand to support growing number of passengers. Various factors affect the energy consumption including efficiency of airport Heating Ventilation and Air conditioning (HVAC) systems, which in turn depends on the efficiency of individual subsystems. In this paper, we present an optimal scheduling method for the central plant system at Dallas Fort Worth airport, involving chillers, pumps, and a thermal energy storage (TES) system. A model predictive control (MPC) problem is formulated to minimize both energy and demand charge costs while satisfying the cooling needs of the airport. The proposed Mixed-Integer Nonlinear Programming (MINLP) formulation includes performance curve based models for chillers and pumps and a simplified state of charge model for TES. The formulation also includes predictions of cooling load and chilled water return temperature. Simulation results for a month in summer show savings around 10% compared to the baseline. Initial recommendations based on insights from simulation results to the manual operation procedures resulted in significant savings. Field test results show a 7% chiller efficiency improvement.

Sustainable efficiency in cities in China—An interaction model among water, energy, and industry

With the inclusion of “Building Inclusive, safe, Resilient and Sustainable Cities and human Settlements” (SDG11) in the United Nations Sustainable Development Goals (SDGS), the movement to promote sustainable development from an urban perspective is growing globally. Many studies examine urban sustainability efficiency from multiple dimensions, but scant attention targets the interaction among various dimensions. This research combines the water-energy-industry subsystem to evaluate the sustainable development performance of 29 provinces in China from 2018 to 2020. The results show that 1) a water system plays an important role in promoting a city's overall sustainable performance. 2) Urban sustainable efficiency has the characteristics of low value aggregation and high value dispersion in space. 3) Regional and sub-system sustainability efficiencies exhibit clear heterogeneity. 4) Rainfall improves the sustainable efficiency of cities, mainly through water systems. 5) The coupling between water and industrial subsystems is better than that between energy and industrial subsystems, and the coupling between the central region subsystem is the best. This paper offers a new perspective for understanding the current state of sustainability in China's provinces and provides more specific suggestions for improving regional sustainability efficiency in the future.

Analysis of coupling characteristics of clean heating systems based on complementary solar, geothermal, and wind energy

In order to overcome the limitations of traditional clean energy utilization methods, this paper proposed an innovative technical solution for a combined heating system that cleverly integrated solar, wind, and geothermal energy to achieve complementarity and synergized among them, thereby ensuring stable and efficient energy utilization. First, a comprehensive mathematical model was developed for the entire heating system, encompassing solar thermal subsystem, geothermal subsystem, wind power generation subsystem, and a second-stage reheating subsystem. Subsequently, Ebsilon simulation software was utilized to cleverly couple these subsystems together, with corresponding boundary conditions set to ensure the overall efficiency and stability of the system. Based on meteorological data and geothermal resource parameters from a typical heating season in Zhengzhou, Henan Province, China, this paper thoroughly analyzed the variations in key performance indicators such as the photothermal conversion efficiency of solar thermal subsystem and the heating capacity of geothermal subsystem. This provided valuable insight for optimizing the design of heating system. The results indicated that during the daylight hours of the heating season, both the photothermal conversion efficiency and the heat supply from the solar thermal subsystem exhibited an increasing trend as solar radiation increased. Among them, the photothermal conversion efficiency peaked at 76.013%, while the maximum heat supply output reached 40.311 kW. When solar direct radiation was relatively weak, the system primarily relied on the heat release process of the thermal storage tank to maintain heating, with a minimum heat supply of 27.268 kW. During nighttime hours of the heating season, the geothermal subsystem dominated the heating process, with a maximum heat supply of 125.556 kW. Additionally, for every 5 °C increased in geothermal water temperature, the heat supply from the geothermal subsystem increased by an average of 6.553 kW, demonstrating excellent heating response performance. Therefore, the integrated clean heating system that combines solar, geothermal, and wind energy not only significantly improves the utilization efficiency of clean energy but also enhances the heating stability of the integrated clean energy coupling system to a certain extent. The clean heating technical solution proposed in the paper had a theoretical total heating capacity of 19 680 kW during the heating season. When converted, this equates to a substitution of 6.9 tons of standard coal, resulting in a reduction of carbon dioxide emissions by 17.94 tons. This demonstrates the considerable cleanliness and environmental benefits of the proposed heating system. This study provides a valuable reference for the engineering application of renewable energy in the field of clean heating.

Reassessment of industrial eco-efficiency in China under the sustainable development goals: A meta two-stage parallel entropy dynamic DDF-DEA model

As the path of industrial eco-efficiency (IEE) needs to be re-examined from a multi-dimensional perspective, this research opens the internal “black box” of China's industrial eco-economic system driven by sustainable development goals (SDGs) and decomposes IEE into industrial production and sustainable development stages. It further divides the industrial production stage into two parallel subsystems of water use efficiency (WUE) and energy efficiency (EE) and derives SDG6 efficiency (SDG6E) and SDG7 efficiency (SDG7E) in the sustainable development stage respectively. The paper proposes a meta two-stage parallel entropy dynamic DDF-DEA model to re-measure IEE of 30 provinces in China from 2015 to 2021, discusses the relationship between overall efficiency and stage efficiency, and by using the Tobit model explores various types of influencing factors by subregion. The results show that the modified DDF-DEA model can explore China's IEE more accurately under SDGs. China's IEE is more stable from 2015 to 2021, with the efficiency value always fluctuating between 0.59 and 0.64, the overall level is low, and there is more room for improvement. There are significant inter-provincial differences in IEE and efficiency inertia. In more than 75% of the provinces SDG7E constrains IEE improvement, while the dynamic evolution of IEE and its subsystem efficiency varies across regions. Environmental regulation is a common factor affecting IEE across the country and in the east, central, and west regions, whereas the level of economic development, openness to the outside world, and urbanization rate are differential factors affecting IEE across the country and in the three major regions. This study offers new perspectives for exploring the path of IEE enhancement and providing empirical references for the collaborative construction of industrial ecological civilization.

Analysis of the Physical Phenomena and Modelling Procedures of Building Heating and Cooling Emission System Energy Losses

An important research issue in assessing the energy performance of buildings concerns the modelling of the interaction between the built environment and the heating/cooling emission systems. Several methods can be used to evaluate the effect of the heating emitter characteristics, including the possible embedment in the building structure, non-uniform space temperature distribution, and the accuracy of the indoor temperature control. Generally, technical standards specify simplified, yet insufficiently validated methods, based on tabulated values. This paper outlines the main simplified procedures for assessing the efficiency of the emission subsystem, with a particular focus on the hydronic systems. It describes the essential datasets required for the analysis and highlights the interaction with phenomena related to the emitter heat loss. The simplified calculation procedures are then methodologically compared with detailed simulation tools, such as EnergyPlus, to identify differences and limitations in the models. The main discrepancies in the procedures and the required input data are highlighted, and possible strategies for improving the simplified methods are presented. A building representative of the European residential building stock is then analysed in the Italian climate using different calculation procedures. The results, in terms of thermal output of the emitter, are then analysed and compared.

Assessment of the level of socio-economic development of the Rostov region based on the balance of regional subsystems

Subject. The conditions determining the balanced development of regional subsystems depend on multiple factors that influence the degree of regional development of a certain region. In today's world, the balanced development of regional subsystems directly affects the level of socio-economic development of the regional economy. Objectives. Justification of a methodological approach to assessing the region’s level of socio-economic development through the prism of the balance of its subsystems (social, environmental, and economic). Methodology. The research methodology is based on a systematic approach, and in this work we used the following: general scientific and special analytical methods: logical analysis, used in the study of methods for assessing the balance of regional development; structural and logical analysis, allowing to organise and clarify the terminology in the conceptual framework of the “balanced development of the region”; generalisation and grouping (while selecting statistical indicators). Economic-mathematical and economic-statistical methods were also used to analyse and assess the relation between indicators, including the method of index correlations. It allows determining the degree of one indicator influencing another and evaluating their correlation. The method of visualisation was used to clearly demonstrate the results of the study and analytical data. It helped to present the obtained results in graphical or diagrammatic form so as to better understand their meaning and make conclusions. Comparative and economic analysis was used to analyse the balance of the region's component subsystems (social, environmental, and economic). Comparative analysis allows determining the differences and similarities between these components and assess their impact on the overall development of the region. Economic analysis identifies economic factors influencing the state of the region and assesses the efficiency of its subsystems’ operation. The method of expert assessment is used to justify a set of indicators and assess the efficiency of regional subsystems’ operation (social, environmental, and economic), which allows obtaining more objective and substantiated data for the analysis and assessment of the region’s activities. Results. The obtained results indicated that the development system of the Rostov region is imperfect, and social, environmental, and economic subsystems were not balanced. The assessment of the balance of regional development showed a low level of economic activity in the region, which was 1.9 points, being below the average value (from 2 to 3 points). This indicator means that the state of the socio-economic system is unstable, therefore, a mechanism must be created to regulate the balance of the target characteristics of the system. This will serve as a fundamental line for future research. Discussion. The obtained results were compared with the conclusions of researchers who assessed the level of socio-economic development of the region in the specified time periods based on an assessment of the balance of regional subsystems and made forecasts regarding the prospects for regional development. Conclusions. The conducted analysis allowed making conclusions on the informative characteristic in the balance of regional development as a result of the influence of economic, social, and environmental factors on the region’s subsystems; the elemental composition of integral indicators for assessing the balance of regional subsystems in particular and regional development in general, including the informative side of assessing the socio-economic development of the region; and features of the methodological approach based on the scoring of regional development indicators.

Design and Thermodynamic Analysis of a Novel Solar CBS-PVT System Using Film-Based Beam Splitting Technology.

An innovative solar concentrating beam splitting photovoltaic thermal (CBS-PVT) system using a half-trough concentrator (HTC) and a film spectrum filter (FSF) is proposed and studied in this study. The FSF used for this system is designed and its average reflectivity and transmissivity are 0.272 and 0.728 for the full spectrum range. Performance evaluation results of the CBS-PVT system reveal the design correctness of the system. When the N-S solar tracking error (STE) rises to 0.15°, the optical efficiency of the entire CSB-PVT system can be kept at 0.8653, showing good adaptable capacity to the STE. The operation feasibility analysis shows that the PV efficiency of the PV subsystem (PVS) is 0.314 and the overall system efficiency overall is 0.26. Parametric analysis results indicate that when the solar thermal collector tube (TCT) operating temperature rises, the total power and overall efficiency of the CSB-PVT system both rise first and then decrease. When the TCT temperature is about 225 °C, the CBS-PVT system reaches its maximum output power of 1003.6 W and the maximum overall efficiency of 0.261. When the PV cell module (PVCM) temperature increases, the total power and overall efficiency of the CBS-PVT system decrease linearly. When the PVCM temperature rises to 50 °C, the two parameters decrease to 952.9 W and 0.248.

Performance Improvement of a Direct Carbon Fuel Cell through an Irreversible Vacuum Thermionic Generator

A novel hybrid system consisting of a direct carbon fuel cell (DCFC), a thermionic generator (TIG), and a regenerator is developed to recover the exhaust heat from the fuel cell. Expressions for the power output and efficiency of subsystems and the hybrid system are derived. Based on the energy balance equation, the area matching problem between the DCFC and the TIG is discussed and solved. By considering the main irreversibilities, the influences of the DCFC’s current density and the TIG’s voltage on the performance of the hybrid system are revealed. The maximum power output density and the corresponding efficiency of the hybrid system are, respectively, equal to 379 W/m2 and 36%. To enhance the maximum power density of the single DCFC, the optimal regions of the main parameters are determined.

Energy, exergy, economic and environmental assessment of solar photovoltaic direct-drive refrigeration system for electronic device cooling

The cooling systems dissipate the high heat flux of miniaturized and highly integrated electronic devices in order to keep the temperature of the electronic devices within acceptable limits. In this paper, a solar photovoltaic direct-drive refrigeration system with an embedded direct evaporator was designed and tested under different conditions. An energy, exergy, economic and environmental analysis was used to investigate and assess the performance of the presented system based on the experimental data. The results indicate that the highest COP of the proposed system is 8.5 at the compressor speed of 4350 rpm. When the average solar radiation intensity is 776.5 W/m2, the photovoltaic cells generate 1.81 kW h of electricity, where 24.9% of electricity is consumed on the proposed system. The PV cells and compressor need be improved in term of their large exergy destruction (1059.4 W, 86.3 W) and low exergy efficiency (24.9%, 26.8%). The exergy performance of equipment and VCR subsystem is more sensitive to the compressor speed than the heating power. The exergy efficiency of the VCR subsystem reduced by 48.4 %. The payback period is 2.2 years, and the reductions of CO2, SO2 and NOx emissions are 395.1 kg, 11.9 kg and 5.9 kg, respectively.

Cryogenic energy storage characteristics in cascaded packed beds

Energy storage is a key technology required to utilize intermittent or variable renewable energy sources such as wind or solar energy. Liquid air energy storage (LAES) technology has important research value because of its advantages of high energy density and free construction from regional restrictions, and the high efficiency and stable operation of the cold thermal storage subsystem is of great significance for LAES application. Therefore, this paper experimentally studies the operating characteristics of the cryogenic energy storage device in the LAES system. By using a cascaded packed bed to store cryogenic energy in different temperature ranges, different flow rates of fluids with different specific heat capacities can be distributed. Hence, the temperature difference between the heat transfer fluids can be reduced, thereby improving the energy and exergy efficiencies. In this study, the experimental system and operating procedures are detailed herein. The pressure drop correlation of the packed beds under the combined influence of density gradient and frictional losses is obtained. The variations in the temperature fields in the charging and discharging processes are revealed, and the energy and exergy efficiencies are calculated to be 93.13 % and 85.62 % with 0.25-h preservation, and 90.46 % and 76.98 % with 4-h preservation, respectively. The exergy loss mechanism of the packed beds during the holding process is revealed. It is found that axial thermal conduction exergy loss accounts for 21.65 % and 7.04 % of the total loss in the packed beds in the full- and low-temperature regions, respectively.

Energy, exergy, and economic analysis of a solar photovoltaic and photothermal hybrid energy supply system for residential buildings

In this study, a dynamic simulation model is developed based on the mathematical model of a solar photovoltaic and photothermal hybrid energy supply system (PV-PTHS) employing the TRNSYS simulation software. The corresponding operational control strategy for the PV-PTHS is proposed. The impact of different PV and PT areas on the performance and the energy and exergy flows of the PV-PTHS throughout the year are analyzed using simulations. In addition, the dynamic performance of the PV-PTHS on typical days is reported during the heating period, transition period, and cooling period. Also, the monthly exergy performance of the system is comprehensively analyzed. Finally, the cost-effectiveness and energy savings of the PV-PTHS are reported and compared against the single PT and single PV systems. The results show that the energy loss of the PV cells is the highest, followed by the solar collector. However, the exergy efficiency of the collector is lower than that of the PV cell in the PV-PTHS, and the low exergy efficiency of the collector results in a lower exergy efficiency of the PT subsystem (PTS). Considering similar initial investments, the PV power supply ratio of the PV-PTHS is the highest in areas with a large heating load, such as Nagqu and Yinchuan. The heat supply ratio and the cost-effectiveness of the signal PT system are the best. Overall, the proposed PV-PTHS yields the highest primary energy saving ratio (PESR) and the best cost-effectiveness for areas with a small heating load, such as Wuhan and Fuzhou.

Thermoeconomic Analysis of Concentrated Solar Power Plants Based on Supercritical Power Cycles

Solar thermal power plants are an alternative for the future energy context, allowing for a progressive decarbonisation of electricity production. One way to improve the performance of such plants is the use of supercritical CO2 power cycles. This article focuses on a solar thermal plant with a central solar receiver coupled to a partial cooling cycle, and it conducts a comparative study from both a thermal and economic perspective with the aim of optimising the configuration of the receiver. The design of the solar receiver is based on a radial configuration, with absorber panels converging on the tower axis; the absorber panels are compact structures through which a pressurised gas circulates. The different configurations analysed keep a constant thermal power provided by the receiver while varying the number of panels and their dimensions. The results demonstrate the existence of an optimal configuration that maximises the exergy efficiency of the solar subsystem, taking into account both the receiver exergy efficiency and the heliostat field optical efficiency. The evolution of electricity generation cost follows a similar trend to that of the exergy efficiency, exhibiting minimum values when this efficiency is at its maximum.

Development and Research of a Two-Contour Solar System in the Lorawan Network

This article examines the mechanism for researching and improving the energy efficiency of a solar water heating system (SWH) in a building located in Kazakhstan. In this paper, we use data collected from LoRaWAN to obtain information about various environmental and operational aspects of the system under consideration, which determine the possibilities for improving the efficiency of various SWH subsystems and develop management strategies for the effective operation of the entire system. With the help of data collected by IoT, such as water consumption, the schedule of the heat pump and water pump, the availability of solar energy and electricity consumption, we conduct a comprehensive energy audit to analyze the efficiency of subsystems, as well as the performance of the system as a whole. Based on the findings obtained from the data analysis, appropriate management strategies are developed for various subsystems in order to increase the efficiency of the entire system and reduce the operating costs of SWH.

Dynamic Resource Optimization for Energy-Efficient 6G-IoT Ecosystems

The problem of energy optimization for Internet of Things (IoT) devices is crucial for two reasons. Firstly, IoT devices powered by renewable energy sources have limited energy resources. Secondly, the aggregate energy requirement for these small and low-powered devices is translated into significant energy consumption. Existing works show that a significant portion of an IoT device’s energy is consumed by the radio sub-system. With the emerging sixth generation (6G), energy efficiency is a major design criterion for significantly increasing the IoT network’s performance. To solve this issue, this paper focuses on maximizing the energy efficiency of the radio sub-system. In wireless communications, the channel plays a major role in determining energy requirements. Therefore, a mixed-integer nonlinear programming problem is formulated to jointly optimize power allocation, sub-channel allocation, user selection, and the activated remote radio units (RRUs) in a combinatorial approach according to the channel conditions. Although it is an NP-hard problem, the optimization problem is solved through fractional programming properties, converting it into an equivalent tractable and parametric form. The resulting problem is then solved optimally by using the Lagrangian decomposition method and an improved Kuhn–Munkres algorithm. The results show that the proposed technique significantly improves the energy efficiency of IoT systems as compared to the state-of-the-art work.

Inferring Subsystem Efficiencies in Bipartite Molecular Machines.

Molecular machines composed of coupled subsystems transduce free energy between different external reservoirs, in the process internally transducing energy and information. While subsystem efficiencies of these molecular machines have been measured in isolation, less is known about how they behave in their natural setting when coupled together and acting in concert. Here, we derive upper and lower bounds on the subsystem efficiencies of a bipartite molecular machine. We demonstrate their utility by estimating the efficiencies of the F_{o} and F_{1} subunits of ATP synthase and that of kinesin pulling a diffusive cargo.