Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally,but the lack of studies of real environmental conditions on these absorbers is felt...Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally,but the lack of studies of real environmental conditions on these absorbers is felt.The present work investigates the effect of viscoelasticity on the stability and bifurcations of a system attached to a nonlinear energy sink(NES).In this paper,the Burgers model is assumed for the viscoelasticity in an NES,and a linear oscillator system is considered for investigating the instabilities and bifurcations.The equations of motion of the coupled system are solved by using the harmonic balance and pseudo-arc-length continuation methods.The results show that the viscoelasticity affects the frequency intervals of the Hopf and saddle-node branches,and by increasing the stiffness parameters of the viscoelasticity,the conditions of these branches occur in larger ranges of the external force amplitudes,and also reduce the frequency range of the branches.In addition,increasing the viscoelastic damping parameter has the potential to completely eliminate the instability of the system and gradually reduce the amplitude of the jump phenomenon.展开更多
The cubic or third-power(TP)nonlinear energy sink(NES)has been proven to be an effective method for vibration suppression,owing to the occurrence of targeted energy transfer(TET).However,TET is unable to be triggered ...The cubic or third-power(TP)nonlinear energy sink(NES)has been proven to be an effective method for vibration suppression,owing to the occurrence of targeted energy transfer(TET).However,TET is unable to be triggered by the low initial energy input,and thus the TP NES would get failed under low-amplitude vibration.To resolve this issue,a new type of NES with fractional nonlinearity,e.g.,one-third-power(OTP)nonlinearity,is proposed.The dynamic behaviors of a linear oscillator(LO)with an OTP NES are investigated numerically,and then both the TET feature and the vibration attenuation performance are evaluated.Moreover,an analogy circuit is established,and the circuit simulations are carried out to verify the design concept of the OTP NES.It is found that the threshold for TET of the OTP NES is two orders of magnitude smaller than that of the TP NES.The parametric analysis shows that a heavier mass or a lower stiffness coefficient of the NES is beneficial to the occurrence of TET in the OTP NES system.Additionally,significant energy transfer is usually accompanied with efficient energy dissipation.Consequently,the OTP NES can realize TET under low initial input energy,which should be a promising approach for micro-vibration suppression.展开更多
The apparent heat sources (<Q l>) and moisture sinks (<Q 2>) are calculated based on the reanalyzed data of the South China Sea Monsoon Experiment (SCSMEX) from May I to August 31, 1998. It is found that t...The apparent heat sources (<Q l>) and moisture sinks (<Q 2>) are calculated based on the reanalyzed data of the South China Sea Monsoon Experiment (SCSMEX) from May I to August 31, 1998. It is found that the formation and distribution of the atmospheric heat sources are important for the monsoon onset. The earlier onset of the SCS monsoon is the result of enduring atmospheric heating in the Indo-china Peninsula and South China areas. The atmospheric heating firstly appears in the indo-China Peninsula area and the sensible heat is the major one. The 30is0 day periodic oscillation of atmospheric heat sources between the SCS area and the western Pacificwarm pool has a reverse phase distribution before the middle of July and the low frequency oscillation of heat sources in SCS area has an obvious longitudinal propagation. The 30-50 day low frequency oscillation has vital modificatory effects on the summer monsoon evolution during 1998.展开更多
The measurement of atmospheric O_(2)concentrations and related oxygen budget have been used to estimate terrestrial and oceanic carbon uptake.However,a discrepancy remains in assessments of O_(2)exchange between ocean...The measurement of atmospheric O_(2)concentrations and related oxygen budget have been used to estimate terrestrial and oceanic carbon uptake.However,a discrepancy remains in assessments of O_(2)exchange between ocean and atmosphere(i.e.air-sea O_(2)flux),which is one of the major contributors to uncertainties in the O_(2)-based estimations of the carbon uptake.Here,we explore the variability of air-sea O_(2)flux with the use of outputs from Coupled Model Intercomparison Project phase 6(CMIP6).The simulated air-sea O_(2)flux exhibits an obvious warming-induced upward trend(~1.49 Tmol yr−2)since the mid-1980s,accompanied by a strong decadal variability dominated by oceanic climate modes.We subsequently revise the O_(2)-based carbon uptakes in response to this changing air-sea O_(2)flux.Our results show that,for the 1990−2000 period,the averaged net ocean and land sinks are 2.10±0.43 and 1.14±0.52 GtC yr−1 respectively,overall consistent with estimates derived by the Global Carbon Project(GCP).An enhanced carbon uptake is found in both land and ocean after year 2000,reflecting the modification of carbon cycle under human activities.Results derived from CMIP5 simulations also investigated in the study allow for comparisons from which we can see the vital importance of oxygen dataset on carbon uptake estimations.展开更多
One of the most significant considerations in the design of a heat sink is thermal management due to increasing thermal flux and miniature in size.These heat sinks utilize plate or pin fins depending upon the required...One of the most significant considerations in the design of a heat sink is thermal management due to increasing thermal flux and miniature in size.These heat sinks utilize plate or pin fins depending upon the required heat dissipation rate.They are designed to optimize overall performance.Elliptical pin fin heat sinks enhance heat transfer rates and reduce the pumping power.In this study,the Firefly Algorithm is implemented to optimize heat sinks with elliptical pin-fins.The pin-fins are arranged in an inline fashion.The nature-inspired metaheuristic algorithm performs powerfully and efficiently in solving numerical global optimization problems.Based on mass,energy,and entropy balance,three models are developed for thermal resistance,hydraulic resistance,and entropy generation rate in the heat sink.The major axis is used as the characteristic length,and the maximum velocity is used as the reference velocity.The entropy generation rate comprises the combined effect of thermal resistance and pressure drop.The total EGR is minimized by utilizing the firefly algorithm.The optimization model utilizes analytical/empirical correlations for the heat transfer coefficients and friction factors.It is shown that both thermal resistance and pressure drop can be simultaneously optimized using this algorithm.It is demonstrated that the performance of FFA is much better than PPA.展开更多
Forest carbon monitoring and reporting are critical for informing global climate change assessment. The regional estimates of forest carbon attached greater attention, to assess the role of forest in carbon mitigation...Forest carbon monitoring and reporting are critical for informing global climate change assessment. The regional estimates of forest carbon attached greater attention, to assess the role of forest in carbon mitigation. Here using field inventory, we examined the carbon sink and mitigation potential of monospecific Deodar forest in the Kumrat valley, of Hindu Kush Himalaya, Region of Pakistan, at a different elevation. The elevation of monospecific Deodar forest ranges from 2300 to 2700 m (a.s.l). We divided the forest into three elevation classes (that is 2300 - 2400 m (EI) 2400 - 2500 m (EII) and 2500 - 2700 m (EIII) a.s.l respectively). In each elevation class, we laid out 09 sample plots (33*33 m2) for measuring carbon values in living tree biomass (LT), soil (SC), litter, dead wood, cone (LDWC) and understory vegetation (USV). Our results showed that the carbon density at EI was 432.37 ± 277.96 Mg·C-1, while the carbon density at EII and EIII was 668.35 ± 323.94 and 1016.79 ± 542.99 Mg·C-1 respectively. Our finding revealed that the carbon mitigation potential of the forest increases with increasing elevation. Among the different elevation classes, EIII stored significantly higher carbon due to the dominance of mature, old age, larger trees, and the minimum anthropogenic disturbance, whereas EI stored statistically lower carbon because of maximum anthropogenic disturbance, which resulted in the removal of mature and over-mature trees. Furthermore, our correlation analysis between tree height and carbon stock and basal area and LT carbon, underlines that the basal area is the stronger predictor of LT carbon estimation than height. Overall our results highlight that deodar forest stored 716.94 ± 462.06 Mg?C·ha-1. However, the rehabilitation, preservation and sustainable management of disturb forest located at a lower elevation could considerably improve carbon mitigation potential.展开更多
We present a micro-Pirani vacuum gauge using the low-resistivity monocrystal silicon as the heaters and heat sinks fabricated by the post complementary metal oxide semiconductor(CMOS) microelectromechanical system(MEM...We present a micro-Pirani vacuum gauge using the low-resistivity monocrystal silicon as the heaters and heat sinks fabricated by the post complementary metal oxide semiconductor(CMOS) microelectromechanical system(MEMS) process. The metal interconnection of the device is fabricated by a 0.5 μm standard CMOS process on8-inch silicon wafer. Then, a SiO_2-Si low-temperature fusion bonding is developed to bond the CMOS wafer and the MEMS wafer, with the electrical connection realized by the tungsten through silicon via process. Waferlevel AlGe eutectic bonding is adopted to package the Pirani gauge in a non-hermetic cavity to protect the gauge from being damaged or contaminated in the dicing and assembling process, and to make it suitable for actual applications. To increase the accuracy of the test and restrain negative influence of temperature drift, the Wheatstone bridge structure is introduced. The test results show that before capping, the gauge has an average sensitivity of 1.04×10~4 K·W^(-1)Torr^(-1) in dynamic range of 0.01-20 Torr. After capping, the sensitivity of the gauge does not decrease but increases to 1.12×10~4 K·W^(-1)Torr^(-1).展开更多
Wireless sensor networks applications involve a position of inaccessible metropolitan vicinity en-closed by wireless sensor nodes (WSNs)-monitors environmental parameters like battle field surveillance, home applicati...Wireless sensor networks applications involve a position of inaccessible metropolitan vicinity en-closed by wireless sensor nodes (WSNs)-monitors environmental parameters like battle field surveillance, home applications like fire alarm, health monitoring, etc. Energy plays a vital role in Wireless sensor networks. So, we have to concentrate more on balanced energy consumption for maximizing the network lifetime. Minimizing the whole network overhead and vigor disbursement coupled with the multi-hop data reclamation process that ensuring balanced energy consumption among SNs which results in prolonged network lifetime. This can be achieved by forwarding the sensed data to their cluster heads and then filtering the data before sending it to their tryst nodes, which is located in proximity to MS’s trajectory. Sleep and awakening of nodes periodically helps to retain their energy for some more time. The events occurring in any part of the network should be identified by the nodes, while arrangements sleep and active among the nodes. (i.e.) the nodes should be scheduled to sleep, so that the outstanding nodes can take care of the whole network. The eXtensible Randomized Matrix Arithmetic Coding (XRMAC) Technique has been used to enhance the security among all the nodes in the network. Simulation results show that our Proposed Scheme can have better Lifetime, improved throughput, reduced delay compared to other existing methods.展开更多
Wireless Sensor Networks(WSNs)are usually formed with many tiny sensors which are randomly deployed within sensing field for target monitoring.These sensors can transmit their monitored data to the sink in a multi-hop...Wireless Sensor Networks(WSNs)are usually formed with many tiny sensors which are randomly deployed within sensing field for target monitoring.These sensors can transmit their monitored data to the sink in a multi-hop communication manner.However,the‘hot spots’problem will be caused since nodes near sink will consume more energy during forwarding.Recently,mobile sink based technology provides an alternative solution for the long-distance communication and sensor nodes only need to use single hop communication to the mobile sink during data transmission.Even though it is difficult to consider many network metrics such as sensor position,residual energy and coverage rate etc.,it is still very important to schedule a reasonable moving trajectory for the mobile sink.In this paper,a novel trajectory scheduling method based on coverage rate for multiple mobile sinks(TSCR-M)is presented especially for large-scale WSNs.An improved particle swarm optimization(PSO)combined with mutation operator is introduced to search the parking positions with optimal coverage rate.Then the genetic algorithm(GA)is adopted to schedule the moving trajectory for multiple mobile sinks.Extensive simulations are performed to validate the performance of our proposed method.展开更多
Global warming and climate change are the most important ecological issues of our time. The most well-known factor in this phenomenon is the redundancy of carbon dioxide in the atmosphere. Over the past 50 years the a...Global warming and climate change are the most important ecological issues of our time. The most well-known factor in this phenomenon is the redundancy of carbon dioxide in the atmosphere. Over the past 50 years the amount of residual CO2 in the atmosphere has risen from 40% to 45%. Reducing CO2 redundancy requires precise knowledge of the gas sources and sinks throughout the atmosphere. Despite having a leading role in residual gas levels of atmosphere, the diagnosis and types of changes of absorbing carbon dioxide are very much in doubt. Atmospheric measurements of CO2 concentrations are highly precise and provide a reliable measure of increase of CO2 in the atmosphere every year but they do not lead to the location of sources and sinks. Studies about understanding CO2 cycles began mainly around 1990 and most of these studies have been focused on non-spatial analysis. By ignoring the spatial effects, an important property such as closeness (adjacent) has been disregarded. The emission sources of gas are stronger than their sink sources i.e., whenever a sink is adjacent to a strong emission source, the measurements will show a massive existence of CO2 gas in that region although there exists a fine CO2?gas sink at below. Using the global measurements of CO2 and applying spatial analysis approach to “Leave One Out” method, our studies reveal the most probable spots of CO2 sources and sinks and that Negev Desert in Middle East is a distinguished CO2 sink region.展开更多
Today global warming has become one of the most important concerns of environmental science. The redundancy of greenhouse gases in the atmosphere is known as a major factor in this phenomenon. These gases contain wate...Today global warming has become one of the most important concerns of environmental science. The redundancy of greenhouse gases in the atmosphere is known as a major factor in this phenomenon. These gases contain water vapor, carbon dioxide, methane, nitrous oxide, and ozone. The CO2?gas is one of their most effective among these gases. According to scientific warnings, the amount of CO2?gases in the atmosphere has increased by 40% to 45% over the last 50 years. Reducing the abundant gas in the atmosphere requires a good knowledge of related factors involved, including sources that emit gases into the atmosphere and sinks that absorb the gas from the atmosphere. The amount of CO2?gas in the atmosphere has been accurately measured in previous years with great certainty. But the predicted values of emissions from sources and removals by sinks have large ambiguities. As studies show, even the computed residuals trends (which is obtained by subtracting the amounts of sinks from sources) strongly disagree with the trends of the existence of CO2?in the atmosphere. This study as a preliminary review, proposes a method to identify the locations of sources and sinks of carbon dioxide using global statistical information and adding spatial analysis approaches. By applying this method to the data observed from 2000 to 2011 and the extraction of likely sources and sinks, the region of the Black Sea, near Romania recognized as one of the strong points issued and Bukit Kototabang near Indonesia acknowledged as an Impressive CO2?absorption zone.展开更多
Given a wireless sensor network (WSN) in which a mobile sink is used to collect data from the sensor nodes, this paper addresses the problem of selecting a set of stop points that results in low energy usage by the se...Given a wireless sensor network (WSN) in which a mobile sink is used to collect data from the sensor nodes, this paper addresses the problem of selecting a set of stop points that results in low energy usage by the sensor nodes. This paper assumes an approach in which a mobile sink travels along a fixed path and uses a stop-and-collect protocol since this has previously been shown to be an efficient WSN data collection method. The problem of selecting an optimal set of stop points is shown to be an NP-hard problem. Then, an Integer Linear Programming (ILP) formulation is used to derive an optimal algorithm that can be used for small problem instances. Next, a polynomial-time Tabu-search-based heuristic algorithm is proposed. Simulations are used to compare the energy consumption values, computation times and expected network lifetimes when using the optimal ILP algorithm, the proposed heuristic algorithm and several other possible heuristic algorithms. The results show that the proposed heuristic algorithm results in near-optimal energy usage values with low computation times, thereby making it suitable for large-sized WSNs.展开更多
The hybrid manifold micro-pin-fin(MMPF)heat sink combined nozzle jets is an option for large-scale integrated circuits(LSI).The demond for uniform and ultra-high heat flux removal by MMPF heat sink has not been adequa...The hybrid manifold micro-pin-fin(MMPF)heat sink combined nozzle jets is an option for large-scale integrated circuits(LSI).The demond for uniform and ultra-high heat flux removal by MMPF heat sink has not been adequately investigated.This work aims to solve the problem of fluid organization.The proposed basic tiling topologies,including square,regular hexagon,30°rhombus,and 60°rhombus topologies,provide different organized fluid flows and heat transfer patterns.The present study focuses on comparing these topologies according to independent porous medium parameters,such as nozzle pore size D_(Z),flow pore size D_(X,Y),and porosityε.The results show that the square topology achieves the smallest total thermal resistance R_(tot)value of0.0975×10^(-4)K m^2/W,while the hexagon topology achieved the highest value of COP/?T,which was 2033.9 K^(-1).According to the sensitivity analysis results,the optimal total thermal resistance can be obtained by balancing the influences of nozzle pore size,flow pore size,and porosity.The optimal pressure drop can be obtained by maximizing the porosity.展开更多
In this paper,the multi-objective optimization of wavy microchannel heat sinks is performed by combining numerical calculation,prediction algorithm and genetic algorithm.In numerical calculation,the fluid-solid conjug...In this paper,the multi-objective optimization of wavy microchannel heat sinks is performed by combining numerical calculation,prediction algorithm and genetic algorithm.In numerical calculation,the fluid-solid conjugate heat transfer of heat sinks with different parameters are simulated in Fluent.On this basis,the vari-able parameters and objective parameters are used to complete the training of neural network model,which aims to achieve accurate prediction of objective parameters.Finally,the multi-objective genetic algorithm is applied to find the Pareto front according to different requirements on the foundation of the prediction model.Results show that the coefficient of determination of the neural network models are all greater than 0.85,which proves that the prediction model has a high accuracy.The Pareto fronts are obtained by non-dominated sorting genetic algorithm(NSGA-II)with different objective parameters and they reveal that the channel with the optimal performance corresponds to a larger channel width or Reynolds number.In addition,it is also found the dimensionless temperature difference is correlated with Nusselt number.展开更多
1.Introduction Carbon neutrality have become a consensus for all of humanity[1,2].As of April,2023,132 countries have announced carbon neutrality targets[3].To achieve carbon neutrality,efforts need to be made from mu...1.Introduction Carbon neutrality have become a consensus for all of humanity[1,2].As of April,2023,132 countries have announced carbon neutrality targets[3].To achieve carbon neutrality,efforts need to be made from multiple aspects,including decarbonization of the power sector[4,5],electrification of the end-use sectors[6,7],and greening of other industries[8].Ecological carbon sinks play a unique role in these strategies to offset hard-to-reduce greenhouse gas(GHG)emissions by reabsorbing or storing carbon that has already been emitted.展开更多
With recent advances in power electronic packaging technologies,liquid-cooled ceramic heat sinks have been considered as a promising solution for further improving the performance of power electronic devices.In this s...With recent advances in power electronic packaging technologies,liquid-cooled ceramic heat sinks have been considered as a promising solution for further improving the performance of power electronic devices.In this study,several aluminum oxide heat sinks were fabricated and tested using the digital light processing-based ad-ditive manufacturing method,to verify their practical performance.The results showed that the complex cooling structures inside the heat sinks can be completely formed and exhibited high surface quality.The experimental thermal and hydraulic performances of the heat sinks were consistent with the numerically modeled predictions.Furthermore,by exploiting the advantages of additive manufacturing,a direct manifold microchannel(MMC)configuration was designed to reduce the vertical flow of the traditional MMC configuration and achieve an im-proved cooling efficiency.At a constant volumetric flow rate of 1 L/min,the direct MMC configuration achieved a 19.8%reduction in pressure drop and an 11.8%reduction in thermal resistance,as well as a more uniform temperature distribution.展开更多
基金financial support from K.N.Toosi University of Technology,Tehran,Iran。
文摘Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally,but the lack of studies of real environmental conditions on these absorbers is felt.The present work investigates the effect of viscoelasticity on the stability and bifurcations of a system attached to a nonlinear energy sink(NES).In this paper,the Burgers model is assumed for the viscoelasticity in an NES,and a linear oscillator system is considered for investigating the instabilities and bifurcations.The equations of motion of the coupled system are solved by using the harmonic balance and pseudo-arc-length continuation methods.The results show that the viscoelasticity affects the frequency intervals of the Hopf and saddle-node branches,and by increasing the stiffness parameters of the viscoelasticity,the conditions of these branches occur in larger ranges of the external force amplitudes,and also reduce the frequency range of the branches.In addition,increasing the viscoelastic damping parameter has the potential to completely eliminate the instability of the system and gradually reduce the amplitude of the jump phenomenon.
基金Project supported by the National Natural Science Foundation of China(Nos.12122206,11972152,12002122)the Natural Science Foundation of Hunan Province of China(No.2021JJ40092)the Natural Science Foundation of Chongqing of China(No.cstc2021jcyj-msxmX0461)。
文摘The cubic or third-power(TP)nonlinear energy sink(NES)has been proven to be an effective method for vibration suppression,owing to the occurrence of targeted energy transfer(TET).However,TET is unable to be triggered by the low initial energy input,and thus the TP NES would get failed under low-amplitude vibration.To resolve this issue,a new type of NES with fractional nonlinearity,e.g.,one-third-power(OTP)nonlinearity,is proposed.The dynamic behaviors of a linear oscillator(LO)with an OTP NES are investigated numerically,and then both the TET feature and the vibration attenuation performance are evaluated.Moreover,an analogy circuit is established,and the circuit simulations are carried out to verify the design concept of the OTP NES.It is found that the threshold for TET of the OTP NES is two orders of magnitude smaller than that of the TP NES.The parametric analysis shows that a heavier mass or a lower stiffness coefficient of the NES is beneficial to the occurrence of TET in the OTP NES system.Additionally,significant energy transfer is usually accompanied with efficient energy dissipation.Consequently,the OTP NES can realize TET under low initial input energy,which should be a promising approach for micro-vibration suppression.
基金National Key Project of Fundamental Research u SCSMEX" the Research Fund for the Doctoral Program of Higher Education:" Stud
文摘The apparent heat sources (<Q l>) and moisture sinks (<Q 2>) are calculated based on the reanalyzed data of the South China Sea Monsoon Experiment (SCSMEX) from May I to August 31, 1998. It is found that the formation and distribution of the atmospheric heat sources are important for the monsoon onset. The earlier onset of the SCS monsoon is the result of enduring atmospheric heating in the Indo-china Peninsula and South China areas. The atmospheric heating firstly appears in the indo-China Peninsula area and the sensible heat is the major one. The 30is0 day periodic oscillation of atmospheric heat sources between the SCS area and the western Pacificwarm pool has a reverse phase distribution before the middle of July and the low frequency oscillation of heat sources in SCS area has an obvious longitudinal propagation. The 30-50 day low frequency oscillation has vital modificatory effects on the summer monsoon evolution during 1998.
基金the World Climate Recruitment Programme’s (WCRP) Working Group on Coupled Modelling (WGCM)the Global Organization for Earth System Science Portals (GO-ESSP)+2 种基金jointly supported by the National Science Foundation of China (Grant Nos. 41991231, 91937302)the China 111 project (Grant No. B13045)supported by Supercomputing Center of Lanzhou University
文摘The measurement of atmospheric O_(2)concentrations and related oxygen budget have been used to estimate terrestrial and oceanic carbon uptake.However,a discrepancy remains in assessments of O_(2)exchange between ocean and atmosphere(i.e.air-sea O_(2)flux),which is one of the major contributors to uncertainties in the O_(2)-based estimations of the carbon uptake.Here,we explore the variability of air-sea O_(2)flux with the use of outputs from Coupled Model Intercomparison Project phase 6(CMIP6).The simulated air-sea O_(2)flux exhibits an obvious warming-induced upward trend(~1.49 Tmol yr−2)since the mid-1980s,accompanied by a strong decadal variability dominated by oceanic climate modes.We subsequently revise the O_(2)-based carbon uptakes in response to this changing air-sea O_(2)flux.Our results show that,for the 1990−2000 period,the averaged net ocean and land sinks are 2.10±0.43 and 1.14±0.52 GtC yr−1 respectively,overall consistent with estimates derived by the Global Carbon Project(GCP).An enhanced carbon uptake is found in both land and ocean after year 2000,reflecting the modification of carbon cycle under human activities.Results derived from CMIP5 simulations also investigated in the study allow for comparisons from which we can see the vital importance of oxygen dataset on carbon uptake estimations.
基金This research is supported by the Deanship of Scientific Research/Saudi Electronic University[Research Number:7638-HS-2019-1-1-S].Initials of authors who received the grant:N.N.HamadnehW.A.Khan.
文摘One of the most significant considerations in the design of a heat sink is thermal management due to increasing thermal flux and miniature in size.These heat sinks utilize plate or pin fins depending upon the required heat dissipation rate.They are designed to optimize overall performance.Elliptical pin fin heat sinks enhance heat transfer rates and reduce the pumping power.In this study,the Firefly Algorithm is implemented to optimize heat sinks with elliptical pin-fins.The pin-fins are arranged in an inline fashion.The nature-inspired metaheuristic algorithm performs powerfully and efficiently in solving numerical global optimization problems.Based on mass,energy,and entropy balance,three models are developed for thermal resistance,hydraulic resistance,and entropy generation rate in the heat sink.The major axis is used as the characteristic length,and the maximum velocity is used as the reference velocity.The entropy generation rate comprises the combined effect of thermal resistance and pressure drop.The total EGR is minimized by utilizing the firefly algorithm.The optimization model utilizes analytical/empirical correlations for the heat transfer coefficients and friction factors.It is shown that both thermal resistance and pressure drop can be simultaneously optimized using this algorithm.It is demonstrated that the performance of FFA is much better than PPA.
文摘Forest carbon monitoring and reporting are critical for informing global climate change assessment. The regional estimates of forest carbon attached greater attention, to assess the role of forest in carbon mitigation. Here using field inventory, we examined the carbon sink and mitigation potential of monospecific Deodar forest in the Kumrat valley, of Hindu Kush Himalaya, Region of Pakistan, at a different elevation. The elevation of monospecific Deodar forest ranges from 2300 to 2700 m (a.s.l). We divided the forest into three elevation classes (that is 2300 - 2400 m (EI) 2400 - 2500 m (EII) and 2500 - 2700 m (EIII) a.s.l respectively). In each elevation class, we laid out 09 sample plots (33*33 m2) for measuring carbon values in living tree biomass (LT), soil (SC), litter, dead wood, cone (LDWC) and understory vegetation (USV). Our results showed that the carbon density at EI was 432.37 ± 277.96 Mg·C-1, while the carbon density at EII and EIII was 668.35 ± 323.94 and 1016.79 ± 542.99 Mg·C-1 respectively. Our finding revealed that the carbon mitigation potential of the forest increases with increasing elevation. Among the different elevation classes, EIII stored significantly higher carbon due to the dominance of mature, old age, larger trees, and the minimum anthropogenic disturbance, whereas EI stored statistically lower carbon because of maximum anthropogenic disturbance, which resulted in the removal of mature and over-mature trees. Furthermore, our correlation analysis between tree height and carbon stock and basal area and LT carbon, underlines that the basal area is the stronger predictor of LT carbon estimation than height. Overall our results highlight that deodar forest stored 716.94 ± 462.06 Mg?C·ha-1. However, the rehabilitation, preservation and sustainable management of disturb forest located at a lower elevation could considerably improve carbon mitigation potential.
基金Supported by the National High Technology Research and Development Program of China under Grant No 2015AA042602
文摘We present a micro-Pirani vacuum gauge using the low-resistivity monocrystal silicon as the heaters and heat sinks fabricated by the post complementary metal oxide semiconductor(CMOS) microelectromechanical system(MEMS) process. The metal interconnection of the device is fabricated by a 0.5 μm standard CMOS process on8-inch silicon wafer. Then, a SiO_2-Si low-temperature fusion bonding is developed to bond the CMOS wafer and the MEMS wafer, with the electrical connection realized by the tungsten through silicon via process. Waferlevel AlGe eutectic bonding is adopted to package the Pirani gauge in a non-hermetic cavity to protect the gauge from being damaged or contaminated in the dicing and assembling process, and to make it suitable for actual applications. To increase the accuracy of the test and restrain negative influence of temperature drift, the Wheatstone bridge structure is introduced. The test results show that before capping, the gauge has an average sensitivity of 1.04×10~4 K·W^(-1)Torr^(-1) in dynamic range of 0.01-20 Torr. After capping, the sensitivity of the gauge does not decrease but increases to 1.12×10~4 K·W^(-1)Torr^(-1).
文摘Wireless sensor networks applications involve a position of inaccessible metropolitan vicinity en-closed by wireless sensor nodes (WSNs)-monitors environmental parameters like battle field surveillance, home applications like fire alarm, health monitoring, etc. Energy plays a vital role in Wireless sensor networks. So, we have to concentrate more on balanced energy consumption for maximizing the network lifetime. Minimizing the whole network overhead and vigor disbursement coupled with the multi-hop data reclamation process that ensuring balanced energy consumption among SNs which results in prolonged network lifetime. This can be achieved by forwarding the sensed data to their cluster heads and then filtering the data before sending it to their tryst nodes, which is located in proximity to MS’s trajectory. Sleep and awakening of nodes periodically helps to retain their energy for some more time. The events occurring in any part of the network should be identified by the nodes, while arrangements sleep and active among the nodes. (i.e.) the nodes should be scheduled to sleep, so that the outstanding nodes can take care of the whole network. The eXtensible Randomized Matrix Arithmetic Coding (XRMAC) Technique has been used to enhance the security among all the nodes in the network. Simulation results show that our Proposed Scheme can have better Lifetime, improved throughput, reduced delay compared to other existing methods.
基金This work was supported by the National Natural Science Foundation of China(61772454,61811530332,61811540410)It was also supported by the open research fund of Key Lab of Broadband Wireless Communication and Sensor Network Technology(Nanjing University of Posts and Telecommunications)Ministry of Education(No.JZNY201905).
文摘Wireless Sensor Networks(WSNs)are usually formed with many tiny sensors which are randomly deployed within sensing field for target monitoring.These sensors can transmit their monitored data to the sink in a multi-hop communication manner.However,the‘hot spots’problem will be caused since nodes near sink will consume more energy during forwarding.Recently,mobile sink based technology provides an alternative solution for the long-distance communication and sensor nodes only need to use single hop communication to the mobile sink during data transmission.Even though it is difficult to consider many network metrics such as sensor position,residual energy and coverage rate etc.,it is still very important to schedule a reasonable moving trajectory for the mobile sink.In this paper,a novel trajectory scheduling method based on coverage rate for multiple mobile sinks(TSCR-M)is presented especially for large-scale WSNs.An improved particle swarm optimization(PSO)combined with mutation operator is introduced to search the parking positions with optimal coverage rate.Then the genetic algorithm(GA)is adopted to schedule the moving trajectory for multiple mobile sinks.Extensive simulations are performed to validate the performance of our proposed method.
文摘Global warming and climate change are the most important ecological issues of our time. The most well-known factor in this phenomenon is the redundancy of carbon dioxide in the atmosphere. Over the past 50 years the amount of residual CO2 in the atmosphere has risen from 40% to 45%. Reducing CO2 redundancy requires precise knowledge of the gas sources and sinks throughout the atmosphere. Despite having a leading role in residual gas levels of atmosphere, the diagnosis and types of changes of absorbing carbon dioxide are very much in doubt. Atmospheric measurements of CO2 concentrations are highly precise and provide a reliable measure of increase of CO2 in the atmosphere every year but they do not lead to the location of sources and sinks. Studies about understanding CO2 cycles began mainly around 1990 and most of these studies have been focused on non-spatial analysis. By ignoring the spatial effects, an important property such as closeness (adjacent) has been disregarded. The emission sources of gas are stronger than their sink sources i.e., whenever a sink is adjacent to a strong emission source, the measurements will show a massive existence of CO2 gas in that region although there exists a fine CO2?gas sink at below. Using the global measurements of CO2 and applying spatial analysis approach to “Leave One Out” method, our studies reveal the most probable spots of CO2 sources and sinks and that Negev Desert in Middle East is a distinguished CO2 sink region.
文摘Today global warming has become one of the most important concerns of environmental science. The redundancy of greenhouse gases in the atmosphere is known as a major factor in this phenomenon. These gases contain water vapor, carbon dioxide, methane, nitrous oxide, and ozone. The CO2?gas is one of their most effective among these gases. According to scientific warnings, the amount of CO2?gases in the atmosphere has increased by 40% to 45% over the last 50 years. Reducing the abundant gas in the atmosphere requires a good knowledge of related factors involved, including sources that emit gases into the atmosphere and sinks that absorb the gas from the atmosphere. The amount of CO2?gas in the atmosphere has been accurately measured in previous years with great certainty. But the predicted values of emissions from sources and removals by sinks have large ambiguities. As studies show, even the computed residuals trends (which is obtained by subtracting the amounts of sinks from sources) strongly disagree with the trends of the existence of CO2?in the atmosphere. This study as a preliminary review, proposes a method to identify the locations of sources and sinks of carbon dioxide using global statistical information and adding spatial analysis approaches. By applying this method to the data observed from 2000 to 2011 and the extraction of likely sources and sinks, the region of the Black Sea, near Romania recognized as one of the strong points issued and Bukit Kototabang near Indonesia acknowledged as an Impressive CO2?absorption zone.
文摘Given a wireless sensor network (WSN) in which a mobile sink is used to collect data from the sensor nodes, this paper addresses the problem of selecting a set of stop points that results in low energy usage by the sensor nodes. This paper assumes an approach in which a mobile sink travels along a fixed path and uses a stop-and-collect protocol since this has previously been shown to be an efficient WSN data collection method. The problem of selecting an optimal set of stop points is shown to be an NP-hard problem. Then, an Integer Linear Programming (ILP) formulation is used to derive an optimal algorithm that can be used for small problem instances. Next, a polynomial-time Tabu-search-based heuristic algorithm is proposed. Simulations are used to compare the energy consumption values, computation times and expected network lifetimes when using the optimal ILP algorithm, the proposed heuristic algorithm and several other possible heuristic algorithms. The results show that the proposed heuristic algorithm results in near-optimal energy usage values with low computation times, thereby making it suitable for large-sized WSNs.
基金supported by the National Natural Science Foundation of China(Grant No.51876062)the Interdisciplinary Innovation Program of North China Electric Power University。
文摘The hybrid manifold micro-pin-fin(MMPF)heat sink combined nozzle jets is an option for large-scale integrated circuits(LSI).The demond for uniform and ultra-high heat flux removal by MMPF heat sink has not been adequately investigated.This work aims to solve the problem of fluid organization.The proposed basic tiling topologies,including square,regular hexagon,30°rhombus,and 60°rhombus topologies,provide different organized fluid flows and heat transfer patterns.The present study focuses on comparing these topologies according to independent porous medium parameters,such as nozzle pore size D_(Z),flow pore size D_(X,Y),and porosityε.The results show that the square topology achieves the smallest total thermal resistance R_(tot)value of0.0975×10^(-4)K m^2/W,while the hexagon topology achieved the highest value of COP/?T,which was 2033.9 K^(-1).According to the sensitivity analysis results,the optimal total thermal resistance can be obtained by balancing the influences of nozzle pore size,flow pore size,and porosity.The optimal pressure drop can be obtained by maximizing the porosity.
文摘In this paper,the multi-objective optimization of wavy microchannel heat sinks is performed by combining numerical calculation,prediction algorithm and genetic algorithm.In numerical calculation,the fluid-solid conjugate heat transfer of heat sinks with different parameters are simulated in Fluent.On this basis,the vari-able parameters and objective parameters are used to complete the training of neural network model,which aims to achieve accurate prediction of objective parameters.Finally,the multi-objective genetic algorithm is applied to find the Pareto front according to different requirements on the foundation of the prediction model.Results show that the coefficient of determination of the neural network models are all greater than 0.85,which proves that the prediction model has a high accuracy.The Pareto fronts are obtained by non-dominated sorting genetic algorithm(NSGA-II)with different objective parameters and they reveal that the channel with the optimal performance corresponds to a larger channel width or Reynolds number.In addition,it is also found the dimensionless temperature difference is correlated with Nusselt number.
文摘1.Introduction Carbon neutrality have become a consensus for all of humanity[1,2].As of April,2023,132 countries have announced carbon neutrality targets[3].To achieve carbon neutrality,efforts need to be made from multiple aspects,including decarbonization of the power sector[4,5],electrification of the end-use sectors[6,7],and greening of other industries[8].Ecological carbon sinks play a unique role in these strategies to offset hard-to-reduce greenhouse gas(GHG)emissions by reabsorbing or storing carbon that has already been emitted.
基金This study was supported by the National Natural Science Founda-tion of China(Grant.No.52175333)Basic Research Program of China(Grant.No.JCKY∗∗∗∗∗∗∗C102)+1 种基金Tribology Science Fund of the China State Key Laboratory of Tribology,Tsinghua University(Grant.No.SKLT2021B05)This study was also supported by the Ten Dimensions(Guangdong,China)Technology Co.,Ltd.,in the course of the lead-ing project“Additive Manufacturing of Ceramic Heat Sinks”(Grant.No.20232000308).
文摘With recent advances in power electronic packaging technologies,liquid-cooled ceramic heat sinks have been considered as a promising solution for further improving the performance of power electronic devices.In this study,several aluminum oxide heat sinks were fabricated and tested using the digital light processing-based ad-ditive manufacturing method,to verify their practical performance.The results showed that the complex cooling structures inside the heat sinks can be completely formed and exhibited high surface quality.The experimental thermal and hydraulic performances of the heat sinks were consistent with the numerically modeled predictions.Furthermore,by exploiting the advantages of additive manufacturing,a direct manifold microchannel(MMC)configuration was designed to reduce the vertical flow of the traditional MMC configuration and achieve an im-proved cooling efficiency.At a constant volumetric flow rate of 1 L/min,the direct MMC configuration achieved a 19.8%reduction in pressure drop and an 11.8%reduction in thermal resistance,as well as a more uniform temperature distribution.