To improve heating uniformity and anthocyanin content of the blueberry pulp under microwave heating,the intermittent variable power microwave heating technology was introduced in the study.The effects of technology pa...To improve heating uniformity and anthocyanin content of the blueberry pulp under microwave heating,the intermittent variable power microwave heating technology was introduced in the study.The effects of technology parameters in terms of high microwave intensity heating time,intermittent time,low microwave intensity and low microwave intensity heating time on the blueberry pulp quality parameters(heating uniformity,average moisture content,the highest temperature and anthocyanin content)were investigated by using the response surface method.The results showed that the longer heating time under different microwave intensities resulted in the poorer heating uniformity.The intermittent stage promoted heat and mass transfer within the pulp and reduced the temperature difference and moisture gradient within the pulp,which enhanced desired uniformity of temperature and moisture distribution before entering the low microwave intensity heating stage.Therefore,the longer the intermittent time,the greater the heating uniformity.The optimal parameters were developed as high microwave intensity of 4 W·g^(-1),high microwave intensity heating time of 9.86 min,intermittent time of 10 min,low microwave intensity of 2.2 W·g^(-1)and low microwave intensity heating time of 6 min.This research might provide guidance for microwave heating berry fruits.展开更多
The high penetration and uncertainty of distributed energies force the upgrade of volt-var control(VVC) to smooth the voltage and var fluctuations faster. Traditional mathematical or heuristic algorithms are increasin...The high penetration and uncertainty of distributed energies force the upgrade of volt-var control(VVC) to smooth the voltage and var fluctuations faster. Traditional mathematical or heuristic algorithms are increasingly incompetent for this task because of the slow online calculation speed. Deep reinforcement learning(DRL) has recently been recognized as an effective alternative as it transfers the computational pressure to the off-line training and the online calculation timescale reaches milliseconds. However, its slow offline training speed still limits its application to VVC. To overcome this issue, this paper proposes a simplified DRL method that simplifies and improves the training operations in DRL, avoiding invalid explorations and slow reward calculation speed. Given the problem that the DRL network parameters of original topology are not applicable to the other new topologies, side-tuning transfer learning(TL) is introduced to reduce the number of parameters needed to be updated in the TL process. Test results based on IEEE 30-bus and 118-bus systems prove the correctness and rapidity of the proposed method, as well as their strong applicability for large-scale control variables.展开更多
Wave energy has gained its popularity in recent decades due to the vast amount of untapped wave energy resources.There are numerous types of wave energy convertor(WEC)being proposed and to be economically viable,vario...Wave energy has gained its popularity in recent decades due to the vast amount of untapped wave energy resources.There are numerous types of wave energy convertor(WEC)being proposed and to be economically viable,various means to enhance the power generation from WECs have been studied and investigated.In this paper,a novel pontoon-type WEC,which is formed by multiple plate-like modules connected by hinges,are considered.The power enhancement of this pontoon-type WEC is achieved by allowing certain level of structural deformation and by utilizing a series of optimal variable power take-off(PTO)system.The wave energy is converted into useful electricity by attaching the PTO systems on the hinge connectors such that the mechanical movements of the hinges could produce electricity.In this paper,various structural rigidity of the interconnected modules are considered by changing the material Young’s modulus in order to investigate its impact on the power enhancement.In addition,the genetic algorithm optimization scheme is utilized to seek for the optimal PTO damping in the variable PTO system.It is observed that under certain condition,the flexible pontoon-type WEC with lesser connection joints is more effective in generating energy as compared to its rigid counterpart with higher connection joints.It is also found that the variable PTO system is able to generate greater energy as compared to the PTO system with constant/uniform PTO damping.展开更多
As wind power penetration has been gaining in the power grid for decades,a large number of the doubly fed induction generator(DFIG)based wind farms are being established around the globe.The power capacities of these ...As wind power penetration has been gaining in the power grid for decades,a large number of the doubly fed induction generator(DFIG)based wind farms are being established around the globe.The power capacities of these wind farms may vary around hundreds of MW,and most of the wind farms are connected to long transmission cables whose impedances can not be ignored and require careful attention.Several works have investigated the impedance interaction between the DFIG based wind farm and long transmission cables which may unfortunately cause high frequency resonance(HFR).The main contribution of this paper is to investigate the influence of the variable wind farm capacity on the behavior of the HFR when certain transmission cables are provided.It is found out that the potential HFR may happen in certain wind farms,and the larger wind farm capacity causes more severe HFR due to the relatively weaker grid transmission capability.Simulation results based on Matlab/Simulink are given to validate the analysis of HFR.展开更多
The variable polarity power source which incorporates a constant current power and a secondary inverter does not need special apparatus for stabilizing arc. The pulse for stabilizing arc is created by the circuit stru...The variable polarity power source which incorporates a constant current power and a secondary inverter does not need special apparatus for stabilizing arc. The pulse for stabilizing arc is created by the circuit structure itself. The paper analyzes the principle of acquiring the pulse, provides the better method to improve the arc stabilization under smaller welding current. Test shows the arc is highly stable , and the process has no high frequency electromagnetic interference, which is suitable for automatic welding case.展开更多
Variable speed pumped storage machines are used extensively in wind power plant and pumped storage power plant. This paper presents direct torque and flux control(DTFC) of a variable speed pumped storage power plant(V...Variable speed pumped storage machines are used extensively in wind power plant and pumped storage power plant. This paper presents direct torque and flux control(DTFC) of a variable speed pumped storage power plant(VSPSP). By this method both torque and flux have been applied to control the VSPSP. The comparison between VSPSP's control strategies is studied. At the first, a wind turbine with the capacity 2.2 k W and DTFC control strategies simulated then a 250 MW VSPSP is simulated with all of its parts(including electrical, mechanical, hydraulic and its control system) by MATLAB software. In all of simulations, both converters including two-level voltage source converter(2LVSC) and three-level voltage source converter(3LVSC) are applied. The results of applying 2LVSC and 3LVSC are the rapid dynamic responses with better efficiency, reducing the total harmonic distortion(THD) and ripple of rotor torque and flux.展开更多
In order to identify all the appropriate system schemes for the compound split systems formed primarily with a four-port mechanical power split device, power transmission characteristics of the compound split systems ...In order to identify all the appropriate system schemes for the compound split systems formed primarily with a four-port mechanical power split device, power transmission characteristics of the compound split systems was analyzed. Considering the structural symmetry and according to the different connection arrangement of the four ports, compound split system was classified into four types. Using black-box modeling method, the generalized models of the speed ratio, the torque ratio and the power split ratio were established. Moreover, a semi-invert diagram was used to distin- guish the different schemes in each type. The characteristics of the speed ratio, the torque ratio and the power split ratio in each domain were also analyzed and compared. Through the semi-invert dia- gram, a selection method based on the rated-power speed ranges in different schemes was presented and all suitable compound split systems were identified, which can be used as references for the scheme selection of this kind of continuously variable power split transmission.展开更多
The bounded and smooth solitary wave solutions of 10 nonlinear evolution equations with a positive fractional power term of dependent variable are successfully obtained by homogeneous balance principle and with the ai...The bounded and smooth solitary wave solutions of 10 nonlinear evolution equations with a positive fractional power term of dependent variable are successfully obtained by homogeneous balance principle and with the aid of sub-ODEs that admits a solution of sech-power or tanh-power type.In the special cases that the fractional power equals to 1 and 2,the solitary wave solutions of more than 10 important model equations arisen from mathematical physics are easily rediscovered.展开更多
The adaptive algorithm used for echo cancellation(EC) system needs to provide 1) low misadjustment and 2) high convergence rate. The affine projection algorithm(APA) is a better alternative than normalized least mean ...The adaptive algorithm used for echo cancellation(EC) system needs to provide 1) low misadjustment and 2) high convergence rate. The affine projection algorithm(APA) is a better alternative than normalized least mean square(NLMS) algorithm in EC applications where the input signal is highly correlated. Since the APA with a constant step-size has to make compromise between the performance criteria 1) and 2), a variable step-size APA(VSS-APA) provides a more reliable solution. A nonparametric VSS-APA(NPVSS-APA) is proposed by recovering the background noise within the error signal instead of cancelling the a posteriori errors. The most problematic term of its variable step-size formula is the value of background noise power(BNP). The power difference between the desired signal and output signal, which equals the power of error signal statistically, has been considered the BNP estimate in a rough manner. Considering that the error signal consists of background noise and misalignment noise, a precise BNP estimate is achieved by multiplying the rough estimate with a corrective factor. After the analysis on the power ratio of misalignment noise to background noise of APA, the corrective factor is formulated depending on the projection order and the latest value of variable step-size. The new algorithm which does not require any a priori knowledge of EC environment has the advantage of easier controllability in practical application. The simulation results in the EC context indicate the accuracy of the proposed BNP estimate and the more effective behavior of the proposed algorithm compared with other versions of APA class.展开更多
Polynomial functions containing terms with non-integer powers are studied to disclose possible approaches for obtaining their roots as well as employing them for curve-fitting purposes. Several special cases represent...Polynomial functions containing terms with non-integer powers are studied to disclose possible approaches for obtaining their roots as well as employing them for curve-fitting purposes. Several special cases representing equations from different categories are investigated for their roots. Curve-fitting applications to physically meaningful data by the use of fractional functions are worked out in detail. Relevance of this rarely worked subject to solutions of fractional differential equations is pointed out and existing potential in related future work is emphasized.展开更多
We study the blow-up and/or global existence of the following p-Laplacian evolution equation with variable source power where Ω is either a bounded domain or the whole space RN and q（x） is a positive and continuous...We study the blow-up and/or global existence of the following p-Laplacian evolution equation with variable source power where Ω is either a bounded domain or the whole space RN and q（x） is a positive and continuous function defined in with 0 〈 q- infq（x） = q（x） 〈 ∞supq（x） = q＋ 〈 ∞. It is demonstrated that the equation with variable source power has much richer dynamics with interesting phenomena which depends on the interplay of q（x） and the structure of spatial domain Ω, compared with the case of constant source power. For the case that is a bounded domain, the exponent p - 1 plays a crucial role. If q＋ 〉 p - 1, there exist blow-up solutions, while if q＋ p - 1, all the solutions are global. If q-〉 p - 1, there exist global solutions, while for given q- 〈 p - 1 〈 q＋, there exist some function q（x） and such that all nontrivial solutions will blow up, which is called the Fujita phenomenon. For the case Ω = RN the Fujita phenomenon occurs if 1 q＋ q＋ ≤p--1＋p/N, while if q_ 〉 p -- 1 ＋p/N there exist global solutions.展开更多
This study aims to explore a method suitable for welding 7A52 high-strength aluminum alloy plates with continuously varying thicknesses and the causes of microscopic defects in welds in order to improve welding qualit...This study aims to explore a method suitable for welding 7A52 high-strength aluminum alloy plates with continuously varying thicknesses and the causes of microscopic defects in welds in order to improve welding quality.Comparative tests were conducted to analyze weld defects and deformation when welding the aluminum alloy plates with varying thicknesses at constant laser power.The laser power required for melting welds at varying-thickness positions was estimated.Weld defects and deformation when welding aluminum alloy plates with varying thicknesses at con-tinuous variable laser power were detected.The causes of microscopic weld defects during constant-power welding were analyzed.The welding defects and deformation and the welding quality were improved by welding aluminum alloy plates at continuous variable power.展开更多
A numerical model of thermoelectric module （TEM） is created by academic analysis,and the impacts of the resistance ratio and thermoelement size on the output power and thermoelectric efficiency of the TEM are analyz...A numerical model of thermoelectric module （TEM） is created by academic analysis,and the impacts of the resistance ratio and thermoelement size on the output power and thermoelectric efficiency of the TEM are analyzed by the MATLAB numerical calculation.The numerical model is validated by the ANSYS thermal,electrical,and structural coupling simulation.The effects of the variable physical property parameters and contact effect on the output power and thermoelectric efficiency are evaluated,and the concept of aspect ratio optimal domain is proposed,which provides a new design approach for the TEM.展开更多
Climate and weather-propelled wind power is characterized by significant spatial and temporal variability.It has been substantiated that the variability of wind power,in addition to contributing hugely to the instabil...Climate and weather-propelled wind power is characterized by significant spatial and temporal variability.It has been substantiated that the variability of wind power,in addition to contributing hugely to the instability of power grids,can also send the balancing costs of electricity markets soaring.Existing studies on the same establish that curtailment of such variability can be achieved through the geographic aggregation of various widespread production sites;however,there exists a dearth of comprehensive evaluation concerning different levels/scales of such aggregation,especially from a global perspective.This paper primarily offers a fundamental understanding of the relationship between the wind power variations and aggregations from a systematic viewpoint based on extensive wind power data,thereby enabling the benefits of these aggregations to be quantified from a state scale ranging up to a global scale.Firstly,a meticulous analysis of the wind power variations is undertaken at 6 different levels by converting the 7-year hourly meteorological re-analysis data with a high spatial resolution of 0.25◦×0.25◦(approximate 28 km×28 km)into a wind power series globally.Subsequently,the proposed assessment framework employs a coefficient of variation of wind power as well as a standard deviation of wind power ramping rate to quantify the variations of wind power and wind power ramping rate to exhibit the characteristics and benefits yielded by the wind power aggregation at 6 different levels.A system planning example is adopted to illustrate the correlation between the coefficient of variation reduction of wind power and investment reduction,thereby emphasizing the benefits pertaining to significant investment reduction via aggregation.Furthermore,a wind power duration curve is used to exemplify the availability of wind power aggregated at different levels.Finally,the results provide insights into devising a universal approach towards the deployment of wind power,principally along the lines of Net-Zero.展开更多
This paper presents a low power 2.4 GHz transceiver for ZigBee applications.This transceiver adopts low power system architecture with a low-IF receiver and a direct-conversion transmitter.The receiver consists of a n...This paper presents a low power 2.4 GHz transceiver for ZigBee applications.This transceiver adopts low power system architecture with a low-IF receiver and a direct-conversion transmitter.The receiver consists of a new low noise amplifier（LNA） with a noise cancellation function,a new inverter-based variable gain complex filter （VGCF） for image rejection,a passive quadrature mixer,and a decibel linear programmable gain amplifier（PGA）. The transmitter adopts a quadrature mixer and a class-B mode variable gain power amplifier（PA） to reduce power consumption.This transceiver is implemented in 0.18μm CMOS technology.The receiver achieves—95 dBm of sensitivity,28 dBc of image rejection,and -8 dBm of third-order input intercept point（IIP3）.The transmitter can deliver a maximum of＋3 dBm output power with PA efficiency of 30%.The whole chip area is less than 4.32 mm^2. It only consumes 12.63 mW in receiving mode and 14.22 mW in transmitting mode,respectively.展开更多
A loop heat pipe(LHP)is a kind of passive heat transfer device that uses the latent heat of the working fluid and the capillary forces of the capillary wicks.It demonstrates high heat transfer efficiency,long-distance...A loop heat pipe(LHP)is a kind of passive heat transfer device that uses the latent heat of the working fluid and the capillary forces of the capillary wicks.It demonstrates high heat transfer efficiency,long-distance heat transfer,and high pipeline flexibility.The multi-evaporator loop heat pipe(MeLHP)is a special loop heat pipe with multiple evaporators so that heat collection and emission from multiple heat sources can be achieved.In this paper,a new type of the multi-evaporator loop heat pipe prototype with a dual-layer condenser was designed,which can ensure the uniform and symmetrical layout of pipelines.The working temperature was 20℃,and propylene was used as the working fluid.The performance of the same evaporator in a single-loop LHP was considered as a reference.The experiment was conducted under two heating modes,i.e.single-evaporator heating and multi-evaporator heating,and the working stability of the prototype was verified by applying periodic heating power change and adverse elevation condition.It was observed that the prototype can be successfully started in different heating modes with a heat transfer limit of 230 W.In the test,the four loops were different in heat transfer limit due to the differences of flow resistance,and less power distribution to the loop with lowest heat transfer limit was considered to be beneficial to the prototype’s performance.Meanwhile,the prototype showed good heat sharing characteristic as the maximum temperature difference is low(smaller than 2 K in single-evaporator heating mode and 0.5 K in multi-evaporator heating mode).The prototype was of good operational reliability and found to be adaptable to the adverse elevation and cyclic variation of the heating power to a certain extent.展开更多
基金Supported by the National Natural Science Foundation of China(32072352)。
文摘To improve heating uniformity and anthocyanin content of the blueberry pulp under microwave heating,the intermittent variable power microwave heating technology was introduced in the study.The effects of technology parameters in terms of high microwave intensity heating time,intermittent time,low microwave intensity and low microwave intensity heating time on the blueberry pulp quality parameters(heating uniformity,average moisture content,the highest temperature and anthocyanin content)were investigated by using the response surface method.The results showed that the longer heating time under different microwave intensities resulted in the poorer heating uniformity.The intermittent stage promoted heat and mass transfer within the pulp and reduced the temperature difference and moisture gradient within the pulp,which enhanced desired uniformity of temperature and moisture distribution before entering the low microwave intensity heating stage.Therefore,the longer the intermittent time,the greater the heating uniformity.The optimal parameters were developed as high microwave intensity of 4 W·g^(-1),high microwave intensity heating time of 9.86 min,intermittent time of 10 min,low microwave intensity of 2.2 W·g^(-1)and low microwave intensity heating time of 6 min.This research might provide guidance for microwave heating berry fruits.
文摘The high penetration and uncertainty of distributed energies force the upgrade of volt-var control(VVC) to smooth the voltage and var fluctuations faster. Traditional mathematical or heuristic algorithms are increasingly incompetent for this task because of the slow online calculation speed. Deep reinforcement learning(DRL) has recently been recognized as an effective alternative as it transfers the computational pressure to the off-line training and the online calculation timescale reaches milliseconds. However, its slow offline training speed still limits its application to VVC. To overcome this issue, this paper proposes a simplified DRL method that simplifies and improves the training operations in DRL, avoiding invalid explorations and slow reward calculation speed. Given the problem that the DRL network parameters of original topology are not applicable to the other new topologies, side-tuning transfer learning(TL) is introduced to reduce the number of parameters needed to be updated in the TL process. Test results based on IEEE 30-bus and 118-bus systems prove the correctness and rapidity of the proposed method, as well as their strong applicability for large-scale control variables.
文摘Wave energy has gained its popularity in recent decades due to the vast amount of untapped wave energy resources.There are numerous types of wave energy convertor(WEC)being proposed and to be economically viable,various means to enhance the power generation from WECs have been studied and investigated.In this paper,a novel pontoon-type WEC,which is formed by multiple plate-like modules connected by hinges,are considered.The power enhancement of this pontoon-type WEC is achieved by allowing certain level of structural deformation and by utilizing a series of optimal variable power take-off(PTO)system.The wave energy is converted into useful electricity by attaching the PTO systems on the hinge connectors such that the mechanical movements of the hinges could produce electricity.In this paper,various structural rigidity of the interconnected modules are considered by changing the material Young’s modulus in order to investigate its impact on the power enhancement.In addition,the genetic algorithm optimization scheme is utilized to seek for the optimal PTO damping in the variable PTO system.It is observed that under certain condition,the flexible pontoon-type WEC with lesser connection joints is more effective in generating energy as compared to its rigid counterpart with higher connection joints.It is also found that the variable PTO system is able to generate greater energy as compared to the PTO system with constant/uniform PTO damping.
文摘As wind power penetration has been gaining in the power grid for decades,a large number of the doubly fed induction generator(DFIG)based wind farms are being established around the globe.The power capacities of these wind farms may vary around hundreds of MW,and most of the wind farms are connected to long transmission cables whose impedances can not be ignored and require careful attention.Several works have investigated the impedance interaction between the DFIG based wind farm and long transmission cables which may unfortunately cause high frequency resonance(HFR).The main contribution of this paper is to investigate the influence of the variable wind farm capacity on the behavior of the HFR when certain transmission cables are provided.It is found out that the potential HFR may happen in certain wind farms,and the larger wind farm capacity causes more severe HFR due to the relatively weaker grid transmission capability.Simulation results based on Matlab/Simulink are given to validate the analysis of HFR.
基金This research was supported inpart by the Found ation !(No .990 951 1 1 2 )for Research admini stered by HarbinInstituteof Te
文摘The variable polarity power source which incorporates a constant current power and a secondary inverter does not need special apparatus for stabilizing arc. The pulse for stabilizing arc is created by the circuit structure itself. The paper analyzes the principle of acquiring the pulse, provides the better method to improve the arc stabilization under smaller welding current. Test shows the arc is highly stable , and the process has no high frequency electromagnetic interference, which is suitable for automatic welding case.
基金the output of a research project (Title: Application of Doubly Fed Asynchronous machine in Pumped Storage Hydropower Plant in Generate Mode, supported by Islamic Azad University South Tehran Branch)
文摘Variable speed pumped storage machines are used extensively in wind power plant and pumped storage power plant. This paper presents direct torque and flux control(DTFC) of a variable speed pumped storage power plant(VSPSP). By this method both torque and flux have been applied to control the VSPSP. The comparison between VSPSP's control strategies is studied. At the first, a wind turbine with the capacity 2.2 k W and DTFC control strategies simulated then a 250 MW VSPSP is simulated with all of its parts(including electrical, mechanical, hydraulic and its control system) by MATLAB software. In all of simulations, both converters including two-level voltage source converter(2LVSC) and three-level voltage source converter(3LVSC) are applied. The results of applying 2LVSC and 3LVSC are the rapid dynamic responses with better efficiency, reducing the total harmonic distortion(THD) and ripple of rotor torque and flux.
基金Supported by the Ministerial Level Advanced Research Foudation (111044)
文摘In order to identify all the appropriate system schemes for the compound split systems formed primarily with a four-port mechanical power split device, power transmission characteristics of the compound split systems was analyzed. Considering the structural symmetry and according to the different connection arrangement of the four ports, compound split system was classified into four types. Using black-box modeling method, the generalized models of the speed ratio, the torque ratio and the power split ratio were established. Moreover, a semi-invert diagram was used to distin- guish the different schemes in each type. The characteristics of the speed ratio, the torque ratio and the power split ratio in each domain were also analyzed and compared. Through the semi-invert dia- gram, a selection method based on the rated-power speed ranges in different schemes was presented and all suitable compound split systems were identified, which can be used as references for the scheme selection of this kind of continuously variable power split transmission.
基金Supported by the Natural Science Foundation of Education Department of Henan Province of China under Grant No.2011B110013
文摘The bounded and smooth solitary wave solutions of 10 nonlinear evolution equations with a positive fractional power term of dependent variable are successfully obtained by homogeneous balance principle and with the aid of sub-ODEs that admits a solution of sech-power or tanh-power type.In the special cases that the fractional power equals to 1 and 2,the solitary wave solutions of more than 10 important model equations arisen from mathematical physics are easily rediscovered.
文摘The adaptive algorithm used for echo cancellation(EC) system needs to provide 1) low misadjustment and 2) high convergence rate. The affine projection algorithm(APA) is a better alternative than normalized least mean square(NLMS) algorithm in EC applications where the input signal is highly correlated. Since the APA with a constant step-size has to make compromise between the performance criteria 1) and 2), a variable step-size APA(VSS-APA) provides a more reliable solution. A nonparametric VSS-APA(NPVSS-APA) is proposed by recovering the background noise within the error signal instead of cancelling the a posteriori errors. The most problematic term of its variable step-size formula is the value of background noise power(BNP). The power difference between the desired signal and output signal, which equals the power of error signal statistically, has been considered the BNP estimate in a rough manner. Considering that the error signal consists of background noise and misalignment noise, a precise BNP estimate is achieved by multiplying the rough estimate with a corrective factor. After the analysis on the power ratio of misalignment noise to background noise of APA, the corrective factor is formulated depending on the projection order and the latest value of variable step-size. The new algorithm which does not require any a priori knowledge of EC environment has the advantage of easier controllability in practical application. The simulation results in the EC context indicate the accuracy of the proposed BNP estimate and the more effective behavior of the proposed algorithm compared with other versions of APA class.
文摘Polynomial functions containing terms with non-integer powers are studied to disclose possible approaches for obtaining their roots as well as employing them for curve-fitting purposes. Several special cases representing equations from different categories are investigated for their roots. Curve-fitting applications to physically meaningful data by the use of fractional functions are worked out in detail. Relevance of this rarely worked subject to solutions of fractional differential equations is pointed out and existing potential in related future work is emphasized.
基金supported by Shanxi Bairen Plan of China and Ng-Jhit-Cheong Foundation
文摘We study the blow-up and/or global existence of the following p-Laplacian evolution equation with variable source power where Ω is either a bounded domain or the whole space RN and q（x） is a positive and continuous function defined in with 0 〈 q- infq（x） = q（x） 〈 ∞supq（x） = q＋ 〈 ∞. It is demonstrated that the equation with variable source power has much richer dynamics with interesting phenomena which depends on the interplay of q（x） and the structure of spatial domain Ω, compared with the case of constant source power. For the case that is a bounded domain, the exponent p - 1 plays a crucial role. If q＋ 〉 p - 1, there exist blow-up solutions, while if q＋ p - 1, all the solutions are global. If q-〉 p - 1, there exist global solutions, while for given q- 〈 p - 1 〈 q＋, there exist some function q（x） and such that all nontrivial solutions will blow up, which is called the Fujita phenomenon. For the case Ω = RN the Fujita phenomenon occurs if 1 q＋ q＋ ≤p--1＋p/N, while if q_ 〉 p -- 1 ＋p/N there exist global solutions.
基金supported by the Guangxi College Youth Project Foundation(No.2023KY0913)Technology Project of Guizhou Province,Guizhou Science and Technology Cooper-ation Support Project Foundation[2020](No.2Y055)。
文摘This study aims to explore a method suitable for welding 7A52 high-strength aluminum alloy plates with continuously varying thicknesses and the causes of microscopic defects in welds in order to improve welding quality.Comparative tests were conducted to analyze weld defects and deformation when welding the aluminum alloy plates with varying thicknesses at constant laser power.The laser power required for melting welds at varying-thickness positions was estimated.Weld defects and deformation when welding aluminum alloy plates with varying thicknesses at con-tinuous variable laser power were detected.The causes of microscopic weld defects during constant-power welding were analyzed.The welding defects and deformation and the welding quality were improved by welding aluminum alloy plates at continuous variable power.
基金Funded by Guangdong Natural Science Foundation (No.00355991220615019)
文摘A numerical model of thermoelectric module （TEM） is created by academic analysis,and the impacts of the resistance ratio and thermoelement size on the output power and thermoelectric efficiency of the TEM are analyzed by the MATLAB numerical calculation.The numerical model is validated by the ANSYS thermal,electrical,and structural coupling simulation.The effects of the variable physical property parameters and contact effect on the output power and thermoelectric efficiency are evaluated,and the concept of aspect ratio optimal domain is proposed,which provides a new design approach for the TEM.
基金This work was supported partly by the Engineering and Physical Sciences Research Council(EPSRC)under Grant EP/N032888/1 and Grant EP/L017725/1by GEIDCO under Grant 1474100.
文摘Climate and weather-propelled wind power is characterized by significant spatial and temporal variability.It has been substantiated that the variability of wind power,in addition to contributing hugely to the instability of power grids,can also send the balancing costs of electricity markets soaring.Existing studies on the same establish that curtailment of such variability can be achieved through the geographic aggregation of various widespread production sites;however,there exists a dearth of comprehensive evaluation concerning different levels/scales of such aggregation,especially from a global perspective.This paper primarily offers a fundamental understanding of the relationship between the wind power variations and aggregations from a systematic viewpoint based on extensive wind power data,thereby enabling the benefits of these aggregations to be quantified from a state scale ranging up to a global scale.Firstly,a meticulous analysis of the wind power variations is undertaken at 6 different levels by converting the 7-year hourly meteorological re-analysis data with a high spatial resolution of 0.25◦×0.25◦(approximate 28 km×28 km)into a wind power series globally.Subsequently,the proposed assessment framework employs a coefficient of variation of wind power as well as a standard deviation of wind power ramping rate to quantify the variations of wind power and wind power ramping rate to exhibit the characteristics and benefits yielded by the wind power aggregation at 6 different levels.A system planning example is adopted to illustrate the correlation between the coefficient of variation reduction of wind power and investment reduction,thereby emphasizing the benefits pertaining to significant investment reduction via aggregation.Furthermore,a wind power duration curve is used to exemplify the availability of wind power aggregated at different levels.Finally,the results provide insights into devising a universal approach towards the deployment of wind power,principally along the lines of Net-Zero.
基金supported by the Technology Major Project(No.2012ZX03004007-002)the National Natural Science Foundation of China(No. 60976023)the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (No.2012BAH20B02)
文摘This paper presents a low power 2.4 GHz transceiver for ZigBee applications.This transceiver adopts low power system architecture with a low-IF receiver and a direct-conversion transmitter.The receiver consists of a new low noise amplifier（LNA） with a noise cancellation function,a new inverter-based variable gain complex filter （VGCF） for image rejection,a passive quadrature mixer,and a decibel linear programmable gain amplifier（PGA）. The transmitter adopts a quadrature mixer and a class-B mode variable gain power amplifier（PA） to reduce power consumption.This transceiver is implemented in 0.18μm CMOS technology.The receiver achieves—95 dBm of sensitivity,28 dBc of image rejection,and -8 dBm of third-order input intercept point（IIP3）.The transmitter can deliver a maximum of＋3 dBm output power with PA efficiency of 30%.The whole chip area is less than 4.32 mm^2. It only consumes 12.63 mW in receiving mode and 14.22 mW in transmitting mode,respectively.
基金The work presented in this paper is supported by the National Natural Science Foundation of China(Grant No.51776121).
文摘A loop heat pipe(LHP)is a kind of passive heat transfer device that uses the latent heat of the working fluid and the capillary forces of the capillary wicks.It demonstrates high heat transfer efficiency,long-distance heat transfer,and high pipeline flexibility.The multi-evaporator loop heat pipe(MeLHP)is a special loop heat pipe with multiple evaporators so that heat collection and emission from multiple heat sources can be achieved.In this paper,a new type of the multi-evaporator loop heat pipe prototype with a dual-layer condenser was designed,which can ensure the uniform and symmetrical layout of pipelines.The working temperature was 20℃,and propylene was used as the working fluid.The performance of the same evaporator in a single-loop LHP was considered as a reference.The experiment was conducted under two heating modes,i.e.single-evaporator heating and multi-evaporator heating,and the working stability of the prototype was verified by applying periodic heating power change and adverse elevation condition.It was observed that the prototype can be successfully started in different heating modes with a heat transfer limit of 230 W.In the test,the four loops were different in heat transfer limit due to the differences of flow resistance,and less power distribution to the loop with lowest heat transfer limit was considered to be beneficial to the prototype’s performance.Meanwhile,the prototype showed good heat sharing characteristic as the maximum temperature difference is low(smaller than 2 K in single-evaporator heating mode and 0.5 K in multi-evaporator heating mode).The prototype was of good operational reliability and found to be adaptable to the adverse elevation and cyclic variation of the heating power to a certain extent.
