Through equilibrium and non-equilibrium molecular dynamics simulations,we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures.Specifically,...Through equilibrium and non-equilibrium molecular dynamics simulations,we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures.Specifically,we investigated the influence of composition gradient length and heterogeneous particles at the silicene/germanene(SIL/GER)heterostructure interface on heat conduction.Our results indicate that composition graded interface at the interface diminishes the thermal conductivity of the heterostructure,with a further reduction observed as the length increases,while the effect of the heterogeneous particles can be considered negligible.To unveil the influence of composition graded interface on thermal transport,we conducted phonon analysis and identified the presence of phonon localization within the interface composition graded region.Through these analyses,we have determined that the decrease in thermal conductivity is correlated with phonon localization within the heterostructure,where a stronger degree of phonon localization signifies poorer thermal conductivity in the material.Our research findings not only contribute to understanding the impact of interface gradient-induced phonon localization on thermal transport but also offer insights into the modulation of thermal conductivity in heterostructures.展开更多
Heart rate is an important data reflecting human vital characteristics and an important reference index to describe human physical and mental state.Currently,widely used heart rate measurement devices require direct c...Heart rate is an important data reflecting human vital characteristics and an important reference index to describe human physical and mental state.Currently,widely used heart rate measurement devices require direct contact with a person’s skin,which is not suitable for people with burns,delicate skin,newborns and the elderly.Therefore,the research of non-contact heart rate measurement method is of great significance.Based on the basic principle of Photoplethysmography,we use the camera of computer equipment to capture the face image,detect the face region accurately,and detect multiple faces in the image based on multi-target tracking algorithm.Then the region segmentation of the face image is carried out to further realize the signal acquisition of the region of interest.Finally,peak detection,Fourier analysis and wavelet analysis were used to detect the frequency of PPG and ECG signals.The experimental results show that the heart rate information can be quickly and accurately detected even in the case of monitoring multiple face targets.展开更多
Yb^(3+):YAG crystal is one excellent material for developing high-power radiation-balanced lasers(RBLs).An experimental study of the laser cooling performances of YAG crystals with various doping Yb^(3+)concentrations...Yb^(3+):YAG crystal is one excellent material for developing high-power radiation-balanced lasers(RBLs).An experimental study of the laser cooling performances of YAG crystals with various doping Yb^(3+)concentrations,especially for application of RBLs,is reported here.With improved Yb^(3+)doping concentration in YAG crystal,though the resonance absorption coefficient increases,the corresponding external quantum efficiency has been found to decrease with the average fluorescence wavelength being red shifted,which is detrimental to anti-Stokes fluorescence(ASF)cooling.The decrease of the external quantum efficiency can cause the first zero crossing wavelength to red shift,which is not conducive to RBLs.Based on the comprehensive study of the cooling characteristics of the series of Yb^(3+)-doped YAG crystals,the optimal Yb3+doping concentration for ASF cooling has been suggested.展开更多
The inclination angle of the flake particle has a significant impact on the in-plane thermal conductivity of composites.The graphite flake/Al composites(50 vol%)with different inclination angles were fabricated via fl...The inclination angle of the flake particle has a significant impact on the in-plane thermal conductivity of composites.The graphite flake/Al composites(50 vol%)with different inclination angles were fabricated via flake powder metallurgy,and the results show that with increasing the size of Al particle from 25.6 to 50.7μm,the inclination angle of graphite flake decreases from 7.3°to 4.4°,while the in-plane thermal conductivity of composites increases from 473 to 555 Wm-1 K-1.Based on the rules of mixture,an effective model was established to qualify and quantify the relation between the inclination angle and the in-plane thermal conductivity of the corresponding composites.This model can also be applied to other flake particle-reinforced composites.展开更多
Stray magnetic fields with a fixed frequency of 50/60 Hz are ubiquitous in buildings,factories,and power system equipment.Researchers are increasingly focusing on har-vesting electrical energy from stray magnetic fiel...Stray magnetic fields with a fixed frequency of 50/60 Hz are ubiquitous in buildings,factories,and power system equipment.Researchers are increasingly focusing on har-vesting electrical energy from stray magnetic fields to provide sustainable energy for the Internet of Things(IoT)devices.Magneto‐mechano‐electric energy conversion is the most efficient way to convert low‐frequency stray magnetic fields into electricity.In this study,we proposed a hybrid piezo/triboelectric nanogenerator(HP/TENG)on the basis of a cantilever beam to use stray magnetic fields from the surrounding environment.The hybrid nanogenerator provided high output voltage/current and power of∼176 V/375μA and 4.7 mW(matched impedance of 20 kΩ)in a magnetic field environment of 4 Oe.The device provided a stable 3.6 V direct current output by incorporating energy management circuitry to sustainably drive power to commercial wireless temperature/humidity sensors.The HP/TENG has a significant application potential in IoT,which can use stray magnetic energy and a power wireless sensor system.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.12104291)。
文摘Through equilibrium and non-equilibrium molecular dynamics simulations,we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures.Specifically,we investigated the influence of composition gradient length and heterogeneous particles at the silicene/germanene(SIL/GER)heterostructure interface on heat conduction.Our results indicate that composition graded interface at the interface diminishes the thermal conductivity of the heterostructure,with a further reduction observed as the length increases,while the effect of the heterogeneous particles can be considered negligible.To unveil the influence of composition graded interface on thermal transport,we conducted phonon analysis and identified the presence of phonon localization within the interface composition graded region.Through these analyses,we have determined that the decrease in thermal conductivity is correlated with phonon localization within the heterostructure,where a stronger degree of phonon localization signifies poorer thermal conductivity in the material.Our research findings not only contribute to understanding the impact of interface gradient-induced phonon localization on thermal transport but also offer insights into the modulation of thermal conductivity in heterostructures.
文摘Heart rate is an important data reflecting human vital characteristics and an important reference index to describe human physical and mental state.Currently,widely used heart rate measurement devices require direct contact with a person’s skin,which is not suitable for people with burns,delicate skin,newborns and the elderly.Therefore,the research of non-contact heart rate measurement method is of great significance.Based on the basic principle of Photoplethysmography,we use the camera of computer equipment to capture the face image,detect the face region accurately,and detect multiple faces in the image based on multi-target tracking algorithm.Then the region segmentation of the face image is carried out to further realize the signal acquisition of the region of interest.Finally,peak detection,Fourier analysis and wavelet analysis were used to detect the frequency of PPG and ECG signals.The experimental results show that the heart rate information can be quickly and accurately detected even in the case of monitoring multiple face targets.
基金supported by the National Natural Science Foundation of China(Grant Nos.11604100,11834003,61574056,91536218,and 11874151)the Special Financial Grant from the China Postdoctoral Science Foundation(Grant No.2016T90346)111 Project(No.B12024).B.Zhong thanks L.Z.Deng for helpful discussions.
文摘Yb^(3+):YAG crystal is one excellent material for developing high-power radiation-balanced lasers(RBLs).An experimental study of the laser cooling performances of YAG crystals with various doping Yb^(3+)concentrations,especially for application of RBLs,is reported here.With improved Yb^(3+)doping concentration in YAG crystal,though the resonance absorption coefficient increases,the corresponding external quantum efficiency has been found to decrease with the average fluorescence wavelength being red shifted,which is detrimental to anti-Stokes fluorescence(ASF)cooling.The decrease of the external quantum efficiency can cause the first zero crossing wavelength to red shift,which is not conducive to RBLs.Based on the comprehensive study of the cooling characteristics of the series of Yb^(3+)-doped YAG crystals,the optimal Yb3+doping concentration for ASF cooling has been suggested.
基金financially supported by the National Key Research and Development Program of China(Nos.2018YFB0704400,2017YFB0406100)the National Nature Science Foundation of China(Nos.51671129,51971132,51501111,51471106)
文摘The inclination angle of the flake particle has a significant impact on the in-plane thermal conductivity of composites.The graphite flake/Al composites(50 vol%)with different inclination angles were fabricated via flake powder metallurgy,and the results show that with increasing the size of Al particle from 25.6 to 50.7μm,the inclination angle of graphite flake decreases from 7.3°to 4.4°,while the in-plane thermal conductivity of composites increases from 473 to 555 Wm-1 K-1.Based on the rules of mixture,an effective model was established to qualify and quantify the relation between the inclination angle and the in-plane thermal conductivity of the corresponding composites.This model can also be applied to other flake particle-reinforced composites.
基金supported by the State Grid Corporation of China through the Science and Technology Project under Grant 52094020006Z。
文摘Stray magnetic fields with a fixed frequency of 50/60 Hz are ubiquitous in buildings,factories,and power system equipment.Researchers are increasingly focusing on har-vesting electrical energy from stray magnetic fields to provide sustainable energy for the Internet of Things(IoT)devices.Magneto‐mechano‐electric energy conversion is the most efficient way to convert low‐frequency stray magnetic fields into electricity.In this study,we proposed a hybrid piezo/triboelectric nanogenerator(HP/TENG)on the basis of a cantilever beam to use stray magnetic fields from the surrounding environment.The hybrid nanogenerator provided high output voltage/current and power of∼176 V/375μA and 4.7 mW(matched impedance of 20 kΩ)in a magnetic field environment of 4 Oe.The device provided a stable 3.6 V direct current output by incorporating energy management circuitry to sustainably drive power to commercial wireless temperature/humidity sensors.The HP/TENG has a significant application potential in IoT,which can use stray magnetic energy and a power wireless sensor system.
