An E//B neutral particle analyzer(NPA)has been designed and is under development at Sichuan University and Southwestern Institute of Physics.The main purpose of the E//B NPA is to measure the distribution function of ...An E//B neutral particle analyzer(NPA)has been designed and is under development at Sichuan University and Southwestern Institute of Physics.The main purpose of the E//B NPA is to measure the distribution function of fast ions in the HL-2A/3 tokamak.The E//B NPA contains three main units,i.e.the stripping unit,the analyzing unit and the detection unit.A gas stripping chamber was adopted as the stripping unit.The results of the simulations and beam tests for the stripping chamber are presented.Parallel electric and magnetic fields provided by a NdFeB permanent magnet and two parallel electric plates were designed and constructed for the analyzing unit.The calibration of the magnetic and electric fields was performed using a 50 kV electron cyclotron resonance ion source(ECRIS)platform.The detection unit consists of 32lutetium-yttrium oxyorthosilicate(LYSO)detector modules arranged in two rows.The response functions ofα,hydrogen ions(H^(+),H_(2)^(+)and H_(3)^(+))andγfor a detector module were measured with^(241)Am,^(137)Cs and^(152)Eu sources together with the 50 kV ECRIS platform.The overall results indicate that the designed E//B NPA device is capable of measuring the intensity of neutral hydrogen and deuteron atoms with energy higher than 20 keV.展开更多
Solid-state electrolyte Li_(10)GeP_(2)S_(12)(LGPS)has a high lithium ion conductivity of 12 mS cm^(-1)at room temperature,but its inferior chemical stability against lithium metal anode impedes its practical applicati...Solid-state electrolyte Li_(10)GeP_(2)S_(12)(LGPS)has a high lithium ion conductivity of 12 mS cm^(-1)at room temperature,but its inferior chemical stability against lithium metal anode impedes its practical application.Among all solutions,Ge atom substitution of the solid-state electrolyte LGPS stands out as the most promising solution to this interface problem.A systematic screening framework for Ge atom substitution including ionic conductivity,thermodynamic stability,electronic and mechanical properties is utilized to solve it.For fast screening,an enhanced model Dop Net FC using chemical formulas for the dataset is adopted to predict ionic conductivity.Finally,Li_(10)SrP_(2)S_(12)(LSrPS)is screened out,which has high lithium ion conductivity(12.58 mS cm^(-1)).In addition,an enhanced migration of lithium ion across the LSr PS/Li interface is found.Meanwhile,compared to the LGPS/Li interface,LSrPS/Li interface exhibits a larger Schottky barrier(0.134 eV),smaller electron transfer region(3.103?),and enhanced ability to block additional electrons,all of which contribute to the stabilized interface.The applied theoretical atom substitution screening framework with the aid of machine learning can be extended to rapid determination of modified specific material schemes.展开更多
Thermal management of nanoscale quantum dots(QDs)in light-emitting devices is a long-lasting challenge.The existing heat transfer reinforcement solutions for QDs-polymer composite mainly rely on thermal-conductive fil...Thermal management of nanoscale quantum dots(QDs)in light-emitting devices is a long-lasting challenge.The existing heat transfer reinforcement solutions for QDs-polymer composite mainly rely on thermal-conductive fillers.However,this strategy failed to deliver the QDs’heat generation across a long distance,and the accumulated heat still causes considerable temperature rise of QDs-polymer composite,which eventually menaces the performance and reliability of lightemitting devices.Inspired by the radially aligned fruit fibers in oranges,we proposed to eliminate this heat dissipation challenge by establishing long-range ordered heat transfer pathways within the QDs-polymer composite.Ultrahigh molecular weight polyethylene fibers(UPEF)were radially aligned throughout the polymer matrix,thus facilitating massive efficient heat dissipation of the QDs.Under a UPEF filling fraction of 24.46 vol%,the in-plane thermal conductivity of QDs-radially aligned UPEF composite(QDs-RAPE)could reach 10.45 W m^(−1) K^(−1),which is the highest value of QDs-polymer composite reported so far.As a proof of concept,the QDs’working temperature can be reduced by 342.5℃ when illuminated by a highly concentrated laser diode(LD)under driving current of 1000 mA,thus improving their optical performance.This work may pave a new way for next generation high-power QDs lighting applications.展开更多
In order to understand the relationship between breakfast frequency and academic performance of grade 5 and grade 8 students, we conducted an investigation through a multistage cluster sampling design with 16,840 stud...In order to understand the relationship between breakfast frequency and academic performance of grade 5 and grade 8 students, we conducted an investigation through a multistage cluster sampling design with 16,840 students (8017 5th graders and 8823 8th graders) from Mianyang city. Results show that: 1) 71.3% of fifth graders and 59.7% of eighth graders had breakfast every day of the week, and 9.7% of fifth graders and 7.5% of eighth graders had breakfast three times or less per week. 2) The number of times students eat breakfast per week has a significant impact on their comprehensive academic performance, which is reflected in the trend that the more times students eat breakfast, the better their overall academic performance is. Based on this, in order to help students eat breakfast more often, and further improve students’ academic performance, we will strengthen the publicity and education of students’ breakfast knowledge from multiple perspectives.展开更多
Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing ...Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ~2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna’s model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ~2.95 mm to ~1.78 mm and the total spreading time changed from ~511 s to ~0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging.展开更多
In this work,we designed the elliptical thermal cloak based on the transformation thermotics.The local entropy generation rate distribution and entransy dissipation rate distribution were obtained,and the total entrop...In this work,we designed the elliptical thermal cloak based on the transformation thermotics.The local entropy generation rate distribution and entransy dissipation rate distribution were obtained,and the total entropy generation and entransy dissipation of different types of elliptical cloaks were evaluated.We used entropy generation approach and entransy dissipation approach to evaluate the performance of the thermal cloak,and heat dissipation analysis was carried out for models with different parameters.Finally,the optimized elliptical thermal cloak with minimum entropy generation and minimum entransy dissipation is found,and some suggestions on optimizing the structure of elliptical thermal cloak were given.展开更多
Taking heat positively as the information carrier,thermotronics can exempt the long-lasting thermal issue of electronics fundamentally,yet has been faced with the challenging multiplexing integration of diverse functi...Taking heat positively as the information carrier,thermotronics can exempt the long-lasting thermal issue of electronics fundamentally,yet has been faced with the challenging multiplexing integration of diverse functionalities.Here,we demonstrate a spatiotemporal modulation platform to achieve multiplexing thermotronics functionalities based on the thermal-hysteresis vanadium dioxide,including negative-differential thermal emission,thermal diode,thermal memristor,thermal transistor,and beyond.The physics behind the multiplexing thermotronics lies in the thermal hysteresis emission characteristics of the phase-changing vanadium dioxide during the spatiotemporal modulation.The present spatiotemporal modulation is expected to stimulate more exploration on novel functionalities,system integration,and practical applications of thermotronics.展开更多
Jinping Underground laboratory for Nuclear Astrophysics(JUNA) will take the advantage of the ultra-low background of CJPL lab and high current accelerator based on an ECR source and a highly sensitive detector to dire...Jinping Underground laboratory for Nuclear Astrophysics(JUNA) will take the advantage of the ultra-low background of CJPL lab and high current accelerator based on an ECR source and a highly sensitive detector to directly study for the first time a number of crucial reactions occurring at their relevant stellar energies during the evolution of hydrostatic stars. In its first phase, JUNA aims at the direct measurements of^(25)Mg(p,γ)^(26)Al,^(19)F(p,α)^(16)O,^(13)C(α,n)^(16)O and ^(12)C(α,γ)^(16)O reactions. The experimental setup,which includes an accelerator system with high stability and high intensity, a detector system, and a shielding material with low background, will be established during the above research. The current progress of JUNA will be given.展开更多
Minipump is widely used in microfluidics system, active cooling system, etc. But building a high efficiency minipump is still a challenging problem. In this paper, a systematic method was developed to design, characte...Minipump is widely used in microfluidics system, active cooling system, etc. But building a high efficiency minipump is still a challenging problem. In this paper, a systematic method was developed to design, characterize and optimize a particular mechanical minipump. The optimization work was conducted to cope with the conflict between pressure head and hydraulic efficiency by an improved back-propagation neural network （BPNN） with the non-dominated sorting genetic algorithm-II （NSGA-II）. The improved BPNN was utilized to predicate hydraulic performance and, moreover, was modified to improve the prediction accuracy. The NSGA-II was processed for minipump multi-objective optimization which is dominated by four impeller dimensions. During hydraulic optimization, the processing feasibility was also taken into consideration. Experiments were conducted to validate the above optimization methods. It was proved that the optimized minipump was improved by about 24 % in pressure head and 4.75 % in hydraulic efficiency compared to the original designed prototype. Meanwhile, the sensitivity test was used to analyze the influence of the four impeller dimensions. It was found that the blade outlet angle β2 and the impeller inlet diameter Do significantly influence the pressure head H and the hydraulic efficiency η, respec- tively. Detailed internal flow fields showed that the optimum model can relieve the impeller wake and improve both the pressure distribution and flow orientation.展开更多
Effects of tilt angles of reflective cup structure and phosphor surface geometries on light extraction efficiency and angular color uniformity （ACU） of phosphor converted light emitting diodes （pcLED） are investig...Effects of tilt angles of reflective cup structure and phosphor surface geometries on light extraction efficiency and angular color uniformity （ACU） of phosphor converted light emitting diodes （pcLED） are investigated by Monte Carlo ray-tracing simulations. It is found that tilt angles of reflective cup and phosphor surface geometries affect the light extraction efficiency and the ACU distinctly. When the tilt angle varied from 60° to 15°, the light extraction efficiency of LED can achieve the improvements of 13.87%, 18.25% and 14.79% respectively, when the phosphor surface geometry is concave, flat and convex, respectively. It is also found the variety law of phosphor concentrations with the change of tilt angles and phosphor surface geometries to maintain a fixed correlated color temperature （CCT）.展开更多
Wavelength-selective thermal emitters(WS-TEs)have been frequently designed to achieve desired target emissivity spectra,as a typical emissivity engineering,for broad applications such as thermal camouflage,radiative c...Wavelength-selective thermal emitters(WS-TEs)have been frequently designed to achieve desired target emissivity spectra,as a typical emissivity engineering,for broad applications such as thermal camouflage,radiative cooling,and gas sensing,etc.However,previous designs require prior knowledge of materials or structures for different applications and the designed WS-TEs usually vary from applications to applications in terms of materials and structures,thus lacking of a general design framework for emissivity engineering across different applications.Moreover,previous designs fail to tackle the simultaneous design of both materials and structures,as they either fix materials to design structures or fix structures to select suitable materials.Herein,we employ the deep Q-learning network algorithm,a reinforcement learning method based on deep learning framework,to design multilayer WS-TEs.To demonstrate the general validity,three WS-TEs are designed for various applications,including thermal camouflage,radiative cooling and gas sensing,which are then fabricated and measured.The merits of the deep Q-learning algorithm include that it can(1)offer a general design framework for WS-TEs beyond one-dimensional multilayer structures;(2)autonomously select suitable materials from a self-built material library and(3)autonomously optimize structural parameters for the target emissivity spectra.The present framework is demonstrated to be feasible and efficient in designing WS-TEs across different applications,and the design parameters are highly scalable in materials,structures,dimensions,and the target functions,offering a general framework for emissivity engineering and paving the way for efficient design of nonlinear optimization problems beyond thermal metamaterials.展开更多
Optical constants, including scattering coefficient, absorption coefficient, asymmetry parameter and reduced scattering coefficient, of cerium-doped yttrium aluminium garnets （YAG：Ce） phosphor blended with SiO2 par...Optical constants, including scattering coefficient, absorption coefficient, asymmetry parameter and reduced scattering coefficient, of cerium-doped yttrium aluminium garnets （YAG：Ce） phosphor blended with SiO2 particle for white light-emitting diode （LED） packages were calculated based on Mie theory in this study. Calculation processes were presented in detail. Variations of the optical constants with the changes of phosphor weight fraction, dopant weight fraction, phosphor particle radius and SiO2 particle radius, were shown and analyzed separately. It was found that the asymmetry parameter is the intrinsic characteristic of the particles, and the increase of the phosphor weight fraction （or concentration） will lead to the increase of the optical constants. It was also discovered that the increase of the dopant weight fraction will enhance the scattering coefficient, but result in the decreases of the reduced scattering coefficient and the absorption coefficient.展开更多
Thermal conductivity of material is one of the basic physical properties and plays an important role in manipu-lating thermal energy.In order to accelerate the prediction of material structure with desired thermal pro...Thermal conductivity of material is one of the basic physical properties and plays an important role in manipu-lating thermal energy.In order to accelerate the prediction of material structure with desired thermal property,machine learning algorithm has been widely adopted.However,in the optimization of multivariable material structure such as different lengths or proportions,the machine learning algorithm may be required to be recon-ducted again and again for each variable,which will consume a lot of computing resources.Recently,it has been found that the thermal conductivity of aperiodic superlattices is closely related to the degree of the structural ran-domness,which can also be reflected in their local pattern structures.Inspired by these,we propose a new pattern analysis method,in which machine learning only needs to be carried out for one time,and through which the optimal structure of different variables with low thermal conductivity can be obtained.To verify the method,we compare the thermal conductivities of the structure obtained by pattern analysis,conventional machine learning,and previous literature,respectively.The pattern analysis method is validated to greatly reduce the prediction time of multivariable structure with high enough accuracy and may promote further development of material informatics.展开更多
As an emerging and energy efficient lighting technology, light-emitting diode （LED） based solid state lighting is expected to significantly reduce global energy consumption and green-house emission for its extraordi...As an emerging and energy efficient lighting technology, light-emitting diode （LED） based solid state lighting is expected to significantly reduce global energy consumption and green-house emission for its extraordinary characteristics compared with traditional light sources, including high luminous efficiency, small size, potentially high device and system reliability, long lifetime, etc. Since the LEDs are unable to be applied before being packaged, the packaging technologies are critically needed in terms of materials selection, process development, co-design with multi-physics consideration, integrated consideration of chip and packaging design. Packaging is therefore essential in enhancing the desired long-term reliability and realizing the full potentials of optical performance of LED devices, which still needs us to conduct more fundamental research. Over the decades, many novel packaging technologies have been proposed and some of them have been commercially applied, yet some of them are still under development.展开更多
基金supported by the National Magnetic Confinement Fusion Energy R&D Program of China(No.2018YFE0310200)National Natural Science Foundation of China(Nos.11705242,11805138 and 12175156)the Fundamental Research Funds for the Central Universities in China(Nos.YJ201820 and YJ201954)。
文摘An E//B neutral particle analyzer(NPA)has been designed and is under development at Sichuan University and Southwestern Institute of Physics.The main purpose of the E//B NPA is to measure the distribution function of fast ions in the HL-2A/3 tokamak.The E//B NPA contains three main units,i.e.the stripping unit,the analyzing unit and the detection unit.A gas stripping chamber was adopted as the stripping unit.The results of the simulations and beam tests for the stripping chamber are presented.Parallel electric and magnetic fields provided by a NdFeB permanent magnet and two parallel electric plates were designed and constructed for the analyzing unit.The calibration of the magnetic and electric fields was performed using a 50 kV electron cyclotron resonance ion source(ECRIS)platform.The detection unit consists of 32lutetium-yttrium oxyorthosilicate(LYSO)detector modules arranged in two rows.The response functions ofα,hydrogen ions(H^(+),H_(2)^(+)and H_(3)^(+))andγfor a detector module were measured with^(241)Am,^(137)Cs and^(152)Eu sources together with the 50 kV ECRIS platform.The overall results indicate that the designed E//B NPA device is capable of measuring the intensity of neutral hydrogen and deuteron atoms with energy higher than 20 keV.
基金support from the National Natural Science Foundation of China (No.51806072)。
文摘Solid-state electrolyte Li_(10)GeP_(2)S_(12)(LGPS)has a high lithium ion conductivity of 12 mS cm^(-1)at room temperature,but its inferior chemical stability against lithium metal anode impedes its practical application.Among all solutions,Ge atom substitution of the solid-state electrolyte LGPS stands out as the most promising solution to this interface problem.A systematic screening framework for Ge atom substitution including ionic conductivity,thermodynamic stability,electronic and mechanical properties is utilized to solve it.For fast screening,an enhanced model Dop Net FC using chemical formulas for the dataset is adopted to predict ionic conductivity.Finally,Li_(10)SrP_(2)S_(12)(LSrPS)is screened out,which has high lithium ion conductivity(12.58 mS cm^(-1)).In addition,an enhanced migration of lithium ion across the LSr PS/Li interface is found.Meanwhile,compared to the LGPS/Li interface,LSrPS/Li interface exhibits a larger Schottky barrier(0.134 eV),smaller electron transfer region(3.103?),and enhanced ability to block additional electrons,all of which contribute to the stabilized interface.The applied theoretical atom substitution screening framework with the aid of machine learning can be extended to rapid determination of modified specific material schemes.
基金supported by the National Natural Science Foundation of China(52106089).
文摘Thermal management of nanoscale quantum dots(QDs)in light-emitting devices is a long-lasting challenge.The existing heat transfer reinforcement solutions for QDs-polymer composite mainly rely on thermal-conductive fillers.However,this strategy failed to deliver the QDs’heat generation across a long distance,and the accumulated heat still causes considerable temperature rise of QDs-polymer composite,which eventually menaces the performance and reliability of lightemitting devices.Inspired by the radially aligned fruit fibers in oranges,we proposed to eliminate this heat dissipation challenge by establishing long-range ordered heat transfer pathways within the QDs-polymer composite.Ultrahigh molecular weight polyethylene fibers(UPEF)were radially aligned throughout the polymer matrix,thus facilitating massive efficient heat dissipation of the QDs.Under a UPEF filling fraction of 24.46 vol%,the in-plane thermal conductivity of QDs-radially aligned UPEF composite(QDs-RAPE)could reach 10.45 W m^(−1) K^(−1),which is the highest value of QDs-polymer composite reported so far.As a proof of concept,the QDs’working temperature can be reduced by 342.5℃ when illuminated by a highly concentrated laser diode(LD)under driving current of 1000 mA,thus improving their optical performance.This work may pave a new way for next generation high-power QDs lighting applications.
文摘In order to understand the relationship between breakfast frequency and academic performance of grade 5 and grade 8 students, we conducted an investigation through a multistage cluster sampling design with 16,840 students (8017 5th graders and 8823 8th graders) from Mianyang city. Results show that: 1) 71.3% of fifth graders and 59.7% of eighth graders had breakfast every day of the week, and 9.7% of fifth graders and 7.5% of eighth graders had breakfast three times or less per week. 2) The number of times students eat breakfast per week has a significant impact on their comprehensive academic performance, which is reflected in the trend that the more times students eat breakfast, the better their overall academic performance is. Based on this, in order to help students eat breakfast more often, and further improve students’ academic performance, we will strengthen the publicity and education of students’ breakfast knowledge from multiple perspectives.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.51606074,51625601,and 51576078)the Ministry of Science and Technology of the People’s Republic of China(Grant No.2017YFE0100600)the Creative Research Groups Funding of Hubei Province(Grant No.2018CFA001)
文摘Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ~2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna’s model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ~2.95 mm to ~1.78 mm and the total spreading time changed from ~511 s to ~0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51606074 and 51625601)the Fund from the Ministry of Science and Technology of China(Grant No.2017YFE0100600)
文摘In this work,we designed the elliptical thermal cloak based on the transformation thermotics.The local entropy generation rate distribution and entransy dissipation rate distribution were obtained,and the total entropy generation and entransy dissipation of different types of elliptical cloaks were evaluated.We used entropy generation approach and entransy dissipation approach to evaluate the performance of the thermal cloak,and heat dissipation analysis was carried out for models with different parameters.Finally,the optimized elliptical thermal cloak with minimum entropy generation and minimum entransy dissipation is found,and some suggestions on optimizing the structure of elliptical thermal cloak were given.
基金Supported by the National Natural Science Foundation of China(Grant No.52076087)the Applied Basic Frontier Program of Wuhan City(Grant No.2020010601012197)。
文摘Taking heat positively as the information carrier,thermotronics can exempt the long-lasting thermal issue of electronics fundamentally,yet has been faced with the challenging multiplexing integration of diverse functionalities.Here,we demonstrate a spatiotemporal modulation platform to achieve multiplexing thermotronics functionalities based on the thermal-hysteresis vanadium dioxide,including negative-differential thermal emission,thermal diode,thermal memristor,thermal transistor,and beyond.The physics behind the multiplexing thermotronics lies in the thermal hysteresis emission characteristics of the phase-changing vanadium dioxide during the spatiotemporal modulation.The present spatiotemporal modulation is expected to stimulate more exploration on novel functionalities,system integration,and practical applications of thermotronics.
基金supported by the National Natural Science Foundation of China(Grant Nos.11490560 and 11321064)the National Basic Research Program of China(Grant No.2013CB834406)
文摘Jinping Underground laboratory for Nuclear Astrophysics(JUNA) will take the advantage of the ultra-low background of CJPL lab and high current accelerator based on an ECR source and a highly sensitive detector to directly study for the first time a number of crucial reactions occurring at their relevant stellar energies during the evolution of hydrostatic stars. In its first phase, JUNA aims at the direct measurements of^(25)Mg(p,γ)^(26)Al,^(19)F(p,α)^(16)O,^(13)C(α,n)^(16)O and ^(12)C(α,γ)^(16)O reactions. The experimental setup,which includes an accelerator system with high stability and high intensity, a detector system, and a shielding material with low background, will be established during the above research. The current progress of JUNA will be given.
文摘Minipump is widely used in microfluidics system, active cooling system, etc. But building a high efficiency minipump is still a challenging problem. In this paper, a systematic method was developed to design, characterize and optimize a particular mechanical minipump. The optimization work was conducted to cope with the conflict between pressure head and hydraulic efficiency by an improved back-propagation neural network （BPNN） with the non-dominated sorting genetic algorithm-II （NSGA-II）. The improved BPNN was utilized to predicate hydraulic performance and, moreover, was modified to improve the prediction accuracy. The NSGA-II was processed for minipump multi-objective optimization which is dominated by four impeller dimensions. During hydraulic optimization, the processing feasibility was also taken into consideration. Experiments were conducted to validate the above optimization methods. It was proved that the optimized minipump was improved by about 24 % in pressure head and 4.75 % in hydraulic efficiency compared to the original designed prototype. Meanwhile, the sensitivity test was used to analyze the influence of the four impeller dimensions. It was found that the blade outlet angle β2 and the impeller inlet diameter Do significantly influence the pressure head H and the hydraulic efficiency η, respec- tively. Detailed internal flow fields showed that the optimum model can relieve the impeller wake and improve both the pressure distribution and flow orientation.
基金The authors would like to acknowledge the financial support in part from the Major State Basic Research Development Program of the Ministry of Science and Technology of China （No. 2011CB013105）, and in part by the National Natural Science Foundation of China （Grant No. 2011AA03A109）.
文摘Effects of tilt angles of reflective cup structure and phosphor surface geometries on light extraction efficiency and angular color uniformity （ACU） of phosphor converted light emitting diodes （pcLED） are investigated by Monte Carlo ray-tracing simulations. It is found that tilt angles of reflective cup and phosphor surface geometries affect the light extraction efficiency and the ACU distinctly. When the tilt angle varied from 60° to 15°, the light extraction efficiency of LED can achieve the improvements of 13.87%, 18.25% and 14.79% respectively, when the phosphor surface geometry is concave, flat and convex, respectively. It is also found the variety law of phosphor concentrations with the change of tilt angles and phosphor surface geometries to maintain a fixed correlated color temperature （CCT）.
基金support by National Natural Science Foundation of China(52211540005,52076087,52161160332)Natural Science Foundation of Hubei Province(2023AFA072)+3 种基金the Open Project Program of Wuhan National Laboratory for Optoelectronics(2021WNLOKF004)Wuhan City Science and Technology Program(2020010601012197)Knowledge Innovation Shuguang Program.W.L.acknowledges the financial support from Key Research and Development plan of Hubei Province(2021BGE037)J.S.acknowledges the financial support from JSPS Bilateral Joint Research Projects(120227404).
文摘Wavelength-selective thermal emitters(WS-TEs)have been frequently designed to achieve desired target emissivity spectra,as a typical emissivity engineering,for broad applications such as thermal camouflage,radiative cooling,and gas sensing,etc.However,previous designs require prior knowledge of materials or structures for different applications and the designed WS-TEs usually vary from applications to applications in terms of materials and structures,thus lacking of a general design framework for emissivity engineering across different applications.Moreover,previous designs fail to tackle the simultaneous design of both materials and structures,as they either fix materials to design structures or fix structures to select suitable materials.Herein,we employ the deep Q-learning network algorithm,a reinforcement learning method based on deep learning framework,to design multilayer WS-TEs.To demonstrate the general validity,three WS-TEs are designed for various applications,including thermal camouflage,radiative cooling and gas sensing,which are then fabricated and measured.The merits of the deep Q-learning algorithm include that it can(1)offer a general design framework for WS-TEs beyond one-dimensional multilayer structures;(2)autonomously select suitable materials from a self-built material library and(3)autonomously optimize structural parameters for the target emissivity spectra.The present framework is demonstrated to be feasible and efficient in designing WS-TEs across different applications,and the design parameters are highly scalable in materials,structures,dimensions,and the target functions,offering a general framework for emissivity engineering and paving the way for efficient design of nonlinear optimization problems beyond thermal metamaterials.
文摘Optical constants, including scattering coefficient, absorption coefficient, asymmetry parameter and reduced scattering coefficient, of cerium-doped yttrium aluminium garnets （YAG：Ce） phosphor blended with SiO2 particle for white light-emitting diode （LED） packages were calculated based on Mie theory in this study. Calculation processes were presented in detail. Variations of the optical constants with the changes of phosphor weight fraction, dopant weight fraction, phosphor particle radius and SiO2 particle radius, were shown and analyzed separately. It was found that the asymmetry parameter is the intrinsic characteristic of the particles, and the increase of the phosphor weight fraction （or concentration） will lead to the increase of the optical constants. It was also discovered that the increase of the dopant weight fraction will enhance the scattering coefficient, but result in the decreases of the reduced scattering coefficient and the absorption coefficient.
基金This work was supported by National Natural Science Foundation of China(52076087)the Ministry of Science and Technology of the People’s Republic of China(2017YFE0100600)Wuhan City Science and Technology Program(2020010601012197).
文摘Thermal conductivity of material is one of the basic physical properties and plays an important role in manipu-lating thermal energy.In order to accelerate the prediction of material structure with desired thermal property,machine learning algorithm has been widely adopted.However,in the optimization of multivariable material structure such as different lengths or proportions,the machine learning algorithm may be required to be recon-ducted again and again for each variable,which will consume a lot of computing resources.Recently,it has been found that the thermal conductivity of aperiodic superlattices is closely related to the degree of the structural ran-domness,which can also be reflected in their local pattern structures.Inspired by these,we propose a new pattern analysis method,in which machine learning only needs to be carried out for one time,and through which the optimal structure of different variables with low thermal conductivity can be obtained.To verify the method,we compare the thermal conductivities of the structure obtained by pattern analysis,conventional machine learning,and previous literature,respectively.The pattern analysis method is validated to greatly reduce the prediction time of multivariable structure with high enough accuracy and may promote further development of material informatics.
文摘As an emerging and energy efficient lighting technology, light-emitting diode （LED） based solid state lighting is expected to significantly reduce global energy consumption and green-house emission for its extraordinary characteristics compared with traditional light sources, including high luminous efficiency, small size, potentially high device and system reliability, long lifetime, etc. Since the LEDs are unable to be applied before being packaged, the packaging technologies are critically needed in terms of materials selection, process development, co-design with multi-physics consideration, integrated consideration of chip and packaging design. Packaging is therefore essential in enhancing the desired long-term reliability and realizing the full potentials of optical performance of LED devices, which still needs us to conduct more fundamental research. Over the decades, many novel packaging technologies have been proposed and some of them have been commercially applied, yet some of them are still under development.
