Intra porous fibrous membranes have enhanced metal ionic adsorption and oil separation abilities than those of intra nonporous fibrous membrane.In this paper,we prepared highly intra porous fibrous poly(vinylidene flu...Intra porous fibrous membranes have enhanced metal ionic adsorption and oil separation abilities than those of intra nonporous fibrous membrane.In this paper,we prepared highly intra porous fibrous poly(vinylidene fluoride)(PVDF)membranes using an innovated water-mediated electrospinning approach.FTIR-ATR and XRD techniques confirmed the conversion of non-polarα-phase to polarβ-phase in electrospun membranes.The porous fibrous membrane M–16 had adsorbed oil almost 120%and metal adsorption around 15%,12%,5%,13%respectively for Pb^(2+),Cd^(2+),Cu^(2+)and Zn^(2+),which are larger than the counterpart of nonporous M–18.The nonporous fibrous membranes have better peak to peak output voltage(Vp-Vp)2 to 3 times than the porous fibrous membranes(M–16).The results show apparent potential applications in wastewater/oil spill treatment as well as piezoelectric sensors.展开更多
Pb_(x)Sr_(1-x)TiO_(3)(x=0.30,0.35,0.40,0.45,0.50 and 0.55)ceramics were fabricated by a solid-state reaction route.Xeray diffraction data at room temperature show PST samples shift from cubic to tetragonal phase with ...Pb_(x)Sr_(1-x)TiO_(3)(x=0.30,0.35,0.40,0.45,0.50 and 0.55)ceramics were fabricated by a solid-state reaction route.Xeray diffraction data at room temperature show PST samples shift from cubic to tetragonal phase with the increase of Pb^(2+) content.The microstructures were observed by scanning electron microscopy.Dielectric measurement was employed to investigate the ferroelectriceparaelectric phase transition behavior.Temperature dependent polarizationeelectric field hysteresis loops were conducted to study the electrocaloric effect(ECE)of the ferroelectric ceramics by indirect methods over a wide temperature range.Direct measurement of temperature change(DT)at room temperature for all samples can achieve 0.79e1.86 K.What's more,a giant ECE(△T=2.05 K,EC strength(△T/△E)=0.51×10^(-6) K m/V,under 40 kV/cm)was obtained in the sample of x=0.35 near phase transition temperature.Our results suggest that the ceramics are promising cooling materials with excellent EC properties for energy related applications.展开更多
As the fundamental energy storage components in electronic systems,dielectric capacitors with high power densities were demanded.In this work,the anti-ferroelectric Pb_(0.89)La_(0.06)Sr_(0.05)(Zr_(0.95)Ti_(0.05))O_(3)...As the fundamental energy storage components in electronic systems,dielectric capacitors with high power densities were demanded.In this work,the anti-ferroelectric Pb_(0.89)La_(0.06)Sr_(0.05)(Zr_(0.95)Ti_(0.05))O_(3)(PLSZT)ceramics and thin film capacitor were successfully fabricated by a solid-state reaction route and pulsed laser deposition method,respectively.The ferroelectric,dielectric,energy-storage properties,and temperature stability of anti-ferroelectric PLSZT capacitor were investigated in detail.By compared with the PLSZT ceramic(energy storage density is 1.29 J/cm^(3) with an efficiency of 78.7%under 75 kV/cm),the anti-ferroelectric PLSZT thin film capacitors exhibited the enhanced energy storage density of 52.6 J/cm^(3) with efficiency of 67.7%under an electric field as high as 2068.9 kV/cm,and the enhanced energy-storage temperature stabilities from room temperature(RT)to more than 200℃ were demonstrated,and the oxygen defects mechanism and size effect were discussed.Moreover,the fast charging(~0.05 μs)and discharging(~0.15 μs)time were certified for the anti-ferroelectric PLSZT film capacitor.These findings broaden the horizon for PLSZT anti-ferroelectrics in high energy storage properties and show promising for manufacturing pulse power capacitor.展开更多
Solid-state cooling technology based on electrocaloric effect(ECE)has been advanced as an alternative to replace the vapour-compression approach to overcome the releasing of the global warming gases.However,the develo...Solid-state cooling technology based on electrocaloric effect(ECE)has been advanced as an alternative to replace the vapour-compression approach to overcome the releasing of the global warming gases.However,the development in high ECE materials is still a challenge.In this work,polarization merging strategy was proposed to achieve a large ECE in xBa(Sn_(0.07)Ti_(0.93))O_(3)–(1−x)Ba(Hf_(0.1)Ti_(0.9))O_(3) ferroelectric ceramics,where x=0,0.2,0.4,0.6,0.8,and 1.Ba(Sn_(0.07)Ti_(0.93))O_(3) with an orthorhombic phase and Ba(Hf_(0.1)Ti_(0.9))O_(3) with a rhombohedral phase at room temperature were prepared beforehand as precursors,and phase-coexisted xBSnT–(1−x)BHfT ceramics were formed via a solid-state reaction approach.Phase coexisting structures were confirmed using the X-ray diffraction.The merged polarization was confirmed by the dielectric and ferroelectric properties.Optimal ECEs were obtained for 0.2BSnT–0.8BHfT ceramics,i.e.,adiabatic temperature change DT=2.16±0.08 K at 80℃and 5 MV/m,and DT=3.35±0.09 K at 80℃and 7 MV/m.展开更多
The effect of a N,N-dimethylformamide(DMF)/acetone solvent system(3:7,4:6,5:5,6:4,7:3)and spinning medium(air and water)on the membrane morphology and the structure-property relationship were investigated.A facile met...The effect of a N,N-dimethylformamide(DMF)/acetone solvent system(3:7,4:6,5:5,6:4,7:3)and spinning medium(air and water)on the membrane morphology and the structure-property relationship were investigated.A facile method was optimized to generate a porous,polymer-fiber membrane via the combinative effect of electrospinning and thermally inducing phase separation of the DMF/acetone(4:6)solvent system in a water medium.The attenuated total reflection(ATR)-Fourier transform infrared(FTIR)results showed an increased b-phase compared to the pristine poly(vinylidene fluoride)(PVDF).The XRD and DSC results further confirmed that the co-existing a-and b-phases in the pristine PVDF were converted into a unique b-phase in the electrospun membranes.In addition,the solvent uptake percentage of the DMF/acetone(4:6)solvent system in a water medium(540)is much greater than that in an air medium(320),and over two times better than that of commercial polyethylene(PE)membranes(190).Similarly,the discharge capacity of the PVDF membrane separator prepared with the DMF/acetone(4:6)solvent system in a water medium is higher than that of the air medium.This enhancement of solvent uptake might be due to the interconnected porous morphology present in the water medium.展开更多
(Ba_(1-x)Sr_(x))(MnyTi1-y)O_(3)(BSMT)ceramics with x=35,40 mol%and y=0,0.1,0.2,0.3,0.4,0.5 mol%were prepared using a conventional solid-state reaction approach.The dielectric and ferroelectric properties were characte...(Ba_(1-x)Sr_(x))(MnyTi1-y)O_(3)(BSMT)ceramics with x=35,40 mol%and y=0,0.1,0.2,0.3,0.4,0.5 mol%were prepared using a conventional solid-state reaction approach.The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field(P-E)hysteresis loop measurements,respectively.The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed.The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1-0.4 mol%of manganese ions in(BaSr)TiO_(3)(BST)specimens.A maximum electrocaloric effect(ECE)of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)^(-1)was directly obtained at~21℃and 50 kV/cm in Ba_(0.6)Sr_(0.4)Mn_(0.001)Ti_(0.999)O_(3) sample,offering a promising ECE material for practical refrigeration devices working at room temperature.展开更多
Unveiling the active site of an electrocatalyst is fundamental for the development of efficient electrode material.For the two-electron water oxidation to produce H_(2)O_(2),competitive reactions,including four-and on...Unveiling the active site of an electrocatalyst is fundamental for the development of efficient electrode material.For the two-electron water oxidation to produce H_(2)O_(2),competitive reactions,including four-and one-electron water oxidation and surface reconstruction derived from the high-oxidative environment co-existed,leading to great challenges to identify the real active sites on the electrode.In this work,Ti/TiO_(2)-based electrodes calcined under air,nitrogen,or urea atmospheres were selected as electrocatalysts for two-electron water oxidation.Electrochemical analyses were applied to evaluate the catalytic activity and selectivity.The morphological and current change on the electrode surface were determined by scanning electrochemical microscopy,while the chemical and valence evolutions with depth distributions were tested by XPS combined with cluster argon ion sputtering.The results demonstrated that Ti/TiO_(2) nanotube arrays served as the support,while the functional groups of carbonyl groups and pyrrolic nitrogen derived from the co-pyrolysis with urea were the active sites for the H_(2)O_(2) production.This finding provided a new horizon to design efficient catalysts for H_(2)O_(2) production.展开更多
并行矩阵乘法是线性代数中最重要的基本运算之一,同时也是许多科学应用的基石.随着高性能计算(HPC)向E级计算发展,并行矩阵乘法的通信开销所占比重越来越大.如何降低并行矩阵乘法的通信开销,提高并行矩阵乘的可扩展性是当前研究的热点之...并行矩阵乘法是线性代数中最重要的基本运算之一,同时也是许多科学应用的基石.随着高性能计算(HPC)向E级计算发展,并行矩阵乘法的通信开销所占比重越来越大.如何降低并行矩阵乘法的通信开销,提高并行矩阵乘的可扩展性是当前研究的热点之一.本文提出一种新型的分布式并行稠密矩阵乘算法,即2.5D版本的PUMMA(Parallel Universal Matrix Multiplication Algorithm)算法,该算法是通过将初始的进程分成c组,利用计算节点的额外内存,在每个进程组上同时存储矩阵A、B和执行1/c的PUMMA算法,最后通过规约操作来得到矩阵乘的最终结果.本文基于BLACS(Basic Linear Algebra Communication Subprograms)通信库实现了一种从2D到2.5D的新型数据重分配算法,与PUMMA算法相结合,最终得到2.5D PUMMA算法,可直接替换PDGEMM(Parallel Double-precision General Matrix-matrix Multiplication),具有良好的可移植性.与国际标准算法库ScaLAPACK(Scalable Linear Algebra PACKage)中的PDGEMM等经典2D算法相比,本文算法缩减了通信次数,提高了数据局部性,具有更好的可扩展性.在进程数较多时,例如4096进程时,系统测试表明相对PDGEMM的加速比可达到2.20~2.93.进一步地,本文将2.5D PUMMA算法应用于加速计算对称三对角矩阵的特征值分解,其加速比可达到1.2以上.本文通过大量数值算例分析了2.5D PUMMA算法的性能,并给出了实用性建议和总结了未来的工作.展开更多
The electrocaloric effect(ECE)is the adiabatic temperature change or isothermal entropy change caused by the polarization change of a dielectric material when subjected to a change of external electric field.The elect...The electrocaloric effect(ECE)is the adiabatic temperature change or isothermal entropy change caused by the polarization change of a dielectric material when subjected to a change of external electric field.The electrostrictive effect is a form of elastic deformation of a dielectric induced by an electric field,associated with those components of strain which are independent of reversal field direction.It was found that both the ECE,e.g.,adiabatic temperature change,and the electrostrictive strain in poly(vinylidene fluoridetrifluoroethylenechlorofluoroethylene)(P(VDF-TrFE-CFE))terpolymers are proportional to the square of the electric field.The adiabatic temperature changeΔT of ECE versus electric field can be illustrated using a modified BelovGoryaga equation.ΔT is proportional to E^(2) when E is small.For electrostrictive effect,the rigid-ion model assumes that the anharmonic movement of the ions leads to the quadratic strainelectric field relation.The quotient of electrostrictive coefficient Q over the phenomenological coefficientis empirically a constant,indicating that the larger the electrostrictive coefficient,the larger the ECE,which opens a new way to find out new electrocaloric materials.展开更多
The electrocaloric effect(ECE)in lead-free BaSn_(x)Ti_(1-x)O_(3)(BSnT,x=0.05,0.10 and 0.15)ceramics were investigated using a direct ECE measurement.Results indicate that the maximum ECE occurs near the Curie temperat...The electrocaloric effect(ECE)in lead-free BaSn_(x)Ti_(1-x)O_(3)(BSnT,x=0.05,0.10 and 0.15)ceramics were investigated using a direct ECE measurement.Results indicate that the maximum ECE occurs near the Curie temperature and it slightly shifts towards high temperatures.The directly measured ECE is larger than that calculated using the Maxwell relation and P-E loops.A maximum electrocaloric efficiencyΔT=ΔE=0.49-10-6 KmV-1 was procured for the composition with x=0.15 at T=299.2 K.And it also shows a broad peak in the temperature range of 250–320 K.展开更多
Organic and inorganic relaxor ferroelectrics used for electrocaloric effect(ECE)applications areintroduced.Relaxor ferroelectrics offer several advantages for ECE devices,e.g.,infinite stateswithout applying electric ...Organic and inorganic relaxor ferroelectrics used for electrocaloric effect(ECE)applications areintroduced.Relaxor ferroelectrics offer several advantages for ECE devices,e.g.,infinite stateswithout applying electric field,field-induced large polarization,no-hysteresis ofheating and cooling,small-hysteresis polarization loss,room temperature phase transition,and broad temperaturerange.The ECE in relaxor ferroelectrics under a high electric field can be described using a theorysimilar to that for first-order phase transition materials.Large ECE was observed directly inhigh-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)68/32 mol%copolymers,P(VDF-TrFE-CFE)(CFE-chlorofluoroethylene)59.2/33.6/7.2 mol%terpolymers,P(vDF-TrFE-CFE)-P(VDF-CTFE)(CTFE-chlorotrifluoroethylene)95/5 wt%terpolymer blended films,and(PbLa)(ZrTi)O_(3)(PLZT)ceramic thin films.ECE reported inPb(Sc_(1/2)Ta_(1/2))O_(3)(PST),Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)(PMN-PT)thin films is also summarized.Finally,the perspective of ECE devices is llustrated.展开更多
基金This work was supported by the Natural Science Foundation of China(Grant No.51372042,51872053)Guangdong Provincial Natural Science Foundation(2015A030308004)+1 种基金the NSFCGuangdong Joint Fund(Grant No.U1501246)the Dongguan City Frontier Research Project(2019622101006)and the Advanced Energy Science and Technology Guangdong Provincial Laboratory Foshan Branch-Foshan Xianhu Laboratory Open Fund-Key Project(Grant No.XHT2020-011).
文摘Intra porous fibrous membranes have enhanced metal ionic adsorption and oil separation abilities than those of intra nonporous fibrous membrane.In this paper,we prepared highly intra porous fibrous poly(vinylidene fluoride)(PVDF)membranes using an innovated water-mediated electrospinning approach.FTIR-ATR and XRD techniques confirmed the conversion of non-polarα-phase to polarβ-phase in electrospun membranes.The porous fibrous membrane M–16 had adsorbed oil almost 120%and metal adsorption around 15%,12%,5%,13%respectively for Pb^(2+),Cd^(2+),Cu^(2+)and Zn^(2+),which are larger than the counterpart of nonporous M–18.The nonporous fibrous membranes have better peak to peak output voltage(Vp-Vp)2 to 3 times than the porous fibrous membranes(M–16).The results show apparent potential applications in wastewater/oil spill treatment as well as piezoelectric sensors.
基金the National Natural Science Foundation of China(Grant Nos.11574057 and 51604087)the Guangdong Provincial Natural Science Foundation of China(Grant No.2016A030313718)the Science and Technology Program of Guangdong Province of China(Grant Nos.2016A010104018,and 2017A010104022).
文摘Pb_(x)Sr_(1-x)TiO_(3)(x=0.30,0.35,0.40,0.45,0.50 and 0.55)ceramics were fabricated by a solid-state reaction route.Xeray diffraction data at room temperature show PST samples shift from cubic to tetragonal phase with the increase of Pb^(2+) content.The microstructures were observed by scanning electron microscopy.Dielectric measurement was employed to investigate the ferroelectriceparaelectric phase transition behavior.Temperature dependent polarizationeelectric field hysteresis loops were conducted to study the electrocaloric effect(ECE)of the ferroelectric ceramics by indirect methods over a wide temperature range.Direct measurement of temperature change(DT)at room temperature for all samples can achieve 0.79e1.86 K.What's more,a giant ECE(△T=2.05 K,EC strength(△T/△E)=0.51×10^(-6) K m/V,under 40 kV/cm)was obtained in the sample of x=0.35 near phase transition temperature.Our results suggest that the ceramics are promising cooling materials with excellent EC properties for energy related applications.
基金financially supported by National Natural Science Foundation of China(NSFC)(Grant Nos.51702055,62073084,11904056,and 51604087)the Guangdong Provincial Natural Science Foundation of China(Grant No.2016A030313718)+1 种基金the Science and Technology Program of Guangdong Province of China(Grant Nos.2016A010104018 and 2017A010104022)Special Funds for the Cultivation of Guangdong College Students’Scientific and Technological Innovation(Climbing Program Special Funds,Grant No.pdjh2020a0174,pdjh2019a0147).
文摘As the fundamental energy storage components in electronic systems,dielectric capacitors with high power densities were demanded.In this work,the anti-ferroelectric Pb_(0.89)La_(0.06)Sr_(0.05)(Zr_(0.95)Ti_(0.05))O_(3)(PLSZT)ceramics and thin film capacitor were successfully fabricated by a solid-state reaction route and pulsed laser deposition method,respectively.The ferroelectric,dielectric,energy-storage properties,and temperature stability of anti-ferroelectric PLSZT capacitor were investigated in detail.By compared with the PLSZT ceramic(energy storage density is 1.29 J/cm^(3) with an efficiency of 78.7%under 75 kV/cm),the anti-ferroelectric PLSZT thin film capacitors exhibited the enhanced energy storage density of 52.6 J/cm^(3) with efficiency of 67.7%under an electric field as high as 2068.9 kV/cm,and the enhanced energy-storage temperature stabilities from room temperature(RT)to more than 200℃ were demonstrated,and the oxygen defects mechanism and size effect were discussed.Moreover,the fast charging(~0.05 μs)and discharging(~0.15 μs)time were certified for the anti-ferroelectric PLSZT film capacitor.These findings broaden the horizon for PLSZT anti-ferroelectrics in high energy storage properties and show promising for manufacturing pulse power capacitor.
基金supported by the National Natural Science Foundation of China(Grant Nos.51872053,52272105,and 52202130)the Guangdong Provincial Natural Science Foundation(Grant No.2015A030308004)+3 种基金the NSFC–Guangdong Joint Fund(Grant No.U1501246)the Dongguan City Frontier Research Project(Grant No.2019622101006)the Advanced Energy Science and Technology Guangdong Provincial Laboratory Foshan Branch–Foshan Xianhu Laboratory Open Fund-Key Project(Grant No.XHT2020-011)the Open Project Program of Guangdong Provincial Key Laboratory of Electronic Functional Materials and Devices,Huizhou University(Grant No.EFMD2022004Z).
文摘Solid-state cooling technology based on electrocaloric effect(ECE)has been advanced as an alternative to replace the vapour-compression approach to overcome the releasing of the global warming gases.However,the development in high ECE materials is still a challenge.In this work,polarization merging strategy was proposed to achieve a large ECE in xBa(Sn_(0.07)Ti_(0.93))O_(3)–(1−x)Ba(Hf_(0.1)Ti_(0.9))O_(3) ferroelectric ceramics,where x=0,0.2,0.4,0.6,0.8,and 1.Ba(Sn_(0.07)Ti_(0.93))O_(3) with an orthorhombic phase and Ba(Hf_(0.1)Ti_(0.9))O_(3) with a rhombohedral phase at room temperature were prepared beforehand as precursors,and phase-coexisted xBSnT–(1−x)BHfT ceramics were formed via a solid-state reaction approach.Phase coexisting structures were confirmed using the X-ray diffraction.The merged polarization was confirmed by the dielectric and ferroelectric properties.Optimal ECEs were obtained for 0.2BSnT–0.8BHfT ceramics,i.e.,adiabatic temperature change DT=2.16±0.08 K at 80℃and 5 MV/m,and DT=3.35±0.09 K at 80℃and 7 MV/m.
基金supported by the Natural Science Foundation of China(Grant No.51372042,51872053)Guangdong Provincial Natural Science Foundation(2015A030308004)the NSFCGuangdong Joint Fund(Grant No.U1501246).
文摘The effect of a N,N-dimethylformamide(DMF)/acetone solvent system(3:7,4:6,5:5,6:4,7:3)and spinning medium(air and water)on the membrane morphology and the structure-property relationship were investigated.A facile method was optimized to generate a porous,polymer-fiber membrane via the combinative effect of electrospinning and thermally inducing phase separation of the DMF/acetone(4:6)solvent system in a water medium.The attenuated total reflection(ATR)-Fourier transform infrared(FTIR)results showed an increased b-phase compared to the pristine poly(vinylidene fluoride)(PVDF).The XRD and DSC results further confirmed that the co-existing a-and b-phases in the pristine PVDF were converted into a unique b-phase in the electrospun membranes.In addition,the solvent uptake percentage of the DMF/acetone(4:6)solvent system in a water medium(540)is much greater than that in an air medium(320),and over two times better than that of commercial polyethylene(PE)membranes(190).Similarly,the discharge capacity of the PVDF membrane separator prepared with the DMF/acetone(4:6)solvent system in a water medium is higher than that of the air medium.This enhancement of solvent uptake might be due to the interconnected porous morphology present in the water medium.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51372042 and 51872053)the Guangdong Provincial Natural Science Foundation(Grant No.2015A030308004)+2 种基金the NSFC–Guangdong Joint Fund(Grant No.U1501246)the Dongguan City Frontier Research Project(Grant No.2019622101006)the Advanced Energy Science and Technology Guangdong Provincial Laboratory Foshan Branch-Foshan Xianhu Laboratory Open Fund-Key Project(Grant No.XHT2020-011).
文摘(Ba_(1-x)Sr_(x))(MnyTi1-y)O_(3)(BSMT)ceramics with x=35,40 mol%and y=0,0.1,0.2,0.3,0.4,0.5 mol%were prepared using a conventional solid-state reaction approach.The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field(P-E)hysteresis loop measurements,respectively.The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed.The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1-0.4 mol%of manganese ions in(BaSr)TiO_(3)(BST)specimens.A maximum electrocaloric effect(ECE)of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)^(-1)was directly obtained at~21℃and 50 kV/cm in Ba_(0.6)Sr_(0.4)Mn_(0.001)Ti_(0.999)O_(3) sample,offering a promising ECE material for practical refrigeration devices working at room temperature.
基金Project(2021JJ30792) supported by the Natural Science Foundation of Hunan Province,ChinaProject(52170031) supported by the National Natural Science Foundation of ChinaProject supported by the Fundamental Research Funds for the Central Universities,China。
文摘Unveiling the active site of an electrocatalyst is fundamental for the development of efficient electrode material.For the two-electron water oxidation to produce H_(2)O_(2),competitive reactions,including four-and one-electron water oxidation and surface reconstruction derived from the high-oxidative environment co-existed,leading to great challenges to identify the real active sites on the electrode.In this work,Ti/TiO_(2)-based electrodes calcined under air,nitrogen,or urea atmospheres were selected as electrocatalysts for two-electron water oxidation.Electrochemical analyses were applied to evaluate the catalytic activity and selectivity.The morphological and current change on the electrode surface were determined by scanning electrochemical microscopy,while the chemical and valence evolutions with depth distributions were tested by XPS combined with cluster argon ion sputtering.The results demonstrated that Ti/TiO_(2) nanotube arrays served as the support,while the functional groups of carbonyl groups and pyrrolic nitrogen derived from the co-pyrolysis with urea were the active sites for the H_(2)O_(2) production.This finding provided a new horizon to design efficient catalysts for H_(2)O_(2) production.
文摘并行矩阵乘法是线性代数中最重要的基本运算之一,同时也是许多科学应用的基石.随着高性能计算(HPC)向E级计算发展,并行矩阵乘法的通信开销所占比重越来越大.如何降低并行矩阵乘法的通信开销,提高并行矩阵乘的可扩展性是当前研究的热点之一.本文提出一种新型的分布式并行稠密矩阵乘算法,即2.5D版本的PUMMA(Parallel Universal Matrix Multiplication Algorithm)算法,该算法是通过将初始的进程分成c组,利用计算节点的额外内存,在每个进程组上同时存储矩阵A、B和执行1/c的PUMMA算法,最后通过规约操作来得到矩阵乘的最终结果.本文基于BLACS(Basic Linear Algebra Communication Subprograms)通信库实现了一种从2D到2.5D的新型数据重分配算法,与PUMMA算法相结合,最终得到2.5D PUMMA算法,可直接替换PDGEMM(Parallel Double-precision General Matrix-matrix Multiplication),具有良好的可移植性.与国际标准算法库ScaLAPACK(Scalable Linear Algebra PACKage)中的PDGEMM等经典2D算法相比,本文算法缩减了通信次数,提高了数据局部性,具有更好的可扩展性.在进程数较多时,例如4096进程时,系统测试表明相对PDGEMM的加速比可达到2.20~2.93.进一步地,本文将2.5D PUMMA算法应用于加速计算对称三对角矩阵的特征值分解,其加速比可达到1.2以上.本文通过大量数值算例分析了2.5D PUMMA算法的性能,并给出了实用性建议和总结了未来的工作.
基金This work was supported by the "100 Talents Scheme" fund at the Guangdong University of Technology.
文摘The electrocaloric effect(ECE)is the adiabatic temperature change or isothermal entropy change caused by the polarization change of a dielectric material when subjected to a change of external electric field.The electrostrictive effect is a form of elastic deformation of a dielectric induced by an electric field,associated with those components of strain which are independent of reversal field direction.It was found that both the ECE,e.g.,adiabatic temperature change,and the electrostrictive strain in poly(vinylidene fluoridetrifluoroethylenechlorofluoroethylene)(P(VDF-TrFE-CFE))terpolymers are proportional to the square of the electric field.The adiabatic temperature changeΔT of ECE versus electric field can be illustrated using a modified BelovGoryaga equation.ΔT is proportional to E^(2) when E is small.For electrostrictive effect,the rigid-ion model assumes that the anharmonic movement of the ions leads to the quadratic strainelectric field relation.The quotient of electrostrictive coefficient Q over the phenomenological coefficientis empirically a constant,indicating that the larger the electrostrictive coefficient,the larger the ECE,which opens a new way to find out new electrocaloric materials.
基金supported by the Natural Science Foundation of China(Grant Nos.51872053 and 51372042)Guangdong Provincial Natural Science Foundation(2015A030308004)the NSFC-Guangdong Joint Fund(Grant No.U1501246)。
文摘The electrocaloric effect(ECE)in lead-free BaSn_(x)Ti_(1-x)O_(3)(BSnT,x=0.05,0.10 and 0.15)ceramics were investigated using a direct ECE measurement.Results indicate that the maximum ECE occurs near the Curie temperature and it slightly shifts towards high temperatures.The directly measured ECE is larger than that calculated using the Maxwell relation and P-E loops.A maximum electrocaloric efficiencyΔT=ΔE=0.49-10-6 KmV-1 was procured for the composition with x=0.15 at T=299.2 K.And it also shows a broad peak in the temperature range of 250–320 K.
基金the US DoE,Office of Basic Energy Sciences,Division of Materials Science and Engineering under Award No.DE-FG02-07ER46410.
文摘Organic and inorganic relaxor ferroelectrics used for electrocaloric effect(ECE)applications areintroduced.Relaxor ferroelectrics offer several advantages for ECE devices,e.g.,infinite stateswithout applying electric field,field-induced large polarization,no-hysteresis ofheating and cooling,small-hysteresis polarization loss,room temperature phase transition,and broad temperaturerange.The ECE in relaxor ferroelectrics under a high electric field can be described using a theorysimilar to that for first-order phase transition materials.Large ECE was observed directly inhigh-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)68/32 mol%copolymers,P(VDF-TrFE-CFE)(CFE-chlorofluoroethylene)59.2/33.6/7.2 mol%terpolymers,P(vDF-TrFE-CFE)-P(VDF-CTFE)(CTFE-chlorotrifluoroethylene)95/5 wt%terpolymer blended films,and(PbLa)(ZrTi)O_(3)(PLZT)ceramic thin films.ECE reported inPb(Sc_(1/2)Ta_(1/2))O_(3)(PST),Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)(PMN-PT)thin films is also summarized.Finally,the perspective of ECE devices is llustrated.
