自触发射电阵列的设计是宇宙线大气簇射的射电探测所面临的机遇和难题之一,例如由背景源产生高振幅的瞬时噪声会导致射电阵列的误触发,而阵列设计需要避免由噪声导致的误触发.大气簇射射电信号独有的偏振特征为解决阵列的误触发问题提...自触发射电阵列的设计是宇宙线大气簇射的射电探测所面临的机遇和难题之一,例如由背景源产生高振幅的瞬时噪声会导致射电阵列的误触发,而阵列设计需要避免由噪声导致的误触发.大气簇射射电信号独有的偏振特征为解决阵列的误触发问题提供了解决方案,而利用信号偏振特征解决阵列误触发的方法的前提是射电信号的电场重建.由于背景噪声也会通过天线响应耦合到最终的观测数据中,这对正确重建射电信号的电场构成不可忽视的挑战.基于GRAND(Giant Radio Array for Neutrino Detection)验证阵列GP300(GRAND-Proto 300)的样机,结合模拟软件ZHAireS(ZHS AIR-shower Extended Simulations)模拟大气簇射产生的射电信号,耦合三极化天线的真实响应并使用最小二乘法重建电场,研究了射电信号的偏振特性,最终统计了以偏振为基础的天线的触发效率.展开更多
Boron nuclei in cosmic rays(CRs)are believed to be mainly produced by the fragmentation of heavier nuclei,such as carbon and oxygen,via collisions with the interstellar matter.Therefore,the boron-tocarbon flux ratio(B...Boron nuclei in cosmic rays(CRs)are believed to be mainly produced by the fragmentation of heavier nuclei,such as carbon and oxygen,via collisions with the interstellar matter.Therefore,the boron-tocarbon flux ratio(B/C)and the boron-to-oxygen flux ratio(B/O)are very essential probes of the CR propagation.The energy dependence of the B/C ratio from previous balloon-borne and space-based experiments can be well described by a single power-law up to about 1 TeV/n within uncertainties.This work reports direct measurements of B/C and B/O in the energy range from 10 Ge V/n to 5.6 TeV/n with 6 years of data collected by the Dark Matter Particle Explorer,with high statistics and well controlled systematic uncertainties.The energy dependence of both the B/C and B/O ratios can be well fitted by a broken power-law model rather than a single power-law model,suggesting the existence in both flux ratios of a spectral hardening at about 100 Ge V/n.The significance of the break is about 5.6σand 6.9σfor the GEANT4 simulation,and 4.4σand 6.9σfor the alternative FLUKA simulation,for B/C and B/O,respectively.These results deviate from the predictions of conventional turbulence theories of the interstellar medium(ISM),which point toward a change of turbulence properties of the ISM at different scales or novel propagation effects of CRs,and should be properly incorporated in the indirect detection of dark matter via anti-matter particles.展开更多
Molybdenum ditelluride （MoTe2） has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taki...Molybdenum ditelluride （MoTe2） has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taking advantage of high-κ screening effect, we have fabricated back-gated MoTe2 transistors on an Al2O3 high-κ dielectric and systematically investigated the electronic and optoelectronic proper- ties. A high current on/off ratio exceeding 106 is achieved in the Al2O3-based MoTe2 transistors, and the hole mobility is demonstrated to be 150 cm2 V^-1 s^-1, compared to 0.2-20 cm^2 V^-1 s^-1 ever obtained from back-gated MoTe2 transistors in the literatures. Moreover, a considerable hole concentration of 1.2 × 10^13 cm 2 is attained in our Al2O3-based MoTe2 transistors owing to the strong gate control capa- bility, leading to a high on-state hole current of 6.1 μA μm^-1. After optimization, our Al2O3-based MoTe2 phototransistor exhibits outstanding photodetective performance, with a high responsivity of 543 AW^-1 and a high photogain of 1,662 at 405 nm light illumination, which are boosted around 419 times compared to the referential SiO2-based control devices. The mechanisms of photoconductivity in the Al2O3-based MoTe2 phototransistors have been analyzed in detail, and the photogating effect is considered to play an important role. This work may provide useful insight to improve carrier mobility in two-dimensional layered semiconductors and open opportunities to facilitate the development of high-performance photodetectors in the future.展开更多
A new capacitance probe is developed for measuring local moisture content in wet porous media. The measurement principle, sensor structure of the probe, dynamic response characteristics and calibration procedure are d...A new capacitance probe is developed for measuring local moisture content in wet porous media. The measurement principle, sensor structure of the probe, dynamic response characteristics and calibration procedure are discussed in detail. The experimental results show that the probe can be used to measure the local moisture content in wet porous media.展开更多
文摘自触发射电阵列的设计是宇宙线大气簇射的射电探测所面临的机遇和难题之一,例如由背景源产生高振幅的瞬时噪声会导致射电阵列的误触发,而阵列设计需要避免由噪声导致的误触发.大气簇射射电信号独有的偏振特征为解决阵列的误触发问题提供了解决方案,而利用信号偏振特征解决阵列误触发的方法的前提是射电信号的电场重建.由于背景噪声也会通过天线响应耦合到最终的观测数据中,这对正确重建射电信号的电场构成不可忽视的挑战.基于GRAND(Giant Radio Array for Neutrino Detection)验证阵列GP300(GRAND-Proto 300)的样机,结合模拟软件ZHAireS(ZHS AIR-shower Extended Simulations)模拟大气簇射产生的射电信号,耦合三极化天线的真实响应并使用最小二乘法重建电场,研究了射电信号的偏振特性,最终统计了以偏振为基础的天线的触发效率.
基金funded by the Strategic Priority Science and Technology Projects in Space Science of Chinese Academy of Sciences(CAS)supported by the National Natural Science Foundation of China(11921003,11903084,12003076,12022503,12103094,and 12220101003)+7 种基金the Strategic Priority Science and Technology Projects of CAS(XDA15051100)the CAS Project for Young Scientists in Basic Research(YSBR-061)the Youth Innovation Promotion Association of CASthe Natural Science Foundation of Jiangsu Province(BK20201107)the Program for Innovative Talents and Entrepreneur in Jiangsusupported by the Swiss National Science Foundation(SNSF),Switzerlandthe National Institute for Nuclear Physics(INFN),Italythe European Research Council(ERC)under the European Unions Horizon 2020 research and innovation programme(851103)。
文摘Boron nuclei in cosmic rays(CRs)are believed to be mainly produced by the fragmentation of heavier nuclei,such as carbon and oxygen,via collisions with the interstellar matter.Therefore,the boron-tocarbon flux ratio(B/C)and the boron-to-oxygen flux ratio(B/O)are very essential probes of the CR propagation.The energy dependence of the B/C ratio from previous balloon-borne and space-based experiments can be well described by a single power-law up to about 1 TeV/n within uncertainties.This work reports direct measurements of B/C and B/O in the energy range from 10 Ge V/n to 5.6 TeV/n with 6 years of data collected by the Dark Matter Particle Explorer,with high statistics and well controlled systematic uncertainties.The energy dependence of both the B/C and B/O ratios can be well fitted by a broken power-law model rather than a single power-law model,suggesting the existence in both flux ratios of a spectral hardening at about 100 Ge V/n.The significance of the break is about 5.6σand 6.9σfor the GEANT4 simulation,and 4.4σand 6.9σfor the alternative FLUKA simulation,for B/C and B/O,respectively.These results deviate from the predictions of conventional turbulence theories of the interstellar medium(ISM),which point toward a change of turbulence properties of the ISM at different scales or novel propagation effects of CRs,and should be properly incorporated in the indirect detection of dark matter via anti-matter particles.
基金supported by the National Key Research and Development Program of China(2016YFA0302300,016YFA0200400)the National Science and Technology Major Project of China(2016ZX02301001)+1 种基金the National Natural Science Foundation of China(61306105)the Tsinghua University Initiative Scientific Research Program
文摘Molybdenum ditelluride （MoTe2） has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taking advantage of high-κ screening effect, we have fabricated back-gated MoTe2 transistors on an Al2O3 high-κ dielectric and systematically investigated the electronic and optoelectronic proper- ties. A high current on/off ratio exceeding 106 is achieved in the Al2O3-based MoTe2 transistors, and the hole mobility is demonstrated to be 150 cm2 V^-1 s^-1, compared to 0.2-20 cm^2 V^-1 s^-1 ever obtained from back-gated MoTe2 transistors in the literatures. Moreover, a considerable hole concentration of 1.2 × 10^13 cm 2 is attained in our Al2O3-based MoTe2 transistors owing to the strong gate control capa- bility, leading to a high on-state hole current of 6.1 μA μm^-1. After optimization, our Al2O3-based MoTe2 phototransistor exhibits outstanding photodetective performance, with a high responsivity of 543 AW^-1 and a high photogain of 1,662 at 405 nm light illumination, which are boosted around 419 times compared to the referential SiO2-based control devices. The mechanisms of photoconductivity in the Al2O3-based MoTe2 phototransistors have been analyzed in detail, and the photogating effect is considered to play an important role. This work may provide useful insight to improve carrier mobility in two-dimensional layered semiconductors and open opportunities to facilitate the development of high-performance photodetectors in the future.
文摘A new capacitance probe is developed for measuring local moisture content in wet porous media. The measurement principle, sensor structure of the probe, dynamic response characteristics and calibration procedure are discussed in detail. The experimental results show that the probe can be used to measure the local moisture content in wet porous media.
