The Wide Field Survey Telescope(WFST) is a dedicated photometric surveying facility being built jointly by University of Science and Technology of China(USTC) and the Purple Mountain Observatory(PMO). It is equipped w...The Wide Field Survey Telescope(WFST) is a dedicated photometric surveying facility being built jointly by University of Science and Technology of China(USTC) and the Purple Mountain Observatory(PMO). It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for highquality image capture over a 6.5-square-degree field of view. The installation of WFST near the summit of Saishiteng mountain in the Lenghu region is scheduled in summer of 2023, and the operation is planned to start three months later. WFST will scan the northern sky in four optical bands(u, g, r and i) at cadences from hourly/daily in the deep high-cadence survey(DHS) program, to semi-weekly in the wide field survey(WFS) program. During a photometric night, a nominal 30 s exposure in the WFS program will reach a depth of 22.27, 23.32, 22.84, and 22.31(AB magnitudes) in these four bands, respectively, allowing for the detection of a tremendous amount of transients in the low-z universe and a systematic investigation of the variability of Galactic and extragalactic objects. In the DHS program, intranight 90 s exposures as deep as 23(u) and 24 mag(g), in combination with target of opportunity follow-ups, will provide a unique opportunity to explore energetic transients in demand for high sensitivities, including the electromagnetic counterparts of gravitational wave events, supernovae within a few hours of their explosions,tidal disruption events and fast, luminous optical transients even beyond redshift of unity. In addition, the final 6-year co-added images, anticipated to reach g■25.8 mag in WFS or 1.5 mags deeper in DHS, will be of fundamental importance to general Galactic and extragalactic science. The highly uniform legacy surveys of WFST will serve as an indispensable complement to those of the Vera C. Rubin Observatory's Legacy Survey of Space and Time(LSST) that monitors the southern sky.展开更多
Blue-emission(~480 nm)CsPbBr_(3) nanoparticles with ultra-small size(~2.1 nm)are synthesized using the liquid nitrogen freezing with the ligand of dodecylbenzene sulfonic acid(DBSA).Asymmetric narrow emissions at the ...Blue-emission(~480 nm)CsPbBr_(3) nanoparticles with ultra-small size(~2.1 nm)are synthesized using the liquid nitrogen freezing with the ligand of dodecylbenzene sulfonic acid(DBSA).Asymmetric narrow emissions at the low energy side,with the full width at half-maximum of~20 nm,are observed in solution and film at room temperature.The spectral asymmetry is mainly ascribed to phonon vibronic replica with averaged phonon energy of~40 meV.Moreover,exciting this CsPbBr_(3) nanoparticles solution using linearly polarized 6 ns pulsed laser at 355 nm,we observe polarized emission with polarization degree(P_(PL))of~7%,and P_(PL) decreases more than 20%in the vibronic progression.However,the P_(PL) goes to zero in frozen solutions as well as in films.Thus we speculate the polarized emission is due to the photoinduced re-alignment of nanoparticles,and the diminished P_(PL) at the phonon side band may be due to the non-adiabatic electronic-to-vibronic transitions.The novel phenomena from the ultra-small CsPbBr_(3) nanoparticle demonstrated in this work may provide fundamental insights into its photophysics with direct implications for optoelectronics.展开更多
We successfully designed and synthesized two BDT-BT-T （BDT=benzo[1,2-b：4,5-b＇]dithiophene, BT-T=4,7-dithien-2-yl-2,1,3-benzothia- diazole） based polymers as the electron donor for application in all-polymer solar ...We successfully designed and synthesized two BDT-BT-T （BDT=benzo[1,2-b：4,5-b＇]dithiophene, BT-T=4,7-dithien-2-yl-2,1,3-benzothia- diazole） based polymers as the electron donor for application in all-polymer solar cells （all-PSCs）. By adopting N2200 as the electron acceptor, we system- atically investigated the impact of fluorination on the charge transfer, transport, blend morphology and photovoltaic properties of the relevant alI-PSCs. A best power conversion efficiency （PCE） of 3.4% was obtained for fluorinated PT-BT2F/N2200 （BT2F=difluorobenzo[c][1,2,5]thiadiazole） alI-PSCs in com- parison with that of 2.7% in non-fluorinated PT-BT/N2200 （BT=benzothiad（azole） based device. Herein, all-polymers blends adopting either non-fluori- nated PT-BT or fluorinated PT-BT2F exhibit similar morphology features. In depth optical spectrum measurements demonstrate that molecular fluorina- tion can further enhance charge transfer between donor and acceptor polymer. Moreover, all-polymer blends exhibit improved hole mobilities and more balanced carriers transport when adopting fluorinated donor polymer PT-BT2F. Therefore, although the PCE is relatively low, our findings may become important in understanding how subtle changes in molecular structure impact relevant optoelectronic properties and further improve the performance of all-PSCSs.展开更多
Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device perf...Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device performance.Nevertheless,the physical picture of interlayer coupling effect during incorporation of monolayer(1L-)hBN is not explicit yet.In this article,spectroscopic ellipsometry was used to experimentally obtain the broadband excitonic and critical point properties of WS_(2)/MoS_(2)and WS_(2)/hBN/MoS_(2)van der Waals heterostructures.We find that 1L-hBN can only slightly block the interlayer electron transfer from WS_(2)layer to MoS_(2)layer.Moreover,insertion of 1L-hBN weakens the interlayer coupling effect by releasing quantum confinement and reducing efficient dielectric screening.Consequently,the exciton binding energies in WS_(2)/hBN/MoS_(2)heterostructures blueshift comparing to those in WS_(2)/MoS_(2)heterostructures.In this exciton binding energies tuning process,the reducing dielectric screening effect plays a leading role.In the meantime,the quasi-particle(QP)bandgap remains unchanged before and after 1L-hBN insertion,which is attributed to released quantum confinement and decreased dielectric screening effects canceling each other.Unchanged QP bandgap as along with blueshift exciton binding energies lead to the redshift exciton transition energies in WS_(2)/hBN/MoS_(2)heterostructures.展开更多
Foothold identification is a key ability for legged robots that allows generating terrain adaptive behaviors(e.g.,gait and control parameters)and thereby improving mobility in complex environment.To this end,this pape...Foothold identification is a key ability for legged robots that allows generating terrain adaptive behaviors(e.g.,gait and control parameters)and thereby improving mobility in complex environment.To this end,this paper addresses the issue of foothold characterization and identification over rugged terrain,from the terrain geometry point of view.For a terrain region that might be a potential foothold of a robotic leg,the characteristic features are extracted as two first-order partial derivatives and two curvature parameters of a quadric regression surface at this location.These features are able to give an intuitive and,more importantly,accurate characterization towards the specific geometry of the ground location.On this basis,a supervised learning technique,Support Vector Machine(SVM),is employed,seeking to Ieam a foothold identification policy from human expert demonstration.As a result,an SVM classifier is leamt using the extracted features and human-demonstrated labels,which is able to identify whether or not a certain ground location is suited as a safe foot support for a robotic leg.It is shown that over 90%identification rate can be achieved with the proposed approach.Finally,preliminary experiment is implemented with a six-legged robot to demonstrate the effectiveness of the proposed approach.展开更多
基金supported by the Cyrus Chun Ying Tang Foundationsthe Major Science and Technology Project of Qinghai Province(Grant No.2019ZJ-A10)+4 种基金the 111 Project for“Observational and Theoretical Research on Dark Matter and Dark Energy”(Grant No.B23042)the National Natural Science Foundation of China(Grant Nos.11833007,12073078,12173088,12192221,12192224,12233008,12273036,and 12273113)the Frontier Scientific Research Program of Deep Space Exploration Laboratory(Grant No.2022-QYKYJH-HXYF-012)the support from the USTC Research Funds of the Double First-Class Initiative(Grant No.YD2030002009)Project for Young Scientists in Basic Research of the Chinese Academy of Sciences(Grant No.YSBR-061),respectively。
文摘The Wide Field Survey Telescope(WFST) is a dedicated photometric surveying facility being built jointly by University of Science and Technology of China(USTC) and the Purple Mountain Observatory(PMO). It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for highquality image capture over a 6.5-square-degree field of view. The installation of WFST near the summit of Saishiteng mountain in the Lenghu region is scheduled in summer of 2023, and the operation is planned to start three months later. WFST will scan the northern sky in four optical bands(u, g, r and i) at cadences from hourly/daily in the deep high-cadence survey(DHS) program, to semi-weekly in the wide field survey(WFS) program. During a photometric night, a nominal 30 s exposure in the WFS program will reach a depth of 22.27, 23.32, 22.84, and 22.31(AB magnitudes) in these four bands, respectively, allowing for the detection of a tremendous amount of transients in the low-z universe and a systematic investigation of the variability of Galactic and extragalactic objects. In the DHS program, intranight 90 s exposures as deep as 23(u) and 24 mag(g), in combination with target of opportunity follow-ups, will provide a unique opportunity to explore energetic transients in demand for high sensitivities, including the electromagnetic counterparts of gravitational wave events, supernovae within a few hours of their explosions,tidal disruption events and fast, luminous optical transients even beyond redshift of unity. In addition, the final 6-year co-added images, anticipated to reach g■25.8 mag in WFS or 1.5 mags deeper in DHS, will be of fundamental importance to general Galactic and extragalactic science. The highly uniform legacy surveys of WFST will serve as an indispensable complement to those of the Vera C. Rubin Observatory's Legacy Survey of Space and Time(LSST) that monitors the southern sky.
基金supported by startup funding at Fudan University,National Natural Science Foundation of China (Nos.62074079,61774039)large instrument equipment open fund of Nanjing University of Science and Technology.
文摘Blue-emission(~480 nm)CsPbBr_(3) nanoparticles with ultra-small size(~2.1 nm)are synthesized using the liquid nitrogen freezing with the ligand of dodecylbenzene sulfonic acid(DBSA).Asymmetric narrow emissions at the low energy side,with the full width at half-maximum of~20 nm,are observed in solution and film at room temperature.The spectral asymmetry is mainly ascribed to phonon vibronic replica with averaged phonon energy of~40 meV.Moreover,exciting this CsPbBr_(3) nanoparticles solution using linearly polarized 6 ns pulsed laser at 355 nm,we observe polarized emission with polarization degree(P_(PL))of~7%,and P_(PL) decreases more than 20%in the vibronic progression.However,the P_(PL) goes to zero in frozen solutions as well as in films.Thus we speculate the polarized emission is due to the photoinduced re-alignment of nanoparticles,and the diminished P_(PL) at the phonon side band may be due to the non-adiabatic electronic-to-vibronic transitions.The novel phenomena from the ultra-small CsPbBr_(3) nanoparticle demonstrated in this work may provide fundamental insights into its photophysics with direct implications for optoelectronics.
基金This work was supported jects （No. 2016YFA0202402）, by the National Key Research Pro- the Natural Science Foundation of Jiangsu Province of China （BK20170337）, the National Natural Science Foundation of China （Nos. 51761145013 and 61674111）, and ＂111＂ projects. And we also acknowledge the Collaborative Innovation Center of Suzhou Nano Science and Technology, the Priority Academic Program Development of Jiangsu Higher Educa- tion Institutions （PAPD）.
文摘We successfully designed and synthesized two BDT-BT-T （BDT=benzo[1,2-b：4,5-b＇]dithiophene, BT-T=4,7-dithien-2-yl-2,1,3-benzothia- diazole） based polymers as the electron donor for application in all-polymer solar cells （all-PSCs）. By adopting N2200 as the electron acceptor, we system- atically investigated the impact of fluorination on the charge transfer, transport, blend morphology and photovoltaic properties of the relevant alI-PSCs. A best power conversion efficiency （PCE） of 3.4% was obtained for fluorinated PT-BT2F/N2200 （BT2F=difluorobenzo[c][1,2,5]thiadiazole） alI-PSCs in com- parison with that of 2.7% in non-fluorinated PT-BT/N2200 （BT=benzothiad（azole） based device. Herein, all-polymers blends adopting either non-fluori- nated PT-BT or fluorinated PT-BT2F exhibit similar morphology features. In depth optical spectrum measurements demonstrate that molecular fluorina- tion can further enhance charge transfer between donor and acceptor polymer. Moreover, all-polymer blends exhibit improved hole mobilities and more balanced carriers transport when adopting fluorinated donor polymer PT-BT2F. Therefore, although the PCE is relatively low, our findings may become important in understanding how subtle changes in molecular structure impact relevant optoelectronic properties and further improve the performance of all-PSCSs.
基金the National Natural Science Foundation of China(Nos.11674062,61775042,and 61774040)the Fudan University-CIOMP Joint Fund(Nos.FC2019-004,FC2019-006,and FC2018-002)+2 种基金the National Key R&D Program of China(No.2018YFA0703700)the Shanghai Municipal Science and Technology Commission(No.18JC1410300)the Shanghai Municipal Natural Science Foundation(No.20ZR1403200).
文摘Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device performance.Nevertheless,the physical picture of interlayer coupling effect during incorporation of monolayer(1L-)hBN is not explicit yet.In this article,spectroscopic ellipsometry was used to experimentally obtain the broadband excitonic and critical point properties of WS_(2)/MoS_(2)and WS_(2)/hBN/MoS_(2)van der Waals heterostructures.We find that 1L-hBN can only slightly block the interlayer electron transfer from WS_(2)layer to MoS_(2)layer.Moreover,insertion of 1L-hBN weakens the interlayer coupling effect by releasing quantum confinement and reducing efficient dielectric screening.Consequently,the exciton binding energies in WS_(2)/hBN/MoS_(2)heterostructures blueshift comparing to those in WS_(2)/MoS_(2)heterostructures.In this exciton binding energies tuning process,the reducing dielectric screening effect plays a leading role.In the meantime,the quasi-particle(QP)bandgap remains unchanged before and after 1L-hBN insertion,which is attributed to released quantum confinement and decreased dielectric screening effects canceling each other.Unchanged QP bandgap as along with blueshift exciton binding energies lead to the redshift exciton transition energies in WS_(2)/hBN/MoS_(2)heterostructures.
基金This work was supported by National Natural Science Foundation of China(Grant No.51805074)State Key Laboratory of Robotics and System(HIT)(Grant No.SKLRS-2018-KF-02)+2 种基金China postdoctoral Science Foundation(Grant Nos.2018M631799 and 2019T120213)Fundamental Research Funds for the Central Universities(Grant No.N2003001)Natural Science Foundation of Liaoning Province(Grant No.2019-BS-090).
文摘Foothold identification is a key ability for legged robots that allows generating terrain adaptive behaviors(e.g.,gait and control parameters)and thereby improving mobility in complex environment.To this end,this paper addresses the issue of foothold characterization and identification over rugged terrain,from the terrain geometry point of view.For a terrain region that might be a potential foothold of a robotic leg,the characteristic features are extracted as two first-order partial derivatives and two curvature parameters of a quadric regression surface at this location.These features are able to give an intuitive and,more importantly,accurate characterization towards the specific geometry of the ground location.On this basis,a supervised learning technique,Support Vector Machine(SVM),is employed,seeking to Ieam a foothold identification policy from human expert demonstration.As a result,an SVM classifier is leamt using the extracted features and human-demonstrated labels,which is able to identify whether or not a certain ground location is suited as a safe foot support for a robotic leg.It is shown that over 90%identification rate can be achieved with the proposed approach.Finally,preliminary experiment is implemented with a six-legged robot to demonstrate the effectiveness of the proposed approach.
