分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2023-12-15 合作期刊: 《Research in Astronomy and Astrophysics》
摘要: The Swift/XRT detected the X-ray afterglow of long burst GRB 220117A, which began to rebrighten 300 s after triggering and followed a single power-law decay segment after thousands of seconds of the orbital observation gap. This segment is different from the shallow decay segment (plateau) and flare, and may belong to a giant X-ray bump. We investigated this segment by the fall-back accretion model and found that the model can interpret this segment with reasonable parameter values. Within this physical model scenario, the fall-back accretion rate reaches a peak value ∼1.70 ×10−5M⊙ s−1 around 300 s in the central engine frame, which is compatible with the late mass supply rate of some low-metallicity massive progenitor stars. The initial black hole (BH) spin is and implies that this re-brightening signature requires a larger BH spin. The total accretion mass during the fall-back process is Macc = (3.09 ± 0.02) × 10−2M⊙. The jet energy from the fall-back accretion is (9.77 ± 0.65) × 1052 erg, with a ratio of 0.066 to the isotropic-equivalent radiation energies of the GRB prompt phase in the 1–104 keV band. The fall-back radius rp corresponding to the peak time of fall-back tp is (3.16 ± 0.05) × 1010 cm, which is consistent with the typical radius of Wolf–Rayet stars. In summary, our results provide additional support for the origin of the long burst from the core collapse of Wolf–Rayet stars, and its late central engine activity is likely due to the fall-back accretion process.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The physical properties of two-dimensional (2D) materials may drastically vary with their thickness profiles. Current thickness profiling methods for 2D material (e.g., atomic force microscopy and ellipsometry) are limited in measurement throughput and accuracy. Here we present a novel high-speed and high-precision thickness profiling method, termed Transmission-Matrix Quantitative Phase Profilometry (TM-QPP). In TM-QPP, picometer-level optical pathlength sensitivity is enabled by extending the photon shot-noise limit of a high sensitivity common-path interferometric microscopy technique, while accurate thickness determination is realized by developing a transmission-matrix model that accounts for multiple refractions and reflections of light at sample interfaces. Using TM-QPP, the exact thickness profiles of monolayer and few-layered 2D materials (e.g., MoS2, MoSe2 and WSe2) are mapped over a wide field of view within seconds in a contact-free manner. Notably, TM-QPP is also capable of spatially resolving the number of layers of few-layered 2D materials.
分类: 生物学 >> 动物学 提交时间: 2017-11-07 合作期刊: 《古脊椎动物学报》
摘要: Our systematic revision of Anhuichelys Yeh, 1979, based on abundant new material from the Paleocene of Qianshan Basin, Anhui Province, China provides evidences for its assignment to the stem Testudinidae. Anhuichelys contains three species in the Paleocene of Qianshan Basin: A. siaoshihensis Yeh, 1979 from the Early Paleocene of Wanghudun Formation, A. tsienshanensis Yeh, 1979 from both Wanghudun and Doumu formations and A. doumuensis sp. nov. from the Middle Paleocene Doumu Formation. A. xinzhouensis Chen, 1983 from the Paleocene of Xinzhou, Hubei Province is synonymized with A. tsienshanensis. Associated with a terrestrial vertebrate fauna, Anhuichelys is likely a land turtle and also the first testudinoid to develop the hinge on the shell.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: To develop highly sensitive, stable and repeatable surface-enhanced Raman scattering (SERS) substrates is crucial for analytical detection, which is a challenge for traditional metallic structures. Herein, by taking advantage of the high surface activity of 1T' transition metal telluride, we have fabricated high-density gold nanoparticles (AuNPs) that are spontaneously in-situ prepared on the 1T' MoTe2 atomic layers via a facile method, forming a plasmonic-2D material hybrid SERS substrate. This AuNP formation is unique to the 1T' phase, which is repressed in 2H MoTe2 with less surface activity. The hybrid structure generates coupling effects of electromagnetic and chemical enhancements, as well as excellent molecule adsorption, leading to the ultrasensitive (4*10^-17 M) and reproducible detection. Additionally, the immense fluorescence and photobleaching phenomena are mostly avoided. Flexible SERS tapes have been demonstrated in practical applications. Our approach facilitates the ultrasensitive SERS detection by a facile method, as well as the better mechanistic understanding of SERS beyond plasmonic effects.