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浏览/检索结果: 共140条，第1-10条 帮助

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Preliminary Design of a New Type of Power Supply Similar to Flat-Top Pulsed High Magnetic Fields 期刊论文  OAI收割
IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 2022, 卷号: 32
作者:  Fei, Wei
  |  收藏  |  浏览/下载：35/0  |  提交时间：2022/12/23
Precipitation variation since 1748 CE in the central Lesser Khingan Mountains, Northeast China 期刊论文  OAI收割
ECOLOGICAL INDICATORS, 2021, 卷号: 129, 页码: 8
作者:  Li, Mingqi;  Deng, Guofu;  Shao, Xuemei;  Yin, Zhi-Yong
  |  收藏  |  浏览/下载：40/0  |  提交时间：2021/11/05
Precipitation variation since 1748 CE in the central Lesser Khingan Mountains, Northeast China 期刊论文  OAI收割
ECOLOGICAL INDICATORS, 2021, 卷号: 129, 页码: 8
作者:  Li, Mingqi;  Deng, Guofu;  Shao, Xuemei;  Yin, Zhi-Yong
  |  收藏  |  浏览/下载：19/0  |  提交时间：2021/11/05
Soil detachment capacity by rill flow for five typical loess soils on the Loess Plateau of China 期刊论文  OAI收割
SOIL & TILLAGE RESEARCH, 2021, 卷号: 213, 页码: 12
作者:  Shen, Nan;  Wang, Zhanli;  Guo, Qi;  Zhang, Qingwei;  Wu, Bing
  |  收藏  |  浏览/下载：50/0  |  提交时间：2021/11/05
Continuous Expansions of Yangtze River Islands After the Three Gorges Dam Tracked by Landsat Data Based on Google Earth Engine 期刊论文  OAI收割
IEEE ACCESS, 2020, 卷号: 8, 页码: 92731-92742
作者:  Sun, Jinyan;  Xu, Nan;  Ding, Lei;  Ma, Yue;  Liu, Zhengjia
  |  收藏  |  浏览/下载：35/0  |  提交时间：2021/07/09
The braking index of PSR B0540-69 and the associated pulsar wind nebula emission after spin-down rate transition 期刊论文  OAI收割
Monthly Notices of the Royal Astronomical Society, 2020, 卷号: 494, 页码: 1865-1870
作者:  HXMT
  |  收藏  |  浏览/下载：66/0  |  提交时间：2022/02/08
stars: magnetic field  stars: neutron  pulsars: general  Astrophysics  - High Energy Astrophysical Phenomena  Abstract: In 2011 December, PSR B054-69 experienced a spin-down rate transition (SRT), after which the spin-down power of the pulsar increased by $\sim 36{{\ \rm per\ cent}}$. About 1000 d after the SRT, the X-ray luminosity of the associated pulsar wind nebula (PWN) was found to brighten by $32\pm 8{{\ \rm per\ cent}}$. After the SRT, the braking index n of PSR B0540-69 changes from n = 2.12 to 0.03 and then keeps this value for about five years before rising to n = 0.9 in the following years. We find that most of the current models have difficulties in explaining the measured braking index. One exceptive model of the braking index evolution is the increasing dipole magnetic field of PSR B0540-69. We suggest that the field increase may result from some instabilities within the pulsar core that enhance the poloidal component at the price of toroidal component of the magnetic field. The increasing dipole magnetic field will result in the X-ray brightening of the PWN. We fit the PWN X-ray light curve by two models: one assumes a constant magnetic field within the PWN during the brightening and the other assumes an enhanced magnetic field proportional to the energy density of the PWN. It appears that the two models fit the data well, though the later model seems to fit the data a bit better. This provides marginal observational evidence that magnetic field in the PWN is generated by the termination shock. Future high-quality and high-cadence data are required to draw a solid conclusion.  
Constraining the X-Ray-Infrared Spectral Index of Second-timescale Flares from SGR 1935+2154 with Palomar Gattini-IR 期刊论文  OAI收割
The Astrophysical Journal, 2020, 卷号: 901, 页码: L7
作者:  HXMT
  |  收藏  |  浏览/下载：27/0  |  提交时间：2022/02/08
Radio transient sources  Magnetars  Soft gamma-ray repeaters  2008  992  1471  Astrophysics - High Energy Astrophysical Phenomena  Astrophysics - Instrumentation and Methods for Astrophysics  Abstract: The Galactic magnetar SGR 1935+2154 has been reported to produce the first example of a bright millisecond-duration radio burst (FRB 200428) similar to the cosmological population of fast radio bursts (FRBs). The detection of a coincident bright X-ray burst represents the first observed multiwavelength counterpart of an FRB. However, the search for similar emission at optical wavelengths has been hampered by the high inferred extinction on the line of sight. Here, we present results from the first search for second-timescale emission from the source at near-infrared (NIR) wavelengths using the Palomar Gattini-IR observing system in the J band, enabled by a novel detector readout mode that allows short exposure times of ?0.84 s with 99.9% observing efficiency. With a total observing time of ?12 hr (?47,728 images) during its 2020 outburst, we place median 3Ҡlimits on the second-timescale NIR fluence of ?18 Jy ms (13.1 AB mag). The corresponding extinction-corrected limit is ?125 Jy ms for an estimated extinction of AJ = 2.0 mag. Our observations were sensitive enough to easily detect an NIR counterpart of FRB 200428 if the NIR emission falls on the same power law as observed across its radio to X-ray spectrum. We report nondetection limits from epochs of four simultaneous X-ray bursts detected by the Insight-HXMT and NuSTAR telescopes during our observations. These limits provide the most stringent constraints to date on fluence of flares at 1014 Hz, and constrain the fluence ratio of the NIR emission to coincident X-ray bursts to RNIR ? 0.025 (fluence index ?0.35).  
An underlying clock in the extreme flip-flop state transitions of the black hole transient Swift J1658.2-4242 期刊论文  OAI收割
Astronomy and Astrophysics, 2020, 卷号: 641, 页码: A101
作者:  HXMT
  |  收藏  |  浏览/下载：65/0  |  提交时间：2022/02/08
accretion  accretion disks  black hole physics  X-rays: binaries  time  Astrophysics - High Energy Astrophysical Phenomena  Abstract:
Aims: Flip-flops are top-hat-like X-ray flux variations, which have been observed in some transient accreting black hole binary systems, and feature simultaneous changes in the spectral hardness and the power density spectrum (PDS). They occur at a crucial time in the evolution of these systems, when the accretion disc emission starts to dominate over coronal emission. Flip-flops remain a poorly understood phenomenon, so we aim to thoroughly investigate them in a system featuring several such transitions.
Methods: Within the multitude of observations of Swift J1658.2-4242 during its outburst in early 2018, we detected 15 flip-flops, enabling a detailed analysis of their individual properties and the differences between them. We present observations by XMM-Newton, NuSTAR, Astrosat, Swift, Insight-HXMT, INTEGRAL, and ATCA. We analysed their light curves, searched for periodicities, computed their PDSs, and fitted their X-ray spectra, to investigate the source behaviour during flip-flop transitions and how the interval featuring flip-flops differs from the rest of the outburst.
Results: The flip-flops of Swift J1658.2-4242 are of an extreme variety, exhibiting flux differences of up to 77% within 100 s, which is much larger than what has been seen previously. We observed radical changes in the PDS simultaneous with the sharp flux variations, featuring transitions between the quasi-periodic oscillation types C and A, which have never been observed before. Changes in the PDS are delayed, but more rapid than changes in the light curve. Flip-flops occur in two intervals within the outburst, separated by about two weeks in which these phenomena were not seen. Transitions between the two flip-flop states occurred at random integer multiples of a fundamental period of 2.761 ks in the first interval and 2.61 ks in the second. Spectral analysis reveals the high and low flux flip-flop states to be very similar, but distinct from intervals lacking flip-flops. A change of the inner temperature of the accretion disc is responsible for most of the flux difference in the flip-flops. We also highlight the importance of correcting for the influence of the dust scattering halo on the X-ray spectra.  
Approach to the Geopolitical Influences of Great Powers in Southeast Asia: Case Studies of China and the US 期刊论文  OAI收割
CHINESE GEOGRAPHICAL SCIENCE, 2019, 卷号: 29, 期号: 2, 页码: 341-351
作者:  Qin Qi;  Cheng Shengkui;  Li Fei;  Zhang Shuwen;  Wu Liang
  |  收藏  |  浏览/下载：67/0  |  提交时间：2019/05/22
Approach to the Geopolitical Influences of Great Powers in Southeast Asia: Case Studies of China and the US 期刊论文  OAI收割
CHINESE GEOGRAPHICAL SCIENCE, 2019, 卷号: 29, 期号: 2, 页码: 341-351
作者:  Qin Qi;  Cheng Shengkui;  Li Fei;  Zhang Shuwen;  Wu Liang
  |  收藏  |  浏览/下载：16/0  |  提交时间：2019/05/22