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Synchronous X-ray/Optical QPOs from the Black Hole LMXB MAXI J1820+070 期刊论文 OAI收割
Monthly Notices of the Royal Astronomical Society, 2021
作者: HXMT

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black hole physics Low Mass X-ray Binaries accretion accretion discs stars: individual (MAXI J1820+070) Astrophysics - High Energy Astrophysical Phenomena Abstract: We present high-speed optical photometry from SAAO and SALT on the black hole LMXB MAXI J1820+070 (ASSASN-18ey), some of it simultaneous with NICER, Swift and Insight-HXMT X-ray coverage. We detect optical Quasi-Periodic Oscillations (QPOs) that move to higher frequencies as the outburst progresses, tracking both the frequency and evolution of similar X-ray QPOs previously reported. Correlated X-ray/optical data reveal a complex pattern of lags, including an anti-correlation and a sub-second lag that evolve over the first few weeks of outburst. They also show correlated components separated by a lag equal to the QPO period roughly centered on zero lag, implying that the inter-band variability is strongly and consistently affected by these QPOs at a constant phase lag of roughly ±Ю The synchronisation of X-ray and optical QPOs indicates that they must be produced in regions physically very close to each other we thus propose that they can be explained by a precessing jet model, based on analogies with V404 Cyg and MAXI J1348-630.

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

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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.

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

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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.

烟台牟平海洋牧场季节性低氧对大型底栖动物群落的生态效应 期刊论文 OAI收割
生物多样性, 2019, 卷号: 27, 期号: 2, 页码: 200-210
作者: 李宝泉

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低氧群落结构群落恢复敏感种机会种 hypoxia community structure community recovery sensitive species opportunistic species Hypoxia is a common phenomenon in the world's oceans, especially in the shallow waters of coastal zones. Rates of hypoxia are increasing due to global climatic changes and anthropogenic activities. Hypoxia can cause mass mortality of marine animals and can have severe negative impacts on marine ecosystems. To better understand the effects of hypoxia on macrobenthic communities, a survey was carried out in the Muping Marine Ranch (Yantai) during June, August and September of 2016. Results showed that seasonal hypoxia led to changes in benthic community structure, especially in terms of species composition and dominant species. The dominant species were Polychaeta Lumbrinereis latreilli, Sternaspis scutata and Mollusca Endopleura lubrica in summer. The opportunistic species Lumbrinereis latreilli increased, whereas, sensitive species such as Leptomya minuta, Glycera chirori, Upogebia major, Pontocrates altamarimus, Eriopisella sechellensis decreased during the hypoxic period of August. Hypoxia also reduced biodiversity indices. The effect of hypoxia on abundance and biomass were not significant, mainly because of the increase in the opportunistic Lumbrinereis latreilli, which counteracted the decline in abundance and biomass of other species. Individual physiological tolerance to hypoxia was different among species. Lumbrinereis latreilli showed higher tolerance to hypoxia in dissolved oxygen (DO) = 1.0 mg/L compared to other species. Some sensitive species, such as Leptomya minuta, Upogebia major, Pontocrates altamarimus and Eriopisella sechellensis showed lower tolerance when DO < 2.5 mg/L. When DO increased to 2.5 mg/L, the macrobenthic community start to recover gradually. The recovery extent and time needed were closely related to the degree of seasonal hypoxia.

Application of interferometry measurement in large-scale optic-electrical theodolite (EI CONFERENCE) 会议论文 OAI收割
2012 International Conference on Sensors, Measurement and Intelligent Materials, ICSMIM 2012, December 26, 2012 - December 27, 2012, Guilin, China
作者: Sun Z.

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Interferometry is a very important method in high accuracy measurement for optical system. This article briefly introduced the conception of interferometry and took a product of 4D Technology as an example to carry on the measurement. A large-scale optic-electrical Theodolite in assemblage was measured and its primary mirror was 400mm in diameter. With the analysis of the results some micro adjustments of the mechanical structure proceed and it made the system perform better. The final results of the whole system is 1.061 in P-V value and 0.1136 in RMS value (=632.8nm) this meets the demand of optical design and practical application. The result demonstrates that interferometry is a good way to be utilized and optimize in the procedure of assemble. (2013) Trans Tech Publications Switzerland.

Structural design of large aperture rectangular mirror for space telescope (EI CONFERENCE) 会议论文 OAI收割
2nd International Conference on Civil Engineering and Transportation, ICCET 2012, October 27, 2012 - October 28, 2012, Guilin, China
作者: Li Z.; Li Z.

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Structural design of large aperture mirror is one of the key technologies for space telescope development. To meet the requirements of high stiffness strength and thermal dimensional stability some factors such as support scheme materials selection lightweight design and flexible support design were taken into account. The three supports location of the mirror was determined according to the modal analytical solution. By adjusting the parameters of flexure hinge influences of gravity assembly stress and thermal stress on the mirror were reduced obviously. Finite element analysis (FEA) results indicate that the surface accuracy reach to rms10.2nm and 10.8nm under the gravity along optical axis direction and 5C uniform temperature rise respectively the fundamental frequency of the mirror component is 268Hz. Dynamics test shows that the first order natural frequency is 256Hz which shows an error less than 5% compared to FEA results. (2013) Trans Tech Publications Switzerland.

Longitudinal control law design and simulation of fixed-wing UAV (EI CONFERENCE) 会议论文 OAI收割
2012 International Conference on Measurement, Instrumentation and Automation, ICMIA 2012, September 15, 2012 - September 16, 2012, Guangzhou, China
作者: Duan Z.

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Taken some fixed-wing UAV as the study object the aircraft movement was broken down into the longitudinal movement and lateral movement according to the linearized small perturbation principle the longitudinal control law design method was discussed using root locus which belonged to classical control theory. The six degrees of freedom nonlinear model simulation result shows that: the control parameters designed are reasonable the simulation profile is fully consistent with the setting profile the control effect of pitch angle loop and altitude loop meets with the indices requirements the method is mature and reliable easy to realize in engineering. (2013) Trans Tech Publications Switzerland.

STEP Mission: Search for Terrestrial Exo-Planets 会议论文 OAI收割
European Planetary Science Congress 2013,, London, UK, 2013
Chen D.; Wu; J.; Li B.

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Search for Terrestrial Exo-Planest (hereafter STEP) mission is a latest advanced research project in Chinese Strategic Pioneer Program (SPP) on Space Science. STEP aims at the nearby earth-alike planets detection comprehensive research on the planetary system and some astrometry research with 0.5 uas precision in the space which will get the fruitful achievements in the exo-planetary and astrometry research fields. STEP will take the Space Astrometry technique in the optical band. The FOV is 0.44 degree based on 1.2m primary and focus length is 50m. The special metrology technique will be taken to reach 0.5 uas astrometry precision which will be idea for terrestrial exo-planets detection. The mission will take the L2 orbit.

A new algorithm for solving the best-fit sphere of optical aspherical surface (EI CONFERENCE) 会议论文 OAI收割
2nd International Conference on Advances in Materials and Manufacturing, ICAMMP 2011, December 16, 2011 - December 18, 2011, Guilin, China
作者: Lin J.; Lu M.

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To solve the best-fit sphere (BFS) accurately is one of the technological keys for the generating and testing of optical aspherical surfaces. This paper presents a new algorithm for solving the BFS of aspherical surfaces to suppress some deficiencies in the existing BFS algorithms. In the proposed approach it is not only suitable for the conic surface a BFS is constructed but also for higher order aspheres. The obtained asphericity and material removal function is more suitable for the machining and test. (2012) Trans Tech Publications which passes through both sides of endpoints in the section o -?xy of the aspherical surfaces Switzerland. the center of the BFS is shifted along the x-axis and its radius of curvature is automatically computed. The variable step size method is proposed to speed up the convergence of the iteration. Through numerically solving the BFS of conic and cubic surface the advantages of the proposed approach are verified. The results show that the proposed approach is of rapid convergence and high accuracy

An improved hyperspectral classification algorithm based on back-propagation neural networks (EI CONFERENCE) 会议论文 OAI收割
2012 2nd International Conference on Remote Sensing, Environment and Transportation Engineering, RSETE 2012, June 1, 2012 - June 3, 2012, Nanjing, China
作者: Yu P.; Yu P.

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In this paper a new method is proposed to improve the classification performance of hyperspectral images by combining the principal component analysis (PCA) genetic algorithm (GA) and artificial neural networks (ANNs). First some characteristics of the hyperspectral remotely sensed data such as high correlation high redundancy etc. are investigated. Based on the above analysis we propose to use the principal component analysis to capture the main information existing in the hyperspectral images and reduce its dimensionality consequently. Next we use neural networks to classify the reduced hyperspectral data. Since the back-propagation neural network we used is easy to suffer from the local minimum problem we adopt a genetic algorithm to optimize the BP network's weights and the threshold. Experimental results show that the classification accuracy is improved and the time of calculation is reduced as well. 2012 IEEE.