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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.

Comparison of simulated backgrounds with in-orbit observations for HE, ME, and LE onboard Insight-HXMT 期刊论文 OAI收割
Astrophysics and Space Science, 2020, 卷号: 365, 页码: 158
作者: HXMT

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Insight-HXMT Geant4 simulation Background observation Astrophysics - Instrumentation and Methods for Astrophysics Abstract: Insight-HXMT, the first X-ray astronomical satellite in China, aims to reveal new sources in the Galaxy and to study fundamental physics of X-ray binaries from 1 to 250 keV. It has three collimated telescopes, the High Energy X-ray telescope (HE), the Medium Energy X-ray telescope (ME), and the Low Energy X-ray telescope (LE). Before the launch, in-orbit backgrounds of these three telescopes had been estimated through Geant4 simulation, in order to investigate the instrument performance and the achievement of scientific goals. In this work, these simulated backgrounds are compared with in-orbit observations. Good agreements are shown for all three telescopes. For HE, (1) the deviation of the simulated background rate after two years of operation in space is 5 % from the observation (2) the total background spectrum and the relative abundance of the 67 keV line show long-term increases both in simulations and observations. For ME, (1) the deviation of simulated background rate is within 15 % from the observation, and (2) there are no obvious long-term increase features in the background spectra of simulations and observations. For LE, the background level given by simulations is also consistent with observations. The consistencies of these comparisons validate that the Insight-HXMT mass model, i.e., space environment components and models adopted, physics processes selected, and detector constructions built, is reasonable. However, the line features at 7.5 and 8.0 keV, which are obvious in the observed spectra of LE, are not evident in simulations. This might result from uncertainties in the LE constructions.

Simulating ocean acidification and CO2 leakages from carbon capture and storage to assess the effects of pH reduction on cladoceran Moina mongolica Daday and its progeny 期刊论文 OAI收割
CHEMOSPHERE, 2016, 卷号: 155, 页码: 621-629
作者: Wang, Zaosheng; Wang, Youshao; Yan, Changzhou

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CO2-driven acidification Rank species sensitivity Reproduction Intrinsic rate of natural increase Progeny Macromolecule contents

The Yangtze finless porpoise: On an accelerating path to extinction? 期刊论文 OAI收割
BIOLOGICAL CONSERVATION, 2014, 卷号: 172, 期号: -, 页码: 117-123
作者: Mei, Zhigang; Zhang, Xinqiao; Huang, Shiang-Lin; Zhao, Xiujiang; Hao, Yujiang

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Yangtze finless porpoise Census Line transect survey Population abundance Intrinsic rate of increase Extinction risk

Research on the torque characteristic of disc micromotor on axial magnetic field (EI CONFERENCE) 会议论文 OAI收割
2012 2nd International Conference on Consumer Electronics, Communications and Networks, CECNet 2012, April 21, 2012 - April 23, 2012, Three Gorges, China
Liu B.

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In order to increase the electromagnetic torque density of micromotor with axial magnetic field numerical analysis of permanent magnetic field and electromagnetic torque were deduced and the key factors of increasing torque density of micromotor was obtained. The numerical analysis of three-dimensional magnetic field in air gap produced by spliced sector permanent magnetic poles is done and the way of improving flux density and permanent magnet use efficiency are given through investigating the influence of magnet thickness height of air gap and pole interval rate and other parameters to air gap flux density and leakage flux. Based on the test of axial magnetic field and torque characteristic of micromotor the analysis of micromotor magnetic field and calculation of torque are verified meanwhile using the plane stator with 0.7mm thickness assemble micromotor having minimum air gap height of 1mm and its torque constant up to 3.8mNm/A. 2012 IEEE.

Energy transfer in Y3Al5O12:Ce 3, Pr3+ and CaMoO4:Sm3, Eu 3 phosphors (EI CONFERENCE) 会议论文 OAI收割
作者: Wang L.; Wang X.-J.; Zhang X.; Zhang X.; Zhang X.

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Non-radiative energy transfers (ET) from Ce3 to Pr3+ in Y3Al5O12:Ce3 Pr3+ and from Sm3 to Eu3 in CaMoO4:Sm3 Eu3 are studied based on photoluminescence spectroscopy and fluorescence decay patterns. The result indicates an electric dipoledipole interaction that governs ET in the LED phosphors. For Ce3 concentration of 0.01 in YAG:Ce3 Pr3+ the rate constant and critical distance are evaluated to be 4.510-36 cm 6 s-1 and 0.81 nm respectively. An increase in the red emission line of Pr3+ relative to the yellow emission band of Ce 3 on increasing Ce3 concentration is observed. This behavior is attributed to the increase of spectral overlap integrals between Ce3 emission and Pr3+ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce3 concentration. In CaMoO4:Sm3 Eu3 Sm 3Eu3 transfer occurs from 4G5/2 of Sm3 to 5D0 of Eu3. The rate constant of 8.510-40 cm6 s-1 and the critical transfer distance of 0.89 nm are evaluated. 2010 Elsevier B.V. All rights reserved.

Research on infrared dim-point target detection and tracking under sea-sky-line complex background (EI CONFERENCE) 会议论文 OAI收割
International Symposium on Photoelectronic Detection and Imaging 2011: Advances in Infrared Imaging and Applications, May 24, 2011 - May 24, 2011, Beijing, China
作者: Dong Y.-X.; Zhang H.-B.; Li Y.; Li Y.; Li Y.

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Target detection and tracking technology in infrared image is an important part of modern military defense system. Infrared dim-point targets detection and recognition under complex background is a difficulty and important strategic value and challenging research topic. The main objects that carrier-borne infrared vigilance system detected are sea-skimming aircrafts and missiles. Due to the characteristics of wide field of view of vigilance system the target is usually under the sea clutter. Detection and recognition of the target will be taken great difficulties.There are some traditional point target detection algorithms such as adaptive background prediction detecting method. When background has dispersion-decreasing structure the traditional target detection algorithms would be more useful. But when the background has large gray gradient such as sea-sky-line sea waves etc.The bigger false-alarm rate will be taken in these local area.It could not obtain satisfactory results. Because dim-point target itself does not have obvious geometry or texture feature in our opinion from the perspective of mathematics the detection of dim-point targets in image is about singular function analysis.And from the perspective image processing analysis the judgment of isolated singularity in the image is key problem. The foregoing points for dim-point targets detection its essence is a separation of target and background of different singularity characteristics.The image from infrared sensor usually accompanied by different kinds of noise. These external noises could be caused by the complicated background or from the sensor itself. The noise might affect target detection and tracking. Therefore the purpose of the image preprocessing is to reduce the effects from noise also to raise the SNR of image and to increase the contrast of target and background. According to the low sea-skimming infrared flying small target characteristics the median filter is used to eliminate noise improve signal-to-noise ratio then the multi-point multi-storey vertical Sobel algorithm will be used to detect the sea-sky-line so that we can segment sea and sky in the image. Finally using centroid tracking method to capture and trace target. This method has been successfully used to trace target under the sea-sky complex background. 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

United steering of control moment gyros for small satellite with limited gimbal rate (EI CONFERENCE) 会议论文 OAI收割
2010 IEEE International Conference on Information and Automation, ICIA 2010, June 20, 2010 - June 23, 2010, Harbin, Heilongjiang, China
Xu K.; Jin G.; Chen C.

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Single Gimbal Control Moment Gyroscopes (SGCMG) can could provide large control torque and quick attitude maneuver rate to small satellites without any increase in power volume and mass which will help small satellites become more powerful. Singularity avoidance and failure steering are two important problems to SGCMGs and also the main focus in this field. A new united steering law for SGCMGs with capabilities of singularity avoidance and quick transition of singularity surfaces is developed in this paper. To ensuring the existence of null motion the commanded output of controller was changed real-timely as the variation of singularity measurement of SGCMGs which can avoid the gimbal angle rate saturation. This developed steering law could help the SGCMGs provide real-time control toques in spite of limitation of gimbal angle rate. Simulation analysis is conducted for a certain 4-SGCMG system mounted on a small satellite. Simulation results indicate that the steering law is very effective in singularity avoidance. 2010 IEEE.

The design of high-speed optical fiber communication system based on PCI bus (EI CONFERENCE) 会议论文 OAI收割
2010 2nd IEEE International Conference on Advanced Management Science, ICAMS 2010, July 9, 2010 - July 11, 2010, Chengdu, China
作者: Zhang L.-G.; Zhang L.-G.; He X.

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In order to increase the transmission distance and reduce noise effectively a communication system with the optical fiber interface is developed in this paper. In the system the PCI bus is adopted as the connection bus between the underlying optical fiber transceiver module circuitry and host computer using the WDM driver. The FPGA is the core logic of the whole system responsible for data transmission and timing logic control. The module structure and the design method of the PCI bus the principle and the design of optical interface module and the bottom-driven development are described in this paper. The experiment results show that the system has basically meet requirement targets. It can achieve the maximum transfer rate of 40MBps when running in the DMA mode. With long transmission distance strong antiinterference and high scalability this system has stable and reliable performance. 2010 IEEE.

Driving techniques for high frame rate CCD camera (EI CONFERENCE) 会议论文 OAI收割
Electronic Imaging and Multimedia Technology V, November 12, 2007 - November 15, 2007, Beijing, China
Guo W.; Jin L.; Xiong J.

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This paper describes a high-frame rate CCD camera capable of operating at 100 frames/s. This camera utilizes Kodak KAI-0340 an interline transfer CCD with 640(vertical)480(horizontal) pixels. Two output ports are used to read out CCD data and pixel rates approaching 30 MHz. Because of its reduced effective opacity of vertical charge transfer registers interline transfer CCD can cause undesired image artifacts such as random white spots and smear generated in the registers. To increase frame rate a kind of speed-up structure has been incorporated inside KAI-0340 then it is vulnerable to a vertical stripe effect. The phenomena which mentioned above may severely impair the image quality. To solve these problems some electronic methods of eliminating these artifacts are adopted. Special clocking mode can dump the unwanted charge quickly then the fast readout of the images cleared of smear follows immediately. Amplifier is used to sense and correct delay mismatch between the dual phase vertical clock pulses the transition edges become close to coincident so vertical stripes disappear. Results obtained with the CCD camera are shown.