We have observed three near-Earth objects(NEOs), 2017 VR12, Camillo and Midas, during 2018.The observations were made with the 1-m telescope, operated by Yunnan Observatories, over two nights.Their precise astrometric...We have observed three near-Earth objects(NEOs), 2017 VR12, Camillo and Midas, during 2018.The observations were made with the 1-m telescope, operated by Yunnan Observatories, over two nights.Their precise astrometric positions are derived from 989 CCD observations. The theoretical positions of asteroids are retrieved from the Jet Propulsion Laboratory(JPL) Horizons System and Institut de M′ecanique C′eleste et de Calcul des ′Eph′em′erides(IMCCE). The positions of three asteroids are measured with respect to stars in the Gaia DR2 star catalog. For 2017 VR12, the means(O-C) of right ascension and declination are -0.090′′and-0.623′′respectively based on the published JPL ephemeris, but the corresponding means(O-C) are 3.122′′and-0.636′′based on the published IMCCE ephemeris. The great difference in declination could be explained by several factors.(1) The degraded CCD images caused by the fast apparent motion of the objects lead to a reduction in positioning accuracy.(2) The poor timing system may introduce systematic errors, especially in the high speed direction.(3) The asteroid may be perturbed by Earth when it approaches the Earth too closely. These astrometric results demonstrate that the centroid centering method can reduce the dispersion of non-Gaussian images as compared with the PSF modeling method.For Camillo and Midas, the astrometric results are consistent based on the two ephemerides. Implementing a high-precision timing system, and analyzing some astronomical effects and geometric distortions in CCD images should be carefully considered in future works.展开更多
12Cr2Mo1VR钢板生产的流程为100 t EAF-LF-VOD-CC-ESR-轧制工艺。电渣重熔过程中,采用熔速降低(160~180)kg/h及氮气保护等工艺;轧制过程采用低速大压下量轧制工艺;轧后采用650~700℃长时保温扩氢退火工艺;热处理采用930-950℃正火(加速...12Cr2Mo1VR钢板生产的流程为100 t EAF-LF-VOD-CC-ESR-轧制工艺。电渣重熔过程中,采用熔速降低(160~180)kg/h及氮气保护等工艺;轧制过程采用低速大压下量轧制工艺;轧后采用650~700℃长时保温扩氢退火工艺;热处理采用930-950℃正火(加速冷却)+680-700℃回火工艺。生产的钢板表面质量良好,探伤级别满足NB/T47013.3-2015及第1号修改单TⅠ级要求,钢板成分、显微组织均匀,力学性能满足技术要求。展开更多
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 11503083 and 11403101)
文摘We have observed three near-Earth objects(NEOs), 2017 VR12, Camillo and Midas, during 2018.The observations were made with the 1-m telescope, operated by Yunnan Observatories, over two nights.Their precise astrometric positions are derived from 989 CCD observations. The theoretical positions of asteroids are retrieved from the Jet Propulsion Laboratory(JPL) Horizons System and Institut de M′ecanique C′eleste et de Calcul des ′Eph′em′erides(IMCCE). The positions of three asteroids are measured with respect to stars in the Gaia DR2 star catalog. For 2017 VR12, the means(O-C) of right ascension and declination are -0.090′′and-0.623′′respectively based on the published JPL ephemeris, but the corresponding means(O-C) are 3.122′′and-0.636′′based on the published IMCCE ephemeris. The great difference in declination could be explained by several factors.(1) The degraded CCD images caused by the fast apparent motion of the objects lead to a reduction in positioning accuracy.(2) The poor timing system may introduce systematic errors, especially in the high speed direction.(3) The asteroid may be perturbed by Earth when it approaches the Earth too closely. These astrometric results demonstrate that the centroid centering method can reduce the dispersion of non-Gaussian images as compared with the PSF modeling method.For Camillo and Midas, the astrometric results are consistent based on the two ephemerides. Implementing a high-precision timing system, and analyzing some astronomical effects and geometric distortions in CCD images should be carefully considered in future works.
文摘12Cr2Mo1VR钢板生产的流程为100 t EAF-LF-VOD-CC-ESR-轧制工艺。电渣重熔过程中,采用熔速降低(160~180)kg/h及氮气保护等工艺;轧制过程采用低速大压下量轧制工艺;轧后采用650~700℃长时保温扩氢退火工艺;热处理采用930-950℃正火(加速冷却)+680-700℃回火工艺。生产的钢板表面质量良好,探伤级别满足NB/T47013.3-2015及第1号修改单TⅠ级要求,钢板成分、显微组织均匀,力学性能满足技术要求。
