BVRI CCD photometry of the poorly studied open cluster NGC 6724 has been carried out down to a limiting magnitude of V-20 mag. The stars of the cluster have been observed using the Newtonian focus （f/4.84） of the 74...BVRI CCD photometry of the poorly studied open cluster NGC 6724 has been carried out down to a limiting magnitude of V-20 mag. The stars of the cluster have been observed using the Newtonian focus （f/4.84） of the 74-inch telescope at Kottamia Astronomical Observatory in Egypt. Also, the 2MASS - JHK system is used to confirm the results we obtained. The main photometric parameters have been estimated for the present object; the diameter is found to be 6 arcmin, the distance is 15304-60pc from the Sun and the age is 900＋50Myr. The optical reddening E（B - V） = 0.65 mag, while the infrared reddening is E（J - H） = 0.20 mag. The slope of the mass function distribution and the relaxation time estimations indicate that cluster NGC 6724 is dynamically relaxed.展开更多
In the present work, recalibration of the National Institute for Standards （NIS, Egypt） working standard lamps from Osram Inc. and their associated expanded uncertainty budget were done. A set-up composed of ...In the present work, recalibration of the National Institute for Standards （NIS, Egypt） working standard lamps from Osram Inc. and their associated expanded uncertainty budget were done. A set-up composed of an integrating sphere, a standard photometer and a group of five luminous flux standard lamps ranged from 25 to 200 W calibrated and traceable to the National Physical Laboratory （NPL, UK） is used to measure and recalibrate the total luminous flux for these five working standard lamps. After recalibration, NIS （Egypt） maintains the national scales for luminous flux in lumen.展开更多
针对ORB-SLAM2(Oriented FAST Rotated BRIEF SLAM2)系统中相机位姿求解精度不高,只能生成稀疏地图的问题,提出了一种在ORB-SLAM2系统框架上将稠密的直接法和原系统采用的稀疏特征法结合在一起求解相机位姿,并生成稠密地图的方法。该方...针对ORB-SLAM2(Oriented FAST Rotated BRIEF SLAM2)系统中相机位姿求解精度不高,只能生成稀疏地图的问题,提出了一种在ORB-SLAM2系统框架上将稠密的直接法和原系统采用的稀疏特征法结合在一起求解相机位姿,并生成稠密地图的方法。该方法改进之处包括:在原系统使用的第三方图优化库g2o(General Graph Optimization)中创建一条新的稠密约束一元边,将稠密直接法的光度误差约束加入到图优化库g2o中;跟踪相机时先通过稠密直接法计算相邻两帧图像之间相机的旋转变换,再利用改进后的图优化库g2o同时最小化特征法的重投影误差和直接法的光度误差,优化求解6DOF(Degree of Freedom)相机位姿;在ORB-SLAM2系统框架上添加稠密重建线程,将周围场景的重建结果实时反馈给用户。在TUM RGB-D和ICL-NUIM数据集上的测试结果表明,本文方法在一定程度上提高了ORB-SLAM2系统中相机位姿的求解精度,不仅可生成稀疏地图,还可重建更高精度的稠密地图。展开更多
文摘BVRI CCD photometry of the poorly studied open cluster NGC 6724 has been carried out down to a limiting magnitude of V-20 mag. The stars of the cluster have been observed using the Newtonian focus （f/4.84） of the 74-inch telescope at Kottamia Astronomical Observatory in Egypt. Also, the 2MASS - JHK system is used to confirm the results we obtained. The main photometric parameters have been estimated for the present object; the diameter is found to be 6 arcmin, the distance is 15304-60pc from the Sun and the age is 900＋50Myr. The optical reddening E（B - V） = 0.65 mag, while the infrared reddening is E（J - H） = 0.20 mag. The slope of the mass function distribution and the relaxation time estimations indicate that cluster NGC 6724 is dynamically relaxed.
文摘本文提出了以计算多弥散体散射光强分布的一种递推公式,目的在于减少对Mic 系数 a_1、b_1和π_1、τ_1的计算工作量.计算了几种散射截面,其结果与有关文献的数据符合很好.计算中发现,Mic 无穷级数的收敛性与微粒的相对折射率的关系不明显,但与无因次直径α有关.并得出相对散射光强 I/I_0-散射角θ、无因次直径α及相对折射率 m 的三组曲线,其中,把根据 Fraunhofer 衍射理论计算的曲线与根据 Mic 散射理论计算的曲线作了比较,可以看出,当用 Fraunhofer 衍射理论代替 Mic 散射理论处理散射问题时,是可以找到参数(θ、α、m)的适用范围的,并且能确定其误差的大小.
文摘In the present work, recalibration of the National Institute for Standards （NIS, Egypt） working standard lamps from Osram Inc. and their associated expanded uncertainty budget were done. A set-up composed of an integrating sphere, a standard photometer and a group of five luminous flux standard lamps ranged from 25 to 200 W calibrated and traceable to the National Physical Laboratory （NPL, UK） is used to measure and recalibrate the total luminous flux for these five working standard lamps. After recalibration, NIS （Egypt） maintains the national scales for luminous flux in lumen.
文摘针对ORB-SLAM2(Oriented FAST Rotated BRIEF SLAM2)系统中相机位姿求解精度不高,只能生成稀疏地图的问题,提出了一种在ORB-SLAM2系统框架上将稠密的直接法和原系统采用的稀疏特征法结合在一起求解相机位姿,并生成稠密地图的方法。该方法改进之处包括:在原系统使用的第三方图优化库g2o(General Graph Optimization)中创建一条新的稠密约束一元边,将稠密直接法的光度误差约束加入到图优化库g2o中;跟踪相机时先通过稠密直接法计算相邻两帧图像之间相机的旋转变换,再利用改进后的图优化库g2o同时最小化特征法的重投影误差和直接法的光度误差,优化求解6DOF(Degree of Freedom)相机位姿;在ORB-SLAM2系统框架上添加稠密重建线程,将周围场景的重建结果实时反馈给用户。在TUM RGB-D和ICL-NUIM数据集上的测试结果表明,本文方法在一定程度上提高了ORB-SLAM2系统中相机位姿的求解精度,不仅可生成稀疏地图,还可重建更高精度的稠密地图。
