Astronomical relativistic reference systems with multipolar expansion: the global one

With the rapid development of techniques for astronomical observations, the precision of measurements has been significantly increasing. Theories describing astronomical relativistic reference systems, which are the foundation for processing and interpreting these data now and in the future, may require extensions to satisfy the needs of these trends. Besides building a framework compatible with alternative theories of gravity and the pursuit of higher order post-Newtonian approximation, it will also be necessary to make the first order post-Newtonian multipole moments of celestial bodies be explicitly expressed in the astronomical relativistic reference systems. This will bring some convenience into modeling the observations and experiments and make it easier to distinguish different contributions in measurements. As a first step, the global solar system reference system is expressed as a multipolar expansion and the post-Newtonian mass and spin moments are shown explicitly in the metric which describes the coordinates of the system. The full expression of the global metric is given.

Combination of terrestrial reference frames based on space geodetic techniques in SHAO:methodology and main issues

Based on years of input from the four geodetic techniques （SLR, GPS, VLBI and DORIS）, the strategies of the combination were studied in SHAO to generate a new global terrestrial reference frame as the material realization of the ITRS defined in IERS Conventions. The main input includes the time series of weekly solutions （or fortnightly for SLR 1983-1993） of observational data for satellite techniques and session-wise normal equations for VLBI. The set of estimated unknowns includes 3- dimensional Cartesian coordinates at the reference epoch 2005.0 of the stations distributed globally and their rates as well as the time series of consistent Earth Orientation Parameters （EOPs） at the same epochs as the input. Besides the final solution, namely SOL-2, generated by using all the inputs before 2015.0 obtained from short-term observation processing, another reference solution, namely SOL- 1, was also computed by using the input before 2009.0 based on the same combination of procedures for the purpose of comparison with ITRF2008 and DTRF2008 and for evaluating the effect of the latest six more years of data on the combined results. The estimated accuracy of the x-component and y-component of the SOL- 1 TRF-origin was better than 0.1 mm at epoch 2005.0 and better than 0.3 mm yr- 1 in time evolution, either compared with ITRF2008 or DTRF2008. However, the z-component of the translation parameters from SOL-1 to ITRF2008 and DTRF2008 were 3.4 mm and -1.0 ram, respectively. It seems that the z-component of the SOL-1 TRF-origin was much closer to the one in DTRF2008 than the one in ITRF2008. The translation parameters from SOL-2 to ITRF2014 were 2.2, -1.8 and 0.9 mm in the x-, y- and z-components respectively with rates smaller than 0.4 mmyr-1. Similarly, the scale factor transformed from SOL-1 to DTRF2008 was much smaller than that to ITRF2008. The scale parameter from SOL-2 to ITRF2014 was -0.31 ppb with a rate lower than 0.01 ppb yr-1. The external precision （WRMS） compared with IERS EOP 08 C04 of the combined EOP series was smaller than 0.06 mas for the polar motions, smaller than 0.01 ms for the UT1-UTC and smaller than 0.02 ms for the LODs. The precision of the EOPs in SOL-2 was slightly higher than that of SOL-1.

A two scaled numerical method for global analysis of high dimensional nonlinear systems

This paper first analyzes the features of two classes of numerical methods for global analysis of nonlinear dynamical systems, which regard state space respectively as continuous and discrete ones. On basis of this understanding it then points out that the previously proposed method of point mapping under cell reference (PMUCR), has laid a frame work for the development of a two scaled numerical method suitable for the global analysis of high dimensional nonlinear systems, which may take the advantages of both classes of single scaled methods but will release the difficulties induced by the disadvantages of them. The basic ideas and main steps of implementation of the two scaled method, namely extended PMUCR, are elaborated. Finally, two examples are presented to demonstrate the capabilities of the proposed method.

THE PRINCIPLES OF LEAST ACTION OF VARIABLE MASS NONHOLONOMIC NONCONSERVATIVE SYSTEM IN NONINERTIAL REFERENCE FRAMES

This paper presents the generalized principles of least action of variable mass nonholonomic nonconservative system in noninertial reference frame, proves the equivalence between Holder form and Suslov form, and then obtains differential equations of motion of variable mass nonholonomic nonconservative system in noninertial reference frame.

Micro-arcsecond Celestial Reference Frames:definition and realization——Impact of the recent IAU Resolutions

The adoption of the International Celestial Reference System （ICRS）, based on Very Long Baseline Interferometry （VLBI） observations of extragalactic radiosources by the International Astronomical Union （IAU） since 1998 January 1, opened a new era for astronomy. The ICRS and the corresponding frame, the International Celestial Reference Frame （ICRF）, replaced the Fundamental Catalog （FK5） based on positions and proper motions of bright stars, with the Hipparcos cat- alog being adopted as the primary realization of the ICRS in optical wavelengths. According to its definition, the ICRS is such that the barycentric directions of distant extragalactic objects show no global rotation with respect to these objects; this pro- vides a quasi-inertial reference for measuring the positions and angular motions of the celestial objects. Other resolutions on reference systems were passed by the IAU in 2000 and 2006 and endorsed by the International Union of Geodesy and Geophysics （IUGG） in 2003 and 2007, respectively. These especially concern the definition and re- alization of the astronomical reference systems in the framework of general relativity and transformations between them. First, the IAU 2000 resolutions refined the con- cepts and definition of the astronomical reference systems and parameters for Earth＇s rotation, and adopted the IAU 2000 precession-nutation. Then, the IAU 2006 resolutions adopted a new precession model that is consistent with dynamical theories; they also addressed definition, terminology or orientation issues relative to reference systems and time scales that needed to be specified after the adoption of the IAU 2000 resolutions. An additional IUGG 2007 resolution defined the International Terrestrial Reference System （ITRS） so that it strictly complies with the IAU recommendations. Finally, the IAU 2009 resolutions adopted a new system of astronomical constants and an improved realization of the ICRF. These fundamental changes have led to significant improvements in the fields of astrometry, celestial mechanics, geodynam- ics, geodesy, etc. Of special interest are the improvements in the model for variations in Earth＇s rotation, which, in turn, can provide better knowledge of the dynamics of the Earth＇s interior. These have also contributed to a significant improvement in the accuracy of the ephemerides of the solar system bodies as determined from modern measurements, with a large number of scientific applications. This paper recalls the main aspects of the recent IAU resolutions on reference systems as well as their con- sequences on the concepts, definitions, nomenclature and models that are suitable for the definition, realization and transformation of reference frames at a microarcsecond level.

INTEGRATION METHOD FOR THE DYNAMICS EQUATION OF RELATIVE MOTION OF VARIABLE MASS NONLINEAR NONHOLONOMIC SYSTEM

In this paper, the integration methods of dynamics equations of relative motion of variable mass nonlinear nonholonomic system are given such as the gradient method, the single-component method and the field method. Firstly, the dynamics equations are written in the canonical form and the field form. Secondly, the gradient method, the single-component method and the field method are used to integrate the dynamics equations of the corresponding constant mass holonomic system in inertial reference frame respectively. With the restriction of nonholonomic constraints to the initial conditions being considered, the solutions of the dynamics equations of variable mass nonlinear nonholonomic system in noninertial reference frame are obtained.

Leveraging the Empirical Wavelet Transform in Combination with Convolutional LSTM Neural Networks to Enhance the Accuracy of Polar Motion Prediction

High-precision polar motion prediction is of great significance for deep space exploration and satellite navigation.Polar motion is affected by a variety of excitation factors,and nonlinear prediction methods are more suitable for polar motion prediction.In order to explore the effect of deep learning in polar motion prediction.This paper proposes a combined model based on empirical wavelet transform(EWT),Convolutional Neural Networks(CNN)and Long Short Term Memory(LSTM).By training and forecasting EOP 20C04 data,the effectiveness of the algorithm is verified,and the performance of two forecasting strategies in deep learning for polar motion prediction is explored.The results indicate that recursive multi-step prediction performs better than direct multi-step prediction for short-term forecasts within 15 days,while direct multi-step prediction is more suitable for medium and long-term forecasts.In the 365 days forecast,the mean absolute error of EWT-CNN-LSTM in the X direction and Y direction is 18.25 mas and 15.78 mas,respectively,which is 23.5% and 16.2% higher than the accuracy of Bulletin A.The results show that the algorithm has a good effect in medium and long term polar motion prediction.

KPI考核方法在炼化设备防腐管理中的应用与研究

本文运用KPI考核方法,将设备完整性管理的持续改进理念、全面腐蚀管理思路、量化考核评比方法等内容应用于炼化企业设备防腐管理工作之中。通过研究KPI相关理论知识与炼化企业的实际生产情况,合理设定了能覆盖现在前沿的炼化设备防腐监检测手段和腐蚀完整性管理系统的12个设备防腐管理KPI考核指标,并给出了详细的指标考核方法和排名规则,明确了考核原则和考核要求。通过在国内某炼化企业开展设备防腐管理KPI指标考核方法的试点和推广工作,证明了12个设备防腐管理KPI考核指标在试点试验和推广应用阶段实施的有效性。设备防腐管理KPI考核指标的设定和实施可以形成专业级的设备完整性管理体系绩效指标,对炼化企业的设备防腐管理水平提升具有积极的借鉴意义和参考价值。

空调系统风平衡调试技术研究

针对基准风口法在空调系统分平衡调试工作中的局限性,以基准风口法为基础总结了一套实用的现场调试方法“风量调节法”,即从超设计风量的风口调起,依次调到风量最小的风口,如此循环反复,直至每个风口都达到设计值;有效地降低了风管系统阻力,提高了调试工作成功率。

A method for calculating probability of collision between space objects

A method is developed to calculate probability of collision. Based on geometric features of space objects during the encounter, it is reasonable to separate the radial orbital motions from those in the cross section for most encounter events that occur in a near-circular orbit. Therefore, the probability of collision caused by differences in both altitude of the orbit in the radial direction and the probability of collision caused by differences in arrival time in the cross section are calculated. The net probability of collision is expressed as an explicit expression by multiplying the above two components. Numerical cases are applied to test this method by comparing the results with the general method. The results indicate that this method is valid for most encounter events that occur in near-circular orbits.

Systematic differences in position and proper-motion between the PPMX and UCAC3 catalogs

Considered to be extensions of the Hipparcos reference system, PPMX and UCAC3 are two of the most important astrometric catalogs released in current years. Extensive analyses of these two large catalogs have been made in order to determine the local and overall systematic biases. The regional and magnitude dependent differences in stellar position and proper motion are comparable to random errors and are even larger in the northern hemisphere. The global orientation bias vector ε between the two systems is also significant （up to 17 mas）, which shows the overall differences of the PPMX and UCAC3 catalogs and their reference systems. On the other hand, the term for the global rotation vector a; is small （tenths of mas per year）： it is reasonable to believe that the PPMX and UCAC3 reference frames do not rotate with respect to each other. Because of plate dependent and field-to-field errors in the UCAC3 catalog, we suggest that positions and proper motions of UCAC3 stars in the northern hemisphere （δ 〉 -20°） should be used with caution.

The dynamical architecture and habitable zones of the quintuplet planetary system 55 Cancri

We perform numerical simulations to study the secular orbital evolution and dynamical structure of the quintuplet planetary system 55 Cancri with the self-consistent orbital solutions by Fischer and coworkers. In the simulations, we show that this system can be stable for at least 108 yr. In addition, we extensively investigate the planetary configuration of four outer companions with one terrestrial planet in the wide region of 0.790AU 〈 a 〈 5.900AU to examine the existence of potential asteroid structure and Habitable Zones （HZs）. We show that there are unstable regions for orbits about 4：1, 3：1 and 5：2 mean motion resonances （MMRs） of the outermost planet in the system, and several stable orbits can remain at 3：2 and 1：1 MMRs, which resembles the asteroid belt in the solar system. From a dynamical viewpoint, proper HZ candidates for the existence of more potential terrestrial planets reside in the wide area between 1.0 AU and 2.3 AU with relatively low eccentricities.

永磁同步电机无位置传感器控制现状和展望

永磁同步电机(PMSM)的无位置传感器控制是当前电机控制领域的研究热点。针对永磁同步电机无位置传感器控制中基于反电动势观测以及电感凸极性的位置估计方法进行归纳总结。分别对滑模观测器法、模型参考自适应法、龙伯格观测器法、扩展卡尔曼滤波器法、无迹卡尔曼滤波器法和高频信号注入法的基本理念进行了介绍,通过比较每种方法的优势和不足,并根据其缺点归纳了目前主要的改进方法,并阐述了全速范围内两大控制方法的结合策略,且对无位置传感器控制的研究趋势进行了展望。

相控阵测控技术(五):相控阵测控系统的附加误差分析法

在相控阵测控系统中,由于角度误差对测速、测距误差耦合效应等的影响,使测速/测距误差加大。为分析这些特殊误差,提出了附加误差分析法和基准阵元法,用相控阵中的基准阵元等效机扫天线,以此作为比较基准,从而分析得到对机扫天线测控系统相控阵化后增加的各项附加误差,总的误差等于该附加误差与原机扫天线测控系统误差之和。该方法继承了机扫天线测控系统测速、测距精度分析的成熟理论,聚焦到了相控阵化后的特殊问题,物理概念较为清晰,具有较大的工程实用意义。

LNG模块管线Hook-up尺寸控制测量技术

LNG模块在建造场地完成建造并托运后,需在项目总组场地进行管线Hook-up的对接,因此建造场地管线Hook-up尺寸控制非常重要。以某大型LNG模块项目为例,分析了在LNG模块建造过程中管线Hook-up对接点尺寸控制的重点和难点。结合项目应用实践,探讨了LNG模块建造阶段管线对接点(Hook-up)尺寸控制测量的方法和技术。基于测量技术中的后方交会原理,给出了管线Hook-up尺寸控制的解决方案。

感应电机高性能矢量控制转子时间常数在线辨识研究

为解决感应电机参数离线辨识不准或随电机运行工况的变化而产生较大变化影响控制系统性能的问题,本文详细仿真分析并验证了参数变化对转子磁链及调速系统的影响,提出了基于模型参考自适应的无功功率模型转子时间常数在线辨识方法,对感应电机矢量控制平台进行了仿真分析,并验证了该方法的有效性。

计时观测测量脉冲星参数的数学模型与精度估计

脉冲星计时观测能够精确测量脉冲星自转参数和天体测量参数.概述了脉冲星计时模型和利用最小二乘拟合测量脉冲星各个参数并估计其方差的数学方法.在黄道坐标系导出了脉冲星各个参数误差与计时残差之间关系的数学表达式.给出了脉冲星黄经、黄纬和周年视差测量精度与脉冲星黄纬绝对值之间的关系曲线.讨论了脉冲星各个天体测量参数测量精度与脉冲星纬向参数本身的关系.

血清肌酐常规测定方法和临床应用的研究进展

血清肌酐常规测定方法从化学法——碱性苦味酸终点比色法发展为两点动力学法,使内源性非肌酐物质的干扰下降。与化学法比较,肌酐酶法分析不同程度提高了血清肌酐测定的特异性、灵敏度和线性测量范围。化学法与酶法间存在系统误差,参考范围不能通用。血清肌酐的生物学变异和分析变异较大,测定结果临床应用要注意其相对性。

MEMS陀螺随机误差补偿在提高姿态参照系统精度中的应用

为提高航姿系统姿态角测量精度,论文对MEMS陀螺随机误差的测试和补偿进行了研究。运用Allan方差方法分析了MEMS陀螺各项随机误差的特性,建立了针对MEMS陀螺的随机误差补偿模型。采用Allan方差辨识算法完成对各项随机误差的分离,获取速率随机游走(RRW)和角度随机游走(ARW)噪声方差值。通过设计的卡尔曼滤波器对MEMS陀螺随机误差进行实时估计补偿,利用姿态解算算法得到随机误差补偿前和补偿后各3个方向的姿态角。实验结果表明经误差补偿后系统的静态偏航角测量精度提高了3倍、横滚角提高了4倍、俯仰角提高了12倍。

基于序分量提取的无功和谐波电流同步坐标检测方法

为研究无功补偿和谐波抑制的关键技术中的无功、不对称和谐波电流检测与计算方法,提出基于序分量提取的同步坐标法。研究结果表明:采用无锁相环的广义dq0变换,能准确提取出基波及整数次谐波正、负序以及零序分量;根据不同的无功补偿目标,能准确地检测出基波正序有功电流和基波正序无功电流,分开基波正序无功电流、不对称与谐波电流,实现分别补偿;该法可用于三相三线制和四线制电力系统以及不对称系统;理论推导和仿真结果验证所提方法的正确性。