基于ASP技术的毕业生就业网的设计与实现

随着通信技术、网络技术和多媒体技术的不断发展 ,各种交互式多媒体系统已成为一个研究热点 .本系统采用基于B/S体系结构 ,对基于ASP的毕业生就业网结构作了阐述 ,并简要探讨了该系统的设计思想、实现方法和关键技术。     

多模多频卫星导航系统码偏差统一定义与处理方法

精确处理和修正观测量偏差（OSB）是有效发挥多模多频优势,提升GNSS服务和应用效能的前提和基础，已成为国内外卫星导航高精度定位领域研究的热点问题之一。国际GNSS服务组织（IGS）和国际大地测量协会（IAG）专门成立了工作组推动相关工作。然而，目前有关观测量偏差处理的方法仍存在着定义不统一、求解不严密、使用不便捷等突出问题，给实时高精度定位应用带来诸多不利因素。针对此，首先阐述了中国科学院（CAS）电离层分析中心码偏差产品的定义、估计策略和使用方法，然后给出了部分精度评估和分析。结果表明：CAS、CODE和DLR发布的码偏差参数一致性优于0.30ns，CAS码偏差月稳定性优于0.15ns。相关工作对于推动多模多频GNSS在电离层监测、高精度定位和授时定时等领域的应用具有重要参考价值。     

Future spacelift projection

In 1996 the NASA Advisory Council asked for a comprehensive look at future launch projections out to the year 2030 and beyond. In response to this request NASA sponsored a study at The Aerospace Corporation to develop long-range space transportation models for future commercial and government applications, and to analyze the design considerations and desired characteristics for future space transportation systems. Follow-ons to present space missions as well as a wide array of potential new space applications are considered in the study. This paper summarizes the space transportation system characteristics required to enable various classes of future missions. High reliability and the ability to achieve high flight rates per vehicle are shown to be key attributes for achieving more economical launch systems. Technical, economic and policy implications are also discussed.     

用PROLOG实现数据库智能检索系统DBINRES

本系统将人工智能技术与数据库技术结合起来,建立逆向演绎的推理机构,实现数据库智能检索。采用“分类树”技术组织数据库;应用最小平方估计法建立有效的启发式评价函数,在此基础上变传统的深度优先搜索为启发式图搜索,从而有效地提高了系统的效率。由于采用MICRO-PROLOG语言编制,本系统具有较强的逻辑推理与检索能力。     

应用端部效应改善的LS+NN模型进行日长变化预报

现有ΔLOD(Delta Length-Of-Day,日长变化)预报模式在进行周期项与残差项拟合分离时,通常没有考虑LS(Least Squares,最小二乘)拟合序列的端部效应,预报精度难以取得较大提高。针对端部效应现象,首先采用时间序列分析模型在ΔLOD序列两端进行数据延拓,构成一个新序列,然后用新序列求得LS外推模型系数,再结合LS外推模型和NN(Neural Network,神经网络)对原始ΔLOD序列进行预测。算例表明,在ΔLOD序列两端增加延拓数据,能有效改善LS拟合序列的端部效应;端部效应改善的LS+NN模型的预报精度明显优于常规LS+NN模型,精度最大提高了17.86%。该方法不仅适用于LS+NN模型,也适用于LS外推模型与其他模型的组合。     

What is the optimum solar proxy for long-term ionospheric investigations?

The problem of optimum solar proxy is important for long-term and/or climatological studies of ionospheric parameters. Here we focus on possibly different optimum solar proxies for different ionospheric parameters, as they are affected by partly different spectral ranges of solar ionizing radiation. We use yearly average values of foF2 and foE of four European stations with long (1976–2014) and high-quality data (Juliusruh, Pruhonice, Rome, Slough/Chilton), and the global total electron content (G-TEC). Four solar proxies are used: F10.7, Mg II, solar Lymna-alpha flux Fα and sunspot numbers. The most important finding is that the optimum solar proxies are different for different ionospheric parameters. The most suitable solar proxy for foF2 is found to be Mg II, whereas for foE F10.7 evidently outperforms Mg II. Fα and sunspot numbers perform slightly worse but none of four solar proxies performs poorly. F10.7 is favored for G-TEC, to some extent surprisingly, as previous results favored rather Mg II.     

Prediction of ionospheric total electron content using adaptive neural network with in-situ learning algorithm

The Ionospheric Total Electron Content is responsible for the group delay of the signals from the Navigation satellites. This delay causes ranging error, which in turn degrades the accuracy of position estimated by the receivers. For critical applications, single frequency receivers resort to Satellite Based Augmentation Systems in order to have improved accuracy and integrity. The performance of these systems in terms of accuracy can be improved if predictions of the delays are available simultaneously with real measurements. This paper attempts to predict the Total Electron Content using adaptive recurrent Neural Network at three different locations of India. These locations are selected at the magnetic equator, at the equatorial anomaly crest and outside the anomaly range, respectively. In-situ Learning Algorithm has been used for tracking the non-stationary nature of the variation. Prediction is done for different prediction intervals. It is observed that, for each case, the mean and root mean square values of prediction errors remain small enough for all practical applications. Analysis of Variance is also done on the results.     

Ionospheric differential error determination using ray tracing for a short baseline

Since the United States government discontinued Selective Availability (SA) on 1 May 2000, ionospheric effects have been responsible for the largest errors in GPS systems. The standard Differential GPS (DGPS) method is incapable of completely eliminating the ionospheric error. This paper describes a new approach to determine the differential ionospheric error between geographically distributed receiver stations. The ray paths of GPS signals were simulated using a modified Jones 3D ray tracing programme that includes the effect of the geomagnetic field. A Nelder–Mead optimisation algorithm was embedded in the program to precisely determine the satellite-to-station path. A realistic ionospheric model is essential for accurate ray tracing results and for estimates of differential error that are accurate on sub-centimetre scales. Here, the ionospheric model used in the ray tracing programme was developed by fitting realistic ionosphere profiles with a number of exponential functions. Results were compared to the theoretical approach. Results show that the differential delay is about 1–5 cm at low elevation angles for a short baseline of 10 km, as reported in other literature. This delay is often neglected in DGPS application. The differential delay also shows a pattern similar to that predicted by the Klobuchar model. The method proposed here can be used to improve future GPS applications.     

The occurrence of the mid-latitude ionospheric trough in GPS-TEC measurements

Simultaneous GPS observations from about 150 stations of European Permanent Network (EPN) have been used for studying dynamics of latitudinal profiles and structure of mid-latitude ionospheric trough (MIT). For the analyses, the TEC maps over Europe were created with high spatial and temporal resolution. The latitudinal profiles were produced from TEC maps with one-hour interval for geographic latitude range from 35N to 75N. The structure of latitudinal profiles relates to the occurrence of the ionospheric trough. The location of the trough depends on season, local time, and both geophysical and geomagnetic conditions. The trough structure in GPS-TEC demonstrates a smooth shape. The trough occurrence as a distinguished structure is more distinct during winter. The relation of TEC in the trough minimum to the equator and polar walls amounted to a factor of 2–4.