共查询到20条相似文献，搜索用时 125 毫秒
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网络时间协议(NTP)是一种非常重要的互联网授时方法。目前,基于NTP的网络授时系统已经在互联网上被广泛应用。但是NTP在快速发展的同时也暴露出很多安全性问题。根据网络时间协议的安全需求针对性地加入安全算法,对于提高网络时间服务系统的安全性十分重要。文章首先介绍了网络时间协议的基本工作原理,分析了网络时间服务系统存在的安全漏洞,介绍了NTP安全模型。其次,实现了客户端和服务器软件,并在此基础上加入RSA算法,确保NTP数据包在传输的过程中不会被截取和更改。利用实验数据,对加入RSA算法后的网络时间服务系统性能进行了详细分析。最后阐明了安全性对于网络时间服务体系的重要意义。 相似文献
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GPS时间比对数据的归化 总被引：2，自引：1，他引：1
胡锦伦 《中国科学院上海天文台年刊》1995,(16):193-201
根据时间实验室在不同时刻接收的GPS时间比对数据，采用三次样条函数的归化方法，本文给出了UTC 0^h的本地时间尺度与BlockⅠ和BlockⅡ卫星的GPS时间差，这些归化结果与世界上一些时间中心（国际计量局（BIPM）时间部、美国海军天文台（USNO）等）的结果比较表明：当取样时间为1天时，国际时间同步的不确定度优于50ns;SA(Selective Availability）效应的影响减少到50ns以内，因此，这种方法是一种精确的有效的方法。 相似文献
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在高精度星地激光时间比对中,为了降低星载设备的研制难度,采用了无门控星载激光探测器。根据星地先验钟差、卫星距离和系统延迟量,精确计算地面激光发射时刻,使得激光信号能在星载计时器星钟开门信号之后短时间内到达星载探测器,使星载计时器关门,这样可以大大降低背景噪声影响,获得有效数据。该文研究了精确控制地面激光发射时刻的方法,包括激光发射时刻计算和激光控制器硬件的实现,该方法已在星地激光时间比对在轨试验中得到了成功应用,控制精度在20ns以内,满足了试验的要求。 相似文献
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相对论框架中的时间计量 总被引：8，自引：0，他引：8
介绍了原时、坐标时等相对论框架中时间计量的基本概念，讨论了时间尺度的基本定义与实现，如地球时（TT）、国际原子时（TAI）、时钟调整和时间比对等。 相似文献
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阐述了一种用于时间同步系统的高性能数字移相系统的设计方案和实现过程,该系统采用直接数字合成（DDS）技术,其同步精度小于100 ns,移相精度可达5×10-10 s,同时能够实现精度为10-6 Hz的频率调节。该系统是为时间同步系统设计,并可广泛应用到军用、电力、通信等领域中。 相似文献
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在采用ＧＰＳ进行共视时问比对过程中，当两站位置相隔不大长（小于１０００ｋｍ）时，由于卫星轨道误差、电离层和对流层延迟修正的误差可减少至只有几纳秒，可以主为接收天线位置的误差是其主要误差来源．利用ＧＰＳ本身的时间比对数据，不必增加别的数据来源和设备，采用相对定位的方法可提高定位精度，从而提高时间比对的精度．本文利用日本（ＣＲＬ）和北京天文台（ＢＡＯ）之间五天的共视时间比对数据，对（ＢＡＯ）的天线坐标进行修正．在水平方向和高程方向的修正偏差分别为２．９ｍ和５．６ｍ．如果试验数据足够，修正６４效果会更好． 相似文献
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The Solar Weather Browser (SWB) is a standalone, open-source software tool designed to display solar images with context overlays.
It was originally developed for the space-weather forecast activities of the Solar Influence Data analysis Center (SIDC) but
it is more generally well suited to display the output of solar-feature recognition methods. The SWB is also useful in the
context of distributed solar-image archives, where it could play the role of a quick-look viewer. The SWB allows the user
to visually browse large solar data sets and investigate the solar activity for a given date. It has a client – server design
that minimizes the bandwidth from the network to the user’s monitor. The server processes the data using the SolarSoft library
and distributes them through a Web server to which the SWB client connects. The client is readily available for Linux, Mac
OS X, and Windows at . We discuss the software technology embedded in the SWB as well as its use for solar physics and space weather. 相似文献
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在标准的Client/Server结果中,数据库处理由Server来承担,Client运行用户接口程度,直接和用户交互,并向Seerver发送数据库请求,而在增强型Client/Server结构的DBMS（简写为ECS－DBMS）中,充分利用了可以利用的Client资料,包括长久存储器,对于数据库中经常使用数据,客户机可以将这些数据拷贝并存储到自己久存储器,对于数据库中经常使用数据,客户机可以将这些数据拷贝并存储到自己的磁盘中,以免下次使用这些数据时再去访问Server,另外,客户机的磁盘中,还可以存储该客户自己的专用数据,这样便可以提高系统的性能,由于公共数据都存放在Server中,数据一致性的维护也由Server来承担,当Server中出现更新时,Server要将更新的内容传递给需要该更新的Clients,以替换客户机磁盘中的旧数据,针对ECS－DBMS,介绍并提出几种Server更新传播策略,并通过计算机模拟试验分析这些策略的性能。 相似文献
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In recent years much effort has been devoted to constructing systems for sharing resources within the solar physics community. Several advanced archives and data analysis systems do exist, but there is low availability of data visualization tools for displaying simultaneous multi instruments/wavelengths solar data. Meanwhile map server technology has received great attention by the IT researcher and geophysical community. In this paper we discuss a possible use of an open source environment for building spatially enabled Internet applications for the visualization and analysis of solar physics data sets. We present the preliminary status of the MINVIT (Multi Instrumental Visualization Tool) project, which shall be able to merge images and information produced by different instruments in a single/synoptic image available on-line. Moreover, the tool is designed in order to allow the visualization of the temporal evolution of data. We further discuss the possible integration into the grid framework, focusing on a middleware able to query EGSO resources such us UOC and SEC in order to include data from several space and ground-based solar observatories. 相似文献
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C. Mendoza M. J. Seaton P. Buerger A. Bellorín M. Meléndez † J. González L. S. Rodríguez F. Delahaye E. Palacios A. K. Pradhan C. J. Zeippen 《Monthly notices of the Royal Astronomical Society》2007,378(3):1031-1035
Codes to compute mean opacities and radiative accelerations for arbitrary chemical mixtures using the Opacity Project recently revised data have been restructured in a client–server architecture and transcribed as a subroutine library. This implementation increases efficiency in stellar modelling where element stratification due to diffusion processes is depth dependent, and thus requires repeated fast opacity re-estimates. Three user modes are provided to fit different computing environments, namely, a web browser, a local workstation and a distributed grid. 相似文献
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介绍了无线应用协议(WAP)的工作原理、体系结构以及WAP的新应用——WAP手机无线授时的模拟实现。它是通过无线通信协议,以无线标记语言编写主程序,采用动态连接的方式调用VC 的时间通信程序来完成WAP手机的无线接时。对于用户来说,只要拥有具有WAP功能的手机,键入他要访问的WAP内容服务器的统一资源定位器(URL),就可以非常快捷、方便地获得时间信息服务。 相似文献
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O. V. Verkhodanov Ya. V. Naiden V. N. Chernenkov N. V. Verkhodanova 《Astrophysical Bulletin》2014,69(1):113-120
We describe the architecture of the developed computing web server http://cmb.sao.ru allowing to synthesize the maps of extended radiation on the full sphere from the spherical harmonics in the GLESP pixelization grid, smooth them with the power beam pattern with various angular resolutions in the multipole space, and identify regions of the sky with given coordinates. We describe the server access and administration systems as well as the technique constructing the sky region maps, organized in Python in the Django web-application development framework. 相似文献
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Zhi Hong Ce Yu Jie Wang Jian Xiao Chenzhou Cui Jizhou Sun 《Experimental Astronomy》2016,42(3):387-405
Astronomy has always been, and will continue to be, a data-based science, and astronomers nowadays are faced with increasingly massive datasets, one key problem of which is to efficiently retrieve the desired cup of data from the ocean. AQUAdexIM, an innovative spatial indexing and querying method, performs highly efficient on-the-fly queries under users’ request to search for Time Series Images from existing observation data on the server side and only return the desired FITS images to users, so users no longer need to download entire datasets to their local machines, which will only become more and more impractical as the data size keeps increasing. Moreover, AQUAdexIM manages to keep a very low storage space overhead and its specially designed in-memory index structure enables it to search for Time Series Images of a given area of the sky 10 times faster than using Redis, a state-of-the-art in-memory database. 相似文献
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《Monthly notices of the Royal Astronomical Society》1998,295(4):737-737
The Editorial Board is now in a position to receive the TEX/LATEX files of accepted Monthly Notices papers by file transfer protocol (FTP), as an alternative to submission on floppy disk. A password-protected Monthly Notices directory has been set up on the FTP server at the publisher, Blackwell Science, for this purpose. 相似文献