Study on pressure wave propagation in two-phase flow in liquid oxygen feed pipe between pumps

A study on the character of pressure wave propagation was proposed for the gas liquid oxygen two-phase flow in the pipe between pumps.According to the practical working conditions,the homogenous model based on the compressibility theory regarding a single bubble in an infinite liquid,and Redlich-Kwong gas equation was derived a model for the low temperature and high pressure case,especially considering the change of the ratio of density of gas to one of liquid.The numerical tests were conducted.The results not only show the agreement between numerical simulation for this model and experiment at the normal temperature and pressure is good,but also show that the modifications of the model for the low temperature and high pressure condition are necessary.The study is of reference to further study of oscillation restrain and relative pipe tests.      

无线传感器网络中的跨层路由协议

为了减少无线传感器网络中的干扰产生,降低由此引起多次重传后的分组丢弃从而导致的额外重传时延和能量消耗,改善网络的传输效率和能量效率,提出了一种基于跨层设计的干扰感知路由(IAR,Interference-Aware Routing)协议.与现有的基于竞争的路由协议不同,IAR协议引入节点干扰度和能量度作为选路代价,通过干扰和能量感知的路由选择机制实现路由建立.利用节点收到的发送请求、清除发送和应答分组的计数作为干扰度的计算依据,从而在路由选择中避开了干扰易发生区域;利用下一跳候选节点的初始和剩余能量作为能量度的计算依据,从而均衡了各节点的能量消耗,延长了整个网络的寿命.仿真结果表明,与动态码字路由和ad-hoc按需距离矢量路由协议相比,IAR协议提高了能量效率、改善了网络的吞吐量、分组投递率和时延等性能.     

LEO/MEO双层卫星网的分层动态路由算法

由低轨LEO(Low Earth Orbit)和中轨MEO(Medium Earth Orbit)卫星构成的双层卫星网络具有较好的组网通信性能.利用MEO和LEO卫星在长、短距通信中的优势,提出一种分层、分布式的双层卫星网动态路由算法.通过控制链路状态信息的洪泛,LEO卫星只需掌握局部拓扑即可完成短距业务通信,长距通信业务则由MEO卫星承载.将星间链路的剩余生存时间因素引入路径权重中,路由计算的路径是综合考虑了时延与持续时间双重因素的最优路径.仿真结果表明该算法在时延、路由开销、网络业务流分布等方面都具有较好的性能,并且易于系统实现.      

Using only observation station data for PPP ambiguity resolution by UPD estimation

This article proposes a new method for uncalibrated phase delay (UPD) estimation to improve the accuracy of precise point positioning (PPP), which uses only observation station data. This means that the station used to generate the UPDs is the same station to which they are applied. First, dual-frequency observation equations based on a raw PPP model are developed. Then, the UPDs are calculated from integer linear combinations of float ambiguities. Third, with the UPD corrections, the least-squares ambiguity decorrelation adjustment (LAMBDA) method is utilized to obtain the integer ambiguities. Since only observation station data are used for UPD estimation, the partial ambiguity resolution (PAR) method is adopted to increase the possibility of finding a subset of integer ambiguities. The UPD estimation and ambiguity resolution are performed in each epoch. To obtain the correct integer ambiguity, the ratio test and success rate (bootstrapping) are used to evaluate the estimated integer ambiguity. Finally, by treating the integer ambiguities as constants, fixed solutions can be obtained. Quality control is also applied throughout the entire data processing procedure to obtain high quality float and fixed solutions. Data from 22 stations of the International Global Navigation Satellite System (GNSS) Service (IGS) in East Asia on day of year (DOY) 206, 2017, are used to verify the feasibility of this method. The experimental results show that compared with the float solution, the proposed method can significantly improve the accuracy in the east, north and up directions by 24%, 21% and 18% for static PPP and 36%, 18% and 34% for dynamic PPP, respectively. However, the accuracy of the proposed method is still lower than that of the fixed solutions obtained by the PRIDE-PPPAR software, in which the fractional cycle bias is computed based on reference network data. These findings sufficiently show that the proposed method can offer better solution accuracy than the float solution. However, the quality of the UPDs estimated only from observation station data is not as good as that of the estimates obtained based on reference network data.     

中美大学生职业生涯规划指导模式的比较

多年的高校扩招,使大学生就业难成为全社会持续关注的热点.就业难的主要原因是人职难以匹配,其症结可归结为大学生没有清晰的职业发展目标,缺乏职业规划.大学生职业生涯规划指导在我国起步较晚,仅有十几年的时间,这一工作尚处于摸索阶段,难免问题多、效果不佳;而大学生职业生涯规划起源于美国,已经有上百年的发展历史,美国并且已经探索出一套行之有效的职业生涯规划指导模式.文章对中美高校职业生涯规划指导进行分析和对比,查找我国职业生涯规划指导存在的问题,总结美国职业生涯规划教育的经验,通过借鉴美国高校的经验,并结合我国的实际情况,探索适合我国大学生职业生涯规划指导的新模式.     

Update Chain-based Approach for Checking Route Oscillation of BGP

This paper presents a novel approach for checking route oscillation of border gateway protocol(BGP) quickly,by which the privacy of routing policies of autonomous system(AS) can be respected.Firstly,route update chain tag(RUCT) is constructed to track the forwarding of update report,and local routing library is made to record the changing history of update report.Then route oscillation can be identified by analyzing correlative state of RUCT and local routing library.The characteristic of this approach is that an arbitrary AS can check route oscillation alone only by sharing its network ID,which greatly respects the pri-vacy of routing policies for each AS.This paper shows that both looping in RUCT and consecutive positive-negative report in local record are sufficient conditions for route oscillation.Comparative experiments demonstrate the availability and efficiency of the proposed approach.     

基于职业能力的高职酒店管理专业培养模式构建

重视学生职业能力的培养，学生才能真正成为人才，企业才会真正满意。某学院酒店管理专业一直以来始终坚持以培养学生的职业能力为核心；依靠学校和酒店企业二个平台，以学校教育为：主，以酒店培训为辅；构建以职业能力培养为核心的课程体系。通过积极推进教学改革的实践，该学院酒店管理专业取得了一定的成效。     

民用飞机设备可靠性设计

民用飞机可靠性设计的目标是保证飞机达到规定的可靠性定量指标和定性要求,以提高飞机的可靠度,降低运营费用,使飞机具有良好的经济性和市场竞争能力。民用飞机由数量巨大的各种设备组成,设备的可靠性是飞机可靠性的重要保证。     

低压环境下过热流体喷雾特性实验

为了研究低压环境下燃料的过热度、喷射压力和喷嘴几何结构对喷雾形状和液滴索特尔平均直径等喷雾特性的影响,测量了不同环境压力下的煤油泡点温度,并给出了环境压力和泡点温度的经验关系式。将过热的航空煤油通过直射式喷嘴喷入低压容器中,进行了不同喷射条件下的喷雾实验。使用高速摄影仪和激光粒度仪进行拍摄和测量,得到了一系列的粒子索特尔平均直径数据和喷雾图片。结果表明,过热度的增加、喷射压力的增加和喷嘴长径比的减小都能够改善煤油的喷射雾化效果。     

0.66m直径对旋式轴流风机的设计和性能估算

对旋式轴流风机具有压力增益大、效率高、结构简单和轴向尺寸小等优点 ,但目前还缺乏现成的设计方法可供借鉴 ,为此笔者提出了一个可行的设计思路及方法 ,即按照常规单级后扭型和预扭型风机 ,分别设计对旋式风机的前后两级桨叶 ,然后修正它们之间的相互干扰。给出了这种设计方法的要点。讨论了两级桨叶的负载分配和前后桨叶各参数之间的关系。根据前后两级桨叶绕流过程的不同 ,重点考虑了它们之间的相互干扰 ,提出修正干扰的方法。进行风机性能估算 ,对缩短研制周期、及时修改设计参数、提高设计水平都是很有益的。样机试验表明 ,风机的设计和性能估算都是成功的