某型飞机起落架收放系统仿真与性能分析

起落架收放系统的性能对整机的安全性和舒适性具有直接影响。以国产在研某型飞机起落架收放系统为研究对象,利用该型飞机起落架收放机构的数学模型,采用LMS Virtual.Lab Rev的Motion模块和LMS Imagine.Lab AMESim软件进行起落架机构3D和起落架液压控制系统1D联合仿真,利用该联合仿真模型研究气动载荷对起落架收放系统的影响和上位锁阻尼参数对起落架收放性能的影响。结果表明:采用理论计算数值能够实现起落架在有限时间里的收放任务,考虑了气动载荷情况的仿真结果符合实际趋势;上位锁阻尼可作为优化设计的优先选取参数。     

Comparison of the roles of nucleotide synthesis, polymerization, and recombination in the origin of autocatalytic sets of RNAs

Ribozymes that act as polymerases and nucleotide synthases are known experimentally, even though no fully self-replicating system has yet been found. If the RNA World hypothesis is true, ribozymes must have arisen initially from within a random abiotic polymerization system. To investigate the origin of the RNA world, we studied a mathematical model of a chemical reaction system describing RNA polymerization. It is supposed that, in absence of ribozymes, polymerization occurs at a small spontaneous rate, and that in the presence of polymerase ribozymes, polymerization occurs at a faster rate that is proportional to the ribozyme concentration. Chains must be longer than a minimum threshold length in order to have the possibility of acting as ribozymes. The reaction system has two stable states that we term dead and living. The dead state is controlled by the small spontaneous rate and has negligible concentration of ribozymes. The living state has high concentration of ribozymes, and the reaction rates are determined by the ribozymes; thus, the system is autocatalytic. Concentration fluctuations in a finite volume can cause a transition to occur from the dead to the living state, that is, an origin of life occurs within this model. We also consider ribozymes that catalyze nucleotide synthesis. We show that living and dead states arise in the presence of synthase ribozymes in the same way as for polymerases. It has been proposed that recombination reactions are a way of generating long RNA chains in the early stages of life. We show that if the possibility of random reversible recombination reactions is added to our model, this does not lead to an increase in long polymer concentration. Thus, if recombination is fully reversible, there is no autocatalytic state controlled by recombination. Nevertheless, recombination can play an important role in ribozyme synthesis if there is an additional process that keeps the recombination reactions out of equilibrium. We modeled a case studied experimentally in which building block strands of moderate length associate due to RNA secondary structure formation. A recombination reaction then occurs between these strands to form a longer sequence that catalyzes its own formation via the recombination reaction. This system has an autocatalytic state, and it is possible for it to arise within our random polymerization system. If complexes formed by associations of shorter strands can act as catalysts without the requirement that the strands be covalently linked, this would alleviate the need for synthesis of very long strands; hence, it makes the emergence of an autocatalytic system from an abiotic random polymerization system much more likely.     

脉冲纹影技术及其在超声速燃烧室流场显示中的应用

超声速燃烧室内部流场具有流速快、温度高、背景光辐射强等特点,其流场显示较为困难.为此设计了一套脉冲纹影系统,该系统通过缩短曝光时间来冻结流场;另一方面,利用脉冲火花光源在短曝光时间内脉冲放电能量远高于燃烧室背景辐射能量的特点,有效消除了燃烧室背景辐射的影响.利用该系统对马赫数3.0的超临界煤油燃烧流场结构进行研究,得到了超临界煤油燃烧过程的清晰流场结构图像及其演化过程.     

基于二维微扫描镜的平视显示系统研究

平视显示系统是一种目前普遍运用于航空器上的飞行辅助器,它能使飞行员不用低头就可以看到仪表上的重要信息.针对传统平视显示系统体积大、生产成本高等不足,提出一种基于二维微扫描镜的平视显示系统.通过对二维微扫描镜的振动频率与平视显示图像的稳定性、分辨率、刷新率之间关系的分析研究,初步实现基于二维微扫描镜的平视显示系统的搭建,并成功完成一个常见标志的成像,证明基于二维微扫描镜的平视显示系统的可行性.     

U形渡槽槽体结构风载体形系数的风洞试验研究

本文对于U形渡槽槽体结构模型进行了风洞实验研究 ,得出了U形渡槽槽体结构的风压分布和风载体型系数。风洞试验结果表明U形渡槽槽体的风压分布和风载体形系数同槽体的高宽比和流场状况有关 ,在同一流场状况下槽体的风载体形系数随着槽体的高宽比变化。本文的试验结果为渡槽结构的抗风设计提供了参考依据。     

一种数字式无汞气压计的检定

以二等液体压力计做标准器，介绍数字式无汞气压计的检定及其检定数据的处理方法。     

SERF陀螺仪研究进展及关键技术

SERF(Spin Exchange Relaxation Free)陀螺仪利用电子自旋在惯性空间的定轴性敏感载体转动信息,具有超高精度、小体积的特点,已成为国内外惯性技术领域的研究热点之一.本文介绍了SERF陀螺仅的基本原理,回顾了SERF陀螺仪的国内外发展历程,指出SERF陀螺仪发展需要解决原子气室抗弛豫、核自旋磁场补偿闭环和高精度的信号检测三个关键技术,并展望了SERF陀螺仪在未来潜在的应用前景.     

民用无线电发射信号对电磁环境的影响

对世界范围内的典型民用无线电业务进行了归纳分析,在空域、时域、频域和能量域等详细参数计算的基础上,分析了民用发射信号对电磁环境中电子设备接收机的影响,并提出了多种建议方法以最大限度地减小民用发射信号对电子设备系统设计的影响。     

MBOC数字中频调制的FPGA实现

MBOC（6，1，1／11）调制是Compass系统与GPS和Galileo系统互操作的信号调制方式。文章采用FPGA实现了MBOC的数字中频调制，通过将FPGA实现的数据与Matlab仿真数据做比对，分析了由于量化带来的信号波形的幅度、功率谱密度和自相关函数等方面的误差。结果表明，采用14位量化时带来的误差很小，可以满足导航信号的设计要求。     

时滞依赖状态的脉冲中立型发展微分包含

目的主要考虑一类时滞依赖状态的脉冲中立型发展微分包含;方法在公理化定义的相空间上,利用Ba-nach空间中发展系统理论结合相应的不动点定理;结果时滞依赖状态的中立型泛函微分至少有一个温和解;结论建立此类问题温和解的存在性。