演播同步系统测试

在演播室视频系统中,要使摄像机信号和外来信号等所有信号源的画面在切换台平滑切换而不产生抖动、撕裂等现象,必须把全部信号源调整到同一个同步相位。本文介绍了数字模拟混合系统、数字高标清混合系统的同步定时测试的相关标准及定义。

作息时间与广播自动控制系统的研制

采用PLC控制与CMMS4 0 4 0制成的时钟脉冲发生器相结合的方式 ,研制开发了作息时间与广播自动控制系统 。

HOW DIFFERENT VARIABLES AFFECT THE ACCURACY OF HAND-TIMING

To analyze the process of hand-timing and the resulting data collected from the hand-timing computer system(HTCS),including the timing operator′s reaction times of starting and stopping the watch,the results from the timing,the simulated electronic timing,the major factor that affects the time-keeper′s accuracy of time-keeping were studied,i.e.the stability of the timekeeper′s reaction time,rather than the time-keeper′s reation time.The leading cause that inflicts error between the hand-time-keeping and the electrionic time-keeping consists in the pitfall that the time-keeper makes a wrong judgment in stopping the watch.The analytical results provide theoretic gist for the selection and training of time-keeping operators.

Improved Circular Correlation Methods for Acquisition in Software GPS Receiver

In this paper the authors explore the Global Positioning System （GPS） signal acquisition and tracking algorithms used in software GPS receiver. Acquisition time is the most important parameter in evaluating the performance of a software GPS receiver in terms of its speed. A trade-off study is done to seek a good balance between the acquisition accuracy and the processing time. The frequency-domain acquisition method by circular correlation, used in a software GPS receiver, has been improved by studying the power spectrum of the Coarse Acquisition （C/A） code alone. The analysis of C/A code reveals that its power spectrum is symmetrical; hence only half the points are required to perform circular correlation. Besides, either half of the spectrum is asymmetrical where a larger amount of power is concentrated in almost one-quarter of the spectrum on its either sides. This further reduces the number of points used to perform correlation. Comparative results of MATLAB simulation of full-size, half-size and quarter-size circular correlation done on actual data stored on hard disk are provided, and they agree with those obtained using GPS receiver. Further reduction in acquisition time has been achieved by investigating the effect of length of the noncoherent pre-integration period. The improved acquisition methods pave way for further development of new algorithms to enhance software GPS receiver performance.

Function of shoulder muscles of driver in vehicle steering maneuver

In order to study the function of muscles of driver shoulder during vehicle steering, identification of relations between electromyograph (EMG) activity of 10 shoulder muscles and steering force was performed. The procedure was to perform controlled steering maneuver by right hand in a driving simulator, and based on analyzing the EMG data with steering force in the steering wheel plane, the function was identified. It was found that muscle function depends strongly on both steering rotation and steering torque directions. In clockwise steering, the long head of triceps brachii was the prime mover and an important contributor to clockwise moment, while the sternocostal portion of the pectoralis major, the lateral head of triceps brachii, biceps brachii and teres major were the important stabilizers or fixators. In contrast, in counterclockwise steering, the anterior, middle and posterior deltoid, the clavicular portion of the pectoralis major and infraspinatus were the prime movers and also the important contributors to counterclockwise moment, while the sternocostal portion of the pectoralis major, the lateral head of triceps brachii, biceps brachii and teres major were the important stabilizers or fixators. We conclude that the prime movers are primarily a consequence of steering direction, while the stabilizers or fixators are primarily constant. These results can be used to improve the neuromuscular model and estimate the steering comfort of driver.

Numerical Modelling of a Supersonic Axial Turbine Stator

In order to improve the turbocharging process,a supersonic axial turbine stator was modelled numerically with a pulsatile inlet mass flow.The main objectives of the study were to find out how pulsation affects the flow field and the performance of the stator.At the beginning of the study,a supersonic turbine stator was modelled using three different techniques:quasi-steady,time-accurate with constant boundary conditions and time-accurate with a pulsatile inlet mass flow.The time-averaged and quasi-steady flow fields and performance were compared,and the flow field and stator performance with a pulsatile inlet mass flow was studied in detail at different time-steps.A hysteresis-like behaviour was captured when the total-to-static pressure ratio and efficiency were plotted as a function of the inlet mass flow over one pulse period.The total-to-static pressure ratio and efficiency followed the sinusoidal shape of the inlet flow as a function of time.It was also concluded that the stator efficiency decreases downstream from the stator trailing edge and the amplitude of the pulsating mass flow is decreased at the stator throat.

Flow computations of multi-stages by URANS and flux balanced mixing models

The quasi-steady methods based on mixing models have been widely applied to flow computations of turbomachinery multi- stages in aerospace engineering. Meanwhile, the unsteady numerical simulation has also been used due to its ability in obtaining time-dependent flow solutions. In the paper, two different mixing treatments and the corresponding flux balanced ones are presented to exchange the flow solutions on the interfaces between adjacent blade rows. The four mixing treatments are then used for flow computations of a subsonic 1.5-stage axial turbine and a quasi-l.5-stage transonic compressor rotor. The results are compared with those by unsteady numerical method, which is implemented by using the sliding mesh technique. The effects of the quasi-steady and unsteady computation methods on the conservation of flow solutions across the interfaces are presented and addressed. Furthermore, the influence of mixing treatments on shock wave and flow separation of the transonic compressor rotor is presented in detail. All the results demonstrate that the flux balanced mixing treatments can be used for multi-stage flow computations with improved performance on interface conservation, even in the complex flows.