A detection algorithm of frequency jumps for GNSS satellite clocks
As the frequency and time reference of space satellites, satellite clock has a direct influence on GNSS service performance. Any anomaly of the atomic clock behavior on board the satellites causes errors for user position. Therefore, it is necessary to detect clock anomaly. Frequency jumps are one of the most common anomalies in atomic clocks of on-board satellites, which appear due to space radiation, temperature change and other factors. In this paper, a detection algorithm of frequency jumps based on the batch least squares residues is proposed. Performance of the new algorithm is analyzed and verified by numerical simulation. The detection algorithm of frequency jumps for satellite clocks proposed in this paper is helpful to GNSS satellite clock autonomous integrity monitoring.
The dynamic Allan variance
We present and discuss the dynamic Allan variance, a measure of the time-varying stability of an atomic clock. First, the dynamic Allan variance is mathematically defined, then its behavior is extensively tested on simulated and experimental data. The results prove the validity and the effectiveness of the proposed new tool.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.