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Position and Orientation System (POS) is the key sensor of remote-sensing system. It is a typically Strapdown Inertial Navigation System (SINS) and Global Navigation Satellite System (GNSS) integrated measurement system, which provides high-precision position and attitude parameters. The gravity disturbance vector is one of the main error sources of high-precision SINS. The error propagation of POS is analyzed. It shows that the vertical component of the gravity disturbance vector is introduced into the POS horizontal channel through the vertical deflections, which leads to the error of the attitude measurement of the POS. In this article, a new real-time gravity compensation method is proposed, which includes the gravity disturbance as the error states of POS Kalman filter, and the accurate gravity disturbance model is constructed by a “Block-Time Variation” Markov Model (B-TV-MM) based on high-precision gravity map, whose resolution is enhanced by a new interpolation method based on Gaussian Process Regression (GPR). A flight experiment was conducted to evaluate the efficiency of the proposed method and the results showed that the proposed method performs better compared with other real-time gravity compensation methods.

Many studies have accessed the association between methionine synthase (MTR) A2756G polymorphism and neural tube defect (NTD). However, the conclusions are inconsistent. Our study aimed to clarify the nature of the genetic risks contributed by this polymorphism for NTD using meta-analysis. We searched electronic literature from the PubMed, EMBASE, and Medline databases, from which 10 articles were selected according to the inclusion criteria. The meta-analysis was conducted in 3 groups, namely, NTD patients, mothers with NTD offspring and fathers with NTD offspring. Pooled odds ratios (ORs) and 95% confidence intervals were used to evaluate the strength of the association and the result was corrected by multiple testing. To sum up, no associations between the MTR A2756G polymorphism and NTD risk were found among the 3 groups in all genetic models. However, as their sample size is not large enough, this result needs further research.