Prediction of eukaryotic protein subcellular multi- localisation with a combined KNN-SVM ensemble classifier

Proteins may exist in or shift among two or more different subcellular locations, and this phenomenon is closely related to biological function. It is challenging to deal with multiple locations during eukaryotic protein subcellular localisation prediction with routine methods; therefore, a reliable and automatic ensemble classifier for protein subcellular localisation is needed. We propose a new ensemble classifier combined with the KNN (K-nearest neighbour) and SVM (support vector machine) algorithms to predict the subcellular localisation of eukaryotic proteins from the GO (gene ontology) annotations. This method was developed by fusing basic individual classifiers through a voting system. The overall prediction accuracies thus obtained via the jackknife test and resubstitution test were 70.5 and 77.6% for eukaryotic proteins respectively, which are significantly higher than other methods presented in the previous studies and reveal that our strategy better predicts eukaryotic protein subcellular localisation

Real-Time BDS-3 Clock Estimation with a Multi-Frequency Uncombined Model including New B1C/B2a Signals

The global system of BDS (BeiDou Navigation Satellite System), i.e., BDS-3, is characterized with a multi-frequency signal broadcasting capability, which was demonstrated as beneficial for GNSS (Global Navigation Satellite System) data processing. However, research on real-time BDS-3 clock estimation with multi-frequency signals is quite limited, especially for the new B1C and B2a signals. In this study, we developed models for BDS-3 multi-frequency real-time data processing, including the uncombined model for clock estimation and the GFIF (Geometry-Free Ionosphere-Free) combined model for IFCB (Inter-Frequency Clock Bias) determination. Based on the models, simulated real-time numerical experiments with about 80 global IGS (International GNSS Service) network stations are conducted for validation and analysis. The results indicate that: (1) the uncombined model with multi-frequency signals can achieve comparable accuracy with the traditional dual-frequency IF model in terms of clock estimation, and the double-differenced clock STDs (Standard Deviations) are generally less than 0.05 ns with post-processed clocks as a reference; (2) unlike the B1C and B1I/B3I signals, the satellite IFCBs generated from multi-frequency clock estimation show apparent temporal variations for B2a and B1I/B3I signals, further investigation with GFIF models confirm the variations mainly result from the errors of receiver antenna corrections. Therefore, we addressed the feasibility of the uncombined model and the importance of accurate antenna information in the multi-frequency data processing

A Second-Order Time-Difference Position Constrained Reduced-Dynamic Technique for the Precise Orbit Determination of LEOs Using GPS

In this paper, we propose a new reduced-dynamic (RD) method by introducing the second-order time-difference position (STP) as additional pseudo-observations (named the RD_STP method) for the precise orbit determination (POD) of low Earth orbiters (LEOs) from GPS observations. Theoretical and numerical analyses show that the accuracies of integrating the STPs of LEOs at 30 s intervals are better than 0.01 m when the forces (<10−5 ms−2) acting on the LEOs are ignored. Therefore, only using the Earth’s gravity model is good enough for the proposed RD_STP method. All unmodeled dynamic models (e.g., luni-solar gravitation, tide forces) are treated as the error sources of the STP pseudo-observation. In addition, there are no pseudo-stochastic orbit parameters to be estimated in the RD_STP method. Finally, we use the RD_STP method to process 15 days of GPS data from the GOCE mission. The results show that the accuracy of the RD_STP solution is more accurate and smoother than the kinematic solution in nearly polar and equatorial regions, and consistent with the RD solution. The 3D RMS of the differences between the RD_STP and RD solutions is 1.93 cm for 1 s sampling. This indicates that the proposed method has a performance comparable to the RD method, and could be an alternative for the POD of LEOs

The Impact of Eclipsing GNSS Satellites on the Precise Point Positioning

When satellites enter into the noon maneuver or the shadow crossing regimes, the actual attitudes will depart from their nominal values. If improper attitude models are used, the induced-errors due to the wind-up effect and satellite antenna PCO (Phase Center Offset) will deteriorate the positioning accuracy. Because different generations of satellites adopt different attitude control models, the influences on the positioning performances deserve further study. Consequently, the impact of three eclipsing strategies on the single-system and multi-GNSS (Global Navigation Satellite System) Precise Point Positioning (PPP) are analyzed. According to the results of the eclipsing monitor, 65 globally distributed MGEX (Multi-GNSS EXperiment) stations for 31-day period in July 2017 are selected to perform G/R/E/C/GR/GREC PPP in both static and kinematic modes. The results show that the influences of non-nominal attitudes are related to the magnitude of the PCO values, maximum yaw angle differences, the duration of maneuver, the value of the sun angle and the satellite geometric strength. For single-system, using modeled attitudes rather than the nominal ones will greatly improve the positioning accuracy of GLONASS-only and BDS-only PPP while slightly contributions to the GPS-only and GALILEO-only PPP. Deleting the eclipsing satellites may sometimes induce a longer convergence time and a worse solution due to the poor satellite geometry, especially for GLONASS kinematic PPP when stations are located in the low latitude and BDS kinematic PPP. When multi-GNSS data are available, especially four navigation systems, the accuracy improvements of using the modeled attitudes or deleting eclipsing satellites are non-significant

The Impact of Yaw Attitude of Eclipsing GPS/GALILEO Satellites on Kinematic PPP Solutions and Their Correction Models

When GPS/GALILEO satellite runs to the position where it is approximately collinear with the sun and the earth, it is difficult for the satellite to keep nominal attitude, so it will show abnormal yaw attitude for a period of time. Based on the precision orbit and clock correction products offered by different analysis centers, we design different attitude correction strategies for satellite that is in abnormal yaw attitude period, select 10-day measured data from 7 MGEX stations distributed globally, and analyze the influence of antenna phase center offset and phase wind-up of GPS/GALILEO satellite on residuals of observations and kinematic PPP positioning result in this paper. The research results show that when the satellite is in abnormal yaw attitude period, adopting nominal yaw attitude can have an impact up to 8 cm and 11 cm on the residuals of GPS/GALILEO satellite observations. GPS/GALILEO satellite is in model yaw attitude during the period and its positioning accuracy of kinematic PPP positioning results in three directions of E, N and U shows an increasing rate of 13.30%, 15.77% and 12.98%, respectively in comparison with that in nominal yaw attitude. Comparing with satellite deletion strategy, the accuracy of kinematic PPP positioning results in three directions of E, N and U when the satellite is in model yaw attitude shows an increasing rate of 5.399%, 4.430% and 5.992%, respectively