The unscented Kalman filter (UKF) is widely used to address the nonlinear problems in target tracking. However, this standard UKF shows unstable performance whenever the noise covariance mismatches. Furthermore, in consideration of the deficiencies of the current adaptive UKF algorithm, this paper proposes a new adaptive UKF scheme for the time-varying noise covariance problems. First of all, the cross-correlation between the innovation and residual sequences is given and proven. On this basis, a linear matrix equation deduced from the innovation and residual sequences is applied to resolve the process noise covariance in real time. Using the redundant measurements, an improved measurement-based adaptive Kalman filtering algorithm is applied to estimate the measurement noise covariance, which is entirely immune to the state estimation. The results of the simulation indicate that under the condition of time-varying noise covariances, the proposed adaptive UKF outperforms the standard UKF and the current adaptive UKF algorithm, hence improving tracking accuracy and stability.

a b s t r a c tMagnetic solid-phase extraction (MSPE) using magnetic multi-walled carbon nanotubes (mag-MWCNTs) as adsorbents, coupled with high-performance liquid chromatography-diode-array detector (HPLC-DAD), was developed for the simultaneous separation and determination of six types of sulfonylurea herbicides (SUs) in environmental water samples. Several variables affecting MSPE efficiency were systematically investigated, including the type and volume of desorption solvent, sample solution pH, salt concentration, amount of mag-MWCNTs, and extraction and desorption time. Response surface was employed to assist in the MSPE optimization. Under optimized conditions, excellent linearity was achieved in the range of 0.05-5.0 g/L for all six SUs, with coefficients of correlation r > 0.9994, and preconcentration factors ranging from 178 to 210. Limits of detection and quantification were 0.01-0.04 g/L and 0.03-0.13 g/L, respectively. The intra-day and inter-day precision (relative standard deviations, n = 6, %) at three spiked levels were 2.0-11.0% and 2.1-12.9% in terms of peak area, respectively. The method recoveries at three fortified concentrations were obtained within 76.7-106.9% for reservoir water samples and 78.2-105.4% for tap water samples. The developed MSPE-HPLC method demonstrated high sensitivity, repeatability, simplicity, rapidity, and excellent practical applicability.

In this study, C 18 -functionalized magnetic silica nanoparticles (Fe 3 O 4 @SiO 2 @C 18 MNPs) based magnetic solid phase extraction (MSPE) was successfully developed for the determination of microcystin-LR (MC-LR) in reservoir water samples followed by high performance liquid chromatography-diode array detection (HPLC-DAD). After the extraction, the adsorbent can be conveniently and rapidly separated from aqueous samples by an external magnet. The main factors influencing the extraction efficiency including the amount of the MNPs, the extraction time, the pH of sample solution and desorption conditions were optimized to obtain high recoveries and extraction efficiency.

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