Assessment of ionospheric corrections for PPP-RTK using regional ionosphere modelling
MEASUREMENT SCIENCE AND TECHNOLOGY
Authors: Psychas, D.; Verhagen, S.; Liu, X.; Memarzadeh, Y.; Visser, H.
Abstract
This paper presents an analysis of the ionospheric corrections required to get a significant improvement in PPP-RTK performance. The main aim was to determine the improvement in the position precision and time-to-first-fix in the PPP-RFK user side using ionospheric corrections computed from a network. The study consists of two main steps. The first one includes an empirical investigation of the ionosphere model precision necessary to greatly improve the PPP-RTK performance in a simulated environment in terms of precision and convergence time. In the second one, an optimal ionosphere representation was developed to provide precise ionospheric corrections by parameterizing the ionospheric slant delays after the PPP-RTK network processing in terms of ionosphere model coefficients and differential code biases using real GNSS measurements. Experimental results demonstrate that the proposed methodology can be used for reliable regional ionosphere modeling and satellite code bias estimation, due to the consistency of the satellite code bias estimates with those provided from the International GNSS Service Analysis Centres, the high stability of the estimated receiver and satellite code biases and the low least-squares residuals of the network-based ionosphere modeling solution. Finally, it has been shown that the precision of ionospheric corrections at zenith needs to be better than 5 cm to enable faster PPP-RTK solutions.
Importance of Riboflavin Kinase in the Pathogenesis of Stroke
CNS NEUROSCIENCE & THERAPEUTICS
Authors: Zou, Ying-Xin; Zhang, Xiu-Hua; Su, Feng-Yun; Liu, Xia
Abstract
Aims To explore risk factors for stroke independent of hypertension and the relationship between riboflavin kinase (RFK) and stroke. Methods Gene expression profiling in the brains of spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP) was comparatively analyzed by gene chips. The differentially expressed gene RFK was further verified by q-PCR and Western blot. The protective role of RFK-regulated flavins (including riboflavin, flavin mononucleotide, and flavin adenine dinucleotide) in stroke was observed in middle cerebral artery occlusion (MCAO) mice. Influence of flavins on apoptosis and death in oxygen and glucose deprivation (OGD)-treated neurons was examined by flow cytometry. Bax and Bcl-2 proteins were detected by Western blot. Results Of the 76 differentially expressed genes, 41 genes were upregulated, and 35 genes were downregulated in SHRSP as compared with SHR. RFK was significantly downregulated in SHRSP. Flavins markedly decreased infarct area in MCAO mice, inhibited apoptosis and death in OGD-treated neurons, and decreased Bax protein expression. Conclusions Physiological downregulation of RFK may be a new potential risk factor for stroke, which probably affects the absorbance and utility of riboflavin and further destroys the protective effect of flavins on stroke. RFK might act as a therapeutic target for stroke.