China is strongly dependent on railway transportation, but the frost heaving of the subgrade in cold regions has seriously affected the safety and comfort of trains. Moisture content is an essential parameter in the subgrade frost heave. Non-destructive and efficient geophysical methods have great potential in measuring the moisture content of railway subgrade. In this paper, we use the common mid-point (CMP) measurement of ground penetrating radar (GPR) to estimate the propagation velocity of electromagnetic waves in a subgrade application. We establish a synthetic model to simulate the railway subgrade structure. The synthetic CMP gathers acquired from shallow and thin layers are seriously disturbed by multiple waves and refraction waves, which make the routine velocity analysis unable to provide accurate velocities. Through the analysis of numerical simulation results, it is found that the primary reflection waves, multiple waves, and refraction waves are dominant in different offset ranges of CMP gather. Therefore, we propose a solution of the optimal gather at a certain range of offset dominated by the primary reflection wave to calculate the velocity spectrum and extract the accurate velocities for the subgrade model. The relative dielectric constants of the corresponding layers are calculated after the stacking velocities are converted into the interval velocities. Then, the moisture content is obtained by the Topp formula, which expresses the relationship between dielectric constant and moisture content. Finally, we apply the optimal gather scheme and the above interpretation process to the GPR data acquired at the railway site, and we form a long moisture content profile of the railway subgrade. Compared with the polarizability measured by the induced polarization (IP) method, it is found that the regions with high moisture content correspond to polarizability anomalies with different strengths. The comparison shows the reliability of GPR results to some extent.
The objective of this short communication was the relationship between vitamin D and precocious puberty (PP). In this study, a comprehensive search of multiple databases was performed to identify studies focused on the association between vitamin D deficiency and PP. Studies that compared serum vitamin D levels between patients with PP and controls were selected for the systematic meta-analysis. The main outcome was the mean difference in serum vitamin D levels between PP and controls. Vitamin D-deficient subjects were more likely to develop PP. Our findings suggest that PP may be linked to vitamin D deficiency. Thus, providing supplements of vitamin D to PP patients may improve their nutritional status and prevent diseases. But, the amount of vitamin D required is uncertain, so it is important to be careful when taking vitamin D supplements.
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