Search

Perfluorooctane sulfonate (PFOS), a new kind of persistent organic pollutant, is widely distributed in the environment and exists in various organisms, where it is also a neurotoxic compound. However, the potential mechanism of its neurotoxicity is still unclear. To examine the role of epigenetics in the neurotoxicity induced by PFOS, SK-N-SH cells were treated with different concentrations of PFOS or control medium (0.1% DMSO) for 48 h. The mRNA levels of DNA methyltransferases (DNMTs) and Brain-derived neurotrophic factor (BDNF), microRNA-16, microRNA-22, and microRNA-30a-5p were detected by Quantitative PCR (QPCR). Enzyme Linked Immunosorbent Assay (ELISA) was used to measure the protein levels of BDNF, and a western blot was applied to analyze the protein levels of DNMTs. Bisulfite sequencing PCR (BSP) was used to detect the methylation status of the BDNF promoter I and IV. Results of MTT assays indicated that treatment with PFOS could lead to a significant decrease of cell viability, and the treated cells became shrunk. In addition, PFOS exposure decreased the expression of BDNF at mRNA and protein levels, increased the expression of microRNA-16, microRNA-22, microRNA-30a-5p, and decreased the expression of DNMT1 at mRNA and protein levels, but increased the expression of DNMT3b at mRNA and protein levels. Our results also demonstrate that PFOS exposure changes the methylation status of BDNF promoter I and IV. The findings of the present study suggest that methylation regulation of BDNF gene promoter and increases of BDNF-related-microRNA might underlie the mechanisms of PFOS-induced neurotoxicity.

Based on the terrain observation by progressive scans (TOPS) mode, an efficient full-aperture image formation algorithm for focusing wide-swath spaceborne TOPS data is proposed. First, to overcome the Doppler frequency spectrum aliasing caused by azimuth antenna steering, the range-independent derotation operation is adopted, and the signal properties after derotation are derived in detail. Then, the azimuth deramp operation is performed to resolve image folding in azimuth. The traditional dermap function will introduce a time shift, resulting in appearance of ghost targets and azimuth resolution reduction at the scene edge, especially in the wide-swath coverage case. To avoid this, a novel solution is provided using a modified range-dependent deramp function combined with the chirp-z transform. Moreover, range scaling and azimuth scaling are performed to provide the same azimuth and range sampling interval for all sub-swaths, instead of the interpolation operation for the sub-swath image mosaic. Simulation results are provided to validate the proposed algorithm., Competing Interests: The authors declare no conflict of interest.

Global Navigation Satellite System (GNSS)-based bistatic Synthetic Aperture Radar (SAR) recently plays a more and more significant role in remote sensing applications for its low-cost and real-time global coverage capability. In this paper, a general imaging formation algorithm was proposed for accurately and efficiently focusing GNSS-based bistatic SAR data, which avoids the interpolation processing in traditional back projection algorithms (BPAs). A two-dimensional point target spectrum model was firstly presented, and the bulk range cell migration correction (RCMC) was consequently derived for reducing range cell migration (RCM) and coarse focusing. As the bulk RCMC seriously changes the range history of the radar signal, a modified and much more efficient hybrid correlation operation was introduced for compensating residual phase errors. Simulation results were presented based on a general geometric topology with non-parallel trajectories and unequal velocities for both transmitter and receiver platforms, showing a satisfactory performance by the proposed method.

In this work, the staggered SAR technique is employed for high-speed platform highly-squint SAR by varying the pulse repetition interval (PRI) as a linear function of range-walk. To focus the staggered SAR data more efficiently, a low-complexity modified Omega-k algorithm is proposed based on a novel method for optimal azimuth non-uniform interpolation, avoiding zero padding in range direction for recovering range cell migration (RCM) and saving in both data storage and computational load. An approximate model on continuous PRI variation with respect to sliding receive-window is employed in the proposed algorithm, leaving a residual phase error only due to the effect of a time-varying Doppler phase caused by staggered SAR. Then, azimuth non-uniform interpolation (ANI) at baseband is carried out to compensate the azimuth non-uniform sampling (ANS) effect resulting from continuous PRI variation, which is further followed by the modified Omega-k algorithm. The proposed algorithm has a significantly lower computational complexity, but with an equally effective imaging performance, as shown in our simulation results.