Non-orthogonal multiple access (NOMA) is deemed to have a superior spectral efficiency and polar codes have became the channel coding scheme for control channel of enhanced mobile broadband (eMBB) in the fifth generation (5G) communication systems. In this paper, NOMA combined with polar codes is used to achieve secure transmission. Both degraded wiretap channel and non-degraded wiretap channel are considered, where an eavesdropper intercepts the communication between base station (BS) and users. For the degraded wiretap channel scenario, a secure polar encoding scheme is proposed in NOMA systems with power allocation to achieve the maximum secrecy capacity. With regard to the non- degraded wiretap channel, a polar encoding scheme with multiple-input-single-output (MISO) system is proposed, where artificial noise is generated at BS to confuse the eavesdropper's channel via transmit beam- forming. The security and the secure rate are employed respectively in order to measure the secrecy performance. We prove that the proposed schemes for each scenario can achieve the secure rate and can transmit the signal securely and reliably. The simulation results show that the eavesdropper hardly decoding the secure signal when the legitimate receiver can decode the signal with very low block error rate (BLER).
Atmospheric concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), and polybrominated diphenyl ethers (PBDEs) were measured in Taizhou, a large electronic equipment waste (e-waste) recycling area in East China. The mean concentrations (in summer and winter) of PCDD/Fs (0.45 and 0.39 pg WHO-TEQ m−3, where WHO-TEQ is the toxic equivalent set by the World Health Organisation), PBDD/Fs (0.22 and 0.18 pg WHO-TEQ m−3), and PBDEs (270 and 225 pg m−3) in this region have declined compared with those in 2005, due to regulations on primitive e-waste recycling activities. However, these concentrations remain higher than the historically highest levels in Europe and North America. The congener profiles of 2,3,7,8-substituted PCDD/Fs were similar, with OCDD, 1,2,3,4,6,7,8-HpCDF, OCDF, and 1,2,3,4,6,7,8-HpCDD being the most abundant congeners at all sites. The PCDD/F homologue profiles in the present study were different from those typically observed at non-e-waste locations, indicating a distinct source in this region. Seasonal differences were found in the lower brominated PBDE profiles. These differences indicate that the PBDE emission sources in summer (e.g., strong evaporation sources) differed from those in winter. However, the relatively steady congener profiles of the highly brominated PBDEs suggest that these PBDEs were controlled primarily by similar emission mechanisms. The lifetime excess cancer risks from exposure to PCDD/Fs and PBDD/Fs via inhalation ranged from 0.7 × 10−5 to 5.4 × 10−5, or approximately 80 cancer cases in the Taizhou population.
Based on a band gap reference source in 0.18um process, a single particle transient current model is used to simulate single particle bombardment to conduct circuit level simulation. A single particle sensitivity analysis is carried out on the whole band gap reference source circuit and the internal sensitive nodes are confirmed by simulation verification. Finally, the method based on filtering and isolation is used to strengthen the sensitive nodes against single particle transient, which can effectively suppress the abnormal SET output voltage.
Groundwater denitrification is challenged by a lack of electron donors and usually requires additional energy input or chemical agents. The microbial electrolysis cells (MECs) provide an effective electronic compensation technique for the remediation of nitrate-contaminated electron-donor-lacking groundwater via the hydrogen-trophic denitrification process by converting organic pollutions to clean H2 gas. In this study, we combine a single chamber microbial electrolysis cell (MECs) as a hydrogen production unit with a permeable bio-reactive barrier (PRB) for in-situ hydrogenotrophic denitrification of groundwater. The semi-hydrophobic PTFE-coated granular activated carbons (GAC) and hydrophilic GAC were filled as biocarriers in PRBs. The PTFE-coated GAC makes the denitrification performance of PRB insensitive to hydrogen partial pressure within the tested range of 0.01 to 0.04 MPa and achieved effluent nitrate concentration < 20 mg L–1 within 12 h (The Water Quality Standard for Drinking Water Sources in China). The gas production in MECs was actively pumped to PRBs and spontaneously achieve negative pressure on the MEC side and positive pressure on the PRB side. The negative pressure improved current density by 18.6 ± 0.7% in MECs and the MEC-PRB hybrid system could reduce 85.0 ± 0.8% of nitrate in actual groundwater with an effluent concentration of 15.0 ± 0.8 mg L–1 at 72 h. Compared with PRB connected with an H2 generator (H2-PRB), MEC-PRB obtained higher diversity in biocommunity with both methylotrophic denitrifiers and hydrogenotrophic denitrifiers. This work demonstrated the feasibility of matching MEC and PRB as a novel hybrid system for organic pollution degradation and effective nitrogen removal in electron-donor-lacking groundwater.
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