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This paper reports the fertility intension of women based on data from the national fertility survey in 2017 in China (CFS 2017), after implementation of the universal two-child policy, and analyses major related factors. The reported ideal number of children is 1.96 in average, and the intended number of children is 1.76, with obvious differences among different regions. The ideal number of children is highly correlated with the intended number of children, and intended number of children is related to number of children women already have. Women who have had one child intend to have fewer children than women who have not yet had a child. Women who have not yet had any child intend to have 1.60 children in average. The preference of boy varies by intended number of children.

An actively reconfigurable broadband terahertz (THz) metamaterial functional device based on the phase-change material vanadium dioxide (VO2) and two-dimensional graphene material is theoretically proposed and demonstrated. The device has excellent tolerance under oblique incidence. When the VO2 is in the metallic state, and the Fermi energy of graphene is fixed at 0.1 eV, the designed device acts as a broadband THz absorber in the transverse magnetic (TM) polarization mode. The absorptance bandwidth exceeds 0.55 THz with a complete absorption intensity of more than 90%. In this state, the absorber operates as a broadband modulator with the total modulation depth exceeding 91.5% as the continually decreased conductivity of VO2 from 200000 S/m to 10 S/m. In the transverse electric (TE) polarization process, the structure behaves as a dual-band absorber with two perfect absorption peaks. When the conductivity of VO2 is changed, the tunable absorber can also be regarded as an absorptance modulator, with a maximum modulation intensity of 92.1%. Alternatively, when VO2 behaves as an insulator at room temperature in the TE polarization mode, a strong broadband electromagnetically induced transparency (EIT) window is obtained, with a bandwidth exceeding 0.42 THz in the transmittance spectrum. By varying the Fermi energy of graphene from 0 to 0.9 eV, the EIT-like window or broadband transmission spectrum (in TM mode) can be switched. The results indicate that the device can also be operated as a modulator in the transmission mode. The impedance matching theory is used, and electric field distributions are analyzed to quantify the physical mechanism. An advantage of the manipulation of the polarization angle is that the modulation performance of the proposed multi-functional THz device can be regulated after fabricated.

Based on China fertility survey 2017, this report presents the national fertility level, age-specific fertility rate and parity distribution. The survey results show that during 2006-2016 the mean ages at first marriage and first birth increased by 2.7 and 2.6 years respectively. From 2006 to 2011, the total fertility rate was around 1.60-1.70, and experienced notable fluctuations during 2012-2016. Compared the agespecific fertility in 2006 with in 2011, the curve in 2016 shifted significantly to the right side. Affected by the relaxation of the fertility policy, the proportion of second births among the total births had increased year by year since 2012.

LoRa wireless technology is a revolutionary wireless network access technology with a wide application prospect. An identification method for Lora devices based on physical layer fingerprinting is proposed to provide identities for authentication. Contrary to previous works, a differential constellation trace figure is established from the radio frequency (RF) fingerprinting features of LoRa devices, which transforms the feature matching to the image recognition. A classification method based on Euclidean distance of clustering center of LoRa signal is performed to analyze the differential constellation trace figure. The experimental results show that six LoRa transmission modules can be recognized accurately, and even in a low signal-to-noise ratio (SNR) environment, the different LoRa devices can still be distinguished and identified effectively.