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The self-noise level of a seismometer can determine the performance of the seismic instrument and limit the ability to use seismic data to solve geoscience problems. Accurately measuring and simultaneously comparing the self-noise models from different types of seismometers has long been a challenging task due to the constraints of observation conditions. In this paper, the self-noise power spectral density (PSD) values of nine types of seismometers are calculated using four months of continuous seismic waveforms from Malingshan seismic station, China, and nine self-noise models are obtained based on the probability density function (PDF) representation. For the seismometer STS-2.5, the self-noise levels on the horizontal channels (E–W and N–S) are significantly higher than that on the vertical channel (U–D) in the microseism band (0.1 Hz to 1 Hz), which is a computing bias caused by the misalignment between the sensors in the horizontal direction, while the remarkably elevated noise on the horizontal channels at the low frequencies (<0.6 Hz) may originate from the local variation of atmospheric pressure. As for the very broadband seismometers Trillium-Horizon-120 and Trillium-120PA, and the ultra-broadband seismometers Trillium-Horizon-360 and CMG-3T-360, there is a trade-off between the microseism band range and low-frequency range in the PSD curves of the vertical channel. When the level of self-noise in the microseism band is high, the self-noise at low frequencies is relatively low. Although compared with the other very broadband seismometers, the self-noise level of the vertical component of the STS-2.5 is 3 dB to 4 dB lower at frequencies less than 1 Hz, the self-noise level of the STS-2.5 at high frequencies (>2 Hz) is slightly higher than others. From our observations, we conclude that the nine seismometers cannot reach the lowest noise level in all frequency bands within the working range. [ABSTRACT FROM AUTHOR]

Objective: To assess the efficacies of proximal femoral nail antirotation (PFNA) versus dynamic hip screw (DHS) for intertrochanteric fracture in elders., Methods: The databases of PubMed, Embase, CENTRAL, CBM, CNKI and WANFANG were searched for the relevant randomized controlled trials (RCTs) up to May 18, 2013. After quality evaluation and data extraction by two authors independently, meta-analyses were performed with the RevMan5.1 software. And the levels of evidence were evaluated by the GRADEprofile 3.6 software., Results: A total of 17 studies (n = 1 344) were included and there were 656 patients in PFNA group and 688 in DHS respectively. Meta-analyses showed that, as compared with DHS, PFNA could significantly decrease fixation failure rate (odds ratio (OR) = 0.26, 95% confidence interval (CI) = [0.12, 0.57], P = 0.0008), reduce average fracture healing time (weighted mean difference (WMD) = -15.11, 95%CI = [-24.36, -5.85], P = 0.001), improve excellent and good rate for Harris score (OR = 0.29, 95%CI = [0.15, 0.56], P = 0.0002), yield a higher Harris score (WMD = 6.88, 95%CI = [0.96, 12.80], P = 0.02) and reduce the rate of coxa vara (OR = 0.40, 95%CI = [0.18,0.92], P = 0.03). However, there was no statistical significance in 1-year mortality, postoperative nonunion and delayed union, postoperative femoral head necrosis, postoperative femoral fractures or femoral head necrosis. The importance of outcomes was "critical". And the level of evidences based on the GRADE approach was from "very low" to "low"., Conclusion: PFNA is superior to DHS. Due to the limitations of the included studies, more large-sample and high-quality RCTs are required. And subgroup analysis based on fracture types should be performed.