A sequential sparse polynomial chaos expansion using Bayesian regression for geotechnical reliability estimations

Polynomial chaos expansions (PCEs) have been widely employed to estimate failure probabilities in geotechnical engineering. However, PCEs suffer from two deficiencies: (a) PCE coefficients are solved by the least-square minimization method which easily causes overfitting issues; (b) building a high order PCE is often computationally expensive. In order to overcome the aforementioned drawbacks, the Bayesian regression technique is employed to evaluate PCE coefficients, which not only provides a sparse solution but also avoids overfitting. With the aid of the predictive means and variances given by Bayesian analysis, a learning function is proposed to sequentially select the most informative samples that are critical to build a PCE. This sequential learning scheme can highly enhance the computational efficiency of PCEs. Besides, importance sampling (IS) is incorporated into the sequential learning (SL)-PCEs to deal with geotechnical problems with small failure probabilities. The proposed method of SL-PCE-IS is applied to three illustrative examples, which shows that the improved PCE method is more effective and efficient than the common PCEs method, leading to accurate estimations of small failure probabilities using fewer training samples.     

Using data‐driven methods to explore the predictability of surface soil moisture with FLUXNET site data

Soil moisture (SM) is a key variable of land surface‐atmosphere interactions. Data‐driven methods have been used to predict SM, but the predictability of SM has not been well evaluated. This study investigated what variables and methods can be used to better predict SM for leading times of 7 days or longer with a global coverage of FLUXNET site data for the first time. Three machine‐learning models, that is, Bayesian linear regression, random forest, and gradient boosting regression tree, are used for the prediction. Variables including atmospheric forcing, surface soil temperature, time variables (year, day of year, and hour), the Fourier transformation of time variables, and lagged SM (7‐ to 14‐day lagged) were sequentially added into models. A framework with five experiments is designed for factorial exploration of SM predictability. A stepwise method was used to build the best models for each site. The performance of regression models became better when adding more explaining variables in most cases. The results showed that from 50 to 95% of variation of the best models can be explained. The important explaining variables are lagged surface SM, followed by day of year, year, soil temperature, and atmospheric forcing. The predictability of SM depends highly on SM memory characteristics and the persistence of seasonality. The effect of SM memory characteristics on SM prediction as an initial condition question has been widely discussed in this paper. Our results also provide an insight that mechanisms of seasonality effects on SM should be also paid more attention to.     

Measurement and analysis of rotation in close binaries. I. Observations and results

A set of close binaries have been observed using the same instrumental configuration at Kitt Peak National Observatory, USA. The rotation velocities for 99 components in 75 binaries, derived by two methods, are given here, including 55 components for the first time. These high-accuracy velocities provide a reliable observational basis for investigating synchronism in binaries and the various synchronizing mechanisms.     

华北陆块南缘富碱侵入岩岩石组合及时空分布

华北陆块南缘（河南段）出露的富碱侵入岩类集中分布于卢氏－确山一线。岩石类型主要分为三大类：①碱性岩类，即含有似长石或碱性暗色矿物的正长岩类；②碱性花岗岩类，包括钠铁闪石花岗岩以及孪生的钾长花岗岩类；③石英正长岩类，包括碱性长石为主的石英正长岩、英碱正长岩和花岗正长（斑）岩类。在空间上构成一条富碱岩浆岩带，据岩石组合自北而南划为三个亚带：北部碱性岩亚带、中部碱性花岗岩类亚带和南部石英正长（斑）岩亚带。在形成时间上富碱岩浆活动集中于晚元古代末期（７００Ｍａ±）和海西晚期（３００Ｍａ±）。     

浙江A村金矿的矿化特征及成矿条件分析

本文阐述了A村金矿点的地质环境及其金矿化特征和矿化类型，认为该金矿点是与花岗岩类岩石有关的金矿化类型。关在研究其成矿条件的基础上，提出了若干寻找同类型金矿的找矿标志。     

自转对恒星物理量的影响

自转本身是恒星的基本物理量之一，同时影响恒星的其它许多物物量，包括对恒星半径、形状和体积的影响；对光度、包指数、谱线轮廓、等值宽度、偏振度等观测量的影响；对引力加速度、元素丰度的影响；对恒星内部结构，如中心压力、温度、密度的影响。这些将会影响到恒星在Ｈ—Ｒ图上的位置，演化路径以及年龄和寿命等。因此，无论是理论模型还是实测研究，对自转快的恒星应该进行自转影响的修正。     

Plastic zones and characteristics-line families for openings in elasto-plastic rock mass

Summary Numerical solutions of the plastic zone and deformation distribution along tunnel wall due to excavation are presented in this paper. These solutions are obtained from elasto-plastic finite-element analysis, which assumes the Hoek-Brown or Mohr-Coulomb criteria, and the analyzation is performed to simulate a tunnel section far away from the excavation face, where the three-dimensional effect can be neglected. Factors, including the effects of anisotropy in the initial stress state and the tunnel shape on the plastic zone around an excavated tunnel have been examined. Furthermore, a concept called the characteristic-line family of rock mass is proposed to describe the varying relations between normalized stress and normalized deformation at various points on the tunnel wall in gradual unloading process due to excavation. The characteristic-line family of rock mass appears to depend on the rock mass property and the tunnel's characteristics.     

Changes of marine productivity and sedimentary environment recorded by biogenic components in the Antarctica Ross Sea since the last deglaciation

Journal of Oceanology and Limnology - Changes in the marine productivity and sedimentary environment since the last deglaciation in the Ross Sea are presented in this paper. Opal has replaced...     

Radiation-induced defects in quartz. II. Single-crystal W-band EPR study of a natural citrine quartz

Single-crystal electron paramagnetic resonance (EPR) spectra of a natural citrine quartz without any artificial irradiation, measured at W-band frequencies (∼94 GHz) and temperatures of 77, 110 and 298 K, allow better characterization of three previously-reported Centers (#6, #7 and B) and discovery of three new defects (B′, C′ and G′). The W-band EPR spectra reveal that Centers #6 and #7 do not reside on twofold symmetry axes, contrary to results from a previous X-band EPR study. The W-band spectra also show that the previously reported Center B is a mixture of two defects (B and B′) with similar g matrices but different-sized ²⁷Al hyperfine structures. Center C′ has similar principal g values to the previously reported Center C but is distinct from the latter by a larger ²⁷Al hyperfine structure with splittings from 0.10 to 0.22 mT. Also, Center G′ has a similar g matrix to the previously reported Center G but a different ²⁷Al hyperfine structure with splittings from 0.41 to 0.53 mT. These spin-Hamiltonian parameters, together with observed thermal properties and microwave-power dependence, suggest that Centers #6 and #7 probably represent O₂³⁻ type defects. Centers B and B′ are probably superoxide radicals (O₂⁻) with the unpaired spin localized on the same pair of oxygen atoms around a missing Si atom but linked to a substitutional Al³⁺ ion each at different neighboring tetrahedral sites. Similarly, Centers G and G′ are most likely superoxide radicals with the unpaired spin localized on another pair of oxygen atoms around a missing Si atom and linked to a substitutional Al³⁺ ion each at different neighboring tetrahedral sites. Center C′ is probably an ozonide radical associated with a missing Si atom and linked to a substitutional Al³⁺ ion at the neighboring tetrahedral site. This study exemplifies the value of  high-frequency EPR for discrimination of  similar defect centers and determination of  small local structural distortions that are often difficult to resolve in conventional  X- and Q-band EPR studies.     

GNSS精密单点定位技术及应用进展

综合分析讨论了GNSS精密单点定位(PPP)技术及应用的最新进展。重点对GNSS精密单点定位实数解、固定解、实时精密单点定位、PPP-RTK和多频多系统精密单点定位等5个方面的核心关键技术和实现方法进行了总结和讨论。结合PPP技术的特点和优势,论述了PPP在低轨卫星定轨、地震、对流层和电离层等方面的典型应用。针对多频多系统GNSS的最新发展动态,展望了PPP技术今后的发展趋势,并指出了精密单点定位技术和推广应用还有待进一步研究的问题。