基于最小二乘支持向量机的城市桥梁震害预测模型研究

针对地震中城市桥梁震害状态具有较强的非线性、复杂性的特点,采用了具有RBF核函数的最小二乘支持向量机(LS-SVM)算法。在大量收集我国地震中城市桥梁震害资料的基础上,将此算法引入桥梁的震害预测中,选取了地震烈度、上部结构、地基失效程度、支座类型、墩台高度、桥梁跨数和场地类别等因素作为模型的特征输入向量,建立了最小二乘支持向量机的桥梁震害预测模型。通过反复地样本训练及模型参数设置,仿真结果表明,该方法具有一定的准确度和可行性。基于最小二乘支持向量机的桥梁震害预测方法是一种可以用于地震中桥梁震害预测的良好方法。     

Effects of surface drag on low-level frontogenesis within baroclinic waves

Using a three-dimensional nonhydrostatic mesoscale numerical model (MM5), the evolution and structures of baroclinic waves with and without surface drag in case of dry and moist atmosphere are simulated, with special emphases on the effects of surface drag on the low-level frontal structure and frontogenesis. There are two different effects of surface drag on the low-level frontogenesis in the dry case. On one hand, the surface drag weakens the low-level frontogenesis and less inclined to develop the baroclinic wave due to the dissipation. But on the other hand, the surface drag induces a strong ageostrophic flow, which prolongs the low-level frontogenesis and finally leads to the enhancement of cold front. Compared with the no surface drag case, the surface drag increases the frontal slope espe- cially in the boundary layer, where the front is almost vertical to the surface, and then enhances the prefrontal vertical motion. All these conclusions expanded the analytical theory of Tan and Wu (1990). In the moist atmosphere, the influence of surface drag on frontal rainbands is also obvious. The surface drag weakens the convection, and reduces the energy dissipation near the surface when the initial relative humidity is relatively weak. At this time, the confluence induced post-frontal updrafts moves across the cold front and reinforces the prefrontal convection, which is beneficial to the maintenance of the rainband in cold sector. Given the enhancement of relative humidity, the moist convection domi- nates the low-level frontogenesis while the retardation of surface drag on energy dissipation is not obvious, therefore the effects of surface drag on the low-level frontogenesis and precipitation are re- duced.     

Geochemistry and SHRIMP U‐Pb Zircon Dating of Mafic Rocks North of Zunhua City,Eastern Hebei,North China Craton: Paleoproterozoic Gabbro rather than Neoarchean Ophiolite

Abundant mafic-ultramafic blocks and dikes occur in the area north of Zunhua City, eastern Hebei Province, and were previously suggested to be part of a late Archean ophiolitic assemblage. We employed SHRIMP zircon dating and a geochemical study on these mafic and surrounding rocks to test the ophiolite hypothesis. The SHRIMP data suggest that three metagabbro samples were metamorphosed at ～1.8 Ga. Numerous ～2.5 Ga zircons display strong oscillatory zoning, characteristic of zircons from granitoid rocks but not from gabbro, so we suggest that these are xenocrystic grains. The age of these xenocrystic zircons and their metamorpbic rims suggests that these mafic blocks formed in Paleoproterozoic. The surrounding gneiss of intermediate composition also contains 2.5 Ga zircons with oscillatory zoning and 1.8 Ga metamorphic rims. Fractionated REE patterns and Nb, Ta, Zr, Hf negative anomalies to variable extent were observed in the mafic blocks and surrounding rocks, also supporting a significant difference in the chemistry of ophiolitic rocks. Our data suggest that many mafic blocks in northern Zunhua are not part of a late Archean ophiolite complex but part of a tectonically dismembered Paleoproterozoic intrusive gabbro complex. This study shows that late Paleoproterozoic metamorphism occurred in the western part of eastern Hebei Province.     

塔城地区1960-2018年季节性冻土的变化特征及影响因子分析

利用1960-2018年塔城地区9个气象观测站冻土深度及同期气温观测资料,采用数理统计方法分析了其分布状况、变化特征及其与气象因子的关系,结果表明：近59a塔城地区最大冻土深度均在120cm以上,大值区主要分布在中部、南部及托里,冻结初日最早出现于9月上旬,最晚结束于5月中旬;年最大冻土深度除额敏以4.00cm/10a的速率显著增多外,其余各站均表现为减少趋势,其中克拉玛依减幅最大;月际变化中1月、2月、5月、9月、10月仅个别站表现为增多趋势,其余站表现为减少趋势,而3月、4月、11月、12月9站均表现为一致的减少趋势;塔城地区最大冻土深度年际变异系数均表现为中等变异性,表明其对气候变化的响应较敏感;平均冻土深度年代际变化呈现“浅-深-浅-浅-浅-浅”的变化趋势,从1980年代开始平均冻土深度逐渐变浅;影响最大冻土深度变化的因子主要有年（月）平均气温、平均最低气温及气温日较差。     

Experimental Study of An Aquaculture Net Cage in Waves and Current

Model experiments of a floating fish cage subjected to waves and current have been performed. The objective was to study the dynamic behaviour of the fish cage model in waves and current. The fish cage model was composed of a model net, a flexible floating collar of the circular plastic type and a weight system. It was found that there are many wave periods in which cancellation of the wave-induced forces on the model occur. These cancellation wave periods are within the range of dimensioning wave periods commonly used for testing of fish farm structures and hence are important to be aware of. Large deformations of the net under realistic wave and current conditions were observed, where contact between the net and other parts of the structure were identified. This may cause damages to the net due to abrasion.     

A framework for computer vision-based health monitoring of a truss structure subjected to unknown excitations

Computer vision(CV) methods for measurement of structural vibration are less expensive, and their application is more straightforward than methods based on sensors that measure physical quantities at particular points of a structure. However, CV methods produce significantly more measurement errors. Thus, computer vision-based structural health monitoring(CVSHM) requires appropriate methods of damage assessment that are robust with respect to highly contaminated measurement data. In this paper a...     

基于CT表现的孤立性肺结节良恶性预测模型的研究

目的:筛选并分析影响肺结节良恶性的因素,建立预测模型、验证该模型并与梅奥模型、Brock模型对比。方法:回顾性分析2015年1月至2017年12月深圳市人民医院有病理结果的孤立性肺结节病例319例,其中229例作为建模组（A组）,90例作为验证组（B组）,分析A组病例性别、年龄、直径、吸烟史、毛刺、位于上叶、边界不清楚、分叶征、空泡征、血管集束征、胸膜凹陷征、含磨玻璃密度及钙化,通过单因素分析及Logistic回归分析,筛选出独立影响因子,并建立回归方程。用B组资料进行验证并将B组资料分别代入本研究模型、梅奥模型及Brock模型进行对比。结果:单因素分析示年龄、直径、毛刺、上叶、边界不清楚、分叶、空泡、血管集束征、胸膜凹陷征、是否含有磨玻璃密度在良恶性结节中的差异具有统计学意义（P<0.05）,Logistic回归分析示有毛刺、有分叶、边界不清楚和含有磨玻璃密度为恶性孤立性肺结节的独立影响因素,并据此建立的回归方程ROC曲线下面积为0.894,其灵敏度为91.3％,特异度为77.3％,阳性似然比为4.02,阴性似然比为0.11,阳性预测值为80.8％,阴性预测值为89.5％;本研究模型与梅奥模型的差异有统计学意义（P=0.0049）,与Brock模型差异没有统计学意义（P=0.79）。结论:有毛刺、有分叶、边界不清楚和含有磨玻璃密度为恶性孤立性肺结节的独立影响因素,据此建立的回归方程具有较高的诊断效能。本研究建立的模型诊断效能优于梅奥模型,与Brock模型诊断效能相当。