本文从垂直分辨率、时间更新频率和要素完整性三个方面,对水平网格距为1 km的华南区域短时临近预报模式(TRAMSRUC1 km:Tropical Region Assimilation Model for South China SeaThe Rapid Update Cycle1 km)中的初始场和侧边界方案进行...本文从垂直分辨率、时间更新频率和要素完整性三个方面,对水平网格距为1 km的华南区域短时临近预报模式(TRAMSRUC1 km:Tropical Region Assimilation Model for South China SeaThe Rapid Update Cycle1 km)中的初始场和侧边界方案进行改进研究。首先选择一次华南飑线个例进行敏感性试验,研究结果表明:(1)提高初始场和侧边界的垂直分辨率以后,模式对飑线内部中小尺度对流系统引起的强降水中心的模拟结果明显更加接近实况,而增加中低层的垂直分辨率对预报的改进起到了主要作用。(2)将模式侧边界时间更新频率从6 h一次提高到1 h一次以后,模式侧边界要素场的逐小时剧烈变化信息可以比较完整的保留下来。在使用高时间分辨率的侧边界条件进行模拟时,粤西沿海地区的水汽辐合明显加强,这对原来模式预报飑线移速偏慢现象会有改善作用。(3)当模式侧边界条件具有较高的时空分辨率时,进一步补充垂直速度和云微物理变量的侧边界条件对于飑线模拟结果的影响并不明显。总的来说,提高初始场和侧边界的垂直分辨率以及增加侧边界更新的时间分辨率,对于区域高分辨率模式对这次华南飑线预报效果的改进具有重要意义,而忽略垂直速度和云微物理量的侧边界条件则是一种可以接受的简化。在个例研究的基础上,利用改进后的初、边界条件进行为期一个月(2019年4月份)的批量试验,评估结果表明新方案对于逐小时降水空间分布和日变化特征的模拟均有明显改善。展开更多
目的探讨急性主动脉夹层患者首发症状与院前延迟的关系,为临床实施院前针对性健康教育提供参考。方法选取急性主动脉夹层患者488例,收集患者首发症状、一般资料、疾病相关因素、院前相关因素及院前时间,分析首发症状与院前延迟的关系。...目的探讨急性主动脉夹层患者首发症状与院前延迟的关系,为临床实施院前针对性健康教育提供参考。方法选取急性主动脉夹层患者488例,收集患者首发症状、一般资料、疾病相关因素、院前相关因素及院前时间,分析首发症状与院前延迟的关系。结果患者院前时间为135.5(48.3,1735.5)min,其中院前时间≤150 min 253例(51.8%),>150 min(即院前延迟)235例(48.2%);首发症状多为胸背痛[146例(29.9%)],其次为胸前痛124例(25.4%)、腹痛121例(24.8%)。Logistic回归分析发现自觉病情严重程度、胸背痛是院前延迟的保护因素(P<0.01),腹痛、四肢麻木/疼痛是急性主动脉夹层患者院前延迟的危险因素(P<0.05,P<0.01)。结论急性主动脉夹层患者常以胸背痛为首发症状,腹痛与四肢麻木/疼痛非典型症状是导致急性主动脉夹层患者出现院前延迟的主要因素。需对公众加强疾病相关知识的健康教育,早期采取正确的应对方式,积极就医,缩短院前时间。展开更多
Under repeated train-induced loads, cement and emulsified asphalt mortar(CA mortar) as a viscoelastic material has a time-dependent deformation, part of which is irreversible. This could lead to debonding between the ...Under repeated train-induced loads, cement and emulsified asphalt mortar(CA mortar) as a viscoelastic material has a time-dependent deformation, part of which is irreversible. This could lead to debonding between the mortar layer and the track slab. Based on the theory of viscoelasticity and the analytical method of the time hardening law(THL), the viscoelastic deformation behavior of CA mortar was studied. Using ABAQUS, we established a solid model of China railway track system(CRTS) Ⅰ prefabricated slab track, with CA mortar at different initial Young’s moduli under cyclic loading corresponding to the influence of actual train loads. The results reveal that the fitted parameters of the THL for CA mortar are suitable for describing its viscoelastic deformation. As the initial Young’s modulus increases, the strain difference before and after cyclic loading gradually decreases, and the displacement difference increases from 0.2 mm to 0.6 mm. The deformation mainly occurs at the end of a mortar layer with longitudinal distribution of about 2.5 times the fasteners’ spacing. It follows that the viscoelastic performance of CA mortar is one of the most important reasons that cause debonding underneath the track slab. Therefore, we suggest that the adverse effects of viscoelastic behavior of CA mortar should be considered when researching such deformation and damage.展开更多
文摘本文从垂直分辨率、时间更新频率和要素完整性三个方面,对水平网格距为1 km的华南区域短时临近预报模式(TRAMSRUC1 km:Tropical Region Assimilation Model for South China SeaThe Rapid Update Cycle1 km)中的初始场和侧边界方案进行改进研究。首先选择一次华南飑线个例进行敏感性试验,研究结果表明:(1)提高初始场和侧边界的垂直分辨率以后,模式对飑线内部中小尺度对流系统引起的强降水中心的模拟结果明显更加接近实况,而增加中低层的垂直分辨率对预报的改进起到了主要作用。(2)将模式侧边界时间更新频率从6 h一次提高到1 h一次以后,模式侧边界要素场的逐小时剧烈变化信息可以比较完整的保留下来。在使用高时间分辨率的侧边界条件进行模拟时,粤西沿海地区的水汽辐合明显加强,这对原来模式预报飑线移速偏慢现象会有改善作用。(3)当模式侧边界条件具有较高的时空分辨率时,进一步补充垂直速度和云微物理变量的侧边界条件对于飑线模拟结果的影响并不明显。总的来说,提高初始场和侧边界的垂直分辨率以及增加侧边界更新的时间分辨率,对于区域高分辨率模式对这次华南飑线预报效果的改进具有重要意义,而忽略垂直速度和云微物理量的侧边界条件则是一种可以接受的简化。在个例研究的基础上,利用改进后的初、边界条件进行为期一个月(2019年4月份)的批量试验,评估结果表明新方案对于逐小时降水空间分布和日变化特征的模拟均有明显改善。
文摘目的探讨急性主动脉夹层患者首发症状与院前延迟的关系,为临床实施院前针对性健康教育提供参考。方法选取急性主动脉夹层患者488例,收集患者首发症状、一般资料、疾病相关因素、院前相关因素及院前时间,分析首发症状与院前延迟的关系。结果患者院前时间为135.5(48.3,1735.5)min,其中院前时间≤150 min 253例(51.8%),>150 min(即院前延迟)235例(48.2%);首发症状多为胸背痛[146例(29.9%)],其次为胸前痛124例(25.4%)、腹痛121例(24.8%)。Logistic回归分析发现自觉病情严重程度、胸背痛是院前延迟的保护因素(P<0.01),腹痛、四肢麻木/疼痛是急性主动脉夹层患者院前延迟的危险因素(P<0.05,P<0.01)。结论急性主动脉夹层患者常以胸背痛为首发症状,腹痛与四肢麻木/疼痛非典型症状是导致急性主动脉夹层患者出现院前延迟的主要因素。需对公众加强疾病相关知识的健康教育,早期采取正确的应对方式,积极就医,缩短院前时间。
基金Project supported by the National Natural Science Foundation of China(No.51578472)。
文摘Under repeated train-induced loads, cement and emulsified asphalt mortar(CA mortar) as a viscoelastic material has a time-dependent deformation, part of which is irreversible. This could lead to debonding between the mortar layer and the track slab. Based on the theory of viscoelasticity and the analytical method of the time hardening law(THL), the viscoelastic deformation behavior of CA mortar was studied. Using ABAQUS, we established a solid model of China railway track system(CRTS) Ⅰ prefabricated slab track, with CA mortar at different initial Young’s moduli under cyclic loading corresponding to the influence of actual train loads. The results reveal that the fitted parameters of the THL for CA mortar are suitable for describing its viscoelastic deformation. As the initial Young’s modulus increases, the strain difference before and after cyclic loading gradually decreases, and the displacement difference increases from 0.2 mm to 0.6 mm. The deformation mainly occurs at the end of a mortar layer with longitudinal distribution of about 2.5 times the fasteners’ spacing. It follows that the viscoelastic performance of CA mortar is one of the most important reasons that cause debonding underneath the track slab. Therefore, we suggest that the adverse effects of viscoelastic behavior of CA mortar should be considered when researching such deformation and damage.
