The tallest sand dune worldwide is located in the Badain Jaran Desert(BJD),China,and has been standing for thousands of years.Previous studies have conducted limited physical exploration and excavation on the formatio...The tallest sand dune worldwide is located in the Badain Jaran Desert(BJD),China,and has been standing for thousands of years.Previous studies have conducted limited physical exploration and excavation on the formation of sand dunes and have proposed three viewpoints,that is,bedrock control,wind dominance,and groundwater maintenance with no unified conclusion.Therefore,this study analyzed the underlying bedding structure of sand dunes in the BJD.Although the bedrock of sand dunes is uplifted and wind controls the shape of dunes,the main cause of dune formation is groundwater that maintains the deposition of calcareous sandstone and accumulation of aeolian sand.According to water transport model and vapor transports in the unsaturated zone of sand dunes,capillary water transport height is limited with film water constituting the main form of water in dunes.Chemical properties and temperature of groundwater showed that aquifers in different basins receive relatively independent recharge from deep sources in the crater.Result of dune formation mechanism is of considerable importance in understanding groundwater circulation and provides a new perspective on water management in arid desert areas.展开更多
数字化制造转型背景下,MBD(Model Based Definition)理念快速推动三维数字模型的深化应用与设计研制体系的深入协同。针对复杂装备传统检验业务中效率低、精度差和特征点不全等问题,文章分析了多种非接触式三维测量技术的工作原理与系...数字化制造转型背景下,MBD(Model Based Definition)理念快速推动三维数字模型的深化应用与设计研制体系的深入协同。针对复杂装备传统检验业务中效率低、精度差和特征点不全等问题,文章分析了多种非接触式三维测量技术的工作原理与系统架构,基于典型机加零部件产品的实测数据多维度评判各类检测技术的性能差异,探索面向MBD设计的高精度三维质量检测解决方案。从而贯通三维数模在设计制造检验环节的数据链路,建成稳定、可靠、高效率的检验能力。展开更多
文摘目的本研究通过列线图构建普通人群罹患重度阻塞性睡眠呼吸暂停(obstructive sleep apnea,OSA)风险的预测模型,探究重度OSA的独立危险因素,指导临床早期诊断和治疗。方法回顾性纳入1656名患者,并按7∶3将其随机分为训练集与验证集。根据呼吸暂停低通气指数>30次/h将患者分为重度OSA与非重度OSA组。用最小绝对收缩、选择算子(the least absolute shrinkage and selection operator,Lasso)和逻辑回归(logistic regression,LR)对所有备选预测因子进行进一步筛选,基于LR建立重度OSA患者的预测模型,在验证集中对列线图模型进行验证,使用C指数、校准曲线和决策曲线分析(Decision Curve Analysis,DCA)评价列线图的区分能力、校准性和临床有效性。此外,我们将该模型与临床上广泛使用的问卷,包括STOP-Bang、柏林问卷通过受试者工作曲线进行了比较。结果通过单因素及多因素Logistic回归分析和Lasso Logistic回归确定吸烟、憋气病史、BMI、腰围、打鼾病史、Epworth嗜睡量表(Epworth sleepiness scale,ESS)作为纳入列线图的预测因子。该模型曲线下面积(area under the curve,AUC)=0.795(95%CI:0.769~0.820),Hosmer-Lemeshow检验提示模型校准良好(χ2=3.942,P=0.862)。DCA曲线显示,该模型对患者是有益的,当阈值概率>18%时,该模型对患者的净获益优于柏林问卷或STOP-Bang量表。临床影响曲线(Clinical Impact Curve,CIC)分析显示了该预测模型的临床有效率,当阈值概率大于82%预测评分概率值时,预测模型判定为重度OSA高风险人群与实际罹患重度OSA人群高度匹配,证实该预测模型临床有效率较高。结论相较于临床常用量表,本研究建立的模型在预测重度OSA方面具有更好的识别能力,可应用于普通人群的OSA早期筛查,有助于及早识别重度OSA,保护患者免受OSA的严重后果,减轻社会负担。
基金This work was funded by the National Natural Science Foundation of China(61771183).
文摘The tallest sand dune worldwide is located in the Badain Jaran Desert(BJD),China,and has been standing for thousands of years.Previous studies have conducted limited physical exploration and excavation on the formation of sand dunes and have proposed three viewpoints,that is,bedrock control,wind dominance,and groundwater maintenance with no unified conclusion.Therefore,this study analyzed the underlying bedding structure of sand dunes in the BJD.Although the bedrock of sand dunes is uplifted and wind controls the shape of dunes,the main cause of dune formation is groundwater that maintains the deposition of calcareous sandstone and accumulation of aeolian sand.According to water transport model and vapor transports in the unsaturated zone of sand dunes,capillary water transport height is limited with film water constituting the main form of water in dunes.Chemical properties and temperature of groundwater showed that aquifers in different basins receive relatively independent recharge from deep sources in the crater.Result of dune formation mechanism is of considerable importance in understanding groundwater circulation and provides a new perspective on water management in arid desert areas.
文摘数字化制造转型背景下,MBD(Model Based Definition)理念快速推动三维数字模型的深化应用与设计研制体系的深入协同。针对复杂装备传统检验业务中效率低、精度差和特征点不全等问题,文章分析了多种非接触式三维测量技术的工作原理与系统架构,基于典型机加零部件产品的实测数据多维度评判各类检测技术的性能差异,探索面向MBD设计的高精度三维质量检测解决方案。从而贯通三维数模在设计制造检验环节的数据链路,建成稳定、可靠、高效率的检验能力。
