Large-scale low-frequency rainfall regimes and their transition modes in summertime over China

It is well known that the predictable period of daily weather is generally within 2-3 weeks, so spatio-temporal mean predictands have to be employed in the monthly, seasonal, and annual predictions. At present, rainfall patterns (RPs)[1-5] are the key for…     

基于自监督学习的交通数据补全算法

区域高速公路网收费站数量众多,每日产生海量收费数据,但由于设备、网络等因素,部分站点数据传输存在延迟现象,在此情况下已传输的数据往往不能满足实时流量预测的要求。为了实现实时交通数据补全和动态交通流量预测,文中首先提出了一种基于自监督学习的用于高速公路交通流量数据缺失补全的方法,该方法采用了基于注意力机制的时间序列模型（Seq2Seq-Att）;然后使用自监督学习方式对模型进行训练;最后,以广东省高速公路网的80个收费站为例,验证方法的可靠性。结果表明：文中的数据补全方法能够灵活捕捉交通数据中的缺失情况,并根据数据自身的内在关联性,给出合理的补全值;该方法总体优于其他方法,且在不同缺失率下都有较好表现,总体MAPE约为17.7%、WMAPE为12.8%;在高缺失率情况下,该方法相比于其他补全方法有明显的优势。交通量预测结果表明,使用该方法补全的数据进行交通流预测的预测精度接近使用完整数据的情况。     

Rainfall spectrum change in North China and its possible mechanism

The seasonal distribution of the rainfall in North China has changed greatly since 1977, with more rainfall in spring and less in July, August, and September (JAS). Wavelet analysis showed that the JAS rainfall underwent an abrupt spectrum change in the mid-1960s. Its interannual variability has declined while the interdecadal component has become the dominant mode, associated with the dry climate. Correlation analysis found that the JAS rainfall is negatively correlated with the departures of the 500 hPa geopotential height significantly over the northwest and southwest of China, and positively correlated with the suer monsoon over eastern China. Therefore, the interdecadal ascending of the air pressure in northwestern China and the monsoon decaying over East Asia in the past 20 years may be the two major causes of North China drought.     

面积贴合法在希腊数学中的几何起源和作用

面积贴法是欧几里得《几何原本》中的重要方法，它甚至涉及希腊数学的起源问题，以往的数学史家多用”几何代数“观点来解释这个问题。实际上，仔细分析面积贴合法在《几何原本》中的地位和中以看出它起源于毕达哥拉斯学派的面积几何学，是纯粹的几何命题，与解代数方程无关。     

Spatiotemporal distribution and decadal change of the monthly temperature predictability limit in China

Based on the nonlinear Lyapunov exponent and nonlinear error growth dynamics, the spatiotemporal distribution and decadal change of the monthly temperature predictability limit （MTPL） in China is quantitatively analyzed. Data used are daily temperature of 518 stations from 1960 to 2011 in China. The results are summarized as follows： （1） The spatial distribution of MTPL varies regionally. MTPL is higher in most areas of Northeast China, southwest Yunnan Province, and the eastern part of Northwest China. MTPL is lower in the middle and lower reaches of the Yangtze River and Huang-huai Basin. （2） The spatial distribution of MTPL varies distinctly with seasons. MTPL is higher in boreal summer than in boreal winter. （3） MTPL has had distinct decadal changes in China, with increase since the 1970s and decrease since 2000. Especially in the northeast part of the country, MTPL has significantly increased since 1986. Decadal change of MTPL in Northwest China, Northeast China and the Huang-huai Basin may have a close relationship with the persistence of temperature anomaly. Since the beginning of the 21st century, MTPL has decreased slowly in most of the country, except for the south. The research provides a scientific foundation to understand the mechanism of monthly temperature anomalies and an important reference for improvement of monthly temperature prediction.     

学缘对高校教师流动性作用的实证研究——基于Web内容分析数据

采用"毕业校与现任职校关系"和"现任职校学术层次"等学缘和地位指标,对通过Web内容分析得到的我国大学教师流动数据(有效个案数2 354人)进行统计分析,并建立相应的统计模型。模型分析结果表明,教师自校率(毕业于现职校的教师占该校教师总人数的比率)过高是导致我国大学教师校际流动性过低的一个原因,学缘越近,教师通过流动进入该校越容易。我国大学教师校际流动是学缘庇护下的能力流动。     

Subcellular localization of several heavy metals of Hg, Cd and Pb in human liver

Liver, as an important metabolic and detoxicological organ of human body, can be used as a good bioindicator for evaluating body burden of environmental pollutants. Its elemental contents and their chemical forms are closely related to the status of human health and disease. In this paper, the liver samples collected from normal subjects were separated to different subcellular fractions of nuclei, mitochondria, lysosome, microsome and cytosol by differential centrifugation. Then their concentrations of heavy metals of As, Pb, Cd, and Hg were determined by atomic absorption and atomic fluorescent spectroscopy. Our results show no significant difference with literature ones when comparing their gross concentrations. In the case of their subcellular distribution, the Hg concentrations are higher in mitochondrial, microsomal and cytosolic fractions; the Cd concentrations are higher in cytosolic and mitochondrial fractions, while As highest in nuclear fraction. The highest concentration of Pb is found in microsomal fraction with similarity to Fe. Mercury in liver is mainly in the form of inorganic, and methylmercury ranged from 9% to 50% with the average value of 20.9% 13.3%. These results indicate that the cellular distribution and the accumulated target organelles are quite different among these heavy metals, which suggest their various pathways and toxic mechanism in vivo.     

基于系统关联性的高速公路大中型货车到达量多尺度预测

近年来，交通流中大中型货车流量占比逐渐增大，对城市交通的影响日愈增加，准确、及时的大中型货车到达量预测对精确的城市交通管控具有重要意义。针对该问题，本文提出了考虑系统关联性的高速公路大中型货车到达量多尺度预测方法：考虑高速公路网的系统关联性，对高速公路收费站进、出口大中型货车流量的时空关联性进行分析，构建神经网络模型学习空间权重与时间权重；每一时间步将输入与空间权重、时间权重融合，并设置偏置项修正后得到该时间步预测结果；各时间步预测结果对应求和得到最终预测结果。实验结果表明：所用方法在15、30、60 min的时间尺度下预测精度分别达到90.92%、92.48%、94.33%,优于其他对比模型，实用性和有效性均得到了保证。