物流业发展对产业结构优化的实证分析 ——基于空间面板杜宾模型

目前,我国正处于产业结构优化升级和实现经济发展方式转变的关键时期。物流业作为第三产业的重要组成部分,具有有效降低经济运行成本、提高运作效率和促进产业结构升级的作用。文章首先对省域产业结构合理化和产业结构高级化空间依赖性进行了检验。然后,基于我国1997―2010年30个省级面板数据,通过引入因变量空间滞后项和自变量空间滞后项,构建空间面板杜宾模型,从产业结构合理化和产业结构高级化2个方面分析物流业发展对产业结构优化的影响。研究结果表明：我国产业结构合理化和产业结构高级化存在着显著为正的空间溢出效应,东部、中部和西部地区存在着明显的空间差异;物流业的发展不仅能够显著促进当地产业结构合理化和产业结构高级化进程,而且对邻近地区产业结构优化具有正向的空间溢出效应。最后,文章有针对性地提出了政策建议。     

城市化与经济发展的关系模式——对钱纳里模型的参数重估

以钱纳里模型为基础,基于1990-2009 年20 年间世界149 个国家或地区的经验数据,采用双对数模型,引入城市化自身时间序列变量,回归了城市化与经济发展水平之间关系的标准型式。研究表明:城市化与经济发展水平的定量关系型式在过去50 年发生了显著变化,钱纳里模型中标准发展型式已不能直接用来比较当前城市化与经济发展的关系;1990-2009 年间,人均GNI值位于1000~10000 美元区间时,城市化率从17.78%变化至60.36%,关系匹配值也相应变化,但是城市化率的饱和值仍然保持在75%左右;较小人口规模国家的城市化受经济发展水平影响大于大国和中等国家。     

阿克达拉大气本底站气流轨迹模拟研究

 利用1994—2002年NCEP再分析资料和HYSPLIT v4.7轨迹模式模拟了阿克达拉大气本底站的气团三维后向轨迹;采用簇分析方法对计算出的数千条后向轨迹进行了聚类归并,得到反映气流轨迹主要特征的数条轨迹;按垂直层次和季节分别作图,并进行分析。主要研究了该站近9 a来不同季节距地面100 m和1 000 m的近地面边界层气流轨迹的特征、各方向轨迹出现的频数及当地天气形势和地面天气系统与气流轨迹的关系;并且把该地的轨迹与地面观测和附近气象站的探空观测历史风向玫瑰图作了对比。揭示了该站气流轨迹的季节分布特征,天气系统的位置和移动路径以及大地形对轨迹的影响。结合该站周边城镇的分布和发展规模以及气团移动的轨迹,分析对阿克达拉大气本底站的可能影响,为建立区域大气本底站提供科学的选址依据;为今后在该站开展进一步的研究提供近地层大气气团移动方向和速度背景参考资料;同时,通过实例把轨迹模式模拟方法予以简介,希望其在气体污染物和沙尘的溯源与追踪研究以及对空气污染敏感设施站址的选择、具有污染排放源设施建设的环境评价中得到应用。     

Emplacement mechanism of gravity flows inferred from high resolution Lidar data: The 1944 Somma–Vesuvius lava flow (Italy)

A Digital Terrain Model derived from high resolution Lidar data allows the determination of the morphometric and physical parameters of a lava flow erupted from the Somma–Vesuvius volcano in 1944. The downstream variation of morphometric parameters including slope, aspect, relative relief, thickness, width, and cross sectional area is analyzed, and the changes in viscosity, velocity and flow rate are estimated. The aims of the analyses are to recognize different flow surfaces, to reconstruct the flow kinematics, and to obtain information on the mechanism of emplacement. The results indicate that the 1944 lava flow can be divided in three sectors: a near vent sector (NVS) characterized by a toe-like surface, an intermediate sector (IS) with an ‘a’ātype brittle surface, and a distal sector (DS) with a sheet-like ductile surface. Lateral leveés and channels do not occur in NVS, whereas they are well developed in IS. In DS, leveés increase with an increasing distance from the vent. Fold-like surfaces occur in NVS and DS, reflecting local shortening processes due to a decrease in the slope of the substratum and overflows from the main channel. IS and DS emplaced between March 18 and 21, 1944, whereas NVS emplaced on March 19 and partly covered IS. The morphometric and physical parameters indicate that IS moved in a ‘tube’-like regime, whereas DS emplaced in a 'mobile crust' regime. The IS to DS transition is marked by an increase in velocity and the flow rate, and by a decrease in thickness, width, cross sectional area, and viscosity. This transition is due to an abrupt increase in the slope of the substratum. The estimated velocity values are in good agreement with the measurements during the 1944 eruption. The analysis used here may be extended to other lava flows. Some gravity flows (debris/mud flows, floods, and avalanches) have rheological properties and shapes similar to those of lavas, and the same process-form relationships may apply to these flows. The approach used here may be therefore useful for evaluating hazards from various gravity currents.     

CMIP5耦合模式对欧亚大陆冬季雪水当量的模拟及预估

基于美国冰雪资料中心(NSIDC)提供的卫星遥感雪水当量资料,评估了26个CMIP5(Coupled Model Inter-comparison Project)耦合模式对1981~2005年欧亚大陆冬季雪水当量的模拟能力,在此基础上应用多模式集合平均结果,预估了21世纪欧亚大陆雪水当量的变化情况。结果表明,CMIP5耦合模式对欧亚大陆冬季雪水当量空间分布具有一定的模拟能力,能够再现出欧亚大陆冬季雪水当量由南向北递增、青藏高原积雪多于同纬度其他地区的特征;就雪水当量的幅值而言,几乎所有模式均显著低估了西伯利亚中部雪水当量的大值中心,对中国东北地区雪水当量的模拟也显著偏低,但模式对乌拉尔山以西的东欧平原、我国北方及蒙古地区冬季雪水当量的模拟却比卫星遥感资料显著偏大,此外模式对堪察加半岛及以北的西伯利亚东北部地区的雪水当量也明显偏大。对于青藏高原地区,虽然部分模式可以模拟出青藏高原东部的雪水当量大值区,但大多数模式对青藏高原西部雪水当量的模拟却明显偏大,存在虚假的大值中心。对遥感反演资料的EOF(Empirical Orthogonal Function)分解表明,对于EOF第一个模态所对应欧亚大陆全区一致的年代际变化特征,仅有少数模式具有一定的模拟能力,大多数模式以及多模式集合的结果均未能予以反映;对应于欧亚大陆雪水当量年际变化的EOF第二模态而言,仅有少数模式(如俄罗斯的INMCM4)具有一定的再现能力,绝大多数模式对该模态及其时间演变的特征没有模拟能力。比较CMIP5多模式的集合预估结果与1981~2005年基准时段的雪水当量,可以发现在RCP4.5排放情景下,西伯利亚中东部地区的雪水当量相对于基准时段显著增加,区域平均的增加量在21世纪前、中、后期分别为4.1mm、5.4 mm和6.8 mm,且随时间增加得更显著;对90°E以西的欧洲大陆和青藏高原地区,其雪水当量则相对减少,减少的幅度和显著性也随时间而增大。就雪水当量的相对变化而言,在欧亚大陆东北部存在雪水当量相对变化的大值区,在21世纪后期相对变化显著区大都在5%~10%;但在青藏高原、斯堪的纳维亚半岛进和东欧平原,并没有发现雪水当量相对变化的髙值区,这是由于这些区域冬季雪水当量的幅值较大的缘故。RCP8.5情景下欧亚大陆雪水当量的变化特征与RCP4.5相类似,只是变化的幅度更大。     

北京市城六区2018年空气质量数值预报效果评估

为更好地改进提高模式预报性能,评估了新一代WRF-CMAQ（Weather Research and Forecasting model-Community Multi-scale Air Quality model）模式系统的不同网格分辨率预报产品对2018年北京市城六区空气质量预报结果的影响。分析表明:（1）基于首要污染物为PM2.5的预报数据集,模式系统1 km网格分辨率（BJ01）和3 km网格分辨率（BJ03）等级准确率优于官方预报结果,模式系统BJ01和BJ03区域4天内预报等级准确率均达到50%以上,24 h内准确率达60%以上,官方预报24 h内等级准确率为59%。本文引入预报综合评分法,基于IAQI（Individual Air Quality Index）和等级级别正确性双因素的预报综合评分结果显示,模式系统BJ03得分75.0分最高,BJ01次之,优于官方预报结果,模式9 km网格分辨率（BJ09）得分69.1分最低。（2）基于模式系统2018年长时间序列预报结果分析表明:模式系统预报的PM2.5浓度与实测的变化趋势较为一致,其中模式系统BJ03结果与实测PM2.5浓度相关系数达0.76,覆盖区域较大的BJ03和BJ09对PM2.5浓度峰值模拟较好。中重度污染过程的PM2.5浓度峰值模式预测误差表明,不同分辨率模式预报峰值误差的变化趋势基本一致,覆盖区域更大的粗分辨率模式预报结果高于覆盖区域小的细分辨率模式预报结果。与预报综合评分结果一致,统计分析结果也表明BJ03区域预报效果最好,平均偏差为0.83 μg/m3;而BJ01区域预报整体偏低,BJ09区域预报整体偏高。（3）基于不同网格分辨率预报效果的空间差异性分析表明:同一站点在不同分辨率上表现不一致,BJ01区域中农展馆站表现最好,BJ03区域中万柳站表现最好,BJ09区域中东四站表现最好。     

邓肯-张E-B模型参数对软土路堤沉降计算结果的影响

有限单元法是计算路堤沉降常见的数值计算方法,其土体模型参数的准确性是计算结果可靠性高的保证。邓肯-张E-B模型是岩土工程分析计算中常用的一种非线性弹性模型。本文针对模型参数敏感性进行大量非线性有限元计算,得到了各参数与路堤沉降和侧向位移之间的关系,确定了该模型中影响软基路堤沉降和侧向变形的主要参数。     

Simulated Heat Content Variability in the Upper Layers of the Tropical Indian Ocean

Ocean General Circulation Model (OGCM) simulations from 1970–2007 are used to study the upper ocean heat content variability in the Tropical Indian Ocean (TIO). Model computed heat contents up to 50 m (denoted by HC50 m hereafter) representing upper ocean heat content and 300 m (HC300 m) representing heat content up to thermocline depth are first compared with heat contents computed from observations of two buoys in the TIO. It is found that there is good agreement between the model and observations. Fourier analysis of heat content is carried out in different regions of TIO. The amplitudes of semi-annual variability for HC50 m and HC300 m are observed to be greater than those for the annual variability in the Bay of Bengal, while in the Arabian Sea there is a mixed result. Heat content tendency is known to be governed by net surface heat flux and horizontal as well as vertical heat transports. For understanding the relative importance of these processes, a detailed analysis of these terms in the tendency equation is carried out. Rossby wave is observed in the annual mode of heat transport while equatorial jet and Kelvin waves are observed in the semi-annual mode of heart transport. Finally, the correlation between heat content and sea surface temperature (SST) and sea level anomaly (SLA), taken one at a time, is computed. It is found that the correlation improves significantly when both these quantities are together taken into account.     

Study the Mechanism of Surface Chlorophyll–a Variability in the Southern Tropical Indian Ocean Using an OGCM

Eleven years (1997–2007) of SeaWiFS observations and Ocean General Circulation Model sensitivity experiments are used to understand chlorophyll–a variability in the southern tropical Indian Ocean. The strong offshore Ekman transport forced by anomalous southeasterly winds are responsible for inducing higher chlorophyll-a in the eastern equatorial Indian Ocean. In the case of the southwest tropical Indian Ocean, Rossby waves and local upwelling are responsible for lifting the phytoplankton from deep chlorophyll maxima to the surface. Both intraseasonal dynamical response and interannual forcing are responsible for the phytoplankton blooming in the western basin, whereas the interannual forcing is mainly responsible in the east.