A Test on Two Codes for Extrapolating Solar Linear Force-free Magnetic Fields

We evaluate the performances of two newly-implemented codes for extrapolating the solar linear force-free magnetic fields, by measuring their quantified responses to the lower boundary vector field data on a finite region using analytical models. The codes are based on two boundary integral formulas with different mechanisms in utilizing the transverse boundary field: the first one only utilizes the transverse boundary field to derive the value of the force-free parameter, while the other one explicitly utilizes the whole transverse boundary field, in addition to the vertical field component. Studies on the test cases show that both of the codes could reproduce the analytical model fields with reasonable accuracy within the valid domain, provided a sufficient amount of data is available at the lower boundary. The code utilizing explicitly all three components of the boundary field shows generally better performances and requires a smaller boundary-data area in order to achieve the same degree of accuracy in the metric quantities such as the normalized vector error, vector correlation, vector angular difference, and magnetic energy; however, the accuracy in the divergence-free metric and especially the force-free metric are less ideal.     

物质点强度折减法边坡失稳判据选择方法

用物质点强度折减法求解边坡安全系数时,需要选择一定的失稳判据,而采用不同的失稳判据获得的安全系数通常存在一定差异.为此,采用物质点强度折减法对两个边坡算例进行了稳定性分析,对比研究了文献中常用的4种边坡失稳判据(计算不收敛、特征点位移突变、塑性应变贯通及界限值判据)在计算边坡安全系数时的合理性及适用性.同时,将Spen...     

多个超高阶重力场模型精度分析

分析了国际和国内公布的EGM2008、GECO、Eigen6c4、UGM2005、DQM2000d和DQM2006等超高阶重力场模型的内符合精度;利用中国境内的实测GPS/水准数据对各类模型进行了外符合精度检验;结合不同的方法对系统差进行了处理;最后基于试验区数据讨论了不同模型之间频谱组合方法对高程异常计算结果的改善情况。实验表明,Eigen-6C4模型具有更高的内符合精度,国内公布的UGM2005和DQM2006两种模型精度相当;本文提出的十参数法相比于传统四参数方法精度获得了4.6%~22.20%的提升;GECO模型和Eigen-6C4模型在实验区内外符合精度较好;不同模型之间的频谱组合可以在一定程度上提高试验区内模型确定高程异常的精度。     

显著度模型的地标提取方法综述

针对地标显著度模型的构成、计算方法及存在的突出问题,该文在对国内外大量文献进行分析研究的基础上,系统综述了基于显著度模型提取地标的方法。指出了现有研究中存在的主要问题和不足,围绕感知显著度、认知显著度、上下文显著度、总体显著度的计算方法,进行了较为深入的研究,并针对性地提出了解决方案。     

资源枯竭型城市空间扩展进程研究——以淮北市为例

城市空间扩展是衡量新型城镇化背景下城市化进程的重要指标之一,对于研究资源枯竭型城市的可持续发展也有重要的意义。以遥感影像为基础,结合ArcGIS和Matlab软件实现建成区范围的自动提取;选取城市化强度、重心和紧凑度等指标,分析资源枯竭型城市空间扩展的时空特征;结合研究区实际情况和部分统计数据探讨了城市空间扩展驱动机制。结果表明：1992-2016年,淮北市建成区面积由13.64 km²增加到130.19 km²,净增8.54倍。城市化强度水平处于中等程度,城市扩展强度处于较高的水平,城市土地利用集约程度不高;重心总体呈现出东偏的姿态,建成区用地紧凑度逐渐下降。经济及人口、政府决策、交通水平和采煤塌陷区分别是研究区城市空间扩展的驱动机制、引导机制、内生机制和限制机制。     

Ecosystem Carbon Allocation of a Temperate Mixed Forest and a Subtropical Evergreen Forest in China

Ecosystem carbon allocation can indicate ecosystem carbon cycling visually through its quantification within different carbon pools and carbon exchange. Using the ecological inventory and eddy covariance measurement applied to both a mature temperate mixed forest in Changbai Mountain (CBM) and a mature subtropical evergreen forest in Dinghu Mountain (DHM), we partitioned the ecosystem carbon pool and carbon exchange into different components, determined the allocation and analyzed relationships within those components. Generally, the total carbon stock of CBM was slightly higher than that of DHM due to a higher carbon stock in the arbor layer at CBM. It was interesting that the proportions of carbon stock in vegetation, soil and litter were similar for the two mature forests. The ratio of vegetation carbon pool to soil carbon stock was 1.5 at CBM and 1.3 at DHM. However, more carbon was allocated to the trunk and root from the vegetation carbon pool at CBM, while more carbon was allocated to foliage and branches at DHM. Moreover, 77% of soil carbon storage was limited to the surface soil layer (0-20 cm), while there was still plentiful carbon stored in the deeper soil layers at DHM. The root/shoot ratios were 0.30 and 0.25 for CBM and DHM, respectively. The rates of net ecosystem productivity (NPP) to gross ecosystem productivity (GPP) were 0.76 and 0.58, and the ratios of ecosystem respiration (Re) to GPP were 0.98 and 0.87 for CBM and DHM, respectively. The net ecosystem carbon exchange/productivity (NEP) was 0.24 t C ha^-1 yr^-1 for CBM and 3.38 t C ha^-1 yr^-1 for DHM. Due to the common seasonal and inter-annual variations of ecosystem carbon exchange resulting from the influence of environmental factors, it was necessary to use the long record dataset to evaluate the ecosystem sink capacity.     

Influence of the Boreal Summer Intraseasonal Oscillation on Extreme Temperature Events in the Northern Hemisphere

The impact of the boreal summer intraseasonal oscillation (BSISO) on extreme hot and cool events was investigated, by analyzing the observed and reanalysis data for the period from 1983 to 2012. It is found that the frequency of the extreme events in middle and high latitudes is significantly modulated by the BSISO convection in the tropics, with a 3–9-day lag. During phases 1 and 2 when the BSISO positive rainfall anomaly is primarily located over a northwest–southeast oriented belt extending from India to Maritime Continent and a negative rainfall anomaly appears in western North Pacific, the frequency of extreme hot events is 40% more than the frequency of non-extreme hot events. Most noticeable increase appears in midlatitude North Pacific (north of 40°N) and higher-latitude polar region.Two physical mechanisms are primarily responsible for the change of the extreme frequency. First, an upper-tropospheric Rossby wave train (due to the wave energy propagation) is generated in response to a negative heating anomaly over tropical western North Pacific in phases 1 and 2. This wave train consists of a strong high pressure anomaly center northeast of Japan, a weak low pressure anomaly center over Alaska, and a strong high pressure anomaly center over the western coast of United States. Easterly anomalies to the south of the two strong midlatitude high pressure centers weaken the climatological subtropical jet along 40°N, which is accompanied by anomalous subsidence and warming in North Pacific north of 40°N. Second, an enhanced monsoonal heating over South Asia and East Asia sets up a transverse monsoonal overturning circulation, with large-scale ascending (descending) anomalies over tropical Indian (Pacific) Ocean. Both the processes favor more frequent extreme hot events in higher-latitude Northern Hemisphere. An anomalous atmospheric general circulation model is used to confirm the tropical heating effect.     

室内可见光通信频域均衡技术DSP方法对比分析

对3种室内可见光通信传输技术的数字信号处理方法（DSP）,包括正交频分复用（OFDM）、单载波频域均衡（SCFDE）与单载波频分复用（SCFDM）进行了对比分析.通过峰值功率比（PAPR）和计算复杂度比较了3种方法的优劣.分析结果表明,SCFDE和SCFDM具有较低的PAPR,但SCFDM计算复杂度较高.此外,还使用白光LED灯针对3种调制解调方法建立了实验模型.实验结果表明,在VLC传输系统中,由于低PAPR特性,使得SCFDE和SCFDM在误码率（BER）和Q值方面的性能优于OFDM.     

Mobility Sequence of Chemical Elements During Loess Weathering—Pedogenesis,Weinan,Shaanxi Province,China

The distribution of chemical elements in the Weinan loess section shows that: (1) carbonate is the critical constituent affecting loess chemistry. The leaching of carbonates may cause “apparent” enrichment of some other constituents. (2) CaCO₃, SiO₂, FeO, MgO, K₂O and Na₂O are mobile while Al₂O₃, Fe₂O₃ and TiO₂ are inert components. The mobility sequence may follow the order of CaCO₃>FeO>MgO>Na₂O>K₂O>SiO₂>Al₂O₃>TiO₂>Fe₂O₃. (3) No obvious migration is noticed of iron, except changes in valence and forms, during the pedogenic process. Little iron has been supplied to paleosol from precipitation. (4) Carbonates and, to a lesser extent, iron are most sensitive to, and can be therefore used as good indicators of, environmental changes. This research project was financially supported by the National Natural Science Foundation of China (Grant No. 49672137).     

用黄土地球化学参数进行古气候定量估算的初步尝试

尝试了用表土地球化学转换函数恢复渭南剖面最近１３万ａ米的古温度,古降水。结果显示：（１）全新世适宜期及末次间冰期时,降水量显著增加,渭南地区的年降水量可大于７００ｍｍ（２）末次冰期时降水量明显低于全新世适宜期及末次间冰期,但是这一时期有一些次一级的变化;特别与深海Ｏ同位素阶段４对应的时期不仅降水量显著降低,而且还有更次一级的变化;（３０全新世适宜期时,渭南地区的年平均温度在１２－１４℃左右,末次冰