不同部位室管膜瘤MRI特征的对比分析

目的对比分析不同部位室管膜瘤的年龄分布及其MRI特征。材料和方法回顾性分析经病理证实的58例室管膜瘤,所有患者均行了MRI平扫和增强扫描,分析患者的年龄分布并在MRI图像上观察肿瘤大小、位置、生长方式、信号特点,有无囊变和出血及肿瘤的强化方式。结果58例室管膜瘤中,27例(46.6%)位于幕上,患者年龄大部分分布在30-50岁之间,侧脑室占20例;20例(34.5%)位于幕下,年龄分布多在20岁以前,绝大多数位于四脑室;11例(18.9%)位于脊髓内。不同部位室管膜瘤信号特征无明显差异性,96.3%幕上、95%幕下、45.5%室管膜瘤呈不均匀显著强化,70.4%幕上、55%幕下、18.2%脊髓室管膜瘤可见瘤内囊变,45.5%的脊髓室管膜瘤可见脊髓本身继发性囊变。29.6%幕上、20%幕下及9%脊髓室管膜瘤可见瘤内出血。80%侧脑室肿瘤侵及对侧侧脑室,四脑室室管膜瘤中,16例沿着侧脑室正中孔浸润,12例通过外侧孔累及桥小脑角,全部脊髓室管膜瘤沿脊髓长轴中心性生长,1例终丝室管膜瘤合并有椎间孔扩大。结论不同部位室管膜瘤在好发年龄、囊变及强化方式存在着差异,可塑性生长是脑室内室管膜瘤的显著特征,了解这些差异有助于术前正确诊断。     

中国低纬度地区电离层闪烁效应模式化研究

GPS（Global Positioning System）周跳是一种GPS信号异常现象.研究发现一定仰角以上的GPS周跳与电离层闪烁有关,是强电离层闪烁造成的GPS载波信号短时失锁现象,因此其可作为表征电离层闪烁效应的参量.本文通过分析由中国低纬度地区GPS台站原始观测数据提取的GPS周跳发生率与地方时、季节、太阳活动以及磁活动之间的关系,开展电离层闪烁效应与这几种参量之间关系的模式化研究.研究结果表明：（1）周跳发生率存在着地方时分布,发生时段主要在日落19：00LT后到午夜02：00LT之前,发生次数在22：00LT左右达到极大,然后缓慢减少,这一变化特点可以用自变量为地方时的Chapman函数形式来描述;（2）周跳发生率存在年变化特点,主要发生在年积日45~135天（春分季节）和225~315天（秋分季节）,可以通过高斯函数来描述每个分季闪烁效应的变化特点;（3）可以利用太阳辐射指数F10.7作为描述周跳随太阳活动周变化的参量,根据周跳随太阳活动周的变化特点,我们使用一个以F10.7为自变量的三次函数来描述这种变化;（4）电离层闪烁与磁活动的关系比较复杂,由于大多数情况下表现为磁活动对电离层闪烁的抑制作用,在本研究中使用一个以地磁活动指数Ap为自变量的的平方根函数来拟合这种变化.     

库姆塔格沙漠羽毛状沙丘剖面特征

在库姆塔格沙漠羽毛状沙丘分布区选取典型地段作为观测区,运用全站仪测量了观测区羽毛状沙丘地形特征。结果如下：（1） 构成羽毛状沙丘羽轴的沙垄由首尾相连的变形的新月形沙丘构成,其走向为N55°E;新月形沙丘的平均高度为17.65 m,西北翼角的平均长度为72 m,均长于东南翼角。（2） 沙垄的纵断面（SW→NE）表现出明显的波动性,波长在50～100 m之间,波高在10～25 m之间。（3） 沙垄的平均宽度为127.69 m,平均坡度为12.59°;西北坡平均坡长为71.74 m,平均坡度为11.65°,东南坡平均坡长为59.05 m,平均坡度为13.52°。（4） 羽毛状沙丘的“羽枝”部分是由地形平缓的穹状大沙波首尾相连构成,并未像遥感影像一样呈现出明暗相间的羽毛状图案。大沙波的平均宽度为641.34 m,其纵断面相对平缓,2个波峰之间的距离在400 m左右,波峰高度为1～3 m,平均坡长为322.37 m,平均坡度为1.28°,仅为沙垄的10%。     

Stability and changes in astaxanthin ester composition from Haematococcus pluvialis during storage

In this paper, we investigated the effects of temperature, oxygen, antioxidants, and corn germ oil on the stability of astaxanthin from Haematococcus pluvialis under different storage conditions, and changes in the composition of astaxanthin esters during storage using high performance liquid chromatography and spectrophotometry. Oxygen and high temperatures （22-25~C） significantly reduced the stability of astaxanthin esters. Corn germ oil and antioxidants （ascorbic acid and vitamin E） failed to protect astaxanthin from oxidation, and actually significantly increased the instability of astaxanthin. A change in the relative composition of astaxanthin esters was observed after 96 weeks of long-term storage. During storage, the relative amounts of free astaxanthin and astaxanthin monoesters declined, while the relative amount of astaxanthin diesters increased. Thus, the ratio of astaxanthin diester to monoester increased, and this ratio could be used to indicate if astaxanthin esters have been properly preserved. If the ratio is greater than 0.2, it suggests that the decrease in astaxanthin content could be higher than 20%. Our results show that storing algal powder from H. pluvialis or other natural astaxanthin products under vacuum and in the dark below 4~C is the most economical and applicable storage method for the large-scale production of astaxanthin from H. pluvialis. This storage method can produce an astaxanthin preservation rate of at least 80% after 96 weeks of storage.     

证据权模型中两种预测单元划分方式对比

证据权模型作为一种数据综合方法已被广泛应用于矿产资源定量预测与评价。在模糊证据权基础上,发展了基于地质单元思想的矢量证据图层构建和数据综合方法,并通过实例作具体阐述：它以矿点缓冲区图层作为训练图层,以各证据变量图层在空间上的叠置所形成的唯一地质单元作为评价对象,统一计算各个证据变量的证据权重,进而基于地质单元进行证据综合和后验概率成图。与基于栅格（或规则格网）的模型不同,基于矢量证据权模型以具有明确地质内涵的地质单元（而非规则网格单元）为预测单元,易于解释,并且消除了边界误差;相比基于规则格网划分所得到的成矿单元,以矿床（点）缓冲区作为训练对象,提高了已知矿点的代表性。实例表明：若预测单元大小为初始栅格大小整数倍,各缓冲等级平均面积计算误差为0.26%,否则面积平均误差达到6%;即使在预测单元大小为初始栅格大小整数倍情况下,矿点平均计算误差也达到4.78%。因此,基于地质单元思想的证据权预测单元划分方法在精度上优于基于栅格或规则格网方法。     

Tidal level response to sea-level rise in the yangtze estuary

The rise of tidal level in tidal reaches induced by sea-level rise has a large impact on flood control and water supply for the regions around the estuary.This paper focuses on the variations of tidal level response along the tidal reaches in the Yangtze Estuary,as well as the impacts of upstream discharge on tidal level response,due to the sea-level rise of the East China Sea.Based on the Topex/Poseidon altimeter data obtained during the period 1993～2005,a stochastic dynamic analysis was performed and a forecast model was run to predict the sea-level rise of the East China Sea.Two-dimensional hydrodynamic numerical models downscaling from the East China Sea to estuarine areas were implemented to analyze the rise of tidal level along the tidal reaches.In response to the sea-level rise,the tidal wave characteristics change slightly in nearshore areas outside the estuaries,involving the tidal range and the duration of flood and ebb tide.The results show that the rise of tidal level in the tidal reaches due to the sea-level rise has upstream decreasing trends.The step between the stations of Zhangjiagang and Shiyiwei divides the tidal reaches into two parts,in which the tidal level response declines slightly.The rise of tidal level is 1～2.5 mm/a in the upper part,and 4～6 mm/a in the lower part.The stations of Jiangyin and Yanglin,as an example of the upper part and the lower part respectively,are extracted to analyze the impacts of upstream discharge on tidal level response to the sea-level rise.The relation between the rise of tidal level and the upstream discharge can be fitted well with a quadratic function in the upper part.However,the relation is too complicated to be fitted in the lower part because of the tide dominance.For comparison purposes,hourly tidal level observations at the stations of Xuliujing and Yanglin during the period 1993～2009 are adopted.In order to uniform the influence of upstream discharge on tidal level for a certain day each year,the hourly tidal level observations are corrected by the correlation between the increment of tidal level and the increment of daily mean upstream discharge.The rise of annual mean tidal level is evaluated.The resulting rise of tidal level at the stations of Xuliujing and Yanglin is 3.0 mm/a and 6.6 mm/a respectively,close to the rise of 5 mm/a according to the proposed relation between the rise of tidal level and the upstream discharge.     

钢弹簧浮置板道床在西安地铁中减振效果分析

西安地铁二号线绕行通过西安钟楼,为降低地铁长期运营对钟楼的振动影响,在钟楼段采用钢弹簧浮置板道床进行减振。主要以地铁二号线运行影响下对钟楼的振动监测数据为基础,通过对钢弹簧浮置板道床段和普通道床段的振动实测值比较与分析,得出隧道内减振段和普通段的振动差异,以此评价钢弹簧浮置板道床在地铁应用中的减振效果。     

放牧强度对科尔沁沙地沙质草地植被的影响

为了研究科尔沁沙地沙质草地在不同放牧强度下植被特征的变化规律,比较了围封、中度放牧、重度放牧3种条件下的植被盖度、群落组成、物种多样性、地上/地下生物量和凋落物量等植被特征的变化特征。结果表明:(1)围封、中度放牧和重度放牧沙质草地的优势植物均为一年生植物,但围封和中度放牧中多年生禾本科植物优势度高于重度放牧,重度放牧沙质草地一年生植物所占优势度最大;(2)放牧强度对沙质草地植被盖度、地上生物量及凋落物量有显著影响。随着放牧强度的增加,植被盖度、地上生物量和凋落物量均降低;(3)围封、中度放牧和重度放牧沙质草地物种丰富度及多样性差异均不显著;(4)放牧强度和土壤深度及其交互作用均能影响地下生物量。随着放牧强度的增加,总的地下根系生物量减小。而重度放牧草地中, 3个土壤深度间地下根系生物量差异不显著。放牧改变了沙质草地植物群落的组成、极大降低了植被盖度和生产力;尤其是重度放牧急剧增加了一年生植物的优势、且对浅层根分布的减少影响最大。     

广义S变换地震信号时频分析

广义S变换继承和发展了S变换的优点,其引入了λ、p两个参数,对S变换中固定的基本小波进行了推广和扩展,使得其时窗更灵活多变,在一定程度上提高了非平稳信号分析处理的时频分辨率。通过线性调频信号模拟测试对比,证实了广义S变换的信号聚焦能力明显优于S变换,能够更好地刻画信号的局部特性。最后,以某区二维单炮地震数据为例进行了地震信号的广义S变换时频分析,取得了良好效果。     

Urban expansion in China and its effect on cultivated land before and after initiating “Reform and Open Policy”

Urbanization in China has expanded at an unprecedented speed since the declaration of "Reform and Open Policy"and presented many challenges. Unbalanced regional development, appearance of super megacities and concomitant problems,and conflicts between urbanization and cultivated land protection are three critical problems that Chinese urbanization has to face. To develop new plans for foreseeable future urbanization in China, it is critical to understand the evolving history of cities across China. This study maps urban expansion of 60 typical Chinese cities based on large amount of remote sensing data and the labor-intensive image interpretation method, in order to understand the history of urban expansion from the 1970 s to 2013.Results showed that area of cities expanded 5.23 times compared to their area in the 1970 s. Urban expansion in China accelerated three times(1988–1996, 1999–2006, and 2009–2011) and decelerated three times(1997–1998, 2007–2008, and 2012–2013) over the 40 years. The urban area of South China expanded most significantly 9.42 times, while the urban area in Northeast China expanded only 2.37 times. The disparity among different administrative ranks of cities was even greater than(3.81 times) the differences among different regions. Super megacities have been continuously expanding at a fast rate(8.60-fold), and have not shown obvious signs of slowing down. The proportion of cultivated land among the land sources for urban expansion decreased to a small extent in the 1990 s, but cultivated land continues to be the major land source for urban expansion. Effective future urbanization needs controlling the expansion scale of large cities and reasonably developing medium and small cities, as well as balancing regional development.