64层锥束CT扫描的优化系统

近年来X射线断层成像(CT)技术获得了突飞猛进的发展,自1998年推出4层螺旋CT后,CT扫描设备在容积覆盖,空间分辨率,扫描速度,切片数方面取得了长足进展.这不仅给医学应用带来了深远的影响,同时也给CT系统设计提出了巨大的挑战.容积CT(VCT)的设计过程引入了各种策略来战胜其复杂性.这些方法学包括:理论分析,系统性能预测的图像分析工具,各种基于专家背对背评价的参数优化.本文论述了64层CT系统设计中的一些考虑因素及优化过程.这些设计过程保证了锥束CT的优化性能.首批客户的应用反馈显示了我们设计实践的有效率性.     

沪昆客专克地坝陵河特大桥工程地质问题及对策研究

克地坝陵河双线特大桥为沪昆客专贵州段内重点控制工程之一。桥梁工程穿越区内地形、地质条件异常复杂,受地形切割地层及地质构造等多种因素综合控制,区内危岩落石、滑坡、岩堆、岩溶等工程地质问题频发。利用测绘、物探、钻探等资料,对桥址区内主要工程地质的类型、规模、危害性以及防治对策等方面进行深入分析、研究。研究成果不仅能为铁路选线提供依据,而且对围岩落石问题的处理及桥梁工程设计、施工以及运营都具有重大意义。     

离散Hopfield神经网络的稳定性

研究离散Ｈｏｐｆｉｅｌｄ神经网络的串行稳定性和并行稳定性，分别提出了条件较弱的串行稳定性和并行稳定性的新判据．     

交流电弧直读发射光谱法测定地球化学样品中银、硼、锡、钼、铅的方法研究

本文建立了交流电弧直读原子发射光谱法测定地球化学样品中银、硼、锡、钼、铅的分析方法。以K2S2O7、NaF、Al2O3、碳粉为缓冲剂,Ge为内标,优选了分析线对,曝光时间为25s,同时扣除分析线和内标线背景。选取国家一级地球化学标准物质（GBW07103、GBW07104、GBW07107、GBW07312、GBW07302a、GBW07304a、GBW07305a、GBW07307a、GBW07406、GBW07446、GBW07454、GBW07456）作为标准系列,以对数坐标二次曲线拟合标准曲线,并采取两次平行分析取平均值的计算方法。方法检出限为:Ag:0011×10-6、B:054×10-6、Sn:019×10-6、Mo:0034×10-6、Pb:066×10-6,精密度为:Ag:401%～833%、B:377%～786%、Sn:294%～817%、Mo:303%～1094%、Pb:201%～1111%。经岩石、水系沉积物、土壤国家一级标准物质验证,测定值与认定值符合。本方法操作简便、工作效率高,是一种新的测定地球化学样品中银、硼、锡、钼、铅的分析方法,可推广应用于大批量地球化学样品的分析测试。     

Effects of gully erosion and gully filling on soil degradation in the black soil region of Northeast China

Gully erosion has caused soil degradation and even reduced soil productivity.However,only few studies on the effects of gully erosion and artificial controlling measures on soil degradation in the Black Soil Region of Northeast China are available.Thus,this study explores the relationships between gully erosion,gully filling and soil parameters.Two sets of soil samples were collected in the field at:(1) 72 sample points in the gully erosion study area,60 sample points in the ephemeral and classical gully erosion area(3,518 m2),12 sample points in the deposition zone(443 m2),(2)10 reference points along a slope unaffected by gully erosion representing the original situation before the gully was formed.All soil samples were analyzed for gravel content(GC),soil organic matter(SOM),total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),and available potassium(AK).The soil property values on unaffected slope were fitted by the polynomial curves as the reference values in no gully erosion area.The interpolated soil property values in gully eroded study area were compared with these polynomial curves,respectively,and then,changes of soil property values were analyzed.Gully erosion caused an increase in GC and a decrease in SOM,TN,AN,AP and AK.The change of GC,SOM,TN,AN,AP,AK was 8.8%,-9.04 g kg-1,-0.92 g kg-1,-62.28 mg kg-1,-29.61 mg kg-1,-79.68 mg kg-1.The soil property values in the study area were below optimal values.Thus,we concluded that gully erosion and gully filling caused both on-site and off-site soil degradation.Soil degradation area was 0.65 % of the cultivated land.In addition,it was proved that gully filling were an improper soil and water conservation measure,which seems to exacerbate the problem.Thus,it is suggested that soil where soil is deep is moved to fill the gully,and then the area around the filled gullies should be covered by grass for preventing the formation and development of the gully.     

冀中坳陷深县凹陷主伸展期的构造调节带及其对沉积环境的控制作用

深县凹陷沙河街组发育的构造调节带控制着沉积体系的迁移路径和平面展布。根据断层的组合特点与断距变化,可将构造调节带分同向、对向、背向及单线4大类。同向和单线调节带主要发育在北部何庄-兵曹-崔家庄一带,规模小,数量多; 对向调节带发育在榆科地区和赵家庄地区,规模较大,分布稀疏。背向调节带极不发育。伸展作用的不均一性以及地层力学性质差异是形成调节带的主要因素。单线调节带控制小规模的沉积体穿过断层进入汇水盆地,如衡水断层下降盘中的水下扇; 同向调节带控制何庄-西魏村、田家庄、东阳乡等辫状河三角洲的入湖路径和展布特征; 对向调节带控制深湖的形成,如赵家庄一带的深湖; 而背向调节带造成的正地形起到了阻隔物源作用。     

Urban Residential Land Value Analysis： Case Danyang, China

The research attempts to find out how the location of the CBD(central business district), the dis- tance to the main roads, the distribution of the public facilities, and the urban land-use pattern influence the urban residential land value variations. The study begins by identifying the influences into two categories: general circumstance and micro/neighboring circumstances. Benchmark price and market land value are tested to be the results influenced by general circumstance and both the influential range and the influential force of individual land-use are investigated and compared. At last explicit case comparisons are also taken for testing the result. The finding of the research is not only useful for understanding the spatial patterns of land values, but also beneficial for the policy-makers concerning land administration and urban planning.     

Continental- Margin Structure of Northeast China and Its Adjacent Areas

The continental margin of Northeast China and its adjacent areas is composed of two tectonic belts. The inner belt is a collage made up of fragments resulting from breakup of an old land with the north part related to the evolution of the Palaeo-Asian Ocean and the south part to the evolution of the Palaeo - Pacific Ocean. The outer belt is a Mesozoic terrane, which is a melange made up of fragments of the Late Palaeozoic to Early Mesozoic oceanic crust and the Late M esozoic trench accumulations.There existed another ocean-the Palaeo - Pacific Ocean during the period from the closing of the Palaeo-Asian Ocean to the opening of the modern Pacific Ocean or from the Devonian to Jurassic, and the ocean-floor spreading of the Palaeo - Pacific Ocean led to the formation of the above-mentioned tectonic belts. The development of the strike-slip fault system after the Late Jurassic and the formation of an epicontinental volcano -plutonic rock belt in the Late Cretaceous to Early Tertiary are attributed to the i     

Photosynthetic characteristics of spring ephemerals in the desert ecosystem of Dzungaria Basin,northwest China

Spring ephemerals have the highest photosynthetic rates in higher plants. Gas exchanges and related environmental factors of four typical spring ephemerals, Eremopyrum orientale, Malcolmia scorpioides, Tetracme quadricormis and Arnebia decumbens were measured in their natural environments in the Gurbantunggut Desert of the Dzungaria Basin, northwestern China. Diurnal variations in net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (gs), and water use efficiency (WUE) were analyzed at individual leaf level for these species. P _N of E. orientale and M. scorpioides showed a bimodal diurnal pattern, whereas that of T. quadricormis and A. decumbens showed a unimodal pattern, with the maximum value occurred at noon (around 12:00). E of all four species showed a unimodal pattern. Higher WUE in the morning was related to higher P _N and lower E. The maximum value of gs appeared in early morning, and then decreased gradually during the daytime. The highest photosynthetically active radiation (PAR) occurred at 14:00, but there was a 2 h lag between the highest temperatures of air and leaf and the highest PAR. The maximum net photosynthetic rate (P _Nmax) of the four spring ephemerals were 18.44, 32.03, 33.17, and 20.04 μmolCO₂ m⁻² s⁻¹, respectively. The present study revealed that the midday depression of photosynthesis of E. orientale and M. scorpioides was mainly due to non-stomatal limitation, whereas that of T. quadricormis and A. decumbens was mainly due to stomatal limitation during 14:00–16:00 followed by non-stomatal limitation after 16:00. Our results illustrated that the change of E was consistent with the diurnal fluctuation of air temperature, but the diurnal change of P _N was affected by the whole microclimate, i.e. temperature, relative humidity (RH), PAR, etc.     

三轴压缩条件下三峡坝基岩石破裂的分形特征

根据分形理论,系统地研究了在三轴压缩条件下三峡坝基岩石破裂系和破损物的分形结构。结果表明,在三轴压缩条件下,岩石脆性破裂的破裂系和岩石破损物的粒度分布均有很好的统计自相似性。在不同的围压和应变率下,岩石脆性破裂的分维值各不相同,体现了岩石脆性断裂机制的差异性。分维可作为描述岩石脆性断裂的定量参数