黄淮海地区乡村人—地—业协调发展格局与机制   总被引：8，自引：0，他引：8  

程明洋  刘彦随  蒋宁 《地理学报》2019,74(8):1576-1589

乡村在社会中占有重要地位,但乡村衰败目前已成为世界性问题,因此,乡村振兴需破解乡村病问题。现有乡村研究主要关注乡村单一系统、乡村转型或乡村特定问题的研究,对乡村系统自身、乡村各子系统之间关系及其驱动乡村发展逻辑的研究则显匮乏。基于黄淮海地区县域数据,选取乡村人—地—业3个子系统,利用耦合协调度模型刻画了乡村内部系统耦合协调度的空间格局,并对人—地—业驱动乡村发展的内在逻辑进行了探讨。结果发现：① 黄淮海地区大部分县域乡村人—地—业发展处于高水平耦合阶段,在空间格局上形成了4条明显的高值轴带,且乡村系统发展水平呈逐年上升趋势。② 黄淮海地区乡村耦合协调水平整体较高,但大部分处于勉强协调或初级协调阶段,耦合协调水平较高的县域主要集中在经济较发达地区。③ 黄淮海地区乡村耦合协同关系可分为低协调水平—土地发展领先型、中协调水平—人口发展领先型和高协调水平—人业发展引领型3种类型,其中产业在黄淮海地区乡村协调发展中至关重要。④ 乡村人—地—业的协调发展可有效激活“四力”,为乡村可持续发展奠定了基础。本研究为理解乡村系统自身、破解乡村问题及实现乡村可持续发展提供了参考。  相似文献   

A two-dimensional analytical model of vertical water entry for asymmetric bodies with flow separation     

《Applied Ocean Research》2019

The vertical water entry of asymmetric two-dimensional bodies with flow separation is considered. As long as there is no flow separation, linearised Wagner's theory combined with the modified Logvinovich model has been shown to provide computationally fast and reliable estimates of slamming loads during water entry. Tassin et al. [11] introduced the fictitious body continuation (FBC) concept as a way to extend the use of Wagner's model to separated flow configurations, but they only considered symmetric bodies. In the present study, we investigate the ability of the FBC concept to provide accurate estimates of slamming loads for asymmetric bodies. In this case, flow separation may not occur simultaneously on both sides of the body. During an intermediate phase, slamming loads are governed by a competition between the local drop in pressure due to partial flow separation and the ongoing expansion of the wetted area. As a first benchmark for the model, we consider the water entry of an inclined flat plate and compare the FBC estimates with the results of a nonlinear model. Then, we consider the case of a foil and compare the FBC results with computational fluid dynamics predictions. In both cases, we find that the FBC model is able to provide reliable estimates of the slamming loads.  相似文献   

球面距离计算方法及精度比较     

樊东卫  何勃亮  李长华  韩军  许允飞  崔辰州 《天文研究与技术》2019,(1):69-76

球面距离(角间距)计算是天文或地理学中极常用的计算之一,也是目标查找、锥形检索、交叉证认等方法的基础。数学上,通过球面几何可以直接计算出两点的距离,前人已经推导出了多个复杂程度不一的计算方法。但是由于计算机的精度有限,在进行数值计算时有舍入误差,导致公式计算结果出现偏差。对几个常用的球面距离计算公式进行了考察,测试并对比它们在不同计算环境下的精度与优缺点。此外还展示并比较了几种常用天文软件包、数据库的球面距离计算方法,以期有助于天文工作者选择适合自己当前需要的计算方法。  相似文献   

三氟乙酸锂-15-冠醚-5体系电迁移法分离锂同位素          下载免费PDF全文

黄超驰  孙进贺  张茜  张鹏瑞  汪词明  薛子轩  景燕  贾永忠 《盐湖研究》2021,29(3):83-89

锂同位素(6 Li和7 Li)在核工业中有着重要作用.锂汞齐法是目前唯一实现锂同位素工业化生产的方法,然而由于汞的使用,该方法具有较大的环境风险.开发绿色高效的锂同位素分离方法对国家能源安全具有重要意义.在本论文中,制备了溶解锂盐的冠醚溶液,并以其作为阳极液,施加电场驱动锂离子向阴极液迁移;与溶有15-冠醚-5的锂盐水...  相似文献   

酉阳河流域典型年汛期的基流分割研究   总被引：2，自引：0，他引：2  

雷宇宽 《水文》2021,41(1):35-41

基流分割是水文学研究中的重难点问题之一,目前基流分割也存在许多方法.基于酉阳河典型年汛期实测日平均流量资料,分别采用Chapman-Maxwell改进方程数字滤波法一次滤波(参数N=1)以及二次滤波(参数N=2)、BFI(f)法、HYSEP固定步长法、HYSEP滑动步长法、HYSEP局部最小值法进行基流分割并对其结果进...  相似文献   

巢湖沉积植硅体组合及中全新世以来的环境演变   总被引：1，自引：0，他引：1  

范斌  许世远  俞立中  蒋辉  冉莉华 《湖泊科学》2006,18(3):273-279

尽管以前对眼虫进行过大量的形态发育研究和基于核糖体RNA基因的系统发育分析,但对于株系之间的关系仍然知之甚少．因其形态特征有限并且易变,很难鉴定眼虫的相似种和同种内不同的株．作者利用微卫星DNA指纹图谱,在七株眼虫中扩增了七个微卫星DNA位点,成功扩增的六个微卫星引物都得到了四到八个条带．从微卫星DNA指纹图谱计算得到的相似性系数范围从0．000到0．957．根据相似性系数得到的树状结构,七株眼虫在距离为0．9346处分为三支:E．mutabilis,E．intermedia和E．gracilis．其中,五株E．gracilis分为两组:来自日本的和美国的．不同地区的株得到不同的基因型,并初步分析了它们之间的关系．研究表明七株眼虫根据微卫星DNA指纹图谱被明显区分开．微卫星DNA指纹图谱具有很高的分辨率,是鉴定和区分原生动物相似种和同种内不同株的一种有用的新方法．  相似文献   

APPLICATION OF UNIT HYDROGRAPH TECHNIQUES TO SOLUTE TRANSPORT IN CATCHMENTS     

C. J. BARNES  M. BONELL 《水文研究》1996,10(6):793-802

Current models of solute movement in catchments are based on rainfall–runoff models and are consequently biased towards processes which determine the magnitude and timing of water flux. It is shown here that the instantaneous unit hydrograph (IUH), or runoff response function, obtained from a hydrograph is fundamentally different from the residence time distribution which governs the response to solutes/tracers. Using hydrometric and tracer data obtained from a small (25 ha) catchment in the humid tropics a modification of the IUH technique is demonstrated which also allows approximate modelling of the tracer data. New features of the modified conceptual model are identified with known hillslope processes.  相似文献   

FLOOD MODELLING WITH GIS-DERIVED DISTRIBUTED UNIT HYDROGRAPHS     

I. MUZIK 《水文研究》1996,10(10):1401-1409

The concept of a spatially distributed unit hydrograph is based on the fact that the unit hydrograph can be derived from the time–area curve of a watershed by the S-curve method. The time–area diagram is a graph of cumulative drainage area contributing to discharge at the watershed outlet within a specified time of travel. Accurate determination of the time–area diagram is made possible by using a GIS. The GIS is used to describe the connectivity of the links in the watershed flow network and to calculate distances and travel times to the watershed outlet for various points within the watershed. Overland flow travel times are calculated by the kinematic wave equation for time to equilibrium; channel flow times are based on the Manning and continuity equations. To account for channel storage, travel times for channel reaches are increased by a percentage depending on the channel reach length and geometry. With GIS capability for rainfall mapping, the assumption of a uniform spatial rainfall distribution is no longer necessary; hence the term, spatially distributed unit hydrograph. An example of the application for the Waiparous Creek in the Alberta Foothills is given. IDRISI is used to develop a simple digital elevation model of the 229 km² watershed, using 1 km × 1 km grid cells. A grid of flow directions is developed and used to create an equivalent channel network. Excess rainfall for each 1 km × 1 km cell is individually computed by the Soil Conservation Service (SCS) runoff curve method and routed through the equivalent channel network to obtain the time–area curve. The derived unit hydrograph gave excellent results in simulating an observed flood hydrograph. The distributed unit hydrograph is no longer a lumped model, since it accounts for internal distribution of rainfall and runoff. It is derived for a watershed without the need for observed rainfall and discharge data, because it is essentially a geomorphoclimatic approach. As such, it allows the derivation of watershed responses (hydrographs) to inputs of various magnitudes, thus eliminating the assumption of proportionality of input and output if needed. The superposition of outputs is retained in simulating flood hydrographs by convolution, since it has been shown that some non-linear systems satisfy the principle of superposition. The distributed unit hydrograph appears to be a very promising rainfall runoff model based on GIS technology.  相似文献   

一种适用于沉积有机质族组分分离的微型柱色谱法   总被引：12，自引：2，他引：10  

徐世平  孙永革 《地球化学》2006,35(6):681-688

硅胶-氧化铝柱色谱是广泛采用的沉积有机质组分分离方法。但在常规柱色谱分离方法中,存在吸附剂、溶剂使用量过大、烷烃/芳烃组分交叉严重等问题。介绍一种微型柱色谱分离法,其分离效果与常规方法的效果基本相同或略有改善,吸附剂用量与样品的比例由100～250降低为25～50,洗脱溶剂与样品的比例由1800～4600降低至250～500。同时,操作程序进一步简化,分析成本和对环境的污染程度大幅度降低。  相似文献   

基于UF、GFC及RP-HPLC的长牡蛎(Crassostrea gigas)蛋白抗衰老小分子活性肽(Zel'ner)的纯化及结构解析     

何定芬  谢超  梁佳  梁瑞萍  李海波 《海洋与湖沼》2020,51(1):141-147

牡蛎肉质鲜美,营养丰富,具有很高的食用价值。本研究以舟山长牡蛎(Crassostreagigas)为研究对象,以DPPH自由基清除率为测试指标,通过UF、GFC及RP-HPLC等技术,对牡蛎蛋白酶解液进行分离纯化,获得牡蛎蛋白小分子肽样品,并对其氨基酸组成进行营养性评价。研究结果表明:浓度为30%—100%的硫酸铵处理酶解液的分离效果明显优于低于浓度为30%硫酸铵的分离效果,其DPPH自由基清除率达到52.43%;纯化后得到两种牡蛎蛋白小分子肽分别标记为组分a(Mw1kDa)和组分b(1kDaMw3kDa);组分a中牡蛎蛋白小分子肽分子量分布主要为1995.2Da、1258.9Da、1023.3Da、398.1Da;对牡蛎蛋白小分子肽组分a进行检测,发现其中氨基酸种类及含量丰富,其中必需氨基酸(EAA)含量为18.863%,总氨基酸含量(TAA)为43.3748%,必需氨基酸占总氨基酸43.49%,必需氨基酸与非必需氨基酸(NEAA)的比例为76.95%,风味氨基酸(FAA)含量为18.9147%,占总氨基酸含量的43.61%。综上可见,牡蛎蛋白小分子肽具有极高的营养价值和市场经济效益,此研究为牡蛎蛋白抗衰老小分子活性肽(Zel'ner)的开发提供了新的思路和方向。  相似文献