A moving PIV system for ship model test in a towing tank

A moving particle image velocimetry (PIV) system was successfully developed and used in a large towing tank for ship model tests to observe velocity fields near ship models. The experimental method involved adjustable optical devices for various test conditions and a special particle-seeding device. The streamwise and cross-streamwise flow fields of a yacht model and a tanker model were measured. Ship type, bottom shape, and towing speed were found to be the causes of problems affecting optical access and image quality. Possible solutions, deeper optical ducts, dark painting color, and pre-processed analysis method, were proposed and discussed.     

Plane Symmetric Domain Wall in Lyra Geometry

In this paper general solutions are found for domain walls in Lyra geometry in the plane symmetric spacetime metric given by Taub. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying displacement field β. It is also shown that the results obtained by Rahaman et al [IJMPD, 10, 735 (2001)] are particular case of our solutions. Finally, the geodesic equations and acceleration of the test particle are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Streamflow permanence in headwater streams across four geomorphic provinces in Northern California

Mountainous headwater streams represent a substantial proportion of the global stream network. These small streams may flow episodically, seasonally, or perennially, providing diverse values and services. Given their broad importance and growing pressures on terrestrial and aquatic resources, we must improve our understanding of the drivers of flow permanence to facilitate informed land and water management decisions. We used field observations from >10 cross-sections in each of 101 non-fish bearing, headwater streams across four geomorphic provinces in Northern California to quantify flow permanence and network connectivity during the summer low flow period in 2018. At each stream cross-section, we noted the presence or absence of streamflow and used this information to classify streams as perennial (continuous streamflow in all cross-sections) or non-perennial and connected (surface water in the most downstream cross-section) or disconnected. At each cross-section, we also quantified channel size (width and depth) and grain size. We coupled field observations with geospatial data of catchment physiography, hydrology, and climate in random forest models to investigate controls of flow permanence and network connectivity. Potential drivers of flow permanence or network connectivity included in our models were channel geometry, grain size, slope, aspect, elevation, annual and seasonal precipitation, air temperature, and topographic wetness index. We found more perennial streams in the Klamath Mountains and Sierra Nevada than in the Cascades and N. Coast regions. Streams in the Klamath were the most connected followed by streams in the N. Coast, Sierra Nevada, and Cascades. The most important variables for predicting flow permanence were channel grain size, winter 2018 precipitation, and drainage area. Comparatively, the most important variables for predicting network connectivity were winter and spring 2018 precipitation, grain size, and bankfull depth. Our study illustrated the complexity of the processes that drive flow permanence and highlighted the uncertainty in projecting the precense of water in streams across diverse regions.     

论辽河群层序的有序性

从排列顺序、基本地层单位、稳定的岩性变化面或标志层、相变、层控矿床、褶皱构造六个方面分析,表明辽河群层序是有序的。辽河群遭受三次变形,即:下降阶段的下部构造层次的变形,有压扁作用和重结晶作用,形成广域流劈理和区域变质岩;上升阶段的中间构造层次(A)的变形,有重力滑动形成的不协调褶皱、顺层剪切形成的韧性剪切带与层内(片内)褶皱和水平拉张形成的拉伸线理与线状构造;褶皱阶段的中间构造层次(B)的变形,有局部出现劈理的平行褶皱与相似褶皱并存,伴生有逆冲型韧性剪切带和逆冲-推覆构造。这种两次垂直运动变形和一次水平挤压运动变形的构造模式是决定辽河群层序有序性的构造基础。流劈理不是拉伸、轴面片理、多期构造作用的构造置换等成因机制形成的,而是在垂直压扁下化学成因的产物,可称顺层片理或构造层理。流劈理的成因机制是讨论辽河群层序有序性的核心问题。     

Flow frequency responses to hardwood-to-grass conversion and subsequent succession

A 8.9 ha (22 acre) catchment at the Coweeta Hydrologic Laboratory in western North Carolina was cleared of hardwood forest in 1958 and 1959 and seeded to Kentucky 31 fescue grass in 1959 and 1960. Grass production was high in years when fertilizer was applied and water yield was very similar to that expected from the original forest cover. as grass production declined, so water yields rose, with important increases in the magnitude of both low frequency flows and, particularly, in baseflow. in 1967 and 1968, when all vegetation was deadened in the catchment, the discharge levels in all flow frequency classes were higher. Natural revegetation was then allowed and water yields gradually declined towards the expected level, although there remained a tendency for winter flows to remain higher, and for summer flows to be lower than expected. This paper updates the earlier work of Hibbert (1969) and uses flow duration curves to extend his results.     

试用“稳定流”评价区域化探异常

出露地表或近地表的矿体,在遭受风化剥蚀作用时,稳定地向水系补充矿化物质,形成在矿体附近具有浓集中心,含量向下游逐渐衰减的水系沉积物异常,对这种异常的形成作用称之为“稳定流”。应用这一概念,可以筛选化探异常。进一步根据“稳定流”的长度和强度,还能够近似定量地推断未知矿化区面金属量(Ps)以及建立典型矿床水系沉积物元素分带序列,为寻找隐伏矿体,评价区域化探异常提供了一种新的方法。     

A projective approach to orbit determination from three sight-lines

Concepts from projective geometry are used to provide a coherent framework for the determination of orbits from observation data comprising lines of sight at three known times. A novel way of presenting the results in a finite diagram is introduced, The effectiveness of the approach is demonstrated by an example, using a simple spreadsheet. A computer-graphic implementation is recommended.     

最小水流能量损失率理论在河相关系中的应用

本文介绍最小水流能量损失率理论的变分法基础。用该理论导出了航道整治工程前后的河相关系式,并将之用于预估东平水道航道整治工程后的河相。实测值与预估值的比较表明,该理论和该河相关系式是可信的。     

Voronoi tessellation on the ellipsoidal earth for vector data

Voronoi tessellation, and its dual the Delaunay triangulation, provide a cohesive framework for the study and interpretation of phenomena of geographical space in two and three dimensions. The planar and spherical solutions introduce errors in the positional accuracy of both Voronoi vertices and Voronoi edges due to errors in distance computations and the path connecting two locations with planar lines or great circle arcs instead of geodesics. For most geospatial applications the introduction of the above errors is insignificant or tolerable. However, for applications where the accuracy is of utmost importance, the ellipsoidal model of the Earth must be used. Characteristically, the introduction of any positional error in the delimitation of maritime zones and boundaries results in increased maritime space for one state at the expense of another. This is a situation that may, among others, have a serious impact on the financial activities and the relations of the states concerned. In the context of previous work on maritime delimitation we show that the Voronoi diagram constitutes the ideal solution for the development of an automated methodology addressing the problem in its entirety. Due to lack of a vector methodology for the generation of Voronoi diagram on the ellipsoid, the aforementioned solution was constrained by the accuracy of existing approaches. In order to fill this gap, in this paper we deal with the inherent attributes of the ellipsoidal model of the Earth, e.g. the fact that geodesics are open lines, and we elaborate on a methodology for the generation of the Voronoi diagram on the ellipsoid for a set of points in vector format. The resulting Voronoi diagram consists of vertices with positional accuracy that is only bounded by the user needs and edges that are comprised of geodesics densified with vertices equidistant to their generators. Finally, we present the implementation of the proposed algorithm in the Python programming language and the results of two case studies, one on the formation of closest service areas and one on maritime boundaries delimitation, with the positional accuracy set to 1 cm.     

Geophysical characterization of the León-Chinandega aquifer,Nicaragua

Electrical geophysical surveys in the mode of vertical electrical soundings (VES) and continuous vertical electrical soundings (CVES) were conducted in the León-Chinandega plains, northwestern Nicaragua, in order to obtain detailed information about the geometry of the different hydrogeological layers in the aquifer and depth to the basement. A total of 51 VES were carried out within the plains. The results show a complex structure towards the north east of the area, and the southwestern part of the plains presents a smoother stratification. The geoelectrical measurements and borehole information indicate that the basement topography is characterized by hills and deep valleys with highly variable basement depths. Fifty CVES where done in a smaller area in the center of the plain. The resistivity data yielded considerable information revealing the existence of two main geo-electrical units. The combined interpretation of geological and geophysical data shows an environment typical of sedimentary volcanic coastal plains. The information collected during this investigation provides valuable data for estimating the fresh-water resources of the León-Chinandega aquifer system and for development of a groundwater management plan.