吐哈盆地硫磺山铜多金属矿床表生黄钾铁矾~(40)Ar/~(39)Ar定年及对风化、地貌演化及古气候的启示

黄钾铁矾是干旱—半干旱地区硫化物矿床氧化带中一种常见表生含钾硫酸盐矿物,对其进行~(40)Ar/~(39)Ar年代学研究,不仅可以直接限定硫化物矿床次生富集的时间,还可以为区域地貌形成演化和古气候演变等重大地质事件提供关键的年代学信息。本文对中国新疆吐哈盆地硫磺山铜多金属矿床氧化带中三个表生黄钾铁矾样品进行了~(40)Ar/~(39)Ar定年,第一次获得了始新世的风化矿物的年龄。结合已发表的年龄数据显示:在吐哈盆地,海拔较高的矿床氧化带剖面(如硫磺山矿床)记录了基岩的持续和较完整的区域风化事件,这些老的风化年龄的存在证明了剥蚀并不是均匀的,即其地貌演化遵循的是斜坡后退模型。对于吐哈盆地的古气候,这些表生硫酸盐的年龄表明:始新世以来吐哈盆地曾多次出现过有利于化学风化和硫化物矿床次生富集的干旱—半干旱气候,且主要集中在以下几个时期:27.7~23.3 Ma、16.4~14.7 Ma、11~7.8 Ma,之后气候开始向极端干旱气候转变,4.1~3.3 Ma之后吐哈盆地可能已经流行大规模的极端干旱气候。     

Tracing sediment redistribution across a break in slope using rare earth elements

Experimentally determined spatial patterns of soil redistribution across a break in slope derived using 10 rare earth element (REE) oxides as sediment tracers are presented. An erosion experiment was conducted using simulated rainfall within a laboratory slope model measuring 2·5 m wide by 6 m long with a gradient of 15° declining to 2°. Soil was tagged with multiple REE and placed in different locations over the slope and at the end of the experiment REE concentrations were measured in samples collected spatially. A new method was developed to quantify the erosion and deposition depths spatially, the relative source contributions to deposited sediment and the sediment transport distances. Particle‐size selectivity over an area of net deposition was also investigated, by combining downslope changes in particle‐size distributions with changes in sediment REE composition within a flow pathway. During the experiment, the surface morphology evolved through upslope propagation of rill headcuts, which gradually incised the different REE‐tagged zones and led to sediment deposition at the break in slope and the development of a fan extending over the shallow slope segment. The spatial patterns in REE concentrations, the derived erosion and deposition depths, the relative source contributions to deposition zones and the sediment transport distances, corroborate the morphological observations and demonstrate the potential of using REE for quantifying sediment transport processes. Copyright © 2010 John Wiley & Sons, Ltd.     

A new series solution method for two-dimensional elastic wave scattering along a canyon in half-space

This paper presents a semi-analytical method for studying the two-dimensional problem of elastic wave scattering by surface irregularities in a half-space. The new method makes use of the member of a c-completeness family of wave functions to construct the scattering fields, and then applies equal but opposite tractions to those of the foregoing constructed scattering fields on the horizontal surface of the half-space to produce additional scattering fields. These additional scattering fields are a series of Lamb's solutions. Thus the whole scattering field constructed in the series automatically satisfies the Navier equations, the condition of zero traction on the half-space surface, and the radiation boundary conditions at infinity. Using the traction-free conditions along the canyon surface, the coefficients of the series solutions are determined via a least-squares method. For incident P, SV, and Rayleigh waves, the numerical results are presented for the scattering displacements in the vicinity of a semi-circular canyon in the half-space.     

Contested and congested spaces: Exploring authenticity in New Zealand farmers' markets

This paper considers issues of authenticity as they apply to the evolution of farmers' markets in New Zealand. Following a discussion of the nature of authenticity and its deployment by farmers' market organisations in several jurisdictions, a two‐part case study is presented. An analysis of the strategies adopted by Farmers' Markets New Zealand to ‘protect its brand’ nationally and an examination of the disputation of authenticity in the Marlborough Farmers' Market reveals the potential of the ‘authenticity project’ to be a lightning rod for heightened tension and the fracturing of the relationship between competing interests in New Zealand farmers' markets.     

Undocumented Students’ Narratives of Liminal Citizenship: High Aspirations,Exclusion, and “In-Between” Identities

This study illustrates how national immigration policy relegates undocumented immigrant children to spaces of liminal citizenship, which shape their aspirations for higher education. Recognizing the power of migrant narratives, and the importance of privileging youths’ voices through children's geographies, we present the narratives of undocumented high school students from several rural North Carolina communities. Despite various barriers facing undocumented students, most have high academic aspirations. Students construct new forms of citizenship, legitimating their claims to higher education access through their achievement. Their liminal status, however, contributes to the formation of conflicted, “in-between” identities.     

Constructing Alterity in Ile De France?

Abstract

The aim of the article is to determine whether the Walt Disney Company has manufactured a landscape “other” to French culture around its parks in the Eastern Paris Basin. Val d'Europe is contentiously constructed by three main groups, not just one enterprise: the French state, the Walt Disney Company and local and regional governments, as well as by present and future residents, within the constraints of a contract based on French laws. The Company's investment has been a tremendous boost to the French state's project but did not lead to Disneyfication of the Briard landscape of agricultural lands in the Eastern Paris basin. In Val d'Europe the French state did not abdicate its authority in favor of commoditization of Paris as a global metropolis. The French state and French culture were never “weak” and overwhelmed.     

Multi‐scale spatiotemporal analyses of moose–vehicle collisions: a case study in northern Vermont

Moose–vehicle collisions (MVCs) pose a serious safety and environmental concern in many regions of Europe and North America. For example, in the state of Vermont, one‐third of all reported MVCs resulted in motorist injury or fatality while collisions have increased from two in 1982 to 164 in 2002. Our work used a MVC dataset from 1983 to 1999 in the Northeastern Highlands of Vermont (four major roads) to perform space, time and spatiotemporal analyses and guide future mitigation strategies. An adapted kernel density estimator was implemented for exploratory analyses to detect high density collision hotspots on roads. The kernel in space showed seven major density peaks which varied in magnitude and spread between roads. The kernel estimator in time for all roads showed an exponentially increasing trend with annual periodicity and a seasonal cyclic component, where the majority of collisions occurred from May to October. Spatiotemporal kernel estimation exhibited discontinuous density hotspots in time and space suggesting changing animal movement patterns across roads. We used an adapted Ripley's K‐function to test the hypothesis that MVCs clustering occurred at multiple scales in space, in time and in space–time combined. Statistically significant spatial clustering was evident on all roads at spatial scales from 2 to 10 km. A more consistent clustering in time occurred on all roads at a scale distance of 5 years. Similar to the kernel estimation, annual periodicity was also evident. Positive space–time clustering was present at small spatial (5 km) and temporal scales (2 years) indicating that where MVCs occur is also influenced by when they occur. In retrospect, using multiple road lengths, and the combined kernel estimation and Ripley's K‐function in time and space, provided a powerful methodology to study varying spatiotemporal patterns of wildlife collisions along roads. This can greatly assist transportation planners in identifying optimal mitigation strategies along specific roads, such as deciding on location and spatial length for permanent and expensive measures (e.g. crossing structures and associated fencing) versus less permanent and inexpensive structures (e.g. wildlife signage and reduced speed limits).     

Hydrological characteristics of vegetated river flows: a laboratory flume study

Abstract

Laboratory flume experiments were undertaken to measure the vertical profiles of mean flow velocity for three different flow discharges and four different stem densities of Hydrilla verticillata. The data were used to calculate three parameters, namely Manning's roughness coefficient, the Reynolds number and the Froude number. In addition, empirical equations were obtained for the vertical distribution of measured flow velocity within the transitional zone and above the plant canopy. The results show that: (a) the vertical distribution of measured flow velocity exhibits three zone profiles; (b) Manning's roughness coefficient decreases with increasing depth-averaged flow velocity; (c) the relationship between Manning's roughness coefficient and the depth-averaged flow velocity is within the smooth left inverse curve; (d) Manning's roughness coefficient significantly changes with increasing density of Hydrilla; (e) the Froude number is independent of the density of Hydrilla; and (f) both the Reynolds number and the Froude number increase with increasing depth-averaged flow velocity.

Citation Shi, J.Z., Li, Y.-H., Hughes, J.M.R., and Zhao, M., 2013. Hydrological characteristics of vegetated river flows: a laboratory flume study. Hydrological Sciences Journal, 58 (5), 1047–1058.

Editor Z.W. Kundzewicz     

A large class of non-zonal oceanic flows satisfying the arnold-blumen sufficient condition for stability

Abstract

Recently Andrews has discussed an example of a topographically-forced non-zonal now satisfying the Arnold-Blumen sufficient condition for stability. At large distances from the topographic centre this flow becomes purely zonal and westward. After underlining the richness of solutions of the Andrews model, the present paper goes on to show that Andrews' technique can be applied successfully to a model where the vertical profile of static stability resembles those found in the ocean. In particular we obtain a large class of hydrodynamic stable flows, forced by the bottom topography, for continuously stratified fluids (two layers each with uniform Brunt-Väisälä frequency).     

The instability of barotropic circular vortices

Abstract

The linear, normal mode instability of barotropic circular vortices with zero circulation is examined in the f-plane quasigeostrophic equations. Equivalents of Rayleigh's and Fjortoft's criteria and the semicircle theorem for parallel shear flow are given, and the energy equation shows the instability to be barotropic. A new result is that the fastest growing perturbation is often an internal instability, having a finite vertical scale, but may also be an external instability, having no vertical structure. For parallel shear flow the fastest growing perturbation is always an external instability; this is Squire's theorem. Whether the fastest growing perturbation is internal or external depends upon the profile: for mean flow streamfunction profiles which monotonically decrease with radius, the instability is internal for less steep profiles with a broad velocity extremum and external for steep profiles with a narrow velocity extremum. Finite amplitude, numerical model calculations show that this linear instability analysis is not valid very far into the finite amplitude range, and that a barotropic vortex, whose fastest growing perturbation is internal, is vertically fragmented by the instability.