Subaqueous “yardangs”: analogs for aeolian yardang evolution

Landforms, morphologically similar to aeolian yardangs but formed by erosion of bedrock by currents on an estuarine rock platform, are described for the first time. The geometries of the “yardangs” are described and related to semi-lemniscate shapes that minimize hydraulic drag. The processes of bedrock erosion by the reversing sediment-laden tidal currents are described, and a semi-quantitative model for landform evolution is proposed. The model casts doubt on the “simple” role of the maximum in the two-dimensional vertical suspended sediment flux distribution and the consequent distribution of potential kinetic energy flux in the process of shaping the rock wall facing the ebb flow. Rather, although the kinetic energy flux increases away from the bed, the sediment becomes finer and abrasion likely is insignificant compared with coarse sand abrasion lower in the profile. In addition, the vertical distribution of sediment flux is mediated by topographic forcing which raises the elevation at which bed load intersects the yardang prow. Consequent erosion leads to ebb-facing caprock collapse and yardang shortening. In contrast, the role of ebb-flow separation is paramount in mediating the abrasion process that molds the rock surface facing the flood flow. The length of yardangs is the least conservative dimension, reducing through time more rapidly than the height and width. Width is the more conservative dimension which implies that once the caprock is destroyed, scour over the obstacle is significant in reducing body height, more so than scour of the flanks which reduces width. The importance of vertical fissures in instigating the final breakdown of smaller yardangs and their extinction is noted. Similarities to aeolian yardang geometries and formation principles and processes are noted, as are the differences. The model has implications for aeolian yardang models generally

Consuming gardens: Representations of paradise, nostalgia and postmodernism

This paper unravels the types of relationships people have with their gardens. This is achieved through a review of previous literature on the topic, coupled with a theoretical contextualisation which utilises postmodern concepts, notably that of Jameson's 'nostalgic return' (1989). To illustrate the relevance of these concepts to an understanding of gardening the paper turns to a number of gardening 'texts' and 'spaces' to decipher the ways in which gardens are consumed within contemporary culture. It argues that representations of gardens cohere around two key motifs: the search for paradise and the imagined return to a long-forgotten past

Harnessing the fishery potential of man-made lakes for the partial commercialisation of Niger River Basin Development Authority, Minna, Nigeria

Niger River Basin Development Authority Minna (NRBDA) is one of the eleven river basins in Nigeria now undergoing transition towards partial commercialisation. In the light of this the need to be self-sustaining through exploration and exploitation of every possible areas along their operation to yield revenue cannot be over-emphasized. Therefore it is most pertinent to consider fisheries activities along their water bodies as one of the major sources of revenue by organising the local fishermen operating along the water into cooperative bodies and made to pay for fishing rights. Strategies to accomplish this objective is highlighted. The need to embark on aquaculture projects by construction of fish ponds at suitable sites along the reservoirs and developing the recreational potentials of their water bodies as sources of revenue is also stresse

Sulphur isotopic evidence for the genesis of the Au-Ag-Sb-W mineralization of the Fairbanks mining district, Alaska

Introduction -- Sampling and analytical technique -- Results and discussions -- References.Sulphur dioxide from sulphides was extracted for analysis by oxidation with Cuprous oxide at 1070º C, using essentially the method described by Robinson and Kusakabe (1975). The isotopic analyses of the purified sulphur dioxide were made on a modified Micromass 602 mass spectrometer with heated inlet system. The results were corrected for isobaric interference assuming a constant oxygen isotopic content and instrumental crosstalk (Coleman, 1977; 1980) and expressed in conventional del notation with respect to the Canon Diablo meteoritic troilite standard

River Ouse: fisheries drought report 1996

The basis for undertaking this study was to examine factors and potential impacts affecting fish and fishing in relation to low flow drought conditions and what other impacts may arise as a result of further reduced flows resulting from abstraction. The study formed the basis of a three year project to concentrate on effects relating to potable water abstractions at Moor Monkton by YWS. To fully evaluate the possible effects on fisheries the study set out to encompass fish population surveys from fry to adult stock, analysis of angler catch data, reports from anglers and river reports from Environment Agency Fisheries staff. In order to evaluate any effects of drought and abstraction a three year study was instigated to examine fish populations. Fish population surveys were conducted at six sites in which the triennial rolling programme formed the basis of site selection. Multi-method sampling techniques were carried out at several sites in order to evaluate capture efficiency. Roach were prolific above the weir at Linton-on-Ouse, with gudgeon, perch and small bream also well represented. Roach dominated catches on the R.Ouse below Linton, with perch and bleak also relatively abundant. Low flows were not thought to be directly correlated to successful recruitment of coarse fish, rather the associated high temperatures during drought conditions showing a strong positive effect with most species exhibiting growth rates above their long-term average. At this stage in the study there are no clear indications that the drought has caused any deleterious effects to coarse fish populations or marked changes in species composition, with evidence of good recruitment by several species, indicating that the higher temperatures have generally been beneficial to recruitment. However, the indication that dace did not benefit as well as other coarse fish under these conditions may suggest some species are affected more than others. The successful strong recruitment of most coarse fish suggests that, in future, fisheries will be supported by the 1995 year-class

The head-body weight and head-body length relationship of Synodontis schall (Bloch and Schneider 1801) in Asa Lake, Ilorin, Nigeria

A total of 710 specimens of Synodontis schall were analyzed for the head body weight and head body length relationship. The head constituted 40% of the total body weight and 30% of the total body length. The mean head weight for male and female computed was 23.90g and 29.13g respectively. Head weight in both male and female was significantly different (P0.05). Fat accumulation in the body tissue was prominent in the females than males usually before the breeding season. The significance of the cephalo-nuchal shield in the bony head of Synodontis species compared with some other catfishes in the lake was also discusse

Properties of Information Carrying Waves in Cosmology

Recently we studied the effects of information carrying waves propagating through isotropic cosmologies. By information carrying we mean that the waves have an arbitrary dependence on a function. We found that the waves introduce shear and anisotropic stress into the universe. We then constructed explicit examples of pure gravity wave perturbations for which the presence of this anisotropic stress is essential and the null hypersurfaces playing the role of the histories of the wave-fronts in the background space-time are shear-free. Motivated by this result we now prove that these two properties are true for all information carrying waves in isotropic cosmologies.Comment: 15 pages, Latex File, accepted for publication in Physical Review