1,380 research outputs found
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Scaling and intermittency in ocean turbulence: analysis of coastal water optical properties and sea surface temperature (SST)
No full textWe consider here some scaling and intermittency properties of oceanic turbulence, with a general aim of considering the impact of turbulence on the bio-optical dynamics. For that purpose, we tried two different approaches, using in situ and satellite data. For the in situ study we adopted one dimensional and for the satellite two dimensional approaches. Different techniques such as Fourier power spectrum, Empirical mode of decomposition (EMD), Hilbert spectral analysis (HSA) have been used for analyzing the intermittency characteristics of the in situ data. For analyzing the multi-scale properties of the satellite images, we have considered Structure functions (SF) and Fourier power spectrum (1D and 2D). The general objective is to understand the multi-scale oceanic variability using scaling tools developed in the field of intermittent turbulence studies
The organization of industry in the P.R. China: A new start or resort to old concepts?
No full textThe Chinese have let it be known since the death of Mao Zedong and the purge of the “Gang of Four” that they would in future draw on credits from foreign governments as well as other sources to finance imports of technology. According to western conjectures China’s capital requirements may be between US $ 25 and 50 bn or even a good deal higher. Many observers have taken the view that the Chinese have thereby put all their former development principles behind them. The author of the following article was in the P.R. China about the middle of this year at the invitation of the National Planning Commission. His assessment is that the P.R. China is far from embarking on an entirely new course in its development policy
Amphibian diversity, distribution and conservation in the Ethiopian highlands : morphological, molecular and biogeographic investigation on Leptopelis and Ptychadena (Anura)
No full textLittle is known about the diversity, distribution and population status of Ethiopian amphibians in general, and most of the existing knowledge is based on field data recorded about three decades ago or earlier. There are almost no genetic data available for molecular systematics studies. Species of the Tree Frogs (Leptopelis Günther 1859) and Grassland Frogs (Ptychadena Boulenger 1917) are solely distributed in Africa (mainly sub-Saharan), with 52 and 53 known species, respectively. Six species of Leptopelis and thirteen species of Ptychadena were recorded in Ethiopia. Together these two genera comprise 30% of all known species of amphibians in Ethiopia. Many of these species (five Leptopelis and five Ptychadena) are said to be endemic to the Ethiopian Highlands that are part of the Eastern Afromontane Biodiversity Hotspot. Geographically, the Ethiopian Highlands are bisected by the Rift Valley, and further fragmented by valleys and gorges, and comprise the highest concentration of elevated ground in Africa. Earlier taxonomic studies were mainly based on morphological and ecological studies, making it difficult to identify most species in museum collections or during field work. In addition, limited sampling from the geographic areas of each species made it difficult to make good estimates of the ranges of species, and to prioritize them for conservation.
The main objectives of this study are, using Leptopelis and Ptychadena as model taxa, 1) to explore the diversity and phylogeography of some amphibians in the Ethiopian Highlands and parts of the Rift Valley; 2) to preliminarily explain the geo-climatic events that are associated with the evolutionary history of these taxa; and 3) to re-evaluate the conservation status of species and their habitats by associating phylogenetic, biogeographic and ecological information. We tested hypotheses pertaining to correspondence of traditional morphological taxonomy versus molecular phylogeny, biogeographic distinctness of distribution patterns, evolutionary history of diversification, and evaluation of conservation status of species and populations in the highlands.
The field sampling conducted between 2006 and 2010 from several localities across and within the Ethiopian Rift Valley was substantial, but not enough, to fully assess the phylogeography of the above genera. This assessment, conducted for the first time for Ethiopian Leptopelis and Ptychadena, was done using partial mitochondrial DNA sequences of the 12S and 16S genes. Estimation of phylogenetic relationships and divergence times was made using Maximum Likelihood and Maximum Parsimony methods. Morphological observations were made on fresh collections, holotypes and non-type museum materials. Biogeographic patterns were assessed using geographic distribution data. Geographic and spatial data were combined with new phylogenetic groupings to assess geographic ranges and habitat status of populations and species. We followed a new approach of ‘elevation-based’ extent of occurrence (instead of the simple polygons applied in the IUCN Red List maps) to estimate geographic ranges. Results were compared and evaluated with previous reports and online database.
Despite the wide taxonomic variation between the studied genera (Leptopelis and Ptychaena), we found similarities in some of their major taxonomic problems, as well as evolutionary, biogeographic and conservation aspects. The similarities are in: overlaps in many morphological characters (conservatism) among different species; misleading variation in some physical features within a population/species (homoplasy); monophyly of highland endemic species; cryptic phylo-groups embedded within known clades; relatively low genetic distance between species and recent evolutionary divergence times; habitat status and threats for survival of populations.
In both genera, the reconstructed phylogenetic relationships showed that the highland endemic species form well-supported monophyletic groups: the ‘Ethiopian Highland Leptopelis species group’, and the ‘Ptychadena cooperi species group’. Cryptic diversity of highland endemics was revealed, highlighting the possibility of having six candidate species (at least two Leptopelis and four Ptychadena) awaiting description. Two presumed lowland endemic species of Ptychadena (P. filwoha and P. harenna) were genetically found to be conspecific with other widely distributed (non-endemic) lowland species (P. mascareniensis and P. anchietae, respectively).
Wide overlaps in several morphological features made identification of some closely related species populations difficult. New diagnostic features were identified to characterize some of the most difficult groups (e.g., presence of spicules in males of P. neumanni contrasted with absence in P. erlangeri or P. nana).
As compared with some other African species for which molecular data are available, relatively small evolutionary distances were found among the highland species within each genus, explained by a possibly very recent radiation as estimated in the corresponding divergence times. Diversification of the highland endemics was probably associated with formation of the Ethiopian Highlands by volcanic activities and uplifting, and accompanying climatic changes between 30 and 6 Mya.
We observed congruence of phylogenetic groups with clear patterns of geographic distribution, allowing us to identify distinct biogeographic categories that can potentially serve as units for conservation of Ethiopian amphibians. The Rift Valley and major river gorges appear important horizontal barriers delimiting geographic ranges of most species. There is no considerable vertical (altitudinal) segregation of the highland populations in the two genera.
The highland Leptopelis and Ptychadena comprise more diverse endemic species (16) than known before (10), contributing substantially to the biodiversity value of the Ethiopian Highlands. While range extension is revealed for some species in the current study, there is unfortunately a substantial reduction for others from what has been proposed previously. Land cover data and our field observation of many parts of the country for about two decades indicate that large parts of the suitable highland habitats for most species of Leptopelis and Ptychadena are severely degraded and fragmented by human activities. Lakes are drying, levels of rivers are decreasing, and the wooded and grassland vegetation of the highlands and the Rift Valley is being lost. Our revised assessment of populations showed that nine of the 16 studied species appear to be threatened at different levels. This implies an urgent need for revision of existing conservation status of these taxa to protect them in rapidly changing environments. Further work is needed in the areas of phylogeography, taxonomy, and natural history of populations and species in areas that are not covered in this study
Constant approximation for virtual backbone construction with guaranteed routing cost in wireless sensor networks
No full textEconomic potential of the P.R. Spring oil-impregnated deposit, Uinta Basin, Utah
No full textreportThe P.R. Spring oil-impregnated sandstone (tar sand) deposit is located in the southeastern portion of the Uinta Basin, approximately 50 miles northwest of Grand Junction, Colorado. These oil impregnated sandstones are in the Eocene Green River Formation and five zones have been identified. These zones consist of one or more lenticular beds of lacustrine sandstone, separated by intervals of barren lithologies. The degree of impregnation of individual beds within the five zones is controlled by the lateral extent of the bed, its porosity and permeability, and the distance the oil has migrated within the bed. The degree of saturation varies both laterally and vertically. The purpose of this report was to 1) determine the total hydrocarbon content of each zone in blocks of 640 acres or less, and 2) relate this data to current economic and mining feasibility. This study incorporates the results of 38 measured sections and 26 core holes. The oil extracted from the P.R. Spring tar sands is a naturally occurring, brown to black, highly viscous or solid mixture of hydrocarbons. Its composition indicates that the oil was formed in situ or migrated only a short distance. The author has calculated the total barrels of oil in place for the deposit to be approximately 3.3 billion barrels. This is less than other published calculations of 3.7 and 4.0 to 4.5 billion barrels (Byrd, 1967; Ritzma, 1974). Problems associated with the method of economic recovery of the oil remain to be solved. Only the southeastern corner of the field is strip rninable. Other areas will probably have to be exploited by in situ recovery methods and several are being tested. The only known active operation in P.R. Spring is by Bighorn Oil, located in the southeastern part of the deposit. Their operation consists of an open-pit mine and a 200-barrel-per-day extraction plant utilizing a solvent solution process. Surface water availability in the area is limited, but may be sufficient if storage, reuse and ground-water potential are considered. Oil extraction will require a fuel supply, possibly from generated coke and other byproduct fuels generated by the tar refining process or by local natural gas or coal production. Further work is needed in the area, specifically more core holes and associated analyses. Strategic drilling in T. 11 S., R. 22 and 24 E., and T. 12 S., R. 22 E., could be used to verify assumed saturation
Obivius Nationale Relatietest: Bachelor Eindverslag
No full textBachelor Eindverslag (MKT) over het bouwen van een web-applicatie t.b.v. Nescio's Hermitage bv, onder begeleiding van Peter van NieuwenhuizenMKTMediamaticsElectrical Engineering, Mathematics and Computer Scienc
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