280 research outputs found

    Assessment of the environmental condition, Ecosystem service provision and sustainability of use of two wetlands in the Kamiesberg uplands:

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    This report is one of the outputs of the Wetland Health and Importance (WHI) research programme which was funded by the Water Research Commission. The WHI represents Phase II of the National Wetlands Research Programme and was formerly known as “Wetland Health and Integrity”. Phase I, under the leadership of Professor Ellery, resulted in the “WET-Management” series of publications. Phase II, the WHI programme, was broadly aimed at assessing wetland environmental condition and socio-economic importance

    IGR J19552+0044: A new asynchronous short period polar: "Filling the gap between intermediate and ordinary polars"

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    Based on XMM--Newton X-ray observations IGR J19552+0044 appears to be either a pre-polar or an asynchronous polar. We conducted follow-up optical observations to identify the sources and periods of variability precisely and to classify this X-ray source correctly. Extensive multicolor photometric and medium- to high-resolution spectroscopy observations were performed and period search codes were applied to sort out the complex variability of the object. We found firm evidence of discording spectroscopic (81.29+/-0.01m) and photometric (83.599+/-0.002m) periods that we ascribe to the white dwarf (WD)\ spin period and binary orbital period, respectively. This confirms that IGR J19552+0044 is an asynchronous polar. Wavelength-dependent variability and its continuously changing shape point at a cyclotron emission from a magnetic WD with a relatively low magnetic field below 20 MG. The difference between the WD spin period and the binary orbital period proves that IGR J19552+0044 is a polar with the largest known degree of asynchronism (0.97 or 3%).Comment: 9 pages, 10 figures, A&A accepte

    Annual Clovers Around the World: Current Status and Future Prospects

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    This paper reviews the distribution and importance of annual clover (Trifolium) species for pasture and fodder production systems globally. Of the 158 recorded annual Trifolium species, 65.2% are endemic to the Mediterranean basin and surrounding areas, 14.6% to sub-Saharan Africa, 17.7% to the United States of America and 2.5% to Chile. Fourteen species have been commercialised, while other endemic and naturalised annual clovers are also utilised. Key species for self-regenerating pastures include T. subterraneum, T. michelianum and T. respinatum var. resupinatum, while major dual-purpose grazing and fodder species include T. incarnatum, T. vesiculosum, T. alexandrinum and T. respinatum var. majus. Less important commercial species include T. hirtum, T. squarrosum, T. nigrescens and T. cherleri. Australian scientists have also recently domesticated T. glanduliferum, T. spumosum, T. purpureum and T. dasyurum. The areas sown to annual clovers may increase in future years, due to increasing nitrogen (N) fertiliser costs, environmental concerns with N runoff. Climate change brings new challenges and opportunities for annual clovers. The forage plant genetic resource centres will be crucial for developing new adapted cultivars

    The Genetic Structure and History of Africans and African Americans.

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    Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, four African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting historical migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (approximately 71%), European (approximately 13%), and other African (approximately 8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies
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