Dedekinds „Bunte Bemerkungen“ zu Kroneckers „Grundzüge“

Ohne Zusammenfassung Vorgelegt von M. Kline The work of H. Edwards was supported by part by the U. S. National Science Foundation Grant SOC-7905162 and by the Vaughn Foundation.     

Early human occupation of the Red Sea coast of Eritrea during the last interglacial

The geographical origin of modern humans is the subject of ongoing scientific debate. The 'multiregional evolution' hypothesis argues that modern humans evolved semi-independently in Europe, Asia and Africa between 100,000 and 40,000 years ago, whereas the 'out of Africa' hypothesis contends that modern humans evolved in Africa between 200 and 100 kyr ago, migrating to Eurasia at some later time. Direct palaeontological, archaeological and biological evidence is necessary to resolve this debate. Here we report the discovery of early Middle Stone Age artefacts in an emerged reef terrace on the Red Sea coast of Eritrea, which we date to the last interglacial (about 125 kyr ago) using U-Th mass spectrometry techniques on fossil corals. The geological setting of these artefacts shows that early humans occupied coastal areas and exploited near-shore marine food resources in East Africa by this time. Together with similar, tentatively dated discoveries from South Africa this is the earliest well-dated evidence for human adaptation to a coastal marine environment, heralding an expansion in the range and complexity of human behaviour from one end of Africa to the other. This new, wide-spread adaptive strategy may, in part, signal the onset of modern human behaviour, which supports an African origin for modern humans by 125 kyr ago.     

A novel cancer therapy using a M?ssbauer-isotope compound

Cancer radiotherapy uses high doses of ionizing radiation (1-10(2) Gy; 10(2)-10(4) rad) because only a small fraction of the absorbed dose leads to lethal double-strand breaks in DNA. These breaks are more efficiently produced by Auger electrons (1-10 eV nm-1) generated in proximity to the DNA. The energy of these electrons (on average 21 electrons for the decay of 125I) is dissipated within 10-100 nm of the Auger event and produces multiple double-strand DNA breaks. A single Auger event can be lethal to a cell and is comparable to more than 10(5) photon absorption events in conventional radiotherapy. We now report that 57Fe(III).bleomycin, administered to malignant cells in vitro and in vivo and irradiated with resonant M?ssbauer gamma rays (14.4 keV), causes ablation of the malignant cells, presumably by Auger cascade, with extremely small radiation doses--about 10(-5) Gy. As a basis for comparison, about 5 Gy is necessary to achieve a similar effect with conventional radiotherapy.     

The detection of carbonation by the Drosophila gustatory system

There are five known taste modalities in humans: sweet, bitter, sour, salty and umami (the taste of monosodium glutamate). Although the fruitfly Drosophila melanogaster tastes sugars, salts and noxious chemicals, the nature and number of taste modalities in this organism is not clear. Previous studies have identified one taste cell population marked by the gustatory receptor gene Gr5a that detects sugars, and a second population marked by Gr66a that detects bitter compounds. Here we identify a novel taste modality in this insect: the taste of carbonated water. We use a combination of anatomical, calcium imaging and behavioural approaches to identify a population of taste neurons that detects CO2 and mediates taste acceptance behaviour. The taste of carbonation may allow Drosophila to detect and obtain nutrients from growing microorganisms. Whereas CO2 detection by the olfactory system mediates avoidance, CO2 detection by the gustatory system mediates acceptance behaviour, demonstrating that the context of CO2 determines appropriate behaviour. This work opens up the possibility that the taste of carbonation may also exist in other organisms.     

An arid-adapted middle Pleistocene vertebrate fauna from south-central Australia

How well the ecology, zoogeography and evolution of modern biotas is understood depends substantially on knowledge of the Pleistocene. Australia has one of the most distinctive, but least understood, Pleistocene faunas. Records from the western half of the continent are especially rare. Here we report on a diverse and exceptionally well preserved middle Pleistocene vertebrate assemblage from caves beneath the arid, treeless Nullarbor plain of south-central Australia. Many taxa are represented by whole skeletons, which together serve as a template for identifying fragmentary, hitherto indeterminate, remains collected previously from Pleistocene sites across southern Australia. A remarkable eight of the 23 Nullarbor kangaroos are new, including two tree-kangaroos. The diverse herbivore assemblage implies substantially greater floristic diversity than that of the modern shrub steppe, but all other faunal and stable-isotope data indicate that the climate was very similar to today. Because the 21 Nullarbor species that did not survive the Pleistocene were well adapted to dry conditions, climate change (specifically, increased aridity) is unlikely to have been significant in their extinction.     

Stream denitrification across biomes and its response to anthropogenic nitrate loading

Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated, causing more bioavailable nitrogen to enter groundwater and surface waters. Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins, indicating that substantial sinks for nitrogen must exist in the landscape. Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favour microbial denitrification. Here we present data from nitrogen stable isotope tracer experiments across 72 streams and 8 regions representing several biomes. We show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of in-stream nitrate that is removed from transport. Our data suggest that the total uptake of nitrate is related to ecosystem photosynthesis and that denitrification is related to ecosystem respiration. In addition, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks.     

载畜率对短花针茅荒漠草原土壤物理特性的影响

放牧对土壤物理特性的影响至关重要.为了研究放牧对土壤物理特性的影响,在内蒙古荒漠草原上开展了不同绵羊载畜率放牧试验.试验采取完全随机区组设计,设置4个不同载畜率处理,3次重复.4个处理分别是对照(CK)、轻度放牧(LG)、中度放牧(MG)和重度放牧(HG),相应的载畜率分别是0,0.15,0.30和0.45只羊/(公顷·月).放牧时间为每年6月-11月.从2004年到2006年的放牧期间,每月测定一次土壤含水量和土壤容重,土壤紧实度和机械组成每年秋季测定一次.通过对测定数据的分析表明,土壤表层(0-10cm)的含水量从对照到轻度放牧显著(p＜0.05)增加,然后随着载畜率的增大明显(p＜0.05)降低.土壤容重在不同载畜率条件下没有明显变化(p＞0.05),但土壤紧实度随载畜率的增加显著(p＜0.05)增大.中度和重度放牧显著降低了土壤黏粒的含量(p＜0.05).重度放牧加快了草地土壤水分的损失,进而增加了土壤的紧实度,使草地土壤发生退化.载畜率和土壤水分是影响荒漠草原可持续管理的关键因子,轻度载畜率是实现草地的可持续发展的最适宜载畜率.