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X-ray spectroscopy is an important tool for understanding the extreme photoionization processes that drive the behaviour of non-thermal equilibrium plasmas in compact astrophysical objects such as black holes 1-4. Even so, the distance of these objects from the Earth and the inability to control or accurately ascertain the conditions that govern their behaviour makes it difficult to interpret the origin of the features in astronomical X-ray measurements. Here, we describe an experiment that uses the implosion 5 driven by a 3 TW, 4 kJ laser system 6 to produce a 0.5 keV blackbody radiator that mimics the conditions that exist in the neighbourhood of a black hole. The X-ray spectra emitted from photoionized silicon plasmas resemble those observed from the binary stars Cygnus X-3 (refs 7, 8) and Vela X-1 (refs 9-11) with the Chandra X-ray satellite. As well as demonstrating the ability to create extreme radiation fields in a laboratory plasma, our theoretical interpretation of these laboratory spectra contrasts starkly with the generally accepted explanation for the origin of similar features in astronomical observations. Our experimental approach offers a powerful means to test and validate the computer codes used in X-ray astronomy. X-ray spectroscopy with an X-ray satellite is the main observational method to give information about compact objects, especially black holes. Black holes are indirectly studied by observing the X-ray continuum from a heated accretion disc and the X-ray fluorescence from the ambient gas of the stellar wind and the surface of a companion star in their binary systems. To derive physical properties from the observations, X-ray astronomers rely on non-local-thermodynamical-equilibrium (LTE) atomic physics in a cold ambient gas subject to an extreme radiation field, for which the mean radiation temperature is of the order of 1 keV. Theoretical models have been developed on the basis of the observed spectra 1-4 and complex computer codes were developed to analyse the observed X-ray spectra 12-16. The underlying assumption of these models is that the spectrum originates from a photoionized plasma. In other words, the intense radiation from the compact object photoionizes the gas, and generates a relatively low-electron-temperature highly ionized non-LTE plasma. However, laboratory experiments on non-LTE photoionized plasmas
An analytical model of femtosecond K(alpha) x-ray generation from laser-irradiated foils is presented. Expressions are found for the photon emission yield in both forward and backward directions in integral form as a function of hot-electron temperature and target thickness. It is found that for any given target material, there is a foil thickness and a hot-electron temperature at which the K(alpha) emission is maximized. Conversion efficiencies are consistent with contemporary measurements of K(alpha) radiation produced with femtosecond lasers.
We investigated the functional significance of plant performance (dry mass, photosynthesis) in plant defence (resistance and tolerance) against pathogen infection, and potential negative cross-resistance between herbicide resistance and plant defence against disease. We compared isonuclear triazine-herbicide-resistant (TR) and -susceptible (TS) biotypes of Senecio vulgaris, in the presence and absence of infection by the rust Puccinia lagenophorae. In a growth chamber study with two reduced irradiance levels, rust infection had a severe effect on plant performance with infected plants having 55% less dry mass and 54% reduced whole-plant photosynthesis than non-infected plants. The TR biotype was more susceptible (reduced resistance) to the pathogen, but the biotypes did not differ in their ability to compensate for rust infection (tolerance). TR plants were less productive than TS plants when grown non-shaded (ca. 10% full sunlight) but not when shaded (ca. 5% full sunlight). This is especially important for situations, where S. vulgaris grows under the crop canopy (e.g. in maize). Here, very low light levels might contribute to a numerical increase of TR relative to TS plants even when only occasionally treated with triazine. Whole-plant photosynthesis was reduced by 21% in TR plants as compared to the TS biotype, and by 59% in plants grown in the shaded as compared to the non-shaded treatment. When whole-plant photosynthesis values were corrected for the estimated leaf area of plants, we found no significant variation between biotypes, shade treatments or rust treatments. In experimental mixed TR:TS field populations, the proportion of TR plants decreased more rapidly in rust-infected populations than uninfected. This finding, together with the lower resistance in the TR than the TS biotype to the rust fungus observed in the growth chamber experiment, may indicate negative cross-resistance, which is a potential tool in the management of herbicide-resistant weeds. Published in "Basic and Applied Ecology 9(5): 577-587 , 2008" which should be cited to refer to this work. 1 http://doc.rero.ch isonukleare Triazinherbizid-resistente (TR) und -empfindliche (TS) Biotypen von Senecio vulgaris, mit und ohne Infektion durch den Rostpilz Puccinia lagenophorae. ZusammenfassungIn einer Klimakammer-Studie mit zwei reduzierten Beleuchtungsstufen hatte Rostpilzinfektion einen starken Einfluss auf die Pflanzenleistung: infizierte Pflanzen hatten 55% weniger Biomasse als nicht-infizierte Pflanzen, und eine um 54% reduzierte Gesamt-Pflanzen-Photosyntheserate. Der TR-Biotyp reagierte empfindlicher auf Pathogeninfektion (reduzierte Resistenz), aber die Biotypen unterschieden sich nicht in ihrer Fa¨higkeit, fu¨r Rostpilzinfektion zu kompensieren (Toleranz). Die TR-Pflanzen waren weniger produktiv als die TS-Pflanzen, wenn diese unbeschattet (ca. 10% volles Sonnenlicht) wuchsen, jedoch nicht, wenn sie beschattet (ca. 5% volles Sonnenlicht) waren. Dies ist von besonderer Bedeutung fu¨r Situationen, bei denen S. vulgaris unter ...
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