Difference between heartwood and sapwood
Forest Products Laboratory (U.S.)
1919
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88,386 records were found.
Collimated relativistic outflows-also known as jets-are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for gamma-ray bursts. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downs...
A c. 5500 year record of peatland development and vegetation change was generated from a core recovered from an Agrostis magellanica peat bog on subantarctic Marion Island, using palynomorph, plant macrofossil, and tephra analyses. Two tephra horizons (both 17 cm thick) were identified and dated to ca. 2900 cal. BP and ca. 1700 cal. BP. Succession of the vegetation as a consequence of tephra deposition, particularly by the pioneer Azorella selago, appears to have been very slow, lasting as long as c. 700 yr. The slow pace of vegetation succession highlights the sensitivity of the indigenous Marion Island flora to environmental change, and the vulnerability to
the spread of alien invasive species.
