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Gregori G Ravasio A Murphy CD Schaar K Baird A Bell AR Benuzzi-Mounaix A Bingham R Constantin C Drake RP Edwards M Everson ET Gregory CD Kuramitsu Y Lau W Mithen J Niemann C Park HS Remington BA Reville B Robinson AP Ryutov DD Sakawa Y Yang S Woolsey NC Koenig M Miniati F 《Nature》2012,481(7382):480-483
The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations. Although other mechanisms may also operate, currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about 10(-21)?gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations, astrophysical environments can effectively be reproduced in the laboratory. Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields sufficiently to affect galaxy evolution. 相似文献
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The consumption of cruciferous vegetables has long been associated with a reduced risk in the occurrence of cancer at various
sites, including the prostate, lung, breast and colon. This protective effect is attributed to isothiocyanates present in
these vegetables, and sulforaphane (SF), present in broccoli, is by far the most extensively studied to uncover the mechanisms
behind this chemoprotection. The major mechanism by which SF protects cells was traditionally thought to be through Nrf2-mediated
induction of phase 2 detoxification enzymes that elevate cell defense against oxidative damage and promote the removal of
carcinogens. However, it is becoming clear that there are multiple mechanisms activated in response to SF, including suppression
of cytochrome P450 enzymes, induction of apoptotic pathways, suppression of cell cycle progression, inhibition of angiogenesis
and anti-inflammatory activity. Moreover, these mechanisms seem to have some degree of interaction to synergistically afford
chemoprevention.
Received: 10 November 2006; received after revision 15 January 2007; accepted 5 February 2007 相似文献
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