4,401 research outputs found
Results from the arable crop rotation study at Oak Park 2000 - 2007
An organic rotation trial was established at Oak Park in 2000. The crop sequence in the seven year rotation was: two years grass-clover, winter wheat, potatoes, winter oats, lupins and spring barley. The grass-clover, which supplies nitrogen to the system, also provides vegetation which of late is cut and mixed with cereal straw to produce compost. The compost replaced sheep manure which was available up to 2007. Manure was applied to potato plots prior to cultivation for the period 2002 to 2007 and to barley plots from 2005 to 2007. The average yield of crops over the period of the rotation was: winter wheat 5.9 t/ha, potatoes 32.7 t/ha, winter oats 5.8 t/ha, lupins 2.4 t/ha and spring barley 4.5 t/ha. Triticale, which was grown in one of the plots designated for winter wheat, had an average yield of 7.5 t/ha. Lupins have been unsatisfactory due to uncompetitiveness with weeds and lateness of maturity
H I observations of the peculiar galaxy NGC 660
The authors present observations of H I emission from the peculiar galaxy NGC 660. H I was detected in the companion galaxy UGC 01195 as well. Sixteen hours of observations were obtained with the VLA telescope of the National Radio Astronomy Observatory during December 1986 and March 1987
Reconciling magnetoelectric response and time-reversal symmetry in non-magnetic topological insulators
A delicate tension complicates the relationship between the topological
magnetoelectric effect in three-dimensional topological
insulators (TIs) and time-reversal symmetry (TRS). TRS underlies a particular
topological classification of the electronic ground state of a
bulk insulator and the associated quantization of the magnetoelectric
coefficient calculated using linear response theory, but according to standard
symmetry arguments simultaneously forbids any physically meaningful
magnetoelectric response. This tension between theories of magnetoelectric
response in bulk and finite-sized materials originates from the distinct
approaches required to introduce notions of polarization and orbital
magnetization in those fundamentally different environments. In this work we
argue for a modified interpretation of the bulk linear response calculations in
non-magnetic TIs that is more plainly consistent with TRS, and use this
interpretation to discuss the effect's observation - still absent over a decade
after its prediction. Our analysis is reinforced by microscopic bulk and thin
film calculations carried out using a simplified but still realistic model for
the well established VVI (V (Sb,Bi) and VI (Se,Te)) family of
non-magnetic TIs. We conclude that the topological
magnetoelectric effect in non-magnetic TIs is activated by
magnetic surface dopants, and that the charge density response to magnetic
fields and the orbital magnetization response to electric fields in a given
sample are controlled in part by the configuration of those dopants.Comment: 30 pages, 5 figure
- …