7,423 research outputs found
Single spin asymmetry for the Drell-Yan process
We calculated the single spin asymmetries for the reaction
in the framework of twist-3 QCD for
HERA energies. The necessary imaginary phase is produced by the on-shell
contribution of the quark propagator, while the long distance part is analogous
to that providing the direct photon asymmetry calculated by J. Qiu and G.
Sterman. The asymmetry turns out to be generally of the order percent.Comment: 7 pages, 4 figures, LaTe
Magnetic anisotropies and magnetization reversal of the CoCrFeAl Heusler compound
Magnetic anisotropies and magnetization reversal properties of the epitaxial
Heusler compound CoCrFeAl (CCFA) deposited on Fe and Cr
buffer layers are studied. Both samples exhibit a growth-induced fourfold
anisotropy, and magnetization reversal occurs through the formation of stripy
domains or 90 degree domains. During rotational magnetometric scans the sample
deposited on Cr exhibits about 2 degree sharp peaks in the angular dependence
of the coercive field, which are oriented along the hard axis directions. These
peaks are a consequence of the specific domain structure appearing in this
particular measurement geometry. A corresponding feature in the sample
deposited on Fe is not observed.Comment: 11 pages, 7 figure
Light structures phototroph, bacterial and fungal communities at the soil surface
The upper few millimeters of soil harbour photosynthetic microbial communities that are structurally distinct from those of underlying bulk soil due to the presence of light. Previous studies in arid zones have demonstrated functional importance of these communities in reducing soil erosion, and enhancing carbon and nitrogen fixation. Despite being widely distributed, comparative understanding of the biodiversity of the soil surface and underlying soil is lacking, particularly in temperate zones. We investigated the establishment of soil surface communities on pasture soil in microcosms exposed to light or dark conditions, focusing on changes in phototroph, bacterial and fungal communities at the soil surface (0–3 mm) and bulk soil (3–12 mm) using ribosomal marker gene analyses. Microbial community structure changed with time and structurally similar phototrophic communities were found at the soil surface and in bulk soil in the light exposed microcosms suggesting that light can influence phototroph community structure even in the underlying bulk soil. 454 pyrosequencing showed a significant selection for diazotrophic cyanobacteria such as Nostoc punctiforme and Anabaena spp., in addition to the green alga Scenedesmus obliquus. The soil surface also harboured distinct heterotrophic bacterial and fungal communities in the presence of light, in particular, the selection for the phylum Firmicutes. However, these light driven changes in bacterial community structure did not extend to the underlying soil suggesting a discrete zone of influence, analogous to the rhizosphere
Ray-tracing in pseudo-complex General Relativity
Motivated by possible observations of the black hole candidate in the center
of our galaxy and the galaxy M87, ray-tracing methods are applied to both
standard General Relativity (GR) and a recently proposed extension, the
pseudo-complex General Relativity (pc-GR). The correction terms due to the
investigated pc-GR model lead to slower orbital motions close to massive
objects. Also the concept of an innermost stable circular orbit (ISCO) is
modified for the pc-GR model, allowing particles to get closer to the central
object for most values of the spin parameter than in GR. Thus, the
accretion disk, surrounding a massive object, is brighter in pc-GR than in GR.
Iron K emission line profiles are also calculated as those are good
observables for regions of strong gravity. Differences between the two theories
are pointed out.Comment: revised versio
Experimental tests of pseudo-complex General Relativity
Based on previous publications exploring pseudo-complex General Relativity
(pc-GR) we present a selection of observable consequences of pc-GR and possible
ways to experimentally access them. Whenever possible we compare the results to
Einstein's GR and differences are worked out in detail. We propose experimental
tests to check the predictions of pc-GR for the orbital frequency of test
particles, the gravitational redshift effect and the last stable orbit. We will
show that the orbital frequency of test particles at a given radius in pc-GR is
in general lower compared to standard GR. Also the effect of frame dragging is
modified (weakened) in pc-GR. Concerning the gravitational redshift of a
radiation emitting object we find that it is also lower in pc-GR than in
standard GR. Eventually the classical concept of a last stable orbit has to be
modified in pc-GR.Comment: submitted for publication to the Monthly Notices of the Royal
Astronomical Societ
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