599 research outputs found
Nitrogen-fixation technology for increased agricultural sustainability
Non-Peer ReviewedThe advent of the world energy crisis in 1973 aroused interest in the potential of nitrogen-fixation for increasing agricultural production. Since then, sustainable agriculture has become the focus of attention. Sustainable agriculture involves design and management of procedures which work with natural processes to conserve resources, and minimize waste and environmental damage, while maintaining farm profitability. As agriculture moves towards greater sustainability, the potential role of nitrogen-fixation processes increases. As a result, the agronomic significance of nitrogen-fixation has generated renewed scientific excitement in this area of microbial-plant interaction. A number of significant advances in applied nitrogen-fixation technology have been made: improved rhizobial delivery systems, increased nitrogen-fixation capacities, greater yield and improved quality of legumes, and better definition of the role of nitrogen-fixation in N cycling. Shifts in agricultural sustainability that involve these improved nitrogen-fixation technologies require continued research efforts to assess the levels of resource conservation, impacts on the environment and the economic consequences
Single vortices observed as they enter NbSe
We observe single vortices as they penetrate the edge of a superconductor
using a high-sensitivity magneto-optical microscope. The vortices leap across a
gap near the edge, a distance that decreases with increasing applied field and
sample thickness. This behaviour can be explained by the combined effect of the
geometrical barrier and bulk pinning.Comment: 2 pages, 1 figure, M2S-Rio proceeding
Onset of transcription of the aminopeptidase N (leukemia antigen CD 13) gene at the crypt/villus transition zone during rabbit enterocyte differentiation
AbstractThe sequence of a cDNA clone (2.82 kbp) of rabbit intestinal aminopeptidase N (CD 13) is reported. Using the corresponding anti-sense RNA probe, the distribution of aminopeptidase N mRNA along the crypt/villus axis of the rabbit small intestine was studied by in situ hybridization. The aminopeptidase N gene is expressed along the whole length of the villus with a maximum at its base. Expression was not detected in the crypt cells. The distribution of aminopeptidase N mRNA correlates with the presence of active enzyme as monitored by histochemical staining. The results are compatible with onset of transcription of the aminopeptidase N gene at the crypt/villus transition zone during the enterocyte differentiation
Onset of transcription of the aminopeptidase N (leukemia antigen CD 13) gene at the crypt/villus transition zone during rabbit enterocyte differentiation
AbstractThe sequence of a cDNA clone (2.82 kbp) of rabbit intestinal aminopeptidase N (CD 13) is reported. Using the corresponding anti-sense RNA probe, the distribution of aminopeptidase N mRNA along the crypt/villus axis of the rabbit small intestine was studied by in situ hybridization. The aminopeptidase N gene is expressed along the whole length of the villus with a maximum at its base. Expression was not detected in the crypt cells. The distribution of aminopeptidase N mRNA correlates with the presence of active enzyme as monitored by histochemical staining. The results are compatible with onset of transcription of the aminopeptidase N gene at the crypt/villus transition zone during the enterocyte differentiation
Geometric K-Homology of Flat D-Branes
We use the Baum-Douglas construction of K-homology to explicitly describe
various aspects of D-branes in Type II superstring theory in the absence of
background supergravity form fields. We rigorously derive various stability
criteria for states of D-branes and show how standard bound state constructions
are naturally realized directly in terms of topological K-cycles. We formulate
the mechanism of flux stabilization in terms of the K-homology of non-trivial
fibre bundles. Along the way we derive a number of new mathematical results in
topological K-homology of independent interest.Comment: 45 pages; v2: References added; v3: Some substantial revision and
corrections, main results unchanged but presentation improved, references
added; to be published in Communications in Mathematical Physic
Two-pronged kill mechanism at the end-Triassic mass extinction
High-resolution biomarker and compound-specific isotope distributions coupled with the degradation of calcareous fossil remnants reveal that intensive euxinia and decalcification (acidification) driven by Central Atlantic magmatic province (CAMP) activity formed a twopronged kill mechanism at the end-Triassic mass extinction. In a newly proposed extinction interval for the basal Blue Lias Formation (Bristol Channel Basin, UK), biomarker distributions reveal an episode of persistent photic zone euxinia (PZE) that extended further upward into the surface waters. In the same interval, shelly taxa almost completely disappear. Beginning in the basal paper shales of the Blue Lias Formation, a Lilliput assemblage is preserved consisting of only rare calcitic oysters (Liostrea) and ghost fossils of decalcified aragonitic bivalves. The stressors of PZE and decalcification parsimoniously explain the extinction event and inform possible combined causes of other biotic crises linked to emplacement of large igneous provinces, notably the end-Permian mass extinction, when PZE occurred on a broad and perhaps global scal
Atom gratings produced by large angle atom beam splitters
An asymptotic theory of atom scattering by large amplitude periodic
potentials is developed in the Raman-Nath approximation. The atom grating
profile arising after scattering is evaluated in the Fresnel zone for
triangular, sinusoidal, magneto-optical, and bichromatic field potentials. It
is shown that, owing to the scattering in these potentials, two
\QTR{em}{groups} of momentum states are produced rather than two distinct
momentum components. The corresponding spatial density profile is calculated
and found to differ significantly from a pure sinusoid.Comment: 16 pages, 7 figure
Atom-optics hologram in the time domain
The temporal evolution of an atomic wave packet interacting with object and
reference electromagnetic waves is investigated beyond the weak perturbation of
the initial state. It is shown that the diffraction of an ultracold atomic beam
by the inhomogeneous laser field can be interpreted as if the beam passes
through a three-dimensional hologram, whose thickness is proportional to the
interaction time. It is found that the diffraction efficiency of such a
hologram may reach 100% and is determined by the duration of laser pulses. On
this basis a method for reconstruction of the object image with matter waves is
offered.Comment: RevTeX, 13 pages, 8 figures; minor grammatical change
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