1,759 research outputs found
Factors Affecting Italian Ryegrass (\u3cem\u3eLolium multiflorum\u3c/em\u3e L.) Seed Distribution
Italian ryegrass (Lolium multiflorum L.) can be a productive and high-quality cool-season forage in the Southern Great Plains of the U.S.A, if it is managed to produce sufficient seed for effective reestablishment without compromising forage yield. Before the re-seeding dynamics of Italian ryegrass can be modeled an understanding of seed production, seed-shed, and seed dispersal is necessary. Here two factors affecting Italian ryegrass seed dispersal and distribution are examined – wind and cultivation practice (mowing and raking)
The Effect of Harvest Management on Forage Production and Self-Reseeding Potential of Italian Ryegrass (Lolium Multiflorum L.)
Italian ryegrass (Lolium multiflorum L.) (IRG) can be managed to produce a seed output sufficient for effective re-establishment, without compromising forage yield, it may provide an alternative to perennial cool-season grasses in the Southern Great Plains of the U.S.A. The reduction in cost of replanting and avoidance of cultivation offered by a self-seeding crop may be particularly useful in low-input production systems. We examined the effect of dates of initial harvest in spring and of partial harvests on forage yield, seed output and re-establishment of Italian ryegrass
Overseeding Unimproved Warm-Season Pasture with Cool- and Warm-Season Legumes to Enhance Forage Productivity
Overseeding forage legumes into existing warm-season pasture may help to reduce cool-season forage deficit on small and resource-limited small farms in the southern Great Plains of the United States. Unimproved warm-season grass pastures were overseeded with Korean lespedeza (Lespedeza stipulacea Maxim) were not overseeded with summer legume. These same plots were subsequently overseeded with hairy vetch (Vicia villosa Roth), crownvetch (Coronilla varia L.), black medic (Medicago lupulina L.) or ladino white clover (Trifolium repens L.) or, not overseeded with cool-season legume. Including lespedeza in a forage mixture increased total forage yield by an average of 15%, or 1700 kg ha-1 over 4 years. Overseeding with cool-season legumes provided a net benefit in total annual forage yield of 0.75 kg for each 1.0 kg of legume produced. Yield increases resulting from overseeding with hairy vetch or black medic were largely limited to the harvest season following sowing, while overseeded crownvetch or white clover provided limited short- to medium-term yield benefit. Improvement of low-productivity pasture resulting from legume introduction is likely to be slow and will require sustained management input to ensure the presence of a productive legume plant stand
Radial Color Gradients in K+A Galaxies in Distant Clusters of Galaxies
Galaxies in rich clusters with z 0.3 are observed to have a higher
fraction of photometrically blue galaxies than their nearby counterparts. This
raises the important question of what environmental effects can cause the
termination of star formation between z 0.3 and the present. The star
formation may be truncated due to ram-pressure stripping, or the gas in the
disk may be depleted by an episode of star formation caused by some external
perturbation. To help resolve this issue, surface photometry was carried out
for a total of 70 early-type galaxies in the cluster Cl1358+62, at z
0.33, using two-color images from the Hubble Archive. The galaxies were divided
into two categories based on spectroscopic criteria: 24 are type K+A (e.g.,
strong Balmer lines, with no visible emission lines), while the remaining 46
are in the control sample with normal spectra. Radial color profiles were
produced to see if the K+A galaxies show bluer nuclei in relation to their
surrounding disks. Specifically, a linear gradient was fit to the radial color
profile of each galaxy. We find that the K+A galaxies on average tend to have
slightly bluer gradients towards the center than the normals. A
Kolmogorov-Smirnov two-sample test has been applied to the two sets of color
gradients. The result of the test indicates that there is only a 2%
probability that the K+A and normal samples are drawn from the same parent
distribution. There is a possible complication from a trend in the apparent
magnitude vs. color gradient relation, but overall our results favor the
centralized star formation scenario as an important process in the evolution of
galaxies in dense clusters.Comment: 16 pages, 12 figures, accepted for publication in A
Evolution of level density step structures from 56,57-Fe to 96,97-Mo
Level densities have been extracted from primary gamma spectra for 56,57-Fe
and 96,97-Mo nuclei using (3-He,alpha gamma) and (3-He,3-He') reactions on
57-Fe and 97-Mo targets. The level density curves reveal step structures above
the pairing gap due to the breaking of nucleon Cooper pairs. The location of
the step structures in energy and their shapes arise from the interplay between
single-particle energies and seniority-conserving and seniority-non-conserving
interactions.Comment: 9 pages, including 5 figure
Critical Behavior of the Meissner Transition in the Lattice London Superconductor
We carry out Monte Carlo simulations of the three dimensional (3D) lattice
London superconductor in zero applied magnetic field, making a detailed finite
size scaling analysis of the Meissner transition. We find that the magnetic
penetration length \lambda, and the correlation length \xi, scale as \lambda ~
\xi ~ |t|^{-\nu}, with \nu = 0.66 \pm 0.03, consistent with ordinary 3D XY
universality, \nu_XY ~ 2/3. Our results confirm the anomalous scaling dimension
of magnetic field correlations at T_c.Comment: 4 pages, 5 ps figure
A vortex description of the first-order phase transition in type-I superconductors
Using both analytical arguments and detailed numerical evidence we show that
the first order transition in the type-I 2D Abelian Higgs model can be
understood in terms of the statistical mechanics of vortices, which behave in
this regime as an ensemble of attractive particles. The well-known
instabilities of such ensembles are shown to be connected to the process of
phase nucleation. By characterizing the equation of state for the vortex
ensemble we show that the temperature for the onset of a clustering instability
is in qualitative agreement with the critical temperature. Below this point the
vortex ensemble collapses to a single cluster, which is a non-extensive phase,
and disappears in the absence of net topological charge. The vortex description
provides a detailed mechanism for the first order transition, which applies at
arbitrarily weak type-I and is gauge invariant unlike the usual field-theoretic
considerations, which rely on asymptotically large gauge coupling.Comment: 4 pages, 6 figures, uses RevTex. Additional references added, some
small corrections to the tex
Greenland ice sheet annual motion insensitive to spatial variations in subglacial hydraulic structure
We present ice velocities observed with global positioning systems and TerraSAR-X/TanDEM-Xin a land-terminating region of the southwest Greenland ice sheet (GrIS) during the melt year 2012–2013, toexamine the spatial pattern of seasonal and annual ice motion. We find that while spatial variability in theconfiguration of the subglacial drainage system controls ice motion at short timescales, this configurationhas negligible impact on the spatial pattern of the proportion of annual motion which occurs duringsummer. While absolute annual velocities vary substantially, the proportional contribution of summermotion to annual motion does not. These observations suggest that in land-terminating margins of the GrIS,subglacial hydrology does not significantly influence spatial variations in net summer speedup.Furthermore, our findings imply that not every feature of the subglacial drainage system needs to beresolved in ice sheet models
Staggered fermions and chiral symmetry breaking in transverse lattice regulated QED
Staggered fermions are constructed for the transverse lattice regularization
scheme. The weak perturbation theory of transverse lattice non-compact QED is
developed in light-cone gauge, and we argue that for fixed lattice spacing this
theory is ultraviolet finite, order by order in perturbation theory. However,
by calculating the anomalous scaling dimension of the link fields, we find that
the interaction Hamiltonian becomes non-renormalizable for ,
where is the bare (lattice) QED coupling constant. We conjecture that
this is the critical point of the chiral symmetry breaking phase transition in
QED. Non-perturbative chiral symmetry breaking is then studied in the strong
coupling limit. The discrete remnant of chiral symmetry that remains on the
lattice is spontaneously broken, and the ground state to lowest order in the
strong coupling expansion corresponds to the classical ground state of the
two-dimensional spin one-half Heisenberg antiferromagnet.Comment: 30 pages, UFIFT-HEP-92-1
Ethane steam reforming over a platinum/alumina catalyst: effect of sulphur poisoning
In this study we have examined the adsorption of hydrogen sulfide and methanethiol over platinum catalysts and examined the effect of these poisons on the steam reforming of ethane. Adsorption of hydrogen sulfide was measured at 293 and 873 K. At 873 K the adsorbed state of hydrogen sulfide in the presence of hydrogen was SH rather than S, even though the Pt:S ratio was unity. The effect of 11.2 ppm hydrogen sulfide or methanethiol on the steam reforming of ethane was studied at 873 K and 20 barg. Both poisons deactivated the catalyst over a number of hours, but methanethiol was found to be more deleterious, reducing the conversion by almost an order of magnitude, possibly due to the co-deposition of sulfur and carbon. Changes in the selectivity revealed that the effect of sulfur was not uniform on the reactions occurring, with the production of methane reduced proportionally more than the other products, due to the surface sensitivity of the hydrogenolysis and methanation reactions. The water-gas shift reaction was affected to a lesser extent. No regeneration was observed when hydrogen sulfide was removed from the feedstream in agreement with adsorption studies. A slight regeneration was observed when methanethiol was removed from the feed, but this was believed to be due to the removal of carbon rather than sulfur. The overall effect of sulfur poisoning was to reduce activity and enhance hydrogen selectivity
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