3,357 research outputs found
A study of local approximation for polarization potentials
We discuss the derivation of an equivalent \textit{l}-independent
polarization potential for use in the optical Schr\"{o}dinger equation that
describes the elastic scattering of heavy ions. Three diffferent methods are
used for this purpose. Application of our theory to the low energy scattering
of the halo nucleus Li from a C target is made. It is found that
the notion of \textit{l}-independent polarization potential has some validity
but can not be a good substitute for the \textit{l}-dependent local equivalent
Feshbach polarization potential.Comment: 8 pages, 4 figure
Large Scale Flows from Orion-South
Multiple optical outflows are known to exist in the vicinity of the active
star formation region called Orion-South (Orion-S). We have mapped the velocity
of low ionization features in the brightest part of the Orion Nebula, including
Orion-S, and imaged the entire nebula with the Hubble Space Telescope. These
new data, combined with recent high resolution radio maps of outflows from the
Orion-S region, allow us to trace the origin of the optical outflows. It is
confirmed that HH 625 arises from the blueshifted lobe of the CO outflow from
136-359 in Orion-S while it is likely that HH 507 arises from the blueshifted
lobe of the SiO outflow from the nearby source 135-356. It is likely that
redshifted lobes are deflected within the photon dominated region behind the
optical nebula. This leads to a possible identification of a new large shock to
the southwest from Orion-S as being driven by the redshifted CO outflow arising
from 137-408. The distant object HH 400 is seen to have two even further
components and these all are probably linked to either HH 203, HH 204, or HH
528. Distant shocks on the west side of the nebula may be related to HH 269.
The sources of multiple bright blueshifted Herbig-Haro objects (HH 202, HH 203,
HH 204, HH 269, HH 528) remain unidentified, in spite of earlier claimed
identifications. Some of this lack of identification may arise from the fact
that deflection in radial velocity can also produce a change in direction in
the plane of the sky. The best way to resolve this open question is through
improved tangential velocities of low ionization features arising where the
outflows first break out into the ionized nebula.Comment: Astronomical Journal, in press. Some figures are shown at reduced
resolution. A full-resolution version is available at
http://ifront.org/wiki/Orion_South_Outflows_Pape
Interplay of static and dynamic effects in 6He+ 238U Fusion
We investigate the influence of the neutron halo and the breakup channel in
6He + 238U fusion at near-barrier energies. To include static effects of the
2n-halo in 6He nuclei, we use a single-folding potential obtained from an
appropriate nucleon-238U interaction and a realistic 6He density. Dynamical
effects arising from the breakup process are then included through
coupled-channel calculations. These calculations suggest that static effects
dominate the cross section at energies above the Coulomb barrier, while the
sub-barrier fusion cross section appears to be determined by coupling to the
breakup channel. This last conclusion is uncertain due to the procedure
employed to measure the fusion cross-section.Comment: 13 pages, 4 figure
Fine Scale Temperature Fluctuations in the the Orion Nebula and the t^2 Problem
We present a high spatial resolution map of the columnar electron temperature
(Tc) of a region to the south west of the Trapezium in the Orion Nebula. This
map was derived from Hubble Space Telescope images that isolated the primary
lines of HI for determination of the local extinction and of the OIII lines for
determination of Tc. Although there is no statistically significant variation
of Tc with distance from the dominant ionizing star theta1-Ori-C, we find small
scale variations in the plane of the sky down to a few arcseconds that are
compatible with the variations inferred from comparing the value of Te derived
from forbidden and recombination lines, commonly known as the t^2 problem. We
present other evidence for fine scale variations in conditions in the nebula,
these being variations in the surface brightness of the the nebula,
fluctuations in radial velocities, and ionization changes. From our Tc map and
other considerations we estimate that t^2=0.028 +-0.006 for the Orion nebula.
Shadowed regions behind clumps close to the ionization front can make a
significant contribution to the observed temperature fluctuations, but they
cannot account for the t^2 values inferred from several methods of temperature
determination. It is shown that an anomalous broadening of nebular emission
lines appears to have the same sense of correlation as the temperature
anomalies, although a causal link is not obvious.Comment: 53 pages, 13 images, many of the images have been downgraded to be
able to fit within the astro-ph file size limit
Quark Delocalization, Color Screening, and Nuclear Intermediate Range Attraction
We consider the effect of including quark delocalization and color screening,
in the nonrelativistic quark cluster model, on baryon-baryon potentials and
phase shifts. We find that the inclusion of these additional effects allows a
good qualitative description of both.Comment: 10 pages, LaTeX, 4 figures in PostScript after text, LA-UR-91-215
Use of Genuine Sources of Ergot Resistance in Species of the \u3ci\u3edilatata\u3c/i\u3e Group of \u3ci\u3ePaspalum\u3c/i\u3e
Paspalum dilatatum Poir. (dallisgrass) is an excellent C4 forage for summer production, highly productive with a wide distribution within warm-temperate regions. P. dilatatum is native to South America with special relevance for milk and meat production since its forage quality is superior to that of other C4 forage grasses and it shows tolerance to frost and water stress. In situations of temperate and warm temperate climate, the presence of these species plays a key role in the ecological stability of the system due to the complementarity of the growth cycles between winter and summer grasses. Claviceps paspali (ergot) is a fungus that mainly parasitizes Paspalum spp., generating a structure called sclerotia, in which indole-diterpenoid alkaloids are isolated. Despite the excellent forage characteristics of Paspalum species, there is a need for the generation of varieties able to overcome two major limitations that were identified early on in this species, such as ergot susceptibility and seed production. With this objective, selected genotypes were crossed between apomictic and sexual species of different ploidy using P. malacophyllum as a source of immunity. Immunity to ergot has been evaluated in the field for two years in different representative regions of Uruguay and the accessions that did not get sick were selected as pollen donors. Crosses made with P. flavescens showed a germination percentage ranging between 1.7 and 7.09, while in P. dilatatum var. ChirĂș the range was reduced between 0.99 and 1.25 according to the employed parents. The hybrid nature of the progeny is being verified by microsatellites and functional markers associated with immunity and DNA content estimated by flow cytometry. This work aims to generate the basis to transfer immunity from P. malacophyllum in selected genotypes of Paspalum species predominant in Pampa biome and to improve seed production
Dynamics aspect of subbarrier fusion reaction in light heavy ion systems
Subbarrier fusion of the 7Li + 12C reaction is studied using an
antisymmetrized molecular dynamics model (AMD) with an after burner, GEMINI. In
AMD, 7Li shows an \alpha + t structure at its ground state and it is
significantly deformed. Simulations are made near the Coulomb barrier energies,
i.e., E_{cm} = 3 - 8 MeV. The total fusion cross section of the AMD + GEMINI
calculations as a function of incident energy is compared to the experimental
results and both are in good agreement at E_{cm} > 3 MeV. The cross section for
the different residue channels of the AMD + GEMINI at E_{cm} = 5 MeV is also
compared to the experimental results.Comment: Talk given by Meirong Huang at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
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