907 research outputs found
Neutron skin of 208Pb, nuclear symmetry energy, and the parity radius experiment
A precise determination of the neutron skin thickness of a heavy nucleus sets
a basic constraint on the nuclear symmetry energy (the neutron skin thickness
is the difference of the neutron and proton rms radii of the nucleus). The
parity radius experiment (PREX) may achieve it by electroweak parity-violating
electron scattering (PVES) on 208Pb. We investigate PVES in nuclear mean field
approach to allow the accurate extraction of the neutron skin thickness of
208Pb from the parity-violating asymmetry probed in the experiment. We
demonstrate a high linear correlation between the parity-violating asymmetry
and the neutron skin thickness in successful mean field forces as the best
means to constrain the neutron skin of 208Pb from PREX, without assumptions on
the neutron density shape. Continuation of the experiment with higher precision
in the parity-violating asymmetry is motivated since the present method can
support it to constrain the density slope of the nuclear symmetry energy to new
accuracy.Comment: 4 pages, 3 figures, some changes in text and references, version to
appear in Phys. Rev. Let
Origin of the neutron skin thickness of 208Pb in nuclear mean-field models
We study whether the neutron skin thickness (NST) of 208Pb originates from
the bulk or from the surface of the nucleon density distributions, according to
the mean-field models of nuclear structure, and find that it depends on the
stiffness of the nuclear symmetry energy. The bulk contribution to NST arises
from an extended sharp radius of neutrons, whereas the surface contribution
arises from different widths of the neutron and proton surfaces. Nuclear models
where the symmetry energy is stiff, as typical relativistic models, predict a
bulk contribution in NST of 208Pb about twice as large as the surface
contribution. In contrast, models with a soft symmetry energy like common
nonrelativistic models predict that NST of 208Pb is divided similarly into bulk
and surface parts. Indeed, if the symmetry energy is supersoft, the surface
contribution becomes dominant. We note that the linear correlation of NST of
208Pb with the density derivative of the nuclear symmetry energy arises from
the bulk part of NST. We also note that most models predict a mixed-type
(between halo and skin) neutron distribution for 208Pb. Although the halo-type
limit is actually found in the models with a supersoft symmetry energy, the
skin-type limit is not supported by any mean-field model. Finally, we compute
parity-violating electron scattering in the conditions of the 208Pb parity
radius experiment (PREX) and obtain a pocket formula for the parity-violating
asymmetry in terms of the parameters that characterize the shape of the 208Pb
nucleon densities.Comment: 11 pages, 4 figures; minor stylistic changes in text, new Ref. [56]
added (new measurement of the neutron skin thickness of 208Pb
The Hubble Diagram of the Calan/Tololo Type Ia Supernovae and the value of Ho
The Calan/Tololo supernova survey has discovered ~30 Type Ia supernovae out
to z~0.1. Using BVI data for these objects and nearby SNe Ia, we have shown
that there exists a significant dispersion in the intrinsic luminosities of
these objects. We have devised a robust chisquare minimization technique
simultaneously fitting the BVI light curves to parametrize the SN event as a
function of (tb,m, m15(B)) where tb is the time of B maximum, m is the peak BVI
magnitude corrected for luminosity variations, and m15(B) is a single parameter
describing the whole light curve morphology. When properly corrected for
m15(B), SNe Ia prove to be high precision distance indicators,yielding relative
distances with errors 7-10%. The corrected peak magnitudes are used to
construct BVI Hubble diagrams (HD), and with Cepheid distances recently
measured with the HST to four nearby SNe Ia (37C, 72E, 81B, 90N) we derive a
value of the Hubble constant of 63.1+/-3.4 (internal) km/s/Mpc. This value is
~10-15% larger than the value obtained by assuming that SNe Ia are perfect
standard candles. As we have shown in Paper V, there is now strong evidence
that galaxies with younger stellar population appear to host the
slowest-declining, and therefore most luminous SNe Ia. Hence, the use of Pop I
objects such as Cepheids to calibrate the zero point of the SNe Ia HD can
easily bias the results toward luminous SNe Ia, unless the absolute
magnitude-decline relation is taken into account.Comment: 32 pages, figures attached, all tables available, to appear in the
Astronomical Journa
Analysis of bulk and surface contributions in the neutron skin of nuclei
The neutron skin thickness of nuclei is a sensitive probe of the nuclear
symmetry energy having multiple implications for nuclear and astrophysical
studies. However, precision measurements of this observable are difficult. The
analysis of the experimental data may imply some assumptions about the bulk or
surface nature of the formation of the neutron skin. Here, we study the bulk or
surface character of neutron skins of nuclei following from calculations with
Gogny, Skyrme, and covariant nuclear mean-field interactions. These
interactions are successful in describing nuclear charge radii and binding
energies but predict different values for neutron skins. We perform the study
by fitting two-parameter Fermi distributions to the calculated self-consistent
neutron and proton densities. We note that the equivalent sharp radius is a
more suitable reference quantity than the half-density radius parameter of the
Fermi distributions to discern between the bulk and surface contributions in
neutron skins. We present calculations for nuclei in the stability valley and
for the isotopic chains of Sn and Pb.Comment: 13 pages, 9 figure
The Absolute Luminosities of the Calan/Tololo Type Ia Supernovae
We examine the absolute luminosities of 29 SNe Ia in the Calan/Tololo survey.
We confirm a relation between the peak luminosity of the SNe and the decline
rate as measured by the light curve, as suggested by Phillips (1993). We derive
linear slopes to this magnitude-decline rate relation in BV(I)kc colors, using
a sample with Bmax-Vmax < 0.2 mag. The scatter around this linear relation (and
thus the ability to measure SNe Ia distances) ranges from 0.13 mag (in the I
band) to 0.17 mag (in the B band). We also find evidence for significant
correlations between the absolute magnitudes or the decline rate of the light
curve, and the morphological type of the host galaxy.Comment: 21 pages, 4 figures, to appear in the Astronomical Journa
Analysis of bulk and surface contributions in the neutron skin of nuclei
The neutron skin thickness of nuclei is a sensitive probe of the nuclear
symmetry energy having multiple implications for nuclear and astrophysical
studies. However, precision measurements of this observable are difficult. The
analysis of the experimental data may imply some assumptions about the bulk or
surface nature of the formation of the neutron skin. Here, we study the bulk or
surface character of neutron skins of nuclei following from calculations with
Gogny, Skyrme, and covariant nuclear mean-field interactions. These
interactions are successful in describing nuclear charge radii and binding
energies but predict different values for neutron skins. We perform the study
by fitting two-parameter Fermi distributions to the calculated self-consistent
neutron and proton densities. We note that the equivalent sharp radius is a
more suitable reference quantity than the half-density radius parameter of the
Fermi distributions to discern between the bulk and surface contributions in
neutron skins. We present calculations for nuclei in the stability valley and
for the isotopic chains of Sn and Pb.Comment: 13 pages, 9 figure
The Morphology of Type Ia Supernovae Light Curves
We present a family of six BVI template light curves for SNe Ia for days -5
and +80, based on high-quality data gathered at CTIO. These templates display a
wide range of light curve morphologies, with initial decline rates of their B
light curves between m15(B)=0.87 mag and 1.93 mag. We use these templates to
study the general morphology of SNe Ia light curves. We find that several of
the main features of the BVI templates correlate tightly with m15(B). In
particular, the V light curves, which are probably a reasonably good
approximation of the bolometric light curves, display an orderly progression in
shapes between the most-luminous, slowest-declining events and the
least-luminous, fastest-declining SNe. This supports the idea that the observed
spectroscopic and photometric sequences of SNe Ia are due primarily to one
parameter. Nevertheless, SNe with very similar initial decline rates do show
significant differences in their light curve properties when examined in
detail, suggesting the influence of one or more secondary parameters.Comment: 32 pages, 15 figures, to appear in the Astronomical Journa
Fungal inoculation effect on post-harvest sugarcane residue decomposition under field conditions
Fungal inoculation effect on post-harvest sugarcane residue (SCR) decomposition in field conditions was studied. In vitro interaction between selected fungi was determined by direct confrontation. Mycelial growth response to different concentrations of herbicides and urea was also assessed. Fungal combinations did not show inhibitory effects. Bjerkandera sp. Y-HHM2 and Myrothecium sp. S-3.20 growth decreased in 2.4-D agar plates. However, Pleurotus sp. Y- RN3 showed a stimulation in 10 ppm 2.4-D agar plates. The biggest growth in ametrine supplemented cultures was observed in Pleurotus sp. Y-RN3. Evaluation of increasing urea concentrations on mycelial growth showed that 5,000 ppm significantly inhibits mycelial growth. The field assay under rainfed condition showed that post-harvest SCR decomposition rate significantly increases in Y-HHM2, Y-RN3 and Y-HHM2/Y-RN3/S-3.20 treatments. This is the first report on the capability of Bjerkandera sp. Y-HHM2 and Pleurotus sp. Y-RN3 to accelerate post-harvest SCR decomposition in rainfed conditions at field scale, suggesting that these fungi might be useful tools in the sugarcane crop system.Fil: Maza, Marianela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Instituto Nacional de TecnologĂa Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de InvestigaciĂłn Animal del Chaco Semiárido; Argentina. Universidad Nacional de Tucumán. Facultad de AgronomĂa y Zootecnia. Sanidad Vegetal. Cátedra FitopatologĂa; ArgentinaFil: Medina, M.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. EstaciĂłn Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Plasencia, Adriana MarĂa. Universidad Nacional de Tucumán. Facultad de AgronomĂa y Zootecnia; ArgentinaFil: Amoroso, Maria Julia del R.. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Tucumán. Planta Piloto de Procesos Industriales MicrobiolĂłgicos; ArgentinaFil: Yasem, Marta Graciela. Universidad Nacional de Tucumán. Facultad de AgronomĂa y Zootecnia. Sanidad Vegetal. Cátedra FitopatologĂa; Argentin
Near-infrared photometry of isolated spirals with and without an AGN. I: The Data
We present infrared imaging data in the J and K' bands obtained for 18 active
spiral galaxies, together with 11 non active galaxies taken as a control
sample. All of them were chosen to satisfy well defined isolation criteria so
that the observed properties are not related to gravitational interaction. For
each object we give: the image in the K' band, the sharp-divided image
(obtained by dividing the observed image by a filtered one), the difference
image (obtained by subtracting a model to the observed one), the color J-K'
image, the ellipticity and position angle profiles, the surface brightness
profiles in J and K', their fits by bulge+disk models and the color gradient.
We have found that four (one) active (control) galaxies previously classified
as non-barred turn out to have bars when observed in the near-infrared. One of
these four galaxies (UGC 1395) also harbours a secondary bar. For 15 (9 active,
6 control) out of 24 (14 active, 10 control) of the optically classified barred
galaxies (SB or SX) we find that a secondary bar (or a disk, a lense or an
elongated ring) is present. The work presented here is part of a large program
(DEGAS) aimed at finding whether there are differences between active and non
active galaxies in the properties of their central regions that could be
connected with the onset of nuclear activity.Comment: Accepted for publication in Astronomy & Astrophysics Supplement
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