484 research outputs found
Nuclear neutrino energy spectra in high temperature astrophysical environments
Astrophysical environments that reach temperatures greater than 100
keV can have significant neutrino energy loss via both plasma processes and
nuclear weak interactions. We find that nuclear processes likely produce the
highest-energy neutrinos. Among the important weak nuclear interactions are
both charged current channels (electron capture/emission and positron
capture/emission) and neutral current channels (de-excitation of nuclei via
neutrino pair emission). We show that in order to make a realistic prediction
of the nuclear neutrino spectrum, one must take nuclear structure into account;
in some cases, the most important transitions may involve excited states,
possibly in both parent and daughter nuclei. We find that the standard
technique of producing a neutrino energy spectrum by using a single transition
with a Q-value and matrix element chosen to fit published neutrino production
rates and energy losses will not accurately capture important spectral
features.Comment: 11 pages, 17 figure
Neutrino Spectra from Nuclear Weak Interactions in -Shell Nuclei Under Astrophysical Conditions
We present shell model calculations of nuclear neutrino energy spectra for 70
-shell nuclei over the mass number range . Our calculations
include nuclear excited states as appropriate for the hot and dense conditions
characteristic of pre-collapse massive stars. We consider neutrinos produced by
charged lepton captures and decays and, for the first time in tabular form,
neutral current nuclear deexcitation, providing neutrino energy spectra on the
Fuller-Fowler-Newman temperature-density grid for these interaction channels
for each nucleus. We use the full -shell model space to compute initial
nuclear states up to 20 MeV excitation with transitions to final states up to
35-40 MeV, employing a modification of the Brink-Axel hypothesis to handle high
temperature population factors and the nuclear partition functions.Comment: 15 pages, 8 figures. Until data available at JINA-CEE, contact GWM
for spectra data file
Neutrino Pair Emission from Hot Nuclei During Stellar Collapse
We present shell-model calculations showing that residual interaction-induced
configuration mixing enhances the rate of neutral current de-excitation of
thermally excited nuclei into neutrino-antineutrino pairs. Though our
calculations reinforce the conclusions of previous studies that this process is
the dominant source of neutrino pairs near the onset of neutrino trapping
during stellar collapse, our shell-model result has the effect of increasing
the energy of these pairs, possibly altering their role in entropy transport in
supernovae.Comment: 9 pages, 8 figure
Modification of the Brink-Axel Hypothesis for High Temperature Nuclear Weak Interactions
We present shell model calculations of electron capture strength
distributions in A=28 nuclei and computations of the corresponding capture
rates in supernova core conditions. We find that in these nuclei the Brink-Axel
hypothesis for the distribution of Gamow-Teller strength fails at low and
moderate initial excitation energy, but may be a valid tool at high excitation.
The redistribution of GT strength at high initial excitation may affect capture
rates during collapse. If these trends which we have found in lighter nuclei
also apply for the heavier nuclei which provide the principal channels for
neutronization during stellar collapse, then there could be two implications
for supernova core electron capture physics. First, a modified Brink-Axel
hypothesis could be a valid approximation for use in collapse codes. Second,
the electron capture strength may be moved down significantly in transition
energy, which would likely have the effect of increasing the overall electron
capture rate during stellar collapse.Comment: 15 pages, 19 figure
Composition Effects on Kilonova Spectra and Light Curves: I
The merger of neutron star binaries is believed to eject a wide range of
heavy elements into the universe. By observing the emission from this ejecta,
scientists can probe the ejecta properties (mass, velocity and composition
distributions). The emission (a.k.a. kilonova) is powered by the radioactive
decay of the heavy isotopes produced in the merger and this emission is
reprocessed by atomic opacities to optical and infra-red wavelengths.
Understanding the ejecta properties requires calculating the dependence of this
emission on these opacities. The strong lines in the optical and infra-red in
lanthanide opacities have been shown to significantly alter the light-curves
and spectra in these wavelength bands, arguing that the emission in these
wavelengths can probe the composition of this ejecta. Here we study variations
in the kilonova emission by varying individual lanthanide (and the actinide
uranium) concentrations in the ejecta. The broad forest of lanthanide lines
makes it difficult to determine the exact fraction of individual lanthanides.
Nd is an exception. Its opacities above 1 micron are higher than other
lanthanides and observations of kilonovae can potentially probe increased
abundances of Nd. Similarly, at early times when the ejecta is still hot (first
day), the U opacity is strong in the 0.2-1 micron wavelength range and kilonova
observations may also be able to constrain these abundances
Survival of dental implants in patients with oral cancer treated by surgery and radiotherapy: a retrospective study
BACKGROUND:
The aim of this retrospective study was to evaluate the survival of dental implants placed after ablative surgery, in patients affected by oral cancer treated with or without radiotherapy.
METHODS:
We collected data for 34 subjects (22 females, 12 males; mean age: 51 ± 19) with malignant oral tumors who had been treated with ablative surgery and received dental implant rehabilitation between 2007 and 2012. Postoperative radiation therapy (less than 50 Gy) was delivered before implant placement in 12 patients. A total of 144 titanium implants were placed, at a minimum interval of 12 months, in irradiated and non-irradiated residual bone.
RESULTS:
Implant loss was dependent on the position and location of the implants (P = 0.05-0.1). Moreover, implant survival was dependent on whether the patient had received radiotherapy. This result was highly statistically significant (P < 0.01). Whether the implant was loaded is another highly significant (P < 0.01) factor determinin
Variability of Moderate Luminosity Active Galactic Nuclei at z=0.36
We monitored 13 moderate luminosity active galactic nuclei at z=0.36 to
measure flux variability, explore feasibility of reverberation mapping, and
determine uncertainties on estimating black hole mass from single-epoch data.
Spectra and images were obtained with approximately weekly cadence for up to 4
months, using the KAST spectrograph on the 3-m Shane Telescope. In broad band
we detect peak-to-peak variations of 9-37% and rms variations of 2-10%. The
observed flux variability in the g' band (rest-frame 2800-4000\AA) is
consistent with that in the r' band (rest-frame 4000-5200\AA), but with larger
amplitude. However, after correcting for stellar light dilution, using Hubble
Space Telescope images, we find nuclear variability of 3-24% (rms variation)
with similar amplitudes in the g' and r' bands within the errors. Intrinsic
flux variability of the H line is also detected at the 3-13% level,
after accounting for systematic errors on the spectrophotometry. This
demonstrates that a reverberation mapping campaign beyond the local universe
can be carried out with a 3-m class telescope, provided that sufficiently long
light curves are obtained. Finally, we compare the H FWHM measured from
mean spectra with that measured from single-epoch data, and find no bias but an
rms scatter of 14%, mostly accounted for by the uncertainty on FWHM
measurements. The propagated uncertainty on black hole mass estimates, due to
the FWHM measurement errors using low S/N (10--15 per pixel) single-epoch
spectra, is 30%.Comment: 12 pages, 7 figures, accepted by Ap
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