1,768 research outputs found
Imaging of fuel mixture fraction oscillations in a driven system using acetone PLIF
Measurements of fuel mixture fraction are made for a jet flame in an acoustic chamber. Acoustic forcing creates a
spatially-uniform, temporally-varying pressure field which results in oscillatory behavior in the flame . Forcing is at 22,27, 32, 37, and 55 Hz. To asses the oscillatory behavior, previous work included chemiluminescence, OH PUF, nitric oxide PUF imaging, and fuel mixture fraction measurements by infrared laser absorption. While these results illuminated what was happening to the flame chemistry, they did not provide a complete explanation as to why these things were happening. In this work, the fuel mixture fraction is measured through PUF of acetone, which is introduced into the fuel stream as a marker. This technique enables a high degree of spatial resolution of fuel/air mixture value. Both non-reacting and reacting cases were measured and comparisons are drawn with the results from the previous work. It is found that structure in the mixture fraction oscillations is a major contributor to the magnitude of the flame oscillations
Gamma-Ray Bursts Black hole accretion disks as a site for the vp-process
We study proton rich nucleosynthesis in windlike outflows from gamma-ray
bursts accretion disks with the aim to determine if such outflows are a site of
the vp-process. The efficacy of this vp-process depends on thermodynamic and
hydrodynamic factors. We discuss the importance of the entropy of the material,
the outflow rate, the initial ejection point and accretion rate of the disk. In
some cases the vp-process pushes the nucleosynthesis out to A~100 and produces
light p-nuclei. However, even when these nuclei are not produced, neutrino
induced interactions can significantly alter the abundance pattern and cannot
be neglected.Comment: 9 pages, 16 figures, accepted for publication in Phys. Rev.
Supernova Inelastic Neutrino-Nucleus Cross Sections from High-Resolution Electron Scattering Experiments and Shell-Model Calculations
Highly precise data on the magnetic dipole strength distributions from the
Darmstadt electron linear accelerator for the nuclei 50Ti, 52Cr and 54Fe are
dominated by isovector Gamow-Teller-like contributions and can therefore be
translated into inelastic total and differential neutral-current
neutrino-nucleus cross sections at supernova neutrino energies. The results
agree well with large-scale shell-model calculations, validating this model.Comment: 5 pages, 4 figures, RevTeX 4, version accepted in Phys. Rev. Letter
On the Design and Development of Object-oriented Scheduling Systems
In this paper, we describe the architecture of an object-oriented scheduling system. First,
a mathematical framework is presented that is based on set theory and graph theory. Then
a number of basic as well as more specialized methods are defined which can be applied
on the entities of any decision support system. The principal objects of a scheduling system
are defined, as well as the methods specifically designed for the manipulation of the schedules.
The object base design, the schedule generator design and the user interface design are
then discussed in detail.Information Systems Working Papers Serie
Influence of light nuclei on neutrino-driven supernova outflows
We study the composition of the outer layers of a protoneutron star and show that light nuclei are present in substantial amounts. The composition is dominated by nucleons, deuterons, tritons and alpha particles; 3He is present in smaller amounts. This composition can be studied in laboratory experiments with new neutron-rich radioactive beams that can reproduce similar densities and temperatures. After including the corresponding neutrino interactions, we demonstrate that light nuclei have a small impact on the average energy of the emitted electron neutrinos, but are significant for the average energy of antineutrinos. During the early post-explosion phase, the average energy of electron antineutrinos is slightly increased, while at later times during the protoneutron star cooling it is reduced by about 1 MeV. The consequences of these changes for nucleosynthesis in neutrino-driven supernova outflows are discussed
Parity-Projected Shell Model Monte Carlo Level Densities for fp-shell Nuclei
We calculate parity-dependent level densities for the even-even isotopes
58,62,66 Fe and 58 Ni and the odd-A nuclei 59 Ni and 65 Fe using the Shell
Model Monte Carlo method. We perform these calculations in the complete fp-gds
shell-model space using a pairing+quadrupole residual interaction. We find
that, due to pairing of identical nucleons, the low-energy spectrum is
dominated by positive parity states. Although these pairs break at around the
same excitation energy in all nuclei, the energy dependence of the ratio of
negative-to-positive parity level densities depends strongly on the particular
nucleus of interest. We find equilibration of both parities at noticeably lower
excitation energies for the odd-A nuclei 59 Ni and 65 Fe than for the
neighboring even-even nuclei 58 Ni and 66 Fe.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
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