109,044 research outputs found
A model comparison of resonance lifetime modifications, a soft equation of state and non-Gaussian effects on correlations at FAIR/AGS energies
HBT correlations of pairs at FAIR/AGS energies are investigated
by using the UrQMD transport model and the CRAB analyzing program. Three
different possible sources (treatment of resonance lifetimes, a soft equation
of state and non-Gaussian effects) to understand the HBT puzzle are
investigated. Firstly, we find that different treatments of the resonance decay
time can not resolve the HBT time-related puzzle, however it can modify the HBT
radii at low transverse momenta to some extent to explain the data slightly.
Secondly, with a soft equation of state with momentum dependence, the measured
transverse momentum dependent HBT radii and ratio can be described
fairly well. Thirdly, non-Gaussian effects are visible in the calculated
correlation function. Using the Edgeworth expansion, one finds that the
non-Gaussian effect is strongest in the longitudinal direction and weakest in
the sideward direction.Comment: 18 pages, 6 figures. To be published in J.Phys.
Antikaon flow in heavy-ion collisions: the effects of absorption and mean fields
We study antikaon flow in heavy-ion collisions at SIS energies based on the
relativistic transport model (RVUU 1.0). The production of antikaons from both
baryon-baryon and pion-baryon collisions are included. Taking into account only
elastic and inelastic collisions of the antikaon with nucleons and neglecting
its mean-field potential as in the cascade model, a strong antiflow or
anti-correlation of antikaons with respect to nucleons is seen as a result of
the strong absorption of antikaons by nucleons. However, the antiflow of
antikaons disappears after including also their propagation in the attractive
mean-field potential. The experimental measurement of antikaon flow in
heavy-ion collision will be very useful in shedding lights on the relative
importance of antikaon absorption versus its mean-field potential.Comment: 12 pages, 2 postscript figures omitted in the original submission are
included, to appear in Phys. Rev.
Antiproton production in Ni+Ni collisions at 1.85 GeV/nucleon
Antiproton production in Ni+Ni collisions at 1.85 GeV/nucleon is studied in
the relativistic Vlasov-Uehling-Uhlenbeck model. The self-energies of the
antiproton are determined from the nucleon self-energies by the G-parity
transformation. Also, the final-state interactions of the antiproton including
both rescattering and annihilation are explicitly treated. With a soft nuclear
equation of state, the calculated antiproton momentum spectrum is in good
agreement with recent experimental data from the heavy-ion synchrotron at GSI.
The effect due to the reduced nucleon and antinucleon masses in a medium is
found to be more appreciable than in earlier Bevalac experiments with lighter
systems and at higher energies.Comment: 10 pages, 4 figures available upon request to [email protected].
TAMUNT-940
Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs
A novel method of applying a two-dimensional Fourier transform (2D-FFT) to SEM was developed to map the CNT orientation in pre-formed arrays. Local 2D-FFTs were integrated azimuthally to determine an orientation distribution function and the associated Herman parameter. This approach provides data rapidly and over a wide range of lengthscales. Although likely to be applicable to a wide range of anisotropic nanoscale structures, the method was specifically developed to study CNT veils, a system in which orientation critically controls mechanical properties. Using this system as a model, key parameters for the 2D-FFT analysis were optimised, including magnification and domain size; a model set of CNT veils were pre-strained to 5%, 10% and 15%, to vary the alignment degree. The algorithm confirmed a narrower orientation distribution function and increasing Herman parameter, with increasing pre-strain. To validate the algorithm, the local orientation was compared to that derived from a common polarised Raman spectroscopy. Orientation maps of the Herman parameter, derived by both methods, showed good agreement. Quantitatively, the mean Herman parameter calculated using the polarised Raman spectroscopy was 0.42 ± 0.004 compared to 0.32 ± 0.002 for the 2D-FFT method, with a correlation coefficient of 0.73. Possible reasons for the modest and systematic discrepancy were discussed
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