Can the nuclear symmetry potential at supra-saturation densities be negative?

In the framework of an Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, for the central $^{197}$Au+$^{197}$Au reaction at an incident beam energy of 400 MeV/nucleon, effect of nuclear symmetry potential at supra-saturation densities on the pre-equilibrium clusters emission is studied. It is found that for the positive symmetry potential at supra-saturation densities the neutron to proton ratio of lighter clusters with mass number $A\leq3$ ($(n/p)_{A\leq3}$) is larger than that of the weighter clusters with mass number $A>3$ ($(n/p)_{A>3}$), whereas for the negative symmetry potential at supra-saturation densities the $(n/p)_{A\leq3}$ is \emph{smaller} than that of the $(n/p)_{A>3}$. This may be considered as a probe of the negative symmetry potential at supra-saturation densities.Comment: 5 pages, 3 figures, 1 table, to be publishe

Supersymmetric Kerr--anti-deSitter solutions

We prove the existence of one quarter supersymmetric type IIB configurations that arise as non-trivial scaling solutions of the standard five dimensional Kerr-AdS black holes by the explicit construction of its Killing spinors. This neutral, spinning solution is asymptotic to the static anti-deSitter space-time with cosmological constant $-\textstyle{\frac{1}{\ell^2}}$, it has two finite equal angular momenta $J_1=\pm J_2$, mass $M=\textstyle{\frac{1}{\ell}} (|J_1|+|J_2|)$ and a naked singularity.We also address the scaling limit associated with one half supersymmetric solution with only one angular momentum.Comment: 15 pages, no figure

Hydrogen enhanced thermal fatigue of y-titanium aluminide

A study of hydrogen enhanced thermal fatigue cracking was carried out for a gamma-based Ti-48Al-2Cr alloy by cycling between room temperature and 750 or 900 °C. The results showed that hydrogen can severely attack the gamma alloy, with resulting lifetimes as low as three cycles, while no failures were observed in helium for test durations of over 4000 cycles. The severity of hydrogen attack strongly depends on the upper limit of the temperature cycled and the cleanliness of the hydrogen. Specifically, the large scatter of life times at 750 °C (ranging from 36 to more than 3000 cycles) have resulted from the competition between surface oxidation and hydrogen attack. The results suggest that an understanding of the combined actions of thermal cycling and hydrogen degradation is needed for assessing materials for high temperature applications in hydrogen