8,118 research outputs found
Relationship between the symmetry energy and the single-nucleon potential in isospin-asymmetric nucleonic matter
In this contribution, we review the most important physics presented
originally in our recent publications. Some new analyses, insights and
perspectives are also provided. We showed recently that the symmetry energy
and its density slope at an arbitrary density
can be expressed analytically in terms of the magnitude and momentum dependence
of the single-nucleon potentials using the Hugenholtz-Van Hove (HVH) theorem.
These relationships provide new insights about the fundamental physics
governing the density dependence of nuclear symmetry energy. Using the isospin
and momentum (k) dependent MDI interaction as an example, the contribution of
different terms in the single-nucleon potential to the and
are analyzed in detail at different densities. It is shown that the
behavior of is mainly determined by the first-order symmetry
potential of the single-nucleon potential. The density
slope depends not only on the first-order symmetry potential
but also the second-order one . Both the
and at normal density are
constrained by the isospin and momentum dependent nucleon optical potential
extracted from the available nucleon-nucleus scattering data. The
especially at high density and momentum affects
significantly the , but it is theoretically poorly understood and
currently there is almost no experimental constraints known.Comment: 9 pages, 6 figures, Review paper, Contribution to the "Topical Issue"
on "Nuclear Symmetry Energy" in European Physical Journal
Delineating effects of tensor force on the density dependence of nuclear symmetry energy
In this talk, we report results of our recent studies to delineate effects of
the tensor force on the density dependence of nuclear symmetry energy within
phenomenological models. The tensor force active in the isosinglet
neutron-proton interaction channel leads to appreciable depletion/population of
nucleons below/above the Fermi surface in the single-nucleon momentum
distribution in cold symmetric nuclear matter (SNM). We found that as a
consequence of the high momentum tail in SNM the kinetic part of the symmetry
energy is significantly below the well-known Fermi gas
model prediction of approximately . With about 15%
nucleons in the high momentum tail as indicated by the recent experiments at
J-Lab by the CLAS Collaboration, the is negligibly small.
It even becomes negative when more nucleons are in the high momentum tail in
SNM. These features have recently been confirmed by three independent studies
based on the state-of-the-art microscopic nuclear many-body theories. In
addition, we also estimate the second-order tensor force contribution to the
potential part of the symmetry energy. Implications of these findings in
extracting information about nuclear symmetry energy from nuclear reactions are
discussed briefly.Comment: Talk given by Chang Xu at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Could the 21-cm absorption be explained by the dark matter suggested by Be transitions?
The stronger than expected 21-cm absorption was observed by EDGES recently,
and another anomaly of Be transitions would be signatures of new
interactions. These two issues may be related to each other, e.g., pseudoscalar
mediated fermionic millicharged dark matter (DM), and the 21-cm absorption
could be induced by photon mediated scattering between MeV millicharged DM and
hydrogen. This will be explored in this paper. For fermionic millicharged DM
with masses in a range of , the
p-wave annihilation would be dominant during DM
freeze-out. The s-wave annihilation is tolerant by constraints from CMB and the 21-cm absorption. The
millicharged DM can evade constraints from direct detection experiments. The
process of with the invisible decay could be employed to search for the millicharged DM, and future high
intensity sources, such as NA62, will do the job.Comment: 6 pages, 2 figures, the accepted version, EPJ
Why is the nuclear symmetry energy so uncertain at supra-saturation densities?
Within the interacting Fermi gas model for isospin asymmetric nuclear matter,
effects of the in-medium three-body interaction and the two-body short-range
tensor force due to the meson exchange as well as the short-range
nucleon correlation on the high-density behavior of the nuclear symmetry energy
are demonstrated respectively in a transparent way. Possible physics origins of
the extremely uncertain nuclear symmetry energy at supra-saturation densities
are discussed.Comment: Added discussions and revised format. Version to appear in Phys. Rev.
C (2010
Characterising gene regulation during epileptogenesis in different models of epilepsy
As epilepsy develops an enormous range of changes occurs in neurons. This process, epileptogenesis, involves complex spatiotemporal alterations of neuronal homeostasis and neural networks. The molecular mechanism of epileptogenesis remains obscure and gene regulation during the epileptogenic process dynamically controls various signalling and functional pathways which play an important role in defining the mechanisms of epilepsy. This thesis explores gene regulation in different in vitro models of seizure like activity, and further focuses on the temporal profiles of molecular changes during an in vivo model of epilepsy. We seek to identify important regulators of epileptogenesis which may be the targets for further study of the mechanism of epilepsy in human. The High-K+, Low-Mg2+, Kainic acid, and Pentylenetetrazole models were used to elicit seizure like activity in cortical neuronal cultures. The tetanus toxin (TeNT) model of focal neocortical epilepsy in rats was utilised to characterise gene regulation in different time points: acute, subacute and chronic stages (48-72 hours, 2 weeks, and 30 days after first spontaneous seizure, respectively). A set of candidate genes relevant to epilepsy was selected to analyse changes in mRNA expression during these in vitro and in vivo models. The mRNA expression of the different candidate genes reveals diverse regulatory behaviours in different models, as well as at different time points during the process of epileptogenesis. The cell culture model treated with Low-Mg2+ for 72 hours displayed the most similar mRNA expression profile to the in vivo model of TeNT neocortical epilepsy during subacute to chronic stages. Furthermore, in the in vivo model, GFAP, mTOR, REST, and SNAP-25 are all temporarily apparently up-regulated during epileptogenesis, while CCL2 is strongly up-regulated later when epilepsy is established. Transient down-regulation of BDNF in the acute stage, and the distinctly lower expression of GABRA5 in late stage suggest that this GABAergic signalling pathway may be down-regulated in the late phase of epileptogenesis. Our work highlights how different candidate genes are differentially regulated during epileptogenesis, and how the regulation of individual genes changes as epileptogenesis progresses
- β¦