8,303 research outputs found
Extended Skyrme Equation of State in asymmetric nuclear matter
We present a new equation of state for infinite systems (symmetric,
asymmetric and neutron matter) based on an extended Skyrme functional
constrained by microscopic Brueckner-Bethe-Goldstone results. The resulting
equation of state reproduces with very good accuracy the main features of
microscopic calculations and it is compatible with recent measurements of two
times Solar-mass neutron stars. We provide all necessary analytical expressions
to facilitate a quick numerical implementation of quantities of astrophysical
interest
Linear response in infinite nuclear matter as a tool to reveal finite size instabilities
Nuclear effective interactions are often modelled by simple analytical
expressions such as the Skyrme zero-range force. This effective interaction
depends on a limited number of parameters that are usually fitted using
experimental data obtained from doubly magic nuclei. It was recently shown that
many Skyrme functionals lead to the appearance of instabilities, in particular
when symmetries are broken, for example unphysical polarization of odd-even or
rotating nuclei. In this article, we show how the formalism of the linear
response in infinite nuclear matter can be used to predict and avoid the
regions of parameters that are responsible for these unphysical instabilities.Comment: Based on talk presented at 18th Nuclear Physics Workshop "Maria and
Pierre Curie", 2011, Kazimierz, Polan
Nuclear response for the Skyrme effective interaction with zero-range tensor terms. II. Sum rules and instabilities
The formalism of linear response theory for Skyrme forces including tensor
terms presented in article [1] is generalized for the case of a Skyrme energy
density functional in infinite matter. We also present analytical results for
the odd-power sum rules, with particular attention to the inverse energy
weighted sum rule, , as a tool to detect instabilities in Skyrme
functionals.Comment: Submitted to Phys. Rev.
Spurious finite-size instabilities in nuclear energy density functionals: spin channel
It has been recently shown, that some Skyrme functionals can lead to
non-converging results in the calculation of some properties of atomic nuclei.
A previous study has pointed out a possible link between these convergence
problems and the appearance of finite-size instabilities in symmetric nuclear
matter (SNM) around saturation density.
We show that the finite-size instabilities not only affect the ground state
properties of atomic nuclei, but they can also influence the calculations of
vibrational excited states in finite nuclei. We perform systematic fully-self
consistent Random Phase Approximation (RPA) calculations in spherical
doubly-magic nuclei. We employ several Skyrme functionals and vary the
isoscalar and isovector coupling constants of the time-odd term
. We determine critical values of these
coupling constants beyond which the RPA calculations do not converge because
RPA the stability matrix becomes non-positive.By comparing the RPA calculations
of atomic nuclei with those performed for SNM we establish a correspondence
between the critical densities in the infinite system and the critical coupling
constants for which the RPA calculations do not converge. We find a
quantitative stability criterion to detect finite-size instabilities related to
the spin term of a functional. This
criterion could be easily implemented into the standard fitting protocols to
fix the coupling constants of the Skyrme functional
Fitting Skyrme functionals using linear response theory
Recently, it has been recently shown that the linear response theory in
symmetric nuclear matter can be used as a tool to detect finite size
instabilities for different Skyrme functionals. In particular it has been shown
that there is a correlation between the density at which instabilities occur in
infinite matter and the instabilities in finite nuclei. In this article we
present a new fitting protocol that uses this correlation to add new additional
constraint in Symmetric Infinite Nuclear Matter in order to ensure the
stability of finite nuclei against matter fluctuation in all spin and isospin
channels. As an application, we give the parameters set for a new Skyrme
functional which includes central and spin-orbit parts and which is free from
instabilities by construction.Comment: Proceeding of 19th Nuclear Physics Workshop "Marie & Pierre Curie"
Kazimierz 201
Understanding fragility in supercooled Lennard-Jones mixtures. II. Potential energy surface
We numerically investigated the connection between isobaric fragility and the
properties of high-order stationary points of the potential energy surface in
different supercooled Lennard-Jones mixtures. The increase of effective
activation energies upon supercooling appears to be driven by the increase of
average potential energy barriers measured by the energy dependence of the
fraction of unstable modes. Such an increase is sharper, the more fragile is
the mixture. Correlations between fragility and other properties of high-order
stationary points, including the vibrational density of states and the
localization features of unstable modes, are also discussed.Comment: 13 pages, 13 figures, minor revisions, one figure adde
Pairing correlations of cold fermionic gases at overflow from a narrow to a wide harmonic trap
Within the context of Hartree-Fock-Bogoliubov theory, we study the behavior
of superfluid Fermi systems when they pass from a small to a large container.
Such systems can be now realized thanks to recent progress in experimental
techniques. It will allow to better understand pairing properties at overflow
and in general in rapidly varying external potentials
A Role for Late Meristem Identity2 in the Reproductive Development of Arabidopsis
The switch from producing vegetative structures--branches and leaves--to producing reproductive structures--flowers--is a crucial developmental transition that significantly affects the reproductive success of flowering plants. In Arabidopsis thaliana , this transition is in large part controlled by the meristem identity regulator LEAFY (LFY) and the LFY direct target APETALA1 (AP1 ). The molecular mechanisms by which LFY orchestrates a precise and robust switch to flower formation is not well understood. Here we show that the R2R3 MYB transcription factor and direct LFY target LATE MERISTEM IDENTITY2 ( LMI2 ) plays a role in the meristem identity transition. Like LFY, LMI2 directly activates AP1 ; moreover LMI2 and LFY physically interact. LFY, LMI2 and AP1 are connected in a feed-forward and positive feedback loop network. We propose that these intricate regulatory interactions direct not only the precision of this critical developmental transition, but also contribute to its robustness and irreversibility.
Subsequent to the meristem identity transition floral primordia undergo a growth period prior to floral organogenesis. This growth phase is maintained in part by the flowering-time genes SHORT VEGETATIVE PHASE (SVP), AGAMOUS-LIKE24 (AGL24) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). Eventually, these flowering-time genes are downregulated by AP1. This downregulation results in the termination of meristematic activity and the onset of floral differentiation. In the absence of AP1, ectopic expression of SVP, AGL24 and SOC1 prevents differentiation and leads to the development of floral meristems in the axils of the first whorl organs. These floral meristems give rise to branched flowers. Here we present a possible role for LMI2 during floral primordia growth. Similar to SVP, AGL24 and SOC1, AP1 downregulates LMI2 in young flower primordia thus preventing the development of branched flowers. LMI2 acts in the same pathway as SVP, AGL24 and SOC1 and the similar expression patterns of LMI2 and SVP as well as the direct binding of LMI2 to SVP suggests a link between LMI2 and the pathways that maintain primordia growth during early flower development
Nuclear response for the Skyrme effective interaction with zero-range tensor terms. III. Neutron matter and neutrino propagation
The formalism of the linear response for the Skyrme energy density functional
including tensor terms derived in articles [1,2] for nuclear matter is applied
here to the case of pure neutron matter. As in article [2] we present
analytical results for the response function in all channels, the Landau
parameters and the odd-power sum rules. Special emphasis is given to the
inverse energy weighted sum rule because it can be used to detect non physical
instabilities. Typical examples are discussed and numerical results shown.
Moreover, as a direct application, neutrino propagation in neutron matter is
investigated through its neutrino mean free path at zero temperature. This
quantity turns out to be very sensitive to the tensor terms of the Skyrme
energy density functional
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