410 research outputs found
Spin- and isospin-polarized states of nuclear matter in the Dirac-Brueckner-Hartree-Fock model
Spin-polarized isospin asymmetric nuclear matter is studied within the
Dirac-Brueckner-Hartree-Fock approach. After a brief review of the formalism,
we present and discuss the self-consistent single-particle potentials at
various levels of spin and isospin asymmetry. We then move to predictions of
the energy per particle, also under different conditions of isospin and spin
polarization. Comparison with the energy per particle in isospin symmetric or
asymmetric unpolarized nuclear matter shows no evidence for a phase transition
to a spin ordered state, neither ferromagnetic nor antiferromagnetic.Comment: 8 pages, 6 figure
Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XI: Stabilizing neutron stars against a ferromagnetic collapse
We construct a new Hartree-Fock-Bogoliubov (HFB) mass model, labeled HFB-18,
with a generalized Skyrme force. The additional terms that we have introduced
into the force are density-dependent generalizations of the usual and
terms, and are chosen in such a way as to avoid the high-density
ferromagnetic instability of neutron stars that is a general feature of
conventional Skyrme forces, and in particular of the Skyrme forces underlying
all the HFB mass models that we have developed in the past. The remaining
parameters of the model are then fitted to essentially all the available mass
data, an rms deviation of 0.585 MeV being obtained. The new model thus
gives almost as good a mass fit as our best-fit model HFB-17 ( = 0.581
MeV), and has the advantage of avoiding the ferromagnetic collapse of neutron
stars.Comment: accepted for publication in Physical Review
Visualizing the Doppler Effect
The development of Information and Communication Technologies suggests some
spectacular changes in the methods used for teaching scientific subjects.
Nowadays, the development of software and hardware makes it possible to
simulate processes as close to reality as we want. However, when we are trying
to explain some complex physical processes, it is better to simplify the
problem under study using simplified pictures of the total process by
eliminating some elements that make it difficult to understand this process. In
this work we focus our attention on the Doppler effect which requires the
space-time visualization that is very difficult to obtain using the traditional
teaching resources. We have designed digital simulations as a complement of the
theoretical explanation in order to help students understand this phenomenon.Comment: 16 pages, 8 figure
Spin Polarized Asymmetric Nuclear Matter and Neutron Star Matter Within the Lowest Order Constrained Variational Method
In this paper, we calculate properties of the spin polarized asymmetrical
nuclear matter and neutron star matter, using the lowest order constrained
variational (LOCV) method with the , , and
potentials. According to our results, the spontaneous phase transition to a
ferromagnetic state in the asymmetrical nuclear matter as well as neutron star
matter do not occur.Comment: 21 pages, 11 figure
Spin instabilities of infinite nuclear matter and effective tensor interactions
We study the effects of the tensor force, present in modern effective nucleon-nucleon interactions, in the spin instability of nuclear and neutron matter. Stability conditions of the system against certain very low energy excitation modes are expressed in terms of Landau parameters. It is shown that in the spin case, the stability conditions are equivalent to the condition derived from the spin susceptibility, which is obtained as the zero-frequency and long-wavelength limit of the spin response function calculated in the random phase approximation. Zero-range forces of the Skyrme type and finite-range forces of M3Y and Gogny type are analyzed. It is shown that for the Skyrme forces considered, the tensor effects are sizable and tend to increase the spin instability, which appears at smaller densities than in the case that the tensor is not taken into account. On the contrary, the tensor contribution of finite-range forces to the spin susceptibility is small or negligible for both isospin channels of symmetric nuclear matter as well as for neutron matter. A comparison with the spin susceptibility provided by realistic interactions is also presented
Nuclear liquid-gas phase transition and supernovae evolution
It is shown that the large density fluctuations appearing at the onset of the
first order nuclear liquid-gas phase transition can play an important role in
the supernovae evolution. Due to these fluctuations, the neutrino gas may be
trapped inside a thin layer of matter near the proto-neutron star surface. The
resulting increase of pressure may induce strong particle ejection a few
hundred milliseconds after the bounce of the collapse, contributing to the
revival of the shock wave. The Hartree-Fock+RPA scheme, with a finite-range
nucleon-nucleon effective interaction, is employed to estimate the effects of
the neutrino trapping due to the strong density fluctuations, and to discuss
qualitatively the consequences of the suggested new scenario.Comment: version2 - precise that nuclear liquid-gas phase transition is 1st
order and the unique instable mode is isoscala
Neutron Fermi Liquids under the presence of a strong magnetic field with effective nuclear forces
Landau's Fermi Liquid parameters are calculated for non-superfluid pure
neutron matter in the presence of a strong magnetic field at zero temperature.
The particle-hole interactions in the system, where a net magnetization may be
present, are characterized by these parameters in the framework of a multipolar
formalism. We use either zero- or finite-range effective nuclear forces to
describe the nuclear interaction. Using the obtained Fermi Liquid parameters,
the effect of a strong magnetic field on some bulk magnitudes such as
isothermal compressibility and spin susceptibility is also investigated.Comment: 20 pages, 10 figure
Deep Chronnectome Learning via Full Bidirectional Long Short-Term Memory Networks for MCI Diagnosis
Brain functional connectivity (FC) extracted from resting-state fMRI
(RS-fMRI) has become a popular approach for disease diagnosis, where
discriminating subjects with mild cognitive impairment (MCI) from normal
controls (NC) is still one of the most challenging problems. Dynamic functional
connectivity (dFC), consisting of time-varying spatiotemporal dynamics, may
characterize "chronnectome" diagnostic information for improving MCI
classification. However, most of the current dFC studies are based on detecting
discrete major brain status via spatial clustering, which ignores rich
spatiotemporal dynamics contained in such chronnectome. We propose Deep
Chronnectome Learning for exhaustively mining the comprehensive information,
especially the hidden higher-level features, i.e., the dFC time series that may
add critical diagnostic power for MCI classification. To this end, we devise a
new Fully-connected Bidirectional Long Short-Term Memory Network (Full-BiLSTM)
to effectively learn the periodic brain status changes using both past and
future information for each brief time segment and then fuse them to form the
final output. We have applied our method to a rigorously built large-scale
multi-site database (i.e., with 164 data from NCs and 330 from MCIs, which can
be further augmented by 25 folds). Our method outperforms other
state-of-the-art approaches with an accuracy of 73.6% under solid
cross-validations. We also made extensive comparisons among multiple variants
of LSTM models. The results suggest high feasibility of our method with
promising value also for other brain disorder diagnoses.Comment: The paper has been accepted by MICCAI201
Lowest Order Constrained Variational Calculation of the Polarized Nuclear Matter with the Modern Potential
The lowest order constrained variational method is applied to calculate the
polarized symmetrical nuclear matter properties with the modern
potential performing microscopic calculations. Results based on the
consideration of magnetic properties show no sign of phase transition to a
ferromagnetic phase.Comment: 19 pages, 6 figure
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