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 $t_1$ and $t_2$ 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 $\sigma$ of 0.585 MeV being obtained. The new model thus gives almost as good a mass fit as our best-fit model HFB-17 ($\sigma$ = 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 $AV_{18}$, $Reid93$, $UV_{14}$ and $AV_{14}$ 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 AV18AV_{18} Potential

The lowest order constrained variational method is applied to calculate the polarized symmetrical nuclear matter properties with the modern $AV_{18}$ 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