Density dependence of the symmetry free energy of hot nuclei

The density and excitation energy dependence of symmetry energy and symmetry free energy for finite nuclei are calculated microscopically in a microcanonical framework, taking into account thermal and expansion effects. A finite-range momentum and density-dependent two-body effective interaction is employed for this purpose. The role of mass, isospin, and equation of state (EOS) on these quantities is also investigated; our calculated results are in consonance with the available experimental data.

Theoretical study of elastic electron scattering off stable and exotic nuclei

Results for elastic electron scattering by nuclei, calculated with charge densities of Skyrme forces and covariant effective Lagrangians that accurately describe nuclear ground states, are compared against experiment in stable isotopes. Dirac partial-wave calculations are performed with an adapted version of the ELSEPA package. Motivated by the fact that studies of electron scattering off exotic nuclei are intended in future facilities in the commissioned GSI and RIKEN upgrades, we survey the theoretical predictions from neutron-deficient to neutron-rich isotopes in the tin and calcium isotopic chains. The charge densities of a covariant interaction that describes the low-energy electromagnetic structure of the nucleon within the Lagrangian of the theory are used to this end. The study is restricted to medium- and heavy-mass nuclei because the charge densities are computed in mean-field approach. Because the experimental analysis of scattering data commonly involves parameterized charge densities, as a surrogate exercise for the yet unexplored exotic nuclei, we fit our calculated mean-field densities with Helm model distributions. This procedure turns out to be helpful to study the neutron-number variation of the scattering observables and allows us to identify correlations of potential interest among some of these observables within the isotopic chains.

Comment on "Influence of bulk properties on the surface structure of finite nuclei"

We comment on a recent paper by Uma Maheswari et al. in which it is claimed that quantal calculations of the half-infinite nuclear matter, in contrast to semiclassical approximations, exhibit an unusually strong dependence of the 90%10% surface thickness of the density profile on the Fermi momentum kF at saturation. This conclusion was carried over to the surface incompressibility. On the contrary we find essential agreement between semiclassical and quantal results and very weak dependence on kF of the quantities in question.

Hysteresis and return-point memory in deterministic cellular automata

We have investigated hysteresis and the return-point memory (RPM) property in deterministic cellular automata with avalanche dynamics. The RPM property reflects a partial ordering of metastable states, preserved by the dynamics. Recently, Sethna et al. [Phys. Rev. Lett. 70, 3347 (1993)] proved this behavior for a homogeneously driven system with static disorder. This Letter shows that the partial ordering and the RPM can be displayed as well by systems driven heterogeneously, as a result of its own evolution dynamics. In particular, we prove the RPM property for a deterministic 2D sandpile automaton driven at a central site.

The influence of the symmetry energy on the giant monopole resonance of neutron-rich nuclei analyzed in Thomas-Fermi theory

We analyze the influence of the density dependence of the symmetry energy on the average excitation energy of the isoscalar giant monopole resonance (GMR) in stable and exotic neutron-rich nuclei by applying the relativistic extended Thomas-Fermi method in scaling and constrained calculations. For the effective nuclear interaction, we employ the relativistic mean field model supplemented by an isoscalar-isovector meson coupling that allows one to modify the density dependence of the symmetry energy without compromising the success of the model for binding energies and charge radii. The semiclassical estimates of the average energy of the GMR are known to be in good agreement with the results obtained in full RPA calculations. The present analysis is performed along the Pb and Zr isotopic chains. In the scaling calculations, the excitation energy is larger when the symmetry energy is softer. The same happens in the constrained calculations for nuclei with small and moderate neutron excess. However, for nuclei of large isospin the constrained excitation energy becomes smaller in models having a soft symmetry energy. This effect is mainly due to the presence of loosely-bound outer neutrons in these isotopes. A sharp increase of the estimated width of the resonance is found in largely neutron-rich isotopes, even for heavy nuclei, which is enhanced when the symmetry energy of the model is soft. The results indicate that at large neutron numbers the structure of the low-energy region of the GMR strength distribution changes considerably with the density dependence of the nuclear symmetry energy, which may be worthy of further characterization in RPA calculations of the response function.

Scaling in relativistic Thomas-Fermi approach for nuclei

By using the scaling method we derive the virial theorem for the relativistic mean field model of nuclei treated in the ThomasFermi approach. The ThomasFermi solutions statisfy the stability condition against scaling. We apply the formalism to study the excitation energy of the breathing mode in finite nuclei with several relativistic parameter sets of common use.

Woody Allen i l'esperit de la tragèdia grega: de Crimes and Misdemeanors a Match Point

Nombrosos són ja els estudis que s'han centrat en l'anomenat "cinema seriós" de Woody Allen i, entre ells, paga la pena de mencionar el que Pau Gilabert Barberà, autor d'aquest article, va escriure (2006) sobre el que, en opinió seva, és el llegat sofístic subjacent en el guió de Crimes and Misdemeanors. En aquesta ocasió, el seu objectiu és analitzar la trajectòria fluctuant del director americà en relació a la tragèdia grega, des de la convicció que, només així, és possible revelar la seva empatia amb l'esperit tràgic dels grecs i comprendre la seva necessitat de presentar aquell gènere literari com un paradigma des del qual entendre les grandeses i misèries del món contemporani.

Woody Allen and the Spirit of the Greek Tragedy: from Crimes and Misdemeanors to Match Point

Many studies have already paid attention to what is called the "serious films" by Woody Allen and, among them, it is also worth mentioning the one written by the very Pau Gilabert Barberà (2006), which is devoted to the Sophistic legacy underlying in his opinion the screenplay of Crimes and Misdemeanors. On this occasion, his aim is to analyse the fluctuating sight of the American director with regard to the Greek tragedy. Indeed, Gilabert is convinced that, only in this way, it is possible to reveal the true Allen¿s sympathy with the tragic spirit of the Greeks, as well as to understand his urge to present that ancient literary genre as a paradigm with the help of which one can evaluate the greatness and misery of our contemporary world.

Woody Allen y el espíritu de la tragedia griega: de Crimes and Misdemeanors a Match Point

Numerosos son ya los estudios que se han centrado en el llamado "cine serio" de Woody Allen y, entre ellos, cabe mencionar el que Pau Gilabert Barberà, autor de este artículo, escribió (2006) sobre lo que, en su opinión, es el legado sofístico subyacente en el guión de Crimes and Misdemeanors. En esta ocasión, su objetivo es analizar la trayectoria fluctuante del director americano en relación con la tragedia griega, desde la convicción de que, sólo así, es posible revelar su empatía con el espíritu trágico de los griegos y comprender su necesidad de presentar aquel género literario como un paradigma desde el cual entender las grandezas y miserias del mundo contemporáneo.

Symmetries and fixed point stability of stochastic differential equations modeling self-organized criticality

A stochastic nonlinear partial differential equation is constructed for two different models exhibiting self-organized criticality: the Bak-Tang-Wiesenfeld (BTW) sandpile model [Phys. Rev. Lett. 59, 381 (1987); Phys. Rev. A 38, 364 (1988)] and the Zhang model [Phys. Rev. Lett. 63, 470 (1989)]. The dynamic renormalization group (DRG) enables one to compute the critical exponents. However, the nontrivial stable fixed point of the DRG transformation is unreachable for the original parameters of the models. We introduce an alternative regularization of the step function involved in the threshold condition, which breaks the symmetry of the BTW model. Although the symmetry properties of the two models are different, it is shown that they both belong to the same universality class. In this case the DRG procedure leads to a symmetric behavior for both models, restoring the broken symmetry, and makes accessible the nontrivial fixed point. This technique could also be applied to other problems with threshold dynamics.

Front form and point form formulation in P.R.M. noninteractions theorems

The front form and the point form of dynamics are studied in the framework of predictive relativistic mechanics. The non-interaction theorem is proved when a Poincar-invariant Hamiltonian formulation with canonical position coordinates is required.

Finite-size scaling investigation of the liquid-liquid critical point in ST2 water and its stability with respect to crystallization.

The liquid-liquid critical point scenario of water hypothesizes the existence of two metastable liq- uid phases low-density liquid (LDL) and high-density liquid (HDL) deep within the supercooled region. The hypothesis originates from computer simulations of the ST2 water model, but the stabil- ity of the LDL phase with respect to the crystal is still being debated. We simulate supercooled ST2 water at constant pressure, constant temperature, and constant number of molecules N for N ≤ 729 and times up to 1 μs. We observe clear differences between the two liquids, both structural and dynamical. Using several methods, including finite-size scaling, we confirm the presence of a liquid-liquid phase transition ending in a critical point. We find that the LDL is stable with respect to the crystal in 98% of our runs (we perform 372 runs for LDL or LDL-like states), and in 100% of our runs for the two largest system sizes (N = 512 and 729, for which we perform 136 runs for LDL or LDL-like states). In all these runs, tiny crystallites grow and then melt within 1 μs. Only for N ≤ 343 we observe six events (over 236 runs for LDL or LDL-like states) of spontaneous crystal- lization after crystallites reach an estimated critical size of about 70 ± 10 molecules.