Finite size effects in Neutron Star and Nuclear matter simulations

In this work we study molecular dynamics simulations of symmetric nuclear matter using a semi-classical nucleon interaction model. We show that, at sub-saturation densities and low temperatures, the solutions are non-homogeneous structures reminiscent of the ``nuclear pasta'' phases expected in Neutron Star Matter simulations, but shaped by artificial aspects of the simulations. We explore different geometries for the periodic boundary conditions imposed on the simulation cell: cube, hexagonal prism and truncated octahedron. We find that different cells may yield different solutions for the same physical conditions (i.e. density and temperature). The particular shape of the solution at a given density can be predicted analytically by energy minimization. We also show that even if this behavior is due to finite size effects, it does not mean that it vanishes for very large systems and it actually is independent of the system size: The system size sets the only characteristic length scale for the inhomogeneities. We then include a screened Coulomb interaction, as a model of Neutron Star Matter, and perform simulations in the three cell geometries. In this case, the competition between competing interactions of different range produces the well known nuclear pasta, with (in most cases) several structures per cell. However, we find that the results are affected by finite size in different ways depending on the geometry of the cell. In particular, at the same physical conditions and system size, the hexagonal prism yields a single structure per cell while the cubic and truncated octahedron show consistent results with more than one structure per cell. In this case, the results in every cell are expected to converge for systems much larger than the characteristic length scale that arises from the competing interactions.Comment: 17 pages, 10 figure

Isoscaling and the nuclear EOS

Experiments with rare isotopes are shedding light on the role isospin plays in the equation of state (EoS) of nuclear matter, and isoscaling -an straight-forward comparison of reactions with different isospin- could deliver valuable information about it. In this work we test this assertion pragmatically by comparing molecular dynamics simulations of isoscaling reactions using different equations of state and looking for changes in the isoscaling parameters; to explore the possibility of isoscaling carrying information from the hot-and-dense stage of the reaction, we perform our study in confined and expanding systems. Our results indicate that indeed isoscaling can help us learn about the nuclear EoS, but only in some range of excitation energies

Beyond Nuclear Pasta: Phase Transitions and Neutrino Opacity of Non-Traditional Pasta

In this work, we focus on different length scales within the dynamics of nucleons in conditions according to the neutron star crust, with a semiclassical molecular dynamics model, studying isospin symmetric matter at subsaturation densities. While varying the temperature, we find that a solid-liquid phase transition exists, that can be also characterized with a morphology transition. For higher temperatures, above this phase transition, we study the neutrino opacity, and find that in the liquid phase, the scattering of low momenta neutrinos remain high, even though the morphology of the structures differ significatively from those of the traditional nuclear pasta.Comment: 12 pages, 10 figure

Effect of nicotin, cystosin, lobelin, coniin, piperidin and quaternary ammonias on adrenal secretion

Nicotin is the type of a group of substances, one of whose characteristic properties is the capacity first to stimulate then to paralyze sympathetic ganglion cells (Langley, 1890, 1896, 1919; Langley and Dickinson, 1889, 1890). The adrenals receive sympathetic innervation by means of the major splanchnics and accessorily through the minor splanchnics. The adrenal medulla has a common embryological origin with the sympathetic ganglia Epinephrin produces sympathico-mimetic effects. All these facts lend a special interest to the study of the influence of nicotin and drugs of similar properties on adrenal secretion.Fil: Houssay, Bernardo Alberto. Administracion Nacional de Laboratorios E Institutos de Salud "dr. Carlos G. Malbran". Instituto Nacional de Epidemiologia. Departamento de Investigacion.; Argentina. Universidad de Buenos Aires. Facultad de Medicina; ArgentinaFil: Molinelli, E. A.. Universidad de Buenos Aires; ArgentinaReceived for publication January 18, 1926fond

Adrenal secretion produced by asphixia

Asphyxia produces a marked epinephrin discharge. This fact reported by several authors has been denied by others. Our present observations confirm the existence and give some insight into the cause of this phenomenon.Fil: Houssay, Bernardo Alberto. Universidad de Buenos Aires; ArgentinaFil: Molinelli, E. A.. Universidad de Buenos Aires; ArgentinaUnidad documental simpl

Adrenal discharge produced by drugs injected into the adrenal

When studying the effects of nicotin on adrenal secretion it was found that the injection of this drug into the adrenal gland produced a marked increase of the epinephrin secretion. In this paper the effects of several other drugs have been studied by the same method.Fil: Houssay, Bernardo Alberto. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Molinelli, E. A.. Universidad de Buenos Aires; Argentinafond

A fast - Monte Carlo toolkit on GPU for treatment plan dose recalculation in proton therapy

In the context of the particle therapy a crucial role is played by Treatment Planning Systems (TPSs), tools aimed to compute and optimize the tratment plan. Nowadays one of the major issues related to the TPS in particle therapy is the large CPU time needed. We developed a software toolkit (FRED) for reducing dose recalculation time by exploiting Graphics Processing Units (GPU) hardware. Thanks to their high parallelization capability, GPUs significantly reduce the computation time, up to factor 100 respect to a standard CPU running software. The transport of proton beams in the patient is accurately described through Monte Carlo methods. Physical processes reproduced are: Multiple Coulomb Scattering, energy straggling and nuclear interactions of protons with the main nuclei composing the biological tissues. FRED toolkit does not rely on the water equivalent translation of tissues, but exploits the Computed Tomography anatomical information by reconstructing and simulating the atomic composition of each crossed tissue. FRED can be used as an efficient tool for dose recalculation, on the day of the treatment. In fact it can provide in about one minute on standard hardware the dose map obtained combining the treatment plan, earlier computed by the TPS, and the current patient anatomic arrangement