Galactic Outflows and the pollution of the Galactic Environment by Supernovae

We here explore the effects of the SN explosions into the environment of star-forming galaxies like the Milky Way. Successive randomly distributed and clustered SNe explosions cause the formation of hot superbubbles that drive either fountains or galactic winds above the galactic disk, depending on the amount and concentration of energy that is injected by the SNe. In a galactic fountain, the ejected gas is re-captured by the gravitational potential and falls back onto the disk. From 3D nonequilibrium radiative cooling hydrodynamical simulations of these fountains, we find that they may reach altitudes up to about 5 kpc in the halo and thus allow for the formation of the so called intermediate-velocity-clouds (IVCs) which are often observed in the halos of disk galaxies. The high-velocity-clouds that are also observed but at higher altitudes (of up to 12 kpc) require another mechanism to explain their production. We argue that they could be formed either by the capture of gas from the intergalactic medium and/or by the action of magnetic fields that are carried to the halo with the gas in the fountains. Due to angular momentum losses to the halo, we find that the fountain material falls back to smaller radii and is not largely spread over the galactic disk. Instead, the SNe ejecta fall nearby the region where the fountain was produced, a result which is consistent with recent chemical models of the galaxy. The fall back material leads to the formation of new generations of molecular clouds and to supersonic turbulence feedback in the disk.Comment: 10 pages, 5 figures; paper of invited talk for the Procs. of the 2007 WISER Workshop (World Space Environment Forum), Alexandria, Egypt, October 2007, Spa. Sci. Rev

Influence of flow confinement on the drag force on a static cylinder

The influence of confinement on the drag force $F$ on a static cylinder in a viscous flow inside a rectangular slit of aperture $h_0$ has been investigated from experimental measurements and numerical simulations. At low enough Reynolds numbers, $F$ varies linearly with the mean velocity and the viscosity, allowing for the precise determination of drag coefficients $\lambda_{||}$ and $\lambda_{\bot}$ corresponding respectively to a mean flow parallel and perpendicular to the cylinder length $L$. In the parallel configuration, the variation of $\lambda_{||}$ with the normalized diameter $\beta = d/h_0$ of the cylinder is close to that for a 2D flow invariant in the direction of the cylinder axis and does not diverge when $\beta = 1$. The variation of $\lambda_{||}$ with the distance from the midplane of the model reflects the parabolic Poiseuille profile between the plates for $\beta \ll 1$ while it remains almost constant for $\beta \sim 1$. In the perpendicular configuration, the value of $\lambda_{\bot}$ is close to that corresponding to a 2D system only if $\beta \ll 1$ and/or if the clearance between the ends of the cylinder and the side walls is very small: in that latter case, $\lambda_{\bot}$ diverges as $\beta \to 1$ due to the blockage of the flow. In other cases, the side flow between the ends of the cylinder and the side walls plays an important part to reduce $\lambda_{\bot}$: a full 3D description of the flow is needed to account for these effects

Asymmetric core combustion in neutron stars and a potential mechanism for gamma ray bursts

We study the transition of nuclear matter to strange quark matter (SQM) inside neutron stars (NSs). It is shown that the influence of the magnetic field expected to be present in NS interiors has a dramatic effect on the propagation of a laminar deflagration (widely studied so far), generating a strong acceleration of the flame in the polar direction. This results in a strong asymmetry in the geometry of the just formed core of hot SQM which resembles a cylinder orientated in the direction of the magnetic poles of the NS. This geometrical asymmetry gives rise to a bipolar emission of the thermal neutrino-antineutrino pairs produced in the process of SQM formation. The neutrino-antineutrino pairs annihilate into electron-positron pairs just above the polar caps of the NS giving rise to a relativistic fireball, thus providing a suitable form of energy transport and conversion to gamma emission that may be associated to short gamma ray bursts (GRBs).Comment: 2 figure

Modelo arquitectónico desde la vista de información para apoyar la interoperabilidad de herramientas software que soportan la mejora de procesos de software

(Eng) Diverse software tools that support the software process improvement (SPI) not interoperate between them, that is to say, the exchange of information between the different tools is deficient, making it difficult to sequence and automatic re-use of information of SPI initiatives. In this article we present an architectural model from the information view to support the interoperability of software tools that support the stages of diagnosing the process and formulating improvements. The model establishes architecture that describes the type of information that can be exchanged these tools, as well as the structure of the data, their possible values, its semantics, and the restrictions imposed on the use and interpretation of such information. The architectural model is composed of a set of schemas, raised in conceptual form, which can be used by organizations that wish to develop software tools to interoperate, which provide support in a comprehensive way to diagnosing the process and formulating improvements of the SPI cycle. These schemas were evaluated using the qualitative method Focus Group.(Spa) La gran mayoría de herramientas software que soportan la mejora de procesos de software (SPI) no interoperan entre ellas, es decir, el intercambio de información entre las diferentes herramientas es deficiente, lo que dificulta la secuencia y reutilización automática de la información de las iniciativas de SPI. En este artículo presentamos un modelo arquitectónico desde la vista de información para apoyar la interoperabilidad de las herramientas software que soportan las etapas de Diagnóstico de procesos y Formulación de mejoras. El modelo establece la arquitectura que describe el tipo de información que pueden intercambiar estas herramientas, así como la estructura de los datos, sus posibles valores, su semántica, y las restricciones impuestas sobre la utilización e interpretación de dicha información. El modelo arquitectónico está constituido por un conjunto de esquemas planteados de forma conceptual, el cual puede ser utilizado por organizaciones que deseen desarrollar herramientas software que interoperen entre sí, las cuales brinden soporte de manera integral al Diagnóstico y Formulación del ciclo de SPI. Estos esquemas fueron evaluados utilizando el método cualitativo Focus Group

The daily life of a researcher introduced with an online data analysis experience based on visual programming

A common criticism for the Italian higher education system is the gap that separates it from the employment landscape. To improve this situation, our department and schools are sponsoring internships, to expose the students to the work life. Groups of two high school students are invited to work with researchers for a week. A tutor introduces them to the research theme and proposes related activities. In order not to require previous experience with programming languages, the visual programming language Blockly is used as the development toolkit, for its suitability for educational activities. We present the development of new functionalities for Blockly purposely for the project: online reading data from a real detection system, interactive analysis, and online data visualization. The activity was successfully experienced by the students hosted in the research group. The actual implementation of the analysis algorithm was quickly achieved, even with no prior experience with data analysis. We bypassed the difficulties related to the syntax of programming languages, by employing Blockly and our added features; this allowed us to focus on the fundamental concepts. The students enjoyed the whole experience and were very proactive asking relevant questions and proposing ideas

Calculation of the energy spectrum of a two-electron spherical quantum dot

We study the energy spectrum of the two-electron spherical parabolic quantum dot using the exact Schroedinger, the Hartree-Fock, and the Kohn-Sham equations. The results obtained by applying the shifted-1/N method are compared with those obtained by using an accurate numerical technique, showing that the relative error is reasonably small, although the first method consistently underestimates the correct values. The approximate ground-state Hartree-Fock and local-density Kohn-Sham energies, estimated using the shifted-1/N method, are compared with accurate numerical self-consistent solutions. We make some perturbative analyses of the exact energy in terms of the confinement strength, and we propose some interpolation formulae. Similar analysis is made for both mean-field approximations and interpolation formulae are also proposed for these exchange-only ground-state cases.Comment: 18 pages, LaTeX, 2 figures-ep