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

On the two-dimensional rotational body of maximal Newtonian resistance

We investigate, by means of computer simulations, shapes of nonconvex bodies that maximize resistance to their motion through a rarefied medium, considering that bodies are moving forward and at the same time slowly rotating. A two-dimensional geometric shape that confers to the body a resistance very close to the theoretical supremum value is obtained, improving previous results.Comment: This is a preprint version of the paper published in J. Math. Sci. (N. Y.), Vol. 161, no. 6, 2009, 811--819. DOI:10.1007/s10958-009-9602-

Mathematical retroreflectors

Retroreflectors are optical devices that reverse the direction of incident beams of light. Here we present a collection of billiard type retroreflectors consisting of four objects; three of them are asymptotically perfect retroreflectors, and the fourth one is a retroreflector which is very close to perfect. Three objects of the collection have recently been discovered and published or submitted for publication. The fourth object - notched angle - is a new one; a proof of its retroreflectivity is given.Comment: 32 pages, 19 figure

Noether's Symmetry Theorem for Variational and Optimal Control Problems with Time Delay

We extend the DuBois-Reymond necessary optimality condition and Noether's symmetry theorem to the time delay variational setting. Both Lagrangian and Hamiltonian versions of Noether's theorem are proved, covering problems of the calculus of variations and optimal control with delays.Comment: This is a preprint of a paper whose final and definite form will appear in the international journal Numerical Algebra, Control and Optimization (NACO). Paper accepted for publication 15-March-201

Modelo de análise não linear material de pórticos de betão armado : calibração das relações constitutivas

No presente trabalho é sumariamente descrito um modelo de análise não linear material destinado à simulação do comportamento de pórticos de betão armado. As barras podem ter secção qualquer, variável ao longo do seu eixo, sendo discretizadas por elementos de Timoshenko 3D. As secções transversais são discretizadas em quadriláteros, dando origem a um modelo de fibras. A influência na resposta de alguns parâmetros das leis constitutivas dos materiais foi avaliada com base na comparação com resultados experimentais

Comportamento de vigas de betão armado de secção oca submetidas a flexão, corte e torção

Neste trabalho são descritos ensaios de vigas de betão armado submetidas a flexão, corte e torção. Estes ensaios fazem parte de um trabalho de investigação experimental e numérico relativo ao comportamento não linear material de estruturas de betão armado. Os resultados obtidos são apresentados e discutidos. Para determinar as principais características do betão e do aço foram também realizados ensaios de compressão uniaxial em provetes cilíndricos de betão simples, ensaios de flexão sob três pontos de carga em vigas entalhadas de betão simples e ensaios de tracção em varões de aço

Crack constitutive model for the prediction of punching failure modes of fiber reinforced concrete laminar structures

The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.The authors wish to acknowledge the support provided by the Portuguese Science and Technology Foundation (FCT) by means of the project PTDC/ECM/73099/2006 "CUTINEMO-Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures". The first author acknowledges the financial support of FCT, PhD Grant number SFRH/BD/23326/2005

Characterization of bioactive colored materials produced from bacterial cellulose and bacterial pigments

A Bacterial Cellulose (BC) film was developed and characterized as a potential functional bioactive material. BC films, obtained from a microbial consortium of bacteria and yeast species, were functionalized with the bacterial pigment prodigiosin, produced by Serratia plymuthica, and flexirubin-type pigment, from Chryseobacterium shigense, which exhibit a wide range of biological properties. BC was successfully functionalized at 15% over the weight of the fiber at 40 °C during 60 min, and a color strength of 1.00 ± 0.01 was obtained for BC_prodigiosin and 0.38 ± 0.02 for BC_flexirubin-type pigment. Moreover, the BC films showed moderate hydrophilic character following alkaline treatment, which was maintained after both pigments were incorporated. The porosity and mechanical performance of the functionalized BC samples also remained unaffected. Furthermore, the BC samples functionalized with prodigiosin presented antibacterial activity and were able to inhibit the growth of pathogenic bacteria Staphylococcus aureus and Pseudomonas aeruginosa, with inhibition rates of 97.89 ± 0.60% and 85.12 ± 0.17%, respectively, while BC samples functionalized with flexirubin-type pigment exhibited the highest antioxidant activity, at 38.96 ± 0.49%. This research provides an eco-friendly approach to grant BC film-based material with color and advantageous bioactive properties, which can find application in several fields, especially for medical purposes.This work was funded by the Portuguese Foundation for Science and Technology (FCT), I.P./MCTES through national funds (PIDDAC), in the scope of the FibEnTech Research Unit project (UIDB/00195/2020) and of the 2C2T Research Unit Project (UIDB/00264/2020). L.F.A. Amorim also acknowledges the doctoral fellowship (PD/BD/128417/2017) from Portuguese Foundation for Science and Technology (FCT), co-financed by the European Social Fund (FSE), through the Regional Operational Program of the Center (Centro2020)