Gravitational waves from coalescing massive black holes in young dense clusters

HST observations reveal that young massive star clusters form in gas-rich environments like the Antenn{\ae} galaxy which will merge in collisional processes to form larger structures. These clusters amalgamate and if some of these clusters harbour a massive black hole in their centres, they can become a strong source of gravitational waves when they coalesce. In order to understand the dynamical processes that are into play in such a scenario, one has to carefully study the evolution of the merger of two of such young massive star clusters and more specifically their respective massive black holes. This will be a promising source of gravitational waves for both, LISA and the proposed Big Bang Observer (BBO), whose first purpose is to search for an inflation-generated gravitational waves background in the frequency range of $10^{-1}-1$ Hz. We used high-resolution direct summation $N-$body simulations to study the orbital evolution of two colliding globular clusters with different initial conditions. Even if the final eccentricity is almost negligible when entering the bandwidth, it will suffice to provide us with detailed information about these astrophysical events.Comment: Based on contribution at the Sixth International LISA Symposium, 7 page

Improving bioethical decision-making with a little help from legal argumentation

The most appropriate method for clinical decision-making is deliberation. The deliberative procedure aims to achieve wise and prudent decisions about health care taking into account facts, values and norms. Since deliberative reasoning is shared by healthcare professions, ethics and law, this paper introduces the structure and features of the bioethical deliberative procedure and suggests to improve it with some contributions from legal science and theories of argumentation.El método más adecuado para la toma de decisiones biomédicas es la deliberación. El procedimiento deliberativo pretende alcanzar decisiones prudentes y razonables tras tomar en consideración hechos, valores y normas. Al ser la racionalidad deliberativa un rasgo compartido por las profesiones asistenciales, la ética y el derecho, el presente artículo expone la estructura y las características del método bioético deliberativo y propone mejorarla mediante algunas contribuciones de la ciencia jurídica y las teorías de la argumentación

Gravitational waves from coalescing massive black holes in young dense clusters

HST observations reveal that young massive star clusters form in gas-rich environments like the Antenn{\ae} galaxy which will merge in collisional processes to form larger structures. These clusters amalgamate and if some of these clusters harbour a massive black hole in their centres, they can become a strong source of gravitational waves when they coalesce. In order to understand the dynamical processes that are into play in such a scenario, one has to carefully study the evolution of the merger of two of such young massive star clusters and more specifically their respective massive black holes. This will be a promising source of gravitational waves for both, LISA and the proposed Big Bang Observer (BBO), whose first purpose is to search for an inflation-generated gravitational waves background in the frequency range of $10^{-1}-1$ Hz. We used high-resolution direct summation $N-$body simulations to study the orbital evolution of two colliding globular clusters with different initial conditions. Even if the final eccentricity is almost negligible when entering the bandwidth, it will suffice to provide us with detailed information about these astrophysical events

Liquid-glass transition in equilibrium

We show in numerical simulations that a system of two coupled replicas of a binary mixture of hard spheres undergoes a phase transition in equilibrium at a density slightly smaller than the glass transition density for an unreplicated system. This result is in agreement with the theories that predict that such a transition is a precursor of the standard ideal glass transition. The critical properties are compatible with those of an Ising system. The relations of this approach to the conventional approach based on configurational entropy are briefly discussed.Comment: 5 pages, 3 figures, version accepted for publication in the Physical Review

First Principle Computation of Random Pinning Glass Transition, Glass Cooperative Length-Scales and Numerical Comparisons

As a guideline for experimental tests of the ideal glass transition (Random Pinning Glass Transition, RPGT) that shall be induced in a system by randomly pinning particles, we performed first-principle computations within the Hypernetted chain approximation and numerical simulations of a Hard Sphere model of glass-former. We obtain confirmation of the expected enhancement of glassy behaviour under the procedure of random pinning, which consists in freezing a fraction $c$ of randomly chosen particles in the positions they have in an equilibrium configuration. We present the analytical phase diagram as a function of $c$ and of the packing fraction $\phi$, showing a line of RPGT ending in a critical point. We also obtain first microscopic results on cooperative length-scales characterizing medium-range amorphous order in Hard Spere glasses and indirect quantitative information on a key thermodynamic quantity defined in proximity of ideal glass transitions, the amorphous surface tension. Finally, we present numerical results of pair correlation functions able to differentiate the liquid and the glass phases, as predicted by the analytic computations.Comment: Working draft, comments are welcom

How Turing parasites expand the computational landscape of digital life

Why are living systems complex? Why does the biosphere contain living beings with complexity features beyond those of the simplest replicators? What kind of evolutionary pressures result in more complex life forms? These are key questions that pervade the problem of how complexity arises in evolution. One particular way of tackling this is grounded in an algorithmic description of life: living organisms can be seen as systems that extract and process information from their surroundings in order to reduce uncertainty. Here we take this computational approach using a simple bit string model of coevolving agents and their parasites. While agents try to predict their worlds, parasites do the same with their hosts. The result of this process is that, in order to escape their parasites, the host agents expand their computational complexity despite the cost of maintaining it. This, in turn, is followed by increasingly complex parasitic counterparts. Such arms races display several qualitative phases, from monotonous to punctuated evolution or even ecological collapse. Our minimal model illustrates the relevance of parasites in providing an active mechanism for expanding living complexity beyond simple replicators, suggesting that parasitic agents are likely to be a major evolutionary driver for biological complexity.Comment: 13 pages, 8 main figures, 1 appendix with 5 extra figure

Stability and evolution of super-massive stars (SMS)

Highly condensed gaseous objects with masses larger than 5x10^4 M_sun are called super-massive stars. In the quasistationary contraction phase, the hydrostatic equilibrium is determined by radiation pressure and gravitation. The global structure is that of an n=3 polytrope at the stability limit. Small relativistic corrections for example can initiate a free fall collapse due to the 'post Newtonian' instability. Since the outcome of the final collapse -A super-massive black hole or hypernova- depends sensitively on the structure and the size of the object, when the instability sets in, it is important to investigate in more detail the contraction phase of the SMS. If the gaseous object is embedded in a dense stellar system, the central star cluster, the interaction and coupling of both components due to dynamical friction changes the energy balance and evolution of the SMS dramatically. Dynamical friction between stars and gas, which can be estimated semi-analytically (see Just et al. 1986), has three different effects on the two-component system. We discuss in which evolutionary stages and parameter range these interaction processes are relevant and how they can influence the stability and evolution of the SMS.Comment: 6 pages, 1 figure, needs eas.cls (included). EAS Publ. Series, Vol. 10 EDP, Paris in pres