9,530 research outputs found
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 artÃculo expone
la estructura y las caracterÃsticas del método bioético deliberativo y propone mejorarla mediante
algunas contribuciones de la ciencia jurÃdica y las teorÃas 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
Hz. We used high-resolution direct summation 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
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 Hz. We used high-resolution direct summation 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 of randomly chosen particles in the positions they have
in an equilibrium configuration. We present the analytical phase diagram as a
function of and of the packing fraction , 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
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