13,564 research outputs found
Connectionism Reconsidered: Minds, Machines and Models
In this paper the issue of drawing inferences about biological cognitive systems on the basis of connectionist simulations is addressed. In particular, the justification of inferences based on connectionist models trained using the backpropagation learning algorithm is examined. First it is noted that a justification commonly found in the philosophical literature is inapplicable. Then some general issues are raised about the relationships between models and biological systems. A way of conceiving the role of hidden units in connectionist networks is then introduced. This, in combination with an assumption about the way evolution goes about solving problems, is then used to suggest a means of justifying inferences about biological systems based on connectionist research
Adaptive evolution on neutral networks
We study the evolution of large but finite asexual populations evolving in
fitness landscapes in which all mutations are either neutral or strongly
deleterious. We demonstrate that despite the absence of higher fitness
genotypes, adaptation takes place as regions with more advantageous
distributions of neutral genotypes are discovered. Since these discoveries are
typically rare events, the population dynamics can be subdivided into separate
epochs, with rapid transitions between them. Within one epoch, the average
fitness in the population is approximately constant. The transitions between
epochs, however, are generally accompanied by a significant increase in the
average fitness. We verify our theoretical considerations with two analytically
tractable bitstring models.Comment: 16 pages, 4 eps figures, Latex (academic press style file), submitted
to the Bulletin of Mathematical Biolog
Equivalence scales reconsidered – an empirical investigation
Households can differ in size and needs. A reliable assessment of inequality in living standards, therefore, necessitates the conversion of the original heterogeneous into an artificial quasi-homogeneous population. Ebert and Moyes (2003) and Shorrocks (2004) theoretically explore the properties of two conversion strategies, i.e., to calculate household equivalent incomes and then to weight household units by their size vs. their needs. We use data from the Luxembourg Income Study for examining the sensitivity of the Gini and the Theil index to the chosen conversion strategy, and explain our results by means of an inequality decomposition by household types. Country inequality rankings are sensitive to the conversion strategy applied. The decomposition analysis reveals the underlying mechanisms. We find inequality estimates typically to be lower in the size-weighted distribution compared to needs-weighting. This is driven by relatively higher weights of large household units in case of size weighting in combination with inequality being typically below average among households with children.income distribution, inequality, inequality decomposition, equivalence scale.
Decoherence and wave function collapse
The possibility of consistency between the basic quantum principles of
quantum mechanics and wave function collapse is reexamined. A specific
interpretation of environment is proposed for this aim and applied to
decoherence. When the organization of a measuring apparatus is taken into
account, this approach leads also to an interpretation of wave function
collapse, which would result in principle from the same interactions with
environment as decoherence. This proposal is shown consistent with the
non-separable character of quantum mechanics
Evolution of Canalizing Boolean Networks
Boolean networks with canalizing functions are used to model gene regulatory
networks. In order to learn how such networks may behave under evolutionary
forces, we simulate the evolution of a single Boolean network by means of an
adaptive walk, which allows us to explore the fitness landscape. Mutations
change the connections and the functions of the nodes. Our fitness criterion is
the robustness of the dynamical attractors against small perturbations. We find
that with this fitness criterion the global maximum is always reached and that
there is a huge neutral space of 100% fitness. Furthermore, in spite of having
such a high degree of robustness, the evolved networks still share many
features with "chaotic" networks.Comment: 8 pages, 10 figures; revised and extended versio
Liquid-gas phase transition in hot nuclei studied with INDRA
Thanks to the high detection quality of the INDRA array, signatures related
to the dynamics (spinodal decomposition) and thermodynamics (negative
microcanonical heat capacity) of a liquid-gas phase transition have been
simultaneously studied in multifragmentation events in the Fermi energy domain.
The correlation between both types of signals strongly supports the existence
of a first order phase transition for hot nuclei.Comment: 9 pages, 2 figures, Invited talk to Nucleus-nucleus 2003 Moscow June
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