37,002 research outputs found
The origins and physical roots of life’s dual – metabolic and genetic – nature
This review paper aims at a better understanding of the origin and physical foundation of life’s dual – metabolic and genetic – nature. First, I give a concise ‘top-down’ survey of the origin of life, i.e., backwards in time from extant DNA/RNA/protein-based life over the RNA world to the earliest, pre-RNA stages of life’s origin, with special emphasis on the metabolism-first versus gene/replicator-first controversy. Secondly, I critically assess the role of minerals in the earliest origins of bothmetabolism and genetics. And thirdly, relying on the work of Erwin Schrödinger, Carl Woese and Stuart Kauffman, I sketch and reframe the origin of metabolism and genetics from a physics, i.e., thermodynamics, perspective. I conclude that life’s dual nature runs all the way back to the very dawn and physical constitution of life on Earth. Relying on the current state of research, I argue that life’s origin stems from the congregation of two kinds of sources of negentropy – thermodynamic and statistical negentropy. While thermodynamic negentropy (which could have been provided by solar radiation and/or geochemical and thermochemical sources), led to life’s combustive and/or metabolic aspect, the abundant presence of mineral surfaces on the prebiotic Earth – with their selectively adsorbing and catalysing (thus ‘organizing’) micro-crystalline structure or order – arguably provided for statistical negentropy for life to originate, eventually leading to life’s crystalline and/or genetic aspect. However, the transition from a prebiotic world of relatively simple chemical compounds including periodically structured mineral surfaces towards the complex aperiodic and/or informational structure, specificity and organization of biopolymers and biochemical reaction sequences remains a ‘hard problem’ to solve
Towards adaptive multi-robot systems: self-organization and self-adaptation
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The development of complex systems ensembles that operate in uncertain environments is a major challenge. The reason for this is that system designers are not able to fully specify the system during specification and development and before it is being deployed. Natural swarm systems enjoy similar characteristics, yet, being self-adaptive and being able to self-organize, these systems show beneficial emergent behaviour. Similar concepts can be extremely helpful for artificial systems, especially when it comes to multi-robot scenarios, which require such solution in order to be applicable to highly uncertain real world application. In this article, we present a comprehensive overview over state-of-the-art solutions in emergent systems, self-organization, self-adaptation, and robotics. We discuss these approaches in the light of a framework for multi-robot systems and identify similarities, differences missing links and open gaps that have to be addressed in order to make this framework possible
The case of the trapped singularities
A case study in bifurcation and stability analysis is presented, in which
reduced dynamical system modelling yields substantial new global and predictive
information about the behaviour of a complex system. The first smooth pathway,
free of pathological and persistent degenerate singularities, is surveyed
through the parameter space of a nonlinear dynamical model for a
gradient-driven, turbulence-shear flow energetics in magnetized fusion plasmas.
Along the route various obstacles and features are identified and treated
appropriately. An organizing centre of low codimension is shown to be robust,
several trapped singularities are found and released, and domains of
hysteresis, threefold stable equilibria, and limit cycles are mapped.
Characterization of this rich dynamical landscape achieves unification of
previous disparate models for plasma confinement transitions, supplies valuable
intelligence on the big issue of shear flow suppression of turbulence, and
suggests targeted experimental design, control and optimization strategies.Comment: 21 pages, 12 figures, 34 postscript figure file
Order out of Randomness : Self-Organization Processes in Astrophysics
Self-organization is a property of dissipative nonlinear processes that are
governed by an internal driver and a positive feedback mechanism, which creates
regular geometric and/or temporal patterns and decreases the entropy, in
contrast to random processes. Here we investigate for the first time a
comprehensive number of 16 self-organization processes that operate in
planetary physics, solar physics, stellar physics, galactic physics, and
cosmology. Self-organizing systems create spontaneous {\sl order out of chaos},
during the evolution from an initially disordered system to an ordered
stationary system, via quasi-periodic limit-cycle dynamics, harmonic mechanical
resonances, or gyromagnetic resonances. The internal driver can be gravity,
rotation, thermal pressure, or acceleration of nonthermal particles, while the
positive feedback mechanism is often an instability, such as the
magneto-rotational instability, the Rayleigh-B\'enard convection instability,
turbulence, vortex attraction, magnetic reconnection, plasma condensation, or
loss-cone instability. Physical models of astrophysical self-organization
processes involve hydrodynamic, MHD, and N-body formulations of Lotka-Volterra
equation systems.Comment: 61 pages, 38 Figure
On the Nature and Shape of Tubulin Trails: Implications on Microtubule Self-Organization
Microtubules, major elements of the cell skeleton are, most of the time, well
organized in vivo, but they can also show self-organizing behaviors in time
and/or space in purified solutions in vitro. Theoretical studies and models
based on the concepts of collective dynamics in complex systems,
reaction-diffusion processes and emergent phenomena were proposed to explain
some of these behaviors. In the particular case of microtubule spatial
self-organization, it has been advanced that microtubules could behave like
ants, self-organizing by 'talking to each other' by way of hypothetic (because
never observed) concentrated chemical trails of tubulin that are expected to be
released by their disassembling ends. Deterministic models based on this idea
yielded indeed like-looking spatio-temporal self-organizing behaviors.
Nevertheless the question remains of whether microscopic tubulin trails
produced by individual or bundles of several microtubules are intense enough to
allow microtubule self-organization at a macroscopic level. In the present
work, by simulating the diffusion of tubulin in microtubule solutions at the
microscopic scale, we measure the shape and intensity of tubulin trails and
discuss about the assumption of microtubule self-organization due to the
production of chemical trails by disassembling microtubules. We show that the
tubulin trails produced by individual microtubules or small microtubule arrays
are very weak and not elongated even at very high reactive rates. Although the
variations of concentration due to such trails are not significant compared to
natural fluctuations of the concentration of tubuline in the chemical
environment, the study shows that heterogeneities of biochemical composition
can form due to microtubule disassembly. They could become significant when
produced by numerous microtubule ends located in the same place. Their possible
formation could play a role in certain conditions of reaction. In particular,
it gives a mesoscopic basis to explain the collective dynamics observed in
excitable microtubule solutions showing the propagation of concentration waves
of microtubules at the millimeter scale, although we doubt that individual
microtubules or bundles can behave like molecular ants
Scalable aggregation predictive analytics: a query-driven machine learning approach
We introduce a predictive modeling solution that provides high quality predictive analytics over aggregation queries in Big Data environments. Our predictive methodology is generally applicable in environments in which large-scale data owners may or may not restrict access to their data and allow only aggregation operators like COUNT to be executed over their data. In this context, our methodology is based on historical queries and their answers to accurately predict ad-hoc queries’ answers. We focus on the widely used set-cardinality, i.e., COUNT, aggregation query, as COUNT is a fundamental operator for both internal data system optimizations and for aggregation-oriented data exploration and predictive analytics. We contribute a novel, query-driven Machine Learning (ML) model whose goals are to: (i) learn the query-answer space from past issued queries, (ii) associate the query space with local linear regression & associative function estimators, (iii) define query similarity, and (iv) predict the cardinality of the answer set of unseen incoming queries, referred to the Set Cardinality Prediction (SCP) problem. Our ML model incorporates incremental ML algorithms for ensuring high quality prediction results. The significance of contribution lies in that it (i) is the only query-driven solution applicable over general Big Data environments, which include restricted-access data, (ii) offers incremental learning adjusted for arriving ad-hoc queries, which is well suited for query-driven data exploration, and (iii) offers a performance (in terms of scalability, SCP accuracy, processing time, and memory requirements) that is superior to data-centric approaches. We provide a comprehensive performance evaluation of our model evaluating its sensitivity, scalability and efficiency for quality predictive analytics. In addition, we report on the development and incorporation of our ML model in Spark showing its superior performance compared to the Spark’s COUNT method
Methodologies for self-organising systems:a SPEM approach
We define ’SPEM fragments’ of five methods for developing self-organising multi-agent systems. Self-organising traffic lights controllers provide an application scenario
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