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Accelerator-Driven System, ADS, belong to the new generation of advanced reactors being developed that promise to drastically reduce the life of radioactive waste by, for example, the transmutation process. Subcritical reactor designs of the ADS type have attracted worldwide attention and are the subject of research and development in several countries. The purpose of this work is to simulate transients associated with ADS. It adopted the neutron diffusion model that leads the spatial kinetics equations. These equations are solved by the known numerical method of finite differences. The simulations are performed considering transients related to the variations in the intensity of the proton flux provided by the particle accelerator acting in a sub-critical reactor in three-dimensional geometry for two energy groups and six groups of delayed neutron precursors.

In order to develop systems capable of artificial evolution, we need to identify which systems can produce complex behavior. We present a novel classification method applicable to any class of deterministic discrete space and time dynamical systems. The method is based on classifying the asymptotic behavior of the average computation time in a given system before entering a loop. We were able to identify a critical region of behavior that corresponds to a phase transition from ordered behavior to chaos across various classes of dynamical systems. To show that our approach can be applied to many different computational systems, we demonstrate the results of classifying cellular automata, Turing machines, and random Boolean networks. Further, we use this method to classify 2D cellular automata to automatically find those with interesting, complex dynamics. We believe that our work can be used to design systems in which complex structures emerge. Also, it can be used to compare various versions of existing attempts to model open-ended evolution (Channon, 2006 ; Ofria & Wilke, 2004 ; Ray, 1991). [ABSTRACT FROM AUTHOR]

We consider a new mechanism for the removal of angular momentum from an X-ray binary system and the change in its orbital period—the mass loss in the form of a wind from an accretion disk. A powerful wind from a disk is observed in X-ray transients and is predicted by models. We have obtained an analytical estimate for the increase in the orbital period of a binary system with a wind from the disk during an outburst; quantitative estimates are given for the systems XTE J1118 480, A0620 00, and GRS 1124 68. The rates of increase in the period are comparable in absolute value to the observed rates of secular decrease in the period. We also compare the predicted rates of change in the period of a binary system due to the mass transfer into the disk and the outflow from the second Lagrange point with the observed ones. We conclude that the above-mentioned mechanisms cannot explain the observed secular decrease in the period, and it is necessary to consider a circumbinary disk that removes the binary's angular momentum. [ABSTRACT FROM AUTHOR]

Conservation Biology fosters the study of Earth's ecosystems and biodiversity aiming at protecting species and their habitats from menaces causing the erosion of biotic interactions and extinctions. Its ultimate goal is to preserve biodiversity and promote sustainable ecological management maintaining both ecosystem's resilience and services. Ecosystems display complex patterns in time and space due to the intrinsic nonlinear nature of their interactions and can suffer regime shifts driven by the agents of global change. During the last decades, Ecology has turned from the equilibrium metaphor to the paradigm of non-equilibrium dynamics. This involves putting into the scene multiple stable states, nonlinear regime shifts, stochasticity, and ecological transients. These aspects are also crucial for biological conservation since they play a fundamental role in species' persistence, ecosystems' resilience, and in detecting warning signals prior to either the collapse or the recovery of the ecosystem. In this contribution, we discuss ecological regime shifts caused by tipping points in real ecosystems. Then, we provide information on some known dynamical features from theoretical ecology and dynamical systems theory associated to tipping points, mainly given by transient phenomena and the characteristic statistical patterns tied to early warning signals. These features are illustrated with a single-species mathematical model including facilitation and immigration. We also introduce and provide evidence of late warning signals as a way to identify when a tipping point has been surpassed but the system still remains in a transient state and recovery may be still possible. Our main goal is to near non-equilibrium concepts in Ecology to the conservationist community and promote bridges between such concepts and the management and conservation of ecosystems. • Ecosystems can suffer abrupt regime shifts driven by tipping points. • Even reducing or eliminating stressors that trigger tipping points, ecosystems may not return to their previous states. • To avoid the impacts of tipping points conservation policies may need to monitor the indicators of ecosystems' resilience. • We discuss how tipping points properties impact on ecosystems' conservation, management, and restoration. • We introduce late warning signals (LWS) and provide preliminary evidence of their existence. [ABSTRACT FROM AUTHOR]