65,515 research outputs found

    Runtime verification for biochemical programs

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    The biochemical paradigm is well-suited for modelling autonomous systems and new programming languages are emerging from this approach. However, in order to validate such programs, we need to define precisely their semantics and to provide verification techniques. In this paper, we consider a higher-order biochemical calculus that models the structure of system states and its dynamics thanks to rewriting abstractions, namely rules and strategies. We extend this calculus with a runtime verification technique in order to perform automatic discovery of property satisfaction failure. The property specification language is a subclass of LTL safety and liveness properties

    Free-fall accretion and emitting caustics in wind-fed X-ray sources

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    In wind-fed X-ray binaries the accreting matter is Compton cooled and falls freely onto the compact object. The matter has a modest angular momentum ll and accretion is quasi-spherical at large distances from the compact object. Initially small non-radial velocities grow in the converging supersonic flow and become substantial in the vicinity of the accretor. The streamlines with l>(GMR)1/2l>(GMR_*)^{1/2} (where MM and RR_* are the mass and radius of the compact object) intersect outside RR_* and form a two-dimensional caustic which emits X-rays. The streamlines with low angular momentum, l<(GMR)1/2l<(GMR_*)^{1/2}, run into the accretor. If the accretor is a neutron star, a large X-ray luminosity results. We show that the distribution of accretion rate/luminosity over the star surface is sensitive to the angular momentum distribution of the accreting matter. The apparent luminosity depends on the side from which the star is observed and can change periodically with the orbital phase of the binary. The accretor then appears as a `Moon-like' X-ray source.Comment: 8 pages, accepted to MNRA

    Physical picture of the gapped excitation spectrum of the one-dimensional Hubbard model

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    A simple picture for the spectrum of the one-dimensional Hubbard model is presented using a classification of the eigenstates based on an intuitive bound-state Bethe-Ansatz approach. This approach allows us to prove a "string hypothesis" for complex momenta and derive an exact formulation of the Bethe-Ansatz equations including all states. Among other things we show that all gapped eigenstates have the Bethe-Ansatz form, contrary to assertions in the literature. The simplest excitations in the upper Hubbard band are computed: we find an unusual dispersion close to half-filling.Comment: 22 pages, revtex, 4 eps-figure

    Where Is Scientific Evidence in Support of Refuge Size Reduction for Pyramided Bt Crops?

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    Genetically modified plants expressing insecticidal Cry proteins originating from a soil-dwelling bacterium Bacillus thuringiensis (Bt) provide a powerful tool for managing insect pests. Unfortunately, insect ability to develop resistance to insecticidal proteins potentially jeopardizes its long-term efficiency. Review of registration materials submitted by plant biotech industry to the U.S. Environmental Protection Agency and the existing scientific literature shows that currently available evidence in support of reducing refuge for the pyramided genetically modified corn plants to 5% of the total crop area is essentially limited to predictions of a single unpublished mathematical model developed &#x201c;in-house&#x201d; by the industry scientists. Additional research and a more extensive (and open) scientific discussion will be of great benefit for ensuring sustainable use of this technology

    Realistic description of causality in truly complex hierarchical structures

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    In his recent essay article entitled "Physics, Complexity and Causality" (Nature 435, 743; 2005) George Ellis states that despite well-known successes of physics "we still do not have a realistic description of causality in truly complex hierarchical structures". Whereas one can only support the author's view that such description is increasingly desirable, the main statement suffers from essential incompleteness, since a realistic, mathematically rigorous and universally applicable description of detailed cause-effect links in truly complex systems, including e.g. emergent consciousness dynamics, does exist and is easily accessible through internet sources. As these results have been successfully presented at many international conferences (and even published!), the true problem is not the absence of realistic complexity description, but its intentional neglect, without any scientific objection, by the same physics establishment that insists (rightly) upon the necessity of that "new kind of science". As today's science has started to strongly modify the whole depth of unreduced dynamic complexity at all its levels using purely empirical, blind technology, further intentional rejection of consistent understanding of the real world complexity inevitably leads to destructive, catastrophically growing consequences