Tunneling rate fluctuations induced by non-linear resonances: a quantitative treatment based on semiclassical arguments

We investigate the tunneling process between two symmetric stable islands of a forced pendulum Hamiltonian in the weak chaos regime. We show that when the tunneling doublet is quantized over a classical non-linear resonance the tunneling rate strongly deviates from the semiclassical prediction. This mechanism is responsible for the irregular dependence of the tunneling rate on the system parameters. The weak-chaos condition allows us to make a theoretical prediction which agrees very well with the numerical results. This opens up a possible avenue to a general theory on the dependence of quantum tunneling on classical chaos.Comment: 4 pages, 2 figure

The anatomy of a collaborative writing tool for public participation in democracy

Two approaches to online collaborative writing for the formulation of norms (laws, bills) are discussed: a Wikipedia-like approach and a structured approach

Graphite/epoxy composite for building Bipolar Plates

Bipolar plates (BPs) are important components of Proton Exchange Membrane Fuel Cells (PEMFC). Graphite-epoxy composites, having a better corrosion resistance than metal-based BPs and better mechanical properties than graphite BPs, are a promising alternative. In this study, we tried to develop graphite-epoxy composites meeting the technical US DOE targets for 2020, with a proper choice of manufacturing conditions that ensure a good compromise between conductivity, flexural strength, and gas permeability. In particular, we studied the influence of the filler to binder ratio, changed the molding temperature and time, and investigated the effects of increasing pressure both on in-plane conductivity and on helium permeability. We found that both formulation and molding pressure are crucial in determining the permeability of the graphite-epoxy composites, whereas molding temperature and time seem to play a minor role

Reactive oxygen species and transcript analysis upon excess light treatment in wild-type Arabidopsis thaliana vs a photosensitive mutant lacking zeaxanthin and lutein

<p>Abstract</p> <p>Background</p> <p>Reactive oxygen species (ROS) are unavoidable by-products of oxygenic photosynthesis, causing progressive oxidative damage and ultimately cell death. Despite their destructive activity they are also signalling molecules, priming the acclimatory response to stress stimuli.</p> <p>Results</p> <p>To investigate this role further, we exposed wild type <it>Arabidopsis thaliana </it>plants and the double mutant <it>npq1lut2 </it>to excess light. The mutant does not produce the xanthophylls lutein and zeaxanthin, whose key roles include ROS scavenging and prevention of ROS synthesis. Biochemical analysis revealed that singlet oxygen (¹O₂) accumulated to higher levels in the mutant while other ROS were unaffected, allowing to define the transcriptomic signature of the acclimatory response mediated by ¹O₂which is enhanced by the lack of these xanthophylls species. The group of genes differentially regulated in <it>npq1lut2 </it>is enriched in sequences encoding chloroplast proteins involved in cell protection against the damaging effect of ROS. Among the early fine-tuned components, are proteins involved in tetrapyrrole biosynthesis, chlorophyll catabolism, protein import, folding and turnover, synthesis and membrane insertion of photosynthetic subunits. Up to now, the <it>flu </it>mutant was the only biological system adopted to define the regulation of gene expression by ¹O₂. In this work, we propose the use of mutants accumulating ¹O₂by mechanisms different from those activated in <it>flu </it>to better identify ROS signalling.</p> <p>Conclusions</p> <p>We propose that the lack of zeaxanthin and lutein leads to ¹O₂accumulation and this represents a signalling pathway in the early stages of stress acclimation, beside the response to ADP/ATP ratio and to the redox state of both plastoquinone pool. Chloroplasts respond to ¹O₂accumulation by undergoing a significant change in composition and function towards a fast acclimatory response. The physiological implications of this signalling specificity are discussed.</p

Semiclassical chaos, the uncertainty principle, and quantum dissipation

Article on semiclassical chaos, the uncertainty principle, and quantum dissipation

Quantum Irreversibility and Chaos [Phys. Rev. Lett. 67, 2593 (1991)]

Corrections to an equation printed with a typographical error in Quantum Irreversibility and Chaos, Physical Review Letters 67, 2593 (1991)

Towards the Thermodynamics of Localization Processes

We study the entropy time evolution of a quantum mechanical model, which is frequently used as a prototype for Anderson's localization. Recently Latora and Baranger [V. Latora, M. Baranger, Phys. Rev.Lett. 82, 520(1999)] found that there exist three entropy regimes, a transient regime of passage from dynamics to thermodynamics, a linear in time regime of entropy increase, namely a thermodynamic regime of Kolmogorov kind, and a saturation regime. We use the non-extensive entropic indicator recently advocated by Tsallis [ C. Tsallis, J. Stat. Phys. 52, 479 (1988)] with a mobile entropic index q, and we find that with the adoption of the ``magic'' value q = Q = 1/2 the Kolmogorov regime becomes more extended and more distinct than with the traditional entropic index q = 1. We adopt a two-site model to explain these properties by means of an analytical treatment and we argue that Q =1/2 might be a typical signature of the occurrence of Anderson's localization.Comment: 13 pages, 8 figures submitted to Phys. Rev.