8,520 research outputs found

    Plasticity in current-driven vortex lattices

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    We present a theoretical analysis of recent experiments on current-driven vortex dynamics in the Corbino disk geometry. This geometry introduces controlled spatial gradients in the driving force and allows the study of the onset of plasticity and tearing in clean vortex lattices. We describe plastic slip in terms of the stress-driven unbinding of dislocation pairs, which in turn contribute to the relaxation of the shear, yielding a nonlinear response. The steady state density of free dislocations induced by the applied stress is calculated as a function of the applied current and temperature. A criterion for the onset of plasticity at a radial location rr in the disk yields a temperature-dependent critical current that is in qualitative agreement with experiments.Comment: 11 pages, 4 figure

    Spontaneous patterns in coherently driven polariton microcavities

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    We consider a polariton microcavity resonantly driven by two external lasers which simultaneously pump both lower and upper polariton branches at normal incidence. In this setup, we study the occurrence of instabilities of the pump-only solutions towards the spontaneous formation of patterns. Their appearance is a consequence of the spontaneous symmetry breaking of translational and rotational invariance due to interaction induced parametric scattering. We observe the evolution between diverse patterns which can be classified as single-pump, where parametric scattering occurs at the same energy as one of the pumps, and as two-pump, where scattering occurs at a different energy. For two-pump instabilities, stripe and chequerboard patterns become the dominant steady-state solutions because cubic parametric scattering processes are forbidden. This contrasts with the single-pump case, where hexagonal patterns are the most common arrangements. We study the possibility of controlling the evolution between different patterns. Our results are obtained within a linear stability analysis and are confirmed by finite size full numerical calculations.Comment: 15 pages, 9 figure

    On the Role of Science in the Postindustrial Society. "Logos" - the Empire Builder

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    The hypothesis that language and DNA represent two stages of the same evolutionary path is briefly evaluated. Volterra equations, so useful in describing the dynamics of competing systems are, in fact, equally efficient in describing social behavior, as shown in numerous examples. The emergence of language first, and science later, interpreted as a metalanguage, are attributed to a "hypercyclization" of basic competing utterances in analogy of hypercyclization of quasi-species of replicating molecules in Manfred Eigen's theory of DNA development and evolution

    On Decarbonization: Historically and Perspectively

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    The possibility that CO2 emitted as a consequence of burning fossil fuels may have an impact on climate stimulated a lot of research on the evolution of the emissions and the possibility of remedies. Here we analyze first the evolution of CO2 emission historically, by looking at the mix and quantity of fuels used. This mix evolves from wood to nuclear energies with an intermezzo of coal, oil and gas, the fossils. The intermezzo lasts about 400 years. These fuels are made of carbon and hydrogen in different proportion and we have discovered that the ratio evolves in favor of hydrogen following a simple logistic for more than 200 years, formally pointing to a pure hydrogen economy for the end of this century. That fact that hydrogen has to emerge as the central fuel is shown here to evolve out of the history of fuels consumption. Nuclear appears to have the quintessential characteristics to be the primary energy source

    Environmental Problems and Technological Opportunities

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    The argument of the paper is that environmental problems are a direct consequence of a certain Weltanschauung Christianism brought into Western societies. Fairly simple solutions exist for the large ecological problems generated by the intrusion of humanity in the ecosphere, including at the limit an almost complete withdrawal. Because cultural changes have long time constants, there is no hope of short-term application of the solutions. Ecologists have to learn thinking long term and recognize that perseverance is more important than argument

    On Energy and Agriculture

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    Energy analysis shows that, since the neolithic, agriculture has developed as a technology to reduce the amount of land necessary to support a given population. All technical discoveries and inventions were eventually bent to this final objective: intensification. The ratio of food-energy output per energy input, on the other hand, did remain remarkably constant, around a value of 40, till agriculture operated on a bootstrap basis. Basically, after World War II, the large-scale use of fossil fuels via machines and fertilizers drastically changed the trends, leading to an escalation in energy consumption per unit of product. The trend appears reversible, and the proper processes to be supported in view of a judicious long-term energy management are indicated

    Logos, il Creatore di Imperi

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    On the Long-Term History of Energy Markets and the Chances for Natural Gas

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    In this paper, Cesare Marchetti presents a review of the development of world energy markets over the last two centuries. This is then used as a springboard for projections of the likely future penetration of natural gas. Marchetti's hypothesis is that society can be viewed as an ensemble of component structures engaged in Darwinian competition; his analysis leads to interesting and perhaps surprising conclusions on long-term energy price stability, the future role of natural gas, and the vexed question of whether or not there really is a global energy shortfall
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