6,430 research outputs found

    Detection of QED vacuum nonlinearities in Maxwell's equations by the use of waveguides

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    We present a novel method for detecting nonlinearities, due to quantum electrodynamics through photon-photon scattering, in Maxwell's equation. The photon-photon scattering gives rise to self-interaction terms, which are similar to the nonlinearities due to the polarisation in nonlinear optics. These self-interaction terms vanish in the limit of parallel propagating waves, but if instead of parallel propagating waves the modes generated in wavesguides are used, there will be a non-zero total effect. Based on this idea, we calculate the nonlinear excitation of new modes and estimate the strength of this effect. Furthermore, we suggest a principal experimental setup.Comment: 4 pages, REVTeX3. To appear in Phys. Rev. Let

    Asia's Sovereign Wealth Funds and Reform of the Global Reserve System

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    This paper explores the potential contribution of Asia’s sovereign wealth funds (SWFs) to the reform of the global foreign exchange reserve system. By diversifying the investment of Asia’s huge reserves into non-dollar denominated assets, Asian SWFs can help to dilute the dominant role of the US dollar as the global reserve currency. At the same time, by exposing reserve managers to a more diverse mix of currencies and asset classes, SWFs will better prepare them for the less dollar-centric global reserve system of the future. In addition to SWFs, other innovative policy options for more active reserve management include transferring some surplus reserves into national pension funds or into exchange traded funds which are distributed among local investors. Regardless of the exact form of more profit-oriented reserve management, it will require that countries build up a critical mass of skills and expertise in wealth preservation and management.Foreign exchange reserves, global reserve system, global financial architecture, pension fund, exchange traded fund

    A possibility to measure elastic photon--photon scattering in vacuum

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    Photon--photon scattering in vacuum due to the interaction with virtual electron-positron pairs is a consequence of quantum electrodynamics. A way for detecting this phenomenon has been devised based on interacting modes generated in microwave waveguides or cavities [G. Brodin, M. Marklund and L. Stenflo, Phys. Rev. Lett. \textbf{87} 171801 (2001)]. Here we materialize these ideas, suggest a concrete cavity geometry, make quantitative estimates and propose experimental details. It is found that detection of photon-photon scattering can be within the reach of present day technology.Comment: 7 pages, 3 figure

    High-power radiating plasma

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    The physical principles underlying the use of radiating plasmas for the optical pumping of lasers are described. Particular consideration is given to the properties of radiating plasmas; radiation selectivity; the dynamics, equilibrium, and stability of radiating plasmas; the radiative Reynolds number; and experimental results on radiating discharges

    The place of the Sun among the Sun-like stars

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    Context. Monitoring of the photometric and chromospheric HK emission data series of stars similar to the Sun in age and average activity level showed that there is an empirical correlation between the average stellar chromospheric activity level and the photometric variability. In general, more active stars show larger photometric variability. Interestingly, the measurements and reconstructions of the solar irradiance show that the Sun is significantly less variable than indicated by the empirical relationship. Aims. We aim to identify possible reasons for the Sun to be currently outside of this relationship. Methods. We employed different scenarios of solar HK emission and irradiance variability and compared them with available time series of Sun-like stars. Results. We show that the position of the Sun on the diagram of photometric variability versus chromospheric activity changes with time. The present solar position is different from its temporal mean position as the satellite era of continuous solar irradiance measurements has accidentally coincided with a period of unusually high and stable solar activity. Our analysis suggests that although present solar variability is significantly smaller than indicated by the stellar data, the temporal mean solar variability might be in agreement with the stellar data. We propose that the continuation of the photometric program and its expansion to a larger stellar sample will ultimately allow us to constrain the historical solar variability.Comment: 10 pages, 5 figures, accepted for publication in Astronomy&Astrophysic

    Some System Approaches to Water Resources Problems III. Optimal Control of Dam Storage

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    Some stochastic aspects of dam storage theory are considered in this paper. In particular optimal control based on some reliable lower estimates of unknown (uncertain) system parameters with the corresponding operational program is developed. Also, statistical equilibrium in dam storage (random) processes are analyzed and general conditions for such a phenomenon are established

    Some approximation problems in the theory of stationary processes

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    AbstractIn this paper, necessary and sufficient conditions for the regularity of a general (multivariate) stationary process are obtained. These subsume all the known criteria of regularity for such processes
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