801 research outputs found

    Transformation of electromagnetically induced transparency into absorption in a thermal potassium optical cell with spin preserving coating

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    We report a new experimental approach where an order of magnitude enhancement of the electromagnetically induced absorption (EIA) resonance contrast, thus making it similar to that of the EIT resonance contrast is observed under the same conditions. The EIA signal results from the interaction of a weak probe beam with a ground state that has been driven by the pump (counter-propagating) beam. Probe absorption spectra are presented where the laser frequency is slowly detuned over the D 1 line of 39 K vapor contained in a cell with a PDMS antirelaxation coating. In addition to the frequency detuning, a magnetic field orthogonal to the laser beams is scanned around zero value at a higher rate. With both laser beams linearly polarized, an EIT resonance is observed. However, changing the pump beam polarization from linear to circular reverses the resonance signal from EIT to EIA

    A simple model for simulation of growth and development in grapevine (Vitis vinifera L.). 2. Model validation

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    A simple model for the simulation of growth and development of Sangiovese vines has been presented in a previous paper. In this paper the model is validated to examine whether the description of the physiological relationships in the model describe the growth of grapevine (cv. Sangiovese) realistically. Furthermore, the model was adapted and validated for the simulation of growth of another cultivar (cv. Cabernet Sauvignon). Comparisons of simulated and experimental data for both cultivars reveal that the model made good predictions of vine growth for the whole growing season

    A simple model for simulation of growth and development in grapevine (Vitis vinifera L.). 1. Model description

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    A simple simulation model for growth of grapevine (Vitis vinifera L. cv. Sangiovese) is presented which mainly bases on analytical results from field experiments with plants free of visible stress and diseases. In the model leaf area development is defined as a function of temperature, biomass accumulation as a function of intercepted radiation and fruit growth is calculated from a linear increase of the fruit biomass index with time. The assumptions are discussed and comparisons between simulated and measured results are shown

    Conversion of bright magneto-optical resonances into dark at fixed laser frequency for D2 excitation of atomic rubidium

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    Nonlinear magneto-optical resonances on the hyperfine transitions belonging to the D2 line of rubidium were changed from bright to dark resonances by changing the laser power density of the single exciting laser field or by changing the vapor temperature in the cell. In one set of experiments atoms were excited by linearly polarized light from an extended cavity diode laser with polarization vector perpendicular to the light's propagation direction and magnetic field, and laser induced fluorescence (LIF) was observed along the direction of the magnetic field, which was scanned. A low-contrast bright resonance was observed at low laser power densities when the laser was tuned to the Fg=2 --> Fe=3 transition of Rb-87 and near to the Fg=3 --> Fe=4 transition of Rb-85. The bright resonance became dark as the laser power density was increased above 0.6mW/cm2 or 0.8 mW/cm2, respectively. When the Fg=2 --> Fe=3 transition of Rb-87 was excited with circularly polarized light in a second set of experiments, a bright resonance was observed, which became dark when the temperature was increased to around 50C. The experimental observations at room temperature could be reproduced with good agreement by calculations based on a theoretical model, although the theoretical model was not able to describe measurements at elevated temperatures, where reabsorption was thought to play a decisive role. The model was derived from the optical Bloch equations and included all nearby hyperfine components, averaging over the Doppler profile, mixing of magnetic sublevels in the external magnetic field, and a treatment of the coherence properties of the exciting radiation field.Comment: 9 pages, 7 figure

    Operational Numerical Weather Prediction systems based on Linux cluster architectures

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    The progress in weather forecast and atmospheric science has been always closely linked to the improvement of computing technology. In order to have more accurate weather forecasts and climate predictions, more powerful computing resources are needed, in addition to more complex and better-performing numerical models. To overcome such a large computing request, powerful workstations or massive parallel systems have been used. In the last few years, parallel architectures, based on the Linux operating system, have been introduced and became popular, representing real“high performance–low cost” systems. In this work the Linux cluster experience achieved at the Laboratory for Meteorology and Environmental Analysis (LaMMA-CNR-IBIMET) is described and tips and performances analysed

    Optical response of a misaligned and suspended Fabry-Perot cavity

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    The response to a probe laser beam of a suspended, misaligned and detuned optical cavity is examined. A five degree of freedom model of the fluctuations of the longitudinal and transverse mirror coordinates is presented. Classical and quantum mechanical effects of radiation pressure are studied with the help of the optical stiffness coefficients and the signals provided by an FM sideband technique and a quadrant detector, for generic values of the product Ď–Ď„\varpi \tau of the fluctuation frequency times the cavity round trip. A simplified version is presented for the case of small misalignments. Mechanical stability, mirror position entanglement and ponderomotive squeezing are accommodated in this model. Numerical plots refer to cavities under test at the so-called Pisa LF facility.Comment: 14 pages (4 figures) submitted to Phys. Rev.

    Stationary entanglement between two movable mirrors in a classically driven Fabry-Perot cavity

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    We consider a Fabry-Perot cavity made by two moving mirrors and driven by an intense classical laser field. We show that stationary entanglement between two vibrational modes of the mirrors, with effective mass of the order of micrograms, can be generated by means of radiation pressure. The resulting entanglement is however quite fragile with respect to temperature.Comment: 15 pages, 3 figure
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