774 research outputs found

    A principal possibility for computer investigation of evolution of dynamical systems with independent on time accuracy

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    Extensive N-body simulations are among the key means for the study of numerous astrophysical and cosmological phenomena, so various schemes are developed for possibly higher accuracy computations. We demonstrate the principal possibility for revealing the evolution of a perturbed Hamiltonian system with an accuracy independent on time. The method is based on the Laplace transform and the derivation and analytical solution of an evolution equation in the phase space for the resolvent and using computer algebra.Comment: Eur Phys Journ C (in press), to match the version to appear, 7 pages, 3 fig

    Anti-solar differential rotation on the active sub-giant HU Virginis

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    Measuring surface differential rotation (DR) on different types of stars is important when characterizing the underlying stellar dynamo. It has been suggested that anti-solar DR laws can occur when strong meridional flows exist. We aim to investigate the differential surface rotation on the primary star of the RS CVn binary HU Vir by tracking its starspot distribution as a function of time. We also aim to recompute and update the values for several system parameters of the triple system HU Vir (close and wide orbits). Time-series high-resolution spectroscopy for four continuous months was obtained with the 1.2-m robotic STELLA telescope. Nine consecutive Doppler images were reconstructed from these data, using our line-profile inversion code iMap. An image cross-correlation method was applied to derive the surface differential-rotation law for HU Vir. New orbital elements for the close and the wide orbits were computed using our new STELLA radial velocities (RVs) combined with the RV data available in the literature. Photometric observations were performed with the Amadeus Automatic Photoelectric Telescope (APT), providing contemporaneous Johnson-Cousins VV and II data for approximately 20 years. This data was used to determine the stellar rotation period and the active longitudes. We confirm anti-solar DR with a surface shear parameter α\alpha of -0.029 ±\pm 0.005 and -0.026 ±\pm 0.009, using single-term and double-term differential rotation laws, respectively. The best fit is achieved assuming a solar-like double-term law with a lap time of \approx 400 d. Our orbital solutions result in a period of 10.387678 ±\pm 0.000003 days for the close orbit and 2726 ±\pm 7 d (\approx 7.5 yr) for the wide orbit. A Lomb-Scarge (L-S) periodogram of the pre-whitened VV-band data reveals a strong single peak providing a rotation period of 10.391 ±\pm 0.008 d.Comment: Accepted for publication in A&

    Pre-determining the location of electromigrated gaps by nonlinear optical imaging

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    In this paper we describe a nonlinear imaging method employed to spatially map the occurrence of constrictions occurring on an electrically-stressed gold nanowire. The approach consists at measuring the influence of a tightly focused ultrafast pulsed laser on the electronic transport in the nanowire. We found that structural defects distributed along the nanowire are efficient nonlinear optical sources of radiation and that the differential conductance is significantly decreased when the laser is incident on such electrically-induced morphological changes. This imaging technique is applied to pre-determined the location of the electrical failure before it occurs.Comment: 3 figure

    Micropropagation of grapevine (Vitis vinifera L.) seedless cultivar 'Parvana' through lateral bud development

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    Factors affecting successful establishment in vitro, rapid proliferation, rooting and acclimatization of grapevine seedless cultivation 'Parvana' were studied. A treatment combination of 2.0 % calcium hypochlorite for 7 minutes plus 70 % ethanol for 3 minutes was found to be effective with 75.0 % of aseptic culture establishment in vitro. The highest number of new microshoots (4.5) was obtained in a culture medium (Gambourg's B5 modification) supplemented with 0.6 mg∙L-1 BAP + 0.2 mg∙L-1 KIN + 0.5 mg∙L-1 GA3. Presence of GA3 in combination with BAP and KIN promoted elongation of shoots. A concentration of 0.4 mg/l IAA in half strength of MS (Murashige and Skoog) proved to be the best for rooting (84.4 % root induction, 4.66 roots with 7.9 cm length). In vitro rooted plantlets were successfully acclimatized, with 82.2 % survival rate in plastic pots containing garden soil, sand and peat moss(1:1:1). In this study an efficient micro propagation technique of grapevine seedless cultivar 'Parvana' was successfully achieved through lateral bud culture. Such a technique would be useful for large scale plant production and in vitro conservation

    Coherent Control of Light Scattering from Nanostructured Materials by Second-Harmonic Generation

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    We introduce an active, all-optical method for controlling the intensity and directionality of light scattering from single nanostructures. The method is based on the coherent interplay between linear light scattering and second-harmonic generation. The intensity and directionality of scattered light can be controlled by the phase delay and the relative angle between excitation beams. We discuss the principle of this coherent control technique and perform numerical model calculations