144 research outputs found
Quantum diffusion on a cyclic one dimensional lattice
The quantum diffusion of a particle in an initially localized state on a
cyclic lattice with N sites is studied. Diffusion and reconstruction time are
calculated. Strong differences are found for even or odd number of sites and
the limit N->infinit is studied. The predictions of the model could be tested
with micro - and nanotechnology devices.Comment: 17 pages, 5 figure
Deflection of coronal rays by remote CMEs: shock wave or magnetic pressure?
We analyze five events of the interaction of coronal mass ejections (CMEs)
with the remote coronal rays located up to 90^\circ away from the CME as
observed by the SOHO/LASCO C2 coronagraph. Using sequences of SOHO/LASCO C2
images, we estimate the kink propagation in the coronal rays during their
interaction with the corresponding CMEs ranging from 180 to 920 km/s within the
interval of radial distances form 3 R. to 6 R. . We conclude that all studied
events do not correspond to the expected pattern of shock wave propagation in
the corona. Coronal ray deflection can be interpreted as the influence of the
magnetic field of a moving flux rope related to a CME. The motion of a
large-scale flux rope away from the Sun creates changes in the structure of
surrounding field lines, which are similar to the kink propagation along
coronal rays. The retardation of the potential should be taken into account
since the flux rope moves at high speed comparable with the Alfven speed.Comment: Accepted for Publication in Solar Physic
Detection of Gravitational Redshift on the Solar Disk by Using Iodine-Cell Technique
With an aim to examine whether the predicted solar gravitational redshift can
be observationally confirmed under the influence of the convective Doppler
shift due to granular motions, we attempted measuring the absolute spectral
line-shifts on a large number of points over the solar disk based on an
extensive set of 5188-5212A region spectra taken through an iodine-cell with
the Solar Domeless Telescope at Hida Observatory. The resulting heliocentric
line shifts at the meridian line (where no rotational shift exists), which were
derived by finding the best-fit parameterized model spectrum with the observed
spectrum and corrected for the earth's motion, turned out to be weakly
position-dependent as ~ +400 m/s near the disk center and increasing toward the
limb up to ~ +600 m/s (both with a standard deviation of sigma ~ 100 m/s).
Interestingly, this trend tends to disappear when the convectiveshift due to
granular motions (~-300 m/s at the disk center and increasing toward the limb;
simulated based on the two-component model along with the empirical
center-to-limb variation) is subtracted, finally resulting in the averaged
shift of 698 m/s (sigma = 113 m/s). Considering the ambiguities involved in the
absolute wavelength calibration or in the correction due to convective Doppler
shifts (at least several tens m/s, or more likely up to <~100 m/s), we may
regard that this value is well consistent with the expected gravitational
redshift of 633 m/s.Comment: 28 pages, 12 figures, electronic materials as ancillary data (table3,
table 4, ReadMe); accepted for publication in Solar Physic
Selection of bee species for environmental risk assessment of GM cotton in the Brazilian Cerrado
Comportamento ingestivo diurno de novilhos em pastejo submetidos a nĂveis crescentes de suplementação energĂ©tica
The Origin, Early Evolution and Predictability of Solar Eruptions
Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt
Large-Eddy Simulations of Magnetohydrodynamic Turbulence in Heliophysics and Astrophysics
We live in an age in which high-performance computing is transforming the way we do science. Previously intractable problems are now becoming accessible by means of increasingly realistic numerical simulations. One of the most enduring and most challenging of these problems is turbulence. Yet, despite these advances, the extreme parameter regimes encountered in space physics and astrophysics (as in atmospheric and oceanic physics) still preclude direct numerical simulation. Numerical models must take a Large Eddy Simulation (LES) approach, explicitly computing only a fraction of the active dynamical scales. The success of such an approach hinges on how well the model can represent the subgrid-scales (SGS) that are not explicitly resolved. In addition to the parameter regime, heliophysical and astrophysical applications must also face an equally daunting challenge: magnetism. The presence of magnetic fields in a turbulent, electrically conducting fluid flow can dramatically alter the coupling between large and small scales, with potentially profound implications for LES/SGS modeling. In this review article, we summarize the state of the art in LES modeling of turbulent magnetohydrodynamic (MHD) ows. After discussing the nature of MHD turbulence and the small-scale processes that give rise to energy dissipation, plasma heating, and magnetic reconnection, we consider how these processes may best be captured within an LES/SGS framework. We then consider several special applications in heliophysics and astrophysics, assessing triumphs, challenges,and future directions
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