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401.
Polar plumes appear as elongated objects starting at the solar polar regions. Here we analyze these objects from a sequence of images taken simultaneously by the three spacecraft telescopes STEREO/EUVI A and B, and SOHO/EIT. We establish a method capable of automatically identifying plumes in solar EUV images close to the limb at 1.01?–?1.39?R ⊙ in order to study their temporal evolution. This plume-identification method is based on a multiscale Hough-wavelet analysis. Then two methods to determine the 3D localization and structure of the plumes are discussed: first, tomography using filtered back-projection and including the differential rotation of the Sun and, second, conventional stereoscopic triangulation. We show that tomography and stereoscopy are complementary for studying polar plumes. We also show that this systematic 2D identification and the proposed methods of 3D reconstruction are well suited to identify plumes individually and also to analyze the distribution of plumes and inter-plume regions. Finally, the results are discussed, focusing on plume position and cross-sectional area. 相似文献
402.
Hydrogen bonding in topaz-OH, Al2SiO4(OH)2, was investigated by IR spectroscopic analysis of the temperature dependence of the OH-stretching frequencies. Low-temperature
spectra ranging from −196 to −160°C prove the existence of four non-equivalent H-positions in the crystal structure from the
occurrence of four different OH-bands. With increasing temperature, these bands merge first, above −160°C, into two OH-bands
and then above 400°C into one asymmetric broad band. Shifting of the OH-bands is caused by thermally induced hydrogen order–disorder.
Low temperature fixes the protons in their positions; increasing temperature induces proton movement and allows switching
between the different positions. Autocorrelation analysis of the IR spectra reveals two phase transitions, one at about −155°C
from P1 to Pbn2
1
characterized as static–dynamic change and the second at about 380°C from Pbn2
1
to Pbnm caused by disordering of the protons. The increasing symmetry with temperature is due to advanced proton movement and dynamical
averages over the proton distribution densities. 相似文献
403.
The aqueous mobility and potential bioavailability of metals and metalloids in road runoff in a ‘wet–dry’ tropical location
were assessed by analysing metal and metalloid concentrations in particulate, total dissolved and labile dissolved phases
in runoff waters. Road-derived Al, Cu, Pb, Sb and Zn concentrations were substantially elevated in runoff when compared to
receiving creek waters. Median dissolved concentrations in road runoff exceeded those in creek waters by up to an order of
magnitude. Leaching experiments of road sediments confirmed that several metals and metalloids were released in high concentrations
from road sediments. Labile Zn and Cu concentrations measured by diffusion gradients in thin films (DGT) showed that almost
all dissolved Zn and up to half of dissolved Cu in runoff waters and in road sediment leachate were potentially bioavailable.
Comparisons of dissolved metal concentrations in receiving waters affected by road runoff with ecosystem guideline levels,
indicated a risk of reaching toxic levels of Cu and Zn in the receiving waters in the absence of adequate treatment or dilution.
Low dilution rates of road runoff are likely to occur during late ‘dry’ season/early ‘wet’ season storms which have the potential
to produce high metal concentrations derived from long periods of accumulation of road sediment at a time when creek flow
rates are at their annual minimum. 相似文献