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101.
The effect of particle-particle interaction on the adiabatic index γ for an electron-positron plasma is considered. An improved method for numerically calculating the Hartree-Fock exchange integral is presented and its relativistic asymptotics is determined. An approximation formula is derived for the correlation part of the interaction in the low-density limit. This formula includes degeneracy and the positron component. 相似文献
102.
A high-velocity ionized outflow and XUV photosphere in the narrow emission line quasar PG1211+143 总被引:1,自引:0,他引:1
K. A. Pounds J. N. Reeves A. R. King K. L. Page P. T. O'Brien M. J. L. Turner 《Monthly notices of the Royal Astronomical Society》2003,345(3):705-713
We report on the analysis of a ∼60-ks XMM–Newton observation of the bright, narrow emission line quasar PG1211+143. Absorption lines are seen in both European Photon Imaging Camera and Reflection Grating Spectrometer spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C. The observed line energies indicate an ionized outflow velocity of ∼24 000 km s−1 . The highest energy lines require a column density of N H ∼ 5 × 1023 cm−2 , at an ionization parameter of log ξ∼ 3.4 . If the origin of this high-velocity outflow lies in matter being driven from the inner disc, then the flow is likely to be optically thick within a radius of ∼130 Schwarzschild radii, providing a natural explanation for the big blue bump (and strong soft X-ray) emission in PG1211+143. 相似文献
103.
Slavek M. Rucinski 《Monthly notices of the Royal Astronomical Society》2006,368(3):1319-1322
The luminosity function for contact binary stars of the W UMa type is evaluated on the basis of the All Sky Automated Survey (ASAS) photometric project covering all stars south of δ=+ 28° within a magnitude range 8 < V < 13 . Lack of colour indices enforced a limitation to 3374 systems with P < 0.562 d (i.e. 73 per cent of all systems with P < 1 d ) where a simplified MV (log P ) calibration could be used. The spatial density relative to the main-sequence FGK stars of 0.2 per cent, as established previously from the Hipparcos sample to V = 7.5 , is confirmed. While the numbers of contact binaries in the ASAS are large and thus the statistical uncertainties small, derivation of the luminosity function required a correction for missed systems with small amplitudes and with orbital periods longer than 0.562 d; the correction, by a factor of 3, carries an uncertainty of about 30 per cent. 相似文献
104.
C. S. M. Turney K. Van Den Burg S. Wastegrd S. M. Davies N. J. Whitehouse J. R. Pilcher C. Callaghan 《第四纪科学杂志》2006,21(4):335-345
High‐precision correlation of palaeoclimatic and palaeoenvironmental records is crucial for testing hypotheses of synchronous change. Although radiocarbon is the traditional method for dating late Quaternary sedimentary sequences, particularly during the last glacial–interglacial transition (LGIT; 15–9 ka), there are inherent problems with the method, particularly during periods of climate change which are often accompanied by major perturbations in atmospheric radiocarbon content. An alternative method is the use of tephras that act as time‐parallel marker horizons. Within Europe, numerous volcanic centres are known to have erupted during the LGIT, providing considerable potential for high‐precision correlation independent of past radiocarbon fluctuations. Here we report the first identification of the Vedde Ash and Askja Tephra in Ireland, significantly extending the known provenance of these events. We have also identified two new horizons (the Roddans Port Tephras A and B) and tentatively recognise an additional horizon from Vallensgård Mose (Denmark) that provide crucial additional chronological control for the LGIT. Two phases of the Laacher See Tephra (LST) are reported, the lower Laacher See Tephra (LLST) and probably the C2 phase of the Middle Laacher See Tephra (MLST‐C2) indicating a more northeasterly distribution of this fan than reported previously. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
105.
106.
Analyses of primary and early diagenetic fluid inclusions in the halite from the Late Ordovician Mallowa Salt, Canning Basin, Western Australia indicate a Ca‐rich composition and high concentration of parent brines in the basin which were close to sylvite and carnallite precipitation. The salt‐bearing series in the sampled interval was overheated up to 62 °C. The recorded differences in gas compositions result from the input of several gas sources including dispersed organic matter in the salt series and hydrocarbon deposits in the underlying rocks. The high concentration of the brines in fluid inclusions does not allow quantitative reconstruction of the chemical composition of Late Ordovician parent seawater. Using the information from Early Cambrian and Late Silurian basins as a proxy, however, the new data indicate that Late Ordovician seawater was undoubtedly Ca‐rich and, in comparison with modern seawater, had a similar K content, considerably lower Mg content (c. 30%), approximately three times the Ca content and one‐third the SO4 content. 相似文献
107.
108.
In laboratory investigations with model waters, the behaviour of selected cation-exchange resins (Amberlite 200 C, Duolite C-25, Lewatit S-100, Wofatit KPS and Wofatit KS-10) is tested. The usable volume capacity of the resins in the forms of H, Na and NH4 as well as the water content and the total volume capacity after 25 cycles of loading/regeneration are determined. It is recommended to use Amberlite 200 C and Wofatit KS-10. 相似文献
109.
110.