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991.
Down‐faulting at the north‐west margins of the Gulf of Aqaba is inferred to have triggered a catastrophic sedimentary event at 2.3 ka that killed the Elat fringing coral reef. Whereas segments of the Holocene reef were perfectly fossilized and preserved beneath a veneer of siliciclastic sediments, other segments were abraded, settled by nomads, and later re‐submerged under 4 m of water. Repeated damage triggered by down‐throwing earthquakes degenerate the fringing reefs of the north‐west end of the gulf. Conversely, on the north‐eastern and southern parts of the gulf, where earthquakes uplift the margins, modern reefs are thriving, attached to uplifted fossil reef terraces. Therefore, coastal subsidence moderates the development of fringing coral reefs during the late Holocene sea‐level stand still. 相似文献
992.
A statistical study is made of the magnetic field directional discontinuities observed in early 1976 onboard Helios 1 and 2. Strong day-to-day variations of occurrence rates are found on either tangential (TD) or rotational (RD) discontinuities. No large variation (if any) is found versus either heliocentric distance or heliographic latitude. This contradicts previous findings obtained by the same technique on Pioneer 8 data in 1968–69; however, reasons are given to expect different results, under different solar conditions. The most interesting results come from the study of the morphology of discontinuities: first of all, the orientation of TD's and RD's normals (identified by a minimum variance technique) are strongly organized by the average magnetic field, following their progressive directional change when approaching the Sun. The inclination (θ n ) and azimuthal (? n ) distributions are gaussian and strongly peaked along the field lines for RD's; as regards TD's the normals are perpendicular to the average field and follow its progressive variation; the θ n distribution is isotropic in solid angle, which is interpreted as evidence of crossing of flux tubes on the order of one/hour. Implications of this interpretation in contrast with a turbulent approach are also discussed. 相似文献
993.
Roberto De Propris Matthew Colless John A. Peacock Warrick J. Couch Simon P. Driver Michael L. Balogh Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Nicholas Cross Gavin Dalton George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,351(1):125-132
994.
Here we report the spectral characteristics of the high and low states of the pulsar 4U 0114 + 65 and examine the change in
the parameters of the spectral model. A power law and a photoelectric absorption by material along the line of sight together
with a high energy cut-off suffice to describe the continuum spectrum in both the states. A fluorescence iron line at ∼6.4
keV is present in the high as well as in the low state, though it is less intense in the latter. The photon index, cut-off
energy and e-folding energy values hardly show any discernible change over the states. We compare these spectral characteristics
as observed with ASCA with those of other satellites. We also compare the spectral characteristics of 4U 0114 + 650 with other
X-ray sources which show intensity variation at different time scales. 相似文献
995.
M. R. Krbetschek J. Götze G. Irmer U. Rieser T. Trautmann 《Mineralogy and Petrology》2002,76(3-4):167-177
Summary ?Feldspar specimens covering the whole Or–Ab–An ternary have been investigated by cathodoluminescence (CL), photoluminescence
(PL), radioluminescence (RL) and radiophosphorescence (RP) spectrometry. A red luminescence emission, which is commonly explained
by Fe3+ lattice defects, is a characteristic feature of all the spectra. Different shifts of the peak-wavelength between ∼680–750 nm
(1.82–1.65 eV) were observed with varying feldspar composition. Despite the dependence of the peak position on the Ca/Na ratio,
initially described for CL in the 1970s, there is also a shift induced by changing NaK composition. The observed effects can
be explained by known relations that the peak position of the red luminescence emission in feldspars can be affected both
by the structural state of the feldspar and the site occupancy of the trivalent iron. In the case of alkali feldspars another
factor may influence the peak-shift. The incorporation of the larger potassium ion causes non-linear variations of the cell
dimensions and therefore Fe–O bond distance. The behaviour of the red peak-shift dependent on the feldspar composition is
not equal for all types of luminescence investigated. This is most likely caused by the different luminescence excitation
mechanism.
Received December 3, 2001; revised version accepted March 25, 2002 相似文献
996.
Coronal heating by nanoflares is presented by using observational, analytical, numerical simulation and statistical results.
Numerical simulations show the formation of numerous current sheets if the magnetic field is sheared and bipoles have unequal
pole strengths. This fact supports the generation of nanoflares and heating by them. The occurrence frequency of transients
such as flares, nano/microflares, on the Sun exhibits a power-law distribution with exponent α varying between 1.4 and 3.3.
For nanoflares heating α must be greater than 2. It is likely that the nanoflare heating can be reproduced by dissipating
Alfven waves. Only observations from future space missions such as Solar-B, to be launched in 2006, can shed further light
on whether Alfven waves or nanoflares, heat the solar corona. 相似文献
997.
U. Hopp 《Astrophysics and Space Science》1980,72(1):233-236
By star counts on four plates with different limiting magnitudes, it was found that the relative frequency of Main-Sequence stars increases from the centre of the cluster to the boundary. It is shown that the stars of NGC 7789 are separated according to their masses. 相似文献
998.
999.
1000.
The scientific objective of the system presented in this paper is to conduct in situ measurements of environmental parameters and to support several marine in situ experiments which are carried out in order to investigate the interaction between the sea and the sea bottom in shallow-water ecosystems. Automated in situ measurements are carried out by means of the radio-controlled data acquisition and control system "OBS" which is mounted on an unattended platform in the western Baltic. The shore station, at a distance of about 25 km, is located at the Institute of Applied Physics of Kiel University and is equipped with a central computer for real-time data retrieval and remote programming. Part of the OBS system is a vertical scanning profiling system which provides measurements of temperature, electrical conductivity, turbidity, scalar irradiance, downwelling and upwelling irradiance, pH, and dissolved oxygen in a water column of about 10-m depth. The vertical resolution is 10 cm. Profiling depth range was automatically determined from the shore by means of an adjustable upper depth limit, in order to protect the probes from surface waves. The research conducted here requires simultaneous measurements of various environmental parameters. This is done by about 20-30 fixed probes mounted on the platform in the air and in the water as well on the sea bottom in the neighborhood of the platform. The radio-controlled data acquisition system serves all probes and samples the sensors repeatedly in time. 相似文献