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251.
In Quaternary studies, tephras are widely used as marker horizons to correlate geological deposits. Therefore, accurate and precise dating is crucial. Among radiometric dating techniques, luminescence dating has the potential to date tephra directly using glass shards, volcanic minerals that formed during the eruption or mineral fragments that originate from the shattered country rock. Moreover, sediments that frame the tephra can be dated to attain an indirect age bracket. A review of numerous luminescence dating studies highlights the method's potential and challenges. While reliable direct dating of volcanic quartz and feldspar as a component in tephra is still methodically difficult mainly due to thermal and athermal signal instability, red thermoluminescence of volcanic quartz and the far-red emission of volcanic feldspar have been used successfully. Furthermore, the dating of xenolithic quartz within tephra shows great potential. Numerous studies date tephra successfully indirectly. Dating surrounding sediments is generally straightforward as long as samples are not taken too close to the tephra horizons. Here, issues arise from the occurrence of glass shards within the sediments or unreliable determination of dose rates. This includes relocation of radioelements, mixing of tephra into the sediment and disregarding different dose rates of adjacent material. 相似文献
252.
A data archive of GPS navigation messages 总被引:2,自引:1,他引:1
Since 18 June 2007 navigation data messages transmitted by the GPS constellation are recorded by five receivers within GeoForschungsZentrum’s
global groundstation network. We describe the recording, processing, validation, analysis and archiving of the navigation
data. During the 197 days between 18 June 2007 and 31 December 2007 a total of 125,723,666 subframes were collected. By taking
into consideration that the same data set frequently is observed by two or more receivers concurrently, 65,153,955 unique
subframes could be extracted from the observations. With an estimated 88,099,200 subframes transmitted by the constellation
during this time period a data yield of about 74% was achieved. Simulation studies suggest that with two additional GPS receivers,
which are scheduled for addition to the network in 2008, about 95% of the transmitted subframes will be retrieved. The message
data archive is open to the scientific community for non-commercial purposes and may be accessed through GFZ’s Information
System and Data Center ().
相似文献
G. BeyerleEmail: |
253.
Positioning fisheries in a changing world 总被引:1,自引:1,他引:0
R. Quentin Grafton Ray Hilborn Lori Ridgeway Dale Squires Meryl Williams Serge Garcia Theodore Groves James Joseph Kieran Kelleher Tom Kompas Gary Libecap Carl Gustaf Lundin Mitsutaku Makino Thorolfur Matthiasson Richard McLoughlin Ana Parma Gustavo San Martin Ben Satia Carl-Christian Schmidt Maree Tait Lin Xiu Zhang 《Marine Policy》2008,32(4):630-634
Marine capture fisheries face major and complex challenges: habitat degradation, poor economic returns, social hardships from depleted stocks, illegal fishing, and climate change, among others. The key factors that prevent the transition to sustainable fisheries are information failures, transition costs, use and non-use conflicts and capacity constraints. Using the experiences of fisheries successes and failures it is argued only through better governance and institutional change that encompasses the public good of the oceans (biodiversity, ecosystem integrity, sustainability) and societal values (existence, aesthetic and amenity) will fisheries be made sustainable. 相似文献
254.
A. Pastorello P. A. Mazzali G. Pignata S. Benetti E. Cappellaro A. V. Filippenko W. Li W. P. S. Meikle A. A. Arkharov G. Blanc F. Bufano A. Derekas M. Dolci N. Elias-Rosa R. J. Foley M. Ganeshalingam A. Harutyunyan L. L. Kiss R. Kotak V. M. Larionov J. R. Lucey N. Napoleone H. Navasardyan F. Patat J. Rich S. D. Ryder M. Salvo B. P. Schmidt V. Stanishev P. Székely S. Taubenberger S. Temporin M. Turatto W. Hillebrandt 《Monthly notices of the Royal Astronomical Society》2007,377(4):1531-1552
255.
Darije Maričić Bojan Vršnak Andrew L. Stanger Astrid M. Veronig Manuela Temmer Dragan Roša 《Solar physics》2007,241(1):99-112
We analyze the relationship between the acceleration of coronal mass ejections (CMEs) and the energy release in associated
flares, employing a sample of 22 events in which the CME kinematics were measured from the pre-eruption stage up to the post-acceleration
phase. The data show a distinct correlation between the duration of the acceleration phase and the duration of the associated
soft X-ray (SXR) burst rise, whereas the CME peak acceleration and velocity are related to the SXR peak flux. In the majority
of events the acceleration started earlier than the SXR burst, and it is usually prolonged after the SXR burst maximum. In
about one half of the events the acceleration phase is very closely synchronized with the fastest growth of the SXR burst.
An additional one quarter of the events may be still considered as relatively well-synchronized, whereas in the remaining
quarter of the events there is a considerable mismatch. The results are interpreted in terms of the feedback relationship
between the CME dynamics and the reconnection process in the wake of the CME. 相似文献
256.
Diatom and chrysophyte cyst-based reconstructions of the dates of spring and autumn lake-mixing enabled us to estimate spring
(STanom) and autumn (ATanom) temperature anomalies as well as ice-cover of the last ca. 4,000 years in a lake sediment core (Oberer Landschitzsee, 2,076
m a.s.l.) from the southern slopes of the Austrian Central Alps. The two independently inferred temperature anomalies were
significantly correlated. On average, spring and autumn temperatures were lower during the two millennia B.C than during 0–1,300
A.D. Marked spring and autumn temperature minima occurred at about 1,300 and 600 B.C. At about 1,300 A.D, STanom declined again. Spring-temperature anomalies during Roman and Medieval times equaled or slightly exceeded the modern values
and paralleled tree-line and glacier fluctuations. The de-coupling of autumn and spring climates, which began during the Medieval
period, might indicate changes in major circulation modes. It was assumed that the North-Atlantic influence, triggering winter-rain
climate in the Northern Mediterranean, became weaker during Medieval times, resulting in a trend towards warmer autumns and
overall more continental climate conditions in the study area. Four pulses of land use, inferred from indicator pollen, occurred
during (1) the Early to Late Bronze, (2) the transition from Late Bronze to Early Iron Age (Hallstatt), (3) Late Iron Age
(La Tène, Celtic time) to Roman times, and (4) during high to late Medieval times. Climate seemed to be an important, though
complex, trigger of Alpine land use. 相似文献
257.
H.-J. Götze R. El-Kelani S. Schmidt M. Rybakov M. Hassouneh H.-J. Förster J. Ebbing DESERT Group 《International Journal of Earth Sciences》2007,96(2):289-302
A 3D interpretation of the newly compiled Bouguer anomaly in the area of the “Dead Sea Rift” is presented. A high-resolution
3D model constrained with the seismic results reveals the crustal thickness and density distribution beneath the Arava/Araba
Valley (AV), the region between the Dead Sea and the Gulf of Aqaba/Elat. The Bouguer anomalies along the axial portion of
the AV, as deduced from the modelling results, are mainly caused by deep-seated sedimentary basins (D > 10 km). An inferred zone of intrusion coincides with the maximum gravity anomaly on the eastern flank of the AV. The intrusion
is displaced at different sectors along the NNW–SSE direction. The zone of maximum crustal thinning (depth 30 km) is attained
in the western sector at the Mediterranean. The southeastern plateau, on the other hand, shows by far the largest crustal
thickness of the region (38–42 km). Linked to the left lateral movement of approx. 105 km at the boundary between the African
and Arabian plate, and constrained with recent seismic data, a small asymmetric topography of the Moho beneath the Dead Sea
Transform (DST) was modelled. The thickness and density of the crust suggest that the AV is underlain by continental crust.
The deep basins, the relatively large intrusion and the asymmetric topography of the Moho lead to the conclusion that a small-scale
asthenospheric upwelling could be responsible for the thinning of the crust and subsequent creation of the Dead Sea basin
during the left lateral movement. A clear segmentation along the strike of the DST was obtained by curvature analysis: the
northern part in the neighbourhood of the Dead Sea is characterised by high curvature of the residual gravity field. Flexural
rigidity calculations result in very low values of effective elastic lithospheric thickness (t
e < 5 km). This points to decoupling of crust in the Dead Sea area. In the central, AV the curvature is less pronounced and
t
e increases to approximately 10 km. Curvature is high again in the southernmost part near the Aqaba region. Solutions of Euler
deconvolution were visualised together with modelled density bodies and fit very well into the density model structures.
An erratum to this article can be found at 相似文献
258.
259.
K. Frhlich T. Schmidt M. Ern P. Preusse A. de la Torre J. Wickert Ch. Jacobi 《Journal of Atmospheric and Solar》2007,69(17-18):2238
Five years of global temperatures retrieved from radio occultations measured by Champ (Challenging Minisatellite Payload) and SAC-C (Satelite de Aplicaciones Cientificas-C) are analyzed for gravity waves (GWs). In order to separate GWs from other atmospheric variations, a high-pass filter was applied on the vertical profile. Resulting temperature fluctuations correspond to vertical wavelengths between 400 m (instrumental resolution) and 10 km (limit of the high-pass filter). The temperature fluctuations can be converted into GW potential energy, but for comparison with parameterization schemes GW momentum flux is required. We therefore used representative values for the vertical and horizontal wavelength to infer GW momentum flux from the GPS measurements. The vertical wavelength value is determined by high-pass filtering, the horizontal wavelength is adopted from a latitude-dependent climatology. The obtained momentum flux distributions agree well, both in global distribution and in absolute values, with simulations using the Warner and McIntyre parameterization (WM) scheme. However, discrepancies are found in the annual cycle. Online simulations, implementing the WM scheme in the mechanistic COMMA-LIM (Cologne Model of the Middle Atmosphere—Leipzig Institute for Meteorology) general circulation model (GCM), do not converge, demonstrating that a good representation of GWs in a GCM requires both a realistic launch distribution and an adequate representation of GW breaking and momentum transfer. 相似文献
260.
J. L. Fanselow R. C. Hartman Peter Meyer P. J. Schmidt 《Astrophysics and Space Science》1971,14(2):301-313
A balloon borne counter telescope with a gas Cerenkov counter is used to measure the energy of primary cosmic ray electrons between 2 and 200 GeV. Electrons are identified by the characteristic electron-photon shower which they produce in a 15 radiation length deep stack of high-Z material interleaved with scintillation counters. Calibrations with monoenergetic electrons up to 14 GeV and monoenergetic protons up to 28 GeV from accelerators are used to develop criteria to statistically separate electrons from proton induced events. The results from six balloon flights (total exposure time 63 hours) are combined to obtain the electron energy spectrum. Up to about 30 GeV the spectrum measured in this experiment can be directly checked with calibrations and agrees well with results from other experiments. Above this energy the flux reported here is somewhat higher than the determinations reported by most other authors. We do not attach significance to an apparent flattening of the energy spectrum above 50 GeV. There is no evidence for a steepening of the spectrum at energies below 200 GeV.Work supported in part by the National Aeronautics and Space Administration grant NGL 14-001-005.Also Department of Physics.NSF trainee (1965–1969). 相似文献