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571.
The zonally averaged UK Meteorological Office (UKMO) zonal mean temperature and zonal winds for the latitudes 8.75°N and 60°N are used to investigate the low-latitude dynamical response to the high latitude sudden stratospheric warming (SSW) events that occurred during winter of the years 1998–1999, 2003–2004 and 2005–2006. The UKMO zonal mean zonal winds at 60°N show a short-term reversal to westward winds in the entire upper stratosphere and lower mesosphere and the low-latitude winds (8.75°N) show enhanced eastward flow in the upper stratosphere and strong westward flow in the lower mesosphere during the major SSW events at high latitudes. The mesosphere and lower thermosphere (MLT) zonal winds acquired by medium frequency (MF) radar at Tirunelveli (8.7°N, 77.8°E) show a change of wind direction from eastward to westward several days before the onset of SSW events and these winds decelerate and weak positive (eastward) winds prevail during the SSW events. The time variation of zonal winds over Tirunelveli is nearly similar to the one reported from high latitudes, except that the latter shows intense eastward winds during the SSW events. Besides, the comparison of daily mean meridional winds over Tirunelveli with those over Collm (52°N, 15°E) show that large equatorial winds are observed over Tirunelveli during the 2005–2006 event and over Collm during the 1998–1999 events. The variable response of MLT dynamics to different SSW events may be explained by the variability of gravity waves. 相似文献
572.
Chara Ch. Mitropoulou Nikos D. Lagaros Manolis Papadrakakis 《Bulletin of Earthquake Engineering》2010,8(6):1375-1396
The basic objective of this study is the assessment of the European seismic design codes and in particular of EC2 and EC8
with respect to the recommended behaviour factor q. The assessment is performed on two reinforced concrete multi-storey buildings, having symmetrical and non-symmetrical plan
view respectively, which were optimally designed under four different values of the behaviour factor. In the mathematical
formulation of the optimization problem the initial construction cost is considered as the objective function to be minimized
while the cross sections and steel reinforcement of the beams and the columns constitute the design variables. The provisions
of Eurocodes 2 and 8 are imposed as constraints to the optimization problem. Life-cycle cost analysis, in conjunction with
structural optimization, is believed to be a reliable procedure for assessing the performance of structures during their life
time. The two most important findings that can be deduced are summarized as follows: (1) The proposed Eurocode behaviour factor
does not lead to a more economical design with respect to the total life-cycle cost compared to other values of q (q = 1, 2). (2) The differences of the total life-cycle cost values may be substantially greater than those observed for the
initial construction cost for four different q (q = 1, 2, 3, 4). 相似文献
573.
Ad. A. Aliev V. Yu. Lavrushin S. V. Kokh E. V. Sokol O. L. Petrov 《Lithology and Mineral Resources》2017,52(5):358-368
Geochemical studies of pyrite crystals from the mud volcanic ejecta in Azerbaijan were studied. It is shown that all of them have cubic shape. Determination of the sulfur isotope composition revealed a wide variation range of δ34S values from–27.0 to +26.4‰. Signs of spatial zonation were recorded in the distribution of δ34S values—lower values are confined to the present-day coastline of the Caspian Sea. Appearance of pyrite with a high share of 34S is attributed to sulfate reduction that takes place in an environment with excess organic matter. It is supposed that the isotopically heavy sulfides represent the “neck” facies that are formed at the periphery of mud volcanic conduits at the contact of the hydrocarbon-rich mud volcanic fluids with stratal waters of host sediments. 相似文献
574.
I. K. Kozakov A. B. Kuznetsov Ch. Erdenegargal E. B. Salnikova I. V. Anisimova Ju. V. Plotkina A. M. Fedoseenko 《Stratigraphy and Geological Correlation》2017,25(5):479-491
The formation stages of high-grade metamorphic complexes and the related granitoids of the Dzabkhan terrane basement are considered. The age data (U–Pb method, TIMS) of zircons from the trondhjemite block of the eastern part of the Dzabkhan terrane, which is directly overlain by the dolomite sequence of the Tsagaan Oloom Formation, are given. Trondhjemites yield the U–Pb zircon age of 862 ± 3 Ma. In their structural position, they are assigned to typical postmetamorphic formations that determine the formation and cratonization of rocks of the host block. The geochronological study of trondhjemites gives grounds to distinguish fragments of the continental crust in the Dzabkhan terrane basement, the formation of which occurred at different periods of time: ~860 and ~790 Ma. Geological–geochronological and Sm?Nd isotope–geochemical studies indicate that the Dzabkhan terrane basement is not a single block of the Early Precambrian continental crust, but a composite terrane, comprising Neoproterozoic ensialic and island-arc structural and compositional complexes. Correlation of Sr isotopic characteristics with the 87Sr/86Sr variation curve in the Neoproterozoic and Cambrian seawater shows that carbonate deposits accumulated at the eastern margin of the Dzabkhan terrane near the end of the Neoproterozoic, 700–550 Ma, and in the central part of the terrane in the Early Cambrian, 540–530 Ma. 相似文献
575.
576.
A new isostatic model of the lithosphere and gravity field 总被引:2,自引:0,他引:2
Based on the analysis of various factors controlling isostatic gravity anomalies and geoid undulations, it is concluded that it is essential to model the lithospheric density structure as accurately as possible. Otherwise, if computed in the classical way (i.e. based on the surface topography and the simple Airy compensation scheme), isostatic anomalies mostly reflect differences of the real lithosphere structure from the simplified compensation model, and not necessarily the deviations from isostatic equilibrium. Starting with global gravity, topography and crustal density models, isostatic gravity anomalies and geoid undulations have been determined. The initial crust and upper-mantle density structure has been corrected in a least squares adjustment using gravity. To model the long-wavelength (>2000 km) features in the gravity field, the isostatic condition (i.e. equal mass for all columns above the compensation level) is applied in the adjustment to uncover the signals from the deep-Earth interior, including dynamic deformations of the Earths surface. The isostatic gravity anomalies and geoid undulations, rather than the observed fields, then represent the signals from mantle convection and deep density inhomogeneities including remnants of subducted slabs. The long-wavelength non-isostatic (i.e. the dynamic) topography was estimated to range from –0.4 to 0.5 km. For shorter wavelengths (<2000 km), the isostatic condition is not applied in the adjustment in order to obtain the non-isostatic topography due to regional deviations from classical Airy isostasy. The maximum deviations from Airy isostasy (–1.5 to 1 km) occur at currently active plate boundaries. As another result, a new global model of the lithosphere density distribution is generated. The most pronounced negative density anomalies in the upper mantle are found near large plume provinces, such as Iceland and East Africa, and in the vicinity of the mid-ocean ridge axes. Positive density anomalies in the upper mantle under the continents are not correlated with the cold and thick lithosphere of cratons, indicating a compensation mechanism due to thermal and compositional density. 相似文献
577.
Integrated adjustment of CHAMP, GRACE, and GPS data 总被引:16,自引:3,他引:13
Various types of observations, such as space-borne Global positioning system (GPS) code and phase data, accelerometer data, K-band range and range-rate data, and ground-based satellite laser ranging data of the CHAllenging Minisatellite Payload (CHAMP) and GRAvity Climate Experiment (GRACE) satellite missions, are used together with ground-based GPS code and phase data in a rigorous adjustment to eventually solve for the ephemerides of the CHAMP, GRACE, and GPS satellites, geocenter variations, and low-degree gravity field parameters. It turns out that this integrated adjustment considerably improves the accuracy of the ephemerides for the high and low satellites, geocenter variations, and gravity field parameters, compared to the case when the adjustment is carried out stepwise or in individual satellite solutions.Acknowledgments. This study has been supported by the German Ministry of Education and Research through the Geotechnologies Programme grants 03F0333A/CHAMP and 03F0326A/GRACE. 相似文献
578.
579.
The rotation of the magnetic axes of sunspot groups is studied as a function of the expansion and contraction of the groups along their magnetic axes. In general, except for the extreme values of tilt-angle change, slow rates of rotation of the magnetic axes are associated with low values of expansion or contraction, and faster rotation of the magnetic axes is associated with rapid expansion or contraction. The direction of rotation of the magnetic axes is related to expansion or contraction in the sense that would be predicted by the Coriolis force. A comparison of the effect at high and low latitudes shows a difference that further supports the Coriolis force hypothesis, and an examination of the amplitude of the effect also suggests that the Coriolis force may be a factor in the tilt-angle rotation of spot groups.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation. 相似文献
580.
It is observed that while there exists a strong correlation between the decay constant and the exciter duration for isolated type III radio bursts, it is absent for those type III radio bursts which are preceded by type IIIb radio bursts. A possible theoretical explanation for the presence of correlation in one case and lack of it in the other is proposed. 相似文献