Modelling the effects of changes in the Earth's magnetic field from 1957 to 1997 on the ionospheric hmF2 and foF2 parameters     

Ingrid Cnossen  Arthur D. Richmond   《Journal of Atmospheric and Solar》2008,70(11-12):1512-1524

We have modelled the effects of changes in the Earth's magnetic field on the ionosphere as have occurred from 1957 to 1997 using the NCAR Thermosphere–Ionosphere–Electrodynamics General Circulation Model. Previous studies that attempted to quantify these effects used a constant wind field, so that any electro-dynamical coupling processes could not be accounted for. Using TIE-GCM we can account for these processes. We find substantial changes in the F2 layer peak height hmF2 (up to ±20 km) and critical frequency foF2 (up to ±0.5 MHz) over the Atlantic Ocean and South America, purely due to changes in the Earth's magnetic field (i.e. unrelated to greenhouse gas cooling effects, which are often held responsible for long-term trends in hmf2 and fof2). These would make up a significant contribution to observed long-term trends in these areas and therefore must be taken into account in their interpretation. Modelled trends of hmF2 and foF2 exhibit a strong seasonal and diurnal variation, highlighting the importance of separating data with respect to season and local time. Most of the modelled changes in hmF2 and foF2 can be related to changes in plasma transport up or down magnetic field lines driven by neutral winds, changes, which are mostly caused by changes in the inclination of the field, though changes in declination and neutral wind also play a role. Changes in the vertical component of the E×B drift seem to have little effect on hmF2 and foF2.  相似文献   

Soil–foundation–structure interaction and vulnerability assessment of the Neoclassical School in Rhodes,Greece     

Anna Karatzetzou  Dimitris Pitilakis  Meta Kržan  Vlatko Bosiljkov 《Bulletin of Earthquake Engineering》2015,13(1):411-428

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Acquiring reference parameters of masonry for the structural performance analysis of historical buildings   总被引：1，自引：1，他引：0  

Meta Kržan  Samo Gostič  Serena Cattari  Vlatko Bosiljkov 《Bulletin of Earthquake Engineering》2015,13(1):203-236

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Chronic exposure of adults and embryos of Pandalus borealis to oil causes PAH accumulation, initiation of biomarker responses and an increase in larval mortality     

Renée Katrin Bechmann  Bodil Katrine Larsen  Ingrid Christina Taban  Per Møller 《Marine pollution bulletin》2010,60(11):2087-2098

Adult shrimps (Pandalus borealis) and their embryos were exposed to an oil-water dispersion (OWD) at concentrations of 0.015, 0.06 and 0.25 mg/L using a continuous flow system. Lysosomal membrane stability was analysed in haemocytes using the neutral red retention assay and an alkaline unwinding assay was used to measure DNA damage in hepatopancreas tissue. Exposure to oil induced concentration and time dependent biomarker responses in adult shrimps together with the accumulation of PAH in their tissues. Oil exposure of shrimp embryos caused increased mortality in the resultant larvae, even if the larvae were kept in clean water after hatching. There were minor differences observed in larval stage development times in the first part of the experiments. The fatty acid composition of embryos exposed to oil was different to that of non-exposed larvae. PAH tissue concentration and biomarker responses correlated to the reduced survival of the shrimp larvae.  相似文献   

Seasonal variability of benthic indices: an approach to test the applicability of different indices for ecosystem quality assessment     

Reiss H  Kröncke I 《Marine pollution bulletin》2005,50(12):1490-1499

In recent studies, several benthic biological indices were developed or used to assess the ecological quality status of marine environments. In the present study the seasonal variability of several univariate and multimetric indices was studied on a monthly scale (September 2000 until May 2002) in different areas of the North Sea such as the German Bight, the Oyster Ground and the Dogger Bank. The stations were chosen to reflect a gradient in the hydrographic regime, temperature and organic matter supply. The seasonal variability was highest for the univariate indices such as the Shannon–Wiener Index and the Hurlbert Index. Thus, due to sensitivity to recruitment the corresponding ecological status ranged from ‘good’ to ‘poor’ depending on the season. For the multimetric indices such as the AMBI or the BQI the seasonal variability and the corresponding ecological status were low. The results are discussed concerning possible consequences for ecological quality assessment especially related to the Water Framework Directive (WFD).  相似文献   

Zircon ages,geochemistry, and Nd isotopic systematics of pre-Variscan orthogneisses from the Erzgebirge,Saxony (Germany), and geodynamic interpretation     

B.?MingramEmail author  A.?Kr?ner  E.?Hegner  O.?Krentz 《International Journal of Earth Sciences》2004,93(5):706-727

High grade granitoid orthogneisses occur in several metamorphic units of the Erzgebirge in the Saxothuringian Zone of the Variscan Belt. The determination of protolith ages and the geochemical characterization of these rocks permit a reconstruction of the Neoproterozoic to early Palaeozoic magmatic and geodynamic history of the Erzgebirge. Single zircon Pb-Pb evaporation and SHRIMP ages combined with major and trace element data and Sm-Nd isotope systematics indicate at least two discrete magmatic events concealed in the so-called red gneisses, one at ~550 Ma in rocks of the medium pressure—medium temperature (MP-MT) unit and the other at ~500–480 Ma in rocks of the high pressure units. The transition zones comprise both Neoproterozoic granitoids and early Palaeozoic metarhyolites. The granitoid gneisses represent Neoproterozoic calc-alkaline granitoids with REE patterns similar to those produced in Andean-type continental margins. The early Palaeozoic muscovite gneisses are geochemically distinct from the older granitoids and may be derived from melts generated in a back-arc setting. Initial _Nd values in all samples overlap and range from –4.1 to –9.2, corresponding to crustal sources with average residence times of 1.5 to 1.9 Ga. Zircon xenocryst ages as old as 2992 Ma provide evidence for Grenvillian, Svecofennian-Birimian-Aazonian and older age components and suggest an association of the Erzgebirge with Avalonia.B. Mingram and A. Kröner have shared senior authorship  相似文献   

Effects of linking up of discontinuities on fracture growth and groundwater transport   总被引：3，自引：1，他引：2  

Agust?GudmundssonAgust.Gudmundsson@gwdg.de" title="agust.gudmundsson@geol.uib.no  Agust.Gudmundsson@gwdg.de" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author  Otilie?Gjesdal  Sonja?L.?Brenner  Ingrid?Fjeldskaar 《Hydrogeology Journal》2003,11(1):84-99

It is proposed that the growth of fractures is the basic process for generating and maintaining permeability in solid rock (bedrock). Many extension fractures grow as hydrofractures, whereas many shear (and extension) fractures grow through the formation of transverse fractures that connect the adjacent tips of existing fractures. In a boundary-element analysis, the hydrofractures are modeled as being driven open by a fluid overpressure that varies linearly from 10 MPa at the fracture centre to 0 MPa at the fracture tip. The host rock has a uniform Young's modulus of 10 GPa, a Poisson's ratio of 0.25, and is dissected by vertical joints and horizontal contacts, each of which is modeled as an internal spring of stiffness 6 MPa m⁻¹. The number of joints and contacts, and their location with respect to the hydrofracture tip are varied in different model runs. The results of the analyses indicate that the tensile stresses generated by overpressured hydrofractures open up joints and contacts out to considerable distances from the fracture tip, so that they tend to link up to form a hydraulic pathway. Using the same Young's modulus, Poisson's ratio, and internal spring constant for joints as in the hydrofracture models, boundary-element models were made to study the interaction stresses that cause neighbouring joints to become interconnected through the growth of linking transverse fractures that, ultimately, may evolve into shear fractures. The models were subjected to tensile stress of 6 MPa acting normal to the joint planes as the only loading. The offset (horizontal distance) and underlap (vertical distance) between the adjacent tips of the joints were varied between model runs. The results show a concentration of tensile and shear stresses in the regions between the neighbouring tips of the joints, but these regions become smaller when the underlap of the joints decreases and changes to overlap. These stress-concentration regions favour the development of transverse (mostly shear) fractures that link up the nearby tips of the joints, so as to form a segmented shear or extension fracture. Analytical results on aperture variation of a hydrofracture in a homogeneous, isotropic rock are compared with boundary-element results for a hydrofracture dissecting layered rocks. The aperture is larger where the hydrofracture dissects soft (low Young's modulus) layers than where it dissects stiff layers. Aperture variation may encourage subsequent groundwater-flow channeling along a pathway generated by a hydrofracture in layered rocks. Electronic Publication  相似文献   

On the complex spatial structure of a gradual microwave burst     

V. M. Bogod  A. N. Korzhavin  Sh. B. Akhmedov  H. Aurass  J. Hildebrandt  A. Krüger 《Solar physics》1990,129(2):351-361

We present a discussion of the gradual burst event on May 13,1985 which is based on observations of the RATAN-600 telescope at ten fixed frequencies in the range between 37.5 and 0.95 GHz (0.8 and 31.6 cm wavelength) and on time profiles of patrol observations of the Observatory for Solar Radio Astronomy at Tremsdorf near Potsdam. This up to now most complete data set allows new conclusions on the extended spectral/spatial structure of the source region.There is strong evidence that only less than 24% of the microwave flux from this event is emitted by an excessive small-scale burst source while the bulk of the burst emission comes from a larger region consisting of two major components covered by the source area of the S-component radiation. The different components of the burst and S-component radiation are analyzed.  相似文献   

Meteoritic material on the moon     

Edward Anders  R. Ganapathy  Urs Krähenbühl  John W. Morgan 《Earth, Moon, and Planets》1973,8(1-2):3-24

Three types of meteoritic material are found on the Moon: micrometeorites, ancien planetesimal debris from the ‘early intense bombardment’, and debris of recent, crater-forming projectiles. Their amounts and compositions have been determined from trace element studies. The micrometeorite component is uniformly distributed over the entire lunar surface, but is seen most clearly in mare soils. It has a primitive, C1-chondrite-like composition, and comprises 1-1.5% of mature soils. Apparently it represents cometary debris. The mean annual influx rate is 2.4 × 10^?9 g cm^?2 yr^?1. It shows no detectable time variation or dependence on selenographic position. The ancient component is seen in highland breccias and soils more than 3.9 AE old. It has a fractionated composition, with volatiles depleted relative to siderophiles. The abundance pattern does not match that of any known meteorite class. At least two varieties exist (LN and DN, with Ir/Au, Re/Au 0.25-0.5 and > 0.5 the C1 value). Both seem to represent the debris of planetesimals that produced the mare basins and highland craters during the first 700 Myr of the Moon's history. It appears that the LN and DN objects impacted at less then 10 km s^?1, had diameters less than 100 km, contained more than 15% Fe, and were not internally differentiated. Both were depleted in volatiles; the LN objects also in refractories (Ir, Re). This makes it unlikely that the LN bodies served as important building blocks of the Moon. The crater-forming component has remained elusive. Only a possible hint of this component has been seen, in ejecta from Dune Crater and Apollo 12 KREEP glasses of Copernican (?) origin.  相似文献   

Optical constants of the mixture of ices     

T. Mukai  W. Krätschmer 《Earth, Moon, and Planets》1986,36(2):145-155

The Maxwell-Garnett mixing rule (MG) was applied to estimate the optical constant m ^* of the mixture of ices. A fairly good agreement between the resulting values of m ^* and those of our laboratory measurements suggests that the MG rule becomes a powerful tool to derive the unknown optical constants of natural dirty-ice, when there are no chemical bonds between the guest and host materials. Our results would provide the knowledge of the optical constants of dirty-ice for studies of icy substances on the surface of satellites, cometary nucleus and interplanetary dust grains based on their reflectance spectra.  相似文献