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861.
Aleksander Brzeziński 《Journal of Geodesy》2007,81(6-8):543-551
A simple digital filter is derived for application to studies concerning geophysical excitation of nutation. Attention is
focused on the inverse solution, i.e., inferring the excitation function from the time-series of the celestial pole offsets
observed by very long baseline interferometry (VLBI). Filter properties are discussed by comparing its transfer function with
that of the original differential equation of nutation. An excellent agreement in both the amplitude and phase response is
shown at frequencies between −5 and + 5 cycles per year, which is the frequency band with expected geophysical signals. The
difference appears at higher frequencies, leading to a spurious oscillation produced by the filter. This undesired effect
is considered and the algorithm enabling its removal is described. 相似文献
862.
We investigate uncertainties about conventional petroleum resources and substitutes for conventional petroleum, focusing on
the impact of these uncertainties on future greenhouse gas (GHG) emissions. We use examples from the IPCC Special Report on
Emissions Scenarios as a baseline for comparison. The studied uncertainties include, (1) uncertainty in emissions factors
for petroleum substitutes, (2) uncertainties resulting from poor knowledge of the amount of remaining conventional petroleum,
and (3) uncertainties about the amount of production of petroleum substitutes from natural gas and coal feedstocks. We find
that the potential effects of a transition to petroleum substitutes on GHG emissions are significant. A transition to low-quality
and synthetic petroleum resources such as tar sands or coal-to-liquids synfuels could raise upstream GHG emissions by several
gigatonnes of carbon (GtC) per year by mid-century unless mitigation steps are taken. 相似文献
863.
Lindsay R. Kendall John W. Ewart Paul N. Ulrich Adam G. Marsh 《Estuaries and Coasts》2007,30(1):154-162
Delaware's Inland Bays comprise a large estuarine system with a restricted access to the Atlantic Ocean (Indian River Inlet).
As part of a local oyster stock enhancement and restoration effort, we conducted a survey for the protozoan pathogenPerkinsus marinus (Dermo) in oysters from a newly established reef. Using standardized methods for the polymerase chain reaction (PCR) amplification
of the non-transcribed spacer (NTS) region, we were surprised to find no detectable titers of this pathogen in the 30 oysters
sampled in the first year of the project. The detection threshold of the PCR coupled with chemiluminescent detection was 30
fgP. marinus NTS DNA. We were able to detect a trace presence of this pathogen in a few hard clams (Mercenaria mercenaria) from the same locale, indicating that aPerkinsus sp. was present in the Inland Bay system. Subsequent monitoring of the reef system using a fluid thioglycollate assay over
3 yr revealed no epizootic outbreaks of this pathogen within the planted oyster population. Two large mortality episodes that
did appear in the oyster population were attributable to abiotic conditions and not pathogen exposure. This study emphasizes
that all potential sources of mortality in the environment are important to consider when designing oyster seeding projects.
In the Delaware Inland Bays,P. marinus does not appear to have a large enough oyster host population to become a significant disease threat at present. Because
of the low parasite incidence levels in the Inland Bay system in 2000, the James Farm oyster reef restoration project presents
an ideal model system to follow the population dynamics between an oyster-host population and a latent or reservoir pathogen
population. 相似文献
864.
Results of centimeter-wavelength RATAN-600 observations of several hundred NVSS objects with a wide range of flux densities are presented. Changes in spectral-index distributions from strong-to faint-object populations are estimated. In the transition from strong to faint radio sources, the number of steep-and ultrasteep-spectrum objects decreases and the minimum between steep-and flat-spectrum objects, which was first discovered in the 1970s, becomes less distinct. A less certain increase in the fraction of inverted-spectrum objects is also found. Comparison with theoretical models of radio-source evolution suggests that the decrease in the number of steep-and ultrasteep-spectrum objects can be naturally explained by a sharp decrease in the fraction of classical FRII radio galaxies. The decrease in the sharpness of the minimum may be due to the growing contribution from the population with spectral indices 0.7–0.5, which is usually identified with starbust galaxies. The small increase in the fraction of inverted-spectrum radio sources can be attributed to the growing number of objects with active nuclei. Our spectrum-based conclusions are confirmed by the morphology of the FIRST Catalog images. The number of radio sources associated with supermassive black holes in the Early Universe is estimated using data from the SDSS Catalog. 相似文献
865.
Ongoing tectonic reactivation of the Outer Carpathians and its impact on the foreland: Results of borehole breakout measurements in Poland 总被引:1,自引:0,他引:1
The direction of present-day maximum horizontal compression (= SHmax = tectonic stress) was interpreted for 62 wells in Poland, using the method of borehole breakout analysis of 4-arm and 6-arm dipmeter logs. The study area covers complex tectonic junction of the Carpathian orogen and its foreland, which comprises the East European Craton (EEC) divided by the Teisseyre–Tornquist zone (TTZ) from the Palaeozoic platform of western Poland. For this area, frequent deviation of the SHmax direction from NW–SE characteristic for the Atlantic ridge push has been interpreted in terms of the ALCAPA tectonic push. In the Upper Silesian segment of the Polish Outer Carpathians (POC), NNE–SSW-oriented SHmax in the accretionary wedge differs significantly from NNW–SSE SHmax in the autochthonous basement. The above discrepancy points to uncoupled type of the suture in this segment of the POC. In this scenario the ALCAPA push involves the nappes and is compensated in the top of the basement, which is expressed by systematic SHmax rotations. In the accretionary wedge of the eastern Małopolska segment, SHmax follows the trend perpendicular to the strike of nappes. It is in general agreement with NNE–SSW-oriented SHmax in the autochthonous basement that also parallels the ALCAPA push direction. Similarity in stress orientation between these structural levels implies coupled suture zone in this segment of the POC. Further to the north, ALCAPA push is transmitted into the foreland plate where it causes N–S orientation of SHmax, as determined for sedimentary cover of the EEC. Within the Baltic portion of the EEC, further SHmax rotation towards the intermediate NNW–SSE position suggests balance between the ALCAPA push and the ridge push components. Within the TTZ, common SHmax rotations from N–S to NW–SE indicate structurally controlled accommodation of the ALCAPA push. In the Palaeozoic platform of western Poland, Mesozoic complex of the Fore-Sudetic Monocline reveals NNE–SSW-directed SHmax that differs from NW–SE-oriented SHmax in the Variscan accretionary wedge. Here, mechanical decoupling along Zechstein evaporates is likely.
Presented set of breakout data from Poland shows that recent compressive reactivation of the Carpathians exerts strong impact on the stress field of the foreland plate at a distance of 700 km from the suture. Due to this effect, the Fore-Carpathian stress domain within the North European stress province can be discriminated. 相似文献
866.
867.
Jeleńska M. Kądziałko-Hofmokl M. Żelaźniewicz A. 《Studia Geophysica et Geodaetica》2003,47(2):419-434
Studia Geophysica et Geodaetica - The paper presents the Apparent Polar Wander Path (APWP) for the West Sudetes for the period from Devonian to Carboniferous. The data used for construction of the... 相似文献
868.
Piotr
roda Wojciech Czuba Marek Grad Aleksander Guterch Edward Gaczy
ski POLONAISE Working Group 《Tectonophysics》2002,360(1-4):169-185
This paper reports the results of 3-D tomographic modelling of crustal structure in the Trans European Suture Zone region (TESZ) of Poland, eastern Germany and Lithuania. The data are the product of a large-scale seismic experiment POLONAISE'97, which was carried out in 1997. This experiment was designed to provide some 3-D coverage. The TESZ forms the boundary between the Precambrian crustal terranes of the East European Craton (EEC) and the younger Phanerozoic terranes to the southwest. The 3-D results generally confirm the earth models derived by earlier 2-D analyses, but also add some important details as well as a 3-D perspective on the structure. The velocity model obtained shows substantial horizontal variations of crustal structure across the study area. Seismic modelling shows low (<6.1 km/s) velocities suggesting the presence of sedimentary rocks down to a depth of about 20 km in the Polish basin. The shape of the basin in the vicinity of the profile P4 shows significant asymmetry. Three-dimensional modelling also allowed tracing of horizontal irregularities of the basin shape as well as variations of the Moho depth not only along profiles, but also between them. The slice between P2 and P4 profiles shows about 10-km variations of the Moho over a 100-km interval. The crustal thickness varies from about 30 km in SW, beneath the Palaeozoic platform, to about 42 km beneath East European Craton in NE. High seismic velocities of about 6.6 km/s were found in the depth range 2–10 km, which coincides with K
trzyn anorthosite massif. The results of this 3-D seismic modelling of the POLONAISE'97 data will ultimately be supplemented by inversion of seismic data from previous experiments. 相似文献
869.
Fractal analysis of faults network, tremor foci spatial distribution as well as the Gutenberg-Richter relationship could further explain whether the biggest seismic events are connected with recent tectonic activity. Fractality of fault systems geometry, as a first step of the analysis, was tested fro a part of the USCB embodying the main structural units. The cluster analysis and the box counting methods were employed.The calculated fractal dimension of fault network was 1.98 for the whole area yet for considered structural units it was close to 1.6. The results point to similarity of studied fault pattern to river network. Faults within selected tectonic units make separate sets which have a distinct geometry and origin. The value of 1.6 is an upper limit to the fracture geometry of rocks that can be explained on the basis of Griffith energy balance concept. 相似文献
870.
We performed high-pressure experiments on the crystallization of water ice I and III in the ammonia-water (NH3)x(H2O)(1−x) system, and apply the results to the interiors of icy bodies in the Solar System. Phase equilibrium lines between an entirely liquid solution and a liquid solution in which water ice forms (liquidus lines) were determined for ammonia concentration by mass X equal to 0.034, 0.0472, 0.111, 0.176, and 0.229. Growth-melting of ice I as well as ice III crystals were observed. Application of the results to icy satellites that are potential bearers of ammonia shows that ammonia admixture decreases the depth of the liquidus surface. A shift of the liquidus temperature within a satellite depends on three parameters: the ammonia concentration, X; the temperature gradient, α; and the product of density and gravity, ρg. 相似文献