Local geoid computation from gravity using the fast fourier transform technique     

D. Nagy  R. J. Fury 《Journal of Geodesy》1990,64(3):283-294

Model computations were performed for the study of numerical errors which are interjected into local geoid computations byFFT. The gravity field model was generated through the attractions of granitic prisms derived from actual geology. Changes in sampling interval introduced only0.3 cm variation in geoid heights. Although zero padding alone provided an improvement of more than5 cm in theFFT generated geoid, the combination of spectral windowing (tapering) and padding further reduced numerical errors. For theGPS survey of Franklin County, Ohio, the parameters selected as a result of model computations, allow large reduction in local data requirements while still retaining the centimeter accuracy when tapering and padding is applied.  相似文献   

Amino acids derived from Titan tholins     

Khare BN  Sagan C  Ogino H  Nagy B  Er C  Schram KH  Arakawa ET 《Icarus》1986,68(1):176-184

An organic heteropolymer (Titan tholin) was produced by continuous dc discharge through a 0.9 N2/0.1 CH4 gas mixture at 0.2 mbar pressure, roughly simulating the cloudtop atmosphere of Titan. Treatment of this tholin with 6N HCl yielded 16 amino acids by gas chromatography after derivatization of N-trifluroacetyl isopropyl esters on two different capillary columns. Identifications were confirmed by GC/MS. Glycine, aspartic acid, and alpha- and beta-alanine were produced in greatest abundance; the total yield of amino acids was approximately 10(-2), approximately equal to the yield of urea. The presence of "nonbiological" amino acids, the absence of serine, and the fact that the amino acids are racemic within experimental error together indicate that these molecules are not due to microbial or other contamination, but are derived from the tholin. In addition to the HCN, HC2CN, and (CN)2 found by Voyager, nitriles and aminonitriles should be sought in the Titanian atmosphere and, eventually, amino acids on the surface. These results suggest that episodes of liquid water in the past or future of Titan might lead to major further steps in prebiological organic chemistry on that body.  相似文献   

Kinematics of the Dadeldhura klippe shear zones (W Nepal): implications for the foreland evolution of the Himalayan metamorphic core     

Borja Antolín  Laurent Godin  Klaus Wemmer  Carl Nagy 《地学学报》2013,25(4):282-291

Mapping combined with structural analyses in the foreland edge of the metamorphic core of the Himalayas in SW Nepal highlights the existence of two north‐dipping shear zones with opposite sense of shear. Here, the metamorphic core is mainly affected by non‐coaxial top‐to‐the‐south sense of shear at temperatures between 450 °C and 550 °C that switch to a top‐to‐the‐north sense of shear at the top of the metamorphic core. We regionally correlate this upper shear zone with the South Tibetan detachment system. Ar‐dating on white mica indicates that both shear zones operated between 23 Ma and 17 Ma. Restoration of the folded South Tibetan detachment in far western Nepal yields a minimum dip‐slip distance of 190 km, compatible with predictions made by models of extrusion of a weak mid‐crustal channel. Our results support an orogenic model in which channel flow in the hinterland coexisted with thrust wedge mechanics in the foreland.  相似文献   

The scales of variability of stream fish assemblages at tributary confluences     

I. Czeglédi  P. Sály  P. Takács  A. Dolezsai  S. A. Nagy  T. Erős 《Aquatic Sciences - Research Across Boundaries》2016,78(4):641-654

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Planetary ENA imaging: Effects of different interaction models for Mars     

H. Gunell  M. Holmström  E. Kallio  A.F. Nagy 《Planetary and Space Science》2006,54(2):117-131

We present and compare energetic neutral atom (ENA) images that are calculated from plasma parameters given by three different simulation models of the interaction between the solar wind and Mars. The images are calculated by combining a model for the ion flow with a model of the neutral atmosphere using the cross-sections for the charge exchange collisions. The three ion models are: an empirical model that is based on Phobos 2 measurements; a three-dimensional hybrid simulation; and a three-dimensional MHD simulation. For the empirical and MHD models the images are obtained by integration of the ENA emission along lines of sight to a virtual ENA instrument. In the case of the hybrid model images are obtained by summing the contributions from all ions, whose positions, velocities, and weights are saved in files at regular intervals.Differences between the models can be detected in the images, for example the hybrid model produces ENA emissions from a larger region than the MHD model does. An asymmetry in the oxygen ion density develops in the hybrid model and can be seen in the oxygen ENA images. The images are influenced by finite gyro radius effects, which are included in the hybrid model but not in the other two. The total production rates of hydrogen ENAs are , , and for the empirical, hybrid and MHD models respectively.This study shows the importance of considering both the type of simulation model used and the proper inclusion of relevant physical phenomena and boundary conditions, when modelling the interaction between planets and the solar wind. Although the different models agree fairly well in terms of macroscopic plasma parameters they produce ENA images that differ substantially.  相似文献   

Origin of CO2 and carbonate veins in mantle-derived xenoliths in the Pannonian Basin     

A. Demény  L. Dallai  M.-L. Frezzotti  T.W. Vennemann  A. Embey-Isztin  G. Dobosi  G. Nagy 《Lithos》2010,117(1-4):172-182

The origin and evolution of CO₂ inclusions and calcite veins in peridotite xenoliths of the Pannonian Basin, Hungary, were investigated by means of petrographic investigation and stable isotope analyses. The fluid inclusions recovered in paragenetic olivine and clinopyroxene belong to distinct populations: type A (texturally early) inclusions with regular shapes (often with negative crystal forms) forming intragranular trails; type B (texturally late) inclusions defining randomly oriented trails that reach grain boundaries. Type B inclusions are often associated with silicate melt (type C) inclusions. Stable carbon isotope compositions in inclusion-hosted CO₂ were obtained by vacuum crushing followed by conventional dual inlet as well as continuous flow mass spectrometry in order to eliminate possible lab artifacts. Olivines, clino- and orthopyroxenes of the host peridotite have oxygen isotope compositions from 5.3 to 6.0‰ (relative to V-SMOW), without any relationship with xenolith texture. Some of the xenoliths contained calcite in various forms: veins and infillings in silicate globules in veins, secondary carbonate veins filling cracks and metasomatic veins with diffuse margins. The former two carbonate types have δ¹³C values around –13‰ (relative to V-PDB) and low Sr contents (< 0.5 wt.%), whereas the third type,veins with high-temperature metasomatic features have a δ¹³C value of –5.0‰ and high Sr contents up to 3.4 wt.%. In spite of the mantle-like δ¹³C value and the unusually high Sr content typical for mantle-derived carbonate, trace element compositions have proven a crustal origin. This observation supports the conclusions of earlier studies that the carbonate melt droplets found on peridotite xenoliths in the alkaline basalts represent mobilized sedimentary carbonate. The large δ¹³C range and the ¹²C-enrichment in the carbonates can be attributed to devolatilization of the migrating carbonate or infiltration of surficial fluids containing ¹²C-rich dissolved carbon.Carbon isotope compositions of inclusion-hosted CO₂ range from –17.8 to –4.8‰ (relative to V-PDB) with no relation to the amount of CO₂ released by vacuum crushing. Low-δ¹³C values measured by stepwise heating under vacuum suggest that the carbon component is pristine and not related to surficial contamination, and that primary mantle fluids with δ¹³C values around –5‰ were at least partly preserved in the xenoliths. Tectonic reworking and heating by the basaltic magma resulted in partial CO₂ release and local ¹³C-depletion.  相似文献   

Petrographical, geochemical and geochronological constraints on igneous clasts and sediments hosted in the Oligo-Miocene Bakony Molasse, Hungary: evidence for a Paleo-Drava River system     

K. Benedek  Z. Nagy  I. Dunkl  C. Szabó  S. Józsa 《International Journal of Earth Sciences》2001,90(3):519-533

The provenance of igneous clasts and arenitic sediment enclosed within the Bakony Molasse was studied using geochemical and geochronological methods. The majority of igneous clasts were eroded from the Oligocene Periadriatic magmatic belt. A part of the andesite material has Eocene formation age. Rhyolitic pebbles originated from Permian sequences of the Greywacke zone or the Gurktal Alps. Apatite fission track (FT) ages from the sandstone matrix (age clusters at ~75 and ~30 Ma) are typical for the Austroalpine nappe pile and for the cooling ages of Periadriatic magmatic belt. Variscan detrital zircon FT ages indicate source areas that had not suffered Alpine metamorphism, such as the Bakony Mountains, Drauzug and the Southern Alps. Another group of detrital zircon grains of Late Triassic-Jurassic FT age (mean: ~183 Ma) marks source zones with Mesozoic thermal overprint such as the Gurktal Alps and some Austroalpine regions. Zircon grains with Oligocene FT age (mean: ~34.7 Ma) were derived from the Periadriatic intrusives and their contact zones. On the basis of the new data, we propose that the ancestor of the recent Drava River had already existed in Oligo-Miocene time and distributed eroded material of the southern Eastern Alps to the east.  相似文献