The PONAM project     

Christian Hjort  Krstin Malmberg Persson 《Boreas: An International Journal of Quaternary Research》1994,23(4):281-281

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Observations on the occurrence, size, and feeding of pelagic larvae of the common wolffish (Anarhichas lupus) in western Finnmark, northern Norway     

Falk-Petersen  I.-B.; Haug  T.; Moksness  E. 《ICES Journal of Marine Science》1990,46(2):148-154

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Atmospheric trace species measured above haute-provence observatory     

Pierre Marche  Christian Meunier 《Planetary and Space Science》1983,31(7):731-733

Trace species have been measured in June 1981, at the “Observatoire de Haute-Provence” Chiran station, 1905 m high, with a ground based high resolution i.r. spectrometer, using the Sun as a source. Column abundance amounts are given for methane, formaldehyde, hydrogen chloride and hydrogen fluoride.  相似文献   

Spatial dispersion of Faraday rotation and its connexion with mode coupling     

Christian Mätzler 《Solar physics》1973,32(1):241-255

It is shown that the lack of linear polarization in the microwave radiation of solar bursts (reported in a earlier paper) may be explained by spatial dispersion of Faraday rotation. The maximum source diameter s without noticeable destruction of linear polarization is determined by the electron density and the magnetic field strength in the volume, where the linear polarization is generated. In the case where linear polarization is produced by the radiation source, s is smaller than only 20 km. In the other case where linear polarization is produced by mode coupling in a quasi-transverse magnetic field in the corona, the s-values are found to range from 10 to 6000 km, which is still much smaller than the generally adopted sizes of microwave burst sources. The second case has been investigated for several models of magnetic fields.  相似文献   

Stochastic ground water flow simulation with a fracture zone continuum model   总被引：3，自引：0，他引：3  

Langevin CD 《Ground water》2003,41(5):587-601

A method is presented for incorporating the hydraulic effects of vertical fracture zones into two-dimensional cell-based continuum models of ground water flow and particle tracking. High hydraulic conductivity features are used in the model to represent fracture zones. For fracture zones that are not coincident with model rows or columns, an adjustment is required for the hydraulic conductivity value entered into the model cells to compensate for the longer flowpath through the model grid. A similar adjustment is also required for simulated travel times through model cells. A travel time error of less than 8% can occur for particles moving through fractures with certain orientations. The fracture zone continuum model uses stochastically generated fracture zone networks and Monte Carlo analysis to quantify uncertainties with simulated advective travel times. An approach is also presented for converting an equivalent continuum model into a fracture zone continuum model by establishing the contribution of matrix block transmissivity to the bulk transmissivity of the aquifer. The methods are used for a case study in west-central Florida to quantify advective travel times from a potential wetland rehydration site to a municipal supply wellfield. Uncertainties in advective travel times are assumed to result from the presence of vertical fracture zones, commonly observed on aerial photographs as photolineaments.  相似文献   

Holocene environmental change at Lake Njulla (999 m a.s.l.), northern Sweden: a comparison with four small nearby lakes alongan altitudinal gradient     

Christian Bigler  Evastina Grahn  Isabelle Larocque  Adam Jeziorski  Roland Hall 《Journal of Paleolimnology》2003,29(1):13-29

We assess Holocene environmental change at alpine Lake Njulla(68°22N, 18°42E, 999 m a.s.l.) innorthernmost Sweden using sedimentary remains of chironomid head capsules anddiatoms. We apply regional calibration sets to quantitatively reconstruct meanJuly air temperature (using chironomids and diatoms) and lake-water pH(using diatoms). Both chironomids and diatoms infer highest temperatures(1.7–2.3°C above present-day estimates, includinga correction for glacio-isostatic land up-lift by0.6°C) during the early Holocene (c.9,500–8,500 cal. yrs BP). Diatoms suggest a decreasing lake-waterpH trend (c. 0.6 pH units) since the early Holocene. Usingdetrended canonical correspondence analysis (DCCA), we compare the Holocenedevelopment of diatom communities in Lake Njulla with four other nearby lakes(Lake 850, Lake Tibetanus, Vuoskkujávri, Vuolep Njakajaure) locatedalong an altitudinal gradient. All five lakes show similar initial DCCA scoresafter deglaciation, suggesting that similar environmental processes such ashigh erosion rates and low light availability associated with high summertemperature appear to have regulated the diatom community, favouring highabundances of Fragilaria species. Subsequently, the diatomassemblages develop in a directional manner, but timing and scale ofdevelopment differ substantially between lakes. This is attributed primarily todifferences in the local geology, which is controlling the lake-waterpH. Imposed on the basic geological setting, site-specific processessuch as vegetation development, climate, hydrological setting andin-lake processes appear to control lake development in northernSweden.  相似文献   

Sub-Cm Subsidence Measurements With The Wide-Angle Airborne Laser Ranging System     

Oliver Bock  Christian Thom 《Surveys in Geophysics》2001,22(5-6):537-548

The Wide-Angle Airborne Laser Ranging System (WA-ALRS) is aninstrument developed at IGN with the aim of measuring landsubsidence with sub-cm accuracy. The instrument provides rangemeasurements that are used to estimate the co-ordinates of aground-based network of cube-corner retroreflectors (CCRs).Millimeter accuracy on relative radial co-ordinates has beendemonstrated in a ground-based experiment and centimeter accuracyhas been obtained in a recent airborne experiment. The mainlimitation in the latter experiment came from the low link budgetat longer distances. In this paper we analyze the performanceexpected with two different detector modules (avalanchephotodiodes with amplifiers). Laboratory measurements are used tocharacterize detector parameters and estimate ranging accuracy.Numerical simulations predict a 2–3 mm accuracy in the verticalco-ordinate with these detectors combined to a 2-km aircraftaltitude, a 20 laser beam divergence, a 250-m CCR separation and 10³ measurements per CCR.  相似文献   

An audiomagnetotelluric study of the Meugueur-Meugueur ring structure, Aïr, Niger: ring dyke or cone sheet?     

Michel Ritz  William L. Brown  Christian Moreau  Daniel Ohnenstetter 《Journal of Applied Geophysics》1996,34(4):229-236

Three radial audiomagnetotelluric (AMT) sounding profiles were carried out across the narrow, 65-km diameter troctolitic Meugueur-Meugueur ring structure, central Aïr, Niger, to study its electrical configuration; one profile extended across the bedrock into the large Ofoud complex situated slightly off geographical centre within the ring. Apparent resistivity data from 27 sites ranged from isotropic to strongly anisotropic. In nearly all soundings, one- and two-dimensional modelling indicated the presence of a major zone of low resistivity (60–600 Ωm), about 200 m thick, dipping steeply inwards at an angle of 65–80° and extending to a depth of at least 2–5 km. This layer, overlain and underlain by rocks of higher resistivities in excess of 5000 Ωm, is taken to be the outer contact. A highly resistive body, about 200 m in width, dipping inwards to a depth of at least 4 km is taken to be the Meugueur-Meugueur intrusion, which is thus interpreted to be a cone sheet.  相似文献   

Adsorption of polar aromatic hydrocarbons on synthetic calcite   总被引：1，自引：0，他引：1  

Lene Madsen  Laila Grahl-Madsen  Christian Grøn  Ida Lind  John Engell 《Organic Geochemistry》1996,24(12):1151-1155

The wettability of hydrocarbon reservoirs depends on how and to what extent the organic compounds are adsorbed onto the surfaces of calcite, quartz and clay. A model system of synthetic calcite, cyclohexane and the three probe molecules: benzoic acid, benzyl alcohol and benzylamine, have been studied by adsorption experiments. The results clearly demonstrate the differences in the adsorption behaviour between probes with different functional groups of varying polarity and acidity. The maximum adsorption decreases in the order: benzoic acid, benzyl alcohol and benzylamine. The order of magnitude of ΔG° for the adsorption process implies the formation of a strong bond between the calcite surface and the adsorbate molecules.  相似文献   

Significance of subtidal sediments to heterotrophically-mediated oxygen and nutrient dynamics in a temperate estuary     

William M. Rizzo  Robert R. Christian 《Estuaries and Coasts》1996,19(2):475-487

Sediment-water exchanges of ammonium (NH₄ ⁺), nitrate + nitrite (NO_x ^?), filterable reactive phosphorus (FRP, primarily ortho-phosphate), and oxygen (O₂) under aphotic (heterotrophic) conditions were determined at 2–5 stations in the Neuse River Estuary, from 1987 to 1989. Shallow (1 m), sandy stations were sampled along the salinity gradient. Fluxes from deep (>2 m) sites were compared to the shallow sites in two salinity zones. Grain size became finer and organic content increased with depth in the oligohaline zone but not in the mesohaline zone. Net release of NH₄ ⁺ and FRP occurred at all sites. Fluxes varied from slight uptake to releases of 200–500 μmol m^?2 h^?1 (NH₄ ⁺) and 150–900 μmol m^?2 h^?1 (FRP). Net NO_x ^? exchange was near zero, but were ±100 μmol m^?2 h^?1 over the year. Release of NH₄ ⁺ and FRP from the shallow sandy stations decreased with distance down the estuary, but O₂ uptake did not change. The deeper oligohaline site had twofold higher rates of NH₄ ⁺ and FRP release and O₂ uptake than the shallow site, but no differences occurred between depths in the mesohaline zone. Temperature and organic content were important controls for all fluxes, but water column NO_x ^? concentration was also important in regulating NO_x ^? exchanges. Ratios of oxygen consumption to NH₄ ⁺ release were near the predicted ratio (Redfield model) at oligohaline sites but increased down estuary at mesohaline sites. This may be due to greater nitrification rates promoted by autotrophy in the sediments.  相似文献