Polarization in cyclotron radiation in strong magnetic fields     

Luidmila Semionova  Denis Leahy  Jorge Paez 《中国天文和天体物理学报》2010,10(10)

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Interaction between tectonic and erosion processes on the morphogenesis of an Alpine valley: geological and geophysical investigations in the lower Romanche valley (Belledonne massif, western Alps)     

Olivier Le Roux  Stéphane Schwartz  Jean François Gamond  Denis Jongmans  Pierre Tricart  Michel Sebrier 《International Journal of Earth Sciences》2010,99(2):427-441

In the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides, from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone (SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited structures, the BMF and the SFZ.  相似文献   

Tropical cyclones in the SW Indian Ocean. Part 2: structure and impacts at the event scale     

Denis S. Chang-Seng  Mark R. Jury 《Meteorology and Atmospheric Physics》2010,106(3-4):163-178

The southwest Indian Ocean (5°–20°S, 45°–70°E) experiences frequent tropical cyclones (TC) in the December–March season. In this paper, TC composite and case-study structure and impacts are studied using daily oceanic and atmospheric fields from model-reanalyzed data, satellite remote sensing, and in situ station data. The TC environment is characterized according to mean track: W-, SW-, and S-moving. Case studies of TC are investigated, and impacts such as storm surge and rainfall are evaluated through comparison of ‘real’ and ‘model’ datasets in the period since 1998. The northern sub-tropical jet stream is found to influence the intensity and track of TC in the SWIO. The composite SW-moving TC maintains intensity compared to the other tracks, which decline in strength. Variability is found in TC rainfall distribution, with maximum intensity in a spiral band 1–2 days before peak intensity, based on satellite estimates. There is a re-establishment of equatorial rainfall in the case of southward moving TC after peak intensity. The W-moving TC lacks monsoon inflow compared to the recurving TC. Comparisons are made between low-resolution model-estimated rainfall, various satellite products, and station-observed rainfall. TC spiral rain-band intensity is found to be similar to that reported elsewhere in the tropics, based on a limited sample of TRMM PR data and station reports. The satellite-derived daily rainfall out-performs NCEP reanalysis due to low resolution and underestimated diabatic heating. Similarly, the circulation within a 300-km radius of the composite TC is poorly resolved by re-analysis; winds, swells, and storm surges are too low by a factor of two compared with QuikSCAT and in situ measurements. This work will offer ways to adjust operational forecasts of winds, rainfall, and swells around tropical cyclones, so that TC risk and impacts are better managed.  相似文献   

Results of a microearthquake study,one year before the El Asnam earthquake of October 10, 1980     

Denis Hatzfeld  Merzouk Ouyed 《Tectonophysics》1982,89(4):T33-T36

In November 1979, five portable instruments were installed in the El Asnam area. During a ten-day recording period, nine events of magnitude 0.5 to 1.9 were located in the focal region of the 1980 earthquake. All but one of the events occurred in the north western block defined by the main fault. A composite fault-plane solution agrees with the mechanism of the main shock. No abnormal behaviour of the $\text{V}{}_{\mathrm{p}}\text{V}{}_{\mathrm{s}}$ ratio was observed.  相似文献   

Ostracode-based reconstruction from 23,300 to about 20,250 cal yr BP of climate, and paleohydrology of a groundwater-fed pond near St. Louis, Missouri   总被引：1，自引：0，他引：1  

Brandon Curry  Denis Delorme 《Journal of Paleolimnology》2003,29(2):199-207

The water chemistry of a groundwater-fed sinkhole-pond near St. Louis, Missouri, and its associated climate during the last glaciation are reconstructed by comparison with autecological data of modern ostracodes from about 5,500 sites in Canada. A 4.8-m succession of fossiliferous sediment yielded ostracode assemblages that collectively are generally found today in ponds in North America including the species Cyclocypris ampla, C. laevis, Cypridopsis vidua, Candona crogmaniana, C. distincta, and C. ohioensis. Fossils of Picea needles and the ostracode Cyclocypris sharpei imply that best analog sites for the succession are in central to south-central Canada. The pond formed 23,300 ± 400 cal yr BP when a sinkhole became plugged by a clay bed about 1 m thick. By about 20,250 cal yr BP, the pond had desiccated and was buried by loess. The sediment accumulation rate was about 0.18 cm/yr, and each sample interval (6 cm) represents a time slice of 33 years. Data from this record provides the first fairly high resolution proxy record of the glacial paleoclimate of the mid-latitude of North America. The analog data indicate the water in the hydrologically-open spring-fed pond was less than 1 m deep. The paleoclimatic reconstructions imply gradually drier conditions and uniform, cool temperatures. The shallow water depth indicates that the temperature reconstruction is robust with mean annual temperatures (MATs) that ranged between 0.8 and 3.9°C, and mean July temperatures that ranged from 16.8 and 18.1°C. Other estimated climatic parameters include mean annual precipitation (MAP; 430 to 840 mm/yr), and moisture balance (P-E; –111 to 298 mm/yr). Compared to values measured today at St. Louis, the MAP was about 400 mm less, MAT about 10°C cooler, and P-E, about the same. These values are consistent with other published reconstructions based on modern analog analysis of fossil beetles and pollen, and paleothermometry based on amino acid racemization. The total dissolved solids (TDS) progressively increased from about 87 to 431 mg/L. Changes in TDS reflect either the balance between the relative inputs of karst groundwater and overland flow, or changes in the duration of water-rock interaction associated with the groundwater. The postulated long-term 900 ± 200 year cyclicity of growing-season moisture and temperature, attributed to El Niño-Southern Oscillation cycles, is not expressed in the reconstructed hydrologic or climatic data. This is attributed, in part, to the mediating effect on temperature by monothermic groundwater input to this flow-through system.  相似文献   

Prévision des crues éclair     

Valérie Estupina Borrell  Jacques Chorda  Denis Dartus 《Comptes Rendus Geoscience》2005,337(13):1109-1119

Flash-flood events resulting from paroxystic meteorological events concentrated in time and space are insufficiently documented as they produce destructive effects. They are hardly measurable and present single features that are not transposable to another event. In the South of France, the flash flood of November 1999 gives a perfect illustration of these characteristics. The physical complexity of the process and consequently the volume and the variety of the data to take into account are incompatible with the real time constraint allocated to the forecasters confronted to the occurrence of such phenomena. So, we have to make choices to afford acceptable simplifications to the complete mechanical model. MARINE (‘Modélisation de l'Anticipation du Ruissellement et des Inondations pour des évéNements Extrêmes’) is the operational and robust tool we developed for flash-flood forecasting. This model complies with the criterions of real-time simulation. It is a physically based distributed model composed of two parts: first the flood runoff process simulation in the upstream part of the basin modelled from a rainfall–runoff approach, then the flood propagation in the main rivers described by the Saint-Venant equations. It integrates remote sensed data – Digital Elevation Model, land-use map, hydrographic network for the observations from satellites and the rainfall evolution from meteorological radar. The main goal of MARINE is to supply real time pertinent information to the forecasters. Results obtained on the Orbieu River (Aude, France) show that this model is able to supply pertinent flood hydrograph with a sufficient precision for the forecasting service to take the appropriate safety decisions. Furthermore, MARINE has already been tested in the French National Flood Forecasting Service of Haute-Garonne in real conditions. To cite this article: V. Estupina Borrell et al., C. R. Geoscience 337 (2005).  相似文献   

Use of Systematic, Palaeoflood and Historical Data for the Improvement of Flood Risk Estimation. Review of Scientific Methods   总被引：2，自引：0，他引：2  

Gerardo Benito  Michel Lang  Mariano Barriendos  M. Carmen Llasat  Felix Francés  Taha Ouarda  Varyl Thorndycraft  Yehouda Enzel  Andras Bardossy  Denis Coeur  Bernard Bobée 《Natural Hazards》2004,31(3):623-643

The catastrophic floods recently occurring in Europe warn of the critical need forhydrologic data on floods over long-time scales. Palaeoflood techniques provideinformation on hydrologic variability and extreme floods over long-time intervals(100 to 10,000 yr) and may be used in combination with historical flood data (last1,000 yr) and the gauge record (last 30–50 yr). In this paper, advantages anduncertainties related to the reconstruction of palaeofloods in different geomorphologicalsettings and historical floods using different documentary sources are described.Systematic and non-systematic data can be combined in the flood frequency analysisusing different methods for the adjustment of distribution functions. Technical toolsintegrating multidisciplinary approaches (geologic, historical, hydraulic and statistical)on extreme flood risk assessment are discussed. A discussion on the potential theoreticalbases for solving the problem of dealing with non-systematic and non-stationary data ispresented. This methodology is being developed using new methodological approachesapplied to European countries as a part of a European Commission funded project (SPHERE).  相似文献   

Hydrous ferric oxide precipitation in the presence of nonmetabolizing bacteria: Constraints on the mechanism of a biotic effect     

Denis G. Rancourt  Pierre-Jean Thibault  Denis Mavrocordatos  Gilles Lamarche 《Geochimica et cosmochimica acta》2005,69(3):553-577

We have used room temperature and cryogenic ⁵⁷Fe Mössbauer spectroscopy, powder X-ray diffraction (pXRD), mineral magnetometry, and transmission electron microscopy (TEM), to study the synthetic precipitation of hydrous ferric oxides (HFOs) prepared either in the absence (abiotic, a-HFO) or presence (biotic, b-HFO) of nonmetabolizing bacterial cells (Bacillus subtilis or Bacillus licheniformis, ∼10⁸ cells/mL) and under otherwise identical chemical conditions, starting from Fe(II) (10⁻², 10⁻³, or 10⁻⁴ mol/L) under open oxic conditions and at different pH (6-9). We have also performed the first Mössbauer spectroscopy measurements of bacterial cell wall (Bacillus subtilis) surface complexed Fe, where Fe(III) (10^−3.5-10^−4.5 mol/L) was added to a fixed concentration of cells (∼10⁸ cells/mL) under open oxic conditions and at various pH (2.5-4.3). We find that non-metabolic bacterial cell wall surface complexation of Fe is not passive in that it affects Fe speciation in at least two ways: (1) it can reduce Fe(III) to sorbed-Fe²⁺ by a proposed steric and charge transfer effect and (2) it stabilizes Fe(II) as sorbed-Fe²⁺ against ambient oxidation. The cell wall sorption of Fe occurs in a manner that is not compatible with incorporation into the HFO structure (different coordination environment and stabilization of the ferrous state) and the cell wall-sorbed Fe is not chemically bonded to the HFO particle when they coexist (the sorbed Fe is not magnetically polarized by the HFO particle in its magnetically ordered state). This invalidates the concept that sorption is the first step in a heterogeneous nucleation of HFO onto bacterial cell walls. Both the a-HFOs and the b-HFOs are predominantly varieties of ferrihydrite (Fh), often containing admixtures of nanophase lepidocrocite (nLp), yet they show significant abiotic/biotic differences: Biotic Fh has less intraparticle (including surface region) atomic order (Mössbauer quadrupole splitting), smaller primary particle size (magnetometry blocking temperature), weaker Fe to particle bond strength (Mössbauer center shift), and no six-line Fh (6L-Fh) admixture (pXRD, magnetometry). Contrary to current belief, we find that 6L-Fh appears to be precipitated directly, under a-HFO conditions, from either Fe(II) or Fe(III), and depending on Fe concentration and pH, whereas the presence of bacteria disables all such 6L-Fh precipitation and produces two-line Fh (2L-Fh)-like biotic coprecipitates. Given the nature of the differences between a-HFO and b-HFO and their synthesis condition dependences, several biotic precipitation mechanisms (template effect, near-cell environment effect, catalyzed nucleation and/or growth effect, and substrate-based coprecipitation) are ruled out. The prevailing present view of a template or heterogeneous nucleation barrier reduction effect, in particular, is shown not to be the cause of the large observed biotic effects on the resulting HFOs. The only proposed mechanism (relevant to Fh) that is consistent with all our observations is coprecipitation with and possible surface poisoning by ancillary bacteriagenic compounds. That bacterial cell wall functional groups are redox active and the characteristics of biotic (i.e., natural) HFOs compared to those of abiotic (i.e., synthetic) HFOs have several possible biogeochemical implications regarding Fe cycling, in the photic zones of water columns in particular.  相似文献   

Modes of thickening of analogue weak lithospheres   总被引：4，自引：2，他引：4  

Florence Cagnard  Jean-Pierre Brun  Denis Gapais 《Tectonophysics》2006,421(1-2):145-160

Several compressional contexts, such as those involving juvenile or thickened crust, are expected to be associated with rather hot lithospheres whose mechanical behaviour remains poorly documented. In this paper, we present a series of analogue models dedicated to compression of lithospheres characterized by a thin upper brittle crust overlying a weak ductile crust and a ductile sub-Moho mantle. The models show that (1) deformation is controlled by the ductile layers that undergo distributed thickening, (2) thrust systems are limited to the upper brittle crust, (3) thrusting induces burial and stacking of upper crust pop-downs. The overall deformation patterns can be basically interpreted in terms of pop-down thrusting of the brittle crust and pure-shear type ductile flow of crust and mantle. Moreover, the models show that the sinking of supracrustal units does not require inverse density profiles but can be simply driven by compression. Model deformation patterns are consistent with those shared by many ancient belts, including not only Archaean granite–greenstone belts, but also more generally Paleoproterozoic ones. They provide also insights on deformation modes that may characterize modern thickened and abnormally hot domains like High Plateaus.  相似文献   

Effects of food particle size on Perca fluviatilis larval growth     

Lakhdar Tamazouzt  Claude Leray  Anne-Marie Escaffre  Denis Terver 《Aquatic Sciences - Research Across Boundaries》1998,60(2):89-98

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