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81.
Fluid theories explain the origin of region-2 field-aligned currents as the closure of the ring current, driven itself by the azimuthal pressure gradients generated in the magnetospheric ring plasma by the sunward convection. Although the structure of pressure gradients appears experimentally complex, observations confirm that a close connection exists between the region-2 field-aligned currents and the ring current. The fluid linear theory of the adiabatic transport by convection of the ring plasma gives a first estimate of this process, and leads ultimately to phase quadrature (in terms of magnetic local time) between the region-2 field-aligned currents and the convection potential. When significant non-adiabatic processes are taken into account, such as precipitations at auroral latitudes, the theoretical phase difference rotates toward opposition. We determine experimentally the phase relationship between the region-2 field-aligned currents and the convection potential from recent statistics, depending on the magnetic activity index Kp, and performed from the EISCAT data base. For geometrical reasons of sufficient probing of region 2, it is only computed in the case of a moderate magnetic activity corresponding to 2\leqKp<4. Region-2 field-aligned currents are found to be in phase opposition with the convection electrostatic potential at auroral latitudes. This confirms the importance of non adiabatic processes, especially ion losses, in the generation of region-2 field-aligned currents, as theoretically suggested. 相似文献
82.
Logging and continuous coring are carried out when drilling and looking for materials such as gravels, sand, and clay or in order to evaluate the fracture state of a deep site intended for waste storage. However, in some cases of non-consolidated formations, the results may be disappointing because of the borehole conditions. Full waveforms, as seismic signals, provide information about physical parameters of the grounds crossed by the sonic tool, and this information is almost independent of borehole conditions. Traditional displays in variable area or density show the wave arrival times and the frequencies with depth; for variable density, a color scale permits to see clustered instantaneous phases.In order to determine precisely and simultaneously the three signal parameters (arrival time, frequency, and amplitude) in the depth-propagation time domain, a 3-D visualization software has been developed. The “view” parameters, which give a nice display of the 3-D→2-D projection of the signals in a parallel perspectives relative to depth, are estimated on the monitor screen in an interactive way. A larger size version of the software is available for displaying in detail the acoustic signals for the whole borehole. However, this program needs a large computer, and the maximum size of the drawing depends on the computer memory available for use.The comparison between traditional and 3-D displays shows that without previous preprocessing, the 3-D visualization (1) shows the very small and continuous variations of amplitude (and, therefore, of attenuation) with depth better; and (2) can bring out interferences and “energetic peaks” by simply changing the “view” parameters. As the attenuation of the different waves is directly determined, fresh zones can be distinguished immediately from fracture zones and hard ground from soft ground. The geometry of major fracturing can be deduced directly from graphical representation; i.e. open or closed, and horizontal or oblique fractures. The calculation of their “vertical thickness” is straightfoward. Microfractures, induced by drilling or otherwise, are not detected, but microfractured rocks are detectable. 相似文献
83.
84.
M. C. Reymond 《Rock Mechanics and Rock Engineering》1975,7(1):1-16
RésuméEtude de la fissuration des eprouvettes sous contraintes en laboratoire et des massifs rocheux en carrières par une methode d'emission acoustique Différentes étapes successives de l'évolution de la roche ont été établies lors d'essais en laboratoire par la technique d'émission acoustique. La dernière phase s'avère d'un grand interêt et peut être comparée aux phénomènes prémonitoires des éboulements qui précèdent la rupture dans les carrières.Un processus d'investigation du comportement du massif rocheux dans les carrières a été défini par la technique de sismique réfraction. D'après l'enregistrement des microbruits, on observe deux phases: une période active suivie d'une période d'amortissement qui traduit une restabilisation du massif, excepté lorsqu'un éboulement se produit quelques minutes après un tir.Les résultats trouvent une application pratique en mécanique des roches dans la conception d'un dispositif de surveillance des sites géologiques dont le principe est basé sur la technique d'emission acoustique.
Avec 12 figures 相似文献
SummaryMechanism of Brittle Fracture of Rock During Uniaxial Compression in Laboratory in a Quarry by an Acoustic Emission Technic Different following stages of brittle fractures of rock were established during experiments in laboratory by using audible noises. The latter stage is very interesting and an analogy was established with premonitory crackles preceding the rupture of rock in quarries.A method for the investigation of the evolution of rocks in quarries was established by technical seismic refraction.Two stages are observed: A sensitive crackle, then die oscillations damp down which displays a stabilisation of rock, except when a falling takes place a few minutes after a crash.This theory is applied in rocks mechanism by means of a detection crackles device of which fundamental mechanics are determined by technical acoustic emission.
ZusammenfassungErfassung des Sprödbruchverhaltens von Fels während einachsiger Druckversuche im Labor und im Steinbruch mittels einer akustischen Methode Durch die Interpretation von Geräuschen wurden bei Laborversuchen verschiedene, aufeinanderfolgende Stadien im Bruchverhalten von Fels festgestellt. Der Endzustand ist interessant; es wurde eine Analogie zu den warnenden Geräuschen, die einem Felsbruch in Steinbrüchen vorangehen, gefunden. Darauf wurde eine Methode aufgebaut, die auf Schallbrechung beruht und zur Überwachung der Entwicklung im Fels dient.Es können zwei Stadien beobachtet werden: ein intensives Knistern, dann eine Dämpfung, die eine Stabilisierung des Felsens ausdrückt, ausgenommen der Fall, daß wenige Minuten nach einem Krach ein Bergsturz eintritt.Diese Theorie wird in der Felsmechanik mittels einer speziellen Apparatur angewendet, die es erlaubt, fundamentale Verhaltensgrundsätze unter Anwendung von akustischer Emission festzustellen.
Avec 12 figures 相似文献
85.
86.
Characterization of water in synthetic rhyolitic glasses and natural melt inclusions by Raman spectroscopy 总被引:3,自引:1,他引:2
Aliouka?Chabiron Jacques?PirononEmail author Dominique?Massare 《Contributions to Mineralogy and Petrology》2004,146(4):485-492
Raman spectroscopy was used to analyze quantitatively water in silicate glasses and melt inclusions and to monitor H2O–OH speciation. Calibration is based on synthetic glasses with various water contents (0.02–7.67% H2O); water determination and OH–H2O differentiation on the area of the Si–O broad band at 468 cm–1 and the asymmetric O–H band at 3,550 cm–1. Each Raman spectrum has been decomposed into four Gaussian + Lorentzian components centered at 3,330, 3,458, 3,560, and 3,626 cm–1 using the Levenberg–Marquardt algorithm. These components are interpreted to be two different types of H2O molecule sites. The influence of the temperature on the loss of water is more important for molecular water than for the hydroxyl groups. The H2O–OH partition confirms the typical evolution of water speciation in rhyolitic glasses as a function of the bulk water content. Method limitations have been studied for the application to natural melt inclusions.Editorial responsibility: T.L Grove 相似文献
87.
Georg?M.?PartzschEmail author Dominique?Lattard Catherine?McCammon 《Contributions to Mineralogy and Petrology》2004,147(5):565-580
One of the most widely used methods to estimate magmatic oxygen fugacity involves the use of empirical equations relating fO2 to the iron redox state in quenched silicate liquids; however none of the equations have been calibrated experimentally under subliquidus conditions at temperatures and oxygen fugacities that are relevant to natural magmas. To address this problem, we tested two empirical relationships [Eq. (1) in Kress and Carmichael 1991; Eq. (6) in Nikolaev et al. 1996] on synthetic glasses synthesized from a ferrobasaltic and a transitional alkali-basaltic composition at sub- to superliquidus temperatures (1,132–1,222°C) and controlled oxygen fugacities (FMQ=–2 to +1.4). Fe3+/Fe was determined using conventional and milliprobe Mössbauer spectroscopy, and verified using wet chemical analysis on selected samples. For the ferrobasaltic bulk composition SC1-P, both empirical models reproduce the Fe3+/Fe ratio of the quenched liquids generally within 0.03 for sub- as well as superliquidus temperatures, although agreement is worse at higher oxygen fugacities (FMQ>+1) at subliquidus temperatures. For the transitional alkali-basaltic composition 7159V-P, both models reproduce the Fe3+/Fe ratio of the quenched liquids generally within 0.04, although agreement is worse for both models at high oxygen fugacities (FMQ>+1). Such behaviour may be related to a change in melt structure, where a progressive change in Fe3+ coordination is inferred to occur as a function of Fe3+/Fe based on Mössbauer center shifts. Recasting the data in terms of oxygen fugacity shows that calculated oxygen fugacities deviate from those actually maintained during the equilibration of the sample material by generally no more than 0.5 log-bar unit, with maximum deviations that only rarely exceed one log-bar unit.Editorial responsibility: J. Hoefs 相似文献
88.
A. Benmoussa J.-F. Hochedez W. K. Schmutz U. SchÜhle M. NeslÁdek Y. Stockman U. Kroth M. Richter A. Theissen Z. Remes K. Haenen V. Mortet S. Koller J. P. Halain R. Petersen M. Dominique M. D’Olieslaeger 《Experimental Astronomy》2003,16(3):141-148
Fabrication, packaging and experimental results on the calibration of metal-semiconductor-metal (MSM) photodetectors made on diamond are reported. LYRA (Lyman- RAdiometer onboard PROBA-2) will use diamond detectors for the first time in space for a solar physics instrument. A set of measurement campaigns was designed to obtain the XUV-to-VIS responsivity of the devices and other characterizations. The measurements of responsivity in EUV and VUV spectral ranges (40–240 nm) have been carried out by the Physkalisch-Technische Bundesanstalt (PTB) in Germany at the electron storage ring BESSY II. The longer wavelength range from 210 to 1127 nm was measured with monochromatic light by using a Xe-lamp at IMO-IMOMEC. The diamond detectors exhibit a photoresponse which lie in the 35–65 mA/W range at 200 nm (corresponding to an external quantum efficiency of 20–40%) and indicate a visible rejection ratio (200–500 nm) higher than four orders of magnitude. 相似文献
89.
90.
Pascal Bertran Dominique Bonnissent Daniel Imbert Pierre Lozouet Nathalie Serrand Christian Stouvenot 《Comptes Rendus Geoscience》2004,336(16):14
A 2.5-m-thick sequence of lake sediments at the Étang de Grand-Case, Saint Martin (French West Indies) is studied here. Significant hydrological budget fluctuations allows distinction of three main climatic periods: (1) an overall dry period (4200 BP–2300 BP), characterised by carbonated mud, gypsum and storm sand layers; (2) a wet phase (2300 BP–1150 BP) dominated by organic mud; and (3) a more complex phase (1150 BP to present), with detrital inputs due to human activities. Comparison with other regional high-resolution records shows that similar climate modifications typify the whole Mesoamerican and Caribbean area. The climatic phenomena that are implicated in the variations of both precipitation and hurricane frequency over the Lesser Antilles are due to the latitudinal displacement of the inter-tropical convergence zone. These data give new support to the hypothesis of the existence of a correlation between peopling phases and climate variations in the Caribbean as previously proposed by some archaeologists. To cite this article: P. Bertran et al., C. R. Geoscience 336 (2004). 相似文献