Test of the vibrational modelling for the λ-type transitions: Application to the α-β quartz transition     

Joëlle Castex  Michel Madon 《Physics and Chemistry of Minerals》1995,22(1):1-10

Vibrational modelling is at the present time the only known way to predict the heat capacities of the Earth's mantle minerals at high-pressure and high-temperature. To test the validity of this method for λ-type transitions, we have applied it to the α-β quartz transition (T ₀=846±1 K). Raman spectra of quartz were recorded up to 900 K. Measured frequency shifts of the α-quartz Raman modes were then used in conjunction with available high-pressure Raman data to calculate intrinsic mode anharmonicity, through the parameter a _i=(?Lnv_i/?T)_v. Vibrational modelling of the heat capacity at constant volume, Cv, and at constant pressure, Cp, including anharmonic corrections deduced from the a _i parameters, are compared to experimental data. Taking into account the soft-mode associated to the α-β quartz transition, the model reproduces the excess of Cp related to the transition. Then, this study confirms that detecting a soft-mode from vibrational data allows one to predict λ-type transitions. However, when modelling the thermodynamic properties, the contribution of a soft-mode cannot be established from spectroscopic data. Therefore, one needs first to determine this contribution in order to predict the heat capacities of Earth's mantle minerals displaying λ-type transitions. In α-quartz, this contribution has been determined as 0.007% of the total number of the optic modes in the model of the density of states.  相似文献   

Chronostratigraphy and paleoclimatic meaning of cryogenic deformations in the Central European loess     

Brigitte van Vliet-Lanoë Dr. 《GeoJournal》1991,24(2):157-163

Cryoturbations in loess reflect cold and wet environments but not necessarily permafrost. Only flat bottomed cryoturbations are indicative of it. Outside the permafrost zone they occur during the wet period of the last glaciation: during the early Weichselian, the lower pleniglacial, the end of the middle pleniglacial and the late glacial. Their morphology ist related to the frost susceptibility of the superimposed layers, expressed in form of differential frost heaving, ruled by the drainage quality and the frost susceptibility gradient. Their diagenesis is discussed.  相似文献   

U-Pb dating of an early paleozoic bimodal magmatism in the french Massif Central and of its further metamorphic evolution     

Christian Pin  Joël Lancelot 《Contributions to Mineralogy and Petrology》1982,79(1):1-12

In the Marvejols area (Southern french Massif Central), the gneissic Marvejols supergroup is overthrust on the metasedimentary “Série du Lot”, deposited in part prior to 540 Ma. The allochtonous terranes are characterized by the occurrence of a leptyno-amphibolitic group, a complex association of mafic and felsic rocks of igneous and sedimentary derivation. A 480±10 Ma age has been obtained by U-Pb dating of zircons, for the crystallization of both mafic and felsic meta-igneous rocks. These rocks were emplaced during an important extensional tectonics. Relics of eclogites, pyrigarnites, coronite gabbros and HP-trondhjemites are clear evidence for a further HP-HT event dated at 415±6 Ma on zircons from a HP trondhjemite. Subsequently, the Marvejols supergroup underwent an amphibolite facies metamorphism with incipient mobilization dated at 345±10 Ma. Rifting and thinning of the continental crust in Cambro-Ordovician times appears to be a major geodynamic feature which could account for the thermal events often referred to the “Caledonian” orogeny. The Silurian (415 Ma) age of the HP episode is clearly older than the main Variscan tectonometamorphic event; it is in agreement with Rb-Sr dating of the Moldanubian granulites and with some radiometric data from Southern Brittany (France). These results point to a compressive phase, probably in a subduction context, in view of the high pressures reached (15–20 Kb), after the Cambro-Ordovician distensive phase. The main final tectono-metamorphic paroxysm (blocking of subduction process and continental collison ?) is not prior to the end of Devonian (340–350 Ma) and is related to the Variscan orogeny s.s  相似文献   

The atmospheric electric agitation and its origin     

H. Israël 《Pure and Applied Geophysics》1959,42(1):140-142

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Remarks concerning the “ten-year-period” of atmospheric electricity     

Prof. Dr. Hans Israël 《Meteorology and Atmospheric Physics》1968,17(1):88-89

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Buchbesprechungen     

F. Steinhauser  W. Mörikofer  H. Israël  M. Toperczer 《Meteorology and Atmospheric Physics》1953,6(1):114-128

Ohne Zusammenfassung  相似文献   

Hans Benndorf †     

H. Israël  M. Toperczer 《Meteorology and Atmospheric Physics》1953,6(1):111-113

Ohne Zusammenfassung

---

Hans Benndorf

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Multi-wavelength observations of the onset phase of a coronal mass ejection     

Innes  D.E.  Inhester  B.  Srivastava  N.  Brekke  P.  Harrison  R.A.  Matthews  S.A.  Noëns  J.C.  Schmieder  B.  Thompson  B.J. 《Solar physics》1999,186(1-2):337-361

The structure and dynamics of the initial phases of a coronal mass ejection (CME) seen in soft X-ray, extreme ultraviolet and optical emission are described. The event occurred on the SW limb of the Sun in active region AR 8026 on 9 April 1997. Just prior to the CME there was a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging Telescope (EIT) reveal the emergence of a candle-flame shaped extreme ultraviolet (EUV) cavity at the time of the flare. Yohkoh images, taken about 15 min later, show that this cavity is filled with hot X-ray emitting gas. It is most likely that this is the site of the flare. Almost simultaneous to the flare, an H surge or small filament eruption occurs about 50 arc sec northwards along the limb from the EUV cavity. At both the site of the core of the hot, EUV cavity and the filament ejection are X-ray jets. These jets seem to be connected by hot loops near their bases. Both jets disappear within a few minutes of one another.Clear evidence of the CME first appeared in the Large Angle Spectrometric Coronagraph (LASCO) and EIT images 40 min after the flare and onset of the filament ejection. It seems to come from a region between the two X-ray jets. This leads to the speculation that magnetic field reconnection near one footpoint of a loop system triggers reconnection near its other footpoint. The loop system is destabilized and ultimately gives rise to the CME. This possibility is supported by magnetic field and H images taken when the active region was at disk center which show that the active region had a double bipole structure with dark H filaments between the bipoles.  相似文献   

Flexible Automatic Scheduling for Autonomous Telescopes: The MAJORDOME     

Mathieu Bringer  Michel Boër  Cedric Peignot  Gérard Fontan  Colette Mercé 《Experimental Astronomy》2001,12(1):33-48

We have developped a new method for the scheduling ofastronomical automatic telescopes, in the framework of theautonomous TAROT instrument. The MAJORDOME software canhandle a variety of observations, constrained, periodic,etc., and produces a timeline for the night, which may bemodified at any time to take into account the specificconditions of the night. The MAJORDOME can also handletarget of opportunity observations without delay.  相似文献   

A Note on Extension Variances in IR2     

Chadœuf  Joël  Moran  Chris  Goulard  Michel 《Mathematical Geosciences》1998,30(6):575-587

Matheron (1971) proposed an approximation of the extension variance in IR. We propose in this note an extension of this formula in IR ² , based on a MacLaurin formula. Its application is shown in an example, the estimation of the maximum depressional storage of a soil surface.  相似文献