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Michel Magny Matthieu Honegger et Laurent Chalumeau 《Eclogae Geologicae Helvetiae》2005,98(2):249-259
Resume. Les fouilles archéologiques réalisées de 1998 à 2002 sur le site néolithique de Marin-Les Piécettes sur la rive nord-ouest
du lac de Neuchatel ont offert l’opportunité d’observer deux séquences sédimentaires intéressantes pour la reconstitution
des variations holocènes du niveau du lac, en particulier au cours de la période correspondant au changement de cours de l’Aar
en direction du nord-est, vers 5650–5500 cal BP. La géométrie des corps sédimentaires et les changements lithologiques permettent
de reconna?tre plusieurs phases majeures de bas niveaux relatifs du plan d’eau vers 6870, 5660, 5060–3990, 3580, 2280, 1640
et 1170 cal BP. Le site néolithique de Marin-Les Piécettes s’est développé vers 5454–5433 cal BP à la faveur d’un court épisode
de bas niveau du lac qui a interrompu une importante phase de haut niveau au début du Subboréal. Les événements paléohydrologiques
identifiés à Marin-Les Piécettes apparaissent cohérents avec ceux reconstitués sur le site de Montilier au bord du lac de
Morat, ainsi qu’avec les variations paléohydrologiques reconstituées à partir des lacs du Jura, du Plateau suisse et des Préalpes
du Nord fran?aises. Ceci suggère qu’ils témoignent d’un signal climatique. La séquence sédimentaire de Marin-Les Piécettes
met enfin en évidence la formation d’un cordon littoral sur la rive nord-ouest du lac juste après 5660 cal BP.
Manuscrit re?u le 22 septembre 2004 Révision acceptée le 11 mars 2005 相似文献
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Second and sub-second structures were simultaneously detected in optical, radio and hard X-ray (HXR) band, respectively by
the GanYu Station of Purple Mountain Observatory, Nobeyama Radio Observatory, and RHESSI satellite in the November 1, 2004 flare (Ji et al., in Astrophys. J. 636:L173, 2006), which may be contributed to the energy transport of the continuous heat flux from the hot corona or chromosphere evaporation
and of the accelerated electrons. The linear correlations between the amplitudes of these fluctuations and their flare emissions,
and those between the cross-correlation coefficients of the fluctuations at two H
α
kernels, or two radio frequencies, or two X-ray energies and their flare emissions may support the causal relationship of
the flare and these time structures. While, the cross-correlations of the fluctuations at three different bands suggest that
the fluctuations are caused by the common thermal or nonthermal processes in the flare. Moreover, some new features of the
fluctuations are reported in the flare: (1) The sub-second fluctuations in radio and HXR bands have a same timescale, which
is evidently larger than that in H-alpha band. The difference may be explained by the downward movements of nonthermal electrons
or the upward motion of chromosphere evaporation. (2) The power-law distributions of the amplitudes of the second and the
sub-second structures are obtained at optical, radio and HXR bands with different indices. (3) The peak-to-peak correspondence
of Stokes I and V components in the sub-second structures at radio band suggests that they may be resulted from a periodical
particle acceleration and particle injection in this event. However, the second structures may be caused by the modulations
of Alfvén waves with an upward speed of 103 km/s. 相似文献
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The kinetics of monodomain order-disorder processes in monoclinic (I2/c) BaAl2Ge2O8-feldspar have been investigated by X-ray powder diffraction, Hard Mode IR Spectroscopy, and TEM darkfield imaging on quenched
samples. Compared to the behaviour predicted by the TDGL approximation ordering kinetics observed at low temperatures slow
down significantly when equilibrium is approached. Such a delay is not observed in disordering experiments starting from essentially
ordered cation distributions. The deviation from TDGL behaviour is interpreted in terms of partial order parameter conservation
in a non-uniformly ordered phase. Modifications to the uniform TDGL rate equation are tested against the available data. An
activation energy of 352 ± 28 kJ/mol is obtained for Al,Ge ordering. The mixing coefficient ξc
2/ξ2, which describes the degree of order parameter conservation, is obtained as a function of temperature. While this coefficient
vanishes in the vicinity of the transformation temperature T
tr, it saturates towards a level of ξc
2/ξ2≈0.4 for T→0. ξ
c
2/ξ2 determines the kinetic stability of ordered clusters quenched from T≈T
tr.
Received: 21 April 1999 / Revised, accepted: 19 July 1999 相似文献
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Energetic charged particles, which are often observed in solar active regions, may be also produced in interplanetary space due to the decoupling of ions and electrons in plasma. The Hall term in general Ohm's law is generally thought to be responsible for the decoupling of electrons and ions in plasma during magnetic reconnection. In this paper, a Hall MHD model is developed to study energetic charged particle events produced during fluctuations in the interplanetary magnetic field intensity. Two energetic charged particle events are used to test this model. It is concluded that the Hall effect does not only play the important role in the process of magnetic reconnection, but also in energetic charged particle events produced during fluctuations in the interplanetary magnetic field intensity. 相似文献
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At MHD scales density fluctuation in the solar wind generally have a relative amplitude less than 0.1. The nearly incompressible MHD theory would seem then appropriate to describe a major part of the compressive turbulence at these scales. As a test of the theory, we focus on the scaling properties of density fluctuations with turbulent Mach numbers and on the level of correlation between density and temperature fluctuations. Our findings do not appear in favour of an extended applicability of the nearly incompressible theory to MHD compressive turbulence in the solar wind. 相似文献
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中昆仑山区距今一万七千年以来湖面波动研究 总被引：3，自引：0，他引：3
根据湖盆地貌、湖泊沉积物分析,本文指出:中昆仑山区的封闭湖泊17000年以来湖面在总体下降过程中,出现了3期相对高湖面,近期湖泊仍在收缩咸化,未来仍将继续达一趋势。 相似文献
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We investigate here the fluctuations in the total, open and closed solar magnetic flux (SMF) for the period 1971–1999 by means of the maximum entropy method in the frequency range 5×10−9–10−7 Hz (6 yr to 120 days). We use monthly data for the total, open and closed magnetic solar fluxes. Periodicities found in the series are similar showing that there is some relationship between the fluxes. The most important finding of this work is the existence of fluctuations at around 1.3 and 1.7 yr in the SMF with alternating importance during consecutive even and odd solar cycles. These fluctuations are directly related with variations present in cosmic rays, solar wind parameters and geomagnetic activity indexes. A quasi-triennial periodicity previously found in sunspots and other solar phenomena is also of importance. The SMF is generated by the action of the solar dynamo; therefore, it is through the magnetic flux that the solar dynamo influences several heliospheric phenomena. 相似文献
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Fluctuations and Variations in Coastal Marine Environments 总被引：2，自引：0，他引：2
Abstract. The manifold aspects of variability of coastal marine ecosystems are reviewed, with special reference to the response of species and communities. Fluctuations are defined as recurrent modifications in community structure, for instance due to seasonality, whereas variations are defined as changes permanently leading from a given community to a different one. Both patterns are described and linked to the interaction between life history traits and environmental factors. Resting stages are proposed to play a still underestimated role in the dynamics of coastal communities, especially for plankton. Rare species are considered as an essential constant of communities, being the source of potential variation and alternance in the contribution to the standing biomass. 相似文献
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