The Performance of MEFOS, the ESO Multi-Object Fibre Spectrograph     

P. Felenbok  J. Guérin  A. Fernandez  V. Cayatte  C. Balkowski  R.C. Kraan-Korteweg 《Experimental Astronomy》1997,7(2):65-85

We are describing a new multi-fibre positioner, MEFOS, that was in generaluse at the La Silla Observatory, and implemented at the prime focus of theESO 3.6 m telescope. It is an arm positioner using 29 arms in a one degreefield. Each arm is equipped with an individual viewing system for accuratesetting and carries two spectroscopic fibres, one for the astronomical objectand the other one for the sky recording needed for sky subtraction. Thespectral fibres intercept 2.5 arcsec on the sky and run from the prime focusto the Cassegrain, where the B&C spectrograph is located. Afterdescribing the observational procedure, we present the first scientificresults.  相似文献   

The Importance of Photospheric Intense Flux Tubes for Coronal Heating     

Démoulin  P.  Priest  E. R. 《Solar physics》1997,175(1):123-155

Dissipation of magnetic energy in the corona requires the creation of very fine scale-lengths because of the high magnetic Reynolds number of the plasma. The formation of current sheets is a natural possible solution to this problem and it is now known that a magnetic field that is stressed by continous photospheric motions through a series of equilibria can easily form such sheets. Furthermore, in a large class of 3D magnetic fields without null points there are locations, called quasi-separatrix layers (QSLs), where the field-line linkage changes drastically. They are the relevant generalisation of normal separatrices to configurations without nulls: along them concentrated electric currents are formed by smooth boundary motions and 3D magnetic reconnection takes place when the layers are thin enough. With a homogenous normal magnetic field component at the boundaries, the existence of thin enough QSL to dissipate magnetic energy rapidly requires that the field is formed by flux tubes that are twisted by a few turns. However, the photospheric field is not homogeneous but is fragmented into a large number of thin flux tubes. We show that such thin tubes imply the presence of a large number of very thin QSLs in the corona. The main parameter on which their presence depends is the ratio between the magnetic flux located outside the flux tubes to the flux inside. The thickness of the QSLs is approximately given by the distance between neighbouring flux tubes multiplied by the ratio of fluxes to a power between two and three (depending on the density of flux tubes). Because most of the photospheric magnetic flux is confined in thin flux tubes, very thin QSLs are present in the corona with a thickness much smaller than the flux tube size. We suggest that a turbulent resistivity is triggered in a QSL, which then rapidly evolves into a dynamic current sheet that releases energy by fast reconnection at a rate that we estimate to be sufficient to heat the corona. We conclude that the fragmentation of the photospheric magnetic field stimulates the dissipation of magnetic energy in the corona.  相似文献   

A new airborne polar Nephelometer for the measurements of optical and microphysical cloud properties. Part I: Theoretical design     

J. F. Gayet  O. Crépel  J. F. Fournol  S. Oshchepkov 《Annales Geophysicae》1997,15(4):451-459

A new optical sensor, the airborne Polar Nephelometer, is described. The sensor is designed to measure the optical and microphysical parameters of clouds containing either water droplets or ice crystals or a mixture of these particles ranging in size from a few micrometers to about 500 m diameter. The probe measures the scattering phase function of an ensemble of cloud particles intersecting a collimated laser beam near the focal point of a paraboloïdal mirror. The light scattered from polar angles from 3.49° to 169° is reflected onto a circular array of 33 photodiodes. The signal processing electronics and computer storage can provide one measurement of the scattering phase function every 100 ms or every 0.2 ms. The first part of the paper describes the theoretical design of a prototype version of the probe.  相似文献   

Two-dimensional structure of mountain wave observed by aircraft during the PYREX experiment     

J. L. Attié  A. Druilhet  P. Durand  B. Bénech 《Annales Geophysicae》1997,15(6):823-839

This study presents an experimental analysis from aircraft measurements above the Pyrenees chain during the PYREX experiment. The Pyrenees chain, roughly WE oriented, is a major barrier for northerly and southerly airflows. We present a case of southerly flow (15 October 1990) and three successive cases of northerly flows above the Pyrenees (14, 15 and 16 November 1990) documented by two aircraft. The aircraft have described a vertical cross section perpendicular to the Pyrenean ridge. This area is described via the thermodynamical and dynamical fields which have a horizontal resolution of 10 km. Three methods for computing the vertical velocity of the air are presented. The horizontal advection terms which play a role in the budget equations are also evaluated. The altitude turbulence zone of 15 October are shown via turbulent fluxes, turbulent kinetic energy (TKE), dissipation rate of TKE and inertial length-scale. A comparison of results obtained by eddy-correlation and inertial-dissi-pation method is presented. The experimental results show a warm and dry downdraft for the southerly flow with large values for advection terms. All the mountain wave cases are also shown to present an important dynamical perturbation just above the Pyrenees at upper altitudes.  相似文献   

The Frequency Dependence of Harmonic Fluid Flow Through Networks of Cracks and Pores     

Y. Bernabé 《Pure and Applied Geophysics》1997,149(3):489-506

—The "dynamic" permeability k(ω) of heterogeneous networks of cracks, tubes and spheres, was determined by numerically simulating the harmonic flow of an interstitial fluid for a wide range of frequencies. For comparison with previous works, this procedure was applied to the 100 network realizations used in Bernabé (1995). In most cases, the calculated frequency dependence of the real and imaginary parts of k(ω) was consistent with the JKD model (Johnson et al., 1987), showing a transition from "viscous", macroscopic flow at low frequencies to "inertial" flow at high frequencies. The viscous skin depth δ _c at the transition was found to be proportional to the critical capillary radius r _c from a capillary invasion (Katz and Thompson, 1986). A simple explanation is that these two length scales arise from the same percolation problem. On the other hand, δ _c was not well correlated with the JKD parameter Λ. The conclusion is that Λ and δ _c (or r _c ?) are two independent parameters, derived from two unrelated approaches (i.e., weighted averaging and percolation theory). Finally, an attempt was made to relax the initial assumptions of a rigid solid matrix and an incompressible fluid. It was observed that the effect of the fluid compressibility could occasionally be very large, especially when networks with large amounts of storage pore space were considered.  相似文献   

Formation of vivianite in holocene clay sediments     

I. Th. Rosenqvist 《Lithos》1970,3(4):327-334

Concretions of vivianite attaining 0.5 g occur in the upper 4 m of the bottom sediments of the Åsrum lake, Vestfold, S. Norway. The vivianite-bearing zone is of lacustrine origin. Vivianite is absent in the underlying lagunal and marine sediments. Electro-chemical and chemical data are given for the interstitial water and the clay.

Solubility product of vivianite is determined. The equilibrium constant is K = 10⁻⁴⁰ for the reaction 3 Fe⁺⁺ + 2 HPO₄⁻ + 2 OH⁻ = vivianite. The concretions grew by diffusion from a slightly supersaturated interstitial water phase. The degree of supersaturation is calculated. The stability relations of vivianite and hydroxyl apatite are discussed.  相似文献   

La phase de la composante annuelle des niveaux des rivières de la plaine de l'Est Européen     

M.elle Aimée Péreau 《Pure and Applied Geophysics》1950,16(1-2):38-46

Résumé L'étude publiée intéresse l'ensemble des échelles hydrométriques de la plaine de l'Est européen. Les moyennes mensuelles des niveaux ont été élaborées par la méthode d'analyse par combinaisons linéaires d'ordonnées, due à M. et MmeLabrouste, afin de définir la phase de la composante annuelle. La carte de la répartition de la phase et les profils de celle-ci le long des cours d'eau, montrent que cette répartition est commandée par le relief, ainsi que par la marche saisonnière des températures, ce qui permet d'expliquer les particularités constatées par les causes naturelles: altitudes, forme et extension du bassin, etc.

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Summary The research deals with the hydrographic observations of the East-Europe's plain. The monthly means of the water level have been elaborated after the method of Mr. and Mrs.Labrouste with the aim to determine the phase of the yearly component. The map of the phase distribution and the profiles along the streams shows that this distribution is governed by the physiography, as well as by the seasonal course of the temperatures, what can permit to explain the observed particularities.

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Beziehungen der ansteckenden Krankheiten zur Witterung mit besonderer Berücksichtigung derHeine-Medinschen Epidemien in Ungarn in den Jahren 1931–1947     

Endre Réthly 《Theoretical and Applied Climatology》1950,2(3):279-290

Zusammenfassung Einleitend werden verschiedene ungarische Arbeiten über den Zusammenhang zwischen Witterung und Krankheiten kritisch besprochen. Nach einer Übersicht über die verschiedenen Ansichten über die Abhängigkeit der Poliomyelitis von der Witterung wird eine 17jährige Statistik aus Ungarn über Witterungseinflüsse auf diese Krankheit untersucht. Es konnte kein Zusammenhang mit der Temperatur, mit dem Wechsel des Witterungscharakters und mit Fronten oder Abgleitflächen nachgewiesen werden. In den an Poliomyelitisfällen reichsten Jahren waren trockene Monate etwas häufiger. Es zeigen sich schwache Anzeichen für eine Doppelwelle während einer Sonnenfleckenperiode. Die Krankheit trat in den kühleren und niederschlagsreicheren nördlichen und nordöstlichen Teilen des Landes am häufigsten auf.

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Summary At first divers Hungarian papers on the relations between weather and diseases are critically discussed. After giving a survey of the different opinions as to the influence of weather upon poliomyelitis, a 17 years statistics from Hungary is investigated in this respect. No connection could be found, however, neither with the temperature and the change of weather character nor with fronts or surfaces of subsidence. Most poliomyelitis cases occurred in years in which dry months were a little more frequent. There are slight indications of a double wave during a sunspot period. The disease was found to be most frequent in the northern and north-eastern regions being relatively cooler and richer in precipitation.

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Résumé On examine tout d'abord différentes études hongroises concernant les relations entre le temps météorologique et les maladies. Après un aperçu sur les diverses opinions émises au sujet de la poliomyélite et de sa dépendance à l'égard du temps, on étudie sur le même sujet une statistique de 17 ans établie en Hongrie. On n'a pas pu prouver de relation avec la température, avec les changements de temps, ni avec les fronts ou les surfaces de subsidence. Les années les plus riches en poliomyélite ont eu un peu plus de mois secs. De faibles indices parlent en faveur d'une double période à l'intérieur de la période des taches solaires. La maladie a été la plus fréquente dans les parties nord et nord-est du pays qui sont aussi les plus froides et les plus humides.

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Recent variations in the general circulation as related to glacier retreat in northern Scandinavia     

Dr. C. C. Wallén 《Pure and Applied Geophysics》1950,18(1):175-178

Summary A review is given of the investigations on variations in the general circulation in middle latitudes made byWillett andPetterssen. According toWillett a «high-index» type of circulation pattern with a strong zonal flow has probably caused the recent climatic improvement in the northern latitudes while the «low-index» type with meridional flow would create a cooling off in the same areas. According toPetterssen an other type of «low-index» pattern with a weak zonal flow and strong meridional exchange of air has been the essential cause of the warming up of the northern latitudes in Europe. This implies that the definition of the «low-index» type is not clear and gives rise to misunderstanding. Making use of our experience on glacier retreat in northern Scandinavia it is concluded that thePetterssen type of circulation more probably than the «high-index» type has caused the warming-up in the North Atlantic area from which the retreat of the glaciers has followed.  相似文献   

Contribution a la tectonique du Bassin houiller de la Sarre: Recherche du tracé au sol de la Faille de la Sarre et de la Faille de la Rosselle (Faille Felsberg)     

N. Théobald 《International Journal of Earth Sciences》1953,41(1):191-200

Zusammenfassung Es werden genauere Angaben gemacht über den Verlauf des Saarsprungs und des Felsbergsprunges an der Erdoberfläche. Der Saarsprung konnte von Bous bis Burbach verfolgt werden. Der Felsbergsprung verfolgt sich nach SE bis in den Rosselsprung.Das Vorkommen von Oberrotliegendem scheint an diese Verwerfungen gebunden zu sein. Es sind Zerrungsspalten, die während der Hauptfaltungsphase (saalische Phase nachStille) des Saar-Nahe-Beckens aufgebrochen sind. Es ist aber anzunehmen, daß sie während des Oberrotliegenden aktiv waren. Sie wurden nach Ablagerung der Trias neu belebt.  相似文献