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781.
782.
Alberta Albertella Federica Migliaccio Fernando Sansó 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):1-15
An artificial satellite, flying in a purely gravitational field is a natural probe, such that, by a very accurate orbit determination, would allow a perfect estimation of the field. A true satellite experiences a number of perturbational, non-gravitational forces acting on the shell of the spacecraft; these can be revealed and accurately measured by a spaceborne accelerometer. If more accelerometers are flown in the same satellite, they naturally eliminate (to some extent) the common perturbational accelerations and their differences are affected by the second derivatives of the gravity fields only (gradiometry). The mission GOCE is based on this principle. Its peculiar dynamical observation equations are reviewed. The possibility of estimating the gravity field up to some harmonic degree (200) is illustrated. 相似文献
783.
784.
Conodont colour alteration index (CAI) data in Upper Ordovician rocks from several areas of the Variscan domain in the Iberian Peninsula indicate conditions ranging from diagenesis to low-grade metamorphism. In most of the areas, where studies using other indicators, such as illite crystallinity (IC) or where vitrinite reflectance are lacking, the CAI method has permitted a preliminary estimation of the metamorphic grade. In the Almadén syncline (Central-Iberian Zone), where IC studies are available, the thermal conditions inferred from CAI data agree with those obtained by the IC method. In the Puertollano–Almuradiel syncline, the thermal interval obtained primarily from fluid inclusions (270–370°C) overlaps considerably with that obtained from CAI data (180–340°C). In general, cleavage in rocks is present in anchizonal or epizonal conditions, whereas in diagenetic conditions with CAI 2.5, cleavage is scarce. The conodont texture changes with increasing metamorphism, and apatite recrystallisation appears in general with CAI 5. Variation of CAI values within a single sample and/or within short stratigraphic distances observed at several localities is due to hydrothermal activity. 相似文献
785.
Spain is a relatively large European country (ca. 500,000 km2) with extensive semiarid areas in which there exists a large number of good aquifers. In some areas, these aquifers are intensively
developed and are the most important sources of fresh water. Nevertheless, groundwater development and protection has rarely
been duly considered by the Spanish Water Administration, despite the pressure to remedy this situation by various groups
of experts, some of them members of the Water Administration. The Spanish Committee of the International Association of Hydrogeologists
(IAH) has been very active during the last decade in promoting activities to spread groundwater science, technology, and management
in Spain and outside, mostly in Latin America, and in trying to orient water policy toward issues of groundwater. These activities
include mainly the organization of technical and scientific meetings on current topics such as groundwater in the new Water
Act, overexploitation, groundwater in water-resources planning, groundwater pollution, natural-recharge estimation and others.
The impact of these activities on the recent water policy of Spain seems significant, and the experience gained may be applicable
to other countries.
Received, February 1997 · Revised, July 1997 · Accepted, July 1997 相似文献
786.
787.
R. J. García López 《Astrophysics and Space Science》1998,263(1-4):365-368
ODIN is an international consortium constituted to design and build a first-light multi-purpose optical intermediate dispersion
spectrograph for the Gran Telescopio Canarias (GTC, 10-m) to be installed at the Observatorio del Roque de los Muchachos (La
Palma). This instrument should fulfill an important fraction of the needs of the Spanish astronomical community in optical
spectroscopy performed at large telescopes, and must be highly competitive in a variety of research fields. We are proposing
a spectrograph that will be capable of providing multi-object observations by means of optical fibers, integral field spectroscopy,
and also multi-integral fields. It will be mounted at the Nasmyth focus of the GTC. One of the main drivers of our proposal
is to cover the whole visible range allowed by the atmospheric cut-off with the highest efficiency, particularly at the UV
end.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
788.
We present some insight on the ionization structure of the circumstellar disks around Be type stars based on the study of
Balmer decrements for absorption-corrected emission lines. Owing to this analysis, three different ionization zones in the
envelope are proposed: the inner one, completely ionized, of about ∼ 5R*, an intermediate recombination zone extending up to ∼ [10 - 20]R*, and an outer extended zone of neutral H.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
789.
Using a recent determination of the X-ray luminosity function of galaxy clusters, accurate mass deposition rates and LX in cooling flow clusters from the literature, and reliable constraints on the star fomation episodes in cooling flows obtained
by our group, we quantify the relevance of such star formation in comparison with the SFR in the local universe. We conclude
that the SFR density in CF is ≲ 0.1% the total local reference.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
790.
This paper considers driven resonant nonlinear slow magnetohydrodynamic (MHD) waves in dissipative steady plasmas. A theory developed by Ruderman, Hollweg, and Goossens (1997) is used and extended to study the effect of steady flows on the nonlinear resonant behaviour of slow MHD waves in slow dissipative layers. The method of matched asymptotic expansions is used to describe the behaviour of the wave variables in the slow dissipative layer. The nonlinear analogue of the connection formulae for slow MHD waves obtained previously by Goossens, Hollweg, and Sakurai (1992) and Erdélyi (1997) in linear MHD, are derived. The effect of an equilibrium flow results partly in a Doppler shift of the available frequency for slow resonance and partly in the modification of the width of the dissipative layer. 相似文献