Factors controlling beryllium-7 at Jungfraujoch in Switzerland   总被引：5，自引：0，他引：5  

P. ZANIS  E. SCHUEPBACH  H. W. GÄGGELER  S. HÜBENER  L. TOBLER 《Tellus. Series B, Chemical and physical meteorology》1999,51(4):789-805

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Anthropogenic versus natural sources of atmospheric sulphate from an Alpine ice core   总被引：1，自引：0，他引：1  

BY M. SCHWIKOWSKI  A. DÖSCHER  H.W. GÄGGELER  U. SCHOTTERER 《Tellus. Series B, Chemical and physical meteorology》1999,51(5):938-951

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Abrupt climate changes: from the past to the future – a review     

T. F. Stocker 《International Journal of Earth Sciences》1999,88(2):365-374

 A review of climatic variability is given with a focus on abrupt changes during the last glacial. Evidence from palaeoclimatic archives suggests that these were most likley due to reorganisations of the atmosphere–ocean system. The mechanisms responsible for these changes are presented. Their implication for future climate changes is discussed in light of recent climate model simulations. Received: 24 June 1998 / Accepted: 27 November 1998  相似文献   

Long-term simulations of thermal and hydraulic characteristics in a mountain massif: The Mont Blanc case study, French and Italian Alps   总被引：3，自引：2，他引：1  

J. C. Maréchal  P. Perrochet  L. Tacher 《Hydrogeology Journal》1999,7(4):341-354

 The use of hydrothermal simulation models to improve the prediction of water inflows in underground works during drilling is tested in the Mont Blanc tunnel, French and Italian Alps. The negative thermal anomaly that was observed during the drilling of this tunnel in 1960 is reproduced by long-term, transient hydrothermal simulations. Sensitivity analysis shows the great inertia of thermal phenomena at the massif scale. At the time of tunnel drilling, the massif had not reached thermal equilibrium. Therefore, a set of simulation scenarios, beginning at the end of the last glacial period, was designed to explain the anomaly encountered in the tunnel in 1960. The continuous cooling of alpine massifs due to infiltration of waters from the surface has occurred for 12,000 years and is expected to continue for about 100,000 years. Comparisons of water-discharge rates simulated in the tunnel with those observed indicate that this hydrothermal method is a useful tool for predicting water inflows in underground works. Received, May 1998 · Revised, March 1999 · Accepted, April 1999  相似文献   

The Kinematics and Origin of smr Stars     

M. Grenon 《Astrophysics and Space Science》1999,265(1-4):331-336

Ages and kinematics are revised for SMR stars ([M/H] >+0.30) common to NLTT and HIPPARCOS catalogues. The origin of MR to SMR stars appears heterogeneous: part of them, of intermediate age, were formed few kpc inside the solar orbit, from slowly enriched gas, whereas the oldest SMRs were born early, closer to the galactic center where the metal-enrichment had been fast. Perturbations by the galactic bar explain the peculiar motions of local SMRs as well as their outwards migration. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

M4–18: the planetary nebula and its WC10 central star     

Orsola De Marco  Paul A. Crowther 《Monthly notices of the Royal Astronomical Society》1999,306(4):931-942

We present a detailed analysis of the planetary nebula M4–18 (G146.7+07.6) and its WC10-type Wolf–Rayet (WR) central star, based on high‐quality optical spectroscopy (WHT/UES, INT/IDS, WIYN/DensPak) and imaging ( HST /WFPC2). From a non-LTE model atmosphere analysis of the stellar spectrum, we derive T _eff=31 kK,     v _∞=160 km s⁻¹ and abundance number ratios of H/He<0.5, C/He=0.60 and O/He=0.10. These parameters are remarkably similar to those of He 2–113 ([WC10]). Assuming an identical stellar mass to that determined by De Marco et al. for He 2–113, we obtain a distance of 6.8 kpc to M4–18 [ E ( B−V )=0.55 mag from nebular and stellar techniques]. This implies that the planetary nebula of M4–18 has a dynamical age of ∼3100 yr, in contrast to ≥270 yr for He 2–113. This is supported by the much higher electron density of the latter. These observations may be reconciled with evolutionary predictions only if [WC]-type stars exhibit a range in stellar masses.
Photoionization modelling of M4–18 is carried out using our stellar WR flux distribution, together with blackbody and Kurucz energy distributions obtained from Zanstra analyses. We conclude that the ionizing energy distribution from the WR model provides the best consistency with the observed nebular properties, although discrepancies remain.  相似文献   

New constraints on a triaxial model of the Galaxy     

Maartje Sevenster  Prasenjit Saha  David Valls-Gabaud  Roger Fux 《Monthly notices of the Royal Astronomical Society》1999,307(3):584-594

We determine the most likely values of the free parameters of an N -body model for the Galaxy developed by Fux via a discrete–discrete comparison with the positions on the sky and line-of-sight velocities of an unbiased, homogeneous sample of OH/IR stars. Via Monte Carlo simulation, we find the plausibility of the best-fitting models, as well as the errors on the determined values. The parameters that are constrained best by these projected data are the total mass of the model and the viewing angle of the central bar, although the distribution of the latter has multiple maxima. The other two free parameters, the size of the bar and the (azimuthal) velocity of the Sun, are less well-constrained. The best model has a viewing angle of ∼ 44°, a semimajor axis of 2.5 kpc (corotation radius 4.5 kpc, pattern speed 46 km s⁻¹ kpc⁻¹), a bar mass of 1.7×10¹⁰ M_⊙ and a tangential velocity of the local standard of rest of 171 km s⁻¹. We argue that the lower values that are commonly found from stellar data for the viewing angle (∼25°) arise when too few coordinates are available, when the longitude range is too narrow or when low latitudes are excluded from the fit. The new constraints on the viewing angle of the Galactic bar from stellar line-of-sight velocities decrease further the ability of the distribution of the bar to account for the observed microlensing optical depth toward Baade's window: our model reproduces only half the observed value. The signal of triaxiality diminishes quickly with increasing latitude, fading within approximately 1 scaleheight (≲3°). This suggests that Baade's window is not a very appropriate region in which to sample bar properties.  相似文献   

Fuzzy factorial analysis of snow avalanches     

Claude Jaccard 《Natural Hazards》1990,3(4):329-340

The mutual influence of 21 factors pertaining to terrain, weather, forest and snowpack have been discussed by 10 experts. The semantic (nil, weak, medium, high) evaluations are translated as membership degrees of fuzzy sets, and averaged between the experts by taking their fuzzy expectation value, yielding a 21 × 21 fuzzy matrix for direct interactions. Fuzzy successive multiplications and additions of the matrix give the indirect interactions. The activity and the passivity of the factors with respect to avalanches is represented by directed weighted graphs, and the average semantic values by a 4 × 4 matrix: the activity (passivity) is weak (strong) for tree damage; medium (nil) for altitude; medium (weak) for ground shape; medium (medium) for vegetation, soil, wind, microclimate, tree type, vertical distribution and mechanics of trees, snowpack distribution and snow gliding; strong (nil) for ground inclination and exposition, weather; strong (medium) for heat, precipitation, horizontal distribution of trees, snowpack constitution and stability.  相似文献   

Authigenic aluminium phosphate-sulphates in sandstones of the Mitterberg Formation, Northern Calcareous Alps, Austria     

CHRISTOPH SPÖTL 《Sedimentology》1990,37(5):837-845

Complex aluminium phosphate-sulphate minerals of the hinsdalite group have been identified as early diagenetic precipitates in Late Permian sandstones of the Northern Calcareous Alps, western Austria. According to their chemical composition they can be regarded as solid solutions between woodhouseite, svanbergite, crandallite and goyazite. The model proposed for their origin involves the dissolution of detrital apatite in a low-pH environment and subsequent precipitation of aluminium phosphate-sulphate minerals, which clearly pre-date syntaxial quartz cementation of the sediment. Their occurrence probably has been overlooked in other sandstones showing diagenetic apatite dissolution. The recognition of such minerals could provide a significant insight into early phosphate diagenesis.  相似文献   

The SOMS model and its application to Lake Neuchâtel     

E. A. H. Zuur  D. E. Dietrich 《Aquatic Sciences - Research Across Boundaries》1990,52(2):115-129

A three-dimensional numerical circulation model (SOMS) based on primitive equations is described. The algorithm, by which Coriolis and vertical diffusion terms are treated implicitly while mass is still conserved exactly (algebraically), is discussed in detail. The model is applied to Lake Neuchâtel (Switzerland), to determine the general circulation under influence of the most prevailing wind.  相似文献