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1.
Anita Enmark Thomas Berkefeld Oskar von der Lühe Torben Andersen 《Experimental Astronomy》2006,21(2):87-99
A simulation model of the adaptive optics of the German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife, is
presented. The model uses modules from the integrated model of the Euro50 extremely large telescope, and includes submodels
of a Shack-Hartmann wavefront sensor, a de-formable mirror, a tip-tilt mirror, high-voltage amplifier low-pass filters, a
reconstructor and a controller. We investigate the impact on the closed loop bandwidth of changes in controller configuration
and certain system parameters, such as low pass filter bandwidth and camera integration and readout time. Control strategies
were tested on simple models before implementation on the full VTT model. Using the models, different control strategies are
compared. 相似文献
2.
Summary ?In the south-eastern Altenbergkar–Silbereck area in the eastern Tauern window (Lungau, Salzburg) structurally controlled
precious-metal (Au–Ag) mineralization is hosted in marbles of the Permo(?)-Mesozoic Silbereck Formation and in the underlying
Variscan Central gneiss. During the Alpine otogeny both lithologies were affected by ductile deformation (shearing, D1; folding,
D2/D3) and subsequent brittle deformation (tension gashes, D4; normal faulting, D5) related to the uplift and exhumation of
the Tauern window. Mineralization is controlled by brittle D4 structures. NE–SW trending steeply dipping tension gashes of
the “Tauerngoldgang” type occur within the Central gneiss. Three different marble-hosted ore types following fracture systems
as well as foliation and bedding planes can be distinguished: 1) metasomatic replacement ores, 2) ores in tension gashes and
3) ores in talc-bearing structures, often containing high-grade gold and silver mineralization (native gold in association
with Ag–Pb–Bi–sulfosalts). Four stages of mineralization can be distinguished which occur in all ore types: arsenopyrite–pyrite–pyrrhotite
(first stage), Au–(Ag–Pb–Bi–sulfosalts) (second stage), base-metal sulfides and tetrahedrite–tennantite (third stage) and
Ag-rich galena (fourth stage). Preliminary fluid inclusion data indicate temperatures of ore formation well above 300 °C (346 °C
mean) for the second stage within the Central gneiss and temperatures between 310 and 230 °C for the second and third stages
in the marble.
Received October 12, 2001; revised version accepted September 5, 2002
Published online March 10, 2003 相似文献
3.
4.
The aim of the present paper is to analyze the light variation as well as the period changes of the eclipsing binary RZ Cas. New photometric elements are computed using the frequency-domain method. The possibility of the light-time effect and the apsidal motion is discussed. 相似文献
5.
C. Christiansen F. Gertz M. J. C. Laima L. C. Lund-Hansen T. Vang C. Jürgensen 《Environmental Geology》1997,29(1-2):66-77
The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of
P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000
tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m–2 yr–1) and 477 ton of P (on average 0.9 g m–2 yr–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension
frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than
net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic
matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of
organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive
sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate
from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity
(56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic
N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively.
Received: 10 July 1995 · Accepted: 19 January 1996 相似文献
6.
A coupled deterministic hydrological and water temperature model, CEQUEAU, was modified to include soil temperature and crown closure in its calculation of local advective terms in the heat budget. The modified model was than tested to verify its sensitivity to these modifications. An analysis of the heat budget of a small forested catchment in eastern Canada revealed that the advective term related to interflow plays a significant role in the daily water heat budget, providing on average 28% of the local advective budget (which also includes advective heat terms from surface runoff and groundwater) and nearly 14% of the total heat budget (which includes all radiative terms at the water surface, convection and evaporation, as well as the local advective terms). Relative sensitivity indices (RSIs) were used to verify the impact of the newly introduced parameters and variables. Among them, parameters related to the forest cover (crown closure and leaf area index) have a maximum RSI of ?0·6; i.e. a 100% increase in value produces a 60% decrease in the local advective term. Parameters with the greatest influence are the volume of water contributing to interflow and the amplitude of the net radiative flux at the soil surface, which, if doubled, would double the contribution of the local interflow advective term to the heat budget. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
Ulrich Hopp Regina E. Schulte-Ladbeck Jürgen Kerp 《Astrophysics and Space Science》2003,284(2):647-650
We are investigating the hypothesis that Compact High-Velocity Clouds (CHVCs) are the left-over building blocks of Local Group
galaxies. To this end, we are searching for their embedded stellar populations using FORS at the VLT. The search is done with
single-star photometry in V and I bands, which is sensitive to both, young and old, stellar populations. Five CHVCs of our
sample have been observed so far down to I=24. We pointed the VLT towards the highest HI column density regions, as determined
in Effelsberg radio data. In an alternate approach, we searched 2MASS public data towards those 5 CHVCs down to K=16. While
the VLT data probe the central regions out to distance moduli of about 27, the 2MASS data are sensitive to a population of
red giant stars to distance moduli of about 20. The 2MASS data, on the other hand, cover a much wider field of view than the
VLT data (radius of 1 degree versus FORS field of 6.8 arcmin). We did not find a stellar population intrinsic to the CHVCs
in either data. In this paper, we illustrate our search methods.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
E. Tóth F. Deak C. S. Gyurkócza Z. S. Kasztovszky R. Kuczi G. Marx B. Nagy S. Oberstedt L. Sajó-Bohus C. S. Sükösd G. Toth N. Vajda 《Environmental Geology》1997,31(1-2):123-127
A steady radon exhalation is assumed in most publications. In a village of North-East Hungary, however, high radon concentrations
have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of geochemical phenomena.
Received: 20 November 1995 · Accepted: 18 June 1996 相似文献
9.
S. P. Plunkett G. E. Brueckner K. P. Dere R. A. Howard M. J. Koomen C. M. Korendyke D. J. Michels J. D. Moses N. E. Moulton S. E. Paswaters O. C. St. Cyr D. G. Socker D. Wang G. M. Simnett D. K. Bedford D. A. Biesecker C. J. Eyles S. J. Tappin R. Schwenn P. L. Lamy A. Llebaria 《Solar physics》1997,175(2):699-718
We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line
transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light.
Two of these events, with speeds >25 km s-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with
erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly
different appearance and is more gradual than the other two, with a projected outward speed <10 km s-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line
corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from
close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic
regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of
these events to recent X-ray observations of CMEs is briefly discussed.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702 相似文献
10.
The bump in the ultraviolet part of the interstellar extinction curve provides a great challenge in the modelling of interstellar dust. Its shape can be well approximated by a classical dispersion profile with a total halfwidth of 48 nm centred at 217 nm. Apart from few slightly deviating cases the parameters of the band seem to be surprisingly constant in the solar neighbourhood.The equivalent widthW of the 217 nm band shows a very tight correlation with the colour excessE(B-V). Studies of correlations with the strength of diffuse interstellar bands gave no conclusive results as to the nature of the band.The most common interpretation of the 217 nm feature as originating from small graphite grians meets several difficulties. No final decision on the carrier can be made at present.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986. 相似文献