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101.
The HCN emission features near 3 μm recently detected by Geballe et al. (2003, Astrophys. J. 583, L39) are analyzed with a model for fluorescence of sunlight in the ν3 band of HCN. The emission spectrum is consistent with current knowledge of the atmospheric temperature profile and the HCN distribution inferred from millimeter-wave observations. The spectrum is insensitive to the abundance of HCN in the thermosphere and the thousand-fold enhancement relative to photochemical models suggested by Geballe et al. (2003, Astrophys. J. 583, L39) is not required to explain the observations. We find that the spectrum can be matched with temperatures from 130 to 200 K, with slightly better fits at high temperature, contrary to the temperature determination of 130±10 K of Geballe et al. (2003, Astrophys. J. 583, L39). The HCN emission spectrum is sensitive to the collisional de-excitation probability, P10, for the ν3 state and we determine a value of 10−5 with an accuracy of about a factor of two. Analysis of absorption lines in the C2H2ν3 band near 3 μm, detected in the same spectrum, indicate a C2H2 mole fraction near 0.01 μbar of 10−5 for P10=10−4. The derived mole fraction, however, is dependent upon the value adopted for P10 and lower values are required if P10 at Titan temperatures is less than its room temperature value. 相似文献
102.
Many authors use magnetic-field models to extrapolate the field in the solar corona from magnetic data in the photosphere. The accuracy of such extrapolations is usually judged qualitatively by eye, where a less judgemental quantitative approach would be more desirable. In this paper, a robust method for obtaining the best fit between a theoretical magnetic field and intensity observations of coronal loops on the solar disk will be presented. The method will be applied to Yohkoh data using a linear force-free field as an illustration. Any other theoretical model for the magnetic field can be used, provided there is enough freedom in the model to optimize the fit. 相似文献
103.
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
104.
LOVISA ZILLÉN IAN SNOWBALL PER SANDGREN TANIA STANTON 《Boreas: An International Journal of Quaternary Research》2003,32(4):612-626
Varved lake sediments can be used to set multiple environmental proxies within a calendar year time scale. We undertook a systematic survey of lakes in the Province of Värmland, west central Sweden, with the aim of finding continuous varved lake sediment sequences covering the majority of the Holocene. In Fennoscandia, such sediments have previously only been recorded in northern Sweden and in southern and central Finland. By following a selective process and fieldwork we discovered three new varved sites (i.e. Furskogstjärnet, Mötterudstjärnet and Kälksjön). We found that lakes with varved sediments have several common lake morphometry properties and lake catchment characteristics such as maximum water depth, maximum water depth/lake surface area ratio, catchment soil types, altitude and number of inflows. Varve chronologies, supported by AMS-14 C dating and tephrochronology were established for two of the sediment profiles. These varve chronologies are the longest geological records with an annual resolution known to exist in Sweden. In Furskogstjärnet, the AMS- 14 C dates based on terrestrial plant macrofossils at several levels deviate significantly from the varve based time-depth curve. In Motterudstjarnet, a fully reasonable time-depth model based on the 14 C dates gives older ages in the lower part of the sequence compared to the varve chronology. These results highlight that seemingly acceptable AMS radiocarbon dates may be erroneous. They also point to the fact that varved lake sediments are reliable geological archives with respect to chronological control and accuracy. Thus, these archives should be of prime interest for studies of climate and environmental change undertaken with the aim of providing sub-decadal resolution proxy data sets. 相似文献
105.
N. Ivanova K. Belczynski J. M. Fregeau F. A. Rasio 《Monthly notices of the Royal Astronomical Society》2005,358(2):572-584
We study the evolution of binary stars in globular clusters using a new Monte Carlo approach combining a population synthesis code ( startrack ) and a simple treatment of dynamical interactions in the dense cluster core using a new tool for computing three- and four-body interactions ( fewbody ). We find that the combination of stellar evolution and dynamical interactions (binary–single and binary–binary) leads to a rapid depletion of the binary population in the cluster core. The maximum binary fraction today in the core of a typical dense cluster such as 47 Tuc, assuming an initial binary fraction of 100 per cent, is only ∼ 5–10 per cent. We show that this is in good agreement with recent Hubble Space Telescope observations of close binaries in the core of 47 Tuc, provided that a realistic distribution of binary periods is used to interpret the results. Our findings also have important consequences for the dynamical modelling of globular clusters, suggesting that 'realistic models' should incorporate much larger initial binary fractions than has usually been the case in the past. 相似文献
106.
R. M. Hueckstaedt S. H. Batha M. M. Balkey N. D. Delamater J. R. Fincke R. L. Holmes N. E. Lanier G. R. Magelssen J. M. Scott J. M. Taccetti C. J. Horsfield K. W. Parker S. D. Rothman 《Astrophysics and Space Science》2005,298(1-2):255-259
Observations of the interstellar medium reveal a dynamic realm permeated by shocks. These shocks are generated on a large
range of scales by galactic rotation, supernovae, stellar winds, and other processes. Whenever a shock encounters a density
interface, Richtmyer-Meshkov instabilities may develop. Perturbations along the interface grow, leading to structure formation
and material mixing. An understanding of the evolution of Richtmyer-Meshkov instabilities is essential for understanding galactic
structure, molecular cloud morphology, and the early stages of star formation. An ongoing experimental campaign studies Richtmyer-Meshkov
mixing in a convergent, compressible, miscible plasma at the Omega laser facility. Cylindrical targets, consisting of a low
density foam core and an aluminum shell covered by an epoxy ablator, are directly driven by fifty laser beams. The aluminum
shell is machined to produce different perturbation spectra. Surface types include unperturbed (smooth), single-mode sinusoids,
multi-mode (rough), and multi-mode with particular modes accentuated (specified-rough). Experimental results are compared
to theory and numerical simulations. 相似文献
107.
108.
Abstract Zircons have been studied from different layers of migmatites (from Arvika, western Sweden and Nelaug, southern Norway) and from a paragneiss (from Arvika) associated with one of the migmatites. The main purpose of the investigation is to establish whether or not information about zircons can help in the elucidation of the parentage and rock-forming processes of migmatites.
The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting. 相似文献
The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting. 相似文献
109.
Sara L. Ellison 《Monthly notices of the Royal Astronomical Society》2006,368(1):335-340
The number of z ∼ 1 damped Lyα systems (DLAs, log N (H i ) ≥ 20.3) per unit redshift is approximately 0.1, making them relatively rare objects. Large, blind QSO surveys for low-redshift DLAs are therefore an expensive prospect for space-borne ultraviolet telescopes. Increasing the efficiency of these surveys by pre-selecting DLA candidates based on the equivalent widths (EWs) of metal absorption lines has previously been a successful strategy. However, the success rate of DLA identification is still only ∼35 per cent when simple EW cut-offs are applied, the majority of systems having 19.0 < log N (H i ) < 20.3. Here, we propose a new way to pre-select DLA candidates. Our technique requires high-to-moderate-resolution spectroscopy of the Mg ii λ2796 transition, which is easily accessible from the ground for 0.2 ≲ z ≲ 2.4. We define the D -index, the ratio of the line equivalent width to velocity spread, and measure this quantity for 19 DLAs and eight sub-DLAs in archival spectra obtained with echelle spectrographs. For the majority of absorbers, there is a clear distinction between the D -index of DLAs compared with sub-DLAs (Kolmogorov–Smirnov probability = 0.8 per cent). Based on this pilot data sample, we find that the D -index can select DLAs with a success rate of up to 90 per cent, an increase in selection efficiency by a factor of 2.5 compared with a simple EW cut. We test the applicability of the D -index at lower resolution and find that it remains a good discriminant of DLAs for full width at half-maximum (FWHM) ≲ 1.5 Å. However, the recommended D -index cut-off between DLAs and sub-DLAs decreases with poorer resolution and we tabulate the appropriate D -index values that should be used with spectra of different resolutions. 相似文献
110.
B. Ahmed G. J. Alner H. Araujo J. C. Barton A. Bewick M. J. Carson D. Davidge J. V. Dawson T. Gamble S. P. Hart R. Hollingworth A. S. Howard W. G. Jones M. K. Joshi V. A. Kudryavtsev T. B. Lawson V. Lebedenko M. J. Lehner J. D. Lewin P. K. Lightfoot I. Liubarsky R. Lüscher J. E. McMillan B. Morgan G. Nicklin S. M. Paling R. M. Preece J. J. Quenby J. W. Roberts M. Robinson N. J. T. Smith P. F. Smith N. J. C. Spooner T. J. Sumner D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented. 相似文献