Sand beach energetics: An ecosystem approach towards a high energy interface     

A. McLachlan  T. Erasmus  A.H. Dye  T. Wooldridge  G. Van der Horst  G. Rossouw  T.A. Lasiak  L. McGwynne 《Estuarine, Coastal and Shelf Science》1981,13(1):11-25

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A 2‐D constitutive model for cyclic interface behaviour     

Giuseppe Mortara  Marc Boulon  Vito Nicola Ghionna 《国际地质力学数值与分析法杂志》2002,26(11):1071-1096

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The ratio of total to selective absorption in dark clouds     

D. C. B. Whittet  I. G. Van Breda 《Astrophysics and Space Science》1975,38(1):L3-L8

Evidence relating to the value ofR=A _V/E_B-V appropriate to discrete dark clouds in the interstellar medium is discussed. The polarimetric method of evaluatingR recently proposed by Serkowski, Mathewson and Ford gives results consistent with extinction curve determinations. A value ofR～4.4 appears to apply to the most reddened stars in the ? Oph complex, suggesting the existence of an upper size limit for the grains. If the grains grow by accretion of the heavier elements from the surrounding gas, as suggested by Carrasco, Strom and Strom, then the availability of material sets a limitation on mantle growth consistent with the observed increase inR.  相似文献   

Line blanketing and opacity probability distribution function     

J. Van Paradijs  M. S. Vardya 《Astrophysics and Space Science》1975,33(1):L9-L12

Advantages and limitations of using opacity probability distribution function (OPDF) in computations of model atmospheres for cool stars have been examined. It is concluded that a direct approach, in which a large number of frequency points are taken, may be more appropriate relative to OPDF.  相似文献   

Test for planetary influences on solar activity     

L. A. Dingle  G. Van Hoven  P. A. Sturrock 《Solar physics》1973,31(1):243-246

A method due to Schuster is used to test the hypothesis that solar activity is influenced by tides raised in the Sun's atmosphere by planets. We calculate the distribution in longtitude of over 1000 flares occurring in a 61/2 yr segment of solar cycle 19, referring the longitude system in turn to the orbital positions of Jupiter and Venus. The resulting distributions show no evidence for a tidal effect.  相似文献   

Formaldehyde polymers in comets     

V. Vanýsek  N. C. Wickramsinghe 《Astrophysics and Space Science》1975,33(2):L19-L28

The possibility that crystalline formaldehyde polymers are present in cometary dust is discussed. In common with most other parent molecules proposed for comets, (H₂CO) _n is difficult to detect, even if it is present in relatively high concentrations. The optical properties of these polymers in the visual and infrared regions are similar to those of silicate grains, and crystalline formaldehyde polymers provide no emission at 6 cm wavelength. The lifetime of gaseous H₂CO in the solar radiation field is too short, and the expected transitions in the microwave region would be too weak to be detected. However, the available data concerning the physical properties of comets indicate that polymerized formaldehyde cannot be ruled out as a major constituent of cometary material.  相似文献   

A search for OB stars in supernova remnants     

Sidney Van den Bergh 《Journal of Astrophysics and Astronomy》1980,1(1):67-70

A massive binary, in which the primary becomes a supernova, should leave a luminous secondary near the centre of its remnant. Contrary to expectation no statistically significant excess of OB stars is, however, found near the centres of optically visible galactic supernova remnants.  相似文献   

A comparison of computed and observed line profiles and flash intensities in the photosphere-chromosphere transition region     

E. L. J. Van Dessel 《Solar physics》1970,15(2):322-337

This paper mainly deals with the development of a method for the interpretation of eclipse observations in the extreme limb - lower chromosphere transition region. We compute line profiles emitted by a column of 1 cm² cross section along the line of sight and, by integration, profiles and total (flash) intensities from a slice of 1 cm width beyond the Moon's edge, at various heights with respect to the solar limb. The solar models used are mentioned in Section 1; method and approximations are described in Section 2. Calculations have been made for some Fei lines with various equivalent widths (Table I); the results are discussed in Section 3. It appears that the method enables one to distinguish between the various models. Particularly line intensities just inside the limb are very important.We compared our computed results with some observations made by Houtgast (Section 4). The main conclusion is that a BCA-type temperature distribution alone does not agree with observations; we have to assume an excitation temperature of Holweger's type.Investigation performed at the Astronomical Institute, Utrecht; present address: Royal Belgian Observatory, 1180 Brussels.  相似文献   

Aircraft observations of Venus' near-infrared reflection spectrum: Implications for cloud composition     

James B. Pollack  Edwin F. Erickson  Fred C. Witteborn  Charles Chackerian  Audrey L. Summers  Warren Van Camp  Betty J. Baldwin  Gordon C. Augason  Lawrence J. Caroff 《Icarus》1974,23(1):8-26

We have obtained measurements of Venus' reflection spectrum in the 1.2 to 4.1-μm spectral region from a NASA-Ames operated Lear jet. This was accomplished by observing both Venus and the sun with a spectrometer that contained a circular, variable interference filter, whose effective spectral resolution was 2%. The aircraft results were compared with computer generated spectra of a number of cloud candidates. The only substance which gave an acceptable match to the profile of Venus' strong 3-μm absorption feature, was a water solution of sulfuric acid, that had a concentration of 75% or more H₂SO₄ by weight. However, our spectra also show a modest decline in reflectivity from 2.3 μm towards 1.2-μm wavekength, which is inconsistent with the flat spectrum of sulfuric acid in this spectral region. We hypothesize that this decline is due to impurities in the sulfuric acid droplets.We also compared our list of cloud candidates with several other observed properties of the Venus clouds. While this comparison does not provide as unique an answer as did our analysis of the 3-μm band, we find that, in agreement with the results of Young (1973) and Sill (1973), concentrated sulfuric acid solutions are compatible with these additional observed properties of the Venus clouds. We conclude that the visible cloud layer of Venus is composed of sulfuric acid solution droplets, whose concentration is 75% H₂SO₄, or greater, by weight.  相似文献   

The structure of coronal magnetic loops     

Riccardo Giachetti  Gerard Van Hoven  Claudio Chiuderi 《Solar physics》1977,55(2):371-386

We present the second part of a complete theory for the plasma and field structure of a cool coronal arch, corresponding to those observed in the EUV from Skylab. The global magneto-hydrodynamic (MHD) stability of a previously described equilibrium-loop model is evaluated, and compared with that of an unmodified ambient force-free field. The influence of the photospheric boundary condition is also evaluated, producing a specification of stability limits which depend on the relative field and plasma pressures and scale widths. The resulting restrictions on the allowable field configuration of a coronal loop are then compared with observed values. The implications of this general method for deducing small-scale coronal magnetic-field structure from the measured plasma profile of an emissive feature are also described.  相似文献