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51.
Virgil E. Barnes 《Meteoritics & planetary science》1990,25(3):149-159
Abstract— Fifty-odd years of tektite research are reviewed, proceeding from the discovery of the first North American tektites in 1936. This included the early recognition that tektites were terrestrial objects rather than meteorites and that the glassy particles in tektites were fused quartz (lechatelierite). Later, during National Science Foundation-supported research, it was found that some tektites appeared to have formed as puddles of melt, that the content and character of bubbles in lechatelierite can be used as a relative temperature scale, that rayed bubbles in tektites formed from hydrous minerals, that bubbles in tektites formed chiefly from water which was absorbed into the walls of the bubbles leaving vacuums, and that “fingers” in the surficial part of some tektites may have formed by differential volatilization. Some unpublished observations and adventures are briefly reported. 相似文献
52.
Anomalies of some tidal waves of UT1 总被引:1,自引:0,他引:1
Summary. The M f and M m waves of UT1 have been analysed from the BIH data during the period 1967.0 to 1984.0 in order to derive the Love number k .
These analyses performed during successive intervals of this period show some anomalies in the values of the Love number k derived from the Mf wave. Large variations with time of the amplitude and the phase appear for this wave while the values derived from the M m wave present a good stability during the whole period.
The spectrum of the UT1-residuals (as obtained by removing the theoretical zonal tidal UT1 terms) shows the existence of a perturbation wave near the Mf period. This wave lies in the range 13.5–13.9 day according to the analysed interval; it could be related with the perturbation wave noticed by some authors near the M f gravimetric wave. 相似文献
These analyses performed during successive intervals of this period show some anomalies in the values of the Love number k derived from the M
The spectrum of the UT1-residuals (as obtained by removing the theoretical zonal tidal UT1 terms) shows the existence of a perturbation wave near the M
53.
Laser-induced plasmas in various gas mixtures were used to simulate lightning in other planetary atmospheres. This method of simulation has the advantage of producing short-duration, high-temperature plasmas free from electrode contamination. The laser-induced plasma discharges in air are shown to accurately simulate terrestrial lightning and can be expected to simulate lightning spectra in other planetary atmospheres. Spectra from 240 to 880 nm are presented for simulated lightning in the atmospheres of Venus, Earth, Jupiter, and Titan. The spectra of lightning on the other giant planets are expected to be similar to that of Jupiter because the atmospheres of these planets are composed mainly of hydrogen and helium. The spectra of Venus and Titan show substantial amounts of radiation due to the presence of carbon atoms and ions and show CN Violet radiation. Although small amounts of CH4 and NH3 are present in the Jovian atmosphere, only emission from hydrogen and helium is observed. Most differences in the spectra can be understood in terms of the elemental ratios of the gas mixtures. Consequently, observations of the spectra of lightning on other planets should provide in situ estimates of the atmospheric and aerosol composition in the cloud layers in which lightning is occuring. In particular, the detection of inert gases such as helium should be possible and the relative abundance of these gases compared to major constituents might be determined. 相似文献
54.
Observations of the brightness, color, and polarization of the fuor V1057 Cyg over more than 30 years are presented and briefly discussed. Variability of the linear polarization was found. 相似文献
55.
R. Surendiranath N. Kameswara Rao Ram Sagar J. S. Nathan K. K. Ghosh 《Journal of Astrophysics and Astronomy》1990,11(2):151-166
bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M)
0 = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1)
× 108 years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor
mass of the planetary nebula on the main sequence is ≥2.5M⊙
Based on observations obtained with the Vainu Bappu Telescope. 相似文献
56.
Steven N. Ward 《Geophysical Journal International》1985,81(2):409-428
Summary. This paper explores the middle ground between complex thermally-coupled viscous flow models and simple corner flow models of island arc environments. The calculation retains the density-driven nature of convection and relaxes the geometrical constraints of corner flow, yet still provides semianalytical solutions for velocity and stress. A novel aspect of the procedure is its allowance for a coupled elastic lithosphere on top of a Newtonian viscous mantle. Initially, simple box-like density drivers illustrate how vertical and horizontal forces are transmitted through the mantle and how the lithosphere responds by trench formation. The flexural strength of the lithosphere spatially broadens the surface topography and gravity anomalies relative to the functional form of the vertical flow stresses applied to the plate base. I find that drivers in the form of inclined subducting slabs cannot induce self-driven parallel flow; however, the necessary flow can be provided by supplying a basal drag of 1–5 MPa to the mantle from the oceanic lithosphere. These basal drag forces create regional lithospheric stress and they should be quantifiable through seismic observations of the neutral surface. The existence of a shallow elevated phase transition is suggested in two slab models of 300 km length where a maximum excess density of 0.2 g cm−3 was needed to generate an acceptable mantle flow. A North New Hebrides subduction model which satisfies flow requirements and reproduces general features of topography and gravity contains a high shear stress zone (75 MPa) around the upper slab surface to a depth of 150 km and a deviatoric tensional stress in the back arc to a depth of 70 km. The lithospheric stress state of this model suggests that slab detachment is possible through whole plate fracture. 相似文献
57.
CHUDongsheng LIANGMeng SHIXin ZHANGLing 《中国海洋大学学报(英文版)》2004,3(1):106-110
1 Introduction Inrecentyearstherehasbeengrowingresearchin terestinthetwo dimensional (2 D )systemtheory .The 2 Dsystemsmayfindapplicationsinareassuchasmarineseismicdataprocessingandimageprocessing .Althoughmoreandmorevaluableresultshavebeengained ,mos… 相似文献
58.
MICHAEL K. WEISBERG MICHAEL E. ZOLENSKY MARTIN PRINZ 《Meteoritics & planetary science》1997,32(6):791-801
Abstract— Fayalitic olivine (Fa54–94) is a ubiquitous component in the matrix of Krymka (LL3.1) as well as in other highly unequilibrated chondrites (ordinary and carbonaceous). In Krymka, the fayalitic olivine has an unusual anisotropic platy morphology that occurs in at least five types of textural settings that can be characterized as: (1) isolated platelets, (2) clusters of platelets, (3) euhedral to subhedral crystals, (4) overgrowths of platelets on forsteritic olivine, and (5) fluffy (porous) aggregates. From transmission electron microscope (TEM) investigation, the direction of elongation of the platy olivine overgrowths on forsteritic olivine substrates is along the c axis and in most cases it corresponds with the c axis of the substrate olivine, which suggests that the fayalitic olivine grew in this unusual morphology and is not a replacement product of preexisting material. The fayalitic olivine in the matrix of Krymka is compositionally similar to olivine with platy morphology in the matrix of some CV3 chondrites and both have similar Fe/Mn ratios, but important morphological differences indicate that their relationship needs to be explored further. Textural and compositional data indicate that the fayalitic olivine in the matrix of Krymka, as well as in some other unequilibrated ordinary chondrites, formed prior to final lithification of the meteorite and probably prior to parent body accretion. We find that formation of the fayalitic olivine by vapor-solid growth provides the best explanation for our observations and data and is the only feasible mechanism for the formation of fayalitic olivine in the matrix of Krymka. We propose that the fayalitic olivine formed by vaporization and recondensation of olivine rich-dust, during a period of enhanced dust/gas ratio in the nebula. 相似文献
59.
We report intermediate resolution H spectroscopy of the black hole candidate Nova Muscae 1991 during quiescence. We classify the companion star as a K3-K4V which contributes 85±6 percent to the total flux from the binary. The photospheric absorption lines are broadened by 106±13 kms−1 with respect to template field stars, leading to a system mass ratio of q =M1/M2 = 7.8−2.0+3.4. Doppler imaging of the H line shows strong emission coming from the secondary star (EW=3.1±0.6Å) which we associate with chromospheric activity. However, the hot-spot is not detected and this may indicate a lower mass transfer rate than in other X-ray transients of comparable orbital periods. The surface brightness distribution of the accretion disk in H follows a relation I∝R−1.1, less steep than typically observed in cataclysmic variables. Updated system parameters are also presented. 相似文献
60.
Harker David E. Woodward Charles E. McMURTRY Craig W. Goetz J. A. Pipher J. L. Forrest W. J. 《Earth, Moon, and Planets》1997,78(1-3):259-264
We present 1- to 5-μm broadband and CVF images of comet Hale-Bopp taken 1997 February 10.5 UT, 50 days before perihelion.
All the images exhibit a nonspherical coma with a bright “ridge” in the direction of the dust tail approximately 10″ from
the coma. Synthetic aperture spectrophotometry implies that the optically important grains are of a radius ≤0.4 μm; smallest
radius for any comet seen to date. The variation of the integrated surface brightness with radial distance from the coma (ρ)
in all the images closely follows the “steady state” ρ−1 model for comet dust ablation (Gehrz and Ney, 1992). The near-infrared colors taken along the dust tail are not constant
implying the dust grain properties vary with coma distance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献