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991.
W. Winkelmans 《GeoJournal》1993,29(2):203-208
The International Geographical Union Reports
IGU Commission on the Organisation of Industrial Space 相似文献992.
J. Ingrin 《Physics and Chemistry of Minerals》1993,20(1):56-62
A study of polytypism in synthetic polycrystalline pseudowollastonite has been made using conventional and high resolution transmission electron microscopy (TEM and HRTEM). Three polytypes of 2, 4 and 6-layers coexist in the one sample in the form of lamellae parallel to (001). From the electron microscopy images the lamellae are interpreted as combinations of the stacking fault vectors: 1/3 [010], 1/6 [310] and 1/6 [3 $\bar 1$ 0], which are probably all equivalent at high temperatures. The polytype lamellae are stable even after prolonged annealing at high temperatures greater than 1700K. These observations suggest that the most frequently reported 4-layer polytype is not the only high-temperature stable polytype. No evidence of melt is detected in samples annealed in the regime where premelting behaviour of pseudowollastonite has previously been reported (above 1600 K). 相似文献
993.
An occurrence of ardennite in quartz veins in piemontite schist,Western Otago,New Zealand 总被引:1,自引:0,他引:1
Summary Ardennite of complex composition: (Mn2+
3.488Ca0.509Ba0.002)=4(Mg0.916916 Fe3+
0.165 Mn3+
0.099Cu0.033Ni0.009Zn0.006 Ti0.008Al4.764)=6(As5+
0.823V5+
0.022P0.005B0.069Al0.042Si5.039)=6O21.81(OH)6.17 occurs in crack-seal quartz veins in quartz-albite-piemontite-spessartine-phengitehematite-chlorite-rutile-tourmaline ± calcite schist of the Haast Schist Group near Arrow Junction, western Otago, New Zealand. The Mn2+/Mn3+-ratio is sensitive to calculations and to accuracy of analyses. Boron is detected in ardennite for the first time. Other properties include = 1.734(3), = 1.735(3), = 1.751(3), 2VZ = 30(2)°;a = 8.721(1),b = 5.816(1),c = 18.545(3) Å,V = 940.7(2) Å3. Associated mineral phases are spessartine, hematite, piemontite containing 0.7% SrO and 0.06% PbO, and phengite. Later-stage vein minerals comprise chlorite, albite, and manganoan calcite which were deposited under less highly oxidizing conditions. Digenite with minor intergrown covellite occurs in small amount with manganoan calcite and quartz in a cross-cutting late-stage veina chalcopyrite and native copper occur in other late-stage veins. Arsenic and other components of the ardennite and associated minerals are derived from highly oxidized ferromanganese oxide- and hydroxide-bearing siliceous pelagic sediments that formed the protolith for the piemontite schist. The veins formed at a relatively early stage after metamorphism peaked in the chlorite zone of the greenschist facies under conditions that have been estimated at about 4.5 kbar, 390 °C.
With 4 Figures 相似文献
Vorkommen von Ardennit in Quarzgängen aus Piemontit-Schiefern, West-Otago, Neuseeland
Zusammenfassung Ardennit mit der Zusammensetzung (Mn2+ 3.488Ca0.509Ba0.002)=4(Mg0.916Fe3+ 0.165Mn3+ 0.099Cu0.033Ni0.009Zn0.006 Ti0.008Al4.764)=6(As5+ 0.823V5+ 0.022P0.005B0.069Al0.042Si5.039)=6O21.81(OH)6.17 tritt in Crack-seal-Quarzgängen in Quarz-Albit-Piemontit-Spessartin-Phengit-Hämatit-Chlorit-Rutil-Turmalin ± Calcit-Schiefern der Haast Schiefer-Gruppe nahe der Arrow Junction, West-Otago, Neuseeland, auf. Die Proportionen von Mn2+/Mn3+ hängen von der Kalkulation und der Genauigkeit der Analyse ab. Bor wird zum ersten Mal im Ardennit bestimmt. Andere Eigenschaften sind: = 1.734(3), = 1.735(3), = 1.751(3), 2Vz = 30(2)°; a = 8.721(1), b = 5.816(1), c = 18.545(3) Å, V = 940.7(2) Å3. Assoziierte Mineralphasen sind Spessartin, Hämatit, Piemontit, der 0.7% SrO und 0.06% PbO enthält und Phengit. Spät gebildete Gangmineralien, wie Chlorit, Albit und Mn-Calcit, sind unter geringer oxidierenden Bedingungen entstanden. Digenit mit etwas Covellin tritt in kleinen Mengen zusammen mit Mn-Calcit und Quartz in einem querschlägigen Gang auf, Chalcopyrit und gediegenes Kupfer kommen in anderen späten Gängen vor. Arsen und andere Komponenten des Ardennites and der assoziierten Minerale können von hochoxidierten, Fe-Mn-Oxid- und Hydroxyd-führenden, Sireichen, pelagischen Sedimenten hergeleitet werden, die das Ausgangsgestein für den Piemontit darstellen. Die Gänge wurden in einem relativ frühen Stadium, nach dem Metamorphosehöhepunkt, innerhalb der Chloritzone der Grünschiefer-Fazies, unter ungefähr 4.5 kbar und 390°C, gebildet.
With 4 Figures 相似文献
994.
G. B. Valsecchi E. Perozzi A. E. Roy B. A. Steves 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):373-380
In a simplified model of the Earth-Moon-Sun system based on the restricted circular 3-dimensional 3-body problem, it is possible to find numerically a set of 8 periodic orbits whose time evolutions closely resemble that of the Moon's orbit. These orbits have a period of 223 synodic months (i.e. the period of the Saros cycle known for more than two millennia as a means of predicting eclipses), and are characterized by a secular rotation of the argument of perigee . Periodic orbits of longer durations exhibiting this last feature are very abundant in Earth-Moon-Sun dynamical models. Their arrangement in the space of the mean orbital elements- for various values of the lunar mean motion is presented. 相似文献
995.
G. Hahn C. -I. Lagerkvist B. A. Lindblad 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):131-141
By using theD-criterion Lindblad (1992) has identified 14 asteroid families from a sample of 4100 numbered asteroids with proper elements from Milani and Kneevi (1990). Taxonomic types and other physical properties for a significant number of objects in five of the families show strong homogeneity within each family, further strengthening their internal relationship.To test the hypothesis of a common origin in, e.g., a catastrophic collision event, we have set out to integrate the orbits of the members of the Maria, Dora and Oppavia-Gefion families over some 106 years. The mean distance for the Maria family is close to the 3:1 mean-motion resonance with Jupiter, while the other two families lie close to the 5:2 resonance.We used a simplified solar system model which included the perturbations by Jupiter and Saturn only and implemented Everhart's variable stepsize integrator RA15. All close encounters between the family members (within 0.1 AU) were recorded as well. Preliminary results from integrations over 4×105 years are presented here.The statistics of close encounters show pronounced peaks for several members within each family, while for others no significant levels above the background of random encounters or even very low frequencies were found. This indicates a subclustering within the families. Quite a lot of very close (<0.005 AU) mutual encounters are found, which suggest that, at least for the larger members in a family, the mutual gravitational interactions could be of some importance for the real orbital evolutions.The encounter statistics between the Dora and Oppavia family members suggest a possible interrelationship between this two groups. 相似文献
996.
John D. Hadjidemetriou 《Celestial Mechanics and Dynamical Astronomy》1993,56(4):563-599
A mapping model is constructed to describe asteroid motion near the 3 : 1 mean motion resonance with Jupiter, in the plane. The topology of the phase space of this mapping coincides with that of the real system, which is considered to be the elliptic restricted three body problem with the Sun and Jupiter as primaries. This model is valid for all values of the eccentricity. This is achieved by the introduction of a correcting term to the averaged Hamiltonian which is valid for small values of the ecentricity.We start with a two dimensional mapping which represents the circular restricted three body problem. This provides the basic framework for the complete model, but cannot explain the generation of a gap in the distribution of the asteroids at this resonance. The next approximation is a four dimensional mapping, corresponding to the elliptic restricted problem. It is found that chaotic regions exist near the 3 : 1 resonance, due to the interaction between the two degrees of freedom, for initial conditions close to a critical curve of the circular model. As a consequence of the chaotic motion, the eccentricity of the asteroid jumps to high values and close encounters with Mars and even Earth may occur, thus generating a gap. It is found that the generation of chaos depends also on the phase (i.e. the angles andv) and as a consequence, there exist islands of ordered motion inside the sea of chaotic motion near the 3 : 1 resonance. Thus, the model of the elliptic restricted three body problem cannot explain completely the generation of a gap, although the density in the distribution of the asteroids will be much less than far from the resonance. Finally, we take into account the effect of the gravitational attraction of Saturn on Jupiter's orbit, and in particular the variation of the eccentricity and the argument of perihelion. This generates a mixing of the phases and as a consequence the whole phase space near the 3 : 1 resonance becomes chaotic. This chaotic zone is in good agreement with the observations. 相似文献
997.
N. Markova 《Astrophysics and Space Science》1993,201(1):61-70
The morphology and variability of 13 helium lines in the P Cygni optical spectrum have been studied in detail over a period of three years. It is found that most lines in the sample have often shown profiles with a complicated structure: discrete components are superposed on a broader underlying P Cyg profile. Multiple sets of components were frequently observed. The radial velocity of the discrete components varies with time. In this article the velocity evolution of two sets of components is studied in detail and the corresponding velocity laws are derived. It is found that the velocity variations in the helium and hydrogen discrete components are correlated. The recurrence timescale for the appearance of new helium components is estimated.An attempt is made for a qualitative interpretation of the obtained results. 相似文献
998.
It has been argued that the loss-cone-driven electron cyclotron maser instability can account for the properties of millisecond microwave spike bursts observed during some solar flares. However, as it propagates outward from the corona, maser radiation undergoes gyroresonance absorption when its frequency is a harmonic of the local electron-cyclotron frequency. Existing analytical models using slab geometries predict that this absorption should be sufficiently strong to prevent the radiation from being seen at the observed levels, except under highly restrictive conditions or for unrealistic plasma parameters. A more comprehensive analysis is presented here to determine if and when maser radiation can escape to produce microwave spike bursts. This analysis employs numerical raytracing and incorporates propagation and absorption of fundamental maser emission in a realistic model of a coronal flux loop. It is found that ranges of physical conditions do exist under which maser radiation can escape to an observer and that these conditions are much more limiting for fundamental emission in the extraordinary ()-mode than in the ordinary (o)-mode. Detailed investigation implies that escaping radiation in the -mode is highly directional and chiefly observable toward the center of the solar disk, while escapingo-mode radiation is found to emerge from the corona over a much wider range of directions, with some cases corresponding to radiation observable near the solar limb. 相似文献
999.
The so-called inverse planetary problem can be stated as follows: given the distances from the centre, masses, and radii of (say) three planets of a planetary system, find the optimum polytropic index, mass, and radius of their star, and also other quantities of interest, which depend either explicitly or implicitly on the foregoing ones (e.g., central and mean density, central and mean pressure, central and mean temperature, etc.). It is hereafter tacitly assumed that the system is opaque with respect to observations concerning periods of planetary otbits; hence, we cannot have any relevant estimates due to the well-known period laws. In the present paper, the inverse planetary problem is treated numerically on the basis of the so-called global polytropic model, developed recently by the first author. 相似文献
1000.
This is a quantitative investigation of the electron beam effect on the hydrogen line profiles and continuum intensity distribution during the impulsive phase of flares. The flaring atmosphere is suggested to be a hydrogenic one and its physical condition corresponds to the gas dynamics problem solution. The radiative transfer, steady-state and particle conservation equations are solved for the three-level hydrogen model atoms with continua. Return-current losses were neglected. Hydrogen line profiles are found to be slightly sensitive to nonthermal impacts with beam electrons in the cores and more sensitive in the wings. With the initial energy flux,F
0, rising and energy spectral index, , decreasing, the wing intensities begin to increase, and the H lines are shown to have rather extended wings as is often observed. The hydrogen continua are shown to be strongly affected by nonthermal impacts. The bigger the value ofF
0 and the smaller the value of , the greater absolute intensities of the hydrogen continua heads. This effect is more noticeable for the Balmer and Paschen continua. The head intensity slopes of them can be used for determination of these electron beam parameters on depths of the hydrogen emission origin and their following comparison with the same parameters for the coronal heights from the X-ray observations. 相似文献