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71.
Isolated isothermal spheres of N gravitationally interacting points with equal mass are believed to be stable when density contrasts do not exceed 709. That stability limit does not, however, take into consideration fluctuations of temperature near the onset of instability. These are important when N is finite.
Here we correlate global mean quadratic temperature fluctuations with the onset of instability. We show that such fluctuations trigger instability when the density contrast reaches a value near 709×exp(−3.3 N−1/3 ). These lower values of limiting density contrasts are significantly smaller than 709 when N is not very large, and this suggests (i) that numerical calculations with small N may not reflect correctly the onset of core collapse in clusters with large N , and (ii) that a greater number of globular clusters than is normally believed may already be in an advanced stage of core collapse, because most of the observed globular clusters with parameters that fit quasi-isothermal configurations are close to marginal stability. 相似文献
Here we correlate global mean quadratic temperature fluctuations with the onset of instability. We show that such fluctuations trigger instability when the density contrast reaches a value near 709×exp(−3.3 N
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Kazumasa Aoki Yukio Isozaki Daisuke Kofukuda Tomohiko Sato Atsushi Yamamoto Kenshi Maki Shuhei Sakata Takafumi Hirata 《地学学报》2014,26(2):139-149
By comparing detrital zircon U–Pb age spectra of coeval fore‐arc and back‐/intra‐arc basin sandstones, we identified the overall distributary pattern of terrigenous clastic material within the Cretaceous arc system of SW Japan. Abundant Proterozoic (c. 1500–2500 Ma) detrital grains from the interior of East Asia are present in the Cretaceous intra‐arc basin. However, after a barrier mountain range formed during batholith emplacement, Proterozoic clastics were rarely transported into the fore‐arc domain. Episodic batholith formation in Pacific‐type orogens likely played a major role in controlling terrigenous supply routes between coeval back‐arc and fore‐arc domains. The Cretaceous orogen in Japan thus provides a good template for analysing the tectono‐sedimentary development of other arc‐related basins. 相似文献
76.
Yoshiaki Kon Mihoko Hoshino Kenzo Sanematsu Sayaka Morita Maiko Tsunematsu Nobuyuki Okamoto Nobuhiko Yano Mikiya Tanaka Tetsuichi Takagi 《Resource Geology》2014,64(1):47-57
We have conducted geochemical and mineralogical investigations of the rare earth and yttrium (REY)‐rich mud from the Minami‐Torishima area in the Pacific in order to clarify the concentration of REY and their host‐phase in the mud. X‐ray diffraction analysis shows that the mud is mainly composed of phillipsite, fluorapatite, quartz, albite, illite and montmorillonite. Whole‐rock CaO, P2O5 and total REY contents of the mud are positively correlated. Relative abundance of apatite is also positively correlated to P2O5 and total REY contents. These correlations suggest that apatite is the main host of the P2O5 and REY in the mud. We make in situ compositional analyses of constituent minerals in the REY mud. The results show that the apatite is abundant in REY (9300–32,000 ppm) and is characterized by a negative Ce anomaly and enrichment in heavy rare‐earth elements. This abundance and composition of REY of the mud is similar those of fish debris apatites. In contrast, phillipsite is less abundant in REY (60–170 ppm). Therefore we conclude that the main REY host phase of the mud is apatite. 相似文献
77.
Akira Monkawa Takashi Mikouchi Eisuke Koizumi Kazumasa Sugiyama Masamichi Miyamoto 《Meteoritics & planetary science》2006,41(9):1321-1329
Abstract— In order to elucidate the formation of low‐H kaersutites in Martian meteorites, the Fe3+/ΣFe ratio of Chassigny kaersutites in magmatic inclusions was directly determined by the synchrotron microXANES analysis. XANES analysis for standard kaersutites with known Fe3+/ΣFe ratios shows a linear relationship between centroid energy positions of XANES pre‐edge spectra and the Fe3+/ΣFe ratio. Based on the linear relationship, the Fe3+/ΣFe ratio of Chassigny kaersutites is estimated to be about 0.05. The low Fe3+/ΣFe ratio clearly suggests that low‐H kaersutites in Chassigny are not likely to be formed by the oxidation‐dehydrogenation reactions. The low‐H content of the Chassigny kaersutites is mainly due to the presence of a Ti oxy‐component. 相似文献
78.
In this paper we investigate the Doppler shifts of the metallic lines for a 3B white-light flare on September 19, 1979. The results show that there is no systematic shift at the line center, while there may appear some asymmetry at the line wing. A possible heating process of this flare is proposed to interpret the observed spectral features. 相似文献
79.
Noam I. Libeskind Shaun Cole Carlos S. Frenk Takashi Okamoto Adrian Jenkins 《Monthly notices of the Royal Astronomical Society》2007,374(1):16-28
We investigate the properties of satellite galaxies formed in N -body/SPH simulations of galaxy formation in the ΛCDM cosmology. The simulations include the main physical effects thought to be important in galaxy formation and, in several cases, produce realistic spiral discs. In total, a sample of nine galaxies of luminosity comparable to the Milky Way was obtained. At magnitudes brighter than the resolution limit, MV =−12 , the luminosity function of the satellite galaxies in the simulations is in excellent agreement with data for the Local Group. The radial number density profile of the model satellites, as well as their gas fractions also match observations very well. In agreement with previous N -body studies, we find that the satellites tend to be distributed in highly flattened configurations whose major axis is aligned with the major axis of the (generally triaxial) dark halo. In two out of three systems with sufficiently large satellite populations, the satellite system is nearly perpendicular to the plane of the galactic disc, a configuration analogous to that observed in the Milk Way. The discs themselves are perpendicular to the minor axis of their host haloes in the inner parts, and the correlation between the orientation of the galaxy and the shape of the halo persists even out to the virial radius. However, in one case the disc's minor axis ends up, at the virial radius, perpendicular to the minor axis of the halo. The angular momenta of the galaxies and their host halo tend to be well aligned. 相似文献
80.
To study the accretional growth of rimmed chondrules and their agglomerates in the solar nebula, we measured the restitution coefficients, ε, and the sticking velocities to a porous silica layer, vc, by impacting the silica layer with a glass ball at velocities from 0.1 to 80 m s?1. We used a porous silica layer covering a basalt block with thicknesses ranging from 1/5 of the glass ball radius to equal to the glass ball radius as a rimmed chondrule analogue, and the porosity of the silica layer was set to be 70%, 80%, 85%, and 90%. Collisional experiments were conducted by means of the free fall method or by the use of a spring gun or a gas gun, allowing us to vary the impact velocity. We used a laser displacement meter to estimate the impact and rebound velocities as well as the acceleration during the collision at impact velocities below 1 m s?1. As a result, the sticking velocity, vc, of 90%- and 85%- porosity layers with a thickness equal to 1/2 of the glass ball diameter was 0.44 and 2.4 m s?1, respectively. On the other hand, we found a distinct barrier to sticking for smaller-porosity layers: the silicate layer with a porosity smaller than 80% never exhibited sticking at any impact velocity below 1 m s?1. Instead, we observed a rebound effect with restitution coefficients larger than 0.2. In the case of a silica layer with a porosity smaller than 80%, we observed the sub-sticking condition defined by ε < 0.1 at velocities extending from 5 m s?1 to 70 m s?1. 相似文献