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971.
972.
Dilatancy and contact surface damage are important phenomena affecting the behaviour of rock joints and other geological discontinuities. Effective constitutive laws that incorporate these behaviours have recently been developed but require the specification of new material parameters that govern damage of asperity surfaces. Determination of the parameters that control damage is currently a difficulty that confronts practitioners. This brief will summarize the findings of Hutson and Dowding's investigation of joint surface asperity degradation and elaborate on the implications for application. 相似文献
973.
974.
Michael R. Rampino 《Icarus》2002,156(2):562-569
The largest explosive volcanic eruptions (supereruptions) produce >1000 km3 of ejected material and ≥1000 Mt (1015 g) of submicron atmospheric aerosols and dust. These eruptions may be capable of creating global climatic disturbances sufficient to cause severe problems for world agriculture and modern civilization. Supereruptions are estimated to occur on average about every 50,000 years, which is about twice the frequency of impacts by comets and asteroids ≥1 km diameter predicted to cause similar climatic effects. Prediction, prevention, and mitigation of global volcanic climatic disasters may be potentially more difficult than planetary protection from the threat of large impacts, so that explosive volcanism might limit the longevity of technological civilizations. 相似文献
975.
Michael Feast 《Astrophysics and Space Science》1994,217(1-2):169-175
The possibilities for detecting distant,highly reddened, cepheids as well as OB star clusters and associations in the surveys is considered and the value of such work for galactic structure problems is outlined. 相似文献
976.
通过对新疆阿尔泰南缘地球物理场特征-深部构造-已知大型矿床分布规律的系统研究,认为该地区不同属性的地质块体受3组基底构造控制,即EW向、NE向和NW向3组基底构造系,并认为该地区已知大型-超大型矿床同样受这3组深部构造系的控制.最后对阿尔泰地区进行了大型、超大型多金属矿床成矿预测. 相似文献
977.
Michael Feast Patricia Whitelock John Menzies 《Monthly notices of the Royal Astronomical Society》2002,329(1):L7-L12
A globular cluster distance scale based on Hipparcos parallaxes of subdwarfs has been used to derive estimates of M K for cluster Miras, including one in the Small Magellanic Cloud (SMC) globular cluster NGC 121. These lead to a zero-point of the Mira infrared period–luminosity (PL) relation, PL( K ), in good agreement with that derived from Hipparcos parallaxes of nearby field Miras. The mean of these two estimates together with data on LMC Miras yields a Large Magellanic Cloud (LMC) distance modulus of in evident agreement with a metallicity-corrected Cepheid modulus .
The use of luminous asymptotic giant branch (AGB) stars as extragalactic population indicators is also discussed. 相似文献
The use of luminous asymptotic giant branch (AGB) stars as extragalactic population indicators is also discussed. 相似文献
978.
979.
Fumiaki Nakata Richard G. Bower Michael L. Balogh David J. Wilman 《Monthly notices of the Royal Astronomical Society》2005,357(2):679-686
We investigate the evolution of the star formation rate in cluster galaxies. We complement data from the Canadian Network for Observational Cosmology 1 (CNOC1) cluster survey (0.15 < z < 0.6) with measurements from galaxy clusters in the Two-degree Field (2dF) galaxy redshift survey (0.05 < z < 0.1) and measurements from recently published work on higher-redshift clusters, up to almost z = 1 . We focus our attention on galaxies in the cluster core, i.e. galaxies with r < 0.7 h −1 70 Mpc . Averaging over clusters in redshift bins, we find that the fraction of galaxies with strong [O ii ] emission is ≲20 per cent in cluster cores, and the fraction evolves little with redshift. In contrast, field galaxies from the survey show a very strong increase over the same redshift range. It thus appears that the environment in the cores of rich clusters is hostile to star formation at all the redshifts studied. We compare this result with the evolution of the colours of galaxies in cluster cores, first reported by Butcher and Oemler. Using the same galaxies for our analysis of the [O ii ] emission, we confirm that the fraction of blue galaxies, which are defined as galaxies 0.2 mag bluer in the rest-frame B – V than the red sequence of each cluster, increases strongly with redshift. Because the colours of galaxies retain a memory of their recent star formation history, while emission from the [O ii ] line does not, we suggest that these two results can best be reconciled if the rate at which the clusters are being assembled is higher in the past, and the galaxies from which it is being assembled are typically bluer. 相似文献
980.