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1.
Some Bianchi Type IX string cosmological models with bulk viscous fluid for massive string is investigated. To get a determinate
solution, a supplementary condition a=b
n, between metric potentials, is used wherea and b are function of time alone. A particular solution for n=0 is also discussed. The behaviour of the model in presence and absence
of bulk viscosity, is discussed. The physical and implications of the model is also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Methane, a potential biosignature, has recently been detected in the martian atmosphere. This Note focuses on field investigations/operational simulations and laboratory studies which resulted in successful detection of methane within arid terrestrial soils, as distinct from the usual methanogen environment, but in at least partial analogy to martian conditions. 相似文献
3.
Gregory P. Marchildon Suren Kulshreshtha Elaine Wheaton Dave Sauchyn 《Natural Hazards》2008,45(3):391-411
Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using
climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought
is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger
region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought.
These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the
Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both
organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover,
these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents
of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective
institutional adaptation. 相似文献
4.
5.
Archaeological investigations in Camels Back Cave, western Utah, recovered a series of small-mammal bone assemblages from stratified deposits dating between ca. 12,000 and 500 14C yr B.P. The cave's early Holocene fauna includes a number of species adapted to montane or mesic habitats containing grasses and/or sagebrush (e.g., Lepus townsendii, Marmota flaviventris, Reithrodontomys megalotis, and Brachylagus idahoensis) which suggest that the region was relatively cool and moist until after 8800 14C yr B.P. Between ca. 8600 and 8100 14C yr B.P. these mammals became locally extinct, taxonomic diversity declined, and there was an increase in species well-adapted to xeric, low-elevation habitats, including ground squirrels, Lepus californicus and Neotoma lepida. The early small-mammal record from Camels Back Cave is similar to the 11,300–6000 14C yr B.P. mammalian sequence from Homestead Cave, northwestern Utah, and provides corroborative data on Bonneville Basin paleoenvironments and mammalian responses to middle Holocene desertification. 相似文献
6.
7.
Regions and sustainable development: regional planning matters 总被引:1,自引:0,他引:1
This paper looks at how the term 'sustainable development' has been used in the process of regional plan making over the past decade. It emphasizes the differing geographies of these debates within England, in terms of how sustainable development has been used to justify different types of approach in different parts of the country. Both drawing on and challenging recent work on state theory, the paper argues the need to see regional planning as a part of a multi-scalar governance system, whose importance should not be underestimated. 相似文献
8.
Dave A.Yuen Benjamin J. Kadlec Evan F. Bollig Witold Dzwinel Zachary A. Garbow Cesar R. S. da Silva 《Visual Geosciences》2005,10(1):1-12
We present a web client-server service WEB-IS, which we have developed for remote analysis and visualization of seismic data consisting of both small magnitude events and large earthquakes. We show that the problem-solving environment (PSE) intended for prediction of large magnitude earthquakes can be based on this WEB-IS idea. The clustering schemes, feature generation, feature extraction techniques and rendering algorithms form a computational framework of this environment. On the other hand, easy and fast access both to the seismic data distributed among distant computing resources and to computational and visualization resources can be realized in a GRID framework. We discuss the usefulness of NaradaBrokering (iNtegrated Asynchronous Real-time Adaptive Distributed Architecture) as a middleware, allowing for flexibility and high throughput for remote visualization of geophysical data. The WEB-IS functionality was tested both on synthetic and the actual earthquake catalogs. We consider the application of similar methodology for tsunami alerts. 相似文献
9.
Massimo Chiaradia Dave Banks Robert Cliff Robert Marschik Antoine de Haller 《Mineralium Deposita》2006,41(6):565-573
The origin of the hypersaline fluids (magmatic or basinal brine?), associated with iron oxide (Cu–U–Au–REE) deposits, is controversial. We report the first chlorine and strontium isotope data combined with Cl/Br ratios of fluid inclusions from selected iron oxide–copper–gold (IOCG) deposits (Candelaria, Raúl–Condestable, Sossego), a deposit considered to represent a magmatic end member of the IOCG class of deposit (Gameleira), and a magnetite–apatite deposit (El Romeral) from South America. Our data indicate mixing of a high δ 37Cl magmatic fluid with near 0‰ δ 37Cl basinal brines in the Candelaria, Raúl–Condestable, and Sossego IOCG deposits and leaching of a few weight percent of evaporites by magmatic-hydrothermal (?) fluids at Gameleira and El Romeral. The Sr isotopic composition of the inclusion fluids of Candelaria, Raúl–Condestable, and El Romeral confirms the presence of a non-magmatic fluid component in these deposits. The heavy chlorine isotope signatures of fluids from the IOCG deposits (Candelaria, Raúl–Condestable, Sossego), reflecting the magmatic-hydrothermal component of these fluids, contrast with the near 0‰ δ 37Cl values of porphyry copper fluids known from the literature. The heavy chlorine isotope compositions of fluids of the investigated IOCG deposits may indicate a prevailing mantle Cl component in contrast to porphyry copper fluids, an argument also supported by Os isotopes, or could result from differential Cl isotope fractionation processes (e.g. phase separation) in fluids of IOCG and porphyry Cu deposits. 相似文献
10.
The axisymmetric formulation of the governing equations for geomechanics in the framework of smoothed particle hydrodynamics (SPH) is presented in this study. Two forms of SPH discretization for the motion equations, which are labeled as form I and form II, are proposed, and the methods to compute the hoop stress and strain terms including hoop strain rate and the acceleration introduced by the hoop stress are compared. To avoid possible singularity problem near the axis of symmetry, a perfectly smooth contact along with ghost particles are applied to prevent the real particles from overly approaching the axis of symmetry to remove this potential singularity. In addition, the Mohr–Coulomb constitutive model is implemented into the SPH formulation in describing soil behavior. Four numerical tests are carried out to validate and compare the accuracy and stability of the proposed algorithms, and their results are compared with analytical solutions and results from FEM analysis. The performance in these comparisons suggests that SPH II with hoop terms computed through direct hoop method is more stable than the others, and the adoption of contact for the symmetric axis is efficient in eliminating the singularity problem. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献