Diamonds: geology, gemmology, technology     

Andrew Fleet  Alan Hart  Frances Wall 《Geology Today》2006,22(1):23-28

Diamonds – rough stones, cut stones, host rocks, historical jewellery, contemporary jewellery, and hi-tech materials – were the stars of an exhibition at the Natural History Museum in London in 2005, the biggest of its kind the Museum had ever staged. Why diamonds are so rare, how they have been valued through history, and the links between the unique properties of diamond and its use were the key themes of the exhibition.  相似文献   

A kinematical approach to dark energy studies     

David Rapetti  Steven W. Allen  Mustafa A. Amin  Roger D. Blandford 《Monthly notices of the Royal Astronomical Society》2007,375(4):1510-1520

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The frequency of wide binaries among the southern barium stars     

Roger B. Culver  Philip A. Ianna 《Astrophysics and Space Science》1988,142(1-2):199-201

Summary All of the barium and marginal barium stars in the 1972 MacConnell, Frey, and Upgren (1972: MFU) list of such objects which are located south of the celestial equator were examined for visual duplicity. Over 200 objects were observed, and a total of six possible candidates for wide pair visual binaries were found. Of these, four are most likely optical in nature. These data suggest that the incidence of wide binaries among barium stars is of the order of 1%.  相似文献   

Unified 3D critical state bounding-surface plasticity model for soils incorporating continuous plastic loading under cyclic paths. Part I: Constitutive relations     

Roger S. Crouch  John P. Wolf 《国际地质力学数值与分析法杂志》1994,18(11):735-758

The unified three-dimensional (3D) critical state bounding-surface plasticity model gUTS enables clays, silts and sands to be treated within a single framework. Furthermore, loose and dense states of a particular soil subjected to a wide range of confinements are viewed as a single material defined by the same set of constants. The model is able to handle both monotonic and complex cyclic paths including those involving a rotation of the principal stress directions. The model incorporates the following features: combined use of radial and deviatoric mapping rules and the use of an apparent normal consolidation line for sands; use of a non-associated flow rule where the ratio of the rates of volumetric plastic strain to deviatoric plastic strain is a function only of the ratio of deviatoric to mean effective stresses and the Lode angle; adoption of a bi-linear critical state line projected onto the plane of the void ratio versus logarithm of mean effective stress; inclusion of a sub-elliptic, or super-elliptic, segment in the plastic dilatancy surface for stress ratios less than critical; use of elliptic segments in the deviatoric planes; movement of the projection centre in the deviatoric mapping region and incorporation of a plastic stiffening effect for cyclic paths which repeatedly load in the same deviatoric direction.  相似文献   

On the long-term motion of Pluto     

Paul E. Nacozy  Roger E. Diehl 《Celestial Mechanics and Dynamical Astronomy》1974,8(4):445-454

A modified periodic orbit of the third kind is introduced that is closely related to periodic orbits of the third kind as defined by Poincaré. It is shown that Pluto librates about the periodic orbit with apparent stability. This further explains the librational motion of the resonant argument of Pluto and the avoidance of a Pluto-Neptune close approach as found by Cohen and Hubbard and the long-term motion of Pluto and the librational motion of the perihelion as found by Williams and Benson. With libration about a periodic orbit, the numerical solution of Williams and Benson can be extrapolated to longer times in the past and future.  相似文献   

Organic nitrogen and caloric content of detritus: II. Microbial biomass and activity     

Roger B. Hanson 《Estuarine, Coastal and Shelf Science》1982,14(3):325-336

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Mineral magnetic analyses as a means of lithostratigraphic correlation and provenance indication of glacial diamicts: Intra- and interunit variation     

John Walden  John P. Smith  Roger V. Dackombe 《第四纪科学杂志》1992,7(3):257-270

Mineral magnetic analyses are applied to a series of diamict samples taken from the Quaternary sequence in the Isle of Man in order to assess the relative magnitude of the intra-and inter-unit variation of the magnetic properties. The results are analysed both qualitatively and quantitatively and show that the level of intra-unit variation is significantly less than the level of inter-unit variation. The intra-unit variation detected appears to show some relationship to the basic stratigraphy. Previous correlations based upon field evidence of diamict units exposed upon the east and west coasts of the Isle of Man are supported by their mineral magnetic properties. The statistically significant differences in the magnetic mineralogy of the stratigraphically lower Wyllin and Shellag Tills and the upper Orrisdale, Ballavarkish and Ballaquark Tills suggests distinct provenances for these two suites of sediments, allowing potential source areas to be suggested. These source areas are consistent with published data on ice flow directions in the Irish Sea Basin during the Devensian.  相似文献   

General Relativistic Magnetoionic Theory     

Avery Broderick  Roger Blandford 《Astrophysics and Space Science》2003,288(1-2):161-173

We have developed methods for tracing rays and performing radiative transfer through a magneto active plasma in a general relativistic environment. The two electromagnetic plasma modes propagate differently due to a combination of dispersive and gravitational effects. We have found that, when given an appropriate environment surrounding the central black hole, it is indeed possible to generate a significant degree of circular polarisation without an appreciable amount of linear polarisation due to these effects alone.  相似文献   

Volumetric strain in relation to particle displacements for body and surface waves in a general viscoelastic half-space     

Roger D. Borcherdt 《Geophysical Journal International》1988,93(2):215-228

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Mineralium Deposita Referees 1992     

Kathy Tixier  Roger Beckie 《Mineralium Deposita》1993,28(1):76-76

Mineralium Deposita Referees 1992  相似文献