Criteria for the detection of lunar cryptomaria     

Irene Antonenko  James W. Head  John F. Mustard  B. Ray Hawke 《Earth, Moon, and Planets》1995,69(2):141-172

Cryptomaria are mare basalt deposits hidden or obscured by superposed higher albedo material or variations in albedo. They represent a record of the earliest mare volcanism, and may be a significant volumetric contribution to the volcanic and magmatic history of the Moon. In order to assess their global distribution and significance, criteria for the identification of cryptomaria are developed and techniques for locating them are described. These criteria and techniques include the presence of dark halo craters, identification by spectral mixing analysis, identification by geochemical evidence, association with light plains units, location within basin topography, proximity to known mare, relation to mascons indicated by gravity anomalies, and identification of the source of an obscuring agent, such as crater ejecta. On the basis of these criteria and techniques, several types of cryptomare are recognized, depending on the nature of ejecta and mare materials. Cryptomaria may be formed when maria are obscured by coverings of proximal or distal basin ejecta, or by crater ejecta dusting, or when ejecta covers over basalts which lack a distinctive 1µm absorption band. Using these concepts we outline three case studies: 1) the Schiller-Schickard region adjacent to the Orientale basin, classified as a basin-ejecta cryptomare and grading from distal to proximal, with possible crater-ejecta covering occurring in the southwestern portion of the region, 2) the Balmer basin, classified as a crater-ejecta-dusting cryptomare, and 3) the Australe basin, in which two types of cryptomare were identified: a) crater-ejecta-dusting on old mare patches and b) possible distal-basin-ejecta covering even older mare material. These case studies provide criteria for the further global identification and classification of cryptomaria and stress the need for utilization of multiple criteria and data sets.  相似文献   

Herbig Ae/Be stars     

T. P. Ray 《Astrophysics and Space Science》1994,216(1-2):71-86

Herbig Ae/Be stars are the higher mass counterparts of the T Tauri stars. In comparison with the latter, however, relatively little is known about them. After a historical introduction, we briefly review their optical and UV spectroscopic properties. We consider the evidence for and against disks around Herbig Ae/Be stars; the existence of which remains highly controversial. We also examine in-depth their interaction with the surrounding medium as manifested through optical outflows. It is shown that although there are similarities with analogous outflows from lower mass young stars, those from Herbig Ae/Be stars may be more poorly collimated. Jets, however, are found in at least some cases.  相似文献   

Growth rate and life span of Eocene/Oligocene Nummulites tests: inferences from Sr/Ca ratio     

S. Sarangi  A. Sarkar  M. M. Sarin  S. K. Bhattacharya  M. Ebihara  & A. K. Ray 《地学学报》2001,13(4):264-269

The problem of growth rate and life span of Nummulites foraminifers, attaining giant sizes during the Eocene, has been addressed by analysing their Sr/Ca ratio across the Eocene/Oligocene Boundary (EOB) of Kutch, western India. The Eocene ratio (˜ 1) rapidly decreases during the Oligocene (˜ 0.5) and is coincident with the extinction of most of the Eocene Nummulites species, a rapid enrichment of δ¹⁸O and decrease in both test size and species diversity across the boundary. The high Sr/Ca ratio in Eocene foraminifers can be explained by their rapid growth under a favourable climatic condition. The climatic deterioration (e.g. δ¹⁸O cooling) across the boundary and during the early Oligocene possibly forced the Nummulites to adopt a slower growth rate (and stunted growth). The rapid growth of the Eocene Nummulites indicates that the giant sizes of these protists need not necessarily involve a large life span.  相似文献   

The bolometric light curve of SN 1993J and the nature of its progenitor     

A. Ray  K. P. Singh  F. K. Sutaria 《Journal of Astrophysics and Astronomy》1993,14(2):53-63

We have constructed the bolometric light curve of SN 1993J based on UBVRI(JHK) photometric data obtained from various sources and assumingA _V = 0 and a distance modulus of 27.6. Effective temperatures and photosphere radius at various times have been obtained from detailed blackbody fits. The bolometric light curve shows two maxima. The short rise time to the second maximum, and the luminosities at the minimum and the second maximum are used to constrain the properties of the progenitor star. The total mass of the hydrogen envelope M_H, in the star is found to be ≲ 0.2 M_⊙ at the time of explosion, and the explosion ejected about 0.05 M_⊙ of Ni⁵⁶. Thin hydrogen envelope combined with a sufficient presupernova luminosity suggest that the exploding star was in a binary with a probable period range of 5yr ≤P _orb ≤ 11yr.  相似文献   

Propagation of plane relativistic shock waves in the presence of a magnetic field     

G. Deb Ray  T. K. Chakraborty 《Astrophysics and Space Science》1978,56(1):119-128

In this paper we obtain similarity solutions for the propagation of plane relativistic shock waves in the presence of a transverse magnetic field for the medium, where the nucleon number density obeys a power law of distance from the plane of explosion. The shock surface moves with constant velocity and the total energy of the disturbance is dependent on time. The solutions are applicable only to an isothermal medium or a cold gas.  相似文献   

A review of the synthesis and characterisation of pillared clays and related porous materials for cracking of vegetable oils to produce biofuels     

J. Theo Kloprogge  Loc V. Duong  Ray L. Frost 《Environmental Geology》2005,47(7):967-981

This paper presents an overview of the modification of clay minerals by propping apart the clay layers with an inorganic complex. This expanded material is converted into a permanent two-dimensional structure, known as pillared clay or shortly PILC, by thermal treatment. The resulting material exhibits a two-dimensional porous structure with acidic properties comparable to that of zeolites. Synthetic as well as natural smectites serve as precursors for the synthesis of Al, Zr, Ti, Fe, Cr, Ga, V, Si and other pillared clays as well as mixed Fe/Al, Ga/Al, Si/Al, Zr/Al and other mixed metal pillared clays. Biofuels form an interesting renewable energy source, where these porous, catalytically active materials can play an important role in the conversion of vegetable oils, such as canola oil, into biodiesel. Transesterification of vegetable oil is currently the method of choice for conversion to biofuel. The second part of this review focuses on the catalysts and cracking reaction conditions used for the production of biofuel. A distinction has been made in three different vegetable oils as starting materials: canola oil, palm oil and sunflower oil.  相似文献   

Volcanism in Mare Fecunditatis and Mare Crisium: Ar-Ar age studies     

Vera A. Fernandes  Ray Burgess 《Geochimica et cosmochimica acta》2005,69(20):4919-4934

The laser ⁴⁰Ar/³⁹Ar dating technique has been applied to five Luna 16 basalt fragments and one impact glass, and nine Luna 24 basalt fragments and one breccia. The textures of these basalts are fine-grained ophitic and coarse-grained basalts. The samples contain high levels of solar and lunar atmospheric argon acquired during their residence on the lunar surface. These trapped argon components are predominantly released at low temperature steps and can be distinguished from radiogenic and cosmogenic released at intermediate and high temperature steps. The apparent ages obtained for Luna 16 samples span a narrow range of 3.29 to 3.38 Ga. A young age of 0.988 Ga was obtained for a basaltic impact glass indicating the age of an impact event in the vicinity of Luna 16 landing site. The ages obtained for Luna 24 samples suggest the existence of at least three periods of volcanism occurring over a protracted interval of between 3.45 and 2.52 Ga. The long period of volcanism suggested for the Mare Crisium was likely due to a combination of geophysical and geochemical features in the surrounding and underlying areas of the Crisium Basin. Attempts at dating three Luna 20 samples were inconclusive due to their high trapped argon contents.  相似文献   

Migration and gender identity among Chinese skilled male migrants to Australia     

Ray Hibbins 《Geoforum》2005,36(2):167-180

This paper reports on a study of the effects of migration on constructions of masculinities among Chinese skilled male migrants to Australia over the past 50 years. Data were collected in in-depth, semi-structured interviews of a sample of 40 Chinese male migrants in Brisbane city. The respondents came from a variety of countries of origin and varied in marital status, sexuality, age and previous migration experiences as well as duration of settlement in Australia. Because of an immigration policy based on a points system for measuring skill potential among migrants, these informants were of middle to upper-middle socio-economic status. Core ideas which emerged from the study included: Chineseness; insularity; the centrality of family, kin and friendship networks; Chinese males in the workplace; the division of labour in the household; employment and the fears of unemployment. These Chinese skilled male migrants displayed qualities of hegemonic masculinity in their households where traditional Chinese division of labour persisted. The markers of masculinity included: centrality of work and education; being a successful provider and protector; the accumulation of wealth and power. Unlike local hegemonic variants of masculinity these males placed little emphasis on sport, sexual prowess and performance and alcohol consumption. There were no ambitions among this sample of males to model local variants of masculinities, however gay males in the sample while experiencing marginalisation, racism and homophobic behaviour at the hands of local hegemonically masculine males, were more like the local dominant males in terms of an emphasis on sexual performance and preferences for well-muscled and fit bodies. Gay males in the Chinese sample found it necessary to restrict their social circles and physical locales. This Australian study has demonstrated the importance of the cultural sensitivity of concepts in doing comparative studies, and of considering sexuality as a dimension of identity in migration research that seems to assume a heteronormativity in its samples.  相似文献   

Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters?     

Jim Ray  Jan Kouba  Zuheir Altamimi 《Journal of Geodesy》2005,79(9):505-511

Combinations of station coordinates and velocities from independent space-geodetic techniques have long been the standard method to realize robust global terrestrial reference frames (TRFs). In principle, the particular strengths of one observing method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and accurate co-location ties are available. More recently, the methodology has been extended to combine time-series of results at the normal equation level. This allows Earth orientation parameters (EOPs) to be included and aligned in a fully consistent way with the TRF. While the utility of such multi-technique combinations is generally recognized for the reference frame, the benefits for the EOPs are yet to be quantitatively assessed. In this contribution, which is a sequel to a recent paper on co-location ties (Ray and Altamimi in J Geod 79(4–5): 189–195, 2005), we have studied test combinations of very long baseline interferometry (VLBI) and Global Positioning System (GPS) time-series solutions to evaluate the effects on combined EOP measurements compared with geophysical excitations. One expects any effect to be small, considering that GPS dominates the polar motion estimates due to its relatively dense and uniform global network coverage, high precision, continuous daily sampling, and homogeneity, while VLBI alone observes UT1-UTC. Presently, although clearly desirable, we see no practical method to rigorously include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, our results, which are the first of this type, indicate that more accurate polar motion from GPS contributes to improved UT1-UTC results from VLBI. The situation with combined polar motion is more complex. The VLBI data contribute directly only very slightly, if at all, with an impact that is probably affected by the weakness of the current VLBI networks (small size and sparseness) and the quality of local ties relating the VLBI and GPS frames. Instead, the VLBI polar motion information is used primarily in rotationally aligning the VLBI and GPS frames, thereby reducing the dependence on co-location tie information. Further research is needed to determine an optimal VLBI-GPS combination strategy that yields the highest quality EOP estimates. Improved local ties (including internal systematic effects within the techniques) will be critically important in such an effort.  相似文献   

Characterizing frictional behavior for use in predicting the seismic response of unattached equipment     

S. Ray Chaudhuri  T.C. Hutchinson   《Soil Dynamics and Earthquake Engineering》2005,25(7-10):591-604

Characterizing friction is a fundamentally important aspect of modeling the seismic response of a body resting on any mechanical interface. In the context of rigid bodies mounted within building structures, the numerous types of elements and interfaces encountered in practice require specific characterization before any modeling assumptions can be undertaken. To this end, in this paper, the specific problem of characterizing the frictional behavior for a variety of small equipment types typically found in Biological and Chemical Science laboratories is studied using two different methods of testing. A simple approach is presented to determine the instantaneous coefficients of friction considering inertial effects. Resulting coefficients of static friction μ_s and kinetic friction μ_k for these types of equipment and their plausible range of uncertainty are presented. Analytical comparisons with shake table experiments, using mean frictional resistance values, illustrate that reasonable estimations of time history response can be determined. The accuracy of the prediction increases as the effects of stick-slip are minimized.  相似文献