Five supernova survey galaxies in the southern hemisphere. II. the supernova rates     

A. A. Hakobyan  A. R. Petrosian  G. A. Mamon  B. McLean  D. Kunth  M. Turatto  E. Cappellaro  F. Mannucci  R. J. Allen  N. Panagia  and M. Della Valle 《Astrophysics》2011,54(3):301-314

  相似文献   

The second byurakan survey galaxies. i. the optical database     

M. Gyulzadyan  B. McLean  V. Zh. Adibekyan  R. J. Allen  D. Kunth  A. Petrosian  J. A. Stepanian 《Astrophysics》2011,54(1):15-25

A database for the entire catalog of the Second Byurakan Survey (SBS) galaxies is presented. It contains new measurements of their optical parameters and additional information taken from the literature and other databases. The measurements were made using I_pg (near-infrared), F_pg (red), and J_pg (blue) band images from photographic sky survey plates obtained by the Palomar Schmidt telescope and extracted from the STScI Digital Sky Survey (DSS). The database provides accurate coordinates, morphological type, spectral and activity classes, apparent magnitudes and diameters, axial ratios and position angles, as well as number counts of neighboring objects in a circle of radius 50 kpc. The total number of individual SBS objects in the database is now 1676. The 188 Markarian galaxies that were re-discovered by SBS are not included in this database. We also include redshifts that are now available for 1576 SBS objects, as well as 2MASS infrared magnitudes for 1117 SBS galaxies.  相似文献   

Retention of uranium in complexly altered zircon: An example from Bancroft,Ontario     

Lutz Nasdala  John M. Hanchar  Dieter Rhede  Allen K. Kennedy  Tamás Váczi 《Chemical Geology》2010,269(3-4):290-300

Mesoproterozoic (~ 1050 Ma; Stenian) zircon crystals from the Saranac Prospect, Bancroft, Ontario, contain up to ~ 1 wt.% U and ~ 0.15 wt.% Th and, correspondingly, they are for the most part extensively radiation-damaged (calculated total α-doses 2.3?35.3 × 10¹⁸/g). The crystals show textures of complex, intense chemical alteration that is attributed to multiple, low-T replacement events along fluid-controlled reaction fronts. Centers of crystals appear totally replaced; the primary zoning is virtually erased and the material has high porosity and numerous inclusions. Interior regions surrounding the central reworked areas still exhibit primary igneous-type zoning; in those regions the alteration emanates from fractures and then follows the more radiation-damaged growth zones. Altered areas are typically recognized by their high porosity, low BSE intensity, and deficient analytical totals. Those regions often have lost a significant fraction of their radiogenic Pb. They are in general somewhat depleted in Zr, Si, and U, and are notably enriched in Ca and Fe. Element maps reveal elevated concentrations of Al and Y within filled fractures. Our observations indicate that the fluid-driven ion exchange is mainly controlled by the accessibility of micro-areas with elevated levels of radiation damage to transporting fluids via “fast pathways”. Most importantly, there is apparent Zr?Si?U equilibrium between initially existing and newly formed zircon. The retention of U after the chemical replacement (94 ± 14% relative to the original U content in the respective zones) does not significantly fall below the retention of two major cations Zr (95 ± 4%) and Si (95 ± 2%). In spite of the partially extreme hydrothermal alteration overprinting, the original U zoning in the crystals is well preserved. These observations suggest that preferential chemical leaching of U from zircon is clearly not a general feature of this mineral. This in turn seems to question the general validity of hydrothermal experiments to low-T, fluid-driven alteration of zircon in geological environments. The observed apparent immobility of U may affect the interpretation of U?Pb discordance in zircon, and the performance assessment of this mineral as potential waste form for actinides.  相似文献   

The complex age of orthogneiss protoliths exemplified by the Eoarchaean Itsaq Gneiss Complex (Greenland): SHRIMP and old rocks   总被引：1，自引：0，他引：1  

Kenji Horie  Allen P. Nutman  Clark R.L. Friend  Hiroshi Hidaka 《Precambrian Research》2010

Field studies integrated with cathodoluminescence petrography and SHRIMP U–Pb dating of zircons from >150 orthogneisses and metatonalites from the Eoarchaean Itsaq Gneiss Complex (southern West Greenland) shows that only a minority contain ≥3840 Ma zircons, whereas the majority carry only younger ones. Rocks containing ≥3840 Ma zircons vary from very rare single-phase metatonalites to more common complexly banded tonalitic migmatites. The former metatonalites have simple oscillatory-zoned ≥3840 Ma zircon with limited recrystallisation and overgrowth, whereas the more common migmatites have much more complicated zircon populations with both ≥3840 Ma and 3650–3600 Ma oscillatory-zoned zircon, more extensive recrystallisation and widespread complex core-rim multiple growth relationships.  相似文献   

Preface to special issue of Precambrian Research on the impact of SHRIMP on understanding the Precambrian     

Allen P. Nutman 《Precambrian Research》2010

  相似文献   

An investigation of aspects of mine waste from a kyanite mine,Central Virginia,USA     

Mark Paul Speeg Krekeler  C. Scott Allen  Lance E. Kearns  J. Barry Maynard 《Environmental Earth Sciences》2010,61(1):93-106

Kyanite Mining Corporation, located in Dillwyn, Virginia has been in operation for over 50 years and their local operation is the largest kyanite mine in the world. As part of the processing at this location, a magnetic separate is generated and a minimum estimation of 3.57 million tons of waste has accumulated. Currently no use for the magnetic separate has been identified. We investigated eight representative samples of the magnetic mine waste which varied in color from a dark tan to black, to determine if the waste could be recycled as an ore or could be used as an environmental media. Mineralogical investigations indicate the composition of the magnetic mine waste is dominated by magnetite, kyanite, lesser amounts of hematite and charcoal. Magnetite occurs as fine grained crystals and as inclusions in kyanite. Hematite occurs largely as botryoidal textures, as discrete grains, and as coatings on kyanite grains. Fe-oxide spheres ranging in diameter from approximately 5–100 μm are common and may compose up to 10% in some samples. Titanium dioxide was rarely observed as coatings on silicate mineral grains. Energy dispersive spectroscopy analysis on magnetite crystals indicates they have end-member compositions. Bulk property investigations indicate that grain size distributions of samples are primarily unimodal with 20–40% of material being between 0.600 and 0.250 mm. Hydraulic conductivity values of samples investigated vary between 0.0036 and 0.0077 cm/s and are broadly consistent with those expected of sands with similar grain size distributions. In addition to the magnetic waste stream a light blue, water soluble, amorphous Cu sulfate occurs as a coating on surfaces of boulders. The coating is composed of rounded interlocking particles 5–60 μm in diameter. This material is of some environmental concern for freshwater invertebrates, but can be managed using sorption media. Hyperspectral data were gathered of the magnetic separate, kyanite ore samples, and the light blue Cu sulfate. The signatures of the kyanite ore, the blue mineral coating, and a mixture of the two provide spectral fingerprints that an imaging spectrometer could exploit for rapid detection and subsequent environmental monitoring.  相似文献   

Studies in fluviatile sedimentation: Lateral variation in some fining-upwards cyclothems from the Red Marls,Pembrokeshire     

J. R. L. Allen 《Geological Journal》1974,9(1):1-16

The lateral lithological variability of 18 stratigraphically close fluviatile cyclothems is analysed in three ways: (1) qualitatively, (2) by means of the upwards facies transition probability matrix, and (3) using the non-parametric Mann-Whitney U statistic. Some cyclothems are relatively very uniform over lateral distances comparable with 100 cyclothem thicknesses, whereas others have a lateral variability similar to the variability characteristic of the set of cyclothems. Hence some amongst stratigraphically close cyclothems are considered to show real differences, which may be attributed to allocyclic environmental factors operating on a relatively large time scale. The variation within cyclothems can be explained by shorter term autocyclic factors.  相似文献   

A quantitative technique for assessing the roundness of pottery sherds in water currents     

J. R. L. Allen 《Geoarchaeology》1989,4(2):143-155

The shape property of transposed pottery sherds that changes most rapidly due to wear during water transport in natural sedimentary environments is roundness, the degree of curvature of edges and corners. of the many methods for the measurement of particle roundness, which are briefly reviewed, that proposed by Wadell (1932, 1933) is considered to specify roundness best. A simple and rapid procedure for the measurement of the Wadell projection roundness is described, which yields roundness values having a precision of the order of a few percent, the precision improving with the degree of roundness. the technique is therefore suitable for the analysis of large samples of transposed and transported sherds.  相似文献