Photoluminescence of zircon (ZrSiO4) doped with REE3+ (REE = Pr, Sm, Eu, Gd, Dy, Ho, Er)     

Henrik Friis  Adrian A. Finch  C. Terry Williams  John M. Hanchar 《Physics and Chemistry of Minerals》2010,37(6):333-342

The photoluminescence properties of synthetic zircon, ZrSiO₄, doped with REE³⁺ (REE = Pr, Sm, Eu, Gd, Dy, Ho, Er) were investigated using combined excitation and emission spectroscopy. All samples showed luminescence characteristics of intra-ion energy transitions, similar to other lanthanide-doped materials. However, the relative intensities were dependent on the energy of excitation and the presence of charge-transfer bands were inferred from excitation spectra. From the data, we conclude that the lanthanides in zircon occur in more than one type of coordination. Energy transfer between different lanthanides was observed in some co-doped samples and emissions that were unassigned in previous studies have been assigned to specific lanthanides based on excitation spectroscopy.  相似文献   

δB, Sr, Mg and B in a modern Porites coral: the relationship between calcification site pH and skeletal chemistry     

Nicola Allison  Adrian A. Finch 《Geochimica et cosmochimica acta》2010,74(6):1790-6360

Sr/Ca, B/Ca, Mg/Ca and δ¹¹B were determined at high spatial resolution across ∼1 year of a modern Hawaiian Porites lobata coral by secondary ion mass spectrometry (SIMS). We observe significant variations in B/Ca, Mg/Ca, Sr/Ca and δ¹¹B over short skeletal distances (nominally equivalent to periods of <20 days). This heterogeneity probably reflects variations in the composition of the extracellular calcifying fluid (ECF) from which the skeleton precipitates. Calcification site pH (total scale) was estimated from skeletal δ¹¹B and ranged from 8.3 to 8.8 (± ∼0.1) with a mean of ∼8.6. Sr/Ca and B/Ca heterogeneity is not simply correlated with calcification site pH, as might be expected if Ca-ATPase activity increases the pH and decreases the Sr/Ca and B(OH)₄⁻/CO₃²⁻ ratios of the ECF. We produced a simple model of the ECF composition and the skeleton deposited from it, over a range of calcium transport and carbonate scenarios, which can account for these observed geochemical variations. The relationship between the pH and Sr/Ca of the ECF is dependent on the concentration of DIC at the calcification site. At higher DIC concentrations the ECF has a high capacity to buffer the [H⁺] changes induced by Ca-ATPase pumping. Conversely, at low DIC concentrations, this buffering capacity is reduced and ECF pH changes more rapidly in response to Ca-ATPase pumping. The absence of a simple correlation between ECF pH and skeletal Sr/Ca implies that calcification occurred under a range of DIC concentrations, reflecting variations in the respiration and photosynthesis of the coral and symbiotic zooxanthellate in the overlying coral tissues. Our observations have important implications for the use of coral skeletons as indicators of palaeo-ocean pH.  相似文献   

An example of fingerprint detection of greenhouse climate change     

DJ Karoly  JA Cohen  GA Meehl  JFB Mitchell  AH Oort  RJ Stouffer  RT Wetherald 《Climate Dynamics》1994,10(1-2):97-105

As an example of the technique of fingerprint detection of greenhouse climate change, a multivariate signal or fingerprint of the enhanced greenhouse effect is defined using the zonal mean atmospheric temperature change as a function of height and latitude between equilibrium climate model simulations with control and doubled CO₂ concentrations. This signal is compared with observed atmospheric temperature variations over the period 1963 to 1988 from radiosonde-based global analyses. There is a significant increase of this greenhouse signal in the observational data over this period.These results must be treated with caution. Upper air data are available for a short period only, possibly too short to be able to resolve any real greenhouse climate change. The greenhouse fingerprint used in this study may not be unique to the enhanced greenhouse effect and may be due to other forcing mechanisms. However, it is shown that the patterns of atmospheric temperature change associated with uniform global increases of sea surface temperature, with El NinoSouthern Oscillation events and with decreases of stratospheric ozone concentrations individually are different from the greenhouse fingerprint used here.  相似文献   

Modelling mineral size reduction in the closed-circuit ball mill at the Pine Point Mines concentrator     

J.A. Finch  J. Ramirez-Castro 《International Journal of Mineral Processing》1981,8(1):61-78

Using plug flow material transport and a cumulative-basis rate-of-breakage parameter, overall size reduction through the closed-circuit ball mills at the Pine Point and Gibraltar concentrators was simulated over a wide range of operating conditions. The rate-of-brakage parameter was related to particle size by a power law, the exponent (n) being: Pine Point, n = 1.043 ± 0.026, and Gibraltar, n = 0.747 ± 0.020. The success of this approach probably stems from the high (> 1.5) circulating load ratios encountered.By analogy individual mineral size reduction at Pine Point was examined. A similar rate-of-breakage parameter versus size relationship was found. Pyrite was the hardest mineral, but fine galena was equally resistant. However, the approximation that mineral and overall rates of breakage were the same gave an adequate fit to the mineral size reduction. This was emphasized by combining with a cyclone model to simulate cyclone overflow mineral size distribution. A more accurate cyclone model is shown to be more important in simulating mineral deportment at Pine Point.Complementary laboratory batch grinding tests were conducted on rod mill discharge and ball mill feed samples. Sufficient agreement with the first-order hypothesis was observed to analyse the rate-of-breakage parameter. The kinetics was similar for both samples and in turn similar to the plant-derived kinetics in terms of relative mineral rates-of-breakage and the relationship of the rate-of-breakage parameter with particle size.  相似文献   

Elastic properties from acoustic and volume compression experiments     

Jay D. Bass  Robert C. Liebermann  Donald J. Weidner  Stephen J. Finch 《Physics of the Earth and Planetary Interiors》1981,25(2):140-158

Hydrostatic compression data for a number of high-pressure phases of oxides and silicates, which have been studied independently by acoustic techniques, have been analyzed by least-squares fitting of the Birch-Murnaghan equation of state to determine the zero-pressure bulk modulus K₀ and its pressure derivative K′₀ for each material. The standard deviations of K₀ and K′₀ so determined are generally underestimated unless the experimental errors in the measurements of volume and pressure are explicitly included. When the values of K₀ determined from the acoustic and compression techniques are consistent, test results for quartz and rutile demonstrate that constraining K₀ to be equal to the acoustic value significantly improves both the accuracy and the precision of K′₀ obtained from the compression data. Similar analyses for high-pressure phases (e.g., pyrope garnet and silicate spinels) indicate that by combining the acoustic and P-V data, the standard deviation of K′₀ is typically reduced by a factor of three. Thus, we conclude that this approach does allow precise determinations of K′₀ even when neither technique alone is able to resolve this parameter. For some materials, however, the P-V and acoustic experiments do not define mutually consistent values of K₀, invalidating any combination of these data. The compression data for stishovite clearly exhibit run to run effects, and we infer that systematic errors are present in some of the P-V data which are responsible for many of the interlaboratory inconsistencies. Such systematic biases in the P-V data can at least be partially compensated for by performing several duplicate experimental runs.  相似文献   

Calculation of the visible-UV absorption spectra of hydrogen sulfide,bisulfide, polysulfides,and As and Sb sulfides,in aqueous solution     

JA?TossellEmail author 《Geochemical transactions》2003,4(1):28

Recently we showed that visible-UV spectra in aqueous solution can be accurately calculated for arsenic (III) bisulfides, such as As(SH)₃, As(SH)₂S^- and their oligomers. The calculated lowest energy transitions for these species were diagnostic of their protonation and oligomerization state. We here extend these studies to As and Sb oxidation state III and v sulfides and to polysulfides S _n ^2- , n = 2–6, the bisulfide anion, SH^-, hydrogen sulfide, H₂S and the sulfanes, S _n H₂, n = 2–5. Many of these calculations are more difficult than those performed for the As(iii) bisulfides, since the As and Sb(v) species are more acidic and therefore exist as highly charged anions in neutral and basic solutions. In general, small and/or highly charged anions are more difficult to describe computationally than larger, monovalent anions or neutral molecules. We have used both Hartree-Fock based (CI Singles and Time-Dependent HF) and density functional based (TD B3LYP) techniques for the calculations of absorption energy and intensity and have used both explicit water molecules and a polarizable continuum to describe the effects of hydration. We correctly reproduce the general trends observed experimentally, with absorption energies increasing from polysulfides to As, Sb sulfides to SH^- to H₂S. As and Sb(v) species, both monomers and dimers, also absorb at characteristically higher energies than do the analogous As and Sb(III)species. There is also a small reduction in absorption energy from monomeric to dimeric species, for both As and Sb III and v. The polysufides, on the other hand, show no simple systematic changes in UV spectra with chain length, n, or with protonation state. Our results indicate that for the As and Sb sulfides, the oxidation state, degree of protonation and degree of oligomerization can all be determined from the visible-UV absorption spectrum. We have also calculated the aqueous phase energetics for the reaction of S₈ with SH^- to produce the polysulfides, S _n H^-, n = 2–6. Our results are in excellent agreement with available experimental data, and support the existence of a S₆ species.  相似文献   

Strontium in coral aragonite: 1. Characterization of Sr coordination by extended absorption X-ray fine structure     

Adrian A. Finch  Nicola Allison  Steven R. Sutton  Matthew Newville 《Geochimica et cosmochimica acta》2003,67(6):1197-1202

Aragonite was analyzed from Porites lobata, Pavona gigantea, Pavona clavus, and Montastrea annularis corals by Sr K-edge extended absorption X-ray fine structure (EXAFS) and compared with aragonite, strontianite, and mechanically mixed standards. Bulk analyses were performed and data compared with equivalent micro-EXAFS analyses on small (∼400 μm³) analytical volumes with a microfocused X-ray beam. As a result of the architecture of the coral skeleton, the crystals within the microanalytical volume are not randomly oriented, and the microanalytical X-ray absorption spectra show orientational dependence. However, refinement of bulk and microanalytical data provided indistinguishable interatomic distances and thermal vibration parameters in the third shell (indicative of Sr speciation). The Sr K-edge EXAFS of all the coral samples refine, within error, to an ideally substituted Sr in aragonite, in contrast to previous studies, in which significant strontianite was reported. Some samples from that study were also analyzed here. Strontianite may be less widely distributed in corals than previously thought.  相似文献   

华北北部中生代岩墙群   总被引：27，自引：19，他引：27  

邵济安  张履桥 《岩石学报》2002,18(3):312-318

岩墙群是深源岩浆浅侵位的产物，它可提供有关壳-幔演化的重要信息。通过华北北部大同早中生代碳酸岩-煌斑岩岩墙群、赤峰早中生代闪长玢岩岩墙群、林西中生代辉绿岩岩墙群、京北晚中生代双峰式岩墙群的对比研究，揭示了华北中生代存在的两次底侵作用及其相关的伸展作用。华北早、晚中生代岩墙群与晋北地区元古代岩墙群的初步对比，从一个侧面反映了华北壳幔的演变。  相似文献   

Palaeoenvironmental records from fossil corals: The effects of submarine diagenesis on temperature and climate estimates     

Nicola Allison  Adrian A. Finch  David A. Clague 《Geochimica et cosmochimica acta》2007,71(19):4693-4703

The geochemistry of coral skeletons may reflect seawater conditions at the time of deposition and the analysis of fossil skeletons offers a method to reconstruct past climate. However the precipitation of cements in the primary coral skeleton during diagenesis may significantly affect bulk skeletal geochemistry. We used secondary ion mass spectrometry (SIMS) to measure Sr, Mg, B, U and Ba concentrations in primary coral aragonite and aragonite and calcite cements in fossil Porites corals from submerged reefs around the Hawaiian Islands. Cement and primary coral geochemistry were significantly different in all corals. We estimate the effects of cement inclusion on climate estimates from drilled coral samples, which combine cements and primary coral aragonite. Secondary 1% calcite or ∼2% aragonite cement contamination significantly affects Sr/Ca SST estimates by +1 °C and −0.4 to −0.9 °C, respectively. Cement inclusion also significantly affects Mg/Ca, B/Ca and U/Ca SST estimates in some corals. X-ray diffraction (XRD) will not detect secondary aragonite cements and significant calcite contamination may be below the limit of detection (∼1%) of the technique. Thorough petrographic examination of fossils is therefore essential to confirm that they are pristine before bulk drilled samples are analysed. To confirm that the geochemistry of the original coral structures is not affected by the precipitation of cements in adjacent pore spaces we analysed the primary coral aragonite in cemented and uncemented areas of the skeleton. Sr/Ca, B/Ca and U/Ca of primary coral aragonite is not affected by the presence of cements in adjacent interskeletal pore spaces i.e. the coral structures maintain their original composition and selective SIMS analysis of these structures offers a route to the reconstruction of accurate SSTs from altered coral skeletons. However, Mg/Ca and Ba/Ca of primary coral aragonite are significantly higher in parts of skeletons infilled with high Mg calcite cement. We hypothesise this reflects cement infilling of intraskeletal pore spaces in the primary coral structure.  相似文献   

A test of the Tate equation to predict bubble size at an orifice in the presence of frother     

Jose R. Hernandez-Aguilar  Ryan CunninghamJames A. Finch 《International Journal of Mineral Processing》2006

Air bubbles of uniform size (ca. 1 mm diameter) were generated at a submerged orifice (glass capillary) under controlled frequency (down to ca. 0.06 s^− 1) in aqueous solutions of frother (Dowfroth 250). The bubbles were sized with an imaging technique. One objective was to establish whether the Tate equation (static balance between buoyancy and capillary forces) could be used as a standard sizing calibration method. Another aim was to verify whether with decreasing surface tension (due to increasing frother concentration) the anticipated decrease in bubble size agreed with the equation prediction. An effect of frother was detected compatible with the role of surface tension but divided into two concentration regions, seemingly the result of a gradual change in bubble shape and wetting: > 6 ppm the bubble holds a spherical shape and the capillary appeared to be completely wetted while at ≤ 6 ppm a degree of non-wetting and bubble distortion (neck formation just prior to detachment) were apparent, supported by qualitative observations. In addition, at > 6 ppm the Tate value was only approached by decreasing the bubble frequency but not attained. Plausible causes for the failure to reach the predicted size are discussed.  相似文献