78 resultados para U-PB SHRIMP GEOCHRONOLOGY


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The objective of this research is to determine the molecular structure of the mineral hinsdalite using vibrational spectroscopy. The mineral hinsdalite (Pb,Sr)Al3(PO4,SO4)2(OH)6 is a hydroxy phosphate-sulphate mineral belonging to the beudantite subgroup of alunites. The mineral is interesting because it contains two oxyanions, phosphate and sulphate, which is unusual. The formation of hinsdalite offers a mechanism for the removal of phosphate from the environment. The mineral has been characterised by Raman spectroscopy and infrared spectroscopy. The spectra are then related to the molecular structure of the mineral. Bands at various wavenumbers are assigned to the different vibrational modes of hinsdalite, which were then associated to the molecular structure of the mineral. Bands were primarily assigned to phosphate and sulphate stretching and bending modes. The Raman spectrum is characterised by an intense sharp band at 982 cm-1 with a component band at 997 cm-1 assigned to the ν1 (PO4)3- symmetric stretching modes. Two symmetric stretching modes for both phosphate and sulphate supported the concept of non-equivalent phosphate and sulphate units in the mineral structure. Bands in the OH stretching region enabled hydrogen bond distances to be calculated. Hinsdalite is characterised by disordered phosphate/sulphate tetrahedra and non-equivalent phosphate units are observed in the vibrational spectrum of hinsdalite.

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Estimates of the half-life to convergence of prices across a panel of cities are subject to bias from three potential sources: inappropriate cross-sectional aggregation of heterogeneous coefficients, presence of lagged dependent variables in a model with individual fixed effects, and time aggregation of commodity prices. This paper finds no evidence of heterogeneity bias in annual CPI data for 17 U.S. cities from 1918 to 2006, but correcting for the “Nickell bias” and time aggregation bias produces a half-life of 7.5 years, shorter than estimates from previous studies.

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The CDKN2 gene, encoding the cyclin dependent kinase inhibitor p16, is a tumour suppressor gene involved in melanoma and maps to chromosome band 9p22. Mutations or interstitial deletions of this gene have been found both in the germline of familial melanoma cases and somatically in melanoma cell lines. Previous mutation analyses of melanoma cell lines have indicated a high frequency of C:G to T:A transitions, with all of these mutations occurring at dipyrimidine sites. Including three melanoma cell lines carrying tandem CC to TT mutations, the spectrum of mutations so far reported indicates a possible role for u.v. radiation in the mutagenesis of this gene in some tumours. To further examine this hypothesis we have characterised mutations of the CDKN2 gene in 30 melanoma cell lines. Nineteen lines carried complete or partial homozygous deletions of the gene. Of the remaining cell lines, eight were shown by direct sequencing of PCR products from exon 1 and exon 2 to carry a total of nine different mutations of CDKN2. Two cell lines carried tandem CC to TT mutations and a high rate of C:G to T:A transitions was observed. This study provides further evidence for the role of u.v. light in the genesis of melanoma, with one target being the CDKN2 tumour suppressor gene.

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The presence of arsenic in the environment is a hazard. The accumulation of arsenate by a range of cations in the formation of minerals provides a mechanism for the accumulation of arsenate. The formation of the tsumcorite minerals is an example of a series of minerals which accumulate arsenate. There are about twelve examples in this mineral group. Raman spectroscopy offers a method for the analysis of these minerals. The structure of selected tsumcorite minerals with arsenate and sulphate anions were analysed by Raman spectroscopy. Isomorphic substitution of sulphate for arsenate is observed for gartrellite and thometzekite. A comparison is made with the sulphate bearing mineral natrochalcite. The position of the hydroxyl and water stretching vibrations are related to the strength of the hydrogen bond formed between the OH unit and the AsO43- anion. Characteristic Raman spectra of the minerals enable the assignment of the bands to specific vibrational modes.

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Purpose - The purpose of this paper is to examine the possibility of an inverted U-shaped relationship between job demands and work engagement, and whether social support moderates this relationship. Design/methodology/approach – This study uses 307 technical and information technology (IT) managers who responded to an online survey. Multiple regressions are employed to examine linear and curvilinear relationship among variables. Findings – Overall, results support the applicability of the quadratic effect of job demands on employee engagement. However, only supervisor support, not colleague support, moderated the relationship between job demands and work engagement. Originality/value – The paper is the first to shed light on the quadratic effect of job demands on work engagement. The findings have noteworthy implications for managers to design optimal job demands that increase employee engagement.

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The volcanic succession on Montserrat provides an opportunity to examine the magmatic evolution of island arc volcanism over a ∼2.5 Ma period, extending from the andesites of the Silver Hills center, to the currently active Soufrière Hills volcano (February 2010). Here we present high-precision double-spike Pb isotope data, combined with trace element and Sr-Nd isotope data throughout this period of Montserrat's volcanic evolution. We demonstrate that each volcanic center; South Soufrière Hills, Soufrière Hills, Centre Hills and Silver Hills, can be clearly discriminated using trace element and isotopic parameters. Variations in these parameters suggest there have been systematic and episodic changes in the subduction input. The SSH center, in particular, has a greater slab fluid signature, as indicated by low Ce/Pb, but less sediment addition than the other volcanic centers, which have higher Th/Ce. Pb isotope data from Montserrat fall along two trends, the Silver Hills, Centre Hills and Soufrière Hills lie on a general trend of the Lesser Antilles volcanics, whereas SSH volcanics define a separate trend. The Soufrière Hills and SSH volcanic centers were erupted at approximately the same time, but retain distinctive isotopic signatures, suggesting that the SSH magmas have a different source to the other volcanic centers. We hypothesize that this rapid magmatic source change is controlled by the regional transtensional regime, which allowed the SSH magma to be extracted from a shallower source. The Pb isotopes indicate an interplay between subduction derived components and a MORB-like mantle wedge influenced by a Galapagos plume-like source.

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An important issue facing Canadians today is crime control and prevention. Research done in the late 1980s and early 1990s by three sociologists shows that Canadian federal criminal justice policies and practices adopted by the Mulroney government from 1984 to 1990 were inconsistent with US ‘law and order’ models in place at that time. However, since the mid‐1990s, Canadian federal and provincial governments have mimicked some US authoritarian and gender‐blind means of curbing crime. The main objective of this paper is to provide some key examples of criminal justice policy transfer from the USA in Canada. At first glance, Canada may appear to be a ‘kinder, gentler nation,’ but not to the extent assumed by many, if not most, outside observers.

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Our Counselling and ISS team organised, in early December, 2011 a celebration of two years of art workshops and activities provided for our University post-graduate research students. The workshops had a number of benefits. They were to raise awareness of biodiversity and forests as well as providing a forum for engaging with others and an opportunity to belong to a semi-regular group. The 2010 theme had been the United Nations International Year of Biodiversity and the 2011 theme had been the United Nations International Year of Forests.

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Our Counselling and ISS team organised, in early December, 2011 a celebration of two years of art workshops and activities provided for our University post-graduate research students. The workshops had a number of benefits. They were to raise awareness of biodiversity and forests as well as providing a forum for engaging with others and an opportunity to belong to a semi-regular group. The 2010 theme had been the United Nations International Year of Biodiversity and the 2011 theme had been the United Nations International Year of Forests.

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In this paper, we address the puzzle of the relationship between age and happiness. Whilst the majority of psychologists have concluded there is not much of a relationship at all, the economic literature has unearthed a possible U-shape relationship with the minimum level of satisfaction occurring in middle age (35–50). In this paper, we look for a U-shape in three panel data sets, the German Socioeconomic Panel (GSOEP), the British Household Panel Survey (BHPS) and the Household Income Labour Dynamics Australia (HILDA). We find that the raw data mainly supports a wave-like shape that only weakly looks U-shaped for the 20–60 age range. That weak U-shape in middle age becomes more pronounced when allowing for socio-economic variables. When we then take account of selection effects via fixed-effects, however, the dominant age-effect in all three panels is a strong happiness increase around the age of 60 followed by a major decline after 75, with the U-shape in middle age disappearing such that there is almost no change in happiness between the age of 20 and 50.