525 research outputs found

    Oxygen isotope geochemistry of the second HSDP core

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    Oxygen isotope ratios were measured in olivine phenocrysts (~1 mm diameter), olivine microphenocrysts (generally ~100–200 µm diameter), glass, and/or matrix from 89 samples collected from depths down to 3079.7 m in the second, and main, HSDP core (HSDP-2). Olivine phenocrysts from 11 samples from Mauna Loa and 34 samples from the submarine section of Mauna Kea volcano have delta18O values that are similar to one another (5.11 ± 0.10‰, 1sigma, for Mauna Loa; 5.01 ± 0.07‰, for submarine Mauna Kea) and within the range of values typical of olivines from oceanic basalts (delta18O of ~5.0 to 5.2‰). In contrast, delta18O values of olivine phenocrysts from 20 samples taken from the subaerial section of Mauna Kea volcano (278 to 1037 mbsl) average 4.79 ± 0.13‰. Microphenocrysts in both the subaerial (n = 2) and submarine (n = 24) sections of Mauna Kea are on average ~0.2‰ lower in delta18O than phenocrysts within the same stratigraphic interval; those in submarine Mauna Kea lavas have an average delta18O of 4.83 ± 0.11‰. Microphenocrysts in submarine Mauna Kea lavas and phencrysts in Mauna Loa lavas are the only population of olivines considered in this study that are typically in oxygen isotope exchange equilibrium with coexisting glass or groundmass. These data confirm the previous observation that the stratigraphic boundary between Mauna Loa and Mauna Kea lavas defines a shift from “normal” to unusually low delta18O values. Significantly, they also document that the distinctive 18O-depleted character of subaerial Mauna Kea lavas is absent in phenocrysts of submarine Mauna Kea lavas. Several lines of evidence suggest that little if any of the observed variations in delta18O can be attributed to subsolidus alteration or equilibrium fractionations accompanying partial melting or crystallization. Instead, they reflect variable proportions of an 18O-depleted source component or contaminant from the lithosphere and/or volcanic edifice that is absent in or only a trace constituent of subaerial Mauna Loa lavas, a minor component of submarine Mauna Kea lavas, and a major component of subaerial Mauna Kea lavas. Relationships between the delta18O of phenocrysts, microphenocrysts, and glass or groundmass indicate that this component (when present) was added over the course of crystallization-differentiation. This process must have taken place in the lithosphere and most likely at depths of between ~5 and 15 km. We conclude that the low-delta18O component is either a contaminant from the volcanic edifice that was sampled in increasingly greater proportions as the volcano drifted off the center of the Hawaiian plume or a partial melt of low-delta18O, hydrothermally altered perdotites in the shallow Pacific lithosphere that increasingly contributed to Mauna Kea lavas near end of the volcano's shield building stage. The first of these alternatives is favored by the difference in delta18O between subaerial and submarine Mauna Kea lavas, whereas the second is favored by systematic differences in radiogenic and trace element composition between higher and lower delta18O lavas

    Bistability patterns and nonlinear switching with very high contrast ratio in a 1550 nm quantum dash semiconductor laser

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    We report on the experimental observation of optical bistability (OB) and nonlinear switching (NS) in a nanostructure laser; specifically a 1550 nm quantum dash Fabry-Perot laser subject to external optical injection and operated in reflection. Different shapes of optical bistability and nonlinear switching, anticlockwise and clockwise, with very high on-off contrast ratio (up to 180:1) between output states were experimentally measured. These results added to the potential of nanostructure lasers for enhanced performance offer promise for use in fast all-optical signal processing applications in optical networks. © 2012 American Institute of Physics

    Psychometric properties of the Persian version of the Fatigue Impact Scale (FIS-P) in patients with Multiple Sclerosis

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    Objectives: This study was designed to evaluate the psychometric features of the Persian version of the Fatigue Impact Scale (FIS-P) tool when used in Iranian MS patients. Methods: 140 MS patients and the equivalent number of healthy controls completed the following assessments: FIS-P, Fatigue Severity Scale (FSS), SF-36 questionnaire and the Mini-Mental State Examination (MMSE). Results: A significant inverse correlation between FIS and the quality of life (SF-36 assessment tool), as well as a positive and significant correlation with the FSS were noted. The Intraclass Correlation Coefficient (ICC) values for the inter-rater reliability for the physical, cognitive, and social sections and the whole questionnaire were 0.89, 0.86, 0.95 and 0.98, respectively. The FIS Persian version was shown to possess a high reliability (with a Cronbach's alpha of 0.953). Likewise, the ICC values for the testretest reliability were 0.86, 0.87, 0.92 and 0.93 for the physical, cognitive, social subscales and the whole questionnaire, respectively. This suggested a high reliability for the FIS-P. Discussion: With a proper validity and reliability, the Persian-version of FIS retains the capability for being used in the assessment of fatigue and evaluation of the treatment and rehabilitation effects on fatigue-related symptoms among Persian-speaking patients with MS

    ALMA Observations of the IRDC Clump G34.43+00.24 MM3: DNC/HNC Ratio

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    We have observed the clump G34.43+00.24 MM3 associated with an infrared dark cloud in DNC JJ=3--2, HN13^{13}C JJ=3--2, and N2_2H+^+ JJ=3--2 with the Atacama Large Millimeter/submillimeter Array (ALMA). The N2_2H+^+ emission is found to be relatively weak near the hot core and the outflows, and its distribution is clearly anti-correlated with the CS emission. This result indicates that a young outflow is interacting with cold ambient gas. The HN13^{13}C emission is compact and mostly emanates from the hot core, whereas the DNC emission is extended around the hot core. Thus, the DNC and HN13^{13}C emission traces warm regions near the protostar differently. The DNC emission is stronger than the HN13^{13}C emission toward most parts of this clump. The DNC/HNC abundance ratio averaged within a 15×1515^{\prime\prime} \times 15^{\prime\prime} area around the phase center is higher than 0.06. This ratio is much higher than the value obtained by the previous single-dish observations of DNC and HN13^{13}C JJ=1--0 (\sim0.003). It seems likely that the DNC and HNC emission observed with the single-dish telescope traces lower density envelopes, while that observed with ALMA traces higher density and highly deuterated regions. We have compared the observational results with chemical-model results in order to investigate the behavior of DNC and HNC in the dense cores. Taking these results into account, we suggest that the low DNC/HNC ratio in the high-mass sources obtained by the single-dish observations are at least partly due to the low filling factor of the high density regions.Comment: accepted to Ap
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