Oxygen isotope geochemistry of the second HSDP core

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

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

Evidence of a possible reversion of the geomagnetic field registered during the late holocene in the province of Chubut, Argentina

Paleomagnetic studies were carried out on sediments sampled at an archaeological excavation sited on Angostura Blanca, Piedra Parada Valley, Province of Chubut (42°30'S, 69°42'W). The archaeological traces show the occupation of the site during the late holocene; this is confirmed by the C1 dating of sanóles obtained on the site (2140+50 years). The usual laboratory techniques for paleomagnetic studies were applied to isolate the directions of the stable remanent magnetization (measurements of natural remanent magnetization, demagnetization by increasing temperatures, measurements of residual remanent magnetization after each step of demagnetization). Using the isolated directions, which represent the directions of the geomagnetic field during the deposition and consolidation of the sediments, the virtual geomagnetic poles were obtained. The analysis of the results shows evidence of a possible record of a reversed polarity event on the studied sediments. This conclusion, if it is confirmed by other paleomagnetic data, would agree with the existence of the Etrussia excursion, recorded in Russia, on sediments of about 2700 years.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

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

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