Sr2V3O9 and Ba2V3O9: quasi one-dimensional spin-systems with an anomalous low temperature susceptibility

The magnetic behaviour of the low-dimensional Vanadium-oxides Sr2V3O9 and Ba2V3O9 was investigated by means of magnetic susceptibility and specific heat measurements. In both compounds, the results can be very well described by an S=1/2 Heisenberg antiferromagnetic chain with an intrachain exchange of J = 82 K and J = 94 K in Sr2V3O9 and Ba2V3O9, respectively. In Sr2V3O9, antiferromagnetic ordering at T_N = 5.3 K indicate a weak interchain exchange of the order of J_perp ~ 2 K. In contrast, no evidence for magnetic order was found in Ba2V3O9 down to 0.5 K, pointing to an even smaller interchain coupling. In both compounds, we observe a pronounced Curie-like increase of the susceptibility below 30 K, which we tentatively attribute to a staggered field effect induced by the applied magnetic field. Results of LDA calculations support the quasi one-dimensional character and indicate that in Sr2V3O9, the magnetic chain is perpendicular to the structural one with the magnetic exchange being transferred through VO4 tetrahedra.Comment: Submitted to Phy. Rev.

Factors associated with serum 25-hydroxyvitamin D concentrations in older people in Europe: the EUREYE study.

BACKGROUND/OBJECTIVES: We aimed to describe serum 25-hydroxyvitamin D (25OHD) concentrations in older Europeans and to investigate associations between 25OHD and lifestyle factors, including dietary intake and supplement use. SUBJECTS/METHODS: Men and women aged ≥ 65 years were recruited from seven centres across north to south Europe. Serum 25OHD2 and 25OHD3 concentrations were measured by liquid chromatography tandem mass spectrometry (LC-MS/MS) in 4495 samples and total 25OHD (25OHD2 + 25OHD3) was adjusted for season of blood collection. RESULTS: The mean (25th, 75th quartile) of seasonally adjusted 25OHD was 46 (34, 65) nmol/L, with the highest concentration of 25OHD in Bergen [61 (49, 79) nmol/L], and the lowest in Paris [36 (24, 57) nmol/L)]. Vitamin D deficiency (25-50 nmol/L) and vitamin D insufficiency (50-75 nmol/L) were found in 41 and 33% of the population, respectively. In multivariable analysis controlled for confounders, seasonally adjusted 25OHD concentrations were significantly (p < 0.05) lower in smokers and participants with self-reported diabetes and higher with increasing dietary vitamin D, and supplement use with fish liver oil, omega-3, and vitamin D. Additionally, in further analysis excluding Bergen, 25OHD was associated with higher intakes of oily fish and increasing UVB exposure. We observed low concentrations of 25OHD in older people in Europe. CONCLUSIONS: Our findings of the higher 25OHD concentrations in supplement users (omega-3 fish oil, fish liver oil, vitamin D) add to current recommendations to reduce vitamin D deficiency. We were unable to fully assess the role of dietary vitamin D as we lacked information on vitamin D-fortified foods

Acoustic backscatter from zooplankton and fish explored through an optimized model framework

The purpose of this work has been to test complementary methods in order to classify marine organisms, with particularly attention to zooplankton and fish. Algorithms to separate fish and zooplankton have been developed and implemented at IMR and at IRD. A novel optimised model framework based on known scattering models are used to classify zooplankton and to separate these from fish. Acoustic data from up to 6 frequencies were collected to test the scattering model framework, while concurrent biological samples from multi-net oblique or horizontal MOCNESS tows, WP2 vertical net hauls and pelagic trawl were also obtained and analysed. Great attention are given on one side to the inter calibration and the comparability of all the frequencies, and to the space and time coherence between the samples collected and the acoustical data which are processed. All algorithms involve zooplankton scattering models, the high-pass ones from Stanton, or the more complex ones like the truncated fluid sphere from Holliday or the DWBA set of models from Chu and Stanton. A set of reliable acoustical and biological data has been chosen in order to proceed to comparisons between the results of the acoustic data processing through the classification algorithms and the results of the biological processing

Pressure Induced Phase Transition in PbTiO3 Studied by X-ray Absorption Spectroscopy at the Ti K edge

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An investigation into the zooplankton composition of a prominent 38-kHz scattering layer in the North Sea

This study aims to determine the contribution made by zooplankton to acoustic scattering layers, which are particularly strong at 38 kHz, in the northern North Sea in summer. It uses a combination of net sampling and forward and inverse acoustic modelling of data collected at 38, 120 and 200 kHz in July 2003. Zooplankton samples were collected from regions of strong acoustic scattering in depths to similar to 50 m, using a undulating towed (U-tow) vehicle. Acoustic data recorded simultaneously were scrutinized to determine actual backscattering, expressed as mean volume backscattering strength (MVBS) (dB). This observed MVBS (MVBSobs) was compared with backscattering predicted by application of appropriate acoustic models (MVBSpred) to sampled densities of zooplankton. In all instances, MVBSobs was greater than MVBSpred, with the difference considerably more pronounced at 38 kHz. There was a weak correlation between MVBSpred and MVBSobs at all three frequencies, with the greatest correlation (r = 0.450, P = 0.545) at 120 kHz. A number of candidate acoustic models were inverted in order to infer the most likely type of scatterer. In most cases, scatterers with a gas inclusion were predicted by this method. Potential sources of inconsistencies between MVBSpred and MVBSobs were identified which, when considered alongside the presented forward and inverse solutions, indicate that 38 kHz scattering in particular must be due to sources other than sampled zooplankton.</p

An investigation into the zooplankton composition of a prominent 38-kHz scattering layer in the North Sea

This study aims to determine the contribution made by zooplankton to acoustic scattering layers, which are particularly strong at 38 kHz, in the northern North Sea in summer. It uses a combination of net sampling and forward and inverse acoustic modelling of data collected at 38, 120 and 200 kHz in July 2003. Zooplankton samples were collected from regions of strong acoustic scattering in depths to similar to 50 m, using a undulating towed (U-tow) vehicle. Acoustic data recorded simultaneously were scrutinized to determine actual backscattering, expressed as mean volume backscattering strength (MVBS) (dB). This observed MVBS (MVBSobs) was compared with backscattering predicted by application of appropriate acoustic models (MVBSpred) to sampled densities of zooplankton. In all instances, MVBSobs was greater than MVBSpred, with the difference considerably more pronounced at 38 kHz. There was a weak correlation between MVBSpred and MVBSobs at all three frequencies, with the greatest correlation (r = 0.450, P = 0.545) at 120 kHz. A number of candidate acoustic models were inverted in order to infer the most likely type of scatterer. In most cases, scatterers with a gas inclusion were predicted by this method. Potential sources of inconsistencies between MVBSpred and MVBSobs were identified which, when considered alongside the presented forward and inverse solutions, indicate that 38 kHz scattering in particular must be due to sources other than sampled zooplankton.</p

Pressure Induced Phase Transition in PbTiO3 Studied by X-ray Absorption Spectroscopy at the Ti K edge

International audienc