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

Early Validation Framework for Critical and Complex Process-Centric Systems

International audienceGuaranteeing the correctness of the future system is of vital importance for the development of critical and complex systems. Rigorous software development methodologies are used for such systems, where formal methods for the verification of properties guarantee the required level of correctness. For process-centric, critical and complex systems, one needs continuous observation of the process (through simulation and visualization) both during the development for correctness and afterwards for process improvement. We present a framework with associated methodology and tools, for the development of process-centric critical and complex systems. This early validation methodology promotes formal verification of the process model alongside agent-oriented simulation and visualization of the process models in a distributed context. Moreover, the process simulation technique proposed in the methodology allows step-wise replacement of the simulated components with the actual system services. We explain the proposed methodology using an adaptation of a real-life case-study from the military sector

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

High pressure crystallographic structures of Ras give insight on high-energy states involved in interactions with regulators

CERVOXY COLLNational audienc

Partially Bounded Context-Aware Verification

International audienceModel-checking enables the formal verification of software systems. Powerful and automated, this technique suffers, however, from the state-space explosion problem because of the exponential growth in the number of states with respect to the number of interacting components. To address this problem, the Context-aware Verification (CaV) approach decomposes the verification problem using environment-based guides. This approach improves the scalability but it requires an acyclic specification of the verification guides, which are difficult to specify without losing completeness. In this paper, we present a new verification strategy that generalises CaV while ensuring the decomposability of the state-space. The approach relies on a language for the specification of the arbitrary guides, which relaxes the acyclicity requirement, and on a partially-bounded verification procedure. The effectiveness of our approach is showcased through a case-study from the aerospace domain, which shows that the scalability is maintained while easing the conception of the verification guides

X-ray absorption spectroscopy on titanate perovskites at the Ti K edge

The Ti K edge X-ray absorption has been measured under high pressure at room temperature for ATiO3 perovskites (A = Ca, Sr, Ba and Pb). The pre-edge features have been used to determine the local distortion around the Ti atom as a function of applied features. The ferroelectric local instability decreases when pressure is increased (PbTiO3 ) and eventually vanishes at high pressure (BaTiO3 ). The antiferrodistorsive instability remains unchanged under pressure for CaTiO3 and appears above 5 GPa for SrTiO3 . Moreover, it is shown that at room pressure SrTiO3 was locally ferroelectric. A new phase appears for SrTiO3 above 14 GPa with a strong deformation of the oxygen octahedron