The Influence of Meteorology on the Spread of Influenza: Survival Analysis of an Equine Influenza (A/H3N8) Outbreak

The influences of relative humidity and ambient temperature on the transmission of influenza A viruses have recently been established under controlled laboratory conditions. The interplay of meteorological factors during an actual influenza epidemic is less clear, and research into the contribution of wind to epidemic spread is scarce. By applying geostatistics and survival analysis to data from a large outbreak of equine influenza (A/H3N8), we quantified the association between hazard of infection and air temperature, relative humidity, rainfall, and wind velocity, whilst controlling for premises-level covariates. The pattern of disease spread in space and time was described using extraction mapping and instantaneous hazard curves. Meteorological conditions at each premises location were estimated by kriging daily meteorological data and analysed as time-lagged time-varying predictors using generalised Cox regression. Meteorological covariates time-lagged by three days were strongly associated with hazard of influenza infection, corresponding closely with the incubation period of equine influenza. Hazard of equine influenza infection was higher when relative humidity was <60% and lowest on days when daily maximum air temperature was 20–25°C. Wind speeds >30 km hour−1 from the direction of nearby infected premises were associated with increased hazard of infection. Through combining detailed influenza outbreak and meteorological data, we provide empirical evidence for the underlying environmental mechanisms that influenced the local spread of an outbreak of influenza A. Our analysis supports, and extends, the findings of studies into influenza A transmission conducted under laboratory conditions. The relationships described are of direct importance for managing disease risk during influenza outbreaks in horses, and more generally, advance our understanding of the transmission of influenza A viruses under field conditions

Sur les phases d'Aurivillius (études structurales et transitions de phases)

Les phases d'Aurivillius (Bi2O2)2+(Am-1BmO3m+l)2- sont des composés ferroélectriques, orthorhombiques à température ambiante et tétragonaux à haute température. Une étude à l'ambiante de composés dits relaxeurs montre que ces derniers sont caractérisés par une structure moyenne très peu déformée proche de la structure prototype avec un affaiblissement des liaisons Bi-O entre le bloc perovskite et la couche (Bi2O2)2+. Des cations autres que Bi3+ apparaissent présents dans cette couche. Microstructuralement, il existe des désordres impliquant des fluctuations locales de composition pouvant être à l'origine du comportement relaxeur. Une étude en température combinant plusieurs techniques permet d'obtenir des informations sur la transition de phase FE-PE et montre une grande diversité de comportement. Plus particulièrement, des monocristaux des composés SrBi2Ta2O9, SrBi2Nb2O9 et Bi4Ti2,8Cr0,2O12 sont étudiés par DRX et microcopie optique. L'utilité de ces deux techniques est discutée.Aurivillius phases, with general formula (Bi2O2)2+(Am-1BmO3m+l)2- can be ferroelectric or relaxor materials. They display orthorhombic symmetry at room temperature and tetragonal at high temperature. Structural study of ferroelectric and relaxor compounds at room temperature show that relaxors' structure is legs distorted than that of ferroelectrics. Their fluorite slabs are independent and contain non-bismuth cations. Disorder in relax ors is showed using TEM analysis. It leads to local variations of structure which can be responsible for relaxor behaviour. Phase transition study cannot be carried out systematically for such compounds. The case of SrBi2Ta2O9, SrBi2Nb2O9 and Bi4Ti2,8Cr0,2O12 is considered, and additional information is given about other Aurivillius phases.LIMOGES-BU Sciences (870852109) / SudocLIMOGES-ENSCI (870852305) / SudocSudocFranceF

Crystal structure of the Aurivillius phases in the system Bi4Ti3O12-PbTiO3

International audienceThe crystal structure of four Aurivillius phases within the pseudo-binary system Bi4Ti3O12-PbTiO3 is examined using a 3 + 1D approach where these phases are treated as commensurately modulated layered structures. The structure of PbBi4Ti4O15, Pb2Bi4Ti5O18, Pb3Bi4Ti6O21 and PbBi8Ti7O27 are refined by the Rietveld method using XRPD data from single phased powders. The structure of Pb3Bi4Ti6O21 and PbBi8Ti7O27 is reported for the first time. When the lead content increases, the structure gets less distorted and approaches the prototype paraelectric phase in an apparent close relation with the onset of a "relaxor-like" ferroelectric behaviour. For these relaxor compounds, SAED investigation evidences the existence of a disorder in the form of micro-twinning

Crystal structure of the Aurivillius phases in the system Bi4Ti3O12-PbTiO3

International audienceThe crystal structure of four Aurivillius phases within the pseudo-binary system Bi4Ti3O12-PbTiO3 is examined using a 3 + 1D approach where these phases are treated as commensurately modulated layered structures. The structure of PbBi4Ti4O15, Pb2Bi4Ti5O18, Pb3Bi4Ti6O21 and PbBi8Ti7O27 are refined by the Rietveld method using XRPD data from single phased powders. The structure of Pb3Bi4Ti6O21 and PbBi8Ti7O27 is reported for the first time. When the lead content increases, the structure gets less distorted and approaches the prototype paraelectric phase in an apparent close relation with the onset of a "relaxor-like" ferroelectric behaviour. For these relaxor compounds, SAED investigation evidences the existence of a disorder in the form of micro-twinning

Structural evolution in three and four-layer Aurivillius solid solutions: A comparative study versus relaxor properties

International audienceTwo solid solutions of three-layer BaxBi4xNbxTi3xO12 (0 x 1.2) and four-layer Aurivillius compounds (Na0.5Bi0.5)1xBaxBi4Ti4O15 (0 x 1), which both present a ferroelectric to relaxor-like transition with increasing x, were synthesized by solid state reaction. The evolution of their crystal structures, as a function of x, was performed using Rietveld refinements from X-ray powder diffraction data. As x increases, the average crystal structures become less distorted with respect to the archetypal high temperature tetragonal one and the coordination number of Bi3þ in M2O2 layers continuously changes from {4 þ 2} to {4}. The relaxor behaviour which appears in samples for a tolerance factor t > 0.96 is associated with a general static disorder in A and M sites together with the presence of some Ba2þ cations in M2O2 layers (less than 10%)

Structure versus relaxor properties in Aurivillius type compounds

International audienceStructure refinements inMIIBi4Ti4O15 (MII = Ca, Ba), Bi4−xBaxTi3−xNbxO12, (Na0.5Bi0.5)1−xBaxBi4Ti4O15 and Bi4Ti3O12–PbTiO3 systems are used to report structural features of relaxor Aurivillius phases. In compounds with relaxor-like behaviour, the average structure is almost undistorted, closed to the archetypal HT paraelectric phase, with a tolerance factor 0.996. The coordination number of Bi3+ in fluorite layers changes from {4+2} for ferroelectrics to {4} for relaxors. Transmission Electron Microscopy reveals some characteristic features of relaxors such as micro-twinning, shearing-type defects which attest from the existence of a compositional inhomogeneity and a disorder at a local scale

Structural and electrical properties of 0.57PSN-0.43PT ceramics prepared by mechanochemical synthesis and sintered at low temperature

International audienceIn this investigation we show that the dielectric, ferroelectric and piezoelectric properties of stoichiometric 0.57Pb(Sc1/2Nb1/2)O3-0.43PbTiO3 (0.57PSN-0.43PT) ceramics prepared by mechanochemical synthesis are comparable or even better than the properties of 0.57PSN-0.43PT ceramics with Nb doping, which was proposed to enhance the electrical properties. Here, the stoichiometric ceramic was sintered to 97% of theoretical density at a temperature of 1000 ◦C, which is 200-300 ◦C lower than previously reported. The dielectric constant ε, remnant polarization Pr, piezoelectric coefficient d33, coupling coefficients kp and kt and mechanical quality factor Qm of the ceramics prepared by mechanochemical synthesis were 2200, 43 C/cm2, 570 pC/N, 0.71, 0.56 and 38, respectively. The effects of the poling field on the structural and electrical properties of the 0.57PSN-0.43PT ceramics were investigated. The results show that the ratio of the monoclinic to the tetragonal phases is influenced by the application of the poling electric field. The non-poled ceramics contain 71% of the monoclinic phase and 29% of the tetragonal phase. The highest d33, kp and kt were measured for ceramics poled at an electric field of 3 kV/mm. For these poled ceramics a phase determination of 86% monoclinic phase and 14% tetragonal phase was obtained from Rietveld refinements. © 2011 Elsevie

Crystal structure and phase transitions of sodium potassium niobate perovskites

International audienceThis paper presents the crystal structure and the phase transitions of K x Na 1-x NbO 3 (0.4. X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100-800K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° °). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phaseboundary region. With increasing temperature, the samples underwent first-order monoclinictetragonal and tetragonal-cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K

Phase transition sequence in ferroelectric Aurivillius compounds investigated by single crystal X-ray diffraction

International audienceThe investigation of the phase transition sequence in SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) is reported using single-crystal X-ray diffraction. By monitoring specific reflections as a function of temperature, sensitive either to the superstructure formation or to polar displacements, it was possible to check the existence or not of an intermediate phase. This latter was confirmed in SBT, but within experimental accuracy could not be detected in SBN