sensing characteristics of hematite and barium oxide doped hematite films towards ozone and nitrogen dioxide

Abstract Hematite (α-Fe2O3) and barium oxide doped hematite (BaO-Fe 2 O 3 ) thin films were investigated as ozone (O 3 ) and nitrogen dioxide (NO 2 ) sensing materials. Fe 2 O 3 and BaO-Fe 2 O 3 films were deposited by radio- frequency sputtering using pure Fe 2 O 3 , and 1-2% BaO doped Fe 2 O 3 targets. The 700 °C (1 hour) annealed films showed significant responses to O 3 at temperatures ranging from 150 °C to 300 °C. Although, hematite is an n-type semiconductor, the Fe 2 O 3 and BaO-Fe 2 O 3 films exhibit p-type behavior to O 3 and n- type behavior to NO 2 at the studied concentration ranges in this work. The response to oxidizing gases is not strictly an increase in resistance due to a conversion from n-type to p-type depending on gas concentrations. This effect is more visible with increasing Ba concentration

Local shell-to-shell energy transfer via nonlocal Interactions in fluid turbulence

In this paper we analytically compute the strength of nonlinear interactions in a triad, and the energy exchanges between wavenumber shells in incompressible fluid turbulence. The computation has been done using first-order perturbative field theory. In three dimension, magnitude of triad interactions is large for nonlocal triads, and small for local triads. However, the shell-to-shell energy transfer rate is found to be local and forward. This result is due to the fact that the nonlocal triads occupy much less Fourier space volume than the local ones. The analytical results on three-dimensional shell-to-shell energy transfer match with their numerical counterparts. In two-dimensional turbulence, the energy transfer rates to the near-by shells are forward, but to the distant shells are backward; the cumulative effect is an inverse cascade of energy.Comment: 10 pages, Revtex

Comparaison du taux cellulaire et de la sensibilité antimicrobienne des germes responsables de mammite subclinique bovine entre les filières conventionnelle et biologique

A comparison of somatic cell count and antimicrobial susceptibility of subclinical mastitis pathogens in organic and conventional dairy herds.Bovine subclinical mastitis is the most important disease affecting dairy cows. The fluctuating increase in somatic cell count (SCC) that occurs causes major economic losses in dairy industry. This comparative study between conventional and organic dairy herds was conducted in the aim to better characterize which consequences might have different management practices on SCC but also on the frequency of pathogens isolated and their antimicrobial susceptibility. Four conventional and four organic herds, with bulk milk SCC >300x103cells/ml were selected, in which respectively 47 and 44 cows were investigated. Each quarter was sampled 3 times at 15 days interval for SCC, microbiological analysis and antimicrobial susceptibility. In both herd categories, major pathogens isolated were by order of importance Streptococcus uberis, Staphylococcus aureus and Streptococcus dysgalactiae with a great impact on SCC. Coagulase negative staphylococci were the most frequent minor germs and had a moderated but real impact on SCC. In certified organic dairy farms, the three most frequently isolated major pathogens were significantly more susceptible to antimicrobials in vitro. This study suggests that the limited use of antibiotics in organic dairy herds could explain, at least in part, the lower resistance obtained from analysed isolates.La mammite subclinique est une pathologie de première importance chez la vache laitière. L’élévation persistante du taux cellulaire qui en résulte engendre d’énormes pertes économiques pour toute la filière laitière. L’objectif de cette étude était de comparer les filières conventionnelle et biologique afin de déterminer les conséquences que des pratiques d’élevage différentes peuvent avoir sur les taux cellulaires ainsi que sur la fréquence des germes isolés et leur sensibilité aux antibiotiques. Quatre exploitations laitières conventionnelles et 4 biologiques avec des taux cellulaires de lait de tank >300x103 cellules/ml ont été sélectionnées, parmi lesquelles 47 et 44 vaches respectivement ont été investiguées. Chaque quartier a été prélevé 3 fois à 15 jours d’intervalle pour les analyses cellulaires, bactériologiques et de sensibilité aux antibiotiques. Quelle que soit la filière, les germes majeurs rencontrés étaient par ordre d’importance Streptococcus uberis, Staphylococcus aureus et Streptococcus dysgalactiae et leur impact sur le taux cellulaire était très important. Les staphylocoques coagulase négative étaient les germes mineurs les plus fréquents et avaient un impact sur le taux cellulaire non négligeable. La sensibilité moyenne aux antibiotiques testés in vitro était significativement plus élevée en filière biologique pour les trois germes majeurs les plus fréquemment rencontrés. Cette étude suggère que l’usage moins abondant des antimicrobiens dans les exploitations biologiques sélectionnées pourrait expliquer, du moins en partie, les moindres taux d’antibiorésistance retrouvés

Formaldehyde gas sensor based on nanostructured nickel oxide and the microstructure effects on its response

NiO nanostructures can be used as a promising material for semiconductor gas sensor to detect formaldehyde at low concentrations (< 1 ppm). Here, the effect of the morphology of the synthesized NiO nanostructures on gas sensing properties is studied and discussed. NiO nanostructures have been synthesized by thermal decomposition of precursors obtained by two different chemical precipitation methods and a sol-gel technique. Thick films of the synthesized NiO nanostructures were deposited by spray coating on alumina substrates fitted with gold interdigitated electrodes and a platinum heater. The gas sensing properties of those NiO films were studied for low concentrations of formaldehyde gas at different working temperatures. A clear difference in response characteristics was observed between the samples prepared by different synthesis routes

Plasmon-enhanced tilted fiber Bragg gratings with oriented silver nanowire coatings

(TFBG) covered by silver nanowires aligned perpendicularly to the fiber axis. TBFGs are a convenient way to measure surrounding refractive index, as they provide intrinsic temperature-insensitivity and preserve the optical fiber structural integrity. With bare TFBGs, sensitivity is about 60 nm/RIU (refractive index unit) while when coated with a gold thin film, surface plasmon resonance can be excited leading to a sensitivity about 600 nm/RIU. In our case, we show that localized plasmon resonances can be excited on silver nanowires. These nanowires (100 nm diameter and about 2.5 μm length) were synthetized by polyol process (ethylene glycol reducing silver nitrate in the presence of poly (vinyl pyrrolidone and sodium chloride). The nanowires were aligned and deposited perpendicularly to the fiber axis on the gratings using the Langmuir-Blodgett technique in order to maximise the coupling between azimuthally polarized light modes and the localized plasmons. Excitation of surface plasmons at wavelengths around 1.5 μm occurred, leading to a dip in the polarization dependent losses of the grating. This dip is highly dependent of the surrounding refractive index, leading to a sensitivity of 650 nm/RIU, which is a 10-fold increase compared to bare gratings. We obtain results equal or slightly higher than those obtained using a gold layer on TFBGs. In spite of the comparable bulk refractometric sensitivity, the use of these oriented nanowire layers provide significantly higher contact surface area for biochemical analysis using bioreceptors, and benefit from stronger polarization selectivity between azimuthal and radially polarized modes

Surface plasmon resonances in oriented silver nanowire coatings on optical fibers

Silver nanowires 1-3 μm in length and diameters of 0.04-0.05 μm were synthesized by a polyol process and deposited on a single mode optical fiber with the Langmuir-Blodgett technique. For nanowire surface coverage of ∼40% and partial orientation of their long axis obtained by controlling the deposition parameters, the optical properties of the nanowire coating become identical to those of a uniform metal coating obtained by sputtering or evaporation. Excitation of the nanowires by the polarized evanescent field of fiber cladding modes at near-infrared wavelengths near 1.5 μm results in surface plasmon-like resonances in the transmission spectrum of the optical fiber. The polarization-dependent loss (PDL) spectrum of the tilted fiber Bragg grating used to excite the cladding modes shows a pronounced characteristic dip indicative of a plasmon resonance for radially polarized light waves and complete shielding of light for azimuthally polarized light. The PDL dip shifts at a rate of 650 nm/(refractive index unit) when the surrounding refractive index is changed, a 10-fold increase compared to uncoated fiber gratings and similar to that of uniform metal coated gratings. The advantage of the nanowire approach is to provide a much increased contact surface area for biomolecular recognition-based immunosensing

Co-precipitation synthesis by malonate route, structural characterization and gas sensing properties of Zn-doped NiO

Zn-doped NiO powders have been prepared via pyrolysis at 500°C of zinc-nickel malonate precursors prepared by co-precipitation using different molar ratios of Zn/Ni (0.01 - 0.04 and 0.1). Structural characterization of the powders was performed by X-ray powder Diffraction (XRD) and Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS). The results confirm that a single phase of Ni1-xZnxO (x=0.01-0.04, 0.1) is formed. Electrical measurements reveal that its activation energy decreases with increasing amount of Zn. Gas-sensing measurements reveal that the optimal operating temperature is 300 °C and that the use of 2 % Zn as a dopant improved the gas-sensing properties