Genesis,structural, and transport properties of La<Subscript>2</Subscript>Mo<Subscript>2-x</Subscript>W<Subscript>x</Subscript>O<Subscript>9</Subscript> prepared via mechanochemical activation

Fast oxide-ion conductors La₂Mo_2-xW_xO₉ (x = 0–1) have been prepared using mechanochemical activation (MA) of starting oxides in a high-power planetary ball mill. Studies of La₂Mo_2-xW_xO₉ genesis and structural properties using thermal analysis, XRD, SEM, IR, and Raman spectroscopy have revealed that MA results in the formation of an amorphous precursor, while the cubic β-phase is formed after calcination at 700–900 °C. Due to a high dispersion of powders, high-density pellets of W-LAMOX ceramics have been obtained already after sintering at 950 °C. Their electrical conductivity measured by the impedance spectroscopy depends on the W concentration being sufficiently high (up to 5.6?10^?3 S/cm at 630 °C) at temperatures below 650 °C.     

Properties of a Co/Cu/Co spin-valve system prepared by an optimized 193 nm pulsed laser deposition process

Layered CoO/Co(7 nm)/Cu(6 nm)/Co(7 nm) spin-valve systems capped by a 5 nm boron top layer, which exhibit giant magnetoresistance (GMR), were prepared by pulsed laser deposition (PLD) with a 193 nm ArF excimer laser. To reduce atomic intermixing at the various layer interfaces, the areal energy density of the laser was lowered to 4.2 J/cm² for the first 2 nm of the intermediate Cu and the Co top layers, while applying 11 J/cm² for the rest. By this procedure, a clear improvement of the GMR could be accomplished as compared to an identical reference system prepared by exclusively applying the high value of 11 J/cm², pointing to the importance of minimizing interface mixing.Additionally, the effect of the laser intensity on the areal density and shape of m-sized droplets co-deposited onto the substrates by PLD was studied. It turned out that for the two limiting values applied in the present case, no negative influence of the droplets on the magnetic hysteresis of pure Co layers or spin-valve systems could be observed. PACS 81.15.Fg; 75.47.Np; 75.70.Cn     

Surface properties and abhesion of undecyl oxazoline block and homopolymers

The surface properties of three undecyl oxazoline homopolymers and two phenyl/undecyl oxazoline block copolymers (as comparison) were studied. After coating on glass slides and annealing, all films had a low critical surface energy of 21 dynes/cm. Water contact angles were higher than 107° for the most hydrophobic films. The deduction that the polymer surfaces contained close-packed methyl groups was further confirmed by electron spectroscopy chemical analysis (ESCA) angle profiling on an annealed undecyl oxazoline homopolymer film. A model was developed for the variation of elemental ratios as a function of photoelectron take-off angle. This verified that the polymer films had the polymer backbones parallel to the surface with the undecyl tails oriented toward the surface. When these block and homopolymers were coated on copy paper and glass slides, the peel strengths of pressure-sensitive adhesives with these surfaces were very low for short dwell times at room temperature. At long dwell times or at elevated temperatures, the peel strengths remained low for the homopolymers but increased greatly for the block copolymers to values higher than those in the tape on glass. After 24 h at 70°C, ESCA analysis showed that the adhesive diffused into the phenyl block domains of the diblock copolymer, generating high peel strength and cohesive failure. However, under the same annealing conditions, the triblock copolymer showed adhesive failure while peel strength increased. ESCA analysis showed very litle diffusion of the adhesive into the triblock copolymer. The homopolymers were stable toward vinyl acetate type adhesives even at elevated temperature; they were abhesive up to 100°C with no interdiffusion.     

Yield ratio for the two 241Pu fission isomers in the 242(γ, n) reaction

The half-lives and yield ratios for the two ²⁴¹Pu fission isomers have been measured in the ²⁴²Pu(γ, n) reaction. The observed half-life for the long-lived isomer $\text{(T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 20.5 ± 2.2 μs)}$ is in agreement with previous data, and the existence of a short-lived 34 ± 7 ns isomer in ²⁴¹Pu could be confirmed. The measured yield ratios are Y_iso/Y_pr = (9.2 ± 0.8) × 10^?5 and Y_iso/Y_pr = (3.7 ± 0.7) × 10^?5, respectively. From a statistical model analysis of the isomeric fission yield ratio, Y^long_iso/Y^short_iso = 2.5 ± 0.6, a spin assignment for the two isomers is attempted. Possible spin combinations are compared with single-particle shell-model calculations and with available spectroscopic data for the other even-odd Pu isotopes.     

Immunochemical analysis of 3-phenoxybenzoic acid,a biomarker of forestry worker exposure to pyrethroid insecticides

Pyrethroid insecticides widely used in forestry, agricultural, industrial, and residential applications have potential for human exposure. Short sample preparation time and sensitive, economical high-throughput assays are needed for biomonitoring studies that analyze a large number of samples. An enzyme-linked immunosorbent assay (ELISA) was used for determining 3-phenoxybenzoic acid (3-PBA), a general urinary biomarker of exposure to some pyrethroid insecticides. A mixed-mode solid-phase extraction reduced interferences from acid hydrolyzed urine and gave 110 ± 6% recoveries from spiked samples. The method limit of quantification was 2 μg/L. Urine samples were collected from forestry workers that harvest pine cone seeds where pyrethroid insecticides were applied at ten different orchards. At least four samples for each worker were collected in a 1-week period. The 3-PBA in workers classified as high, low, or no exposure based on job analysis over all sampling days was 6.40 ± 9.60 (n = 200), 5.27 ± 5.39 (n = 52), and 3.56 ± 2.64 ng/mL (n = 34), respectively. Pair-wise comparison of the differences in least squares means of 3-PBA concentrations among groups only showed a significant difference between high and no exposure. Although this difference was not significant when 3-PBA excretion was normalized by creatinine excretion, the general trend was still apparent. No significant differences were observed among days or orchards. This ELISA method using a 96-well plate was performed as a high-throughput tool for analyzing around 300 urine samples measured in triplicate to provide data for workers exposure assessment.