62 research outputs found
Natural and released inoculum levels of entomopathogenic fungal biocontrol agents in soil in relation to risk assessment and in accordance with EU regulations
Coherent matter wave inertial sensors for precision measurements in space
We analyze the advantages of using ultra-cold coherent sources of atoms for
matter-wave interferometry in space. We present a proof-of-principle experiment
that is based on an analysis of the results previously published in [Richard et
al., Phys. Rev. Lett., 91, 010405 (2003)] from which we extract the ratio h/m
for 87Rb. This measurement shows that a limitation in accuracy arises due to
atomic interactions within the Bose-Einstein condensate
Assessing the mechanisms of common Pb incorporation into titanite
Common Pb, the portion of non-radiogenic Pb within a U bearing mineral, needs to be accurately accounted for in order to subtract its effect on U-Pb isotopic ratios so that meaningful ages can be calculated. The propensity to accommodate common Pb during crystallization, or later, is different across the range of U bearing minerals used for geochronology. Titanite frequently accommodates significant amounts of common Pb. However, the most appropriate method to correct for this requires knowledge on the mechanism and timing of common Pb incorporation; information that is commonly difficult to extract. In this study, the spatial and compositional distribution of trace elements (including Pb) in metamorphic titanites from a Greenland amphibolite is investigated on the grain- to nano-scale. Titanites have an isotopically similar signature for both common and radiogenic-Pb in all grains but significantly different quantities of the non-radiogenic component. Microstructural and compositional examination of these grains reveals undeformed, but high common Pb (F207%) titanites have homogeneous element distributions on the atomic scale suggesting common Pb is incorporated into titanite during its growth and not during later processes. In contrast, deformed titanite comprising low-angle boundaries, formed by subgrain rotation recrystallization, comprise networks of dislocations that are enriched in Mg, Al, K and Fe. Smaller cations may migrate due to elastic strain in the vicinity of the dislocation network, yet the larger K cations more likely reflect the mobility of externally-derived K along the orien tation interface. The absence of Pb enrichment along the boundary indicates that either Pb was too large to fit into migrating lattice dislocations or static low-angle boundaries and/or that there was no external Pb available to diffuse along the grain boundary. As the common Pb composition is distinctly different to regional Pb models, the metamorphic titanite grew in a homogeneous Pb reservoir dominated by the break-down of precursor U-bearing phases. The different quantity of common Pb in the titanite grains indicates a mineral-driven element partitioning in an isotopically homogeneous metamorphic reservoir, consistent with low U, low total REE and flat LREE signatures in high F207% analyses. These results have implications for the selection of appropriate common Pb corrections in titanite and other accessory phases
Cichlid biogeography: comment and review
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72313/1/j.1467-2979.2004.00148.x.pd
Poly(styrene-b-isobutylene-b-styrene) Block Copolymers Produced by Living Cationic Polymerization. Part III. Dynamic Mechanical and Tensile Properties of Block Copolymers and Ionomers Therefrom
Poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymers prepared by living carbocationic polymerization and ionomers therefrom were analyzed using dynamic mechanical analysis (DMA) and tensile testing. The study encompassed five block copolymer samples, each with a PIE center block of approximately 52,000 g/mol, and PS weight fractions ranging from 0.127 to 0.337. Ionomers were prepared from two of these materials by lightly sulfonating the PS outer blocks. Sulfonation levels varied from 1.7 to 4.7 mol% and the sodium and potassium neutralized forms were compared to the parent block copolymers. DMA of the block copolymer films indicated the existence of a third phase attributed to PIE chains near the PS domain interface which experience reduced mobility due to their firm attachment to the hard PS domain. The relative amount of this phase decreased in samples with larger PS blocks, while the temperature of the associated transition increased. Tensile testing showed increased tensile strength but decreased elongation at break with larger PS blocks. DMA of the ionomers indicated improved dynamic modulus at temperatures above 90 degreesC. Tensile testing of the ionomers indicated slight improvements in tensile strength with little loss in elongation at break. (C) 2000 Elsevier Science Ltd. All rights reserved
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Crystallisation ages in coeval silicic magma bodies: 238U-230Th disequilibrium evidence from the Rotoiti and Earthquake Flat eruption deposits, Taupo Volcanic Zone, New Zealand
The timescales over which moderate to large bodies of silicic magma are generated and stored are addressed here by studies of two geographically adjacent, successive eruption deposits in the Taupo Volcanic Zone, New Zealand. The earlier, caldera-forming Rotoiti eruption (>100 km3 magma) at Okataina volcano was followed, within months at most, by the Earthquake Flat eruption (10 km3 magma) from nearby Kapenga volcano; both generated non-welded ignimbrite and coeval widespread fall deposits. The Rotoiti and Earthquake Flat deposits are both crystal-rich high-silica rhyolites, with sparse glass-bearing granitoid fragments also occurring in Rotoiti lag breccias generated during caldera collapse. Here we report 238Uâ230Th disequilibrium data on whole rocks and mineral separates from representative Rotoiti and Earthquake Flat pumices and the co-eruptive Rotoiti granitoid fragments using TIMS and in situ zircon analyses by SIMS. Multiple-grain zircon-controlled crystallisation ages measured by TIMS from the Rotoiti pumice range from 69±3 ka (350 ka, with a pronounced peak at 70â90 ka. The weighted mean of isochrons is 83±14 ka, in accord with the TIMS data. One glass-bearing Rotoiti granitoid clast yielded an age of 57±8 ka by TIMS (controlled by Th-rich phases that, however, are not apparently present in the juvenile pumices). Another glass-bearing Rotoiti granitoid yielded SIMS zircon model ages peaking at 60â90 ka, having a similar age distribution to the pumice. Age data from pumices are consistent with a published 64±4 ka eruptive age (now modified to 62±2 ka), but chemical and/or mineralogical data imply that the granitoid lithics are not largely crystalline Rotoiti rhyolite, but instead represent contemporaneous partly molten intrusions reflecting different sources in their chemistries and mineralogies. Similarly, although the Earthquake Flat eruption immediately followed (and probably was triggered by) the Rotoiti event, age data from juvenile material are significantly different. A multiple-grain zircon-controlled crystallisation age measured by TIMS from a representative pumice is 173±5 ka, while SIMS model ages range from 70â26+34 ka to >350 ka, with a peak at 105 ka. These age data coupled with previously published geochemical and isotopic data show that the Rotoiti and Earthquake Flat deposits were erupted from independent, unconnected magma bodies
Poly(styrene-b-isobutylene-b-styrene) Block Copolymers and Ionomers Therefrom: Morphology as Determined by Small-Angle X-Ray Scattering and Transmission Electron Microscopy
Solvent-cast films of poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymers and block ionomers were analyzed using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Four block copolymer samples with center block molecular weights of 52,000 g mol(-1) and PS volume fractions (phi(PS)) ranging from 0.17 to 0.31 were studied. Block ionomers were produced by lightly sulfonating the PS outer blocks of the PS-PIB-PS block copolymers. Sulfonation levels were 1.5 and 3.4 mol%, and sodium and potassium counterions were studied. All samples exhibited hexagonally packed cylinders of PS within the PIE matrix. Cylinder spacing was in the range 32-36 nm for most samples, while cylinder diameters varied from 14 to 21 nm. Pored analysis of the scattering data indicated the presence of isolated phase mixing and sharp phase boundaries. (C) 2000 Elsevier Science Ltd. All rights reserved
Poly(styrene-b-isobutylene-b-styrene) Block Copolymers Produced by Living Cationic Polymerization - I. Compositional Analysis
Poly(styrene-b-isobutylene-b-styrene) block copolymers made through controlled-living cationic polymerization using the Bu-t-m-DCC-TiCl4 initiating system in 60/40 (v/v) hexane-methyl chloride cosolvents were analyzed using curve-resolution software in conjunction with high-resolution g.p.c. Fractional precipitation and selective solvent extraction were applied to a representative sample in order to confirm the identity of contaminating species. The block copolymers were found to consist of 70-75 wt% of the target molecule, and about 20 wt% of coupled (and higher Linked) block copolymers formed by intermolecular electrophilic aromatic substitution linking reactions occurring during the styrene polymerization. Minor contaminants were identified as diblock copolymer and low molecular weight polystyrene homopolymer. (C) 1999 Elsevier Science Ltd. All rights reserved
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