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Large celestine orebodies formed by early-diagenetic replacement of gypsified stromatolites (Upper Miocene, Montevive–Escúzar deposit, Granada Basin, Spain
No full textThe Montevive and the Escúzar stratabound celestine orebodies in the Upper Miocene evaporite succession of the intramontane Granada Basin (Spain) constitute one of the largest strontium deposits in the world. Celestine occurs within a gypsum/anhydrite–halite evaporite sequence where it replaces gypsum and gypsified stromatolites preserving carbonate peloids. 87Sr/86Sr and δ34S values in the Montevive celestine deposit are close to those reported for the saline unit (Chimeneas Halite; marine to nonmarine) but higher than those of the overlying gypsum unit (Agrón Gypsum; nonmarine). 87Sr/86Sr and δ34S isotope values in the Escúzar celestine deposit match the nonmarine values recorded in the upper part of the Agrón Gypsum. The similarity in isotope values between celestine and the corresponding gypsum host in the Escúzar deposit points to early-diagenetic mineralization. According to that, both orebodies are diachronous. Gypsum pseudomorphs and molds, intraformational breccias and karst structures in these celestine deposits point to dissolved gypsum as the main sulfate source. Diagenetic–hydrothermal CaCl2 brines are interpreted to be the main strontium source. The spatial relationship between gypsified stromatolites and the ore deposits suggests the existence of coeval thermal springs related to fractures, bordering the saline lake. The proposed model envisages gypsum dissolution by SO42 −-poor and Sr2 +-rich, CaCl2 diagenetic–hydrothermal water discharging in coastal ponds at times of dry periods and low meteoric water inflow. The increase in SO42 − concentration by gypsum dissolution and the low solubility of SrSO4 would lead to celestine precipitation replacing gypsum and gypsified stromatolites. © 2014 Elsevier B.V
Validation of a numerical model used to predict phase distribution and residual stress in ferritic steel weldments
No full textNumerical finite element analyses were combined with experimental observation of a single-pass autogenous beam weld in SA508 Gr.3 Cl.1 ferritic steel. Two weldment sets were prepared using different weld heat inputs, resulting in different post-weld residual stress and ferritic phase distributions. Neutron diffraction was employed to measure the residual stress distribution while microhardness measurements were used to measure the post-weld phase distribution in each weldment. In both cases, the numerical model accurately predicts the ferritic phase distribution and residual stress field. Model predictions illustrate how the higher cooling rates associated with a faster torch speed result in an increased martensite volume fraction within the weldment. Consideration of both the transformation kinetics and transformation plasticity are proven to significantly improve model accuracy when comparing measured and predicted residual stress profiles. © 2014, Acta Materialia Inc
AFM and Ellipsometry Studies of Ultra Thin Ti Film Deposited on a Silicon Wafer
No full textAn ultra- thin Ti film with a thickness of less than 30 nm was deposited on the surface of a silicon wafer by the filtered arc deposition system. A novel technique was adopted to create a height step between the coated area and non-coated area (silicon wafer) during deposition. The surface morphology and thickness of the film was detected by atomic force microscopy (AFM). The AFM results showed that the deposited film formed a smooth structure on the silicon wafer and the height step between the coating and silicon wafer was clear enough to give the thickness of the deposited film. The composition of the deposited film was detected by a combined use of Ellipsometry and AFM. Natural oxidisation of Ti (TiO2) was found on the top of the Ti film after deposition, and the thickness of TiO2 was determined by ellipsometry to be about 0.6 nm. Trans Tech Publications. © 2014, Trans Tech Publications
Holocene changes in vegetation composition in northern Europe: why quantitative pollen-based vegetation reconstructions matter
No full textWe present pollen-based reconstructions of the spatio-temporal dynamics of northern European regional vegetation abundance through the Holocene. We apply the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using fossil pollen records from eighteen sites within five modern biomes in the region. The eighteen sites are classified into four time-trajectory types on the basis of principal components analysis of both the REVEALS-based vegetation estimates (RVs) and the pollen percentage (PPs). The four trajectory types are more clearly separated for RVs than PPs. Further, the timing of major Holocene shifts, rates of compositional change, and diversity indices (turnover and evenness) differ between RVs and PPs. The differences are due to the reduction by REVEALS of biases in fossil pollen assemblages caused by different basin size, and inter-taxonomic differences in pollen productivity and dispersal properties. For example, in comparison to the PPs, the RVs show an earlier increase in Corylus and Ulmus in the early-Holocene and a more pronounced increase in grassland and deforested areas since the mid-Holocene. The results suggest that the influence of deforestation and agricultural activities on plant composition and abundance from Neolithic times was stronger than previously inferred from PPs. Relative to PPs, RVs show a more rapid compositional change, a largest decrease in turnover, and less variable evenness in most of northern Europe since 5200 cal yr BP. All these changes are primarily related to the strong impact of human activities on the vegetation. This study demonstrates that RV-based estimates of diversity indices, timing of shifts, and rates of change in reconstructed vegetation provide new insights into the timing and magnitude of major human disturbance on Holocene regional vegetation, features that are critical in the assessment of human impact on vegetation, land-cover, biodiversity, and climate in the past. © 2014, Elsevier Ltd
Ultramicroporous MOF with high concentration of vacant CuII sites
No full textAn ultramicroporous metal–organic framework (MOF) is reported that contains 0.35 nm nanotube-like channels with an unprecedented concentration of vacant CuII coordination sites. The nonintersecting, narrow channels in [Cu3(cdm)4] (cdm = C(CN)2(CONH2)−) align in two perpendicular directions, structurally resembling copper-doped carbon nanotubes with CuII embedded in the walls of the channels. The combination of ultramicroporosity with the exposed CuII coordination sites gives size-based selectivity of CO2 over CH4, based on pore-size distribution and modeling. Neutron powder diffraction and molecular dynamics simulations show the close packing of single rows of guests within the tubular nanostructure and interaction of CO2 with the exposed metal sites. © 2014, American Chemical Society
Formation of Liquid-Crystalline Structures in the Bile Salt–Chitosan System and Triggered Release from Lamellar Phase Bile Salt–Chitosan Capsules
No full textNanostructured capsules comprised of the anionic bile salt, sodium taurodeoxycholate (STDC), and the biocompatible cationic polymer, chitosan, were prepared to assess their potential as novel tailored release nanomaterials. For comparison, a previously studied system, sodium dodecyl sulfate (SDS), and polydiallyldimethylammonium chloride (polyDADMAC) was also investigated. Crossed-polarizing light microscopy (CPLM) and small-angle X-ray scattering (SAXS) identified the presence of lamellar and hexagonal phase at the surfactant–polymer interface of the respective systems. The hydrophobic and electrostatic interactions between the oppositely charged components were studied by varying temperature and salt concentration, respectively, and were found to influence the liquid-crystalline nanostructure formed. The hexagonal phase persisted at high temperatures, however the lamellar phase structure was lost above ca. 45 °C. Both mesophases were found to dissociate upon addition of 4% NaCl solution. The rate of release of the model hydrophilic drug, Rhodamine B (RhB), from the lamellar phase significantly increased in response to changes in the solution conditions studied, suggesting that modulating the drug release from these bile salt–chitosan capsules is readily achieved. In contrast, release from the hexagonal phase capsules had no appreciable response to the stimuli applied. These findings provide a platform for these oppositely charged surfactant and polymer systems to function as stimuli-responsive or sustained-release drug delivery systems. © 2014, American Chemical Society
Direct synthesis of chromium perovskite oxyhydride with a high magnetic-transition temperature
No full textWe report a novel oxyhydride SrCrO2H directly synthesized by a high-pressure high-temperature method. Powder neutron and synchrotron X-ray diffraction revealed that this compound adopts the ideal cubic perovskite structure equation image with O2−/H− disorder. Surprisingly, despite the non-bonding nature between Cr 3d t2g orbitals and the H 1s orbital, it exhibits G-type spin ordering at TN≈380 K, which is higher than that of RCrO3 (R=rare earth) and any chromium oxides. The enhanced TN in SrCrO2H with four Cr-O-Cr bonds in comparison with RCr3+O3 with six Cr-O-Cr bonds is reasonably explained by the tolerance factor. The present result offers an effective strategy to tune octahedral tilting in perovskites and to improve physical and chemical properties through mixed anion chemistry. © 2014, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Development of a large-area silicon α-particle detector
No full textCircular ion-implanted silicon detector of α-particles with a large, 5-cm2, sensitive area has been developed. An advantage of the detector is that the detector surface is easily cleanable with chemicals. The hardened surface of the detector shows no signs of deterioration of the spectroscopic and electrical characteristics upon repeated cleaning. The energy resolution along the diameters of the detector was (1.0±0.1)% for the 5.486-MeV α-particles. Detailed tests of the charge collection efficiency and uniformity of the detector entrance window were also performed with a 5.5-MeV He2+ microbeam. © 2014, Elsevier Ltd
Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling
No full textWe present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1° × 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover–climate interactions, biodiversity and human resources. © 2014, The Author
Design and implementation of a differential scanning calorimeter for the simultaneous measurement of small angle neutron scattering
No full textFor almost 30 years, at synchrotron facilities, it has been possible to perform small-angle x-ray scattering experiments whilst simultaneously measuring differential scanning calorimetry (DSC). However, a range of challenges exist to enable the collection of simultaneous small-angle neutron scattering (SANS) and DSC data associated not only with intrinsic flux limitations but also scattering geometry and thermal control. The development of a DSC
(temperature range ca. −150 ◦C to 500 ◦C) suitable for SANS is detailed here and its
successful use is illustrated with combined measurements on a binary blend of normal alkanes in which one component has been deuterium labelled. © 2014, IOP Publishing Lt