On the Deformation of Dendrites During Directional Solidification of a Nickel-Based Superalloy

Abstract: Synchrotron X-ray imaging has been used to examine in situ the deformation of dendrites that takes place during the solidification of a nickel-based superalloy. By combining absorption and diffraction contrast imaging, deformation events could be classified by their localization and permanence. In particular, a deformation mechanism arising from thermal contraction in a temperature gradient was elucidated through digital image correlation. It was concluded that this mechanism may explain the small misorientations typically observed in single crystal castings

Exploring subsurface fluid flow and active dewatering along the oceanic plate boundary between Africa and Eurasia (Gloria Fault)

R/V Meteor cruise M162 was conducted as a systematic continuation of ongoing work dedicated to understand if and howfluid flow through crust and sedimentscontinues along transform-type plate boundaries and fracture zones away from mid-ocean ridges and continental margins. Central target was the Gloria Fault in the central Northeast Atlantic. Previous findings along the eastern continuation of the Gloria Fault revealed fault-controlled fluid advection and mud volcanism along strike-slip faults in the Horseshoe Abyssal Plain and the Gulf of Cadiz, where fluid geochemistry revealed the admixture of fluids from deeply buried oceanic crust and oldest sediments on top of it. TheGloria Fault itselfis an old, reactivated, and seismically active oceanic fracture zone. During M162 a systematic survey along the main trace of the Gloria Fault between the Azores Plateau and the Madeira-Tore Rise was carried out, including sub-bottom profiler surveys, heat flow transects, gravity corer sampling, as well as video-guided CTD and multicorer deployments. In accordance to recently recorded seismic activity along the fault, there isevidence for tectonic motion both in sub-bottom profiler records and sediment cores. Heat flow measurements revealed values significantly elevated above the background in many places, predominantly along the main fault trace and other active faults.Ina number of placesfluid geochemistry revealed enhanced diagenetic processes in the sediments, implying the potential relation to upward-directed fluid flow. In summary, cruise M162revealed the first complementary data set on heat flow and fluid geochemistry along an oceanic fault zone, which will further our understanding on themes like the alteration of oceanic lithosphere and crust-ocean element exchange

Good to be bad : should we be worried by the sharing economy?

We develop the notion of a legitimacy tipping point to demonstrate how informal economy practices are being utilized by innovative sharing economy ventures to gain a competitive advantage that is subsequently leveraged to reconfigure formal institutional arrangements. Companies who are able to scale rapidly can afford to contravene regulations, provided they have public support. When they reach a certain size, in terms of investment and customer numbers, regulators are forced into a reactive position where novel business models are legitimized. This raises an important question for regulators and entrepreneurs as to whether subverting business regulation is being viewed as a viable source of competitive advantage by scaling firms

Environmental quality standards for trace metals in the aquatic environment

The scientific basis for the regulation of metals that are potentially toxic to aquatic life is widely debated, especially with respect to bioavailability. Environmetal Quality Standards (EQSs) based on total metal concentrations and laboratory toxicity data for conditions unrepresentative of field situations, may both underprotect and overprotect. The setting of EQSs could be informed by knowledge about dose-response relationships in the field. The work described in this report was performed to attempt to establish dose-response relationships for macroinvertebrates and diatoms in streamwaters contaminated to different extents with trace metals (nickel, copper, zinc, cadmium, lead). Different possible variables were used to express metal concentrations and bioavailability. The results obtained were then used to evaluate different approaches to EQS setting. We carried out field studies of the ecology and chemistry of upland streams, influenced by past mining activity. We conducted field sampling and performed analyses at carefully-chosen field sites, and analysed the data to attempt to establish quantitative relationships between the chemical and ecological variables. The chosen sites were perceived to have several advantages, notably similarity in their physical characteristics, appreciable ranges of water and metal chemistries, and the absence of other pollutants. Therefore they made it possible to explore the effects of differences in streamwater chemistry on ecological response, with few confounding factors. The ecological part of the field work was conducted in Spring 2006, and comprised sampling and enumeration of benthic invertebrates and diatoms. Chemical characterisation of the streamwaters was achieved by repeated sampling during the 6 weeks before the ecological fieldwork. As well as carrying out conventional chemical analyses, we also used analytical speciation techniques (Diffusive Gradients in Thin films, DGT, and the Donnan Membrane Technique, DMT), and applied the WHAM chemical speciation model to calculate free metal ion activities and other variables. We collected separate samples of key invertebrate taxa and analysed them for metal body burdens, and we collected samples of stream bryophytes and analysed them for metals. In another supporting study, we collected water samples from the study sites and used them in laboratory toxicity experiments with an algal and a daphnid species. We carried out a literature review of metal mixture effects, to aid interpretation of field data from those sites (the majority) where more than one metal may exert a toxic effect. We also reviewed methods for setting EQSs. The chemical compositions of the study streams covered appreciable ranges of acidity, alkalinity, total ionic concentration and DOC concentration. The nutrient concentrations were sufficiently low for there to be negligible effects on either macroinvertebrates or diatoms. Suspended particulate matter concentrations were in the range 0 - 50 mg l-1. As expected because of the historical mining activities, most of the streamwaters were contaminated with trace metals, at levels exceeding EQS values. The study sites included several acid streamwaters, some of which were contaminated with trace metals, but all of which had high levels of aluminium. The results of DGT and DMT measurements, and of chemical speciation calculations, indicated that zinc and cadmium are present largely in inorganic forms in the streamwaters, whereas there was appreciable organic complexation of aluminium, copper and lead, and to a lesser extent nickel. The metal contents of both bryophytes and macroinvertebrates varied considerably with streamwater chemistry. The metal contents of both types of organism were approximately predictable using chemical speciation concepts, which is direct evidence that biota respond to the chemistry of the medium. Analysis of the relationships between ecological and chemical variables, and of the results of the laboratory toxicity measurements, led to the following conclusions. 1. Toxic metals were demonstrated to reduce species numbers of both macroinvertebrates and diatoms in the field. 2. Laboratory tests confirmed that 8 of the streamwaters in which field effects were observed contained metals at toxic concentrations. 3. The macroinvertebrate community provides an effective and sensitive tool for detecting metal toxicity. In the study sites, toxicity could be attributed definitely to Al and Zn, and there was some evidence of toxic effects due to H+ and Cu. 4. For diatoms, which were less sensitive than macroinvertebrates, the most likely toxicant was zinc, but cadmium may also have been active. 5. A function combining free metal ion concentrations and pH provided the best solution-based measure of metal toxicity towards macroinvertebrates, because it accounted best for aluminium effects. 6. Toxicity towards diatoms was expressed best, in terms of solution concentrations, by either total dissolved metal concentration or the metal concentration measured by DGT. 7. The field data permitted the formulation and partial parameterisation of the Toxicity Binding Model (TBM), which is based on Biotic Ligand Model principles, but applicable to mixtures of metals. The model permits clear toxicity thresholds to be identified, and quantifies the contributions of different metals to the overall toxicity. 8. Because of the dominant effect of zinc, among the trace metals, the available data did not permit conclusions to be drawn about the effect of chemical speciation on copper or lead toxicity. However, the finding that aluminium effects are best expressed in terms of the free ion, and the promising results from the TBM, imply that speciation-based measures provide the best way to describe the toxic effects of metals in the field. We considered the implications of the results of this work in the assessment and setting of Environmental Quality Standards for metals in freshwaters. The following points can be made. A. The results of the present study add significant weight to the use of bioavailability and chemical speciation in deriving EQSs. B. A full assessment of the effects of toxic metals in contemporary waters requires knowledge about past “pristine” conditions. In the contaminated streamwaters of the present study, dissolved concentrations of trace metals were considerably higher (by 10 to 1000 times) than those estimated for similar uncontaminated sites under pristine conditions. As well as solution concentrations, calculated loadings of biotic ligands with toxic metals can be compared, and when this is done with the TBM it appears that at present-day uncontaminated sites the loadings can be substantial, not much lower than threshold values. C. If bioavailability and chemical speciation are to be used in EQS setting, the biotic ligand approach is currently the best way forward. Although its application relies on calculations, the chemical speciation results can be tested with in situ analytical devices (DGT and DMT), lending robustness to the method. D. There may be regulatory advantages to confining EQS setting to individual metals. However, the results of the present study suggest a significant role of “natural” Al in field toxicity, and this implies that the issue of mixtures should be addressed. This can be done using biotic ligand concepts. E. By showing that metal toxicity operates in the field, with dose-response relationships, and in line with bioavailability and chemical speciation concepts, the study provides support for metals regulation through EQSs. It further shows that targeted fieldwork can provide the information necessary for EQS evaluation and modification

In Situ Speciation Measurements of Trace Metals in Headwater Streams

Concentrations of Al, Fe, Mn, Ni, Cu, Cd, Pb, and Zn were measured using DGT (diffusive gradients in thin-films) devices deployed in situ in 34 headwater streams in Northern England. Mean values of filtered samples analyzed by ICP-MS (inductively coupled plasma mass spectrometry) were used, along with DOC (dissolved organic carbon), pH and major ions, to calculate the distribution of metal species using the speciation code WHAM. DGT-measured concentrations, [Me]DGT, of Zn and Cd were generally similar to concentrations in filtered samples, [Me]filt. For the other metals, [Me]DGT was similar to or lower than [Me]filt. Calculation of the maximum dynamic metal from the speciation predicted using WHAM showed that most of the lower values of [Cu]DGT could be attributed to the dominance of Cu−fulvic acid complexes, which diffuse more slowly than simple inorganic species. Similar calculations for Al, Pb, and Mn were consistent with appreciable proportions of these metals being present as colloids that are not simple complexes with humic substances. Differences between WHAM predictions and the measured [Ni]DGT indicated that WHAM used with the default binding parameters underestimates Ni binding to natural organic matter. Plots of [Me]DGT versus the ratio of bound metal to DOC provided slight evidence of heterogeneous binding of Pb and Cu, while results for Mn, Cd, and Zn were consistent with weak binding and complete lability

High-resolution analysis of polyacrylamide gels for trace metals in two dimensions using diffusive gradients in thin-films (DGT) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

A simple method for the analysis of polyacrylamide diffusive gradients in thin film (DGT) gels by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), employing a novel use of 115In internal standardization, has been developed. This method allows the determination of Co, Ni, Cu, Zn, Cd, and Pb concentrations (at the DGT filter face) or fluxes in sediments at a spatial resolution of 100 μm. Single-layered gels, using an optimized laser defocus of 4000 μm at 400 mJ power, showed high precision (generally 10%) and a linear response during solution deployment. Of the elements Sc, In, Ba, La, Ce, and Tb, Ba most closely tracked variations in laser energy and showed the highest analytical precision but could not be used as an internal standard due to its elevated presence in natural sediments. Therefore, internal standardization, necessary to normalize data collected on different days, was carried out using 115In contained within a second layer of backing gel and dried along with the analyte layer as a dual-gel disk. This multilayered gel standard required a laser defocus setting of 1000 μm and a laser power of 800 mJ. Analytical precision for a 64-spot ablation grid at 100-μm spacing was 10%. Verification of this method was carried out on DGT sediment probes deployed in Priest Pot (English Lake District). Results obtained by conventional slicing techniques and aqueous elution agreed with laser ablation results when the different sampling areas were considered. The elution results varied by a factor of <2, whereas the laser ablation technique showed a variability of 4, indicating localized elevated concentrations of Co. This higher resolution LA-ICPMS method could ultimately lead to an improved understanding of the geochemical processes responsible for metal uptake and release in sediments

Interpretation of in situ speciation measurements of inorganic and organically complexed trace metals in freshwater by DGT

The dynamic speciation technique, diffusive gradients in thin-films (DGT), has been used in freshwater to determine simultaneously, from a single set of in situ measurements, (1) the equilibrium distribution of metal ions between simple inorganic complexes and larger organic complexes and (2) information on the rates of dissociation of these complexes. DGT devices with different diffusion layer thicknesses (0.3, 0.54, 1.34, and 2.14 mm) were used to estimate the in situ dissociation kinetics. Information on the species distribution was obtained by using two types of gel, which allow relatively free (polyacrylamide, APA) and more retarded (restricted, RES) diffusion of the metal complexes. The full theoretical basis of the technique is developed and applied to in situ measurements of Mn, Fe, Co, Ni, Cu, Cd, and Pb in a pristine river (Wyre, U.K.), with high DOC(15mg L(-1)), assuming that organic complexes are dominated by fulvic acid. These first DGT measurements that do not rely on assumptions about complex lability or the distribution of species, are compared to total dissolved measurements, previously reported speciation calculations and measurements using alternative speciation techniques. Examination of calculation consistency suggests that the effective mean diffusion coefficients of metal complexes with organic matter under in situ conditions may be larger than those measured in the laboratory using extracted fulvic acid

The beta(2)-subtype of adrenoceptors mediates inhibition of pro-fibrotic events in human lung fibroblasts

Fibrosis is part of airway remodelling observed in bronchial asthma and COPD. Pro-fibrotic activity of lung fibroblasts may be suppressed by beta-adrenoceptor activation. We aimed, first, to characterise the expression pattern of beta-adrenoceptor subtypes in human lung fibroblasts and, second, to probe beta-adrenoceptor signalling with an emphasis on anti-fibrotic actions. Using reverse transcription PCR, messenger RNA (mRNA) encoding beta(2)-adrenoceptors was detected in MRC-5, HEL-299 and primary human lung fibroblasts, whereas transcripts for beta(1)- and beta(3)-adrenoceptors were not found. Real-time measurement of dynamic mass redistribution in MRC-5 cells revealed beta-agonist-induced G(s)-signalling. Proliferation of MRC-5 cells (determined by [H-3]-thymidine incorporation) was significantly inhibited by beta-agonists including the beta(2)-selective agonist formoterol (-logIC(50), 10.2) and olodaterol (-logIC(50), 10.6). Formoterol's effect was insensitive to beta(1)-antagonism (GCP 20712, 3 mu M), but sensitive to beta(2)-antagonism (ICI 118,551; apparent, pA (2), 9.6). Collagen synthesis in MRC-5 cells (determined by [H-3]-proline incorporation) was inhibited by beta-agonists including formoterol (-logIC(50), 10.0) and olodaterol (-logIC(50), 10.3) in a beta(2)-blocker-sensitive manner. alpha-Smooth muscle actin, a marker of myo-fibroblast differentiation, was down-regulated at the mRNA and the protein level by about 50% following 24 and 48 h exposure to 1 nM formoterol, a maximally active concentration. In conclusion, human lung fibroblasts exclusively express beta(2)-adrenoceptors and these mediate inhibition of various markers of pro-fibrotic cellular activity. Under clinical conditions, anti-fibrotic actions may accompany the therapeutic effect of long-term beta(2)-agonist treatment of bronchial asthma and COPD