Anodic dissolution of metals in oxide-free cryolite melts

The anodic behavior of metals in molten cryolite-alumina melts has been investigated mostly for use as inert anodes for the Hall-Héroult process. In the present work, gold, platinum, palladium, copper, tungsten, nickel, cobalt and iron metal electrodes were anodically polarized in an oxide-free cryolite melt (11%wt. excess AlF3 ; 5%wt. CaF2) at 1273 K. The aim of the experiments was to characterize the oxidation reactions of the metals occurring without the effect of oxygen-containing dissolved species. The anodic dissolution of each metal was demonstrated, and electrochemical reactions were assigned using reversible potential calculation. The relative stability of metals as well as the possibility of generating pure fluorine is discussed

Electrochemical oxidation of binary copper-nickel alloys in cryolite melts

Anodic oxidation of copper, nickel and two copper-nickel alloys was studied in cryolite melts at 1000°C. In an oxide-free melt, anodic dissolution of each material was observed, and the dissolution potential increases with the content of copper. SEM characterization of a Cu55-Ni45 alloy showed that nickel is selectively dissolved according to a de-alloying process. In an alumina-containing melt, a partial passivation occurs at the copper-containing electrodes, at potentials below the oxygen evolution potential. A passive film forms on the copper electrode, while on the nickel electrode no dense oxide layer develops. Copper-nickel alloys were found to form a mixed oxide layer. At higher potentials, the formation of oxygen bubbles on the electrodes results in a degradation of the passive films and a strong corrosion

First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017

In the first spectroscopic campaign for a PG 1716 variable (or long-period pulsating subdwarf B star), we succeeded in detecting velocity variations due to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained during 40 nights on 2-m class telescopes in Arizona, South Africa,and Australia. The target,PG1627+017, is one of the brightest and largest amplitude stars in its class.It is also the visible component of a post-common envelope binary.Our final radial velocity data set includes 84 hours of time-series spectroscopy over a time baseline of 53 days. Our derived radial velocity amplitude spectrum, after subtracting the orbital motion, shows three potential pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and 7037.3s.Only one of the features is statistically likely to be real,but all three are tantalizingly close to, or a one day alias of, the three strongest periodicities found in the concurrent photometric campaign. We further attempted to detect pulsational variations in the Balmer line amplitudes. The single detected periodicity of 7209 s, although weak, is consistent with theoretical expectations as a function of wavelength.Furthermore, it allows us to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme weakness of g-mode pulsations in these stars,we conclude that anything beyond simply detecting their presence will require larger telescopes,higher efficiency spectral monitoring over longer time baselines,improved longitude coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full abtrac

Implications of climate change for ecological reference conditions, thresholds and classification systems for European lakes

This report focuses on potential effects of climate change on ecological reference conditions and on ecological responses to nutrient pressures in lakes, especially threshold-type and non-linear responses. Reference conditions and thresholds responses are both fundamental for na-tional ecological classification systems according to the European Water Framework Direc-tive (WFD), for defining reference values and management targets (Good/Moderate class boundary) respectively. Effects of climate change on these components therefore have impor-tant implications for assessment of ecological status and management of lakes. We have addressed the effects of climate change on lakes by an extensive literature review, as well as by analysing palaeolimnological datasets, large-scale European datasets and long-term time series for four individual lakes in Norway, Estonia and Germany (case studies). The cli-matic changes considered include increased temperature, increased precipitation (and conse-quently increased content of organic matter) and reduced precipitation (and consequently re-duced water levels and increased salinity). The literature review describes effects of climate change on reference conditions for each biological quality element (BQE; phytoplankton, macrophytes, macroinvertebrates and fish); of these phytoplankton and fish tend to be most sensitive to climate change. Results from new palaeolimnological analyses suggest that nutrients are the dominant driver of diatom compositional change, and there is insufficient evidence to suggest how reference conditions should be modified in light of climate change. Nonetheless further work is required to explore the relationship between diatoms and climate change in more detail. Analysis of chlorophyll a (chl-a) in European reference lakes suggest that under future climatic condi-tions, increased temperature in combination with increased TP (due to increased winter pre-cipitation) will lead to increased chl-a concentrations, although the effects will vary with the lake type (notably the humic level). Large-scale analysis of cyanobacteria in North-European lakes, considering both lake typology and climatic variables, suggest that the risk of exceed-ing regulatory thresholds for cyanobacteria will increase with future higher temperature, but also that this tendency to some degree might be compensated by increased precipitation. The four case studies provide more detailed examples of interactions between climatic factors and nutrient pressures on plankton communities, and demonstrate some of the complexity in-volved in ecological responses to climate change in lakes. Finally, the report provides a set of recommendations for river basin management, considering impacts of climate change on ref-erence conditions and ecological thresholds, and the implications for WFD-based classifica-tion systems

Ecosystem effects of thermal manipulation of a whole lake, Lake Breisjøen, southern Norway (THERMOS project)

International audienceWe conducted a 3-year artificial deepening of the thermocline in the dimictic Lake Breisjøen, southern Norway, by means of a large submerged propeller. An adjacent lake served as untreated reference. The manipulation increased thermocline depth from 6 to 20 m, caused a significant increase in the heat content, and delayed ice-on by about 20 days. There were only minor changes in water chemistry. Concentrations of sulphate declined, perhaps due to greater reduction of sulphate at the sediment-water interface. Concentrations of particulate carbon and nitrogen decreased, perhaps due to increased sedimentation velocity. Water transparency increased. There was no significant change in concentration of phosphorus, the growth-limiting nutrient. There were few significant changes in principal biological components. Phytoplankton biomass and productivity did not change, although the chlorophyll-a concentration showed a small decrease. Phytoplankton species richness increased, and the species composition shifted. Growth of periphyton increased. There was no change in the macrophyte community. The manipulation did not affect the zooplankton biodiversity, but caused a significant shift in the relative abundance (measured as biomass) in the two major copepod species. The manipulation did not affect the individual density, but appeared to have changed the vertical distribution of zoobenthos. Fish populations were not affected. The lake is oligotrophic and clearwater and the manipulation did not change the supply of phosphorus, and thus there were only minor changes in lake chemistry and biology. Effects might be larger in eutrophic and dystrophic lakes in which internal processes are stronger

OSIRIS: A Decade of Scattered Light

Into year 11 of a 2-yr mission, OSIRIS is redefining how limb-scattered sunlight can be used to probe the atmosphere, even into the upper troposphere

Resolving the ancestry of Austronesian-speaking populations

There are two very different interpretations of the prehistory of Island Southeast Asia (ISEA), with genetic evidence invoked in support of both. The “out-of-Taiwan” model proposes a major Late Holocene expansion of Neolithic Austronesian speakers from Taiwan. An alternative, proposing that Late Glacial/postglacial sea-level rises triggered largely autochthonous dispersals, accounts for some otherwise enigmatic genetic patterns, but fails to explain the Austronesian language dispersal. Combining mitochondrial DNA (mtDNA), Y-chromosome and genome-wide data, we performed the most comprehensive analysis of the region to date, obtaining highly consistent results across all three systems and allowing us to reconcile the models. We infer a primarily common ancestry for Taiwan/ISEA populations established before the Neolithic, but also detected clear signals of two minor Late Holocene migrations, probably representing Neolithic input from both Mainland Southeast Asia and South China, via Taiwan. This latter may therefore have mediated the Austronesian language dispersal, implying small-scale migration and language shift rather than large-scale expansion

Observations of the pulsating subdwarf B star Feige 48: Constraints on evolution and companions

Since pulsating subdwarf B (sdBV or EC14026) stars were first discovered (Kilkenny et al, 1997), observational efforts have tried to realize their potential for constraining the interior physics of extreme horizontal branch (EHB) stars. Difficulties encountered along the way include uncertain mode identifications and a lack of stable pulsation mode properties. Here we report on Feige 48, an sdBV star for which follow-up observations have been obtained spanning more than four years, which shows some stable pulsation modes. We resolve the temporal spectrum into five stable pulsation periods in the range 340 to 380 seconds with amplitudes less than 1%, and two additional periods that appear in one dataset each. The three largest amplitude periodicities are nearly equally spaced, and we explore the consequences of identifying them as a rotationally split l=1 triplet by consulting with a representative stellar model. The general stability of the pulsation amplitudes and phases allows us to use the pulsation phases to constrain the timescale of evolution for this sdBV star. Additionally, we are able to place interesting limits on any stellar or planetary companion to Feige 48.Comment: accepted for publication in MNRA