Determination of the molar extinction coefficient for the ferric reducing/antioxidant power assay

The FRAP reagent contains 2,4,6-tris(2-pyridyl)-s-triazine, which forms a blue-violet complex ion in the presence of ferrous ions. Although the FRAP (ferric reducing/antioxidant power) assay is popular and has been in use for many years, the correct molar extinction coefficient of this complex ion under FRAP assay conditions has never been published, casting doubt on the validity of previous calibrations. A previously reported value of 19.800 is an underestimate. We determined that the molar extinction coefficient was 21,140. The value of the molar extinction coefficient was also shown to depend on the type of assay and was found to be 22,230 under iron assay conditions, in good agreement with published data. Redox titration indicated that the ferrous sulfate heptahydrate calibrator recommended by Benzie and Strain, the FRAP assay inventors, is prone to efflorescence and, therefore, is unreliable. Ferrous ammonium sulfate hexahydrate in dilute sulfuric acid was a more stable alternative. Few authors publish their calibration data, and this makes comparative analyses impossible. A critical examination of the limited number of examples of calibration data in the published literature reveals only that Benzie and Strain obtained a satisfactory calibration using their method. (C) 2011 Elsevier Inc. All rights reserved.

Fitness reduction and potential extinction of wild populations of Atlantic salmon, Salmo salar, as a result of interactions with escaped farm salmon.

The high level of escapes from Atlantic salmon farms, up to two million fishes per year in the North Atlantic, has raised concern about the potential impact on wild populations. We report on a twogeneration experiment examining the estimated lifetime successes, relative to wild natives, of farm, F1 and F2 hybrids and BC1 backcrosses to wild and farm salmon. Offspring of farm and hybrids (i.e. all F1 , F2 and BC1 groups) showed reduced survival compared with wild salmon but grew faster as juveniles and displaced wild parr, which as a group were significantly smaller. Where suitable habitat for these emigrant parr is absent, this competition would result in reduced wild smolt production. In the experimental conditions, where emigrants survived downstream, the relative estimated lifetime success ranged from 2% (farm) to 89% (BC1 wild) of that of wild salmon, indicating additive genetic variation for survival . Wild salmon primarily returned to fresh water after one sea winter (1SW) but farm and hybrids produced proportionately more 2SW salmon. However, lower overall survival means that this would result in reduced recruitment despite increased 2SW fecundity. We thus demonstrate that interaction of farm with wild salmon results in lowered fitness, with repeated escapes causing cumulative fitness depression and potentially an extinction vortex in vulnerable populations.

Atomic oxygen surface loss coefficient measurements in a capacitive/inductive radio-frequency plasma

Spatially resolved measurements of the atomic oxygen densities close to a sample surface in a dual mode (capacitive/inductive) rf plasma are used to measure the atomic oxygen surface loss coefficient beta on stainless steel and aluminum substrates, silicon and silicon dioxide wafers, and on polypropylene samples. beta is found to be particularly sensitive to the gas pressure for both operating modes. It is concluded that this is due to the effect of changing atom and ion flux to the surface. (C) 2002 American Institute of Physics.

Measurements of the XUV mass absorption coefficient of an overdense liquid metal

The increase in the XUV mass absorption coefficient of liquid aluminium, produced by high-power-laser shock-compression, is measured using XUV laser radiography. At a photon energy of 63 eV a change in the mass absorption coefficient by up to a factor of similar to2.2 is determined at densities close to twice that of solid and electron temperatures of the order of 1 eV. Comparison with hydrodynamic simulations indicate that the absorption coefficient scales with density as rho (1.3 +/-0.2).

An assessment of the earth pressure coefficient in overconsolidated clays

The determination of the earth pressure coefficient K 0 in a natural clay deposit is a problem of considerable significance in geotechnical engineering. While the methods for evaluation of K 0 are reliable for normally consolidated soils, significant difficulties still exist in evaluating K 0 in overconsolidated clays, given that it is influenced by the stress history of the material, together with the age, structure, mineralogical composition and depositional environment. Indeed, some of these factors are responsible for the soil becoming anisotropic. The existing framework for prediction of K 0 in overconsolidated soils does not account for any influences caused by anisotropy. The work reported in this paper evaluates the validity of a revised relationship between K 0oc and OCR (overconsolidation ratio) using data obtained from laboratory investigations. The tests were performed on reconstituted and undisturbed samples of Belfast Upper Boulder Clay, London Clay and Gault Clay. Tests were also performed on reconstituted samples of kaolin. The values of K 0oc were determined using various approaches, including on-sample measurements. The results have confirmed that reliable predictions of K 0oc can be made using the proposed relationship.

Coefficient of consolidation by plotting velocity against displacement

A method is presented for estimating the initial compression, the final compression and the coefficient of consolidation from an observed, experimental consolidation response, using a plot of velocity versus displacement and the conventional Taylor plot of compression versus the square root of time. Goodness of fit measures indicate that the method produces good agreement between fitted and measured displacement values, at least up until the point where the impact of secondary compression on the overall displacement response becomes significant.

Extinction risk from climate change

Climate change over the past ,30 years has produced numerous shifts in the distributions and abundances of species1,2 and has been implicated in one species-level extinction3. Using projections of species’ distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth’s terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a powerlaw relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15–37% of species in our sample of regions and taxa will be ‘committed to extinction’. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction (,18%) than mid-range (,24%) and maximum change (,35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse

Determining the Reaeration Coefficient and Hydrodynamic Properties of Rivers Using Inert Gas Tracers

Various contaminants which can be aerobically degraded find their way directly or indirectly into surface water bodies. The reaeration coefficient (K2) characterises the rate at which oxygen can transfer from the atmosphere across the air-water interface following oxygen depletion in a water body. Other mechanisms (like advection, dispersion and transient storage) determine how quickly the contaminants can spread in the water, affecting their spatial and temporal concentrations. Tracer methods involving injection of a gas into the water body have traditionally been used for direct (in-situ) measurement of K2 in a given reach. This paper shows how additional modelling of tracer test results can be used to quantify also hydrodynamic mechanisms (e.g. dispersion and storage exchange coefficients, etc.). Data from three tracer tests conducted in the River Lagan (Northern Ireland) using an inert gas (krypton, Kr) are re-analysed using two solute transport models (ADM, TSM) and an inverse-modelling framework (OTIS-P). Results for K2 are consistent with previously published values for this reach (K2(20)~10-40 d-1). The storage area constituted 30-60% of the main cross-section area and the storage exchange rate was between 2.5×10-3-3.2×10-3s-1. The additional hydrodynamic parameters obtained give insight into transport and dispersion mechanisms within the reach.