Solar wind helium, neon, and argon isotopic and elemental composition: Data from the metallic glass flown on NASA’s Genesis mission

Solar wind (SW) helium, neon, and argon trapped in a bulk metallic glass (BMG) target flown on NASA’s Genesis mission were analyzed for their bulk composition and depth-dependent distribution. The bulk isotopic and elemental composition for all three elements is in good agreement with the mean values observed in the Apollo Solar Wind Composition (SWC) experiment. Conversely, the He fluence derived from the BMG is up to 30% lower than values reported from other Genesis bulk targets or in-situ measurements during the exposure period. SRIM implantation simulations using a uniform isotopic composition and the observed bulk velocity histogram during exposure reproduces the Ne and Ar isotopic variations with depth within the BMG in a way which is generally consistent with observations. The similarity of the BMG release patterns with the depth-dependent distributions of trapped solar He, Ne, and Ar found in lunar and asteroidal regolith samples shows that also the solar noble gas record of extraterrestrial samples can be explained by mass separation of implanted SW ions with depth. Consequently, we conclude that a second solar noble gas component in lunar samples, referred to as the “SEP” component, is not needed. On the other hand, a small fraction of the total solar gas in the BMG released from shallow depths is markedly enriched in the light isotopes relative to predictions from implantation simulations with a uniform isotopic composition. Contributions from a neutral solar or interstellar component are too small to explain this shallow sited gas. We tentatively attribute this superficially implanted gas to low-speed, current-sheet related SW, which was fractionated in the corona due to inefficient Coulomb drag. This fractionation process could also explain relatively high Ne/Ar elemental ratios in the same initial gas fraction.     

Phthalic acid complexation and the dissolution of forsteritic glass studied via in situ FTIR and X-ray scattering

Multiple Internal Reflection Fourier Transform Infra-Red (MIR-FTIR) spectroscopy was developed and used for in situ flow-through experiments designed to study the process of organic acid promoted silicate dissolution. In tandem with the FTIR analysis, ex situ X-ray scattering was used to perform detailed analyses of the changes in the surface structure and chemistry resulting from the dissolution process. Phthalic acid and forsteritic glass that had been Chemically Vapour Deposited (CVD) onto an internal reflection element were used as reactants, and the MIR-FTIR results showed that phthalic acid may promote dissolution by directly binding to exposed Mg metal ion centers on the solid surface. Integrated infrared absorption intensity as a function of time shows that phthalic acid attachment apparently follows a t^1/2 dependence, indicating that attachment is a diffusive process. The diffusion coefficient of phthalic acid was estimated to be approximately 7 × 10⁻⁶ cm² s⁻¹ in the solution near the interface with the glass. Shifts in the infrared absorption structure of the phthalate complexed with the surface compared to the solute species indicate that phthalate forms a seven-membered ring chelate complex. This bidentate complex efficiently depletes Mg from the glass surface, such that after reaction as much as 95% of the Mg may be removed. Surface depletion in Mg causes adsorbate density to fall after an initial attachment stage for the organic ligand. In addition, the infrared analysis shows that silica in the near surface polymerizes after Mg removal, presumably to maintain charge balance. X-ray reflectivity shows that the dissolution rate of forsteritic glass at pH 4 based on Mg removal in such flow-through experiments was equal to 4 × 10⁻¹² mol cm⁻² s⁻¹ (geometric surface area normalized). Reflectivity also shows how the surface mass density decreases during reaction from 2.64 g cm⁻³ to 2.2 g cm⁻³, consistent with preferential loss of Mg from the surface. Auxiliary batch experiments with forsteritic glass films deposited onto soda glass were also completed to add further constraints to the mechanism of reaction. By combining reflectivity with diffuse scatter measurements it is shown that the primary interface changes little in terms of atomic-scale roughness even after removal of several hundred angstroms of material. These measurements unequivocally show how a dicarboxylic acid bonds to and may chelate the dissolution of a magnesium-bearing silicate. At the molecular level the solid surface retreat may best be described by a depinning model where Mg is preferentially removed and residual silica tetrahedra polymerize and act to episodically “pin” the surface.     

GMOs and their contexts: A comparison of potential and actual performance of GM crops in a local agricultural setting

In this paper, I argue that genetically modified organisms (GMOs) have inherent potential to contribute to socially and environmentally sustainable agriculture by virtue of their ‘biological embeddedness’. Their actual ‘performance’ and how this contributes to sustainability depends on the ‘mutual shaping’ of technology and context. While much attention has been given to the design context of GMOs, this paper considers the influence of the application context and of users. A case study investigating the use of insect-resistant and herbicide-tolerant GM cotton in the cotton-growing region of New South Wales in Australia is presented. The study was based on focus groups with farmers and other stakeholders in a cotton-growing community. It demonstrated a range of direct and indirect effects of GM cotton use, both positive and negative for sustainability, and the ways in which these effects were influenced by the local social context. The influences of the biotechnology industry context, in limiting the contributions that gene technologies can make to sustainability, were also considered, and remedies suggested. I argue that the polarity of the GM debate is hindering progress on these issues, and that a more balanced approach to our analysis of GMOs is necessary in order to fully understand, and to influence, their role in the future of rural spaces.     

Airports, mobility and the calculative architecture of affective control

Drawing on work surrounding the theorisation of concepts such as mobility, affect and emotion, the paper argues that their control is now being intertwined in places like airports which are employing a number of techniques that engineer affects. Airport affect is enacted, in one way, by planning and designing the situational affective context one inhabits - throwing up structures of ethological possibility that shape capacities for the corporeal body to move and be moved. It is shown that the engineering of airport affect is premised upon a wider discursive framework of calculation and indeterminacy, and that selective techniques summon a number of different modalities of control. The paper concludes with a series of implications for the understanding of power, and the study of mobility, emotion and affect.     

Atmospheric mercury near Salmon Falls Creek Reservoir in southern Idaho

Gaseous elemental mercury (GEM) and reactive gaseous mercury (RGM) were measured over 2-week seasonal field campaigns near Salmon Falls Creek Reservoir in south-central Idaho from the summer of 2005 through the fall of 2006 and over the entire summer of 2006 using automated Tekran Hg analyzers. GEM, RGM, and particulate Hg (HgP) were also measured at a secondary site 90 km to the west in southwestern Idaho during the summer of 2006. The study was performed to characterize Hg air concentrations in the southern Idaho area for the first time, estimate Hg dry deposition rates, and investigate the source of observed elevated concentrations. High seasonal variability was observed with the highest GEM (1.91 ± 0.9 ng m⁻³) and RGM (8.1 ± 5.6 pg m⁻³) concentrations occurring in the summer and lower values in the winter (1.32 ± 0.3 ng m⁻³, 3.2 ± 2.9 pg m⁻³ for GEM, RGM, respectively). The summer-average HgP concentrations were generally below detection limit (0.6 ± 1 pg m⁻³). Seasonally averaged deposition velocities calculated using a resistance model were 0.034 ± 0.032, 0.043 ± 0.040, 0.00084 ± 0.0017 and 0.00036 ± 0.0011 cm s⁻¹ for GEM (spring, summer, fall and winter, respectively) and 0.50 ± 0.39, 0.40 ± 0.31, 0.51 ± 0.43 and 0.76 ± 0.57 cm s⁻¹ for RGM. The total annual RGM + GEM dry deposition estimate was calculated to be 11.9 ± 3.3 μg m⁻², or about 2/3 of the total (wet + dry) deposition estimate for the area. Periodic elevated short-term GEM (2.2–12 ng m⁻³) and RGM (50–150 pg m⁻³) events were observed primarily during the warm seasons. Back-trajectory modeling and PSCF analysis indicate predominant source directions to the SE (western Utah, northeastern Nevada) and SW (north-central Nevada) with fewer inputs from the NW (southeastern Oregon and southwestern Idaho).     

The passivation of calcite by acid mine water. Column experiments with ferric sulfate and ferric chloride solutions at pH 2

Column experiments, simulating the behavior of passive treatment systems for acid mine drainage, have been performed. Acid solutions (HCl or H₂SO₄, pH 2), with initial concentrations of Fe(III) ranging from 250 to 1500 mg L⁻¹, were injected into column reactors packed with calcite grains at a constant flow rate. The composition of the solutions was monitored during the experiments. At the end of the experiments (passivation of the columns), the composition and structure of the solids were measured. The dissolution of calcite in the columns caused an increase in pH and the release of Ca into the solution, leading to the precipitation of gypsum and Fe–oxyhydroxysulfates (Fe(III)–SO₄–H⁺ solutions) or Fe–oxyhydroxychlorides (Fe(III)–Cl–H⁺ solutions). The columns worked as an efficient barrier for some time, increasing the pH of the circulating solutions from 2 to 6–7 and removing its metal content. However, after some time (several weeks, depending on the conditions), the columns became chemically inert. The results showed that passivation time increased with decreasing anion and metal content of the solutions. Gypsum was the phase responsible for the passivation of calcite in the experiments with Fe(III)–SO₄–H⁺ solutions. Schwertmannite and goethite appeared as the Fe(III) secondary phases in those experiments. Akaganeite was the phase responsible for the passivation of the system in the experiments with Fe(III)–Cl–H⁺ solutions.     

Memorial landscapes: analytic questions and metaphors

Over the past two decades, geographers have probed the intersection of collective memory and urban space. Their sustained interest in the subject reflects an understanding of the social condition of commemoration and the important role that space plays in the process and politics of collective memory. Along with other critical social scientists, geographers envision these public symbols as part of larger cultural landscapes that reflect and legitimate the normative social order. A review of the extant literature indicates that geographers scrutinize memorial landscapes through three conceptual lenses that may be understood via the metaphors of ‘text,’ ‘arena,’ and ‘performance.’ These metaphors are in turn mobilized through a series of analytic questions that serve to identify the interests served and denied by landscape ‘texts,’ the ‘arenas’ in which they are produced, and the ways in which they are enacted via ‘performance.’ This article’s synopsis of the subfield’s predominant metaphors and its attendant questions contributes to the ongoing cultural geographic project of articulating and implementing methods for interpreting landscapes as open-ended symbolic systems.

Millennium-long recession of limestone facades in London

Historical data on the temperature and precipitation data for London has been combined with output from the Hadley Model to estimate the climate of London for the period 1100–2100 CE. This has been converted to other parameters such as freeze–thaw frequency and snowfall relevant to the weathering of stone facades. The pollutant concentrations have been estimated for the same period, with the historical values taken from single box modelling and future values from changes likely given current policy within the metropolis. These values are used in the Lipfert model to show that the recession from karst weathering dominates across the period, while the contributions of sulphur deposition seem notable only across a shorter period 1700–2000 CE. Observations of the late seventeenth century suggest London architects witnessed a notable increase in the recession rate and attributed “fretting quality” to “smoaks of the sea-coal”. The recession rates measured in the late twentieth century lend some support to the estimates from the Lipfert model. The recession looks to increase only slightly, and frost shattering will decrease while salt weathering is likely to increase.     

Flexural isostatic response of the Alps to increased Quaternary erosion recorded by foreland basin remnants,SE France

We test the hypothesis that flexural isostatic compensation of the mass removed by enhanced Quaternary erosion is responsible for uplift of the Western European Alps and their forelands. We use two well‐preserved and well‐dated (1.8 Ma) abandonment surfaces of foreland basin remnants in SE France (the Chambaran and Valensole plateaux) as passive benchmarks for tilting of the foreland. Estimating their initial slope from morphometric scaling relationships, we determine bulk post‐depositional tilting of 0.5–0.8% for these surfaces. The calculated isostatic response of the Alpine lithosphere to erosional unloading, using the method recently proposed by Champagnac et al. [Geology 35 (2007) 195–198] , yields a predicted tilting of 0.3–0.4% in the considered areas, explaining approximately half of the determined post‐depositional tilting. Such long‐term deformation being insensitive to cyclic loading/unloading because of glaciations, we suspect the other half to be related to as yet undetermined long‐wavelength and long‐lived tectonic process(es).