Detection of C2HD and the D/H ratio on Titan

We report here the first detection of mono-deuterated acetylene (acetylene-d1, C₂HD) in Titan's atmosphere from the presence of two of its emission bands at 678 and 519 cm⁻¹ as observed in CIRS spectral averages of nadir and limb observations taken between July 2004 and mid-2007. By using new laboratory spectra for this molecule, we were able to derive its abundance at different locations over Titan's disk. We find the C₂HD value () to be roughly constant with latitude from the South to about 45° N and then to increase slightly in the North, as is the case for C₂H₂. Fitting the 678 cm⁻¹ν₅ band simultaneously with the nearby C₂H₂ 729 cm⁻¹ν₅ band, allows us to infer a D/H ratio in acetylene on Titan with an average of the modal values of 2.09±0.45×¹⁰⁻⁴ from the nadir observations, the uncertainties being mainly due to the vertical profile used for the fit of the acetylene band. Although still subject to significant uncertainty, this D/H ratio appears to be significantly larger than the one derived in methane from the CH₃D band (upper limit of 1.5×¹⁰⁻⁴; Bézard, B., Nixon, C.A., Kleiner, I., Jennings, D.E., 2007. Icarus, 191, 397-400; Coustenis, A., Achterberg, R., Conrath, B., Jennings, D., Marten, A., Gautier, D., Bjoraker, G., Nixon, C., Romani, P., Carlson, R., Flasar, M., Samuelson, R.E., Teanby, N., Irwin, P., Bézard, B., Orton, G., Kunde, V., Abbas, M., Courtin, R., Fouchet, Th., Hubert, A., Lellouch, E., Mondellini, J., Taylor, F.W., Vinatier, S., 2007. Icarus 189, 35-62). From the analysis of limb data we infer D/H values of (at 54° S), (at 15° S), (at 54° N) and (at 80° N), which average to a mean value of 1.63±0.27×¹⁰⁻⁴.     

Applying Geography Course Projects to Issues in City Resilience and Global Connectivity

Globalization would appear to be a subject that easily could be addressed in geography classrooms, yet this is not always the case. In terms of pedagogy, many geographers are concerned whether the field has been adequately engaging various components of this topic (e.g., connectivity, core-periphery), especially in terms of making the subject matter relevant to students. This article presents the results of a recent course project situated at the intersection of city-level resilience to hazards and connectivity with the global economy, utilizing SWOT analysis. The student projects demonstrated that this comparatively simple analytical tool was a useful means for exploring and integrating key topics in globalization and urban-economic geography, while also facilitating a problem-based learning environment.     

Spatial and Temporal Patterns Associated with Permitted Tree Removal in Austin,Texas, 2002–2011

A wide-ranging set of physical, urban, demographic, socioeconomic, and policy characteristics determines the spatial distribution of urban forests. Information on the characteristics surrounding tree removals on both public and private properties has received less attention in the literature. The purpose of this research was to analyze the spatiotemporal trends and geographic patterns of tree removals in Austin, Texas, between 2002 and 2011 in an effort to understand how site-specific characteristics influence urban tree removal and affect the overall distribution of Austin's urban forest. We examined permitted tree removals using a geographic information system (GIS) as well as spatial and statistical analyses. Specifically, we evaluated the degree to which variables related to various physical, urban, and socioeconomic conditions predicted tree removals. The results indicate that permitted tree removals and their associated characteristics in Austin have varied over the ten-year study period. Permitted tree removals increased over the study period and took place in the urban core and along the urban periphery. Permitted tree removals were more likely to be undertaken by college graduates and owner-occupants and to occur in more densely populated areas, closer to major streets, and on properties with older structures. The results of this research provide urban forest professionals with information on the location and intensity of permitted tree removals and the significant characteristics driving urban tree loss.     

Japan’s urban singles: negotiating alternatives to family households and standard housing pathways

In comparison to other advanced economies, the rise of people living alone in Japan has been late and rapid, with singletons now accounting for almost half of all households in major cities. The normative and structural frameworks surrounding standard family-household formation, however, remain formidable, reducing life-course opportunities for non-family formers. This paper considers the household and housing pathways being negotiated by younger-adults living independently. In addition to various secondary data sources, we draw on qualitative interviews with 35 individuals from 28 Tokyo households in addressing manifestations of, and resistance to, atomisation and individualisation in the Japanese context. Our analysis focuses on meanings and practices of homemaking among renters and buyers in the growing sector of single-person dwellings, as well as the recent emergence of commercial shared housing . This analysis provides a contrast to discourses surrounding the “singles boom” and “the growing appeal of living alone” in Western cities.     

The new hominid skeleton from Sterkfontein,South Africa: age and preliminary assessment

A new hominid skeleton from Sterkfontein Member 2 attaches to foot bones recovered from loose blocks during the 1980s and first described in 1995. Several flowstone horizons are present above and below the skeleton and have given clear palaeomagnetic signatures. Five changes in magnetic polarity have been identified; when constrained by the available biostratigraphy, this sequence can be placed confidently between 3.22 and 3.58 Ma. Interpolation of sedimentation rates over the small intervals between reversals allows this range to be reduced to 3.30–3.33 Ma. The skeleton is thus the oldest yet discovered and is considered to belong to a species of Australopithecus other than africanus. Copyright © 1999 John Wiley & Sons, Ltd.     

Probabilistic domain decomposition for the solution of the two-dimensional magnetotelluric problem

Probabilistic domain decomposition is proposed as a novel method for solving the two-dimensional Maxwell’s equations as used in the magnetotelluric method. The domain is split into non-overlapping sub-domains and the solution on the sub-domain boundaries is obtained by evaluating the stochastic form of the exact solution of Maxwell’s equations by a Monte-Carlo approach. These sub-domains can be naturally chosen by splitting the sub-surface domain into regions of constant (or at least continuous) conductivity. The solution over each sub-domain is obtained by solving Maxwell’s equations in the strong form. The sub-domain solver used for this purpose is a meshless method resting on radial basis function-based finite differences. The method is demonstrated by solving a number of classical magnetotelluric problems, including the quarter-space problem, the block-in-half-space problem and the triangle-in-half-space problem.     

Spatial and Temporal Patterns in <Emphasis Type="Italic">Thalassia testudinum</Emphasis> Leaf Tissue Nutrients at the Chandeleur Islands,Louisiana, USA

Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows.     

Numerical Analysis of Thermal Remediation in 3D Field‐Scale Fractured Geologic Media

Thermal methods are promising for remediating fractured geologic media contaminated with volatile organic compounds, and the success of this process depends on the coupled heat transfer, multiphase flow, and thermodynamics. This study analyzed field‐scale removal of trichloroethylene (TCE) and heat transfer behavior in boiling fractured geologic media using the multiple interacting continua method. This method can resolve local gradients in the matrix and is less computationally demanding than alternative methods like discrete fracture‐matrix models. A 2D axisymmetric model was used to simulate a single element of symmetry in a repeated pattern of extraction wells inside a large heated zone and evaluate effects of parameter sensitivity on contaminant recovery. The results showed that the removal of TCE increased with matrix permeability, and the removal rate was more sensitive to matrix permeability than any other parameter. Increasing fracture density promoted TCE removal, especially when the matrix permeability was low (e.g., <10^?17 m²). A 3D model was used to simulate an entire treatment zone and the surrounding groundwater in fractured material, with the interaction between them being considered. Boiling was initiated in the center of the upper part of the heated region and expanded toward the boundaries. This boiling process resulted in a large increase in the TCE removal rate and spread of TCE to the vadose zone and the peripheries of the heated zone. The incorporation of extraction wells helped control the contaminant from migrating to far regions. After 22 d, more than 99.3% of TCE mass was recovered in the simulation.     

Constraints on Mercury’s Na exosphere: Combined MESSENGER and ground-based data

We have used observations of sodium emission obtained with the McMath-Pierce solar telescope and MESSENGER’s Mercury Atmospheric and Surface Composition Spectrometer (MASCS) to constrain models of Mercury’s sodium exosphere. The distribution of sodium in Mercury’s exosphere during the period January 12-15, 2008, was mapped using the McMath-Pierce solar telescope with the 5″ × 5″ image slicer to observe the D-line emission. On January 14, 2008, the Ultraviolet and Visible Spectrometer (UVVS) channel on MASCS sampled the sodium in Mercury’s anti-sunward tail region. We find that the bound exosphere has an equivalent temperature of 900-1200 K, and that this temperature can be achieved if the sodium is ejected either by photon-stimulated desorption (PSD) with a 1200 K Maxwellian velocity distribution, or by thermal accommodation of a hotter source. We were not able to discriminate between the two assumed velocity distributions of the ejected particles for the PSD, but the velocity distributions require different values of the thermal accommodation coefficient and result in different upper limits on impact vaporization. We were able to place a strong constraint on the impact vaporization rate that results in the release of neutral Na atoms with an upper limit of 2.1 × 10⁶ cm⁻² s⁻¹. The variability of the week-long ground-based observations can be explained by variations in the sources, including both PSD and ion-enhanced PSD, as well as possible temporal enhancements in meteoroid vaporization. Knowledge of both dayside and anti-sunward tail morphologies and radiances are necessary to correctly deduce the exospheric source rates, processes, velocity distribution, and surface interaction.