Solid-state astrochemistry in star-forming regions

Surface-catalysed chemical reactions, the molecules they form, and the implications for star formation were key themes in an international workshop on "Solid-state chemistry in star-forming regions" at the Lorentz Centre, Leiden University, the Netherlands from 14–17 April 2003. Helen Fraser, David Williams, Ian Sims, Anita Richards and Jeremy Yates report.     

Towards better integration of ecology in palaeoecology: from proxies to indicators,from inference to understanding

The special issue titled “Putting the Ecology into Palaeoecology” stems from a session with that name that was held at the 2015 International Paleolimnological Association meeting (International Paleolimnology Symposium) in Lanzhou, China. We briefly describe the motivation for the session, and summarise the contributions to this special issue. Additionally, we discuss our perceptions and concerns about the progress, challenges and future directions of palaeolimnology, stressing the importance of meaningful integration of ecological principles and thinking into palaeoapproaches.     

Refining the palaeoecology of lacustrine testate amoebae: insights from a plant macrofossil record from a eutrophic Scottish lake

Lakes are common natural systems for which sedimentation is considered to be relatively simple, generally dominated by fluvial processes along the margin and prevailing low-energy settling in the central, deeper parts. However, for many lakes, higher-energy wind-driven processes dominate. As such, a new category of lakes is proposed, herein referred to as wind-driven waterbodies (WWB). WWB display a sedimentation largely dominated by wave related processes and wind-induced lake-scale water circulation evidenced by the construction of beach ridges, spits or cuspate spits along their shorelines, and by sediment drifts, sedimentary shelf progradation and erosional surfaces in their deeper, offshore domains. WWB are observed worldwide, they share a common physiography that favours wind-forced hydrodynamics and related sedimentation patterns. This physiography is expressed by the I_WWB index, a ratio of the maximum representative fetch relative to mean basin depth. It is proposed that an index value greater than three favours the evolution of a lake as a WWB. The WWB concept represents a new end-member in an alternative, sedimentologically-based lake classification that is proposed in this paper.     

An investigation into the efficiency of particle size separation using Stokes’ Law

The accuracy of gravimetric fractionation as a means of obtaining size fractions from marine sediments has been explored. Analysis of the particle size distribution and sediment properties of fractions obtained using this method was undertaken. This has highlighted the extent to which experimental artefacts rather than variations in sediment characteristics may adversely affect the efficiency of the fractionation process. Copyright © 1999 John Wiley & Sons, Ltd.     

Evaluating practical macrophyte control tools on small agricultural waterways in Canterbury,New Zealand

Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species.     

Plastic hinge analysis for lightly reinforced and unconfined concrete structural walls

Poor performance of lightly reinforced and unconfined concrete structural walls have been observed in recent earthquake events. This research investigates the displacement capacity of such walls by comparing the results of a series of state-of-the-art finite element analyses for a range of different structural walls to that estimated using plastic hinge analyses. The common expressions used in estimating the yield curvature, yield displacement and plastic displacement are scrutinised for these types of walls. Some recommendations are given to improve the prediction of the displacement capacity of lightly reinforced and unconfined rectangular and C-shaped walls for flexural actions using a plastic hinge analysis. Importantly, a parameter has been recommended to be used in a “modified” approach for estimating the nominal yield displacement of lightly reinforced concrete walls. Different expressions are also recommended depending on the amount of longitudinal reinforcement used in the wall in comparison to that required to initiate secondary cracking. This is important for providing better estimations of the displacement capacity of RC structural wall buildings in low-to-moderate seismic regions such that vulnerability studies can be conducted.     

On the treatment of uncertainty in seismic vulnerability and portfolio risk assessment

In a related study developed by the authors, building fragility is represented by intensity‐specific distributions of damage exceedance probability of various damage states. The contribution of the latter has been demonstrated in the context of loss estimation of building portfolios, where it is shown that the proposed concept of conditional fragility functions provides the link between seismic intensity and the uncertainty in damage exceedance probabilities. In the present study, this methodology is extended to the definition of building vulnerability, whereby vulnerability functions are characterized by hazard‐consistent distributions of damage ratio per level of primary seismic intensity parameter—Sa(T₁). The latter is further included in a loss assessment framework, in which the impact of variability and spatial correlation of damage ratio in the probabilistic evaluation of seismic loss is accounted for, using test‐bed portfolios of 2, 5, and 8‐story precode reinforced concrete buildings located in the district of Lisbon, Portugal. This methodology is evaluated in comparison with current state‐of‐the‐art methods of vulnerability and loss calculation, highlighting the discrepancies that can arise in loss estimates when the variability and spatial distributions of damage ratio, influenced by ground motion properties other than the considered primary intensity measure, are not taken into account.     

Organic carbon fluxes of a glacier surface: A case study of Foxfonna,a small Arctic glacier

Arctic glaciers are rapidly responding to global warming by releasing organic carbon (OC) to downstream ecosystems. The glacier surface is arguably the most biologically active and biodiverse glacial habitat and therefore the site of important OC transformation and storage, although rates and magnitudes are poorly constrained. In this paper, we present measurements of OC fluxes associated with atmospheric deposition, ice melt, biological growth, fluvial transport and storage (in superimposed ice and cryoconite debris) for a supraglacial catchment on Foxfonna glacier, Svalbard (Norway), across two consecutive years. We found that in general atmospheric OC input (averaging 0.63 ± 0.25 Mg a^-1 total organic carbon, i.e. TOC, and 0.40 ± 0.22 Mg a^-1 dissolved organic carbon, i.e. DOC) exceeded fluvial OC export (0.46 ± 0.04 Mg a^-1 TOC and 0.36 ± 0.03 Mg a^-1 DOC). Early in the summer, OC was mobilised in snowmelt but its release was delayed by temporary storage in superimposed ice on the glacier surface. This delayed the export of 28.5% of the TOC in runoff. Biological production in cryoconite deposits was a negligible potential source of OC to runoff, while englacial ice melt was far more important on account of the glacier's negative ice mass balance (–0.89 and –0.42 m a^-1 in 2011 and 2012, respectively). However, construction of a detailed OC budget using these fluxes shows an excess of inputs over outputs, resulting in a net retention of OC on the glacier surface at a rate that would require c. 3 years to account for the OC stored as cryoconite debris. © 2018 John Wiley & Sons, Ltd.     

The age of the meteorite recovery surfaces of Roosevelt County,New Mexico,USA

Abstract— We have obtained minimum age estimates for the sand units underlying the two largest meteorite deflation surfaces in Roosevelt County, New Mexico, USA, using thermoluminescence dating techniques. The dates obtained ranged from 53.5 (±5.4) to 95.2 (±9.5) ka, and must be considered lower limits for the terrestrial ages of the meteorites found within these specific deflation surfaces. These ages greatly exceed previous measurements from adjacent meteorite-producing deflation basins. We find that Roosevelt County meteorites are probably terrestrial contemporaries of the meteorites found at most accumulation zones in Antarctica. The apparent high meteorite accumulation rate reported for Roosevelt County by Zolensky et al. (1990) is incorrect, as it used an age of 16 ka for all Roosevelt County recovery surfaces. We conclude that the extreme variability of terrestrial ages of the Roosevelt County deflation surfaces effectively precludes their use for calculations of the meteorite accumulation rate at the Earth's surface.