Assessment of hurricane wind performance and potential design modifications for informally constructed housing in Puerto Rico

This study assesses the wind performance of various housing typologies representing informal construction practices in Puerto Rico to suggest modifications to enhance housing resilience in hurricanes. Based on fieldwork and interviews, the study defined four base housing typologies and possible variations in design and construction details. Each house was assessed using performance-based static wind analysis of potentially critical components. The results show that the initial governing failure mode in all base house typologies considered is roof panel loss due to tear-through at the fasteners, with subsequent governing failures being panel loss due to failures at the purlin-to-truss connections and failures of the truss-to-wall connections. In-plane wall failures and masonry uplift failures were both found to occur at much higher wind speeds than roof failures. To improve the hurricane performance, several feasible modifications are suggested, including installing hurricane straps at both the truss-to-wall and the purlin-to-truss connections, as well as improving the panel-fastener interface. In the construction of new roofs, this study found that using reduced spacing between roof members, hip roofs instead of gable roofs, and higher roof slopes leads to improved performance. These recommendations can make houses built through informal construction processes safer and more resilient to hurricanes as a form of climate adaptation.

     

Behavior of Dry-Mixed and Permeated Laponite-Treated Sand: From Small Strains to Critical State

Geotechnical and Geological Engineering - Laponite—a synthetic nanoclay with (2:1) layer structure—has shown promise for the improvement of granular deposits susceptible to earthquake...     

Ion Implants as Matrix‐Appropriate Calibrators for Geochemical Ion Probe Analyses

Ion microprobe elemental and isotopic determinations can be precise but difficult to quantify. Error is introduced when the reference material and the sample to be analysed have different compositions. Mitigation of such ‘matrix effects’ is possible using ion implants. If a compositionally homogeneous reference material is available which is ‘matrix‐appropriate’ (i.e., close in major element composition to the sample to be analysed, but having an unknown concentration of the element, E, to be determined) then ion implantation can be used to introduce a known amount of an E isotope, calibrating the E concentration and producing a matrix‐appropriate calibrator. Nominal implant fluences (ions cm^?2) are inaccurate by amounts up to approximately 30%. However, ion implantation gives uniform fluences over large areas; thus, it is possible to ‘co‐implant’ an additional reference material of any bulk composition having known amounts of E, independently calibrating the implant fluence. Isotope ratio measurement standards can be produced by implanting two different isotopes, but permil level precision requires postimplant calibration of the implant isotopic ratio. Examples discussed include (a) standardising Li in melilite; (b) calibrating a ²⁵Mg implant fluence using NIST SRM 617 glass and (c) using Si co‐implanted with ²⁵Mg alongside NIST SRM 617 to produce a calibrated measurement of Mg in Si.     

Subtidal flow and its variability at the entrance to a subtropical lagoon

Spatial and temporal variability of the subtidal exchange flow at West Pass, an inlet at the entrance to a subtropical lagoon (St. Andrew Bay, Florida), was studied using moored and towed current velocity profiles and hydrographic data. Towed and hydrographic measurements were captured over one diurnal tidal cycle to determine intratidal and spatial changes in flow. Hydrographic profiles over the tidal cycle showed that tidal straining modified density stratification asymmetrically, thus setting up the observed mean flow within the inlet. During the towed survey, the inlet's mean flow had a two-layer exchange structure that was moderately frictional and weakly influenced by Coriolis accelerations. Moored current profiles revealed the additional contribution to the dynamics from centrifugal accelerations. Along channel residual flows changed between unidirectional and exchange flow, depending on the forcing from the along-estuary wind stress and, to a lesser extent, the spring–neap tidal cycle. Increases in vertical shear in the along channel subtidal flow coincided with neap tides and rain pulses. Lateral subtidal flows showed the influence on the dynamics of centrifugal accelerations through a well-developed two-layer structure modulated in magnitude by the spring–neap tidal cycle.     

Synergistic toxic effects of zinc pyrithione and copper to three marine species: Implications on setting appropriate water quality criteria

Zinc pyrithione (ZnPT) is widely applied in conjunction with copper (Cu) in antifouling paints as a substitute for tributyltin. The combined effects of ZnPT and Cu on marine organisms, however, have not been fully investigated. This study examined the toxicities of ZnPT alone and in combination with Cu to the diatom Thalassiosira pseudonana, polychaete larvae Hydroides elegans and amphipod Elasmopus rapax. Importantly, ZnPT and Cu resulted in a strong synergistic effect with isobologram interaction parameter lambda>1 for all test species. The combined toxicity of ZnPT and Cu was successfully modelled using the non-parametric response surface and its contour. Such synergistic effects may be partly due to the formation of copper pyrithione. It is, therefore, inadequate to assess the ecological risk of ZnPT to marine organisms solely based on the toxicity data generated from the biocide alone. To better protect precious marine resources, it is advocated to develop appropriate water quality criteria for ZnPT with the consideration of its compelling synergistic effects with Cu at environmentally realistic concentrations.     

Interactive effects of hypoxia and polybrominated diphenyl ethers (PBDEs) on microbial community assembly in surface marine sediments

Hypoxia alters the oxidation–reduction balance and the biogeochemical processes in sediments, but little is known about its impacts on the microbial community that is responsible for such processes. In this study, we investigated the effects of hypoxia and the ubiquitously dispersed flame-retardant BDE47 on the bacterial communities in marine surface sediments during a 28-days microcosm experiment. Both hypoxia and BDE47 alone significantly altered the bacterial community and reduced the species and genetic diversity. UniFrac analysis revealed that BDE47 selected certain bacterial species and resulted in major community shifts, whereas hypoxia changed the relative abundances of taxa, suggesting slower but nonetheless significant community shifts. These two stressors targeted mostly different taxa, but they both favored Bacteroidetes and suppressed Gammaproteobacteria. Importantly, the impacts of BDE47 on bacterial communities were different under hypoxic and normoxic conditions, highlighting the need to consider risk assessments for BDE47 in a broader context of interaction with hypoxia.     

Processes at the margins of supraglacial debris cover: Quantifying dirty ice ablation and debris redistribution

Current glacier ablation models have difficulty simulating the high-melt transition zone between clean and debris-covered ice. In this zone, thin debris cover is thought to increase ablation compared to clean ice, but often this cover is patchy rather than continuous. There is a need to understand ablation and debris dynamics in this transition zone to improve the accuracy of ablation models and the predictions of future debris cover extent. To quantify the ablation of partially debris-covered ice (or ‘dirty ice’), a high-resolution, spatially continuous ablation map was created from repeat unmanned aerial systems surveys, corrected for glacier flow in a novel way using on-glacier ablation stakes. Surprisingly, ablation is similar (range ~ 5 mm w.e. per day) across a wide range of percentage debris covers (~ 30–80%) due to the opposing effects of a positive correlation between percentage debris cover and clast size, countered by a negative correlation with albedo. Once debris cover becomes continuous, ablation is significantly reduced (by 61.6% compared to a partial debris cover), and there is some evidence that the cleanest ice (<~ 15% debris cover) has a lower ablation than dirty ice (by 3.7%). High-resolution feature tracking of clast movement revealed a strong modal clast velocity where debris was continuous, indicating that debris moves by creep down moraine slopes, in turn promoting debris cover growth at the slope toe. However, not all slope margins gain debris due to the removal of clasts by supraglacial streams. Clast velocities in the dirty ice area were twice as fast as clasts within the continuously debris-covered area, as clasts moved by sliding off their boulder tables. These new quantitative insights into the interplay between debris cover characteristics and ablation can be used to improve the treatment of dirty ice in ablation models, in turn improving estimates of glacial meltwater production. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Pilot-Scale Electrochemical Treatment of a 1,4-Dioxane Source Zone

Electrochemical treatment is a promising emerging technology in which direct current is applied to drive the degradation of aqueous contaminants. Several bench-scale studies have demonstrated the capability of electrochemical oxidation to fully mineralize refractory organics such as pesticides and perfluorinated compounds. However, insights into large-scale design and field performance are critically lacking. Here, we designed six pilot-scale reactors and tested their performance and efficiency for the treatment of groundwater contaminated with 1,4-dioxane (1,4-DX) at concentrations exceeding 1000 mg/L. Anode surface area-normalized degradation rates increased with increasing potential applied, while the process was more energy-efficient per mass unit removed at low potentials. While not all 1,4-DX was completely mineralized, the detected ring-opening intermediates are known to be readily biodegradable. Analyses of potential by-products from chloride oxidation revealed the generation of chloromethanes and perchlorate at low mg/L concentrations. Towards the end of the 8.5-month pilot test, decreasing currents and degradation rates indicated progressing passivation of the electrodes, likely due to cathodic carbonate precipitation and/or poisoning by the uniquely high organic carbon load of this source zone groundwater. The findings of our study demonstrate that electrochemical groundwater remediation is a capable approach for the treatment of persistent organic pollutants. Our pilot-scale test provides practitioners with a basis for evaluating its efficiency under site-specific conditions and collecting critical performance metrics for technology scale-up.