The seasonal cycle of arsenic in estuarine and nearshore waters of the South Atlantic Bight

Arsenic concentrations vary with season on the continental shelf of the South Atlantic Bight. During periods of high winds in the winter and early spring, inorganic arsenic concentrations are reduced to as little as 20% of typical open ocean concentrations by sorption onto resuspended sediments or incorporation into phytoplankton. In the early fall, arsenic sequestered in sediments in the spring is regenerated and returned to the water column, creating elevated arsenic concentrations in the nearshore zone that are up to 50% greater than open ocean concentrations. Arsenic in the adjacent estuaries is nearly conservative over the seasonal cycle, although its distribution in the estuaries is greatly affected by the seasonal changes in arsenic concentrations in the nearshore waters.     

Observation-based blended projections from ensembles of regional climate models

We consider the problem of projecting future climate from ensembles of regional climate model (RCM) simulations using results from the North American Regional Climate Change Assessment Program (NARCCAP). To this end, we develop a hierarchical Bayesian space-time model that quantifies the discrepancies between different members of an ensemble of RCMs corresponding to present day conditions, and observational records. Discrepancies are then propagated into the future to obtain high resolution blended projections of 21st century climate. In addition to blended projections, the proposed method provides location-dependent comparisons between the different simulations by estimating the different modes of spatial variability, and using the climate model-specific coefficients of the spatial factors for comparisons. The approach has the flexibility to provide projections at customizable scales of potential interest to stakeholders while accounting for the uncertainties associated with projections at these scales based on a comprehensive statistical framework. We demonstrate the methodology with simulations from the Weather Research & Forecasting regional model (WRF) using three different boundary conditions. We use simulations for two time periods: current climate conditions, covering 1971 to 2000, and future climate conditions under the Special Report on Emissions Scenarios (SRES) A2 emissions scenario, covering 2041 to 2070. We investigate and project yearly mean summer and winter temperatures for a domain in the South West of the United States.     

Seismic response of steel frame structures with hybrid passive control systems

The concept of the hybrid passive control system is studied analytically by investigating the seismic response of steel frame structures. Hybrid control systems consist of two different passive elements combined into a single device or system. The hybrid systems investigated in this research consist of a rate‐dependent damping device paired with a rate‐independent energy dissipation element. The innovative configurations exploit individual element strengths and offset their weaknesses through multiphased behavior. A nine‐story, five‐bay steel moment‐frame was used for the analysis. Six different seismic resisting systems were analyzed and compared. The conventional systems included a special moment‐resisting frame (SMRF) and a dual SMRF–buckling‐restrained brace (BRB) system. The final four configurations are hybrid passive systems. The different hybrid configurations utilize a BRB and either a high‐damping rubber damper or viscous fluid damper. The analyses were run in the form of an incremental dynamic analysis. Several damage measures were calculated, including maximum roof drift, base shear, and total roof acceleration. The results demonstrate the capability of hybrid passive control systems to improve structural response compared with conventional lateral systems and to be effective for performance‐based seismic design. Each hybrid configuration improved some aspect of structural response with some providing benefits for multiple damage measures. The multiphased nature provides improved response for frequent and severe seismic events. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental determination of the chromium-aluminum mixing parameter in garnet

The equilibrium Grossular + Quartz = Anorthite + 2 Wollastonite was used to obtain the mixing properties of Cr and Al in grossular-uvarovite solid solutions by determining displacement of the univariant boundary curve for measured values of $\text{x}{}_{\mathrm{gross}}{}^{\mathrm{gt}}$. Experiments were performed in a piston cylinder apparatus with initial garnet compositions Gr₁₀₀, Gr₈₀Uv₅₀, Gr₅₀Uv₅₀, and Gr₂₀Uv₈₀. Reversals were obtained in the temperature range 1040°C–1320°C and corrected pressure range 10–17 kbar. Results indicate that grossular-uvarovite solutions can be modeled as nearly ideal two-site solid solutions. W_G^Cr,Al of +200 to + 1000 cal/mole is consistent with our experimental results.     

Precipitate flotation of copper as the sulfide,using recyclable amphoteric surfactants

An experimental study was made to identify surfactants which are effective for removal of copper from dilute aqueous solution (100–500 ppm) by precipitate flotation as the sulfide, and which at the same time can be recovered from the CuS product for recycle. Batch flotation experiments confirmed that a cationic surfactant was necessary for flotation of CuS from such dilute suspensions; however, no satisfactory way could be found for recovering cationic surfactants from the CuS. This led to consideration of amphoteric surfactants, which are cationic at low pH and anionic at high pH. It was found that a change to negative, rather than simply neutral, charge was required for efficient surfactant recovery. It was further found, through the assistance of experiments in which the CuS suspension was agitated with solvents, that certain functional groups which interact chemically with the CuS surface should also be absent from the surfactant molecule. Following this logic, Amphoterge K-2 (Lonza Chemical Co.) was identified as a suitable surfactant, provided CuS was precipitated with S^2? in excess. Tests established that 95% of adsorbed Amphoterge K-2 could be recovered by raising the pH to 11 and boiling the suspension for one hour, followed by decanting. Surfactant thus recovered was effective in a second flotation test. Foamate solids settled rapidly; such behavior would help reduce the consumption of chemicals for the pH change.Column flotation studies were made using Amphoterge K-2 for removal of Cu²⁺ present at 100 ppm and pH = 2. High removals of CuS could be obtained at concentrations of surfactant above about 25 ppm, for which conditions a substantial fraction of the surfactant remains in solution rather than being adsorbed onto the CuS. The recovery of CuS would be improved by introducing the surfactant in a separate feed, below the feed of CuS suspension. Adding some surfactant in the CuS feed, as well as in a lower feed, gave an even better recovery of CuS (99.8%) at sufficiently high surfactant loadings.     

Paleomagnetic stratigraphy of Pliocene Centerville Beach section,northern California

Samples from the upper two-thirds of the approximately 1900 m thick Neogene section exposed south of Centerville Beach on the northern California coast have predominantly reversed detrital remanent magnetism. Fossil evidence suggests a lower Pliocene through lower Pleistocene age for the section. The combined paleomagnetic and fossil data indicate that a large part of the section was deposited during the Matayama reversed epoch (2.4-0.7 million years ago). Samples from correlative sections exposed a few kilometers inland from the Centerville Beach section have a predominantly normal polarity and appear to have been remagnetized. The Centerville Beach section is important because it may serve as a standard with which to compare both other on-land Pliocene sections from western North America and nearby Deep Sea Drilling Project cores.     

Light requirements of seagrassesHalodule wrightii andSyringodium filiforme derived from the relationship between diffuse light attenuation and maximum depth distribution

The correspondence between maximum depth of growth (Z_max) for two seagrases,Halodule wrightii andSyringodium filiforme, and the attenuation of diffuse photosynthetically active radiation (K_dPAR) were evaluated over a 3.5-yr period in the southern Indian River Lagoon, Florida. The lower limit of seagrass depth distribution was controlled by light availability. Both species grew to the same maximum depth, indicating they have similar minimum light requirements. Based on average annual values of K_dPAR, estimates of seagrass minimum light requirements ranged from 24% to 37% of the light just beneath the water surface (I_o), much hgiehr than a photic zone for many phytoplankton and macroalgae (1–5% incident light). In less transparent waters of Hobe Sound, where turbidity (NTU) and color (Pt-Co) had their highest concentrations, minimum light requirements for growth were greatest. These results suggest that more sophisticated optical models are needed to identify specific water quality constituents affecting the light environment of seagrasses. Water quality criteria and standards needed to protect seagrasses from decreasing water transparency must be based on parameters that can be routinely measured and reasonably managed.     

Emerging fisheries,emerging fishery interactions with sea turtles: A case study of the large-mesh gillnet fishery for flounder in Pamlico Sound,North Carolina,USA

Emerging fisheries and changes in fishery practices are not always readily apparent, nor are their impacts on non-target species such as seabirds, sea turtles, and marine mammals. Data from several different sources led managers to discover high rates of sea turtle bycatch in an inshore large-mesh gillnet fishery in North Carolina, USA, particularly the emerging deep-water gillnet fishery. This paper reviews the history of how increased numbers of observed stranded sea turtles in 1999 led to the discovery that turtles were becoming entangled in the large-mesh gillnet fishery in Pamlico Sound, North Carolina. It also demonstrates how a variety of data sets from fisheries observers, aerial surveys, and fisheries statistics programs contributed to shaping management of the large-mesh gillnet fishery in Pamlico Sound to decrease turtle bycatch and now point towards the need of additional assessment of gillnet bycatch in other parts of North Carolina. Finally, potential approaches are discussed for a more timely detection of future fishery conflicts and development of a plan to reduce otherwise inevitable bycatch and disruptions to fishing effort.     

An investigation into the effects of damping and nonlinear geometry models in earthquake engineering analysis

The growing emphasis of considering the behavior of structures at extreme performance states, such as collapse, has necessitated the characterization of the effects of varying attributes of the structural model. One source of variability that has not previously been considered is variability in the mathematical model. This study investigated the effects of changing the geometric nonlinearity approach and damping model on a four‐story buckling restrained braced frame, a four‐story steel moment resisting frame, and an eight‐story steel moment resisting frame. The variations in behavior are quantified using the maximum interstory drift ratio as the performance metric and qualified by comparing the relative displaced shapes and component response histories at the collapse performance state. Copyright © 2015 John Wiley & Sons, Ltd.     

Paraffin hydrocarbon patterns in petroleum-polluted mussels

This paper explains how modern analytical techniques can be used to detect hydrocarbons in marine organisms at extremely low concentrations, below those detectable by taste or smell.