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Unlike nearly all engineered materials which contain bonds that weaken under load, biological materials contain "catch" bonds which are reinforced under load. Consequently, materials, such as the cell cytoskeleton, can adapt their mechanical properties in response to their state of internal, non‐equilibrium (active) stress. However, how large‐scale material properties vary with the distance from equilibrium is unknown, as are the relative roles of active stress and binding kinetics in establishing this distance. Through course‐grained molecular dynamics simulations, the effect of breaking of detailed balance by catch bonds on the accumulation and dissipation of energy within a model of the actomyosin cytoskeleton is explored. It is found that the extent to which detailed balance is broken uniquely determines a large‐scale fluid‐solid transition with characteristic time‐reversal symmetries. The transition depends critically on the strength of the catch bond, suggesting that active stress is necessary but insufficient to mount an adaptive mechanical response. [ABSTRACT FROM AUTHOR]

The hypoxic zone on the Louisiana Continental Shelf (LCS) forms each summer due to nutrient‐enhanced primary production and seasonal stratification associated with freshwater discharges from the Mississippi/Atchafalaya River Basin (MARB). Recent field studies have identified highly productive shallow nearshore waters as an important component of shelf‐wide carbon production contributing to hypoxia formation. This study applied a three‐dimensional hydrodynamic‐biogeochemical model named CGEM (Coastal Generalized Ecosystem Model) to quantify the spatial and temporal patterns of hypoxia, carbon production, respiration, and transport between nearshore and middle shelf regions where hypoxia is most prevalent. We first demonstrate that our simulations reproduced spatial and temporal patterns of carbon production, respiration, and bottom‐water oxygen gradients compared to field observations. We used multiyear simulations to quantify transport of particulate organic carbon (POC) from nearshore areas where riverine organic matter and phytoplankton carbon production are greatest. The spatial displacement of carbon production and respiration in our simulations was created by westward and offshore POC flux via phytoplankton carbon flux in the surface layer and POC flux in the bottom layer, supporting heterotrophic respiration on the middle shelf where hypoxia is frequently observed. These results support existing studies suggesting the importance of offshore carbon flux to hypoxia formation, particularly on the west shelf where hypoxic conditions are most variable. Plain Language Summary: Formation of hypoxia, or low dissolved oxygen, is a seasonal occurrence on the Louisiana Continental Shelf associated with stratification of the water column and excess nutrient loads delivered via the Mississippi and Atchafalaya River systems. Frequently referred to as "dead zones," bottom‐water hypoxia results in stress or death of aquatic organisms, especially those that cannot move to areas with more oxygen. To study the sources and distribution of organic matter that supports oxygen consumption, we applied a three‐dimensional hydrodynamic‐biogeochemical model named CGEM (Coastal Generalized Ecosystem Model). CGEM simulations between 2003 and 2007 successfully simulated spatial and temporal patterns of hypoxia and important biological processes that control its formation. Our simulations revealed that highly productive nearshore waters serve as a source of organic matter that supports oxygen consumption offshore. We identified seasonal bottom‐layer currents that transport organic matter offshore and interannual variations in river discharge that influence biological production and bottom‐layer oxygen consumption offshore. The ecological processes described in this study increase our understanding of how nearshore processes affect the development and maintenance of offshore hypoxia. Key Points: Simulation models describe ecological processes controlling spatial patterns in production and respiration and effect on hypoxiaOffshore organic matter flux from highly productive nearshore areas supports increased respiration offshoreOffshore carbon flux is an important driver of oxygen demand and resulting hypoxia at intermediate depths where hypoxia commonly occurs [ABSTRACT FROM AUTHOR]

Benthic invertebrate community composition was surveyed across the salinity gradient of the Pensacola Bay Estuary in Florida during summer 2016. Macrofauna densities ranged from 1000 to 9300 individuals m−2, with highest densities occurring at the upper estuary and the lowest in the mid‐ and lower estuary. Taxonomic richness and Shannon diversity were lowest in the upper estuary and increased along the salinity gradient. Small‐bodied, near‐surface infaunal polychaete species (e.g., Mediomastus ambiseta and Paraprionospio alata) dominated the macrofaunal community in fine sediment areas. We calculated the Gulf of Mexico Benthic Index of Biological Integrity for each site and compared the index scores with those from Environmental Monitoring and Assessment Program ‐ Estuaries, an earlier benthic assessment model. Condition evaluations by the different models did not match across all sites in this study; however, scores consistently indicated that most sites were at or near degraded levels, implying that Pensacola Bay represents a marginal habitat for a "healthy" benthic macrofauna community. This study provided new information about the benthic communities and sediments in the Pensacola Bay estuary. Integr Environ Assess Manag 2020;16:245–256. Published 2019. This article is a US Government work and is in the public domain in the USA. KEY POINTS: Study describes benthic communities in the Pensacola Bay system, in the Gulf of Mexico (GOM), and evaluates habitat condition using 2 benthic index approaches, i.e., GOM Benthic Index of Biological Integrity (B‐IBI) and Environmental Monitoring and Assessment Program ‐ Estuaries (EMAP‐E).Results of this study suggest that more systematic testing and reference site assessments are needed to make the GOM B‐IBI more useful for environmental management applications, particularly for high‐salinity regions of northern Florida estuaries with muddy sediments.Until the GOM B‐IBI can be refined to include panhandle‐specific metrics, the EMAP‐E index may be the most appropriate model for assessing the benthic habitat condition in this region. [ABSTRACT FROM AUTHOR]

The aims of this study were to assess the perceptions of dental students, faculty members, and patients about the benefits and pitfalls of intraoral camera use and to compare the completion rate of treatment planned posterior crowns with and without intraoral camera use in a predoctoral dental clinic. From July 2016 to June 2017, all 60 fourth‐year dental students at one U.S. dental school were encouraged to use the intraoral camera in treatment planning with patients in the school clinic. Perceptions of the students, their patients, and the faculty members supervising the treatment planning were assessed with a survey at the end of the treatment planning appointment. The completion rate of treatment planned posterior crowns was determined by recalling all posterior teeth that were treatment planned for a single unit crown at a specific period of time compared to the number of the same crowns completed for the same patients at a specific period of time, using the electronic health record, with and without camera use. Of the 60 students, 51 completed 198 surveys (85% response rate); 35 faculty members completed 64 surveys, and 202 patients completed one survey each (response rates for those groups could not be calculated). The survey results suggested that the students, faculty, and patients viewed intraoral camera use in a positive way. However, faculty perceptions were a little lower than those of patients and students, and a significant number of faculty members were neutral. The completion rate of posterior planned crowns was significantly higher (p=0.0005) when intraoral cameras were used to present images to patients than when cameras were not used. In this study, intraoral camera use in a predoctoral clinic was perceived positively by students and patients but more neutrally by faculty, and it increased the completion rate of planned posterior crowns. [ABSTRACT FROM AUTHOR]

In aquatic systems, time series of dissolved oxygen (DO) have been used to compute estimates of ecosystem metabolism. Central to this open-water method is the assumption that the DO time series is a Lagrangian specification of the flow field. However, most DO time series are collected at fixed locations, such that changes in DO are assumed to reflect metabolism and that effects of advection or mixing are negligible. A weighted regression model was applied to remove variability in DO time series from tides, thereby helping to partially relax this assumption and improve metabolism estimates. The method offers a distinct advantage over traditional deconvulution methods by targeting the periodicity of the tidal component while preserving the true biological signal. The model was first applied to simulated DO time series with specified biological and physical characteristics, and then applied to 1 yr of continuous monitoring data from four stations within the National Estuarine Research Reserve System. The correlation of DO and metabolism estimates with tides was greatly reduced after using weighted regression. The model was especially effective when the magnitude of tidal influence was high and correlations between tidal change and the solar cycle were low at the time scales of interest. The model was less robust when tides and the solar cycle were correlated for protracted periods. By reducing the effects of physical transport on metabolism estimates, there may be increased potential to empirically relate metabolic rates to causal factors on timescales of several days to several weeks. [ABSTRACT FROM AUTHOR]

Here we report uranium and thorium isotopic ratios and elemental concentrations measured in solid reference materials from the USGS (BHVO-2G, BCR-2G, NKT-1G), as well as those from the MPI-DING series (T1-G, ATHO-G). Specifically created for microanalysis, these naturally-sourced glasses were fused from rock powders. They cover a range of compositions, elemental concentrations and expected isotopic ratios. The U-Th isotopic ratios of two powdered source materials (BCR-2, BHVO-2) were also characterised. These new measurements via multi-collector thermal ionisation mass spectrometry and multi-collector inductively coupled plasma-mass spectrometry can now be used to assess the relative performance of techniques and facilitate comparison of U-Th data amongst laboratories in the geoscience community for in situ and bulk analyses. [ABSTRACT FROM AUTHOR]

Incorporating growth into contemporary material functionality presents a grand challenge in materials design. The F‐actin cytoskeleton is an active polymer network that serves as the mechanical scaffolding for eukaryotic cells, growing and remodeling in order to determine changes in cell shape. Nucleated from the membrane, filaments polymerize and grow into a dense network whose dynamics of assembly and disassembly, or "turnover," coordinates both fluidity and rigidity. Here, the extent of F‐actin nucleation is varied from a membrane surface in a biomimetic model of the cytoskeleton constructed from purified protein. It is found that nucleation of F‐actin mediates the accumulation and dissipation of polymerization‐induced F‐actin bending energy. At high and low nucleation, bending energies are low and easily relaxed yielding an isotropic material. However, at an intermediate critical nucleation, stresses are not relaxed by turnover and the internal energy accumulates 100‐fold. In this case, high filament curvatures template further assembly of F‐actin, driving the formation and stabilization of vortex‐like topological defects. Thus, nucleation coordinates mechanical and chemical timescales to encode shape memory into active materials. [ABSTRACT FROM AUTHOR]

Dissolved inorganic carbon (DIC), total alkalinity (TAlk), pH, and dissolved oxygen (DO) were determined in the Mississippi River plume during five cruises conducted in the spring, summer, and fall. In contrast to many other large rivers, both DIC and TAlk were higher in river water than in seawater. Substantial losses of DIC, relative to TAlk, occurred within the plume, particularly at intermediate salinities. DIC removal was accompanied by high DO, high pH, and nutrient depletion, and was attributed to high phytoplankton production. As a result, the carbonate saturation in the plume became much higher than in ocean and river waters. A mixing model was used to determine DIC removal. We provide evidence that the use of a two-end-member (river and ocean) mixing model was valid during late summer and fall (low discharge period). However, for other periods we used salinity and TAlk to delineate a mixing model that included two river end members and an ocean end member. Net community production rates in the plume, estimated using a box model, peaked in the summer and were among the highest reported to date for large river plumes. In the summer and fall, biological production in the river plume consumed a majority of the available nutrients, whereas during the spring only a small fraction of the available nutrients were consumed in the plume. Biological production was the dominant process influencing pH and carbonate saturation state along the river-ocean gradient, whereas physicochemical dynamics of mixing played an important role in controlling the TAlk and DIC distributions of this large river plume. [ABSTRACT FROM AUTHOR]