Nanowrinkled Carbon Aerogels Embedded with FeN x Sites as Effective Oxygen Electrodes for Rechargeable Zinc-Air Battery.

Rational design of single-metal atom sites in carbon substrates by a flexible strategy is highly desired for the preparation of high-performance catalysts for metal-air batteries. In this study, biomass hydrogel reactors are utilized as structural templates to prepare carbon aerogels embedded with single iron atoms by controlled pyrolysis. The tortuous and interlaced hydrogel chains lead to the formation of abundant nanowrinkles in the porous carbon aerogels, and single iron atoms are dispersed and stabilized within the defective carbon skeletons. X-ray absorption spectroscopy measurements indicate that the iron centers are mostly involved in the coordination structure of FeN4, with a minor fraction (ca. 1/5) in the form of FeN3C. First-principles calculations show that the FeN x sites in the Stone-Wales configurations induced by the nanowrinkles of the hierarchically porous carbon aerogels show a much lower free energy than the normal counterparts. The resulting iron and nitrogen-codoped carbon aerogels exhibit excellent and reversible oxygen electrocatalytic activity, and can be used as bifunctional cathode catalysts in rechargeable Zn-air batteries, with a performance even better than that based on commercial Pt/C and RuO2 catalysts. Results from this study highlight the significance of structural distortions of the metal sites in carbon matrices in the design and engineering of highly active single-atom catalysts

Decomposition of the Leinster-Cobbold Diversity Index

The Leinster and Cobbold diversity index possesses a number of merits; in particular, it generalises many existing indices and defines an effective number. We present a scheme to quantify the contribution of richness, evenness, and taxonomic similarity to this index. Compared to the work of van Dam (2019), our approach gives unbiased estimates of both evenness and similarity in a non-homogeneous community. We also introduce a notion of taxonomic tree equilibration which should be of use in the description of community structure.Comment: 10 pages, 1 figur

Ruthenium atomically dispersed in carbon outperforms platinum toward hydrogen evolution in alkaline media.

Hydrogen evolution reaction is an important process in electrochemical energy technologies. Herein, ruthenium and nitrogen codoped carbon nanowires are prepared as effective hydrogen evolution catalysts. The catalytic performance is markedly better than that of commercial platinum catalyst, with an overpotential of only -12 mV to reach the current density of 10 mV cm-2 in 1 M KOH and -47 mV in 0.1 M KOH. Comparisons with control experiments suggest that the remarkable activity is mainly ascribed to individual ruthenium atoms embedded within the carbon matrix, with minimal contributions from ruthenium nanoparticles. Consistent results are obtained in first-principles calculations, where RuCxNy moieties are found to show a much lower hydrogen binding energy than ruthenium nanoparticles, and a lower kinetic barrier for water dissociation than platinum. Among these, RuC2N2 stands out as the most active catalytic center, where both ruthenium and adjacent carbon atoms are the possible active sites

Estimating half-saturation constants of microzooplankton grazing in the sea

This study is a preliminary step to estimate microzooplankton grazing half-saturation constants (K) from dilution experiments in which nonlinear feeding kinetics occurred. In 528 dilution experiments, 96 experiments show significantly concave curves and only 22 experiments show convex curves. The average Chl a concentrations in the experiments which show concave curves were significantly higher than those showing linear and convex curves. The estimated values of K vary three orders of magnitude and are are log-log linearly related with ambient Chl a concentrations.Poster presented at Ocean Sciences Meeting 2016, the Oceanography Society, ASLO, AGU, New Orleans, Louisiana, USA, Feb. 21-26, 201

Decomposing diversity into measures of evenness, similarity, and richness

It has long been recognized that diversity has many measurable aspects, such as richness, evenness, and similarity among species. However, given a diversity index, it is unclear whether it necessarily can be decomposed into components that reflect these different aspects. Here, we present a scheme to decompose the Leinster and Cobbold diversity index, which subsumes and generalizes many other indices, into the components of richness, evenness and taxonomic similarity. Our approach addresses the problem that in general a vector of equal relative abundances does not maximize diversity. Furthermore, our approach uses all available information to give unbiased estimates of both evenness and similarity

Diel vertical migration promotes zooplankton horizontal patchiness

Spatial patchiness of plankton enhances fishery production and carbon export in the ocean. While diel vertical migration (DVM) has been identified as an important factor contributing to vertical patchiness, its effect on horizontal patchiness has never been investigated. We use a simple individual based zooplankton model to examine the effect of DVM on the horizontal patchiness of four zooplankton groups with differing DVM patterns in a two-dimensional ocean circulation model. We find that zooplankton horizontal patchiness can be induced by two mechanisms: 1) in stratified waters, DVM can synchronize zooplankton vertical positions with the horizontal current velocities that drive them, resulting in horizontal patchiness; and 2) migrating zooplankton tend to aggregate in deep waters when they encounter sea bottom. Due to these mechanisms, zooplankton horizontal patchiness may be ubiquitous in the ocean, enhancing secondary production and fisheries

Optimality-based approach for computationally efficient modeling of phytoplankton growth, chlorophyll-to-carbon, and nitrogen-to-carbon ratios

To increase the efficiency of computing phytoplankton growth rate (μ), chlorophyll-to-carbon (θ) and nitrogen- to-carbon ratios (QN) in three-dimensional ocean circulation models, it is preferable to directly calculate θ and QN from ambient environmental factors instead of treating them as independent tracers. Optimality-based modeling has emerged as a novel and efficient approach to fulfill this task. However, it is still unclear precisely how the response of optimality-based models differs from conventional models. We compare a recent optimality- based phytoplankton model (PAHLOW model), based on which the familiar Droop function can be derived, to a commonly used Monod-type (MONOD) model. The two models generate similar patterns of μ with some im- portant differences. Compared to the MONOD model, the PAHLOW model predicts higher μ under light lim- itation. The PAHLOW model also predicts that θ decreases with decreasing light under dim light and predicts decreasing QN with increasing light even at constant nutrient levels. Compared to the MONOD model, these features of the PAHLOW model qualitatively agree better with laboratory data. The PAHLOW model also suffers from a few shortcomings including the underestimation of θ under very low light and two times of computation time compared to the MONOD model. The two models generate striking differences of QN and θ in a one- dimensional implementation. Validation of such patterns will require more direct in situ measurements of μ, θ and QN

PIBM 1.0: An individual-based model for simulating phytoplankton acclimation, diversity, and evolution in the ocean

Phytoplankton is a diverse group of photosynthetic organisms and accounts for almost half of global primary produc-tion. However, most existing marine ecosystem models incorporate limited phytoplankton diversity, overlook phytoplankton evolution, and treat phytoplankton as concentrations instead of particles. Here we present an individual-based phytoplankton model that captures three dimensions of phytoplankton traits (size, temperature, and light affinities) and allows phytoplankton cells to mutate in a one-dimensional (1D) water column. Other components of this ecosystem include dissolved inorganic nitrogen, twenty size classes of zooplankton, and detritus, all modelled as Eulerian fields. This hybrid plankton model can reproduce the general seasonal patterns of nutrients, chlorophyll, and primary production in the subtropical ocean. We expect that this model will be a useful tool for studying phytoplankton physiology, diversity and evolution in the ocean

Seasonal variability of mesozooplankton feeding rates on phytoplankton in subtropical coastal and estuarine waters

In order to understand how mesozooplankton assemblages influenced phytoplankton in coastal and estuarine waters, we carried out a monthly investigation on mesozooplankton composition at two contrasting stations of Hong Kong coastal and estuarine waters and simultaneously conducted bottle incubation feeding experiments. The assemblage of mesozooplankton was omnivorous at both stations with varying carnivory degree (the degree of feeding preference of protozoa and animal food to phytoplankton) and the variations of carnivory degree were significantly associated with microzooplankton biomass (ciliates for the coastal station, both ciliates and dinoflagellates for the estuarine stations) and physical environmental parameters (primarily salinity). High carnivory was primarily due to high composition of noctilucales, Corycaeus spp., Oithona spp. and Acartia spp. Results of feeding experiments showed that grazing impacts on phytoplankton ranged from -5.9 to 17.7%, while the mean impacts were just < 4% at both stations. The impacts were size-dependent, by which mesozooplankton consumed around 9% of large-sized phytoplankton while indirectly caused an increase of 4% of small-sized phytoplankton. Mesozooplankton clearance rate on phytoplankton, calculated from the log response of chlorophyll a concentrations by the introduction of bulk grazers after 1-day incubation, was significantly reduced by increasing carnivory degree of the mesozooplankton assemblage. The mechanism for the reduction of mesozooplankton clearance rate with increasing carnivory degree was primarily due to less efficient of filtering feeding and stronger trophic cascades due to suppression of microzooplankton. The feeding rates of mesozooplankton on microzooplankton were not obtained in this study, but the trophic cascades indirectly induced by mesozooplankton carnivorous feeding can be observed by the negative clearance rate on small-sized phytoplankton. Overall, the main significance of this study is the empirical relationship between carnivory degree and clearance rate, which allow researchers to potentially predict the herbivory of mesozooplankton in the nature without conducting feeding experiments

Evidence of partial thermal compensation in natural phytoplankton assemblages

Whether phytoplankton growth is solely constrained by temperature (hotter is better) or compensated by thermal adaptation is still under debate. We measured the temperature sensitivity of natural phytoplankton communities at both short‐term and seasonal timescales using temperature manipulation experiments. The activation energy across communities (mean ± SE: E i = 0.51 ± 0.12 eV, Q10 = 1.98) is significantly lower than that within communities (E a = 0.80 ± 0.10 eV, Q10 = 2.80). Moreover, using a larger dataset of phytoplankton growth rates measured in (sub)tropical waters, we estimated the across‐community activation energy as 0.33 ± 0.06 eV (Q10 = 1.56), which is also lower than E a . Our study is the first to suggest the “hotter is partially better” for natural phytoplankton communities, indicating that the phytoplankton communities can show some thermal adaptation capability. Our results highlight the importance of incorporating the differential temperature sensitivities at different timescales into the biogeochemical models to better evaluate how marine ecosystems will respond to climate changes