Effects of quenching on phase transformations and ferroelectric properties of 0.35BCZT-0.65KBT ceramics

© 2019 Elsevier Ltd Solid solutions of 0.35(Ba,Ca)(Zr,Ti)O3-0.65(K0.5Bi0.5)TiO3 (BCZT-KBT) having various Ca and Zr contents were synthesized by solid state reaction. The sintered ceramics exhibited interesting features comprising core-shell type microstructures and relaxor ferroelectric behaviour. The influence of air-quenching on structure and electrical properties has been systematically investigated. The results indicate that the compositional heterogeneity in the shell regions, for the slow-cooled state, was reduced by air quenching. Improvements are evident in ferroelectric tetragonal phase content, accompanied by increased polarisation values and depolarisation temperatures. Comparing the results obtained for two BCZT compositions, it was demonstrated that the stability of the ferroelectric tetragonal phase in slow-cooled BCZT-KBT samples was improved for the ceramic with lower Ca and Zr concentrations, denoted x = 0.06, comparing with that for higher levels, denoted x = 0.15. Furthermore, the electric field-induced ferroelectric state in the quenched ceramic with x = 0.06 was found to be more stable during heating, yielding an enhanced depolarisation temperature

Solvent-switchable continuous-breathing behaviour in a diamondoid metal–organic framework and its influence on CO2 versus CH4 selectivity

Understanding the behaviour of flexible metal–organic frameworks (MOFs)—porous crystalline materials that undergo a structural change upon exposure to an external stimulus—underpins their design as responsive materials for specific applications, such as gas separation, molecular sensing, catalysis and drug delivery. Reversible transformations of a MOF between open- and closed-pore forms—a behaviour known as ‘breathing’—typically occur through well-defined crystallographic transitions. By contrast, continuous breathing is rare, and detailed characterization has remained very limited. Here we report a continuous-breathing mechanism that was studied by single-crystal diffraction in a MOF with a diamondoid network, (Me2NH2)[In(ABDC)2] (ABDC, 2-aminobenzene-1,4-dicarboxylate). Desolvation of the MOF in two different solvents leads to two polymorphic activated forms with very different pore openings, markedly different gas-adsorption capacities and different CO2 versus CH4 selectivities. Partial desolvation introduces a gating pressure associated with CO2 adsorption, which shows that the framework can also undergo a combination of stepped and continuous breathing

The Influence of Pupil Alignment on Spectator Address in Manet's Portraiture

Participants judged 94 portraits painted by Édouard Manet (70), Gustave Courbet (12) and Henri Fantin-Latour (12) for horizontal and vertical pupil misalignment and gaze ambiguity (Experiment 1) and focal point of gaze (Experiment 2). Eye movements were also measured as participants considered the extent to which sitters in the same portraits acknowledged viewers (spectators; Experiment 3). The results showed Manet portraits to be frequently painted with misaligned pupils that are associated with gaze ambiguity, especially when misaligned on the vertical axis. This ambiguity of gaze was associated with the average focal point of gaze as being judged further up and to the left of the centre for ambiguous relative to non-ambiguous portraits. These decisions in relation to portraits displaying ambiguous gaze were associated with increased eye-movements to the eye region relative to those portraits not displaying ambiguity. Finally, ratings of acknowledgement taken in Experiment 3 correlated with those of gaze ambiguity taken in Experiment 1. The results are interpreted in terms of the role of eye gaze in influencing spectatorship of portraits and, specifically, Fried’s theory of the ‘double relation’ (Fried 1980; Fried 1996) between painting and spectator in the paintings of Manet

Laboratory exploration of mineral precipitates from Europa's subsurface ocean

The precipitation of hydrated phases from a chondritic-like Na-Mg-Ca-SO4-Cl solution is studied using in situ synchrotron X-ray powder diffraction, under rapid (360 K hour−1, T = 250-80 K, t = 3 hours) and ultra-slow (0.3 K day−1, T= 273-245K, t = 242 days) freezing conditions. The precipitation sequence under slow cooling initially follows the predictions of equilibrium thermodynamics models, however after ∼ 50 days at 245 K, the formation of the highly hydrated sulphate phase Na2Mg(SO4)2·16H2O, a relatively recent discovery in the Na2Mg(SO4)2-H2O system, was observed. Rapid freezing, on the other hand, produced an assemblage of multiple phases which formed within a very short timescale (≤4 minutes, ∆T = 2 K) and, although remaining present throughout, varied in their relative proportions with decreasing temperature. Mirabilite and meridianiite were the major phases, with pentahydrite, epsomite, hydrohalite, gypsum, bl¨odite, konyaite and loweite also observed. Na2Mg(SO4)2·16H2O was again found to be present and increased in proportion relative to other phases as the temperature decreased. Results are discussed in relation to possible implications for life on Europa and application to other icy ocean worlds

Coastal stormwater wet pond sediment nitrogen dynamics

Wet ponds are a common type of stormwater control measure (SCM) in coastal areas of the southeastern US, but their internal nitrogen dynamics have not been extensively studied. Using flow-through intact sediment core incubations, net sediment N2 fluxes before and after a nitrate addition from five wet ponds spanning a range of ages (3.25–10 years old) were quantified through membrane inlet mass spectrometry during early summer. Multiple locations within a single wet pond (6.16 years old) were also sampled during ambient conditions in late summer to determine the combined effects of depth, vegetation, and flow path position on net N2 fluxes at the sediment-water interface. All pond sediments had considerable rates of net nitrogen fixation during ambient conditions, and net N2 fluxes during nitrate-enriched conditions were significantly correlated with pond age. Following a nitrate addition to simulate storm conditions, younger pond sediments shifted towards net denitrification, but older ponds exhibited even higher rates of net nitrogen fixation. The pond forebay had significantly higher rates of net nitrogen fixation compared to the main basin, and rates throughout the pond were an order of magnitude higher than the early summer experiment. These results identify less than optimal nitrogen processing in this common SCM, however, data presented here suggest that water column mixing and pond sediment excavation could improve the capacity of wet ponds to enhance water quality by permanently removing nitrogen

Living shorelines enhance nitrogen removal capacity over time

Living shorelines are nature-based solutions to coastal erosion that can be constructed as salt marshes with fringing oyster reefs. Each of these habitats can decrease the potential for eutrophication through increased nitrogen (N) removal via denitrification. However, the development of N cycling over time has not been studied in living shorelines. This research measured denitrification rates in a chronosequence of living shorelines spanning 0–20 years in age in Bogue Sound, NC. Analyses were conducted seasonally from summer 2014 to spring 2015 along an elevation transect through the salt marsh, oyster reef, and adjacent sandflat at all sites. Gas fluxes (N2 and O2) from sediment core incubations were measured with a membrane inlet mass spectrometer (MIMS) to assess denitrification and sediment oxygen demand. Fluxes of dissolved nutrients and the greenhouse gas N2O were measured. Sediment properties, inundation frequency, oyster filtration rates, and marsh grass stem density were also quantified. There was no significant difference in denitrification rates among habitats. N removal consistently increased from the 0- to 7-year-old sites. Denitrification efficiency was always greater than 50% and positive N2O fluxes were negligible. Our results suggest that living shorelines increase net N removal within a relatively short time period following construction, without introducing deleterious greenhouse gas emissions. This demonstrates that living shorelines can play an important role in estuarine N cycling and management

Non-Native Marsh Grass (Phragmites australis) Enhances Both Storm and Ambient Nitrogen Removal Capacity in Marine Systems

Marshes play a key role in global nitrogen cycling at the land–water margin. Invasive species are generally considered detrimental as they alter ecosystems they invade, but recent studies have shown some established invasive species can enhance certain ecosystem functions. The European haplotype of Phragmites australis is an aggressive and widespread invasive plant species in North America. We hypothesized that P. australis may play an important role in marsh nitrogen cycling by promoting higher rates of sediment denitrification compared with native marsh species. Seasonal measurements of sediment dissolved gas (N2 and O2) fluxes at three sites within the Albemarle-Pamlico Region of North Carolina compared sediments from invasive P. australis, native Spartina alterniflora, and/or Juncus roemarianus, and unvegetated sediments. In a marine tidal site, annual net denitrification in sediments associated with upland P. australis was highest compared to lower elevation marsh species or unvegetated sediments under ambient (139 μmol N2-N m−2 h−1) and nitrate enriched (219 μmol N2-N m−2 h−1) conditions. N2 fluxes were lower in sediments from two brackish marshes and did not differ between associated species, unvegetated sediments, or between high or low organic matter sites. Treatments with elevated nitrate showed enhanced net denitrification in most sediments at the marine site, suggesting the capacity to remove additional nitrate delivered episodically. Additionally, N2 fluxes measured before and after Hurricane Florence showed an increase in denitrification in P. australis sediments after the hurricane. Ecosystem value for this nitrogen removal service in the marine tidal site was estimated at US$ 266–426 *ha−1*yr−1. These results demonstrate an important role for invasive P. australis in coastal nitrogen cycling in marine environments and provide landscape context for potential biogeochemical impacts of this invasion

Nitrogen cycling processes within stormwater control measures: A review and call for research

Stormwater control measures (SCMs) have the potential to mitigate negative effects of watershed development on hydrology and water quality. Stormwater regulations and scientific literature have assumed that SCMs are important sites for denitrification, the permanent removal of nitrogen, but this assumption has been informed mainly by short-term loading studies and measurements of potential rates of nitrogen cycling. Recent research concluded that SCM nitrogen removal can be dominated by plant and soil assimilation rather than by denitrification, and rates of nitrogen fixation can exceed rates of denitrification in SCM sediments, resulting in a net addition of nitrogen. Nitrogen cycling measurements from other human-impacted aquatic habitats have presented similar results, additionally suggesting that dissimilatory nitrate reduction to ammonium (DNRA) and algal uptake could be important processes for recycling nitrogen in SCMs. Future research should directly measure a suite of nitrogen cycling processes in SCMs and reveal controlling mechanisms of individual rate processes. There is ample opportunity for research on SCM nitrogen cycling, including investigations of seasonal variation, differences between climatic regions, and trade-offs between nitrogen removal and phosphorus removal. Understanding nitrogen dynamics within SCMs will inform more efficient SCM design and management that promotes denitrification to help mitigate negative effects of urban stormwater on downstream ecosystems

The Effects of Urbanization and Retention-Based Stormwater Management on Coastal Plain Stream Nutrient Export

Stormwater nutrient pollution can be more effectively managed if there is a predictable link between urbanization and pollutant export. The goal of this study was to determine the effects of increased watershed impervious surface cover (ISC) and retention-based stormwater management on stream discharge and nutrient export from coastal plain streams in the southeastern United States. To quantify coastal plain stream nutrient export, measurements of stream discharge and concentrations of dissolved nutrients, particulate nitrogen, and algal biomass (as chlorophyll a) were collected during baseflow and stormflow for four years from five streams on Marine Corps Base Camp Lejeune near Jacksonville, North Carolina. The study streams had watersheds that spanned a range of ISC (1–38%) and included an urban watershed drained extensively by stormwater ponds. Urban streams had higher rates of annual discharge than less impacted streams due to elevated discharge at all rates of flow, more cumulative discharge at high flows, and dampened seasonal patterns. Streams with higher watershed ISC had higher rates of annual export of all measured nutrients due to increased stream discharge and concentrations of inorganic and particulate nitrogen. The relative importance of dissolved organic nitrogen decreased with watershed ISC, but it was still the dominant form of nitrogen export in every study stream except the stream that was dominated by particulate nitrogen export from stormwater pond algal production. Based on these findings, this study suggests that stormwater management emphasizing stormwater harvesting and evapotranspiration, increased wetland area, and decreased anthropogenic nutrient sources could reduce nutrient export from urban coastal plain streams