ALBERT

Beschreibung: Abstract A series of five realistic, nested, hydrostatic numerical ocean model simulations are used to study semidiurnal internal tide generation and propagation from the continental slope, through the shelf break and to the midshelf adjacent to Point Sal, CA. The statistics of modeled temperature and horizontal velocity fluctuations are compared to midshelf observations (30‐ to 50‐m water depth). Time‐ and frequency‐domain methods are used to decompose internal tides into components that are coherent and incoherent with the barotropic tide, and the incoherence fraction is 0.5–0.7 at the midshelf locations in both the realistic model and observations. In contrast, the incoherence fraction is at the most 0.45 for a simulation with idealized stratification, and neither atmospheric forcing nor mesoscale currents. Negligible conversion from barotropic to baroclinic energy occurs at the local shelf break. Instead, the dominant internal tide energy sources are regions of small‐scale near‐critical to supercritical bathymetry on the Santa Lucia escarpment (1,000–3,000 m), 70–80 km from the continental shelf. Near the generation region, semidiurnal baroclinic energy is primarily coherent and rapidly decays adjacent to the shelf break. In the realistically forced model, incoherent energy is less than 10% in the generation region, with a steady increase in incoherence fraction from the continental slope to the midshelf. Backward ray tracing from the midshelf to the Santa Lucia escarpment identifies multiple energy pathways potentially leading to spatial interference. As internal tides shoal on the predominantly subcritical slope/shelf system, temporally variable stratification and Doppler shifting from mesoscale and submesoscale features appear equally important in leading to the loss of coherence.

Beschreibung: Abstract Variability of the flow across the Solomon Sea's southern entrance was examined using end point subsurface moorings and seafloor pressure sensors, reconstructed velocity profiles based on satellite‐derived surface velocity and bottom pressure‐derived subsurface velocity, and 1993–2017 proxy volume transport based on satellite altimetry. The reconstructed velocity correctly represents the fluctuating surface flow and subsurface core providing a high‐frequency continuous observing system for this sea. The mean equatorward volume transport over 0‐ to 500‐m depth layer is 15.2 Sv (1 Sv ≡ 106 m3/s) during July 2012 to May 2017. The measurements resolve the full spectrum of the volume transport including energetic subseasonal variability that fluctuates by as much as 25 Sv over one week. At low‐frequency timescales, the study finds that linear Rossby waves forced by Ekman pumping in the interior of the Pacific influence not only seasonal fluctuations as found by previous studies but also interannual variability. As found previously, the El Niño–Southern Oscillation highly influences interannual volume transport. During the 2015/2016 El Niño, observations show the seasonal cycle to be suppressed from the second half of 2014, prior to the mature phase of the El Niño, to September 2016 along with an increase in across‐transect transport. At subseasonal timescales, local Ekman pumping and remote wind stress curl are responsible for a third of the subseasonal variance. The study highlights the importance of high‐frequency observations at the southern entrance of the Solomon Sea and the ability of a linear Rossby model to represent the low‐frequency variability of the transport.

Beschreibung: Abstract A direct method is presented to obtain the meridional overturning and heat transport in oceanic basins from observations under the sole assumptions of geostrophy and hydrostatics,. The method is made possible because of the rising Argo float displacements data base which can provide a reference level at 1000 dbar for the time mean circulation at 1° × 1° resolution. To achieve the overturning and heat transport objectives, the absolute geostrophic time mean circulation must have non divergent barotropic transports and this requires the solutions of two Poisson equations with suitable boundary conditions, one for the geopotential at 1000 dbar and one for the barotropic streamfunction. Applied to the subpolar Atlantic for the period 2000‐2009, an overturning of 16‐18 Sv is found around 40o‐50oN, a meridional heat transport of 0.59 PW is found at 40oN (0.23 PW at 60oN) so that on average ~50 Wm‐2 are exported from ocean to atmosphere to feed the atmospheric storm track. The zonally averaged flow (the overturning) falls short of explaining the observed heat transport and the barotropic component of the circulation accounts for up to 50% of the heat transport poleward of 55oN. With the rising Argo float data base, the method offers high potential to reconstruct the World Ocean time mean circulation and its heat transport away from the equator at higher resolution. The drawback is that it requires in some critical places additional current observations on the shallow shelves which are not sampled by the Argo floats.

Beschreibung: Abstract Here we present an observation‐based study of the coupled land‐ocean regions of influence for the transformation of precipitation over land into coastal river plume structure in the Gulf of Mexico (GoM). First, we locate the regions on land for which precipitation and runoff generation have the strongest relationship with local river discharge. Then we map, on average, the apparent unique contribution of individual river discharge forcing to specific features of river plume structure across the GoM. To this end, we employ a spatial‐temporal lagged correlation analysis that relates satellite‐based precipitation, soil moisture, and sea surface salinity observations to in situ river discharge for the three primary freshwater input sources for the GoM. On land, we find a likely source region for the northeastern GoM in the southeastern Mississippi basin at 16‐day lead time, a likely source region for the northeastern GoM in the Mobile Bay basin at 3‐day lead time and a likely source region for the Central GoM from the Texas basin region at 4‐day lead time. In the ocean, we find statistically significant regions of distinct contribution for each of the three sources of freshwater on plume structure at lag times from weeks to several months. Though a statistical approach is limited in its interpretability, this result advances progress toward a predictive framework for mapping of the impacts of hydrological flood events from land into the ocean using observations alone.

Beschreibung: Abstract This paper evaluates the intraseasonal variability of sea surface temperature (SST) along the Sumatra‐Java southern coast using available satellite‐derived oceanic and atmospheric data combined with output from a numerical model. The result reveals that the intraseasonal variability of SST is greater during boreal summer–fall (June–October) than during boreal winter–spring (November–May). Composite analysis shows a correlation between positive/negative intraseasonal SST variabilities and coastal downwelling/upwelling, as well as onshore/offshore Ekman transport during summer–fall. During this period, with the significantly increasing role of oceanic advection, oceanic processes are evidently enhanced and dominate the intraseasonal variability of SST. Meanwhile, the contribution of atmospheric processes drops by 67%. During winter–spring, the intraseasonal SST is primarily contributed by atmospheric processes but has a nonsignificant relationship with sea level anomalies. Intraseasonal SST anomalies vary out of phase with surface wind anomalies. The result also shows a relatively small contribution by vertical processes throughout the year, with the maximum in April and the minimum during August–September. Further analysis reveals that the alternating dominance of atmospheric and oceanic processes on intraseasonal variability of SST is responsible for the seasonality along the Sumatra‐Java southern coast. Moreover, the result indicates that the seasonality in intraseasonal SST is different in the eastern Indonesian Seas, which tends to be relatively strong in boreal winter. Distinct dominance of atmospheric and oceanic processes in intraseasonal SST is the main reason for these differences in seasonal variation characteristics.

Beschreibung: Abstract In this work, cobalt phosphide (CoP) nanoparticles were successfully decorated on an ultrathin g‐C3N4 nanosheet photocatalysts by in situ chemical deposition. The built‐in electric field formed by heterojunction interface of the CoP/g‐C3N4 composite semiconductor can accelerate the transmission and separation of photogenerated charge‐hole pairs and effectively improve the photocatalytic performance. TEM, HRTEM, XPS, and SPV analysis showed that CoP/g‐C3N4 formed a stable heterogeneous interface and effectively enhanced photogenerated electron‐hole separation. UV‐vis DRS analysis showed that the composite had enhanced visible light absorption than pure g‐C3N4 and was a visible light driven photocatalyst. In this process, NaH2PO2 and CoCl2 are used as the source of P and Co, and typical preparation of CoP can be completed within 3 hours. Under visible light irradiation, the optimal H2 evolution rate of 3.0 mol% CoP/g‐C3N4 is about 15.1 μmol h−1. The photocatalytic activity and stability of the CoP/g‐C3N4 materials were evaluated by photocatalytic decomposition of water. The intrinsic relationship between the microstructure of the composite catalyst and the photocatalytic performance was analyzed to reveal the photocatalytic reaction mechanism.

Beschreibung: Abstract High volume fraction SiC nanowires‐reinforced SiC composites (SiCNWs/SiC) were prepared by hybrid process of chemical vapor infiltration and polymer impregnation/pyrolysis in this research. SiCNWs networks are first to be made promising a high volume fraction (20 vol%), and the pyrolytic carbon (PyC) interphase with 5 nm is designed on SiCNWs surface to optimize the bonding condition between SiCNWs and SiC matrix. Nanoindentation shows a modulus of 494 ± 14 GPa of SiCNWs/SiC composites without interphase comparing to the one with PyC interphase of 452 ± 13 GPa. However, the 3‐point bending test shows a higher strength of the composite with PyC interphase (273 ± 32 MPa) comparing with the one without interphase (240 ± 38 MPa). The fracture surface is observed under SEM, which shows a longer SiCNWs pullout of the composite with PyC interphase. The energy dissipation during the 3‐point bending test is calculated by the length of nanowire pull‐out, it demonstrates that the SiCNWs with PyC interphase possess better performance for toughening composite. Further characterization proves that the PyC interphase can give SiCNWs/SiC composites higher fracture toughness (4.49 ± 0.44 MPa·m1/2) than the composites without interphase (3.66 ± 0.28 MPa·m1/2).

Beschreibung: Here, we report a multicolor PersL phosphor Sr Ga GeO :Pr .The PersL color can be tuned from deep red to blue. It reveals that the multicolor luminescence of the phosphor is essentially associated with the crossrelaxation effect of Pr . What's more,the PersL lifetime of the multicolor phosphor can be also tuned. Based on the unique features of Sr Ga GeO :Pr phosphor, some luminescent images are fabricated for dynamic multicolor anticounterfeiting. Abstract Persistent luminescence (PersL) phosphor is a glow‐in‐the‐dark material that has been widely applied. Here, we report a multicolor PersL phosphor Sr2Ga2GeO7:Pr3+. The PersL color can be tuned from deep red to blue. It reveals that the luminescent color modulation of the Sr2Ga2GeO7:Pr3+ phosphor is essentially associated with the cross‐relaxation effect of Pr3+ in the host with low‐phonon assistance energy. The PersL lifetime of the multicolor phosphors can be also tuned. Based on the unique features of Sr2Ga2GeO7:Pr3+ phosphor, some simple PersL images are fabricated to emit dynamic multicolor information, and it shows that the PersL image even depicts dynamic multicolor anticounterfeiting.

Beschreibung: Abstract Although great advance has been made in glass science, predicting luminescence properties of laser glass poses a significant challenge for scientists due to the complex relationship between the composition, structure, and properties of the rare earth ions doped laser glasses. The development of high‐performance laser glass usually relies on intuition and trial‐and‐error. Recently, with the proposal of the materials genome engineering, the “glass genome” has also attracted much attention. Here, the structure of the Nd3+ doped B2O3‐Li2O laser glasses was analyzed using Fourier transform infrared spectra and nuclear magnetic resonance, revealing that the glass contains similar glass‐forming ion‐centered coordination polyhedron structure groups to the neighbor congruent glassy compounds. The structure and properties of glass largely depend on the neighbor congruent glassy compounds. Therefore, the structure and luminescence properties of Nd3+ doped B2O3‐Li2O and B2O3‐MgO‐Li2O laser glasses can be quantitatively predicted via the neighbor congruent glassy compounds. The predictive values are in good agreement with the experimental data, which indicates that our approach is an effective way to predict the structure and luminescence properties of Nd3+ doped borate laser glasses.

Beschreibung: Abstract The Surface Water Ocean Topography (SWOT) satellite mission is planned for launch in 2021. It will use the technique of radar interferometry to measure sea surface height over a 120‐km‐wide swath with a 20‐km gap around the satellite's nadir track. The oceanographic objectives of the mission are to study ocean circulation at scales down to 15 km. To prepare for the evaluation of the mission's performance, we are undertaking a series of studies to explore the efficacy of an assimilative high‐resolution modeling system for estimating the state of the ocean based on independent observations from both spaceborne and in situ measurements. The system is based on the heritage of a multiscale approach to data assimilation by the Regional Ocean Modeling System. Observing System Simulation Experiments were first conducted in the setup of an identical twin experiment to assess the system's performance near the calibration/validation site of SWOT off the coast of California. The system was applied to a nested model domain with 1‐km resolution. Simulated satellite observations of SSH, sea surface temperature, salinity, in situ observations of upper ocean temperature, and salinity by profiling floats and a dedicated notional array of station‐keeping gliders were assimilated by the system. The results indicate that such an observing system can accurately estimate the state of the ocean, and in particular SSH for the evaluation of SWOT performance.

Beschreibung: Abstract Sea ice data assimilation can greatly improve forecasts of Arctic sea ice evolution. Many previous sea ice data assimilation studies were conducted without assimilating ocean state variables, even though the sea ice evolution is closely linked to the oceanic conditions, both dynamically and thermodynamically. Based on the method of a localized ensemble error subspace transform Kalman filter, satellite‐retrieved sea ice concentration and sea ice thickness are assimilated into an Arctic sea ice‐ocean model. As a new addition, sea surface temperature (SST) data are also assimilated. The additional assimilation of SST improves not only the simulated ocean temperature in the mixed layer of the ocean substantially but also the accuracy of sea ice edge position, sea ice extent, and sea ice thickness in the marginal sea ice zone. The improvement in the simulated potential temperature in the upper 1,000 m can be attributed to the enhanced vertical convection processes in the regions where the assimilated observational SST is colder than the simulated SST without assimilation. The improvements in the sea ice edge position and sea ice thickness simulations are primarily caused by the SST data assimilation reducing biases in the simulated SST and the associated coupled ocean‐sea ice processes. Our investigation suggests that, due to the complex interaction between the sea ice and ocean, assimilating ocean data should be an indispensable component of numerical polar sea ice forecasting systems.

Beschreibung: Abstract Despite the importance of the large‐scale Atlantic circulation for the climate system and sea level, most of the interior flow field is only known qualitatively, and neither the mean nor the variability and trends are quantified. We investigate the meridional flow field in the western Atlantic at 47°N between 44°W and 31°W, combining moored pressure inverted echo sounders and current meter moorings with lowered acoustic Doppler current profiler and Argo data. Correlations with altimetry are used to extend each of the transport time series back to 1993. At the Canadian continental margin the boundary current exports −23.1 ± 1.5 Sv to the south. Nearby, the northward flowing North Atlantic Current (NAC) imports 105.9 ± 3.4 Sv into the subpolar gyre. Constrained mainly by topography, about half of that flow recirculates in close proximity to the NAC (−58.8 ± 3.9 Sv). NAC and recirculation are significantly anticorrelated. The flow east of 37°W (−27.8 ± 2.1 Sv) has no permanent regional features and is not correlated to the NAC. The sum of the interior components (19.3 ± 3.3 Sv) shows a significant trend in the time period 1993–2018 of −0.60 Sv/year. This decline is dominated by the significant increase of the southward flow east of 37°W (−0.44 Sv/year). The trends of the other individual components are not significant, but the sum of the interior and boundary current transport is (−0.71Sv/year). The trends are most likely caused by regionally different warming.

Beschreibung: Abstract Mixing in the ocean and shelf seas is critical for the vertical distribution of dynamically active properties, such as density and biogeochemical tracers. Eight different decadal simulations are used to assess the skill of vertical Turbulent Mixing Schemes (TMS) in a 3D regional model of tidally active shelf seas. The TMS differ in the type of stability functions used and in the Ozmidov/Deardorff/Galperin limiter of the turbulence length scales. We review the dependence of the critical Richardson and Prandtl numbers to define the “diffusiveness” of the TMS. The skill in representing bias and variability of stratification profiles is assessed with 5 different metrics: surface and bottom temperatures; pycnocline depth, thickness and strength. The assessment is made against hydrography from three datasets (28,000 profiles in total). Bottom and surface temperatures are found to be as sensitive to TMS choice as to horizontal resolution or heat flux formulation, as reported in other studies. All TMS under‐represent the pycnocline depth and benthic temperatures. This suggests physical processes are missing from the model, and these are discussed. Different TMSs show the best results for different metrics, and there is no outright winner. Simulations coupled with an ecosystem model show the choice of TMS strongly affects the ecosystem behaviour: shifting the timing of peak chlorophyll by one month, showing regional chlorophyll differences of order 100%, and redistributing the production of chorophyll between the pycnocline and mixed layer.

Beschreibung: Abstract Ba2Ti9O20 single‐phase ceramics were prepared by reaction sintering method using TiO2 and BaCO3 as raw materials after heat treating at 1150°C for 10h. Furthermore, the formation mechanism and microstructure evolution of Ba2Ti9O20 ceramics prepared by reaction sintering method were investigated. The formation behavior of Ba2Ti9O20 phase was analyzed from the perspective of diffusion, where the reaction activation energy required for the process was calculated to be about 386.17kJ/mol. Combined with the scanning electron microscopy and the energy dispersive spectrometer, it was revealed that the pores on Ba2Ti9O20 grains in the process of reaction sintering might be caused by the absence of oxygen element. Meanwhile, the reason for the roughness of ceramic surface was that the local inhomogeneous distribution of barium on the surface of Ba2Ti9O20 grain leaded to the enrichment of titanium.

Beschreibung: Abstract Two dimensional (2D) SnS2/MoS2 heterojunction with a 2D/2D novel structure were used as electrodes materials for enhanced supercapacitor performance. Compared with the sole SnS2, the as‐prepared 2D/2D SnS2/MoS2 layered heterojunction has exhibited great improvement in supercapacitor properties. This novel structure can effectively prevent agglomeration and stacking in electrochemical process, and 2D/2D structure is beneficial to intercalation and desorption of ions in electrochemical processes. The experiment result shows that MoSn5 (Samples with 5% Mo:Sn mole ratios) display a specific capacitance of 466.6 F/g at the current Density of 1 A/g in 0.5M Potassium hydroxide solution, an impressive cycling stability with 88.2 % capacitance retention at current density of 4 A/g. In addition, the as‐fabricated symmetric supercapacitor exhibited high energy density of 115 Wh kg‐1 at the power density of 2230 W kg‐1. This work provides a fundamental investigation of 2D/2D layered material synergistic effect on the electrochemical process.

Beschreibung: Abstract Freeze casting is an established method for fabricating porous ceramic structures with controlled porosity and pore geometries. Herein, we developed a novel freeze casting and freeze drying process to fabricate tubular anode supports for solid oxide fuel cells (SOFCs). Freeze casting was performed by injecting aqueous anode slurry to a dual‐purpose freeze casting and freeze drying mold wrapped with peripheral coils for flowing a coolant. With the use of an ice barrier layer, proper control of the experimental setup, and adjustments in the drying temperature profile, complete drying of the individual anode tubes was achieved in four hours. The freeze‐cast anode tubes contained radially aligned columnar pore channels, thus significantly enhancing the gaseous diffusion. SOFC single cells with conventional Ni/yttria‐stabilized zirconia (YSZ)/strontium‐doped lanthanum manganite (LSM) materials were prepared by dip coating the thin functional layers onto the anode support. Single‐cell tests showed that the concentration polarization was low owing to the highly porous anode support with directional pores. With H2/N2 (1:1) fuel, maximum power densities of 0.47, 0.36, and 0.27 W/cm2 were recorded at 800, 750, and 700 °C, respectively. Our results demonstrate the feasibility of using freeze casting to obtain tubular SOFCs with desired microstructures and fast turn‐around times. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract During the Lagrangian submesoscale experiment (LASER), 1000 drifters were launched to sample the surface ocean flow in the northern Gulf of Mexico. Due to half a dozen strong winter storms, about 40% of the drifters lost their drogue. This unintended situation facilitated documentation of both near surface (5 cm) and deeper (60 cm) flows. These depths are relevant to transport of oil spills, as well as marine debris, such as micro plastics, a rapidly‐growing environmental problem. Here, we improve the surface Lagrangian current prediction by combining a state‐of‐the‐art ocean forecast model with wind and wave data. The ocean surface velocities are obtained from the Navy Coordinate Ocean Model (NCOM) at 1 km horizontal resolution, while the wind and wave fields are from the UWIN‐CM coupled atmosphere‐wave‐ocean model. Two Lagrangian parameterizations are tested: one is based on Ekman dynamics, and the other directly on the surface winds. LASER dataset is then used to assess the performance of these formulations, as a function of wind/wave conditions, as well as geographic region. It is found that incorporation of wind and wave data into the ocean circulation model can lead to major prediction improvement, by reducing the average two‐day separation from the modeled and real LASER trajectories by a factor ranging from 1.4 to 4.9. This is a significant improvement for applications, where a rapid deployment of assets is needed, such as oil spill response, or other tracking problems.

Beschreibung: Abstract The observed seasonal and intraseasonal evolution of near‐surface meteorological and oceanographic variables in the Andaman Sea (AS) during March 2014 to December 2017 is examined using moored buoy observations at 10.5°N, 94°E. The amplitude of temperature inversions is very weak (0.2°C to 0.4°C) and they appeared primarily during winter and latter part of summer. The net surface heat flux plays a primary role and vertical processes term contributes secondarily to determine the seasonal ML heat storage variability. Consistent with the seasonal variations of formation and strength of temperature inversion, vertical processes term shows a positive tendency during winter. The sea surface salinity (SSS) shows large amplitude intraseasonal variability during fall and winter and it is attributed to the variability of horizontal circulation in the presence of large lateral SSS gradients at the mooring location. The sea surface temperature (SST) shows the presence of strong intraseasonal variability between 20–80 days, though its amplitude of oscillation is distinctly higher during May–October than November–April. Bandpass filtered (20–80 days) time series of different components of the ML heat budget shows that the net surface heat flux primarily determines the intraseasonal ML heat storage variability. Our analysis further shows that during May–October, both net shortwave radiation and latent heat flux together determine the modulation of the intraseasonal net surface heat flux. In contrast, latent heat flux acts as the sole factor to determine the modulation of the intraseasonal net surface heat flux during November–April.

Beschreibung: Abstract The upper oceanic thermal response induced by Tropical Cyclone Phailin (9th‐14th October 2013) under the influence of East India Coastal Current (EICC) and a cyclonic eddy are investigated and contrasted with the response from open ocean region using a high‐resolution HYbrid Coordinate Ocean Model (HYCOM) simulation. There is significant cooling (7°C) inside the cold core eddy and negligible cooling (0.5°C) within the EICC region characterized by the shallow and deeper thermocline, respectively. Our analysis of mixed layer heat budget terms showed that the horizontal advection plays a significant role in determining the temperature tendency for the location within the EICC, in contrary to the general dominance of vertical processes as reported in previous studies during the cyclone period. The analysis for the locations Inside Eddy (IE) and Open Ocean (OO) concur with the previous studies showing the dominance of vertical processes towards the temperature tendency. Further, near the coast, the surface cooling is minimal compared to the subsurface cooling, dominantly seen between 50m to 100m depth. This disparity indicates that the factors responsible for the surface temperature anomalies are different from those of subsurface. Our analysis of thermal signatures after the passage of cyclone showed that the EICC and cyclonic eddy contributes to the faster advection of cold wake and recovery of SST to the pre‐storm state.

Beschreibung: Abstract Defect engineering plays an important role in property modification for piezoelectric materials. In this work, we pay much attention to the effect of Nb non‐stoichiometry on structure and properties of typical 0.95(K0.45Na0.55)Nb1+xO3‐0.05Bi0.5Na0.5HfO3 ceramics. Large piezoelectric constant (d33~425 pC/N and d33*~ 482 pm/V) together with high Curie temperature (TC~315 ºC) have been achieved in the ceramics with excess Nb content (x=0.01). However, the ceramics with deficient Nb element have seriously suppressed cryogenic εr‐T curves and deteriorated electrical properties. Multi‐scale characterizations including phase structure, microstructure, defect structure and domain structure have been adopted to explain the corresponding phenomenon. Defect complex of VNb'''''‐Vo.. caused by deficient Nb induces clamped domain wall motion, leading to blocked polarization vector and poor electrical properties. On the contrary, the enhanced properties for the ceramics with excess Nb are attributed to easier domain switching due to the suppressed vacancies. We believe that defect engineering, for example non‐stoichiometry, can not only modulate electrical properties but also help us to understand some fundamental and critical problems about KNN‐based ceramics. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The paper by Lee et al (J Am Ceram Soc 102:4555‐4561, 2019) reports on semiconductor quantum dots (QDs) obtained in a silicate glass matrix by a novel modification of the solid‐state precipitation technique and characterized by a variety of techniques. Based on their experimental data, we critically discuss their assessment of the QDs obtained as CdSe/Cd1−xZnxSe core/shell structures. By analyzing their results (in particular, Raman scattering data) and comparing them to other data available in literature, we show that the data presented give no evidence for the formation of core/shell structures and conclude that the authors obtained rather homogeneous Cd1−xZnxSe QDs without any noticeable compositional gradient.

Beschreibung: Abstract Solid‐oxide fuel cells (SOFCs) have the potential to increase electricity generation efficiency, but traditional SOFCs supported by nickel cermets suffer from reliability challenges due to weaker mechanical strength caused by cracking after redox cycling. To solve this problem, a new ceramic anode material, SrFe0.2Co0.4Mo0.4O3−δ (SFCM) combined with Ce0.9Gd0.1O2 (GDC), was evaluated for conductivity and mechanical strength at SOFC operating conditions and after redox cycling. Fracture toughness of SFCM was determined to be (0.124 ± 0.023) MPa√m at room temperature in air, increasing to (0.286 ± 0.038) MPa√m at 600°C. A mixture of SFCM:GDC showed fracture toughness between the two materials, following SFCM's trend with temperature. The SFCM‐GDC anode supported half‐cell strength increases by 31% from room temperature to 600°C as intrinsic stresses remaining from sintering are relaxed and thermal expansion pushes existing cracks closed. Exposure to reducing gasses decreases strength by 29% compared to ambient, due to oxygen vacancy formation and microstructural flaw changes. It is found that SFCM‐GDC based cells tolerate cycling well because of phase stability but weaken from 34.3 to 22.4 MPa due to uniform growth of critical microstructural flaws.

Beschreibung: Abstract Photoluminescence of rare earth ions doped glasses could be enhanced by diverse Ag species such as Ag+ ions, Ag+‐Ag+ pairs, Ag nano‐clusters (NCs) and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ions doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, the Ag+ ions and Ag NCs were selectively prepared in the Sm3+ doped borosilicate glass via the Ag+‐Na+ ion exchange. The influence of AgNO3/NaNO3 ratio in the molten salt on the Ag existing states was investigated. The results demonstrate the isolated Ag+ ions exist in the Sm3+ doped borosilicate glass when the ratio of AgNO3/NaNO3 is 1/1000. The Ag NCs are formed in the Sm3+ doped borosilicate glass when the AgNO3/NaNO3 ratio is 1/10. The influences of Ag+ ions or Ag NCs on the photoluminescence of Sm3+ were systematically investigated. The results show that the photoluminescence of Sm3+ was enhanced by the energy transfer from Ag+ ions or Ag NCs to Sm3+. This article is protected by copyright. All rights reserved.

Beschreibung: Journal of the American Ceramic Society, EarlyView.

Beschreibung: Abstract The Eu3+ ions doped (1‐x)Na0.5Bi0.5TiO3‐xSrTiO3 (Eu‐NBT‐xSTO) thin films were prepared on Pt/Ti/SiO2/Si substrates. Raman analysis reveals that the phase structure may undergo a phase evolution of rhombohedral → rhombohedral + tetragonal (morphotropic phase boundary) → tetragonal with increasing content of STO. The SEM images show that the uniformity and high density of Eu‐NBT‐xSTO films were increased by adding STO, resulting in a pronounced effect on energy‐storage properties. The ɛ‐T curves confirm that a high phase transition diffuseness of γ= 2.02±0.03 and 1.98±0.03 was achieved in Eu‐NBT‐0.24STO and Eu‐NBT‐0.3STO films, respectively. Further, a large recoverable energy‐storage density of 31.5 J/cm3 with an efficiency of 64% was obtained in Eu‐NBT‐0.3STO film, which also exhibited good thermal stability in the temperature range between ‐60 °C and 80 °C as well as long‐term stability up to 1×108 switching cycles. These results suggest that the Eu‐NBT‐xSTO films may be used in the novel and advanced energy‐storage capacitors. This article is protected by copyright. All rights reserved.

Beschreibung: No abstract is available for this article.

Beschreibung: Abstract A unique feature of cordierite is the negative thermal expansion of its c‐axis, while the a‐ and b‐axes show positive thermal expansion behavior. The thermal expansion mechanism of cordierite has been investigated in many theoretical studies, but the effect of Ti or Ge doping has not yet been studied theoretically. Here, we investigate the thermal expansion behavior of Ti‐ and Ge‐doped cordierite by ab initio molecular dynamics (AIMD) simulation. The computational cost of AIMD simulation for cordierite doped with Ti or Ge is challenging due to the many different configurations of crystal models. We overcame this computational difficulty by separating the respective models into groups with identical symmetry, then we performed the MD simulation for each different symmetry crystal model. To understand the mechanism of the negative thermal expansion of the c‐axis, we investigated the changes of all the bond lengths and angles. We found that the negative thermal expansion of the c‐axis is coupled with the increase in the O‐Al‐O angle and the shrinkage of the O‐Si‐O angle at the T1 site in cordierite, which suggests rotation of the six‐membered ring. This studyprovides insight into the mechanism of thermal expansion of cordierite with Ti and Ge doping. Moreover, the approach presented here can be generally applied to investigate the thermal expansion behavior of other ceramic materials within reasonable accuracy and computational cost. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Lateral nanoindentation provides access to the scratch hardness of glass surfaces. The specific sensitivity of the scratching experiment to surface mechanical properties can be enhanced when the local load at the tip apex is reduced. Here, we report on ramp‐load scratch tests on a range of silicate glasses using a sphero‐conical tip shape. Similar as with regular scratching experiments using sharp indenters, such tests create a sequence of micro‐ductile, micro‐cracking, and micro‐abrasive regimes. Detailed investigation of the indenter displacement h and of the lateral force FL as recorded in situ, however, reveals pronounced deviations in comparison to Vickers or Berkovich scratching experiments. Most notably, this includes an abrupt increase in both h and FL at moderate normal load, marking the onset of ductile fracture, and a yield point at the transition from fully elastic deformation to the elastic‐plastic regime at low load. For the range of examined silicate glasses, we find that structural cohesion controls yielding, whereas scratch‐induced fracture and micro‐abrasion are dominated by the volume density of bond energy.

Beschreibung: Abstract Heat transfer at the interfacial contact is a dominant factor in the thermal behavior of glass during nonisothermal glass molding process. Recent research is developing reliable numerical approaches to quantify contact heat transfer coefficients. In most previous studies, however, both theoretical and numerical models of thermal contact conductance in glass molding attempted to investigate this factor by either omitting surface topography or simplifying the nature of contact surfaces. In fact, the determination of the contact heat transfer coefficient demands a detailed characterization of the contact interface including the surface topography and the thermo‐mechanical behavior of the contact pair. This paper introduces a numerical approach to quantify the contact heat transfer by means of a microscale simulation at the glass‐mold interface. The simulation successfully incorporates modeling of the thermo‐mechanical behaviors and the three‐dimensional topographies from actual surface measurements of the contact pair. The presented numerical model enables the derivation of contact heat transfer coefficients from various contact pressures and surface finishes. Numerical predictions of these coefficients are validated by transient contact heat transfer experiments using infrared thermography to verify the model. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract In the (Bi1‐xCex)VO4 (0 ≤ x ≤ 1) system, we found that the (Bi1‐xCex)VO4 (0 ≤ x ≤ 0.1) belongs to the monoclinic scheelite phase and the (Bi1‐xCex)VO4 (0.7 ≤ x ≤ 1) belongs to the tetragonal zircon phase, while the (Bi1‐xCex)VO4 (0.1 〈 x 〈 0.7) belongs to the mixed phases of both monoclinic scheelite and tetragonal zircon structure. Interestingly, two components with near‐zero temperature coefficient of resonant frequency (TCF) appeared in this system. In our previous work, a near‐zero TCF of ~ +15 ppm/oC was obtained in a (Bi0.75Ce0.25)VO4 ceramic with a permittivity (εr) of ~ 47.9, a Qf (Q = quality factor = 1/dielectric loss; f = resonant frequency) value of ~18,000 GHz (at 7.6 GHz). Furthermore, in the present work, another temperature stable microwave dielectric ceramic was obtained in (Bi0.05Ce0.95)VO4 composition sintered at 950 °C and exhibits good microwave dielectric properties with a εr of ~ 11.9, a Qf of ~ 22,360 GHz (at 10.6 GHz), a near‐zero TCF of ~ +6.6 ppm/oC. The results indicate that this system might be an interesting candidate for microwave device applications. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract BiFeO3‐BaTiO3 (BF‐BT) solid solutions are lead‐free candidates for high‐temperature piezoelectric applications. BF‐BT ceramics with compositions near the morphotropic phase boundary (MPB) separating rhombohedral (R) and pseudo‐cubic (PC) phases were fabricated by the conventional high temperature sintering method, and their thermal stability and aging properties were studied in detail. BF‐BT ceramics with rhombohedral (R) phase show much better thermal stability and aging properties than those with pseudo‐cubic (PC) or coexistence of PC and R phases. The thermal degradation and aging rates of BF‐BT ceramics with R phase are on the order of 1% and 1.2% per decade, respectively. X‐ray diffraction results reveal that the domain state of poled rhombohedral BF‐BT ceramics is stable up to its Curie temperature, which is responsible for the high thermal stability. The Rayleigh analysis shows that the low aging rate is attributed to the low domain wall contribution to the overall piezoelectric response. The high thermal stability and low aging rates indicate that the lead‐free BF‐BT ceramics with R phase are potential candidates for sensor and transducer applications over a broad temperature range.

Beschreibung: Abstract In this report, a mixed‐metal cation‐based halide perovskite (HP) CsPb1−xTixBr3 quantum dots (QDs) were first embedded in the B–Si–Zn glasses using a traditional approach of melt quenching and heat treating. A battery of test results such as photoluminescence, X‐ray diffraction, and time‐resolved attenuation prove that Ti ions do not destroy the properties of CsPbBr3, and they are successfully doped into CsPbBr3. At the same time, the doping of Ti ions also reduces the toxicity of lead. By altering the ratio of Pb/Ti, we determined the optimum ratio of CsPb0.7Ti0.3Br3 QDs through experimental data. Due to the excellent optical properties and stability of CsPb0.7Ti0.3Br3 QDs glass, it was designed to construct the white‐light emitting diode device with tunable color coordinate, color rendering index, correlated color temperature, and a high luminous efficiency compared with CsPbBr3 QDs glass, which may be a promising candidate for the field of lighting and displays.

Beschreibung: Abstract The south Indian Ocean (SIO) is a region of strong air‐sea heat loss due to the unique ocean circulation pattern influenced by the Indonesian Throughflow. In this study, the seasonal variation of the surface layer heat budget in the eastern SIO is investigated using 2 years of measurements from a mooring at 25°S, 100°E, the only colocated upper ocean and surface meteorology time series in the subtropical Indian Ocean. The mooring data are combined with other in situ and satellite data to examine the role of air‐sea fluxes and ocean heat transport on the evolution of mixed layer temperature using heat budget diagnostic models. Results show that on seasonal timescales, mixed layer heat storage in the eastern SIO is mostly balanced by a combination of surface fluxes and turbulent entrainment with a contribution from horizontal advection at times. Solar radiation dominates the seasonal cycle of net surface heat flux, which warms the mixed layer during austral summer (67 Wm‐2) and cools it during austral winter (‐44 Wm‐2). Entrainment is in good agreement with the heat budget residual for most of the year. Horizontal advection is spatially variable and appears to be dominated by the presence of mesoscale eddies and possibly annual and semi‐annual Rossby waves propagating from the eastern boundary. Results from the 2‐year mooring‐based data analysis are in reasonably good agreement with a 12‐year regional heat budget analysis around the mooring location using ocean reanalysis products.

Beschreibung: Abstract The spatial distributions of biogenic dimethylated sulfur compounds (BDSCs), including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide, were determined in the Yellow Sea and Bohai Sea during a survey in April–May 2014 and the occurrence and fate of BDSCs in the surface seawater were investigated. The concentrations of DMS and DMSP were significantly correlated with the stocks of chlorophyll a and a decreasing trend was observed from the inshore to the offshore areas. In situ incubation experiments indicated that more than half of the degraded dissolved DMSP (DMSPd) was transformed into DMS. Irradiation experiments showed that the photooxidation of DMS under ultraviolet B, ultraviolet A, and visible light accounted for 23.9%, 71.8%, and 4.3% of the total photooxidation of DMS, respectively. The sea‐to‐air fluxes of DMS ranged from 0.24 to 34.11 μmol m−2 day−1 with a mean of 8.84 μmol m−2 day−1. A comparison of the DMS production rate and main removal rates indicated that bioproduction cannot completely maintain the removal of DMS and might not be the only but the primary source of DMS in the surface seawater. Additionally, the average turnover times of microbial consumption, photooxidation, and sea‐to‐air exchange of DMS were 1.53, 1.16, and 4.28 day and the contributions of the three removal pathways were 40.0%, 41.2%, and 18.8% respectively; this indicated that microbial consumption and photooxidation played dominant roles in controlling the removal of DMS from the surface seawater.

Beschreibung: Abstract Due to their superior piezo‐responses (strain S〉0.3%), bismuth sodium titanate (BNT)‐based relaxor ferroelectrics have received much attention. Compared to other chemical elements, tantalum (Ta) doping provides superior electro‐strain for these ferroelectrics, while the effect of Ta2O5 as oxide additive has been rarely reported. Herein, lead‐free piezoceramics of Bi0.5(Na0.72K0.22Li0.06)0.5TiO3‐xTa2O5 (BNKLT‐xTa2O5, x=0‐0.015) are synthesized. We study the effects of Ta2O5 addition on the crystal structure, piezoelectric responses, dielectric properties, and ferroelectric properties of BNKLT ceramics. All of the ceramics exhibit a typical perovskite structure, and Ta2O5 diffuses into the BNKLT lattice to form a uniform solid solution. The addition of Ta2O5 can make the grains more regular and uniform, while excess Ta2O5 result in finer grains. The undoped BNKLT ceramics show good ferroelectric and piezoelectric properties (remnant polarization Pr=22.5 μC/cm2 and piezoelectric coefficient d33=250 pC/N); however, the addition of Ta2O5 leads to an clear degradation in d33 and Pr. Meanwhile, the addition of an appropriate Ta2O5 amount leads to an increase in the electro‐strain, and the unipolar strain reaches 0.385% under 60 kV/cm for x=0.003, together with a higher normalized strain (d33*=Smax/Emax) of 633 pm/V (x=0.003). The enhanced strain behaviors can be attributed to the coexistence of the ferroelectric and relaxor states, and an excellent electrostriction coefficient Q33 (Q33=S/P2) value of 0.038 m4C‐2 is obtained under 60 kV/cm for x=0.003. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The primary goal of this study is to characterize the influence of the pore saturated gas media and their physical properties on the elasticity of porous ceramic materials. Resonant ultrasound spectroscopic (RUS) measurements were performed on test specimens of alumina with ~40% porosity, zirconia with ~48% porosity and sintered fully dense zirconia to determine the hydrostatic pressure dependent macroscopic elasticity. Here we report the variation of elasticity of porous and full dense samples over approximately five orders of magnitude (800 ‐ 0.02 psi) in absolute pressure. The time evolution of mechanical equilibrium of the porous materials at low pressure and high temperature conditions will also be discussed. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Calcium‐Silicate‐Hydrates (C‐S‐H) gel, the main binding phase in cementitious materials, has a complex multiscale texture. Despite decades of intensive research, the relation between C‐S‐H's chemical composition and mesoscale texture remains experimentally limited to probe and theoretically elusive to comprehend. While the nanogranular texture explains a wide range of experimental observations, understanding the fundamental processes that control particles' size and shape are still obscure. This paper strives to establish a link between the chemistry of C‐S‐H nanolayers at the molecular level and formation of C‐S‐H globules at the mesoscale via the potential‐of‐mean‐force (PMF) coarse‐graining approach. We propose a new thermo‐mechanical load cycling scheme that effectively packs polydisperse coarse‐grained nanolayers and creates representative C‐S‐H gel structures at various packing densities. We find that the C‐S‐H nanolayers percolate at ~ 0% packing fraction, significantly below the percolation of ideal hard contact oblate particles and rather close to that of overlapping ellipsoids. The agglomeration of C‐S‐H nanolayers leads to the formation of globular clusters with the effective thickness of ~ 5nm, in striking agreement with small angle neutron and X‐ray scattering measurements as well as nanoscale imaging observations. The study of pore structure and local packing distribution in the course of densification shows a transition from a connected pore network to isolated nanoporosity. Furthermore, the calculated mechanical properties are in excellent agreement with statistical nanoindentation experiments, positioning nanolayered morphology as a finer description of C‐S‐H globule models. Such high‐resolution description becomes indispensable when investigating phenomena that involve internal building blocks of globules such as shrinkage and creep. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Calcium silicate hydrate (C–S–H) is the main hydration product of cement and the most important binder that plays a pivotal role in the mechanical properties of concrete. However, one of the major drawbacks of C–S–H is its high brittleness and low flexural strength due to its disordered structure at the nano‐ and micro‐scales. Therefore, this study adopts graphene oxide (GO) to modify the structure of C–S–H, and investigates the effects of synthetic methods on the structure of C–S–H–GO composites. In this study, the highly ordered C–S–H–GO composite is successfully synthesized and exhibits itself the high toughness. Moreover, the formation mechanism of the highly ordered C–S–H–GO composite is explored and discussed, which provides a new insight into the design of high‐toughness cement‐based materials.

Beschreibung: Abstract A large production of anomalous dense water in the North Western Mediterranean Sea during winter 2005 led to a widespread abrupt shift in Western Mediterranean deep waters characteristics. This new configuration, the so‐called Western Mediterranean Transition (WMT), involved a complex thermohaline structure that was tracked over time through a deep hydrographic station located NE of Minorca Island, sampled 37 times between 2004 and 2017. In this study, the thermohaline evolution of the WMT signal is analysed in detail. Using a 1‐D diffusion model sensitive to double‐diffusive mixing phenomena, the contribution to the heat and salt budgets of the deep Western Mediterranean in terms of ventilation and diffusive transference from the intermediate layers above is disentangled. Results show distinct stages in the evolution of the deep waters, driven by background diffusion and intermittent injections of new waters. The progression of a multi‐layered structure in the deep ocean is well represented through existing parameterizations of salt fingering and diffusive layering processes, and makes it possible to infer an independent estimate of regional background diffusivity consistent with current knowledge. Overall, the deep layers of the Western Mediterranean underwent substantial warming (0.059°C) and salt increase (0.021) between 2004 and 2017, mostly dominated by injections of dense waters in the 2005–2006 and 2011–2013 periods. Thus, within the WMT period, heat uptake rate in the deep Western Mediterranean was substantially higher than that of the intermediate levels in the global ocean.

Beschreibung: The Nowotny phase Mo Si C (x = 0.9‐0.764) was found to be catalytically active in electrochemical water splitting. The electrocatalytic activity of the Mo Si C /C/SiC nanocomposite with respect to the hydrogen evolution reaction was characterized by low overpotentials of 22 and 138 mV vs reversible hydrogen electrode for applying 1 and 10 m A cm of current density, respectively, which exceeds that of most Mo‐based electrocatalysts and shows a high stability (over 90 %) during 35 h. Abstract The ternary Nowotny phase (NP), with a composition Mo3+2xSi3C0.6 (x = 0.9‐0.764), is found to be catalytically active in the field of electrochemical water splitting. The NP embedded in a porous SiC/C nanocomposite matrix is synthesized via a single‐source‐precursor approach which involves the reaction of allylhydridopolycarbosilane with MoO2(acac)2. Thermal treatment of the single‐source‐precursor up to 1400°C in a protective atmosphere results in the in situ formation of nanocrystalline Mo3+2xSi3C0.6 immobilized in a thermally and corrosion‐stable SiC/C matrix. The weight fractions of the observed crystalline phases Mo3+2xSi3C0.6 and SiC amount to ca. 28 (26) and 72 (74) wt%, respectively, when prepared at 1400°C (1350°C). The porosity of the formed nanocomposite is adjusted by the addition of polystyrene (PS) as a pore former to the single‐source‐precursor resulting in a specific surface area up to 206 m2/g. The electrocatalytic activity of the Mo3+2xSi3C0.6/C/SiC nanocomposite with respect to the hydrogen evolution reaction (HER) is characterized by low over potentials of 22 and 138 mV vs reversible hydrogen electrode (RHE) for applying 1 and 10 mA cm−2 of current density, respectively. The analyzed electrocatalytic performance exceeds that of most Mo‐based electrocatalysts and shows high stability (over 90%) during 35 hours.

Beschreibung: Abstract Making illumination light sources become comfortable to the human eye is a long‐term effort, which justifies the current research on warm white‐light‐emitting diodes (w‐LEDs). In this work, a novel phosphor for w‐LEDs, namely SrGa12O19: Dy3+(SGO: Dy3+), with a low‐color temperature (CT) was designed and synthesized. The crystal structure, the luminescence properties, the thermoluminescence properties and the stability of SGO: Dy3+ were investigated. We demonstrate outstanding luminescent characteristics and excellent stabilities. The intensity of emission light keep remained when excited by a flickering light source with a chopping speed or off‐time of a few seconds, which indicates that the SGO: Dy3+ phosphor has anti‐flicker properties that will be useful for potential applications, as LEDs driven by alternating current (AC‐LED). The chromaticity coordinates and the correlated color temperature (CCT) of SGO: Dy3+ phosphors with different Dy3+ concentrations are close with an optimal doping at 4.00 mol% Dy3+ for chromaticity coordinate (0.4269, 0.4348) and a lowest CCT of 3361 K. The perfect weatherability of this phosphor was also confirmed since the phosphorescence intensity and the color were stable at high temperature and in a high humidity environment. The performance obtained shows that SGO: Dy3+ is a suitable candidate for illumination sources that are beneficial to human health.

Beschreibung: Abstract We use a numerical model, already validated for this purpose, to simulate the effect of wave frequency spread on wave transformation and swash amplitudes. Simulations are performed for planar beach slope cases and for offshore wave spectra whose frequency spread changes over realistic values. Results indicate that frequency spread, under normally approaching waves, affects swash amplitudes. For moderately dissipative conditions, the significant infragravity swash increases for increasing values of the offshore frequency spread. The opposite occurs under extremely dissipative conditions. The numerical analysis suggests that this inverted pattern is driven by the effect that different distributions of incoming long‐wave energy have on low‐frequency wave propagation and dissipation. In fact, with large frequency spreads, wave groups force relatively short subharmonic waves that are strongly enhanced in the shoaling zone. This process leads to an infragravity swash increase for increasing frequency spread under moderately dissipative conditions, in which low‐frequency energy dissipation in shallow water is negligible or small. However, under extremely dissipative conditions, the significant low‐frequency energy dissipation associated with large frequency spreads overturns the strong energy growth in the shoaling zone eventually yielding an infragravity swash decrease for increasing frequency spread.

Beschreibung: Abstract Buoyant microplastic in the ocean can be submerged to deeper layers through biofouling and the consequent loss of buoyancy or by wind‐induced turbulent mixing at the ocean surface. Yet the fact that particles in deeper layers are transported by currents that are different from those at the surface has not been explored so far. We compute 10‐year trajectories of 1 million virtual particles with the Parcels framework for different particle advection scenarios to investigate the effect of near‐surface currents on global particle dispersal. We simulate the global‐scale transport of passive microplastic for (i) particles constrained to different depths from the surface to 120‐m depth, (ii) particles that are randomly displaced in the vertical with uniform distribution, (iii) particles subject to surface mixing, and (iv) for a 3‐D passive advection model. Our results show that the so called “garbage patches” become more “leaky” in deeper layers and completely disappear at about 60‐m depth. At the same time, subsurface currents can transport significant amounts of microplastic from subtropical and subpolar regions to polar regions, providing a possible mechanism to explain why plastic is found in these remote areas. Finally, we show that the final distribution in the surface turbulent mixing scenario with particle rise speed wr = 0.003 m/s is very similar to the distribution of plastic at the surface. This demonstrates that it is not necessary to incorporate surface mixing for global long‐term simulations, although this might change on more local scales and for particles with lower rise speeds.

Beschreibung: Abstract The dynamics of shoal‐channel estuaries require consideration of lateral gradients and transport, which can create significant intratidal variability in stratification and circulation. When the shoal‐channel system is strongly coupled by tidal exchange with mudflats, marshes, or other habitats, the gradients driving intratidal stratification variations are expected to intensify. To examine this dynamic, hydrodynamic data were collected from 27 January 2017 to 10 February 2017 in Lower South San Francisco Bay, a small subembayment fringed by extensive shallow vegetated habitats. During this deployment, salinity variations were captured through instrumentation of six stations (arrayed longitudinally and laterally) allowing for mechanisms of stratification creation and destruction to be calculated directly and compared with observed time variability of stratification at the central station. We present observation‐based calculations of longitudinal straining, longitudinal advection, lateral straining, and lateral advection. The time dependence of stratification was observed directly and calculated by summing measured longitudinal and lateral mechanisms. We found that the stratification dynamics switch between being longitudinally dominated during the middle of ebb and flood tides to being laterally dominated during the tidal transitions. This variability is driven by the interplay between tidally variable lateral density gradients and turbulent mixing. Relatively constant along‐estuary density gradients are differentially advected during flood and ebb tides, resulting in maximal lateral density gradients around tidal transitions. Simultaneous decrease in turbulent mixing at slack tides allows lateral density‐driven exchange to stratify the estuary channel at the slack after flood. At the end of ebb, barotropic forcing drives negatively buoyant shoal waters toward the channel.

Beschreibung: Abstract In most places extreme high tides undergo a clear seasonal variation. It is well known that semidiurnal tides tend to peak during equinox seasons, and diurnals during solstice seasons. This is a consequence of the solar and lunar declinations, which when large maximize diurnal tides at the expense of semidiurnals. The semiannual range modulation of tidal extremes for a pure semidiurnal tide is determined mainly by the amplitude of the K2 constituent; a pure diurnal is determined mainly by P1. Mixed tidal regimes tend to experience maxima very roughly around the times of solstice, but not always, with the semiannual modulation generally a complicated function of constituent amplitudes and phases. These modulations are here mapped worldwide by analyzing tidal extremes predicted with a global tide model. The known 4.4‐year modulation in extreme tides is a consequence of declinational and perigean effects coming in and out of phase. The phase of the 4.4‐year modulation is controlled by the phase of the semiannual modulation, irrespective of whether the tide is diurnal, semidiurnal, or mixed.

Beschreibung: Abstract The three‐dimensional structure of the offshore export of Mississippi River (MR) waters is documented for the first time with in situ data. Numerical simulations and satellite data in the Gulf of Mexico (GoM) are also employed to study two pathways that were detected in summer of 2015, along the eastern and western sides of the Loop Current (LC). The initial formation of offshore branches was primarily due to the interaction of the anticyclonic LC and LC Eddy (which were close to the MR Delta and the Louisiana‐Texas shelf‐slope, respectively) with riverine waters that had been advected eastward by westerly winds (which reduced the westward buoyancy‐driven currents). The interaction of anticyclonic circulation patterns with cyclones (LC Frontal Eddies) was found to influence the dynamics and structure of the branches. Thickness variability and other vertical characteristics of the brackish plumes were investigated from their origin in the northern GoM through their extension in the Straits of Florida. In particular, offshore branch thickness increased near the LC and LC Frontal Eddy fronts. The two types of pathways revealed different factors contributing to the low‐salinity waters. Besides the MR input, precipitation contributed to the eastern pathway, while waters from additional northern GoM rivers contributed to the western pathway. The study offers new insights on the processes that control the formation and the offshore (southward) advection of low‐salinity waters. These processes have implications on the properties of waters hundreds of kilometers from the northern river sources, extending to the southern Gulf and the Straits of Florida.

Beschreibung: Abstract The Scotia Sea is the site of one of the largest spring phytoplankton blooms in the Southern Ocean. Past studies suggest that shelf‐iron inputs are responsible for the high productivity in this region, but the physical mechanisms that initiate and sustain the bloom are not well understood. Analysis of profiling float data from 2002 to 2017 shows that the Scotia Sea has an unusually shallow mixed‐layer depth during the transition from winter to spring, allowing the region to support a bloom earlier in the season than elsewhere in the Antarctic Circumpolar Current. We compare these results to the mixed‐layer depth in the 1/6° data‐assimilating Southern Ocean State Estimate and then use the model output to assess the physical balances governing mixed‐layer variability in the region. Results indicate the importance of lateral advection of Weddell Sea surface waters in setting the stratification. A Lagrangian particle release experiment run backward in time suggests that Weddell outflow constitutes 10% of the waters in the upper 200 m of the water column in the bloom region. This dense Weddell water subducts below the surface waters in the Scotia Sea, establishing a sharp subsurface density contrast that cannot be overcome by wintertime convection. Profiling float trajectories are consistent with the formation of Taylor columns over the region's complex bathymetry, which may also contribute to the unique stratification. Furthermore, biogeochemical measurements from 2016 and 2017 bloom events suggest that vertical exchange associated with this Taylor column enhances productivity by delivering nutrients to the euphotic zone.

Beschreibung: Abstract Upper‐ocean dynamics in the Northern Indian Ocean (NIO) depend on changes in the magnitude and location of the high salinity waters of the Arabian Sea and low salinity waters of the Bay of Bengal. The large sea surface salinity (SSS) differences between these two basins are related to the surface freshwater flux (evaporation minus precipitation), which is positive (negative) in the Arabian Sea (Bay of Bengal). To quantify large‐scale salinity changes on decadal time scale over the whole water column and to study trends in salinity and volume transport, we have analyzed Simple Ocean Data Assimilation (SODA) reanalysis product, HYbrid Coordinate Ocean Model (HYCOM) simulations, European Centre for Medium‐Range Weather Forecasting's ERA‐Interim reanalysis product, and riverine streamflow data from the National Centers for Atmospheric Research's Global River Flow and Continental Discharge Dataset for the NIO. We find increased freshening conditions in the Bay of Bengal and salinification conditions in the Arabian Sea that would support a stronger zonal SSS difference in the NIO but that it is partially compensated by positive (negative) salt transports into the Bay of Bengal (BoB) (Arabian Sea). Empirical orthogonal function analysis of SODA SSS indicates that the main factors of SSS variability are Indian Ocean Dipole and El Niño‐Southern Oscillation and seasonal currents. The trends in the volume transport reveal decadal changes in zonal equatorial currents in HYCOM and Somali Current in SODA.

Beschreibung: Abstract The exhibited geometry of catalytic substrates can have a significant influence on the chemical activity and efficiency. Controlling their geometry can be challenging using the traditional techniques. In this work, we propose new and novel catalytic substrates with architected and controllable topologies based on the minimal surfaces framework. A novel design approach and an additive manufacturing (AM) technique were proposed to manufacture the catalytic substrates using ceramic materials. After 3D printing, their mechanical and flow properties were investigated experimentally. An elastic‐plastic‐damage coupled model was employed to investigate the underlying deformation mechanism of the investigated substrates. Results showed that the CLP substrate exhibited the highest mechanical properties as well as the least pressure drop among the tested substrates. Also, numerical simulations showed that the strut‐based substrates exhibit stress localization which leads to faster failure, while stress is distributed more homogeneously in the sheet‐based substrates. While the model showed to have a good agreement in the experimental and simulation stress‐strain responses, the damage mechanism was not fully captured by the numerical simulations. This was attributed mainly to the process‐induced defects in the form of microcracks and microvoids that can alter the nature of deformation and damage.

Beschreibung: Abstract The degradation of mechanical properties due to sintering is one of the major issues during high temperature service of thermal barrier coating system for advanced gas turbines. In this study, a constitutive model was developed by the variational principle, based on the experimentally observed microstructure features of suspension plasma‐sprayed thermal barrier coatings. The constitutive model was further implemented in finite element analysis software, in order to investigate the effect of vertical cracks. The evolution of microstructure during sintering, coating shrinkage and mechanical degradation were predicted. The numerical predictions of Young's modulus were generally in agreement with experimental results. Furthermore, the effect of vertical cracks on the strain tolerance and sintering resistance were discussed. It was confirmed that the introduction of vertical cracks contributed to the improvement of both properties.

Beschreibung: Abstract Hollandite has been studied as a candidate ceramic waste form for the disposal of high‐level radioactive waste due to its inherent leach resistance and ability to immobilize alkaline‐earth metals such as Cs and Ba at defined lattice sites in the crystallographic structure. The chemical and structural complexity of hollandite‐type phases developed for high‐level waste immobilization limits the systematic experimental research that is required to understand phase development due to the large number of potential additives and compositional ranges that must be evaluated. Modeling the equilibrium behavior of the complex hollandite‐forming oxide waste system would aid in the design and processing of hollandite waste forms by predicting their thermodynamic stability. Thus, a BaO–Cs2O–TiO2–Cr2O3–Al2O3–Fe2O3–FeO–Ga2O3 thermodynamic database was developed in this work according to the CALPHAD methodology. The compound energy formalism was used to model solid solution phases such as hollandite while the two‐sublattice partially ionic liquid model characterized the oxide melt. Results of model optimizations are presented and discussed including a 1473 K isothermal BaO–Cs2O–TiO2 pseudo‐ternary diagram that extrapolates phase equilibrium behavior to regions not experimentally explored.

Beschreibung: Abstract Suppression of charge recombination by thin amorphous alumina layers on metal oxide semiconductors has demonstrated a vital role in electronic appliances beside its role as an insulator. This study reports effect of amorphous alumina (Al2O3) on the structural, electrical, and optical properties of stannous oxide (SnO2). The samples for the present study are prepared as nanofibers by electrospinning a polymeric solution containing aluminum and stannous precursors and subsequent annealing; six samples with varying concentrations of aluminum and stannous are considered. A crystal‐amorphous SnO2/Al2O3 hybrid system was confirmed by both XRD and XPS analysis. Both BET and Mott‐Schottky analysis showed increase in the surface area and conduction band minimum of the sample with increase in the Al content, however, at the expense of its electrical conductivity. The electron lifetime of the sample increased with increase in the Al content, but the electron transport time increase with decrease in the electrical conductivity of the sample. Both Urbach energy measurement and Stoke's shift showed generation of deeper trap state with increase in the Al content. Investigation on sample photovoltaic performance showed that the loss in electrical conductivity of the sample can be compensated by the improved surface area to a certain extent. Interestingly, a composite nanofiber containing equal molar fraction of aluminum and stannous showed orders of magnitude higher photocurrent despite its similar resistivity as that of pure alumina fibers, which is shown to originate from a Fermi energy gradient at the Al2O3/SnO2 interface.

Beschreibung: Abstract Ba0.875Ca0.125Ti0.95Sn0.05O3 (BCT‐Sn) was examined for photocatalytic, piezocatalytic, and piezo‐photocatalytic effects. BCT‐Sn powder was poled through corona poling and it was found that poling induces significant impact on photocatalysis. This material was also able to degrade dye (Methylene blue) using poled powder under ultrasonication (piezocatalysis). There was a remarkable effect in dye degradation which is a clear indication of the importance of piezocatalytic behavior in catalytic reactions. Moreover, the piezo‐photocatalytic effect (piezocatalysis + photocatalysis) was also investigated. Results suggested an enormous scope of ferroelectric materials in the field of catalysis.

Beschreibung: Abstract A novel pale‐yellow Ba2ZnGe2O7:Bi3+ phosphor with site‐selected excitation and small thermal quenching was synthesized by conventional solid‐state sintering. The crystal structure and luminescence properties have been investigated in detail for the first time using XRD patterns, photoluminescence spectra, diffuse reflection spectra, decay curves, and temperature‐dependent emission spectra. The results reveal that the excitation spectrum of Ba2ZnGe2O7:Bi3+ phosphor locates in the near‐ultraviolet region of 300‐400 nm, and its emission shows an obvious site‐selective excitation phenomenon since Bi3+ ions occupy two different crystallographic sites in the Ba2ZnGe2O7 host. When excited under 360 nm, the phosphors show a pale‐yellow emission in the range of 400‐700 nm with the maximum peaking at 520 nm, while when excited under 316 nm, the phosphors show a blue emission in the range of 400‐700 nm with the maximum peaking at 480 nm. In addition, the emission of Ba2ZnGe2O7:Bi3+ can also be easily controlled by changing the Bi3+ concentration. The Ba2ZnGe2O7:Bi3+ phosphor has small thermal quenching, and its emission intensity only decreases by 2% at 200°C. The results indicate that this novel pale‐yellow Ba2ZnGe2O7:Bi3+ phosphor could be conducive to the development of white light‐emitting diodes.

Beschreibung: Abstract The binding of Na+, K+, and Li+ by magnesium silicate hydrate (M–S–H) was investigated in batch sorption experiments. Sorption isotherms and cation exchange measurements indicated the binding of alkalis in cation exchange sites compensating the negative surface charge of M–S–H. Higher pH values led to further deprotonation of the silanol groups and a higher alkali uptake by M–S–H. No significant incorporation of alkalis in the main silica or magnesium oxide sheets was observed. However, the silica sheets were less polymerized in the presence of higher alkali hydroxide concentrations.

Beschreibung: Abstract Large‐strain multilayer actuators (MLAs) were fabricated by tape‐casting 0.91(Na1/2 Bi1/2)TiO3–0.06BaTiO3–0.03AgNbO3 (NBT‐BT–3AN) lead‐free incipient piezoceramics co‐fired with Pt inner electrodes. Microstructures, dielectric properties, unipolar and bipolar strain, as well as fatigue properties of the MLAs were investigated. It was found that the actuator consisting of 15 ceramic layers with individual thicknesses of 114 μm could output a large unipolar strain of 0.3% and a dynamic displacement of 5 μm at 6 kV/mm at room temperature. It exhibited excellent cycling stability and provided a high strain of 0.23% after 107 cycles at 6 kV/mm. Moreover, these MLAs still can deliver a strain of 0.20% at 125°C.

Beschreibung: Abstract (0.96‐x)K0.48Na0.52NbO3‐0.04Bi0.5Na0.5ZrO3‐xLaFeO3 ceramics (abbreviated as KNN‐BNZ‐LF1000x) with enhanced piezoelectric performance and temperature stability were prepared by the conventional solid‐state sintering method. It was found that the incorporation of LaFeO3 gradually shifted the O‐T phase boundary toward room temperature, while maintaining the Curie temperature above 300°C. The optimal piezoelectricity was found at x = 0.006, with relatively high piezoelectric constant d33 of 345 pC/N as well as a high level of unipolar strain (0.126% at 3 kV/mm). Benefiting from the diffused phase transition induced by appropriate amount of LaFeO3 content, the KNN‐BNZ‐LF6 sample possessed greatly enhanced the temperature stability of , which varied less than 8% in the temperature range of 20°C‐100°C.

Beschreibung: Abstract Degradation of thermal barrier coatings (TBCs) in gas‐turbine engines due to calcium–magnesium–aluminosilicate (CMAS) glassy deposits from various sources has been a persistent issue since many years. In this study, state of the art electron microscopy was correlated with X‐ray refraction techniques to elucidate the intrusion of CMAS into the porous structure of atmospheric plasma sprayed (APS) TBCs and the formation and growth of cracks under thermal cycling in a burner rig. Results indicate that the sparse nature of the infiltration as well as kinetics in the burner rig are majorly influenced by the wetting behavior of the CMAS. Despite the obvious attack of CMAS on grain boundaries, the interaction of yttria‐stabilized zirconia (YSZ) with intruded CMAS has no immediate impact on structure and density of internal surfaces. At a later stage the formation of horizontal cracks is observed in a wider zone of the TBC layer.

Beschreibung: An effective and facile dip‐loading approach was adopted to fabricate Au nanoparticle (NPs) @TiO2 nanotube arrays (NTAs) heterostructured films with improved H2 generation rate under visible light. Abstract Au nanoparticle (NPs)@TiO2 nanotube arrays (NTAs) heterostructured films with enhanced H2 generation rate under full spectrum were synthesized, by using a controllable and facile dip‐loading approach. Size of the Au NPs was well‐distributed around 7 nm, and the TiO2 NTAs were found vertically aligned. Due to LSPR effect and Schottky contact, the as‐prepared Au NPs@TiO2 NTAs heterostructured films exhibited improved H2 generation abilities as well as photocatalytic degradation abilities. H2 evolution rate of the obtained samples (effective area: 5.25 cm2) reached 74.56 μmol/h, which was 38 times higher than that of the raw TiO2 NTAs. And the Au NPs@TiO2 NTAs samples also showed an obvious advantage over the raw TiO2 NTAs, in methyl orange degradation under UV illumination. Repetition experiments were further carried out to ensure the dip‐loading method was a reliable fabrication process, and the amount of Au particles attached on TiO2 tube walls could be manipulated by changing the dip‐loading cycle times.

Beschreibung: Abstract In this study, TiO2 nanorod arrays (TNR), Ag quantum dots (QDs) sensitized with TNR TiO2/Ag, bismuth oxyhalide (BiOI) nanosheets, and Ag QDs co‐modified with TNR and TiO2/BiOI/Ag (TBA) were prepared by a stepwise process. The morphological, structural, compositional, optical, photocatalytic (PC), and photoelectrochemical (PEC) properties of the samples were investigated. The TBA‐2 sample exhibited the highest photocurrent density (281.8 μA/cm2) and photodegradation efficiency (93.3%), with values 9.7 times and 2.25 times higher than those for TNR, respectively. The improvement in sample performance can be attributed to the formation of a heterojunction between BiOI and TiO2, thereby enhancing the absorption of visible light and improving the charge separation efficiency; Ag QDs limit interfacial electron‐hole pair recombination. The experimental results show that TBA can effectively promote light‐induced carrier transport and visible light absorption, while inhibiting the recombination rate of the electron‐hole pairs, PEC, and PC.

Beschreibung: Abstract The drastic reduction in dimensions in thin films, together with the low crystallization temperatures used, normally results in a large reduction in the grain size. It has been reported that relaxor ferroelectric states are stabilized at room temperature for fine‐grained ceramics and films that behave as normal ferroelectrics for large grains. In this work, the effects of the grain size reduction on the relaxor characteristics are analyzed for a composition that is already a canonical relaxor with a nonergodic state at room temperature: (Bi0.5Na0.5)1‐xBaxTiO3 (BNBT). The comparison of the local polar ordering within BNBT grains studied with piezoresponse force microscopy on large‐grained ceramics and fine‐grained thin films shows that the development of stable long‐range ferroelectric order with the application of an electric field is hampered due to the small grain size of the grains. The ergodic character of the high‐temperature phase is thus stabilized at room temperature, following a similar mechanism as the one discussed for other noncanonical relaxors.

Beschreibung: Abstract In this work, we have prepared a novel (K0.5Na0.5)0.99‐xPrxYb0.01NbO3 (abbreviated as KNN:xPr3+/0.01Yb3+, x = 0.0006, 0.0008, 0.001, 0.002, 0.003, and 0.004) ceramics, which possess visible UC emissions, photochromic (PC) and optical thermometric properties. Under the excitation of a 980‐nm diode laser, all the samples show the featured emissions of Pr3+ ions and the UC emission intensity is greatly dependent on the Pr3+ doping content. The optimal UC luminescence intensity is obtained at x = 0.001. All the prepared samples show a strong PC reaction, and a large luminescence quenching degree (ΔRt) of 74.94% is found. The optical thermometric properties of both the irradiated and unirradiated KNN:0.001Pr3+/0.01Yb3+ ceramics in the temperature range of 123‐573 K have been investigated via measuring the temperature‐dependent UC emission spectra of green emissions, which originate from the two 3P1 and 3P0 thermally coupled levels. It has been found that the prepared samples have both excellent PC behaviors and temperature‐sensing performances. These results suggest that the KNN:xPr3+/0.01Yb3+ ceramics are promising candidates for the applications in PC reaction and thermometers.

Beschreibung: Abstract In this work, we present a general sol‐gel protocol for the synthesis of highly porous monolithic transition metal borides via carbothermal conversion of the organic/inorganic interpenetrating networks (IPNs). The formation of organic/inorganic IPNs is clearly demonstrated by simple oxidation and boiling water treatment. A series of transition metal boride porous monoliths, including CrB2, ZrB2, TiB2, Cr3C2/CrB, and ZrB2/ZrC with porosities ranging from 70% to 85% and pore sizes ranging from 0.5 to 35 μm, have been prepared. In each case, a porous hybrid monolith is obtained by drying the wet gel under ambient pressure. It is believed that the formation of organic/inorganic IPNs strengthens the gel network, so that it can withstand the severe changes during desiccation to give out a monolithic xerogel. Samples are characterized by TG‐DSC, XRD, SEM, EDS, TEM, BET, and MIP, and the ceramic monoliths are shown to be well defined and rather homogeneous.

Beschreibung: Abstract Sr2[Ti1−x(Al0.5Nb0.5)x]O4 (x = 0, 0.10, 0.25, 0.30, 0.5) ceramics were synthesized by a standard solid‐state reaction process. Sr2[Ti1−x(Al0.5Nb0.5)x]O4 solid solutions with tetragonal Ruddlesdon‐Popper (R‐P) structure in space group I4/mmm were obtained within x ≤ 0.50, and only minor amount (1‐2 wt%) of Sr3Ti2O7 secondary phase was detected for the compositions x ≥ 0.25. The temperature coefficient of resonant frequency τf of Sr2[Ti1−x(Al0.5Nb0.5)x]O4 ceramics was significantly improved from 132 to 14 ppm/°C correlated with the increase in degree of covalency (%) with increasing x. The dielectric constant ɛr decreased linearly with increasing x, while high Qf value was maintained though it decreased firstly. The variation tendency of Qf value was dependent on the trend of packing fraction combined with the microstructure. Good combination of microwave dielectric properties was achieved for x = 0.50: ɛr = 25.1, Qf = 77 580 GHz, τf = 14 ppm/°C. The present ceramics could be expected as new candidates of ultra‐high Q microwave dielectric materials without noble element such as Ta.

Beschreibung: A small addition of TaC into HfC (or vice versa) induces a great improvement in materials properties of (Hf1‐xTax)C. Abstract Bond characteristics, mechanical properties, and high‐temperature thermal conductivity of ultrahigh‐temperature ceramics (UHTCs), hafnium carbide (HfC), tantalum carbide (TaC), and their solid solution composites, were investigated using first‐principles calculations. Mulliken analyses revealed that Ta formed stronger covalent bonds with C than did Hf. Bond overlap analyses indicated that the Hf–C bond possessed mixed covalent and ionic bond characteristics, compared with the more covalent character of the Ta–C bond. Consequently, the overall elastic properties were enhanced with increasing number of Ta–C bonds in the composites. The overall metallicity of the composites also increased with increasing TaC content; thus, the mechanical properties did not improve monotonically. Our results indicate that adding a small amount of TaC to HfC or vice versa to produce a composite would create a new UHTC with greatly improved elastic and mechanical properties as well as high‐temperature thermal conductivity.

Beschreibung: Abstract The charge compensation mechanisms that occur when Li+ substitutes a 2+ element in superionic conductor (MgCoNiCuZn)O high‐entropy oxide have been studied using a combination of thermogravimetric analysis and X‐ray photoemission spectroscopy. Depending on the concentration of Li+ in the compound, the charge compensation involves first partial oxidation of Co2+ into Co3+ for low fraction of Li+, and then a combination of both the oxidation of cobalt and the formation of oxygen vacancies for large fraction of Li+.

Beschreibung: Abstract HBO2‐II ceramics were prepared by cold sintering with 10wt% dehydrated ethanol as the transient liquid phase. When the processing temperature is 30°C, the relative density of the mechanically robust HBO2‐II ceramics increases from 77.5% to 84.5% with increasing the uniaxial pressure from 200 to 500 MPa. It changes less than 0.2% for higher pressure up to 700 MPa. Under a constant uniaxial pressure of 500 MPa, the relative density further increases to 94.7% for the processing temperature of 120°C. HBO2‐I is observed as the secondary phase when the processing temperature is 150°C. In comparison, the compacts prepared in the absence of ethanol are fragile, and the relative densities are 78.5%‐84.5% for the processing temperatures of 30‐120°C and uniaxial pressure of 500 MPa. It is indicated that ethanol promotes the densification significantly through the dissolution‐precipitation mechanism. The permittivity increases with increasing the processing temperature, while the Qf value decreases. The optimal properties with the relative density of 94.7%, εr = 4.21, Qf = 47 500 GHz, and τf = −70.0 ppm/°C were obtained in the single‐phase HBO2‐II ceramics cold sintered at 120°C under 500 MPa for 10 minutes. The relative density and Qf value are significantly higher than those of the HBO2‐II ceramic prepared by sintering the H3BO3 compact at 180°C for 2 hours (70.3% and 32 700 GHz, respectively). The results indicate that the nonaqueous solvent can also be used as the transient liquid phase for cold sintering, so that more materials that are unstable or insoluble in water can be densified by this method.

Beschreibung: Abstract Self‐healing capability in wet oxygen atmospheres is the key issue for long term service of SiC/SiC composites in aero‐engines. Polymer derived SiBCN ceramic (PDC SiBCN) was introduced into SiC fiber reinforced SiC as a self‐healing component to obtain SiC/(SiC‐SiBCN)x composites by a newly developed method, namely chemical vapor infiltration combined with polymer infiltration online pyrolysis (CVI + PIOP) process. The weight loss behavior and three‐point bending performance of the samples under different temperatures (1200, 1300 and 1400°C) and different wet oxygen partial pressures were tested up to 100 hours to demonstrate the oxidation behavior of the samples in wet oxygen environments. According to these tests, the antioxidant capacities of samples prepared from different preforms were compared. It has been found that the 2D plain weave samples with higher density have the best resistance to wet oxygen corrosion while the 2D plain weave samples have the worst resistance to wet oxidation and the antioxidant capacities of 2D satin weave samples is between them.

Beschreibung: Abstract Low‐permittivity ZnAl2‐x(Zn0.5Ti0.5)xO4 ceramics were synthesized via conventional solid‐state reaction method. A pure ZnAl2O4 solid‐state solution with an Fd‐3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn0.5Ti0.5]3+ for Al3+ effectively lowered the sintering temperature of the ZnAl2O4 ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (εr = 9.1, Q × f = 115,800 GHz and τf = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl2O4 ceramics.

Beschreibung: Abstract A series of Dy3+/Eu3+ single‐ and co‐doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt‐quenching method. A compact glass structure is obtained by the addition of Dy3+/Eu3+ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy3+/Eu3+ fill in the interspaces of glass network and contribute to the conversion of [BO3] to [BO4]. Dy3+/Eu3+ co‐doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white‐emitting glasses have proved the existence of energy transfer. The average lifetime of Dy3+ decreases from 0.251 to 0.165 ms with the increasing Eu3+ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy3+/Eu3+ co‐doped glass shifts from cyan to white with increasing excitation wavelength. A white‐light emission is obtained when the concentration of Dy3+ and Eu3+ equals to 4% and 2%, respectively. Moreover, the Dy3+/Eu3+ co‐doped calcium borosilicate glass shows high‐thermal stability and it may be applicable for high‐quality white LEDs based on high power near ultraviolet (n‐UV) LED chip in the future.

Beschreibung: Abstract Freeze‐casting is a technique used to produce structures with anisotropic porosity in the form of well‐defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La0.66Ca0.26Sr0.07 Mn1.05O3. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze‐casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non‐gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB®.

Beschreibung: Abstract The interannual variability and trends of the Alaska Gyre and Gulf of Alaska (GOA) circulation are examined using meridional geostrophic transport from Argo temperature and salinity (2004–2017) and altimetric sea surface height (1993–2017). More than half of the top 1,500 m meridional transport variability in the Alaska Gyre is accounted for by a statistical mode strongly correlated with the Pacific Decadal Oscillation (PDO) index, consistent with the PDO exerting a major influence on North Pacific sea surface temperature variability. During a positive phase of the PDO, the zero‐transport streamline separating the subtropical from the Alaska Gyre is shifted to the south from its mean position, while more transport is diverted northward, associated with a stronger and larger Alaska Gyre. Additionally, over the 25‐year altimetric record there is a linear, increasing trend in strength of the Alaska Gyre (but not in areal extent), accompanied by an increasing trend for the incoming North Pacific Current. The effect of the PDO transport mode on GOA circulation is weak. Temperature and salinity volume averaged for the GOA covary with the PDO index, with warmer and fresher waters during a positive phase. Despite correlated anomalies for temperature, salinity, and northward transport into the GOA, however, geostrophic advection from the south contributes only minimally to the interannual variations of water properties in the GOA. An exception was the marine heat wave of 2013/2014 and its aftermath when temperature advection from the south played a more appreciable role for warming and subsequent cooling of the GOA.

Beschreibung: Abstract A new method for the detection of sea ice using GNSS‐R (Global Navigation Satellite Systems Reflectometry) is presented and applied to 33 months of data from the U.K. TechDemoSat‐1 mission. This method of sea ice detection shows the potential for a future GNSS‐R polar mission, attaining an agreement of over 98% and 96% in the Antarctic and Arctic, respectively, when compared to the European Space Agency's Climate Change Initiative sea ice concentration product. The algorithm uses a combination of two parameters derived from the delay‐Doppler Maps to quantify the spread of power in delay and Doppler. Application of thresholds then allows sea ice to be distinguished from open water. Differences between the TechDemoSat‐1 sea ice detection and comparison data sets are explored. The results provide information on the seasonal and multiyear changes in sea ice distribution of the Arctic and Antarctic. Future potential and applications of this technique are discussed.

Beschreibung: Abstract A strong decrease of volume and density of North Pacific Subtropical Mode Water (NPSTMW) in 1999, was analyzed in a regional high‐resolution (0.1°) numerical ocean circulation model simulation. Both shoaling of the bottom, and deepening of the top of the NPSTMW layer contributed equally to volume decrease. They were locally governed by different physical processes, but both seem to be associated with basin‐wide changes in wind. A westward propagating negative thermocline depth anomaly, that developed in the Central Pacific when the Pacific Decadal Oscillation index changed from a positive to a negative phase in 1998, caused shoaling of the bottom of the NPSTMW layer. Deepening of the top of the NPSTMW layer was due to an increase in the near surface stratification, caused by an increase in wind‐driven lateral heat transport convergence by the Kuroshio Extension jet starting in 1997. Both processes increased the potential vorticity (PV) in the NPSTMW region, decreasing the volume of water in the NPSTMW density range that satisfied the low PV constraint that is part of the definition of "mode water”. The strong near‐surface density decrease provided preconditioning for preferential surface formation of a lighter variety of NPSTMW, further decreasing its density. It also resulted in decrease of the outcrop window in the NPSTMW density range, strongly reducing its formation rate in 1998 and 1999 despite strong surface heat loss.

Beschreibung: Abstract Off the coast of central Chile, subsurface anticyclonic eddies are a salient feature of the oceanic circulation, transporting a significant fraction of coastal water that is rich in nutrients and poor in dissolved oxygen offshore. In this study, the formation mechanism of these eddies is analyzed through a high‐resolution (~0.3 km) and low‐resolution (~3 km) oceanic model that realistically simulate the regional mean circulation, including the Peru‐Chile Undercurrent (PCUC). An analysis of the vorticity and eddy kinetic energy in both simulations indicated that the subsurface eddies can be triggered through a combination of processes that are associated with instabilities of the PCUC. In the high‐resolution simulation, we observed that the interaction between the PCUC and topographic slope generates anticyclonic vorticity and potential vorticity close to zero in the bottom boundary layer. The separation of the undercurrent from the slope favors the intensification of anticyclonic vorticity. It reaches magnitudes that are larger than the planetary vorticity while kinetic energy is converted from the PCUC to the eddy flow. These processes set the necessary conditions for the development of centrifugal instabilities, which can form submesoscale structures. The coalescence of submesoscale structures generates a subsurface anticyclonic mesoscale eddy. In the low‐resolution simulations (〉3 km) centrifugal instabilities are not simulated, and the barotropic conversion of the mean kinetic energy into eddy kinetic energy appears as the main process of eddy formation. We showed that the vertical structure of these eddies is sensitive to the spatial resolution of the model.

Beschreibung: Abstract Oceans are an important natural source of the greenhouse gas nitrous oxide (N2O). The isotopomer signature of N2O provides a useful tool to differentiate the production processes of N2O in the oceans. Here we present the distribution of the concentration and stable isotopic composition of dissolved N2O in the water column of the shelf and slope region of the northern South China Sea (SCS) in June 2015. Dissolved N2O concentrations in surface waters ranged from 6.9 to 9.1 nM with an average of 7.7 ± 0.6 nM (136 ± 10% saturation). Higher N2O was found at the region influenced by coastal water entrained by eddies. Vertical profiles of dissolved N2O showed a general increase with depth below the mixed layer and reached a broad peak (23–29 nM) at around 700 m coinciding with the nitrate maximum and oxygen minimum. The SP values measured for N2O ranged between 10.2‰ and 18.8‰, suggesting that dissolved N2O in the water column had been produced from both nitrification (ammonium oxidation) and nitrifier denitrification (nitrite reduction). Nitrification dominated in the intermediate water (120–1,000 m) while nitrifier denitrification dominated in the euphotic zone. The sea‐to‐air fluxes of N2O were estimated to be 7.0 ± 6.1 and 6.9 ± 6.5 μmol m−2 day−1 using two different gas transfer relationships. N2O emissions from the shelf and slope regions of the northern SCS were estimated to be 0.25 Tg N2O year−1, suggesting that coastal areas like the SCS are net sources of N2O to the atmosphere.

Beschreibung: Abstract Here, we select simple Er3+‐doped tellurite glass as model system to systematically explore the up‐conversion, down‐shifting mechanisms with different excitations (980 nm and 447 nm), respectively. We observe for the first time, to the best of our knowledge, that tunable photo‐luminescence occurs from green to red & NIR region, rather than merely from the long‐accepted green to red region. Direct evidence of selective energy transfer mechanism is expounded in detail, and its potential applications are demonstrated. In addition, we provide evidence that the cross‐relaxation process between dopant ions can enhance photo‐luminescence in Er3+ doped tellurite glasses with high dopant concentrations, whereas the crucial reason for emission decrease is the energy loss long‐distance energy migration. These fundamental insights into the photophysical processes in heavily doped photonic glasses will broaden the applications of rare‐earth‐doped materials ranging from optical communications to medical imaging. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract We present in situ observations of mean and turbulent bottom stresses in a shallow, wave‐ and current‐driven flow over a cohesive sediment bed on the eastern shoals of South San Francisco Bay. Data from a Nortek Vectrino Profiler deployed with its measurement volume overlapping the bed allowed us to calculate mean velocity profiles and turbulent Reynolds stresses over a 1.5 cm profile with 1 mm vertical resolution. Additional acoustic instrumentation and pressure sensors provided mean current and wave data. From these observations we found that biological roughness elements protruding from the sediment bed result in a mean velocity profile qualitatively similar to that found in canopy shear mixing layers. Despite fundamental differences between this measured velocity structure and that assumed by wave‐current boundary layer models, we also found that the addition of waves to mean currents increases the net drag felt by the flow. The near‐bed momentum flux was often dominated by a wave‐induced component, which was generated by interactions between the wavy flow and the rough bed. Finally, we estimated the friction velocity using several different calculation methods and compared results to the measured bottom stress. This analysis revealed that traditional methods (e.g. log law fitting and point turbulence measurements) are consistent with one another when measuring the stress outside the wave boundary layer, but were all poor approximations of the total stress at the bed.

Beschreibung: Abstract For ice concentrations less than 85%, internal ice stresses in the sea ice pack are small and sea ice is said to be in free drift. The sea ice drift is then the result of a balance between Coriolis acceleration and stresses from the ocean and atmosphere. We investigate sea ice drift using data from individual drifting buoys as well as Arctic‐wide gridded fields of wind, sea ice and ocean velocity. We perform probabilistic inverse modeling of the momentum balance of free‐drifting sea ice, implemented to retrieve the Nansen number, scaled Rossby number and stress turning angles. Since this problem involves a non‐linear, under‐constrained system, we used a Monte Carlo guided search scheme ‐ the Neighbourhood Algorithm ‐ to seek optimal parameter values for multiple observation points. We retrieve optimal drag coefficients of CA = 1.2×10‐3 and CO = 2.4×10‐3 from ten‐day averaged Arctic‐wide data from July 2014 that agree with the AIDJEX standard, with clear temporal and spatial variations. Inverting daily‐averaged buoy data give parameters that, whilst more accurately resolved, suggest that the forward model over‐simplifies the physical system at these spatial and temporal scales. Our results show the importance of the correct representation of geostrophic currents. Both atmospheric and oceanic drag coefficients are found to decrease with shorter temporal averaging period, informing the selection of drag coefficient for short time‐scale climate models.

Beschreibung: Abstract In this work, the influence of starting particle size and sintering conditions on the microstructures and dielectric properties of BaTiO3‐based ceramics coated with 0.3Bi(Zn1/2Ti1/2)O3‐0.7BaTiO3 were investigated to reveal the core‐shell structure by using high resolution transmission electron microscopy technique coupled with energy‐dispersive spectrometer analysis. The ion‐diffusion behavior plays a critical role in the formation and evolution of the core‐shell structure and, therefore, significantly influences the dielectric properties. When using starting powders containing BaTiO3 particles larger than 100 nm in size and sintering for shorter dwelling times (0.5‐2.0 hours), a core‐shell structure could be formed and retained owing to the limited diffusion behavior, enabling BaTiO3‐based ceramics to meet the X8R specification for multilayer ceramic capacitors applications at high temperatures. However, when using 80 nm BaTiO3 nanopowders and further extending the dwelling time to 6.0 hours, more driving energy was provided to prompt ion diffusion, which led to the compositional inhomogeneity becoming homogenized.

Beschreibung: Abstract Scientific and societal interest in the relationship between the Atlantic Meridional Overturning Circulation (AMOC) and United States (US) east coast sea level has intensified over the past decade, largely due to: 1) projected, and potentially ongoing, enhancement of sea‐level rise associated with AMOC weakening; and 2) the potential for observations of US east coast sea level to inform reconstructions of North Atlantic circulation and climate. These implications have inspired a wealth of model‐ and observation‐based analyses. Here, we review this research, finding consistent support in numerical models for an anti‐phase relationship between AMOC strength and dynamic sea level (DSL). However, simulations exhibit substantial along‐coast and inter‐model differences in the amplitude of AMOC‐associated DSL variability. Observational analyses focusing on shorter (generally less than decadal) timescales show robust relationships between some components of the North Atlantic large‐scale circulation and coastal sea‐level variability, but the causal relationships between different observational metrics, AMOC, and sea level are often unclear. We highlight the importance of existing and future research seeking to understand relationships between AMOC and its component currents, the role of ageostrophic processes near the coast, and the interplay of local and remote forcing. Such research will help reconcile the results of different numerical simulations with each other and with observations, inform the physical origins of covariability, and reveal the sensitivity of scaling relationships to forcing, timescale, and model representation. This information will, in turn, provide a more complete characterization of uncertainty in relevant relationships, leading to more robust reconstructions and projections.

Beschreibung: Abstract Ba{[Gax,Tax]Ti(1−2x)}O3 ceramics with x equal to 0, 0.0025, 0.005, 0.01, 0.025, and 0.05 have been prepared by conventional solid‐state reaction. Structural and dielectric characterization have been performed to investigate the effect of dipole‐pair substitution concentration on the macroscopic dielectric properties. Ba{[Gax,Tax]Ti(1−2x)}O3 evolves from a classic ferroelectric to a diffuse phase transition (DPT) as x increases. Ba{[Gax,Tax]Ti(1−2x)}O3 for x ≥ 0.01 possesses diffuseness parameters comparable to Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) and recently reported (Ba0.97Pr0.03)(Ti0.9425Ce0.05)O3 (BPTC), yet it lacks the frequency and temperature dependence of Tm necessary to be a strictly defined relaxor ferroelectric. Additionally, Ba{[Ga0.05,Ta0.05]Ti0.9}O3 possesses a relative permittivity, ɛr, of 700 ± 16% and dissipation factor less than 0.05 at 10 kHz within the temperature range [−75°C, 120°C]. In comparison to BaTiO3, Ba{[Gax,Tax]Ti(1−2x)}O3 possesses enhanced electrical resistivity at and above room temperature. In situ XRD, including Rietveld refinement, have been performed to determine the lattice parameter, coefficient of thermal expansion, and phase transition temperature (Tc) of each composition within the temperature range [RT, 1000°C], thus linking the dielectric properties with the material's structure. These studies have been corroborated by temperature‐dependent Raman spectroscopy to compare the Tc determined by electrical and structural characterization. The properties of Ba{[Gax,Tax]Ti(1−2x)}O3 are discussed in context with available models that describe donor and acceptor dopants spatially separated in the parent matrix, inter‐relating lattice parameter, Curie temperature, and other material properties.

Beschreibung: Abstract High‐accuracy spectrophotometric pH measurements were taken during a summer cruise to study the pH dynamics and its controlling mechanisms in the northern Gulf of Mexico in hypoxia season. Using the recently available dissociation constants of the purified m‐cresol purple (Douglas & Byrne, 2017, https://doi.org/10.1016/j.marchem.2017.10.001; Müller & Rehder, 2018, https://doi.org/10.3389/fmars.2018.00177), spectrophotometrically measured pH showed excellent agreement with pH calculated from dissolved inorganic carbon (DIC) and total alkalinity over a wide salinity range of 0 to 36.9 (0.005 ± 0.016, n = 550). The coupled changes in DIC, oxygen, and nutrients suggest that biological production of organic matter in surface water and the subsequent aerobic respiration in subsurface was the dominant factor regulating pH variability in the nGOM in summer. The highest pH values were observed, together with the maximal biological uptake of DIC and nutrients, at intermediate salinities in the Mississippi and Atchafalaya plumes where light and nutrient conditions were favorable for phytoplankton growth. The lowest pH values (down to 7.59) were observed along with the highest concentrations of DIC and apparent oxygen utilization in hypoxic bottom waters. The nonconservative pH changes in both surface and bottom waters correlated well with the biologically induced changes in DIC, that is, per 100‐μmol/kg biological removal/addition of DIC resulted in 0.21 unit increase/decrease in pH. Coastal bottom water with lower pH buffering capacity is more susceptible to acidification from anthropogenic CO2 invasion but reduction in eutrophication may offset some of the increased susceptibility to acidification.

Beschreibung: Abstract Interannual variability of Ocean Heat Content (OHC) is intimately linked to ocean water mass changes. Water mass characteristics are imprinted at the ocean surface and are modulated by climate variability on interannual to decadal time scales. In this study, we investigate the water mass change and their variability using an isopycnal decomposition of the OHC. For that purpose, we address the thickness and temperature changes of these water masses using both individual temperature‐salinity profiles and optimal interpolated products from Argo data. Isopycnal decomposition allows us to characterize the water mass interannual variability and decadal trends of volume and OHC. During the last decade (2006–2015), much of interannual and decadal warming is associated with Southern Hemisphere Subtropical Mode Water and Subantarctic Mode Water, particularly in the South Pacific Eastern Subtropical Mode Water, the Southeastern Indian Subantarctic Mode Water, and the Southern Pacific Subantarctic Mode Water. In contrast, Antarctic Intermediate Water in the Southern Hemisphere and North Atlantic Subtropical Mode Water in the Northern Hemisphere have cooled. This OHC interannual variability is mainly explained by volume (or mass) changes of water masses related to the isopycnal heaving. The forcing mechanisms and interior dynamics of water masses are discussed in the context of the wind stress change and ocean adjustment occurring at interannual time scale.

Beschreibung: Abstract Revolutionary observational arrays, together with a new generation of ocean and climate models, have provided new and intriguing insights into the Atlantic Meridional Overturning Circulation (AMOC) over the last two decades. Theoretical models have also changed our view of the AMOC, providing a dynamical framework for understanding the new observations and the results of complex models. In this paper we review recent advances in conceptual understanding of the processes maintaining the AMOC. We discuss recent theoretical models that address issues such as the interplay between surface buoyancy and wind forcing, the extent to which the AMOC is adiabatic, the importance of mesoscale eddies, the interaction between the middepth North Atlantic Deep Water cell and the abyssal Antarctic Bottom Water cell, the role of basin geometry and bathymetry, and the importance of a three‐dimensional multiple‐basin perspective. We review new paradigms for deep water formation in the high‐latitude North Atlantic and the impact of diapycnal mixing on vertical motion in the ocean interior. And we discuss advances in our understanding of the AMOC's stability and its scaling with large‐scale meridional density gradients. Along with reviewing theories for the mean AMOC, we consider models of AMOC variability and discuss what we have learned from theory about the detection and meridional propagation of AMOC anomalies. Simple theoretical models remain a vital and powerful tool for articulating our understanding of the AMOC and identifying the processes that are most critical to represent accurately in the next generation of numerical ocean and climate models.

Beschreibung: Abstract Transverse‐vertical structure and temporal variability of the Kuroshio current across the Tokara Strait during 2003–2012 measured by a ferryboat acoustic Doppler current profiler with a 2‐km horizontal resolution and a two‐day interval are presented. The Kuroshio passing through the Tokara Strait exhibits a multicore velocity structure. Its seasonal volume transport variation is biannual for baroclinic components relative to 700 m, peaking in July and December–January. However, the barotropic transport component exhibits an annual cycle with a maximum in December. Empirical orthogonal function analysis of the cross‐sectional velocity is performed. The first two empirical orthogonal function modes reveal the north‐south shift of the Kuroshio current axis and the change in Kuroshio volume transport, respectively. Temporal variabilities of the leading two modes correspond to those of the Kuroshio Position Index and the sea level difference across the strait, respectively. The third empirical orthogonal function mode, with a relatively smaller horizontal scale, was examined in terms of turbulent mixing. The banded structure captured by this mode is likely induced by flow‐topography interaction because islands in the Kuroshio route could cause horizontal and vertical flow separation. Additional analysis based on high‐resolution reanalysis data suggested that (1) inertial instability, which is expected in the areas with negative Ertel's potential vorticity, arises to enhance vertical mixing around the islands in the Tokara Strait, and (2) when the Kuroshio directly impinges the islands, flow divergence in the lee of the islands drives upwelling and leads to uplift of isotherms.

Beschreibung: Abstract Ab initio molecular dynamics simulations are executed to probe the short‐range order and the electrical features of the liquid and amorphous boron subarsenide (B12As2). A drastic volume swelling of ~40% is witnessed for the liquid state, relative to the crystal. The density of the melt is found to be close to that of liquid boron. As the temperature applied is gradually decreased, the volume progressively decreases and a glass‐transition zone at around 1400 K is observed. About 14% volume expansion is perceived for the amorphous phase. Due to the drastic density (volume) difference between the liquid and amorphous forms, their atomic structure is found to be different from each other. In the liquid phase at 2500 K, the mean coordination number (CN) of B and As atoms is 4.4 and 2.5, correspondingly. During the solidification process, both average CNs steadily increase and reach values of 5.5 (B‐atom) and 4.14 (As‐atom) at 300 K. The pentagonal pyramid‐like motifs barely survive at 2500 K but during the quenching process they develop progressively and some of which lead to the formation of B12 clusters. In the amorphous state, the chain‐like and A7‐like As‐As clusters are observed. Nonetheless, the noncrystalline state is proposed to be partially similar to the crystalline structure. The liquid state shows a metallic character while the amorphous form presents a semiconducting nature having an energy band gap much smaller than that of the crystalline phase.

Beschreibung: Abstract Near‐inertial waves (NIWs), a fundamental oceanic response to wind forcing, play an important role in dynamical processes related to ocean mixing and hence have attracted sustained interest. Herein, we investigate temporally and spatially varying NIW distributions in the mixed and deep layers of the East/Japan Sea (EJS) using high‐resolution hourly‐wind‐forced data‐assimilated ocean model outputs. Temporally, the kinetic energy of NIWs in the mixed and deep layers is higher in fall and winter than in spring and summer, showing maxima in December, corresponding to wind forcings of both wind stress and wind‐current resonance. Spatially, the NIW energy in the mixed layer is higher on the northern side of the subpolar front (SPF), although there are no significant spatial differences in the wind forcings. Because of intensive background currents and their vorticities in the upper layer on the southern side of the SPF, vertical transfer of NIW energy is facilitated, shown by a shorter e‐folding decay time scale of NIWs in the mixed layer on the southern side of the SPF. The NIW kinetic energy in the deep layer of 400–1,000 m is higher on the southern side than on the northern side, an opposite spatial pattern to that in the mixed layer, but consistent with a previous observational study. Our results confirm that energetic anticyclonic circulations with negative relative vorticity in the upper layer on the southern side enable vertical penetration of NIW energy from the mixed layer to the deep layer more effectively.

Beschreibung: Abstract We have used digital holographic tomography (DHT) to study the refractive index (density) changes occurring under Vickers indentations in silica, soda‐lime, and non‐alkaline aluminoborosilicate glasses. The measurements confirm that the maximum refractive index (density) is not constant but increases with load up to 300 gf. At higher loads (500 gf and 1 kgf), a subsurface (median) crack in soda‐lime glass is observed with no apparent surface trace. The appearance of this crack reduces the maximum refractive index (density) observed. In addition, the vertical cross section of the 3D refractive index (density) map has been successfully obtained using a square fiber sample and lateral observation. These results clearly demonstrate a promising potential of DHT to evaluate the shape and the density distribution of the structurally modified zone in a Vickers‐indented glass.

Beschreibung: Abstract Weakly coupled relaxors based on compositions (1‐x) BaTiO3‐xBiMeO3, where Me is a metal ion, have attracted attention as potential candidates for high‐temperature high‐energy density capacitors. However, the necessary Bi content is typically high with x = 0.3‐0.4. In order to reduce problems associated with compatibility for base metal electrodes and due to additional problems due to Bi volatility, it is desirable to lower the Bi content in the overall composition for these materials. Here, we have explored a possible way to reduce BiMeO3 content through additional A‐site substitutions viz. Ca and Sn. The relaxor nature and energy storage properties of Sn‐modified (Ba,Ca)(Ti)O3‐BiScO3 ceramics were determined from their dielectric and ferroelectric behaviors. The material showed attractive properties in terms of a frequency‐independent (200 Hz‐1 MHz) dielectric response from room temperature to 200°C, extremely low loss and high‐energy storage efficiency. The structural phenomena underlying the functional properties of Sn‐modified (Ba,Ca)TiO3‐BiScO3 are characterized from temperature‐dependent X‐ray diffraction and pair distribution function analysis. In broader terms, the study illustrates the potential for tailoring relaxor behavior in Pb‐free ferroelectrics by combining phenomena, such as quantum fluctuations and lone pair stereochemical effect associated with different solid‐solution substitutions.

Beschreibung: Steps involved for investigation of the effect of AD processing at the substrate interface using NaCl coating. Abstract Aerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron‐sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the film‐substrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron‐sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking.

Beschreibung: Abstract Silicon carbide fiber reinforced MoSi2 matrix composite (SiCf/MoSi2) is prepared by liquid silicon infiltration at 1450°C. SiC fiber preform is first impregnated with phosphomolybdic acid (PMA) solution in ethyl alcohol. After calcinations, the PMA is converted into MoO3. Following the heating in hydrogen atmosphere, the MoO3 is reduced into metallic Mo, leading to a porous SiCf/Mo. The porous preform is then infiltrated with liquid silicon above silicon melting point to produce SiCf/MoSi2. The microstructure evolution and the underlying mechanism are studied. It is found that MoSi2 is formed by dissolution‐precipitation. Through multiple impregnation‐calcination cycles, a fully dense SiCf/MoSi2 can be obtained with MoSi2 as the continuous matrix phase. The presence of Mo is found to significantly reduce the attack of liquid silicon the silicon carbide fiber reinforcements.

Beschreibung: Abstract 8 mol% yttria‐stabilized zirconia (8YSZ) ceramic is an oxide ion conductor at atmospheric pressure but shows the onset of p‐type semiconduction, in addition to the preexisting oxide ion conduction, on application of a dc bias in the range 4‐66 Vcm−1 and at temperatures in the range 150°C‐750°C. The p‐type behavior is attributed to the location and hopping of holes on oxygen. This contrasts with the commonly observed introduction of n‐type conduction under reducing conditions and high fields. The hole conductivity increases with both dc bias and pO2. Its occurrence may contribute to the early stages of flash phenomena in 8YSZ ceramics.

Beschreibung: Abstract BiMn3Cr4O12 shows an unusual joint multiferroicity, which facilitates the coexistence of considerable ferroelectric polarization and remarkable magnetoelectric coupling in a single‐phase multiferroic material. Based on first‐principles calculations, we investigate the two different types of ferroelectric phase transitions in the BiMn3Cr4O12 material. Our results show that the first ferroelectric phase transition is driven by soft mode and leads BiMn3Cr4O12 into the Cm space group. The predicted ferroelectric polarization in single crystal is about ~9.8 μC/cm2. With the emergence of spin order on both Mn and Cr sublattices, it is the polar Cm structure that triggers the exchange striction mechanism and therefore results in a large type‐II multiferroicity (~1.1 μC/cm2). In addition, the intrinsic direction of the spin‐driven ferroelectric polarization is always opposite to that of the existing Cm phase structure. Our results imply a feasible strategy in searching/designing novel type‐II multiferroics with large ferroelectric polarization.

Beschreibung: The crystal structure of Li5La3Ta2O12 and PL spectrum of Li5La3Ta2O12:Mn4+ phosphor with the chromaticity diagram and picture under UV 365 nm lamp. Abstract Li5La3Ta2O12:Mn4+ (LLTO:Mn4+) phosphors are prepared in air via high‐temperature solid‐state method and investigated for their crystal structures and luminescence properties. LLTO:Mn4+ phosphor under excitation at 314 nm shows deep‐red emission peaking at 714 nm due to the 2E→4A2 transition of Mn4+ ion. The excitation bands in the range 220 ‐ 570 nm are attributed to the Mn4+ ‐ O2‐ charge‐transfer band and the 4A2g→4T1g, 2T2g, and 4T2g transitions of Mn4+, respectively. The optimal Mn4+ ion concentration is ~0.4 mol%. The concentration quenching mechanism in LLTO:Mn4+ phosphor is electric dipole‐dipole interaction. The luminous mechanism and temperature quenching phenomenon are explained by the Tanabe‐Sugano energy level diagram and the configurational coordinate diagram of Mn4+ in the octahedron, respectively. The experimental results indicate that LLTO:Mn4+ phosphor has a potential application prospect as candidate of deep‐red component in light‐emitting diode (LED) lighting.

Beschreibung: Abstract The effect of the substitution of Na2O with K2O on the viscosity and structure of molten CaO‐SiO2‐CaF2‐based mold fluxes containing alkali‐oxides at high temperatures has been studied. The CaO/SiO2 mass ratio (C/S) and CaF2 were fixed at 0.8 and 10 mass pct., respectively. The total alkali‐oxide was fixed at 20 mass pct. By systematically substituting the Na2O with K2O, the K2O/(Na2O + K2O) mass ratio was modified between 0.0 and 1.0. Using the rotating spindle method to measure the viscosity at high temperatures, the viscosity was found to increase with higher K2O/(Na2O + K2O). From the slope of the temperature dependence of the viscosity, an apparent activation energy was calculated and increased with higher K2O/(Na2O + K2O), from 96 to 154 kJ/mol, due to the cation size effect on the resistance to shearing. Using Raman spectroscopy of as‐quenched fluxes, the mole fraction of Q3 was found to increase, while the mole fractions of Q2 and Q0 decreased with higher K2O/(Na2O + K2O). The nonbridged oxygen per silicon cation (NBO/Si) decreased from 1.97 to 1.58 with increasing K2O/(Na2O + K2O), suggesting greater complexity of the flux structure with higher K2O/(Na2O + K2O), resulting in a higher viscosity.

Beschreibung: Abstract A novel tantalate red‐emitting phosphors NaCa1‐xEuxTiTaO6 (x = 0.02‐0.50) is synthesized via the traditional solid‐state reaction sintering. The photoluminescence properties, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and thermal stability are characterized in detail. Photoluminescence spectra show strong red emission monitored at 614 nm at λex = 395 nm. The spectral properties exhibit excellent color purity and chromaticity coordinate (CIE) characteristics. White light‐emitting diodes (w‐LEDs) device are fabricated by the prepared phosphors and show high quality of color‐rendering index. The investigated results suggest that the Eu3+‐doped NaCaTiTaO6 phosphors can be as potential substitute red phosphors for w‐LEDs.

Beschreibung: Abstract Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase. Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase.

Beschreibung: Abstract ZnO thin films were deposited via atomic layer deposition (ALD) using H2O and H2O2 as oxidants with substrate temperatures from 100°C to 200°C. The ZnO films deposited using H2O2 (H2O2‐ZnO) showed lower growth rates than those deposited with H2O (H2O‐ZnO) at these temperature range due to the lower vapor pressure of H2O2, which produces fewer OH− functional groups; the H2O2‐ZnO films exhibited higher electrical resistivities than the H2O‐ZnO films. The selection of H2O2 or H2O as oxidants was revealed to be very important for controlling the electrical properties of ALD‐ZnO thin films, as it affected the film crystallinity and number of defects. Compared to H2O‐ZnO, H2O2‐ZnO exhibited poor crystallinity within a growth temperature range of 100‐200°C, while H2O2‐ZnO showed a strong (002) peak intensity. Photoluminescence showed that H2O2‐ZnO had more interstitial oxygen and fewer oxygen vacancies than H2O‐ZnO. Finally, both kinds of ZnO thin films were prepared as transparent resistive oxide layers for CIGS solar cells and were evaluated.

Beschreibung: Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into CuCl2 + HCl aqueous solution through the comproportionation reaction between Cu and [Cu(OH)4]2‐ ions. Abstract We demonstrate that Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into an aqueous solution of CuCl2 and HCl at room temperature. The Cl− ions induce oxidative extraction of Ca from CaSi2 to form siloxene and trigger the reductive deposition of Cu particles. All particles are then gradually oxidized to form Cu2O particles under optimized conditions as follows. A trace amount of residual CaSi2 is dissolved in the solution, which provides OH− ions, and a portion of the formed Cu particles are dissolved as [Cu(OH)4]2− ions. Accordingly, Cu2O particles would be formed through the comproportionation reaction between Cu and [Cu(OH)4]2− ions in the solution. However, under conditions with an excess amount of Cl− ions results in further oxidation of Cu to also form Cu2Cl(OH)3. Thus, CaSi2 acts as an effective reduction and/or oxidation mediator to tune the number of Cl− and OH− ions and control the oxidation state of Cu.