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  • Articles  (12,234)
  • Wiley  (12,234)
  • American Meteorological Society
  • Cambridge University Press
  • 2020-2024  (9)
  • 2010-2014  (10,906)
  • 1995-1999  (1,319)
  • Geophysical Research Letters  (4,699)
  • Journal of the American Ceramic Society  (2,688)
  • 4905
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  • Articles  (12,234)
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  • 1
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    Projections of global changes in precipitation extremes from CMIP5 models (2013)
    Wiley
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    Publication Date: 2013-09-10
    Description: [1]  Precipitation extremes are expected to increase in a warming climate, thus it is essential to characterise their potential future changes. Here we evaluate eight high-resolution Global Climate Model simulations in the twentieth century and provide new evidence on projected global precipitation extremes for the 21 st century. A significant intensification of daily extremes for all seasons is projected for the mid and high latitudes of both hemispheres at the end of the present century. For the subtropics and tropics, the lack of reliable and consistent estimations found for both the historical and future simulations might be connected with model deficiencies in the representation of organised convective systems. Low inter-model variability and good agreement with high-resolution regional observations are found for the twentieth century winter over the Northern Hemisphere mid and high latitudes.
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  • 2
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    Mid-depth mixing linked to north atlantic current variability (2013)
    Wiley
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    Publication Date: 2013-09-10
    Description: [1]  Repeated observations at the subpolar front west of the Mid-Atlantic Ridge show a link between the position of the North Atlantic Current (NAC), and the spatial distribution of finescale variance, diapycnal diffusivity, and integrated energy dissipation. Observational data were collected during three cruises. A single branch of the NAC was found in 2008, approximately at 50 ∘ 30Õ N, and two branches were observed in 2010 and 2011, with alternating intensities. Shear variance was elevatedbelow the core of the NAC in all cases, resulting in an average diapycnal diffusivity that is higher by a factor of 3 compared to the averages north and south of the NAC. The integrated energy dissipation has maxima at or south of the fronts; background dissipation is highest during 2008, also the year with the highest surface eddy kinetic energy.
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  • 3
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    The role of synoptic eddies in the tropospheric response to stratospheric variability (2013)
    Wiley
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    Publication Date: 2013-09-10
    Description: [1]  The tropospheric response to sudden stratospheric warmings (SSWs) is analyzed in an idealized model setup regarding the respective roles of planetary-scale and synoptic-scale waves. The control model run includes a full interactive wave spectrum, while a second run includes interactive planetary-scale waves but only the time-mean synoptic-scale wave forcing from the control run. In both runs the tropospheric response is characterized by the negative phase of the respective tropospheric annular mode. But given their different latitudinal structure, the control run shows the expected response, i.e. an equatorward shift of the tropospheric jet, whereas the response in the absence of interactive synoptic eddies is characterized by a poleward jet shift. This opposite jet shift is associated with a different planetary wave variability that couples with the zonal flow between the stratosphere and the surface. These results indicate that the synoptic eddy feedback is necessary for the observed tropospheric response to SSWs.
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  • 4
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    Density-driven transport in the umbrella region of volcanic clouds: implications for tephra dispersion models (2013)
    Wiley
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    Publication Date: 2013-09-10
    Description: [1]  Large explosive volcanic eruptions can generate ash clouds from rising plumes that spread in the atmosphere around a Neutral Buoyancy Level (NBL). These ash clouds spread as inertial intrusions and are advected by atmospheric winds. For low mass flow rates, tephra transport is mainly dictated by wind advection, because ash cloud spreading due to gravity current effects is negligible (passive transport). For large mass flow rates, gravity driven transport at the NBL can be the dominant transport mechanism. Conditions under which the passive transport assumption is valid have not yet been critically studied. We analyze the conditions when gravity-driven transport is dominant in terms of the cloud Richardson number. Moreover, we couple an analytical model that describes cloud spreading as a gravity current with an advection–diffusion model. This coupled model is used to simulate the evolution of the volcanic cloud during the climatic phase of the 1991 Pinatubo eruption.
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  • 5
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    Geographical versus dynamically defined boundary layer cloud regimes and their use to evaluate general circulation model cloud parameterizations (2013)
    Wiley
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    Publication Date: 2013-09-10
    Description: [1]  Regimes of tropical low-level clouds are commonly identified according to large-scale subsidence and lower tropospheric stability (LTS). This definition alone is insufficient for the distinction between regimes and limits the comparison of low-level clouds from CloudSat radar observations and the ECHAM5 GCM run with the COSP radar simulator. Comparisons of CloudSat radar cloud altitude-reflectivity histograms for stratocumulus and shallow cumulus regimes, as defined above, show nearly identical reflectivity profiles because the distinction between the two regimes is dependent upon atmospheric stability below 700 hPa and observations above 1.5 km. Regional subsets, near California and Hawaii for example, have large differences in reflectivityprofiles than the dynamically defined domain; indicating different reflectivity profiles exist under a given large-scale environment. Regional subsets are better for the evaluation of low-level clouds in CloudSat and ECHAM5 as there is less contamination between 2.5 km to 7.5 km from precipitating hydrometeors which obscured cloud reflectivities.
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  • 6
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    Deep moist atmospheric convection in a sub-kilometer global simulation (2013)
    Wiley
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    Publication Date: 2013-09-11
    Description: [1]  Deep moist atmospheric convection is a key element of the weather and climate system for transporting mass, momentum, and thermal energy. It has been challenging to simulate convection realistically in global atmospheric models, because of the large gap in spatial scales between convection (10 0  km) and global motions (10 4  km). We conducted the first ever sub-kilometer global simulation and described the features of convection. Through a series of grid-refinement resolution testing, we found that an essential change for convection statistics occurred around 2-km grid spacing. The convection structure, number of convective cells, and distance to the nearest convective cell dramatically changed at this resolution. The convection core was resolved using multiple grids in simulations with grid spacings less than 2.0 km.
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  • 7
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    El Nino, the 2006 Indonesian Peat Fires, and the distribution of atmospheric methane (2013)
    Wiley
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    Publication Date: 2013-09-11
    Description: [1]  Dry conditions from a moderate El Nino during the fall of 2006 resulted in enhanced burning in Indonesia with fire emissions of CO approximately 4–6 times larger than the prior year. Here we use new tropospheric methane and CO data from the Aura Tropospheric Emission Spectrometer (TES) and new CO profile measurements from the Terra Measurements of Pollution in the Troposphere (MOPITT) satellite instruments with the GEOS-Chem model to estimate methane emissions of 4.25 +/− 0.75 Tg for October-November 2006 from these fires. Errors in convective parameterization in GEOS-Chem, evaluated by comparing MOPITT and GEOS-Chem CO profiles, are the primary uncertainty of the emissions estimate. The El Nino related Indonesian fires increased the tropical distribution of atmospheric methane relative to 2005, indicating that tropical biomass burning can compensate for expected decreases in tropical wetland methane emissions from reduced rainfall during El Nino as found in previous studies.
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  • 8
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    Genesis of hurricane sandy (2012) simulated with a global mesoscale model (2013)
    Wiley
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    Publication Date: 2013-09-11
    Description: [1]  In this study, we investigate the formation predictability of Hurricane Sandy (2012) with a global mesoscale model. We first present five track and intensity forecasts of Sandy initialized at 00Z October 22-26, 2012, realistically producing its movement with a northwestward turn prior to its landfall. We then show that three experiments initialized at 00Z Oct. 16-18 captured the genesis of Sandy with a lead time of up to six days and simulated reasonable evolution of Sandy's track and intensity in the next two-day period of 18Z Oct. 21-23. Results suggest that the extended lead time of formation prediction is achieved by realistic simulations of multi-scale processes, including (1) the interaction between an easterly wave and a low-level westerly wind belt (WWB); (2) the appearance of the upper-level trough at 200-hPa to Sandy's northwest. The low-level WWB and upper-level trough are likely associated with a Madden-Julian Oscillation.
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  • 9
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    The influence of water vapor absorption in the 290-350 nm region on solar radiance: Laboratory studies and model simulation (2013)
    Wiley
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    Publication Date: 2013-09-11
    Description: [1]  Water vapor is an important greenhouse gas in the earth's atmosphere. Absorption of the solar radiation by water vapor in the near UV region may partially account for the up to 30% discrepancy between the modeled and the observed solar energy absorbed by the atmosphere. But the magnitude of water vapor absorption in the near UV region at wavelengths shorter than 384 nm is not known. We have determined absorption cross sections of water vapor at 5 nm intervals in the 290-350 nm region, by using cavity ring-down spectroscopy. Water vapor cross section values range from 2.94 × 10 -24 to 2.13 × 10 -25  cm 2 /molecule in the wavelength region studied. The effect of the water vapor absorption in the 290-350 nm region on the modeledradiation flux at the ground level has been evaluated using radiative transfer model.
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  • 10
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    Atmosphere drives recent interannual variability of the Atlantic meridional overturning circulation at 26.5°N (2013)
    Wiley
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    Publication Date: 2013-09-12
    Description: [1]  The RAPID-MOCHA array has observed the Atlantic Meridional overturning circulation (AMOC) at 26.5°N since 2004. During 2009/2010, there was a transient 30% weakening of the AMOC driven by anomalies in geostrophic and Ekman transports. Here, we use simulations based on the Met Office Forecast Ocean Assimilation Model (FOAM) to diagnose the relative importance of atmospheric forcings and internal ocean dynamics in driving the anomalous geostrophic circulation of 2009/10. Data assimilating experiments with FOAM accurately reproduce the mean strength and depth of the AMOC at 26.5°N. In addition, agreement between simulated and observed stream functions in the deep ocean is improved when we calculate the AMOC using a method that approximates the RAPID observations. The main features of the geostrophic circulation anomaly are captured by an ensemble of simulations without data-assimilation. These model results suggest that the atmosphere played a dominant role in driving recent interannual variability of the AMOC.
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  • 11
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    Contribution of the pacific decadal oscillation to global mean sea level trends (2013)
    Wiley
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    Publication Date: 2013-09-13
    Description: [1]  Understanding and explaining the trend in GMSL has important implications for future projections of sea level rise. While measurements from satellite altimetry have provided accurate estimates of GMSL, the modern altimetry record has only now reached twenty years in length, making it difficult to assess the contribution of decadal to multi-decadal climate signals to the global trend. Here, we use a sea level reconstruction to study the twenty-year trends in sea level since 1950. In particular, we show that the Pacific Decadal Oscillation (PDO) contributes significantly to the twenty-year trends in GMSL. We estimate the PDO contribution to the GMSL trend over the past twenty years to be approximately 0.49 ± 0.25 mm/year, and find that removing the PDO contribution reduces the acceleration in GMSL estimated over the past sixty years.
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  • 12
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    North Pacific Gyre Oscillation and the Occurrence of Western North Pacific Tropical Cyclones (2013)
    Wiley
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    Publication Date: 2013-09-14
    Description: [1]  This study examines links between the North Pacific Gyre Oscillation (NPGO) and the occurrence of tropical cyclones (TCs) in the western North Pacific (WNP) at both inter-annual and decadal scales. The major findings are summarized as follows: (1) NPGO makes significant impacts on the WNP TC frequency at both inter-annual and decadal time scales. The impacts of NPGO on the TC activity are more profound than those exerted by the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation. (2) Niño 3 plays a more important role than Niño 3.4 and Niño 4 in modulating the decadal WNP TC activity. (3) Positive low-level relative vorticity and weak zonal vertical wind shear are responsible for the increase in the WNP TC activity in negative NPGO phases. This study indicates that the NPGO and Niño 3 indices should be key factors for building a scheme for decadal prediction of occurrences of WNP TCs.
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  • 13
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    Changes in electrical resistivity track changes in tectonic plate coupling (2013)
    Wiley
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    Publication Date: 2013-09-17
    Description: [1]  Inter-plate coupling on the Hikurangi subduction margin along the east coast of New Zealand's North Island changes north to south from almost uncoupled to locked. Clay-rich sediments and aqueous-fluids at the subduction interface have been invoked as key factors in the frictional processes that control inter-plate coupling. Here we use magnetotelluric (MT) data to show that the subduction interface in the weakly coupled region is electrically conductive, but is resistive in the locked region. These results indicate the presence of a layer of fluid- and clay-rich sediments in the weakly coupled region and support the idea that the presence of fluid and hydrated clays at the interface is a major factor controlling plate coupling.
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  • 14
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    A new type of Doppler velocity fluctuations in HF ground scatter from the polar cap (2013)
    Wiley
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    Publication Date: 2013-09-17
    Description: [1]  We report a new type of variations in Doppler velocity of HF ground scatter echoes from the polar cap at f ~10 mHz. Similar fluctuations from lower latitudes are usually associated with large-scale dayside Pc3-4 ULF waves. However, the polar cap oscillations exhibit a puzzling anisotropy in spatial coherence along and across the radar's line-of-sight. Furthermore, in contrast to Pc3-4 waves, these fluctuations show no ground magnetic signatures and display a pronounced gap in power/occurrence around local noon. We hypothesize that localized, ≤100 km, auroral particle precipitations near the radar site can modulate Doppler shift of the radio waves entering the ionosphere. In the ground scatter returns, due to the geometrical spread of the rays propagating through the ionosphere to the ground, these variations would appear to have a much larger line-of-sight scale.
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  • 15
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    Synthesis of ZrC–SiC Powders by a Preceramic Solution Route (2013)
    Wiley
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    Publication Date: 2013-09-17
    Description: Homogenous liquid precursor for ZrC – SiC was prepared by blending of Zr ( OC 4 H 9 ) 4 and Poly[(methylsilylene)acetylene]. This precursor could be cured at 250°C and converted into binary ZrC – SiC composite ceramics upon heat treatment at 1700°C. The pyrolysis mechanism and optimal molar ratio of the precursor were investigated by XRD. The morphology and elements analyses were conducted by SEM and corresponding energy-dispersive spectrometer. The evolution of carbon during ceramization was studied by Raman spectroscopy. The results showed that the precursor samples heat treated at 900°C consisted of t- ZrO 2 (main phase) and m- ZrO 2 (minor phase). The higher temperature induced phase transformation and t- ZrO 2 converted into m- ZrO 2 . Further heating led to the formation of ZrC and SiC due to the carbothermal reduction, and the ceramic sample changed from compact to porous due to the generation of carbon oxides. With the increasing molar ratios of C / Zr , the residual oxides in 1700°C ceramic samples converted into ZrC and almost pure ZrC – SiC composite ceramics could be obtained in ZS-3 sample. The Zr , Si , and C elements were well distributed in the obtained ceramics powders and particles with a distribution of 100 ~ 300 nm consisted of well-crystallized ZrC and SiC phases.
    Print ISSN: 0002-7820
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 16
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    Application of a new data operator-splitting data assimilation technique to the 3D VERB diffusion code and CRRES measurements (2013)
    Wiley
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    Publication Date: 2013-09-20
    Description: [1]  In this study we present 3D data assimilation using CRRES data and 3D Versatile Electron Radiation Belt Model using a newly developed operator-splitting method. Simulations with synthetic data show that the operator-splitting Kalman filtering technique proposed in this study can successfully reconstruct the underlying dynamic evolution of the radiation belts. The method is further verified by the comparison with the conventional Kalman filter. We applied the new approach to 3D data assimilation of real data, to globally reconstruct the dynamics of the radiation belts using pitch-angle, energy, and L-shell dependent CRRES observations. An L-shell time cross-sections of the global data assimilation results for nearly equatorially mirroring particles and high and low values of the first adiabatic invariants clearly show the difference between the radial profiles of phase space density. At μ  = 700 MeV/G cross-section of the global reanalysis shows a clear peak in the phase space density, while at lower energy of 70 MeV/G the profiles are monotonic. Since the radial profiles are obtained from one global reanalysis, the differences in the profiles reflect the differences in the underlying physical processes responsible for the dynamic evolution of the radiation belt energetic and relativistic electrons.
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  • 17
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    Feasibility of Tropical Cyclone Intensity Estimation Using Satellite-borne Radiometer Measurements: an Observing System Simulation Experiment (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: [1]  This study evaluates the potential of a proposed technique in using satellite-borne radiometer measurements and weather analyses to estimate the intensity of tropical cyclones. This theory shows that intensity is essentially directly related to the temperature deficit of cloud-top versus sea-surface, and the surplus in saturation entropy in the eyewall versus its surroundings. The eyewall entropy estimate comes from measurements of cloud-top temperature and pressure, and the analysis provides the environmental saturation entropy. An Observing Systems Simulation Experiment (OSSE) was conducted and the results were compared to those from previous studies using cloud-profiling radar altimetry measurements. The use of cloud-top pressure measurements may produce more accurate results. Inherent challenges still require caution in considering operational implementation.
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  • 18
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    Structural evolution of monsoon clouds in the Indian CTCZ (2013)
    Wiley
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    Publication Date: 2013-09-22
    Description: [1]  Structural evolution of monsoon clouds in the core monsoon region of India has been examined using multi-sensor data. Invigoration of warm clouds above 4.5 km (occurring in only 15.4% days of the last 11 monsoon seasons) is associated with a transition from negative to positive normalized rainfall anomaly. Cloud top pressure reduces with an increase in aerosol optical depth at a higher rate of invigoration in drier condition (characterized by large fraction of absorbing aerosols) than wet condition. Cloud effective radius for warm clouds does not show any significant change with an increase in aerosol concentration in presence of high liquid water path, probably due to strong buffering role of meteorology. The structural evolution of monsoon clouds is influenced by both dynamic and microphysical processes that prolong the cloud lifetime, resulting in infrequent rainfall. Our results call for improved representation of aerosol and cloud vertical structures in the climate models to resolve this issue.
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  • 19
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    Ultra-Broad Temperature Stability Obtained with Ce-Doped BaTiO3-Based Ceramics (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: Ce -doped BaTiO 3 -based ceramics were prepared and studied to satisfy ultra-broad temperature stability (from −55°C to 300°C, capacitance variation rate based on C 20°C is within ±15%). The sample with 0.6 mol% CeO 2 succeeds to achieve this performance with a remarkably high ceiling temperature of 300°C. Meanwhile, the sample has good dielectric and electrical properties at room temperature (ε r  = 1667, tanδ = 1.478%, ρ V  = 5.9 × 10 12  Ω·cm). Ce ion can substitute for Ti ion as Ce 4+ or Ba ion as Ce 3+ . The substitution decreases the spontaneous polarization of BaTiO 3 , and then weakens the ferroelectricity of BaTiO 3 . As a result, the temperature stability of samples is improved obviously. Besides, CeO 2 addition promotes the formation of exaggerated grains, which are consisting of Ba 6 Ti 17 O 40 .
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  • 20
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    Mineralogical Composition of Clinker as an Indicator of Sulfate Resistance: A Rietveld XRD/Takashima Approach (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: This study aims to optimize quantitative X-ray diffraction (XRD) mineralogical analysis of the minority phases in clinker. The proposed method consists of applying Rietveld quantitative refinement to the XRD patterns for both clinker and the insoluble residue remaining after it is attacked with methanol and salicylic acid (Takashima method). The method was tested with industrial clinker and the same material after modifying its mineralogy by refiring at 1500°C followed by slow cooling. The findings showed that the C 4 AF / C 3 A ratios for quickly and gradually cooled clinker were much higher when the clinker diffractograms were refined with the Rietveld procedure than when the proposed method was used. The proportion of C 3 A found with the proposed method was ≈2.8-fold higher than when Rietveld only was applied to the diffractograms for clinkers. Taken together, the refinement data for the two materials (clinker and Takashima residua) revealed that Rietveld quantitative XRD applied to clinker underestimates the low C 3 A content. These findings are supported by postsulfate attack durability studies conducted on cements prepared with the two clinkers.
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  • 21
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    The Effect of Electric Poling on the Performance of Lead-Free (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 Piezoceramics (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: The effect of increasing poling fields on the properties of (1− x )BZT– x BCT compositions across the morphotropic phase boundary (MPB) is studied using large signal polarization and strain, small signal permittivity and piezoelectric coefficient, and XRD measurements. Successive poling causes charge carrier migration inducing an internal bias field, which becomes large with respect to the coercive field resulting in biased ferroelectric and ferroelastic switching. Improvements in piezoelectric coefficient of 9% are significantly smaller in the tetragonal 60BCT composition compared with the improvement of approximately 50% in the rhombohedral 40BCT and MPB 50BCT compositions. While the properties continue to change with increased poling fields, the remnant ferroelastic domain texture parallel to the field direction, as observed from XRD, stays approximately constant. The improvement in overall domain alignment leading to largely enhanced intrinsic piezoelectricity originates from the alignment of 180° domains and possibly non-180° domains in grains with orientations inclined to the electric field. As a result, poling is most effective in BZT–BCT materials that have low coercive fields, show low distortions and possess more polarization orientations, such as compositions in the rhombohedral phase field or near the MPB.
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  • 22
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    Impedance Spectroscopy and Dielectric Properties of Flash Versus Conventionally Sintered Yttria-Doped Zirconia Electroceramics Viewed at the Microstructural Level (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: The defect chemistry-modulated dielectric properties of dense yttria-doped zirconia ceramics prepared by conventional sintering (at 1350°C–1500°C) and electric field-assisted flash sintering (55 V/cm at 900°C) were studied by impedance spectroscopy. While the bulk dielectric properties from both sets of samples showed only small and insignificant changes in conductivity and permittivity, respectively, a huge increase of these properties was measured for the grain boundaries in the flash sintered specimens. A close analysis of these results suggests that flash sintering reduced grain-boundary thickness (by about 30%), while increasing the concentration of oxygen vacancies near these interfaces (by about 49%). The underlying mechanism proposed is electric field-assisted generation and accommodation of defects in the space-charge layers adjacent to the grain surface. The changes in measured permittivity are attributed to the boundary thickness effect on capacitance, while conductivity involved variations in its defect density-dependent intrinsic value, accounting for changes also observed in grain-boundary relaxation frequencies. Therefore, in terms of modifications to the specific dielectric properties of these materials, the overall consequence of flash sintering was to considerably lower the semi-blocking character of the grain boundaries.
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  • 23
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    Nanoscaled Interface Between Microgold Particles and Biphase Glass-Ceramic Matrix (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: This article presents a detailed study on the nanoscaled interface between microelongated gold particles (GP) and biphase leucite/feldspar glass-ceramic matrix. The glass-ceramic composite with a nonuniform GP distribution was processed through hot-pressing under vacuum using a commercial dental ceramic furnace for glass-ceramic dental crown manufacturing. Heat treatments at 900°C, 1100°C, and 1300°C were conducted, and microstructural features along the interface were used to verify the chemical reactions between GP and glass-ceramic matrix. It was observed that the amorphous glass-ceramic matrix had nanoscaled biphase structures, and the distributed nanoscaled amorphous leucite phase was attracted to GP during hot-pressing, and was more reactive with GP than the feldspar phase. The thickness of the interfacial phase formed through chemical reactions between GP and glass-ceramic matrix is around 30 nm. The chemically bonded interface has contributed significantly toward the substantial improvements in both strength and toughness of the GP-reinforced glass-ceramic matrix composite. Characterization techniques, including X-ray diffraction and field-emission scanning electron Microscopy, incorporating X-ray microanalysis using energy dispersive spectrometry, have been employed in this study.
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    North American Winter-Spring Storms: Modeling Investigation on Tropical Pacific Sea Surface Temperature Impacts (2013)
    Wiley
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    Publication Date: 2013-10-01
    Description: [1]  An increased frequency and intensity of winter and spring storms have recently manifested over a broad area of North America—along the east coast of the U.S. especially, though global mean storm tracks are suggested to shift northward. To understand these changes, we have conducted atmospheric model experiments, examining the response of North American storm activity to the elevated tropical Pacific sea surface temperature (SST) associated with El Niño. The results indicate that, when tropical Pacific SST increases, there are more numerous intense storms over southwestern, southeastern, and northwestern North America, but fewer weaker storms over the northeast. Transient eddy analysis of the general circulation demonstrates consistent changes, suggesting systematic changes from large-scale general circulation to synoptic-scale storms. These changes can be attributed to enhanced lower tropospheric baroclinicity, to which the southward shift and an intensification of extratropical jet streams make a major contribution.
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    The response of methane hydrate beneath the seabed offshore Svalbard to ocean warming during the next three centuries (2013)
    Wiley
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    Publication Date: 2013-10-01
    Description: [1]  Methane is a potent greenhouse gas and large-scale rapid release of methane from hydrate may have contributed to past abrupt climate change inferred from the geological record. The discovery in 2008 of over 250 plumes of methane gas escaping from the seabed of the West Svalbard continental margin at ~400 m water depth (mwd), suggests that hydrate is dissociating in the present-day Arctic. Here, we model the dynamic response of hydrate-bearing sediments over a period of 2300 yr and investigate ocean warming as a possible cause for present-day and likely future dissociation of hydrate, within 350-800 mwd, west of Svalbard. Future temperatures are given by two climate models, HadGEM2 and CCSM4, and scenarios, Representative Concentration Pathways (RCPs) 8.5 and 2.6. Our results suggest that over the next three centuries 5.3-29 Gg yr -1 of methane may be released to the Arctic Ocean on the West Svalbard margin.
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    Spatial and temporal patterns of simulated slow slip events on the Cascadia megathrust (2013)
    Wiley
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    Publication Date: 2013-10-01
    Description: [1]  In recent years it has been discovered that sections of the subduction interface slip aseismically in slow slip events, during which stress is intermittently transferred to the section of the subduction zone that generates large or great earthquakes. Within the Cascadia subduction zone the magnitude and frequency of SSEs and accompanying tectonic tremor exhibit complex patterns that vary systematically with depth. However the loading mechanisms and interactions that precede great subduction earthquakes are poorly understood. Here we present results from physics-based simulations that reproduce the continuum of SSE characteristics reported for the Cascadia subduction zone. The simulations provide a basis for understanding the interactions that control both the observed complex patterns of SSEs and stress transfer to the seismogenic section that produce great earthquakes.
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    In-situ observations of supercooled liquid clouds over the Southern Ocean during the HIAPER Pole-to-Pole Observation (HIPPO) campaigns (2013)
    Wiley
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    Publication Date: 2013-10-01
    Description: [1]  Clouds over the Southern Ocean exist in a pristine environment that results in unique microphysical properties. However, in-situ observations of these clouds are rare, and the dominant precipitation processes are unknown. Uncertainties in their life cycles and radiative properties make them interesting from a weather and climate perspective. Data from the standard cloud physics payload during the HIAPER Pole-to-Pole Observations (HIPPO) global transects provide a unique snapshot the nature of low-level clouds in the Southern Ocean. High quantities of supercooled liquid water (up to 0.47gm –3 ) were observed in clouds as cold as –22 °C during two flights in different seasons and different meteorological conditions, supporting climatologies inferred from satellite observations. Cloud droplet concentrations were calculated from mean droplet size and liquid water concentrations, and were in the range of 30–120 cm –3 , which is fairly typical for the pristine Southern Ocean environment. Ice in non- or lightly-precipitating clouds was found to be rare, while drizzle drops with diameter greater than 100  μ m formed through warm rain processes were widespread. Large, pristine crystals were commonly seen in very low concentrations below cloud base.
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    Evidence of active mantle flow beneath South China (2013)
    Wiley
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    Publication Date: 2013-10-01
    Description: [1]  The India-Eurasia collision is responsible for producing the Himalayan Mountains and Tibetan plateau and has been hypothesized to have significant far field influences, including driving the Baikal rift and the eastward extrusion of South China. However, quantification of lithospheric buoyancy forces and integrated effect of tractions acting at base of the lithosphere are unable to explain the observed surface motions within South China. We present 198 new SKS shear-wave splitting observations beneath South China and invert these data along with published GPS data to solve for the sub-asthenospheric flow field beneath South China to assess the role of small-scale convection here. We find a 15-20 mm/yr southwestward-directed mantle flow towards the Burma slab. This flow is consistent with the mantle response of slab retreat over the past 25ma, and counter flow due to subduction of Burma/Sunda slabs demonstrating the importance of localized mantle convection on present day plate motions.
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    Raman Spectroscopy of Anhydrous and Hydrated Calcium Aluminates and Sulfoaluminates (2013)
    Wiley
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    Publication Date: 2013-10-02
    Description: Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the identification of anhydrous, hydrated, and carbonated phases in cement-based materials has been demonstrated. In the present work, the application of micro-Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C 12 A 7 , CA 2 , C 2 AS, cubic- C 3 A , C 4 AF, and C 4 A 3 ; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet ( C 3 AH 6 ); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O–H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature.
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    Solvothermal Synthesis of Acmite Conversion Coatings on Steel (2013)
    Wiley
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    Publication Date: 2013-10-02
    Description: Acmite ( NaFeSi 2 O 6 ) films were formed on steel coupons via solvothermal reaction of silica, sodium hydroxide, and 1, 4-butanediol in an autoclave under autogenous pressure. Systematic variation in processing variables led to homogenous coatings comprised of pinacoidal acmite grains with an average grain size of ~33 μm. The coatings were produced on the steel coupons from reactant conditions of 0.635 m SiO 2 , 2.546 m NaOH , and 3.087 m 1,4-butanediol for 72 h at 240°C.
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    Recovering coseismic point ground tilts from collocated high-rate GPS and accelerometers (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Rotational along with translational and strain measurements are essential for a complete description of the motion of a deformable body in a seismic event. We propose a new seismogeodetic approach where collocated high-rate GPS and accelerometer measurements are combined to estimate permanent and dynamic coseismic ground tilts at a point, whereas at present only dynamic tilts are measured with either a dense seismic array or an expensive ring laser gyroscope. We estimate point tilts for a five-story structure on a shake table subjected to 13 earthquake strong-motion records of increasing intensity. For the most intense record from the 2002 M7.9 Denali earthquake, we observe a peak-to-peak dynamic tilt of 0.12°, and a permanent tilt of 0.16° for the structure's roof. Point tilts derived from networks of collocated GPS and accelerometers can be used to estimate the rotational component of seismic wavefield for improved earthquake source characterization.
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    Can we distinguish canonical El Niño from Modoki? (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Following the recent discovery of the “Modoki” El Niño, a proliferation of studies and debates has ensued concerning whether Modoki is dynamically distinct from “Canonical” El Niño, how Modoki impacts and teleconnections differ, and whether Modoki events have been increasing in frequency or amplitude. Three decades of reliable, high temporal–resolution observations of coupled ocean–atmosphere variability in the equatorial Pacific reveal a rich diversity of El Niños. Although central and eastern Pacific sea surface temperature (SST) anomalies appear mechanistically separable in terms of local and remote forcing, their frequent overlap precludes robust classifications. All observed El Niños appear to be a mixture of locally (central Pacific) and remotely forced (eastern Pacific) SST anomalies. Submonthly resolution appears essential for this insight and for the proper dynamical diagnosis of El Niño evolution, thus the use of long–term monthly reconstructions for classification and trend analysis is strongly cautioned against.
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    Aquarius and SMOS Detect Effects of an Extreme Mississippi River Flooding Event in the Gulf of Mexico (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Sea surface salinity (SSS) measurements from the Aquarius/SAC-D satellite and SMOS mission were used to document the freshening associated with the record 2011 Mississippi River flooding event in the Gulf of Mexico (GoM). Assessment of the salinity response was aided by additional satellite observations, including MODIS chlorophyll-a (chl-a) and ocean surface currents, and a passive tracer simulation. Low SSS values associated with the spreading of the river plume were observed 1–3 months after peak river discharge which then receded and became unidentifiable from satellite observations 5 months after maximum discharge. The seasonal wind pattern and general circulation of the GoM dramatically impacted the observed salinity response, transporting freshwater eastward along the Gulf coast and entraining low salinity waters into the open GoM. The observed salinity response from Aquarius was consistent with SMOS SSS, chl-a concentrations, and the passive tracer simulation in terms of the pathway and transit time of the river plume spreading. This study is the first successful application of satellite SSS to study salinity variation in marginal seas.
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    Estuarine acidification and minimum buffer zone – a conceptual study (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  This study uses a simulation method to explore how estuarine pH is affected by mixing between river water, anthropogenic CO 2 enriched seawater, and by respiration. Three rivers with different levels of weathering products (Amazon, Mississippi, and St. Johns) are selected for this simulation. The results indicate that estuaries that receive low to moderate levels of weathering products (Amazon and St. Johns) exhibit a maximum pH decrease in the mid-salinity region as a result of anthropogenic CO 2 intrusion. This maximum pH decrease coincides with a previously unrecognized mid-salinity minimum buffer zone (MBZ). In addition, water column oxygen consumption can further depress pH for all simulated estuaries. We suggest that recognition of the estuarine MBZs may be important for studying estuarine calcifying organisms and pH-sensitive biogeochemical processes.
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    Wavy Magnetodisk in Saturn's Outer Magnetosphere (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  A simple wavy magnetodisk model can explain periodicities in energetic charged particles observed in Saturn's outer magnetosphere (〉20 R S ). The model's free parameters are the tilt of magnetodisk in inner magnetosphere (~1.8°), speed of outgoing spiral wave (~8 R S /hr), critical radius (~10 R S ), and period of rotation (10.64 hours). The fidelity of the model is not judged by a least squares fit to the actual data, but rather by the model's accuracy in reproducing the Lomb periodogram of the periodicities. The model accurately simulates the main spectral feature near ~10.7 hours plus a secondary (“dual”) period near ~10.95 hours. The ability of the wavy magnetodisk with one period to produce the observed dual periodicity in the observations suggests that models having “dual” periods need not be invoked to explain some of the periodicities in Saturn's outer magnetosphere.
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    An analytical formula for the longitudinal resonance frequencies of a fluid-filled crack (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  The fluid-filled crack model has been widely used to interpret the peak frequencies of long-period (LP) seismic events at volcanoes. Up to now, numerical methods have been used to compute resonant frequencies in the model. We propose a simple analytical formula for the longitudinal resonance frequencies of a fluid-filled crack. We evaluated the formula by comparing its results with the resonant frequencies computed by finite difference method (FDM) code. The comparison revealed that the formula well describes the resonant frequencies of both 2D and 3D cracks. The formula enables simple and rapid estimates of the fluid properties and geometries of LP source cracks.
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    Sound velocity of hexagonal close-packed iron up to core pressures (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  We determined the compressional velocity of hcp-Fe using high resolution inelastic X-ray scattering (IXS) combined with in-situ X-ray powder diffraction (XRD): our measurements extend up to 174 GPa at room temperature, to 88 GPa at 700 K, and to 61.5 GPa at 1000 K. Our data, including those obtained at high temperature, are well described by a linear relation to density, extending the range of verification of Birch's law, and suggesting only small temperature dependence up to 1000 K. This result, once compared to the PREM seismologically based model, indicates that there is either a strong temperature effect on Birch's law above 1000 K, or that the composition of the core is rather different than expected, containing, e.g. heavy impurities. Noting that both recent theoretical calculations and shock-wave velocity measurements are consistent with modification of Birch's law at high temperature, we favor the former explanation.
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    Properties of an Infrared-Transparent MgO:Y2O3 Nanocomposite (2013)
    Wiley
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    Publication Date: 2013-09-07
    Description: A 50:50 vol% MgO – Y 2 O 3 nanocomposite with ~150 nm grain size was prepared in an attempt to make 3–5 μm infrared-transmitting windows with increased durability and thermal shock resistance. Flexure strength of the composite at 21°C is 679 MPa for 0.88 cm 2 under load. Hardness is consistent with that of the constituents with similar grain size. For 3-mm-thick material at 4.85 μm, the total scatter loss is 1.5%, forward scatter is 0.2%, and absorptance is 1.8%. Optical scatter below 2 μm is 100%. Variable intensity OH absorption (~6% absorptance) is observed near 3 μm. The refractive index is ~0.4% below the volume-fraction-weighted average of those of the constituents. Thermal expansion is equal to the volume-fraction-weighted average of expansion of the constituents. Specific heat capacity is equal to the mass-fraction-weighted average of heat capacities of the constituents. Thermal conductivity lies between those of the constituents up to 1200 K. Elastic constants lie between those of the constituents. The Hasselman mild thermal shock resistance parameter for the composite is twice as great as that of common 3–5 μm window materials, but half as great as that of c -plane sapphire.
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    Understanding non-linear tropical precipitation responses to CO2 forcing (2013)
    Wiley
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    Publication Date: 2013-09-10
    Description: [1]  Using a traceable framework of idealised GCM experiments, a non-linear dependence of tropical precipitation pattern change on CO 2 forcing is identified. These non-linearities are relatively large and widespread throughout the tropics, and so should not be neglected in projections of future precipitation change. This has implications for the use of pattern-scaling and simple climate models to produce precipitation projections, and for physical understanding of precipitation change across forcing scenarios. The non-linearities can be understood by considering that processes which cause precipitation change, such as increasing moisture, a weakening circulation, and convergence zone shifts, interact in a non-linear manner even when individual processes arequasi-linear. Three driver interactions are identified: ‘warm-shift’, ‘warm-weak’ and ‘shift-weak’. Combined with Clausius-Clapeyron non-linearity in moisture increase, these interactions drive the non-linear pattern change. A strong convergence feedback response substantially amplifies the non-linearity. This analysis is limited to ocean regions, as mechanisms are simpler than over land.
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    Detection of acoustic-gravity waves in lower ionosphere by VLF radio waves (2013)
    Wiley
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    Publication Date: 2013-09-10
    Description: [1]  We present a new method to study harmonic waves in the low ionosphere (60 - 90 km) by detecting their effects on reflection of very low frequency (VLF) radio waves. Our procedure is based on amplitude analysis of reflected VLF radio waves recorded in real time, which yields an insight into the dynamics of the ionosphere at heights where VLF radio waves are being reflected. The method was applied to perturbations induced by the solar terminator motions at sunrises and sunsets. The obtained results show that typical perturbation frequencies found to exist in higher regions of the atmosphere are also present in the lower ionosphere, which indicates a global nature of the considered oscillations. In our model atmosphere, they turn out to be the acoustic and gravity waves with comparatively short and long periods, respectively.
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    Paleogeographic controls on the onset of the Antarctic Circumpolar Current (2013)
    Wiley
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    Publication Date: 2013-09-11
    Description: [1]  Development of the Antarctic Circumpolar Current (ACC) during the Cenozoic is controversial in terms of timing and its role in major climate transitions. Some propose that the development of the ACC was instrumental in the continental scale glaciation of Antarctica and climate cooling at the Eocene/Oligocene boundary. Here we present climate model results that show a coherent ACC was not possible during the Oligocene due to Australasian paleogeography, despite deep water connections through the Drake Passage and Tasman Gateway and the initiation of Antarctic glaciation. The simulations of ocean currents compare well to paleoenvironmental records relating to the physical oceanography of the Oligocene and provide a framework for understanding apparently contradictory dating of the initiation of the ACC. We conclude that the northward motion of the Australasian land masses and the reconfiguration of the Tasman Seaway and Drake Passage are necessary preconditions for the formation of a strong, coherent ACC.
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    Permanently enhanced dynamic triggering probabilities as evidenced by two M ≥ 7.5 earthquakes (2013)
    Wiley
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    Publication Date: 2013-09-11
    Description: [1]  The M 7.7 Haida Gwaii earthquake radiated waves that likely dynamically triggered the M 7.5 Craig earthquake, setting two precedents. Firstly, the triggered earthquake is the largest dynamically triggered shear failure event documented to date. Secondly, the events highlight a connection between geologic structure, sedimentary troughs that act as waveguides, and triggering probability. The Haida Gwaii earthquake excited extraordinarily large waves within and beyond the Queen Charlotte Trough, which propagated well into mainland Alaska and likely triggering the Craig earthquake along the way. Previously, focusing and associated dynamic triggering have been attributed to unpredictable source effects. This case suggests that elevated dynamic triggering probabilities may exist along the many structures where sedimentary troughs overlie major faults, such as subduction zones’ accretionary prisms and transform faults’ axial valleys. Although data are sparse, I find no evidence of accelerating seismic activity in the vicinity of the Craig rupture between it and the Haida Gwaii earthquake.
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    Numerical and statistical evidence for long-range ducted gravity wave propagation over Halley, Antarctica (2013)
    Wiley
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    Publication Date: 2013-09-12
    Description: [1]  Abundant short-period, small-scale gravity waves have been identified in the mesosphere and lower thermosphere over Halley, Antarctica, via ground-based airglow image data. Although many are observed as freely-propagating at the heights of the airglow layers, new results under modeled conditions reveal that a significant fraction of these waves may be subject to reflections at altitudes above and below. The waves may at times be trapped within broad thermal ducts, spanning from the tropopause or stratopause to the base of the thermosphere (~140 km), which may facilitate long-range propagation (~1000 s of km) under favorable wind conditions.
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    Multi-model seasonal forecasting of global drought onset (2013)
    Wiley
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    Publication Date: 2013-09-13
    Description: [1]  The capability of seasonal forecasting of global drought onset at local scales (1-degree) has been investigated using multiple climate models with 110 realizations. Climate models increase the global mean probability of drought onset detection from the climatology forecast by 31%-81%, but only increase equitable threat score by 21%-50% due to a high false alarm ratio. The multi-model ensemble increases the drought detectability over some tropical areas where individual models have better performance, but cannot help more over most extra-tropical regions. On average, less than 30% of the global drought onsets can be detected by climate models. The missed drought events are associated with low potential predictability and weak antecedent ENSO signal. Given the high false alarms, the reliability is very important for a skillful probabilistic drought onset forecast. This raises the question of whether seasonal forecasting of global drought onset is essentially a stochastic forecasting problem.
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    The K-derived MLT-sector geomagnetic indices (2013)
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    Publication Date: 2013-09-13
    Description: [1]  New sub-auroral K -derived sector indices are proposed. They are based upon the K local geomagnetic activity indices from the planetary am network stations, and their derivation scheme draws directly from that of am indices. Four Magnetic Local Time (MLT) sectors are considered, leading to four different K -derived MLT-sector indices: the aσ Dawn (03-09 MLT), aσ Noon (09-15 MLT), aσ Dusk (15-21 MLT) and aσ Midnight (21-03 MLT) indices. They cover more than 4 solar cycles and, thus, allow robust statistical analysis. Statistical studies of the whole aσ data series and case studies for two geomagnetic storms are presented. These analyses clearly show that the four aσ have specific behaviors, and that it is possible to get insight into both the statistical properties of the physical processes responsible for the observed geomagnetic activity and contribution to the dynamics of a given storm.
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    Extratropical forcing of El Niño/Southern Oscillation asymmetry (2013)
    Wiley
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    Publication Date: 2013-09-13
    Description: [1]  Boreal-winter near-surface atmospheric circulations over the Hawaiian region are known to influence the state of the tropical Pacific and initiate the development of El Niño/Southern Oscillation (ENSO) events. Here we show that these same preceding near-surface circulations have an additional influence on the longitudinal position of the resultant ENSO-related sea-surface temperatures (SSTs) as well, with warm (cold) events systematically shifted to the east (west) of the typical SST anomalies. In influencing this positioning, these atmospheric circulations in turn modify the near and far-field climate responses to these SSTs such that during warm events, the typical ENSO-related responses east (west) of the dateline are generally enhanced (reduced); conversely, during cold events the typical ENSO-related responses are generally reduced (enhanced). The fact that the extratropical atmospheric circulations in question influence the asymmetry of ENSO extremes with a 12-month lead time carries important implications for predicting the socio-economic impacts of these events.
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    Post-eruption chemical evolution of a volcanic caldera lake: Karymsky Lake, Kamchatka (2013)
    Wiley
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    Publication Date: 2013-09-17
    Description: [1]  The 1996 short-lived subaqueous eruption at the Karymsky caldera lake suddenly changed the composition of the lake water. The lake with the surface area of ~10 km 2 and a volume of ~0.5 km 3 became acidic, increased its salinity to ~1000 mg/kg, and became dominated by SO 4 2- and Ca 2+ . Since the eruption, the lake chemistry has evolved in a predictable manner described by simple box model. As a result of dilution by incoming SO 4 -Ca-Mg poor water, SO 4 , Ca and Mg concentrations follow a simple exponential decrease with a characteristic time close to the residence time of the lake. Na, K and Cl decrease relatively significantly slower indicating a continuing input of these constituents into the lake that was initiated during the eruption. Thus, the dynamics of two groups of lake water solutes can be predicted by a simple box model for water and solute mass balance.
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    Land-use change and nitrogen feedbacks constrain the trajectory of the land carbon sink (2013)
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    Publication Date: 2013-09-17
    Description: [1]  Our understanding of Earth's carbon-climate system depends critically upon interactions between rising atmospheric CO 2 , changing land use, and nitrogen limitation on vegetation growth. Using a global land model we show how these factors interact locally to generate the global land carbon sink over the past 200 years. Nitrogen constraints were alleviated by N 2 fixation in the tropics and by atmospheric nitrogen deposition in extra-tropical regions. Non-linear interactions between land-use change and land carbon and nitrogen cycling originated from three major mechanisms: (i) a sink foregone that would have occurred without land-use conversion; (ii) an accelerated response of secondary vegetation to CO 2 and nitrogen, and (iii) a compounded clearance loss from deforestation. Over time, these non-linear effects have become increasingly important and reduce the present-day net carbon sink by ~40% or 0.4 PgC yr -1 .
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    NAL phase in K-rich portions of the lower mantle (2013)
    Wiley
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    Publication Date: 2013-09-19
    Description: [1]  The stability of the K-rich new aluminous (NAL) phase was examined on the join Na 1.00  Mg 2.00 Al 4.80 Si 1.15 O 12 –K 1.00  Mg 2.00 Al 4.80 Si 1.15 O 12 (Na100–K100) up to 144 GPa by X-ray diffraction in a laser-heated diamond-anvil cell. Single-phase K100 and Na50K50 NAL were formed up to the lower mantle conditions, and the NAL phase coexisted with the calcium ferrite-type phase at 120 GPa and 2300 K for the Na75K25 bulk composition. This is a striking contrast to the K-free (Na100) NAL that becomes unstable above 27 GPa at 1850 K, which suggests that potassium stabilizes NAL at significantly higher pressures. K-rich NAL may host potassium in the lower mantle that contains K 2 O more than 0.09 wt%. In addition, the NAL phase likely formed owing to partial melting in the ultralow velocity zone or because of a basal magma ocean. Future seismological observations may clarify whether NAL is a radiogenic heat source above the core–mantle boundary.
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    A new wave scheme for trajectory simulations of stratospheric water vapor (2013)
    Wiley
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    Publication Date: 2013-09-19
    Description: [1]  We have developed a new wave scheme particularly aiming to provide better temperature fields with realistic variability for trajectory modeling of dehydration processes in the tropical tropopause layer (TTL). The new scheme includes amplitude-phase interpolation and amplification of waves in reanalysis data. Amplification factors are based on statistical variability differences between reanalysis data and radiosonde observations at 24 tropical locations during 1997-2013 boreal winters. We show that conventional linear interpolation of temperatures in the vertical coordinate degrades wave amplitudes and variability. Amplitude-phase interpolation in Fourier space greatly mitigates the problem found in linear interpolation. Furthermore, amplitudes of existing waves in reanalyses were amplified to generate realistic variability. In addition to improvements in variability, the scheme lowers cold point temperatures and raises cold point tropopause heights. Having realistic variability with the new approach will reduce uncertainties in simulations of TTL cirrus clouds and stratospheric water vapor.
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    High ozone concentrations on hot days: The role of electric power demand and NOx emissions (2013)
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    Publication Date: 2013-09-19
    Description: [1]  High ambient temperatures intensify photochemical production of tropospheric ozone, leading to concerns that global warming may exacerbate smog episodes. This widely-observed phenomenon has been termed the climate penalty factor (CPF). A variety of meteorological and photochemical processes have been suggested to explain why surface ozone increases on hot days. Here, we quantify an anthropogenic factor previously overlooked: the rise of ozone precursor emissions on hot summer days due to high electricity demand. Between 1997 and 2011, power plant emissions of NO x in the eastern U.S. increased by ~2.5-4.0%/°C, raising surface NO x concentrations by 0.10-0.25 ppb/°C. Given an ozone production efficiency (OPE) of ~8 mol/mol based on the 2011 NASA DISCOVER-AQ campaign, at least 1/3 of the CPF observed in the eastern U.S. can be attributed to the temperature dependence of NO x emissions. This finding suggests that controlling emissions associated with electricity generation on hot summer days can mitigate the CPF.
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    Preparation of Y2Si2O7/ZrO2 Composites and Their Composition – Mechanical Properties – Tribology Relationships (2013)
    Wiley
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    Publication Date: 2013-09-19
    Description: In this work, novel Y 2 Si 2 O 7 / ZrO 2 composites were developed for structural and coating applications by taking advantage of their unique properties, such as good damage tolerance, tunable mechanical properties, and superior wear resistance. The γ- Y 2 Si 2 O 7 / ZrO 2 composites showed improved mechanical properties compared to the γ- Y 2 Si 2 O 7 matrix material, that is, the Young's modulus was enhanced from 155 to 188 GPa (121%) and the flexural strength from 135 to 254 MPa (181%); when the amount of ZrO 2 was increased from 0 to 50 vol%, the γ- Y 2 Si 2 O 7 / ZrO 2 composites also presented relatively high facture toughness (〉1.7 MPa·m 1/2 ), but this exhibited an inverse relationship with the ZrO 2 content. The composition–mechanical property–tribology relationships of the Y 2 Si 2 O 7 / ZrO 2 composites were elucidated. The wear resistance of the composites is not only influenced by the applied load, hardness, strength, toughness, and rigidity but also effectively depends on micromechanical stability properties of the microstructures. The easy growth of subcritical microcracks in Y 2 Si 2 O 7 grains and at grain boundaries significantly contributes to the macroscopic fracture toughness, but promotes the pull-out of individual grains, thus resulting in a lack of correlation between the wear rate and the macroscopic fracture toughness of the composites.
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    Correction to “Field-aligned currents associated with dipolarization fronts” (2013)
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    Publication Date: 2013-09-20
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    Temperature Gradient Introduced Ferroelectric Self-Poling in BiFeO3 Ceramics (2013)
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    Publication Date: 2013-09-21
    Description: The as-prepared BiFeO 3 ceramic shows a piezoelectric d 33 coefficient of −14 pC/N, that is, an obvious ferroelectric self-poling phenomenon. The temperature gradient between the two surfaces of BiFeO 3 ceramic was intentionally enlarged when BiFeO 3 was prepared with a rapid liquid sintering method. This temperature gradient and the corresponding thermal strain can introduce defect dipoles through separating bismuth vacancies from oxygen vacancies. A mass of these dipoles introduce a macroscopic internal electric field ( E in ) which downward poles BiFeO 3 ceramic during its cooling down process. As expected, an E in of 〉10 kV/cm is confirmed by the asymmetrical polarization/strain versus electric field curves.
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    Effect of Ba Content on the Stress Sensitivity of the Antiferroelectric to Ferroelectric Phase Transition in (Pb,La,Ba,)(Zr,Sn,Ti)O3 Ceramics (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: The effect of Ba content on the stress sensitivity of the antiferroelectric to ferroelectric phase transition in ( Pb 0.94− x La 0.04 Ba x )[( Zr 0.60 Sn 0.40 ) 0.84 Ti 0.16 ] O 3 ceramics is investigated through monitoring electric field-induced polarization and longitudinal strain under compressive prestresses. It is found that incorporation of Ba significantly suppresses the stress sensitivity of the phase transition, as manifested by slight decreases under prestresses up to 100 MPa in the maximum polarization ( P m ) and longitudinal strain ( x m ). The energy storage density is even increased under the mechanical confinement in compositions x  = 0.02 and 0.04. X-ray diffraction, transmission electron microscopy, and dielectric measurements indicate that the suppressed stress sensitivity is associated with the disruption of micrometersized antiferroelectric domains into nanodomains and the transition from antiferroelectric to relaxor behavior.
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    Enhancement of Interparticle Exchange Coupling in CoFe2O4/CoFe2 Composite Nanoceramics Via Spark Plasma Sintering Technology (2013)
    Wiley
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    Publication Date: 2013-09-21
    Description: Powders and nanoceramics composed of composites of CoFe 2 O 4 , CoFe 2 , and a small amount of FeO were prepared by heating CoFe 2 O 4 powder in reducing atmosphere and by sintering the product of reducing reaction at 350°C via spark plasma sintering technology. In the powders, increase in the molar ratios of CoFe 2 : CoFe 2 O 4 and a great change in magnetic parameters were observed with the change in heating temperature from 300°C to 400°C, and the dominance of dipole interaction over exchange coupling in the interparticle interactions was confirmed by the steps in magnetic hysteresis loops and the negative Henkel plots. However, in the nanoceramics, significant enhancement in exchange coupling was found when the sintering temperature was raised to 500°C and 650°C, which was confirmed by both the positivity of Henkel plot and the single-phase style of the magnetic hysteresis loop.
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    Optimization of Gas Adsorption Porosimetry for Geopolymer Analysis (2013)
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    Publication Date: 2013-09-21
    Description: Gas adsorption porosity measurement of geopolymers (GPs) is required for quantitative understanding of such mesoporous structures, but the complex nature of the GP system makes analysis difficult. Previous results in the literature are often ambiguous or contradictory. A systematic investigation of metakaolin GP gas adsorption results was conducted to optimize the use of this measurement technique and verify that results match known theory about GP structure. It was found that GP undergoes structural change upon degassing at 100°C or higher. If and only if this change is prevented by degassing at a lower temperature could it be shown that specific surface area and total gas adsorption increases with both increasing curing temperature and decreased Si : Al ratio. This observation is consistent with previous suggestions of increased zeolitic character under these conditions, where previous gas adsorption investigations had not observed this expected relationship. Hydrogen physisorption is proposed as a substitute technique for micropore isotherms in GPs due to the difficulty of removing trace gasses from GPs and the measurement effect of such gasses at high vacuum. A hydrogen physisorption isotherm qualitatively resembled an equivalent nitrogen micropore isotherm.
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    Rupture complexity of the Mw 8.3 Sea of Okhotsk earthquake: Rapid triggering of complementary earthquakes? (2013)
    Wiley
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    Publication Date: 2013-09-24
    Description: [1]  We derive a finite slip model for the 2013 M w 8.3 Sea of Okhotsk Earthquake (Z = 610 km) by inverting calibrated teleseismic P-waveforms. The inversion shows that the earthquake ruptured on a 10° dipping rectangular fault zone (140 km × 50 km) and evolved into a sequence of 4 large sub-events (E1-E4) with an average rupture speed of 4.0 km/s. The rupture process can be divided into two main stages. The first propagated south, rupturing sub-events E1, E2 and E4. The second stage (E3) originated near E2 with a delay of 12 s and ruptured northwards, filling the slip-gap between E1 and E2. This kinematic process produces an overall slip pattern similar to that observed in shallow swarms, except it occurs over a compressed time span of about 30s and without many aftershocks, suggesting that sub-event triggering for deep events is significantly more efficient than for shallow events.
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    Seismic transect across the Lomonosov and Mendeleev ridges: Constraints on the geological evolution of the Amerasia Basin, Arctic Ocean (2013)
    Wiley
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    Publication Date: 2013-09-24
    Description: [1]  We report on seismic and petrological data that provide new constraints on the geological evolution of the Amerasia Basin. A seismic reflection profile across the Makarov Basin, located between the Mendeleev and Lomonosov ridges, shows a complete undisturbed sedimentary section of Mesozoic/Cenozoic age. In contrast to the Mendeleev Ridge, the margin of the Lomonosov Ridge is wide and shows horst and graben structures. We suggest that the Mendeleev Ridge is most likely volcanic in origin and support this finding with a 40 Ar/ 39 Ar isotopic age for a tholeitic basalt sampled from the central Alpha/Mendeleev Ridge. Seismic reflection data for the Makarov Basin show no evidence of compressional features consistent with the Lomonosov Ridge moving as a microplate in the Cenozoic. We propose that the Amerasia Basin moved as a single tectonic plate during the opening of the Eurasia Basin.
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    Scaling relations of seismic moment, rupture area, average slip, and asperity size for M ~ 9 subduction-zone earthquakes (2013)
    Wiley
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    Publication Date: 2013-09-24
    Description: [1]  Scaling relations for seismic moment M 0 , rupture area S , average slip D , and asperity size S a were obtained for large, great, and giant ( M w  = 6.7–9.2) subduction-zone earthquakes. We compiled the source parameters for seven giant ( M w  ~ 9) earthquakes globally for which the heterogeneous slip distributions were estimated from tsunami and geodetic data. We defined S a for subfaults exhibiting slip greater than 1.5 times D . Adding 25 slip models of 10 great earthquakes around Japan, we recalculated regression relations for 32 slip models: S  = 1.34 × 10 −10   M 0 2/3 , D  = 1.66 × 10 −7   M 0 1/3 , S a  = 2.81 × 10 −11   M 0 2/3 , and S a / S  = 0.2, where S and S a are in km 2 , M 0 is in Nm, and D is in m. These scaling relations are very similar to those obtained by Murotani et al. (2008) for large and great earthquakes. Thus, both scaling relations can be used for future tsunami hazard assessment associated with a giant earthquake.
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    Characterization of nucleation during laboratory earthquakes (2013)
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    Publication Date: 2013-09-24
    Description: [1]  We observe the nucleation phase of in-plane ruptures in the laboratory. We show that the nucleation is composed of two distinct phases, a quasi-static and an acceleration stage, followed by dynamic propagation. We propose an empirical model which describes the rupture length evolution: the quasi-static phase is described by an exponential growth while the acceleration phase is described by an inverse power law of time. The transition from quasistatic to accelerating rupture is related to the critical nucleation length, which scales inversely with normal stress in accordance with theoretical predictions, and to a critical surfacic power, which may be an intrinsic property of the interface. Finally, we discuss these results in the frame of previous studies and propose a scaling up to natural earthquake dimensions.
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    Effect of the Eu3+ Addition on Photoluminescence and Microstructure of ZnO–CdO–TeO2 Glasses (2013)
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    Publication Date: 2013-09-24
    Description: In this work, the role of europium doping of glasses formulated in the ternary system ZnO – CdO – TeO 2 is described. The Eu -doped oxide glasses were prepared by the conventional melt-quenching method and by using three different compositions. Structural studies reveal that there exists a good affinity between Cd and some rare earth (RE) ions to form the crystalline phase. The X-ray diffraction (XRD) diagrams display that the structure of these glasses is amorphous and with the increase in CdO content and the compatibility of Eu 3+ , there is a tendency to form nanocrystals of CdTe 2 O 5 . The scanning electron microscopic (SEM) observation of their microstructure confirms the presence of phase separation. Differential thermal analysis (DTA) of these glasses showed small exothermic peaks noted around 450°C for the V2 glass and 480°C for V1 and V3 glasses, which could be attributed to the formation of these crystals. The infrared spectra showed a main absorption band around 800–600 cm −1 corresponding to the Te – O stretching mode in TeO 4 and TeO 3 groups. By optical absorption (OA), the band gap ( E g ) for each glass was determined; these values were 3.27, 3.14, and 3.3 eV for the V1–V3 glasses, respectively. Furthermore, the presence of Eu 3+ was detected in the 370–470 nm short-range wavelengths. The photoluminescence (PL) experiments of the glasses showed light emission due to the following transitions: 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4.
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    Effects of lunar cumulate mantle overturn and megaregolith on the expansion and contraction history of the Moon (2013)
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    Publication Date: 2013-10-01
    Description: [1]  Gravity anomalies derived from recent GRAIL data suggest the presence of early volume expansion of the Moon. The absence of identifiable thrust faults limits the total net contraction that has occurred. These observations provide constraints on the lunar thermal evolution which raise questions for giant impact origin of the Moon. To study the lunar expansion/contraction history, we perform 3D thermochemical mantle evolution models, with solidifying core overlain by a layer of ilmenite-bearing cumulates (IBC) resulting from mantle overturn after magma ocean solidification. Our models focus on the effects of the overturn-produced density stratification with a deep heat-producing element (HPE) distribution and a top insulating megaregolith layer. The deep HPE can cause an early expansion up to 1.5 km radius due to the heating of the deep mantle. This HPE distribution also reduces the present-day contraction by ~7 km. Compared to the models without overturn, an end-member model with a stable IBC-rich layer on the core-mantle boundary shows an overall present-day contraction as small as 1.1 km. The low thermal conductivity of megaregolith also affects the present-day contraction, reducing it by ~ 3 km.
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    The multiple spots of the Ganymede auroral footprint (2013)
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    Publication Date: 2013-10-01
    Description: [1]  The interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere, called the satellite footprints. So far, footprints have been detected for Io, Europa, Ganymede and Enceladus. These footprints are usually seen as single spots. However, the Io footprint, the brightest one, displays a much more complex morphology made of at least three different spots and an extended tail. Here, we present Hubble Space Telescope FUV images showing evidence for a second spot in the Ganymede footprint. The spots separation distance changes as Ganymede moves latitudinally in the plasma sheet, as is seen for the Io footprint. This indicates that the processes identified at Io are universal. Moreover, for similar Ganymede System III longitudes, the distance may also vary significantly with time, indicating changes in the plasma sheet density. We identified a rapid evolution of this distance ~8 days after the detection of a volcanic outburst at Io, suggesting that such auroral observations could be used to estimate the plasma density variations at Ganymede.
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    Low-order stochastic model and “past-noise forecasting” of the Madden-Julian oscillation (2013)
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    Publication Date: 2013-10-01
    Description: [1]  This paper presents a predictability study of the Madden-Julian Oscillation (MJO) that relies on combining empirical model reduction (EMR) with the “past-noise forecasting” (PNF) method. EMR is a data-driven methodology for constructing stochastic rotect low-dimensional models that account for nonlinearity, seasonality, and serial correlation in the estimated noise, while PNF constructs an ensemble of forecasts that accounts for interactions between (i) high-frequency variability (“noise”), estimated here by EMR; and (ii) the low-frequency mode (LFM) of MJO, as captured by singular-spectrum analysis (SSA). A key result is that — compared to an EMR ensemble driven by generic white noise — PNF is able to considerably improve prediction of MJO phase. When forecasts are initiated from weak MJO conditions, the useful skill is of up to 30 days. PNF also significantly improves MJO prediction skill for forecasts that start over the Indian Ocean.
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    Proton Conductivity in Solid Solution 0.7(CaWO4)–0.3(La0.99Ca0.01NbO4) and Ca(1−x)LaxW(1−y)TayO4 (2013)
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    Publication Date: 2013-10-02
    Description: The conductivity of nominal CaWO 4 , CaW 0.99 Ta 0.01 O 4–δ , 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ), and Ca 0.9 La 0.1 WO 4+δ has been studied by means of a.c. impedance measurements. Proton conductivity was observed for CaW 0.99 Ta 0.01 O 4–δ , which displayed exothermic hydration with enthalpy and entropy of –82 kJ/mol and –120 J/molK, respectively. The proton mobility in CaW 0.99 Ta 0.01 O 4–δ was low, with enthalpy and preexponential factor of mobility of 82 kJ/mol and 0.7 cm 2 K/Vs. The high enthalpy of mobility is interpreted to reflect association between the acceptor dopant and protonic defects, whereas the low preexponential factor of mobility may reflect a lower proton concentration than assumed. Rietveld refinement indicated low solubilities of La on Ca -site and Ta on W-site. Proton conductivity was also observed in undoped CaWO 4 , however, not in Ca 0.9 La 0.1 WO 4+δ . The conductivity of 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ) behaved much like that of undoped LaNbO 4 , likely due to a very low acceptor dopant concentration.
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    Preparation and Electric Properties of Bi0.5Na0.5TiO3–Bi(Al0.5Ga0.5)O3 Lead-Free Piezoceramics (2013)
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    Publication Date: 2013-10-02
    Description: A new lead-free BNT-based piezoelectric ceramics of (1 −  x ) Bi 0.5 Na 0.5 TiO 3 – x Bi ( Al 0.5 Ga 0.5 ) O 3 ( x  = 0, 0.02, 0.03, 0.04, and 0.05) were synthesized using a conventional ceramic fabrication method. Their structures and electrical properties were investigated. All the samples show a typical ferroelectric P ( E ) loops and S ( E ) curves at room temperature. The optimal properties are obtained at the composition of the x  = 0.03. The substitution of Bi ( Al 0.5 Ga 0.5 ) O 3 enhances piezoelectric constant and increases Curie temperature from 58 pC/N and 310°C of pure BNT to 93 pC/N and 325°C of the x  = 0.03. The temperature-dependent P ( E ) loops and S ( E ) curves of 0.97BNT–0.03BAG indicate that phase transition from ferroelectric to antiferroelectric takes place over a very wide temperature region from 80°C to 180°C. The results show that the introduction of BAG improves the electrical properties of BNT.
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    Seismic Evidence for Lithospheric Modification Beneath the Mojave Neovolcanic Province, Southern California (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  The Mojave Neovolcanic Province (MNVP), located in the Mojave block of southern California, comprises late Miocene to Quaternary small-volume basaltic centers. Geochemistry indicates an asthenospheric source for the MNVP beginning in the late Miocene, but no physical evidence of missing mantle lithosphere has been presented. We utilize receiver functions and ambient noise tomography to image the lithosphere beneath the Mojave block. Regionally, we find thin crust that thickens distal to sites of MNVP volcanism. Shear wave velocities between 40 and 75 km depth are consistent with the presence of mantle lithosphere in the southern Mojave block and very thin or missing mantle lithosphere to the north. With one exception, MNVP volcanoes lie along this sharp boundary. Our observations, together with the established geologic history and geochemistry of the MNVP, can be explained by small-scale edge-driven convection producing ongoing lithospheric removal within the Mojave block. Our results provide another example of lithospheric instability that occurs in response to rapid changes in mantle dynamics induced by major changes in tectonic plate geometry.
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    Ferromagnetism of iron under pressure to 21.5 GPa (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Computational, Mössbauer and synchrotron radiation experiments arrive at disparate conclusions regarding the magnetic state of the high-pressure, hexagonal closed packed, phase of iron, which likely comprises the bulk composition of Earth's inner core. Using a non-magnetic, moissanite anvil cell together with a superconducting magnetometer, we measured the remanent magnetization of iron in response to applied magnetic fields under pressure up to 21.5 GPa at room temperature. Two independent experiments using different pressure transmission media reveal a higher remanent magnetization at 21.5 GPa than at initial conditions, which could be attributed to a distorted hexagonal closed packed phase grown during the martensitic transition. Upon both compression and decompression, the remanent magnetization of the body centered cubic phase increases several times over initial conditions while the coercivity of remanence remains mostly invariant with pressure.
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    Investigation of cosmic ray–cloud connections using MISR (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Numerous empirical studies have analyzed International Satellite Cloud Climatology Project (ISCCP) data and reached contradictory conclusions regarding the influence of solar-modulated galactic cosmic rays on cloud fraction and cloud properties. The Multiangle Imaging SpectroRadiometer (MISR) instrument on the Terra satellite has been in continuous operation for 13 years and thus provides an independent (and previously unutilized) cloud dataset to investigate purported solar–cloud links. Furthermore, unlike many previous solar–climate studies that report cloud fraction MISR measures albedo, which has clearer climatological relevance. Our long-term analysis of MISR data finds no statistically significant correlations between cosmic rays and global albedo or globally averaged cloud height, and no evidence for any regional or lagged correlations. Moreover, epoch superposition analysis of Forbush decreases reveals no detectable albedo response to cosmic ray decreases, thereby placing an upper limit on the possible influence of cosmic ray variations on global albedo of 0.0029 per 5% decrease. The implications for recent global warming are discussed.
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    Large-scale climate control of zooplankton transport and biogeography in the Kuroshio-Oyashio Extension region (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  We studied decadal-scale climate control of zooplankton biogeography driven by Kuroshio Extension (KE) dynamics using long-term zooplankton data and an advection model driven with currents from the Earth Simulator eddy-resolving ocean model. Passive tracer model experiments indicated that warm-water species transported from the south were retained in the Kuroshio-Oyashio Extension (KOE) region during years with a weak KE. A 2.5-year lag in the North Pacific Gyre Oscillation (NPGO) index was significantly correlated with the KE strength and with warm-water species abundance. These findings indicate that climate signals from the central and eastern North Pacific propagated westward, influencing not only transport in the KOE region but also regional ecosystem variability. Because the NPGO controls important aspects of the transport dynamics and ecosystem variability in the eastern North Pacific, this study provides additional evidence that large-scale climate patterns drive coherent changes in ecosystems throughout the North Pacific by impacting regional-scale transport dynamics.
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    Bidirectional exchange of methyl halides between tropical plants and the atmosphere (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Using a stable isotope tracer technique, we studied the exchange of methyl chloride (CH 3 Cl) and methyl bromide (CH 3 Br) between plants and the atmosphere in a tropical rainforest in Malaysia. Most plant species examined showed not only production but also consumption of CH 3 Cl with a large net emission overall. In contrast, CH 3 Br consumption was comparable to its production, so the net emission was small. The rates of CH 3 Cl and CH 3 Br consumption were highly correlated with each other, and their ratio was consistent with reported values in terrestrial ecosystems, where microorganisms are responsible for the consumption. Such microorganisms might participate in the consumption we observed, as the consumption rates were faster in saplings, whose leaves were generally covered by epiphytic microorganisms, than in healthy looking leaves of mature trees.
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    A mid-crustal ramp-fault structure beneath the Taiwan tectonic wedge illuminated by the 2013 Nantou earthquake series (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Taiwan's active mountain belt is a spotlight for orogenic studies and was first used to test the critical-taper wedge mechanics. The concept of an orogenic wedge above a shallow detachment surface has been highly influential on current understanding of orogenic processes in Taiwan. However, the recent M L 6.2 and M L 6.5 2013 Nantou reverse-faulting earthquakes in central Taiwan nucleated below the proposed detachment indicating that active mountain building is occurring below the orogenic wedge. We estimate the coseismic slip distributions and fault geometry using the uniform stress drop slip inversions. The earthquakes occur on essentially the same 30° dipping fault plane ramping up from ~20 km depth near a cluster of 1999 Chi-Chi earthquake aftershocks to the shallow detachment and the Chi-Chi fault plane. The fault could be a deep extension of a mature shallow fault or a newly-developed deep ramp fault that is not reflected in the surface geology.
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    Large-scale simulations of snow albedo masking by forests (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Comparisons between climate models have found large differences in predictions for the albedo of forested regions with snow cover, leading to uncertainty in the strength of snow albedo feedbacks on climate change predicted by these models. To explore this uncertainty, three commonly used methods for calculating the albedo of vegetated surfaces are compared, taking observed snow and vegetation distributions as inputs. Surprisingly, all three methods produce similar results and compare reasonably well with observations over seasonally snow covered regions of the Northern Hemisphere. It appears that some climate models use unrealistic parameter values, and snow albedo masking need not be as large a source of uncertainty as it is in current climate projections.
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    An information-theoretic perspective on teleconnections (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  A classical paradigm for terrestrial climate variability involves remote sea-surface temperature forcing, communicated to receptor regions via atmospheric teleconnections. Here, the teleconnection link is abstracted in terms of Shannon's information-theoretic measure “channel capacity.” An upper bound on the channel capacity for DJF seasonal precipitation teleconnections with sea surface temperature in the NINO3.4 region, when both variables are tercile-quantized, is estimated as one bit, meaning that it is only marginally possible to distinguish reliably between two NINO3.4 input states on the basis of observed precipitation output amounts, the central tercile acting principally to degrade reliability. A relationship between the channel capacity in a continuous model and the correlation coefficient is established; the corresponding nonlinear transformation provides a useful shift in perspective on the communication of information as such via teleconnections.
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    The shallow structure beneath Montserrat (W.I.) from new Bouguer gravity data (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  Although the persistently active Soufrière Hills Volcano (Montserrat, West Indies) is one of the most extensively studied active stratovolcanoes, a local Bouguer gravity map of the volcano and the island of Montserrat has yet to be constructed. We collected 157 new gravity data, which we analysed and inverted in order to constrain the island's subsurface density distribution. Our model results reveal high-density material beneath the centres of the extinct volcanic complexes – presumably related to exposed dome cores – while the volcanic flanks and the active Soufrière Hills Volcano are underlain by low-density material. Volcaniclastic deposits and subsurface melt aggregations, respectively, may explain these negative gravity anomalies. Our results are in good agreement with previous structural observations from seismic tomography, yet a higher spatial density of the gravity survey network has allowed us to additionally capture smaller, shallow-seated anomalies in the gravity field that relate to tectonic structures and fluvial filling deposits.
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    Comprehensive model of short- and long-term slow slip events in the Shikoku region of Japan, incorporating a realistic plate configuration (2013)
    Wiley
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    Publication Date: 2013-10-04
    Description: [1]  We numerically simulate slow slip events (SSEs) in the Shikoku region of Japan, incorporating the configuration of the subducting plate. We adopt a rate- and state-dependent friction law with cut-off velocities, assuming a frictional parameter distribution based on observed long-term SSEs and nonvolcanic tremors that reflects the slip of short-term SSEs. Our model reproduces recurrences of long- and short-term SSEs and segments of short-term SSEs. In our simulation, short-term SSEs’ transition from episodic to continuous slip is reproduced. This feature is consistent with tremor activity recently reported in both Shikoku and Cascadia. In addition to the long-term SSEs in the Bungo Channel, our model also reproduces newly found long-term SSEs in central Shikoku, and predicts that these SSEs recur during the interseismic period between megathrust earthquakes. Our model comprehensively reproduces various SSEs and their characteristics as reported in the Shikoku region.
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    Inner shelf intrusions of offshore water in an upwelling system affect coastal connectivity (2013)
    Wiley
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    Publication Date: 2013-10-05
    Description: [1]  Poleward warm-water flows around Point Conception are an important transport mechanism linking biogeographic provinces along central California. These flows are initiated by relaxation of upwelling winds; the intensity and duration of upwelling is an important driver of how far north warm water penetrates against the prevailing surface currents. In this paper we present evidence of offshore surface water intrusions to the inner shelf, 130 km north of Point Conception, near Cambria, California. Satellite observations show that the intrusions originate as eddies generated offshore along the upwelling front. These eddies may form as submesoscale instabilities or by interaction of upwelling centers with offshore waters. The intrusions move southern watersto the central California inner shelf farther northward than is typical for a coastal relaxation plume, and therefore inner shelf connectivity and ecology may be governed over timescales and distances longer than those set by the intermittent relaxation of upwelling winds.
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    Rupture history of the 2013 Mw 6.6 Lushan earthquake constrained with local strong motion and teleseismic body and surface waves (2013)
    Wiley
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    Publication Date: 2013-10-05
    Description: [1]  The rupture history of the April 20, 2013 Mw 6.6 Lushan (China) earthquake is constrained by inverting waveforms of local strong motion, teleseismic broadband body waves, and long period surface waves. This earthquake ruptured a blind thrust fault oriented N210 o E (along the Longmenshan fault zone) and dipping 40 o to the NW. The inverted slip distribution is heterogeneous, dominated by a slip patch with a roughly right triangular shape, which spans a depth range of 5-20 km and accounts for two-thirds of the total seismic moment (8.9x10 18 Nm). The rupture initiated roughly at the middle of the triangle's hypotenuse and, during the first 4 s, propagated mainly in along-strike and down-dip directions, towards a peak slip of 1.2 m. Despite a large number of fatalities and economic loss, the estimated static and apparent stress drops of the Lushan earthquake are 1.5 MPa and 0.35 MPa, considerably low with respect to other similar intra-plate earthquakes.
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    Electrical and Thermal Transport Properties of Iron and Iron-Silicon Alloy at High Pressure (2013)
    Wiley
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    Publication Date: 2013-10-05
    Description: [1]  The efficiency of heat transfer by conduction in Earth's core controls the dynamics of convection and limits the power available for the geodynamo. We have measured the room temperature electrical resistivity of iron and iron-silicon alloy to 60 GPa and present a new model of the resistivity at the high pressures and temperatures relevant to Earth's core. The model is compared with available shock wave data and theoretical studies. For a power law and linear temperature dependence of electrical resistivity, the calculated thermal conductivity at the core mantle boundary is ~67-145 W/m/K for pure Fe, and ~41-60 W/m/K for Fe-9wt.%Si. Impurities in the core have a strong effect on the transport properties of iron that could significantly impact core thermal models. The models describing the data indicate higher thermal conductivity at core pressure than previously suggested, requiring additional energy sources in the past to operate the geodynamo.
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    Two-dimensional simulation of ionospheric variations in the vicinity of the epicenter of the Tohoku-oki earthquake on 11 March 2011 (2013)
    Wiley
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    Publication Date: 2013-10-05
    Description: [1]  Unusual ionospheric variations were observed in the M9.0 Tohoku-oki earthquake on 11 March 2011. Among various kinds of features in the ionosphere, significant depletion of TEC near the epicenter was observed after the earthquake. Although previous studies have suggested that the coseismic ionospheric variations are associated with atmospheric perturbation caused by vertical displacement of the sea surface, the mechanism of the TEC depletion has not been fully understood. In this paper, a two-dimensional nonlinear nonhydrostatic compressible atmosphere–ionosphere model is employed to investigate the ionospheric variations in the vicinity of the epicenter. The simulation results reveal that an impulsive pressure pulse produced by a sudden uplift of the sea surface leads to local atmospheric expansion in the thermosphere and that the expansion of the thermosphere combined with the effect of inclined magnetic field lines in the ionosphere causes the sudden TEC depletion above the epicenter region.
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    Rapid Submarine Melting Driven by Subglacial Discharge, LeConte Glacier, Alaska (2013)
    Wiley
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    Publication Date: 2013-10-05
    Description: [1]  We show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers. This buoyant discharge draws in warm seawater, entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice. To capture the effects of subglacial discharge on submarine melting, we conducted four days of hydrographic transects during late summer 2012 at LeConte Glacier, Alaska. A major rainstorm allowed us to document the influence of large changes in subglacial discharge. We found strong submarine melt fluxes that increased from 9.1 ± 1.0 to 16.8 ± 1.3 m d −1 (ice face equivalent frontal ablation) as a result of the rainstorm. With projected continued global warming and increased glacial runoff, our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems. These effects must be considered when modeling glacier response to future warming and increased runoff.
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    Moderate-magnitude earthquakes induced by magma reservoir inflation at Kīlauea Volcano, Hawai‘i (2013)
    Wiley
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    Publication Date: 2013-10-05
    Description: [1]  Although volcano-tectonic (VT) earthquakes often occur in response to magma intrusion, it is rare for them to have magnitudes larger than ~ M4. On 24 May 2007, two shallow M4+ earthquakes occurred beneath the upper part of the east rift zone of Kīlauea Volcano, Hawai‘i. An integrated analysis of geodetic, seismic and field data, together with Coulomb stress modeling, demonstrates that the earthquakes occurred due to strike-slip motion on pre-existing faults that bound Kīlauea Caldera to the southeast and that pressurization of Kīlauea's summit magma system may have been sufficient to promote faulting. For the first time, we infer a plausible origin to generate rare moderate-magnitude VTs at Kīlauea by reactivation of suitably oriented pre-existing caldera-bounding faults. Rare moderate to large-magnitude VTs at Kīlauea and other volcanoes can therefore result from reactivation of existing fault planes due to stresses induced by magmatic processes.
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    Critical role for mesoscale eddy diffusion in supplying oxygen to hypoxic ocean waters (2013)
    Wiley
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    Publication Date: 2013-10-05
    Description: [1]  Estimates of the oceanic lateral eddy diffusion coefficient A redi vary by more than an order of magnitude, ranging from less than a few hundred m 2 /s to thousands of m 2 /s. This uncertainty has first-order implications for the intensity of oceanic hypoxia, which is poorly simulated by the current generation of Earth System Models. Using satellite-based estimate of oxygen consumption in hypoxic waters to estimate the required diffusion coefficient for these waters gives a value of order 1000 m 2 /s. Varying A redi across a suite of Earth System Models yields a broadly consistent result given a thermocline diapycnal diffusion coefficient of 1x10 -5  m 2 /s.
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    A Nondestructive Methodology for the Study of Colored Enamels: Insights into Manufacturing and Weathering Processes (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: We studied ancient enamels on gilded copper from a collection of archeological horse harness pendants of the Museo Instituto Valencia de Don Juan (Madrid, Spain) to test the benefits of a new, nondestructive analytical methodology based on chemometric analysis (i.e., Principal Component Analysis, PCA) on micro-ATR-FTIR spectral data and chemical quantification using SEM-EDS. The novelty of this approach was threefold: (i) PCA allowed the discrimination of the different harness pendants of known origin and attributed to the 14th and 15th centuries according to the chemical complex composition, nanostructure, glass weathering, and/or coloring mechanisms of each colored enamel, separately (i.e., red, purple, blue, and white), (ii) it is a cheap, easily available and nondestructive methodology that enables us to (iii) draw archeological conclusions about the quality of the manufacturing process, reassess the chronology of these objects and attempt to attribute them to different workshops according to the different traditional recipes identified. In particular, the enamels were made of alkali and/or alkaline earth lead-glass with a wide range of chemical compounds in the form of pigments or opacifiers. Two types of coloring mechanisms were identified, colloidal particles such as copper-ruby for red enamels, and ionic mechanisms such as Fe (II) and Co (II) to achieve a blue pigments; Mn (III) in the purple pigment; and two kind of white enamels were identified, i.e., tin oxide as an opacifier and uranium oxide. In addition, we established the reason for the poor state of conservation of some of the enamels by means of the identification of depolymerization and ion exchanges, well-known harmful effects of glass weathering, and finally a chronology was assigned for some of these pieces according to the enamel composition.
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    A Study on Crystallization Kinetics of Thermoelectric Bi2Se3 Crystals in Ge–Se–Bi Chalcogenide Glasses by Differential Scanning Calorimeter (2013)
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    Publication Date: 2013-06-06
    Description: Novel glass-ceramics with embedded thermoelectric Bi 2 Se 3 crystals were prepared from glass matrices in the Ge 20 Se 100− x Bi x ( x  = 5, 10, 12 mol%) system. Based on DSC results performed at different heating rates, characteristic activation energies ( E c ) and Avrami exponents ( n ) were obtained and analyzed by using Kissinger's relation, Ozawa's method, Augis–Bennett approximation and Matusita–Sakka theory. XRD results showed that pure Bi 2 Se 3 crystalline phase precipitated upon annealing at different temperatures for various time. The crystal size and crystalline fraction in the samples could be tuned by controlling the annealing time.
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    Low Temperature Synthesis of High Alumina Cements by Novel Co-Melt Precursors and Their Implementation as Castables with Some Micro Fine Additives (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: In the present investigations nano size high alumina cements (HAC) were prepared by very effective co-melt precursor sintering technique from their metal nitrate precursors. The prime cementing phases observed were CA, CA 2 , and C 12 A 7 . The addition of nano structured cements in refractory castables has improved the thermo-chemical-mechanical properties to a significant extent. Each batch of low cement castables (LCC) was prepared from calcined Chinese bauxite, HAC, and superfine additives. The effect of HAC in bauxite castable with the additives similar to Silicon Carbide, reactive alumina, and micro-fine silica on the sinterability and properties of these castables was investigated. Physical properties such as apparent porosity and bulk density, mechanical properties such as hot modulus of rupture (HMOR), cold and hot modulus of rupture (CMOR), and cold crushing strength (CCS) of hydrated and sintered castables were studied. The sintered castables were also characterized for their solid phase compositions and microstructure using X-ray diffraction (XRD) and FE-SEM, respectively. In the castables new phases such as mullite, α-alumina were formed at the expense of bauxite and silica. Solid solution of mullite formed at high temperature acts as a bonding phase and is accounted for high HMOR, CMOR, and CCS values. These excellent properties of such castables may enable their uses in various applications such as refractory lining for fabrication of steel, aluminium, copper, glass, cement, chemicals, and ceramics.
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    The simulated tropospheric annular modes show no long-term response to external forcing over the past millennium (2013)
    Wiley
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    Publication Date: 2013-06-07
    Description: [1]  This study analyzes whether the imprint of external forcings can be detected in the long-term evolution of the main atmospheric circulation patterns in climate simulations over the last millennium. The external forcing is not found to significantly add variability in any frequency band compared to control simulations where the external drivers are kept constant. Additionally, a method designed to detect a common signal in the time evolution of these circulation patterns among all simulations is proposed, and employed to demonstrate that the null hypothesis of an evolution dominated by internal variability can not be rejected regardless of the time smoothing applied to the series. Given that the fingerprint of external forcings on atmospheric circulation has been successfully detected in simulations of the 20th century climate and in future climate change projections, we argue that either the effect of past natural forcing is too small, state-of-the-art climate models underestimate their climate sensitivity, or the anthropogenic forcing qualitatively differs from the natural forcing in its effect on main circulation patterns.
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    High-speed rupture in the first 20 s of the 2011 Tohoku earthquake, Japan (2013)
    Wiley
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    Publication Date: 2013-06-07
    Description: [1]  The 2011 Tohoku earthquake produced tens of meters of fault slip near the Japan Trench, which generated devastating tsunami. The rupture process before the huge slip is still unclear due to a lack of resolution. Here I perform a multiscale slip inversion analysis to examine the first 10 and 20 s of the rupture process and the whole rupture process at different scales. The result shows that 4 s after the initiation, this earthquake started with a relatively high-speed rupture that had a peak slip-rate faster than 1 m/s and rupture velocity comparable to 3 km/s. 14 s after the initiation, the rupture propagation direction changed from northward to westward, near the edge of the M 7.3 foreshock coseismic slip area. The stress release by the foreshock may contribute to the complex small-scale rupture propagation, which may appear to be a slow rupture propagation when only looking at long-period data.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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    Nutrient variability in Subantarctic Mode Waters forced by the Southern Annular Mode and ENSO (2013)
    Wiley
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    Publication Date: 2013-06-08
    Description: [1]  As the primary source of nutrients to the global thermocline, Subantarctic Mode Waters (SAMWs) play a key role in primary production and climate. Here we use repeat hydrographic WOCE/CLIVAR data to quantify interannual SAMW nutrient variability and its forcing. Pacific sector SAMW nutrients were significantly correlated with the Southern Annular Mode (SAM) and wind stress curl anomalies associated with a faster meridional overturning circulation (MOC). A stronger MOC results in greater upwelling of nutrients at high latitudes, increased Ekman transport of nutrients equatorward, and subduction of higher preformed nutrient loads in SAMWs. Australian sector SAMWs were significantly correlated with ENSO, likely due to its modulation of transport in the East Australian Current extension. Interannual variability in SAMW nutrients impacts downstream tropical export production by as much as 5-12% of the annual mean.
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    Topics: Geosciences , Physics
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    High Conductivity Electrolyte: Zn2GeO4 (2013)
    Wiley
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    Publication Date: 2013-06-11
    Description: Zn 2 GeO 4 ceramic materials were synthesized by the solid-state method. Zn 2 GeO 4 powders were investigated with X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Oxygen defects in the Zn 2 GeO 4 ceramics were investigated by photoluminescence, Raman, and EDS spectra. Conductivity of Zn 2 GeO 4 was 0.18 S/cm at low temperature of 773 K, and its activation energy was 0.49 eV. The results showed that Zn 2 GeO 4 was a promising low-temperature electrolyte with high conductivity.
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    Electronic ISSN: 1551-2916
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    Identification of a widespread Kamchatkan tephra: A middle Pleistocene tie-point between Arctic and Pacific paleoclimatic records (2013)
    Wiley
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    Publication Date: 2013-06-12
    Description: [1]  Very few age controls exist for Quaternary deposits over the vast territory of the East Russian Arctic, which hampers dating of major environmental changes in this area and prevents their correlation to climatic changes in the Arctic and Pacific marine domains. We report a newly identified ~177 ka old Rauchua tephra, which has been dispersed over an area of 〉1,500,000 km 2 and directly links terrestrial paleoenvironmental archives from Arctic Siberia with marine cores in the northwest Pacific, thus permitting their synchronization and dating. The Rauchua tephra can help to identify deposits formed in terrestrial and marine environments during the oxygen isotope stage 6.5 warming event. Chemical composition of volcanic glass from the Rauchua tephra points to its island-arc origin, while its spatial distribution singles out the Kamchatka volcanic arc as a source. The Rauchua tephra represents a previously unknown, large (magnitude 〉6.5) explosive eruption from the Kamchatka volcanic arc.
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    Opposite CMIP3/5 trends in the wintertime Northern Annular Mode explained by combined local sea-ice and remote tropical inuences (2013)
    Wiley
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    Publication Date: 2013-06-12
    Description: [1]  A crucial challenge in climate studies is to determine how warming trends due to anthropogenic forcing may affect the natural modes of atmospheric variability. In the Northern extratropics, the leading pattern of atmospheric dynamics is known as the Northern Annular Mode (NAM), often computed as the first Empirical Orthogonal Function of sea-level pressure (SLP) or geopotential height at 500mb (Z500). Here we compare wintertime NAM changes estimated from previous (CMIP3) versus ongoing (CMIP5) generations of multi-model projections for the twenty-first century, under similar emission scenarios (SRES A2 vs. RCP 8.5). CMIP3 projections exhibited a positive NAM trend, albeit this response differed between SLP and Z500, whereas CMIP5 projections rather reveal a negative trend, especially for Z500. We show that the CMIP3/5 discrepancies are mostly explained in early winter by the local consequence of faster Arctic sea ice loss in CMIP5, and in late winter by the remote influence through teleconnection of stronger warming in the Western tropical Pacific. The attribution of CMIP3/5 discrepancies to the differences in emission scenarios is assessed by investigating NAM responses in common 1%-CO2 idealized experiments.
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    Tailoring the Piezoelectric and Relaxor Properties of (Bi1/2Na1/2)TiO3–BaTiO3 via Zirconium Doping (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94( Bi 1/2 Na 1/2 ) TiO 3 –6 Ba ( Zr x Ti 1− x ) O 3 (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric-field-induced transition of the average crystal structure from pseudo-cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm 2 at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature T F-R , above which the field-induced transformation from the relaxor to ferroelectric state becomes reversible.
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    Processing and Properties of Eu3+-Doped Barium Bismuth Titanate (BaBi4Ti4O15) Glass–Ceramic Nanocomposites (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: Precursor glasses for the ferroelectric barium bismuth titanate ( BaBi 4 Ti 4 O 15 ) (BBiT) have been prepared by the melt-quench technique in the SiO 2 – K 2 O – BaO – Bi 2 O 3 – TiO 2 (SKBBT) glass system with and without Eu 2 O 3 doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction (XRD), electron microscopy (FE-SEM, TEM), and FT-IR reflectance spectroscopy. FE-SEM images show the formation of randomly oriented hexagonal rod-shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT-IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm −1 . The activation energy of crystallization ( E c ) varies from 295 to 307 kJ/mol. The dielectric constants (ε r ) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat-treated GCs show higher ε r values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5 D 0 → 7 F 2 transition. An intense 466 nm excitation band corresponding to the 7 F 0 → 5 D 2 transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat-treatment times led to a 15-fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu 3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam 0.5 ) values obtained in the GCs are high and suitable for structural applications.
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    Enhancing the Superconducting Properties of Magnesium Diboride Without Doping (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: Carbon doping is known to be very effective for enhancing the high-field properties of magnesium diboride, MgB 2 , but not for the low-field properties. Here, we report that both the high- and the low-field properties can be improved simultaneously without doping by increasing the initial magnesium partial pressure, by simply reducing the size of the magnesium particles. It is shown that in situ processed bulk MgB 2 sintered with fine magnesium powders has superior superconducting properties compared with a bulk sample fabricated using coarse magnesium lumps. The change in the lattice parameters was almost negligible; however, a clear increase in lattice strain can be observed for the sample sintered with fine magnesium powders. The increase in the lattice strain results in an enhancement of the high-field properties. Furthermore, it has also been found that the low-field critical current density is not reduced, but rather slightly increased for the fine magnesium powder sample. This is due to a closer linkage among the grains that drastically improves grain connectivity. These findings demonstrate that the initial growth mechanism of MgB 2 is very crucial for its superior superconducting properties, and it especially indicates the importance of magnesium vapor pressure.
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    Alumina Region of the Lithium Aluminosilicate System: A New Window for Temperature Ultrastable Materials Design (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: Revisiting classic phase diagrams and chemical phase relations in the solid state of a very well-studied oxide system, such as the lithium aluminosilicate (LAS) system, can open a new window for the design of new advanced materials with improved properties. Crystal chemistry and phase equilibria are used to demonstrate the ability to design materials with particular desired properties in the alumina-rich corner of the LAS phase diagram. The experimental results demonstrate the alumina and β-eucryptite solid-state compatibility.
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    Annealing Effect on the Properties of Cu(In0.7Ga0.3)Se2 Thin Films Grown by Femtosecond Pulsed Laser Deposition (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: This work reports the crystallization, microstructure, and surface composition of Cu In 0.7 Ga 0.3 Se 2 (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X-ray diffraction, Raman scattering, UV-visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuS e initially formed on the as-deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as-deposited and annealed films as demonstrated by preliminary tests.
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    Formation Mechanisms of Ti3SnC2 Nanolaminate Carbide Using Fe as Additive (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: Reactive sintering of 3 Ti : Sn :2 C and 3Ti:Sn:2C:0.6Fe powder mixtures is studied in the temperature range 510°C–1200°C under argon. It is demonstrated that the recently discovered Ti 3 SnC 2 phase is formed, provided that Fe is added to a 3 Ti : Sn :2 C reactant mixture within the synthesis conditions used. Using dilatometric and X-Ray diffraction analyses, the formation mechanism of Ti 3 SnC 2 is discussed. Results show that at low temperature (about 510°C), tin is consumed to form Fe x Sn y intermetallics. At high temperature (about 1060°C), tin is newly available to form Ti 3 SnC 2 due to the melting of Fe x Sn y . Then, the intermediate phases, TiC and Ti 2 SnC , and/or Ti 5 Sn 3 , TiC , C , and Ti are dissolved in the ( Fe  +  Sn ) liquid phase and Ti 3 SnC 2 very likely precipitate from the melt. The second part of the study deals with the optimization of the Fe content in the initial 3Ti:Sn:2C reactant powder mixture to synthesize samples with larger Ti 3 SnC 2 content by hot isostatic pressing.
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    Effects of Non-Stoichiometry on the Microstructure, Oxygen Vacancies, and Piezoelectric Properties of CuTa2O6-Doped NKN Ceramics (2013)
    Wiley
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    Publication Date: 2013-06-06
    Description: The effects of non-stoichiometry on the microstructure, oxygen vacancies, and piezoelectric properties of ( Na 0.5 K 0.5 ) x NbO 3 (NK x N, where x  =   0.98, 1.00, 1.01, and 1.02) ceramics doped with sintering aid CuTa 2 O 6 (CT) doping were investigated. X-ray diffraction (XRD) patterns indicated that a secondary phase formed in CT-doped NK x N (NK x NCT) ceramics with x  〈   1.00 and that a pure phase was obtained with x  ≥   1.00. The grain size of NK x NCT ceramics increased with increasing x value due to the formation of a liquid phase. The internal bias field, activation energy, and Raman analysis for NK x NCT ceramics showed that the number of induced oxygen vacancies increased with decreasing x value. The high mechanical quality factor ( Q m ) value obtained for NK x NCT ceramics did not correspond to a higher concentration of oxygen vacancies, illustrating that the suitable compensation (excess Na and K ) is more important than the concentration of oxygen vacancies to obtain the ceramics with high Q m values. The NK x NCT ceramics with x  =   1.01 exhibited excellent piezoelectric properties, with k p and Q m values of 39.9% and 2,070, respectively.
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