Inversion for the density–depth profile of Dome A, East Antarctica, using frequency-modulated continuous wave radar

The density–depth relationship of the Antarctic ice sheet is important for establishing a high-precision surface mass balance model and predicting future ice-sheet contributions to global sea levels. A new algorithm is used to reconstruct firn density and densification rate by inverting monostatic radio wave echoes from ground-operated frequency-modulated continuous wave radar data collected near four ice cores along the transect from Zhongshan Station to Dome A. The inverted density profile is consistent with the core data within 5.54% root mean square error. Due to snow redistribution, the densification rate within 88 km of ice core DT401 is correlated with the accumulation rate and varies greatly over horizontal distances of <5 km. That is, the depth at which a critical density of 830 kg m−3 is reached decreases and densification rate increases in high-accumulation regions but decreases in low-accumulation regions. This inversion technique can be used to analyse more Antarctic radar data and obtain the density distribution trend, which can improve the accuracy of mass-balance estimations.

Fabrication of Highly Transparent Y2O3 Ceramics with CaO as Sintering Aid

Highly transparent Y2O3 ceramics were successfully fabricated with CaO as sintering aid. The microstructure evolution, optical transmittance, hardness and thermal conductivity of the Y2O3 ceramics were investigated. It was found that doping a small amount (0.01–0.15 wt.%) of CaO could greatly improve the densification rate of Y2O3. With an optimized CaO dosage of 0.02 wt.% combined with the low temperature vacuum sintering plus hot isostatic pressing (HIP-ing), Y2O3 ceramics with in-line transmittance of 84.87% at 1200 nm and 81.4% at 600 nm were obtained.

Snowpack modelling in central Italy: analysis and comparison of high-resolution WRF-driven Noah LSM and Alpine3D simulations

&lt;p&gt;Italy is a territory characterized by complex orography. Its main mountain chains are the Alps, which identify the northern Italian border, and the Apennines, which cross the entire Italian peninsula ranging from north-west to south-east. The major Apennines peaks reach almost 3000 meters and are located in central Italy, in the Abruzzo region. The near Mediterranean sea is an important source of moisture, which permits to this region to experience a substantial snow cover during winter. Thanks to the orientation of the Apennines chain and the height of its peaks the Abruzzo region is characterized by different climate types. This affects the precipitation patterns and the snowpack evolution, resulting in high regional variability of the snow cover. The goal of this study is to investigate the snow cover evolution in the Abruzzo region, using and comparing different snowpack models. To this end we have used the Weather Research and Forecasting (WRF) model to drive the Noah Land Surface Model (LSM) and the sophisticated three-dimensional snow cover model Alpine3D to simulate the snow cover evolution at regional scale. Noah LSM is already on-line coupled with WRF, but this is not the case for Alpine3D. Thus we have modified and used the interfacing library MeteoIO to force Alpine3D with the meteorological data simulated with WRF, off-line coupling the two models. We have validated the WRF simulation using a dense network of automatic weather stations (AWS), obtaining good agreement between simulated and observed data. We have found that the snow depth simulated with Noah LSM presents a negative bias, caused by the inability of the model to reproduce correctly the snow densification rate. Instead, Alpine3D is capable to better reproduce the observed densification rate, thanks to its more detailed description of the snow metamorphism processes. However, the snow depth simulated with Alpine3D presents a negative bias, caused by an underestimation of the new snow depth, which has a negative impact on the entire simulation.&lt;/p&gt;

Effect of (Tb+Y)/Al ratio on Microstructure Evolution and Densification Process of (Tb0.6Y0.4)3Al5O12 Transparent Ceramics

(Tb0.6Y0.4)3Al5O12 transparent ceramics were successfully fabricated by solid-state reactive sintering using Tb4O7, Y2O3, and α-Al2O3 powders as raw materials. The effect of (Tb+Y)/Al ratio on microstructure evolution and densification process was investigated in detailed. The results showed that the grain growth kinetics were significantly affected by (Tb+Y)/Al ratio. Al-rich and Tb-rich phases appeared in part of the samples of different ratios. Particularly, excess aluminum increased the diffusing process, leading to a higher densification rate, while samples with excess terbium ratios displayed a smaller grain size and lower relative density. The optical quality was highly related to the amount of the secondary phase produced by different (Tb+Y)/Al ratios. Finally, (Tb0.6Y0.4)3Al5O12 transparent ceramics have been fabricated through pre-sintering in vacuum, followed by hot isostatic sintering (HIP), and the best transmittance of sample with a 4 mm thickness was approximately 78% at 1064 nm.

Characterization of MgAl2O4 sintered ceramics

Single phase MgAl2O4 was made from a one-to-one molar ratio of MgO and Al2O3 powders mixed using ball-milling. Mixtures of MgO and Al2O3 were subsequently treated in planetary ball mill for 30, 60, 90 and 120 minutes in air. The aim of this study was to examine phase composition, microstructure, and densification behavior of sintered specimens. After sintering in dilatometer at 1500?C, the powder was converted to single phase MgAl2O4. The results show that mechanical activation improved the densification behavior of MgAl2O4 sintered specimens, and it reduced the onset temperature for sintering by approx. 100?C. Based on dilatometer data, powders were subsequently densified at 1450?C by hot pressing. Almost ?ll specimens exhibited full density, while sample activated for 30 minutes showed the fastest densification rate.

A set of constitutive functions for dried body to predict entire deformation process of ceramic products during firing

Purpose The purpose of this paper is to propose a set of constitutive functions for dried bodies for accurate prediction of the entire deformation process of ceramic products during firing and to present relevant methods for determining their coefficients from a series of respective thermo-mechanical analysis (TMA) tests. Design/methodology/approach The function forms of the sintering-induced strain rate, viscoplastic multiplier and elastic modulus are formulated in order with reference to empirical data of relative densities. Separate TMA tests are conducted to identify their coefficients, while a stairway thermal cycle test is carried out to identify the parameters in the densification rate. Then, various finite element analyses (FEA) are performed for accuracy confirmation. Findings The performances of the present constitutive functions along with the identified material parameters were validated in comparison with the relevant test results. It has then been confirmed that these functions enable us to some extent to accurately estimate the non-mechanical and mechanical deformations of dried bodies during firing. Also, by performing FEA of an actual sanitary ware product, the applicability and capability of the proposed set of constitutive functions could be demonstrated. Practical implications The present methodology with the proposed constitutive functions is a simple, but reliable and practical approach for simulating the deformation process of arbitrary ceramic products subjected to firing and applicable for practical applications in various engineering fields. Originality/value The constitutive functions of the viscoplastic multiplier and elastic modulus, which enable us to properly characterize the mechanical behavior of dried bodies subjected to firing, are originally formulated in analogy with that of the sintering-induced strain.

Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities

The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas–ice age difference is essential to documenting the phasing between CO2 and temperature changes, especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ15N of air measured in ice cores. All firn densification models applied to deglaciations show a large disagreement with δ15N measurements at several sites in East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ15N suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model–data mismatch for the gas trapping depth evolution over the last deglaciation at the coldest sites in East Antarctica (Vostok, Dome C), while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ15N evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in the coldest conditions. The inclusion of impurity effects improves the agreement between modelled and measured δ15N at cold East Antarctic sites during the last deglaciation, but deteriorates the agreement between modelled and measured δ15N evolution at Greenland and Antarctic sites with high accumulation unless threshold effects are taken into account. We thus do not provide a definite solution to the firnification at very cold Antarctic sites but propose potential pathways for future studies.

Densification Behaviors in the Early Stage of Spark Plasma Sintering of 3Y-TZP Nanoceramics

The early-stage sintering behaviours of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramics during spark plasma sintering (SPS) was investigated using different pressure and heating regimes.It was found that dependent neither on pressure value (20~100 MPa) nor heating rates higher than 50 °C/min, the maximum densification rate had always been observed at rather similar ~78% of theoretical density (TD), where the grain growth was rather moderate. A novel intensive-particle-rearrangement mechanism was proposed to dominate the rapid densification of early-stage SPS process, by which yielded the considerable faster densification rate than those achievable by diffusion-related processes.Present findings showed the possibility of particle rearrangement in high density compacts and the effects of classic particle rearrangement should be re-evaluated in nanoceramic sintering.