We present a StyleGAN2‐based deep learning approach for 3D shape generation, called SDF‐StyleGAN, with the aim of reducing visual and geometric dissimilarity between generated shapes and a shape ...collection. We extend StyleGAN2 to 3D generation and utilize the implicit signed distance function (SDF) as the 3D shape representation, and introduce two novel global and local shape discriminators that distinguish real and fake SDF values and gradients to significantly improve shape geometry and visual quality. We further complement the evaluation metrics of 3D generative models with the shading‐image‐based Fréchet inception distance (FID) scores to better assess visual quality and shape distribution of the generated shapes. Experiments on shape generation demonstrate the superior performance of SDF‐StyleGAN over the state‐of‐the‐art. We further demonstrate the efficacy of SDF‐StyleGAN in various tasks based on GAN inversion, including shape reconstruction, shape completion from partial point clouds, single‐view image‐based shape generation, and shape style editing. Extensive ablation studies justify the efficacy of our framework design. Our code and trained models are available at https://github.com/Zhengxinyang/SDF‐StyleGAN.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
The effects of microstructure on crack resistance and toughening mechanism of an ultra-low carbon steel were investigated. The microstructures were controlled via thermal-mechanical control ...processing (TMCP) and heat-treatments. Distribution of stress concentration, microcracks formation and propagation during Charpy impacting were investigated in detail. The results indicate that the lath martensitic structure provided a higher yield stress together with a better impact property, compared to the polygonal ferritic structure. The high strength can be attributed to the high density of dislocations in the lath martensitic structure introduced by quenching. The instrumented Charpy impact results indicated that the crack initiation energy in the lath martensitic structure was similar to that in the ferritic structure while the crack propagation energy was significantly greater than that in the ferritic structure, leading to the high toughness of the steel with the lath martensitic structure. Local stress concentration distributed uniformly in lath martensitic structure, leading to the homogeneous nucleation of microcrack. The high crack propagation energy in the lath martensitic structure can be attributed to the high fraction of high angle grain boundaries and fine effective grains, which deflected the cleavage crack propagation direction.
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•60 °C decrement in DBTT was obtained through controlling microstructure.•The lath martensite provides a good combination of strength and toughness.•The high crack propagation energy of lath martensite benefits to the good toughness.•HAGB and EGS deflect the cleavage crack propagation direction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Ensemble Kalman inversion (EKI) is an adaption of the ensemble Kalman filter (EnKF) for the numerical solution of inverse problems. Both EKI and EnKF suffer from the ‘subspace property’, ...i.e. the EKI and EnKF solutions are linear combinations of the initial ensembles. The subspace property implies that the ensemble size should be larger than the problem dimension to ensure EKI’s convergence to the correct solution. This scaling of ensemble size is impractical and prevents the use of EKI in high-dimensional problems. ‘Localization’ has been used for many years in EnKF to break the subspace property in a way that a localized EnKF can solve high-dimensional problems with a modest ensemble size, independently of the number of unknowns. Here, we study localization of the EKI and demonstrate how a localized EKI (LEKI) can solve high-dimensional inverse problems with a modest ensemble size. Our analysis is mathematically rigorous and applies to the continuous time limit of the EKI. Specifically, we can prove an intended ensemble collapse and convergence guarantees with an ensemble size that is
less
than the number of unknowns, which sets this work apart from the current state-of-the-art. We illustrate our theory with numerical experiments where some of our mathematical assumptions may only be approximately valid.
Solid oxide cells are electrochemical devices used for the conversion of chemical energy to electrical energy (Solid Oxide Fuel Cells-SOFC) and vice versa (Solid Oxide Electrolysis Cells-SOEC). ...However, long-term performance degradation impedes the widespread commercialization of the technology. To investigate the effects of operation mode on the degradation of Ni/yttria-stabilized zirconia (YSZ) electrodes, two cells from the same production batch are tested for 1000 h at 800 °C; one as SOFC and the other as SOEC. The cells are fed with the same gas composition at the fuel inlet side (p(H2O)/p(H2) = 0.5/0.5) while the direction of the current (±1 A cm−2) is reversed. It is found that Ni coarsening occurs to a similar extent in both operation modes while Ni depletion is only observed in SOEC mode, in the region close to the electrode/electrolyte interface. Here, the Ni/(Ni + Zr + Y) atomic ratio decreases from ~0.49 before operating the cell to ~ 0.28 and the SOEC shows a pronounced decrease in percolating triple phase boundaries (TPBs). The wettability of Ni on YSZ is studied and hypotheses are presented to correlate the phenomena of Ni coarsening and Ni depletion with the cell operation mode.
•The effect of the operation mode (SOEC, SOFC) on SOC degradation was investigated.•Ni coarsening occurs regardless of the SOC operation mode.•Ni depletion at the electrode/electrolyte interface is observed only in SOEC mode.•Ni depletion is a major cause of SOEC performance degradation.•A gradient in Ni/YSZ contact angle as the main driving force for Ni depletion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nanoscale precipitation and its influence on the strengthening mechanisms in low-carbon ultra-high-strength steel, hot-rolled at different temperatures and subjected to various isothermal aging ...conditions, are studied. The steel has a yield strength of ∼1730 MPa and elongation-to-failure of ∼13% under the peak aging condition, of which ∼740 MPa is contributed by precipitation strengthening. The precipitation strengthening mechanisms, including both the shearing mechanism and the Orowan mechanism, are quantitatively analyzed based on the mechanical properties and precipitate properties determined by small-angle neutron scattering, and atom probe tomography (APT). The APT results show that the average Guinier radius of the nanoscale precipitates under the peak aging condition is 1.4 nm at a number density of 6.19 × 1023m−3. These nanoscale precipitates consist of a Cu-enriched core, in which the depletion of Fe and enrichment of Cu change monotonically towards the center of the precipitates, whereas the concentrations of Ni, Al, and Mn exhibit diffused enrichment near the precipitate-matrix interfaces. Until the peak aging, precipitation strengthening mainly arises from shearing mechanism, among which the order and modulus strengthening mechanisms play the most significant role. Beyond peak aging, the shearing mechanism is not valid and the Orowan mechanism is the dominant contributor to the increase in yield strength due to the coarsening of the precipitates. The effect of the matrix microstructure on strength is also addressed and discussed.
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•740 MPa increment in yield strength is obtained through precipitation strengthening.•The precipitates consist of Cu-enriched core encased by Ni(Al,Mn) phase.•Precipitation strengthening is contributed by shear mechanism under and at the peak aging.•Orowan mechanism dominates the increase in yield strength beyond peak aging.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) are important factors of soil fertility. However, effects of the combined chemical fertilizer and ...organic manure or straw on these factors and their relationships are less addressed under long-term fertilizations. This study addressed changes in SOC, TN, MBC and MBN at 0–20cm soil depth under three 17years (September 1990–September 2007) long-term fertilization croplands along a heat and water gradient in China. Four soil physical fractions (coarse free and fine free particulate organic C, cfPOC and ffPOC; intra-microaggregate POC, iPOC; and mineral associated organic C, MOC) were examined under five fertilizations: unfertilized control, chemical nitrogen (N), phosphorus (P) and potassium (K) (NPK), NPK plus straw (NPKS, hereafter straw return), and NPK plus manure (NPKM and 1.5NPKM, hereafter manure). Compared with Control, manure significantly increased all tested parameters. SOC and TN in fractions distributed as MOC>iPOC>cfPOC>ffPOC with the highest increase in cfPOC (329.3%) and cfPTN (431.1%), and the lowest in MOC (40.8%) and MTN (45.4%) under manure. SOC significantly positively correlated with MBC, cfPOC, ffPOC, iPOC and MOC (R2=0.51–0.84, P<0.01), while TN with cfPTN, ffPTN, iPTN and MTN (R2=0.45–0.79, P<0.01), but not with MBN, respectively. Principal component analyses explained 86.9–91.2% variance of SOC, TN, MBC, MBN, SOC and TN in each fraction. Our results demonstrated that cfPOC was a sensitive SOC indicator and manure addition was the best fertilization for improving soil fertility while straw return should take into account climate factors in Chinese croplands.
•Assessed the effects of 17years fertilization on SOC, TN and its fractions.•Manure increased all indexes but straw return had no effects on all indexes at GZL.•Chemical fertilization had no effects on TN but decreased MBC in GZL and QY.•cfPOC was the most sensitive indicator and MOC, MTN was the main sequestrated form.•Straw return was site-dependent and manure was the best for improving soil quality.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We investigate how ideas from covariance localization in numerical weather prediction can be used in Markov chain Monte Carlo (MCMC) sampling of high-dimensional posterior distributions arising in ...Bayesian inverse problems. To localize an inverse problem is to enforce an anticipated “local” structure by (i) neglecting small off-diagonal elements of the prior precision and covariance matrices; and (ii) restricting the influence of observations to their neighborhood. For linear problems we can specify the conditions under which posterior moments of the localized problem are close to those of the original problem. We explain physical interpretations of our assumptions about local structure and discuss the notion of high dimensionality in local problems, which is different from the usual notion of high dimensionality in function space MCMC. The Gibbs sampler is a natural choice of MCMC algorithm for localized inverse problems and we demonstrate that its convergence rate is independent of dimension for localized linear problems. Nonlinear problems can also be tackled efficiently by localization and, as a simple illustration of these ideas, we present a localized Metropolis-within-Gibbs sampler. Several linear and nonlinear numerical examples illustrate localization in the context of MCMC samplers for inverse problems.
•We explain how to use localization for the numerical solution of Bayesian inverse problems by Markov chain Monte Carlo (MCMC).•We prove dimension independence of MCMC samplers under simplifying assumptions.•The notion of high-dimension we discuss is different from what is usually assumed in function space MCMC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Highlights • Treadmill exercise prevents impairment of spatial learning and memory in aged APP/PS1 mice. • Synaptic plasticity is involved in exercise-induced cognitive improvement in aged AD mice. • ...Alterations in soluble Aβ levels may contribute to the beneficial effects of treadmill exercise.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. The efficiency of thermoelectric materials depends directly on the ...average ZT (dimensionless figure of merit) over a certain temperature range, which historically has been challenging to increase. Here we report that 2.5% K-doped PbTe0.7S0.3 achieves a ZT of >2 for a very wide temperature range from 673 to 923 K and has a record high average ZT of 1.56 (corresponding to a theoretical energy conversion efficiency of ~20.7% at the temperature gradient from 300 to 900 K). The PbTe0.7S0.3 composition shows spinodal decomposition with large PbTe-rich and PbS-rich regions where each region exhibits dissimilar types of nanostructures. Such high average ZT is obtained by synergistically optimized electrical- and thermal-transport properties via carrier concentration tuning, band structure engineering and hierarchical architecturing, and highlights a realistic prospect of wide applications of thermoelectrics.
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