Engineering topics
Li, Qing
Publications and source records attributed to Li, Qing.
Correlation approach for quality assurance of additive manufactured parts based on optical metrology
Surface topography and surface finish are two significant factors for evaluating the quality of products in additive manufacturing (AM). AM parts are fabricated layer by layer, which is quite different from traditional formative or subtractive methods. Despite rapid progress in additive manufacturing and associated optical metrology for quality control and in-situ monitoring, limited research has been conducted to investigate the reliability of 3D surface measurement data. The surface topologies scanned by multiple optical systems demonstrated significant differences due to varying sampling mechanisms, resolutions, system noises, etc. The 3D datasets should be trustworthy in order to extract parameters for quality assurance or feedback control from 3D surface measurements. In this paper, we set up new standards to evaluate the reliability of 3D surface measurement data and analyze the variation in the topographical profile. In this study, two non-contact optical methods based on Focus Variation Microscopy (FVM) and Structured Light System (SLS) were adopted to measure the surface topography of the target components. The two optical metrology systems generated two entirely different point cloud datasets. Statistical methods were applied to test the difference between the data obtained from the two systems. By using a data analytics approach for comparison, it was found that the surface roughness estimated from the point cloud data sets of FVM and SLS has no significant difference, though the point cloud data sets were completely different. This paper provides standard validation approach to evaluate the plausibility of metrology data from in-situ real-time surface analysis for process planning of AM.
The DOE E3SM Coupled Model Version 1: Description and Results at High Resolution
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Comparing Ocean Surface Boundary Vertical Mixing Schemes Including Langmuir Turbulence
Six recent Langmuir turbulence parameterization schemes and five traditional schemes are implemented in a common single-column modeling framework and consistently compared. These schemes are tested in scenarios versus matched large eddy simulations, across the globe with realistic forcing (JRA55-do,WAVEWATCH-III simulated waves) and initial conditions (Argo), and under realistic conditions as observed at ocean moorings. Traditional non-Langmuir schemes systematically underpredict large eddy simulation vertical mixing under weak convective forcing, while Langmuir schemes vary in accuracy. Under global, realistic forcing Langmuir schemes produce 6% (–1% to 14% for 90% confidence) or 5.2 m (–0.2 m to 17.4 m for 90% confidence) deeper monthly mean mixed layer depths than their non-Langmuir counterparts, with the greatest differences in extratropical regions, especially the Southern Ocean in austral summer. Discrepancies among Langmuir schemes are large (15% in mixed layer depth standard deviation over the mean): largest under wave-driven turbulence with stabilizing buoyancy forcing, next largest under strongly wave-driven conditions with weak buoyancy forcing, and agreeing during strong convective forcing. Non-Langmuir schemes disagree with each other to a lesser extent, with a similar ordering. Langmuir discrepancies obscure a cross-scheme estimate of the Langmuir effect magnitude under realistic forcing, highlighting limited understanding and numerical deficiencies. Maps of the regions and seasons where the greatest discrepancies occur are provided to guide further studies and observations.
The DOE E3SM Coupled Model Version 1: Description and Results at High Resolution
This study provides an overview of the coupled high-resolution Version 1 of the Energy Exascale Earth System Model (E3SMv1) and documents the characteristics of a 50-year-long high-resolution control simulation with time-invariant 1950 forcings following the HighResMIP protocol. In terms of global root-mean-squared error metrics, this high-resolution simulation is generally superior to results from the low-resolution configuration of E3SMv1 (due to resolution, tuning changes, and possibly initialization procedure) and compares favorably to models in the CMIP5 ensemble. Ocean and sea ice simulation is particularly improved, due to better resolution of bathymetry, the ability to capture more variability and extremes in winds and currents, and the ability to resolve mesoscale ocean eddies. The largest improvement in this regard is an ice-free Labrador Sea, which is a major problem at low resolution. Interestingly, several features found to improve with resolution in previous studies are insensitive to resolution or even degrade in E3SMv1. Most notable in this regard are warm bias and associated stratocumulus deficiency in eastern subtropical oceans and lack of improvement in El Niño. Another major finding of this study is that resolution increase had negligible impact on climate sensitivity (measured by net feedback determined through uniform +4K prescribed sea surface temperature increase) and aerosol sensitivity. Cloud response to resolution increase consisted of very minor decrease at all levels. Large-scale patterns of precipitation bias were also relatively unaffected by grid spacing.
Tungsten‐Doped L1 0 ‐PtCo Ultrasmall Nanoparticles as a High‐Performance Fuel Cell Cathode
Abstract The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt‐alloy with a Pt‐skin. The synthesis of ultrasmall and ordered L1 0 ‐PtCo nanoparticle ORR catalysts further doped with a few percent of metals (W, Ga, Zn) is reported. Compared to commercial Pt/C catalyst, the L1 0 ‐W‐PtCo/C catalyst shows significant improvement in both initial activity and high‐temperature stability. The L1 0 ‐W‐PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 °C, which is superior to the DOE 2020 targets. EXAFS analysis and density functional theory calculations reveal that W doping not only stabilizes the ordered intermetallic structure, but also tunes the Pt‐Pt distances in such a way to optimize the binding energy between Pt and O intermediates on the surface.
Tungsten‐Doped L1 0 ‐PtCo Ultrasmall Nanoparticles as a High‐Performance Fuel Cell Cathode
Abstract The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt‐alloy with a Pt‐skin. The synthesis of ultrasmall and ordered L1 0 ‐PtCo nanoparticle ORR catalysts further doped with a few percent of metals (W, Ga, Zn) is reported. Compared to commercial Pt/C catalyst, the L1 0 ‐W‐PtCo/C catalyst shows significant improvement in both initial activity and high‐temperature stability. The L1 0 ‐W‐PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 °C, which is superior to the DOE 2020 targets. EXAFS analysis and density functional theory calculations reveal that W doping not only stabilizes the ordered intermetallic structure, but also tunes the Pt‐Pt distances in such a way to optimize the binding energy between Pt and O intermediates on the surface.
Taming the stability of Pd active phases through a compartmentalizing strategy toward nanostructured catalyst supports
The design and synthesis of robust sintering-resistant nanocatalysts for high-temperature oxidation reactions is ubiquitous in many industrial catalytic processes and still a big challenge in implementing nanostructured metal catalyst systems. Herein, we demonstrate a strategy for designing robust nanocatalysts through a sintering-resistant support via compartmentalization. Ultrafine palladium active phases can be highly dispersed and thermally stabilized by nanosheet-assembled γ-Al2O3 (NA-Al2O3) architectures. The NA-Al2O3 architectures with unique flowerlike morphologies not only efficiently suppress the lamellar aggregation and irreversible phase transformation of γ-Al2O3 nanosheets at elevated temperatures to avoid the sintering and encapsulation of metal phases, but also exhibit significant structural advantages for heterogeneous reactions, such as fast mass transport and easy access to active sites. This is a facile stabilization strategy that can be further extended to improve the thermal stability of other Al2O3-supported nanocatalysts for industrial catalytic applications, in particular for those involving high-temperature reactions.
Atomic Arrangement Engineering of Metallic Nanocrystals for Energy-Conversion Electrocatalysis
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An investigation of the reduction of TiO 2 by Mg in H 2 atmosphere
Hydrogen assisted magnesiothermic reduction (HAMR) of TiO 2 is a promising new process developed recently to produce Ti metal with low cost and less energy consumption. Here this work focuses on the understanding and optimization of the reduction process to control the quality of the reduced product. TiO 2 precursor particles with different relative densities were prepared, and the effects of the relative densities on reduction by Mg in H 2 were studied. The changes of oxygen contents vs. reduction time at various temperatures were investigated. The phase transformations during the reduction were analyzed both theoretically and experimentally. The relationship between the morphology of the reduced products and the relative densities of the TiO 2 precursors was analyzed by SEM characterization and the likely reason for the morphology evolution was discussed.
The Influence of Fabrication Methods on Structure and Microwave Absorption Property of Fe{sub 3}O{sub 4}/rGO Composites
In this study, flake graphite is used as raw material and oxidized to produce graphene oxide (GO), and then two kinds of ferroferric oxide/reduced graphene oxide (Fe{sub 3}O{sub 4}/rGO) composites are fabricated with one-step and two-step methods, respectively. The influence of composite methods on structure and performance is investigated by FT-IR, XRD, SEM, TEM, and testing of electromagnetic parameters. The results show that there are many advantages in the one-step method for fabrication of Fe{sub 3}O{sub 4}/rGO composite, such as the composite process is simplified, the time is shortened, and the Fe{sub 3}O{sub 4}/rGO composite fabricated with the one-step method has the best microwave impedance matching property in the frequency range of 2.5–6 GHz. At the same time, it can be found that there is the Fe–O–C bond in Fe{sub 3}O{sub 4}/rGO composites fabricated with the one-step method, which results in two ways of physical recombination and chemical bonding between Fe{sub 3}O{sub 4} and rGO sheet particulates. In addition, when the mass ratio of GO and FeCl{sub 3} is 1:10, the R{sub L} value of the Fe{sub 3}O{sub 4}/rGO composite fabricated with the one-step method is minimum, and the increase of sample thickness is beneficial to improve the impedance matching property of Fe{sub 3}O{sub 4}/rGO composite in the frequency range of 2.5–6 GHz.
p21-activated kinase 4 as a switch between caspase-8 apoptosis and NF-κB survival signals in response to TNF-α in hepatocarcinoma cells
PAK4 is overexpressed in a variety of human cancers and considered a promising candidate for therapeutic target. However, its functions remain poorly understood, especially in liver carcinogenesis which could be triggered by inflammation. In the present study, endogenous PAK4 was knockdown using siRNA in HepG2 and SK-Hep1 cells. The two cell lines performed reduced cell viability, altered cell cycle composed of decreased S and arrest in G2, and apoptosis. Meanwhile, expression of NF-κB p65 in the nuclei and caspase-8 activity did not show significant differences from control. However, after treating cells with TNF-α, an inflammatory cytokine, we investigated repressed nuclear expression and localization of NF-κB p65, and induced apoptosis with increased caspase-8 activity in PAK4-knockdown cells. The findings revealed that ablation of PAK4 inhibited cell viability via blocking cell cycle and progressing apoptosis. The apoptosis was partially dependent upon caspase-8 concomitant with attenuated NF-κB survival signal due to stimulus of TNF-α. It suggests that PAK4 as target is a switch between caspase-8 apoptosis and NF-κB survival signals induced by TNF-α in hepatocarcinoma cells.
Self-assembly directed one-step synthesis of [4]radialene on Cu(100) surfaces
The synthetic challenges of radialenes have precluded their practical applications. Here, we report a one-step synthetic protocol of [4]radialene on a copper surface. High-resolution scanning tunneling microscopy measurements reveal that such catalytic reaction proceeds readily with high selectivity at the temperature below 120 K. First-principles calculations show that the reaction pathway is characterized by firstly the cooperative inter-molecular hydrogen tautomerization and then the C–C bond formation. The feasibility of such cyclotetramerization reaction can be interpreted by the surface effect of Cu(100), which firstly plays an important role in directing the molecular assembly and then serves as an active catalyst in the hydrogen tautomerization and C–C coupling processes. This work presents not only a novel strategy to the scant number of synthetic methods to produce [4]radialenes via a novel [1 + 1 + 1 + 1] reaction pathway, but also a successful example of C–C bond coupling reactions guided by the surface-induced C–H/π assembly.
On the temperature equation in a phase change pseudopotential lattice Boltzmann model
We report that in a recent paper by Gong et al. [19], the researchers claimed that in the previous models the derivation of the target temperature equation for liquid–vapor phase change is paradoxical because the equations of state for ideal gases and non-ideal gases are applied simultaneously, and therefore they proposed a modified pseudopotential lattice Boltzmann (LB) model for liquid–vapor phase change. Here, in this technical note we clarify that the modified phase change pseudopotential LB model proposed by Gong et al. was based on a misunderstanding of the derivations in the previous studies as well as a mistake that they employed e=c v T, where e is the internal energy, to the derive the temperature equation for non-ideal gases.
Geometries, stabilities and electronic properties of photo sensitized (CdS) 2n (n=5–27) nanoclusters
As advanced materials for energy storage or conversion applications, metal sulfides with hollow structures are as widely used as supercapacitors and sensors. The geometries and electronic properties of (CdS) 2n (n = 5–27) nanocages are calculated here by density functional theory with the gradient corrected Perdew-Burke-Ernzerh of exchange-correlation functional and including the relativistic effect. The obtained results showed that the inner radius and charge-transfers, surface stabilities along with ionic semiconductor and metallic properties of the hollowed (CdS) 2n are increased as cage size being increased. The distinct metallic features in large-size (CdS) 2n are revealed. Particularly, the calculated energy gaps for (CdS) 2n are generally decreased as the size of (CdS) 2n being increased, together with absorption spectra moving from short to long wavelength. The photon to current conversion efficiency related energy conversion is discussed. Interestingly, the encapsulated double-layer CdS nanocages have bigger capacity for energy conversion than the monolayer nanocages.