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6. Fragility crossover mediated by covalent-like electronic interactions in metallic liquids

Author

Hui-Ru Zhang, Liang Gao, Yu-Hao Ye, Jia-Xin Zhang, Tao Zhang, Qing-Zhou Bu, Qun Yang, Zeng-Wei Zhu, Shuai Wei, and Hai-Bin Yu

Subjects
metallic glass, fragility, fast scanning calorimetry, density functional theory, deep learning potential, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

Fragility is one of the central concepts in glass and liquid sciences, as it characterizes the extent of deviation of viscosity from Arrhenius behavior and is linked to a range of glass properties. However, the intervention of crystallization often prevents the assessment of fragility in poor glass-formers, such as supercooled metallic liquids. Hence experimental data on their compositional dependence are scarce, let alone fundamentally understood. In this work, we use fast scanning calorimetry to overcome this obstacle and systematically study the fragility in a ternary La–Ni–Al system, over previously inaccessible composition space. We observe fragility dropped in a small range with the Al alloying, indicating an alloying-induced fragility crossover. We use x-ray photoelectron spectroscopy, resistance measurements, electronic structure calculations, and DFT-based deep-learning atomic simulations to investigate the cause of this fragility drop. These results show that the fragility crossover can be fundamentally ascribed to the electronic covalency associated with the unique Al–Al interactions. Our findings provide insight into the origin of fragility in metallic liquids from an electronic structure perspective and pave a new way for the design of metallic glasses.

Published
2024
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9. A Supremum-Norm Based Test for the Equality of Several Covariance Functions

Author

Guo, Jia, Zhou, Bu, and Zhang, Jin-Ting

Subjects
Statistics - Methodology, Statistics - Applications, Statistics - Computation
Abstract

In this paper, we propose a new test for the equality of several covariance functions for functional data. Its test statistic is taken as the supremum value of the sum of the squared differences between the estimated individual covariance functions and the pooled sample covariance function, hoping to obtain a more powerful test than some existing tests for the same testing problem. The asymptotic random expression of this test statistic under the null hypothesis is obtained. To approximate the null distribution of the proposed test statistic, we describe a parametric bootstrap method and a non-parametric bootstrap method. The asymptotic random expression of the proposed test is also studied under a local alternative and it is shown that the proposed test is root-$n$ consistent. Intensive simulation studies are conducted to demonstrate the finite sample performance of the proposed test and it turns out that the proposed test is indeed more powerful than some existing tests when functional data are highly correlated. The proposed test is illustrated with three real data examples., Comment: arXiv admin note: text overlap with arXiv:1609.04231

Published
2016

11. Influence of Hydrodynamics on the Composition and Reactivity of Particulate Organic Matter in a Large River Influenced Ocean Margin

Author

Guo, Jinqiang, Zhou, Bu, Achterberg, Eric P., Song, Jinming, Duan, Liqin, Li, Xuegang, Yuan, Huamao, Guo, Jinqiang, Zhou, Bu, Achterberg, Eric P., Song, Jinming, Duan, Liqin, Li, Xuegang, and Yuan, Huamao

Abstract

Marginal seas influenced by large rivers are characterized by complex hydrodynamic and organic matter cycling processes. However, the impacts of hydrodynamics on the composition and reactivity of particulate organic matter (POM) remain unclear. Here we conducted a comprehensive study on the bulk, molecular and biological properties of suspended POM in the Changjiang Estuary and adjacent area subjected to strong currents, eddies as well as typhoons during spring and autumn. D/L‐enantiomers of particulate amino acids (PAA) were analyzed to evaluate the bioreactivity of POM and quantify bacterial‐derived organic carbon. We found that POM bioavailability as indicated by carbon‐normalized yields of PAA (PAA‐C%) reflected the ecosystem productivity. Relatively high PAA‐C% values (20−35%) were observed in productive areas influenced by Changjiang River plume, cyclonic eddies and typhoons, likely related to the enhanced nutrient availability arising from hydrodynamic processes. In contrast, the oligotrophic Taiwan Warm Current‐influenced regions featured relatively low POM bioavailability (PAA‐C% < 10%) despite typhoons facilitating water mixing. The PAA‐C% values showed a significant positive correlation with extracellular enzyme activity, indicating that bioavailable POM can rapidly stimulate heterotrophic transformation. Hot spots of elevated bioavailable POM showed high contributions of bacterial organic carbon. A large portion (∼2/3) of bacterial organic carbon was present in the form of bacterial detritus, suggesting that patches of these biological hot spots represent important sites of carbon sequestration. Together, our findings indicate that fresh POM production is largely controlled by nutrient supply driven by hydrodynamic processes, with important implications for carbon sequestration in the dynamic ocean margins. Plain Language Summary Marginal seas are subject to complex hydrodynamic processes and play an important role in carbon sequestration. Disentangling

Published
2024
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19. Surface Coating Modification of Lithium-Rich Manganese-Based Oxide as Cathode Material for Lithium-Ion Batteries

Author

Sheng Zhou Bu, Yu Xing Long, Liang Bin Zhang, Mei Yan Lu, Yue Mei Li, Dan Wei, Yong Peng Xia, Yu Mei Luo, Shu Jun Qiu, Fen Xu, Li Xian Sun, and Hai Liang Chu

Subjects
Mechanics of Materials, Mechanical Engineering, General Materials Science
Abstract

Lithium-rich manganese-based oxides (Li1.2Mn0.54Ni0.13Co0.13O2, LMNCO) as cathode materials were prepared by the sol-gel method. Then, LMNCO was coated with γ-basic manganese oxide (γ-MnOOH) to form the composite cathodes. Through the structural characterization and performance test, it is found that the composite cathode with 10% γ-MnOOH coating exhibits the best electrochemical performance. After 50 cycles at 0.1 C (1 C = 200 mA g-1), the specific discharge capacity is 264.4 mAh g-1 with capacity retention of 96.1%. Even at a high current density of 1C, its discharge capacity reaches up to 200.5 mAh g-1 after 30 cycles, which suggests that surface coating of γ-MnOOH is an effective strategy for further enhancing the electrochemical performance of LMNCO.

Published
2023
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24. Rapid Cycling of Bacterial Particulate Organic Matter in the Upper Layer of the Western Pacific Warm Pool

Author

Guo, Jinqiang, Zhou, Bu, Achterberg, Eric Pieter, Yuan, Huamao, Song, Jinming, Duan, Liqin, Li, Xuegang, Guo, Jinqiang, Zhou, Bu, Achterberg, Eric Pieter, Yuan, Huamao, Song, Jinming, Duan, Liqin, and Li, Xuegang

Abstract

Bacterial metabolism largely drives the sequestration of refractory organic matter in the ocean. However, a lack of understanding exists regarding the abundance and reactivity of bacterial particulate organic matter (POM). Here we report the bacterial contributions to suspended POM collected in the oligotrophic Western Pacific Warm Pool (WPWP). Around 27% of particulate organic carbon (POC) and ∼39% of particulate nitrogen (PN) in the surface ocean were derived from bacteria. Most of the bacterial POM (∼87%) was labile or semi-labile, and ∼85% of bacterial POM was removed between depths of ∼100–300 m. Bacterial POM constituted only ∼8% and ∼13% of refractory POC and PN, respectively. The rapid cycling of bacterial POM in upper waters was likely related to oligotrophic conditions and facilitated by higher temperatures in the WPWP. Taken together, these observations indicate that bacterial POM plays a crucial role in supplying energy for bacterial respiration. Key Points We assess bacterial contributions to suspended particulate organic matter (POM) in the Western Pacific Warm Pool on the basis of D-amino acid biomarkers Bacterial organics constitute 27% of surface ocean particulate organic carbon (POC) and 39% of particulate nitrogen (PN), but majority (∼87%) is labile or semi-labile Rapid cycling of bacterial POM in the upper ocean results in a contribution of only ∼8% to refractory POC and ∼13% to PN

Published
2023
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28. Sishen Pill Ameliorates Dextran Sulfate Sodium (DSS)-Induced Colitis with Spleen-Kidney Yang Deficiency Syndromes: Role of Gut Microbiota, Fecal Metabolites, Inflammatory Dendritic Cells, and TLR4/NF-κB Pathway

Author

Ge, Wei, primary, Zhou, Bu-Gao, additional, Zhong, You-Bao, additional, Liu, Su-Qing, additional, Huang, Jia-Qi, additional, Yuan, Wang-Yuan, additional, Xie, Chang-Ying, additional, Liu, Duan-Yong, additional, Wang, Hai-Yan, additional, and Zuo, Zheng-Yun, additional

Published
2022
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32. Structural length-scale of β relaxation in metallic glass

Author

Qun Yang, Shuai Wei, Yang Yu, Hui-Ru Zhang, Liang Gao, Qing-Zhou Bu, Narges Amini, Yu-Dong Cheng, Fan Yang, Alexander Schoekel, and Hai-Bin Yu

Subjects
General Physics and Astronomy, metallic glasses, ddc:530, polyamorphous transition, Physical and Theoretical Chemistry, structure–property relationship, secondary (β) relaxation
Abstract

The journal of chemical physics 157(18), 184504 (2022). doi:10.1063/5.0123202, Establishing the structure–property relationship is an important goal of glassy materials, but it is usually impeded by their disordered structure and non-equilibrium nature. Recent studies have illustrated that secondary (β) relaxation is closely correlated with several properties in a range of glassy materials. However, it has been challenging to identify the pertinent structural features that govern it. In this work, we show that the so-called polyamorphous transition in metallic glasses offers an opportunity to distinguish the structural length scale of β relaxation. We find that, while the glass transition temperature and medium-range orders (MROs) change rapidly across the polyamorphous transition, the intensity of β relaxation and the short-range orders (SROs) evolve in a way similar to those in an ordinary reference glass without polyamorphous transition. Our findings suggest that the MRO accounts mainly for the global stiffening of the materials and the glass transition, while the SRO contributes more to β relaxation per se., Published by American Institute of Physics, Melville, NY

Published
2022
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42. An $\boldsymbol{L^{2}}$-norm based test for high-dimensional two-way MANOVA

Author

Zhang Jin-Ting, Guo Jia, and Zhou Bu

Subjects
Clustering high-dimensional data, Dimension (vector space), General Mathematics, Null distribution, Test statistic, Applied mathematics, Inverse, Invariant (mathematics), Statistic, Mathematics, Test (assessment)
Abstract

In this paper, we propose and study an $L^{2}$-norm based test for high-dimensional two-way MANOVA where there are fewer observations than the dimension. The test statistic is constructed by removing the inverse sample covariance matrix in the Wald-type statistic for the general linear hypothesis.We propose to approximate the null distribution of our test statistic by using the well-known Welch-Satterthwaite chi-squared approximation and discuss the relationship between chi-squared approximation and the commonly-used normal approximation. The $L^{2}$-norm based test is also shown to admit several invariant properties under certain transformations. The asymptotic and approximate powers of the proposed test are investigated. Simulation studies and real data applications show that the proposed test performs well for high-dimensional data.

Published
2020
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48. A Simple Two-Sample Test in High Dimensions Based on L2-Norm.

Author

Zhang, Jin-Ting, Guo, Jia, Zhou, Bu, and Cheng, Ming-Yen

Subjects
ASYMPTOTIC normality, APPROXIMATION error
Abstract

Testing the equality of two means is a fundamental inference problem. For high-dimensional data, the Hotelling's T2-test either performs poorly or becomes inapplicable. Several modifications have been proposed to address this issue. However, most of them are based on asymptotic normality of the null distributions of their test statistics which inevitably requires strong assumptions on the covariance. We study this problem thoroughly and propose an L2-norm based test that works under mild conditions and even when there are fewer observations than the dimension. Specially, to cope with general nonnormality of the null distribution we employ the Welch–Satterthwaite χ2-approximation. We derive a sharp upper bound on the approximation error and use it to justify that χ2-approximation is preferred to normal approximation. Simple ratio-consistent estimators for the parameters in the χ2-approximation are given. Importantly, our test can cope with singularity or near singularity of the covariance which is commonly seen in high dimensions and is the main cause of nonnormality. The power of the proposed test is also investigated. Extensive simulation studies and an application show that our test is at least comparable to and often outperforms several competitors in terms of size control, and the powers are comparable when their sizes are. for this article are available online. [ABSTRACT FROM AUTHOR]

Published
2020
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