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277 results on '"Niu, Yanyan"'

4. Total squared mean curvature of immersed submanifolds in a negatively curved space

Author

Niu, Yanyan and Xu, Shicheng

Subjects
Mathematics - Differential Geometry, 53C21, 53C42
Abstract

Let $n\ge 2$ and $k\ge 1$ be two integers. Let $M$ be an isometrically immersed closed $n$-submanifold of co-dimension $k$ that is homotopic to a point in a complete manifold $N$, where the sectional curvature of $N$ is no more than $\delta<0$. We prove that the total squared mean curvature of $M$ in $N$ and the first non-zero eigenvalue $\lambda_1(M)$ of $M$ satisfies $$\lambda_1(M)\le n\left(\delta +\frac{1}{\operatorname{Vol} M}\int_M |H|^2 \operatorname{dvol}\right).$$ The equality implies that $M$ is minimally immersed in a metric sphere after lifted to the universal cover of $N$. This completely settles an open problem raised by E. Heintze in 1988., Comment: 13 pages

Published
2021

10. Gap theorem on K\'ahler manifold with nonnegative orthogonal bisectional curvature

Author

Ni, Lei and Niu, Yanyan

Subjects
Mathematics - Differential Geometry
Abstract

In this paper we prove a gap theorem for K\"ahler manifolds with nonnegative orthogonal bisectional curvature and nonnegative Ricci curvature, which generalizes an earlier result of the first author. We also prove a Liouville theorem for plurisubharmonic functions on such a manifolds, which generalizes a previous result of L.-F. Tam and the first author., Comment: 14 pages

Published
2017

18. Electrochemical Determination of Rutin on a Gold Microsphere—Taro Stalk Porous Carbon Modified Carbon Ionic Liquid Electrode (CILE).

Author

Chen, Yuxue, Weng, Wenju, Jiao, Guosong, Cheng, Hui, Niu, Yanyan, Li, Guangjiu, and Sun, Wei

Subjects
IONIC liquids, TARO, RUTIN, ELECTROCHEMICAL sensors, GOLD
Abstract

As an abundant, inexpensive, and renewable biomass raw material, taro [Colocasia esculenta (L.) Schott] stalks were employed as a simple biochar template due to their porous structure. A composite composed of gold microsphere and taro stalk derived porous carbon (Au-MS@TSPC) was used to construct an electrochemical sensor for the sensitive determination of rutin. Under the optimized conditions, the sensor exhibited a wide linear range from 0.12 to 10.0 μmol·L−1 with a detection limit of 0.0265 μmol·L−1. The sensor demonstrated good selectivity and was applied to the determination of rutin in human serum with recoveries from 94.0% to 105.8%. The fabrication of Au-MS@TSPC in this study provides a promising approach for the subsequent utilization of taro stalks. [ABSTRACT FROM AUTHOR]

Published
2024
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26. Sharp differential estimates of Li-Yau-Hamilton type for positive $(p,p)$-forms on K\'ahler manifolds

Author

Ni, Lei and Niu, Yanyan

Subjects
Mathematics - Differential Geometry
Abstract

In this paper we study the heat equation (of Hodge-Laplacian) deformation of $(p, p)$-forms on a K\"ahler manifold. After identifying the condition and establishing that the positivity of a $(p, p)$-form solution is preserved under such an invariant condition we prove the sharp differential Harnack (in the sense of Li-Yau-Hamilton) estimates for the positive solutions of the Hodge-Laplacian heat equation. We also prove a nonlinear version coupled with the K\"ahler-Ricci flow and some interpolating matrix differential Harnack type estimates for both the K\"ahler-Ricci flow and the Ricci flow.

Published
2010

32. Stability and Rheological Properties of the Hydroxypropyl Methyl Cellulose-Based Graft Copolymer/Halocynthia roretziDrasche-Based Cellulose Nanocrystal/Sodium Dodecyl Sulfate Dispersion for Enhanced Heavy Oil Recovery

Author

Niu, Yanyan, Fu, Xin, Zhu, Yifei, Meng, Fanjun, Ma, Qinglin, Song, Cui, Zhang, Qian, and Che, Yuju

Abstract

As a “green” displacing agent, nanocellulose is enriched, nontoxic, biodegradable, and environmentally friendly; therefore, the development and potential application of nanocellulose in oilfield chemistry have attracted widespread attention in recent years. In this study, a thermothickening copolymer synthesized in our laboratory called hydroxypropyl methyl cellulose-based graft (PHAD) copolymer was chosen to mix with Halocynthia roretziDrasche-based cellulose nanocrystals (TCNCs), and anionic surfactant sodium dodecyl sulfate (SDS) was added to improve the stability of the displacing agent. After the optimal SDS concentration was confirmed, PHAD/TCNCs/SDS dispersions containing 0.05–0.15 wt % TCNCs can be stable for a long time. Hence, the rheological performance of dispersions containing 0.05–0.15 wt % TCNCs was investigated systematically, and the results revealed that the PHAD/TCNCs/SDS dispersions had outstanding thermothickening ability, salt resistance, shear resistance, and viscoelastic property in a simulated oil reservoir circumstance, and the interaction mechanism among PHAD, TCNCs, and SDS was analyzed. Finally, a core flooding test was conducted, and the obtained data showed that the oil recovery of dispersion was 21.5%, which is higher than the control dispersion without TCNCs, confirming that the PHAD/TCNCs/SDS dispersions have significant practical application prospects.

Published
2024
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38. Inhibition and Removal of Mature Mixed-Bacteria Biofilms on Voice Prostheses by Sodium Selenite [Corrigendum]

Author

Zhang,Yongli, Niu,Yanyan, Huo,Hong, Wang,Jian, Jin,Xiaofeng, Yang,Hua, Zhang,Yongli, Niu,Yanyan, Huo,Hong, Wang,Jian, Jin,Xiaofeng, and Yang,Hua

Abstract

Zhang Y, Niu Y, Huo H, Wang J, Jin X, Yang H. Infect Drug Resist. 2022;15:7799–7810. The authors have advised that there was an error in the Funding section on page 7809. Line 2, the text “XDA1601040201” should read “XDA16040301”. The authors apologize for this error.

Published
2023

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