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- 저자 : Liu Tianqing (검색결과 6 건)
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Weighted rank estimation for nonparametric transformation models with doubly truncated data
Liu Tianqing,원소휘,Sun Jianguo 한국통계학회 2021 Journal of the Korean Statistical Society Vol.50 No.1
Doubly truncated data often arise when event times are observed only if they fall within subject-specifc intervals. We analyze doubly truncated data using nonparametric transformation models, where an unknown monotonically increasing transformation of the response variable is equal to an unknown monotonically increasing function of a linear combination of the covariates plus a random error with an unspecifed log-concave probability density function. Furthermore, we assume that the truncation variables are conditionally independent of the response variable given the covariates and leave the conditional distributions of truncation variables given the covariates unspecifed. For estimation of regression parameters, we propose a weighted rank (WR) estimation procedure and establish the consistency and asymptotic normality of the resulting estimator. The limiting covariance matrix of the WR estimator can be estimated by a resampling technique, which does not involve nonparametric density estimation or numerical derivatives. A numerical study is conducted and suggests that the proposed methodology works well in practice, and an illustration based on real data is provided.
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Variable selection for semiparametric accelerated failure time models with nonignorable missing data
Liu Tianqing,Yuan Xiaohui,Sun Liuquan 한국통계학회 2024 Journal of the Korean Statistical Society Vol.53 No.1
The regularization approach for variable selection was well developed for semipara- metric accelerated failure time (AFT) models, where the response variable is right censored. In the presence of missing data, this approach needs to be tailored to dif- ferent missing data mechanisms. In this paper, we propose a flexible and generally applicable missing data mechanism for AFT models, which contains both ignorable and nonignorable missing data mechanism assumptions. We propose weighted rank (WR) estimators and corresponding penalized estimators of regression parameters under this missing data mechanism. An advantage of the WR estimators and cor- responding penalized estimators is that they do not require specifying a missing data model for the proposed missing data mechanism. The theoretical properties of the WR and corresponding penalized estimators are established. Comprehensive simulation studies and a real data application further demonstrate the merits of our approach.
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Zhifeng Liu,Jingjing Ji,Dong Zheng,Lei Su,Tianqing Peng,Jing Tang 생화학분자생물학회 2020 Experimental and molecular medicine Vol.52 No.-
To explore the role of calpain and its signaling pathway in lipopolysaccharide (LPS)-induced acute kidney injury (AKI), animal models of endotoxemia were established by administration of LPS to mice with endothelial-specific Capn4 knockout (TEK/Capn4−/−), mice with calpastatin (an endogenous calpain inhibitor) overexpression (TgCAST) and mice with myeloid-specific Capn4 knockout (LYZ/Capn4−/−). Mouse pulmonary microvascular endothelial cells (PMECs) were used as a model of the microvascular endothelium and were stimulated with LPS. Renal function, renal inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) expression, cellular apoptosis, plasma and renal levels of NO and reactive oxygen species (ROS), and phosphorylation of mitogenactivated protein kinase (MAPK) family members (p38, ERK1/2, and JNK1/2) were examined. Moreover, a calpain inhibitor, calpastatin overexpression adenoviruses and MAPK inhibitors were used. Significant renal dysfunction was induced by LPS stimulation, and recovery was observed in TEK/Capn4−/− and Tg-CAST mice but not in LYZ/ Capn4−/− mice. Endothelial Capn4 knockout also abrogated the LPS-induced increases in renal iNOS expression, caspase-3 activity and apoptosis and plasma and renal NO and ROS levels but did not obviously affect renal eNOS expression. Moreover, LPS increased both calpain and caspase-3 activity, and only the expression of iNOS in PMECs was accompanied by increased phosphorylation of p38 and JNK. Inhibiting calpain activity or p38 phosphorylation alleviated the increased iNOS expression, NO/ROS production, and cellular apoptosis induced by LPS. These results suggest that endothelial calpain plays a protective role in LPS-induced AKI by inhibiting p38 phosphorylation, thus attenuating iNOS expression and further decreasing NO and ROS overproduction-induced endothelial apoptosis.
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Variable selection for single-index models based on martingale difference divergence
Yuan Xiaohui,Wang Yue,Wang Yiming,Liu Tianqing 한국통계학회 2024 Journal of the Korean Statistical Society Vol.53 No.1
In this paper, we consider variable selection for single-index models via martin- gale difference divergence. The important covariates are selected by maximizing penalized martingale difference divergence objective functions with fixed tuning parameters. To choose tuning parameters, we propose to use a BIC criterion. The consistency of the variable selection procedure with LASSO, SCAD and ALASSO penalties and asymptotic properties of the resulting estimators are established. The performance of the proposed procedure is assessed through extensive simulation studies. Finally, we apply the proposed method to real data sets.
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Kedong Song,Liying Li,Lili Ji,Siyuan Li,Chunfeng Mu,Yiwei Wang,Tianqing Liu 한국통합생물학회 2016 Animal cells and systems Vol.20 No.5
Fabrication and transplantation of tissue-engineered bones in a rotating wall vessel bioreactor (RWVB) was studied in the present study aiming to repair segmental bone defects. Osteoblasts were transfected with green fluorescent protein prior to seeding on bio-derived porous bone scaffolds at a density of 1 × 106 cells/mL and cultured in an RWVB for one week. For comparison, constructs were also cultured in a static condition. Morphology and structure of fabricated bones were examined using an inverted microscope, scanning electron microscope and histology analysis via hematoxylin–eosin and toluidine blue staining. Moreover, an animal model for repairing segmental bone defects of a Zelanian rabbit was used to assess the efficacy and biosafety of fabricated bones. In conclusion, tissue-engineered bones grew favorably in RWVB. In animal study, a preliminary repair of bone defects was noticed only in the experimental group after 4 weeks of implantation. Using RWVB, the fabricated tissue-engineered bone constructs were approved with better bio-capability in repairing the segmental bone defect.
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