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Articles by J. Qin
Total Records ( 3 ) for J. Qin
  Z Hu , D. A Follmann and J. Qin

Model misspecification can be a concern for high-dimensional data. Nonparametric regression obviates model specification but is impeded by the curse of dimensionality. This paper focuses on the estimation of the marginal mean response when there is missingness in the response and multiple covariates are available. We propose estimating the mean response through nonparametric functional estimation, where the dimension is reduced by a parametric working index. The proposed semiparametric estimator is robust to model misspecification: it is consistent for any working index if the missing mechanism of the response is known or correctly specified up to unknown parameters; even with misspecification in the missing mechanism, it is consistent so long as the working index can recover E(Y | X), the conditional mean response given the covariates. In addition, when the missing mechanism is correctly specified, the semiparametric estimator attains the optimal efficiency if E(Y | X) is recoverable through the working index. Robustness and efficiency of the proposed estimator is further investigated by simulations. We apply the proposed method to a clinical trial for HIV.

  X.S. Wu , H. Wu , B.C. Li , G.Y. Zhou , S.Y. Sun , J. Qin , G.H. Chen and H.H. Musa
  To isolate, purify and culture spermotogonia from chicken testicular tissues, a procedure of enzymatic digestion and percoll density centrifugation was adopted for the single cell suspension to obtain purified spermatogonia. The results showed that, using the same purification method, the purity of spermatogonia gained from 6 days old chicken embryo was more than from 13, 15 and 19 days of age; adhesion purification step led to a harvest of 82% of total spermatogonia, which was 15.6% higher than that of direct isolation method; the adhesion time and survival time of spermotogonia before percoll density gradient centrifugation was earlier and longer than after precoll density gradient centrifugation.
  Y. Jiao , Z.-H. Peng , J.-Y. Zhang , J. Qin and C.-P. Zhong
  An in vivo method for islet visualization using magnetic resonance imaging (MRI), using superparamagnetic iron oxide (SPIO), has been described. Herein we have developed a protocol that uses cationic liposomes to increase the efficiency of islet cell labeling by SPIO in vitro. Fresh islet cells were incubated in RPMI-1640 medium, to which had been added a range of concentrations of ferucarbotran, a SPIO contrast agent. At each SPIO concentration, duplicate samples were incubated with versus without addition of cationic liposomes. We measured intracellular iron concentration, cell viability, and insulin-release function after labeling. We observed that the amount of iron bound to islet cells increased as the concentration of added SPIO increased. The presence of liposomes increased labeling efficiency at each SPIO concentration. In vitro MRI confirmed the effect of liposomes to improve labeling efficiency of islet cells by SPIO.
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