The effect of cryogenic and heating treatment on the solution properties of rigid polymer nitrocellulose(NC)indilute tetrahydrofuran solution were studied with a sealed viscometer and a size exclusion chromatograph(SE...The effect of cryogenic and heating treatment on the solution properties of rigid polymer nitrocellulose(NC)indilute tetrahydrofuran solution were studied with a sealed viscometer and a size exclusion chromatograph(SEC),respectively.The experimental results show that the relative viscosity of NC solution decreases after repeated freezing-thawing treatment.The decreased viscosity value of NC could not be restored but decreased further after the solution beingre-heated.The experimental results of SEC are fully consistent with that of viscosity measurements.It is believed that theeffect of two treatments on NC solution both causes the apparent hydrodynamic volume to decrease.But they are assumed tobe ascribed to different mechanisms.展开更多
To tackle multi collinearity or ill-conditioned design matrices in linear models, adaptive biased estimators such as the time-honored Stein estimator, the ridge and the principal component estimators have been studied...To tackle multi collinearity or ill-conditioned design matrices in linear models, adaptive biased estimators such as the time-honored Stein estimator, the ridge and the principal component estimators have been studied intensively. To study when a biased estimator uniformly outperforms the least squares estimator, some sufficient conditions are proposed in the literature. In this paper, we propose a unified framework to formulate a class of adaptive biased estimators. This class includes all existing biased estimators and some new ones. A sufficient condition for outperforming the least squares estimator is proposed. In terms of selecting parameters in the condition, we can obtain all double-type conditions in the literature.展开更多
基金This work was financially supported by the funds of Jiangsu ScienceTechnology Department(JH03-013,JHjd03-008).
文摘The effect of cryogenic and heating treatment on the solution properties of rigid polymer nitrocellulose(NC)indilute tetrahydrofuran solution were studied with a sealed viscometer and a size exclusion chromatograph(SEC),respectively.The experimental results show that the relative viscosity of NC solution decreases after repeated freezing-thawing treatment.The decreased viscosity value of NC could not be restored but decreased further after the solution beingre-heated.The experimental results of SEC are fully consistent with that of viscosity measurements.It is believed that theeffect of two treatments on NC solution both causes the apparent hydrodynamic volume to decrease.But they are assumed tobe ascribed to different mechanisms.
基金Supported by a grant from The Research Grants Council of Hong Kong HKU7181/02H.The authors wishes to thank the referees for the constructive comments
文摘To tackle multi collinearity or ill-conditioned design matrices in linear models, adaptive biased estimators such as the time-honored Stein estimator, the ridge and the principal component estimators have been studied intensively. To study when a biased estimator uniformly outperforms the least squares estimator, some sufficient conditions are proposed in the literature. In this paper, we propose a unified framework to formulate a class of adaptive biased estimators. This class includes all existing biased estimators and some new ones. A sufficient condition for outperforming the least squares estimator is proposed. In terms of selecting parameters in the condition, we can obtain all double-type conditions in the literature.
