Generalized Linear Mixed Models with Gaussian Mixture Random Effects: Inference and Application.

We propose a new class of generalized linear mixed models with Gaussian mixture random effects for clustered data. To overcome the weak identifiability issues, we fit the model using a penalized Expectation Maximization (EM) algorithm, and develop sequential locally restricted likelihood ratio tests to determine the number of components in the Gaussian mixture. Our work is motivated by an application to nationwide kidney transplant center evaluation in the United States, where the patient-level post-surgery outcomes are repeated measures of the care quality of the transplant centers. By taking into account patient-level risk factors and modeling the center effects by a finite Gaussian mixture model, the proposed model provides a convenient framework to study the heterogeneity among the transplant centers and controls the false discovery rate when screening for transplant centers with non-standard performance.

A preliminary study on the rheological properties of human ejaculate and changes during liquefaction.

AIM: To study the changes in rheological properties, namely the parameters of the hysteresis loops and yield stress versus time for human semen after ejaculation. METHODS: Ejaculates were obtained from volunteers and immediately put into the test cup of a Brookfield Programmable DV-11 Rheometer, by which the hysteresis loops and yield stress were determined. RESULTS: (1) Yield stress values dropped down from more than 3000 mPa to 60 mPa in about 5 minutes after ejaculation; (2) The shape of the hysteresis loops of shear stress versus shear rate was changed from the counter-clockwise direction, that enclosed a large area, into the clockwise direction, that enclosed a very small area. CONCLUSION: Human ejaculate originally possesses semi-solid or visco-elastic body behavior and in 5 minutes after liquefaction, it becomes a thixotropic fluid or shearing thinning fluid with very low viscosity.