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Articles by R. Yu
Total Records ( 2 ) for R. Yu
  V Chesnokova , C Wong , S Zonis , A Gruszka , K Wawrowsky , S. G Ren , A BenShlomo and R. Yu

Pituitary tumor transforming gene (PTTG) encodes a securin protein critical in regulating chromosome separation. PTTG-null (PTTG–/–) mice exhibit pancreatic β-cell hypoplasia and insulinopenic diabetes. We tested whether PTTG deletion causes β-cell senescence, resulting in diminished β-cell mass. We examined β-cell mass, proliferation, apoptosis, neogenesis, cell size, and senescence in PTTG–/– and WT mice from embryo to young adulthood before diabetes is evident. The roles of cyclin-dependent kinase inhibitors and DNA damage in the pathogenesis of diabetes in PTTG–/– mice were also addressed. Relative β-cell mass in PTTG–/– mice began to decrease at 2–3 wk, whereas β-cell proliferation rate was initially normal but decreased in PTTG–/– mice beginning at 2 months. Apoptosis was also much more evident in PTTG–/– mice. At 1 month, β-cell neogenesis was robust in wild-type mice but was absent in PTTG–/– mice. In addition, the size of β-cells became larger and macronuclei were prominent in PTTG–/– animals. Senescence-associated β-galactosidase was also active in PTTG–/– β-cells at 1 month. Cyclin-dependent kinase inhibitor p21 was progressively up-regulated in PTTG–/– islets, and p21 deletion partially rescued PTTG–/– mice from development of diabetes. mRNA array showed that DNA damage-associated genes were activated in PTTG–/– islets. We conclude that β-cell apoptosis and senescence contribute to the diminished β-cell mass in PTTG–/– mice, likely secondary to DNA damage. Our results also suggest that ductal progenitor β-cells are exhausted by excessive neogenesis induced by apoptosis in PTTG–/– mice.

  B. Li , E. Baudoin , R. Yu , Z.W. Sun , Z.S. Li , X.S. Bai , M. Alden and M.S. Mansour
  The structure and dynamics of a turbulent partially premixed methane/air flame in a conical burner were investigated using laser diagnostics and large-eddy simulations (LES). The flame structure inside the cone was characterized in detail using LES based on a two-scalar flamelet model, with the mixture fraction for the mixing field and level-set G-function for the partially premixed flame front propagation. In addition, planar laser induced florescence (PLIF) of CH and chemiluminescence imaging with high speed video were performed through a glass cone. CH and CH2O PLIF were also used to examine the flame structures above the cone. It is shown that in the entire flame the CH layer remains very thin, whereas the CH2O layer is rather thick. The flame is stabilized inside the cone a short distance above the nozzle. The stabilization of the flame can be simulated by the triple-flame model but not the flamelet-quenching model. The results show that flame stabilization in the cone is a result of premixed flame front propagation and flow reversal near the wall of the cone which is deemed to be dependent on the cone angle. Flamelet based LES is shown to capture the measured CH structures whereas the predicted CH2O structure is somewhat thinner than the experiments.
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