Product Distributions Following Hyperthermal Collisions Between C2H4 And O(3P)

Transient Diode Laser Absorption Spectroscopy (TDLAS) was used to perform vibrational state population studies of the CO2 product from the hyperthermal reaction between C2H4 and O(3P) at room temperature using O3 as the O-atom precursor. Photodissociation of O3 using a frequency quadrupled Q-switch Nd:YAG laser pulse at 266 nm produced O(3P) atoms at high velocities which subsequently reacted with C2H4, producing several primary and secondary products including CO2. The CO2 product was detected using high-resolution TDLAS under five unique sets of reaction conditions. The vibrational distribution of the CO2 product did not follow a Boltzmann distribution at all five sets of conditions. The experiments showed a distribution in which there was a surprisingly high population in the (1000) (symmetric stretching) state compared with the other states probed, all of which contained bend excitation. In general, the CO2 population in the (1000) state was about 15-20% more populated than the Boltzmann distribution predicts. A possible explanation for this result may lie in the mechanism of CO2 evolution from the C2H4 + O(3P) reaction.

Low-density lipoprotein apolipoprotein B100 turnover in hypopituitary patients with GH deficiency: a stable isotope study

Epidemiological studies suggest that hypopituitary patients have an increased risk for cardiovascular mortality. The dyslipidaemia associated with this condition is often characterised by an increase in total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol (LDL-C) and may contribute to these findings. The underlying mechanisms are not fully elucidated.

Monotone Constrained Tensor-product B-spline with application to screening studies

When different markers are responsive to different aspects of a disease, combination of multiple markers could provide a better screening test for early detection. It is also resonable to assume that the risk of disease changes smoothly as the biomarker values change and the change in risk is monotone with respect to each biomarker. In this paper, we propose a boundary constrained tensor-product B-spline method to estimate the risk of disease by maximizing a penalized likelihood. To choose the optimal amount of smoothing, two scores are proposed which are extensions of the GCV score (O'Sullivan et al. (1986)) and the GACV score (Ziang and Wahba (1996)) to incorporate linear constraints. Simulation studies are carried out to investigate the performance of the proposed estimator and the selection scores. In addidtion, sensitivities and specificities based ona pproximate leave-one-out estimates are proposed to generate more realisitc ROC curves. Data from a pancreatic cancer study is used for illustration.

Longitudinal data on telomere length in leukocytes from newborn baboons support a marked drop in stem cell turnover around 1 year of age

Stem cells of various tissues are typically defined as multipotent cells with 'self-renewal' properties. Despite the increasing interest in stem cells, surprisingly little is known about the number of times stem cells can or do divide over a lifetime. Based on telomere-length measurements of hematopoietic cells, we previously proposed that the self-renewal capacity of hematopoietic stem cells is limited by progressive telomere attrition and that such cells divide very rapidly during the first year of life. Recent studies of patients with aplastic anemia resulting from inherited mutations in telomerase genes support the notion that the replicative potential of hematopoietic stem cells is directly related to telomere length, which is indirectly related to telomerase levels. To revisit conclusions about stem cell turnover based on cross-sectional studies of telomere length, we performed a longitudinal study of telomere length in leukocytes from newborn baboons. All four individual animals studied showed a rapid decline in telomere length (approximately 2-3 kb) in granulocytes and lymphocytes in the first year after birth. After 50-70 weeks the telomere length appeared to stabilize in all cell types. These observations suggest that hematopoietic stem cells, after an initial phase of rapid expansion, switch at around 1 year of age to a different functional mode characterized by a markedly decreased turnover rate.