7-Substituted pyrrolo[2,3-d]pyrimidines for the synthesis of new 1-deazapyrimido[1,2,3-cd]purines

Few examples of new heterocyclic 1-deazapyrimido[1,2,3-cd]purine derivatives were synthesized by intramolecular cyclization of methyl 7-(oxiran-2-ylmethyl)-7H-pyrrolo[2,3-d]pyrimidine-6-carboxylates. The latter were obtained by iodolactonization of 7-allylpyrrolo[2,3-d]pyrimidine-6-carboxylic acids

Laminar Flow Friction and Heat Transfer in Non- Circular Ducts and Channels Part II: Thermal Problem

A detailed review and analysis of the thermal characteristics of laminar developing and fully developed flow in non-circular ducts is presented. New models are proposed which simplify the prediction of Nusselt numbers for three fundamental flows: the combined entrance problem, the Graetz problem, and thermally fully developed flow in most non-circular duct geometries found in heat exchanger applications. By means of scaling analysis it is shown that the complete problem may be easily analyzed by combining the asymptotic results for short and long ducts. By means of a new characteristic length scale, the square root of cross-sectional area, the effect of duct shape has been reduced. The new model has an accuracy of ± 10 percent, or better, for most common duct shapes. Both singly and doubly connected ducts are considered

Temperature dependence of the probability of "small heating" and total losses of ucns on the surface of fomblin oils of different molecular mass

We measured the temperature dependence of the probability of small heating and total losses of UCNs on the PFPE Fomblin Y surface with various molecular masses Mw=2800, 3300, 6500 amu in the temperature range of 100-300 K. The probability of small heating sharply decreases with increasing Mw and decreasing temperature. The probability of total loss weakly decreases with decreasing temperature and takes the minimum value at Mw=3300 amu. As this oil provides a homogeneous surface with minimal probabilities of small heating and total losses of UCNs, it is the preferred candidate for experiments on measuring the neutron lifetime