The Effect of Laminar Flow on Rotor Hover Performance

The topic of laminar flow effects on hover performance is introduced with respect to some historical efforts where laminar flow was either measured or attempted. An analysis method is outlined using combined blade element, momentum method coupled to an airfoil analysis method, which includes the full e(sup N) transition model. The analysis results compared well with the measured hover performance including the measured location of transition on both the upper and lower blade surfaces. The analysis method is then used to understand the upper limits of hover efficiency as a function of disk loading. The impact of laminar flow is higher at low disk loading, but significant improvement in terms of power loading appears possible even up to high disk loading approaching 20 ps f. A optimum planform design equation is derived for cases of zero profile drag and finite drag levels. These results are intended to be a guide for design studies and as a benchmark to compare higher fidelity analysis results. The details of the analysis method are given to enable other researchers to use the same approach for comparison to other approaches

Follow-up of a suspected excess of brain tumours among Namibian children

The original publication is available at http://www.samj.org.zaTo the Editor: The aim of this follow-up study was to further investigate a suggested excess of childhood brain tumours (CBT) among Herero children in Namibia from 1983 to 1988. Incidence rates of primary brain tumours among Herero children were found to be 4 times higher than rates among Namibian children in any of the 10 other tribal groups or among children of European origin. The causes of CBTs remain largely unknown. The only established causes are ionizing radiation and predisposing inherited syndromes. A particularly compelling hypothesis is that exposure during gestation to N-nitroso compounds (NOCs) may lead to the development of CBT. This hypothesis was suggested by experimental work in which 100% production of nervous system (NS) tumours in rat offspring resulted from transplacental exposure to the neurocarcinogen ethylnitrosourea (ENU) or to low levels of the precursor compounds sodium nitrite and ethyl urea added to the food and drinking water of pregnant rat

Nucleon-Nucleon Scattering from Effective Field Theory

We perform a nonperturbative calculation of the 1S0 NN scattering amplitude using an effective field theory (EFT) expansion. The expansion we advocate is a modification of what has been used previously; it is no a chiral expansion in powers of the pion mass. We use dimensional regularization throughout and the MS-bar subtraction scheme; our final result depends only on physical observables. We show that the EFT expansion of the quantity |p|cot delta(p) converges at momenta much greater than the scale that characterizes the derivative expansion of the EFT Lagrangian. Our conclusions are optimistic about the applicability of an EFT approach to the quantitative study of nuclear matter.Comment: Revised discussion of power counting in the EFT expansion. Tex file uses harvmac, epsf macros, 35 pages with 9 postscript figure