Vapor ingestion in Centaur liquid-hydrogen tank

Vapor ingestion phenomena were investigated using scale models of the Centaur liquid hydrogen tank to determine the height of the free surface of the liquid when vapor is intially ingested into the tank outlet. Data are compared with an analysin and, is general the agreement is very good. Predictions are presented for minimum liquid levels required in the Centaur liquid hydrogen tank in order to prevent vapor ingestion when restarting the engines in space and the quantities of liquid remaining in the tank at vapor ingestion during main engine firing

Contoured tank outlets for draining of cylindrical tanks in low-gravity environment

An analysis is presented for defining the outlet contour of a hemispherical-bottomed cylindrical tank that will prevent vapor ingestion when the tank is drained. The analysis was used to design two small-scale tanks that were fabricated and then tested in a low gravity environment. The draining performance of the tanks was compared with that for a tank with a conventional outlet having a constant circular cross-sectional area, under identical conditions. Even when drained at off-design conditions, the contoured tank had less liquid residuals at vapor ingestion than the conventional outlet tank. Effects of outflow rate, gravitational environment, and fluid properties on the outlet contour are discussed. Two potential applications of outlet contouring are also presented and discussed

Effect of throttling on interface behavior and liquid residuals in weightlessness

An experimental investigation was conducted to study liquid-vapor interface behavior and subsequent vapor ingestion in a flat-bottomed cylindrical tank following a single-step throttling in outflow rate in a weightless environment. A throttling process in which the final Weber number was one-tenth of the initial Weber number tended to excite large-amplitude symmetric slosh, with the amplitude generally increasing as initial Weber number increased. As expected, liquid residuals were lower than those obtained without throttling and, for moderate values of initial Weber number, could be adequately predicted by assuming that all draining took place at the final Weber number. At large values of Weber number, residuals tended to be lower than this predicted value

Do peer Groups Matter? Peer Groups versus Schooling Effects on Academic Attainment

In this paper we estimate an educational production function. Educational attainment is a function of three types of inputs: peer group, parental and schooling. We find that conventional measures of school quality are not good predictors for academic attainment, once we control for peer group effects. Parental qualities also have strong effects on academic atainment. This academic attainment is then a key determinant of subsequent labour market success, as measured by earnings.

Attainment in Secondary School

This paper studies attainment in secondary schools. We estimate an education production function in which attainment depends upon parental inputs, peer group inputs and schooling inputs. We find that the most powerful parental input is parental interest in children, as assessed by teachers. We find a strong peer group effect. The school pupil-teacher ratio does not enter significantly. The only strongly endogenous variable is initial attainment. We argue that this is due to measurement error. There is some evidence that parental interest is endogenous but we do not find peer group variables to be so.

A Model of Intervention in Childhood

This paper describes a model and resulting simulations to assess the appropriate age structure of intervention in childhood on the theme: should we intervene early or late? We use asset theory approaches to construct a general model of state investment whose aim is to reduce inequality in human capital. We set out the key parameters of such a model, clarifying the assumptions that must be made by state planners or economists in assessing the relative value of targeted investment at different ages in the presence of a range of elements of uncertainty. We simulate the model showing how the age-investment schedule will vary under different assumptions. Early investment is highly valued because of the likely decline with age in effectiveness but the trade-offs are strongly moderated by other important assumptions around which there is uncertainty or are choice variables of the state planner.

Factor Residuals in SUR Regressions: Estimating Panels Allowing for Cross Sectional Correlation

This paper describes a method for estimating panels by imposing a factor structure on the residuals. The method allows SUR estimation of panel models by providing a full-rank estimator of the system covariance matrix when the usual estimate is rank-deficient. We charactersie completely the circumstances when this is possible. When the usual estimator is of full rank, our procedure provides a more parsimonious representation of the covariance matrix, which can lead to efficiency gains in finite samples. Monte Carlo analysis of convergence regressions and PPP regressions in the Heston-Summers data-set indicates that the proposed estimator has better performance in terms of RMSE and bias than standard panel or SUR estimators (where available), as well as offering unbiased inference.Panel data, cross sectional correlation, factor analysis