Potassium-Rankine Power Conversion Subsystem Modeling for Nuclear Electric Propulsion

A potassium-Rankine power conversion system model was developed under Contract No. NAS3-25808 for the NASA-LeRC. This model predicts potassium-Rankine performance for turbine inlet temperatures (TIT) from 1200 - 1600 K, TIT to condenser temperature ratios from 1.25-1.6, power levels from 100 to 10,000 kWe, and lifetimes from 2-10 years. The model is for a Rankine cycle with reheat for turbine stage moisture control. The model assumes heat is supplied from a lithium heat transport loop. The model does not include a heat source or a condenser/heat rejection system model. These must be supplied by the user

Two Jovian-Mass Planets in Earthlike Orbits

We report the discovery of two new planets: a 1.94 M_Jup planet in a 1.8-year orbit of HD 5319, and a 2.51 M_Jup planet in a 1.1-year orbit of HD 75898. The measured eccentricities are 0.12 for HD 5319 b and 0.10 for HD 75898 b, and Markov Chain Monte Carlo simulations based on derived orbital parameters indicate that the radial velocities of both stars are consistent with circular planet orbits. With low eccentricity and 1 < a < 2 AU, our new planets have orbits similar to terrestrial planets in the solar system. The radial velocity residuals of both stars have significant trends, likely arising from substellar or low-mass stellar companions.Comment: 32 pages, including 11 figures and 5 tables. Accepted by Ap

Bottom water variability in the Samoa Passage

The Samoa Passage (near 10S, 170W) is the channel through which the coldest, saltiest, densest bottom water approaches the North Pacific Ocean from its southern source. Over the past 25 years, three hydrographic sections have been made across the passage. A section occupied in 1968 shows little sign of modified North Atlantic Deep Water (NADW) within the northward flowing Lower Circumpolar Water (LCPW). In contrast, a section occupied in 1987 shows a strong negative curvature in -S (potential temperature-salinity) and a local maximum in salinity characteristic of NADW. A third section occupied in 1992 reveals a marginal NADW signature. The three sections are objectively mapped and very fine-scale bivariate areal -S censuses are made for a quantitative comparison of differences in water-mass structure. The strength of the NADW signature could fluctuate over a wide range of time-scales. However, these data are consistent with decadal variability, with no NADW signal in the passage in 1968, a strong signal in 1987, and a weak one in 1992. The geostrophic volume transport through the passage is 1.0 ± 0.2, 5.6 ± 1.3, and 4.8 ± 0.6 × 106 m3•s−1 below a zero-velocity surface (ZVS) of = 1.2°C for the 1968, 1987, and 1992 sections respectively. The transport estimates, made for comparison with those from velocity data presently being collected by a current meter array in the passage, are sensitive to variations in the choice of ZVS

Equation-free implementation of statistical moment closures

We present a general numerical scheme for the practical implementation of statistical moment closures suitable for modeling complex, large-scale, nonlinear systems. Building on recently developed equation-free methods, this approach numerically integrates the closure dynamics, the equations of which may not even be available in closed form. Although closure dynamics introduce statistical assumptions of unknown validity, they can have significant computational advantages as they typically have fewer degrees of freedom and may be much less stiff than the original detailed model. The closure method can in principle be applied to a wide class of nonlinear problems, including strongly-coupled systems (either deterministic or stochastic) for which there may be no scale separation. We demonstrate the equation-free approach for implementing entropy-based Eyink-Levermore closures on a nonlinear stochastic partial differential equation.Comment: 7 pages, 2 figure