Magnetically controlled mass loss from extrasolar planets in close orbits

We consider the role magnetic fields play in guiding and controlling mass-loss via evaporative outflows from exoplanets that experience UV irradiation. First we present analytic results that account for planetary and stellar magnetic fields, along with mass-loss from both the star and planet. We then conduct series of numerical simulations for gas giant planets, and vary the planetary field strength, background stellar field strength, UV heating flux, and planet mass. These simulations show that the flow is magnetically controlled for moderate field strengths and even the highest UV fluxes, i.e., planetary surface fields $B_P\gtrsim 0.3$ gauss and fluxes $F_{UV}\sim10^{6}$ erg s$^{-1}$. We thus conclude that outflows from all hot Jupiters with moderate surface fields are magnetically controlled. The inclusion of magnetic fields highly suppresses outflow from the night-side of the planet. Only the magnetic field lines near the pole are open and allow outflow to occur. The fraction of open field lines depends sensitively on the strength (and geometry) of the background magnetic field from the star, along with the UV heating rate. The net effect of the magnetic field is to suppress the mass loss rate by (approximately) an order of magnitude. Finally, some open field lines do not allow the flow to pass smoothly through the sonic point; flow along these streamlines does not reach steady-state, resulting in time-variable mass-loss.Comment: Accepted for publication in MNRAS, 20 pages, 13 figure

Standing on Academic Shoulders: Measuring Scientific Influence in Universities

This article measures scientific influence by means of citations to academic papers. The data source is the Institute for Scientific Information (ISI); the scientific institutions included are the top 110 U.S. research universities; the 12 main fields that classify the data cover nearly all of science; and the time period is 1981-1999. Altogether the database includes 2.4 million papers and 18.8 million citations. Thus the evidence underlying our findings accounts for much of the basic research conducted in the United States during the last quarter of the 20th century. This research in turn contributes a significant part of knowledge production in the U.S. during the same period. The citation measure used is the citation probability, which equals actual citations divided by potential citations, and captures average utilization of cited literature by individual citing articles. The mean citation probability within fields is on the order of 10-5. Cross-field citation probabilities are one-tenth to one-hundredth as large, or 10-6 to 10-7. Citations between pairs of citing and cited fields are significant in less than one-fourth of the possible cases. It follows that citations are largely bounded by field, with corresponding implications for the limits of scientific influence. Cross-field citation probabilities appear to be symmetric for mutually citing fields. Scientific influence is asymmetric within fields, and occurs primarily from top institutions to those less highly ranked. Still, there is significant reverse influence on higher-ranked schools. We also find that top institutions are more often cited by peer institutions than lower-ranked institutions are cited by their peers. Overall the results suggest that knowledge spillovers in basic science research are important, but are circumscribed by field and by intrinsic relevance. Perhaps the most important implication of the results are the limits that they seem to impose on the returns to scale in the knowledge production function for basic research, namely the proportion of available knowledge that spills over from one scientist to another.

Cornea organoids from human induced pluripotent stem cells.

The cornea is the transparent outermost surface of the eye, consisting of a stratified epithelium, a collagenous stroma and an innermost single-cell layered endothelium and providing 2/3 of the refractive power of the eye. Multiple diseases of the cornea arise from genetic defects where the ultimate phenotype can be influenced by cross talk between the cell types and the extracellular matrix. Cell culture modeling of diseases can benefit from cornea organoids that include multiple corneal cell types and extracellular matrices. Here we present human iPS cell-derived organoids through sequential rounds of differentiation programs. These organoids share features of the developing cornea, harboring three distinct cell types with expression of key epithelial, stromal and endothelial cell markers. Cornea organoid cultures provide a powerful 3D model system for investigating corneal developmental processes and their disruptions in diseased conditions

Unmanned Multiple Exploratory Probe System (MEPS) for Mars observation. Volume 2: Calculations and derivations

This volume of the final report on the unmanned Multiple Exploratory Probe System (MEPS) details all calculations, derivations, and computer programs that support the information presented in the first volume

Unmanned Multiple Exploratory Probe System (MEPS) for Mars observation. Volume 1: Trade analysis and design

This report presents the unmanned Multiple Exploratory Probe Systems (MEPS), a space vehicle designed to observe the planet Mars in preparation for manned missions. The options considered for each major element are presented as a trade analysis, and the final vehicle design is defined

Research on the external fluid mechanics of ocean thermal energy conversion plants : report covering experiments in a current

This report describes a set of experiments in a physical model study to explore plume transport and recirculation potential for a range of generic Ocean Thermal Energy Conversion (OTEC) plant designs and ambient conditions. Tests were conducted in a thermally-stratified 12 m x 18 m x 0.6 m basin, at an undistorted length scale ratio of 1:300, which allowed the upper 180 m of the ocean to be studied. Conditions which have been tested include a range of plant sizes (nominally 200 MWe - 600 MWe); a range of discharge configurations (mixed vs. non-mixed evaporator and condenser flows, multiple vs. radial slot discharge port(s), variation of discharge-intake separation and variation of discharge angle); and a range of ambient current speeds (0.15 - 1.0 m/s), and density profiles (surface mixed layers of 31 to 64 m). The tests described herein complement those reported previously (Adams et al., 1979) for a stagnant-ambient environment.Measurements included temperature, dye concentration and visual observations from still and motion pictures. Results derived from these measurements are presented in tables and graphs in prototype dimensions for direct use by OTEC designers. Many of the results are also analyzed and presented in non-dimensional terms to extend their generality. No significant recirculation was observed for any tests with a discharge directed with a vertical (downward) component. For tests with a horizontal discharge, recirculation was observed to be a complex function of a number of parameters. For sufficiently shallow discharge submergence, low to moderate current speeds, and with plants employing a radial slot discharge, recirculation could result from dynamic pressures caused by the proximity of the free surface - despite the negative plume buoyancy. This mode was labelled "confinement-induced" recirculation and led to measurements of direct recirculation ranging from 25% to 40%.For certain combinations of ambient current speed and generally positive plume buoyancy (resultIng from deeper discharge submergence), the plume was observed to billow upward resulting in "current-induced" recirculation. This was observed for both radial slot and multiple port discharge configurations although somewhat greater recirculation was observed with the former configuration. Measured recirculation for current-induced recirculation fell in the range 0 to 10% with a peak occurring at intermediate current speeds of about 0.5 m/s. Experiments with a mixed evaporator and condenser discharge showed less tendency for direct recirculation of either type than the separate (evaporator only) discharges, but the effects of recirculation, as measured by the drop in evaporator intake temDerature (below the ambient temperature at the level of the intake) were not very different. A simple mathematical model, based on the governing length scales, was successfully calibrated to the observed values of direct recirculation for the radial discharge case.Various measures of plume transport were summarized to help designers predict the impact of OTEC operation on the environment and to establish guidelines for spacing of multiple plants. Minimum near field dilutions were observed in the range between 5 and 10 indicating that the peak concentration of any chemicals contained in the discharge would be between 10 and 20% of the discharge concentration. Near field horizontal and vertical dimensions of the plume wake were found to be correlated with a length scale derived from discharge kinematic momentum flux and ambient current speed. The rise and fall of the equilibrium plume elevation (above or below the discharge elevation) was found to be governed by a ratio of length scales based on the ambient density profile and the discharge kinematic momentum and buoyancy fluxes