Performance assessment of low pressure nuclear thermal propulsion

A low pressure nuclear thermal propulsion (LPNTP) system, which takes advantage of hydrogen dissociation/recombination, was proposed as a means of increasing engine specific impulse (Isp). The effect of hydrogen dissociation/recombination on LPNTP Isp is examined. A two-dimensional computer model was used to show that the optimum chamber pressure is approximately 100 psia (at a chamber temperature of 3,000 K), with an Isp approximately 15 s higher than at 1,000 psia. At high chamber temperatures and low chamber pressures, the increase in Isp is due to both lower average molecular weights caused by dissociation and added kinetic energy from monatomic hydrogen recombination. Monatomic hydrogen recombination increases the Isp more then hydrogen dissociation. Variations in the mole fraction of monatomic hydrogen are similar to variations in static pressure along the axial nozzle position. Most recombination occurs close to the nozzle throat. Practical variations in nozzle geometry have minimal impact on recombination. Other models which can simulate a wider range of nozzle designs should be used in the future. The uncertainty of the hydrogen kinetic reaction rates at high temperatures (approximately 3,000 K) affects the accuracy of the analysis and should be verified with simple bench tests

Safe, Affordable, Nuclear Thermal Propulsion Systems

The fundamental capability of Nuclear Thermal Propulsion (NTP) is game changing for space exploration. A first generation Nuclear Cryogenic Propulsion Stage (NCPS) based on NTP could provide high thrust at a specific impulse above 900 s, roughly double that of state of the art chemical engines. Characteristics of fission and NTP indicate that useful first generation systems will provide a foundation for future systems with extremely high performance. The role of the NCPS in the development of advanced nuclear propulsion systems could be analogous to the role of the DC-3 in the development of advanced aviation. Progress made under the NCPS project could help enable both advanced NTP and advanced Nuclear Electric Propulsion (NEP)

Effect of smoke on subcanopy shaded light, canopy temperature, and carbon dioxide uptake in an Amazon rainforest

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95278/1/gbc1694.pd

The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multi-band instrument which makes use of light from 600 to 2500nm allowing for coronagraphic direct exoplanet imaging of the inner 3 lambda/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1 lambda/D. Non-common path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate, NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid 2016) can take deeper exposures and/or perform angular, spectral and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable sub-diffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory.Comment: Accepted for publication, 20 pages, 10 figure

Improved Color-Temperature Relations and Bolometric Corrections for Cool Stars

We present new grids of colors and bolometric corrections for F-K stars having 4000 K < Teff < 6500 K, 0.0 < log g < 4.5 and -3.0 < [Fe/H] < 0.0. A companion paper extends these calculations into the M giant regime. Colors are tabulated for Johnson U-V and B-V; Cousins V-R and V-I; Johnson-Glass V-K, J-K and H-K; and CIT/CTIO V-K, J-K, H-K and CO. We have developed these color-temperature (CT) relations by convolving synthetic spectra with photometric filter-transmission-profiles. The synthetic spectra have been computed with the SSG spectral synthesis code using MARCS stellar atmosphere models as input. Both of these codes have been improved substantially, especially at low temperatures, through the incorporation of new opacity data. The resulting synthetic colors have been put onto the observational systems by applying color calibrations derived from models and photometry of field stars which have Teffs determined by the infrared-flux method. The color calibrations have zero points and slopes which change most of the original synthetic colors by less than 0.02 mag and 5%, respectively. The adopted Teff scale (Bell & Gustafsson 1989) is confirmed by the extraordinary agreement between the predicted and observed angular diameters of the field stars. We have also derived empirical CT relations from the field-star photometry. Except for the coolest dwarfs (Teff < 5000 K), our calibrated, solar-metallicity model colors are found to match these and other empirical relations quite well. Our calibrated, 4 Gyr, solar-metallicity isochrone also provides a good match to color-magnitude diagrams of M67. We regard this as evidence that our calibrated colors can be applied to many astrophysical problems, including modelling the integrated light of galaxies. (abridged)Comment: To appear in the March 2000 issue of the Astronomical Journal. 72 pages including 16 embedded postscript figures (one page each) and 6 embedded postscript tables (18 pages total

Investigation of Isoprene Dynamics During the Day‐to‐Night Transition Period

At the University of Michigan Biological Station during the 2016 AMOS field campaign, isoprene concentrations typically peak in the early afternoon (around 15:00 local time, LT) under well‐mixed conditions. However, an end‐of‐day peak (around 21:00 LT) occurs on 23% of the campaign days, followed by a rapid removal (from 21:00–22:00 LT) at rate of 0.57 hr−1 during the day‐to‐night transition period. During the end‐of‐day peak, in‐canopy isoprene concentrations increase by 77% (from 3.5 to 6.2 ppbv) on average. Stratification and weak winds (<3.4 m s−1 at 46 m) significantly suppress turbulent exchanges between in‐ and above‐canopy, leading to accumulation of isoprene emitted at dusk. A critical standard deviation of the vertical velocity (σw) of 0.14, 0.2, and 0.29 m s−1 is identified to detect the end‐of‐day peak for the height of 13, 21, and 34 m, respectively. In 85% of the end‐of‐day cases, the wind speed increases above 2.5 m s−1 after the peak along with a shift in wind direction, and turbulence is reestablished. Therefore, the wind speed of 2.5 m s−1 is considered as the threshold point where turbulence switches from being independent of wind speed to dependent on wind speed. The reinstated turbulence accounts for 80% of the subsequent isoprene removal with the remaining 20% explained by chemical reactions with hydroxyl radicals, ozone, and nitrate radicals. Observed isoprene fluxes do not support the argument that the end‐of‐day peak is reduced by vertical turbulent mixing, and we hypothesize that horizontal advection may play a role.Key PointsLow turbulent mixing during clear and calm nights leads to accumulation of isoprene within the canopyTurbulent mixing accounts for 80% of the observed nighttime isoprene loss ratesIsoprene flux measurements did not capture the majority of the removal of the accumulated isoprenePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163406/2/jgrd56554.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163406/1/jgrd56554_am.pd

The Relationship of Left Ventricular Trabeculation to Ventricular Function and Structure Over a 9.5-Year Follow-Up The MESA Study

Left ventricular (LV) trabeculation is highly variable among individuals and is increased in some diseases (e.g., congenital heart disease or cardiomyopathies), but its significance in population-representative individuals is unknown

Poor survival outcomes in HER2 positive breast cancer patients with low grade, node negative tumours

We present a retrospective analysis on a cohort of low-grade, node-negative patients showing that human epidermal growth factor receptor 2 (HER2) status significantly affects the survival in this otherwise very good prognostic group. Our results provide support for the use of adjuvant trastuzumab in patients who are typically classified as having very good prognosis, not routinely offered standard chemotherapy, and who as such do not fit current UK prescribing guidelines for trastuzumab

Comment on the narrow structure reported by Amaryan et al

The CLAS Collaboration provides a comment on the physics interpretation of the results presented in a paper published by M. Amaryan et al. regarding the possible observation of a narrow structure in the mass spectrum of a photoproduction experiment.Comment: to be published in Physical Review