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DOE OSTI2025

Risk of longer-term endocrine and metabolic conditions in the Deepwater Horizon Oil Spill Coast Guard cohort study – five years of follow-up

Abstract Introduction Long-term endocrine and metabolic health risks associated with oil spill cleanup exposures are largely unknown, despite the endocrine-disrupting potential of crude oil and oil dispersant constituents. We aimed to investigate risks of longer-term endocrine and metabolic conditions among U.S. Coast Guard (USCG) responders to the Deepwater Horizon (DWH) oil spill. Methods Our study population included all active duty DWH Oil Spill Coast Guard Cohort members ( N = 45,224). Self-reported spill exposures were ascertained from post-deployment surveys. Incident endocrine and metabolic outcomes were defined using International Classification of Diseases (9th Revision) diagnostic codes from military health encounter records up to 5.5 years post-DWH. Using Cox proportional hazards regression, we estimated adjusted hazard ratios (aHR) and 95% confidence intervals (CIs) for various incident endocrine and metabolic diagnoses (2010–2015, and separately during 2010–2012 and 2013–2015). Results The mean baseline age was 30 years (~ 77% white, ~ 86% male). Compared to non-responders ( n = 39,260), spill responders ( n = 5,964) had elevated risks for simple and unspecified goiter (aHR = 2.09, 95% CI: 1.29–3.38) and disorders of lipid metabolism (aHR = 1.09, 95% CI: 1.00–1.18), including its subcategory other and unspecified hyperlipidemia (aHR = 1.10, 95% CI: 1.01–1.21). The dysmetabolic syndrome X risk was elevated only during 2010–2012 (aHR = 2.07, 95% CI: 1.22–3.51). Responders reporting ever ( n = 1,068) vs. never ( n = 2,424) crude oil inhalation exposure had elevated risks for disorders of lipid metabolism (aHR = 1.24, 95% CI: 1.00–1.53), including its subcategory pure hypercholesterolemia (aHR = 1.71, 95% CI: 1.08–2.72), the overweight, obesity and other hyperalimentation subcategory of unspecified obesity (aHR = 1.52, 95% CI: 1.09–2.13), and abnormal weight gain (aHR = 2.60, 95% CI: 1.04–6.55). Risk estimates for endocrine/metabolic conditions were generally stronger among responders reporting exposure to both crude oil and dispersants (vs. neither) than among responders reporting only oil exposure (vs. neither). Conclusion In this large cohort of active duty USCG responders to the DWH disaster, oil spill cleanup exposures were associated with elevated risks for longer-term endocrine and metabolic conditions.

Denic-Roberts, Hristina↗

NASA NTRS1994

Comprehensive stellar population models and the disentanglement of age and metallicity effects

The construction of detailed models for intermediate and old stellar populations is described. Input parameters include metallicity (-2 less than (Fe/H) less than 0.5), single-burst age (between 1.5 and 17 Gyr), and initial mass function (IMF) exponent. Quantities output include broadband magnitudes, spectral energy distributions, surface brightness fluctuation magnitudes, and a suite of 21 absorption feature indices. The models are checked against a wide variety of available observations. Examinations of model output yield the following conclusions. (1) If the percentage change delta age/delta Z approximately equals 3/2 for two populations, they will appear almost identical in most indices. A few indices break this degeneracy by being either more abundance sensitive (Fe4668, Fe5015, Fe5709, and Fe5782) or more age sensitive (G4300, H beta, and presumably higher order Balmer lines) than usual. (2) Present uncertainties in stellar evolution are of the same magnitude as the effects of IMF and Y in the indices studied. (3) Changes in abundance ratios (like (Mg/Fe)) are predicted to be readily apparent in the spectra of old stellar populations. (4) The I-band flux of a stellar population is predicted to be nearly independent of metallicity and only modestly sensitive to age. The I band is therefore recommended for standard candle work or studies of M/L in galaxies. Other conclusions stem from this work. (1) Intercomparison of models and observations of two TiO indices seem to indicate variation of the (V/Ti) ratio among galaxies, but it is not clear how this observation ties into the standard picture of chemical enrichment. (2) Current estimates of (Fe/H) for the most metal-rich globulars that are based on integrated indices are probably slightly too high. (3) Colors of population models from different authors exhibit a substantial range. At solar metallicity and 13 Gyr, this range corresponds to an age error of roughly +/- 7 Gyr. Model colors from different authors applied in a differential sense have smaller uncertainties. (4) In the present models the dominant error for colors is probably the transformation from stellar atmospheric parameters to stellar colors. (5) Stellar B - V is difficult to model, and current spreads among different authors can reach 0.2 mag. (6) If known defects in the stellar flux library are corrected, the population model colors of this work in passbands redder than U would be accurate to roughly 0.03 mag in an absolute sense. These corrections are not made in the tables of model output.

Worthey, Guy↗

NASA NTRS2007

The NASA-Sponsored Study of Cataract in Astronauts (NASCA). Relationship of Exposure to Radiation in Space and the Risk of Cataract Incidence and Progression. Report 1: Recruitment and Methodology

The NASA Study of Cataract in Astronauts (NASCA) is a five-year, multi-centered, investigation of lens opacification in populations of U.S. astronauts, military pilots, and ground-based (nonaviator) comparison participants. For astronauts, the explanatory variable of most interest is radiation exposure during space flight, however to properly evaluate its effect, the secondary effects of age, nutrition, general health, solar ocular exposure, and other confounding variables encountered in non-space flight must also be considered. NASCA contains an initial baseline, cross-sectional objective assessment of the severity of cortical (C), nuclear (N), and posterior subcapsular (PSC) lens opacification, and annual follow-on assessments of severity and progression of these opacities in the population of astronauts and in participants sampled from populations of military pilots and ground-based exposure controls. From these data, NASCA will estimate the degree to which space radiation affects lens opacification for astronauts and how the overall risks of each cataract type for astronauts compared with those of the other exposure control groups after adjusting for differences in age and other explanatory variables.

Chylack, Leo T.↗

DOE OSTI2014

Organ localization: Toward prospective patient-specific organ dosimetry in computed tomography

Purpose: With increased focus on radiation dose from medical imaging, prospective radiation dose estimates are becoming increasingly desired. Using available populations of adult and pediatric patient phantoms, radiation dose calculations can be catalogued and prospectively applied to individual patients that best match certain anatomical characteristics. In doing so, the knowledge of organ size and location is a required element. Here, the authors develop a predictive model of organ locations and volumes based on an analysis of adult and pediatric computed tomography (CT) data. Methods: Fifty eight adult and 69 pediatric CT datasets were segmented and utilized in the study. The maximum and minimum points of the organs were recorded with respect to the axial distance from the tip of the sacrum. The axial width, midpoint, and volume of each organ were calculated. Linear correlations between these three organ parameters and patient age, BMI, weight, and height were determined. Results: No statistically significant correlations were found in adult patients between the axial width, midpoint, and volume of the organs versus the patient age or BMI. Slight, positive linear trends were found for organ midpoint versus patient weight (max r{sup 2} = 0.382, mean r{sup 2} = 0.236). Similar trends were found for organ midpoint versus height (max r{sup 2} = 0.439, mean r{sup 2} = 0.200) and for organ volume versus height (max r{sup 2} = 0.410, mean r{sup 2} = 0.153). Gaussian fits performed on probability density functions of the adult organs resulted in r{sup 2}-values ranging from 0.96 to 0.996. The pediatric patients showed much stronger correlations overall. Strong correlations were observed between organ axial midpoint versus age, height, and weight (max r{sup 2} = 0.842, mean r{sup 2} = 0.790; max r{sup 2} = 0.949, mean r{sup 2} = 0.894; and max r{sup 2} = 0.870, mean r{sup 2} = 0.847, respectively). Moderate linear correlations were also observed for organ axial width versus height (max r{sup 2} = 0.772, mean r{sup 2} = 0.562) and for organ volume versus height (max r{sup 2} = 0.781, mean r{sup 2} = 0.601). Conclusions: Adult patients exhibited small variations in organ volume and location with respect to height and weight, but no meaningful correlation existed between these parameters and age or BMI. Once adulthood is reached, organ morphology and positioning seem to remain static. However, clear trends are evident between pediatric organ locations versus age, height, and weight. Such information can be incorporated into a matching methodology that may provide the highest probability of representing the anatomy of a patient undergoing a clinical exam to prospectively estimate the radiation dose.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2019

Decadal carbon decomposition dynamics in three peatlands in Northern Minnesota

The uppermost portion of the peat profile, an area of active diagenetic processes, is exceedingly important for understanding peatland dynamics and the diagenesis and geochemistry of atmospherically-deposited materials. In this study, we investigated high resolution carbon (C) accrual and peat decomposition rates at two Sphagnum-rich ombrotrophic bogs and one fen in northern Minnesota, USA by analyzing 1 cm increments from 30 cm thick intact frozen blocks of peat soil. We conducted radiocarbon analysis of Sphagnum cellulose to determine peat age and net C accumulation at each depth interval. Calibrated peat ages were determined using CALIBomb and a compilation of calibration datasets for the pre-bomb period. We fit data with a negative exponential accumulation model and used model-derived parameters to estimate net primary productivity (NPP) and a peat decomposition rate constant k. FTIR spectroscopy and C:N were used to derive humification indices and to chemically characterize the peat. NPP ranged from 180 to 266 g C m -2 year -1 , k ranged from 0.015 to 0.019 year -1 . Net C accumulation rates ranged from 112 to 174 g C m -2 year -1 at 25 years and 70 to 113 g C m -2 year-1 at 50 years. Mass loss was up to 55% during the first 50 years of peat accumulation. Decomposition is greater at depth in the bogs—where 25 cm of peat correspond to 55 years of peat accumulation—than in the fen, where peat age is approximately 25 years at 25 cm depth. Lastly, information on fine-scale variations in peat mass decomposition and loss across ombrotrophic bogs and a fen help interpret other diagenetic processes in peatlands.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2015

Dose–Volume Relationships Associated With Temporal Lobe Radiation Necrosis After Skull Base Proton Beam Therapy

Purpose: We evaluated patient and treatment parameters correlated with development of temporal lobe radiation necrosis. Methods and Materials: This was a retrospective analysis of a cohort of 66 patients treated for skull base chordoma, chondrosarcoma, adenoid cystic carcinoma, or sinonasal malignancies between 2005 and 2012, who had at least 6 months of clinical and radiographic follow-up. The median radiation dose was 75.6 Gy (relative biological effectiveness [RBE]). Analyzed factors included gender, age, hypertension, diabetes, smoking status, use of chemotherapy, and the absolute dose:volume data for both the right and left temporal lobes, considered separately. A generalized estimating equation (GEE) regression analysis evaluated potential predictors of radiation necrosis, and the median effective concentration (EC50) model estimated dose–volume parameters associated with radiation necrosis. Results: Median follow-up time was 31 months (range 6-96 months) and was 34 months in patients who were alive. The Kaplan-Meier estimate of overall survival at 3 years was 84.9%. The 3-year estimate of any grade temporal lobe radiation necrosis was 12.4%, and for grade 2 or higher radiation necrosis was 5.7%. On multivariate GEE, only dose–volume relationships were associated with the risk of radiation necrosis. In the EC50 model, all dose levels from 10 to 70 Gy (RBE) were highly correlated with radiation necrosis, with a 15% 3-year risk of any-grade temporal lobe radiation necrosis when the absolute volume of a temporal lobe receiving 60 Gy (RBE) (aV60) exceeded 5.5 cm{sup 3}, or aV70 > 1.7 cm{sup 3}. Conclusions: Dose–volume parameters are highly correlated with the risk of developing temporal lobe radiation necrosis. In this study the risk of radiation necrosis increased sharply when the temporal lobe aV60 exceeded 5.5 cm{sup 3} or aV70 > 1.7 cm{sup 3}. Treatment planning goals should include constraints on the volume of temporal lobes receiving higher dose. The EC50 model provides suggested dose–volume temporal lobe constraints for conventionally fractionated high-dose skull base radiation therapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2020

Quantile-specific heritability of sibling leptin concentrations and its implications for gene-environment interactions

“Quantile-dependent expressivity” occurs when the effect size of a genetic variant depends upon whether the phenotype (e.g., leptin) is high or low relative to its distribution. Leptin concentrations are strongly related to adiposity, whose heritability is quantile dependent. Whether inheritance of leptin concentrations is quantile dependent, and whether this explains the greater heritability in women than men in accordance with their greater adiposity, and explains other gene-environment interactions, remains to be determined. Therefore, leptin and leptin receptor concentrations from 3068 siblings in 1133 sibships from the Framingham Heart Study Third Generation Cohort were analyzed. Free leptin index (FLI) was calculated as the ratio of leptin to soluble leptin receptor concentrations. Full-sib (β FS ) regression slopes were robustly estimated by quantile regression with nonparametric significance assigned from 1000 bootstrap samples. The analyses showed β FS increased significantly with increasing percentiles of the offspring’s age- and sex-adjusted leptin distribution (P linear = 0.0001), which was accelerated at the higher concentrations (P quadratic = 0.0003). β FS at the 90th percentile (0.418 ± 0.066) was 4.7-fold greater than at the 10th percentile (0.089 ± 0.032, P difference = 3.6 × 10 –6 ). Consistent with quantile-dependent expressivity, the β FS was greater in female sibs, which was attributable to their higher leptin concentrations. Reported gene-environment interactions involving adiposity and LEP , LEPR , MnSOD , PPARγ , PPARγ2 , and IRS-1 polymorphisms were consistent with quantile-dependent expressivity of leptin concentrations. β FS for leptin receptor concentrations and free leptin index also increased significantly with increasing percentiles of their distributions (P linear = 0.04 and P linear = 8.5 × 10 –6 , respectively). In conclusion, inherited genetic and shared environmental effects on leptin concentrations were quantile dependent, which likely explains male–female differences in heritability and some gene-environment interactions.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Sea-level rise in Southwest Greenland as a contributor to Viking abandonment

The first records of Greenland Vikings date to 985 CE. Archaeological evidence yields insight into how Vikings lived, yet drivers of their disappearance in the 15th century remain enigmatic. Research suggests a combination of environmental and socioeconomic factors, and the climatic shift from the Medieval Warm Period (~900 to 1250 CE) to the Little Ice Age (~1250 to 1900 CE) may have forced them to abandon Greenland. Glacial geomorphology and paleoclimate research suggest that the Southern Greenland Ice Sheet readvanced during Viking occupation, peaking in the Little Ice Age. Counterintuitively, the readvance caused sea-level rise near the ice margin due to increased gravitational attraction toward the ice sheet and crustal subsidence. We estimate ice growth in Southwestern Greenland using geomorphological indicators and lake core data from previous literature. We calculate the effect of ice growth on regional sea level by applying our ice history to a geophysical model of sea level with a resolution of ~1 km across Southwestern Greenland and compare the results to archaeological evidence. The results indicate that sea level rose up to ~3.3 m outside the glaciation zone during Viking settlement, producing shoreline retreat of hundreds of meters. Sea-level rise was progressive and encompassed the entire Eastern Settlement. Moreover, pervasive flooding would have forced abandonment of many coastal sites. These processes likely contributed to the suite of vulnerabilities that led to Viking abandonment of Greenland. Sea-level change thus represents an integral, missing element of the Viking story.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2017

Eight new luminous z ≥ 6 quasars discovered via SED model fitting of VISTA, WISE and Dark Energy Survey Year 1 observations

We present the discovery and spectroscopic confirmation with the ESO NTT and Gemini South telescopes of eight new 6.0 < z < 6.5 quasars with z$_{AB}$ < 21.0. These quasars were photometrically selected without any star-galaxy morphological criteria from 1533 deg$^{2}$ using SED model fitting to photometric data from the Dark Energy Survey (g, r, i, z, Y), the VISTA Hemisphere Survey (J, H, K) and the Wide-Field Infrared Survey Explorer (W1, W2). The photometric data was fitted with a grid of quasar model SEDs with redshift dependent Lyman-{\alpha} forest absorption and a range of intrinsic reddening as well as a series of low mass cool star models. Candidates were ranked using on a SED-model based $\chi^{2}$-statistic, which is extendable to other future imaging surveys (e.g. LSST, Euclid). Our spectral confirmation success rate is 100% without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants the method allows large data sets to be processed without human intervention and without being over run by spurious false candidates. We also present a robust parametric redshift estimating technique that gives comparable accuracy to MgII and CO based redshift estimators. We find two z $\sim$ 6.2 quasars with HII near zone sizes < 3 proper Mpc which could indicate that these quasars may be young with ages < 10$^6$ - 10$^7$ years or lie in over dense regions of the IGM. The z = 6.5 quasar VDESJ0224-4711 has J$_{AB}$ = 19.75 is the second most luminous quasar known with z > 6.5.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Sap flux measurements in wet tropical forests: unique challenges and opportunities

Tropical rainforests often have great tree species and functional diversity, complex age and stand structure, deep active sapwood, and potential factors that reduce transpiration, such as frequent cloud cover and wet leaves. Such factors generate challenges for estimating transpiration from sap flux measurements. In fact, upscaling approaches have rarely been attempted for diverse tropical forests. Thus, the objective of this paper is to build upon past efforts to scale transpiration and optimize strategies for wet tropical forests. Over a five-year period, we instrumented 44 trees with heat dissipation sap flow sensors within a premontane wet tropical rainforest in Costa Rica (5000 mm MAP). Given high diversity, few instrumented trees belonged to the same species, genus, or even family. In a subset of trees, radial profiles across the full range of active xylem were examined. Measurements were scaled to the stand in two plots using sapwood area. In association with extensive micrometeorological measurements, only ~10% of rainfall was transpired from this forested watershed due to persistent low radiation, evaporative demand, and frequent wet canopy conditions. Contrary to temperate trees, we observed minimal flow reductions in deeper sapwood among the largest trees, whose water use amounted to nearly 80% of the total stand water use, even though they contributed less than 15% to total stand basal area. We found that transpiration was suppressed when leaves were wet, even after accounting for lower vapor pressure deficit and reduced solar radiation. Since soil moisture conditions at this site remain continually above deficit levels, flow reversal has been assumed to be minor and thus has not yet been investigated. The driest month on record resulted in higher, not lower transpiration. Given the high diversity of these forests, herein we propose practical and innovate approaches to group trees by function or degree of canopy exposure. Finally, these efforts are critical for accurate scaling of measurements from individual sensors to stands and for improving global land surface models that increasingly partition canopy components to better represent these functionally and structurally diverse ecosystems.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2017

Absolute Dimensions of the Eccentric Eclipsing Binary V541 Cygni

We report new spectroscopic and photometric observations of the main-sequence, detached, eccentric, double-lined eclipsing binary V541 Cyg (P = 15.34 days, e = 0.468). Using these observations together with existing measurements, we determine the component masses and radii to better than 1% precision: M{sub 1}=2.335{sub −0.013}{sup +0.017} M{sub ⊙}, M{sub 2}=2.260{sub −0.013}{sup +0.016} M{sub ⊙}, R{sub 1}=1.859{sub −0.009}{sup +0.012} R{sub ⊙}, and R{sub 2}=1.808{sub −0.013}{sup +0.015} R{sub ⊙}. The nearly identical B9.5 stars have estimated effective temperatures of 10650 ± 200 K and 10350 ± 200 K. A comparison of these properties with current stellar evolution models shows excellent agreement at an age of about 190 Myr and [Fe/H] ≈ −0.18. Both components are found to be rotating at the pseudo-synchronous rate. The system displays a slow periastron advance that is dominated by general relativity (GR), and has previously been claimed to be slower than predicted by theory. Our new measurement, ω-dot =0.859{sub −0.017}{sup +0.042} deg century{sup −1}, has an 88% contribution from GR and agrees with the expected rate within the uncertainties. We also clarify the use of the gravity darkening coefficients in the light-curve fitting Eclipsing Binary Orbit Program (EBOP), a version of which we use here.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Velocity Dispersion, Size, Sérsic Index, and D{sub n}4000: The Scaling of Stellar Mass with Dynamical Mass for Quiescent Galaxies

We examine the relation between stellar mass, velocity dispersion, size, Sérsic index, and D{sub n}4000 for a volume-limited sample of ∼40,000 quiescent galaxies in the SDSS. At a fixed stellar mass, galaxies with higher D{sub n}4000 have larger velocity dispersions and smaller sizes. D{sub n}4000 is a proxy for stellar population age, thus these trends suggest that older galaxies typically have larger velocity dispersions and smaller sizes. We combine velocity dispersion and size into a dynamical mass estimator, σ{sup 2}R. At a fixed stellar mass, σ{sup 2}R depends on D{sub n}4000. The Sérsic index is also correlated with D{sub n}4000. The dependence of σ{sup 2}R and Sérsic index on D{sub n}4000 suggests that quiescent galaxies are not structurally homologous systems. We derive an empirical correction for non-homology which is consistent with the analytical correction derived from the virial theorem. After accounting for non-homologous galactic structure, we measure M{sub ∗}∝M{sub d}{sup 0.998±0.004}, where M {sub *} is the stellar mass and M {sub d} is the dynamical mass derived from the velocity dispersion and size; stellar mass is directly proportional to dynamical mass. Quiescent galaxies appear to be in approximate virial equilibrium, and deviations of the fundamental plane parameters from the expected virial relation may result from mass-to-light ratio variations, selection effects, and the non-homology of quiescent galaxies. We infer the redshift evolution of velocity dispersion and size for galaxies in our sample assuming purely passive evolution. The inferred evolution is inconsistent with direct measurements at higher redshifts. Thus quiescent galaxies do not passively evolve. Quiescent galaxies have properties that are consistent with standard galaxy formation in ΛCDM. They form at different epochs and evolve modestly, increasing their size, velocity dispersion, and Sérsic index after they cease star formation.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Optimizing stadium evacuation by integrating geocomputation and affordance theory

Football is culturally and economically important in the United States, and football stadiums are part of the country's critical infrastructure, thus receiving government protection against hazard events. In this project, an agent-based evacuation model was implemented to optimize evacuation time from The University of Southern Mississippi's M.M. Roberts Stadium (football) by accounting for evacuees’ age, gender, physical fitness, alcohol consumption, and prior experience with hazard events. The findings revealed that (i) the age and gender of an individual impact his/her locomotion speed and (ii) evacuation route choice is influenced by evacuees’ perception of its safety and effectiveness. The estimated evacuation times for all evacuees to exit only the stadium and the stadium plus the surrounding campus were 20.82 and 165.01 minutes, respectively. Both of these times were shorter than the evacuation times determined by models employing location-unspecific locomotion speeds. One-way analysis of variance revealed that there were statistically significant differences between use of location-specific and location-unspecific within-stadium evacuation times (p ≤ 0.001 with α = 0.05). These results suggest that using local data is vital to accurately estimate evacuation time.

99 GENERAL AND MISCELLANEOUS↗

NASA NTRS1977

Turbulent viscosity and Jupiter's tidal Q

A recent estimate of tidal dissipation by turbulent viscosity in Jupiter's convective interior predicts that the current value of the planet's tidal Q is roughly 5 million. We point out a fundamental error in this calculation, and show that turbulent dissipation alone implies that at present Q is about 50 trillion. Our reduced estimate for the rate of tidal dissipation shows conclusively that tidal torques have produced only negligible modifications of the orbits of the Galilean satellites over the age of the solar system.

Goldreich, P.↗

NASA NTRS1986

Towards a theory for Neptune's arc rings

It is proposed that the incomplete rings of Neptune consist of a number of short arcs centered on the corotation resonances of a single satellite. The satellite must have a radius of the order of 100 km or more and move on an inclined orbit. Corotation resonances are located at potential maxima. Thus, mechanical energy dissipated by interparticle collisions must be continually replenished to prevent the arcs from spreading. It is shown that each corotation resonance is associated with a nearby Lindblad resonance, which excites the ring particles' orbital eccentricity, thus supplying the energy required to maintain the arc. The ultimate energy reservoir is the satellite's orbital energy. Therefore, interaction with the arcs damps the satellite's orbital inclination. The self-gravity of the arcs limits their contraction and enforces a relation between arc length and mass. The estimated arc masses are so small, of the order of 10 to the 16th g, that the satellite's orbital inclination suffers negligible decay over the age of the solar system. The inferred surface mass densities are comparable to those found in the major rings of Saturn and Uranus.

Goldreich, P.↗

NASA NTRS1989

Tropical forest biomass and successional age class relationships to a vegetation index derived from Landsat TM data

Forest stand structure and biomass data were collected using conventional forest inventory techniques in tropical, subtropical, and warm temperate forest biomes. The feasibility of detecting tropical forest successional age class and total biomass differences using Landsat-Thematic mapper (TM) data, was evaluated. The Normalized Difference Vegetation Index (NDVI) calculated from Landsat-TM data were not significantly correlated with forest regeneration age classes in the mountain terrain of the Luquillo Experimental Forest, Puerto Rico. The low sun angle and shadows cast on steep north and west facing slopes reduced spectral reflectance values recorded by TM orbital altitude. The NDVI, calculated from low altitude aircraft scanner data, was significatly correlated with forest age classes. However, analysis of variance suggested that NDVI differences were not detectable for successional forests older than approximately 15-20 years. Also, biomass differences in young successional tropical forest were not detectable using the NDVI. The vegetation index does not appear to be a good predictor of stand structure variables (e.g., height, diameter of main stem) or total biomass in uneven age, mixed broadleaf forest. Good correlation between the vegetation index and low biomass in even age pine plantations were achieved for a warm temperate study site. The implications of the study for the use of NDVI for forest structure and biomass estimation are discussed.

Sader, Steven A.↗

NASA NTRS1995

The formation of protostellar disks. 2: Disks around intermediate-mass stars

Hydrodynamical calculations of the evolution of a collapsing, rotating axisymmetric 10 solar masses molecular clump, including the effects of radiative acceleration but without magnetic fields, are represented. The initial cloud is assumed to be uniformly rotating, centrally condensed sphere with rho is proportional to r(exp -2). Several cases are considered, in which both the overall clump size and the total amount of angular momentum are varied. The calculations show how a warm, quasi-hydrostatic disk surrounding a central unresolved core of only a few solar masses forms and grows in size and mass. The disk is encased in two distinct accretion shock fronts, both of which are several scale heights above the equatorial plane. At the end of the calculation of our standard case, the central unresolved region is found to have a mass of 2.7 solar masses and a ratio of rotational to gravitational energy of approximately 0.45, sufficiently large to be unstable to nonaxisymmetric perturbations. In addition, the inner portions of the disk containing most of the mass are unstable according to the local Toomre criterion, implying that also in this region nonaxisymmetric perturbations will lead to rapid evolution. Under the assumption that gravitational torques would transport angular momentum out of this region, a central core of less than or approximately 8 solar masses with a stable disk of greater than or approximately = 2 solar masses should result. Frequency-dependent radiative transfer calculations of the standard case at selected ages show how the continuum spectrum of the structure depends on the disk's orientation and age and how the observed isophotal contours vary with wavelength. Because of the strong dependence on viewing angle, continuum spectra alone should not be used to estimate the evolutionary stage of development of these objects. Comparable results were obtained for the other cases considered.

Yorke, Harold W.↗

NASA NTRS1998

The Problem of Hipparcos Distances to Open Clusters: Constraints from Multicolor a Main-Sequence Fitting - Report 1

Parallax data from the Hipparcos mission allow the direct distance to open clusters to be compared with the distance inferred from main-sequence (MS) fitting. There are surprising differences between the two distance measurements. indicating either the need for changes in the cluster compositions or reddening, underlying problems with the technique of MS fitting, or systematic errors in the Hipparcos parallaxes at the 1 mas level. We examine the different possibilities, focusing on MS fitting in both metallicity-sensitive B-V and metallicity-insensitive V-I for five well-studied systems (the Hyades, Pleiades, alpha Per, Praesepe, and Coma Ber). The Hipparcos distances to the Hyades and alpha Per are within 1 sigma of the MS-fitting distance in B-V and V-I, while the Hipparcos distances to Coma Ber and the Pleiades are in disagreement with the MS-fitting distance at more than the 3 sigma level. There are two Hipparcos measurements of the distance to Praesepe; one is in good agreement with the MS-fitting distance and the other disagrees at the 2 sigma level. The distance estimates from the different colors are in conflict with one another for Coma but in agreement for the Pleiades. Changes in the relative cluster metal abundances, age related effects, helium, and reddening are shown to be unlikely to explain the puzzling behavior of the Pleiades. We present evidence for spatially dependent systematic errors at the 1 mas level in the parallaxes of Pleiades stars. The implications of this result are discussed.

Pinsonneault, Marc H.↗