Improved Algorithms for Radar-based Reconstruction of Asteroid Shapes

We describe our implementation of a global-parameter optimizer and Square Root Information Filter (SRIF) into the asteroid-modelling software SHAPE. We compare the performance of our new optimizer with that of the existing sequential optimizer when operating on various forms of simulated data and actual asteroid radar data. In all cases, the new implementation performs substantially better than its predecessor: it converges faster, produces shape models that are more accurate, and solves for spin axis orientations more reliably. We discuss potential future changes to improve SHAPE's fitting speed and accuracy.Comment: 12 pages, 9 figure

The Albedo, Size, and Density of Binary Kuiper Belt Object (47171) 1999 TC36

We measured the system-integrated thermal emission of the binary Kuiper Belt Object 1999 TC36 at wavelengths near 24 and 70 microns using the Spitzer space telescope. We fit these data and the visual magnitude using both the Standard Thermal Model and thermophysical models. We find that the effective diameter of the binary is 405 km, with a range of 350 -- 470 km, and the effective visible geometric albedo for the system is 0.079 with a range of 0.055 -- 0.11. The binary orbit, magnitude contrast between the components, and system mass have been determined from HST data (Margot et al., 2004; 2005a; 2005b). Our effective diameter, combined with that system mass, indicate an average density for the objects of 0.5 g/cm3, with a range 0.3 -- 0.8 g/cm3. This density is low compared to that of materials expected to be abundant in solid bodies in the trans-Neptunian region, requiring 50 -- 75% of the interior of 1999 TC36 be taken up by void space. This conclusion is not greatly affected if 1999 TC36 is ``differentiated'' (in the sense of having either a rocky or just a non-porous core). If the primary is itself a binary, the average density of that (hypothetical) triple system would be in the range 0.4 -- 1.1 g/cm3, with a porosity in the range 15 -- 70%.Comment: ApJ, in press (May, 2006

Measuring the impact of a mindfulness-based stress reduction intervention on perceived stress and study skills of social work graduate students

This multi-component study incorporated the following: (1) an integrated study measuring the impact of a Mindfulness-Based Stress Reduction intervention (MBSR) on potential stressors, appraised stress levels and adaptation to stress of MSW students enrolled in the Louisiana State University School of Social Work through a pretest posttest group design using time-series data to evaluate meditation practice; (2) a pretest posttest group design which examined changes in self-regulated learning skills; and (3) a cross-sectional survey which explored students self-reported reasons for not participating in the MBSR randomized control group study offered prior to the current study. Sample size for the integrated study was 12 females at pretest and 3 at posttest. Sample size for the survey was 56 male and female MSW students. Descriptive univariate statistics were used to summarize data addressing subjects’ potential stressors, appraised stressful situations, and adaptation to stress. Univariate statistics were used to summarize data collected about subjects’ implementation of self-reported, self-regulated learning skills. Time-series data for the pretest posttest group design were plotted on graphs for visual analysis of Psychological Stress measure (PSM-9) stress scores and subjects’ time spent meditating. A strong association emerged between Perceived Stress Scale (PSS) and PSM-9 scores, indicating that high levels of appraised stress were associated with high levels of adaptation to stress. A negative association emerged between PSS and Motivational Strategies for Learning Questionnaire (MSLQ) scores, indicating that higher stress levels were related to lower self-regulated learning skills. In spite of extreme data, results of the group study implementing a pretest posttest group design suggested increases in meditation time and decreases in stress levels during the intervention phase for two of three subjects. Associations emerged between enrollment in field internship and lack of interest in the study, lack of interest in participation in the study, and the inability to commit to daily meditation time. Low annual income and having dependent children in the home were associated with students’ inability to commit to daily meditation time

Yarkovsky Drift Detections for 247 Near-Earth Asteroids

The Yarkovsky effect is a thermal process acting upon the orbits of small celestial bodies, which can cause these orbits to slowly expand or contract with time. The effect is subtle (da/dt ~ 10^-4 au/My for a 1 km diameter object) and is thus generally difficult to measure. We analyzed both optical and radar astrometry for 600 near-Earth asteroids (NEAs) for the purpose of detecting and quantifying the Yarkovsky effect. We present 247 NEAs with measured drift rates, which is the largest published set of Yarkovsky detections. This large sample size provides an opportunity to examine the Yarkovsky effect in a statistical manner. In particular, we describe two independent population-based tests that verify the measurement of Yarkovsky orbital drift. First, we provide observational confirmation for the Yarkovsky effect's theoretical size dependence of 1/D, where D is diameter. Second, we find that the observed ratio of negative to positive drift rates in our sample is 2.34, which, accounting for bias and sampling uncertainty, implies an actual ratio of $2.7^{+0.3}_{-0.7}$. This ratio has a vanishingly small probability of occurring due to chance or statistical noise. The observed ratio of retrograde to prograde rotators is two times lower than the ratio expected from numerical predictions from NEA population studies and traditional assumptions about the sense of rotation of NEAs originating from various main belt escape routes. We also examine the efficiency with which solar energy is converted into orbital energy and find a median efficiency in our sample of 12%. We interpret this efficiency in terms of NEA spin and thermal properties.Comment: 27 pages, 9 figures, published in the Astronomical Journal, 159, 92, 202

Arterial Elastin as Seen with Scanning Electron Microscopy: A Review

All large arteries contain elastin, collagen, and muscle which can be seen with light microscopy and transmission electron microscopy. Elastin forms an internal elastic lamina (IEL) in all arteries, but also forms multiple fenestrated sheets in the media of the aorta and other large arteries. The fenestrations in the media are larger than those in the IEL. The adventitial elastin is more fibrous and often contains tubular elastin surrounding vasa vasorum when prepared by removing all non-elastin by placing the aorta in 0.1 N NaOH at 70-75°C for five hours. The fenestrations are larger near branches and in an experimentally created poststenotic dilatation. Atherosclerosis appears associated with both new elastin formation in early atherosclerosis and elastolysis in late disease

A ring as a model of the main belt in planetary ephemerides

We assess the ability of a solid ring to model a global perturbation induced by several thousands of main-belt asteroids. The ring is first studied in an analytical framework that provides an estimate of all the ring's parameters excepting mass. In the second part, numerically estimated perturbations on the Earth-Mars, Earth-Venus, and Earth-Mercury distances induced by various subsets of the main-belt population are compared with perturbations induced by a ring. To account for large uncertainties in the asteroid masses, we obtain results from Monte Carlo experiments based on asteroid masses randomly generated according to available data and the statistical asteroid model. The radius of the ring is analytically estimated at 2.8 AU. A systematic comparison of the ring with subsets of the main belt shows that, after removing the 300 most perturbing asteroids, the total main-belt perturbation of the Earth-Mars distance reaches on average 246 m on the 1969-2010 time interval. A ring with appropriate mass is able to reduce this effect to 38 m. We show that, by removing from the main belt ~240 asteroids that are not necessarily the most perturbing ones, the corresponding total perturbation reaches on average 472 m, but the ring is able to reduce it down to a few meters, thus accounting for more than 99% of the total effect.Comment: 18 pages, accepted in A&

Live Organ and Tissue Transplants from Minor Donors in Massachusetts

This article examines the system of providing court approval for organ and tissue transplants from minor donors as it operates in Massachusetts. It focuses principally on the substantive interests of prospective donors and on the extent to which the current procedures afford them adequate protection. It begins by examining the requirement of consent and demonstrates the necessity of judicial authorization of minor donors\u27 participation in transplant procedures. Next, it analyzes the current Massachusetts practice and assess its capacity to afford minor donors adequate protection from the possible dangers of serving as an organ or tissue donor. It suggests that the Massachusetts system has not adequately protected minor transplant donors.This article concludes by proposing a number of reforms in the present practice to increase its capacity to protect minor donors