Near-Earth Asteroid Satellite Spins Under Spin-Orbit Coupling

We develop a fourth-order numerical integrator to simulate the coupled spin and orbital motions of two rigid bodies having arbitrary mass distributions under the influence of their mutual gravitational potential. We simulate the dynamics of components in well-characterized binary and triple near-Earth asteroid systems and use surface of section plots to map the possible spin configurations of the satellites. For asynchronous satellites, the analysis reveals large regions of phase space where the spin state of the satellite is chaotic. For synchronous satellites, we show that libration amplitudes can reach detectable values even for moderately elongated shapes. The presence of chaotic regions in the phase space has important consequences for the evolution of binary asteroids. It may substantially increase spin synchronization timescales, explain the observed fraction of asynchronous binaries, delay BYORP-type evolution, and extend the lifetime of binaries. The variations in spin rate due to large librations also affect the analysis and interpretation of lightcurve and radar observations.Comment: 12 pages, 11 figures, Published in A

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

Limits to ion energy control in high density glow discharges: Measurement of absolute metastable ion concentrations

Unprecedented demands for uniformity, throughput, anisotropy, and damage control in submicron pattern transfer are spurring development of new, low pressure, high charge density plasma reactors. Wafer biasing, independent of plasma production in these new systems is intended to provide improved ion flux and energy control so that selectivity can be optimized and damage can be minimized. However, as we show here, an inherent property of such discharges is the generation of significant densities of excited, metastable ionic states that can bombard workpiece surfaces with higher translational and internal energy. Absolute metastable ion densities are measured using the technique of self-absorption, while the corresponding velocity distributions and density scaling with pressure and electron density are measured using laser-induced fluorescence. For a low pressure, helicon-wave excited plasma, the metastable ion flux is at least 24% of the total ion flux to device surfaces. Because the metastable ion density scales roughly as the reciprocal of the pressure and as the square of the electron density, the metastable flux is largest in low pressure, high charge density plasmas. This metastable ion energy flux effectively limits ion energy and flux control in these plasma reactors, but the consequences for etching and deposition of thin films depend on the material system and remain an open question

Possibilities and Prospects: The Debate Over a Guaranteed Income

The idea of a guaranteed income has a long and respectable history in Canadian political and economic thought. Recently, in the face of both wide criticism of the Canadian income security system and growing recognition of the unacceptability of current poverty rates, there has been a resurgence in calls for implementation of a Canadian guaranteed income. But the idea is a controversial one; progressive activists, academics, and politicians disagree about the desirability and the practicality of a guaranteed income. This report: Traces the history of guaranteed income proposals in Canada; Catalogues both the most common reasons supporting advocacy of a guaranteed income and the most telling concerns raised by the notion; Provides an overview of basic dimensions along which proposals for a guaranteed income differ and sets out models that capture much of the range of proposals in the current debate; and Suggests a number of other social welfare measures that should be central elements of any reform program, but that guaranteed income debates often ignore. The term “guaranteed income” refers to a specific although broad category of social reform. As a starting place for discussion, the idea of a guaranteed income is used to signal reform proposals that advocate some variant of an income benefit scheme in which the state provides a minimum level of basic income on a continuing basis to every adult, irrespective of personal circumstances or need, with no or very few conditions attached. Proponents of a guaranteed income cite a range of reasons supporting the idea: A fix to poverty; Liberty and individual opportunity; Social and democratic citizenship; Gender equality; Shared social ownership; A flexible and just labour market; and Environmental sustainability

Slow carbon and nutrient accumulation in trees established following fire exclusion in the southwestern United States.

Increasing tree density that followed fire exclusion after the 1880s in the southwestern United States may have also altered nutrient cycles and led to a carbon (C) sink that constitutes a significant component of the U.S. C budget. Yet, empirical data quantifying century-scale changes in C or nutrients due to fire exclusion are rare. We used tree-ring reconstructions of stand structure from five ponderosa pine-dominated sites from across northern Arizona to compare live tree C, nitrogen (N), and phosphorus (P) storage between the 1880s and 1990s. Live tree biomass in the 1990s contained up to three times more C, N, and P than in 1880s. However, the increase in C storage was smaller than values used in recent U.S. C budgets. Furthermore, trees that had established prior to the 1880s accounted for a large fraction (28-66%) of the C, N, and P stored in contemporary stands. Overall, our century-scale analysis revealed that forests of the 1880s were on a trajectory to accumulate C and nutrients in trees even in the absence of fire exclusion, either because growing conditions became more favorable after the 1880s or because forests in the 1880s included age or size cohorts poised for accelerated growth. These results may lead to a reduction in the C sink attributed to fire exclusion, and they refine our understanding of reference conditions for restoration management of fire-prone forests

Planetary Bistatic Radar

Planetary radar observations offer the potential for probing the properties of characteristics of solid bodies throughout the inner solar system and at least as far as the orbit of Saturn. In addition to the direct scientific value, precise orbital determinations can be obtained from planetary radar observations, which are in turn valuable for mission planning or spacecraft navigation and planetary defense. The next-generation Very Large Array would not have to be equipped with a transmitter to be an important asset in the world's planetary radar infrastructure. Bistatic radar, in which one antenna transmits (e.g., Arecibo or Goldstone) and another receives, are used commonly today, with the Green Bank Telescope (GBT) serving as a receiver. The improved sensitivity of the ngVLA relative to the GBT would improve the signal-to-noise ratios on many targets and increase the accessible volume specifically for asteroids. Goldstone-ngVLA bistatic observations would have the potential of rivaling the sensitivity of Arecibo, but with much wider sky access.Comment: 11 pages, 2 figures, To be published in the ASP Monograph Series, "Science with a Next-Generation VLA", ed. E. J. Murphy (ASP, San Francisco, CA

Capabilities of Earth-based radar facilities for near-Earth asteroid observations

We evaluated the planetary radar capabilities at Arecibo, the Goldstone 70-m DSS-14 and 34-m DSS-13 antennas, the 70-m DSS-43 antenna at Canberra, the Green Bank Telescope, and the Parkes Radio Telescope in terms of their relative sensitivities and the number of known near-Earth asteroids (NEAs) detectable per year in monostatic and bistatic configurations. In the 2015 calendar year, monostatic observations with Arecibo and DSS-14 were capable of detecting 253 and 131 NEAs respectively, with signal-to-noise ratios (SNRs) greater than 30/track. Combined, the two observatories were capable of detecting 276 NEAs. Of these, Arecibo detected 77 and Goldstone detected 32, or 30% and 24% the numbers that were possible. The two observatories detected an additional 18 and 7 NEAs respectively, with SNRs of less than 30/track. This indicates that a substantial number of potential targets are not being observed. The bistatic configuration with DSS-14 transmitting and the Green Bank Telescope receiving was capable of detecting about 195 NEAs, or ~50% more than with monostatic observations at DSS-14. Most of the detectable asteroids were targets of opportunity that were discovered less than 15 days before the end of their observing windows. About 50% of the detectable asteroids have absolute magnitudes > 25, which corresponds diameters < ~30 m.Comment: 12 pages, 7 figures, Accepted to A

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&

Mass and density of B-type asteroid (702) Alauda

Observations with the adaptive optics system on the Very Large Telescope reveal that outer main belt asteroid (702) Alauda has a small satellite with primary to secondary diameter ratio of $\sim$56. The secondary revolves around the primary in 4.9143 $\pm$ 0.007 days at a distance of 1227 $\pm$ 24 km, yielding a total system mass of (6.057 $\pm$ 0.36) $\times$ 10$^{18}$ kg. Combined with an IRAS size measurement, our data yield a bulk density for this B-type asteroid of 1570 $\pm$ 500 kg~m$^{-3}$.Comment: In press, ApJ 2011. 6 pages, 4 figure

Standardized on-road tests assessing fitness-to-drive in people with cognitive impairments: A systematic review.

The on-road assessment is the gold standard because of its ecological validity. Yet existing instruments are heterogeneous and little is known about their psychometric properties. This study identified existing on-road assessment instruments and extracted data on psychometric properties and usability in clinical settings. A systematic review identified studies evaluating standardized on-road evaluation instruments adapted for people with cognitive impairment. Published articles were searched on PubMed, CINHAL, PsycINFO, Web of Science, and ScienceDirect. Study quality and the level of evidence were assessed using the COSMIN checklist. The collected data were synthetized using a narrative approach. Usability was subjectively assessed for each instrument by extracting information on acceptability, access, cost, and training. The review identified 18 published studies between 1994 and 2016 that investigated 12 different on-road evaluation instruments: the Performance-Based Driving Evaluation, the Washington University Road Test, the New Haven, the Test Ride for Practical Fitness to Drive, the Rhode Island Road Test, the Sum of Manoeuvres Score, the Performance Analysis of Driving Ability, the Composite Driving Assessment Scale, the Nottingham Neurological Driving Assessment, the Driving Observation Schedule, the Record of Driving Errors, and the Western University's On-road Assessment. Participants were mainly male (64%), between 48 and 80 years old, and had a broad variety of cognitive disorders. Most instruments showed reasonable psychometric values for internal consistency, criterion validity, and reliability. However, the level of evidence was poor to support any of the instruments given the low number of studies for each. Despite the social and health consequences of decisions taken using these instruments, little is known about the value of a single evaluation and the ability of instruments to identify expected changes. None of the identified on-road evaluation instruments seem currently adapted for clinical settings targeting rehabilitation and occupational priorities rather than road security alone. PROSPERO registration number CRD42018103276