Photophoresis boosts giant planet formation

In the core accretion model of giant planet formation, a solid protoplanetary core begins to accrete gas directly from the nebula when its mass reaches about 5 earth masses. The protoplanet has at most a few million years to reach runaway gas accretion, as young stars lose their gas disks after 10 million years at the latest. Yet gas accretion also brings small dust grains entrained in the gas into the planetary atmosphere. Dust accretion creates an optically thick protoplanetary atmosphere that cannot efficiently radiate away the kinetic energy deposited by incoming planetesimals. A dust-rich atmosphere severely slows down atmospheric cooling, contraction, and inflow of new gas, in contradiction to the observed timescales of planet formation. Here we show that photophoresis is a strong mechanism for pushing dust out of the planetary atmosphere due to the momentum exchange between gas and dust grains. The thermal radiation from the heated inner atmosphere and core is sufficient to levitate dust grains and to push them outward. Photophoresis can significantly accelerate the formation of giant planets.Comment: accepted in Astronomy and Astrophysics, 201

Detection of Pulsed X-ray Emission from PSR B1706-44

We report the first detection of pulsed X-ray emission from the young, energetic radio and Gamma-ray pulsar PSR B1706-44. We find a periodic signal at a frequency of f = 9.7588088 +/- 0.0000026 Hz (at epoch 51585.34104 MJD), consistent with the radio ephemeris, using data obtained with the High Resolution Camera on-board the Chandra X-ray Observatory}. The probability that this detection is a chance occurrence is 3.5E-5 as judged by the Rayleigh test. The folded light curve has a broad, single-peaked profile with a pulsed fraction of 23% +/- 6%. This result is consistent the ROSAT PSPC upper limit of < 18% after allowing for the ability of Chandra to resolve the pulsar from a surrounding synchrotron nebula. We also fitted Chandra spectroscopic data on PSR B1706-44, which require at least two components, e.g., a blackbody of temperature T(infinity) between 1.51E6 K and 1.83E6 K and a power-law of Gamma = 2.0 +/- 0.5. The blackbody radius at the nominal 2.5 kpc distance is only R(infinity) = 3.6 +/- 0.9 km, indicating either a hot region on a cooler surface, or the need for a realistic atmosphere model that would allow a lower temperature and larger area. Because the power-law and blackbody spectra each contribute more than 23% of the observed flux, it is not possible to decide which component is responsible for the modulation in the spectrally unresolved light curve.Comment: 6 pages, 4 figures, Latex, emulateapj. Published version. Includes an updated radio ephemeris and presents the absolute radio/X-ray phase alignmen

Inefficient education spending in public school districts: a case for consolidation

This paper estimates scale economies for Arkansas school districts. Large economies of scale exist in teacher salary and supply costs, as well as total costs. Our results suggest that districts, especially rural districts, would experience measurable cost-savings from consolidation. We simulate a hypothetical rural school district consolidation to obtain cost-saving estimates from consolidation. Simulations indicate that districts could save an average of 34 percent in average variable costs. At the state level, consolidation of rural districts in Arkansas could annually save million. However, consolidation of school districts may increase various implicit costs to students and local communities.Education

Book Review: Cuban Convents in the Age of Enlightened Reform, 1761-1807

Review of Cuban Convents in the Age of Enlightened Reform, 1761-1807 by John J. Clune, Jr

Kant\u27s theory of the social contract.

The thesis of my dissertation is that Kant\u27s theory of the social contract, which is the central concept of his political philosophy, provides, when suitably reconstructed, an adequate theoretical foundation for liberal democracy. I take liberal democracy to consist of three components: first, the rule of law; second, democratic self-rule (either representative, direct, or some combination of the two); and third, the recognition and institutional guarantee of the rights of individuals. In the dissertation, I take as my starting point Kant\u27s conception of autonomy. For Kant, the idea of the social contract explains how individual moral agents can maintain their autonomy in the context of community. The social contract resolves the conflict between moral autonomy and political authority by defining a model of civil society in which free, equal, and independent rational agents collectively legislate the public laws that are to govern their external relations, which are essentially property relations. Ideal civil society, then, is a condition of maximum equal freedom for rational agents who interact with one another

Mental Health Policies and Practices: Student Services Leaders Connect the Dots

This research explored the perceptions of student affairs and services (SAS) leaders in relation to the effectiveness of policies and practices that assist students with mental health problems. Many students enter post-secondary schools with existing conditions that may or may not be clinically recognized. These mental health impairments and disabilities can manifest as permanent, sporadic, or temporary impairments. The emergence and magnitude of mental illness in early adulthood make post-secondary institutions key environments in which to intervene more proactively. Providing access to comprehensive mental health supports is vital for meeting students’ increasing needs. To investigate how post-secondary leaders are responding to these needs, a qualitative single case study was conducted at one college in Ontario. Thematic analysis was used to examine transcripts and documentary evidence. Researcher notes served as a third source of data. Four participant-derived themes emerged in this study. They were (a) Developing Contextual Understanding: Complexity of Needs; (b) Developing the Culture: It Takes the Whole Community; (c) Developing People and Supports: On the Same Page; and (d) Developing the Organization: Connecting the Dots. These areas were viewed as chief priorities for ensuring learning, success & positive mental health. There were four major findings: (a) Students’ mental health affected learning & success. Their needs were complex, growing & not being fully met; (b) Mental health policies & practices must be responsive to individual & collective needs & driven by a student-centred, contextually specific approach & shared commitment to success; (c) Some students & faculty misunderstood mental health. Student services leaders played a key role in filling this gap by initiating data-driven preventive & promotional measures; and (d) The lack of a mental health policy acted as a barrier to meeting students’ needs. The SAS leaders proposed three key areas for improvement at the college: (a) expanding students’ awareness of mental health and the support alternatives; (b) building the faculty’s knowledge of mental health, the accommodation process, and the available mental health services; and (c) introducing a college mental health policy centred on these knowledge mobilization and capacity building efforts. SAS leaders have been identified as important agents for introducing awareness-raising activities, reducing barriers, and providing resources that positively influence students’ mental health. This research contributes knowledge to the mental health and student services disciplines. The goals were to inform policies and practices and provide guidance for developing and implementing services and supports that are devoted to college students with mental health impairments and disabilities