6,288 research outputs found

    Search for Dust Emission from (24) Themis Using the Gemini-North Telescope

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    We report the results of a search for a dust trail aligned with the orbit plane of the large main-belt asteroid (24) Themis, which has been reported to have water ice frost on its surface. Observations were obtained with the GMOS instrument on the Gemini-North Observatory in imaging mode, where we used a chip gap to block much of the light from the asteroid, allowing us to take long exposures while avoiding saturation by the object. No dust trail is detected within 2' of Themis to a 3-sigma limiting surface brightness magnitude of 29.7 mag/arcsec^2, as measured along the expected direction of the dust trail. Detailed consideration of dust ejection physics indicates that particles large enough to form a detectable dust trail were unlikely to be ejected as a result of sublimation from an object as large as Themis. We nonetheless demonstrate that our observations would have been capable of detecting faint dust emission as close as 20" from the object, even in a crowded star field. This approach could be used to conduct future searches for sublimation-generated dust emission from Themis or other large asteroids closer to perihelion than was done in this work. It would also be useful for deep imaging of collisionally generated dust emission from large asteroids at times when the visibility of dust features are expected to be maximized, such as during orbit plane crossings, during close approaches to the Earth, or following detected impact events.Comment: 11 pages, 4 figures, accepted for publication in PAS

    Aspects of oviposition in the fowl

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    Each part of the hen's oviduct possesses to some extent, the properties of secretion and. moti- lity. Those secretions of the oviduct which contri bute to egg formation have been studied by several authors but the mechanics of egg formation have so far received little attention. The oviduct may be considered to show two types of movement: relatively slow, propulsive movements by means of which the egg is moved as far as the uterus, and relatively quick, expulsive movements which constitute the process of oviposition. The object of this work is to describe some aspects of the physiology of these latter movements, to suggest possible ways in which they are controlled and to compare them with similar movements observed during mammalian parturition

    A derivative formula for the free energy function

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    We consider bond percolation on the Zd{\bf Z}^d lattice. Let MnM_n be the number of open clusters in B(n)=[−n,n]dB(n)=[-n, n]^d. It is well known that EpMn/(2n+1)dE_pM_n / (2n+1)^d converges to the free energy function κ(p)\kappa(p) at the zero field. In this paper, we show that σp2(Mn)/(2n+1)d\sigma^2_p(M_n)/(2n+1)^d converges to −(p2(1−p)+p(1−p)2)κ′(p)-(p^2(1-p)+p(1-p)^2)\kappa'(p).Comment: 8 pages 1 figur
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