10,411 research outputs found

    Modeling the coma of 2060 Chiron

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    Observations of comet-like activity and a resolved coma have established that 2060 Chiron is a comet. Determinations of its radius range from 65 to 200 km. This unusually large size for a comet suggests that the atmosphere of Chiron is intermediate to the tightly bound, thin atmospheres typical of planets and satellite and the greatly extended atmospheres in free expansion typical of cometary comae. Under certain conditions it may gravitationally bind an atmosphere that is thick compared to its size, while a significant amount of gas escapes to an extensive exosphere. These attributes coupled with reports of sporadic outbursts at large heliocentric distances and the identification of CN in the coma make Chiron a challenging object to model. Simple models of gas production and the dusty coma were recently presented but a general concensus on many basic features has not emerged. Development was begun on a more complete coma model of Chiron. The objectives are to report progress on this model and give the preliminary results for understanding Chiron

    NICMOS Imaging of the Dusty Microjansky Radio Source VLA J123642+621331 at z = 4.424

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    We present the discovery of a radio galaxy at a likely redshift of z = 4.424 in one of the flanking fields of the Hubble Deep Field. Radio observations with the VLA and MERLIN centered on the HDF yielded a complete sample of microjansky radio sources, of which about 20% have no optical counterpart to I < 25 mag. In this Letter, we address the possible nature of one of these sources, through deep HST NICMOS images in the F110W (J) and F160W (H) filters. VLA J123642+621331 has a single emission line at 6595-A, which we identify with Lyman-alpha at z = 4.424. We argue that this faint (H = 23.9 mag), compact (r = 0.2 arcsec), red (I - K = 2.0) object is most likely a dusty, star-forming galaxy with an embedded active nucleus.Comment: Accepted for publication in Astrophysical Journal Letters. 11 pages, 4 figures, uses aastex v5.0 and psfi

    Dual Instantons

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    We show how to map the Belavin-Polyakov instantons of the O(3)-nonlinear σ\sigma-model to a dual theory where they then appear as nontopological solitons. They are stationary points of the Euclidean action in the dual theory, and moreover, the dual action and the O(3)-nonlinear σ\sigma-model action agree on shell.Comment: 13 page

    What Goods Do Countries Trade? A Quantitative Exploration of Ricardo’s Ideas

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    The Ricardian model predicts that countries should produce and export relatively more in industries in which they are relatively more productive. Though one of the most celebrated insights in the theory of international trade, this prediction has received little attention in the empirical literature since the mid-1960s. The main reason behind this lack of popularity is the absence of clear theoretical foundations to guide the empirical analysis. Building on the seminal work of Eaton and Kortum (“Technology, Geography, and Trade”, Econometrica, 70, 1741–1779 2002), we offer such foundations and use them to quantify the importance of Ricardian comparative advantage. In the process, we also provide a theoretically consistent alternative to Balassa's (1965, “An Empirical Demonstration of Classical Comparative Cost Theory”, Review of Economics and Statistics, 45, 231–238) well-known index of “revealed comparative advantage”

    Composite Fermions with Orbital Magnetization

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    For quantum Hall systems, in the limit of large magnetic field (or equivalently small electron band mass mbm_b), the static response of electrons to a spatially varying magnetic field is largely determined by kinetic energy considerations. This response is not correctly given in existing approximations based on the Fermion Chern-Simons theory of the partially filled Landau level. We remedy this problem by attaching an orbital magnetization to each fermion to separate the current into magnetization and transport contributions, associated with the cyclotron and guiding center motions respectively. This leads to a Chern-Simons Fermi liquid description of the ν=12m\nu=\frac{1}{2m} state which correctly predicts the mbm_b dependence of the static and dynamic response in the limit mb0m_b \rightarrow 0.Comment: 4 pages, RevTeX, no figure
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