Opportunity cost and prudentiality : a representative-agent model of futures clearinghouse behavior

Includes bibliographic references (p. 31-38)

Opportunity cost and prudentiality : an analysis of futures clearinghouse behavior

Margin deposits, which serve as collateral to protect the clearinghouse, are typically the most important tool for risk management. The authors develop a model that explains how creating a futures clearinghouse may allow traders simultaneously to reduce both the risk of default and the total amount of margin that members post. Optimal margin levels are determined by the need to balance the deadweight costs of default against the opportunity cost of holding additional margin. Both costs are a consequence of market participants'imperfect access to capital markets. The simultaneous reduction in default risk and in the opportunity cost of margin deposits is possible because the creation of the clearinghouse facilitates multilateral netting. The authors characterize the conditions under which multilateral netting will dominate bilateral netting. They also show that it is credible for the clearinghouse to expel members who default, further reducing the risk of default. Finally, they show that it may (but need not) be optimal for the clearinghouse to monitor the financial condition of its members. If monitoring occurs, it will reduce the amount of margin required, but need not affect the probability of default. The empirical tests run by the authors indicate that the opportunity cost of margin plays an important role in determining margin. The relationship between volatility and margins indicates that participants face an upward-sloping opportunity cost for margin, which appears to more than offset the effects that monitoring and expulsion would be expected to have on margin setting.Environmental Economics&Policies,Banks&Banking Reform,International Terrorism&Counterterrorism,Economic Theory&Research,Insurance&Risk Mitigation

Time-resolved Ultraviolet Spectroscopy of the M-dwarf GJ 876 Exoplanetary System

Extrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide more realistic inputs for atmospheric models of planets orbiting low-mass stars, we present new near- and far-ultraviolet (NUV and FUV) spectroscopy of the M-dwarf exoplanet host GJ 876 (M4V). Using the COS and STIS spectrographs aboard the Hubble Space Telescope, we have measured the 1150-3140A spectrum of GJ 876. We have reconstructed the stellar HI LyA emission line profile, and find that the integrated LyA flux is roughly equal to the rest of the integrated flux (1150-1210A + 1220-3140A) in the entire ultraviolet bandpass (F(LyA)/F(FUV+NUV) ~0.7). This ratio is ~ 2500x greater than the solar value. We describe the ultraviolet line spectrum and report surprisingly strong fluorescent emission from hot H2 (T(H2) > 2000 K). We show the light-curve of a chromospheric + transition region flare observed in several far-UV emission lines, with flare/quiescent flux ratios >= 10. The strong FUV radiation field of an M-star (and specifically LyA) is important for determining the abundance of O2 -- and the formation of biomarkers -- in the lower atmospheres of Earth-like planets in the habitable zones of low-mass stars.Comment: 6 pages, 4 figures. ApJL accepte

From e-Portfolio of competencies towards processes of accompanied academic teaching and learning

En el marco de la formación inicial para la docencia, se implementa el ePortafolio de competencias como dispositivo para apoyar el desarrollo profesional de los estudiantes en prácticas, que realizan una escritura reflexiva con acompañamiento. Nuestro artículo presenta dos estudios: uno desarrollado en la Universidad de Lleida, España y el otro en la Universidad de Sherbrooke, Quebec, Canadá, con estudiantes en prácticas de 2º y 4º curso, respectivamente, que editan sus ePortfolios de competencias profesionales. Se explican las características de las plataformas y del dispositivo. Seguidamente, se presenta la metodología y los resultados del estudio. Sobre estos, subrayaremos la importancia del acompañamiento y la orientación, dos aspectos esperados por los practicantes, el compromiso en la escritura reflexiva y el desarrollo profesional próximo.No marco da formação inicial para a docência, implementa-se o ePortafolio de concorrências como dispositivo para apoiar o desenvolvimento profissional dos estudantes em práticas, que realizam uma escritura reflexiva com acompanhamento. Nosso artigo apresenta dois estudos: um desenvolvido na Universidade de Lleida, Espanha e o outro na Universidade de Sherbrooke, Quebec, Canadá, com estudantes em práticas de 2º e 4º curso, respectivamente, que editam seus ePortfolios de concorrências profissionais. Explicam-se as características das plataformas e do dispositivo. Seguidamente, apresenta-se a metodologia e os resultados do estudo. Sobre estes, sublinharemos a importância do acompanhamento e a orientação, dois aspectos esperados pelos praticantes, o compromisso na escritura reflexiva e o desenvolvimento profissional próximo.In teacher education programs, the resource of ePortfolio of competencies is used in order to support the professional development of student teachers with the help of reflexive writing. This article presents two studies, one realized at Lleida University with 2nd year student teachers and the other one at Sherbrooke University with 4th year student teachers who have produced their own ePortfolio of professional competencies. The attributes of the digital platforms are explained. The methodology and some results of the studies are reflected in a constructed dialogue. Among the results obtained are underlined, the importance of scaffolding advice wished by student teachers, investment in reflexive writing and proximal professional development

Multiwavelength Observations of Swift J1753.5-0127

We present contemporaneous X-ray, ultraviolet, optical and near-infrared observations of the black hole binary system, Swift J1753.5-0127, acquired in 2012 October. The UV observations, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope, are the first UV spectra of this system. The dereddened UV spectrum is characterized by a smooth, blue continuum and broad emission lines of CIV and HeII. The system was stable in the UV to <10% during our observations. We estimated the interstellar reddening by fitting the 2175 A absorption feature and fit the interstellar absorption profile of Ly$\alpha$ to directly measure the neutral hydrogen column density along the line of sight. By comparing the UV continuum flux to steady-state thin accretion disk models, we determined upper limits on the distance to the system as a function of black hole mass. The continuum is well fit with disk models dominated by viscous heating rather than irradiation. The broadband spectral energy distribution shows the system has declined at all wavelengths since previous broadband observations in 2005 and 2007. If we assume that the UV emission is dominated by the accretion disk the inner radius of the disk must be truncated at radii above the ISCO to be consistent with the X-ray flux, requiring significant mass loss from outflows and/or energy loss via advection into the black hole to maintain energy balance.Comment: To appear in the Ap