The Sizes of Kuiper Belt Objects

One of the most fundamental problems in the study of Kuiper belt objects (KBOs) is to know their true physical size. Without knowledge of their albedos we are not able to distinguish large and dark from small and bright KBOs. Spitzer produced rough estimates of the sizes and albedos of about 20 KBOs, and the Herschel space telescope will improve on those initial measurements by extending the sample to the ~150 brightest KBOs. SPICA's higher sensitivity instruments should allow us not only to broaden the sample to smaller KBOs but also to achieve a statistically significant sample of KBO thermal light curves (Herschel will measure only six objects). A large sample covering a broad range of sizes will be key to identify meaningful correlations between size and other physical and surface properties that constrain the processes of formation and evolution of the solar system.Comment: 6 pages, 6 figures, Proc. Workshop "The Space Infrared Telescope for Cosmology and Astrophysics: Revealing the Origins of Planets and Galaxies

Time-Resolved Near-Infrared Photometry of Extreme Kuiper Belt Object Haumea

We present time-resolved near-infrared (J and H) photometry of the extreme Kuiper belt object (136108) Haumea (formerly 2003 EL61) taken to further investigate rotational variability of this object. The new data show that the near-infrared peak-to-peak photometric range is similar to the value at visible wavelengths, \Delta m_R = 0.30+/-0.02 mag. Detailed analysis of the new and previous data reveals subtle visible/near-infrared color variations across the surface of Haumea. The color variations are spatially correlated with a previously identified surface region, redder in B-R and darker than the mean surface. Our photometry indicates that the J-H colors of Haumea (J-H=-0.057+/-0.016 mag) and its brightest satellite Hi'iaka (J-H=-0.399+/-0.034 mag) are significantly (>9 sigma) different. The satellite Hi'iaka is unusually blue in J-H, consistent with strong 1.5 micron water-ice absorption. The phase coefficient of Haumea in the J-band is found to increase monotonically with wavelength in the range 0.4<lambda<1.3. We compare our findings with other Solar system objects and discuss implications regarding the surface of Haumea.Comment: 10 pages, 10 figures, 6 tables. Accepted for publication in The Astronomical Journal (2008 November 28

Extinction in the Coma of Comet 17P/Holmes

On 2007 October 29 the outbursting comet 17P/Holmes passed within 0.79 arcsec of a background star. We recorded the event using optical, narrowband photometry and detect a 3% to 4% dip in stellar brightness bracketing the time of closest approach to the comet nucleus. The detected dimming implies an optical depth tau~0.04 at 1.5 arcsec from the nucleus and an optical depth towards the nucleus center tau_n<13.3. At the time of our observations, the coma was optically thick only within rho<~0.01 arcsec from the nucleus. By combining the measured extinction and the scattered light from the coma we estimate a dust red geometric albedo p_d=0.006+/-0.002 at 16 deg phase angle. Our measurements place the most stringent constraints on the extinction optical depth of any cometary coma.Comment: 5 pages, 3 figures, 2 table. Accepted for publication in ApJ

Dual boundary element method for axisymmetric crack analysis

In this paper a dual boundary element formulation is developed and applied to the evaluation of stress intensity factors in, and propagation of, axisymmetric cracks. The displacement and stress boundary integral equations are reviewed and the asymptotic behaviour of their singular and hypersingular kernels is discussed. The modified crack closure integral method is employed to evaluate the stress intensity factors. The combination of the dual formulation with this method requires the adoption of an interpolating function for stresses after the crack tip. Different functions are tested under a conservative criterion for the evaluation of the stress intensity factors. A crack propagation procedure is implemented using the maximum principal stress direction rule. The robustness of the technique is assessed through several examples where results are compared either to analytical ones or to BEM and FEM formulations

Analysis of the Predictors of Default for Portuguese Firms

The paper presents an insolvency risk analysis of Portuguese companies with three techniques: logistic regression, discriminant analysis and support vector machines (SVM). It identifies the most critical predictors of default based on the accounting, employee and debt concentration data. A comparison of the three methods reveals a superiority of SVM. Non-financial information such as employee data and the debt concentration index appear to be strong predictors of default.

Credit Risk and Capital Requirements for the Portuguese Banking System

In this study, an assessment of the impact of Basel II capital requirement rules driven by credit risk of non-financial firms is performed. Intervals of variation for the risk drivers are established such that capital requirements for firms' credit risk under Basel II exceed capital requirements under Basel I. Moreover, a characterization of the Portuguese Banking system, which includes a description of corporate credit and its associated probabilities of default, and the computation of capital requirements are performed.

Statistical Arbitrage with Default and Collateral

In this paper we study the implications of the absence of statistical arbitrage opportunities (SAO) in a two-period incomplete market economy where default is allowed but there are collateral requirements. We study the existence of state price deflators and the existence of a solution for the individual optimality problem, obtaining modified versions of the fundamental theorems of asset pricing. Then, we address the existence of equilibrium.

Heidegger, technology and sustainability: between intentionality, accountability and empowerment

Transition is the adequate term for characterising contemporary societies. Norms and values are in transit, led by a technological revolution, which is, in itself, the tip of the iceberg of millenary social and cultural changes. Heidegger, one of the leading philosophers of the twentieth century, captured this tension between social change and innovative technology and showed that the Western civilisation was captive of ontological instances whose role was already pin-pointed by Greek Antiquity philosophy but which went underground with Modernity. The product of Heidegger’s work was a revolution in Western thought, which found echoes across all areas of society. Taking Husserl’s call for “back to the things themselves”, Heidegger’s impact has empowered the calls for more sustainable and resilient societies. Sustainability models, with its three pillars of environmental, economic and social sustainability, are directly dependent upon the role of technology and of information science in shaping current patterns of production and consumption in contemporary societies. Industrial, academic and political discourses already voice such taken for granted assumptions. Nevertheless, it is crucial to clarify and to highlight the links between economic evolution and progress, social change and the catalysing role of technology, taken as an enabler of human action.info:eu-repo/semantics/publishedVersio