Trust beyond reputation: A computational trust model based on stereotypes

Models of computational trust support users in taking decisions. They are commonly used to guide users' judgements in online auction sites; or to determine quality of contributions in Web 2.0 sites. However, most existing systems require historical information about the past behavior of the specific agent being judged. In contrast, in real life, to anticipate and to predict a stranger's actions in absence of the knowledge of such behavioral history, we often use our "instinct"- essentially stereotypes developed from our past interactions with other "similar" persons. In this paper, we propose StereoTrust, a computational trust model inspired by stereotypes as used in real-life. A stereotype contains certain features of agents and an expected outcome of the transaction. When facing a stranger, an agent derives its trust by aggregating stereotypes matching the stranger's profile. Since stereotypes are formed locally, recommendations stem from the trustor's own personal experiences and perspective. Historical behavioral information, when available, can be used to refine the analysis. According to our experiments using Epinions.com dataset, StereoTrust compares favorably with existing trust models that use different kinds of information and more complete historical information

Discovery of the Eclipsing Detached Double White Dwarf Binary NLTT 11748

We report the discovery of the first eclipsing detached double white dwarf (WD) binary. In a pulsation search, the low-mass helium core WD NLTT 11748 was targeted for fast (approx 1 minute) differential photometry with the Las Cumbres Observatory's Faulkes Telescope North. Rather than pulsations, we discovered approx 180 s 3%-6% dips in the photometry. Subsequent radial velocity measurements of the primary white dwarf from the Keck telescope found variations with a semi-amplitude K_1 = 271 +/- 3 km/s, and confirmed the dips as eclipses caused by an orbiting WD with a mass M_2 = 0.648-0.771 M_sun for M_1 = 0.1-0.2 M_sun. We detect both the primary and secondary eclipses during the P_orb = 5.64 hr orbit and measure the secondary's brightness to be 3.5% +/- 0.3% of the primary at SDSS-g'. Assuming that the secondary follows the mass-radius relation of a cold C/O WD and including the effects of microlensing in the binary, the primary eclipse yields a primary radius of R_1 = 0.043-0.039 R_sun for M_1 = 0.1-0.2 M_sun, consistent with the theoretically expected values for a helium core WD with a thick, stably burning hydrogen envelope. Though nearby (at approx 150 pc), the gravitational wave strain from NLTT 11748 is likely not adequate for direct detection by the Laser Interferometer Space Antenna. Future observational efforts will determine M_1, yielding accurate WD mass-radius measurement of both components, as well as a clearer indication of the binary's fate once contact is reached.Comment: 5 pages, 3 figures: Accepted to ApJ Letters, 2010 May 11. v2 corrects a typo in ephemeris and impliments redline correction