In a distributed web service integration environment, the selection of web services should be based on their reputation and quality-of-service (QoS). Various trust models for web services have been proposed to evaluate the reputation of web services/service providers. Current mechanisms are based on tracing the feedbacks to the past behaviors of web services. However, very few of them consider the robustness and attackresiliency of the trust models. In this paper, we present an attack resilient distributed trust management system in a web service management environment. The proposed attack resilient trust model uses two vectors to capture the behavior and the trustworthiness of a web service/service provider based on our analysis on the possible attacks against the trust models. We also present a set of experiments that show the effectiveness of our trust model in detecting malicious behavior of service providers. 1
The thermal buckling of an axially restrained composite column that is exposed to a heat flux due to fire is studied by both analytical and experimental means. The column is exposed to fire from one-side and the resulting heat damage, the charred layer formation and non-uniform transient temperature distribution are calculated by the thermal model developed by Gibson et al. (Revue de l'Institute Francais du Petrole 50:69-74, 1995). For the thermal buckling analysis, the mechanical properties of the firedamaged (charred) region are considered negligible; the degradation of the elastic properties with temperature (especially near the glass transition temperature of the matrix) in the undamaged layer, is accounted for by using experimental data for the elastic moduli. Due to the non-uniform stiffness and the effect of the ensuing thermal moment, the structure behaves like an imperfect column, and responds by bending rather than buckling in the classical Euler (bifurcation) sense. Another important effect of the non-uniform temperature is that the neutral axis moves away from the centroid of the cross section, resulting in another moment due to eccentric loading, which would tend to bend the structure away from the fire. In order to verify the mechanical response, the compressive buckling behavior of the same material subjected to simultaneous high intensity surface heating and axial compressive loading were investigated experimentally. Fire exposure was simulated by subjecting the surface of rectangular specimens to radiant heating in a cone calorimeter. Heat flux levels of 25 kW/m 2 , 50 kW/m 2 and 75 kW/m 2 were studied. All specimens exhibited buckling and subsequent catastrophic failure, even at compressive stresses as low as 3.5 MPa under a surface heat flux of 25 kW/m 2 . Details of the experimental procedure, including modifications made to a cone calorimeter to allow simultaneous mechanical loading are presented.
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