On the origin of the featureless soft X-ray excess emission from the Seyfert 1 galaxy ESO~198--G24

We present medium and high resolution X-ray spectral study of a Seyfert 1 galaxy ESO~198--G24 using a long (122 ks) XMM-Newton observation performed in February 2006. The source has a prominent featureless soft X-ray excess below 2\kev. This makes the source well suited to investigate the origin of the soft excess. Two physical models -- blurred reflection, and optically thick thermal Comptonization in a warm plasma, describe the soft-excess equally well resulting in similar fits in the 0.3-10\kev band. These models also yield similar fits to the broad-band UV (Optical Monitor) and X-ray data. XMM-Newton observations performed in 2000, 2001 and 2006 on this source show flux variability. From 2001 to 2006, the UV flux increased by $\sim23\%$ while the 2-10\kev X-ray flux as well as the soft-excess flux decreased by ~ 20. This observation can be described in the blurred reflection scenario by a truncated accretion disk whose inner-most radius had come closer to the blackhole. We find that the best-fit inner radius of the accretion disk decreases from R_{in}=4.93_{-1.10}^{+1.12}R_G to R_{in}<2.5R_G from 2001 to 2006. This leads to an increase in the UV flux and compressing the corona, leading to reduction of the powerlaw flux and therefore the soft-excess. The blurred reflection model seems to better describe the soft-excess for this source.Comment: Accepted for publication in the MNRA

Creep Life Prediction of Modified 9Cr-1Mo Steel under Multiaxial State of Stress

AbstractCreep life prediction of modified 9Cr-1Mo steel under multiaxial state of stress has been carried out in the present investigation. Creep tests were carried out on smooth and notched specimens of modified 9Cr-1Mo steel in the stress range 150 - 230MPa at 873K. The creep rupture life was found to be higher in the presence of notch than that of smooth specimens indicating ‘notch strengthening’ behaviour. The extent of strengthening tends to saturate for relatively sharper notches. Finite element analysis was used to estimate the variation of stresses across the notch throat plane. As the stresses varied across the notch throat plane, the stresses at the skeletal point were used for estimating the representative stress. The models proposed by Cane, Hayhurst and Nix were examined for creep life prediction under multiaxial state of stress. The von-Mises stress was found to predominantly govern the creep rupture life of the steel. The creep rupture life has been predicted based on Cane's model using finite element analysis and continuum damage mechanics