Thin accretion disc with a corona in a central magnetic field

We study the steady-state structure of an accretion disc with a corona surrounding a central, rotating, magnetized star. We assume that the magneto-rotational instability is the dominant mechanism of angular momentum transport inside the disc and is responsible for producing magnetic tubes above the disc. In our model, a fraction of the dissipated energy inside the disc is transported to the corona via these magnetic tubes. This energy exchange from the disc to the corona which depends on the disc physical properties is modified because of the magnetic interaction between the stellar magnetic field and the accretion disc. According to our fully analytical solutions for such a system, the existence of a corona not only increases the surface density but reduces the temperature of the accretion disc. Also, the presence of a corona enhances the ratio of gas pressure to the total pressure. Our solutions show that when the strength of the magnetic field of the central neutron star is large or the star is rotating fast enough, profiles of the physical variables of the disc significantly modify due to the existence of a corona.Comment: Accepted for publication in Astrophysics & Space Scienc

Frequency and field dependence of the irreversibility line in a yttrium barium copper oxide (YBa2Cu3O7-δ) film

The irreversibility line of an epitaxial YBa2Cu3O7-d film was determined using AC susceptibility experiments. It is shown that the irreversibility line depends on both the amplitude of the AC field and the measuring frequency. We argue that, therefore this line represents a crossover from pinning to flow regimes. The power law behaviour which is predicted by flux creep is only found in a limited field range and is dependent on hAC

Reliability prediction through bayesian inference based on product change

This paper provides a methodology to determine the reliability of a system, when only limited information about the system (in this case a patient table of a medical scanning system) is available. With this methodology, Bayesian inference, different sources of information (expert knowledge and field data) can be combined, and the uncertainty that is inherent to reliability prediction when only little information is available can be depicted. In order to use the information that can be provided by experts, the expert knowledge first has to be quantified, which has also been done in this case study. It is found that it is possible to quantify expert knowledge about reliability performance over time of the subsystem. However, the process to do that (elicitation process) is a difficult process to control, because of the different issues that play a role. Also, in this case, the design of the subsystem under study had already been defined, which could have influenced the ease of elicitation. Furthermore, it is shown that it is possible to predict the reliability performance of the new table over time based either solely expert knowledge and one reliability indicator (without further data), or based on a combination of data and expert knowledge. Also the possibility to depict the uncertainty regarding the prediction and its reduction when more information becomes available is shown. © 2009 IEEE

Tumor accumulation of radiolabeled bevacizumab due to targeting of cell- and matrix-associated VEGF-A isoforms.

Contains fulltext : 81037.pdf (publisher's version ) (Open Access)PURPOSE: Vascular endothelial growth factor-A (VEGF-A) is one of the most important factors inducing angiogenesis in tumors. Nine splice-variant isoforms of VEGF-A have been identified, each having different properties. Recently, we showed that radiolabeled anti-VEGF monoclonal antibody, bevacizumab, accumulates specifically in VEGF-A expressing tumors. In this study, we investigated in a nude mouse model which VEGF-isoforms are responsible for tumor accretion. MATERIALS AND METHODS: The humanized anti-VEGF-A antibody, A.4.6.1. (bevacizumab), was radiolabeled with In-111. The originally VEGF-negative Mel57 tumor was transfected with different VEGF isoforms (VEGF-121, VEGF-165, and VEGF-189). The obtained melanoma xenografts specifically expressing different VEGF-isoforms were used in mice. The bevacizumab uptake was examined in biodistribution studies and by gamma-camera imaging. RESULTS: The tumor cell line expressing VEGF-121 did not show specific uptake, most likely as a result of the fact that this isoform is freely diffusible. Tumors expressing VEGF-165 and -189 were clearly visualized by using gamma-camera imaging. CONCLUSION: The accumulation of radiolabeled bevacizumab in the tumor is due to interaction with VEGF-A isoforms that are associated with the tumor cell surface and/or the extracellular matrix. Scintigraphic imaging of the expression of these VEGF isoforms may thus be useful to predict response to angiogenic therapy