Assessing the relationship between hepatitis C virus and porphyria cutanea tarda

Thesis (M.A.)--Boston UniversityPorphyria cutanea tarda (PCT) is the most common form of porphyria, diseases that arise from decreased activity levels of enzymes in the heme biosynthetic pathway. Unlike other porphyrias that are caused by genetic mutations, PCT is often caused by exogenous factors, which include alcohol abuse, human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infection. Many studies have shown that there is an overlap in the population of patients who have PCT and HCV infection. HCV infection, in particular, causes inflammation and fibrosis in the liver, and disrupts overall homeostasis of the body, especially with respect to iron metabolism. Both diseases present symptoms that are either the cause or the effect of iron overloading in the liver. Iron overloading leads to oxidative stress in the body which further propagates symptoms of PCT and HCV. This review will investigate the causes, symptoms, and treatment modalities for patients with PCT and HCV infection. It will also evaluate the risk factors, such as iron overload and oxidative stress, which may contribute to the overlap among patient populations with the two diseases

Generalized matrix-based Bayesian network for multi-state systems

To achieve a resilient society, the reliability of core engineering systems should be evaluated accurately. However, this remains challenging due to the complexity and large scale of real-world systems. Such complexity can be efficiently modelled by Bayesian network (BN), which formulates the probability distribution through a graph-based representation. On the other hand, the scale issue can be addressed by the matrix-based Bayesian network (MBN), which allows for efficient quantification and flexible inference of discrete BN. However, the MBN applications have been limited to binary-state systems, despite the essential role of multi-state engineering systems. Therefore, this paper generalizes the MBN to multi-state systems by introducing the concept of composite state. The definitions and inference operations developed for MBN are modified to accommodate the composite state, while formulations for the parameter sensitivity are also developed for the MBN. To facilitate applications of the generalized MBN, three commonly used techniques for decomposing an event space are employed to quantify the MBN, i.e. utilizing event definition, branch and bound (BnB), and decision diagram (DD), each being accompanied by an example system. The numerical examples demonstrate the efficiency and applicability of the generalized MBN

CDM, Feedback and the Hubble Sequence

We have performed TreeSPH simulations of galaxy formation in a standard LCDM cosmology, including effects of star formation, energetic stellar feedback processes and a meta-galactic UV field, and obtain a mix of disk, lenticular and elliptical galaxies. The disk galaxies are deficient in angular momentum by only about a factor of two compared to observed disk galaxies. The stellar disks have approximately exponential surface density profiles, and those of the bulges range from exponential to r^{1/4}, as observed. The bulge-to-disk ratios of the disk galaxies are consistent with observations and likewise are their integrated B-V colours, which have been calculated using stellar population synthesis techniques. Furthermore, we can match the observed I-band Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk galaxies, (M/L_I), is about 0.8. The ellipticals and lenticulars have approximately r^{1/4} stellar surface density profiles, are dominated by non-disklike kinematics and flattened due to non-isotropic stellar velocity distributions, again consistent with observations.Comment: 6 pages, incl. 4 figs. To appear in the proceedings of the EuroConference "The Evolution of Galaxies: II - Basic Building Blocks", Ile de La Reunion (France), 16-21 October 2001 (Slightly updated version). A much more comprehensive paper about this work with links to pictures of some of the galaxies can be found at http://babbage.sissa.it/abs/astro-ph/020436

Are spiral galaxies optically thin or thick?

The opacity of spiral galaxies is examined by modelling the dust and stellar content of individual galaxies. The model is applied to five late-type spiral galaxies (NGC 4013, IC 2531, UGC 1082, NGC 5529 and NGC 5907). Having analyzed a total of seven galaxies thus far, the five galaxies mentioned above plus UGC 2048 and NGC 891 presented in (Xilouris et al. 1997, 1998), we are able to draw some general conclusions, the most significant of which are: 1) The face-on central optical depth is less than one in all optical bands indicating that typical spiral galaxies like the ones that we have modelled would be completely transparent if they were to be seen face-on. 2) The dust scaleheight is about half that of the stars, which means that the dust is more concentrated near the plane of the disk. 3) The dust scalelength is about 1.4 times larger than that of the stars and the dust is more radially extended than the stars. 4) The dust mass is found to be about an order of a magnitude more than previously measured using the IRAS fluxes, indicating the existence of a cold dust component. The gas-to-dust mass ratio calculated is close to the value derived for our Galaxy. 5) The derived extinction law matches quite well the Galactic extinction law, indicating a universal dust behaviour.Comment: 13 pages. Accepted for publication in A&

Modeling, system identification, and control of ASTREX

The modeling, system identification and controller design aspects of the ASTREX precision space structure are presented in this work. Modeling of ASTREX is performed using NASTRAN, TREETOPS and I-DEAS. The models generated range from simple linear time-invariant models to nonlinear models used for large angle simulations. Identification in both the time and frequency domains are presented. The experimental set up and the results from the identification experiments are included. Finally, controller design for ASTREX is presented. Simulation results using this optimal controller demonstrate the controller performance. Finally the future directions and plans for the facility are addressed