Maximum likelihood estimation of single X-ray point-source parameters in ROSAT data

The point source parameter estimation via Maximum Likelihood Estimation in ROSAT data is docu men ted. The infall of X-ray photons is treated as a Poisson process. Based on the Poisson model, the log-likelihood function for unbinned data is derived. The adopted source and background models are explained. In the chosen parameterization, the Maximum Likelihood equations and their numerical solution are expounded. The performance of the method is illustrated by an example and tests on simulated observations

EXSAS user's guide Extended scientific analysis system to evaluate data from the astronomical X-ray satellite ROSAT

For data evaluation support of ROSAT observers the ROSAT Scientific Data Center (RSDC) at the Max-Planck Institut fuer Extraterrestrische Physik (MPE) in Garching has set up a Standard Processing and Analysis System (SASS) routinely applied to all data and the Extended Scientific and Analysis System (EXSAS) for individual interactive data analysis work of the ROSAT observers. Although EXSAS has been developed specifically for data analysis of the ROSAT instruments, its structural design is sufficiently general to serve equally well also data from other X-ray and XUV instruments. EXSAS has been built on top of the well-known and widely accepted ESO-MIDAS environment and is thus available to the many astronomical sites already using MIDAS. This edition 4 of the EXSAS User's Manual describes the status of the EXSAS software as released in July 1994. With this release the versatility of the package is enhanced and insufficiencies are corrected. (orig./AKF)Available from TIB Hannover: RA 234:ET(257) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Membrane Elasticity in Giant Vesicles with Fluid Phase Coexistence

Biological membranes are known to contain compositional heterogeneities, often termed rafts, with distinguishable composition and function, and these heterogeneities participate in vigorous transport processes. Membrane lipid phase coexistence is expected to modulate these processes through the differing mechanical properties of the bulk domains and line tension at phase boundaries. In this contribution, we compare the predictions from a shape theory derived for vesicles with fluid phase coexistence to the geometry of giant unilamellar vesicles with coexisting liquid-disordered (L(d)) and liquid-ordered (L(o)) phases. We find a bending modulus for the L(o) phase higher than that of the L(d) phase and a saddle-splay (Gauss) modulus difference with the Gauss modulus of the L(o) phase being more negative than the L(d) phase. The Gauss modulus critically influences membrane processes that change topology, such as vesicle fission or fusion, and could therefore be of significant biological relevance in heterogeneous membranes. Our observations of experimental vesicle geometries being modulated by Gaussian curvature moduli differences confirm the prediction by the theory of Juelicher and Lipowsky

Biomimetic block copolymer membranes

Amphiphilic block copolymer membranes, classified as vesicles, are nano-aggregates receiving a lot of scientific interest due to their wide range of potential applications extending from biomedicine (e.g., drug delivery, imaging, nanoreactors) to material science (biosensors, electronics). This chapter summarizes the principles of vesicle formation, various membrane-forming copolymer systems and their properties as well as common techniques for vesicle preparation and characterization. Copolymer membranes with responsiveness to external stimuli are particularly attractive for use in drug delivery and are, therefore, also discussed. In addition, the chapter reviews recent examples of vesicles encapsulating proteins, enzymes and therapeutics as prospective systems for bio-applications