Ultraluminous X-ray Sources and Their Nebulae

One of the interesting features of Ultraluminous X-ray sources is that many of them are surrounded by luminous nebulae exhibiting diverse observational properties. In different cases the nebulae are photoionized or shock-powered. Generally, the two energy sources appear to coexist. ULX bubble nebulae may be considered a new class of shock-powered nebulae similar to upscaled versions of stellar wind bubbles. Their expansion rates support constant energy influx rather than single powerful events like Hypernova explosions.Comment: 6 pages, 1 figure, to appear in the proceedings of "Cool discs, hot flows: The Varying Faces of Accreting Compact Objects", Funasdalen, Sweden, 2008, ed. M. Axelsson (New York: AIP

Weighted maximal regularity estimates and solvability of non-smooth elliptic systems I

We develop new solvability methods for divergence form second order, real and complex, elliptic systems above Lipschitz graphs, with $L_2$ boundary data. The coefficients $A$ may depend on all variables, but are assumed to be close to coefficients $A_0$ that are independent of the coordinate transversal to the boundary, in the Carleson sense $\|A-A_0\|_C$ defined by Dahlberg. We obtain a number of {\em a priori} estimates and boundary behaviour results under finiteness of $\|A-A_0\|_C$. Our methods yield full characterization of weak solutions, whose gradients have $L_2$ estimates of a non-tangential maximal function or of the square function, via an integral representation acting on the conormal gradient, with a singular operator-valued kernel. Also, the non-tangential maximal function of a weak solution is controlled in $L_2$ by the square function of its gradient. This estimate is new for systems in such generality, and even for real non-symmetric equations in dimension 3 or higher. The existence of a proof {\em a priori} to well-posedness, is also a new fact. As corollaries, we obtain well-posedness of the Dirichlet, Neumann and Dirichlet regularity problems under smallness of $\|A-A_0\|_C$ and well-posedness for $A_0$, improving earlier results for real symmetric equations. Our methods build on an algebraic reduction to a first order system first made for coefficients $A_0$ by the two authors and A. McIntosh in order to use functional calculus related to the Kato conjecture solution, and the main analytic tool for coefficients $A$ is an operational calculus to prove weighted maximal regularity estimates.Comment: This is an extended version of the paper, containing some new material and a road map to proofs on suggestion from the referee

Federated Robust Embedded Systems: Concepts and Challenges

The development within the area of embedded systems (ESs) is moving rapidly, not least due to falling costs of computation and communication equipment. It is believed that increased communication opportunities will lead to the future ESs no longer being parts of isolated products, but rather parts of larger communities or federations of ESs, within which information is exchanged for the benefit of all participants. This vision is asserted by a number of interrelated research topics, such as the internet of things, cyber-physical systems, systems of systems, and multi-agent systems. In this work, the focus is primarily on ESs, with their specific real-time and safety requirements. While the vision of interconnected ESs is quite promising, it also brings great challenges to the development of future systems in an efficient, safe, and reliable way. In this work, a pre-study has been carried out in order to gain a better understanding about common concepts and challenges that naturally arise in federations of ESs. The work was organized around a series of workshops, with contributions from both academic participants and industrial partners with a strong experience in ES development. During the workshops, a portfolio of possible ES federation scenarios was collected, and a number of application examples were discussed more thoroughly on different abstraction levels, starting from screening the nature of interactions on the federation level and proceeding down to the implementation details within each ES. These discussions led to a better understanding of what can be expected in the future federated ESs. In this report, the discussed applications are summarized, together with their characteristics, challenges, and necessary solution elements, providing a ground for the future research within the area of communicating ESs

Short term aperiodic variability of X-ray binaries: its origin and implications

In this review I briefly describe the latest advances in studies of aperiodic variability of accreting X-ray binaries and outline the model which currently describe the majority of observational appearances of variability of accreting sources in the best way. Then I concentrate on the case of luminous accreting neutron star binaries (in the soft/high spectral state), where study of variability of X-ray emission of sources allowed us to resolve long standing problem of disentangling the contribution of accretion disk and boundary/spreading layer components to the time average spectrum of sources. The obtained knowledge of the shape of the spectrum of the boundary layer allowed us to make estimates of the mass and radii of accreting neutron stars.Comment: 11 pages, 5 figures. Proceedings article of the conference "Cool Discs, Hot Flows: The Varying Faces of Accreting Compact Objects", Ed. M. Axelsson, AIP Conference Proceedings 105

Federated Embedded Systems – a review of the literature in related fields

This report is concerned with the vision of smart interconnected objects, a vision that has attracted much attention lately. In this paper, embedded, interconnected, open, and heterogeneous control systems are in focus, formally referred to as Federated Embedded Systems. To place FES into a context, a review of some related research directions is presented. This review includes such concepts as systems of systems, cyber-physical systems, ubiquitous computing, internet of things, and multi-agent systems. Interestingly, the reviewed fields seem to overlap with each other in an increasing number of ways