26,987 research outputs found
Specification of multiparty audio and video interaction based on the Reference Model of Open Distributed Processing
The Reference Model of Open Distributed Processing (RM-ODP) is an emerging ISO/ITU-T standard. It provides a framework of abstractions based on viewpoints, and it defines five viewpoint languages to model open distributed systems. This paper uses the viewpoint languages to specify multiparty audio/video exchange in distributed systems. To the designers of distributed systems, it shows how the concepts and rules of RM-ODP can be applied.\ud
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The ODP ¿binding object¿ is an important concept to model continuous data flows in distributed systems. We take this concept as a basis for multiparty audio and video flow exchanges, and we provide five ODP viewpoint specifications, each emphasising a particular concern. To ensure overall correctness, special attention is paid to the mapping between the ODP viewpoint specifications
Discovery of GRS 1915+105 variability patterns in the Rapid Burster
We report the discovery of two new types of variability in the neutron star
low-mass X-ray binary MXB 1730-335 (the 'Rapid Burster'). In one observation in
1999, it exhibits a large-amplitude quasi-periodic oscillation with a period of
about 7 min. In another observation in 2008, it exhibits two 4-min long 75 per
cent deep dips 44 min apart. These two kinds of variability are very similar to
the so-called or 'heartbeat' variability and the variability,
respectively, seen in the black hole low-mass X-ray binaries GRS 1915+105 and
IGR J17091-3624. This shows that these types of behavior are unrelated to a
black hole nature of the accretor. Our findings also show that these kinds of
behaviour need not take place at near-Eddington accretion rates. We speculate
that they may rather be related to the presence of a relatively wide orbit with
an orbital period in excess of a few days and about the relation between these
instabilities and the type II bursts.Comment: Accepted for publication in MNRAS letter
Constructing simply laced Lie algebras from extremal elements
For any finite graph Gamma and any field K of characteristic unequal to 2 we
construct an algebraic variety X over K whose K-points parameterise K-Lie
algebras generated by extremal elements, corresponding to the vertices of the
graph, with prescribed commutation relations, corresponding to the non-edges.
After that, we study the case where Gamma is a connected, simply laced Dynkin
diagram of finite or affine type. We prove that X is then an affine space, and
that all points in an open dense subset of X parameterise Lie algebras
isomorphic to a single fixed Lie algebra. If Gamma is of affine type, then this
fixed Lie algebra is the split finite-dimensional simple Lie algebra
corresponding to the associated finite-type Dynkin diagram. This gives a new
construction of these Lie algebras, in which they come together with
interesting degenerations, corresponding to points outside the open dense
subset. Our results may prove useful for recognising these Lie algebras.Comment: We made many corrections suggested by a referee, and extended our
results to positive characteristic greater than
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