197,704 research outputs found
First proper motions of thin dust filaments at the Galactic Center
Context: L'-band (3.8 micron) images of the Galactic Center show a large
number of thin filaments in the mini-spiral, located west of the mini-cavity
and along the inner edge of the Northern Arm. One possible mechanism that could
produce such structures is the interaction of a central wind with the
mini-spiral. Additionally, we identify similar features that appear to be
associated with stars. Aims: We present the first proper motion measurements of
the thin dust filaments observed in the central parsec around SgrA* and
investigate possible mechanisms that could be responsible for the observed
motions. Methods: The observations have been carried out using the NACO
adaptive optics system at the ESO VLT. The images have been transformed to a
common coordinate system and features of interest were extracted. Then a
cross-correlation technique could be performed in order to determine the
offsets between the features with respect to their position in the reference
epoch. Results: We derive the proper motions of a number of filaments and 2
cometary shaped dusty sources close (in projection) to SgrA*. We show that the
shape and the motion of the filaments does not agree with a purely Keplerian
motion of the gas in the potential of the supermassive black hole at the
position of SgrA*. Therefore, additional mechanisms must be responsible for
their formation and motion. We argue that the properties of the filaments are
probably related to an outflow from the disk of young mass-losing stars around
SgrA*. In part, the outflow may originate from the black hole itself. We also
present some evidence and theoretical considerations that the outflow may be
collimated.Comment: accepted for publication by A&
The 'black box' problem in the study of participation
Research on citizen participation has been guided by two core issues: first, the observation of a widening repertory of modes of participation, and second, the argument that participation is not an undifferentiated phenomenon, but must be conceived as an inherently multidimensional reality. In this article, we argue that conventional participation research has focused too one-sidedly on quantitatively expanding the range of types of activities, while the complex dimensionality is not reflected in the measures used. We formulate a methodological critique by using the metaphor of the 'black box', which refers to the implicit and unquestioned assumption that distinct types of activities and associations represent homogeneous and consistent realities that do not warrant further analytical decomposition. Surveys of participation allocate individuals to different 'participation boxes' by means of a binary logic, leaving a void of what is actually happening inside the boxes. To conclude, we reflect upon the fundamental dilemmas the black box of participation raises for theory and research, and offer conceptual and methodological keys to unlock the participation box
Factors Influencing Oviposition in \u3ci\u3eAedes Triseriatus\u3c/i\u3e (Diptera: Culicidae)
Five factors associated with natural oviposition sites were tested for their attractancy to ovipositing Aedes triseriatus, including dyed oviposition water, presence of decaying organic matter, a dark oviposition container, water in which conspecific larvae have been reared to the 4th instar and the presence of eggs on the balsa wood oviposition substrate. A replicated fractional factorial design was used to examine the effects of the above factors on oviposition behavior in laboratory experiments. Regression analysis showed dyed oviposition water and eggs on the oviposition substrate to be statistically significant attractants for ovipositing A. triseriatus females. The attraction to dyed oviposition water indicated that dyed water in oviposition traps may greatly increase their competiveness with naturally occurring oviposition sites
A Product Oriented Modelling Concept: Holons for systems synchronisation and interoperability
Nowadays, enterprises are confronted to growing needs for traceability,
product genealogy and product life cycle management. To meet those needs, the
enterprise and applications in the enterprise environment have to manage flows
of information that relate to flows of material and that are managed in shop
floor level. Nevertheless, throughout product lifecycle coordination needs to
be established between reality in the physical world (physical view) and the
virtual world handled by manufacturing information systems (informational
view). This paper presents the "Holon" modelling concept as a means for the
synchronisation of both physical view and informational views. Afterwards, we
show how the concept of holon can play a major role in ensuring
interoperability in the enterprise context
N-body simulations of gravitational dynamics
We describe the astrophysical and numerical basis of N-body simulations, both
of collisional stellar systems (dense star clusters and galactic centres) and
collisionless stellar dynamics (galaxies and large-scale structure). We explain
and discuss the state-of-the-art algorithms used for these quite different
regimes, attempt to give a fair critique, and point out possible directions of
future improvement and development. We briefly touch upon the history of N-body
simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu
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