86,588 research outputs found
On the stable configuration of ultra-relativistic material spheres. The solution for the extremely hot gas
During the last stage of collapse of a compact object into the horizon of
events, the potential energy of its surface layer decreases to a negative value
below all limits. The energy-conservation law requires an appearance of a
positive-valued energy to balance the decrease. We derive the internal-state
properties of the ideal gas situated in an extremely strong, ultra-relativistic
gravitational field and suggest to apply our result to a compact object with
the radius which is slightly larger than or equal to the Schwarzschild's
gravitational radius. On the surface of the object, we find that the extreme
attractivity of the gravity is accompanied with an extremely high internal,
heat energy. This internal energy implies a correspondingly high pressure, the
gradient of which has such a behavior that it can compete with the gravity. In
a more detail, we find the equation of state in the case when the magnitude of
the potential-type energy of constituting gas particles is much larger than
their rest energy. This equation appears to be identical with the
general-relativity condition of the equilibrium between the gravity and
pressure gradient. The consequences of the identity are discussed.Comment: 12 pages (no figure, no table) Changes in 3-rd version: added an
estimate of neutrino cooling and relative time-scale of the final stage of
URMS collaps
Attentive monitoring of multiple video streams driven by a Bayesian foraging strategy
In this paper we shall consider the problem of deploying attention to subsets
of the video streams for collating the most relevant data and information of
interest related to a given task. We formalize this monitoring problem as a
foraging problem. We propose a probabilistic framework to model observer's
attentive behavior as the behavior of a forager. The forager, moment to moment,
focuses its attention on the most informative stream/camera, detects
interesting objects or activities, or switches to a more profitable stream. The
approach proposed here is suitable to be exploited for multi-stream video
summarization. Meanwhile, it can serve as a preliminary step for more
sophisticated video surveillance, e.g. activity and behavior analysis.
Experimental results achieved on the UCR Videoweb Activities Dataset, a
publicly available dataset, are presented to illustrate the utility of the
proposed technique.Comment: Accepted to IEEE Transactions on Image Processin
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Letter processing and font information during reading: beyond distinctiveness, where vision meets design
Letter identification is a critical front end of the
reading process. In general, conceptualizations of the identification process have emphasized arbitrary sets of distinctive features. However, a richer view of letter processing incorporates principles from the field of type design, including an emphasis on uniformities across letters within a font. The importance of uniformities is supported by a small body of research indicating that consistency of font increases letter identification efficiency. We review design concepts and the relevant literature, with the goal of stimulating further thinking about letter processing during reading
The architectures of seeing and going:or, are cities shaped by bodies or minds? And is there a syntax ofspatial cognition?
In my first paper to this Symposium, it was argued that the human cognitive subjectplayed a key part the shaping and working of the city. The key mechanism was thesynchronisation of diachronically experienced (and usually diachronically created)information into higher order pictures of spatial relations, the guiding form for whichwas an abstracted notion of a grid formed by linearised spaces. This notion wasargued to be both perceptual and conceptual, serving at once as an abstractedrepresentation of the space of the city and as a means of solving problems, such asnavigational problems. In this paper, the question addressed is where the notion ofthe ideal grid comes from, why it has the properties it does, and what it has to dowith the real grids of cities, which are commonly of the 'deformed' or 'interrupted'rather than 'ideal' kinds (Hillier, 1996). The answer, it is proposed, lies in the verynature of complex spaces, defining these as spaces in which objects are placed so asto partially block seeing and going, and, in particular, in certain divergences in thelogics of metric and visual accessibility in such spaces. The real grid, deformed orinterrupted, is, it is argued the practical resolution of these divergent logics, and theideal grid its abstract resolution. In both resolutions, however, the resolution is moreon the terms of the visual than the metric, suggesting that cognitive factors are morepowerful than metric factors in shaping the space of the city. The question is thanraised: do people have or acquire the concept of the grid, perhaps as some kind ofperceptual-conceptual invariance of spatial experience in complex spaces, and dothey use it as a model to interact with complex spatial patterns of the urban kind?This possibility is examined against the background of current opinion in the cognitivesciences
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