13,758 research outputs found
A Simple Particle Action from a Twistor Parametrization of AdS_5
The SO(4,2) isometries of AdS_5 are realized non-linearly on its
horospherical coordinates (x^m,\rho). On the other hand, Penrose twistors have
long been known to linearly realize these symmetries on 4-dimensional Minkowski
space, the boundary of AdS_5, parametrized by x^m. Here we extend the twistor
construction and define a pair of twistors, allowing us to include a radial
coordinate in the construction. The linear action of SO(4,2) on the twistors
induces the correct isometries of AdS_5. We apply this new construction to the
study of the dynamics of a massive particle in AdS_5. We show that in terms of
the twistor variables the action takes a simple form of a 1-dimensional gauge
theory. Our result might open up the possibility to find a simple worldvolume
action also for the string propagating on AdS_5.Comment: 11 pages, LaTe
On the run? Growing up in modern mobile societies. John Urry interviewt von Claus J. Tully
Das hier veröffentlichte Interview wurde am Rande des 32. Kongresses der Deutschen Gesellschaft für Soziologie am 7. Oktober 2004 in München geführt. Thema des Gesprächs ist die Ausformung sozialer Bezüge unter dem Eindruck einer modernen, netzwerkmäßig organisierten mobilen und kommunikativen Gesellschaft. Im Interview wird der Frage nachgegangen, wie sich das Aufwachsen von Kindern und Jugendlichen im Kontext von Familie und lokalen Bezügen unter diesen Bedingungen verändert. In seinen Büchern "The Tourist Gaze" von 1990 und "Consuming Places" (1995) thematisiert er die gewandelte Bedeutung von Orten. 1994 expliziert er gemeinsam mit Lash in "Economies of Signs and Space" die These der generellen Mobilisierung von Symbolen und der Menschen, die der mobilen Ökonomie dienen. In "Sociology beyond Society" (1999) argumentiert John Urry im Sinne der Castells\u27schen Netzgesellschaften, dass wir soziales Leben nicht länger mit den vertrauten und letztlich statischen Kategorien beschreiben können. Auch in seinem jüngsten Buch "Global Complexity" (2004) plädiert er für eine neue Sichtweise auf Nationen, Orte, Regionen im Dienste sozialwissenschaftlicher Begriffsbildung vor dem Hintergrund globaler Verschränkung. (DIPF/Orig.
Evolution of Resource Competition between Mutually Dependent Digital Organisms
We study the emergence and dynamics of competing strains of digital organisms in a world with two depletable resources. Consumption of one resource produces the other resource as a by-product, and vice versa. As a consequence, two types of mutually dependent organisms emerge that each prey on the waste product of the other. In the absence of mutations, that is, in a purely ecological setting, the abundances of the two types of organisms display a wide range of different types of oscillations, from regular
oscillations with large amplitude to irregular oscillations with amplitudes ranging from small to large. In this regime,
time-averaged abundance levels seem to be controlled by the
relative fitness of the organisms in the absence of resources. Under mutational pressure, on the other hand, populations evolve that seem to avoid the oscillations of intermediate to large amplitudes. In this case, the relative fitness of the organisms in the presence of resources plays an important role in the time-averaged abundance levels as well
Desirability to characterize process capability
Over the past few years continuously new process capability indices have been developed, most of them with the aim to add some feature missed in former process capability indices. Thus, for nearly any thinkable situation now a special index exists which makes choosing a certain index as difficult as interpreting and comparing index values correctly. In this paper we propose the use of the expected value of a certain type of function, the so-called desirability function, to assess the capability of a process. The resulting index may be used analogously to the classical indices related to Cp, but can be adapted to nearly any process and any specification. It even allows a comparison between different processes regardless of their distribution and may be extended straightforwardly to multivariate scenarios. Furthermore, its properties compare favorably to the properties of the ?classical? indices. --
SSME fuelside preburner two-dimensional analysis
The flow field within the fuelside preburner of the Space Shuttle Main Engine is calculated using a reacting flow code (REACT2D). Inlet and modeling parameters involved in the numerical calculation are systematically varied to establish the sensitivity of the calculated exit temperature profile. It is found that differences in the inlet equivalence ratio have a large effect on the turbine inlet temperature profile. A variety of preburner inlet modeling changes such as inlet turbulence level, modeling the gases as burned, unburned, premixed, or unmixed, are shown to have a smaller effect on the calculated turbine inlet temperature profile. Also, the form of finite differencing used is shown to have an effect on the temperature profile
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