17,265 research outputs found
Research and development activities in unified control-structure modeling and design
Results of work sponsored by JPL and other organizations to develop a unified control/structures modeling and design capability for large space structures is presented. Recent analytical results are presented to demonstrate the significant interdependence between structural and control properties. A new design methodology is suggested in which the structure, material properties, dynamic model and control design are all optimized simultaneously. The development of a methodology for global design optimization is recommended as a long term goal. It is suggested that this methodology should be incorporated into computer aided engineering programs, which eventually will be supplemented by an expert system to aid design optimization. Recommendations are also presented for near term research activities at JPL. The key recommendation is to continue the development of integrated dynamic modeling/control design techniques, with special attention given to the development of structural models specially tailored to support design
Dynamical Disentanglement across a Point Contact in a Non-Abelian Quantum Hall State
We analyze tunneling of non-Abelian quasiparticles between the edges of a
quantum Hall droplet at Landau level filling fraction nu=5/2, assuming that the
electrons in the first excited Landau level organize themselves in the
non-Abelian Moore-Read Pfaffian state. We formulate a bosonized theory of the
modes at the two edges of a Hall bar; an effective spin-1/2 degree of freedom
emerges in the description of a point contact. We show how the crossover from
the high-temperature regime of weak quasiparticle tunneling between the edges
of the droplet, with 4-terminal R_{xx} scaling as T^{-3/2}, to the
low-temperature limit, with R_{xx} - h/(10 e^2) scaling as -T^4, is closely
related to the two-channel Kondo effect. We give a physical interpretation for
the entropy of \ln(2\sqrt{2}) which is lost in the flow from the ultraviolet to
the infrared.Comment: 4 pages, 1 figur
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