23,158 research outputs found
Dilations and constrained algebras
It is well known that unital contractive representations of the disk algebra
are completely contractive. Let A denote the subalgebra of the disk algebra
consisting of those functions f whose first derivative vanishes at 0. We prove
that there are unital contractive representations of A which are not completely
contractive, and furthermore provide a Kaiser and Varopoulos inspired example
for A and present a characterization of those contractive representations of A
which are completely contractive. In the positive direction, for the algebra of
rational functions with poles off the distinguished variety V in the bidisk
determined by (z-w)(z+w)=0, unital contractive representations are completely
contractive.Comment: New to version 2 is a proof of rational dilation for the
distinguished variety in the bidisk determined by (z-w)(z+w)=
Active damping application to the shuttle RMS
Control Structure Interaction (CSI) is a relatively new technology developed over the last 10 to 15 years for application to large flexible space vehicles. The central issue is recognition that high performance control systems necessary for good spacecraft performance may adversely interact with the dynamics of the spacecraft structures, a problem increasingly aggravated by the large size and reduced stiffness of modern spacecraft structural designs. The CSI analysis and design methods were developed to avoid interactions while maintaining spacecraft performance without exceeding structural capabilities, but they remain largely unvalidated by hardware experiments or demonstrations, particularly in-space flight demonstrations. One recent proposal for a low cost flight validation of CSI technology is to demonstrate active damping augmentation of the Space Shuttle Remote Manipulator System (RMS). An analytical effort to define the potential for such an active damping augmentation demonstration to improve the structural dynamic response of the RMS following payload maneuvers is described. It is hoped that this study will lead to an actual inflight CSI test with the RMS using existing shuttle hardware to the maximum extent possible. By using the existing hardware, the flight demonstration results may eventually be of direct benefit to actual Space Shuttle RMS operations, especially during the construction of the Space Station Freedom
Active vibration damping of the Space Shuttle remote manipulator system
The feasibility of providing active damping augmentation of the Space Shuttle Remote Manipulator System (RMS) following normal payload handling operations is investigated. The approach used in the analysis is described, and the results for both linear and nonlinear performance analysis of candidate laws are presented, demonstrating that significant improvement in the RMS dynamic response can be achieved through active control using measured RMS tip acceleration data for feedback
Slepton Flavor Physics at Linear Colliders
If low energy supersymmetry is realized in nature it is possible that a first
generation linear collider will only have access to some of the superpartners
with electroweak quantum numbers. Among these, sleptons can provide sensitive
probes for lepton flavor violation through potentially dramatic lepton
violating signals. Theoretical proposals to understand the absence of low
energy quark and lepton flavor changing neutral currents are surveyed and many
are found to predict observable slepton flavor violating signals at linear
colliders. The observation or absence of such sflavor violation will thus
provide important indirect clues to very high energy physics. Previous analyses
of slepton flavor oscillations are also extended to include the effects of
finite width and mass differences.Comment: 7 pages, no figures, uses RevTeX4. Contribution to Snowmass 200
A Stochastic Compartmental Model for Fast Axonal Transport
In this paper we develop a probabilistic micro-scale compartmental model and
use it to study macro-scale properties of axonal transport, the process by
which intracellular cargo is moved in the axons of neurons. By directly
modeling the smallest scale interactions, we can use recent microscopic
experimental observations to infer all the parameters of the model. Then, using
techniques from probability theory, we compute asymptotic limits of the
stochastic behavior of individual motor-cargo complexes, while also
characterizing both equilibrium and non-equilibrium ensemble behavior. We use
these results in order to investigate three important biological questions: (1)
How homogeneous are axons at stochastic equilibrium? (2) How quickly can axons
return to stochastic equilibrium after large local perturbations? (3) How is
our understanding of delivery time to a depleted target region changed by
taking the whole cell point-of-view
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