83,126 research outputs found
Adaptation and Resilience of Interdependent Infrastructure Systems: a Complex Systems Perspective
The effects of disruption upon one or more components in interdependent infrastructure systems and the ability of
the system to return to normal operations, is investigated in this paper. This addresses the concept of resilience, and
examines the trade-off between redundancy and efficiency, as well as the adaptive ability of a system to respond to
disruptions and continue to operate, albeit not necessarily as it did initially
Intelligent redundant actuation system requirements and preliminary system design
Several redundant actuation system configurations were designed and demonstrated to satisfy the stringent operational requirements of advanced flight control systems. However, this has been accomplished largely through brute force hardware redundancy, resulting in significantly increased computational requirements on the flight control computers which perform the failure analysis and reconfiguration management. Modern technology now provides powerful, low-cost microprocessors which are effective in performing failure isolation and configuration management at the local actuator level. One such concept, called an Intelligent Redundant Actuation System (IRAS), significantly reduces the flight control computer requirements and performs the local tasks more comprehensively than previously feasible. The requirements and preliminary design of an experimental laboratory system capable of demonstrating the concept and sufficiently flexible to explore a variety of configurations are discussed
Studies in a Random Noise Model of Decoherence
We study the effects of noise and decoherence for a double-potential well
system, suitable for the fabrication of qubits and quantum logic elements. A
random noise term is added to the hamiltonian, the resulting wavefunction found
numerically and the density matrix obtained by averaging over noise signals.
Analytic solutions using the two-state model are obtained and found to be
generally in agreement.
In particular, a simple formula for the decoherence rate in terms of the
noise parameters in the two-state model is reviewed and verified for the full
simulation with the multi-level system. The formalism is extended to describe
multiple sources of noise or different "dephasing" axes at the same time.
Furthermore, the old formula for the "Turing-Watched Pot" effect is generalized
to the case where the environmental interactions do not conserve the "quality"
in question.
Various forms for the noise signal are investigated. An interesting result is
the importance of the noise power at low frequency. If it vanishes there is, in
leading order, no decoherence. This is verified in a numerical simulation where
two apparently similar noise signals, but differing in the power at zero
frequency, give strikingly different decoherence effects. A short discussion of
situations dominated by low frequency noise is given.Comment: 27 pages, 10 figures. New section added on Very Low Frequency Noise,
with two additional figures. Conclusions, Abstract modified accordingly.
Various other small editorial changes and clarification
Positive psychology and romantic scientism: Reply to comments on Brown, Sokal, & Friedman (2013)
This is a response to five comments [American Psychologist 69, 626-629 and
632-635 (2014)] on our article arXiv:1307.7006.Comment: PDF, 9 page
The persistence of wishful thinking: Response to "Updated thinking on positivity ratios"
This is a response to Barbara Fredrickson's comment [American Psychologist
68, 814-822 (2013)] on our article arXiv:1307.7006.
We analyze critically the renewed claims made by Fredrickson (2013)
concerning positivity ratios and "flourishing", and attempt to disentangle some
conceptual confusions; we also address the alleged empirical evidence for
nonlinear effects. We conclude that there is no evidence whatsoever for the
existence of any "tipping points", and only weak evidence for the existence of
any nonlinearity of any kind. Our original concern, that the application of
advanced mathematical techniques in psychology and related disciplines may not
always be appropriate, remains undiminished.Comment: LaTeX2e, 10 pages including 6 Postscript figure
Phase 2 and 3 wind tunnel tests of the J-97 powered, external augmentor V/STOL model
Static and forward speed tests were made in a 40 multiplied by 80 foot wind tunnel of a large-scale, ejector-powered V/STOL aircraft model. Modifications were made to the model following earlier tests primarily to improve longitudinal acceleration capability during transition from hovering to wingborne flight. A rearward deflection of the fuselage augmentor thrust vector was shown to be beneficial in this regard. Other augmentor modifications were tested, notably the removal of both endplates, which improved acceleration performance at the higher transition speeds. The model tests again demonstrated minimal interference of the fuselage augmentor on aerodynamic lift. A flapped canard surface also showed negligible influence on the performance of the wing and of the fuselage augmentor
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