711 research outputs found
Kramers-Kronig, Bode, and the meaning of zero
The implications of causality, as captured by the Kramers-Kronig relations
between the real and imaginary parts of a linear response function, are
familiar parts of the physics curriculum. In 1937, Bode derived a similar
relation between the magnitude (response gain) and phase. Although the
Kramers-Kronig relations are an equality, Bode's relation is effectively an
inequality. This perhaps-surprising difference is explained using elementary
examples and ultimately traces back to delays in the flow of information within
the system formed by the physical object and measurement apparatus.Comment: 8 pages; American Journal of Physics, to appea
Reactive control of autonomous drones
Aerial drones, ground robots, and aquatic rovers enable mobile applications that no other technology can realize with comparable flexibility and costs. In existing platforms, the low-level control enabling a drone's autonomous movement is currently realized in a time-triggered fashion, which simplifies implementations. In contrast, we conceive a notion of reactive control that supersedes the time-triggered approach by leveraging the characteristics of existing control logic and of the hardware it runs on. Using reactive control, control decisions are taken only upon recognizing the need to, based on observed changes in the navigation sensors. As a result, the rate of execution dynamically adapts to the circumstances. Compared to time-triggered control, this allows us to: i) attain more timely control decisions, ii) improve hardware utilization, iii) lessen the need to overprovision control rates. Based on 260+ hours of real-world experiments using three aerial drones, three different control logic, and three hardware platforms, we demonstrate, for example, up to 41% improvements in control accuracy and up to 22% improvements in flight time
Non-universality of elastic exponents in random bond-bending networks
We numerically investigate the rigidity percolation transition in
two-dimensional flexible, random rod networks with freely rotating cross-links.
Near the transition, networks are dominated by bending modes and the elastic
modulii vanish with an exponent f=3.0\pm0.2, in contrast with central force
percolation which shares the same geometric exponents. This indicates that
universality for geometric quantities does not imply universality for elastic
ones. The implications of this result for actin-fiber networks is discussed.Comment: 4 pages, 3 figures, minor clarifications and amendments. To appear in
PRE Rap. Com
Adaptive Control Based on Retrospective Cost Optimization
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83558/1/AIAA-46741-507.pd
Glucose regulation and pain in older people-The Helsinki Birth Cohort Study
Aims: To assess if individuals with diabetes or prediabetes report more pain or have increased use of pain medication compared to normoglycaemic individuals. Methods: Using cross-sectional data, we studied 928 men and 1075 women from the Helsinki Birth Cohort Study in 2001-2004 at a mean age of 61.5 years. Glucose regulation was assessed with a 2-h 75 g oral glucose tolerance test, and applying World Health Organization criteria, participants were defined as having normoglycaemia, prediabetes (impaired fasting glucose or impaired glucose tolerance), newly diagnosed diabetes or previously diagnosed diabetes. Self-reported pain intensity and interference during the previous 4 weeks was estimated using the RAND 36-Item Health Survey 1.0. Information on use of pain medication during the past 12 months was obtained from the Social Insurance Institution of Finland. Results: There was no difference in pain intensity or interference between glucose regulation groups for neither men nor women after adjusting for covariates (age, body mass index, education years, Beck Depression Inventory and physical activity). In addition, use of pain medication was similar between glucose regulation groups. Conclusions: Although pain is a common symptom in the general population, impairments in glucose regulation alone does not seem to increase pain among older individuals. (c) 2021 The Authors. Published by Elsevier Ltd on behalf of Primary Care Diabetes Europe. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe
Modularity in signaling systems
Modularity is a property by which the behavior of a system does not change upon interconnection. It is crucial for understanding the behavior of a complex system from the behavior of the composing subsystems. Whether modularity holds in biology is an intriguing and largely debated question. In this paper, we discuss this question taking a control system theory view and focusing on signaling systems. In particular, we argue that, despite signaling systems being constituted of structural modules, such as covalent modification cycles, modularity does not hold in general. As in any engineering system, impedance-like effects, called retroactivity, appear at interconnections and alter the behavior of connected modules. We further argue that while signaling systems have evolved sophisticated ways to counter-act retroactivity and enforce modularity, retroactivity may also be exploited to finely control the information processing of signaling pathways. Testable predictions and experimental evidence are discussed with their implications
TRES: A modular representation of schedulers, tasks, and messages to control simulations in simulink
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