On a Kelvin-Voigt Viscoelastic Wave Equation with Strong Delay

An initial-boundary value problem for a viscoelastic wave equation subject to a strong time-localized delay in a Kelvin & Voigt-type material law is considered. Transforming the equation to an abstract Cauchy problem on the extended phase space, a global well-posedness theory is established using the operator semigroup theory both in Sobolev-valued $C^{0}$- and BV-spaces. Under appropriate assumptions on the coefficients, a global exponential decay rate is obtained and the stability region in the parameter space is further explored using the Lyapunov's indirect method. The singular limit $\tau \to 0$ is further studied with the aid of the energy method. Finally, a numerical example from a real-world application in biomechanics is presented.Comment: 34 pages, 4 figures, 1 set of Matlab code

Appearance-based localization for mobile robots using digital zoom and visual compass

This paper describes a localization system for mobile robots moving in dynamic indoor environments, which uses probabilistic integration of visual appearance and odometry information. The approach is based on a novel image matching algorithm for appearance-based place recognition that integrates digital zooming, to extend the area of application, and a visual compass. Ambiguous information used for recognizing places is resolved with multiple hypothesis tracking and a selection procedure inspired by Markov localization. This enables the system to deal with perceptual aliasing or absence of reliable sensor data. It has been implemented on a robot operating in an office scenario and the robustness of the approach demonstrated experimentally

Measurement of Subcellular CA2+ Redistribution in Cardiac Muscle In Situ: Time Resolved Rapid Freezing and Electron Probe Microanalysis

To directly assess the physiological roles of sarcoplasmic reticulum (SR) and miitochondria (MT), we have utilized energy dispersive electron probe microanalysis (EPMA) on ultrathin freeze-dried cryosections from isolated papillary muscles, rapidly frozen at precise time points of the contractile cycle. Using this approach, we can detect redistribution of subcellular Ca2+ during the cardiac contractile cycle. Changes in Ca2+ of less than 1.0 mmol/kg dry wt can be detected. By determining the variability of the Ca2+ measurements in preliminary experiments, we have also demonstrated that it is possible to optimize experimental design, i.e., to predict the number of animals per treatment group and the number of X-ray spectra per animal that are required in order to detect a specified Ca2+ difference. Quantitative EPMA of rapidly frozen contracting papillary muscle has also allowed us to correlate the Ca2+ content of SR and MT with the contractile state of the muscle. Our results show a decrease of 40% in the amount of Ca2+ stored in the junctional SR during a cardiac muscle twitch, thus providing direct evidence for a role of the SR as a primary site of Ca2+ release. In addition, we have demonstrated dissociation between MT Ca2+ uptake and activation of regulatory enzymes, such as pyruvate dehydrogenase, indicating that MT Ca2+ uptake is not required for activation of MT metabolism

The evolution of representation in simple cognitive networks

Representations are internal models of the environment that can provide guidance to a behaving agent, even in the absence of sensory information. It is not clear how representations are developed and whether or not they are necessary or even essential for intelligent behavior. We argue here that the ability to represent relevant features of the environment is the expected consequence of an adaptive process, give a formal definition of representation based on information theory, and quantify it with a measure R. To measure how R changes over time, we evolve two types of networks---an artificial neural network and a network of hidden Markov gates---to solve a categorization task using a genetic algorithm. We find that the capacity to represent increases during evolutionary adaptation, and that agents form representations of their environment during their lifetime. This ability allows the agents to act on sensorial inputs in the context of their acquired representations and enables complex and context-dependent behavior. We examine which concepts (features of the environment) our networks are representing, how the representations are logically encoded in the networks, and how they form as an agent behaves to solve a task. We conclude that R should be able to quantify the representations within any cognitive system, and should be predictive of an agent's long-term adaptive success.Comment: 36 pages, 10 figures, one Tabl

Self-calibration and improving image fidelity for ALMA and other radio interferometers

This manual is intended to help ALMA and other interferometer users improve images by recognising limitations and how to overcome them and deciding when and how to use self-calibration. The images provided by the ALMA Science Archive are calibrated using standard observing and data processing routines, including a quality assurance process to make sure that the observations meet the proposer's science requirements. This may not represent the full potential of the data, since any interferometry observation can be imaged with a range of resolutions and surface brightness sensitivity. The separation between phase calibration source and target usually limits the target dynamic range to a few hundred (or 50--100 for challenging conditions) but if the noise in the target field has not reached the thermal limit, improvements may be possible using self-calibration. This often requires judgements based on the target properties and is not yet automated for all situations. This manual provides background on the instrumental and atmospheric causes of visibility phase and amplitude errors, their effects on imaging and how to improve the signal to noise ratio and image fidelity by self-calibration. We introduce the conditions for self-calibration to be useful and how to estimate calibration parameter values for a range of observing modes (continuum, spectral line etc.). We also summarise more general error recognition and other techniques to tackle imaging problems. The examples are drawn from ALMA interferometric data processed using CASA, but the principles are generally applicable to most similar cm to sub-mm imaging.Comment: 76 pages, 55 figures, ALMA Memo serie