On designing observers for time-delay systems with nonlinear disturbances

This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2002 Taylor & Francis LtdIn this paper, the observer design problem is studied for a class of time-delay nonlinear systems. The system under consideration is subject to delayed state and non-linear disturbances. The time-delay is allowed to be time-varying, and the non-linearities are assumed to satisfy global Lipschitz conditions. The problem addressed is the design of state observers such that, for the admissible time-delay as well as non-linear disturbances, the dynamics of the observation error is globally exponentially stable. An effective algebraic matrix inequality approach is developed to solve the non-linear observer design problem. Specifically, some conditions for the existence of the desired observers are derived, and an explicit expression of desired observers is given in terms of some free parameters. A simulation example is included to illustrate the practical applicability of the proposed theory.The work of Z. Wang was supported in part by the University of Kaiserslautern of Germany and the Alexander von Humboldt Foundation of Germany

Trajectory generation for road vehicle obstacle avoidance using convex optimization

This paper presents a method for trajectory generation using convex optimization to find a feasible, obstacle-free path for a road vehicle. Consideration of vehicle rotation is shown to be necessary if the trajectory is to avoid obstacles specified in a fixed Earth axis system. The paper establishes that, despite the presence of significant non-linearities, it is possible to articulate the obstacle avoidance problem in a tractable convex form using multiple optimization passes. Finally, it is shown by simulation that an optimal trajectory that accounts for the vehicle’s changing velocity throughout the manoeuvre is superior to a previous analytical method that assumes constant speed

Evolution of surface gravity waves over a submarine canyon

The effects of a submarine canyon on the propagation of ocean surface waves are examined with a three-dimensional coupled-mode model for wave propagation over steep topography. Whereas the classical geometrical optics approximation predicts an abrupt transition from complete transmission at small incidence angles to no transmission at large angles, the full model predicts a more gradual transition with partial reflection/transmission that is sensitive to the canyon geometry and controlled by evanescent modes for small incidence angles and relatively short waves. Model results for large incidence angles are compared with data from directional wave buoys deployed around the rim and over Scripps Canyon, near San Diego, California, during the Nearshore Canyon Experiment (NCEX). Wave heights are observed to decay across the canyon by about a factor 5 over a distance shorter than a wavelength. Yet, a spectral refraction model predicts an even larger reduction by about a factor 10, because low frequency components cannot cross the canyon in the geometrical optics approximation. The coupled-mode model yields accurate results over and behind the canyon. These results show that although most of the wave energy is refractively trapped on the offshore rim of the canyon, a small fraction of the wave energy 'tunnels' across the canyon. Simplifications of the model that reduce it to the standard and modified mild slope equations also yield good results, indicating that evanescent modes and high order bottom slope effects are of minor importance for the energy transformation of waves propagating across depth contours at large oblique angles

A Framework For Memory Performance Prediction From Brain Volume In Preterm-Born Adolescents

With advances in medical care, higher numbers of extremely preterm-born babies are now surviving, however the rate of neurodevelopmental and neurological complications has not improved at the same rate and the relative rate of disabilities and health problems is increasing, with associated high costs for health care systems and education. Understanding brain development after early birth is of great importance to be able to make informed decisions. Many studies have associated different areas of the preterm brain with poor cognitive performance, however it is less clear whether these associations persist into adult life. In this study, we investigate how well cortical volumes describe memory performance in 133 19 year-old adolescents, 61% of whom were born extremely preterm. We employ LASSO to identify brain regions that better explain memory performance. The brain regions identified by LASSO explained 27% and 32% of the variance in the visual working memory scores and the visual short term memory respectively. Furthermore, the correlation between the predicted scores and validation scores is statistically significant and it is 58% for the visual working memory task and 56% for the visual short term memory task

The study of ionospheric anomalies in Japan area during 1998–2010 by Kon et al.: An inaccurate claim of earthquake-related signatures?

The problem of identifying precursory signals of earthquakes in the hope of mitigate the seismic hazard is a very important topic, but inaccurate documentations of precursory signatures decrease the credibility of this field of research. The statistical analysis by Kon et al. (2011) shows that there is tendency of positive total electron content (TEC) anomalies to occur 1–5 days before 52 M > 6 earthquakes which struck Japan during 1998–2010. Kon et al. (2011) also report in detail three selected case studies claiming the occurrence of TEC anomalies possibly related to large and destructive earthquakes. This paper casts doubts on the possibility that in the three cases the TEC disturbances were caused by seismic events suggesting that these TEC changes could be induced by normal variations of the global geomagnetic activity. As a consequence, also the results of the Superimposed Epoch Analysis performed by Kon et al. (2011) could be seriously influenced by global magnetospheric signals

Calorimetric Investigation of CeRu2Ge2 up to 8 GPa

We have developed a calorimeter able to give a qualitative picture of the specific heat of a sample under high pressure up to approximately 10 GPa. The principle of ac-calorimetry was adapted to the conditions in a high pressure clamp. The performance of this technique was successfully tested with the measurement of the specific heat of CeRu2Ge2 in the temperature range 1.5 K<T<12 K. The phase diagram of its magnetic phases is consistent with previous transport measurements.Comment: 5 pages, 4 figure

Working time flexibility components and working time regimes in Europe: using company-level data across 21 countries

Working time ?exibility comprises a wide variety of arrangements, from part-time, overtime, to long-term leaves. Theoretical approaches to grouping these arrangements have been developed, but empirical underpinnings are rare. This article investigates the bundles that can be found for various ?exible working time arrangements, using the Establishment Survey on Working Time and Work–Life Balance, 2004/2005, covering 21 EU member states and 13 industries. The results from the factor analyses con?rmed that working time arrangements can be grouped into two bundles, one for the employee-centred arrangements and second for the employer-centred arrangements, and that these two bundles are separate dimensions.Wealso tested the stability of the factor analysisoutcome, showing that although we ?nd some deviations from the pan-Europe and pan-industry outcome, the naming of the components as ?exibility for employees and ?exibility for employers can be considered rather stable. Lastly, we ?nd three country clusters for the 21 European countries using the bundle approach. The ?rst group includes the Northern European countries along side Poland and Czech Republic, the second group the continental European countries with UK and Ireland, and lastly, the southern European countries with Hungary and Slovenia

A network-based analysis of the preterm adolescent brain using PCA and graph theory

The global increase in the rate of premature birth is of great concern since it is associated with an increase in a wide spectrum of neurologic and cognitive disorders. Neuroimaging analyses have been focused on white matter alterations in preterm subjects and findings have linked neurodevelopment impairment to white matter damage linked to premature birth. However, the trajectory of brain development into childhood and adolescence is less well described. Neuroimaging studies of extremely preterm born subjects in their adulthood are now available to investigate the long-term structural alterations of disrupted neurodevelopment. In this paper, we examine white matter pathways in the preterm adolescent brain by combining state-of-the-art diffusion techniques with graph theory and principal component analysis (PCA). Our results suggest that the pattern of connectivity is altered and differences in connectivity patterns result in more vulnerable premature brain network