Stability borders of feedback control of delayed measured systems

When stabilization of unstable periodic orbits or fixed points by the method given by Ott, Grebogi and Yorke (OGY) has to be based on a measurement delayed by $\tau$ orbit lengths, the performance of unmodified OGY method is expected to decline. For experimental considerations, it is desired to know the range of stability with minimal knowledge of the system. We find that unmodified OGY control fails beyond a maximal Ljapunov number of $\lambda_{max}=1+\frac{1}{\tau}$. In this paper the area of stability is investigated both for OGY control of known fixed points and for difference control of unknown or inaccurately known fixed points. An estimated value of the control gain is given. Finally we outline what extensions have to be considered if one wants to stabilize fixed points with Ljapunov numbers above $\lambda_{max}$.Comment: 5 pages LaTeX using revtex and epsfig (4 figs included). Revised versio

Electronic Performance Support for E-Learning Analysis and Design

Corporate instructional designers often follow an instructional systems design (ISD) process to plan, create, and implement training programs. Increased demand for elearning as a replacement or addition to classroom training means that, in the current corporate environment, instructional designers are called upon to produce a wide variety of instructional formats and have to make more decisions during the ISD process. E-learning is evolving into a total performance improvement solution rather than simply as a means to delivering distance training and consequently, in an effort to achieve business goals, many corporations are turning to it as a cost effective way to deliver training and support to employees and customers. Corporate e-learning applications can incorporate knowledge management and electronic performance support as well as support for multiple formats of online learning, adding to the complexity of the instructional designer\u27s job and the ISD process. While the ISD process is well documented and numerous operational models exist, instructional designers often have difficulty in its application given the complexity of an e-learning application. The study analyzed the impact of an experimental electronic performance support system (EPSS) on the performance of e-learning instructional designers. An EPSS intended to provide assistance during the analysis and design stages of an e-learning project was created to aid corporate instructional designers make tradeoffs among time, cost, and quality of various analysis and design procedures and techniques. Formative reviews by instructional designers experienced in e-learning added to the validity of the contents of the EPSS. Summative evaluator’s pilot tested the EPSS by using it in conjunction with the analysis and design activities of three corporate e-learning projects. Evaluation results indicated that an instructional design EPSS can help designers sequence and prioritize tasks, allocate time and resources to task execution, and focus tasks on user performance and client goals

Analysis of water vapor adsorption in soils by means of a lysimeter and numerical modeling

Daily temperature oscillations can cause adsorption (and desorption) of atmospheric water vapor by soils. The resulting daily fluctuations in the amount of liquid water in the soil can be measured by high-precision weighing lysimeters. We analyzed the data of a lysimeter in a sandy dune sediment in southern Spain using Codebright, a thermohydraulic numerical model for unsaturated flow that takes into account water, vapor, and heat transport in the soil, as well as soil–atmosphere interactions such as precipitation, evaporation, and solar radiation. The analysis shows that daily temperature oscillations, psychrometrics, and soil water retention can explain the fluctuations of the amount of liquid water in the soil. The retention curve, especially its driest part, is essential for the existence of these fluctuations. The fluctuations could not be reproduced by a model using the van Genuchten retention curve with a constant residual saturation. On the other hand, satisfactory results could be obtained by models using retention curves that at their driest part still show a change of saturation with suction. Moreover, the models suggest within the top few decimeters of the soil a pattern of alternating bands of condensation and evaporation, which follows the daily temperature oscillations that fade out deeper in the soil.We are very grateful to André Peters for providing the AWAT filter and give special thanks to Daniel Jesus Martínez, Fernando Ruiz Bermudo, and Antonio Nicolas Martínez for their excellent technical assistance and support.We are grateful for the support and collaboration of the Biological Station of Doñana, the Biological Reserve of Doñana, and the administration of the Doñana National Park. The contract of Lidia Molano Leno (PEJ-2014-A-68763) was financed by the Ministry of Economy, Industry and Competitiveness of Spain (MINECO) and co-financed by the European Investment Bank (EIB) and the European Social Fund (ESF). Likewise, this work has been financed by the CLIGRO Project (MICINN, CGL2016-77473-C3-1-R) of the Spanish National Plan for Scientific and Technical Research and Innovation. The infrastructure has been co-financed by European Research Funds (SE Scientific Infrastructures and Techniques and Equipment 2013, IGME13-1E-2113).Peer ReviewedPostprint (published version