61 research outputs found
Friction modeling, identification and compensation
No full textHigh-precision tracking requires excellent control of slow motion and positioning. Recent advances have provided dynamic friction models that represent almost all experimentally observed properties of friction. The state space formulation of these new mathematical descriptions has the property that the state derivatives are continuous functions. This enables the application of established theories for nonlinear systems. The existence of locally stable fixed points does not imply for nonlinear systems the absence of limit cycles (periodic orbits) or unstable solutions. Therefore, global properties of PI velocity and PID position control are analyzed using a passivity and Lyapunov based approach. These linear control laws are then extended by nonlinear components based on the friction model considered. The applications presented in this work are in the domains of mechatronics and machine-tools.LAContact the author at the following address: friedhelm.altpeter(_AT_)ieee.or
A Service of zbw Leibniz-Informationszentrum Wirtschaft Leibniz Information Centre for Economics Age-Dependent Skill Formation and Returns to Education: Simulation Based Evidence Age-Dependent Skill Formation and Returns to Education: Simulation Based Evi
No full textStandard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in Age-Dependent Skill Formation and Returns to Education: Simulation Based Evidence Friedhelm Pfeiffer Karsten Reuß The Institute for the Study of Labor (IZA) in Bonn is a local and virtual international research center and a place of communication between science, politics and business. IZA is an independent nonprofit company supported by Deutsche Post World Net. The center is associated with the University of Bonn and offers a stimulating research environment through its research networks, research support, and visitors and doctoral programs. IZA engages in (i) original and internationally competitive research in all fields of labor economics, (ii) development of policy concepts, and (iii) dissemination of research results and concepts to the interested public. D I S C U S S I O N P A P E R S E R I E S IZA Discussion Papers often represent preliminary work and are circulated to encourage discussion. Citation of such a paper should account for its provisional character. A revised version may be available directly from the author. This study integrates findings from neurobiology and psychology on early childhood development and self-regulation to assess returns to education. Our framework for evaluating the distribution of age-specific returns to investments in cognitive and noncognitive skills is a lifecycle simulation model based on the technology of skill formation (Cunha and Heckman JEL Classification: J21, J24, J3
Mutational analysis of SGPL1: In silico modelling (The analysis results will be shared with Prof. Friedhelm Hildebrandt, Harvard medical school, Division of Nephrology Boston Children's Hospital). These results ( were approved in OAK before), that were shared with Prof. Friedhelm Hildebrandt is now a part of full manuscript for publication with Prof. Friedhelm Hildebrandt as corresponding author . Honnappa Srinivas and Rainer Wilken are the co-authors from NIBR. Please find attached the full manuscript.
No full textSphingosine-1-phosphate lyase (SGPL1), a key enzyme of sphingolipid metabolism, catalyzes the irreversible decomposition of sphingosine-1-phosphate (S1P) by a retro-aldol fragmentation that yields hexadecanaldehyde and phosphoethanolamine. . Its main substrate sphingosine-1-phosphate (S1P) acts both extracellularly, by binding G protein-coupled receptors of the lysophospholipid receptor family, and inside the cell, as a second messenger. Therefore, S1P takes part in regulating various cellular processes and its levels are tightly regulated.
SGPL1 is a symmetric homodimer; two subunits form a tightly intertwined dimer with both chains contributing to the catalytic cavity defined by the covalently bound cofactor pyridoxal phosphate (PLP). Two mutations (R222Q and S346Ile) were found in individuals from families with nephrotic syndrome (unpublished data, Prof. Friedhelm Hildebrandt, Harvard medical school, Division of Nephrology Boston Children's Hospital). To understand the structural changes due to these mutations, we have performed an in silico modelling analysis. The published SGPL1 structure (PDB accession 4Q6R) served as a basis for our in silico model analysis to derive qualitative measure of protein stability and dimer affinity
Single State Elasto-Plastic Friction Models
No full textFor control applications involving small displacements and velocities, friction modeling and compensation can be very important. In particular, the modeling of presliding displacement (motion prior to fully developed slip) can play a pivotal role. In this paper, it is shown that existing single-state friction models exhibit a nonphysical drift phenomenon which results from modeling presliding as a combination of elastic and plastic displacement. A new class of single state models is defined in which presliding is elasto-plastic: under loading, frictional displacement is first purely elastic and then transitions to plastic. The new model class is demonstrated to substantially reduce drift while preserving the favorable properties of existing models (e.g., dissipativity) and to provide a comparable match to experimental data
Motion stabilization in the presence of friction and backlash: a hybrid system approach
No full textIn this paper a hybrid system approach is considered to deal with backlash and
friction induced nonlinearities in mechanical control systems. To describe the low velocity
frictional behaviour a linearized friction model is proposed. The novelty of this study is that
based on the introduced friction model, the stability theorems developed for hybrid systems can
directly be applied for controller design of mechanical systems in the presence of Stribeck friction
and backlash. During the controller design it is assumed that the size of the backlash gap is
unknown and the load side position and velocity cannot be measured. For motion control an LQ
controller is applied. A condition is formulated for the control law parameters to guarantee the
asymptotic stability of the control system. Simulation measurements were performed to confirm
the theoretical results
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