control based on saturated time-delay systems theory of mach number in wind tunnels

Producción CientíficaA proposal for the regulation of the Mach number in wind tunnels using static state feedback for saturated systems with delays is presented here. As these systems can be precisely represented by a time-delay model with saturating inputs, a general solution for discrete delayed systems with saturating input is first derived. This general solution is based on modeling the saturation using a Lyapunov functional, using free weighting matrices and maximizing the set of admissible initial conditions. The application of this solution to the control of the Mach number in a wind tunnel is then presented, illustrating the design procedures.MiCInn Project DPI2014-54530-

Robust H∞ Control of Takagi–Sugeno Systems with Actuator Saturation

Producción CientíficaThe robust static output feedback control for continuous-time Takagi–Sugeno systems subject to actuator saturation is solved here, including H∞ performance guarantees. Based on a polytopic model of the saturation, sufficient conditions are proposed for designing these controllers in terms of Linear Matrix Inequalities. With the aid of some special derivations, bilinear matrix inequalities are converted into a set of linear matrix inequalities which can be solved easily without requiring iterative algorithms or equality constraints, moreover, the output matrix of the considered system does not require to be full row rank. Finally, some examples are presented to show the validity of the proposed methodology

Allosteric rescue of catalytically impaired ATP phosphoribosyltransferase variants links protein dynamics to active-site electrostatic preorganisation

Funding: This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) [Grant BB/M010996/1] via EASTBIO Doctoral Training Partnership studentships to B. J. R. and G. F., by Stiftelsen Olle Engkvist Byggmästare [Grant 190-0335] and the Knut and Alice Wallenberg Foundation [Grants 2018.0140 and 2019.0431] to S.C.L.K., and by the European Union’s Horizon 2020 Research and Innovation Programme via a Marie Sklodowska-Curie fellowship [Grant 890562] to M.C. The simulations were enabled by resources provided by the Swedish National Infrastructure for Supercomputing (SNIC, UPPMAX), partially funded by the Swedish Research Council [Grant 2016-07213].ATP phosphoribosyltransferase catalyses the first step of histidine biosynthesis and is controlled via a complex allosteric mechanism where the regulatory protein HisZ enhances catalysis by the catalytic protein HisGS while mediating allosteric inhibition by histidine. Activation by HisZ was proposed to position HisGS Arg56 to stabilise departure of the pyrophosphate leaving group. Here we report active-site mutants of HisGS with impaired reaction chemistry which can be allosterically restored by HisZ despite the HisZ:HisGS interface lying ~20 Å away from the active site. MD simulations indicate HisZ binding constrains the dynamics of HisGS to favour a preorganised active site where both Arg56 and Arg32 are poised to stabilise leaving-group departure in WT-HisGS. In the Arg56Ala-HisGS mutant, HisZ modulates Arg32 dynamics so that it can partially compensate for the absence of Arg56. These results illustrate how remote protein-protein interactions translate into catalytic resilience by restoring damaged electrostatic preorganisation at the active site.Publisher PDFPeer reviewe

Closed-Loop Control of Fluid Flow: a Review of Linear Approaches and Tools for the Stabilization of Transitional Flows

International audienceFlow control is concerned with the targeted manipulation of intrinsic flow behavior to optimally satisfy prescribed objectives. This article will give an overview of the most common tools for the design of control strategies. We focus on linear control that is aimed at stabilizing fixed points of the Navier-Stokes equations, such as those existing in the case of transitional flows. Key steps to build a Galerkin-based and a data-based model will be presented and illustrated on two generic flow configurations: flow over an open cavity and over a backward-facing step. In the former case, a feedback configuration will result and particular attention will be paid to performance measures and robustness analyses. For the latter case, a feedforward setup has been chosen and a system-identification method will be employed to extract the fluid behavior from data sequences, via statistical learning techniques

Development in a biologically inspired spinal neural network for movement control

In two phases, we develop neural network models of spinal circuitry which self-organises into networks with opponent channels for the control of an antagonistic muscle pair. The self-organisation is enabled by spontaneous activity present in the spinal cord. We show that after the process of self-organisation, the networks have developed the possibility to independently control the length and tension of the innerated muscles. This allows the specification of joint angle independent from the specification of joint stiffness. The first network comprises only motorneurons and inhibitory interneurons through which the two channels interact. The inhibitory interneurons prevent saturation of the motorneuron pools, which is a necessary condition for independent control. In the second network, however, the neurons in the motorneuron pools obey the size-principle, which is a threat to the desired invariance of joint angle for varying joint stiffness, because of the different amplification of inputs in the case these inputs are not equal. To restore the desired invariance the second network ha.s been expanded with Renshaw cells. The manner in which they are included in the circuitry corrects the problem caused by the addition of the size-principle. The results obtained from the two models compare favourably with the FLETE-model for spinal circuitry (Bullock & Grossberg, 1991; Bullock et al., HJ93; Bullock & Contreras-Vidal, 1993) which has been successful in explaining several phenomena related to motor control.Fulbright Scholarship; Office of Naval Research (N00014-92-J-1309, N00014-95-1-0409

Analysis and feedback control of magnetic bearings with reference to flywheel energy storage.

Bibliography: leaves 132-136.In high speed applications magnetic bearings offer many potential advantages over mechanical bearings. The type of magnetic bearing most suitable for energy storage flywheels is selected and analysed for the purpose of designing feedback control loops. A nonlinear as well as a small signal linear model of the "current driven" magnetic bearing with unlaminated magnetic components is derived. Subsequently describing functions characterising the small- as well as large signal behaviour of the same bearing in the "voltage driven" mode, are obtained. It is shown that workable results are obtained for most practical situations by using linear systems theory, although the magnetic bearing is a nonlinear device. The describing function model enables the designer to identify the mechanisms leading to limit cycles under adverse operating conditions. Feedback control loops designed around the small signal characteristics produce practical results in the case of the "voltage driven" mode which are superior to that of the "current driven" case. An essential refinement, where energy losses and vibrations arising from rotor imbalance are eliminated, is described. A discrete time filtering technique is used. Two experimental models were built and fully tested in order to verify the above theoretical approaches

An economic policy for the fifth long wave

The paper starts by reviewing a recent contribution on long-waves, in order to recall the essential points of a theory that, better than any other, is able to explain the long term development of capitalist economies. Considering that the present technological revolution in ICT is part of the broad phenomenon of a new long wave, it follows that the main focus of economic policy should be to support the diffusion of the new technological style and to favour the institutional changes required by such an objective. On the basis of a selective view of what is deemed crucial to foster the full implementation of the new long wave, four broad guidelines are suggested: (i) a Keynesian policy for demand; (ii) a policy to re-establish the primacy of productive capital through systematic concerted open market operations to regulate liquidity in the financial markets; (iii) a reconstruction of the employment relationship that, while taking into consideration the requirements of the new technological paradigm, preserves the essential features of the “European social model”; a targeted flexibility of labour, that contrasts with the all-out market flexibility that results from the neoclassical theory, is also suggested; (iv) a regime for intellectual property rights that avoids the drawbacks – both ethical and economic – of current US practices.long-waves