Application of a Fractional Order Integral Resonant Control to increase the achievable bandwidth of a nanopositioner

The congress program will essentially include papers selected on the highest standard by the IPC, according to the IFAC guidelines www.ifac-control.org/publications/Publications-requirements-1.4.pdf, and published in open access in partnership with Elsevier in the IFAC-PapersOnline series, hosted on the ScienceDirect platform www.sciencedirect.com/science/journal/24058963. Survey papers overviewing a research topic are also most welcome. Contributed papers will have usual 6 pages length limitation. 12 pages limitation will apply to survey papers.Publisher PD

Integral Resonant Control for vibration damping and precise tip-positioning of a single-link flexible manipulator

Peer reviewedPostprin

A robust control scheme for flexible arms with friction in the joints

A general control scheme to control flexible arms with friction in the joints is proposed in this paper. This scheme presents the advantage of being robust in the sense that it minimizes the effects of the Coulomb friction existing in the motor and the effects of changes in the dynamic friction coefficient. A justification of the robustness properties of the scheme is given in terms of the sensitivity analysis

Phosphorelays provide tunable signal processing capabilities for the cell

Achieving a complete understanding of cellular signal transduction requires deciphering the relation between structural and biochemical features of a signaling system and the shape of the signal-response relationship it embeds. Using explicit analytical expressions and numerical simulations, we present here this relation for four-layered phosphorelays, which are signaling systems that are ubiquitous in prokaryotes and also found in lower eukaryotes and plants. We derive an analytical expression that relates the shape of the signal-response relationship in a relay to the kinetic rates of forward, reverse phosphorylation and hydrolysis reactions. This reveals a set of mathematical conditions which, when satisfied, dictate the shape of the signal-response relationship. We find that a specific topology also observed in nature can satisfy these conditions in such a way to allow plasticity among hyperbolic and sigmoidal signal-response relationships. Particularly, the shape of the signal-response relationship of this relay topology can be tuned by altering kinetic rates and total protein levels at different parts of the relay. These findings provide an important step towards predicting response dynamics of phosphorelays, and the nature of subsequent physiological responses that they mediate, solely from topological features and few composite measurements; measuring the ratio of reverse and forward phosphorylation rate constants could be sufficient to determine the shape of the signal-response relationship the relay exhibits. Furthermore, they highlight the potential ways in which selective pressures on signal processing could have played a role in the evolution of the observed structural and biochemical characteristic in phosphorelays

Two-degrees-of-freedom PI2D controller for precise nanopositioning in the presence of hardware-induced constant time delay

This work was supported in part by the Spanish Agencia Estatal de Investigacion (AEI) under Project DPI2016-80547-R (Ministerio de Economia y Competitividad) and in part by the European Social Fund (FEDER, EU), and in part by the Spanish FPU12/00984 Program (Ministerio de Educacion, Cultura y Deporte).Peer reviewedPostprin

Fractional order implementation of Integral Resonant Control – A nanopositioning application

This paper was sponsored by the Spanish FPU12/00984 Program (Ministerio de Educacion, Cultura y Deporte). It was also sponsored by the Spanish Government Research Program with the Project DPI2012-37062-CO2-01 (Ministerio de Economia y Competitividad) and by the European Social Fund.Peer reviewedPostprin

Unlimited multistability and Boolean logic in microbial signalling

The ability to map environmental signals onto distinct internal physiological states or programmes is critical for single-celled microbes. A crucial systems dynamics feature underpinning such ability is multistability. While unlimited multistability is known to arise from multi-site phosphorylation seen in the signalling networks of eukaryotic cells, a similarly universal mechanism has not been identified in microbial signalling systems. These systems are generally known as two-component systems comprising histidine kinase (HK) receptors and response regulator proteins engaging in phosphotransfer reactions. We develop a mathematical framework for analysing microbial systems with multi-domain HK receptors known as hybrid and unorthodox HKs. We show that these systems embed a simple core network that exhibits multistability, thereby unveiling a novel biochemical mechanism for multistability. We further prove that sharing of downstream components allows a system with n multi-domain hybrid HKs to attain 3n steady states. We find that such systems, when sensing distinct signals, can readily implement Boolean logic functions on these signals. Using two experimentally studied examples of two-component systems implementing hybrid HKs, we show that bistability and implementation of logic functions are possible under biologically feasible reaction rates. Furthermore, we show that all sequenced microbial genomes contain significant numbers of hybrid and unorthodox HKs, and some genomes have a larger fraction of these proteins compared with regular HKs. Microbial cells are thus theoretically unbounded in mapping distinct environmental signals onto distinct physiological states and perform complex computations on them. These findings facilitate the understanding of natural two-component systems and allow their engineering through synthetic biology

Understanding the CO Preoxidation and the Intrinsic Catalytic Activity of Step Sites in Stepped Pt Surfaces in Acidic Medium

In order to deepen the knowledge about the origin of the CO preoxidation process and the intrinsic catalytic activity of Pt superficial steps toward CO oxidation, a series of CO stripping experiments were performed on stepped Pt electrodes in acidic medium. For the occurrence of CO preoxidation, it was found that it arises (reproducibly) whenever four interconnected conditions are simultaneously fulfilled: (1) CO adsorption at potentials lower than about 0.2 V; (2) on surfaces saturated with COads; (3) in the presence of traces of CO in solution; (4) in the presence of surface steps. If any of these four conditions is not satisfied, the CO preoxidation pathway does not appear, even though the steps on the electrode surface are completely covered by CO. By controlling the removal of the CO adlayer (voltammetrically), we show that once the CO adlayer has been partially oxidized, the (111) terrace sites of stepped surfaces are released earlier than the (110) step sites. Moreover, if (110) steps are selectively decorated with CO, its oxidation occurs only at potentials ∼150 mV higher than the CO preoxidation peak. Our results systematically demonstrate that step sites are less active to oxidize CO than those ones responsible for the CO preoxidation process. Once the sites responsible for the CO preoxidation are made free, there is no apparent motion of the remaining adsorbed CO layer, suggesting that the activation of the surface controls the whole process, rather than the diffusion of COads toward hypothetically “most active sites”. Voltammetric and chronoamperometric experiments performed on partially covered CO adlayers suggest that adsorbed CO behave as a motionless species during its oxidation, in which the CO adlayer is removed piece by piece. By means of in situ FTIR experiments, the stretching frequency of CO selectively adsorbed on (110) step sites was examined. Band frequency results confirm that those molecules adsorbed on steps are fully coupled with the adsorbed CO on (111) terraces when the surface reaches full coverage.M.J.S. Farias is grateful to the CNPq (Brazil) (grants 200390/2011-2 and 313402/2013-2) for the financial support. G. A. Camara acknowledges financial assistance from CNPq (grants 305494/2012-0 and 405695/2013-6) and FUNDECT (grant 23/200.583/2012). J. M. Feliu thanks the MINECO (Spain) project CTQ2013-44083-P

On the oxidation of isopropanol on platinum single crystal electrodes. A detailed voltammetric and FTIR study

Isopropanol oxidation is studied on platinum single crystals using electrochemical techniques and FTIR spectroscopy at different isopropanol concentrations. Isopropanol oxidation is found to be facilitated by the presence of adsorbed OH on the electrode surface, which reacts with an isopropanol molecule to yield the adsorbed alkoxide. Thus, when sulfuric acid is used as the supporting electrolyte instead of perchloric acid, oxidation currents diminish drastically since sulfate hinders OH adsorption. Kinetic measurements reveal that the chemical reaction between adsorbed OH and isopropanol is the rate-determining step in the mechanism. Voltammetric and FTIR experiments show that acetone is the major product of the reaction. On the Pt(111) surface, acetone is produced exclusively, and oxidation currents are controlled by diffusion since, on this electrode, acetone is not adsorbed and the adsorbed OH mobility is high. The adsorption of acetone-related species on the Pt(110) surface, which partially block the surface, leads to slightly lower currents. On the other hand, the Pt(100) electrode is the one showing significant rates for the C–C bond cleavage, yielding adsorbed CO and other species. Although this route is a minor path, the surface blockage by these species leads to a significant diminution of the currents.This research was funded by Ministerio de Ciencia e Innovación (Spain) grant number PID2019-105653 GB-I00) and Generalitat Valenciana (Spain) grant number PROMETEO/2020/063. RMAA acknowledges the financial support from Generalitat Valenciana (CDEIGENT/2019/018). DSM thanks the Government of Argelia for the award of a doctoral fellowship to support her studies at the University of Alicante

Understanding the electrochemical hydrogenation of acetone on Pt single crystal electrodes

The heterogeneous upgrading of biomass by means of electrocatalytic hydrogenation is an attractive way to refine products for industrial and pharmaceutical purposes. Also, the efficient electrochemical reduction of carbonyl compounds can act as hydrogen vectors, and therefore energy vectors. In this manuscript, we render further fundamental insights into the electrochemical reduction of acetone as a model molecule of carbonyl compounds. The structural sensitivity of the reaction is demonstrated by using platinum single crystal electrodes with low Miller indices and stepped electrodes with (110) terraces and either (111) or (100) monoatomic steps. Among the basal planes, Pt(110) is the only one active for the electroreduction of acetone. The inclusion of (111) steps on the (110) terraces does not significantly alter the behavior of Pt(110), but increasing the (100) step density has been observed to decrease the activity. We attribute this different performance to a geometrical effect of the active sites. By using different supporting electrolytes, we have found that sulfate competes with acetone for the surface sites, thus modifying the adlayer interfacial structure and hampering acetone reactivity.This research was funded by Ministerio de Ciencia e Innovación (Spain) grant number PID2019-105653GB-I00), Generalitat Valenciana (Spain) grant number PROMETEO/2020/063. RMAA. acknowledges the financial support from Generalitat Valenciana (CDEIGENT/2019/018)