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See detailA Nonlinear Model-Predictive Motion Planning and Control System for Multi-Robots in a Microproduction System with Safety Constraints and a Global Long-Term Solution
Wangmanaopituk, Suparchoek; Voos, Holger UL; Kongprawchnon, Waree

in Kasetsart Journal. Natural Sciences (2014), 48(2), 283-293

The manufacturing of microsystems such as micromotors and micropumps among other examples is a very important emerging market. One big challenge in microproduction is mass customization, that is, the ... [more ▼]

The manufacturing of microsystems such as micromotors and micropumps among other examples is a very important emerging market. One big challenge in microproduction is mass customization, that is, the automated production of a large variety of products that are highly adapted to special customer needs in small batch sizes. These requirements call for a highly flexible manufacturing system. This study focuses on the multi-robot coordination of the resulting flexible microproduction system which is solved here by the application of a multi-agent system. Additionally, all robots additionally applied the proposed nonlinear model predictive control approach on a local real-time level to solve problems associated with path-following and collision avoidance in parallel, while also considering differential constraints on single robots, such as velocity constraints, in this specific application. The global longterm motion planning approach was also considered as an optimization problem. [less ▲]

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See detailNonlinear Observation and Control of a Lightweight Robotic Manipulator Actuated by Shape Memory Alloy (SMA) Wires
Quintanar Guzman, Serket UL

Doctoral thesis (2019)

In the last decade, the industry of Unmanned Aerial Vehicles (UAV) has gone through immense growth and diversification. Nowadays, we find drone based applications in a wide range of industries, such as ... [more ▼]

In the last decade, the industry of Unmanned Aerial Vehicles (UAV) has gone through immense growth and diversification. Nowadays, we find drone based applications in a wide range of industries, such as infrastructure, agriculture, transport, among others. This phenomenon has generated an increasing interest in the field of aerial manipulation. The implementation of aerial manipulators in the UAV industry could generate a significant increase in possible applications. However, the restriction on the available payload is one of the main setbacks of this approach. The impossibility to equip UAVs with heavy dexterous industrial robotic arms has driven the interest in the development of lightweight manipulators suitable for these applications. In the pursuit of providing an alternative lightweight solution for the aerial manipulators, this thesis proposes a lightweight robotic arm actuated by Shape Memory Alloy (SMA) wires. Although SMA wires represent a great alternative to conventional actuators for lightweight applications, they also imply highly nonlinear dynamics, which makes them difficult to control. Seeking to present a solution for the challenging task of controlling SMA wires, this work investigates the implications and advantages of the implementation of state feedback control techniques. The final aim of this study is the experimental implementation of a state feedback control for position regulation of the proposed lightweight robotic arm. Firstly, a mathematical model based on a constitutive model of the SMA wire is developed and experimentally validated. This model describes the dynamics of the proposed lightweight robotic arm from a mechatronics perspective. The proposed robotic arm is tested with three output feedback controllers for angular position control, namely a PID, a Sliding Mode and an Adaptive Controller. The controllers are tested in a MATLAB simulation and finally implemented and experimentally tested in various different scenarios. Following, in order to perform the experimental implementation of a state feedback control technique, a state and unknown input observer is developed. First, a non-switching observable model with unknown input of the proposed robotic arm is derived from the model previously presented. This model takes the martensite fraction rate of the original model as an unknown input, making it possible to eliminate the switching terms in the model. Then, a state and unknown input observer is proposed. This observer is based on the Extended Kalman Filter (EKF) for state estimation and sliding mode approach for unknown input estimation. Sufficient conditions for stability and convergence are established. The observer is tested in a MATLAB simulation and experimentally validated in various different scenarios. Finally, a state feedback control technique is tested in simulation and experimentally implemented for angular position control of the proposed lightweight robotic arm. Specifically, continuous and discrete-time State-Dependent Riccati Equation (SDRE) control laws are derived and implemented. To conclude, a quantitative and qualitative comparative analysis between an output feedback control approach and the implemented state feedback control is carried out under multiple scenarios, including position regulation, position tracking and tracking with changing payloads. [less ▲]

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See detailNonlinear optical properties of Rb2ZnCl4 in the incommensurate and ferroelectric phases
Sanctuary, Roland UL; Jundt, D.; Baumert, J. et al

in Physical Review. B, Condensed Matter and Materials Physics (1985), 32(3), 1649-1660

Nonlinear optical properties of Rb2ZnCl4 are measured for the incommensurate and ferroelectric phases by means of second-harmonic generation experiments. In the temperature range of the ferroelectric lock ... [more ▼]

Nonlinear optical properties of Rb2ZnCl4 are measured for the incommensurate and ferroelectric phases by means of second-harmonic generation experiments. In the temperature range of the ferroelectric lock-in phase, the nonlinear optical coefficients d33, d32, and d24 and the Miller coefficients are determined using the wedge technique and are shown to be proportional to the spontaneous polarization. In the incommensurate phase of Rb2ZnCl4, the order of magnitude of the second-harmonic intensity corresponding to nonlinear optical coefficients allowed by the local point-group symmetry is estimated to be at least 107 times smaller than the second-harmonic intensity generated in quartz and thus difficult to detect. Furthermore, it is shown that quasi-phase-matching of the fundamental and second-harmonic waves in the incommensurate phase is limited to a very small temperature range of TC [less ▲]

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See detailNonlinear protocols for distributed consensus in directed networks of dynamic agents
Li, Yumei UL; Voos, Holger UL; Darouach, Mohamed

in Journal of the Franklin Institute (2015), 352(9), 3645-3669

This paper deals with the distributed consensus problem of multi-agent systems. While existing work mainly considers the design of linear protocols, we derive nonlinear protocols for directed networks of ... [more ▼]

This paper deals with the distributed consensus problem of multi-agent systems. While existing work mainly considers the design of linear protocols, we derive nonlinear protocols for directed networks of dynamic agents with fi xed and switched topologies, respectively. The obtained nonlinear protocols have the same effectiveness as the existing linear protocols, however they can satisfy the input constraints of real world physical systems, as well as the state value restrictions of agents, which ensure the smooth communication of the whole network and the correct data transmission among agents under the limited bandwidth. In contrast to most existing approaches that commonly use the Lyapunov function theory in order to prove the consensus problem, simple and effective mathematical methods are developed here for this purpose. Based on the equivalent in fi nitesimal functions and differentials as well as linear approximations as comparatively simple mathematical tools, we prove that the distributed consensus is asymptotically reachable and derive the group decision values. For balanced topology structures, these nonlinear protocols in particular guarantee that the agents asymptotically reach an average-consensus. Furthermore, the obtained protocols relax the constraints on the communication links among the agents. Finally, simulations comprising the vertical alignment maneuver of a team of unmanned aerial vehicles (UAVs) and the phase synchronization of three oscillators are studied, respectively. The simulation results underline that the developed nonlinear protocols are effective and feasible for distributed consensus in directed networks of dynamic multi-agent systems. [less ▲]

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See detailNonlinear Protocols for Output Performance Value Consensus of Multi-Agent Systems
Li, Yumei UL; Guan, Xinping; Hua, Changchun

in The 30th Chinese Control Conference (2011)

This paper investigates output performance value consensus issue, which is a new necessarily considered issue for cooperative and coordinate control of multi-agent systems with fixed topology. Based on ... [more ▼]

This paper investigates output performance value consensus issue, which is a new necessarily considered issue for cooperative and coordinate control of multi-agent systems with fixed topology. Based on Lyapunov theory, this paper presents nonlinear protocols for output performance value consensus of systems and proves the asymptotic consensus is reachable. Simulation example shows the nonlinear protocols are effective for output performance value consensus of multi-agent systems [less ▲]

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See detailNonlinear Tracking and Landing Controller for Quadrotor Aerial Robots
Voos, Holger UL; Bou-Ammar, Haitham

in IEEE Multi-conference on Systems and Control, Yokohama, Japan, 8-10 Sept. 2010 (2010)

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See detailNonlinear transport through a dynamic impurity in a strongly interacting one-dimensional electron gas
Schmidt, Thomas UL; Komnik, A.

in Phys. Rev. B (2007), 76

We analyze the transport properties of a Luttinger liquid with an embedded impurity of explicitly time-dependent strength. We employ a radiative boundary condition formalism to describe the coupling to ... [more ▼]

We analyze the transport properties of a Luttinger liquid with an embedded impurity of explicitly time-dependent strength. We employ a radiative boundary condition formalism to describe the coupling to the voltage sources. Assuming the impurity time dependence to be oscillatory, we present a full analytic perturbative result in impurity strength for arbitrary interaction parameter calculated with the help of Coulomb gas expansion (CGE). Moreover, a full analytic solution beyond the above restriction is possible for a special nontrivial interaction strength which has been achieved independently by full resummation of CGE series as well as via refermionization technique. The resulting nonlinear current-voltage characteristic turns out to be very rich due to the presence of the additional energy scale associated with the impurity oscillation frequency. In accordance with the previous studies, we also find an enhancement of the linear conductance of the wire to values above the unitary limit G0=2e2/h. [less ▲]

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See detailNonlocalization Properties of Time Operators Transformations
Sorger, Ulrich UL; Suchanecki, Zdzislaw UL

in International Journal of Theoretical Physics (2015), 54(4), 787-800

It is presented a general approach to the problem of extension of time operators and the associated Lambda transformations on singular measures. It is also shown that Lambda transformations defined on ... [more ▼]

It is presented a general approach to the problem of extension of time operators and the associated Lambda transformations on singular measures. It is also shown that Lambda transformations defined on function spaces having the Urysohn property are non localized. Particular attention has been devoted to time and Lambda operators associated with the Walsh-Paley system and to a characterization of their domain and non locality. [less ▲]

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See detailA nonparametric ACD model
Cosma, Antonio UL; Galli, Fausto

in Chevalier, Julien; Goutte, Stephane; Guerreiro, David (Eds.) et al Financial Mathematics, Volatility and Covariance Modelling (2019)

We propose a fully nonparametric approach to the analysis of the Autocorrelated Conditional Duration (ACD) process applied to durations between financial events. We use a recursive algorithm to estimate ... [more ▼]

We propose a fully nonparametric approach to the analysis of the Autocorrelated Conditional Duration (ACD) process applied to durations between financial events. We use a recursive algorithm to estimate the nonparametric specification. In a Monte Carlo experiment, we analyse its forecasting performance and compare it with a correctly and a mis-specified parametric estimator. On a real dataset, the nonparametric estimator seems to mildly overperform in terms of predictive power. The nonparametric analysis can also provide guidance on the choice between alternative parametric specifications. In particular, once intraday seasonality is directly modelled in the conditional duration function, the nonparametric approach provides insights into the time-varying nature of the dynamics in the model that the standard procedures of deseasonalization may lead one to overlook. [less ▲]

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See detailNonparametric Estimation of Additive Models with Homogenous Components
Hardle, Wolfgang; Kim, Woocheol; Tripathi, Gautam UL

in Economic Essays: A Festschrift for Werner Hildenbrand (2009)

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See detailNonparametric Estimation of Homogenous Functions
Tripathi, Gautam UL; Kim, Woocheol

in Econometric Theory (2003), 19

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See detailNonparametric estimation of returns to scale
Severini, Thomas A.; Tripathi, Gautam UL

Presentation (2014, January 30)

Detailed reference viewed: 67 (2 UL)
See detailNonparametric estimation of returns to scale
Severini, Thomas A.; Tripathi, Gautam UL

Scientific Conference (2013)

Detailed reference viewed: 42 (6 UL)
See detailNonparametric estimation of returns to scale
Severini, Thomas A.; Tripathi, Gautam UL

Scientific Conference (2013)

Detailed reference viewed: 31 (3 UL)
See detailNonparametric estimation of returns to scale
Severini, Thomas A.; Tripathi, Gautam UL

Scientific Conference (2014, July 11)

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See detailAn Nonparametric Evaluation of SysML-Based Mechatronic Conceptual Design
Chami, Mohammad; Bou Ammar, Haitham; Voos, Holger UL et al

in Proceedings, 24th Benelux Conference on Artificial Intelligence (2012)

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See detailA nonsynonymous SNP in the ITGB3 gene disrupts the conserved membrane-proximal cytoplasmic salt bridge in the αIIbβ3 integrin and cosegregates dominantly with abnormal proplatelet formation and macrothrombocytopenia
Ghevaert, Cedric; Salsmann, Alexandre UL; Watkins, Nicholas A. et al

in Blood (2008), 111(7), 3407-3414

We report a 3-generation pedigree with 5 individuals affected with a dominantly inherited macrothrombocytopenia. All 5 carry 2 nonsynonymous mutations resulting in a D723H mutation in the beta3 integrin ... [more ▼]

We report a 3-generation pedigree with 5 individuals affected with a dominantly inherited macrothrombocytopenia. All 5 carry 2 nonsynonymous mutations resulting in a D723H mutation in the beta3 integrin and a P53L mutation in glycoprotein (GP) Ibalpha. We show that GPIbalpha-L53 is phenotypically silent, being also present in 3 unaffected pedigree members and in 7 of 1639 healthy controls. The beta3-H723 causes constitutive, albeit partial, activation of the alphaIIbbeta3 complex by disruption of the highly conserved cytoplasmic salt bridge with arginine 995 in the alphaIIb integrin as evidenced by increased PAC-1 but not fibrinogen binding to the patients' resting platelets. This was confirmed in CHO alphaIIbbeta3-H723 transfectants, which also exhibited increased PAC-1 binding, increased adhesion to von Willebrand factor (VWF) in static conditions and to fibrinogen under shear stress. Crucially, we show that in the presence of fibrinogen, alphaIIbbeta3-H723, but not wild-type alphaIIbbeta3, generates a signal that leads to the formation of proplatelet-like protrusions in transfected CHO cells. Abnormal proplatelet formation was confirmed in the propositus's CD34+ stem cell-derived megakaryocytes. We conclude that the constitutive activation of the alphaIIbbeta3-H723 receptor causes abnormal proplatelet formation, leading to incorrect sizing of platelets and the thrombocytopenia observed in the pedigree. [less ▲]

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See detailNontargeted Elucidation of Metabolic Pathways Using Stable-Isotope Tracers and Mass Spectrometry
Hiller, Karsten UL; Metallo, Christian M.; Kelleher, Joanne K et al

in Analytical Chemistry (2010)

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See detailNontidal ocean loading: amplitudes and potential effects in GPS height time series
van Dam, Tonie UL; Collilieux, X.; Wuite, J. et al

in Journal of Geodesy (2012), 86(11), 1043-1057

Ocean bottom pressure (OBP) changes are caused by a redistribution of the ocean’s internal mass that are driven by atmospheric circulation, a change in the mass entering or leaving the ocean, and/or a ... [more ▼]

Ocean bottom pressure (OBP) changes are caused by a redistribution of the ocean’s internal mass that are driven by atmospheric circulation, a change in the mass entering or leaving the ocean, and/or a change in the integrated atmospheric mass over the ocean areas. The only previous global analysis investigating the magnitude of OBP surface displacements used older OBP data sets (van Dam et al. in J Geophys Res 129:507–517, 1997). Since then significant improvements in meteorological forcing models used to predict OBP have been made, augmented by observations from satellite altimetry and expendable bathythermograph profiles. Using more recent OBP estimates from the Estimating the Circulation and Climate of the Ocean (ECCO) project, we reassess the amplitude of the predicted effect of OBP on the height coordinate time series from a global distribution of GPS stations. OBP-predicted loading effects display an RMS scatter in the height of between 0.2 and 3.7 mm, larger than previously reported but still much smaller (by a factor of 2) than the scatter observed due to atmospheric pressure loading. Given the improvement in GPS hardware and data analysis techniques, the OBP signal is similar to the precision of weekly GPS height coordinates. We estimate the effect of OBP on GPS height coordinate time series using the MIT reprocessed solution, mi1. When we compare the predicted OBP height time series with mi1, we find that the scatter is reduced over all stations by 0.1 mm on average with reductions as high as 0.7 mm at some stations. More importantly we are able to reduce the scatter on 65 % of the stations investigated. The annual component of the OBP signal is responsible for 80 % of the reduction in scatter on average.We find that stations located close to semi-enclosed bays or seas are affected by OBP loading to a greater extent than other stations. [less ▲]

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See detailNon‐cognitive vs. cognitive predictors for academic success –opportunities and limits of self‐assessments illustrated by the Viennese products
Kubinger, K. D.; Weitensfelder, Lisbeth; Frebort, Martina et al

Scientific Conference (2012)

Detailed reference viewed: 28 (0 UL)