A method for robustness analysis of controlled nonlinear systems

This paper presents an approach to analyzing robustness properties of nonlinear systems under feedback control. The core idea is to apply numerical bifurcation analysis to the closed-loop process, using the controller/observer tuning parameters, the set points, and parameters describing model uncertainty (parametric as well as unmodeled dynamics) as bifurcation parameters. By analyzing the Hopf bifurcation and saddle-node bifurcation loci with respect to these parameters, bounds on the controller tuning are identified which can serve as a measure for the robustness of the controlled system. These bounds depend upon the type as well as the degree of mismatch that exists between the plant and the model used for controller design.The method is illustrated by analyzing three control systems which are applied to a continuously operated stirred tank reactor: a state feedback linearizing controller and two output feedback linearizing controllers. While model uncertainty has only a minor effect on the tuning of the state feedback linearizing controller, this does not represent a very realistic scenario. However, when an observer is implemented in addition to the controller and an output feedback linearizing scheme is investigated, it is found that the plant-model mismatch has a much more profound impact on the tuning of the observer than it has on the controller tuning. In addition, two observer designs with different level of complexity are investigated and it is found that a scheme which makes use of additional knowledge about the system will not necessarily result in better stability properties as the level of uncertainty in the model increases. These investigations are carried out using the robustness analysis scheme introduced in this paper.     

Testing hybrid systems with TTCN-3 embedded

A testing language typically provides a set of test automation statements that allows for a systematic definition and automatic application of stimulation data (i.e. messages or signals) to a system under test. Moreover, it eases the assessment of the system’s reaction by providing customizable evaluation statements and functions. TTCN-3, the Testing and Test Control Notation, already provides universal and powerful concepts to describe tests for discrete, message-based systems. However, software-based control systems that are used to control physical processes often show continuous quantities that can be only poorly stimulated and assessed by means of the currently available language constructs in TTCN-3. In this article, we show how this problem can be solved by extending the TTCN-3 language. We introduce an extension of TTCN-3, namely TTCN-3 embedded, that provides concepts and constructs that directly address the specification of tests for continuous and hybrid real time systems. The extension includes the notion of streams that can be used to represent continuous quantities over time. In addition, TTCN-3 has been extended with the concepts of stream-based ports, sampling, equation systems, and with additional control flow structures. The concepts are integrated with standard TTCN-3 and allow for defining test cases that handle continuous quantities, as well as discrete state changes and the exchange of messages within the same concept space. The feasibility of the approach is shown by providing a small example from the automotive industry.     

Plane-strain fracture toughness of epoxies at different loading rates

The plane-strain fracture toughness of two common epoxy systems of different ductility were determined at different loading rates, according to ASTM E 399 for metallic materials. The ASTM standard was applicable, but underestimated slightly the specimen thickness required for K_Ic. K_Ic decreased with an increasing loading rate and with an increasing yield stress. The fracture surfaces were all very smooth as long as plane-strain conditions prevailed.     

Ideas in the Workplace: A New Approach Towards Organizing the Fuzzy Front End of the Innovation Process

This article pinpoints requirements for organizing the fuzzy front end of the innovation process. The author derived the conditions for computer‐aided idea management from benchmarking the fuzzy front ends of several German and European companies and proposes differentiating between general and company‐specific requirements for organizing the fuzzy front end. It is suggested that structuring the fuzzy front end involves low financial investment but highly sensitive and transparent leadership. Using specific properties of ideas in the workplace as springboards, considerations on further new requirements for successful idea management are developed. Placing a particular emphasis on the interface between the idea owner and the idea‐adoption system, an ‘idea types’ model is developed, which defines four different extreme types of employees and their inclinations to solve problems. An extended set of requirements for managing ideas in the workplace as a useful instrument in creation and implementation of idea‐pipelines in companies and in checking software programmes for idea management or the early stages of new product development programmes is presented.     

Industrially-styled room-temperature pulsed laser deposition of titanium-based coatings

Titanium-based compounds are widely used as coating materials for mechanical, tribological, electrical, optical, catalytic, sensoric, micro-electronical applications due to their exceptionally physical and chemical properties. Recently, the trend of using temperature-sensitive materials like polymers and tool steels with the highest hardness demands new low-temperature coating techniques for protective surface finishing as well as for surface functionalization, but up to now there is lack of industrially scaled vacuum coating techniques at temperatures below 50 °C. An alternative for overcoming this problem is the pulsed laser deposition (PLD) technique, which was up-scaled for industrial demands at Laser Center Leoben of JOANNEUM RESEARCH Forschungsgesellschaft mbH.The current paper summarizes the application of the industrially-scaled PLD technique on the deposition of the presently most important Ti-based coatings: metallic titanium, titanium nitride (TiN), titanium oxide (TiO₂) and titanium carbonitride (TiCN). PLD coating allows, even at room temperature, the formation of film structures of Zone-T type of Thornton's structure zone model, both on substrates aligned normal and parallel to the incident vapor flux. The high-energetic deposition conditions are revealed by the occurrence of (2 2 0) textures for the fcc TiN-based films. The dense grown structure affects advantageously the tribological behavior—generally, low wear rates and (for TiCN) very low friction coefficients were found. For TiO₂ coatings, growing as a mixture of β-TiO₂ and amorphous phases, the easily reproducible change of deposition parameters in the room-temperature PLD allows large differences in the optical transmission and electrical resistance.     

Implied Open-circuit Voltage Imaging via a Single Bandpass Filter Method—Its First Application in Perovskite Solar Cells

A novel, camera-based method for direct implied open-circuit voltage (iV_OC) imaging via the use of a single bandpass filter (s-BPF) is developed for large-area photovoltaic solar cells and precursors. The photoluminescence (PL) emission is imaged using a narrow BPF with centre energy inside the high-energy tail of the PL emission, utilising the close-to-unity and nearly constant absorptivity of typical photovoltaic devices in this energy range. As a result, the exact value of the sample's absorptivity within the BPF transmission band is not required. The use of an s-BPF enables a fully contactless approach to calibrate the absolute PL photon flux for spectrally integrated detectors, including cameras. The method eliminates the need for knowledge of the imaging system spectral response. Through an appropriate choice of the BPF centre energy, a range of absorber compositions or a single absorber with different surface morphologies, such as planar and textured, can be imaged, all without the need for additional detection optics. The feasibility of this s-BPF method is first validated. The relative error in iV_OC is determined to be ≤1.5%. The method is then demonstrated on device stacks with two different perovskite compositions commonly used in single-junction and monolithic tandem solar cells.     

Optimization and Filtering for Human Motion Capture

Local optimization and filtering have been widely applied to model-based 3D human motion capture. Global stochastic optimization has recently been proposed as promising alternative solution for tracking and initialization. In order to benefit from optimization and filtering, we introduce a multi-layer framework that combines stochastic optimization, filtering, and local optimization. While the first layer relies on interacting simulated annealing and some weak prior information on physical constraints, the second layer refines the estimates by filtering and local optimization such that the accuracy is increased and ambiguities are resolved over time without imposing restrictions on the dynamics. In our experimental evaluation, we demonstrate the significant improvements of the multi-layer framework and provide quantitative 3D pose tracking results for the complete HumanEva-II dataset. The paper further comprises a comparison of global stochastic optimization with particle filtering, annealed particle filtering, and local optimization.     

Designing automation for complex work environments under different levels of stress

This article examines the effectiveness of different forms of static and adaptable automation under low- and high-stress conditions. Forty participants were randomly assigned to one of four experimental conditions, comparing three levels of static automation (low, medium and high) and one level of adaptable automation, with the environmental stressor (noise) being varied as a within-subjects variable. Participants were trained for 4?h on a simulation of a process control environment, called AutoCAMS, followed by a 2.5-h testing session. Measures of performance, psychophysiology and subjective reactions were taken. The results showed that operators preferred higher levels of automation under noise than under quiet conditions. A number of parameters indicated negative effects of noise exposure, such as performance impairments, physiological stress reactions and higher mental workload. It also emerged that adaptable automation provided advantages over low and intermediate static automation, with regard to mental workload, effort expenditure and diagnostic performance. The article concludes that for the design of automation a wider range of operational scenarios reflecting adverse as well as ideal working conditions needs to be considered.     

An executable formal semantics for UML-RT

We propose a formal semantics for UML-RT, a UML profile for real-time and embedded systems. The formal semantics is given by mapping UML-RT models into a language called kiltera, a real-time extension of the \(\pi \)-calculus. Previous attempts to formalize the semantics of UML-RT have fallen short by considering only a very small subset of the language and providing fundamentally incomplete semantics based on incorrect assumptions, such as a one-to-one correspondence between “capsules” and threads. Our semantics is novel in several ways: (1) it deals with both state machine diagrams and capsule diagrams; (2) it deals with aspects of UML-RT that have not been formalized before, such as thread allocation, service provision points, and service access points; (3) it supports an action language; and (4) the translation has been implemented in the form of a transformation from UML-RT models created with IBM’s RSA-RTE tool, into kiltera code. To our knowledge, this is the most comprehensive formal semantics for UML-RT to date.     

Properties of BaxSr1−x TiO3 films grown by rf magnetron sputtering on sapphire with an SrTiO3 sublayer

Results are presented of experiments to deposit barium strontium titanate films on an r-cut sapphire substrate with a strontium titanate sublayer. It is shown that the use of a strontium titanate sublayer can ensure that the dielectric properties of barium strontium titanate films have a weak temperature dependence over a wide temperature range. Moreover, the parameters of the films are consistent with those required to fabricate microwave microelectronics devices. Pis’ma Zh. Tekh. Fiz. 25, 1–5 (July 26, 1999)