Backstepping-based tracking control of the vertical gradient freeze crystal growth process

The vertical gradient freeze crystal growth process is the main technique for the production of high quality compound semiconductors that are vital for today's electronic applications. A simplified model of this process consists of two 1D diffusion equations with free boundaries for the temperatures in crystal and melt. Both phases are coupled via an ordinary differential equation that describes the evolution of the moving solid/liquid interface. The control of the resulting two-phase Stefan problem is the focus of this contribution. A flatness-based feedforward design is combined with a multi-step backstepping approach to obtain a controller that tracks a reference trajectory for the position of the phase boundary. Specifically, based on some preliminary transformations to map the model into a time-variant PDE-ODE system, consecutive decoupling and backstepping transformations are shown to yield a stable closed loop. The tracking controller is validated in a simulation that considers the actual growth of a Gallium arsenide single crystal.Comment: 6 pages, 5 figure

Backstepping Control of Coupled General Hyperbolic-Parabolic PDE-PDE Systems

This paper considers the backstepping state feedback and observer design for hyperbolic and parabolic PDEs, which are bidirectionally interconnected in a general coupling structure. Both PDE subsystems consist of coupled scalar PDEs with the heterodirectional hyperbolic PDE subsystem subject to actuation and sensing. By making use of a multi-step approach to construct the transformation into a stable target system, it is shown that a backstepping state feedback and observer design only requires to solve the well-known kernel equations for the hyperbolic and parabolic subsystems as well as additional decoupling equations. The latter are standard initial boundary value problems for parabolic PDEs. This significantly facilitates the well-posedness analysis and the numerical computation of the backstepping controller. Exponential stability is verified for the state feedback loop, the observer error dynamics, and the closed-loop system using an observer-based compensator. The proposed backstepping design procedures are demonstrated for numerical examples.Comment: 8 pages, 6 figures, journal paper under revie

The uORF-containing thrombopoietin mRNA escapes nonsense-mediated decay (NMD)

Platelet production is induced by the cytokine thrombopoietin (TPO). It is physiologically critical that TPO expression is tightly regulated, because lack of TPO causes life-threatening thrombocytopenia while an excess of TPO results in thrombocytosis. The plasma concentration of TPO is controlled by a negative feedback loop involving receptor-mediated uptake of TPO by platelets. Furthermore, TPO biosynthesis is limited by upstream open reading frames (uORFs) that curtail the translation of the TPO mRNA. uORFs are suggested to activate RNA degradation by nonsense-mediated decay (NMD) in a number of physiological transcripts. Here, we determine whether NMD affects TPO expression. We show that reporter mRNAs bearing the seventh TPO uORF escape NMD. Importantly, endogenously expressed TPO mRNA from HuH7 cells is unaffected by abrogation of NMD by RNAi. Thus, regulation of TPO expression is independent of NMD, implying that mRNAs bearing uORFs cannot generally be considered to represent NMD targets

Green Space Visits among Adolescents: Frequency and Predictors in the PIAMA Birth Cohort Study.

Green space may influence health through several pathways, for example, increased physical activity, enhanced social cohesion, reduced stress, and improved air quality. For green space to increase physical activity and social cohesion, spending time in green spaces is likely to be important

The questionnaire design process in the European Human Biomonitoring Initiative (HBM4EU)

This document was created for the HBM4EU project. HBM4EU has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 733032. The Swiss participation in this European Program is funded by the Swiss State Secretary for Education Research and Innovation (SERI).Background: Designing questionnaires is a key point of epidemiological studies assessing human exposure to chemicals. The lack of validated questionnaires can lead to the use of previously developed and sub-optimally adapted questionnaires, which may result in information biases that affect the study’s validity. On this ground, a multidisciplinary group of researchers developed a series of tools to support data collection within the HBM4EU initiative. The objective of this paper is to share the process of developing HBM4EU questionnaires, as well as to provide researchers with harmonized procedures that could help them to design future questionnaires to assess environmental exposures. Methods: In the frame of the work package on survey design and fieldwork of the HBM4EU, researchers carried out procedures necessary for the development of quality questionnaires and related data collection tools. These procedures consisted of a systematic search to identify questionnaires used in previous human biomonitoring (HBM) studies, as well as the development of a checklist and evaluation sheet to assess the questionnaires identified. The results of these evaluations were taken into consideration for the development of the final questionnaires. Results: The main points covered by each of the sections included in HBM4EU questionnaires are described and discussed in detail. Additional tools developed for data collection in the HBM4EU (e.g. non-responder questionnaire, satisfaction questionnaire, matrix-specific questionnaire) are also addressed. Special attention is paid to the limitations faced and hurdles overcome during the process of questionnaire development. Conclusions: Designing questionnaires for use in HBM studies requires substantial effort by a multidisciplinary team to guarantee that the quality of the information collected meets the study’s objectives. The process of questionnaire development described herein will contribute to improve the harmonization of HBM studies within the social and environmental context of the EU countries.European Union's Horizon 2020 research and innovation programme 733032Swiss State Secretary for Education Research and Innovation (SERI

Alternde Gesellschaften in Europa. Empirische Untersuchungen mit Daten des SHARE

Dieser Band präsentiert drei ausgewählte empirische Studien, die im Rahmen des Bevölkerungswissenschaftlichen Forschungspraktikums an der Universität Bamberg entstanden sind. Der erste Beitrag beschäftigt sich mit „familialen Transferregimes“ in Europa, dem privaten Äquivalent zu öffentlichen Wohlfahrtsstaatsregimes. Im Mittelpunkt der Analyse steht die Frage, ob und wie sich osteuropäische Länder von nord-, west- und südeuropäischen Regimetypen unterscheiden. Der zweite Beitrag untersucht, ob sich ältere Menschen nach dem Renteneintritt gleichbleibend, vermehrt oder seltener ehrenamtlich engagieren. Der dritte Beitrag konzentriert sich ebenfalls auf die Effekte des Renteneintritts. Diese Arbeit geht der Frage nach, ob die Verrentung für ältere Menschen ein stressauslösendes Ereignis ist, das den gesundheitlichen Abbau beschleunigt. Die Autorinnen und Autoren untersuchen diese aktuellen sozialwissenschaftlichen Fragestellungen mit Daten der ersten beiden Wellen des Survey of Health, Ageing and Retirement in Europe (SHARE)

A carbon-nanotube based nano-furnace for in-situ restructuring of a magnetoelectric oxide

We present current-voltage (I-V) characteristics of an individual carbon nanotube (CNT) filled with Cr₂O₃, a multi-functional magnetic oxide relevant to spintronics. We demonstrate that a filled CNT during a two probe I-V scan in suspended geometry, can be used like a nano-furnace for controlled restructuring of the oxide encapsulate. With proper utilization of Joule heating during I-V scans, the encapsulate, initially in the form of a polycrystalline nano-wire, converts to beads, nano-crystals and sheets within the CNT. These morphological phases are formed and preserved by controlling the amplitude, rate and holding time of the bias voltage. The sequential restructuring, observed in real time by Transmission Electron Microscopy (TEM), is also accompanied by a substantial enhancement in the current flowing through the CNT. We further demonstrate that advantageously tailoring the morphology of the encapsulate is linked to this current enhancement and can be a route for heat dissipation in nano devices. Magnetization measurements reveal that Cr₂O₃, a well known antiferromagnetic and magnetoelectric, when confined within CNT, exhibits logarithmic time dependence. This slow magnetization dynamics is associated to a pinning mechanism that points towards the possibility of stress induced moments in this system. These measurements elucidate novel magnetic properties of the encapsulate