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Individual Mobility and Public Transport Subsidies
(2025) Andor, Mark A.; Flintz, Joschka; Vance, Colin
Politicians around the world are looking for ways to reduce the negative externalities of the transport sector. Subsidization of public transport is a popular remedy, but evidence on the associated causal effects remains scant.
Based on a randomized controlled trial that tracks mobility behavior continuously via a mobile app, this study provides causal evidence on how individuals modify their mobility patterns when provided with temporary cost-free access to public transport. We further explore whether such access induces enduring shifts in mobility behavior after the reinstatement of regular fares. We randomly provide roughly half of our around 420 participants - whose selection targeted car users - with a one-month public transport ticket for their local area, and %Leveraging monitor travel behavior across all modes over three months. We find a statistically significant average increase of about two trips per month using public transport during the subsidization period. The rise in public transport utilization, however, is not paralleled by a reduction in car usage, nor does it yield a persistent alteration in mobility behavior in the subsequent month after the ticket expires.
System theoretical analyses of voltage stability in power electronics-dominated hybrid power systems
(2024) Liemann, Sebastian; Rehtanz, Christian; Becker, Christian
The massive integration of power electronic de-vices at the load and generation side is changing the dynamics and stability of power systems. In particular, power electronic loads can threaten voltage stability in the event of major disturbances, such as short circuits, due to their low voltage sensitivity. In addition, the ancillary services of decommissioned conventional power plants have to be taken over by grid-forming converters. Since power electronic converters and loads can discretely change their dynamics during disturbances, e.g. by current limitation or disconnection with zero power consumption, additional challenges for voltage stability arise. Therefore, in this thesis, hybrid system theory is used as a modelling basis to explicitly analyse the complex interactions between continuous and discrete dynamics in such events. It is examined how the theory of hybrid systems can extend the system theory of voltage stability and how it can support its assessment in the short and long term. Furthermore, since there is only a small overlap between conventional voltage stability dynamics and power electronics dynamics, it is not clear whether phasor or electromagnetic transient models should be used. Therefore, grid-forming converters and power electronic loads are modelled for both types. The simulation results show that phasor models may still be suitable for grid-forming converters, while electromagnetic transient models are needed for power electronic loads. In addition, the results demonstrate that the current limitation of grid-forming converters can lead to voltage instability in the short and long term. However, by applying stability-enhancing control methods, the instability induced by the converter can be avoided. The disconnection of power electronic loads during short circuits can initially stabilise the system due to the reduced power consumption. Yet, their potential fast power recovery during the fault can lead to instability or delayed voltage recovery afterwards. The combined simulation of grid-forming converters and power electronic loads show that the simultaneous occurrence of current limitation and fast power recovery can be a serious threat to short- and long-term voltage stability.
Real‐time optimization using machine learning models applied to the 4,4′‐diphenylmethane diisocyanate production process
(2023-04-03) Ehlhardt, Jens; Ahmad, Afaq; Wolf, Inga; Engell, Sebastian
In this work, the optimal time-varying allocation of steam in a large-scale industrial isocyanate production process is addressed. This is a problem that falls into the category of real-time optimization (RTO). The application of RTO in practice faces two problems: First the available rigorous process models may not be suitable for use in real-time connected to the process. Second, there is always a mismatch between the predictions of the model and the behavior of the real plant. We address the first problem by training a neural net model as a surrogate to data generated by a rigorous simulation model so that the model is simple to implement and short execution times result. The second problem is tackled by adapting the optimization problem based on measured data such that convergence to the optimal operating conditions for the real plant is achieved.
Continuous phase separation of stable emulsions from biphasic whole-cell biocatalysis by catastrophic phase inversion
(2023-03-27) Janssen, Lisa; Sadowski, Gabriele; Brandenbusch, Christoph
The main bottleneck for the industrial implementation of highly promising multi-phase whole-cell biocatalytic processes is the formation of stable Pickering-type emulsions, hindering efficient downstream processing. Especially for the crucial step of phase separation, state-of-the-art processes require time-consuming and costly process steps (excessive centrifugation/use of de-emulsifiers). In contrast, using the phenomenon of catastrophic phase inversion (CPI), efficient phase separation can be achieved by addition of an excess dispersed phase within minutes. To show applicability of CPI as an innovative process step, a fully automated lab-scale prototype was designed and constructed within this work. A simple mixer-settler set-up enabled a continuous phase separation using CPI termed applied catastrophic phase inversion (ACPI). Test runs were conducted using emulsions from biphasic whole-cell biocatalysis (Escherichia coli JM101 and Pseudomonas putida KT2440 cells). Solvents used included n-heptane, ethyl oleate or 1-octanol as organic phase. These investigations revealed ideal process settings for a stable ACPI process (e.g., flow/stirring rates and volumetric phase ratios between organic and water phase). The knowledge of the CPI point is most crucial, as only the inverted state of emulsion is successfully destabilized.
How modern working environments shape attendance behaviour: a longitudinal study on weekly flexibilization, boundaryless work and presenteeism
(2023-04-06) Poethke, Ute; Klasmeier, Kai N.; Radaca, Elvira; Diestel, Stefan
In the face of technological advancements, flexibilization and boundaryless work have become integral parts of modern occupational settings. Simultaneously, current research indicates a considerable increase in presenteeism—the behaviour of working while sick. Meta-analytic findings indicate two main drivers for presenteeism: a high work motivation and an impaired state of health and psychological well-being. Research on flexibilization and boundaryless work shows that these job conditions enhance employees' work motivation but also impair employees' health. Based on conservation of resources theory and Miraglia and John's (J Occupational Health Psychol, 21, 2016, 261) dual-path model on antecedents of presenteeism, we investigate how both job conditions affect attendance behaviour (absenteeism and presenteeism) via motivation and well-being by conducting a weekly diary study over the course of 9 weeks. In total, 284 people provided data on flexibilization, boundaryless work, flow experience, well-being, absenteeism and presenteeism (N = 2284 week-level). Multilevel mediational analyses revealed that flexibilization prevents presenteeism, whereas boundaryless work can increase presenteeism. The results further revealed support for the health impairment path at the within-person and between-person levels whereas the motivational path was not supported at the within-person level. Our results offer several theoretical and practical implications for how modern work shape attendance behaviour.