Helmut Schmidt University / University of the Federal Armed Forces Hamburg
Recent publications
The use of Lamb waves for the determination of component states and damage detection in thin-walled structures is a generally accepted method in today’s Structural Health Monitoring. Although the behavior of Lamb waves has been dealt with in depth, there are still topics where research is needed, for example, the influence of prestress on Lamb wave propagation. In order to gain profound insight into this area, experimental methods and results on wave propagation under the influence of prestress have been presented in previous work by the authors. These results are characterized by the use of a 2d Fourier transform to evaluate the observation of this behavior over large frequency ranges. Based on these results, the work presented here deals with a 2d numerical modeling approach of the wave propagation in a prestressed structure. The focus is on analyzing the suitability of linear and non-linear material models for reproducing the wave velocity changes. For this purpose, the numerically obtained results for different material models are compared with experimental data. The numerical data is generated using a FE model which combines a nonlinear static computation for the prestress and a linear eigenfrequency computation for the dispersion behaviour of Lamb waves. Finally, the comparison of simulated and experimental data will provide a well-founded basis for further numerical analysis on this topic.
The congruency sequence effect (CSE) and the proportion congruency effect (PCE) are typical findings in experimental conflict protocols. Given the ever-increasing number of, in part, radically different mechanisms proposed to explain either effect, a unified system for describing candidate mechanisms appears desirable. In this article, we show that such a system can be derived by focusing on functional similarities among all mechanisms capable of explaining either effect. The latter perspective reveals the adaptive dynamic that all such mechanisms share. This shared dynamic allows describing each mechanism by addressing the same questions about how this dynamic is implemented. We contend that this description system facilitates comparisons between mechanisms, and relating the discourse on the CSE and PCE to other lines of discourse. First, we introduce the adaptive dynamic and the questions about its implementation. Then, we answer these questions for exemplary cases. Finally, we discuss the utility of the proposed system.
Intense phase-locked terahertz (THz) pulses are the bedrock of THz lightwave electronics, where the carrier field creates a transient bias to control electrons on sub-cycle time scales. Key applications such as THz scanning tunnelling microscopy or electronic devices operating at optical clock rates call for ultimately short, almost unipolar waveforms, at megahertz (MHz) repetition rates. Here, we present a flexible and scalable scheme for the generation of strong phase-locked THz pulses based on shift currents in type-II-aligned epitaxial semiconductor heterostructures. The measured THz waveforms exhibit only 0.45 optical cycles at their centre frequency within the full width at half maximum of the intensity envelope, peak fields above 1.1 kV cm ⁻¹ and spectral components up to the mid-infrared, at a repetition rate of 4 MHz. The only positive half-cycle of this waveform exceeds all negative half-cycles by almost four times, which is unexpected from shift currents alone. Our detailed analysis reveals that local charging dynamics induces the pronounced positive THz-emission peak as electrons and holes approach charge neutrality after separation by the optical pump pulse, also enabling ultrabroadband operation. Our unipolar emitters mark a milestone for flexibly scalable, next-generation high-repetition-rate sources of intense and strongly asymmetric electric field transients.
The Kingdom of Saudi Arabia (KSA) has vast geothermal energy resources. When developed, these markedly strengthen the country's goals of achieving a carbon-neutral economy. To demonstrate the feasibility and techno-economic performance of small-scale, hydrothermal well doublet systems for direct use in KSA, we perform reservoir and wellbore flow and heat-transport simulations as well as an economic analysis. The maximum permissible flowrate is constrained to avoid thermoelastic fracturing in the near-wellbore region. Reservoir conditions of a sedimentary basin along the Red Sea coast (near Al Wajh) provide an ideal study case to which we add economic parameters considered representative for KSA. We derive a Levelized Cost of Heat (LCOH) ranging from 49 to 128 $/MWh for 50-mD hydrothermal doublet systems with an optimal well spacing of 600 m and a flowrate ranging from 110 kg/s to 50 kg/s. LCOH is strongly influenced by decreasing reservoir transmissivity. Also, a minimum injection temperature is required to avoid thermoelastic fracturing. Our economic analysis further highlights that capacity factor and well-drilling cost have the greatest impact on LCOH. Thus, this study provides a guide and workflow to conduct techno-economic investigations for decision-making, risk mitigation, optimizing geothermal-energy-extraction and economic-performance conditions of hydrothermal doublet systems.
The present paper analyses the effect of an inhomogeneous surface temperature distribution on the operation of a thermoelectric generator (TEG), experimentally and numerically. In the steady-state measurements, a spatially inhomogeneous temperature distribution is imposed on the colder surface of the TEG. The hotter surface temperature distribution is kept homogeneous. The maximum-to-minimum difference in the TEG cold side surface temperature distribution has been changing between 10 °C and 25 °C during the measurements, while the difference of the area averaged cold surface temperature to the hot side temperature has been varying within the range 70 °C and 150 °C. Tests are also performed with homogeneous cold side temperature distributions. Measurements with the variable and uniform cold side temperatures are compared. The comparison shows that a local surface variation within the considered ranges does not have a noticeable effect on the TEG performance. A finite element method (FEM) based computational model is developed and validated based on the measured data. Using the FEM model, it has been possible to increase the applied temperature inhomogeneity to higher levels beyond those, which were possible in the experiments. The FEM model predicts a deviation at very high temperature inhomogeneity on the cold side, which can be justified with the temperature dependency of the material properties.
This work proposes an effective thermal activation method with low technical effort for industrially produced titanium-iron-manganese powders (TiFeMn) for hydrogen storage. In this context, the influence of temperature and particle size of TiFeMn on the activation process is systematically studied. The results obtained from this investigation suggest that the activation of the TiFeMn material at temperatures as low as 50 °C is already possible, with a combination of “Dynamic” and “Static” routines, and that an increase to 90 °C strongly reduces the incubation time for activation, i.e. the incubation time of the sample with the two routines at 90 °C is about 0.84 h, while ∼ 277 h is required for the sample treated at 50 °C in both “Dynamic” and “Static” sequences. Selecting TiFeMn particles of larger size also leads to significant improvements in the activation performance of the investigated material. The proposed activation routine makes it possible to overcome the oxide layer existing on the compound surface, which acts as a diffusion barrier for the hydrogen atoms. This activation method induces further cracks and defects in the powder granules, generating new surfaces for hydrogen absorption with greater frequency, and thus leading to faster sorption kinetics in the subsequent absorption-desorption cycles.
Common count distributions, such as the Poisson (binomial) distribution for unbounded (bounded) counts considered here, can be characterized by appropriate Stein identities. These identities, in turn, might be utilized to define a corresponding goodness-of-fit (GoF) test, the test statistic of which involves the computation of weighted means for a user-selected weight function f. Here, the choice of f should be done with respect to the relevant alternative scenario, as it will have great impact on the GoF-test's performance. We derive the asymptotics of both the Poisson and binomial Stein-type GoF-statistic for general count distributions (we also briefly consider the negative-binomial case), such that the asymptotic power is easily computed for arbitrary alternatives. This allows for an efficient implementation of optimal Stein tests, that is, which are most powerful within a given class of weight functions. The performance and application of the optimal Stein-type GoF-tests is investigated by simulations and several medical data examples.
  • M. C. MeijersM. C. Meijers
  • J. StouthardJ. Stouthard
  • A. W. M. EversA. W. M. Evers
  • [...]
  • L. M. van VlietL. M. van Vliet
To alleviate anti-cancer treatment burden in advanced breast cancer, patient-clinician communication strategies based on nocebo-effect mechanisms are promising. We assessed distinct/combined effects on psychological outcomes (e.g. anxiety; main outcome) and side-effect expectations of (1) nocebo information about the (non)pharmacological origin of side effects, and (2) clinician-expressed empathy through reassurance of continuing support. Furthermore, we explored whether information and empathy effects on side-effect expectations were mediated by decreased anxiety. In a two-by-two experimental video-vignette design, 160 cancer patients/survivors and healthy women watched one of four videos differing in level of nocebo information (±) and empathy (±). Regression and mediation analysis were used to determine effects of information/empathy and explore anxiety’s mediating role. Anxiety was not influenced by empathy or information (Stai-state: p = 0.295; p = 0.390, VAS p = 0.399; p = 0.823). Information improved (specific) side-effect coping expectations (p < 0.01). Empathy improved side-effect intensity expectations (p < 0.01 = specific; p < 0.05 = non-specific/partial) and specific side-effect probability expectations (p < 0.01), and increased satisfaction, trust, and self-efficacy (p < 0.001). No mediating effects were found of anxiety on expectations. Mainly empathy, but also nocebo information improved psychological outcomes and—mainly specific—side-effect expectations. Exploring the power of these communication elements in clinical practice is essential to diminish the anti-cancer treatment burden in advanced breast cancer.
In bildungspolitischen Verlautbarungen und pädagogischer Praxis zeigt sich eine enge Verbindung zwischen Diskursen um Migration und um ‚Fähigkeit‘. In dem Beitrag nehmen wir diese Verbindung als Fähigkeitsordnungen in der frühen Kindheit und Konstruktionen um migrantisierte Kindheiten in den Blick. Mit Rassismus, Ableismus und ihrer Intersektion als theoretischem Bezugsrahmen analysieren wir zwei Ausschnitte aus Beobachtungsprotokollen, die in einer Kita entstanden sind und mit denen wir die Praxis der Verunfähigung des migrantisierten Kindes als ein Ergebnis konzeptualisieren – eine Praxis, die mit ihren sinnstiftenden Gelegenheitsstrukturen Handlungsspielräume für die Diagnose eines (sonderpädagogischen) Förderbedarfs eröffnet.
Background Adverse events of chemotherapy may be caused by pharmacodynamics or psychological factors such as negative expectations, which constitute nocebo effects. In a randomized controlled trial, we examined whether educating patients about the nocebo effect is efficacious in reducing the intensity of self-reported adverse events. Methods In this proof-of-concept study, N = 100 outpatients (mean age: 60.2 years, 65% male, 54% UICC tumour stage IV) starting first-line, de novo chemotherapy for gastrointestinal cancers were randomized 1:1 to a nocebo education (n = 49) or an attention control group (n = 51). Our primary outcome was patient-rated intensity of four chemotherapy-specific and three non-specific adverse events (rated on 11-point Likert scales) at 10-days and 12-weeks after the first course of chemotherapy. Secondary outcomes included perceived control of adverse events and tendency to misattribute symptoms. Results General linear models indicated that intensity of adverse events differed at 12-weeks after the first course of chemotherapy (mean difference: 4.04, 95% CI [0.72, 7.36], p = .02, d = 0.48), with lower levels in the nocebo education group. This was attributable to less non-specific adverse events (mean difference: 0.39, 95% CI [0.04, 0.73], p = .03, d = 0.44) and a trend towards less specific adverse events in the nocebo education group (mean difference: 0.36, 95% CI [− 0.02, 0.74], p = .07, d = 0.37). We found no difference in adverse events at 10-days follow-up, perceived control of adverse events, or tendency to misattribute non-specific symptoms to the chemotherapy. Conclusions This study provides first proof-of-concept evidence for the efficacy of a brief information session in preventing adverse events of chemotherapy. However, results regarding patient-reported outcomes cannot rule out response biases. Informing patients about the nocebo effect may be an innovative and clinically feasible intervention for reducing the burden of adverse events. Trial registration Retrospectively registered on March 27, 2018 to the German Clinical Trial Register (ID: DRKS00009501).
AI in the Navy? Dreams of the future or state-of-the-art? Here, two approaches for the use of ML procedures on ships are presented and possible prerequisites for creating awareness for them. Condition monitoring using the example of power generation and the identification of other naval vessels serve to illustrate ML-based cyber-physical systems and their benefits. With their good results, both methods testify to the advantages for the Navy to increasingly deal with the use of AI on board in the future.
Ten different thermodynamic properties of the noble gas krypton were calculated by Monte Carlo simulations in the isothermal-isobaric ensemble using a highly accurate ab initio pair potential, Feynman–Hibbs corrections for quantum effects, and an extended Axilrod–Teller–Muto potential to account for nonadditive three-body interactions. Fourteen state points at a liquid and a supercritical isotherm were simulated. To obtain results representative for macroscopic systems, simulations with several particle numbers were carried out and extrapolated to the thermodynamic limit. Our results agree well with experimental data from the literature, an accurate equation of state for krypton, and a recent virial equation of state (VEOS) for krypton in the region where the VEOS has converged. These results demonstrate that very good agreement between simulation and experiment can only be achieved if nonadditive three-body interactions and quantum effects are taken into account.
The Impostor Phenomenon describes people characterized by a non-self-serving attributional bias towards success. In this experimental between-subjects design, we conducted a bogus intelligence test in which each subject was assigned to a positive or negative feedback condition. Our sample consisted of N=170 individuals (51% female). The results showed that the impostor expression moderates the influence of feedback on locus of causality and stability attribution. ‘Impos- tors’ show an external-instable attributional style regarding success and an internal-stable attributional style regarding failure. Therefore, the relationship between the impostor expression and its characteristic attribution patterns could be experimentally validated for the first time. In addition, we investigated whether the IP is linked to the performance-related construct mindset. We found a positive correlation between the IP and fixed mindset. Possible causes for these findings are discussed.
Popular models for time series of count data are integer-valued autoregressive (INAR) models, for which the literature mainly deals with parametric estimation. In this regard, a semiparametric estimation approach is a remarkable exception which allows for estimation of the INAR models without any parametric assumption on the innovation distribution. However, for small sample sizes, the estimation performance of this semiparametric estimation approach may be inferior. Therefore, to improve the estimation accuracy, we propose a penalized version of the semiparametric estimation approach, which exploits the fact that the innovation distribution is often considered to be smooth, i.e. two consecutive entries of the PMF differ only slightly from each other. This is the case, for example, in the frequently used INAR models with Poisson, negative binomially or geometrically distributed innovations. For the data-driven selection of the penalization parameter, we propose two algorithms and evaluate their performance. In Monte Carlo simulations, we illustrate the superiority of the proposed penalized estimation approach and argue that a combination of penalized and unpenalized estimation approaches results in overall best INAR model fits.
Behavioral activation (BA) interventions systematically encourage positive and value-based activities. Engaging in them is an effective way to counteract negative affect, but it is unknown whether there are subtypes of activities that may have differential effects on mood. This study investigated the factorial structure of 99 potentially rewarding activities used in an online BA intervention during the COVID-19 lockdown. About 3624 German-speaking participants evaluated a list of 99 activities that were easy to apply. We analyzed the initially 99 activities by means of confirmatory factor analysis. Since activities can either be seen as reflective or formative indicators, a reflective as well as a formative model was analyzed. Although the range of chosen activities differed clearly between respondents, a one-factor model provided the best fit. It seems that a general "activity" factor is more important for explaining whether people choose a certain activity or not, than specific characteristics of the activity itself.
Due to different rheological behavior of human synovial fluid and the test mediums for in vitro examinations, wear tests cannot replicate the in vivo situation completely. The standards for wear testing indicate calf serum as in vitro test medium. However, these standards do not contain precise information on the main constituent components and the rheological properties. In this study, bovine calf serum and newborn calf serum with a protein concentration of 20 g/L, both approved for wear testing defined by the International Organization for Standardization (ISO), were characterized according to their rheological properties to detect differences before and during tribological simulation. The rheological behavior was determined at five defined intervals of a tribological test. The two test fluids differ in their rheological properties before and during the test and can therefore lead to deviating results in tribological testing. Furthermore, both test media changes considerably over test duration. At a test duration of 0.5 Mio cycles, both fluids have changed so that there is no longer any difference between them in terms of rheological properties. These changes could be attributed to denaturation and degradation of proteins. Thus, the choice of medium impacts tribological test results which should be considered for the interpretation of these studies.
Liking and pleasantness are common concepts in psychological emotion theories and in everyday language related to emotions. Despite obvious similarities between the terms, several empirical and theoretical notions support the idea that pleasantness and liking are cognitively different phenomena, becoming most evident in the context of emotion regulation and art enjoyment. In this study it was investigated whether liking and pleasantness indicate behaviourally measurable differences, not only in the long timespan of emotion regulation, but already within the initial affective responses to visual and auditory stimuli. A cross-modal affective priming protocol was used to assess whether there is a behavioural difference in the response time when providing an affective rating to a liking or pleasantness task. It was hypothesized that the pleasantness task would be faster as it is known to rely on rapid feature detection. Furthermore, an affective priming effect was expected to take place across the sensory modalities and the presentative and non-presentative stimuli. A linear mixed effect analysis indicated a significant priming effect as well as an interaction effect between the auditory and visual sensory modalities and the affective rating tasks of liking and pleasantness: While liking was rated fastest across modalities, it was significantly faster in vision compared to audition. No significant modality dependent differences between the pleasantness ratings were detected. The results demonstrate that liking and pleasantness rating scales refer to separate processes already within the short time scale of one to two seconds. Furthermore, the affective priming effect indicates that an affective information transfer takes place across modalities and the types of stimuli applied. Unlike hypothesized, liking rating took place faster across the modalities. This is interpreted to support emotion theoretical notions where liking and disliking are crucial properties of emotion perception and homeostatic self-referential information, possibly overriding pleasantness-related feature analysis. Conclusively, the findings provide empirical evidence for a conceptual delineation of common affective processes.
This work provides a framework for predicting fracture of catalyst coated membrane (CCM) due to coupled electro-chemo-mechanical degradation processes in proton exchange membrane water electrolysis (PEMWE) cells. Electrolysis in the catalyst layer (CL) bulk, diffusion of Hydrogen proton through the membrane (MEM), mechanical compression at the interface with the porous transport layer (PTL) generate micro-cracks that influence the catalyst degradation. Based on the experimental observations, we propose theoretical formulations along with the constitutive framework to help understanding and providing a reliable description of the stated multi-physics problem. The computational modeling of crack formation in the CL bulk is achieved in a convenient way by continuum phase-field formulations to fracture, which are based on the regularization of sharp crack discontinuities. The model performance is demonstrated through two representative boundary value problems, representing the cell setup and working of the PEMWE cell.
Although, uncommitted dating via online apps is widespread, most people find value in long-term, trusting relationships. From a social and evolutionary point of view, it has been theorized that mating strategies, and, in particular, short-term strategies make some relationships more vulnerable than others. In our study, we examined short- and long-term relationship orientation and their association with relationship quality. We analysed data from 395 heterosexual couples using the actor-partner-interdependence model in order to explore effects on individuals and couples. Results demonstrated that short-term orientation was associated with lower levels of relationship quality and an increased likelihood of complaints about the partner and the relationship. Long-term relationship orientation, on the other hand, was associated with higher levels of relationship quality. In addition, higher levels of sexual satisfaction mediate the association between short-term orientation and relationship quality. In-depth analyses revealed gender- and couple effects.
The emergence of cities in specific locations depends on both geographical features (such as elevation and proximity to rivers) and institutional factors (such as centrality within an administrative region). In this paper, we analyse the importance of these factors at different levels of the urban hierarchy. To do so, we exploit a unique data set on the location of cities of different status in imperial China from 221 BCE to 1911 CE, a geographically diverse empire with a long history of centralised rule. Developing a stylised theoretical model, we combine econometrics with machine learning techniques. Our results suggest that the higher a city is in the urban hierarchy, the less important are local geographical features compared to institutional factors. At the lower end of the scale, market towns without government responsibilities are most strongly shaped by geographical characteristics. We also find evidence that many cities of political importance in imperial times still enjoy a special status nowadays, underlining the modern relevance of these historical factors.
Institution pages aggregate content on ResearchGate related to an institution. The members listed on this page have self-identified as being affiliated with this institution. Publications listed on this page were identified by our algorithms as relating to this institution. This page was not created or approved by the institution. If you represent an institution and have questions about these pages or wish to report inaccurate content, you can contact us here.
1,532 members
Tanja Klenk
  • Economics and Social Sciences
Thomas Carraro
  • Department of Mathematics
Fabian Paetzel
  • Faculty of Economics and Social Sciences
Holstenhofweg 85, 22043, Hamburg, Germany
Head of institution
Prof. Dr. Klaus Beckmann
+49 40 6541 1
+49 40 6541 2869