De puber en de pedagoog

While the First World War raged outside, fifteen-year-old Jaap Kann sat indoors and struggled with his schoolwork. He was the terror of his teachers and consistently failed his subjects. Rather than studying, he preferred dreaming of building airplanes and joining the war effort. Concerned about his future, Jaap’s wealthy parents hired Otto Barendsen—a psychologist and pedagogue—to provide daily homework supervision. Over several years, Barendsen meticulously kept a diary of their sessions, chronicling not only his attempts to motivate Jaap but also their conversations, Jaap’s emotional development, and his inner world. Inspired by the ideals of progressive pedagogy, Barendsen hoped to establish himself as a pedagogical writer in the tradition of Jan Ligthart and Theo Thijssen. For this ambition, Jaap was a golden subject. He was a typical teenager and attended the very first ‘lyceum’ of the Netherlands, where early theories of adolescent psychology inspired efforts to redesign education. As Barendsen prepared his envisioned book on adolescents, a profound friendship grew between the rebellious teenager and his idealistic tutor

Insulin-like growth factor binding protein 7 (IGFBP7), a link between heart failure and senescence

Aims: Insulin like growth factor binding protein 7 (IGFBP7) is a marker of senescence secretome and a novel biomarker in patients with heart failure (HF). We evaluated the prognostic value of IGFBP7 in patients with heart failure and examined associations to uncover potential new pathophysiological pathways related to increased plasma IGFBP7 concentrations. Methods and results: We have measured plasma IGFBP7 concentrations in 2250 subjects with new‐onset or worsening heart failure (BIOSTAT‐CHF cohort). Higher IGFBP7 plasma concentrations were found in older subjects, those with worse kidney function, history of atrial fibrillation, and diabetes mellitus type 2, and in subjects with higher number of HF hospitalizations. Higher IGFBP7 levels also correlate with the levels of several circulating biomarkers, including higher NT‐proBNP, hsTnT, and urea levels. Cox regression analyses showed that higher plasma IGFBP7 concentrations were strongly associated with increased risk of all three main endpoints (hospitalization, all‐cause mortality, and combined hospitalization and mortality) (HR 1.75, 95% CI 1.25–2.46; HR 1.71, 95% CI 1.39–2.11; and HR 1.44, 95% CI 1.23–1.70, respectively). IGFBP7 remained a significant predictor of these endpoints in patients with both reduced and preserved ejection fraction. Likelihood ratio test showed significant improvement of all three risk prediction models, after adding IGFBP7 (P < 0.001). A biomarker network analysis showed that IGFBP7 levels activate different pathways involved in the regulation of the immune system. Results were externally validated in BIOSTAT‐CHF validation cohort. Conclusions: IGFPB7 presents as an independent and robust prognostic biomarker in patients with HF, with both reduced and preserved ejection fraction. We validate the previously published data showing IGFBP7 has correlations with a number of echocardiographic markers. Lastly, IGFBP7 pathways are involved in different stages of immune system regulation, linking heart failure to senescence pathways

Wave-Induced Current in a Seakeeping Basin

During tests in MARIN’s wave basins, it was observed that large-scale current patterns may develop under the influence of wave generation and absorption. The velocity of these currents is very low, so they generally do not influence the behaviour of models. However, for specific experiments at low speeds — wave added resistance tests with small models or current drag tests — a residual current may influence the results significantly. A good understanding of the residual circulation in a wave basin is essential to improve the quality of the tests performed. The wave-induced current patterns were observed during tests in MARIN’s Seakeeping and Manoeuvring Basin (SMB). The patterns may develop in several ways under the influence of waves in a basin. End effects of Stokes drift (mass transport due to second-order wave effects) can play a role, as the water has to return at the end of the basin. The SMB has the capability to generate oblique waves. It therefore has a wave-damping beach along two sides of the basin. Similar to ‘real’ beaches, they may cause alongshore currents and rip currents under the influence of oblique and perpendicular waves respectively. During the tests, floaters in the form of oranges were distributed in the basin after wave generation. They were tracked using a camera system. The images were processed such that the surface current patterns in the basin were visualized, and an estimate of the velocities was obtained. Additional local acoustic current meter measurements were used to check the order of magnitude of these velocities. Based on these tests, it was concluded that different patterns may occur in the basin, with the largest velocities after oblique wave generation. Typical surface velocities are in the order of 1 to 2 cm/s, non-uniformly distributed over the basin. Due to this non-uniformity and because decay is slow (memory effects), very sensitive added resistance and current drag tests may have to be corrected for a measured current velocity in the future.</jats:p

Finding Dangerous Waves—Review of Methods to Obtain Wave Impact Design Loads for Marine Structures

AbstractGreen water and slamming wave impacts can lead to severe damage or operability issues for marine structures. It is therefore essential to consider their probability and loads in design. This is difficult, as impacts are both hydrodynamically complex and relatively rare. The complexity requires high-fidelity modeling (experiments or CFD), whereas a statistically sound analysis of rare events requires long durations. High-fidelity tools are too demanding to run a Monte–Carlo simulation; low-fidelity tools do not include sufficient physical details. The use of extreme value theory and/or multi-fidelity modeling is therefore required. The present paper reviews the state-of-the-art methods to find wave impact design loads, which include response-conditioning methods, screening methods, and adaptive sampling methods. Their benefits and shortcomings are discussed, as well as challenges for the wave impact problem. One challenge is the role of wave non-linearity. Another is the validation of the different methods; it is hard to obtain long-duration high-fidelity wave impact data.</jats:p

How to Deal With Basin Modes When Generating Irregular Waves on Shallow Water

Modeling shallow-water waves in a basin with a finite length and width introduces challenges related to low-frequency (LF) waves, especially for testing of moored vessels with long natural periods. Waves in this frequency range are also present in reality, as for instance bound set-down waves and unbound free waves formed by the geometry bathymetry. In model basins, additional unwanted LF wave components will be formed as a side-product of the wave generation and due to the basin geometry though. Standing waves over the basin length and width (basin modes) can generally be identified, which are difficult to dampen using beaches. This is the case for every wave basin, as they all have finite dimensions. Moored structures generally have natural frequencies in the LF range, which may be excited by basin modes with similar frequencies. It is therefore important to understand the natural modes of a basin before tests with moored structures in shallow water are done. The energy of these basin modes increases and their natural frequency decreases with decreasing water depth (waves travel slower in shallow water). Generally, it can be said that the issues with basin modes are present on very shallow water (typically ∼15–30 m water depth full-scale for structures with a length around 200 m at a scale around 1 to 40). The smaller the basin for the same water depth, the higher the basin mode frequencies and the higher the likelihood of resonance problems. The energy and frequencies of the basin modes and their relevance for specific tests depend on the effective length and width of the basin, the water depth, wave conditions and the (mooring stiffness of) the structure under consideration. The influence of these variables is evaluated in the current study. Tests were done in MARIN’s Offshore Basin (OB), but most of the results are also expected to be applicable to other basins. The observed basin mode frequencies during these tests were compared to the theoretical values, and an overview of the unwanted LF wave content as a function of water depth, wave height and period is presented. The energy and shape of individual basin modes is also discussed. Considering these results, a practical approach for future basin projects on shallow water is described.</jats:p

Evaluation of Directional Analysis Methods for Low-Frequency Waves to Predict LNGC Motion Response in Nearshore Areas

Because LNG terminals are located increasingly close to shore, the importance of shallow-water effects associated with low-frequency (LF) waves increases as well. The LF wave spectrum in these areas is generally complex, with multiple frequency peaks and/or directional peaks due to LF wave interaction with the shore. Both free and bound LF waves at the same frequency can be present. Since LF waves are potentially very significant for moored vessel motions, it is important to include their effect in an early stage of the terminal design. This requires an efficient and relatively simple tool able to estimate the LF wave spectrum in nearshore areas. The benefit of such a procedure with respect to state-of-the-art response methods is the ability to include the LF free wave distribution in a local wave field in the vessel response calculation. The objectives of the present study are to identify such a tool, and to evaluate the use of its output as input for a vessel motion calculation. Three methods, designed for the determination of wave spectra of free wave-frequency (WF) waves, were applied to artificial LF wave fields for comparison of their performance. Two stochastic methods, EMEP (Hashimoto et al., 1994) and BDM (Hashimoto et al., 1987) and one deterministic method, r-DPRA (De Jong and Borsboom, 2012) were selected for this comparison. The foreseen application is beyond the formal capabilities for which these three methods were intended. However, in this study we have investigated how far we can take these existing methods for the determination of directional LF wave spectra. Sensitivity analyses showed that the EMEP method is the most suitable method of the three for a range of LF wave fields. The reconstructed LF wave spectra using EMEP resembled the input spectra most closely over the whole range of water depths and frequencies, although its performance deteriorated with increasing water depth and wave frequency. Subsequently, a first effort was made to use the information in the reconstructed EMEP LF wave spectrum of a representative shallow-water wave field for a first estimate of the motions of a moored LNG carrier. The results were acceptable. This is a first indication that EMEP output might be used to calculate the motions of an LNG carrier moored in shallow water.</jats:p