PurposeTo compare agreement of different evaluation methods of magnetic resonance (MR) 4D flow-derived diastolic transmitral and myocardial peak velocities as well as their ratios, using echocardiography as reference. MethodsIn this prospective study, 60 subjects without symptoms of cardiovascular disease underwent echocardiography and non-contrast 3 T MR 4D flow imaging of the heart. Early- (E) and late-diastolic (A) transmitral peak filling velocities were evaluated from 4D flow data using three different strategies: 1) at the mitral valve tips in short-axis orientation (SA-method), 2) between the mitral valve tips in 4-chamber orientation (4-chamber-method), and 3) as maximal velocities in the transmitral inflow volume (max-velocity-method). Septal, lateral and average early-diastolic myocardial peak velocities (e’) were derived from the myocardial tissue in the vicinity of the mitral valve. 4D flow parameters were compared with echocardiography by correlation and Bland-Altman analysis. ResultsAll 4D flow-derived E, A and E/A values correlated with echocardiography (r = 0.65–0.73, 0.75–0.83 and 0.74–0.86, respectively). While the SA- and 4-chamber-methods substantially underestimated E and A compared to echocardiography (p < 0.001), the max-velocity-method provided E (p = 0.13) and E/A (p = 0.07) without significant bias. Septal, lateral and average e’ from 4D flow as well as the max-velocity-method-derived E/e’ correlated with echocardiographic measurements (r = 0.64–0.81) and showed no significant bias (p = 0.26–0.54). ConclusionMR 4D flow imaging allows precise and accurate evaluation of transmitral and myocardial peak velocities for characterization of LV diastolic function without significant bias to echocardiography, when transmitral velocities are assessed from the transmitral inflow volume. This enables the use of validated echocardiography threshold values.

ObjectivesThe magnetic resonance (MR) 4D flow imaging–derived left atrial (LA) acceleration factor α was recently introduced as a means to non-invasively estimate LA pressure. We aimed to investigate the association of α with the severity of left ventricular (LV) diastolic dysfunction using echocardiography as the reference method.MethodsEchocardiographic assessment of LV diastolic function and 3-T cardiac MR 4D flow imaging were prospectively performed in 94 subjects (44 male/50 female; mean age, 62 ± 12 years). LA early diastolic peak outflow velocity (vE), systolic peak inflow velocity (vS), and early diastolic peak inflow velocity (vD) were evaluated from 4D flow data. α was calculated from α = vE / [(vS + vD) / 2]. Mean parameter values were compared by t-test; diagnostic performance of α in predicting diastolic (dys)function was investigated by receiver operating characteristic curve analysis.ResultsMean α values were 1.17 ± 0.14, 1.20 ± 0.08, 1.33 ± 0.15, 1.77 ± 0.18, and 2.79 ± 0.69 for grade 0 (n = 51), indeterminate (n = 9), grade I (n = 13), grade II (n = 13), and grade III (n = 8) LV diastolic (dys)function, respectively. α differed between subjects with non-advanced (grade < II) and advanced (grade ≥ II) diastolic dysfunction (1.20 ± 0.15 vs. 2.16 ± 0.66, p < 0.001). The area under the curve (AUC) for detection of advanced diastolic dysfunction was 0.998 (95% CI: 0.958–1.000), yielding sensitivity of 100% (95% CI: 84–100%) and specificity of 99% (95% CI: 93–100%) at cut-off α ≥ 1.58. The AUC for differentiating grade III diastolic dysfunction was also 0.998 (95% CI: 0.976–1.000) at cut-off α ≥ 2.14.ConclusionThe 4D flow–derived LA acceleration factor α allows grade II and grade III diastolic dysfunction to be distinguished from non-advanced grades as well as from each other.Clinical relevance statementAs a single continuous parameter, the 4D flow–derived LA acceleration factor α shows potential to simplify the multi-parametric imaging algorithm for diagnosis of advanced LV diastolic dysfunction, thereby identifying patients at increased risk for cardiovascular events.Key Points• Detection of advanced diastolic dysfunction is typically performed using a complex, multi-parametric approach.• The 4D flow–derived left atrial acceleration factor α alone allows accurate detection of advanced left ventricular diastolic dysfunction.• As a single continuous parameter, the left atrial acceleration factor α could simplify the diagnosis of advanced diastolic dysfunction.

Quantification of thin film adhesion to their substrates is crucial to ascertain reliable multi-material components, which are typically encountered in technologically relevant structures such as microelectronic devices. Metal-polymer interfaces have gained increased attention in the past since they open a new research field towards developing flexible electronic devices, yet their quantification is often experimentally challenging since standard routes to assess adhesion such as nanoindentation-based techniques or four-point bending may not be applicable due to lack of rigidity. In the present study interface adhesion of nominally 150 nm thin WTi films sputtered onto polyimide, part of a multi-material stack consisting of brittle and compliant materials, was determined experimentally. Upon contactless removal of the bilayer by etching a sacrificial layer, originally part of the multilayer stack, the WTi film showed cracks and buckles, which could be characterized by atomic force and confocal laser scanning microscopy. Hence, two models to quantify adhesion were compared: the model of tensile induced delamination – typically employed for metal films on compliant substrates – and the model of Hutchinson and Suo, which is usually applied on spontaneously formed, straight buckles. The first model reveals adhesion values for the native WTi-polyimide interface of 2.4 ± 0.8 J/m2 and the latter model 4.7 ± 2.3 J/m2. The slight difference in adhesion results, which are both rooted in the same theory, could be rationalized by the fact that the model for tensile induced delamination gives a measure of the lower bound of the adhesion energy. The overall rather lower adhesion values could be explained by additional transmission electron microscopy investigations conducted on the cross section of the interface, which reveals no interlinking morphology and a flat interface.

Although often discussed, the role of threading dislocations (TDs) in the degradation of lateral GaN-on-Si p-GaN HEMTs under reverse bias stress test (RBST) has never been clearly shown in experiment until today. Here we present a novel test concept to establish a direct correlation between dislocations and degradation sites in RBST and demonstrate it on lateral p-GaN/AlGaN/GaN PIN diodes. By scaling down structures down to ~500 nm width, the point of degradation is always forced to be located at a defined position, independent of the local position of TDs. Furthermore, an integrated serial p-GaN resistor has been implemented with the PIN diode, which effectively limits the current and protects the device from a large meltdown due to parasitic capacitances and enables TEM analysis of structural degradation. A large quantity of lateral PIN devices exhibit a similar time-to-breakdown under RBST, indicating the intrinsic nature of this failure mode. Planar TEM analysis of a degraded and failed device clearly reveals structural damages and a breakdown of the AlGaN barrier as the failure signature. A combined planar and cross-sectional TEM lamella analysis approach of the expected failure site was introduced and applied. The results unambiguously show, that the observed degradation in the AlGaN barrier, which is attributed to the intrinsic failure mode, is not directly linked to the position of a dislocation.

PurposeThe simplified modeling of many physical processes results in a second-order ordinary differential equation (ODE) system. Often the damping of these resonating systems cannot be defined in the same simplified way as the other parameters due to the complexity of the physical effects. The purpose of this paper is to develop a mathematically stable approach for damping resonances in nonlinear ODE systems.Design/methodology/approachModifying the original ODE using the eigenvalues and eigenvectors of a linearized state leads to satisfying results.FindingsAn iterative approach is presented, how to modify the original ODE, to achieve a well-damped solution.Practical implicationsThe method can be applied for every physical resonating system, where the model complexity prevents the determination of the damping.Originality/valueThe iterative algorithm to modify the original ODE is novel. It can be used on different fields of the physics, where a second-order ODE is describing the problem, which has only measured or empirical damping.

Cord-rubber materials are used in crucial components of rail vehicles, such as air spring bellows in secondary suspension. A detailed understanding of the material behaviour of these components is thus of the utmost importance at an early stage of development. In general, a minor knowledge of the fatigue behaviour is currently all that is available today, while empirical methods involving designer experiences are in most cases essential requirements for this work. The design can be carried out more efficiently based on a representative cord-rubber composite specimen than on an entire air spring bellow. In this paper, the design of such representative specimens is shown taking different geometries and test conditions into consideration. It is found, that a flat specimen design is suitable for analysing the base material under different loading scenarios. The design and optimisation of the specimen geometry was carried out using finite element analysis, which was validated by means of optical strain measurement. The test procedure for the specimen was designed to provide a sound transferability to experimental testing of the components. A fracture pattern study was carried out using radiography and micro computed tomography. The results show, that the dominant damage mechanism is the separation of the layers from each other, denoted as delamination. In conclusion, the developed specimen is well suited for further investigations of the composite material. Furthermore, it will significantly accelerate the development of new air springs and new layups in particular. Future work will focus on a systematic investigation of the fatigue behaviour of the cord-rubber composite air-spring bellows based on the fatigue data of the representative specimens designed in this work.