Forecasting Graph Signals with Recursive MIMO Graph Filters

Forecasting time series on graphs is a fundamental problem in graph signal processing. When each entity of the network carries a vector of values for each time stamp instead of a scalar one, existing approaches resort to the use of product graphs to combine this multidimensional information, at the expense of creating a larger graph. In this paper, we show the limitations of such approaches, and propose extensions to tackle them. Then, we propose a recursive multiple-input multiple-output graph filter which encompasses many already existing models in the literature while being more flexible. Numerical simulations on a real world data set show the effectiveness of the proposed models

Forecasting Models for Graph Processes: A Study on the Multi-Dimensional Case

In the current Big Data era, large amounts of data are collected from complex systems, such as sensor networks and social networks. The emerging field of graph signal processing (GSP) leverages a network structure (graph) to process signals on an irregular domain. This thesis studies the forecasting of multi-dimensional graph processes, i.e., where each entity in the network carries a multivariate time series. Recent research has proposed to use product graphs to model the dependencies between different variables in multi-dimensional graph processes and employ them in graph-based vector autoregressive models to predict future values. A problem with these product graph-based models is that they can be too restrictive. In this work, it is proposed to combine product graph-based models with multiple one-dimensional models to implement more estimation flexibility. To further increase the degrees of freedom, the use of multiple-input-multiple-output graph filters is also proposed. The proposed models are implemented and tested on synthetic and real-world data sets, which shows an improved forecasting performance compared to state-of-the-art alternatives.Electrical Engineerin

A Wireless Charging solution for the Zebro

The Zebro is a six legged autonomous robot, designed to be deployed in swarms. Charging the battery is still done manually. To further increase the autonomous abilities of the Zebro, a wireless charging station and module is designed. The charging station is fully modular and interconnected by charging pads. This opens the possibility of charging multiple Zebro's simultaneously. The charging module consists of a receiver and Battery Management System inside the Zebro.In this thesis, both the transmitter and receiver side of the Wireless Power Transfer (WPT) system is designed. The transmitter and receiver must be perfectly aligned for high efficiency in a wireless charging setup. The positioning of the Zebro is not highly accurate, therefore the design of an inductive WPT system using SS-topology compensation is presented. Also, possible solutions improving the efficiency of the power transfer and the WPT system is proposed in this thesis. These improvements include coil optimization, object detection, circuit damage protection and implementation into the overall system

Quantitative flow ratio for immediate assessment of nonculprit lesions in patients with ST‐segment elevation myocardial infarction—An iSTEMI substudy

Objectives: We evaluated the diagnostic performance of quantitative flow ratio (QFR) assessment of nonculprit lesions (NCLs) based on acute setting angiograms obtained in patients with ST-segment elevation myocardial infarction (STEMI) with QFR, fractional flow reserve (FFR), and instantaneous wave-free ratio (iFR) in the staged setting as reference. Background: QFR is an angiography-based approach for the functional evaluation of coronary artery lesions. Methods: This was a post-hoc analysis of the iSTEMI study. NCLs were assessed with iFR in the acute setting and with iFR and FFR at staged (median 13 days) follow-up. Acute and staged QFR values were computed in a core laboratory based on the coronary angiography recordings. Diagnostic cut-off values were ≤0.80 for QFR and FFR, and ≤0.89 for iFR. Results: Staged iFR and FFR data were available for 146 NCLs in 112 patients in the iSTEMI study. Among these, QFR analysis was feasible in 103 (71%) lesions assessed in the acute setting with a mean QFR value of 0.82 (IQR: 0.73–0.91). Staged QFR, FFR, and iFR were 0.80 (IQR: 0.70–0.90), 0.81 (IQR: 0.71–0.88), and 0.91 (IQR: 0.87–0.96), respectively. Classification agreement of acute and staged QFR was 93% (95%Cl: 87–99). The classification agreement of acute QFR was 84% (95%CI: 76–90) using staged FFR as reference and 74% (95%CI: 65–83) using staged iFR as reference. Conclusions: Acute QFR showed a very good diagnostic performance with staged QFR as reference, a good diagnostic performance with staged FFR as reference, and a moderate diagnostic performance with staged iFR as reference

Quantitative flow ratio for immediate assessment of nonculprit lesions in patients with ST-segment elevation myocardial infarction—An iSTEMI substudy

Objectives: We evaluated the diagnostic performance of quantitative flow ratio (QFR) assessment of nonculprit lesions (NCLs) based on acute setting angiograms obtained in patients with ST-segment elevation myocardial infarction (STEMI) with QFR, fractional flow reserve (FFR), and instantaneous wave-free ratio (iFR) in the staged setting as reference. Background: QFR is an angiography-based approach for the functional evaluation of coronary artery lesions. Methods: This was a post-hoc analysis of the iSTEMI study. NCLs were assessed with iFR in the acute setting and with iFR and FFR at staged (median 13 days) follow-up. Acute and staged QFR values were computed in a core laboratory based on the coronary angiography recordings. Diagnostic cut-off values were ≤0.80 for QFR and FFR, and ≤0.89 for iFR. Results: Staged iFR and FFR data were available for 146 NCLs in 112 patients in the iSTEMI study. Among these, QFR analysis was feasible in 103 (71%) lesions assessed in the acute setting with a mean QFR value of 0.82 (IQR: 0.73–0.91). Staged QFR, FFR, and iFR were 0.80 (IQR: 0.70–0.90), 0.81 (IQR: 0.71–0.88), and 0.91 (IQR: 0.87–0.96), respectively. Classification agreement of acute and staged QFR was 93% (95%Cl: 87–99). The classification agreement of acute QFR was 84% (95%CI: 76–90) using staged FFR as reference and 74% (95%CI: 65–83) using staged iFR as reference. Conclusions: Acute QFR showed a very good diagnostic performance with staged QFR as reference, a good diagnostic performance with staged FFR as reference, and a moderate diagnostic performance with staged iFR as reference

The Power of Flash Mob Research Conducting a Nationwide Observational Clinical Study on Capillary Refill Time in a Single Day

BACKGROUND: Capillary refill time (CRT) is a clinical test used to evaluate the circulatory status of patients; various methods are available to assess CRT. Conventional clinical research often demands large numbers of patients, making it costly, labor-intensive, and time-consuming. We studied the interobserver agreement on CRT in a nationwide study by using a novel method of research called flash mob research (FMR). METHODS: Physicians in the Netherlands were recruited by using word-of-mouth referrals, conventional media, and social media to participate in a nationwide, single-day, "nineto-five," multicenter, cross-sectional, observational study to evaluate CRT. Patients aged >= 18 years presenting to the ED or who were hospitalized were eligible for inclusion. CRT was measured independently (by two investigators) at the patient's sternum and distal phalanx after application of pressure for 5 s (5s) and 15 s (15s). RESULTS: On October 29, 2014, a total of 458 investigators in 38 Dutch hospitals enrolled 1,734 patients. The mean CRT measured at the distal phalanx were 2.3 s (5s, SD1.1) and 2.4 s (15s, SD1.3). The mean CRT measured at the sternum was 2.6 s (5s, SD1.1) and 2.7 s (15s, SD1.1). Interobserver agreement was higher for the distal phalanx (k value, 0.40) than for the sternum (k value, 0.30). CONCLUSIONS: Interobserver agreement on CRT is, at best, moderate. CRT measured at the distal phalanx yielded higher interobserver agreement compared with sternal CRT measurements. FMR proved a valuable instrument to investigate a relatively simple clinical question in an inexpensive, quick, and reliable manner