"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:426494ed-d770-48f4-8181-3c6f0b57a3a1","http://resolver.tudelft.nl/uuid:426494ed-d770-48f4-8181-3c6f0b57a3a1","Vortex modes and vortex-induced vibration of a long, flexible riser","Xu, J.","","2009","","construction","","journal article","","","","","","","","","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","Ship Hydromechanics and Structures","","",""
"uuid:14df7e55-a0dc-412a-bac1-4af3736f372c","http://resolver.tudelft.nl/uuid:14df7e55-a0dc-412a-bac1-4af3736f372c","Bedform evolution around a submarine pipeline and its effects on wave-induced forces under regular waves","Xu, J.","","2010","","hydrodynamics","","journal article","","","","","","","","","Mechanical, Maritime and Materials Engineering","Marine and Transport Technology","Ship Hydromechanics and Structures","","",""
"uuid:9f4c083d-5b67-488c-ada6-0c5876afcf60","http://resolver.tudelft.nl/uuid:9f4c083d-5b67-488c-ada6-0c5876afcf60","A 160μW 8-Channel Active Electrode System for EEG Monitoring","Xu, J. (TU Delft Electronic Instrumentation); Yazicioglu, Refet Firat (IMEC); Grundlehner, Bernard (Stichting IMEC Nederland); Harpe, Pieter (Eindhoven University of Technology); Makinwa, K.A.A. (TU Delft Electronic Instrumentation); Van Hoof, Chris (IMEC)","","2011","This paper presents an active electrode system for gel-free biopotential EEG signal acquisition. The system consists of front-end chopper amplifiers and a back-end common-mode feedback (CMFB) circuit. The front-end AC-coupled chopper amplifier employs input impedance boosting and digitally-assisted
offset trimming. The former increases the input impedance of the active electrode to 2 G at 1 Hz and the latter limits the chopping induced output ripple and residual offset to 2 mV and 20 mV respectively. Thanks to chopper stabilization, the active electrode achieves 0.8 μVrms (0.5-100 Hz) input referred noise. The use of a back-end CMFB circuit further improves the CMRR of the active electrode readout to 82 dB at 50 Hz. Both front-end and back-end
circuits are implemented in a 0.18 μm CMOS process and the total current consumption of an 8-channel readout system is 88 μA from 1.8 V supply. EEG measurements using the proposed active electrode system demonstrate its benefits compared to passive electrode systems, namely reduced sensitivity to cable motion artifacts and mains interference.","Elektrotechniek; Techniek","en","journal article","","","","","","Accepted Author Manuscript","","","","","Electronic Instrumentation","","",""
"uuid:474d8991-7e57-49e9-80aa-a71066cb884a","http://resolver.tudelft.nl/uuid:474d8991-7e57-49e9-80aa-a71066cb884a","A mesoscale modelling perspective of cracking process and fracture energy under high strain rate in tension","Weerheijm, J.; Lu, Y.; Xu, J.","","2013","This paper presents a numerical modelling study on the simulation of the cracking process and fracture energy in concrete under high strain rate. To capture the stress wave effect and the damage evolution at the meso-length scale, both a homogeneous model with a millimetreresolution mesh and an explicit heterogeneous mesoscale model with random polygon aggregates are employed. The tendency of development of a) discrete multiple cracks, and b) spread tensile damage across adjacent element layers, in the high strain rate tension regime is scrutinised. This phenomenon generally gives rise to an increase in the dynamic fracture energy, which is consistent with experimental observations. Relative comparison between the homogeneous and heterogeneous mesoscale simulations suggests a sensible effect of the mesoscopic heterogeneity in the dynamic fracture process.","concrete; dynamic tension; high strain rate; fracture energy; mesoscale model","en","conference paper","Cimne","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:82d083dc-b287-437f-8066-b2ce9b7da015","http://resolver.tudelft.nl/uuid:82d083dc-b287-437f-8066-b2ce9b7da015","A Wearable 8-Channel Active-Electrode EEG/ETI Acquisition System for Body Area Networks","Xu, J (External organisation); Mitra, S (External organisation); Matsumoto, A (External organisation); Patki, S (External organisation); van Hoof, C (External organisation); Makinwa, K.A.A. (TU Delft Electronic Instrumentation)","","2014","br","Active electrode; chopper amplifier; dry electrode; EEG monitoring; electrode-tissue impedance","en","journal article","","","","","","Accepted Author Manuscript","","","","","Electronic Instrumentation","","",""
"uuid:6acba056-8bfb-44ce-9af8-60e991ae52b1","http://resolver.tudelft.nl/uuid:6acba056-8bfb-44ce-9af8-60e991ae52b1","Robot Mood is Contagious: Effects of Robot Body Language in the Imitation Game","Xu, J.; Broekens, D.J.; Hindriks, K.V.; Neerincx, M.A.","","2014","Mood contagion is an automatic mechanism that induces a congruent mood state by means of the observation of another person's emotional expression. In this paper, we address the question whether robot mood displayed during an imitation game can (a) be recognized by participants and (b) produce contagion effects. Robot mood was displayed by applying a generic framework for mood expression using body language. By modulating the set of available behavior parameters in this framework for controlling pose and motion dynamics, the gestures performed by the humanoid robot NAO were adjusted to display either a positive or negative mood. In the study performed, we varied both mood as well as task difficulty. Our results show that participants are able to differentiate between positive and negative robot mood. Moreover, self-reported mood matches the mood of the robot in the easy task condition. Additional evidence for mood contagion is provided by the fact that we were able to replicate an expected effect of negative mood on task performance: in the negative mood condition participants performed better on difficult tasks than in the positive mood condition, even though participants’ self-reported mood did not match that of the robot.","mood expression; nonverbal cues; behavioral cues; body language; social robots; Human Robot Interaction (HRI)","en","conference paper","ACM","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Intelligent Systems","","","",""
"uuid:e18df776-27fb-425a-ace3-6f702c6975af","http://resolver.tudelft.nl/uuid:e18df776-27fb-425a-ace3-6f702c6975af","A 15-Channel digital active electrode system for multi-parameter biopotential measurement","Xu, J. (Holst Centre); Büsze, Benjamin (Holst Centre); Van Hoof, Chris (IMEC); Makinwa, K.A.A. (TU Delft Electronic Instrumentation); Yazicioglu, Refet Firat (IMEC)","","2015","This paper presents a digital active electrode (DAE) system for multi-parameter biopotential signal acquisition in portable and wearable devices. It is built around an IC that performs analog signal processing and digitization with the help
of on-chip instrumentation amplifiers, a 12 bit ADC and a digital interface. Via a standard bus, up to 16 digital active electrodes (15-channels) can be connected to a commercially available microcontroller, thus significantly reducing system
complexity and cost. In addition, the DAE utilizes an innovative functionally DC-coupled amplifier to preserve input DC signal, while still achieving state-of-the-art performance: 60 nV/sqrt(Hz) input-referred noise and 350 mV electrode-offset tolerance. A common-mode feedforward scheme improves the CMRR of an
AE pair from 40 dB to maximum 102 dB.","Active electrode; biopotential measurement; digital interface; DC-coupled amplifier; common-mode feedforward (CMFF)","en","journal article","","","","","","","","","","","Electronic Instrumentation","","",""
"uuid:061e1563-5a89-4593-8142-d798212b7423","http://resolver.tudelft.nl/uuid:061e1563-5a89-4593-8142-d798212b7423","Mood contagion of robot body language in human robot interaction","Xu, J.; Broekens, D.J.; Hindriks, K.V.; Neerincx, M.A.","","2015","The aim of our work is to design bodily mood expressions of humanoid robots for interactive settings that can be recognized by users and have (positive) effects on people who interact with the robots. To this end, we develop a parameterized behavior model for humanoid robots to express mood through body language. Different settings of the parameters, which control the spatial extent and motion dynamics of a behavior, result in different behavior appearances expressing different moods. In this study, we applied the behavior model to the gestures of the imitation game performed by the NAO robot to display either a positive or a negative mood. We address the question whether robot mood displayed simultaneously with the execution of functional behaviors in a task can (a) be recognized by participants and (b) produce contagion effects. Mood contagion is an automatic mechanism that induces a congruent mood state by means of the observation of another person’s emotional expression. In addition, we varied task difficulty to investigate how the task load mediates the effects. Our results show that participants are able to differentiate between positive and negative robot mood and they are able to recognize the behavioral cues (the parameters) we manipulated. Moreover, self-reported mood matches the mood expressed by the robot in the easy task condition. Additional evidence for mood contagion is provided by the fact that we were able to replicate an expected effect of negative mood on task performance: in the negative mood condition participants performed better on difficult tasks than in the positive mood condition, even though participants’ self-reported mood did not match that of the robot.","human robot interaction (HRI); mood expression; nonverbal cues; behavioral cues; body language; social robots","en","journal article","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Intelligent Systems","","","",""
"uuid:c5802c94-a984-474c-8703-698e056086ad","http://resolver.tudelft.nl/uuid:c5802c94-a984-474c-8703-698e056086ad","Affective Body Language of Humanoid Robots: Perception and Effects in Human Robot Interaction","Xu, J.","Neerincx, M.A. (promotor)","2015","","human robot interaction; social robots; bodily expression; nonverbal cues; affective expression; mood expression; behavior model; body language; artificial intelligence; humanoid robots","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Intelligent Systems","","","",""
"uuid:be785ee1-eef0-44b0-aa72-2f5c658b13c9","http://resolver.tudelft.nl/uuid:be785ee1-eef0-44b0-aa72-2f5c658b13c9","Model Predictive Control for continuous piecewise affine systems using optimistic optimization","Xu, J. (TU Delft Team Bart De Schutter); van den Boom, A.J.J. (TU Delft Team Bart De Schutter); Busoniu, L (Technical University of Cluj-Napoca); De Schutter, B.H.K. (TU Delft Team Bart De Schutter)","Chiu, George (editor); Johnson, Katie (editor); Abramovitch, Danny (editor)","2016","This paper considers model predictive control for continuous piecewise affine (PWA) systems. In general, this leads to a nonlinear, nonconvex optimization problem. We introduce an approach based on optimistic optimization to solve the resulting optimization problem. Optimistic optimization is based on recursive partitioning of the feasible set and is characterized by an efficient exploration strategy seeking for the optimal solution. The advantage of optimistic optimization is that one can guarantee bounds on the suboptimality with respect to the global optimum for a given computational budget. The 1-norm and ∞-norm objective functions often considered in model predictive control for continuous PWA systems are continuous PWA functions. We derive expressions for the core parameters required by optimistic optimization for the resulting optimization problem. By applying optimistic optimization, a sequence of control inputs is designed satisfying linear constraints. A bound on the suboptimality of the returned solution is also discussed. The performance of the proposed approach is illustrated with a case study on adaptive cruise control.","Optimization; Partitioning algorithms; Linear programming; Predictive control; Complexity theory; Prediction algorithms; Cruise control","en","conference paper","IEEE","","","","","Accepted Author Manuscript","","","","","Team Bart De Schutter","","",""
"uuid:dde2e340-1359-46fd-b490-e3ad29df49ca","http://resolver.tudelft.nl/uuid:dde2e340-1359-46fd-b490-e3ad29df49ca","Receding-horizon control for max-plus linear systems with discrete actions using optimistic planning","Xu, J. (TU Delft Team Bart De Schutter); Busoniu, L (Technical University of Cluj-Napoca); van den Boom, A.J.J. (TU Delft Team Bart De Schutter); De Schutter, B.H.K. (TU Delft Team Bart De Schutter)","Cassandras, Christos G. (editor); Giua, Alessandro (editor); Li, Zhiwu (editor)","2016","This paper addresses the infinite-horizon optimal control problem for max-plus linear systems where the considered objective function is a sum of discounted stage costs over an infinite horizon. The minimization problem of the cost function is equivalently transformed into a maximization problem of a reward function. The resulting optimal control problem is solved based on an optimistic planning algorithm. The control variables are the increments of system inputs and the action space is discretized as a finite set. Given a finite computational budget, a control sequence is returned by the optimistic planning algorithm. The first control action or a subsequence of the returned control sequence is applied to the system and then a receding-horizon scheme is adopted. The proposed optimistic planning approach allows us to limit the computational budget and also yields a characterization of the level of near-optimality of the resulting solution. The effectiveness of the approach is illustrated with a numerical example. The results show that the optimistic planning approach results in a lower tracking error compared with a finite-horizon approach when a subsequence of the returned control sequence is applied.","Planning; Optimal control; Linear systems; Linear programming; Aerospace electronics; Algorithm design and analysis","en","conference paper","IEEE","","","","","Accepted Author Manuscript","","","","","Team Bart De Schutter","","",""
"uuid:0f80a5f1-d81f-4f1d-b6ae-01289f8dfef0","http://resolver.tudelft.nl/uuid:0f80a5f1-d81f-4f1d-b6ae-01289f8dfef0","Low-Power Active Electrodes for Wearable EEG Acquisition","Xu, J. (TU Delft Electronic Instrumentation)","Makinwa, K.A.A. (promotor); van Hoof, C (promotor); Delft University of Technology (degree granting institution)","2016","","","en","doctoral thesis","","","","","","","","","","","Electronic Instrumentation","","",""
"uuid:678fa285-e3cf-4308-a210-5af4dabbfae3","http://resolver.tudelft.nl/uuid:678fa285-e3cf-4308-a210-5af4dabbfae3","Active Electrodes for Wearable EEG Acquisition: Review and Design Methodology","Xu, J. (TNO); Mitra, Srinjoy (University of Glasgow); Van Hoof, Chris (IMEC); Yazicioglu, Refet Firat (GlaxoSmithKline); Makinwa, K.A.A. (TU Delft Microelectronics)","","2017","Active electrodes (AEs), i.e., electrodes with built-in readout circuitry, are increasingly being implemented in wearable healthcare and lifestyle applications due to AEs' robustness to environmental interference. An AE locally amplifies and buffers μV-level EEG signals before driving any cabling. The low output impedance of an AE mitigates cable motion artifacts, thus enabling the use of high-impedance dry electrodes for greater user comfort. However, developing a wearable EEG system, with medical grade signal quality on noise, electrode offset tolerance, common-mode rejection ratio, input impedance, and power dissipation, remains a challenging task. This paper reviews state-of-the-art bio-amplifier architectures and low-power analog circuits design techniques intended for wearable EEG acquisition, with a special focus on an AE system interfaced with dry electrodes.","Active electrode (AE); brain–computer interface; common-mode rejection ratio (CMRR); dry electrodes; electroencephalography (EEG); instrumentation amplifier (IA)","en","journal article","","","","","","Accepted Author Manuscript","","","","Microelectronics","","","",""
"uuid:7ae33605-2335-4e53-b691-69cccd44e4d7","http://resolver.tudelft.nl/uuid:7ae33605-2335-4e53-b691-69cccd44e4d7","Near-optimal control with adaptive receding horizon for discrete-time piecewise affine systems","Xu, J. (TU Delft Team Bart De Schutter); Buşoniu, Lucian (Technical University of Cluj-Napoca); De Schutter, B.H.K. (TU Delft Team Bart De Schutter)","Dochain, D (editor); Henrion, D (editor); Peaucelle, D (editor)","2017","We consider the infinite-horizon optimal control of discrete-time, Lipschitz continuous piecewise affine systems with a single input. Stage costs are discounted, bounded, and use a 1 or ∞-norm. Rather than using the usual fixed-horizon approach from model-predictive control, we tailor an adaptive-horizon method called optimistic planning for continuous actions (OPC) to solve the piecewise affine control problem in receding horizon. The main advantage is the ability to solve problems requiring arbitrarily long horizons. Furthermore, we introduce a novel extension that provides guarantees on the closed-loop performance, by reusing data (“learning”) across different steps. This extension is general and works for a large class of nonlinear dynamics. In experiments with piecewise affine systems, OPC improves performance compared to a fixed-horizon approach, while the data-reuse approach yields further improvements.","near-optimality analysis; nonlinear predictive control; optimistic planning; piecewise affine systems","en","conference paper","Elsevier","","","","","","","","","","Team Bart De Schutter","","",""
"uuid:fbc34ac3-cedf-42be-8d6f-dac1d8cb0a32","http://resolver.tudelft.nl/uuid:fbc34ac3-cedf-42be-8d6f-dac1d8cb0a32","Design of 3D Wireless Power Transfer System Based on 3D Printed Electronics","Hou, T. (TU Delft Mechatronic Design; School of Mechatronic Engineering and Automation); Xu, J. (TU Delft Mechatronic Design); Elkhuizen, W.S. (TU Delft Mechatronic Design); Wang, C.C. (Chinese University of Hong Kong); Jiang, Jiehui (Shanghai Institute for Advanced Communication and Data Science; Shanghai University); Geraedts, Jo M.P. (TU Delft Mechatronic Design); Song, Y. (TU Delft Mechatronic Design)","","2019","2D coil design limits the use of wireless power transfer (WPT) in many products with freeform outer shapes. In this paper, enabled by 3D printed electronics, we propose a systematic approach to design and fabricate 3D coils for WPT. Based on the circular spiral and rectangular spiral patterns, 3D receiver and transmitter coils can be generated on an arbitrarily selected region of a product and its offset, respectively. Mathematical models are proposed to estimate the self-inductance and the mutual-inductance of the 3D arbitrarily shaped coils for 3D WPT. This leads to a new design approach of a 3D WPT system. Several sets of 3D printed WPT systems were designed, simulated, and prototyped to demonstrate the effectiveness of the proposed design approach as well as the mathematical models. The calculation speed of the proposed mathematical models is 30 times faster than the simulation, and compared with the measurement results, the calculation results have mean absolute errors of 2.63% and 4.45% regarding the self- and the mutual-inductance, where the simulation results have mean absolute errors of 1.20% and 2.38%, respectively. Measurements also indicate that with a 5V input, the prototypes are able to deliver 1-watt power at an efficiency ranging between 20.9% and 25.3%. It was concluded that the proposed approach is feasible and promising for designing and manufacturing WPT using 3D printed electronics.","3D coil; 3D printed electronics; design; IPT; WPT; OA-Fund TU Delft","en","journal article","","","","","","","","","","","Mechatronic Design","","",""
"uuid:87bafdf4-a16e-4abd-8e81-c349cf95f9f2","http://resolver.tudelft.nl/uuid:87bafdf4-a16e-4abd-8e81-c349cf95f9f2","Optimization and model-based control for max-plus linear and continuous piecewise affine systems","Xu, J. (TU Delft Team Bart De Schutter)","De Schutter, B.H.K. (promotor); van den Boom, A.J.J. (copromotor); Delft University of Technology (degree granting institution)","2019","This PhD thesis considers the development of optimization and model-based control techniques for max-plus linear (MPL) and continuous piecewise affine (PWA) systems. The three main topics investigated in this thesis are as follows: 1. Optimistic optimization and planning for model-based control of MPL systems; 2. Optimistic optimization for MPC of continuous PWA systems; 3. MPC for stochastic MPL systems with chance constraints","Model predictive control (MPC); Max-plus linear systems; piecewise affine systems; Optimistic optimization","en","doctoral thesis","","978-94-6186-953-1","","","","","","","","","Team Bart De Schutter","","",""
"uuid:6f4365e5-bb22-4523-b023-c894c421f3cc","http://resolver.tudelft.nl/uuid:6f4365e5-bb22-4523-b023-c894c421f3cc","Analysis and control of max-plus linear discrete-event systems: An introduction","De Schutter, B.H.K. (TU Delft Delft Center for Systems and Control; TU Delft Team Bart De Schutter); van den Boom, A.J.J. (TU Delft Team Bart De Schutter); Xu, J. (TU Delft Team Bart De Schutter); Safaei Farahani, S. (TU Delft Energie and Industrie)","","2020","The objective of this paper is to provide a concise introduction to the max-plus algebra and to max-plus linear discrete-event systems. We present the basic concepts of the max-plus algebra and explain how it can be used to model a specific class of discrete-event systems with synchronization but no concurrency. Such systems are called max-plus linear discrete-event systems because they can be described by a model that is “linear” in the max-plus algebra. We discuss some key properties of the max-plus algebra and indicate how these properties can be used to analyze the behavior of max-plus linear discrete-event systems. Next, some control approaches for max-plus linear discrete-event systems, including residuation-based control and model predictive control, are presented briefly. Finally, we discuss some extensions of the max-plus algebra and of max-plus linear systems.","Analysis of discrete-event systems; Max-plus algebra; Max-plus linear systems; Model predictive control; Model-based control of max-plus linear systems; Residuation-based control; Survey","en","journal article","","","","","","","","","","Delft Center for Systems and Control","Team Bart De Schutter","","",""
"uuid:27fb86b1-db06-449f-af0e-f9df9e34f290","http://resolver.tudelft.nl/uuid:27fb86b1-db06-449f-af0e-f9df9e34f290","The influence of the angle of attack on passenger comfort","Ping, Y. (Student TU Delft); Yao, X. (TU Delft Mechatronic Design); Xu, J. (TU Delft Mechatronic Design); Li, Juntian (External organisation); Song, Y. (TU Delft Mechatronic Design); Vink, P. (TU Delft Materials and Manufacturing)","Mansfield, Neil (editor)","2021","The angle of attack (AOA) of an airplane changes the direction of the gravitational force on passengers and thereby might influence passengers’ flying experience. However, the contribution of the AOA regarding comfort/discomfort is not fully explored. In this paper, we aim to fill this knowledge gap by identifying the relationships between the perceived comfort/ discomfort of passengers and the AOA of the plane during the take-off and climbing phases of a flight. An
experiment is conducted in a Boeing 737 fuselage where 10 participants were recruited. Each participant experiences 3 setups of seats with different AOAs (3, 14 and 18 degrees) for 20 minutes, respectively. Participants were asked to complete several sets of questionnaires during each session, and their heart rate and the pressure on the seat and the backrest were recorded as well. Experiment results indicated that participants experienced 14-degree as the most comfortable angle with the lowest discomfort, which might be useful for airlines in setting up the take-off and climbingprocedure.","Seat inclination; Comfort; Take-off/climbing","en","conference paper","","","","","","","","","","","Mechatronic Design","","",""
"uuid:079385f5-e19a-4832-a755-679213f7705f","http://resolver.tudelft.nl/uuid:079385f5-e19a-4832-a755-679213f7705f","Virtual Resistor Active Damping with Selective Harmonics Control of LCL-Filtered VSCs","Wu, Y. (TU Delft DC systems, Energy conversion & Storage); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage); Shekhar, A. (TU Delft DC systems, Energy conversion & Storage); Xu, J. (Shanghai Jiao Tong University); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2021","LCL filter is widely adopted for strict standard compliance of grid-tied voltage source converters (VSCs). The third order low-pass filtering provides great attenuation for the high frequency harmonics generated by the power electronics guaranteeing low output currents noise injection into the grid. A major concern of the implementation of the LCL-filter is to safeguard the system stability by providing effective damping of the filter resonances. Active damping methods are preferred because it does not result in substantial power losses as it would result by the utilization of passive damping circuits. Capacitor-current active damping (CCAD) technique can be effective while realizing only a proportional feedback. However, the suitable feedback gain for maintaining stability remains to be identified. Another control issue related to the grid-tied VSC is the harmonics compensation of the currents due to the grid voltage distortion. Therefore, this paper proposes an improved resonator with phase compensation to suppress the harmonics distortion while maintaining stability with properly design capacitor current feedback. The capacitor feedback gain for stability is analytically derived in this paper. The proposed control scheme is verified by both simulation and experimental results.","Capacitor-current feedback Active damping (CCAD); Harmonics resonator; LCL filter; VSC","en","conference paper","IEEE","","","","","Accepted author manuscript","","","","","DC systems, Energy conversion & Storage","","",""
"uuid:7230080d-3df1-4408-952b-9f28a0a7fc2e","http://resolver.tudelft.nl/uuid:7230080d-3df1-4408-952b-9f28a0a7fc2e","A Multi-Sensor Information Fusion Method Based on Factor Graph for Integrated Navigation System","Xu, J. (TU Delft Interactive Intelligence); Yang, Gongliu (Beihang University); Sun, Yiding (Beihang University); Picek, S. (TU Delft Cyber Security)","","2021","The current navigation systems used in many autonomous mobile robotic applications, like unmanned vehicles, are always equipped with various sensors to get accurate navigation results. The key point is to fuse the information from different sensors efficiently. However, different sensors provide asynchronous measurements, some of which even appear to be nonlinear. Moreover, some sensors are vulnerable in specific environments, e.g., GPS signal is likely to work poorly in interior space, underground, and tall buildings. We propose a multi-sensor information fusion method based on a factor graph to fuse all available asynchronous sensor information and efficiently and accurately calculate a navigation solution. Assuming the sensor measurements and navigation states in a navigation system as factor nodes and variable nodes in a factor graph, respectively, the update of the states can be implemented in the framework of the factor graph. The proposed method is experimentally validated using two different datasets. A comparison with Federated Filter, which has been widely used in integrated navigation systems, demonstrates the proposed method’s effectiveness. Additionally, analyzing the navigation results with data loss verifies that the proposed method could achieve sensor plug and play in software.","Integrated navigation; multi-sensor; information fusion; factor graph; plug and play","en","journal article","","","","","","","","","","","Interactive Intelligence","","",""
"uuid:9d056d82-4134-40ef-9908-b01ec75b0649","http://resolver.tudelft.nl/uuid:9d056d82-4134-40ef-9908-b01ec75b0649","Carrier-based Generalized Discontinuous PWM Strategy for Single-Phase Three-Legs Active Power Decoupling Converters","Xu, J. (Shanghai Jiao Tong University; Ministry of Education); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage); Gao, Fei (Shanghai Jiao Tong University; Ministry of Education); Tang, Houjun (Shanghai Jiao Tong University; Ministry of Education); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2021","Three-legs active power decoupling (APD) converters are widely studied in the single-phase grid-connected systems to enhance the circuit lifetime by creating an alternative path for the typical existing dc-side power pulsating ripple. Therefore, this reduces the requirement of smoothing dc capacitors allowing compact designs even with the implementation of long life metalized film technology. In this article, to allow enhancement of the system power density by improving power conversion efficiency and thus reducing the requirement of thermal management of the semiconductors, a carrier-based generalized discontinuous PWM strategy is proposed. This method detects the converter ac currents and ac reference voltages to determine the optimum clamped duration in each one of the three bridge-legs, which will minimize the converter overall switching losses. The proposed modulation method is analyzed and validated on a PLECS simulation and a 2 kVA single-phase three-legs APD converter.","Active power decoupling (APD); discontinuous pulsewidth modulation (DPWM); single-phase","en","journal article","","","","","","","","","","","DC systems, Energy conversion & Storage","","",""
"uuid:34769f1e-5b7f-45b2-a760-961d81af7e6a","http://resolver.tudelft.nl/uuid:34769f1e-5b7f-45b2-a760-961d81af7e6a","Explainability-based Backdoor Attacks against Graph Neural Networks","Xu, J. (TU Delft Cyber Security); Xue, Minhui (University of Adelaide); Picek, S. (TU Delft Cyber Security)","","2021","Backdoor attacks represent a serious threat to neural network models. A backdoored model will misclassify the trigger-embedded inputs into an attacker-chosen target label while performing normally on other benign inputs. There are already numerous works on backdoor attacks on neural networks, but only a few works consider graph neural networks (GNNs). As such, there is no intensive research on explaining the impact of trigger injecting position on the performance of backdoor attacks on GNNs. To bridge this gap, we conduct an experimental investigation on the performance of backdoor attacks on GNNs. We apply two powerful GNN explainability approaches to select the optimal trigger injecting position to achieve two attacker objectives - high attack success rate and low clean accuracy drop. Our empirical results on benchmark datasets and state-of-the-art neural network models demonstrate the proposed method's effectiveness in selecting trigger injecting position for backdoor attacks on GNNs. For instance, on the node classification task, the backdoor attack with trigger injecting position selected by GraphLIME reaches over 84% attack success rate with less than 2.5% accuracy drop.","backdoor attacks; explainability; graph neural networks","en","conference paper","Association for Computing Machinery (ACM)","","","","","","","","","","Cyber Security","","",""
"uuid:041e7a1c-a7aa-4024-8986-edefe0354e60","http://resolver.tudelft.nl/uuid:041e7a1c-a7aa-4024-8986-edefe0354e60","The development of a low-cost photogrammetry-based 3D hand scanner","Yang, Y. (TU Delft Mechatronic Design; Shanghai University); Xu, J. (TU Delft Mechatronic Design); Elkhuizen, W.S. (TU Delft Mechatronic Design); Song, Y. (TU Delft Mechatronic Design)","","2021","Acquiring an accurate 3D scan of the human hand is a challenging task, mainly due to the complicated geometry and the instability of the hand. In this paper, we present a low-cost photogrammetry-based scanner that is designed for scanning the human hand. The scanner has fifty modules, each has a Raspberry Pi with an 8-megapixels camera. They are uniformly positioned in two parallel frames and 96% of a hand surface can be viewed by at least 3 cameras. Using the timestamp method, we synchronize the shutters of the 50 cameras within the range of 80 ms to minimize the influence of the instability of the hand. Moreover, the scanner is easy to build with its modular design, and easy to operate with a laptop that is connected to the system by WiFi. Using a 3D printed prosthetic hand, we compared the 3D scanning accuracy of the proposed scanner with the Artec Spider® scanner. The mean absolute error between the two scans is 0.62 ± 0.28 mm. It is concluded that the proposed hand scanner can be used as a low-cost yet accurate tool in many applications, such as personalized product design.","3D scan; Photogrammetry; Raspberry Pi","en","journal article","","","","","","","","","","","Mechatronic Design","","",""
"uuid:59e39aa0-02ec-43db-848d-bdf9f0e3f751","http://resolver.tudelft.nl/uuid:59e39aa0-02ec-43db-848d-bdf9f0e3f751","(Fe,Co)2(P,Si) rare-earth free permanent magnets: From macroscopic single crystals to submicron-sized particles","Yibole, H. (Inner Mongolia Normal University China); Lingling-Bao, B. (Inner Mongolia Normal University China); Xu, J. (TU Delft Mechanical, Maritime and Materials Engineering; Inner Mongolia Normal University China); Alata, H. (Inner Mongolia Normal University China); Tegus, O. (Inner Mongolia Normal University China); Hanggai, W. (External organisation); van Dijk, N.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Guillou, F. (Inner Mongolia Normal University China)","","2021","While rare-earth magnets exhibit unchallenged hard-magnetic properties, looking for alternatives based on inexpensive elements of non-critical supply remains of utmost interest. Here, we demonstrate that (Fe,Co)2(P,Si) single crystals combine a large magnetocrystalline anisotropy (K1 ≈ 0.9 MJ m−3 at 300 K), high Curie temperatures (TC up to 560 K) and an appreciable saturation specific magnetization (101 A m2 kg−1) leading to a theoretical |BH|max ≈ 165 kJ m-3, making them promising candidate materials as rare-earth-free permanent magnets. Our comparison between (Fe,Co)2P and (Fe,Co)2(P,Si) single crystals highlights that Si substitution reduces the low-temperature magnetocrystalline anisotropy, but strongly enhances TC, making the latter quaternary alloys most favorable for room temperature applications. Submicron-sized particles of Fe1.75Co0.20P0.75Si0.25 were prepared by a top-down ball-milling approach. While the energy products of bonded particles are to this point modest, they demonstrate that permanent magnetic properties can be achieved in (Fe,Co)2(P,Si) quaternary alloys. This work correlates the development of permanent magnetic properties to a control of the microstructure. It paves the way toward the realization of permanent magnetic properties in (Fe,Co)2(P,Si) alloys made of economically competitive Fe, P and Si elements, making these materials desirable for applications.","Magnetic properties; Magnetism; Nanomaterials; Single crystal","en","journal article","","","","","","","","2023-10-20","Mechanical, Maritime and Materials Engineering","","RST/Fundamental Aspects of Materials and Energy","","",""
"uuid:f383ef06-68e6-4f0c-98fa-60425d41358b","http://resolver.tudelft.nl/uuid:f383ef06-68e6-4f0c-98fa-60425d41358b","A Hybrid Modulation Featuring Two-phase Clamped Discontinuous PWM and Zero Voltage Switching for 99% Efficient DC-Type EV Charger","Xu, J. (Shanghai Jiao Tong University); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage); Wang, Yong (Shanghai Jiao Tong University); Gao, Fei (Shanghai Jiao Tong University); Tang, Houjun (Shanghai Jiao Tong University); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2022","Two-stage AC-DC converters are considered as a prominent solution for DC-type electric vehicle (EV) chargers. However, this kind of architecture suffers from high switching losses with large heatsink and DC-link capacitor volume. To relieve this issue, this paper presents a new hybrid modulation for DC-type EV chargers, where a two-phase clamped discontinuous pulse-width-modulation (DPWM) in the front-end circuit is cooperated with the variable frequency triangular-current mode (TCM) zero voltage switching (ZVS) or its simplified implementation, i.e., boundary-ZVS (B-ZVS) strategy, in the back-end circuit. The former can stop the switching actions in the front-end stage during two-thirds of the grid period, while the AC currents are at their highest values, which can yield to the best switching loss reduction and deliver high power factor operation. Besides, TCM-ZVS or B-ZVS modulations can achieve ZVS turn-on action for all semiconductors during all operating range in the DC-DC stage to further reduce the power losses on the semiconductors. With such characteristics, the proposed strategies can reduce the switching losses of the system to the best extent, and thus allow an enhancement of the system power density by improving the power conversion efficiency. The proposed strategy is described, analyzed, validated, and benchmarked in a 5kW SMD SiC MOSFET-based two-stage AC-DC converter. A 99% power efficiency can be achieved with the solution implementing the TCM-ZVS strategy at an output voltage of 400V and rated power.","Electric vehicle (EV); two-stage AC-DC converter; discontinuous pulse width modulation (DPWM); , zero voltage switching (ZVS)","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","DC systems, Energy conversion & Storage","","",""
"uuid:099dfc1a-0f2c-448a-9465-f37ef3112a2b","http://resolver.tudelft.nl/uuid:099dfc1a-0f2c-448a-9465-f37ef3112a2b","Optimal Periodic Variable Switching PWM for Harmonic Performance Enhancement in Grid-Connected Voltage Source Converters","Wu, Y. (TU Delft DC systems, Energy conversion & Storage); Xu, J. (TU Delft DC systems, Energy conversion & Storage; Shanghai Jiao Tong University); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage); Stecca, M. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2022","Variable switching frequency PWM (VSFPWM) modulation can be advantageously implemented in industrial applications, such as renewable energy, motor drives, and uninterrupted power supply (UPS) systems, to reduce the injected current harmonic amplitudes, to suppress audible noise, and to improve semiconductor power efficiency. In this article, the usage of periodic VSFPWM methods in a voltage source converter (VSC) is proposed, analyzed, and benchmarked in terms of harmonic spectrum spreading, following the IEEE-519 current harmonic standard for the connection to the distribution grid. Particular attention is paid to the influence of VSFPWM on the ac filter design. First, the analytical model of the voltage harmonic spectrum generated by a three-phase three-wire two-level VSC implementing several periodic VSFPWM methods is derived. Subsequently, a design guideline for the commonly used LCL filter in the grid-tied VSC application is proposed, which minimizes the size requirement of the necessary components. The voltage spectrum models of the proposed VSFPWM method and the optimal switching profiles are verified by MATLAB/Simulink simulations and a 5-kW three-phase two-level VSC hardware demonstrator. The study shows that the ac filter power density for the studied VSFPWM methods can be greatly increased when compared with the conventional and widely employed constant switching frequency continuous PWM strategies.","filter design; optimal design; spectrum model; Variable switching frequency PWM (VSF-PWM)","en","journal article","","","","","","","","","","","DC systems, Energy conversion & Storage","","",""
"uuid:6463eadd-f857-4292-97a8-a80b0df8d4e9","http://resolver.tudelft.nl/uuid:6463eadd-f857-4292-97a8-a80b0df8d4e9","Hybrid Si/SiC Switch Modulation with Minimum SiC MOSFET Conduction in Grid Connected Voltage Source Converters","Stecca, M. (TU Delft DC systems, Energy conversion & Storage); Tan, Changyu (Student TU Delft); Xu, J. (TU Delft DC systems, Energy conversion & Storage); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Palensky, P. (TU Delft Intelligent Electrical Power Grids)","","2022","In this article, a hybrid Si/Si carbide (SiC) switch (HyS) modulation with minimum SiC MOSFET conduction (mcHyS) is experimentally characterized, so as to derive its conduction and switching performance. These are later used to derive a silicon (Si) area analytical model for the HyS configuration. The chip area model is used to benchmark the mcHyS modulation concepts against single-technology switches and typical HyS modulation when considering the implementation of a 100-kW two-level voltage-source converter (VSC) deployed for three industrial applications: photovoltaic inverter, electric vehicle fast-charging station, and battery storage systems for grid ancillary service. The two additional switching events of the SiC MOSFET, which differentiate the mcHyS modulation from the typical HyS one, are proven to happen in soft switching; therefore, the mcHyS switching performances are not penalized. Furthermore, the analysis presented shows how the studied mcHyS modulation performs against the single semiconductor technology and the typical HyS solution in terms of cost and power conversion efficiency. More specifically, it is shown that the HyS solutions are particularly competitive versus the full Si-based VSCs when the application at hand often operates at low partial loads. Finally, a 10-kW two-level VSC assembled with mcHyS is tested, so as to compare its efficiency versus single-technology switches.","Double-pulse test (DPT); grid-connected voltage-source converter (VSC); grid connected; SiC MOSFET","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-02-28","","","DC systems, Energy conversion & Storage","","",""
"uuid:4d78313f-452a-4986-9ea0-9f19517e4cfe","http://resolver.tudelft.nl/uuid:4d78313f-452a-4986-9ea0-9f19517e4cfe","A Carrier-based Two-Phase-Clamped DPWM Strategy With Zero-Sequence Voltage Injection for Three-Phase Quasi-Two-Stage Buck-Type Rectifiers","Xu, J. (Shanghai Jiao Tong University); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage; TU Delft Electrical Sustainable Energy); Wu, Y. (TU Delft DC systems, Energy conversion & Storage); Gao, Fei (Shanghai Jiao Tong University); Wang, Y. (TU Delft Statistics; Shanghai Jiao Tong University); Tang, Houjun (Shanghai Jiao Tong University); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2022","A three-phase buck-type rectifier features a step-down ac-dc conversion function, which is considered as a prominent solution for electric vehicle chargers and telecommunication systems integrated to the grid above 380 V line to line. However, traditional solutions for those applications employ cascaded architectures with an ac-dc boost-type stage and a dc-dc buck-type stage, which may suffer from high switching losses and large dc-link capacitor volume. To relieve this issue, a straightforward carrier-based two-phase-clamped discontinuous pulsewidth modulation (DPWM) strategy with generalized zero-sequence voltage injection is proposed in this article for the commonly employed cascaded circuit. This method can stop the switching actions in the front-end stage during two-third of the grid period, which can yield to the best switching loss reduction. The operations of the front- and back-end converter stages become highly coupled to each other, which reduces the size requirement of the capacitor in the dc link. Therefore, the equivalent circuit behaves as a quasi-two-stage buck-type rectifier allowing an enhancement of the system power density by improving power conversion efficiency and by reducing the volume of passive components and heat sink. The proposed carrier-based two-phase-clamped DPWM strategy is described, analyzed, validated, and compared with different pulsewidth modulation methods on PLECS-based simulation and a 5-kW prototype.","buck-type rectifier; Capacitors; Carrier-based; discontinuous pulsewidth modulation (DPWM); Phase modulation; Pulse width modulation; Switches; Switching loss; Voltage; Voltage control; zero-sequence voltage injection","en","journal article","","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:ed9603ee-97b4-4942-9741-75cad042b471","http://resolver.tudelft.nl/uuid:ed9603ee-97b4-4942-9741-75cad042b471","Can You Hear It? Backdoor Attacks via Ultrasonic Triggers","Koffas, S. (TU Delft Cyber Security); Xu, J. (TU Delft Cyber Security); Conti, M. (TU Delft Cyber Security; Università degli Studi di Padova); Picek, S. (TU Delft Cyber Security; Radboud Universiteit Nijmegen)","","2022","This work explores backdoor attacks for automatic speech recognition systems where we inject inaudible triggers. By doing so, we make the backdoor attack challenging to detect for legitimate users and, consequently, potentially more dangerous. We conduct experiments on two versions of a speech dataset and three neural networks and explore the performance of our attack concerning the duration, position, and type of the trigger. Our results indicate that less than 1% of poisoned data is sufficient to deploy a backdoor attack and reach a 100% attack success rate. We observed that short, non-continuous triggers result in highly successful attacks. Still, since our trigger is inaudible, it can be as long as possible without raising any suspicions making the attack more effective. Finally, we conduct our attack on actual hardware and saw that an adversary could manipulate inference in an Android application by playing the inaudible trigger over the air.","backdoor attacks; inaudible trigger; neural networks","en","conference paper","Association for Computing Machinery (ACM)","","","","","","","","","","Cyber Security","","",""
"uuid:53dbc38a-4b79-4b0d-a247-bb30db5ecd48","http://resolver.tudelft.nl/uuid:53dbc38a-4b79-4b0d-a247-bb30db5ecd48","Computational Design for Digitally Fabricated 3D Inductive Power Transfer Coils","Xu, J. (TU Delft Emerging Materials); Doubrovski, E.L. (TU Delft Mechatronic Design); Geraedts, Jo M.P. (TU Delft Emerging Materials); Song, Y. (TU Delft Emerging Materials)","","2022","The geometric shapes and the relative position of coils influence the performance of a three-dimensional (3D) inductive power transfer system. In this paper, we propose a coil design method for specifying the positions and the 3D shapes of a pair of coils to transmit the desired power. Given region of interests (ROIs) for designing the transmitter and the receiver coils on two surfaces, the transmitter coil is generated around the center of its ROI. The center of the receiver coil is estimated as a random seed position in the corresponding 3D surface. At this position, we use the heatmap method with electromagnetic constraints to iteratively extend the coil until the desired power can be transferred via the set of coils. In each step, the shape of the extension, i.e., a new turn of the receiver coil, is found as a spiral curve based on the convex hulls of the 2D projected adjacent turns along their normal direction. Then, the optimal position of the receiver coil is found by maximizing the efficiency of the system. In the next step, the position and the shape of the transmitter coil are optimized based on the fixed receiver coil using the same method. This optimization process iterates until an optimum is reached. Simulations and experiments with digitally fabricated prototypes were conducted and the effectiveness of the proposed 3D coil design method was verified.","computer aided design; physics-based simulations","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Mechatronic Design","","",""
"uuid:76e7e236-66c8-493b-959c-543c57ae2175","http://resolver.tudelft.nl/uuid:76e7e236-66c8-493b-959c-543c57ae2175","More is Better (Mostly): On the Backdoor Attacks in Federated Graph Neural Networks","Xu, J. (TU Delft Cyber Security); Wang, R. (TU Delft Cyber Security); Koffas, S. (TU Delft Cyber Security); Liang, K. (TU Delft Cyber Security); Picek, S. (TU Delft Cyber Security; Radboud Universiteit Nijmegen)","","2022","Graph Neural Networks (GNNs) are a class of deep learning-based methods for processing graph domain information. GNNs have recently become a widely used graph analysis method due to their superior ability to learn representations for complex graph data. Due to privacy concerns and regulation restrictions, centralized GNNs can be difficult to apply to data-sensitive scenarios. Federated learning (FL) is an emerging technology developed for privacy-preserving settings when several parties need to train a shared global model collaboratively. Although several research works have applied FL to train GNNs (Federated GNNs), there is no research on their robustness to backdoor attacks.
This paper bridges this gap by conducting two types of backdoor attacks in Federated GNNs: centralized backdoor attacks (CBA) and distributed backdoor attacks (DBA). Our experiments show that the DBA attack success rate is higher than CBA in almost all cases. For CBA, the attack success rate of all local triggers is similar to the global trigger, even if the training set of the adversarial party is embedded with the global trigger. To explore the properties of two backdoor attacks in Federated GNNs, we evaluate the attack performance for a different number of clients, trigger sizes, poisoning intensities, and trigger densities. Finally, we explore the robustness of DBA and CBA against two state-of-the-art defenses. We find that both attacks are robust against the investigated defenses, necessitating the need to consider backdoor attacks in Federated GNNs as a novel threat that requires custom defenses.","backdoor attacks; graph neural networks; federated learning","en","conference paper","Association for Computing Machinery (ACM)","","","","","","","","","","Cyber Security","","",""
"uuid:47a3bca4-3f36-4a4c-b531-164b0a7607fc","http://resolver.tudelft.nl/uuid:47a3bca4-3f36-4a4c-b531-164b0a7607fc","Label-Only Membership Inference Attack against \\Node-Level Graph Neural Networks","Conti, M. (TU Delft Cyber Security; University of Padua); Li, Jiaxin (University of Padua); Picek, S. (TU Delft Cyber Security); Xu, J. (TU Delft Cyber Security)","","2022","Graph Neural Networks (GNNs), inspired by Convolutional Neural Networks (CNNs), aggregate the message of nodes' neighbors and structure information to acquire expressive representations of nodes for node classification, graph classification, and link prediction. Previous studies have indicated that node-level GNNs are vulnerable to Membership Inference Attacks (MIAs), which infer whether a node is in the training data of GNNs and leak the node's private information, like the patient's disease history. The implementation of previous MIAs takes advantage of the models' probability output, which is infeasible if GNNs only provide the prediction label (label-only) for the input.
In this paper, we propose a label-only MIA against GNNs for node classification with the help of GNNs' flexible prediction mechanism, e.g., obtaining the prediction label of one node even when neighbors' information is unavailable. Our attacking method achieves around 60\% accuracy, precision, and Area Under the Curve (AUC) for most datasets and GNN models, some of which are competitive or even better than state-of-the-art probability-based MIAs implemented under our environment and settings. Additionally, we analyze the influence of the sampling method, model selection approach, and overfitting level on the attack performance of our label-only MIA. All of those three factors have an impact on the attack performance. Then, we consider scenarios where assumptions about the adversary's additional dataset (shadow dataset) and extra information about the target model are relaxed. Even in those scenarios, our label-only MIA achieves a better attack performance in most cases. Finally, we explore the effectiveness of possible defenses, including Dropout, Regularization, Normalization, and Jumping knowledge. None of those four defenses prevent our attack completely.","Machine learning; Membership inference attack; Graph neural networks","en","conference paper","Association for Computing Machinery (ACM)","","","","","","","","","","Cyber Security","","",""
"uuid:e6b6efd9-f4bf-46bc-b8ab-06ca714a9386","http://resolver.tudelft.nl/uuid:e6b6efd9-f4bf-46bc-b8ab-06ca714a9386","A Mode-Switching Based Phase Shift Control for Optimized Efficiency and Wide ZVS Operations in Wireless Power Transfer Systems","Zhu, G. (TU Delft DC systems, Energy conversion & Storage); Dong, J. (TU Delft DC systems, Energy conversion & Storage); Shi, W. (TU Delft DC systems, Energy conversion & Storage); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage; University of Twente); Xu, J. (TU Delft DC systems, Energy conversion & Storage; Shanghai Jiao Tong University); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2022","This article proposes a mode-switching-based phase shift control (MS-PSC) for wireless power transfer (WPT) systems, which is able to achieve power regulation, load matching, and wide ZVS operations simultaneously without using additional dc-dc converters. Based on the mode transitions between the full-bridge, mixed-bridge, and half-bridge modes of both the inverter and the rectifier, the MS-PSC method guarantees a wide-range ZVS with minimized circulation of reactive power. Therefore, the system efficiency is improved over a wider power range compared to the conventional triple-phase-shift (TPS) control and the existing hybrid modulation control. The principles of different operating modes are analyzed. Then, the implementation of the proposed MS-PSC method and the mode selection strategy are presented. Finally, the effectiveness of the proposed MS-PSC method is validated in a WPT prototype. Experimental results show that the proposed MS-PSC method can achieve a high overall efficiency in a wide power range. Compared with the conventional TPS control, the MS-PSC method further optimizes the efficiency in 10%-63% of the rated power, with efficiency improvements ranging from 1.5% to 6%. As a result, the system efficiency remains at 93.5%-96.1% in the power range of 1-10 kW, with the transformer coupling coefficient k = 0.19.","Control systems; DC-DC power converters; Inverters; Load matching; mode switching; power regulation; Rectifiers; Regulation; Voltage control; wireless power transfer (WPT); zero -voltage-switching (ZVS); Zero voltage switching","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-06-26","","","DC systems, Energy conversion & Storage","","",""
"uuid:ab4acc85-8c8d-4195-91f1-921a9f12bc4d","http://resolver.tudelft.nl/uuid:ab4acc85-8c8d-4195-91f1-921a9f12bc4d","Crystal structures and magnetic properties of Fe1.93-xCoxP1-ySiy compounds","Bao, L. L. (Inner Mongolia Normal University China); Yibole, H. (Inner Mongolia Normal University China); Xu, J. (Inner Mongolia Normal University China); Ou, Z. Q. (Inner Mongolia Normal University China); Haschuluu, O. (Inner Mongolia Normal University China); Tegus, O. (Inner Mongolia Normal University China); van Dijk, N.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Guillou, F. (Inner Mongolia Normal University China)","","2022","In view of the interest that (Fe,Co)2(P,Si) compounds have as potential permanent magnets, their structural and magnetic phase diagrams are explored focusing on establishing the range where the hexagonal Fe2P-type structure is observed. In Fe1.93-xCoxP1-ySiy, the highest Si content prior entering a mixed phase domain is y ≈ 0.5. At high Si content but low Co for Fe substitutions, a structural distortion leading to a body-centered orthorhombic structure occurs. At high Co contents, when the Fe2P unit cell reaches a critical volume of about 102.4 Å3, the samples crystallize in a Co2P-type orthorhombic structure. Within the Fe2P-type structural range, the evolution of the unit-cell volume appears to follow the Vegard's law, but this hides strongly anisotropic changes. Simultaneous Co for Fe and Si for P substitutions increase the range where the hexagonal structure is observed in comparison to ternary Fe2(P,Si) and (Fe,Co)2P. The samples are ferromagnetic, but with Curie temperatures showing an unusual evolution, uncorrelated to the c/a ratio of the lattice parameters. At low Si content, TC increases with Co for Fe substitutions. For y = 0.2, the evolution is not significant, while at high Si content TC systematically decreases with the increase in Co. Large Si and Co substitutions lead to a swift weakening of the magnetocrystalline anisotropy until the easy axis anisotropy turns from the c axis toward the a-b plane. This study guides future investigations by restricting the range where desirable properties for permanent magnetic applications can be expected to 0.1 ≲ x ≲ 0.3 and 0.1 ≲ y ≲ 0.3.","Crystal structure; Magnetic measurements; Permanent magnets; Phase diagrams","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","RST/Fundamental Aspects of Materials and Energy","","",""
"uuid:1e074235-2ccf-470a-9806-2371e918ca39","http://resolver.tudelft.nl/uuid:1e074235-2ccf-470a-9806-2371e918ca39","Poster: Clean-label Backdoor Attack on Graph Neural Networks","Xu, J. (TU Delft Cyber Security); Picek, S. (TU Delft Cyber Security; Radboud Universiteit Nijmegen)","","2022","Graph Neural Networks (GNNs) have achieved impressive results in various graph learning tasks. They have found their way into many applications, such as fraud detection, molecular property prediction, or knowledge graph reasoning. However, GNNs have been recently demonstrated to be vulnerable to backdoor attacks. In this work, we explore a new kind of backdoor attack, i.e., a clean-label backdoor attack, on GNNs. Unlike prior backdoor attacks on GNNs in which the adversary can introduce arbitrary, often clearly mislabeled, inputs to the training set, in a clean-label backdoor attack, the resulting poisoned inputs appear to be consistent with their label and thus are less likely to be filtered as outliers. The initial experimental results illustrate that the adversary can achieve a high attack success rate (up to 98.47%) with a clean-label backdoor attack on GNNs for the graph classification task. We hope our work will raise awareness of this attack and inspire novel defenses against it.","backdoor attacks; graph classification; graph neural networks","en","conference paper","Association for Computing Machinery (ACM)","","","","",".","","","","","Cyber Security","","",""
"uuid:0e4d11be-9c34-4602-98e0-79be8aaeb57f","http://resolver.tudelft.nl/uuid:0e4d11be-9c34-4602-98e0-79be8aaeb57f","AGIC: Approximate Gradient Inversion Attack on Federated Learning","Xu, J. (Student TU Delft); Hong, C. (TU Delft Dataintensive Systems); Huang, J. (TU Delft Dataintensive Systems); Chen, Lydia Y. (TU Delft Dataintensive Systems); Decouchant, Jérémie (TU Delft Dataintensive Systems)","Ceballos, Cristina (editor); Torres, Hector (editor)","2023","Federated learning is a private-by-design distributed learning paradigm where clients train local models on their own data before a central server aggregates their local updates to compute a global model. Depending on the aggregation method used, the local updates are either the gradients or the weights of local learning models, e.g., FedAvg aggregates model weights. Unfortunately, recent reconstruction attacks apply a gradient inversion optimization on the gradient update of a single mini- batch to reconstruct the private data used by clients during training. As the state-of-the-art reconstruction attacks solely focus on single update, realistic adversarial scenarios are over- looked, such as observation across multiple updates and updates trained from multiple mini-batches. A few studies consider a more challenging adversarial scenario where only model updates based on multiple mini-batches are observable, and resort to computationally expensive simulation to untangle the underlying samples for each local step. In this paper, we propose AGIC, a novel Approximate Gradient Inversion Attack that efficiently and effectively reconstructs images from both model or gradient updates, and across multiple epochs. In a nutshell, AGIC (i) approximates gradient updates of used training samples from model updates to avoid costly simulation procedures, (ii) leverages gradient/model updates collected from multiple epochs, and (iii) assigns increasing weights to layers with respect to the neural network structure for reconstruction quality. We extensively evaluate AGIC on three datasets, namely CIFAR-10, CIFAR- 100 and ImageNet. Our results show that AGIC increases the peak signal-to-noise ratio (PSNR) by up to 50% compared to two representative state-of-the-art gradient inversion attacks. Furthermore, AGIC is faster than the state-of-the-art simulation- based attack, e.g., it is 5x faster when attacking FedAvg with 8 local steps in between model updates.","Reconstruction attack; Federated Learning; Federated Averaging","en","conference paper","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Dataintensive Systems","","",""
"uuid:69e1c1f3-9049-432f-acb1-e40b8b65184f","http://resolver.tudelft.nl/uuid:69e1c1f3-9049-432f-acb1-e40b8b65184f","Rethinking the Trigger-injecting Position in Graph Backdoor Attack","Xu, J. (TU Delft Cyber Security); Abad, Gorka (Radboud Universiteit Nijmegen; Ikerlan research centre); Picek, S. (TU Delft Cyber Security; Radboud Universiteit Nijmegen)","","2023","Backdoor attacks have been demonstrated as a security threat for machine learning models. Traditional backdoor attacks intend to inject backdoor functionality into the model such that the backdoored model will perform abnormally on inputs with predefined backdoor triggers and still retain state-of-the-art performance on the clean inputs. While there are already some works on backdoor attacks on Graph Neural Networks (GNNs), the backdoor trigger in the graph domain is mostly injected into random positions of the sample. There is no work analyzing and explaining the backdoor attack performance when injecting triggers into the most important or least important area in the sample, which we refer to as trigger-injecting strategies MIAS and LIAS, respectively. Our results show that, generally, LIAS performs better, and the differences between the LIAS and MIAS performance can be significant. Furthermore, we explain these two strategies’ similar (better) attack performance through explanation techniques, which results in a further understanding of backdoor attacks in GNNs.","backdoor attack; trigger-injecting position; graph neural networks","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-02-02","","","Cyber Security","","",""
"uuid:ec6f34ad-2c77-4132-ad23-ef59cfcba1a0","http://resolver.tudelft.nl/uuid:ec6f34ad-2c77-4132-ad23-ef59cfcba1a0","Comfort Wearables for In-Flight Sitting Posture Recognition","Yao, X. (TU Delft Emerging Materials); Yang, Y. (TU Delft Mechatronic Design; Shanghai University); Vledder, G. (TU Delft Emerging Materials); Xu, J. (TU Delft Emerging Materials); Song, Y. (TU Delft Emerging Materials); Vink, P. (TU Delft Emerging Materials)","","2023","Wearables are used to recognize human activities in various applications. However, there is limited evidence on the comfort feelings in using wearables, which is crucial for the adoption and long-term engagement of users in those applications. In this paper, we propose the concept of comfort wearables in the context of in-flight posture recognition. A comfort wearable and a tight-fit version, using identical hardware and software architecture, were prototyped and tested by 35 participants in a Boeing 737 cabin. During the usage of each wearable, participants were asked to perform seven frequently observed in-flight sitting postures and report their overall comfort/discomfort afterwards. A multilayer perceptron neural network was used to classify those activities. Experiment results indicated that participants appreciated the comfort wearable, rating it with significantly higher comfort scores and lower discomfort scores. Cross-validation results also revealed that using the comfort wearable achieved even better accuracy (74.8%) than using the tight-fit wearable (65.8%) in posture recognition. Outcomes of the study demonstrate that ergonomic design and technical accuracy are not competing factors in the wearable design and highlight the opportunities for designing and using comfort wearables in broader contexts.","Losse-fit; tight-fit; ergonomics; accelerometer; IMU; wearability","en","journal article","","","","","","","","","","","Emerging Materials","","",""
"uuid:fa8734e9-ba92-472b-9eab-65f3c5a24817","http://resolver.tudelft.nl/uuid:fa8734e9-ba92-472b-9eab-65f3c5a24817","Watermarking Graph Neural Networks based on Backdoor Attacks","Xu, J. (TU Delft Cyber Security); Koffas, S. (TU Delft Cyber Security); Ersoy, Oǧuzhan (Radboud Universiteit Nijmegen); Picek, S. (Radboud Universiteit Nijmegen)","","2023","Graph Neural Networks (GNNs) have achieved promising performance in various real-world applications. Building a powerful GNN model is not a trivial task, as it requires a large amount of training data, powerful computing resources, and human expertise. Moreover, with the development of adversarial attacks, e.g., model stealing attacks, GNNs raise challenges to model authentication. To avoid copyright infringement on GNNs, verifying the ownership of the GNN models is necessary.This paper presents a watermarking framework for GNNs for both graph and node classification tasks. We 1) design two strategies to generate watermarked data for the graph classification task and one for the node classification task, 2) embed the watermark into the host model through training to obtain the watermarked GNN model, and 3) verify the ownership of the suspicious model in a black-box setting. The experiments show that our framework can verify the ownership of GNN models with a very high probability (up to 99%) for both tasks. We also explore our watermarking mechanism against an adaptive attacker with access to partial knowledge of the watermarked data. Finally, we experimentally show that our watermarking approach is robust against a state-of-the-art model extraction technique and four state-of-the-art defenses against backdoor attacks.","","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-01-31","","","Cyber Security","","",""
"uuid:2fd60cc5-4aca-4339-b51a-e11b227d133d","http://resolver.tudelft.nl/uuid:2fd60cc5-4aca-4339-b51a-e11b227d133d","Effectiveness of BMP-2 and PDGF-BB Adsorption onto a Collagen/Collagen-Magnesium-Hydroxyapatite Scaffold in Weight-Bearing and Non-Weight-Bearing Osteochondral Defect Bone Repair: In Vitro, Ex Vivo and In Vivo Evaluation","Xu, J. (Erasmus MC); Fahmy-Garcia, Shorouk (Erasmus MC); Wesdorp, Marinus A. (Erasmus MC); Forte, Lucia (Fin-Ceramica Faenza); De Luca, Claudio (Fin-Ceramica Faenza); Filardo, Giuseppe (Rizzoli Orthopaedic Institute); Labberté, Margot (University College Dublin); Kok, Joeri (Eindhoven University of Technology); Nickel, Joachim (Universitätsklinikum Würzburg); van Osch, G.J.V.M. (TU Delft Biomaterials & Tissue Biomechanics; Erasmus MC)","","2023","Despite promising clinical results in osteochondral defect repair, a recently developed bi-layered collagen/collagen-magnesium-hydroxyapatite scaffold has demonstrated less optimal subchondral bone repair. This study aimed to improve the bone repair potential of this scaffold by adsorbing bone morphogenetic protein 2 (BMP-2) and/or platelet-derived growth factor-BB (PDGF-BB) onto said scaffold. The in vitro release kinetics of BMP-2/PDGF-BB demonstrated that PDGF-BB was burst released from the collagen-only layer, whereas BMP-2 was largely retained in both layers. Cell ingrowth was enhanced by BMP-2/PDFG-BB in a bovine osteochondral defect ex vivo model. In an in vivo semi-orthotopic athymic mouse model, adding BMP-2 or PDGF-BB increased tissue repair after four weeks. After eight weeks, most defects were filled with bone tissue. To further investigate the promising effect of BMP-2, a caprine bilateral stifle osteochondral defect model was used where defects were created in weight-bearing femoral condyle and non-weight-bearing trochlear groove locations. After six months, the adsorption of BMP-2 resulted in significantly less bone repair compared with scaffold-only in the femoral condyle defects and a trend to more bone repair in the trochlear groove. Overall, the adsorption of BMP-2 onto a Col/Col-Mg-HAp scaffold reduced bone formation in weight-bearing osteochondral defects, but not in non-weight-bearing osteochondral defects.","animal model; biocompatible materials; bone morphogenetic proteins; osteochondral lesion; platelet-derived growth factor; regenerative medicine; tissue engineering; weight-bearing","en","journal article","","","","","","","","","","","Biomaterials & Tissue Biomechanics","","",""
"uuid:4c515da8-6d44-45d9-bf8a-5c80b1a10eae","http://resolver.tudelft.nl/uuid:4c515da8-6d44-45d9-bf8a-5c80b1a10eae","Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair","Zhou, Liangbin (The Hong Kong Polytechnic University; Chinese University of Hong Kong); Xu, J. (Erasmus MC); Schwab, Andrea (Erasmus MC); Tong, Wenxue (Chinese University of Hong Kong); Zheng, Lizhen (Chinese Academy of Sciences; Chinese University of Hong Kong); Li, Zhuo (Chinese University of Hong Kong); Xu, Shunxiang (Chinese University of Hong Kong); van Osch, G.J.V.M. (TU Delft Biomaterials & Tissue Biomechanics; Erasmus MC); Wen, Chunyi (The Hong Kong Polytechnic University); Qin, Ling (Chinese Academy of Sciences; Chinese University of Hong Kong)","","2023","As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.","Articular cartilage (AC) repair; Biochemical cues; Endogenous stem/progenitor cells (ESPCs); Regenerative biomaterials","en","review","","","","","","","","","","","Biomaterials & Tissue Biomechanics","","",""
"uuid:5e8c3656-a2c5-46ed-81c3-7a311767c7b8","http://resolver.tudelft.nl/uuid:5e8c3656-a2c5-46ed-81c3-7a311767c7b8","in-situ3He neutron spin filters at JCNS, status and updates","Babcock, E. (Forschungszentrum Jülich GmbH); Salhi, Z. (Forschungszentrum Jülich GmbH); Feoktystov, A. (Forschungszentrum Jülich GmbH); Bannenberg, L.J. (TU Delft RID/TS/Instrumenten groep); Parnell, S.R. (TU Delft RID/TS/Instrumenten groep); Alba Venero, D. (ISIS Facility); Hutanu, V. (Rheinisch-Westfälische Technische Hochschule; Technische Universität München); Thoma, H. (Rheinisch-Westfälische Technische Hochschule); Xu, J. (Rheinisch-Westfälische Technische Hochschule)","","2023","The JCNS has been developing and using in-situ polarized neutron spin filters for many applications. The system used for analysis on MARIA and polarization for TOPAS were completed about 10 years ago with the MARIA system in standard operation for users and the TOPAS system employed for a long measurement on the POLI instrument. In the meantime we are progressing on several new in-situ polarizers based on these first two but with additional innovations. The KWS-1 analyzer device which was recently used in tests at TU Delft and ISIS is essentially a 50%-sized copy of the MARIA device. The two devices in construction for polarization and analysis on POLI for hot neutrons feature magic-boxes with angled plates on both the entrance and exit sides to minimize overal length and the polarizer device will employ an additional passive magnetic shield of soft iron so that it can operate inside the stray field area of a 8-T vertical (compensated) sample magnet. We will summarize the current status of our 3He neutron spin filters and provide extra focus on the technical aspects and measured performance characteristics of the new devices for KWS-1 and POLI in particular.","","en","journal article","","","","","","","","","","","RID/TS/Instrumenten groep","","",""
"uuid:91fb5f6e-910a-4997-bc0e-3b53a123b9f0","http://resolver.tudelft.nl/uuid:91fb5f6e-910a-4997-bc0e-3b53a123b9f0","Modulating design parameters to drive cell invasion into hydrogels for osteochondral tissue formation","Schwab, Andrea (Erasmus MC; AO Research Institute Davos, Davos); Wesdorp, Marinus A. (Erasmus MC); Xu, J. (Erasmus MC); Abinzano, Florencia (University Medical Center Utrecht); Loebel, Claudia (University of Pennsylvania); Levato, Riccardo (University Medical Center Utrecht; Universiteit Utrecht); Eglin, David (University of Twente; University Jean Monnet); Narcisi, Roberto (Erasmus MC); Malda, Jos (University Medical Center Utrecht; Universiteit Utrecht); van Osch, G.J.V.M. (TU Delft Biomaterials & Tissue Biomechanics; Erasmus MC)","","2023","Background: The use of acellular hydrogels to repair osteochondral defects requires cells to first invade the biomaterial and then to deposit extracellular matrix for tissue regeneration. Due to the diverse physicochemical properties of engineered hydrogels, the specific properties that allow or even improve the behaviour of cells are not yet clear. The aim of this study was to investigate the influence of various physicochemical properties of hydrogels on cell migration and related tissue formation using in vitro, ex vivo and in vivo models. Methods: Three hydrogel platforms were used in the study: Gelatine methacryloyl (GelMA) (5% wt), norbornene hyaluronic acid (norHA) (2% wt) and tyramine functionalised hyaluronic acid (THA) (2.5% wt). GelMA was modified to vary the degree of functionalisation (DoF 50% and 80%), norHA was used with varied degradability via a matrix metalloproteinase (MMP) degradable crosslinker and THA was used with the addition of collagen fibrils. The migration of human mesenchymal stromal cells (hMSC) in hydrogels was studied in vitro using a 3D spheroid migration assay over 48h. In addition, chondrocyte migration within and around hydrogels was investigated in an ex vivo bovine cartilage ring model (three weeks). Finally, tissue repair within osteochondral defects was studied in a semi-orthotopic in vivo mouse model (six weeks). Results: A lower DoF of GelMA did not affect cell migration in vitro (p = 0.390) and led to a higher migration score ex vivo (p < 0.001). The introduction of a MMP degradable crosslinker in norHA hydrogels did not improve cell infiltration in vitro or in vivo. The addition of collagen to THA resulted in greater hMSC migration in vitro (p = 0.031) and ex vivo (p < 0.001). Hydrogels that exhibited more cell migration in vitro or ex vivo also showed more tissue formation in the osteochondral defects in vivo, except for the norHA group. Whereas norHA with a degradable crosslinker did not improve cell migration in vitro or ex vivo, it did significantly increase tissue formation in vivo compared to the non-degradable crosslinker (p < 0.001). Conclusion: The modification of hydrogels by adapting DoF, use of a degradable crosslinker or including fibrillar collagen can control and improve cell migration and tissue formation for osteochondral defect repair. This study also emphasizes the importance of performing both in vitro and in vivo testing of biomaterials, as, depending on the material, the results might be affected by the model used. The translational potential of this article: This article highlights the potential of using acellular hydrogels to repair osteochondral defects, which are common injuries in orthopaedics. The study provides a deeper understanding of how to modify the properties of hydrogels to control cell migration and tissue formation for osteochondral defect repair. The results of this article also highlight that the choice of the used laboratory model can affect the outcome. Testing hydrogels in different models is thus advised for successful translation of laboratory results to the clinical application.","Cartilage; Cells; Hydrogels; Regenerative medicine; Tissue engineering","en","journal article","","","","","","","","","","","Biomaterials & Tissue Biomechanics","","",""
"uuid:6f94c28c-fbae-458e-a757-6331d1561b25","http://resolver.tudelft.nl/uuid:6f94c28c-fbae-458e-a757-6331d1561b25","Incorporating strontium enriched amorphous calcium phosphate granules in collagen/collagen-magnesium-hydroxyapatite osteochondral scaffolds improves subchondral bone repair","Xu, J. (Erasmus MC); Vecstaudza, Jana (Riga Technical University); Wesdorp, Marinus A. (Erasmus MC); Labberté, Margot (University College Dublin); Salerno, Manuela (Rizzoli Orthopaedic Institute); Kok, Joeri (Eindhoven University of Technology); van Rietbergen, Bert (Eindhoven University of Technology); van Osch, G.J.V.M. (TU Delft Biomaterials & Tissue Biomechanics; Erasmus MC); Locs, Janis (Riga Technical University); Brama, Pieter A.J. (University College Dublin)","","2024","Osteochondral defect repair with a collagen/collagen-magnesium-hydroxyapatite (Col/Col-Mg-HAp) scaffold has demonstrated good clinical results. However, subchondral bone repair remained suboptimal, potentially leading to damage to the regenerated overlying neocartilage. This study aimed to improve the bone repair potential of this scaffold by incorporating newly developed strontium (Sr) ion enriched amorphous calcium phosphate (Sr-ACP) granules (100–150 μm). Sr concentration of Sr-ACP was determined with ICP-MS at 2.49 ± 0.04 wt%. Then 30 wt% ACP or Sr-ACP granules were integrated into the scaffold prototypes. The ACP or Sr-ACP granules were well embedded and distributed in the collagen matrix demonstrated by micro-CT and scanning electron microscopy/energy dispersive x-ray spectrometry. Good cytocompatibility of ACP/Sr-ACP granules and ACP/Sr-ACP enriched scaffolds was confirmed with in vitro cytotoxicity assays. An overall promising early tissue response and good biocompatibility of ACP and Sr-ACP enriched scaffolds were demonstrated in a subcutaneous mouse model. In a goat osteochondral defect model, significantly more bone was observed at 6 months with the treatment of Sr-ACP enriched scaffolds compared to scaffold-only, in particular in the weight-bearing femoral condyle subchondral bone defect. Overall, the incorporation of osteogenic Sr-ACP granules in Col/Col-Mg-HAp scaffolds showed to be a feasible and promising strategy to improve subchondral bone repair.","Amorphous calcium phosphate; Osteochondral defect; Regenerative medicine; Strontium; Tissue engineering","en","journal article","","","","","","","","","","","Biomaterials & Tissue Biomechanics","","",""