Fabrication of flexible intracranial aneurysm models using stereolithography 3D printing. - In: Current directions in biomedical engineering, ISSN 2364-5504, Bd. 9 (2023), 1, S. 395-398
The use of 3D printing technology for medical applications is becoming increasingly popular. Recent stereolithography (SLA)-based printing methods allow the generation of complex structures with a high surface quality. This is particularly useful for applications in the neurovascular field, where sophisticated structures are involved. In this study patient-specific intracranial aneurysm models are extracted based on medical image data und printed as thin-walled vascular phantom models. For this purpose, two commercially available 3D printers are used to print flexible vascular models with three different silicone-like elastic resins (Ultracur3D FL 300, Prusament Flex80 and Formlabs Elastic 50A) of various Shore hardness. Three aneurysm models of different size and complexity are chosen. To evaluate the geometric accuracy of the flexible models, angiographic measurements are performed for an exemplary case and morphological parameters are extracted from the generated 3D models. The printed results demonstrate a successful generation of hollow aneurysm phantoms. There are dependencies regarding the print quality from the model to platform positioning for two materials. The quantitative geometric accuracy analysis shows notable differences between the materials. The extracted morphological parameter values for all materials show a mean decrease compared to the original reference model of aneurysm volume (4.5 %) and maximum diameter (1.0 %) as well as an increase of ostium area (6.0 %) and maximum height (4.9 %). However, Formlabs Elastic 50A in particular exhibits just slight reductions with respect to the reference model, with a mean decrease for all parameters of 5.7 % as well as no dependence on printing position and resulting artifacts. The study investigates the feasibility of using SLA-based 3D printing to generate realistic flexible aneurysm phantoms. In this context, the Formlabs Elastic 50A could be identified as potentially applicable for phantom creation in terms of reproducible quality and geometric validity.
https://doi.org/10.1515/cdbme-2023-1099
Review of battery storage and power electronic systems in flexible A-R-OPF frameworks. - In: Electronics, ISSN 2079-9292, Bd. 12 (2023), 14, 3127, S. 1-15
This paper provides an overview of power electronics and its applications in various fields, emphasizing power conditioning and minimizing losses for high energy efficiency. It discusses the distinction between unidirectional and bidirectional converters and their applications in power systems. The significance of unidirectional and bidirectional power flow in different scenarios is explored. The importance of battery storage systems (BSSs) for grid stabilization, frequency regulation, and renewable energy integration is highlighted. The paper focuses on flexible active-reactive optimal power flow (A-R-OPF) frameworks in battery storage and power electronic systems, reviewing existing research, identifying gaps, and offering new perspectives. It addresses the challenges and potential of grid-scale energy storage for reliable and cost-effective power systems with high renewable energy penetration. The need for energy curtailment, demand response, and smart grid implementation is discussed. The paper emphasizes comprehensive coordination, new power lines, European collaboration, and smart grid implementation to meet the dynamic needs of Europe’s power grids.
https://doi.org/10.3390/electronics12143127
Why temporal inference stimulation may fail in the human brain: a pilot research study. - In: Biomedicines, ISSN 2227-9059, Bd. 11 (2023), 7, 1813, S. 1-25
Temporal interference stimulation (TIS) aims at targeting deep brain areas during transcranial electrical alternating current stimulation (tACS) by generating interference fields at depth. Although its modulatory effects have been demonstrated in animal and human models and stimulation studies, direct experimental evidence is lacking for its utility in humans (in vivo). Herein, we directly test and compare three different structures: firstly, we perform peripheral nerve and muscle stimulation quantifying muscle twitches as readout, secondly, we stimulate peri-orbitally with phosphene perception as a surrogate marker, and thirdly, we attempt to modulate the mean power of alpha oscillations in the occipital area as measured with electroencephalography (EEG). We found strong evidence for stimulation efficacy on the modulated frequency in the PNS, but we found no evidence for its utility in the CNS. Possible reasons for failing to activate CNS targets could be comparatively higher activation thresholds here or inhibitory stimulation components to the carrier frequency interfering with the effects of the modulated signal.
https://doi.org/10.3390/biomedicines11071813
Human-sized quantitative imaging of magnetic nanoparticles with nonlinear magnetorelaxometry. - In: Physics in medicine and biology, ISSN 1361-6560, Bd. 68 (2023), 15, 155002, S. 1-10
Objective. Magnetorelaxomety imaging (MRXI) is a noninvasive imaging technique for quantitative detection of magnetic nanoparticles (MNPs). The qualitative and quantitative knowledge of the MNP distribution inside the body is a prerequisite for a number of arising biomedical applications, such as magnetic drug targeting and magnetic hyperthermia therapy. It was shown throughout numerous studies that MRXI is able to successfully localize and quantify MNP ensembles in volumes up to the size of a human head. However, deeper regions that lie far from the excitation coils and the magnetic sensors are harder to reconstruct due to the weaker signals from the MNPs in these areas. On the one hand, stronger magnetic fields need to be applied to produce measurable signals from such MNP distributions to further upscale MRXI, on the other hand, this invalidates the assumption of a linear relation between applied magnetic field and particle magnetization in the current MRXI forward model which is required for the imaging procedure. Approach. We tackle this problem by introducing a nonlinear MRXI forward model that is also valid for strong magnetic excitation fields. Main results. We demonstrate in our experimental feasibility study that scaling up the imaging region to the size of a human torso using nonlinear MRXI is possible. Despite the extreme simplicity of the imaging setup applied in this study, an immobilized MNP sample with 6.3 cm3 and 12 mg Fe could be localized and quantified with an acceptable quality. Significance. A well-engineered MRXI setup could provide much better imaging qualities in shorter data acquisition times, making nonlinear MRXI a viable option for the supervision of MNP related therapies in all regions of the human body, specifically magnetic hyperthermia.
https://doi.org/10.1088/1361-6560/ace304
Road parameter estimation with drone-vehicle communication. - In: SAE technical papers, ISSN 2688-3627, (2023), SAE technical paper 2023-01-0664, S. 1-7
The presented study is dedicated to the technology supporting vehicle state estimation and motion control with a concept drone, which helps the vehicle in sensing the surroundings and driving conditions. This concept allows also extending the functionality of the sensors mounted on the vehicle by replacing or including additional parameter observation channels. The paper discusses the feasibility of such a drone-vehicle interaction as well as demonstrates several design configurations. In this regard, the paper presents a general description of the proposed drone system that assists the vehicle and describes an experiment in measuring the profile of the road with a range sensor. The results obtained in the experiment are described in terms of the accuracy to be achieved using the drone and are compared with other studies, which use the methods of estimation from the sensors mounted on the vehicle. The proposed measurement concept can be applied to a large number of vehicle systems such as adaptive cruise control, active or semi-active suspension, and wheel slip control. The road profile is captured in real-time by a drone, and the telemetry data is processed by the host computer.
https://doi.org/10.4271/2023-01-0664
Transparency and traceability for AI-based defect detection in PCB production. - In: Modelling and development of intelligent systems, (2023), S. 54-72
Automatic Optical Inspection (AOI) is used to detect defects in PCB production and provide the end-user with a trustworthy PCB. AOI systems are enhanced by replacing the traditional heuristic algorithms with more advanced methods such as neural networks. However, they provide the operators with little or no information regarding the reasoning behind each decision. This paper explores the research gaps in prior PCB defect detection methods and replaces these complex methods with CNN networks. Next, it investigates five different Cam-based explainer methods on eight selected CNN architectures to evaluate the performance of each explainer. In this paper, instead of synthetic datasets, two industrial datasets are utilized to have a realistic research scenario. The results evaluated by the proposed performance metric demonstrate that independent of the dataset, the CNN architectures are interpretable using the same explainer methods. Additionally, the Faster Score-Cam method performs better than other methods used in this paper.
https://doi.org/10.1007/978-3-031-27034-5_4
Spatiotemporal phase slip patterns for visual evoked potentials, covert object naming tasks, and insight moments extracted from 256 channel EEG recordings. - In: Frontiers in integrative neuroscience, ISSN 1662-5145, Bd. 17 (2023), 1087976, S. 01-20
Phase slips arise from state transitions of the coordinated activity of cortical neurons which can be extracted from the EEG data. The phase slip rates (PSRs) were studied from the high-density (256 channel) EEG data, sampled at 16.384 kHz, of five adult subjects during covert visual object naming tasks. Artifact-free data from 29 trials were averaged for each subject. The analysis was performed to look for phase slips in the theta (4-7 Hz), alpha (7-12 Hz), beta (12-30 Hz), and low gamma (30-49 Hz) bands. The phase was calculated with the Hilbert transform, then unwrapped and detrended to look for phase slip rates in a 1.0 ms wide stepping window with a step size of 0.06 ms. The spatiotemporal plots of the PSRs were made by using a montage layout of 256 equidistant electrode positions. The spatiotemporal profiles of EEG and PSRs during the stimulus and the first second of the post-stimulus period were examined in detail to study the visual evoked potentials and different stages of visual object recognition in the visual, language, and memory areas. It was found that the activity areas of PSRs were different as compared with EEG activity areas during the stimulus and post-stimulus periods. Different stages of the insight moments during the covert object naming tasks were examined from PSRs and it was found to be about 512 ± 21 ms for the ‘Eureka’ moment. Overall, these results indicate that information about the cortical phase transitions can be derived from the measured EEG data and can be used in a complementary fashion to study the cognitive behavior of the brain.
https://doi.org/10.3389/fnint.2023.1087976
Editorial: Functional assessments of the ocular circulation. - In: Frontiers in medicine, ISSN 2296-858X, Bd. 10 (2023), 1222022, S. 01-04
https://doi.org/10.3389/fmed.2023.1222022
Trusted implementation and enforcement of application security policies. - In: E-Business and Telecommunications, (2023), S. 362-388
Although system-level security policies are enforced directly in many modern operating systems, they do not provide adequate support for application-level security policies. Application software uses objects of higher abstraction requiring individual security policies with application-specific semantics. While frameworks assist in application policy implementation, developers are still responsible for their application’s security architecture which often leads to large and heterogeneous application trusted computing bases rendering protection from unauthorized manipulation hard to achieve. This work contributes to improving this situation. We present AppSPEAR - an application-level security policy enforcement architecture tailorable to application requirements. To foster streamlined and tool-supported security engineering workflows, we moreover present a policy specification language (DynaMo), a corresponding Rust source code generation approach, and a developer framework leveraging Rust and Intel SGX for trusted and memory-safe AppSPEAR implementation and policy integration.
https://doi.org/10.1007/978-3-031-36840-0_16
Putting the pieces together: model-based engineering workflows for attribute-based access control policies. - In: E-Business and Telecommunications, (2023), S. 249-280
Although being well-adopted and in widespread use, attribute-based access control (ABAC) remains a hard-to-master security paradigm in application software development. Despite considerable research towards ABAC policy engineering and ABAC policy correctness, this mainly is because there is still no unified workflow to encompass both the versatility of application domains and the strong guarantees promised by formal modeling methods. This work contributes to improving this situation. By presenting a flexible, yet highly formalized modeling scheme for designing and analyzing ABAC policies (DABAC), a reference implementation in Rust (dabac-rs), and a reference architecture for its integration into applications (AppSPEAR) including developer support (appspear-rs), we put together loose pieces of a tool-supported model-based security engineering workflow. The effectiveness of our approach is demonstrated based on a real-world engineering scenario.
https://doi.org/10.1007/978-3-031-36840-0_12