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Discrete Event Simulation in R using the ‘Simmer’ Package for Health Economic Modelling:A Tutorial and Illustration in Colon Cancer
Get PDFDiscrete event simulation (DES) provides enhanced flexibility over modelling techniques that have been traditionally used for assessing health-economic outcomes, making it a particularly interesting technique for modelling complex clinical pathways. Discrete event simulation also facilitates consideration of resources and capacity constraints, making it suitable for addressing a wide range of research questions in health care and beyond. However, those unfamiliar with DES often perceive it to be more complex compared to traditional health-economic modelling techniques, such as state-transition modelling. To address this perceived complexity, this tutorial provides a detailed illustration of implementing DES in the open-source R software using the simmer package, through a case study in colon cancer. The tutorial is aimed at those who have a conceptual model that they want to implement as a DES in R, and are looking for practical guidance. It discusses methodological aspects related to DES and individual-level modelling in general that have not been extensively covered in literature, the conceptual model structure and corresponding pseudocode, data analysis, model implementation, and the deterministic and probabilistic analysis of the model. The documented code provides all building blocks required to develop a wide range of DES models in R using the simmer package.</p
Estimating sagittal knee and ankle moment during running using only inertial measurement units:a top-down inverse dynamics approach
Get PDFThe net joint moment is a commonly investigated kinetic quantity in running but currently requires force plates and optical motion capture. This study proposes a physics-based top-down inverse dynamics method to estimate net sagittal knee and ankle moment across three speeds using only inertial measurement units (IMUs). This method does not require musculoskeletal modelling, machine learning, pressure insoles, or centre of pressure. The top-down method was validated against a 2D IMU-driven/3D marker-driven OpenSim model and an IMU-based bottom-up inverse dynamics approach. Strong correlations were found for the top-down net sagittal knee (0.87–0.96) and ankle moment (0.83–0.90) during stance. Maximum knee extension moment showed similar values during stance compared to IMU-based references, while maximum ankle plantar flexion moment was significantly higher. The marker-driven OpenSim model showed overall significantly lower values. This study highlights the potential of top-down inverse dynamics in calculating net sagittal knee moment during running using only IMUs, while the sagittal ankle moment was less accurate and needs a different approach. This method could potentially be used for running (i.e. providing feedback) during training sessions. However, a deeper understanding of upper body kinematics and kinetics is needed, as the top-down method is highly dependent on upper body movement.</p
Impact of Defects on the Low-Field Electron Mobility in GaN-on-Si HEMTs
Get PDFIn this work, we investigate the field and temperature dependence of the electron mobility in aluminum-gallium-nitride/gallium-nitride (AlGaN/GaN) high electron mobility transistors (HEMTs) realized on GaN-on-silicon (Si) substrates. For this purpose we employ an extraction method to eliminate parasitic and fringing effects. Our results show that especially at low fields the temperature dependence of the mobility, and consequently that of the specific on-resistance, is strongly affected by stress-induced charged dislocation scattering. For explaining the mobility behaviour at low fields, the subthreshold operation regime of the HEMTs has also been analyzed. An interface trap density at the AlGaN/GaN interface (Nit) of ~ 6.9 x 1010 cm−2 has been extracted independent of the temperature which is close to the extracted dislocation density from mobility measurements. This suggests that the relatively high dislocation density in the GaN layer, which is a consequence of the still imperfect buffer layer in the GaN-on-Si substrate that is used to accommodate the strain difference, has an impact on Nit, thus subthreshold swing, in addition to the mobility reduction.</p
Locomotion of paired spermatozoa during flagellar synchronisation
Get PDFMicroorganisms, such as spermatozoa, exhibit rich behaviours when in close proximity to each other. However, their locomotion is not fully understood when coupled mechanically and hydrodynamically. In this study, we develop hydrodynamic models to investigate the locomotion of paired spermatozoa, predicting the fine structure of their swimming. Experimentally, sperm pairs are observed to transition between different modes of flagellar synchronisation: in-phase, anti-phase and lagged synchronisation. Using our models, we assess their swimming performances in these synchronisation modes in terms of average swimming speed, average power consumption, and swimming efficiency. The swimming performances of paired spermatozoa are shown to depend on their flagellar phase lag, flagellar waveforms, and the mechanical coupling between their heads.</p
Integration of Visual SLAM in Robot-Assisted Minimally Invasive Surgery:Advances, Challenges, and Solutions
Get PDFRobot-assisted surgery (RAS) has demonstrated notable advancements in visualization, instrument dexterity, ergonomic improvements, and decreased infection risks when compared to conventional surgical methods. However, within minimally invasive surgery (MIS) contexts, RAS encounters notable challenges in navigating surgical tools effectively. Recent advancements in robot navigation techniques have transitioned from rudimentary wheel odometry and dead reckoning to sophisticated Visual SLAM (Simultaneous Localization and Mapping) methods, capable of addressing complex indoor and outdoor environments. Nevertheless, the integration of Visual SLAM within Robot-Assisted Minimally Invasive Surgery (RAMIS) applications remains substantially restricted due to various factors, including limited field of view, challenges in stereopsis, soft tissue deformations, insufflation effects, and instrument occlusions. This study provides an extensive overview of ongoing efforts towards the development of Visual SLAM algorithms tailored for establishing precise RAMIS systems. It delves into the encountered challenges, delineates the essential features required for establishing a precise Visual SLAM-driven RAMIS system, and explores a diverse range of approaches, which can potentially enhance Visual SLAM functionality within RAMIS contexts.</p
Influence of Gait Speed on Inter-Joint Coordination in People with and Without Parkinson’s Disease
Get PDFBackground: The influence of gait speed on lower-extremity coordination while walking in people with Parkinson’s disease (pwPD) is poorly understood. This study sought to investigate the relationship between gait speed and hip–knee coordination and coordination variability in older adults and pwPD. Methods: A total of 27 pwPD and 21 healthy older adults were recruited. Participants walked in a straight line at slow, preferred, and fast walking speeds. Gait data were collected using inertial measurement units, and the kinematics of the hip and knee were calculated. Coordination and coordination variability at the hip–knee joint pair were determined using continuous relative phase. A repeated measures two-way ANCOVA tested the impact of gait speed on coordination and coordination variability, while group differences were evaluated using statistical parametric mapping (SPM). Results: Neither the healthy older adults nor the pwPD adjusted their hip–knee coordination in response to changes in gait speed. pwPD also displayed a trend towards restricted hip and knee joint excursion compared to older adults, which may further limit their ability to adapt gait strategies. Conclusions: These findings suggest that interventions addressing both joint excursion and motor adaptability may be important for improving gait function in individuals with Parkinson’s disease. Real-world applicability can be found in the potential of wearable sensors to become a valuable tool in routine clinical practice for both diagnosis and ongoing management. Trial registration: The study is registered in the German Clinical Trials Register (DRKS00022998).</p
Analysis of the Impact of Renewable Energy Sources and Energy Storage Systems on Multi-Stage Transmission Network Expansion Planning
Get PDFThis paper presents a mathematical model to solve the multi-stage transmission network expansion planning (MTNEP) problem considering renewable energy sources (RES) and the allocation of energy storage systems (ESSs). Given the stochastic nature of both renewable energy sources and demand, the implementation of representative periods (RPs) is proposed. RPs represent the behavior of the electrical power system over time series, including short-term variations, demand and RES correlations, and geographic factors, offering feasible computational complexity to solve the MTNEP problem. The proposed model is formulated as a deterministic equivalent mixed-integer linear programming (MILP) model for a set of RPs. The MILP model optimizes investments in transmission lines (TLs) and ESSs. Furthermore, the MILP model incorporates active power losses through piecewise linearization and N-1 security constraints. A method is developed to reduce the combinatorial search space to deal with high-dimensional problems. The Garver’s 6-bus system, a modified IEEE 24-bus test system, and the northern Colombian transmission system are used to validate the proposed model. An extensive analysis of the impact of RES and ESSs on MTNEP is presented. Simultaneous optimization of TLs and ESSs provides better and cheaper MTNEPs compared to traditional methods. The effectiveness of ESSs in integrating RES, shifting electricity, reducing/delaying investments (especially when considering N - 1 security constraints) and alleviating grid congestion is evidenced. This shows that ESSs have great potential as reinforcement and flexibility elements in the MTNEP problem.</p
Additional Carbon Dioxide Removal by Oxygenated Dialysis Fluid:Insights for the Development of a Novel Lung and Kidney Assist Device
Get PDFRenOx, a novel artificial lung and kidney assist device, combines gas exchange and dialysis fibers for integrated respiratory and renal support, with dialysis fibers intended for toxin clearance and filtration. However, when kidney support is not needed, dialysis fibers could be repurposed for additional respiratory support for patients in exacerbated cases, and to compensate losses in CO2transfer caused by the partial replacement of gas exchange fibers by dialysis fibers. We analyzed the feasibility of extracorporeal gas transfer via dialysis membranes with fully oxygenated and decarboxylated dialysis fluid in a closed circuit, quantifying O2and CO2exchange during standardized in-vitro tests with blood. Oxygenated dialysate was pumped through a dialyzer with a similar dialysis fiber area (0.6 m2) to the RenOx (adult size). Gas transfer efficiency was evaluated at blood-to-dialysate flow ratios of 1, 3, and 6. Average CO2removal from 12 to 35 ml/Lbloodwas achieved by adjusting blood-to-dialysate flow ratio, approaching the full metabolic requirement of adult patients (40 ml/Lblood). Maximum oxygen supply was 15 ml/Lblood. Blood pH and hematocrit were within physiological range. This study proposes a simple method to enhance lung support in the RenOx, advancing research on CO2removal by dialysis.</p