333 research outputs found
Modelling statistical wave interferences over shear currents
No full textWave forecasting in ocean and coastal waters commonly relies on spectral models based on the spectral action balance equation. These models assume that different wave components are statistically independent and as a consequence cannot resolve wave interference due to statistical correlation between crossing waves, as may be found in, for instance, a focal zone. This study proposes a statistical model for the evolution of wave fields over non-uniform currents and bathymetry that retains the information on the correlation between different wave components. To this end, the quasi-coherent model (Smit & Janssen, J. Phys. Oceanogr., vol. 43, 2013, pp. 1741-1758) is extended to allow for wave-current interactions. The outcome is a generalized action balance model that predicts the evolution of the wave statistics over variable media, while preserving the effect of wave interferences. Two classical examples of wave-current interaction are considered to demonstrate the statistical contribution of wave interferences: (1) swell field propagation over a jet-like current and (2) the interaction of swell waves with a vortex ring. In both examples cross-correlation terms lead to development of prominent interference structures, which significantly change the wave statistics. Comparison with results of the SWAN model demonstrates that retention of cross-correlation terms is essential for accurate prediction of wave statistics in shear-current-induced focal zones.Environmental Fluid Mechanic
The trade-off between accuracy and accessibility of syphilis screening assays.
No full textThe availability of rapid and sensitive methods to diagnose syphilis facilitates screening of pregnant women, which is one of the most cost-effective health interventions available. We have evaluated two screening methods in Tanzania: an enzyme immunoassay (EIA), and a point-of-care test (POCT). We evaluated the performance of each test against the Treponema pallidum particle agglutination assay (TPPA) as the reference method, and the accessibility of testing in a rural district of Tanzania. The POCT was performed in the clinic on whole blood, while the other assays were performed on plasma in the laboratory. Samples were also tested by the rapid plasma Reagin (RPR) test. With TPPA as reference assay, the sensitivity and specificity of EIA were 95.3% and 97.8%, and of the POCT were 59.6% and 99.4% respectively. The sensitivity of the POCT and EIA for active syphilis cases (TPPA positive and RPR titer ≥ 1/8) were 82% and 100% respectively. Only 15% of antenatal clinic attenders in this district visited a health facility with a laboratory capable of performing the EIA. Although it is less sensitive than EIA, its greater accessibility, and the fact that treatment can be given on the same day, means that the use of POCT would result in a higher proportion of women with syphilis receiving treatment than with the EIA in this district of Tanzania
Sero-epidemiological status and risk factors of toxoplasmosis in pregnant women in Northern Vietnam
No full textBackground: In Vietnam, few studies have determined the epidemiological status of toxoplasmosis in pregnant women and no routine prenatal screening is in place. This study was conducted to evaluate the seroprevalence of this zoonotic parasitic infection in pregnant women in Northern Vietnam and to assess the association with awareness, risk factors and congenital toxoplasmosis.
Methods: Approximately 800 pregnant women were included in the study from two hospitals, one in Hanoi and one in Thai Binh province, which is known to have a dense cat population. Serological immunoglobulin G (IgG) and immunoglobulin M (IgM) detection was performed to estimate the seroprevalence of toxoplasmosis and sero-incidence of maternal and congenital toxoplasmosis. In addition, a survey was conducted about awareness, clinical history, presentation of signs and symptoms relating to toxoplasmosis and to detect biologically plausible and socio-demographic risk factors associated with toxoplasmosis. Associations with seroprevalence were assessed using univariable and multivariable analysis.
Results: The mean IgG seroprevalence after the full diagnostic process was 4.5% (95% confidence interval(CI): 2.7–7.0) and 5.8% (95% CI: 3.7–8.6) in Hanoi and Thai Binh hospital, respectively, and included one seroconversion diagnosed in Thai Binh hospital. Only 2.0% of the pregnant women in Hanoi hospital and 3.3% in Thai Binh hospital had heard about toxoplasmosis before this study.
Conclusion: Since the percentage of seronegative, and thus susceptible, pregnant women was high and the awareness was low, we suggest to distribute information about toxoplasmosis and its prevention among women of child bearing age. Furthermore, future studies are recommended to investigate why such a low seroprevalence was seen in pregnant women in Northern Vietnam compared to other countries in South East Asia and globally
Discrete and metric divisorial gonality can be different
No full textThis paper compares the divisorial gonality of a finite graph G to the divisorial gonality of the associated metric graph Γ(G,1) with unit lengths. We show that dgon(Γ(G,1)) is equal to the minimal divisorial gonality of all regular subdivisions of G, and we provide a class of graphs for which this number is strictly smaller than the divisorial gonality of G. This settles a conjecture of M. Baker [3, Conjecture 3.14] in the negative.Discrete Mathematics and Optimizatio
Simulating gait with the 3R60 knee prosthesis and a control moment gyroscope
No full textDeveloping a new knee prosthesis requires thorough testing. Forward dynamics simulation can be valuable in the development process. It can reduce the need for intermediate prototypes and tests. Currently, there are 3D simulations of healthy walking and kinematic models of common prosthesis like the 3R60. However, they have not yet been combined. Such a model could function as a baseline for newly developed prostheses. It would also open possibilities for researchers to modify the prosthesis design by analyzing different scenarios in simulations. In this paper an existing 3D neuromuscular model of a healthy human is adjusted so that it represents a trans-femoral amputee with a 3R60. The model is simulated walking with an average velocity of 0.9 m/s and 1.2 m/s. The performance of the model is evaluated by comparing gait differences between the healthy and amputee model to findings from literature. The simulated amputee gait agrees well with literature, especially for a velocity of 1.2m/s. When walking 0.9 m/s the model oscillates in the coronal plane, suggesting it has difficulty maintaining balance. Furthermore, a case study was done on fall prevention using a controlmoment gyroscope embedded in the prosthetic shank. The control moment gyroscope increases the ability to flex and extend the prosthetic knee, which can help with fall prevention. With the added control moment gyroscope the gait at 1.2 m/s became more symmetric. A fall was prevented after a trip using a control moment gyroscope, however, this simulation is numerically too sensitive to draw conclusions.https://github.com/nathantim/amputee_gait_simulation GitHub repositoryMechanical Engineering | Systems and Contro
Hundreds of variants clustered in genomic loci and biological pathways affect human height
No full textMost common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits(1), but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait(2,3). The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P<0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways
Optimising the Decentralisation of Periodic Event-Triggered Control
No full textEvent-Triggered Control (ETC) is a control method where the controller is only updated when necessary. The control inputs are kept fixed until a state-dependent event triggers their re-computation. The triggering condition is designed to guarantee the stability and desired performance of the control system. This prevents the excessive use of scarce communication and energy resources. To fully take advantage of these savings when dealing with a (physically) distributed system, it is vital to decentralise the triggering condition. A decentralised triggering condition can be checked locally at the nodes of the system using the locally available states, eliminating the need to send updated sensor measurements to a central location constantly. However, the decentralisation of the triggering condition needs to be optimised for the state of the system to fully take advantage of the possible resource savings. This thesis provides a framework to optimally decentralise quadratic triggering conditions for Periodic Event-Triggered Control (PETC) systems in the absence and presence of bounded disturbances. In addition, a method of constructing a region-based map of such optimisations is provided, making it feasible to implement the optimisation approach on larger systems without needing more powerful hardware.Mechanical Engineering | Systems and Contro
Fast relative sensor orientation estimation in the presence of real-world disturbances
No full textWe present a novel approach to estimate the relative sensor orientation from inertial sensors placed on connected body segments. Drift in the relative orientation estimates obtained by integrating the gyroscope measurements is corrected solely by incorporating common information in the inertial sensor measurements due to the connection of the body segments. We solve the estimation problem using a complementary filtering implementation to reduce the computational complexity. We study its robustness under common real-world model violations, e.g., soft tissue artifacts and spikes in the acceleration signals due to impacts. The efficacy of the method is illustrated with numerical simulations and is compared to a multiplicative extended Kalman filter implementation, both with and without outlier rejection. In addition, a human experiment strengthened the simulation results under realistic sensor errors.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.Medical Instruments & Bio-Inspired TechnologyTeam Manon Ko
Compliant shape adaptive chicory gripping: for robotic sorting processes
No full textThis thesis contains the design process of a compliant shape adaptive chicory gripper for robotic sorting processes. The robotic sorting line consists of an input and output conveyor-belt. The input line contains unsorted chicories which are scanned by a robotic vision system. Overhead FlexPicker robots, equipped with chicory grippers, sort the chicories size by size onto the output line. The output line can contain a transportation crate or flowpack in which the chicories will be packed and shipped after sorting. Chicories are vulnerable for internal and external damages when touching the outer skin which makes robotic sorting difficult. The acceleration forces performed by the robot requires a strong but gentle grip on the chicory without any damaging marks. By designing a specific compliant shape adaptive gripper, sorting can be done faster, cheaper and more accurate than manual sorting. Current patents, academic literature or business applications had no solution for this chicory gripping problem. The design process for a suitable gripper started with an analysis of current patents and literature within compliant gripping in general. This provided insights in the the possibilities of compliant gripping. Based on the design requirements for the robot sorting setup, several concepts are obtained and selected. The concepts have been translated into four working gripper prototype layouts which are evaluated on force and damage requirements. Based on the results of these experiments, a first iteration prototype was made. Three additional optimizing iterations were needed to result in a prototype which reached the damage and force requirements. Further evaluation of this prototype proved a sufficient performance on robustness, endurance, operational speed and food grade requirements. The iteration 4 prototype reached therefore 17 of the total 19 gripper design requirements. To be able to accomplish the two remaining requirements, several recommendations are provided for a final gripper end product which is ready for industrial application
A New Quantitative Analysis for Prostheses Research and Evaluation: A Sensor Fusion Approach
No full textProblem: Due to high rejection rates regarding prostheses’ use, the assessment of the amputee’s use of the prosthesis has become more critical. Today’s prosthesis research is limited to assessing a users’ performance to perform tasks in a controlled environment. Therefore, these studies cannot wholly assess how the prosthesis is used in the daily lives of amputees. Purpose: The purpose of this thesis project is to create, test, and examine the performance of methods that can be used to enhance prostheses' research and evaluation. Results: We have created several enhancements and extensions regarding prosthesis research and evaluation for three sensor scenarios. In the first scenario, we only use an accelerometer, which allowed us to create a new method for creating a vector magnitude (VM) that can show us what type of arm movement is made; additionally, we created a novel scoring system to determine the intensity of movements that are performed. In our second scenario, we used an additional gyroscope, which opened up possibilities for using more advanced Sensor Fusion (SF) techniques. We created an accurate tilt estimation algorithm that remains robust against high levels of gyroscope noise, accelerometer outliers, and measurement model violations. With the gyroscope, we were also able to create a VM from rotational velocity, which displays information about the arms’ rotational movement. Additionally, we created a novel scoring system that also shows the intensity of the performed movements. Our last scenario considers the use of two Inertial Measurement Units (IMUs); we present a novel algorithm for estimating the relative sensor orientation. This algorithm uses a joint kinematic estimation method that incorporates the connection between adjacent segments within a SF algorithm that remains accurate in the vicinity of common real-world disturbances, among which are; high levels of gyroscope noise, accelerometer outliers, and Soft-Tissue-Artifacts (STA). Conclusion: The best way to enhance the analysis for prostheses research and evaluation is to start incorporating gyroscopes into the research process. This can either be in the form of the single sensor case or the double sensor system. The additional gyroscope(s) will enable the use the SF techniques and methods as discussed in this report.Mechanical Engineering | Systems and Contro
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