Estimation of hydraulic conductivity and its uncertainty from grain-size data using GLUE and artificial neural networks

peer reviewedaudience: researcher, professionalVarious approaches exist to relate saturated hydraulic conductivity (Ks) to grain-size data. Most methods use a single grain-size parameter and hence omit the information encompassed by the entire grain-size distribution. This study compares two data-driven modelling methods, i.e.multiple linear regression and artificial neural networks, that use the entire grain-size distribution data as input for Ks prediction. Besides the predictive capacity of the methods, the uncertainty associated with the model predictions is also evaluated, since such information is important for stochastic groundwater flow and contaminant transport modelling. Artificial neural networks (ANNs) are combined with a generalized likelihood uncertainty estimation (GLUE) approach to predict Ks from grain-size data. The resulting GLUE-ANN hydraulic conductivity predictions and associated uncertainty estimates are compared with those obtained from the multiple linear regression models by a leave-one-out cross-validation. The GLUE-ANN ensemble prediction proved to be slightly better than multiple linear regression. The prediction uncertainty, however, was reduced by half an order of magnitude on average, and decreased at most by an order of magnitude. This demonstrates that the proposed method outperforms classical data-driven modelling techniques. Moreover, a comparison with methods from literature demonstrates the importance of site specific calibration. The dataset used for this purpose originates mainly from unconsolidated sandy sediments of the Neogene aquifer, northern Belgium. The proposed predictive models are developed for 173 grain-size -Ks pairs. Finally, an application with the optimized models is presented for a borehole lacking Ks data

Vaccines against toxoplasma gondii : challenges and opportunities

Development of vaccines against Toxoplasma gondii infection in humans is of high priority, given the high burden of disease in some areas of the world like South America, and the lack of effective drugs with few adverse effects. Rodent models have been used in research on vaccines against T. gondii over the past decades. However, regardless of the vaccine construct, the vaccines have not been able to induce protective immunity when the organism is challenged with T. gondii, either directly or via a vector. Only a few live, attenuated T. gondii strains used for immunization have been able to confer protective immunity, which is measured by a lack of tissue cysts after challenge. Furthermore, challenge with low virulence strains, especially strains with genotype II, will probably be insufficient to provide protection against the more virulent T. gondii strains, such as those with genotypes I or II, or those genotypes from South America not belonging to genotype I, II or III. Future studies should use animal models besides rodents, and challenges should be performed with at least one genotype II T. gondii and one of the more virulent genotypes. Endpoints like maternal-foetal transmission and prevention of eye disease are important in addition to the traditional endpoint of survival or reduction in numbers of brain cysts after challenge

Association of C-reactive protein and muscle strength in the English Longitudinal Study of Ageing

Sarcopenia has been associated with systemic inflammation and a range of other biological risk factors. The purpose of this study was to assess the systemic inflammation–muscle strength relationship in a large representative community-based cohort of older adults, and to determine the independence of this association from other biological and psychosocial risk factors. Participants were 1,926 men and 2,260 women (aged 65.3 ± 9.0 years) from the English Longitudinal Study of Ageing, a study of community dwelling older adults. We assessed hand grip strength and lower body strength (time required to complete five chair stands). Biological measures included C-reactive protein (CRP), fibrinogen, cholesterol, haemoglobin, glycated haemoglobin, adiposity, and blood pressure. Approximately 33% of the sample demonstrated elevated concentrations (≥3 mg/L) of CRP. After adjustments for age, smoking, physical activity, education, inflammatory diseases, and all other biological factors, elevated CRP was associated with poorer hand grip strength and chair stand performance in women but only chair stand performance in men. Low haemoglobin levels were consistently associated with poorer performance on both tests in women and men. These results confirm an independent association between low grade systemic inflammation (as indexed by CRP) and muscle strength that appears to be more robust in women