Parameter estimation and uncertainty quantification of a fiber-reinforced concrete model by means of a multi-level Bayesian approach

The paper presents a procedure for the stochastic calibration of a cracked hinge model on the basis of an extensive experimental campaign performed on a large group of nominally identical fiber-reinforced specimens. The calibration is carried out in a multi-level Bayesian framework that allows to quantify and separate several uncertainty contributions affecting model parameters. Indeed, the variability in the experimental response for nominally identical specimens due to the material heterogeneity represents a significant uncertainty contribution as well as model error. The former can be quantified at the hyper-parameter level of the multi-level framework. The presented results highlight the good agreement of the numerical predictions with the experimental data and the superior performance of the multi-level framework compared to that of the classical single-level framework. We also perform analyses to explore the impact of the prior parameter model conditioned on hyper-parameters and assess the minimum number of specimen datasets needed to quantify the inherent variability of model parameters

Modeling soil nitrate accumulation and leaching in conventional and conservation agriculture cropping systems

Nitrate is a major groundwater inorganic contaminant that is mainly due to fertilizer leaching. Compost amendment can increase soils' organic substances and thus promote denitrification in intensively cultivated soils. In this study, two agricultural plots located in the Padana plain (Ferrara, Italy) were monitored and modeled for a period of 2.7 years. One plot was initially amended with 30 t/ha of compost, not tilled, and amended with standard fertilization practices, while the other one was run with standard fertilization and tillage practices. Monitoring was performed continuously via soil water probes (matric potential) and discontinuously via auger core profiles (major nitrogen species) before and after each cropping season. A HYDRUS-1D numerical model was calibrated and validated versus observed matric potential and nitrate, ammonium, and bromide (used as tracers). Model performance was judged satisfactory and the results provided insights on water and nitrogen balances for the two different agricultural practices tested here. While water balance and retention time in the vadose zone were similar in the two plots, nitrate leaching was less pronounced in the plot amended with compost due to a higher denitrification rate. This study provides clear evidence that compost addition and no-tillage (conservation agriculture) can diminish nitrate leaching to groundwater, with respect to standard agricultural practices

A statistical approach for modeling individual vertical walking forces

This paper proposes a statistical approach for modeling vertical walking forces induced by single pedestrians. To account for the random nature of human walking, the individual vertical walking force is modeled as a series of steps and the gait parameters are assumed to vary at each step. Walking parameters are statistically calibrated with respect to the results of experimental tests performed with a force plate system. Results showed that the walking parameters change during walking and are correlated with each other. The force model proposed in this paper is a step-by-step model based on the description of the multivariate distribution of the walking features through a Gaussian Mixture model. The performance of the proposed model is compared to that of a simplified load model and of two force models proposed in the literature in a numerical case study. Results demonstrate the importance of an accurate modeling of both the single step force and the variability of the individual walking force

Surrogate-based bayesian model updating of a historical masonry tower

This paper presents the surrogate-based Bayesian model updating of a historical masonry bell tower. The finite element model of the structure is updated on the basis of the modal properties experimentally identified thanks to a vibration test. In a general context, model updating results are highly affected by several uncertainties, regarding both the experimental measures and the model. Stochastic approaches to model updating, as the one based on Bayes' theorem, enable to quantify the uncertainties associated to the updated parameters and, consequently, to increase the reliability of the identification. The major drawback of Bayesian model updating is the high computational effort requested to compute the posterior distribution of parameters. For this reason, the paper proposes to integrate the classical procedure with a surrogate model. A Gaussian surrogate is employed for the approximation of the posterior distribution of parameters and the performances of the proposed method are compared to those of an Bayesian numerical method proposed in literature

PEG reimplantation after Buried Bumper Syndrome: a case report

Percutaneous endoscopic gastrostomy (PEG) is the method of choice to provide long-term enteral nutrition for patients with impossibility to be fed orally. Although it is considered a routine and safe procedure, potential complications exist, which are generally classified into three major categories: endoscopic technical difficulties, PEG procedure-related complications and late complications associated with PEG tube use, such as buried bumper syndrome (BBS). BBS is a potentially life-threatening complication, occurring in 0.3% to 2.5% of cases. Additional complications related to BBS may present, such as wound infection, peritonitis, and necrotizing fasciitis. Once resolved the acute complication, an adequate feeding method should be prompted for the patient, among whom PEG remains of choice. After tissue inflammation, fibrosis may prevent a standard endoscopic procedure for the new implantation, therefore endoscopists should modulate procedures to obtain successful and safe results. A combined surgical-and endoscopic strategy could resolve implantation difficulties ensuring a safe and simple procedure. We present here a case of BBS complicated with abdominal wall cellulitis in a paraplegic 35-year-old-man who was admitted to our hospital. (www.actabiomedica.it)

Can the plasma PD-1 levels predict the presence and efficiency of tumor-infiltrating lymphocytes in patients with metastatic melanoma?

Background: The immune response in melanoma patients is locally affected by presence of tumor-infiltrating lymphocytes (TILs), generally divided into brisk, nonbrisk, and absent. Several studies have shown that a greater presence of TILs, especially brisk, in primary melanoma is associated with a better prognosis and higher survival rate. Patients and Methods: We investigated by enzyme-linked immunosorbent assay (ELISA) the correlation between PD-1 levels in plasma and the presence/absence of TILs in 28 patients with metastatic melanoma. Results: Low plasma PD-1 levels were correlated with brisk TILs in primary melanoma, whereas intermediate values correlated with the nonbrisk TILs, and high PD-1 levels with absent TILs. Although the low number of samples did not allow us to obtain a statistically significant correlation between the plasma PD-1 levels and the patients' overall survival depending on the absence/presence of TILs, the median survival of patients having brisk type TILs was 5 months higher than that of patients with absent and nonbrisk TILs. Conclusions: This work highlights the ability of measuring the plasma PD-1 levels in order to predict the prognosis of patients with untreated metastatic melanoma without a BRAF mutation at the time of diagnosis

Citalopram-Induced Long QT Syndrome and the Mammalian Dive Reflex

Abstract While SCUBA diving, a 44-year-old Caucasian patient had an abnormal cardiac rhythm, presumably Tor-sade de Pointes (TdP), during the initial descent to depth. Upon surfacing, she developed ventricular fibrillation and died. The patient had been treated for mild depression for nearly a year with citalopram 60 mg per day, a drug known to cause prolonged QT interval. She had also been treated with two potentially hepatotoxic drugs. Liver impairment causes selective loss of cytochrome P450 (CYP) 2C19 activity, the major pathway for metabolism of citalopram. The post mortem blood level of citalopram was 1300 ng/ mL. The patient was found to be an intermediate metabo-lizer via CYP2D6, the major pathway for metabolism of desmethylcitalopram; the level of which was also abnormally high. It is suggested that drug-induced long QT syndrome (DILQTS), caused by citalopram, combined with the mammalian dive reflex triggered malignant ventricular rhythms resulting in the patient&#39;s death. It is further suggested that, in general, the dive reflex increases the risk of fatal cardiac rhythms when the QT interval is prolonged by drugs. Key Points Long-term high dosage and impaired metabolism apparently accounted for accumulation of high, but presumably non-lethal levels, of citalopram and desmethylcitalopram in a 44-year-old woman who died while SCUBA diving.</div