Analysis of Stress Concentration in Functionally Graded Plates with Linearly Increasing Young's Modulus.

In this article, the strain and stress analyses of functionally graded plates with circular holes that are subject to a uniaxial far-field traction load are analytically considered. The Young's modulus is assumed to vary linearly along the radial direction around the hole. The adoption of such a type of inhomogeneity variation can be justified as follows. Firstly, and among all the possible variations of stiffness, the linear one is indeed the simplest inhomogeneity distribution. Surprisingly however, according to our knowledge extent, the associated elastic fields were not yet addressed in the literature. Secondly, a linearly varying stiffness could reasonably imply a remarkable advantage from a technological point of view. In fact, unlike nonlinearly varying stiffness plates, manufacturing routes are only required to handle constant variations throughout the radial domain. After recalling the basic equations for plane stress elasticity, the displacement, strain, and stress fields around the hole were numerically tackled and discussed for different stiffness ratios. A comparison was also carried out with other Young's modulus distributions that have been commonly employed in the literature.

Cyclic Plasticity and Low Cycle Fatigue of an AISI 316L Stainless Steel: Experimental Evaluation of Material Parameters for Durability Design.

AISI 316L stainless steels are widely employed in applications where durability is crucial. For this reason, an accurate prediction of its behaviour is of paramount importance. In this work, the spotlight is on the cyclic response and low-cycle fatigue performance of this material, at room temperature. Particularly, the first aim of this work is to experimentally test this material and use the results as input to calibrate the parameters involved in a kinematic and isotropic nonlinear plasticity model (Chaboche and Voce). This procedure is conducted through a newly developed calibration procedure to minimise the parameter estimates errors. Experimental data are eventually used also to estimate the strain-life curve, namely the Manson-Coffin curve representing the 50% failure probability and, afterwards, the design strain-life curves (at 5% failure probability) obtained by four statistical methods (i.e., deterministic, "Equivalent Prediction Interval", univariate tolerance interval, Owen's tolerance interval for regression). Besides the characterisation of the AISI 316L stainless steel, the statistical methodology presented in this work appears to be an efficient tool for engineers dealing with durability problems as it allows one to select fatigue strength curves at various failure probabilities depending on the sought safety level.

A Dynamic Programming Setting for Functionally Graded Thick-Walled Cylinders.

Material property variation in non-homogeneous internally pressurized thick-walled cylinders is investigated within the context of dynamic programming theory. The material is assumed to be linear, elastic, isotropic, and functionally graded in the radial direction. Based on the plane stress hypothesis, a state space formulation is given and the optimal control problem is stated and solved by means of Pontryagin's Principle for different objective functionals. Optimal Young's modulus distribution is found to be piecewise linear along the radial domain. A brief digression on the possible existence of switching points is addressed. Finally, a numerical example is performed within a special class of derived optimal solutions, showing promising results in terms of equivalent stress reduction with respect to the most used variations in literature.

Early osteopontin levels predict mortality in patients with septic shock.

BACKGROUND: Inflammatory biomarkers could be useful to stratify the risk of sepsis adverse outcome and potentially improving the clinical management. Here, we investigated the prognostic role of the inflammatory molecule osteopontin (OPN) in patients with severe sepsis with and without septic shock. MATERIAL AND METHODS: This is a sub-analysis of 957 patients with sepsis/septic shock from the Albumin Italian Outcome Sepsis (ALBIOS) study. Alongside demographic, clinical, and laboratory data, we assessed plasmatic values of OPN at day 1, 2 and 7 after enrolment. The primary outcome was the predictive role of OPN values at day 1on death for any cause at 28 days after enrolment. RESULTS: Plasma OPN values at day 1 were higher in patients with septic shock and correlated with the severity of multi-organ dysfunction. Once categorized for 28-day mortality, survivors were characterized by lower OPN levels at each time point and statistically significant drop overtime (p<0.001 for all). Similarly, OPN reduction during the first 7 days was associated with reduced hospitalization and mortality overtime. Multivariate logistic and Cox regression models confirmed plasma OPN at day 1 as predictor of both 28- and 90-day mortality and infection resolution as well, independently of demographic, clinical and therapeutic variables. However, this prognostic value was limited to septic shock patients. CONCLUSIONS: In patients with septic shock, OPN plasma levels at day 1 predict a poor clinical outcome. These results provide the rationale for future pathophysiological studies aimed at clarifying the mechanisms triggered by OPN in septic shock (ALBIOS ClinicalTrials.gov Identifier: NCT00707122).

Intraparenchymal ventricular diverticula in chronic obstructive hydrocephalus: prevalence, imaging features and evolution.

BACKGROUND: Intraparenchymal cavities communicating with the ventricles may appear in patients with chronic obstructive hydrocephalus despite no identifiable surgerical, vascular or traumatic causes. The rate, features, pathogenesis, evolution and clinical impact of intraparenchymal diverticula have not been outlined, yet. METHODS: Brain MRIs of 130 patients (mean age: 11.3 years; age range: 0-67; 60 females) with chronic obstructive hydrocephalus were analyzed. The pathogenesis, neurosurgical treatment, ventricle size, signs of transependymal reabsorption and septum pellucidum integrity of the hydrocephalus were recorded. Subarachnoid outpouching of the ventricles, post-hemorrhagic parenchymal cavities, paths of ventricular shunting and cavities not communicating with the ventricles were excluded. Of patients with intraparenchymal diverticula, all previous available CT and MRI scans were evaluated. RESULTS: Eight patients (6.2 %, mean age: 18.7 years; age range: 2-42) harbored 11 intraparenchymal diverticula sprouting from the temporal (6), occipital (3) or frontal (2) horns of the lateral ventricles. Intraparenchymal diverticula were more frequent in males (p = 0.04) and older patients (18.7 ± 12.7 vs 11.3 ± 9.8 years, p = 0.04). Their presence or evolution (mean neuroradiological follow-up 3.6 years; range: 0-8) showed a trend of association with hydrocephalus severity (bifrontal index) and did not correlate with the surgical treatment. In three patients the diverticula progressed during follow-up. One patient presented with hemiparesis consistent with the intraparenchymal lesion and improved after ventricular shunting. A DTI study revealed that the cortico-spinal tract was partly included in the septum between the ventricle and the intraparenchymal diverticulum. CONCLUSIONS: Clinicians dealing with chronic severe obstructive hydrocephalus should be aware of ventricular intraparenchymal diverticulation. Studies aiming at clarifying their pathogenesis and proper management are warranted.