A new yield criteria including the effect of lode angle and stress triaxiality

AbstractAccording to several experiments reported in the literature, the elastoplastic behaviour of metals depends not only on the first stress invariant (triaxiality) for the ductile damage and on the second stress invariant (equivalent von Mises stress) for the yield, but also on the third stress invariant (normalized Lode angle X) which may affect at the same time the yielding and the ductile failure.In this paper a new yield model is presented, where the yield surface depends on the Lode Angle and, eventually, also on the triaxiality ratio.The proposed model is identified by a calibration parameter expressing the degree of nonlinearity of the yield with respect to the Lode angle, and a calibration function expressing the maximum variability of the hardening stress at the two extremities of the Lode angle range, corresponding to the uniaxial and to the pure shear stress states.The proposed model has been tested against several experimental data from the literature on the Titanium alloy Ti6Al4V, including mixed tension-torsion loading which allowed to control the evolution of X and to confine its values into different narrow ranges for better investigating the Lode angle effects on the yield response

INTERACTION OF STRAIN RATE AND NECKING ON THE STRESS-STRAIN RESPONSE OF UNIAXIAL TENSION TESTS BY HOPKINSON BAR

Abstract The effect of the necking combined to that of the strain rate is analysed in dynamic split Hopkinson bar (SHTB) tests, by both experiments and finite elements. Experiments from the literature by Noble et al. are considered here together with other tests ran at the University of Catania. Two different characterization procedures are used for modeling the materials, leading to strain and strain rate-dependent flow stress according to the Johnson-Cook model for the Remco Iron by Noble et al., and to an MLR-based calibration for the FeN steel implemented by fortran subroutines, respectively. After satisfactory validation of the finite elements results and of the dynamic hardening models via comparison to the experimental stress-strain, a detailed investigation on the way the necking perturbation of the stress interacts with the strain rate is carried out, expecially investigating how the ratio of the flow stress/true stress evolves with the strain and the strain rate. Special modifications are introduced to the subroutine modeling the strain rate-promoted dynamic amplification of the stress; the related response from finite elements confirms the outcomes of previous papers, unveiling a new feature of the dynamic stress in SHTB tests and providing new information about the suitability and the accuracy of the modern procedures for the dynamic stress-strain characterization

Short-Term Neurodevelopmental Outcome in Term Neonates Treated with Phenobarbital versus Levetiracetam: A Single-Center Experience

BACKGROUND: Phenobarbital (PB) has been traditionally used as the first-line treatment for neonatal seizures. More recently, levetiracetam (LEV) has been increasingly used as a promising newer antiepileptic medication for treatment of seizures in neonates. OBJECTIVES: The aim of our study was to compare the effect of PB vs. LEV on short-term neurodevelopmental outcome in infants treated for neonatal seizures. METHOD: This randomized, one-blind prospective study was conducted on term neonates admitted to the Neonatal Intensive Care Unit of S. Bambino Hospital, University Hospital "Policlinico-Vittorio Emanuele," Catania, Italy, from February 2016 to February 2018. Thirty term neonates with seizures were randomized to receive PB or LEV; the Hammersmith Neonatal Neurological Examination (HNNE) was used at baseline (T0) and again one month after the initial treatment (T1). RESULTS: We found a significantly positive HNNE score for the developmental outcomes, specifically tone and posture, in neonates treated with LEV. There was no significant improvement in the HNNE score at T1 in the neonates treated with PB. CONCLUSION: This study suggests a positive effect of levetiracetam on tone and posture in term newborns treated for neonatal seizures. If future randomized-controlled studies also show better efficacy of LEV in the treatment of neonatal seizures, LEV might potentially be considered as the first-line anticonvulsant in this age grou

Microsurgical Disconnection of Ruptured Intracranial Pial Arteriovenous Fistula Guided by Indocyanine Green Videoangiography.

Intracranial arteriovenous fistulas, rare causes of spontaneous intracerebral bleeding, are direct communications between an arterial feeder and an arterialized vein that drains a normal brain. Arteriovenous disconnection is the only effective treatment for this type of vascular malformation, which is often reached microsurgically due to the difficult endovascular access. Intraoperative indocyanine green videoangiography (ICG-VA) is a valuable help in identifying the arterialized draining vein and its direct communication with the arterial feeder and in confirming real-time interruption of the fistula. We describe the case of a 46-year-old man presenting with sudden onset of headache and left arm motor and sensory deficits associated with a frontoparietal hematoma evacuated 1 week earlier in another institution. Digital subtraction angiography showed a direct communication between an anterior parietal branch of the right middle cerebral artery and a parietal vein. Given the difficulty to reach the point of the fistula endovascularly because of the small caliber and tortuosity of the arterial feeder, as well as the short and relatively rapid flow through the arteriovenous communication, we decided to proceed with microsurgical treatment. Under intraoperative neurophysiologic monitoring the fistula was located with the aid of ICG-VA and interrupted (Video 1). Both control ICG-VA and postoperative angiogram confirmed resolution of the fistula. At a 3-month follow-up the patient had a complete neurologic recovery

static and dynamic response of titanium alloy produced by electron beam melting

Abstract The suitability of Titanium alloys for many specialized applications requiring excellent performances at both static and dynamic strain rates, benefits of modern manufacturing technologies like the additive manufacturing, oriented toward the obtainment of complicated component shapes. The EBM methodology for the production of Ti6Al4V components is based on the localized melting of alloy powders by way of guided electron beams scanning the powder volume by successive planar trajectories; for this reason, the whole production process may confer a certain degree of anisotropy to the components. The material behavior of the EBM alloy may be orientation-dependent in terms of stress-strain elastoplastic response as well as in terms of damage sensitivity and ductile fracture under given triaxiality histories. The static and dynamic behavior of a sintered Ti6Al4V alloy is investigated here by way of quasistatic tension-torsion tests and dynamic tensile Hopkinson bar (SHTB) tests. The outcome of the latter experiments, compared to similar tests results from the literature concerning Ti alloy obtained by classical metallurgical techniques, gives some indications about how the technological process may affect the final performance of the material and the component

Berry Characterisation of cv Shiraz According to Position on the Rachis

In this study, characterisation of the physical and compositional parameters of berries located in differentpositions on the rachis of Shiraz/R99 bunches was done. Berries were divided according to position onthe rachis (apical, median and basal) and berry weight, resulting in four berry weight classes, averaging0.86 g, 1.29 g, 1.74 g and 2.26 g and 0.74, 1.18, 1.59 and 2.09 cm3, respectively. The berries were analysedindividually. The fresh weight of the berries comprised approximately 4% seeds, 20% skin and 76% flesh.Different percentage distributions were found for each class of berry weight and according to position onthe rachis. From the top to the bottom rachis position, an increase in skin proportion value and a decreasein flesh and seed proportion value occurred. Skins decreased and flesh increased in proportion from thesmallest to the largest berry size. The seed maintained a relatively stable proportion, irrespective of berrysize. Larger berries had more flesh compared to skin than smaller berries. A higher level of soluble solidsoccurred in the shoulder to middle bunch area (28.7 °B and 28.6 °B, respectively) than in the bottom area(27.6 °B). It is extremely difficult to obtain uniform berry size and composition under field conditions.Continuous efforts are required to reduce variation and the potential negative impact on wine quality andconsistency of wine style

Anthocyanin variation in individual 'Shiraz' berries as affected by exposure and position on the rachis

This study was done on 'Shiraz'/Richter 99 grapes with the intention to define the variation of skin anthocyanin content in a single berry. The effects of berry position (on the rachis), berry exposure, berry weight category, part of the skin of a single berry, and their interactions, were analysed. The anthocyanin concentration of externally facing berries decreased and that of the internally facing berries increased from the apical part to the basal part of the bunch. Highest values were recorded in internally facing berries and lowest values in the externally facing (exposed) berries, of the basal rachis area. Anthocyanin values of small berries seemed to decrease from the apical part of the rachis to the basal part, whereas those of the larger berries generally increased. Anthocyanin distribution in the skin of a single berry was similar for all the berry weight categories. The median concentric layer of the berry showed the highest anthocyanin concentration. The study showed significant intra-berry variation, indicating that even at full ripeness stage there is still variation in every single smaller or larger berry. The results highlighted the very complicated management challenges to grape producers to increase bunch uniformity in quantity and quality.

Blood pressure and cardiac autonomic nervous system in obese type 2 diabetic patients: Effect of metformin administration

Background: Hyperinsulinemia/insulin resistance and elevated plasma free fatty acids (FFA) levels are involved in the hypertension and cardiac sympathetic overactivity. Metformin improves insulin action and lower plasma FFA concentrations. We investigate the possible effect of metformin on arterial blood pressure (BP) and cardiac sympathetic nervous system. Methods: One hundred twenty overweight type 2 diabetic patients were treated by placebo (n = 60) + diet or metformin (850 mg twice daily) (n = 60) + diet for 4 months, to evaluate the effect of metformin treatment on the cardiac autonomic nervous system. Insulin resistance was measured by the Homeostasis Model Assessment (HOMA) index. Heart rate variability (HRV) assessed cardiac sympathovagal balance. Results: Metformin treatment, but not placebo treatment, was associated with a decrease in fasting plasma glucose (P < .05), insulin (P < .05), triglyceride (P < .05), and FFA (P < .03) concentrations and HOMA index (P < .03). Metformin treatment was also associated with a significant improvement in cardiac sympathovagal balance but not in mean arterial BP. Furthermore, in a multivariate analysis, delta change in sympathovagal balance index (LF/HF ratio) were associated with delta change in plasma FFA concentrations and HOMA index independently of gender and delta change in plasma triglyceride and HbA1c concentrations. Conclusions: Our study demonstrated that metformin treatment might be useful for improving cardiac sympathovagal balance in obese type 2 diabetic patients

Regional Development of Glioblastoma: The Anatomical Conundrum of Cancer Biology and Its SurgicalImplication

Glioblastoma (GBM) are among the most common malignant central nervous system (CNS) cancers, they are relatively rare. This evidence suggests that the CNS microenvironment is naturally equipped to control proliferative cells, although, rarely, failure of this system can lead to cancer development. Moreover, the adult CNS is innately non-permissive to glioma cell invasion. Thus, glioma etiology remains largely unknown. In this review, we analyze the anatomical and biological basis of gliomagenesis considering neural stem cells, the spatiotemporal diversity of astrocytes, microglia, neurons and glutamate transporters, extracellular matrix and the peritumoral environment. The precise understanding of subpopulations constituting GBM, particularly astrocytes, is not limited to glioma stem cells (GSC) and could help in the understanding of tumor pathophysiology. The anatomical fingerprint is essential for non-invasive assessment of patients' prognosis and correct surgical/radiotherapy planning

Cell Shortening and Calcium Homeostasis Analysis in Adult Cardiomyocytes via a New Software Tool

Intracellular calcium (Ca2+) is the central regulator of heart contractility. Indeed, it couples the electrical signal, which pervades the myocardium, with cardiomyocytes contraction. Moreover, alterations in calcium management are the main factors contributing to the mechanical and electrical dysfunction observed in failing hearts. So, simultaneous analysis of the contractile function and intracellular Ca2+ is indispensable to evaluate cardiomyocytes activity. Intracellular Ca2+ variations and fraction shortening are commonly studied with fluorescent Ca2+ indicator dyes associated with microscopy techniques. However, tracking and dealing with multiple files manually is time-consuming and error-prone and often requires expensive apparatus and software. Here, we announce a new, user-friendly image processing and analysis tool, based on ImageJ-Fiji/MATLAB® software, to evaluate the major cardiomyocyte functional parameters. We succeeded in analyzing fractional cell shortening, Ca2+ transient amplitude, and the kinematics/dynamics parameters of mouse isolated adult cardiomyocytes. The proposed method can be applied to evaluate changes in the Ca2+ cycle and contractile behavior in genetically or pharmacologically induced disease models, in drug screening and other common applications to assess mammalian cardiomyocyte functions