Titanium corrosion in molten glasses : Part 2. Electrochemical study and corrosion mechanismus

In situ electrochemical experiments are carried out to determine the mechanisms of pure titanium corrosion in molten glasses. The corrosion layers formed at the metal/glass interface are systematically reported. The formal potentials of the TiIII/TiII and TiIV/TiIII redox couples are respectively positioned at -1.0 V and -0.7 V by coupling square wave voltammetry measurements and polarization of titanium rods. The potential of the BIII/B0 couple is estimated to be near -1.4 V. The results obtained by immersion tests and electrochemical measurements in glasses are compared. They are consistent in terms of corrosion rate variations and morphology of the corrosion scales. The corrosion mechanisms are described in the form of successive redox reactions between the glass and the substrate followed by diffusion of the formed species into the titanium substrate. It is demonstrated that Ti does not form spontaneously protective scales when immersed in molten glass and that protection can not be reached by either anodic or cathodic polarization

Numerical modelling of entangled carbon fibre material under compression

A new entangled cross-linked material was recently developed in order to present a new core material that can resolve the drawbacks of the honeycomb. The optimization of entangled carbon fibres requires a deep understanding of the influence of the parameters of a fibre network on its macroscopic behaviour. This paper presents a 3D finite element model to investigate the compressive behaviour of this fibrous material. The current work focuses on a representative volume element (RVE) with appropriate boundary conditions and initial fibre distribution close to that of the experimental test. The morphology of the RVE is examined before loading. The simulation results show a good correlation with the experimental data in terms of stress–strain curves. The descriptors of the morphology such as the distance between contacts and fibre orientation are studied under compression loading

Numerical modelling of shear hysteresis of entangled cross-linked carbon fibres intended for core material

The analysis of an entangled cross-linked fibrous material at low deformation is explored as way of predicting the shear behaviour, especially the shear hysteresis. This paper presents a 3D finite element model to characterize the carbon fibre network rigidified by epoxy cross-links. The morphology of the representative volume element (RVE) is studied to guarantee that it is representative of the actual material that was characterized experimentally. Two steps are simulated, namely the initial compression during the shaping and before the polymerization of the epoxy resin and the cyclic shear testing of the material with its rigidified network of fibres. A numerical simulation of an RVE is used to present a description of the measured hysteresis loop that is decomposed of linear and nonlinear parts. A comparison between the numerical prediction and the experiment data is discussed. Even if the 3D numerical model under-predict the average shear stiffness of the material, it can capture the complex shapes of the measured hysteresis loops at different strain amplitudes

Numerical analysis of shear stiffness of an entangled cross-linked fibrous material

The objective of this paper is to understand and study the effect of morphological parameters on the shear stiffness of an entangled cross-linked fibrous material made with carbon fibres where some of the contacts are bonded by the epoxy resin. This current work presents a 3D finite element model using ABAQUS/Standard in order to characterize the mechanical behaviour of different carbon fibre networks rigidified by epoxy cross-links. Numerical simulations are achieved on a representative volume element (RVE) with the orientation distribution of the fibres based on a tested sample. Since not all the strands are perfectly separated, an equivalent diameter of fibre is determined to obtain the rigidity experimen- tally measured in shear. Then, an investigation of the influence of morphological descriptors, such as the distance between cross-links, distribution fibre orientations and junction properties, is carried out. For the entangled cross-linked fibrous material with a small fibre volume fraction, the relationship between the shear stiffness and the fibre volume fraction is a linear function whereas the relation between the shear stiffness and the distance between junctions is a power law with exponent of −3/2. The shear stiff- ness depends slightly on the twisting joint stiffness, and its relationship with the tension joint stiffness is a logarithmic function. The effect of fibre stiffness is also investigated by taking Young’s modulus values corresponding to those of glass fibres, inox fibres or aramid fibres. A linear function is obtained between the shear stiffness and the Young’s modulus. These results are consistent with the analytical models in the literature for a cross-linked fibrous material

Nevirapine versus Efavirenz for patients co-infected with HIV and Tuberculosis: A Randomised Non-Inferiority Trial

BACKGROUND: In countries with a high incidence of HIV and tuberculosis co-infection, nevirapine and efavirenz are widely used as antiretroviral therapy but both interact with antituberculosis drugs. We aimed to compare efficacy and safety of a nevirapine-based antiretroviral therapy (started at full dose) with an efavirenz-based regimen in co-infected patients. METHODS: We did a multicentre, open-label, randomised, non-inferiority trial at three health centres in Maputo, Mozambique. We enrolled adults (≥18 years) with tuberculosis and previously untreated HIV infection (CD4 cell counts <250 cells per μL) and alanine aminotransferase and total bilirubin concentrations of less than five times the upper limit of normal. 4-6 weeks after the start of tuberculosis treatment, we randomly allocated patients (1:1) with central randomisation, block sizes of two to six, and stratified by site and CD4 cell count to nevirapine (200 mg twice daily) or efavirenz (600 mg once daily), plus lamivudine and stavudine. The primary endpoint was virological suppression at 48 weeks (HIV-1 RNA <50 copies per mL) in all patients who received at least one dose of study drug (intention-to-treat population); death and loss to follow-up were recorded as treatment failure. The non-inferiority margin for the difference of efficacy was 10%. We assessed efficacy in intention-to-treat and per-protocol populations and safety in all patients who received study drug. This study is registered with ClinicalTrials.gov, number NCT00495326. FINDINGS: Between October, 2007, and March, 2010, we enrolled 285 patients into each group. 242 (85%) patients in the nevirapine group and 233 (82%) patients in the efavirenz group completed follow-up. In the intention-to-treat population, 184 patients (64·6%, 95% CI 58·7-70·1) allocated nevirapine achieved virological suppression at week 48, as did 199 patients (69·8%, 64·1-75·1) allocated efavirenz (one-sided 95% CI of the difference of efficacy 11·7%). In the per-protocol population, 170 (70·0%, 63·8-75·7) of 243 patients allocated nevirapine achieved virological suppression at week 48, as did 194 (78·9%, 73·2-83·8) of 246 patients allocated efavirenz (one-sided 95% CI 15·4%). The median CD4 cell count at randomisation was 89 cells per μL. 15 patients substituted nevirapine with efavirenz and six patients substituted efavirenz with nevirapine. 20 patients allocated nevirapine (7%) had grade 3-4 increase of alanine aminotransferase compared with 17 patients allocated efavirenz (6%). Three patients had severe rash after receipt of nevirapine (1%) but no patients did after receipt of efavirenz. 18 patients in the nevirapine group died, as did 17 patients in the efavirenz group. INTERPRETATION: Although non-inferiority of the nevirapine-regimen was not shown, nevirapine at full dose could be a safe, acceptable alternative for patients unable to tolerate efavirenz. FUNDING: French Research Agency for HIV/AIDS and hepatitis (ANRS)

Relationship between paramacular thinning, cerebral vasculopathy, and hematological risk factors in sickle cell disease

PurposeTo identify risk factors for sickle cell maculopathy due to hematological parameters (especially anemia and hemolysis) or cerebral vasculopathy.MethodsThis retrospective study was conducted at a Referral Center. The follow-up included optical coherent tomography/optical coherent tomography angiography, neuro-radiological imaging, and a hematological assessment (hemoglobin, hemoglobin S level, reticulocytes, mean corpuscular volume, bilirubin, and lactate dehydrogenase).ResultsHundred and thirty-two sickle cell patients were included. Maculopathy was observed in 127 eyes of SS patients and 10 eyes of SC patients (p &lt; 0.001), unrelated to peripheral retinopathy. Cerebral vasculopathy was more frequent in SS patients (p &lt; 0.001) and was also associated with the presence of maculopathy (p = 0.049), and it was related to peripheral retinopathy (p &lt; 0.001). All biological parameters significantly differed according to the genotype (p &lt; 0.001) but not according to the presence of cerebral vasculopathy or maculopathy. In the multivariate analysis, reticulocytes and bilirubin were associated with the presence of cerebral vasculopathy and maculopathy.ConclusionThe data obtained were consistent with the role of anemia or hemolysis markers in cerebral vasculopathy and macular involvement. As a trend of hemolysis appears to be a risk factor for these complications, this validates the use of preventive plasmapheresis in these patients