Magnetite and its galvanic effect on the corrosion of carbon steel under carbon dioxide environments

Carbon dioxide corrosion, which can cause premature failure of oil and gas pipelines, is an imperative health, safety and environmental issue in the oil and gas industry. Extensive studies have been conducted to understand the formation and role of iron carbonate scale, which is the most probable scale formation under CO2 corrosion. This scale can be protective toward the carbon steel pipelines. However, many post failure studies and ex-situ corrosion product scale analyses have shown the presence of thick corrosion product scale that consists mainly of black magnetite scale.The formation of magnetite scales from carbon dioxide corrosion of oil and gas carbon steel pipelines at temperatures below 100oC has not been studied or investigated comprehensively despite the fact that magnetite is often found in pipelines. The observation of rapid corrosion failures and the associated corrosion product scale on the ruptured pipelines has instigated this PhD research to determine the mechanism of the formation of corrosion product scale and the galvanic effect of the magnetite scale in causing an accelerated corrosion.Consequently, the mechanism of the formation of corrosion product scale on carbon steel under anaerobic conditions was studied. Preliminary studies on the corrosion product scales were conducted in an autoclave at 150oC. The morphology and the properties of the corrosion product scales were analysed using Raman spectroscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Ex-situ analysis showed that the scale formed in a pH 5.5 anaerobic brine solution saturated with a low partial pressure of carbon dioxide gas comprised a mixture of magnetite (Fe3O4) and iron carbonate (FeCO3). Whereas, the scale formed under the same temperature and solution pH, but in the absence of carbonate or bicarbonate species, consists only of magnetite. However, results from ex-situ analysis cannot be relied upon to conclusively prove the state of the surface in-situ. Therefore, a jet impingement cell that incorporates the capability of applying electrochemical measurements was used as an autoclave.The autoclave tests were replicated with in-situ electrochemical monitoring in the jet impingement cell to study the corrosion process and the scale development. The test temperature was set at 80oC to closely simulate the operating temperature in most oil and gas production fields. The morphology of the scales was examined under a Field Emission Scanning Electron Microscope (FESEM) since the SEM was not able to resolve nanometer structures on the surface. The FESEM clearly resolved the porous lath-like structure of chukanovite (Fe2(OH)2CO3), iron carbonate and ultrafine nanometer crystals on the scale surface formed under low partial pressure of carbon dioxide. On the other hand, the carbon steel surface, which was corroded in the absence of carbonate species at pH 5.5, was fully covered with nanometer crystalline magnetite that was only detectable under the FESEM. The identity of the iron compounds was confirmed using Synchrotron Radiation Grazing Incidence X-ray Diffraction (SR-GIXRD).An in-situ SR-GIXRD study on the corrosion of carbon steel under low partial pressure of carbon dioxide gas was carried out, incorporating EIS. This combined approach showed a strong correlation of the phase development as detected on the SR-GIXRD to the electrochemical behaviour on the impedance spectra. The development of the porous chukanovite and magnetite was found in association with a higher corrosion rate of the carbon steel before the steel was passivated by the combined corrosion product scale. Both in-situ and ex-situ studies have shown that magnetite (Fe3O4) and chukanovite (Fe2(OH)2CO3) are formed at the early stage of scale development via electrochemical and hydrolysis reactions in mildly acidic conditions before iron carbonate exceeds it solubility limit and precipitates rapidly over the carbon steel surface.The galvanic effect of coupling the magnetite to carbon steel was studied. The coupling was found to cause galvanic corrosion of the carbon steel. The cathode to anode surface area ratio of the magnetite/mild steel couple and the solution pH, inter-related to the partial pressure of carbon dioxide, were investigated and found to be contributing factors to the rate of galvanic corrosion. The galvanic corrosion was cathodically controlled by magnetite. The self corrosion rate of the carbon steel was reduced with increasing pH but the galvanic corrosion rate did not seem to be affected by the high pH. This prompted the suggestion of the possibility of magnetite itself partaking in self reduction and contributing to the galvanic current.Following the hypothesis that magnetite undergoes reductive dissolution in acidic carbon dioxide solution, studies were carried out to study on the reductive behaviour of magnetite. Cyclic voltammetry was used to investigate the reductive-oxidative behaviour of magnetite at different solution pH. The results show that magnetite does undergo reduction when it is polarized cathodically. Ferric ion in the magnetite lattice reduces to ferrous ion that can diffuse from the solid lattice in acid solution or form hydroxide compounds. The semiconductivity of magnetite was investigated using the Mott-Schottky technique, illustrating a conversion from an n-type semiconductor to a p-type semiconductor when the magnetite was reduced cathodically.In view of the galvanic effect from the magnetite scale, corrosion inhibitors that are commonly used to control carbon dioxide corrosion in the oil and gas industries were tested for their inhibition efficiency against this galvanic corrosion. Generic inhibitors as well as industrial formulated inhibitors were tested. Some inhibition was observed, but all materials failed to achieve a confidence level of at least 90% of inhibition efficiency

Factors Driving Customer Satisfaction for Shopee Malaysia

The Covid-19 pandemic caused the e-commerce adoption rate to skyrocket. Shopee Malaysia was among the few e-commerce platforms that have managed to ride the wave of the e-commerce boom in Malaysia. This study aimed to examine the factors that drive customer satisfaction for Shopee Malaysia, including customer understanding, customer service, and technology. The study used a quantitative method through an online survey. In total, 164 participants took part in this research. The results indicate that although customer understanding contributes significantly towards customer service, it does not influence customer satisfaction unless through customer service or technology. Customer service and technology are significant predictors of customer satisfaction. Additionally, technology is a strong mediator for the relationships of customer understanding and customer service with customer satisfaction. Therefore, Shopee Malaysia needs to improve the areas of its e-commerce platform technology since it significantly impacts customer satisfaction. It is hoped that Shopee Malaysia and other interested parties can benefit from the results of this study

Does segmentation always improve model performance in credit scoring?

Credit scoring allows for the credit risk assessment of bank customers. A single scoring model (scorecard) can be developed for the entire customer population, e.g. using logistic regression. However, it is often expected that segmentation, i.e. dividing the population into several groups and building separate scorecards for them, will improve the model performance. The most common statistical methods for segmentation are the two-step approaches, where logistic regression follows Classification and Regression Trees (CART) or Chi-squared Automatic Interaction Detection (CHAID) trees etc. In this research, the two-step approaches are applied as well as a new, simultaneous method, in which both segmentation and scorecards are optimised at the same time: Logistic Trees with Unbiased Selection (LOTUS). For reference purposes, a single-scorecard model is used. The above-mentioned methods are applied to the data provided by two of the major UK banks and one of the European credit bureaus. The model performance measures are then compared to examine whether there is improvement due to the segmentation methods used. It is found that segmentation does not always improve model performance in credit scoring: for none of the analysed real-world datasets, the multi-scorecard models perform considerably better than the single-scorecard ones. Moreover, in this application, there is no difference in performance between the two-step and simultaneous approache

Comprehensive translational assessment of human-induced pluripotent stem cell derived cardiomyocytes for evaluating drug-induced arrhythmias

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) hold promise for assessment of drug-induced arrhythmias and are being considered for use under the comprehensive in vitro proarrhythmia assay (CiPA). We studied the effects of 26 drugs and 3 drug combinations on 2 commercially available iPSC-CM types using high-throughput voltage-sensitive dye and microelectrode-array assays being studied for the CiPA initiative and compared the results with clinical QT prolongation and torsade de pointes (TdP) risk. Concentration-dependent analysis comparing iPSC-CMs to clinical trial results demonstrated good correlation between drug-induced rate-corrected action potential duration and field potential duration (APDc and FPDc) prolongation and clinical trial QTc prolongation. Of 20 drugs studied that exhibit clinical QTc prolongation, 17 caused APDc prolongation (16 in Cor.4U and 13 in iCell cardiomyocytes) and 16 caused FPDc prolongation (16 in Cor.4U and 10 in iCell cardiomyocytes). Of 14 drugs that cause TdP, arrhythmias occurred with 10 drugs. Lack of arrhythmic beating in iPSC-CMs for the four remaining drugs could be due to differences in relative levels of expression of individual ion channels. iPSC-CMs responded consistently to human ether-a-go-go potassium channel blocking drugs (APD prolongation and arrhythmias) and calcium channel blocking drugs (APD shortening and prevention of arrhythmias), with a more variable response to late sodium current blocking drugs. Current results confirm the potential of iPSC-CMs for proarrhythmia prediction under CiPA, where iPSC-CM results would serve as a check to ion channel and in silico modeling prediction of proarrhythmic risk. A multi-site validation study is warranted

Absorption Enhancement in Organic-Inorganic Halide Perovskite Films with Embedded Plasmonic Gold Nanoparticles

We report on the numerical analysis of solar absorption enhancement in organic-inorganic halide perovskite films embedding plasmonic gold nanoparticles. The effect of particle size and concentration is analyzed in realistic systems in which random particle location within the perovskite film and the eventual formation of dimers are also taken into account. We find a maximum integrated solar absorption enhancement of ∼10% in perovskite films of 200 nm thickness and ∼6% in 300 nm films, with spheres of radii 60 and 90 nm, respectively, in volume concentrations of around 10% in both cases. We show that the presence of dimers boosts the absorption enhancement up to ∼12% in the thinnest films considered. Absorption reinforcement arises from a double contribution of plasmonic near-field and scattering effects, whose respective weight can be discriminated and evaluated from the simulations.Peer Reviewe

Middle ear microbiome differences in indigenous Filipinos with chronic otitis media due to a duplication in the A2ML1 gene

Middle ear microbial profiles of indigenous Filipinos with chronic otitis media. All panels compare carriers with non-carriers of the A2ML1 duplication variant. Panel description: (A) ι-diversity by observed OTUs; (B) ι-diversity by the Shannon diversity index; (C) β-diversity from unweighted UniFrac principal coordinate analysis; (D) β-diversity from weighted UniFrac principal coordinate analysis. (PDF 1019 kb

A positron emission tomography imaging study to confirm target engagement in the lungs of patients with idiopathic pulmonary fibrosis following a single dose of a novel inhaled αvβ6 integrin inhibitor

© 2020 The Author(s). Background: Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disease with poor prognosis and a significant unmet medical need. This study evaluated the safety, pharmacokinetics (PK) and target engagement in the lungs, of GSK3008348, a novel inhaled alpha-v beta-6 (αvβ6) integrin inhibitor, in participants with IPF. Methods: This was a phase 1b, randomised, double-blind (sponsor unblind) study, conducted in the UK (two clinical sites, one imaging unit) between June 2017 and July 2018 (NCT03069989). Participants with a definite or probable diagnosis of IPF received a single nebulised dose of 1000 mcg GSK3008348 or placebo (ratio 5:2) in two dosing periods. In period 1, safety and PK assessments were performed up to 24 h post-dose; in period 2, after a 7-day to 28-day washout, participants underwent a total of three positron emission tomography (PET) scans: Baseline, Day 1 (~ 30 min post-dosing) and Day 2 (~ 24 h post-dosing), using a radiolabelled αvβ6-specific ligand, [18F]FB-A20FMDV2. The primary endpoint was whole lung volume of distribution (VT), not corrected for air volume, at ~ 30 min post-dose compared with pre-dose. The study success criterion, determined using Bayesian analysis, was a posterior probability (true % reduction in VT > 0%) of ≥80%. Results: Eight participants with IPF were enrolled and seven completed the study. Adjusted posterior median reduction in uncorrected VT at ~ 30 min after GSK3008348 inhalation was 20% (95% CrI:-9 to 42%). The posterior probability that the true % reduction in VT > 0% was 93%. GSK3008348 was well tolerated with no reports of serious adverse events or clinically significant abnormalities that were attributable to study treatment. PK was successfully characterised showing rapid absorption followed by a multiphasic elimination. Conclusions: This study demonstrated engagement of the αvβ6 integrin target in the lung following nebulised dosing with GSK3008348 to participants with IPF. To the best of our knowledge this is the first time a target-specific PET radioligand has been used to assess target engagement in the lung, not least for an inhaled drug. Trial registration: Clinicaltrials.gov: NCT03069989; date of registration: 3 March 2017

Ribosomal DNA copy loss and repeat instability in ATRX-mutated cancers

ATRX (alpha thalassemia/mental retardation X-linked) complexes with DAXX to deposit histone variant H3.3 into repetitive heterochromatin. Recent genome sequencing studies in cancers have revealed mutations in ATRX and their association with ALT (alternative lengthening of telomeres) activation. Here we report depletion of ATRX in mouse ES cells leads to selective loss in ribosomal RNA gene (rDNA) copy number. Supporting this, ATRX-mutated human ALT-positive tumors also show a substantially lower rDNA copy than ALT-negative tumors. Further investigation shows that the rDNA copy loss and repeat instability are caused by a disruption in H3.3 deposition and thus a failure in heterochromatin formation at rDNA repeats in the absence of ATRX. We also find that ATRX-depleted cells are reduced in ribosomal RNA transcription output and show increased sensitivity to RNA polymerase I (Pol I) transcription inhibitor CX5461. In addition, human ALT-positive cancer cell lines are also more sensitive to CX5461 treatment. Our study provides insights into the contribution of ATRX loss of function to tumorigenesis through the loss of rDNA stability and suggests the therapeutic potential of targeting Pol I transcription in ALT cancers.This work was supported by the Norwegian Cancer Society and the Research Council of Norway (to P.C.); an Australia Research Council Future Fellowship award (to L.H.W.); National Health and Medical Research Council Program Grant 1053792 (to R.B.P. and R.D.H.), senior research fellowships (to R.B.P. and R.D.H.), and a project grant (to L.H.W.); and a Cure Brain Cancer Foundation Australia project grant (to L.H.W. and H.P.J.V.)

The changing seroepidemiology of enterovirus 71 infection among children and adolescents in Singapore

<p>Abstract</p> <p>Background</p> <p>Enterovirus 71 (EV71) has caused recurrent epidemics of hand, foot and mouth disease among children in Singapore. Between August 2008 and July 2010, we conducted a survey to estimate the seroprevalence of EV71 infection among children and adolescents aged 1-17 years. We compared our EV71 seroepidemiologic findings with a previous study conducted in 1996-1997.</p> <p>Methods</p> <p>The survey involved the prospective collection of 1,200 residual sera from Singapore residents aged 1-17 years in two hospitals. Neutralizing antibodies to EV71 were detected by the microneutralization test. The geometric mean titer (GMT) of EV71 antibodies and 95% confidence intervals (CI) were calculated and compared by age groups. Statistical significance was taken as <it>P </it>< 0.05.</p> <p>Results</p> <p>The overall EV71 antibody prevalence was 26.9% (95% CI: 24.5-29.5%). It increased significantly from 14.3% in children aged 1-6 years to 27.8% in those aged 7-12 years, and reached 38.8% in adolescents aged 13-17 years. The seroconversion rate differed by about 12% between the consecutive age groups. The GMT of EV71 antibodies was higher among primary school children aged 7-12 years in our study than that among the 6-12 year age group in the 1996-1997 study.</p> <p>Conclusions</p> <p>Higher antibody titers were observed in children aged 1-6 years than those in the other two age groups, indicating that most of the infections had been acquired during early childhood. EV71 infection is common among children and adolescents in Singapore, with 39% infected by the time they are in secondary school (13-17 years of age).</p