Analyses of oxide films grown on AISI 304L stainless steel and Incoloy 800HT exposed to supercritical water environment

Supercritical water (SCW) is being considered as a cooling medium for the next generation nuclear reactors because it provides high thermal efficiency and plant simplification. However, materials corrosion has been identified as a critical problem due to the oxidative nature of supercritical water. Thus, for safety using of these nuclear reactor systems a systematic study of candidate materials corrosion is needed. As in other high temperature environments, corrosion in SCW occurs by the growth of an oxide layer on the materials surface. The current work aims to evaluate oxidation behavior of AISI 304L SS and Incoloy 800HT in water at supercritical temperatures in the range 723-873 K under a pressure of 25 MPa for up to 1680 h. After exposure to deaerated supercritical water, the samples were investigated using gravimetry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). Oxide films grown on these materials have a layered structure with an outer layer consisting of a mixture of iron oxide/iron-nickel spinel oxides and an inner layer consisting of chromium oxide in the case of Incoloy 800HT and nickel-chromium spinel oxide in the case of AISI 304L SS. The mass gains for Incoloy 800HT at all temperatures were small, while comparatively with AISI 304L SS which exhibited higher oxidation rates. In the same time the results obtained by EIS indicate the best corrosion resistance of oxides grown on Incoloy 800HT surface.     

Optical properties of titanium oxide films obtained by cathodic arc plasma deposition

Structural and optical properties of nanometric titanium oxide(TixOy) films obtained by cathodic arc plasma deposition were investigated. Phase analysis by x-ray diffraction and Fouriertransform infrared spectroscopy showed the presence of anatase, rutile, Ti_2O_3, Ti_4O_7 and amorphous phases. Scanning electron microscopy images showed well-developed surface morphology with nano-patterns. Spectroscopic ellipsometry revealed film thicknesses of 53 and50 nm, variable refractive indices dependent on the light wavelength and close to zero extinction coefficients for wavelengths higher than 500 nm. On the basis of ultraviolet–visible spectroscopy data and using the Tauc equation, band gap values for direct and indirect electron transitions were determined.     

Comparative study of natural carob fibre and psyllium husk in rats. Influence on some aspects of nutritional utilisation and lipidaemia

The effects of the addition of 100 g kg⁻¹ of psyllium husk (PSY), cellulose (CEL) or natural carob fibre (NCF) to a semi‐synthetic diet on fat (FD) and nitrogen (NF) digestibility coefficients, metabolic nitrogen utilisation (MNU), net nitrogen utilisation (NNU) and total serum cholesterol and triglyceride levels, were studied in male ‘Wistar’ rats. No significant differences were observed between the three fibres with respect to the weight increase of the animals or MNU. Significant differences were recorded for the FD of the NCF group (0.91±0.01) compared to the CEL group (0.95±0.01), as well as on ND (0.88±0.00 NCF group, 0.88±0.00 PSY group and 0.95±0.00 CEL group) and NNU. None of these indexes showed differences between the groups PSY and NCF. For the serum cholesterol levels, there were no significant differences between the non‐hypercholesterolaemic groups fed PSY, CEL or NCF; in those in which hypercholesterolaemia was induced (cholesterol and bile bovine 8.3 g kg⁻¹), significantly lower values were found in the NCF group (166±17 mg dl⁻¹ ) than in the PSY group (343±61 mg dl ⁻¹) and in the CEL group (386±48 mg dl⁻¹). © 1999 Society of Chemical Industry     

Theoretical study of a catalytic mechanism using cyclic and derivative chronopotentiometric techniques with spherical electrodes

A general analytical solution for a pseudo-first order catalytic process in chronopotentiometric techniques (reversal chronopotentiometry, cyclic chronopotentiometry and reciprocal derivative chronopotentiometry) when using spherical electrodes of any size is presented. The evolution from transient to stationary potential-time responses, characterized by the disappearance of the periodical signal in the neighbourhood of the steady state, is analyzed in cyclic and reversal chronopotentiometry. From reversal potential-time responses, the reciprocal derivative dt^1/2/dE-E curves - which are more sensitive than traditional dt/dE-E curves - have been obtained. The characteristic peaks presented by the dt^1/2/dE-E curves are quantitatively related to the rate constants of the chemical reaction and show a very different behaviour in catalytic and EC processes, allowing the easy discrimination between both mechanisms. Several types of working curves have been proposed to obtain the rate constants of the chemical reaction in a catalytic process.     

An unexpected sulfinate–sulfonate mixed coordination polymer of copper(II)

By reaction of copper nitrate trihydrate and 2,2′-dipyridyldisulfide in both aerobic and anaerobic conditions, the mixed [{Cu(2-pySO₂)₂}_n]–[{Cu(2-pySO₃)₂}_n] coordination polymer of copper(II) (1) has been synthesized. The X-ray diffraction analysis indicates that complex 1 exhibits an infinite one-dimensional polymeric chain consisting of [Cu(C₅H₄N)₂] building units connected by SO₂/SO₃ groups. The atom which has been labelled O3 is only present in 60% of the molecules. Complex 1 exhibits a very weak ferrogmagnetic spin coupling (zJ = +0.40 cm⁻¹).     

Sentiment analysis and Twitter: a game proposal

Pervasive sensing of people’s opinions is becoming critical in strategic decision processes, as it may be helpful in identifying problems and strengthening strategies. A recent research trend is to understand users’ opinions through a sentiment analysis of contents published in the Twitter platform. This approach involves two challenges: the large volume of available data and the large variety of used languages combined with the brevity of texts. The former makes manual analysis unreasonable, whereas the latter complicates any type of automatic analysis. Since sentiment analysis is a difficult process for computers, but it is quite simple for humans, in this article, we transform the sentiment analysis process into a game. Indeed, we consider the game with a purpose approach and we propose a game that involves users in classifying the polarity (e.g., positive, negative, neutral) and the sentiment (e.g., joy, surprise, sadness) of tweets. To evaluate the proposal, we used a dataset of 52,877 tweets, we developed a Web-based game, we invited people to play the game, and we validated the results through two different methods: ground-truth and manual assessment. The obtained results showed that the game approach is effective in measuring people’ sentiments and also highlighted that participants liked to play the game.     

Natural perception in dynamic stereoscopic augmented reality environments

Notwithstanding the recent diffusion of the stereoscopic 3D technologies for the development of powerful human computer interaction systems based on augmented reality environment, with the conventional approaches an observer freely moving in front of a 3D display could experience a misperception of the depth and of the shape of virtual objects. Such distortions can cause eye fatigue and stress for entertainment applications, and they can have serious consequences in scientific and medical fields, where a veridical perception of the scene layout is required. We propose a novel technique to obtain augmented reality systems capable to correctly render 3D virtual objects to an observer that changes his/her position in the real world and acts in the virtual scenario. By tracking the positions of the observer’s eyes, the proposed technique generates the correct virtual view points through asymmetric frustums, thus obtaining the correct left and right projections on the screen. The natural perception of the scene layout is assessed through three experimental sessions with several observers.     

Artificial intelligence models to stratify cardiovascular risk in incident hemodialysis patients

End stage renal disease condition increases the risk of cardiovascular disease. The mortality rates among hemodialysis patients are 20% higher than the general population, thus in recent years the preservation of the cardiovascular system has become a major point of focus for nephrology care in patients. Cardiovascular events jeopardize the life of a dialysis patient and must therefore be prevented. The aim of this study is to develop forecast models that can predict the cardiovascular outcome of incident hemodialysis (HD) patients. Data relating to the treatment methods and the physiological condition of patients was collected during the first 18 months of renal replacement therapy and then used to predict the insurgence of cardiovascular events within a 6-month time window. Information regarding 4246 incident hemodialysis patients was collected. A Lasso logistic regression model and a random forest model were developed and used for predictive comparison. Every forecast model was tested on 20% of the data and a 5-fold cross validation approach was used to validate the random forest model. Random forest showed higher performance with AUC of the ROC curve and sensitivity higher than 70% in both the temporal windows models, proving that random forests are able to exploit non-linear patterns retrieved in the feature space. Out of bag estimates of variable importance and regression coefficients were used to gain insight into the models implemented. We found out that malnutrition and an inflammatory condition strongly influence cardiovascular outcome in incident HD patients. Indeed the most important variables in the model were blood test variables such as the total protein content, percentage value of albumin, total protein content, creatinine and C reactive protein. Age of patients and weight loss in the first six months of renal replacement therapy were also highly involved in the prediction. A greater understanding of the mechanisms involved in the insurgence of cardiovascular events in dialysis patients can ensure physicians to intervene in the appropriate manner when a high-risk cardiovascular condition is identified.     

Approximation algorithms for a hierarchically structured bin packing problem

In this paper we study a variant of the bin packing problem in which the items to be packed are structured as the leaves of a tree. The problem is motivated by document organization and retrieval. We show that the problem is NP-hard and we give approximation algorithms for the general case and for the particular case in which all the items have the same size.