In vivo assessment of the corrosion of nickel–titanium orthodontic archwires by using scanning electron microscopy and atomic force microscopy

This study was undertaken to assess in vivo the corrosion in two commercial nickel–titanium (NiTi) orthodontic archwires removed from the oral cavity of patients using fluoride mouthwashes. Five volunteers took part in this study on the corrosion behavior of two brands of NiTi archwires (3M and AO (brand of archwire)) during use of two mouthwashes with neutral sodium fluoride 1.1%, one with acidulated fluoride 1.1%, and one with placebo and a control group. Each patient used one mouthwash in three different periods of time for 1 min a day for 30 days. The archwires were assessed with scanning electron microscopy and atomic force microscopy for qualitative and quantitative analysis. The values obtained with atomic force microscopy (AFM) were submitted to normality test, two‐way analysis of variance, and Tukey's test at a significance level of 5%. The AFM images showed a gradual qualitative increase in the roughness of both types of wire between the treatments: control < placebo < neutral fluoride < acidulated fluoride. The arithmetic average of the roughness and root mean square of the roughness were similar. As for 3M archwires, only the acidulated fluoride group differed statistically from the others. As for AO archwires, the control and placebo groups did not differ from each other, but differed from the other fluoride treatments. The group using neutral fluoride also differed significantly from the acidulated fluoride group. 3M archwires were not affected by daily oral challenges. AO archwires were not affected by daily oral challenges either; their association with fluoride, either neutral or acidulated, increased their roughness.     

Analysis of high voltage step-up nonisolated DC–DC boost converters

A high voltage step-up nonisolated DC–DC converter based on coupled inductors suitable to photovoltaic (PV) systems applications is proposed in this paper. Considering that numerous approaches exist to extend the voltage conversion ratio of DC–DC converters that do not use transformers, a detailed comparison is also presented among the proposed converter and other popular topologies such as the conventional boost converter and the quadratic boost converter. The qualitative analysis of the coupled-inductor-based topology is developed so that a design procedure can be obtained, from which an experimental prototype is implemented to validate the theoretical assumptions.     

MIL-100(Fe) Sub-Micrometric Capsules as a Dual Drug Delivery System

Nanoparticles of metal–organic frameworks (MOF NPs) are crystalline hybrid micro- or mesoporous nanomaterials that show great promise in biomedicine due to their significant drug loading ability and controlled release. Herein, we develop porous capsules from aggregate of nanoparticles of the iron carboxylate MIL-100(Fe) through a low-temperature spray-drying route. This enables the concomitant one-pot encapsulation of high loading of an antitumor drug, methotrexate, within the pores of the MOF NPs, and the collagenase enzyme (COL), inside the inter-particular mesoporous cavities, upon the formation of the capsule, enhancing tumor treatment. This association provides better control of the release of the active moieties, MTX and collagenase, in simulated body fluid conditions in comparison with the bare MOF NPs. In addition, the loaded MIL-100 capsules present, against the A-375 cancer cell line, selective toxicity nine times higher than for the normal HaCaT cells, suggesting that MTX@COL@MIL-100 capsules may have potential application in the selective treatment of cancer cells. We highlight that an appropriate level of collagenase activity remained after encapsulation using the spray dryer equipment. Therefore, this work describes a novel application of MOF-based capsules as a dual drug delivery system for cancer treatment.     

Anti‐Oxygen Leaking LiCoO2

LiCoO₂ is a prime example of widely used cathodes that suffer from the structural/thermal instability issues that lead to the release of their lattice oxygen under nonequilibrium conditions and safety concerns in Li‐ion batteries. Here, it is shown that an atomically thin layer of reduced graphene oxide can suppress oxygen release from Li_xCoO₂ particles and improve their structural stability. Electrochemical cycling, differential electrochemical mass spectroscopy, differential scanning calorimetry, and in situ heating transmission electron microscopy are performed to characterize the effectiveness of the graphene‐coating on the abusive tolerance of Li_xCoO₂. Electrochemical cycling mass spectroscopy results suggest that oxygen release is hindered at high cutoff voltage cycling when the cathode is coated with reduced graphene oxide. Thermal analysis, in situ heating transmission electron microscopy, and electron energy loss spectroscopy results show that the reduction of Co species from the graphene‐coated samples is delayed when compared with bare cathodes. Finally, density functional theory and ab initio molecular dynamics calculations show that the rGO layers could suppress O₂ formation more effectively due to the strong C? O_cathode bond formation at the interface of rGO/LCO where low coordination oxygens exist. This investigation uncovers a reliable approach for hindering the oxygen release reaction and improving the thermal stability of battery cathodes.     

Thermo-Metallurgical Modeling of Nodular Cast Iron Cooling Process

A new numerical model to describe the microstructural evolution of a eutectic nodular cast iron during its cooling is presented. In particular, equiaxial solidification assuming an independent nucleation of austenite and graphite nodules is considered. In this context, the austenite has dendritic growth whereas the graphite grows with a spherical shape. After solidification occurs, the model assumes that the graphite nodules present in the cast iron continue growing since the carbon content in austenite decreases. Once the stable eutectoid temperature is reached, the alloy undergoes the austenite-ferrite transformation. The nucleation of the ferrite takes place at the contour of the spherical graphite nodules where austenite has low carbon concentration. A ferrite shell surrounding the graphite nodules is formed afterward by means of a process governed by carbon diffusion. Then, a ferrite-pearlite competitive transformation occurs when the temperature is below the metastable temperature. This thermo-metallurgical model is discretized and solved by means of the finite element method. The model allows the computation of cooling curves, fraction evolution for each component, and size and distribution of graphite nodules. The present numerical results are compared with experiments using standardized Quick-cup-type cups, and satisfactory numerical predictions of the final microstructure and cooling curves are achieved.     

Photophysics of polyaniline: Sequence-length distribution dependence of photoluminescence quenching as studied by fluorescence measurements and Monte Carlo simulations

The dependence of the fluorescence quenching of electropolymerized poly(aniline-co-m-chloroaniline) with polymer composition has been investigated. Fluorescence emission in polyaniline is quenched when the polymer is oxidized (brought to emeraldine state); the copolymers exhibit decreasing quenching as chloroaniline contents increases. Quenching shows a strong decrease in the presence of 0.1% m-chloroaniline monomers in the feed. The presence of dichloroaniline units in the copolymer was confirmed by XPS measurements and a terpolymerization reaction scheme was developed, obtaining the kinetic parameters. By Monte Carlo simulation the sequence length distributions for different compositions were obtained and compared; it was found that quenching, for low aniline contents, requires aniline sequences of at least three units. The strong decrease in quenching at low m-chloroaniline contents is attributed to a double effect: breaking of conjugation in the emeraldine form by the presence of the chlorinated unit, and a disruption of the close chain packing in the crystalline domains, preventing state delocalization and thus efficient quenching.     

Comparative study between large-scale and small-scale electrochemical potentiokinetic reactivation performed on AISI 316L austenitic stainless steel

This work optimizes the application of electrochemical potentiokinetic reactivation (EPR) to assess the degree of sensitization (DOS) of AISI 316L and compares the large-scale and small-scale EPR with the aim of improving the study of the different zones of AISI 316L welded joints by using an electrochemical minicell. The optimized EPR allows to discriminate better than the standardized EPR among different DOS. Small-scale EPR shows greater sensitivity to assess the DOS than large-scale EPR: (i) at lower deformation levels; (ii) for shorter sensitization times; (iii) when localized microstructural regeneration is caused by the combined effect of deformation and subsequent sensitization.