Search

We critically examined the performance of probabilistic streamflow forecasting in the prediction of flood events in 19 subbasins of the Doce River in Brazil using the Eta (4 members, 5 km spatial resolution) and European Centre for Medium‐Range Weather Forecasts (ECMWF; 51 members, 32 km resolution) weather forecast models as inputs for the MHD‐INPE hydrological model. We observed that the shapes and orientations of subbasins influenced the predictability of floods due to the orientation of rainfall events. Streamflow forecasts that use the ECMWF data as input showed higher skill scores than those that used the Eta model for subbasins with drainage areas larger than 20,000 km2. Since the skill scores were similar for both models in smaller subbasins, we concluded that the grid size of the weather model could be important for smaller catchments, while the number of members was crucial for larger scales. We also evaluated the performance of probabilistic streamflow forecasting for the severe flood event of late 2013 through a comparison of observations and streamflow estimations derived from interpolated rainfall fields. In many cases, the mean of the ensemble outperformed the streamflow estimations from the interpolated rainfall because the spatial structure of a rainfall event is better captured by weather forecast models. [ABSTRACT FROM AUTHOR]

Abstract: Composite materials allow one to associate fragile and ductile phases in order to obtain a good combination of properties. In situ composites obtained through eutectic transformation may present a combination of phases under a condition of equilibrium. Samples of the eutectic Ni–Ni3Si alloy were arc-melted and characterized in the as cast and directionally solidified (DS) conditions. The as cast microstructure was refined and uniform, while the DS microstructure was aligned in the direction of heat extraction and presented a plane solid/liquid interface. The alloy displayed an interesting combination of relatively high strength and tensile ductility at room temperature (3.7% total strain; UTS=810MPa), and a modulus of elasticity E =264MPa. High temperature tests showed that the yield strength decreased almost linearly as the temperature rose. No brittle to ductile transition temperature was found. [Copyright &y& Elsevier]

Presenting high fracture toughness is a decisive condition to any structural material, and when considering brittle alloys, the Vickers indentation method to determine fracture toughness is an interesting alternative. Like many other intermetallics, the Al3Nb–Nb2Al eutectic alloy shows high strength at high temperatures and low fracture toughness at room temperature. Al3Nb–Nb2Al samples, both in the as-solidified condition and in the directionally solidified condition, had their hardness and fracture toughness determined by the Vickers indentation method. Lower values of hardness were found when higher loads were used, and fracture toughness was found to be about 2.0 MPa m1/2. The as-solidified condition is harder and less tough, and when fracture occurs, cracks always develop by cleavage. [Copyright &y& Elsevier]

Abstract: The aim of this work is to present correlations between Vickers indentation cracks and fracture toughness of an Al3Nb+Nb2Al+AlNbNi in situ composite. Correlations between the resulting crack parameters and indentation load suggested that the radial-median model resulted in a better fit to the experimental data. The hardness value was found to change according to the indentation load applied. Low indentation loads resulted in high hardness values, while the application of higher loads decreased the hardness. Experimental results indicate that Vickers hardness varied from 8.6 to 9.5GPa, which is due to the indentation size effect (ISE). Fracture toughness was calculated based on several models and the results were found to vary in a broad range of values. The fracture toughness obtained from Vickers indentation was in the order of 1.65–2.26MPam1/2. [Copyright &y& Elsevier]

Abstract: The eutectic alloy Al3(Nb,Cr)+Cr(Al,Nb) forms an in situ composite and the Al3Nb presents high specific strength and low oxidation rate that may be improved by the combination with other phases. The purpose of this work is to investigate physical, mechanical and oxidation properties of the eutectic alloy. Therefore, Rietveld analysis was carried out for furnace cooled and water quenched samples and oxidation tests were performed on directional solidified samples. Compressive tests were performed for the eutectic alloy and also for the Nb–74.8% Cr–24.6% Al alloy in the as-cast condition. The alloy presents 12.9% Cr(Al,Nb) at room temperature, retained from the transformation Cr(Al,Nb) to Al(Nb)Cr2. The combination of Al3Nb with Cr(Al,Nb) and Al(Nb)Cr2 considerably improves mechanical behaviour, leading the yield strength to 1525MPa at 800°C and 925MPa at 900°C. The oxidation tests showed the formation of several oxides at all temperatures studied and that from 900°C on alfa Al2O3 is formed both in air and O2 except under O2 at 1000°C. It is believed that the Cr(Al,Nb) phase acts as an Al reservoir for the formation of the various Al2O3 scales. [Copyright &y& Elsevier]

Abstract: The system Nb–Cr–Al was investigated in the region near the Al3(Nb,Cr)+Cr(Al,Nb) eutectic and the liquidus projection of that region was determined based on the microstructural characterization of arc melted alloys. The characterization utilized scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and X-ray diffraction (XRD). The results allowed one to determine three primary solidification liquidus surfaces ((Cr,Al)2Nb, Cr(Al,Nb) and Al3(Nb,Cr)), that are originated from the binary systems Cr–Nb, Cr–Al and Al–Nb. It is proposed the occurrence of the invariant reaction L+(Cr,Al)2Nb⇆Al3(Nb,Cr)+Cr(Al,Nb) and of a point of minimum, which involves a three phase reaction, L⇆Al3(Nb,Cr)+Cr(Al,Nb). All alloys studied showed formation of the Al3(Nb,Cr)+Cr(Al,Nb) eutectic as the last solidification step with Al(Nb)Cr2 precipitating from Cr(Al,Nb). [Copyright &y& Elsevier]

Abstract: An attractive alternative method for the manufacture of high temperature structural materials may be achieved from a eutectic transformation found in the Fe–Al–Nb system, which generates the (Fe, Al)2Nb and (Fe, Al, Nb)ss solid phases. Eutectic and off-eutectic samples from the Fe–Al–Nb system were prepared by arc melting under argon atmosphere, which were subsequently directionally solidified using a vertical Bridgman crystal growth unit. The ingots obtained were investigated using optical and electron scanning microscopy with the purpose to evaluate the effect of the growth condition on the microstructure. Primarily, the growth mode of the (Fe, Al)2Nb/(Fe, Al, Nb) eutectic was considered by examining off-eutectic samples. The solidification experiments carried out under different conditions revealed that the microstructure of this system is very sensitive to a growth rate variation. At a low growth rate, the eutectic microstructure was regular, even though several types of defects were found. As the growth rate was increased, a transition from lamellar to fibrous morphology was observed. Some aspects of this transition were also evaluated. [Copyright &y& Elsevier]

Abstract: In situ composite materials obtained by directional growth of eutectic alloys usually show improved properties, that make them potential candidates for high temperature applications. The eutectic alloy found in the Al–Nb system is composed of the two intermetallic phases Al3Nb (D022) and Nb2Al (D8b). This paper describes the directional solidification of an Al–Nb eutectic alloy using a Bridgman type facility at growth rates varying from 1.0 to 2.9 cm/h. Longitudinal and transverse sections of grown samples were characterized regarding the solidification microstructure by using optical and scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-ray diffraction. Despite both phases being intermetallic compounds, the eutectic microstructure obtained was very regular. The results obtained were discussed regarding the effect of the growth rate on the microstructure, lamellar–rod transition and variation of phase volume fraction. [Copyright &y& Elsevier]

A little-studied p-type ternary oxide semiconductor, copper(I) tungstate (Cu 2 WO 4 ), was assessed by a combined theoretical/experimental approach. A detailed computational study was performed to solve the long-standing debate on the space group of Cu 2 WO 4 , which was determined to be triclinic P 1. Cu 2 WO 4 was synthesized by a time-efficient, arc-melting method, and the crystalline reddish particulate product showed broad-band absorption in the UV-visible spectral region, thermal stability up to ∼260 °C, and cathodic photoelectrochemical activity. Controlled thermal oxidation of copper from the Cu(I) to Cu(II) oxidation state showed that the crystal lattice could accommodate Cu 2+ cations up to ∼260 °C, beyond which the compound was converted to CuO and CuWO 4 . This process was monitored by powder X-ray diffraction and X-ray photoelectron spectroscopy. The electronic band structure of Cu 2 WO 4 was contrasted with that of the Cu(II) counterpart, CuWO 4 using spin-polarized density functional theory (DFT). Finally, the compound Cu 2 WO 4 was determined to have a high-lying (negative potential) conduction band edge underlining its promise for driving energetic photoredox reactions.

In this study, we explored the Ti-Nb-Fe system to find an optimal cost-effective composition with the lowest elastic modulus and the lowest added Nb content. Six Ti-(31-4x)Nb-(1+0.5x)Fe ingots were prepared and Nb was substituted with Fe, starting at Ti-31Nb-1.0Fe and going up to Ti-11Nb-3.5Fe (wt%). The ingots were subjected to cold rolling, recrystallization and solution treatment, followed by water-quenching (WQ), furnace cooling (FC) or step-quenching to 350°C, which caused massive formation of isothermal ω phase. All the water-quenched alloys displayed athermal ω phase, which is apparently the result of fully collapsed β phase. The Fe content improved the compressive strength of the alloys. In the FC alloys, substitution with Fe favored the formation of α phase instead of ω phase, giving rise to a solute-rich β phase with a lattice parameter of 0.3249nm. Among the FC alloys, the lowest modulus of 83±4GPa was obtained in the Ti-19Nb-2.5Fe alloy, which exhibited fine and well dispersed α precipitation and absence of ω phase. DSC experiments indicated that the experimental alloys showed varying phase stability during heating., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

β-type Ti alloys containing Nb are exciting materials for numerous orthopedic and dental applications due to their exceptional mechanical properties. To improve their cytocompatibility properties (such as increasing bone growth and decreasing infection), the surfaces of such materials can be optimized by adding elements and/or nanotexturing through anodization. Because of the increasing prevalence of orthopedic implant infections, the objective of this in vitro study was to add Sn and create unique nanoscale surface features on β-type Ti alloys. Nanotubes and nanofeatures on Ti-35Nb and Ti-35Nb-4Sn alloys were created by anodization in a HF-based electrolyte and then heat treated in a furnace to promote amorphous structures and phases such as anatase, a mixture of anatase-rutile, and rutile. Samples were characterized by SEM, which indicated different morphologies dependent on the oxide content and method of modification. XPS experiments identified the oxide content which resulted in a phase transformation in the oxide layer formed onto Ti-35Nb and Ti-35Nb-4Sn alloys. Most importantly, regardless of the resulting nanostructures (nanotubes or nanofeatures) and crystalline phase, this study showed for the first time that adding Sn to β-type Ti alloys strongly decreased the adhesion of Staphylococcus aureus (S. aureus; a bacteria which commonly infects orthopedic implants leading to their failure). Thus, this study demonstrated that β-type Ti alloys with Nb and Sn have great promise to improve numerous orthopedic applications where infection may be a concern., (© 2015 Wiley Periodicals, Inc.)

The correlation between the composition, aging heat treatments, microstructural features and mechanical properties of β Ti alloys is of primary significance because it is the foundation for developing and improving new Ti alloys for orthopedic biomaterials. However, in the case of Ti-Mo alloys, this correlation is not fully described in the literature. Therefore, the purpose of this study was to experimentally investigate the effect of composition and aging heat treatments on the microstructure, Vickers hardness and elastic modulus of Ti-Mo alloys. These alloys were solution heat-treated and water-quenched, after which their response to aging heat treatments was investigated. Their microstructure, Vickers hardness and elastic modulus were evaluated, and the results allow us to conclude that stabilization of the β phase is achieved with nearly 10% Mo when a very high cooling rate is applied. Young's modulus was found to be more sensitive to phase variations than hardness. In all of the compositions, the highest hardness values were achieved by aging at 723K, which was attributed to the precipitation of α and ω phases. All of the compositions aged at 573K, 623K and 723K showed overaging within 80h., (© 2013 Published by Elsevier Ltd.)

beta-Ti alloys are highly attractive metallic materials for biomedical applications due to their high specific strength, high corrosion resistance and excellent biocompatibility, including low elastic modulus. This work aims to clarify the hardening mechanism of a beta-Ti-Nb-Zr-Ta alloy using different characterization techniques. Ingots (50 g) of Ti-35Nb-7Zr-5Ta (wt.%) alloy were arc furnace melted in an Ar((g)) atmosphere, homogenized, hot rolled, solubilized and finally aged at several temperatures from 200 to 700 degrees C for 4 h. Microstructure characterization was performed using X-ray diffraction, optical microscopy, scanning and high resolution transmission electron microscopy (HR-TEM). The 4 h aging showed that the highest hardness values were found when aged at 400 degrees C and the HR-TEM images confirmed splitting of spots on the Fourier space map, which indicated the presence of a coherent interface between separated phases (beta and beta') and explains the hardening mechanism of the alloy. Through geometric phase analysis analysis, using the HR-TEM image, the localized strain map showed 5-10 nm domains of the beta and beta' phases. The combination of suitable values of yield strength, hardness and low Young's modulus makes Ti-35Nb-7Zr-5Ta alloy suitable for medical applications as a metallic orthopedic implant., (Copyright 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Trying to find out the clinical elements that define the precise indication ofr a jejunal biopsy, 28 children with several pathological conditions were studied. They were 12 cases of kwashiorkor, 11 cases with chronic diarrhea, two cases of chronic pancreatitis, 2 cases with ferropenic anemia resistant to the oral treatment with iron and one case of chilous ascitis. It is concluded that only in those cases in which the biopsy is the precise medium for diagnosis is where it would be indicated, such as intestinal lymphangiectasis or in those cases with signs or evidence of malabsorption without diarrhea. The chronic diarrhea per se does not seem to be a formal indication for biopsy.