Modification of as-cast Al-Mg/B4C composite by addition of Zr

Zirconium was used in Al-Mg/B4C composite to improve compocasting efficiency by increasing particle incorporation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results revealed that by addition of zirconium a reaction layer containing Zr, Al, B and C is formed on the interface of B4C-matrix. X-ray diffraction (XRD) analysis of extracted particles unveiled that the ZrB2 phase is the main constituent of this layer. Formation of ZrB2 is an exothermic reaction which can rise temperature locally around particles and agglomerates. Rising temperature around agglomerates in conjunction with turbulent flow of melt facilitates agglomerates wetting and dissolving into molten aluminum. As the result, final product contains more uniformly distributed B4C particles. Besides enhancing compocasting efficiency, addition of Zr and formation of reaction layer by improving particle matrix bonding quality, led to increase in ultimate tensile strength and elongation of the composite around 8% and 30%, respectively. SEM observations of the fracture surfaces confirmed that a proper bonding presents at the interface of particles and matrix in presence of Zr.Peer ReviewedPostprint (author's final draft

Autoregression as a means of assessing the strength of seasonality in a time series

BACKGROUND: The study of the seasonal variation of disease is receiving increasing attention from health researchers. Available statistical tests for seasonality typically indicate the presence or absence of statistically significant seasonality but do not provide a meaningful measure of its strength. METHODS: We propose the coefficient of determination of the autoregressive regression model fitted to the data ([Image: see text]) as a measure for quantifying the strength of the seasonality. The performance of the proposed statistic is assessed through a simulation study and using two data sets known to demonstrate statistically significant seasonality: atrial fibrillation and asthma hospitalizations in Ontario, Canada. RESULTS: The simulation results showed the power of the [Image: see text] in adequately quantifying the strength of the seasonality of the simulated observations for all models. In the atrial fibrillation and asthma datasets, while the statistical tests such as Bartlett's Kolmogorov-Smirnov (BKS) and Fisher's Kappa support statistical evidence of seasonality for both, the [Image: see text] quantifies the strength of that seasonality. Corroborating the visual evidence that asthma is more conspicuously seasonal than atrial fibrillation, the calculated [Image: see text] for atrial fibrillation indicates a weak to moderate seasonality ([Image: see text] = 0.44, 0.28 and 0.45 for both genders, males and females respectively), whereas for asthma, it indicates a strong seasonality ([Image: see text] = 0.82, 0.78 and 0.82 for both genders, male and female respectively). CONCLUSIONS: For the purposes of health services research, evidence of the statistical presence of seasonality is insufficient to determine the etiologic, clinical and policy relevance of findings. Measurement of the strength of the seasonal effect, as can be determined using the [Image: see text] technique, is also important in order to provide a robust sense of seasonality

Dynamic deformation response of Al-Mg and Al-Mg/B4C composite at elevated temperatures

The dynamic deformations at high temperatures of Al-3 wt%Mg alloy and Al-3 wt%Mg/B4C composites with different volume fractions and particle sizes were studied using a dilatometer deformation instrument and a split Hopkinson pressure bar operating at strain rates of 10–1000 1/s. A comprehensive analytical procedure was developed to correct the effects of adiabatic heating, friction at interface of the specimen and bars, and strain rate variation, on flow stress curves. Then based on corrected data, a physical based constitutive equation was developed for modeling and prediction of flow stress. It was observed that composites in comparison with single phase alloy, after initial straining, showed lower hardening rate which is unexpected. EBSD micrographs and finite element analysis were used to investigate microstructural evolution and deformation condition around particles. It was concluded that particle fracture during deformation which is more expectable in larger particles, and also higher adiabatic heating in composite and not recrystallization related phenomena, are the main reasons for softening of stress flow curves at large deformation.Peer ReviewedPostprint (author's final draft

Microstructural investigation of Al-Mg/B4C composite deformed at elevated temperature

The microstructure evolution of Al-3wt.%Mg reinforced with 10¿vol% B4C during isothermal compression at temperatures ranging 300–500¿°C at strain rates of 0.001–10 s-1 was investigated by electron backscatter diffraction (EBSD). According to the results, at strain rates lower than 0.01 s-1 and temperatures higher than 400¿°C, the grain size distribution in the microstructure is uniform, dynamic recovery is the predominant softening mechanism and continues recrystallization through lattice rotation is responsible for grain refinement. However, during deformation at higher strain rates or lower temperatures, deformation zones appeared in special locations around particles where microstructure is formed by recovered and hardened grains, and particle stimulating nucleation leaded to partially discontinues dynamic recrystallization which in turns promoted finer average grain and sub-grain size than those in single phase Al-Mg alloy. Moreover, it was found that the variation of grain and sub-grain size with deformation parameters (Zener-Holloman parameter (Z)) can be described by a power law type equation rather than by an initially expected exponential expression.Peer ReviewedPostprint (author's final draft

Time-dependent Mechanics and Lagrangian submanifolds of Dirac manifolds

A description of time-dependent Mechanics in terms of Lagrangian submanifolds of Dirac manifolds (in particular, presymplectic and Poisson manifolds) is presented. Two new Tulczyjew triples are discussed. The first one is adapted to the restricted Hamiltonian formalism and the second one is adapted to the extended Hamiltonian formalism

In-situ nanocomposite in friction stir welding of 6061-T6 aluminum alloy to AZ31 magnesium alloy

Prior to friction stir welding (FSW), silicon carbide (SiC) nanopowders were placed inside the groove on the adjacent side of magnesium sheet. In order to make a good distribution of these nanoparticles, first, friction stir processing (FSP) with a pinless tool was conducted on this side. Second, using a frustum pin tool, a combination of two travel speeds (25 and 35¿mm/min) and three rotation speeds (550, 600 and 650¿rpm) were employed to obtain the optimal conditions for FSW of AZ31 magnesium alloy to 6061 aluminum alloy. The joint fabricated at 35¿mm/min and 650¿rpm, exhibited improvement of 28% in tensile strength and enhancement about three times in elongation, compared with the joint without nanoparticles. SiC nanoparticles had an effective role on the grain refining of the stirred zone and improving the microstructural characteristics of the banded structure zone. Due to the decreased grain size and the presence of ceramic nanoparticles (SiC) with high value of hardness, the hardness level of the reinforced samples was greater than that of the non-reinforced samples. Fracture of the non-reinforced sample was completely brittle, while in the reinforced samples, fracture features changed to the ductile mode.Peer ReviewedPostprint (author's final draft

The Effects of Static and Dynamic Stretching on Postural Stability, Hip Flexibility, and Power

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Structural Characterization of the Extracellular Domain of CASPR2 and Insights into Its Association with the Novel Ligand Contactin1

Contactin-associated protein-like 2 (CNTNAP2) encodes for CASPR2, a multidomain single transmembrane protein belonging to the neurexin superfamily that has been implicated in a broad range of human phenotypes including autism and language impairment. Using a combination of biophysical techniques, including small angle x-ray scattering, single particle electron microscopy, analytical ultracentrifugation, and bio-layer interferometry, we present novel structural and functional data that relate the architecture of the extracellular domain of CASPR2 to a previously unknown ligand, Contactin1 (CNTN1). Structurally, CASPR2 is highly glycosylated and has an overall compact architecture. Functionally, we show that CASPR2 associates with micromolar affinity with CNTN1 but, under the same conditions, it does not interact with any of the other members of the contactin family. Moreover, by using dissociated hippocampal neurons we show that microbeads loaded with CASPR2, but not with a deletion mutant, co-localize with transfected CNTN1, suggesting that CNTN1 is an endogenous ligand for CASPR2. These data provide novel insights into the structure and function of CASPR2, suggesting a complex role of CASPR2 in the nervous system

Molecular metabolic response of diet-induced obese mice to a polyphenol mixture beverage based on Mediterranean Diet consumption

Podeu consultar el III Workshop anual INSA-UB complet a: http://hdl.handle.net/2445/118993Sessió 1. Pòster núm.

On the Hamilton-Jacobi Theory for Singular Lagrangian Systems

We develop a Hamilton-Jacobi theory for singular lagrangian systems using the Gotay-Nester-Hinds constraint algorithm. The procedure works even if the system has secondary constraints.Comment: 36 page