In situ TEM study of mechanical behaviour of twinned nanoparticles

There is strong interest in studying changes in mechanical properties with reducing grain size. The rational is that consequent dislocation glide cannot be sustained, resulting in an increase in material strength. However, this comes with the cost of a reduction in ductility. It has been shown that coherent twin boundaries in nanostructured Cu improve the ductility to 14% [Lu et al., Science 324 (2009) p. 349]. In this paper, we report for the first time the compression of individual nanoparticles using an in situ force probing holder in the transmission electron microscope. Four types of nanoparticles were tested, three with twin boundaries (decahedra, icosahedra and a single twin) and one free of defects (octahedral). Our results indicate the yield strength of the twinned nanoparticles is between 0.5 and 2.0 GPa. The total malleability for the twinned particles range from 80 to 100%. In addition, experimental results were reproduced by MD simulations of the compression phenomena and suggest that the outstanding mechanical properties are related with partial dislocation multiplication at twin boundaries.     

Modeling Insurgent Dynamics Including Heterogeneity

Despite the myriad complexities inherent in human conflict, a common pattern has been identified across a wide range of modern insurgencies and terrorist campaigns involving the severity of individual events—namely an approximate power-law x ^?α with exponent α≈2.5. We recently proposed a simple toy model to explain this finding, built around the reported loose and transient nature of operational cells of insurgents or terrorists. Although it reproduces the 2.5 power-law, this toy model assumes every actor is identical. Here we generalize this toy model to incorporate individual heterogeneity while retaining the model’s analytic solvability. In the case of kinship or team rules guiding the cell dynamics, we find that this 2.5 analytic result persists—however an interesting new phase transition emerges whereby this cell distribution undergoes a transition to a phase in which the individuals become isolated and hence all the cells have spontaneously disintegrated. Apart from extending our understanding of the empirical 2.5 result for insurgencies and terrorism, this work illustrates how other statistical physics models of human grouping might usefully be generalized in order to explore the effect of diverse human social, cultural or behavioral traits.     

Mid‐ and Near‐Infrared Spectroscopic Determination of Carbon in a Diverse Set of Soils from the Brazilian National Soil Collection

Abstract

Calibrations for soil carbon content measured by combustion (total carbon, TC) and chromate oxidation by a modified Walkley‐Black method (Walkley‐Black carbon, WBC) from the Brazilian National Soil Collection were made using Fourier‐transform near (1100 to 2500 nm; NIRS) and mid‐infrared diffuse reflectance (2,500 to 25,000 nm; DRIFTS) spectroscopy combined with partial least squares (PLS). Calibration sets of sample populations of different carbon ranges, soil taxonomic classes, and soil textural groups were established. These are for TC ranges between 0.4 to 555.0, 0.4 to 99.1, and 0.4 to 39.9 g kg^?1: for WBC 0.2 to 401.0, 0.2 to 66.0, and 0.2 to 66.0, and 0.2 to 30.0 g kg^?1: for soil taxonomic classes Ferralsols and Acrisols; and for soil textural groups very clayey, clayey, and medium textures were examined. Calibrations obtained for the largest TC and WBC ranges were better compared to the lower ones, but lower root mean squared deviation (RMSD) and relative difference (RD=RMSD/mean value) were found for the lower carbon ranges. Taxonomic soil class was not an adequate criterium for calibration set formation. Soil texture had effect on calibrations, especially using NIR, because of the particle size effect to which NIR was more sensitive than mid‐IR. In general, DRIFTS showed better performance than NIRS. NIRS only outperformed DRIFTS when used with calibration set fairly homogeneous in its particle size distribution. Results demonstrated that while calibrations can be developed using either DRIFTS or NIRS for even a very diverse set of soil samples, which will determine C over a wide range of concentrations inherent in such a diverse set, it is desirable to seperate sample populations by soil textural properties and choose the adequate spectral range (NIR or mid‐IR) based on the textural group, for calibration development to achieve more accurate results.     

Synthesis,Characterization, and Antimicrobial Activity oF The Ligand 3-Methylpyrazole- 4-Carboxaldehyde Thiosemicarbazone and Its Pd(II) Complex

Abstract

The synthesis and characterization of a new palladium(II) complex [Pd(MePhPzTSC)₂] and its corresponding ligand 3-methylpyrazole-4-carboxaldehyde thiosemicarbazone (MePhPzTSC) are described. The bidentate ligand is coordinated to Pd(II) through the azomethine nitrogen atoms and sulfur in the form of thiol by deprotonation of the NH-C = S. The antimicrobial activity of these new compounds was evaluated against gram-negative (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa) and gram-positive (Staphylococcus aureus and Bacillus thuringiensis) bacteria and two yeast strains (Candida albicans and Saccharomyces cerevisiae). Coordination of the ligand to the metallic ion showed improved antimicrobial activity compared to the free ligand. For the gram-positive bacteria the antimicrobial activity of the complex was higher than that of the positive control used.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the following free supplemental files: Additional figures and tables]     

NMR‐based conformational analysis of perezone and analogues

Complete assignment of the ¹H NMR chemical shift and coupling constant values of perezone (1), O‐methylperezone (2) and 6‐hydroxyperezone (3) was carried out by total‐line‐shape‐fitting calculations using the PERCH iterative spectra analysis software (PERCH Solutions Ltd., Kuopio, Finland). The resulting simulated spectra for the three compounds showed strong similarity to their corresponding experimental spectra. Particularly, all vicinal, allylic and homoallylic coupling constant values for the side chain of the three compounds were very similar, thus revealing that the conformation of these three molecules in solution is indeed almost identical. This fact is in agreement with extended side chain conformations over folded chain conformations because 1, 2 and 3 undergo completely different intramolecular cycloaddition reactions. In addition, results of double pulsed field gradient spin echo NOESY 1D experiments performed on perezone (1) were unable to provide evidence for folded conformers. Copyright © 2013 John Wiley & Sons, Ltd.     

Finite element method applied to the quenching of steel cylinders using a multi-phase constitutive model

Heat treatment processes are usually employed to control the mechanical properties of steels and quenching is one of the most common treatments. This article deals with the modeling and simulation of quenching in steel cylinders using a multi-phase constitutive model. Finite element method is employed for spatial discretization. Numerical simulations are carried out by considering an iterative process associated with the operator split technique. Initially, a verification procedure is of concern establishing a comparison between numerical and experimental data, presenting a good agreement. Afterward, notched steel cylinders are treated evaluating the influence of notches in quenched pieces. Temperature, phase transformations and stresses are monitored during the quenching in order to give a general idea of the thermomechanical behavior of the process.     

Unfolding the role of iron in Li-ion conversion electrode materials by 57Fe M?ssbauer spectroscopy

⁵⁷Fe M?ssbauer spectroscopy is particularly useful in the study of oxide and oxalate conversion anode materials for Li-ion batteries. After reduction in lithium test cells, all these materials showed M?ssbauer spectra ascribable to iron atoms in two different environments with superparamagnetic relaxation. The spectra recorded at 12?K revealed the ferromagnetic character in agreement with particle sizes of ca. 5?nm. The two types of iron can be ascribed then to surface and core atoms. Core iron atoms play an important role to retain high faradic capacity values for a large number of cycles. These atoms are preserved from irreversible reactions with the electrolyte and hence they promote a high reversibility and rate capability.