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The effect of Nb content on the corrosion behavior of in-situ (Ti0.45Zr0.31Be0.17Cu0.07)100−xNbx (x = 4, 6, 8, 10, and 12) was evaluated in 0.5 mol/L H2SO4, 0.6 mol/L NaCl, and 1 mol/L NaOH solutions. A dual-phase microstructure which composed of an amorphous matrix and dendrites was observed. Electrochemical measurements in each corrosion medium showed the same trend. The corrosion resistance first increased and then decreased with the addition of Nb content from 4 to 12 at.%. The results show the best corrosion resistance in terms of × = 8 for the alloys. Notably, Nb addition improved the pitting-corrosion resistance of samples in a chloride-containing solution, whereas spontaneous passivation occurred in chloride-free solutions. A preferential solution was observed in the amorphous matrix region in NaCl solution, but a part of dark spots and dents appeared on the surface after the polarization in chloride-free solutions. X-ray photoelectron spectroscopic measurements showed that Nb addition promoted the formation of metal oxide on the surface film, thus inducing a superior corrosion resistance for the bulk metallic glass matrix composites.

Soil aggregation is one of the most important factors affecting soil organic carbon (SOC) stabilization, and the stability of aggregates depends in part on soil microbial diversity and composition. Interactions between the soil bacterial community and SOC content in soil aggregates after afforestation are poorly understood. In this study, we investigated difference in the diversity of soil bacterial with high-throughput 16S rRNA sequencing, as well as the SOC content in soil aggregates representing a chronosequence of 42, 27, and 17 years of Robinia pseudoacacia L. succession (RP42, RP27, and RP17), and in farmland (FL) soil for comparison (millet (Setaria italica) and soybean (Glycine max) rotation).The SOC content in RP17, RP27, and RP42 plots were significantly higher than that of FL by an average of 85.57%, 142.37%, and 76.69% in large macro-aggregates (>1 mm), small macro-aggregates (0.25–1 mm), and micro-aggregates (

Both the mass density (1.37 kgm/m 3) and sp3/sp2+sp3 bonding fraction (0.15) were determined for an unusual nanoporous amorphous carbon consisting of curved single graphitic sheets. A combination of High-Resolution Transmission Electron Microscopy (HRTEM) and Parallel Electron Energy Loss Spectroscopy (PEELS) was used. The values of these two parameters provide important constraints for the determination of the structure of this relatively low density variety of nanoporous carbon. The results are relevant also in the search for negatively-curved Schwarzite-related carbon structures. New data are also presented for Highly-Oriented Pyrollytic Graphite (HOPG), Chemically Vapour Deposited (CVD) diamond, C60, Glassy Carbon (GC) and Evaporated Amorphous Carbon (EAC); these are compared with the results for NAC. Kramers-Kronig Analysis (KKA) of the low-loss PEELS data shows that the band gaps of both NAC and EAC are collapsed relative to that of CVD diamond.

Structures in phyllotaxy are generalized using some concepts from lattice theory. A minimal lattice model is introduced to simulate the dynamics of the morphology of phyllotaxis. Numerical results indicate that the lattice divergences, which are equivalent to the divergence angle as used in phyllotaxy, converge to constant numbers for most of the growth rate and initial conditions. These numbers are associated with the noble numbers which are related to the general Fibonacci sequence. A method is developed to derive the lattice divergence as a sequence expressed in a recurrence formula. An analytical solution of the latter is obtained which reveals the convergence and asymptotic values of the sequence.

High-resolution (0.2 nm) images are used to locate chemical domains occurring with length scales of 1–5 nm in the dielectric relaxor lead magnesium niobate (PMN). The experimental HRTEM images are analysed using computer simulations and image matching in order to clarify and characterize the nature of the chemical ordering. Madelung electrostatic energy calculations are used to rank a set of structural models for possible ordered and disordered distributions of Nb and Mg over the B sites of perovskite ABO3. Next, the chemical domain textures are modelled using next-nearest-neighbour Ising (NNNI) models and Monte Carlo methods. These simulations allow us to understand and quantify the local structures of clusters of Nb and Mg atoms and how these interact to form chemical domain walls and other configurations including charged chemical defects. This results in a preferred model for the B-site distribution (the extended NNNI model), which is used for image simulations. Both HRTEM many-beam bright- and dark-field and single-beam dark-field TEM images are obtained and compared with the experimental images. The final result is a realistic atomic model for the Nb, Mg distribution of PMN.

In Douady and Couder’s experiment [Phys. Rev. Lett. 68, 2098, (1992)], spiral phyllotactic-like patterns were formed by magnetic dipoles dropped sequentially into a vertical magnetic field. The dipoles move radially with constant velocity limited by frictional forces in a silicone oil. This paper presents an analysis of the stability of this self-organized growth process using a second nearest neighbor (SNN) interaction approximation. A recurrence formula is written for the divergence angle; i.e. the angle defined by successive radial vectors. Further analysis of the dynamics reveals conditions for convergence of the recurrence formula. The limit of the divergence angle sequence includes a fractional part of 2π which is the ratio of pairs of Fibonacci numbers. It also includes a term which varies linearly with a growth parameter µ, defined in the text. The system is stable within the SNN approximation. Even richer dynamical behaviors, including that observed experimentally, require higher order approximations.

Elementary properties of spiral lattices are evaluated in reciprocal space. The relative merits of direct space object data, Fourier transforms and power spectra (diffraction patterns) are discussed and applied to the identification of the radial law for three distinct naturally-occurring spiral structures.

A convention for labelling the handedness of the generating spiral and an algorithm for determining the chirality of visible spiral structures is derived. Some applications to common natural structures, as well as some unusual cases are described.