Structure of Unsupported Small Palladium Nanoparticles

A tight binding molecular dynamics calculation has been conducted to study the size and coordination dependence of bond length and bond energy of Pd atomic clusters of 1.2–5.4 nm in diameter. It has been found that the bond contraction associated with bond energy increases in the outermost layer about 0.24 nm in a radial way, yet in the core interior the bond length and the bond energy remain their corresponding bulk values. This surface bond contraction is independent of the particle size

Grain boundary precipitation induced by grain crystallographic misorientations in an extruded Al-Mg-Si-Cu alloy

The grain boundary precipitation induced by grain crystallographic misorientations in an extruded Al-Mg-Si-Cu alloy was investigated by electron back-scattering patterns and high resolution transmission electron microscopy. The results showed that compared with the recrystallization cube {1 0 0}〈0 0 1〉 texture, the deformation brass {1 1 0}〈1 1 2〉 texture prevailed in the microstructure. The brass texture mainly contributed for the formation of low angle grain boundaries, where the pre-β″/β′ phases were formed during precipitation. The recrystallization cube texture predominately induced the formation of high angle grain boundaries, where the Q′/Q phases related to the corrosion were precipitated. And, high and low grain boundary was 23.5% and 76.5% proportion in the microstructure, respectively. Finally, it was believed that in order to improve the resistance to intergranular corrosion of alloy, the recrystallization cube {1 0 0}〈0 0 1〉 texture should be inhibited as far as possible.Hunan Provincial Innovation Foundation for Postgraduate (CX2010B044), P.R. China

Quantum phase transition in magnetic nanographenes on a lead superconductor

Quantum spins, referred to the spin operator preserved by full SU(2) symmetry in the absence of the magnetic anistropy, have been proposed to host exotic interactions with superconductivity4. However, spin orbit coupling and crystal field splitting normally cause a significant magnetic anisotropy for d/f-shell spins on surfaces6,9, breaking SU(2) symmetry and fabricating the spins with Ising properties10. Recently, magnetic nanographenes have been proven to host intrinsic quantum magnetism due to their negligible spin orbital coupling and crystal field splitting. Here, we fabricate three atomically precise nanographenes with the same magnetic ground state of spin S=1/2 on Pb(111) through engineering sublattice imbalance in graphene honeycomb lattice. Scanning tunneling spectroscopy reveals the coexistence of magnetic bound states and Kondo screening in such hybridized system. Through engineering the magnetic exchange strength between the unpaired spin in nanographenes and cooper pairs, quantum phase transition from the singlet to the doublet state has been observed, in consistent with quantum models of spins on superconductors. Our work demonstrates delocalized graphene magnetism host highly tunable magnetic bound states with cooper pairs, which can be further developed to study the Majorana bound states and other rich quantum physics of low-dimensional quantum spins on superconductors.Comment: 13 pages, 4figure

Relationship between microstructure, properties and reaction conditions for Cu-TiB2 alloys prepared by in situ reaction

Three Cu-TiB2 alloys (0.45, 1.6, 2.5 wt.% TiB2) have been prepared by a combination of in situ reaction and rapid solidification under optimized conditions. The relationship between microstructure, properties and in situ reaction condition for these Cu-TiB2 alloys was investigated and analyzed by modeling. It is shown that the distribution and size of TiB2 particles are strongly dependent on the choice of in situ reaction conditions and solute concentration; specifically, the size and aggregation level of TiB2 particles tend to increase as the volume per cent of TiB2 in the three Cu-TiB2 alloys increases when the same in situ reaction conditions are used. The forming, coarsening and aggregation models of TiB2 particles are established. The mechanical properties of three Cu-TiB2 alloys are directly related to the distribution and size of TiB2 particles, the change in the grain size and the residual solute concentration. A composite model reveals the separate contributions of these parameters to the mechanical properties. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Recrystallization characteristics of a fine grained copper alloy

Recrystallization characteristics of severe cold rolled Cu-0.23 vol%Al2O3 alloy were investigated through the examination of properties and microstructure. A special change of mechanical and physical properties was observed during the annealing process, which is different from previous reports of particle-containing alloys. On the basis of metallographic, fracture observations and TEM microstructure, nature of recrystallization behavior and kinetic analysis, it was deduced that its diffusion activation energy in the nucleation process is higher than that in the growth process for the high temperature annealing. (C) 2009 Elsevier BM. All rights reserved

The safety analysis of transportation vehicles carrying prefabricated units under the action of gusts

The prefabricated-unit industry has developed rapidly and the safety of vehicles carrying prefabricated units has received extensive attention. In order to evaluate the safety of vehicles carrying prefabricated units under the action of gusts, the roughness of road surfaces was simulated by the sinusoid superposition method. Furthermore, the wind load was simulated by the harmonic synthesis method. The analysis model of the 13-DOF vehicle was established, and the wind-vehicle-road system was formed. In addition, the safety of the vehicles carrying prefabricated units under gusts was analyzed. It is demonstrated that when a vehicle encounters a sudden gust during driving, lateral deviation of the body will occur. The contact force on the windward side wheel will drop sharply and the wheel is easy to get off the ground, which decides whether a rollover accident happens or not. It sheds light on the safety analysis for ultra-wide and overweight vehicles under gust action

The safety analysis of transportation vehicles carrying prefabricated units under the action of gusts

The prefabricated-unit industry has developed rapidly and the safety of vehicles carrying prefabricated units has received extensive attention. In order to evaluate the safety of vehicles carrying prefabricated units under the action of gusts, the roughness of road surfaces was simulated by the sinusoid superposition method. Furthermore, the wind load was simulated by the harmonic synthesis method. The analysis model of the 13-DOF vehicle was established, and the wind-vehicle-road system was formed. In addition, the safety of the vehicles carrying prefabricated units under gusts was analyzed. It is demonstrated that when a vehicle encounters a sudden gust during driving, lateral deviation of the body will occur. The contact force on the windward side wheel will drop sharply and the wheel is easy to get off the ground, which decides whether a rollover accident happens or not. It sheds light on the safety analysis for ultra-wide and overweight vehicles under gust action