Response of a Two-Degree-of-Freedom Vibration System with Rough Contact Interfaces

This paper is focused on the influence of the rough contact interfaces on the dynamics of a coupled mechanical system. For this purpose, a two-degree-of-freedom model of a coupled seismic-vibrator-rough-ground system is proposed with which the nonlinear vibration properties are analyzed. In this model, the force-deflection characteristic of the contact interfaces is determined by finite element analysis. By analyzing the undamped free vibration, it was found that the variation of the second-order natural frequency with amplitude increases with rougher contact interfaces; however, the amplitude has little influence on the first-order natural frequency of the system. For the harmonic excited analysis, the jump frequencies and hysteretic region both decrease with rougher contact interfaces. Moreover, it is inferred from the bifurcation diagrams that, increasing the excitation force, the system can bring about chaotic motions on rough contact interfaces.

Direct observation of crystallization and melting with colloids

We study the kinetics of crystal growth and melting of two types of colloidal crystals: body-centered cubic (BCC) crystals and face-centered cubic (FCC) crystals. A dielectrophoretic “electric bottle” confines colloids, enabling precise control of the motion of the interface. We track the particle motion, and by introducing a structural order parameter, we measure the jump frequencies of particles to and from the crystal and determine from these the free-energy difference between the phases and the interface mobility. We find that the interface is rough in both BCC and FCC cases. Moreover, the jump frequencies correspond to those expected from the random walk of the particles, which translates to collision-limited growth in metallic systems. The mobility of the BCC interface is greater than that of the FCC interface. In addition, contrary to the prediction of some early computer simulations, we show that there is no significant asymmetry between the mobilities for crystallization and melting.

Diffusion and Equilibration of Site-Preferences Following Transmutation of Tracer Atoms

Using the method of perturbed angular correlation of gamma rays, diffusional jump-frequencies of probe atoms can be measured through relaxation of the nuclear quadrupole interaction. This was first shown in 2004 for jumps of tracer atoms that lead to reorientation of the local electric field-gradient, such as jumps on the connected a-sublattice in the L12 crystal structure. Studies on many such phases using the 111In/Cd PAC probe are reviewed in this paper. A major finding from a 2009 study of indides of rare-earth elements, In3R, was the apparent observation of two diffusional regimes: one dominant for heavy-lanthanide phases, R= Lu, Tm, Er, Dy, Tb, Gd, that was consistent with a simple model of vacancy diffusion on the In a-sublattice, and another for light-lanthanides, R= La, Ce, Pr, Nd, that had no obvious explanation but for which several alternative diffusion mechanisms were suggested. It is herein proposed that the latter regime arises not from a diffusion mechanism but from transfer of Cd-probes from In-sites where they originate to R-sites as a consequence of a change in site-preference of 111Cd-daughter atoms from In-sites to R-sites following transmutation of 111In. Support for this transfer mechanism comes from a study of site-preferences and jump-frequencies of 111In/Cd probes in Pd3R phases. Possible mechanisms for transfer are described, with the most likely mechanism identified as one in which Cd-probes on a-sites transfer to interstitial sites, diffuse interstitially, and then react with vacancies on b-sites. Implications of this proposal are discussed. For indides of heavy-lanthanide elements, the Cd-tracer remains on the In-sublattice and relaxation gives the diffusional jump-frequency.

Jump-based estimation for nonlinear stiffness and damping parameters

To overcome the limitation that only stiffness nonlinearity can be estimated via jump frequencies, this work introduces jump amplitudes as a supplement condition in the estimation of both stiffness and damping nonlinearities. An estimation method is proposed for a single-degree-of-freedom system containing both stiffness and damping nonlinearities. The idea may be applied to other nonlinear systems. The method is based on the measurements of both jump frequencies and jump amplitudes of the system subject to swept-sine excitations respectively in frequency and in amplitude. The experimental data yield frequency response curves at a fixed excitation amplitude and amplitude response curves at a fixed frequency. Based on the measured jump frequencies and jump amplitudes of the displacements, the system parameters can be determined by the method of harmonic balance. A numerical example is presented to demonstrate the application of the proposed approach and to check approximate explicit analytical expressions of the parameter estimation. To validate the effectiveness of the proposed approach, an experiment is performed on a vibration isolator with strongly nonlinear stiffness and damping. The estimation results show that the proposed method can estimate the stiffness and the damping parameters of the system with strong nonlinearities. Hence exploiting the knowledge about nonlinear jump phenomena is a promising approach to parameter estimations.

Jump and Lunge Frequencies Analysis during Men’s Single Badminton Matches: Implications on Physical Conditioning Training

The objective of this study is to determine the jump and lunge frequencies performed during men’s single badminton matches during world class level tournament. Players’ jump frequencies were calculated in the whole matches. Lunge frequencies were presented in the position performed in the court. The findings of this study will be beneficial as it can be used as a reference for developing training program besides technical and tactical plan during real matches.

Impurity Diffusion in Highly-Ordered Intermetallic Compounds Studied by Nuclear Quadrupole Interactions

Diffusion of impurity atoms depends on the sublattices occupied, active diffusion mechanisms, and jump frequencies to neighboring sites. The method of perturbed angular correlation of gamma rays (PAC) has been applied over the past decade to study impurity diffusion through measurement of nuclear quadrupole interactions (NQI) at nuclei of 111In/Cd probe atoms. Extensive measurements have been made on highly-ordered compounds having the L12 crystal structure, including In3R, Sn3R, Ga3R, Al3R and Pd3R phases (R= rare-earth element). Measurements in thermal equilibrium at high temperature served to determine lattice locations of 111In parent probe-atoms, through characteristic NQIs, and to measure diffusional jump-frequencies of 111Cd daughter probe-atoms, through relaxation of the NQI. This paper summarizes results of the jump-frequency measurements and relates them to the conventional diffusivity that can be determined, for example, from penetration profiles of tracer species. In spite of chemical similarities of the series of rare-earth phases studied, remarkably large variations in jump frequencies have been observed especially along series of In3R and Pd3R phases. Most phases appear as “line compounds” in binary phase diagrams, but large differences in site-preferences and jump-frequencies were observed for samples prepared to have the opposing limiting phase boundary compositions. Comparisons of jump-frequencies measured at opposing boundary compositions can give insight into the predominant microscopic diffusional mechanisms of the impurity. A change in diffusion mechanism was proposed in 2009 to explain jump-frequency systematics for In3R phases. An alternative explanation is proposed in the present paper based on site-preferences of 111Cd daughter probes newly observed along the parallel Pd3R series. The diffusivity can be expressed as the product of a jump-frequency such as measured in these studies and a correlation factor for diffusion that depends on the diffusion mechanism. The correlation factor can be modeled for the L12 structure and diffusion sublattice of interest using a five-frequency model originally proposed for metals. Although the correlation factor is an essential parameter for the diffusion of impurities, it has never been measured. It is suggested that values of the correlation factor can be determined feasibly by combining results of jump-frequency measurements such as the present ones with diffusivity measurements made for the same host-impurity systems.

Cu Precipitation Dynamics in an Fe-1.18%Cu Alloy

The precipitation of copper during aging at 600oC in high-purity Fe-Cu alloy was examined by means of transmission electron microscopy (TEM).Nano-scale copper-rich clusters with a B2-like structure were observed during heat treatment. These micro structural features play an important role in precipitation strengthening. In addition, the precipitation process has been analyzed in terms of the evolution of microstructure by a Monte Carlo method. A description of the coherent precipitation of copper in iron, based on a vacancy diffusion mechanism, thermally activated jump frequencies and cohesive energy is discussed in order to deal with simultaneous precipitation of metastable and stable phases in Cu-containing steel during aging. This analysis gives an estimation of the precipitation dynamics, as well as the evolution of Cu precipitates across a wide range of temperatures.

Diffusion in LanCoIn3n+2 Phases Studied by Perturbed Angular Correlation

Jump frequencies of 111In/Cd tracer atoms were measured for a series of layered phases LanCoIn3n+2 using the technique of perturbed angular correlation of gamma rays (PAC). The frequencies were determined by analysis of nuclear quadrupole relaxation produced by fluctuating electric field gradients. Samples were synthesized having nominal values n= 1, 2, 3, 5 and , with n= corresponding to the L12 phase LaIn3. The phases form heuristically from LaIn3 by replacing every (n+1)th (100) mixed plane of La and In atoms with a plane of Co-atoms. For the n=1 phase, LaCoIn5, jump frequencies were too small to detect. Two signals were observed, one for indium atoms next to the Co-planes and the other for more distant indium atoms. No relaxation was observed for atoms next to the Co-planes, indicating that there is no diffusion across the Co-planes. With increasing n, jump rates for the other In-atoms increased toward values observed for LaIn3. Jump frequency activation enthalpies for n= 3 and 5 were observed to be the same as for n=, suggesting the same diffusion mechanism. However, the jump-frequency prefactors were found to be smaller for small n, which is attributed to reductions in the connectivity of the diffusion sublattice. We conclude that diffusion in the layered phases is remarkably similar to diffusion in LaIn3 once the reduced connectivity is taken into account.