Thermal conductivity of an alloy in relation to the observed cooling rate and glass-forming ability

The glass-forming ability (GFA) of an alloy in this case is the largest diameter of a rod which can be cast fully glassy. The present work shows that the thermal conductivity of a liquid alloy has a strong effect on GFA by influencing the cooling rate upon mould casting. The initial cooling rates (for the first 70–100?K of temperature decrease), obtained for Cu-, Zr- and Au-based bulk glass-forming alloys in the liquid state, are found to scale linearly with the thermal conductivities of the liquid base elements. However the low cooling rate found for Ni-based alloy suggests that the heat transfer at the melt–mould interface may also influence the cooling rate. The low thermal conductivity of Ni-based alloys and the correspondingly low cooling rate obtained compared to Cu-based counterparts explains their lower GFA. In the literature, many factors influencing the GFA of alloys have been discussed. To these factors, the present study adds the thermal conductivity of the molten alloy and the melt–mould heat-transfer coefficient. Moreover, the cooling rate depends on temperature and, thus, the critical cooling rate itself is not a suitable parameter for indicating GFA. The cooling can be better described by an appropriate fitting of the cooling curve to an exponential temperature decay function.     

Phase transformation behaviour in continuously cooled Zr65Al7.5Ni10Cu17.5− x Pd x (x = 0 − 17.5) glass-forming alloys and consequences for structure and property control

Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr₆₅Al_7.5Ni₁₀Cu_{17.5? x} Pd _x (x?=?0???17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x?=?5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x?=?17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural relaxation during continuous heating, could be fabricated for the low-Pd alloy (x?=?5). Plasticity was found to increase proportionally with the relaxation enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7 mm in diameter for the high-Pd alloy (x?=?17.5).     

Excitation and decay dynamics of 1s2s inner-shell double-vacancy states of neon atoms

The photo-excitation and Auger decay processes of inner-shell double vacancy states 1s2s2p^6（1,3^S）3s3p of neutral neon atoms have been studied theoretically. Multi-configuration Dirac-Fock （MCDF） calculations have been carried out, with electron correlation effects taken into consideration. The relaxation of core and excited orbitals and configuration interaction are found to be crucial to creating the double vacancy states by single photo-absorption. The predominant decay paths for the double vacancy states turn out to be of the LLM Auger decay to 1s 2s^22p^53s（3p）, KLL Auger decay to 1s^22s2p^43s3p, and KLM Auger decay to 1s^22p^63s（3p）. They lead to further Auger decay, creating the neon ions of multiple charge states. For both double and single vacancy states the spectator type of Auger process is dominated in all the Auger decay processes. Theoretical Anger electron spectra are presented for further investigations, experimental and theoretical.     

Magnetic behavior of Fe0.2Mg0.8TiO3 and Fe0.3Mg0.7TiO3 probed by Mössbauer timescale

Magnetization and Mössbauer measurements have been made on a diluted antiferromagnets Fe_xMg_1?xTiO₃ with x=0.2, 0.3 and 0.7. It has been demonstrated that this system exhibits a spin glass or a reentrant spin glass like behavior in the samples with x around the percolation concenrration x_c≈0.25. It has been shown that various sizes of magnetic clusters are formed well above the transition temperatures determined by the magnetization measurements in the samples with x near x_c. The behavior of Fe_0.2Mg_0.8TiO₃ is discussed as a typical cluster glass.     

Extended string field theory for massless higher-spin fields

We propose a new gauge field theory which is an extension of ordinary string field theory by assembling multiple state spaces of the bosonic string. The theory includes higher-spin fields in its massless spectrum together with the infinite tower of massive fields. From the theory, we can easily extract the minimal gauge-invariant quadratic action for tensor fields with any symmetry. As examples, we explicitly derive the gauge-invariant actions for some simple mixed symmetric tensor fields. We also construct covariantly gauge-fixed action by extending the method developed for string field theory.     

Surface contouring by phase-shifting digital holography

Surface contouring by phase-shifting digital holography is proposed that provides surface height from a change of reconstructed object phases due to the tilt of object illumination. Surface height from a reference plane is directly obtained from the phase change. Its sensitivity depends on the tilt angle as well as on the initial incident angle. By proper selection of the angles we can derive surface height without phase unwrapping. The sensitivity can be enhanced by increasing the tilt angle. Then we need phase unwrapping that is sensitive to noise due to laser speckles in the reconstructed images. This noise could be suppressed by selecting phase values at points of the maximum product of amplitudes before and after the illumination change in the course of data reduction from 1024×1024 to 512×512 and by selecting paths for phase unwrapping by looking for the intensity maximum. The observed height resolution is 20 μm. Effects of numerical focusing have also been investigated. The present method has the same sensitivity as the fringe projection method, but it has larger measurement depth and is also applicable to the deformation measurement with the same arrangement.     

Applying a Mode Selector to Improve the Pulse-Compression Performance of Asymmetric-Coupled-Waveguide-Based Dispersion Compensators

An InGaAsP slab-type asymmetric-coupled-waveguide-based dispersion compensator with a mode selector has been designed and fabricated. The mode selector is necessary to select either a symmetric [with a positive group-velocity dispersion (GVD)] or antisymmetric (with a negative GVD) supermode. These supermodes exist simultaneously in the dispersion-compensation region of the device. Pulse-compression experiments were used to test the dispersion compensator, evaluating the function of the mode selector. A theoretical study of the experimental results shows that the mode selector obtains a very strong selectivity (nearly 100%) for the antisymmetric supermode.     

Current-driven resonant excitation of magnetic vortices

A magnetic vortex core in a ferromagnetic circular nanodot has a resonance frequency originating from the confinement of the vortex core. By the micromagnetic simulation including the spin-transfer torque, we show that the vortex core can be resonantly excited by an ac (spin-polarized) current through the dot and that the resonance frequency can be tuned by the dot shape. The resistance measurement under the ac current successfully detects the resonance at the frequency consistent with the simulation.