Dendritic and eutectic growth in Sb<Subscript>60</Subscript>Ag<Subscript>20</Subscript>Cu<Subscript>20</Subscript> ternary alloy

The rapid solidification of Sb60Ag20Cu20 ternary alloy was realized by high undercooling method, and the maximum undercooling is up to 142 K (0.18TL). Within the wide undercooling range of 40-142 K, the solidified microstructures are composed of (Sb), θand ε phases. High undercooling enlarges the solute solubility of (Sb) phase, which causes its crystal lattice to expand and its crystal lattice constants to increase. Primary (Sb) phase grows in two modes at small undercoolings non-faceted dendrite growth is the main growth form; whereas at large undercoolings faceted dendrite growth takes the dominant place. The remarkable difference of crystal structures between (Sb) and θphases leads to (θ Sb) pseudobinary eutectic hard to form, whereas strips of θform when the alloy melt reaches the (θ Sb) pseudobinary eutectic line. The cooperative growth of θand ε phases contributes to the formation of (ε θ) pseudobinary eutectic easily. In addition, the crystallization route has been determined via microstructural characteristic analysis and DSC experiment.     

Semiconductor quantum dots in high magnetic fields

We review and extend the composite fermion theory for semiconductor quantum dots in high magnetic fields. The mean-field model of composite fermions is unsatisfactory for the qualitative physics at high angular momenta. Extensive numerical calculations demonstrate that the microscopic CF theory, which incorporates interactions between composite fermions, provides an excellent qualitative and quantitative account of the quantum dot ground state down to the largest angular momenta studied, and allows systematic improvements by inclusion of mixing between composite fermion Landau levels (called Λ levels).     

Transient thermal characterization of micro/submicroscale polyacrylonitrile wires

In this work, the thermal diffusivity of single polyacrylonitrile (PAN) wires with diameters from 4.62 μm down to 324 nm is measured by using our recently developed transient electro-thermal technique. The wires span from 23 μm to 126.2 μm in our measurement. Since PAN wires are dielectric, a thin Au film is coated on the surface of the wires to make them conductive. In the experiment, a step current (with ∼2 μs rising time) is fed to the sample. The sample is heated and takes a certain time to reach its steady thermal state. The temperature rising response of the sample is sensed by measuring the resistance change of the thin Au coating. From the average temperature evolution of the sample, the thermal diffusivity can be extracted. Three PAN wires with different diameters are synthesized using the electro-spinning technique and are measured to obtain their thermal diffusivities (around 1.53×10^-7 m²/s), which are slightly smaller than the bulk value. PACS 65.80.+n; 66.30.Xj; 44.10.+i     

Beta decay of <Superscript>115</Superscript>In to the first excited level of <Superscript>115</Superscript>Sn: Potential outcome for neutrino mass

Recent observation of β decay of ¹¹⁵In to the first excited level of ¹¹⁵Sn with an extremely low Q _β value (Q _β ≤ O(1) [keV]) could be used to set a limit on neutrino mass. To give a restriction potentially competitive with those extracted from experiments with ³H (≃2 eV) and ¹⁸⁷Re (≃15 eV), the atomic mass difference between ¹¹⁵In and ¹¹⁵Sn and energy of the first ¹¹⁵Sn level should be remeasured with higher accuracy (possibly of the order of ∼1 eV). The text was submitted by the authors in English.     

Simple Analog Complementary Metal Oxide Semiconductor Circuit for Generating Motion Signal

We proposed in this study a novel analog complementary metal oxide semiconductor (CMOS) circuit for generating a motion signal when an object moves, which is a simple structure. The proposed unit circuit was constructed using a previously proposed edge detection circuit and a novel proposed circuit for generating a motion signal which accepts an edge signal. The part for generating the motion signal was constructed using six metal oxide semiconductor (MOS) transistors and one capacitor. Results obtained by the simulation program with integrated circuit emphasis (SPICE) and the measured results of a test circuit constructed with discrete MOS transistors and the test circuit fabricated with a 1.2 μm CMOS process showed that the proposed unit circuit can output pulsed current (motion signal) when an object moves on the circuit. It was clarified from the SPICE results that the two-dimensional network constructed with proposed unit circuits can output motion signals. The size of the novel unit circuit is expected to be about 110 × 110μm² obtained by the 1.2 μm CMOS process. It is possible to arrange 90 × 90 unit circuits on a chip which has an area of 1 × 1cm². The aperture ratio is expected to be about 21%, which is twice as large as that of the previously proposed circuit. An integrated circuit for image processing in real time can thus be realized by applying the two-dimensional network constructed with the proposed circuits.     

Monitoring of Paint Drying Process by Digital Speckle Correlation

The state of drying paint is monitored from the dynamic behaviors of the speckle pattern arising from laser illumination of the region inspected. Temporal variation of the peak height of the cross-correlation function between successive frames taken with a fixed interval is plotted until the peak maintains a stationary maximum value. We used a speckle pattern in the diffraction field for monitoring of a single region and that in the image field for simultaneous monitoring of various regions. Both the normal and the phase-only algorithms were compared for cross-correlation computation. The former showed more distinct variation of peak height.     

Ionic conduction and effect of cation doping in Tl<Subscript>4</Subscript>HgI<Subscript>6</Subscript>

The ionic conduction properties of undoped and doped Tl₄HgI₆ were investigated using electrical conductivity, dielectrics, differential scanning calorimetry, and X-ray diffraction techniques. The heavy Tl⁺-ions diffusion was activated at high temperature, whereas low conductivity at the lower temperature suggested electronic contribution in undoped Tl₄HgI₆. The partial replacement of heavy Tl⁺ ion by suitable cations (Ag⁺ and Cu⁺) enhanced the conductivity by several orders of magnitude, whereas diminution in conductivity results with increasing dopants’ concentration in Tl₄HgI₆. These results can be interpreted in terms of a lattice contraction and vacancy–vacancy interaction (leading to the cluster formation), respectively. The dielectric values of undoped Tl₄HgI₆ system gradually increasing with temperature, followed by a sharp change, were observed around 385 K and can be explained on the basis of increasing number of space charge polarization and ions jump orientation effects. The activation energy of undoped and doped Tl₄HgI₆ systems were calculated, and it was found that ionic conductivity activation energy for 5 mol% of cation dopants is much lower than that of undoped one, and also 10 mol% doped Tl₄HgI₆ systems.     

Ultra fine carbon nitride nanocrystals synthesized by laser ablation in liquid solution

Crystalline carbon nitride nanopowders and nanorods have been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation of a graphite target in liquid ammonia solution. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FTIR) were used to systematically study the morphology, nanostructure and chemical bonding. The experimental composition and structure of the nanoparticles are consistent with the theoretical calculations for α-C₃N₄. After 2 h ablation the particles had a size distribution ∼8–12 nm, whereas after 5 h ablation the particles had grown into nanorod-like structures with a crystalline C₃N₄ tip. A formation mechanism for these nanorods is proposed whereby nanoparticles are first synthesized via rapid formation of an embryonic particle, followed by a slow growth, eventually leading to a one-dimensional nanorod structure.     

The PMD of sinusoidally spun fibers in the presence of random birefringence perturbations

Although fiber spinning is known to reduce polarization mode dispersion (PMD) effects in optical fibers, relatively few studies have been performed of the dependence of the reduction factor on the strength of random birefringence fluctuations. In this paper, we apply a general mathematical model of random fiber birefringence to sinusoidally spun fibers. We find that while even in the presence of random birefringence perturbations the maximum reduction of PMD is still obtained when the phase matching condition is satisfied, the degree of PMD reduction and the probability distribution function of the DGD both vary with the random birefringence profiles.     

Atomic displacements due to interstitial hydrogen in Cu and Pd

The density functional theory (DFT) is used to study the atomic interactions in transition metal-based interstitial alloys. The strain field is calculated in the discrete lattice model using Kanzaki method. The total energy and hence atomic forces between interstitial hydrogen and transition metal hosts are calculated using DFT. The norm-conserving pseudopotentials for H, Cu and Pd are generated self-consistently. The dynamical matrices are evaluated considering interaction up to first nearest neighbors whereas impurity-induced forces are calculated with M₃₂H shell (where M = Cu and Pd). The atomic displacements produced by interstitial hydrogen at the octahedral site in Cu and Pd show displacements of 7.36% and 4.3% of the first nearest neighbors respectively. Both Cu and Pd lattices show lattice expansion due to the presence of hydrogen and the obtained average lattice expansion ΔV/V = 0.177 for Cu and 0.145 for Pd.