Local structural analysis of hopeite crystals by the EXAFS curve-fitting method

Structural analysis of hopeite crystals was performed by the extended X-ray absorption fine structure (EXAFS) curve fitting method. Two types of hopeite crystals, Zn₃(PO₄)₂·4H₂O and Zn_3-xMn_x(PO₄)₂·4H₂O which is doped by manganese, were studied. Fourier transform of EXAFS gave Zn-O bond distances of 0.146 nm for the former and 0.144 nm for the latter. The real bond distances were determined by the reverse operation of Fourier transform and curve-fitting. By this procedure, the real bond distances of Zn-O were determined to be 0.194 and 0.196 nm, respectively. These distances indicated a Zn-O bond in [ZnO₄] of tetrahedral structure. Although the Mn-O bond distance in Zn_3-xMn_x(PO₄)₂·4H₂O was found to be 0.162 nm by the Fourier transform of EXAFS, the reverse operation of Fourier transform gave a real bond distance of 0.215 nm for the Mn-O bond in the hopeite crystal. The data supported the idea that the Mn-O bond refered to [MnO₂(H₂O)₄] of the octahedral structure in the crystal. The coordination numbers of the zinc and manganese components clarified their local structure in hopeite crystals.     

Structural refinement of gray iron by electromagnetic vibrations

Simultaneous imposition of alternating electric and stationary magnetic fields on a molten metal will induce a vibrating motion in the liquid, which can lead to the formation and collapse of cavities and affect the solidification structure. Following earlier works on Al-Si alloys, the process is used to refine the microstructure of gray iron. It is found that in addition to the refinement of columnar-dendritic structure of primary austenite into a fine and homogeneous one, the eutectic cell structure is also extensively refined. The effects of the two main parameters involved in the process, that is, the frequency and the intensity of vibrations are, for the first time, quantitatively presented. The refinement of the cells proceeds as the frequency is increased up to about 500 Hz, where a reverse trend starts and results in a complete termination of the effects at about 10 kHz. The increase in the number of cells because of the increase in the intensity of vibrations shows a sharp jump at an electromagnetic pressure of about 10⁵ Pa, where the cavitation phenomenon is more likely to occur by overcoming the static pressure. However, increasing the electromagnetic pressure to higher values does not essentially result in a considerable further refinement, implicating the existence of a limit in the process of structural refinement by the cavitation phenomenon.     

Three-dimensional analysis of the interface between an Sn-8wt.%Zn-3wt.%Bi solder and a substrate by using an angle-lapping method

The validity of application of the angle-lapping method to investigate the microstructure between an Sn-8wt.%Zn-3wt.%Bi Pb-free solder and an Auimmersed Ni-7.0%P plate or a Cu substrate was studied using transmission electron microscopy. The method enabled a three-dimensional analysis of the interface layers. The morphology of the Au layer was clarified as an intermetallic compound with Zn with numerous voids that looked like cracks spreading in all directions. Sn and Bi could diffuse into the interface layer only when the Ni-P plate was used, but Ni did not diffuse actively and formed a narrow interface layer. When a Cu substrate was used, Cu diffused, rather than Sn or Bi, and formed a relatively wide interface layer. These results were obtained with the angle-lapping method.     

Servo System Using Optical Serial Transmission in Control Loop for Industrial Robots

A new servo system suitable for robot control is proposed. An optical serial transmission is applied in its servo-control loops to reduce the number of signal cables and the cable length between the robot mechanism and the controlling equipment, as well as to increase flexibility for expanding control functions.     

On‐chip neural cell cultivation using agarose‐microchamber array constructed by a photothermal etching method

We have developed a novel method for on‐chip cultivation of neural cells in a flexible agarose‐microchamber array on a glass slide. The agarose microchamber is a micrometer‐order cavity constructed on the surface of an agarose layer by molding a 50‐µm‐high square/circular micro‐cast of thick SU‐8 photoresist. In addition, the shape of the agarose microchamber was rearranged by using the photothermal etching method, in which we used an infrared (1064‐nm) focused laser beam as the heat source to melt and remove a portion of agarose gel at the heating spot. With the photothermal etching method, we can also manufacture narrow tunnel‐shaped channels between microchambers. When nerve cells were cultured on the agar‐microchamber array chip, the nerve cells in two adjacent microchambers connected through the photothermal‐etched channel after 48 hours of cultivation. Those results suggest the potential of an agarose‐microchamber array integrated with the photothermal etching method for the next stage of single cell cultivation and measurement of nerve cells, such as real‐time control of cell interactions during cultivation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 37–42, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10215     

A Remark on Intramolecular Transfer of an Injected Electron in C60 and C70

A simple analysis on the intramolecular transfer of an injected electron into C₆₀ and C₇₀ has been performed based on the concept of orbital interaction. This analysis contains the partitioning of each fullerene into three parts and the examination of the frontier molecular orbital interaction for propagation of an injected electron into the whole Cgo or C70 molecule. This electron transfer process is shown to be “one-way” from energetical point of view.     

Polymer whispering gallery mode lasers

We study the emission properties of dye doped polymer microspheres. Under the weak excitation condition, emission exhibits resonant features characteristic to the spherical cavity modes. By the systematic analyses with the Lorenz-Mie calculation, we determine the mode indices of all the resonance lines. From the line width analyses, we determine the effective concentration of dye molecules. Under the pulsed pumping, we observe lasing. Spheres with dye molecule in the entire sphere show complicated spectra indicating the multi-mode lasing. We demonstrate the mode elimination by using a stratified structure. A 20 μm diameter sphere which has the dye doped shell shows very simple lasing by the lowest order number modes of spherical cavity mode. A small sphere of 5 μm in diameter shows single mode lasing behavior. The observed spontaneous coupling coefficient is about 30% which agrees with the calculated value.