Visualization of the vortical structure of a circular jet excited by axial and azimuthal perturbations

The vortical structure of a circular water jet was investigated by a flow visualization technique. The jet was excited by axial and azimuthal perturbations to stabilize and enhance the large-scale axisymmetric and streamwise vortices. A laser fluorescent dye and a laser light sheet were used to visualize the vortical structure, and the whole view of the structure was captured by applying the Taylor hypothesis to the cross-sectional images and by scanning a laser light sheet in the streamwise direction. The visualized images reveal the details of the complicated structure of axisymmetric and streamwise vortices, and it is confirmed that the streamwise vortices have fundamental effect on the entrainment of ambient fluid. From the images, the length of jet boundary was calculated to estimate the mixing effect. The result suggests that the jet mixing is significantly increased by the break-down of the vortices enhanced by axial and azimuthal perturbations. We also discussed the jet diffusion effect in consideration of the jet widths obtained by velocity measurement. The result indicates that the vortical structure including streamwise vortices plays an important role to enhance diffusion.     

Total synthesis of (S)-(+)-ent-phomapyrones B and surugapyrone B

Phomapyrone B ( 1 ), the 2-pyrones isolated from the phytopathogenic fungus Leptosphaeria maculans, has been synthesized as the enantiomeric form starting from (S)-2-methylbutanol ( 4 ). Surugapyrone B ( 3 ) isolated from Streptmyces sp. USF-6280 as an antioxidant has also been synthesized as a natural form. The absolute configuration of phomapyrone B ( 1 ) was estimated to be the (R)-form and that of surugapyrone B ( 3 ) being the (S)-form. A series of 2-pyrone derivatives 17 have been synthesized through the established procedure and their DPPH radical-scavenging activities have also been evaluated.     

Cyclization from Higher Excited States of Diarylethenes Having a Substituted Azulene Ring

The cyclization reaction of diarylethenes having an azulene ring occurs only via higher excited states. Novel diarylethenes having an azulene ring with a strong donor or acceptor were synthesized and examined in these reactions. A derivative having an electron-donating 1,3-benzodithiol-2-ylidenemethyl group at the 1-position of the azulene ring showed photochromism, whereas neither a derivative having a π-conjugated electron-donating group at the 3-position of the azulene ring nor derivatives having a π-conjugated electron-withdrawing group at the 1- or 3-position of the azulene ring showed any photochromism. The photoreactivities of these compounds were explained by calculating forces and bond orders on the excited states using density functional theory (DFT) and time-dependent (TD)-DFT.     

ASACUSA MUSASHI: New progress with intense ultra slow antiproton beam

Our group “ASACUSA MUSASHI” has established an efficient way for accumulating antiprotons and extracting them as intense ultra-slow mono-energetic beams at the CERN-AD facility. This novel beam opens new frontiers for investigating a variety of physics. For realizing H? spectroscopy and the test for charge-parity-time symmetry, we have also developed the cusp trap, a combination of an anti-Helmholz superconducting coil and a multi-ring electrode trap, for trapping both antiprotons and positrons and then synthesizing antihydrogens. Recently, the cusp trap was practically used to accumulate antiprotons. The last piece for synthesizing antihydrogens in the cusp trap is the positron accumulator. We have developed a compact system to effectively accumulate positrons based on N₂ gas-buffer scheme with a specially designed high precision cylindrical multi-ring electrode trap. The recent progress of the developing work is an important milestone for upcoming antihydrogen science of ASACUSA MUSASHI.     

Improved sound absorption performance of three-dimensional MPP space sound absorbers by filling with porous materials

Because microperforated panels (MPPs), which can be made from various materials, provide wide-band sound absorption, they are recognized as one of the next-generation absorption materials. Although MPPs are typically placed in front of rigid walls, MPP space sound absorbers without a backing structure, including three-dimensional cylindrical MPP space absorbers (CMSAs) and rectangular MPP space absorbers (RMSAs), are proposed to extend their design flexibility and easy-to-use properties. On the other hand, improving the absorption performance by filling the back cavity of typical MPP absorbers with porous materials has been shown theoretically, and three-dimensional MPP space absorbers should display similar improvements. Herein the effects of porous materials inserted into the cavities of CMSAs and RMSAs are experimentally investigated and a numerical prediction method using the two-dimensional boundary element method is proposed. Consequently, CMSAs and RMSAs with improved absorption performances are illustrated based on the experimental results, and the applicability of the proposed prediction method as a design tool is confirmed by comparing the experimental and numerical results.     

Effect of Sr addition to La-based perovskite-type oxide as an electrode material for zirconia-based amperometric-type NOx sensor

The sensing characteristics of an amperometric NOx sensor with yttria-stabilized zirconia and a La-based perovskite-type oxide sensing electrode were examined. La_1-xSr_xMO₃ (M = Co, Mn, x = 0, 0.2, 0.4, 0.6) were synthesized using the spray pyrolysis method. The NO₂ response of a sensor fabricated with La_1-xSr_xMnO₃ increased with increasing amount of Sr, and the trend was in contrast to that of the sensors fabricated with La_1-xSr_xCoO₃. LaSr_0.2MnO₃ was determined to be the most appropriate material for the sensor in terms of a high NO₂ response and low O₂ current. In order to discuss the effects of Sr addition to La-based perovskite oxides for the sensor, NO adsorption and desorption properties of oxides and the relationship between the oxidation number of the B-site cation and Sr substitution were examined using temperature-programmed desorption and X-ray photoelectron spectroscopy, respectively.     

Investigation on non-optically bleachable components of ESR aluminium signal in quartz

Electron Spin Resonance (ESR) can be used as a method to estimate the age of sediment deposition using the paramagnetic centre related to aluminium impurities in quartz. This so-called Al-centre can be partially optically bleached and its signal intensity decreases in relation to time exposure to solar light, until it reaches a plateau value corresponding to a residual signal. This signal can be attributed to “Deep Aluminium Traps” (DAT) which cannot be reset by an exposure to sunlight. In this study, we have investigated the behaviour of the DAT signal in samples from different origins and ages. The intensity of the DAT signal has been isolated from the total aluminium signal by the exposure of different quartz samples to simulated solar light. We observed that the DAT intensities were sample dependant and therefore it should be determined for each sample. Moreover, DAT intensities of Pleistocene volcanic quartz increase with gamma laboratory irradiation, whereas DAT intensities of sedimentary quartz do not vary with added artificial doses. This suggests that DAT in quartz extracted from sediments must be inherited from the primary source of the quartz, and were saturated at the time of sedimentation. We thereby validate the ESR dating of quartz sediment protocol used so far.     

Electronic structures in coupled two quantum dots by 3D-mesh Hartree-Fock-Kohn-Sham calculation

To study the electronic structures of quantum dots in the framework of self-interaction-free including three dimensional effects, we adopt the theory of nonlocal effective potential introduced by Kohn and Sham [#!ks65!#]. For utilizing the advantageous point of the real space (3D) mesh method to solve the original nonlinear and nonlocal Hartree-Fock-Kohn-Sham (HFKS)-equation, we introduce a linearization of the equation in the local form by introducing the local Coulomb potentials which depend on explicitly the two single particle states. In practice, for solving the local form HFKS-equation, we use the Car-Parrinello-like relaxation method and the Coulomb potentials are obtained by solving the Poisson equation under proper boundary conditions. Firstly the observed energy gap between triplet- and singlet-states of N = 4 in DBS [#!tarucha96!#] is discussed to reproduce the addition energies and chemical potentials depending the magnetic field. Next the coupling between two-quantum dots in TBS [#!aht97!#] is studied by adding the square barrier between two dots. The spin-degeneracy [#!aht97!#] measured in gate-voltage depending on magnetic field is well reproduced in the limit of small mismatch. Finally, the electronic states in the ring structure are calculated and discussed how the ring size and magnetic field affect to the structures. Received 30 November 2000     

The synthesis of tricarbonyl iron complexes of 6,7-dimethylene- cycloheptadienium ion and tropoquinodimethanes

The synthesis and spectroscopic characterization of the title complexes correspond to isoelectronic system of o-quinodi-methane complex are described.