Stability of charged metal clusters in the vicinity of an ionic charge

Stability of highly charged metal clusters in the electric field of an external ion is investigated with the classical liquid drop model. We study the optimum shape of the cluster which has a local minimum of the total energy, taking account of the effects of the surface charge polarization on the Coulomb energy and the cluster deformation on the surface energy. We find that the cluster deformation greatly affects the total energy of the system and that a cluster with a fissility larger than some critical value 0.7-0.8 can become unstable against deformation. We investigate the local competition between the Coulomb force and the surface tension at the cluster surface and show that the surface charge polarization which is induced by the external electric field significantly affects the shape of the cluster and its stability. Received 5 November 2002 / Received in final form 27 January 2003 Published online 11 March 2003 RID="a" ID="a"e-mail: hamada@konan-u.ac.jp     

Robustness to head misalignment of virtual sound imaging systems

When binaural sound signals are presented with two loudspeakers, the listener's ears are required to be in the relatively small region which is under control of the system. Misalignment of the head results in inaccurate synthesis of the binaural signals. Consequently, directional information associated with the acoustic signals is inaccurately reproduced. When the two loudspeakers are placed close together, the spatial rate of change of the generated sound field is much smaller than that generated by two loudspeakers spaced apart. Therefore, the performance of such a system is expected to be more robust to misalignment of the listener's head. Robustness of performance is investigated here with respect to head displacement in three translational and three rotational directions. A comparison is given between systems consisting of two loudspeakers either placed close together or spaced apart. The extent of effective control with head displacement and the resulting deterioration in directional information is investigated in the temporal and spectral domain by analyzing synthesized binaural signals. Subjective localization experiments are performed for cases in which notable differences in performance are expected from the previous analysis. It is shown that the system comprising two loudspeakers that are close together is very robust to misalignment of the listener's head.     

Rotational Analyses of Several Infrared Bands of NH(2)Cl

The high-resolution absorption spectra of several infrared bands of NH(2)Cl molecule have been observed and analyzed. Rotational lines of amino wagging and scissoring fundamental bands are split by about 0.2 cm(-1) through the amino inversion motion. The shape of the inversion potential and the barrier height are considered by comparing the results of the experimental observations and an ab initio MO calculation. The amino twisting band of amine molecule has been observed for the first time in the gas phase. The intensity of the transition seems to be induced through a Coriolis interaction with the intense amino wagging band. Copyright 2000 Academic Press.     

Ab initio materials design for transparent-conducting-oxide-based new-functional materials

Based upon ab initio electronic structure calculations for delafossite CuAlO₂ and ZnO, we report on the design of new-functional materials for transparent conducting oxides (TCO), such as (i) low-resistive p-type ZnO and CuAlO₂ by co-doping, (ii) high-efficiency thermoelectric power in CuAlO₂ (ZT>3) by p-type doping, (iii) half-metallic ferromagnetism in transition-metal-impurity doped CuAlO₂ and ZnO-based diluted magnetic semiconductors, and (iv) CaO, MgO, SrO and BaO based DMS without transition metal impurities. We also discuss the implementation of the self-interaction correction to our materials design method. PACS 61.72.Bb; 61.72.Jj; 71.15.Mb; 72.15.Jf; 82.75.-d     

First-principles molecular dynamics simulation of biased electrode/solution interface

First-principles molecular dynamics simulations have been carried out for water in contact with Pt(1 1 1) surface. To apply negative bias potential to the water/Pt interface, excess electrons were added to our slab model using the recently developed computational scheme called “effective screening medium (ESM)”. Water molecules located away from the surface reoriented themselves to screen the electric field, but they responded differently near the surface. Water molecules nearest to the surface, forming a distinct layered structure with the hydrogen atom directed to the surface, increased the density with increasing field. On these bases, we discuss microscopic aspects of the electric double layer.     

Influence of intramolecular vibrations in charge redistribution at the pentacene-graphite interface

We have investigated the relation between the intramolecular vibrational modes of pentacene and the charge redistribution at the pentacene-graphite interface by using high-resolution electron-energy-loss-spectroscopy. The three main vibrational peaks shift to lower energies as the pentacene film thickness decreases. In order to discuss this energy shift, we have calculated the vibrational energies of a free pentacene molecule by changing its charge state. We have also calculated the vibrational energies of a pentacene molecule adsorbed on a graphite sheet by changing the pentacene-graphite distance. Taking the experimental and calculation results into account, we conclude that the observed energy shifts result from an intramolecular charge redistribution. The present results indicate that the effect of an intramolecular charge redistribution is essential to discuss the origin of an energy shift observed in a vibrational study of an organic molecule/substrate interface.     

First-Principles Calculation of Lattice Dynamics of bcc and hcp Iron Under High Pressures

Lattice dynamics and electron-phonon coupling are calculated for non-magnetic hcp iron at 100 GPa by a first-principles linear response full-potential LMTO method. Superconducting transition temperature is estimated to be less than 0.5 K. For ferromagnetic bcc iron lattice dynamical calculations are performed for 9.8 GPa as well as for ambient pressure. The results of calculation reproduce well the pressure dependence of phonon dispersion curves observed by neutron scattering measurements.     

Reversible photoswitching in a cell-sized vesicle

A photosensitive amphiphilic molecule can switch the shape of an assembled vesicle as determined by microscopic observation. Photoisomerization induces a change in membrane fluctuation behavior or a morphological transition between ellipsoid and bud shapes, depending on the asymmetrical degree of the initial shape. The mechanism of this reversible photoswitching in the vesicle morphology is interpreted in terms of a change in the effective cross-sectional area of the photosensitive molecule.     

Sur les immeubles triangulaires et leurs automorphismes

Résumé  Les travaux de J. Tits ont conduit à la classification complète des immeubles euclidiens de dimension supérieure ou égale à 3. L’ensemble de ces immeubles à isomorphisme près est dénombrable et paramétré par les corps locaux qui leur correspondent. Dans cet article nous nous intéressons aux immeubles triangulaires, qui sont euclidiens de dimension 2 et pour lesquelles une paramétrisation analogue est impossible. Nous construisons une lamination Λ sur un espace topologique localement compact séparé, dont l’espace des feuilles est l’ensemble des immeubles triangulaires à isomorphisme près. On considère ainsi les immeubles triangulaires comme points d’un espace dont Λ est une désingularisation naturelle. Nous établissons des résultats de chirurgie sur les immeubles triangulaires à données locales fixées. Ils entra?nent par exemple que Λ est topologiquement transitive. Nous montrons qu’un immeuble triangulaire générique au sens de Baire a un groupe d’automorphismes trivial et qu’il contient toutes les géométries locales possibles. L’espace des immeubles triangulaires à isomorphisme près est un nouvel exemple d’espace non commutatif. Le second auteur a été en partie financé par JSPS.