Application of a high-performance,special-purpose computer,GRAPE-2A,to molecular dynamics

The special-purpose computer GRAPE-2A accelerates the calculation of pairwise interactions in many-body systems. This computer is a back-end processor connected to a host computer through a Versa Module Europe (VME) bus. GRAPE-2A receives coordinates and other physical data for particles from the host and then calculates the pairwise interactions. The host then integrates an equation of motion by using these interactions. We did molecular dynamics simulations for two systems of liquid water: System 1 (1000 molecules), and System 2 (1728 molecules). The time spent for one step of molecular dynamics was 3.9 s (System l), and 10.2 s (System 2). The larger the molecular system, the higher the performance. The speed of GRAPE-2A did not depend on the formula describing the pairwise interaction. The cost performance was about 20 times better than that of the fastest workstations available today, and GRAPE-2A cost only $22,000. © 1994 by John Wiley & Sons, Inc.     

Solid-state photoelectron transfer in powdery nanocomposites comprised of a sensitiser, photoacid generators and silica nanoparticles

The dry beads milling of a mixture of 9,10-dipropoxyanthracene (DPA) as an electron donor and surface-modified silica nanoparticles was conducted in the absence or in the presence of a photoacid generator (PAG) as an electron acceptor to give powdery nanocomposites. Fluorescence measurements indicated no mechanochemical change in the crystal structure of DPA after the nanohybridisation. The co-milling with PAG resulted in solid-state fluorescence quenching, whereas quenching efficiency was considerably dependent on the nature of PAG. The solid-state sensitised photoacid generation through the electron transfer was demonstrated by the solid-state photocolouration of leuco-dye of crystal violet lactone.     

Determination of thyroid hormones in pharmaceutical preparations,after derivatization with 9-anthroylnitrile,by high-performance liquid chromatography with fluorescence detection

Fast ion-exchange chromatography has been developed and applied to the separation of common inorganic anions. Using a didodecyldimethylammonium bromide (DDAB) coated short (30 mm x 4.6 mm) ODS analytical column (3-microm particle size) and a 5 mM phthalate eluent (pH 7.5) the isocratic separation of nine common anions in 160 s was possible, with the first seven anions, including phosphate, chloride and sulphate, separated within 65 s. Detection was achieved using indirect UV at 279 nm. The high capacity, highly hydrophobic ion-exchange coating demonstrated excellent stability over time, even at elevated temperatures (45 degrees C) and exhibited unusual selectivity for common anions (retention order=fluoride, carbonate, phosphate, chloride, bromate, nitrite, sulphate, bromide and nitrate). The developed chromatography was successfully applied to the rapid analysis of river water and seawater samples.     

Surface-mediated photoalignment of discotic liquid crystals on azobenzene polymer films

This paper describes a simple strategy for the formation of photoaligned and micropatterned discotic liquid crystal (DLC) film on the surface of photoirradiated azobenzene-containing polymer thin film. The key material for the surface-mediated photoalignment of the DLCs was poly[4-(4-cyanophenylazo)phenyl methacrylate] (pMAzCN). Optical anisotropy was generated in a pMAzCN film by oblique exposure to nonpolarized light which resulted in angle-selective photoisomerization and reorientation of the azobenzenes. Subsequent annealing of the film at 240 degrees C enhanced the photoaligned state of the p-cyanoazobenzenes due to strong intermolecular dipole-dipole interaction and semicrystalline nature of the pMAzCN. This combination of photoirradiation and subsequent annealing of the pMAzCN film made it possible to realize the surface-assisted orientation control of a DLC molecule, which displays both columnar (Col) and discotic nematic (N(D)) phases over 152 degrees C. When the pMAzCN film was exposed to linearly polarized light from the surface normal, the DLC molecules showed homeotropic orientation with the director perpendicular to the substrate surface. In the contrast, oblique irradiation of the pMAzCN film with nonpolarized light gave rise to tilted DLC orientation with well-ordered optical birefringence at the N(D) phase. Rapid cooling from the N(D) phase produced a well-aligned glassy N(D) state at room temperature, which was adequately stable for 10 months even though no covalent cross-linking among the DLCs was performed. The spatial orientation of photoaligned DLCs in both their bulk film and in their interface region was characterized by means of optical birefringence, X-ray diffraction, and fluorescence measurements. At the N(D) phase, the DLC molecules were aligned in a hybrid manner such that their tilt angles varied throughout the thickness of DLC film. The direction of tilted DLCs was opposite to the propagation of the actinic nonpolarized light. The photoaligned DLC films exhibited polarized fluorescence emission with an s-polarized/p-polarized intensity ratio of 4.1, despite the nonpolarized excitation of only DLC at outmost surface. These results indicate that the three-dimensionally aligned azobenzene moieties of the pMAzCN thin film were transferred to the tilted DLC molecules at air/DLC interface. Finally, we demonstrated micrometer-scale photopatterned orientation of DLC molecules on the pMAzCN surface by oblique nonpolarized irradiation of the film through a photomask.     

Molecular origin of viscoelasticity and chain orientation of glassy polymers

Dynamic birefringence and dynamic viscoelasticity of poly(4-methyl styrene) and poly(4-t-butyl styrene) were measured to investigate the molecular origin of viscoelasticity around the glass transition zone. The data were analyzed with a modified stress-optical rule: The birefringence and the stress were separated into two component functions of different molecular origins. One component is related to the orientation of the main chain axis and the other one to the rotation of the repeating units about the main chain axis. The strain dependence of the two characteristic orientation functions in the glassy zone was estimated and the orientation mechanism of repeating units was discussed.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.     

Fermi surfaces and quasi-particle band dispersions of the iron pnictides superconductor KFe2As2 observed by angle-resolved photoemission spectroscopy

We have performed an angle-resolved photoemission study of the iron pnictide superconductor KFe₂As₂ with . Most of the observed Fermi surfaces show almost two-dimensional shapes, while one of the quasi-particle bands near the Fermi level has a strong dispersion along the k_z direction, consistent with the result of a band-structure calculation. However, hole Fermi surfaces α and ζ are smaller than those predicted by the calculation while other Fermi surfaces are larger. These observations are consistent with the result of a de Haas-van Alphen study and a theoretical prediction on inter-band scattering, possibly indicating many body effects on the electronic structure.