Synthesis of the glycan moiety of ganglioside HPG-7 with an unusual trimer of sialic acid as the inner sugar residue

The glycan moiety of ganglioside HPG-7, isolated from the sea cucumber (Holothuria pervicax), was synthesized for the first time. The characteristic substructure, a trisialic acid sequence embedded in the glycan, was deliberately constructed by utilizing suitably differentiated sialyl units for various synthetic purposes. Finally, a pentasaccharide was successfully delivered as the hexyl glycoside.     

The role of intermolecular hydrogen bond on dielectric properties in hydrogen-bonded material 5-bromo-9-hydroxyphenalenone: theoretical investigation

Dielectric properties of the hydrogen-bonded material, 5-bromo-9-hydroxyphenalenone (C(13)H(7)O(2)Br; BrHPLN), are investigated theoretically by means of electronic structure calculations and Monte Carlo simulations. The density functional calculations of BrHPLN crystals have revealed that the polarization per one molecule can be about 1.7 times larger than that of the isolated monomer. It is also found that there exists significant electron density (0.01 e bohr(-3)) in an intermolecular C-H···O region, which, together with the interatomic distances of 2.39 ? for H···O and 3.34 ? for C···O, suggests the existence of intermolecular weak hydrogen bonding that may enhance the molecular polarization. The induced polarization effects in various intermolecular configurations are evaluated with the Fragment Molecular Orbital method. In addition to the π-π stacking interactions, two types of "in plane" intermolecular weak hydrogen-bonding configurations are found to affect the molecular dipole moment most significantly. These effects are efficiently included in a Monte Carlo simulation method in terms of "dipole corrections" as functions of both the intermolecular arrangements and the intramolecular proton configurations. The application to the dielectric phase transition of a BrHPLN crystal shows that the dipole corrections almost double the transition temperature, toward better agreement with experiments, and qualitatively affect the temperature dependence of the dielectric constant. Discussions are given to support that the results will remain adequate and consistent even after explicit inclusion of the quantum tunneling effects.     

Effects of disorder on modulated quantum Hall systems

The Hall conductivity and the localization length are calculated for weakly modulated two-dimensional systems within the lowest Landau level approximation. We find that the fractal character of the Hofstadter butterfly is reflected on the coincidence in the localization and the Hall conductivity among a series of fluxes φ+2n with integers n.     

Multiwalled carbon nanotubes mass-produced by dc arc discharge in He–H2 gas mixture

Uniform cathode deposits (longer than 15 mm), containing multiwalled carbon nanotubes (MWNTs) inside, were produced by dc arc discharge evaporation with a computer-controlled feeder of a pure-carbon electrode without a metal catalyst in a He–H₂ gas mixture. The purification of MWNTs was carried out to remove amorphous carbon and carbon nanoparticles. High-resolution transmission electron microscopy observations and Raman scattering studies show that the MWNTs possess a high crystallinity and a mean outermost diameter of ∼ ∼10 nm. It has been confirmed that the current density in the electron field emission from a purified MWNT mat can reach 77.92 mA/cm², indicating that the purified MWNTs are a promising candidate electron source in a super high-luminance light-source tube or a miniature X-ray source.     

Multistage automodulation using decreasing length cavities

It is observed that the length of a coaxial cavity strongly affects the induced gap voltage and the level of automodulation. For high-frequency automodulation for a beam with slow rise-time, a series of cavities with decreasing lengths is proposed.     

Vertices of Degree 5 in a Contraction Critically 5-connected Graph

An edge of a k-connected graph is said to be k-contractible if the contraction of the edge results in a k-connected graph. A k-connected graph with no k-contractible edge is said to be contraction critically k-connected. We prove that a contraction critically 5-connected graph on n vertices has at least n/5 vertices of degree 5. We also show that, for a graph G and an integer k greater than 4, there exists a contraction critically k-connected graph which has G as its induced subgraph.     

Unitarily invariant norms related to the numerical radius

We determine the maximum in the class of unitarily invariant norms ∥·∥ such that w(A) ? ∥A∥ for all n-square matrices A. Here w(A) denotes the numerical radius of A.     

Inelastic scattering on 12Be and disappearance of the N = 8 magic number

Experimental studies on in-beam γ-ray spectroscopy using a ¹²Be radioactive beam are presented. Inelastic scattering of the neutron-rich ¹²Be nucleus on ²⁰⁸Pb, ¹²C, and (CH₂)_n targets has been studied by measuring de-excitation γ-rays in coincidence with scattered particles. The level schemes and transition probabilities are determined for low-lying excited states in ¹²Be. The present paper presents a brief review of the spectroscopic results, which may be associated with the N = 8 shell quenching near the drip line. Received: 1 May 2001 / Accepted: 4 December 2001