Association schemes of quadratic forms

A new class of association schemes attached to quadratic forms is obtained. In terms of a graph, those schemes are distance regular but generally not distance transitive.     

ESR study of thermal history and dating of a stone tool

Electron spin resonance (ESR) of Fe³⁺ ions and of radiation-induced centers in quartz (E’, peroxy and Al centers) was studied to distinguish between burnt and unburnt stone tools and to determine their age. The yellow stone tool with a reddish edge discovered at the paleolithic site in Kamitakamori, northern Japan, was investigated. The ESR spectrum intensity of Fe³⁺ ions around g=4.3 and the color of the material changed at 600°C and 240°C, respectively, which indicates that the red part was heated at 240–600°C. The E′ center in the red part was used for dating because isochronal annealing experiments showed low thermal stability of the Al center and overlap of broad signals at g=2.0086 onto the peroxy center. Assuming the same efficiency of defect formation in the red part as of that in the laboratory-heated material at 450°C, the obtained age of 520–770 ka is in concordance with the ages of the tephra layers at the site.     

Thermal effect in metamorphic rock around an intrusion zone with ESR studies

Hornfels, and intrusion rocks were studied with electron spin resonance (ESR) as a function of the distance from an intrusion zone in Mino Natural Park, Osaka, Japan. The temperature distribution in metamorphic rocks around an intrusion zone was calculated based on a simplified model of one-dimensional thermal conduction. The age as well as the thermal effect due to an intrusion rock were assessed using ESR signal intensities of paramagnetic defect centers (E’, oxygen-hole, and Al) in quartz grains. Geothermal heating effects are observable more than ten million years later for stable detects such as the E’ center.     

Contractible edges inn-connected graphs with minimum degree greater than or equal to [5n/4]

It is proved that ifG is ann-connected graph with minimum degree greater than or equal to [5n/4],n 4, thenG has an edgee such that the graph obtained fromG by contractinge is stilln-connected.Dedicated to Professor Nagayoshi Iwahori on his 60th birthday     

Characterization of inclusion complexation of various tetraalkylammonium chlorides with cucurbit[7]uril by external high-pressure studies

The inclusion constants of tetraalkylammonium salts (ASs) with cucurbit[7]uril (CB[7]) were determined at high-pressures using methylene blue as a chemical indicator. CB[7] formed 1:1 inclusion complexes with ASs. We found a characteristic dependence of the alkyl chain substituents in ASs on the inclusion equilibrium, which was responsible for the formation of clathrate hydrates of the AS in bulk. Furthermore, we examined the effects of external high pressures on the CB[7] inclusion complexations of ASs having different alkyl chain lengths. Pressure dependence experiments allowed us to calculate the reaction volume (ΔV) upon inclusion; i.e., the volume change (ΔV_desolv) accompanying desolvation around the guest molecules and the volume change (ΔV_repel) caused by the water molecules repelled from the CB[7] cavity. The volumetric study for the inclusion of ASs with CB[7] showed that in the tetraheptylammonium ion, one arm (alkyl chain) was encapsulated in the CB[7] cavity, while in other ASs, two arms were located in the cavity. NMR measurements of the complexes and pressure-dependent studies provided unique information on the structures of the inclusion complexes of ASs with CB[7].     

ESR studies of mylonite at San Andreas Fault,California

The dating of the San Andreas Fault, California based on a qualitative analysis of EPR spectra of mylonite has been carried out.     

Polar and Hydrogen-Bonding Effects of Alcohols on the Emission Spectrum of Styrene–Triethylamine System

The emission spectra of styrene (ST)–triethylamine (TEA) systems were measured under steady-state illumination conditions in some tetrahydrofuran (THF)–protic solvent mixtures. The fluorescence spectrum of the ST–TEA system in THF consists of two bands (band A at 304 nm (fluorescence of ST) and band B at 460 nm (emission from an exciplex)). The intensity of band A increased and that of band B decreased with increasing amounts of protic solvents in THF–protic solvent mixtures. The increase in the intensity of band A was explained by the decrease in the concentration of free amine owing to the hydrogen-bonding interaction (or protonation) between TEA and protic solvents. The decrease in the intensity of band B was considered to be caused by the decrease in the concentration of free amine upon the addition of protic solvents and the enhanced conversion of the exciplex to an ion pair with increasing solvent polarity. The polar effect was expressed as a function of the relative permittivity of the solution.     

Controlling the incorporation and release of C60 in nanometer-scale hollow spaces inside single-wall carbon nanohorns

We succeeded in large-scale preparation of single-wall carbon nanohorns (SWNH) encapsulating C60 molecules in a liquid phase at room temperature using a "nano-precipitation" method, that is, complete evaporation of the toluene from a C60-SWNH-toluene mixture. The C60 molecules were found to occupy 6-36% of the hollow space inside the SWNH, depending on the initial quantity of C60. We showed that the C60 in C60@SWNHox was quickly released in toluene, and the release rate decreased by adding ethanol to toluene. Numerical analysis of the release profiles indicated that there were fast and slow release processes. We consider that the incorporation quantity and the release rate of C60 were controllable in/from SWNHs because SWNHs have large diameters, 2-5 nm.     

Preparation and properties of some water-soluble cobalt (III)–poly-4-vinylpyridine complexes

Water-soluble cobalt(III) chelates having a polymeric ligand such as cis-[Co(en)_2-PVPCl]Cl₂ and cis-[Co-(trien)PVPCl]Cl₂ (PVP = poly-4-vinylpyridine) were prepared by substitution reactions between cobalt(III) chelate and PVP in water–alcohol solution. PVP of different degrees of polymerization was used as the ligand in preparation of these complexes. The PVP complexes were identified and their properties ascertained by microanalysis and by a study of the infrared, ultraviolet, visible, and PMR spectra. Most of the characteristic properties of these complexes may be ascribed to the polymeric structure of the PVP ligand.