Hamiltonian cycles on random lattices of arbitrary genus

A Hamiltonian cycle of a graph is a closed path that visits every vertex once and only once. It has been difficult to count the number of Hamiltonian cycles on regular lattices with periodic boundary conditions, e.g. lattices on a torus, due to the presence of winding modes. In this paper, the exact number of Hamiltonian cycles on a random trivalent fat graph drawn faithfully on a torus is obtained. This result is further extended to the case of random graphs drawn on surfaces of an arbitrary genus. The conformational exponent y is found to depend on the genus linearly.     

Organic hybrid of chlorinated polyethylene and hindered phenol. II. Influence of the chemical structure of small molecules on viscoelastic properties

The viscoelastic properties and stabilities of those properties of organic hybrids consisting of chlorinated polyethylene (CPE) and tetrakis[methylene‐3‐(3‐5‐di‐tert‐butyl‐4‐hydroxy phenyl)propionyloxy]methane (AO‐60) and triethylene glycol bis[3‐(3‐tert‐butyl‐4‐hydroxy‐5‐methyl phenyl)propionyloxy] (AO‐70) were investigated. The CPE/AO‐70 hybrids show only one transition, whereas for the CPE/AO‐60 hybrids, one novel relaxation appears above the glass‐transition temperature of CPE. This relaxation on the higher temperature side in the mechanical spectrum for CPE/AO‐60 is associated with the appearance of the AO‐60‐rich phase. Furthermore, the stabilities of the viscoelastic properties and microstructures of the organic hybrids consisting of CPE and multifunctional hindered phenols are dominated by the strength of the intermolecular interaction between CPE and phenols and the conformations of the middle skeletal parts of hindered phenols. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1496–1503, 2000     

Biological activity of chitosan–sugar hybrids: specific interaction with lectin

The specific interactions between lectins and chitosan–sugar hybrids, the synthesized chitosan derivatives linking carbohydrate residue to the amino group of chitosan, were investigated. The specific bindings of chitosan‐L ‐fucose (Fuc) hybrid with Ulex europaeus agglutinin I (UEA I, a lectin specific to L ‐Fuc), and chitosan‐N‐acetyl‐D ‐glucosamine (D ‐GlcNAc) hybrid with Concanavalin A (Con A, a lectin specific to D ‐glucose, D ‐mannose and D ‐GlcNAc), were confirmed by a surface plasmon resonance technique. The microscopic observation of Pseudomonas aeruginosa, which was preincubated with the fluorescein isothiocyanate‐labeled chitosan‐L ‐Fuc hybrid, showed bacteria aggregation. The aggregation was thought to be resulted from the specific interaction of the L ‐Fuc residue of the hybrid with PA‐II lectin on the surface of P. aeruginosa. The chitosan‐L ‐Fuc hybrid inhibited P. aeruginosa growth more effectively in comparison with the other hybrids or unmodified chitosan. The enhancement of antimicrobial activity of chitosan‐L ‐Fuc hybrid could be attributed to the specific binding between PA‐II lectin of P. aeruginosa and L ‐Fuc residue of the L ‐Fuc hybrid. Copyright © 2000 John Wiley & Sons, Ltd.     

Biodegradation of chitin with enzymes and vital components

Chitin from squid pen was effectively degraded by the chitinase from Bacillus sp. PI-7S, while the degradation of chitin with lysozyme proceeded very slowly. Among the various vital components studied, the degradation of chitin from squid pen was performed not by canine serum, canine tela subcutanea, canine tela liver, and equine serum but by bovine serum and caprine serum. Noteworthy is the fact that chitin sponge subcutaneously implanted in dog reported not to have chitinase was degraded in ca. 14 days.     

Light-off Performance of Three-Way Catalysts Before and After Accelerated Aging Test with an Engine-Dynamometer

This study demonstrates the reaction behavior during the purification of model automotive exhaust gases over Pd catalysts before and after thermal degradation. In particular, to investigate the relationship between the Pd state and the reaction behavior of Pd/Al₂O₃ and Pd/CeO₂−ZrO₂ (CZ), operando X-ray absorption spectroscopy measurements were performed during purifying exhaust gases over real and model catalysts mimicking the degradation of Pd particles and CZ supports after accelerated aging tests. The NO reduction activity of the aggregated Pd metal species was as high as that of the highly dispersed Pd species, but hydrocarbon (HC) poisoning was significantly enhanced by the aggregation of Pd metal particles caused by thermal aging. The existence of a three-phase boundary (TPB) between the CZ, the Pd particles, and the gas phase strongly affected the catalytic activity at low temperatures, and the presence of a sufficient TPB facilitated the combustion of unburned HCs owing to the oxygen storage performance of CZ. Thus, the TPB reduced the poisoning of the precious metal surface by HC species at low temperatures. Therefore, the findings of this study will facilitate the development of next-generation gas purification catalysts with high activity and durability.     

meso‐Diketopyripentaphyrin and Diketopyrihexaphyrin as Macrocyclic Tripyrrinone Ligands for NiII Ions

We report expanded porphyrins with pyridine rings and two neighboring carbonyl groups, which allow Ni^II ions to coordinate to the tripyrrinone‐type NNNO coordination structure with Ni?O bonds. The selectivity of tripyrrinone is superior to other pyrrolic or pyridinic cavities of expanded porphyrins. Introduction of α‐carbonyl pyridine next to the tripyrrolic conjugated structure is a powerful strategy for regioselective metalation of flexible expanded porphyrinoids.     

Spontaneous ignition of ultra-fine magnesium powder without an original oxide coat at room temperature in O2/N2 mixture streams

To examine the pyrophoric characteristics of Mg powder, we generated ultra-fine Mg particles (average particle diameter: about 0.3 μm) without an original oxide coat in an Ar stream. The ignition of the powder was measured by using the impinging O₂/N₂ mixture streams over a wide range of the experimental parameters: pressure, oxygen concentration and velocity of the streams. The Mg powder was found to ignite even at room temperature. The spontaneous ignition temperatures in the range of 278  324 K were insensitive to all the experimental parameters. The ignition delay time had a tendency to decrease with increasing experimental parameters.The ignition process of the Mg powder was found to be controlled by the surface reaction rate without an oxide coat. We proposed a new ignition hypothesis considering a critical oxide thickness on the Mg powder particles at the transition temperature from protective to non-protective nature: that is, the ignition of the Mg powder occurs when the powder temperature rises above the transition temperature before surface reactions form a protective oxide coat with the critical thickness on the individual particle surfaces. According to this hypothesis, an ignition model of Mg powder cluster was developed, and the relation between the spontaneous critical ignition temperature and the ultra-fine powder size, depending on the critical thickness of the protective oxide coat, was clarified. The critical oxide thickness was estimated.     

SQUID sensor application for small metallic particle detection

High-Tc superconducting quantum interference device (SQUID) is an ultra-sensitive magnetic sensor. Since the performance of the SQUID is improved and stabilized, now it is ready for application. One strong candidate for application is a detection system of magnetic foreign matters in industrial products or beverages. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. If this happens, the manufacturer of the product suffers a great loss recalling products. The outer dimension of metallic particles less than 100 μm cannot be detected by an X-ray imaging, which is commonly used for the inspection. Ionization of the material is also a big issue for beverages in the case of the X-ray imaging. Therefore a highly sensitive and safety detection system for small foreign matters is required. We developed detection systems based on high-Tc SQUID with a high-performance magnetic shield. We could successfully measure small iron particles of 100 μm on a belt conveyer and stainless steel balls of 300 μm in water. These detection levels were hard to be achieved by a conventional X-ray detection or other methods.     

Masking mechanisms of bitter taste of drugs studied with ion selective electrodes

The masking mechanisms of the bitter taste of propantheline bromide (PB) and oxyphenonium (OB) bromide by native and modified cyclodextrins, saccharides, surfactants, organic acids, nonionic and anionic polymers, and other compounds were investigated with ion selective electrodes. The intensity of the bitter taste for a mixed solution of cyclodextrin with PB or OB was quantitatively explained from the observed electromotive force with the following assumptions: the complex and the masking agent do not have any tastes and the bitter taste is independent of other tastes. Sodium dodecyl sulfate reduced the bitter taste remarkably, and this reduction was also explicable on the basis of the same mechanism. Sodium taurodeoxycholate enhanced the bitter taste, because of its strong bitterness, although it formed 1 : 1 complexes with PB and OB. The masking mechanism of saccharides was ascribed to overcoming the weak bitterness of the drug by the strong sweetness. Lambda-carrageenan suppressed the bitter taste remarkably. This suppression was ascribed to the binding of PB and OB to lambda-carrageenan, the effect of the solution viscosity on the bitter taste, and the covering of the bitter taste receptor by lambda-carrageenan. It was suggested that the moderate masking by other polymers was attributable to the effect of the solution viscosity or the receptor covering. Native and modified beta-cyclodextrins, sodium dodecyl sulfate, lambda-carrageenan, Tween 20, and sodium carboxymethyl cellulose are good masking agents for the bitter tastes of PB and OB. The drug ion selective electrode is a useful tool for understanding of the masking mechanism of the bitter taste, screening of masking agents, and estimation of appropriate concentrations of the masking agents.     

Effect of the moisture content in aerosol on the spray performance of Stmerin D HFA preparations

Stmerin D, a pressurized metered dose inhaler (MDI) for treatment of asthma, contains CFCs (chlorofluorocarbons) as a propellant. For the CFC replacement study, two formulations were prepared using hydrofluoroalkanes (HFA-134a and HFA-227) and the effect of storage on the spray performance was investigated under accelerated stress conditions. Drug stability, moisture content and spray performances such as the emitted dose uniformity and aerodynamic particle size distribution were evaluated. Drug content did not change after 3 months storage at 40 degrees C/75% RH. However, the emitted dose uniformity varied and the respirable fraction (RF) was reduced remarkably. While stored at 40 degrees C/ambient for 3 months, no change was observed in either drug content or spray performances. This study clarified that the moisture content in the canister played an important role on the spray performance, and it changed not only the emitted dose uniformity but also the particle size distribution. Consequently, in order to improve the stability of the spray performance of aerosol prepared with HFAs, moisture permeation into the canister must be controlled.