Long Time Behaviour of Unstable Multilevel Systems in Presence of Zero Energy Resonance

Long time behaviour of the survival probability for unstable multilevel systems is studied based on the N-level Friedrichs model in the presence of zero energy resonance, that means the divergence of the resolvent at zero energy. With resort to the technique developed by Jensen and Kato [Duke Math. J. 46, 583 (1979)], the zero energy resonance of this model is characterized by the zero energy eigenstate that does not belong to the Hilbert space. It is then shown that for some kinds of the form factors, logarithmically slower decay of the survival probability can be realized.     

Continuous reactor system of monosized colloidal particles

A reactor system, which continuously hydrolysed the metal alkoxide in an alcohol solution, was designed using an electromagnetic stirrer and an ageing tube. Several monosized colloidal particles were produced by this reactor system, which had high reproducibility and reliability for long-term production. The relation between powder characteristics and experimental parameters such as reagent concentration, mixing rate, ageing time, temperature, was investigated. These parameters had an effect on the particle size, size distribution, morphology and state of agglomeration. It is possible to control the particle size to between 0.1 and 1.0 μm by varying the experimental conditions. A narrower size distribution of powders was obtained by using an electromagnetic stirrer with greater flow rate. Physical and chemical properties of monosized colloidal particles obtained by this reactor were comparable to those of monosized colloidal particles obtained by the batch process.     

Velocity and turbulence measurements in a cylindrical bath subject to centric bottom gas injection

Laser Doppler velocimeter (LDV) measurements were made to clarify the fluid flow behavior in a bath subject to centric bottom gas injection. Correlations of the axial mean velocity and turbulence components in the gas-liquid two-phase flow region,i.e., in the bubbling jet region, were proposed as functions of the inner diameter of nozzle, gas flow rate, and densities of gas and liquid. Measured values of the flow rate, momentum, and kinetic energy of water rising upward were approximated satisfactorily by these empirical correlations. In addition, the Reynolds shear stress was calculated and compared with measured values. Formerly Graduate Student, Osaka University,     

Nano-strip grating lines self-organized by a high speed scanning CW laser

After a laser annealing experiment on Si wafer, we found an asymmetric sheet resistance on the surface of the wafer. Periodic nano-strip grating lines (nano-SGLs) were self-organized along the trace of one-time scanning of the continuous wave (CW) laser. Depending on laser power, the nano-trench formed with a period ranging from 500 to 800 nm with a flat trough between trench structures. This simple method of combining the scanning laser with high scanning speed of 300 m min(-1) promises a large area of nanostructure fabrication with a high output. As a demonstration of the versatile method, concentric circles were drawn on silicon substrate rotated by a personal computer (PC) cooling fan. Even with such a simple system, the nano-SGL showed iridescence from the concentric circles.     

Anti-obesity and anti-diabetic effects of ethanol extract of Artemisia princeps in C57BL/6 mice fed a high-fat diet

Artemisia princeps is commonly used as a food ingredient and in traditional Asian medicine. In this study, we examined the effects of long-term administration of an ethanol extract of A. princeps (APE) on body weight, white adipose tissue, blood glucose, insulin, plasma and hepatic lipids, and adipocytokines in C57BL/6 mice fed a high-fat diet. Daily feeding of a 1% APE diet for 14 weeks normalized elevated body weight, white adipose tissue, and plasma glucose and insulin levels, and delayed impaired glucose tolerance in mice a fed high-fat diet. These events were not observed in mice fed a control diet containing 1% APE. Liver triglyceride and cholesterol levels were similar in mice fed a 1% APE-diet and those fed a control diet. In the high-fat diet groups, APE inhibited hepatic fatty acid synthase (FAS) and suppressed the elevation of plasma leptin, but had no effect on adiponectin levels. These findings suggest that the regulation of leptin secretion by APE may inhibit FAS activity with subsequent suppression of triglyceride accumulation in the liver and adipose tissues. Inhibition of lipid accumulation can, in turn, lead to improvements in impaired glucose tolerance.     

Occurrence of paralytic shellfish poison (PSP)-producing dinoflagellate Alexandrium tamarense in Hiroshima Bay, Hiroshima Prefecture, Japan, during 1993-2004 and its PSP profiles

To assess levels of shellfish intoxication by the paralytic shellfish poison (PSP)-producing dinoflagellate Alexandrium tamarense, potential health risks to human shellfish consumers and the possible need for regulatory intervention, yearly variations of maximum cell density of this species were examined from 1993 to 2004 in Kure Bay and Kaita Bay, which are located within Hiroshima Bay, Hiroshima Prefecture, Japan. The seawater temperature was determined concomitantly. In Kure Bay, maximum concentrations of 1,400 and 1,300 cells/mL at 0 and 5 m depths were observed on 21 and 24 April 1997. In Kaita Bay, remarkably high concentrations above 1,000 cells/mL of A. tamarense were observed in two out of three years investigated. These facts suggest that the environment in both bays is favorable for the propagation of A. tamarense. The temperature range at which the natural population of A. tamarense blooms was generally from 12 to 16 degrees C. Four strains (ATKR-94, -95, -97 and -01) from Kure Bay and one strain (ATKT-97) from Kaita Bay were established. The strain ATKR-94, cultured in modified SW-2 medium at 15 degrees C for 15 days, showed a specific toxicity of 33.8 x 10(-6) MU/cell. The toxins in all five strains exist almost exclusively as beta-epimers (C2 (PX2 or GTX8), GTX3, dcGTX3 and GTX4), which accounted for 54.9 to 73.0 mol% of the total. The corresponding a-epimers (C1 (PX1 or epi-GTX8), GTX2, dcGTX2 and GTX1) accounted for 6.0 to 28.9 mol%. The toxin profiles of ATKR-97 and ATKT-97 were characterized by unusually high proportions of low-potency sulfocarbamoyl toxin, which comprised 62.4 and 68.2 mol%, respectively, of total toxins. In the toxic bivalves, the low-toxicity sulfocarbamoyl components, major components of A. tamarense, were present in amounts of only a few percent, suggesting that in vivo conversion of PSP occurs after ingestion. A comparison of the toxin profiles of the causative dinoflagellate and contaminated bivalves showed that PSP components exist in the bivalves in the form of alpha-epimers, presumably owing to accumulation or storage of the toxins.     

Effect of cross-flow on the frequency of bubble formation from a single-hole nozzle

Bubble formation from a single-hole nozzle placed vertically upward in a rotating water bath was investigated using a high-speed video camera. Air was used as the working gas. The measured values of the frequency of bubble formation, f _B, were compared with those observed in a stationary bath, f _B0. The velocity of cross-flow, ν_θ, affected the bubble formation significantly when it exceeded a critical value, ν_θc . The ratio of f _B to f _B0 was unity for ν_θ≦ν_θc , but it changed in a complex manner for ν_θ>ν_θc . In the latter case, when the air flow rate Q _g was relatively low, f _B/f _B0 became larger than unity irrespective of Q _g, and an empirical correlation of f _B/f _B0 was proposed as a function of ν_θ and the inner diameter of the nozzle, d _ni. As the gas flow rate increased, f _B/f _B0 decreased monotonically and became smaller than unity, and an empirical correlation of f _B/f _B0 was derived as a function of Q _g, ν_θ, and d _ni. These empirical correlations could approximate the measured values of f _B/f _B0 within a scatter of −15 to +20 pct.     

Improvement of fatigue-crack growth resistance by grain-boundary reaction precipitates at high temperature

Effects of grain-boundary reaction precipitates on fatigue-crack growth rate were investigated using austenitic 21 wt% Cr-4 wt% Ni-9wt% Mn heat-resisting steel at 973 K in air. Grain boundaries were serrated by-the grain-boundary reaction precipitates. The crack growth rate was considerably decreased by these precipitates, especially at low crack growth rates. Fatigue cracks extended to the serrated grain boundaries or to the interface between the grain-boundary reaction nodule and the grain. Therefore, the cracks grew along zigzag paths, and brittle intergranular fracture was inhibited. The decrease in the fatigue-crack growth rate was explained by these changes in fracture mode.