Breakdown Phenomena in Point-to-Point Gaps

Measurements with multiple techniques delineating the complete sequence of events from the primary streamer to the formation of the spark channel for relatively small point-to-point gaps are reported. The pulsed potential with 0.4 μs rise time and 1800 μs decay time was applied to the point-to-point gap, of which length was changed from 6 to 14 cm. The light pulses were observed by 5 photomultipliers as well as current and potential wave. It is shown that the spark channel can be materialized through the following three processes: 1) initial process, in which the primary, the secondary, and the tertiary streamers develop from both point electrodes into gap, and the ionizing wave bridges the gap; 2) intermediate process, in which the dark period proceeds with ion and electron movement if the applied potential is around the mean breakdown potential, or in the other case, the ``leader' develops from the anode with the help of ionizing waves; and 3) final process, in which the channel is highly ionized at first by the ionizing wave, then gas heating, to lead the formation of a spark channel. On the bases of the measurements of streamer speed and current, the ion and electron density were calculated. It is estimated that starting with the primary streamer with an electron density of 1012 cm-3, the electron density in the streamer channel is augmented by the ionizing wave up to 1012cm -3 when the gap is bridged by the ionizing wave.     

The dilute solution properties of maleic anhydride and maleic acid copolymers: 1. Light scattering, osmotic pressure and viscosity measurements

Dilute solution behaviour of poly(maleic anhydride-co-ethyl vinyl ether) and poly(maleic acid-co-ethyl vinyl ether) has been investigated by light scattering, osmotic pressure, and viscosity measurements. The molecular weights ($\text{M}\text{?}{}_{\mathrm{w}}$ and $\text{M}\text{?}{}_{\mathrm{n}}$), the second virial coefficients A₂, and the intrinsic viscosities [η] have been determined for three states of this copolymer: anhydride-form, H-form, and Na-salt independently. The constants in the Mark-Houwink relations were obtained for the above three states under different solvent conditions. The molecular weight of the anhydride-form is found to be higher than that of the acid-form or the Na-salt, suggesting the degradation in a process of hydrolysis. The second virial coefficient A₂ as well as the Mark-Houwink relation indicates that the anhydride-form and H-form behave as flexible polymer chains in good solvents. However, the polymer coil of Na-salt is highly expanded even at saturated NaCl concentration.     

Reduction and Sintering of a Nickel–Dispersed-Alumina Composite and Its Properties

High-density nickel–dispersed-alumina (Al₂O₃/nickel) composites with superior mechanical properties were obtained by the hydrogen reduction and the hot pressing of alumina–nickel oxide (Al₂O₃/NiO) mixed powders. The mixtures were prepared by using NiO or nickel nitrate (Ni(NO₃)₂· n H₂O) as a dispersion source of nickel metal. Microstructural investigations of the composite fabricated using nitrate powder revealed that fine nickel particles, } 100 nm in diameter, dispersed homogeneously at the matrix grain boundaries, forming the intergranular nanocomposite. High strength (.1 GPa) and high-temperature hardness were registered for the composite that contained a small amount of nickel dispersion. The ferromagnetic properties of nickel, such as high coercive force, were observed, because of the fine magnetic dispersions, which indicates a functional value of structural composites.     

The effects of infusion of trieicosapentaenoyl-glycerol emulsion on extravascular lung water during myocardial ischemia and reperfusion in dogs

To test the effects of eicosapentaenoic acid (EPA) infusion on pulmonary edema induced by coronary ligation and reperfusion, extravascular lung water (EVLW) was measured in situ by the thermal-dye double indicator dilution method in dogs. In the control group of five dogs, 30 mL of a 10% soybean oil emulsion was infused through a leg vein. One hour after infusion, the left anterior descending coronary artery below the first diagonal branch was ligated for 15 min and then reperfused for 30 min. In the EPA group, six dogs were similarly treated with an emulsion of a 10% trieicosapentaenoyl-glycerol (90% pure). EVLW, pulmonary capillary wedge pressure, mean pulmonary artery pressure, mean blood pressure, and cardiac index were measured before and 15 min after coronary ligation, and 15 min and 30 min after coronary reperfusion. There were no significant differences in the hemodynamic indices between the two groups. EVLW significantly increased up to two times of baseline during coronary ligation in the control group (P< 0.05) and more during reperfusion (P<0.01), whereas EVLW did not increase in the EPA group. In conclusion, EPA inhibited EVLW accumulation and may be useful for ameliorating one of the ischemia-reperfusion-induced complications, pulmonary edema.     

Characterization of morphology and mechanical properties of block copolymers using atomic force microscopy: Effects of processing conditions

The effect of preparation methods and processing conditions on morphology and mechanical properties of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymer were investigated with atomic force microscopy (AFM) tapping mode and nanomechanical mapping, tensile testing, and gel permeation chromatograph (GPC). It was found that the samples prepared by solution casting and melt processing show large difference in morphology and mechanical properties. High shear rate does not induce alignment of lamellar block copolymer melts but leads to serious degradation of SEBS. As increase of rotational speed from 0 to 400 rpm, the molecular weight including M_n and M_w decreases from 67,100 to 26,000 and 70,000 to 43,000, respectively. Such large molecular weight decrease causes greatly decreased tensil strength but there is almost no evident effect on the well-phase separated morphology and Young's modulus of the SEBS. The Young's modulus distribution revealed by nanomechanical mapping becomes narrow as the increase of rotational speed. The amount of SEBS molecular having higher Young's modulus, which play a very important role in tensile strength of SEBS, also decreases.     

Stimulation of THP-1 Macrophages with LPS Increased the Production of Osteopontin-Encapsulating Exosome

Osteopontin (OPN) mediates bone remodeling and tissue debridement. The OPN protein is cleaved, but it is unclear how full-length (FL)-OPN or its cleaved form perform their biological activities in target cells. We, therefore, performed the molecular characterization of OPN in exosomes (Exo). The Exo were isolated from lipopolysaccharide (LPS)-stimulated phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 macrophages. The Exo were also isolated from PMA-differentiated THP-1 macrophages. The Exo were identified using the qNano multiple analyzer (diameter 59–315 nm) and western blotting with a CD9 antibody. LPS-stimulated cells produced more particles than non-stimulated cells. The presence of the FL or the cleaved form of OPN was confirmed using western blot analysis. A mixture of FL and cleaved OPN was also measured using an ELISA system (Ud-OPN) and their presence in the Exo was confirmed. Ud/FL ratios became low after LPS stimulation, indicating the enhanced encapsulation of FL-OPN in the Exo by LPS. These findings suggest that LPS stimulation of human macrophages facilitates the synthesis of FL-OPN, which is cleaved in cells or the Exo after release. These findings indicate that Exo is a suitable vehicle to transfer OPN to the target cells.     

Potential bile acid metabolites. 24. An efficient synthesis of carboxyl-linked glucosides and their chemical properties

A facile and efficient synthesis of the carboxyl-linked glucosides of bile acids is described. Direct esterification of unprotected bile acids with 2,3,4,6-tetra-O-benzyl-d-glucopyranose in pyridine in the presence of 2-chloro-1,3,5-trinitrobenzene as a coupling agent afforded a mixture of the α- and β-anomers (ca. 1∶3) of the 1-O-acyl-d-glucoside benzyl ethers of bile acids, which was separated effectively on a C₁₈ reversedphase chromatography column (isolated yields of α- and β-anomers are 4–9% and 12–19%, respectively). Subsequent hydrogenolysis of the α- and β-acyl glucoside benzyl ethers on a 10% Pd−C catalyst in acetic acid/methanol/EtOAc (1∶2∶2, by vol) at 35°C under atmospheric pressure gave the corresponding free esters in good yields (79–89%). Chemical specificities such as facile hydrolysis and transesterification of the acyl glucosides in various solvents were also discussed.     

Selectivity and mechanism for skeletal isomerization of alkanes over typical solid acids and their Pt-promoted catalysts

Selectivities for skeletal isomerizations of n-butane and n-pentane catalyzed by typical solid acids such as Cs_2.5H_0.5PW₁₂O₄₀ (Cs2.5), SO₄²⁻/ZrO₂, WO₃/ZrO₂, and H-ZSM-5 and their Pt-promoted catalysts were compared. High selectivities for n-butane and low selectivity for n-pentane were observed over Cs2.5 and SO₄²⁻/ZrO₂, while H-ZSM-5 was much less selective, and WO₃/ZrO₂ was highly selective for both reactions. The Pt-promoted solid acids were usually selective for these reactions in the presence of H₂ except for Pt-H-ZSM-5 for n-butane isomerization. Both the acid strength and pore structure would be factors influencing the selectivity. Mechanism of skeletal isomerization of n-butane was investigated by using 1,4-¹³C₂-n-butane over Cs2.5 and Pt–Cs2.5. It was concluded that n-butane isomerization proceeded mainly via monomolecular pathway with intramolecular rearrangement on Pt–Cs2.5, while it occurred through bimolecular pathway with intermolecular rearrangement on Cs2.5. The higher selectivity on Pt–Cs2.5 would be brought about by the monomolecular mechanism. In the skeletal isomerization of cyclohexane, Pt–Cs2.5/SiO₂ was highly active and selective, while Pt–Cs2.5 was less selective. Control in the acid strength of Cs2.5 by the supporting would be responsible for the high selectivity.     

Dietary conjugated linolenic acid in relation to CLA differently modifies body fat mass and serum and liver lipid levels in rats

The present study compared the effect of dietary conjugated linolenic acid (CLNA) on body fat and serum and liver lipid levels with that of CLA in rats. FFA rich in linoleic acid, α-linolenic acid, CLA, or CLNA were used as experimental fats. Male Sprague-Dawley rats (4 wk old) were fed purified diets containing 1% of one of these experimental fats. After 4 wk of feeding, adipose tissue weights, serum and liver lipid concentrations, serum tumor necrosis factor (TNF)-α and leptin levels, and hepatic β-oxidation activities were measured. Compared with linoleic acid, CLA and, more potently, CLNA were found to reduce perirenal adipose tissue weight. The same trend was observed in the weight of epididymal adipose tissue. CLNA, but not CLA, was found to significantly increase serum and liver IG concentrations. Serum FFA concentration was also increased in the CLNA group more than in the other groups. The activity of β-oxidation in liver mitochondria and peroxisomes was significantly higher in the CLNA group than in the other groups. Thus, the amount of liver TG exceeded the ability of hepatic β-oxidation. Significant positive correlation was found between the adipose tissue weights and serum leptin levels in all animals (vs. perirenal: r=0.557, P<0.001; vs. epididymal: r=0.405, P<0.05). A less significant correlation was found between adipose tissue weights and serum TNF-α level (vs. perirenal: r=0.069, P<0.1; vs. epididymal: r=0.382, P<0.05). Although the mechanism for the specific effect of CLNA is not clear at present, these findings indicate that in rats CLNA modulated the body fat and TG metabolism differently from CLA.     

Defect and Mixed Conductivity in Nanocrystalline Doped Cerium Oxide

The results obtained from a study on the microstructure and the electrical properties of Gd-doped CeO₂ thin films were reported. Dense, nanocrystalline films on sapphire substrates are prepared using a polymeric precursor spin coating technique. The electrical conductivity was studied as a function of temperature and oxygen activity and correlated with the grain size. For nanocrystalline Gd-doped CeO₂ thin films, the ionic conductivity increased with decreasing activation energy as the grain size decreased. A conductivity model was developed to analyze P _O2 behavior of the electrical conductivity. Using the conductivity model, the hopping energy of electron conduction and the enthalpy of oxygen vacancy formation were determined for different microstructures.