Dielectric breakdown characteristics of cryogenic nitrogen gasabove liquid nitrogen

We measured the DC dielectric breakdown characteristics of cryogenic nitrogen gas above a liquid nitrogen surface for needle-to-plane and sphere-to-plane electrode configurations. Experimental results revealed that the DC breakdown voltage of cryogenic nitrogen gas increased, as the distance from the gap axis to the liquid nitrogen surface diminished, i.e. as the liquid nitrogen surface got closer to the gap. The breakdown voltage proved to be enhanced not only by the temperature drop of nitrogen gas due to the existence of liquid nitrogen, but also by an effect of vapor mist arising from vaporization of liquid nitrogen. For the quasi-uniform electrode configuration, the relation between breakdown voltage and the gas density times the gap spacing agreed well with the Paschen curve for nitrogen with both the temperature falling and the vapor-mist density considered. For the nonuniform needle electrode, positive breakdown voltage was higher than negative one; the polarity effect was interpreted in terms of the electric field relaxation at the tip of the positive needle resulting from partial discharges observed only for the positive needle     

Conversion of alkyl radicals to allyl radicals in irradiated single crystal mats of polyethylene

The decay of alkyl radicals, the conversion of alkyl radicals to allyl radicals and the trapping of allyl radicals in irradiated single crystal mats of polyethylene have been studied by electron spin resonance (e.s.r.). It has been suggested that in the crystal core alkyl radicals react with trans-vinylene double bonds and are converted into trans-vinylene allyl radicals; at the crystal surface, alkyl radicals react with vinyl end groups and are converted into allyl radicals with vinyl end groups. The decay of radical pairs and the formation of trans-vinylene double bonds are discussed.     

Oxidative dehydrogenation of ethane over some titanates based perovskite oxides

A series of perovskite catalysts have been tested for the oxidative dehydrogenation of ethane. The composition of these catalysts covered CaTi_1–x Fe _x O_3–, with 0 x 0.4, SrTi_1–x Fe _x O_3–, with 0 x 1.0, as well as mixtures of these. The latter catalysts containing more basic Sr metal showed higher selectivity to ethene than the former catalysts containing Ca. A few catalysts with Co on B-sites in the lattice were tested, but lost their stability above 923 K, resulting in a substantial change in the product selectivity. The perovskites gained activity when Fe was introduced in the lattice to form hypervalent ions (Fe⁴⁺) which are believed to play a role in the catalytic activity of these materials.     

Effectiveness and biocompatibility of a novel biological adhesive application for repair of meniscal tear on the avascular zone

We have investigated the effectiveness and safety of a newly developed biological adhesive for repair of meniscal tear. The adhesive was composed of disuccinimidyl tartrate (DST) as a crosslinker and human serum albumin (HSA) as a hardener. To determine adequate concentration, bonding strength was measured using a tensiometer 5 min after applying the adhesive on the avascular zone tear of porcine meniscus; it was compared with the strengths of commercially available cyanoacrylate-based and fibrin-based adhesives. In vivo examination was performed using Japanese white rabbits, creating longitudinal tears on the avascular zone of meniscus and applying DST–HSA adhesive. Three months after operation the rabbits were sacrificed and tension test and histological evaluation were performed. Bonding strength was measured in three porcine meniscus groups: (i) only suturing, (ii) suturing after applying the adhesive on surface and (iii) suturing using an adhesive-soaked suture. The optimum concentrations were 0.1 mmol of DST and 42 w/v% of HAS. Bonding strength was greatest with cyanoacrylate-based adhesive, followed by DST–HSA adhesive, and fibrin-based adhesive. No inflammation was observed in the synovium or surrounding tissues 3 months after using the DST–HSA adhesive. Bonding strength was greatest with DST–HSA adhesive-soaked suturing group (77 ± 6 N), followed by suturing only group (61 ± 5 N) and surface adhesive application group (60 ± 8 N). The newly developed DST-HSA adhesive is considered safe and may be effective in enforcement of bonding of avascular zone tear of the meniscus.     

Titanium powder prepared by magnesiothermic reduction of Ti2+ in molten salt

A process to produce titanium powder from Ti²⁺ in the molten salt was confirmed experimentally. It consists of two steps. In the first step, titanium (IV) chloride gas dissolves in the molten salt as the titanium (II) chloride by reacting chemically with the metallic titanium or magnesium. In the second step, this molten salt is exposed to the metallic reductant Mg for the final reduction to the metallic Ti powder. Experimentally, the feed of TiCl₄ gas and the subsequent reaction with Ti prepared the molten salt containing 5 to 10 mass pct Ti²⁺. By Mg reduction of this salt, the well-isolated fine Ti particles were recovered. The powder morphology and particle size depended on the Ti²⁺ concentration, reduction temperature, time, and concentration of the by-product MgCl₂. The stirring by argon gas bubbling effectively grew the fine and round particles to a few tens of microns in size.     

Target-cell specificity of fusogenic liposomes: membrane fusion-mediated macromolecule delivery into human blood mononuclear cells

Fusogenic liposome, a unique vector prepared by fusing ultraviolet-inactivated Sendai virus and liposome, is known to efficiently deliver content into various animal cells through membrane fusion. In this study, we examined the target-cell specificity of fusogenic liposome (FL)-mediated macromolecule delivery into human blood cells using diphtheria toxin fragment A (DTA) as a probe. Among the peripheral blood mononuclear cells (PBMC), FL was able to deliver its encapsulates into CD14+ monocytes and CD4-/CD8- T-cells, but not into CD19+ B-lymphocytes, CD4+ T-cells or CD8+ T-cells. The susceptibility of human leukemia cell lines to FL was similar to that of PBMC; the order of the reactivity was U937 (monoblastic leukemia)>MOLT4, Jurkat (T-lymphoma)>Daudi, BALL1 (B-lymphoma)>K562 (erythroblastic leukemia). Interestingly, FL showed similar binding activity to all of these leukemia cell lines. These findings indicate that, among blood cells, monocytes, monoblastic leukemia cells, CD4-/CD8- T-cells and T-lymphoma cells are preferable targets for FL-mediated macromolecule delivery. This is the first demonstration of the existence of non-permissive cells against FL. Our results also suggest that some molecules on target-cells other than the binding targets of SV-derived protein may participate in fusion between FL and cells.     

A Gibbs-sampler approach to estimate the number of faults in asystem using capture-recapture sampling [software reliability]

A new recapture debugging model is suggested to estimate the number of faults in a system, ν, and the failure intensity of each fault, φ. The Gibbs sampler and the Metropolis algorithm are used in this inference procedure. A numerical illustration suggests a notable improvement on the estimation of ν and φ compared with that of a removal debugging model     

Temporal development of partial discharge and its application tobreakdown prediction in SF6 gas

The authors measured the temporal change of partial discharge (PD) characteristics leading to breakdown in SF₆ gas for AC voltage application. At the final stage close to the breakdown, positive PD pulses with relatively high magnitude began to take place in the phase region near the applied voltage peak. This event was interpreted in terms of the change of PD type in SF₆ gas from streamer to leader. Optical observation also revealed that PD type transition occurred. With the results considered, the mechanisms of PD were discussed. Moreover, they discussed the possibility of breakdown prediction in GIS. An attempt was made to find a breakdown prediction parameter which characterized the change of PD type: the ratio R_L of maximum charge to the average charge of PD pulses appearing in the phase region near the peak in positive half cycle. It was found that R_L allowed to predict the time to breakdown successfully within the error of 4~20%     

Impact of surface modification by addition of self-assembled monolayer for carrier transport of quaterrylene thin films

Quaterrylene field-effect transistors (FETs) were formed on a silicon oxide (SiO₂) layer and on an octadecyltrichlorosilane self-assembled monolayer (OTS-SAM). To elucidate the transport mechanisms in the respective devices, we examined the dependence of carrier mobility on film thickness and temperature. On the OTS surface, a marked increase in the carrier mobility was observed in the initial layers, indicating that the accumulated carriers were distributed closer to the interface than were those on the SiO₂ surface. Moreover, the carrier transport in the respective devices exhibited distinct behaviors in the low temperature range, particularly in the initial layers. On the SiO₂ surface the carrier mobility depended strongly on temperature; the value drastically declined with the decreasing temperature from 300 K down to 60 K. On the OTS surface, the carrier mobility showed temperature-independent transport below 210 K. This maintenance of the carrier transport at low temperatures was caused by the termination of the trap-state density near the interface. These results clearly reveal that the OTS treatment effectively helped improve the interface properties because of a reduction in the density of the carrier traps, dramatically facilitating the carrier transport in the initial layers.