EFFECT OF DISTRIBUTOR ON BUBBLE SIZE AND BUBBLE RISE VELOCITY IN THE SLUGGING REGIME OF A SEMI-CYLINDRICAL GAS-SOLID FLUIDIZED BED†

A semi-cylindrical fluidized bed of 15 cm internal diameter, equipped with a transparent flat glass plate for the front wall, was employed to visually observe bubbles in the bubbling to slugging transition regime and in the slugging regime. Five kinds of perforated distributors were used to investigate the effect of distributor type on the bubble size and the bubble rise velocity. The average bubble size was not affected by distributor type in these flow regimes, and could be predicted by Darton et al's correlation (1974)of hole number 22. In other words, this comes from the inapplicability of the correlation to the slugging regime. The bubble rise velocity agreed well with Allahwala et al's correlation (1979) and was not affected by the type of distributor.     

Influence of ion source configuration and its operation parameters on the target sputtering and implantation process

In the work, investigation of the features and operation regimes of sputter enhanced ion-plasma source are presented. The source is based on the target sputtering with the dense plasma formed in the crossed electric and magnetic fields. It allows operation with noble or reactive gases at low pressure discharge regimes, and, the resulting ion beam is the mixture of ions from the working gas and sputtering target. Any conductive material, such as metals, alloys, or compounds, can be used as the sputtering target. Effectiveness of target sputtering process with the plasma was investigated dependently on the gun geometry, plasma parameters, and the target bias voltage. With the applied accelerating voltage from 0 to 20 kV, the source can be operated in regimes of thin film deposition, ion-beam mixing, and ion implantation. Multi-component ion beam implantation was applied to α-Fe, which leads to the surface hardness increasing from 2 GPa in the initial condition up to 3.5 GPa in case of combined N(2)-C implantation. Projected range of the implanted elements is up to 20 nm with the implantation energy 20 keV that was obtained with XPS depth profiling.     

Inactivation of Bacillus subtilis spores in soybean milk by radio-frequency flash heating

An apparatus to pasteurize soybean milk using radio-frequency flash heating (RF-FH) was developed. An electrode surface was covered with a 50-μm thick Teflon film, and 28 MHz RF-FH was applied to soybean milk flowing through the electrode.     

YHp as a highly stable,hyper-copy,hyper-expression plasmid constructed using a full 2-μm circle sequence in cir0 strains of Saccharomyces cerevisiae

In the yeast Saccharomyces cerevisiae, the yeast episomal plasmid (YEp), containing a partial sequence from a natural 2-μm plasmid, has been frequently used to induce high levels of gene expression. In this study, we used Japanese sake yeast natural cir⁰ strain as a host for constructing an entire 2-μm plasmid with an expression construct using the three-fragment gap-repair method without Escherichia coli manipulation. The 2-μm plasmid contains two long inverted repeats, which is problematic for the amplification by polymerase chain reaction. Therefore, we amplified it by dividing into two fragments, each containing a single repeat together with an overlapping sequence for homologous recombination. TDH3 promoter-driven yEmRFP (TDH3p-yEmRFP) and the URA3 were used as a reporter gene and a selection marker, respectively, and inserted at the 3′ end of the RAF1 gene on the 2-μm plasmid. The three fragments were combined and used for the transformation of sake yeast cir⁰ ura3^- strain. The resulting transformant colonies showed a red or purple coloration, which was significantly stronger than that of the cells transformed with YEp-TDH3p-yEmRFP. The 2-μm transformants were cultured in YPD medium and observed by fluorescence microscopy. Almost all cells showed strong fluorescence, suggesting that the plasmid was preserved during nonselective culture conditions. The constructed plasmid maintained a high copy state similar to that of the natural 2-μm plasmid, and the red fluorescent protein expression was 54 fold compared with the chromosomal integrant. This vector is named YHp, the Yeast Hyper expression plasmid.     

Contribution of shape on ignition of polymeric materials

The contribution of the shape and size of polymers towards ignition for four kinds of polymers, PP (polypropylene), HIPS (rubber reinforced polystyrene), ABS (acrilonitril‐butadiene‐styrene copolymer) and PC (bisphenor‐A type polycarbonate) was studied. The critical heat flux (CHF), which means that the specimen ignites after infinite time, depended on the shape and kind of polymer at the plane position heating. But it was not affected by these conditions at the side position heating. The CHF and other phenomena of ignition were analyzed and the two regions in one of which the shape and the kind of polymer affects them and in another region they was not affected. It will be useful to design electrical parts that reduce fire risks. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Carrier separation analysis for clarifying carrier conduction and degradation mechanisms in high-k stack gate dielectrics

The carrier conduction and the degradation mechanism in n⁺gate p-channel metal-insulator-semiconductor field-effect-transistors with HfAlO_X (Hf: 60 at.%, Al: 40 at.%)/SiO₂ dielectric layers have been investigated using carrier separation method. Since gate current depends on substrate bias and both electron and hole currents are independent of temperature over the range of 25–150 °C, the conduction mechanism for both currents is controlled by a tunneling process. As the interfacial SiO₂ layer (IL) thickness increases in a fixed high-k layer thickness (T_high-k), a dominant carrier in the leakage current changes from hole to electron around 2.2-nm-thick IL. This is due to an asymmetric barrier height for electrons and holes at the SiO₂/Si interface. On the contrary, in the case of a fixed IL thickness of 1.3 nm, the hole current is dominant in the leakage current, regardless of T_high-k. It is shown that the dominant carrier in the leakage current depends on the structure of the high-k stack. Both electron and hole currents for the stress-induced-leakage-current (SILC) state increase slightly relative to the initial currents, which means that the trap generation in the high-k stack occurs near both the conduction band edge of n⁺poly-Si gate and the valence band edge of Si substrate. The electron current at soft breakdown (SBD) state dramatically increases over that for the SILC state, while the hole currents for both the SILC state and SBD are almost the same. This indicates that the defect sites generated in the high-k stack after SBD are located at energies near the conduction band edge of n⁺poly-Si gate. Both the defect generation rate and the defect size in the HfAlO_X/SiO₂ stacks are large compared with those in SiO₂. It is inferred that, in high-k dielectric stack, the defect generation mainly occurs in the high-k side rather than the IL side, and the defect size larger than the case of SiO₂ could be related to a larger dielectric constant of the high-k layer.     

Degradation of SiC-MESFETs by irradiation

The impact of radiation source dependence on the device performance degradation of 4H-SiC MESFETs (Metal Schottky Field Effect Transistors), which have been irradiated at room temperature with 2-MeV electrons and 20-MeV protons, is studied. The damage coefficient for protons is about three orders of magnitude larger than that for electrons. The radiation source dependence of the device performance degradation is attributed to the difference of mass and the possibility of nuclear collision for the formation of lattice defects. From thermal annealing of electron-irradiated MESFETs, it is found that the recovery of the drain current characteristics principally takes place from 100 °C, and that the drain current recovers to the pre-rad value after 200 °C annealing. It is concluded that the degradation of the drain current is mainly sensitive to the radiation-induced decrease of the Schottky barrier height at the gate contact.