Surface modification of steel surfaces by electron beam excited plasma processing

The nitriding performance of low power electron beam excited plasma is investigated by characterizing the surface of nitrided low alloy Cr-Mo steels. In this research, a particular attention was given to the effect of the acceleration voltage and processing time on the composition and hardness of the processed samples. In an attempt to maximize the dissociation of N₂, the acceleration voltages applied in our experiments were set within a range that corresponds to the maximum dissociation cross-section of N₂. The results show that the peak intensity of the alpha Fe observed for the unprocessed sample decreases as the acceleration voltage increases. Moreover, the peak intensities depicting the formation of the nitride compound layers, Fe₄N and Fe₃N phases, increases with the acceleration voltage of the electron beam. Consequently, the surface hardness of the treated low alloy steel was increased by more than two times that of the unprocessed specimen.     

Comparative studies on Ar and He closed-cycle MHD power plants combined with fossil fuel

Comparative studies on Ar and He closed-cycle MHD power plants combined with fossil fuel are performed. The sizes of a regenerative heat exchanger and a boiler are expected to be smaller for He than for Ar. The pressure loss of a working gas in a regenerative heat exchanger is reduced for He. The purification subsystem for He is expected to be more compact and economical than that for Ar; but a larger compressor is required for He than for Ar.     

Chiral selection in supercoiling and wrapping of DNA

This paper gives an account of our recent studies on the mechanisms for chiral selection in super-coiling and wrapping of DNA. We first present a compact model of double-stranded DNA (Model 1), which consists of two elastic chains that mutually intertwine in a right-handed manner to form a double-stranded helix. Numerical analysis of this model suggests an intrinsic propensity of DNA to writhe in the left direction upon bending. Based on this asymmetric elasticity of DNA, we present a further simplified model of DNA (Model 2), which is a single-chained homopolymer with the propensity to writhe in the left direction upon bending. This simplified model is incorporated into a Langevin dynamics study to explore the origin of the uniform left-handed wrapping of DNA around a nucleosome core particle in nature. We finally show that the propensity of DNA to writhe in the left direction upon bending gives rise to the selective left-handed wrapping, provided that the size of the core particle is appropriate. This result suggests the fundamental significance of the asymmetric elasticity of helical biopolymers in their structural dynamics and functions.     

Chiral recognition ability of oligopeptide derivatives consisting of glutamyl residues

The effect of the constituting amino acid residue [Glu(OBzl)] number on the chiral recognition ability was investigated. Chiral recognition sites were prepared from oligopeptide derivatives (constituting amino acid residue number = three–five) by adopting alternative molecular imprinting. It was made clear that with a constituting amino acid residue number of four, the tetrapeptide derivative of Glu(OBzl) is the best candidate material to generate a chiral recognition site among eight types of oligopeptide derivatives in the study. The affinity constant between Ac‐L ‐Trp and a chiral recognition site ranged from 3.4 × 10³ to 1.08 × 10⁴ mol^?1 dm³, depending on the number of Glu(OBzl) residues in an oligopeptide derivative. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1302–1309, 2005     

Superconducting digital electronics

Single-flux quantum logic (SFQ) circuits, in which a flux quantum is used as an information carrier, have the possibility for opening the door to a new digital system operated at over 100-GHz clock frequency at extremely low power dissipation. The SFQ logic system is a so-called pulse logic, which is completely different from the level logic for semiconductors like CMOS, so circuit design technologies for SFQ logic circuits have to be newly developed. Recently, much progress in basic technologies for designing SFQ circuits and operating circuits at high speeds has been made. With advances in these design tools, large-scale circuits including more than several thousand junctions can be easily operated with the clock frequency of more than several tens of gigahertz. High-end routers and high-end computers are possible applications of SFQ logic circuits because of their high throughput nature and the low power dissipation of SFQ logic. In this paper, recent advances of SFQ circuit design technologies and recent developments of switches for high-end routers and microprocessors for high-end computers that are considered possible applications for SFQ logic will be described.     

Effects of Samarium Oxide Addition on the Phase Composition, Microstructure, and Electrical Resistivity of Aluminum Nitride Ceramics

The phase composition, microstructure, and electrical resistivity of hot-pressed AlN ceramics with 0–4.8 wt% Sm₂O₃ additive were investigated. The phase composition was approximately consistent with that estimated from the Sm₂O₃–Al₂O₃ phase diagram using the amount of added Sm₂O₃ and oxygen content of the AlN raw material. When sintered at more than 1800°C, the AlN ceramics with 1.0–2.9 wt% Sm₂O₃ additive contained an Sm-β-alumina phase wetting the grain boundaries, and their electrical resistivity considerably decreased to 10¹⁰–10¹²Ω·cm. This resistivity decrease was caused by the continuity of the Sm-β-alumina phase with a resistivity lower than that of bulk AlN.     

Optical Resolution Membranes from Polysulfones Bearing Alanine Derivatives as Chiral Selectors

Polysulfones bearing a derivative of alanyl residue employed as chiral selectors were prepared by polymer modification. The specific rotation ([α]_D) of the polysulfone with a derivative of D ‐alanyl residue (PSf‐Ac‐D ‐Ala) was determined to be 2.87 deg · cm² · g^?1 (c = 1.00 g · dL^?1 in DMF) and that with L ‐alanyl residue (PSf‐Ac‐L ‐Ala) to be ‐2.36 deg · cm² · g^?1 (c = 1.00 g · dL^?1 in DMF). The membrane from PSf‐Ac‐D ‐Ala preferentially adsorbed the D ‐isomer of Glu from racemic mixture of Glu and vice versa. Chiral separation ability was studied by applying a potential difference as a driving force for membrane transport. The permselectivity of PSf‐Ac‐D ‐Ala toward D ‐Glu (α_D/L) was determined to be 1.40, and that of PSf‐Ac‐L ‐Ala toward the L ‐isomer (α_L/D) to be 1.48 at 18.0 V, reflecting their adsorption selectivity.

     

The Effectiveness of Latent Semantic Analysis for Building Up a Bottom-up Taxonomy from Folksonomy Tags

In this paper, we evaluate the effectiveness of a semantic smoothing technique to organize folksonomy tags. Folksonomy tags have no explicit relations and vary because they form uncontrolled vocabulary. We discriminates so-called subjective tags like “cool” and “fun” from folksonomy tags without any extra knowledge other than folksonomy triples and use the level of tag generalization to form the objective tags into a hierarchy. We verify that entropy of folksonomy tags is an effective measure for discriminating subjective folksonomy tags. Our hierarchical tag allocation method guarantees the number of children nodes and increases the number of available paths to a target node compared to an existing tree allocation method for folksonomy tags.