Cloning and heterologous expression of a glucodextranase gene from Arthrobacter globiformis I42, and experimental evidence for the catalytic diad of the recombinant enzyme

The gene encoding a glucodextranase from Arthrobacter globiformis I42 was cloned and, subsequently, heterologously expressed in Escherichia coli. This glucodextranase gene consists of 1048 amino acid residues with a calculated molecular mass of 109,135 Da. The roles of two residues at the active site of A. globiformis I42 glucodextranase were examined by site-directed mutagenesis. Glutamic acid residues 458 and 656, which are part of the apparent catalytic residues, were found to be essential for hydrolase activity.     

Electrochemical detection of nonlabeled oligonucleotide DNA using biotin-modified DNA(ss) on a streptavidin-modified gold electrode

In the electrochemical detection of nonlabeled DNA, it is important to control the bonding at the interface between the DNA and the electrode. Atomic force microscope (AFM) was taken for the commonly used thiol-modified DNA on a gold surface. It was found that the coverage of the DNA was very low. On the other hand, a streptavidin-modified gold electrode provided a much better alternative where DNA hybridization resulted in large changes in the electrochemical reaction responses. This work demonstrates that streptavidin-modified gold electrodes could be used in the development of a new electrochemical protocol for the detection of nonlabeled DNA.     

Production of anti-CD2 chimeric antibody by recombinant animal cells

Expression vectors for chimeric anti-CD2 antibody were constructed in order to clarify the importance of the expression ratio of heavy (H-) and light (L-) chains of antibody to antibody production in animal cells. The antibody genes were introduced into cells using plasmid DNA vectors or replication-defective retroviral vectors. Productivity was maximal when the expression ratio of H-and L-chains was 1:1, and decreased when the ratio was not equal. We also examined the expression of antibody using one-packed vectors in which the bicistronic expression of H- and L-chain genes was mediated by an internal ribosomal entry site (IRES) sequence derived from encephalomyocarditis virus (EMCV). The translation efficiency was unbalanced between 5'Cap- and IRES-dependent genes. Using the retroviral vectors, it was estimated that the IRES-dependent translation efficiency was 5-fold lower than the 5'Cap-dependent translation efficiency. The cells exhibiting an unbalanced expression of H- and L-chains tended to accumulate H-chain protein.     

Surface potential contrasts between silicon surfaces covered and uncovered with an organosilane self-assembled monolayer

Surface potentials of Si substrates covered with a organosilane self-assembled monolayers (SAMs) were measured with reference to the substrate uncovered with the SAM using Kelvin probe force microscopy. Based on a photolithographic technique, the reference surface was prepared in a micrometer scale on each of the samples. SAMs were prepared from n-octadecyltrimethoxysilane [ODS: CH3(CH2)17Si(OCH3)3], 3,3,3-trifluoropropyltrimethoxysilane [FAS3: CF3(CH2)2Si(OCH3)3], heptadecafluoro-1,1,2,2-tetahydro-decyl-1-trimethoxysilane [FAS17: CF3(CF2)7(CH2)2Si(OCH3)3] or n-(6-aminohexyl) aminopropyltrimethoxysilane [AHAPS: H2N(CH2)6NH(CH2)3Si(OCH3)3) by chemical vapor deposition. Potentials of the surfaces covered with ODS-, FAS3- and FAS17-SAMs became more negative than the uncovered Si substrate, while the surface covered with AHAPS-SAM showed a more positive surface potential than the reference. The potential contrasts of these SAMs to the reference were -25, -170, -225 and +50 mV for ODS-, FAS3-, FAS17- and AHAPS-SAMs, respectively. These results almost agreed with potentials expected from the dipole moments of the corresponding precursor molecules estimated by ab initio molecular orbital calculation, except for FAS3-SAM. Despite FAS3 molecule having a larger dipole moment than FAS17 molecule, the surface potential contrast of FAS3-SAM was smaller than that of FAS17-SAM, since surface coverage of FAS3-SAM was relatively incomplete compared with the other SAMs.     

Consolidation of machined magnesium alloy chips by hot extrusion utilizing superplastic flow

An examination of consolidation conditions by hot extrusion of AZ31 magnesium alloy machined chips was conducted to enhance the bonding of individual chips, in order to improve the mechanical properties. Hot extrusions were carried out in the superplastic and non-superplastic region. Microstructural observations revealed that grain refinement was attained by extruding machined chips, and the grain sizes of the chip-extruded materials were smaller than 5 m. The interfaces of individual chips of extruded materials were not identified when the chips were extruded in the superplastic region. The ultimate tensile strength was about 300 MPa and elongation-to-failure was about 10% for chip-extruded materials that were extruded in the superplastic region. These materials were comparable with the as-received alloy with respect to the room temperature strength, although the ductility was reduced to half. It was confirmed that chip consolidation utilizing superplastic flow is useful to enhance the bonding of individual grains.     

Pressure dependence of surface wave-excited plasma column sustained along metal rod antenna

A novel method was proposed to generate high-density microwave-excited plasma along metal surfaces. In our previous work, 2.45 GHz microwaves were confirmed to propagate as surface waves along the interface between overdense (>10¹¹ cm^–3) plasma and a graphite rod biased at a negative voltage against a grounded chamber. The generated plasma showed columnar structure surrounding the rod surface, and thus it was called metal-antenna surface wave-excited plasma (MASWP) column. In this work, the effect of gas pressure on the spatial distribution of MASWP column was investigated. It was confirmed that the length of MASWP column became longer along a graphite rod (25 cm in length and 1 cm in diameter) with increasing gas pressure. In particular, at an Ar gas pressure of 33 Pa, we obtained a long plasma column covering the entire surface of the rod with a negative voltage of −150 V and an input microwave power of 100 W. The same tendency, or the extension of MASWP column with increasing gas pressure was also confirmed by using a copper rod and a stainless-steel rod instead of the graphite rod. This indicates that the extension of MASWP column with increasing gas pressure occurs independently of antenna materials.     

Evaluation of corrosion fatigue crack propagation life at low-pressure steam turbine rotor groove

The corrosion fatigue crack propagation life of Christmas-tree type rotor groove with three hooks is studied. Each corner of the hook can be a candidate for crack initiation site therefore the condition where cracks initiate and propagate simultaneously at several hook corners must be considered. When a blade is inserted in the rotor groove, narrow gap is introduced unavoidably between the rotor groove and the blade root. The effect of this narrow gap on the crack behavior must also be considered. A procedure was presented to assess the crack initiation and propagation behavior under such a condition. Using the procedure, crack initiation and propagation behavior was evaluated for several gap conditions. It was revealed that the gap condition had little effect on the relation between crack depth at the third hook corner and life consumption ratio (ratio of loading cycle to final failure life). A corrosion fatigue test was performed using a rotor groove model specimen, and the results were compared with the evaluation results.     

Secure cooperation in a distributed robot system using active RFIDs

In this article, we develop a distributed robotic system that can provide various services in a real environment using ad-hoc networked active radio frequency identifications (RFIDs). These services are derived from a large amount of data acquired from sensors connected to active RFIDs. The primary advantage of this method is that it facilitates the construction of a real-environment monitoring system. Furthermore, a human's status and position can easily be identified by fitting active RFIDs to subjects. However, a security system is required for a radio ad-hoc network and a cooperation system between active RFIDs. In our research, we developed a multirobot cooperating system as a multiagent system and applied it to an active RFID, which has limited resources. We also developed a security system for active RFID communication that can be executed using limited resources. We then integrated the multiagent system and security system. We also constructed a robotic environment that can provide various services using active RFIDs and then evaluated it. This work was presented in part at the 10th International Symposium on Artificial Life and Robotics, Oita, Japan, February 4–6, 2005     

Can robots get “memberships” by social interaction?

To investigate how robots behave as social entities, we analyze the interaction of humans and “Muu,” an embodied artificial entity. Specifically, our purpose is to find the salient patterns of behavior that distinguish the robot from humans in the course of an interaction. Through exploratory observations, we identify such salient patterns as the manner of repetitions and the address mismatch. We discuss how the social display of such patterns as “marked” features plays a very important role in mutual interaction. This work was presented in part at the 10th International Symposium on Artificial Life and Robotics, Oita, Japan, February 4–6, 2005     

Hierarchical parallel processing of large scale data clustering on a PC cluster with GPU co-processing

This paper presents an effective scheme for clustering a huge data set using a PC cluster system, in which each PC is equipped with a commodity programmable graphics processing unit (GPU). The proposed scheme is devised to achieve three-level hierarchical parallel processing of massive data clustering. The divide-and-conquer approach to parallel data clustering is employed to perform the coarse-grain parallel processing by multiple PCs with a message passing mechanism. By taking advantage of the GPU’s parallel processing capability, moreover, the proposed scheme can exploit two types of the fine-grain data parallelism at the different levels in the nearest neighbor search, which is the most computationally-intensive part of the data-clustering process. The performance of our scheme is discussed in comparison with that of the implementation entirely running on CPU. Experimental results clearly show that the proposed hierarchial parallel processing can remarkably accelerate the data clustering task. Especially, GPU co-processing is quite effective to improve the computational efficiency of parallel data clustering on a PC cluster. Although data-transfer from GPU to CPU is generally costly, acceleration by GPU co-processing is significant to save the total execution time of data-clustering.