NDE of degradation of thermal barrier coating by means of impedance spectroscopy

Nondestructive evaluation of thermal barrier coating (TBC) degradation during service operation has received a wide attention for service life prediction of advanced gas turbines. In this work, TBC on nickel base superalloy degraded at various degrees by thermal aging is investigated. Particularly, TBC and Metal–Chromium–Aluminum–Yttrium alloy (McrAlY) (M indicates iron (Fe), cobalt (Co), nickel (Ni) or these combinations) bond coating interface where a detrimental reaction takes place and forms various reaction products during thermal aging, is studied in detail. Formation kinetics and physical properties of the reaction layer are evaluated by means of Impedance Spectroscopy (IS). Specimens aged at higher temperature and a longer aging time shows larger impedance. The impedance behavior of TBC and bond coating is found to be markedly changed by the formation of the reaction layer. Physical properties and thickness of the reaction layer are evaluated using the change of the impedance. A mechanistic interpretation of the cause of change in the physical properties and IS behavior are described.     

Polyion Complex Fiber and Capsule Formed by Self‐Assembly of Chitosan and Poly(α,L‐glutamic acid) at Solution Interfaces

Different characteristic surface structures such as spherical capsules, regularly spaced droplets and fibers are formed by electrostatic polysaccharide interaction between chitosan and poly(α,L ‐glutamic acid) via polyion complex (PIC) formation. Spherical droplet‐like PIC capsules of varying diameters form in solutions. Some dyes adsorb on the surface of the capsules, while other dyes and benzoic acid derivatives penetrate into the capsules. The PIC fiber can be prepared by reactive‐spinning at the solution interface, followed by gravity and by removing water in ethanol. The tensile strength of the fiber is 11.2 kg·mm^–2 (1.48 g·denier^–1) and the knotting strength is 2.15 kg·mm^–2 (0.30 g·d^–1). By reaction with an organic cross‐linking agent, ethylene glycol diglycidyl ether (EGDE), the tensile strength of the fiber can be increased to 18.1 kg·mm^–2 (3.14 g·d^–1), and by reacting with hexamethylene diisocyanate (HMDI), the knotting strength of the fiber can be increased to 7.58 kg·mm^–2 (0.89 g·d^–1). The interaction energies (work of adsorption, W_ads) of PLG and chitosan in aqueous solution were estimated by a surface chemical approach, and a relationship between the W_ads values and the tensile strengths of the PIC fibers and the W_ads indicated that the higher W_ads system gives the higher tensile strength. The PIC fiber can be dyed by four different dyeing procedures such as direct and vat dyeings. When the cross‐linked PIC fiber was incubated in an aqueous solution in the presence of endocrine disruptor related compounds such as dibenzofuran and biphenyl, these compounds were accumulated onto and/or into the fibers.     

Teleoperation via computer network

In a teleoperation system, providing force information to a human operator can improve task performance. When a communication block between a master and a slave has a transmission delay, the system is easily destabilized. Anderson and Spong guaranteed passivity in the communication block by using scattering transformation and overcame this instability caused by the time delay. But this method can be applied to the communication block with a constant time delay. In a traditional teleoperation system, its communication block has a constant time delay. But time delay irregularly changes in a computer network because many users share telecommunication lines. This paper shows that the variable time delay destabilizes bilateral master-slave manipulator with scattering transformation and a new compensation method which keeps the time delay constant. This new compensation method has been implemented in a single-axis master-slave manipulator.     

Frequency stabilization of a semiconductor laser under direct FSK modulation: The modulation method and evaluation of stability

The frequency stability of a semiconductor laser deteriorated under direct frequency shift keying (FSK) when stabilization depended entirely upon an external frequency reference. Therefore, the PEAK method was devised for the purpose of improving frequency stability. This method requires two distinct frequency components and, therefore, will not work effectively in a communications system that produces a succession of identical frequencies, as does the FSK method on occasion. This paper, then, explains the results of our comparative analysis of the two modulation methods. The evaluation of frequency stability requires us to use a beat note between two stabilized laser beams, referred to here, as “signal” and “reference,” lasers. The reference laser is stabilized by a method that takes advantage of the magneto-optical effect. This laser restrains the tendency of the beat note frequency to broaden in other stabilization methods, and even makes it possible to predetermine the beat frequency to be employed. The improvement in frequency stability obtained is about one order of magnitude. © 1998 Scripta Technica, Electr Eng Jpn, 125(2): 44–51, 1998     

Application of magneto-optical sensors for fault location in an air-insulated substation bus

A new fault location system using optical current transducers (CTs) to detect faulted sections in the bus bars of directly grounded 275-kV substations has been developed. This system detects fault current by combining optical CTs with wound-type CTs. The new type of optical CT applies a bulk-type Faraday sensor to the combination of windings around a magnetic iron core and a solenoid coil. The optical CT was capable of current measuring over 50 kA. A current differential discriminator combining an optical CT and a wound-type CT verified the operational performance with 40-kA currents. The intended level of fault detection performance was obtained. Based on these results, a system is being made for actual application in 275-kV substations. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(2): 10–17, 1997     

Predicting Tensile Properties of Friction-Stir-Welded 6063 Aluminum with Experimentally Measured Welding Heat Input

This work aims to develop a reliable method to predict mechanical properties of friction-stir-welded 6 xxx-series alloys with experimentally measured welding heat input. A calorimetrical method was utilized to experimentally measure the welding heat input in the friction stir welded of aluminum alloy 6063-T5. Good correlations between the input variables, i.e., welding parameters and physical properties of the materials, and the welding heat inputs obtained with experimental measurements were discovered. The welding heat input can be predicted using the empirical equation derived based on these correlations. Moreover, the results suggested that the thermal conductivities of the welded alloys affected the welding heat input significantly. Mechanical properties, including hardness and tensile properties, of friction-stir-welded aluminum alloy 6063 were in good correlation to the heat input obtained with experimental measurement. These correlations were explained by the evolution of the strengthening precipitates during welding. This work proposed a reliable new route to predict these mechanical responses through the estimation of heat input.     

A neural network parallel algorithm for one‐dimensional gate assignment problems

A near‐optimum parallel algorithm for solving the one‐dimensional gate assignment problem is presented in this paper, where the problem is NP‐hard and one of the most fundamental layout problems in VLSI design. The proposed system is composed of n × n processing elements based on the artificial two‐dimensional maximum neural network for (n + 2)‐gate assignment problems. Our algorithm has discovered improved solutions in the benchmark problems compared with the best existing algorithms. The proposed approach is applicable to other VLSI layout problems such as the PLA (Programmable Logic Array) folding problem. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 71–77, 1999     

X-ray Diffraction Analysis to Explore Molecular Traces of Eccentric Contraction on Rat Skeletal Muscle Parallelly Evaluated with Signal Protein Phosphorylation Levels

We performed X-ray diffraction analyses on rat plantaris muscle to determine if there are strain-specific structural changes at the molecular level after eccentric contraction (ECC). ECC was elicited in situ by supramaximal electrical stimulation through the tibial nerve. One hour after a series of ECC sessions, the structural changes that remained in the sarcomere were evaluated using X-ray diffraction. Proteins involved in cell signaling pathways in the muscle were also examined. ECC elicited by 100, 75, and 50 Hz stimulation respectively developed peak tension of 1.34, 1.12 and 0.79 times the isometric maximal tetanus tension. The series of ECC sessions phosphorylated the forkhead box O proteins (FoxO) in a tension-time integral-dependent manner, as well as phosphorylated the mitogen-activated protein kinases (MAPK) and a protein in the mammalian target of rapamycin (mTOR) pathway in a maximal tension dependent manner. Compared to isometric contractions, ECC was more efficient in phosphorylating the signaling proteins. X-ray diffraction revealed that the myofilament lattice was preserved even after intense ECC stimulation at 100 Hz. Additionally, ECC < 75 Hz preserved the molecular alignment of myoproteins along the myofilaments, while 75-Hz stimulation induced a slight but significant decrease in the intensity of meridional troponin reflection at 1/38 nm⁻¹, and of myosin reflection at 1/14.4 nm⁻¹. These two reflections demonstrated no appreciable decrease with triple repetitions of the standard series of ECC sessions at 50 Hz, suggesting that the intensity decrease depended on the instantaneous maximal tension development rather than the total load of contraction, and was more likely linked with the phosphorylation of MAPK and mTOR signaling proteins.