Numerical evaluation of the ill-posedness of eddy current problems to size real cracks

This study evaluates whether or not eddy current testing is applicable to the sizing of cracks that appear in a general structure. Two 10 mm thick specimens with artificial stress corrosion cracking are prepared, eddy current testing is performed to gather eddy current signals that result from cracking, and numerical inversions are performed to evaluate the maximum depths of the cracking. The inversions estimate the depths of the cracks are 0.8 and 1.6 mm. Although the simulated signals agree well with the measured ones, destructive tests reveal that the true depths are 1.27 and 2.58 mm. Another numerical simulation is conducted to discuss the ill-posedness of the inverse problem of sizing crack depths from eddy current signals. The simulation simply models a crack as a rectangular region with a constant length and uniform conductivity inside and calculates the eddy current signals of 1024 cracks having variety of depths, widths, and conductivities. Analyzing the results of the simulation reveal that information contained in conventional single-frequency eddy current tests is not sufficient to size conductive cracks in a general sense.     

A hierarchy of uniquely parsable grammar classes and deterministic acceptors

We introduce a new class of grammars called uniquely parsable grammars (UPGs). A UPG is a kind of phrase structure grammar having a restricted type of rewriting rules, where parsing can be performed without backtracking. We show that, in spite of such restriction to the rules, UPGs are universal in their generating ability. We then define three subclasses of UPGs. They are M-UPGs (monotonic UPGs), RC-UPGs (UPGs with right-terminating and context-free-like rules), and REG-UPGs (regular UPGs). It is proved that the generating abilities of the classes of M-UPGs, RC-UPGs, and REG-UPGs are exactly characterized by the classes of deterministic linear-bounded automata, deterministic pushdown automata, and deterministic finite automata, respectively. Especially, the class of RC-UPGs gives a very simple grammatical characterization of the class of deterministic context-free languages. Thus, these four classes form a deterministic counterpart of the classical Chomsky hierarchy. Received August 30, 1995 / May 13, 1996     

Removal of radioactive cobalt ion in high temperature water using titanium oxide

The adsorption of Co²⁺ on titanium oxide (TiO₂) has been experimentally evaluated as a function of temperatures in the range 20–280°C. The selectivity experiments showed that corrosion products such as Co²⁺, Ni²⁺ and Mn²⁺ in reactor water are preferentially adsorbed at high temperatures. The data suggest that there are two reaction mechanisms, i.e. an ion exchange reaction at low temperatures, and chemical adsorption with the formation of insoluble cobalt meta-titanate (CoTiO₃) on the TiO₂ surface at high temperatures.     

Application of cryogenic distillation to Krypton-85 recovery

Fundamental and pilot experiments were carried out to develop a ⁸⁵Kr recovery system for nuclear power and fuel reprocessing plants. It consisted of a pretreatment unit to remove oxygen (O₂), acetylene (C₂H₂) and nitrogen oxides (NO_x) from the inlet gas, a cryogenic distillation unit to remove and concentrate ⁸⁵Kr, and a storage unit for recovered ⁸⁵Kr.     

Generation of high photocurrent in three-dimensional silicon quantum dot superlattice fabricated by combining bio-template and neutral beam etching for quantum dot solar cells

We fabricated a three-dimensional (3D) stacked Si nanodisk (Si-ND) array with a high aspect ratio and uniform size by using our advanced top-down technology consisting of bio-template and neutral beam etching processes. We found from conductive atomic microscope measurements that conductivity became higher as the arrangement was changed from a single Si-ND to two-dimensional (2D) and 3D arrays with the same matrix of SiC, i.e., the coupling of wave functions was changed. Moreover, our theoretical calculations suggested that the formation of minibands enhanced tunneling current, which well supported our experimental results. Further analysis indicated that four or more Si-NDs basically maximized the advantage of minibands in our structure. However, it appeared that differences in miniband widths between 2D and 3D Si-ND arrays did not affect the enhancement of the optical absorption coefficient. Hence, high photocurrent could be observed in our Si-ND array with high photoabsorption and carrier conductivity due to the formation of 3D minibands.     

纳米SiO_2改性苯丙复合涂料制备及性能研究

通过偶联接枝技术,用硅烷偶联剂对纳米SiO2胶体和苯乙烯丙烯酸乳液进行了有机无机复合,制备了纳米SiO2改性苯丙复合乳液。采用正交试验法研究了复合乳液、填料和添加剂最优配比,分析了它们影响作用。通过试验考察了复合涂料的耐擦洗、附着力、老化和耐沾污等主要性能。结果表明:通过正交试验优选出的最佳涂料配方为14号配方,具体添加量:A为32%、B为2.5%、C为7.8%、D为7.8%、E为13%、F为3.9%、G为0.78%;复合涂料的附着力可达100%,耐洗刷次数可达22 576次,遮盖力为351.675 g/m2,耐沾污性可达95.8%。     

Stimuli-induced core-corona inversion of micelles of water-soluble poly(sodium 2-(acrylamido)-2-methyl propanesulfonate-b-N-isopropylacrylamide)

Micelles of poly(sodium 2-(acrylamido)-2-methylpropanesulfonate-b-N-isopropylacrylamide) (PAMPS-b-PNIPAM) have been investigated in aqueous solutions using various techniques including dynamic light scattering, scanning electron microscopy, transmission electron microscopy and ζ-potential measurements. It was found that PAMPS-b-PNIPAM produces two distinct types of micelle structures; one is a PAMPS-core/PNIPAM-corona structure and the other is a PNIPAM-core/PAMPS-corona structure. The PAMPS-core micelle with the PNIPAM-corona was obtained by insolubilizing the PAMPS block with ferric ion (Fe³⁺) at room temperature, and the PNIPAM-core micelle with the PAMPS-corona was obtained by increasing the solution temperature above the lower critical solution temperature (LCST) of the PNIPAM block in the absence of the Fe³⁺ ion. We have also found that the inversion from one type to the other is reversible. The transformation from the PAMPS-core micelle to the PNIPAM-core micelle was induced by removing Fe³⁺ ion using ethylenediaminetetraacetic acid followed by elevating the temperature above the LCST of the PNIPAM block, while the reverse transformation was triggered by adding Fe³⁺ ion at a lower temperature.     

Profile reconstruction of simulated natural cracks from eddy current signals

Based upon the fact that internal conductivity of the crack has a serious effect on the eddy current signals, two kinds of inversion schemes that can reconstruct cracks with non-vanishing conductivity from eddy current signals are proposed in this paper. One is a physics-based approach that modifies crack parameters iteratively and the other is a neuronet-based approach. Two models that are supposed to be appropriate models of a natural crack are also proposed. After detailed explanation of the schemes, several reconstruction results using simulated data are presented. The results show these schemes can reconstruct crack profile with high accuracy where not only shape of the crack but also internal conductivity is unknown. Advantages and disadvantages of both schemes are discussed at the end of the paper.