Convective instabilities and transport properties in horizontal fluid layers

This paper concerns the analysis of convective instabilities and fully developed transport properties in Bénard convection. The onset of convective instabilities driven by surface-tension variations and buoyancy forces is analyzed theoretically by using the propagation theory we have developed. Based on these stability criteria, the subsequent transport correlations of fully developed buoyancy-driven convection in horizontal fluid layers are suggested. It is found that the present predictions are compared favorably with existing experimental results.     

Direct Physical Imaging and Chemical Probing of LiFePO4 for Lithium‐Ion Batteries

The control of unexpectedly rapid Li intercalation reactions without structural instability in olivine‐type LiFePO₄ nanocrystals is one of the notable scientific advances and new findings attained in materials physics and chemistry during the past decade. A variety of scientific studies and technological investigations have been carried out with LiFePO₄ to elucidate the origins of many peculiar physical aspects as well as to develop more effective synthetic processing techniques for better electrochemical performances. Among the several features of LiFePO₄ that have attracted much interest, in this article we address four important issues—regarding doping of aliovalent cations, distribution of Fe‐rich secondary metallic phases, nanoparticle formation during crystallization, and antisite Li/Fe partitioning—by means of straightforward atomic‐scale imaging and chemical probing. The direct observations in the present study provide significant insight into alternative efficient approaches to obtain conductive LiFePO₄ nanocrystals with controlled defect structures.     

Synthesis and electroluminescent properties of π-conjugated copolymer based on 10-hexylphenothiazine and aromatic 1,2,4-triazole

A new polymer, poly((10-hexyl-3,7-phenothiazine)-alt-(4-(4-butyl-phenyl)-3,5-diphenyl-4H-[1,2,4]triazole)-3,5-diyl) (PT-TAZ), has been synthesized. In order to improve electron injection/transporting ability, we introduce electronegative 1,2,4-triazole group in the backbone. We also synthesized poly(10-hexylphenothiazine-3,7-diyl) (PT) to compare the physical properties with PT-TAZ. The photoluminescence (PL) maximum wavelength, the band gap energy, and the HOMO energy level of PT-TAZ film were 509 nm, 2.67 eV, and −5.06 eV, respectively, which are very comparable to those of PT. The maximum efficiency and brightness of the electroluminescent (EL) device based on PT-TAZ were 0.247 cd/A and 771 cd/m², respectively, which were significantly higher than those of the device based on the polymer without 1,2,4-triazole (TAZ) as a repeat unit (PT) (1.05 × 10⁻⁴ cd/A and 4.4 cd/m²). This is because TAZ unit improves the electron transporting ability in the emissive layer. The turn-on voltage of brightness of the device based on PT-TAZ was 5.0 V, which was slightly higher than that of the based on PT (4.5 V). This is because the ionization potential of PT-TAZ is very similar to that of PT.     

Sliding mode control of a shear-mode type ER engine mount

This paper presents feedback control characteristics of a shear-mode type electro-rheological (ER) engine mount. The field-dependent yield stress of an arabic gum-based ER fluid is obtained using a couette type electroviscometer, and it is incorporated into the governing equation of motion of the ER engine mount, which is derived from a bond graph model. A sliding mode controller which directly represents the field-dependent damping force is formulated by taking into account the stiffness and damping properties of the systems as parameter uncertainties. The controller is then experimentally realized by imposing a semi-active actuating condition. The effectiveness of the proposed ER engine mount is demonstrated showing capabilities of isolating the vibrations due to sinusoidal and random excitations.     

A case study on detection and sizing of defects in steam generator tubes using eddy current testing

Eddy current testing (ECT) method is widely used to detect various types of defects occurring in nuclear steam generator tubes. Therefore, the reliability of its detection and sizing accuracy for defects should be validated. For this purpose, two tubes with defect signals were pulled from an operating steam generator and destructively examined. The defect type was a circumferential crack for one tube and an intergranular attack (IGA) for the other tube. The plus point coil probe showed a better capability to detect and size both a circumferential crack and a volumetric IGA than pancake and bobbin coil probe. The destructive results are correlated with the ECT results obtained during the in-service inspection.     

Strain hardening behavior during manufacturing of tube shapes by hydroforming

Safe and robust process design relies on knowledge of the evolution of the mechanical properties in a tube during hydroforming. The manufacturing of tubular shapes generally consists of three main stages: bending, preforming, and expansion. The latter is usually called hydroforming. As a result of these three steps, the final product’s strain hardening history is nonlinear. In the present study, the strain hardening behavior during hydroforming was experimentally investigated. The variation of local flow stress and/or local hardness was used as an index of the strain hardening during the various steps and the local flow stress and/or local hardness were used with respective correlations to determine the effective strain. The strain hardening behavior during hydroforming after preforming has been successfully analyzed by using the relationships between hardness, flow stress, and effective strain for variable pre-strains prior to hydroforming. The comparison of predicted hardness with measured hardness confirms that the methodology used in this study is feasible, and that the strain hardening behavior can be quantitatively estimated with good accuracy.     

An experimental study of the mean effective strain in rod (or bar) rolling process

This paper presents an experimental study that investigates the validity of the analytical model [9] for predicting the mean effective strains associated with bar (or rod) rolling. Designed for this purpose were plate and bar rolling experiments which consist of a four-pass groove (oval and round) rolling sequences, which have material at each pass that experience the same amount of mean effective strain. The microstructure and mechanical behaviors of specimens acquired from two types of rolling experiments at 650°C were compared. A parallelism between the mechanical behaviors of a plate-rolled specimen and a bar-rolled specimen has been found at each pass. We therefore concluded that the analytical model has the underlying rationale to be used in the analysis of the rod (or bar) rolling process.     

Enhanced soft subspace clustering integrating within-cluster and between-cluster information

While within-cluster information is commonly utilized in most soft subspace clustering approaches in order to develop the algorithms, other important information such as between-cluster information is seldom considered for soft subspace clustering. In this study, a novel clustering technique called enhanced soft subspace clustering (ESSC) is proposed by employing both within-cluster and between-class information. First, a new optimization objective function is developed by integrating the within-class compactness and the between-cluster separation in the subspace. Based on this objective function, the corresponding update rules for clustering are then derived, followed by the development of the novel ESSC algorithm. The properties of this algorithm are investigated and the performance is evaluated experimentally using real and synthetic datasets, including synthetic high dimensional datasets, UCI benchmarking datasets, high dimensional cancer gene expression datasets and texture image datasets. The experimental studies demonstrate that the accuracy of the proposed ESSC algorithm outperforms most existing state-of-the-art soft subspace clustering algorithms.