A statistical modeling methodology for the analysis of term structure of credit risk and its dependency

This paper presents a statistical modeling methodology for simultaneous estimation of the term structure for the risk-free interest rate, hazard rate, loss given default as well as credit risk dependency structure between bond-issuing industries. A model like this provides a realistic view for the market anticipation of credit risk for corporate bonds and the flexibility in capturing credit risk dependency between industries. Our statistical modeling procedure is carried out without specifying the model likelihood explicitly, and thus robust to the model mis-specification. An empirical analysis is conducted using the financial information on the Japanese bond market data. Numerical results confirm the practicality of the proposed methodology.     

Narrow‐gap field‐sequential TN‐LCD with and without nanoparticle doping

Abstract— The fabrication and demonstration of field‐sequential‐color (FSC) LCDs using modules of narrow‐gap twisted‐nematic (NTN) LCDs with and without doping of newly synthesized PγCyD‐ZrO² nanoparticles is reported. Two types of FSC‐LCDs are demonstrated: one is a direct multiplexed NTN‐LCD and the other is TFT driven. The advantages of FSC‐LCDs include their high legibility even under direct sunlight, and the mechanism for the doping of nanoparticles in LCDs is discussed.     

Creep deformation of TiAl-Si alloys with aligned γ/α 2 lamellar microstructures

Creep tests were conducted on directionally solidified TiAl-Si alloys to discern the effect of lamellar spacing and lamellar orientation on the high-temperature strength. Directional solidification of a Ti-43Al-3Si alloy was used to produce a model microstructure consisting of a single γ/α ₂ lamellar colony of controlled orientation for creep testing. Different heat treatments were used to vary the lamellar spacing and tensile creep tests were performed at 750 °C using applied stresses of 180, 210, and 240 MPa. In addition, ingots with large columnar grains of various lamellar orientation were also tested. The results clearly show the beneficial effect of microstructural control with the aligned microstructure having a much superior creep resistance. Furthermore, for specimens with aligned lamellar microstructure, decreasing the lamellar spacing greatly improved creep resistance, as both the primary creep strain and secondary creep rate are much smaller for materials with the fine lamellar spacing.     

Electrical stability of polyimide siloxane films for interlayer dielectrics in multilevel interconnections

Electrical stability of a polyimide siloxane (PSI) film for ultra-large scale integrated circuit (ULSI) multilevel interconnections is studied. The PSI films, modified by p-aminophenyltrimethoxysilane (APTMS), are designed to have three-dimensional polymer structures through Si–O bonds. It has been revealed that the PSI films are more stable in electrical properties at higher temperatures than 150°C, as compared to the conventional polyimide (PI) films. The electrical conduction mechanism study for the PSI films has revealed that Schottky emission is dominant. Barrier height φ_B obtained from the electrical property for the PSI film was 0.460 eV in the temperatures ranging from 25–250°C. On the other hand, barrier height of 0.422 eV at lower temperatures than 150°C and activation energy of 1.09 eV at higher temperatures than 150°C were obtained for the conventional PI film. The difference in polymer structure is very sensitive to the electrical conduction at high temperature, due to sodium ion migration. The ideal band diagrams of metal-insulator-semiconductor (MIS) structures were also discussed. The optical band gaps for PSI and conventional PI films were 3.320 eV and 3.228 eV, respectively. This result suggests that the band gap of PI films can be enlarged by modification with Si–O components. The differential barrier height between the PSI and conventional PI films is 0.038 eV, and is close to the difference in half of optical band gaps (0.046 eV).     

FEM-BEM superposition method for fracture analysis of quasi-brittle structures

Fracture analysis of civil engineering structures often requires appropriate modeling of discrete cracks propagating in an inhomogeneous or nonlinear material. For example, quasi-brittle materials, such as concrete, are characterized by formation of cracks with fracture process zone under tension and plasticity under compression. Application of either finite element method (FEM) or boundary element method (BEM) to problems involving simultaneously discrete cracks and inhomogeneities or plastic deformations faces certain difficulties. Therefore, we propose the FEM-BEM superposition method, which removes the respective methods disadvantages while keeping their advantages. In the proposed method, the original problem involving both material inhomogeneity or plasticity and discrete cracks is decomposed into two subproblems. The inhomogeneity or inelastic deformation is represented in only one of the subproblems, while the cracks appear only in the other. The former subproblem is analyzed using FEM and the latter one by BEM, so as to utilize the advantages of the two methods. The solution of the original problem is then obtained by superposing the solutions of the two subproblems. In order to verify validity of the proposed method we present numerical results of several examples, including both linear-elastic and nonlinear fracture mechanics. The results are compared with available analytical solutions or with data computed by other numerical methods, showing both accuracy and computational superiority of the proposed method.     

Microstructure and Mechanical Properties of ZrO2(2Y)-Toughened Al2O3 Ceramics Fabricated by Spark Plasma Sintering

Spark plasma sintering (SPS) has been performed for 5 min at 1500°C and 30 MPa using submicrometer-sized Al₂O₃/ZrO₂(2Y) composite powders in the Al₂O₃-rich region. Dense ZrO₂-toughened Al₂O₃ (ZTA) ceramics show excellent mechanical strength; the strength of 1620 MPa is achieved in the ZTA with 50 mol% ZrO₂. The grain size of Al₂O₃ in ZTA decreases from 1.5 to 0.6 m with increased ZrO₂ content. Almost all the ZrO₂ grains (0.3 m) are located in the boundaries of the Al₂O₃ grains. Mechanical properties are discussed, with an emphasis on the relation between t-/m-ZrO₂ ratios and microstructures of ZTA.     

Arsenic ion implantation induced structural effects in C60 films

C₆₀ films grown on Si (001) by vacuum evaporation were implanted with 100 keV positive arsenic ions to various doses in the range 1 × 10¹³ to 1 × 10¹⁵ ions/cm². The structural properties of the implanted films were studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). XPS results indicate the formation of arsenic buried layer within C₆₀ film leading to the anisotropy stress in the film. XRD results reveal the preferential orientation of the film along the (531) plane on implantation and it can be due to the re-alignment of the grains as evidenced by our AFM measurement. AFM measurements also reveal the reduction in the grain size and the surface roughness on implantation.     

Correlation effects in wave function mapping of molecular beam epitaxy grown quantum dots

We investigate correlation effects in the regime of a few electrons in uncapped InAs quantum dots by tunneling spectroscopy and wave function (WF) mapping at high tunneling currents where electron-electron interactions become relevant. Four clearly resolved states are found, whose approximate symmetries are roughly s and p, in order of increasing energy. Because the major axes of the p-like states coincide, the WF sequence is inconsistent with the imaging of independent-electron orbitals. The results are explained in terms of many-body tunneling theory, by comparing measured maps with those calculated by taking correlation effects into account.