Toughness recovery of modified 9Cr–1Mo steel weld metals after long-term thermal ageing and its evaluation by electrochemical measurement

Recently, thermal power plants have tended to operate under higher temperature and pressure steam conditions for CO₂ reduction. Modified 9Cr–1Mo steels are used in the ultra-super critical power plant because of their excellent creep properties. However, the toughness of base metal decreases after long-term thermal ageing at operation temperature. Moreover, toughness of weld metal is lowest in the MIG weldment. In this study, metallurgical factors of toughness of the modified 9Cr–1Mo steel weld metals by thermal ageing at operation temperature were investigated. And the evaluation method of toughness by the electrochemical measurement used with 5% sulphuric acid aqueous solution was investigated.

The weld metal that received post-welding heat treatment (PWHT: 1023 K and 5.4 ks) decreased toughness by thermal ageing in 873 K and 31.5 Ms. However, toughness of the welds after thermal ageing was recovered to the same level as PWHT welds when the thermal aged welds received the same thermal history as PWHT. A lot of the large Laves phase was observed in the weld metal after the thermal ageing. However, almost all of the Laves phase dissolved in parent phase by the same thermal history as PWHT. Therefore, it seemed that the decrease and the recovery of toughness were mainly determined by the behaviour of precipitation of the Laves phase. The peak of the current density (Ip) in the electrochemical measurement appeared in the weld metals that precipitated a lot of large Laves phase. It seemed that appearance of Ip was caused by the dissolution of the Laves phase. A good correlation between toughness and Ip was observed. Therefore, it can be said that toughness of the weld metals is supposed to be predicted using an Ip of the electrochemical measurement.     

Emission of Terahertz Radiation from Two-Dimensional Electron Systems in Semiconductor Nano- and Hetero-Structures

This paper reviews recent advances in emission of terahertz radiation from two-dimensional (2D) electron systems in semiconductor nano-heterostructures. 2D plasmon resonance is first presented to demonstrate intense broadband terahertz emission from InGaP/InGaAs/GaAs and InAlAs/InGaAs/InP material systems. The device structure is based on a high-electron mobility transistor and incorporates the author??s original interdigitated dual-grating gates. Second topic focuses on graphene, a monolayer carbon-atomic honeycomb lattice crystal, exhibiting unique carrier transport and optical properties owing to massless and gapless energy spectrum. Coherent stimulated terahertz emission from femtosecond infrared-laser pumped epitaxial graphene is experimentally observed, reflecting the occurrence of negative dynamic conductivity and population inversion.     

An investigation of methods to improve input/output waveforms in matrix converters

The matrix converter is a three‐phase AC‐to‐AC direct converter without any energy storage requirement such as DC link capacitors. However, the matrix converter has some practical problems such as the necessity for bidirectional power devices, necessity for special commutation sequence, and complexity of the control method. Thus, there are no practical systems in which matrix converters are used. In this paper, the control strategy for matrix converters with basic configuration is investigated so as to realize practical matrix converters. First, the necessity of the phase detector for the input voltage and the output current sensor is pointed out from the viewpoint of realization of the basic operation. With these sensors required in the basic configuration, the instantaneous control of the output current is realized. It is also pointed out that three‐phase switching is effective in improving the input current waveforms. Some methods for implementation of three‐phase switching are proposed. The effectiveness of the proposed control methods is confirmed by some experimental results employing a test system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 55–64, 2005; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20031     

A new low‐power driving method for high‐resolution mobile IPS LCDs

Abstract— High‐resolution displays are now needed for mobile equipment, not only for cell phones but for other devices such as ultra‐mobile PCs (UMPCs) and mobile Internet protocol televisions (IPTVs). A new low‐cost and low‐power driving method for high‐resolution in‐plane‐switching (IPS) liquid‐crystal displays (LCDs) on a low‐temperature polycrystalline‐silicon (LTPS) thin‐film‐transistor (TFT) platform has been developed. Because this method drives common electrodes separated by each line, it can reduce inversion frequency, unlike “dot‐inversion” or “column‐inversion” methods. On the other hand, it was found that horizontal smear is an obstacle to achieve this method. To solve this problem, techniques to optimize the timing of RGB time‐sharing are proposed. A 5‐in. WXGA (1366 × 768) prototype using the new driving method was fabricated, and it was found that the horizontal smear is less than ±1% of the luminance and that the power consumption of the display discharge and charge is 0.245 W.     

Molecular dynamics simulation of physical vapor deposition of metals onto a vertically aligned single-walled carbon nanotube surface

Behaviors of nickel and gold clusters deposited onto a vertically aligned single-walled carbon nanotube film (VA-SWCNT) were investigated by molecular dynamics simulation methods. Brenner potential was applied for carbon–carbon, and bond-order potential was applied for metal–metal and carbon–metal interactions. Their parameters of gold–gold and carbon–gold were derived by density functional theory calculations. After metal clusters were fully annealed, they were deposited onto the flat nanotube surface with small evaporation energy. Nickel clusters spread over the surface; on the other hand, the gold clusters sometimes formed a grain-like structure, especially when they formed a large cluster before arriving at the surface. When another CNT was placed on the vertically aligned surface, nickel clusters spread and formed a smooth surface, as in the case of a VA-SWCNT film; however, gold clusters could not spread but formed a grain-like structure. This result is in good agreement with the experimental and indicates the mechanism for forming a grain-like structure on a VA-SWCNT. To avoid the formation of a grain-like structure on the surface of a SWCNT, the deposition should be carried out under a high vacuum condition and at a low deposition rate for preventing clustering as it obstructs formation of a flat surface.     

Effects of magnetic field on the carrier density distribution of semiconductor power device operated in pulsed power conditions

Turn‐on characteristics of semiconductor power devices are evaluated under external magnetic field to study the effects of external magnetic field generated in a pulsed power circuit. Two pin diodes that have a basic structure of power devices are connected in parallel and driven by a pulsed voltage source. It was found the magnetic field applied to one diode in the perpendicular direction of current‐flow changed the current balance between the diodes. Besides the on‐resistance of a diode was increased under external magnetic field. The carrier‐density distribution inside of the diodes was measured by using a free carrier absorption method. The data show that the carrier‐density distribution changes from nearly the uniform one to the one‐sided one. It can be concluded that the effects of magnetic‐field have to be considered for the evaluation of switching characteristic in pulsed power operations. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 10–16, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10271     

Phenotypical heterogeneity of CD4+CD8+ double-positive chronic T lymphoid leukemia

BACKGROUND: One of the most controversial areas in patient selection and donor allocation is the high-risk patient. Risk factors for mortality and major infectious morbidity were prospectively analyzed in consecutive United States veterans undergoing liver transplantation under primary tacrolimus-based immunosuppression. METHODS: Twenty-eight pre-liver transplant, operative, and posttransplant risk factors were examined univariately and multivariately in 140 consecutive liver transplants in 130 veterans (98% male; mean age, 47.3 years). RESULTS: Eighty-two percent of the patients had postnecrotic cirrhosis due to viral hepatitis or ethanol (20% ethanol alone), and only 12% had cholestatic liver disease. Ninety-eight percent of the patients were hospitalized at the time of transplantation (66% United Network for Organ Sharing [UNOS] 2, 32% UNOS 1). Major bacterial infection, posttransplant dialysis, additional immunosuppression, readmission to intensive care unit (P=0.0001 for all), major fungal infection, posttransplant abdominal surgery, posttransplant intensive care unit stay length of stay (P<0.005 for all), donor age, pretransplant dialysis, and creatinine (P<0.05 for all) were significantly associated with mortality by univariate analysis. Underlying liver disease, cytomegalovirus infection and disease, portal vein thrombosis, UNOS status, Childs-Pugh score, patient age, pretransplant bilirubin, ischemia time, and operative blood loss were not significant predictors of mortality. Patients with hepatitis C (HCV) and recurrent HCV had a trend towards higher mortality (P=0.18). By multivariate analysis, donor age, any major infection, additional immunosuppression, posttransplant dialysis, and subsequent transplantation were significant independent predictors of mortality (P<0.05). Major infectious morbidity was associated with HCV recurrence (P=0.003), posttransplant dialysis (P=0.0001), pretransplant creatinine, donor age, median blood loss, intensive care unit length of stay, additional immunosuppression, and biopsy-proven rejection (P<0.05 for all). By multivariate analysis, intensive care unit length of stay and additional immunosuppression were significant independent predictors of infectious morbidity (P<0.03). HCV recurrence was of borderline significance (P=0.07). CONCLUSIONS: Biologic and physiologic parameters appear to be more powerful predictors of mortality and morbidity after liver transplantation. Both donor and recipient variables need to be considered for early and late outcome analysis and risk assessment modeling.     

Self-assembly of Sn-3Ag-0.5Cu Solder in Thermoplastic Resin Containing Carboxyl Group and its Interconnection

The self-assembly of solder powder on pads is attractive as a novel interconnection method between chips and substrates. However, the solder used in this method is limited to Sn-58Bi and Sn-52In. In contrast, Sn-3Ag-0.5Cu has been relatively less studied despite its wide use as a lead-free solder in assembling semiconductor packages. Hence, here, polymeric materials incorporating Sn-3Ag-0.5Cu solder powder were investigated for the self-assembly of the solder on pads at temperatures up to 260°C in a lead-free reflow process. The self-assembly of the solder was observed with an optical microscope through transparent glass chips placed on substrates covered with the polymeric materials incorporating the solder powder. Differential scanning calorimetry measurements were performed to confirm the behaviors of the reaction of the resins and the melting of the solder. When epoxy resin with a fluxing additive was used as a matrix, self-assembly of the solder was prevented by the cross-linking reaction. Conversely, when thermoplastic resin containing carboxyl groups was used as a matrix, the self-assembly of solder was successfully achieved in the absence of fluxing additives. The shear strength of interconnection using reflowfilm with lamination was sufficient and significantly increased during the reflow process. However, the shear strength of the reflowfilm showed cohesive failure, possibly because of the brittle intermetallic compounds (Ag₃Sn, Au₄Sn) network in bulk was lower than that of conventional solder paste that showed interfacial failure after the reflow process with a rapid cooling rate.     

Friction and Wear Properties of Si3N4/Carbon Fiber Composites with Aligned Microstructure

The friction and wear properties of silicon nitride/carbon fiber composites have been assessed and compared with monolithic Si₃N₄. Three different types of composites have been produced; one in which both the Si₃N₄ grains and the carbon fibers were aligned, one in which only the fibers had alignment, and a third where both the grains and fibers had random orientation. The friction coefficients of all of the composites, following running in, were around 0.2–0.3, typically less than one-third of that of the monolithic material. However there was no significant difference in friction coefficient between the three different types of composite. The specific wear rates of all the materials decreased with sliding distance and those of the composites were lower than the monolithic material. Among the composites, the wear rate of the one with aligned fibers in a randomly oriented Si₃N₄ matrix showed no dependence on sliding direction relative to the fiber alignment, and the specific wear rates of these samples were similar to that of the randomly oriented fiber composite, indicating little effect of fiber alignment alone on the wear properties under the present testing conditions. However, the specific wear rate of the composite with both fiber and grain alignment showed directional dependence. Grain cracking was observed perpendicular to the sliding direction, and the Spara specimen, in which the sliding direction was parallel to the Si₃N₄ grain alignment, showed higher wear rates than the Sperp and N samples of this composite. Such cracks are perpendicular to the major axis of the grains in the Spara sample and are thought to lead to easier removal of grains following their cracking under the tensile stresses induced particularly during the running in period.