Metal Vapor Behavior in GTA Welding of a Stainless Steel Considering the Marangoni Effect

A gas tungsten arc in helium was modeled taking into account the contamination of the plasma by metal vapor from the weld pool. The whole region of gas tungsten arc atmosphere including the tungsten cathode, arc plasma and weld pool was treated using a unified numerical model. The anode was of a low sulfur stainless steel or a high sulfur stainless steel. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of shielding gas and metal vapor. The transient two-dimensional distributions of the temperature, velocity of plasma flow and iron vapor concentration were predicted, together with the weld penetration at the atmospheric pressure. The distribution of the iron vapor is obviously different between the case of a low sulfur stainless steel anode and the case of a high sulfur stainless steel anode. © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

The Role of Hydrogen on the Local Fracture Toughness Properties of 7XXX Aluminum Alloys

High-resolution synchrotron X-ray microtomography has been successfully used to evaluate the local crack driving force at arbitrary crack tip locations as a form of CTOD. This is to our knowledge the first experimental evidence in supporting a correlation between the local fracture toughness associated with the corresponding hydrogen-assisted fracture mode including quasi-cleavage, intergranular, and dimple. Our results have revealed that very small CTOD, of about 1.26 μm, is observed when the crack tip is located in the quasi-cleavage fracture. Compared to quasi-cleavage fracture, the CTOD values increase by a factor of 5 when the crack tip is located in intergranular fracture mode and even greater increase in CTOD (of about 18 times) is observed when the crack tip is located in dimple fracture mode. We also observed that the crack propagation process under the influence of hydrogen deviates greatly from that of standard behavior, where stable crack growth is accompanied by a change in crack tip singularity from the HRR to the RDS. It was concluded that the presence of high concentration of hydrogen ahead of the crack tip increases the slip localization, and thereby reduces crack tip blunting. Hence crack continues to grow before the crack tip becomes fully blunt.     

Round-robin exercise on the three- and four-point flexural strength of thin ceramic plates for power modules

Round-robin exercises on three- and four-point flexural tests were successfully conducted to evaluate the fracture strength of Si₃N₄, Al₂O₃, and AlN thin plates for power modules. A 0.64 mm × 12 mm × 40 mm test specimen was loaded in three-point flexure with a major span of 30 mm or was loaded in four-point flexure with a major/minor span of 30/10 mm. For a 0.32 mm × 12 mm × 20 mm test specimen, both major and minor spans were halved. All test specimens were loaded in a fully articulated fixture provided by the test organizer. Reasonable consistencies in the resultant flexural strength were obtained between laboratories, indicating our new test condition for three- and four-point bending of thin ceramic plates is satisfactory for reliable measurement of the flexural strength.     

Phase relations in silicon and germanium nitrides up to 98 GPa and 2400°C

Phase relations in silicon and germanium nitrides (Si₃N₄ and Ge₃N₄) were investigated using a Kawai-type multianvil apparatus and a laser-heated diamond anvil cell combined with a synchrotron radiation. The pressure-induced phase transition from the β to γ (cubic spinel-type structure) phase was observed in both compositions. We observed the coexistence of the β and γ phases in Si₃N₄ at 12.4 GPa and 1800°C, while the appearance of single phase γ-Ge₃N₄ was observed at pressures above 10 GPa. Our observations under higher pressures revealed that γ-Si₃N₄ and γ-Ge₃N₄ have wide stability fields and no postspinel transition was observed up to 98 GPa and 2400°C in both compositions. Using the room-temperature compression curves of these materials, the bulk moduli (K₀) and their pressure derivatives (K′₀) were determined: K₀ = 317 (16) GPa and K′₀ = 6.0 (8) for γ-Si₃N₄; K₀ = 254 (13) GPa and K′₀ = 6.0 (7) for γ-Ge₃N₄.     

Converting rice husk activated carbon into active material for capacitor using three-dimensional porous current collector

We have successfully applied rice husk activated carbon (RHAC) as an active material for the electric double layer capacitor using a three-dimensional (3D) porous current collector. The capacity and cycle stability were evaluated in a 1.0 mol dm⁻³ tetraethylammonium tetrafluoroborate/propylene carbonate solution in the range of 0-2.5 V. The specific capacity of the RHAC was about 14 mAh g⁻¹ at the 50 mA g⁻¹ discharge rate, corresponding to 19 F g⁻¹ under the present conditions. The RHAC cell using the 3D porous current collector possessed a lower internal resistance and better high-rate discharge properties than the RHAC cell using a conventional aluminum (Al) foil collector. After 5000 cycles of charging and discharging, the RHAC cell with the 3D current collector maintained 95% of its initial capacity, while the capacity of the one with the Al foil collector dropped to only 30%.     

Growth of Phragmites japonica on a sandbar of regulated river: morphological adaptation of the plant to low water and nutrient availability in the substrate

The construction of upstream dams regulates flood magnitudes, reduces the inundation frequency of the riparian zones and curtails the discharge of sediments to the downstream. Adaptation of a Phragmites japonica colony growing at a rarely flooded sandbar (1.4 × 0.25 km) was investigated. Above‐ and belowground biomass was sampled, together with litters on the ground surface of a quadrat and soil in the rhizosphere. Five sampling locations were selected with three locations located in sandy and two in stony areas. The results showed the total biomass and the ratio of above‐ to belowground biomasses were larger at the sandy sites than the stony sites. However, the fraction of root biomass (i.e. root to rhizome ratio) in the belowground biomass at the stony sites was higher than that at the sandy sites. Higher aboveground and total plant biomass in the sandy areas was because the plants had better access to water and nutrients than plants growing in stony beds. A higher proportion of root biomass, at the expense of rhizome biomass, in the belowground biomass of plant growing in stony sites was due to the difficulty in accessing water and inorganic nutrients. The ratios of nitrogen (N) to phosphorus (P) in the plant tissues were mostly between 5 and 10, indicating that plant growth was N limited. Low ratios of total N (TN) to total P (TP) were also recorded in soil samples, where TN was 300–700 mg/kg and TP was 300–350 mg/kg. A wide phenotypic plasticity observed in P. japonica was an importance factor to maximize the plant survival and fitness in frequently disturbed habitats, and this plasticity was the result of both true adjustment and ontogenetic drift. A mitigation effort, aimed to prevent coarsening of the riverbed by supplying sand to the downstream, can actually advance the development of P. japonica colonies. Copyright © 2008 John Wiley & Sons, Ltd.     

High-strength nanocomposite based on fibrillated chemi-thermomechanical pulp

The incompatibility between cellulose fibers and hydrophobic polymers has presented a major obstacle for the fabrication of composites and nanocomposites. In this study, we applied a one-time grinder treatment to disintegrate chemi-thermomechanical pulp (CTMP) and obtained micro- to nano-meter-sized lamellar or fibrous fragments. The CTMP fragments were composed of cellulose microfibrils with high aspect ratios encased in matrix substances including hydrophobic lignin. Furthermore, we produced compression-molded products from the CTMP fragments by thermally plasticizing lignin without any adhesives or resins. The molded products pressed at 180 °C exhibited a plastic-like gloss on the surface and a high bending strength, 221 MPa, which greatly exceeded that of the conventional plant-based binderless boards. The molded products produced here are a novel form of ideal cellulose nanocomposite, which exploited the inherent compatibility between cellulose microfibrils and matrix substances present in CTMP fragments.     

Increased carbonyl protein levels in the stratum corneum of the face during winter

The stratum corneum (SC) is the interface between the body and the environment, and is continuously exposed to oxidative stress that results in carbonyl modification of proteins. We previously developed a simple and non-invasive method to assess the stratum corneum carbonyl protein (SCCP) levels. In this study, we used this method to examine the seasonal changes in the SCCP levels and the relationship between the SCCP level and the physiological condition of the SC. SC was collected from the face of healthy Japanese volunteers by adhesive tape stripping and its carbonyl groups were determined by reaction with fluorescein-5-thiosemicarbazide. The average fluorescence intensity of the SC was calculated as the SCCP level. The SCCP level in the cheek was higher in winter than summer. The SCCP level was negatively correlated with the water content in the SC measured by the conductance and capacitance, and also negatively correlated with the extensibility of the skin measured by a Cutometer, suggesting that the mechanical properties of the skin can be affected by oxidative modification of the SC. These data suggest the involvement of oxidative modification of SC proteins in the generation of rough skin during winter.