Superplastic Property of the Ti–6Al–4V Alloy with Ultrafine‐Grained Heterogeneous Microstructure

Ti–6Al–4V alloy having a heterogeneous microstructure composed of ultrafine‐equiaxed‐α‐grains and fine‐lamellar‐α‐grains is investigated for microstructural changes during superplastic deformation at temperature of 700 °C. The Ti–6Al–4V alloy having an optimum fraction of fine‐lamellar‐α‐grains exhibits an excellent superplastic property and the highest elongation of 583% (tested at 700 °C 10^?3 s^?1). This is mainly due to the optimized activation of grain‐boundary‐sliding and additional accommodation mechanism associated with frequent occurrences of dynamic recrystallization and β precipitation at boundaries during deformation of the heterogeneous starting microstructure. The present result suggests the possibility that optimizing the starting microstructure so as to have an optimum heterogeneous‐microstructure serves as an additional stress accommodation mechanism and leads to a large superplastic elongation.

     

Protective effect of a vitamin E analog, phosphatidylchromanol, against oxidative hemolysis of human erythrocytes

The protective effect of a vitamin E analog, phosphatidylchromanol [1,2-diacyl-sn-glycero-3-phospho-2′-(hydroxyethyl)-2′, 5′,7′,8′-tetramethyl-6′-hydroxychroman; PCh], against oxidative hemolysis of human erythrocytes was examined and was compared with those of vitamin E (α-tocopherol) and 2,2,5,7,8-pentamethyl-6-chromanol (PMC). These three compounds at 50 μM protected the erythrocytes from hemolysis, when erythrocyte suspension (10%, vol/vol) was incubated with a water-soluble radical generator, 2,2′-azobis(2-amidino-propane)-dihydrochloride (75 mM). When erythrocyte suspension was oxidized after pretreatment with these compounds (50 μM) for 30 min followed by washing, PCh protected about 54% of erythrocytes from the hemolysis, while α-tocopherol protected only about 16% of the cells and PMC did not show any protective effect. During preincubation, α-tocopherol, PMC, and PCh were incorporated into the cells at the concentration of 12.6, 3.7, and 16.3 nmol/mg protein, respectively. Moreover, PCh was found in the ghost membrane fraction at a 20% higher level than α-tocopherol, and no PMC was detected in this fraction. These results indicate that phosphatidyl group in PCh accts as an excellent carrier of chromanol moiety into cells as well as an anchor within membranes more efficiently than phytyl group in α-tocopherol. PMC seems to be slightly anchored within membranes because of the lack of hydrophobic side chain. The excellent antihemolytic activity of PCh is likely to be caused by its accumulation within erythrocyte membranes.     

Regulation of Transgene Expression in Tumor Cells by Exploiting Endogenous Intracellular Signals

Recently, we have proposed a novel strategy for a cell-specific gene therapy system based on responses to intracellular signals. In this system, an intracellular signal that is specifically and abnormally activated in the diseased cells is used for the activation of transgene expression. In this study, we used protein kinase C (PKC)α as a trigger to activate transgene expression. We prepared a PKCα-responsive polymer conjugate [PPC(S)] and a negative control conjugate [PPC(A)], in which the phosphorylation site serine (Ser) was replaced with alanine (Ala). The phosphorylation for polymer/DNA complexes was determined with a radiolabel assay using [γ-³²P]ATP. PPC(S)/DNA complexes were phosphorylated by the addition of PKCα, but no phosphorylation of the PPC(A)/DNA complex was observed. Moreover, after microinjection of polymer/GFP-encoding DNA complexes into HepG2 cells at cation/anion (C/A) ratios of 0.5 to 2.0, significant expression of GFP was observed in all cases using PPC(S)/DNA complexes, but no GFP expression was observed in the negative control PPC(A)/DNA complex-microinjected cells at C/A ratios of 1.0 and 2.0. On the other hand, GFP expression from PPC(S)/DNA complexes was completely suppressed in cells pretreated with PKCα inhibitor (Ro31-7549). These results suggest that our gene regulation system can be used for tumor cell-specific expression of a transgene in response to PKCα activity. Daisuke Asai and Jeong-Hun Kang contributed equally to this work.     

Composite Behavior of Lath Martensite Steels Induced by Plastic Strain,a New Paradigm for the Elastic-Plastic Response of Martensitic Steels

Based on high-resolution neutron diffraction experiments, we will show that in lath martensite steels, the initially homogeneous dislocation structure, i.e., homogeneous on the length scale of grain size, is disrupted by plastic deformation, which, in turn, produces a composite on the length scale of martensite lath packets. The diffraction patterns of plastically strained martensitic steel reveal characteristically asymmetric peak profiles in the same way as has been observed in materials with heterogeneous dislocation structures. The quasi homogeneous lath structure, formed by quenching, is disrupted by plastic deformation producing a composite structure. Lath packets oriented favorably or unfavorably for dislocation glide become soft or hard. Two lath packet types develop by work softening or work hardening in which the dislocation densities become smaller or larger compared to the initial average dislocation density. The decomposition into soft and hard lath packets is accompanied by load redistribution and the formation of long-range internal stresses between the two lath packet types. The composite behavior of plastically deformed lath martensite opens a new way to understand the elastic-plastic response in this class of materials.     

Work Hardening,Dislocation Structure,and Load Partitioning in Lath Martensite Determined by <Emphasis Type="Italic">In Situ</Emphasis> Neutron Diffraction Line Profile Analysis

A lath martensite steel containing 0.22 mass pct carbon was analyzed in situ during tensile deformation by high-resolution time-of-flight neutron diffraction to clarify the large work-hardening behavior at the beginning of plastic deformation. The diffraction peaks in plastically deformed states exhibit asymmetries as the reflection of redistributions of the stress and dislocation densities/arrangements in two lath packets: soft packet, where the dislocation glides are favorable, and hard packet, where they are unfavorable. The dislocation density was as high as 10¹⁵ m^?2 in the as-heat-treated state. During tensile straining, the load and dislocation density became different between the two lath packets. The dislocation character and arrangement varied in the hard packet but hardly changed in the soft packet. In the hard packet, dislocations that were mainly screw-type in the as-heat-treated state became primarily edge-type and rearranged towards a dipole character related to constructing cell walls. The hard packet played an important role in the work hardening in martensite, which could be understood by considering the increase in dislocation density along with the change in dislocation arrangement.     

TEM study of the influence of antisite defects on magnetic domain structures in double perovskite Ba2FeMoO6

Magnetic domain structures and crystal structures of double perovskite Ba(2)FeMoO(6) were studied using Lorentz transmission electron microscopy (TEM), dark-field imaging and high-resolution TEM. Two types of magnetic domain structure were observed below the Curie temperature: an ordinary 180 degrees ferromagnetic domain structure and a typical maze-pattern structure. In regions where maze-pattern structures were observed, antiphase boundaries were found by dark-field imaging and high-resolution TEM and develop densely in Fe/Mo-ordering domains, suggesting that Fe/Mo antisite defects affect magnetic domain structures.     

Development of high-resolution single-ion PSD using random access memories

Using heavy-ion microbeam, we have examined the feasibility of a Static Random Memory (SRAM) as an in situ Position Sensitive Detector (PSD) with bit-cell size resolution for extremely low current ion beams. It is found that SRAMs are promising candidates for high-resolution PSD to diagnose an extremely low current ion microbeam.     

A method of designing ac/dc thyristor converter current control systems by using discrete time MRAC with deterministic disturbances

Two design methods of ac/dc thyristor converter current control systems with MRAC (Model Reference Adaptive Control) have been designed. To linearize the input/output relation of the systems, the constant term of the model is considered in different ways. In the first method, a linear transformation of the control input is made while in the second method, the constant term and compensated modeling error are neglected by integral adaptation. Computer simulations and experiments have shown that the control performances of the MRAC systems are much better than that of PI controllers. However, in the first method, since the variable vector is not persistently spanning, the convergence rate of estimated parameters is not as high as expected. The second method has better dynamic characteristics but its stability has not been proved in theory. This paper suggests a new design method in which the constant term is considered as a deterministic disturbance. The feature of this method is that by introducing an equality equation which makes the term of disturbances apparently unobservable, the effect of disturbances can be eliminated and the existing adaptive control scheme without disturbances whose stability has been proved theoretically can be used. Computer simulations and experiments show that the new method can obtain better responses than the old ones.     

The effect of demand response on electricity consumption under the existence of the reference price effect: Evidence from a dynamic pricing experiment in Japan

This paper investigates the effect of demand response on households’ electricity consumption under the existence of the reference price effect. The reference price effect is observed in peak and shoulder hours. Consistent with reference price theory predictions, our results show that the reduction of electricity consumption is greater in the case where the current price is higher than the previous price than in the case where the current price is lower than the previous price.