Masahiro Ikeda

Protein refolding assisted by self-assembled nanogels as novel artificial molecular chaperone.

Molecular chaperone‐like activity for protein refolding was investigated using nanogels of self‐assembly of cholesterol‐bearing pullulan. Nanogels effectively prevented protein aggregation (i.e. carbonic anhydrase and citrate synthase) during protein refolding from GdmCl denaturation. Enzyme activity recovered in high yields upon dissociation of the gel structure in which the proteins were trapped, by the addition of cyclodextrins. The nanogels assisted protein refolding in a manner similar to the mechanism of molecular chaperones, namely by catching and releasing proteins. The nanogels acted as a host for the trapping of refolded intermediate proteins. Cyclodextrin is an effector molecule that controls the binding ability of these host nanogels to proteins. The present nanogel system was also effective at the renaturation of inclusion body of a recombinant protein of the serine protease family.

Low-threshold CW operation of square-shaped semiconductor ring lasers (orbiter lasers)

The CW operation of square-shaped semiconductor ring lasers is demonstrated with a threshold current as low as 6 mA. The ring resonator consists of straight waveguides and four total reflection mirrors. The lasers are fabricated using Br/sub 2/ dry etching on an InGaAs/GaAs strained single-quantum-well graded-index separate-confinement heterostructure wafer. The low-threshold CW operation is due to the high differential gain of the wafer and the low-loss total reflection mirror.<<ETX>>

Control of unidirectional oscillation in semiconductor orbiter lasers

Unidirectional oscillation in a ring-resonator-type semiconductor laser was demonstrated in a square-shaped orbiter laser using an optical feedback mechanism. The bistable switching phenomenon between the unidirectional and bidirectional oscillation was observed synchronized with the switching of the longitudinal lasing mode. A longitudinal-mode bistability results from the compound cavity system formed by the orbiter laser and output waveguide. The feedback light from the output waveguide end interferes with the orbiter lasing light. Switching between the unidirectional and bidirectional oscillation was controlled by injecting a current into the output waveguide, which varies the phase condition of the feedback light.<<ETX>>

A note on the lifespan of solutions to the semilinear damped wave equation

This paper concerns estimates of the lifespan of solutions to the semilinear damped wave equation. We give upper estimates of the lifespan for the semilinear damped wave equation with variable coefficients in all space dimensions.

Null Structure in a System of Quadratic Derivative Nonlinear Schrödinger Equations

We consider the initial value problem for a three-component system of quadratic derivative nonlinear Schrödinger equations in two space dimensions with the masses satisfying the resonance relation. We present a structural condition on the nonlinearity under which small data global existence holds. It is also shown that the solution is asymptotically free. Our proof is based on the commuting vector field method combined with smoothing effects.

A robust embedded ladder-oxide/Cu multilevel interconnect technology for 0.13 μm complementary metal oxide semiconductor generation

A robust embedded ladder-oxide (k=2.9)/copper (Cu) multilevel interconnect is demonstrated for 0.13 µm complementary metal oxide semiconductor (CMOS) generation. A stable ladder-oxide intermetal dielectric (IMD) is integrated by the Cu metallization with a minimum wiring pitch of 0.34 µm, and a single damascene (S/D) Cu-plug structure is applied. An 18% reduction in wiring capacitance is obtained compared with that in SiO2 IMDs. The superior controllability of metal thickness by the S/D process enables us to enhance the MPU maximum frequency easily. The stress-migration lifetime of vias on wide metals for the S/D Cu-plug structure is longer than that for a dual damascene (D/D) structure. Reliability test results such as electromigration (EM), the temperature dependant dielectric breakdown (TDDB) of Cu interconnects, and pressure cooker test (PCT) results are acceptable. Moreover, a high flexibility in a thermal design is obtained.

Enhancement of proopiomelanocortin gene promoter activity by local anesthetics in a pituitary cell line.

Background and Objectives: Corticotropin-releasing hormone (CRH) induces gene expression of proopiomelanocortin, a precursor protein of adrenocorticotropic hormone and &bgr;-endorphin, by elevating intracellular cyclic adenosine 3′,5′-monophosphate (cyclic AMP) level in anterior pituitary cells and immune cells. CRH-induced proopiomelanocortin gene expression plays an important role in stress responses and is affected by a variety of drugs, but it is not known whether local anesthetics can directly affect the gene expression. We hypothesized that local anesthetics may directly affect proopiomelanocortin gene expression and can modulate production of adrenocorticotropic hormone and &bgr;-endorphin. Methods: The authors used mouse pituitary tumor cells stably transfected with approximately 0.7 kilobases of the rat proopiomelanocortin 5′ promoter linked with the luciferase gene. In the presence or absence of local anesthetics (lidocaine, mepivacaine, bupivacaine, and ropivacaine), cells were stimulated by CRH or forskolin. After stimulation, proopiomelanocortin gene promoter activity was assessed as luciferase activity, and cyclic AMP efflux was measured by enzymeimmunoassay. Results: CRH- or forskolin-stimulated proopiomelanocortin promoter activity was significantly enhanced by local anesthetics. Cyclic AMP efflux induced by CRH was not significantly increased by local anesthetics. Conclusions: It was concluded that local anesthetics potentiate the effect of CRH or forskolin on proopiomelanocortin promoter activity without changing the intracellular cyclic AMP level. It might be possible that transcriptional regulation mediated by cyclic AMP is also enhanced by local anesthetics in the other cells.

Low-temperature growth of highly crystalline superconducting ZrN thin film on c-GaN layer by pulsed laser deposition

Superconducting ZrN thin films were fabricated on c-GaN/c-Al2O3 substrates at low growth temperatures ranging from 200 to 300 °C by pulsed laser deposition. ZrN(111) thin films were epitaxially grown on c-GaN/c-Al2O3 substrates, while the growth on c-Al2O3 substrates yielded poorer crystallinity. The use of Zr metal and ZrN targets respectively resulted in higher crystallinity and a higher superconducting transition temperature of up to 7.3 K, indicating that the superconducting transition temperature is not closely related to the crystallinity. The results suggest the usefulness of a GaN layer for the growth of cubic-nitride thin films.

The Cauchy problem for the nonlinear damped wave equation with slowly decaying data

We study the Cauchy problem for the nonlinear damped wave equation and establish the large data local well-posedness and small data global well-posedness with slowly decaying initial data. We also prove that the asymptotic profile of the global solution is given by a solution of the corresponding parabolic problem, which shows that the solution of the damped wave equation has the diffusion phenomena. Moreover, we show blow-up of solution and give the estimate of the lifespan for a subcritical nonlinearity. In particular, we determine the critical exponent for any space dimension.

An asymmetric Y-branching circuit using total reflection for semiconductor integrated optical circuits

A new structure for a compact optical branching circuit is proposed. An asymmetric Y-branching circuit using total reflection is fabricated on an AlGaAs/GaAs wafer. Good branching operation is observed in a single-mode branching circuit with a branching angle of 45 degrees . The exact origins of loss in the branching circuit are also clarified.<<ETX>>